X-ray diffraction on nanocrystalline thin films

1. X-ray diffraction on nanocrystalline thin films David Rafaja Institute of Physical Metallurgy, TU Bergakademie Freiberg (D) Michal Šíma PIVOT a.s. (CZ), PLATIT Advanced Coating Systems Ladislav Havela Department of Electronic Structures, Charles University Prague (CZ)

2. Physical background A contribution to the explanation of the relationship between physical properties and real structure of matters Examples Strong dependence of the mechanical hardness of thin TiN films on deposition conditions (microstructure) Strong dependence of the magnetic behaviour of thin UN films on deposition conditions (microstructure) ISPMA 9, Prague

3. Magnetic susceptibility of UN thin films Sample deposition: Reactive DC sputtering Target voltage: -800 V Ion current: 2.5 mA Plasma was maintained by injecting electrons with energy between -50 and -100 eV Substrate temperatures: -200°C, 20°C, 200°C, 300°C, 350°C, 400°C Deposition rates:  1 Å/s UN single crystals: paramagnetic below 53 K antiferromagnetic below 53 K Thin polycrystalline UN films: development of a ferromagnetic component below 100 K. ISPMA 9, Prague

4. Ti Al N2 + Ar Hardness of Ti1-xAlxN thin films A series of arc deposited Ti1-xAlxN films with increasing aluminium contents Different colour and hardness of the coatings Addition of Aluminium improves the hardness of the films, especially at high temperatures (up to 1000°C) ISPMA 9, Prague

5. Microstructure of thin films • Chemical and phase composition, chemical homogeneity • Residual stress • Stress-free lattice parameter • Preferred orientation of crystallites (texture) • Crystallite size and shape • Microstrain • Macroscopic and microscopic anisotropy of lattice deformation ISPMA 9, Prague

6. Experimental methods • XRD • GAXRD with the parallel beam optics – phase composition and chemical homogeneity, residual stress, stress-free lattice parameters, crystallite size, microstrain, anisotropy of the lattice deformation • /-scan on Eulerian cradle (pole figure) – texture • Symmetrical 2/-scan on Bragg-Brentano diffractometer – crystallite size and microstrain • EPMA with WDX – chemical composition • HRTEM – crystallite size and shape ISPMA 9, Prague

7. Schematic phase diagram of U-N 670 T(°C) 400 UN2 U2N3 U UN 0 Atomic Percent Nitrogen 50 60 67 Phase composition (Uranium nitride) • Phase composition • UN (Fm3m) 80-90 mol.% • U2N3 (Ia3) 10-20% mol.% U2N3 (Ia3) U: 8b (¼, ¼, ¼) U: 24d (-0.018, 0, ¼) N: 48e (0.38, 1/6, 0.398) UN (Fm3m) U: 4a (0, 0, 0) N: 4b (½, ½, ½) Different lattice parameters Negligible differences in intensities ISPMA 9, Prague

8. Phase composition (Ti1-xAlxN) 100 WC 101 WC 100 AlN 200 TiAlN 001 WC 311 TiAlN 222 TiAlN 111 TiAlN 220 TiAlN 110 AlN 111 WC 110 WC 201 AlN 102 WC 112 AlN 103 AlN 200 WC 002 WC 002 AlN 101 AlN Ti4Al41N55 … AlN + Ti1-xAlxN Ti8Al38N54 … AlN + Ti1-xAlxN Ti19Al31N50 …Ti1-xAlxN + AlN Ti26Al24N50 … Ti1-xAlxN + AlN Ti37Al14N49 … Ti1-xAlxN + AlN Ti41Al7N52 … Ti1-xAlxN + AlN (P63mc) Ti55Al2N43 … Ti1-xAlxN(Fm3m) ISPMA 9, Prague

9. Phase composition (Ti1-xAlxN) Diffraction line asymmetry, maximum in Ti37Al14N49 220 TiAlN 110 AlN Ti55Al2N43 Ti41Al7N52 Ti37Al14N49 Ti26Al24N50 Ti19Al31N50 Concentration gradient in Ti1-xAlxN  TiAlN + AlN TiAlN + AlN ISPMA 9, Prague Ti1-xAlxN (Fm3m)

10. n s ay y s a a0 a || sin2y 1 0 2n/(1+n) Residual stress and stress-free lattice parameters Elastic lattice deformation from X-ray diffraction: Bi-axial residual stress in thin films: The sin2-method for cubic thin films: ISPMA 9, Prague

11. HKL n a hkl f y b Residual stress and stress-free lattice parameters easy hard ISPMA 9, Prague

12. Preferred orientation of crystallites PVD Ti1-xAlxN, texture {111} GAXRD at  = 3° Strong anisotropy of lattice deformation 220 111 200 311 422 222 331 420 400 Simulation: fibre texture {111} ISPMA 9, Prague

