Iodine incorporation into polymeric films investigated by angle-resolved XPS

Distribution of elements into subsurface layers (up to 120 angstrom thickness) of polyphenylacetylene (PPA) films doped with I2 vapour has been determined by X-ray photoelectron spectroscopy data using a unique numerical technique. Concentration of incorporated iodine has been shown to increase with exposure time; the concentration profiles are dome-shaped and iodine does not penetrate much into the bulk of PPA films, even when exposed to I2 vapours for 1 h. The depth of the layer corresponding to maximum iodine concentration is directly proportional to the iodine exposure time. The non-homogeneous distribution of the doping species in the polymer may be responsible for the low conductivity observed for heterogeneously doped PPA films.