“Controlling nanotube geometry is necessary to realize the many promised applications of these materials,” said Sungho Jin of the University of California San Diego. “Our new results show that we have taken a step toward understanding how to shape nanotubes to our specifications, an achievement that could greatly enhance their value to society.”

Jin and colleagues reckon the shaped nanotubes could find a use as tips for atomic-force microscopes, small springs, electrical connectors in integrated circuits and as a replacement for the metal alloy solders that form interconnects between microcircuit devices.

“If these interconnections were made with electrically conducting nanotube zigzags, not only would we need much less space to make [them], but the thermal-expansion mismatch wouldn’t matter because the interconnections are flexible,” said Jin. “We call it the compliant nano-interconnect.”

To create the structures, the researchers used plasma-enhanced chemical vapour deposition with a nickel catalyst. Applying an electric field across a pair of electrodes above and below the sample enabled them to control the tubes' growth direction.

Once they had grown an array of carbon nanotubes perpendicular to the substrate, the scientists removed the sample and carried out sputter-etching. This removed the carbon coating that formed on the catalyst particles as deposition stopped. As a result, the researchers were able to restart growth of the nanotubes in a different direction, by altering the orientation of the electric field.

In this way, the team grew carbon nanotubes with a single change of direction, in the form of zigzags and, by continually rotating the electric field during growth, as nanocoils. The scientists also made parallel arrays of T- and Y-shaped nanotubes: these could act as a support for platinum catalyst particles for use in fuel cells.

The researchers reported their work in the Journal of Physical Chemistry B.