Secondary electrons are electrons generated as
ionization products. They are called 'secondary' because they are generated by other radiation (the ''primary''
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
). 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".
Applications
Secondary electrons are also the main means of viewing images in the
scanning electron microscope (SEM). 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" familiar to electron spectroscopists and surface analysts. This distance is on the order of a few nanometers in metals and tens of nanometers in insulators. This small distance allows such fine resolution to be achieved in the SEM.
For
SiO2, for a primary electron energy of 100
eV, the secondary electron range is up to 20 nm from the point of incidence.
See also
*
Delta ray
*
Everhart-Thornley detector
References
{{DEFAULTSORT:Secondary Electrons
Electron states
Ions