Highly sensitive gas sensing material for polar gas molecule based on Janus group-III chalcogenide monolayers: A first-principles investigation

Gas sensors play an indispensable role in industrial, personal safety and environmental protection, and have been widely investigated by researchers. In some cases, the sensitivity of a two-dimensional material sensor can be enhanced by generating vacancies or applying an external electric field. Similar results can be achieved using Janus 2D materials, which have an inherent electric field and are good candidates for high-sensitivity gas sensors. In this study, the electronic and transport properties of Janus group-III chalcogenide monolayers (Ga₂SSe, In₂SSe) were investigated for detecting CO₂ and NO₂ using first-principles calculations. For several parameters that affect the performance of gas sensors, such as adsorption distances, adsorption energies, charge transfers and density of states (DOS), a detailed comparison of Janus group-III chalcogenide monolayers has been provided with their pristine systems, Janus group-III chalcogenide monolayers (Ga₂SSe, In₂SSe) have high selectivity. It was mainly ascribed to the built-in electric field caused by the out-of-plane asymmetric structure of Janus monolayer which enhances the dipole-dipole interaction between the polar gas molecule and the 2D materials. And the variation of transmission spectra of the Janus group-III chalcogenide monolayer before and after adsorbing molecules further proves the feasibility of this kind of material as a high-sensitivity gas sensor.