Influence of primary ion bombardment conditions on the emission of molecular secondary ions

In order to further our understanding of the secondary ion emission behavior from organic surfaces, we have performed a systematic study on the influence of the primary ion parameters. As model sample Irganox 1010 on low density polyethylene (LDPE) was used. Both monoatomic (Ga, Cs, Au) and polyatomic (Au-2, Au-3, SF5, C-60) primary ions were used. Additionally, the primary ion energy was varied. The data were evaluated by calculating secondary ion yields, disappearance cross sections and ion formation efficiencies (yield/damage cross section). The results show that heavier monoatomic ions are more efficient than lighter ones and that polyatomic primary ions are more efficient than monoatomic ones. Highest efficiency values are found for C-60 bombardment at 20 keV. Compared to Ga bombardment the efficiency gain in this case is more than 2000-fold. Additionally it can be shown that the higher efficiency is correlated with a softer ionization, i.e. less fragmentation. The results suggest a much more homogeneous energy distribution in the sample surface by polyatomic primary ions compared to monoatomic ones. (C) 2004 Elsevier B.V. All rights reserved.