Editing Photoelectric effect (section)

==Uses and effects==
===Photomultipliers===
{{Main|Photomultiplier}}
[[File:Photomultiplier schema en.png|thumb|Photomultiplier|alt=]]
These are extremely light-sensitive vacuum tubes with a coated [[photocathode]] inside the envelope. The photo cathode contains combinations of materials such as cesium, rubidium, and antimony specially selected to provide a low work function, so when illuminated even by very low levels of light, the photocathode readily releases electrons. By means of a series of electrodes (dynodes) at ever-higher potentials, these electrons are accelerated and substantially increased in number through [[secondary emission]] to provide a readily detectable output current. Photomultipliers are still commonly used wherever low levels of light must be detected.<ref name="Ref_Timothy">Timothy, J. Gethyn (2010) in Huber, Martin C.E. (ed.) ''Observing Photons in Space'', ISSI Scientific Report 009, ESA Communications, pp. 365–408, {{ISBN|978-92-9221-938-3}}</ref>

===Image sensors===
[[Video camera tube]]s in the early days of [[television]] used the photoelectric effect. For example, [[Philo Farnsworth]]'s "[[Image dissector]]" used a screen charged by the photoelectric effect to transform an optical image into a scanned electronic signal.<ref name="Ref_x">Burns, R. W. (1998) ''Television: An International History of the Formative Years'', IET, p. 358, {{ISBN|0-85296-914-7}}.</ref>

===Photoelectron spectroscopy===
{{Main|Photoemission spectroscopy|Angle-resolved photoemission spectroscopy|X-ray photoelectron spectroscopy}}
[[File:ARPES setup - ultraviolet source - sample holder - electron analyzer.svg|thumb|[[Angle-resolved photoemission spectroscopy]] ([[Angle-resolved photoemission spectroscopy|ARPES]]) experiment. Helium discharge lamp shines ultraviolet light onto the sample in ultra-high vacuum. Hemispherical electron analyzer measures the distribution of ejected electrons with respect to energy and momentum.|alt=]]
Because the kinetic energy of the emitted electrons is exactly the energy of the incident photon minus the energy of the electron's binding within an atom, molecule or solid, the binding energy can be determined by shining a [[monochromatic]] [[X-ray]] or [[Ultraviolet|UV]] light of a known energy and measuring the kinetic energies of the photoelectrons.<ref name="Stefan2003" /> The distribution of electron energies is valuable for studying quantum properties of these systems. It can also be used to determine the elemental composition of the samples. For solids, the kinetic energy and emission angle distribution of the photoelectrons is measured for the complete determination of the [[electronic band structure]] in terms of the allowed binding energies and momenta of the electrons. Modern instruments for angle-resolved photoemission spectroscopy are capable of measuring these quantities with a precision better than 1 meV and 0.1°.{{citation needed|date=November 2023}}

[[Photoelectron spectroscopy]] measurements are usually performed in a high-vacuum environment, because the electrons would be scattered by gas molecules if they were present. However, some companies are now selling products that allow photoemission in air. The light source can be a laser, a discharge tube, or a [[synchrotron radiation]] source.<ref name="Ref_aa">{{cite journal|title=Solid-State Photoelectron Spectroscopy with Synchrotron Radiation|doi=10.1126/science.206.4415.151|year=1979|last1=Weaver|first1=J. H.|last2=Margaritondo|first2=G.|journal=Science|volume=206|issue=4415|pages=151–156|pmid=17801770|bibcode=1979Sci...206..151W|s2cid=23594185}}</ref>

The [[Hemispherical electron energy analyzer|concentric hemispherical analyzer]] is a typical electron energy analyzer. It uses an electric field between two hemispheres to change (disperse) the trajectories of incident electrons depending on their kinetic energies.

