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)
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X-ray diffraction on nanocrystalline thin films David Rafaja Institute of Physical Metallurgy, TU Bergakademie Freiberg (D) Michal Šíma PIVOT a.s. (CZ),
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X-ray diffraction on nanocrystalline thin films
David RafajaInstitute of Physical Metallurgy, TU Bergakademie Freiberg (D)
Michal ŠímaPIVOT a.s. (CZ), PLATIT Advanced Coating Systems
Ladislav HavelaDepartment of Electronic Structures, Charles University Prague (CZ)
ISPMA 9, Prague 2
Physical background
A contribution to the explanation of the relationship between physical properties and real structure of matters
Strong dependence of the magnetic behaviour of thin UN films on deposition conditions (microstructure)
Strong dependence of the mechanical hardness of thin TiN films on deposition conditions (microstructure)
Examples
ISPMA 9, Prague 3
Magnetic susceptibility of UN thin films
T (K)
0 50 100 150 200 250 300
24
242468
10
68
101214
68
101214
468
10Ts = 400 oC
Ts = 350 oC
Ts = 300 oC
Ts = 200 oC
Ts = 20 oC
Ts = -200 oC
(1
0-8 m
3/m
ol)
UN single crystals: paramagnetic below 53 Kantiferromagnetic below 53 K
Thin polycrystalline UN films:development of a ferromagneticcomponent below 100 K.
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
Hardness of Ti1-xAlxN thin filmsA series of arc deposited Ti1-xAlxN films with increasing aluminium contents
Ti Al
N2 + Ar
Addition of Aluminium improves the hardness of the films, especially at high temperatures (up to 1000°C)
Different colour and hardness of the coatings
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
Phase composition (Uranium nitride)
20 30 40 50 60 70
101
102
103
222,
UN31
1, U
N
622
, U2N
3220,
UN
440
, U2N
3
Su
bst
rate
200,
UN
111,
UN
400
, U2N
3
222
, U2N
3
Inte
nsity
(cp
s)
Diffraction angle (o2)
Phase compositionPhase composition
1. UN (Fm3m) 80-90 mol.%2. U2N3 (Ia3) 10-20% mol.%
Inclination of the texture direction (dominated by the geometry of the deposition process)
Dominant phasefcc TiAlN
hex AlN
Crystallite size below 20 nmMinimum: ~ 3.3 nm
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
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
Advanced information on microstructure of thin films
XRD study Lattice parameters + Texture
Structure model Information on distribution of inter-atomic
distances (local probe), but no lateral resolution
nHKL
hkl
2
0
2
0
max|| coscossinsinsin
dg
dg
hk
Microstructure modeland
Texture model
ISPMA 9, Prague 20
Typical features observed in nanocrystalline fcc thin films
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
Needle-like crystallitesSimulation usingHeight: 200 ÅWidth: 40 Å
ISPMA 9, Prague 21
True crystallite sizeSymmetrical XRD
HRTEM35 – 50 Å
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