THERMOCHROMIC AND STRUCTURAL PROPERTIES OF

Transcription

THERMOCHROMIC AND STRUCTURAL PROPERTIES OF ION BEAM SYNTHESIZED VANADIUM
OXIDE NANOCLUSTERS. H. Karl and B. Stritzker, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
Introduction: VO2 undergoes a semiconductor-tometal transition at 68°C, which is marked by a tremendous decrease in electrical resistivity and an important change in optical transmittance and reflectance
in the near infrared spectral region. With this phase
transition the material undergoes also a structural
phase transition (e.g. VO2 transforms from a monoclinic in the semiconducting to a tetragonal structure in the
metallic state).
Nanocomposites consisting of VO2 nanocrystals
(nc-VO2) embedded in SiO2 thin films allow to control
the crystallite size restriction and the coupling of semiconducting and metallic domains, which have strong
influence on the their phase transition [1]. Thin films
of those nanocomposits are very promising materials
for application in active optical wavequides and photonic crystals [2-4].
The unique properties of ion implantation (e.g.
generation of supersaturated impurity concentrations)
allow a phase selective synthesis of VO2 in SiO2 and
other optically transparent host materials [5]. Moreover, ion implantation is predestinated to fabricate planer two-dimensional arrays of buried nc-VO2.
Experiment: V+ and O+ ions with energies of
100 keV and 36 keV respectively were implanted into
200 nm thick thermally grown SiO2 on (100) silicon
substrates. A post-implantation rapid thermal annealing step at 1000°C for 10 min in inertgas atmosphere
resulted in spherical VO2 nanocrystallites located in
the center of the SiO2 layer (Fig. 1). The oxidation
state of V ranging from 2+ to 5+ results in a large number of different vanadium oxide phases. The synthesis
of pure phase VO2 has been achieved by implanting V
and O with a fluence ratio of 1 to 2.
Fig. 1: TEM crossectional image of nc-VO2 embedded
in in the center of 200 nm thick thermally grown SiO2
on (100) silicon.
The effect of the semiconductor-to-metal phase
transition on the optical properties has been determined by spectral ellipsometry in the wavelength
range between 320 and 1700 nm. Figure 2 shows the
Workshop Ion Beam Physics
29th – 31st March 2010
result for the temperature dependence of the extinction
coeffiction at a wavelength of 1200 nm determined on
the basis of an effective medium approximation. A
wide hysteresis of approx. 50°C was found for this
composit.
Fig. 2: Temperature hysteresis of the extinction coefficient for heating (dash dotted line) and cooling (dotted
line) sequence at wavelength of 1200 nm.
The structural changes during the phase transition
have been probed by µ-Raman spectroscopy [6]. The
Raman modes clearly indentify VO2 and its semiconductor-to-metal phase transition with this large hysteresis. The positions of the Raman lines shift due to
thermal expansion towards smaller wavenumbers and
finally vanish at the phase transition to the metallic
state and vice versa.
In the course of this work the properties of the embedded nc-VO2 have been modified by either implantation of dopants like W and Mo or by radiation defects induced by ion implantation of He. In the latter
case, the hysteresis can be completely recovered by a
thermal annealing step. Both techniques allow it to
reduce the hysteresis width whereas the thermodynamic temperature of the phase transition only changes in
the case of W and Mo incorporation.
References: [1] Cao J. et al. Nature Nanotechnology 4 (2009) 732–737. [2] Lopez R., Boatner L.A.,
Haynes T.E. Appl. Phys. Lett. 85 (2004) 1410–1412.
[3] Changhong Chen et al. Appl. Phys. Lett. 93 (2008)
171101. [4] Driscoll T. et al. Appl. Phys. Lett. (2008)
02410. [5] Lopez R. et al. J. Appl. Phys. 92 (2002)
4031. [6] Petrov G. I. et al. Appl. Phys. Lett. 81 (2002)
1023–1025.
O1
SELF-ASSEMBLED ORDERED NANOSTRUCTURES ON Ge BY CLUSTER IRRADIATION. L. Bischoff,
K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam
Physics and Materials Research, POB 51 01 19, 01314 Dresden, Germany, e-mail: [email protected]
Introduction: Surface modification with ion beams is
a well-established technique to create self-organized
regular patterns like ripples and dots [1,2]. The pattern
can be controlled by the kind of ion species as well as
by their energy, fluence and angle of incidence. Future
applications in electronic or optoelectronic nanodevices are under discussion [3]. In this contribution we
present a novel approach, the irradiation with focused
dimer and trimer beams of heavy ions, in particular
Bi2+ and Bi3++. These clusters from a liquid metal ion
source were mass separated in a CANION 31Mplus
FIB system from Orsay Physics and focused onto a Ge
surface. The acceleration voltage of 30 kV corresponds
to energies of 10-15 keV/atom, fluences from 1015 to
1017 cluster/cm2 were applied.
1. Low-angle irradiation: For normal incidence
up to an angle of ~30° dot patterns with a pronounced
short-range order have been found. The dots are crystalline (as confirmed by Raman measurements),
enriched with Bi and have a diameter of 30 nm. The
inter-dot distance is about 50 nm. A new quality of the
dots is their large aspect ratio of ~1. A HR-SEM image
of such a pattern is shown in Fig. 1. Using the same
fluence and energy/atom, irradiation with single Bi+
ions resulted in the well-known porous Ge surface.
Therefore, this new kind of pattern should be caused
by cluster effects, not by single ion impacts. The Bradley-Harper model is obviously not valid, in contrast to
the fabrication of regular 3-4 nm deep holes in Ge by a
5 keV FIB irradiation with monomer Ga-ions [4]. According to a first analysis, the energy density deposited
per volume by the cluster impact cascade must exceed
a threshold value to form this new kind of surface pattern. The threshold energy deposited per Ge atom
coincides with the heat per atom required for Ge melting. Thus, each cluster impact yields to a small melting
pool of <1000 nm³ volume. A model based on such
pools explains the segregation of Bi into the dots. The
Ge surface undulation is caused by a decrease of the
Ge volume of 5% during melting. A Ge flux into the Bi
rich region occurs due to the Bi concentration dependent Ge melt temperature.
2. High-angle irradiation: In the range from 30°
to 60° no structures occur. The surface becomes very
smooth by the heavy cluster beam. Increasing the angle
further leads to the formation of ripples perpendicular
to the beam direction with a wavelength of about
100 nm and a height of 30 nm. Measurements with
back scattered electrons reveal that the top of the ripples is Bi enriched. Fig. 2 presents a ripple structure
made by Bi3++ clusters at an incident angle of 70°. At
still higher angles a transition from ripples to a shingle
structure has been found, which are also perpendicular
to the beam direction. A rotation into ripple pattern
parallel to the beam has been not observed. A shingle
pattern formed at an incidence angle of 80° is shown in
Fig. 3.
Fig. 1: SEM image of regular dot pattern, formed by
30 keV Bi3++ clusters at 0°. Inset: FFT
Fig. 2: SEM image of ripples, made by Bi3++ at 70°.
Fig. 3: SEM image of shingles, made by Bi3++ at 80°.
Acknowledgement: The authors want to thank M.
Krause (FZD) for Raman measurements.
References: [1] Bradley R.M. and Harper J.M.E.
J. Vac. Sci Technol. A 6 (1988) 2390-2395. [2] Facsko
S., Dekorsy T., Koerndt C., Trappe C., Kurz H., Vogt
A., Hartnagel H.L. Science 285 (1999) 1551-1553.
[3] Gago R. et al. Phys. Rev. B 73 (2006) 155414-1-9.
[4] Wei Q. et al. Adv. Mat. 21 (2009) 2865-2869.
O2
Lasers can process materials at submicron length scale
and picosecond time scale. Here, it will be shown that
swift heavy ions can be used for materials processing at
even shorter length and time scales.
The driving forces of nanomaterials processing by
swift heavy ions as identified by our studies are (i) the
materials dependent electronic stopping power, (ii) the
volume change upon melting, (iii) the asymmetric hydrodynamic flow due to stress field hysteresis, as well
as (iv) far-from-equilibrium steady-state solubilities
and strongly anisotropic diffusion coefficients [1]. Size
distributions, shapes and anisotropies of nanoparticles
can be tailored by appropriate tuning of these driving
forces.
The evolution of Au and Ge nanospheres under
swift heavy ion irradiation was studied experimentally
and by atomistic computer simulations. Ge nanospheres
of different sizes embedded in SiO2 show different response (Fig. 1a) to I7+ ion irradiation at 38 MeV [2].
Spheres below a critical size become discus-shaped
(Fig. 1c), very small ones show Ge loss at their equator
(Fig. 1d). Computer simulations based on a model,
which includes the driving forces listed above describe
the Ge shaping (Fig. 1e) and the Au shaping (Fig. 2),
where Au nanospheres of 15 nm diameter elongate to
rods.
Our model describes the ion-induced shape evolution of different elements for different ion species,
energies and fluences quantitatively, where only one fit
parameter describes all experiments. This is a strong
evidence that our model based on classical thermodynamics and hydrodynamics describes the shaping mechanism appropriate.
An even stronger proof is the shape change of nanospheres of critical size under swift heavy ion irradiation (see Fig. 3): For such particles, exclusively central
ion impacts induce shaping, where Au is squeezed out
of the poles. Using critical-size nanospheres with an
unimodal size distributions and changing the ion impact angle during irradiation, tailoring of very exotic
nanoparticle shapes become feasible.
References: [1] Heinig K.-H. et al. Int. Workshop
on Nanostructures in Silica, Sept 6-9, 2009, Ivalo,
Finland (inv. talk) and in prep. for Phys. Rev. B
(2010). [2] Schmidt B. et al. NIMB 267 (2009) 1345.
[3] Awazu K. et al. Phys. Rev. B 78 (2008) 054102.
rel. radius change (Rxy-R0)/R0
Au AND Ge NANOPARTICLE SHAPING BY SWIFT HEAVY ION IRRADIATION. K.-H. Heinig1,
B. Schmidt1, A. Mücklich1, C. Akhmadaliev1, M. Ridgeway2, P. Kluth2, A. Vredenberg3, 1Forschungszentrum Dresden-Rossendorf, Dresden, Germany, 2Australian National University, Canberra , Australia, 3Utrecht University, Utrecht, The Netherlands
0.4
0.3
(e)
0.2
0.1
0.0
-0.1
-0.2
0
1
2
+
3
4
14
38 MeV I fluence (10 cm
5
-2
)
Fig. 1: Ge spheres of different sizes embedded in SiO2
show different response to 1x1014 cm-2 I7+ ion irradiation at 38 MeV (a). Large nanospheres (>35 nm) are
not deformed (b), smaller ones become discs (c), and
very small ones have Ge loss at their equator (d). The
critical sizes as well as the shaping have been modelled
and simulated (e).
Fig. 2: Au nanospheres of 15 nm diameter embedded in
SiO2 are deformed into rods by 54 MeV Ag+ beams
(experimentally found rod length versus initial radius
plotted as full squares). The simulated rod shapes and
their length (open circles) agree nicely with the experiment.
Fig. 3: Au nanospheres of a critical size respond to
central ion impacts only, i.e. Au is squeezed out of the
poles. This feature is seen in experiments (left) [3] as
well as in simulations (right), which provides some
evidence for the validity of the model.
O3
PROTON BEAM WRITING AND APPLICATIONS. R. Feder, F. Menzel, T. Butz, Faculty of Physics and
Geosciences, Linnéstr. 5, 04103 Leipzig, Germany
Proton Beam Writing (PBW) is a direct-writing
process using a focused ion beam to change the physical and chemical properties of an irradiated area. It is
similar to direct writing using electrons, but due to the
higher mass, protons penetrate deeper and experience
lower straggling, which increases the aspect ratio of the
created structures. Whereas optical or UV-lithography
is limited by interference effects the minimal structure
size using PBW is only defined by the beam size and
the sample material. It is also possible to create 3dimensional structures utilizing the energy dependency
of the stopping cross section or the well-defined ion
range. PBW, not restricted to resist materials, offers a
large number of applications by patterning semiconductors, polymers or biological substances like AGAR.
