The role of atomic-scale surface-roughness features ("adatoms") in the surface-enhanced Raman scattering (SERS) effect has been examined. We use a thin, low-temperature evaporation technique in ultrahigh vacuum to generate a surface with a high density of adatoms and fail to observe SERS signals from this surface. Only thicker films, with larger surface-roughness features, show SERS signals. This observation supports surface plasmon or electromagnetic mechanisms for SERS and demonstrates that adatoms play a limited role in the enhancement.

• Received 26 May 1981

DOI:https://doi.org/10.1103/PhysRevB.24.2289