Influence of CO, H 2 , and H 2 S adsorption on the electronic, optical, and thermoelectric properties of Li-decorated silicene/germanene heterostructures

Density functional theory calculations were performed to investigate the effects of CO, H2, and H2S adsorption on the electronic, optical, and thermoelectric properties of Li-decorated silicene/germanene heterostructures. Unlike previous studies focusing on adsorption behaviour or individual physical properties, this work provides a unified assessment of adsorption-induced electronic, optical, and thermoelectric changes. Comparative analyses show that Li decoration selectively modifies molecule-surface interactions, with CO exhibiting the most favourable adsorption among the investigated gas molecules (Ea = −0.213 eV), owing to its larger charge transfer, more pronounced charge redistribution, and enhanced hybridisation between C-2p/O-2p and Li-Si-Ge states. CO adsorption induces a magnetic moment of 0.47 μB arising from spin-polarized C-2p and O-2p orbitals, significantly alters the electronic structure, enhances the dielectric response in the low-energy infrared-to-visible region, and increases ultraviolet absorption. Semiclassical Boltzmann transport calculations within the constant relaxation time approximation reveal pronounced thermoelectric responses primarily for CO adsorption. These results demonstrate the potential of Li-decorated silicene/germanene heterostructures for selective CO sensing and tunable optoelectronic devices operating across a broad infrared-to-ultraviolet spectral range.