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Nanotech development brings closer era of nanowire electronic devices, much smaller computer chips
05 February 2002

By Robert Sanders, Media Relations



Scanning transmission electron microscope (STEM) image of two heterostructure nanowires. The light and dark striations along the wires are alternating regions of silicon and silicon/germanium. Junctions between different materials can be engineered to make electronic devices such as light emitting diodes or transistors.
PHOTO CREDIT: Peidong Yang/UC Berkeley

Berkeley - Scientists at the University of California, Berkeley, announced this week a development that could significantly shrink computer chips, promising electronic devices on a single nanowire less than one-hundredth the width of a human hair.

The researchers have found a way to mate different materials along the length of a single nanowire using manufacturing techniques common in the semiconductor industry. With this ability, a single nanowire could be a complete device, incorporating transistor junctions, light-emitting diodes and even lasers.

The development takes electronics from the two-dimensional world of today's chips into the one-dimensional world of nanowires.

"This is a major advancement in the field of one-dimensional nanostructure research. The impact could be tremendous," predicts Peidong Yang, assistant professor of chemistry at UC Berkeley and a faculty scientist in the Materials Science Division at Lawrence Berkeley National Laboratory.

Yang and graduate students Yiying Wu and Rong Fan reported their results in the February issue of the peer-reviewed journal Nano Letters, a publication of the American Chemical Society.

The issue reports similar work by a Swedish team. The two groups independently made lattices that they say will for the first time enable nanowires to be constructed with otherwise incompatible materials. Such mixed bundles are essential to making electronics and other devices on an increasingly smaller scale.

These reports show that nanowire devices could soon be routinely and cheaply built using little more than a special mixture of gases deposited on a foundation material.

"Because you can mix these materials, one wire could be a device itself as opposed to needing multiple wires to make a device," said Larry Bock, president and CEO of Nanosys, Inc., a Palo Alto-based company co-founded by Yang that hopes to commercialize nanowire technology.

Whereas today "you could cross two different wires - one p-doped and one n-doped - and create a device like a light emitting diode, you could do all this on one wire" with nanowire technology, he said.

Bock predicts a nanowire device will be on the market within three to four years. Less than a year old, Nanosys is developing nanowire devices for chemical sensing, optoelectronics - lasers and light emitting diodes - and, in the long term, nanoelectronics.

Yang and his colleagues developed a way to fabricate "superlattice" nanowire, so named because the nanowire's cylinder-shaped nanoscopic bundle interweaves substances with different compositions and properties. As a result, well-defined junctions and interfaces with potentially important functionalities are incorporated within individual nanowires.

Nanotechnologists have long sought such a means to bring together materials on the nanoscopic scale that otherwise would be structurally incompatible. Much like conventional builders, nanoengineers mix and match a mélange of elements in hopes of creating entirely new classes of nanoscale products or systems that could revolutionize everything from energy production to manufacturing and assembly. In the field of electronics and optics, mastery of these nanoscale "heterostructures" should lead to devices too small to see with the naked eye, but equal to or better than today's hand-size electronics.

The team of nine Swedish scientists working in the Materials Chemistry and Solid State Physics Departments in Lund University's Nanometer Consortium used related but different methods than their California peers. In both cases, manufacture is relatively straightforward and results in stable nanowires that can operate at room temperature.

The California scientists went a step further, however. "We've successfully made nanoscale junctions within individual [nano]wires, putting different materials together, embedding junctions directly in the wires," Yang said. "The next step is to use the wires as submicroscopic components for various optoelectronic devices. These are definite first steps, but critical ones."

Today's personal computers rely on a series of small junctions that connect components that have properties necessary for proper functioning. Given the laws of physics and real-world manufacturing demands, radically scaling down such functionality is difficult. The research findings in California and Sweden promise to make nanowire production both rapid and economical. In just one hour, millions of nanowires can be made at minimal expense.

"Growing" a nanowire can be done either with vapor deposition from a stockpile of specialty gases, or with a laser aimed at a target material to produce a specific vapor, or both. In either case, the gases are directed toward and then condense on a substrate material, like silicon. Because the technique is precisely controlled, the resultant nanowire can be customized according to function or composition. Thus, single nanowires can control current flow, emit light, process or store information or dissipate heat - but at extremely small scales.

The work is funded by the Camille and Henry Dreyfus Foundation, the 3M Corporation, the National Science Foundation, the U.S. Department of Energy and UC Berkeley.


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