Anomalous, low-frequency Raman scattering from localized acoustic vibrations of roughness features on a metal surface are observed. The observed mode frequency shifts with excitation frequency and with the index of refraction of the surrounding medium. The shifts arise from resonant laser excitation of localized dipolar plasmons. This resonant optical coupling is a key to the phenomenon of enhanced Raman scattering from molecules adsorbed on rough metal surfaces.

• Received 24 April 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.355