Work function: Difference between revisions

Revision as of 16:52, 28 April 2022

Revision as of 01:35, 11 July 2022

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* Absolute methods employ electron emission from the sample induced by photon absorption (photoemission), by high temperature (thermionic emission), due to an electric field ([[field electron emission]]), or using [[quantum tunneling|electron tunnelling]].

* Relative methods make use of the [[contact potential difference]] between the sample and a reference electrode. Experimentally, either an anode current of a diode is used or the displacement current between the sample and reference, created by an artificial change in the capacitance between the two, is measured (the [[Kelvin probe force microscope|Kelvin Probe]] method, [[Kelvin probe force microscope]]). However, absolute work function values can be obtained if the tip is first calibrated against a reference sample.<ref name="calib">{{Cite journal | last1 = Fernández Garrillo | first1 = P. A. | last2 = Grévin | first2 = B. | last3 = Chevalier | first3 = N. | last4 = Borowik | first4 = Ł. | title = Calibrated work function mapping by Kelvin probe force microscopy | doi = 10.1063/1.5007619 | journal = Review of Scientific Instruments | volume = 89 | issue = 4 | pages = 043702 | year = 2018 | pmid = 29716375|bibcode = 2018RScI...89d3702F| url = https://hal.archives-ouvertes.fr/hal-02277068/file/Garrillo_2018_1.5007619.pdf }}</ref>

=== Methods based on thermionic emission ===

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=== Temperature dependence of the electron work function ===

The electron behavior in metals varies with temperature and is largely reflected by the electron work function. A theoretical model for predicting the temperature dependence of the electron work function, developed by Rahemi et al. <ref>{{cite journal|last1=Rahemi|first1=Reza|last2=Li|first2=Dongyang | title=Variation in electron work function with temperature and its effect on the Young's modulus of metals| journal=Scripta Materialia| date=April 2015|volume=99|issue=2015|pages=41–44 | doi=10.1016/j.scriptamat.2014.11.022 | arxiv=1503.08250|s2cid=118420968 }}</ref> explains the underlying mechanism and predicts this temperature dependence for various crystal structures via calculable and measurable parameters. In general, as the temperature increases, the EWF decreases via <math display="inline">\varphi(T)=\varphi_0-\gamma\frac{(k_\text{B}T)^2}{\varphi_0}</math> and <math>\gamma</math> is a calculable material property which is dependent on the crystal structure (for example, BCC, FCC). <math>\varphi_0</math> is the electron work function at T=0 and <math>\beta</math> is constant throughout the change.

== References ==