Surface Analysis of LaB6 Single Crystal Thermionic Emitters

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Abstract
Surface analysis of heated LaB6 thermionic emitter is made by means of Auger electron spectroscopy. Changes in surface state with changing emitter temperature and ambient oxygen pressure are investigated. The emitter temperature is varied from room temperature to 1700°C, and the oxygen pressure from 1×10-5 Pa to 7×10-3 Pa. With the increase of temperature the emitter surface passes through four states depending on oxygen pressure, before it reaches a clean state. Among them a state is particularly noteworthy that the emitter surface is covered with a layer of lanthanum oxide just before assuming the clean surface state. A surface state diagram is shown. The optimum conditions of emitter temperature and oxygen gas pressure to exhibit high emission properties are described.

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