Orientational probing of polymeric thin films by NEXAFS: Calculations on polytetrafluoroethylene

We demonstrate the possibility for orientational probing of polymeric thin films by means of computer simulations of near-edge x-ray-absorption fine structure spectra. Using a recently developed algorithm for static exchange calculations of core-excited states we study the near-edge carbon and fluorine K absorption in polytetrafluoroethylene. Unpolarized and polarization-selected results for oligomers including up to five fluoroethylene subunits are presented. Through experimental comparision we confirm that the polytetrafluoroethylene (Teflon) polymer sample used in previous experimental studies is highly oriented, that the zig-zag structure prevails over the helical structure, and that the polymer chain is directed along the assumed slide direction. It is shown how experimental information can be used to determine if the carbon plane is perpendicular or orthogonal to the substrate surface.