Introduction to nanocomposite

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Introduction to nanocomposite thin film
coatings Witold Gulbinski
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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
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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
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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)

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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 its 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.

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Crystallite size measurement accuracy
Conventional diffractometer (FWHM 0.10 at 20
2?) Accurate Size Range lt 45 nm Rough Upper Limit
90 nm Monochromatic Lab X-ray (Cu Ka FWHM
0.05 at 20 2?) Accurate Size Range lt 90nm Rough
Upper Limit lt 180 nm Synchrotron (? 0.8 A,
FWHM 0.01 at 20 2?) Accurate Size Range lt 233
nm Rough Upper Limit 470 nm
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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 its maximum intensity. Integral
Breadth (ß) - The width of a rectangle with the
same height and area as the diffraction peak.
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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 K?/
/FWHM cos ? d crystallite size K Scherrer
somewhat arbitrary value that falls in the range
0.87-1.0 ? the wavelength of the
radiation FWHM of a reflection (in radians)
located at 2?.
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 1100 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
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Increasing Copper Strength
Jonathon Shanks, Michigan State University
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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. 
• for the single crystal sample at a displacement
  of 12.3 Angstrom,
• b) for the 12nm 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/PHYS549/549l
ectures/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/PHYS549/549l
ectures/film2.html
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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/PHYS549/549l
ectures/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
http//www.uccs.edu/tchriste/courses/PHYS549/549l
ectures/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 MeTi, W,
  V)
• n-MeN/n-nitride for example n-TiN/n-BN
• n-MeC/a-C or a-CH for example TiC/DLC
  TiC/a-CH, Mo2C/a-CH
• 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-CH

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Deposition of nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science
239 (2005) 302310
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Mo2C-MoC/a-CH nanocomposite thin films
XRD
XPS
Gulbinski, W. et al.., Inzynieria Materialowa 6
(2003) 490
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Mo2C-MoC/a-CH nanocomposite thin films
Friction coefficient vs. test temperature
Gulbinski, W. et al.., Inzynieria Materialowa 6
(2003) 490
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TiC/a-CH nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science
239 (2005) 302
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TiC/a-CH nanocomposite thin films
Gulbinski, W. et al.., Applied Surface Science
239 (2005) 302
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TiC/a-CH 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-CH 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