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Nano-generator could power tiny devices. 19:00 13 April 2006
The nanowires convert movement into current (Image: Georgian Institute of Technology)
simple "nano-generator" that converts movement into electricity could
let nanoscale devices draw power from their surroundings, researchers
nano-devices must use conventional power sources built on a much larger
scale. But a nano-generator could, for example, let a tiny medical
implant draw power from the movement of a patient''s arteries.
nano-generator, developed by researchers at the Georgia Institute of
Technology, Atlanta, US, consists of an array of flexible zinc oxide
nanowires. Each is 50 nanometres in diameter and 300 nanometres in
length (a nanometre is a billionth of metre). As each wire bends, its
crystalline structure builds up electrical charge in response to
mechanical stress - an phenomenon known as the piezoelectric effect.
charge up the nanowires, the researchers gently bent them using the tip
of an atomic force microscope. "One side of the nanowire is compressed
and the other is stretched," explains Jinhui Song, a member of the
research team. "The deformation of the crystal structure on the surface
of the wire causes charge to build up. The stretched side becomes
positive, and the compressed side negative."
the tip was in contact with the positive, stretched, part of the wire
the charge could not escape. This is because of the electrical
properties of the junction between the platinum tip of the microscope,
and the semiconducting nanowire. But when the tip moved over to the
negative, compressed side of the wire, the charge could escape, making
it act like a nanoscopic power source.
Billionths of a watt
single nanowire can only produce around half a picowatt, or one hundred
billionths of a watt.
But 200 nanowires can be squeezed into a 10
square micron area, to produce 10 picowatts. That is enough to power a
nanoscopic device like a nanotube-based gas sensor, the researchers
Shaffer, a nanotechnologist at Imperial College London, UK, says the
generator could make a useful addition to the growing array of
nano-components already created by scientists. But he adds that
researchers have yet to work out how to link many of these components
assembling lots of small pieces, but a big challenge for the future
will be how to build these components into working systems," Shaffer
told New Scientist. "In this case, it will be necessary work out how to connect up these wires to the electronic components."
Shaffer notes that a recently announced method for embedding electronic
transistors within nanowires could be a solution. The technique,
revealed in March 2006 by researchers from IBM, the University of
Florida and Columbia University in the US, could be used to connect the
generator to an electronic circuit, Shaffer says.Before
tacking this issue, however, the Georgia Institute of Technology team
are keen to get as much power as possible from their generator. This
could involve using lots of nanowires at once or finding a way of
keeping contact with the wires for longer while they vibrate. "The
current system captures only around 20% of the available mechanical
energy," Song says.
Journal reference: Science (vol 312, p 242)