Tungsten Disulfide

Tungsten disulfide (WS₂) in bulk has been used for many years as a dry lubricant due to how it exhibits similar properties to Molybdenum Disulfide (MoS₂), such as a low coefficient of friction, high chemical stability, and thermal stability. In 1992, it was discovered that the structure of WS₂ made it capable of forming nanotube structures. These nanotubes were the first examples of WS₂ being used as a low-dimensional material.

After the discovery of simple mechanical exfoliation techniques to isolate single layers of 2-D materials, it was possible to study the properties of WS₂ flakes. It was shown that, just like MoS₂, the band-gap of WS₂ change from an indirect band-gap of 1.4eV to a direct band-gap of 2eV when changing from a bulk material to a 2-D material. Due to its band-gap, WS₂ is seen as a significantly interesting material for many areas of application.

Just like MoS₂, WS₂ possesses a high on/off ratio in field-effect transistors, controllable spin and valley polarisation, strong geometrical confinement of excitons, and tunable photoluminescence. Additionally, WS₂ could lead to increased interest in areas such as photodetectors and multi-junction photovoltaics.