Relevance of Rabi splitting effect for tunable enhancement of Raman scattering in self-assembled silver – Fullerene nanocomposite films

Abstract

We report on detection of plasmon-enhanced Raman scattering (PERS) in self-assembled AgxC60 nanocomposite films and on evolution of this effect with increase of the Ag concentration, x, in the interval of 2<x < 25. Optical absorption spectra show that origin of the PERS effect is closely related with dipolar plasmonic mode generated by uniform 3D-ensemble of Ag nanoparticles, which arise in the C60-based matrix during the film deposition. Careful analysis of the absorption spectra designates features of strong coupling between dipolar plasmon mode and the C60 low-energy exciton suggesting energy exchange between the arisen high- and low-energy polaritonic states. Evaluation of dispersion spectra of the polaritons revealed anti-crossing effect as a sign of the strong plasmon-exciton coupling with Rabi splitting energy of about 300 meV. In frames of the recently-reported quantum-electrodynamics model, the detected PERS effect was ascribed to abundant population of the low-energy polaritonic states caused by asymmetric transitions between the low- and high-energy polaritons. The obtained PERS-spectra display sensitivity of the C60 vibrational modes to the x-driven plasmonic field strength, which demonstrates some reduction at higher x due to charge transfer through C60 molecular junctions. The evident tunability of PERS suggests an emerging potential of the self-assembled AgxC60 films for their application in molecular electronics and molecular photochemistry.