GOALI: Understanding the Microstructural Evolution and High-Temperature Behavior of Osmium-Ruthenium Coatings for Dispenser Cathodes

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The research objective of this award is an improved understanding of osmium-ruthenium coatings during their fabrication and service in dispenser cathodes. These cathodes, which serve as electron sources in devices such as traveling wave tubes and cathode ray tubes, must withstand demanding environmental conditions including vacuum, high operational temperature and high current density. The osmium-ruthenium films undergo significant microstructural changes during processing and initial service, but must remain intact to maintain electron emission from the cathode. Topics of fundamental scientific importance include the effects of thin film microstructure on the diffusion of refractory metals, as well as the effects of film texture on electron work function. There are also several industrially relevant issues, including how to achieve enhanced emission, longer lifetime and/or lower operating temperature. By systematically investigating the effects of microstructure on the compositional stability and emission properties of annealed and conditioned cathodes, a scientific, microstructure-based understanding of osmium-ruthenium film coatings will be built.The knowledge gained from this project will help advance the dispenser cathode industry from an empirical field with decades of experience, to a field with scientific understanding and the ability to tailor new coatings for improved performance. This project will establish the knowledge needed for a fundamental shift in cathode manufacturing and also mitigate the effects of increasing material costs. If successfully implemented, the results of this research will lead to improved devices for the dispenser cathode industry. This will enable lowered production costs and improved yield, and will benefit customers by increasing cathode lifetime and reliability. The project will enhance both graduate and undergraduate education by providing research experience that has a direct and tangible impact on industry and by providing industrially relevant materials problems for the capstone design course taught by the PI.