X-ray photoelectron and Auger spectroscopy study of some vanadium oxides

A detailed investigation of ${\mathrm{V}}_2$ ${\mathrm{O}}_5$, V${\mathrm{O}}_2$, ${\mathrm{V}}_2$ ${\mathrm{O}}_3$, and V metal is presented. The vanadium core lines in the x-ray photoelectron spectra are anomalously wide for ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ and V${\mathrm{O}}_2$. It is shown that this is a consequence of the narrow $3d$ band in these materials and the relatively strong core-hole $3d$ Coulomb interaction. The influence of electron correlation effects in the $3d$ band on the core linewidths is discussed. The valence bands are compared to band-structure calculations and the difference in the band structure above and below the semiconductor-metal transition is discussed. The Auger results are discussed in terms of the $3d$ partial density of states. It is found that there is a large amount of $d$ character in the $\mathrm{O}-2p$ region of the valence band. Also the average "on-site" Coulomb interaction of $3d$ electrons is obtained from the Auger spectra and is discussed in terms of electron correlation effects.