SERS from the point of view of the Molecule & the Antenna

Surface Enhanced Raman Spectra (SERS) recorded on plasmonic substrate is often accompanied with broad background, origin of which is extensively deliberated. Moreover, fluctuation in the spectra is regarded as a signature of single molecule response. The plasmonic junctions typically evolve and so does the local near field, which the molecule experiences. The molecular signature indicates presence of complicated near field, as well as the background is characterized via electronic Raman of the metal. The understanding of the entire spectra is based on the molecular response, metal response and their coupling. Polarized SERS measurements on single Au or Ag nanodimer equipped with some reporter molecule shows that the emission constituting the continuum is polarized. In a metal, bulk states can only result in scattering which is unpolarized, however, the surface states of the metal can be responsible for Raman. We assign the continuua to Raman of plasmons. The polarization decomposition of the intimately related molecular and plasmonic SERS allows mechanistic assignments of the scattering process and the nature of accessible plasmons in the prototypical dumbbell antenna