Far-field interaction of focused relativistic electron beams in electron energy loss spectroscopy of nanoscopic platelets

TL;DR

This paper develops a quantum scattering theory for focused relativistic electron beams interacting with nanoscopic platelets, revealing new radiative excitation mechanisms and enhancements in electron energy loss spectra.

Contribution

It introduces a novel quantum mechanical model that accounts for edge scattering and radiative excitations in electron energy loss spectroscopy of nanostructures.

Findings

Discovery of radiative electromagnetic excitations above surface plasmon peaks

Enhanced electron energy loss probabilities at spectral gaps

Potential for far-field detection of nanostructure excitations

Abstract

A quantum mechanical scattering theory for relativistic, highly focused electron beams near nanoscopic platelets is presented, revealing a new excitation mechanism due to the electron wave scattering from the platelet edges. Radiative electromagnetic excitations within the light cone are shown to arise, allowed by the breakdown of momentum conservation along the beam axis in the inelastic scattering process. Calculated for metallic (silver and gold) and insulating (SiO2 and MgO) nanoplatelets, new radiative features are revealed above the main surface plasmon-polariton peak, and dramatic enhancements in the electron energy loss probability at gaps of the 'classical' spectra, are found. The corresponding radiation should be detectable in the vacuum far-field zone, with e-beams exploited as sensitive 'tip-detectors' of electronically excited nanostructures.