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 ({reversed tilde equals}10³-10⁴ 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 based 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.