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

The molecular orientation of perfluoroicosane (PFI), n-C20F42, 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 PFT 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 CF3 groups of the sample.