World's smallest electric motor

Medford/Somerville, Mass. – If you’re struggling integrating a bulky electric motor into an assembly, a team of chemical engineers at Tufts University’s School of Arts and Sciences may have a new option. The team has developed the world’s first single molecule electric motor, which measures only 1 nanometer across, beating out the current world record holder’s 200 nanometer motor. A single strand of human hair is about 60,000 nanometers wide.

According to E. Charles H. Sykes, Ph.D., associate professor of chemistry at Tufts and senior author on the paper published online in Nature Nanotechnology, the team plans to submit the Tufts-built electric motor to Guinness World Records.

“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,” Sykes said. “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.”

Sykes and his colleagues were able to control a molecular motor with electricity by using a low-temperature scanning tunneling microscope (LT-STM) that uses electrons instead of light to “see” molecules. The team used the metal tip on the microscope to provide an electrical charge to a butyl methyl sulfide molecule that had been placed on a conductive copper surface. This sulfur-containing molecule had carbon and hydrogen atoms radiating off to form what looked like two arms, with four carbons on one side and one on the other. These carbon chains were free to rotate around the sulfur-copper bond.

The team determined that by controlling the temperature of the molecule they could directly impact its rotation. At temperatures around 5 Kelvin (K) – about minus 450 degrees Fahrenheit (ºF) – the Tuft researchers were able to track the rotations of the motor and analyze the data.

However, the Tufts researchers say further breakthroughs will need to be made before molecular electric motors have a practical application. While the motor spins much faster at higher temperatures, the added speed makes it difficult to measure and, therefore, control its rotation.

“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,” said Sykes. “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.”
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