Prof. Xiaoqing Pan, Invited Speaker
Department of Materials Science & Engineering Department of Physics & Astronomy UC Irvine Materials Research Institute
In this talk, I will first present our TEM studies of the polarization ordering and electronic properties of domain walls and novel polarization states in multiferroic thin films. We found that the charged domain walls can be created or erased by an electrical bias, and the local polarization state and electric charge density distribution strongly depend on boundary conditions. We directly observed a strongly anisotropic polarization-induced conductivity at a ferroelectric/insulator (BiFeO3/TbScO3) interface, caused by an alternating polarization associated with the domains, producing either electron or hole doping of the interface. We also revealed a spin-polarized 2DEG forms at the PZT/STO interface, which is strongly localized, due to the interplay between Coulomb interaction and band bending, and can be tuned by the polarization. I will also present our in-situ TEM studies of nanostructured catalysts using a MEMS-based gas cell. We reveal details of a counter-intuitive core-shell formation process in platinum-cobalt nanoparticles at elevated temperature under oxygen at atmospheric pressure with the atomic resolution. Initial segregation of a thin platinum, rather than cobalt oxide, surface layer occurs concurrently with ordering of the intermetallic core, followed by the layer-by-layer growth of a platinum shell via Ostwald ripening during the oxygen annealing treatment. Calculations based on density functional theory demonstrate that this process follows an energetically favorable path. These findings are useful for the future design of structured Pt alloy catalysts.