Tecnologie di Sintesi di Materiali Nanostrutturati

Tecnologie di Sintesi di Materiali Nanostrutturati
Leander Tapfer
Unità Materiali e Nuove Tecnologie
ENEA, Brindisi
Introduzione
Processi e Tecnologie di Sintesi – Strategie per la realizzazione
di Nanostrutture e Materiali Nanostrutturati
Tecnologie di Sintesi nell’Unita Materiali e Nuove Tecnologie
Processi di Lavorazione Meccanica (Stato Solido)
Processi di Deposizione Fisica e in Fase di Vapore
Processi di Sintesi Chimica
Processi di Sintesi utilizzando Fasci Ionici (Impiantazione)
Synthesis Strategies - 1
nanostructured materials
bottom-up construction
top-down construction
assembling from nano-building blocks
‘sculpturing’ (fragmentation) from bulk
physical vapor deposition
chemical vapor deposition
chemical synthesis (e.g., sol-gel, colloids)
powder/aerosol compaction
Lithographic/etching processes
mechanical attrition (ball milling)
structuring by irradiation processes
Nanoparticle Synthesis Strategies - 2
SOLID-STATE PROCESSES
GAS-PHASE PROCESSING
High-Energy Milling
Mechanochemical Synthesis
Chemical Vapor Deposition
Gas Condensation with Thermal Evaporation
Vacuum Evaporation on Running Liquids (VERL)
Thermal Plasma Synthesis
Combustion Synthesis
WET CHEMICAL PROCESSES
Chemical Precipitation
Colloidal Synthesis
Sol-Gel Processing
Thermochemical Synthesis
Sonochemical Synthesis
Langmuir-Blodgett Deposition
SURFACE & THIN FILM MODIFICATION
BY HIGH ENERGY BEAMS
Laser Beams
Electron Beams
Ion Beams
VACUUM SYNTHESIS
Electron-Beam Evaporation
Sputtering
Laser Ablation
Cluster Beam Deposition
ION BEAM SYNTHESIS
Ion Implantation
Ion Irradiation
Criteria for the Selection of the Synthesis Process
Properties
Electrical
Magnetic
Optical & Electronic
Catalytic
Mechanical
Ordering Degree
Ordered nanostructures:
2D or 3D arrays
Layered or multilayered
Quantity & Scale-up
Production rate (quantity/time)
Production cost
High Energy Ball Milling
tecniche di macinazione ad alta energia
trasferimenti di energia meccanica a substrati in polvere
provocando trasformazioni chimico-fisiche e strutturali
E’ possibile:
⇒ partire da polveri microcristalline provocandone la destrutturazione
in domini nanoscopici
⇒ promuovere la formazione di nuove fasi stabili e/o metastabili
(meccanosintesi)
Sintesi di ferrite di manganese nanostrutturata
Fe2O3 + MnO = MnFe2O4
∆G25°C = - 5.118 kcal/mol
• reazione allo stato solido attivata
meccanicamente
• atmosfera inerte (Ar)
• energia trasferita ~10-2 J/urto
• temperatura ambiente
L ≈ 5 nm
equivalente sferico delle particelle:
∅ ≈ 100 nm
Evaporation
evaporation of metal atoms from a solid source ⇒ deposit on a substrate
substrate
source
sublimation of source material at high temperature
sources:
Ohmically - heated filament (W, Mo)
Electron-beam heated source material
impingement is line-of-sight from source onto substrate
Gas transport at 10-6 torr is ballistic / molecular
Molecular mean free path ?mfp >> chamber dimensions
sticking probability of atoms hitting the substrate is near unity
BaF2-Ag composite film: Ag clusters embedded in BaF2 matrix
advantage of BaF2 matrix:
?
?
?
?
low dielectric constant e=7.3 at RT
large band gap (10 - 11 eV)
correct stoichiometric ratio in film deposited via thermal evaporation
melting point at 1352°C
⇒ matrix is thermally stable after post-growth thermal annealing processes
BaF2 25nm
Ag 1.2 – 7 nm
periods:
4-5
Silice substrate
experimental details
base pressure
0.8 mPa
deposition temperature
80°C
deposition rate
0.01 nm/sec
annealing condition
T=500°C, t=1
AFM image
Average Ag particle dimension:
∅ ≈ 7 - 10nm
Experimental XRD patterns of an as-grown
(red line) and annealed (black line) sample.
According to the simulations: increase of the
Ag coherent domain size after annealing (from
∅ ≈ 8 nm to 28 nm)
Optical Absorption BaF2-Ag multilayer
as grown multilayers
? broad plasmon resonance peak
? red shift in the absorption peak position
with increased silver-layers thickness
(from 560 nm to 490 nm)
? from the band positions:
polarization factor Lm ≈1
(the Ag clusters flat plates with their
normals parallel to the optical beam).
