Dr. Marco Buongiorno-Nardelli leans over his computer in Cox Hall,
scanning the results flashing across the screen from a state away.
Hes exploring the feasibility of using carbon nanotubes in nanoscale
electronic devices, and is using the Oak Ridge supercomputer to run
his own suite of codes simulating electron transport in nanotubes.
Although carbon nanotubes are very small objects on the human scale,
simulation of their behavior is possible only on a very large-capacity
The biggest supercomputer in the Research Triangle area, located at
MCNC, has one-
teraflop capacity, handling one trillion floating point calculations
per second. But the reigning supercomputer at ORNL is an IBM Power
4, nicknamed Cheetah, which has six teraflops of computing
power. ORNL has recently acquired a test Cray X1 system, which could
be expanded and made even faster in the next few years, bringing ORNLs
capacity to ten
teraflopsChristmas for a certain young theoretical physicist.
Buongiorno-Nardelli came to the U.S. from Italy as a post-doc in 1995.
He became an
assistant professor in the College of Physical and Mathematical Sciences
at NC State in 2001, having already begun his interaction with ORNL
the year before. He now holds one of the two new positions shared
between NC State and ORNL.
With a young family, Buongiorno-Nardelli was concerned about working
for organizations in two different states. But a new high-speed fiber-optic
link 10,000 times faster than todays fastest networks has been
set up to connect ORNL, the Atlanta gigapop, and the Research
Triangle. Now, there is no difference between my sitting in
a control room in Oak Ridge and my lab in Raleigh, says Buongiorno-Nardelli.
He splits his time by teaching one semester
at NC State, then spending a week a month at Oak Ridge in the following
semester, and more time there in summer. There is no substitute
for the face-to-face interaction with the scientists at Oak Ridge,
he maintains, so I visit as often as I can.
Using the ORNL supercomputer, Buongiorno-Nardelli predicted that it
would be possible to build a nano-rheostat, similar to a dimmer light
switch. In such a device, a carbon nanotubea cylinder resembling
rolled-up chicken wire because its carbon atoms are arranged in a
hexagonal configurationis placed on a sheet of graphite whose
carbon atoms also have a hexagonal arrangement (see illustration on
Computational simulations verified that the interface between a carbon
nanotube and graphite gives tunable resistance. If you place
the carbon cylinder on the graphite sheet so that the carbon atoms
of both are aligned, a current will flow at the interface, Buongiorno-Nardelli
says. As you rotate the carbon cylinder on the graphite sheet,
changing the angle between the atoms in the system, you get increased
electrical resistance and reduced current flow. As the atoms become
aligned, you get low resistance
and high current flow. His theoretical predictions agreed with
experimental results at the University of North Carolina at Chapel
Hill, and were published in Science magazine in 2000.
Buongiorno-Nardelli and his NC State colleagues are also computationally
modeling a proposed molecular memory cell that would allow laptop
computer batteries to last 100 times longer than todays batteries.
Were not actually making things, explains Buongiorno-Nardelli.
Were simulating nanoscopic pieces for experimentalists
to use in fabricating devices. This is such a great opportunity to
be a part of the interplay between theory and experiment.
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