Supplemental material: Appl. Phys. Lett.
Symmetry-dependent interfacial reconstruction to compensate polar
discontinuity at perovskite oxide interfaces (LaAlO3/SrTiO3,
LaAlO3/CaTiO3)
Joohwi Lee,1,+ Jong Kwon Choi,2,+ Seon Young Moon,1 Jaehong Park,1,3 Jin-Sang Kim,1
Cheol Seong Hwang,3 Seung-Hyub Baek,1,4 Jung-Hae Choi,1,* and Hye Jung Chang2,4*
1
Electronic Materials Research Center, Korea Institute of Science and Technology,
Seoul 136-791, Korea
2
Advanced Analysis Center, Korea Institute of Science and Technology,
Seoul 136-791, Korea
3
Department of Materials Science and Engineering and Inter-university Semiconductor
Research Center, Seoul National University, Seoul 151-744, Korea
4
Department of Nanomaterials Science and Technology, Korea University of Science and
Technology, Daejeon, 305-333, Republic of Korea
1
1. Transformation into pseudocubic cell
The orthorhombic cells of CaTiO3 (CTO) and LaAlO3 (LAO) were transformed into
the pseudocubic 2×2×2 supercell in order to describe the heterostructures. Equation S.1 is the
transformation matrix from orthorhombic CTO to psuedocubic.
 a p   1 1 0  a0 
  
 
 bp    0 0 1 b0 
 c   1 1 0  c 
 0 
 p 
(S.1)
where a0, b0, and c0 are lattice vectors of the orthorhombic cell while ap, bp, and cp are those of
the transformed pseudocubic cell. The <110> direction of orthorhombic CTO was set to be
parallel to [001] STO which followed the growth direction of SrRuO3 belonging to Pbnm on
cubic SrTiO3 (STO). 1
Equation S.2 shows the transformation matrix of LAO belonging to the space group
of Imma.
 a p   0 1 1  a0 
  
 
 bp    1 0 0   b0 
 c   0 1 1  c 
 0 
 p 
(S.2)
The direction of LAO was on CTO/STO was chosen to minimize the mismatch of the
octahedral tilt. In this case, the Glazer notation2 of CTO is a-b+a-, and that of LAO is a-b0awith respect to the pseudocubic lattice vectors, respectively.
2
2. Computational method and results on optimized structures
The pseudocubic 2×2×2 supercell composed of 8 A-sites and 8 B-site cations, and 24
O atoms were optimized with 3×3×3 Γ-centered k-point sampling before forming the
heterostructure model. Table S-1 shows the optimized structures in this work and previous
reports. Note the lattice parameters from calculations using GGA parameterized by Perdew et
al.9 are always slightly larger than those of experimental values. However, the ratio of the
calculated lattice parameters among STO, CTO and LAO were almost the same with the
experimental values, indicating that the calculations mimic the experimental strain state.
For LAO/STO and LAO/CTO heterostructures, the lattice parameters of the in-plane
strained bulk LAO were used in order to describe the epitaxy on the STO substrate and CTO
film. The in-plane lattice parameter of CTO film was also set as the lattice parameter of STO
to describe the epitaxial CTO film on the STO substrate.
3
Table S-1. Structural information on STO, CTO and LAO.
XCfunctional
Space
Lattice (Å)
Group
Parameters
Glazer
State
References
a
Notation [2]
(pseudocubic)
STO
CTO
GGA
Pm-3m
3.94, 3.94, 3.94
a0a0a0
Bulk
This study
GGA
Pm-3m
3.94, 3.94, 3.94
a0a0a0
Bulk
[3]
exp.
Pm-3m
3.90, 3.90, 3.90
a0a0a0
Bulk
[4]
GGA
Pbnm
3.86, 3.84, 3.86
ab a
Bulk
This study
GGA
P21/m
3.94, 3.94, 3.80
a-b+a-
Strained bulk
This study
3.83, 3.82, 3.83
- + -
Bulk
[5]
- 0 -a
exp.
LAO
- + -a
GGA
Pbnm
Imma
C2/m
LDA
Imma
b
ab a
3.82, 3.81, 3.82
ab a
Bulk
This study
3.94, 3.94, 3.72
a-b+a-
Strained bulk
This study
3.76, 3.73, 3.76
- 0 -
ab a
Bulk
[6]
- - -
Bulk
[7]
exp.
R-3c
3.79, 3.79, 3.79
aaa
exp.
