ARGONNE,
Ill. (August 30, 2005) – Researchers at the U.S.
Department of Energy's Argonne National Laboratory
have combined the world's hardest known material – diamond – with
the world's strongest structural form – carbon nanotubes.
This new process for “growing” diamond and carbon
nanotubes together opens the way for its use in a
number of energy-related applications.
The
technique is the first successful synthesis of
a diamond-nanotube nanocomposite, which means for
the first time this specialized material has been
produced at the nanometer size – one-millionth
of a millimeter, or thousands of times smaller than
the period at the end of this sentence.
The result established for the first time a process
for making these materials a reality, setting the
stage for several fundamental advances in the field
of nanostructured carbon materials.
The resulting material has potential for use in
low-friction, wear-resistant coatings, catalyst supports
for fuel cells, high-voltage electronics, low-power,
high-bandwidth radio frequency microelectromechanical/nanoelectromechanical
systems (MEMS/NEMS), thermionic energy generation,
low-energy consumption flat panel displays and hydrogen
storage.
Diamond is called the hardest material because of
its ability to resist pressure and permanent deformation,
and its resistance to being scratched. Carbon nanotubes,
which consist of sheets of graphitic carbon wrapped
to form tubes with diameters only nanometers in size,
are the strongest structures because they can withstand
the highest tensile force per gram of any known material.
“Diamond is hard because of its dense atomic structure
and the strength of the bonds between atoms,” said
Argonne's John Carlisle, one of the developers of
the new material. “The larger the distance between
atoms, the weaker the links binding them together.
Carbon's bond strength and small size enable it to
form a denser, stronger mesh of atomic bonds than
any other material.”
Diamond has its drawbacks, however. Diamond is a
brittle material and is normally not electrically
conducting. Nanotubes, on the other hand, are incredibly
strong and are also great electrical conductors,
but harnessing these attributes into real materials
has proved elusive.
By integrating these two novel forms of carbon together
at the nanoscale a new material is produced that
combines the material properties of both diamond
and nanotubes.
The
new hybrid material was created using Ultrananocrystalline™ diamond
(UNCD™ ), a novel form of carbon developed at Argonne.
The researchers made the two materials – ultrananocrystalline
diamond and carbon nanotubes – grow simultaneously
into dense thin films.
This
was accomplished by exposing a surface covered
with a mixture of diamond nanoparticles and iron
nanoparticle “seeds” to an argon-rich, hydrogen-poor
plasma normally used to make UNCD. The diamond and
iron “seeds” catalyze the UNCD and carbon nanotube
growth, respectively, and the plasma temperature
and deposition time are regulated to control the
speed at which the composite material grows, since
carbon nanotubes normally grow much faster than ultrananocrystalline
diamond.
“Experimenting with these variables led us to the
right combination,” said Argonne's Jeffrey Elam,
one of the developers. Added another of the developers,
Xingcheng Xiao, “It is possible that the plasma environment
causes local charging effects that cause attractive
forces to arise between the ultrananocrystalline
diamond supergrains and the carbon nanotubes. If
so, such hybrid structures could have interesting
electronic and photonic transport properties.”
The next step is to develop patterning techniques
to control the relative position and orientation
of the ultrananocrystalline diamond and carbon nanotubes
within the material.
“In addition, we hope to understand the structure
and properties of these materials, particularly the
mechanical, tribological and transport properties,” developer
Orlando Auciello said.
The research was featured in the June on the cover
of the peer-reviewed journal, Advanced
Materials .
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 .
For more information , please contact Catherine
Foster (630/252-5580 or cfoster@anl.gov )
at Argonne.
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