At LIPSION we investigate new materials and applications for PBW. The irradiation of PMMA allows
the construction of enclosed micro-channels for microfluidic devices. Patterned AGAR-areas are used as
substrate for the growth of neuronal networks. The
change of the electric properties in different semiconductors by PBW, in connection with electro-chemical
etching, lead to positive or negative structures with
high aspect ratios. Subsequent processes like Niplating or evaporating the developed structures with
metals also offer new possibilities like the production
of micro-meshes or multi-electrode arrays.
O4
ION MICRO-TOMOGRAPHY. M. Rothermel1, T. Andrea1, T. Reinert2, T. Butz1, 1Institute for Experimental
Physics II, Department Nuclear Solid-State Physics, Faculty for Physics and Earth Sciences, Leipzig University,
Linnéstraße 5, D-04103 Leipzig, Germany, [email protected], 2Department of Physics, 1155 Union
Circle, # 311427, University of North Texas, Denton, TX 76203, USA
Ion micro-tomography can be used to determine the
three-dimensional distribution of a sample’s mass density and elemental composition. This information is
obtained by combining the two analytical techniques
scanning transmission ion micro-tomography (STIMT) and particle induced X-ray emission tomography
(PIXE-T). The tomogram is a 3D image of stacked,
reconstructed 2D slices or projections. The projection
data are collected in two consecutive series of measurements, during which the sample is rotated in small
steps. If a complete revolution by 180°/360° is not
possible, the data from missing angles have to be
extrapolated (limited angle tomography). Whereas
STIM uses the energy-loss of each single transmitted
ion to gain contrast, PIXE requires higher ion currents
(since the cross sections of X-ray excitations must be
taken into account), but delivers the elemental information. Using the spatially highly resolved STIM mass
density data, the spatial resolution of the elemental
distribution can be enhanced. Because all ions have to
traverse the sample, the upper limit of the sample size
is given by the range of the ions in the material of typically 10 to 50 µm.
The slices are reconstructed by backprojection of
filtered projections (BFP). Since X-ray absorption and
fluorescence in the sample cannot be taken into account during the reconstruction, they need to be corrected afterwards. The discrete image space reconstruction algorithm [1] iteratively corrects a sketchy
initial tomogram estimated from the experimental reconstruction. The necessary correction factors are calculated comparing the reconstruction of the experimental data with the reconstruction of simulated data. For
the simulated data, sets of STIM projections and PIXE
maps are computed from the sketchy tomogram. These
data sets are processed with the BFP algorithm to get
the simulated reconstruction data.
Besides the basics of tomography we will elucidate
the data processing and present results ranging from
cell biology to materials science.
Reference: [1] Sakellariou A., Cholewa M., Saint
A., Legge G.J.F. Meas. Sci. Technol. 8 (1997) 746758.
O5
PROTON BEAM-INDUCED ULTRATHIN LAYER SPLITTING. O. Moutanabbir, Max Planck Institute of
Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany, Email: [email protected]
Introduction: Proton beams provide unique opportunities for controlled manipulation and integration of
semiconductors materials on foreign platform [1].
These hybrid structures, unattainable by other micro
and nanofabrication processes, open up fully new areas
in advanced electronic, photonic and optoelectronic
devices and offer an additional degree of freedom in
the design and fabrication of high efficiency photovoltaics. As illustrated in Figure 1, this process employs
protons, with a typical energy in the range of 50–
200 keV, to induce a mechanically fragile zone under
the surface of the donor wafer. The implanted wafer is
then bonded to a handle wafer and the obtained pair is
subjected to thermal annealing at a temperature in the
200–500ºC range. During annealing, the interaction of
the implanted species with the radiation damage acts as
an atomic scalpel producing extended internal surfaces
parallel to the bonding interface (Fig. 2). This leads to
the splitting and transfer of a thin layer with a thickness
roughly equivalent to the implantation depth. This
process is commonly known as ion-cut process.
Results and Discussion: In this presentation, I will
describe the current scientific background of the ioncut process as well as its future and potential technological applications. Examples of successful demonstration of the ion-cutting in Si, SiGe, InP, GaAs, AlN, and
GaN will be presented. I will emphasize the current
understanding of the physical mechanisms and atomic
processes governing the proton-induced semiconductor
ultrathin layer splitting. Results from cross-sectional
Transmission Electron Microscopy (XTEM), Atomic
Force Microscopy, vibrational spectroscopies, x-ray
diffraction, ion-channeling and positron annihilation
spectroscopy analyses will be presented and discussed.
In silicon, detailed investigations of the thermoevolution of proton-induced damage have demonstrated that
hydrogen liberated from multivacancies plays the key
role in strain buildup, which is manifested by the reverse annealing in the displacement field measured by
the ion-channeling spectra [2]. However, direct evidence for what precise form the free hydrogen takes is
still missing. Moreover, this free H does not appear to
be essential to feed the sub-surface microcracks, the
key defects are, however, the H-saturated platelets.
Positron annihilation measurements point to large cavities (V4) as plausible sites for hydrogen retrapping.
Interestingly, exploring the ion-cut of silicon at a low
temperature (150 K) provided a strong evidence of the
critical role of the stabilizing effect of dangling bond
passivation by H [3]. These studies have led to a detailed mechanistic picture of the ion-cut process. However, these mechanisms are not universal and depend
strongly on the nature of the materials. Indeed, for instance, in GaN the produced microstructure is funda-
mentally different and mainly characterized by the absence of the reverse annealing [4], which is characteristic of the critical regime leading to silicon splitting
[3]. In addition, the morphology of void-like structures
(believed to be the embryos of sub-surface microcracks) was also found to be very sensitive to the material [5]. This indicates that the intrinsic mechanical
properties as well as the nature of proton-induced defects may be critical in the ion-cut process.
Acknowledgment: This work was supported by
the German Federal Ministry of Education and Research BMBF (Contract Nr. 01BU0624: CrysGaN).
References: [1] Moutanabbir O. and Gösele U.
Annual Review of Materials Research 40 (in press).
[2] Moutanabbir O. et al. PRB 75 (2007) 075201.
[3] Moutanabbir O. et al. PRB 79 (2009) 233202.
[4] Moutanabbir O. et al. APL 93 (2008) 031916.
[5] Moutanabbir O. et al. PRB (in press).
Fig. 1: Schematic illustration of the ion-cut process.
Fig. 2: (a) XTEM image of 50 keV H-implanted GaN
at a fluence of 2.6×1017 cm-2. (b) XTEM image of Himplanted GaN after annealing at 600ºC for 5 min. The
measured atomic displacements and H concentration
depth profiles are superposed.
O6
APPLICATION OF ION BEAM TRIMMING TECHNOLOGY IN SEMICONDUCTOR INDUSTRY.
F. Allenstein, M. Zeuner, M. Demmler, T. Dunger, M. Nestler, Roth & Rau MicroSystems GmbH, Gewerbering 3,
09337 Hohenstein-Ernstthal, Germany
In this paper we present state-of-the-art applications by
using Focussed Broad Ion Beam Sources with a typical
ion beam energy range of 100 V up to 2 kV and beam
currents in a range of about 5 mA up to 500 mA. Many
applications in semiconductor technology are characterized by extreme requirements in terms of film thickness homogeneity. For manufacturing Surface Acoustic
Wave (SAW) and Bulk Acoustic Wave (BAW) devices it is necessary to adjust geometrical dimensions of
different materials with accuracies in the sub-nm range.
Standard film deposition processes do not fulfill these
homogeneity requirements, consequently it is necessary to perform a local correction of dimensions in a
follow-up process [1,2].
Introduction: The authors introduce a new method
of local film thickness trimming and its technical implementation. During the process, the wafer is moved
in front of a focussed ion beam. The local milling rate
is controlled upon the residence time of the ion beam
at certain positions. A modulated velocity profile is
calculated specifically for each wafer, in order to mill
the material at the associated positions to the target
film thickness. Depending on whether an inert or reactive ion beam process is used, it is possible to apply the
IonScan technology for any material desired, such as
Si3N4, SiO2, Al2O3, AlN, W or NiFe.
Principle of ion beam trimming technology: Ion
beam trimming can be performed with either an aperture or a residence time method. In the aperture method, a large surface ion beam gets shaped with a shutter system in its temporal progression. The local ion
dose is controlled in a defined way by variable aperture windows of different size, that are chronologically consecutive. However, the technical effort implementing the aperture method is notably high. At the
same time, the process rates are low due to blanking a
large share of the ion beam. Consequently, the aperture method is normally out of question for use in a
production environment. It is much easier to control
the local removal characteristics by means of the residence time method. The residence time method uses a
focused ion beam, which is moved in relation to the
substrate to be corrected according to a defined motional strategy. It is possible to calculate the required
residence time values at the corresponding positions
and the appropriate motional mode being aware of the
static etch profile of the ion beam. The basic process
arrangement of the residence time method is shown in
Fig. 1. The residence time method does not require
any additional aperture or shutter systems. This method always utilizes the ion beam to its full extent for
etching, and small-sized and economic ion sources are
sufficient. For these reasons, the residence time me-
thod is commonly superior to the aperture method,
both under technological and economic aspects. However, using the residence time method demands a sufficiently low width of the ion beam versus the local
wavelength of the surface errors to be corrected. A 2axis system is required to implement the residence
time method in order to carry out the necessary relative motion between the ion source and the surface.
The layout of the axis system mainly depends on the
motional strategy. Present default is to scan the surface following a meandershaped course (Fig. 1). In
this case, the performance of both axes may be clearly
different, since one of the axes has only a linefeed
function.
Fig. 1: Schematic diagram of film thickness trimming.
Results: IonScan trimming is suitable for a wide
range of applications. Until now main applications are
SAW and BAW manufacturing. The main item of
each BAW device is a piezoelectric film regularly
made of aluminium nitride and contacted by two electrodes. To generate an acoustic resonator, the thickness of the piezoelectric film has to be adjusted to /2
of the wavelength of the transversal acoustic wave.
The frequency gets finally tuned with a small additional mass load, which is deposited onto the upper
electrode as additional film, mostly silicon nitride.
IonScan 800 is capable of adequately trimming of all
films in a BAW stack. The system performance has
been demonstrated for trimming of the Si3N4 mass
load of a Solid Mounted Resonator (SMR). The mean
target frequency of 896 MHz was adjusted by
0.19 MHz, the 1σ standard deviation simultaneously
reduced from 8.29 by a factor of 12 down to
0.70 MHz.
References: [1] Lakin K.M., Kline G.R., McCarron K.T. IEEE Transactions on Microwave Theory
and Techniques 41 (1993) 2139. [2] Aigner R. 2nd
Int. Symp. Acoustic Wave Dev. Fut. Mob. Comm.
Syst., Chiba (Japan) 2004.
O7
ION IMPLANTED SILICON SENSORS REALIZED BY KETEK IN CO-OPERATION WITH FZD.
F. Wiest1, T. Eggert1, R. Fojt1, L. Höllt1, J. Knobloch1, A. Pahlke1, S. Pahlke1, R. Stötter1, B. Schmidt2, H. Lange2,
1
KETEK GmbH, Hoferstr. 3, 81737 Munich, Germany, Phone: +49 89 67346772; Fax: +49 89 67346777; Email:
[email protected],2Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Division of Process Technology, P.O. Box 510119, 01314 Dresden, Germany, Phone: +49 351 260 2726,
Fax: +49 351 260 3285, Email: [email protected]
In 2004 Ketek has established a long term co-operation
with the Research Centre Dresden (FZD) and the Universität der Bundeswehr München (UBW) targeted on
the development of new ion implanted silicon radiation
detectors as well as on their commercialization.
