Single Molecure is tiniest electric motor ever
New Scientiest | 10th September 2011
For the first time, an electric motor has been made from a single molecule. At 1 nanometre long, that makes the organic compound the smallest electric motor ever.
Its creators plan to submit their design to Guinness World Records, but the teeny motor could have practical applications, such as pushing fluid through narrow pipes in “lab-on-a-chip” devices.
Molesules have previously converted energy from light and chemical reactions into directed motion like rolling or flapping.
Electricity has also set an oxygen molecule spinning randomly. But controlled, electrically driven motion – necessary for a device to be classed as a motor had not yet been observed in a single molecule.
To address this, E. Charles Sykes at Tufts University in Boston and collegues turned as asymmetric butylmethyl sulphide, a sulphur atom with a chain of four carbons on one side and a single carbon atom on the other. They anchored the molecule to a copper surface via the sulphur atom, producing a lopsided, horizontal “propeller” that was free to rotata about the vertical copper-sulphur bond.
Above the molecule they placed a metal needle a few atoms wide and its tip. When the flowed a current from this tip, through the molecule, to the conducitive copper below, the molecule converted the electrical energy into rotational energy. It bounced around in jittery hops at a rate of about 50 turns per second.
Because the propeller is asymmetrical, there are two ways it can be oriented with respect to the copper. In one orientation – but not the other – the molecule’s hops were not random but slightly biased towards rotating clockwise, allowing the reasearchers to classify it as a motor.
It’s not clear why the bias occurs but Sykes suspects that an inherent assymmetry in the tip of the metal needle could explain why it only occurs in one molecular orientation. He hopes to harness his motor to fight the friction that slows fluid flow in nanosized tubes<