Electrical conductivity maps in graphene nanoplatelet/silicon nitride composites using conducting scanning force microscopy

Graphene nanoplatelet (GNP)/silicon nitride (Si3N4) ceramic composites containing 12 and 15 wt.% of GNPs are prepared by mixing the nanoplatelets and the ceramic powders in a liquid medium followed by densification of the dried mixture by spark plasma sintering. The electrical conductivity of these composites is investigated at the nanoscale by conducting scanning force microscopy to understand the influence of the carbon phase content when above the percolation threshold. The establishment of a conducting network is revealed from the conduction measured at GNPs emerging at the surface of the composites. Current maps obtained for two orientations of the composites, parallel and perpendicular to the press sintering axis, show a preferential orientation of the nanoplatelets within the ceramic matrix. The effective current per conducting pixel, determined from the corresponding maps, is four times larger for the 15 wt.% GNP composite than for the 12 wt.% one. For the same composite (15 wt.%), differences in the effective current are measured for each of the two probing configurations. These results are interpreted in terms of unbalanced weight and nature of the resistors forming the percolated network.