CAMD 2005 Annual Report - Louisiana State University

Transcription

CAMD
2005 Annual Report
Editor
Lee Ann Murphey
Content Development
Jost Goettert
Josef Hormes
Tracy Morris
John Scott
The J. Bennett Johnston, Sr.,
Center for Advanced Microstructures and Devices
6980 Jefferson Highway
Baton Rouge, LA 70806
www.camd.lsu.edu
Dedicated to the Memory of our Dear
Friend and Colleague
Dr. Roland C. Tittsworth
July 30, 1953 – December 20, 2005
Dedicating this Annual Report to Roland seems like a small thing considering the impact
he had on so many of our lives; however, it is fitting that the manuscript that is written by
CAMD users and staff alike would also be a tribute to this friend whose life was so much
a part of our lives.
Roland was a scientist; he graduated cum laude with a BS in Biochemistry and Molecular
Biology from the University of Maryland Baltimore County in 1989 and with a PhD in
Chemistry from LSU in 1995. His interest in X-ray spectroscopy and its impact on
understanding the structure and function of biologically important molecules began
during his LSU graduate work directed by Professor Brian Hales. It continued for the
remainder of his life.
Roland was a loving family man. He was devoted to his wonderful wife, Pam, his step
sons, Richard and Christian Hull, Richard’s wife Michele and baby daughter Regan, his
sisters, Marian Ervin, Jo Anne Laverdiere and Betty Lee Tasternack and all of the folks
he considered sisters and brothers in Jesus Christ.
Roland was a hard working and loved co-worker at LSU CAMD. He joined us in
September, 1995 as a Research Associate 4, was promoted to Research Associate 5 three
years later and to Assistant Professor- Research and Director of X-ray Sciences in 1999.
Roland, you never took yourself too seriously but you did take friendships seriously.
Thank you for sharing your life with us.
2
Table of Contents
Director’s Comments…………………………………………………………………...……4
CAMD Contact Information…………………………………………………………….…..6
I. Introduction and Accelerator Operations
A. General Comments Regarding 2005…………………..…………………………........7
B. Accelerator Operations………………………………………………………………..8
C. Research Facility Operations………………………………………………………...14
1. Basic Science and Beamlines……………………………………………………14
2. Microfabrication…………………………………………………………………16
II. CAMD Research Infrastructure; Major Equipment and Facility Utilization
A. Introduction……………………………………………………………….................18
B. Basic and Material Sciences at CAMD…………………………………………...…18
1. Infrared through Soft X-ray Beamlines………………………………………..…18
2. The Protein Crystallography Beamline……………………………..……………19
3. X-ray Beamlines; Spectroscopy, Scattering, Tomography and Powder-Diffraction...21
C. MEMS/LiGA Services at CAMD in 2005…….…………………………………….25
D. CAMD Cleanroom…………………………………………………………………..31
III. User Reports and User Activities
A. Basic and Material Sciences
1. Spectroscopy
a. VUV……………………………………………………………………..…..38
b. X-ray……………………………………………………………………...…74
2. X-ray Micro-Tomography…………………………………………………...…132
3. Nanofabrication………………………………………………………………...134
4. Protein Crystallography...………………………………………………………202
B. Microfabrication
1. CAMD Staff Reports on Internal Projects…….…………………………..…...214
2. External User Reports………………………………………………….……....265
C. CAMD Users’ Publications and Presentations………………………………….….288
D. Annual Users Meeting 2005…………………………………………………….….295
E. CAMD User Committee (CUC)…………………………………………………....297
IV. CAMD Facility/Staff
A. Scientists’ Activity (Publications/Presentations)………………………………..….300
B. Facility and Community Programs
1. REU……………………………………………………………………………...309
2. CAMD / CBM2 Summer Workshop: Advanced Technologies for Biomedical Applications..310
3. Open House, Day of Discovery………………………………………………….312
4. CAMD in the community………………………………………………………..327
C. CAMD Facility Tours……………………………………………………………....331
D. CAMD Seminars…………………………………………………………………...332
E. SAC and MAC Executive Summaries for 2005……………………………………334
F. CAMD Budget…………………………………………………………………...…336
G. CAMD Staff Changes………………………………………………………………337
3
Director’s Comments
2005 was one of the most successful years in CAMD’s history!
There have been no major problems with the machine: the accelerator group delivered
more than 5200 h and about 700 amp-hours of user beam with reliability above 90% in
spite of the heavy hurricane season! By further improving beam diagnostics (beam based
alignment, photon beam position monitors, X-ray pin-hole camera, etc.) the beam
stability was improved significantly. This apparently was appreciated by the users as the
number of complaints also decreased significantly!
At present time, there are 11 fully operational beamlines at CAMD:
- 4 beamlines for X-ray lithography
- 4 IR/VUV beamlines (IR, 3m TGM, 6m TGM, 3m NIM)
- 3 X-ray beamlines (DCM, XMP, PX)
The wiggler-based tomography beamline (TOMO) that has two monochromators (a
double multilayer-mirror monochromator mainly for tomography and a grooved single
Si- crystal monochromator mainly for high-energy X-ray spectroscopy) is partly
operational and the multilayer monochromator has just successfully been readjusted. The
problems connected with the monochromator of the SAXS beamline could finally be
solved with support from our colleagues from the Brazilian Light Source so that the final
commissioning should be finished quite soon. There is light at the exit slit of the new
VLSG monochromator and the commissioning should start soon. Finally, also the new
powder diffraction beamline is ready for commissioning. Thus, there is realistic hope that
by the end of summer 2006 all 15 beamlines at CAMD will be fully operational and open
for users. This should be a very good basis for attracting new external users with new
exciting experiments.
The number of users increased once again and we had about 250 (non-CAMD) users
representing about 50 different institutions. I think it is worth mentioning that from this
number there have been about 120 (!) graduate students and about 30 undergraduate
students.
Serious discussions have been started (once again) about the second insertion device that
could/should be installed in the remaining straight section to keep CAMD competitive.
From the user side there seems to be an interest in improving CAMD’s capabilities in the
“soft X-ray” range, i.e. between about 100 eV and 4000 eV. Thus, we are considering a
superconducting multi-pole (30 pole) wiggler with an optimal spectral range of
approximately 1-4 keV and would increase the intensity in the energy range of interest by
more than an order of magnitude. Multi-pole wigglers normally have the drawback that
the opening angle of the available beam is very limited so that it is very difficult to
provide light for more than one beamline. The new design that has been suggested by the
Budker Institute in Novosibirsk overcomes this problem by implementing the opportunity
to split the poles into 3 sections with 10 poles each
4
In spite of the exciting achievements one should not forget the less positive events/facts:
-
Because of the problems in the aftermath of hurricanes Katrina and Rita the 2005
National Synchrotron Radiation Instrumentation Conference that was planned to
be hosted by CAMD had to be canceled on rather short notice: a very frustrating
process for the CAMD people that invested such a lot of work in the planning and
preparation of this event.
-
CAMD’s operational budget remains flat on the same level as for the last 8 years
in spite of increased number of beamlines, users, and beam time provided for
users.
-
There has been no progress regarding SEALS – the CAMD proposal for a new
third generation SR-facility for the Southeast of the US
The budget cuts that hit higher education in Louisiana and that are also valid for CAMD
in the aftermath of the Hurricanes Katrina and Rita in combination with rapidly
increasing power costs have forced us to reduce the hours of user beam by about 50 %(!)
by giving up the well established 24 hours per day operation mode and moving to a 12hours-per-day schedule. This schedule that started on January 2006 and I have no doubts
that this will in a negative way influence the stability and performance of the machine.
This will be the last annual report for which I am writing a forward as CAMD’s Director.
I was in charge of CAMD for more than 6 years and I am in the process of stepping
down. However, I hope to stay affiliated with LSU/CAMD as a (once again) active
scientist and as an advisor whenever advice is asked. My time as director of CAMD was
exciting and challenging. I think CAMD moved forward and in the right direction and it
is now a reliable user facility with a performance very much comparable to the one of the
national SR-facilities. This was achieved with an extremely limited budget and with
minimum staff. I am grateful to all my co-workers, who actually deserve the praise for
what was achieved as they did the hard work! I would also like to use this opportunity to
thank CAMD’s Advisory Committees (Machine, Scientific, Industrial and User) for their
commitment and support: their constructive criticism helped us very often to recognize
weak points and to refocus our efforts whenever that was necessary. Last but not least, I
would also like to thank our loyal users: an SR user facility is useless without a strong
and committed user community. The complaints of our users motivated us very often to
push things forward a little bit harder and we have taken the silence of our users as a sign
that things are running smoothly according to their expectations: there was a lot of silence
in 2005! I hope that with the continued support of all people that care about CAMD, there
will be more exciting and fruitful years to come for the CAMD user community!
Josef Hormes
5
CAMD Contact Information
Mail:
CAMD
Phone:
225/578-8887
Fax:
225/578-6954
Web:
www.camd.lsu.edu
User Interface Coordinator:
(to submit a news item or
arrange a tour of the facility)
Lee Ann Murphey
225/578-4606
[email protected]
6
I. Introduction and Accelerator Operations
A. General Comments Regarding 2005.
The Facility:
The Louisiana State University J. Bennett Johnston, Sr., Center for Advanced
Microstructures and Devices (LSU-CAMD) is a synchrotron-radiation research center of
the Office of Research headed by Vice Chancellor for Research and Graduate Studies
Harold Silverman. The electron-storage ring, which is the heart of CAMD, has been in
operation to produce intense and bright synchrotron radiation since September, 1992.
The facility is located at 6980 Jefferson Highway, Baton Rouge, approximately five miles
from the LSU campus.
The synchrotron-radiation source, an electron storage ring operated at 1.3 GeV, the
200-MeV-linear-accelerator injector and the CAMD Experiment Hall and MechanicalSupport Facility were built with funding provided by a special Congressional
appropriation of $25M made in 1988. The principal operating budget is provided by the
State of Louisiana as a part of the LSU budget. A brief history of the facility is in the
CAMD 2003 Annual Report, p1 (online at http://www.camd.lsu.edu/ ).
Impact of the hurricanes of August-September, 2005:
The National Synchrotron Radiation Instrumentation (SRI) Conference, the biennial
scientific meeting of the eight US synchrotron-light sources, was scheduled to be hosted
by CAMD September 19-23, 2005; however, the hurricanes, Katrina and Rita, displaced
several hundred thousand unfortunate people to Baton Rouge and the accommodations,
which we had reserved for conference lodging and meeting, were no longer available.
The meeting and its associated two workshops were cancelled. The workshops dealt with
electron-beam-position monitoring and with photon detectors. The Detector Workshop
actually was only postponed and moved to the APS, December 8-9. The SRI Meeting
had scheduled ca. 40 talks, invited and contributed, a over 100 poster presentations. The
local organizers of the meeting were Eizi Morikawa, Lee Ann Murphey, and John Scott
with Surendar Paruchuri creating and maintaining a beautiful and very useable (by
registrants, authors and conference organizers) meeting web site.
The cancellation of the 2005 National SRI Conference was not the only CAMD
casualty of the hurricanes; a number of our users from New Orleans universities, UNO,
Tulane and Xavier were displaced both from their homes and university laboratories and
students. Also impacted was the Louisiana budget and, thus, the budgets of the state
universities. At the close of 2005, CAMD was preparing for an approximately 10% cut
to its total annual budget (6% cut in the actual budget plus a 4% projected loss due to
increased utility costs). CAMD staff had only six months to accommodate this projected
financial loss. The major impact to the users was the decision, made jointly by the
CAMD Staff and CAMD User Committee, to change the operation schedule to a 14-day
cycle of nine days of 12-hour user light, one day (Sunday) no beam and three days
machine studies and maintenance. This schedule basically cut the user-beam time by
50%.
7
The Loss of Dr. Roland Tittsworth
We lost our dear friend and colleague, Dr. Roland Tittsworth, who passed from this
life unexpectedly the evening of December 20, 2005. Roland was an important part of
CAMD and was loved and respected by CAMD Staff and Users alike. He will be greatly
missed. He was the Director of the Basic Sciences X-Ray Program.
Dr. Amitava, our Environmental Scientist and a member of Dr. Tittsworth’s staff
agreed to serve as an interim Director of X-ray Sciences. In early 2006, Dr. Roy
accepted the position as permanent director.
B. Accelerator Operations
General Characteristics of the CAMD Electron Storage Ring:
Figure 1.1 is a plan view of the CAMD electron storage ring and Table 1.1 contains
the major operational parameters. The ring is injected by a 200 MeV (operated at 180
MeV) linear accelerator. Stored beam current accumulates over a period of a few
minutes until a limit of up to about 300 mA is attained, at which point the beam energy is
ramped to 1.3 GeV. Although the storage ring can be operated at energies up to 1.5 GeV,
it is operated at this lower energy to achieve optimum reliability by minimizing electronic
stress.
DB
-
Dipole Bending
QA
-
Quadrapole
Achromat
QD
-
Quadrapole
Defocusing
QF
-
Quadrapole
Focusing
SD
-
Sextapole
Defocusing
SF
-
Sextapole
Focusing
LinAc in basement
Figure I.1 Plan view of the CAMD electron storage ring.
8
Table I.1 CAMD Electron Storage-Ring Parameters
Beam Energy (GeV)
1.3
Beam current (mA)
200
Bending radius (meters)
2.928
Critical wavelength, bend magnet (Å)
7.45
Critical energy, bend magnet (keV)
1.66
Critical energy, 7 Tesla wiggler (keV)
7.87
Beam lifetime at 200 mA (hours)
10
Harmonic number
92
Radiative (power) mwatts/mrad/mA
0.014
Injection energy (MeV)
200
Natural emittance (m-rad)
3.5x10-7
For users of synchrotron radiation, certain characteristics of the radiation and, thus,
the specific storage ring need to be known and understood. The radiation that is admitted
down the beamlines from the storage ring ports is described in general in the following
sentences. The beta functions of the CAMD ring are plotted in Figure 1.2. Figures I.3,
1.4 and I.5 are all plots of the radiation characteristics of the synchrotron radiation
emitted from the CAMD ring when operated at the typical parameters of 1.3 GeV and
200 mA beam energy and beam current, respectively. The (simulated) flux curves (0.1%
energy band width), vertical divergence (σz’) and spectral brightness curves are plotted
for both bending-magnet (1.48 Tesla required for the CAMD dipole-bend radius of 2.928
m and electron-beam energy of 1.3 GeV) and single-pole (source is center of fan) superconducting wiggler energized at 7 Tesla. The emittance given in Table I.1 (and 2%
vertical-horizontal coupling in electron beam) and the beta function plots given in Figure
I.2 were used to calculate the flux, divergence angle and brightness. Brightness is
important, especially for a highly focusing beamline, while divergence angle and flux
(e.g., photon/sec/hrz.mrad/eV) are sufficient for rough approximation of the radiation
density profile at a specific distance from the source for a non-focusing beamline
9
Figure I.2. The CAMD storage ring lattice functions as modified to increase the flux
density produced by the wiggler. Half the ring circumference is shown. The wiggler is
located at the extreme right hand edge of the diagram, where the vertical beta function is
seen to bring the beam to a sharp focus.
10
flux (1012photons/sec/mrad/0.1%bw)
10
1.4 8
1
0.1
0.01
0.01
be n d
-tesla
e
magn
g
la wi
7 - te s
t
gler
CAMD Storage Ring
1.3 GeV and 200 mA
0.1
1
10
100
photon energy (keV)
Figure I.3 Simulated synchrotron-radiation-flux curves for synchrotron radiation from
the CAMD source operating as indicated. Note the spectra are normalized to 200 mA
ring current and 1 mrad horizontal acceptance.
10
1
σz' (mrad)
7-tesla wiggler
1.48-tesla bend magnet
0.1
CAMD Storage Ring
1.3GeV
Vertical Photon-Beam Divergence σz'
0.01
0.01
0.1
1
10
100
photon energy (keV)
Figure I.4 Vertical divergence of photon beam, σz’, calculated as a function of photon
energy using beam parameters given in this chapter.
11
brightness (1012photons/sec/mm2/mrad2/0.1%bw)
10
81. 4
1
l
tes
d
en
b
a
et
gn
a
m
7-
l
tes
le
gg
i
aw
r
CAMD Storage Ring
1.3GeV and 200 mA
0.1
0.01
0.1
1
10
100
photon energy (keV)
Figure I.5 Brightness of CAMD radiation produced in bending magnets and wiggler.
Calculations based on machine parameters given in chapter and operation as indicated
Performance
The storage-ring operation cycle during 2005 was 15 days in length with 4 contiguous
days of studies/maintenance. The schedule of operation can be found at the CAMD web
site; http://www.camd.lsu.edu/schedule_beam/beamschedule.htm Usually, the storage
ring was given back to the users during early evening of the last day of the
studies/maintenance period. Figure I.6 is a bar chart showing a month-by-month
scheduled versus actual user-light availability during 2005.
Ring current continued to be good during 2004 with typical injection currents
between 200 and 250 mA with 175 to 220 mA ramped. Life times of 10 hours at 200 mA
were also typical. Figure I.7 shows the monthly radiation delivered to users, plotted as
machine amp-hours. Beam current was integrated only when at least one beamline
shutter was open and beam current was greater than 30 mA.
Figure I.8 is a pie chart analysis of down time, a total of 149 hours, by quantitatively
presenting the sources during 2005. The percentages are with respect to total down time.
12
500.0
Hours per months
400.0
300.0
200.0
100.0
0.0
Jan
Feb
Mar
Apr
May
Jun
Ops Hours
Jul
Aug
Sep
Oct
Nov
Dec
Sched. Hours
Figure I.6 Bar graph comparing scheduled user beam time versus actual delivered beam
time.
120.0
Hours per month and %Efficiency
100.0
80.0
60.0
40.0
20.0
0.0
Jan
Feb
Mar
Apr
May
Jun
Amp Hours
Jul
Aug
Sep
Oct
Nov
Dec
% Efficiency
Figure I.7 Amp hours delivered to users, plotted monthly. Also, the per-cent efficiency
(actual use) is shown beside the delivered radiation.
13
Unkown, 2.1 Facility, 4.1
RIS, 4.4
Misc., 1.1
External, 10.5
Computer, 9.8
Ring, 42.7
Linac, 25.3
Figure I.8 Pie-chart analysis of accelerator “down time” (total of 149 hours) during
2005.
C. Research Facility Operations
1. Basic Science and Beamlines
At a synchrotron-radiation facility, the interface between the electron-storage-ring
radiation source and the users’ experiments are the beamlines. Table I.2 is a listing of
the beamlines that were in operation during a least a part of 2005 or were being installed
and had not yet become operational at the close of 2005. In Chapter II, the beamlines
are described in more detail, particularly those that became operational or whose
installation was began during 2004.
Funding obtained by members of the Basic-Science Staff for three beamline/endstation upgrades, which all are for CAMD-User utilization, totaled ca. $450,000 during
2005. All three grants were funded as LEQSF projects bt the Louisiana Board of
Regents.
14
Table I.2. CAMD Beamlines Available to Users Currently or in Near Future; 2005
[Italics indicate beamline under design, construction or modification]
FTIR & Microscope
Port 1A, 17 mrad
vertical and 50 mrad
horizontal
Micromachining I
Port 2A, 15 mrad
Micromachining II
Port 2B, 5 mrad
Micromachining IV
Port 3A, 10 mrad
Protein
Crystallography
Port 3A, 2 mrad
X-ray
Microtomography
Port 3A,3 mrad, Wiggler
source
3-meter NIM
Port 3B, 70 mrad
IR spectromicroscopy, spatial resolution down to ca. 500 cm-1 is 15x15
µ2. Biology, surface chemistry, environmental science, forensics
Variable-wavelength, variable high-pass (transmittance) and low-pass
(reflectance) filters, Jenoptic DEX02 scanner. Microfabrication
“White-light” beamline, εmax ≈ 4 keV, Jenoptic (first model) scanner.
Microfabrication
Micromachining beamline mounted at the 7- tesla superconducting
wiggler. Ideal for deep resists. Jenoptik DEX03 scanner.
Microfabrication
Installed on wiggler. Constructed with funding from NIH and NSF
acquired by the Gulf Coast Protein Crystallography Consortium ,
Protein Crystallography
Double multi-layer-mirror; ε less-than or equal to 36 keV, X-ray
tomography with ability to choose wavelength to enhance contrast
and make element identification a possibility. Spatial resolution of
less than 5 microns.
High-resolution, high-flux beamline, , range 4 – 40 eV. Scienta
electron analyzer with 10 meV resolution. valence-electron excitation
PGM being modified to
Modification began during 2004 to increase flux and res. and add
VLSGM
circ. pol. Material science.
Port 4A, 7 mrad
Range 15-300 eV with resolving power greater than 2000. High flux,
6-meter TGM
moderate resolution. Material and surface sciences. Operation status
Port 4B, 28 mrad
is awaiting suitable end station commissioning.
Double-crystal monochromator and micro-focus/sample-alignment
X-ray Microprobe
stage. Achieves spatial resolution of 20 µm over range 2 - 15 keV.
Port 5A, 2 mrad
Material-structure and environmental studies. Should be available
summer, 2006.
Range 1-15 keV with resolution from 0.5 eV (low energy) to
EXAFS, DCM
2 eV (high energy), currently configured for EXAFS. MaterialPort 5B, 2 mrad
structure and environmental studies
SAXS/Grz.-Angle XAS Range 1-15 keV, DCM equipped, Commissioning phase. surfacePort 6A, 2 mrad
structure studies:
Range 15 - 350 eV with resolving power greater than 1000.
3-meter TGM
Port 6 B, 24 mrad
.material and surface sciences
X-ray Powder
Double-crystal monochromator and 5-circle goniometer. Under
Diffraction
construction December 2004. Expected to be on-line in summer, 2005.
Port 7A, 3 mrad
“White-light” beamline, scanner & mask/wafer chuck.
Micromachining III
Port 7B, 5 mrad
Microfabrication
15
2. Microfabrication
In the past year the CAMD microfabrication group further reduced internal R&D
efforts related to developing new process skills and material expertise due to a lack of
funding. Main focus was put on tasks associated with funded projects as well as paid
services.
A brief overview of accomplishments in 2005 is provided in the following text and is
complemented by more detailed description in Chapter II and Chapter III.
Research
Throughout the year research in a few dedicated areas was performed focusing on
enhancing the microfabrication service skills. Efforts include:
• x-ray mask fabrication optimizing processing of Silicon-Nitride membrane masks;
large area are now routinely fabricated with high yield and good dimensional control;
• systematic SU8 studies to further improve patterning accuracy of ultra-tall (1mm and
higher) microstructures and initial research using nanoparticle filled SU8 resists for
dedicated functions (higher mechanical stability, electrical conductivity);
Service
The CAMD service team is continuing providing print-shop and other LIGA services
to external customers. In addition, well-defined service modules for substrate preparation,
x-ray masks, electroplating, sample finish, and metrology have been established and are
provided on a regular basis. Generally services provided to academic users and clearly
stated as ‘best effort’ are well-received and give customers some first useful structures to
investigate their performance for MEMS applications. There is a strong interest in LiGA
structures and services for industrial customers. However, working with industry
currently reaches a critical point where requirements for ever higher yield and
reproducibility are expected but the necessary effort for quality control will not be
compensated for. In the coming year CAMD service group will carefully evaluated its
service portfolio and may have to reduce the huge selection of services to a few core
areas with a strong focus on quality assurance. The Clean room and safety staff, as in
previous years, continuously trained new and retrained old users throughout the year
guaranteeing better research results and a safer operation. A major change for the next
year is the introduction of the cost center. Users will now be charged when working at
CAMD. The ‘income’ will be used to support the day-to-day operation, pay for
maintenance and repair, and if possible add new equipment needed.
Program overview
The following overview provides organizational information and will briefly
introduce the main ongoing projects. More details on these and other projects will be
presented in Chapter II and Chapter III.
16
Organizational information
The following CAMD staff members supported the research and service efforts in
2005:
Abhinav Bhushan, Proyag Datta,Yohannes Desta (left CAMD in December 2005),
Yoonyoung Jin, Kun Lian, Zhong-Geng Ling, Changgeng Liu, Shaloma Malveaux, Tracy
Morris, Mark Pease, Varshni Singh, Dawit Yemane .
In addition graduate and undergraduate assistants and student workers were supported by
CAMD funds and joined the team in helping with routine work and research projects:
Tracey Allen (REU student), Lalitha Dabbiru (Southern University), Fareed Dawan
(Southern University), Joshua Fields (REU-student), Sitanshu Gurung (LSU), Jens
Hammacher (FH Chemnitz), Pradeep Khanal (LSU), Evelyn Kornemann
(Fachhochschule Gelsenkirchen), Abhilash Krishna (LSU), Sebastian Mammitzsch
(Fachhochschule Gelsenkirchen), Tyler Mancil (LSU), Etay Rosenzweig (REU student),
Philip Smith (LSU), Liming Sun (LSU), Lena Venkatasami (LSU), Kaiyang Wang
(LSU), Min Zhang (LSU).
Overview of funded projects
The DARPA DSO office is sponsoring a joint project with the University of New
Orleans’ Advanced Research Material Institute (AMRI) and the LSU Health Science
Center, also New Orleans, (Grant MDA 972-03-C-0100) to develop a BioSensor using
magnetic Nanoparticles. The project PI is the CAMD director, Josef Hormes, assisted by
the BioMagneticIC team and progress is reported in several contributions from various
team members. Key partner in this project is NVE Inc. supplying GMR magnetic sensors
and initial collaboration with a group at University of Bielefeld, Germany has started,
too.
New DARPA funding as subcontractor (Contract # 347108) to Sandia National
Laboratory to develop MicroGasAnalyzer sensors (MGA-project) has been granted to
LSU (Prof. Ed Overton, Environmental Studies) and allowed the CAMD group to
continue their efforts in micro GC column fabrication and system integration towards a
handheld ‘GC-sensor’. The Sandia-LSU team successfully met the Phase I milestones
and has received funding for Phase II starting in February 2006. Progress is reported by
A. Bhushan and D. Yemane.
CAMD has also been awarded a subcontract to Southern University’s DoE/NNSA grant
supporting the design and fabrication of novel heat exchangers.
Lastly, the CAMD microfabrication group is a key partner of the recently funded NSF
EPSCoR Center grant (Grant Number EPS-0346411) for LSU’s CBM2 (Center for
BioModular Meso-Scale Systems) and supports a number of CBM2 research projects
with its services.
17
II. CAMD Research Infrastructure; Major Equipment and Facility
Utilization
A. Introduction
This chapter contains description of the research infrastructure from the
standpoint of new equipment and programmatic progress during 2005. Chapter III
contains a more systematic and detailed presentation of the user activities and Chapter
IV contains more detailed information about the staff members.
B.
Basic and Material Sciences at CAMD
Basic and Material Sciences at CAMD are categorized by spectral region and
beamlines.
1. Infrared through soft X-ray beamlines;
There are five beamlines that cover the range from the infrared through the far VUV and
soft X-ray region of the spectrum. The VUV/IR Spectroscopy Staff is under the
leadership of Dr. Eizi Morikawa and consists of him, Dr. Yaroslav Losovyj, and Dr.
Orhan Kizilkaya. We are seeking to expand this staff by at least one scientist. At the
close of 2005, three of the five beamlines were operational; the FTIR, 3-m NIM/Scienta
end-station and 3-m TGM. These three are described below.
a. FTIR spectrometer/microscope beamline which currently allows measurement of
Microspectroscopy to energies as low as 500 cm-1 with spatial resolution of 15x15 µ2.
This beamline was funded as a joint effort by The University of Louisiana at
Lafayette (Departments of Chemistry and Chemical Engineering; the Corrosion Institute)
and LSU CAMD. The beamline was fully operational during 2005 and eight user groups
took advantage of superior brightness of a synchrotron-source FTIR to carry-out
spectromicroscopy at this beamline. Users were from ULL, LSU, Bonn University,
DOW Chemical, University of Nebraska and Tulane.
On June 15, 2005, a workshop was held and attended by 31 researchers interested
in using the FTIR Beamline. The speakers were Lisa Milner from LNLS, Mike Martin
from ALS and Orhan Kizilkaya, the CAMD FTIR Beamline Manager. Attendees were
from LSU, Tulane, ULL, SLU, Southern University and Exxon-Mobil.
b. The 3-m NIM and Scienta 200 end station have been waiting for the dedicated
Scienta end station to be operational for the entire beamline to be considered an
operational beamline. The 3-m normal-incidence-monochromator has been transmitting
high-resolution VUV radiation (4 eV – 40 eV) since 2002. Last year (2004) a concerted
effort was made to bring the commercial Scienta 200 end station into operation. The
VUV Group worked to accomplish this under the lead of Dr. Yaroslav Losovyj. Late in
the year, 2005, it was discovered that a modification (to the magnetic shielding) made
earlier caused damage to the sample manipulator. At the close of 2005, this problem was
being rectified by Dr. Losovyj.
During the limited time that the 3-m NIM was used there were a total of six users
from LSU, University of Nebraska, North Dakota State University and the University of
18
Lviv. Three publications resulted from work on this beamline in 2005.
publications were primarily a result of the early work done in 2004.
These
c. The 3-m TGM beamline continued to be the “work-horse” beamline in the VUV
spectral region. The manager of this beamline is Dr. Yaroslav Losovyj. There were a
total of 25 users of this beamline and Chapter III contains the reports from users of this
beamline. Users came from LSU, Tulane, Xavier of New Orleans, UNO, Louisiana
Tech, University of Nebraska, North Dakota State University, plus several universities
from outside the US. There were 15 papers published from measurements done at this
beamline.
d. The two VUV beamlines not in operation during 2005 are the 6—m TGM and the
PGM. The 6-m TGM, as a beamline, was operational; however, there were problems
with the end stations that were to be used on this beamline. It is hoped that this problem
will be remedied during early 2006. The PGM was completely modified to a varied-linespace-grating high resolution, high-flux beamline during 2005. The 2004 CAMD
Annual Report, Chapter II, provides plans and theoretical operational parameters of
this modified beamline. At the close of 2005, all of the optics and mechanical
components were on hand to complete the beamline (which was accomplished by March
2006). The components remaining include a front-end shutter that will permit selection
of right, left and plane polarized radiation from the CAMD storage ring.
e. Funding received for beamline modification and end station acquisition:
• Acquisition of a photo-electron electron microscope PEEM ($130,000).
• Design, fabrication, installation and commissioning of a dipole chamber which will
allow 50 mrad vertical acceptance of synchrotron at port 1A, the port that supplies
radiation to the FTIR beamline. This should allow far IR as well as higher resolution
spectroscopy to be performed at this beamline ($125,000)
• Fabrication, installation, and commissioning of a second tail at the 3-m NIM
beamline. This will allow experiments not involving the dedicated Scienta end
station to be performed. Equipment to allow utilization of the highly plane polarized
radiation transmitted by this second tail is also included in the grant ($195,000).
2. The Protein Crystallography Beamline;
The Protein-Crystallography Beamline and Program were managed by Dr. Henry
Bellamy and are part of the Gulf Coast Protein Crystallography Consortium (GCPCC);
description at the web site http://www.camd.lsu.edu/gcpcc/GCPCChome.htm . This
beamline is attached to one of the CAMD 7-tesla super-conduction-wiggler ports. A full
description of the beamline’s capabilities can be found at the above web site.
The utilization statistics for 2005 are:
19
Protein Crystallography Beamline Utilization Statistics
•
•
•
•
•
•
•
•
•
•
•
•
•
Total available for user beam
216 days
Actually used by users
91 days
Outside users
18 days
Lost due to beamline equipment failure
14 days
Facilities (includes multilayer installation)
57 days
Unused
54 days
Beam time used by 15 groups
15 groups
From GCPCC (1 FedEx)
12 groups
Outside GCPCC (1 FedEx)
3 groups
Improvements in the operation of the beamline include the following;
New version of beamline control software (MX) configured and installed.
• Can control picomotors and other devices not controlled by previous version.
• Faster response.
Beamline GUI partially rewritten and improved.
Beamline web page updated and expanded.
PCs upgraded to Fedora Core 4.
“FedEX” program initiated.
Wiggler characterized by accelerator group.
Compumotor controllers reprogrammed to have better backlash and acceleration
values.
• Positions more reproducible.
• Position not lost when hitting limit switch.
CCM configuration in MX changed to make energy changes more accurate.
MLM configured in MX to move 2nd multilayer.
MAR dtb modified to provide external ion-chamber readout.
Problems remaining at close of 2005 include the following;
Source point not known exactly.
• Beam at ~1mrad horizontal angle to beamline.
• Vertical position is probably OK.
Can’t measure flux along beamline before hutch.
Flux can vary from fill to fill. Flux at sample does not scale linearly with ring current.
(source point? optics?)
20
•
•
•
•
•
•
•
Multi-layer-mirror monochromator (MLM) not operational.
Focus much larger than sample crystals.
Mar data-collection software has bugs.
• Dose mode unreliable.
• Occasional blank frame.
• GUI has bugs.
• Spontaneous slit movement.
No automatic energy changing for MAD.
Users not taking all of time offered.
Few “outside” users (situation improving).
Wet lab not completed.
3. X-ray beamlines; Spectroscopy, scattering, tomography and powderdiffraction;
The X-ray materials and basic sciences program was directed by Dr. Roland
Tittsworth from 2000 through 2005. The beamline infrastructure consists of five
beamlines, each equipped with an X-ray monochromator. The following table gives the
beamlines and each of their status and location on the storage ring. The reader is referred
to the 2003 CAMD Annual Report for diagrams and operational characteristics of each
beamline; the microtomography beamline description is referenced in its section (web
site that is very informative).
CAMD X-ray Beamlines; Location and Status, 2005
Beamline
Port
Status
Double Crystal Monochromator
5b
Operational
X-ray Micro-Probe
5a
Being Upgraded
Small angle scattering/Grazing
Incidence X-ray Absorption Fine
Structure
6a
Monochromator problem
fixed
Powder Diffraction
7a
Installation/commissioning
Completed by May 2006?
Microtomography
Wiggler
Tomography part working;
Channel-cut crystal
monochromator removed
21
The X-ray Basic and Materials Sciences staff members during 2005 were:
David Alley
Electronic equipment support
Chris Bianchetti
Maintaining/building beamlines, supporting
users
Kyungmin Ham
In charge of tomography beamline
Henning Lichtenberg
Renovating X-ray microprobe
Rusty Louis
Electronic equipment support; building and
maintaining beamlines
Vadim Palshin
Maintaining/building beamlines, supporting
users, beamline scientist
Roland C. Tittsworth
Beamline scientist; leader of X-ray group till
December 20th, 2005.
Amitava Roy
Beamline scientist; interim leader of X-ray
group
a. The X-ray Microtomagraphy Beamline is attached to a port on the CAMD 7-tesla
super-conducting wiggler. The User Group for this beamline is currently limited as the
beamline remained in an alignment/commissioning phase during 2005. Users included:
Chemistry- Les Butler; polymer blend
Civil and Environmental Engineering- Clint Willson; flow in porous system
Medical Physics- Kenneth Hogstrom; radiation dose measurement
Kenneth Matthews; phase contrast
Biology- Dominique Homberger: hooves, cat claw
Geology- Gary Byerly: volcanic glasses
The beamline has a tandem-mounted pair of monochromators; a multi-layer-mirror
monochromator for low-resolution spectroscopic contrast measurement of tomography
and a high-resolution channel-cut crystal monochromator for high-energy X-ray
absorption spectroscopy. At the close of 2005, it was decided to remove the channel-cutcrystal monochromator because of poor characteristics associated with its throughput.
The decision was to use the beamline only for tomography until a better monochromator
for high-resolution spectroscopy studies could be obtained. Upgrades to the operation of
the beamline include:
• Data collection method:
• Semi-automatic data collection; ring current < 70mA, data collection will be
suspended
• Greek golden ratio: efficient way to sample and obtain data even if incomplete set
• Humidity chamber constructed: biological samples for long acquisition times
The web site for microtomography at CAMD; beamline description and diagram, samples
of experimental results and discussion of how to become part of the user team can be
22
found by going to http://www.camd.lsu.edu/beamlines.htm and scrolling down to
“Tomography” and then clicking as indicated.
The beamline has been brought into operation by the beamline manager, Dr.
Kyungmin Ham, the Principal Investigator and Researcher, Professor Les Butler from
LSU Chemistry, and the CAMD Vacuum/Mechanical Group under the direction of Kevin
Morris.
b. The Double-Crystal-Monochromator X-ray-Absorption-Spectroscopy Beamline is
mounted on a CAMD bending magnet and is the “workhorse” beamline for X-ray
absorption spectroscopy (XAS) at CAMD. The important characteristics of this beamline
are:
-Port 5b (bending magnet 5 dipole chamber, port b)
-Lemmonier-Bonn double crystal monochromator for XAS
-Differential ion pump immediately upstream of monochromator (UHV upstream of DIF
with no Be window).
-Kapton window downstream of monochromator, before end station (to enable low
energy operation to ca. 1keV.
-beamline vacuum valving and pumping system to allow rapid (usually < 2hr.) crystal
changes.
-various crystal sets are available, allowing 1.3 keV -14 keV operation
-XAS detection: ion chambers, Lytle fluorescence, TEY
-Canberra 13 element Ge diode array detector in routine operation
-Photon Beam Position Monitor,
The DCM beamline was available for general users during 2005 and generally was
“overbooked” for user time. The users of the DCM in 2003 have supplied reports of their
research (Chapter III).
c. The X-ray Microprobe Beamline was operated successfully as early as 1999 and had
been utilized for Microspectroscopy (spatial resolution smaller than 50x50 µ2. It also
was used to help relieve the pressure on the DCM XAS beamline, which, as mentioned, is
generally “overbooked.” The beamline also has been utilized to obtain excellent XANES
spectra. Over time, the Kirkpatrick-Baez mirror system used for focusing and the rather
stark sample handling system fell out of use and the beamlime became a simple
EXAFS/XANES beamline. In 2004 it was decided to upgrade the microprobe end station
extensively. Improvements include a steel vacuum chamber (usually to be used with He
atmosphere) and remote mirror-alignment system. By the close of 2005 this beamline
was near operation with tasks such as routing control cables through vacuum feedthrough ports remaining to be completed.
d. The Small Angle Scattering/Grazing Incidence X-ray Absorption Fine Structure
(SAX/GIXAFS) Beamline is well behind schedule for being put into operation.
Problems with the double-crystal monochromator and the beamline control system have
prevented this beamline from being brought to a point at which true commissioning can
begin. Part of the problem has been associated with the staffing in the Basic Sciences
Group; for over 6 months, there were no technical staff members available for
programming controls and working with the monochromator. A resignation combined
with the “loan” of a crucial staff member to Microfabrication for an extended period
(which continued to become more extended) caused work to come to a standstill. This
23
lack of staff also slowed work on the X-ray Microprobe, Powder Diffraction and the
newly modified VLSGM beamlines.
The SAX part of this beamline is now in a commissioning phase as the control
system and monochromator problems were remedied near the close of 2005. The
GIXAFS part will be commissioned following the beginning of standard operation of the
SAX end station.
e. The Powder Diffraction Beamline has been under construction and the mechanical
components (double-crystal monochromator, goniometer, vacuum and radiation-safety
systems) have been assembled in the double-hutch enclosure. A compatibility problem
between the commercial control system and the goniometer stepper motors was a major
roadblock at the end of 2005. Optimistic projections are for May, 2006 operation of this
beamline which already has a number of anxious potential users.
24
C. MEMS/LiGA Services at CAMD in 2005
Editor: Jost Goettert
Group Leader: Yohannes Desta
Co-Workers: Proyag Datta, Yoonyoung Jin, Zhong-Geng Ling, Varshni Singh,
Fareed Dawan, Feng Xian
Summary
Since 2001 the MEMS/LiGA Services Group at CAMD has been provided a multitude
of MEMS related services to the MEMS community primarily at LSU but also the wider
LIGA community in the world. The group has pursued this mission and its “customers”
today span the globe from Asia, Europe, and the United States. Thin film deposition;
LIGA substrates; X-ray masks; X-ray lithography; electroplating of Ni, Ni-Fe, Cu, and
Au; mold insert fabrication; hot embossing; and complete LiGA prototyping are all
provided by the group as services.
In the past years research efforts required to develop new processes and transition
them into services have been funded through R&D projects within the DARPA grant. In
2005 this funding was no longer available and consequently a number of R&D projects
including larger format membrane X-ray masks, sub-micrometer X-ray lithography, SU-8
ultra-thick processing and high throughput, hard X-ray (wiggler) lithography couldn’t be
continued. The only project that was completed was nickel-iron electroplating utilizing
the already installed Technotrans electroplating facilities.
The following sections briefly summarize the main activities in 2005 and provide an
overview over our services. It should also be mentioned that the group experienced a
number of technical challenges related to high yield, high quality production of LiGA
parts and, together with the fact that Yohannes Desta, the group leader of the service
group accepted a new position in January 2006, is currently undergoing a reorganization
and consolidation process of its activities. This will most likely result in a reduced
number of services and a tighter quality control program. The team members will also
continue their efforts for strategic partnerships and joint proposals ensuring some R&D
funding to develop new fabrication skills.
Overview of currently provided services
Tables I and II summarize the base processes and process modules offered by the
MEMS/LiGA Services Group at CAMD. All services are offered to customers on a pay
basis. These services are mostly comparable to the ones offered in 20041 with some
minor adjustments marked at the bottom of each table.
1
Y. Desta et al: ‘MEMS/LiGA Services at CAMD in 2004’, CAMD Annual Report 2004.
25
Table I
Services provided by the CAMD Service Group in 2005
Service Type
Materials
Specifications
Contact person
Cr, Au, Cu, Ni, Ti 0-2000 A
Yoonyoung Jin
E-beam deposition
Surface
modification
Ti
2 µm
Yoonyoung Jin
Printshop (X-ray
exposure)
PMMA
SU-8(1)
1-1000 µm
1-3000 µm
Zhong-Geng Ling
Electroplating
Ni
Cu
Au
Ni-Fe
1-5000 µm
1-500 µm
1-100 µm
1-500 µm
Varshni Singh
Varshni Singh
Varshni Singh
Varshni Singh
Hot-embossing
PMMA, PC
CD > 10 µm
Aspect-ratio 10:1
Proyag Datta
Flycutting
PMMA, SU-8
10-1000 µm
Zhong-Geng Ling
Metrology:
Any
< 4“ DIA
Varshni Singh
SEM
Varshni Singh
EDAX
Any
Any
Varshni Singh
WYKO
(1)
Su-8 substrates are to be provided by customer, CAMD is not offering application of thick
(>500µm) SU-8 resists at this time.
Table II
Process modules offered by the CAMD Service Group in 2005
Module Type
Materials
Specifications
Contact person
PMMA
100-1000 µm
Varshni Singh
UDXRL
Substrates
X-ray masks
Au on Be, C, SiNx,
or Kapton
5-40 µm Au thickness,
5 µm CD
Yoonyoung Jin
Jost Goettert
Proyag Datta, Jason
(1)
Guy
(1)
Machined mold inserts made from Brass is a rapid prototyping service provided through
CBM2/Jason Guy; while evaluating the customer’s design and specification CAMD staff is
recommending the most suitable fabrication approach to make a mold insert. Precision machined
mold inserts are especially attractive for microfluidic applications and design iteration.
Mold inserts
Nickel
Brass (machined)
5 µm CD, 4“-6“ DIA
20 µm CD
Table III provides a summary of all the services completed in 2005.
26
Table VI
Summary of service jobs completed in 2005 and compared with service jobs in 2004
Service type
Customers
Number of Jobs 2005 Number of Jobs 2004
Thin film deposition
LSU, Industrial
519 (1591 substrates)
220 (800+ substrates)
UDXRL Substrates
Industrial
5 (27 substrates)
9 (47 substrates)
X-ray masks
LSU, Industrial
21
19
Mold inserts
LSU, Industrial
4
4
Electroplating
LSU, Industrial
46 (112 substrates)
11 (34 substrates)
X-ray Exposure
LSU, Industrial
598 (661 substrates)
52 (202 substrates)
Hot embossing
LSU, Industrial
57 (930 substrates)
26 (200+ substrates)
Metrology
LSU, Industrial
30 (105+ samples)
NA
Fly cutting
Industrial
22 (191 substrates)
NA
Polishing
Industrial
4 (16 substrates)
NA
Overall the number of service jobs has increased and a few new services requested by
our customers have been added. The services related to x-ray LiGA remain on a similar
level compared to 2004 indicating a constant demand in the US market. It should be
noted that there is an increasing demand in the German market due to customers
requiring ultra-precision microparts in special materials and federal funding enabling the
research groups at IMT/Karlsruhe and BESSY to setup up higher throughput, high yield
manufacturing capabilities.
Ni-Fe Alloy Electroplating by Varshni Singh
A large number of MEMS applications (actuators and sensors) incorporate magnetic
alloys such as electrodeposited Ni-Fe alloy. This alloy also has great potential for high
temperature mold insert application as well as high strength and enhanced wear resistance
microstructures. In the present study Ni-Fe alloy samples, with Fe content 5 and 15 at%,
were electrodeposited using a plating bath prepared by mixing nickel sulfate and iron
sulfate. The samples were electrodeposited at a high current density to obtain a high
deposition rate (≥20 µm/hr). Several 500 µm thick samples were deposited in
polymethylmethacyrlate (PMMA) molds structured by deep X-ray lithography on 100
mm-diameter silicon wafers. Titanium, wet-oxidized to improve the adhesion to PMMA,
was used as an electroplating base on the silicon wafers. Uniformity of the composition
of samples was studied along the thickness using an EDS (see Fig.1). EDS and SEM
results show that Ni-Fe alloy with Fe content at least up to 15% can be plated to fabricate
thick MEMS structures (aspect ratio as high as 30) with good uniformity across a 1mm
tall structure. The quality of deposition was comparable to Ni electrodeposited structures.
Micro-hardness tester was used to measure the hardness of the samples to study the effect
of variation in composition on mechanical properties of the alloy. Hardness was found to
be increase with increase in content of Fe. Tribological behavior of the electroplated
samples was analyzed using Pin-on-disc type tribometer, with pin material alumina.
Discs with thickness of more than 250 µm were electroplated and used for wear
27
experiments. Wear results show that harder alloy with higher Fe content has lower
friction coefficient, Fig.2 and higher wear resistance. 2 Efforts in the future will explore
the chances of replacing regular Ni mold insert with higher quality Ni-Fe mold inserts.
Fe: 14.48%
Fe: 15.11%
a
c
Fe: 14.99% Fe: 15.41% Fe: 15.37%
d
b
Figure 1: (a) EDS measurements showing composition along the height of a 1 mm tall
structure, (b-d) Examples of micro-gears plated with Ni-Fe 15% solution.
Pin Materials: Alumina
Pin diameter: 9.5 mm
Speed: 10 m/s
Load: 100 g
Friction Coefficient (µ)
1.0
Ni-Fe 15%
Ni-Fe 05%
0.8
0.6
0.4
0.2
0
100
200
300
400
500
Distance (m)
Figure 2: Wear results for the Ni-Fe electroplated alloy.
2
V. Singh, Y. Desta, Y. Jin, J. Goettert, ‘Development of thick Electrodeposited NiFe MEMS Structures
with Uniform Composition’ Louisiana Materials and Emerging Technologies Conference – December 1213, 2005, Ruston Louisiana.
28
User statistic – x-ray lithography exposures by Zhonggeng Ling
The total number of exposed substrates at all beamlines stayed approximately constant
compared to 2004. The two charts in Fig. 3 below represent the distribution of exposed
substrates by user group (CAMD, External, LSU) at all four beamlines for the years 2004
and 2005. The number of substrates exposed for external users increased primarily due to
the strong interest from HT Micro (see Fig. 4, distribution of substrates from external
users). The CAMD total number of exposed substrates dropped slightly from 280 to 245.
The majority of these substrates were for two funded projects (GC, see contribution this
Annual Report by A. Bhushan and V. Singh) with no active R&D program to further
enhance the X-ray lithography capabilities.
External 50.6%
39% External
17.5%
LSU
10.5%
LSU
CAMD
43.5% CAMD
38.9%
Distribution of all substrates exposed in
Distribution of all substrates exposed in 2004; 2005; total number of substrates was
630.
total number of substrates was 650.
Fig. 3: Distribution of substrates exposed in 2004 (left) and 2005 (right) among user
groups.
HT Micro
56.7%
Fig. 4:
Creatv
MicroTech
1.57%
6.9%
Honeywell
16.9%
Sandia
Distribution
of
External
User
Substrates in 2005; total number of
substrates is 319.
17.9%
MEZZO
The slight increase of external user substrates demonstrates a certain ‘commercial
interest’ in x-ray lithography. While Mezzo’s focus has shifted to making ‘product’
prototypes by addressing packaging and assembly issues of micromachined parts HT
Micro was still in an exploratory mode trying a number of different designs for various
applications.
The charts in Fig. 5 compare the accumulated exposure dose for all samples exposed.
The left chart represents data for 2004 with a total exposure dose of 1.34 x 107 mAmin,
the right one the corresponding information for 2005 with a total exposure dose of 2.105
x 107 mAmin. The increase by approximately 56% is mainly from the high number of
29
thick PMMA samples exposed for the GC project. It is noteworthy that the interest of the
LSU community in using x-ray lithography for their research projects is continuously
declining over the years and shifting to alternative fabrication methods including rapid
prototyping using precision machining and SU-8 UV lithography.
External 26%
External
28.6%
LSU
18.1%
CAMD
65%
55.9%
CAMD
Distribution of total exposure dose at all 4
beamlines among main user groups in 2004.
6.36%
LSU
Distribution of total exposure dose at all 4
beamlines among main user groups in
2005.
Conclusions
2005 has been another productive year for the MEMS/LiGA Services Group at
CAMD. The group has been able to fulfill its main objective of facilitating LIGA related
research at LSU and the world-wide LIGA community by providing the vast processing
expertise of CAMD’s personnel as services. The trend from the previous years continues
in that only few projects demand the full x-ray lithography capability and often use
alternative MEMS approaches, especially for R&D efforts. The CAMD Service Group
also experienced limitation in its efforts to enhance yield and quality. While there are
many technical details impacting these efforts it is very often also a question of costs and
the lack of customer (financial) commitment to sponsor the necessary R&D efforts
required to better understand and execute the processes. All these things considered the
coming year will be very challenging and the CAMD group has to carefully evaluate its
operation.
Acknowledgements
The members of the services group would like to thank all customers and users for
their interest and support of their activities. Special thanks are given to our ‘active’ users
for their interest in working at CAMD and sharing their expertise and knowledge, which
ultimately helps to enhance CAMD’s service capabilities.
30
D. CAMD Cleanroom
The CAMD Cleanroom is currently undergoing major changes in operational structure in
order to better support use of the microfabrication capabilities for LSU, CAMD, and
other users. The cleanroom managing team is committed to providing infrastructure for
standardized processes and research for device development. This infrastructure includes
environment, equipment, and supplies maintenance along with education and training.
User Information
The number of people actively using the cleanroom remained steady, at 63, from 2004 to
2005. The majority of cleanroom users are CAMD staff and LSU students from the
Mechanical Engineering and Electrical and Computer Engineering departments, as
indicated in Fig. 1. Increased participation from students of Prof. Fred Lacy’s group at
Southern University’s Electrical Engineering department and a new PI from LSU’s
Mechanical Engineering department, Prof. Sunggook Park, are also progressing in their
research utilizing CAMD facilities. Also, CBM2 (Center for BioModular Multi-Scale
Systems) is supporting a total of 15 researchers on various projects, making it the largest
external project. In Fig. 1, however, they are listed with the individual PI of the project
and not with CBM2.
Number of Active Users per Group
25
Number of Users
20
15
2004
2005
10
5
A
jm
er
a
LS
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EE
A
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IU
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O
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is
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EE
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EE
an
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Pa
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rk
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LS
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La
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cy
SU
EE
0
Department / Group
Fig 1. Chart of active cleanroom Users and their affiliations.
Operations
Cleanroom activity is monitored from information on machine use, which is derived from
the database created from login of machines inside the cleanroom. Fig. 2 indicates
machine use by each User group. CAMD continues to be the cleanroom’s most active
31
group. However, Fig. 2 also indicates individuals of many external groups work inside
the cleanroom more frequently than CAMD’s staff members. For example, one of LSU’s
Mechanical Engineering groups, led by Prof. Wanjun Wang, uses the equipment half as
much as CAMD Service and Research (55%) but with ¼ the staff size of CAMD’s.
CAMD’s research, funded through external projects, focuses on device integration and
service. Service, by definition, uses standardized processes, which are highly efficient.
The chips for device integration are designed such that processing demands fall within
more routine, thus reliable, procedures and process parameters. This trend reduces the
amount of lab time required inside the cleanroom. Processing research is relatively more
common in the projects of external academic users, which tends to result in increased lab
time.
500,000
Microfabrication Machine Use in 2005
Sum of Duration (Min)
CAMD Service + Research
= 874,803 mins
450,000
Duration of Machine Use (min)
400,000
350,000
300,000
Start Year
250,000
2005
200,000
150,000
100,000
50,000
0
AEE
CHEM
EWEI
MEM
MEN
Mezzo
NANO
WANG
MGA
SUEE
AccountNo
Fig. 2. Chart showing machine use for each group in 2005. For clarity, CAMD
microfabrication staff machine use is not graphed, but is noted. Groups/users using
machines less than 1500 minutes per year were excluded from the chart.
Fig. 3 indicates the change in machine use from calendar years 2004 to 2005, organized
by User group. Total machine use dropped 11% in 2005, relative to 2004. Usage was up
during the first five months of 2005, according to the chart in Fig. 4. The decrease began
in June and lasted through the summer months, primarily due to reduced activity by the
REU (Research Experiences for Undergraduates) summer students. In past years, an
average of 6 REU students working on process development accounted for significant
cleanroom activity. In 2005 only 3 REU students performed microfabrication research
projects, and these primarily required the use of machines located outside of the
cleanroom.
32
Percent Change in Machine Use 2004 to 2005
300%
Total Machine Use Change
= -11%
250%
200%
150%
100%
50%
MicroGas
Analyzer
Wang LSU ME
Nanofabrication
CAMD
MezzoTech
Nik LSU ME
Murphy LSU ME
Khon LSU ME
Kelly LSU ME
Feldman LSU EE
Wei LSU EE
Choi LSU EE
CAMD
Chemistry LSU
-100%
AMRI UNO
-50%
Ajmera LSU EE
0%
Department / Group
Fig. 3. Chart indicates the change in amount of time of machine use 2004 - 2005.
350,000
Monthly Machine Use in 2004 and 2005
300,000
250,000
200,000
Start Year
2004
2005
150,000
100,000
50,000
0
1
2
3
4
5
6
7
8
9
10
11
12
Start Month
Fig. 4. Chart comparing monthly total machine use in 2004 and 2005. The months are
listed chronologically, such as January as month 1, February as month 2, etc.
33
Reduction of machine use during the fall months, as indicated in Fig. 4, is attributed to
the disruptions from Hurricanes Katrina and Rita, which nearly destroyed UNO, New
Orleans, and western Louisiana in August and September. Many factors contributed to
reduction of research and facility operations in the months following the hurricanes.
CAMD operations decreased or were halted entirely during the local power outages
resulting from both Hurricanes. Additionally, the community disruptions contributed to
less focus on lab work and more on personal and civic obligations. Many LSU campus
changes affected LSU PI’s and researchers, due to the influx of displaced students and
researchers from New Orleans and the Gulf Coast. Regrettably, five researchers from
UNO’s AMRI (Advanced Materials Research Institute) are presumed permanently
displaced and have not worked at CAMD since the hurricanes.
50,000
Annual Machine Use 2004 and 2005
40,000
30,000
Start Year
20,000
2004
2005
10,000
Tencor Alpha-Step 50 Surface
Profiler
Quintel UL7000TL Mask Aligner /
Exposure System
Oriel UV Exposure
Station/Aligner
HITACHI S-4500II Field Emission
SEM
Headway Research PWM101
Light Duty Photoresist Spinner
Bransen Plasma Asher
0
Machine Name
Fig. 5. Chart comparing time of use for common machines 2004 and 2005.
Fig. 5 indicates the use of a few processing and metrology machines. As noted in the
previous two graphs, usage was down approximately 11% overall.
Cost Center
A cost center was introduced in November 2005 to the academic community and anyone
else interested. CAMD has worked for many years to create a cost center in order to
allow all Users (including CAMD staff) to contribute their portion of used resources to
the operation and maintenance of the facility. The cost center is a fee schedule in which
rates for each piece of equipment were derived using CAMD’s expense and usage history
according to guidelines provided by the university. Strict guidelines for rate derivation
were provided by PS-103 through LSU’s department of Budget and Planning. Jim Bates,
Director of Sponsored Programs, approved the initial rates and implementation of the
34
cost center in October. Rates are subject to yearly adjustment in order to ensure best
estimates of generated revenue, which are to be kept at or below cost.
During November’s meeting, there were concerns about the ability of currently funded
projects to afford the increase in cost of research, since work at CAMD’s User facility
has historically been free of charge to all Users. The approved rates will apply during a
transition period of 3 months, starting January 2006, in which projects will be invoiced
but not charged. A subsequent meeting in March 2006 will be held to reevaluate costs
and discuss changes that may be needed for affordability. For a historically-accurate
estimate of yearly costs for cleanroom machine use, Fig. 6 indicates costs for a few
different groups for the past two years.
Cost Center Rates Applied to Past Usage
$350,000.00
$309,286
$300,000.00
$250,000.00
$218,596
$200,000.00
$180,629
2004
2005
$150,000.00
$128,214
$100,000.00
$67,736
$50,000.00
$31,112
$15,152$19,087
$5,833 $4,700
$0.00
Wang
Murphy
Soper
CAMD + Service
MGA
Group Leader
Fig. 6. Costs of using cleanroom equipment for various PI’s if current rates were applied
to 2004 and 2005 machine usage.
A new project proposal form was devised in January 2005 that required new Users (and
updates of existing Users) to investigate their project in greater depth, which improved
User awareness of project details and timelines. Due to the cost structure implementation
starting beginning 2006, CAMD will no longer judge project preparation and student
knowledge. CAMD will depend solely on the new User training sessions to prepare
Users on basic chemical knowledge, safety, machine use, and, in the near future,
microfabrication basics. Thus, beginning January 2006, the project proposal form will be
replaced by a simplified Project Routing Sheet, which is used to track basic information
35
on the PI and project. A User Sheet starts New Users on the training path and correlates
existing Users with the project(s) he/she is working.
Many changes and improvements are expected over the next year as CAMD implements
the cost center for all microfabrication equipment. More online training and information
will improve communication and streamline information for Users and visitors.
Improved device tracking will help to predict costs and maintenance schedules. And an
overall increase in User satisfaction with the facility is expected as the CAMD staff
attempts to serve each User in a more efficient and customer-oriented manner.
Training
Specific additions to the Cleanroom Training module were required by the federal
department, EPA. Instruction of the newly implemented HMIS (Hazard Materials
Identification System) hazard specifications was added. This system is additionally
mandated for use campus-wide along with the currently used NFPA (National Fire
Protections Association) system. HMIS includes the code specifications for health risks,
safety precautions, and combinations of the two, as well as specific designation of gloves.
Procedures that were guided by the CAMD’s Safety Committee were also added to
Cleanroom Training to further ensure the safety of cleanroom workers. These procedures
and instructions were related to chemical spills, hood use, broken glass, accidents and
incidents reporting, and chemical labeling. Additionally safety and medical supplies
were added to the cleanroom burn protocol and neutralizing capabilities.
The first Annual Cleanroom Refresher was held in the spring. Instruction on the new
safety and cleanroom protocols were included, along with etiquette and operational
reminders to Users on specific issues that were subsequently improved upon by the
Users.
36
User Reports and
User Activities
37
Basic and Material Sciences
Spectroscopy
VUV
38
The valence electronic structure of Gd@C60
A.N. Caruso1, P. Jeppson1, Robert D. Bolskar2, R. Sabirianov3, P.A. Dowben4 and Ya.B.
Losovyj5
1
Center for Nanoscale Science and Engineering, North Dakota State University,
Fargo, ND 58102 (UNL-AC1205)
[email protected]
2
3
4
5
TDA Research Corporation, Wheat Ridge, Colorado 80033
Department of Physics, University of Nebraska, Omaha, NE 68182-0266
Department of Physics & Astronomy and the Center for Materials Research and
Analysis, University of Nebraska, Lincoln, NE 68588-0111
Center for Advanced Microstructures and Devices, Louisiana State University, Baton
Rouge, LA 70806
Endohedral fullerenes and their solids represent a class of molecules and materials
with extraordinary physical, optical, electronic and magnetic properties. In general, fullerene
materials fulfill the ever surging “nano” interest where size and new phenomena based
applications drive funding. For the endohedral fullerenes specifically, applications such as
MRI contrast agents and magnetoelectric memory are pushing the present applied interest,
while metal-organic synthesis and electronic structure experiment and theory are pushing the
basic science. Some of the questions regarding endohedral molecules are: how the central
atom (typically a metal) hybridizes with its surrounding cage; how many electrons transfer to
the cage; how does the cage existence perturbs the nuclear moment; and, what are the
(intermolecular) interactions between molecule-molecule and molecule-substrate.
Figure 1. Image produced from a density
functional calculation of Gd@C60. Note that the
metal is offset from the central cage position (due
to an image charge) which results in a net dipole.
There has been a good deal of work on the M@Cx molecules, with M= Be, Mg, Ca, Li, Na,
K, La, Ce, Gd, Tm and x=70,74 and 82 but the M@C60 are more difficult to synthesize,
especially for endohedral lanthanides. For Gd@C60, this is the first electronic structure study,
from the only known synthesis by Bolskar et al. [1]. Because of the reduced diameter,
relative to C82, the above interaction questions attain greater precedence and magnitude;
hence, comparison of Gd@C60 with prior work on Gd@C82 and entirely new answers to the
above questions represent the foundation for completing this electronic structure study.
39
Figure 2. Thickness and polarization
dependent photoemission of Gd@C60
adsorbed on Au(111). The TOP
spectra represent clean gold, while
the MIDDLE and BOTTOM spectra
show
progressively
thicker
adsorptions of Gd@C60, but not so
much that the gold features are
suppressed (i.e. less than 25Å). The
red-dots indicate p polarization,
while the black-solid line indicates
s+p incident light polarization.
The thickness dependence is shown in Figure 2 with a suppression of the gold
features and a growth of the carbon 2p. The Gd 4f orbitals, whose position for metallic Gd is
usually -7.8 eV are now shifted away from the Fermi level due to the cage hybridization.
The HOMO and HOMO-1 for C60 that are usually located at -2 and -3eV, and an expected
Gd state close to EF are not visible, possibly due to the extremely thin nature of the adsorbed
layer. The polarization dependence is particularly interesting, as one would not expect an
anisotropy in the transition dipoles of the carbon 2p. Future work with other substrate
surfaces and high energy photons will allow for a more rigorous determination of where
exactly each of the orbitals is lining up and what the valency of the endohedral metal is. For
now, we can only speculate to say that the enhancement with p polarization is indicative of a
d-f hybridization between the Au 5d and Gd 4f or that the Gd is offset in the cage relative to
the substrate in the vertical direction so as to induce an electric dipole normal to the surface.
The above experiments were completed at the Center for Advanced Microstructures
and Devices synchrotron radiation facility in Baton Rouge, LA on beamline 6B1. This work
was supported by the Defense Microelectronics Activity (DMEA) under agreement
DMEA90-02-2-0218 and the NSF through ND EPSCoR grant EPS-0447679. We would
especially like to thank TDA research for proving the Gd@C60 powder.
[1] Robert D. Bolskar, Angelo F. Benedetto, Lars O. Husebo, Roger E. Price, Edward F.
Jackson, Sidney Wallace, Lon J. Wilson and J. Michael Alford, J. Am. Chem. Soc. 125
(2003) 5471
40
Photoemission studies of adsorbed Mn(thiobenzoate)2
Shengming Liu1, D.L. Schulz1, Ya.B. Losovyj2 and A.N. Caruso1
1
2
[email protected]
Rouge, LA 70806
Transition metal centered benzoate complexes are of traditional interest toward
optoelectronic and other charge transfer related applications. Thiobenzoato complexes
with metals in the 2+ state are known to exhibit variable coordination numbers [1] which
coupled to variable isomer/tautomer forms makes for a diverse set of spin states and
charge localization.
S
C
O
Mn
O
C
S
Figure 1. One of the two isomers of bis(thiobenzoato)manganese(II). There are also two
tautomers which provide non-coordinating but protonated bonds on the oxygens or
sulfurs. Our intention here was to synthesize, adsorb and study the isomer above.
Our intention here was to study the valence electronic structure of monolayer and greater
adsorptions of the transition metal complex, bis(thiobenzoato)manganese(II) as shown in
Figure 1. It is also of interest to determine the role played by the benzene rings with
regard to substrate interactions (orientation, coordination) as well as neighbor influence
on multilayer packing.
(b)
Intensity
Intensity (a.u.)
(a)
-35 -30 -25 -20 -15 -10 -5
0
-35 -30 -25 -20 -15 -10 -5
0
E-EF (eV)
E-EF (eV)
Figure 2. Thickness dependent (a) and polarization dependent photoemission (b) of the
molecule shown in Figure 1 adsorbed on Au(111). Both spectra were taken with 90 eV
incident light and the photoelectrons were collected normal to the surface.
41
The thickness dependent photoemission shown in Figure 2a demonstrates the rise of the
benzoate molecular orbitals and the reduction of gold states as the thickness of the
adsorbate increases. At the thickest adsorption (blue) where the gold 5d features are
completely suppressed, a strong insulating character arises with the HOMO at a position
greater than 2 eV below the Fermi level. Future investigations using electron spin and
circularly polarized photons with temperature dependence to probe the candidacy of this
system as a Mott-insulator induced by the existence of magnetic coupling.
The above studies were completed at the Center for Advanced Microstructures
and Devices synchrotron radiation facility in Baton Rouge, Louisiana on the 3m torodial
grating monochromator beamline 6B1.
[1] Rema Devy, Jagadese J. Vittal and Philip A.W. Dean, Inor.Chem. 37 (1998) 6939
42
The Work Function and Conductivity of Doped PEDOT-PEG
Copolymers
A.N. Caruso1, P. Jeppson1, Shawn Sapp2, Silvia Luebben2, D.L. Schulz1 and Ya.B.
Losovyj3
1
[email protected]
2
3
TDA Research Corporation, Wheat Ridge, Colorado 80033
Rouge, LA 70806
The convention in organic light emitting diode (OLED) multilayer structures is to
use indium tin oxide (In2O3:Sn or ITO) as the transparent anode or conductive hole
injection source. Using ITO has led to a string of hurdles that provide an increased
degree of difficulty with respect to fabricating devices as well as reduce the overall
efficiency from manufacturing costs to power consumption. Some of the problems
encountered with ITO are a variability in work function (4.1 – 5.1 eV), large surface
roughness as a bottom electrode and oxidative destruction at the overlying emissive
polymer interface. To counter the above issues, intermediate polymer layers known as
hole transport layers (HTL) have been considered such as polyaniline emeraldine or
poly(3,4-ethylenedioxythiophene) blended with poly(styrenesulfonate) (PEDOT-PSS).
PEDOT-PSS (Figure 1a) is the conventional HTL because it provides a reproducible
work function, can be cast to give a smooth interface and hinders oxidation at the
emissive interface. Unfortunately, PEDOT-PSS is itself corrosive at the ITO interface
due to PSS being a strong acid. Furthermore, from the reported work function values of
PEDOT-PSS (4.7-5.4 eV) relative to ITO, hole injection may be hindered as shown
schematically in Figure 2a. Presented herein is an investigation of the work function and
conductivity of poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOTPEG) doped with perchlorate or para-tuluenesulfonate anions is presented in the context
of OLEDs as an alternative to the high work function and corrosive PEDOT-PSS.
ClO4O
O
O
O
S
S
O
O
+
O
O
+
S
S
B)
S
S
S
O
S
A)
O
O
SO3H SO3H SO3H
SO3-
O
O
O
O
SO3H SO3H SO3H
O
O
ClO4
+
O
O
R
S
O
O
O
y
O
y
O
R
O
R
O
x
perchlorate-doped PEDOT-PEG
-
SO3H SO3H
SO3-
H3C
O
PEDOT-PSS
O
S
S
O
O
O
S
+
x
SO3-
O
S
S
O
O
O
C)
y
S
O
O
O
H3C
O
S
+
+
S
O
SO3-
O
S
S
O
O
O
O
S
R
O
O
O
x
PTS-doped PEDOT-PEG
Figure 1. Structure of PEDOT-PSS (a), structure of perchlorate-doped PEDOT-PEG (b),
and structure of PTS-doped PEDOT-PEG (c).
Intrinsically conducting polymers (ICPs) consist of extended π conjugation along
a molecular backbone or chain. Oxidative doping transforms the chains from neutral
43
species to polycationic with conductivity increasing by several orders of magnitude upon
doping. During oxidation, anions are incorporated as dopants in the polymer by
oxidative polymerization (either chemical or electrochemical) of the conjugated or
aromatic monomer. It has been shown that conductivity increases with doping level,
however few studies have been done to show the relationship between work function and
doping level. Therefore, one outstanding question is what role does “doping” play in π
conjugated systems with respect to work function and conductivity? The study reported
here is designed to understand the mechanisms which control work function dependence
as is important for present and future two and three-terminal organo-electronic devices.
Figure 2. Photoemission at -3V bias of clean gold (solid line), PEDOT-PEG doped with
perchlorate (dashed line) and PEDOT-PEG doped with PTS (dotted line). The inset
indicates the value in binding energy of the secondary photoemission cutoff.
Above are photoemission spectra, used to determine the work function of the
block copolymer poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOTPEG) doped with perchlorate or para-toluenesulfonate anions. The take home message of
this work is that doped PEDOT-PEG may open the door for low band gap emissive
materials that have been otherwise discounted due to their inappropriate match to high
work function or low conductivity standard hole transport materials.
The above experiments were completed at the Center for Advanced
Microstructures and Devices synchrotron radiation facility in Baton Rouge, LA on
beamline 6B1. This work was supported by the Defense Microelectronics Activity
(DMEA) under agreement DMEA90-02-2-0218 and the NSF through ND EPSCoR grant
EPS-0447679.
44
Valence and shallow core photoemission of adsorbed cyclohexasilanes
A.N. Caruso1, S.B. Choi1, D.L. Schulz1, P. Boudjouk1 and Ya.B. Losovyj2
1
2
[email protected]
Rouge, LA 70806
Many polysilane molecules of linear and cyclic symmetry have been studied
under the requisite of chemical vapor deposition precursor toward applications using
amorphous silicon a:SiH or silicon carbide. In this study our primary intention is to
understand the interfacial valence and shallow core electronic nature of cyclic polysilanes
both before and after decomposition. A secondary goal is to determine what molecular
species exist after adsorption to the subtrate (i.e. ring opening, radical formation, etc.).
The intention of such goals are to extract interfacial orbital hybridization and raw spectral
density information relative to the Fermi level so as to determine binding energies of SiH, Si-Si, Si-C and residual H and C amounts.
R
Si
R
R
R Si
Si
R
R
R
Si
Si R
R
Si
R
Figure 1. Chair conformation of the D3d
Si6H12 with R=H and the Si6(CH3)12 molecule
with R= CH3.
R
R
For molecules such as silane (SiH4), that are traditional CVD precursors toward forming
amorphous silicon, removing all of the hydrogen to achieve good conductivity and
mobility is a challenge [1]. Furthermore, the energy of dissociation of SiH4 to form a-Si
is high relative to Si6H12 due to the weaker Si-Si bonds. For silicon carbide, the
challenge lies in forming the Si-C bond, rather than the carbon (easily) desorbing as an
alkyl group [2] upon precursor adsorption.
Si6H12
Shown below in Figures 2 and 3 are the core and valence band photoemission spectra of
very thin adsorbed Si6H12 (initial state) on Au(111). Figure 2 shows the development of
Figure 2. Shallow core photoemission of Si6H12
on Au(111) completed with 120 eV incident
photon energy and s+p polarization.
