Work Function in Field Emission. Chemisorption

Abstract

Analogs to the contact potential are calculated for the work function increase in field emission caused by polar chemisorbates. It is found that the discreteness of the dipoles constituting the layer leads to a work function increment smaller than the corresponding contact potential. The discrepancy becomes more marked at low coverages and high fields. A simple Fermi‐Thomas calculation for estimating the depolarization of the electron cloud at a metal surface is given. It is probable that observed depolarizations of oxygen and nitrogen on tungsten can be explained in terms of this factor. The effect of the high fields used in cold emission on the work function is estimated and found to be of the order of 0.1 volt. Arguments are presented to show that a recent explanation of the fall in heats of chemisorption with coverage may need revision.