Paper #2 in the current Hot Ten reports a remarkable way of making ribbon-like metal oxide fibers, which the authors refer to as "nanobelts" because they have a rectangular cross-section. They have widths of 30 to 300 nanometers and can grow up to a millimeter or more in length, and can be synthesized with a large degree of control over their structure. The belt-like morphology appears to be a common structural characteristic for this family of semiconducting oxides.

Nanobelts can be made simply by evaporating the metal oxide at a high temperature, and under a reduced pressure flow of argon. For example, zinc oxide powder of 99.99% purity was heated at 1400° C for two hours to yield a mass of long wool-like fibers that grew on an alumina plate placed downstream of the flow of argon gas. Paper #2 reports how the fibers were investigated by various techniques, such as transmission electron microscopy, and were shown to be pure, structurally uniform, crystalline, and free from dislocations.

The discovery of carbon nanotubes in 1991 launched science into the realm of one-dimensional nanomaterials, and for a time it seemed as if carbon would be the only element to produce such materials. Then came paper #2, the first to report a radically different class of semiconductors. Nanobelts are unlike nanowires in that they are truly structurally controlled, with well-defined growth direction and regular side surfaces.

The most important character of these nanobelts is that they are semiconducting, and their conductivity, bandgap, surface properties, and optical properties can be tuned by introducing oxygen vacancies. This offers huge advantages for making functional nano devices, and Wang says that so far they have fabricated field-effect transistors, and ultra-sensitive nano-size gas sensors, and nanocantilevers, based on individual nanobelts.

Speaking to Science Watch, Wang outlined his plans for the future. "My research will focus on two aspects: the application and integration of nanobelt materials with other microsystems; and applications of nanobelts in biomedical science." Ultimately Wang sees his nanobelts as playing a part in tackling one of the most intractable problems that face humans today: "One day we may use these materials for in-situ, real-time, non-destructive and remote monitoring within the human body, using them to detect cancer cells—and this might even be possible by sensing a single such cell. Meanwhile we are concentrating on developing nanobelt structures for improving the performance of micro- and nano-electromechanical systems."

The research reported in #2 has naturally attracted a lot of interest from industry because of possible sensor applications, but nanobelts could also find use in optoelectronics devices, transducers, and as surface-active catalysts. So far eight provisional patents have been taken out to protect the new technology, and Wang and his colleagues are in the process of setting up a company to make biodetectors using nanobelts.

Wang’s research is clearly going places as his output of research papers shows, some being singled out for special mention, such as his paper in Microscopy and Microanalysis (see Z.L. Wang, et al., 8[6]: 467-74, 2002) on the structures of oxide nanobelts and nanowires, which the journal selected as the best paper it had published that year. More recently, the news pages of Nature featured a paper in Applied Physics Letters (see W.L. Hughes, et al., 82[17]: 2886-8, 2003] which reports of the use of a nanobelt as a nanocantilever. Wang’s most recent discovery is of structurally controlled piezo- and ferro-electric materials, which promise to stimulate yet more scientific and technological interest. But it is another paper that may give Georgia Tech even more media spin, and that reports "nanowindmills" which Wang and his team made from zinc sulfide (see C. Ma, et al., Advanced Materials, 15[3]: 228-231, 2003).