The Contact Difference of Potential Between Barium and Silver. The External Work Function of Silver

Abstract

A method has been developed for measuring contact differences of potential between metal surfaces in which both surfaces are prepared by thermal vaporization in a gettered vacuum. The design of the tubes permitted them to be immersed in liquid air during the measurements. The fresh surfaces were measured immediately (2-3 seconds) after they were formed and the reproducibility of the contact potential difference determined by measuring in alternation films formed in fractional distillations of the two metals. Barium surfaces were reproducible to ±0.002 volt and constant to ±0.001 volt. The silver surfaces were reproducible to ±0.02 volt and constant to ±0.001 volt. The contact difference of potential at liquid-air temperature between microcrystalline barium and silver is found to be 1.94±0.02 volts. Combination of this result with the value 2.39 volts found for the work function of barium in measurements on tungsten-barium places the work function of microcrystalline silver at 4.33±0.05 equivalent volts, as compared to 4.08 volts for the thermionically determined heat function (Goetz) and 4.74 volts for the work function of thermally etched silver wires measured photoelectrically (Winch). A valid comparison of these three values will be possible only after the variations of the work functions with temperature and with crystal surface structure have been determined.