Atomic structure and electronic properties of perovskite *surfaces and *interfaces

ABO3 type perovskites have been crucial in modern technology due to their functions in electronic devices, catalysis and environmental interactions. Surfaces and interfaces in perovskites introduce a whole new array of useful properties. To achieve a fundamental understanding of interface-related phenomena in this class of materials, local characterizations of charge distribution and defect segregation at submicron or atomic levels are required. This work lays the foundation for scanning probe analysis of perovskite surfaces and interfaces in ultrahigh vacuum condition. Standard scanning probe methods, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM), along with Kelvin probe force microscopy (KPFM) and scanning impedance microscopy (SIM) were used in this study. High angle SrTiO3 grain boundaries, as a model for perovskite interfaces, were characterized by electron microscopy and low temperature four-point transport measurement. Experimentally determined boundary charge was consistent with theoretical calculations. Furthermore, we discovered a positive temperature coefficient of resistivity effect at these grain boundaries, which is ascribed to the formation of dielectric polarization in the vicinity of the grain boundary. The boundary charge and its limitation on transport were directly observed with KPFM. An extensive study of SrTiO3 (001) and BaTiO3 (001) surfaces were carried out with low energy electron diffraction, STM and NC-AFM. It is found that several mechanisms are responsible for the formation of SrTiO 3 surface reconstructions and that the c(6x2) reconstruction is not due to oxygen vacancies but TixOy clusters on Sr-O plane. Reconstructions on BaTiO3 (001) were successfully produced and locally observed with scanning probe microscopy. Their formation mechanism is ascribed to oxygen vacancy induced ordering.