Correlation between surface potentials and surface oxygen exchange coefficents of CeO2

本研究的目的是探讨典型氧离子导体CeO2的表面费米能级位置、电离势和功函数与氧表面交换速率之间可能存在的关系。由于被吸附的氧的能级（相对于带边）预计直接依赖于底物的功函数，它们决定了电子是否转移到被吸附的氧上，这很可能是一个决定速率的步骤。为了检验可能的相关性，CeO2的功函数将被系统地确定为掺杂和氧分压对不同表面取向和末端的函数。为此，将采用磁控溅射法制备不同掺杂的多晶和外延CeO2薄膜。在不打破真空条件的情况下，用光电子能谱法测定表面化学成分和表面电位。表面电位的变化将通过沉积条件的变化和沉积后的氧化还原处理来确定。利用二次离子质谱法测量18O示踪剂交换以及电导率弛豫实验，对相同制备的薄膜和烧结陶瓷试样的氧表面交换率进行了研究。交换条件的设置将类似于在功函数分析期间建立的条件。

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.