The
topmost spectra (BLACK) represents clean
Au(111), while the RED and GREEN are for
progressively thicker adsorptions of Si6H12; the
bottom spectra (BLUE) is after 60 seconds of
zero order light incident on the GREEN
adsorption thickness.
45
Figure 3. (LEFT) Angle resolved photoemission of Si6H12 adsorbed on Au(111)
completed with p polarization and 55 eV incident light. Spectra (a) represents clean gold
while (b), (c) and (d) represent progressively thicker adsorptions. All spectra were
collected along surface normal to preserve symmetry of the final state. (RIGHT) Angle
resolved polarization dependent photoemission of gaseous Si6H12 adsorbed on Au(111)
taken with hv=55 eV. The solid line represents p polarization while the dots are for s+p
polarization. Note that the adsorption is less than 25 Å as some gold is still apparent in
the photoemission intensity.
the Si 2p at -100 eV and the reduction of the Au 4f states at -84/87 eV as the gaseous
Si6H12 is adsorbed (red and green) and decomposed (blue). As a thicker layer is
developed the Si 2p shifts from -99.79 eV (red) to -100.57 eV (red); upon exposure to
white light, the Si 2p shifts back toward lower binding energy at -99.86 eV (blue). The
shift toward higher binding energy is commensurate with the formation of a silicon
hydride, although we must first confirm whether ring opening, Si-Si or Si-H bond
scission, Au-Si charge transfer or bond formation or a combination of the above effects
have occurred to make a rigorous determination of the hydride type and mechanism of
formation. The polarization dependent spectra (Figure 3 RIGHT) demonstrates the
existence of symmetry selection rules from the enhancement in the spectral region -4.5 to
-2.5 eV. Such polarization dependence, although convoluted with the Au 5d orbitals,
indicates that the ring does NOT open upon adsorption. If one considers that such
spectral features at -4.5 to -2.5 eV are represented by the Si 3p while the feature at -10 eV
is the Si 3s, then enhancement in s+p polarization (45˚ photon incidence relative to 70˚
incidence from normal or p polarization) makes sense and should represent the σ-SiSi
bonding. Also, because there exists an enhancement at the Si 3p, the ring should exist in
a planar conformation as otherwise in the chair or boat conformation, the photoemission
intensity would yield equal densities for each polarization. Ultimately, further studies
with thicker adsorptions, temperature and decomposition dependence will be required to
make a more rigorous determination of the adsorbed species, decomposition mechanisms
and residual hydrogen content. For now, it is a surprising result that the ring does not
open upon adsorption, leading to a large host of questions regarding ordering and the
differences between interfacial and bulk electronic structures. One difficult but exciting
46
experiment would be to observe a low energy electron diffraction (LEED) or STM
pattern in both the submonolayer to monolayer coverage range (without decomposing by
electron bombardment).
Si6(CH3)12
In an effort to study a unique precursor toward forming silicon carbide and as a
comparison to cyclic Si6H12 we present photoemission of the adsorbed phenyl based
analog dodecamethylcyclohexasilane Si6(CH3)12 on Au(111). The core level spectra
(Figure 4) reveal a shift toward lower binding energy for the Si 2p from -99.24 eV (red)
to -98.64 eV (green) as thickness increases; upon decomposition, due to white light
exposure, the Si 2p shifts to -98.85 eV (blue). Such values of the thick adsorbed layer
(green) Si 2p3/2 relative to crystalline silicon are low by ~0.9 eV and are not indicative of
carbide or hydride formation which would tend to stabilize.
Figure 4. Shallow core photoemission of
Si6(CH3)12 on Au(111) completed with 120
eV incident photon energy and s+p
polarization. The bottom spectra (BLACK)
represents clean Au(111), while the RED and
GREEN are for progressively thicker
adsorptions of Si6H12; the bottom spectra
(BLUE) is after 60 seconds of zero order light
incident on the GREEN adsorption thickness.
Figure 5 contains the valence band photoemission where a gradual decrease of the gold
photoemission contributions, their complete obscurity and polarization dependence of
such is shown. The feature at -15.1 eV is attributed to the C 2s, while the molecular
orbital at -7eV is due to C-H from the C 2p with a remaining hybridization between C 2p
and Si 3p making up the remaining orbitals within 5 eV of EF. Both the carbon 2s and 2p
exhibit a polarization enhancement with p polarization, while the feature at -2 eV is
enhanced with s+p polarized light; the remaining silicon features are show no
polarization dependence. Due to the complexity of this molecule, calculations will be
required in order to apply symmetry and selection rules for determination of the
adsorbate conformation, orientation and overall condition. It is interesting and somewhat
amazing that for such an outrageous molecule (twelve methyls bound to a central silicon
ring) a symmetry dependence is observed at all, especially for a coverage that exceeds the
photoelectron mean free path (~25Å). Hence, the interplay between σ (Si 3p) and π (C
2p) conjugation which leads to such an ordered structure is interesting both electronically
and physically.
47
Figure 5. (LEFT) Angle resolved photoemission of Si6(CH3)12 adsorbed on Au(111)
completed with p polarization and 55 eV incident light. The black spectra represents
clean gold while red, green and blue represent progressively thicker adsorptions. All
spectra were collected along surface normal to preserve symmetry of the final state.
(RIGHT) Angle resolved polarization dependent photoemission of gaseous Si6(CH3)12
adsorbed on Au(111) taken with hv=55 eV. The solid line represents p polarization while
the dots are for s+p polarization. Note that the adsorption is greater than 25 Å as the gold
orbitals are no longer apparent.
[1] J.J. Koulmann, F. Ringeisen, M. Alaoui and D. Bolmont, Phys. Rev. B 41 (1996) 3878
[2] D.G.J. Sutherland, L.J. Terminello, J.A. Carlisle, I. Jimenze, F.J. Himpsel, K.M.
Baines, D.K. Shuh and W.M. Tong, J. Appl. Phys. 82 (1997) 3567
The above data was collected at the Center for Advanced Microstructures and Devices
synchrotron radiation facility in Baton Rouge, LA on beamline 6B1. This work was
supported by the Defense Microelectronics Activity (DMEA) under agreement
DMEA90-02-2-0218 and the NSF through ND EPSCoR grant EPS-0447679.
48
The valence electronic structure of two metalloporphyrin analogs:
cobalt and nickel tetramethyldibenzotetraazaannulene
A.N. Caruso1, S.B. Choi1, L. Jarabek1 and Ya.B. Losovyj2
1
2
[email protected]
Rouge, LA 70806
Metal centered macrocyclic (metallocycles) compounds are of past and present
interest for a host of electronic and opto-electronic reasons. The most well known
metallocycles are the metalloporphyrin and metallophthalocyanine molecules as used in
thin film form for organic light emitting diodes, transistors, solar cells and gas sensing
devices. In addition to their electronic properties such metallocycles possess excellent
physical structure properties such as, ability to form supramolecular assemblies (due to
their high symmetry and pi delocalization) and are easily deposited using traditional
evaporation techniques.
CH3
CH3
N
Figure 1. Tetraazaannulene with
methyl units at the R positions. The
two metals studied here are Co and Ni
in the 2+ state.
N
M
N
CH3
N
CH3
A lesser studied metallocycle, compared to the porphyrin and phthalocyanine are
the tetraazaannulene (TAA) complexes (Figure 1). The TAA are considered highly
conjugated (in comparison to highly saturated) and delocalized ligand systems that
exhibit strong coordination to metal centers [1]. The resultant molecules with hydrogen
only termination are found to be highly planar while those with strong steric R groups
will form a saddle geometry. In addition, the TAA metallocycles differ from their C4v
cousins by forming unusual spin states in the 1+, 2+ or 3+ state that have been identified
as stable radicals (polarons) [2]. It is for the above reasons and lack of experimental
results, that we believe these molecules represent a possible diamond in the rough with
respect to metal-organic magnetic materials development of which the first step is an
electronic structure investigation. Hence, we present a valence band electronic structure
Nickel(II)
study
of
adsorbed
(NiC22H22N4)
[7,16dihydro6,8,5,17tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinato(2)N5,N9,N14,N18]
and
(CoC22H22N4)
Cobalt(II)
[7,16dihydro6,8,5,17tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinato(2)N5,N9,N14,N18] hereafter refereed to as NiTMTAA and CoTMTAA. The NiTMTAA
and CoTMTAA molecules were adsorbed from sublimed vapor onto a Au(111) single
crystal cooled to 100 K. All of the photoemission reveal very similar character and
response with respect to the strict nitrogen and carbon orbitals. The remaining sections
will highlight the differences observed between the cobalt and nickel centers.
49
Figure 2. Shallow core photoemission of NiTMTAA (LEFT) and CoTMTAA (RIGHT)
completed with hv=120 eV and p polarization. All photoelectrons were collected normal
to the substrate so as to preserve the final state symmetry and provide a parallel
wavevector equal to zero. The top spectra represents clean Au, while the middle and
bottom spectra are for thin and thicker adsorptions of the molecules in question.
Both core level spectra possess the dominate features at -18 eV due to the the C
2s. The broad spectral density located from -40 to -70 eV represents the various 3p states
of the respective transition metals coupled and degeneracy lifted. For Ni the 3p1/2 and
3p3/2 is expected to fall at -68 and -66.2 eV, while for Co we expect the -59.9 and -58.9
eV. For CoTMTAA there is definitely a small peak centered around -58 eV, but it is very
hard to extract much from the NiTMTAA at -67 eV. Unfortunately, the secondary
photoyield and highly insulating character of both molecules make a rigorous
determination of the metal 3p levels not possible.
Figure 3. Thickness dependent valence band photoemission of NiTMTAA (LEFT) and
CoTMTAA (RIGHT) adsorped on Au(111) completed with 55 eV incident light and p
polarization. Black represent clean Au, while red, green, blue and violet represent
progressively thicker adsorption of the respective molecule.
The thickness dependent spectra (Figure 3) reveal a slightly more stable molecule
for NiTMTAA relative to the CoTMTAA due to the C 2p existing at higher binding
50
energy for nickel versus cobalt. This stability is also echoed from thermal gravimetric
analysis where the Co complex decomposed at a lower temperature and is also found to
be sensitive to atmosphere. The highly insulating character of these molecules is shown
by the photoemission onset existing at about -2.0 eV. Placement of the HOMO is
uncertain at this time, where theory calculations, coupled with the polarization
depedendent photoemission will help determine whether a molecular orbital or defect
state is responsible for the photoemission onset.
One of the most amazing results from this work is shown in Figure 4 for the
difference in polarization dependent photoemission between the Ni and Co complexes.
From the photoemission enhancements, it is clear that the NiTMTAA retains a great deal
of symmetry while the CoTMTAA has a reduced symmetry. Such a result makes sense
within a square planar configuration (C4v) for the Ni 2+ relative to a possible saddle
geometry (C2v or lower) for the Co 2+. Conversely, crystal structure determinations have
shown that in the bulk, both the Co and Ni complex exist in the saddle geometry, which
suggests that the NiTMTAA could exist in the saddle while the CoTMTAA has little or
no point group assignment. Upon comparison with point group based calculations, the
configuration and possible orientation with respect to surface normal will become more
clear.
Figure 4. Polarization dependent photoemission of NiTMTAA (LEFT) and CoTMTAA
(RIGHT) completed with hv=55 eV for the thickest coverage. The normalization is
somewhat incomparable due to the extreme secondary in the NiTMTAA spectra taken
with lower photon flux.
The above studies were completed at the Center for Advanced Microstructures
and Devices synchrotron radiation facility in Baton Rouge, Louisiana on the 3m torodial
grating monochromator beamline 6B1.
[1]
[2]
Marvin C. Weiss, Guy Gordon and Virgil L. Goedken, Inorganic Chemistry 16
(1977) 305
Alan R. Cutler, Carl S. Alleyne and David Dolphin, Inorganic Chemistry 24
(1985) 2276.
51
Modifying Materials Properties of Metal Oxides by Doping:
Photoemission studies at the 3m-TGM beamline
Erie H. Morales, Jimi Burst, Khabibulakh Katsiev, Matthias Batzill, and Ulrike Diebold
Department of Physics, Tulane University, New Orleans, LA 70118
Email: [email protected], [email protected]
PRN: TU-UD0904
In last year’s report we described studies investigating the surface properties of reduced
and stoichiometric SnO2 surfaces and the interaction of water with TiO2 and SnO2. These
studies are now published; see references [1-6]. In the period of the current report we
extended our studies on the same materials by modifying the materials properties by
dopants. In particular we investigated the influence of nitrogen-doping on the electronic
structure of TiO2, cobalt-doping of SnO2, and the growth of palladium on SnO2(101). In
the following we give brief summaries of these works in progress.
1. Nitrogen-doping of TiO2
Nitrogen-doping of TiO2 has been proposed to reduce the band-gap of TiO2. Narrowing
of the band gap of TiO2 would allow a more efficient harvesting of the solar light in
photocatalytic applications of TiO2 and thus is of enormous practical interest. Our studies
aimed to clarify the effect N-doping has on the electronic structure of TiO2. We found
that N-doping induced localized band gap states at the valence band maximum of pure
TiO2 which explains the increased absorption of visible light in doped TiO2. More
interestingly though, N-doping also decreases the oxygen vacancy-defect formationenergy. This results in a thermal instability of doped TiO2 and may cause degradation of
N-doped TiO2 photocatalysts. These results are accepted for publication in Phys. Rev.
Lett. [7].
2. Palladium-growth on SnO2
Palladium is an important additive in SnO2 based solid state gas sensing materials and as
a heterogeneous catalyst. Our combined scanning tunneling microscopy (STM) and
ultraviolet photoemission spectroscopy (UPS) studies showed that Pd wets the reduced
SnO2(101) surface but grows as 3D clusters on the stocihiometric SnO2(101) surface.
UPS measurements indicate a downward shift of the Pd-5d states forming a band gap at
low Pd-coverage on the reduced SnO2 surface. This behavior may be explained by a
hybridization of the Pd valence electrons with the occupied Sn-5s states of the reduced
Sn-surface atoms. Such a hybridization of electronic states also implies a strong
interaction between Pd and the SnO2 surface and thus is consistent with the unusual
wetting of an oxide by a metal. The observed strong downward shift of the Pd d-band has
important implications for the catalytic activity of Pd.
3. Cobalt-doping of SnO2
Cobalt-doped SnO2 is a dilute ferromagnetic material with a Curie temperature above
room temperature. Such semiconducting ferromagnets are sought for applications in
future spintronic devices. We have grown epitaxial Co-doped SnO2 thin films on alumina
substrates by oxygen plasma assisted MBE and characterized their properties by various
techniques in collaboration with other groups. One technique we utilized has been UPS at
CAMD for the characterization of the valence band of differently doped SnO2 films.
From these studies we could deduce the position of the Co d-band. The position of this
52
state is important for a fundamental understanding of the ferromagnetic coupling in dilute
ferromagnetic materials. The predominate theory for ferromagnetism (see e.g. J.M.D.
Coey, M. Venkatesan, and C.B. Fitzgerald, Nature Materials 4, 173 (2005)) in dilute
oxides is that high spin state, dilute Co2+ cations couple their spin via the defect band
associated with oxygen vacancies. For this to work either the Co-3d majority or the
minority band has to overlap with the O-vacancy defect band. Our measurements suggest
that for Co-doped SnO2 the Co-3d minority band causes the splitting of the O-vacancy
defect band and thus causes the high Curie temperature in this material.
53
The Electronic Structure of 1,2-PCB10H11 Molecular Films: precursor
to a novel semiconductor (UNBD1203 and UNJB1203)
Snjezana Balaz,1 Dimtcho I. Dimov,2 N.M. Boag,1,2 Kyle Nelson,3 Benjamin Montag,3
J.I. Brand,3 and P.A. Dowben1
1
Dept, of Physics and Astronomy and the Center for Materials Research and Analysis,
Behlen Laboratory of Physics, University of Nebraska, P.O. Box 880111, Lincoln, NE
68588-0111 U.S.A. [email protected]
2
Chemistry and Nanotechnology, Institute for Materials Research, Cockcroft Building,
University of Salford, Salford M5 4WT, United Kingdom
3
College of Engineering and Technology, N245 Walter Scott Engineering Center, 17th &
Vine Streets, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511,
[email protected]
The ability to generate semiconducting grades of boron carbide by plasma
enhanced chemical vapor phase deposition (PECVD) of carboranes permits the
development of corrosion resistant, high temperature devices with many applications
including neutron detection. It is now clear that these boron carbides, of approximate
stoichiometry “C2B10Hx” (where x represents up to ~5% molar fraction of hydrogen),
exhibit a range of electronic properties (e.g. p-type or n-type) presumably as a result of
differing electronic structures originating in differences in polytype (molecular structure).
These films may be doped “conventionally” with dopants such as iron, vanadium [12],
chromium and nickel, however, main group doping has not been so successful.
The difficulties in using main group elements as dopants in semiconducting boron
carbides led to the exploration of the dimeric complex phosphorus bridged orthocarborane (1,2-C2B10H10PCl)2 [1,2] as a precursor with ‘built–in’ dopant (P). Although
this produced a boron carbide with a significantly larger band gap than the undoped
material, phosphorus inclusion was disappointingly variable and never higher than 3%,
suggestive of loss during deposition [1,2]. Since “C2B10Hx” is undoubtedly built up of
icosahedral cages, we felt that a precursor that contains a phosphorus atom as an integral
part of the cage structure might prove more satisfactory in regard to phosphorus
incorporation in the final film. Accordingly, we have instigated studies using a variety of
main group substituted carboranes (heterocarboranes) to determine the suitability of these
materials as precursors for doped boron carbide.
1,2-PCB10H11 adsorbs on Au and Ag substrates to generate thin films with the
Fermi level (chemical potential) placed closer to the lowest unoccupied molecular orbital
than has been observed with closo-1,2-dicarbadodecarborane (1,2-C2B10H12,
orthocarborane) adsorbed on Co, Cu or Ag. Both 1,2-PCB10H11 and 1,2-C2B10H12
molecular films exhibit an unoccupied molecular defect state just above the Fermi level.
The vibrational modes, observed in infra-red absorption, are close to the values expected
for the isolated 1,2-PCB10H11 molecule. Consistent with the placement of the Fermi level
in the molecular films, fabrication of heterojunction diodes from partially
dehydrogenated 1,2-PCB10H11 indicates that the resultant PCB10Hx semiconductor film is
more n-type than the corresponding boron carbide semiconductor formed from 1,2C2B10H12, orthocarborane.
[1]
D.N. McIlroy, S.-D. Hwang, K. Yang, N. Remmes, P.A. Dowben, A.A.Ahmad,
N.J. Ianno, J.Z. Li, J.Y. Lin and H.X. Jiang, Appl. Phys. A 67, 335-342 (1998).
[2]
P. Lunca-Popa, J.I. Brand, S. Balaz, Luis G. Rosa, N.M. Boag, M. Bai, B.W.
Robertson and P.A. Dowben, J. Phys. D: Appl. Phys. 38, 1248-1252 (2005)
54
Strain induced half-metal to semiconductor transition in GdN
(UN-PD1203-1)
Chun-gang Duan, R. F. Sabiryanov, Jianjun Liu, W. N. Mei
Department of Physics, University of Nebraska at
Omaha, Omaha, Nebraska 68182-0266
P. A. Dowben
Department of Physics and Center for Materials Research and Analysis, University of
Nebraska at Lincoln, Lincoln, Nebraska 68588, e mail: [email protected]
Electronic and transport properties of the rare-earth nitrides have long been a
challenge to investigators: the nitrides are difficult to fabricate into single phase crystals
and the experimental picture of their electronic structures is far from clear. Although
most rare-earth nitrides have shown to be semi-metallic, there are still uncertainties about
GdN. An appealing property of GdN is that it is ferromagnetic with a large gap at the
Fermi energy in the minority spin states, according to the electronic structure calculations
based on the local density approximation (LDA). At the same time GdN is semi-metallic
in majority spin states with electron and hole pockets at the Fermi surface. This latter
property has led to some interest in GdN as a possible candidate for spin-dependent
transport devices, exploiting the spin filter, giant magnetoresistance or tunneling
magnetoresistance effects.
An accurate description of the electronic structure of rare-earth compounds is a
very challenging problem because of their unfilled 4f shells. Calculations based on local
spin density approximation (LSDA) are well known to underestimate the band gap in
semiconductors. Thus LSDA and similar computational methods may not be able to
correctly describe whether a highly correlated system, like GdN, is semi-metallic or
semiconducting at the equilibrium volume. Nonetheless, if we are interested in the trend
of how the electronic and magnetic properties vary with the change of volume, we can
obtain a reasonable picture for GdN from LSDA with additional Hubbard correlation
terms describing on-site electron-electron repulsion associated with the 4f narrow bands
(LSDA+U approach). Actually, due to the fact that the f states of this system are exactly
half occupied, there is no orbital moment and the anisotropic and multipole effects are
minimal. As a result, GdN is the ideal material to study the magnetic exchange
interactions in rare-earth nitrides [1].
We have show that applying stress can influence significantly the electronic and
magnetic properties of GdN [1]. We have investigated the electronic structure and
magnetic properties of GdN as a function of unit cell volume. Based on the firstprinciples calculations of GdN, we observe that there is a transformation in conduction
properties associated with the volume increase: first from half-metallic to semi-metallic,
then ultimately to semiconducting. We have also shown that applying stress can alter the
carrier concentration as well as mobility of the holes and electrons in the majority spin
channel. In addition, we found that the exchange parameters depend strongly on lattice
constant, thus the Curie temperature of this system can be enhanced by applying stress or
doping impurities. Using the first-principles approaches, we demonstrated that the system
exhibits nominal “half-metallic” band structure at the equilibrium lattice constant, and
then semi-metallic and/or semiconducting character develops with increasing lattice
55
constant. We note that the magnetic properties are also extremely sensitive to the volume
variations, i.e., the exchange interactions are at first ferromagnetic, then the calculated
Figure 1. Comparison between the calculated DOS (majority spin: solid line, minority spin: dotted line) at
theoretical lattice constant (a = 4.92 Å) and the photoemission spectra for nitrogen on Gd(0001). The new
photoemission features that are not attributable to the Gd(0001) substrate compare well with the calculated
DOS for GdN. Features with strong N 2p weight are indicated. Binding energies for experiment are shifted to
higher binding energies as expected with a final state spectroscopy of a correlated electron system, but the
shift is roughly uniform for key features of the photoemission spectra (taken for both s and p polarized light).
magnitudes of exchange parameters reduce substantially with increasing volume,
suggesting that the Curie temperature is reduced with an increase in lattice constant. The
energy levels of 4f states are crucial in determining the accurate exchange parameters.
Our calculation on equilibrium structure of GdN, based on the present U parameter, gives
the unoccupied 4f states 5 eV above EF and occupied 4 f states 6 eV below, which
agrees well with the experimental situation [1], thus provides a reliable support to our
magnetic properties study on GdN.
[1]
Chun-gang Duan, R.F. Sabiryanov, Jianjun Liu, W.N. Mei, P.A. Dowben and
J.R. Hardy, Physical Review Letters 94 (2005) 237201
56
Single crystal ice grown on the surface of the ferroelectric polymer
poly(vinylidene fluoride) (70%) and trifluoroethylene (30%)
(UN-PD1203-3)
Luis G. Rosa,a Jie Xiao,a Ya.B. Losovj,b Yi Gao,c Ivan N. Yakovkin,d Xiao C. Zeng,c
and P. A. Dowbena
a
Department of Physics and Astronomy and the Center for Materials Research and
Analysis, Behlen Laboratory of Physics, University of Nebraska-Lincoln, Lincoln,
Nebraska 68588-0111; e mail: [email protected]
b
Rouge, LA 70806
c
Department of Chemistry, 536 Hamilton Hall, University of Nebraska, Lincoln NE
68588-0304
d
Institute of Physics of National Academy of Sciences of Ukraine, Prospect Nauki 46,
Kiev 03028, Ukraine
Because of biomedical and polymer
electronic devices, studies of adsorbates (in
particular water) on polymer surfaces are of
considerable interest, but are presently quite
limited.
Detailed studies of adsorbate
chemistry on polymer surfaces have proven to
be difficult to undertake because of the
complexities associated with the ordering of
polymer surfaces. Through technical advances
in making crystalline polymers, this situation is
changing.
Water ice is observed to order at the
copolymer ferroelectric
poly(vinylidenefluoride-trifuoroethylene)
surface. The successful growth of crystalline
thin films of water on these polymer surfaces
implicates water to polymer dipole interactions.
These ice thin films are sufficiently ordered for
experimental identification of the wave vector
dependence in the electronic band structure of
hexagonal ice. The significant band dispersion,
of about 1 eV (Figure 1), suggests strong
overlap of molecular orbitals between adjacent
water molecules in the ice film. The presence
of dipole interactions with adsorbate water is
consistent with the possibility of water acting
Figure 1. (a) Compilation of the band dispersion as a
function of wave vector k, providing an experimental
as a spectator to surface ferroelectric transitions
lattice parameter of 2.9 Å along the surface normal. (b)
in this system.
The band structure calculation for cubic ice, adapted
from G.P. Parravicini and L. Resca [1].
The P(VDF-TrFE; 70:30) films are very
well ordered, as illustrated in the scanning
tunneling microscopy image in Figure 2d. This,
no doubt, aids in the formation of an ordered
ice layer. With the formation of an ordered ice layer, details of the electronic structure
57
can now be probed. While some dispersion was observed in prior photoemission studies
of ice, also on the order of 1 eV, the results were not very compelling and a preferential
Figure 2. The structure of the ice on PVDF-TrFE predicted by DFT methods at the interface (a) and from the
top (c) showing the honey combed structure. Semiempirical calculations of the ice layer on the ferroelectric
polymer (b) result in a similar 2.8 Å lattice spacing along the surface normal for the ice layer. The PVDFTrFE is well ordered as indicated in (d) from the STM of the ferroelectric polymer surface.
orientation of the water molecules was not obtained. Our study continues to add to the
contention that water, in constrained geometries, will adopt unusual crystallographic
order [2].
[1]
G. Pastori-Parravicini, L. Resca, Phys. Rev. B 8, 3009-3023 (1973)
[2]
Luis G. Rosa, Jie Xiao, Ya.B. Losovyj, Yi Gao, I.N. Yakovkin, Xiao C. Zeng
and P.A. Dowben, Journ. Am. Chem. Soc. 127, 17261-17265 (2005)
58
Abnormal Temperature Dependence of Photoemission Intensity
Mediated by Thermally Driven Reorientation of a Monomolecular Film
(UN-PD1203-3)
D.-Q. Feng1, D. Wisbey1, Y. Tai3, Ya. B. Losovyj2, M. Zharnikov3 and P.A. Dowben1*
1) Dept. of Physics and Astronomy and the Center for Materials Research and Analysis,
University of Nebraska-Lincoln, Lincoln, NE 68588-0111, e mail: [email protected]
2) Center for Advanced Microstructures and Devices, Louisiana State University, 6980
Jefferson Highway, Baton Rouge, LA 70806, e mail: [email protected]
3) Angewandte Physikalische Chemie, Universität Heidelberg, Im Neuenheimer Feld
253, D-69120 Heidelberg, Germany
Although organic adsorbates and thin films are generally regarded as “soft”
materials, the effective Debye temperature, indicative of the dynamic motion of the
lattice normal to the surface, can be very high, e.g., in the multilayer film formed from
[1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT) [1]. The effective Debye temperature,
determined from core level photoemission from the all carbon arene rings, is comparable
to that of graphite, and follows the expected Debye-Waller behavior for the core level
photoemission intensities with temperature. We associate this rigidity to the stiffness of
the benzene rings, and the ordering in the ultrathin multilayer molecular thin film [1].
Figure 1. Logarithm of the C 1s (a) and S 2p (b) total photoemission intensities for the [1,1’;4’,1”-terphenyl]4,4”-dimethanethiol (TPDMT) (triangles), and biphenyldimethyldithiol (BPDMT) (black dots and circles
indicating two different representative sets of data) as a function of temperature. The effective Debye
temperatures for the multilayer BPDMT films were determined to be 1397±110 K from C 1s core level
intensity and 456±50 K from the S 2p signal.
Temperature assisted conductivity and molecular configurational changes can
both occur in molecular systems and need not always be directly correlated. In addition,
electron-phonon coupling in molecular systems must of necessity consider local point
59
group symmetry effects. Setting aside these known complications, failure to obey an
expected temperature dependence of the photoemission intensities, consistent with the
Debye-Waller scattering, can provide a very strong indication of molecular
conformational changes. An interesting candidate to prove this hypothesis is selfassembled monolayer (SAM) of [1,1’;4’,1”-terphenyl]-4,4”-dimethanethiol (TPDMT),
which exhibit structural and conformational changes upon metal evaporation and
temperature variation.
With the example of a monomolecular film formed from [1,1’;4’,1”-terphenyl]4,4”-dimethanethiol, we show that pronounced deviations from Debye-Waller
temperature behavior are possible and are likely caused by temperature dependent
changes in molecular orientation. The molecular orientation for the terphenyl backbone
of TPDMT in the single layer SAM film is more “upright” (but we note not perfectly so)
while BPDMT is oriented nearly parallel to the substrate with the planes of benzene rings
oriented normal to the surface. Taking into account the results presented in Figure 1, we
can assume that the temperature dependent variation of the Debye temperature of the
TPDMT film is mediated by temperature dependent changes in orientation and
conformation of its molecular constituents.
Strong deviations from the expected Debye-Waller behavior occur in the
vicinity of 260-270 K, about the temperature where there are the subtle changes in the
light polarization dependent photoemission. Taken together, we surmise that temperature
dependent structural changes are most likely responsible for TPDMT violating the
Debye-Waller behavior. Not all changes in molecular orientation result in such
significant deviations in Debye behavior as is observed here. Structural changes for
TPDMT must differ from molecules like polyhexylthiophene [1] in that with increasing
temperature, there is an increase in intermolecular interaction [2]. Such intermolecular
interactions lead to an increase in the rigidity of the molecular film, as opposed to the
expected decrease in intermolecular interaction expected with a molecule like regioregular polyhexyl thiophene (P3HT) [1].
[1]
[2]
D.Q. Feng, R. Rajesh, J. Redepenning and P.A. Dowben, Applied Physics
Letters 87 (2005) 181918
D.-Q. Feng, D. Wisbey, Y. Tai, Ya. B. Losovyj, M. Zharnikov and P.A.
Dowben, J. Phys. Chem. B (2006), in press
60
Geometric and Electronic Structure of Self-Assembled Monolayers
Grown on Noble Metal Substrates:
Dodecanethiol on Au, Ag, Cu, and Pt
Heike Geisler and Lauren Powell
Dept. of Chemistry, Xavier University, New Orleans, LA 70125
Shawn Huston, Tim Sweeney, Daniel Borst and Carl A. Ventrice, Jr.
Department of Physics, University of New Orleans, New Orleans, LA 70148
Yaroslav Losovyj
CAMD, Louisiana State University, Baton Rouge, LA 70806
(PRN: XU-HG 1206)
Intensity (arb. units)
The electronic structure of dodecanethiol (C12H25SH) self-assembled monolayers
(SAMs) on Au(111), Ag(111), Cu(111), and Pt(111)) substrates has been studied using
angle-resolved ultra-violet photoelectron spectroscopy at the 3m-TGM of the CAMD
synchrotron. The geometric structure of the SAMs was measured via low energy electron
diffraction (LEED) at UNO and the 3m-TGM endstation. The SAMs were grown both
by vapor deposition in UHV and in solution. The electronic structure of the fully
saturated SAM is similar on all of these substrates, with peaks observed at binding
energies of 6.5, 10, 14, and 20 eV,
as shown in Fig. 1. The geometric
structure of the molecular films at
intermediate coverages is different
for each substrate. Growth on Au
Cu(111)
proceeds through a well-ordered
lying-down phase followed by a
disordered phase and a well-ordered
√3 standing-up phase at saturation.
Ag(111)
Initial growth on Pt(111) shows first
a p(2x2)symmetry followed by a √3
Au(111)
symmetry, which indicates that the
initial growth is via standing-up
phases on Pt. This is followed by a
Pt(111)
disordered phase at saturation.
Films on Ag and Cu show a great
deal of disorder at all stages of
growth. The lack of angular
dependence of the ARUPS
20
10
0
Binding Energy (eV)
emissions from the substrate bands
of Ag and Cu indicate that the
Fig.1: ARUPS spectra of solution grown dodecanethiol
adsorption of dodecanethiol on
SAMs
grown on Cu, Ag, Au, and Pt substrates. The
these substrates induces a
spectra were taken at normal emission with p-polarized
disordering of the outer most layer
light at an incident angle of 45˚ and 55 eV photon energy.
of the metal atoms.
61
Infrared Micropectroscopy studies of bio-functionalized oxide surfaces
O. Kizilkaya and M. Pease
Louisiana State University, Baton Rouge, Louisiana 70806
The patterned bifunctionalized oxide surfaces on the GMR sensor have been studied with
infrared microscopy technique in order to understand and characterize the bonding
interaction of polymer with biomolecules. The Thermo Nicolet Continuum Fourier
transform infrared (IR) spectromicroscope on IR beamline has been employed to
characterize the chemical structure of micro-contact printed polyethyleneimine (PEI), an
organic polymer that has a high density of amino groups, and biotin attached to PEI dots
on four different oxide substrates (SiO2, Si3N4, Al2O3, AlN) by use of microfludic
platform developed at CAMD. The inset in figure 1 shows the optical view image of
biotinated PEI micro-dot on which IR spetra measured. Fig. 1 shows the IR spectrum of
PEI/S3iN4 (top spectrum) and biotinated PEI/Si3N4 (bottom spectrum) microdots taken
with reflection mode. The dots on other substrates have also revealed the same absorption
bands seen in Fig. 1 except a cutoff on Al2O3 and AlN for frequencies above 2500cm-1.
In PEI/Si3N4 IR spectrum (top spectrum), the peaks at 3360 and 3260cm-1 are attributed
to NH2 antisymmetric and symmetric stretching modes and the peak at 1570cm-1 is
associated to NH2 deformation mode. These two modes indicate that we have primary
amine structure bonded on the Si3N4 surface. The peaks at 2932 and 2841cm-1 are due to
methylene antisymmetric and symmetric and the one at 1458cm-1 is arisen from bending
(scissoring) mode of methylene functional group. A strong carbonyl absorption peak
(C=O) is appeared at 1640cm-1 in the IR spectrum (see bottom spectrum in Fig. 1) after
biotin bonded to polymer/Si3N4 dot. The existence of carbonyl bond is clear indicative of
attachement of biotin biomolecule to PEI polymer.
Fig. 1
62
Infrared Characterization of Localized Corrosion Products
Richard S. Perkins1, James D. Garber1, Brett Rodrigue1, O. Kizilkaya2, E. Morikawa2, J.
Scott2
1
2
UL Lafayette Corrosion Center, Lafayette, LA 70504-4370
The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices,
Louisiana State University, Baton Rouge, LA 70806
Failure of devices due to corrosion often comes about because of localized corrosion, or
pitting. Though general corrosion may occur across a metal surface, pitting corrosion
occurs at a faster rate at certain locations. A better understanding of the pitting process
should lead to better ways to predict and control it. One important aspect of localized
corrosion is the corrosion products that form. The nature of these products has a bearing
on the progress of the corrosion reaction.
We have begun an infrared study of these corrosion products in the system composed of
an iron foil in an aqueous carbonate/bicarbonate buffer through which gaseous carbon
dioxide is bubbled. This system is an important one in the oil industry. By adjusting the
buffer components and the partial pressure of carbon dioxide, the pH can be controlled.
Our ultimate aim is to obtain infrared spectra of the products of general corrosion and
pitting corrosion under in-situ conditions.
We have obtained spectra of products under ex-situ conditions. Samples were prepared,
stored in nitrogen, and within 24 hours studied with the infrared beamline and
microscope. These data should serve as a guide in interpreting spectra from in-situ
studies. The samples were prepared two ways. Some were left in the buffer/CO2 system
and allowed to corrode. A faster and more convenient method of obtaining samples is to
hold the iron sample at a fixed potential in the buffer/CO2 system. The fixed potentials
are chosen with the help of a published Pourbaix diagram[1] of the system and cyclic
voltammograms obtained by us prior to constant potential control. Spectra can be
obtained for systems near the corrosion potential as well at more anodic potentials where
other products may form.
Reflectance spectroscopy was done and reflectance spectra obtained. Interpretation of
these spectra is aided by published reflectance spectra. There has been recent interest in
reflectance spectroscopy of iron compounds. It is important in studying surfaces on other
planets and their satellites.
A sample holder (electrochemical cell) suitable for use with the microscope has been
fabricated and will be used to obtain in-situ spectra.
[1] A. Ikeda, M. Ueda, and S. Mukai, Advances in CO2 Corrosion, vol. 1, pp.39-51,
National Association of Corrosion Engineers, 1984.
63
Spatially resolved determination of metabolic activity of rust fungi on
leaves using synchrotron radiation based IR-microspectroscopy
Alexander Prange1,2, Orhan Kizilkaya1, Harald Engelhardt3, Erich-Christian Oerke4,
Ulrike Steiner4, and Josef Hormes1
1
Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson
Hwy., Baton Rouge, LA 70806, USA
2
Microbiology and Food Hygiene, Niederrhein University of Applied Sciences, Rheydter Straße
277, 41065 Mönchengladbach, Germany
3
Max-Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
4
INRES, Phytomedicine, University of Bonn, Nussallee 9, D-53115 Bonn, Germany
Correspondence to: A. Prange, e-mail: [email protected]; PNR GMX-AP1206IR
Introduction
Over 6000 plants species are infected by various types of fungi, and losses worldwide from plant
disease outbreaks are estimated to exceed $ 1 billion per year. Knowledge of the molecular basis
of the interaction between pathogenic fungi and their host plants is a crucial prerequisite for
understanding the nature of damage caused during pathogenesis and for a targeted screening of
crop protection agents. In this project we applied synchrotron radiation based Infra-red (IR)
spectroscopy to characterisize the host-pathogen interaction of the bean rust Uromyces
appendiculatus with bean leaves. The goal of the project is to receive spatially resolved
information about changes of the “organic matter” (e.g. proteins and carbohydrates) which is
caused by the host-plant interaction.
Material and Methods
Experimental. Measurements were carried out at CAMDs IR-microspectroscopy beamline with
a spatial resolution of 70 µm x 70 µm in reflection and/or transmission mode. In general, mid-IR
radiation from storage rings is at least one order of magnitude brighter than for conventional
sources allowing spatially resolved experiments with a resolution near the diffraction limit of 3 –
10 µm (Jamin et al., 1998; Dumas et al., 2000). Mid-infrared spectroscopy – covering the
wavelength range from about 3 to 15 µm – measures the contribution of vibrational signatures
from particular organic and inorganic functional groups. These local vibrational modes are very
sensitive to small chemical changes as the ones caused by certain diseases (Miller et al., 2003).
Thus it is a very valuable technique for biological applications (e.g. Raab and Vogel, 2004). A
“slight” drawback of IR spectroscopy is the fact that in many cases plant tissues have to be
cleared of pigments and waxes prior to measurements. It is also important to notice that because
of the penetration depth of mid-IR radiation the majority of spectral features originate from cell
walls of the epidermis.
Samples. The bean rust Uromyces appendiculatus was cultivated on planta under greenhouse
conditions at INRES-Phytomedicine, Bonn University. Samples were used directly for the
measurements without any special preparation.
64
Preliminary Results and Discussion
At the IR-microspectroscopy beamline at CAMD the first spatially resolved mid-IR spectra of
bean leaves infected by Uromyces appendiculatus have been recorded with a resolution of about
70 x 70 µm2. Experiments were carried out mainly in reflection mode (Fig. 1) but some also in
transmission mode (Fig. 2). Fig. 2 shows in a direct comparison the spectra of the infected area
and of a visibly healthy area. There are obvious differences in the intensity distribution between
1800 and 2800 cm-1 and around 1250 cm-1 indicating higher amounts of lipids in the intact bean
leaf and more saccharides in the rusted leaf area. Both these facts can be correlated with a model
for fungal nutrition proposed by Solomon et al. (2003). Fig. 2 shows the IR transmission
spectrum of a green bean leaf. The spectrum is less noisy, than those recorded in reflection mode.
However, is has to be kept in mind, that water from the plant cells is dominating in the spectrum.
Therefore, the sample preparation (e.g. freeze drying) will be improved, but one can obtain
already some important information from the spectrum as indicated in the figure.
Amide A
-OH (H2O)
more lipids in the
healthy leaf
more saccharides
in the rusted area
-CH2 / -CH3
Amide-I (protein)
-OH (H2O)
Amide-II
(protein)
C-OH
P-O-C
C-H
C-O
(sugars,
phosphates
-C=O
-COOand others
P=O
C-O
magenta line: rust on bean leaf
green line: healthy bean leaf
Fig. 1: Mid-IR spectra of bean leaves infected by Uromyces
bean leafs appendiculatus (resolution 70 x 70 µm2 )
(x-axis: wavenumbers 1/cm; y-axis: % reflectance).
Fig. 2: Mid-IR spectrum of
in transmission mode
(resolution 70 x 70 µm2 ).
Outlook
The project will be continued in 2006. Besides bean rust, wheat rust will be included in the investigation.
Using IR-microspectroscopy, “line scans” (uninfected area – rust pustule – uninfected area) with a
resolution of at least 25 x 25 µm2 will be carried out.
References
Dumas, P., Carr, G.L. and Williams, G.P. (2000). Enhancing the lateral resolution in infrared
microspectrometry by using synchrotron radiation: applications and perspectives. Analysis 28, 68
Jamin, N., Dumas, P., Moncuitt, J., Fridman, W.-H., Teillaud, J.-L., Carr, G.L. and Williams, G.P. (1998).
Highly resolved chemical imaging of living cells by using synchrotron infrared microspectrometry.
Proc. Natl. Acad. Sci. 95, 4837.
Miller, L.M., Smith, D.G. and Carr, G.L. (2003). Synchrotron-based biological microspectroscopy: From
the mid-infrared through the far-infrared regimes. J. Biolog. Phys. 29, 219.
Raab, T.K. and Vogel, J.P. (2004). Ecological and agricultural applications of Synchrotron IR microscopy.
Infrared Phys. Technol. 45, 393.
Solomon, P.S., Kar-Chun, T. and Oliver, R.P. (2003). The nutrient supply of pathogenic fungi; a fertile
field of study. Mol. Plant Pathol. 4, 203.
65
Characterization of the Electronic Structure of MEH-PPV
PRN#IfM-SS0505 “Conjugated Polymer Optoelectronic Technology”
Sandra Selmic,1 David Keith Chambers,1 Srikanth Karanam,1 Orhan Kizilkaya,2 and
Ya.B. Losovyj2
1
Louisiana Tech University, Institute for Micromanufacturing, Electrical Engineering
Program
P.O. Box 10137, 911 Hergot Ave, Ruston, LA 71272
e mail: [email protected]
2
Center for Advanced Microstructures and Devices, Louisiana State University, 6980
Jefferson Highway, Baton Rouge, LA 70806
Polymer material analysis included measurement of absorption, index of refraction,
conductivity, and electronic structure. All these measurements were done in the Institute
for Micromanufacturing (IfM) of Louisiana Tech University except the electronicstructure measurements done at the synchrotron in the Center for Advanced
Microstructures & Devices (CAMD) at Louisiana State University. We analyzed
polymer/fullerene and polymer/nanocrystal compounds for photovoltaic device
applications. We focused on the following materials: polymer poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), PbSe nanocrystals, and fullerene
[6,6]-phenyl-C60-butyric-acid-methyl-ester (PCBM).
Temperature Dependence
75% MEH-PPV PCBM at 70eV
60000
70000
Temperature Dependence
Pure MEH-PPV at 70eV
60000
100°C
Relative Intensity (a.u.)
40000
85°C
30000
ambient
20000
50000
210°C
50000
100°C
40000
ambient
0°C
30000
-89°C
-100°C
20000
10000
-150°C
-240°C
0
0
10
20
30
40
50
Binding Energy (eV)
60
70
10000
-240°C
80
60
50
40
30
20
Binding Energy (eV)
10
0
-10
Fig. 1. Temperature dependence of the binding energy in the PCBM doped MEH-PPV
(left) and pure MEH-PPV (right).
Temperature dependence of the highest occupied molecular orbit (HOMO) structure of
pure MEH-PPV and MEH-PPV doped with PCBM are given in Figure 1. The HOMO
level band filling is evident as temperature increases, both in MEH-PPV/PCBM and pure
MEH-PPV films. This is similar to the HOMO level band filling as temperature
increases seen for MEH-PPV/PbSe films. The energy dependence of the PbSe and MEHPPV doped with PbSe nanocrystals are given in Fig. 2. We observed a marked energy
dependent dispersion, an indication of molecular ordering perpendicular to the film
surface, in the energy dependent spectra of pure PbSe nanocrystals. There is little
dispersion in the PbSe-MEH-PPV blend films. This indicates the ordering is decreased in
66
these blends. We also observed an interesting migration of the core density of states
feature in the blends from around 45eV binding energy to around 30eV binding energy as
we sweep the incident energy from 60eV-80eV.
40000
Energy Dependence
Pure PbSe at 70eV
35000
30000
80eV
50000
80eV
78eV
25000
78eV
Energy Dependence
50% MEH-PPV-PbSe
60000
40000
76eV
20000
74eV
72eV
15000
70eV
72eV
70eV
20000
68eV
10000
76eV
74eV
30000
68eV
66eV
66eV
10000
64eV
5000
64eV
62eV
0
80
62eV
0
60eV
70
60
50
40
30
20
Binding Energy (eV)
10
0
-10
70
60eV
60
50
40
30
20
Binding Energy (eV)
10
0
-10
Fig. 2. Binding energy dispersion of PbSe and MEH-PPV doped with PbSe.
Polarization-temperature dependence in PCBM and MEH-PPV/PCBM is shown in Fig. 3.
Polarization Dependence
Pure PCBM
60000
Polarization
75% MEH-PPV PCBM
70eV at Ambient Temperature
24000
50000
22000
unpolarized
40000
s+5°
30000
20000
20000
18000
unpolarized
16000
s+5°
s+20
14000
10000
s+10°
60
50
40
30
20
10
0
s+30
12000
70
-10
Binding Energy (eV)
60
50
40
30
20
Binding Energy (eV)
10
0
-10
Fig. 3. Polarization-temperature dependence in PCBM and MEH-PPV/PCBM.
We observed a strong polarization dependence of PCBM films, both in pure and MEHPPV blend films. The strong preferential P (parallel to films surface) orientation is
consistent in 75% MEH-PPV films both at ambient and low (-240°C) temperatures. This
indicates little change in preferential molecular orientation with changes in temperature.
67
Electronic Structure of Silver Nanowires on Cu(110)
W. Zhao, R.L Kurtz, Y. Losovyi, P.T. Sprunger ([email protected]), Department of Physics
and Astronomy & Center for Advanced Microsctroctures and Devices, Louisiana State
University, 202 Nicholson Hall, Louisiana State University, Baton Rouge, LA 70808
(00
1)
Self-assembled nanomaterials with reduced dimensionality, or at least one dimension that
is on the nanoscale, such as one-dimensional nanowires, have been studied intensively in
recent years. The nanostructured materials are promising
building
blocks
for
manufacturing
devices
of
nanoelectronics and photonics from a bottom-up approach.
STM results (see figure) show that the Ag nanowires grown
(11
0)
on Cu(110) are approximately 2 nm (~12 nm) in height
(width). However, the nanowires orientate with the long
axis parallel to the [1̄10] substrate direction and posses an
anisotropic morphology with aspect ratio up to 20:1. The
strong anisotropic shape of the self-organized nanowires
500
suggests a strong difference between the Ag band structure
along and perpendicular to the nanowires. To investigate
this idea, we have performed angle-resolved photoemission
spectroscopy (ARPES) on Ag nanowires grown on Cu(110)
at the 3m NIM beamline with use of the Scienta Endstation.
(110)
1}
{11
{33
2}
25
23
101
Previous STM results (top) show
the overall morphology of Ag nanowires (bright protrusions). The
model (bottom) shows details
nanowire’s proposed structure.
Consistent with the STM results, our ARPES results (see
below) that the valence bands within the Ag nanowire are
strongly anisotropic with clear band dispersion in the alongwire direction, but no dispersion in the across-wire direction. This strongly suggests that
the valence electrons of Ag behave one-dimensionally in the lateral plane (along the
wire) and have little interaction with the lattice along the across-wire direction
(perpendicular to the wire).
With the ability to rotate the sample Form the ARPES studies of the Ag/Cu(110)
nanowire system, it is demonstrated the electronic structure of the Ag(110) nanowire on
Cu(110) considerably deviates from that of bulk Ag band structure in energy dispersion
behavior and even in increased energy band number. The most obvious dispersion
behavior deviation is that the photoelectron spectra show dispersion in the vertical (or
(110)) and the lateral [1̄10] (or along-wire) direction (top figure- next page), but absence
of dispersion in the lateral [001] (or across-wire) direction because of the limited
dimension of the nanowire width (~ 200 Å in average; bottom figure – next page).
Therefore the dimensionality of the band structure of the Ag(110) nanowire crystal is
decreased to two dimensional in the vertical plane formed by the cross lines parallel to
the vertical [110] and the lateral [1̄10] directions. This results is in accordance with the
STM results.
68
a) Angle-dependent photoelectron spectra from Ag/Cu(110) nanowires (21±5 ML) taken with light beam towards the [110]
direction (along-wire) at photon energy of 16 eV.; b) same except with photon beam towards the [001] direction (acrosswire) at photon energy of 16 eV: absence of Ag-d-band dispersion in across-wire direction, contrasting to that of the
along-wire direction; c) Band structure map for the two high-symmetry directions across the (110) surface Brillouin zone,
indicating band dispersion in the along-wire direction and absence of dispersion in the across-wire direction. d) Normal
emission photoelectron spectra from the same Ag/Cu(110) nanowires with photon beam towards the along-wire direction
( A [001]) at photon energy of 14 eV ~ 31 eV
69
4f-5d hybridization in a high k dielectric material HfO2 and evidence for
phonon effects in the electronic bands of granular Fe3O4
Yaroslav Lozovyy1 and Jinke Tang2,
1
Center for Advanced Microstructure and Devices, Louisiana State University, Baton
Rouge, LA 70806, [email protected]
2
Department of Physics, University of New Orleans, New Orleans, LA 70148,
[email protected]
PRN: UNO-JT1205
While intra-atomic f-d hybridization is expected, experimental confirmation of f-d
hybridization leading to 4f band structure has been limited to 5f systems and compound
systems with very shallow 4f levels. It has been demonstrated that core 4f state can
contribute to the valence band structure in wide band gap dielectric HfO2. In spite of the
complications of sample charging, we found evidence of symmetry in the shallow 4f
levels and wave vector dependent band dispersion, the latter consistent with the crystal
structure of HfO2. The HfO2 thin films were grown on silicon substrates by pulse laser
deposition at substrate temperature of approximate 700 °C, with base vacuum 5 x10-7 torr
and growth rate of about 0.15 Å/s. X-ray diffraction patterns show that the resulting
HfO2 films are single monoclinic phase with strong texture growth. Transmission
electron microscopy images reveal columnar growth of the HfO2 crystallites within the
films.
30
20
10
EF 30
25
20
Binding Energy (eV)
Left: Photoemission spectra of the powder pile taken at different light polarizations.
○ denotes s+p polarized light and ● corresponds to p-polarized light.
Right: 4f’s core level region. Photon energy was 80 eV.
The Verwey nonmetal to metal transition appears to be enhanced, rather than
suppressed, in high quality nanogranular Fe3O4 samples made in our labs. This indicates
that even in a granular system that magnon and phonon effects are present and cannot be
70
completely suppressed. The implication of such interaction is that the electron spin
polarization of iron magnetite, supposedly a half-metal, will be reduced. Nanocrystalline
(50 nm) magnetite thin films were fabricated by pulsed laser deposition (PLD) and
characterized by X-ray diffraction, magnetometry, transmission electron microscopy and
transport measurements. The magnetic properties of the films have been previously
reported.
Nanogranular Fe3O4films prepared
by pulsed laser deposition
(311)
30
5
0
10
20
30
40
50
2θ (degree)
71
(440)
(220)
10
(511)
(400)
15
(422)
20
(111)
Intensity (counts)
25
60
70
Energy Level Alignment at Arylthiol/Metal Interfaces
Christopher Zangmeister♣ and Roger van Zee
National Institute of Standards and Technology, Gaithersburg, Maryland
Carl Ventrice
University of New Orleans, New Orleans, Louisiana
Heike Geissler
Xavier University of Louisiana, New Orleans, Louisiana
The interactions at molecule/metal interfaces control the energy alignment of the valence
molecular states with respect to the metal Fermi level. The engineering of macroscopic
organic-electronic devices has benefited greatly from study of the factors that control the
energy-level alignment of those weakly interacting interfaces. Understanding the factors
that govern this energy mismatch, referred to as the charge-injection barrier, is also a
requirement for innovation of molecular-based electronic devices. However, far less work
has been done on the tightly-bound molecule/metal interfaces used in molecular
nanoelectronics. This study investigated the energy-level alignment of an arylthiol chemisorbed on Group IIB and IIIB metals.
For a molecule adsorbed on a surface, the charge transport barriers are referenced to the
highest occupied molecular orbital and lowest unoccupied molecular orbital and are
referred to as the hole (ΦB,hole) and electron injection (ΦB,elec) barriers, respectively. In the
case of minimal electronic-charge rearrangement, ΦB,hole can be estimated by aligning the
vacuum levels of the molecule and the metal. In this case, ΦB,hole is the difference
between the molecular ionization energy (IE) and the metal work function (ΦM), as
shown in Fig. 1. Investigations of weakly adsorbed molecules on a variety of metal and
semiconductor surfaces have shown that, in most cases, this model fails to accurately
predict ΦB,hole. An interface dipole (∆) is invoked to explain the shifting the vacuum
level. The expression for the charge-injection barrier then becomes ΦB,hole = IE - ΦM - ∆.
The magnitude of the shift can be
quantified by differentiating this
a
b
∆
equation with respect to ΦM
leading to:
d Φ B ,hole d Φ M + d ∆ d Φ M = −1 .
Φ
Φ
M
M
I.E.
The quantity S B = d Φ B ,hole d Φ M
is called the interface slope parameter and S D = d ∆ d Φ M dipole
slope parameter. The case of
SB = −1 corresponds to vacuum
level alignment or the SchottkyMott limit. Conversely, in the case
when ΦB,hole is pinned to a
constant energy, SB=0.
♣
I.E.
ΦB, hole
ΦB, hole
Figure 1. Vacuum alignment at an interface (a), and the effect of an
interface dipole.
[email protected]
72
SH
We have measured SB to determine whether
thiolate bound monolayers are closer to the
Schottky-Motts or the pinning limit.
Arylthiolates have been used in numerous
device prototypes and are known to form
ordered, densely-packed monolayers on
each of the surfaces studied here. A model
molecular
wire,
[tri-(phenyleneethynylene)thiol or “triPET”], was used to
determine SB. Monolayers of triPET were grown on
single crystals of Cu, Au, Pt, and Ag. Then ΦB,hole was
determined from the photoemission spectra of each
Counts
d
c
monolayer sample. The three-meter toriodal-grating monochromator (3m-TGM) beamline was used for these experiments.
b
The 55 eV photon energy spectrum of triPET adsorbed on each
The spectrum of triPET
on Pt has a large contribution from the
substrate resulting from low molecular
coverage, see Pt spectrum low binding
energy region in Figure 2d. The values of
ΦB,hole, extracted from these spectra, are
surface is shown in Figure 2.
10
8
6
4
2
0
Binding Energy (eV)
Figure 2. Photoemission spectra of triPET (upper right) on
a) Ag, b) Cu, c) Au, and d) Pt, where dashed line shows
clean Pt.
plotted for each metal in Figure 3. The holeinjection barrier is linear in work function
across the metal series, with the value of SB
determined as −0.76. These data are
evidence that the interface dipole is an important factor controlling energy-level alignment in these monolayers.
The relationship above shows that
SB + SD = −1. This equality holds only if the
interface dipole is the sole factor responsible
for the vacuum level shift. In future work at
CAMD, we plan to measure d ∆ d Φ M to
determine whether this is the case for these
systems. In the meantime, the results of this
study show that the hole-injection barrier,
ΦB,hole, changes linearly with metal work
function and that the best energy-level
alignment is achieved with large work function metals.
73
2.75
Vacuum alignment, S = 1
2.50
2.25
2.00
1.75
1.50
1.25
1.00
∆ (eV)
12
ΦB, hole Onset (eV)
a
S = 0.76 ± 0.11
0.75
0.50
Fermi alignment, S = 0
4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2
ΦM (eV)
Figure 3. ΦB,hole vs. ΦM. Squares are measured values.
Vertical lines show ∆ for each. Dashed lines represent
vacuum level alignment and Fermi level pinning.
Spectroscopy
X-ray
74
Hyperaccumulation and Reduction of Cr (VI) to Cr (III) From a
Hydroponic Solution by Seashore paspalum (Paspalum vaginatum): A
Phytoremediation study using XAS
Chris Bianchetti1, Roland Tittsworth1, Amativa Roy1, David Wall2, and Josef Hormes1
1 Center for Advanced Microstructures and Devices (CAMD) 6980 Jefferson Hwy.
Baton Rouge LA, 70806
2 Louisiana State University Agronomy
Cr (VI) is a known carcinogen and is extremely toxic even in trace amounts. Since Cr
contamination is found at more than half of all the EPA superfund sites [1], it is
important to develop environmentally safe methods to remediate Cr contamination. One
promising technique is phytoremediation. Phytoremediation uses plants to extract and
sequester harmful contaminants. In this phytoremediation study, seashore paspalum
(Paspalum vaginatum) was chosen for its rapid rate of growth, and potential for
utilization in coastal restoration. The P. vaginatum cuttings were grown in rock wool and
subsequently transferred into a hydroponic medium that contained a 250 ppm (4807.5
micromolar) concentration of Cr (VI). After a seven days growing period the seashore
paspalum were harvested and examined using X-ray Absorption Spectroscopy (XAS),
and Inductively Coupled Plasma Emission Spectroscopy (ICP ES). X-ray Absorption
Near Edge Spectroscopy (XANES) spectra indicate that the P. vaginatum exposed to Cr
(VI) not only extracted the Cr (VI) from solution, but the extracted Cr (VI) was reduced
to Cr (III). Extended X-ray Absorption Fine Structure (EXAFS) spectra were recorded in
order to determine the possible neighboring atoms, and there bond lengths. P. vaginatum
samples were dried and then tested by ICP ES to determine the concentration of Cr in the
roots, stems, and leaves. The ICP ES results showed that the P. vaginatum had a Cr
concentration of 438 ppm (8422.74 µmol), 33 ppm (634.59 µmol), and 70 ppm (1346.1
µmol) in the roots, stem, and leaves, respectively. With such a substantial concentration
of Cr in the roots and the leaves P. vaginatum can be considered a hyperaccumulator of
Cr.
3.5
3.0
Seashore Paspalum Leaves
Exposed to 250 ppm Cr (VI)
Cr (III) acetylacetonate
3.0
2.5
Cr (III) Nitrate
5990 eV
Seashore Paspalum Roots
5990 eV
2.5
2.0
2.0
Seashore Paspalum Roots
1.5
Absorption
Absorption
Cr Foil
Na2Cr(VI)O4
Seashore Paspalum Stems
1.5
Na2Cr(VI)O4
1.0
1.0
0.5
0.5
0.0
0.0
5960
5980
6000
6020
6040
6060
6080
6100
5960
Energy (eV)
5980
6000
6020
6040
6060
6080
6100
Energy (eV)
Cr (VI) has a distinctive pre edge peak at 5993 eV. This pre-edge peak is only
present in Cr compounds that are in +VI oxidation state. Figure 1 shows several standard
Cr compounds that were collected during the experiment. The only compound that has a
pre-edge is Sodium Chromate. Therefore it is a trivial matter to determine if the Cr in a
75
Cr containing sample is in the +VI oxidation state. When the P. vaginatum roots, stems,
and leaves are examined it is apparent that there is not any Cr (VI) in the P. vaginatum
due to the lack of the Cr (VI) pre-edge peak. Also it is apparent that the edge position of
the P. vaginatum roots, stems, and leaves correspond to that of Cr (III). With The
elevated concentration of Cr in the leaves, stems, and roots indicates P. vaginatum’s
ability to hyperaccumulate Cr from a hydroponic system. It appears that the P. vaginatum
stored the Cr in the stems, and roots but some Cr was also detected in the leaves. Cr Kedge XANES reveals that P. vaginatum can hyperaccumulate Cr (VI) and reduce Cr (VI)
to Cr (III). The P. vaginatum roots exhibit dramatic hyperaccumulation of Cr, and are
able to absorb close to twice the Cr concentration from the hydroponic solution. The
ability to extract and store a high concentration of contaminants from the environment
classifies P. vaginatum as a hyperaccumulator. We have obtained preliminary results
which indicate that P. vaginatum can also hyperaccumulate As from a hydroponic
solution.
76
Speciation of Lead and Arsenic of Soil and Plants Employed for
Phytoremediation at Barber Orchard, NC
PRN WCU-DB0106
Principal Investigator: David Butcher
Department of Chemistry & Physics
Western Carolina University
Cullowhee, NC 28723
Voice: (828) 227-7646
Email: [email protected]
Co-Principal Investigator: James Bolick (M.S. Student)
Barber Orchard is a Superfund site located in Haywood County, NC. For the first
90 years of the twentieth century, it was a commercial apple orchard. Throughout this
period, a variety of pesticides were employed at this location, including lead arsenate. In
the 1990s, 37 homes were constructed on this site. The pollutant of greatest concern is
arsenic, as soil concentration levels above 40 mg/kg are considered a serious threat to
human health.
Phytoremediation, which involves the use of green plants to collect pollutants
from soil, is an alternative approach to conventional remediation techniques (excavation
of soil). Its principal advantage is cost. Commercially available Chinese brake fern
(Pteris vittata) and moonlight ferns (Pteris cretica cv Mayii) were evaluated to determine
its suitability for phytoextraction of arsenic at Barber Orchard. Bench scale studies have
illustrated the application of electrodic phytoremediation for the remediation of lead
using Indian mustard. Current experiments involve the use of a hydroponic system to
characterize the uptake of arsenic. All of these experiments involved analysis by
inductively coupled plasma – optical emission spectrometry, which determines the total
form of lead and arsenic present.
We conducted two sets of experiments at CAMD during 2005. On September 19,
preliminary studies were performed on arsenic standards and brake fern samples for
arsenic. These studies demonstrated that the concentrations in the plant samples were
detectable by X-ray fluorescence.
We then returned on November 1-3 to analyze moonlight ferns that were grown in
our hydroponic system while exposed to various chemical forms of arsenic. The goal
was to determine whether the form in the hydroponic solution affected the form of
arsenic present in the plant tissue. The ferns were exposed to 200 µM solutions of
arsenic (III), arsenic (V), organic arsenic, arsenic (III) and arsenic (V), or arsenic (III) and
organic arsenic. The samples were analyzed by x-ray fluorescence at CAMD. We also
analyzed soil samples from Barber Orchard to characterize the chemical form(s) of
arsenic present in the soil. We are currently in the process of analyzing these data as part
of Mr. Bolick’s M.S. thesis research.
We have not currently published any papers, made any presentations, or written
any proposals based on this research.
77
Synchrotron X-ray Absorption Spectroscopy (XAS) for Understanding
Dopant Effects in Ti-doped NaAlH4
Tabbetha A. Dobbins1, Roland Tittsworth2, Scott A. Speakman3, Joachim Schneibel3
1
Lousiana Tech University, Institute for Micromanufacturing, P.O. Box 10137, Ruston,
LA 71272, U.S.A.
2
Louisiana State University, Center for Advanced Microstructures and Devices, 6980
Jefferson Hwy., Baton Rouge, LA 70806, U.S.A.
3
Oak Ridge National Laboratory; Oak Ridge, TN, 37831, USA
Contact: [email protected]
PRN: LaTech-TD0505
INTRODUCTION
We report studies concerning the time frame for catalytic reactions between NaAlH4
(sodium alanate) and TiCl3 during high energy milling. Spectral features in x-ray
absorption spectra were analyzed for samples milled for various times (0 minutes, 1
minute, 5 minutes, 25 minutes, and 125 minutes). A structural transition from Ti3+ to Ti0
is observed within the first 5 minutes of milling. The Ti0 structure persists for samples
milled for times longer than 5 minutes—even after those samples underwent a subsequent
single hydrogen desorption/absorption cycle. Samples milled for less than 5 minutes
retain Ti3+. For samples milled for 1 minute, the Ti-K edge position shifts from Ti3+ to
Ti0 after a single desorption/absorption cycle. However, the first coordination sphere
around the Ti0 absorber occurs at longer distances for 1 minute milled sample. These
results hint at the formation of Ti0 pure metallic clusters upon desorption/adsorption
cycling of 1 minute milled sample. Previously reported x-ray absorption spectroscopy
studies have demonstrated the structural transition from Ti3+ (in TiCl3) to Ti0 (determined
to be TiAl3 found at the surface of the alanate powder). Aluminum deficiency on the
NaAlH4 lattice is responsible for controlling hydrogen absorption capacity. These timeresolved spectroscopy studies suggest the possibility for controlling aluminum
deficiency, while still maintaining titanium activation of the alanate powder, by
manipulating the coordination environment of the titanium dopant during the first five
minutes of high energy milling. Specifically, a possible approach to mitigating aluminum
deficiency during doping would be to introduce an alternative species to which the to Ti3+
catalyst would form a metallic bond after the TiCl3 has attached at the surface of the
sodium alanate powder and before the Ti3+ forms the TiAl3 intermetallic species.
Several researchers report mechanisms for the role of the catalyst in Ti-doped NaAlH4.116
Experimentally, x-ray and neutron scattering—as well as FTIR— studies have been
used to study the positioning of hydrogen and metallic ions in complex metal hydrides.
Among these studies, many researchers have used x-ray absorption spectroscopy (XAS)
to elucidate the problem.5-7, 11, 12 Using XAS, Graetz et al.7 have observed TiAl3 at the
surface of NaAlH4 powders after several desorption/absorption cycles. Other researchers
have observed TiAl3 formation using x-ray diffraction and NMR studies.3, 16 It was
hypothesized that Al-H bonds were weakened in this structure--- thus influencing
hydrogen desorption kinetics.9, 10 Although the NaAlH4 atomic model has been well
78
established using Rietveld refinement, controversy remains regarding the exact role of
Ti3+ dopants in the NaAlH4 complex hydride system. Furthermore, the formation of
TiAl3 phase is believed to be responsible for lower than theoretical absorption capacities
upon desorption /absorption cycling.3 Here, we report on the time scale for the structural
evolution in the local environment of TiCl3 introduced to NaAlH4 by x-ray absorption
spectra (XAS) collected from samples milled for a variety of times. Such studies may
eventually enable the manipulation of the transition metal dopant in order to optimize its
kinetic enhancement effect—while reducing its potential for Al depletion from NaAlH4
powders.
RESULTS AND DISCUSSION
Since H- is found in the first coordination sphere around Al in the NaAlH4 crystal
structure, desorption reactions to release H2 gas from the structure yields metallic
aluminum product. The Al3+-H- bond lengths have been reported as 1.55Ǻ.17 The Na+
cation also has 4 neighboring H- ions at 1.88-2.00Ǻ distance. After doping with Ti
species, x-ray absorption studies have reported the formation of TiAl3.7, 11, 12
1.8
Normalized Absorption (a.u.)
1.6
1.4
1.2
1.0
0.8
0.6
0
Ti Foil (Ti )
0
0.4
TiAl3 (Ti )
0.2
TiN (Ti )
0.0
TiO2 (Ti )
3+
4+
4960
4970
4980
4990
5000
5010
5020
Photon Energy (eV)
Figure 1. Absorption edge positions for standards occurring at 4966eV for Ti foil, at
4966eV for TiAl3, at 4969eV for TiN and at 4978eV for TiO2.
1.2
1.0
0.8
0.6
0.4
0 minute mill time (blended)
1 minute mill time
5 minute mill time
25 minute mill time
125 minute mill time
0.2
0.0
4960
4970
4980
4990
5000
5010
5020
Photon Energy (eV)
Figure 2. Absorption edge positions for samples milled for 0 minutes, 1 minute, 5
minutes, 25 minutes, and 125 minutes. Absorption edge position shifted after a mill
time between 1 and 5 minutes. The shift occurred from a K-edge position
representative of the Ti3+ standard (at 4969 eV) to a K-edge position representative
of Ti0 standards (at 4966 eV).
79
1 Minute Mill Time (Blended)
1.2
1.0
0.8
0.6
0.4
0.2
1 minutes mill time (Blended)
Cycled
0.0
1.2
125 Minutes Mill Time
5 Minutes Mill Time
1.2
1.0
0.8
0.6
0.4
0.2
5 minutes mill time
Cycled
4970
4980
4990
5000
5010
5020
0.8
0.6
0.4
0.2
25 minutes mill time
Cycled
0.0
0.0
4960
1.0
4960
4970
Photon Energy (eV)
4980
4990
5000
5010
4960
5020
4970
4980
4990
5000
5010
5020
Photon Energy (eV)
Photon Energy (eV)
Figure 3. Absorption edge position before and after a single H2 desorption/absorption
cycle.
1 Minute Mill Time (Blended)
1.67A
20x10
As Milled
Cycled
2.47A
-3
400x10
As Milled
Cycled
2.27A
2.10A
10
5
10
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
200
100
0
0
0.0
As Milled
Cycled
2.20A
300
5
0
-6
2.15A
15
FT(χ(k))
15
FT(χ(k))
25 Minutes Mill Time
5 Minutes Mill Time
-3
FT(χ(k))
20x10
0.0
1.0
2.0
R(Å)
3.0
4.0
R(Å)
5.0
6.0
7.0
8.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
R(Å)
Figure 4. Fourier Transform of χ(k) signal—indicator of distance to first coordination
shell around the Ti3+ or Ti0 species. Data are not phase shift (δj(k)) corrected—thus,
only qualitative trends in the radial distribution function is offered by the analysis and
distances to the first coordination shell should not be taken as absolute..
Comparisons of the normalized absorption data of various standards (Figures 1) and
samples milled for various times (Figure 2) reveals the absorption edge corresponding to
the metallic Ti0 at 4966 eV for samples milled for 5 minutes, 25 minutes and 125
minutes. For blended samples and those milled for 1 minute, the absorption edge occurs
at 4969eV—which corresponds to Ti3+. After one desorption/absorption cycle, the Ti0
chemical state persists for samples milled for 5 minutes or longer (Figure 3). However,
the sample milled for 1 minute undergoes a chemical shift from the Ti3+ to the Ti0 state
after a single desorption/absorption cycle.
Formation of a hydride-rich TiAl3
intermetallic phase has been reported previously to account for the phase to which the Ti0
belongs.6, 11, 12 The formation of this intermetallic phase is known to reduce the overall
hydrogen absorption capacity for doped samples.3 The distance to the first coordination
sphere around the Ti0 (after a single desorption/absorption cycle) is shown in Figure 4.
The sample milled for 1 minute shows a longer distance to the first coordination shell (at
2.50 Angstroms) relative to those milled for longer times (at ~2.26Angstroms). Others
report distances for Ti-Ti at 2.98Angstroms6 and Ti-Al at 2.80Angstroms10. We believe
that the longer distance revealed by XAS is strong evidence that metallic Ti0 clusters
form after the single desorption/absorption cycle in the sample milled for 1 minute. That
is, the formation of Ti0 clusters occurs for “undermilled” samples (i.e. samples milled for
times below which Ti3+ shifts to Ti0 oxidation state). For samples milled for longer
times, the shorter distance observed by XAS suggest the formation of the TiAl3
intermetallic phase after the single desorption/absorption cycle. It remains to be explored
as to whether the Ti0 remains situated at the surface of the NaAlH4 powder—as reported
80
8.0
by others for samples milled for longer times.3, 7, 9, 10 These results are significant in that
they suggest that there may be a brief period of time (or “induction period”) during which
the dopant may be chemically altered by reactants in order to bypass Ti-Al formation—
while permitting the Ti to attach at the NaAlH4 particle surface for facilitating the Al-H
bond weakening—a mechanism for the role of the dopant suggested by Iniguez et al.9, 10
ACKNOWLEDGMENTS
We thank Mr. Christopher Bianchetti (CAMD) for his kind help in our XAS
measurements. Funding for this project is provided by the Department of Energy, Office
of Basic Energy Sciences (Contract No.: DE-FG02-05ER46246). Partial support is
provided by National Science Foundation, Division of Materials Research (Contract No.:
DMR-0508560) and the Louisiana State Board of Regents Office of Sponsored Research
(Contract No.: LEQSF(2005-08)RD-A-20). JHS acknowledges the support of the
Laboratory Directed Research and Development Program of Oak Ridge National
Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy
under Contract No. DE-AC05-00OR22725.
