Molecules are incorrigible fidgeters. Let loose in a gas, they store their heat by zigging and zagging; when trapped in a solid, they wiggle against their neighbors. Now, scientists have discovered molecules with an entirely new type of motion: They spontaneously spin at the dizzying pace of more than several million times a second. The twirling molecules, described in today's issue of Science, could become a prototype for the world's tiniest, and entirely frictionless, bearing.
The discovery was serendipitous. A team from IBM's Research Laboratory in Zurich, Switzerland, and several European universities was investigating a new way to store data. They had wanted to coat a copper surface with a layer of propeller-shaped molecules--complex organic molecules each just 2 nanometers across. Then they planned to enter binary information by flattening selected molecules with the tip of a scanning tunneling microscope (STM).
But, after trying to create a layer just one molecule thick, the researchers noticed gaps where the copper surface was exposed. Normally, the STM could spot only the three-bladed propellers, but "in those voids, we observed ring-shaped molecules," says IBM's Jim Gimzewski. These, they surmised, might be the blurred images of spinning propellers. They confirmed their hunch by observing individual molecules as they started to rotate (another way to store heat) then stopped after being jammed by other loose molecules.
The whirling dervishes aren't likely to appear in molecular motors anytime soon. "This is still basic research, but we may be able to apply it to devices in a decade or so," says Cees Dekker of the Technical University of Delft in the Netherlands. In the meantime, he adds, they could be useful in the lab for studying the mechanics of molecular bearings.