Ionization probability of sputtered cluster anions: C n− and Si n−

Abstract

The yields of negatively charged carbon C n − ( n≤21) and silicon Si n − ( 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 Δ Φ were determined in situ from the shifts of the sputtered ions’ emission-energy spectra; the total change Δ Φ amounted to ∼2.7 eV for graphite and to ∼2.3 eV for silicon. For C n − anions the lowering of Φ induces an exponential increase of the ionization probability P −, whereas for Si n − ions P − is also enhanced by the lowering of the WF, but no distinct exponential scaling of P − with Δ Φ is observed.