Fundamental Behavior of Electric Field Enhancements in the Gaps Between Closely Spaced Nanostructures

TL;DR

This paper reveals that electric field enhancement in nanostructure gaps is due to a transverse waveguide mode, providing a universal semianalytic model applicable across various materials and geometries.

Contribution

It introduces a universal semianalytic equation describing electric field enhancement in nanogaps, independent of material or shape, including effects of surface plasmons.

Findings

The enhancement is caused by a transverse waveguide mode.

The derived equation applies broadly across different nanostructures.

Validation with metallic antennas and nanoparticle dimers confirms the model.

Abstract

We demonstrate that the electric field enhancement that occurs in a gap between two closely spaced nanostructures, such as metallic nanoparticles, is the result of a transverse electromagnetic waveguide mode. We derive an explicit semianalytic equation for the enhancement as a function of gap size, which we show has a universal qualitative behavior in that it applies irrespective of the material or geometry of the nanostructures and even in the presence of surface plasmons. Examples of perfect electrically conducting and Ag thin-wire antennas and a dimer of Ag spheres are presented and discussed.