Nanowire Made to Order

BOSTON--Electrical switches the size of molecules could help shrink computer chips. But until now, researchers had no way to wire up components so small. At a meeting of the Materials Research Society here yesterday, scientists described a pair of techniques for wiring up nano-sized chips--one that uses electric fields, the other DNA. Though no working molecular devices have been rigged up, experts say the approaches are a harbinger of miniscule circuitry that could lead to computers far more powerful than those available today.

For their nanowiring experiments, a team led by electrical engineer Theresa Mayer of Pennsylvania State University, University Park, first grew gold and platinum rods a mere 30 billionths of a meter wide and up to several millionths of a meter long. Linking these rods required an innovative scaffold: a pair of electrodes that resemble two combs with interlaced teeth. The researchers coated these electrodes with a layer of insulation and placed a thin gold square atop the center of each tooth. Finally, they immersed the apparatus in a solution containing their tiny metal rods.

A voltage applied between the electrodes induced a type of electrical attraction between the gold pads and the metal rods, causing the rods to bridge adjacent gold squares. When the rods were shorter than the gap between squares, several rods lined up to form a bridge, which turned out to be the most energetically favorable arrangement of the rods. The researchers "welded" these rods into wires by enriching the solution with gold ions that filled in the junctions. In other experiments, the researchers hooked up DNA strands to the tips of their metal rods. Rods would then link up when they bound to complementary DNA strands--offering another technique for delicately positioning metal wires.

"This was really nice work," says Zhenan Bao, an advanced electronics specialist at Lucent Technologies Bell Laboratories in Murray Hill, New Jersey. The ability to direct the positioning of nanowires is likely to add steam to the already fast moving field of molecular electronics, says Bao. "It's the future direction the [molecular electronics] field will take."

--ROBERT F. SERVICE