Transcript Document

Introduction to nanocomposite
thin film coatings
Witold Gulbiński
Nanomaterials…..
What are they?
- bulk materials or thin films with the grain (crystallite) size
below 100nm
What makes them unique?
- their properties (mechanical, electrical, magnetic, optical)
strongly differ from macrocystalline materials
What are some applications?
- hard, wear resistant and low friction coatings, dielectics,
magnetic devices
International Student’s Summer School „Nanotechnologies in materials engineering”
Warsaw - Koszalin 2006
Witold Gulbiński
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How to measure the grain/crystallite size?
TEM, AFM, STM
X-ray diffraction line broadening analysis
By analyzing this broadening it is possible to extract information
about the microstructure of a material.
Sources of Line Broadening
 Instrumental Broadening
 Crystallite Size Broadening
 Strain Broadening
Methods of Analysis
 Simplified Integral Breadth Methods
 Fourier Methods
http://fusedweb.pppl.gov/CPEP
International Student’s Summer School „Nanotechnologies in materials engineering”
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Sources of Line Broadening
Instrumental Broadening
 Non ideal optics
 Wavelength Dispersion
 Axial Divergence od the X-ray beam
 Detector resolution
Finite Crystallite Size
Extended Defects Extended Defects
 Stacking Faults
Lattice Strain (microstrain)
International Student’s Summer School „Nanotechnologies in materials engineering”
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Witold Gulbiński
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Typical instrumental broadening
FWHM – Full Width at Half Maximum of the peak
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Peak broadening - Finite Crystallite Size
 A perfect crystal would extend in all directions to infinity, so
we can say that no crystal is perfect due to it’s finite size.
 This deviation from perfect crystallinity leads to a
broadening of the diffraction peaks.
 However, above a certain size (~0.1 - 1 micron) this type of
broadening is negligible.
 Crystallite size is a measure of the size of a coherently
diffracting domain. Due to the presence of polycrystalline
aggregates crystallite size is not generally the same thing
as particle size.
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Finite Crystallite Size
Line broadening analysis is most accurate when the
broadening due to crystallite size effects is at least twice the
contribution due to instrumental broadening.
We could also estimate a rough upper limit for
reasonable accuracy by looking at the crystallite size that
lead to broadening equal to the instrumental broadening.
International Student’s Summer School „Nanotechnologies in materials engineering”
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Crystallite size measurement accuracy
Conventional diffractometer (FWHM ~ 0.10° at 20° 2θ)
Accurate Size Range < 45 nm
Rough Upper Limit = 90 nm
Monochromatic Lab X-ray (Cu Kα FWHM ~ 0.05° at 20° 2θ)
Accurate Size Range < 90nm
Rough Upper Limit < 180 nm
Synchrotron (λ = 0.8 A, FWHM ~ 0.01° at 20° 2θ)
Accurate Size Range < 233 nm
Rough Upper Limit = 470 nm
International Student’s Summer School „Nanotechnologies in materials engineering”
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Measures of Line Broadening
The width of a diffraction line can be estimated by more than
one criterion.
The two most common width than one criterion. parameters
are:
Full Width at Half Maximum (FWHM) - ) - The width of the
peak at 1/2 it’s maximum intensity.
Integral Breadth (β) - The width of a rectangle with the same
height and area as the diffraction peak.
International Student’s Summer School „Nanotechnologies in materials engineering”
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Calculation of crystallite size
Scherrer (1918) first observed that small crystallite size could
give rise to line broadening. He derived a well
known equation for relating the crystallite size to the
broadening, which is called the Scherrer Formula.
d = Kλ/{ /{FWHM cos θ}
d = crystallite size
K = Scherrer somewhat arbitrary value that falls in the range
0.87-1.0
λ = the wavelength of the radiation
FWHM of a reflection (in radians) located at 2θ.
Now we are able to measure crystallite size!
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From micro- to nanograin bulk materials
COPPER
• Copper is a “model
material”
– Very well known bulk
properties
– Many uses
• Normal copper is
microstructured
– Grain size is 1–100
microns
Jonathon Shanks, Michigan State University
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From micro- to nano-grain bulk materials
COPPER
Metals can be made into nanocrystalline materials that
perform better than regular metals.
- Roll copper at the temperature of liquid nitrogen
- Then, heat to around 450K
Result:
- structure with micrometer sized grains and
nanocrystalline grains
- Increased strength and hardness of metal because
of the nanocrystalline grains
- high ductility
www.research.ibm.com/ journal/rd/451/murray.html
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Increasing Copper Strength
• Plastic deformation of copper introduces
work-hardening (copper gets stronger) and
reduces the grain size
• Hall-Petch relation predicts materials get
stronger as grain size decreases:
y = 0 + KHPd-1/2
(Yield strength is inversely proportional to grain size)
Jonathon Shanks, Michigan State University
International Student’s Summer School „Nanotechnologies in materials engineering”
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Witold Gulbiński
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Increasing Copper Strength
Material
Yield Strength
Cold Worked Copper
393 MPa
400 nm Copper
443 MPa
100 nm Nanograin Copper
900 MPa
10 nm Nanograin Copper
2.9 GPa
Jonathon Shanks, Michigan State University
International Student’s Summer School „Nanotechnologies in materials engineering”
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Witold Gulbiński
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Increasing Copper Strength
Hall-Petch relation
y = 0 + KHPd-1/2
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A molecular dinamics simulated copper sample before (a) and after (b) 10%
deformation. 16 grains, 100,000 atoms; average grain size: 5nm
J. Schiotz et al., Nature, 391 (1998) 561
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Reverse Hall-Petch
effect (for Copper)
J. Schiotz et al., Nature, 391 (1998) 561
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Molecular Dynamics
(MD) simulation
Zone beneath the indenter.
a) for the single crystal sample at a
displacement of 12.3 Angstrom,
b) b) for the 12~nm grain sample at a
displacement of 11.9 Angstrom.
