Neutralization of intermediate-velocity Li emerging from Cs- and oxygen-covered Si (1 0 0) and GaAs (1 1 0) surfaces

Abstract

Neutral fractions were measured for intermediate-velocity ( v∼0.6−2 v 0, v 0: Bohr velocity 2.2×10 8 cm/s) Li emerging from Si (1 0 0) and GaAs (1 1 0) surfaces on which Cs and oxygen atoms were adsorbed to modify the electronic states of the surface. The obtained neutral fractions do not always correlate with the change in the work function induced by the adsorbates, especially when the Cs-saturated Si (1 0 0) and GaAs (1 1 0) surfaces are exposed to oxygen. The fact is inconsistent with the expectation of the resonant-neutralization model. The change in the neutral fraction induced by the oxygen adsorption gives information on the mechanism of charge exchange. At v< v 0, the final charge states of the emerging ions are sensitive to the valence-electron spatial density on the surface. At v> v 0, Li + ions capture electrons from the inner shells of atoms in subsurface layers as well as in the surface layer.