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Photoelectron- and Thermionic- Emission Microscopy of Barium/Scandium Thin Films on Tungsten

Published online by Cambridge University Press:  01 February 2011

Joel M. Vaughn  and
Martin Kordesch
Joel M. Vaughn
Affiliation:
jv218100@ohio.edu, Ohio University, Physics and Astronomy, Clippinger Labs RM 251B, Athens, OH, 45701, United States
Martin Kordesch
Affiliation:
kordesch@ohio.edu, Ohio University, Physics and Astronomy, Clippinger Labs RM 251B, Athens, OH, 45701, United States
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Abstract

Commercial scandium oxide doped thermionic cathodes have demonstrated current densities over 100 A/cm2. In order to understand the effect of Sc- and Ba- oxides on the emissivity of these cathodes we have imaged thin films of scandium oxide and barium oxide on tungsten foils using photoelectron emission microscopy and thermionic emission microscopy. Arrays of 100 um × 100 um squares of scandium and 25 um × 25 um squares of barium, 200 nm thick, were sputter deposited onto 50 um thick sheets of tungsten foil. Imaging squares of different sizes gives an unequivocal identification of each material and a completely consistent comparison of each material and cathode structure under identical conditions in one image.

The metal squares oxidize in air before imaging. Each sample was heated in situ in a Bauer-Telieps style LEEM/PEEM used primarily in the ThEEM mode. The barium oxide squares emit below 875 K, and diffuse over the scandium below 875 K. Thermionic emission from scandium oxide squares is observed at temperatures significantly larger than 875 K. Failure of the barium oxide film cathode is through barium desorption. AES spectra show that the Sc does not desorb.

While the origin of reduced emission temperature is commonly believed to be a result of a low work function monolayer of Ba and Sc oxides, in our study, the benefits of a combined Ba/Sc cathode are present in a thick (multi-layer), layered structure of barium oxide on top of a thick scandium oxide layer.

Keywords

thermionic emissionBaSc
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1088: Symposium W – Advances and Applications of Surface Electron Microscopy , 2008 , 1088-W03-09
Copyright
Copyright © Materials Research Society 2008

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