P. Granholm et al., LANGMUIR-BLODGETT-FILMS OF POLYANILINE - FABRICATION AND TRANSPORT STUDIES, Physical review. B, Condensed matter, 55(20), 1997, pp. 13658-13663
Langmuir-Blodgett films of polyaniline have been fabricated and charac
terized electrically and optically. We found that the doping level of
the films. determined from optical-absorption spectra, can be controll
ed by adding HCl or camphorsulfonic acid. The addition of neutral KCl
salt to the subphase enhances the doping. A systematic effect of the a
cid on the isotherm was found, and related to the size of the correspo
nding counter ion. The conductivity of the doped films was studied as
a function of film thickness, temperature (77 K < T < 300 K), and elec
tric field (0 < F less than or equal to 10(5) V/cm). The low-field con
ductivity obeyed the behavior ln sigma(T)proportional to -(T-0/T)(1/2)
over the whole temperature range measured, and ln sigma(F)proportiona
l to F1/(1+nu) with nu approximate to 0.9 at higher fields. The result
s suggest three-dimensional variable-range hopping in a parabolic quas
igap,possibly a Coulomb gap.