Diffusion of iodine into polyethylene implanted with 150 keV As + ions

Abstract

The iodine depth profiles and the sheet resistivity were studied on polyethylene implanted with 150 keV As + ions to the doses of 1 × 10 12–1 × 10 15 cm −2 and then exposed to iodine vapours for 4 hours at the temperature of 90°C. For lower implanted doses the iodine content in the radiation damaged layer increases with the dose, it achieves a maximum for the dose of 1 × 10 14 cm −2, and for still higher doses it decreases significantly. The iodine depth profiles change dramatically from “bumpy” ones for the doses below 1 × 10 14 cm −2 to “depleted” ones, exhibiting a pronounced concentration maximum at the depth of 300 nm, for higher implanted doses. The iodine depth profiles differ strongly from those expected from classical Fickian diffusion. The iodine doping leads to an immediate decrease of the sheet resistivity of radiation damaged polyethylene by about three orders of magnitude. A spontaneous increase of the sheet resistivity as a function of the time elapsed from the diffusion was observed together with iodine inward migration. The data obtained seem to support a concept of enhanced mobility of iodine atoms in the radiation damaged surface layer and their trapping on defects produced by ion impact.