Atomic resolution HOLZ-STEM imaging of atom position modulation in oxide heterostructures

Magnus Nord,Juri Barthel,Christopher S Allen,Damien Mcgrouther,Angus I Kirkland,Ian Maclaren

doi:10.1016/j.ultramic.2021.113296

Magnus Nord, Juri Barthel + Show 4 more

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https://doi.org/10.1016/j.ultramic.2021.113296

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Abstract

It is shown that higher order Laue zone (HOLZ) rings in high energy electron diffraction are specific to individual columns of atoms, and show different strengths, structure and radii for different atom columns along the same projection in a structure. An atomic resolution 4-dimensional STEM dataset is recorded from a <110> direction in a perovskite trilayer, where only the central LaFeO3 layer should show a period doubling that gives rise to an extra HOLZ ring. Careful comparison between experiment and multislice simulations is used to understand the origins of all features in the patterns. A strong HOLZ ring is seen for the La-O columns, indicating strong La position modulation along this direction, whereas a weaker ring is seen along the O columns, and a very weak ring is seen along the Fe columns. This demonstrates that atomic resolution HOLZ-STEM is a feasible method for investigating the 3D periodicity of crystalline materials with atomic resolution.

Highlights

Scanning transmission electron microscopy (STEM) has had a sub stantial impact on the characterisation of materials
Advances have been made towards resolving extended features along the direction of the electron beam using scanning confocal electron microscopy [15, 16], and variable angle detection has been used to determine the vertical position of single dopants or vacancies [17,18]
It was speculated that the behaviour of electrons channelling along distinct columns in the structure would lead to an observable difference in the higher order Laue zone (HOLZ) rings

Summary

Introduction

Scanning transmission electron microscopy (STEM) has had a sub stantial impact on the characterisation of materials. The high angle diffraction events that form these rings arise from diffraction vectors that are a significant angle away from being perpendicular to the electron beam direction, and contain information about the ordering of the crystal along the beam direction It was previously the orised that it might be possible to use these to prove a period doubling along the core of a 90◦ partial dislocation in silicon, and simulations. It was speculated that the behaviour of electrons channelling along distinct columns in the structure would lead to an observable difference in the HOLZ rings We extend this previous work by performing 4D-HOLZ-STEM imaging at atomic resolution. All the column-resolved diffraction patterns have been simulated using a mul tislice approach at the same spatial resolution in order to provide an understanding of the origins of the features therein

Experimental

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Conclusions