Linearly polarized carbon k-edge x-ray absorption spectroscopic study of heavily p-doped polyacetylene film with preferred orientation

The structures of polyacetylene (PA) films with oriented chains have been intensively investigated with linearly polarized carbon K-edge near edge x-ray absorption fine structure (NEXAFS) for the first time. The angular dependence of linearly polarized peak feature has been observed from normal to glancing incidence, with respect to the stretched direction of the PA film. The polymeric chain orientation of the stretched trans-PA has been determined with the strong angular dependence of π*_C-C, σ*_C-H, and π*_C-C resonance. Heavily doped PA films with 6% FeCl₄^- or ClO₄^- show different near-edge peak features from the undoped PA films, especially in the energy region of ∼285 eV corresponding to electronic transition of C 1s electron to unoccupied π*_C-C molecular level. Upon doping, the resonance peak position for sp² hybridization of unsaturated C-C bonding is shifted to higher energy and the peak intensity is reduced significantly, which indicates that the cleavage of conjugated π bonds by p-doping occurs in the trans polymeric chain reducing the alternating double bond chain length. Although the peak features for σ*_C-H and σ*_C-C have been effectively changed, no angular dependence of the NEXAFS spectra are observed in the doped PAs. © Physica Scripta 2005.