ARGONNE , Ill. (Jan. 3, 2006) – Researchers at the
U.S. Department of Energy's Argonne National Laboratory
have found that gold "shines" in a different way
at the nanoscale, and the insights may lead to new
optical chips for computers or for switches and routers
in fiber networks.
The nanoscale refers to a size one-billionth of
a meter, or about 70,000 times smaller than the width
of a human hair. Materials that small exhibit entirely
different properties from conventional materials.
Specifically, temperature, electricity and magnetism
are completely different from that of conventional
materials, and could form the basis of new technologies.
The Argonne researchers examined the characteristics
of photoluminescence – the emission of light when
electrons are stimulated -- in gold nanorods, and
found that they could control the wavelength of the
light emitted by the material, making it possible
to use as a light source inside an optical chip,
allowing transmission of information through light. "The
light emitted is dependent on the shape of the gold
nanorods," said Gary Wiederrecht, Argonne scientist
and leader of the research team.
The gold nanorods are about 20 nanometers wide and
range from 70 to 300 nanometers long. The rod-like
shape of the material is important, Wiederrecht explained,
because the rod shape determines the energy of the
collective electronic excitations that radiate light.
Thus, photoluminescence at different wavelengths
is achieved in nanorods of differing lengths. The
rod shape also produces enhanced absorption of the
illumination, increasing the light intensity and
also concentrating that intensity to levels high
enough to create luminescence. "The rods have strong
absorption characteristics in the near-infrared range," Wiederrecht
said. The experimenters used an ultrafast titanium-sapphire
laser beam at 800 nanometers to create the photoluminescence.
The research is published in the Dec. 31, 2005,
issue of Physical Review Letters .
While the research has future implications for technological
advances, Wiederrecht is quick to explain that his
group has done basic research -- an examination of
the material for a fundamental understanding of its
characteristics. The longer-term implications of
the work include the ability to produce nanoscale
light sources for faster and smaller optical devices
and novel photoluminescent sensors.
"Because materials at the nanoscale behave so differently
from conventional materials, we're starting all over
again, in a way, to understand how and why these
nanomaterials function," Wiederrecht said.
Other members of the research team are lead author
Alexandre Bouhelier of Argonne's Chemistry Division
and the Center for
Nanoscale Materials and Renaud Bachelot, Gilles
Lerondel , Sergei Kostcheev and Pascal Royer, all
of the Laboratoire de Nanotechnologie et d'Instrumentation
Optique in Troyes, France.
The nation's first national laboratory, Argonne
National Laboratory conducts basic and applied scientific
research across a wide spectrum of disciplines, ranging
from high-energy physics to climatology and biotechnology.
Since 1990, Argonne has worked with more than 600
companies and numerous federal agencies and other
organizations to help advance America's scientific
leadership and prepare the nation for the future.
Argonne is managed by the University
of Chicago for the U.S.
Department of Energy 's Office
of Science .
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