Work function values from contact potential difference measurements

Abstract

Attempts to refer all reliable contact potential difference measurements to the reference value 4.545 ev of the work function of polycrystalline tungsten showed that two measurements were still required. These have been carried out, and give the results (a) - 0.25 ± 0.02 v, and (b) - 0.110 ± 0.010 v for the contact potential differences between tungsten and silver films on (a) glass and (b) tantalum substrates, respectively. An incidental result is the contact potential difference between tungsten and tantalum foils, - 0.327 ± 0.020 v. With the help of the first two results a table has been compiled of all work functions derived from reliable contact potential difference measurements, in which every value is based on the standard tungsten reference. Inter-comparisons between values in the table show that there is a tendency for the work function of vacuum-deposited films to rise in the substrate sequence glass, tungsten, tantalum. This is attributed to different degrees of preferred orientation in the substrate surface, with consequent epitaxial effect on the film.