===Night vision devices===
Photons hitting a thin film of alkali metal or [[semiconductor]] material such as [[gallium arsenide]] in an [[image intensifier]] tube cause the ejection of photoelectrons due to the photoelectric effect. These are accelerated by an [[electrostatic field]] where they strike a [[phosphor]] coated screen, converting the electrons back into photons. Intensification of the signal is achieved either through acceleration of the electrons or by increasing the number of electrons through secondary emissions, such as with a [[micro-channel plate]]. Sometimes a combination of both methods is used. Additional kinetic energy is required to move an electron out of the conduction band and into the vacuum level. This is known as the [[electron affinity]] of the photocathode and is another barrier to photoemission other than the forbidden band, explained by the [[band gap]] model. Some materials such as gallium arsenide have an effective electron affinity that is below the level of the conduction band. In these materials, electrons that move to the conduction band all have sufficient energy to be emitted from the material, so the film that absorbs photons can be quite thick. These materials are known as negative electron affinity materials.{{citation needed|date=November 2023}}

===Spacecraft===
The photoelectric effect will cause [[spacecraft]] exposed to sunlight to develop a positive charge. This can be a major problem, as other parts of the spacecraft are in shadow which will result in the spacecraft developing a negative charge from nearby plasmas. The imbalance can discharge through delicate electrical components. The [[static electricity|static charge]] created by the photoelectric effect is self-limiting, because a higher charged object does not give up its electrons as easily as a lower charged object does.<ref>{{cite book
| last=Lai
| first=Shu T.
| title=Fundamentals of Spacecraft Charging: Spacecraft Interactions with Space Plasmas
| publisher=Princeton University Press
| edition=illustrated
| year=2011
| pages=1–6
| isbn=978-0-691-12947-1
}}</ref><ref name="Ref_ab">{{cite news|url=http://holbert.faculty.asu.edu/eee460/spacecharge.html|title=Spacecraft charging|work=Arizona State University}}</ref>

===Moon dust===
Light from the Sun hitting lunar dust causes it to become positively charged from the photoelectric effect. The charged dust then repels itself and lifts off the surface of the [[Moon]] by [[electrostatic levitation]].<ref name="Ref_ac">[https://science.nasa.gov/science-news/science-at-nasa/2005/30mar_moonfountains/ Bell, Trudy E., "Moon fountains"], NASA.gov, 2005-03-30.</ref><ref name="Ref_ad">[http://www.spacedaily.com/reports/Dust_Gets_A_Charge_In_A_Vacuum.html Dust gets a charge in a vacuum]. spacedaily.com, July 14, 2000.</ref> This manifests itself almost like an "atmosphere of dust", visible as a thin haze and blurring of distant features, and visible as a dim glow after the sun has set. This was first photographed by the [[Surveyor program]] probes in the 1960s,<ref>{{cite conference |title= Horizon-Glow and the Motion of Lunar Dust| author=Criswell D.R. |year=1973 |publisher=Springer, Dordrecht |book-title=Photon and Particle Interactions with Surfaces in Space |location=Noordwijk, the Netherlands |conference=6th Eslab Symposium | editor=R. J. L. Grard | doi=10.1007/978-94-010-2647-5_36}}</ref> and most recently the [[Chang'e 3]] rover observed dust deposition on lunar rocks as high as about 28&nbsp;cm.<ref>{{cite journal |author=Yan Q. |author2=Zhang X. |author3=Xie L. |author4=Guo D. |author5=Li Y. |author6=Xu Y. |author7=Xiao Z. |author8=Di K. |author9=Xiao L. | title=Weak Dust Activity Near a Geologically Young Surface Revealed by Chang'E-3 Mission | journal=Geophysical Research Letters | volume=46 | pages=9405–9413 | doi=10.1029/2019GL083611 | year=2019| issue=16 | bibcode=2019GeoRL..46.9405Y | doi-access=free }}</ref> It is thought that the smallest particles are repelled kilometers from the surface and that the particles move in "fountains" as they charge and discharge.<ref>{{cite journal | title=A dynamic fountain model for lunar dust | doi=10.1016/j.asr.2005.04.048 | journal=Advances in Space Research | volume=37 | issue=1 | year=2006 | pages=59–66 | author1=Timothy J. Stubbs | author2=Richard R. Vondrak | author3=William M. Farrell| bibcode=2006AdSpR..37...59S | hdl=2060/20050175993 | s2cid=56226020 | hdl-access=free }}</ref>