2HMoS2

2H-MoS2 is a polymorph of molybdenum disulfide (MoS2) in which the structure consists of stacked, sulfur-atom–chlorinated layers with molybdenum in a trigonal prismatic coordination. The “2H” designation refers to a hexagonal polytype with two layers per repeating unit along the c-axis and AB-like stacking. In its bulk form, 2H-MoS2 is the most common phase of the natural mineral molybdenite. It is semiconducting, in contrast to the metallic 1T phase of MoS2.

Structure and crystal chemistry: Each Mo atom is sandwiched between two sheets of sulfur atoms, forming S–Mo–S layers held together by van der Waals forces. The bulk crystal belongs to the space group P6_3/mmc and exhibits lattice parameters roughly a = 3.16 Å and c ≈ 12.3 Å. The two-layer repeating unit gives rise to layered quasi-two-dimensional properties that are sensitive to thickness.

Electronic properties: Bulk 2H-MoS2 has an indirect bandgap around 1.2 eV, while a monolayer transitions to a direct bandgap near 1.8–1.9 eV due to quantum confinement and reduced interlayer coupling. This thickness-dependent band structure leads to strong photoluminescence in monolayer form and makes 2H-MoS2 suitable for optoelectronic applications. The material also exhibits pronounced spin–orbit coupling and valley-related phenomena in few-layer forms.

Synthesis and processing: 2H-MoS2 can be obtained from bulk crystals via mechanical or liquid exfoliation to produce few-layer and monolayer flakes. Large-area monolayers can be grown by chemical vapor deposition on various substrates, enabling scalable device fabrication.

Applications: 2H-MoS2 is used in field-effect transistors, photodetectors, and flexible electronics, where its sizable on/off ratio and thickness-tunable optical response are advantageous. As a catalyst, 2H-MoS2 is less active for hydrogen evolution than the metallic 1T phase, but remains of interest in composite catalysts and doped or phase-engineered configurations.