Optical properties of two-dimensional transition metal dichalcogenides

Abstract

The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the research on their potential applications in the fields of logic nanoelectronics and high-performance nanophotonics. Many body effects are of great significance in 2-dimensional TMDs, especially when thinned down to a monolayer. As a result, the exciton-related phenomena are prominent in TMD monolayers, which distinguish the monolayers significantly from their bulk counterparts. This thesis systematically studies the optical properties in semiconducting, monolayer TMDs, including Raman spectroscopy, photoluminescence (PL), and optical absorption. In order to further understand the excitononic properties in 2-dimensional TMDs, we took monolayer MoS2 as an example, and studied its exciton behaviors with different carrier densities and dielectric environments through PL measurements with the help of electrochemical gating and non-ionic solvent immersion. Our findings are helpful to understand better the tightly bound excitons in low-dimensional systems and to provide a simple approach to controlling the generation of excitons and trions (charged excitons) selectively and separately.