Probing exciton species in atomically thin WS₂-graphene heterostructures

We report on a detailed study of temperature-dependent photoluminescence spectroscopy of monolayer WS₂ grown on epitaxial graphene. The study reveals for the first time the intrinsic excitonic effects of WS₂ supported on one- and two-layer graphene (2LG) from room temperature to 83 K, with both excitons and trions evidenced in the entire temperature range and temperature-independent trion dissociation. All emission peaks exhibit a shift towards higher energy with decreasing temperature due to band gap renormalisation induced by electron-phonon interaction. A highly linear dependence of the photoluminescence with the excitation power is found for both WS₂ on one- and 2LG, confirming the excitonic nature of associated transitions and the high crystal quality of the WS₂-graphene heterostructure.