Electronic, mechanical and gas sensing properties of two-dimensional γ-SnSe.

Two-dimensional (2D) materials are excellent candidates for advanced flexible electronics and gas sensors. Herein, we systematically investigate the layer-dependent electronic structures, mechanical properties and gas sensing characteristics of the newly synthesized γ-SnSe based on first-principles calculations. Bulk γ-SnSe is a typical van der Waals layered material with an indirect narrow band gap, while monolayer and multilayer γ-SnSe can be obtained through mechanical exfoliation due to its low cleavage energy. The band gap of γ-SnSe gradually increases with decreasing layers, reaching a value of 2.25 eV for the monolayer due to weakened interlayer coupling. Mechanical analysis reveals strong anisotropy in multilayer γ-SnSe, whereas the monolayer exhibits a negative Poisson's ratio (-0.023/-0.025). Additionally, based on the analysis of electronic structures, adsorption energies and charge transfer of the host materials after adsorption of various gases, it is found that the γ-SnSe monolayer demonstrates enhanced sensitivity and selectivity towards NO, NO2, and SO2 compared to CO, CO2, H2S and NH3. These findings highlight the potential of γ-SnSe as an excellent gas-sensitive material for the detection of nitrogen oxides and sulfur dioxide.