Surface and Interface Reconstruction in Functional Oxides

Junsoo Shin,1,2 Albina Borisevich,1 Vincent Meunier,3 Jing Zhou,4 E. Ward Plummer,5 Sergei V. Kalinin,3 and Arthur P. Baddorf3

1-Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
2-Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996
3-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
4-Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071
5-Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803

Achievement

This work combines several microscopy techniques capable of atomic resolution to provide unprecedented insight into the structure of surfaces and interfaces during the layer-by-layer growth of BaTiO3 films on SrRuO3. This pairing combines the classic ferroelectric material, BaTiO3, which spontaneously polarizes in one of several possible directions, with the most common conducting oxide, SrRuO3, and has been the subject of numerous investigations. By combining in situ measurements of in-plane surface structure, ex situ cross-sectional microscopy and spectroscopy, and first-principles simulations, we provide the first atomic scale structure of the SrRuO3 surface and its impact on the interface with several layers of BaTiO3. Surprisingly, the SrRuO3 surface, which had previously been thought to have ideal perovskite termination, is actually reconstructed at atomic length scales. This reconstruction increases the oxygen concentration and persists in the SrRuO3-BaTiO3 interface. This study presents a new archetype for identification of stoichiometry and interface structure in oxides, required for control of functional properties.

Significance

Advances in atomically controlled oxide growth have generated new classes of materials with unique physical properties highly sensitive to abrupt interfaces. The extreme sensitivity of oxides to electron concentration is coupled to charge transfer, structure, and spin and has recently been shown to produce spectacular behavior including interface-mediated conduction,1-3 superconductivity,4 magnetism,5 and phase transitions6,7 despite parent materials lacking these attributes. In the last decade, there has been a tremendous amount of high-profile work on these systems; however, in all cases the films were grown and cross-sections were studied only a posteriori, for example by electron microscopy. The structure at the surface of the oxide and interface remained an enigma, even though this controls the behavior in oxide heterostructures. Very few atomic scale studies of interface structures exist for complex oxides, due to the need for multiple tools to probe subsurface features, the need for a highly controlled environment, and the insulating nature of many oxides. We have performed the first atomic level analysis of an oxide interface combining in-plane structure using scanning tunneling microscopy, cross-sectional structure with aberration-corrected scanning transmission electron microscopy, and first principles density functional theory. The unexpected restructuring of the SrRuO3 surface into SrO rows changes the structure of the interface with BaTiO3. Only with this level of analysis can we control the interface and consequently formulate strategies to capture the exciting possibilities of functional oxides with nanoscale dimensions.

Credit

This work was published in ACS Nano 4, 4190 (2010), doi: 10.1021/nn1008337. Research was sponsored by the Division of Materials Science and Engineering and at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. This work was also partially sponsored by the Department of Energy Grant DE-SC0002136.

Surface and Interface Reconstruction in Functional Oxides

Junsoo Shin, Albina Y. Borisevich, Vincent Meunier, Jing Zhou, E. Ward Plummer, Sergei V. Kalinin, and Arthur P. Baddorf, “Oxygen-Induced Surface Reconstruction of SrRuO3 and Its Effect on the BaTiO3 Interface,” ACS Nano 4, 4190 (2010), doi: 10.1021/nn1008337

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