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Dear Colleagues,
The past decade has been a very exciting time for electron crystallography. Once limited to inorganic materials resistant to radiation damage, electron crystallography is now being applied to less-robust crystals, including hybrid materials, pharmaceutical molecules, and even proteins, using the transmission electron microscope.
The recent progress owes much to advances in instrumentation. Hardware and software originally developed for electron tomography in the imaging mode are employed to acquire diffraction data analogous to data collection in X-ray crystallography. Low-dose imaging, developed for imaging protein samples, avoids non-essential exposure of the sample to the electron beam. Cryo-electron microscopy, renowned for protein structural resolution by single-particle analysis, not only allows protein crystals to be preserved in their native hydrated state, but also limits the radiation damage when crystals are exposed to the electron beam. Lastly, the availability of hybrid pixel detectors for electron microscopes has definitely accelerated the expansion of the use of electron crystallography on radiation-sensitive materials.
With all these advances, many areas are under active development. Whereas conventional X-ray crystallography requires crystals of over a micron in size, electron diffraction is limited to thin crystals due to the mean-free path of the electron. Beyond the range of optical microscopes, the detection of crystals in this size range is a challenge. The production of nanocrystals—especially well-diffracting ones—requires a different approach than in conventional crystallography. Electron microscopy grid preparation techniques for these nanocrystals are also being optimized. Detectors are constantly being improved, allowing for larger detector area and better tolerance for higher electron energy. X-ray crystallography software, which most data analyses of electron diffraction rely on, is being tuned to truly adapt to electron crystallography. Information from electron diffraction that are unavailable from X-ray diffraction (e.g., charge state) is being exploited. Potential problems, such as dynamical scattering, are also being tackled. This Special Issue gives us an opportunity to get an overview of these topics.
We welcome all contributions covering the application of electron crystallography to a broad range of radiation-sensitive materials and the development in the different areas of this exciting and quickly expanding discipline.
Dr. Guy Schoehn
Dr. Dominique Housset
Dr. Wai Li Ling
Guest Editors
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