Carbon nanotubes stretch out
Context: Little more than a nanometer wide, carbon nanotubes have become superstars of the nano world: unusually strong, electrically conductive, and stable at high temperatures. Fibers composed of nanotubes should outperform those made from any existing material. However, the length of the tubes – most are only tenths of a millimeter long – requires that they be lined up for peak performance. Now, researchers at Los Alamos National Laboratory and Duke University have created nanotubes that are centimeters long, and whose length is checked only by the size of the chamber used to create them.
Methods and Results: The Los Alamos team synthesized the nanotubes by flowing ethanol vapors at 900 degreesC over an iron catalyst spotted onto a silicon wafer. Tubes grew from these catalyst spots; the catalyst was pushed along the wafer surface in the direction of the gas flow. The longest tubes grew to four centimeters as straight lines across the length of the silicon wafer, terminating only at the wafer’s edge.
Why it matters: Bundles of carbon nanotubes, spun as fi bers, have been promoted for applications where high strength and low weight are critical, from sporting equipment like golf clubs or tennis rackets to science fiction dreams of “elevators” extending into outer space. Although the shorter tubes have many promising applications in their own right, bundles of them have failed to perform up to their potential because of weak links between the tubes. Lengthening the tubes reduces these problems, bringing researchers closer to exploiting the remarkable strength and conductivity of nanotube bundles. But the Los Alamos and Duke researchers have done more than advance a technology; they have done the unthinkable, building individual molecules as long as a paper clip.
Source: Zheng, L. X. et al. (2004) Ultralong single-wall carbon nanotubes. Nature Materials 3:673-6.