EBSD Technology (Electron BackScatter Diffraction)

EBSD is the acronym for electron backscatter diffraction*. This technology adds microstructural analysis capabilities to scanning electron microscopes. It is usually used to examine the crystallographic orientation of crystalline materials. Before the introduction of EBSD this type of analysis was mainly performed by X-ray diffraction techniques, now electrons in the SEM can be used as well.

The performance of EBSD analyses requires the installation of an EBSD detector, like one of Bruker's e^-Flash detectors, on the SEM-sample chamber. An EBSD detector is equipped with a phosphorescent screen that registers the electrons diffracted by the specimen. The produced image is then recorded by a fast CCD-camera.

Electron Backscatter Diffraction Patterns

What is registered are so-called electron backscatter diffraction patterns (EBSP). These can be best observed under specific geometrical conditions. In order to fulfill these conditions the sample has to be tilted by approximately 70° towards the screen of the EBSD detector, which is mounted (in case of the e-Flash: more or less) horizontally. Also, samples have to be highly polished for optimum analytical results.

Bragg condition

If electrons impinge on the sample they can interact with the lattice of the crystallite they hit. If this interaction fulfills the so-called Bragg condition the according electrons are diffracted into well-defined directions. The multitude of electrons diffracted under different angles produces the bands which form an EBSD pattern.

Each of the bands corresponds to a crystal lattice plane that diffracted the electrons. It can be indexed by the Miller indices of that lattice plane. One therefore speaks of indexing an EBSP to identify crystal structure and determine orientation of the analyzed crystallite.

EBSP - Additional information on crystal lattice perfection

Apart from structure and orientation information EBSPs contain additional information on crystal lattice perfection, like local strain, deformation, and of course also on grain boundaries (if the orientation changes abruptly).

There are a number of options to display results of EBSD analyses. This can either be in form of point results, like the patterns themselves, collections of point results, like pole figures and inverse pole figures and also as two-dimensional orientation maps. The latter are composed of point measurements on a grid, very much like X-ray elemental mapping.

*Also sometimes referred to as backscatter Kikuchi diffraction (BKD).