Electron beam shaping: how to control the e-beam propagation along atomic columns

TL;DR

This paper analyzes how high-energy electron beams with different shapes propagate along atomic columns in GaN crystals, using simulations to understand channeling phenomena and beam control.

Contribution

It introduces a detailed comparison of Bloch wave and multislice simulations for shaped electron beams, including Bessel and Gaussian probes, to improve beam control along atomic columns.

Findings

Bessel beams' propagation can be described by free space properties.

Gaussian probes optimize coupling to 1s Bloch states.

Insights into channeling phenomena and probe oscillations.

Abstract

In this work we report on a detailed analysis of the propagation of high energy electron beams having different shapes in a model system, namely [100] oriented zincblende GaN crystal. The analyses are based on the comparison between a reformulated Bloch wave and multislice simulations and mainly focus on Bessel beams. In fact, considering the simplicity of the Bessel beam momentum spectrum and the symmetry of the material it is possible in some cases to give a simple description of the propagation and explain it on the bases of the free space properties of each beam. This analysis permits a deeper understanding of the channeling phenomena and of the probe intensity oscillation along the propagation direction. For comparison we will also consider two additional relevant cases of the well-known aperture limited beams and a newly introduced Gaussian probes. The latter can be shown to be the optimal probe for coupling to 1s Bloch states and obtain minimal spread along columns.