"So far, innovations for delivering nanoscale power sources are almost non-existent," Zhong Lin Wang of Georgia Institute of Technology told nanotechweb.org, "while huge emergent needs for nanoscale sensing devices continue for biological and defence applications. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy, such as body movement or muscle stretching, vibration energy, such as acoustic or ultrasonic wave, and hydraulic energy, such as body fluid and blood flow, into electric energy that will be used to power nanodevices without using a battery."

Wang believes the nanowires could also have a huge impact in miniaturizing integrated nanosystems by reducing the size of the power generator and improving its efficiency and power density.

To create the nanogenerator, Wang and colleague Jinhui Song made an array of aligned zinc oxide nanowires on an α-Al2O3 substrate using a vapour-liquid-solid process and gold nanoparticles as a catalyst. The nanowires were 200–500 nm long and a thin film of ZnO also grew on the substrate.

Next the researchers used an atomic force microscope tip to bend the nanowires. This created a voltage when the resulting piezoelectric charges in the nanowires discharged as the wires straightened up. The power generators were around 17–30% efficient.

"This [is] the first work achieving nano-scale energy conversion by nanotechnology," said Wang, who is affiliated to Peking University and the National Centre for Nanoscience and Technology, China. "This is also the first example that shows the coupling of piezoelectric and semiconducting properties is the key for the piezoelectric discharge process."

According to Wang, the technology can also be applied for building wireless, self-powered sensors by harvesting energy from the environment or can be used to generate electricity by body movement.

"You could envision having these nanogenerators in your shoes to produce electricity as you walk," Wang said. "This could be beneficial to soldiers in the field, who now depend on batteries to power their electrical equipment. As long as the soldiers were moving, they could generate electricity."

Now the team hopes to develop the technology in two ways – creating self-powering nanodevices and nanosystems in biological systems and making a large-power-output electricity generator for biomedical, defence and civil applications.

The researchers reported their work in Science.