Argonne National Laboratory

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Heteroepitaxy and Emergent Functionalities of Complex Oxide Thin-Films and Interfaces

Materials Science Seminar
Liang Qiao, Oak Ridge National Laboratory
September 6, 2013 11:00AM to 12:00PM
Building 223, Room S105
 Complex oxides represent a very important class of materials and exhibit broad range of electronic, magnetic and optical behaviors. Their richness in functionalities, along with superior stability, wide abundance, and environmental friendly nature, uniquely suit them for a number of strategically important applications, which are not possible for conventional semiconductors. Recent advance of cutting-edge thin-film epitaxy and in-situ atomic-scale characterization techniques have now made it possible for precise control of material synthesis and perfecting their properties for future information technology and energy-related applications.  

In this talk, I will focus on the emergent interfacial structural and electronic properties of several La-based ABO3 polar/nonpolar oxides heterojunctions, prepared by both low-energetic MBE and high-energetic PLD. Due to chemical solubility and inherent polar discontinuity, these material systems are prevent from forming structurally and chemically abrupt interfaces, as evidenced by angle-resolved XPS, high-resolution RBS, probe-corrected HAADF-STEM/EELS, and DFT calculations. By replacing the B-site cation from simple Al to 3d transition metals, we inject a new degree of freedom into the band structure — partially occupied d orbitals — and, thus, enable other mechanisms of charge redistribution.

Based on photoemission technique, residual electric field inside polar films is extracted and energy-level band alignment of these heterojunctions is reconstructed. It is shown that the intrinsic polarity mismatch induced built-in potential can be utilized to tune the band alignment at these heterojunctions, especially for systems involving low band gap polar oxides. I will also introduce our recent research on tuning optical properties of complex oxides towards energy applications and interesting correlation between octahedral tilts and induced magnetic ordering at epitaxial cobaltites.