Surface analysis of DC oxygen plasma treated or chromium evaporated poly(ethylene terephthalate) foils by soft X-ray absorption spectroscopy (NEXAFS)

Surface modified biaxially stretched poly(ethylene terephthalate) (PET) foils have been analysed by surface sensitive soft X-ray absorption (NEXAFS) spectroscopy. Generally, an orientation of polymer chain segments can be detected by a variation of the angle between the linearly polarized synchrotron light beam and the surface normal of the investigated sample (angle resolved NEXAFS spectroscopy). Biaxially stretched PET foils have been found to be characterized by angle dependent NEXAFS C and O K-edge spectra. This angle dependence was interpreted to be a result of a preferential orientation of the PET chain segments at the surface wherein the plane defined by the benzene ring is parallel to the surface plane. In the course of chromium deposition or low pressure O2 DC plasma treatment that preferential orientation is continuously diminished. This is interpreted to be a structural effect of the respective treatment.