Etching time-controlled Ag-assisted chemical etching of porous silicon for enhanced surface-enhanced Raman scattering...

Porous silicon (PSi) with tunable structural and optical properties has fabricated through Ag-assisted electrochemical anodization at constant current density of 13 mA cm^-2 via varying the etching time from 30 to 60 min. The influence of etching duration on the morphology, crystal structure, optical behavior, and SERS performance of PSi has investigated. SEM revealed the formation of uniform sponge-like porous network, with porosity increasing from 28.3% to 73.8% as the etching time increased, accompanied via progressive pore enlargement and improved surface connectivity. XRD confirmed the preservation of the crystalline Si (111) structure at 2θ ≈ 28.59°, while diffraction peak broadening indicated gradual reduction in crystallite size due to nanostructure formation. Optical measurements demonstrated pronounced reduction in reflectivity in the UV-visible region, attributed to enhanced light trapping through multiple internal reflections and graded refractive-index profile. The optical band gap increased from 1.134 eV for bulk silicon to 2.60 eV for the sample etched for 60 min, confirming the quantum confinement effect associated with silicon nanocrystallites. The SERS performance has evaluated using MB as probe molecule, where characteristic Raman bands at 449, 502, 893, 1396, and 1626 cm^-1 have identified. The substrate etched for 60 min exhibited the highest Raman enhancement owing to its larger surface area, higher porosity, improved analyte adsorption, enhanced optical confinement, and charge-transfer interactions. Compared with the reference Au nanoparticle substrate, the fabricated porous silicon produced stronger Raman signals under identical measurement conditions. These results demonstrate that controlled pore engineering enables the fabrication of highly sensitive, reproducible, and cost-effective PSi substrates for SERS-based chemical sensing, biosensing, and integrated photonic applications.