The study of defect-related surface reaction on metal oxide model system utilizing ambient pressure X-ray photoelectron spectroscopy

Abstract

The development of surface characterization techniques can contribute to significant progress in cutting-edge science regarding sustainable energy conversion and environment-friendly technology at the molecular level. In the last decade, the advanced operando observation tools have been widely utilized in structural, compositional, and thermodynamic behavior observations at the gas-solid interface in surface science and heterogeneous catalysis. In particular, the synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) plays an important role in fundamental investigations of complicated reactions to reveal physicochemical properties on the material surface under the more realistic condition. In this thesis, I will introduce technical details on the hemispherical electron analyzer equipped with the differential pumping system to build high-flux photon delivery into the analysis chamber at elevated pressure conditions. By using AP-XPS, surface chemical states and interfacial structures have been studied on representative metal oxide model systems such as Ga2O3-x, SrTiO3 (001), and SrRuO3/SrTiO3 (001). The core-level spectra analysis results highlight that the surface redox process and the variation of bandgap on the Ga2O3-x during post-annealing process, the nature of electron depletion and band bending with vacancy formation on the SrTiO3 (001) substrate, and the influence of surface migration of lattice oxygen process at the SrRuO3-SrTiO3 interface on the structural phase transition. Those observed phenomena at the surface show that the bunch of reactive molecules’ interaction at the gas-solid interface could affect the surface electronic structure near the Fermiedge on the condensed matter, which provides more reliable spectroscopic evidence for understanding energy conversion issues on the surface in the real world.