Abstract
We use conductive atomic force microscopy (CAFM) to study the origin of long-range conductivity in model transparent conductive electrodes composed of networks of reduced graphene oxide (rGO(X)) and silver nanowires (AgNWs), with nanoscale spatial resolution. Pristine networks of rGO(X) (1-3 monolayers-thick) and AgNWs exhibit sheet resistances of similar to 100-1000 k Omega/square and 100-900 Omega/square, respectively. When the materials are deposited sequentially to form bilayer rGO(X)/AgNW electrodes and thermally annealed at 200 degrees C, the sheet resistance reduces by up to 36% as compared to pristine AgNW networks. CAFM was used to analyze the current spreading in both systems in order to identify the nanoscale phenomena responsible for this effect. For rGO(X) networks, the low intra-flake conductivity and the inter-flake contact resistance is found to dominate the macroscopic sheet resistance, while for AgNW networks the latter is determined by the density of the inter-AgNW junctions and their associated resistance. In the case of the bilayer rGO(X)/AgNWs' networks, rGO(X) flakes are found to form conductive "bridges" between AgNWs. We show that these additional nanoscopic electrical connections are responsible for the enhanced macroscopic conductivity of the bilayer rGO(X)/AgNW electrodes. Finally, the critical role of thermal annealing on the formation of these nanoscopic connections is discussed. Published by AIP Publishing.