Electron-energy-loss- and ultraviolet-photoemission-spectroscopy study of theVNxsystem

Reflection electron-energy-loss spectroscopy (ELS) and ultraviolet-photoemission spectroscopy (UPS) have been used to study the electronic properties of ${\mathrm{VN}}_x(0.0\mathrm{}\le x<\mathrm{}0.96)$. Polycrystalline samples of several compositions have been fabricated with special care to avoid oxygen contamination. ELS is used to examine the collective oscillations ("plasmons") of the valence electrons, and one-electron core-level excitations, while angle-integrated UPS experiments using the resonance lines of He and Ne are used to probe the valence-band density of states. The ELS experiments are the first of this type on any of the transition-metal nitrides or carbides, while the UPS results are the first reported for ${\mathrm{VN}}_x$. Good overall agreement is found with the calculated density of states of Neckel et al. The experimental results seem to indicate that composition changes result in a reshaping of the hybridized $(\mathrm{V}-3d)+(\mathrm{N}-2p)$ valence band rather than a simple rigid-band—like shift of the Fermi level.