Introduction to nanocomposite thin film coatings Witold Gulbiński

Introduction to nanocomposite thin film coatings

Witold Gulbiński

2International Student’s Summer School „Nanotechnologies in materials engineering”

Warsaw - Koszalin 2006 Witold Gulbiń[email protected]

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



http://fusedweb.pppl.gov/CPEP

How to measure the grain/crystallite size?

TEM, AFM, STMX-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



Sources of Line BroadeningInstrumental 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)



Typical instrumental broadening

FWHM – Full Width at Half Maximum of the peak



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.



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 forreasonable accuracy by looking at the crystallite size that lead to broadening equal to the instrumental broadening.



Crystallite size measurement accuracy

Conventional diffractometer (FWHM ~ 0.10° at 20° 2θ)Accurate Size Range < 45 nmRough Upper Limit = 90 nm

Monochromatic Lab X-ray (Cu Kα FWHM ~ 0.05° at 20° 2θ)Accurate Size Range < 90nmRough Upper Limit < 180 nm

Synchrotron (λ = 0.8 A, FWHM ~ 0.01° at 20° 2θ)Accurate Size Range < 233 nmRough Upper Limit = 470 nm



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.

10

International Student’s Summer School „Nanotechnologies in materials engineering”Warsaw - Koszalin 2006

Witold Gulbiń[email protected]

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 thebroadening, which is called the Scherrer Formula.

d = Kλ/{ /{FWHM cos θ}

d = crystallite sizeK = Scherrer somewhat arbitrary value that falls in the range 0.87-1.0 λ = the wavelength of the radiationFWHM of a reflection (in radians) located at 2θ.

Now we are able to measure crystallite size!

11



From micro- to nanograin bulk materialsCOPPER

• 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

12



From micro- to nano-grain bulk materialsCOPPER

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

13



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

14




Material Yield Strength

Cold Worked Copper 393 MPa400 nm Copper 443 MPa

100 nm Nanograin Copper 900 MPa

10 nm Nanograin Copper 2.9 GPa

Jonathon Shanks, Michigan State University

15




Hall-Petch relation

y = 0 + KHPd-1/2

16



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

17



Reverse Hall-Petch effect (for Copper)

J. Schiotz et al., Nature, 391 (1998) 561

18



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.

Molecular Dynamics (MD) simulation

http://sb2.epfl.ch/instituts/akarimi/small.html

19



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

20



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

21



Thin film growth - island growth model

3. Mixed growth (Stranski - Krastanov)- initially layer by layer - then three dimensional islands are formed


22



Picture of simulated island growth

23



Grain size dependence on deposition conditions

Grain size typically increases with:

- increasing film thickness,

- increasing substrate temperature,

- increasing annealing temperature,

- decreaseing deposition rate


24



Structural zone models of thin film growth

Movchan-Demischin (1969)

25




Thornton (1974)

26




Messier (1984)

27



Structural zone models

of thin film growth

Zone Temperature Diffusion Other processes Structure

I T<0.2-0.3 Tm limited Small grains, many voids

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


28



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

29



Structure-performance relations in nanocomposite thin films

J. Patscheider et al.., Surf. Coat. Technol. 146-147 (2001) 201

30



Structure-performance relations in nanocomposite thin films

J. Patscheider et al.., Surf. Coat. Technol. 146-147 (2001) 201

31



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

32



Deposition of nanocomposite thin films

Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302–310

33



290 288 286 284 282 280 278

Inte

nsyw

ność

(j.u

.)

Energia wiązania (eV)

= 100%

= 64%

= 46%

= 25%

C1sC1s

284,2284,2a-Ca-C

283,0283,0MoCMoC

30 35 40 45 50 55 60 65 70

Inte

nsyw

ność

(j.u

.)

Kąt dyfrakcji 2 [°]

= 100%

= 64%

= 46%

= 25% = 33%

-MoC(101)

-Mo2C(100)

-Mo2C(100)

Mo(110)

Mo2C-MoC/a-C:H nanocomposite thin films

XRD XPSGulbinski, W. et al.., Inżynieria Materiałowa 6 (2003) 490

34



0 50 100 150 200 250 300 350 400 4500,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

Wsp

ółcz

ynni

k ta

rcia

m

Temperatura [°C]

= 100%= 100%

= 25%= 25%

= 46%= 46% = 33%= 33%

= 64%= 64%

Mo2C-MoC/a-C:H nanocomposite thin films

Friction coefficient vs. test temperature

Gulbiński, W. et al.., Inżynieria Materiałowa 6 (2003) 490

35



TiC/a-C:H nanocomposite thin films

Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302

36





37





38



Mo2N/Ag nanocomposite thin films

Gulbinski, W. et al.., Surf. Coat. Technol. (2006) in press

39



Mo2N/Ag nanocomposite thin films

Gulbinski, W. et al.., Surf. Coat. Technol. (2006) in press

40



Ni/a-C:H nanocomposite thin films

S. Kukielka et al.. Surf.Coat. Technol. 200/22-23 (2006) 6258-6262

41



Ti-Si-C nanocomposite thin films

W. Gulbinski et al.. Surf. Coat. Technol. 180-181 (2004) 341

42




W. Gulbinski et al.. Surf. Coat. Technol. 180-181 (2004) 341

W. Gulbinski et al.. Surf. Coat. Technol. 200 (2006) 4179

43




W. Gulbinski et al.. Surf. Coat. Technol. 200 (2006) 4179

44



CONCLUSIONS

Nanocrystalline or nanocomposite thin films show:

enhanced hardness,

enhanced ductility,

high toughness,

low friction

unusual dielectric and magnetic properties

Documents

Introduction to nanocomposite thin film coatings Witold Gulbiński