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

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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

Substrate temperatures: -200°C, 20°C, 200°C, 300°C, 350°C, 400°C

Deposition rates: 1 Å/s

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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

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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

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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

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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.%

UN (Fm3m)U: 4a (0, 0, 0)N: 4b (½, ½, ½)

U2N3 (Ia3)

U: 8b (¼, ¼, ¼)U: 24d (-0.018, 0, ¼)N: 48e (0.38, 1/6, 0.398)

Different lattice parametersNegligible differences in intensities

0 Atomic Percent Nitrogen 50 60 67

670

T(°C)

400

U UN U2N

3

UN

2

Schematic phase diagram of U-NSchematic phase diagram of U-N

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Phase composition (Ti1-xAlxN)

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)

001

WC

100

WC

101

WC

110

WC

002

WC

111

WC

200

WC

102

WC

100

AlN

002

AlN

101

AlN 11

0 A

lN

103

AlN

112

AlN

201

AlN

111

TiA

lN

200

TiA

lN

220

TiA

lN 311

TiA

lN22

2 T

iAlN

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Phase composition (Ti1-xAlxN)

Diffraction line asymmetry, maximum in Ti37Al14N49

Concentration gradient in Ti1-xAlxN TiAlN + AlN

Ti1-xAlxN (Fm3m)

TiAlN + AlN

Ti55Al2N43

Ti41Al7N52

Ti37Al14N49

Ti26Al24N50

Ti19Al31N50

110

AlN

220

TiA

lN

ISPMA 9, Prague 10

Residual stress and stress-free lattice parameters

2sinsincos1

1sinsin2sincos

1

2313332211

332

332

22122

110

0

EE

EEd

dd

22212

211

22112

0

0332313

sin2sincos

sin1

0

EEd

dd

Elastic lattice deformation from X-ray diffraction:

Bi-axial residual stress in thin films:

12sin1 2

0 E

aa

The sin2-method for cubic thin films:

sin2

0 1

a

a

a ||

a0

2

ns

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Residual stress and stress-free lattice parameters

nHKL

hkl

2

0

2

0

dg

dghk

hk

12

123

23

22

22

21442

1121144

121

23

23

22

22

21442

1121111

4

2

SSSSG

SSSSE

hk

hk

2

cossinsincoscoscos iiii

ea

sy

ha

rd

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Preferred orientation of crystallitesPVD Ti1-xAlxN, texture {111}

GAXRD at = 3°

Strong anisotropy of lattice deformation

111

200

220

311

222

400

331

420 42

2

Simulation: fibre texture {111}

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Preferred orientation of crystallitesPVD Ti1-xAlxN, texture {100}

GAXRD at = 3°

No anisotropy of lattice deformation111

200

220

311

222

400

331 42

0

422

Simulation: fibre texture {100}

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Preferred orientation of crystallites

-0.5 0 0.5

-0.5

0

0.5

TiA lN -1 (111)

m ax = 4330bei (0°,0°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -1 (200)

m ax = 2092bei (55°,80°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -1 (220)

m ax = 557bei (35°,-45°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -5 (111)

m ax = 374bei (60°,60°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -5 (200)

m ax = 1050bei (15°,70°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -5 (220)

m ax = 209bei (25°,60°)

“111”

“100”

111 200 220

111010

100

001

110

101 011

Ti1-xAlxNPVD

-0.5 0 0.5

-0.5

0

0.5

TiA lN -3 (111)

m ax = 1805bei (10°,5°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -3 (200)

m ax = 2225bei (40°,10°)

-0.5 0 0.5

-0.5

0

0.5

TiA lN -3 (220)

m ax = 648bei (30°,85°)

010 100

001

110

101 011

~ 30°

010

001

100

111

100

010

001

110

101

011

100

111_111

_111

__111

_101

_011

011

101

001

_101

_011

011

101

~ 30°

~ 30°

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Crystallite size and microstrain

Williamson-Hall plot

0.0 0.2 0.4 0.6 0.8 1.0

5

10

15

20

25

30

Lin

e b

roa

de

nin

g (

10-3

Å-1)

sin

1/D

~eCrystallite size Microstrain

Scherrer formula Line broadening only due to the crystallite size. Microstrain is neglected.

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.

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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

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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 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

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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

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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

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Typical features observed in nanocrystalline fcc thin films

D < 0

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

Needle-like crystallitesSimulation usingHeight: 200 ÅWidth: 40 Å

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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)

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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

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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