3D Electron Backscatter Diffraction (3D EBSD)

Electron Backscatter Diffraction (EBSD) provides information from the sample surface. However, there is often a requirement to get the same type of information from a 3D volume, in order to study grain structures, 3D grain sizes and interface boundaries. Depending on the size of the volume of interest, this can be achieved in several ways: For large scale features it is possible to use mechanical sectioning techniques to expose a new surface at different depths of the sample, and to analyse at these different depths. Alternatively, carefully controlled broad ion beam milling can be used to incrementally remove layers of material. Both of these techniques have recently been automated (in some cases with the use of a robot arm to transfer the sample from the scanning electron microscope (SEM) to the polishing rig), enabling efficient generation of 3D microstructures on the scales of 100s μm to mm.

For smaller scale features, it is not practical to take the sample out of the SEM chamber and then reposition it to collect more data. A solution is to use an SEM combined with a focused ion beam (FIB-SEM), where the ion column is used to mill away the surface between each EBSD map.

This process is also typically automated. To achieve this the sample must be placed in a geometry suitable for both milling, with the ion beam parallel to the sample surface, and for EBSD data collection.

Geometry set up for automated 3D EBSD using a FIB-SEM. The illustration shows the set-up for the EBSD acquisition step; for the FIB milling, the sample would be rotated 180° and tilted so that the ion beam is parallel to the surface to be analysed.