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Title: Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern

Abstract

We report on a unique experimental method to determine thermionic work functions of major crystal planes of single crystal zirconium carbide. Applications for transition metal carbides could include cathodes for advanced thermionic energy conversion, radiation immune microcircuitry, {beta}-SiC substrates or high current density field emission cathodes. The primary emphasis of this paper is the analytical method used, that of computer processing a digitized image. ZrC single crystal specimens were prepared by floating zone arc refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr=0.92. A 0.075 cm hemispherical cathode was prepared and mounted in a thermionic projection microscope (TPM) tube. The imaged patterns of thermally emitted electrons taken at various extraction voltages were digitized and computer analyzed to yield currents and corresponding emitting areas for major crystallographic planes. These data were taken at pyrometrically measured temperatures in the range 1700{lt}{ital T}{lt}2200 K. Schottky plots were then used to determine effective thermionic work functions as a function of crystallographic direction and temperature. Work function ordering for various crystal planes is reported through the TPM image processing method. Comparisons are made with effective thermionic and absolute (FERP) work function methods. To support the TPM image processing method, clean tungsten surfaces weremore » examined and results are listed with accepted values.« less

Authors:
; ; ; ; ; ; ; ;  [1];  [2]
  1. Linfield Research Institute, Linfield College, McMinnville, OR (USA)
  2. Department of Applied Physics and Electrical Engineering, Oregon Graduate Center, Beaverton, OR (USA)
Publication Date:
OSTI Identifier:
6881867
Resource Type:
Journal Article
Journal Name:
Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (USA)
Additional Journal Information:
Journal Volume: 8:3; Journal ID: ISSN 0734-2101
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ZIRCONIUM CARBIDES; THERMIONIC EMISSION; CRYSTAL LATTICES; EXPERIMENTAL DATA; IMAGE PROCESSING; VERY HIGH TEMPERATURE; WORK FUNCTIONS; CARBIDES; CARBON COMPOUNDS; CRYSTAL STRUCTURE; DATA; EMISSION; FUNCTIONS; INFORMATION; NUMERICAL DATA; PROCESSING; TRANSITION ELEMENT COMPOUNDS; ZIRCONIUM COMPOUNDS; 360204* - Ceramics, Cermets, & Refractories- Physical Properties

Citation Formats

Mackie, W A, Hinrichs, C H, Cohen, I M, Alin, J S, Schnitzler, D T, Carleson, P, Ginn, R, Krueger, P, Vetter, C G, and Davis, P R. Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern. United States: N. p., 1990. Web. doi:10.1116/1.576759.
Mackie, W A, Hinrichs, C H, Cohen, I M, Alin, J S, Schnitzler, D T, Carleson, P, Ginn, R, Krueger, P, Vetter, C G, & Davis, P R. Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern. United States. doi:10.1116/1.576759.
Mackie, W A, Hinrichs, C H, Cohen, I M, Alin, J S, Schnitzler, D T, Carleson, P, Ginn, R, Krueger, P, Vetter, C G, and Davis, P R. Tue . "Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern". United States. doi:10.1116/1.576759.
@article{osti_6881867,
title = {Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern},
author = {Mackie, W A and Hinrichs, C H and Cohen, I M and Alin, J S and Schnitzler, D T and Carleson, P and Ginn, R and Krueger, P and Vetter, C G and Davis, P R},
abstractNote = {We report on a unique experimental method to determine thermionic work functions of major crystal planes of single crystal zirconium carbide. Applications for transition metal carbides could include cathodes for advanced thermionic energy conversion, radiation immune microcircuitry, {beta}-SiC substrates or high current density field emission cathodes. The primary emphasis of this paper is the analytical method used, that of computer processing a digitized image. ZrC single crystal specimens were prepared by floating zone arc refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr=0.92. A 0.075 cm hemispherical cathode was prepared and mounted in a thermionic projection microscope (TPM) tube. The imaged patterns of thermally emitted electrons taken at various extraction voltages were digitized and computer analyzed to yield currents and corresponding emitting areas for major crystallographic planes. These data were taken at pyrometrically measured temperatures in the range 1700{lt}{ital T}{lt}2200 K. Schottky plots were then used to determine effective thermionic work functions as a function of crystallographic direction and temperature. Work function ordering for various crystal planes is reported through the TPM image processing method. Comparisons are made with effective thermionic and absolute (FERP) work function methods. To support the TPM image processing method, clean tungsten surfaces were examined and results are listed with accepted values.},
doi = {10.1116/1.576759},
journal = {Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (USA)},
issn = {0734-2101},
number = ,
volume = 8:3,
place = {United States},
year = {1990},
month = {5}
}