Evidence is presented that coldly deposited Ag films are highly porous and that the pores persist up to 170 K but are heated out at 250 K. Diffusion of adsorbed pyridine into the pores is negligible below 60 K but readily takes place at 130 K. Theoretical results on the classical electromagnetic enhancement of the Raman cross section within the pores as well as a survey of published surface-enhanced Raman-scattering data lead the authors to conclude that the surface-enhanced Raman-scattering active sites of coldly deposited Ag films are within the pores.

• Received 27 July 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.2314