KEYWORDS
hydrogen storage, Alanates, EXAFS, XANES
REFERENCES
1.
Anton D.L., Hydrogen Desorption Kinetics in Transition Metal Modified NaAlH4. Journal of Alloys and
Compounds 2003, 356-357, 400-404.
2.
Bogdanovic B.; Brand R.A.; Marjanovic A.; Schwickardi M.; Tolle J., Metal-doped Sodium Aluminum
Hydrides as Potential New Hydrogen Storage Materials. Journal of Alloys and Compounds 2000, 302, 36-58.
3.
Bogdanovic B.; Felderhoff M.; Germann M.; Hartel M.; Pommerin A.; Schuth F.; Weidenthaler C.;
Zibrowius B., Investigation of Hydrogen Discharging and Recharging Processes of Ti-doped NaAlH4 by X-ray
Diffraction Analysis (XRD) and Solid-State NMR Spectroscopy. Journal of Alloys and Compounds 2003, 350, 246255.
4.
Bogdanovic B.; Schwickardi M., Ti-Doped NaAlH4 as a Hydrogen-Storage Material-- Preparation by TiCatalyzed Hydrogenation of Aluminum Powder in Conjunction iwth Sodium Hydride. Applied Physics A 2001, 72,
221-223.
5.
Bruster E.; Dobbins T.A.; Tittsworth R.; Anton D., Decomposition Behavior of Ti-doped NaAlH4 Studied
using X-ray Absorption Spectroscopy at the Titanium K-edge. Mater. Res. Soc. Symp. Proc. 2005, 837, N3.4.1.
6.
Fichtner M.; Fuhr O.l.; Kircher O.; Rothe J., Small Ti Clusters for Catalysis of Hydrogen Exchange in
NaAlH4. Nanotechnology 2003, 14, 778-785.
7.
Graetz J.; Reilly J.J.; Johnson J.; Ignatov A.Yu; Tyson T.A., X-ray Absorption Study of Ti-Activated Sodium
Aluminum Hydride. Applied Physics Letters 2004, 85, (3), 500-502.
8.
Gross K.J.; Thomas G.J.; Jensen C.M., Catalyzed Alanates for Hydrogen Storage. Journal of Alloys and
Compounds 2002, 330-332, 683-690.
9.
Iniguez J.; Yildirim T.; Udovic T.J.; Sulic M.; Jensen C.M., Structure and Hydrogen Dynamics of Pure and
Ti-doped Sodium Alanate. Physical Review B 2004, 70, 06101.
10.
Iniguez J.; Yildirim T., First-Principles Study of Ti-Doped Sodium Alanate Surface. Applied Physics Letters
2005, 86, 103109.
11.
Leon A.; Kircher O.; Rothe J.; Fichtner M., Chemical State and Local Structure Around Titanium Atoms in
NaAlH4 Doped with TiCl3 Using X-ray Absorption Spectroscopy. J. Phys. Chem B 2004, 108, 16372-16376.
12.
Leon A.; Rothe J.; D., S.; Fichtner M., Comparative Study of NaAlH4 Doped with TiCl3 or Ti13.6THF by
Ball Milling Using XAS and XPS. Chemical Engineering Transactions 2005, 8, 171-176.
13.
Sandrock G.; Gross K.; Thomas G.; Jensen C.; Meeker D.; Takara S., Engineering Considerations in the use
of Catalyzed Sodium Alanates for Hydrogen Storage. Journal of Alloys and Compounds 2002, 330-332, 696-701.
14.
Sandrock G.; Gross K.; Thomas G., Effect of Ti-Catalyst Content on the Reversible Hydrogen Storage
Properties of the Sodium Alanates. Journal of Alloys and Compounds 2002, 339, 299-308.
15.
Leon A.; Kircher O.; Fichtner M.; Rothe J.; Schild D., Study of the Evolution of the Local Structure around
Ti Atoms in NaAlH4 Doped with TiCl3 or Ti13.6THF by Ball Milling Using XAS and XPS Spectroscopy. J. Phys.
Chem. B 2005, Accepted for Publication.
16.
Weidenthaler C.; Pommerin A.; Felderhoff M.; Bogdanovic B.; Schuth F., On the State of the Titanium and
Zirconium in Ti- or Zr-doped NaAlH4 Hydrogen Storage Material. Phys. Chem. Chem. Phys 2003, 5, 5149-5153.
17.
Cotton F.A.; Wilkinson G., Advanced Inorganic Chemistry. Wiley and Sons Publishers: New York, NY,
1988.
81
XANES/EXAFS Study of Transition Metal Cationic (Ca2+, Fe3+, and
Mn2+) Dopants in Polymer Films during Layer-by-Layer Nanoassembly
Vimal Kamineni, Tabbetha A. Dobbins, Yuri Lvov
Lousiana Tech University, Institute for Micromanufacturing, P.O. Box 10137, Ruston,
LA 71272, U.S.A.
Contact: [email protected]
PRN: LaTech-TD0505
INTRODUCTION
With the growing economic turbulence of existing hydro-carbon fuels and their pollution
in the atmosphere, the governments of the world are looking for a safer and environment
friendly fuel. From, the research done in testing a lot of options for the fuel of the future
hydrogen is leading the race by a large margin. Hydrogen has water vapor as by-product,
which is eco-friendly.
There are various methods for storing hydrogen fuel, but the safest and for more effective
method is by storing them in the form of metal hydrides. Metal hydrides are heavy
compounds with various kinds of metals and hydrogen present in them. There are a vast
number of metal hydrides that can be prepared, but our scope of interest is in using
lighter metal halides with higher weight percentage of hydrogen. Of all these metal
hydrides sodium aluminum hydride, lithium aluminum hydride and magnesium
aluminum have higher weight percentage of hydrogen. These metal hydrides need to be
used as commercial fuels so they should easily absorb and desorb hydrogen under
optimum working conditions. Out of these metal hydrides sodium aluminum hydride is
the best fuel for the forward and backward reaction involved in the storage of hydrogen.
The storage and the kinetics is further improved by using titanium metal as a catalyst.
There are various methods of adding titanium to the metal hydrides. Some of the methods
are ball milling, sputtering and layer-by-layer technology. In future studies, layer-bylayer (LbL) nanoassembly will explored as a means to coat NaAlH4 colloidal particles
with salts of titanium and other metals. Coating colloidal particles with polyelectrolyte
films has been achieved by Sukhorukov et al.1 After the hydride particles have been
coated, the oxidation state of the metals on the NaAlH4 micron colloidal particles will be
explored EXAFS and XANES. In these studies, the feasibility of coating metal salts
using a method developed for polyelectrolyte deposition is explored.
EXPERIMENTAL
Layer-by-layer (LbL) nanoassembly is used to deposit uniform multilayer thin films (~5
nm or more) from polyelectrolyte solutions adsorbed onto silicon substrates.1,2 During
the assembly process, coulombic interactions between polymeric cations and anions lead
to film growth. We have used XANES and EXAFS to examine the oxidation state and
local environment of metallic cations added to LbL polyelectrolyte assemblies. The
metal salts used were 0.5 M of each FeCl3, MnCl2, and CaCl2. Samples were prepared by
alternately adsorbed poly(styrenesulfonate) (called PSS) (in 2 mg/mL aqueous) and
polyaniline hydrochloride (called PAH) (in 2 mg/mL aqueous). The metal salts were
added to the PSS polyanion aqueous solution.
82
Analysis shows local sulfate (SO2-) formation around all three the cations (i.e Fe3+, Mn2+,
and Ca2+) (preliminary analysis performed via comparison with the sulfate standard).
Metal cation additions are known to improve adsorption and to reduce film thickness,
however, these reports represent the earliest work in using x-ray absorption spectroscopy
to define the binding sites of metal cations.1
3.5
2
1.6
0.5M FeCl2 in film
Fe2(SO4)3 Standard
1.4
0.5M CaCl2 in Film
CaSO4 Standard
0.5M MnCl2 in Film
MnSO4 Standard
1.8
3
1
0.8
0.6
0.4
1.6
1.2
1.4
1.2
1
0.8
0.6
2.5
2
1.5
1
0.4
0.5
0.2
0.2
0
0
0
7
7.2
7.4
Energy (keV)
7.6
6.5
6.55
6.6
6.65
Energy (keV)
6.7
4
4.1
4.2
4.3
4.4
4.5
Energy (keV)
Figure 1. Comparison of Mx+-PSS/PAH Films with sulfate standards. (Mx+=Fe3+, Mn2+,
and Ca2+)
ACKNOWLEDGMENTS
We thank Dr. Amitava Roy (CAMD) and Mr. Christopher Bianchetti (CAMD) for kind
help in our XAS measurements. We thank Ms. Katherine Keeton for help in LbL sample
preparation. Funding for this project is provided by the National Science Foundation,
Division of Materials Research (Contract No.: DMR-0508560). Partial support is
provided by the Department of Energy, Office of Basic Energy Sciences (Contract No.:
DE-FG02-05ER46246) and the Louisiana State Board of Regents Office of Sponsored
Research (Contract No.: LEQSF(2005-08)RD-A-20).
KEYWORDS
polyelectrolytes, layer by layer, EXAFS, XANES
REFERENCES
1. Schukin D., Sukhorukov, G.B. Micron Scale Hollow Polyelectrolyte Capsules with Nanosized Magnetic
Fe3O4 Inside, Langmuir V19 (2003) 4427-4431.
2. Decher G., “Fuzzy nanoassemblies: Toward layered polymeric multicomposites”, Science 227 pp 12321237 (1997).
3. Lvov Y., Ariga K., Onda M., Ichinose I., Kunitake T., “A Careful Examination of the Adsorption Step in
the Alternate Layer-by-Layer Assembly of Linear Polyanion and Polycation”, Colloids and Surfaces A:
Physicochemical and Engineering Aspects 146 pp 337-346 (1999).
4. Dhullipudi R.B., Lvov Y.M., Adiddela S., Zheng Z., Gunasekaran R.A., Dobbins T.A., “Noncovalent
Functionalization of Single-Walled Carbon Nanotubes using Alternate Layer-by-Layer Polyelectrolyte
Adsorption for Nanocomposite Fuel Cell Electrodes”, Materials Research Society Symposium –
Proceedings 837, paper N3.27.1 (2005).
83
New Catalysts for Methylketone Manufacture
Craig Plaisance*, Kerry Dooley, Amitava Roy1
Louisiana State University, Gordon A & Mary Cain Department of Chemical
Engineering, Baton Rouge, LA 70808 USA and 1Center for Advanced Microstructures &
Devices 6980 Jefferson Hwy., Baton Rouge, LA 70806 USA
E-mail:[email protected]; PRN - ChE-KD0705; ChE-KD0306
INTRODUCTION
The aim of this work is the determination of electronic structure and coordination
environment of Ce and dopant atoms in pure and doped (K, Co, Pd) mixed metal oxide
catalysts used for the manufacture of methylketones by acid/acid and acid/aldehyde
condensations. XANES and EXAFS spectra were collected at room temperature and at
420°C (a typical reaction temperature), in both inert and reducing environments.
EXPERIMENTAL
Synchrotron radiation emitted by the Electron storage ring of the Center for Advanced
Microstructure and Devices (CAMD) in Baton Rouge running at 1.3 GeV with an
average current of 100mA was used. The spectra were obtained in transmission mode
with ionization chambers measuring the incident beam intensity before and the
transmitted beam intensity after the sample cell. A third ionization chamber was used for
calibration with a standard. The spectra were taken by pressing the catalyst samples into
self-supporting wafers, and then loading them into an XAS (X-ray Absorption
Spectroscopy) cell. First, a scan was taken at room temperature. The wafer was heated to
~420°C in a flow of N2, and scanned at this temperature. The sample was then reduced
for 15 minutes in an atmosphere of 10% H2 (balance N2) and another scan was taken. For
the Ce LIII edge, spectra (XANES and EXAFS) were taken from 5525-6145 eV. For the
Co K edge in transmission mode, spectra were taken from 7550-8700 eV. In
fluorescence mode, spectra were taken from 7559-8710 eV. The raw spectra were
background corrected and normalized using WinXAS1 for XANES analysis. For EXAFS
analysis, Athena was used to subtract a smooth background function with Fourier
components less than 1 Å. The data were then converted to k-space to get χ(k).
The total number of days of beamtime used for the 2005 calendar year was three.
RESULTS AND INTERPRETATION
The normalized XANES data shown in Figure 1 were fitted with model functions
consisting of a Lorentzian and an arctangent to describe the two white lines originating
from Ce(IV) at 5728 eV and 5736 eV and the single white line originating from Ce(III) at
5725 eV.2 From such functions, the ratio of Ce(III) to Ce(IV) is estimated from the peak
area ratio. The presence of two white lines at the Ce(IV) edge is ascribed to a mixed
valence state of Ce, which consists of a superposition of f0 and f1L states, where L is a
hole in the ligand band.3 The low energy white line results from the transition to a d1f1L
84
final state and the high energy white line results from the transition to a d1f0 final state.
The intensity ratio of these two lines is equal to the amplitude ratio of the two oneelectron states in the initial state. In addition to these two lines, a shoulder is present
about 4 eV below the first line that is thought to arise from crystal field splitting of the Ce
d orbitals by the oxygen coordination shell.
2.5
undoped
Normalized Absorption
0.8% Pd
0.8% Co
2.0
2.4% Co
1.5
1.0
0.5
0.0
5720
5725
5730
5735
5740
Photon Energy (eV)
Figure 1. XANES spectra of catalysts taken at 420°C in reducing conditions
The 0.8% Pd and 0.8% Co catalysts have a higher intensity peak or shoulder
corresponding to Ce(III) than does the undoped sample, while the catalyst containing
2.4% Co has a lower intensity shoulder, as do the K-containing samples (not shown
here). These differences in the number of oxygen vacancies in the Ce coordination shell
are roughly correlated with catalytic activity for ketonization reactions at early times
onstream.
Two methods were used to estimate the number of oxygen vacancies from the XANES
data: (1) the method of Takahashi et al.;2 (2) linear fits using the WinXAS package.1
Takahashi et al. used physical mixtures of Ce(III) oxalate and Ce(SO4)2 to derive a linear
correlation between relative peak areas and relative amount of Ce(III) in Ce(III)/Ce(IV)
mixtures. Following normalization and background removal, each white line was fitted
with a Lorentzian and an arctangent. The centers of each function were fixed relative to
each other, and the width of each function was also set according to the standards. The
relative amplitudes of the two white lines in Ce(IV) were also fixed. Three parameters
were fitted, the edge position and the amplitudes of Ce(III) and Ce(IV). The areas under
the corresponding Lorentzians were used in the correlation. It is assumed that the
XANES spectrum of a Ce(III) atom adjacent to an oxygen vacancy in reduced CeO2 is
85
similar to Ce(III) in the salt, and that the spectrum of Ce(IV) in CeO2 is the same as in
Ce(SO4)2. But in comparing the spectra of CeO2 and Ce(SO4)2, it is seen that the
shoulder present in CeO2 due to the crystal field is not present in Ce(SO4)2, so the
amount of Ce(III) (oxygen vacancies) in supported CeOx will be overestimated by this
method.
WinXAS was also used to calculate the relative amounts of the two valence states by
matching the XANES spectra to linear combinations of the spectra of the CeO2 and
Ce(III) acetate standards. The first assumption here is the same as the first assumption of
the Takahashi et al. method. The second assumption is that Ce in the catalyst, mostly
present on the surface, gives the same spectrum as in the bulk. Since the shoulder and the
lower energy white line are slightly more intense in larger crystals,6 and since these
features are at energies close to that of the Ce(III) white line, this method should
underestimate Ce(III) in the catalyst (the catalyst should give a spectrum closer to that of
smaller crystals, because the CeO2 is approximately monolayer). Therefore, the number
of oxygen vacancies predicted by the Takahashi et al. and WinXAS methods should
bound the actual number of vacancies.
The trends in the average number of oxygen vacancies in the coordination shell adjacent
to each Ce atom (8 oxygen atoms maximum) are shown in Figure 2. The two methods of
quantification often give close values, but the WinXAS method always predicts the
smaller number of vacancies. Treatment with H2 increased the number of vacancies, in
some cases even more if the treatment time was lengthened. For example, in catalysts
that had been used for two full days the number of vacancies was found to be in the 1.21.3 range. Therefore under the reducing reaction conditions, supported CeO2 is quite
defective. The number of vacancies for the CeO2/Al2O3 (corresponding to ~40%
reduction of CeO2 to Ce2O3) and the 0.8% Pd catalyst (corresponding to ~45-48%
reduction of CeO2 to Ce2O3) are both similar to measured values from previous work, for
CexZr1-xO2 and Pd/CexZr1-xO2 reduced at 500°C in H2.7
EXAFS data for the Co K-edge were fitted using WinXAS and Artemis,1 to theoretical
spectra for a Co atom substituted into CeO2, generated by FEFF6.4 Data were fitted in
the R-space range of 0.9 – 4.8 Å derived from the Fourier-transformed region of k-space
from 3.0 – 9.4 Å-1. Data in k-space were obtained by subtracting background Fourier
components of less than 1.0 Å. In the fit done in Artemis, the spectra were further
refined by including background parameters in the fitting process. The k, k2 and k3
weighted spectra of each set were simultaneously fit to reduce correlation between
coordination number and Debye-Waller factors in Artemis. In WinXAS, only k and k2
weighted spectra were used.
86
1.0
WinXAS (N2)
Oxygen Vacancies per Ce atom
Takahashi (N2)
WinXAS (H2)
0.8
Takahashi (H2)
0.6
0.4
0.2
0.0
undoped
3% K2O
0.8% Pd
0.8% Co
2.4% Co
Figure 2. Average number of oxygen vacancies around each Ce atom as determined by
XANES using the Takahashi and WinXAS methods.
The model used in regression included parameters for the radial distances and DebyeWaller factors of the first five shells and the coordination numbers of the first oxygen
shell. The theoretical model substituted half of the Ce atoms in the second shell with Co
atoms, although the relative number of each was allowed to vary during the fit. A
different radial distance was used for the Ce and Co sub-shells but the same DebyeWaller factor was used for both. The coordination number of oxygen atoms in the third
shell was highly correlated with the Debye-Waller factor; to produce a reasonable fit, the
coordination number was fixed at 21 (3 vacancies), since XANES indicate approximately
this number. The coordination numbers of the fourth and fifth shells were fixed at 6 and
24 respectively. The electron amplitude reduction factor (0.9) was determined by fitting
a Co foil standard in WinXAS.
Scattering paths with up to four coplanar legs were included in the model. WinXAS
correlates the parameters for the multiple scattering (MS) paths to those of the single
scattering (SS) paths. In Artemis, the amplitudes of the MS paths were assumed to vary
proportionally with the coordination number for each atom in the path. The path lengths
for MS paths were determined from the SS path lengths by assuming the scattering angle
does not change with path length. The Debye-Waller factors for MS paths were taken as
the average of the Debye-Waller factors for each atom in the path.
The Co EXAFS spectra in R-space for the Co/CeO2/Al2O3 catalysts are shown in Figure
3; the fitting parameters obtained using Artemis are given in Table 1. The first five
coordination shells expected for Co added to a CeO2 lattice appear in the spectra. It was
found that at least half of the Ce atoms in the second shell are substituted by Co,
indicating that dispersion of Co within the lattice is not homogeneous, and is less so for
the 2.4% Co catalyst, as expected. There are roughly four oxygen atoms in the first
87
coordination shell of Co, compared to six for CoO. For both samples, fitting using either
the WinXAS or Artemis packages gave similar numbers. The results suggest that for
both samples there is intimate association of much of the Co with a CeOx phase,
especially for the 2.4% Co. This was borne out in the results of Fig. 2, where the addition
of Co at the 2.4 wt% level affected the reduction of CeO2 less than 0.8% Co or the 0.8%
Pd, a result that was contrary to expectation.
1.5
Data
1.0
Fit
-3
χ (R) (Å )
0.5
0.0
-0.5
-1.0
-1.5
0
1
2
3
4
5
R (Å)
1.5
Data
1.0
Fit
-3
χ (R) (Å )
0.5
0.0
-0.5
-1.0
-1.5
0
1
2
3
4
5
R (Å)
Figure 3. Fourier-transformed (k2 weighted magnitude and real parts) EXAFS for Co K
of 0.8% Co (top) and 2.4% Co (bottom) Co/CeO2/Al2O3. The fit obtained using
88
Artemis is shown
Table 1. Fitted EXAFS parameters for 0.8% Co (top) and 2.4%
Co (bottom) CeO2/Al2O3 catalysts using Artemis.
Shell
O (1)
Co (2)
Ce (2)
O (3)
Ce (4)
O (5)
CN
4.4 ± 1.9
5.2 ± 3.3 b
6.8 ± 3.3 b
21 a
6a
24 a
R (Å)
1.95 ± 0.04
3.07 ± 0.05
3.20 ± 0.07
3.88 ± 0.13
4.70 ± 0.21
5.41 ± 0.57
σ (Å)
0.009 ± 0.008
0.014 ± 0.003 3
0.014 ± 0.003 3
0.031 ± 0.026
0.020 ± 0.030
0.050 ± 0.140
O (1)
Co (2)
Ce (2)
O (3)
Ce (4)
4.4 ± 2.4
7.2 ± 4.4 b
4.8 ± 4.4 b
21 a
6a
1.95 ± 0.05
3.03 ± 0.08
3.19 ± 0.09
3.85 ± 0.16
4.72 ± 0.21
0.006 ± 0.009
0.012 ± 0.005 3
0.012 ± 0.005 3
0.028 ± 0.031
0.013 ± 0.027
O (5)
24 a
5.45 ± 0.47
0.029 ± 0.082
a
Value fixed within regression
Sum constrained to 12 within regression
3
Set equal during fitting
b
REFERENCES
1. T. Ressler, WinXAS (2004).
2. Y. Takahashi, H. Shimizu, H. Kagi, H. Yoshida, A. Usui, M. Nomura, Earth and
Planetary Sci. Lett., 182, 201-207 (2000). Y. Takahashi, H. Sakami, M. Nomura,
Analytica Chemica Acta, 468, 345-354 (2002).
3. A. V. Soldatov, T. S. Ivanchenko, S. Della Longa, A. Kotani, Y. Iwamoto, A.
Bianconi, Phys. Rev. B, 50(8), 5074-5080 (1992).
4. B. Ravel, Artemis (2004). M. Newville, IFEFFIT (2004).
5. E. Fonda, D. Andreatta, P. E. Colavita, G. Vlaic, Journal of Synchrotron Radiation,
6(1), 34-42 (1999).
6. P. Nachimuthu, W.C. Shih, R.S. Liu, L.Y. Jang, J.M. Chen, J. Solid State Chem. 149
(2000) 408.
7. A. Norman, V. Perrichon, A. Bensaddik, S. Lemaux, H. Bitter, D. Koningsberger,
Top. Catal. 16-17 (2001) 363.
89
Auger Electron Radiotherapy and Dosimetry
Joseph P. Dugas1, Scott Oves1, Erno Sajo1, Frank Carroll2,3, and Kenneth R. Hogstrom1,4
[email protected]; [email protected]; [email protected]; [email protected];
[email protected]
1. Louisiana State University, Department of Physics and Astronomy, 202 Nicholson
Hall, Baton Rouge, LA, 70803
2. Department of Radiology and Radiological Sciences, Vanderbilt University Medical
Center, 1221 21st Ave. S., Nashville, TN 37235-2675
3. MXISystems Inc., 7226 White Oak Drive, Fairview, TN, 37062
4. Mary Bird Perkins Cancer Center, 4950 Essen Lane, Baton Rouge, LA, 70809
PRN: Phy-KH0606
Overview. A collaboration of personnel from LSU Medical Physics, Vanderbilt
University/MXISystems (Fairview, TN), and CAMD was founded in 2005 with aims to
study: (1) monochromatic Auger electron radiotherapy, dosimetry, and treatment
planning; and (2) phase contrast imaging. Specific aims of the project under examination
at CAMD in 2005 are:
Aim 1: Determination of monochromatic x-ray beam properties to provide
physical data for theoretical calculations and designing future experiments
including: beam intensity (# x-rays·s-1), mean energy (keV), spatial (x-y)
distribution, and beam divergence.
Aim 2: Measurement of the central axis depth dose for a broad beam (3×3 cm2) in
a homogeneous plastic phantom (PMMA) and an inhomogeneous phantom
(PMMA and bone plastic) for comparison to Monte Carlo calculations.
Aim 3: Verification of dose distributions in phantom simulations of small animals
as preparation for future animal trials.
Administrative Progress. Several research staff members were hired to work on the
project including a postdoctoral researcher (Mar. 2005), radiation biologist (Dec. 2005),
and graduate student (May 2005). The first meeting of collaboration members was held at
CAMD in May 2005 to define project goals, delineate collaborators’ respective roles, and
determine appropriate CAMD facilities. The tomography beamline, overseen by Drs. Les
Butler and Kyungmin Ham, was deemed most suitable since its monochromatic 10-35
keV x-ray range allows access to the 33.2 keV k-edge of iodine. In November 2005, a
CAMD project proposal was submitted and accepted for beam time. All appropriate LSU
Medical Physics personnel have gained access privileges to CAMD (cards and badges).
Research Progress. Much of 2005 was devoted to design and testing of experiments to
accomplish the specific aims, documentation of the tomography workspace, procurement
of necessary equipment, and experimental apparatus design and fabrication. However,
aim-specific research progress is detailed below.
Aim 1. A small (1 inch diameter × 1 mm thick crystal), thin-window (0.010 inch Be) NaI
detector was purchased for use in determining beam intensity and mean energy via
90
acquisition of the beam’s Compton scattered spectrum. On-site energy calibration of this
detector with a sealed Am-241 radioactive source required approval, which was obtained
in November of 2005. Equipment testing in Dec. 2005 detected insignificant background
radiation during energy calibration at CAMD (Fig. 1).
200
180
160
Detector Counts
140
120
100
80
60
40
3 cm
20
0
0
10
20
30
40
50
60
70
80
Energy (keV)
Figure 2: Five second exposure of
radiochromic film to an uncollimated
beam. Beam is 3.1 cm × 1 mm (thin,
dark bottom line) with an appreciable
second component (top, thick line).
Figure 1: Energy calibrated Am241 spectrum acquired with a 1”
diameter × 1 mm thick NaI
scintillation detector at CAMD.
Aim 2. An initial measurement estimated the mean dose to air from an un-collimated, 15
keV, monochromatic x-ray beam to be approximately 110 cGy·s-1 over a 1 mm × 6.2 mm
area. This corresponds to a fluence estimate of 3.4×1011 photons·cm-2·s-1 (Aim 1).
Additionally, analytical calculations and MCNP5 Monte Carlo simulations of the depth
dose in a water phantom have been performed for comparison to CAMD measurements.
Since experiments have been planned utilizing radiochromic film for both dose
measurements and beam divergence, samples of GAFChromic EBT film (ISP, Wayne,
NJ) were obtained and preliminary exposures performed (Fig. 2). These exposures
verified the film’s utility to the proposed experiments and confirmed the uncollimated
beam size of 3.1 cm long × 0.8 mm high. Film exposures also provided an initial
estimate of dose via correlation to optical density versus dose curves. Equipment
procured for dose measurements include a film scanner (Epson 1680) and acquisition
software to read the film, a Wellhöfer-Scanditronix 0.23 cm3 Farmer-type ionization
chamber, and a modified Keithley 614 electrometer.
91
The electronic structure studies of Pd nanoparticle by VUV
photoemission and X-ray Fluorescence Spectroscopy
O. Kizilkaya, M. Ono, C. Bianchetti, C. Kumar and E. Morikawa
J. Bennett Johnston, Sr. Center for Advanced Microstructures and Devices,
Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806
Intensity (Arb. Units)
The electronic structure of the valence bands of thin films of sulfobetaine (SB-12)
stabilized Pd nanoparticles on a gold surface were
prepared by evaporation of colloidal solution of the
SB12/Pd
nanoparticles in water and investigated by ultraviolet
photoemission spectroscopy (UPS).
Photoemission
UPS
spectra were taken using the light dispersed by a 3-meter
toroidal grating monochromator beamline at CAMD.
Molecular orbital (MO) calculations were performed for
analyzing the photoemission features in measured spectra.
The photoemission spectrum of the stabilized Pd
nanoparticles films measured at the photon energy of 80
eV is presented in Fig. 1 together with the DOS obtained
DOS
by ab initio MO calculation for the model structure. The
good agreement between the measured photoemission
spectrum and the calculated DOS leads to the conclusion
40
30
20
10
0
that the observed photoemission spectrum is entirely
Binding Energy (eV)
dominated by the SB12 surfactant molecules.
H3C
H2
C
C
H2
H2 O
H2 H H2
OH
C
C
C
S
C
N
H2
O
CH3
Fig.1
No photoemission feature from the core Pd
nanoparticles was observed. This fact suggests strongly
that the Pd nanoparticles core is completely surrounded
by the surfactant molecules which are closely packed.
Gold
This also indicates that the surfactant thickness is at
Sputtering time
least more than a typical value for the electron mean
120 sec.
free path (~5 Å) upon the photoemission event.
The sample films were degraded by ion
bombardments in situ. The sputtering with neon gas
60 sec.
was conducted with electron beam conditions of 1 kV
and 5 mA. The ion beam strength was kept low enough
30 sec.
to ensure gradual degradation to the films. The UPS of
Pristine
the pristine films degrades as increasing the sputtering
time as seen from Fig. 2. Two major processes are
evident; intensity loss at all peaks, and appearance of
new peak at the lower binding energy region. The new
30
20
10
0
peak appearing at the low binding energy is clearly due
Binding Energy (eV)
to photoemission from Au substrate. The characteristic
Fermi energy edge is seen as soon as small area of the
Fig.2
Au substrate surface is exposed by the ion
bombardments. The photoemission intensity from Au increases as increasing the film
Intensity (Arb. Units)
Pd
92
Intensity (Log)
degradation until it dominates the whole UPS spectrum. This degradation investigation
strongly assures that photoemission from the pristine films involves no contribution from
the Au substrate. Thus, it can be concluded firmly that the thin films prepared from the
evaporation were very uniform. It is noted that no photoemission feature from Pd is seen
during the film degradation. Possibly the intense photoemission from Au hinders
emission peaks from small concentration of the Pd particles in the films.
Qualitative analysis of
the
nanoparticles
were
performed by conducting X-ray
6
Pd foil
Pd nanoparticle
fluorescence spectroscopy to
5
confirm that Pd atoms present
in the samples by associating
4
measured
spectrum
with
3
characteristic X-ray emission
lines of Pd atoms. The
2
measurements carried out at
DCM beamline at CAMD with
1
use of 4800 eV of incident
0
beam energy. Figure 3 shows
0
1000
2000
3000
4000
5000
6000
fluorescence spectra of Pd foil
Energy (eV)
used as reference and Pd
Fig. 3
nanoparticle. The characteristic
X-ray emission lines (Lα-Lγ) of Pd atom are located between 2800-3300 eV. Having the
same characteristic lines clearly prove the existence of Pd metals in the nanoparticle.
93
Spatially resolved XANES spectroscopy of sulfur speciation in wheat
leaves infected by Puccinia triticina and X-ray fluorescence analysis
Alexander Prange1,2, Henning Lichtenberg1, Chris M. Bianchetti1, Erich-Christian
Oerke3, Ulrike Steiner3, Heinz-W. Dehne3, Hartwig Modrow4 and Josef Hormes1
1
Center for Advanced Microstructures and Devices, Louisiana State University, 6980
Jefferson Hwy., Baton Rouge, LA 70806, USA
2
Microbiology and Food Hygiene, Niederrhein University of Applied Sciences,
Rheydter Straße 277, 41065 Mönchengladbach, Germany
3
INRES, Phytomedicine, University of Bonn, Nussallee 9, D-53115 Bonn, Germany
4
Institute of Physics, University of Bonn, Nussallee 12, D-53115 Bonn, Germany
Correspondence to: A. Prange, e-mail: [email protected]; PNR GMXAP1206XMP
Introduction
This work describes the application of XANES spectroscopy for the characterization of
interactions of biotrophic plant pathogens with their hosts as exemplified by the brown
rust Puccinia triticina colonizing wheat leaves (recently published: Prange et al., 2005).
Spatially resolved X-ray Absorption Near Edge Structure (XANES) spectroscopy was
used to detect changes in sulfur metabolism induced by leaf rust infections. A significant
accumulation of sulfate occurred at the site of the sporulating urediniosori of P. triticina.
Some minor changes in the spectra were observed for the non-visibly colonized tissue
neighboring the rust sori when compared with non-infected leaf areas. As the spectra for
isolated urediniospores and the healthy leaf areas did not fit the spectra of the
urediniosori, a significant impact of the biotrophic pathogen on sulfur metabolism of
wheat has been shown. Spatially resolved XANES spectroscopy will extend the range of
qualitative and quantitative methods for in situ investigations of host-pathogen
interactions, thus may contributing to enlarge our knowledge about the metabolism of
diseased plants.
Material and Methods
Experimental. Spatially resolved XANES spectra were acquired in fluorescence mode at
the X-ray microprobe (XMP) beamline of CAMD. Spectra were recorded with a
resolution of about 100 µm x 100 µm for (A) the center of urediniosori, (B) the nonvisibly infected leaf tissue bordering the uredinal sorus and (C) uninfected leaf areas (cf.
Fig 1). A Canberra single element Ge-detector (GUL 0110P) was used as a fluorescence
detector. To achieve the required spatial resolution, the monochromatic beam was
focused by a Kirkpatrick-Baez double mirror system. Details on beamline and focusing
system are described in Moelders et al. (2001) and references therein. To reduce
absorption of the monochromatisized beam in air, during measurements, this arrangement
was in a home-made flow box filled with helium. The spectra were recorded with step
widths of 0.5 eV in the pre-edge region between 2440-2468 eV, 0.1 eV between 24682485 eV and 0.3 eV between 2485-2520 eV according to the spectral features and with an
integration time of 3 s per data point and normalized at 2510 eV. All fluorescence
excitation spectra have been smoothed using the FFT-smoothing routine which is part of
the ORIGIN program. Reference spectra (Fig. 2) were recorded in transmission mode. X-
94
ray emission spectra were recorded at XMP: 600 sec, excitation energy 7.35 keV. Spectra
were normalized at 2960 eV (Ar Kα-emission line).
Samples. Wheat (Triticum aestivum L.), cv. ‘Dekan’ highly susceptible to Puccinia
triticina (Eriks.), was grown under greenhouse conditions (21 ± 3°C, 16 h photoperiod).
At growth stage (GS) 12-13 leaves were inoculated with an aqueous suspension (ca. 105
spores mL-1) of P. triticina urediniospores; plants were incubated for 24 h under 100 %
relative humidity before returning to greenhouse conditions. Diseased leaves were
investigated 12 days after inoculation when uredinial sori had erupted through the plant
cuticle producing abundant spores. Uredinospores were harvested by brushing infected
leaves, passed through a 40 µm mesh and stored at 4°C.
Fig. 1: Left: Wheat leaf infected with Puccinia triticina and exact position of the areas where the
sulfur K-edge XANES spectra have been taken (cf. Fig. 2): (A) center of uredinial sorus; (B) nonvisibly infected leaf tissue bordering the uredinial sorus; (C) non-infected leaf area between
infection sites. Right: Uredinospores of P. triticina.
95
Fig. 2: Sulfur K-edge XANES spectra of the reference compounds (top to bottom): cystine (a),
glutathione (oxidized form) (b), glutathione (reduced form) (c), cysteine (d), methionine (e),
dimethylsulfoxide (f), cysteic acid (g) and zinc sulfate (h).
Results and Discussion
The variation in fluorescence spectra of the three wheat leaf regions of interest is given in
Fig. 2.
In the center of sporulating rust pustules, a strong structure in the spectrum at an energy
of about 2481.4 eV is observed (Fig. 3). This structure is not present in either healthy leaf
areas or symptomless colonized areas as well as in isolated urediniospores. From Fig. 2,
it can be derived that this is correlated to an increased amount of sulfate (S+VI) in the
sample.
The increase of the sulfate species in response to fungal development is confirmed when
comparing the spectra for the region bordering the sporulating sorus. As compared to
healthy leaf areas, in this symptomless infected area just a slight increase in the
corresponding energy range was observed.
Fig. 3: Sulfur K-edge spectra (smoothed, 7-point setting): isolated Puccinia triticina
urediniospores (solid line), P. triticina sporulating rust pustule on the wheat leaf (dash line), nonvisibly infected leaf tissue bordering the uredinial sorus (dash+dot line), non-infected area of
wheat leaf (dot line). Original data without smoothing of P. triticina sporulating rust pustule on
the wheat leaf (thin, dash+dot+dot line)
Apart from the sulfate, at all sites a resonance located at about 2472.9 eV contributes to
the spectra, which can be assigned to the amino acids cysteine and methionine (C-S-H;
C-S-C) of the proteins (cf. Fig. 3). The results presented can still imply a) that
biochemical interactions between fungus and host tissue have been identified or b) that
sulfate is a dominant species of sulfur contained in the spores, as a considerable part of
96
the fluorescence signal from infected leaf tissue may be due to the interaction of the
incoming radiation with the spores of the fungus. Therefore, if the spores themself
contained sulfate and a slightly different composition of different ”zero-valent” sulfur
species, the superposition of the signals obtained from leaf and fungus might be
responsible for the sulfate peak in the spectrum obtained at the infected site.
In contrast to this assumption, the XANES spectrum of isolated fungal urediniospores,
also displayed in Fig. 4, showed hardly any contribution of sulfate, but its first strong
resonance which is shifted to slightly lower energy (≈ 2471.7 eV) indicating a higher
amount of C-S-S-C-containing compounds (cf. Fig. 3).
Also spatially resolved X-ray fluorescence spectra have been measured in a line-scan
across an infected wheat leaf as shown in Fig. 4. X-ray fluorescence mapping of elements
on leaves (wheat and bean) with host-pathogen interactions will be continued, with
special regard on sulfur, phosphorus and iron will be
Fig. 4: SR-excited (7.35 keV) spatially resolved (~ 100 x 100 µm2)X-ray fluorescence
spectra of a Puccinia triticina infected wheat leave. The figure shows the elements that can be
measured (Ar from the air! P and S are here not shown) and the differences in concentration when
moving the excitation spot across the infected area.
References
Moelders, N., Schilling, P.J., Wong, J., Roos, J.W. and Smith, I.L. (2001). X-ray fluorescence
mapping and micro-XANES spectroscopic characterization of exhaust particulates emitted
from auto engines burning MMT-added gasoline. Environ. Sci. Technol. 35, 3122.
Prange, A., Oerke, E.-C., Steiner, U., Bianchetti, C. M., Hormes, J. and Modrow, H. (2005).
Spatially resolved sulfur K-edge XANES spectroscopy for the in situ-characterization of the
fungus-plant interaction Puccinia triticina and wheat leaves. J. Phytopathol. 153, 627.
97
Iron-based Catalysts for Fischer-Tropsch Synthesis
A. Roy1, C. Bianchetti1, J.J. Spivey2
J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices,
Louisiana State University, Baton Rouge, Louisiana, 70806
2
Department of Chemical Engineering, Louisiana State University, Baton Rouge,
Louisiana, 70803
1
Introduction
The Fisher-Tropsch synthesis (FTS) is an attractive route for the production of
clean transportation fuels and high molecular weight hydrocarbons from synthesis gas
(H2 + CO). Recent studies have shown that there are sufficient domestic reserves of coal
to supply most of U.S. fuel needs for many years using FTS. Like coal, many types of
biomass can be converted to fuels and chemicals using FTS. Biomass and coal based FT
processes are advantageous economically and environmentally (Dry 1999; Marano 2001;
Tijmensen et al. 2002). However coal and biomass conversion via FTS requires a
practical, durable catalyst.
The Fe catalysts are usually synthesized from precipitated hematite (Fe2O3) which
temporarily converts to magnetite (Fe3O4) and finally to iron carbide (FeCx) during
activation. Activation is performed with CO or H2/CO. A typical Fe catalyst has low
initial activity and it is only after an induction period of many hours that the activity
reaches its maximum. After activation and induction of a Fe catalyst, there can be an
initial rapid decrease in activity due to deactivation to a relatively stable pseudo-steadystate activity. However, even at this more stable state, the catalyst continues to deactivate
with time-on-stream (TOS). This may be on the order of a few percent per week, which
is undesirable.
During preparation, copper is often added to Fe catalysts to facilitate its reduction
to a lower oxidation state. Unlike other metal catalysts like Co, or Ru, the active catalytic
form of iron FTS catalyst is not the metallic form. Recent research suggests that the key
factor determining Fe activity for FTS and long-term catalyst activity is the carburized Fe
surface. Thus, production and maintenance of the carburized Fe surface appears to be
key in shaping initial and long-term activity. The effect of the second metal (Me) on the
state of the Fe carbide or on the formation of Fe-Me mixed carbides appears important.
While single metal carbides have been extensively characterized, mixed-metal carbides
are less well understood, especially at temperatures less than 400oC. Fe is known to form
a number of mixed metal carbides.
Experimental Procedures
Table 1. Catalysts, their preparation conditions, and absorption edges investigated
98
Calcined at 300C CO pre-treated at 280C for 12 Comments
for 5 hours
hours and passivated in 2% O2 in
He
Catalyst
Absorption Edges
Absorption Edges
100Fe/5Cu/17Si
Fe, Cu
Fe, Cu
90Fe/10Cr/5Cu/17Si
Fe, Cu, Cr
Fe, Cu, Cr
100Fe/5Cu/4.2K/11SiO2
Fe, Cu
Fe, Cu
90Fe/10Mo/5Cu/17Si
Fe, Cu, Mo
Fe, Cu, Mo
The catalysts studied and their preparation conditions are listed in Table 1.
Table 2. Data collections parameters
Edge
Energy Range (eV)
Step Size (eV)
Integration Time
(sec)
Chromium
K
5850,5980,6040,6990
3,0.3,2
1.0
Iron
K
6955,7100,7170,8100
3.0,0.3,2.0
1,1,1
Copper
K
8830,8960,9040,9880
3.0,0.4,2.0
1.0
Molybdenum
L
2420,2510,2550,2600
2.0,0.3,2.0
1.0
The data collection parameters are provided in Table 2. The concentrations of the
elements were such that measurement in transmission was possible. Germanium 220 (Ge
220) crystals were used for all elements, except molybdenum, for which indium
antimonide 111 (InSb) crystals were used. The heavier elements were analyzed in air,
while helium was flowed through the chamber to minimize X-ray absorption for
molybdenum.
Figure 1. Fe K edge of all catalysts
99
The iron K edge spectra of all catalysts are plotted in Figure 1. The spectrum of iron
metal (aqua marine) is also shown for comparison. Before pre-treatment, all of them have
the same oxidation state. Pre-treatment reduces the oxidation state to a very similar level
in all catalysts except the chromium-bearing one, where the average oxidation state is
little higher. Pre-treatment of all these catalysts should yield some form of iron carbides,
along with other iron phases. Suitable iron carbide standards have yet to be measured.
Absorption (normalized)
1.5
Copper K Edge
1.0
Copper Foil
100Fe _ 5Cu _ 17Si
100Fe-5cu-17si pre
90Fe-10Mo-5Cu-17Si
90Fe-10Mo-5Cu-17Si pre
Fe-5Cu-4.2 K-11SiO2
90Fe-5Cu-4.2 K-11SiO2
Fe-10Cr-5Cu-17Si
0.5
90fe-10cr-5cu-17si pre
0.0
8960
8980
9000
9020
9040
Photon Energy (eV)
Figure 2. Copper K edge in all catalysts
Figure 2 shows the copper K edge spectra in copper-containing catalysts. The K
edge for copper metal is also shown. Similar to the iron-bearing catalysts, copper K edge
also shows reduction after pre-treatment, however, the edge location varies quite widely.
The pre-treatment process appears to reduce the Mo-bearing catalyst the most.
100
100 Fe/5 Cu/17 Si Iron K Edge
1.6
0.4
Calcined
Pre-Treated
Fe Metal
0.2
0.0
0.4
Real
Fourier Transform
Magnitude
0.6
0.0
1.2
0.8
0.4
XANES
0.0
7100
7125
7150
7175
7200
Photon Energy (eV)
-0.4
Imaginary
0.4
0.0
-0.4
0
1
2
3
4
5
6
r' (r + r, Angstrom)
Figure 3. Evolution of iron speciation in one catalyst
100 Fe/5 Cu/17 Si Copper K Edge
1.6
0.6
Pre-Treated
Cu Metal
0.4
0.2
0.0
0.4
1.2
0.8
0.4
XANES
Real
0.0
0.0
-0.4
8975
9000
9025
9050
Photon Energy (eV)
-0.8
0.4
Imaginary
Fourier Transform
Magnitude
Calcined
0.0
-0.4
0
1
2
3
4
5
6
r' (r + r, Angstrom)
Figure 4. Evolution of copper speciation in one catalyst.
101
90 Fe/10 Cr/5 Cu/17 Si Chromium K Edge
1.6
0.4
Calcined
Pre-Treated
Cr Metal
0.2
0.0
0.4
Real
Fourier Transform
Magnitude
0.6
1.2
0.8
Cr+6
0.4
XANES
0.0
0.0
6000
-0.4
6025
6050
Photon Energy (eV)
Imaginary
0.4
0.0
-0.4
0
1
2
3
4
5
6
r' (r + ∆ r, Angstrom)
6
Mo LIII Edge
4
Mo metal
Calcined
Pre-Treated
2
0
2505
2520
2535
2550
Photon Energy (eV)
Figure ?.
The split in the LIII while line of molybdenum is indicative of its coordination (Lede et
al. 2002). Figure ? shows that the separation in the white line is clearly changing, thus the
coordination is also changing. The pre-treatment process is also changing the overall
oxidation state.
102
References
Dry , M. E. (1999). "Fischer-Tropsch reactions and the environment." Applied Catalysis A 189: 185-190.
Lede, E. J., F. G. Requejo, et al. (2002). "XANES Mo L-edges and XPS study of mo
loaded in HY zeolite." Journal of Physical Chemistry B 106(32): 7824-7831.
Marano, J. J. a. C., J.P. (2001). Life-cycle Greenhouse-Gas Emission Inventory for FT
Fuels, DOE/NETL.
Tijmensen, M. J. A., A. P. C. Faaij, et al. (2002). "Exploration of the possibilities for
production of Fischer Tropsch liquids and power via biomass gasification."
Biomass & Bioenergy 23(2): 129-152.
103
Gordaite in a New Environment: in a Salt Bath as a Corrosion Product
of Copper Paint-Coated Steel Plate and Microbially Influenced
Corrosion
Amitava Roy1, Caroline Metosh-Dickey2, Christopher Bianchetti1, Roland Tittsworth1,
Ralph Portier2, and Orhan Kizilkaya1
1
2
Center of Advanced Microstructures and Devices, Louisiana State University, 6980
Jefferson Highway, Baton Rouge, Louisiana, LA 70806
Department of Environmental Studies, School of the Coast and Environment, Louisiana
State University, 6980 Jefferson Highway, Baton Rouge, Louisiana, LA 70893
Introduction
Microbially influenced corrosion and growth on structures, ships and historical fishery
areas is an endemic problem in all aquatic systems. Some of the earliest materials to be used to
prevent biofouling were heavy metals and metal amalgams. Ships were clad with copper and
later copper alloys in an effort to prevent growth of micro and macroscopic organisms on ships
hulls. Metals claddings were expensive, however, and added significant weight to sea going
ships.
There has been a resurgence in the use of metallic copper as an antifouling material via
the application of small copper pieces in new epoxy coatings. These newer epoxies are not
designed to ablate but to hold the copper in place without the negative corrosive effects that can
occur between some metals and copper. Additionally, this coating is not designed to leach but to
create a low energy surface that inhibits attachment of traditional fouling organisms.
Bacterial growth on surfaces in marine environments has generally initiated higher
benthic organisms colonization since bacteria serve as the grazing food source for many of these
species. In recent years, however, the picture of bacterial biofilm generation enhancing
biofouling has become confused in the presence of toxic agents. The exudation of mucopolysaccharide films by bacteria can act to protect the organism as well as help it to maintain its
surface attachment. This film can serve as a sink for various materials including toxicants and
heavy metals thus sequestering toxicants from affecting the bacterium. These exo-polymers
have also been shown to be particularly good at chelating and holding copper. As a
consequence, copper concentrations can increase significantly in biofilms causing any organism
grazing on the biofilm to be discouraged from attaching, i.e., a dose-response situation.
We recently examined the deposit formed on such epoxy-coated steel plates immersed
in artificial seawater. The examination was part of a experiment to study the efficacy of a copper
flake embedded epoxy coating. To our surprise, the principal phase in the corrosion product
appears to be gordiate. Gordiate is a hydrated sodium zinc chloro-sulfate whose crystal structure
was first formally described only in 1997 (Schluter et al. 1997); since then it has been discovered
in a slag heap in Germany (Jahn and Witzke 1999); A calcium variety has been reported from
slag dumps in Italy (Burns et al. 1998); An unidentified mineral specimen from the Juan de Fuca
Ridge has recently also been identified as gordaite (Nasdala et al. 1998).
104
Experimental Method
FT-IR Spectro-Microscopy
A Thermo Electron Nicolet continuµm FT-IR spectro-microscope was used in this study.
The microscope is attached to a Nicolet 670 Spectrometer, which utilizes synchrotron infrared
source. The synchrotron ring is located at the J. Bennett Johnston Sr., Center for Advanced
Microstructures and Devices (CAMD), Louisiana State University, Baton Rouge, Louisiana. The
ring operates at 1.3 GeV. The current in the ring typically ranged between 200 to 100 mA. In
mid infrared range, for a 10 µm spot, the intensity of the focused beam is at least a 1,000 times
more than in a conventional globar source.
The spectra were collected in the reflection mode. The crust scraped from the steel
surface was sprinkled on a gold-coated slide. The background was collected from the gold slide.
Each spectrum is the average of at least 250 scans.
Figure 1
Figure 1 shows the steel plates before and after immersion in the artificial seawater.
Within 30 days, a grayish crust developed on the plate surface. The crust was approximately ??
cm thick.
Microscopy
A representative photomicrograph of the crust, obtained with a stereomicroscope in
reflected light, is shown in Figure 2a. Black nodules (ca. 2 mm across) are observed which are
filled with white translucent crystals (5 to 10 µm in diameter). The translucent crystals appeared
to have filled the voids in the nodules. Repeated washing with distilled water removed some of
the deposits from the interior of the nodules.
105
106
Figure 2
Scanning electron microscopy at low magnifications shows the same nodular
structure of the crust (Figure 2b). When viewed at slightly higher magnification, the
nodule walls appears to have a layered structure, each layer being a few tens of µm thick.
Apart from the hexagonal crystals, other morphologies are also present (Figure 2d).
Observations at moderately higher magnifications indicated the presence of locally
abundant colonies of bacilli. A culture of these bacteria has shown them to be both grampositive and –negative.
781
1438
984
839
1105
1024
1670
1637
Absorbance
Crystals
Bulk powder
1112
3515
3460
3407
3343
FTIR Spectro-Microscopy
3500
3000
1500
Wavenumber (cm-1)
1000
Figure 3
The FTIR spectra of the colorless crystals were obtained by focusing the infrared
beam to a 15 µm x 15 µm spot in the microscope. There is remarkable similarity
between the FTIR spectra provided by Nasdala et al. (Nasdala et al. 1998) and ours. All
the major H2O, OH and sulfate bands can be matched and their intensities are roughly
similar. Very similar bands are present in both the colorless crystals and the dark
nodules, suggesting that they are compositionally very similar.
Concluding Statements
Gordaite is the principal reaction product in the process. There is very little, if any, other
phases.
This may be the first reported association of gordaite with bacteria.
References Cited
Burns, P. C., A. C. Roberts, et al. (1998). "The crystal structure of Ca[Zn8(SO4)(2)(OH)(12)Cl-2]H2O)(9), a new phase from slag dumps at Val Varenna,
Italy." European Journal Of Mineralogy 10(5): 923-930.
Jahn, S. and T. Witzke (1999). "Secondary minerals of zinc and copper in heaps of
kupferschiefer ores at Helbra, Sachsen-Anhalt, Germany: First occurrence of
cuprian gordaite." Chemie Der Erde-Geochemistry 59(3): 223-232.
Nasdala, L., T. Witzke, et al. (1998). "Gordaite NaZn4(SO4)(OH)6Cl.6H2O: Second
occurrence in the Juan de Fuca Ridge, and new data." American Mineralogist
83(9-10): 1111-1116.
Schluter, J., K. H. Klaska, et al. (1997). "Gordaite, NaZn4(SO4)(OH)6Cl.6H2O, a new
mineral from the San Francisco Mine, Antofagasta, Chile." Neues Jahrbuch Fur
Mineralogie-Monatshefte(4): 155-162.
Gordaite in a New Environment: in a Salt Bath as a Corrosion Product
of Copper Paint-Coated Steel Plate and Microbially Influenced
Corrosion
Amitava Roy1, Caroline Metosh-Dickey2, Christopher Bianchetti1, Roland Tittsworth1,
Ralph Portier2, and Orhan Kizilkaya1
1
Center of Advanced Microstructures and Devices, Louisiana State University, 6980
Jefferson Highway, Baton Rouge, Louisiana, LA 70806
2
Department of Environmental Studies, School of the Coast and Environment, Louisiana
State University, 6980 Jefferson Highway, Baton Rouge, Louisiana, LA 70893
Introduction
Microbially influenced corrosion and growth on structures, ships and historical fishery
areas is an endemic problem in all aquatic systems. Some of the earliest materials to be used to
prevent biofouling were heavy metals and metal amalgams. Ships were clad with copper and
later copper alloys in an effort to prevent growth of micro and macroscopic organisms on ships
hulls. Metals claddings were expensive, however, and added significant weight to sea going
ships.
There has been a resurgence in the use of metallic copper as an antifouling material via
the application of small copper pieces in new epoxy coatings. These newer epoxies are not
designed to ablate but to hold the copper in place without the negative corrosive effects that can
occur between some metals and copper. Additionally, this coating is not designed to leach but to
create a low energy surface that inhibits attachment of traditional fouling organisms.
Bacterial growth on surfaces in marine environments has generally initiated higher
benthic organisms colonization since bacteria serve as the grazing food source for many of these
species. In recent years, however, the picture of bacterial biofilm generation enhancing
biofouling has become confused in the presence of toxic agents. The exudation of mucopolysaccharide films by bacteria can act to protect the organism as well as help it to maintain its
surface attachment. This film can serve as a sink for various materials including toxicants and
heavy metals thus sequestering toxicants from affecting the bacterium. These exo-polymers
have also been shown to be particularly good at chelating and holding copper. As a
consequence, copper concentrations can increase significantly in biofilms causing any organism
grazing on the biofilm to be discouraged from attaching, i.e., a dose-response situation.
We recently examined the deposit formed on such epoxy-coated steel plates immersed
in artificial seawater. The examination was part of a experiment to study the efficacy of a copper
flake embedded epoxy coating. To our surprise, the principal phase in the corrosion product
appears to be gordiate. Gordiate is a hydrated sodium zinc chloro-sulfate whose crystal structure
was first formally described only in 1997 (Schluter et al. 1997); since then it has been discovered
in a slag heap in Germany (Jahn and Witzke 1999); A calcium variety has been reported from
slag dumps in Italy (Burns et al. 1998); An unidentified mineral specimen from the Juan de Fuca
Ridge has recently also been identified as gordaite (Nasdala et al. 1998).
Experimental Method
X-Ray Absorption Spectroscopy
The XAS spectra were collected at the CAMD Double Crystal Monochromator beamline
for the elements copper, zinc and sulfur. The measurements were conducted in air for the heavier
elements, while helium was flowed during sulfur measurement. The concentrated specimens
were analyzed in transmission and those with low concentrations were analyzed in fluorescence
by a thirteen-element high purity germanium detector. Specimens were prepared by smearing a
very thin layer of the powder onto a Kapton™ tape. Ge 220 crystals were used in the
monochromator for the heavy elements, while InSb 111 crystals were used for sulfur. For copper
and zinc, XANES spectra were collected from 200 eV below the edge to up to 20 eV below the
edge in 3eV steps; from – 20 eV to 60 eV above the edge in 0.3 eV steps; and 60 eV above the
edge to 300 eV above the edge in 3 eV steps. For copper EXAFS, the range over which data
could be collected was limited by the zinc K edge at 9659 eV. Thus only several hundred eV of
data could be collected. The steps were 3 eV below the edge and 2 eV above the edge up to
9659 eV. For the sulfur, the scan ranged from -70 to -10 eV below the edge in 1.5eV steps, from
10eV to 30 eV above the edge in 0.2 eV steps, and from 30 eV to 125 eV above the edge in 1.5
eV steps. The counting time was 1 second at each step. The spectra were analyzed by Athena
and resulted suite of software (Ravel and Newville 2005).
Figure 1
Figure 1 shows the steel plates before and after immersion in the artificial seawater.
Within 30 days, a grayish crust developed on the plate surface. The crust was approximately ??
cm thick.
Microscopy
A representative photomicrograph of the crust, obtained with a stereomicroscope in
reflected light, is shown in Figure 2a. Black nodules (ca. 2 mm across) are observed which are
filled with white translucent crystals (5 to 10 µm in diameter). The translucent crystals appeared
to have filled the voids in the nodules. Repeated washing with distilled water removed some of
the deposits from the interior of the nodules.
Figure 2
Scanning electron microscopy at low magnifications shows the same nodular structure of
the crust (Figure 2b). When viewed at slightly higher magnification, the nodule walls appears to
have a layered structure, each layer being a few tens of µm thick. Apart from the hexagonal
crystals, other morphologies are also present (Figure 2d). Observations at moderately higher
magnifications indicated the presence of locally abundant colonies of bacilli. A culture of these
bacteria has shown them to be both gram-positive and –negative.
X-Ray Analysis
105
106
Cu Kα
Copper excitation
Zinc Excitation
105
Intensity
Intensity
104
Zn Kα
Fe Kα
103
Ar Kα
Cr Kα
104
Fe Kβ
Cr Kβ
Ar Kβ
102
Ca Kα
Ca Kβ
103
101
100
2
4
6
102
10
8
Energy (eV)
Figure 3
Figure 3 shows the X-ray fluorescence spectra of the crust collected during XAS
measurements. Elements below argon are not observed due to absorption of the X-rays in air.
Apart from zinc and copper, minor amounts of iron and chromium are also observed in the
spectra. Presumably these elements are extracted from the steel plate. Calcium in the corrosion
product must be coming from the simulated seawater. Considering the amount of chromium
usually present in steel relative to iron, its amount in the residue is quite high.
250
Al Kα
Na Kα Zn Lα
Nodule Surface
S Kα
50
Cl Kα
100
P Kα
Cl Kα
S Kα
P Kα
Al Kα
Mg Kα
Cu Lα
100
Crust
150
Cu Lα
Colorless crystals
O Kα
Intensity (cps)
200
150
50
C Kα
Crust
Na Kα Zn Lα
C Kα
O Kα
Intensity (cps)
200
Mg Kα
250
0
0
0
1
2
3
8
10
0
1
Energy (keV)
Figure 4 – X-micro-analyses in the SEM
2
Energy (keV)
3
8
10
Energy dispersive X-ray micro-analysis of the crust, obtained in the variable pressure
SEM, is shown in Figure 4. Elementally, the analyses of the crystals and the nodule surface are
very similar. Some of the carbon signal may also be derived from the substrate used to mount the
material. The sodium Kα and zinc Lα peaks cannot be differentiated because of their almost
identical energy.
X-Ray Absorption spectroscopy
Corrossion
product
Zn(OH)2
ZnO
a
Zinc foil
9640
9660
9680
9700
Photon Energy (eV)
A
B
Crust
CuO
b
Cu2O
8960
8980
9000
9020
Photon Energy (eV)
9040
Figure 5 – X-ray absorption near edge (XANES) spectra of (a) copper and (b) zinc K
edges of the crust
Fluorescence (normalized)
The zinc K edge XANES spectrum of the crust is shown in Figure 5a. The edge
energy of the crust suggests that all the zinc is in +II oxidation state. The white line for
the crust is stronger than that of ZnO or Zn(OH)2. The XANES spectrum of copper in
the crust, along with those of copper oxides in +I and +II oxidation states, is shown in
Figure 5b. The distinct pre-edge peak seen in Cu2O is absent in the spectrum of the crust,
suggesting that copper in the crust is in +II oxidation state. The edge energy of the
spectrum also corresponds well with +II oxidation state. The peak B is usually due to the
immediate neighbor around the central atom. The low intensity of this peak in the crust
probably suggests that copper is not located in a well-defined crystallographic position.
In gordaite, zinc is both tetrahedrally and octahedrally coordinated. In tetrahedral
coordination, three oxygen atoms are present at a distance of 1.955 Å, and one chlorine
atom is at a distance of 2.279 Å. In octahedral coordination, the oxygen distance varies
from 2.026 to 2.434 Å. Severe absorption of copper X-rays in the pre-dominantly zinc
matrix of the crust reduced the amplitude of copper EXAFS oscillations. The best fit
using Artemis (Ravel and Newville 2005) had a ψ2= 0.27. With coordination fixed as
octahedral, the best fit yields Cu-O distances of 1.93, 1.94 and 2.76 Å, with two atoms in
each shell. Thus if any copper substitution of zinc occurs in gordaite, the octahedron is
highly distorted.
8
6
E0 = 2480.97 eV
4
2
0
2460
2480
2500
2520
Photon Energy (eV)
Figure 6
The sulfur K edge spectrum of the crust was obtained in fluorescence. No other
species of sulfur, except that of sulfate, was detected. Thus no sulfur-reducing or
oxidizing bacteria are involved with the corrosion process.
References Cited
Burns, P. C., A. C. Roberts, et al. (1998). "The crystal structure of Ca[Zn8(SO4)(2)(OH)(12)Cl-2]H2O)(9), a new phase from slag dumps at Val Varenna,
Italy." European Journal Of Mineralogy 10(5): 923-930.
Jahn, S. and T. Witzke (1999). "Secondary minerals of zinc and copper in heaps of
kupferschiefer ores at Helbra, Sachsen-Anhalt, Germany: First occurrence of
cuprian gordaite." Chemie Der Erde-Geochemistry 59(3): 223-232.
Nasdala, L., T. Witzke, et al. (1998). "Gordaite NaZn4(SO4)(OH)6Cl.6H2O: Second
occurrence in the Juan de Fuca Ridge, and new data." American Mineralogist
83(9-10): 1111-1116.
Ravel, B. and M. Newville (2005). "ATHENA, ARTEMIS, HEPHAESTUS: data
analysis for X-ray absorption spectroscopy using IFEFFIT." Journal Of
Synchrotron Radiation 12: 537-541.
Schluter, J., K. H. Klaska, et al. (1997). "Gordaite, NaZn4(SO4)(OH)6Cl.6H2O, a new
mineral from the San Francisco Mine, Antofagasta, Chile." Neues Jahrbuch Fur
Mineralogie-Monatshefte(4): 155-162.
Phosphate Removal by Kaolinite- Bentonite Media
Jia Ma1, Amitava Roy2 and John Sansalone1
1
Department of Civil and Environmental Engineering, Louisiana State University,
Baton Rouge, Louisiana, 70803
2
Introduction
As one of the essential elements on earth, phosphorus has been regarded as the
major growth limiting nutrient. However excessive amount of phosphorus in water bodies
such as urban streams and lake reservoirs is directly responsible for eutrophication (algal
blooms, depletion of dissolved oxygen and deterioration of water quality). Eutrophication
is considered as one of the most important environmental problems. A better understanding
of the detrimental influence of eutrophication caused by phosphorus has led to more
stringent regulation of phosphorus level in receiving waters and stimulated the demand for
more efficient and cost effective removal of phosphorus. The maximum contaminant level
(MCL) of phosphorus in lake reservoirs was 0.1 mg/L as recommended by EPA (1986).
Complying with this standard is apparently difficult considering the significant amounts of
waters and discharges around the world that exceed this level. Removal of phosphorus
from urban rainfall-runoff has become a priority in many areas of the USA for suitable
discharge to receiving waters.
Economical sorption materials for effective phosphorus removal from aqueous
solution such as urban rainfall-runoff, has attracted great attention lately., A range of
adsorbents has been investigated for phosphate adsorption, including: aluminas (Gangoli
and Thodos 1973),
aluminum hydroxide (Galinada and Yoshida 2004), aluminum oxide (Huang 1977),
synthetic boehmite (Tang et al. 1996), gibbsite (Gimsing et al. 2004), goethite (Juang and
Chung 2004; Rietra et al. 2001), amorphous calcium silicate (Southam et al. 2003),
polymeric hydrogels (Kofinas and Kioussis 2003), fly ash (Deborah and Marcia 1979),
iron oxide tailings (Zeng et al. 2004) and blast furnace slag (Hisashi et al. 1986). It was
found that lower concentrations of
Sorption by aluminum species is credited to the presence of Al-OH and functional
groups on the mineral surface (Shin et al. 2004). Given the complexity of surface
composition and structure, many interactions are likely to occur, including specific
chemical adsorption (surface complexation involved with ligand exchange) and
precipitation; nonspecific physical adsorption (ion exchange relevant to electrostatic forces)
driven by the surface charge and surface area of adsorbent. When surface complexation
phenomenon occurs, the surface complexes formed can be classified as inner and outer
sphere complexes depending on the type of affinity of phosphate to an active surface site.
Formation of these surface complexes is mostly dependent on the degree of surface
protonation and/or dissociation. Johnson et aL (2002) used P NMR to study the adsorption
of phosphate on y-A1203 and concluded that the adsorption is complex, with evidence of
outer- and inner- sphere complexes and surface precipitation.
Aluminum oxide coated media (AOCM) represents a group of aluminum oxide
coated or impregnated substrates with high porosity and large specific surface area were
developed to selectively bind the phosphorus anion onto and into the media matrix,
permitting subsequent removal from an aqueous stream. This engineered media must fulfill
requirements of economy, provide a medium of desired hydraulic conductivity, provide
desired P adsorption capacity, reduce P concentrations to targeted levels, and be able to
retain the P without desorption.
The AOCM media proved quite successful in the laboratory in removal of
phosphorus from synthetic stormwater.
Experimental Procedure
AOCM Preparation
Sorbent media utilized in this study was a specific form of AOCM. This media was
prepared from clay material and aluminum oxide. Clay expanded with a blowing agent was
fired into bricks at 1000°C . The cooled bricks were crushed and sieved to yield to three
size ranges of substrate: 0.85 - 2 mm, 2 - 4.75 mm and 4.75 - 9.5 mm using ASTM
standard sieves No. 1/4 inch (4.75-mm opening), No. 10 mesh (2.00-mm opening) and No.
20 mesh (0.85-mm opening). The resulting substrate is a stable, highly porous, lightweight
media of low organic content. The sorbent substrate was then coated with an aluminum salt
to produce the sorbent media (AOCM) utilized in this study. The effect of media size of
AOCM on phosphorus adsorption was examined using these three size categories: 0.85 - 2
mm; 2 - 4.75 mm and 4.75 - 9.5 mm by sieving. Such a size range of AOCM is suitable for
the potential adsorption cartridge filter usage.
The same powder was used for thermal analysis, X-ray powder diffractometry,
and FTIR analysis. It was prepared by grinding the particles initially with an agate mortar
and pestle, and subsequently in a micronizing mill. The average particle size is expected
to be in the 5 to 10 µm range.
X-Ray Absorption Spectroscopy
The XAS spectra were also collected at the CAMD Double Crystal
Monochromator beamline. The phosphorus K edge is at approximately 2150 eV. The
peak of aluminum phosphate white line (2149? eV) was used for calibration. Due to the
low concentration of phosphorus, the measurements were made in fluorescence. A nineelement high purity germanium detector was used. A low atomic number inert gas,
helium, was flowed through the chamber. . InSb 221 (?) crystals were used in the
monochromator. XANES spectra were collected from 2050 eV to up to 2140 eV in 2eV
steps; from 2140 eV to 2180 eV above in 0.2 eV steps; and 2180 eV to 2450 eV in 3 eV
steps. The integration time in each region was 3, 5, and 3 seconds respectively. Each
measurement was repeated at least ten times. The spectra were analyzed by Athena and
resulted suite of software (Ravel and Newville, 2005).
Specimens were prepared by smearing a very thin layer of the powder onto a
Kapton™ tape. The mm-size media was gently crushed in an agate mortar and pestle.
The used media was quite moist.
X-Ray Absorption Near Edge Structure
4
2148
Before Use
After Use
0
2140
2150
2160
2170
2180
Photon Energy (eV)
A
Phosphorus
K Edge XANES
Fe+III(PO4).2H2O
CaHPO4.2H2O
AlPO4
KH2PO4
D
B C
Ca5(PO4)3(OH, F, Cl)
2130
2140
2150
2160
2170
Photon Energy (eV)
2180
Figure 1. Phosphorus K edge XANES spectra of KB media, before and after treatment
(left), and of some standard minerals (right).
Figure 1 shows the phosphorus K edge absorption spectra of the treatment media,
before and after treatment. A comparison of the spectra with those of the standards shows
that the edge position does not change after its use in treatment and the peak height of the
white line is reduced after treatment. The peak width is also a lot narrower, similar to the
iron phosphate, strengite. Further data analysis is in progress.
References
Ravel, B., and Newville, M. (2005) ATHENA, ARTEMIS, HEPHAESTUS: data analysis
for X-ray absorption spectroscopy using IFEFFIT. Journal Of Synchrotron
Radiation, 12, 537-541.
Speciation of Iron, copper and Zinc in Katrina Sediments from New
Orleans
Amitava Roy1, Christopher Bianchetti1, Roland Tittsworth1, and John Pardue2
1
2
Department of Civil and Environmental Engineering, Louisiana State University,
Baton Rouge, Louisiana, 70803
Introduction
Hurricane Katrina, a Category 4 storm on the Saffir-Simpson scale, struck the
Gulf Coast on August 29th, 2005. The storm surge resulted in a breach of the levee
system in New Orleans at two locations, which flooded up to 80% of the city. The flood
water was sampled in the Mid-City and Lakeview areas of New Orleans within days. The
concentrations of metals like iron, zinc and copper in the flood water were often elevated
compared to EPA drinking water standards (Pardue et al., 2005).
The sediment deposited from the flood water was sampled as soon as the water
receded in the Mid-City region. The Lakeview area was sampled within weeks. Optical
microscopy showed that sand-size quartz, often enclosed in asphalt, is the dominant
component of the sediment in the Mid-City location. At Lakeview sample sites, clay
minerals formed an important component of the sediment, though quartz was also
voluminous.
Figure 1. Iron K edge XANES of Katrina Sediments
1.5
Copper K Edge XANES
of some Stadards
1.0
Copper foil
0.5
Cu (II) Oxide
Cu (I) Oxide
0.0
8960
8980
9000
9020
Photon Energy (eV)
9040
1.5
Copper K Edge XANES
of Katrina Sediments
1.0
NO 4
NO 5
NO 7
NO 8
NO 9
0.5
NO 2
NO 6
0.0
8960
8980
9000
9020
Photon Energy (eV)
9040
Figure 2. Copper K edge XANES of Katrina Sediments
Figure 3. Zinc K edge XANES of Katrina Sediments
3000
2500
NO 4
NO 8
NO 7
2000
Counts
NO 9
1500
NO 5
NO 2
1000
NO 3
NO 6
500
0
5.4
5.6
Energy (keV)
Figure 4. Chromium Kα peak in Mid-City New Orleans samples.
