First-principles probing of Au-doped WS2 monolayer as a superb CO sensor with high selectivity and fast diffusion

Doping with noble metals is considered to be an effective strategy to improve the gas sensitivity of 2D WS2 materials. In this work, the adsorption properties of CO, CO2, NH3 and SO2 on both pure and Au-doped WS2 monolayers are investigated in detail by first-principles calculations. The results show that the adsorption energy of CO on the WS2 monolayer doped with an Au atom is significantly lower than that of the pure WS2 monolayer (−0.15 eV reduced to −0.35 eV). From analysis of the adsorption configuration, it can be found that the CO molecule and WS2/Au monolayer form a new C = S double bond with a bond length of 2.067 Å due to chemisorption, and the calculated results of charge density difference (CDD) and electron localization function (ELF) also show that there exists the charge transfer and electron co-existence occur between them. Further, the density of states (DOS) of the WS2/Au monolayer shifts towards the lower energy state after adsorbing the CO molecule, indicating excellent CO detection sensitivity. On the other hand, both before and after doping with an Au atom, the WS2 monolayer always exhibits weak physical adsorption and insignificant changes in electronic properties for CO2, NH3 and SO2 molecules. Finally, the calculated diffusion coefficients indicate that the CO molecules diffuse more easily on the surface of the WS2/Au monolayer than the other three gases. These findings provide a theoretical basis for the Au-doped WS2 monolayer to improve the detection performance for CO.