Neutralization of slow multicharged ions at a clean gold surface: Electron-emission statistics.

Abstract

Emission of slow electrons (${\mathit{E}}_{\mathit{e}}$\ensuremath{\le}60 eV) induced by impact of slow multicharged ions (impact velocity ${\mathit{v}}_{\mathit{p}}$\ensuremath{\le}2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ m/s) onto an atomically clean, polycrystalline gold surface has been studied both experimentally and by numerical simulation, based on the resulting electron-emission statistics. The projectile ions (${\mathrm{N}}^{\mathit{q}+}$, q=5,6; ${\mathrm{Ne}}^{\mathit{q}+}$, q=5--10; ${\mathrm{Ar}}^{\mathit{q}+}$, q=5--16; ${\mathrm{Kr}}^{\mathit{q}+}$, q=5--10; ${\mathrm{Xe}}^{\mathit{q}+}$, q=6,8,10; ${\mathrm{I}}^{\mathit{q}+}$, q=16,20,23,25) have been extracted from a recoil ion source pumped by the GSI UNILAC heavy-ion accelerator in Darmstadt, Germany. We discuss the shape of the experimentally obtained electron-emission statistics and, by means of numerical simulation based on the classical over-the-barrier model put forward recently by Burgd\"orfer, Lerner, and Meyer [Phys. Rev. A 44, 5674 (1991)], identify the various processes contributing to the ``above-surface'' electron emission, i.e., taking place until projectile impact on the surface. In particular, for impact of slow (E\ensuremath{\ge}50 eV) ${\mathrm{Ar}}^{12+}$ we show that most of the emitted electrons have energies below 50 eV, with the above-surface-produced fast Auger electrons being a small minority of less than 1%.