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The Next Big Thing:
Nanobelts Join the World of the Ultra-Small

First came nanotubes, then nanowires, nanoclusters and nanoparticles. Now please welcome nanobelts to the growing, but still very small, world of nanometer-scale structures.

photo by Gary Meek A new class of structures known as "nanobelts" (inset) may have applications in sensors, flat-panel displays and "smart" windows. A team of researchers including Zhong Wang, Zhengwei Pan and Zurong Dai produce oxide-based nanobelts in a high-temperature furnace. (300-dpi JPEG version - 843k)

Microscope image shows a clump of ribbon-like nanobelts. (Larger JPEG version - 121k)

In March, Georgia Tech researchers reported in the journal Science that they had created a new class of structures just 10 to15 nanometers thick and 30 to 300 nanometers wide. Dubbed "nanobelts," the new structures could be the basis for inexpensive ultra-small sensors, components for improved flat-panel displays and "smart" windows for controlling the amount of heat and light entering buildings.

Produced from semiconducting metal oxides, nanobelts offer important advantages over other nanoscale structures in electronic applications. Chemically pure, structurally uniform and largely defect-free with surfaces that don't require protection against oxidation, each nanobelt is made up of a single crystal.

"This is a vitally important area of nanotechnology," says Zhong L. Wang, director of Georgia Tech's Center for Nanoscience and Nanotechnology and a professor in the School of Materials Science and Engineering. "If we are successful at these applications, it may lead to major technological advances in nano-size sensors and functional devices with low power consumption and high sensitivity."

Wang and colleagues have so far produced nanobelts from oxides of zinc, tin, indium, cadmium and gallium. They believe other semiconducting oxides may also be used to make the structures.

"The crystallographic structure varies a great deal from one oxide to another, but they all have a common characteristic as part of a family of materials that have ribbon-like structures with a narrow rectangular cross-section," Wang explains. "In comparison to the cylindrical symmetric nanowires and nanotubes reported in the literature, these are really a distinctive group of materials."

Researchers begin production of the nanobelts by placing commercially available metal oxide powders in the center of an alumina tube. As argon or nitrogen gas flows through it, the tube is heated in a furnace to temperatures just below the melting point of the powders, approximately 1,100 to 1,400 degrees Celsius. The powders evaporate, then form the crystalline nanobelts as they return to solid phase on an alumina plate in a cooler part of the furnace. No purification is needed.

Finished nanobelts resemble clumps of cotton. Despite their origin in normally brittle oxides, the structures are flexible and can be bent 180 degrees without breaking.

For more information, contact Zhong Wang, School of Materials Science and Engineering, Georgia Tech, Atlanta, GA 30332-0245. (Telephone: 404-894-8008) (E-mail: zhong.wang@mse.gatech.edu)