Method makes double nanotubes

Carbon nanotubes are a promising nanotechnology building block. The tubes are made from rolled-up sheets of carbon atoms, have useful optical, electrical and mechanical properties, and can be smaller than 1 nanometer in diameter. A nanometer is one millionth of a millimeter, or the span of 10 hydrogen atoms.

Carbon nanotubes can be grown as single tubes or multiwall tubes, which are made up of successively smaller nested tubes.

Researchers from Shinshu University in Japan, the Institute for Scientific and Technology Research at San Luis Potosi in Mexico, and the Massachusetts Institute of Technology have found a way to fabricate pure batches of double-walled carbon nanotubes.

Mixed batches of nanotubes are commonly available; pure batches of double-walled carbon nanotubes have proved more difficult to produce.

The process makes it possible to better investigate the properties of double-walled carbon nanotubes, according to the researchers. In theory, double-walled nanotubes should be more thermally and chemically stable than their single-walled cousins but with the better electrical and optical properties of single-walled tubes. Double-walled carbon nanotubes could eventually be used in gas sensors, electron emitters for displays and scientific instruments, electronic devices like transistors and light-emitting diodes, and composite materials.

The researchers' method purifies a mix of single and double-walled nanotubes using hydrochloric acid, then oxidation at 500 degrees Celsius. The process results in paper-like sheets of densely-packed bundles of double-walled nanotubes.

Double walled carbon nanotubes will be ready to be used in simple applications in two to five years, according to the researchers. The work appeared in the February 3, 2005 issue of Nature.