The effect of adsorbate-adsorbate interactions on stimulated desorption yields

Abstract

A treatment is given of the effect of lateral interactions between adsorbed species on the desorption yield from surfaces. In a number of well-studied systems, e.g. H/W(100), Mo(100), CO/Ni, W, and O/W(100), Mo(100), it is observed that after an initial linear increase of electron stimulated ion desorption yield at very low coverage, a region of negative differential ion yield with increasing coverage is encountered. The yield achieves a maximum and then decreases with further coverage as the coverage exceeds a quarter to a half monolayer depending upon the system. Here we present model calculations based on the hypothesis that this decreasing yield is due to lateral delocalization of the desorption causing excitation as the interaction between adsorbed species increases. A specific application is the H/W(100) system where we find that a simple model indicates that such delocalization could cause a decrease in the desorption yield in excess of one order of magnitude in going from a quarter monolayer to a half monolayer coverage. Several experimental tests of this model are suggested.