Electromagnetic interaction between a metallic nanoparticle and surface in tunnelling proximity modelling and experiment

TL;DR

This paper models and experimentally investigates the electromagnetic interactions between a metallic nanoparticle and a surface in tunneling proximity, revealing how these interactions influence plasmon resonances and field localization.

Contribution

It introduces a simulation approach for localized surface plasmon resonances near a metal surface and compares these with experimental observations from tunneling microscopy.

Findings

Modes show significant red-shifting with increasing nanoparticle radius

Field enhancement exhibits oscillatory spatial variation near the surface

Localization degree depends mainly on nanoparticle radius

Abstract

We simulate the localized surface plasmon resonances of an Au nanoparticle within tunneling proximity of a Au substrate and demonstrate that the modes may be identified with those responsible for light emission from a scanning tunneling microscope. Relative to the modes of an isolated nanoparticle these modes show significant red-shifting, extending further into the infrared with increasing radius, primarily due to a proximity-induced lowering of the effective bulk plasmon frequency. Spatial mapping of the field enhancement factor shows an oscillatory variation of the field, absent in the case of a dielectric substrate; also the degree of localization of the modes, and thus the resolution achievable electromagnetically, is shown to depend primarily on the nanoparticle radius with only a weak dependence on wavelength.