Band Structure of Layer Crystals NbSe₂ and MoS₂ and an Interpretation of Their Optical Spectra

Abstract

Abstract The optical functions a and ε 2 ω 2 of NbSe 2 and MoS 2 are deduced from reflectivity measurements between 2 and 70 eV. Basing on the results of photoemission studies and band structure calculations, an experimental model is proposed of the density of states for both the valence and conduction bands. As expected, the optical behaviours of NbSe 2 and MoS 2 are very similar. The shape of the ε; 2 ω 2 curve in the high energy range (30 to 50 eV) corresponding to deep level excitations describes the density of states of the conduction band in spite of some broadening of the structure. This broadening is not of experimental origin.