MoS2

MoS2, or molybdenum disulfide, is a layered transition metal dichalcogenide (TMDC). Each layer consists of a plane of molybdenum atoms sandwiched between two planes of sulfur atoms, forming a trigonal prismatic coordination. The layers are bonded by weak van der Waals forces, which allows exfoliation to single or few-layer thicknesses and stacking in various polytypes.

Bulk MoS2 has an indirect bandgap of about 1.2 eV, while a monolayer exhibits a direct bandgap around 1.8–1.9 eV. This transition leads to strong light emission from monolayers, making MoS2 attractive for optoelectronic applications. In devices, MoS2 is a semiconductor with relatively modest electron mobility that depends on thickness, defects, and the substrate. Reported mobilities span a broad range, typically well below graphene’s, and performance is highly tunable through engineering of the dielectric environment and doping.

Preparations include mechanical exfoliation from bulk crystals to obtain high-quality monolayers, chemical vapor deposition (CVD) for scalable, large-area films, and liquid-phase or chemical exfoliation for dispersions. The standard 2H phase is semiconducting, whereas a metastable 1T phase is metallic; the 1T phase can be induced by intercalation or chemical treatment and may be reversible under certain conditions.

Applications span electronics, optoelectronics, and catalysis. In transistors and photodetectors, monolayer MoS2 offers a sizable on/off ratio and light sensitivity. For catalysis, edge sites in MoS2 act as active centers for the hydrogen evolution reaction. The material is also used as a dry lubricant and in energy storage contexts due to its layered structure and chemical stability.

MoS2 is generally stable in air, though edge sites and defect-rich areas can be more reactive, and long-term stability can depend on environmental conditions and processing.