Goals:

The special interest group on electron crystallography is to promote electron diffraction and imaging as a standard technique for crystallographic solution of materials, molecules and bio-structures and provide a forum of discussion for further development of electron crystallography.

Electron Crystallography: The Situation, Challenge and Future:

Electron diffraction and imaging are powerful techniques for imaging three-dimensional structures and determination of difficult structures in both materials science and biology. Recent developments in microscopy technology have significantly improved quantitative analysis of electron diffraction intensities and brought new types of highly accurate electron diffraction techniques for structure determination, refinement and construction of three-dimensional structure of macromolecules.

Electron beam is uniquely different from X-ray and neutron scattering from its ability to form images and small probes (angstroms). Equally important, electrons interact very strongly with matter through the strong Coulomb potential. Because of this, electrons are very sensitive to bonding electrons at low scattering angle and to nuclei at high scattering angle. As result of the strong interaction, multiple scattering or dynamic effect often needs to be included in the interpretation in electron diffraction. Complication in the relationship between diffraction intensity and structure factor from multiple scattering has been a major obstacle in the wider application of electron beams as a major structure solution tool. However, recent development with the development of advanced algorithms show that multiple scattering effect can be effectively included in the structure refinement process and can be used to advantage for high accuracy measurement of structure factors to give details about bonding electrons. Experimental techniques for electron intensity collection by procession also reduce the dynamic effects.

High-resolution electron imaging at atomic resolution provide the phase information and three-dimensional morphology. 3-D reconstruction and tomography are established techniques for reconstruction of cell structures and single macromolecules. Direct determination of structure from high resolution images has been proved feasible a number of important inorganic structures. Phase extension in combination with electron diffraction data can be used to further improve the accuracy of method.

Rapid developments in electron microscope technology promises sub-angstrom electron imaging resolution and better and fast data collection with electron energy filtering and parallel detectors. Meanwhile, the trend toward nano- and bio-science and technology demands the development of diffraction techniques for single molecules, clusters, nanocrystals and other low-dimensional objects. Electron beam has the imaging and diffraction capabilities at the length scale critical to these areas and is well positioned to meet these challenges.

Areas of Focus:

Electron microscopy and diffraction is a flexible technique with diverse fields of applications. The special interest group on electron crystallography will focus the following common areas of interest that cross the boundary of materials science and biology and promote cross-disciplinary exchange:

1) Development of electron diffraction theory and novel imaging techniques
2) Electron data collection
3) Structure determination of difficult crystals
4) 3-D tomography and structure determination of biological macromolecules
5) Structure determination of low-dimensional objects, including surfaces, clusters, wires and tubes
6) Structure determination of ill-defined crystals, such as modulated structures, amorphous materials, and quasicrystals