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X-ray diffraction on nanocrystalline thin films

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Macroscopic and microscopic anisotropy of lattice deformation ... is related to the anisotropy of elastic constants and to the orientation of crystallites ... – PowerPoint PPT presentation

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Title: 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)
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
-200C, 20C, 200C, 300C, 350C,
400C 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.
4
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
1000C)
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

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

7
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
8
Phase composition (Ti1-xAlxN)
100 WC
101 WC
100 AlN
001 WC
200 TiAlN
311 TiAlN
222 TiAlN
111 TiAlN
220 TiAlN
110 AlN
111 WC
110 WC
201 AlN
102 WC
112 AlN
002 WC
200 WC
103 AlN
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)
9
Phase composition (Ti1-xAlxN)
Diffraction line asymmetry, maximum in Ti37Al14N49
220 TiAlN
110 AlN
Ti55Al2N43 Ti41Al7N52 Ti37Al14N49 Ti26Al24N50 Ti19
Al31N50
Concentration gradient in Ti1-xAlxN ? TiAlN AlN
TiAlN AlN
Ti1-xAlxN (Fm3m)
10
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
11
Residual stress and stress-free lattice parameters
easy
hard
12
Preferred orientation of crystallites
PVD Ti1-xAlxN, texture 111 GAXRD at ?
3 Strong anisotropy of lattice deformation
111
220
200
311
422
222
331
420
400
Simulation fibre texture 111
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
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
15
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.
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
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
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
19
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
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 lt 0
Needle-like crystallites Simulation using Height
200 Å Width 40 Å
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)
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

23
Acknowledgements
  • Grant Agency of the Czech Republic (Project
    number 106/03/0819)
  • European Community (Program HPRICT-200100118)
  • 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
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