Researchers have built a motor from a single molecule, copying one of the oldest machines known, the Archimedes screw. That device is a rotating spiral used for more than 2,000 years to move water uphill. In the new motor, electrons take the place of water: when a current flows through a spiral-shaped molecule, the molecule starts to rotate. This work is published in Nature.
The molecule measures only a few millionths of a millimetre and can bind to gold surfaces through sulfur atoms. Researchers stretched individual molecules between two atomically fine gold tips. By adjusting the distance between the tips, the team could stretch or compress the molecular screw.
When a voltage was applied, the molecule rotated, and reversing the polarity of the voltage reversed the direction. The researchers say this is the first current-driven molecular motor fixed between two metal electrodes with a controllable direction of rotation.
Rotation raises the current
The rotating molecule also conducted electricity far better than a stationary one. To find out why, researchers ran quantum mechanical simulations on a supercomputer. They found that conductance depends strongly on the molecule's angle of rotation and can rise by up to 100 times during rotation. Surprisingly, the positions that conduct best are ones the molecule avoids when at rest, and only rotation makes them accessible. A simplified model reproduces both the rotation and the current increase.
The finding matters because it demonstrates a new operating principle for machines at the limits of miniaturisation: an electric current generates a directed rotation, and that rotation in turn controls the current. According to the team, this could support future molecular electronic components, spintronics (electronics that exploit the spin of electrons rather than only their charge) and microfluidic systems. It also gives scientists a new way to study physical processes on an atomic scale.