Mirror enhanced directional out-coupling of SERS by remote excitation of a nanowire-nanoparticle cavity

TL;DR

This paper demonstrates mirror-enhanced, directional SERS from a nanowire-nanoparticle junction on a mirror, revealing how a mirror influences plasmon modes and emission directionality through experimental and numerical analysis.

Contribution

It introduces a remote excitation configuration for SERS using a mirror to control emission directionality and studies the effects of multiple hotspots and plasmon modes.

Findings

Mirror presence reduces angular spread of emission.

Multiple gap plasmon modes have unique momentum signatures.

Mirror enhances directionality of molecular emission.

Abstract

We report on the experimental observation of mirror enhanced directional surface enhanced Raman scattering (SERS) from a self-assembled monolayer of molecules coupled to a nanowire-nanoparticle (NW-NP) junction on a mirror in remote excitation configuration. Placing NW-NP junction on a metallic mirror generates multiple gap plasmon modes which have unique momentum space scattering signatures. We perform Fourier plane imaging of SERS from NW-NP on a mirror to understand the effect of multiple hotspots on molecular emission. We systematically study the effect of ground plane on the directionality of emission from NW-NP junction and show that the presence of a mirror drastically reduces angular spread of emission. The effect of multiple hotspots in the geometry on directionality of molecular emission is studied using 3D numerical simulations. The results presented here will have implications in understanding plasmon hybridization in the momentum space and its effects on molecular emission.