PINWHEEL. A molecule of hexa-tert-butyl decacyclene resembles a minirotor, 1.5 nanometers in diameter. In this scanning tunneling microscope image, the molecule is spinning so fast that the individual blades have blurred and it looks like a doughnut, or torus.

IBM scientists at the Zurich Research Laboratory report on a pinwheel smaller than a pin's head in the journal Science. The structure is a single molecule of hexa-tert-butyl decacyclene (HB-DC): six bulky t-butyl blades fan out from a central benzene ring. Steric interactions between the hydrogen atoms on the blade's tips make them twist like those on a propeller.

James K. Gimzewski and colleagues deposited enough HB-DC molecules on a clean copper surface to nearly cover it, but not quite. Then they studied them using a scanning tunneling microscope in an ultrahigh vacuum.

Some HB-DC molecules bonded together into a tight crystal lattice, but where there were nanoscopic voids, the molecules had a bit more freedom. Here the group observed individual atoms that, instead of having the classic six-lobed shape, resembled doughnuts. Their conclusion: these molecules were spinning at speeds too fast for the camera to catch--and so the lobes blurred into a single loop. The molecules around them served as a bearing of sorts.

This minirotor is much smaller than many classical micromachines, which measure in the tens of micrometers. It works in a dry state and appears to be wearless, because it weighs a mere 1.33 x 10 -24 kilograms. To make it rotate takes nothing more than a nudge from a scanning tunneling microscope tip.

Image: J.K. GIMZEWSKI and C. JOACHIM, IBM Research Division, Zurich Research Laboratory, Ruschlikon, Switzerland.