MODIFICATION OF POLYETHYLENE PROPERTIES BY IMPLANTATION WITH F+ IONS AND IODINATION

Polyethylene samples implanted with 150 keV F+ ions to the doses 10(11 )-10(15) Cm-2 were doped with iodine by exposing them to iodine vapors at 90 degrees C for 3 h. The iodine depth profiles, measured by Ruthe rford back-scattering techniques, evolve dramatically with increasing implanted doses, from ''bumpy'' profiles at lower fluences to a ''depl eted'' one comprising two concentration maxima with no iodine in betwe en observed at highest dose. The areal density of iodine incorporated into the 500-nm thick surface layer is proportional to the ion dose fo r the doses less than or equal to 1 X 10(13) cm(-2) and it achieves a saturation or declines at higher doses. The results support the concep t of enhanced iodine diffusion in the radiation-damaged surface layer and its trapping on the radiation defects within. The sheet resistivit y of as-implanted PE is practically constant, independent of the impla nted dose. Iodine doping of the ion-implanted PE samples results in im mediate, strong decrease of the sheet resistivity by 3-4 orders of mag nitude which, however, is not stable. The measured temperature depende nce of the sheet resistance indicates p-semiconducting character of io n-implanted and iodinated samples at the temperatures below the PE mel ting point. The iodine redistribution and/or escape with increasing te mperature is observed. (C) 1996 John Wiley & Sons, Inc.