Iodine diffusion and trapping in polyethylene implanted with 150 keV F + and As + ions to different fluences

Polyethylene samples irradiated with 150 keV F ⁺ and As ⁺ ions to the fluences of 10 ¹¹-10 ¹⁵ cm ^-2 were exposed to iodine vapour at 90°C for 4 h and the depth profiles of incorporated iodine were determined using the Rutherford back-scattering technique. For the implanted fluences ≤10 ¹³ cm ^-2, the iodine content increases proportionally to the implanted ion fluence, and the average numbers of iodine atoms incorporated per ion are 5.2 × 10 ³ and 1.1 × 10 ⁴ for F ⁺ and As ⁺ irradiation, respectively. For higher implanted fluences the increase in the iodine uptake is much slower and for the highest fluences the iodine content even declines. The iodine depth profiles evolve dramatically with increasing ion fluence. For the fluences ≤10 ¹⁴ cm ^-2 and both ion species, "bumpy" profiles are observed which, at higher fluences, change into "depleted" ones comprising two concentration maxima with no iodine in between. The profile change is due to a gradual degradation of polymer structure taking place at higher implanted fluences. A simple phenomenological model is suggested describing the profile evolution over the whole range of the fluences used.