First principle investigation on gas sensing properties of MoS2/ZnO heterojunction

MoS2/ZnO heterojunction is theoretically constructed based on density functional theory (DFT). The adsorption and electrical properties of MoS2/ZnO heterojunction after adsorbing six toxic gas molecules (CO, NO, NO2, SO2, H2S and NH3) are investigated, including adsorption energy, energy gap, density of states, charge density difference, planar-average charge density, total charge density, work function and recovery time. The results suggest that the adsorption energy of MoS2/ZnO for six gas molecules are significantly increased compared with intrinsic MoS2. Especially, the adsorption energy of the heterojunction for NO2, SO2, H2S and NH3 reach to −0.88, −0.98, −0.79 and −1.08 eV, respectively, indicating that the adsorption behavior is changed from physisorption to chemisorption. In addition, after adsorption of gas molecules (CO, NO, NO2, SO2, H2S and NH3), the energy gap of MoS2/ZnO is decreased to 0.793, 0.964, 0.834, 0.864, 0.804 and 0.770 eV, respectively, which indicates that the conductivity of MoS2/ZnO is improved. The adsorption distance (D) is also decreased after adsorption gases, especially for H2S gas molecule (0.797 Å). In addition, the work function (WF) of adsorption system is decreased and the charge transfer is increased. These results indicate that the interaction between MoS2/ZnO and gas molecules is stronger than that of intrinsic MoS2. Therefore, MoS2/ZnO has potential application for gas sensor to detect toxic gas molecules.