X-ray absorption spectroscopy of layer transition-metal disulfides

Abstract

We have measured the x-ray $K$ absorption spectra of $\mathrm{S}$ and the ${L}_{\mathrm{III}}$ absorption spectra of Nb and Mo in layer transition-metal disulfides (Ti${\mathrm{S}}_{2}$, V${\mathrm{S}}_{2}$, Zr${\mathrm{S}}_{2}$, Nb${\mathrm{S}}_{2}$, Mo${\mathrm{S}}_{2}$, and Hf${\mathrm{S}}_{2}$, using a Yohan-type curved-crystal spectrometer. These spectra reflect the electronic band structures of these materials very well and exhibit the large peak originating in the empty "$d$" bands and the broad peak originating in the "metal $\mathrm{sp}$" bands. In combination with the photoemission spectra and the band calculations, we obtain information on detailed band structures of both occupied and empty states, which were not inconsistent with the other experimental results, such as the reflectivity and the energy-loss spectra. We could also obtain information on band character, owing to the selection rules and the localization property of an x-ray spectrum. The results obtained suggest the strong covalency of these materials.