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Visualizing twisted 2D materials with electron channelling contrast imaging

Nature Reviews Physics volume 7, page 134 (2025)Cite this article

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Twisting two-dimensional (2D) materials to form moiré superlattices provides an additional degree of freedom for tuning materials’ optoelectronic properties and studying correlation effects in flat electronic bands. At small twist angles (≤1.1°), where interesting phenomena appear, atomic reconstruction leads to the formation of large domains (up to micrometres in diameter). Correlating the moiré-induced electronic effects to the underlying structural domains requires a direct, non-destructive visualization technique. Scanning probe microscopy (SPM) methods allow visualization of moiré superlattices, however they rely on close range interactions between the tip and surface. Thus, scanning probe microscopy cannot probe lattices which are interfaced with other materials to form devices (for example twisted van der Waals (vdW) crystals encapsulated with dielectrics, contacts or gates). Furthermore, optical microscopy techniques can probe lattices interfaced with other materials, allowing device–property characterization. Yet, these methods lack sufficient spatial resolution for correlating properties with directly imaged atomically reconstructed twisted 2D materials’ domains.

CMSEI of twisted vdW heterostructures acquires images with secondary electrons of low energies (<50 eV), collected on an Everhart–Thornley detector. Orienting specimens to the ideal tilt angle is necessary to optimize the difference in electron channelling conditions for different stacking domains, thereby creating secondary electron contrast to reveal crystallographic reconstruction in twisted vdW heterostructures. Imaging is robust to thin encapsulation and so can be used to understand transport behaviour for encapsulated electronic device heterostructures. It is also compatible with in situ observation of electric field induced domain reconstruction, since the twisted vdW heterostructure can still be imaged when covered by a dielectric and top gate electrode. However, the low-energy secondary electron signal detected by the Everhart–Thornley detector has a small penetration distance and is subsequently sensitive to surface topography, as well as surface charging. Therefore, twisted moiré superlattice features are obscured in the presence of significant surface contamination, charging, trapped hydrocarbon bubbles and/or other strong topographic features.

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Acknowledgements

The author thanks R. Gorbachev, J. Howarth, N. Clark, T. Hashimoto, A. Pollard and S. J. Haigh for discussions and advice. This project has received funding from the European Union under the Horizon 2020 framework (grant EvoluTEM 715502), from the Engineering and Physical Sciences Research Council grants (EP/ S021531/1, EP/S030719, EP/ V007033/1, EP/V001914/1 and EP/P009050/1, EP/Y024303/1) and from the UK National Physical Laboratory (NPL).

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  1. Department of Materials, Faculty of Science and Engineering, University of Manchester, Manchester, UK

    Evan Tillotson

  2. National Graphene Institute, University of Manchester, Manchester, UK

    Evan Tillotson

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  1. Evan Tillotson
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Correspondence to Evan Tillotson.

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Tillotson, E. Visualizing twisted 2D materials with electron channelling contrast imaging. Nat Rev Phys 7, 134 (2025). https://doi.org/10.1038/s42254-025-00810-y

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