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 (${\mathit{E}}_{\mathit{e}}$≤50 eV) electrons due to the impact of slow (${\mathit{v}}_{\mathit{p}}$≤5×${10}^5$ m/s) highly charged ions [${\mathrm{Ar}}^{\mathit{q}+}$ (q≤18), ${\mathrm{Xe}}^{\mathit{q}+}$ (q≤51), and ${\mathrm{Th}}^{\mathit{q}+}$ (q≤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.