Work-function dependence of above-surface neutralization of multicharged ions

Measurements have been made of projectile K-Auger-electron emission during interactions of 60-keV N⁶⁺ ions grazingly incident on a Au(011) single crystal whose work function was modified by submonolayer deposits of Cs. K Auger spectra were obtained for incidence angles in the range 0.3^∘{}--5^∘{}, using clean, as well as cesiated, Au surfaces whose work function had been reduced by as much as 3.3 eV. For incidence angles smaller than 5^∘{}, an enhancement on the above-surface K Auger component, relative to that observed for ``clean'' Au, could be discerned with decreasing surface work function, which appears to saturate below 0.7^∘{} (corresponding to an inverse perpendicular velocity of about 200 a.u.^-1) at approximately 30--35 %. The experimental results are compared with modeling studies of the work-function dependence of above-surface neutralization and projectile K Auger emission, using a simulation based on the classical over-the-barrier model that was modified to treat the case of a ``two-component'' surface. The simulation results agree qualitatively with the experimental results up to v_⊥^-1=200. At higher inverse perpendicular velocities, the simulated enhancement continues to increase and exceeds the clean Au result by more than a factor of 2 at v_⊥^-1=1000. Speculations about possible reasons for this discrepancy will be presented.