Electrical conductivities of multi-wall carbon nano tubes

Electrical conductivities of individual multi-wall carbon nano tubes have been measured using a micro manipulator by two probe method. The nano tubes are 15~50 nm in diameter and longer than 20 μm in length. The resistance of tubes is several kΩ per μm, which gives the average conductivity as 1,000~2,000 S/cm. The current-voltage characteristics at high field are also studied until the dielectric breakdown takes place. It is found that the enormously large current density more than 106 A/cm2 can flow in a piece of individual nano tubes. The temperature dependence of conductivity of the individual nano tube has been also measured. The preliminary result that the tube with low resistance shows metallic behavior and that of high resistance exhibits semiconductive behavior indicates the various helicities for the multi wall nano tubes too.