The miniature shuttle device consists of a carbon nanotube covered with a shorter concentric nanotube which can move back and forth along the longer tube, and to which a metal cargo can be attached.
By keeping the two ends of the long nanotube at different temperatures, a thermal gradient is set up which causes the shuttle to move from the hotter to the colder end of the long tube. And this movement can be controlled with a precision of less than the diameter of an atom, say the researchers.
“The main result of our study is that at the nanoscale it is possible to exert control over the direction of motion of a mobile object by controlling the temperature of its surroundings,” says Eduardo Hernández. “Or, more precisely, by controlling the way in which the temperature of its surroundings changes.”
Adrian Bachtold adds: “The contact surface between the two nanotubes has a certain corrugation, which depends on the actual structure of the tubes. This offers an additional possibility of control over the motion, as it can favour rotation as well as translation of the outer tube.”
Heat engines are normally thought of in thermodynamic terms, where the the observed behaviour is a statistical property of a very large number of molecules. What the Catalan scientists, together with colleagues in Austria and Switzerland, have shown is that heat gradients can be important also for nanoscale objects, and particularly when their motion is restricted to one dimension.
Further reading: “Subnanometer Motion of Cargoes Driven by Thermal Gradients along Carbon Nanotubes”, Barreiro et al., Science (2008).
Figure: This nanoscale motor consists of a long nanotube covered with a shorter concentric nanotube that shuttles along its length under the influence of a temperature difference between the ends of the longer tube (source: Universitat Autònoma de Barcelona).
Article first published in Nanomaterials News.