||1.4 - 2.01 eV 
||Tungsten sulphide, Tungsten sulfide, Tungsten (IV) sulfide
|Classification / Family
Transition metal dichalcogenides (TMDCs), 2D Semiconductor Materials, NIR band-gap, Nano-electronics, Nano-photonics, Transistors, Photovoltaics, Materials science
||Synthetic - Chemical Vapour Transport (CVT)
||1250 °C (lit.)
One of the most distinctive features of tungsten disulfide (WS2) is its performance as a lubricant, even under harsh conditions (e.g. high temperature and high pressure). Its coefficient of friction (CoF) of 0.03 is nearly unmatched.
Depending on the techniques used in its preparation, exfoliated 2D WS2 layers have three crystal phases: octahedral (1T) and hexagonal (2H and 3R). Such phases provide opportunities for structure engineering at an atomic level to develop new optoelectronic properties. It is known that the 2H (antiparallel) and 3R (parallel) hexagonal phases are semiconducting.
Of the two hexagonal phases, 2H is the more stable form. The octahedrally-coordinated 1T phase is not stable in a bulk form, and is associated solely with single-layer films. It is believed that the 1T phase is metallic and can be transformed from 2H WS2 by electron doping (e.g. by electron irradiation or lithium ion intercalation).
Nanosheets and nanoparticles prepared from electronic pure WS2 powders find applications in nanoelectronics, optoelectronics, gas-sensing devices, hydrogen evolution reactions, and energy storage devices. Like most TMDCs, they are of great interest in condensed matter physics and are widely explored for their photonic and optoelectronic properties.
Tungsten disulfide (WS2) powder is obtained via the CVT method, with a purity in excess of 99.995% achieved.
WS2 powder is suitable for liquid chemical exfoliation to prepare WS2 nanosheets and nanoparticles down to few-layer films. WS2 powder is also used for the preparation of mono-layer and few-layer films via chemical vapour deposition (CVD).
Literature and Reviews
Controlled Synthesis and Transfer of Large-Area WS2 Sheets: From Single Layer to Few Layers, A. Elı´as et al., ACS Nano, 7 (6), 5235–5242 (2013); DOI: 10.1021/nn400971k.
An effective liquid-phase exfoliation approach to fabricate tungsten disulfide into ultrathin two dimensional semiconducting nanosheets, R. Jha et al., J. Mater. Sci., 52:7256–7268 (2017); DOI 10.1007/s10853-017-0962-4.
Enhanced Catalytic Activities of Surfactant Assisted Exfoliated WS2 Nanodots for Hydrogen Evolution, X Zhao et al., ACS Nano 2016, 10, 2159−2166; DOI: 10.1021/acsnano.5b06653.
Cost-effective liquid-phase exfoliation of molybdenum disulfide by prefreezing and thermal-shock, L. Taran et al., Adv. Powder Tech., 28, 2996–3003 (2017); DIO: 10.1016/j.apt.2017.09.010.
Enhanced catalytic activity in strained chemically exfoliated WS2 nanosheets for hydrogen evolution, D. Voiry et al., Nat. Mater., 12, 850–855 (2013); DOI: 10.1038/NMAT3700.