Monolayer MoS2 for nanoscale photonics

Transition metal dichalcogenides are two-dimensional semiconductors with strong in-plane covalent and weak out-of-plane interactions, resulting in exfoliation into monolayers with atomically thin thickness. This creates a new era for the exploration of two-dimensional physics and device applications. Among them, MoS2 is stable in air and easily available from molybdenite, showing tunable band-gaps in the visible and near-infrared waveband and strong light-matter interactions due to the planar exciton confinement effect. In the single-layer limit, monolayer MoS2 exhibits direct band-gaps and bound excitons, which are fundamentally intriguing for achieving the nanophotonic and optoelectronic applications. In this review, we start from the characterization of monolayer MoS2 in our group and understand the exciton modes, then explore thermal excitons and band renormalization in monolayer MoS2. For nanophotonic applications, the recent progress of nanoscale laser source, exciton-plasmon coupling, photoluminescence manipulation, and the MoS2 integration with nanowires or metasurfaces are overviewed. Because of the benefits brought by the unique electronic and mechanical properties, we also introduce the state of the art of the optoelectronic applications, including photoelectric memory, excitonic transistor, flexible photodetector, and solar cell. The critical applications focused on in this review indicate that MoS2 is a promising material for nanophotonics and optoelectronics.