13. Preferred orientation of crystallites PVD Ti1-xAlxN, texture {100} GAXRD at  = 3° No anisotropy of lattice deformation 200 111 220 311 420 422 222 331 400 Simulation: fibre texture {100} ISPMA 9, Prague

14. Preferred orientation of crystallites 111 200 220 110 010 100 110 111 010 “111” 100 ~ 30° 101 101 011 011 001 001 100 110 ~ 30° 100 011 Ti1-xAlxN PVD 010 111 010 001 101 001 011 _ 111 111 ~ 30° 011 _ 111 101 _ 101 101 _ 101 “100” 100 001 _ 011 __ 111 _ 011 ISPMA 9, Prague

15. ~e 1/D Crystallite size and microstrain Line broadening only due to the crystallite size. Microstrain is neglected. Scherrer formula Williamson-Hall plot Crystallite size Microstrain Warren-Averbach or Krivoglaz methods Fourier analysis of diffraction profiles taken in symmetrical geometry Problems with low intensity of diffraction lines in thin films and with preferred orientation of crystallites. ISPMA 9, Prague

16. Microstructure of UN thin films Increasing substrate temperature Relaxation of the stress-free lattice parameter Relaxation of the residual stress Relaxation of the microstrain Weaker texture At high Ts: Development of large crystallites Changes in the real structure of PVD UN thin films are predominantly caused by non-equilibrium deposition conditions ISPMA 9, Prague

17. Microstructure of Ti1-xAlxN thin films Increasing Al-contents Decreasing stress-free lattice parameter (cell volume) Increasing residual stress Increasing microstrain Decreasing crystallite size Inclination of the texture direction (dominated by the geometry of the deposition process) Dominant phase fcc TiAlN hex AlN Changes in the real structure of PVD UN thin films are due to the changes in the aluminium stoichiometry and due to the geometry of the deposition process Crystallite size below 20 nm Minimum: ~ 3.3 nm ISPMA 9, Prague

18. Typical features observed in nanocrystalline fcc thin films • Fan-like distribution (scatter) of the “cubic” lattice parameters … is caused by mechanical interaction between neighbouring crystallites (compressive residual stress) … is related to the anisotropy of elastic constants and to the orientation of crystallites • Large compressive residual stress … is probably caused by atoms built in the host structure and by mechanical interaction between regions with different lattice parameters … is apparently increased by anisotropy of the lattice deformation top view top view ISPMA 9, Prague

19. HKL n a hkl f y b Advanced information on microstructure of thin films Microstructure model and Texture model XRD study  Lattice parameters + Texture  Structure model  Information on distribution of inter-atomic distances (local probe), but no lateral resolution ISPMA 9, Prague

20. Typical features observed in nanocrystalline fcc thin films PVD TiAlN films, GAXRD at =3° • Negative crystallite size … anisotropic shape of crystallites … overestimated microstrain … coherent neighbouring crystallites • Large microstrain … anisotropic shape of crystallites … mutual coherence of neighbouring nano-crystals • Why nano-crystals develop in thin films ? … very high density of structure faults caused by the deposition process  nano-crystallites with large residual stress (local decomposition of TiAlN) … plastic deformation during the deposition because of large residual stress  nano-crystallites with large residual stress D < 0 Needle-like crystallites Simulation using Height: 200 Å Width: 40 Å ISPMA 9, Prague

21. True crystallite size HRTEM 35 – 50 Å Symmetrical XRD Spatial modulation of interplanar spacing (chemical composition)  large residual stress (interaction between coherent domains)  large microstrain, “negative” crystallite size (large coherent domains with many structure faults) ISPMA 9, Prague

22. Relationship between deposition conditions, microstructure and physical properties • Residual stress change of the lattice parameter related to macroscopic directions, anisotropic variations of the inter-atomic distances • Stress-free lattice parameter change of the inter-atomic distances, indicates changes in stoichiometry • Preferred orientation of crystallites  macroscopic anisotropy of physical properties, effect on the local lattice deformation • Crystallite size different effect of the grain boundaries • Microstrain local deformation of the crystal lattice, fluctuations in the inter-atomic distances ISPMA 9, Prague

23. Acknowledgements • Grant Agency of the Czech Republic (Project number 106/03/0819) • European Community (Program HPRI–CT-2001–00118) • DFG (Priority Programme number 1062) • Dr. T. Gouder, ITU Karlsruhe • Dr. V. Klemm, Dr. D. Heger, Dipl.-Phys. G. Schreiber, Mrs. U. Franzke and Mrs. B. Jurkowska, TU BA Freiberg ISPMA 9, Prague