Slow-particle-induced kinetic electron emission from a clean metal surface: A comparison for neutral and ionized projectiles

Abstract

Electron emission from a clean gold surface bombarded by slow (v1 a.u.) neutral or singly charged atoms has been investigated both experimentally and theoretically. The determination of electron-emission statistics for 1--16-keV ${\mathrm{H}}^{+}$, ${\mathrm{H}}^{0}$, ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{He}}^{+}$, ${\mathrm{He}}^{0}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{Ne}}^{0}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{Ar}}^{0}$, respectively, delivered accurate total electron-emission yields, which are consistently higher for positively charged ions than for the corresponding isoenergetic neutral atoms. It was assured that potential emission could not be responsible for the observed differences. ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ bombardment at low impact energy causes equal yields as for ${\mathrm{H}}^{0}$, but for higher kinetic energy even the yields for ${\mathrm{H}}^{+}$ are surpassed. The results are explained with a semiempirical theory for heavy-particle-induced electron emission, assuming different screening of projectile cores by the accompanying electron(s) during the continuous change of projectile charge upon penetration of the solid. For ${\mathrm{H}}^{+}$,${\mathrm{H}}^{0}$ bombardment a quantitative description of the experimentally observed effects could be achieved by calculation of the stopping power for slow projectiles in different charge states, together with the electron-capture and -loss cross sections for these projectiles colliding with the target atoms.