Epitaxial and graphoepitaxial growth of materials on highly orientated PTFE substrates

The mechanism by which friction-deposited, highly orientated poly(tetrafluoroethylene) (PTFE) films promote orientated growth of materials was investigated. For this purpose, transmission electron microscopy was used to determine the orientation of polyethylene and 1,4-bis-2-(5-phenyloxazolyl)benzene (POPOP) crystals grown from the vapour phase onto the single crystal like PTFE films. Electron diffraction patterns revealed that the polyethylene crystals adopted an orientation that minimized the lattice mismatch at the interface between this material and the PTFE substrate. On the other hand, the POPOP crystals aligned in a fibre pattern, implying that orientated growth occurred because of the grating-shaped surface topography of the PTFE films. Evidently, the latter films were capable of promoting orientated growth of materials by a graphoepitaxial mechanism or conventional epitaxy, depending on the material used.