Electronic structure of thermally oxidized tungsten

Abstract

The electronic structure of thermally oxidized tungsten used as an emitter in thermal ionization of organic molecules is studied. Tungsten foil was thermally oxidized at oxygen pressure 1 Torr and temperature 950 K. The photoemission spectra from the valence band and O 2s and W 4f core levels are studied under synchrotron excitation with the photon energies 100 ÷ 600 eV. It is shown that thermal oxidation of tungsten leads to the formation in the W near-surface region various tungsten oxides with an oxidation state from 6+ to 4+. In this case, mainly tungsten oxides with an oxidation state of 6+ are formed on the surface, the proportion of which gradually decreases with distance from the surface with an increase in tungsten oxides with an oxidation state of 4+.