Molecular “Archimedes Screw” Spins When Electrified, Reverses Direction on Voltage Flip
Researchers have built a spiral‑shaped molecule that rotates under electric current and can change its spin direction by swapping voltage polarity.
Scientists have created a molecular motor that spins when electricity passes through it and can reverse its direction by flipping the voltage. The device draws inspiration from the ancient Archimedes screw, adapting the rotating spiral concept to a single molecule.
From Ancient Engineering to Molecular Scale
Earlier electrically driven molecular motors, first reported in 2011, required a scanning tunneling microscope tip and operated on surfaces. The new design abandons that approach, instead using a spiral‑shaped molecule that mimics the screw’s helical geometry.
Design and Construction
The central component is a spiral molecule engineered by Prof. Michael Pittelkow’s group at the University of Copenhagen. The molecule measures only a few millionths of a millimeter and attaches to gold surfaces via sulfur atoms.
At the Weizmann Institute of Science, Prof. Oren Tal and Dr. Anil Kumar Singh positioned individual molecules between two atomically sharp gold tips. By adjusting the gap between the electrodes, they could stretch or compress the molecular screw.
Electrical Activation and Direction Control
When a voltage is applied across the gold tips, the researchers observed rotation of the molecule. Reversing the voltage polarity caused the rotation to switch direction. This marks the first demonstration of a molecular motor that is driven by an electrical current, firmly linked to two metal electrodes, and capable of controllable directional rotation.
How the Spin Is Generated
Electrons traveling through the spiral transfer angular momentum to the molecular framework, analogous to airflow turning a wind turbine. The handedness of the spiral—right‑ or left‑threaded—determines the response to the electron flow, and once the applied voltage exceeds a threshold, the rotation becomes continuous.
Unexpected Conductivity Boost
The experiments also revealed that the rotating molecule conducts electricity more efficiently than when it is stationary. This raises questions about the internal mechanisms at play during rotation.
While molecular machines have long been hailed as a frontier for miniaturization, and the field earned a Nobel Prize in Chemistry in 2016, this achievement demonstrates a concrete step toward functional, electrically powered nanodevices.
