Electron Backscatter Diffraction

Electron backscatter diffraction (EBSD) is a microanalytical technique for SEM to study crystal structure and crystal orientation of sample surface down to nanoscale. EBSD provides valuable information on crystalline and polycrystalline specimens that help researchers characterise and understand properties of materials. The EBSD  provides information about local crystal orientation, phase, characterisation of grain morphology, grain boundary, as well as orientation texture, internal stresses and defects in samples and many others can be determined with this microanalytical technique.  
The EBSD principle is based on a Kikuchi-like electron diffraction of focused electron beam. Electrons from the primary beam are diffracted on crystal planes while leaving the sample surface as backscattered electrons.  The intensity of backscattered signal is therefore modulated by the diffraction condition of the crystal and forms a diffraction pattern specific for local crystal structure and its orientation.
The pattern is captured on a fluorescent screen of fast EBSD. In a typical setup the electron beam of the SEM or FIB-SEM system impinges a flat polished surface of the sample which is tilted by 70° and facing the EBSD screen. This high tilt of the sample maximises the yield of diffracted electrons in order to obtain the best contrast of diffraction patterns. The fluorescent screen is placed close the sample and almost perpendicular to the beam axis. A focusing optics and a fast digital camera are behind this screen. 

The image of the pattern is synchronized with a beam scanning and further processed by dedicated software, which can automatically detect the orientation according the Kikuchi lines position and width. The results of EBSD measurements are shown in the so-called crystal orientation maps which are obtained by extracting information on crystal orientation from diffraction patterns at each point of the scanned region of interest. Such maps consist of colour-coded points, each colour corresponding to a specific crystal orientation, phase or other parameter.  For texture evaluation an orientation distribution function can be calculated out of the map data and shown as orientation density in various diagrams such as pole figures.

A grain is identified as a region of the sample where the crystal orientation is the same within a certain orientation angle tolerance. In this way, the EBSD provides complete quantitative microstructural information of the specimen. The EBSD technique can also be combined with energy dispersive x-ray spectrometry (EDS) for more precise phase identification – based on both, elemental composition and crystallography. Combining EBSD with FIB-SEM serial sectioning (i.e. FIB-slicing followed by EBSD data acquisition of each new surface), a 3D EBSD sample reconstruction can be achieved.

 
Electron Backscatter Diffraction
Microstructure of UFG copper after annealing at 473 K EBSD map