First-principles study on the gas-sensing mechanism of monolayer GaSe toward nitrogen-containing toxic gases

To meet the demands of industrial emission assessment and real-time environmental monitoring for toxic gas detection, there is a strong demand for the development of gas-sensing materials with enhanced sensitivity and selectivity. Two-dimensional materials exhibit significant advantages in gas sensing due to the large surface-to-volume ratio, rich active sites, and flexible electronic characteristics. In this work, the adsorption behaviors and sensing mechanisms of four nitrogen-containing toxic gases (NO, NO₂, NH₃, and N₂O) on monolayer GaSe were systematically explored based on density functional theory calculations. By comparing different high-symmetry adsorption sites, the most energetically stable adsorption geometries for each gas molecule were determined, and the results indicate that all four gases are adsorbed via physisorption. Bader charge analysis reveals that only NH₃ acts as an electron donor, whereas NO₂ extracts the largest amount of charge (0.15 e) from the GaSe monolayer. Work function calculations show that NO adsorption induces the most pronounced change, with a reduction of 1.24 eV (22.47%), reflecting strong modulation of the electronic structure. Further analyses of the electronic band structure and density of states indicate that NO and NO₂ adsorption induces pronounced electronic perturbation near the Fermi level and significant band-gap narrowing, thereby enhancing the electrical response of monolayer GaSe. Recovery time analysis indicates that the system possesses good reversibility. Consequently, monolayer GaSe exhibits excellent sensitivity and promising application potential, particularly for NO gas detection.