Correlation between surface potentials and surface oxygen exchange coefficents of CeO2

这个提议的目的是研究原型氧离子导体CeO2的表面费米能级位置、电离势和功函数与氧表面交换率之间的可能关联。由于被吸附的氧物种(相对于带边)的能级预计直接取决于底物的功函数，它们决定了电子向被吸附物种的转移是否可能，最有可能是一个速率决定步骤。为了考察可能的关联，CeO2的功函数将被系统地确定为不同表面取向和端面的掺杂和氧分压的函数。为此，我们将采用磁控溅射的方法制备不同掺杂的多晶和外延CeO2薄膜。然后，在不破坏真空条件的情况下，通过光电子能谱来确定表面化学成分和表面电位。通过改变沉积条件和沉积后的氧化还原处理，可以确定沉积过程中和沉积后表面电位的变化。用~(18)O示踪交换测量和二次离子质谱仪以及电导弛豫实验研究了相同制备的薄膜和烧结陶瓷样品上的氧表面交换率。交换条件的设置类似于功函数分析过程中建立的条件。

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.