Nanosprings: Helical Nanostructures Could be Actuators & Transducers in Future Nanosystems

Dubbed "nanosprings," the new structures have piezoelectric and electrostatic polarization properties that could make them useful in small-scale sensing and micro-system applications.

Just 10 to 60 nanometers wide and 5-20 nanometers thick - but up to several millimeters long - the new structures are similar to but smaller than the "nanobelts" first reported by Georgia Tech scientists two years ago in the journal Science. The new helical structures and their potential applications were described in the journal Nano Letters. The research was supported by the National Science Foundation and NASA.

"These structures are very different from our original nanobelts and are a major step toward a new system of nanostructures," said Zhong L. Wang, director of Georgia Tech's Center for Nanoscience and Nanotechnology and a professor in the School of Materials Science and Engineering. "Piezoelectric and polar-surface dominated smart materials based on zinc oxide are important because they could be the transducers and actuators for future generations of nanoscale devices."

The piezoelectric properties of the new structures could make them useful in detecting and measuring very small fluid flows, tiny strain/stress forces, high-frequency acoustical waves and even air flows that would otherwise be imperceptible. When deflected by the flow of air or fluids, the nanosprings would produce small but measurable electrical voltages.

"They could be used to measure pressure in a bio-fluid or in other biomedical sensing applications," said Wang. "You could use them to measure nano- or pico-newton forces."

The piezoelectric properties could also make the structures useful as actuators in micro-systems and nanosystems, where applying voltage would induce strains. "In micromechanical systems, these structures could provide the coupling between an electrical signal and a mechanical motion," Wang noted.

Semiconductor-based nanostructures that rely on electrostatic forces have gained widespread research interest, but Wang said development of nanomaterials for piezoelectric actuators have lagged. The new nanosprings could therefore give designers of future nanoscale systems more options.

Beyond their piezoelectric properties, the new structures also display unusual electrostatic polarization, with positively and negatively charged surfaces across the thickness of the nanoribbon. This electrical charge could be used to attract specific molecules, potentially allowing the nanosprings to be used as biosensors to detect single molecules or cells.