EPITAXIAL AND GRAPHOEPITAXIAL GROWTH OF MATERIALS ON HIGHLY ORIENTATED PTFE SUBSTRATES

The mechanism by which friction-deposited, highly orientated poly(tetr afluoroethylene) (PTFE) films promote orientated growth of materials w as investigated. For this purpose, transmission electron microscopy wa s used to determine the orientation of polyethylene and 1,4-bis-2-(5-p henyloxazolyl)benzene (POPOP) crystals grown from the vapour phase ont o the single crystal like PTFE films. Electron diffraction patterns re vealed that the polyethylene crystals adopted an orientation that mini mized 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 th e 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 t he material used.