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UCSD Jacobs School of Engineering

UCSD Engineering Professor Named to Scientific American 50 List

November 15, 2006 -- A UC San Diego materials scientist has been named to the 2006 Scientific American 50, a list of top scientists and innovators published annually by the popular-science magazine. Prabhakar Bandaru, a professor in the Jacobs School of Engineering’s Materials Science Program was recognized in the “chicken-wire electronics” category for demonstrating a radically new kind of nanotube-based transistor and switching device.

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Customized Y-shaped Carbon Nanotubes Can Compute. UCSD Jacobs School of Engineering professor Sungho Jin (left), professor Prabhakar Bandaru, and postdoctoral fellow Chiara Daraio.
The magazine’s editor in chief John Rennie said the list “pays tribute to individuals and organizations who, through their efforts in research, business, and policy-making, are driving advances in science and technology that lay groundwork for a better future. Not only does our list honor these prime movers - it shines a spotlight on the critical fields that are benefiting from their achievements.”

Bandaru and colleagues at UCSD and Clemson University investigate nanotube electronics and reported in Nature Materials in 2005 that Y-shaped nanotubes can behave like transistors. Microscopic switches made with such nanotubes could offer a way to shrink the size of transistors beyond that possible with conventional silicon microelectronics, and offer new types of functionality.

Real icon: Y nanotubes

UCSD researchers explain in this video how they analyzed the properties of Y-shaped nanotubes.
Length: 3:40

Nanotubes are fullerene-like cylindrical structures, consisting of hexagonal subunits with carbon atoms at the corners, arranged in a chicken-wire pattern - a bonding arrangement that makes nanotubes stronger than diamond. Nanotubes are so named because they are only a few nanometers in diameter, and their superior properties make them candidates for use in nanotechnology, electronics, optics, and other applications.

Scientific American announced its list on Nov. 13 and the list is available at the magazine’s Website and will be published in the magazine’s December 2006 issue, which is expected at newsstands Nov. 21.

Bandaru has focused his research on the underlying physics and chemistry of modern materials, focusing primarily on the electrical, magnetic, and optical properties at the nanoscale. “I feel very honored to be included in this list, and this recognition is also a credit to many people who have helped me, including my collaborators and colleagues at UCSD and fellow researchers at other institutions who also study nanotubes,” said Bandaru. “It’s interesting that the Scientific American editors call the graphitic structures we work with ‘chicken wire.’ I wish they were as easy to handle as chicken wire.”

Schematic drawing of a single-walled carbon nanotube showing the chicken-wire molecular architecture. Credit: NASA Glenn Research Center
Industry experts predict that fundamental technological and financial limits will prevent the makers of conventional metal oxide semiconductor transistors to reduce their size much further. The Y-shaped nanotubes investigated by Bandaru are only a few tens of nanometers thick and can be made as thin as a few nanometers.

The Y-shaped nanotube transistors were initially grown as straight elements. Titanium-modified iron catalyst particles added to the synthesis mixture were then attached to the straight nanotubes, nucleating additional growth, which continued like branches growing from a tree trunk. Consequently, the nascent nanotubes assumed a Y-shape with the catalyst particle gradually becoming absorbed at the junction of the stem and two branches.

Experiments conducted in Bandaru’s lab showed that the movement of electrons through the Y-junction can be finely controlled, or gated, by applying a voltage to the stem. Bandaru hypothesized that positive charge applied to the stem enhances the flow of electrons through the two arms, producing a strong “on” signal. Then, when the polarity of the charge is reversed, the movement of electrons through the arms essentially stops, creating an “off” signal. Such binary logic is the basis of nearly all transistors.

Bandaru is continuing to study new categories of Y-shaped nanotubes that have geometry-dependent electrical effects. “Large-scale assembly of hundreds, thousands, or even millions of these tubes is still an unsolved technical issue,” he said. “In addition to the use of nanotubes for electronics, we’re also looking into using nanotubes as fluid-flow sensors.”

Founded in 1845, Scientific American is the oldest continuously published magazine in the U.S. Editorial contributors to the magazine have included more than 100 Nobel laureates.

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