Enhanced Raman scattering by crystal violet molecules and benzoic acid molecules adsorbed on Ag nanocrystals was measured by employing the attenuated total reflection method. The Ag nanocrystals were deposited directly on a glass substrate by the gas condensation method. Scanning electron microscopy images show that they were evenly distributed over the surface of the substrate. Films composed of Ag nanocrystals were found to be good enhancers of Raman signals. No obvious frequency shift with respect to the ''normal'' Raman lines was observed in the enhanced Raman spectra, thus indicating that the enhancement effect is mainly electromagnetic in nature. The enhancement factor depends on the laser excitation line used. Under our experimental conditions the enhancement obtained from Ag nanocrystals of mean grain size about 15 nm is an order of magnitude greater than that obtained from a flat Ag thin film of mass thickness about 56 nm. The excitation profile obtained using benzoic acid molecules shows an intensity maximum at about 500 nm, which may be linked to an effect caused by the aggregation of Ag nanocrystals.
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY