A molecular "handle" could soon be used to move carbon nanotubes without damaging their electrical properties. It could ultimately provide a novel way of constructing nanoscale computer circuitry, say researchers.

Nanotechnologists currently attach benzene-ring molecules to nanotubes chemically, to make them easier to manipulate. However, this distorts the tubes and also affects their valuable ability to conduct electricity.

"Those molecules really kill the conduction of tubes with metallic properties," explains Nicola Marzari, a materials scientist at Massachusetts Institute of Technology in the US, who developed the novel molecular manipulators with colleague Young-Su Lee.

Carbon nanotubes are made from rolled sheets of carbon in which each atom is joined to three others. Benzene-ring molecules cause problems because they add an extra bond to one of the carbon atoms, ruining a tube's conductivity by altering the flow of individual electrons.

Protruding atoms

Marzari and Lee used a supercomputer to model the behaviour of different atoms and molecules. Simulations revealed that certain molecules with protruding carbon or nitrogen atoms should bind to nanotubes without affecting electrical conductivity.

These molecules attach by bonding one atom to two adjacent carbon ones, providing a bridge between the carbon atoms while breaking the bond between them. The effect is that conduction goes back to normal.

Marzari says it should be relatively simple to test the technique using real molecules, as chemists have already proved it works on buckyballs – spherical carbon structures made up of 60 carbon atoms in the shape of a soccer ball.

The ability to manoeuvre conducting nanotubes without harming them could lead to new electronic devices, he adds. "Nanotubes can carry an enormous amount of charge without damage," Marzari told New Scientist. "Companies are researching how they can be used because they perform better than metals like copper."

Light switch

Buckyball experiments also suggest it should be possible to control the conductivity of nanotubes by attaching a light-absorbing molecule using the same technique.

"Light energy can be passed down the attached molecule and reform the bond between the carbons it is joined to," Marzari says. This should completely change the tube's conductivity, and another burst of light ought to reverse the effect.

The MIT team's findings could be put into action right away, says Andrew Alexander, who works on nanotubes at Edinburgh University in the UK. "The reactions they are talking about have actually been done before for different reasons," he told New Scientist. "If I were working in that area I'd be heading to the lab to try this right away."