  Recent advances in synthesis and electrical characterization of nanofibers
and nanotubes made out of various conjugated polymers attract attention of the
research community to studies of transport properties of these materials. In
this work we present a theoretical analysis of electron transport in polymer
nanofibers assuming them to be in conducting state. We treat a conducting
polymer as a network of metallic-like grains embedded in poorly conducting
environment, which consists of randomly distributed polymeric chains. We
analyze the contribution from intergrain electron resonance tunneling via
intermediate states localized on the polymeric chains between the grains.
Correspondingly, we apply the quantum theory of conduction in mesoscopic
systems to analyze this transport mechanism. We show that the contribution of
resonance electron tunneling to the intergrain electron transport may be
predominating, as follows from experiments on the electrical characterization
of single polyaniline nanofibers. We study the effect of temperature on the
transport characteristics. We represent the thermal environment as a phonon
bath coupled to the intermediate state, which provides electron tunneling
between the metallic-like grains. Using the Buttiker model within the
scattering matrix formalism combined with the nonequilibrium Green's functions
technique, we show that temperature dependencies of both current and
conductance associated with the intergrain electron tunneling, differ from
those typical for other conduction mechanisms in conducting polymers. Also, we
demonstrate that under certain conditions the phonon bath may cause suppression
of the original intermediate state accompanied by emergence of new states for
electron tunneling. The temperature dependencies of the magnitudes of the peaks
in the transmission corresponding to these new states are analyzed.
