Electronic structure of ReS2 and ReSe2 from first-principles calculations, photoelectron spectroscopy, and electrolyte electroreflectance

The electronic structures of ReS2 and ReSe2 single crystals are investigated using a first-principles density of-states (DOS) calculation, ultraviolet photoelectron spectroscopy (UPS), and electrolyte electroreflectance (EER). The total and partial DOS were calculated by the full-potential linearized-augmented-plane-wave method. From the calculations, the main contribution near the band edge of Re X-2 (X = S,Se) is determined to be dominated by the nonbonding Re d orbitals. The valence-band DOS is experimentally verified by the UPS measurements. EER measurements were performed in the energy range of 1.3-6 eV. The EER spectra exhibit sharp derivativelike structures in the vicinity of the band-edge excitonic transitions as well as higher-lying interband transitions. Transition energies are determined accurately. From the experimental and the theoretically calculated results, probable energy-band structures of ReS2 and ReSe2 are constructed. [S0163-1829(99)07847-9].