Correlation between surface potentials and surface oxygen exchange coefficents of CeO2

点击翻译按钮获取中文摘要

The aim of this proposal is to investigate the possible correlation between the surface Fermi level position, ionization potential, and work function and the oxygen surface exchange rate of the prototypical oxygen-ion conductor, CeO2. As the energy levels of adsorbed oxygen species (relative to the band edges) are expected to depend directly on the work function of the substrate, they govern whether electron transfer to the adsorbed species, most likely a rate determining step, is possible or not. To examine the possible correlation, the work function of CeO2 will be determined systematically as a function of doping and oxygen partial pressure for various surface orientations and terminations. Differently doped polycrystalline and epitaxial thin CeO2 films will be prepared by magnetron sputtering for this purpose. The surface chemical composition and the surface potentials will then be determined by means of photoelectron spectroscopy without breaking vacuum conditions. The variation of surface potentials will be established during and after deposition through variation of deposition conditions and post-deposition oxidation and reduction treatments. The oxygen surface exchange rate will be investigated on identically prepared thin films as well as on sintered ceramic specimens by means of 18O tracer exchange measurements with secondary ion mass spectrometry as well as with conductivity relaxation experiments. The conditions for exchange will be set analogously to those established during work function analysis.