Janus AsP monolayers: a promising 2D platform for NO and NO₂ gas sensing

Two-dimensional Janus AsP monolayers have attracted considerable interest due to their structural asymmetry and tunable electronic properties. In this study, the gas sensing performance of Janus AsP monolayers toward N₂, CO₂, H₂O, NO, and NO₂ was systematically investigated using first-principles calculations combined with nonequilibrium Green's function simulations. The calculation reveals weak physical interactions with common background gases (N₂, CO₂, and H₂O), whereas NO and NO₂ molecules exhibit stronger adsorption, significant charge transfer, and pronounced band gap modulation. In particular, NO₂ exhibits a strong physisorption energy of -0.69 eV, which surpasses those of conventional AsP and even its complex doped counterparts, thereby highlighting its potential for reversible sensing applications. Notably, the adsorption of the NO and NO₂ molecules induces spin polarization in the substrate, resulting in an asymmetric spin-resolved density of states and the formation of new impurity states near the Fermi level. Electronic transport calculations show enhanced electrical conductivity and substantial I-V responses for NO and NO₂ adsorption, highlighting both sensitivity and potential selectivity. The reversible nature of the physical adsorption, confirmed by charge density difference and electron localization function analyses, further supports practical sensor applications. These findings demonstrate that Janus AsP is a promising candidate for high-performance nitrogen oxide detection and provides theoretical guidance for the design of next-generation 2D material-based gas sensors.