Electrical conductivity and thermopower of Cu–SiO2 nanogranular films

We have measured the thermopower S and electrical conductivity σ in a series of Cux(SiO2)1−x nanogranular films between 2 and 300 K with Cu volume fraction x varying from 0.43 up to 1.0. At low temperatures, disorder-enhanced electron–electron interaction effects dictate the behavior of σ. A crossover of the temperature dependence from σ∝T to σ∝T1/3 is observed as x is lowered and the metal–insulator transition is approached. S is small, shows linear temperature dependence, and is rather insensitive to the change of x. Effects of annealing are also discussed.