ABSTRACT
Plasmons are quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons. e origin of the enormous Raman enhancement is produced by at least two main mechanisms that contribute to the surface-enhanced Raman scattering (SERS) eect: (1) an electromagnetic (EM) eect occurring near metal surface structures associated with large local elds caused by EM resonances, oen referred to as surface plasmons, and (2) a chemical eect involving a scattering process associated with chemical interactions between the molecule and the metal surface. When a metallic nanostructured surface is irradiated by an incident EM eld (e.g., a laser beam), conduction electrons are displaced into frequency oscillations equal to those of the incident light. ese oscillating electrons, called surface plasmons, produce a secondary electric eld, which adds to the incident eld. ese elds can be quite large (106-to 107-fold, or even up to 1015-fold enhancement at hot spots). When these oscillating electrons become spatially conned, as is the case for isolated metallic nanospheres or otherwise roughened metallic surfaces (nanostructures), there is a characteristic frequency (the plasmon frequency) at which there is a resonant response of the collective oscillations to the incident eld. is condition yields intense localized elds that can interact with molecules in contact with or near the metal surface [1-4]. In an eect analogous to a lightning rod eect, secondary elds can become concentrated at high curvature points on the roughened metal surface.
