Many MindedA single molecule spins between gold tips when current flows through it
A team has built a motor from a single molecule that rotates when electric current passes through it. Switching the voltage polarity reverses the direction of rotation. The design borrows from the Archimedes screw, the rotating spiral traditionally used to lift water. The authors describe it as the first molecular motor driven by electric current, firmly connected to two metal electrodes, with controllable rotation direction.
The spiral molecule was designed by Prof. Michael Pittelkow's group at the University of Copenhagen. It is a few millionths of a millimeter long and binds to gold through sulfur atoms. At the Weizmann Institute of Science, Prof. Oren Tal and Dr. Anil Kumar Singh placed single molecules between two atomically sharp gold tips, and changed the gap to stretch or compress the molecule. Once the applied voltage passes a threshold, rotation becomes continuous. Electrons crossing the molecule transfer angular momentum to it, which drives the spin.
For energy, the interest is in converting electrical current into controlled motion at the smallest possible scale. Conductivity depends on the molecule's angle and rises by up to 100 times during rotation. Simulations by Prof. Fabian Pauly's group at the University of Augsburg showed that highly conductive orientations are ones the molecule avoids at rest, and rotation makes them reachable. The earlier electrically driven molecular motors, made in 2011, worked on surfaces and needed a scanning tunneling microscope tip. The authors name molecular electronic components, spintronics and microfluidic systems as possible uses.
The caveats are real. The applications are potential, not demonstrated. The rotation was inferred from current measurements, and simulations were needed to understand what happened inside the contact. Watch for whether anyone turns this into a working device component.
Source: ScienceDaily