Nanotube conveyor belts

Carbon nanotubes shuffle atoms and molecules into place.

Scanning probe microscopes can be used to order atoms or molecules on surfaces within a small target area, but what is the best way to deliver the particles? US researchers now report that multi-walled carbon nanotubes (MWNTs) could be used as conveyor belts to move metal atoms. Alex Zettl’s group at the University of California at Berkeley attached indium nanocrystals to MWNTs and placed the nanotubes between electrodes set up in the sample chamber of an electron microscope. Applying a voltage to the tubes, they observed that the In particles at one end of the tube gradually disappeared, while those at the other end grew.

A distillation process, whereby the In evaporates at the warmer end of the tube and condenses at the cold end, would have been the simplest explanation. But the team ruled this out by reversing the voltage. Now, with the temperature gradient unchanged, the In atoms migrated in the opposite direction, clearly following the voltage rather than the temperature. While some details of this mass transport remain unclear, the authors present a model that depicts the mobile In atoms as a 2D gas coating the surface of the nanotube. The voltage dictates the directionality of their movement, effectively creating conveyor belts between the existing crystals.

If one could place a target site at the end of a nanotube, this would immediately create a nanoscale soldering iron.

Michael Gross