Density Functional Theory Analysis of Gas Adsorption on Monolayer and Few Layer Transition Metal Dichalcogenides: Implications for Sensing

First-principles calculations are performed to compare the adsorption of CO, NH3, NO, and NO2 molecules on monolayer, bilayer, and heterobilayer MoS2 and WS2, using van der Waals corrected density functional theory. Only minor differences are demonstrated for the adsorption behaviors of the monolayer and bilayer systems despite fundamental differences in the electronic structure (direct versus indirect band gap). We also show that NO2 binds stronger to the sensor materials than the other gas molecules, resulting in enhanced charge transfer. Adsorption of paramagnetic NO and NO2 has significant impact on the electronic states, in contrast to adsorption of nonmagnetic CO and NH3.