Electrical characterization of in situ polymerized polyaniline thin films

The alternating conductivity, σ*(f) = σ′(f) + iσ″(f), of in situ polymerized polyaniline thin films doped with hydrochloric acid, deposited on top of an interdigitated gold line array previously deposited on glass substrates, were measured in the frequency (f) range between 0.1 Hz to 10 MHz and in the temperature range from 100 to 430 K. The results for σ′(f) are typical of a disordered solid material: for frequencies lower than a certain hopping frequency γhop, log[σ′(f)] is frequency-independent rising almost linearly for in log f > γhop. A master curve was thus obtained by plotting the real component of the conductivity using normalized scales σ′(f)/σdc and f/γhop, which is indicative of a single process operating in the whole frequency range. An expression encompassing the conduction through a disordered structure taken from previous random free energy barrier model for hopping carriers, as well a dielectric function to represent the capacitive behavior of the PAni was employed to fit the experimental results. The dielectric constant and activation energy for hopping carriers were obtained as function of the polymer doping level.