Contact Potential Difference between Iron and Nickel and their Photoelectric Work Functions

Abstract

Specimens of electrolytic iron and electrolytic nickel were outgassed by intensive heat treatment in high vacuum and the contact potential difference between them measured by the Kelvin null method. An apparatus is described by means of which the photoelectric long wave limits could be determined on the same specimens and under identical conditions as used for the contact potential measurements. The photoelectric long wave limits were determined in one case by using filters in the path of the light and in a second case by the method of plotting the photoelectric sensitivity curves obtained using monochromatic illumination of the metals. The results remained unchanged between 300 and 750 hours of heating in the first case and between 400 and 600 hours in the second. The equilibrium value of the contact potential difference was Fe-Ni+0.21\ifmmode\pm\else\textpm\fi{}0.01 volt. The photoelectric long wave limits determined by the second method were 2620A\ifmmode\pm\else\textpm\fi{}10A for the iron and 2500A\ifmmode\pm\else\textpm\fi{}10A for the nickel. The corresponding work functions are 4.71\ifmmode\pm\else\textpm\fi{}0.02 volts for the iron and 4.93\ifmmode\pm\else\textpm\fi{}0.02 volts for the nickel. Using the method published by Fowler the work functions were 4.77 volts for the iron and 5.01 volts for the nickel. The difference in these work functions by either method is equal to the measured contact potential difference between the metals within the limits of error of the photoelectric measurements.