Limit possible electric field in plasmon nanogap resonator

TL;DR

This paper develops a theoretical model for ultra-narrow plasmonic gaps formed by a metal cylinder on a metal surface, predicting huge local electromagnetic field enhancements useful for sensing applications.

Contribution

It introduces a new theory for plasmons in ultra-narrow nanogaps and estimates the maximum electric field enhancement achievable in such structures.

Findings

Resonance conditions for the plasmon in the nanogap are derived.

Maximum electric field enhancement scales with material permittivities and losses.

Potential applications include SERS sensing and infrared spectroscopy.

Abstract

We propose the theory of the plasmon excited in ultra-narrow plasmonic gap formed by a metal cylinder on a metal surface, that generates a huge resonant local electromagnetic field in optical frequencies. Resonance conditions are found. The maximum possible enhancement of the electric field in the nanogap is estimated as $\left|E_{max} \right|/ \left| E_{0} \right| \propto \left| \varepsilon_m \right|^{3} \varepsilon_{d}^{-1} \left( \Im \varepsilon_{m}\right) ^{-2}$ A simple ultranarrow-gaped resonator can be used for SERS sensing and infrared spectroscopy of adsorbed molecules. We assume that a plasmonic nanogap is simplest and most straightforward way to increase flexibility as well as sensitivity of the plasmon-enhanced spectroscopes.