Identifying conducting phase from the insulating matrix in percolating metal-insulator nanocomposites by conducting atomic force microscopy

We present a study on mapping conducting networks and identifying the metallic phase in percolating metal-insulator nanocomposites Ni-x(SiO2)(1-x) and Fe-x(SiO2)(1-x) by conductingatomic force microscopy (C-AFM). The conducting networks (CNs) were mapped via current images using the constant bias mode of C-AFM. By combining the topographic and electric current images simultaneously, the conducting phase can be identified from the insulator matrix. A rapid increase of the conducting phase was observed when x crossed the percolation threshold x,. Therefore the percolation was directly "seen" on a nanometer scale. With this technique, C-AFM is not only a "topographic profiler" but also a "chemical profiler" if the volume fraction of metal phase exceeds the percolation threshold. The factors limiting the lateral resolution will also be discussed.