Sn quantum dots for optical gas sensing: DFT insight into CO and NO adsorption and charge transfer mechanisms

In this study, the structural, electronic and optical properties of stannene quantum dots (QDSn) before and after CO and NO adsorption were investigated using density functional theory (DFT) implemented in the Quantum ESPRESSO package. The results show that QDSn possesses high structural stability with a cohesive energy of [Formula: see text] [Formula: see text]eV and no significant imaginary frequencies in the phonon spectrum. After adsorption, the adsorption distances are 2.542[Formula: see text]Å for CO and 1.881[Formula: see text]Å for NO, with corresponding adsorption energies of [Formula: see text]0.175[Formula: see text]eV and [Formula: see text]0.526[Formula: see text]eV, indicating a much stronger interaction for NO. Charge density difference and Bader charge analyses reveal significant charge transfer at the Sn atoms near the adsorption site, especially in the QDSn-NO system. The band structure and density of states indicate the emergence of new states near the Fermi level and band gap modulation after adsorption. Optical properties, including the dielectric function, absorption spectrum, and JDOS (joint density of states), show pronounced changes in the 1–3[Formula: see text]eV range, particularly for NO, suggesting potential applications in visible-light optical gas sensing. These results demonstrate that QDSn is a promising material for selective gas sensor development based on electronic structure modulation and optical response variation.