COMBINED HERM AND EELS STUDIES OF THE ELECTRON BEAM INDUCED REDUCTION OF MAXIMAL-VALENCE TRANSITION-METAL OXIDES.

High resolution electron microscopy has been used in conjunction with electron energy loss spectroscopy to follow the beam-induced reduction of WO//3, V//2O//5 and CuO, all of which are maximal valence oxides. All three oxides underwent reduction, although there are differences in the reduction pathway: WO//3 is reduced directly to the metal by loss of oxygen from the surface layers; CuO is reduced to the metal via at least two intermdiate oxides (Cu//4O//3 and Cu//2O); and V//2O//5 forms a reduced oxide (possibly V//6O//1//3) and then remains stable. It was possible to drill holes in V//2O//5 with an intense, small electron probe (using a field-emission electron gun) provided the sample had previously only been exposed to an electron dose below a critical value ( less than 10**8 e/nm**2). Preliminary doses higher than this critical value rendered the oxide immune to hole drilling (but not to a subsequent reduction to the stable oxide mentioned above), suggesting that holes can only be drilled while the material retains the original V//2O//5 structure.