Practical Electron Microscopy and Database

Backscattered electrons are defined as electrons scattered by high angles that they reverse their travel direction. The emission of electrons, by the surface of a solid object when it is bombarded by electrons, was discovered in 1902 by the German physicists L. Austin and H. Starke. The electron beam bombarding the object are called primary beam, and the emitted electrons are called secondary electrons. These electrons’ energy and momentum prove to be sufficiently great to surmount the potential barrier on the surface of the object and leave the surface. The reflected electrons without energy loss are called elastical backscattering electrons and the reflected electrons with energy loss are called in-elastical backscattering electrons. All three groups of electrons are present in the recorded electron flow.

According to Rutherford scattering cross-section, we have,
            ------------------------------- [4821]
where,
           T -- The kinetic energy of incident electrons.
           θ -- The scattering angle.
Due to the T⁻² dependence in Equation 4821, the probability of the electron backscattering is small for incident electrons, at several hundred keV, passing through thin specimens.

Therefore, the properties of secondary electrons are known to depend on:
         i) The energy of incident electrons,
         ii) the surface material.

Backscattered electrons (BSE) provide information about chemical composition (Z contrast), topography, and crystallography (via channeling).

In accurate EDS quantifications, the appropriate corrections such as stopping power, back-scattering, X-ray absorption and secondary X-ray fluorescence within the specimen, should be evaluated and applied to the raw EDS data.

Table 4821. Existence of backscattering electrons in nature.