ELECTRON AFFINITY

Updated 05-May-2020.

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Quantum photoyield of diamond(111)—A stable negative-affinity emitter: Quantum photoyield and secondary-electron distributions are presented for an unreconstructed diamond (111) surface (type-IIb, gem-quality blue-white semiconductor). This chemically inert surface exhibits a negative electron affinity, resulting in a stable quantum yield that increases linearly from photothreshold (5.5 eV) to ̃20% at 9 eV, with a very large yield of ̃40%-70% for 13≲h ν≲35 eV. For all photon energies, secondary-electron energy distributions show a dominant ̃0.5-eV-wide emission peak at the conduction-band minimum (∆^<min></min>₁=5.50±0.05 eV above the valence-band maximum Γ₂₅‘). In contrast with recent self-consistent calculations <article>[J. Ihm, S. G. Louie, and M. L. Cohen, Phys. Rev. B 17, 769 (1978)]</article> no occupied intrinsic surface states with ionization energies in the fundamental gap (the Fermi level was 1 eV above Γ₂₅‘) were observed. Likewise, the measured photothreshold (E_vac-Γ₂₅‘) is significantly smaller than calculated (7.0±0.7 eV).

My botty best at summarizing from Wikipedia: the electron affinity (Eea) of an atom or molecule is defined as the amount of energy released when an electron is attached to a neutral atom in the gaseous state to form a negative ion a list of the electron affinities was used by Robert S. Mulliken to develop an electronegativity scale for atoms . other theoretical concepts that use electron affinity include electronic chemical potential and chemical hardness . electron capture for almost all non-noble gas atoms involves the release of energy . confusion arises in mistaking Eea for a change in energy, E . positive values listed in tables negative values typically arise for the capture of a second electron, but also for the nitrogen atom . if the value assigned to Eea is negative, the negative sign implies a reversal of direction . negative the energy change for the process X X + e Since almost all detachments (require +) an amount of energy listed on the table, those detachement reactions are endothermic the electron affinities of noble gases have not been conclusively measured . they may or may not have slightly negative values . in group 18, added electrons are unstable, tending to be ejected very quickly . electron affinity follows the same “left-right” trend as electronegativity . electron affinity does not decrease when progressing down the rows of the periodic table . the following data are quoted in kJ/mol . for a semiconductor-vacuum interface, electron affinity is typically denoted by EEA or . a silicon crystal surface has electron affinity 4.05 eV, whereas an isolated silicon atom has electron the electron affinity does depend on the surface termination (crystal face, surface chemistry, etc.) and is strictly a surface property . in semiconductor physics, primary use of electron affinity is not in the analysis of semiconductor– negative electron affinity is desired to obtain efficient cathodes that can supply electrons to the vacuum with little energy loss . for one illustration of the apparent effect of surface termination on electron emission, see Figure 3 in Marchywka Effect Chemistry: A Molecular Approach (2nd Edn.). New Jersey: Pearson Prentice Hall. ISBN 0-13-100065-9. pp. 348–349.