Tunable electronic and optical properties of gas molecules adsorbed monolayer graphitic ZnO: Implications for gas sensor and environment monitoring

摘要

Due to the large surface area and the peculiar electronic characters, great attention has been paid to 2D materials for the gas sensing applications. Here, using the hybrid density functional calculations, we systematically study the adsorptions of gas molecules on the monolayer graphitic ZnO (g-ZnO), including CO, H_2, H_2O, H_2S, NH_3, NO, NO_2, O_2, and SO_2. For most of the molecules, g-ZnO shows superior sensing performance to the well-known MoS_2, black phosphorus, blue phosphorus, antimo-nene, and germanene. H_2S, NO, NO_2, and SO_2 act as charge acceptors, and CO, H_2, H_2O, and NH_3 serve as charge donors. These molecules also induce distinct modifications to the electronic structures, work functions, and optical adsorptions. NO, NO_2, and O_2 form flat bands in the bandgaps of the spin-up or spin-down states, whereas other molecules mainly tune the bandgaps and the orbital couplings. In particular, g-ZnO is most likely to adsorb the atmospheric pollutant SO_2, which has the strongest interaction through hybridizing its widely broadened 2p orbitals with the 3d orbitals of g-ZnO. Moreover, the improved visible light absorption is demonstrated in the NO_2 adsorbed g-ZnO. Our results not only confirm that the electronic and optical properties of g-ZnO can be effectively tuned by the selective adsorption of gas molecules but also provide insightful guidance for the potential application of g-ZnO in the field of gas sensors.