MoS2 is a two-dimensional crystal that belongs to the family of transition metal dichalcogenides (TMDCs), which are materials composed of a transition metal atom (such as Mo, W, Nb, etc.) and two chalcogen atoms (such as S, Se, Te, etc.). TMDCs have attracted a lot of attention in recent years because of their diverse and tunable properties, such as semiconductivity, metallicity, and magnetism. MoS2 is one of the most studied TMDCs because it has a direct bandgap in the monolayer limit, which makes it suitable for optoelectronic and photovoltaic applications. MoS2 also exhibits strong light-matter interactions, spin-orbit and Coulomb interactions, valley-selectivity, and superconductivity under certain conditions. The optical properties of MoS2 depend on various factors, such as the number of layers, the stacking order, the presence of defects, the choice of substrate, the temperature, the strain, the doping level, and the applied magnetic field. Raman and photoluminescence (PL) spectroscopy are powerful techniques to probe these optical properties and reveal the underlying physics and mechanisms of MoS2 and other TMDCs.
Using a Linkam HFS600E-PB4 to modulate the temperature, the researchers discovered an anomalous behaviour of the A1g mode in Raman spectra and an intensity enhancement in PL spectra of MoS2 with temperature, and explained them by considering sulfur vacancies and intervalley charge transfer.
