Talk:Work function

Misleading/confusing statement in opening paragraph

This isn't my field, but I can't see how, "The work function is not a characteristic of a bulk material, but rather a property of the surface of the material (depending on crystal face and contamination)" isn't either confusing or simply wrong, depending on how one interprets it. The equation in the definition, -e(phi) - Ef, relates the work function to the Fermi level, which *is* dependent on the bulk material. If surface contamination dominates the work function to the extent that the bulk material is irrelevant, then the contaminant itself essentially becomes the bulk material. Perhaps something like, "The work function is a measured quantity dependent on a material's Fermi level and the characteristics of the surface on which it is being measured" would be more useful. Alt Livingston (talk) 21:37, 18 December 2016 (UTC)

Hmm, that sentence could be written better. The point is that for a given blob of conductor (constant Ef throughout), -e(phi) varies from surface to surface. Thus, the work function is also surface-depndent. (Indeed Ef has nothing to do with the surface material or bulk material, it is just the applied electrochemical potential). --Nanite (talk) 23:11, 18 December 2016 (UTC)

Work function on a glass surface

This is a question about work fonction for a glass surface: How does the work function change when the glass surface is 'wet' i.e. it is covered with few monolayers of water?

How doe the work function change when the glass surface is covered by some deposits? How does this change depends on the composition of these depostits? Will be very grateful for any information or for suggestions how to make such measurements.. Adam Para, para@fnal.gov

The question is 4 years old now, but an answer anyway - Yes, the work function can change, for example when a charge transfer from adsorbate to the surface occurs. One can reason that, when adsorbate electrons are transferred the surface, the work function will decrease, and vice versa. In the case of water adsorption this effect might be smaller then compared to ion adsorption, when the dipole of the surface will not be changed too much by the presence of the water.

See for example the paper concerning water and alkali metal ions on graphite is given in J. Chem. Phys. 125, 014708 (2006)

-- Mipmip 11:27, 27 November 2006 (UTC)

Work function between two materials

doing some research:

"defines characteristics of contact between two materials featuring different work function; for conductor-semiconductor contact determines whether contact is ohmic or rectifying."

Actually the ionization potential and work function of any metal is the same, but it is different for semiconductors or insulators. In fact work function is defined as the energy required to remove an electron from Fermi level to Vacuum level(energy level differences), but ionization potential is the energy required to remove the electron from the bottom of the conduction band to vaccuum level. I hope that I have clearly written to you, if not pleaze advice me.

http://arxiv.org/abs/physics/0207116

Dependence on charge of material

does the work function depend on the charge of the material? i would imagine it does. - Omegatron 20:45, May 20, 2005 (UTC)

looks like it does: "The same process will charge a spacecraft orbiting in the sunlight positively, to a few volts. Sunlight knocks out electrons from the surface and a few manage to escape, leaving the spacecraft positively charged; the situation then stabilizes, because the positive charge prevents any more electrons from leaving." - Omegatron 21:46, May 20, 2005 (UTC)

No, it tells you how much charge or voltage you would need to apply to the material to get an electron off. This is briefly mentioned as "retarding potential" in the article. 128.111.74.89 (talk) 21:43, 25 September 2008 (UTC)

equation issues

the equation needs to have all the terms defined. - Omegatron 20:45, May 20, 2005 (UTC)

changed 'metal' to 'conductor' in definition

Semiconductors for example have an associated work function so 'metal' in the definition is not strictly correct. I have changed it to 'conductor' which I believe to be more accurate. Andrew Gray Edinburgh University

Define the terms on the formula

This comment was left on the page:

You need to say what "N" is. You need to identify explicitly "V". From your definition I do not think it is the vacuum level. Also the fermi energy and the chemical potential (neither of which you define and assume the reader knows) aren't always the same thing. This is a place where people come to find out things they don't know. Define all your terms. A derivation would be nice.

I am postint it here, where it belongs -- Marco ^✉ 16:45, 8 October 2005 (UTC)

Surface effect is important for work function

I changed the definition and gave a new formula for work function because the original one did not take surface effect into account, which is important. Work function is not simply negative Fermi energy due to the "double charge layer" on the conductor surface. There is a very good description in Ashcroft's text book concerning this.

origin of term

does anyone have any idea where this term comes from? it kind of stands out relative to the names of other material properties.

Good question - why is it named a "function" if it is really just a "value"? —Preceding unsigned comment added by 24.28.74.115 (talk) 05:22, 16 March 2010 (UTC)

caesium

how come caesium is quoted as two different work function 1.9 eV in text and 2.14 eV in the table. which is correct? --Liamstone (talk) 06:38, 9 May 2008 (UTC)

according to http://symp15.nist.gov/pdf/p563.pdf, it is approximately 1.95eV

the CRC value of 2.14eV apparently refers to work done in 1969; an old AIP handbook lists both values and refers to work done in 1964. It looks to me like the CRC table is based on a 1977 JAppliedP paper by Michaelson (48, 4729) Tkirkman (talk) —Preceding comment was added at 17:45, 24 May 2008 (UTC)

delete?

"A saturation state of the filament current is reached, where a minor change in the filament current does not affect the beam current. The electron gun is then operated with the filament current very near the potential to overcome the work function (W)(Goldstein, 2003)"

For any normal material (and certainly for W as the data of Jones & Langmuir showed long ago) more filament current results in higher temperature (say, $T\propto {\sqrt {I}}$ )...so I always affects T

"filament current..near..potential" amps cannot be volts!

