Scientists belt out a novel nanostructure For several years, researchers have

been creating a variety of microscopic tubes and wires just tens of atoms wide. They hope someday to use these cre- ations as components in extraordinarily small sensors, electronics, and other mi- croscopic machines. Now, their toolbox has another promising miniature compo- nent: the nanobelt.

The ribbonlike structure can be made from various semiconducting metal oxides including zinc oxide and tin oxide, says materials scientist Zhong Lin Wang of the Georgia lnstitute of Technology in Atlanta. He and his colleagues report their belt-

Scanning electron microscopy shows a muss of zinc oxide nanobelts (left), while trunsrnission electron microscopy reveals a single, flexible belt (right). The dark lines in the single belt indicate strain.

making handiwork in the March 9 Scmc~. Chemist William E. Buhro of Washing-

ton University in St. Louis says he’s sur- prised by the uniformity of the nanobelts despite their different compositions. Wang’s group “has synthesized a wide va- riety of compounds having different crys- tal structures, and they all managed to form with this same kind of a ribbon or belt morphology,” Buhro says.

Each belt, just 30 to 300 nanometers wide and 10 to 15 nanometers thick, is made of a single crystal that has a rectan- gular cross section. The structures, which grow as much as a few millimeters in length, are flexible enough to bend in half, says Wang.

He and his coworkers made the nanobelts by evaporating metal oxide powders under high temperature in a gas-swept alumina tube. They strictly controlled such conditions as pressure and the duration of the procedure.

Wang says that the process is simple and does not require catalysts, so the belts could be made in industrial quantities.

In the procedure, the metal oxide de- posited as a white wool-like clump near one end of the cylinder, the team reports. Microscope observations then revealed that each 5-to-10-gram mass of material contains crystals in the new nanobelt

Dinosaur fossil yields feathery s t r u w s The oldest known bird, Archaeopteryx

lifhographica, lived roughly 150 million years ago and had modem feathers. But no one knows what earlier feathers may have looked like.

“To have an incredibly new and com- plex thing suddenly arise with no known antecedents is tough to explain,” says

but dismissed the possibility that the two could be related (SN 10/26/96, p. 260 6/27/98, p. 404).

aments is a feather,” says Prum. What’s L

found feather antecedents on the mains of Sinomithosaurus

Liaoning, China. Although the Sinornithosaurus fossil is Researchers found these brunched,

younger than that of Azhaeopteryx, the newly described structures could repre sent precursors that evolved into Ar- chaeopteryx’s feathers, the team argues in the March 8 NATURE. Both creatures may have emerged from a common ancestor that had rudimentary feathers.

In recent years, earthed dinosaur r be covered in a layer of “dinofuzz,” notes Lawrence Witmer, a paleontologist at Ohio University in Athens. But these wispy hairlike structures are so unlike modern feathers that skeptics have all

e snucturtes near the skull of a n-year-old dinosaur.

more, some of the filaments found on Sinornithosaunrs are bound into tufts, like down, he adds.

The researchers found fossils of the downy structures near the dinosaur’s skull. On other parts of the body, they found a different featherlike structure made up of multiple filaments attached along a central shaft. “This is the first view of what some primitive feathers may have looked like,” says Prum.

shape, says Wang. The belts formed from oxides of indium, cadmium, gallium, and lead, as well as zinc and tin.

Buhro says that he’s very interested in learning the details of how the nanobelts form from the various metal oxides. “What mechanistic or energetic factors are responsible for this unusual morphol- ogy?” he wonders.

The semiconducting belts might have electronic and optical properties handy for the development of a variety of micro- scopic devices, says Wang. For example, he speculates that the belts eventually could be developed as components of a nanosize sensor for use in medical or in- dustrial settings. These oxides change their conductivity in a predictable way when they encounter specific chemicals or gases, he points out.

However, Buhro stresses that any talk of applications, “at this point, would be purely speculative and far, far from this initial discovery.”

Wang harks back to the 1991 discovery of the first carbon nanotubes, which spawned an ongoing cascade of research and development (SN: 7/29/00, p. 71). He thinks that the belts will be the next big thing in nanoscale materials science. “[They] will spark a lot of research in the next few years because everyone can make [them], and a lot of people already study the properties of these oxides,” says Wang. 4 Gorman

Same researchers hold that feathers

feathers showed

. ”This is simply an

MARCH 10,2001 SCIENCE NEWS, VOL. 159 149