Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS₂and WS₂ Monolayers

Due to the two dimensional confinement of electrons in a monolayer of 2D materials, the properties of monolayer can be controlled by electrical field formed on the monolayer surface. F₄ TCNQ was evaporated on MoS₂ and WS₂ monolayer forming dipoles between strong acceptor, F₄TCNQ, and monolayers of MoS₂or WS₂. The strong acceptor attracts electrons (charge transfer) and decreases the number of the ionized excitons. Free excitons undergo radiative recombination in both MoS₂and WS₂. Moreover, the photoluminescence enhancement is stronger in WS₂ where the exciton-phonon coupling is weaker. The theoretical model indicates that the surface dipole controls the radiative exciton recombination and enhances photoluminescence radiation. Deposition of F₄TCNQ on the 2D monolayers enables a convenient control of the radiative exciton recombination and leads to the applications of these materials in lasers or LEDs.