Abstract

Os–Ru thin films with varying concentrations of W were sputter deposited in order to investigate their structure–property relationships. The films were analyzed with x-ray diffraction to investigate their crystal structures, and a Kelvin probe to investigate their work functions. An Os–Ru–W film with ∼30 at. % W yielded a work function maximum of approximately 5.38 eV. These results align well with other studies that found work function minima from thermionic emission data on M-type cathodes with varying amounts of W in the coatings. Furthermore, the results are consistent with other work explaining energy-level alignment and charge transfer of molecules on metal oxides. This may shed light on the mechanism behind the “anomalous effect” first reported by Zalm et al., whereby a high work function coating results in a low work function for emitting cathode surfaces. An important implication of this work is the potential for the Kelvin probe to evaluate the effectiveness of dispenser cathode coatings.

Document Type

Article

Publication Date

3-2015

Notes/Citation Information

Published in Journal of Vacuum Science & Technology A, v. 33, no. 2, article 021405, p. 1-7.

Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

The following article appeared in Journal of Vacuum Science & Technology A, v. 33, no. 2, article 021405, p. 1-7 and may be found at http://dx.doi.org/10.1116/1.4905499

Digital Object Identifier (DOI)

http://dx.doi.org/10.1116/1.4905499

Funding Information

This material was based upon work supported by the National Science Foundation under Grant No. CMMI-0928845. Use of the XPS was supported by the National Science Foundation under Grant No. 0814194.

Additional Files
1.tif (758 kB)
Fig. 1 HIGH-RES. (Color online) UHV Kelvin probe showing the tip and sample configuration. The probe tip vibrates vertically above the sample. The sample must be grounded with respect to the tip and remain free of any vibration.
Figure 1.pptx (222 kB)
Fig. 1 POWERPOINT. (Color online) UHV Kelvin probe showing the tip and sample configuration. The probe tip vibrates vertically above the sample. The sample must be grounded with respect to the tip and remain free of any vibration.
2.tif (129 kB)
Fig. 2 HIGH-RES. (Color online) Concentration gradient of W–Os–Ru ternary alloy films deposited on Mo–Re and porous W substrates. The composition for every sample was determined using XPS and select samples were measured with EDS as a cross-check, which gave similar compositions.
Figure 2.pptx (75 kB)
Fig. 2 POWERPOINT. (Color online) Concentration gradient of W–Os–Ru ternary alloy films deposited on Mo–Re and porous W substrates. The composition for every sample was determined using XPS and select samples were measured with EDS as a cross-check, which gave similar compositions.
3.tif (331 kB)
Fig. 3 HIGH-RES. (Color online) XRD scans of W–Os–Ru ternary alloys indicating a shift in the HCP peak position with increasing W concentration (starting from the bottom, peaks indicated by arrows) and showing the formation of a BCT phase (arrows above the top two XRD scans).
Figure 3.pptx (144 kB)
Fig. 3 POWERPOINT. (Color online) XRD scans of W–Os–Ru ternary alloys indicating a shift in the HCP peak position with increasing W concentration (starting from the bottom, peaks indicated by arrows) and showing the formation of a BCT phase (arrows above the top two XRD scans).
4.tif (90 kB)
Fig. 4 HIGH-RES. (Color online) Comparison of variations in <em>c</em> and <em>a</em> lattice parameters with W concentration. The variation in <em>c/a</em> ratio is also shown plotted against the right axis. The <em>c</em> lattice parameter increases over 3.5 times faster than the <em>a</em> lattice parameter, indicating that the unit cell expands primarily along the <em>c</em> axis as W is added to the HCP Os–Ru phase.
Figure 4.pptx (98 kB)
Fig. 4 POWERPOINT. (Color online) Comparison of variations in <em>c</em> and <em>a</em> lattice parameters with W concentration. The variation in <em>c/a</em> ratio is also shown plotted against the right axis. The <em>c</em> lattice parameter increases over 3.5 times faster than the <em>a</em> lattice parameter, indicating that the unit cell expands primarily along the <em>c</em> axis as W is added to the HCP Os–Ru phase.
5.tif (197 kB)
Fig. 5 HIG-RES. (Color online) Work function and composition relationship for W–Os–Ru ternary alloys. The alloys are in the as-deposited state, with no surface or thermal treatment. The work function exhibits a peak near 30 at. % W in the W–Os–Ru alloy system and shows a sharper drop in work function at a composition corresponding to the appearance of the σ-phase. The dashed sloped line indicates the continuation of the second linear region from the piecewise fit, to show that the measured work function decreases more rapidly above 60 at. % W.
Figure 5.pptx (109 kB)
Fig. 5 POWERPOINT. (Color online) Work function and composition relationship for W–Os–Ru ternary alloys. The alloys are in the as-deposited state, with no surface or thermal treatment. The work function exhibits a peak near 30 at. % W in the W–Os–Ru alloy system and shows a sharper drop in work function at a composition corresponding to the appearance of the σ-phase. The dashed sloped line indicates the continuation of the second linear region from the piecewise fit, to show that the measured work function decreases more rapidly above 60 at. % W.
6.tif (85 kB)
Fig. 6 HIGH-RES. (Color online) Work function trend of W–Ir alloys with respect to W concentration. There is a peak in the work function at approximately 40 at. % W. This is similar to the peak observed in the W–Os–Ru system, albeit at a slightly higher W content and with a higher value of work function.
Figure 6.pptx (85 kB)
Fig. 6 POWERPOINT. (Color online) Work function trend of W–Ir alloys with respect to W concentration. There is a peak in the work function at approximately 40 at. % W. This is similar to the peak observed in the W–Os–Ru system, albeit at a slightly higher W content and with a higher value of work function.
7.tif (205 kB)
Fig. 7 HIGH-RES. (Color online) XPS spectrum of W–Os–Ru (51 at. % W) in the as-deposited state. The inset region for W 4f peaks indicates that the alloy surface is partially oxidized. All peaks for major species are labeled. Other peaks can be attributed to core levels of W, Os, or Ru. Additional W–Os–Ru alloy compositions yielded similar spectra.
Figure 7.pptx (92 kB)
Fig. 7 POWERPOINT. (Color online) XPS spectrum of W–Os–Ru (51 at. % W) in the as-deposited state. The inset region for W 4f peaks indicates that the alloy surface is partially oxidized. All peaks for major species are labeled. Other peaks can be attributed to core levels of W, Os, or Ru. Additional W–Os–Ru alloy compositions yielded similar spectra.
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