Silicon Drift Detector (SDD): SDDs are widely
used in XRF, TXRF, electron microprobe analysis
systems and synchrotron applications. The big benefit
of SDDs compared to other X-ray detectors as Si(Li)s
or pin-diodes is the spectroscopic performance principally being independent of the sensitive area. Ketek
offers silicon drift detectors with sizes varying from 10
to 100 mm2 whereby the large area devices become
more and more attractive for most of the applications.
Energy resolution below 130 eV for the Manganese K
line and peak to background values of more than
10.000 can be achieved for devices with active areas of
100 mm2 when cooled down to -60°C. This temperature can be already realized by a Peltier element integrated into the detector module, since the thermal
budget of this evacuated device is well-optimized.
Count rate dependency of the energy resolution and the
peak position is negligible up to count rates of 100.000
counts per second.
Silicon Photomultiplier (SiPM): SiPMs are single
photon sensitive devices built from an avalanche photodiode (APD) array on common Si substrates,
whereby the APDs are operated in Geiger modus
(above break down voltage).
All applications for this sensor are connected with
fast low level light sensing like e.g. the indirect gamma
radiation detection by a scintillator.
The first SiPM prototypes, which have been realized by Ketek in co-operation with FZD, show promising values for photon detection efficiency, dark rate
and optical cross talk. Now this detector shall be further optimized for PET application.
1400
1 p.e.
SiPM Type 120B
Size: 1 mm x 1mm
Temp.: 22.5 °C
2 p.e.
Number of Events
1200
3 p.e.
1000
800
0 p.e.
600
4 p.e.
400
5 p.e.
200
6 p.e.
7 p.e. 8 p.e.
Counts [1/eV]
10000
1000
65 mm² SDD
collimated to 50 mm²
FWHM 126 eV
P/B 12420
Peaking time 16 µs
Chip temperature -60°C
0
100
200
300
400
500
600
700
Fig. 2: Single photon spectra from a Ketek SiPM device taken at room temperature. The device has an active area of 1.0 mm x 1.0 mm. The pixel size is
120 µm x 120 µm.
100
10
1
1
2
3
800
QDC Channel
4
5
6
7
8
Energy [keV]
Fig. 1: Spectrum of the Manganese K - and K -line.
Active Vitus detector area is 50 mm2. The chip temperature of -60°C is achieved with an integrated thermoelectric cooler.
O8
OXIDATION PROTECTION OF TITANIUM ALUMINIDES AND Ni-BASE SUPERALLOYS AT HIGH
TEMPERATURES BY FLUORINE ION IMPLANTATION – PRINCIPLES AND APPLICATIONS. H.-E.
Zschau and M. Schütze, DECHEMA e. V., Karl-Winnacker-Institut, Theodor-Heuss-Allee 25, D-60486 Frankfurt
am Main, Germany, Email: [email protected]
The presentation focuses on the application of ion
beams in the field of oxidation protection of materials
developed for high temperature environments. The
Gamma-Titanium Aluminides (44-50% Al) are expected to substitute the presently used Ni-base superalloys at temperatures between 700-1100°C due to their
excellent specific strength and their specific weight
reduced by a factor of 50%. To overcome the poor
oxidation resistance of TiAl at temperatures above
750°C ion beams are used for surface modification. By
F-ion implantation and oxidation (24 h/900°C) the
formation of a protective alumina scale can be
achieved. The effect can be explained by the preferred
formation of volatile Al-Fluorides and their oxidation
on the surface. The thermodynamic model [1] predicted the fluorine effect for TiAl within a corridor of
total fluorine amount in terms of partial pressures. To
meet this condition in terms of F-concentration (in at.%) numerous Monte Carlo simulations of the Fimplantation depth profiles by using T-DYN software
were performed to obtain a suitable set of implantation
parameters [2]. The PIGE technique (Proton Induced
Gamma-ray Emission) was applied to verify the implantation profiles. The values of 2x1017 F cm-2 /
20 keV were identified to be an optimal parameter set.
The time behaviour of the fluorine concentration at the
metal/oxide interface was studied. Parameters were
formulated and determined proofing the long-term stability of the fluorine effect [3]. The technological potential is pointed out by considering other methods of
F-application (liquid phase, gas phase).
The Ni-base superalloys with Al-contents of less
than 10 wt.-% are widely used in high temperature
technology due to their beneficial mechanical properties. In contrast to this their oxidation resistance may
be insufficient at temperatures above 1000°C. Oxidation of these Ni-base alloys does not form a pure continuous alumina protective scale on the surface, but
rather a complex layer structure. This structure is characterized by internal oxidation. However, the formation of a dense continuous alumina scale without significant internal oxidation would theoretically be possible, if a “critical“ Al-concentration Nc is realized.
This critical value Nc was calculated from Wagner„s
oxidation theory [4] for Ni-base alloys to be less than
10 wt.-%.
In this work a new concept for the formation of a
protective alumina scale on the surface is presented.
The change of the alumina formation from a discontinuous internal to a continuous dense protective external oxide scale can be achieved by an “artificial” increase of the Al-activity on the surface. This can be
realized via the halogen effect. Thermodynamical cal-
culations show the existence of a region for a positive
fluorine effect for the Ni-based alloy IN 738 and
IN 939 at temperatures between 900-1200°C. These
results had to be transformed into fluorine calculations
by a screening using ion implantation. Following combined Monte Carlo calculations, fluorine implantations,
PIGE–measurements of the fluorine profiles and oxidation at 1050°C an optimal set of implantation parameters was found [5]. The oxidation mechanism was
changed into the formation of a dense protective alumina scale (Fig. 1). The oxidation protection was
shown
by
mass
gain
measurements
of
1000 h/1050°C/air showing alumina kinetics after an
incubation time.
Cr2O3
Internal Al2O3
Nitrides
Alloy
Spinel
Alloy
external Al2O3
Fig. 1: Cross-section of alloy IN 738. Top figure: Untreated sample after oxidation (48 h/1050°C). Bottom
figure: Implanted sample (7.5 x 1016 F cm-2) after oxidation of 60 h/1050°C.
References: [1] Donchev A., Gleeson B., Schuetze M. Intermetallics 11 (2003) 387. [2] Zschau H.-E.,
Gauthier V., Schütze M., Baumann H. and Bethge K.
Proc. Internat. Symposium Turbomat, Bonn, 17.19.6.2002, 210-214. [3] Zschau H.-E. and Schütze M.
MRS Symposium Proceedings Volume 1128 (2009)
165-170. [4] Whittle D.P. Oxid. Metals 4 (1972) 171179. [5] Zschau H.-E., Renusch D., Masset P. and
Schütze M. NIMB 267 (2009) 1662-1665.
O9
A CHARACTERISATION OF ELECTRONIC PROPERTIES OF ALKALINE-TEXTURIZED
POLYCRYSTALLINE SILICON SOLAR CELLS USING IBICC. A.M. Jakob, R. Thies, D. Spemann,
N. Barapatre, J. Vogt and T. Butz, University of Leipzig, Institute for Experimental Physics II, Nuclear Solid State
Physics, Linnéstr. 5, 04103 Leipzig, GERMANY, [email protected]
In this study, electronic properties of p-type alkalinetexturized polycrystalline silicon solar cells were investigated using IBICC analysis. With this technique quantitative information on minority carrier diffusion
lengths and mean minority carrier capture cross sections of lattice defects generated by high energy protons
were obtained. Since lateral IBICC measurements
could not be performed on these samples angularresolved IBICC was used to quantify the electronic
diffusion lengths. For this purpose, the experimental
data were fitted using a simulation based on the RamoShockley-Gunn theorem and the assumption of an
abrupt pn-junction. In order to determine the mean minority carrier capture cross section of proton-induced
lattice defects, the loss of charge collection efficiency
(CCE) was plotted vs. the accumulated ion dose. As
will be demonstrated, a simple model based on charge
carrier diffusion and Shockley-Read-Hall recombination is able to fit the CCE loss well. However, this
model is not capable to differentiate between various
defect types.
Furthermore, spatially and energetically highly resolved IBICC-maps of grain boundaries were recorded.
A comparison with PIXE-maps shows that there is no
correlation observable between CCE variations at grain
boundaries and metallic impurities within the PIXE
detection limits of a few ppm. On the contrary, there is
an evident correlation to the morphology of the sample's surface as was observed by comparing IBICCmaps with SEM-micrographs. Local CCE fluctuations
are dominated by the interaction of charge carrier diffusion processes and the sample surface morphology.
Neither recombination mechanisms on impurities nor
on grain boundaries are significant for local CCE variations on the p-type alkaline-texturized silicon solar
cells investigated here.
Top: IBICC-map of a p-type alkaline-texturized silicon
solar cell (1800 keV He+ ions); Bottom: SEMmicrograph of the same region. Correlations between
the sample’s topology and local CCE variations are
clearly visible.
O10
TUNING THE PHYSIOCHEMICAL PROPERTIES OF MICA SURFACES BY LOW ENERGY ION
BOMBARDEMENT. A. Keller1, M.D. Dong1, M. Fritzsche2, M. Ranjan2, S. Facsko2, Y. Yu3, Q. Liu3, Y.-M. Li3,
and F. Besenbacher1, 1 Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, Ny Munkegade, DK8000 Aarhus C, Denmark, [email protected], 2Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, PO Box 510119, 01314 Dresden, Germany, 3Key Lab of Bioorganic Phosphorus Chemistry & Chemical Biology, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China
Many biochemical in-vivo processes are catalyzed by
the presence of surfaces and influenced by the different physiochemical surface properties, e.g. amyloid
aggregation that can occur on hydrophilic cell membranes and on the hydrophobic interior of lipid bilayers [1]. Therefore, detailed studies of the influence of
the hydrophilicity and hydrophobicity on these
processes are necessary. However, tuning the hydropho-bicity of a biological model surface represents an
expe-rimental challenge. In the past, this has mainly
been achieved by chemically modifying the model
surface [2] or by using different types of surfaces [1].
For example, it has been shown that amyloid fibrillation, which plays an important role in several neurodegenerative diseases, follows different pathways on
hydrophilic mica and hydrophobic graphite surfaces,
respectively [1]. However, also the different chemical
properties of the model surfaces and their crystalline
structure were found to affect amyloid fibril formation. Therefore, it is hard to separate the influence of
the hydrophobicity from that of the chemical environment.
Muscovite mica is a material that is commonly
used as a model surface in the study of biomolecules
at the solid-liquid interface. Crystalline muscovite
mica has a layered structure consisting of negatively
charged alumi-no-silicate sheets that are bound to alternating layers of K+ ions. Mica can thus be easily
cleaved, which yields an atomically flat hydrophilic
surface. Under aqueous conditions the outermost K+
ions are exchanged in solu-tion, leaving a surface with
a negative net charge. The charged mica surface is
ideally suited for the adsorption and immobilization of
positively charged biomolecules like proteins.
In this work, we have utilized low energy ion bombardment to tune the hydrophobicity of mica surfaces.
During sub-keV noble gas ion bombardment, the first
few nanometers of the crystalline mica surface are
amorphized. This results in a reduced charging of the
surface in aqueous solution [3]. In addition, preferential sputtering leads to an enrichment of Al in the surface [3]. Here, we show that the ion-induced amorphization also makes the mica surface hydrophobic, resulting in a contact angle of about 60° compared to a
contact angle of close to 0° for the freshly cleaved and
of < 30° for the uncleaved oxidized mica surface, respectively (see insets of Fig. 1). Our results indicate
that this mechanism also works at a very low ion energy of 25 eV where sputtering can be neglected. Thus,
low energy ion bombardment enables the tuning of the
hydrophobicity of mica surfaces without changing their
chemical composition. By using mica surfaces modified in this way, we investigate the influence of hydrophobicity on the surface induced aggregation of the
islet amyloid polypeptide (IAPP), which is asso-ciated
with the occurrence of type II diabetes mellitus and
find that the hydrophobicity induces the formation of
aggregates of different conformation (see Fig. 1).
a
b
Fig. 1: IAPP aggregates on (a) uncleaved mica (contact angle < 30°) and (b) ion bombarded mica (contact
angle ~ 60°) after 4 hours of incubation. The insets
show water droplets on the surfaces.
