The impact of LSP–SPP coupling on the electric field enhancement of a composite SERS substrate consisting of an Au 2D sinusoidal grating and Ag colloidal nanoparticles

Abstract

In this study, a composite Surface-Enhanced Raman Scattering (SERS) substrate, consisting of an Au 2D sinusoidal grating and Ag colloidal nanoparticles (AgNPs-Au2DSG), was designed. The impact of the coupling of surface plasmon polariton (SPP) and localized surface plasmon (LSP) on electric field enhancement of the composite substrate, insensitive to the polarization of incident light, is thoroughly discussed and studied. FDTD simulations showed that the maximum enhancement factor (EF) of the substrate appeared at the LSP–SPP coupling resonance frequencies. For the incident light of TM at 785 nm, the substrate had a larger hot spot area and EF when the AgNP radius was 50∼60 nm. By adapting the size of the AgNPs, the SPP–LSP coupling can be optimized to offer greater electric enhancement at the wavelengths of interest, contributing to the practical improvement of SERS detection.