Introduction to nanocomposite thin film coatings Witold Gulbiński

1. Introduction to nanocomposite thin film coatings Witold Gulbiński

2. 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

3. How to measure the grain/crystallite size? • TEM, AFM, STM • X-ray diffraction line broadening analysis • By analyzingthis 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

4. 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)

5. Typical instrumental broadening FWHM – Full Width at Half Maximum of the peak

6. 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 finitesize. • This deviation from perfect crystallinity leads to abroadening of the diffraction peaks. • However, above a certain size (~0.1 - 1 micron) this type of broadening isnegligible. • Crystallite size is a measure of the size of a coherentlydiffracting domain. Due to the presence of polycrystallineaggregates crystallite size is not generally the samething as particle size.

7. Finite Crystallite Size • Line broadening analysis is most accurate when the broadening due to crystallite size effects isat 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.

8. Crystallite size measurement accuracy Conventionaldiffractometer (FWHM ~ 0.10° at 20° 2θ) Accurate Size Range < 45 nm Rough Upper Limit = 90nm 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 = 470nm

9. 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 ofthe peak at 1/2 it’s maximum intensity. Integral Breadth (β)- The width of a rectangle with thesame height and area as the diffraction peak.

10. 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!

11. 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

12. From micro- to nano-grain bulk materials COPPER Metals can be madeintonanocrystalline materials that performbetter than regular metals. • Roll copper at the temperature of liquidnitrogen • Then, heat to around 450K Result: - structure with micrometersized grains and nanocrystallinegrains - Increased strength and hardness ofmetal because of the nanocrystallinegrains - 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. Increasing Copper Strength Jonathon Shanks, Michigan State University

15. Increasing Copper Strength 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. Molecular Dynamics (MD) simulation • Zone beneath the indenter.  • for the single crystal sample at a displacement of 12.3 Angstrom, • b) for the 12~nm grain sample at a displacement of 11.9Angstrom. Only non-FCC atoms are shown. 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 http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html

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 http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html

24. Structural zone models of thin film growth Movchan-Demischin (1969)

25. Structural zone models of thin film growth Thornton (1974)

26. Structural zone models of thin film growth Messier (1984)

27. Structural zone models of thin film growth http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/film2.html

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. -MoC (101) a = 100% Intensywność (j.u.) b-Mo2C (100) a = 64% b-Mo2C (100) a = 46% Mo (110) a = 33% a = 25% 30 35 40 45 50 55 60 65 70 Kąt dyfrakcji 2J [°] C1s Intensywność (j.u.) a = 100% a = 64% 283,0 MoC a = 46% 284,2 a-C a = 25% 290 288 286 284 282 280 278 Energia wiązania (eV) Mo2C-MoC/a-C:H nanocomposite thin films XRD XPS Gulbinski, W. et al.., Inżynieria Materiałowa 6 (2003) 490

34. 0,7 a = 25% a = 33% 0,6 a = 46% a = 64% m 0,5 0,4 Współczynnik tarcia 0,3 a = 100% 0,2 0,1 0,0 0 50 100 150 200 250 300 350 400 450 Temperatura [°C] 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. TiC/a-C:H nanocomposite thin films Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302

37. TiC/a-C:H nanocomposite thin films Gulbinski, W. et al.., Applied Surface Science 239 (2005) 302

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. 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

43. Ti-Si-C nanocomposite thin films 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