Transport properties of chemically synthesized polypyrrole thin films

The electronic transport in polypyrrole thin films chemically synthesized from the vapor phase is studied as a function of temperature as well as of electric and magnetic fields. We find distinct differences in comparison with the behavior of both polypyrrole films prepared by electrochemical growth as well as of the bulk films obtained from conventional chemical synthesis. For small electric fields F, a transition from Efros-Shklovskii variable range hopping to Arrhenius activated transport is observed at 30 K. High electric fields induce short-range hopping. The characteristic hopping distance is found to be proportional to 1/root F. The magnetoresistance R(B) is independent of F below a critical magnetic field, above which F counteracts the magnetic-field-induced localization.