Electrochemical phenomena, SERS

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. 

Special mention must be made of SERS studies of carbonates, carbon, and graphitic layers on surfaces. Cooney et have reported the appearance of Raman vibrational structures associated with the presence of carbon species on the SERS-active surfaces, in electrochemical systems. They even suggest that a graphitic layer formed on the surface is responsible for the SERS phenomenon itself. Tsang et also discuss the broad bands seen in SERS at 1350 and 1550 cm in terms of amorphous carbon. In the UHV systems, Pockrand and Otto report carbonate impurities exhibiting enhanced Raman scattering. They find that these impurities are incorporated into the sample below the surface. DelPriore et find by XPS several layers of carbon and oxygen on SERS-active vapor-deposited surfaces in the UHV. 

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