? at higher value of silver thickness:
a second peak at about 440 nm due to a
broader distribution of the clusters size
post-annealing multilayers
annealing process at 500°C for 1hour
? pronounced plasmon resonance peak
(419 nm to 430 nm)
? simulation by Maxwell-Gernett theory:
increase of cluster mean size
? polarization factor decreases to Lm ≈1/3
(the Ag clusters are almost spherical)
? accordance with the results obtained by
X-ray diffraction Rietveld analysis
Hot Filament CVD (HF-CVD)
MKS Gas Control Unit
647 B
Deionised Water
Hydrogen Generator
H 9200 Air Products
MKS 1179A
Mass-Flo® Controller
MKS 1179A
Mass-Flo® Controller
Methane
Nitrogen
~
Gas in
MKS Baratron® 722A
Absolute Pressure Trasducer
Penning Gauge
Leybold-Heraeus Ionivac IM25
DC Power Supply
5 KW – 250 A
Pirani
Gauge
Cooling Water
Progettato e realizzato da
MAT-TEC Casaccia
&
MAT-ING Faenza
Process Chamber
Combivac
CM33
Filament
Temperature Measurement
IR Pyrometer Land System 4
Substrate
Temperature Measurement
Type K Thermocouple
Rotary Process
Pump
Gas out
Turbomolecular
Pumping Group
Gas out
synthesis of diamond
Process parameters:
H2 + (2- 0.3%) CH4
Tsubstrate: 700-900°C
Tfilament:
2300°C
Ptot:
0.5-3 Pa
macrocrystalline structure
Realization of diamond films of
macro-crystalline & nanocrystalline
structure
nanocrystalline structure
un esempio di applicazione:
fibre di carbonio rivestite di diamante
Progetto PROMOMAT L.449 MIUR
Synthesis of carbon nanotubes by HF-CVD
Fabrication of Ni clusters on Si surface by thermal treatment of thin Ni films
deposited by RF sputtering
Ni clusters as catalysts
SEM micrograph
catalytic metal particles ⇒ growth of
carbon nanotubes
RF Sputtering
∅ ≈ 10- 40nm)
Ni particles (∅
Schematic diagram of growth model
•
•
•
Formation of nucleation process;
cap growth;
mechanism for vertical alignment
HF-CVD process parameters:
H2+ (10%) CH4
Tsub: 600°C
Ptot: 0.5 Pa
Arc-Discharge
Fabrication of Fullerenes and Carbon Nanotubes
Fullerene (C70)
D. R. Huffman and W. Krätschmer (1990)
Carbon Nanotubes
arc-discharge performed in liquid nitrogen environment
? a method that ensures a very stable reaction occurring over many hours
? the productivity of raw material is of the order of 2g/hour
applied voltage
20 - 22 V
graphite electrode
∅ = 5 mm
liquid nitrogen
MW-CNT structure & morphology
HREM
TEM image
XRD profile
Langmuir-Blodgett
?
?
?
?
Known for about a century, but recently applied in Self-Assembly
Monolayer or layer of organic layer on a solid substrate
Advantage in creating a network of two components
Enhance the properties from components
Langmuir trough
Langmuir deposition
?
?
?
?
?
Made by nature, through hydrophobic interactions
Fold and unfold depends on the environment
Folding and unfolding define various functioning of organisms
Addition of design lipids, can start this self- assembly
Design molecules give control over desired pattern
incorporation of Carbon Nanotubes within highly ordered Cadmium
Behenate Multilayers deposited by LB technique
behenic acid
fabrication of highly ordered
carbon nanotubes – LB film composites
layer sequence (6 monolayers Cd-behenate – 1 sheet of CNT
optical micrographs - compression pressure (15mN/m)
loose packing
X-ray reflectivity
⇓
satellite peaks
⇓
high order in
composite structure
is preserved
5 periods
compact
10 periods
defects: exfoliations from the surface
Sol-Gel process
un precursore metallo-organico ed un solvente sono mischiati
per formare una soluzione colloidale
Sol-Gel Synthesis
sols ⇒ solvent evaporation ⇒ gelation process ⇒ formation of a film
densification by thermal
treatment (≈ 500°C)
small particle size in the sol (nm range)
small particle size in the sol
(nm range)
Nanostructured Films and Nanoparticles Dispersed in Glass by Sol-Gel
Nanostructured TiO2 films
X-ray diffraction & Rietveld Analysis
Nanostructured phase: ∅≈3-5nm)
∅≈
Nanoparticles (Au) in silica
⇓
doped glasses
TEM imaging
Colloidal Synthesis
chemical bath deposition process
synthetic procedure:
synthesize nanocrystalline sample by high-temperature
(100-300°C) solution-phase route
narrow the NC sample size distribution by
size-selective precipitation
deposition of nanocrystalline dispersions
⇒ self-assembling
formation of ordered nanocrystal assemblies
⇒ 2D and 3D ordered structures (superlattices)
C.B. Murray
(2001)
thiol-stabilized Au nanocrystals
Au nanocrystals capped by thiols
inorganic core (Au NC)
organic shell (thiol molecules)
self-assembled superstructure
of Au clusters
- regular array (2D, 3D structure) -
core/shell structure modification:
inorganic/inorganic materials
(e.g., Au/silica)
imposed ordering:
layer by layer deposition
(e.g., Langmuir - Blodgett)
XPS Analysis
Au-Au doublet:
Au-S doublet:
TEM image
⇒ crystalline
⇒ Au - thiol
Average diameter:
∅ ≈ 2.5±0.5nm
HREM image
Polymeric Nanospheres for Photonic Crystals Application
by
Emulsion Polymerization technique
monomer droplets
? Monomer is insoluble in
water and is dissolved in a
co-solvent which forms an
emulsion in water
(droplets).
