Langmuir-Blodgett films of polyaniline: Fabrication and transport studies

Langmuir-Blodgett films of polyaniline have been fabricated and characterized electrically and optically. We found that the doping level of the films, determined from optical-absorption spectra, can be controlled by adding HCl or camphorsulfonic acid. The addition of neutral KCl salt to the subphase enhances the doping. A systematic effect of the acid on the isotherm was found, and related to the size of the corresponding counter ion. The conductivity of the doped films was studied as a function of film thickness, temperature (77 K300 K), and electric field (0{}10⁵ V/cm). The low-field conductivity obeyed the behavior ln {σ}(T){∝}-(T₀/T)1/2 over the whole temperature range measured, and ln {σ}(F){∝}F^1/(1+ν) with {ν}{≈}0.9 at higher fields. The results suggest three-dimensional variable-range hopping in a parabolic quasigap, possibly a Coulomb gap.