DIRECT IMAGING OF THE PERCOLATION NETWORK IN A 3-DIMENSIONAL DISORDERED CONDUCTOR-INSULATOR COMPOSITE

We have directly imaged the percolation network at the surface of a three-dimensional carbon-black-polymer composite using an electric force microscope. At intermediate length scales the conductive area exposed at the surface increases with surface area according to a power law corresponding to a three-dimensional infinite cluster of fractal dimension D = 2.6 +/- 0.1. This value is in good-agreement with the scaling theory prediction, D = 2.53. At large length scales the behavior is homogenous with the classical exponent D = 3.