Band gap modulation of transition-metal dichalcogenide MX2 nanosheets by in-plane strain

•The bandgap of MX2 nanosheets can be widely tuned by applying in-plane strain.•Compared to WX2, MoX2 needs a smaller critical tensile strain for the band gap close.•MSe2 needs a smaller critical compressive strain than MS2 for the bandgap close.•The critical strain difference among the layer thickness is not much.•The mechanism of the bandgap close under tensile and compressive strain is different.

The electronic properties of quasi-two-dimensional honeycomb structures of MX2 nanosheets (M=Mo, W and X=S, Se) subjected to in-plane biaxial strain have been investigated using first-principles calculations. We demonstrate that the band gap of MX2 nanosheets can be widely tuned by applying tensile or compressive strain, and these ultrathin materials undergo a universal reversible semiconductor-metal transition at a critical strain. Compared to WX2, MoX2 need a smaller critical tensile strain for the band gap close, and MSe2 need a smaller critical compressive strain than MS2. Taking bilayer MoS2 as an example, the variation of the band structures was studied and the semiconductor-metal transition involves a slightly different physical mechanism between tensile and compressive strain. The ability to tune the band gap of MX2 nanosheets in a controlled fashion over a wide range of energy opens up the possibility for its usage in a range of application.

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