Weird Wires of Gold

Ever since carbon nanotubes were discovered in 1991, these strange molecules have fascinated physicists. Now the bizarre world of the ultrathin has a second inhabitant: minuscule gold wires, described in the 28 July issue of Science. The gold atoms arranged themselves in a way never seen before, almost the same structure as so-called carbon nanotubes--conferring great strength and rigidity. But the gold nanowires, of course, easily conduct electricity, making them an ideal candidate for wiring components of future nanotechnological devices.

Carbon nanotubes are minuscule, rolled-up sheets of carbon atoms with properties, such as a near absence of friction, that continue to amaze physicists (ScienceNOW, 31 July). Some researchers had argued that structures made of materials other than carbon, if small enough, would also display entirely new characteristics. Yukihito Kondo and Kunio Takayanagi from Exploratory Research for Advanced Technology in Tokyo decided to check out what happens with gold.

The team used an electron beam to punch holes into a very thin gold film; they then used a transmission electron microscope to focus on the bridgelike structures between neighboring holes, while the electron beam carved them thinner and thinner. Eventually, they had produced wires with diameters of about 1 nanometer, roughly the size of carbon nanotubes. Observing the wires with the electron microscope, they found a structure very similar to that of nanotubes: helical layers of atoms arranged in chickenwire-like lattices. The only difference is that the gold wire was not hollow like a carbon nanotube.

The team isn't sure yet why gold can take this strange shape. But the wires could make useful components for all kinds of molecular machines, Kondo says. Not only are they rigid, but, unlike carbon nanotubes, they are "ideal conductors" of electricity, he says. The team also plans to investigate nanowires made of other metals and even semiconductors. Indeed, metallic nanowires are "a whole new nanoworld to be explored," say physicists Erio Tosatti and Santi Prestipino of the International Center for Theoretical Physics in Trieste, Italy, in a Perspective in the same issue. "When matter is reduced to just a few layers of atoms ..." the duo concludes, "there is room for surprises."

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