Logarithmic behavior of the conductivity of electron-beam deposited granular Pt/C nanowires

We found that granular Pt/C composite nanowires have a logarithmic temperature dependence of conductivity in a wide range of temperatures. The logarithmic dependence can be explained by Coulomb interaction between Pt grains in a conductive carbon matrix. We stress the difference of the conductivity mechanism in the composite nanogranular material and known mechanisms in bulk metals/semiconductors and low-dimensional systems, including logarithmic dependence in systems with two-dimensional weak localization. Our observations show that local voltage fluctuations between grains result in the log(T) dependence for the samples with high conductivity (annealed nanowires), while the samples with low conductivity (as fabricated nanowires) appear to be insulators with a Coulomb gap.