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Tom Willhammar Department of Materials and Environmental Chemistry, Stockholm University, Sweden

Electron crystallography - a versatile tool for structure elucidation at the sub-micrometer scale

Knowledge about the atomic structure of materials is essential in order to understand its properties, improve its design and develop applications. Modern materials with increasing complexity increases the demands on structural characterization. Using electrons as probes for structure elucidation introduces two significant benefits, which makes it a versatile complement to well established methods based on X-ray and neutron scattering. Firstly, electrons interacts much stronger with matter compared to other types of probes, decreasing the necessary volume to obtain single crystal data. Secondly, the nature of electrons as being charged particles can be used to control the beam in a precise manner, which enables the formation of images with atomic resolution as well as mapping of features at the nanoscale. Several recent methodological developments provide new opportunities to obtain structural knowledge. It is now possible to obtain three dimensional (3D) single-crystal electron diffraction data from crystals down towards the nano-regime. This data can be used for structure determination of specimens where conventional methods struggle and has been applied on a significant number of new specimens, including numerous porous materials such as zeolites and metal-organic frameworks (MOFs) as well as pharmaceuticals and other organic compounds. [1,2] A second emerging tool is scanning electron diffraction, where microstructural information can be achieved with a few nanometer resolution. This method has recently been applied to studies of the crystalline microstructure of highly beam sensitive soft materials such as cellulose nanofibers.[3] The possibility of image formation enables studies of atomic arrangements at the local scale. This is of importance, especially for structure determination of specimens containing structural disorders and lack of periodicity.[4] These opportunities, utilizing modern electron microscopy, provide a unique toolbox for studies of specimens with complex structures and is highly complementary to other tools for structural characterization.

References
[1] Willhammar et.al. Adv. Func. Mater. 24 182 (2014)
[2] Lu, Willhammar et.al. Nature Comms. 11 1546 (2020)

[3] Willhammar et.al. ChemRxiv (2020) chemrxiv.org/articles/preprint/Local_Crystallinity_in_Twisted_Cellulose_Nanofibers/12639686