"When an electron gains energy, it jumps from one energy level to another in "quantum leaps." This process is called exciting an electron, and the higher energy levels are called "excited states" while the bottom level is called "ground state.""

true, but not really relevant as ejection is to a continuum of states..perhaps just a link to Electron excitation Tkirkman (talk) —Preceding comment was added at 17:32, 10 May 2008 (UTC)

I checked the cited source (Goldstein, 2003) out of our library and have determined that the cited material relates to the electron gun of an electron microscope. It is referring to the complex interaction of the Wehneit cylinder (or grid cap) and bias resistor that is used to focus the electron beam from the heated filament; it is not a fundamental part of thermionic emission or the work function. I am therefore going to edit the document to delete this material. Tkirkman (talk) —Preceding comment was added at 14:49, 9 June 2008 (UTC)

Proofs

Can anyone cite the equations from which most of the math here has been derived, for example, the integrals, differentials, from which the simple algebraic equations were derived? There are an aweful lot of stated equations which include constants with no showing of proof that these are completely valid and are standing definitions. Hence the discrepancies in the table.

Corrections

Also, in one statement "In the case of water adsorption this effect might be smaller then compared to ion adsorption" the statement is grammatically incorrect, it should be "In the case of water adsorption this effect might be smaller than compared to ion adsorption" "then" is a declarator [If a>b ; where ";" replaces 'then'] and "than" is a comparative [a>b where 'than' replaces '>']. The whole: If a is great than b then do the next step.

Inconsistency in Richardson Constant

The article states an exact number for the Richardson constant during the thermionic discussion, and then states that it's material specific during the later discussion on measurement techniques. It's possible that both are right to some extent (see this abstract http://www3.interscience.wiley.com/journal/112433017/abstract?CRETRY=1&SRETRY=0), but a sentence explaining the "real world" variations from theory should be included possibly in both places, perhaps?Grj23 (talk) 00:38, 1 July 2009 (UTC)

Work function definition

The opening line of the article states: "In solid-state physics, the work function (sometimes spelled workfunction) is the minimum energy (usually measured in electronvolts) needed to remove an electron from a solid ..."

However, it appears that a more precise definition in textbooks (for example, this reference) is that the work function is the energy difference between the vacuum energy level and the Fermi level of a solid. In a metal, because the Fermi level is in the conduction band, then this does indeed correspond to the energy required to remove an electron. However, in an insulator the Fermi level is in the band gap (no electron population) and so the energy required to remove an electron is now the energy difference between the vacuum energy level and the valence band, i.e. E_vac - E_V (Ga2re2t (talk) 12:34, 9 October 2012 (UTC))

Discussions of "vacuum level" are dangerous, because it sounds unique, but is not. For example, if I have a chunk of tungsten with a (111) crystallographic facet on one part of the surface and a (100) crystallographic facet on another part of the surface, and I have an electron sitting in the middle of the chunk, what is its workfunction? Well, it has a different value depending on which facet it gets pulled out of. That is hard to reconcile with the definition "the energy difference between the vacuum energy level and the fermi level". People use that definition anyway, and can get away with it because different facet workfunctions are usually only slightly different. :-P

(The crystal sets up a small electric field in the vacuum outside it, related to its spatially-varying surface dipole, so different parts of the vacuum have different voltages.)

Anyway, it sounds like the simplest solution is to change the wording: "the minimum energy needed to remove an electron from a solid (at the Fermi level) to a point immediately outside the solid surface", right? --Steve (talk) 19:42, 10 October 2012 (UTC)

The definition of work function is has two forms. You are talking about the surface work function, however there is also the work function defined by the energy required to move an electron from the Fermi level to 'infinity', in practice simple away from the sample surface. These values are rarely the same, the book by Holtz and Shulte "Workfunctions of Metals" covers this topic well. 128.250.0.195 (talk) 07:10, 6 April 2016 (UTC)

Moving the electron away to infinity would depend on the potential you apply at infinity... I don't see how that number could be an intrinsic property of the material. For example an electron ejected from an electron gun is accelerated to hundreds or thousands of eV as it moves away to infinity. But OK, I see maybe you are referring to the electron being far enough away to not be affected by image forces. That is indeed one of the sticky points about work function, especially when ambient electric fields are present (Schottky effect and all that). --Nanite (talk) 07:18, 6 April 2016 (UTC)

Wrong numbers in table?

I don't have access to the edition of the Handbook of Chemistry and Physics used as reference for the table in section 8, but comparing some of the numbers with the current edition shows big discrepancies for Silver: instead of 4.26-4.74 the current edition shows 4.52-4.74. Since 4.26 also shows up for Al in the next cell, I wonder if it's just a copy/paste error. I don't currently have the time to redo the entire table with the newer edition, and I can't just edit the one number without invalidating the reference. Lmartin78 (talk) 01:19, 24 February 2017 (UTC)

Add comment about Arrhenius Equation maybe??

I noticed in the Methods based on thermionic emission and Work function of cold electron collector sections that the equations looked strikingly similar to those of the Arrhenius equation, so I ran a Ctrl+F search for "Arrh" and got nothing. Would someone with deeper understanding of the equations involved be able to either edit in how they are related, or possibly explain why neither of these two articles reference each other as using very-similar equations? PolymathGirl (talk) 16:23, 18 April 2018 (UTC)

@Bush6984: The way I see it is like this: both the Arrhenius equation and thermionic emission both inherit from a more fundamental law of thermal excitation, which is the Boltzmann distribution. That's where the exponential term comes from. They're not entirely similar however --- you'll notice in the case of thermionic emission there is also a T^2 prefactor (which turns out to come from the three-dimensionality of the emission process). --Nanite (talk) 20:17, 18 April 2018 (UTC)

Liquid Surface Work Function?

Characterizing work function as solid state physics seems inadequate. "The same work function was found for solid or liquid mercury." Jim Bowery (talk) 18:02, 27 July 2020 (UTC)

References