Scientists scale down Archimedes screw to molecular dimensions

An international team of researchers has made a breakthrough in nanotechnology by developing an unusual molecular motor that rotates when an electric current passes through it. Inspired by the ancient Archimedes screw, this tiny machine can even reverse its direction of rotation when the voltage polarity is flipped.

• Researchers developed a molecular motor based on the Archimedes screw driven by electric current.
• The spiral molecule was created at the University of Copenhagen and tested at the Weizmann Institute of Science.
• Flipping voltage polarity reverses rotation direction, while conductivity increases about a hundredfold.

Design and mechanism of the molecular motor

At the core of the new motor is a specially designed spiral molecule created by Professor Mikael Pittelkov's group at the University of Copenhagen. Its length is just a few millionths of a millimeter, and thanks to sulfur atoms, the molecule can anchor itself securely to gold surfaces.

At the Weizmann Institute in Israel, researchers led by Professor Oren Tal and Dr. Anil Kumar Singh placed individual molecules between two gold electrodes with atomic-scale tips. By adjusting the distance between the electrodes, they could stretch or compress the molecular screw.

Experimental observations and quantum calculations

When scientists applied electrical voltage, measurements showed that the molecule began to spin. Although direct visual observation of the rotation was impossible, cyclic transitions between conductivity states were measured and confirmed by quantum-mechanical calculations and potential energy landscape models.

Crucially, the direction of rotation could be reversed simply by swapping the voltage polarity. When the applied voltage exceeded a certain threshold, the movement transitioned into continuous and stable rotation driven by the passing electrons.

Connection between rotation and electrical conductivity

The rotating molecule conducted electric current significantly more efficiently than a stationary one. Calculations revealed a close relationship between the molecule's rotation angle and its ability to conduct current, which can increase by up to two orders of magnitude—about 100 times—during rotation.

The reason behind this proved to be unexpected: certain positions where electric current passes most easily are simultaneously states that the molecule naturally avoids when at rest. Continuous rotation makes these highly conductive configurations accessible.

Significance and future implications of the breakthrough

This research represents the first demonstration of an electrically driven molecular motor firmly connected to two metal electrodes and capable of rotating in a controlled direction. Electrons transfer angular momentum to the molecular structure just like airflow drives a turbine.

For modern nanotechnology, this achievement lays the groundwork for creating advanced molecular machines capable of performing useful work at the microscopic level. While practical commercial applications are still ahead, the fundamental physics of nanoscale motors is becoming increasingly clear.