Work Function of Cesium-Covered Nickel—Thermionic and Photoelectric Measuring Techniques

The work function of cesium-covered nickel has been measured by the thermionic and photoelectric methods. A modulated light beam technique allowed the measurement of the photoelectric emission currents in the presence of thermionic currents that were 106 times larger. The minimum work function of cesium-covered nickel was determined to be 1.42±0.05 eV by the thermionic method at a nickel temperature of 530°K and a cesium reservoir temperature of 333°K. The results obtained by the photoelectric method were, on the average, 0.05 eV lower than the values determined by the thermionic method. The discrepancy is expected because of the bias introduced to both methods by local variations in work function. The agreement of the data obtained by the two methods indicates that the Richardson constant is close to the assumed value of 120 A/cm2·deg2. The work was undertaken as a first step toward the improvement of cesium-filled thermionic generators by lowering the collector work function.