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Dreaming of Nanowires

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Image: Georgia Institute of Technology

As the push to miniaturize electronic devices has mounted, engineers have dreamed of wires no wider than a nanometer. The smaller the wires, the more features they can fit on a single silicon chip, the more speed the device gains and the less energy it uses. But these dreams have been interrupted by some very real nightmares: when features become that small, they no longer obey the usual laws of physics; instead weird quantum behavior comes into play.

Some new results from researchers at the Center for Computational Materials Science at the Georgia Institute of Technology and the IBM T. J. Watson Research Center, however, should help electrical engineers sleep more peacefully. Using a giant supercomputer, they ran large-scale simulations of just how silicon nanowires no more than a few atoms wide and attached to aluminum leads would actually work in the quantum world.

Their predictions offer several interesting insights: because atomic orbitals in the leads and the silicon combine, finite conductance might plague nanowires shorter than one nanometer in length, like the one illustrated above. (Teal balls depict aluminum atoms; yellow balls are silicon; blue balls are hydrogen.) So-called Schottky barriers, which form between the two materials and prevent a flow of electrons, shouldn't prove so high that dangerous voltages are required to cross them. Doping--a common practice for optimizing today's semiconductors--might not present a problem if nanowires can be made from silicon clusters that, like carbon fullerenes, envelop the dopants. And the wavelike nature of electrons may interfere with the electric conductance through nanowires in certain configurations.

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