Probing electron conduction at the microscopic level in percolating nanocomposites by conducting atomic-force microscopy

We have studied systematically the conductance distribution in nanocomposite ${\mathrm{Ni}}_x{(\mathrm{S}\mathrm{i}\mathrm{O}}_2{)}_{1-x}$ thin films with $x$ near the percolation threshold $x_c$ by conducting atomic-force microscopy. We have experimentally demonstrated that there exists power-law and exponential dependences of the conductance distribution in low- and high-conductance regions, respectively. The conductance distribution was found to be independent of the bias, indicating that Ohmic behavior was satisfied at the microscopic level. Quantitative analysis further suggests that the tunneling effect leads to the power-law distribution of conductance in the low-conductance region.