Work function variation of tungsten in barium plus cesium and strontium plus cesium vapor environments

Abstract

The variation of the electron work function of tungsten in barium, cesium, strontium and their vapor combinations has been experimentally determined in a thermionic diode incorporating independently controlled barium (or strontium) and cesium reservoirs. The data show that in the single vapor cases the work function variation is defined, within experimental error, by T s/ T v for the regions investigated. For the case of combined vapors, the work function is defined by both ratios, T s/ T v1 and T s/ T v2, where T v1 and T v2 are the temperatures of the reservoirs generating each vapor, respectively. Furthermore, it is shown that with increasing barium (or strontium) vapor pressure a region of constant φ s is established in the φ s versus T s/ T cs plot. For example: at T Ba = 700 °K and T s = 2050 °K, φ s is essentially affected by T/ T cs, however, at T Ba = 1000°K and T s = 1800°K, φ s is constant at 3.0 eV, for T s/ T cs equal or greater to 2.8 and decreases for values less than this. The point of department from the constant line for low barium or strontium pressures falls very close to the line of φ s versus T s/ T cs for tungsten when taken in the absence of barium or strontium vapors. However, at high barium or strontium pressures this point crosses over the line of the Cs-on-W system. Data plotted in the form of φ s versus T s/ T Ba and T s/ T sr and φ s versus T s/ T cs and other related information are given.