Momentum-Resolved Surface Enhanced Raman Scattering from a Nanowire-Nanoparticle Junction Cavity

Herein experimental evidence of directional surface enhanced Raman scattering from molecules situated inside a single nanowire-nanoparticle junction cavity is reported. The emission is confined to a narrow range of wavevectors perpendicular to the axis of the cavity. In addition to this, the molecules excite multiple guided modes of the nanowire which are imaged using leakage radiation Fourier microscopy. The emission wavevectors are further characterized as a function of output polarization. The excited guided modes of the wire show interesting polarization signatures. All the results are corroborated using finite element method based numerical simulations. Essentially, an important connection between gap-cavity enhanced Raman scattering and its directionality of emission is provided. The results may be of relevance in understanding the cavity electrodynamics at the nanoscale and molecular coupling to extremely small gaps between a 1D and a 0D plasmonic nanostructure.