Thermoelectric power and field-effect mobility in self-assembled films of poly- and oligoanilines

Thin conducting films of polyanilines and oligoanilines were deposited by using a layer-by-layer self-assembly process. Conductivity, thermoelectric power and field-effect measurements were performed on the films. The highest conductivities were around 1 S cm⁻¹ at room temperature. The conductivity was studied as a function of temperature and was found to obey the T^-12 law of variable-range hopping. The thermoelectric power of the films was initially n-type in air at room temperature, but changed its sign to p-type under vacuum or with time. A linear temperature dependence was observed and related to the contribution from metallic polymer chain segments. The field effect, measured using thin film transistor structures, was always n-type and the field-effect mobilities about 10⁻⁶-10⁻³cm2 V⁻¹ S⁻¹. The Coulomb gap model gives a good description of the system still lacking an expression for the field effect.