Surface enhanced raman scattering at electrodes: A status report

Abstract

AbstractProgress during the first decade of surface enhanced Raman scattering (SERS) is briefly reviewed. Examples of SERS of adsorbed H2O. OH−, and H3O+ on Ag electrodes which have undergone an oxidation‐reduction cycle (ORC) are discussed in some detail in order to bring out the unique and general features of SERS in an electrochemical system. Experimental techniques to further enhance the SERS signal, as well as to decrease the SERS signal after an ORC, are reviewed as such results can provide clues to possible surface enhancement mechanisms. The two enhancement mechanisms (electromagnetic and charge transfer) are presented in a unified but simplistic picture which involves the nearly free s,p‐electron band and the more localized d‐electron band for the noble metals (Ag, Cu, and Au). The role of the intraband transitions in the electromagnetic and charge transfer enhancement processes is discussed in terms of the wave‐vector uncertainty associated with the Raman dipole located on or near the surface and with the localized metal clusters which are often referred to as SERS‐active sites. Several examples are cited in which experiments initially designed to prove the presence of one enhancement mechanism end up proving the existence of both enhancement mechanisms. Progress expected in the SERS field during the next decade is also suggested.