2HWS2

2HWS₂, also known as hexagonal tungsten disulfide, is a layered transition‑metal dichalcogenide with the empirical formula WS₂. The “2H” notation indicates a two‑layer hexagonal (trigonal prismatic) unit cell in which tungsten atoms are sandwiched between two planes of sulfur atoms. Each tungsten atom is coordinated in a trigonal prismatic environment by six sulfide ions, while the layers are stacked along the crystallographic c‑axis and held together by weak van der Waals forces.

The material can be produced by several methods. Conventional solid‑state synthesis involves heating a stoichiometric mixture of tungsten and sulfur powders at temperatures around 800–900 °C under controlled atmospheres. Liquid‑phase approaches, such as solvothermal or hydrothermal synthesis, allow the growth of nanocrystals and flakes at lower temperatures. Chemical vapor deposition (CVD) on substrates such as SiO₂/Si or sapphire is widely used to produce large‑area monolayer or few‑layer films, which are essential for electronic and optoelectronic device fabrication.

2HWS₂ exhibits a direct band gap of approximately 2.0 eV in monolayer form and an indirect band gap of about 1.3 eV in bulk. Its layered structure grants it mechanical flexibility, high in‑plane electrical conductivity, and strong anisotropic optical absorption. Consequently, the material is employed in transistors, photodetectors, and flexible electronics. Additionally, its lubricating properties—stemming from the ease of interlayer shear—make it useful as a solid lubricant and in tribological applications. Recent research explores 2HWS₂ for catalysis, particularly in hydrogen evolution reactions, and for energy storage devices such as supercapacitors and batteries.