Selective sensing of NH₃ and NO₂ on WSe₂ monolayers based on defect concentration regulation

Defect engineering is an important method to control material properties. In this paper, large-scale sampling density functional theory (DFT) was used to investigate the adsorption and sensing behavior of NH₃ and NO₂ on a WSe₂ monolayer, with a focus on the effect of selenium vacancy concentration. The results demonstrate that selectivity is inhibited on a perfect monolayer due to the similar adsorption energy of the two gases, NH₃ and NO₂, while selectivity can be obtained for both of them under different selenium vacancy concentrations (NH₃ about 2-5.6%, NO₂ about >8.3%). It is believed that the good match between the unique surface structure of the double-color (double-charged) wave wheel disk-like structure of the WSe₂ monolayer and the molecular structure of both of the two representative molecules, NH₃ and NO₂, contributes dominantly to the unusual performance. The results demonstrate that one kind of material-WSe₂ monolayer-can perform selective sensing of both NH₃ and NO₂, respectively, using only defect adjustment. It is particularly important to acquire the selectivity to NH₃ in the mixture of NO₂ and NH₃. It also provides opportunities for understanding materials and patterned catalyst design.