CONDUCTIVITY BARRIERS AND TRANSMISSION ELECTRON-MICROSCOPY ON HIGHLY CONDUCTING POLYACETYLENE

Individual fibrils were extracted from the bulk of high-sigma samples of Naarmann polyacetylene by using a special preparation technique and subsequently studied with transmission electron microscopy (TEM) both before and after gas phase doping with iodine. Doping induces constrictions in the fibrils, an effect also found in SEM after solution doping of polyacetylene films. The TEM results indicate inhomogeneous doping within the fibrils, showing highly doped regions separated by non-doped regions, which are typically 1 - 3 nm wide. In this context, it is interesting that the temperature dependence of the dc conductivity of Naarmann polyacetylene doped to maximum with iodine can be fitted with the Sheng formula within a model of a heterogeneously conducting material consisting of highly conducting regions separated by insulating barriers. Within a phenomenological model, barrier widths are derived, which are comparable to the widths of the undoped regions observed with TEM.