First-Principles Investigation of Fluorination-Induced Electronic and Optical Tuning in Gear-Like Armchair Silicon Nanotubes: Implications for CMOS-Compatible Nanoelectronic and Optoelectronic Applications

Fluorination provides a powerful route to stabilize gear-like armchair silicon nanotubes and tailor their electronic and optical properties. First-principles calculations reveal that distinct adsorption geometries under full and half coverages yield contrasting outcomes: dual-surface full fluorination enhances sp 3 bonding and widens the band gap, interior full fluorination mitigates curvature and narrows it, while half fluorination breaks sublattice symmetry, giving rise to metallic or narrow-gap states dominated by π-like orbitals at nonfluorinated sites. The optical spectra exhibit pronounced polarization anisotropy, with fluorination-induced shifts spanning from the infrared to the ultraviolet, underscoring chemical functionalization as a versatile means of tuning optoelectronic responses.