Exponential behavior of the Ohmic transport in organic films

An exponential dependence of conductance on thickness and temperature was found in the low voltage, Ohmic regime of copper (CuPc) and cobalt (CoPc) phthalocyanine, sandwiched between palladium and gold electrodes, unlike ever claimed in organic materials. A comparison with conventional models fails to explain all the data with a single set of parameters. On the other hand, a model which incorporates tunneling between localized states with thermally-induced overlap agrees with the data, and decouples the contributions to conductance from the electrode-film interface and the bulk of the film. Work supported by AFOSR, DOE and the UCOP program on carbon nanostructures.