Dealloying Ag-Al alloy to prepare nanoporous silver as a substrate for surface-enhanced raman scattering: Effects of structural evolution and surface modification

Sensitive detection of molecules by using the surface-enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag-Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5× 10⁵ was observed on bare NPS obtained by dealloying Ag₃₀Al₇₀ in 2.5 wt% HCl at room temperature followed by 15 min aging at around 85°C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6× 10⁸ owing to strong near-field coupling between the ligaments and nanoparticles.