| Summary: | The adsorption types of ten kinds of gas molecules (O<sub>2</sub>, NH<sub>3</sub>, SO<sub>2</sub>, CH<sub>4</sub>, NO, H<sub>2</sub>S, H<sub>2</sub>, CO, CO<sub>2</sub>, and NO<sub>2</sub>) on the surface of SiSe monolayer are analyzed by the density-functional theory (DFT) calculation based on adsorption energy, charge density difference (CDD), electron localization function (ELF), and band structure. It shows high selective adsorption on SiSe monolayer that some gas molecules like SO<sub>2</sub>, NO, and NO<sub>2</sub> are chemically adsorbed, while the NH<sub>3</sub> molecule is physically adsorbed, the rest of the molecules are weakly adsorbed. Moreover, stress is applied to the SiSe monolayer to improve the adsorption strength of NH<sub>3</sub>. It has a tendency of increment with the increase of compressive stress. The strongest physical adsorption energy (−0.426 eV) is obtained when 2% compressive stress is added to the substrate in zigzag direction. The simple desorption is realized by decreasing the stress. Furthermore, based on the similar adsorption energy between SO<sub>2</sub> and NH<sub>3</sub> molecules, the co-adsorption of these two gases are studied. The results show that SO<sub>2</sub> will promote the detection of NH<sub>3</sub> in the case of SO<sub>2</sub>-NH<sub>3</sub>/SiSe configuration. Therefore, SiSe monolayer is a good candidate for NH<sub>3</sub> sensing with strain engineering.
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