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

The systematic study of structures with gold and silver nanoparticles (MeNPs) of various shapes and dielectric functions immobilized onto the silver grating is performed. The structures may serve as double resonance SERS (surface-enhanced Raman spectroscopy) systems with coupling between surface plasmon polariton (SPP) supported by the silver grating and localized surface plasmons (LSPs) excited on the grafted metal 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 the 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 a significant SERS signal is produced by R6G or BFDT molecules. Properties of the prepared structures are simulated using the Finite-difference time-domain method (FDTD). The measured and simulated SERS data are in reasonable agreement, the measured values being lower than those calculated.