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||1.2 eV -1.4 eV 
||Tungsten Selenide, Tungsten (IV) Selenide
|Classification / Family
Transition metal dichalcogenides (TMDCs), 2D Semiconductor Materials, Nano-electronics, Nano-photonics, Materials Science
||Synthetic - Chemical Vapour Transport (CVT)
||> 1200 °C
Bulk tungsten diselenide (WSe2) has a high absorption coefficient, high photostability, and a band-gap of 1.2 eV. It is an indirect band-gap semiconducting material that can be both n- and p-doped. The ambipolar nature of WSe2 makes it possible to create electronic devices that include p−n junctions or complementary logic circuits.
Tungsten diselenide single layers are composed of a layer of tungsten atoms positioned between two layers of selenium atoms, with each tungsten atom coordinating through strong covalent-ionic bonds to six selenium atoms in a trigonal prismatic geometry. As occurs in graphene, black phosphorus and other TMDC materials, multuilayer structures are stabilised by weak Van de Waal forces. These forces are strong enough to hold layers together, but weak enough to allow mechanical exfoliation.
With a lattice structure similar to MoSe2, WSe2 single layers are semiconductors with a trigonal (2H) structure. By reacting with n-butyllithium, the 2H-WS2 can undergo a phase change to 1T-WSe2 (this process being totally reversible).
Monolayer or few-layer WS2 films that are mechanically exfoliated from bulk WS2 crystals have been explored for applications in FETs, electrochemical cells, thermoelectrics, sensors, and light-emitting diodes.
The energy gap of WSe2 (1.2 - 1.4 eV) makes it perfect for applications in photovoltaics and solar cells.
Tungsten disulfide WS2 is manufactured via chemical vapour transport (CVT) crystallisation, with a purity in excess of 99.999%.
Tungsten disulfide WS2 can be used to create monolayer and few-layer WS2 by mechanical or liquid exfoliation.
Literature and Reviews
Layer-dependent electronic structure of an atomically heavy two-dimensional dichalcogenide, P-C. Yeh et al., Phys. Rev. B 91, 041407 (2015); DOI: 10.1103/PhysRevB.91.041407.
Strain-Induced Indirect to Direct Bandgap Transition in Multilayer WSe2,
S. B. Desai et al., Nano Lett., 14 (8), 4592–4597 (2014); DOI: 10.1021/nl501638a.
Large-Area Synthesis of Highly Crystalline WSe2 Monolayers and Device Applications, J. Huang et al., ACS Nano, 8 (1), 923–930 (2014); DOI: 10.1021/nn405719x.
Preparation and Applications of Mechanically Exfoliated Single-Layer and Multilayer MoS2 and WSe2 Nanosheets, H. Li et al., Acc. Chem. Res., 47, 1067−1075 (2014); DIO: 10.1021/ar4002312.
Large-area synthesis of monolayer WSe2 on a SiO2/Si substrate and its device applications, J. Huang et al., Nanoscale, 7, 4193 (2015); DOI: 10.1039/c4nr07045c.