Only non-FCC atoms are shown.
http://sb2.epfl.ch/instituts/akarimi/small.html
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From bulk materials to thin films
- how to deposit nanocrystalline thin films
What are thin film growth models?
How to control thin film growth?
- How to control grain size?
a) by substrate temperature
b) by deposition rate
c) by annealing temperature
d) by film thickness
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Thin film growth - island growth model
1. Island growth (Volmer - Weber)
- three dimensional islands are formed
WHY:
- film atoms more strongly bound to each other than to substrate
- and/or slow diffusion
2. Layer by layer growth (Frank - van der Merwe)
- generally highest crystalline quality
WHY:
- film atoms more strongly bound to substrate than to each other
- and/or fast diffusion
http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html
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Thin film growth - island growth model
3. Mixed growth (Stranski - Krastanov)
- initially layer by layer
- then three dimensional islands are formed
http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html
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Witold Gulbiński
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Picture of simulated island growth
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Grain size dependence on deposition conditions
Grain size typically increases with:
- increasing film thickness,
- increasing substrate temperature,
- increasing annealing temperature,
- decreaseing deposition rate
http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html
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Structural zone models of thin film growth
Movchan-Demischin (1969)
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Structural zone models of thin film growth
Thornton (1974)
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Structural zone models of thin film growth
Messier (1984)
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Structural zone models
of thin film growth
Zone
Temperature
Diffusion
Other processes
Structure
I
T<0.2-0.3 Tm
limited
T
T<0.2-0.5 Tm
surface
renucleation during
growth
Mixed size
fibrous grains,
fewer voids
II
T<0.3-0.7 Tm
surface
grain boundary
migration
Columnar
grains
III
T<0.5 Tm
bulk + surface
recrystalization
Large grains
Small grains,
many voids
http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html
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Nanocrystalline thin films
 Single component (metals deposited at low temperatures)
 Binary and multicomponent alloys (limited solubility promotes
nucleation and segregation of phases),
 Carbides, nitrides, and oxides of metals deposited at high rates
and low temperatures
 NANOCOMPOSITES
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Structure-performance relations in
nanocomposite thin films
J. Patscheider et al.., Surf. Coat. Technol. 146-147 (2001) 201
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Structure-performance relations in
nanocomposite thin films
J. Patscheider et al.., Surf. Coat. Technol. 146-147 (2001) 201
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Nanocomposite thin films
 n-MeN/a-nitride (nMeN/a-Si3N4, where: Me=Ti, W, V)
 n-MeN/n-nitride; for example: n-TiN/n-BN
 n-MeC/a-C or a-C:H; for example: TiC/DLC; TiC/a-C:H, Mo2C/a-C:H
 n-MeN/metal, for example: ZrN/Cu, CrN/Cu, Mo2N/Cu, Mo2N/Ag
 n-WC + n-WS2/DLC
 n-MeC/a-SiC, for example: TiC/a-SiC/a-C:H
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Deposition of nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302–310
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Mo2C-MoC/a-C:H nanocomposite thin films
-MoC
(101)
Intensywność (j.u.)
Intensywność (j.u.)
C1s
a = 100%
b-Mo2C
(100)
a = 64%
b-Mo2C
(100)
a = 46%
a = 25%
35
40
45
50
55
Kąt dyfrakcji 2J [°]
a = 64%
283,0
MoC
Mo
(11
0)
a = 33%
30
a = 100%
a = 46%
284,2
a-C
60
65
70
290
288
XRD
286
284
a = 25%
282
280
278
Energia wiązania (eV)
XPS
Gulbinski, W. et al.., Inżynieria Materiałowa 6 (2003) 490
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Mo2C-MoC/a-C:H nanocomposite thin films
0,7
a = 25%
a = 33%
a = 46%
a = 64%
Współczynnik tarcia m
0,6
0,5
0,4
0,3
a = 100%
0,2
0,1
0,0
0
50
100
150
200
250
300
Temperatura [°C]
350
400
450
Friction coefficient vs. test temperature
Gulbiński, W. et al.., Inżynieria Materiałowa 6 (2003) 490
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TiC/a-C:H nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302
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TiC/a-C:H nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302
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TiC/a-C:H nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302
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Mo2N/Ag nanocomposite thin films
Gulbinski, W. et al.., Surf. Coat. Technol. (2006) in press
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Mo2N/Ag nanocomposite thin films
Gulbinski, W. et al.., Surf. Coat. Technol. (2006) in press
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Ni/a-C:H nanocomposite thin films
S. Kukielka et al.. Surf.Coat. Technol. 200/22-23 (2006) 6258-6262
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Ti-Si-C nanocomposite thin films
W. Gulbinski et al.. Surf. Coat. Technol. 180-181 (2004) 341
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Ti-Si-C nanocomposite thin films
W. Gulbinski et al.. Surf. Coat. Technol. 180-181 (2004) 341
W. Gulbinski et al.. Surf. Coat. Technol. 200 (2006) 4179
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Ti-Si-C nanocomposite thin films
W. Gulbinski et al.. Surf. Coat. Technol. 200 (2006) 4179
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CONCLUSIONS
Nanocrystalline or nanocomposite thin films show:
 enhanced hardness,
 enhanced ductility,
 high toughness,
 low friction
 unusual dielectric and magnetic properties
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