Abstract
Crystallographic defects such as dislocations can significantly alter material properties and functionality. However, imaging these imperfections during operation remains challenging due to the short length scales involved and the reactive environments of interest. Bragg coherent diffractive imaging (BCDI) has emerged as a powerful tool capable of identifying dislocations, twin domains, and other defects in 3D detail with nanometer spatial resolution within nanocrystals and grains in reactive environments. However, BCDI relies on phase retrieval algorithms that can fail to accurately reconstruct the defect network. Here, we use numerical simulations to explore different guided phase retrieval algorithms for imaging defective crystals using BCDI. We explore different defect types, defect densities, Bragg peaks, and guided algorithm fitness metrics as a function of signal-to-noise ratio. Based on these results, we offer a general prescription for phasing of defective crystals with no a priori knowledge.
Highlights
Phase retrieval in coherent diffraction imaging (CDI) is a non-convex optimization problem in which convergence to the true solution is not guaranteed
The most common practice for Bragg coherent diffractive imaging (BCDI) phase retrieval is to alternate between error reduction (ER) and Hybrid Input-Output (HIO) while utilizing the Shrinkwrap algorithm[32] to update the support
Bragg coherent diffraction data from defective crystals were simulated under the kinematic approximation using an atomistic model assuming a plane wave illumination[41]
Summary
We use numerical simulations to explore different guided phase retrieval algorithms for imaging defective crystals using BCDI. We explore different defect types, defect densities, Bragg peaks, and guided algorithm fitness metrics as a function of signal-to-noise ratio. Based on these results, we offer a general prescription for phasing of defective crystals with no a priori knowledge. We discuss the results of this procedure for the case of a perfect edge dislocation in a facetted nanocrystal with Wulff geometry From this atomic model, coherent Bragg diffraction about a (1–11) Bragg peak was calculated and used to test the guided algorithm fitness metrics.
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