Determining the structure/property relation at oxide interfaces by means of advanced TEM spectroscopy and imaging

Abstract

The study of novel physical properties appearing when two materials are interfaced has become one of the major fields of research in solid state physics over the last decade. For example, in the strive for novel non‐silicon based electronics, the discovery of the formation of a conductive layer right at the interface region between 2 insulators (for example LaAlO 3 and SrTiO 3 ); a so‐called two‐dimensional electron gas (2DEG) or two dimensional electron liquid appears. Another important example of such emergent phenomena is the appearance of interface magnetism or superconductivity. As the materials involved in those new physical phenomena are often complex oxides, many factors such as strain, oxygen stoichiometry, cation intermixing, oxygen octahedral coupling.…[1,2] have to be considered when discussing their origin. The exact understanding of those phenomena is a key factor in order to turn these research ideas into working devices and in order to search for the most optimal materials. In parallel, advances in electron microscopy instrumentation and techniques such as the introduction of aberration‐correctors of the probe‐forming lens have made it possible to achieve sub‐angstrom spatial resolution allowing the study of materials on an atom column by atom column basis. High Angle Annular Dark Field (HAADF) combined with Annular Bright Field (ABF) imaging have made it possible to study and understand respectively the cationic and the oxygen sub‐lattices in these materials. As a first example, in the case of a (La,Sr)MnO 3 (LSMO) film grown on a NdGaO 3 (NGO) substrate, the magnetic easy axis of the LSMO film can be reversed by adding a SrTiO 3 (STO) buffer layer between the substrate and the film. Using the statistical analysis of STEM ABF images, we could reveal that even one single STO layer is enough to remove the transferred octahedral tilt of NGO into the LSMO film reversing its magnetic easy axis from the a to the b axis(see ref 1 and figure 1). In a second part, The appearance of superconductivity in a superlattice of (Sr,Ca)CuO 2 (SCCO) and BaCuO 2 (BCO) will be investigated. Comparing two different heterostructures where 8 layers of SCCO are sandwiched with STO (no superconductivity) and BCO (superconductivity) the effect of the structure of the different layers (orientation of the CuO 2 in the form of planes or chains) on the appearance of superconductivity will be presented.