artifacts in the characterization of skin layers and ultrathin films by x-ray diffraction x. marti,...
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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 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
Substrate
Thin film, t < 10 nm
Incoming X-rays
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
Samples grown at ICMAB
|ESL(w)|2 = |ES(w) + EL(w)|2 |E0SL(w)|2 = |ES(w)|2 + |EL(w)|2
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
How relevant this issue could be (2/2):
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
How relevant this issue could be (2/2):
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
Measured peak is at ……w = 22.24 deg
The corresponding “c” is at… 21.84 deg !!!
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
How relevant this issue could be (2/2):
Sample courtesy of A. Gruverman
STO
SRO2BTO
SRO1
I0
21.84 deg 4.14 Angstrom (fit)
22.24 deg 4.07 Angstrom (peak-pick)
Measured peak is at ……w = 22.24 deg
The corresponding “c” is at… 21.84 deg !!!
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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
Scenario # 2: a thin skin layer of a substrate
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
),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
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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)
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
Measured Corrected
Changing the angles
BULK SKIN
Changing the energy(no refraction correction required)
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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!
xavi.mr@gmail.com
EMRS, Warsaw, SEPT 2011xavi.mr@gmail.com
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
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