Fig. 4: Characterization of FEP films.

a The molecular structure diagrams of several FEP films structures are given by a Fourier transform infrared (ATR-FTIR) spectrum. b C 1 s XPS spectra of FEP films. c 2D-WAXD patterns of FEP films. d X-ray diffraction (XRD) pattern of FEP films. e The o-Ps lifetime and free volume radius of FEP are calculated by positron lifetime spectrum. Source data are provided as a Source Data file.