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

The surface structure of polytetrafluoroethylene (PTFE) upon α‐particle irradiation has been investigated at doses in the range of 1 × 10 7 to 1 × 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 4 He 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 α‐ doses less than 1 × 10 9 Rad, followed by increased fragmentation and unsaturation at α‐ doses greater than 1 × 10 9 Rad. Throughout the irradiation regime, scission is a constant factor promoting cross‐linking, branching, and unsaturation. However, at α‐doses greater than 1 × 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 α ‐particle field, an upper exposure limit of ∼10 10 Rad is essential for nominal retention of molecular structure. Finally, a quantitative relationship between α‐ dose and characteristic fragment ion intensity is developed. Copyright © 2005 John Wiley & Sons, Ltd.