The effects of the local dielectric environment on the surface-enhanced Raman-scattering enhancement factor of benzoic acid adsorbed on silver oblate spheroids are studied experimentally and modeled theoretically. Silver-island films were annealed to produce spheroidal-shaped particles which exhibit well resolved resonances in absorption spectra. These resonances are shifted in different amounts by the depolarizing interaction with the substrate. An additional dielectric film has been deposited between the particles and substrate in order to measure the effects of proximity on the surface-enhanced Raman signal. Experimental observations on germanium and silicon are presented and found to be in agreement with calculations involving only the surface-plasmon excitation on the particles.

• Received 20 June 1990

DOI:https://doi.org/10.1103/PhysRevB.43.4605