Editing Electron microscope (section)

=== Backscattered electrons ===
Backscattered electrons (BSE) are those emitted back out from the specimen due to beam-specimen interactions where the electrons undergo [[Elastic scattering|elastic]] and [[Inelastic scattering|inelastic]] scattering. They have energies from 50 eV up to the energy of the primary beam by conventional definition. Backscattered electrons can be used for both imaging and to form an [[electron backscatter diffraction]] (EBSD) image that can be used to determine the crystallographic structure of the specimen.<ref name=":1" />[[File:EBSD_(001)_Si.png|thumb|Electron backscatter diffraction pattern for (001) single crystal silicon crystals taken at 20kV using Oxford S2 detector]]

Since heavy elements (high atomic number) backscatter electrons more strongly than light elements (low atomic number), and thus appear brighter in the image, BSEs are used to detect contrast between areas with different chemical compositions.<ref name=":1" />  Dedicated backscattered electron detectors are positioned above the sample in a "doughnut" type arrangement, concentric with the electron beam, maximizing the solid angle of collection. BSE detectors are usually either of scintillator or of semiconductor types. When all parts of the detector are used to collect electrons symmetrically about the beam, atomic number contrast is produced. However, strong topographic contrast is produced by collecting back-scattered electrons from one side above the specimen using an asymmetrical, directional BSE detector; the resulting contrast appears as illumination of the topography from that side. Semiconductor detectors can be made in radial segments that can be switched in or out to control the type of contrast produced and its directionality.<ref name=":1" />