Chennai: Scientists at IIT Madras used an electric current to turn a single, screw-shaped molecule — and found that its rotation enables more current flow through it. The finding could help researchers design electronic switches as small as a molecule.The researchers placed a molecule called helicene between two gold electrodes, the contacts through which electricity enters and leaves a circuit. Helicene has a spiral shape, like a tiny screw, said Anil Kumar Singh, an assistant professor of physics at IIT Madras, who was part of the international study published in the scientific journal Nature. To hold the molecule, the team used a method called a mechanically controllable break junction. They opened a tiny gap between gold contacts and suspended the molecule across it so they could adjust the gap with precision.When the team applied a voltage, the molecule moved through a repeating sequence of positions – movement driven by the electric current. As the molecule rotated, it reached positions that allowed electrons — the particles that carry electric charge — to pass through more easily. “An exciting aspect of this work is that molecular motion is not merely a consequence of electrical transport. It can also facilitate the passage of electrons through the molecule,” Singh said.The researchers found they could control the direction of the motion. In all 122 cases where they could identify the direction, the molecule followed the same sequence. Reversing the voltage reversed that sequence. Above a certain voltage, the current rose sharply. Measurements and calculations indicated that the molecule shifted from moving in steps between preferred positions to rotating continuously. The current through the intact molecule-and-electrode connection increased by up to about 100 times.The study draws on an old mechanical idea: the Archimedean screw. Traditionally used to lift water, the device can also work in reverse, allowing flowing water to drive its rotation. The researchers explored a related link between flow and motion, but with electric charge and a single molecule.The work, however, remains a laboratory demonstration, not a device ready for everyday use, scientists said. “This is a fundamental proof-of-principle demonstration, rather than a technology ready for practical use,” Singh said.The findings, however, could eventually inform molecular switches or components that regulate current.