? Initiator or catalyst is
dissolved in water.
? Polymerisation starts in
polymeric nanospheres
initiator
water phase and polymers
coalesce and segregate
resulting in the formation
of colloidal particles.
? Material: PMMA (polymethylmethacrylate)
? Experimental parameters: reaction time, temperature, reactants concentration
Preparation of nanospheres crystals
Reaction
products
are
purified and solvent is slowly
evaporated producing a bulk
ordered nanospheres crystal
? Crystalline domains dimensions of the order of some microns
? Nanospheres size dependence on reaction time
Polymeric nanospheres for photonic crystals application
Photonic crystals are three-dimensional, ordered, sub-visible light wavelength
lattices that can control the propagation of light in the manner that atomic crystals
control electrons.
Photonic crystals ⇒ manipulate light producing many interesting effects such as
inhibition of spontaneous emission or localization of light thus opening the
possibility of many device applications.
Optical devices such as rejection filters,
filters optical filters,
filters limiters,
limiters and switches can be
fabricated with applications such as performance-improvement in lasers,
lasers and optical
signal processing in the communication industry.
A viable method for photonic crystal production is from self-assembling colloidal
crystals.
Applications ⇒ Photonics (photonic crystals)
Micrographs (crossed polars, interference colors) are both taken in
transmission normal to the film plane. As predicted, crystals grow in the
viewing direction (A) or in the film plane (B), depending on drying
geometry.
Ion Beam Synthesis (IBS)
Ion Beams for
Fabrication and Modification
of Nanocrystals
Ion Implantation
Ion Irradiation
far-from-equilibrium state
⇒ high supersaturation
⇒ high interface energy
“driven system”
⇒ non-equilibrium process
Annealing
⇓
Relaxation towards equilibrium
self-organization
Steady-state: competition
⇓
Collisional mixing ⇔ diffusion
pattern formation
Fabrication of
Nanocrystals
Modification of
Nanocrystals
Implantation
chamber
In2+
ion implantation parameters:
energy: 320 keV
dose: 1÷2 x1017 ions/cm2
silica
TEM micrograph in cross-section
surface
ion-implanted surface layer
∼200nm)
(∼
crystalline In nanoparticles
(bi-modal distribution)
silica
Rutherford Back-Scattering
maximum In-concentration
at a depth of 107nm
10
8
6
4
surface
3
concentration (atoms/cm )
12
RBS
simulation
“profile”
2
0
0
50
100
150
depth (nm)
200
250
300
Cluster diameter (nm)
40
X-Ray Diffraction & Rietveld analysis
In nanoparticle size
30
Melting point of bulk Indium
⇓
156.61°C
20
10
Dopo il ciclo
after
thetermico
thermal cycle
0
20
40
60
80
100
120
140
160
180
200
Temperature (°C)
structural stability: nanoparticle - matrix
melting behavior of nanoparticles
ro
0,005
0,004
Microstrain
crystalline In
0,003
0,002
0,001
Microstrain in In nanoparticles
0,000
20
40
60
80
100
120
Temperature (°C)
140
160
180
200
liquid In
Contributi:
C. Alvani, M. Alvisi, F. Antolini, P. Aversa,
•
Cappello, L. Capodieci, F. Cardellini, C. Colella, F. Cleri, V. Contini,
R. D’Amato*, Th. Dikonimos Makris, T. Di Luccio, G. Ennas, M. Falconieri,
M.C. Ferrara, R. Giorgi, A. La Barbera, N. Lisi, R. Marazzi, M. Massaro,
G. Mattei°, S. Mazzarelli, P. Mazzoldi°,
A. Mevoli, A. L. Mirenghi, A. Montone, P. Morales, T. Nocco,
F. Padella, M. Palmisano, M. Pentimalli, E. Pesce, L. Petrucci, L. Pilloni,
M. Re, A. Rizzo, P. Rotolo, M.V. Russo*, E. Salernitano, F. Sarto, G. Scalia,
M.A. Tagliente, I. Venditti*, M. Vittori-Antisari, M. Volpe
(*) Dip. di Chimica, Università “La Sapienza” Roma
(°) Dip. di Fisica, Università di Padova