Applying a small electrical current to a carbon nanotube moves indium particles along the tube like a conveyor belt. This movement solves the issue of efficient assembly of nanostructures currently plaguing researchers.
Indium metal is thermally evaporated onto a bundle of carbon nanotubes. The bundle is placed inside a transmission electron microscope, where a tungsten tip on the end of a nanomanipulator approaches a nanotube. Once physical contact is made, voltage is applied between the tip and the other end of the nanotube, creating a circuit.
Real-time video shows an indium particle disappearing, while a particle next to it grows. The large particle also disappears, replaced by another further to the right. The thermally driven indium atoms move along the nanotube, until all the indium piles up at the end. In the future, this nanosized conveyor belt could be aimed anywhere scientists want to deliver mass atom by atom. Also, if voltage increases, the indium's temperature rises and the metal moves from left to right more quickly. “It's the equivalent of turning a knob with my hand and taking macroscale control of nanoscale mass transport,” says Chris Regan of the Materials Sciences Div. “It's also reversible: We can change the current's polarity and drive the indium back to its original position,” he adds.
The research lays the groundwork for high-throughput construction of atomic-scale optical, electronic, and mechanical devices that will power the growing field of nanotechnology.