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

Abstract

X-ray photoelectron (XPS), emission (XES), and absorption (XAS) spectroscopy methods were used to study the electronic structure of WO x compounds over the range 2.0≤x≤3.0. The XPS core-level binding energies (BEs) and valence-band structures for the tungsten oxides were determined. The XES O Kα 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 WO 3 to WO 2. 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 1s core-level spectra increase in the sequence WO 3→WO 2. 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 WO x , where 2.0≤x≤2.77. The sub-band intensity increased significantly in the sequence WO 2.77→WO 2.3→WO 2. The XPS O 1s core-level BEs remain constant (within experimental error) for all the tungsten oxides studied. Both the O Kα band and the XPS valence-band spectra broaden somewhat in the sequence WO 3→WO 2. The inflection point of the W L III absorption spectra shifted almost monotonously towards higher energies when going from WO 2 to WO 3.