Work function investigations of alkali-coadsorbate systems

The authors have measured the work function changes induced by the coadsorption of oxygen or carbon monoxide with sodium as a function of alkali precoverage for the systems O 2 /Na/Cu(111), O 2 /Na/Ni(111), O 2 /Na/Cu(110), and CO/Na/Ni(111). In agreement with results for many other related systems, they observe anomalous work function decreases for initial doses of both O 2 and CO for high alkali precoverages. Their results are inconsistent with the standard explanations. They propose a new model in which the work function changes can be accounted for by a competition between two elements; a work function increase due to the coadsorbate and a decrease due to coadsorbate-induced undepolarization of the alkali overlayer.