Precession Electron Diffraction in the Transmission Electron Microscope

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• Dr Alex Eggeman, Dept of Materials Science & Metallurgy, University of Cambridge
• Tuesday 20 October 2009, 15:00-16:00
• Pfizer Seminar Room [4th floor], Materials Science and Metallurgy, Department of.

If you have a question about this talk, please contact Dr Jonathan Barnard.

There is currently great interest in the use of precession electron diffraction for acquiring high quality crystallographic information because of the seeming ability to remove dynamical effects from recorded intensities, usually a significant problem for direct structure solution. The precession geometry uses the upper deflectors to tilt the incident beam away from a dynamical zone-axis and then rotate the tilted beam to produce a hollow-cone of illumination. The lower deflectors then de-scan the precessed beams to recover the original zone-axis geometry. In this way it is possible to reduce the effect of strong coherent multi-beam conditions on the overall diffraction pattern.

The reduction in dynamical effects in the recorded diffraction intensities has an important role in improving the ability of researchers to successfully recover structures. In addition to this, there are other useful applications such as gathering point-group information about a sample and acquiring zone-axis data from beam sensitive samples.

In this talk I will introduce the historic motivation for precession electron diffraction and go through to show some of our recent results from known and unknown materials. In addition I aim to show some of the ways in which we are looking to determine the optimum conditions for using precession on a sample and possible avenues for improving it’s application.

This talk is part of the Electron Microscopy Group Seminars series.

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