We observe trajectory dependent neutralization of 1 keV He+ ions scattered from the Pb(111) surface. Varying the azimuthal angle of the ion trajectories we observe neutralization by charge densities of the next and second next neighbors of the target atom occurring at polar angles between 40 and 15 degrees. This corresponds to ion-neighbor distances between 2.3 Å and 1 Å. We adjust a three parameter neutralization model for Pb to fit the trajectory dependence of the survival probability for the well known Pb(111) surface geometry. Good agreement with experimental results is found only if a shell like neutralization region is centered at a radius of 1.46 Å. In regard to the spatial distribution of the neutralization rate we consider the Pb 6sp electrons to be the source of the long distance neutralization that leads to the trajectory dependence. The same neutralization model is then applied for a structural analysis of ultra thin Pb films evaporated on Cu(100), where we confirm the existence of a Pb-Cu surface alloy on the c(4x4) Pb/Cu(100) and the existence of a Pb overlayer on the c(2x2) Pb/Cu(100). It turns out that the neutralization model developed for Pb atoms embedded in the (111) surface holds also for adsorbed Pb atoms.
Corresponding author: P. Varga (varga).
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