Surface plasmon polaritons models

The electromagnetic enhancement mechanism features the major contribution to the overall enhancement of SERS. It is based on the generation of an electromagnetic field at the surface of nanostructured metal surfaces due to the interaction of an incident electromagnetic field and the excitation of localized surface plasmon polaritons. To explain this phenomenon in more detail, a simple model can be used. A simple metal nanosphere with a size smaller than the wavelength of the incident light is considered for this purpose. This metal nanosphere is surrounded by a medium or vacuum with a dielectric constant Eq, and all appearing processes are assumed to be quasi-static. The dielectric constant inside the metal nanosphere is independent of the size of the sphere and is described as follows ... 

One may classify the various proposed models in several ways. One way is to differentiate between models that focus on the role of the electric field E and the emission G terms (these two are related), on the one hand, and those that emphasize the role of changes in the Raman polarizability tensor, on the other. The former discuss the enhancement in terms of amplified fields, due to the presence of the surface, which act on the scattering molecule and its emission being further amplified by the surface. These are the local field and emission enhancement models (LFE). The difference between the various models which belong to this group is in the identification of the specific excitation in the solid which is responsible for the amplification plasmon polaritons, shape resonances, electron holes, etc. 

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