The speciation of iron, zinc, copper, and chromium was studied by X-ray
absorption near edge structure (XANES). The white line intensity in the zinc XANES
spectra is stronger in the Mid-City samples compared to those from Lakeview. The
former were also moist, while the Lakeview samples were dry. Zinc appears to be mostly
122
+II oxidation state but in some samples a higher metallic component is found. Iron
XANES spectra are very uniform (similar to goethite) in the sediment from the Lakeview
area but shows more variation at the Mid-City sites. Chromium XANES spectra could be
obtained from the Lakeview samples only, which seemed to have a strong metallic
component. Similarly, only Mid-City samples yielded useful copper XANES spectra. The
spectra show a strong +II oxidation state component along with a variable amount of
metallic component.
One sample from the Mid-City area, close to the Superdome, has reduced oxidation state
for all the elements measured.
References
Pardue, J.H., Moe, W.M., McInnis, D., Thibodeaux, L.J., Valsaraj, K.T., Maciasz, E., van
Heerden, I., Korevec, N., and Yuan, Q.Z. (2005) Chemical and Microbiological
Parameters in New Orleans Floodwater Following Hurricane Katrina ES&T, Web
Edition(October 11th).
123
Sulfur Speciation in Some Cementitious Materials
Amitava Roy
J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices, Louisiana
State University, 6980 Jefferson Highway, Baton Rouge, LA 70806
Introduction
Sulfur species, particularly in sulfate form, exert a strong influence on the
dimensional stability of cementitious materials though volumetrically they constitute a
minor role. For example, the sulfate containing phase ettringite is strongly implicated in
sulfate attack in concrete and cement-stabilized soil, even though the exact mechanism is
not fully understood (Famy and Taylor, 2001). It is not easy to monitor the sulfate phases
in cementitious materials as some of it may exist in solid solution. Apart from ettringite,
the calcium silicate hydrate and monosulfate can contain some of the sulfate. In addition,
some of the original sulfates phases such as gypsum and anhydrite may remain. If a
sulfite sludge from a coal-fired power plant is used in some form of stabilization, the
speciation of sulfur will be different.
Granulated blast furnace slag also has a different speciation for sulfur. During hydration
of cement, the presence of blast furnace slag provides a reducing environment. It has
been documented that during solidification/stabilization of hexavalent chromiumcontaining wastes, the chromium is reduced to the relatively benign +III oxidation state
(Bajt et al., 1993). During the hydration process of blast furnace slag, the interior of the
slag changes into a dark green color. A freshly broken slag mass usually smells of
hydrogen sulfide. When a slag does not react properly (accompanied by no strength
gain), no such color change is observed. Coarse slag aggregate can potentially supply
sulfate by oxidation of calcium sulfide in it (Van Dam et al., 2003).
X-ray absorption spectroscopy, which can detect all types of speciation of sulfur,
has been applied in to soil humic substances and petroleum to study the speciation of
sulfur in those materials. To date, it has not been applied to cement chemistry. When a
mixture of portland cement and blast furnace slag is used, is the Eh still reducing, at what
proportions does the reducing environment change, and how long can the reducing
environment last? These questions have implications for the long term storage of
hazardous wastes in cements.
Experimental Methods
The sulfur spectra were collected at the J. Bennett Johnston, Sr., Center for
Advanced Microstructures and Devices, Louisiana State University, Baton Rouge,
Louisiana. Depending on the concentration, the spectra were collected either in
transmission or fluorescence. Indium antimonide (InSb) crystals were used in the double
crystal monochromator. The data collection parameters were: -70 eV to -10 eV in 1.5 eV
steps, from -10 eV to 30 eV in 0.2 eV steps, and from 30 eV to 125 eV in 1.5 eV steps.
Helium was flowed through the sample chamber at a pressure slightly higher than
atmospheric. A 13-element solid state high purity germanium detector was used for
fluorescence signal detection.
124
A
Normalized (fluorescence)
16
Sulfur K Edge XANES
Activated by Calcium
Hydroxide Solution
water/solids = 0.4
12
13 months old
8
18 hours old
Class C Fly Ash
4
C
B
D
Gypsum
Ettringite
0
2470
2480
2490
2500
2510
Photon Energy (eV)
Figure 1
Figure 1 shows the sulfur K edge XANES spectra of a Class C fly ash, before and
after its reaction with calcium hydroxide. The spectra of gypsum and ettringite, a reactant
and ettringite a product of this type of hydration reaction, are also shown for comparison.
Ettringite spectrum does not show any strong secondary peaks beyond the white line. The
XANES spectra for the Class fly ash shows somewhat similar features as that of
gypsum’s, but the intensities are lower. Hydration of Class C fly ash produces a much
stronger white line, which gets more intense with time, from 18 hours to 13 months. The
peak locations are also slightly different. The peak B, which is absent in the 18-hour-old
sample, is more pronounced in the 18-month-old spectrum.
A
Sulfur K Edge
XANES
Ca(OH)2
Activation
Sulfur K Edge
XANES
E
D
C
White
Bluish
Green
B
GGBFS
2460
NaOH
Activation
A
D
E
White
C
Bluish
B
Green
GGBFS
2470
2480
2490
2500
2510
2460
Photon Energy (eV)
2470
2480
2490
2500
Photon Energy (eV)
125
2510
Figure 2. The vertical scale is identical in both.
Granulated blast furnace slag is obtained by quenching the slag in an ironproducing plant. For natural magmas of similar composition, where sulfur is immiscible,
researchers have found that sulfur speciates in sulfide and sulfate forms (Paris et al.,
2001). The BFS glass shows a similar phenomenon. BFS has a strong sulfate peak and a
broad sulfide peak (Figure 2. Sulfur in silicate magmas exist in two state sulfide and
sulfate, the ration depending on oxygen fugacity. In some magmatic rocks though the
conditions were quite oxidizing, some sulfide persists. This was probably due to local
reducing conditions. This reasoning certainly applies to activated BFS.
Figure 2 also shows the sulfur K edge XANES spectra of granulated blast furnace
slag reacted with calcium hydroxide and sodium hydroxide. The sodium hydroxide
solution is five Normal (pH – 14.72), while a saturated solution of calcium hydroxide has
a pH of 12.5. The interior of the solidified, reacted mass has a dark green color and there
is a colorless to light yellowish brown rind of variable thickness. In specimens cured for
months the rind is only a few mm thick.
After activation by both alkaline solutions the broad peak is reduced and minor,
better defined peaks form. These peaks are stronger in the rind. The white line is always
stronger in the rind. Compared to calcium hydroxide activation, the white line is broader
and less intense in the sodium hydroxide reacted BFS.
References
Bajt, S., Clark, S.B., Sutton, S.R., Rivers, M.L., and Smith, J.V. (1993) Synchrotron XRay Microprobe Determination of Chromate Content Using X-Ray-Absorption
near-Edge Structure. Analytical Chemistry, 65(13), 1800-1804.
Famy, C., and Taylor, H.F.W. (2001) Ettringite in hydration of Portland cement concrete
and its occurrence in mature concretes. ACI Materials Journal, 98(4), 350-356.
Paris, E., Giuli, G., Carroll, M.R., and Davoli, I. (2001) The valence and speciation of
sulfur in glasses by X-ray absorption spectroscopy. Canadian Mineralogist, 39,
331-339.
Van Dam, T.J., Peterson, K.R., Sutter, L.L., and Housewright, M.E. (2003) Deterioration
in Concrete Pavements Constructed with Slag Coarse Aggregate. Transportation
Research Record(1834), 8-15.
126
Investigation of the Local Geometric Structure of Mn Impurity Atoms
in Si: a Dilute Magnetic Semiconductor
Carl A. Ventrice, Jr.
Department of Physics, University of New Orleans, New Orleans, LA 70148
Heike Geisler
Department of Chemistry, Xavier University, New Orleans, LA 70125
Martin Bolduc, C. Awo-Affouda, and Vincent P. LaBella
College of Nanoscale Science and Engineering, Univ. at Albany, Albany, NY 12203
Roland Tittsworth
CAMD/LSU, Baton Rouge, LA 70806
(PRN: UNO-CV1205)
The local atomic structure of Mn impurities in Mn-implanted Si samples has been
studied using extended x-ray absorption fine structure (EXAFS) spectroscopy at the
DCM beamline at CAMD. These measurements are being used to provide information
about the nature of the ferromagnetism that is observed in this system. It is well
documented that ferromagnetic behavior in an ideal dilute magnetic semiconductor
(DMS) strongly depends on the local atomic structure around the impurity atoms. This
remains a challenging issue for the fabrication of novel generation of spintronic devices.
EXAFS provides information regarding the charge state, bond distance, coordination and
type of neighboring atoms around the Mn impurities.
The samples are p-type silicon wafers (~1019 cm-3) that are implanted with Mn+ ions
at 350 keV. The Mn peak concentration reaches 0.1 - 0.8 Mn atomic % (~1021 cm-3) at
~250 nm below the surface. This results in ferromagnetism that remains persistent above
400 K. After annealing, the Mn forms
crystallites of up to 8 nm in size, as seen
in high-resolution transmission electron
microscopy (TEM) images. The current
focus of this research is to try to
determine the composition of these
clusters and their role in the
ferromagnetic behavior of the DMS.
Representative EXAFS spectra for a Mn
doped Si DMS and a Mn reference
Mn Reference
Mn doped Si(100)
sample are shown in Fig. 1. Since the
Mn absorption edge of both samples is
the same, the implanted Mn is in a
6500
6600
6700
conducting state. However, the intensity
Energy (eV)
modulation after the near edge region is
dramatically different for the DMS Fig. 1: EXAFS spectra for a Mn doped Si sample
sample. This indicates that the Mn is that exhibits ferromagnetic behavior and a Mn
forming a manganese silicide cluster, not reference sample.
a phase-separated elemental Mn. Since
there are several stable phases of manganese silicide, modeling of the EXAFS intensity
modulations is being undertaken to determine the composition of the nanoparticles.
127
Speciation of Arsenic in the Common Marsh Fern, Thelypteris palustris.
LaShunda L. Anderson ([email protected]) and Maud Walsh ([email protected]);
Louisiana State University Department of Agronomy
and Environmental Management 70803
PRN # AGR-MW-1205
Arsenic contamination of soils and groundwater poses a widespread threat to
ecological and human health in Louisiana and around the world. Phytoremediation, the
use of plants to decontaminate soils or water, has the potential to be a cost-effective, nonintrusive method for the remediation of many Louisiana environments, including
endangered coastal wetlands affected by petrochemical discharges, agricultural sites
contaminated by arsenic-based pesticides and urban brownfield sites rendered unsafe by
unregulated manufacturing processes
Our research focuses on the ability of common Louisiana plants to accumulate
arsenic in sufficient quantities to effectively remediate soils without costly excavation
and incineration. The discovery of an arsenic-hyperaccumulating fern (Ma et al., 2001)
and the potential applications for soil remediation has stimulated investigations into the
abilities of other ferns to accumulate arsenic (Meharg, 2003). Other plants have been
researched to assess their ability to tolerate and accumulate arsenic. The marsh fern was
chosen for arsenic uptake and speciation studies due to its ease of propagation, various
environmental habitats it can survive in and the recent discovery of arsenic accumulating
ferns.
Marsh ferns were propagated in the greenhouse from roots. Marsh fern roots were
sewn into ½ gallon plastic pots containing Scotts® Metrol Mix 300 or medium grade
vermiculite that was thoroughly mixed with Osmocote® extended time release fertilizer.
Thirty-six marsh ferns were randomly chosen from the rootlings and placed into a 36 unit
gravitational fed hydroponic system that contained Foxfarm ® GrowBig Hydroponic
Concentrate (3-2-6) hydroponic solution mixed at the concentration rate of 15 ml (2
tablespoons) per 3.8 L (1 gallon) of water . Potassium arsenate (KH2AsO4 ) was added to
the hydroponic nutrient solution to achieve arsenic treatment concentrations of 250 ppb
and 500 ppb. A greenhouse insect infestation destroyed all above ground biomass so only
fern roots from each treatment level were analysed by XANES
As a result of above-biomass destruction, a second hydroponic study was
conducted so that the above-ground biomass could be analysed. In this study, twelve
marsh ferns potted in vermiculitewere placed into dishpans filled with four liters of
arsenic solution. Potassium arsenate (KH2AsO4 ) was added to water to achieve arsenic
treatment concentrations of 250 ppb and 500 ppb. Aquarium air pumps were inserted into
the arsenic solution of each dishpan to decrease algae formation. Arsenic solution was
changed at approximately one week. At two weeks of arsenic exposure, fronds from each
treatment level was harvested for XANES analysis
Roots and fronds of ferns were examined with XANES to determine arsenic
speciation. Standards used for XANES analysis are sodium arsenate, arsenate oxide, and
arsenic oxide. Two samples of exposed roots were placed between individual layers of
Kapton tape. Roots were found to contain arsenate when sample chart readings were
128
similar to the arsenate oxide standard peak. One fern root that was exposed to 250 ppb
did appear similar to any of the standard peaks (Figure 1 & Figure 2). This maybe be due
to pressure washing did not remove all soil particles from the root sample or it may
contain a arsenic-thiol group contamination. Fern fronds that were exposed to 250 and
500ppb of arsenic had detection levels below the capable detection limits for XANES
analysis.
T2R1 #3
T2R1 #2
T3R1 #1
T3R1 #2
3.0
2.5
Absorption
2.0
1.5
1.0
0.5
0.0
11840
11860
11880
11900
11920
Energy (eV)
Figure 1: XANES analysis of roots exposed to 250ppb (T2) and 500 ppb (T3) of
arsenic
As (III) Oxide
As (V) Oxide
Sodium Asrenate
T2R1#3
2.5
Absorption
2.0
1.5
1.0
0.5
0.0
11840
11860
11880
11900
11920
Energy (eV)
Figure 2: Arsenic standards for XANES analysis of roots exposed to 250 ppb
and 500ppb arsenic treatment levels
129
250
200
150
As (ppm) 100
50
0
*
BLOCK1 *
500ppb R3
*
BLOCK 2
500ppb R2
*
BLOCK 3
500ppb R1
*
250ppb R3
BLOCK 4
250ppb R2
Treatments
250 ppb, R1
0ppb R3
0 ppb R2
0 ppb R1
-50
Graph 1: ICP-MS concentrations of marsh fern root samples used in XANES
analysis
130
Speciation of Phosphorus Compounds in Typical Louisiana Calcareous Soils
Using XANES
J. J. Wang1, D.L. Harrell1, and Amitava Roy2. 1LSU Agriculture Center and LSU
Department of Agronomy and Environmental Management, Sturgis Hall, Baton Rouge,
LA, 70810, [email protected], [email protected] 2LSU Center for Advanced
Microstructures and Devices, 6980 Jefferson Hwy., Baton Rouge, LA 70806,
[email protected]. PRN: Agr-JW040.
It has been generally accepted that Fe and Al bound phases control the solubility and
mobility of P in acidic soils while Ca bound phases are the controlling factor in
calcareous environments. However, recent evidence from wet chemistry has showed that
Fe oxides may play an equally important role in P retention in calcareous soils. The
objective of this study is to use XANES techniques to identify P controlling minerals in
some typical Louisiana calcareous soils. Results are presented in Figure1.
The P K-XANES spectra for 17 standards along with the four calcareous and one
biosolids-impacted soil samples were collected at the Double Crystal Monochromator
(DCM) equipped with two InSb (111) crystals that were slightly detuned. In general, the
spectra obtained for common Fe, Al, and Ca phosphate minerals showed unique features
which could be used to identify the various phosphate forms. On the other hand, the P KXANES spectra for P sorbed on Fe and Al oxide surfaces lacked unique spectral features
and could not be used to distinguish among these P species. Principal component
analysis (PCA) indicated that it would take five orthogonal components to describe the
variation in the XANES spectra of each soil sample. Target transformation determined
that several of the 17 P standards used had SPOIL values < 1, indicating that they were
the most probable components which could improve the fitting when included in the data
matrix. Consequently, only the five P standards with the lowest SPOIL values
determined by target transformation were generally used in the fittings. Resulting
normalized relative percentages of each standard species were summed grouped into the
following categories: phosphates sorbed on Fe-/Al-oxides plus organic P, crystalline Fe/Al-phosphates, and Ca phosphates (Ca minerals and P sorbed on CaCO3). Nearly
identical least-squares linear combination fitting (LCF) results occurred when P sorbed
on ferrihydrite was substituted with P sorbed on gibbsite illustrated insensitivity of
XANES analysis to distinguish between the metal oxide sorbed P phases. Since the
Commerce and Norwood soils contained broad white line peaks as compared to other
soils, the less intense featured CaCO3 sorbed P rather than the intense featured
hydroxyapatite was used in LCF analysis. The LCF fitting of original soil XANES
spectra suggests that most of the Fe-/Al-P were in sorbed forms. There was no strengite
found in all soils but variscite was possibly present in Mer Rouge and Jeanerette soils.
The LCF analysis also showed that the Norwood and Commerce soils contained Ca-P
mostly in sorbed form associated with CaCO3 or as Ca-hydroxyphosphate. The Mer
Rouge soil contained Ca-P in the form of Ca-hydroxyphosphate while the Jeanerette
contained Ca-P in both the hydroxyapatite and Ca-hydroxyphosphate forms. A highly
significant correlation was found between the total Ca-P determined by least-squares
LCF of P K-XANES spectra of the soils and the Ca-P determined by the HCl-P
extraction of the sequential chemical fractionation procedure (R2 = 0.89, P = 0.016).
Likewise a significant correlation (R2 = 0.81, P = 0.0383) was found between the sum of
131
relative percentage of total Fe-/Al-P plus organic P determined by XANES fitting and the
relative percentage of Fe-/Al-P from the NaOH-P fraction of the chemically sequential
fractionation procedure. Generally, least-squares LCF of XANES spectra estimated more
Ca-P as well as Fe-/Al-P and than was determined by chemical fractionation. Since
chemical fractionation contained a large residual-P fraction which could not be
partitioned into chemically defined P forms, XANES estimates of soil total Caphosphates and the total Fe-/Al-P species was more effective than the chemical P fraction
procedure even though XNAES could not differentiate P sorbed onto Fe or Al oxides.
The LCF fitting of the Commerce soil after fractionation indicated that total Ca-P
increased after the NaOH-P and CBD-P extraction as expected. However, the LCF
fitting of the Savannah soil showed that total Ca-P declined after the NaOH-P extraction
and then slightly increased after the subsequent CBD-P extraction. Analysis of P KXANES spectra were limited due to the insensitivity of PCA and target transformation
and the noisy soil spectra due to the low total P content in soils such as Norwood after
fractionation. Although we eliminated testing all possible standard combinations by only
using reference components with SPOIL values < 1, a software package allowing the
simultaneous determination of the best least-squares fit of large possible standard
combinations could enhance our least-squares analysis.
4
6
M e r R o u g e (1 )
Normalized absorption
3
2
1
S a v a n n a h (1 )
S a v a n n a h
L e a s t- s q u a r e s L C F
C a - h y d r o x y p h o s p h a te
P o n fe r r ih y d r ite
P o n h e m itite
h y d r o x y a p a tite
v a r is c ite
5
Normalized adsorption
M e r R o u g e
P o n g ib s ite
P o n h e m itite
v a r is c ite
N a - p h y ta te
4
3
2
1
0
0
2 1 4 5
2 1 5 0
2 1 5 5
2 1 6 0
2 1 6 5
2 1 4 5
2 1 5 0
2 1 5 5
2 1 6 0
2 1 6 5
3 .5
2 .5
2 .0
1 .5
1 .0
C o m m e r c e (3 )
C
L
C
P
P
P
P
4
J e a n e r e tte
P o n g ib s ite
P o n h e m itite
h y d r o x y a p a tite
v a r is c ite
J e a n e r e tte (1 )
3 .0
3
o m m e rc e
e a s t- s q u a r e s L C F
a - h y d r o x y p h o s p h a te
o n g ib s ite
o n h e m itit
o n fe r r ih y d r it
o n C a C O 3
2
1
0 .5
0 .0
0
2 1 4 5
2 1 5 0
2 1 5 5
2 1 6 0
2 1 4 5
2 1 6 5
2 1 5 0
2 1 5 5
2 1 6 0
2 1 6 5
E n e r g y (E v )
N o r w o o d
(3 )
N o rw o o d
P o n g ib s ite
P o n C a C O 3
P o n h e m itite
v a r is c ite
4
3
2
1
0
2 1 4 5
2 1 5 0
2 1 5 5
2 1 6 0
2 1 6 5
E n e r g y (E v )
Figure 1. Least-squares LCF of each soil P K-XANES spectra along with the residuals of
each standard species used in the fitting.
132
X-ray
Micro-Tomography
133
Tomography for 3D Chemical Analysis
Kyungmin Hama and Les Butlerb
aCAMD, [email protected] and bDepartment of Chemistry, LSU, [email protected];
Chem-LB1206
In 2005, the tomography beamline was turned off for a move and upgrade, and came
back on-line in August, 2005, and accepted friendly proposals in October, 2005. The
current upgrades are roughly 90% finished, though another equipment proposal is
pending which may lead to another round of upgrades. Relative to other synchrotron
tomography beamlines in the world operating with pin-hole type optics, the CAMD
instrument has comparable resolution (4.5 micron), good horizontal field-of-view, but a
constricted (1 mm) vertical field-of-view.
The newly installed high-throughput
multilayer monochromator (funded by NSF MRI-0216875) does yield the desired fast
shutter speeds over 6 to 35 keV. Because of the monochromator upgrade, the beamline
moved from a bending magnet to the 7 Tesla wiggler. Data acquisition software was
rewritten, converting from tomography with fixed rotation angle increment to a Greek
golden ratio algorithm for angle increments that are optimized for rapid image acquisition
[Köhler, 2004; Matej, 2004].
More details are at the tomography web site:
http://tomo.camd.lsu.edu
The chemical analysis project was funded by NSF in July, 2005, and has commenced
with analysis of some previously acquired data. In a blend of fiberglass, nylon, and
Albemarle flame retardant HP-3010G (a short chain brominated polystyrene), we are
finding excellent blending, extending from the surface of each glass fiber into the bulk
nylon. To perform this analysis, we have written several new 3D image analysis
programs to: (a) correct images for gain, offset, and spatial distortions, (b) use a
combination of segmentation and diffusion to mask out fiberglass from the concentration
calculations, and (c) measure concentration in directions normal to the fiberglass/polymer
interface. In summary, this work more than substantially increases the total volume of
data analyzed and the scope of analysis tools generated, relative to our first
publication.[Ham, 2004]
K. Ham, et al., Chemistry of Materials, (2004) 16, 4032-4042.
T. Köhler, IEEE Nuclear Science Symposium Conference Record, (2004) 6, 3961-3965.
S. Matej, et al., IEEE Trans. Med. Imag. (2004) 23(4), 401-412.
134
Nanofabrication
135
Targeting Breast Cancer Cells and Their Metastases through
Luteinizing Hormone Releasing Hormone (LHRH) Receptors Using
Magnetic Nanoparticles
Carola Leuschner a, Challa S. S. R. Kumarb, Josef Hormes,b and William Hansela
Pennington Biomedical Research Center, LSU System, Baton Rouge, LA 70808, USA;
b
Center for Advanced Microstructures and Devices, 6980 Jefferson Hwy, Baton Rouge,
LA 70806.
a
Breast cancer is the most common cause of cancer death in women; more than
75% of patients die from skeletal metastases.1 The accurate diagnosis of metastatic
disease is, therefore, crucial for monitoring treatment success in cancer patients.
Sensitive and noninvasive methods for early detection of metastases need to be
developed. Noninvasive detection methods include mammography, ultrasound, magnetic
resonance imaging (MRI), and nuclear imaging techniques such as positron emission
tomography (PET), SPECT (single-photon emission tomography), and computed
tomography (CT). Of these MRI is the most promising, as this technique is independent
of tissue depth and does not require radioisotopes. Contrast agents, such as gadolinium
chelates or iron oxide, can increase the sensitivity of MR images.2,3
Signal amplification can be achieved by increasing intracellular concentrations of
the contrast agent or the particle size.4,5 Dextran-coated iron oxide particles of 62–150 nm
diameter (Endorem or AMI125) accumulated mainly in the liver and spleen after
intravenous injection and were used in patients for the diagnosis of liver metastases.6-9 In
these applications the contrast agent accumulated in healthy tissue and enhanced the
resolution of the MR image between malignant and healthy tissue.10 However,
accumulation in and binding of nanoparticles to the target cells was either absent or
nonspecific. Therefore these applications were limited to liver, spleen, and intestinal
diagnostics. In clinical trials iron oxide particles caused no side effects or toxicities.6-9
To increase the intracellular concentration of iron oxide nanoparticles in
disseminated cancer cells in peripheral organs, particles need to be designed that have the
following characteristics: (1) high specificity to the target cells, (2) reduced size (less
than 50 nm) (3) long circulation time in vivo, and (4) surface coating to avoid recognition
and internalization by the macrophages of the reticulo endothelial system.11 Long
circulating dextran coated iron oxide nanoparticles of 10-nm diameter were incorporated
into cancer cells and macrophages in vitro at ranges between 0.01–100 pg/cell depending
on particle type, composition, and cell type tested.12,13 The uptake of such nanoparticles
in tumor cells and macrophages reached 0.01–0.1 pg Fe/cell for tumor cells and 0.97 pg
Fe/cell for macrophages.12
Examples for targeted delivery of iron oxide particles to cancer cells have been
described previously: Dextran-coated monocrystalline iron oxide nanoparticles linked to
transferrin increased the iron accumulation in rat glioma cells compared to free
particles;14 similar effects were observed when iron oxide particles linked to folate
targeted and accumulated in cancer cells.15,16 The targeted iron particle uptake in cancer
cells resulted in various iron contents and was dependent on the type of receptor targeted.
Dextran coated nanoparticles of less than 10 nm diameter resulted in 0.9-1.3 pg Fe/cell,
whereas Her2/neu targeting in the same cells increased the uptake by a factor of 2.17
Dextran-coated monocrystalline iron oxide nanoparticles (MION) linked to transferrin
resulted in a 10-fold increased accumulation in rat glioma cells compared to free
particles.14 In contrast, human fibroblasts did not incorporate transferrin-linked MIONs;
instead, these particles remained on the surface membrane.18
136
Most human breast cancers and most likely their metastases (60%) express
receptors for luteinizing hormone releasing hormone (LHRH).19,20 Metastases and
disseminated cells derived from breast cancer xenografts of estrogen independent MDAMB-435S.luc cells in the presence and absence of the primary tumor have been detected
and characterized and were specifically targeted by LHRH-lytic peptide conjugates.20
LHRH is a decapeptide and belongs to the gonadotropins. The amino acid sequence of
the human LHRH is Glu His Trp Ser Tyr Gly Leu Arg Pro Gly. Upon release from the
hypothalamus, LHRH stimulates release and synthesis of the gonadotropin hormones
luteinizing hormone and follicle stimulating hormone, which regulates the endocrine
levels of estrogens and androgens.
We hypothesized that SPIONs decorated with LHRH specifically facilitate
accumulation of particles at the tumor/metastatic cells and promote their incorporation
through receptor-mediated endocytosis, thus increasing the intracellular contents of
SPION in metastatic cancer cells of peripheral tissues, lymph nodes, and bones. In this
study we compared the intracellular accumulation of SPION and LHRH-SPION in
human breast cancer cells in vitro and tested whether LHRH-SPION specifically target
tumors and lung metastases from human breast cancer xenografts in a nude mouse model.
SPIONs were fabricated as described in Kumar et al. using wet chemical methods
and then conjugated to the carboxylated form of LHRH using carbodiimide chemistries.21
The magnetite nanoparticles were synthesized under inert atmospheric conditions with
the Schlenk technique and these particles have on their surface amine groups, which were
utilized to bind LHRH.
In vitro studies: MDA-MB-435S human breast cancer cells were obtained from
the American Type Culture Collection (Rockville, MD) and cultured as described
previously.20 MDA-MB-435S cells were transfected with exogenous DNA by lipofection
using the plasmid pRC/CMV-luc containing the Photinus pyralis luciferase gene and an
antibiotic resistance gene under transcription control of the cytomegalovirus
promoter.22,23 The stably transfected MDA-MB-435S.luc cells with the highest
expression of the luciferase gene were characterized for their LHRH receptor binding
capacities.20,24 Mouse Sertoli cells (TM4) were cultured as described in Leuschner et
al.24 MDA-MB-435S.luc cells and TM4 cells were grown to 70% confluency in 6 or 24
well plates and were incubated with LHRH-SPION or SPION at 37 and 4 oC in the
presence and absence of LHRH (50 µM). At the end of the incubations the cells were
detached from the culture plates, washed, centrifuged and the cell pellets were
resuspended in HCl (1 M). Iron contents were determined spectrophotometrically after a
Prussian Blue reaction.
In vivo studies: The animal studies were approved by the institutional animal
care and use committee (IACUC), and was in compliance with the principles of
laboratory animal care of the National Institute of Health (NIH), USA. Female nude mice
bearing subcutaneous human breast cancer xenografts (MDA-MB-435S.luc), were
injected into the lateral tail vein with LHRH-SPIONs or SPION (250 mg of Fe/kg of
body weight). Twenty hours after injection the mice were sacrificed, lungs and tumors
weighed and frozen in liquid N2 until further analyses. Metastatic cells in lungs from
xenograft bearing mice were determined by luciferase assays from lung homogenates.22,23
Iron contents were determined spectrophotometrically after a Prussian blue reaction from
cell and lung homogenates and from paraffin embedded and sectioned tissues.
Statistical Analyses: Three separate analyses of the data were conducted. In the
first, the raw data were analyzed using ANOVA. Second, we applied a variancestabilizing transformation (log transform) to the raw data and subsequently conducted an
137
ANOVA. Finally, we obtained the ranks of the data and conducted a Kruskal-Wallis test.
Differences were considered significant at p < 0.05. Rank data and variance stabilizing
transformations were included.
Characteristics of SPION and LHRH-SPION
The superparamagnetic iron oxide nanoparticles had an average diameter of 10 nm,
were nearly monodisperse, and remained superparamagnetic regardless of the binding of
LHRH. The binding of LHRH to SPION was confirmed by FTIR (Fourier transformation
infrared) spectroscopy, XANES, and HPLC analysis, which revealed complete binding
and saturation of the amine surface with the ligand peptides SPIONs showed a higher
saturation magnetization Ms = 72.1 emu/g compared to 30.6 emu/g for the LHRHSPION. The coercive magnetic field, for LHRH-SPION was 6 times greater than for
SPION alone. SPIONs were charged particles (28.05 ± 1.93 mV), whereas LHRHSPIONs were neutral according to their ζ-potential (–2.2 ± 0.58 mV). Unlike other
particles previously fabricated (for review, see ref 11), LHRH-SPION or SPION were not
specifically coated with any polymers or other compounds.
Specificity and Quantification of LHRH-SPION Accumulation in Human Breast
Cancer Cells in vitro
MDA-MB-435S.luc breast cancer cells were incubated with LHRH-SPION with or
without LHRH and SPION for 0.5 or 3 h at 37 oC and 3 h at 4 oC. Each well contained 1
mg of iron (0.33 mg/ml). At this concentration, neither SPIONs or LHRH-SPIONs were
toxic to the cells as determined by cell viability assays (data not shown). Fig. 1 shows
three representative 6- well plates, which illustrates the iron contents from MDA-MB435S.luc cells as indicated by Prussian blue stains for each incubation (one column = 3
wells for control medium, SPION, SPION + LHRH, LHRH-SPION, and LHRH-SPION
+ LHRH) after 3 h. The iron content was highest in samples with the darkest the blue
stain. The amount of iron accumulated in the breast cancer cells increased in all
incubations between 0.5 and 3 h at 37 oC by a factor of 4. The highest iron accumulation
based on the initially present iron concentration (0.3 mg/ml) was observed with LHRHSPION after 3 h (34.8 ± 0.06%) compared to SPION (7.7 ± 0.01%) (p < 0.003 vs
SPION). Co-incubation with LHRH to saturate the cellular LHRH-receptors decreased
the iron accumulation from LHRH-SPION to 18.2 ± 0.24% (p < 0.001). Incubations at 4
o
C resulted in iron accumulation of less than 0.26% regardless of SPION or LHRHSPION incubations.
The specificity of LHRH-SPION uptake into cells was tested in MDA-MB435S.luc breast cancer cells, which express LHRH receptors, and compared to TM4 cells,
which do not express LHRH receptors, and served as a negative control. After 1 h of
incubation, the intracellular iron content reached MDA-MB-435S.luc cells 106 ± 21 pg of
Fe/cell with LHRH-SPION and 37.2 ± 9 pg of Fe/cell with SPION. The addition of free
LHRH to the incubation medium significantly reduced the accumulation of iron particles
to values similar to that of unconjugated SPIONs (Figs. 1 and 2). As expected, TM4 cells
138
Figure 1. Accumulation of SPION and LHRH-SPION in human breast cancer cells.
MDA-MB-435S.luc breast cancer cells were stained for iron in a Prussian blue reaction
after a 3-h incubation at 37 oC with LHRH-SPION and SPION (0.3 mg/ml of Fe) in the
presence and absence of LHRH.
Fig. 2. Intracellular iron contents of MDA-MB-435S.luc and mouse Sertoli cells (TM4)
after incubation at 37 oC with SPION and LHRH-SPION (0.3 mg/ml) in the absence or
presence of LHRH (50 uM) after 1 h. N = 4, (*) p < 0.036 compared to all other
incubations.
accumulated iron particles at similar concentrations independent of LHRH conjugation
(29.6–37.3 pg of Fe/cell).
139
When MDA-MB-435S.luc cells were incubated with LHRH-SPION or SPION at
concentrations between 0 and 400 uM; iron saturation was achieved at a LHRH-SPION
concentration of 48 uM (452.63 pg of Fe/cell). In contrast, unconjugated SPION or the
presence of the same ligand together with LHRH-SPION, resulted in a maximal iron
content of 38 pg of Fe/cell at iron concentrations of more than 50 uM. These values were
significantly higher than iron contents reported previously with dextran-coated iron oxide
nanoparticles, with the highest concentrations reported as 100 pg of Fe/cell.12,13 Her2/neu
targeting resulted in iron contents of 3 pg of Fe/cell.17 Dextran-coated monocrystalline
iron oxide nanoparticles linked to transferrin resulted in a 10-fold increased accumulation
in rat glioma cells compared to free particles,14 although the absolute iron content was
much higher in our experiment.
Targeting Breast Cancer Tumors and Lung Metastases with LHRH-SPION in vivo
The high metastatic potential of MDA-MB-435S breast cancer cells in nude mice
provides an adequate model for studying drug effects and interaction with contrast agents
in vivo. The MDA-MB-435S.luc cell line, transfected with the luciferase gene from the
firefly (Photinus pyralis), offers a sensitive tool for the investigation and detection of
micrometastases and disseminated tumor cells in a nude mouse model. Micrometastases
and tumor cell clusters in homogenates or peripheral organs, lymph nodes, and bones can
be quantified through luciferase assays with sensitivities to less than 10 individual breast
cancer cells per organ.10
The SPIONs and LHRH-SPIONs were injected intravenously into human breast
cancer xenograft-bearing nude mice without causing side effects or toxicities at the
injected concentration of 250 mg/kg. Iron oxide nanoparticles are biologically safe. They
are metabolized into elemental iron and oxygen by hydrolytic enzymes, and the iron joins
the normal body stores and is incorporated into hemoglobin. Acute toxicity has not been
observed, in rats or humans. In rats, 250 mg/kg of iron particles injected intravenously
caused no side effects, in mice 350 mg/kg were well tolerated.25-27
When paraffin embedded lung sections from LHRH-SPION and SPION injected
mice were stained for iron content, only lung metastases from mice having received
LHRH-SPION tested positive for iron, as illustrated by Prussian Blue iron complexes.
SPIONs did not accumulate in lung metastases and were not different to saline injected
controls when tested for iron content (Fig. 3). In contrast the iron content in the lungs
containing metastatic cells reached up to 20% of the injected iron, whereas no LHRHSPION accumulated in lungs of normal mice (<0.09%). Most importantly, the iron
content in lungs was directly dependent on the number of metastatic cells, suggesting that
LHRH-SPION entered the cells through receptor-mediated endocytosis and accumulated
specifically in the metastasized MDA-MB-435S.luc cells of the lungs.
These findings strongly suggest that human breast cancer cells that express
LHRH-receptors are targeted through LHRH-SPIONs and accumulate specifically in
human breast cancer cells in vitro and in vivo. When LHRH-SPION accumulation was
compared to injections of free iron particle (SPION), the targeted approach resulted in a
7.5-fold higher iron concentration in tumors; metastastatic cells in the lungs incorporated
specifically LHRH-SPIONs , whereas no iron accumulation was observed with
unconjugated SPIONs. Further studies are in progress to determine the body distribution
of LHRH-SPION and SPION in vivo and to study the subcellular accumulation of iron
particles in tumors and metastases.
140
Fig. 3. Paraffin-embedded sections from lungs of mice bearing MDA-MB-435S.luc
tumors stained for iron after injection of LHRH-SPION or SPION. (A) Lung section of
untreated tumor-bearing mouse; (B) Lung section tested positive for iron after LHRHSPION injection. (C) Lung section of tumor bearing metastasis positive mouse tested
negative for iron after SPION injection. All lung sections contained luciferase positive
cells, which metastasized from the primary MDA-MB-435S.luc tumor. Iron stains were
conducted with the iron stain kit (Sigma).
SUMMARY
MDA-MB-435S.luc breast cancer cells were specifically targeted through their LHRH
receptors with LHRH-SPION. The amount of iron accumulated in MDA-MB-435S.luc
cells in vitro was 12-fold higher after LHRH-SPION than after free SPION incubation.
The uptake of LHRH-SPIONs was directly dependent on LHRH-receptor expression and
was inhibited in the presence of LHRH. Cell lines which do not express functional
LHRH receptors had similar iron contents when incubated with LHRH-SPION or
SPION. LHRH-SPIONs accumulated in tumor cells and lung metastases from breast
cancer xenograft-bearing mice. Iron accumulation in the lungs was directly dependent on
the number of metastatic tumor cells. MDA-MB-435S.luc breast cancer cells and their
metastases were specifically targeted through their LHRH receptors and incorporated
LHRH-SPIONs at a significantly higher rate than SPION, suggesting a mechanism of
highly specific receptor-mediated endocytosis. LHRH-SPIONs have high potential as
contrast agent for magnetic resonance imaging as they directly accumulate in metastases
from breast cancer tumors.
Acknowledgements
Supported by PBRC/LSU, Nutrition and Chronic Disease Section, pilot project award:
Detection of disseminated cells and micrometastases by ligand conjugated
superparamagnetic iron oxide nanoparticles. PI: Carola Leuschner. Financial
support from the Center of Advanced Microstructures and Devices is gratefully
acknowledged. We thank Dr. Yuri Lvov and his team from the Louisiana Tech
University, Ruston, for providing the measurements for the ζ-potentials.
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143
A TEM Study of Magnetic Nanoparticles Targeting Breast Cancer Cells
and Metastases in vivo
J. Zhou1, C. Leuschner2, C. Kumar3, L. Hayward1, L. Ionescu1, C. Hormes3 and W.O.
Soboyejo1
1
Department of Mechanical and Aerospace Engineering, and Princeton Institute
for the Science and Engineering of Materials, Princeton University, Princeton, NJ
08544 ; 2Pennington Biomedical Research Center, 6400 Perkins Road, Baton
Rouge, Louisiana 70808; 3Center for Advanced Microstructures and Devices,
Louisiana State University, 6980 Jefferson Hwy, Baton Rouge, Louisiana 70806
INTRODUCTION
Mammary adenocarcinoma is the second leading cause of cancer death in women.
At the time of diagnosis 35-40 % of the breast cancer patients already have metastases
[1]. These metastases result from spreading of the primary breast cancer cells through
lymphatic system, venous system, or through direct extension to neighboring organs, as
shown schematically in Figure 1. Breast cancer has the potential to spread to almost any
region of the body. The most common region where breast cancer spreads to is bone.
This is followed by lung and liver. Furthermore, the micrometastases may develop long
duration after removal of the primary tumor. According to the National Cancer Institute,
approximately only 10% to 20% of women with metastatic breast cancer survive the
disease (achieve permanent remission) [2]. It is, therefore, extremely important to
improve early stage detection of breast cancers and the resultant metastases.
Biocompatible magnetic nanoparticles (MNPs) have been widely used for cancer
diagnostics and treatment [3-12]. These include magnetic drug targeting [6],
hyperthermia [7-9], magnetic field assisted radionuclide therapy [10,11], and magnetic
resonance imaging (MRI) contrast enhancement [5,12]. Depending on application
requirements, MNPs may be coated with various functional surface layers. For example,
poly(ethylene glycol) (PEG) coat is used to minimize or eliminate protein adsorption,
leading to increasing circulation times of MNPs in the blood stream [12].
144
Figure 1: Schematic illustration of primary cancer cell spreading into other organs. The
primary cancer cells spread through lymphatic system, venous blood system, or via
extension to neighboring mussel tissues to form sarcoma.
Low molecular weight targeting agents such as folic acid coating helps MNPs to target
specific cancer cells [13]. A recent study has demonstrated that an amphipathic
membrane-disrupting peptide can be targeted to prostate cancer cells using luteinizing
Hormone (LH) [14]. The concentration-dependent toxicity was reduced by linking the
peptides to MNPs when applied to a breast cancer line in vitro experiment. Since
Luteinizing Hormone and Releasing Hormone (LHRH) receptors are over expressed by
cells in several types of cancers including prostate cancer and breast cancer [15], they can
be targeted by MNPs conjugated by LHRH (LHRH-MNPs) [16,17]. Drugs binding to
LHRH-MNPs may also be delivered efficiently to these specific cancer cells [18].
Furthermore, the distribution of metastases will be detected using magnetic resonance
imaging (MRI) if LHRH-MNPs can effectively target cancer cells, because the MRI
images are negatively enhanced by magnetic nanoparticles [3]. However, most relevant
studies were in vitro experiments [4].
In this paper, a study is carried out to investigate the use of LHRH-MNPs in
targeting the primary breast cancer and the resulting metastases in female nude mice
bearing breast tumors. LHRH-MNPs were intravenously injected into tumor bearing
mice. After sacrificing mice, tumors and periphery organs including liver, lung and
145
kidney were collected for analysis. Parts of organs were homogenized, and their iron
contents were determined spectrophotometrically using a Prussian Blue Reaction [18].
Other parts of organs were fixed and stained for transmission electron microscopy (TEM)
analysis. Nanoparticles without surface coatings were also injected into tumor-bearing
mice for control tests. We found that LHRH conjugated MNPs were mainly distributed in
tumors, and associated metastases developed in lung.
MATERIALS AND METHODS
Preparation of LHRH conjugated MNPs
MNPs were synthesized using the Schlenk technique in inert atmospheric
conditions. The LHRH conjugation procedure was reported by Kumar et al. [14]. Briefly,
the magnetic nanoparticles synthesized using this method have on their surface amine
groups which were utilized to covalently bind LHRH. Carbodiimide activation was used
to promote ligand binding. The conjugating process is illustrated schematically in Figure
2. The LHRH-MNPs have been characterized and analyzed using various methods and
techniques that were reported in Ref. [16].
NH2
H2N
H2N
NH2
NH2
NH2
LHRH-HN
LHRH-HN
LHRH
NH-LHRH
NH-LHRH
NH-LHRH
NH-LHRH
NH-LHRH
NH2
Figure 2: Covalent binding of LHRH to MNP nanoparticles with surface amine groups.
H2N
Carbodiimide
activation
LHRH-HN
In vivo experiments
The human breast cancer cell line MDA-MB-435S (established from a human
mammary ductal carcinoma, estrogen independent) were used in this study [14]. They
were obtained from the American Type Culture Collection (Rockville, MD). MDA-MB435S cells were grown in Leibovitz’s L 15 medium, 10% fetal bovine serum, 0.010
mg/ml bovine insulin, 100 IU/ml penicillin, 100 mg/ml streptomycin. The cells were
cultured in tightly closed flasks, and the incubation temperature was 37 °C. The MDAMB-435S cells were stably transfected with the luciferase gene of the firefly Photinus
pyralis with exogenous DNA by lipofection with the plasmid pRC/CMV-luc containing
the Photinus pyralis luciferase gene and an antibiotic resistance gene under transcription
146
control of the cytomegalovirus promoter. The stably transfected MDA-MB-435S.luc cells
were selected with 400 mg/ml G418, and the clones with the highest expression of
luciferase gene were selected.
Female athymic nude mice were used as animal model in this study. At 6 weeks
of age, the mice (N = 10) were subcutaneously implanted with 1 x 106 breast cancer cell
line MDA-MB-435S.luc in the interscapular region [14]. MDA-MB-435S.luc cells
developed solid, vascularized tumors within 10 days after subcutaneous injection, and
had high metastasis potential in nude mice. After bearing cancers for 30 days, the mice
were then injected intravenously with 350 mg/kg of unconjugated MNPs or LHRHMNPs. Animals were then sacrificed 20 hours after nanoparticles injection. Tumors,
livers, lungs and kidneys were collected for subsequent analyses.
Iron determination
The accumulation of magnetic nanoparticles in the tumors and periphery organs
including livers, lungs and kidneys were determined spectrophotometrically in a Prussian
blue reaction that has been described elsewhere [14]. Tissues were also Prussion blue
stained and embedded in paraffin to observe the distribution of LHRH-MNPs in tumors
and lungs. Metastatic cells and their concentrations in organs were determined through
luciferase assays [18].
TEM study of sub-cellular distribution of LHRH-MNPs and MNPs
Tumors, livers, lungs and kidneys were fixed immediately after being removed
from sacrificed animals by immersion in glutaraldehyde (2.5% glutaraldehyde in 0.1 M
sodium cacodylate with 2 mM CaCl2, pH 7.3). These tissue samples were further cut into
small pieces of ~ 1 mm3 and dehydrated using increasing concentrations of ethanol
alcohol, from 25% to 100% ethanol. Tissues were then embedded in resin. TEM
specimens were prepared by cutting 60 nm thick foils from the resins using Ultracut UCT
Microtome (Leica®). The thin slices were then transferred onto copper TEM grids. After
further staining in 1% osmium tetroxide, the samples were ready for TEM observation.
The TEM analysis was carried out in a high resolution TEM (Philips CM 200) equipped
with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy
(EELs). MNPs were identified by EDS analysis, and their sub-cellular distribution was
investigated by bright field TEM micrographs.
147
Iron content in tumors and organs
Iron contents in tumors and peripheral organs including lungs, livers and kidneys
are shown in Figure 3 for tumor-bearing mice intravenously injected with MNPs or
LHRH conjugated MNPs (LHRH-MNPs). Up to 60% of the injected nanoparticles were
found to accumulate in tumors for mice that were injected with LHRH conjugated MNPs
(Figure 3a). In contrast, only ~ 8% of the injected unconjugeted MNPs were distributed
into tumors in mice that were administrated in the same conditions (Figure 3b).
Accumulation of MNPs and LHRH-MNPs in lungs exhibits similar trend. LHRH-MNP
incorporated into the lung tissue reached up to 20% in tumor-bearing mice, while
unconjugated MNPs accumulated in lungs are less than 2.3% of all the injected
nanoparticles.
Unconjugated MNPs accumulated preferably in the livers (55%)
compared to only 5.2% of the LHRH-MNPs remaining in livers 20 hours after the
injection. Similar small portion of nanoparticles distributed into kidneys: 3.3% for
unconjugated MNPs and 3.9% for LHRH-MNPs.
70
60
50
50
Iron Content (%)
Iron Content (%)
60
40
30
20
40
30
20
10
10
0
0
Tumor
Lung
Liver
Kidney
Tumor
Lung
Liver
Kidney
(B)
(A)
Figure 3: Iron contents in tumors, lungs, livers and kidneys: (a) iron content of LHRHMNPs and (b) iron content of MNPs.
148
TEM analysis
TEM analysis was started with tumor cells, since LHRH-MNPs tend to
accumulate in tumors. TEM micrographs obtained from tumors are shown in Figure 4.
Unconjugated MNPs were observed in tumor cells. These individual nanoparticles
distributed inside cells everywhere except cell nucleus (Figure 4a). Similar distribution
was observed for LHRH-MNPs (Figure 4b). However, more LHRH-MNPs accumulate to
form nanoparticle clusters. Although few nanoparticle clusters were observed within cell
membrane (Figure 4c), these particle clusters are mainly associated with cell membranes
(Figure 4b).
X-ray spectrums of nanoparticles were also collected using energy dispersive
spectrum (EDS) system that is installed in Philips CM 200 transmission electron
microscopy (TEM). In EDS analysis, electron beam was focused on the MNPs. A
representative x-ray spectrum is shown in Figure 5. Significant Fe Kα peak was obtained.
Since copper TEM grids were used to support 60 nm thin tissue slices, strong copper Kα
peak also presents in the x-ray spectrum. Osmium Kα peak and Uranium Kα peak were
149
Figure 4: Sub-cellular distribution of MNPs and LHRH-MNPs in tumor cells: (a)
individual MNPs in a tumor cells; (b) individual LHRH- MNPs and in tumor cells and
nanoparticle clusters associated with cell membrane; and (c) LHRH-MNP clusters in
cells.
also observed because osmium tetroxide and uranyl acetate were used for tissue fixing
and staining in specimen preparation for TEM analysis.
Figure 5: An x-ray spectrum collected from magnetite nanoparticles in tumor cells.
150
MNPs and LHRH-MNPs in cells from lung are shown in Figure 6. No observable
MNPs without conjugation were found in the cells from lungs of tumor-bearing mice that
were sacrificed 20 hours after injection of MNPs (Figure 6a). In contrast, a significant
amount of LHRH-MNPs were observed in the cells from lungs of mice that were treated
in the same way (Figure 6b). The LHRH conjugated MNPs accumulate to form
nanoparticles clusters, and these clusters preferably distributed in a local region. A higher
magnification image of one cluster shows individual MNPs in Figure 6c.
Both individual nanoparticles and nanoparticle clusters were observed in liver
cells of mice that were injected with unconjugated MNPs (Figure 7a). Few individual
LHRH-MNPs were also observed in liver cells (Figure 7b). It is important to note that
these individual MNPs were only observed inside cell nucleus. This is true for both
conjugated and unconjugated MNPs.
TEM micrographs of kidney cells are presented in Figure 8. No observable MNPs
were found in kidney cells. This is true for mice injected with either conjugated MNPs or
unconjugated MNPs.
151
Figure 6: Sub-cellular distribution of MNPs and LHRH-MNPs in cells from lungs of
mice bearing tumors for 30 days: (a) no MNPs in lung cells and (b) a significant
amount of LHRH-MNP clusters in cells from lungs; (c) individual LHRH-MNPs in a
nanoparticle cluster.
Discussion
In this study, all mice have been treated in the same way and administrated in the same
conditions. Tumors with size greater than 10 mm were typically developed when bearing
tumors for 30 days. The mice were sacrificed 20 hours after nanoparticles injection, such
that enough time was provided for nanoparticles to reach most organs through blood
stream circulation and diffusion. The results of both TEM study and Prussion Blue
Reaction study suggest that twenty-hour duration is enough to distribute nanoparticles in a
mouse body. Furthermore, it is generally believed that magnetic particles may be removed
from a mouse body by reticulaendothalia system (RES) [3]. However, our results suggest
that MNPs may stay in a mouse body for a longer duration. This could be attributed to the
small sizes of the MNPs that were used in this study, since small size particles tend to be
stable to reticulaendothelia system [4].
Figure 7: Sub-cellular distribution of MNPs and LHRH-MNPs in liver cells from mice
bearing with tumors for 30 days: (a) individual MNPs in the nucleus and nanoparticle
clusters in a liver cell; (b) individual LHRH-MNPs in the nucleus of a liver cell.
152
For mice injected with LHRH-MNPs, a surprisingly high MNPS content (22.2%)
in lungs was found. TEM observation showed accumulation of LHRH-MNPs to form
nanoparticle clusters the cells from lungs of tumor-bearing mice. In contrast, no
nanoparticle clusters were observed in the lungs collected from mouse without tumor 20
hours after nanoparticles injection, even though the mouse was housed in the same
conditions as those used in this study. Luciferase assay study shows that significant
metastases developed in lungs of mice bearing breast tumor for thirty days, and that iron
content is proportional to the amount of metastatic cells [18]. This suggests that both
primary cancer cells and metastatic cells can be detected and targeted through LHRHMNPs. Since MNPs can enhance MRI image contrast, LHRH-MNPs may be used for
early cancer detection [5,12]. Future studies are expected to explore the potential
applications of LHRH conjugated magnetic nanoparticles in MRI imaging.
Figure 8: Sub-cellular distribution of MNPs and LHRH-MNPs in kidney cells from mice
bearing with tumors for 30 days: (a) no MNPs or (b) LHRH-MNPs were observed in
kidney cells.
With current breast cancer detection techniques, 35-40 % of the breast cancer
patients already have occult metastases at the time of diagnosis. Approximately only 10%
to 20% of women with metastatic breast cancer survive the disease (achieve permanent
remission) [3]. These show the importance of the early detection of disseminated tumor
cells and micrometastases. However, the practical tools including micro-computed
153
tomography (µCT) and magnetic resonant imaging (MRI) are limited by their resolution
to find metastases when the concentrations of secondary cancer cells are low at early
stages. It is, therefore, critical to increase the detection resolution. This study shows that
the LHRH conjugated MNPs are able to specifically target the disseminated metastatic
cancer cells, whose contrast is then accordingly increased against the surrounding normal
cells [3-5]. This may result in improved detection resolutions when MRI or µCT is used.
This study also shows that the major of the injected MNPs without conjugation
are collected in liver cells. It is interesting to observe that the MNPs penetrate nuclear
pore and distribute in nucleolus, independent of conjugated coating. However, this
phenomenon was not observed in other organs, suggesting distinct interaction and
movement of MNPs in liver cells. It is, therefore, interesting to study the interaction
mechanisms of MNPs with liver cells in future.
Before closing, it is important to point out that TEM is a powerful tool to study
the sub-cellular distribution of MNPs. To achieve targeted delivery of drugs to subcellular level is critical to improve drug delivery efficiency [19]. Without understanding
the interaction of MNP with cell compartments, it is difficult to deliver DNA and realize
gene therapy [20]. However, only limited information is available for the interaction of
nanoparticles with sub-cellular organelles [21]. One major limit is that most microscopes
used in biology community can not provide high enough resolution to study the
interactions between nanoparticles and sub-cellular structures. TEM overcomes this
obstacle. In this study, TEM micrographs not only provide direct evidence shown the
presence of MNPs in various organs, they also tell us where the MNPs are in cells or
tissues. Moreover, our study shows that individual nanoparticles could either stay in cells
as a single particle or accumulate to form nanoparticle clusters. This is important
complementary to other methods like Prussion Blue Reaction, which can only determine
whether iron is present. A long sample preparing process seems, therefore, to be well
awarded by much more useful and detailed information provided by TEM studies.
CONCLUSIVE REMARKS
In vivo distribution of functionalized magnetic nanoparticles in mice bearing
tumors were studied using Prussion blue reaction and TEM analysis. Results obtained by
the two methods are consistent. Significant accumulation of LHRH-MNPs was observed
154
in both primary breast tumor cancer cells and metastatic cells in lungs. However,
individual LHRH-MNPs were also observed in the nucleuses of liver cells 20 hours after
nanoparticle injection. These results suggest LHRH conjugated magnetic nanoparticles
are able to target both primary breast cancer cells and their resulting metastases in other
organs. Furthermore, accumulation of individual nanoparticles in the nucleus of liver cell
suggests that the LHRH-MNP is a potential carrier for delivering drugs or genes to liver
cells with diseases. The significant results achieved in this study also indicate that TEM
is a powerful tool to study sub-cellular distribution of MNPs and their interactions with
cell compartments.
ACKNOWLEDGEMENTS
This research is supported by The National Science Foundation (NSF DMR0231418). The authors are grateful to and NSF Program Manager (Dr. Carmen Huber)
for their encouragement and support. Appreciation is also extended to Dr. Nan Yao and
Ms. Margaret Bisher for help with sample preparation.
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157
PMMA-STABILIZED COLLOIDAL IRON
NANOPARTICLES
H. Modrow,1, Zh. Guo,2,3 V. Palshin,2 Kh. Olimov,1,4 L. L. Henry, 5 J. Hormes,2 and
Challa S. S. R. Kumar2,
1
Physikalisches Institut, University of Bonn, Nussallee 12, Bonn, D-53115, Germany;
Center for advanced Microstructure and Devices, Louisiana State University, 6980
Jefferson Hwy, Baton Rouge, LA 70806, USA ; 3 Gordon A. and Mary Cain Department
of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA ; 4
Physical-technical institute of SPA “Physics-Sun” of Uzbek Academy of Sciences, ul. G.
Mavlyanova 2b, Tashkent, 700084, Uzbekistan ; 5 Department of Physics, Southern
University and A&M College, LA 70813, USA
2
1 INTRODUCTION
Today, many roads towards the synthesis of metal nanoparticles (NP’s) have been
developed. [1,2] This statement holds even if one limits oneself to wet-chemical
approaches: For example, references [3-12] represent an incomplete list of such routes in
the case of Co NP’s, leading to various particle sizes, different Co phases in the particle
core and core-shell as well as surfactant-stabilized particles. The increasing number of
synthetic approaches has lead to increasing availability of NP’s with “identical” size and
metallic core, as verified typically using transmission electron microscopy. With varying
surfactant molecules the more evidence has appeared that many changes in macroscopic
properties which had been assigned initially to size effects are in fact dependent on the
surface-interaction of the particles. This is evident e.g. from Table 1. More detailed
discussions of such effects, again based on Co NP’s, are found in [13,14]; a broader
review is found e.g. in [15] Also, recent studies show that even secondary processing
steps performed on a previously synthesized, surfactant-stabilized NP, e.g. crosslinking
with spacer molecules, using suitable rest groups of the stabilizing shell, can affect the
electronic structure of the NP core [16,17]. These examples illustrate that it is crucial to
develop a one-step, in situ synthesis whenever it is necessary to ensure that nanoparticle
properties are not modified in further processing steps, i.e. to obtain a product with
exactly the desired properties. At the same time, for any commercial application scale-up
potential of the method, simplicity and the cost efficiency of the entire processing must
be ensured.
158
In this paper, we report a new type of synthesis for PMMA stabilized Fe NPs
which can be utilized for the incorporation of magnetic Fe NP’s into a PMMA matrix.
For this purpose, ex-situ methods are well established, e.g. dispersing the synthesized
magnetic NP’s into organic PMMA solution [18], or polymerization of
methyl
methacrylate monomer in the presence of magnetic NP’s (e.g. [19-23]). In-situ
nanocomposite preparation was reported by high-temperature thermal or high-intensity
ultra-sonochemical decomposition methods [24-26]. Here, the first in-situ roomtemperature synthesis of PMMA-stabilized zero-valent metallic NP’s using a wetchemical reduction route is reported. Compared with the previously known in-situ
methods, this route is more economical, easy to operate due to the room temperature
approach and can be scaled-up easily.
To verify the success of this approach, TEM/SAED, X-ray absorption
spectroscopy and magnetic measurements were performed. Due to their high sensitivity
towards the influence of surface coordination on the (electronic) structure of the NP’s,
which has been reported by now in numerous studies [27-31], the X-ray absorption
spectroscopic data allow for a description of the influence of the stabilizing matrix, which
can also be correlated to the magnetic properties of these particles. As an example of use
of the X-ray absorption spectroscopy for the investigation of iron nanoparticles the works
[32-33] can be mentioned.
2 EXPERIMENTAL
2.1 Synthesis
Chemicals: THF (99.90% pure packaged under nitrogen), FeCl2 (99%), lithium
hydrotriethyl borate as 1M solution in THF, acetone (reagent anhydrous) and ethanol
(reagent anhydrous) were purchased from Aldrich Chemical Company and used without
further purification. PMMA (Poly(methyl methacrylate)) sheets were purchased from
Goodfellow and AIN.
Synthetic procedure: Iron nanoparticles stabilized by PMMA were synthesized by
reduction of FeCl2 in THF with lithium hydrotriethylborate (LiBH(C2H5)3) as a reducing
agent in the presence of PMMA by modifying the wet chemical process reported in the
literature [34]. The reaction was carried out under inert atmospheric conditions using the
Schlenk technique. In a 250 ml three-necked R. B. flask equipped with a flow control
159
inlet adapter and immersed in an ultrasonication bath, PMMA/FeCl2-THF solution (7.1
mM FeCl2) was taken under inert atmospheric conditions. The reducing agent (20 ml
superhydride in 50 ml tetrahydrofuran) was added to the PMMA/FeCl2-THF solution
drop by drop within 30 minutes under ultrasonication and reacted for 1 additional hour.
The PMMA stabilized iron NP’s were precipitated by adding ethanol, the supernatant
solution was removed and the remaining black paste was redissolved again inTHF and
reprecipitated using ethanol. The above process was repeated three times in order to
remove LiCl and possible by- products such as BEt3. The thus obtained black paste was
finally dried under vacuum to obtain a fine powder.
2.2 Characterization
Transmission electron microscopy (TEM) measurements were performed on a JEOL
2010 microscopy with an accelerating voltage of 200 kV. Transmission electron
microscopy (TEM) samples were prepared by dissolving the obtained dried PMMA
stabilized NP’s into tetrahydrofuran (THF) solvent under ultrasonic stirring condition,
then depositing them on an amorphous carbon coated Cu grid and drying under nitrogen
protection condition. Fe weight percentage in the iron NP complex was analyzed by
atomic absorption spectroscopy elemental analysis.
Fe K-edge XANES and EXAFS-spectra were collected at the Double-Crystal
Monochromator (DCM) beamline at the 1.3 GeV electron energy storage ring
synchrotron radiation facility of the Center for Advanced Microstructures & Devices
(CAMD) at Louisiana State University. The experiments were preformed in standard
transmission mode using ionization chambers filled with nitrogen at a pressure of 1 atm.
The monochromator was equipped with Si (311) crystals, and the photon energy was
calibrated relative to the absorption spectrum of a standard iron foil setting the first
inflection point at 7112 eV. Standard XANES data analysis was performed using the
WINXAS97 software package, where raw spectra were normalized and background
corrected by fitting the pre-edge region with a straight line, and the post-edge region with
a third order polynomial.
EXAFS analysis was performed with the use of the UWXAFS (University of
Washington X-Ray absorption fine structure) program package [35-37]. Fitting of
the Fe K-edge EXAFS data was done in R space between 1.5 Å and 3.0 Å using a
Hanning window for the experimental χ(k) spectra weighted by k3 in the k-range
between 2.5 Å-1 and 13.0 Å-1. The value for S02 was determined as 0.72 by fitting
EXAFS data for the iron foil with the known structural parameters (distances and
160
coordination numbers were kept constant from Fe bcc structure) and kept constant
throughout the whole fitting procedure.
Magnetic studies were carried out using a Quantum Design
MPMS-5S superconducting quantum interference device (SQUID) magnetometer.
The magnetization temperature dependence was measured in an applied magnetic
field of 100 G between 4 and 340 K using zero-field-cooled (ZFC) and fieldcooling (FC) procedures. The field dependence of magnetization was measured at
10 K and 300 K. The field cooled (FC) hysteresis loop at 10 K was measured by
cooling the sample from 300 K to 10 K with an applied field of 5 Tesla, removing
the 5 Tesla field and recording the magnetization with the changing magnetic
field. The sample was placed in a gelatin capsule in thin film form in a glove box
before it was inserted in the sample space of the magnetometer.
3 RESULTS AND DISCUSSION
Fig. 1 shows a typical bright field TEM micrograph of the PMMA-stabilized iron NP’s
on amorphous carbon coated copper grid. The NP’s with a mean size of 4.9 nm and a
Fig. 1. TEM micrograph of PMMA stabilized nanoparticles.
standard deviation of ±0.6 nm were observed to the dispersed within the PMMA media.
Selected area electron diffraction as shown in the inset of Fig. 1 has diffraction rings 2, 3
and 4 corresponding to a lattice distance of 2.04 Ǻ (110), 1.43 Ǻ (200) and 1.04 Ǻ (220),
respectively, which is consistent with a bcc metallic iron lattice structure. Ring 1
corresponding to a lattice distance of 2.43 Ǻ can be attributed to the (111) line of cubic
iron oxide (FeO). In the light of the results of X-ray absorption spectroscopy and of the
161
magnetic characterization presented below, this is assumed to be an oxidation induced by
sample preparation and transfer into the TEM machine. Oxidation of samples during the
transfer through air into the electron microscope is well documented. [38]
Fig. 2 shows a comparison between the EXAFS oscillations (in k-space) of the
embedded NP’s and of a bcc iron foil, respectively, using a weight factor of k3. Whereas
the observed structures are identical in position and general shape, the amplitudes are
significantly reduced in the case of the NP’s. This effect is commonly observed in the
40
30
3
-3
χ(k)*k (Å )
20
10
0
-10
-20
3
4
5
6
7
8
9
10
11
12
13
14
-1
k (Å )
Fig. 2. Experimental χ(k) spectra of Fe NP’s (solid line) and bcc Fe foil (dashes)
weighted by k3.
EXAFS analysis of NP’s and can be explained by a combination of surface
effects, increased structural disorder and local defects as is shown, for example, in
EXAFS study of Fe nanoparticles embedded in the amorphous Al2O3 matrix in [32]. The
observations based on the above inspection of the raw EXAFS data are confirmed upon
comparison of the non-phase-corrected radial distribution functions (RDF) obtained from
162
the Fe K-edge EXAFS spectra of the PMMA stabilized NP’s and the bcc iron foil, as
shown in Figure 3. In order to facilitate the comparison, the first data set has been
multiplied by a factor of 2.3. The results of the EXAFS fit, as presented in Table 2,
indicate that the first two bcc Fe-Fe distances (2.48 and 2.86 Å for bcc Fe, respectively)
are reproduced within the error
Size (nm)
TB
Coating
References
no coating (theory)
Dumestre et al., Faraday
(K)
5/
70 /
9
304
Discussions
125, 265 (2004).
4.4
30
Kun et al., Langmuir 14,
DDAB
7140 (1998).
5
200
Verelst et al., Chemistry of
CoO
Materials, 11, 2702 (1999).
5
as above
>300 Polydimethylphenyloxide
5.8
58
trioctylphosphine
Petit et al., Applied Surface
Science, 162, 519 (2000).
9.5
105
9.5
150
oleic acid/trialkyl-
Sun et al., Journal of Applied
phosphine
Physics, 85, 4325 (1999).
oleic acid/triphenyl-
Su et al., Applied Physics A,
phosphine
81, 569 (2005)
Table 1. Variations in blocking temperature (TB) for ≈5nm and ≈9nm Co NP’s as
reported by various authors, illustrating the importance of the surface coordination for
particle properties.
limits of the fit, whereas the coordination numbers are reduced as compared to the
coordination numbers 8 and 6 for bcc Fe, respectively. It should be noted that the ratio of
the coordination numbers for the first two Fe-Fe paths obtained from EXAFS fit of the
PMMA-stabilized iron NP’s, which is 1.34±0.52 (3.9±0.3/2.9±0.9), coincides perfectly
Path
CN
DW factor (Å2)
R (Å)
Fe-O
1.3±0.6
0.0045±0.0034
1.95±0.01
163
∆e0 (eV)
3.40±0.45
R-factor
0.0017
Fe-Fe
3.9±0.3
0.0045±0.0004
2.48±0.01
3.40±0.45
0.0017
Fe-Fe
2.9±0.9
0.0086±0.0023
2.86±0.01
3.40±0.45
0.0017
Table 2. EXAFS first shell fit results for Fe-nanoparticles.
within the error limit with the corresponding ratio value 1.33 (8.0/6.0) for bcc Fe.
Evidently, the only major difference is the fact that some amount of coordination to a soft
backscatterer is observed in the case of the NP’s. According to the fitting result, the
distance at which it is observed is 1.95±0.01 Å, which agrees reasonably well with the
one encountered e.g. for the tetrahedral sites in Fe3O4. The obtained coordination number
is rather low, but this, too, may be interpreted as a sign for a surface coordination rather
than an ironoxide shell. This assumption is also supported by the fact that all other peakpositions in the RDFs are identical. In the RDF of iron-oxides the first Fe-Fe single
scattering peak dominates although it does not form the first coordination shell.
Therefore, if one would be dealing with a core-shell particle with an iron-oxide shell such
a contribution should be visible as well. To facilitate the identification of possible
contributions of that kind, the shortest Fe-Fe single scattering paths for FeO and Fe2O3
have been included in Figure 3 as well. However, in the RDF of the NP’s no
corresponding contribution is observed, ruling out this possibility.
Therefore, the Fe NP RDF indicates that one is in fact dealing with bcc iron and
that no oxide phase is formed during synthesis and/or purification and suggests the
interpretation of the soft backscatterer in terms of a surface coordination.
164
80
60
RDF (Å-4)
d
40
c
20
b
a
0
2
4
6
R(Å)
Fig. 3. Non phase-corrected radial distribution functions (RDF) for a) Fe NP’s in
PMMA, (multiplied by 2.3, dots indicate 1st shell fit); b) alpha iron (bcc Fe) foil, c)
path contributions for 1st Fe-Fe scattering paths in FeO (dots) and Fe2O3 (dashes),
respectively; d) gamma iron (obtained from calculated spectrum).
In order to check whether the structure to which the Fe-O path is fitted could be
explained merely by background effects, a fit without this contribution has also been
attempted. The best result obtained using this approach is displayed in Fig. 4. Evidently,
without an Fe-O path contribution, the structure at R<2 Å cannot be fitted.
165
16
14
RDF (A-4)
12
10
8
6
4
2
0
0
2
4
6
8
10
R(Å)
Fig. 4. EXAFS fit (dashes) of Fe NP’s experimental RDF (solid line) without Fe-O
path contribution (dash & dots) and varying the background (dots).
In Fig 5, a comparison between the Fe K-edge XANES spectra of the NP’s and a
bcc iron foil is presented along with the spectra of the reference oxides FeO and Fe2O3.
Whereas there are deviations from the spectra of the reference foil in the region of the
absorption edge and the first series of strong shape resonances located between about
7152 and 7175 eV, the positions of the maxima of the ocsillations at higher excitation
166
Absorption (a.u.)
1,6
1,2
0,8
0,4
0,0
7100
7125
7150
7175
7200
7225
7250
Energy (eV)
Fig. 5. Fe K-edge XANES spectra of NP’s (solid line), compared to bcc iron foil
(dashes), Fe2O3 (dots) and FeO (dashes & dots).
energy agree completely to those of the iron foil, but are somewhat reduced in intensity
due to surface effects and increased local disorder. In addition to that, as is observed in
Fig 5, no additional structures appear at XANES spectra of Fe NP’s at the energy
positions of the shape resonances of the iron oxides spectra. Any attempt to explain the
reduced pre-edge intensity with the presence of a known oxide phase fails, because the
result unambiguously overestimates the change in white line intensity. Both observations
167
2,8
2,6
2,4
2,2
Absorption (a.u.)
2,0
1,8
1,6
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
7100
7125
7150
7175
7200
7225
7250
Energy (eV)
Fig. 6. Feff8 calculations of Fe K-edge XANES spectra as a function of cluster size.
From top to bottom: 100 atom cluster (solid line), 4 shells (dashes), 3 shells (dots), 2
shells (dash & dots), 1 shell (dash-dot-dot) of neighbours, and experimental XANES of
Fe NP’s (solid line) and Fe foil (dashes).
imply in total agreement with the EXAFS results that none of the iron-oxide phases also
displayed in this figure is present. In fact, the observed spectral changes in the white line
range can be explained by the influence of the NP’s surface coordination. Similar effects
of surfactant influence on NP electronic structure have been reported in literature for
various systems [13-18, 28-31]. To analyze this effect in more detail, ab initio
calculations of the
168
2,8
2,6
2,4
2,2
Absorption (a.u.)
