Study Of Dispenser Cathode With High Emission Current Density

A new type of dispenser cathode with dual-layer (Os-W/Re and Os-Ru/Re) has been developed in order to meet the high electron emission and reliability requirements of high power microwave electron devices for electron emitters.Coating of dispenser cathode is mainly discussed for the aim of high electron emission in this article. The study is based upon the investigation of the structure of coated dispenser cathode and the analysis of its manufacture and examination.Coated dispenser cathode with single coating, binary coating or ternary coating put forward by C. S. AresFang et al. is the dispenser cathode with monolayer. The dispenser cathode with dual-layer using Re as substrate layer and Os-W alloy (or Os-Ru alloy) as upper layer is developed.The emission capability of the dispenser cathode is compared before and after its activation. The result is: the cathode coated with Os-W/Re has better emission performance than the cathode coated with Os-W alloy. Also, the cathode coated with Os-Ru/Re has better emission performance than the cathode coated with Os-Ru alloy.We also discuss the reason of film peeling based on physical structure character of the coating. The surface of each variety of the cathodes is checked with scanning electron microscope (SEM) before and after activation. The SEM analysis shows that the emitting surface of the cathode with Os-W alloy and Os-Ru alloy appears non-adherence (flaking) in many small areas after ageing. In the contrast, the surface of the cathode with dual-layer does not present film peeling under the same conditions. Adhesion of upper layer is improved with Re as a middle layer. This dual-layer coating will ensure better emission uniformity and functional reliability for the dispenser cathode.In the end surface characteristics of the dispenser cathode coated with Os-W/Re are studied with X-ray photoelectron spectroscopy (XPS). The XPS spectra...