-
3.90, 3.90, 3.80
-
a
Film (on STO)
- - +
[8]
Glazer notations of original orthorhombic cells of CTO and LAO are a a c and a a c , respectively. However, ab+a- and a-b0a- were used to adjust the present heterostructures.
b
- - 0
LAO belonging to R-3c was reported to be the stable bulk phase, however, LAO belonging to Imma was used
in this study, which was reported to be stable under the biaxial tensile strain. 6
4
3. STEM observations on the surface termination of STO
In order to find out the termination layer of the STO substrate, the cross-sectional
plane of STO was examined by high angle annular dark field (HAADF) STEM as shown in
Figs. S1(a) and (b) after the deposition of thin amorphous LAO to protect the surface
structure. The Sr atomic column shows higher intensity than Ti one. The line profiles from
each layer (SrO-TiO2-SrO-TiO2…) in Fig. 1(c) reveal the periodic atomic positions. The line
7, which is supposed to be the SrO layer shows a non-periodic profile, while the line 6
corresponding to Ti layer shows the periodic peaks. This means that STO is terminated by
TiO2 layer, which is in agreement with many previous reports.10-16 The observation of the
2DEG in our previous paper17 also provides the indirect evidence of the TiO2-terminated STO,
because the 2DEG phenomena occur only when STO substrate has TiO2-termination.18-20
Although, some previous studies reported the surface reconstruction of TiO2-terminated
STO,21,22 our HAADF images did not indicate any surface reconstruction, which is consistent
with the reflection high-energy electron diffraction (RHEED) image of STO substrate treated
in the same condition with our experiments.23
5
Fig. S1. (Color online) (a) STEM HAADF image of a-LAO/STO taken along the [100]STO
direction showing the termination layer is TiO2 (b) guiding lines to obtain the intensity
profiles and (c) line profiles of each atomic layer indicating the atomic column positions with
intensity peaks.
6
REFERENCES
1
J. C. Jiang, W. Tian, and X. Q. Pan, Q. Gan and C. B. Eom, Appl. Phys. Lett. 72, 2963
(1998).
2
A. M. Glazer, Acta Cryst. A 31, 756 (1975).
3
S. Piskunov, E. Heifets, R. I. Eglitis, and G. Borstel, Comput. Mater. Sci. 29, 165 (2004).
4
Y. A. Abramov, V. G. Tsirelson, V. E. Zavodnik, S. A. Ivanov, and I. D. Brown, Acta Cryst. B
51, 942 (1995).
5
S. Sasaki, C. T. Prewitt, and J. D. Bass, Acta Cryst. C 43, 1668 (1987).
6
A. J. Hatt, and N. A. Spaldin, Phys. Rev. B 82, 195402 (2010).
7
M. Guennou, P. Bouvier, G. Garbarino, and J. Kreisel, J. Phys.: Condens. Matter 23, 395401
(2011).
8
C. Cancellieri, D. Fontaine, S. Gariglio, N. Reyren, A. D. Caviglia, A. Fête, S. J. Leake, S. A.
Pauli, P. R. Willmott, M. Stengel, Ph. Ghosez, and J.-M. Triscone, Phys. Rev. Lett. 107,
056102 (2011).
9
J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).
10
11
T. Matsumoto, H. Tanaka, T. Kawai, and S. Kawai, Surf. Sci. Lett. 278, L153 (1992).
M. Kawasaki, K. Takahashi, T. Maeda, R. Tsuchiya, M. Shinohara, O. Ishiyama, T.
Yonezawa, M. Yoshimoto, and H. Koinuma, Science 266, 1540 (1994).
12
C. L. Chen, Y. Cao, Z. J. Huang, Q. D. Jiang, Z. Zhang, Y. Y. Sun, W. N. Kang, L. M.
7
Dezaneti, W. K. Chu, and C. W. Chu, Appl. Phys. Lett. 71, 1047 (1997).
13
G. Koster, B. L. Kropman, G. J. H. M. Rijnders, D. H. A. Blank, and H. Rogalla, Appl. Phys.
Lett. 73, 2920 (1998).
14
H.-J. Gao, C. L. Chen, B. Rafferty, S. J. Pennycook, G. P. Luo, and C. W. Chu, Appl. Phys.
Lett. 75, 2542 (1999).
15
M. Huijben, A. Brinkman, G. Koster, G. Rijnders, H. Hilgenkamp, and D. H. A. Blank, Adv.
Mater. 21, 1665 (2009).
16
Y. J. Chang, A. Bostwick, Y. S. Kim, K. Horn, and E. Rotenberg, Phys. Rev. B 81, 235109
(2010).
17
S. Y. Moon, D. -H. Kim, H. J. Chang, J. K. Choi, C -Y. Kang, H. J. Choi, S. -H. Hong, S. -H.
Baek, J. -S. Kim, and H. W. Jang, Appl. Phys. Lett. 102, 012903 (2013).
18
N. Nakagawa, H. Y. Hwang, and D. A. Muller, Nat. Mater. 5, 204 (2006).
19
M. Huijben, G. Rijnders, D. H. A. Blank, S. Bals, S. V. Alert, J. Verbeeck, G. V. Tendeloo, A.
Brinkman, and H. Hilgenkamp, Nature Mater. 5, 556 (2006).
20
R. Yamamoto, C. Bell, Y. Hikita, H. Y. Hwang, H. Nakamura, T. Kimura, and Y.
Wakabayashi, Phys. Rev. Lett. 107, 036104 (2011).
21
Q. D. Jiang, and J. Zegenhagen, Surf. Sci. 425, 343 (1999).
22
N. Erdman, K. R. Poeppelmeier, M. Asta, O. Warschkow, D. E. Ellis, L. D. Marks, Nature
419, 55 (2002).
8
23
M. Huijben, A. Brinkman, G. Koster, G. Rijnders, H. Hilgenkamp, and D. H. A. Blank, Adv.
Mater. 21, 1665 (2009).
9