Practical Crystallography with a Transmission Electron Microscope

Abstract: Three-dimensional electron diffraction (3DED) is a powerful technique providing for crystal structure solutions of sub-micron sized crystals too small for structure determination via X-ray techniques. The entry requirement, however, of a transmission electron microscope (TEM) adapted with bespoke software for coordinated sample stage rotation and continuous electron diffraction data acquisition has generally inhibited the wider uptake of 3DED. To address this limitation, we present novel software GiveMeED appropriate for controlled 3DED data acquisition. The collection of useable reflections beyond 0.8 {\AA} makes 3DED crystallographic processing effectively routine, using standard software and workflows derived from single-crystal X-ray diffraction (SCXRD) techniques. A full experimental workflow for 3DED on a conventional TEM is described in practical terms, in combination with direct imaging, and energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), for the return of comprehensive correlative descriptions of crystal morphologies and sample compositions, with due regard for the quantification of electron flux at each stage of the characterisation process. The accuracy and effectiveness of GiveMeED is demonstrated through structure solutions for case study paracetamol, copper(II) phthalocyanine, and percholorocoronene samples, characterised in their near-native states under controlled low dose conditions at either room or cryogenic temperatures, with determined unit cell parameters and atomic connectivity matching accepted literature X-ray structures for these compounds. To promote the wider adoption of 3DED, we make GiveMeED freely available for use and modification, in support of greater uptake and utilisation of structure solution procedures via electron diffraction.