2,0
1,8
1,6
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
-0,2
7100
7125
7150
7175
7200
7225
7250
Energy (eV)
Fig. 7. Feff8 calculations of Fe K-edge XANES spectra for varying model-geometries
for surface-effects (for details see text). From top to bottom: 100 atom cluster (solid
line); surface covered with carbon at iron sites, high occupation (dashes); as before but
lower occupation (dots), reduced distance Fe-C (dash & dots), minimum distance Fe-C
(dash-dot-dot), and experimental XANES of Fe NP’s (solid line) and Fe foil (dashes).
spectra have been performed using the FEFF8 code [39], which has been successfully
applied to a wide variety of systems, including NP’s [40-43]. As a first step, it is
interesting to analyze how many complete iron shells have to be present in the vicinity of
the absorbing atom to start reproducing the shape resonances for bcc Fe foil at the energy
range 7152 eV<E<7175 eV which are missing at XANES spectrum of Fe NP’s. The shell
by shell calculations displayed in Fig.6 prove that even using four complete shells the
spectral features of a bcc iron foil are not reproduced completely yet in the region
169
between 7152 and 7175 eV, indicating that this region is highly sensitive to changes in
the coordination of the iron atoms in general, whereas the following two shape
resonances are present as soon as three complete shells around the absorbing atom are
considered. However, the size-induced effects alone are not sufficient to explain the
observed spectral changes of Fe NP’s, as the intensity of the pre-edge shoulder is not
reduced sufficiently.
Therefore, in the next step one has to study the effect of a surface coordination.
The simplest model for this approach is obtained by cutting the bcc cluster along one axis
–e.g the z-axis- and describing the surface coordination by adding a monolayer of O/C
atoms on the former iron sites in the “unoccupied” half of space. Such an approach, as
shown in Figure 7, leads to changes in the white line region which correspond
qualitatively to the ones observed in the experimental data, i.e. a reduced intensity of the
pre-edge shoulder and an increased intensity of the white line. Therefore, one can
conclude that there is a chemical coordination to/interaction with PMMA, which can
explain the observed changes in geometric structure. However, -as one would expect- the
positions of the shape resonances stay rather similar, only their intensity is slightly
reduced (as expected due to the smaller scattering amplitude of the soft backscatterer).
This mismatch is not surprising, as the assumed distances of the O/C monolayer atoms to
the surface Fe atoms of bcc Fe cluster are different from those obtained in EXAFS fit.
Therefore, the next step is to reduce the distance of the O/C monolayer to the surface Fe
atoms of bcc Fe cluster along the z-axis in order to obtain an improved match for the
distance determined in the EXAFS fit. It should be stressed that the purpose of this
variation is limited to a proof of principle that a large variation in the intensity of the
series of shape resonances between 7150 and 7175 eV can be induced. In fact, it is
evident from Figure 7 that this is the case. In order to obtain a complete reproduction of
the spectrum and allow for a detailed analysis of the Fe-PMMA interaction, as obtained
e.g. in [13, 43], at least a realistic starting point for the real structure of the Fe-PMMA
coordination, obtained using quantum-chemical methods, would be needed.
Still, the XAS data show clearly that one is dealing with bcc Fe NP’s, which are
subject to chemical surface-interaction with the PMMA matrix. Similar types of chemical
interactions between the stabilizer and the nanoparticle surface are well documented in
the literature. For example, it was recently demonstrated that in the case Co nanoparticles
170
stabilized by oleic acid, the two oxygen atoms in the carboxylate are coordinated
symmetrically to the Co atoms [44].
The XAS observations are further confirmed by magnetic measurements, which
were also utilized to indirectly investigate the valence state of the iron NP’s. The Zerofield cooled (ZFC) hysteresis loop at 10 K was compared to the field cooled (FC)
hysteresis loop. A shift towards the applied magnetic field due to the exchange coupling
interaction between the antiferromagnetic shell (FeO) and the ferromagnetic core (Fe)
[e.g. 45-49] has been used as a criterium to identify the oxidation of the magnetic metal
NP’s. In this case the almost overlapping (within the SQUID magnetometer measurement
error) of the ZFC hysteresis loop and the FC (5 Tesla) hysteresis loop, i.e. identical
coercivities, Ms values and Mr/Ms ratios in both ZFC and FC conditions, indicate that the
iron NP’s are free from oxidation, which is consistent with the XANES observations.
The results discussed so far also indicate that the iron NP’s are stable in the
ethanol solvent during the washing process and the subsequent sample preparation
process, unlike the iron oxidation observed in gold coated iron NP’s obtained via
microemulsion technique [50]. This is fully confirmed by the hysteresis loop of the dried
PMMA-Fe NP’s in the film form (see Fig. 8). Saturation magnetization (Ms) was
determined by the extrapolated saturation magnetization obtained from the intercept of
magnetization vs H-1 at high field [6,51]. The obtained saturation magnetization was 84.8
emu/g based on the pure iron NP’s (Iron elemental percentage in the PMMA-Fenanoparticles complex was 7.59%, as determined by atomic absorption elemental
analysis). This saturation magnetization is lower than that of the bulk iron (220 emu/g).
However, it is consistent with the reported magnetization value (25 to 190 emu/g for the
size around 6 nm to 20 nm) for Fe NPs fabricated by vapor deposition techniques, and
with that (82 emu/g) of iron nanoparticles with comparable size (6 nm) synthesized by
thermal decomposition of iron pentacarbonyl [52, 53]. The decreased saturation
171
Fig. 8. Hysteresis loops of PMMA-stabilized Fe nanoparticles at 300 K, and 10 K at
zero field cooled and field cooled at 5 Tesla
magnetization can be attributed to the particle size and the influence of the coating [5256]. Both the non-zero ratio of remnant magnetization (Mr) to saturation magnetization
(Ms): 0.13 (0.36) and coercivity (Hc): 106 Oe (1117) Oe indicate that the blocking
temperature is above room temperature, i.e. ferromagnetic property of the PMMA
stabilized iron NP’s are observed at room temperature, in contrast to sonochemically
synthesized poly (ethylene glycol) stabilized iron NP’s [57] with superparamagnetic
properties.
4 CONCLUSION
The in-situ synthesis of PMMA-stabilized colloidal iron nanoparticles, which form stable
colloids in THF solvent, is reported. PMMA has effectively protected the iron
nanoparticles from agglomeration. PMMA-iron nanoparticles exhibit ferromagnetic
172
property even at room temperature and are likely to have wider applications in the
information storage media, magnetic refrigeration, audio reproduction, ferrofluids,
magnetically guided drug delivery with suitable size less than ~20 nm [46] and other
biomedical applications. The synthetic method is simple and can be used in general for
the synthesis of PMMA-stabilized zero-valent metallic nanoparticles. Changes in the
electronic structure of the product of this synthesis are traced to the influence of
surrounding matrix.
5 ACKNOWLEDGEMENTS
This work was financially supported by a grant from NSF-EPSCoR ((2001-04) RII-03)
and DARPA (Grant No: HR0011-04-C-0068). The authors kindly thank Miss Carol for
the elemental analysis.
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176
Functionalization of Gold and Glass Surfaces with Magnetic Nanoparticles Using
Biomolecular Interactions
Bala G. Nidumolu1, Michelle. C. Urbina1,
Joseph Hormes2, Challa S.S.R. Kumar2, and W. Todd Monroe1
Department of Biological and Agricultural Engineering1
Louisiana State University and LSU AgCenter, Baton Rouge, LA; Center for Advanced
Microstructures and Devices2 Louisiana State University, Baton Rouge, LA
Introduction
Over the past few decades, the study of magnetizeable objects on the nanometer
scale has generated considerable interest in various biotechnological applications. They
have influenced detection and imaging processes such as magnetic resonance imaging
(Artemov, 2003 #2), protein detection (Cao, 2003 #4)(Bucak, 2003 #3), and molecular
and cellular separation and purification (Molday, 1982 #5)(Yang, 2004 #6). They also
have applications in increasing efficiency in site-specific drug delivery (Forbes, 2003
#7)(Lubbe, 2001 #9), cancer treatment (Hilger, 2004 #10)(Zhang, 2005 #11), and in
increasing enzymatic activity(Rossi, 2004 #13)(Pan, 2005 #12). Various types of
nanoparticles are being used in biosensing schemes to show improvements over
microparticles. Nanoparticles have several advantages in detecting biological molecules
compared to microparticles, such as high magnetization per unit weight, ability to remain
in suspension for longer periods of time without aggregation, and faster velocities in
solution (Moller, 2003 #14). Functionalization of magnetic beads with biological
recognition elements that can bind to specific targets has several advantages in the
detection of biomolecules compared to radioactive, electrochemical, optical, and other
methods (Rife, 2003 #15). For example, radioimmunoassay requires expensive
instrumentation and handling of potentially hazardous radioactive materials; whereas,
magnetic bead detection is cheap, efficient, and safe. Biomedical applications using
nanoparticles require narrow size distribution and compatibility with surface modifiers
i.e., nonimmunogenic, nonantigenic and resistant to protein adsorption (Pankhurst, 2003
#16).
The recognition and capture of molecules and particles on solid surfaces has
numerous bioanalytical applications in bio- and immunosensor diagnostic devices (Yam,
2002 #17). The immobilization of bio-recognition molecules, such as nucleic acids,
proteins and other ligands on solid surfaces plays an important role in the development of
177
such devices. Using a system that couples proteins with nanoparticles, the efficiency of
the immobilization can be increased. Here we demonstrate a system for functionalization
of magnetic nanoparticles and planar surfaces followed by binding of functionalized
nanoparticles on the functionalized surfaces in an effort to move towards developing
nanoparticle based bio-recognition schemes.
The biotin and streptavidin couple is an ideal model for these types of
bioconjugation applications because of its high binding affinity (Ka=1015 M-1) and high
specificity (Yam, 2002 #17). Each streptavidin has four binding sites for biotin
positioned in pairs on opposite domains of the protein molecule. These properties
enable streptavidin to act as a bridge between immobilized biotinylated moiety and the
detectable nanoparticles. Magnetite nanoparticles with surface amine residues can be
functionalized with cabodiimide-activated carboxylic group of proteins (Kumar, 2004
#18). Several forms of commercially available thiolated biotin that can be immobilized
onto gold surfaces via sulphur linkages have been evaluated (Pradier, 2002 #19). The
high affinity of gold for sulphur-containing molecules generates well-ordered
monolayers termed self-assembled monolayers (SAMs). In this ongoing effort we
describe the synthesis of streptavidin-functionalized magnetic nanoparticles and
characterize their binding to biotinylated SAMs on gold for biological recognition
applications. Figure 1 shows a schematic of such a magnetic nanoparticle based
functionalization of gold and glass
Magnetite nanoparticles
9.8 ± 4.6nm
Diameter
Streptavidin
O
O
NH
H
N
HN
S
C
O
O
C
NH S
NH
NH
Spacer
Gold slide
S
O
N
H
Aminated glass slide
Figure 1. Scheme showing functionalization of biotinylated gold and glass
surfaces
with streptavidin-modified magnetic nanoparticles.
surfaces. This study has been divided into three parts: part one consists of the synthesis
and functionalization of nanoparticles, part two consists of the functionalization of gold
and glass surfaces with biotin SAMs, and part three consists of specifically binding the
functionalized particles onto the biotinylated gold surfaces. In each part, functionalization
is confirmed using various imaging and spectroscopy techniques.
178
Materials and Methods
Glass substrates with a 50Aº chromium base layer and a 1000Aº evaporated gold
film were purchased from EMF Corporation (Ithaca, NY). (N-(6-(Biotinamido)hexyl)-3'(2'-pyridyldithio)-propionamide (Biotin-HPDP, Pierce Biotechnologies, Rockford, IL),
N-Hydroxysulfosuccinimidobiotin
(sulpho-NHS
biotin,
Pierce
Biotechnologies),
fluorescein-5-isothiocyanate-(FITC) labeled streptavidin (Molecular Probes, Eugene,
OR), tributyl phosphine, N,N-dimethyl formamide (DMF, Sigma), and SuperAmine
coated slides (TeleChem International, Sunnyvale, CA) were used as received.
Magnetite nanoparticles were prepared and protein functionalized using a similar
method as previously described (Kumar, 2004 #18). Briefly, ferrous and ferric salts were
coprecipitated in ammonium hydroxide and then functionalized with FITC-labeled
streptavidin using a standard carboiimide activation followed by magnetic separation.
Biotin-HPDP was reduced with butylphosphine and applied directly onto a gold-coated
slide (Zimmermann, 1994 #21). Nanoparticle capture was performed by spotting 10µl of
the nanoparticle suspension onto the biotinylated surface with a micropipette tip and kept
in the dark for 1h. The substrates were rinsed with HPLC-grade water and dried under
nitrogen.
Sulpho NHS-biotin was immobilized directly on aminated glass slides using a
microcapillary for capture and analysis via fluorescent microscopy. Incubation of the
slide in a 1% solution of bovine serum albumin was used to prevent non-specific
adsorption. The nanoparticle solution was passed through a 0.2µm filter to remove large
aggregates and then deposited onto the entire glass slide. The slides were then kept in the
dark for 2 h, and then washed with deionized water and ethanol. They were then dried
with nitrogen and analyzed as described below.
Characterization of Functionalized Gold Surfaces
The morphology and size of the functionalized particles on gold surfaces were
examined by a JEOL 100CX transmission electron microscope (TEM) at accelerating
voltages up to 80keV. Image analysis to determine nanoparticle diameter was performed
using ImageJ software (NIH, Bethesda, MD). FT-IR spectra were recorded on a US 670
FT-IR at 4cm-1 resolution. Spectra obtained from an 87º incidence angle were baselined
with unmodified gold slides. Purging the system with nitrogen before taking scans
eliminated water and CO2 absorption contributions. For all spectra, 500 scans were
collected and smoothened by 25 to eliminate the background noise.
179
Fluorescent microscopy of functionalized glass surfaces was carried out on an
Eclipse TS100 (Nikon) with a mercury arc lamp and filters with excitation wavelengths
of 492±10nm and emission wavelengths of 525±10nm to collect FITC emission. Phase
and fluorescent images of functionalized nanoparticles immobilized on amine-terminated
glass substrates were acquired at 2X, 10X, and 40X magnifications.
X-ray photoelectron spectroscopy spectra were obtained on an Axis 165
spectrometer equipped with a monochromatic A1K ά X-ray source. A takeoff angle of
90º from the surface was employed for each sample. Survey spectra were recorded with
15KeV pass energy of a 300µm x 800µm spot size. A window pass energy of 20eV was
used to acquire high-resolution spectra. SEM coupled with Energy Dispersive
Spectrometry (EDS, Hitachi Model S-3600N) was used to characterize the functionalized
gold surface SAMs and SAM-nanoparticle complexes at 10µm and 50µm resolution.
Nanoparticle Functionalization
Electron microscopy and FTIR analysis of the functionalized nanoparticles
indicates streptavidin attachment. Image analysis of iron oxide nanoparticles taken with
TEM shows an average diameter of 9.8±4.6nm (Figure 2). Some aggregation of particles
was observed, most likely due to the lack of surfactant in particle synthesis or storage.
Figure 2. Transmission Electron Micrograph streptavidin-modified nanoparticles.
Bar represents 10nm.
180
This fact could be alleviated in the future by use of recent studies using
surfactants during nanoparticle synthesis to achieve monodisperse suspensions of
magnetite (Teng, 2004 #30)(Horak, 2003 #27). Figure 3 compares the FT-IR spectra of
unfunctionalized and functionalized nanoparticles. A reference spectrum of streptavidin
deposited onto the gold surface is also shown as a reference. The characteristic peaks at
3167cm-1 and 1604cm-1 present in spectra of unfuntionalized particles confirm the
presence of amine groups in unfuntionalized nanoparticles. The peak at 561cm-1 from the
magnetite nanoparticles is similar to that seen in other studies (Waldron.R.D, 1955
#22)(Gupta, 2004 #23)(Curtis, 2002 #24). This same peak was shifted to 586cm-1 after
functionalization with streptavidin. The peak at 2948cm-1 in the spectra of functionalized
nanoparticles can be attributed to CH2 stretching.
This peak was not observed in
unfuntionalized particle spectra, confirming nanoparticle -
functionalization with
streptavidin. A further study to decrease the degree of aggregation is
currently in
progress. One possible solution might be use of surfactants such as oleic acid, Sodium
dodecyl sulphate (SDS) to coat the nanoparticle surface during synthesis to prevent them
from aggregation.
Figure 3. FTIR spectra of functionalized and unfunctionalized nanoparticles.
The spectra of free streptavidin is used to confirm the functionalization.
Biotinylation of Gold Surfaces
Biotinylation of gold surfaces using biotin-HPDP was confirmed using FTIR and
X-ray photoelectron spectroscopy (XPS). The FTIR peaks at 2942 cm-1 (Figure 4) were
due to the C – H stretching in CH2 of the alkyl chains. Bands at 1674 cm-1 and 3328cm-1
were due to the amide-I and amide-II bands of biotin-HPDP, similar to those reported
previously with this technique (Pradier, 2002 #20). The band at 538 cm-1 present in the
181
Figure 4. FTIR spectra of deposited and thiol-immobilized biotin-HPDP on gold.
spectra of deposited (non-immobilized) biotin was assigned to the disulphide bond of
biotin-HPDP, and is not seen in the immobilized sample as expected. The carbon 1s,
nitrogen 1s, and oxygen 1s atomic orbital spectra were obtained with XPS for gold
surfaces with and without biotin-HPDP as seen in Figure 5. There is an increase in the
intensities of nitrogen, carbon, and oxygen signals after immobilization of biotin-HPDP.
The respective peaks at 285, 400, and 532 eV were assigned to the CH2, NH, and
carboxylic groups of biotin-HPDP, similar to other findings with this technique (Riepl,
20
b
15
Carbon
a
10
280
285
290
295
Intensity (Counts/Sec)
Intensity (Counts/Sec)
2002 #32).
Intensity(Counts/Sec)
Binding Energy (eV)
34
a
19
530
535
b
30
a
25
390
395
400
405
Figure 5. X-ray photoelectron
spectra of the gold surface before
(a) and after (b) functionalization
with biotin-HPDP.
29
525
Nitrogen
Binding Energy (eV)
Oxygen
24
35
540
Binding energy (eV)
182
410
Nanoparticle Functionalization of Gold and Glass Surfaces
Figure 6 compares the FT-IR spectra of the deposited versus covalently
functionalized nanoparticles on the gold surface. A characteristic peak between 576cm-1
was observed in the spectra of the deposited nanoparticles indicating the presence of iron
oxide (Waldron, 1955 #22). The peak has been slightly shifted to 586cm-1 after capture
by the biotinylated surface, which confirms the presence of nanoparticles immobilized by
Figure 6. FTIR spectra of nanoparticles captured on the biotinylated gold surface or
deposited on non-modified gold.
biomolecular interactions (Curtis, 2002 #24). The peaks at 1600cm-1 and 1660cm-1 are
due to the amide-I stretches of the N-H groups present in biotin-HPDP on the slide for
nanoparticle capture, which are not present on the unmodified deposition slide.
Figure 7 shows a SEM image of nanoparticles bound to the biotinylated gold
surface. The size of the particles was not uniform because of some aggregation, but this
183
Figure 7. Scanning electron micrograph of biotinylated gold surface with aggregated
nanoparticle complexes for elemental analysis.
fact facilitated elemental analysis via Energy Dispersive Spectrometry (EDS). Figure 8
confirms the presence of iron, carbon, and nitrogen, which is consistent with the principle
elements found in the attachment of protein-nanoparticle complexes. The upper and
lower panels in Figure 8 compare elemental analysis of small (x nm) and large (x nm)
particle aggregates. An increase in the EDS signal of iron was observed as the size of the
particle increased. Consequently, there is a higher carbon signal compared to iron
observed in the smaller particles. The possible reason for this might be that particles
aggregated during synthesis would have less streptavidin bound to the exterior of the
complex during functionalization.
184
1000
Au
Intensity
800
600
400
B
C
N
Fe
200
0
0
200
400
600
800
1000
1200
Energy(KeV)
1200
Au
Intensity
1000
A
C
800
600
N
400
200
Fe
0
0
200
400
600
800
1000
1200
Energy(KeV)
Figure 8. Elemental EDS analysis of the biotinylated gold surface with
captured streptavidin-conjugated (A) small and (B) large nanoparticle
aggregates.
Fluorescent microscopy of the nanoparticle-functionalized gold surfaces
described in Figures 6 and 7 was hindered by the high reflectivity of gold as well as its
potential to quench the fluorophore. Thus, glass surfaces proved better at confirming
spatial arrangement of nanoparticle capture via microscopy. Aminated glass surfaces
functionalized with NHS-biotin and then nanoparticle-FITC-streptavidin complexes were
analyzed by phase and fluorescent microscopy as seen in Figure 9. The images show the
specific absorption of streptavidin-conjugated nanoparticles to the biotinylated areas of
the slide, which were regions of approximately 120 µm in diameter. Average fluorescent
intensity of non-functionalized regions was 10±3 RFI, compared to nanoparticlefunctionalized spots with intensities of 113±14 RFU, indicating specific capture at
biotinylated spots.
Figure 10 shows SEM images of functionalized nanoparticles
immobilized on the aminated glass substrate at 200 nm and 500 nm resolutions. The
images show that immobilized particles on glass surfaces were aggregated like those seen
on gold, with an average size of 106±46 nm. These results are similar to a recently
reported larger (200nm) biotinylated magnetic nanoparticle immobilization on
185
biotinylated silicon surfaces using a streptavidin sandwich technique which was showed
functionalization via magnetic force microscopy (Arakaki, 2004 #1).
Phase Images
Fluorescent Images
Functionalized Spots before and after washing
Figure 9. Phase and fluorescent images of nanoparticles captured on the biotinmodified aminated glass slide. Bottom panel shows functionalized spots
before and after extensive washes.
Figure 10. Scanning electron micrographs of functionalized nanoparticles
immobilized on the aminated glass substrate from Figure 9.
Conclusions
Here we describe the functionalization of gold and glass surfaces with
streptavidin-coated magnetic nanoparticles and characterize their binding to biotinylated
SAMs on gold and glass for biological recognition applications. Immobilization of
streptavidin-functionalized magnetic nanoparticles to biotinylated gold and glass surface
was achieved by the strong interaction forces between biotin and streptavidin.
Streptavidin-functionalized nanoparticles, biotinylated surfaces, and combinations of the
186
two were characterized by SEM, XPS, fluorescent microscopy, and FT-IR to confirm
that little functionalization (capture) occurred in non-biotinylated regions of the gold and
glass surfaces compared to the intended sites.
These techniques have application in studying the modification and behavior of
nanoparticles for biological and other applications such as measuring low concentrations
of bacteria, more efficient site-specific drug delivery, detection of proteins, and
separation and purification of biological molecules and cells. While microparticles have
been used widely, nanoparticles show advantages in these applications, such as greater
magnetization per unit weight, and less tendency to settle in microfluidics. Development
and testing of magnetic–based bioassays such as the BARC device, which signal the
specific capture of magnetic particles in close proximity to magnetoresistive elements
may be confirmed and enhanced by utilization of this technique (Edelstein, 2000 #29).
The results of this study have shown that nanoparticles can be functionalized and
immobilized onto specific locations of gold and glass substrates using bimolecular
interactions.
Acknowledgements
This work is supported by the DARPA Bio-MagnetICs Program, NSF EPS-034611
(through the Center for Biomodular Multi-Scale Systems), and the State of Louisiana
Board of Regents Support Fund. We are grateful to Dr. Orhan Kizilkaya, Dr. Jiechao
Jiang, and Cindy Henk for their technical assistance and to Dr. Cristina Sabliov for
critically reading the manuscript.
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190
An Integrated Stacked Micro Fluidic Reactor System for
Nanoparticle Synthesis
1
Jost Goettert, 1 Yujun Song, 1 Proyag Datta, 1 Josef Hormes, 1 Willi Hempelmann 2 and
Challa SSR Kumar.1
Center for advanced Microstructure and Devices, Louisiana State University, 6980 Jefferson Hwy, Baton
Rouge, LA 70806; 2MicroMechatronicTechnologies AG, Eisenfelder Str. 316, D-57080 Siegen, Germany.
Micro reactors are gaining an increasingly important role in specialized chemical
production and process development.1 First successful experiments clearly indicate that
they have also the potential to play a very important role in wet chemical synthesis of
nanoparticles.2 This is mainly due to the fact that micro systems for chemical synthesis
have a significant advantage in terms of increased mass and heat transfer.3 The reduction
in size and the integration of multiple functions provides the potential for producing
devices with capabilities that exceed those of conventional macroscopic systems.
Polymer based micro reactors have the additional advantage of low initial fabrication cost
in combination with the fabrication capability through “inexpensive” replication
technologies such as embossing, casting, or photo- and injection molding. We have
designed and fabricated a user-friendly computer controlled stacked polymeric micro
reactor system for the synthesis of nanoparticles. The reactor system also can be utilized
in general for wet chemical synthesis and process development of specialty chemicals.
This user-friendly system consists of three basic functional blocks for controlled flow
from the chemical container (inlet), a custom made, temperature controlled micro reactor
stack, and an outlet unit to control and optimize all critical reaction parameters. The
system operation is controlled by a computer (see the figure below). Based on the
experimental parameters and conditions developed for the synthesis of Pd nanoparticles
using a single polymeric micro reactor in our laboratory, 2 we are studying issues of
scale-up production utilizing the stacked micro reactor system. We are currently
invetigating its utility in scale-up production of nanoparticles as well as specialty
chemicals.
191
1. Web page Ehrfeld Mikrotechnik, http://www.ehrfeld-mikrotechnik.com/.
2. Y. Song, Challa S.S.R.Kumar, and Josef Hormes, “Synthesis of Pd nanoparticles using a
continuous flow polymeric micro reactor, ” Journal of Nanoscience and nanotechnology,
4(7), 788-793, 2004.
3. Haswell, S. J.; Fletcher, P. D. I.; Greenway, G. M.; Skelton, V.; Styring, P.; Morgan, D. O.;
Wong, S. Y.F.; Warrington, B. H. Micro-chemical reactors: the key to controlling
chemistry.
Special Publication - Royal Society of Chemistry 2000, 250(Automated
Synthetic Methods for Speciality Chemicals), 25-33.
192
Preparation and Conjugation of Magnetic Nanoparticles
Using a Micro-reactor
Hammacher, J., Ozkaya, T., Urbina, M. Jost Goettert and Challa S.S.R.Kumar
Center for Advanced Microstructures and Devices, 6980 Jefferson Hwy, Baton Rouge, LA
70806.
Introduction
The objective was to use a continuous flow micro-reactor to precisely control nanocrystal
growth parameters in order to produce nanoparticles of defined size and attach the
created particles with biochemistry. Magnetic nanoparticles, magnetite, were synthesized
using standard batch processes and micro-reactor processes. Binding of glutaric acid to
the particles was also attempted using several methods, including attachment during
synthesis of nanoparticles and attachment to previously made nanoparticles.
Characterization of the particles was made using TEM, FTIR, TLC, and XRD.
µ-Fluidic Setup and Experiment
The micro-reactor experiments consist of the fluidic construction kit from thinXXS3, two
pumps, and the chemicals needed for the process. The fluidic construction kit consists of
a thinXXS snake mixer slide, a frame, and fluidic interconnections to assemble the snake
mixer slide with the tubing. The slide that was used for the majority of the experiments
was made of clear plastic, COC (cyclo-olefin copolymer), and contains several passive
mixers on a chip (Figure 1). The channels of the mixers differ by length and width. For
this project, channels 2 and 4, 640 µm and 320 µm diameter respectively, were used for
different experiments (Figure 1). A mixer made of SU-8 negative photoresist was used
for another experiment. Two different kinds of pumps were also used, MMT pumps4
(Figure 3) and volumetric syringe pumps5 (Figure 4). Silicone Tubing and a female TubeLuer Connector were used to connect the fluidic mixer chip with the syringes (Figure 2).
Fig. 1: schematic snake mixer
Fig. 2: snake mixer slide
3
http://www.thinxxs.com/products/index_products.html
http://www.micromechatronic.de/index.php?option=content&task=view&id=6&Itemid=29
5
http://www.kdscientific.com/Products/KDS100/kds100.html
4
193
Figure 3: MMT pumps
Figure 4: volumetric syringe pump setup
Preliminary tests were made with colored water at different flow rates and with different
channel sizes in order to test the reliability of the two pumps used, to determine if any
offset would need to be taken into account, and to determine the effects of backpressure.
The pumps were hooked up to the snake mixer slide and adjusted to a certain flow rate.
After switching the pump on, the time was counted for every 0.1 ml of volume of water
that was moved into a 1ml syringe (Figure 5-6). The idea was to prove that two pumps
can create a constant flow in one mixing channel, without decreasing the flowrate. That
means the resulting flowrate should be an addition of the two inlet flows and absolutely
constant.
Pump 1
Snake mixer
1 ml syringe
Pump 2
Fig. 5: schema of the experimental setup
Fig. 6: experimental setup
The results showed that the MMT pumps and syringe pumps, using two sizes of channels,
move the fluid through the channel with the programmed flow rate after about 0.5 ml
(Figure 7, 8, 9). After 0.5 ml, the pressure in the system is reaches an equilibrium and the
flow rate remains constant. The measured flowrate is exact the summation of the
programmed setting of the two pumps. Even the halt time smaller channels have no
effect. They are still large enough to keep the flowrate in the expected range. The error of
the pump is mentioned as less than 1% by the manufacturer. Variations in the
measurements are because of the inexact time measurement. The reasons for these
imprecise measurements are because of the equipment and the reaction time of the user.
Because of the created pressure of the pump, the flow rate will be the same every time, as
long as there are no obstructions in the channels. Due to these results, no offset has to be
programmed for the experiments. It was also found that flow-rate is dependent on
194
channel size, but only at a diameter smaller than those used for the experiments. A test of
a 100 µm diameter channel at 0.1 ml/min and 1 ml/min made the connectors pop off at
about 0.5 ml, showing that the backpressure at this size is too high for both flow-rates.
The flow-rate was also found to be slower than the programmed rate. However, the
channels used in the experiments at 640 µm and 320 µm, did not cause the connectors to
pop off when the water was run at the same flow-rate.
Syringe pump: flowrate measurement Channel 2
MMT: flowrate measurements Channel 2
2.50
fl o w ra te b o th p u m p s i n
m l/m in
flo w ra re b o th p u m p s in
m l/m in
2.50
2.00
1.50
1.00
0.50
0.00
2.00
1.50
1.00
0.50
0.00
0
0.2
0.4
0.6
0.8
1
1.2
0
volume in ml
0.2
0.4
0.6
0.8
1
1.2
volume in ml
Fig. 7: flow-rate channel 2, 640 µm
(syringe pump)
Fig. 8: flow-rate channel 2, 640 µm
(MMT pump)
Syringe pump:flowrate measurement Channel 4
fl o w ra te b o th p u m p s i n
m l/m in
2.50
2.00
1.50
1.00
0.50
0.00
0
0.2
0.4
0.6
0.8
1
1.2
volume in ml
Fig.9: flow-rate channel 4, 320 µm
(syringe pump)
Performance
MMT vs. syringe pumps
The first two micro-reactor experiments of the synthesis of magnetite were made with the
MMT “µ-Dosier” syringe pumps (Figure 3). These pumps should provide a smooth,
continuous, and pulsation-free transport of fluids, which is a big advantage for the
creation of nanoparticles. The pumps work like two integrated syringe pumps with two
directly opposite running pistons. When one side of the pump is pulling the fluid from the
reservoir, the other side is pressing the liquid into the micro-reactor (Figure 10).
The first two experiments were made at flow-rates of 1 ml/min and 0.5 ml/min. The
particles and data collected for these particles, however, are not used in the overall
analysis of particle
195
synthesis using micro-reactors. First, the pumps are
made for mass production, so the dead column in the
tubing is very large. This means that is takes a long
time for the chemicals to arrive at the micro-reactor.
During this time, much of the iron chloride salts
settled in the reservoir, decreasing the chances of
even mixing. Second, it was not possible to
synchronize the pumps because the switch of the
pumps is not calculated by time, but by the position
of the pistons. Because of differences in alignment,
the pumps will never switch at the same time. The
problem with this is that during switching, one pump
loses its pressure immediately, while the liquid from
that pump moves towards the path of least resistance,
Fig. 10: chemical mixing of
which would be towards the second pump, not
magnetite in 640 µm channel
towards the smaller diameter micro-reactor channel.
When this happens, the two solutions mix and form
nanoparticles inside the tubing, then when the pumps switch again, the second pumps
push the particles towards the channel, where they seemed to have clogged the system.
Each time this occurs, the MMT pumps give a non-continuous flow, with inhibit the
reaction to be as even as it should. After this happed twice, the MMT pumps were
replaced by normal volumetric lab syringe pumps (Figure 4) to eliminate the dead
volume and maintain a continuous-flow atmosphere. The first two trials with the syringe
pumps were used to make magnetite at 1 ml/min. In the set-up for the syringe pumps, a
plastic syringe is assembled to the pumps and connected with the Luer-Tube connectors
to the micro-fluidic system (Figure 4). The only disadvantage of these pumps is the
smaller volume that it allows. The limit for the syringe pumps is 60 ml per syringe, while
the limit for the MMT pumps is limited by the sample volume.
Clogging
Persistent problems during the synthesis of the magnetite in the micro-reactor channels
were clogging and the resulting back pressure. It was unclear whether the particles in the
experiment have clogged the channels completely or if they have started to restrict the
channels enough to cause back pressure to build and disengage the connectors to the
channels. Due to the design of the micro-reactor slide, a mixing turbulence seemed to be
created where the two chemical solutions met. Because the particle were created
immediately after the iron chloride salt solution and ammonium hydroxide solution mix
in the reaction chamber, a large amount of particles were created in one area, and perhaps
due to their magnetic properties, the magnetite form cluster which may clog the channels.
The particles also seem to cover the walls of the plastic channels and stick to the
glassware, which demonstrates that the particles may begin to aggregate off the sides of
the channel walls to clog or restrict the channels. This is an important obstacle to
overcome because it restricts the amount of time and the overall mass of sample that can
be made using these micro-reactors. One suggestion would be to use Teflon coated
channels to decrease the amount of magnetite that will stick to the walls. Another
suggestion would be to change the design of the inlet channels, to decrease the amount of
particles made at the start of the channels. To test this theory, an experiment using an SU8 mixer was made. Clogging and surface coating, however, also occurred in this kind of
channels.
196
Experiments also showed that the clogging may be flow-rate dependent; the lower the
rate, the higher to possibility of clogging. While the particles were being made,
observations were made by eye of how clogged the channels were becoming, or how
narrow the path was becoming. For example, at a flow-rate of 0.1 ml/min the restriction
of the channels appeared quicker, around 6 minutes, than that of a flow-rate of 1 ml/min,
which occurred around 16 or 17 minutes. When the experiment was run at 3.5 ml/min
(the maximum which can be achieved with the syringe pumps) the clogging of the
channels appeared to be less significant, during the amount of time it had to run, 14
minutes. To increase the flow-rate in order of magnitude might solve the problem.
Another reason why Teflon channels would help is in the cleaning of the channels. If the
current COC channels are completely clogged, it takes a few days of soaking in HCl
solution in order to dissolve the particles. If the channels are not completely clogged it
still takes about one night in solution to be cleaned well. Teflon channels may decrease
the cleaning time of the channels because the design of the Teflon micro-reactor that
would be used can be opened, therefore making it easier to clean the clogged area. Teflon
is also known to inhibit surface adhesion.
Experimental Details
Magnetite
Magnetite is a superparamagnetic nanoparticles that is made by combining FeCl3 and
FeCl2 with air free nanopure water (Figure 10, brown dilution) and mixing it with
ammonium hydroxide in air-free nanopure water (Figure 10, clear dilution) under an inert
atmosphere. It is created as a black colloid (Figure 10; black dilution), but is decanted
and washed by magnetic separation, then dried under nitrogen into a black powder.
Magnetite – Glutaric Acid
Another series of experiments were made to study the differences of processes in the
attachment of the biochemical glutaric acid, which is used as a spacer in the study of
cancer detection and treatment. In this case magnetite is to be conjugated with glutaric
acid using micro-reactors. Four different micro-reactor processes were made: a two-step
synthesis, a one-step synthesis, a one-step synthesis series, and a two-step binding. All
particles were made using the micro-reactor slide with 640 µm, the syringe pumps, and a
flow-rate of 1 ml/min.
Two-step synthesis
In the two-step synthesis, two syringe pumps, 3 syringes, and two micro-reactor slide
were used. Magnetite was first made in one micro-reactor, where one syringe was filled
with the iron-salt solution and was met with the ammonium hydroxide solution inside the
micro-reactor channels. After going through the micro-reactor slide, the product was
collected in a sample reservoir under nitrogen. While still in solution it was then put into
a clean syringe and pumped into a clean micro-reactor slide, where it meet with the
solution of glutaric acid and EDC from the third syringe. This second step should be
made in a 4°C atmosphere. To do this, the micro-reactor slide was put into a small
container will water at 4°C. The water was changed continuously to maintain a constant
temperature. Prior to use, the syringes were also kept in the chiller at 4°C, then covered
197
with foil during the conjugation. It is noted that the temperature was not likely to have
been held at a constant 4°C. After the pumps stopped, the solution of magnetite and
glutaric acid were collected under nitrogen, kept in the refrigerator overnight to ensure
binding, decanted and washed by magnetic separation, and dried under nitrogen.
One-step synthesis
In the one-step synthesis, two syringe pumps, two syringes, and one micro-reactor mixer
was used. In this process the iron chloride salt solution was mixed with the glutaric acid
and EDC solution prior to exposure to the micro-reactor. It was met the mixture of
ammonium hydroxide and air-free nanopure water while inside the chiller at 4°C to
maintain the correct atmosphere. The resulting solution was then collected in a flask
under nitrogen, kept in the refrigerator overnight, decanted and washed by magnetic
separation, and dried under nitrogen.
One-step synthesis series
The one-step synthesis series consisted of three syringe pumps, three syringes, and two
micro-reactor mixers. The magnetite nanoparticles were made in the first micro-reactor
slide by the same manner as the two-step synthesis. This solution then traveled to the
second mixer slide, which was held in the chiller at 4°C, to meet with the glutaric acid
solution from the third syringe pump. The product was then collected under nitrogen,
kept in the refrigerator overnight, decanted and washed by magnetic separation, and dried
under nitrogen.
Two-step binding
In the two-step binding, two syringe pumps, two syringes, and one micro-reactor mixer
slide was used. In this process, pre-made and dried magnetite particles were bound to, not
synthesizes with, the glutaric acid. Nanopure water was added to magnetite and sonicated
for 30 minutes to ensure an even suspension and decrease the concern for clogging. The
dissolved magnetite was then put into one syringe, while the glutaric acid and EDC
solution was added to the other. They were mixed in the micro-reactor mixer slide in the
chiller at 4°C. The product was kept in the refrigerator overnight, decanted and washed
by magnetic separation, and dried under nitrogen.
TEM: Size distribution
Other research groups have shown that the size, shape, and agglomeration of the
nanoparticles can be controlled through the use of continuous flow micro reactors.[1-4]
TEM pictures of the previously mentioned experiments have shown that these parameters
were not able to fully be controlled. Most of the particles are seen in large clusters and
vary in size. A common trend that was seen was that the particles from the batch process
were more evenly distributed than the particles made using the micro-reactor (Figure 11).
The shape that was seen was mostly spherical, however elliptical particles were common,
and one experiment resulted with squared particles.
More testing would be needed to obtain regulated particles.
198
Figure 11: a) Magnetic Beads made with
Batch process
b) Magnetic beads made with microreactor
Frequency (%)
There was a pattern, however, of the
Gauss Size Distribution of Magnetite
size and size distribution of the
particles based on channel size and
15
chemical dilution. This comparison
640 µm channel,
1/2 concentration
included four types of particles,
broken into two sets. The first set
320 µm channel,
10
1/2 concentration
consists of one normal batch process
and one micro-reactor process in the
batch process,
640 µm channels, both at one
normal
5
concentration
particular concentration. The other set
consists of one micro-reactor process
640 um channel,
normal
concentration
in the 640 µm channels and one
0
micro-reactor process in the 320 µm
0
2
4
6
8 10 12 14 16 18 20
channels, both at a concentration of
Diameter (nm)
half of the first set. A TEM-based
Gauss distribution of the size of
particles was made based on 200
Figure 12: Magnetite size distribution
nanoparticles of each process (Figure
12). The results showed that the micro-reactor-made particles were smaller and had a
better size distribution than the batch process-made particles, and that the particles made
with a lower concentration were also smaller and had even better size distributions.
FTIR Analysis
FTIR spectra was taken to determine if conjugation of glutaric acid to magnetite
occurred. Several samples were analyzed, but they were inconsistent with each other.
There did not appear to be a consistent difference between magnetite and magnetiteglutaric acid particles (Figure 13, 12). The broad peak around 1650 cm-1 should be due
to the C=O stretch of the amide bond between glutaric acid, containing two carboxylic
groups, and magnetite, containing several amine groups. Of particles that were made in
the micro-reactor, one comparison of the spectra of the particles with glutaric acid199
magnetite is shifted to the left of the spectra for magnetite. In another comparison, the
spectra of the particles with glutaric acid are shifted to the right. The other two samples
overlap each other (Figure 13). In the spectra of the particles that were made using the
batch process, a shift to the left occurred in two of the samples, and one sample was
indeterminate (Figure 14).
Title: *Tue Aug 09 12:40:19 2005-MC89
Thu Aug 18 16:52:08 2005
1.1 *Tue Aug 02 12:20:24 2005-MC74
1.0 *Fri Jul 22 17:32:12 2005-MC82-2mg-2
*Tue Aug 09 12:40:19 2005-MC89
0.9 *Tue Aug 09 12:13:07 2005-MC88
*Mon Aug 08 11:47:06 2005-MC87
0.8
Absorbance
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1)
Expanded fingerprint region:
User name: camd
*Tue Aug 02 12:20:24 2005-MC74
*Fri Jul 22 17:32:12 2005-MC82-2mg-2
*Tue Aug 09 12:40:19 2005-MC89
0.06
*Tue Aug 09 12:13:07 2005-MC88
*Mon Aug 08 11:47:06 2005-MC87
0.05
Absorbance
0.07
Collection time: Tue Aug 09 12:41:45 2005
Number of sample scans: 64
Number of background scans: 64
Resolution: 4.000
Sample gain: 8.0
Mirror velocity: 0.6329
Aperture: 69.00
0.04
0.03
0.02
0.01
1800
1600
1400
1200
1000
Wavenumbers (cm-1)
Figure 13: Magnetite and Magnetite-Glutaric Acid, micro-reactor processes
200
Title: *Fri Jul 22 16:43:15 2005-MC80-2mg
Thu Aug 18 16:55:42 2005
*Thu Jul 14 11:28:40 2005-MC69-magnetite-2mg-1
*Thu Jul 14 11:05:46 2005-MC79-glu acid+magnetite-2mg-2
*Fri Jul 22 16:43:15 2005-MC80-2mg
0.7 *Fri Jul 22 17:13:53 2005-MC81-2mg
0.8
A bsorbance
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1)
Expanded fingerprint region:
User name: camd
A bsorbance
*Thu Jul 14 11:28:40 2005-MC69-magnetite-2mg-1
0.030 *Thu Jul 14 11:05:46 2005-MC79-glu acid+magnetite-2mg-2
*Fri Jul 22 16:43:15 2005-MC80-2mg
0.025 *Fri Jul 22 17:13:53 2005-MC81-2mg
Collection time: Fri Jul 22 16:44:54 2005
Number of sample scans: 64
Number of background scans: 64
Resolution: 4.000
Sample gain: 4.0
Mirror velocity: 0.6329
Aperture: 69.00
0.020
0.015
0.010
0.005
1800
1600
1400
1200
1000
Wavenumbers (cm-1)
Figure 14: Magnetite and Magnetite-Glutaric Acid, batch processes
XRD
XRD spectra was taken for two types of particles: magnetite made in the normal batch
process and those made with the micro-reactor (Figure 15). These spectra do not appear
to have a large difference in distribution. With more analysis, XRD can be used to
determine the difference in packing of atoms between the batch and micro-reactor
processes. [2]
201
Magnetite
90
80
70
Intensity
60
50
Batch
process
40
Micro-reactor
process
30
20
10
0
20
30
40
50
60
Theta (*)
Figure 15: XRD spectra a magnetite
TLC
TLC was attempted in the comparison of magnetite and magnetite and glutaric acid, both
made using the normal batch processes. The particles were dissolved in nanopure water
and put onto a silica gel. Acetone was used as the solvent. When tested with magnetite
itself, it appeared that some of the particles had moved with the solvent; however, when
the particles were tested in comparison to glutaric acid and magnetite-glutaric acid, there
did not appear to be any movement. More testing in this area may help to get positive
results in using chromatography to determine conjugation.
References
[1]
[2]
[3]
[4]
X. Z. Lin, A. D. Terepla, H Yang. Nano Lett. 4, 11 (2004).
Y. Song, S. S. R. Kumar, J. Hormes. J. Nanosci. Nanotech. 4, 7 (2004).
J. Wagner, J. M. Kohler. Nano Lett. 5, 4 (2005).
J. Wagner, T. Kimer, G. Mayer, J. Albert, J. M. Kohler. Chem. Eng. J. 101 (2004)
202
Protein
Crystallography
203
Structural biology of interactions between TEM-1 and BLIP
Jihong Wang#, Zhen Zhang*§, Timothy Palzkill*§, and Dar-Chone Chow*#
From the *Structural and Computational Biology and Molecular Biophysics Program,
§Dept of Molecular Virology and Microbiology, and §Dept of Biochemistry and
Molecular Biology, Baylor College of Medicine, Houston, Texas 77030 and the
#Department of Chemistry, University of Houston, 4800 Calhoun road, Houston, Texas
77204
Beta-Lactamase Inhibitory Protein (BLIP) is a natural inhibitor protein that binds to
class-A Beta-Lactamases including TEM-1. The previous studies with alanine scanning
mutagenesis of the TEM-1 contacting residues of BLIP have determined that the binding
of BLIP to TEM-1 has two separate hot spots separated on the concave binding surface.
To understand the nature of the driving forces behind the binding of TEM-1 and BLIP,
we are carrying out the thermodynamic measurements using Isothermal Titration
Calorimetry (ITC) and have completed measurements of bindings between TEM-1 and
10 BLIP mutants. All of them are entropy driven except Y50A. The Ka values show
similar trend as the published values from inhibitory tests. The interactions between
TEM-1 and these mutants have a wide range of heat capacities (–305 ~ -778 Cal٠K1
٠mol-1). These thermodynamic results suggest the bindings of TEM-1 and BLIP mutants
have different nature of driving forces and possible binding-induced conformational
changes. To investigate the structural aspects behind these thermodynamics, we
undertake crystallization of these complexes of TEM-1 and BLIP mutants. The first
complex has been successfully crystallized in several conditions. Some crystals show xray diffraction at a resolution better than 3 angstroms. We have collected x-ray diffraction
data sets from these crystals at CAMD. Currently, data processing for structural
determination is in progress.
204
Structure of a Calmodulin/IQ domain Complex at 1.45 A
Jennifer L. Fallon and Florante A. Quiocho, Verna and Marrs McLean Department of
Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza,
Houston, Texas 77030
(contact: jjffaalllloonn@
@bbccm
m..ttm
mcc..eedduu, ffaaqq@
@bbccm
m..ttm
mcc..eedduu )
Calmodulin is a ubiquitous 17 kDa calcium binding protein whose main function
involves transducing the calcium signal by altering the activities of target enzymes
depending on the presence or absence of calcium ions. In the typical case calmodulin
binds calcium and this calcium-bound calmodulin then binds the target enzyme. The
most well characterized calmodulin-binding domains which occur on these target
enzymes are alpha helices (when Ca2+ calmodulin is bound), which contain large
hydrophobic residues at the one and ten positions or the one and fourteen positions. The
largest class of calmodulin binding domains are the IQ and IQ-like motifs, which usually
contain an isoleucine and a glutamine residue in the sequence along with several other
conserved residues. These sequences typically contain more large hydrophobic residues
than usual and do not have a clear one-ten or one-fourteen spacing motif. The IQ and IQlike calmodulin binding motifs are present in many myosins and ion channels, and the
complex structures and mode of binding of calmodulin were very uncertain prior to this
study.
In order to determine the structure of this complex at high resolution, well diffracting
crystals were required. We were fortunately provided with an excellent sample of the
calmodulin-IQ domain complex by D. Brent Halling and Dr. Susan Hamilton of the
Department of Molecular Physiology and Biophysics at Baylor College of Medicine,
which routinely produced such crystals. A sample of the complex with a mutant version
of the IQ peptide also produced useful crystals.
To determine the complex structure, a native high resolution dataset was collected at the
CAMD GCPCC x ray beamline along with a three wavelength Multiwavelength
Anomalous Dispersion (MAD) derivative dataset on a native crystal soaked overnight in
1 mM lead nitrate. With the assistance of Dr. Henry Bellamy, high quality datasets were
recovered on the first try. These data allowed the phasing of this structure by use of the
CNS software package shortly after returning to Houston. On a subsequent trip to Baton
Rouge data on the mutant complex were obtained with assistance from David Neau. The
structure revealed by these data showed an unexpected mode of binding by calmodulin,
delineated the exact calmodulin binding sequence, and also revealed how calmodulin is
able to accommodate the large hydrophobic residues in these domains. The study has
been published in the peer-reviewed literature1, and the structures along with
experimental details are available from the Protein Data Bank (www.rcsb.org/pdb/) with
access codes 2F3Y and 2F3Z. We are grateful for the assistance of Dr. Bellamy and
David Neau during the data collection.
1. Fallon. J. L., Halling, D. B., Hamilton, S. L., Quiocho, F. A. Structure of Calmodulin
Bound to the Hydrophobic IQ Domain of the Cardiac Ca(v)1.2 Calcium Channel.
Structure (Camb). 2005 Dec; 13(12):1881-6.
205
Crystal Structure of the Hypoxia-Inducible Form of 6-Phosphofructo-2Kinase/Fructose-2,6-Bisphosphatase (PFKFB3): A Possible New Target
for Cancer Therapy*
Song-Gun Kim§, Nathan P. Manes¶, M. Raafat El-Maghrabi¶, and Yong-Hwan Lee§
From the §Department of Biological Sciences, Louisiana State University, Baton Rouge,
Louisiana 70803 and the ¶Department of Physiology and Biophysics, State University of
New York at Stony Brook, Stony Brook, New York 11794-8661
Address correspondence to: Yong-Hwan Lee, Department of Biological Sciences, Louisiana State
University, 202 Life Sciences Bldg, Baton Rouge, LA 70803, Tel. 225 578-0522; Fax. 225 5787258; E-Mail: [email protected]
The hypoxia-inducible form of 6-phosphofructo-2-kinase/fructose-2,6bisphosphatase (PFKFB3), plays a crucial role in the progression of cancerous cells by
enabling their glycolytic pathways even under severe hypoxic conditions. To understand
its structural architecture and to provide a molecular scaffold for the design of new cancer
therapeutics, the crystal structure of the human form was determined. The structure at
2.1 Å resolution shows that the overall folding and functional dimerization are very
similar to those of the liver (PFKFB1) and testis (PFKFB4) forms, as expected from
sequence homology. However, in this structure, the N-terminal regulatory domain is
revealed for the first time among the PFKFB isoforms. With a β-hairpin structure, the Nterminus interacts with the 2-Pase domain to secure binding of fructose-6-phosphate to
the active pocket, slowing down the releases of fructose-6-phosphate from the
phosphoenzyme intermediate product complex. The C-terminal regulatory domain is
mostly disordered leaving the active pocket of the fructose-2,6 bisphosphatase domain
wide-open. The active pocket of the 6-phosphofructo-2-kinase domain has a more rigid
conformation, allowing independent bindings of substrates, fructose-6-phosphate and
ATP, with higher affinities than other isoforms. Intriguingly, the structure shows an
EDTA molecule bound to the fructose-6-phosphate site of the 6-phosphofructo-2-kinase
active pocket, despite its unfavorable liganding concentration, suggesting a high affinity.
EDTA is not removable from the site with fructose-6-P alone but is with both ATP and
fructose-6-P or with fructose-2,6-bisphosphate. This finding suggests a molecule, in
which EDTA is covalently linked to ADP, is a good starting molecule for the
development of new cancer therapeutic molecules.
206
Crystal Structure of the Functionally Distinct Ferritin Homolog Dps-1
from Deinococcus radiodurans*
Song-Gun Kim, Gargi Bhattacharyya, Anne Grove, Yong-Hwan Lee
From the Department of Biological Sciences, Louisiana State University, Baton Rouge,
Louisiana, 70803
Address correspondence to: Yong-Hwan Lee, Department of Biological Sciences, Louisiana State
University, 202 Life Sciences Bldg, Baton Rouge, LA 70803, Tel. 225 578-0522; Fax. 225 5787258; E-Mail: [email protected]
In eubacteria, Dps (DNA protection during starvation) proteins play an important role in
protecting cellular macromolecules from damage by reactive oxygen species (ROS).
Unlike most orthologs which protect DNA by a combination of DNA binding and
prevention of hydroxyl radical formation by sequestration of iron, Dps-1 from the
radiation-resistant Deinococcus radiodurans fails to protect DNA from hydroxyl radicalmediated cleavage through a mechanism inferred to involve continuous release of iron
from the protein core {Grove, 2005 #22}. To address the structural basis for this
unusually facile release of Fe2+, the crystal structure of D. radiodurans Dps-1 was
determined at 2.0 Å resolution by a single wavelength anomalous dispersion phasing
method. Two of four strong anomalous signals per subunit correspond to metal binding
sites within an iron-uptake channel and a ferroxidase site, common features related to the
canonical function of Dps homologs. At the proposed DNA-binding N-terminal region, a
novel metal-binding site is found. Unlike other metal sites, this site is located at the outer
surface of the dodecameric protein sphere and does not involve symmetric association of
protein subunits. Intriguingly, a novel channel-like structure is seen featuring a fourth
metal coordination site that results from 3-fold symmetrical association of protein
subunits through α2 helices. The presence of a metal binding site suggests that this may
be an iron-exit channel. This interpretation is supported by substitution of residues
involved in this ion coordination and the observation that the resultant mutant protein
exhibits significantly attenuated iron-release. We propose that the facile release of iron
from Dps-1 affords an available supply of Fe2+ needed for detoxification of ROS.
Publication:
Kim, S.-G., Bhattacharyya, G., Grove A., and Lee, Y.H. (2006) ‘A novel iron-exit
channel revealed in the structure of the functionally distinct ferritin homolog Dps-1 from
Deinococcus radiodurans’. Submitted
207
Crystal Structure of Minimal MobA
Arthur F. Monzingo, Research Associate
Gregory Sawyer, Postdoctoral Fellow
Jon D. Robertus, Professor
Department of Chemistry & Biochemistry
University of Texas at Austin
1 University Station A5300
Austin, TX 78712
[email protected]
[email protected]
[email protected]
The minimal domain of the relaxase MobA from the bacterial plasmid R1162 has been
crystallized in a form suitable for high resolution structure determination using X-ray
crystallography. Native and several derivative data sets (including MAD data) from the
minimal MobA crystals were collected on the PX beamline. The structure determination
of the protein is ongoing.
208
The crystal structure of the transcriptional regulator HucR from
Deinococcus radiodurans suggests a mechanism for attenuation of DNA
binding by protonation
Tee Bordelon, Steven P. Wilkinson†, Anne Grove, and Marcia E. Newcomer
From the Department of Biological Sciences, Louisiana State University, Baton Rouge,
LA 70803
The hypothetical uricase regulator (HucR) from Deinococcus radiodurans R1, a member
of the MarR family of DNA binding proteins, represses its own expression as well as that
of a uricase. Repression is alleviated upon binding of the substrate for uricase, uric acid.
As uric acid is a potent scavenger of reactive oxygen species, these observations suggest
a novel oxidative stress response mechanism. The crystal structure of HucR in absence of
ligand or DNA at 2.3 Å was determined with multi wavelength anomalous diffraction
data from SeMet Hucr collected at CAMD. The structure reveals a dimer in which the
DNA recognition helices are preconfigured for DNA binding. This configuration of
DNA-binding domains is achieved through an apparently stable dimer interface that,
unlike other MarR homologs, shows little conformational heterogeneity in absence of
ligand. Notably, the stacking of a pair of symmetry-related histidine residues at a central
pivot point at the dimer interface suggests a mechanism for modulation of DNA binding
by pH. HucR-DNA complex formation is significantly attenuated at pH 5.0, consistent
with a functional role of histidine-protonation in regulation of DNA binding.
209
The structures of heme enzymes of a newly described mini-catalase
enzyme family
Svetlana Pakhomova, Alan Brash*, Marcia Newcomer
Department of Biological Sciences, LSU, Baton Rouge, LA 70803
*Vanderbilt School of Medicine
Our recently solved structure of an allene oxide synthase (AOS; Oldham, Brash,
Newcomer, PNAS, 2005) from the soft coral Plexaura Homomalla clearly established a
structural relationship between AOS and catalase: AOS resembles catalase both in terms
of its overall fold (rmsd 1.65 Å for 225 of 373 Cα’s) and heme environment, which is
essentially completely conserved in a context of <15% sequence identity. Yet AOS and
catalase have distinct enzymatic activities, and the basis for the different activities is not
obvious from comparison of the structures. Differences in heme access, heme planarity
and substrate recognition sites are proposed to contribute to the distinct functional
properties of these enzymes. Other mini-catalases proposed to be involved in the
metabolism of endogenous peroxides from Fusarium graminearum, Anabaena,
Mycobacterium avium subsp. paratuberculosis, Helicobacter pylori, and Pseudomonas
aeruginosa have been identified. These enzymes are associated with activities thought to
be restricted to members of the P450 superfamily, heme enzymes with a Cys rather than
Tyr as the proximal heme ligand. The identification of enzymes that are P450-like in
activity, yet structurally dissimilar, is an important contribution towards understanding
how protein environments tune heme activity. These enzymes, like AOS, are expected to
promote the homolysis of the peroxide bound and generate a highly reactive free radical
intermediate. Accordingly, the fate of the intermediate is determined by the shape of the
binding pocket which constrains it. Thus the crystals structures will provide a framework
with which to understand the chemical transformations catalyzed by “mini-catalases.”
We have collected an Fe-MAD data set on the Mycobacterium avium subsp.
paratuberculosis AOS-homologue and solved the structure to 2.4 Å resolution
(R/Rfree=0.194/0.231) with Fe-MAD data collected at CAMD.
210
What features of the mini-catalase allene oxide-synthase (AOS) are
essential for catalysis?
Nathan Gilbert, Alan Brash*, Marcia Newcomer
Department of Biological Sciences, LSU, Baton Rouge, LA 70803
*Vanderbilt School of Medicine
Modest differences in the heme environments of allene oxide synthase (AOS) and
catalase lead to significantly different enzyme chemistries. There are three possible
factors that may contribute to fundamental differences in catalytic mechanisms: the heme
environment, heme conformation, and the nature of the substrate and its fit into the
binding site. As part of an effort to understand how similar heme environments provide
distinct catalytic activities, structural and functional studies on various mutant forms of
AOS designed to test theories of catalytic mechanism are underway. We have initially
focused on the fact that despite an open cavity that cannot exclude the approach of H2O2
to the heme, AOS does not have catalase activity, nor is it rapidly deactivated by
hydrogen peroxide. We have proposed that the fact that the distal His (H66) is H-bonded
to both T66 (an invariant Val in catalase) and N137 protects an otherwise highly
accessible heme. The prediction is then that a T66V mutation will open up the active site
to pseudo-substrates. Indeed, a T66V mutation confers some catalase activity, albeit at a
rate greatly reduced with respect to catalase. A structure of this mutation is necessary in
order to fully understand its consequences and we have screened crystals for AOS:T66V
at CAMD. So far crystal quality has been a problem.
211
Crystal structure of the GAP-related domain of human IQGAP1
Jessica Ricks, Vinodh Kurella and David K. Worthylake
Department of Biochemistry and Molecular Biology, LSU Health Sciences Center, 1901
Perdido St., Room 7101, New Orleans, LA 70112 Phone (504) 568-4733
E-mail [email protected]
IQGAP1 is a widely expressed 190kD molecular scaffold that has an important role in
cell adhesion and cell motility. IQGAP1 possesses at least six distinct interaction
domains including isoleucine and glutamine rich repeats (IQ) and a region of high
sequence homology (16.9% identity, 45% similarity) to the GTPase-activating domain of
p120RasGAP. IQGAP1 has been shown to bind to numerous proteins including F-actin,
calmodulin, Erk2, CLIP-170, β-catenin, E-cadherin, APC, and the Rho-family small
GTPases Cdc42 and Rac1. However, despite possessing a GAP-related domain (GRD),
IQGAP1 has not been shown to accelerate the hydrolysis of GTP on any small GTPase.
Instead, binding of Cdc42 or Rac1 to a region of IQGAP1 that includes the GRD
significantly stabilizes the activated forms of Cdc42 and Rac1 in vitro. Furthermore,
over-expression of IQGAP1 has been shown to increase the amount of activated Cdc42 in
vivo. These results are consistent with a role for IQGAP1 as either a novel Cdc42 (or
Rac1) effector, or as a newly discovered guanine nucleotide exchange factor (activator)
for Cdc42 (or Rac1). To better understand the role of the GRD in IQGAP1 function, we
have crystallized a 43kD fragment of IQGAP1 that encompasses the GRD.
Preliminary diffraction studies at the PX beamline at CAMD demonstrated ≈2.5Å
diffraction for a cryo-protected, native GRD crystal. A full native data set for this crystal
was not pursued because of poor spot shape and split reflections. Since the GRD
construct used contains 10 methionine residues, prior to our trip to CAMD we prepared
and cryo-protected several seleno-methionine substituted crystals. Although these
crystals were much smaller, they diffracted X-rays to approximately 3.0Å. An X-ray
fluorescence experiment indicated that the crystals do indeed contain selenium. It was
then decided to collect as much of a multi-wavelength anomalous dispersion (MAD) data
set as possible prior to the next beam fill. We collected complete data for the "peak"
wavelength and ≈1/2 of the data for the inflection point wavelength. Analysis of a
portion of the peak wavelength data indicated that the crystals belong to space group
P212121 with cell parameters consistent with one GRD molecule per asymmetric unit.
Although we have been significantly delayed by the recent local events, we anticipate
that this project will be quite straight-forward and should be completed soon. In the next
few months we will attempt to utilize the data already obtained at CAMD to acquire
initial phasing for the GRD. We are already in the process of preparing more GRD
crystals (native and SeMet) in order to acquire a more complete, higher resolution MAD
data set, and a high resolution native data set for refinement purposes.
Information acquired during our visit to CAMD was utilized in a Louisiana Board of
Regents RCS grant application submitted November 1st, 2005.
212
Structural Study of a Multifunctional Triterpene/Flavonoid
Glycosyltransferase from Medicago truncatula
Hui Shao, Xianzhi He, Lahoucine Achnine,
Jack W. Blount, Richard A. Dixon, and Xiaoqiang Wang
Plant Biology Division, Samuel Roberts Noble Foundation
2510 Sam Noble Parkway, Ardmore, OK 73401
E-mail: [email protected]
Glycosylation is a ubiquitous reaction controlling the bioactivity and storage of plant
natural products. Glycosylation of small molecules is catalyzed by a superfamily of
glycosyltransferases (GTs) in most plant species studied to date. The crystal structure of
the uridine diphosphate (UDP) flavonoid/triterpene glycosyltransferase UGT71G1 from
Medicago truncatula bound with a UDP molecule was determined using the
multiwavelength anomalous dispersion (MAD) method. A 2.4Å MAD data set from a
SeMet derivative crystal, using three wavelengths, was collected at the GCPCC beamline
at the Center for Advanced Microstructures and Devices (CAMD, Louisiana State
University) using a MAR CCD detector. The structure of UGT71G1 consists of two Nand C-terminal domains with similar Rossmann-type folds. The N-terminal domain
contains a central seven-stranded parallel β sheet flanked by eight α helices on both
sides, and a small two-stranded β sheet. The C-terminal domain contains a six-stranded β
sheet flanked by eight α helices. The two domains pack very tightly and form a deep cleft
with a UDP molecule bound. The structure reveals the key residues involved in
recognition of donor substrate, and, by comparison with other GT structures, suggests
histidine 22 as the catalytic base and aspartate 121 as a key residue which may assist
deprotonation of the acceptor by forming an electron transfer chain with the catalytic
base. Mutagenesis confirmed the roles of these key residues in donor substrate binding
and enzyme activity. Our results provide an initial structural basis for understanding the
complex substrate- and regiospecificities underlying glycosylation of plant natural
products and other small molecules. This information will direct future attempts to
engineer bioactive compounds in crop plants for improving plant, animal and human
health, and facilitate the rational design of GTs to improve the storage and stability of
novel engineered bioactives.
This work was supported by National Science Foundation grant 0416883 and the Samuel
Roberts Noble Foundation.
213
X-ray Diffraction of the Protease Domain of NSP2 from Venezuelan Equine
Encephalitis
Andrew T. Russo, Stanley Watowich
Department of Biochemistry and Molecular Biology
Sealy Center for Structural Biology and Molecular Biophysics
University of Texas Medical Branch, Galveston Texas 77555
Venezuelan equine encephalitis virus (VEEV) is a significant cause of human
illness in Central and South America, with outbreaks occasionally reaching as far as
southern Texas. Human epidemics have occurred as recently as 1995 in Venezuela and
Colombia, with widespread illness and mortality rates of ~1% (Weaver, S.C., et al.,
1996). Several nations , including the USA and the former Soviet union have developed
VEEV in a weaponized form and may have stockpiles of this weapon (Bronze, M.S., et
al., 2002). There is currently no specific treatment for VEEV infection and the vaccine
strain TC-83 provides incomplete protection (Weaver, S.C., et al., 1999). The proteolytic
processing of the VEEV replication complex by NSP2 is essential for viral replication,
making NSP2 an attractive target for development of antiviral drugs to treat VEEV
infection. To date, there is no structural information available on NSP2 from VEE or any
related alphavirus. Availability of a structure for the protease domain of VEEV NSP2
would be of great use in the drug discovery process. We have crystallized the C-terminal
protease domain of VEEV NSP2 (NSP2pro) and have collected a full native dataset on
the PX beamline at CAMD.
214
Microfabrication
CAMD Staff Reports on Internal
Projects
215
Development of a Gas Chromatographic Analytical Instrument for
Ultra-Fast Chemical Analysis
Editors: Abhinav Bhushan, Dawit Yemane, Khalef Hosany,
Chetan Ramesh, Edward Overton
Co-workers: Jost Goettert, Michael Murphy
Supported by a grant from DARPA
Project Summary
The current effort is geared towards building a very small, fast, and reliable gas
chromatographic instrumentation [1] to detect chemical agents in the battlefield. The
project, Micro Gas Analyzers, is funded by the Defense Advanced Research Projects
Agency (DARPA), MTO Office, of the U.S. Department of Defense. The final goal of
the program is to develop a complete, miniaturized GC instrument which has a volume of
2 cm3, can detect analytes down to ppt concentrations in less than 4 seconds with a peak
capacity of 1200, and consume 1 J of power. LSU is partner in this project led by Sandia
National Laboratories, Albuquerque.
Due to the complexity of the sensor, the project has multi-dimensional performance
metrics (milestones) and the tasks are spread over three 18-month phases. For phase I, the
metrics focused on the performance of individual components namely, the column and
the pre-concentrator. The specific milestones were: separation of four analytes and four
interferrents (ranging from C4-C20) in less than 4 seconds, a demonstrated peak capacity
of 20, and a pre-concentrator gain of 1000. In addition to the components, the sensor will
have innovative engineering solutions to provide on-chip hydrogen manufacturing
capability and intelligent electrical and thermal power management important for further
integration towards a complete sensor device.
During the last year, the milestones for the project were successfully accomplished (see
Fig. 1 for the 4 sec separation milestone). Initial separation was demonstrated using a 100
µm diameter, 0.75 m long, silica column with a 0.1 µm thick stationary phase. In order to
improve separation temperature programming with a rate of 300ºC/sec was employed.
Further improvement is expected by using a LiGA fabricated separation column currently
fabricated at CAMD. For various performance reasons, the column should have high
aspect ratio fluidic channels with a very narrow width. They should also be made out of a
material which has good thermal conductivity (Nickel) and can withstand temperatures of
up to 300º C. The current columns are 0.5 - 1 m long, 50 µm wide, and 650 µm tall.
Fabrication
The GC columns were fabricated using the LiGA process. An X-ray mask was fabricated
on a silicon nitride membrane. The devices from this mask have better sidewall quality
than those from a mask on a graphite membrane. Following the column fabrication
process outlined in Fig. 2, a fabrication yield of 85% and more has been achieved. An
SEM cross-section of the sealed columns is shown in Fig. 3.
216
Peak capacity >40, b.p. range = 90 – 228 ºCin <4 sec
3-methylhexane
1,6-dichlorohexane
n-dodecane
1-decanol
Solvent
DMMP
DEMP
DIMP
Toluene
Fig. 1: Separation of 4 analytes and 4 interferrents in under 4 seconds using the microFast GC developed
by Analytical Specialists, Inc.
The experimental setup to test the column performance is shown in Fig. 4. Stainless steel
capillaries with o.d. of 0.016” and i.d. of 0.010” were glued or silver soldered to the
openings in the sealed GC. The carrier gas and the sample were injected at port A and
collected at port D, which was connected to a Flame Ionization Detector (FID). The
detector response was measured using a Keithley 6517A Electrometer (Keithley,
Cleveland, OH), collected at 125 Samples/sec using an A/D board and displayed on a PC.
A continuous flow of the hydrogen carrier gas at the vent carried away the gases
remaining after injection. To inject a sharp sample plug, the vent was closed just prior to
injecting the sample into the column and opened immediately to allow the excess gas to
flow out. At port C, hydrogen was used to sweep the sample through to the detector.
Sealing was checked by measuring the pressure-flow characteristics and observing
dispersion in a methane plug through the column. The inlet head pressure was varied
from 20-55 psi, with the outlet at atmospheric pressure. With a 30 psi inlet pressure, peak
widths ranging from 15-30 ms were obtained with a column dead time of 200 ms for the
0.5 m column and 1 s for the 2 m column. The sharp peaks of methane obtained indicate
that there was no flow across the column tops. Fig. 5 shows the comparison between
theoretical and experimental peak width at half height for a 650 µm tall, 2 m long,
column. The graph suggests that the serpentine turns in the column do not contribute
significantly to the dispersion in the sample plug.
Phase coating of nickel GC columns
In order for the LiGA fabricated column to act as a GC separation column, the column
walls have to be coated with a thin organic layer known as stationary phase. Molecules of
different vapors in the sample diffuse in and out the stationary phase and separate based
upon their relative boiling points. An important factor affecting the separation efficiency
is the phase thickness and the thickness uniformity. For fast separation a thin and uniform
coating is preferred.
While coating on circular capillary columns has been commercialized over the past 50 years or
so, coating on rectangular cross section columns has not been studied and comes with its
own issues. There are two main factors to be investigated: 1) adhesion of the
217
X-rays
k
Step 1: Expose PMMA on a Si substrate
Step 2: Develop exposed PMMA
Fig. 3: SEM image of the cross-section of the
sealed column
Make up gas for detector
Step 3: Electroplate nickel and polish
C
Detector
D
A
B
Sealed µ-column
Sample injection loop
Step 4: Etch substrate, cover bottom side
Step 5: Heat to remove the PMMA
Fig. 2: Schematic for the column fabrication process
using the LIGA process
Fig. 4: Experimental setup for testing the columns
liquid film to the metal columns and 2)
pooling of the liquid in the corners of the
microfabricated rectangular columns [2].
25
Furthermore, uniform coating of metal
20
capillary columns is challenging because of
the presence of a large number of active sites
15
on the surface.
