Drawing Diodes - IEEE Xplore

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cylindrical boule of material— generally silica, although. Orf and his colleagues used a polymer instead. The material is heated until it's soft enough to flow. Then.
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Frequency that microwaves drive the beat of a micromechanical drum built at the U.S. National Institute of Standards and Technology to demonstrate a principle of quantum mechanics.

Drawing Diodes

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according to Edmunds .com CEO Jeremy Anwyl, delivery vans of all sorts make up just 1.9 percent of the U.S. market. But vehicle fleets aren’t just commercial trucks. General Electric said in November it would buy 25 000 electric vehicles, including 12 000 Chevy Volts, for its own use. Plug‑ins serve as rolling “green” ads for companies, but what all fleet buyers really treasure is the lower cost of running on grid power (it’s onefifth to one-third the cost per mile of gasoline). That said, even automakers aren’t convinced the United States will hit its 1 million target. Britta Gross, director of global energy systems and infrastructure commercialization for GM, thinks the country might miss the target by a year or two. But whether the United States hits that mark in 2015 or 2017 may not really matter. Like the moon shot, an audacious goal has been put out there—and the industry is moving smartly toward it, which was hardly the case even five years ago. The biggest determi­ nant of whether Obama’s goal will be met is oil prices. Unrest in oil-­producing regions, plus growing demand from China, could convince consumers who are wary of gas-price levels to take the plunge—or more accurately, the plug. 

—John Voelcker

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at regular intervals along the length of the fiber. “The fact that you Engineers create semiconductor diodes can synthesize a high-­ inside optical fibers temperature compound [the zinc selenide] inside process. The researchers a low-­temperature matrix aterials scientists started by lowering the is very interesting and at MIT say they’ve melting points of the surprising, and as far as I found a way to build components of the compound know, this is the first time it simple semiconductor devices semiconductor zinc selenide— has been demonstrated in the inside a fiber. This new mixing the zinc with tin and context of a fiber,” Fink says. manufacturing process could The fiber drawing process create fibers with logic, image-­ the selenium with sulfur. They drilled slots along the essentially makes large processing, and photovoltaic surface of a solid boule of the structures much smaller and capabilities that could one day polymer polyethylsulfone brings them closer together, lead to smart, self-­powered and inserted tin-zinc wires so it should be possible fabrics, say researchers. into the slots. They then used to lay out fairly complex Nicolas Orf, a researcher evaporation to deposit a thin circuits in the preform to in Yoel Fink’s laboratory at create nanometer-scale MIT, managed to synthesize devices within the fiber. semiconductor materials into With the right reagents, Fink the precursor to an optical says, the process should fiber, so that as the fiber is work to produce a wide drawn out, the semiconductor variety of semiconductor forms into simple diodes materials. That could make with electrical contacts. possible flexible electronic “You could end up with textiles and fibers that can a piece of material that’s a convert light into electricity; kilometer long,” says Fink. perhaps one day a T-shirt “That’s something that really could power a cellphone. could only happen if you “These fibers open can draw the materials.” the door to intriguing Optical fiber is made possibilities,” says John starting with a thick, Ballato, an optical fiber cylindrical boule of material— layer of the selenium sulfide researcher at Clemson generally silica, although on top of the wires and finally University, in South Orf and his colleagues used wrapped the whole thing Carolina. However, the a polymer instead. The with more polymer. This use of polymers and soft material is heated until it’s “preform” was then heated semiconductors and metals soft enough to flow. Then in a vacuum to produce a may limit the amount of it is drawn out into a fiber single, solid structure; it optical power that such that’s often hundreds of was then pulled into fiber. a fiber could handle, he meters long but just a few As the tin zinc and the says. But the drawing micrometers in diameter. selenium sulfide were method “can be considered Engineers have pulled close together during an important step to a been intrigued by the the drawing process, they ‘fiber that does everything’— idea of incorporating underwent a chemical creates, propagates, semiconductors into the reaction, crystallizing into senses, and manipulates fiber, but many useful small chunks of zinc selenide, photons, electrons, semiconductors have high phonons, et cetera.” melting points and won’t flow with tin wires providing electrical contact. The at the temperatures typically  —Neil Savage result was semiconductor used in the drawing process. diodes, the building blocks Fink’s team got around this A version of this article appeared of many circuits, spaced problem by using a multistep online in March.

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april 2011 • IEEE Spectrum • NA

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