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

Mroz, Michael V.; Kordesch, Martin E.; Sadowski, Jerzy T.

doi:10.1116/1.5094258

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)

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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 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.

Authors:

Mroz, Michael V. ^[1];

^[1];

^[2]

Ohio Univ., Athens, OH (United States)
Brookhaven National Lab. (BNL), Upton, NY (United States)

Publication Date:: 2019-04-24

Research Org.:: Brookhaven National Lab. (BNL), Upton, NY (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

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

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.

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                    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.  https://doi.org/10.1116/1.5094258

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                    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.  https://doi.org/10.1116/1.5094258.  https://www.osti.gov/servlets/purl/1508962.

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@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},

  number       = 3,

  volume       = 37,

  place        = {United States},

  year         = {2019},

  month        = {4}

}

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