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Triennial report of International Union of Crystallography Commission on Electron Diffraction

Jan 2002 - Dec 2004

Written Feb 2005 by John C. H. Spence.

The last three years have been a time of great excitement in electron diffraction and microscopy, resulting partly from the boom in nanoscience, and partly from breakthroughs in new instrumentation. These have included the commercial development of aberration-correctors and monochromators, and of field-emission scanning transmission instruments (STEMs) and TEMs capable of imaging and spectroscopy with sub-Angstrom spatial resolution, a long-sought goal finally attained. The field-emission source (brighter than current generation synchrotron/undulator systems) has allowed inner-shell energy-loss spectra and images of individual dopant atoms in crystals to be obtained, while Prof Zewail's Nobel Prize has spurred the development of sub-picosecond electron diffraction systems. The discovery of the carbon nanotube by high-resolution TEM has stimulated much new high-resolution in-situ imaging at high pressures for catalysts, while the new electron precession camera has been fully developed and applied. Oxygen ordering in high-Tc materials and defects at interfaces continue to be imaged at atomic resolution, while a major development has been the achievement of tomographic imaging in materials science by TEM at sub-nanometer resolution for mesoporous materials. The sub-nanometer probe of the STEM, and the much greater sensitivity of electron structure factors to ionicity than X-ray, at low angles, has allowed highly accurate extinction-free quantification of convergent-beam electron diffraction patterns to produce charge-density maps of unprecedented precision for the study of bonding. In biology, cryo-EM has produced whole-cell tomographic images at 5nm resolution, while single-particle work continues to explore the ribosome and other macromolecules and membrane proteins which cannot be crystallised at sub-nanometer resolution.

These years have been crowded with teaching activity and conferences, some of which included the well attended (90 attendees) Erice/NATO school in Sicily in summer 2004 on electron crystallography, and workshops on time-resolved electron diffraction and imaging at Livermore in summer 2004, international and national conferences on electron microscopy in many countries, the 2004 Gordon conference on charge densities, a school on electron crystallography in Berkeley in April 2004, similar schools in Bejing (100 attendees in Dec 2002) and Moscow amongst many others. The European Crystallography Meeting in Budapest (August 2004) held special sessions on electron crystallography. D. Dorset won the Patterson award of the ACA in 2002 for his work in electron crystallography of organic materials. There have been several special issues of journals devoted to electron crystallography and atomic-resolution electron microscopy.

The CED now has a web page, accessed thro the IUCr web page and CED links, which contains a list of teaching materials including books and free software. Also given is a list of conferences and links to web pages of many active research groups , arranged by applications in materials science and biology. The CED commission, chaired by J. Spence, will meet at the IUCr Congress in Florence, 2005.