10
The pooling results in an uneven stationary
5
phase layer which causes excessive peak
0
broadening. Based on the experience with
0
10
20
30
40
50
60
capillary coating and to meet the
Pressure (psig)
Theoretical
C 700
C 800
requirements for separation times of less
Fig. 5: Variation of peak width at half height than 10 seconds the stationary phase film
with inlet pressure for a 2m column and
should be on the order of 0.1 µm,
comparison with theoretical values
homogenously spread over the column’s
inner surface with minimum or no pooling. The columns were coated by static coating,
where the stationary phase is dissolved in a solvent and is filled into the column with one
end closed. As the solvent evaporates under vacuum, it leaves a thin coating on the walls
of the column.
Peak width (ms)
30
218
butane, pentane, and hexane) on a 2m long, 50 µm
wide, 500 µm tall coated microfabricated column.
C8, C10, C12) on a 0.5m long, 50 µm wide,
600 µm tall coated microfabricated column.
Fig. 6 shows the separation of four straight-chain hydrocarbons on a 2 m coated column.
Fig. 7 shows the separation of four other compounds on a 0.5 m coated column. While
separation time is only a few seconds the quality of separation indicates the need to
further improve column coating.
Future work
Both partners successfully met the performance milestones for individual components
and will focus on integrating them in the phase II of the MGA project. In particular
integration of sample pre-concentrator with the column, adding the detector and amplifier
electronics, and building a user-friendly test platform allowing for systematic studies of
column coatings and optimized temperature programming will be main efforts on our
way to meet the phase II milestones.
References:
1) A. Bhushan, D. Yemane, D. Trudell, E. B. Overton, and J. Goettert, “Fabrication of
micro-gas chromatograph columns for fast chromatography”, accepted at
Microsystem Technologies
2) Sumpter, RS and Lee ML (1991), “Enhanced radial dispersion in open tubular column
chromatography”, J. Microcol. Sep., v 3, pp 91-113
219
Development of a micro gas chromatography column in SU-8
Editor: Sebastian Mammitzsch
Co-worker: Abhinav Bhushan, Dawit Yemane, Ed Overton, Jost Goettert
Supported by DARPA
Introduction
This research was topic of a master thesis and focused on developing a multi-layer
SU-8 process to fabricate narrow-bore column for fast, high separation gas
chromatography applications.i The GC column consists of a 2m long serpentine channel
structure with a rectangular cross section of 600µm x 50µm covering an area of
approximately 2 x 4 cm2. The column surface has to be covered with a thin, uniform
layer, so-called stationary phase that will allow separation of a sample mixture into its
components because of different diffusion properties of the individual components into
the phase material. The high aspect ratio (HAR) of 12:1 provides a large cross section
area with relatively low flow resistance and large sample volume. The narrow width
ensures good interaction with the phase material and appropriate separation.
Consequently, a relatively large sample volume is passing through the column resulting
in a sharp peak measured by a column terminating detector.
Fabrication
The HAR column cross section together with the large footprint required many
systematic studies and process modification of the standard SU-8 process, and also used a
combination of optical and x-ray lithography for patterning. The three necessary SU-8
layers were fabricated with three different techniques briefly described here. For more
details please refer to the master thesis.ii The 300 µm thick bottom layer was applied onto
a thick PMMA substrate and structured using standard SU-8 UV lithography. The choice
of a ½” thick PMMA substrate was necessary to allow low stress patterning of multiple
layers throughout several exposure as well as pre-and post bake steps. The 600 µm thick
SU-8 structure layer containing the actual column design was applied on the undeveloped
bottom layer in two steps and structured by x-ray lithography. Bottom and structure layer
were developed simultaneously after completing the post exposure bake. It should be
mentioned that flycutting was employed to precisely adjust the height and flatness of the
different levels as well as to optimize the surface roughness. The third layer was
produced using a modified flexible semi-solid transfer technique. In this step a 100 µm
thick SU-8 layer was spin coated onto a 50 µm thick PEEK foil, partially flood exposed
and dried for approximately 10 min. The open column was then gently pressed into the
semi-soft SU-8 layer without clogging the channels and baked. The process was
completed by removing the PEEK foil, flood exposing all SU-8 layers, and a final post
exposure bake. Optionally, the PMMA substrate could be removed resulting in a free
standing column. Connection of the columns to gas supply and sample gas was obtained
through stainless steel tubes. These tubes were fixed and sealed into the open column
using SU-8 100 as glue.
Fig. 1 illustrates the assembled three layer column and also shows a cross section of
the built device demonstrating that the GC column was successfully structured using the
process described above.
220
SU-8 cap
SU-8 channel structures
stainless steel tube
SU-8 base
Fig. 1: Schematic cross section of the column (left) and cross-sectional image of the
fabricated column in SU-8 (right).
Results
Fig. 2 shows a SU-8 micro column after process completion including the connecting
steel tubes. Preliminary flow tests using hydrogen as carrier gas and sample plugs from
methane and butane showed transition times of approximately 1 s (see Fig. 3) for the
unretained peak and are comparable with similar measurements of nickel structure.iii A
peak width of approximately 25 ms will allow a good separation of a multiple component
mixture after coating the column with the appropriate stationary phase.
peak width: 25 ms
Fig. 2: SU-8 micro column released from Fig. 3: Flow measurements of unretained
PMMA
substrate
and
ready
for methane gas plugs.
measurements.
References
1. See also A. Bhushan et.al.; “Development of a Gas Chromatographic Analytical
Instrument for Ultra-Fast Chemical Analysis” CAMD Annual Report 2005.
2. Sebastian Mammitzsch: “Development of a micro gas chromatography column in SU8,” Master Thesis Fachhochschule Gelsenkirchen, Germany 2005.
3. A. Bhushan et. al.; “Fabrication of Micro-Gas Chromatograph Columns for Fast
Chromatography,” Proc/HARMST2005, Geongju, Korea, June 2005.
221
Bio-Magnetics Interfacing Concepts: A Microfluidic System using
Magnetic Nanoparticles for Quantitative Detection of Biological Species
CAMD BioMagnetICs Team,
PIs: J. F. Hormes, J. Goettert
Louisiana State University
6980 Jefferson Hwy. Baton Rouge, LA70806
DARPA – Project MDA972-03-C-0100
SUMMARY
Continuing last year’s efforts6 the BioMag team has focused this year on three main
aspects of the project: (1) Miniaturized microfluidic/magnetic chips and fluidic handling
system for controlling fluidic flow, (2) Probing of GMR sensors using a dry bead probes,
and (3) continuous development of bio-surfaces compatible with the sensor design. The
next chapters summarize the main results of last year’s work and will also briefly discuss
the next efforts. Additional efforts focusing on synthesis of magnetic nanoparticle and
bio-functioning of these particles is reported in contributions by Challa Kumar elsewhere
in CAMD’s annual report 2005.
The various efforts in the past year have demonstrated the need for a multidisciplinary research team to address the many aspects of the GMR BioSensor
development. Progress in some key areas especially related to integrating microfluidics
with GMR sensors and bio-surface research has matured and allows precise fluid control
required for bio-protocols. However, overall system integration is still a task to be
completed and will require substantial efforts from the group for the remainder of the
project.
6
J. Hormes et. al.:” Bio-Magnetics Interfacing Concepts: A Microfluidic System using Magnetic
Nanoparticles for Quantitative Detection of Biological Species”, CAMD Annual Report 2004.
222
An Approach for GMR Sensor Packaging and Dry Calibration
Editor: Min Zhang
Center for Advanced Microstructures and Devices (CAMD), Louisiana State University
6980 Jefferson Hwy, Baton Rouge, LA 70806, USA
A GMR (Giant Magneto Resistive) sensor is a highly sensitive micron-sized magnetic
field sensing element, whose resistance changes in response to an external magnetic stray
field. Its recent applications in biology and biomedicine emphasize the use of GMR
materials as biosensors to detect the presence as well as the concentration of biomolecules, which were bounded to superparamagnetic particles.
The purpose of this work is to establish a standard GMR sensor packaging and a
sensitivity calibration protocol to get the relationship between the magnitude of GMR
signals and the number of bound particles. A standard DIP IC chip carrier packaging and
superparamagnetic particle embedded microprobes (SPEM) were realized, and standard
calibration protocols were established. The proposed method has four major advantages:
modular approach, a precisely controlled number of mostly single-layered particles on a
microprobe, pristine GMR surface after calibration, and mass fabrication.
The GMR sensor packaging was realized firstly by the wafer-scale microfluidic
packaging, followed by wafer dicing and wire-bonding of the die to a DIP IC chip carrier
(Fig. 1).
Fig. 1: GMR sensor glued and wire bonded to a standard IC chip carrier.
The use of standard IC chip carrier promises benefits in terms of ease of interconnect
and costs over the NVE ‘diving board’ solution, which is a custom-made design.
However, further research is underway to integrate a fluidic connector onto the chip
carrier required for the GMR sensor applications.
223
Dry calibration of GMR sensors
The purpose of this work is to establish a standard sensitivity calibration protocol for
GMR (Giant MagnetoResistive) spin valve sensors using superparamagnetic particle
embedded microprobes (SPEM). Comparing to other calibration methods, such as the use
of MFM (Magnetic Force Microscope)7, sealed fluidic flow cells8, and current lines9, the
proposed SPEM method has four major advantages: no magnetic background, a precisely
controlled number of particles generates the signal, pristine GMR surface after
calibration, and mass fabrication.
The SPEM is made from a glass cantilever (Polymicro Technology®) and a SU-8
cylinder post (Microchem®). The superparamagnetic particles are embedded on the
bottom surface of the SU-8 post. The probe tips were fabricated with diameters from
50µm to 200µm and a height of 500µm. Two fabricated microprobes in Figs. 2.
Glass capillary
Tip with bead layer
Figs. 2: Examples of microfabricated probes with circular (left) and rectangular
(right) cross-section.
For experiments the probe is mounted to a xyz-stage and carefully positioned relative
to the GMR surface. By bringing the probe close to the GMR surface GMR responses can
be measured. Initial sensor testing includes moving the probe up and down relative to the
GMR surface and monitoring the sensor output (Fig. 3). Optimization of the sensor
operating parameters (amplification, current) can also be done in this configuration. Fig.
4 illustrates the sensor response as a function of probe distance for a fixed setup. As can
be seen reasonable signals can be measured up to a distance of 100µm from the surface
for a full coverage probe. By using probes with different numbers of superparamagnetic
particles sensor response as a function of number of beads has been measured as shown
in Fig. 5. These results indicate that the limit of detection for this particular sensor was
approx. 40-50 beads (Ø=2.8µm). In Fig. 6 measurements of GMR sensors with different
active areas were conducted showing that higher signals are measured for smaller sensor
areas.
7
H. Brückl, “Magnetoresistive logic and biochip”, J. Magn. Magn. Mater., vol. 282, p. 219, 2004.
R.L. Edelstein, “The BARC biosensor applied to the detection of biological warfare agents”, Biosensors
and Bioelectronics, vol. 14, p. 805–813, 2000.
9
D.L. Graham, “Single magnetic microsphere placement and detection on-chip using current line designs
with integrated spin valve sensors: Biotechnological applications”, J. of Appl. Phys., vol. 91, nr. 10, p.
7786–7788, 2002.
8
224
Signal of Full Coverage Probe on 50um sensor
-2.5
85
95
105
115
125
-3
GMR sensor signal for
alternating probe positions
relative to the GMR surface.
-3.5
Volt
Fig. 3:
-4
-4.5
-5
Time (sec)
350
5 % S p in V a lv e (2 0 k O h m )
u n d e r 2 0 G a u s s fie ld
& 1 m A b ia s in g c u r r e n t
300
Fig. 4:
Output (mV)
250
GMR sensor signal as a
function of probe distance to
the GMR surface.
200
150
100
50
0
-5 0
0
50
100
150
200
250
300
350
400
D is t a n c e fr o m S e n s o r S u r fa c e ( u m )
Fig. 5:
GMR sensor signal as a
function of probes with
different number of magnetic
beads.
Sensor output (m V)
Sensor Size vs Sensor Signal (10k Amplification)
Fig. 6:
1000
800
600
400
200
0
GMR sensor signals from
different size sensor for a full
coverage probe.
0
50
100
150
200
250
Square sensor dimension
In conclusion these preliminary experiments demonstrate the possibilities of the
SPEM experiments to support GMR sensor research within the BioMag project. It will be
used as a tool in our ongoing research to characterize and optimize the GMR sensor
performance.
225
Fluidic Handling System
Editor: Jens Hammacher
Co-worker: Proyag Datta, Jost Goettert, Changgeng Liu, Mark Pease
Fluidic handling is critical for good and reliable results in a microfluidic sensor
system. Precisely controlling fluid flow rate and volume leads to small dead volume,
short reaction times and low space consumption in the entire system. For the BioMag
project the fluid handling system will control fluid delivery to and from the actual sensor
volume and is important to execute complex bio-chemical protocols. The idea was to buy
off the shelf components and integrate them into the GMR sensor platform.
First of all we tested very small micro
fabricated
pumps
from
Bartels
10
Mikrotechnik (Germany). The pump and
the controller are shown in Fig.1. The
pump consists of a 1.4 mm square plastic
case with two nozzles. One nozzle is the
inlet and the other the outlet. A piezo
membrane acts as an actuator. The
pumping operation of the membrane is
depending on the waveform, the
Fig.1: Bartels micropump and controller.
amplitude, and the frequency of the
driving voltage signal. Typical flow rates
are shown in Fig. 2 as a function of the controller setting. While overall the pumps meet
our requirements of small size, ease of operation and easy integration into the overall
sensor, experiments with different pumps and multiple tests with one pump proved that
the reliability and uniformity cannot meet the stringent needs for the sensor applications.
For example different pumps, represented by different colors in Fig. 2, had up to a factor
of 4 different flow rates for similar operating conditions. Also, repeatability was not as
good as expected indicated by graphs in the same color measured in subsequent runs.
Fig. 2:
Measured flow rates for
different controller settings and
different but nominally identical
pumps.
Due to the limited success in using commercially available micropumps we decided to
change pumping concept. Instead of pressing fluid into the channels using a pump a
vacuum driven system was proposed in which a vacuum pump us sucking the liquid
10
More details about the pump are available from the Bartels webpage at www.bartels-mikrotechnik.de.
226
through the channels (see Fig. 3). Flow regulation is achieved by using valves to connect
the pump to the fluid channels and open/close individual reservoirs, too. An additional
advantage of this concept is that fluid leakage was minimized or completely avoided by
having an under pressure in the fluidic channels.
The system consists of a number of reservoirs (up to 4), active pinch valves
(BioChem, Fig. 4), and a waste reservoir to which a vacuum pump (Sensidyne, Fig. 5) is
connected. The flow is regulated by squeezing the tubing and creating backpressure. The
reservoirs are made of single use syringes, which are interconnected by Luer lock
connectors with the silicone tubing. The tubing is hooked up to the fluidic block using
connectors from ThinXXS.11 A picture of the assembled system is shown in Fig. 6.
Fig.3:
Reservoir 1
Reservoir 2
Reservoir 3
Waste Reservoir
Schematic of the vacuum
driven fluidic handling
system.
Fluidic
Interface
Block
Reservoir 4
Vacuum Pump
Flow Regulator
BioChem
Pinch Valve
Fig. 4: Pinch valves from BioChem.
(www.bio-chemvalve.com/biochem-valve.html)
Fig. 5: Small vacuum pump from
Sensidyne. (http://www.sensidyne.com).
11
More details on microfluidic solutions from ThinXXS is available from their webpage at
www.thinxxs.com.
227
Reservoirs
Valves
Fluidic block
Pump
Controller
Fig.6: Fluidic handling system.
The current system is push button controlled through a custom made electronic box
operating pump and valves. By pushing one of the buttons, the corresponding valve will
be opened and the fluid from this reservoir will be sucked out. By creating backpressure
in the system (squeeze tubing with a bolt and a nut, use a tubing with smaller diameter,
etc.) the flow rate can be adjusted and controlled. A test series, where the backpressure is
created by adding tubing with a smaller diameter (0.008” ID) has been made. These
experiments have been done with two different vacuum pumps. The results are shown in
Fig. 7, left. On the right of Fig. 7 repeatability of flow rate measurements are shown for
multiple measurements with one pump and fixed parameters indicating that this system is
useful for the ongoing research with adjustable flow rates ranging from µl/min to ml/min.
Length of adjusting tube [mm]]
40
stability of the flowrate
35
0.4
flowrate in ml/min
30
25
20
15
10
0.3
0.2
0.1
0
0
5
100
200
300
time in s
0
0
1
2
3
4
5
Flow Rate [ml/min]
Fig.7: Flow rate measurements for different backpressure (left) and repeatability of
measurement for one fixed setup.
228
Modular Vertical Fluidic Stack
Editors: Jens Hammacher, Proyag Datta, Jost Goettert
Co-worker: Jason Guy
A number of Life-Science applications will benefit from the advantages of using
dedicated micro-fluidic chips performing discrete functions. Combining a number of
simple chips in a compact format will offer maximum flexibility and optimized
functionality and will enable systematic research on complex biological systems.
Ongoing research at CAMD proposes basic fluidic chips for simple tasks such as mixing
or splitting of fluids and well-defined micro-micro and micro-macro interfaces.
Combination of multiple chips can be achieved using passive alignment strategies an will
enable customers to build dedicated modules for specific tasks. The customer will take
advantage of already existing chips and can flexibly add new designs that will offer
advanced solutions for BioMEMS research and applications. The vertical fluidic stack is
also providing well-defined interfaces to existing laboratory equipment such as optical
fluorescence microscopes and electrical circuits offering a universal research platform.
The stack consists of several fluidic chips in standard glass slide format (1” x 3”) with
a large variety of basic fluidic functions including mixer, splitter, reservoirs, and
interconnects. A simple macro micro interface with off the shelf fluidic and electrical
interconnections enables user friendly handling and operation. Each slide design is
custom made, but the interconnections are standardized. This allows small fluidic
pathways within and between several layers, which results in minimum dead volume and
lower cost in expensive chemicals.
Fig. 1 shows the concept of the fluidic stack. The left picture shows a complete fluidic
stack with several functional layers. The right picture illustrates the standardized
interconnection layer chip with slots for off the shelf electrical and fluidic connectors.
Fluidic connectors
Electrical connectors
Alignment marks
Fig. 1: Schematic of the fluidic stack.
Depending upon design, minimum feature and material choice, fabrication of microfluidic chips and of the stacks employ a combination of precision micromachining (CNC
229
milling) to manufacture a custom made mold insert (large scale, multi-level) and polymer
LiGA MEMS fabrication (hot embossing) to replicate the fluidic chips. This combination
allows both rapid fabrication of prototypes and small scale series production of chips for
testing and optimization purposes. If needed, CNC machined mold inserts can also be
replaced by LiGA mold inserts or mold inserts that use a combination of both fabrication
techniques. An example for a CNC mold insert is shown in Fig. 2. This mold insert is
used for fabrication the interconnection layer chip with the fluidic and electrical ports.
The special design on this mold insert is a two level structure, which allows 3D molding
(Fig.3) of the inlet ports.
Fig.2: CNC milled mold insert
Fig.3: Conical 3D structure on mold
insert
This design allows using a broad range of polymer materials. The plastic is placed
under the mold insert and by using force and pressure the chips are embossed. A selection
of chips is shown in Fig.4. For comparison a glass slide is shown on the left slide. The
mid left slide is the interconnection layer chip and the both chips to the right side are
basic fluidic structures made in different thickness of polymer material. Prior to stacking
the chips together an appropriate sealing approach has to be considered.
Fig.4: Custom made fluidic chips.
Fig.5: CAMD demonstrator chip
combining various basic fluidic structures
with the interface chip.
At this time different solutions including thermal bonding (permanent), gluing
(permanent), and soft gaskets (latex rubber, PDMS, temporary) are investigated and will
230
be selected depending upon the customer’s need. A thermal bonding solution is shown in
Fig.5.
In conclusion initial results of the newly developed vertical stack concept prove to be
of interested for a number projects in BioMEMS, BioSensor, and Life Science
applications. It also generated some interest for potential users. Two internal applications
at CAMD, use of custom-made polymer micro-fluidic chips (LabWare) for bio-surface
research (see Fig. 6) and development platform for microfluidic research within the
BioMAG project illustrates the usefulness of the concept but also indicates that more
systematic studies are needed including optimization of passive alignment and sealing of
adjacent chips.
Fig. 6: The picture displays custom made chips (LabWare) for bio-surface research.
231
CAMD Fluidic Cartridge and Electronic – a R&D Platform for
Systematic Studies of the GMR Sensor
Editor: Jost Goettert
Task leaders: Mark Pease, Rusty Louis
Co-worker: Proyag Datta, Jens Hammacher
In order to enable systematic studies of bio-functionalized GMR sensors the NVE
electronic board with CAMD fluidic connector, which has been developed in 2004 (for
details see CAMD Annual Report 2004 contribution by J. Hormes et. al.:” Bio-Magnetics
Interfacing Concepts: A Microfluidic System using Magnetic Nanoparticles for
Quantitative Detection of Biological Species”) needed to be replaced with an open, more
versatile and easily accessible system.
Led by Mark and Rusty a team of researchers has developed the CAMD cartridge with
the so-called Dagger board fluid to meet these needs. The NVE diving board fits exactly
into the cartridge (Fig.1). The block consists of two parts, which have slots on each side
to accommodate Helmholtz coils required for the excitation field. The lower part has a
slot which holds the diving board with the mounted GMR sensor (Fig. 2) and the top
block has a slot for the Dagger board (Fig. 3). Both blocks are aligned and fixed using
nuts and bolts. The Dagger board is pressed down onto the GMR sensor using a Silicone
gasket to seal it. Screws will fix it temporary for the experiment. After assembly (Fig. 4)
the system is placed in a shielded electronic box (Fig.5) and electrically connected.
Fig.1: Schematic of the CAMD cartridge.
Fig.2: GMR on diving board attached to
lower part of the block with magnetic coils.
The system is now ready for measurements. Fig. 6 shows the flow of a colored liquid
through the Dagger board and across the GMR sensor.
232
Interface
reservoir
Interface
microfluidic
6 mm
Dagger Board
Fig.3: Dagger board.
Fig.4: Assembled and connected CAMD
cartridge.
Fig.5: Cartridge electrically connected.
Fig.6: Fluid flowing to the GMR sensor
through the Dagger board.
The CAMD electronic data collection box is developed to be a stand alone device. The
box possesses an enhanced noise shielding. A copper shield around the sensor electronic
allows low noise measurements. For calibration and testing purposes, electronic
equipment (power supply for magnetic coils, data acquisition hardware, amplifier, battery
source) is connected to the box as illustrated in Fig. 7. This modular setup offers
maximum flexibility needed for the initial experiments but to be replaced with a PCB
based version at a later phase of the project. The Helmholtz coils are energized with a
very stable current source to provide a homogenous excitation field. The
superparamagnetic beads are magnetized by this field and induce the stray field that
causes the GMR resistance to change delivering the sensor signal.
User friendly software and data acquisition allows automatic testing protocols and
systematic studies of sensor parameters. For calibration purposes the user can quickly
scan multiple excitation fields and calculate the optimum field. The software
continuously collects data and allows export to other software packages for further
evaluation. One example is displayed in Fig. 8 showing the noise signal from the entire
system measured for an extended time period to verify long term stability.
233
Fig. 7: Electronic equipment needed to
Fig. 8: Long-term noise measurement
control and collect GMR sensor data.
illustrating the system stability.
In conclusion the CAMD cartridge provides a user-friendly test platform for GMR
sensors mounted onto NVE’s diving board. Systematic studies should that the
performance is comparable with the more compact NVE electronic board and more
suitable for the needs of investigating bio-functionalized GMR surfaces, which are
studies to be conducted in the near future.
234
Development of an injection micromixer for vertically integrating
into biochemical microfluidic systems
Editor: Changgeng Liu
ABSTRACT
This research was focused on designing, fabricating and testing a modular polymerbased injection micromixer prototype. This micromixer can easily be integrated into the
GMR sensor system and is also compatible with vertical stack concept. This presentation
is addressing some basic aspects of the mixer design related to mixing efficiency.
INTRODUCTION
Microfluidic systems have been widely applied in biochemical, biological and
chemical analysis for their potentials and advantages: small amounts of sample and
reagent, less time consumption, lower cost and high throughput. Besides the micropump,
the micromixer is another important component in a microfluidic system or a micro-TAS.
Mixing on the microscale relies mainly on diffusion due to the laminar behavior at low
Reynolds numbers. Various efforts have been made to improve the mixing process by
introducing geometric irregularities in fluidic channels to create localized eddies and
turbulences. Also there are some good reviews to summarize the history of micromixer
and their applications there is only little research reported to directly integrate the
micromixer into a complex microfluidic system.
DESIGN AND FABRICATION OF A PMMA INJECTION MIXER
The average diffusion time τ over a relevant mixing path d is given as:
τ=
d2
2D
(1)
where D represents diffusion coefficient of solutions. Equation (1) shows that the
diffusion time or the mixing time is proportional to the square of the mixing path. So the
smaller mixing channel feature sizes, the faster becomes the mixing process.
Suppose two water-based liquids are to be mixed in a 100 µm wide channel, and the
diffusivity is 2.4 × 10-5 cm2/s. According to Equation (1), the required mixing time is
more than 2 seconds. However, by splitting one stream into many substreams through
injection nozzles, an injection mixer with only 28 injection nozzles can mix the two
liquids in less than 3 milliseconds as long as the layout of the injection nozzles is
optimized. An injection mixer depicted in Fig. 1 includes two inlets, micronozzles, and a
mixing chamber. In this injection mixer, all micronozzles were arranged symmetrically.
b
a
Outlet
Inlets
Mixing chamber
Nozzles
Fig. 1: 2D layout of micronozzles and 3D schematic model of an injection mixer.
235
By using Coventor software, the performance of the injection mixer has been
simulated. The width and depth of the channels are 100 µm and 200 µm, respectively.
The mixing chamber is 600 µm in width and 800 µm in length. There are 28 injection
nozzles with the diameter of 20 µm. The flow rate of both liquids is 10 µL/s, and
diffusivity is 2.4 × 10-5 cm2/s. The contour and profile of the concentrations of two
liquids at the outlet of the mixing chamber was plotted in Fig. 2.
Fig. 2: Contour and profile of the concentrations of two fluids in a mixer (channel width: 100 µm;
channel depth: 100 µm.
28 nozzles with diameter of 20 µm; flow rate of each fluid: 10 µL/s; Diffusivity: 2.4 ×
10-5 cm2/s)
From the numerical results, along the cross section at the outlet of the mixing chamber
the concentrations of two liquids were narrowed down from 0.3 to 0.7. In fact, regular
arrangement of micronozzles as shown in Fig. 2 is not an efficient layout. From the
contour of the concentrations of two fluids, there are several substreams along the
direction of the axis of the channel merged together, which degraded the efficiency of
mixing.
According to the above analysis and design, a PMMA-based injection mixer was
machined as shown in Fig. 3.
Inlets with standard
connectors
Outlet with
standard connector
Micronozzles &
Mixing chamber
Fig. 3:
Picture of a PMMA-based
injection
mixer
including
standard
¼”-28
interface
connections.
The micronozzles were arranged symmetrically, in parallel with the direction of the
channels. A standard connection protocol with ¼”-28 threads was selected. 28
micronozzles with the diameter of 50 µm were fabricated.
An experimental system was setup to test the mixer as shown in Fig. 4a. By using two
micro diaphragm pumps (MDP 1304, thinXXS corp., 49-6131-6277845), two waterbased red and green liquids were connected to the two inlets of the mixer through the
standard connection, a tubing (1478, 1/16 × .008, Upchurch Scientific, 1-360-679-2528),
a nut (P-218x, FLANGELESS, SHORT, 1/16 IN, 1/4-28), and a ferrule (P-200Nx,
FLANGELESS, 1/16 IN). By adjusting the driving frequencies of the two pumps, the
flow rates of the two liquids can be controlled separately. A microscope with a camera
was used to monitor the status of mixing.
236
Fig. 4b demonstrated the picture of experimental results. Because of the regular
arrangement of the micronozzles, two major substreams of the liquid injected from the
micronozzles were detected, which coincided with the numerical results and which can
be improved by using randomly distributed nozzles.
Micropump
& control unit
a
Microscope
with a camera
Two water-based red
& green liquids
Injection mixer
b
Fig. 4: Experimental setup and pictures of mixing of two water-based red and green
fluids (a: Experimental setup; b: pictures of the testing of the injection mixer).
In the future this PMMA-based injection mixer is ready to be
integrated into the vertical-stacked fluidic as illustrated in Fig. 5.
Macro-micro interfaces
Injection mixer (Developed in this paper)
Cartridge
Pre-concentrator
Micro-micro interfaces
Biosensor (GMR with biofunctionalized surface)
Fig. 5: Schematic design of the vertical-stacking-type cartridges.
237
Hydro-focusing to focus magnetic beads onto GMR surfaces
Editor: Changgeng Liu
Besides embedded magnets or conductive wires attracting beads to the GMR surface
hydro-focusing is an another alternative solution taking advantage of laminar flow
conditions in microfluidic channels. By using SU-8 open channels directly fabricated
onto GMR sensor chips, a PDMS cover layer to seal it, and a specially designed fluidic
connector to interface with reservoirs, the bead solution will be narrowed by the shear
flow and directed down to the surfaces of GMR sensor arrays, where the magnetic beads.
The concept of focusing to the surface is illustrated in Figs. 1 for a simple 2D focusing
and a more advanced 3D focusing where shear flow will be provided from the top as well
as from two sides.
a) 2D hydro-focusing
b) 3D hydro-focusing
Figure 1: Schematics of hydro-focusing the bead solution over to surfaces of GMR sensor
arrays.
Fig. 2 demonstrated a picture of the cartridge for hydro-focusing magnetic bead
solution. Assembly and further experiments are currently conducted.
Fig. 2:
Picture of a special fluidic connector
used for hydro-focusing magnetic bead
solution onto GMR sensors mounted onto
NVE’s diving board.
238
High-Through-Put Assay Development for GMR Sensor System
Editor: Mark Pease
Co-workers: Proyag Datta, Tyler Mancil
Louisiana State University, Baton Rouge, Louisiana 70806
Assays for the detection of biological molecules must be robust, reliable, and highly
reproducible. This often requires that literally thousands of samples must be run before a
biological assay is ready for implementation in a real world setting or for use in an
instrument GMR Biosensor being developed at CAMD.
To achieve this level of through-put, it was necessary to adapt standard immunosandwich biochemistries to the surface of a GMR sensor in such a fashion that the assay
could be run in a 384 well format.
The electronically active element of the CAMD GMR biosensor is a 1.5 mm x 6.0 mm
diced silicon wafer that is coated with SiOx. These “chips” are the substrate for the
immuno-sandwich assay and are glued to white acrylic backbone to form a “24 chip
comb” (Fig. 1a.). The 24 chip comb in combination with a standard 384 well plate is used
to produce all of the surface chemistries as well as conduct the steps of the immunosandwich assay.
In short, primary antibodies were immobilized to the surface of the GMR substrate
with covalent chemistry utilizing reactive aldhydes on the surface of the substrate and
primary amines on the surface of the IgG. Heat killed Salmonella were then captured by
the primary antibodies. After washing removes the unbound Salmonella, protein
congujates of antibody-horse radish peroxidase (IgG-HRP) were bound to the captured
Salmonella. When the immobilized HRP is exposed to luminol substrate (Pierce) a
gently blue glow is produced that is recorded on X-ray film (Fig 1b.). Fig. 1c shows the
dose response curve for the detection of heat killed Salmonella using this technique.
Future work will focus on expanding the number of targets beyond the initial assay for
the detection of heat-killed Salmonella.
Fig. 1a.
Fig. 1b.
239
Fig. 1c.
Large Area Multi Level Polymeric Microfluidic Platform for Microchip
Electrophoresis Fabricated by Use of the LIGA Process
Pradeep Khanal1,2, Yohannes Desta1, Li Zhu2, Proyag Datta1,
Jost Goettet1, and Steven Soper2
1
Center for Advanced Microstructures and Devices (CAMD)
2
Center for BioModular Multi-Scale Systems (CBM2)
Louisiana State University, Baton Rouge, Louisiana
[email protected], 225-578-4618, PRN: ChSS105
Summary
Chip-based analysis systems have been shown to have many advantages over their conventional
analogues including the improved efficiency with regard to sample size, analysis times, cost,
analytical performance, process control, integration, throughput and automation. Microchip
electrophoresis, being considered as a scaled-down version of conventional capillary format, is
particularly attractive for DNA analysis, for example, in DNA sequencing. Parallelism and read
length are the two key parameters for high-throughput DNA sequencing. Previous results on
microchips have demonstrated that short channels are impractical for long-read DNA sequencing
since the separation resolution scales with the square root of the separation length. In order to
achieve long sequencing read length with high-resolution separation efficiency on microchip
while still maintaining the compact size of the chip, turns are incorporated in each channel to
provide the necessary separation length. However, the introduction of multiple turns may
deteriorate the separation efficiency. On the other hand, in order to increase the sample
throughput, parallel separation lanes need to be designed and fabricated on a single chip. The
small-area wafers put limits on the number of channels that can be incorporated. All of these
stimulate the need of fabricating chips with relatively large surface areas, which can easily
accommodate longer separation channels and increase the channel capacity.
To fabricate microstructures of large area, step and rotate technique was used. A large stainless
steel substrate of 6” outer diameter was used as substrate. In order to develop a mold insert with
multiple levels, the upper face was machined to two levels- 4.5” diameter central circular part and
the outer remaining 1.5” circular region at 75 microns deeper than the former. PMMA was
bonded and flycut to 200 microns. A special fixture was designed and built for ‘step and rotate’
exposure at the CAMD XRLM4 beamline. Using a standard 4” X-ray mask and the fixture, the
substrate was exposed 4 times with the aid of the alignment marks of 15 microns resolution. The
sample was developed and then electroplated with nickel. Two-Level Large Area Mold Insert was
hence obtained by polishing and mounting the nickel mold on to the steel substrate. The mold
insert was used to hot emboss PMMA sheets and polymer chips with the complex microstructures
were obtained.
Large Area Mold insert Fact Sheet
Tool diameter:
Microstructure depth:
Critical dimension:
Number of channels:
6”
multi-level, 80 µm center and 175 µm outer structures
15 µm
16
240
Schematic diagram of the fabrication steps
75 µm
(Machined
into 2 levels)
Stainless Steel Substrate
Photo resist (PMMA)
X-ray radiation
First Exposure
X-ray mask
Technotrans Plating
Station with Rotating
Electrode
Alignment mark
Second, third and
fourth exposures
Rotate-and-repeat
exposure unit
Large Format Mold Insert
Electroplated Nickel
Developed PMMA
Machined Nickel Mold Insert
(Microstructures)
Hot-embossed PMMA chip
Design and Fabrication
To fabricate microstructures of large area, rotate-and-repeat technique was used.
The following steps were undertaken.
1. A large stainless steel substrate of 6” outer diameter was machined. In order to build a mold
insert with multi levels, the upper face was machined to two levels- 4.5” diameter central circular
part and the outer remaining 1.5” circular region at 75 microns deeper. This is advantageous since
it is easier to insert injection tube into taller micro channels.
2. PMMA was bonded and flycut to 200 microns.
241
3. A special exposure unit was developed for ‘rotate-and-repeat’ technique. Using a standard 4”
X-ray mask and the exposure unit, the substrate was exposed 4 times with the aid of the
alignment marks of 15 microns resolution.
4. Each exposure was followed by the development process.
5. The sample was then electroplated with nickel.
6. Two-level large area mold insert was hence obtained by polishing and mounting the nickel
mold on to the steel substrate.
7. Mold Insert, thus obtained was used to hot emboss the thermoplastic (PMMA) and the
devices/chips with the complex microstructures were obtained.
The metrology measurements performed with the WYKO RST interference microscope
demonstrate the smooth transition in step height between the two regions.
SEM Image of the step
on the channel in LFMI
75 µm
(2 levels)
Optical Profiler Analysis of 2 levels in
Large Area Mold Insert Channel
Applications:
Large area polymeric chip helps to achieve long sequencing read length with high resolution
separation efficiency and to increase the sample throughput by providing parallel separation lanes
on a single chip. Moreover, LFMI can easily accommodate longer separation channels thereby
increasing the channel capacity. The same rotate-and-repeat exposure technique can be used to
develop other mold inserts of different dimensions with symmetrical microstructures. Larger
mold inserts (>6” diameter) can also be built with this technique.
242
Polymer Molding for Microfluidics
Editor: Proyag Datta
Co-Workers: Jost Goettert, Sitanshu Gurung, Jens Hammacher, Jason Guy, Feng Xu
MEMS technology related to microfluidics is the focus of immense interest because of
the existing and foreseen applications in a variety of fields, the most prominent ones
being life sciences and medicine. Polymer microfluidic chips are a key technology for the
mass production of disposable BioMEMS devices in the future. Microdevices related to
life science applications are finding uses ranging from assays for genetic research to toxin
detection on the battlefield. In order to hasten the rate of research and to promote
commercial advancement of technology based on such polymer chips, it is essential that
the process for fabricating them be well defined. With that goal in mind CAMD
established the capability to mold polymer microstructures with the acquisition of a
Jenoptik HEX02 hot embossing machine in 2002. Since then, hot embossing has been
established as a regular service offered to internal and external customers. Hot embossing
is a polymer molding process that is gaining popularity as a method of replicating
microstructures since it is a low cost process with fast turnaround times suitable for rapid
prototyping.
Establishing standard process parameters for hot embossing is demanding because
bulk effects of the mold insert fixture and molding machine have a dominant influence on
the molding parameters and the properties of the material being molded tend to vary from
batch to batch. A methodology for evaluating and optimizing the parameters for hot
embossing microstructures was developed, based on known material properties and
considering the cumulative behavior of mold, material and machine. Using this method
force-temperature-deflection curves (Fig 1b) were measured in-situ using the HEX02
embossing machine. Data thus acquired was used to fine tuning the hot embossing
process (Fig 1a). This work was presented at HARMST2005.iv
Microfluidic chips for various applications were fabricated over the last year (Fig 2).
One particular application required an opto-fluidic chip with a waveguide integrated in a
polymer microfluidic chip in order to deliver excitation light to fluorescent probes
contained along the length of the fluidic channel. This chip was designed and fabricated
at CAMD using a double sided embossing process illustrated in Fig 3a. The mold inserts
were fabricated by direct micromilling of brass (Fig 3b). The molded chip, Figs 3c and d,
was tested for optical performance and for effective fluorescence excitation of probes
contained in the microfluidics channel. Initial results were promising and the results were
presented at Photonics West 2006, San Jose.v Research on this project continues with
the aim of optimizing performance of the chip and improving the coupling efficiency of
light into the chip.
Polymer molding established at CAMD has proven to be an extremely useful enabling
technology for rapid fabrication of microfluidics chips for biological analysis. Future
research efforts will be aimed towards post-processing of molded chips in order to add
functionality that enhances the present capabilities of the molded chip.
243
Fig 1a: PMMA microstructure embossed under various
conditions of temperature with a force of 5 kN; Width of
the cross-bar pattern is 50µm.
Fig 1b: Displacement as a function of temperature
comparing the behavior of 3 different polymers.
Fig 2a: Microfluidic slides with silicon inserts used
for bio-surface studies on silicon.
Fig 2b: Microfluidic slide used for magnetic
particle separation studies.
Fig 2c: Brass mold insert for exploring microfluidic
phenomenon. Various mixer and splitter structures
are included in the design.
Fig 2d: Polymer microfluidics slides molded at
CAMD by Hot Embossing.
244
Fig 3a: Schematic of double-sided hot embossing used to
fabricate microfluidic chips with integrated waveguide.
Fig 3b: Brass mold insert fabricated by micromilling.
Fluidic Channel
500µm
Waveguide
Fig 3c: Image of molded polymer chip with multiple channels
and integrated waveguides.
Fig 3d: Image of the cross Section of a single fluidic channel
and waveguide.
References
4
Proyag Datta, Jost Goettert; “Methods for Polymer Hot Embossing Process
Development” from the Proceedings of HARMST ’05 June 10-13, 2005, Gyeongju,
Korea, pg 256.
5
Proyag Datta, Feng Xu, Sitanshu Gurung, Steven A Soper and Jost Goettert, “Polymeric
Waveguides for Orthogonal Near Surface Fluorescent Excitation“; Microfluidics,
BioMEMS, and Medical Microsystems IV, from the Proceedings of SPIE Vol. 6112,
2006
245
Single Step Fabrication of an Integrated Optical Waveguide
Editor: Sitanshu Gurung
Co-Workers: Proyag Datta, Jason Guy, Feng Xu
Summary
An optical waveguide is a structure which is used to deliver light from one point to
another. We have shown a novel approach to integrate an optical waveguide into a microfluidic channel so that it forms an integral part of the channel. The purpose of doing so
was to deliver excitation wavelength light to an extended region i.e. along the length of
the fluidic channel. A waveguide is typically made up of an optically clear material of
higher refractive index forming the core and an optically clear material but of lower
refractive index forming the cladding1. Light injected into such a structure gets confined
in the core (apart from some leakage) due to total internal reflection. Light confined can
then be transported from one point to another, hence working as an optical waveguide.
In our design of the integrated optical waveguide, the core is PMMA (η=1.48) and the
aqueous biological media (η=1.33) and air (η=1.0) form the cladding. A cross-section of
the waveguide is shown in Fig. 1. Light injected from one end is transmitted along the
length of the waveguide but as light travels, part of it leaks out of the waveguide (Fig. 2)
into the fluidic microchannel above it. This leaked light will excite any fluorescent probes
bound to the bottom of the microchannel, thus enabling optical detection.2
Polymer molding by hot embossing was the technique used to fabricate the polymer
waveguide 3-4. The Jenoptik HEX02 hot embossing machine is used for this purpose. Hot
embossing starts with fabrication of a mold insert. In our case the mold insert was made
of brass by direct micro milling (Fig. 3). A double sided hot embossing process was
employed to obtain the required waveguide profile (Fig. 4). The top and bottom mold
inserts were aligned using passive alignment to obtain an accuracy of approximately
±20µm. A force of 20kN and an embossing temperature of 165˚C were applied to obtain
a residual thickness of ~500µm of PMMA. Each molded plastic part had 9 microfluidic
channels. The widths of these channels ranged from 50 - 500µm. Each piece was cut to
the shape and size of a standard microscope slide and polished using a Micromesh
abrasive cloth to obtain a smooth, optically clear edge surface (Fig. 5)
The confinement of light in the waveguide was observed by injecting light into one
end of the waveguide through a pin-hole aperture and observing it with an optical
microscope from the other edge of the waveguide (Fig. 6). Performance of the waveguide
was then tested on an optical bench by coupling excitation wavelength light (635nm)
from a laser into the waveguide. The microfluidic channel was filled with a 5 ng/µl
ΦX174/HaeIII DNA digest intercalated with a TOPRO3 dye. The fluorescence emitted
by the dye was observed perpendicular to the length of the channel using an optical
microscope (Fig. 7). Fluorescence intensity along the length of the channel is shown in
Fig. 8.
A novel, single step method of fabricating a polymer waveguide integrated in a
microfluidic channel was demonstrated and its performance was tested, proving it to be a
viable design that merits further improvement and testing.
246
Microfluidic Channel
PMMA Structure
Seal Layer
Air
Waveguiding
Region
Fig.1a: Cross-section of the optical waveguide.
Fig.1b: Image of the waveguide.
Light out
Light leaking
Light In
Fig. 2: Light leaking of the waveguide.
Fig. 3: Brass mold insert.
Fig. 4: Double sided hot embossing.
Fig. 5: A cut and polished waveguide chip.
247
Fig. 6: Confinement of light in the channel.
Fig. 7: Fluorescent image of the DNA dye.
2000
Fluorescence Intensity
1750
1500
1250
1000
0
4
8
12
16
20
Distance from the beginning (mm)
Fig. 8: Variation of fluorescence intensity along the length of the channel.
References:
1.
2.
3.
4.
Choi, C.-G., "Fabrication of optical waveguides in thermosetting polymers using hot embossing".
Journal of Micromechanics and Microengineering, 2004. 14: p. 945-949.
Mogensen, K.B., H. Klank, and J.P. Kutter, "Recent developments in detection for microfluidic
systems". Electrophoresis, 2004. 25(21-22): p. 3498-3512.
Kricka, L.J., et al., "Fabrication of plastic microchips by hot embossing". Lab on a Chip, 2002.
2(1): p. 1-4.
Truckenmuller, R., et al., "Low-cost thermoforming of micro fluidic analysis chips". Journal of
Micromechanics and Microengineering, 2002. 12(4): p. 375-379.
248
Fabricating Microstructures on the Heat Exchangers of Pressurized
Water Reactors Used in Naval Propulsion Systems
Samuel Ibekwe1, Guoqiang Li1,2, ChangGeng Liu3,Su-Seng Pang2, KaYang Wang3, Kun
Lian3
1
Mechanical Engineering Department, Southern University and A&M College, 324 PBS
Pinchback Hall, Baton Rouge, LA70813
2
Mechanical Engineering Department, Louisiana State University, CEBA, Baton Rouge,
LA70803
3
CAMD/LSU, 6980 Jefferson Hwy. Baton Rouge, LA70806
Tel:225-578-9341; Email: [email protected]
Summary
Recently funded through DOE/NNSA professors from Southern University, LSU and
CAMD will explore the possibilities of using High Aspect Ratio Metal Microstructures
for building and integrating highly efficient heat exchangers for use in Pressurized Water
Reactors (PWRs). This contribution briefly introduces into the need for these heat
exchangers and the research planned.
Introduction
The Pressurized Water Reactors (PWRs) were originally developed for naval
propulsion purposes, and then adapted to land-based applications. It has three separate
cooling systems: the reactor coolant system, the steam generator, and the condenser. The
reactor heats the water that flows past the fuel assemblies from a temperature of about
5300 F to a temperature of about 5900 F. Pressure is maintained at approximately 2250 psi
by a pressurizer connected to the reactor coolant system. The water from the reactor is
then pumped to the steam generator through tubes. Coolant water absorbs the heat from
these steam generator tubes, and converts it into steam. The steam then passes through to
the turbines, which is connected to and turns the generator. The steam from the turbines
condenses in a condenser. Fig. 1 illustrates the whole cooling system. The reactor coolant
system is expected to be the only one with radioactive materials in it.
249
Area of interest
Fig. 1: Schematic of PWR coolant systems [1]
The Steam Generator (marked as yellow area in Fig. 1) where the radioactive reactor
cooling system water enters at the bottom, flows through small (1/2-inch
diameter) inverted U-tubes. The water loses its heat as it passes through the U-tubes to
the non-radioactive water outside the tube. Non-radioactive feedwater enters through the
nozzles at the mid-height of the steam generator at a temperature of about 4250 F. The
water flows downward outside a wrapper sheet to the area just above the tubesheet where
the water turns and flows upward past the U-tubes. The water temperature increases and
it turns into steam. A moist steam at about 510-5470 F with pressure of 720-1005 psi is
produced. The moist steam travels upward to steam separators (chevron separators and
swirl vanes) which allow 99.75% purity steam to pass through the steam generator and
the remaining water is directed back to the lower part of the steam generator. The
function of the steam generators is to transfer the heat from the primary coolant to the
secondary feedwater to generate steam for the turbine generator set. Steam generators for
the PWR design are shell and tube heat exchangers with high-pressure primary water
passing through the tube side and lower pressure secondary feedwater as well as steam
passing through the shell side. Therefore, increasing the efficiency of heat exchanger is a
key issue in improving the design of steam generator.
It is well known that larger heat exchanger interface will dramatically increase heatexchanging efficiency. Heat transfer augmentation by pin-fins can be several folds as
compared to the configurations without them. Any improvement in the efficiency of the
heat exchanger and reduction in their size would therefore directly translate into
economic benefits [2]. As compared to macroscale structures, microstructures have
higher surface area to volume ratio. Using microfabrication techniques, such as LIGA,
micro-molding or electroplating, some special microstructures can be fabricated around
the tubes in the heat exchanger of PWR to increase the heat-exchanging efficiency and
reduce the overall size of the heat-exchanger for the given heat transfer rates.
250
According to high fidelity simulations of the thermal transport in the entire system,
optimal design of microstructure patterns and layouts can be worked out.
Current State of Research: Heat transfer applications in Microstructures
Figs. 2 and 3 are the concept drawing of proposed approach of this research. It is
well documented in the past research works [3-11] that the presence of a pin fins array in
a channel enhances the heat transfer significantly.
(a)
(b)
Figs. 2: a) An assembly of micro pin fins to enhance the surface heat transfer, b) A
periodic module of such pin fins to simplify analysis [2].
Such enhancement in the heat transfer behavior is mainly due to (a) the increase in the
wetted surface area available to heat transfer, and (b) the increase in higher convective
heat transfer coefficients because of higher turbulence and mixing. Several fundamental
researches have been done in the past in studying the effects of fin geometrical
parameters, array orientation of fins [12-13], effect of fin shape [14], effect of lateral flow
ejection in pin fin channels [15], and, effect of gap atop an array of fins [16]. Over the
last decade, driven by the rapidly increasing heat dissipation predicament involving
microprocessors, numerous investigations have been conducted on forced convection in
microchannels concerning both single phase [17-20] and boiling (two-phase flow) [2125].
251
(a)
(c)
(b)
Fig. 3: Different patterns of microstructures around cylinder surface (CAMD team:
include also the zoomed circular and square sections. (a) Blade shape, (b) Round posts,
(c) Square posts
Utilization of microfabcrication technologies in the heat exchangers has been limited
so far in the electronics cooling [26]. Miniaturization of the heat exchanger component
was a requirement in the electronics cooling area. Volumetric heat exchanging capacity
as well as efficiency of these components had to match the increasing specific heat
generation rates by the high speed processors. In the naval propulsion systems, the
miniaturization of any system component translates into lowering of the payload for the
same amount of available energy produced. In this research effort, microfabrication of the
pin fins on the heat exchanger tubes in PWR is proposed to enhance the specific capacity
of the heat exchanger.
Research Objectives and Goals
The proposed research is consistent with DOE/NNSA’s current research mission of
“providing the United States Navy with safe, militarily effective nuclear propulsion
plants and to ensure the safe and reliable operation of those plants; and also
supporting United States leadership in science and technology”. The ultimate goal of
this project is to develop the innovative technology and knowledge for economic
exploration of novel microfabrication techniques (specifically LIGA based micromolding
techniques) for producing micromechanical structures using complex engineered
materials that can be successfully utilized in pressurized water reactors of the Naval
Propulsion Systems and hence could contribute to enhancement of its heat transfer
properties, operating efficiency and reduction of the overall payload. In particular, the
252
research objective is to develop novel processing routes for fabricating microstructures in
complex engineered materials that can have good performances in extreme high pressure
and elevated temperature by unifying (a) the LIGA expertise, (b) electroplating
complicated microstructures, (c) high fidelity simulations of the thermal transport in
complex systems, (d) microsample testing, (e) design optimization, and, (f)
comprehensive microscopic and macroscopic structural properties evaluation of the
proposed novel structures.
•
•
•
•
The specific interrelated research and educational tasks proposed are:
Development of microfabrication techniques for producing prototype
micromechanical structures in complex engineered materials:
Research Aspect: Employment of LIGA processes on curved surfaces is still in the
state of infancy. The microfabrication process for curved surfaces
will involve development of novel flexible masks and rotating
substrates.
Education Aspect: The students will be trained at CAMD research facilities to
microfabricate simple features using LIGA techniques. They will
also participate in the summer workshops offered at CAMD.
Employment of optimal fabrication parameters and surface processing techniques to
increase mechanical properties of microstructures under extreme high
pressure/temperature:
Research Aspect: Material selection processes for such harsh environments (high
pressure and temperature) are well known for macroscale
structures. However, such implications for microstructures remain
to be investigated.
Education Aspect: The students will be trained at LSU as well as SU through their
undergraduate and graduate theoretical courses and lab works in
the areas of Material Science. The course work projects would
also involve usage of CAMD facilities for material selection and
design.
Simulation of the thermal transport and heat transfer behavior in complex systems:
Research Aspect: Multiscale calculations that involve length scales spanning from
the microstructure pin-fin dimensions to the overall heat
exchanger dimensions pose several computational and algorithmic
challenges. Applications and numerical algorithms to address such
multiscale issues will be investigated.
Education Aspect: The students will be trained through workshops and short courses
on the simulation techniques and software packages for heat
exchanger problems.
Optimal design for the geometry and arrangement of the microstructures in order to
achieve maximum efficiency:
Research Aspect: Thermodynamic analysis and design optimization of complex pinfin structures in the heat-exchanger systems has been done only at
the macroscopic details. Such analyses that integrate the
microscale to the overall system are rare.
253
Education Aspect: The students will be educated on the numerical optimization,
design and thermodynamic analysis tools through undergraduate
and graduate coursework offered at SU and LSU.
• Experimental techniques for the local material strength behavior of microstructures
(pin fins) and the global structural properties of the overall system:
Research Aspect: Such experimental techniques involve characterization of the
fabricated prototype structures, e.g. measurement of the
displacement and strain on micromechanical systems,
quantification of fatigue properties etc.
Education Aspect: The students will learn various experimental methods to
determine mechanical strength of structures (both macro-scale and
microscopic level) at SU, LSU and CAMD experimental facilities.
Research efforts in the future will explore several fabrication techniques to produce
microstructures around the cylinder surfaces. All these processing methods will be tested
and the optimal one will be selected for final prototypes fabrication.
• Rotating substrates: As a similar processing procedure mentioned above for
microsample fabrication, the microstructure patterns on the cylinder surfaces will be
produced. The critical difference is that when the pattern transfers from the mask to
the substrates, the substrates will be rotated at a certain speed, so that all the round
surfaces will be exposed to X-ray (for X-ray LIGA) or UV radiation (UV-LIGA).
After pattern development, the substrates with pattern transferred will be electroplated
with pure Ni or Ni-based alloys, such as Alloy 600, Kovar, or Invar.
• Flexible mask: By selecting soft polymer film with Au patterns as masks, such as
Kapton (for X-ray) or Maylar (for X-ray and UV light), the mask will be wrapped
around the cylinder surfaces and X-ray or UV light will be used to expose the
photoresist through the mask. Finally the microstructure patterns will be transferred
onto the cylinder surfaces.
• Microimprint: A flat master with microstructure patterns will be fabricated first, and
then an ink such as a photoresist is sprayed onto the master and the tube is rotated
along the master. Correspondingly the microstructure patterns are transferred onto the
cylinder surfaces of the tube.
BIBLIOGRAPHY AND REFERENCES
1. http://www.nrc.gov/, accessed June, (2005).
2. F.P. Incropera and D.P. DeWitt, “Introduction to heat transfer,” 3rd Edition, John
Wiley & Sons Inc., (1996).
3. B.A. Brigham, “The Effect of Channel Convergence on Heat Transfer in a Passage
With Short Pin Fins”, NASA-TM-83201, (1984).
4. M.K. Chyu, “Heat Transfer and Pressure Drop for Short Pin-Fin Arrays with PinEndwall Fillet”, Journal of Heat Transfer, 112, pp. 926-932, (1990).
5. M.K. Chyu, Y.C. Hsing, T.I-P. Shih, V. Natarajan, “Heat Transfer Contributions of
Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition
Modeling”, Journal of Turbomachinery, 121, pp. 257-263, (1999).
6. M.K. Chyu, C.H. Yen, W. Ma, T. I-P. Shih, “Effects of Flow Gap Atop Pin
Elements on The Heat Transfer from Pin Fin Arrays”, Presented at the International
Gas Turbine & Aeroengine Congress & Exhibition, Indianapolis, June 7-10, (1999).
254
7. S.C. Lau, J.C. Han, Y.S. Kim, “Turbulent Heat Transfer and Friction in Pin Fin
Channels With Lateral Flow Ejection”, Journal of Heat Transfer, 111, pp. 51-58,
(1989).
8. D.E. Metzger, C.S. Fan, S.W. Haley, “Effects of Pin Shape and Array Orientation
on Heat Transfer and Pressure Loss in Pin Fin Arrays”, Journal of Engineering for
Gas Turbines and Power, 106, pp. 252-257, (1984).
9. D.E. Metzger, R.A. Berry, J.P. Bronson, “Developing Heat Transfer in Rectangular
Ducts With Staggered Arrays of Short Pin Fins”, Journal of Heat Transfer, 104, pp.
700-706, (1982).
10. D.A. Olson, “Heat Transfer in Thin, Compact Heat Exchangers With Circular,
Rectangular, or Pin-Fin Flow Passages”, Journal of Heat Transfer, 114, pp. 373382, (1992).
11. G.J. VanFossen, “Heat Transfer Coefficients for Staggered Arrays of Short Pin
Fins”, Journal of Engineering for Power, 104, pp. 268-274, (1982).
12. M.K. Chyu, “Heat Transfer and Pressure Drop for Short Pin-Fin Arrays with PinEndwall Fillet”, Journal of Heat Transfer, 112, pp. 926-932, (1990).
13. M.K. Chyu, Y.C. Hsing, T.I-P. Shih, V. Natarajan, “Heat Transfer Contributions of
Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition
Modeling”, Journal of Turbomachinery, 121, pp. 257-263, (1999).
14. M.K. Chyu, C.H. Yen, W. Ma, T. I-P. Shih, “Effects of Flow Gap Atop Pin
Elements on The Heat Transfer from Pin Fin Arrays”, Presented at the International
Gas Turbine & Aeroengine Congress & Exhibition, Indianapolis, June 7-10, (1999).
15. S.C. Lau, J.C. Han, Y.S. Kim, “Turbulent Heat Transfer and Friction in Pin Fin
Channels With Lateral Flow Ejection”, Journal of Heat Transfer, 111, pp. 51-58,
(1989).
16. S.C. Arora and W. Abdel-Messeh, “Characteristics of Partial Length Circular Pin
Fins As Heat Transfer Augmentors for Airfoil Internal Cooling Passages”, Journal
of Turbomachinery, 112, pp.559-565, (1990).
17. W. Qu, G. Mala, L. Dongqing, “Pressure-driven water flows in trapezoidal silicon
microchannels,” Int. J. Heat Mass Transfer, 43 (3), pp. 353–364, (2000).
18. S.M. Ghiaasiaan and T.S. Laker, “Turbulent forced convection in microtubes,” Int.
J. Heat Mass Transfer, 44 (14), pp. 2777–2782, (2001).
19. X.F. Peng and G.P. Peterson, “Convective heat transfer and flow friction for water
flow in microchannel structure,” Int. J. Heat Mass Transfer, 39 (12), pp. 2599–
2608, (1996).
20. S.G. Kandlikar and W.J. Grande, “Evaluation of single phase flow in
microchannels for high flux chip cooling—thermohydraulic performance
enhancement and fabrication technology,” in: Presented at the Second International
Conference on Microchannels and Minichannels, ASME, New York, pp. 67–76,
(2004).
21. L. Zhang, J. Koo, L. Jiang, M. Asheghi, K.E. Goodson, J.G. Santiago,
“Measurements and modeling of two-phase flow in microchannels with nearly
constant heat flux boundary conditions,” J. Microelectromech. Syst., 11 (1), pp. 12–
19, (2002).
22. L. Jiang, M. Wong, Y. Zohar, “Forced convection boiling in microchannel heat
sink,” J. Microelectromech. Syst., 10 (1), pp. 80–87, (2001).
23. S.G. Kandlikar, “Fundamental issues related to flow boiling in minichannels and
microchannels,” Exp. Therm. Fluid Sci., 26, pp. 389–407, (2002).
255
24. S.G. Kandlikar, “Two-phase flow patterns, pressure drop, and heat transfer during
Boiling in minichannels flow passages of compact evaporators,” Heat Transfer
Eng., 23 (1), pp. 5–23, (2002).
25. W. Qu, I. Mudawar, “Flow boiling heat transfer in twophase micro-channel heat
sink—I. Experimental investigation and assessment of correlation methods,” Int. J.
Heat Mass Transfer, 46 (15), pp. 2755–2771, (2003).
26. Y. Peles, A. Kosar, C. Mishra, C.-J. Kuo, and B. Schneider, “Forced convective
heat transfer across a pin fin micro heat sink,” Int. J. Heat Mass Trans., In press,
(2005).
256
X-ray surface modification of silicon-containing fluorocarbon films prepared by
plasma-enhanced chemical vapor deposition
Yoonyoung Jin, Yohannes Desta, Jost Goettert
Center for Advanced Microstructures and Devices (CAMD)
Louisiana State University,
Baton Rouge, Louisiana 70806
[email protected]; PRN: IN-YJ1207
G. S. Lee
Department of Electrical Engineering
University of Texas at Dallas,
Richardson, Texas 75083
P. K. Ajmera
Department of Electrical and Computer Engineering
Louisiana State University,
Baton Rouge, Louisiana 70803
Introduction
Fluorocarbon films offer several desirable properties such as wettability, hardness,
chemical resistance, optical characteristics, and biocompatibility. In particular, it has a
low value for its dielectric constant. These films have recently gained interest not only as
potential interlayer dielectric materials for ultra-large-scale integration (ULSI) devices,
but also as surface coating materials for biomicroelectromechanical systems (BioMEMS).1.2 The x-ray irradiation method offers a unique advantage in achieving surface
modifications in localized areas of microstructures including high-aspect-ratio
microstructures (HARMST).
In the last year, x-ray surface modification of silicon containing fluorocarbon films
(SiCF) has been studied.3 Plasma-enhanced chemical vapor deposition (PECVD) is
utilized to prepare SiCF films. The PECVD process uses tetrafluoromethane (CF4) and
disilane (Si2H6; 5 vol.% in helium) as gas precursors. Surface modification of SiCF films
through x-ray irradiation are of principal interest here. The fabrication of a Ti-membrane
x-ray mask is also introduced for selective x-ray exposures.
X-ray modification
The surface modification of SiCF films via x-ray irradiation was carried out with the xray micromachining III (XRLM3) beamline at the Center for Advanced Microstructures
and Devices (CAMD) at Louisiana State University using light from the bending magnet
(Ec = 1.6 keV). A Ti-membrane x-ray mask, shown in Figs. 1(a) and 1(b), with Au
absorber patterns was fabricated in order to achieve selective surface modification. The
Ti membrane was 3 µm thick and deposited using the rf sputtering system at CAMD.
The films were exposed in contact mode with x-rays at room temperature with a He
ambient of 100 Torr. After the x-ray exposures, the surfaces were tested for hydrophilic
characteristics on the exposed area using water contact angles. Further information for
the chemical bond change study on x-ray dose is available in the Journal of Vacuum
Science and Technology A, vol. 23, No.4, Jul/Aug 2005.
257
Fig. 2(a) shows typical pictures from the measurement of sessile water-drop contact
angles before and after x-ray irradiation. The surface characteristics of SiCF films were
changed by x-ray exposure at room temperature from hydrophobic to hydrophilic. The
average contact angle of sessile water drop on as-deposited SiCF films was 95° ± 2°. The
contact angle after x-ray irradiation with dose of 27.4 kJ/cm3 was changed to 39° ± 3°.
The contact angle of sessile water drop on the film exposed at the x-ray dose of 115.4
kJ/cm3 was similar to that of 27.4 kJ/cm3. The water pattern on the selectively modified
area on the SiCF film, exposed by x-ray with a dose of 27.4 kJ/cm3 is shown in Fig. 2(b).
before
(a)
(b)
~13 µm
after
(c)
(a)
(d)
Water pattern
~8 µm
(e)
(b)
(f)
Fig. 1. Ti-membrane x-ray mask fabricated by UVLIGA process: (a) front-side view of x-ray mask, (b)
back-side view of x-ray mask, (c) results of photoresist
mold in SPR220-7 following UV lithography, (d) details
of feature shown in (c), (e) electroplated Au structures as
absorbers on x-ray mask, and (f) details of feature shown
in (e). After reference [3].
Fig. 2. (a) Typical sessile water-drop contact
angles on SiCF films before and after x-ray
irradiation at the dose of 27.4 kJ/cm3 and (b)
water pattern on the selectively modified area
of the SiCF film. After reference [3].
The water pattern was formed by dipping the exposed sample in DI water and then
withdrawing immediately. The dipping angle between the sample and the surface of the
water was maintained to be perpendicular.
Summary
Surface modifications of PECVD SiCF films for metallization compatibility via x-ray
irradiation were performed. The wet surface modification is a low cost process and is
suitable to modify a large surface area. It requires lithography for selective surface
modification. This makes it difficult to modify sidewall surfaces of high-aspect-ratio
structures (HARMST). Because of the penetrating nature of x-rays, unlike the wet
chemical treatment, x-ray irradiation affects both the surface and the bulk of the
irradiated film. This aspect of x-ray irradiation can be exploited in HARMST MEMS
258
fabrication technology. With x-rays, it is possible to modify selective areas on the
sidewalls of conformal-deposited SiCF film, especially for HARMST MEMS. The x-ray
modification of SiCF films has a high potential for application in MEMS technology,
such as metallization on three-dimensional structures for a bio-chip and self-assembling
of nanoparticles on hydrophilic surfaces, among others.
References
1. K. Endo and T. Tatsumi, Jpn. J. Appl. Phys., Part 1, 37, p1809 (1998).
2. B. Cruden, K. Chu, K. Gleason, and Ambients, J. Electrochemical Society 146 (12), p4597 (1999).
3. Y. Jin, Y Desta, J. Goettert, G. Lee and P. K. Ajmera, J. Vac. Sci. Technol. A., 23 (4) (2005) pp666-670.
259
Fabrication of a Polymer Nano-Composite by X-ray Lithography
Fareed Dawan1,2), Yoonyoung Jin1), Jost Goettert1), Samuel Ibekwe2)
1) Center for Advanced Microstructures and Devices
Louisiana State University and A & M College
6980 Jefferson HWY., Baton Rouge, La., 70806
[email protected], PRN: IN-FD0301
2) Department of Mechanical Engineering
Southern University and A & M College
324 PBS Pinchback Hall, Baton Rouge, La., 70813
Introduction
Polymer nano-composites (PNCs) have, in the past decade, emerged as a new class of
materials due to much improved mechanical, thermal, electrical and optical properties as
compared to their macro- and micro-composites. Recently, PNC technology has been
moved quickly from the mechanical enhancement of the neat resin to multi-functional
applications such as conductive PNCs, microstructures, sensors [1] and actuators [2].
However, there is the challenge in the integration of multi-functional PNC components
into micro-electro-mechanical systems (MEMS). This issue is crucial for low cost, high
precision and high performance PNC-MEMS, along with the traditional issues that are
solely on the mechanical enhancement of the neat resin or the direct replacement of
current filler technology [3, 4].
In the last year, X-ray micromachining of PNC material was initiated for functional
structures for MEMS applications. PNC material was developed for and patterned by Xray lithography, and characterized for its mechanical and structural properties. The
reinforcement component of the composite was carbon black and the polymeric matrix
was SU-8.
Material Selection
Considerations for PNC material selection for X-ray fabrication are reinforcement
particle size and dispersion, X-ray sensitivity, and polymeric viscosity. The PNC consists
of carbon black as the reinforcement and SU-8 5 as the polymeric matrix. Carbon black is
an allotrope of carbon made from the thermal decomposition of acetylene. This form of
carbon has low electrical resistivity, an average particle size of 46 nm, and a large surface
area of 80 m2/g suggesting that to impart its mechanical, thermal, and electrical properties
in a polymeric matrix requires only a low weight percentage. The thermoset polymeric
matrix material, SU-8 5, is a negative photoresist and one of several SU-8 formulations.
The fully cured SU-8 is capable of forming high aspect ratio microstructures for micromechanical parts or bio/chemical resistive structures [5-7].
Sample Preparation, Fabrication and Characterization
The synthesis of the PNC was done by hand mixing carbon black particles into SU-8 5
resin. The composite was then pasted onto a titanium dioxide coated silicon wafer and
soft baked. Pattern exposure by X-rays required the fabrication of an X-ray mask. The Xray mask was fabricated from a graphite membrane, and the PNC was exposed at the
XRLM-2 beam line. Following the exposure, the PNC layer was post-baked and
developed. Preparation of the PNC samples for mechanical testing required the removal
of the samples from the substrate. This was done by Si etching.
Stress-strain
260
characteristics, for both normal SU-8 and CB/SU-8 were tested in agreement to ASTM
standards, using dynamic mechanical analysis (DMA) in 3-point bending mode. Constant
loading was applied with varying strain percentage.
Results
In a first study [8], the necessity patterning PNC using X-rays became apparent after an
initial study was conducted using UV lithography on micro-sized graphite particles
within SU-8. It was observed that UV-lithography of this micro-composite was hardly
possible because of UV light scattering and reduced matrix sensitivity to UV light. This
is shown in Fig. 1. A cross-linked “cap” was formed; reduced cross-linking occurred
below this surface resulting in structural deformation and poor adhesion. Fig. 2 shows Xray lithography of the micro-composite. This resulted in complete cross-linking and
improved adhesion but poor resolution. Fig. 3 shows X-ray patterning of the CB
nanoparticle/SU-8 PNC. This resulted in straight sidewalls improved structural resolution
and an aspect ratio of 5.
5 mm dia.
100 µm width
100 µm width
Poor adhesion
500 µm height
<200 µm thick
Fig. 1. Graphite particle (particle
size: 45 µm) / SU-8 composite by
UV lithography.
500 µm height
Fig. 2. Graphite particle (particle
size: 45 µm) / SU-8 by X-ray
lithography.
Fig. 3. Nanoparticle (CB, size:
46 nm) / SU-8 by X-ray
lithography.
Figs. 4(a) and 4(b) are micrographs with low magnification from the top while a higher
magnification image at an angle using a stereomicroscope is shown in Fig. 4(c). Fig. 4(b)
shows a top-down view of fabricated PNC columns with a width of 43 µm at a pitch of
130 µm. Fig. 4(c) shows the height of the PNC columns at 100 µm.
Support substrate
PNC top
PNC sidewall surface
43 µm
130 µm
(a)
100 µm
(b)
(c)
Fig. 4. Typical X-ray machined PNC microstructures.
The elastic modulus from flexural testing of SU-8 was found to be ~3.2 GPa. The elastic
modulus of the PNC at 15 wt% of carbon black was 15.3 GPa, which is nearly 5 times
that of pure SU-8. This evidently states that the addition of carbon black increased the
elastic modulus (15 GPa) of the SU-8 matrix (3.2 GPa). This shows that the mechanical
properties of SU-8 can be significantly altered.
261
Future work
Future work will extend on the synthesis, fabrication, and the characterization of PNCs.
Synthesis study of the PNC will be directed towards controlling particle dispersion and
composite homogeneity. Fabrication of varying carbon black weight percentages in SU-8
will be conducted. This will include X-ray machining design factors such as exposure
dose optimization and structural reduction rate. Characterization of the X-ray micro
machined PNCs will involve studying mechanical, thermal, and electrical properties.
Additionally, a focus towards development of an application for the PNC in MEMS will
be given.
References
1.
2.
3.
4.
5.
6.
7.
8.
May Tahhan, Van-Tan Truong, Geoffrey M. Spinks, Gordon G. Wallace, Carbon nanotubes and
polyaniline composite actuators, Smart Materials and Structures, Vol. 12, 2003.
Brian Matthews, Jing Li, Stephen Sunshine, Lee Lerner, Jack W. Judy, “Effects of Electrode
Configuration on Polymer Carbon-Black Composite Chemical Vapor Sensor Performance, IEEE
Sensors Journal, Vol. 2, No. 3, 2002.
Zeng, Q. H., Yu, A. B., (Max) Lu, G. Q., Paul, D. R., 2005, “Clay-Based Polymer Nanocomposites:
Research and Commercial Development”, Journal of Nanoscience and Nanotechnology, Vol. 5,
pp.1574-1592.
“Polymer Nanocomposites are the Future”, Institute of Packaging Professionals, URL: www.iopp.org.
Song, Yujun; Kumar, Challa S. S. R., Hormes, Josef, 2004, “Fabrication of an SU-8 based microfluidic
reactor on a PEEK substrate sealed by a 'flexible semi-solid transfer' (FST) process”, Journal of
Micromechanics and Microengineering, 14(7), pp 932-940.
