Sulfur Monovacancies in Liquid-Exfoliated MoS2 Nanosheets for NO2 Gas Sensing

The use of MoS2 nanosheets as a gas sensing material has been reported extensively in recent years. Sulfur vacancies (V-s) are known to play a significant role, but the detailed mechanism is still in dispute. In this work, we tried to investigate the relationship between the V-s and the gas sensing response based on experimental and simulation results. Experimentally, we developed a NO2 gas sensor based on liquid-exfoliated MoS2 nanosheets with the response of 330% at 100 degrees C for 5 ppm NO2 gas. The excellent performance is due to the creation of sulfur vacancies (undercoordinated Mo atoms) at room temperature. From density functional theory (DFT) calculations, a dominant MoS2-NO2 adsorption complex is formed and higher adsorption energy (32.89 meV/Mo) of the NO2 gas molecule on sulfur vacancy-induced MoS2 is obtained. The V-s acts as the singly ionized acceptor level (0.54 eV above the valence band). Finally, a detailed temperature-dependent sensing mechanism for p-type MoS2 nanosheets has been proposed considering the V-s as a single electron acceptor with the (0/-1) charged states. This level is responsible for enhanced NO2 adsorption at low temperatures, and the observed behavior agrees well with the findings of DFT studies.

Automated summary

The study investigates the role of sulfur vacancies in MoS2 nanosheets in gas sensing response, with experiments and simulations showing a correlation between sulfur vacancies and enhanced NO2 adsorption. The findings propose a detailed temperature-dependent sensing mechanism for p-type MoS2 nanosheets considering sulfur vacancies as single electron acceptors.