X-ray and UV photoelectron spectra of the oxides NbO2, MoO2 and RuO2

HeI and Mg Kα_1,2 valence band photoelectron spectra of polycrystalline samples of NbO₂, MoO₂ and RuO₂ are reported. A marked increase is observed in the intensity of the metal 4d structure, relative to that due to oxygen 2p electrons, on changing from X-ray to UV excitation. The superior resolution of the 4d signals in the HeI spectra reveals the presence of the Fermi edge in the metallic oxides MoO₂ and RuO₂. In addition, the HeI spectrum of MoO₂ shows a splitting of the metal 4d signal, confirming established ideas concerning the electronic structure of such materials.