Highly oriented polytetrafluoroethylene films: A force microscopy study

Highly oriented polytetrafluoroethylene (PTFE) thin films might be useful as substrates for oriented growth of well-organized layers of organic materials. In this study, such PTFE films were deposited onto oxide-covered Si wafers by sliding of a PTFE rod at constant speed under controlled conditions of deposition temperature T-d and load W. The morphology of these films was studied down to molecular resolution by atomic force microscopy, and the amount of deposited polymer was measured by nuclear reaction analysis, dependence on T-d and W was investigated. For T-d > 150 degrees C these films consist of straight and very long (> 100 mu m) ribbons parallel to the sliding direction. Their width and their height, i.e. the amount of PTFE, are increasing with T-d and W, so that the substrate can be almost completely covered. These ribbons are crystalline, being bundles of polymer chains with the helix axis parallel to the ribbon length. Known properties of PTFE and our results suggest that the final film formation and the resulting morphology are dependent on crystallization upon cooling and not only on deposition parameters.