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 sp3 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.