Single scan STEM-EMCD in 3-beam orientation using a quadruple aperture

TL;DR

This paper introduces a novel quadruple aperture method for single-scan EMCD in a 3-beam orientation, significantly simplifying data acquisition and improving magnetic characterization accuracy in electron microscopy.

Contribution

The study presents a new quadruple aperture technique enabling simultaneous acquisition of all necessary spectra in a single scan for EMCD experiments, reducing errors from sample drift and damage.

Findings

Successful demonstration of single-scan EMCD using quadruple aperture

Quantitative EMCD results at sub-nm probe size

Comparison of EMCD results across different detector geometries

Abstract

The need to acquire multiple angle-resolved electron energy loss spectra (EELS) is one of the several critical challenges associated with electron magnetic circular dichroism (EMCD) experiments. If the experiments are performed by scanning a nanometer to atomic-sized electron probe on a specific region of a sample, the precision of the local magnetic information extracted from such data highly depends on the accuracy of the spatial registration between multiple scans. For an EMCD experiment in a 3-beam orientation, this means that the same specimen area must be scanned four times while keeping all the experimental conditions same. This is a non-trivial task as there is a high chance of morphological and chemical modification as well as non-systematic local orientation variations of the crystal between the different scans due to beam damage, contamination and spatial drift. In this work, we employ a custom-made quadruple aperture to acquire the four EELS spectra needed for the EMCD analysis in a single electron beam scan, thus removing the above-mentioned complexities. We demonstrate a quantitative EMCD result for a beam convergence angle corresponding to sub-nm probe size and compare the EMCD results for different detector geometries.