Small cavities as major active sites for surface enhanced Raman scattering

Abstract

Recently it has been proposed that extremely small cavities or pores may be important active sites for the surface enhanced Raman scattering (SERS) process on coldly deposited silver films in UHV. There is an interesting correlation between the temperature for annealing out these small cavities and the temperature at which the high-temperature anneal in SERS occurs. In order to further investigate this high-temperature anneal in terms of the cavity site model, experiments have been carried out in which varying amounts of very thin silver films are deposited over the substrate just before the Raman signal reaches a maximum by the high-temperature anneal. Further enhancements are observed when the average thickness of the silver overlayer is about 20 Å. These results are discussed in relation to theoretical considerations based on collective electronic resonances of a small spherical void in the metal near a surface. © 1985.