References: [1] Kowalewski T. and Holtzman
D.M. PNAS 96 (1999) 3688–3693. [2] Zhu M. et al.
JBC 277 (2002) 50914–50922. [3] Buzio R. et al.
Surf. Sci. 601 (2007) 2735–2739.
O11
DOPING OF GERMANIUM BY ION IMPLANTATION AND FLASH LAMP ANNEALING. C. Wündisch1,
M. Posselt1, B. Schmidt1, V. Heera1, A. Mücklich1, W. Skorupa1, T. Clarysse2, E. Simoen2 and H. Hortenbach3,
1
Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, P.O.Box 510119,
D-01314 Dresden, Germany, 2IMEC Kapeldreef 75, B-3001 Leuven, Belgium, 3Qimonda Dresden GmbH & Co
OHG, Fraunhofer-Center Nanoelektronische Technologien (CNT), Königsbrücker Landstrasse 180, D-01099 Dresden, Germany (present adress: SGS Institut Fresenius GmbH, Zur Wetterwarte 10, D-01109 Dresden, Germany)
In the past the lack of stable native germanium oxide
for surface passivation and gate dielectrics as well as
the inability to epitaxially grow sufficiently thick
defect-free germanium layers on silicon hindered the
integration of germanium into the mainstream Si-based
technology. Recent developments, such as high-k
dielectrics and germanium-on-insulator substrates have
made germanium a promising candidate for future high
mobility devices. Therefore, electrical doping of
germanium by ion implantation and subsequent
annealing has drawn a renewed interest. Investigations
on the formation of ultra shallow junctions by ion
beam processing have shown that p+-doping using B
yields junctions that meet the requirements for the
22 nm technology node, whereas the formation of n+junctions by P or As is complicated by the high
diffusivity and the low solubility of the dopants [1].
Recently, the concentration-dependent diffusion of ndopants like P, As and Sb has been explored, and it has
been found that doubly negatively charged vacancies
are the mobile species responsible for the migration of
the dopant atoms [2]. The application of conventional
rapid thermal annealing (RTA) with durations of some
seconds and temperatures above about 500°C leads to
the activation of the n-dopants but their fast
concentration-dependent diffusion can generally not be
prevented. On the other hand it has been shown [3,4]
that both the diffusion and the activation of the dopants
does not depend significantly on the implantation
damage, i.e. using the defect engineering schemes
known from Si technology seems not to be promising.
Therefore, in order to control junction depth and
dopant activation ultra-short annealing by flash lamps
or lasers are currently under investigation.
The present work deals with the application of
millisecond flash lamp annealing (FLA) [5,6] to
samples containing an implanted surface layer of about
100 nm thickness. P or As ions were implanted at an
energy of 30 or 90 keV, respectively, and a fluence of
3x1015 cm-2. The investigations are focused on solid
phase epitaxial recrystallization, dopant redistribution
and dopant activation. The dependence of these effects
on the heat transfer to the sample during FLA as well
as on pre-amorphization and pre-annealing treatment is
discussed. The results are compared to typical data
achievable by RTA. Different characterization methods
were employed. Channeling Rutherford backscattering
spectrometry and cross-sectional transmission electron
microscopy (XTEM) were used to monitor the
recrystallization of the amorphous layers formed
during implantation. The depth distributions of P and
As were measured by secondary ion mass
spectrometry. In order to determine the sheet resistance
variable probe spacing and micro four point probe
measurements were utilized. Selected samples were
studied by XTEM to search for precipitates and endof-range defects. While in RTA the concentration
dependent dopant diffusion hinders the formation of
ultra-shallow n+ layers, FLA does not cause any
diffusion. The maximum activation obtained by FLA is
about 6x1019 and 2x1019 cm-3 for P and As,
respectively. This is about 3-4 times higher than under
typical RTA conditions. However, the activation and
the sheet resistance achieved by FLA do not yet fulfill
the ITRS requirements for the 22 nm technology node.
Possible mechanisms responsible for dopant
deactivation are discussed.
References: [1] Simoen E., Satta A., D’Amore A.,
Janssens T., Clarysse T., Martens K., De Jaeger B.,
Benedetti A., Hoflijk I., Brijs B., Meuris M. and
Vandervorst W. Mater. Sci. Semicond. Processing 9
(2006) 634. [2] Brotzmann S. and Bracht H. J. Appl.
Phys. 103 (2008) 033508. [3] Posselt M., Schmidt B.,
Anwand W., Grötzschel R., Heera V., Mücklich A.,
Wündisch C., Skorupa W., Hortenbach H., Gennaro S.,
Bersani M., Giubertoni D., Möller A. and Bracht H. J.
Vac. Sci. Technolog. B 26 (2008) 430. [4] Koike M.,
Kamata Y., Ino T., Hagishima D., Tatsumura K.,
Koyama M. and Nishiyama A. J. Appl. Phys. 104
(2008) 023523. [5] Skorupa W., Panknin D., Anwand
W., Voelskow M., Ferro G., Monteil Y., Leycuras A.,
Pezoldt J., McMahon R., Smith M., Camassel J.,
Stoemenos J., Polychroniadis E., Godignon P., Mestres
N., Turover D., Rushworth S. and Friedberger A.
Mater. Sci. Forum 175 (2004) 457. [6] Wuendisch C.,
Posselt M., Schmidt B., Heera V., Schumann T.,
Mücklich A., Grötzschel R., Skorupa W., Clarysse T.,
Simoen E. and Hortenbach H. Appl. Phys. Lett. 95
(2009) 252107.
O12
EX SITU n AND p DOPING OF VERTICAL Si NANOWIRES BY ION IMPLANTATION. Xin Ou1,
Pratyush Das Kanungo2 and Michael Zier1, 1Forschungszentrum Dresden-Rossendorf, Bautzner Landstrasse 400,
01328 Dresden, Germany, [email protected], [email protected], 2Max Planck Institute für Mikrostrukturphysik, Weinberg
2, 06120 Halle, Germany, [email protected]
Introduction: Vertical epitaxial short (200-300 nm
long) silicon nanowires (Si NWs) grown by molecular
beam epitaxy on Si(111) substrates were separately ex
situ doped, p- and n-type, by implantation with B, P
and As ions, respectively, at room temperature. Multienergy implantations were used for each case with
fluences in the order of 1013-1014 cm-2 and the NWs
were subsequently annealed by rapid thermal
annealing (RTA). Transmission electron microscopy
showed no residual defect in the volume of the NWs.
Electrical I-V measurements of single NWs with a
Pt/Ir tip inside an SEM showed significant increase of
electrical conductivity of the implanted NWs
compared to that of a nominally undoped NW. The ptype i.e. B implanted, NWs showed the conductivity
expected from the intended doping level. However, the
n-type NWs, i.e. P- and As-implanted ones, showed 12 orders of magnitude lower conductivity. This result,
which was predicted by theory, can be explained by a
stronger dopant segregation and a charge carrier
depletion at the NW surface. Such surface effects are
mainly responsible for the different behavior of the ntype NWs.[1,2]
Moreover, Si NW cross section specimen were
fabricated and investigated by scanning spreading
resistance microscopy (SSRM), a technique that
allows measuring the carrier profiles.
The three-dimensional SSRM profile of a NW was
obtained by measuring the NW cross sections at
different depths along the radial direction. The
achieved three-dimensional carrier profile reveals a
multi-shell structure of the carrier distribution across
the NW diameter, which consists of a lower doped
core region, a higher doped shell region and a carrier
depleted sub-surface region.[3]
Problems to create a good quality p/n junction in
vertical NWs by ion implantation are discussed by
comparison of the experimental and theoretical dopant
distributions across the nanowire.
References: [1] Das Kanungo P., Kögler R.,
Nguyen-Duc K., Zakharov N., Werner P. and Gösele U.
Nanotechnology 20 (2009) 165706. [2] Das Kanungo
P., Kögler R., Werner P., Skorupa W. and Gösele U.,
Nanoscale Res. Lett. 5 (2009) 243-246. [3] Ou X.,
Das Kanungo P., Kögler R., Werner P., Gösele U.,
Skorupa W. and Wang X., Nano Letters 10 (2010)
171-175.
O13
SURFACE PROCESSES IN REACTIVE PLASMAS. A. von Keudell, Research Group Reactive Plasmas, RuhrUniversity Bochum, 44801 Bochum, Germany
Reactive plasmas are a versatile tool for numerous
applications. Based on the non-equilibrium chemistry
in most low pressure and some atmospheric pressure
plasmas, synthesis routes can be tailored to the desired
goal and the surface properties of delicate objects can
be easily altered and modified. At present, however,
the basic understanding of the underlying physical
processes in the plasma and at the surfaces remains still
challenging. Starting with an atomic or molecular precursor gas, a multitude of species is created in the
plasma via dissociation and ionization. All these spe-
cies impinge on plasma exposed surfaces simultaneously and several synergism and anti-synergisms
dominate the overall reaction rate. The isolation of
important reaction pathways is therefore extremely
difficult. Nevertheless, it is possible to gain insight into
relevant plasma processes by combining dedicated
particle beam experiments with especially designed
plasma experiments and diagnostics to identify the
main reacting species and processes. This approach is
reviewed for the plasma deposition of carbonaceous
thin films.
O14
HYDROGEN RETENTION IN MATERIALS: A CRITICAL SAFETY ASPECT IN FUSION RESEARCH.
Joachim Roth, Max-Planck-Institut für Plasmaphysik, EURATOM Association, 85748 Garching, Germany
Introduction: Due to the use of the radioactive hydrogen isotope tritium in thermonuclear fusion reactors, the implantation, retention and permeation of hydrogen through the vessel walls of fusion devices was
considered a problem and studied intensely since the
beginning of plasma-wall interaction (PWI) research in
the 1960s. By the end of the 1980s it became clear,
both from laboratory experiments [1] and from fusion
experiments [2] that the amount of tritium retained in
layers deposited from eroded plasma-facing carbon
components contributes largely to the tritium inventory
in the plasma vessel. Only with the start of the ITER
project, the international tokamak experimental reactor
designed to demonstrate fusion as potential energy
producing technique, the tritium inventory became a
critical issue: safety considerations pose an upper limit
to the amount of tritium in the vacuum vessel equivalent to the total amount of tritium needed for few minutes of plasma operation. A reliable estimate of the
fraction of tritium retained, conditions for the reduction of this fractions and methods for the routine removal of tritium from the vessel became immediately
high priority.
Present status: The presentation demonstrates
the importance of different retention processes, which
comprise the full range of plasma-wall interaction
processes such as implantation and trapping, surface
erosion, plasma transport and co-deposition [3]. It
compares the inventory for different options of the
plasma-facing materials, Be, CFC and W, as function
of plasma operation time in ITER [4] and demonstrates how results obtained 40 years ago are still vital
for the predictions of the tritium inventory in ITER.
References: [1] Scherzer B.M.U., Wang J., Möller W. JNM 162-164 (1989) 1013. [2] Coad J.P., Behrisch, R. JNM 162-164 (1989) 533. [3] Roth J. et al.
PPCF 50 (2008) 103001. [4] Roth J. et al. JNM 390391 (2009) 1.
