100 years anniversary of the oxide cathode - a historical review

Now 100 years have passed, since Arthur Wehnelt published his famous paper entitled: "On the emission of negative ions from glowing metal compounds and related-phenomena". This paper was the start of the oxide cathode, which has become the work horse not only in cathode ray tubes with a production of about 700 million oxide cathodes in 2000, but also in low pressure gas discharge lamps with about 7 billion pieces produced in the same year. A more systematic and detailed investigation of the physical processes in the oxide cathode began about 1920. The studies of Koller and Becker proved, that the emission of the cathode is due to an excess of metallic Ba in the oxide, which is produced during cathode activation. This excess Ba was thought to be present in the form of a monoatomic Ba film, which also exhibits a much lower Ba evaporation rate than bulk Ba. Reimann 1930 and others in the next years found, that there is a close relationship between the electrical conductivity of the coating and the emission. Regarding the theoretical model and basic investigations, new insights have been obtained and some of these was presented at this conference. Thus the oxide cathode still remains a modern and challenging subject despite its 100 years history.