ELECTRON-BEAM-INDUCED REACTIONS AT TRANSITION-METAL OXIDE SURFACES

Electron irradiation of maximally-valent transition-metal oxides within the transmission electron microscope leads to a variety of surface reactions which depend primarily upon the energy and local current density of the incident electron beam. When the oxides Nb2O5, V2O5, TiO2 and WO3 are irradiated at current densities of 5-50 A cm-2 then formation of the respective metallic monoxide is observed. The surface profile imaging technique reveals that the surface monoxide invariably has a well-defined epitaxial relationship with the original oxide. When a small focused probe of extreme current density (congruent-to 10(3)-10(4) A cm-2) is used, reduction beyond the monoxide phase for WO3, V2O5 and TiO2 is observed. Extensive pitting, amorphization and some evidence for the base metal is also found. Measurements have also been performed under uhv conditions and show that sputtering from the exit surface is an important damage mechanism.