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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