Conference

Keywords

Abstract

With the development of fast pixelated electron detectors, four-dimensional scanning transmission electron microscopy (4D-STEM) has become an established technique, enabling the capture of a full diffraction pattern at each probe position. This comprehensive data acquisition opens new pathways in imaging and structural characterisation, including Symmetry STEM (S-STEM) [1], which utilises symmetry elements within diffraction patterns - such as rotation and mirror symmetry - to create images where intensity is related to structural symmetry. S-STEM uses the whole diffraction pattern to extract information about the symmetry of the diffraction patterns, which can be related to the symmetry of the corresponding material volume. Prior studies using pixelated detectors have shown the high sensitivity of S-STEM contrast to local symmetry and its robustness to several experimental parameters, including accelerating voltage, sample thickness and defocus. It can also enable enhanced sensitivity to light elements, even in the presence of heavier elements [1]. However, the relatively slow acquisition rates of pixelated detectors and the big data they generate, pose limitations, especially for real-time imaging applications. In this work, we investigate S-STEM using faster read-out segmented detectors, using both simulations and experimental data. When a segmented detector is used, it can enable faster imaging with a smaller electron budget - a critical advantage for beam sensitive materials. By summing signals within detector segments, the signal generated by symmetry elements can be enhanced under certain conditions, as shown in Figure 1, which compares the same data processed using the whole pattern with that processed by integrating over segments. Figure 1. Comparison of a 180-degree rotation S-STEM image of one-unit-cell of <110> CeB6 generated with 128*128 pixels and 12 segments, using the same experimental 4D-STEM data: (a) CBED pattern recorded with an EMPAD with 128*128 pixels. (b) Post processed CBED pattern in (a) generated by integrating the intensity in 12 segments. (c) S-STEM image using 128*128 pixels and (d) S-STEM image using 12 segments. Comparison of a 180-degree rotation S-STEM image of one-unit-cell of <110> CeB6 generated with 128*128 pixels and 12 segments, using the same experimental 4D-STEM data: (a) CBED pattern recorded with an EMPAD with 128*128 pixels. (b) Post processed CBED pattern in (a) generated by integrating the intensity in 12 segments. (c) S-STEM image using 128*128 pixels and (d) S-STEM image using 12 segments.

Authors

Chao W; Petersen T; Lazar S; Etheridge J

Publisher

ScienceOpen

Publication Date

January 21, 2025

DOI

10.14293/apmc13-2025-0330

Name of conference

Symmetry Scanning Transmission Electron Microscopy using Segmented Detectors
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