Right click to open a feedback form in a new tab to let us know how this document benefits you.Osmium-ruthenium films with different microstructures were deposited onto dispenser cathodes and subjected to 1000 h of close-spaced diode testing. Tailored microstructures were achieved by applying substrate biasing during deposition, and these were evaluated with scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy before and after close-spaced diode testing. Knee temperatures determined from the close-spaced diode test data were used to evaluate cathode performance. Cathodes with a large {10-11} Os-Ru film texture possessed comparatively low knee temperatures. Furthermore, a low knee temperature correlated with a low effective work function as calculated from the close-spaced diode data. It is proposed that the formation of strong {10-11} texture is responsible for the superior performance of the cathode with a multilayered Os-Ru coating.
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. V
Osmium-ruthenium thin films were deposited on porous tungsten pellets, at the same time as cathode assemblies, to investigate possibilities for minimizing interdiffusion. Previous studies had identified promising film characteristics for inhibiting tungsten interdiffusion. For example, it was found that a 5W-substrate-biased film of 550 nm thickness exhibited high structural and compositional stability, and several other films exhibited promising properties as well. These films were produced and annealed, then analyzed for composition. Emission tests of M-type cathode assemblies, coated with the same candidate films, were performed to assess the degree of lifetime improvement imparted by the films to the cathodes.
This technical paper was written and developed when the author(s) was an employee of Semicon Associates, a Ceradyne, Inc. company. Ceradyne, Inc. was acquired by 3M Company on November 28, 2012.
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