Georgia Tech scientists have produced a special type of nanogenerators that can utilize mechanical energy from body movement and blood flow to power the next generation of implantable medical devices, making them self-powered:
Described in the April 14th issue of the journal Science, the nanogenerators produce current by bending and then releasing zinc oxide nanowires – which are both piezoelectric and semiconducting…
The nanogenerators developed by Wang [Zhong Lin Wang, professor in the School of Materials Science and Engineering at the Georgia Institute of Technology -ed.] and graduate student Jinhui Song use the very small piezoelectric discharges created when zinc oxide nanowires are bent and then released. By building interconnected arrays containing millions of such wires, Wang believes he can produce enough current to power nanoscale devices.
To study the effect, the researchers grew arrays of zinc oxide nanowires, then used an atomic-force microscope tip to deflect individual wires. As a wire was contacted and deflected by the tip, stretching on one side of the structure and compression on the other side created a charge separation – positive on the stretched side and negative on the compressed side – due to the piezoelectric effect.
The charges were preserved in the nanowire because a Schottky barrier was formed between the AFM tip and the nanowire. The coupling between semiconducting and piezoelectric properties resulted in the charging and discharging process when the tip scanned across the nanowire, Wang explained.
When the tip lost contact with the wire, the strain was released – and the researchers measured an electrical current. After the strain release, the nanowire vibrated through many cycles, but the electrical discharge was measured only at the instant when the strain was released…
The researchers grew the nanowire arrays using a standard vapor-liquid-solid process in a small tube furnace. First, gold nanoparticles were deposited onto a sapphire substrate placed in one end of the furnace. An argon carrier gas was then flowed into the furnace as zinc oxide powder was heated. The nanowires grew beneath the gold nanoparticles, which serve as catalysts.
The resulting arrays contained vertically-aligned nanowires that ranged from 200 to 500 nanometers in length and 20 to 40 nanometers in diameter. The wires grew approximately 100 nanometers apart, as determined by the placement of the gold nanoparticles.
A film of zinc oxide also grew between the wires on the substrate surface, creating an electrical connection between the wires. To that conductive substrate, the researchers attached an electrode for measuring current flow.
Researchers believe their technology could be utilized in myriads of ways outside the body as well, such as for soldiers in the field, by implanting the generators in shoes or clothing.
A scanning electron microscope image (top) shows an array of zinc oxide nanowires. Middle image shows a schematic of how an AFM tip was used to bend nanowires to produce current. Bottom image depicts output voltages produced by the array as it is scanned by the AFM tip….
The press release…
More from the National Science Foundation…
