Slow light ion irradiation of polymers III: quantification of the etching process beyond the etchant breakthrough threshold

Whereas hitherto most of all papers on ion irradiation of thin polymer foils and their subsequent etching restrict to the study of etchant breakthrough times tB only, we also wanted to quantify the further progress of the etching process beyond these tB times. Therefore, we first defined an additional time t100%, which denotes the maximum etching time up to which etching progress can still be recorded safely by our analytic technique (Transmission Current Spectroscopy). Using these two times, etching of different samples can be well compared with each other to detect common features. When quantifying the etching progress between tB and t100%, a usually smooth and gradual increase of the transmission currents is initially favored. However, at later etching stages, smaller or larger current jumps become more frequent. In earlier discussions on ion irradiation and etching of polymers, there was still the question left open, whether different irradiation and etching directions might affect the measured results, especially when the ion irradiation created some asymmetry between both the front and back sides of the examined foils. When examining SLI-irradiated foils under both possible directional configurations, we found that the majority of all observations indeed points against any directional dependence, though in a few cases it appears to play some role. When studying conventional swift heavy ion (SHI) irradiation of common polymers, the data scattering of both the tB and t100% values of different samples is typically in the {12to1} order of magnitude only. However, when replacing the SHI irradiation with SLI (slow light ions) irradiation in the same samples, the data scattering increases dramatically. Even if one restricts SLI irradiation to the same fluence only, the data straggling of both tB and t100% already covers typically some 2–3 orders of magnitude. When covering all SLI fluences instead, the straggling increases up to 3–4 orders of magnitude. There are a number of arguments that indeed explain this extraordinarily large straggling of the etching times after SLI irradiation.