Resonant charge transfer during scattering of low energy 7Li + from cesiated surfaces

Abstract

Neutral fractions of 2 keV 7Li + ions scattered from cesiated Al(100), Ni(100) and Si(111)-7 × 7 surfaces are measured and compared. For low coverages of Cs adsorbed on Al(100) and Ni(100), there are large differences between the neutral fractions of Li ions singly scattered from substrate and adsorbate atomic sites. These differences disappear as the Cs coverage is increased. This behavior is attributed to an inhomogeneous to homogeneous transition in the surface local electrostatic potential. For Cs adsorbed on Si(111)-7 × 7, on the other hand, the Li neutral fractions for scattering from Si and Cs sites are nearly equal over the entire coverage range. This is attributed to coupling of the exiting Li energy levels to the surface dangling bonds. As a result, the final charge state distribution is insensitive to adsorbate-induced inhomogeneities in the surface potential.