ENHANCED RAMAN-SCATTERING FROM CRYSTAL VIOLET AND BENZOIC-ACID MOLECULES ADSORBED ON SILVER NANOCRYSTALS

Enhanced Raman scattering by crystal violet molecules and benzoic acid molecules adsorbed on Ag nanocrystals was measured by employing the a ttenuated 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 ove r the surface of the substrate. Films composed of Ag nanocrystals were found to be good enhancers of Raman signals. No obvious frequency shi ft with respect to the ''normal'' Raman lines was observed in the enha nced Raman spectra, thus indicating that the enhancement effect is mai nly electromagnetic in nature. The enhancement factor depends on the l aser excitation line used. Under our experimental conditions the enhan cement 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 us ing benzoic acid molecules shows an intensity maximum at about 500 nm, which may be linked to an effect caused by the aggregation of Ag nano crystals.