Plasmon resonance excitation enhances Raman emission and amplifies the molecular vibration on Au (1 1 1) film

Abstract

The enhancement of Raman scattering by localized plasmonic resonances has boosted spectroscopic analysis down to the single-molecule level. Here, the simultaneous measurement of the surface plasmon resonance and surface-enhanced Raman scattering on a flat Au surface is demonstrated. The results emphasize that, under the conditions of plasmon resonance, the electromagnetic field is enhanced, permitting the readout of the surface-enhanced Raman scattering signal.Peaks at different frequencies characterized the spectra of the molecules selected as Raman probes. In the first approach, we explained our findings referring to classical optomechanics. Because the plasmon lifetime and the molecular vibrational have the same magnitude and the molecular dephasing is not expected phenomenon, we fostered the hypothesis that a stronger coupling occurs. In fact, the coupling rate between the monolayer and the plasmon is enhanced with an order of gv0=0.12MHz, which is wider than the laser linewidth and leads to coherent amplification of molecular motion.In conclusion, the possibility to run the SERS in the Kretschmann configuration with flat gold substrates opens endless possibilities in nanophotonics for fundamental investigations and their applications.