O15
HOW CAN ION BEAMS CONTROL MAGNETIC AND OPTICAL NANOSTRUCTURES? Harry Bernas,
CSNSM-CNRS, University Paris-Sud; 91405-Orsay, France, email: [email protected]
This talk is an attempt to relate ion beam physics to
some recent developments in materials science, and to
suggest a few areas in which the controlled use of ion
beam interactions might contribute to new advances. It
is by no means a research program – rather an invita-
tion to discuss and criticize. Some of the mechanisms
by which ion beams affect the synthesis and behavior
of nanostructures are summarized and discussed, with
a view toward studies and applications in novel areas
of nanooptics, plasmonics and ferroics.
O16
POTENTIALS, SPUTTERING, AND SWIFT IONS: COLLABORATION AND INTERPLAY WITH
GERMANY. K. Nordlund, Department of Physics, P. O. Box 43, 00014 University of Helsinki, Finland
The development of the science of ion beam effects in
materials has always involved a close interplay between theory and experiments. For instance, channeling was first predicted by computer simulations, but
quickly became an attractive experimental analysis
method, capable of detecting the lattice location of
impurity atoms in crystals. The results of this analysis
method, in turn, provide very valuable reference point
for modern density-functional theory calculation of
defect properties in solids.
In this talk, I will review some examples of our
own research that have involved an interplay between
simulations and experiments, and also interplay between research in Finland and Germany.
My first topic is a narrative of the low-energy sputtering of carbon under H isotope bombardment in fusion reactors. Experiments carried out since the 1970's
have shown that any carbon-based material in a tomaklike fusion reactor will erode chemically even for very
low energies of the impinging H ions. TRIDYN binary
collision activation computer simulations carried out in
Garching in the 1980's by Eckstein and Möller gave a
good description of the high-energy erosion and dynamic composition changes, but also showed that the
low-energy erosion cannot be physical in origin. Although a temperature dependence of the results indicated that the low-energy erosion might be associated
with thermally activated breaking of weak chemical
bonds, classical and quantum mechanical molecular
dynamics simulations carried out by us around 2000
described a fully athermal mechanism, swift chemical
sputtering, that can explain the low-energy erosion.
Strong experimental for this mechanism came in turn
when in 2004 researchers in Garching found that carbon erosion is essentially the same at 77 and 300 K,
essentially ruling out thermally activated mechanisms
at room temperature.
My second topic is an overview of the development of interatomic potentials, an activity that has its
basis in the framework for potential development laid
out by Albe and Möller in the mid-1990’s and applied
to BN. This framework has been a strong basis for a
long-running collaboration with the Albe group on
joint potential development efforts for numerous materials and application of them in studies of nanoclusters, and now the circle has closed as we are again
studying BN.
My final topic will be a description of the ongoing
quest to understand how swift heavy ions can elongate
nanocrystals in solids, a research line inspired by Heinig a few years ago, that has greatly benefited from
exchanges of ideas with him and other German scientists. While the definite understanding of this effect
still remains elusive, I will describe our recent MD
results that at least give indications of which mechanisms may or may not be relevant.
O17
ION BEAM PHYSICS WITH THE COMPUTER: FROM HARD COATINGS TO NANOSTRUCTURES.
Karsten Albe, Technische Universität Darmstadt, Institut für Materialwissenschaft, Fachgebiet Materialmodellierung, Petersenstr. 32, D-64287 Darmstadt, e-Mail: [email protected]
In the field of ion-solid interaction a general problem is
that measurable quantities are often determined by
highly multiple interactions. Therefore, computer
simulation studies, which allow to directly monitor
trajectories of atoms have become a popular tool over
the last decades. In 1994, when I started as a graduate
student with W. Möller at FZ Rossendorf, U. Littmark
published an article where he questioned the achievements and perspectives of computer simulations studies [1]. Most importantly, he was raising the question
whether computer simulation studies are only a useful
tool for technologists or, whether new physical insights
can be gained.
In this talk, I will try to find answers on this question by looking back into two topics that have been
studied, both in theory and experiment in Rossendorf.
Firstly, I will review the progress made in understanding ion-assisted growth of hard coatings. Special attention is paid to the use of molecular dynamics simulations in modelling ion-assisted thin film growth, including tetrahedral amorphous carbon film deposition
from energetic carbon ions and growth of boron nitride
[2,3].
Secondly, I will show how computer simulations
helped to improve the physical understanding of alloyed nanoparticles, that exhibit structural, thermodynamic, kinetic and functional properties which are particly difficult to reconcile with established perceptions.
In particular, I will address the example of FePt nanoparticles that are a technologically interesting material
because of the high magnetic anisotropy energy in the
chemically ordered L1o phase (fct) and present results
on unexpected effects of ion [4,5].
Finally, the talk will also include some nonscientific notes on the resigning director of the Institute
of Ion Beam Physics and Materials Research.
References: 1 Littmark U. NIMB 90 (1994) 202.
[2] Jäger H.U., Albe K. J. Appl. Phys. 88 (2000) 1129.
[3] Albe K., Möller W. Comp. Mat. Sci. 10 (1998)
111. [4] Müller M., Albe K. Phys. Rev. B 72 (2005)
094203. [5] Järvi T., Kuronen A., Nordlund K., Albe
K. Phys. Rev. B 80 (2009) 132101.
O18
RADIO BIOLOGY AT THE ION MICROPROBE SNAKE. G. Dollinger1, V. Hable1, C. Greubel1, G. Du2,
R. Krücken2, H. Strickfaden3, T. Cremer3, G.A. Drexler4, A.A. Friedl4, T. Schmid5, 1Angewandte Physik und Messtechnik LRT2, UniBw-München, D-85577 Neubiberg, Germany, 2Physik Department E12, TU München, D-85748
Garching, Germany, 3Department Biologie II, LMU-München, D-82152 Martinsried, Germany, 4Strahlentherapie
und Radiologische Onkologie, Klinikum Großhadern LMU-München, D-80336 München, Germany,
5
Strahlentherapie und Radiologische Onkologie, Klinikum Rechts der Isar, TU München, D-81675 München
Methods: The ion microprobe SNAKE, (Superconducting Nanoprobe for Applied nuclear (Kern-) phyics
Experiments) at the Munich 14 MV tandem accelerator is capable to focus ion beams to a spot size of about
0.5 µm (FWHM). SNAKE is mainly used today for
hydrogen microscopy with unrivalled sensitivity [1]
and, discussed here, for radio biology experiments [2].
SNAKE allows the accurate application of an arbitrary dose to a cell nucleus or a substructure of it using
the small spot size in combination with a single ion
preparation. Due to the wide spectrum of ion sorts
(from protons to heavy ions) and ion energies (2–
6 MeV/nucl), the dose average from a single ion deposited in a cell nucleus can be varied by about four orders of magnitude from a few mGy up to about 10 Gy.
By using online state of the art optical phase contrast
and epi-fluorescence microscopy we are able to define
the target of ion irradiation as well as to study dynamics of proteins that are stained by GFP (green fluorescent proteins) (Fig. 1) [3].
We have accomplished wide field irradiation using
microscopic patterns by a fast electrostatic scanning of
the beam. Any arbitrary field geometry can be irradiated when combining the wide field scan with additional movement of the target that is fixed on a motorised stage. Beside cell cultures the wide field irradiation can be used to irradiate artificial tissue or even
tumours in mice which are close to the skin. We have
also accomplished to obtain a nanosecond pulsed beam
for the application of a full irradiation dose of about
3 Gy by a single shot [4]. Actually the beam spot size
for the pulsed beam is limited to about 50 µm in diameter.
Investigations: A main goal of our work is to investigate the cellular response to ionising radiation,
especially the kinetics and dynamics of damaged DNA
and its repair processes. A linewise irradiation allows
analysing the movement of damaged DNA by investigating the evolution of the line pattern. Also kinetics
for the accumulation of repair factors at radiation induced foci can be followed. We use online microscopy
to investigate fast protein accumulation at damaged
DNA that happens within seconds. We show changing
kinetics depending on the stopping force of the ions
(LET: Linear Energy Transfer) and by the time course
of the dose application [5].
a)
b)
5 μm
Fig. 1: (a) HeLa-cell where part of the DNA has been
labelled by red staining. One of the small red spots
has been selected as target for a cross wise irradiation
with 55 MeV carbon as indicated by the white cross.
(b) The green channel of a green fluorescence protein
is superimposed to the red micrograph as ob-served
several minutes after irradiation. The deviation reflects the actual pointing accuracy [3].
References: [1] Reichart P. et al. Science 306
(2004) 1537. [2] Hauptner A. et al. Radiat. Environ.
Biophys. 42 (2004) 237. [3] Hable V. et al. NIM B 267
(2009) 2090. [4] Dollinger G. et al. NIM B 267 (2009)
2008. [5] Greubel C. et al. Radiat. Environ. Biophys.
47 (2008) 423.
O19
CATALYTIC MODEL SYSTEMS STUDIED BY HIGH-RESOLUTION, VIDEO-RATE SCANNING
TUNNELING MICROSCOPY. F. Besenbacher, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark, [email protected]
The development of renewable, sustainable and green
energy resources and the protection of the environment
by reducing emission pollutants are two of the largest
challenges for the human civilization within the next
50 years Besides the well-known energy resources that
power the world today; petroleum, coal, and natural
gas, active research and development exploring alternative energy resources such as solar, biomass, wind,
and hydrogen is currently being performed.
To realize the vision of a clean society and our vision of plentiful, low cost sustainable energy, research
and innovation within the area of the rapidly expanding
fields of nanoscience and nanotechnology, multidisciplinary by nature involving physics, chemistry,
biology, molecular biology, is mandatory. For decades
single-crystal surfaces have been studied under ultrahigh vacuum (UHV) conditions as model systems for
elementary surface processes. This “surface science
approach” has contributed substantially to our understanding of the processes involved in especially catalysis.
In this talk I will show how STM can reveal fundamental processes in relation to catalysis, and how we
can extract quantitative information on surface diffusion of adatoms and molecules [2-4], diffusion of va-
cancies, interstitials and molecules, e.g. water molecules on oxide surfaces [5-7], sintering and diffusion of
nanoclusters on oxide surfaces [7], diffusion of intermediate species [9,10], identification of active sites,
determination of new nanostructures with new novel
catalytic properties from time-resolved, high-resolution
STM images/movies (see www.phys.au.dk/spm) [1].
The atomic-scale information obtained may even lead
to the design of new and improved catalysts in certain
cases [11].
References: [1] Besenbacher F. Reports on Progress in Physics 59 (1996) 1737. [2] Linderoth T. et al.
Phys. Rev. Lett. 78 (1997) 4978. [3] Horch S. et al.
Nature 398 (1999) 1344. [4] Otero R. et al. Nature
Materials 3 (2004) 779. [5] Schaub R. et al. Science
299 (2003) 378 and Science 303 (2004) 511.
[6] Wendt S. et al. Physical Review Letters 96 (2006)
066107. [7] Wendt S. et al. Science 320 (2008) 1755.
[8] Matthey D. et al. Science 315 (2007) 1692.
[9] Kruse Vestergaard E. et al. Phys. Rev. Lett. 88
(2002) 259601. [10] Lauritsen J.V. et al. J. Catal. 197
(2001) 1-5. [11] Kibsgaard J. et al. Journal of the
American Chemical Society 128 (2006) 13950.
[12] Besenbacher F. et al. Science 279 (1998) 1913.
O20
EXPERIMENTAL DESIGN: OPTIMIZING IBA DEPTH PROFILING. U. von Toussaint, T. SchwarzSelinger, M. Mayer and S. Gori, Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany
Ion beam techniques have several compelling features
compared to many other surface analytical techniques.
Arguably the most useful feature is their flexibility e.g.
with respect to projectile species, projectile energy and
incidence angle. However, the systematic exploitation
of these possibilities is still limited and the continuous
adaption of the diagnostic settings based on previous
gained data is a rare exception.
