Suppression of Octahedral Tilts and Associated Changes in Electronic Properties at Epitaxial Oxide Heterostructure Interfaces

A. Y. Borisevich, H. J. Chang, M. Huijben, M. P. Oxley, S. Okamoto, M. K. Niranjan, J. D. Burton, E. Y. Tsymbal, Y. H. Chu, P. Yu, R. Ramesh, S. V. Kalinin, and S. J. Pennycook

Phys. Rev. Lett. 105, 087204 – Published 19 August 2010

Abstract

Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the ${BiFeO}_{3} − {La}_{0.7} {Sr}_{0.3} {MnO}_{3}$ interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition near the interface in ${BiFeO}_{3}$ and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface.

Received 10 February 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.087204

Authors & Affiliations

A. Y. Borisevich^1,*, H. J. Chang¹, M. Huijben^2,3, M. P. Oxley¹, S. Okamoto¹, M. K. Niranjan⁴, J. D. Burton⁴, E. Y. Tsymbal⁴, Y. H. Chu⁵, P. Yu³, R. Ramesh³, S. V. Kalinin¹, and S. J. Pennycook¹

¹Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
³Department of Materials Science and Engineering and Department of Physics, University of California, Berkeley, California 94720, USA
⁴Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
⁵Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30013, Republic of China

^*albinab@ornl.gov

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Vol. 105, Iss. 8 — 20 August 2010

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Images

Figure 1
Lattice parameters from HAADF STEM: (a) image of the $STO / 5 nm$ $LSMO / 50 nm$ BFO thin film, (b) corresponding 2D map of the $c$ lattice parameter (normal to the interface), with lighter color corresponding to higher $c$ values, (c) line profile obtained by averaging all rows of the map in (b) showing an increase in the first few layers of BFO. (d) Image of the $STO / 5 nm LSMO / 3.2 nm BFO$ ultrathin film, (e) corresponding 2D map of the $c$ lattice parameter, (f) line profile obtained by averaging all rows of the map in (e). Image in (d) was rescaled to correct for drift; error bars in (c) and (f) reflect variance between individual rows in the 2D maps. Note that graphs (c) and (f) are presented on the same absolute scale.Reuse & Permissions
Figure 2
Oxygen octahedral rotation angles from BF STEM: (a) image of the $3.2 nm$ $BFO / 5 nm$ $LSMO / STO$ ultrathin film, acquired simultaneously with the HAADF image in Fig. 1d, (b) corresponding 2D map of in-plane octahedral rotation angles in BFO showing checkerboard order (color scale on left); (c) BFO structure in rhombohedral (001) orientation showing the tilt pattern, (d) line profiles obtained from the map in (b) with two checkerboard “sublattices” added up separately: odd (top) and even (bottom); two bad points in the map corresponding to a hole in the sample are taken out of the averaging. The image in (a) was rescaled to correct for drift; the map in (b) was corrected for local Bi-Bi angle variations; error bars in (d) are equal to the standard deviation of local Bi-Bi angles.Reuse & Permissions
Figure 3
Low-loss EELS imaging of the ${SrTiO}_{3} / (La, Sr) {MnO}_{3} / {BiFeO}_{3}$ interface. (a) imaging area; (b) representative spectra (after Fourier-log deconvolution) of the three components showing distinctive signatures and features; (c)–(f) results of the multiple least square fit of the image using BFO, LSMO, and STO spectra from (b) in two energy ranges: core loss (35 to 125 eV): (c) fit coefficient map, (d) $χ^{2}$ map; and plasmonic (5 to 35 eV): (e) fit coefficient map, and (f) $χ^{2}$ map. A region of BFO approximately 2 nm wide shows an anomaly in map (f). Thin lines denote interface positions taken from a simultaneously acquired dark field image. The interfaces appear tilted due to specimen drift during spectrum image acquisition (over 5 min).Reuse & Permissions
Figure 4
Interfacial lattice distortion in ${BiFeO}_{3}$ and its effect on the density of states. (a) DOS by LSDA method, in fully relaxed ${BiFeO}_{3}$ (top) where oxygen octahedron rotations are present and (bottom) in cubic ${BiFeO}_{3}$ where oxygen octahedron rotations are absent; band gap is reduced from 0.44 to 0 eV. (b) DOS by $LSDA + U$ method, $U - J = 3.0 eV$ (top) in fully relaxed ${BiFeO}_{3}$ where oxygen octahedron rotations are present and (bottom) in cubic ${BiFeO}_{3}$ where oxygen octahedron rotations are absent; band gap is reduced from 1.7 to 0.74 eV. The dashed lines indicate the position of the Fermi energy. (c) Additional coupling with LSMO can generate finite density of states within the gap.Reuse & Permissions

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