Enhancement of the positive secondary ion yield during low‐energy, dual‐beam depth profiling of polytetrafluoroethylene with 1‐keV Cs+

Abstract

AbstractThis work documents the behaviour of the positive secondary ion yield of bulk polytetrafluoroethylene (PTFE) under dual‐beam depth profiling conditions employing 1 keV Ar+, Cs+ and SF5+. A unique chemical interaction is observed in the form of a dramatic enhancement of the positive secondary ion yield when PTFE is dual‐beam profiled with 1 keV Cs+. The distinct absence of such an enhancement is noted for comparison on two non‐fluorinated polymers, polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS). The bulk PTFE was probed using 15‐keV, 69Ga+ primary ions in dual beam mode under static conditions; 1‐keV Ar+ (a non‐reactive, light, noble element), Cs+ (a heavier metallic ion known to form clusters) and SF5+ (a polyatomic species) served as the sputter ion species. The total accumulated primary ion dose was of the order of 1015 ions/cm2, which is well beyond the static limit. The enhancement of the positive secondary yield obtained when profiling with 1‐keV Cs+ far exceeds that obtained when SF5+ is employed. An explanation of this apparent reactive ion effect in PTFE is offered in terms of polarisation of CF bonds by Cs+ in the vicinity of the implantation site thereby predisposing them to facile scission. The formation of peculiar, periodic CsxFy+ (where y = x − 1) and CsxCyFz+ clusters that can extend to masses approaching 2000 amu are also observed. Such species may serve as useful fingerprints for fluorocarbons that can be initiated via pre‐dosing a sample with low‐energy Cs+ prior to static 15‐keV Ga+ analysis. Copyright © 2005 John Wiley & Sons, Ltd.