Deducing surface chemistry and annealing conditions from observed nanoparticle shapes: A study of scandate cathodes

Mujan N. Seif, T. John Balk, Matthew Beck

Research output: Contribution to journalArticlepeer-review

Abstract

Since the early 1900s it has been understood that knowledge of the surface energies of stable crystal facets under given chemical conditions allows prediction of the equilibrium shape of the crystal via the Wulff construction. Here, we demonstrate a practical application of an inverse Wulff construction: leveraging computed temperature- and chemical-environment-dependent surface energies to determine the chemical conditions under which particles exhibiting an experimentally observed equilibrated shape were formed. We apply this approach to reveal the chemical conditions required to fabricate high-performing scandate thermionic cathodes. Thermionic cathodes are critical components in vacuum electron devices, and scandate cathodes have exhibited dramatically enhanced performance compared to state-of-the-art cathodes. Despite this, manufacturing difficulties limit their integration into devices. In the following we show that fabrication of high-performing scandate cathodes exhibiting a characteristic W particle shape requires processing in narrow windows of temperature and oxygen partial pressure. We further show that small variations from these conditions result in large changes in cathode work function (and therefore thermionic emission) and that the role of Sc in enhancing emission performance may not be to directly modify surface work functions, but rather to control chemical conditions to stabilize (Sc-free) low work function surface configurations.

Original languageEnglish
Article number154541
JournalApplied Surface Science
Volume605
DOIs
StatePublished - Dec 15 2022

Bibliographical note

Funding Information:
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Matthew Beck reports financial support was provided by Defense Advanced Research Projects Agency.

Funding Information:
This work was financially supported by the Defense Advanced Research Projects Agency (DARPA) Innovative Vacuum Electronics Science and Technology (INVEST) program, under grant number N66001-16-1-4041 . The views, opinions, and/or findings expressed are those of the author(s) and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

Funding Information:
This work was financially supported by the Defense Advanced Research Projects Agency (DARPA) Innovative Vacuum Electronics Science and Technology (INVEST) program, under grant number N66001-16-1-4041. The views, opinions, and/or findings expressed are those of the author(s) and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

Publisher Copyright:
© 2022 Elsevier B.V.

Keywords

  • Experimental/computational approach
  • High temperature surface energies
  • Inverse Wulff construction
  • Nanoparticles
  • Scandate cathodes

ASJC Scopus subject areas

  • Chemistry (all)
  • Condensed Matter Physics
  • Physics and Astronomy (all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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