Abstract
The two-filament bulb technique of Taylor and Langmuir 1) is used to measure cesium coverages on tungsten and rhenium to a monolayer. Fractions θ of a monolayer to small values in the order of 10 −5 for arrival rates to 7.8 × 10 −15 atom/cm 2 · sec are measured by displaying ion desorption pulses on an oscilloscope. Monolayer values of 5 × 10 14 atom/cm 2 and 6.9 × 10 14 atom/cm 2 for tungsten and rhenium, respectively, are obtained. Ion evaporation times for 0 < θ < 0.02 and atom evaporation times for 0 < θ < 0.3 are measured for various arrival rates. The heats of sublimation ΔH S = 18.82 kcal/ mole and vaporization ΔH V = 16.32 kcal/ mole for cesium are obtained by the positive ion method. An analysis is presented which determines a two-dimensional critical point for the adsorbed gas. For Cs-W, the critical temperature T c is evaluated to be 1800° K and for CsRe, T c == 2500° K. The analysis is verified over the range of experimental data.
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