Single nano crystal analysis using automated electron diffraction tomography

Most of hitherto unknown natural phases and many new synthetic compounds can grow only in the form of nanocrystals. X-ray powder diffraction is the most widespread technique for the structural characterization of nanomaterials, but its use is limited by two main restrictions: structural information is projected in one dimension and data come from the whole sample and not from a specific single crystallite. On the other hand, crystallographic methods based on the scattering of accelerated electrons are able to obtain 3-D structural data from single volumes of few tens of nanometers. Automated diffraction tomography is a recently developed method able to record more kinematical and complete electron diffraction data. This method consists in the acquisition of a series of electron diffraction patterns while the sample is rotated around an arbitrary tilt axis by sequential mechanical steps, within the full tilt range of the microscope goniometer. Data collection can be performed on highly beam sensitive materials, as no time is required for orienting the crystal along specific crystallographic orientations and mild illumination conditions are used. In the last years many nanocrystalline materials belonging to different material classes have been characterized by automated diffraction tomography. This review describes the different experimental and analytical approaches used for the determination of inorganic and organic phases and points out the advantages offered by automated diffraction tomography for the characterization of minor phases available only in polyphasic nanomixtures and for the description of domain arrangement in polycrystalline nanocomposites.