Nanoscale devices present a megascale bear of a problem when it comes to energy sources, especially when these devices are intended for implantation in the body.
Georgia Tech researcher Zhong Lin Wang (photo), who also holds positions at Peking University and the National Center for Nanoscience and Technology of China, and graduate student Jinhui Song are working on nanogenerators that produce current mechanically by bending and releasing zinc oxide nanowires, which are both piezoelectric and semiconducting. Interconnected arrays of millions of such wires could produce enough current to run nanoscale devices. Brought to fruition, this technology could resolve the dual issues of power supply bulk and toxicity.
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Wang and Song grew arrays of zinc oxide nanowires and deflected individual wires using an atomic-force microscope (AFM) tip. This created a charge separation, positive on the stretched side and negative on the other. The charges were preserved because a Schottky barrier was formed between the AFM tip and the wire. Coupling between the semiconducting and piezoelectric properties resulted in the charging and discharging process when the tip scanned across the nanowire. When the tip lost contact with the wire, the strain was released and the wire vibrated through many cycles, but the researchers measured a current only at the instant of release. Similar tests on structures that were neither piezoelectric nor semiconducting indicated that the observed effect was truly a piezoelectric-induced discharge process.
Wang estimates that as much as 30% of the mechanical input can be converted to electrical energy for a single cycle of vibration. This would argue for harvesting the energy produced by the body and using it to power implanted medical devices. (http://tinyurl.com/q2k4e)