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Fine-tuning the chemical sharpness of oxide heterostructure interfaces

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Schematic diagram of atomic layer engineering for a chemically sharp oxide interface. Broad interface prepared by conventional growth in high vacuum (left-hand side) and chemically abrupt interface produced by inserting a monolayer grown in high pressure with the rest of the structure grown in vacuum (right-hand side).
In pulsed laser deposition (PLD), a widely used growth technique for epitaxial oxides, inserting a single layer of LaAlO3 grown at high oxygen pressure is found to dramatically enhance the interface abruptness of structures otherwise grown at lower pressure. The ability to control the chemical composition of the interface is crucial for optimizing the physical properties of the heteroepitaxial oxide interfaces that are of great interest for a variety of technologically important applications, including advanced energy materials and novel oxide electronics.

In epitaxial heterostructures, the first layer grown represents the foundation that dictates the degree of ordering and thus the properties of the subsequent layers. The present study of interface formation and strain evolution during the initial growth of LaAlO3 on SrTiO3 found that the behaviour of a vacuum-grown heterostructures can be fundamentally altered by the insertion of a single monolayer of material deposited at high oxygen pressure: the resulting structure shows an atomically sharp interface and an enhanced epitaxial relationship between film and substrate. The data from coherent Bragg rod analysis (COBRA), real time surface x-ray diffraction (SXRD), and scanning transmission electron microscopy (STEM)-based electron energy loss spectroscopy (EELS) confirm the critical role played by the kinetic energy of the laser plume in the formation of chemically-sharp oxide interfaces.

For more information, please contact hnlee@ornl.gov

Woo Seok Choi, Christopher M. Rouleau, Sung Seok A. Seo, Zhenlin Luo, Hua Zhou, Tim T. Fister, Jeffrey A. Eastman, Paul H. Fuoss, Dillon D. Fong, Jonathan Z. Tischler, Gyula Eres, Matthew F. Chisholm, and Ho Nyung Lee, “Atomic layer engineering of perovskite oxides for chemically sharp heterointerfaces,” Advanced Materials, DOI: 10.1002/adma.201202691.