X-ray absorption spectroscopy of layered 4D transition-metal dichalcogenides

Abstract
The authors have measured the metal LIII absorption spectra of layered 4d transition-metal dichalcogenides with the use of a Yohan-type curved-crystal spectrometer. The spectra showed that the metal d orbitals are strongly admixed with the chalcogen p orbitals to form the covalent bonding. The rigid-band model which has been suggested by Wilson and Yoffe (1969) appears to be valid in the first approximation for the unoccupied bands to about 5 eV above the Fermi level, but is not valid for the higher-energy bands. As the atomic number of the chalcogen increases, the bands broaden and overlap each other, probably due to the spin-orbit interaction. The absorption-edge shifts observed can be explained in terms of the energy differences of the bottom of the conduction band or the lowest empty state.