Professor Dave Prior
Electron back scatter diffraction is a technique which we use in a scanning electron microscope, and it enables us to measure the crystal structure and orientation for a very small point on a sample surface. If you have an electron beam coming in an SEM and this electron beam comes down and it hits a sample at a point, the electrons go into a sample and there’s a process which scatters them into every possible direction. Because crystalline materials have preferred lattice planes within them, and you can see the facets on this crystal are defining where some of those lattice planes are, then the diffraction process in crude terms focuses the outcoming electrons in those lattice planes. So this particular lattice plane will have a focused band of electrons coming out in all directions parallel to that. When you deform this, the crystal is allowed to slide on those planes of weakness, and what happens is that certain crystallographic directions get lined up. So if we can measure the way they’re lined up, it can tell us something about what were the temperature conditions, for example, under which the rock deformed and what way was it being pulled or pushed, because the alignment will relate to whether it was pulled out this way or whether it was pulled out that way.
Professor David Prior, Department of Geology, University of Otago.