Editing Work function (section)

== Applications ==

;[[Thermionic emission]]: In thermionic [[electron gun]]s, the work function and temperature of the [[hot cathode]] are critical parameters in determining the amount of current that can be emitted. [[Tungsten]], the common choice for vacuum tube filaments, can survive to high temperatures but its emission is somewhat limited due to its relatively high work function (approximately 4.5 eV). By coating the tungsten with a substance of lower work function (e.g., [[thorium]] or [[barium oxide]]), the emission can be greatly increased. This prolongs the lifetime of the filament by allowing operation at lower temperatures (for more information, see [[hot cathode]]).
;[[Band bending]] models in solid-state electronics: The behavior of a solid-state device is strongly dependent on the size of various [[Schottky barrier]]s and [[heterojunction|band offset]]s in the junctions of differing materials, such as metals, semiconductors, and insulators. Some commonly used heuristic approaches to predict the band alignment between materials, such as [[Anderson's rule]] and the [[Schottky–Mott rule]], are based on the thought experiment of two materials coming together in vacuum, such that the surfaces charge up and adjust their work functions to become equal just before contact. In reality these work function heuristics are inaccurate due to their neglect of numerous microscopic effects. However, they provide a convenient estimate until the true value can be determined by experiment.<ref>[[Herbert Kroemer]], "[https://www.nobelprize.org/nobel_prizes/physics/laureates/2000/kroemer-lecture.html Quasi-Electric Fields and Band Offsets: Teaching Electrons New Tricks]" Nobel lecture</ref><ref>{{cite web|url=http://academic.brooklyn.cuny.edu/physics/tung/Schottky/systematics.htm|title=Barrier Height Correlations and Systematics|website=academic.brooklyn.cuny.edu|access-date=11 April 2018}}</ref>
;Equilibrium electric fields in vacuum chambers: Variation in work function between different surfaces causes a non-uniform electrostatic potential in the vacuum. Even on an ostensibly uniform surface, variations in {{math|''W''}} known as patch potentials are always present due to microscopic inhomogeneities. Patch potentials have disrupted sensitive apparatus that rely on a perfectly uniform vacuum, such as [[Casimir force]] experiments<ref>{{Cite journal | doi = 10.1103/PhysRevA.85.012504| title = Modeling electrostatic patch effects in Casimir force measurements| journal = Physical Review A| volume = 85| issue = 1| pages = 012504| year = 2012| last1 = Behunin | first1 = R. O.| last2 = Intravaia | first2 = F.| last3 = Dalvit | first3 = D. A. R.| last4 = Neto | first4 = P. A. M. | last5 = Reynaud | first5 = S.|arxiv = 1108.1761 |bibcode = 2012PhRvA..85a2504B | s2cid = 119248753}}</ref> and the [[Gravity Probe B]] experiment.<ref>{{Cite journal | doi = 10.1103/Physics.4.43| title = Finally, results from Gravity Probe B| journal = Physics| volume = 4| issue = 43| pages = 43| year = 2011| last1 = Will | first1 = C. M. |arxiv = 1106.1198 |bibcode = 2011PhyOJ...4...43W | s2cid = 119237335}}</ref> Critical apparatus may have surfaces covered with molybdenum, which shows low variations in work function between different crystal faces.<ref name="venables">{{cite web|url=http://venables.asu.edu/qmms/PROJ/metal1a.html|title=Metal surfaces 1a|website=venables.asu.edu|access-date=11 April 2018|archive-date=29 December 2016|archive-url=https://web.archive.org/web/20161229160647/http://venables.asu.edu/qmms/PROJ/metal1a.html|url-status=dead}}</ref>
;[[Contact electrification]]: If two conducting surfaces are moved relative to each other, and there is potential difference in the space between them, then an electric current will be driven. This is because the [[surface charge]] on a conductor depends on the magnitude of the electric field, which in turn depends on the distance between the surfaces. The externally observed electrical effects are largest when the conductors are separated by the smallest distance without touching (once brought into contact, the charge will instead flow internally through the junction between the conductors). Since two conductors in equilibrium can have a built-in potential difference due to work function differences, this means that bringing dissimilar conductors into contact, or pulling them apart, will drive electric currents. These contact currents can damage sensitive microelectronic circuitry and occur even when the conductors would be grounded in the absence of motion.<ref>{{Cite journal | last1 = Thomas Iii | first1 = S. W. | last2 = Vella | first2 = S. J. | last3 = Dickey | first3 = M. D. | last4 = Kaufman | first4 = G. K. | last5 = Whitesides | first5 = G. M. | title = Controlling the Kinetics of Contact Electrification with Patterned Surfaces | doi = 10.1021/ja902862b | journal = Journal of the American Chemical Society | volume = 131 | issue = 25 | pages = 8746–8747 | year = 2009 | pmid =  19499916| bibcode = 2009JAChS.131.8746T | citeseerx = 10.1.1.670.4392 }}</ref>