SETI bioastro: Fw: Cornell News: Single-atom transistor developed

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Date: Fri Jun 14 2002 - 09:37:36 PDT

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Sent: Friday, June 14, 2002 10:46 AM
Subject: Cornell News: Single-atom transistor developed

Cornell scientists create single-atom transistor by implanting
molecule between wires, enabling 'virtual dance of electrons'

EMBARGOED FOR RELEASE: 2 p.m. EDT, June 12, 2002

Contact: David Brand
Office: 607-255-3651

ITHACA, N.Y. ---- A long-sought goal of scientists has been to shrink
the transistor, the basic building block of electronic circuits, to
smaller and smaller size scales. Scientists at Cornell University
have now reached the smallest possible limit: a transistor in which
electrons flow through a single atom.

The Cornell researchers have created a single-atom transistor by
implanting a "designer" molecule between two gold electrodes, or
wires, to create a circuit. When voltage was applied to the
transistor, electrons flowed through a single cobalt atom within the
molecule. Paul McEuen, professor of physics at Cornell, describes the
process by which electrons pass from one electrode to the other by
hopping on and off the atom as "a virtual dance of electrons."

McEuen and his colleagues at Cornell's Center for Materials Research,
including Dan Ralph, associate professor of physics, and graduate
students Jiwoong Park and Abhay Pasupathy, report on their creation
of a single-atom transistor in the latest issue (June 13) of the
journal Nature.

McEuen cautions that the device cannot yet be described as having all
the functions of a traditional transistor, such as amplification. But
he sees a potential application for the new transistor as a chemical
sensor because a change in the environment around the molecule could
cause a measurable alteration of the conductance of the device.

At the heart of the Cornell group's transistor is the "designer
molecule" synthesized by Héctor Abruņa, professor of chemistry
and chemical biology, and graduate student Jonas Goldsmith. At the
molecule's center is a cobalt atom surrounded by carbon and hydrogen
atoms and held in place on either side by molecular "handles" made of
pyridine, a relative of benzene. On their outer side, the "handles"
are attached to sulfur atoms, which act like "sticky fingers," to
bond the molecule to the gold electrodes. Two different molecules
were studied, one with longer "handles" than the other. The shorter
molecule was found to be a more efficient conductor of electrons."As
chemists, we can deliberately design and manipulate molecules to
achieve a specific function," says Abruņa. "This is very important
because we are now able to incorporate the properties of these
molecules into electronic devices."

The challenge faced by the Cornell researchers was to place a
molecule less than two nanometers long (about the length of five
silicon atoms) between two gold electrodes. To do this they used a
technique called electromigration, by which an increasingly large
current is run through a gold wire, forcing the atoms to migrate
until the wire breaks. The molecule is then "sucked" into the gap by
the high electric field present, and the sulfur "sticky fingers" bond
the molecule to the gold. "Using this technique you can very reliably
get wires with a gap on the order of one nanometer," or about three
silicon atoms, says McEuen.

The technique was invented by McEuen and his former postdoctoral
colleague, Hongkun Park, when both were researchers at the University
of California-Berkeley. Park, now at Harvard University, reports in
the same issue of Nature on a similar development in molecular
electronics, using a different molecule. Both teams were able to
start and stop the flow of electrical current by adjusting the
voltage near the bridging molecule.

Although the single-atom transistor demonstrates the potential for
shrinking the size of components well beyond what is possible using
conventional lithographic techniques, says McEuen, there are major
technological hurdles to be overcome in order to build such a
transistor for electronic applications. One problem to be solved, for
example, is gain, the ability to amplify a small signal.

The Cornell group plans next to focus on engineering a molecule with
two different geometries (or shapes) that could act as a switch,
changing between the two forms with the application of a voltage. "No
one has yet put a single molecule in a circuit and activated it
electronically," McEuen observes.

Other collaborators on the Nature paper, titled "Coulomb blockade and
the Kondo effect in single atom transistors," are, at Cornell, James
Sethna, professor of physics; postdoctoral associate Yuval Yaish; and
graduate students Connie Chang and Jason Petta; and Oberlin College
undergraduate Marie Rinkoski. The research was funded by the National
Science Foundation, the Department of Energy, the Department of
Education and the Packard Foundation.

Related World Wide Web sites: The following sites provide
additional information on this news release.

o McEuen Group:


o Ralph Group: <>

oAbruņa Group: <>


The web version of this release, with accompanying photos, may be
found at

Cornell University News Service
Surge 3
Cornell University
Ithaca, NY 14853

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