Photoemission Studies of the Layered Dichalcogenides NbSe2and MoS2and a Modification of the Current Band Models

Ultraviolet photoemission measurements have been used to determine the electronic structure of two of the layered transition-metal dichalcogenides, Nb${\mathrm{Se}}_2$ and Mo${\mathrm{S}}_2$, which show trigonal prismatic coordination. Although the electronic structures of the two materials have rather different character, the results are consistent with a loose interpretation of a rigid-band model. The observed energy of the Fermi level above the valence-band maximum in Mo${\mathrm{S}}_2$ indicates that the splitting between the nonbonding $d$ bands is in excess of 1 eV, a value considerably larger than some previous suggestions.