Crystal clear

Wires just a few nanometers thick are among the technologies that could lead to improvements in memory chips and high-resolution displays. The challenge, however, has been to assemble nanowires in regular patterns in order to build large numbers of devices such as transistors or diodes on a single chip. Babak Nikoobakht of the National Institute of Standards and Technology in Gaithersburg, Md., has now managed to grow nanowires exactly where they’re needed.

Nikoobakht first placed an orderly array of gold nanodroplets on a sapphire crystal surface. He then exposed the droplets to a hot gas of zinc oxide. The droplets acted as catalysts, each one spawning the growth of a zinc oxide crystal just 10 or 15 nm across.

The sapphire’s molecular structure made all the zinc oxide crystals grow on its surface in the same direction, which pushed the gold droplets along. With each nanodroplet acting “like a printer” on the sapphire’s surface, says Nikoobakht, the resulting zinc oxide trails formed a regular array of nanowires. Nikoobakht was able to fine-tune his process to make the nanowires grow to lengths of a few hundreds of nm to 50 microns.

By adding layers of different materials, Nikoobakht was able to use the nanowires as building blocks for transistors and diodes, he reports in the Oct. 30 Chemistry of Materials. He says that the technique might be useful for imprinting high-density memory chips. Because zinc oxide is transparent but can also emit light, the nanowires could also work as components of transparent semiconducting displays, he says.

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