Characterization of PTFE on Silicon Wafer Tribological Transfer Films by XPS, Imaging XPS and AFM

Abstract

Atomic force microscopy (AFM) shows that PTFE-on-silicon wafer tribological transfer films consist of narrow ribbons of PTFE, <1 μm wide and <10 nm high, aligned with the film draw direction. Within the ribbons the PTFE molecular chains are also aligned with the draw direction. Such materials are of interest as substrates for the epitaxial crystallization of polymers and small molecules. X-ray photoelectron spectroscopy demonstrates that the amount of PTFE put down increases with deposition temperature and pressure. The XPS azimuthal angle dependence at low electron take-off angle is consistent with the aligned ribbon morphology. Azimuthal and polar angle dependence and charging studies show that hydrocarbon contamination observed in the XPS spectrum is located on top of the silicon wafer substrate, in the channels between the PTFE ribbons. Imaging XPS confirms the pressure dependence of PTFE coverage, and at low deposition pressure reveals tracks of PTFE ∼100 μm wide, aligned with the film draw direction. Together with the AFM data this leads to a description of PTFE transfer films as fractal materials.