Temperature dependence of the conductivity of Cu:SiO2 composite films.: Experiment and numerical simulation

Experimental data are presented for the temperature dependence of the conductivity of Cu : SiO2 metal-insulator composite films containing 3-nm Cu granules. At low temperatures in the concentration range 17-33 vol % Cu, all of the conductivity curves have a temperature dependence of the form sigma proportional to exp{-(T-0/T)(1/2)}, while at higher temperatures a transition is observed to an activational dependence. A numerical simulation of the conduction in a composite material shows that an explanation of the observed temperature dependence must include the Coulomb interaction and the presence of a rather large random potential. The simulation also yields the size dependence and temperature dependence of the mesoscopic scatter of the conductivities of composite conductors. It is shown that a self-selecting percolation channel of current flow is formed in the region of strong mesoscopic scatter. (C) 2000 MAIK "Nauka/Interperiodica".