Becnel, C., Desta, Y., Kelly, K., 2005, “Ultra-deep x-ray lithography of densely packed SU-8 features:
I. An SU-8 casting procedure to obtain uniform solvent content with accompanying experimental
results”, Journal of Micromechanics and Microengineering, Vol. 15, pp 1242-1248.
Seidemann, V., Rabe, J., Feldmann, M., Buttgenbach, S., 2002, “SU8-micromechanical structures with
in situ fabricated movable parts”, Microsystem Technologies, Vol. 8, No. 4-5, pp 348-350.
Dawan, F., Jin, Y., Singh, V., Desta, Y., Goettert, J., Ibekwe, S., 2005, “Development of Conductive
Polymer Nanocomposite (Carbon Black/SU-8) Micromachining by X-Ray Lithography”, Louisiana
Materials and Emerging Technologies Conference, Louisiana Tech University, December 12-13, 2005.
262
Surface Nanostructures of Commercial Pure Aluminum by Cryogenic
Surface Mechanical Attrition Treatment
K. Y. Wang and K.Lian
Center of Advanced Microstructures and Devices, Louisiana State University,
Abstract
Commercial grade aluminum (AA 1100) plates were subjected to surface mechanical
attrition treatment (SMAT) on both side-surfaces at liquid nitrogen (LN)) and room
temperatures (RT). A layer of ultrafine-grains was obtained at the surface after 10
minutes SMAT in LN and RT. Transmission Electron Microscope examination results
showed that there are nanocrystalline microstructures with an average grain size values of
100nm and 200nm for samples after LN and RT SMATs, respectively. The
microhardness testing results of treated samples showed drastically increasing in hardness
values for both LN and RT surface mechanical attrition treated samples compared to that
of as received coarse-grained (CG) Al. The results also showed that microhardness values
of the LN sample is higher than that of the RT samples. Pin-on-disc wearing test were
performed to evaluate the effects that finalized grains on wear resistances. The friction
coefficient as well as wear rate of the LN sample are slightly lower than that of the RT
sample. The nanocrystalline formation mechanism under different treatment conditions
and their effects on wear behaviors are discussed.
1. Introduction
Mechanical attrition resulted surface severe plastic deformation (SPD) is an effective
processing method for fabricating of various ultrafine-grained structures on the material
surface. This technique imposes intense plastic strains into the surfaces of metals and
alloys. The two significant advantages over other techniques are: it has a potential for
producing large bulk samples without the introduction of any residual porosity and
contamination. Secondly, it can be easily applied to a wide range of metals and alloys.
In present study, commercial grade pure Al plates underwent the surface mechanical
attrition treatment (SMAT) process at both cryogenic and room temperatures. The
microhardness and wear resistant values of as received and processed commercial grade
pure Al samples were measured and their microstructures characterized by TEM and
SEM. The relationships between the processing parameters and resulting microstructures
as well as their mechanical properties are discussed. The mechanism of nanocrystalline
phase formation during cryogenic and room temperatures treatments is also explored.
2. Experimental Procedures
The material used in this work was commercially grade pure Al (AA 1100) rod with
chemical composition (in wt%): 0.35 Si, 0.1 Zn, 0.05 Mg, 0.05 Cu with the balance Al.
The initial grain size was determined to be about 10 µm. The rod was cut into slices of
3.75 mm diameter and 1.5 mm thick. The original sample was polished down to 600 grit
abrasive paper as the final step and washed with acetone in an ultrasonic bath for 30
minutes.
Fig. 1 is a schematic illustration of the SMAT set-up used in the present work. Spherical
304 stainless steel balls with smooth surfaces were placed in a vial that was vibrated by a
263
SPEX 8000 mixer/mill with maximum vibration frequency of close to 50 kHz and
amplitude around 10 mm. The liquid nitrogen was filled inside the vial before the process
and kept spraying on the surface of the vial during the process in order to keep the
processing temperature as low as possible. The vial’s temperature during the processes
was lower than around -190oC.
3. Results and Discussion
Surface layer microstructures of the cryogenic and room temperature SMAT treated
samples are shown in Figs. 2 (a) and (b), respectively. All these micrographs show
typical structures of Al that has undergone large amount of plastic deformation. It can be
clearly measured that the surface average crystalline size values of cryogenic and room
temperature treated samples are around 250nm and 400nm, respectively. The diffraction
pattern shows that only Al is detected in the sample without noticeable impurities. One
can see that the crystalline sizes of the samples processed at cryogenic temperature and
room temperature are very close.
Table 1 shows the results of the Knoop microhardness of the samples processed at
different conditions. One can see that the microhardness increased for the samples
mechanical attrition treated after 10 minutes at cryogenic and room temperature
compared to the original sample. For the different depth of the as-processed samples, the
microhardness near the processed surface is higher than the depth far from the surface. At
the same depth of the sample, the microhardness of the sample processed at cryogenic
temperature is higher than that of the sample processed at room temperature.
Fig. 3 shows the results of wear traces of as-received and as-processed samples at room
and cryogenic temperatures. One can see that the coefficient of friction (COF) of asprocessed sample is pretty lower before the distance of 200m. After running 200m, the
COF of as-processed is close to that of the as-received sample. But the COF of asprocessed is still lower than that of the as-received sample.
4. Conclusions
1.
The surface ultrafine-grained (around 300nm and 400nm, respectively) of CP
aluminum alloys were obtained after cryogenic temperature and room temperature
surface attrition for 10 minutes.
2. The values of the microhardness drastically increased for cryogenic temperature and
room temperature surface attrition treated samples compared to coarse-grained (CG)
Al samples. The microhardness of the cryogenic temperature treated sample is higher
than that of the room temperature treated sample.
3. The friction coefficients of the cryogenic temperature and room temperature treated
samples are both slightly lower than that of the CG Al.
264
Table 1 The Knoop Microhardness of the samples processed at different conditions
Knoop Microhrdness (GPa)
Pure Al
0.32±0.005
Pure Al processed 10min
at cryogenic temperature
0.84±0.006
Pure Al processed 10min
at room temperature
0.62±0.008
15 µm deep from the
processed surface
45 µm deep from the
processed surface
0.32±0.005
0.66±0.007
0.49±0.009
Fig. 1: Schematic illustration of the SMAT process (a) experimental set-up and (b)
localized plastic deformation in the surface layer through impaction by a ball.
Fig. 2 (a) TEM of the sample processed at cryogenic temperature and
(b)TEM of the sample processed at room temperature.
1.4
Coefficient of Friction
1.2
1
0.8
0.6
Pure Al Al2O3 pin 5mm
10cm/s
0.4
Al RM 10min A Al2O3 pin
5mm 10cm/s
0.2
Al LN 10min A Al2O3 pin
5mm 10cm/s
0
0
100
200
300
400
500
600
Sliding Distance (m)
Fig. 3: Friction coefficient as a function of sliding distance.
265
Microfabrication
External User Reports
266
Portable Coordinate Measuring Tool
M. Feldman and L. Jiang, Department of Electrical and Computer Enginering,
Louisiana State University, Baton Rouge, LA 70803-5901,
[email protected], [email protected].
Transparent wafers were prepared by spin coating 1.5 microns of
poly(methylmethacrylate) (PMMA) resist from a toluene solvent. The resist
also contained a Coumarin dye that strongly absorbed blue light but was
transparent to red light. The wafers were patterned using x-ray lithography at
CAMD’s XRLM2 beamline.
Fig. 1. Arrangement of the transparent wafer in the immersion microscope.
The wafers were viewed in an immersion microscope (Fig. 1) in both
transmitted red light and reflected blue light. In blue light the patterns on the
wafers were highly visible (Fig. 2). However, in red light the resist was both
transparent and index matched by the immersion oil, so that an underlying
grating was visible, but the pattern itself could not be seen (Fig. 3).
By capturing video frames from a camera mounted on the microscope the
grating could be used to make precise measurements of the separation
between features in the pattern. A precision of less than 1 nm was
demonstrated.
267
Fig. 2. Image of the dyed PMMA resist taken in reflected blue light. The
separation between features was measured as 9967 ± 1 nm.
Fig. 3. Image of the 1.1 micron grating taken in transmitted red laser light
(633 nm). Only the illumination was changed between the images in Figure 2
and Figure 3. The horizontal “lines” are an unrelated interference artifact.
268
CAMD project title: Microfluidic platforms for genetic-based analysis
Contributing authors: Li Zhu, Pradeep Khanal, Yohannes Desta, Proyag Datta, Jifeng Chen, Donald
Patterson, Mateusz Hupert, Hamed Shadpour, Jost Goettert, Dimitris Nikitopoulos, and Steven A. Soper
Department of Chemistry, Center for Advanced Microstructures and Devices, and Center for BioModular
Multi-Scale Systems, Louisiana State University, Baton Rouge, LA 70803
1. High-throughput microchip capillary array electrophoresis (µ-CAE) system
We are currently developing polymer µ-CAE devices for high throughput sequencing of DNA
samples. In the first approach we have designed and fabricated a 16-channel µ-CAE unit. The critical
attribute of DNA sequencing device is capability to obtain a single base-pair resolution and long (>500
base-pair) read lengths. This can be usually achieved by providing long separation microchannels.
Typically, the microchannels are layout in the serpentine fashion in order to fit long channel into limited
space of microfluidic chip. It has been shown, however, that the separation efficiency can be compromised
with each turn of the microchannel due to sample band spreading. In order to provide a long separation
length and minimize number of microchannel turns we have designed and fabricated a large area (6”
diameter) mold insert (LAMI) using LiGA. A direct exposure of the substrate with dimensions larger than
4” is not possible at CAMD X-ray beam line. The exposure can be achieved by using a rotate-and-repeat
technique. This technique can be used for symmetrical designs and involves use of standard format X-ray
mask with only part of the design present. The mask is repeatedly used to expose X-ray photoresist over the
whole substrate. To aid with alignment process for each exposure we have designed and built a special
exposure unit. It allowed us to achieve 15 µm positional accuracy between individual exposures on the 6 ”
substrate.
Photoresist (PMMA)
Stainless steel substrate
(two levels)
a)
X-ray
radiation
First exposure
X-ray mask
Cathode Capillary input
Development
b)
Alignment
mark
Rotate-and-repeat
Second, third and
fourth exposures
(each followed by
development)
Common anode
c)
Electroplating of
nickel
Mold insert
(nickel structures
welded to steel disc)
Figure 1. Schematic diagram of LAMI fabrication using
rotate-and-repeat technique.
Figure 2. Layout of 16-channel micro-electrophoresis chip. (a)
Schematic of a 16-channel microchip. (b) Detailed diagram of a
single pair of channels. (c) X-ray mask for rotate-and-repeat
exposure.
269
Future directions: Practical application of hot-embossed PMMA 16-channel µ-CAE devices for
sequencing DNA samples.
2. Electrokinetically synchronized polymerase chain reaction microchip fabricated in polycarbonate
We have developed a novel method for DNA thermal amplification using the polymerase chain
reaction (PCR) in an electrokinetically driven synchronized continuous flow PCR (EDS-CF-PCR)
configuration that can be carried out in a microfabricated polycarbonate (PC) chip. The synchronized
format allowed patterning a shorter length microchannel for the PCR compared to nonsynchronized
continuous flow formats, permitting the use of smaller applied voltages when the flow is driven electrically
and also allowed flexibility in selecting the cycle number without having to change the microchip
architecture. A home-built temperature control system was developed to precisely configure three
isothermal zones on the chip for denaturing (95°C), annealing (55°C), and extension (72°C) within a
single-loop channel. DNA templates were introduced into the PCR reactor, which was filled with the PCR
cocktail, by electrokinetic injection. The PCR cocktail consisted of low salt concentrations (KCl) to reduce
the current in the EDS-CF-PCR device during cycling. To control the EOF in the PC microchannel to
minimize dilution effects as the DNA “plug” was shuttled through the temperature zones, Polybrene was
used as a dynamic coating, which resulted in reversal of the EOF. The products generated from 15, 27, 35,
and 40 EDS-CFPCR amplification cycles were collected and analyzed using microchip electrophoresis
with LIF detection for fragment sizing. The results showed that the EDS-CF-PCR format produced results
similar to that of a conventional block thermal cycler with leveling effects observed for amplicon
generation after 25 cycles.
270
Figure 3. Diagrammatic principle of electrokinetic synchronized cyclic
continuous flow PCR process. (a) Sample injection. A DNA (target) was
filled into reservoir 5, and a voltage was applied to the electrodes in
reservoirs 5 (GND) and 6 (+HV). Sample moved across the reactor
channel to fill the offset T injector. (b) Sample cycling. One cycle
included four steps: (1) a voltage was applied to the electrodes in
reservoirs 1 (GND) and 3 (+HV) moving the DNA plug from the bottom
channel to right channel; (2) a voltage was applied between reservoirs 2
(GND) and 4 (+HV) moving the sample from the right to the top
channel; (3) the voltage was then applied between reservoirs 3 (GND)
and 1 (+HV) moving sample from the top to the left channel; (4) the
voltage field was then applied between reservoirs 4 (GND) and 2 (+HV)
causing the sample to move to its starting position. The injection voltage
was 800 V, and the cycling voltage was 1.5 KV.
Figure 4. Electropherograms of PCR products and PCR
markers. (a) Separation of a 500-bp PCR product that was
collected from the EDS-CF-PCR chip. (b) Electropherogram of PCR markers using PMMA microchip. The
migration time of the 500-bp PCR product was 228 s, and
the migration time of a 500-bp DNA marker was 225 s.
Future directions: Fabrication of the EDS-CF-PCR devices with on-chip conductivity detection for realtime monitoring of PCR reaction.
Reference: Chen, J.; Wabuyele, M.; Chen, H.; Patterson, D.; Hupert M. L.; Shadopour H.; Soper, S. A.
Analytical Chemistry 2005, 77(2), 658.
271
MICROFABRICATED CELL SENSOR
Dr. Fred Lacy, Nikhil Modi, Dr. Pradeep K. Bhattacharya
Southern University and A&M College
Pinchback Hall, Room 415
[email protected]
PRN: SU-FL0904
Summary: The goal of this project is to evaluate microcantilever beams composed of
thin films of Lead Zirconium Titanate (PZT) and Platinum, and determine its
performance in a mechanical and microfluidic environment. The structures will function
in different modes of operation and will be designed to detect E. Coli bacteria cells.
Computational analysis is used to determine the sensitivity of these devices in different
modes of operation. This device is evaluated from a fluid flow and mechanical
perspective. The calculations of fluid pressures and velocities inside the microfluidic
chamber provide insight on design optimization of the device as well as process flow for
fabrication. Initial steps have been performed to fabricate this microstructure using
cleanroom equipment and the outcome of that effort is reported.
Use of cleanroom equipment: The only CAMD machines required for the project were
equipment in the cleanroom. Specifically, equipment was used for photolithography and
fabrication of masks (also for optical lithography). Equipment used included the
Headway Research PWM 101 Light Duty Photoresist Spinner, Mann 3600 Pattern
Generator, M326 Mechanical Convection Oven, Nikon Optiphot-88 Optical
Microscope/Image Capture, 6’ VA Polypropylene Chemicals hood, Oriel UV Exposure
Station, and Tencor Alpha-Step 50 Surface Profiler.
Results & Conclusions: A computational analysis of microcantilevers as detectors in a
microfluidic environment has been performed. A piezoelectric substance, PZT, has been
deposited in thin film form on Si substrates, resulting in a Zr:Ti stoichiometric
composition of about 61:39 in the deposited films. The piezoelectric constants of the thin
film demonstrate that improvement of the composition layers is needed. Masks for
photolithography were fabricated and experiments show that it is possible to fabricate
micro sized cantilevers for detection of bacteria cells.
Additionally, a study of the mechanical properties of the detectors has been performed.
Different modes of detection have been studied. An analysis of the physical properties of
a micro-environment that houses these detectors has been performed, and a procedure for
the fabrication of the device has been formulated. The computational study shows that
microcantilevers provide a highly sensitive method of detection of cells.
In conclusion, it should be noted that the experiments performed to calculate pressure and
velocity values associated with fluid flow can be used to study adhesion coefficients of
immobilization agents with binding analytes. Another byproduct of the study is the
significance of a dynamic pressure load on the detection devices and its effect on the long
term functioning of the device. Knowledge of these subsets of the study of
microcantilevers can lead to fabricated devices with greater reliability in adhesion and
optimization of the engineered device. Assuming conservative values for the amount of
forces required to dissociate analytes from the immobilizing agents deposited on
272
cantilevers, calculations shown that reasonable inflow rate for fluid flow into the
microfluidic chamber will not dissociate the adhered cell. Therefore, once these devices
(i.e., microcantilevers in microfluidic chambers) are completely fabricated, they should
make reliable bacteria detection devices.
References
Resonance frequency based micro-oscillator, Ilic, B., Czaplewski, D., Zalalutdinov, M.,
and Craighead, H.G., Neuzil, P., Campagnolo, C., Batt, C., J Vac Sci Tech B 19 (6),
Nov/Dec 2001
Process and Fabrication of a PZT Thin Film Pressure Sensor, Zakar, E., Dubey, M.,
Piekarski, B., Conrad, J., Piekarz, R., Widuta, R., 46th International Symposium,
American Vacuum Society, Oct 1999
273
Fabrication of Patterned 1D Nanostructures Based on Photolithography
Project Number: PRN UNO-FL0706
PI: Feng Li
Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148 Email:
[email protected]; Tel: 504-231-4964
A procedure to fabricate patterns of nanowire arrays based on photolithography and
electrochemical deposition in the pores of anodic alumina membrane has been developed
successfully. After the pores of AAM was modified with photoresist and opened
selectively through photolithography, the porous membranes were converted into
microelectrode to direct the growth of patterns of metal nanowire arrays. The optimized
experimental parameters have also been investigated to control the structures of patterned
nanowire arrays. One of the advantages of our technique developed is patterns of metal
and other nanowire array can be produced at room temperature. Due to the pore structure
of AAM can be controlled conveniently, we can also tune the structure of nanowire in the
pattern together with electrochemical deposition.
A paper is in preparation.
Collaboration at CAMD: Dr. Changgeng Liu
References:
1. Feng Li, Xavier Badel, Jan Linnros and John B. Wiley, Adv. Mater. 2006, 18, 270.
2. Feng Li, Xavier Badel, Jan Linnros and John B. Wiley, Journal American Chemical
Society, 2005, 127, 3268.
3. Feng Li and John B. Wiley, Journal of Materials Chemistry, 2004, 14, 1387.
4. Feng Li, Jibao He, Weilie Zhou and John B. Wiley, Journal of the American
Chemical Society, 2003, 125, 16166.
5. Feng Li, Lianbin Xu, Weilie Zhou, Jibao He, Ray H. Baughman, Anvar A.
Zakhidov and John B. Wiley, , Advanced Materials, 2002, 14, 1528.
274
Developing Molding Replication Technology for Metal-based HighAspect-Ratio Microscale Structures (HARMS)
W.J. Meng, J. Jiang, D.M. Cao
Mechanical Engineering Department, Louisiana State University
Baton Rouge, Louisiana 70803, USA, [email protected], PRN: ME-WM4172
Commercial realization of nontraditional microscale devices and systems, such as microchemical-reactors[1], micro-heat-exchangers[2], and micro-electromagnetic-relays[3],
demands fabrication technologies which can achieve economical mass production of
high-aspect-ratio microscale structures (HARMS) made of metals or ceramics. Al-based
HARMS, by virtue of its favorable combination of thermal conductivity and density, are
important for heat transfer applications. The construction of electromagnetic
microdevices, on the other hand, requires fabrication of Ni- or Fe- based HARMS.
The LiGA approach, combining deep lithography (Lithographie), electrodeposition
(Galvanoformung), and molding replication (Abformung) [4], represents an important
strategy for economical fabrication of metal-based HARMS. We have previously
explored surface engineering of microscale mold inserts by conformal deposition of
nanostructured ceramic coatings over high-aspect-ratio microscale features[5, 6]. With
surface-engineered, microscale, metallic mold inserts, successful HARMS replication by
high temperature compression molding was demonstrated in Pb and Zn[7], as well Al[8].
The successful molding replication of Al-based HARMS, to our knowledge, is a first in
the LiGA field. Alternative fabrication technologies for metal-based HARMS such as
micro-powder-injection-molding[9] and micro-casting[10] involve heat treatments and
multiple processing steps, which can lead to reduced densities and dimensional
inaccuracies. Other subtractive fabrication technologies, such as micro-milling[11] and
laser micromachining[12], are serial in nature and have low production throughput. In
comparison, replication of metal-based HARMS from microscale inserts by compression
molding is faster and simpler, and therefore holds potential advantages in production
throughput and cost.
Typical microscale mold inserts contain three-dimensional microscale features protruding
from the active surface, made up of flat top surfaces and vertical sidewalls. Successful
molding replication of metal-based HARMS involves extensive plastic deformation
within the molded metal. Instrumented micromolding of Pb has been carried out[13],
with a simple model of the mechanics of molding developed in conjunction[14]. The
process of molding starts via elastic contact between the top surfaces of the insert and the
molded metal. As molding progresses, plastic deformation occurs within the molded
metal, which flows around the microscale features on the insert and makes contact with
the feature sidewalls. To preserve fidelity of replication and prolong insert life, no plastic
deformation of the insert should occur during the molding process.
Elastic contact between a half space and a punch with a flat top surface, vertical
sidewalls, and sharp corners at the top surface-sidewall transitions typically leads to high
stress concentrations near the corner locations. These high contact stresses tend to induce
plastic deformation within the mold insert. To avoid such permanent insert damage, it is
thus desirable to fabricate inserts out of materials with high strengths at elevated molding
temperatures. In the conventional LiGA approach, mold inserts are formed by
275
electrodeposition into lithographically defined recesses in polymeric resists. Ni is the
most often used material. Electrodeposition of Ni typically leads to formation of nano/micro- crystals, which undergo significant grain growth if subsequently heated to high
temperatures. Yield strength of electrodeposited Ni microspecimens decreases by more
than 50% over the room-temperature value when the specimens are heated to
~400oC[15]. Attempts to electrodeposit alloys with increased high-temperature strengths
encounter difficulties such as limited composition range and non-optimal micro-/nanoscale structures for high-temperature use.
In 2005, we have explored a hybrid approach to fabricating refractory metal based
HARMS, with a particular emphasis on making mold inserts suitable for hightemperature molding replications. We used the micro-electrical-discharge-machining
(µEDM) technique successfully to fabricate HARMS mold inserts with simple
geometries out of Ta[16]. With additional surface engineering, such Ta inserts have been
used successfully to replicate Cu-based HARMS[16]. Replication of Cu-based HARMS,
to our knowledge, constitutes another record in the LiGA field.
In addition, we have demonstrated in 2005 parallel micropattern generation in refractory
metals with a hybrid LiGA/µEDM approach, in which multiple micropatterns are
generated on the work piece simultaneously with a lithographically-defined, patterned
electrode. The hybrid LiGA/µEDM strategy offers a credible alternative to conventional
LiGA regarding fabrication of meso- and microscale mold inserts, and enables them to
be fabricated out of high-temperature metals/alloys not achievable with
electrodeposition[17].
References:
1
.
R. Knitter, D. Gohring, P. Risthaus, J. Haubelt, Microfabrication of ceramic
microreactors, Microsystem Technologies 7, 85 (2001).
2
.
F. Arias, S. R. J. Oliver, B. Xu, R. E. Homlin, G. M. Whitesides, Fabrication of
metallic heat exchangers using sacrificial polymer mandrils, J. MEMS 10, 107
(2001).
3
.
J. D. Williams, W. Wang, Microfabrication of an electromagnetic power relay
using SU-8 based UV-LIGA technology, Microsystem Technologies 10, 699
(2004).
4
.
M. Madou, Fundamentals of Microfabrication (CRC Press, Boca Raton, Florida,
2000).
5
D. M. Cao, T. Wang, B. Feng, W. J. Meng, K. W. Kelly, Amorphous hydrocarbon
based thin films for high-aspect-ratio MEMS applications, Thin Solid Films
398/399, 553 (2001).
6
.
7
.
D. M. Cao, W. J. Meng, S. J. Simko, G. L. Doll, T. Wang, K. W. Kelly,
Conformal deposition of Ti-containing hydrocarbon coatings over LiGA
fabricated high-aspect-ratio micro-scale structures and tribological characteristics,
Thin Solid Films 429, 46 (2003).
D. M. Cao, D. Guidry, W. J. Meng, K. W. Kelly, Molding of Pb and Zn with
microscale mold inserts, Microsystem Technologies 9, 559 (2003).
276
8
.
9
.
10
.
11
.
12.
13
.
D. M. Cao, W. J. Meng, Microscale compression molding of Al with surface
engineered LIGA inserts, Microsystem Technologies 10, 662 (2004).
L. Merz, S. Rath, V. Piotter, R. Ruprecht, J. Hausselt, Powder injection molding
of metallic and ceramic microparts, Microsystem Technologies 10, 202 (2004).
S. Chung, S. Park, I. Lee, H. Jeong, D. Cho, Replication techniques for a metal
microcomponent having real 3D shape by microcasting process, Microsystem
Technologies 11, 424 (2005).
C. R. Friedrich, M. J. Vasile, The micromilling process for high aspect ratio
microstructures, Microsystem Technologies 2, 144 (1996).
M. Farsari, G. Filippidis, S. Zoppel, G. A. Reider, C. Fotakis, Efficient
femtosecond laser micromachining of bulk 3C-SiC, J. Micromech. Microeng. 15,
1786-1789 (2005).
D. M. Cao, W. J. Meng, K. W. Kelly, High-temperature instrumented microscale
compression molding of Pb, Microsystem Technologies 10, 323 (2004).
14
.
15.
16
.
17.
W. J. Meng, D. M. Cao, G. B. Sinclair, Stresses during micromolding of metals at
elevated temperatures: pilot experiments and a simple model, J. Mater. Res. 20,
161 (2005).
H. S. Cho, K. J. Hemker, K. Lian, J. Goettert, G. Dirras, Measured mechanical
properties of LiGA Ni structures, Sensors and Actuators A103, 59 (2003).
D. M. Cao, J. Jiang, W. J. Meng, J. C. Jiang, W. Wang, Fabrication of highaspect-ratio microscale Ta mold inserts with micro-electrical-dischargemachining, Microsystem Technologies, in press (2006).
D. M. Cao, J. Jiang, R. Yang, W. J. Meng, Fabrication of high-aspect-ratio
microscale mold inserts by parallel µEDM, Microsystem Technologies, in press
(2006).
277
The Design and Fabrication of Novel Micro-Instrument Platforms for
Performing Genetic Analyses
P.-C. Chen1,3, T.Y. Lee1,3, A. Maha1,3, M. Hashimoto2,3, J. Chen2,3, M. Hupert2, J. Guy2,
D.E. Nikitopoulos1,3, S.A. Soper2,3, M.C. Murphy1,2
1
- Department of Mechanical Engineering
2
- Department of Chemistry
3
- Center for Bio-Modular Multi-Scale Systems
PRN: ME MM1204, e-mail: [email protected]
Objectives: Design and fabricate a family of molded polymer instruments modules
that can be stacked together to provide the functionality for complex genetic assays.
Work has focused on the design and prototyping of a series of instrument modules, and
methods for aligning and assembling the modules. Modules for the polymerase chain
reaction (PCR), the ligase detection reaction (LDR), and passive mixing are under
development. Different approaches for fabricating structures for passive alignment of the
modules for assembly are being evaluated. Factors contributing to the tolerance of
injection molded alignment structures are also being characterized.
Results:
PCR development concentrated on two tasks: (1) Improving thermal
management of the existing spiral CFPCR module; and (2) Demonstrating an
electrokinetic shuttle PCR (EKSPCR). The CFPCR devices were hot embossed using a
LIGA-fabricated mold insert.1 Experiments had shown that yield was lower than obtained
from a comparable block thermal cycler run.2 Simulations results indicated that this
might be due to the dwell time of the PCR cocktail in each temperature zone being less
than the optimal values. The CFPCR substrate thickness was reduced to 2 mm to
decrease the thermal capacitance of the system, grooves were milled in the backside of
the substrate along the temperature zone boundaries to increase the resistance to thermal
conduction between temperature zones, and copper plates were placed between the thin
Figure 1.
Finite element simulation prediction of temperature distribution in
modified CFPCR.
278
Figure 2.
IR camera image of the temperature distribution in the modified CFPCR.
film heaters and the fluid channel cover to insure that the boundary condition above the
CFPCR channels was a constant temperature condition, not a constant heat flux. Finite
element simulations (Figure 1) predicted that this would yield sharper transitions between
temperature zones, which was confirmed by experiment (Figure 2). Amplification yield
increased by 50% at the 2 mm/s design velocity.
The CFPCR has two drawbacks a footprint of about 3 cm X 5 cm and a total channel
length for 20 cycles of about 1.5 meters. One objective of the research is to reduce the
modular devices to a size small enough to fit within the footprint of one well of a
microtiter plate (9 mm X 9 mm). The current design is not easily scalable and the fault
free fabrication of the long channel is a challenge. The shuttle PCR (SPCR) was
developed to try and overcome the limitations. There are three constant temperature
zones arranged along a short, straight channel. Instead of passing through a spiral the
cocktail is shuttled between temperature zones; in the prototype electrokinetic drive was
used. A prototype mold insert was milled in brass and hot embossed in polycarbonate at
CBM2. Initial results show lower yield than the CFPCR, which have been attributed to
flow control problems. These are being addressed.
The ligase detection reaction is a two step thermal reaction, but the nominal reaction
times for the two steps are significantly different. Preliminary results indicate that the
sufficient yield can be produced by a micro LDR device.3 A parametric study of time,
temperature, and reagent concentrations is being carried out in a hot embossed
microchamber-type LDR device. Hot embossing is being done at CAMD on the Jenoptik
machine. The results will indicate whether a microchamber or continuous flow type
reactor is more appropriate for further development.
Each of the reactor modules requires mixing of reagents and analyte. In current practice,
the mixing is done off chip and the cocktail injected into the reactor, but with stackable
modules integral mixing units will be necessary at each level. Passive mixers were
designed and evaluated. Simulations in FLUENT were used to characterize the mixing
efficiency of different candidate configurations. The most promising designs were
incorporated on a micro-milled brass insert and test devices embossed.
279
Assembly of molded polymer parts must be accomplished in order to realize the modular
approach. Two investigations are underway addressing some of the issues in assembly.
The first is a characterization of the factors affecting tolerances on feature locations and
feature geometry on injection molded parts. A test pattern consisting of different size
square microfeatures was micro-milled in brass. Tolerances of injection molding of parts
using the test pattern are being measured using the Wyko 3300 at CAMD. Measured
tolerances are being compared to simulated results obtained using Moldflow (Charlotte,
NC). In parallel, methods are being developed to make passive alignment structures that
kinematically constrain the relative motion of two assembled parts. Combinations of vgrooves and spherical ended posts can completely constrain two rigid bodies. One
approach to creating alignment structures on mold inserts is to directly mill them using a
micro-mill. Representative results are shown in Figure 3.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Figure 3.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Milled patterns for spherical post and v-groove in a brass mold insert.
1
Mitchell, M.W., Liu, X., Bejat, Y., Nikitopoulos, D.E., Soper, S.A. and
Murphy,M.C. (2003) “Design and Microfabrication of a Microchip for Continuous Flow
PCR,” in MicroFluidics, BioMEMS, and Medical Microsystems, ed. H. Becker and P.
Wolas, Society of Photo-optical Instrumentation Engineers (SPIE), Volume 4982, pp.
83-98.
2
Hashimoto, M., Chen, P.-C., Mitchell, M.W., Nikitopoulos, D.E., Soper, S.A.,
and Murphy, M.C. (2004) “Rapid PCR in a continuous flow device,” Lab-on-a-Chip,
4(6):638-645.
3
Hashimoto, M. Hupert, M.L., Cheng, Y.-W., Barany, F., Murphy, M.C., Soper,
S.A., (2005) Ligase Detection Reaction/Hybridization assays using three-dimensional
microfluidic networks for the detection of low abundant DNA point mutations, Analytical
Chemistry, 77(10):3243-3255.
280
Center for Bio-Modular Microsystems: Large Area Mold Insert (LAMI)
Fabrication
D. Park2, M. Hupert2, J. Guy2, J.-B. Lee3, M.C. Murphy1,2
1
2
- Center for Bio-Modular Multi-Scale Systems
3
– MicroNano Devices and Systems Laboratory (MiNDS)
University of Texas at Dallas, Richardson, TX 75083
PRN: CBMM-MM01061, e-mail: [email protected]
Objectives: Highly parallelized biochemical analysis is one step toward achieving high
throughput processing of patient samples for diagnostic and treatment monitoring. The
standard microtiter plate, with a 127.76 mm by 85.48 mm footprint, is used to carry out
from 96-1536 reactions in parallel using separate wells. By incorporating micro analysis
devices at each well, the capability of the format could be significantly enhanced. Low
cost replication of the microtiter plates is done through molding, so technology for
making mold inserts containing microdevices at each well of a microtiter plate is needed,
Results:
A UV-lithography based approach was used to develop the large area
mold inserts (LAMIs). Silicon wafers were chosen as the substrate due to flatness and
availability. SU-8 photoresist (MicroChem, Waltham, MA) was spin-coated on 150 mm
Si wafers with e-beam evaporated plating bases. UV exposures were done using the
Quintel aligner in the CAMD cleanroom. Development and post-bake were also carried
out at CAMD. The patterns were filled with electroplated nickel and over-electroplated in
a custom-designed electroplating bath at CBM2. The over-electroplated nickel was
planarized at the Chemical Engineering Shop and lapped at CBM2. The excess SU-8 was
removed using a plasma asher process at the MiNDS laboratory at UT Dallas. A mold
insert photograph is shown in Figure 1(a) and an SEM image of a solid phase reactor
structure at one well in Figure 1(b).
(a)
(b)
Figure 1.
(a) Photograph of 135 mm diameter over-electroplated nickel mold insert;
(b) SEM view of solid phase reactor (SPRI) pattern at each well of the microtiter plate.
281
Electrodeposition of Nanostructured Multilayers
D. Iyer1, D. Palaparti1, M.C. Henk3, E.J. Podlaha-Murphy2, M.C. Murphy1
1
2
- Department of Chemical Engineering
3
- Department of Biological Sciences
PRN: ME MM0604MT, e-mail: [email protected]
Objectives: The primary goal of the project was to understand the thermal expansion
behavior of the electrodeposited Invar-like alloy and determine if the variation of the
CTE could be modulated through the use of copper nanolayers interposed between the
Ni-Fe alloy. Initial work was done on electrodeposited posts.
Results:
X-ray lithography was used to fabricate the pattern of micro-recesses for
the multilayer micro-posts. Stock CQ-grade, high molecular weight (Vista Optics, UK)
polymethylmethacrylate (PMMA), a positive X-ray resist, was bonded to a 100 mm
diameter, copper sputtered alumina substrate using a PMMA bonding solution and fly cut
to a thickness of approximately 100 µm ± 3.5 µm. The X-ray mask, with a gold absorber
and a graphite membrane, was a 130 X 130 grid of circles with a uniform diameter of 100
µm and uniform center-to-center spacing of 300 µm. Exposures were done at CAMD.
Deposition of multilayers was achieved by pulsing currents between two levels, one to
deposit Cu and the other to deposit FeNiCu. A TEM image of the multilayers is shown in
Figure 1(a).
The coefficient of thermal expansion (CTE) for the posts was measured using a thermo
mechanical analyzer (TMA) at Stork Technimet (New Berlin, WI). Displacement was
measured over three heating/cooling cycles from room temperature to 300 oC. The asdeposited material had a negative CTE on the first heating cycle (Figure 1(b)).
Subsequent cycles produced low positive CTE’s comparable to bulk Invar, but no
evidence of transition to higher CTE due to the Curie effect at temperatures between
200 oC and 300 oC.
Figure 1.
(a) TEM image of nanolayers (dark – FeNiCu; light – Cu); (b) CTE as a
function of temperature for as-deposited materal.
282
Fabrication of Thermoelectric Arrays
A.Z. Cygan1, A. Prabhakar1, R. Devireddy1, E.J. Podlaha-Murphy2, M.C. Murphy1
1
2
- Department of Chemical Engineering
PRN: ME MM0604EN, e-mail: [email protected]
Objectives: The goal of this project is to design and fabricate an integrated array of
micro thermocouples and micro Peltier devices. The LIGA and UV-LIGA processes
provide the tools to produce small scale devices in a dense array with a vertical, low
thermal capacitance via layer to connect the instruments to the necessary electronics.
Results:
In the initial work, separate arrays of micro thermocouples and micro
Peltier elements are being fabricated to demonstrate the concepts. Individual devices in
each array are to have a center-to-center distance of 50 micrometers in order to measure
and modulate the temperature of single cells in an engineered tissue construct.
The array of micro thermocouples will be T-type thermocouples with one electrode
copper and one constantan (CuNi). Plating parameters were established using a rotating
Hull cell. Mathematical models were used to determine appropriate dimensions for the
thermocouples that would have sufficiently fast response to track freezing events. The
prototype array uses a conventional planar wiring layer, 3 m and 5 m diameter by 20
m tall electrodes to provide thermal isolation, and a junction layer. The spacing
between the two electrodes in each thermocouple is 5 m. A mask containing patterns
for various diameter posts and inter-post spacing was used first, then a set of five masks
were purchased from Advanced Reproductions (N. Andover, MA): two wiring layer
masks (one for each material), two electrode masks (one for each material), and one
junction layer mask. The wiring and junction layers will be patterned using SPR 1813
Photoresist (Rohm & Haas, Marlborough, MA) and the electrode layer with AZ 4620
(Clariant, Somerville, MA).
The test pattern was used to evaluate the alignment and exposure capabilities of the
Quintel aligner at CAMD. Structures down to 3 m diameter were successfully patterned
and aligned to within +/- one micrometer. Figure 1(a) shows representative test 5 m
diameter posts. Work is underway on fabrication of the whole array. The wiring layer and
copper posts for both 3 and 5 micrometer diameters are shown in Figure 1(b).
Figure 1.
(a) SEM images of aligned nominal 5 µm diameter posts with 5 µm
spacing; (b) Microscope image showing both wiring layers, with copper posts
283
electroplated and the holes for the constantan posts patterned but not filled. The top
structures are 5 µm diameter and the bottom structures are 3 µm.
Fabrication of micro scale arrays of thermoelectric sensors and actuators for
cryobiological applications, A.Z. Cygan, A. Prabhakar, E.J. Podlaha-Murphy, M.C.
Murphy, and R.V. Devireddy, Proceedings of the ASME IMECE 2004, Anaheim, CA,
November 15-20, 2004, IMECE2004-60920.
284
Fabrication of perforated polymer membranes
using imprinting technology
Anish Roychowdhury, Sunggook Park
Department of Mechanical Engineering and Centre for BioModular Multiscale Systems
Louisiana State University, Baton Rouge, LA 70803,
PRN: ME- SP1205, email: [email protected]
Objectives: The ability to imitate architecture of naturally existing matter economically
is important because this will provide platform for various fundamental and applied
research activities. The objective of this proposal is to develop a process for the
production of perforated polymer membranes using imprinting technology. The
perforated membrane structures can be found in many biological systems and thus have
potentials to researches on transport behavior in cell biology and separation of
substances. Such structures can also be used as components in polymer optics and
modular bioanalytic devices. In order to realize low cost production of the membrane
structures, a single step imprinting process is employed, which is combined with semi
conductor micro machining processes. The several technical challenges in this project
include developing and optimizing a series of processes starting from stamp design to
materials choice, imprinting of high aspect ratio patterns, and post- processing.
Results: The first step to realize the membrane structure is to fabricate high quality NIL
stamps with desired structures which can be repeatedly used with damage. Stamps with
microscale features were fabricated via photolithography using microfabrication facilities
at the CAMD cleanroom. After coating S1813 photoresist on a Si wafer, the Quintel UV
exposure station was used to pattern the photoresist. Subsequent deep reactive ion etching
(DRIE) to transfer the resist pattern into Si was performed at the Microelectronic
Research Center at Georgia Tech. Fig.1(a) shows a scanning electron microscope (SEM)
image for the Si stamp with pillars of 9 µm diameter and 8 µm height, where almost
vertical sidewalls and smooth surface were revealed. Using this stamp, imprinting was
performed to define hole structures in a sheet of PMMA (Fig.1(b)) which will be further
processed to perforated membrane structures by micromachining the backside of the
substrate using KOH and HF.
(a)
(b)
Fig.1. SEM images for (a) a Si stamp with pillars of 8µm depth and 9µ diameter and (b)
the corresponding imprinted PMMA using the stamp shown in Fig(a) .
285
CAMD project title: Modular Microfluidic Systems
Multi-channel Polymer Microchip Electrophoresis Devices with
Integrated Conductivity Detection
Contributing Authors: Mateusz Hupert, Hamed Shadpour, Changgeng Liu, Donald
Patterson, Jason Guy, Proyag Datta, and Steven A. Soper
Department of Chemistry, Center for Advanced Microstructures and Devices, and Center
for BioModular Multi-Scale Systems, Louisiana State University, Baton Rouge, LA
70803
High-throughput capabilities are extremely desirable in bio-separations, especially for
genetic and proteomic studies and also for determining the identity and purity of
synthesized substances used in drug discovery. We are particularly interested in the
fabrication of three-dimensional, modular architectures capable of performing series of
bioanalytical processes in parallel. This type of architecture enhances the degree of
integration of the system and also, allows for matching the preferred construction
material with the intended application of each module. Task-specific modules can be
fabricated, tested, and optimized separately before a final assembly of the modular
microsystem takes place.
Herein we report on the fabrication of multi-channel polymer microchip electrophoresis
device with integrated conductivity detection that will be eventually used as purification
module in DNA sequencing system. We have selected conductivity as a detection method
since it provides a universal detection of many analytes without the need for labeling. It is
also scalable, can be easily applied in multichannel format, and uses relatively
inexpensive instrumentation.
The microchip was fabricated in polycarbonate (PC). A high-precision micromilled brass
master was used to hot-emboss microfluidic channels into a polymer substrate.
Conductivity electrodes were patterned onto thin PC sheets using the standard
lithographic techniques (Fig. 1). These patterned PC sheets served as the coverplates for
the microfluidic channels. In order to aid in the alignment process of the microelectrodes
over the microchannel, alignment marks were fabricated on both microchip and
coverplate. The coverplates were thermally annealed to the microfluidic chip. Initial tests
involving injection of KCl solution into the microfluidic channels showed good, leakage
free seal of the microchannels, and capability of gold microelectrodes to detect
conductivity signals.
Future directions: An evaluation of the analytical performance of the multi-channel
polymer microchip electrophoresis device with integrated conductivity detection. An
application of the device in the modular DNA sequencing system.
286
Figure 1. Schematic diagram of electrode fabrication process.
Figure 2. (a) Layout of the 16-channel CEC-chip with conductivity detection (red lines). Channel width: 60
µm, channel depth: 40 µm, electrode width at detection point: 10 – 60 µm, electrode spacing: 5 – 20 µm.
(b) Detailed layout of the separation microchannel with a pair of the conductivity electrodes. (c) Optical
micrograph of PC coverplate with lithographically patterned gold electrodes. (d) Optical micrograph of the
microfluidic channel hot-embossed in PC with annealed coverplate with gold electrodes.
287
Field Emission from Multiwalled Carbon Nanotubes
Abhilash Krishna, Dept. of ECE, LSU, [email protected]
Jeong Tae Ok, Dept. of ECE, LSU, [email protected]
Bingqing Wei - Assistant professor, Dept of ECE, LSU. ([email protected])
PRN: ECE-BW1204
The primary goal of this work was to study the effects of various factors that
influence field emission from multiwalled CNTs. For the set of factors that was chosen
for investigation, a suitable field emission testing system was designed and assembled.
Temperature of the CNTs was observed to have a considerable effect on the field
emission from CNTs. Current saturation is observed at high temperatures. These findings
can prove to be critical if the field emission device is operating in conditions of high
temperature. The effects of variation in ambient pressure and changes in the background
gas species are also studied. The field emission device characteristic is found to be very
sensitive to the ambient gas pressure and more so when the gas species used was helium.
Among Ar, He and N2, it is observed that He is the most suitable for field emission based
device applications. It has been experimentally proven that aligned CNTs are far superior
to random CNTs in terms of field emission characteristics. Effect of different substrate
materials on field emission has also been examined. It has been found that metallic
substrates like stainless steel show promise of better performance. CNT growth
conditions have also been shown to influence their field emission property. Young’s
interference fringes found on the copper anode surface after field emission have been
reported. Emitter and anode degradation as a result of field emission have been observed
as part of this wok. However it is important to note that CNTs are relatively more robust
and less prone to degradation when compared to many other conventional field emitters.
These results can be applied to find a set of optimal parameters that could be used for any
field emission device design in order to get maximum field emitted current density at low
operating voltages.
288
Publications from Users in 2005
Adsorption of water on the TiO2(011)-2x1 reconstructed surface, C. Di Valentin, A.
Tilocca, A. Selloni, T.J. Beck, A. Klust, M. Batzill, Y. Losovyj, U. Diebold , J. Am.
Chem. Soc. 127, 9895 (2005).
Advanced Characterization of the Electronic Structure of MEH-PPV, D. K.
Chambers and S. Selmic, MRS Proceedings, Volume 871E, article I6.20, 2005.
Comment on “Spectral Identification of Thin Film Coated and Solid Form
Semiconductor Neutron detectors” by McGregor and Shultis, S. Hallbeck, A.N.
Caruso, S. Adenwalla, J. Brand, Dongjin Byun, H.X. Jiang, J.Y. Lin, Ya.B. Losovyj, C.
Lundstedt, D.N. McIlroy, W.K. Pitts, B.W. Robertson, and P.A. Dowben, Nuclear
Instruments and Methods in Physics Research A 536 (2005) 228-231.
Comparison of Crystalline Thin Poly(vinylidene (70%) - trifluoroethylene (30%))
Copolymer Films with Short Chain Poly(vinylidene fluoride) films, Jaewu Choi, E.
Morikawa, S. Ducharme and P.A. Dowben, Matt. Lett. 59 (2005) 3599-3603.
Crystal structures of a multifunctional triterpene/flavonoid glycosyltransferase
from Medicago truncatula, H. Shao, X. He, L. Achnine, J.W. Blount, R.A. Dixon, and
X. Wang, Plant Cell, 17(11):3141-54, Nov. 2005.
Deposition of highly hydrogenated carbon films by a modified plasma assisted
chemical vapor deposition technique, B. Shi, W. J. Meng, R. D. Evans, N.
Hershkowitz, Surf. Coat. Technol. 200, 1543-1548 (2005).
Evidence for Multiple Polytypes of Semiconducting Boron Carbide (C2B10) from
Electronic Structure, Petru Lunca-Popa, J.I. Brand, Snjezana Balaz, Luis G. Rosa, N.M.
Boag, Mengjun Bai, B.W. Robertson, and P.A. Dowben, J. Physics D: Applied Physics
38 (2005) 1248-1252.
Evidence for phonon effects in the electronic bands of granular Fe3O4, Ya. B.
Losovyj and J. Tang, Mater. Lett., 59, (2005) 3828, 3 pages.
Gas phase-dependent properties of SnO2 (110), (100), and (101) single crystal
surfaces: structure, composition, and electronic properties, M. Batzill, K. Katsiev,
J.M. Burst, U. Diebold, A.M. Chaka, B. Delley, Phys. Rev. B 72, 165414 (2005).
Ketones from Acid/Aldehyde Condensation Using Metal/CeO2 Catalysts, K.M.
Dooley, A.K. Bhat, A.D. Roy and C.P. Plaisance, Proceedings, 19th North American
Meeting, Catalysis Society, Philadelphia, 2005.
Mercury and C2B10 Icosahedra Interaction, Carolina C. Ilie, Petru Lunca-Popa,
Jiandi Zhang, Bernard Doudin, Peter A. Dowben, Mater. Res. Soc. Symp. Proc. 848
(2005) FF6.5.1-FF6.5.6.
Metal hybridization and electronic structure of Tris(8-hydroxyquinolato)aluminum
(Alq3), A.N. Caruso, D.L. Schulz and P.A. Dowben, Chem. Phys. Lett. 413 (2005) 321.
289
Mixed dissociated/molecular monolayer of water on the TiO2(011)-(2x1) surface,
T.J. Beck, A. Klust, M. Batzill, U. Diebold, C. Di Valentin, A. Tilocca, A. Selloni, Surf.
Sci. Lett. 591, L267 (2005).
Noncollinear spin states and competing interactions in half-metals and magnetic
perovskites, R. Skomski, J. Zhou, P.A. Dowben and D.J. Sellmyer, Journal of Applied
Physics 97 (2005) 10C305.
Noncovalent Functionalization of Single-Walled Carbon Nanotubes using Alternate
Layer-by-Layer Polyelectrolyte Adsorption for Nanocomposite Fuel Cell Electrodes,
R.B. Dhullipudi, Y.M. Lvov, S. Adiddela, Z. Zheng, R.A. Gunasekaran, T.A. Dobbins,
Materials Research Society Symposium – Proceedings 837, paper N3.27.1 (2005).
On the importance of defects in magnetic tunnel junctions, P.A. Dowben and B.
Doudin, in Local Moment Ferromagnets: Unique Properties for Modern Applications,
Lecture Notes in Physics 678, Springer (2005), M. Donath and W. Nolting, editors, pp.
309-326, ISBN number 0075-8450.
Photohole Screening Effects in Polythiophenes with Pendant Groups, D.-Q. Feng,
A.N. Caruso, D.L. Schulz, Ya.B. Losovyj and P.A. Dowben, J. Phys. Chem. B 109
(2005) 16382-16389.
Portable Coordinate Measuring Tool, L. Jiang and M. Feldman, J. Vac. Sci. Technol.
B 23, p. 3056, Nov./Dec. 2005.
Single crystal ice grown on the surface of the ferroelectric polymer poly(vinylidene
fluoride) (70%) and trifluoroethylene (30%), Luis G. Rosa, Jie Xiao, Ya.B. Losovyj,
Yi Gao, I.N. Yakovkin, Xiao C. Zeng and P.A. Dowben, Journ. Am. Chem. Soc. 127
(2005) 17261-17265.
Strain Induced half metal to semiconductor transition in GdN, Chun-gang Duan, R.F.
Sabiryanov, Jianjun Liu, W.N. Mei, P.A. Dowben and J.R. Hardy, Physical Review
Letters 94 (2005) 237201.
The Anomalous “Stiffness” of Biphenydimethyldithiol, D.Q. Feng, R. Rajesh, J.
Redepenning and P.A. Dowben, Applied Physics Letters 87 (2005) 181918.
The Coadsorption and Interaction of Molecular Icosahedra with Mercury, Carolina
C. Ilie, Snjezana Balaz, Luis G. Rosa, Jiandi Zhang, P. Lunca-Popa, Christopher
Bianchetti, Roland Tittsworth, J.I. Brand, B. Doudin, P.A. Dowben, Applied Physics A
81 (2005) 1613-1618.
The Electronic Structure of Oriented poly(2-methoxy-5-(2’-ethyl-hexyloxy)-1,4phenylenevinylene), David Keith Chambers, Srikanth Karanam, Difei Qi, Sandra
Selmic, Ya.B. Losovyj, Luis G. Rosa and P.A. Dowben, Applied Physics A 80 (2005)
483-488.
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The Limits to Spin-Polarization in Finite-Temperature Half-Metallic Ferromagnets,
P.A. Dowben and S.J. Jenkins. in Frontiers in Magnetic Materials, edited by Anant
Narlikar, Springer Verlag (2005) 295-325.
The structure of coral allene oxide synthase reveals a catalase adapted for
metabolism of a fatty acid hydroperoxide, M.L. Oldham, A.R. Brash, & M.E.
Newcomer, Proc Natl Acad Sci U S A 102, 297-302 (2005).
The surface and materials science of tin oxide, M. Batzill, U. Diebold, Prog. Surf. Sci
79, 47 (2005).
Theoretical study of the magnetic ordering in rare-earth compounds with facecentered-cubic structure, Chun-gang Duan, R.F. Sabiryanov, Jianjun Liu, W.N. Mei,
P.A. Dowben and J.R. Hardy, Journal of Applied Physics 97 (2005) 10A915.
Tuning surface properties of SnO2(101) by reduction, M. Batzill, K. Katsiev, J.M.
Burst, Y. Losvoyi, W. Bergermayer, I. Tanaka, and U. Diebold submitted to the Journal
of Physics and Chemistry of Solids, as part of the Proceedings of the Third Meeting of
the Study of Matter at Extreme Conditions (SMEC), May 2005.
Vibronic Coupling in the Valence Band Photoemission of the Ferroelectric
Copolymer: poly(vinylidene fluoride) (70%) and trifluoroethylene (30%), Luis G.
Rosa, Ya.B. Losovyj, Jaewu Choi, and P.A. Dowben, Journal of Physical Chemistry B
109 (2005) 7817-7820.
X-ray Absorption Spectroscopy of Ti-doped NaAlH4 at the Titanium K-edge, E.
Bruster, T.A. Dobbins, R. Tittsworth, D. Anton, Materials Research Society Symposium
– Proceedings 837, paper N3.4.1 (2005).
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Presentations from Users in 2005
Water adsorption on the ZnO(10-10) surface: an experimental and theoretical
investigation of the overlayer structure Presenter: Ulrike Diebold, International
Workshop on Oxide Surfaces, IWOX-4, Torino University (Italy) and Centre Paul
Langevin, Aussois (France), Jan. 04 - January 08, 2005.
Fabrication of microscale two-level surface-engineered mold inserts for MEMS
applications by UV-LiGA and conformal coating deposition, R. Yang, J. Jiang, W.
Wang (presenter), W. J. Meng, presented at the SPIE MOEMS-MEMS2005 Conference
on Micro/Nano Fabrication (#5717-24), January 2005, San Jose, California.
Geometric and Electronic Structure of Self-Assembled Monolayers Grown on Noble
Metal Substrates: Dodecanethiol on Au, Ag, and Pt, T. M. Sweeney, J. M. Burst, P. S.
Robbert, J. W. Hobson, S. M. Huston, C. A. Ventrice, Jr., and H. Geisler, 5th Louisiana
Conference on Advanced Materials and Emerging Technologies (LaCOMET), New
Orleans, Louisiana, January 22, 2005. (Presented by C. A. Ventrice, Jr.).
Scanning Tunneling Microscopy on Metal Oxide Surfaces (Speaker: Ulrike Diebold)
Department of Physics, Loyola University, New Orleans, LA, February 24, 2005.
Water adsorption on the rutile TiO2(011)-(2x1) surface Presenter: Andreas Klust,
Gordon Research Conference, Chemical Reactions at Surfaces, Ventura, CA, Feburary
2005.
Geometric and Electronic Structure of Self-Assembled Monolayers on Noble Metal
Surfaces, B. Hayes, H. Geisler, T. M. Sweeney, J. M. Burst, P. S. Robbert, J. W.
Hobson, S. M. Huston, and C. A. Ventrice, Jr., DARPA/UNO Advanced Materials
Research Institute Symposium, New Orleans, Louisiana, February 3, 2005. (Presented by
H. Geisler).
Growth and Properties of Oxide-supported Nanoclusters (Speaker: Ulrike Diebold),
American Chemical Society Meeting, San Diego, March 22, 2005.
Adsorption and dissociation of water at the rutile TiO2(011)-2x1 surface Presenter:
T.J. Beck, March Meeting of the American Physical Society, March 2005, Los Angeles,
CA.
Surface Electronic Structure of the Compositional Variants of SnO2(101) Presenter:
Matthias Batzill, March Meeting of the American Physical Society, March 2005, Los
Angeles, CA.
Properties of a ferromagnetic semiconductor: epitaxial Co-doped SnO2 films
Presenter: Jimi Burst, March Meeting of the American Physical Society, March 2005,
Los Angeles, CA.
292
Low Energy Electron Diffraction and Photoemission Study of Dodecanethiol on
Pt(111) and Pt(100), T. M. Sweeney, P. S. Robbert, J. W. Hobson, S. M. Huston, C. A.
Ventrice, Jr., and H. Geisler, 2005 March Meeting of the American Physical Society, Los
Angeles, California, March 24, 2005. (Presented by T. M. Sweeney).
The Effect of Arsenic Upon Thelypteris Palustris, The Common Marsh Fern by L.
Anderson and M.Walsh, March 2005 Graduate Poster Presentation.
Surface electronic structure and interface properties of the compositional variants
of SnO2(101) (Speaker: Matthias Batzill) Third meeting of the Study of Matter at
Extreme Conditions (SMEC), Miami Beach, April 17-21, 2005.
Nanoscience and Surfaces: Watching Atoms with Scanning Tunneling Microscopy
(Speaker: Ulrike Diebold) Austrian Scientists and Scholars in North America, ACSINA
2005, Vienna, Austria, April 27 – 29, 2005.
Surface electronic structure and interface properties of the compositional variants
of SnO2(101) Presenter: Matthias Batzill, CAMD Annual Users’ Meeting, April 2005,
Baton Rouge, LA.
Bimodal Pd cluster growth on the reduced SnO2 (101) surface Presenter: Bulat
Katsiev, CAMD Annual Users’ Meeting, April 2005, Baton Rouge, LA.
The Effect of Arsenic Upon Thelypteris Palustris, The Common Marsh Fern by L.
Anderson and M. Walsh, International Conference on the Biogeochemistry of Trace
Elements, April 2005 Poster Presentation (Dr. Walsh Presenter).
Surface Science Investigations of Titanium Dioxide: Relevant for Photocatalysis?
(Speaker: Ulrike Diebold) DoE/BES Catalysis Program Contractor’s Meeting, Rockville
Maryland, May 18 – 21, 2005.
The influence of oxygen composition on the surface functionality of SnO2(101)
Presenter: Ulrike Diebold, Department of Energy/Basic Energy Sciences, Catalysis and
Chemical Transformations Contractors’ Meeting, May 18-21, 2005 – Doubletree Hotel,
Rockville, MD.
Deposition of highly hydrogenated carbon films by a modified plasma assisted
chemical vapor deposition technique, B. Shi (presenter), W. J. Meng, presented at the
International Conference on Metallurgical Coatings and Thin Films (ICMCTF2005), San
Diego, May 2005.
The Adsorption of Water on Single-crystalline Metal Oxide Surfaces (Speaker:
Ulrike Diebold) 89th International Bunsen Discussion Meeting, "Chemical processes at
oxide surfaces: from experiment to theory”, Hennesee, Germany, June 15-17, 2005.
Metal micromolding: further experiments and preliminary finite element analysis,
D. M. Cao, J. Jiang, W. J. Meng (presenter), J. C. Jiang, W. Wang, presented at the HighAspect-Ratio Microscale Structures Technology (HARMST2005) conference, Gyeongju,
South Korea, June 2005.
293
Fabrication of high-aspect-ratio microscale Ta mold inserts with micro-electricaldischarge-machining, D. M. Cao, J. Jiang, W. J. Meng (presenter), J. C. Jiang, W.
Wang, presented at the High-Aspect-Ratio Microscale Structures Technology
(HARMST2005) conference, Gyeongju, South Korea, June 2005.
Structure and Stoichiometry at Metal Oxide Surfaces (Speaker: Ulrike Diebold) 8th
International Conference on the Structure of Surfaces, ICSOS-8, Munich, Germany, 1822 July 2005.
Orientation-dependent surface properties of TiO2: the rutile (011) face (Speaker:
Ulrike Diebold) ASEVA Summer School, WS-17, on Characterization and Properties of
Titanium Dioxide, Avila, Spain, July 25-27, 2005.
Effects of Physical Layout, Temperature and Pressure on Field Emission Properties
of Carbon Nanotubes, Krishna, A. Ok, J. T. and Wei, B.Q., ICMAT 2005 (3rd
International Conference on Materials for Advanced Technologies), July 3-8, 2005,
Singapore.
Prospects for Neutron Tomography and High-Speed Radiography by L. G. Butler,
C. Hubbard, D. Penumadu, ACS Natl. Mtg, Washington DC, August 28 - Sept 1, 2005.
C. Hubbard, D. Penumadu, at the Spallation Neutron Source, Oak Ridge National
Laboratory, Sept 23, 2005.
Surface Structure and Chemistry of TiO2 (Speaker: Matthias Batzill) European
Conference on Surface Science, ECOSS-23, Berlin, Germany, Sept. 4 – 9, 2005.
C. Hubbard, D. Penumadu, at the Spallation Neutron Source User Group Meeting, Oak
Ridge National Laboratory, Oct 11-13, 2005.
Surface Structure and Reactivity of Titanium Dioxide (Speaker: Ulrike Diebold)
Workshop on Opportunities in Nanocatalysis, Brookhaven National Laboratory, October
19 – 21, 2005.
Structure, defects, and adsorption on metal oxide surfaces (Speaker: Ulrike Diebold)
52nd Symposium of the American Vacuum Society, Boston, MA, Oct 5 – Nov 30, 2005.
An Atomic-Scale View of Transition Metal Oxide Surfaces (Speaker: Ulrike Diebold)
Seminar, Department of Chemistry, Princeton University, Princeton, NJ, November 8,
2005.
Surface Investigations of Pure and Doped Transition Metal Oxides (Speaker: Ulrike
Diebold) Condensed Matter Seminar, Department of Physics, University of Maryland,
November 17, 2005.
294
Seminar, Department of Applied Physics, Columbia University, New York, November
18, 2005.
Department of Materials Science and Engineering, Rutgers, The State University of New
Jersey, November 29, 2005.
Bimodal Pd cluster growth on the reduced SnO2 (101) surface Presenter: Bulat
Katsiev, American Vacuum Society, Boston, November 2005.
Tuning surface reactivity of SnO2(101): dissociative and molecular water
adsorption Presenter: Matthias Batzill, American Vacuum Society, Boston, November
2005.
Geometric and Electronic Structure of Self-Assembled Monolayers on Noble Metal
Surfaces: Dodecanthiol on Pt, Au, Ag and Cu, T. M. Sweeney, J. M. Burst, S. M.
Huston, P. S. Robbert, J. W. Hobson, C. A. Ventrice Jr., L. Powell, B. Hayes, H. Geisler,
52nd International Symposium of the American Vacuum Society, Boston ,
Massachusetts, November 1, 2005. (Presented by H. Geisler).
Fe3O4: A Half-Metal or Not?, Presenter: Jinke Tang, Iowa State University, University
of Arkansas, and University of Missouri, Kansas City, November 2005.
Phytoremediation of Arsenic Contaminated Soils by L. Anderson and M. Walsh,
Louisiana Air and Waste Management Society, November 2005 Conference Presenter.
An Atomic-Scale View of Transition Metal Oxides (Speaker: Ulrike Diebold) Seminar,
Center for Functional Nanomaterials, Brookhaven National Laboratory, December 7,
2005.
Oxides, Defects, and Surface Reactivity: What Can We Learn from Atomic-Scale
Studies? (Speaker: Ulrike Diebold) Department of Chemistry, University of Illinois at
Chicago, December 12, 2005.
Ketones from Acid/Aldehyde Condensation Using Metal/CeO2 Catalysts, K.M.
Dooley (speaker), A.K. Bhat, A.D. Roy and C.P. Plaisance, 19th North American
Meeting, Catalysis Society, Philadelphia, 2005.
Atomic Structure and Dynamics at Oxide Surfaces (Speaker: Ulrike Diebold)
Colloquium, Department of Physics and Astronomy, Rutgers, The State University of
New Jersey.
Metal micromolding with surface engineered inserts, D. M. Cao(presenter), J. Jiang,
W. J. Meng, presented at MRS’05 fall meeting (Boston), 2005.
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2005 Annual CAMD User Meeting
April 8, 2005
Schedule
Morning Session, Conference Room, CAMD, 6980 Jefferson Hwy., Baton Rouge, LA:
7:30 – 8:30
Continental Breakfast and Registration
8:30 – 9:00
Status of CAMD
Josef Hormes, CAMD Director
9:00 – 9:15
Status of Microfabrication
Jost Goettert, CAMD Director of Microfabrication
9:15 – 10:00 KEYNOTE SPEAKER
George Phillips, Professor of Biochemistry and of Computer Sciences
University of Wisconsin – Madison
“Using Synchrotron Light to Study Proteins: Trends and Examples”
10:00 – 10:30 Coffee Break
10:30 – 10:50 Fareed Dawan, CAMD/LSU
“Development of Left-Handed Meta-Material Using a UV-LIGA Process
for High Frequency Applications”
10:50 – 11:10 Recipient of the Student Award for Basic Science
Sponsored by IoP, The Institute of Physics
Jason Emory, LSU Department of Chemistry
“Single-Molecule Detection in a High Throughput, Multi-channel Micro
Device as an Approach to Analyzing DNA Point Mutations”
11:10 - 11:30 Diwakar Iyer, LSU Department of Mechanical Engineering
“Electrodeposited Nanoscale Multilayers of Invar with Copper”
11:30 – 11:50 Hamed Shadpour, LSU Department of Chemistry
“Multi-Channel PC Device with Integrated Conductivity Detector for
Analysis of Biological Samples”
11:50 – 1:00 Lunch
Afternoon Session, Conference Room, CAMD, 6980 Jefferson Hwy., Baton Rouge, LA:
1:00 – 1:20
Orhan Kizilkaya, CAMD/LSU
“Status of the Infrared Beamline”
1:20 – 1:40
Snjezana Balaz, University of Nebraska – Lincoln
“A Comparison of the Electronic Structure of Phosphacarborane and
Orthocarborane Molecular Films”
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1:40 – 2:00
Matthias Batzill, Tulane University
“Surface Electronic Structure and Interface Properties of the
Compositional Variants of SnO2(101)”
2:00 – 2:20
Jia Ma, LSU Department of Civil and Environmental Engineering
“Partitioning and Particulate-Bound Distribution of Phosphorus in
Rainfall-Runoff”
2:20 – 2:40
Recipient of the Student Award for Microfabrication
Sponsored by IoP, The Institute of Physics
Craig Plaisance, LSU Department of Chemical Engineering
“New Catalysts for Methylketone Manufacture”
2:40 – 3:00
Luis Rosa, University of Nebraska – Lincoln
“Water Adsorption of a Polymer Surface”
3:00 – 3:20
Khabibullah Katsiev, Tulane University
“Bimodal Pd Cluster Growth on the Reduced SnO2 (101) Surface”
3:20 – 3:40
David Keith Chambers, LaTech University
“Ultraviolet Photoelectron Spectroscopic Study of Semiconductive
Optoelectronic Polymers”
3:40 – 4:10
Report from CAMD User Committee
4:10 – 4:40
Radiation Safety Recertification, CAMD Conference Room
6:00 – 9:00
Social Time and Crawfish Boil, CAMD “Backyard”
Correspondence Address and Phone Numbers:
LSU CAMD
(225) 578-8887 Tel
(225) 578-6954 Fax
Contact: Lee Ann Broussard, User Coordinator
This year’s meeting is sponsored in part by
297
The CAMD Users’ Committee (CUC)
At this writing, the Center for Advanced Microstructures and Devices (CAMD) of
Louisiana State University and A & M College Users’ Committee (CUC) is, as is much
of CAMD, trying to address a state of considerable uncertainty and transition. The CUC
has been led by Peter Dowben (University of Nebraska) aided ably by Les Butler
(Chemistry, LSU) Chair elect. (vice Chair), elected 2005, Snjezana Balaz (Univ. of
Nebraska), student representative, elected 2005, Ulrike Diebold, (Tulane Univ.), elected
2005, Tabbetha Dobbins (LaTech Univ.), Steve Soper (LSU), past chair of the CUC, Carl
Ventrice (Physics, UNO), Wanjun Wang (Mechanical Engineering, LSU), elected 2005,
Weilie Zhou (AMRI, UNO) and recent past members of the CAMD USERS' Committee:
Richard Kurtz (Physics & Astronomy, LSU, and previous past chair of the CUC) and
Marcia Newcomer (Biological Sciences, LSU).
To address to some of the turmoil, a number of initiatives were begun while Steve
Soper was chair of the CUC, but have not yet seen full fruition. Other turmoil has been
the result of the financial fallout from Hurricane Katrina, which has placed budgetary
shortfalls throughout Louisiana, and on CAMD as well. Still, the CUC has been more
active than ever before, and consulted often collectively and individually this past year by
the CAMD and LSU administration.
As part of the budget shortfall, some (hopefully) short lived restrictions in the
CAMD schedule have been put into affect. These changes were done in consultation with
the CUC, after considering a number of plans. Les Bulter went to some considerable
effort (for which he has out great thanks) to try and address these budget shortfalls, but
was, unfortunately, unsuccessful.
The CUC continued to work with the CAMD Administration in scheduling
beamtime. The scheduling of beamtime has been expanded from the VUV beamlines (the
VUV scheduling committee consisting of Eizi Morikawa, [email protected], Phils Sprunger,
[email protected], Carl Ventrice, [email protected], Orhan Kizilkaya, [email protected],
Peter Dowben, [email protected], Rich Kurtz, [email protected], Yaroslav
Losovyj, [email protected]) to the X-ray beamlines, with a committee appointed
consisting of Marcia Newcomer, Les Bulter, and Roland Tittsworth. With Roland
Tittsworth’s much lamented passing, it is hoped that the scheduling committee for X-ray
will not falter and continue in its good works with Amitava Roy, who will be serving in
an interim X-ray Beamlines Manager capacity ([email protected] or (225) 578-6706).
The CUC continued to work with the CAMD Administration in organization of the
CAMD Users’ meeting. Lee Ann Murphey and her colleagues shouldered most of this
organizational burden for the 2005 Users’ Meeting, and it is hoped that the 2006 will
prove to be less burdensome. Nonetheless, the meeting was a success with crawfish to be
had by all and the graduate student prizes being given to Jason Emory (LSU-Chem.) in
micro-fabrication and to Craig Plaisance (LSU-Dept of Chemical Engineering) in basic
sciences in 2005. Graduate student prizes are again planned for the 2006 CAMD Users’
meeting and into the future. The 2005 Users’ meeting continues to have external support
from Oxford-Danfysik and the Institute of Physics.
There was also some input as to how the Microfab cost center will be implemented
at CAMD, but CAMD has prepared a detailed listing of costs for equipment/personnel
usage, and a meeting planned to discuss implementation of these new charges with the
LSU faculty and CAMD was planned.
A CAMD Users’ survey (an initiative of Steve Soper), and the responses have
298
resulted in frequent meetings throughout this past year between a number of LSU faculty,
who use CAMD, and the Vice Chancellor for Research, Harold Silverman. On behalf of
the CUC, both Peter Dowben and Les Butler have met with the CAMD Scientific
Advisory Committee in March (2006), to convey Users’ concerns and peter Dowben had
an opportunity to communicate those concerns to VC Harold Silverman directly in
March.
As we go into the future, we believe that the User will be increasingly consulted
and contribute to the future of CAMD. Such input depends not only on being heard, but
also this depends upon all of the active CAMD users putting forward their opinions and
speaking forth on issues of concern.
299
CAMD Faculty/Staff
300
Scientists’ Activity
(Publications/Presentations)
301
Publications from CAMD staff members in referred journals
2005
A Hybrid Approach for Fabrication of Polymeric BIOMEMS Devices, V. Singh, Y.
Desta, P. Datta, J. Guy, M. Clarke, D.L. Feedback, J. Weimert and J. Goettert; Book of
Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 170-171, 2005,
accepted for publication in Microsystem Technologies.
A Quantitative Study on the Adhesion Property of Cured SU-8 on Various Metallic
Surfaces, Wen Dai, Kun Lian and Wanjun Wang, Microsystem Technologies, Volume-1,
Issue Online First page:46, June 23, 2005. DOI: 10.1007/s00542-005-0587-4.
Adsorption of Water on the TiO2 (011)-(2×1) Reconstructed Surface, Cristiana Di
Valentin, Antonio Tilocca4 and Annabella Selloni, T. J. Beck, Andreas Klust, Matthias
Batzill, Yaroslav Losovyj, Ulrike Diebold, J. Am. Chem. Soc. 127 (27) (2005) pp 98959903.