However, recent advances in Bayesian Experimental Design together with increased computing power
allow optimizing the measurement strategy 'on-thefly', taking into account the results of previous measurements to select the best set-up for the next measurement and to compute the expected information
gain from further measurements.
The application of this approach will be demonstrated for the measurement of deuterium inventory in
plasma-facing materials: Here the nuclear reaction
analysis with 3He holds the promise to derive Deuterium depth profiles up to large depths from a set of
measurements with different energies.
However, the extraction of depth profiles from the
measured data is very sensitive to the quality of the
data and the commonly chosen set of equispaced energies is in hindsight often noticeably inferior to other,
optimized choices. As examples depth profiling of
Deuterium in tungsten and in amorphous hydrocarbonsamples are presented and the results of the different
approaches are compared.
O21
(UHV-)ERDA INVESTIGATION OF NEG COATINGS. Marc Wengenroth1, Markus Bender1, Holger Kollmus1, Walter Assmann2, 1GSI, D-64291 Darmstadt, Germany, [email protected], 2Department of Physics, Ludwig Maximilians University Munich, D-85748 Garching, Germany
Non evaporable getter (NEG) coatings are used to
reach and maintain UHV conditions, very often in
large vacuum installations such as particle accelerator
rings like SIS18 at GSI or the huge spectrometer vessel
of the Karlsruhe Tritium Neutrino experiment
KATRIN. For the GSI future project FAIR, a base
pressure in the lower 10-12 mbar region is necessary to
assure long enough life time of the stored heavy ion
beam. Therefore, NEG coating of the vacuum chambers inside of the magnets is planned [1]. In order to
optimize the NEG sputter coating process and, more
general, to study the hitherto not fully understood
physical processes of pumping and activation, a systematic experimental program has been started. ERDA is
an ideal tool to measure the depth distribution of light
elements, which are the main residual gas components,
in NEG layers of 1 µm thickness, typically.
During pumping one or two mono-layers of gas are
adsorbed, which in turn passivate the getter and prevent further pumping. Reactivation at temperatures
above 200ºC at UHV conditions removes the adsorbed
gas layer from the surface, partly by diffusion into the
NEG material, and prepares a new pumping surface.
Thus, the pumping capacity is limited due to the indiffusion of gas. All these processes could be studied
in a unique manner by ERDA, and in addition the quality of the production process for the NEG layer. Moreover, making use of our UHV-ERDA setup, we studied
the pumping and reactivation behaviour of NEG coatings at real accelerator conditions [2].
References: [1] Bellacioma M.C. et al. Vacuum
82 (2008) 435. [2] Bender M. et al. submitted to Nucl.
Instr. Meth. B
O22
ANALYSIS AND MODIFICATION OF THIN LAYERS BY HEAVY ION BEAMS. I. Bogdanović Radović,
M. Buljan, Z. Siketić, N. Skukan, M. Karlušić and M. Jakšić, Department for experimental physics, Ruđer Bošković
Institute, P.O. Box 180, 10002 Zagreb, Croatia, e-mail: [email protected]
Introduction: Due to the high stopping power that
heavy MeV ions have in materials, they can be successfully used for both, analysis as well as modification of different thin layers. First, an overview of recent improvements in detection systems and analysis
applications will be described. Also, we are presenting
our recent work where the ion beam irradiation has
been used to induce a formation of long-range ordered
quantum dot arrays in amorphous silica matrix.
Modifications of the existing Time-of-flight
Elastic Recoil Detection (TOF ERDA) spectrometer:
Improved detection efficiency for the lightest elements: The reason why TOF-ERDA is not usually used
for H detection is that the efficiency of carbon-foil time
detectors is less than 100% for light elements. The
detection efficiency depends on the energy and electronic stopping power of analyzing recoil atoms in the
foil, and this is particularly critical for hydrogen where
detection efficiency can decrease to only 10%. By covering DLC foils by good electron emitter (LiF), detection efficiency for 400 keV protons has increased to
~60% [1]. This was sufficient that quantitative analysis
of H and its isotopes can be performed simultaneously
with all other lighter elements in the sample in a single
measurement as is shown on Fig. 1.
(~0.1 msr) kinematic correction improves surface
time/depth resolution by ~20%. However, larger benefits can be expected for larger solid angles due to the
fact that the kinematic broadening in that case is dominant contribution to the surface time resolution [2].
Three dimensional imaging of light elements using an elastic coincidence technique: A setup for an
elastic scattering coincidence technique was installed
at an ion microprobe. It was developed for threedimensional (3D) profiling of light elements in heavier
matrices. The technique was demonstrated on 3D imaging of carbon. Recoiled carbon atoms together with
carbon ions scattered from the target were detected in
coincidence using particle detectors placed symmetrically around the beam direction at 45°. Capabilities of
the technique concerning depth resolution and sensitivity were tested by analyzing low amounts of C in thin
Al foil. 3D carbon microscopy with a position resolution in the range of 2-3 m, a sensitivity of around
1 at.%, and a depth resolution of ~100 nm was
achieved [3].
Formation of long-range ordered quantum dot
arrays in amorphous matrix: Twenty alternating
(Ge+SiO2) and SiO2 layers were deposited and irradiated by 3 MeV O ions with the dose of 1×1015 at/cm2
under the angle of 60° with respect to the sample surface. Irradiation induces the nucleation of amorphous
Ge quantum dots in well-ordered chains and the inclination angle of the chains corresponds with the irradiation direction. After the annealing quantum dots crystallize resulting in a 3D array of crystalline Ge quantum dots embedded in SiO2 matrix [4,5]. TEM images
of the multilayer after annealing are shown in Fig. 2
together with the associated GISAXS map.
Fig. 1: TOF-E coincidence spectrum of a deuterium
implanted a-Si:H sample.
Position sensitive detector: TOF ERDA was upgraded by a position sensitive detection system that is
based on microchannel plate detector in order to perform kinematic correction and improve surface
time/depth resolution. Position resolution of the detector was tested for different ions and anode voltages.
TOF spectra of recoiled O from SiO2 and F from CaF2
were collected in coincidence with position sensitive
detector signal. For small solid angles as in our case
Fig. 2: a) and b) TEM images of the multilayer after
annealing, arrows indicate irradiation direction, c) corresponding GISAXS map.
References: [1] Siketić Z. et al. Thin Solid Films
518 (2010) 2617. [2] Siketić Z. et al. accepted for publishing in Rev. of Sci. Instruments. [3] Bogdanović
Radović I. et al. JAP 105 (2009) 074901. [4] Buljan
M. et al. APL 95 (2009) 063104. [5] Buljan M. et al.
PRB 81 (2010) 085321.
O23
STUDY OF THE INITIAL STAGE OF ZrO2 GROWTH ON SiO2 OR TiN SUBSTRATES. F. Munnik,
M. Vieluf, and C. Neelmeijer, Institute of Ion Beam Physics and Materials Research, Forschungszentrum DresdenRossendorf, P.O. Box 510119, 01314 Dresden, Germany, email: [email protected]
High Resolution Rutherford Backscattering Spectrometry (HR-RBS) was used to analyse the interface
of ultrathin high-k ZrO2 layers. This method is ideally
suited for measurements of concentration depth profiles with a depth resolution of 0.3 nm near the surface.
The aim was to study atomic layer deposition
(ALD) growth processes in the initial regime of this
layer on SiO2 and TiN substrates. In order to improve
the quality of the analysis, a method was developed
that takes local thickness variations into account [1].
These thickness variations were extracted from atomic
force microscopy (AFM) measurements (e.g. Fig. 1).
For the ZrO2 layer on SiO2, the roughness was low
and the calculated thickness distribution could be used
directly for the spectrum analysis with SimNRA. The
resulting fits showed that the interface is sharp except
for a small intermediate ZrSiO4 layer and no diffusion
of Zr atoms in SiO2 could be detected.
A quite different behaviour could be observed from
the high resolution spectra for the growth of ZrO2 on
TiN. Measurements of the surface topography of the
TiN layer revealed much larger values for the surface
roughness. This required a method to capture the influence of the surface roughness on the shape of the
high resolution spectrum. A software program [1] was
developed that extracts an energy distribution from
AFM measurements. The topography matrix is used to
calculate path lengths in matter for ions scattered on
surface at each position of the matrix. The path length
differences are converted to an energy distribution.
The application of this program on the Zr spectra on a
TiN substrate revealed large differences between the
measurement and simulated spectra with correction for
roughness. It can, therefore, be concluded that diffusion of Zr into polycrystalline TiN takes place. The
detailed analysis indicates that some of the deposited
Zr atoms diffuse into the TiN layer up to a depth of
3 nm. This occurred for all studied layer thicknesses
and it is already visible after the first ALD reaction
cycle. Such a fast and large diffusion can only be explained by grain-boundary diffusion.
References: [1] Vieluf M., Ph.D. thesis (in German), Technical University Dresden, Germany, submitted.
z:
5.5 nm
-2.3 nm
y: 0.5 µm
x: 0.5 µm
Fig. 1: 3D-AFM image of ZrO2 after one ALD cycle on
20 nm of TiN.
Fig. 2: High resolution RBS spectrum of Zr on ZrO2 after
one ALD cycle on 20 nm of TiN with simulations. The
simulations are with and without the path length variations
extracted from the AFM image (Fig. 1).
O24
ORIGINAL VERSION OR NOT: PIXE-RBS TESTING OF A MEISSEN PORCELAIN BOX. C. Neelmeijer1
and R. Roscher2, 1Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research,
PF 510119, 01314 Dresden, Germany, [email protected], 2Porzellanrestaurierung, Plangasse 8, 01662 Meissen,
Germany
Introduction: The valuation of an artistic object depends decisively on its complete originality. Regarding
the 18th century snuffbox, made from Meissen Porcelain, restorers ask the following question: Are both the
base body but also the hinged cover originals?
a
trum taken from the pink gown on the cover (b) shows
signals from Au, to be characteristic for purple [3].
Corresponding low-intensity Au-peaks cannot be identified for the pink skirt painted on the bottom. This is
because of the superimposed high-intensity Pb-L lines
due to another type of glazing.
Porcelain glazing. The bottom comprises comparatively thick lead containing glazing, hence intense
Pb-L signals are found in the PIXE spectrum.
PIXE
green from leaves of the tree
Zn
c
500
Pb
Lα
Pb
Lβ
bottom
cover
100
Pb
Znβ
200
Pb-L γ
Cu
Co + Feβ
Fe
300
Feβ
Coβ
b
Intensity / Counts
400
Pb
Pb
Pb
0
5
Cover
Visual discrepancies concerning especially the shade
of porcelain glazing raised doubts. In addition, the
onglaze decorations show slight differences in colour
and flow. Assured non-destructive materials analysis
was in demand to clarify the problem.
External Ion Beam Analysis: The 4-MeV proton
beam used in atmosphere and PIXE (Particle Induced
X-Ray Emission) simultaneously with RBS (Rutherford Backscattering Spectrometry) for analysis [1,2]
proved ideal to get convincing answers. Visible marks
due to the beam spot (1 mm2) on the highly sensitive
porcelain were avoided by using only 200 pA beam
intensity and 30 s irradiation time.
Similarities and differences:
Ornamental painting. The ancient Meissen onglaze colour palette is well-known since decades [3].
