Field enhancement in subnanometer metallic gaps

TL;DR

This paper presents a theoretical analysis demonstrating that subnanometer gold gaps can produce extremely high electric field enhancements, exceeding 1000 times, due to hybrid plasmon coupling, aligning with recent experimental observations.

Contribution

It provides a classical FDTD simulation study revealing the mechanism of giant field enhancement in subnanometer metallic gaps, advancing understanding of nano-optical phenomena.

Findings

Field enhancement factors over 1000 in subnanometer gaps

Strong confinement of electric fields within the gap region

Coupling of incident light to hybrid plasmons explains the enhancement

Abstract

Motivated by recent experiments [Ward et al., Nature Nanotech. 5, 732 (2010)], we present here a theoretical analysis of the optical response of sharp gold electrodes separated by a subnanometer gap. In particular, we have used classical finite difference time domain simulations to investigate the electric field distribution in these nanojunctions upon illumination. Our results show a strong confinement of the field within the gap region, resulting in a large enhancement compared to the incident field. Enhancement factors exceeding 1000 are found for interelectrode distances on the order of a few angstroms, which are fully compatible with the experimental findings. Such huge enhancements originate from the coupling of the incident light to the evanescent field of hybrid plasmons involving charge density oscillations in both electrodes.