DETERMINATION OF SURFACE-STRUCTURE AND ORIENTATION OF POLYMERIZED TETRAFLUOROETHYLENE FILMS BY NEAR-EDGE X-RAY ABSORPTION FINE-STRUCTURE, X-RAY PHOTOELECTRON-SPECTROSCOPY, AND STATIC SECONDARY ION MASS-SPECTROMETRY

Films of conventional and radio frequency glow discharge (RFGD) polymerized tetrafluoroethylene (TFE) were examined by ultrasoft X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS),and static secondary ion mass spectrometry (SIMS). The polarization-dependent intensity changes of transitions to C-C and C-F sigma* orbitals in the carbon and fluorine near-edge X-ray absorption fine structure (NEXAFS) spectra revealed different CF2 chain orientations. The surface region of skived poly(tetrafluoroethylene) (PTFE) was composed of CF2 chains oriented along the surface striations present in PTFE. XPS confirmed only CF2 groups were present in the PTFE surface region. Fluorocarbon (FC) films prepared by RFGD deposition of TFE onto substrates placed directly in the visible glow (TFE-I) were randomly oriented. XPS showed the TFE-I films had CF, CF2, and CF3 groups in the surface region. Static SIMS indicated that the TFE-I film surface contained CF3 and C2F5 groups. XPS showed the FC films prepared by RFGD deposition of TFE onto substrates placed downstream from the visible glow (TFE-II) contained approximately 90% CF2 groups. The strong polarization dependence of the C and F NEXAFS spectra of these films indicated the CF2 groups were aligned in vertical chains on the substrate. Static SIMS and XPS results suggested the outermost surface of the CF2 chains are terminated with CF3 groUPs. For thin (50-500 angstrom) FC RFGD films deposited onto polymeric substrates such as poly(methyl methacrylate) or poly(ethylene terephthalate), fluorescence yield detection XAS could be used to examine the substrate, while XPS, static SIMS, and electron yield detection XAS could be used to examine the FC overlayer. These results demonstrate the complementary nature of ultrasoft XAS, XPS, and static SIMS for detailed surface structural characterization of polymers.