Secondary electrons

This radiation can be in the form of ions, electrons, or photons with sufficiently high energy, i.e. exceeding the ionization potential.

Photoelectrons can be considered an example of secondary electrons where the primary radiation are photons; in some discussions photoelectrons with higher energy (>50 eV) are still considered "primary" while the electrons freed by the photoelectrons are "secondary".

The range of secondary electrons depends on the energy.

Plotting the inelastic mean free path as a function of energy often shows characteristics of the "universal curve" [1] familiar to electron spectroscopists and surface analysts.

[2][3] This small distance allows such fine resolution to be achieved in the SEM.

Visualisation of a Townsend avalanche , which is sustained by the generation of secondary electrons in an electric field
Mean free path of low-energy electrons. Secondary electrons are generally considered to have energies below 50 eV. The rate of energy loss for electron scattering is very low, so most electrons released have energies peaking below 5 eV(Seiler, 1983).