XPS, XES and XAS studies of the electronic structure of tungsten oxides

X-ray photoelectron (XPS), emission (XES), and absorption (XAS) spectroscopy methods were used to study the electronic structure of WO, compounds over the range 2.0 less than or equal to x less than or equal to 3.0. The XPS core-level binding energies (BEs) and valence-band structures for the tungsten oxides were determined. The XES O K alpha and XAS W L-III spectra for the compounds were derived. It was established that the XPS O 2s-like sub-band intensity decreases almost monotonously when going from WO3 to WO2. In all the studied tungsten oxides the energy positions of the centers of gravity of the O 2p-like emission bands remain constant. Half-widths of both the XPS W 4f and O Is core-level spectra increase in the sequence WO3 --> WO2. The creation of a sub-band of M-M interactions with a two-peak structure in the near-Fermi region of the XPS valence-band spectra was observed for WOx, where 2.0 less than or equal to x less than or equal to 2.77. The sub-band intensity increased significantly in the sequence WO2.77 --> WO2.3 -->WO2. The XPS O Is core-level BEs remain constant (within experimental error) for all the tungsten oxides studied. Both the O K alpha band and the XPS valence-band spectra broaden somewhat in the sequence WO3 --> WO2. The inflection point of the W L-III absorption spectra shifted almost monotonously towards higher energies when going from WO3 to WO2 . (C) 2000 Elsevier Science S.A. All rights reserved.