Analytical considerations, design, and fabrication of a microfabricated fast GC x
GC system for the DARPA Micro Gas Analyzer (MGA), E. B. Overton, J. Goettert, H.
P. Dharmasena, A. Bhushan, D. Yemane, R. Simonson, D. Wheeler, D. Trudell, S. Dirke,
13th Intl. Conference On-Site Analysis, Arlington VA, January 2005.
Changes in Electronic Structure through a Disorder Transition in Gadolinium
Adlayers on W(112), Ya. Losovyj, P.A. Dowben, J Alloys Comp. 401 (2005) 155-159.
Characterization of size-dependent structural and electronic properties of CTABstabilized cobalt nanoparticles by X-ray absorption spectroscopy, H. Modrow, N.
Palina, C.S.S.R. Kumar, E.E. Doomes, M. Aghasyan, V.Palshin, R. Tittsworth, J.C.
Jiang, J. Hormes, Physica Scripta, T115, 790-793, 2005.
Characterization of the photo-irradiation effects on polystyrene ultrathin films with
ultraviolet photoemission spectroscopy, O. Kizilkaya, M. Ono, and E. Morikawa, J. of
Electron Spectrosc. Relat. Phenom, 151, 34 (2005).
Comment on “Spectral Identification of Thin Film Coated and Solid Form
Semiconductor Neutron detectors” by McGregor and Shultis, S. Hallbeck, A.N.
Caruso, S. Adenwalla, J. Brand, Dongjin Byun, H.X. Jiang, J.Y. Lin, Ya.B. Losovyj, C.
Lundstedt, D.N. McIlroy, W.K. Pitts, B.W. Robertson, and P.A. Dowben, Nuclear
Instruments and Methods in Physics Research A 536 (2005) 228.
Comparison of Crystalline Thin Poly(vinylidene (70%) – trifluoroethylene (30%))
Copolymer Films with Short Chain Poly(vinylidene fluoride), J. Choi, E. Morikawa,
S. Ducharme, and P. Dowben, Material Letters, 59, 3599 (2005).
Contact Voltage in Nanoparticle/Molecule Connections, H. Modrow, S. Modrow, J.
Hormes, N. Waldoefner, and H. Bönnemann, J. Phys. Chem. B, Vol. 109 , 900, 2005.
302
Cr-Diamondlike Carbon Nanocomposite Films: Synthesis, Characterization and
Properties, V. Singh, J.C. Jiang and E.I. Meletis; Thin Solid Films, Vol. 489 (1-2), 2005,
150-158.
Crystalline Ice Grown on the Surface of the Ferroelectric Polymer Poly(vinylidene
fluoride) (70%) and Trifluoroethylene (30%), Luis G. Rosa, Jie Xiao, Yaroslav B. Losovyj, Yi Gao, Ivan N.
Yakovkin, Xiao C. Zeng, and Peter A. Dowben, J. Am. Chem. Soc. 127 (49) (2005) pp 17261 – 17265.
Deep X-ray Lithography of SU-8 Photoresist: Influence of Process Parameters and
Conditions on Microstructure Quality, Y. Desta, H. Miller, J. Goettert, C. Stockhofe,
V. Singh, O. Kizilkaya, Y. Jin, D. Johnson, W. Webber; Book of Abstracts, HARMST05,
June 10-13, 2005, Gyeongju, Korea, pp. 70-71, 2005; June 2005.
Dimensionality in the alloy-de-alloy phase transition of Ag/Cu(110), Kizilkaya O,
Hite DA, Zhao W, Sprunger PT, Laegsgaard E, Besenbacher F, SURFACE SCIENCE
596, 242, 2005.
Directed evolution of a ring-cleaving dioxygenase for polychlorinated biphenyl
degradation, Fortin, Pacal D., Ian Macpherson, David B. Neau, Jeffrey T. Bolin, and
Lindsay D. Eltis, J Biol Chem. 2005 Dec 23;280(51):42307-14.
Direct-LiGA service for prototyping – a status report, B. Loechel, Y. Desta, J.
Goettert; Book of Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 198199, 2005; June 2005.
Displacement synthesis of Cu shells surrounding Co nanoparticles, Z.H. Guo,
C.S.S.R. Kumar, L.L. Henry, E.E. Doomes, J. Hormes, E.J. Podlaha, J. Electrochem. Soc.
152(1), D1, 2005.
Dopand concentration effect on NiO-doped sodium metaphosphate glasses: a
combined X-ray absorption fine structure (XAFS) and UVNIS/NIR spectroscopic
investigation, B. Brendebach, R. Glaum, M. Funke, F. Reinauer, J. Hormes, H. Modrow,
Z. Naturforschung Sect. A- A J. Physical Sci., 60(6), 449, 2005.
Effective Stabilization of Sulfate-Containing Soil: Mineralogical Evidence, Wang, L.,
Roy, A., and Seals, R.K., Journal of the American Ceramic Society. Vol. 88, 1600-1606
(2005).
Electronic, magnetic and geometric properties of functionalized magnetic
nanoparticles, J. Hormes, H. Modrow, H. Bonnemann and Challa S.S.R. Kumar, J.
Appl. Phys. Lett (2005), 97(10), 10R102-10R102-6.
Evidence for phonon effects in the electronic bands of granular Fe3O4, Ya.B. Losovyj
and Jinke Tang, Materials Letters 59 (2005) 3828-3830.
Fabrication of micro-gas chromatograph columns for fast chromatography, A.
Bhushan, D. Yemane, D. Trudell, E. B. Overton, and J. Goettert, Book of Abstracts,
HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 42-43, 2005, accepted for
publication in Microsystem Technologies.
303
Formation and characterisation of Pt nanoparticle networks, F. Wen, N. Waldofner,
W. Schmidt, K. Angermund, H. Bönnemann, S. Modrow, S. Zinoveva, H. Modrow, J.
Hormes, L. Beuermann, S. Rudenkiy, W. Muas-Friedrichs, T. Vad, H.G. Haubold,
European J. Inorg. Chem., 18, 3625, 2005.
HARMST by means of SU-8 Based Optical Lithography and Deep X-ray
Lithography, L. Jian, Y. Desta, J. Goettert, K. Lian, M. Bednarzik, H.-U. Scheunemann,
B. Loechel, H.O. Moser, O. Wilhelmi; Book of Abstracts, HARMST05, June 10-13,
2005, Gyeongju, Korea, pp. 76-77, 2005; June 2005.
High-energy X-ray diffraction study of Ni-doped sodium metaphosphate glasses, H.
Schlenz, F. Reinauer, R. Glaum, J. Neuefeind, B. Brendebach, J. Hormes, J. NonCrystalline Solids, 351(12-13), 1014, 2005.
In situ fabrication of SU-8 movable parts by using PAG diluted SU-8 as the
sacrificial layer, Z. Ling, K. Lian, Book of Abstracts, HARMST05, June 10-13, 2005,
Gyeongju, Korea, pp. 153-154, 2005, accepted for publication in Microsystem
Technologies.
Influence of mycotoxin producing fungi (Fusarium, Aspergillus, Penicillium) on
gluten proteins during suboptimal storage of wheat after harvest and competitive
interactions between field and storage fungi, A. Prange, H. Modrow, J. Hormes, J.
Krämer, P. Kohler, J. Agricultural and Food Chem., 53(17), 6930, 2005.
Interconnected Multi-Level Microfluidic Channels Fabricated Using Low
Temperature Bonding of SU-8 and Multilayer Lithography, Z-C Peng, Z-G Ling, J.
Goettert, J. Hormes, K. Lian; SPIE Photonics West 2005, Proceeding of SPIE Vol. 5718,
209-215.
Investigations into sulfobetaine-stabilized Cu nanoparticle formation: towards
development of a microfluidic synthesis, Y.J. Song, E.E. Doomes, J. Prindle, R.
Tittsworth, J. Hormes, C.S.S.R. Kumar, J. Phys. Chem. B 109, 9330, 2005.
Investigations of different human pathogenic and food contaminating bacteria and
moulds Grown on selenite/selenate and tellurite/tellurate by X-ray absorption
spectroscopy, A. Prange, B. Birzele, J. Hormes, H. Modrow, Food Control, 16(8), 723,
2005.
Investigations on the behaviour of C-60 as a resists in X-ray lithography, H. Klesper,
R. Baumann, J. Bargon, J. Hormes, H. Zumaque-Diaz, G.A. Kohring, Applied Phys. AMaterials Science & Processing 80(7), 1469, 2005.
Layer-by-layer nanoengineered magnetic encapsulation system for drug delivery.
Lu, Zonghuan; Prouty, Malcolm D.; Guo, Zhanhu; Kumar, Challa S. S. R.; Lvov, Yuri
M., MSE Preprints (2005), 93, 656-657.
304
LIGA fabricated high aspect ratio nickel gas chromatograph (GC) columns as a step
towards a portable and fast GC instrument, A. Bhushan, D. Yemane, J. Goettert, and
E. B. Overton, The 5th Harsh-Environment Mass Spectrometry Workshop, Center for
Ocean Technology, College of Marine Science /University of South Florida September
20-23 2005, Lido Beach Sarasota, Florida.
Local structure of composite Cr-containing diamond-like carbon thin films, V.
Singh, V. Palshin, R. Tittsworth and E.I. Meletis; Carbon In Press, Corrected Proof,
Available online 9 December 2005.
Magnetic Switch of Permeability for Polyelectrolyte Microcapsules Embedded with
Co@Au Nanoparticles, Zonghuan Lu, Malcolm D. Prouty, Zhanhu Gao, Vladimir O.
Golub, Challa S.S.R. Kumar, Yuri M. Lvov, Langmuir, 21(5), 2042 -2050, 2005.
Methods for Polymer Hot Embossing Process Development, P. Datta and J. Goettert;
Book of Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 256-257, 2005;
June 2005, accepted for publication in Microsystem Technologies.
Microfluidic Labware forDeveloping Biofunctional Surface on GMR Sensor, M.
Pease, V. Singh, P. Datta, O. Kizilkaya, E. Kornemann and J. Goettert; Book of
Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 94-95, 2005; June 2005,
submitted for publication to Microsystem Technologies.
Performance of the infrared microspectroscopy beamline at CAMD, Kizilkaya O,
Scott JD, Morikawa E, Garber JD, Perkins RS , REVIEW OF SCIENTIFIC
INSTRUMENTS 76,13703, 2005
Photohole Screening Effects in Polythiophenes with Pendant Groups, D.-Q. Feng,
A.N. Caruso, D. L. Shulz, Ya.B. Losovyj, and P. A. Dowben, J. Phys. Chem. B(2005)
109 (34) pp 16382-16389.
Polymer-Based Valves with Tunable Opening Pressures for Biomedical
Applications, C. Liu, Y. Qiu, K. Lian; SPIE Photonics West 2005, Proceeding of SPIE
Vol. 5718, 179-185.
Possibility of the Fermi Level Control by VUV-induced Doping of an Organic Thin
Film: polytetrafluoroethylene, Masaki Ono, Hiroyuki Yamane, Hirohiko Fukagawa,
Satoshi Kera, Daisuke Yoshimura, Eizi Morikawa, Kazuhiko Seki, and Nobuo Ueno,
Proc. Int. Symp. Super-Functionality Organic Devices, IPAP Conf. Series 6, 27-30,
(2005).
Processing-Microstructures-Surface Modification and Resulting Materials
Properties of LIGA Ni, Kun Lian, J.Jiang, Z. Ling, J. Goettert, and J. Hormes; Book of
Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp. 53-54, 2005; June 2005,
accepted for publication in Microsystem Technologies.
305
SEALS: A high brightness, low cost, light source proposal for the Southeastern
USA, V.P. Suller, M. Fedurin, J. Hormes, D. Einfeld, G. Vignola, Nuclear Instr. Methods
in Phys. Research: Sect. A- Accelerators, Spectrometers, Detectors And Assoc.
Equipment, 543(1), 23, 2005.
Sensing Interactions Between Vimentin Antibodies and Antigens for Early Cancer
Detection, C. Milburn, J. Zhou, O. Bravo, C. Kumar, and W. O. Soboyejo,
J.Biomed.Nanotech. 1(1), 30-38, 2005.
Spatially resolved sulphur K-edge XANES spectroscopy for in situ characterization
of the fungus-plant interaction Puccinia tritinca and wheat leaves, A. Prange, E.C.
Oerke, U. Steiner, C.M. Bianchetti, J. Hormes, H. Modrow, J. Phytopathology, 153(10),
627, 2005.
SU-8 3D micro optic components fabricated by inclined UV lithography in water, Z.
Ling, K. Lian, Book of Abstracts, HARMST05, June 10-13, 2005, Gyeongju, Korea, pp.
94-95, 2005, accepted for publication in Microsystem Technologies.
Surface Modification of Silicon Containing Fluorocarbon Films Prepared by Plasma
Enhanced Chemical Vapor Deposition, Y. Jin, Y. Desta, J. Goettert, G. S. Lee and P.
K. Ajmera, J. Vac. Sci. Technol. A, Vol. 23, No. 4, pp666-670, Jul/Aug (2005).
Targeting breast cancer cells and their metastases through luteinizing hormone
releasing hormone (LHRH) receptors using magnetic nanoparticles, C. Leuschner,
C.S.S.R. Kumar, W. Hansel, and J. Hormes, J.Biomed.Nanotech., 1(2), 229-233, 2005.
The Band Offsets of Isomeric Boron Carbide Overlayers, A.N. Caruso, P. LuncaPopa, Y.B. Losovyj, A.S. Gunn, and J.I. Brand, Mater. Res. Soc. Symp. Proc. 836 (2005)
L5.40.1.
The electronic structure and band hybridization of Co/Ti doped BaFe12O19, Natalie
Palina, H. Modrow, R. Müller, J. Hormes, P.A. Dowben and Ya.B. Losovyj, Materials
Letters 60 (2006) 236-240.
The Electronic Structure of Oriented poly(2-methoxy-5-(2,9-ethyl-hexyloxy)-1,4phenylenevinylene), David Keith Chambers, Srikanth Karanam, Difei Qi, Sandra
Selmic, Ya.B. Losovyj, Luis G. Rosa and P. A. Dowben, Appl. Phys. A 80 (2005) 483.
The influence of various coatings on the electronic, magnetic and geometric
properties of Cobalt – nanoparticles, J. Hormes, H. Modrow, H. Bönnemann, C.S.S.R.
Kumar, J. Appl. Physics, 97(10), Art. No. 10R102 Part 3, 2005.
Ultralow-k Silicon Containing Fluorocarbon Films Prepared by Plasma Enhanced
Chemical Vapor Deposition, Y. Jin, P. K. Ajmera, G. S. Lee, V. Singh, Journal of
Electronic Materials, IEEE, Vol. 34, No. 9, pp1193-1205 (2005).
306
UPS Study of VUV-Photodegradation of Polytetrafluoroethylene (PTFE) Ultrathin
Film by using Synchrotron Radiation, Masaki Ono, Hiroyuki, Yamane, Fumimasa
Katagiri, Hirohiko Fukagawa, Satoshi Kera, Daisuke Yoshimura, Koji K. Okudaira, Eizi
Morikawa, Kazuhiko Seki, and Nobuo Ueno, Nucl. Instr. and Meth., B236, 377 (2005).
Vibronic Coupling in the Valence Band Photoemission of the Ferroelectric
Copolymer: poly(vinylidene fluoride) (70%) and trifluoroethylene (30%), Luis G.
Rosa, Ya.B. Losovj, Jaewu Choi, and P.A. Dowben, J. Phys. Chem. B(2005) 109 (16) pp
7817-7820.
Welcome to the Journal of Biomedical Nanotechnology, Kumar, Challa S. S. R., J.
Biomed. Nanotech. (2005), 1(1), 1-2.
X-ray absorption near edge structure (XANES) investigatiuons of MnOy-doped
sodium metaphosphate glasses and crystalline reference materials, B. Brendebach, F.
Reinauer, N. Zotov, M. Funke, R. Glaum, J. Hormes, H. Modrow, J. Non-Crystalline
Solids, 251, 1072, 2005.
Presentations
A TEM Study Biological Distribution of Superparamagnetic Iron Oxide
Nanoparticles, Jikou Zhou, Lauren Heyward, Carola Leuschner, Challa Kumar, Josef
Hormes and Wole O. Soboyejo, 2005 MRS Spring Meeting, March 28- April 1, 2005,
San Fransisco, USA.
An Integrated Stacked Micro Fluidic Reactor System for Nanoparticle Synthesis,
Jost Goettert, Yujun Song, Proyag Datta, Josef Hormes, Willi Hempelmann and
Challa SSR Kumar, 8th International Conference on on Microreaction Technology, April
14th, 2005, Atlanta.
Development of a micro gas chromatography column in SU-8, Sebastian
Mammitzsch, Abhinav Bhushan, Dawit Yemane, Ed Overton, Jost Goettert; Poster
presentation 6th Louisiana Materials and Emerging Technologies Conference, Ruston,
Dec. 2005.
Development of Conductive Polymer Nano-Composite (carbon black/SU-8)
Micromachining by X-ray Lithography, Fareed Dawan, Yoonyoung Jin, V. Singh, Y.
Desta, J. Goettert and S. Ibekwe; Poster presentation 6th Louisiana Materials and
Emerging Technologies Conference, Ruston, Dec. 2005.
Development of Modular, Vertically Stacked Microfluidic Systems, Jens Hammacher,
Proyag Datta, Mark Pease, Rusty Louis, Changgeng Liu, Jost Goettert; Poster
presentation 6th Louisiana Materials and Emerging Technologies Conference, Ruston,
Dec. 2005.
Development of Thick Electrodeposited NiFe MEMS structures with Uniform
Composition, V. Singh, Y. Desta, Y. Jin, J. Goettert; Poster presentation 6th Louisiana
Materials and Emerging Technologies Conference, Ruston, Dec. 2005.
307
Drug Nanoencapsulation and Controlled Release, M. Prouty, Z. Lu, N. Veerabadran,
G. Krishna, A. Yaroslavov, C. Kumar, C. Leuschner, Y. Lvov, Louisiana Materials and
Emerging Technologies Conference, Ruston, Dec 12-13, 2005
Fabrication of a Polymeric Tapered HARMs Array Utilizing a Low-Cost Nickel
Electroplated Mold Insert, I. Song, Y. Jin and P. K. Ajmera, High Aspect Ratio
Microstructure Technology (HARMST), 6th Biennial Workshop (2005).
From Rapid Prototyping to Small Scale Production of Polymer Microchips via Hot
Embossing, Proyag Datta and Jost Goettert; Poster presentation 6th Louisiana Materials
and Emerging Technologies Conference, Ruston, Dec. 2005.
Functionalization and Characterization of Magnetic Nanoparticles for Biological
Engineering Applications, G. Nidumolu, M.C. O'Brien, C.S.S.R. Kumar and W.T.
Monroe, 10th Annual IBE (Institute of biological engineering) meeting, March 4-6, 2005,
Athens, Georgia, USA.
Functionalized magnetic nanoparticles for early breast cancer detection, Jikou
Zhou, Challa S.S.R.Kumar, Carola Leuschner, Josef Hormes and Wole O. Soboyejo,
TMS 2005 Annual Meeting, February 13- 17, 2005, San Fransisco, USA.
Layer-by-layer nanoengineered magnetic encapsulation system for drug delivery,
Lu, Zonghuan; Prouty, Malcolm D.; Guo, Zhanhu; Kumar, Challa S. S. R.; Lvov, Yuri
M. Abstracts of Papers, 230th ACS National Meeting, Washington, DC, United States,
Aug. 28-Sept. 1, 2005, PMSE-390.
LiGA MEMS Capabilities at LSU/CAMD, J. Goettert; Presentation at Jenoptik Special
Session, µTAS2005, Boston, October 2005.
LIGA Microfabrication at CAMD - A Status Report on Capabilities and Projects, J.
Goettert; APS User Meeting, Chicago, May 2005.
Micro fluidic synthesis of metallic nanoparticles, Kumar, Challa; Hormes, Josef; Song,
Yujun. AIChE Spring National Meeting, Conference Proceedings, Atlanta, GA, United
States, Apr. 10-14, 2005 (2005), 137B/1.
Microfabrication at CAMD - LiGA Service and Research Experience, J. Goettert;
Invited talk 6th Louisiana Materials and Emerging Technologies Conference, Ruston,
Dec. 2005.
Microfabrication Technologies - An Overview, J. Goettert; 1 week long Graduate
Level Lecture Series at Fachhochschule Gelsenkirchen, Gelsenkirchen, Germany, Jan.
2005.
Microfabrication Technologies for BioMEMS, J. Goettert; Lecture at the joint
CAMD/CBMM Summer School, LSU, Baton Rouge, July 2005.
308
New techniques in fabrication of SU-8 3D micro structures and movable parts
developed at CAMD, Zhong-Geng Ling,and Kun Lian; Poster presentation 6th Louisiana
Materials and Emerging Technologies Conference, Ruston, Dec. 2005.
Polymer Nano-Composite Micromachining by X-ray Lithography for MEMS
Application, Y. Jin, F. Dawan, S. Ibekwe, J. Goettert, G. Li and E. Woldesenbet,
American Society of Engineering Education-Gulf-Southwest Section 2006 Annual
Conference (submitted in Dec. 2005).
Single Step Fabrication of an Integrated Polymeric Waveguide, Sitanshu Gurung,
Proyag Datta and Jost Goettert; Poster presentation 6th Louisiana Materials and Emerging
Technologies Conference, Ruston, Dec. 2005.
Superparamagnetic Particle Embedded Microprobe (SPEM) for GMR Sensor
Calibration, M Zhang, J Goettert, K Lian, F-J Hormes, P K Ajmera; Poster presentation
6th Louisiana Materials and Emerging Technologies Conference, Ruston, Dec. 2005.
Synchrotron lithography at CAMD, J. Goettert; Workshop on Micro-fabrication
Strategies for Small Devices organized by MiniFAB, Scoresby, September 2005.
Synchrotron Lithography at the CAMD Synchrotron or The CAMD LiGA
Experience, J. Goettert; Workshop on SYNCHROTRON LITHOGRAPHY, organized
by Australian Synchrotron Project and MiniFAB, Scoresby, September 2005;
Synthesis of Magnetic Poly(DL-Lactide-co-Glycolide) Nanoparticles by Emulsion
Evaporation Method, C. Astete, W. Monroe, C. Kumar, and C. M. Sabliov, 10th Annual
IBE (Institute of biological engineering) meeting, March 4-6, 2005, Athens, Georgia,
USA.
Targeting breast cancers and metastases with LHRH and a lytic peptide bound to
iron oxide nanoparticles, Leuschner C., Kumar CSSR, Hansel W, Hormes J., Abstract
262. 17th AACR-EORTC-NCI Conference Molecular Targets and Cancer Therapeutics,
Philadelphia, November 2005.
The use of ligand conjugated superparamagnetic iron oxide nanoparticles (SPION)
for early detection of metastases, Leuschner, C.; Kumar, C.; Urbina, M. O.; Zhou, J.;
Soboyejo, W. Hansel, W.; Hormes, F. NSTI Nanotech 2005, NSTI Nanotechnology
Conference and Trade Show, Anaheim, CA, United States, May 8-12, 2005, 1 5-6.
Ultrafine-Grained Aluminum by Cryogenic Surface Mechanical Attrition
Treatment, K.Y. Wang, J.C.Jiang, C.G. Liu and K.Lian; Poster presentation 6th
Louisiana Materials and Emerging Technologies Conference, Ruston, Dec. 2005.
Updated MEMS/LIGA Services at CAMD, Yohannes Desta, Proyag Datta, Jost
Goettert, Yoonyoung Jin, Zhong-Geng Ling, Varshni Singh; Poster presentation 6th
Louisiana Materials and Emerging Technologies Conference, Ruston, Dec. 2005.
309
Research Experiences for Undergraduates, 2005
The REU Program for the Summer, 2005 was greatly reduced in scope because
we lost our NSF funding as the renewal proposal written in 2004 was rejected. Using
state-budget funds, we were able to support four students; students were from
Southeastern Louisiana University, Southern University, Texas Southern University and
Cornell University. Two students did research in X-ray spectroscopy and two in
Microfabrication.
In September 2005, we submitted another proposal to the Division of Materials
Research at NSF for three-year support of our REU Program. We received word in
March, 2006 that our proposal was recommended for funding and confirmation of
funding of $246 K for three years followed. The NSF Award Abstract for this grant
follows:
Award Abstract for CAMD REU Program - Louisiana State University;
Synchrotron-Radiation-Based Research for Advanced Undergraduate Science and
Engineering Students
PI John D. Scott [email protected]
CAMD web site http://www.camd.lsu.edu/
Address:
CAMD
The Louisiana State University J. Bennett Johnston, Sr., Center for Advanced
Microstructures and Devices (LSU CAMD) REU site is supported by the ASSURE
(Awards to Stimulate and Support Undergraduate Research Experiences) Program of the
Department of Defense through a DoD-NSF partnership. The support grant is managed
by the National Facilities Program in DMR for the summers of 2006-2008. CAMD is the
Southeast’s only synchrotron-radiation (SR) center and utilizes a 1.3 GeV secondgeneration electron synchrotron/storage ring. Each of the ten students selected each year
to participate in this REU Program will choose from among several basic research areas
based on the utilization of SR; spectroscopy from the far infrared (including
spectromicroscopy) to ca. 40 keV in the X-ray region, structure determinations using X
ray techniques such as microtomography, protein crystallography, powder diffraction and
small-angle-X-ray scattering, microfabrication based on X-ray lithography and involving
research and development of biosensors, MEMS devices and fundamental techniques of
the process itself and accelerator and control-system development and studies. The
program will run for ten weeks each summer and includes introduction to general SR
production and utilization, education in and practice of appropriate data acquisition and
analysis, weekly seminars in which REU students are actively involved and end-ofsummer oral and poster presentations of each student’s research. The poster
presentations are a part of a university-wide undergraduate research symposium
involving over 100 students. The Program Administrator is Ms Lee Ann Murphey,
[email protected] .
310
CAMD / CBM2 Summer School: Advanced Technologies for
Biomedical Applications
A week-long conference sponsored by CAMD and CBM2 was held on the LSU campus July 2529, 2005. The workshop was focused on fundamentals of microfabrication and biological
detection, technologies available for device development, and current and developing
applications. The week of lectures culminated in a day of tours and application of beamline and
microfabrication capabilities at CAMD on Friday.
Daily Schedule
2005 CAMD / CBM2 Summer Workshop
Monday
Time
Event
Details
7:00 – 8:00 am
Check-in, Breakfast
Collect binders, literature
8:00 – 9:30 am
Jeff Schloss, KN1
1:15 Talk + 15 min Q&A
9:30 – 9:50 am
Coffee Break
9:50 – 10:55 am
Steve Wereley
1 hr Talk + 5 min Q&A
10:55am –12:00pm
Robin McCarley
12:00 – 1:00 pm
Lunch
1:00 – 2:05 pm
Derek Hansford
2:05 – 2:25 pm
Coffee Break
2:25 – 3:30 pm
Tza-Huei (Jeff) Wang
3:30 – 5:30 pm
Cocktail reception - CAMD/CBM2 posters *
Located at LSU Union/Faculty Club
Tuesday
Time
Event
Details
7:30 – 8:00 am
Breakfast
8:00 – 9:30 am
Mark Burns, KN2
9:30 – 9:50 am
Coffee Break
9:50 – 10:55 am
Jost Geottert
10:55 am – 12:00pm
Helmut Schift
12:00 – 1:00 pm
Lunch
1:00 – 2:05 pm
Harry Stephanou
2:05 – 3:10 pm
Bruce Gale
3:10 – 3:25 pm
Coffee Break
3:25 – 4:30 pm
Jin-Woo Choi
311
Wednesday
Time
Event
Details
7:30 – 8:00 am
Breakfast
8:00 – 9:30 am
Robert Austin, KN3
9:30 – 9:50 am
Coffee Break
9:50 – 10:55 am
Bill Janzen
10:55 am – 12:00pm
Michael Wiggins
12:00 – 1:00 pm
Lunch
1:00 – 2:05 pm
Charles “Fred” Battrell
2:05 – 3:10 pm
Michael McShane
3:10 – 3:25 pm
Coffee Break
3:25 – 4:30 pm
Ajay Malshe
Thursday
Time
Event
Details
7:30 – 8:00 am
Breakfast
8:00 – 9:30 am
Richard Gibbs, KN4
9:30 – 10:35 am
Steve Soper
10:35 – 10: 50 am
Coffee Break
10:50 am – 11:55 pm
Michael J. Cima
11:55 – 1:00 pm
Mark Batzer
1:00 pm
Lunch
boxed for option of eating at Expo
1:00 – 4:00 pm
E&O Expo
Located at Energy
Environmental Building
* Subject to change
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Coast
and
Open House, Day of Discovery
Applied and fun sciences were demonstrated during CAMD’s Sixth Annual Open House
for the public on Saturday, May 7, 2005. There were eleven stations set up to expose
students, teachers, parents, and the public-at-large to specific projects and capabilities in
progress at CAMD.
Station #1
Center for BioModular Multi-scaled Systems (CBM2)
Polymerase Chain Reaction (PCR)
The polymerase chain reaction (PCR) is a technique that allows scientists and researchers
to amplify a specific DNA sequence millions of times in just a few hours. This
technique, developed by Dr. Kary Mullins, is used in study of genetic disease from
diagnosis to detection, forensic medicine and genetic mapping. The PCR analysis
consists of running a DNA sample and specific enzymes through various heat cycles to
separate the DNA molecules into single strands and then to replicate those strands.
CBM2 researchers have reduced the size of the typical lab equipment from table top size
to a box that can be held in your hand. The reduced size of the device diminishes the
time for analysis and the quantities of DNA material and chemicals needed.
DNA (deoxyribose nucleic acid) carries the inherited instructions for the biological
development of all cellular forms of life and many viruses. DNA is often referred to as
the molecule of heredity since it is inherited and is used to reproduce traits to offspring.
DNA Gumdrop Models
DNA is composed of four bases, which are paired and then alternate repeatedly to
comprise the DNA molecule. The bases are referred to as adenine (A), guanine (G),
cytosine (C), and thymine (T). G is usually paired with C, and A is usually paired with T.
DNA models were created by using gumdrops to represent the four bases and toothpicks
to indicate the bonds between the bases. The gumdrop pairs were combined in a ladder
configuration and then twisted into a spiral to form the signature double-helix.
Station #2
Microfabrication
Microfabrication: Mask to Molding
In the past 10 years the semiconductor community has grown from building a transistor
radio to thumb size MP3 players thanks to microfabrication technology.
Microfabrication is a science/technology developed to manufacture small parts and
devices with feature sizes measured in micrometers (one thousandth of a millimeter).
These small parts and microdevices are essential tools used to engineer miniaturized
instruments and microsystem products. The advantages of microsystem products are
generally lower power requirements, better functionality per unit space and time,
improved sensitivity, exponentially increased contact area, and portable accessibility.
Additionally, in most cases, the high-volume fabrication of these devices leads to
reduced, affordable prices. Ink-jet printing heads, compact disks, thin-film magnetic
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heads in hard drives, air bag deployment sensors in automobiles, and incision-free
medical equipment are some examples of Microsystem applications.
At CAMD, we use UV LIGA and X-ray LIGA in order to fabricate micro-parts. LIGA is
a german acronym used to describe the major steps involved in this microfabrication
technique: lithography, electroforming, and molding.
To produce microstructures using the LIGA process, the device design begins with
creation of an optical mask. Preparation of an X-ray mask is accomplished using the
optical mask and UV lithography. A 3-D resist mold is then generated by exposing the
solid X-ray sensitive material to X-rays from synchrotron light through the pattern on the
X-ray mask. This resist mold can then be submerged in an electroplating bath with a
electrical potential applied to ’grow’ metal structures within the resist mold. The
resulting electroplated metal part is the inversion of the resist mold. The metal version
can be the final product or it can be used as a semi-permanent mold for micro-replication.
Micro-replication may include ceramic injection molding, hot-embossing plastics, metal
micro-molding, and many other alternatives.
Demonstration
Lithography is demonstrated in this station with the use of transparencies and photosensitive paper. Designs can be drawn on the transparencies in any pattern. The paper is
then exposed through the transparency with a lamp. After rinsing in water, the resulting
image on the paper is a shadow of the transparency design!
Cleanroom
The CAMD cleanroom is 2500 ft2 of class 100 environment used primarily to support
nano- and microfabrication activity at CAMD, LSU, Southern University, and other
Louisiana institutions. A cleanroom is an environment where airborne particulates are
controlled through an exchange of highly filtered air using a high efficiency particulate
air (HEPA) filtering system, and through minimization of activities that generate
particles. A microfabrication processing lab and metrology machines, used for inspection
and characterization of the micro-structures, are housed inside the cleanroom.
Class 100 maintains less than one hundred particles larger than 0.5 microns in each cubic
foot of air space. In addition to particle control, the cleanroom is temperature and
humidity controlled to 70F and 45% relative humidity. This level of cleanliness is
required to prevent dust particles from interfering with microfabrication processing. If a
particle approximately as large as the features being fabricated is present, then fabrication
will probably not be successful. Similarly, if you are trying to play Monopoly, but your
adult cat sits in the middle of the board, then you probably cannot properly play the
game.
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(S.M. SZE, Semiconductor Devices, Pg. 430)
Demonstration
As humans inside this clean environment, we are the largest source of contaminants.
Gowning is required to contain the lint from our clothing, exfoliated skin, and hair.
Cleanroom gowning was available to visitors to briefly wear and to have a photo.
Microfluidics:
Microfluidic systems are now widely used in biology and biotechnology. Applications
include:
• Analysis of DNA and proteins
• Sorting of cells
• High-throughput screening
• BioMedical devices
• Chemical reactions
• Transfers of small volumes (1nL to 100 nL) of materials (nL = nanoliters)
Typical uses of microfluidic devices require that these systems are inexpensive and
simple to operate.
By using LIGA techniques at CAMD, polymer-based microchips can be fabricated with
low costs. The feature size can be as small as several microns (less than one tenth of the
diameter of human hair).
CAMD is involved in expanding analyses on a chip for modular BioMedical devices.
Similar modular, hand-held systems will be available on the market in the near future.
These devices are successfully designed to decrease analysis time to a few minutes
while requiring only a drop or two of body fluid, resulting in improved sensitivity and
accuracy of test results in a small fraction of the time, while practically eliminating the
manpower, time, and costs of traditional labs. This concept is referred to as ‘point-of315
care’ and it allows immediate action on the results of blood/fluid analysis within minutes
of withdrawing the sample!
Demonstration
A molded microfluidic chip demonstrates fluid transfer for analysis in a micromixer
created at CAMD. A micromixer is a required device in most microfluidic systems
since premixing the sample is usually part of the anaylsis. Differences between mixing
liquids in microscale and macroscale will be explained.
Micro Gas Chromatograph (MicroGC)
In collaboration with the Departments of Environmental Studies and Mechanical
Engineering at LSU, a group at CAMD is building the next generation of gas sensors
which will:
•
•
•
Continuously monitor harmful gases coming out of power plants, chemical industries.
This is very important for Louisiana because of the high density of chemical and
petroleum industries in the state.
Monitor the environment for pollutants, including hydrocarbons emitted by
automobiles and industries.
Issue early warnings for homeland security in the event of terrorists attacking with
chemical weapons.
These miniaturized sensors work on the basis of traditional gas chromatography (GC).
The technique is fairly simple: a mixture of gases is input at one end of a long and thin
tube which is coated with a reactive gel on the inside. While flowing through the tube, the
gases separate into its individual components. Through a GC, it is possible to detect gases
present with up to 1 part per billion parts of other compounds, making it one of the most
sensitive detection techniques currently available.
At CAMD, we are making a micro GC small in size so that
it can be held in hand like a cell phone or PDA. Through
engineering and chemistry, this sensor will be able complete
the analysis in less than five seconds! This is almost 200
times faster than the instruments currently available in the
market. The sensor will be efficient, by using less power and
gas volume, and it will enable soldiers to carry it with them to the field. Analysis time is
drastically reduced for immediate reaction in the field, if necessary, for our soldiers and
citizens!
Demonstration
The microGC is available for inspection and discussion of benefits. The older technology
is also available for comparison.
Sweatstick
The Sweatstick is a micro-device in development at CAMD that is used to perform boneloss analysis. Such a device is a crucial, diagnostic tool designed to indicate bone mineral
density (BMD). This is applicable, for example, during long space flights or extreme
exercise regimens.
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The device accurately measures the Ca2+ concentration in sweat samples obtained in-situ
on the user’s skin. The current patch technology has inherent problems in precisely
determining the collected sweat volume. Therefore, accuracy of the Ca2+ content in the
sweat sample analyzed is questionable. The miniaturized, robust microfluidic skin patch
designed at CAMD collects a precise volume (600 µL) of sweat in tiny honeycomb
geometries that are precision machined using microfabrication techniques
The quantity of Ca2+ in the microfabricated sample is measured using mass spectrometer,
which provides a accurate results of the ion content. Together, the microfabricated
device and accurate ion measurement leads to precise results from the in-situ, easily
accessible samples collected.
The LIGA technique, which uses high aspect ratio, deep X-ray lithography, micro-milling
and molding (hot embossing) was used to form the parts of the Sweatstick. These parts
are packaged and assembled into a small sweatstick device (< 1.5” in diameter). Thanks
to the small size it can be patched on human body (arms, legs, back, etc) relatively easily
to collect the sweat sample.
Demonstration
Assembled Sweatstick and the isolated honeycombed chip are shown and discussed.
Improvements in response time, data collection, and accuracy of results obtained through
this miniaturized device are important to people who closely monitor bone loss.
Tiny Things: All about MEMS and air bags
Tiny devices that can sense their environment, for example, temperature, acceleration,
and rotation, are called MEMS – Micro Electro Mechanical Systems. MEMS are usually
so small that you cannot see them with your naked eyes. The most common MEMS
device is found in your car’s air bags, which is made from a nylon fabric bag, some
‘rocket fuel’ to inflate the bag, and a MEMS sensor to measure acceleration. We call air
bag sensors accelerometers because they measure acceleration. The sensor element in an
air bag is about as small as the diameter of your hair.
Come and learn all about MEMS:
1. Learn how they are built at CAMD,
2. Observe the internal parts of an air bag sensor
(accelerometer) using a microscope and compare it to
the thickness of your hair,
3. Measure the acceleration of a remote controlled toy
truck using an accelerometer by crashing it into a
wall.
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Station #3
Biological Research with BioSensors
Protein Crystallography (PX)
The X-ray crystallography beamline at CAMD allows Users to bring protein crystals to
CAMD and perform experiments. These experiments determine the precise 3-D
positions of atoms in the protein molecule (the protein’s structure).
In an X-ray crystallography experiment, the crystal is placed in the beamline path, where
a narrow beam of high-intensity X-rays hits the crystal and scatters in various directions.
Some of these scattered X-rays strike a detector, producing an array of spots of varying
intensities. A crystallographer then measures the intensity of the spots to calculate a map
of the electron density in the protein. This map is interpreted to reveal the positions of
the atoms in the protein molecule.
Knowledge of the protein structure can provide insight into how the protein recognizes
and binds other molecules, how it functions as an enzyme, and how it evolved. This
information can be used to understand the mechanisms of diseases and to aid in the
development of drugs specifically targeted to treat them. The structures of over 24,000
proteins have been solved by X-ray crystallography, and this number continues to grow
with the use of CAMD’s synchrotron light and infrastructure.
Magnetic Nanoparticles for Targeted Delivery of Anticancer Drugs
Slide 1: Hello, and welcome to the world of nanoscale science and nanotechnology. You
might wonder just what is nanoscience and nanotechnology? Nanotechnology, is a world
in which science and engineering are carried out on a nanometer scale. One Nanometer is
just one one-billionth of the size of a meter. A meter, you might remember, has length of
39.37 inches or 3.28 ft. The human eye has difficulty resolving anything smaller than
one millimeter, about the thickness of a wire used to make a paper clip. The diameter of
that wire is still one million times larger than materials fabricated on the nanoscale.
Imagine, if you can, materials that are thousands of times smaller than the thickness of a
single, human hair. Conceive now, the ability to fabricate devices that are millions of
times smaller than the smallest ant. This is the world of nanotechnology.
Slide 2: At CAMD, scientists are working to develop methods to prepare such tiny
materials, and to use these materials to build devices that are useful in our day to day
world. Here at CAMD, in collaboration with the LSU-Pennington Biomedical Research
Center, research is underway to develop novel technologies for the treatment and
diagnosis of breast cancer using tiny magnets called nanomagnets which are being
attached directly to the anticancer drugs. Using an external magnetic field, these tiny
magnets carrying anticancer drugs can be directed precisely to the site of the tumor. The
ability to use “nano-drugs” in such a way would limit the side-effects of chemotherapy to
the rest of the otherwise healthy body.
Slide 3: Let us now define cancer. Though there are hundreds of different cancers,
cancer is defined as any malignant growth or tumor caused by abnormal and/or
uncontrolled cell division. Such rapidly dividing cells may break off from the primary
tumor and be spread to other parts of the body through the lymphatic system or through
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the blood stream. This is called metastasis. Cancer will be the leading cause of death
overtaking heart disease in the near future. Already, cancer claims 560,000 lives per
year! More Americans will die of cancer in the next 14 months than have perished
cumulatively in every war this nation has ever fought!
Slide 4: Breast cancer is the major cancer among women and it even affects 5% of the
male populace. Approximately one in nine women will develop cancer of the breast. In
addition, in the United States one woman dies from breast cancer every 12 minutes!
Breast Cancer can spread to the bones and lymph nodes. The survival rate with
metastasis is less than 30%. A mammogram can only detect tumors that are at least 2
tenths to 4 tenths of an inch in diameter. Tumors of this size contain millions of cells and
are probably, on average, already two years old when detected. It is obvious then that we
need new technologies that will detect breast cancer at its earliest stage before it has time
to metastasize, a certain death sentence for so many women today..
Slide 5: Scientists are working very hard to find effective solutions to combat cancer.
Here at CAMD, the Nanogroup researchers are doing their bit to fight cancer by
developing innovative Nanomaterials. These materials are being investigated for their
efficacy for breast cancer treatment and diagnosis.
Movie 1: CAMD’s researchers are developing wet chemical methods to prepare
nanomagnets, functionalized with anticancer drugs. What you see in the film clip is a
typical chemical reaction, in a flask that is used for the preparation of nanomagnets made
from the metal Cobalt. Remember, these tiny magnets are billions of times smaller than
size of the smallest fire ant.
Movie 2: Utilizing CAMD’s expertise in microfabrication, a unique polymer based
micro-reactor technology is being developed specifically for the production of
nanomagnets. What, you are see in this next film clip are the microfluidic reactor
channels for nanoparticle production. These channels are 300-400 um wide and 300-700
mm deep. Can you believe that these channels are 300-400 thousand times bigger than
each of the tiny magnets that are being produced in the reactor vessel? That is the
equivalent of bouncing a one inch diameter ball inside the length of ten foot ball fields.
As you can imagine, there is a lot of room in these channels to make many nanoparticles.
That’s the world of nanotechnology - it is truly revolutionary. It is genuinely amazing
that you can produce useful materials on such a tiny scale.
Movie 3: The film clips have shown microfluidic channels on a single micro-reactor chip.
But a single chip can only produce a few milligrams of nanomagnets in one hour.
However, in order to produce nanomagnets on an industrial scale we need to increase the
production. One of way doing this is by linking several micro-reactors by connecting
thousands of such reactors in parallel. All reactors are working together, each generating
its own nanoparticles as seen in the third film clip. Scientists call this “An Integrated
Stacked Micro Fluidic Reactor System for Nanoparticle Synthesis”. Similarly, CAMD
scientists have designed and fabricated a user-friendly computer-controlled stacked (one
on top of the other) polymeric micro-reactor system for the specific purpose of
synthesizing nanoparticles. The reactor system can also be utilized, in general, for wet
chemical synthesis and for the process development of specialty chemicals. This microreactor system consists of three basic functional blocks. The first allows the controlled
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flow from the chemical container (inlet), a custom made temperature-controlled microreactor stack, and an outlet unit to control and optimize all critical reaction parameters.
The system operation is controlled via a computer. In addition to producing
Nanomaterials in large quantities, the micro-reactor system can also be utilized by the
chemical industry for process and product development. It can also be used for the largescale production of specialty chemicals.
Movie 4: Having developed innovative technologies for the production of nanomagnets,
CAMD researchers are working in collaboration with LSU-Pennington Biomedical
research Center scientists to utilize these magnets for both cancer therapy and diagnosis.
These miniature magnets will be functionalized by binding the anticancer drug to the
nanomagnet. The functionalized nanomagnet will then be directed to the breast cancer
tumor only. These manufactured nanoparticles also have the ability to improve the
sensitivity of detection of cancer cells at the early stages of cancer development by
improving the contrast of the image of cancer cells in a well-known technique called
Magnetic Resonance Imaging (MRI). That means, we can detect smaller cancers (with
fewer cells) and hopefully identify and treat cancers before they can metastasize. The
final film clip shows the movement of injected nanomagnets carrying drugs to the breast
cancer tumor site.
You never know what is lurking in the field of nanoscience. The scientific future is bright
and very, very small. So join the revolution and consider becoming an investigator. Help
to develop these futuristic technologies. We at CAMD are delighted that you have taken
the time to visit us to learn about the cutting edge science that we hope one day may help
to improve your life. CAMD invites you, with open arms, to learn and develop these
truly amazing and exciting technologies. Remember, good things do come in small
packages!
Station #4
Optics
The CAMD accelerator (an electron storage ring) is operated for one purpose: to produce
wonderfully bright beams of light spanning the spectrum from infrared to X-ray
wavelengths. This radiation is used by scientists and engineers to make careful
measurements of the constitution, structure and nature of matter and to alter matter to
change its form and construct microscopic devices that are useful to mankind. To guide
the bright light beams from the storage ring to the various experiment stations and to
transform them into useful tools for the particular application needed requires devices
known as beamlines. Focusing the beams, filtering them so that only a narrow range of
energies or wavelengths (monochromatize) get to the experiment and guiding them to the
experiment are only a few examples of what is required to make the bright beams useful
to researchers. The beamlines are quite evident in the CAMD experiment hall; they
constitute the majority of the “furniture.” Not so evident are the optical elements inside
the beamlines. These elements are the mirrors, filters, monochromators and other devices
that make the beamline do what is necessary to give “good” light at the experiment
station.
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Demonstration
Several CAMD beamline scientists will be available to help visitors understand the many
natures of light as well as to help them operate some of the optical devices that are
typically used to “harness” the power of light. Hands-on demonstrations of infrared
detectors, light polarizers, diffraction gratings, light sources, spectrometers and displays
of results of measuring materials with infrared, visible, ultraviolet and X-ray light will be
available at this station.
Station #5
High Voltage
The Van de Graaf Generator
Invented in 1931 by Robert Van de Graaf, an MIT physics student, the Van de Graaf
generators (VDG) were originally used as power supplies for the early particle
accelerators. Prior to the invention of the cyclotron and linear accelerator rings,
researchers used a VDG machine connected to a long vacuum tube to generate the
necessary energy.
The VDG generators come in many sizes from 2-inch versions producing only five
thousand volts to those which are several stories tall and output many megavolts. The
VDG is a relatively simple device modeled somewhat after a printing press. It has a
hollow metal ball for its top, a vertical pipe with a rubber conveyor belt inside which
comes in contact with two rollers and the bottom is a hollow metal box which houses the
electric motor which powers the generator.
Electricity can be simply described as the flow of electrons. While these electrons cannot
be seen, the effects of the energy they give off can. This energy is seen as light. CAMD
is a light source and, while it doesn’t give off light, a VDG uses the flow of electrons to
generate static electricity just as CAMD uses the flow of electrons to create light. The
static electricity is generated as the belt moves inside the column creating a charge. This
charge builds up on the dome and the electricity it generates looks for a way to ground
itself. The negatively charged electrons want to get away from each other and jump to
any conducting object. Ideally the object is touching the dome but the electricity can
jump without touching the dome, if the conditions are right.
Large VDGs are still used today to power high energy X-ray machines for cancer
treatments, make x-ray photos of locomotive engines or sterilize food with gamma rays.
It is also used in science classrooms to study voltage and electric charge.
Various experiments are performed with the help of human subjects to show how the
VDG generates high voltage. This can make your hair stand straight out, make paper
stick to you, and cause metal pie plates to fly.
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Station #6
Vacuum
What does a vacuum have to do with CAMD?
Scientists define a vacuum as any pressure less than the pressure of the atmosphere.
The word vacuum comes from the Latin ‘vacuus’ which means ‘empty’. That’s because
in earlier times people believed that a vacuum was indeed empty, but in reality every
vacuum has some gas particles, even interstellar space.
Imagine the volume inside an 8cm long section of the synchrotron tube (which happens
to be about the volume of an empty can of soda). At atmospheric pressure there are about
1,000,000,000,000,000,000,000 gas particles for our unsuspecting electrons to crash into.
Inside the CAMD synchrotron tube we need to create a less obstructed path for the
electrons to travel so we remove as many of those gas particles as we can, resulting in a
high vacuum. We are able to reduce that number by 1000 billion times. How many
particles does that leave? Find out the answer to this and other vacuum related
conundrums at Station #6
Station #7
Environmental Science at CAMD
Phytoremediation Studies
Unfortunately, pollution from metals is quite extensive in south Louisiana. Arsenic
insecticides have been widely used in agriculture, resulting in soil and water pollution.
Chromium waste from industrial processes has been introduced into the environment.
Mercury from power plants is so common that periodic fish-eating advisories are issued
by the Louisiana Department of Environmental Quality. However, some plants have
recently been discovered which can make these elements less toxic, by taking up
pollutant metals and sequestering the metals in plant tissue. This process is called
phytoremediation. It may be possible to grow appropriate phytoremediative plants on
polluted soil, isolating pollutant metals from the soil in the plants themselves, and then
harvesting the plants for safe disposal. This method shows promise for environmental
clean-up, and may be superior to drastic methods like digging up all of the polluted soil.
At CAMD, we use X-ray Absorption Spectroscopy (XAS) to study the effectiveness of
various phytoremediation methods. XAS is a powerful tool for investigating the
chemical state of a particular element. Each element in the periodic table absorbs x-rays
at a characteristic wavelength. Our synchrotron light source is a broad band tunable light
source, so we can select the appropriate energy range for each specific element we which
investigate. We do this using x-ray optics in our beamlines.
Beamlines are the
equipment we use to get the light from the CAMD storage ring, tune it, and use it for
specific experiments. So, with an x-ray beamline, we have a tool which allows us to
investigate the chemical state of a particular absorbing element in a material, and get
useful structural information on the atomic/molecular level.
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An illustrative example is an experiment utilizing watercress as a potential
phytoremediator for Cr (VI). Chromium can exist in the metallic form, with a formal
charge of 0. It also has common ionic forms, which have a charge of +6 [Cr(VI)] or +3
[Cr(III)]. Cr(VI) is a highly toxic ion, while Cr(III) is not.
Watercress was grown in a hydroponic medium containing Cr(VI) for a period of 2
weeks. The plants were harvested, washed, and examined by x-ray spectroscopy on a
CAMD beamline. Interestingly, it was observed that watercress did take up large
amounts of Cr from the growth medium, and in the process, converted it from the highly
toxic Cr(VI) ion, to the less toxic Cr(III) ion. Below is a Cr XAS spectrum of the growth
medium, the watercress leaves, and a Cr metal foil standard [Cr(0)].
1.50
Absorption
1.25
1.00
This feature
indicates Cr (VI)
0.75
Watercress Leaves [Cr (III)]
Cr (VI) Contaminated Water
Cr (0) Foil
0.50
0.25
0.00
5960
5980
6000
6020
6040
6060
PhotonEnergy (eV)
The Cr XAS spectrum shows that the growth medium [Cr(VI) contaminated water] has
Cr in the +6 ionic form. The watercress leaves exhibit an x-ray spectrum indicative of Cr
in the +3 ionic form. Thus, the XAS shows that the watercress transformed the toxic
Cr(VI) ion to the more benign Cr(III) ion.
Stations #8 and #9
The Accelerator
Electron Beams & Magnetism
CAMD is called a “Light Source” by scientists who perform research here. This light is
produced by a particle accelerator that sends electrons flying down a pipe at nearly the
speed of light! This beam of electrons is produced by high voltage electricity and is
steered and maneuvered using electricity and magnets of various sizes. Without the help
of electricity & magnetism, CAMD’s synchrotron light could not exist.
3D magnetic filed viewer and 2D magnetic film
Magnetism can be visualized with lines tracing out the field that exists around a magnet
connecting its two opposing poles. The magnetic field of a small magnet is traced out by
iron filings suspended in heavy clear oil in the 3D field viewer. Other magnetic effects
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are shown as hand held magnets paint designs in the green 2D magnetic field viewing
film.
Simple electric motor
Magnetic fields are produced by permanent magnets, found in nature and man made, and
by electric currents. Those produced by electric currents are called electro-magnets and
are controllable. They can be used to make electric motors, as is demonstrated by the
simple “coil & magnet” motor.
Electron beam steering
Electro-magnets are used here at CAMD to steer the electron beam in the particle
accelerator. The clear pipe electron beam set-up shows how magnets can cause the
purple glowing electron beam to turn from its normally straight path.
High voltage discharge globe
If the electron beam passes through a continuous magnetic field, it can be steered into a
perfect circle. This is similar to what happens in some particle accelerators. This effect
is shown as the green glowing electron beam in the glass Bainbridge tube is bent into a
perfect circle by the continuous magnetic field of the Hemholtz coils.
High voltage Jacob’s Ladder and Circular electron beam demo
The electron beam is produced and accelerated by high voltage electricity. The high
voltage Jacob’s ladder shows how hot air conducts electricity better than cold air as the
electric arc jumps through the air and travels upward following the rising hot air
produced from the heat of the arc. A more benign demonstration of electricity shows
how high frequency electricity can produce an arc as well but can pass harmlessly
through glass bulbs as well as your over your body!
Synchrotron Light
The thirst for knowledge drives us to explore the world around us. What is our planet made of?
What are the processes that sustain life? How can we explain the properties of matter and
develop new materials? Can we someday conquer viruses, predict natural catastrophes, or
eliminate pollution?
To answer these questions, scientists have developed more powerful instruments capable of
resolving the structure of matter down to the level of atoms and molecules. Synchrotron light
sources reveal invaluable information in numerous fields of research. There are about 50
synchrotrons in the world (8 of those in the US) used by an ever growing number of scientists.
Synchrotron light is extremely bright light at low wavelengths. The picture below indicates where
synchrotron light falls on the electromagnetic spectrum.
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(NSRRC
image)
CAMD’s primary purpose of generating synchrotron light is accomplished with a few electrons
and magnets. Electrons are accelerated in a linear path to nearly the speed of light. The electrons
are then steered to a storage ring that is circular in appearance but has straight segments with
eight turns. The bends in the electron path are induced by large magnets. At each bend, energy is
released in the form of extremely bright synchrotron light and channeled tangentially through
beamlines. Each beamline has a specific purpose, which generally requires filtration or
attenuation of the light to achieve proper conditions for the sample and/or experiment waiting at
the end of the beamline.
Station #10
Superconductivity
A Superconductor is a material through which electrons travel with no resistance.
Because these materials have no electrical resistance, meaning electrons can travel
through them freely, they can carry large amounts of electrical current for long periods of
time without losing energy as heat. Superconducting loops of wire have been shown to
carry electrical currents for several years with no measurable loss.
Superconductivity is a phenomenon observed in several metals and ceramic materials.
When these materials are cooled to temperatures ranging from near absolute zero (-459
degrees Fahrenheit, 0 degrees Kelvin, or -273 degrees Celsius) or liquid nitrogen
temperatures (-321ºF, 77 K, -196ºC), they have no electrical resistance. Recent
discoveries of materials have found superconductivity behavior as high as 125K.
The temperature at which electrical resistance is zero is called the critical temperature
(Tc) and varies with the individual material. For practical purposes, critical temperatures
are achieved by cooling materials with either liquid helium (-452ºF, 4K, -269ºC) or liquid
nitrogen.
The future of superconductivity research is to find materials that can become
superconductors at room temperature. Once this happens, the whole world of electronics,
power, and transportation will be revolutionized.
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Superconducting magnets also support very high current densities with incredibly small
resistance. This characteristic permits magnets to be constructed that generate intense
magnetic fields with little or no electrical power input. Superconductor materials are
used to make the coil windings for superconducting magnets. These superconducting
magnets must be cooled with liquid helium.
At CAMD, a superconductive magnetic insertion device, called a wiggler, is used in the
path of the synchrotron light to ‘harden’ the light by decreasing its wavelength and
increasing its frequency, resulting in increased energy. Three beamlines require the use
of this modified light:
microfabrication wiggler, protein crystallography, and
tomography. CAMD’s wiggler uses liquid Helium for cooling the magnet and a liquid
Nitrogen jacket to insulate the Helium vessel.
Fun with liquid Nitrogen
At -321º F below zero, this stuff is pretty cold. We'll show how low temperature affects
things: turn gasses into liquids and solids, make rubber balls, break flowers like glass,
levitate a superconducting magnet, and how to freeze and thaw hamsters.
You’re sure to get a BOOM out of this demo!
Station #11
Micro-Replication
Micro-Molding
Micro-molding is a powerful technology that allows cost-effective fabrication of
precision micro- and nanostructures in a variety of polymers. Traditionally, injection
molding has been used to fabricate low aspect ratio (short with broad base)
microstructures, as in the case of the Compact Disk. The hot embossing operations at
CAMD are specifically geared towards production of devices which require high aspect
ratio (tall with narrow base) microstructures. Hot embossing is a type of micro-molding
which is performed at CAMD.
In the hot embossing process, a metal stamp (mold insert) is heated and pressed into a
softer plastic material under controlled conditions. This stamp contains very small
features, microstructures, on it. During the stamping process these features are
transferred to the plastic material. The transfer occurs at a high temperature where the
plastic is melted or starts to melt. After that, both the stamp and the plastic are cooled to
the point at which the plastic solidifies when the replicated structure is then demolded
from the mold insert.
At this station we are demonstrating the principles of embossing using a brass stamp as
the mold insert and aluminum foil and Playdoh® as the molded substance.
Electroplating
Electroplating is part of the LIGA (German acronym for lithography, electroplating and
molding) process. Electroplating is used in this process to ‘grow’ the metal device from a
plastic 3-D mold of the inverted microdevice. By definition, electroplating is the
deposition of a metal or metallic alloy on the cathode (plastic mold with conductive base)
326
by electrolysis from a salt solution. The salt solution consists of a metal salt dissolved in
a polar solvent (e.g. water) present in an ionic form.
Electroplating from an aqueous solution is commercially used in decorative metal
applications and automotive, aerospace, and electronic industries. In
microelectromechanical systems (MEMS) fabrication, electroplating must be refined to
completely fill the micrometer-scaled gaps in a way that produces metals with sufficient
physical properties. At CAMD, commercial electroplating equipment was modified to
achieve these high-quality plating requirements.
327
On October 8, 2005, CAMD was one of 26 teams to participate in the first Red Stick
Dragon Boat Regatta at Baton Rouge Beach hosted by The Chamber of Greater
Baton Rouge. The sport of dragon boating is over 2000 years old with its origins
steeped in tradition. The pageantry, the colors, the mechanics of dragon boating are
educational and present a view into the past.
328
Southern gets Navy grant to help build smaller fleet
Advocate - Baton Rouge, La.
Date:
Nov 8, 2005
Start Page:
20.A
Section:
News
(Copyright 2005 by Capital City Press)
A $1.5 million grant from the U.S. Navy will help Southern University's College of
Engineering find ways to build naval fleets with smaller, more efficient machinery, the
school announced this week.
The grant will enable the college, working with other partners, to boost the effectiveness
of the pressurized water reactors used to fabricate ships. The project will involve complex
alloys and micro manufacturing, according to a press release.
"We are very grateful to the U.S. Navy for granting the award and making it possible to
partner with CAMD and the Louisiana State University mechanical engineering
department via personnel and equipment," said mechanical engineering department
Chairman Samuel Ibekwe. "The grant will also enable us to contribute to knowledge in
the area of nuclear reactor pressure vessels and to expand research capabilities." The
Center for Advanced Microstructures and Devices develops tiny instruments used in
scientific research.
Ambassador Linton F. Brooks and Adm. Kirkland H. Donald presented the $1.5 million
check to the college of engineering Thursday.
Reproduced with permission of the copyright owner. Further reproduction or distribution is prohibited without permission.
Copyright © 1992-2006, 2theadvocate.com, WBRZ, Louisiana Broadcasting LLC and The Advocate,
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329
Public gets inside look at best of science LSU research complex holds open
house
Advocate - Baton Rouge, La.
Author:
WILLIAM TAYLOR
Date:
May 8, 2005
Start Page:
2.B
Section:
News
(Copyright 2005 by Capital City Press)
As a little girl, Hillary Spruell was afraid of LSU's J. Bennett Johnston Sr. Center for
Advanced Microstructures and Devices.
The complex hidden behind the trees off Jefferson Highway conjured up for her images
of bio-suited scientists examining aliens like in the movie "ET."
Spruell, now 16, found the reality much different Saturday as she toured the site with
family and friends during the center's annual open house.
"It helps to see it in person," Spruell said.
At the heart of the 45,000-square-foot building lies an electron storage ring using
powerful magnets to produce and control light.
Moving electrons in a circle at near light speed produces synchrotron radiation - intense
light scientists can harness as powerful X-rays, infrared rays and other beams for precise
examinations of tiny molecules.
Potential applications include developing medical technology to diagnose patients using
only drops of blood instead of vials and new approaches to solving environmental
problems by using certain plants to remove chemicals from water or soils.
The scientists don't mind if their work reminds people of the movies.
However, a movie poster used in one display Saturday wasn't from "ET," "Star Wars" or
any other science-fiction flick.
Instead, the scientists wanted visitors to see a connection between their work and "Erin
Brockovich."In that movie, Julie Robert plays a woman who waged a legal battle with a
large company over a power plant that polluted nearby groundwater with Chromium VI,
a highly toxic cancer-causing substance.
Scientists have discovered that watercress plants will remove the chemical from the
ground and in the process convert it to Chromium III, a non-toxic agent that is essential
to human metabolism.
Using the plants to solve environmental problems is called phytoremediation.
330
Harvesting contaminated plants is much more efficient than digging up and hauling off
contaminated dirt, Professor of Research Roland Tittsworth said.
The center's scientists assist other scientists in studying the possibilities by using their
powerful X-rays to provide data.
Tittsworth and Research Associate Vadim Palshin explained that they can focus the Xray on a tiny portion of a leaf to see not only what chemicals are there, but how those
chemicals are interacting with the materials around them.
"You can get information that would otherwise be hidden in the noise," Associate
Professor of Research Amitava Roy said.
Roy added that phytoremediation could help Louisiana.
Scientists are looking at grasses that could help reduce coastal erosion and also remove
mercury from the water, he said.
Shavarsha Kaltakdjian, a Baton Rouge jeweler visiting the open house for the fourth
consecutive year, was impressed with what he saw.
There are even plants that absorb gold and that can be harvested by drying them and then
burning them, he said.
Kaltakdjian brought his 9-year-old son, Alex, with him for the first time.
"He fought me, but once he got here he's been having fun," the father explained.
Alex made DNA models out of gumdrops and toothpicks and enjoyed touching an
electron generator that made his hair stand on end.
The boy was more interested in what the science did than how it worked, the father
conceded.
But some day that could change, Kaltakdjian said.
"This is the greatest thing LSU does, for the kids especially, because this will touch lots
of kids' minds and you never know which direction they will go with it," he said.
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Copyright © 1992-2006, 2theadvocate.com, WBRZ, Louisiana Broadcasting LLC and The Advocate,
Capital City Press LLC, All Rights Reserved. Click here to send comments or questions about 2theadvocate.com.
331
2005 CAMD Facility Tours
January 25
7th-12th grade Home Schoolers
20 people
February 7
Varian
5 people
February 12
LSU Physics Graduate Students
30 people
February 17
LSU IEEE Students
20 people
February 24
ITI Technical College Students
13 people
March 11
Louisiana Technology Park
2 people
March 22
Episcopal High AP Chemistry Students
24 people
March 24
Centerville High School Physics Students
10 students
May 2
LSU Computing Services
5 people
July 26
Student Affiliates of the American Chemical Society
Science summer camp for high school students
25 people
332
2005 CAMD Seminars
January 10
Dr. Sunggook Park
Department of Mechanical Engineering
“Improving Versatility of Nanoimprint Lithography”
February 9
Prof. Fritz Goetz
Fachhochschule Gelsenkirchen, Germany
Institute for Physical Engineering
“Test Chip for Surface Functionalization of Fluidic Structures”
February 11
Prof. M. Graca H. Vicente
Department of Chemistry
“Synthesis of Porphyrin-Based Sensitizers for Cancer Treatment”
February 18
Prof. Gudrun Schmidt
“Structure of Polymer-Clay Hydrogels”
February 25
Dr. Qian Wang
Department of Chemistry & Biochemistry
University of South Carolina
“Self-Assembly of Two Dimensional Bionanoparticles at Liquid-Liquid Interfaces”
March 11
Dr. Jayne Garno
“AFM-Based Nanolithography of ω-Functionalized n-Alkanethiol Self-Assembled
Monolayers”
May 5
Dr. David J. Butcher
Department of Chemistry and Physics
Western Carolina University
“Phytoremediation of Lead and Arsenic at Barber Orchard, NC”
333
July 11
Dr. Richard Sah
Candidate for position of “Machine Group” Leader at CAMD
“The Evolution of Third-Generation Synchrotron Light Sources”
July 12
Dr. Richard Sah
Candidate for position of “Machine Group” Leader at CAMD
“Current Trends in Particle Beam Radiation Therapy”
August 3
Dr. Elena Kondrashkina
Biophysics Collaborative Access Team (BioCAT)
Advanced Photon Source
“Static and Time-Resolved Small-Angle Scattering from Protein Solutions”
August 22
Dr. Diane Blake
Department of Biochemistry
Tulane University Health Sciences Center
“To Affinity and Beyond: Incorporation of Biologicals into Sensors”
October 13
Dr. Annette Summers Engel
Department of Geology & Geophysics
“Better than Lotion: Using Hydrothermal Sinter Deposits to Understand Protection
Against UV Radiation for Early Precambrian Cyanobacteria”
October 14
Dr. Richard J. Field
University of Montana
“The Oscillatory Belousov-Zhabotinsky (BZ) Reaction: Examples of Nonlinear
Dynamics in Chemistry”
October 18
Dr. Nikolay Mezentsev
Budker INP, Russia
“Superconducting Insertion Devices for Light Sources”
334
Report of the Scientific Advisory Committee to CAMD
March 3-4, 2005
Conducted for the
Office of the Interim Vice Chancellor for Research
Harold Silvermann
Members
*Gwyn P. Williams, Chair, Thomas Jefferson National Accelerator Facility
*David Ederer, Tulane University
*Jill Hruby, Sandia National Laboratory
*Tai Chiang, University of Illinois at Urbana-Champaign
*Erik Johnson, Brookhaven National Laboratory
Howard Padmore, Lawrence Berkeley National Laboratory
*Robert Sweet, Brookhaven National Laboratory
*Herman Winick, Stanford Synchrotron Radiation Laboratory & Stanford Linear Accelerator Center
*In attendance at this meeting
Executive Summary
1. During the past 5 years, CAMD has undergone a truly remarkable transformation in terms of
machine operations and reliability. The data presented show operations for calendar year 2004 of
more than 6000 user hours. This would be considered a good achievement for a facility with the
resources of a national laboratory; but is an extraordinary accomplishment for a laboratory the
size of CAMD.
2. CAMD is a cutting edge research tool, representing an investment of roughly $100 million,
providing invaluable training opportunities for graduate and undergraduate students, while having
broad applications to nano-, bio, energy and environmental sciences and technologies.
3. CAMD is well positioned to play a major role in the evolution of facilities in the USA in the
next decade. The US has 8 synchrotron radiation facilities, all of which are predominantly local.
CAMD is the closest synchrotron radiation center for 40% of US population.
4. The SAC recognizes that CAMD has turned around in the last 5 years under the leadership of
Josef Hormes despite a very limited budget. Hormes has the scientific breadth to provide
leadership in the many fields served by CAMD.
5. Our committee has serious concerns about the long-term health and viability of CAMD.
Significant increases in staff and funding are needed to bring it to the level of scientific
productivity, and to develop the user service levels that are typical of other US facilities.
6. The strain in the collegial relationships with the LSU faculty and the CBM2 collaboration in
particular needs to be addressed at the highest level of LSU management.
7. The management and intellectual leadership of CAMD is in jeopardy, and in particular the 2
key positions of director and accelerator leader must be identified and recruited or retained.
8. The committee recognizes with high respect the work of the safety officer, but continues to be
concerned about workload levels and with radiation safety issues on the wiggler beamline.
335
CAMD Machine Advisory Committee Meeting
March 3-4, 2005
Members
*Glenn Decker, Chair, APS/Argonne National Laboratory
*Jeff Corbett, Stanford Synchrotron Radiation Laboratory
*Gerardo d’Auria, Sincrotron Trieste-Italy
Mikael Eriksson, Max Lab-Lund, Sweden
*Richard Heese, NSLS/Brookhaven National Laboratory
*Sam Krinsky, NSLS/Brookhaven National Laboratory
*In attendance at this meeting
Executive Summary
The CAMD staff can be justifiably proud of their accomplishments over the past several years,
which have resulted in a reliable user facility with minimal resources. Operation with 200 mA is
now routine with high availability (>94%), and the orbit is now much better understood and
reproducible. The completion of the quadrupole shunt project has allowed a quantitative
determination of the lattice functions for the first time at CAMD, paving the way to the
commissioning of a new lower emittance lattice with good lifetime last November. This system
has also been crucial in the determination of the absolute beam position (“the golden orbit”)
relative to the quadrupole magnet centers. New diagnostics (in particular for the RF system),
together with a quickly maturing EPICS-based control system will no doubt pave the way to a
better understanding of the machine and ultimately to further improved performance.
Vic Suller’s efforts here have benefited machine operation considerably. The search for an
experienced full time accelerator physicist should continue, including a high visibility preseance
at the particle accelerator conference coming up in May etc., and perhaps DIPAC in June. The
PAC is also an important learning opportunity for accelerator staff members.
Development efforts should be well coordinated with the CAMD resident beamline personnel.
For example a reduction in horizontal beam size at the wiggler source point coupled with an
incremental increase in stored beam current would make the PX beamline more competitive,
attracting users. Fortunately the diagnostics and machine reliability at present are such as to make
the realization of such a goal much more likely than at any time in the past.
Additional diagnostics will continue to be of prime importance in development efforts, for
example an online beam size diagnostic will become invaluable as new lattices are tested,
whether using a pinhole camera or some other technique. Coupling compensation is an important
capability that should be aggressively pursued.
While items such as routine maintenance are no longer viewed as being of the highest priority,
the committee trusts that the staff will continue its efforts to sustain not only high availablility but
in addition a low fault rate. As discussed in earlier reviews, a reliable machine is a necessary
precondition in efforts to attract influential user groups who in turn can add support to efforts to
secure more adequate financial support, which ultimately could lead the way toward a future
regional facility (SEALS). It is commendable that the CAMD staff have achieved the present
high level of reliability with the limited resources available.
336
CAMD Operating Budget 2004/2005
$4.7M
Facility
4%
Outreach Programs
1%
Office Support
1%
Telecommunications
1%
Match Commitments
2%
Utilities
CAMD Research
Salaries
Match Commitments
Telecommunications
Office Support
Outreach Programs
Facility
Utilities
17%
CAMD Research
12%
Salaries
62%
337
Staff Changes During 2005
New Employees in 2005
Accelerator Group
Selim Kazan
Microfabrication Group
Jens Hammacher*
Sebastian Mammitzsch*
Nano Group
W. Rohini deSilva*
Protein Crystallography Group
David Neau*
Spectroscopy Group
David Alley
Employees who left in 2005
Yohannes Desta
Brett Keller
Evelyn Kornemann
Yunjun Song
Christian Stockhofe
*Grant supported
338

CAMD 2005 Annual Report - Louisiana State University

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