Monolayer transition metal dichalcogenides (TMDCs) are two-dimensional semi- conductors that are only three atoms thick. Every atom in these materials belongs to the surface. Because of that, TMDCs are strongly affected by their microenvironment. In this talk we show that excitons, or bound electron/hole pairs, in TMDCs can serve as exquisite probes of the physical and chemical properties of that microenvironment.
First, we show that TMDC excitons are strongly screened by nearby dielectrics. In suspended TMDCs, we approach the behavior of pristine material. We then examine frequency-dependent screening of excitons in TMDC and show that the frequency- dependent dielectric function of the environment can be effectively “sampled” by examining spectral shifts and intensity redistribution between neutral, charged, and defect-bound excitons. Second, we examine near-field energy transfer between TMDCs and nanoscale quantum emitters (semiconductor quantum dots or dye molecules) near it. We show that such energy transfer is very efficient, and that its rate can be controlled through electrical gating. Finally, we show that excitons in TMDCs can be localized on disorder or charge transferred from an external molecule.