Ionization probability of sputtered cluster anions: Cn− and Sin−

The yields of negatively charged carbon Cn− (n≤21) and silicon Sin− (n≤9) cluster ions sputtered by 14.5 keV Cs+ ions from graphite and silicon, respectively, were monitored during the initial stages of Cs incorporation in the near-surface regions of the samples. The associated work function (WF) variations ΔΦ were determined in situ from the shifts of the sputtered ions’ emission-energy spectra; the total change ΔΦ amounted to ∼2.7 eV for graphite and to ∼2.3 eV for silicon. For Cn− anions the lowering of Φ induces an exponential increase of the ionization probability P−, whereas for Sin− ions P− is also enhanced by the lowering of the WF, but no distinct exponential scaling of P− with ΔΦ is observed.