CsI coated C fiber cathodes are promising electron emitters utilized in field emission applications. Ab initio calculations, in conjunction with experimental investigations on CsI-spray coated C fiber cathodes, were performed in order to better understand the origin of the low turn-on E-field obtained, as compared to uncoated C fibers. One possible mechanism for lowering the turn-on E-field is surface dipole layers reducing the work function. Ab initio modeling revealed that surface monolayers of Cs, CsI, , and CsO are all capable of producing low work function C fiber cathodes , yielding a reduction in the turn-on E-field by as much as ten times, when compared to the bare fiber. Although a CsI-containing aqueous solution is spray deposited on the C fiber surface, energy dispersive x-ray spectroscopy and scanning auger microscopy measurements show coabsorption of Cs and I into the fiber interior and Cs and O on the fiber surface, with no surface I. It is therefore proposed that a cesium oxide surface coating is responsible, at least in part, for the low turn E-field and superior emission characteristics of this type of fiber cathode. This layer could be formed during preconditioning heating. surface layers cannot only lower the fiber work function by the formation of surface dipoles (if they are thin enough) but may also enhance surface emission through their ability to emit secondary electrons due to a process of grazing electron impact. These multiple electron emission processes may explain the reported 10–100 fold reduction in the turn-on E-field of coated C fibers.
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15 February 2010
Research Article|
February 24 2010
Surface chemical analysis and ab initio investigations of CsI coated C fiber cathodes for high power microwave sources
Vasilios Vlahos;
Vasilios Vlahos
a)
1Interdisciplinary Materials Science Program,
University of Wisconsin–Madison
, Madison, Wisconsin 53706, USA
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Dane Morgan;
Dane Morgan
2Interdisciplinary Materials Science Program and Department of Materials Science and Engineering,
University of Wisconsin–Madison
, Madison, Wisconsin 53706, USA
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Matthew LaCour;
Matthew LaCour
3
SAIC, Inc.
, Albuquerque, New Mexico 87117, USA
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Ken Golby;
Ken Golby
3
SAIC, Inc.
, Albuquerque, New Mexico 87117, USA
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Don Shiffler;
Don Shiffler
4
Air Force Research Laboratory, AFRL/DEHP
, 3550 Aberdeen SE, Kirtland AFB, New Mexico 87117, USA
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John H. Booske
John H. Booske
5Interdisciplinary Materials Science Program and Department of Electrical and Computer Engineering,
University of Wisconsin–Madison
, Madison, Wisconsin 53706, USA
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a)
Present address: L-3 Communications–Electron Devices Division 960 Industrial Rd., San Carlos, California 94070, USA. Electronic mail: vlahos@wisc.edu.
J. Appl. Phys. 107, 044903 (2010)
Article history
Received:
December 09 2009
Accepted:
December 23 2009
Citation
Vasilios Vlahos, Dane Morgan, Matthew LaCour, Ken Golby, Don Shiffler, John H. Booske; Surface chemical analysis and ab initio investigations of CsI coated C fiber cathodes for high power microwave sources. J. Appl. Phys. 15 February 2010; 107 (4): 044903. https://doi.org/10.1063/1.3304923
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