Automated electron diffraction tomography – development and applications

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Marco E. Ciriotti
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Automated electron diffraction tomography – development and applications

Messaggio da Marco E. Ciriotti » lun 12 ago, 2019 12:29

Referenza:
▪ Kolb, U., Krysiak, Y., Plana.Ruiz, S. (2019): Automated electron diffraction tomography – development and applications. Acta Crystallographica, B75, 463-474.

Abstract:
Electron diffraction tomography (EDT) has gained increasing interest, starting with the development of automated electron diffraction tomography (ADT) which enables the collection of three-dimensional electron diffraction data from nano-sized crystals suitable for ab initio structure analysis. A basic description of the ADT method, nowadays recognized as a reliable and established method, as well as its special features and general applicability to different transmission electron microscopes is provided. In addition, the usability of ADT for crystal structure analysis of single nano-sized crystals with and without special crystallographic features, such as twinning, modulations and disorder is demonstrated.

Conclusion:
The high potential of EDT for crystal structure analysis of nanocrystals, where other diffraction methods such as X-ray single crystal or powder diffraction fail, has been demonstrated many times since 2007, when the development of the first method was described. Here we provide a description of the different approaches and propose to reference all the different acquisition techniques in the general name of EDT. Apart from this survey, we focus on the ADT method developed in our group, which is so far the only method combining STEM imaging for tracking purposes with tomographic diffraction data acquisition. The benefit of this approach is discussed from a technical point of view as well as demonstrated in the case of applications to several classes of materials. This includes the accessibility of crystals down to a size of 20 nm and the possibility of accessing the average structure of the disordered material with a subsequent description of the disorder. In addition, it was demonstrated that ADT is capable of acquiring EDT data from beam-sensitive materials with only weak scattering atoms by using a CCD camera. Especially for phase mixtures, it is important to be able to derive information from all phases, which may not only differ in terms of crystal size but as well by properties such as crystallinity, solubility, stability and bioavailability. As an example, a structure analysis of carbamazepine was successfully performed based on a single ADT data set. The structure, which was refined without any constraint, is in good agreement with those solved by EDT on the basis of significantly larger crystals.
Furthermore, it is demonstrated that ADT provides a high accessibility to structurally complex samples. This is increasingly important for successful tailoring of physical properties for a wide range of applications. The majority of materials used in this respect contain crystalline nano-sized domains, in many cases bearing defects, which drive the desired physical effects. The accuracy of the STEM imaging used in ADT is ideal to access and characterize one by one these single domains.
Beside the large number of materials which have been structurally determined solemnly on the basis of EDT data, the method provides a strong potential to be combined to complementary techniques such high-resolution imaging (HR-TEM/HR-STEM), diffraction methods that provide bulk information, such as XRPD and NMR, as well as to simulation approaches.
Marco E. Ciriotti

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