EMISSION OF ELECTRONS FROM A CLEAN GOLD SURFACE-INDUCED BY SLOW, VERY HIGHLY-CHARGED IONS AT THE IMAGE CHARGE ACCELERATION LIMIT

Total low-energy electron yields for the normal incidence interaction of slow very highly charged ions (Xe-136q+, 21 less-than-or-equal-to q less-than-or-equal-to 51; Th-232q+, 51 less-than-or-equal-to q less-than-or-equal-to 80) with a clean gold surface have been determined from the related measured electron emission statistics. The projectile impact energies could be reduced down to the image charge acceleration limit. The electron emission yield was found to increase proportionally with the increasing projectile charge state in all cases studied, suggesting no saturation in the ability of the Au target to provide necessary electrons within the above surface interaction time (e.g., about 280 electrons/projectile for Th79+ in less than 10(-13) s). Because of the relatively narrow energy distribution and very high charge states of the incident ions, the first clear measurements of image charge acceleration from electron emission yields could be performed. Results of a quantitative study of this acceleration are in good agreement with those of a theoretical model recently developed by J. Burgdorfer et al.