OPTIMUM MASSTHICKNESS OF AG-NANOPARTICLE FILM FOR SURFACE-ENHANCED RAMAN-SCATTERING

Raman scattering from a few monolayers of benzoic acid (BA) enhanced b y a thin layer of Ag-nanoparticles (AGNs) was studied, using a series of AGN films having different massthickness covering a range from 5 to 50 nm. Surface images taken using an atomic force microscope clearly reveal each individual AGN of average size similar to 25 nm. Extinctio n spectra of the AGN films exhibit a surface-plasma resonance peak at similar to 380 nm with a long tail extending to the visible region. Wh en emphasizing the electromagnetic effect, the attenuated total reflec tion configuration was adopted to obtain an enhanced Raman spectrum. A n optimum massthickness for enhancing Raman signal was found to be sim ilar to 15 nm. A semi-empirical formula was also developed to estimate the Raman signals from a few monolayers of BA, hence the enhancement factor. The estimated enhancement factor is in the order of 10(4) for the optimum case. The enhancement is believed to originate from the ex citation of surface plasmons (SPs). (C) 1998 Published by Elsevier Sci ence S.A. All rights reserved.