Meso-scale measurement of the electrical spreading resistance in highly anisotropic media

Abstract

The spreading resistance of circular contacts with a radius in the range from 60 nm to 500 nm has been measured in highly oriented pyrolytic graphite which is known to exhibit an extremely large electrical conductance anisotropy due to the layered structure. The experimental data are compatible with a diffusive transport model characterized by an inverse scaling of the spreading resistance with contact radius with an effective resistivity of ρeff = 5.7 ± 0.3 × 10-5 Ω m. Based on a scaling theory of the conduction in anisotropic media, we infer a ratio of the in-plane to out-of-plane conductance of 3.6 × 104 in agreement with literature. Accordingly, the radius of the effective area probed is on the order of 100 μm, which is much larger than the radius of contact, whereas the penetration depth into the sample is around 1 nm to 5 nm corresponding to 3-15 graphite layers. Remarkably, no deviation from the scaling model is observed despite the fact that only a small number of graphite layers are involved in the conduction.