Role of Au–Ag alloy plasmonic layer thickness over pyramidal silicon in controlling SERS activity

Abstract

In this study, we systematically explore the role played by thickness of SERS functional metallic plasmonic layer over pyramidal Si pre-templates in controlling the SERS behavior. For this purpose, three different thicknesses, i.e., 30, 50, and 70 nm, of Au–Ag alloy nanolayer were investigated over topographically variant pyramidal Si templates. The fabrication of pyramidal templates was followed using a simple and cost-intensive anisotropic wet chemical etch approach by having a variation in etching time. The SERS response of R6G dye probe molecule on these substrates shows a strong dependence on both thickness and template topography. A substantially high SERS contribution comes from the 50 nm-thick film over a surface with dense and small pyramids. An enhancement factor of 8.6 ×106 is observed for this case. Finally, a suitable thickness is proposed for a better SERS response. This work suggests a significant role of thickness in designing potential SERS substrates.