Scientists created a molecular motor inspired by Archimedes' screw that spins when electricity flows through it. The motor, developed by Prof. Michael Pittelkow's group at the University of Copenhagen, consists of a spiral-shaped molecule measuring only a few millionths of a millimeter.
Researchers at the Weizmann Institute of Science, led by Prof. Oren Tal and Dr. Anil Kumar Singh, positioned individual molecules between two gold electrode tips. When voltage was applied, the molecule rotated. Reversing the voltage's polarity reversed the rotation direction. This marks the first demonstration of a molecular motor driven by electrical current, anchored to two metal electrodes, and capable of controlled rotation in both directions.
Theoretical physicists including Prof. Fabian Pauly at the University of Augsburg used quantum mechanical simulations to understand why the rotating molecule conducted electricity much more efficiently than when stationary. Their calculations revealed that conductivity increased by as much as 100 times during rotation. The simulations showed that molecular positions allowing the best electrical flow are positions the molecule naturally avoids when stationary. Rotation makes these highly conductive arrangements accessible.
"The surprising thing is that it is precisely the positions that the molecule avoids when at rest that conduct electricity best. It is only the rotation that makes these positions accessible," explained Léon Martin, a PhD student at the University of Augsburg.
Researchers including Per Hedegård of the Niels Bohr Institute in Copenhagen and Jing-Tao Lü of Huazhong University of Science and Technology developed a theoretical model that recreated both the observed rotation and the increase in electrical current.
"We have shown that an electric current can be used to generate a directed rotation and that this rotation, in turn, controls the current. This is a new operating principle for machines at the very limits of miniaturization," stated Pauly.
The motor could contribute to development of molecular electronic components, spintronics technologies, and microfluidic systems.