Ultimate High Conductivity of Multilayer Graphene Examined by Multiprobe Scanning Tunneling Potentiometry on Artificially Grown High-Quality Graphite Thin Film

With the discovery of graphene, the excellent characteristics of graphite (multilayer graphene), such as high thermal and electric conductivities, heat resistance, and chemical stability, have also been attracting considerable attention again. However, the production of a large-area (>0.1 X 0.1 m(2)) graphite thin film with uniformly high electric conductivity, which will be indispensable in industrial applications, has been difficult because of its breakage occurring during the growth process. Recently, we have succeeded, for the first time, in growing large-area high-quality graphite films with thicknesses from similar to 0.5 to similar to 3 mu m by an industrial method, providing a fundamental platform for examining and utilizing the intrinsic and ultimate characteristics of such a material. Here, as a step toward realizing such efforts, we performed microscopic measurements of electric conductivity by the method of multiprobe scanning tunneling potentiometry we have developed. Using the resistivity along the c-axis, rho(c) = 1.72 +/- 0.04 m Omega.m, which was directly measured for the first time, we determined the resistivity in the ab-plane, rho(ab), to be 0.30 +/- 0.01 mu Omega.m, indicating that the conductance of the graphite thin film we grew is about 1.3 times the previous highest reported value for the highest grade single-crystal natural graphite with an ideal structure without grain boundaries or wrinkles (0.38 mu Omega.m). Both the advantage of multilayer graphene, which is considered to reduce the effect of grain boundaries on conductance, and the decrease in conductance as an effect of wrinkles were directly evaluated.