The development of high-performance gas sensing materials is one of the development trends of new gas sensor technology. In this work, in order to predict the gas-sensitive characteristics of HfSe2 and its potential as a gas-sensitive material, the interactions of nonmetallic element (O, S, Te) doped HfSe2 monolayer and small molecules (NH3 and O3) have been studied by first-principles based on density functional theory. The results show that the adsorption of NH3 and O3 on pristine HfSe2 monolayer is weak, and the adsorption strength can be significantly improved by doping O. And O-HfSe2 is chemical adsorption to O3 with large adsorption energy and transfer charge, and the band gap of O[sbnd]HfSe2 disappears after adsorbing O3, indicating that the adsorption of O3 has a significant effect on the electrical properties of the substrate. These mean that O3 is difficult to recover from the substrate surface, thus preventing O-HfSe2 from developing into a sensitive material for O3 detection. After doping S, the charge transfers and adsorption strength to NH3 are the largest, but it is still small. So, the strain effect on the S-HfSe2/NH3 adsorption system is also studied. The results indicate that the adsorption strength of S-HfSe2 to NH3 can be enhanced by stretching S-HfSe2 along x-axis. After absorbing NH3, the conductivity of x-axis strained S-HfSe2 changes, which suggest its sensitivity. And the predicted recovery times of S-HfSe2 surfaces with εx=4%, 6% and 8% are 0.027 s, 1.153 s and 102.467 s, respectively, which suggests that the S-HfSe2 monolayer has the potential to be developed as a sensitive material for NH3 detection. These adsorption mechanism studies can also serve as a theoretical foundation for the experimental design of gas-sensing materials.@en

In this work, the adsorption of toxic gaseous NO2 and other gas molecules (NO, CO, CO2, N2, O2, SO2) on pristine and X-doped (X = Si, P, S, Te, As) two-dimensional (2D) WSe2 have been detailed studied by performing density functional theory (DFT) calculations. Calculation results of adsorption energies and adsorption distances demonstrate that As-doped 2D WSe2 (As-WSe2) exhibits high selectivity not only towards NO2, but also towards NO and SO2. However, the charge transfer between NO and the substrate is too small to detect, and chemical bond forms between SO2 and the substrate; both phenomena make As-WSe2 substrate more suitable as a substrate material of the NO2 sensor. To eliminate the interference of SO2 on the adsorption of NO2, coexistence of NO2 and SO2 is simulated. Results reveal that although the interaction between SO2 and the As-WSe2 substrate is stronger than that between NO2 and the substrate, SO2 molecule hardly interacts with the substrate when co-adsorbed with NO2. Besides, calculation results of DOS and PDOS further confirm the sensitivity of As-WSe2 towards NO2; and those of the recovery time also highlight the extremely fast recovery rate of As-WSe2 after adsorbing NO2. The present findings make As-WSe2 monolayer a potential substrate material of NO2 gas sensors used in the atmospheric environment.@en