Crystallography of nanocrystalline materials has witnessed a true revolution in the past 10 years, thanks to the introduction of protocols for 3D acquisition and analysis of electron diffraction data. This method provides single-crystal data of structure solution and refinement quality, allowing the atomic structure determination of those materials that remained hitherto unknown because of their limited crystallinity. Several experimental protocols exist, which share the common idea of sampling a sequence of diffraction patterns while the crystal is tilted around a noncrystallographic axis, namely, the goniometer axis of the transmission electron microscope sample stage. This Outlook reviews most important 3D electron diffraction applications for different kinds of samples and problematics, related with both materials and life sciences. Structure refinement including dynamical scattering is also briefly discussed.

Pin the tail on the hydrogens: X-ray diffraction has been the method of choice for determining the positions of atoms within a crystal. However, the technique works better for atoms with higher atomic numbers and requires single crystals of a minimum size. Palatinus et al. used electron diffraction, a technique of increasing importance for analyzing very small crystals, to identify the positions of hydrogen atoms in organic and inorganic materials (see the Perspective by McCusker). Science , this issue p. 166 ; see also p. 136

The study reports a simple and potentially universal strategy for post-synthetic engineering of zeolite crystals. Our strategy includes the generation of point defects in zeolite crystals by preliminary etching with oxalic acid, followed by the development of these defects by NH₄F etching. Several experimental techniques were used to measure and visualize the zeolite framework dissolution as a function of intrinsic and induced defects. It is revealed that the intrinsic defects lead to the extraction of misoriented nano domains, while those introduced by oxalic acid treatment lead further to the formation of small irregular mesopores. The resultant hierarchical zeolite shows substantially improved mesoporosity, in terms of mesopore volume and spatial distribution, and outstanding micropore acid site accessibility. These samples show superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene. Our approach highlights the significance of chemically induced extrinsic defects, which make zeolite dissolution go beyond the limits set by the zeolite structure and synthesis chemistry.

A new search–match procedure has been developed and tested which, in contrast to previously existing methods, does not use a set of lines identified from a diffraction pattern, but an optimized Rietveld fitting on the raw data. Modern computers with multicore processors allow the routine to be fast enough to perform the entire search in a reasonable time using quite large databases of crystal structures. The search–match is done using the crystal structures for all phases and the instrumental geometry, and as such can be applied to every kind of diffraction experiment, including X-rays, thermal/time-of-flight neutrons and electrons. The methodology can also be applied to nanocrystalline samples for which peak identification may be a problem. A web interface has been developed to permit easy testing and evaluation of the procedure. The quality of the results mainly depends on the availability of the sought phase in the structure database. The method permits not only phase identification but also a rapid quantification of the phases and their gross microstructural features, provided the instrumental function is known.