Sulfur Monovacancies in Liquid-Exfoliated MoS<sub>2</sub> Nanosheets for NO<sub>2</sub> Gas Sensing
Rishi Ranjan Kumar, Mohammad Rezwan Habib, Afzal Khan, Po‐Cheng Chen, Thangapandian Murugesan, Shivam Gupta, Aswin kumar Anbalagan, Nyan‐Hwa Tai, Chih‐Hao Lee, Heh‐Nan Lin
Abstract
The use of MoS2 nanosheets as a gas sensing material has been reported extensively in recent years. Sulfur vacancies (VS) 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 VS 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 °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 VS 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 VS 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.