Abstract

Surface-enhanced Raman scattering (SERS) at roughened silver surfaces may be attributed in the main to excitation of plasma resonances within the surface bumps. Colloidal particles exhibit the same phenomenon and have the advantage of being amenable to a complete theoretical analysis and to simple experiments. We describe the theoretical model for enhancement of the Raman signals from molecules located on or near spherical or spheroidal surfaces and also report experimental results with silver hydrosols. With molecular species which absorb strongly over part of the visible spectrum, it is possible to observe both resonance Raman (RR) and normal Raman enhancement from the same system. In some cases these processes overlap, providing a superposition of RR and SERS enhancement. By utilizing two different molecular species, it is also possible to observe separately each process, SERS and RR on the same substrate.

© 1989 Optical Society of America