Defect Reductionin Reduced Graphene Oxide-Metal OxideNanocomposites for Enhanced THz Shielding and Optical Limiting Applications

Abstract With rapid innovations in THz technology and the growth of equipment operating in this frequency range, effective shielding materials are crucial for ensuring stable device functioning. Graphene-based materials stand out for their absorptive shielding ability. The ratio of sp2 to sp3 carbon and tuned oxygen vacancies influences the absorption characteristics. Chemical reduction with different KOH concentrations was utilized to reduce GO to rGO with minimal defects. Increasing KOH molarity considerably diminished defect density, as confirmed by the Raman spectral deconvolution, and the major defects were found to be edge defects. The C/O ratio of the composites was found to increase with the reduction rate. Reducing defects enhanced THz shielding effectiveness (SE) and conductivity, attributing to improved π-conjugation and increased free carrier concentration. The composite with the minimum defect (R3) showed an SE of 36.17 dB, which is purely absorptive. The 2 mm thick nanocomposite pellet R3t2 exhibited an absorption coefficient of 52.71 cm–1 at 0.3 THz. Materials with higher concentrations of free carriers show increased absorption in the nonlinear regime. The Z-scan studies showed that a reduction in defects improved the optical limiting ability of the composites. The composite R3 was found to possess an optical limiting onset of 0.08 J/cm2. The present study focuses on modulating the defect density in graphene-based nanocomposites to improve their THz shielding efficiency and optical limiting potential.