Experimental Evidence of Two-fold Electromagnetic Enhancement Mechanism of Surface-Enhanced Raman Scattering

The surface-enhanced Raman scattering (SERS) electromagnetic (EM) enhancement mechanism is a two-fold enhancement process in which both the incident and scattered Raman fields are enhanced. In this letter, we present new direct evidence of the two-fold EM mechanism by using an Ag nanorod array/SiO₂ dielectric layer/Ag mirror multilayer thin film "local plasmon resonator". The two-fold EM enhancement mechanism of SERS was confirmed by analyzing the optical absorption and Raman scattering spectra of the local plasmon resonator for excitation and scattered light. The effect of light interference was altered by varying the film thickness of the SiO₂ phase control layer (PCL), and the absorbance in the Raman scattering wavelength range was reduced from 90% to 0%. We also demonstrated that the intensity of the background emission is closely related to the enhancement of the scattered field and provides substantial evidence for a two-fold SERS enhancement mechanism.