Smallest diameter carbon nanotubes

Mass-selected carbon ion beam deposition (MSIBD) was used to demonstrate th at the diameter of a carbon nanotube could be as small as 0.4 nm, the theor etical limit predicted but never experimentally reached so far. The deposit ion was performed at an elevated temperature much lower than the high tempe ratures (800-1000 degreesC) needed for deposition of carbon nanotubes by co nventional methods. High-resolution transmission electron microscopy showed that the combination of the stress induced by the ion impact and the C mig ration at the temperature applied formed graphitic sheets with their normal (c axis) parallel to the surface of the silicon substrate. Some sheets clo sed to form multiwall nanotubes. The smallest diameter of the innermost tub e was found to be 0.4 nm. The novel use of MSIBD (a pure method, catalyst f ree, low deposition temperature, easily applied to large surfaces without s urface pretreatment capable of pattern-writing) may significantly advance t he carbon nanostructure technology. (C) 2000 American Institute of Physics. [S0003-6951(00)02244-0].