Nanotubes lengthen to centimeters

Carbon nanotubes are rolled-up sheets of carbon atoms that can be less than one millionth of a millimeter in diameter, are stronger than steel, and have useful electrical and optical properties.

One line of nanotube research has been to find ways to make the tubes grow continuously. Long nanotubes could be used as wires in electronic circuits and woven into macroscopic fibers that could be used to make extremely strong fabrics and rope. One long-range possibility is using ultralong carbon nanotubes fibers to make an elevator to low Earth orbit.

Researchers from Los Alamos National Laboratory and Duke University have found a way to grow very long carbon nanotubes. The researchers have used the method to produce a nanotube that is a record four centimeters long. The method has no apparent length limit, according to the researchers.

The researchers grew the long carbon nanotubes using the common vapor deposition method in combination with a metal catalyst. The process involves flowing ethanol vapor into a furnace at 900 degrees Celsius. The vapor reacts with an iron nanoparticle, causing a single-walled carbon nanotube to grow from the particle in the direction of the gas flow.

The nanotubes ranged from 1.31 to 2.25 nanometers in diameter and grew at a rate of 11 microns, or thousandths of a millimeter, per second.

Key to growing nanotubes long, straight and without defects was a method to keep the nanotubes floating free above the substrate as they grew. Using this setup, the nanotubes grew straight as long as the iron particle did not come into contact with the substrate.

The long nanotubes could be used in practical applications in five to ten years, according to the researchers. The work appeared in the September 12, 2004 issue of Nature.