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1 X-ray Scattering from Thin Films Experimental methods for thin films analysis using X-ray scattering –Conventional XRD diffraction –Glancing angle X-ray diffraction –X-ray reflectivity measurement –Grazing incidence X-ray diffraction X-ray diffraction study of real structure of thin films –Phase analysis –Residual stress analysis –Crystallite size and strain determination –Study of the preferred orientation –Study of the crystal anisotropy

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2 Conventional X-ray diffraction + Reliable information on the preferred orientation of crystallites the crystallite size and lattice strain (in one direction) No information on the residual stress (constant direction of the diffraction vector) Low scattering from the layer (large penetration depth) Diffracting crystallites

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3 Glancing angle X-ray diffraction GAXRD Gold, CuK, 4000 cm -1 Symmetrical mode GAXRD

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4 Other diffraction techniques used in the thin film analysis Conventional diffraction with -scanning q y =0 Grazing incidence X-ray diffraction (GIXRD) q z 0 Conventional diffraction with -scanning q x =0

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5 Penetration depth of X-rays L.G. Parratt, Surface Studies of Solids by Total Reflection of X-rays, Physical Review 95 (1954) 359-369. Example: Gold (CuK ) = 4.2558 10 -5 = 4.5875 10 -6

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6 X-ray reflectivity measurement Si Mo t [Å] [Å] 0.68 19.6 5.8 0.93 236.5 34.0 1.09 14.1 2.7 1.00 5.0 2.7 1.00 2.8 Calculation of the electron density, thickness and interface roughness for each particular layer W The surface must be smooth (mirror-like) Edge of TER Kiessig oscillations (fringes)

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7 Experimental set-up Scintillation detector Flat monochromator Sample Goebel mirror X-ray source Sample rotation, Normal direction Diffraction vector Diffraction angle, 2 Angle of incidence, Sample inclination, Used for XRR, SAXS, GAXRD and symmetrical XRD

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Information on the microstructure of thin films Phase analysis Residual stress analysis Crystallite size and strain determination Study of the preferred orientation Study of the anisotropy in the lattice deformation Investigation of the depth gradients of microstructure parameters

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9 Uranium nitride – phase analysis Phase composition 1.UN, 80-90 mol.% Fm3m, a = 4.8897 Å 2.U 2 N 3, 10-20% mol.% Ia3, a = 10.64 10.68 Å Sample deposition PVD in reactive atmosphere N 2 Heated quartz substrate (300°C) 0 Atomic Percent Nitrogen 50 60 67 800 T(°C) 400 UUN U2N3U2N3 UN 2 Schematic phase diagram

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10 U 2 N 3 versus UN 2 UNUN U 2 N 3 (Ia3), a = 10.66 Å U: 8b (¼, ¼, ¼) U: 24d (-0.018, 0, ¼) N: 48e (0.38, 1/6, 0.398) UN 2 (Fm3m) a = 5.31 Å U: 4a (0, 0, 0) N: 8c (¼, ¼, ¼) Cannot be distinguished in thin films

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11 Uranium nitride – residual stress analysis UN a 0 = (4.926 ± 0.015) Å Compressive residual stress = (1.8 ± 0.8) GPa Strong anisotropy of lattice deformation U 2 N 3 a 0 = (10.636 ± 0.002) Å Compressive residual stress = (6.2 ± 0.1) GPa No anisotropy of lattice deformation GAXRD at =3°

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12 Uranium nitride – anisotropic lattice deformation 111 easy hard UN a 0 = (4.9270 ± 0.0015) Å = (1.0 ± 0.1) GPa directions

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13 UN – anisotropic lattice deformation Dependence of the lattice deformation on the crystallographic direction R.W. Vook and F. Witt, J. Appl. Phys., 36 (1965) 2169. Related to the anisotropy of the elastic constants

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14 UN versus U 2 N 3 UNUN UN (Fm3m) a = 4.93 Å U: 4a (0, 0, 0) N: 4b (½, ½, ½) Anisotropy of the mechanical properties is related to the crystal structure U 2 N 3 (Ia3), a = 10.66 Å U: 8b (¼, ¼, ¼) U: 24d (-0.018, 0, ¼) N: 48e (0.38, 1/6, 0.398)

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15 Methods for the size-strain analysis using XRD Crystallite size Fourier transformation of finite objects (with limited size) Constant line broadening (with increasing diffraction vector) Lattice strain Local changes in the d-spacing Line broadening increases with increasing q (a result of the Bragg equation in the differential form) Scherrer Williamson-Hall Warren-Averbach Krivoglaz P. Klimanek (Freiberg) R. Kuzel (Prague) P. Scardi (Trento) T. Ungar (Budapest) (000) (100) (001) (011) (111) (110) (000) (100) (001) (011) (111) (110)

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16 UN – anisotropic line broadening The Williamson-Hall plot It recognises the anisotropy of the line broadening It is robust (weak intensity, overlap of diffraction lines) It is convenient if the higher-order lines are not available (nanocrystalline thin films, very thin films, GAXRD) 100 111

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17 UN – texture measurement Preferred orientation {110} Reciprocal space mapping

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18 Reciprocal space mapping Measured using CuK radiation A highly textured gold layer

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19 Epitaxial growth of SrTiO 3 on Al 2 O 3 O in SrTiO 3 Sr Al Ti O in Al 2 O 3 Reciprocal space map Atomic ordering in direct space SrTiO 3 : Fm3m 111 axis -3 001 Al 2 O 3 : R-3c

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20 SrTiO 3 on Al 2 O 3 Atomic Force Microscopy Pyramidal crystallites with two different in-plane orientations AFM micrograph courtesy of Dr. J. Lindner, Aixtron AG, Aachen. 111 _ 110 _ 110

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21 TiCN Depth resolved X-ray diffraction TiN TiC TiN WC Absorption of radiation TiC TiN

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22 Surface modification of thin films Gradient of the residual stress in thin TiN coatings (CVD) implanted by metal ions: Y, Mo, W, Al and Cr

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23 Functionally graded materials W. Lengauer and K. Dreyer, J. Alloys Comp. 338 (2002) 194 SEM micrograph courtesy of C. Kral, Vienna University of Technology, Austria Nitrogen – in-diffusion from N 2 N-rich zone of (Ti,W)(C,N) Ti(C,N) N-poor zone of (Ti,W)(C,N) (Ti,W)C

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24 Study of concentration profiles Copper radiation Penetration depth: 1.8 m Molybdenum radiation Penetration depth: 12.5 m The lattice parameter must depend on concentration

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25 Summary Benefits of X-ray scattering... for investigation of the real structure of thin films Length scale between 10 -2 Å and 10 3 Å is accessible (from atomic resolution to the layer thickness) Small and variable penetration depth of X-ray into the solids (surface diffraction, study of the depth gradients) Easy preparation of samples, non-destructive testing Integral measurement (over the whole irradiated area)

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