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 ${\mathrm{N}}^{6+}$ 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${.}^{\mathrm{-}1}$) 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 ${\mathit{v}}_{\mathrm{\perp }}^{\mathrm{-}1}$=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 ${\mathit{v}}_{\mathrm{\perp }}^{\mathrm{-}1}$=1000. Speculations about possible reasons for this discrepancy will be presented.