Stimulated tip-enhanced Raman scattering on single molecule in plasmonic nanocavity

Abstract

Abstract Plasmonic nanocavities formed by a metal nanoparticle located close to a thin metal film or other nanoparticle are of great interest for nanophotonics. Their properties can be used for optical superresolution, optoelectronics, and the creation of new materials with increased non-linearity. However, the interpretation of Raman spectra enhanced by a nanoresonator is complicated by depolarization effects. In this work, the analysis of tip-enhanced Raman scattering (TERS) on a single organic molecule in the plasmonic nanocavity formed by a metal tip and a gold substrate is carried out. The linear and nonlinear regimes of TERS are considered. The reasons for the selective enhancement of Raman spectral bands are analysed using anisotropic molecule of the free base porphyrin (FBP) dye as an example. The observed vibrational symmetry of the molecule changes even greater in nonlinear regime of spectroscopic TERS measurements. We believe that our results are beneficial for the development of the tools to control vibrations of molecules at the nanoscale.