Abstract
Optical conductivity, which originates from the interband transition due to electron-phonon interaction, is one of the powerful tools used for studying the electronic states in layered transition metal dichalcogenides (TMDCs). Here, we report for the first time the optical conductivity of WS 2 , one of the emerging classes of TMDCs, prepared directly on SiO 2 /Si substrate using reflection contrast spectroscopy. The measured optical conductivity at direct excitonic transition point K of the Brillouin zone for monolayer WS 2 shows a value of 0.37 e 2 /pπ in the visible range of the energy spectrum. Our results reveal that the optical conductivity of WS 2 layers is frequency-dependent and show additional features in the conductivity spectra for bilayer to bulk counterparts, signifying a transition from direct band gap to indirect band gap with the evolution of layer numbers as predicted by our calculations.