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Modifications of Polypropylene Induced by the Implantation of Iodine Ions

The polypropylene (PP) samples implanted with I+ ions at the implantation energies of 50, 100 and 150 keV to the fluence of 1×1015 cm-2 were studied using standard RBS (Rutherford backscattering) technique. The surface of the implanted PP samples is heavily damaged and enriched in carbon. The measured projected ranges of iodine atoms are by 10 to 30% lower than the theoretical ones calculated using Monte-Carlo simulation code TRIM (transport of ions in matter) code for pristine PP. The differences may be due to structural changes of polymer during the ion implantation. The range stragglings exceed the theoretical TRIM estimations about twice. The profile broadening is probably due to the diffusion of the iodine atoms through the damaged PP surface layer. In repeated RBS measurements, the iodine diffusion was confirmed with diffusion coefficient of 2.7×10-18 cm2·s-1. Noticeable oxidation of the implanted samples was observed, with majority of the oxygen atoms being trapped in the region of maximum radiation defects. The bulk oxygen concentration profile resembles that of iodine but it is shifted inward by 200-350Å. The relative oxygen content in the bulk is an increasing function of the implantation energy and it exceeds considerably the stoichiometric value for common iodine oxides.