Molecular epitaxy of perfluoroicosane on PTFE tribological transfer films studied by XPS and RAIRS

Abstract

The molecular orientation of perfluoroicosane (PFI), n-C ₂₀ F ₄₂ , vacuum-deposited onto plain substrates (silicon and gold) and onto poly(tetrafluoroethylene) (PTFE) tribological transfer films, has been studied by angle-dependent X-ray photoelectron spectroscopy (XPS) and reflection–absorption IR spectroscopy (RAIRS). On the plain substrates PFI forms an ordered film with the molecular chains oriented perpendicular to the substrate. However, when deposited onto a PTFE tribological transfer film, epitaxial growth occurs such that the PFI chains align with the PTFE chains, parallel to the substrate. For PFI on silicon, XPS reveals a surface chemical shift for the uppermost CF ₃ groups of the sample.