View source for Physics:Secondary electrons

{{short description|Electrons generated as ionization products}}
[[File:Electron avalanche.gif|thumb|Visualisation of a Townsend avalanche, which is sustained by the generation of secondary electrons in an electric field]]

'''Secondary electrons''' are [[Physics:Electron|electron]]s generated as [[Physics:Ionization|ionization]] products. They are called 'secondary' because they are generated by other [[Physics:Radiation|radiation]] (the ''primary'' radiation). This radiation can be in the form of [[Physics:Ion|ion]]s, electrons, or [[Physics:Photon|photon]]s 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&nbsp;[[Physics:Electronvolt|eV]]) are still considered "primary" while the electrons freed by the photoelectrons are "secondary".

[[Image:Electron MFP and Range.PNG|right|thumb|300px|'''Mean free path of low-energy electrons.''' Secondary electrons are generally considered to have energies below 50&nbsp;eV. The rate of energy loss for [[Physics:Electron scattering|electron scattering]] is very low, so most electrons released have energies peaking below 5&nbsp;eV(Seiler, 1983).]]

==Applications==
Secondary electrons are also the main means of viewing images in the [[Physics:Scanning electron microscope|scanning electron microscope]] (SEM). The range of secondary electrons depends on the energy. Plotting the [[Physics:Inelastic mean free path|inelastic mean free path]] as a function of energy often shows characteristics of the "universal curve" <ref>{{cite book | last=Zangwill | first=Andrew | title=Physics at surfaces | url=https://archive.org/details/physicsatsurface00zang | url-access=limited | publisher=Cambridge University Press | publication-place=Cambridge Cambridgeshire New York | year=1988 | isbn=978-0-521-34752-5 | oclc=15855885 | page=[https://archive.org/details/physicsatsurface00zang/page/n30 21]}}</ref> 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.<ref>{{cite journal | last=Seiler | first=H | title=Secondary electron emission in the scanning electron microscope | journal=Journal of Applied Physics | publisher=AIP Publishing | volume=54 | issue=11 | year=1983 | issn=0021-8979 | doi=10.1063/1.332840 | pages=R1–R18| bibcode=1983JAP....54R...1S }}</ref><ref>{{cite journal | last=Cazaux | first=Jacques | title=Some considerations on the secondary electron emission, δ, from e− irradiated insulators | journal=Journal of Applied Physics | publisher=AIP Publishing | volume=85 | issue=2 | date=15 January 1999 | issn=0021-8979 | doi=10.1063/1.369239 | pages=1137–1147}}</ref> This small distance allows such fine resolution to be achieved in the SEM.

For [[Chemistry:Silicon dioxide|SiO<sub>2</sub>]], for a primary electron energy of 100&nbsp;[[Physics:Electronvolt|eV]], the secondary electron range is up to 20&nbsp;nm from the point of incidence.<ref>{{cite journal | last1=Schreiber | first1=E. | last2=Fitting | first2=H.-J. | title=Monte Carlo simulation of secondary electron emission from the insulator SiO2 | journal=Journal of Electron Spectroscopy and Related Phenomena | publisher=Elsevier BV | volume=124 | issue=1 | year=2002 | issn=0368-2048 | doi=10.1016/s0368-2048(01)00368-1 | pages=25–37}}</ref><ref>{{cite journal | last1=Fitting | first1=H.-J. | last2=Boyde | first2=J. | last3=Reinhardt | first3=J. | title=Monte-Carlo Approach of Electron Emission from SiO2 | journal=Physica Status Solidi A | publisher=Wiley | volume=81 | issue=1 | date=16 January 1984 | issn=0031-8965 | doi=10.1002/pssa.2210810136 | pages=323–332| bibcode=1984PSSAR..81..323F }}</ref>

==See also==
*[[Physics:Delta ray|Delta ray]]
*[[Engineering:Everhart-Thornley detector|Everhart-Thornley detector]]

==References==

{{Reflist}}{{Electron microscopy}}{{DEFAULTSORT:Secondary Electrons}}
[[Category:Electron states]]
[[Category:Ions]]

{{Sourceattribution|Secondary electrons}}