Tunable donor and acceptor impurity states in a WSe2 monolayer by adsorption of common gas molecules

A gas sensor of common gas molecules, such as CO, H2O, NH3, O-2, NO and NO2 on a WSe2 monolayer is investigated systematically by using first-principle calculations. The results show that the effects of NH3, H2O, CO adsorption on the electronic structures of the WSe2 monolayer are not obvious; while the adsorption of O-2, NO and NO2 molecules has an obvious influences on electronic structures of the WSe2 monolayer. Moreover, our calculations show that NH3 acts as a charge donor, whereas O-2, CO, H2O, NO and NO2 gas molecules act as an acceptor impurity. In particular, our results also show that NO2 molecule adsorptions can result in an effective p-type doping in the WSe2 monolayer. These results suggest that the carrier type can be tuned effectively in the monolayer WSe2 by adsorption of common gas molecules.