At Tufts University a team of scientists has built what they say is the world's smallest motor -- they're submitting it to the Guinness Book of World Records -- made of a single molecule. The researchers, led by Charlie Sykes, associate professor of chemistry, found that a motor that consists of a single molecule can be powered by a beam of electrons from an electron microscope. The work marks another advance in the science of building useful nanotechnological devices.
The team used a single molecule of butyl methyl sulfide, which contains atoms of carbon, hydrogen and sulphur. The molecule attaches weakly to a piece of copper, a process called adsorbtion (as opposed to absorbtion).
The bond between the sulphur and copper acts like the axle at the center of a wheel. The other atoms radiate like arms. Whenever there is energy to excite the molecule -- such as energy from heat -- the molecule spins. But energy from heat is not the greatest source because it creates random motion. If you saw a group of these molecules on the copper surface, they would spin every which way and rapidly switch between one direction and another.
That's where a scanning tunneling microscope (STM) comes in. An STM essentially fires a beam of electrons at a surface -- that's how it can see objects down to the nanometer scale. In this case, the electrons forma current that drives the tiny molecular motor.
Making a molecule spin wasn't all that Sykes' team wanted to do, however. They also wanted to see if they could measure and control the direction of the spin. For that they had to cool the whole setup down to about five degrees above absolute zero in order to slow the spinning molecules down. The result: you can control the spins, and turn them on and off, just like a real motor.
Sykes says there are practical applications, but that will mean designing some way to get the motors to operate at such low temperatures. And a future step will be getting many of these tiny rotors to operate together, and space them far enough so that they can still spin without interfering with each other.
Image: Sykes Laboratory/Tufts University