Electron backscattered electron diffraction (EBSD)

EBSD is a method for determining the crystallographic orientation of mineral or metal grains relative to one another in a polished thin section. The technique can be used to determine preferred orientations among minerals produced by crystallization and deformation processes.

The method is based on backscattered electrons being channelled by crystalline lattice planes when the angle of an incident electron beam is near 30 degrees (sample tilt 70 degrees). The resulting emission presents an image with a pattern that is characteristic of the mineral's crystallography, and which can be captured by a digital camera. The variety of angles within the image, together with the locations where the bands meet (poles) are indicative of the crystal's symmetry and orientation. The band widths are a measure of the crystal d-spacing – however the EBSD technique is not as sensitive to d-spacing measurement as is traditional x-ray diffraction. For mineral identification, EBSD can only be used together with other information (e.g., x-ray composition).

The EBSD technique is a very powerful researchers' tool, especially when the spatial resolution of the SEM is taken into account. When identity of a mineral is known, the pole geometry can determine the orientation of the lattice to within a single degree. For example, it would be an easy task for EBSD to identify lattice twin planes (not otherwise visible), as well as subtle alignments due to strain or magmatic flow.









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