Comprehensive first principles study on CO and NO gas adsorption effects on the structural, electronic, and optical properties of ASiSn nanoribbons

This paper presents a detailed first-principles investigation of the effects of CO and NO gas molecule adsorption on the structural, electronic, and optical properties of armchair SiSn nanoribbons (ASiSnNRs). Cohesive and adsorption energy calculations indicate that the ASiSnNR structure is thermodynamically stable, with physisorption for CO (−0.01 eV) and chemisorption for NO (−0.68 eV). Electronic band structure analysis reveals that pristine ASiSnNR exhibits semiconducting behavior with a narrow band gap (~0.43 eV), which slightly widens upon CO adsorption and transitions to a metallic state upon NO adsorption, due to strong orbital hybridization and charge transfer effects. Charge density and wave function analyses confirm this mechanism, with particular emphasis on the role of the π* orbital of the CO molecule. The dielectric function, optical absorption, reflection spectra, and joint density of states (JDOS) show significant enhancements in anisotropic optical properties after CO adsorption, especially in the ultraviolet region. These findings suggest the strong potential of ASiSnNRs for selective and highly sensitive gas sensing applications, particularly for the detection of NO.