On tunneling effects in metal-deposited polyethylene-carbon black and polycarbonate-carbon black systems

Electrical conductivity for polyethylene-carbon black, polycarbonate-carbon black composites was measured for conducting compositions well above the percolation limit. Three conductivity methods were employed in our studies: sputtering coated metal electrodes, painted metal electrodes, and the four-point method. Results suggest that while the two latter methods do not modify substantially the material surface, the former method introduces a low conductivity region at the surface. The effect of contact resistance developed during metal coating is discussed in the light of both fluctuation-induced tunneling predictions and "hopping" transport mechanisms. Experimental results favor the tunneling alternative across the evaporated metal-composite interphase.