Helical microtubules of graphitic carbon

The preparation of a new type of finite carbon structure consisting of needlelike tubes is reported. Produced using an arc-discharge evaporation method similar to that used for fullerene sythesis, the needles grow at the negative end of the electrode used for the arc discharge. Electron microscopy reveals that each needle comprises coaxial tubes of graphitic sheets ranging in number from two up to about 50. On each tube the carbon-atom hexagons are arranged in a helical fashion about the needle axis. The helical pitch varies from needle to needle and from tube to tube within a single needle. It appears that this helical structure may aid the growth process. The formation of these needles, ranging from a few to a few tens of nanometers in diameter, suggests that engineering of carbon structures should be possible on scales considerably greater than those relevant to the fullerenes.