PROBING ELECTRON CONDUCTION AT THE MICROSCOPIC LEVEL IN PERCOLATING NANOCOMPOSITES BY CONDUCTING ATOMIC-FORCE MICROSCOPY

We have studied systematically the conductance distribution in nanocom posite Ni-x(SiO2)(1-x) thin films with x near the percolation threshol d x, by conducting atomic-force microscopy. We have experimentally dem onstrated that there exists power-law and exponential dependences of t he conductance distribution in low- and high-conductance regions, resp ectively. The conductance distribution was found to be independent of the bias, indicating that Ohmic behavior was satisfied at the microsco pic level. Quantitative analysis further suggests that the tunneling e ffect leads to the power-law distribution of conductance in the low-co nductance region.