Researchers from the Georgia Institute of Technology, have made single-crystal zinc oxide (ZnO) nanobelts that spontaneously rolled into helical structures. The nanohelixes or nanosprings, have piezoelectric properties and show promise for biomedical applications and in microsystems.
Piezoelectric semiconductors are natural resonators and therefore don't need all the circuitry normal semiconductors need to make them process and emit signals. Physical stimulation causes piezoelectric materials to naturally oscillate at a known frequency. It might therefore be possible to treat the material to attract a protein from a cancer cell and then even a single molecule of that protein could be detected with just one nanospring.
Currently working to exploit this is a collaborative group of multidisciplinary specialists looking to devise a micron-sized "pill" that disperses millions of such nanosprings all through the entire body, and radios through the skin if cancer cells are detected. A prototype of this "pill" is promised by the end of the year.
The nanosprings are also compatible with traditional photolithographic techniques of chip-making and by being grown on-chip, they can be used as highly sensitive transducers.
The nanobelts were grown by a solid-vapour process by evaporating high-purity zinc oxide powder in vacuum at 1,350 degrees C, at which time an argon gas flow is introduced into the furnace. The ring shapes began depositing on a cooler 400- to 500 degrees C alumina substrate, with the thinnest of them forming spiraled nanosprings.
To get the greatest piezoelectric effect, the ZnO nanostructures need a large area of polarized (0001) zinc- and oxygen-terminated surfaces. However, the (0001) surface has a high surface energy and so its growth is energetically unfavourable. With careful control of the experimental conditions, the Georgia team produced structures with more than 90% of the nanobelts having top flat surfaces consisting of polar ±(0001) facets.