On the mechanism of small Sin+andAln+ ( n = 1–3) cluster emission from 3–10 keV Ar + bombarded Al and Si surfaces at increased target current densities

Abstract

Secondary emission of the ion types M n q+ ( M = Si or Al; q = 1, 2; n = 1–3) from 3–10 keV Ar + bombarded polycrystalline Si and Al samples at target current densities ( J p) in the range of 60–800 μ A cm 2 has been studied in detail. For each projectile, the yield ratio of the cluster ions with respect to the singly-charged monomers ( I n + I 1 + ) is observed to be steady only for primary energies ( E) > 9 keV. Below this energy, the ratio rapidly increases in more or less an exponential manner with I p, the effect being most prominent at the lowest E value. This increase in yield ratio with target current density appears to be rather inconsistent with the recombination model, but can be, to some extent, explained within the framework of the direct emission model. Briefly speaking, our results, at least at high J p and low E values are in apparent contradiction to the standing notion that emission of small clusters is best understood within the framework of the recombination model proposed by Konnen.