For the cold field-emission electron gun, the energy distribution of the primary beam captured in an EELS CCD presents an asymmetry characteristic.
What causes this and are there any references?
I'm not sure if this will answer your question
https://www-project.slac.stanford.edu/lc/wkshp/RFBreakdwn/references/fowler.pdf
Not sure if you now have an answer to this question. The answer given previously is not very helpful. The quantity that is measured is the total energy distribution.This is determined by a combination of: (a) the 3-dimensional energy distribution of electrons inside the emitter; and (b) how the transmission probability for emission varies with the so-called "normal energy" (component of electron energy normal to the surface). The mathematics is a bit tricky, and much of the literature is not very helpful. A simple-minded answer is that the fall-off on the right-hand side relates to the fall-off with energy in the Fermi-Dirac distribution function and the fall-off on the left-hand side occurs because the transmission probability deceases as the height of the tunnelling barrier seen by the electron increases.
Some appropriate references are: J.W. Gadzuk & E.W. Plummer, Rev. Mod. Phys. 45, 487 (1973); L.W. Swanson & A.E. Bell, Adv. Electronics Electron Phys. 32, 193 (1973) (see Appendix). There are many other references. Try a search on “field emission energy distributions”.
As Dr. Richard G. Forbes said, this is the total energy distribution of the emitted electrons. For cold field emission experiments, this distribution is characterized to be symmetric and fixed for the clean uncoated electron emitters and if you do your experiment using fixed low temperature (like room temperature or at any temperatures that are not considered to start thermal emissions for the used material) or with variable temperature but with levels that do not affect the Fermi-Dirac distribution of the electrons.
For example, if you use a dielectric material to coat the apex of the emitter you will see a different behaviour of the energy distribution since thermal effects will be considered in this situation. You can see Mousa and Latham 1980-1996 articles to check what are the differences between the two systems and their characteristics. I hope that this answer may help you.
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