Scanning probe microscopy imaging of frequency dependent electrical transport through carbon nanotube networks in polymers

Frequency dependent electrical transport in the conducting networks of single walled carbon nanotubes embedded in polymers was studied by scanning impedance microscopy (SIM). SIM allows current flow in the nanotubes inside the polymer matrix at up to 100 nm below the surface to be imaged directly, providing a non-invasive approach for studying transport in these materials. The conductance of the composite is shown to be limited by a small number of bundle-bundle and bundle-contact junctions. For high frequencies, the SIM phase distribution along the networks is governed by the capacitive interaction between the nanotubes and the substrate and is in agreement with a transmission line model. For low driving frequencies the capacitive coupling to the back gate can be minimized and an approach for determining the potential distribution along the network by accounting for tip-surface capacitance variations is demonstrated. Thus, SIM provides a direct method for characterizing electrical transport through percolation networks formed by nanotube bundles in polymers or, more generally, nanorods in various matrices.