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

Abstract

Measurements have been made of projectile [ital K]-Auger-electron emission during interactions of 60-keV N[sup 6+] ions grazingly incident on a Au(011) single crystal whose work function was modified by submonolayer deposits of Cs. [ital K] Auger spectra were obtained for incidence angles in the range 0.3[degree]--5[degree], 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[degree], an enhancement on the above-surface [ital 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[degree] (corresponding to an inverse perpendicular velocity of about 200 a.u.[sup [minus]1]) at approximately 30--35 %. The experimental results are compared with modeling studies of the work-function dependence of above-surface neutralization and projectile [ital 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 [ital v][sub [perpendicular]][sup [minus]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 [ital v][submore » [perpendicular]][sup [minus]1]=1000. Speculations about possible reasons for this discrepancy will be presented.« less