The Effect of Silver Grating and Nanoparticles Grafting for LSP-SPP Coupling and SERS Response Intensification

Abstract

The systematic study of structures with gold and silver nanoparticles (MeNPs) of various shape and dielectric function immobilized onto the silver grating is performed. The structures may serve as double resonance SERS (Surface-enhanced Raman spectroscopy) systems with the coupling between surface plasmon polaritons (SPPs) supported by the silver grating and localized surface plasmons (LSPs) excited on the grafted metals nanoparticles (MeNPs). The silver grating supports SPP excitation under the 785 nm wavelength illumination. Spherical silver and gold nanoparticles, triangular silver nanoprisms and gold nanorods are prepared and used with the aim to gradually cover the LSP excitation in 400-850 nm wavelength range. MeNPs are grafted through the 4,4'-biphenyldithiol (BFDT) linkers. Rhodamine 6G (R6G) molecules are added onto SERS substrates and located above and between the MeNPs. Several wavelengths (470, 532, and 785 nm) are applied to probe the SERS response. Depending on the nanoparticles type and excitation wavelength the significant SERS signal is produced by R6G or BFDT molecules. The properties of the prepared structures are simulated using Finite-difference time-domain method (FDTD). Measured and simulated SERS data are in reasonable agreement, the measured values being lower than those calculated.