Dislocation electron tomography and precession electron diffraction - minimising the effects of dynamical interactions in real and reciprocal space

Two techniques that explore how minimising the effects of dynamical interactions can lead to an improved understanding of underlying structural information in real and reciprocal space are reviewed and extended. In this special issue dedicated to David Cockayne, the techniques of dislocation tomography and precession electron diffraction described in this paper echo very strongly David's interests in weak-beam imaging of dislocations and structure determination using kinematic diffraction. The weak-beam dark-field (WBDF) technique has been extended to three dimensions to visualise networks of dislocations in a number of materials systems. Some of the issues that arise from using this technique are explored. It is shown how the overall reconstruction can be improved through careful image processing. Using STEM medium-angle annular dark field (MAADF) imaging many of the artefacts seen in the WBDF technique are minimised, with a significant increase in the ease of acquisition and processing the data. Recent developments in precession electron diffraction and the desire to better understand and optimise the technique are reported. In particular, the idea of 'intensity ordering' is explored as a means of judging the likely success of structure determination from precession data.