Carbon nanotubes show superconductivity.

In a discovery that could aid the development of molecular-scale electronic devices, researchers in Hong Kong have made tiny carbon nanotubes that exhibit superconductivity--a characteristic associated with the loss of electrical resistance.

The single-walled nanotubes (SWNTs)--cylinders of carbon with walls one-atom thick--have electronic properties that have intrigued researchers for years. Bundled into so-called ropes, these nanotubes have even demonstrated superconducting traits. Until now, however, no one has shown that an individual carbon nanotube can be a superconductor.

Ping Sheng and other researchers at Hong Kong University of Science and Technology were able to grow individual nanotubes by using the channels in crystals called zeolites as tiny growth chambers. Researchers had recently developed this method for making some of the smallest carbon nanotubes ever--each just 0.4 nanometers (nm), or just a few atoms, across (SN: 12/16/00, p. 398).

Measurements on these smallest of nanotubes revealed that the structures become superconductive when chilled below 15 kelvins, or -258 [degrees] C, Sheng's team reports in the June 29 SCIENCE. Among the traits of superconducting materials that the tubes exhibited was the so-called Meissner effect, in which the material expels magnetic fields, says Sheng.

The researchers followed their experiments with extensive calculations confirming that the nanotubes' behavior follows accepted theories of superconductivity at these low temperatures, adds Sheng.

Superconductive carbon nanotubes are just the kind of molecular components that engineers might someday use to shrink electronic devices to nearly unimaginable dimensions. "These small-diameter nanotubes might be used as conducting wires ... or as the basic material for electronic components of nanosized electronic circuitry," says Sheng.