Comprehensive first principles study on CO and NO gas adsorption effects on the structural, electronic, and optical properties of armchair silicon-tin nanoribbons

This study presents a detailed first-principles investigation of the effects of CO and NO gas adsorption on the structural, electronic and optical properties of armchair silicon-tin nanoribbons (ASiSnNRs). Cohesive and adsorption energy calculations indicated that the ASiSnNR structure was thermodynamically stable, with physisorption for CO (−0.01 eV) and chemisorption for NO (−0.68 eV). Electronic band structure analysis revealed that pristine ASiSnNRs exhibited semiconducting behaviour with a narrow band gap (approx. 0.43 eV), which slightly widened upon CO adsorption and transitioned to a metallic state upon NO adsorption because of the strong orbital hybridization and charge transfer effects. Charge density and wave function analyses confirmed 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 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.