An international team has built a single-molecule motor that rotates when voltage is applied and reverses direction when the voltage’s polarity changes, according to University of Augsburg material published by ScienceDaily. Researchers at the Weizmann Institute of Science in Israel positioned individual spiral-shaped molecules between two gold tips. Sulfur atoms allow the molecules to attach to the gold.
The design takes inspiration from the Archimedes screw, but electrons travel through this molecular spiral instead of water. The University of Augsburg account calls it the first current-driven molecular motor firmly connected to two metal electrodes that can rotate in a controllable direction. That is a narrower claim than the first electrically powered molecular motor: earlier designs operated on surfaces.
Experiments found that the molecule conducted electricity more efficiently while rotating than while stationary. To investigate why, University of Augsburg researchers used quantum-mechanical simulations and calculated that conductance varies with the molecule’s angle, increasing by as much as 100 times during rotation. Léon Martin, one of the researchers, explained that rotation gives the molecule access to positions it avoids at rest, even though those positions conduct best. The 100-fold figure comes from the calculations, rather than a reported measurement of that increase.
