X-rays mark the spot: grain mapping in polycrystals

Large high-quality single crystal samples are invaluable for many reasons: it could be that the purity of your samples is a key factor when searching for a certain phase or that grain boundaries will mean that the results of transport or scattering measurements will have no clear meaning. Typically, production of such single crystal samples starts with a larger polycrystalline sample being cut to pieces. We are uniquely well-equipped at Edinburgh University to produce high-quality polycrystals, but determining the size or location of the single crystals within these for extraction is a slow process. This is usually done by taking Laue x-ray patterns and making careful comparisons of these along the sample surface. By combining modern CCD detectors, which allow direct input of x-ray patterns into PCs, with now-standard image processing capabilities, and a large six-axis automated goniometer, we can automate the search for the single crystals in large polycrystals. I will talk, as an introduction, about how the large samples are produced, and then go over some of the difficulties encountered when trying to adapt the manual search for grains into an automated one, as well as showing an example of the grain maps we can get out. I will also mention how we can overcome the limitations of having a detector with a small surface area, by remapping images and stitching them together to give us larger ones.