Strain-Tunable Gas Sensing Properties of Ag- and Au-Doped SnSe2 Monolayers for the Detection of NO, NO2, SO2, H2S and HCN

In this work, the gas sensing properties and adsorption mechanisms of Ag- and Au-doped SnSe₂ monolayers toward NO, NO₂, SO₂, H₂S, and HCN were systematically investigated via first-principles calculations. The results demonstrate that NO₂ exhibits the strongest interaction and the highest charge transfer in both doped systems, indicating superior sensing selectivity. Biaxial strain (ranging from -8% to 6%) was further applied to modulate adsorption behavior. By evaluating changes in equilibrium height, adsorption energy, charge transfer, and recovery time across ten representative adsorption systems, it was found that both compressive and tensile strains enhance the interaction between gas molecules and doped SnSe₂ monolayers. Specifically, H₂S/Au-SnSe₂ and HCN/Au-SnSe₂ are highly sensitive to tensile strain, while NO/Au-SnSe₂, H₂S/Ag-SnSe₂, NO/Ag-SnSe₂, and NO₂/Ag-SnSe₂ respond more strongly to compressive strain. Systems such as NO₂/Au-SnSe₂, SO₂/Au-SnSe₂, and SO₂/Ag-SnSe₂ respond to both types of strain, whereas HCN/Ag-SnSe₂ shows relatively low sensitivity in charge transfer. Recovery time analysis indicates that NO₂ exhibits the slowest desorption kinetics and is most affected by strain modulation. Nevertheless, increasing the operating temperature or applying appropriate strain can significantly shorten recovery times. While other gas systems show smaller variations, strain engineering remains an effective strategy to tune desorption behavior and enhance overall sensor performance. These findings offer valuable insights into strain-tunable gas sensing behavior and provide theoretical guidance for the design of high-performance gas sensors based on two-dimensional SnSe₂ materials.