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Nano World: Painted-on electronics

By
CHARLES Q. CHOI, UPI Technology Correspondent

NEW YORK, July 13 (UPI) -- The first electronics painted on with liquids to outperform their conventional electronic counterparts are made possible via crystals only nanometers or billionths of a meter in diameter. These light-detecting particles might be used in night vision goggles, digital cameras, biomedical imaging and telecommunications.

"The current ways of growing the semiconductors used in making these electronics, these photodetectors that you have in night vision goggles and digital cameras and telecommunications, are very expensive. Night vision goggles cost $60,000," said researcher Ted Sargent, an electrical engineer at the University of Toronto. "The approach we're taking is much simpler, just painting onto a chip. You can see in the dark, take away the night at a price point potentially everyone can afford."

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Conventional semiconductors rely on growing atomically perfect crystals at 1,000 degrees Celsius and above. While scientists have developed electronics painted on with liquids before that are lower cost, such as lasers and solar cells, these have until now also proven lower in performance. "This is a proof of concept that they can be superior," Sargent said.

Sargent and his colleagues cooked up semiconductor nanoparticles in a flask containing extra-pure oleic acid, the main ingredient in olive oil. Droplets of this solution were then placed on a glass slide and spread out into a smooth, continuous semiconductor film. After bathing the films for two hours in methanol solvent, the oil evaporated, leaving behind an 800-nanometer-thick layer of the light-sensitive nanoparticles.

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At room temperature, the paint-on semiconductor films were roughly 10 times more sensitive to visual and infrared light than the sensors currently used in military night-vision and biomedical imaging. "These are exquisitely sensitive detectors of light," Sargent said. He and his colleagues report their findings in the July 13 issue of the journal Nature.

Sargent emphasized they have not developed images using their devices yet. "We've shown sensors with single pixel detection. Our next big challenge is scaling up to a full image sensor," he said.

In addition to night-vision goggles, infrared detectors are key in telecommunications. Moreover, these infrared detectors could find use in low-cost sensors in biomedical imaging, "as the body is very transparent to infrared light," Sargent said.

"This is a really exciting and important new direction for making both light detection and light emission devices at low costs. This is really the right approach to go with here," said John Joannopoulos, director of the Institute for Soldier Nanotechnologies at the Massachusetts Institute of Technology in Cambridge. "The ability to realize low-cost, paintable, high-performance designer semiconductors for use as short-wavelength infrared detectors and emitters is of enormous value for a wide range of communications, imaging and monitoring applications."

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