Probing of optical near-fields by electron rescattering on the 1 nm scale

TL;DR

This paper introduces a novel electron rescattering method to measure optical near-fields at nanometer scales near metal surfaces, revealing the influence of geometry over plasmon resonances and implications for quantum plasmonics.

Contribution

The study develops a new measurement technique for optical near-fields at ~1 nm scale and provides detailed field enhancement maps for different materials and geometries.

Findings

Optical near-fields are mainly governed by geometric effects.

Good agreement between measurements and Maxwell simulations.

Plasmon resonances have a minor role in near-field enhancement.

Abstract

We present a new method of measuring optical near-fields within ~1 nm of a metal surface, based on rescattering of photoemitted electrons. With this method, we precisely measure the field enhancement factor for tungsten and gold nanotips as a function of tip radius. The agreement with Maxwell simulations is very good. Further simulations yield a field enhancement map for all materials, which shows that optical near-fields at nanotips are governed by a geometric effect under most conditions, while plasmon resonances play only a minor role. Last, we consider the implications of our results on quantum mechanical effects near the surface of nanostructures and discuss features of quantum plasmonics.