Solids which Exhibit SERS

It is often wondered whether SERS is a useful tool in the study of solid surfaces in general or, perhaps, it is only a unique property of silver and its family. In the latter case the utility of SERS would be greatly diminished. From the theoretical point of view it is also extremely interesting to know which solid substrates support SERS. This may be an important clue in elucidating the enhancement mechanism itself. 

One should keep in mind several points when considering the experimental evidence for SERS activity on various solid substrates, in addition to the considerations mentioned in Section II. 1  

SERS is strongly dependent on the excitation frequency, a dependence which varies from solid to solid (see Section II.5), and, in addition, for the same substrate, it depends on the surface preparation procedure adopted. Therefore, the practice is to scan for SERS activity throughout the visible range and the near UV, the classical domain of Raman spectral effects. 

Merely detecting a Raman signal from a solid substrate surface does not necessarily mean that SERS is in effect. Weak signals can be detected due to the improved Raman systems, the larger surface areas on rough surfaces, multilayer formations, and simple reflectivity considerations. 

One is bound to find from time to time unique, specific systems where a special mechanism causes an enhancement of Raman scattering. Such a case, for instance, is probably the enhancement of the Raman scattering of oxygen on polydiacetylene. It is thought to originate from a charge transfer mechanism. In this review such systems will be considered SERS active only if several molecules (of different types) show an enhancement. 

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