SYNOPSISPolyethylene samples implanted with 150 keV F+ ions to the doses 1011-1015 cm-' were doped with iodine by exposing them to iodine vapors a t 90°C for 3 h. The iodine depth profiles, measured by Rutherford back-scattering techniques, evolve dramatically with increasing implanted doses, from "bumpy" profiles at lower fluences to a "depleted" one comprising two concentration maxima with no iodine in between observed at highest dose. The areal density of iodine incorporated into the 500-nm-thick surface layer is proportional to the ion dose for the doses I 1 X 1013 cm-' and it achieves a saturation or declines at higher doses. The results support the concept of enhanced iodine diffusion in the radiationdamaged surface layer and its trapping on the radiation defects within. The sheet resistivity of as-implanted PE is practically constant, independent of the implanted dose. Iodine doping of the ion-implanted PE samples results in immediate, strong decrease of the sheet resistivity by 3-4 orders of magnitude which, however, is not stable. The measured temperature dependence of the sheet resistance indicates p-semiconducting character of ionimplanted and iodinated samples at the temperatures below the PE melting point. The iodine redistribution and/or escape with increasing temperature is observed. 0 1996 John Wiley & Sons, Inc.
I NTRO DU CTlO NSteadily increasing interest in the diffusion of various inorganic agents into polymers is due to several unsolved fundamental problems in the field and to the importance of the process for potential applications in membrane production and microelectronics.'*' The diffusion of different agents from gaseous, liquid, or solid phases is a relatively simple technique of modification of surface properties of polymer^.^,^ Iodine as a dopant has been found to increase electrical conductivity of p~lyethylene,~ p01y-2-ethynylpyridine,~ poly~inylfluoride,~ and cellulose acetate-butyrate. ' The penetration of dopants into polymers may be significantly affected by a prior irradiation with energetic heavy ions leading to dramatic changes in polymer surface ~t r u c t u r e .~ Increased permeation of gases through thin polymer foils irradiated by ener-~~~ * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 60, 1455-1459 (1996) 0 1996 John Wiley & Sons, Inc.CCC 0021-8995/96/091455-05 getic ions is well documented," and an enhanced diffusion of iodine atoms into radiation-damaged polymers has recently been o b s e r~e d .~,~ Previous experimental data on the diffusion of various agents into polymers modified by ion irradiation are rather scarce and the microscopic mechanism of the penetration and trapping of atoms or molecules on radiation defects remains unclear. Also, little is known about the effect of doping on the modified polymer's physical properties, such as electrical conductivity.Here, the structure and electrical conductivity of polyethylene implanted with different doses of 150 keV F+ ions and subsequently doped with iodine are studied wit...