ANGULAR-DISTRIBUTIONS AND CHARGE-EXCHANGE IN NA SCATTERING FROM CLEAN AND CS COVERED AG(111)

An experimental study of 35 eV Na scattering at normal incidence from a clean and Cs covered Ag(111) surface is presented. The measured ion and neutral yield are in quite good agreement with model calculations by Nakanishi et al. using the time-dependent Newns-Anderson model taking into account the Coulomb interaction between electrons of opposite spin occupying the ionization and affinity level. For a complete description local workfunction effects cannot be neglected. With the help of classical trajectory calculations most of the scattering phenomena can be understood, both for the clean and for the cesiated surface. From the measurements a neutralization cross section of 175 +/- 40 angstrom-2 is extracted for each adsorbed Cs atom. The pronounced rainbow scattering observed for the clean surface is masked but does not disappear upon Cs adsorption.