Electron emission and image-charge acceleration for the impact of very highly charged ions on clean gold

We present total yields for emission of slow ([ital E][sub [ital e]][le]50 eV) electrons due to the impact of slow ([ital v][sub [ital p]][le]5[times]10[sup 5] m/s) highly charged ions [Ar[sup [ital q]+] ([ital q][le]18), Xe[sup [ital q]+] ([ital q][le]51), and Th[sup [ital q]+] ([ital q][le]80)] on clean polycrystalline gold. The highly charged ions were produced in the Lawrence Livermore National Laboratory electron-beam ion trap; electron yields have been derived from the respective measured electron emission statistics. The experimental data support a currently accepted scenario for multicharged ion-induced electron emission, which is largely based on a classical over-barrier model. In particular, we are able to distinguish different processes contributing to the total above-surface electron emission. In addition, an ultimate low-impact-energy limit due to projectile self-acceleration toward the metal surface, as a result of the projectile image charge, has been demonstrated and evaluated.