ENHANCED RAMAN-SCATTERING FROM SILVER METAL GRATINGS COATED WITH P-NITROBENZOIC ACID FILMS

The Raman scattering from echelette silver gratings coated with p-nitr obenzoic acid (PNBA) films was measured as a function of the angle of incidence of the exciting laser beam. It was found that on excitation of surface plasmon polaritons (SPPs) on the grating, the Raman scatter ing intensity of the adsorbed PNBA- species is enhanced by a factor of five compared with its intensity at off-resonance angles of incidence . However, an enhancement of about a factor of 10 in our estimation is observed with s-polarized radiation independent of the angle of incid ence, indicating the presence of some supplementary mechanism other th an the high-field intensity of SPP in the enhancement process. No Rama n bands due to PNBA were observed in the thickness range up to 50 nm.