It gives a whole new meaning to the phrase "get your motor running" when the structure in question is just 500 nanometers wide--so small that it would take 300 to match the width of a human hair. But researchers describe such a device today in the journal Nature. The electric rotor could eventually be put to a variety of uses ranging from optical switching to microfluidics.

Alex Zettl of the University of California, Berkeley, and his colleagues fashioned the motor by affixing a multiwalled carbon nanotube to a silicon wafer and attaching a gold square about 200 nanometers wide to the tube. The team then selectively etched parts of the wafer so the metal blade could rotate freely. By varying the voltage applied to different parts of the wafer, the scientists could control how the metal plate moved. (A composite of still images of the rotor taken by a scanning electron microscope is shown above.) "It's the smallest synthetic motor that's ever been made," Zettl notes. "Nature is still a little bit ahead of us--there are biological motors that are equal or slightly smaller in size--but we are catching up."

Unlike some current tiny motors, the authors note that their model is "designed to operate over a wide range of frequency, temperature, and environmental conditions, including high vacuum and harsh chemical environments." The researchers also hope to miniaturize the motor even more, perhaps by a factor of five. "There are many very fundamental questions we are trying to answer," Zettl says. "The flip side is, we've got this incredibly neat little motor that's smaller than any other electric motor--let's try to integrate it into some larger architecture where people are making microelectromechanical devices or nanoelectromechanical devices."