Single Molecule Charges Electric Motor

Tuesday, September 6, 2011 @ 05:09 PM gHale

The smallest electric motor ever devised is now able to churn away. The motor consists of a single molecule just a billionth of a meter across.

This minuscule motor could have applications in engineering nanotechnology and medicine, where tiny amounts of energy can generate power for these motors.

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Tiny rotors based on single molecules have been around, but this is the first that an electric current can individually drive.

“People have found before that they can make motors driven by light or by chemical reactions, but the issue there is that you’re driving billions of them at a time — every single motor in your beaker,” said Charles Sykes, a chemist at Tufts University in Medford, MA.

“The exciting thing about the electrical one is that we can excite and watch the motion of just one, and we can see how that thing’s behaving in real time,” he said.

Sykes and his colleagues were able to control a molecular motor with electricity by using a state of the art, low-temperature scanning tunneling microscope (LT-STM), one of about only 100 in the United States. The LT-STM uses electrons instead of light to “see” molecules.

The world's first single molecule electric motor may potentially create a new class of devices that could be used in applications ranging from medicine to engineering.

The world's first single molecule electric motor may potentially create a new class of devices that could be used in applications ranging from medicine to engineering.

The team used the metal tip on the microscope to provide an electrical charge to a butyl methyl sulfide molecule 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 by controlling the temperature of the molecule they could directly impact the rotation of the molecule. Temperatures around 5 Kelvin (K), or about minus 450 degrees Fahrenheit (ºF), proved to be the ideal to track the motor’s motion. At this temperature, the researchers were able to track all of the rotations of the motor and analyze the data.

While there are foreseeable practical applications with this electric motor, breakthroughs would need to occur in the temperatures at which electric molecular motors operate. The motor spins much faster at higher temperatures, making it difficult to measure and control the rotation of the motor.

“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. Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along,” said Sykes. “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.”

“The next thing to do is to get the thing to do work that we can measure; to couple it to other molecules, lining them up next to one another so they’re like miniature cog-wheels, and then watch the rotation propagation down the chain,” he said.

As well as forming a part of the tiniest machines the world has ever seen, such minute mechanics could be useful in medicine — for example, in the controlled delivery of drugs to targeted locations.

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