ToF-SIMS observation of PTFE surfaces modified by α-particle irradiation

The surface structure of polytetrafluoroethylene (PTFE) upon a-particle irradiation has been investigated at doses in the range of 1 X 10(7) to 1 x 10(11) Rad and compared with the surface structure of the unirradiated polymer. Both neat and 25% fiberglass content PTFE were studied. The samples, maintained at nominal room temperature, were irradiated in vacuum by 5.5 MeV He-4(2+) ions generated in a tandem accelerator beam line. Static time-of-flight SIMS (ToF-SIMS) was employed to probe chemical changes at the surface as a function of the irradiation level. In general, the data are indicative of increased cross-linking at alpha-doses less than 1 x 10(9) Rad, followed by increased fragmentation and unsaturation at alpha-doses greater than 1 x 10(9) Rad. Throughout the irradiation regime, scission is a constant factor promoting cross-linking, branching, and unsaturation. However, at alpha-doses greater than 1 x 10(10) Rad, extreme structural degradation of the polymer becomes evident and is accompanied by conversion to oxygen-functionalized and aliphatic compounds. Thus, for PTFE in an alpha-particle field, an upper exposure limit of similar to 10(10) Rad is essential for nominal retention of molecular structure. Finally, a quantitative relationship between alpha-dose and characteristic fragment ion intensity is developed. Copyright (c) 2005 John Wiley & Sons, Ltd.