Structure And Properties Of Cesium-Coated Surfaces And The Effects Of Hydrogen And Oxygen Implantation

Abstract

Cesium, hydrogen and oxygen adsorption on beryllium clusters are studied using restricted Hartree-Fock (RHF) calculations and ab initio relativistic effective core potentials. The clusters are taken as cylindrical plugs from Be wafers. Cs-, H- and 0-to-substrate internuclear distances are optimized. For each system numerous low-lying electronic states are investigated, and the Mulliken electron populations are analyzed. The calculations are carried out in the context of an experimental study to determine the effects of various adsorbates on the work function of the substrate. Auger electron spectroscopy and experimental work function measurements indicate that H2 does not adsorb on polycrystalline Be, while photoemission and thick Cs overlayer measurements show a 2.3 eV lowering in the work function of Be metal upon Cs adsorption. The continuous oxidation of Cs has been studied using ultraviolet photoelectron spectroscopy and electron spectroscopy by deexcitation of metastable noble gas atoms. Results indicate that the work function of Cs is lowered upon exposure of the surface to small doses of oxygen. RHF calculations show that a 19 atom Be cluster, with three layers of atoms, is too small to adequately model the Be surface, while the 33 atom cluster, a five-layered system, and the 45 atom cluster, a seven-layered system, are more accurate representations of the bulk metal. The emitted electron is clearly seen as vacating a molecular orbital which is localized in the surface layer of the cluster, thereby giving further credence to the model.