2D materials under the microscope(s)*

Interest in transition metal dichalcogenides (TMDs) has been renewed by the discovery of emergent properties when reduced to single, two-dimensional (2D) layers. Here, we use a set of complementary techniques - photoluminescence, Kelvin probe, scanning tunneling and photoelectron spectroscopy – to correlate locally chemical state, electronic structure, and optical properties of 2D-TMDs. Atomic force and scanning tunneling microscopy allowed us to identify unambiguously the atomic and electronic structure of chalcogen and metal vacancies in chemical vapor deposition grown WS₂. Furthermore, we employ spatially and angle resolved photoemission spectroscopy (nano-ARPES) to map variations in band alignment and chemical composition. By correlating this information with photoluminescence data, we reveal the interplay between local material properties, such as defect density or chemical composition, and the formation of charged trions, defect-bound excitons and neutral excitons.