Artifacts in the characterization of skin layers and ultrathin films by X-ray diffraction

$: Artifacts in the characterization of skin layers and ultrathin films by X-ray diffraction$
Artifacts in the characterization of skin layers and ultrathin films by X-ray diffraction

X. Marti, V. HolyCharles University, Prague

P. Ferrer, T. SchulliESRF, Grenoble

J. Herrero-AlbillosBESSY, Berlin

J. Narvaez, G. CatalanCIN2, Barcelona

N. Barrett, CEA, Gif-sur-Yvette

M. AlexeMPI, Halle

EMRS, Warsaw, SEPT [email protected]

D. Pesquera, F. Sanchez, G. Herranz, J. FontcubertaICMAB, Barcelona

Substrate

Thin film, t < 10 nm Out-of-plane parameter?

1 2

Conventional XRD Grazing incidence diffraction

22 22.5 23 23.5 24 24.5 250

1

2

3

4

5

6

Incidence angle

Inte

nsit

y

Lattice parameter(A):3.8282 || Thickness (A):260

22 22.5 23 23.5 24 24.5 25-1

0

1

2

3

4

5

6

Incidence angle In

tens

ity

Lattice parameter(A):3.8254 || Thickness (A):65


22 22.5 23 23.5 24 24.5 250

1

2

3

4

5

6

Incidence angle

Inte

nsit

yLattice parameter(A):3.8282 || Thickness (A):260

Substrate

Thin film, t < 10 nm

Incoming X-rays


Substrate

Thin film, t < 10 nm

Incoming X-rays


10-6

10-3

100

Am

plitude

22.5 23 23.5 24 24.5

10-5

10-3

10-1

Am

pli

tude

Incidence angle (deg)

10-7

10-5

10-3

Am

plitude

a)

b)

c)

S

2S SE ( ) 1

S B B 0S

S S

1sin 2 C

C ·C

l l

L L

LL B

C 2E ( ) exp i 1

2 sin

l t

2L B B 0S B

L L

1sin 2 C 2 sin

C C

l -l

|ESL(w)|2 = |ES(w) + EL(w)|2

|E0SL(w)|2 = |ES(w)|2 + |EL(w)|2


How relevant this issue could be (1/2):

5 10 15 20 25 303.82

3.83

3.84

3.85

3.86

3.87

Bragg peak position

Fitting to |ESL

()|2

Inte

rpla

nar

dist

ance

(A)

Thickness(nm)

Bulk LSMO

Samples grown at ICMAB



|ESL(w)|2 = |ES(w) + EL(w)|2 |E0SL(w)|2 = |ES(w)|2 + |EL(w)|2



5 10 15 20 25 303.82

3.83

3.84

3.85

3.86

3.87

Bragg peak position

Fitting to |ESL

()|2

Inte

rpla

nar

dist

ance

(A)

Thickness(nm)

Bulk LSMO




Samples courtesy of A. Gruverman

STO

SRO2BTO

SRO1

I0

Measured peak is at ……w = 22.24 deg

The corresponding “c” is at… 21.84 deg !!!

20 20.5 21 21.5 22 22.5 23 23.5 2410

-1

100

101

102

103

104

105

106

107

Incidence angle (deg)

Inte

nsit

y



Samples courtesy of A. Gruverman21 21.5 22 22.5 23 23.5

10-5

10-4

10-3

10-2

10-1

100

Incidence angle

Inte

nsity

True lattice parameter

Apparent lattice parameter

STO

SRO2BTO

SRO1

I0





Sample courtesy of A. Gruverman

STO

SRO2BTO

SRO1

I0

21.84 deg 4.14 Angstrom (fit)

22.24 deg 4.07 Angstrom (peak-pick)



FE Measurement courtesy of P. Zubko

1. Small changes of the out-of-plane parameter

2. …and confined in a few (?) nm thick topmost surface

http://henke.lbl.gov/optical_constants/

Single crystal

αi

Ei


Scenario # 2: a thin skin layer of a substrate

http://henke.lbl.gov/optical_constants/


),2/()Re(),Im(/1 zzzz QqaLq

.)1(2)(sin)1(2)(sin)),sin()(sin( 22 nnKqKQ fizfiz

αiEi

Two exit angles: αf , Ψ

Z: perpendicular to surface

(i.e. latitude, longitude)

Primary beam

Pseudocubic reciprocal space coordinates :

qx = K * [ cos(αf) * cos(Ψ) - cos(αI) ] ~ Hqy = K * [ cos(αf) * sin(Ψ) ] ~ Kqz = K * [ sin(αf) + sin(αI) ] ~ LK = 2*π/λ

X

Y

Correction for refraction

To circumvent refraction we scanned both

energy and incidence angle


Color scale indicates the information depth

For the particular case of BiFeO3, for instance:

Measured CorrectedBULK SKIN

Q Q

Changing the energy(no refraction correction required)


Measured Corrected

Changing the angles

BULK SKIN

Changing the energy(no refraction correction required)


Concluding remarks

1) For the extraction of lattice parameters it is highly recommended to fit simultaneously both the substrate and the thin film using a dynamical or semi-kinematical model.

2) For the determination small changes of lattice parameters, in grazing incidence geometry, changing the energy may be more useful than changing the angles

Thank you very much for your attention!

[email protected]


5 10 15 20 25 303.82

3.83

3.84

3.85

3.86

3.87

Bragg peak position

Fitting to |ESL

()|2

Inte

rpla

nar

dist

ance

(A)

Thickness(nm)

Bulk LSMO

Artifacts in the characterization of skin layers and ultrathin films by X-ray diffraction

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