An X-Ray and Ultraviolet Photoemission Study of Vanadium Sulfides in the Series VS1.0-VS1.60

A combined UPS and XPS study was performed on a series of structurally related vanadium sulfides of the NiAs type. The valence band spectra show systematic variations with the metal to sulfur ratio (1.0 to 1.6) such as an increase in the density of states with increasing sulfur content. These findings are discussed using structural information and band structure calculations of VS at the linear Muffin-Tin orbital (LMTO) level. The core level data of S 2p, S 2s, and V 2p exhibit much larger variations than expected from the valence band spectra indicating that the bonding interaction in the VS6 octahedra vary with the elemental composition. The compounds contain a significant amount of dissolved atomic oxygen which forms oxides only after Ar ion bombardment. The presence of nonbonding oxygen was substantiated with XPS and IMR-MS thermal desorption spectroscopy. All data point to an alloy type electronic structure of these metalloid compounds resulting from a vanadium atom network with metallic contacts varying systematically in its topology with chemical composition.