Like other frontier areas, nanotechnology can deliver surprises in which something useful is demonstrated, but not quite in the way intended. European nanotechnology researchers have moved a gold cargo about 500 nm along a carbon nanotube ‘Monorail”. However, the cargo only moves from the center to one end, instead of from one end to the other, because the motive force is not the electric current applied to the nanotube, as intended, but rather phonons from the heat generated by the current. Excerpts from “Nanoscale freighter hauls its first load“, written by David Robson at NewScientist.com news service:
A nanoscale “monorail” that can creep along a nanotube track has shifted its first load, hauling a gold nugget a distance of 0.5 micrometres. The device could be a useful addition to microscopic construction toolkits that researchers hope will advance computing and other fields.
The new device developed by researchers in Spain, Austria and Switzerland is made from two nanotubes nested like the parts of a telescope.
The central tube is one micrometer long and acts as a rail for the second, smaller, 200-nanometre nanotube. The outer “monorail carriage” is driven by applying current to the inner rail, and can move in both directions along the rail — it can also rotate around it.
In trials, the device was used to transport a ball of gold about 250 nanometres wide along the track for a distance of 500 nanometres (0.5 micrometres). It moves at speeds ranging from 0.1 nanometres per second to 1 micrometre per second. The researchers observed the motion using an atomic force microscope.
…”It is the first nano-freighter train,” says Andrea Ferrari, an expert in nano-engineering from the University of Cambridge, UK, who was not involved in the research.
…Ferrari was impressed by the work, saying it advanced previous demonstrations of nanotransport. “However, this is just a first step and significant research and development work is needed to make this a real technology.”
Excerpts from “Nanotube ‘monorail’ moves cargo“, at nanotechweb.org (requires free registration), written by Hamish Johnston:
Carbon nanotubes are sheets of carbon one atom thick that are rolled up into tubes that are only several nanometres in diameter. Adrian Bachtold and colleagues at the Autonomous University of Barcelona along with collaborators at the University of Vienna and the Swiss Federal Institute of Technology in Lausanne built their device using a multiwalled nanotube, which comprises several concentric nanotubes.
The team began by attaching a 1500-nm long multiwalled tube across the trench with metal electrodes. They then used an electrical-breakdown technique to remove several outer layers from most of the nanotube, leaving a short sleeve that could rotate freely and move to and fro along the inner rail.
…Bachtold told physicsworld.com that the team had originally hoped that they could apply a voltage between the electrodes to encourage atomic interactions between the rail and sleeve, causing the sleeve to move in a helical manner in one direction — and then in the other direction when they reversed the voltage. Such motion was expected, according to Bachtold, because the atoms on the inner and outer nanotubes would both be arranged in slightly different spiral configurations.
Instead, the team found that the sleeve always moved away from the centre of the trench. According to Bachtold, the first clue that heat was driving the motion was that the gold cargo particle changed shape by partially melting. The team confirmed the role of heating by doing computer simulations of the system.
…Ramin Golestanian of the University of Sheffield describes the work as “a beautiful experimental result”. However Golestanian, who studies the physics of moving nanoparticles and nanomechanical devices, told physicsworld.com that much more investigation is required to understand the mechanism responsible for the motion and the role of phonons in it.
The research was published in Science (abstract). It seems quite possible that the researchers will improve this device so that it becomes useful for driving nanometer-scale machines, as they intend to do. However, I suspect it would be easier to understand and control an atomically precise cargo hauler of some type.
—Jim
