High resolution electron microscopy has been used in conjunction with electron energy loss spectroscopy to follow the beam-induced reduction of WO3, V2 O5 and CuO, all of which are maximal valence oxides. All three oxides underwent reduction, although there are differences in the reduction pathway: WO3 is reduced directly to the metal by loss of oxygen from the surface layers; CuO is reduced to the metal via at least two intermediate oxides (Cu4 O3 and Cu2O); and V2 05 forms a reduced oxide (possibly V6 O13) and then remains stable. It was possible to drill holes in V2O5 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 (<108 e/nm2). 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 V2O5 structure.
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Long, N.J., Petford-Long, A.K. Combined Hrem and Eels Studies of the Electron Beam Induced Reduction of Maximal-Valence Transition-Metal Oxides.. MRS Online Proceedings Library 74, 299 (1986). https://doi.org/10.1557/PROC-74-299