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

This 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 SF 5 + . 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, 69 Ga + 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 SF 5 + (a polyatomic species) served as the sputter ion species. The total accumulated primary ion dose was of the order of 10 15 ions/cm 2 , 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 SF 5 + is employed. An explanation of this apparent reactive ion effect in PTFE is offered in terms of polarisation of CF bonds by Cs + in the vicinity of the implantation site thereby predisposing them to facile scission. The formation of peculiar, periodic Cs x F y + (where y = x − 1) and Cs x C y F z + 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.