Work function investigations at electrodes with adsorbed layers by measuring contact potential differences in vapor atmosphere

One of the most promising methods for improving the efficiency of thermionic energy converters is to lower the work function of the collector electrode. Investigations in this field require suitable methods for measuring work function values within an atmosphere of adsorbing vapors at low temperatures. A survey of potential theoretical and experimental methods is given and a device and procedure described, developed for measuring contact potential differences at such conditions. Results of work function measurements are reported, concerning bare surfaces of different metallic electrodes and some cermet materials in ultra high vacuum as well as with adsorption layers of cesium, barium, oxygen or mixtures of these adsorbates. The lowest work function values could be observed with cesium adsorption on oxidized electrode surfaces, showing minimum values of about 1,0 eV.