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Metallization and demetallization of clean and oxygen-covered ultrathin alkali metal films on GaAs(1 0 0)
Authors:Peter Fouquet  Gregor Witte
Institution:

a Max-Planck Institut für Strömungsforschung, Bunsenstraße 10, D-37073 Göttingen, Germany

b Ruhr-Universität Bochum, Physikalische Chemie I, Universitätsstraße 150, D-44801 Bochum, Germany

Abstract:The structure and the electronic valence state occupation of ultrathin K, Rb, and Cs films grown on a GaAs(1 0 0)-(4×2) surface have been studied by means of metastable He atom scattering (MHAS), He atom scattering (HAS), and low-energy electron diffraction (LEED) at temperatures ranging from 150 to 400 K. From the survival probability of the scattered He* atoms, detailed information on the coverage-dependent filling of the alkali metal valence states and their emptying upon subsequent exposure to oxygen were derived. These data reveal for K and Rb a nearly linear band filling with increasing coverage starting at about 0.5 ML whereas a more rapid filling is observed for Cs which is almost completed at about 0.7 ML. Subsequent oxygen adsorption causes a demetallization of the metallic alkali metal monolayers. In case of Cs, a distinct minimum of the He* signal appears at an oxygen exposure of about 0.8 L, presumably indicating the onset of subsurface oxidation.
Keywords:Atom — solid scattering and diffraction — elastic  Surface electronic phenomena  Noble gases  Alkali metals  GaAs  Oxygen
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