  We observed a phase transition-like behavior that is marked by the onset of
the realization of the connectivity between two sites on a two-dimensional
cross-section of a three-dimensional percolation cluster. This was found using
contact-resistance atomic force microscopy on carbon black/polymer composites.
The features in the current images, when presented as a function of the cut-off
current, or as a function of the total area covered by the electrically
connected objects, appear to obey a cluster statistics that is similar to the
one predicted and observed in continuum percolation systems.
