Electron donor–acceptor properties of thin polymer films on silicon. II. Tetrafluoroethylene polymerized by RF glow discharge techniques

Metal–insulator–semiconductor (MIS) techniques were used to show that 86–210 nm thick plasma-polymerized tetrafluoroethylene films on silicon stored only negative charge (electron acceptors). This property persisted at a reduced level when a 7 nm thick inner layer of hydrolyzed γ-aminopropyltriethoxysilane was combined with an outer layer of plasma-polymerized tetrafluoroethylene. The dispersion force contribution to the surface energy, γ^d_s, for the fluorocarbon films was found to be 6 mJ/m² (erg/cm²) which is comparable with the lowest values found in the literature. X-ray photoelectron spectroscopy (XPS) revealed a substantial content of ? CF₃ groups in the fluorocarbon films. This finding coupled with the reported effects of noncrystallinity, crosslinking, and branching on the surface energies of fluorocarbon systems were used to explain the low surface energy and electrophilicity of the plasma-deposited poly(tetrafluoroethylene)s.