The role of adsorbed oxygen in secondary emission from metallic substrates
Low energy, ion- and photon-induced secondary electron and anion emission from metallic substrates has been investigated as a function of adsorbate coverage. Sodium positive ions (Na+), with kinetic energies up to 500 eV, and photons, with energies up to 23 eV, are utilized to initiate secondary emi...
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| Format: | Others |
| Language: | English |
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W&M ScholarWorks
1998
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| Online Access: | https://scholarworks.wm.edu/etd/1539623943 https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=3538&context=etd |
| Summary: | Low energy, ion- and photon-induced secondary electron and anion emission from metallic substrates has been investigated as a function of adsorbate coverage. Sodium positive ions (Na+), with kinetic energies up to 500 eV, and photons, with energies up to 23 eV, are utilized to initiate secondary emission. The principal adsorbate is oxygen with coverages ranging from none to a few monolayers.;For ion-induced emission, the secondary electron and negative ion absolute and relative yields from 302 stainless steel and polycrystalline tungsten (W) have been measured as a function of both impact energy and oxygen coverage. Additionally, the yields from a "technical" stainless steel surface, i.e., a surface for which no in-situ cleaning is performed, have been measured. The sputtered anions have been identified by secondary ion mass spectroscopy (SIMS). For both surfaces, adsorbate coverage is found to greatly enhance the electron and anion yields at all impact energies.;In addition, the kinetic energies of the secondary electrons and negative ions have been measured as a function of both impact energy and oxygen coverage. The electron and anion kinetic energy distributions exhibit low most probable energies (1--2 eV) and unique features that are substrate dependent.;Photoelectron kinetic energy distributions for aluminum (Al), molybdenum (Mo), Mo (100) and stainless steel have been measured, as a function of oxygen coverage, in order to ascertain the effects of adsorbed oxygen. Additionally, photon-stimulated anion desorption from oxygen covered Al has been measured as a function of photon energy. This anion desorption is found to have a narrow resonance at approximately 8.75 eV.;The resonance in the photon-induced anion emission is shown to be in direct support of a model proposed to explain the observed ion-induced secondary electron and O- emission from an oxygen covered Al surface. The model invokes a collision-induced excitation, of a surface state, that serves as a precursor to both electron and anion emission. This model is discussed in detail and utilized to explain the emission from oxygen covered stainless steel and tungsten. The results for the technical stainless steel surface are related to those for the oxygen covered surface and the implications for plasma discharge modeling are discussed. |
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