Editing Desorption (section)

===Electron-stimulated desorption===
[[File:Electron Stimulated Desorption Video.webm|thumb|shows the effects of an incident electron beam on adsorbed molecules]]
Electron-stimulated desorption occurs as a result of an electron beam incident upon a surface in vacuum, as is common in [[particle physics]] and industrial processes such as scanning electron microscopy (SEM). At atmospheric pressure, molecules may weakly bond to surfaces in what is known as [[adsorption]]. These molecules may form monolayers at a density of 10<sup>15</sup> atoms/cm<sup>2</sup> for a perfectly smooth surface,.<ref>M. H. Hablanian (1997). ''High-Volume Technology, A Practical Guide''. Second Edition. Marcel Dekker, Inc.</ref>  One monolayer or several may form, depending on the bonding capabilities of the molecules.  If an electron beam is incident upon the surface, it provides energy to break the bonds of the surface with molecules in the adsorbed monolayer(s), causing pressure to increase in the system. Once a molecule is desorbed into the vacuum volume, it is removed via the vacuum's pumping mechanism (re-adsorption is negligible).  Hence, fewer molecules are available for desorption, and an increasing number of electrons are required to maintain constant desorption.

One of the leading models on electron stimulated desorption is described by Peter Antoniewicz<ref name="peter">
Model for electron- and photon-stimulated desorption, Antoniewicz, Peter R., Phys. Rev. B 21.9, pages: 3811—3815, May 1980, American Physical Society, doi = {10.1103/PhysRevB.21.3811},</ref> In short, his theory is that the adsorbate becomes ionized by the incident electrons and then the ion experiences an image charge potential which attracts it towards the surface. As the ion moves closer to the surface, the possibility of electron tunnelling from the substrate increases and through this process ion neutralisation can occur. The neutralised ion still has kinetic energy from before, and if this energy plus the gained potential energy is greater than the binding energy then the ion can desorb from the surface. As ionisation is required for this process, this suggests the atom cannot desorb at low excitation energies, which agrees with experimental data on electron simulated desorption.<ref name="peter" /> Understanding electron stimulated desorption is crucial for accelerators such as the [[Large Hadron Collider]], where surfaces are subjected to an intense bombardment of energetic electrons. In particular, in the beam vacuum systems the desorption of gases can strongly impact the accelerators performance by modifying the secondary electron yield of the surfaces.<ref>Electron Stimulated Desorption of Condensed Gases on Cryogenic Surfaces (September 2005) Dipl. Ing. Herbert Tratnik Matrikelnr. 9226169, page:3 </ref>