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Combined Hrem and Eels Studies of the Electron Beam Induced Reduction of Maximal-Valence Transition-Metal Oxides.

  • Neil J. Long (a1) and Amanda K. Petford-Long (a1)

Abstract

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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References

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1. Hobbs, L.W., in ‘Quantitative Electron Microscopy’ (eds. J.N., Chapman and A.J., Craven, Scottish Universities Summer School in Physics, 1983).
2. Long, N.J., Skiff, W.M., Higgs, A., Carpenter, R.W. and Lyman, C.E., Proc. of 43rd Ann. Meeting of the Electron Microsc. Soc. of Amer. (San Francisco Press, 1985) 408.
3. Long, N.J. and Petford-Long, A.K., Ultramicroscopy, 1986 (in press).
4. Lyman, C.E., Ferretti, A. and Long, N.J., in ‘Analytical Electron Microscopy’ (eds. Williams, D.B. and Joy, D.C., San Francisco Press, 1984) 209.
5. Petford, A.K., Marks, L.D. and O'Keeffe, M., Surf. Sci. 172, 496, (1986).
6. Langell, M.A. and Bernasek, S.L., Phys. Rev. B 23, 1584, 1981.
7. Luscher, P.E., Surface Science, 66, 16, 1977.

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