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Secondary electrons are electrons generated as
Secondary electrons are electrons generated as ionization
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
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
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
. Photoelectron
The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid sta ...
s 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 theinelastic mean free path The inelastic mean free path (IMFP) is an index of how far an electron on average travels through a solid before losing energy.
If a monochromatic primary beam of electrons is incident on a solid surface, the majority of incident electrons lose t ...
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
A delta ray is a secondary electron with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization, and is sometimes used to describe any recoil particle caused by secondary ionization. The ...
* Everhart-Thornley detector
References
{{DEFAULTSORT:Secondary Electrons Electron states Ions