Electronic structures of , and in the real and the hypothetical undistorted structures

Abstract

The transition-metal dichalcogenides (X = S or Se) and with a electron configuration have distorted and structures, respectively, with the Re(Tc) atoms in each layer forming parallelogram-shaped connected clusters (diamond chain). Ab-initio band-structure calculations were performed for and , and the hypothetical undistorted 1T- and 3R- structures. The calculations show that , and are semiconductors with energy gaps of about 1.0 eV, 0.5 eV and 0.7 eV, respectively, while for the undistorted structures the Fermi level is in the partly filled band of and orbitals of the manifold. X-ray photoemission spectra for the core levels and valence band of and are presented. The valence x-ray photoemission spectra showed that is a p-type semiconductor with an energy gap of about 1.5 eV, while is an n-type semiconductor. The experimental results are in good agreement with the band-structure calculations.