Skin layer of BiFeO 3 single crystals
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layer of BiFeO 3 single crystals /arxiv.org/abs/1012.2306 X. Marti, V. Holy Charles University, Prague P. Ferrer ESRF, Grenoble J. Herrero-Albillos BESSY, Berlin J. Narvaez, G. Catalan CIN2, Barcelona N. Barrett, CEA, Gif-sur-Yvette M. Alexe MPI, Halle BiFeO 3 (AF, FE) = BULK SKIN And a general methodology to study skin layers by X-ray grazing incidence diffraction ISIF, Cambridge, AUG 20 [email protected] [email protected]
description
Skin layer of BiFeO 3 single crystals http://arxiv.org/abs/1012.2306. X. Marti, V. Holy Charles University, Prague P. Ferrer ESRF, Grenoble J. Herrero-Albillos BESSY, Berlin J. Narvaez, G. Catalan CIN2, Barcelona N. Barrett, CEA, Gif- sur -Yvette M. Alexe MPI, Halle. - PowerPoint PPT Presentation
Transcript of Skin layer of BiFeO 3 single crystals
Skin layer of BiFeO3 single crystalshttp://arxiv.org/abs/1012.2306
X. Marti, V. HolyCharles University, Prague
P. FerrerESRF, Grenoble
J. Herrero-AlbillosBESSY, Berlin
J. Narvaez, G. CatalanCIN2, Barcelona
N. Barrett, CEA, Gif-sur-Yvette
M. AlexeMPI, Halle
BiFeO3 (AF, FE)
=BULK
SKIN
And a general methodology to study skin layers by X-ray
grazing incidence diffraction
ISIF, Cambridge, AUG 2011
Required: tuneable information depth
BiFeO3
αi
Ei
http://henke.lbl.gov/optical_constants/
Snell’s lawCritical angleGrazing incidence
Required: tuneable information depth
BiFeO3
αi
EiSnell’s lawCritical angleGrazing incidence
http://henke.lbl.gov/optical_constants/
Refraction is relevant at very low incidence angles
To circumvent refraction we proposed scanning both energy and incidence angle
Outline
1. Methodology for energy-dependant grazing incidence diffraction
2. Use on BiFeO3 single crystals
3. Complementary experiments
4. Conclusions
Required: excellent surface of your materials
Peak-to-valley ~ 1 nm
Roughness RMS: 0.73 nm
200nm
Atomic force microscopy Laboratory X-ray reflectivity
Critical angle ~ 0.3
Interface roughness 1.3 nm
Required: BiFeO3 is a good single crystal
Rhombohedrala = 3.964 Åangle = 89.418 °
Identical planes point in many directions
The interplanar distances are the same
Caution: BiFeO3 ferroelastic domains
Interplanar distance
BiFeO3(001)
Identical planes point in many directions
The interplanar distances are the same
Caution: BiFeO3 ferroelastic domains
BiFeO3(001)
“Information” in X-ray diffraction is
(#1) Periodicities
(#2) Directions
The inter-planar distances are a fingerprint of each material/phase/skin
BiFeO3
αi
Ei
Information depth: sample surface
“Information itself”: crystal planes
The inter-planar distances are a fingerprint of each material/phase/skin
We will investigate the set of interplanar distances in the skin and in the bulk, but we skip the orientation of crystal planes
“Information” in X-ray diffraction is
(#1) Periodicities
(#2) Directions
Technical issue 1/2
BiFeO3
αiEi
(hkl)2perpendicular direction
Primary beam
We only align L to be perpendicular to the surface (information depth)
Each location in the real space (Ψ, αf) corresponds to a interplanar distance
Two exit angles: αf , Ψ(i.e. latitude, longitude)
Technical issue 1/2
BiFeO3
αiEi
(hkl)2
Two exit angles: αf , ΨZ: 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
hklzyx dqqqQ 222
Exact Pseudocubic approximation
Technical issue 1/2
BiFeO3
αiEi
(hkl)2
3-D mesh Z: perpendicular to surface
Primary beam X
Y
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
hklzyx dqqqQ 222
Exact Pseudocubic approximation
Technical issue 2/2
Refraction is relevant at very low incidence angles
Enlarges out of plane lattice parameters
Measurement plan: 3-D mesh at two energies and at two incidence angles
To circumvent refraction we propose scanning different energies at fixed incidence angle
Measured Corrected
(hkl)2
3-D mesh
Maps of (102) and (102) reflectionsEach pixel is one inter-planar distance Skin layer of BiFeO3 exists
The inter-planar distances are differentCoincidence after 2 different experimentshklzyx dqqqQ 222
-1
-0.5
0
0.5
1
-0.8-0.6
-0.4-0.2
00.2
0.40.6-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
hk
l
All possible [-2 -1 0 1 2] permutations(combinations,3)x4 ferroelastic domains type-(111)
-0.05
0
0.05
0.22
0.23
0.24
0.25
0.26
0.27
0.280.4
0.42
0.44
0.46
0.48
0.5
0.52
0.54
0.56
0.58
0.6
hk
l
3:0,-1,20.56858...0.0051273,0.25828,0.506511:-1,0,20.56859...-0.0024343,0.25834,0.506514:1,0,20.56405...0.0076131,0.24809,0.506512:0,1,20.56409...-0.0051267,0.24823,0.50651
At the region we measured there are only 4 peaksBut only two Q’s were expected!!!
Skin and bulk are in-plane coherent
Skin and bulk are in-plane coherent
Red rectangle must be the same
Possible changes: α = β, or c
Elongation of c by 0.8%
The distortion angle is preserved
The skin is triclinic
c %
elo
ngat
ion
Q102
/Q-102
0
0.5
1
0.99
0.995
1
Distortion angle (deg)
c %
elo
ngat
ion
Q/Qbulk102
89 89.5 900
0.5
1
0.985
0.99
0.995
1
1.005
Elongation of c by 0.8%
The distortion angle is preserved
The skin is triclinic
Temperature dependence
The skin has its own phase transitions
Ac anomalies seen in 3 samples by 3 different growers !!!
Independent of polishing process
X-ray diffraction Capacitance
BiFeO3 (AF, FE)
=BULK
SKIN
Concluding remarks
We have observed a skin layer in BiFeO3 single crystalsOut of plane parameter expands 0.2% in the topmost interface (~10 nm)
The skin has its own phase transitions
Methodology:
1) Use Q-histograms as fingerprints2) Tune both energy and angle in “grazing incidence”
AcknowledgementsH. Schmidt, P. JégouSpanish Ministerio de Ciencia e Innovación (PI201060E013), Consejo Superior de Investigaciones Científicas (PIE 200960I187), the German Science Foundation (Grant SFB762), Ministry of Education of Czech Republic (MSM0021620834), the Grant Agency of the Czech Republic (P204/11/P339)
),2/()Re(),Im(/1 zzzz QqaLq
.)1(2)(sin)1(2)(sin)),sin()(sin( 22 nnKqKQ fizfiz
