Theory of Work-Function Changes Induced by Alkali Adsorption

Abstract

Changes of the work function due to adsorption of alkali atoms by a high-work-function substrate are studied using a very simple ("jellium") model of the metallic substrate-adsorbate system. A self-consistent quantum-mechanical analysis of the model leads to a work-function-vs-coverage curve with a minimum at a coverage below that of a single full adsorbed layer, and a maximum at completion of the layer. Good agreement with the results of recent measurements is obtained for these extremal values; and, though not designed to treat very low coverages, the model yields an initial dipole moment in satisfactory agreement with experiment. The computed full-layer work function is very nearly equal to that obtained theoretically for the corresponding bulk sample. A study of limiting cases provides a framework for viewing the results of the calculation in a coherent way.