High Selectivity Gas Sensing and Charge Transfer of SnSe₂

SnSe₂ is an anisotropic binary-layered material with rich physics, which could see it used for a variety of potential applications. Here, we investigate the gas-sensing properties of SnSe₂ using first-principles calculations and verify predictions using a gas sensor made of few-layer SnSe₂ grown by chemical vapor deposition. Theoretical simulations indicate that electrons transfer from SnSe₂ to NO₂, whereas the direction of charge transfer is the opposite for NH₃. Notably, a flat molecular band appears around the Fermi energy after NO₂ adsorption and the induced molecular band is close to the conduction band minimum. Moreover, compared with NH₃, NO₂ molecules adsorbed on SnSe₂ have a lower adsorption energy and a higher charge transfer value. The dynamic-sensing responses of SnSe₂ sensors confirm the theoretical predictions. The good match between the theoretical prediction and experimental demonstration suggests that the underlying sensing mechanism is related to the charge transfer and induced flat band. Our results provide a guideline for designing high-performance gas sensors based on SnSe₂.