Surface Enhanced Raman electrochemically roughened silver

In most work on electrochemical systems, use is made of two effects that greatly enhance the Raman signals. One is resonance Raman spectroscopy (RRS), wherein the excitation wavelength corresponds to an electronic transition in an adsorbed molecule on an electrode surface. The other effect is surface-enhanced Raman spectroscopy (SERS), which occurs on certain surfaces, such as electrochemically roughened silver and gold. This effect, discovered by Fleischmann et al. (1974), yields enhancements of 10 to 10 . The vast majority of publications on Raman studies of electrochemical systems use SERS. The limitations of SERS are that it occurs on only a few metals and the mechanism of the enhancement is not understood. There is speculation that only a small part of the surface is involved in the effect. There is a very good review of SERS (Pemberton, 1991). 

Fortunately, in favorable cases enhancement mechanisms operate which increase the signal from the interface by a factor of 105 — 106, so that spectra of good quality can be observed - hence the name surface-enhanced Raman spectroscopy (SERS). However, these mechanisms seem to operate only on metals with broad free-electron-like bands, in particular on the sp metals copper, silver and gold. Furthermore, the electrodes must be roughened on a microscopic scale. These conditions severely limit the applicability of Raman spectroscopy to electrochemical interfaces. Nevertheless, SERS is a fascinating phenomenon, and though not universally applicable, it can yield valuable information on many interesting systems, and its usefulness is expected to increase as instrumentation and preparation techniques improve. 

Surface-enhanced Raman scattering was first observed by Fleischmann, et al. (3) for pyridine adsorbed on a silver surface that had been roughened by repeated electrochemical oxidation and reduction in chloride solution. The... 

Over the past decades, smface enhanced Raman scattering (SERS) has became a valuable spectroscopic technique as a powerful smface diagnostic tool. In 1974 Fleischmann, Hendra, and McQuillan performed the first measurement of a surface Raman spectrum from pyridine adsorbed on an electrochemically roughened silver electrode. It has been explained that some vibrational bands of pyridine are selectively enhanced a million times. This increases the sensitivity of... 

The effective increases in the Raman scattering cross sections, or surface enhancement factors (SEE), are typically about lO fold on electrochemically roughened silver, gold, and copper. Few works have been reported on the other free electron metals such as alkali metals. Many transition metals have relatively weak surface enhancements. Their SEE values depend on the nature of the metal, for example, 10 10" for Pt, Rh, Ni, Co, and Fe, and 10 for Pd. 

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