ESCA Studies of Metal-Oxygen Surfaces Using Argon and Oxygen Ion-Bombardment.

摘要

ESCA has been used to monitor alternations of catalytically and electrochemically important metal-oxygen surfaces following exposure to Ar(+) and O2(+) ion bombardment. This treatment resulted not only in sputtering, but also, in many cases, in reduction to the corresponding metal or lower oxide. A model based on bulk thermodynamic free energy considerations is proposed to explain this phenomenon. We have also exploited this approach to obtain an in-depth concentration profile of various oxidation states of an element, to selectively prepare desired surface oxide compositions, and to aid in interpreting complex O 1s spectra. Results obtained from metal-oxygen surfaces for Ni, Ru and Mo are presented. Ni2O3 and RuO3, which are gross defect structures of the bulk species, are present on NiO and RuO2, respectively, with the former being confined to the surface layers. The MoO2, on the other hand, is covered with a surface layer of MoO3 present as a regular crystal structure. (Author)