Effect of Monolayer Adsorption on the Ejection of Electrons from Metals by Ions

Electron ejection from metals by ions is shown in this work to be a surface-sensitive phenomenon which is profoundly affected by the adsorption of a monolayer of foreign gas on an atomically clean metal surface. Monolayer adsorption is shown to decrease the total electron yield, γᵢ, primarily at the expense of the faster electrons ejected from the metal. Measurements of γᵢ show it to decrease steadily as the monolayer forms and to level off at a value characteristic of the covered surface when the monolayer is completed. Measurements have been made for the adsorption of N₂, H₂, and CO on tungsten. Electron ejection by all the singly-charged ions of the noble gases has been studied. It was possible to clean the tungsten surface in the presence of N₂ and CO but not in H₂. In H₂ the tungsten surface, as judged from γᵢ measurement, was found to be covered with about 75% of a monolayer immediately upon cooling from 2000^∘{}K. It is shown that the effect of monolayer adsorption cannot possibly be simply the result of change in work function. There is also evidence that electrons are ejected in non-Auger processes at higher ion energies when the surface is covered.