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Defect Complexes in CrSBr Revealed Through Electron Microscopy and Deep Learning

Mads Weile1,2,*, Sergii Grytsiuk3, Aubrey Penn4, Daniel G. Chica5, Xavier Roy5, Kseniia Mosina6, Zdenek Sofer6, Jakob Schiøtz7, Stig Helveg2 et al.

Malte Rösner3, Frances M. Ross1,†, and Julian Klein1,‡

  • *Contact author: weile.a.mads@gmail.com
  • †Contact author: fmross@mit.edu
  • ‡Contact author: jpklein@mit.edu
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Phys. Rev. X 15, 021080 – Published 4 June, 2025

DOI: https://doi.org/10.1103/PhysRevX.15.021080

Abstract

Atomic defects underpin the properties of van der Waals materials, and their understanding is essential for advancing quantum and energy technologies. Scanning transmission electron microscopy is a powerful tool for defect identification in atomically thin materials, and extending it to multilayer and beam-sensitive materials would accelerate their exploration. Here, we establish a comprehensive defect library in a bilayer of the magnetic quasi-1D semiconductor CrSBr by combining atomic-resolution imaging, deep learning, and ab initio calculations. We apply a custom-developed machine learning work flow to detect, classify, and average point vacancy defects. This classification enables us to uncover several distinct Cr interstitial defect complexes, combined Cr and Br vacancy defect complexes, and lines of vacancy defects that extend over many unit cells. We show that their occurrence is in agreement with our computed structures and binding energy densities, reflecting the intriguing layer interlocked crystal structure of CrSBr. Our ab initio calculations show that the interstitial defect complexes give rise to highly localized electronic states. These states are of particular interest due to the reduced electronic dimensionality and magnetic properties of CrSBr and are, furthermore, predicted to be optically active. Our results broaden the scope of defect studies in challenging materials and reveal new defect types in bilayer CrSBr that can be extrapolated to the bulk and to over 20 materials belonging to the same FeOCl structural family.

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Popular Summary

Defects at the atomic level can dramatically affect a material’s behavior, changing how it conducts electricity, responds to magnetic fields, or interacts with light. For quantum and spintronic technologies, understanding these defects is crucial. However, studying defects in sensitive, low-dimensional materials like CrSBr has been difficult because they degrade when exposed to air. In this study, we overcome these limitations and directly visualize the atomic-scale defects in bilayer CrSBr, a magnetic semiconductor with potential applications in quantum technologies.

We use atomic-resolution electron microscopy combined with a deep learning algorithm to detect and analyze atomic defects in CrSBr. This approach enables us to identify not only simple vacancy defects but also more complex defect patterns, including mobile chromium atoms forming defect complexes under the electron beam. To interpret and organize these findings, we build a detailed defect library, which can help researchers predict and control how the material behaves. Our analysis suggests that several of the observed defects could serve as quantum emitters—tiny light sources integral to quantum communication and sensing.

This work lays the foundation for using CrSBr in quantum technologies by elucidating its atomic imperfections and potentially making them tunable. Our method can also be extended to study other beam-sensitive layered materials, many of which share a similar crystal structure.

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Phys. Rev. X 15, 021080– Published 4 June, 2025
  • Received 9 September 2024
  • Revised 18 December 2024
  • Accepted 16 April 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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