2 PARAMETER SCALING OF THE CONDUCTIVITY FOR INSULATING GRANULAR PDXC1-X FILMS

Conductivity measurements are reported for thin (t < 32nm) granular PdxC1-x films with x < 0.3 on the insulating side of the metal insulator transition (x(p) = 0.3). The granular films consist of small disconnected metallic Palladium-clusters (PHI almost-equal-to 3nm) embedded in an amorphous Carbon matrix. The temperature dependence of the conductivity follows the form sigma(T) = sigma0.exp(-(T0/T)alpha) with alpha = 1/4 at higher temperatures up to T = 300K and alpha = 1/2 at low temperatures. This is discussed in the framework of electronic hopping transport with and without the influence of a gap in the electronic density of states. The scaling behavior of the conductivity is analysed. Using both scaling parameters sigma0 and T0 the conductivity data for all films with different metal volume fraction x collapse onto one single scaling curve.