3D electron diffraction on nanoparticles with a complex structure

The synthesis of inorganic compounds in form of nanoparticles of few nanometers has opened a new world for chemistry, with discovery of unexpected properties and also of entirely new crystal structures. At the beginning, simple stoichiometries related with crystal structures of low complexity have been mainly explored. As far as nanochemistry grew searching for exotic properties, the exploration has extended towards more complex phase diagrams, where the complexity of the crystal structure is a real challenge. In these cases, the crystallographer is hampered by the limited crystal size that enlarges the powder x-ray diffraction peaks and quite often cannot rely on the knowledge of the bulk structure, which can be different from the nanocrystalline form or even not stable in the same conditions. Conversely, 3D electron diffraction (3D ED) has demonstrated its potential for solving crystallographic problems where the size of the crystal grains was the limiting factor. A 3D ED single crystal diffraction experiment is performed with a beam that can be as small as few hundreds of nanometers, and the collected 3D intensity data sets are suitable for structure solution. We report here the application of 3D ED to extreme cases, where the size of the crystalline grains was smaller or in the range of 100 nm and the powder x-ray diffraction was not able to give a definite answer. The challenge is to establish which is the minimum crystal size that we can investigate in this way. All the nanoparticles we analysed have unknown and not trivial crystal structures.