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Title: Scandium function in “scandate” thermionic cathodes: A microspot synchrotron radiation x-ray photoelectron spectroscopy study of co-adsorbed Ba-Sc-O on W(100)

Abstract

The co-adsorption of barium, scandium and oxygen on W(100) was investigated with micro-Synchrotron radiation X-ray Photoelectron Spectroscopy (μ-SRXPS) in the emission microscope at the Electron-Spectro-Microscopy (ESM) beam line at the National Synchrotron Light Source II. The Ba-Sc-0-W(100) system is a model for “scandate” thermionic electron emitters. The barium 4d (Ba4d), tungsten 4f (W4f) and scandium 3p (Sc3p) levels were observed after metal deposition and adsorption of oxygen. The initial deposits of metallic scandium and barium were confirmed with μSRXPS. After oxygen adsorption, the Sc 3p peaks shifted to higher binding energy (by >4 eV), indicating the formation of Sc 2O 3 or a related compound. After heating to 800 C, the barium 4d peaks were no longer observed. The shifted Sc3p peak was also absent. The results indicate that scandium acts as a cleaning agent to remove oxygen from the tungsten surface. The oxidized scandium is removed by reaction with barium and desorption below 800 C. The temperature of desorption indicates that scandium does not remain on the surface at a temperature where a contribution to the reduction of the surface barrier to electron emission could be expected.

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [2]
  1. Ohio Univ., Athens, OH (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1508962
Report Number(s):
BNL-211590-2019-JAAM
Journal ID: ISSN 0734-2101
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films
Additional Journal Information:
Journal Volume: 37; Journal Issue: 3; Journal ID: ISSN 0734-2101
Publisher:
American Vacuum Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Mroz, Michael V., Kordesch, Martin E., and Sadowski, Jerzy T. Scandium function in “scandate” thermionic cathodes: A microspot synchrotron radiation x-ray photoelectron spectroscopy study of co-adsorbed Ba-Sc-O on W(100). United States: N. p., 2019. Web. doi:10.1116/1.5094258.
Mroz, Michael V., Kordesch, Martin E., & Sadowski, Jerzy T. Scandium function in “scandate” thermionic cathodes: A microspot synchrotron radiation x-ray photoelectron spectroscopy study of co-adsorbed Ba-Sc-O on W(100). United States. doi:10.1116/1.5094258.
Mroz, Michael V., Kordesch, Martin E., and Sadowski, Jerzy T. Wed . "Scandium function in “scandate” thermionic cathodes: A microspot synchrotron radiation x-ray photoelectron spectroscopy study of co-adsorbed Ba-Sc-O on W(100)". United States. doi:10.1116/1.5094258.
@article{osti_1508962,
title = {Scandium function in “scandate” thermionic cathodes: A microspot synchrotron radiation x-ray photoelectron spectroscopy study of co-adsorbed Ba-Sc-O on W(100)},
author = {Mroz, Michael V. and Kordesch, Martin E. and Sadowski, Jerzy T.},
abstractNote = {The co-adsorption of barium, scandium and oxygen on W(100) was investigated with micro-Synchrotron radiation X-ray Photoelectron Spectroscopy (μ-SRXPS) in the emission microscope at the Electron-Spectro-Microscopy (ESM) beam line at the National Synchrotron Light Source II. The Ba-Sc-0-W(100) system is a model for “scandate” thermionic electron emitters. The barium 4d (Ba4d), tungsten 4f (W4f) and scandium 3p (Sc3p) levels were observed after metal deposition and adsorption of oxygen. The initial deposits of metallic scandium and barium were confirmed with μSRXPS. After oxygen adsorption, the Sc 3p peaks shifted to higher binding energy (by >4 eV), indicating the formation of Sc2O3 or a related compound. After heating to 800 C, the barium 4d peaks were no longer observed. The shifted Sc3p peak was also absent. The results indicate that scandium acts as a cleaning agent to remove oxygen from the tungsten surface. The oxidized scandium is removed by reaction with barium and desorption below 800 C. The temperature of desorption indicates that scandium does not remain on the surface at a temperature where a contribution to the reduction of the surface barrier to electron emission could be expected.},
doi = {10.1116/1.5094258},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 3,
volume = 37,
place = {United States},
year = {2019},
month = {4}
}

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This content will become publicly available on April 24, 2020
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