Paper #1 reports that zinc oxide nanowires can act as ultraviolet lasers. Paper #2, first featured in Science Watch in March/April 2002, reports a nanoswitch made of interlocking molecular rings. Paper #3 suggests that carbon nanotubes could be the basis of random access memory for molecular computing. Paper #4 is about ways of growing nanocrystals of cobalt that have magnetic properties; this report was highlighted in Science Watch in July/August 2002. Paper #5 announces that silicon nanowires doped with boron or phosphorus can perform as semiconductors.

However, it is #1 that perhaps has the potential for the widest application. The flexible, one-dimensional nanowires it describes can act as miniaturized, short wavelength, laser light sources and, as such, might one day be used in optical computing, information storage, and microanalysis. Peidong Yang and co-workers in the Department of Chemistry at the University of California, Berkeley, produced this remarkable form of zinc oxide, and his group works in conjunction with the Environmental Energy Technology Division and the Materials Science Division, Lawrence Berkeley National Laboratory, California.

Yang’s nanowires were formed on a sapphire surface using a process known as chemical vapor deposition. They were made by heating a finely ground mixture of zinc oxide and graphite at 900 degrees C in an atmosphere of argon gas. Atoms of zinc and oxygen are volatilized in the process and deposit on the sapphire surface as perfectly formed, ultra fine, hexagonal-shaped wires of zinc oxide with diameters of less than 100 nanometres. The secret of their production is first to imprint on the sapphire surface a thin layer of a gold template. It is from this that the crystals grow, the gold acting as a catalyst to promote the creation of the nanowires. These can be up to 10 microns long (= 10,000 nanometers) and will grow to that length within a few minutes. Paper #1 contains impressive illustrations of these nanowires, taken with a scanning electron microscope.

Semiconductor nanowires offer a unique type of nanoscale building block and are attracting attention worldwide, with a lot of effort going into studying their fundamental physical properties such as electrical transport and light emission. What is unique about Yang’s work is that he was the first to make nanowires that could act as coherent UV-blue nanoscale laser sources and it was this, he says, that explains why paper #1 has attracted so much attention.

More recently, the Yang group has focused on detailed investigation of single nanowire lasing phenomena, mainly using the technique of near field scanning optical microscopy (see J.C. Johnson, et al., J. Phys. Chem. B,105[46]:11387-90, 2001). Earlier this year he published a paper in Nano Letters (see J.C. Johnson, et al., 2[4]:279-83, 2002) on non-linear optical mixing in individual zinc oxide nanowires. Nor is the effect confined to zinc oxide nanowires; the California group has shown that gallium nitride (GaN) can produce crystals exhibiting the same effect. This work is soon to be published in Nature Materials.

Whether this fundamental research will lead to useful applications remains to be seen, but its commercial possibilities are being explored and the nanolaser technology has been licensed to Nanosys, Inc. The hope is that it will be possible to develop integrated nanoscale UV-blue laser sources for "lab-on-a-chip" analysis technology, and possibly for high-definition displays and high-density data storage applications. In the case of analytical applications the nanowires would act as nanoscale UV excitation sources for ultrasenstive molecular detection and sensing.