Investigation of electron emission properties of Ba-activated tungsten cathodes

Abstract

In this work we investigated the electron emission properties of high-pressure discharge lamp cathode tips. The work function (Φ) of the cathode tip was measured by using the Kelvin probe method and by work function spectroscopy (WFS). The Kelvin probe method was used to measure the average work function of tips under atmospheric pressure in air. By WFS we could measure the local work function value of tips in the selected spots under ultra high vacuum conditions. The chemical composition analysis was carried out in the same chamber by Auger electron spectroscopy.The focus of this study is to investigate the influence of sintering temperature of cathodes (1500–1700 °C) and lamp operation time (0–12 000 h) on the work function. The comparison of the work function of both cathodes as a function of operation time originating from the two different ends of the ceramic tube is also considered. In order to understand the structure of the layers on the cathode tips we also give results obtained on a flat tungsten foil covered with Ba-containing emission material. The flat samples were measured using x-ray photoelectron spectroscopy and WFS.

Chemistry of materials science phenomena in high-intensity discharge light sources

“…Beck et al have monitored the work function of HPS lamps as a function of the sintering condition of the emission material and as a function of the aging of the lamp [9]. Beside the conventional Kelvin probe measurement, they have developed the so-called work function spectroscopy (WFS), which is capable of determining the work function with very good spatial resolution.…”