Oxide effects on photoemission from high current GaAs photocathodes

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During four years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO/sub 2/ on the PC's during running at LN/sub 2/ temperatures. Such PC's can be rejuvenated by warming to 90K, i.e., above the CO/sub 2/ desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during ... continued below

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Pages: 18

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Garwin, E.L.; Kirby, R.E.; Sinclair, C.K. & Roder, A. March 1, 1981.

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Description

During four years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO/sub 2/ on the PC's during running at LN/sub 2/ temperatures. Such PC's can be rejuvenated by warming to 90K, i.e., above the CO/sub 2/ desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during in-situ heat cleaning prior to activation. In this mode, As is preferentially evaporated from the GaAs, leaving a Ga/sub 2/O/sub 3/ layer on the surface. This effect has been studied by AES sputter profiling which indicates that the substantial thickness of the oxide layer blocks photoemission. These PC's may only be recovered by chemically removing the oxide layer. A third mode which is not as well characterized appears for thin Ga oxide layers. Properties of these PC's include reduced emission and the presence of a cutoff bias level. Such PC's are also not recoverable in-situ.

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Pages: 18

Notes

NTIS, PC A02/MF A01.

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  • Interdisciplinary surface science conference, Liverpool, UK, 6 Apr 1981

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  • Other: DE81025129
  • Report No.: SLAC-PUB-2715
  • Report No.: CONF-810495-2
  • Grant Number: AC03-76SF00515
  • Office of Scientific & Technical Information Report Number: 6200571
  • Archival Resource Key: ark:/67531/metadc1109211

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • March 1, 1981

Added to The UNT Digital Library

  • Feb. 22, 2018, 7:45 p.m.

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  • May 29, 2018, 4:35 p.m.

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Garwin, E.L.; Kirby, R.E.; Sinclair, C.K. & Roder, A. Oxide effects on photoemission from high current GaAs photocathodes, article, March 1, 1981; California. (digital.library.unt.edu/ark:/67531/metadc1109211/: accessed July 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.