Thermal effects on the work function of cesium adlayers and order—disorder transitions

Abstract

Abstract The increase in the work function minimum of a Cs-O-W(110) surface, which occurs when the temperature is raised at constant cesium coverage, is analyzed through a simple new model which introduces the effect of thermal motion of the adatoms on their mutual field depolarization. The effect on the average individual dipole moment is treated through the Topping formulation. A good fit with the data is obtained when parameters determined from work function measurements at 300 K are used. However the derived distance from the cesium core to the image plane may be too small to be compatible with the oxygen-cesium duolayer concept. The model allows definition of a disorder temperature which strongly increases with increased adatom coverage and dipole moment. Good agreement is found when this disorder temperature is compared with existing data on alkaline earth layers on refractory metals.