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 K < T < 300 K), and electric field (0 < F less than or equal to 10(5) V/cm). The low-field conductivity obeyed the behavior ln sigma(T)proportional to -(T-0/T)(1/2) over the whole temperature range measured, and ln sigma(F)proportional to F1/(1+nu) with nu approximate to 0.9 at higher fields. The results suggest three-dimensional variable-range hopping in a parabolic quasigap,possibly a Coulomb gap.