In conformity with [3] the artist used the pigment copper green for leaves of trees painted on both bottom
and cover (point a). However, the green colourant of
the cover contains Co and Zn, not obtained in the Xray spectrum from the bottom. According to [3] Meissen copper green was made from Cu or brass, an alloy
of Cu and Zn, which are both reduced to ashes. The
addition of Co is mentioned [3] for getting special
shaded green paint. Whether or not such characteristic
differences are also present in the case of the crimson
clothes can not be revealed. Indeed, the PIXE spec-
10
15
20
X-ray energy / keV
The number of lead atoms inside the glazing of the
cover (c) is much lower. The latter gets reflected also
by comparing Pb-Lγ in the presented PIXE spectra
taken from the green leaves painted on glazing. Moreover, RBS taken from pure glazing of the cover makes
clear that the few Pb atoms are situated on the glazing
surface. This is understandable when supposing Pb to
originate from a surface polishing process using Pb
containing polish agent. The discussed difference in
glazing of cover and bottom and especially the considerable Pb-content of the latter, assumable to be
bond as lead oxide, clarifies the apparent discrepancies of shades.
Unfortunately, unglazed positions had not been available for getting compositions of the porcelain body.
Conclusions: Cover and base body of the porcelain
box can not be related to one and the same workmanship. The cover was certainly later on replaced or it
represents completely a later additive. Despite of differences regarding the green pigments of porcelain
paints used on bottom and cover, the box fit the typical
Meissen onglaze colour technology. Therefore, the
question - original version or not - must be answered
by the statement: Certainly not, but there is no doubt
concerning original Meissen handcraft.
References: [1] Neelmeijer C. et al. NIMB 118
(1996) 338-345. [2] Neelmeijer C. and Mäder M.
NIMB 189 (2002) 293-302. [3] Mields M., Keramische Zeitschrift 8 (1963) 453-459.
O25
FIRST RESULTS OF THE NEW M-BRANCH AT GSI PROVIDING IN-SITU ANALYTICAL
TECHNIQUES FOR MATERIALS RESEARCH. D. Severin1, S. Klaumünzer2 C. Trautmann1, R. Neumann1,
1
GSI Helmholtz Centre for Heavy Ion Research, Planckstr. 1, 64291 Darmstadt, Germany, 2Helmholtz Centre Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
The new M-branch at the UNILAC of GSI is devoted to materials research experiments with swift
heavy ions up to uranium and maximum energy
11.4 MeV per nucleon. The three new beamlines are
equipped with various analytical techniques for on-line
and in-situ monitoring of beam-induced modifications,
described in the following.
Beamline M1 is connected to a high-resolution
scanning electron microscope, housing a 5-axes motorised eucentric sample stage which allows the irradiation of a rotating specimen under variable ion beam
incidence. For imaging, the stage is tilted into the
electron beam without exposing the irradiated sample
to air.
Beamline M2 is equipped with a standard 4-circle
x-ray diffractometer (Cu-K ) and a position sensitive
detector (simultaneous measurement of 2 = 3º). Investigation under any angle of incidence enables the quantitative analysis of structural modifications such as
amorphisation or other phase transitions, internal stresses, and textural changes.
At beamline M3, irradiations at high (up to 900°C)
and cryo temperature are possible. In addition, several
state-of-the-art techniques provide in-situ analysis online or during beam-stops. The methods available include, e.g. residual gas analysis, infrared and UV/Vis
spectroscopy, laser reflectometry for stress measurements, and luminescence spectrometry.
Fig. 1: M-branch.
The experimental equipment has been built up in
collaboration with six universities (Darmstadt, Dresden, Göttingen, Heidelberg, Jena, and Stuttgart), and
the Helmholtz Centre Berlin.
First results after one year of operation will be presented and illustrated by examples of the new powerful on-line and in-situ techniques available at the
beamlines. A special focus will be set on the in-situ
XRD studies of S. Klaumünzer concerning ion beam
induced fragmentation and grain rotation of NiO.
O26
FIRST EXPERIMENTS WITH THE NEW IN-SITU SCANNING ELECTRON MICROSCOPE AT THE
UNILAC MATERIALS BRANCH. S. Amirthapandian1,2, F. Schuchart1, R. Ferhati1, N. Guilliard1, T. Weishaar1
and W. Bolse1, 1Institut für Halbleiteroptik und Funktionelle Grenzflächen, Universität Stuttgart, Allmandring 3,
70569 Stuttgart, [email protected], 2on leave from: Indira Gandhi Centre for Atomic Research, Kalpakkam, India
Introduction: During the last 3 years we have set-up
and commissioned an in-situ high-resolution scanning
electron microscope (HRSEM) in the M1-beam line of
the new M-branch at the UNILAC accelerator of the
GSI Helmholtz-Zentrum für Schwerionenforschung.
This facility allows us to investigate the development
of individual μm- and nm-scale structures and objects
in-situ during swift heavy ion (SHI) irradiation by
means of scanning electron microscopy (SEM). The
HRSEM is a standard Zeiss SUPRA 40 and presently
equipped with an annular in-lens detector, an EverhartThornley scintillation detector and a 4-quadrant Sidiode backscattered electron detector. During ion irradiation, the sample can be tilted at any angle with
respect to the ion beam axis and continuously rotated
around its surface normal. A detailed description can
be found in reference [1]. Here we will present the
preliminary results of our first experiments performed
with this new experimental set-up in order to demonstrate its unique potential for the investigation of SHI
induced modifications of solid surfaces and thin films.
SHI-Induced Dewetting (Normal Ion Incidence): Recently we have reported that SHI irradiation
of thin metal-oxide films on Si-substrates results in
dewetting effects [2,3] similar to those observed with
liquid polymer films [4], even though the irradiations
were carried out at 80 K, far below the melting point
of the film material.
In our first experiment with the new set-up we have
investigated dewetting kinetics of a 50 nm thick
Fe2O3-film on Si during irradiation with 3.6 MeV/u
Au-ions. Due to pre-irradiation with 1 Mev/u Au-ions,
the film already exhibited single, well-separated dewetting holes, the growth parameters of were individually measured in this experiment. We found a linear
relationship between the dewetted area and the applied
ion fluence, in contrast to the linear growth in time of
the hole radii in case of liquid polymer films.
Besides the already existing, new holes nucleate and
first exhibit an exponential increase of the dewetted
area before also fading into a linear areal growth. The
width of the rim, formed around the hole by the material removed from the dewetted area, increases with
increasing size of the hole until it finally saturates.
This indicates the transition into a steady state of the
dewetting process, where as much material is dissipating into the surrounding of the rim as is added from
the further growing hole.
In addition to the growth of single separated holes,
we also observed the formation of a wave-like pattern,
the amplitude of which increases with increasing ion
fluence until the wave-troughs reach the Fe2O3-Si interface and give rise to the nucleation of new holes.
This process is very similar to the spinodal dewetting
observed for the liquid polymers, except that in this
cases it is not caused by capillary waves but most
probably by an instability of the surface against periodic deformation due to irradiation induced stresses.
SHI-Induced Dewetting (Oblique Ion Incidence):
Irradiation induced stresses are also the cause for
another phenomenon we have previously observed
when bombarding NiO-films on Si with SHI under
oblique incidence [5]. Here at low fluences a more or
less regular (depending on the irradiation conditions
and the film thickness) crack pattern perpendicular to
the beam direction forms due to the uni-axial in-plane
tensile stresses caused by the solid-liquid-solid transition in the ion tracks. Further irradiation then results in
shrinking of the material between the cracks along the
beam direction and its growth along the surface normal, until finally a lamellae-like pattern is formed
(thickness ~ 100 nm, height ~ 1 μm, distance few μm).
The lamellae-formation is a consequence of the hammering effect [6].
As our second experiment we have investigated the
lamellae-formation of a 100 nm NiO-film on Si under
3.6 Mev/u Xe ions. Besides its lateral shrinking we
could nicely illustrate the formation and break-up of
cross-connections between the lamellae as well as how
the material slips off the substrate. This would be hardly possible in a conventional ex-situ experiment.
Conclusions: With the first experiments performed
at our new in-situ HRSEM SHI irradiation facility at
the UNILAC accelerator of GSI we could demonstrate
the unique potential of this instrument for the study of
SHI induced surface and thin film modifications. The
investigation of the development of individual structures under SHI bombardment allowed us to gain information about the underlying processes, which
would be hardly obtained with conventional ex-situ
experiments. Further experiments on controlled SHI
induced shaping of sub-micron and nano-sized structures are under progress.
References:
[1] Amirthapandian S., Schuchart F., Bolse W. Rev.
Sci. Instr. 81 (2010) in print. [2] Bolse T. et al. NIM B
244 (2006) 115-119. [3] Bolse T. et al. NIM B 245
(2006) 264-268. [4] Seemann R. et al. J. Phys. Condens. Matter 13 (2001) 4915-4923. [5] Bolse W. et
al., Appl. Phys. A 77 (2003) 11-15. [6] Klaumünzer S.
et al. Phys. Rev. Lett. 51 (1983) 1987-1990.
O27
HEAVY ION INDUCED DESORPTION WITH MeV–IONS. Markus Bender*1, Marc Wengenroth1, Holger
Kollmus1, Walter Assmann2, 1GSI, D-64291 Darmstadt, Germany, 2Department of Physics, Ludwig Maximilians
University Munich, D-85748 Garching, Germany
Heavy ion accelerators such as the heavy ion synchrotron SIS 18 at GSI are required to deliver more and
more output ion current. Gas desorption, stimulated by
energetic heavy ions striking the chamber wall is deteriorating the accelerator vacuum and thus limiting the
ion current.
We have investigated the process of heavy ion induced gas desorption at room temperature during recent years in order to minimize the amount of desorbed
gas. Metallic samples with different surface treatments
have been irradiated with various ion beams, and the
desorption yield (desorbed gas molecules per incident
ion) has been measured by means of the pressure rise
during the irradiation. Furthermore, the samples properties have been determined by the ion beam analysis
ERDA.
With these techniques combined, we have proved
that the origin of the desorbed gas is mainly the samples very surface. However, the bulk material plays an
important role for the desorption yield [1]. For example oxidized metals show far higher desorption yields
than pure metals, even though the desorbed gas is not
the sputtered oxide layer.
With the experimental results we were able to draw
the picture of the ion induced desorption as a pure
thermal effect. The impinging ion is heating up an area
around the ion track and gas is desorbed thermally. By
means of the inelastic thermal spike model we are able
to model desorption yields of many metals and to explain the desorption process in detail [2].
References: [1] Bender M. et al. Nucl. Instr. and
Meth. B 256 (2007) 387-391. [2] Bender M. et al.
Nucl. Instr. and Meth. B 267 (2009) 885-890.
O28
STRUCTURAL MODIFICATION OF SWIFT HEAVY ION IRRADIATED AMORPHOUS GERMANIUM
LAYERS.
T. Steinbach1, W. Wesch1, C.S. Schnohr1, P. Kluth2, Z.S. Hussain2, L.L. Araujo2, R. Giulian2,
2
D.J. Sprouster , A.P. Byrne2, M.C. Ridgway2, 1Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena,
Max-Wien-Platz 1, D-07743 Jena, Germany, 2Department of Electronic Materials Engineering, Research School of
Physics and Engineer-ing, The Australian National University, Canberra ACT 0200, Australia
Swift heavy ion (SHI) irradiation of amorphous silicon
(a-Si) at non-perpendicular incidence leads to a nonsaturable plastic flow, which shows a linear dependence on the ion fluence. The positive direction of
flow suggests that a liquid phase of similar density to
that of the amorphous solid must exist [1]. For room
temperature irradiation of amorphous silicon to very
high ion fluence (3x1015 cm-2), the plastic flow is accompanied by swelling due to the formation of voids.
To study the effect of high electronic energy deposition on amorphous germanium (a-Ge) layers, crystalline germanium (c-Ge) wafers were amorphised by ion
irradiation with various germanium ion energies and
fluences at 80 K, resulting in a 3.2 μm thick amorphous layer. A grid of Au was evaporated on the sample
surface, which was then partly masked during the subsequent irradiation. The samples were irradiated with
89 and 185 MeV Au ions at room temperature with ion
beam angles of incidence of 0°, 45° as well as 60° with
respect to the surface normal. The Au ion fluence was
varied between 2x1012 cm-2 and 2.2x1014 cm-2. The
irradiated samples were analysed by optical microscopy, surface profilometry and scanning electron microscopy (SEM), which was used in plan-view as well as
two different cross section geometries (XSEM).
