Self-powered nanowires
Many research teams around the world are building nanodevices of some kind. But these very small devices need very small sources of power to be fully functional. Now, researchers at the University of Illinois at Urbana-Champaign (UIUC) have shown that a single nanowire can produce power by harvesting mechanical energy from its environment. 'Made of piezoelectric material, the nanowire generates a voltage when mechanically deformed.' But don't think that this nanowire, made of an oxide of barium and titanium, and measuring approximately 280 nanometers in diameter and 15 microns long, will be able to power anything more than a nanoscale sensor. It was able to generate an electrical energy of about 0.3 attojoules -- less than one quintillionth of a joule or about 2.8E-25 kilowatt-hour.
You can see on the left a diagram showing "the experimental setup for the piezoelectric charge detection from an individual barium-titanate nanowire" (top) and a "scanning electron microscope image of the suspended nanowire under test" (bottom) (Credit: UIUC). Here is a link to a larger version.
This research work has been driven by Min-Feng Yu, an assistant professor in the Department of Mechanical Science and Engineering at UIUC, who is affiliated with the Beckman Institute for Advanced Science and Technology, and his team. Yu has other research projects.
As you can guess, it was difficult to measure a voltage of 0.3 attojoules. And the researchers had to build an extremely sensitive device. "With the development of this precision testing apparatus, we successfully demonstrated the first controlled measurement of voltage generation from an individual nanowire," said Yu. "The new testing apparatus makes possible other difficult, but important, measurements, as well."
Besides this testing equipment, how did the researchers conduct their experiments with this nanowire? "The nanowire was synthesized in the form of a single crystal of barium titanate, an oxide of barium and titanium used as a piezoelectric material in microphones and transducers, and was approximately 280 nanometers in diameter and 15 microns long. [...] When the researchers’ piezoelectric nanowire was placed across the gap and fastened to the two platforms, the movable platform induced mechanical vibrations in the nanowire. The voltage generated by the nanowire was recorded by high-sensitivity, charge-sensing electronics."
This research work will be published in Nano Letters under the name "Voltage Generation from Individual BaTiO3 Nanowires under Periodic Tensile Mechanical Load." It has already been published online on September 26, 2007. Here is the abstract. "Direct tensile mechanical loading of an individual single-crystal BaTiO3 nanowire was realized to reveal the direct piezoelectric effect in the nanowire. Periodic voltage generation from the nanowire was produced by a periodically varying tensile mechanical strain applied with a precision mechanical testing stage. The measured voltage generation from the nanowire was found to be directly proportional to the applied strain rate and was successfully modeled through the consideration of an equivalent circuit for a piezoelectric nanowire under low-frequency operation. The study, besides demonstrating a controlled experimental method for the study of direct piezoelectric effect in nanostructures, implies also the use of such perovskite piezoelectric nanowires for efficient energy-harvesting applications."
Now, what will be the possible usages for such nanowires? Probably nanoscale sensors.
Sources: University of Illinois at Urbana-Champaign, via EurekAlert!, September 27, 2007; and various websites
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