Smallest electric motor now just a nanometer wide

Chemists at Tufts are on their way to creating an entirely new class of devices to be used in medicine and engineering thanks to their development of the world's first single-molecule electric motor.

Elizabeth Armstrong Moore
Elizabeth Armstrong Moore is based in Portland, Oregon, and has written for Wired, The Christian Science Monitor, and public radio. Her semi-obscure hobbies include climbing, billiards, board games that take up a lot of space, and piano.
Elizabeth Armstrong Moore
2 min read

Way back in the early days of 2011, the world's smallest electric motor was so...big. At 200 nanometers wide, it was a whopping 1/300th the size of a human hair.

Now, chemists at Tufts University's School of Arts and Sciences have smashed that record, which was set in 2005, with this weekend's unveiling of their single-molecule electric motor, which at 1 nanometer wide could be the first in an entirely new class of devices with potential use in medicine and engineering.

The team powered the molecular motor with electricity from a state-of-the-art microscope, which sent an electrical current through the molecule, directing the molecule to rotate in a specific direction. Tufts University

That's right: 1 nanometer. That's been estimated to be about 1/60,000th the size of a strand of human hair--depending, of course, on the hair.

"There has been significant progress in the construction of molecular motors powered by light and by chemical reactions, but this is the first time that electrically driven molecular motors have been demonstrated, despite a few theoretical proposals," said Charles Sykes, associate professor of chemistry at Tufts and senior author of the team's paper, which was published online September 4 in the journal Nature Nanotechnology.

Sykes sums up his team's progress thusly: "We have been able to show that you can provide electricity to a single molecule and get it to do something that is not just random."

The team did this with a rare, state-of-the-art, low-temperature scanning tunneling microscope (LT-STM) that uses electrons, not light, to see molecules. The microscope's metal tip provided the electrical charge to a butyl methyl sulfide molecule, which was on a copper surface.

By controlling the molecule's temperature, the team found that it could exert direct control over the molecule's rotation. Of course, they had to operate at minus 450 degrees Fahrenheit (barely above absolute zero, the coldest theoretic temperature in the universe) to best track the motor's rotations. But in light of the success, the actual logistics seem but a minor nuisance.

"Once we have a better grasp on the temperatures necessary to make these motors function, there could be real-world application in some sensing and medical devices which involve tiny pipes," Sykes said in a news release, adding:

Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along. Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits; these gears could be used in miniature delay lines, which are used in devices like cell phones.

Only time will tell precisely how a motor the size of a molecule will be used, but for now, the potential seems as vast as the motor is small.