Like in the case of amorphous silicon, SHI irradiation
of amorphous germanium at room temperature shows
a positive plastic flow as well (see Fig. 1), demonstrating that liquid polymorphism is common for these two
semiconductors [2].
Fig. 1: The optical micrograph shows the plastic flow
as well as the swelling of the irradiated amorphous
germanium layer during SHI-irradiation with 89 MeV
Au ions under an angle of  = 45° at room temperature. The inset shows the corresponding SEM image
with a higher magnification (scale bar: 5 µm).
However, subsequent to irradiation, a change in
sample surface colour from light brown to black accompanied by swelling of the amorphous layer was
readily apparent with increasing ion fluence (cp. Fig.
1). XSEM revealed the transformation of the initially
homogeneous amorphous germanium layer into a
sponge like porous structure with irregularly shaped
voids thus establishing that the swelling was a consequence of void formation. However, in contrast to
amorphous silicon in amorphous germanium the formation of voids begins at low ion fluence (1012 cm-2).
Fig. 2: Cross-section SEM image parallel to the projection of the ion beam (XSEM 2, cp. Fig. 1) of an aGe sample irradiated at room temperature with
89 MeV Au ions under an angle of 45°.
As a consequence of the void formation a non linear plastic flow process is observed. By means of
cross section SEM (see Fig. 2, cross section parallel to
the projection of the ion beam) it becomes apparent
that within the amorphous germanium layer the voids
do not appear to correspond to the direction of the ion
tracks along which the energy is deposited into the
electronic system of the amorphous germanium layer
but rather reflect the ion beam induced plastic flow
process in positive direction directly [3].
We will discuss the enhanced plastic deformation
and swelling effect as a function of the ion fluence and
electronic energy deposition e. Furthermore, we show
that the swelling depends on the electronic energy deposition, which enables an estimation of an electronic
energy deposition threshold, where the swelling, i.e.
the formation of voids, begins.
References: [1] Hedler A. et al. Nat. Mater. 3
(2004) 804. [2] Wesch W. et al. J. Phys. D: Appl.
Phys. 42 (2009) 115402. [3] Steinbach T., Wesch W.
et al. to be published.
Work supported by BMBF, contract no. 05KK7SJ1
and DAAD, contract no. D/07/15034.
O29
RAMAN AND NANOINDENTATION STUDY OF DEPTH PROFILE OF GeV HEAVY IONS –INDUCED
DAMAGE IN GRAPHITE. M. Tomut1,2,#, I. Manika3, J. Gabrusenoks3, J. Maniks3, R. Zabels3, M. Krause1,4,
K. Schwartz1, C. Trautmann1, 1GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße1, 64291 Darmstadt,
Germany,#[email protected], 2National Institute for Materials Physiscs, 077125 Bucharest-Magurele, Romania,
1
Institute of Solid State Physics, University of Latvia, 8 Kengaraga Street, LV-1063, Riga, Latvia, 4Technische Universität Darmstadt, Petersenstraße 23, 64287 Darmstadt, Germany
A fine-grained isotropic graphite grade with high thermal conductivity and good thermal shock resistance is
chosen as material for the beam catchers and for the
rare isotope production target at the future large-scale
accelerator facility FAIR (Facility for Antiproton and
Ion Research, Darmstadt, Germany) [1]. Ion-induced
radiation damage and thermal stress will be the limiting
factors for the the lifetime of these components. The
radiation damage mechanism is different for target and
for beam catchers. In the target, which works in transmission mode, the primary beam looses energy mostly
by inelastic collisions, while in the beam catchers there
is also an important contribution to damage from nuclear stopping processes. Experimental investigations
have been performed to asses the damage in the two
regimes.
Isotropic polycrystalline graphite samples were irradiated at room temperature with 238U and 197Au ions
with a specific energy of 11.1 MeV/u at the GSI linear
accelerator, UNILAC. Large fluence exposure was
chosen to maximize the damage. The ion range and
energy-loss were calculated using SRIM 2008 code.
For damage characterization, heavy ion-irradiated
samples of R6650 grade graphite as well as freshly
cleaved highly oriented pyrolytic graphite (HOPG,
ZYB grade, NT-MDT) were investigated using Raman
spectroscopy. The evolution of Raman spectra for the
irradiated graphite has been interpreted according to
Ferrari and Robertson [2] in terms of disordering, crystallite size reduction, bending and cross-linking of the
graphitic planes, bond-angle disorder and change in
hybridization. Depth characterization of damage for
the ion-penetrated layer of the polycrystalline graphite
has been performed on cross-section, on a plane cut
parallel to the beam incidence. For HOPG, which
serves as model material due to its well-defined structure and ideal surface conditionsion, the ion-induced
damage evolution with depth has been investigated at
different stages of cleaving. This allowed us to compare damage induced in an ideal graphite layered structure by swift heavy ions, in the surface region where
the stopping process is dominated by electronic excitation and coupling to the lattice and in the displacement
cascades region, at depths approaching the range of the
ions.
Raman characterization of ion-induced damage is
accompanied by studies of hardening on the surface
and cross-section of the ion-irradiated polycrystalline
samples.
Nanoindentation tests were performed using a MTS
G200 nanoindenter with Berkovich diamond tip
(R<20 nm) using the continuous stiffness measurements technique at load resolution <50 nN, displacement resolution <0.001 nm and strain rate 0.05 s-1. The
hardness and Young’s modulus values were an average
of 10 individual tests. The distance between adjacent
impressions was sufficiently large to avoid the interaction of deformation fields. The distances of the indents
from the irradiated surface were measured by optical
microscopy.
The ion-induced hardening on the surface of the
graphite is surprisingly high (up to 500%). For comparison, the ion-induced hardening in LiF, which
serves as a model material in radiation damage studies,
reaches about 200% [3]. This additional strengthening
can be related to increase of the sp3 bond, bending of
graphite layers and layer interconnection via interstitial
atoms, as a result of ion-induced damage. The values
of the Young’s modulus together with Raman spectroscopy results indicate the formation of stronger chemical bonds. The process is favoured by the polishing of
the sample surface before the irradiation. The grain
size reduction by polishing makes the top layer of the
graphite more sensitive to swift heavy-ion induced
damage.
Its magnitude decreases with the distance from
irradiated surface. As we approach the range of the
ions, the hardness of the sample falls below the value
for pristine sample. Hardness values lower than those
for virgin sample near the interface between irradiated
and non-irradiated layer are affected by residual elastic
stresses created due to swelling of irradiated layer.
Tensile stresses are known to reduce both Young’s
modulus and hardness.
References: [1] Henning W. et al. Nuclear Physics A 805 (2008) 502c. [2] Ferrari J. and Robertson
A.C., Phys. Rev. B 61 (1999) 14095. [3] Manika I. et
al. J. Phys. D 41 (2008) 074008.
O30
HEAVY-ION IRRADIATION AT HIGH PRESSURE USING THE PARIS-EDINBURGH PRESS.
M. Burchard1, S. Pabst1, U.A. Glasmacher1#, C. Weikusat1, R. Miletich1, B. Schuster2, C. Trautmann2,
R. Neumann2, 1Institut für Geowissenschaften, Im Neuenheimer Feld 234, 69120 Heidelberg, #[email protected]
Introdution: Up to now, diamond anvil cells (DAC)
have been used for irradiation experiments with swift
heavy ions and the simultaneous application of high
pressures and temperature [1]. DACs allow spectroscopic measurements of the irradiated sample inside the
cell, e.g. by Raman spectroscopy or X-ray diffraction.
However, the drawback is given by their extremely
small sample chamber available for sample volumes of
less than 10-6 mm3. Various measurement techniques
and industrial applications would require larger volumes of irradiated material. Here, we present the results of successful irradiations of samples inside large
volume Paris-Edinburgh presses (PE-press) [2].
The PE-press, which was developed for experimental neutron scattering, offers a defined radiation pathway as well as relatively high maximum pressure limits (up to 25 GPa). Furthermore, the sample chamber
volume reaches up to several mm3 and the sample
handling is relatively easy. Pressure on the material is
increased by an oil pressure pump attached to anvils.
The large chamber volume allows more experiments
such as combining different materials in variable grain
sizes (called mixing experiments), material with sandwich structures of several mm in size, and shear pressure experiments. To avoid severe ion-induced activation of the material within the central pressure cell, the
design of the PE-press was modified by thinning the
cBN-anvils, using a plastic blend at the entrance part
of the open channel, which is used by the swift heavy
ions to penetrate the steal material that is surrounding
the irradiation chamber. Furthermore, ultrapure silver
as secondary pressure medium and capsule material
was used to reduce the activation as well. The sample
chamber was directly drilled into the silver and has a
thin hBN-plate on the bottom and a silver foil on top.
For easy handling during the irradiation and safety
reasons, we developed a metal cave surrounding the
PE-press. We successfully test different steal types
(mat. No. 1.7225, 1.1620 and 14305) to replace the
expensive Cu-Be-alloy commonly used as gaskets materials.
Irradiation was performed with a mixture of zircon
and rutile crystals, a single zircon crystal, and calcite
crystals. All minerals are well-documented to be highly sensitive for radiation induced damage that can easily be detected by Raman spectroscopy [3,4]. The zircon and rutile crystals of several mm in size were
heated prior to the experiment to remove any traces of
previous radiation damage. A pressure of ~6 GPa was
applied to the mixing experiment, of ~7 GPA to the
single zircon crystal, and of 2.9 GPa to the calcite
crystals. Using the equipment available in cave A at
the SIS, the PE-press cell was exposed to Xe ions
(300 MeV/u; 1.5×1012 ions/cm2), 238U (400 MeV/u;
197
1×1012 ions/cm2),
and
Au
(350 MeV/u;
11
2
5×10 ions/cm ).
After the irradiation, the pressure was released and
the crystals were carefully extracted under an optical
microscope. Raman spectra of the irradiated zircon
crystals (mixture experiment), and pristine zircons
from the same batch were acquired with identical measurement parameters. Voigt functions were fitted to
each band (Fig. 1).
Fig. 1: Raman spectra of zircon before and after irradiation under 6 GPa with 1.5×1012 Xe-ions/cm2.
Comparison of the Raman spectra of irradiated and
pristine zircons (Fig. 1) reveals a significant decrease
of band intensity after irradiation. Fitting of each band
furthermore shows an increase of the band width while
the band center is shifted to lower wavenumbers, indicating radiation damage in zircon [3].
References:
[1] Glasmacher U.A., Lang M.,
Keppler H., Langenhorst F., Neumann R., Schardt D.,
Trautmann C., Wagner G.A. Phys. Rev. Lett. 96 (2006)
195701. [2] Weikusat C., Burchard M., Glasmacher
U.A., Klotz S., Miletich R., Trautmann C., Neumann
R. GSI Scientific report Materials 13 (2008) 345.
[3] Zhang M., Salje E.K.H., Farnan I., Graeme-Barber
A., Daniel P., Ewing R.C., Clark A.M., Leroux H. J.
Phys.
Condens.
Matter
12
(2000)
1915.
[4] Nagabhushana H., Prashantha S.C., Nagab-hushana
B.M., Lakshminarasappa B.N., Singh F. Spectrochim.
Acta A 71 (2008) 1070. [5] Lang M., Zhang F., Lian J.,
Trautmann C., Neumann R., Ewing R.C. EPSL 269
(2008) 291.
O31

THERMOCHROMIC AND STRUCTURAL PROPERTIES OF

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