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Fujitsu
Achieves Breakthrough with World's First New Carbon Nanotube
Composite
Other topics:
JCN Newswire
Monday, March 03, 2008
Fujitsu Laboratories Ltd. today announced the successful
formation of a new nano-scale carbon composite featuring a
self-organizing structure[1], by combining carbon nanotubes
and graphene[2] which are both nano-scale carbon structures.
The newly-discovered composite structure is synthesized at a
temperature of 510 C, cooler than for conventional graphene
formed at temperatures too high for electronic device
applications, thereby paving the way for the feasible use of
graphene as a material suitable for future practical use in
electronic devices which are vulnerable to heat. Carbon
nanotubes have properties including high thermal
conductivity and high current-density tolerance[3], while
graphene is known for its high electron mobility. Carbon
nanostructures combining these two materials hold the
promise of creating new potential for material research and
applications.
Details of this technology will be presented at the 34th
Fullerene Nanotubes General Symposium to be held from March
3 to March 5 in Nagoya, Japan. |
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Background
Carbon nanotubes and graphene are both nano-scale structures
consisting of carbon atoms. Graphene is a sheet-like
hexagonal lattice of carbon atoms, while nanotubes can be
described as graphene wrapped into a cylinder with a nano-scale
diameter.
Despite the fact that both are made from the same carbon
atoms, each has very distinct characteristics. Of any
material found in nature, carbon nanotubes feature the
highest thermal conductivity and mechanical strength as well
as the ability to withstand the highest current density,
making them an attractive material for wiring, heat
dissipation, field electron emitters[4], and other potential
applications. Research and development is underway to find
technologies to synthesize carbon nanotubes at temperatures
as low as approximately 400 C, a temperature that would
enable its use in electronic devices vulnerable to heat.
Since the discovery of its high electron mobility in 2004,
graphene has become attractive as a channel material for
future transistors. However, conventional methods for
synthesizing graphene only work at temperatures over 700 C -
considered too high for use in electronic devices - or
involve a time-consuming and unreliable process of stripping
away graphite crystals.
Fujitsu Laboratories is researching ways to develop
electronic devices that take advantage of the superior
properties of carbon nanostructures.
Overview of the New Technology
In order to better understand the growth mechanism of carbon
nanotubes, Fujitsu Laboratories conducted experiments using
chemical vapor deposition, a technique in which a feedstock
gas is heat-cracked in a vacuum chamber to synthesize film
or structures on a substrate. This resulted in the formation
and discovery of aligned growth[5] multi-walled carbon
nanotubes[6] featuring layers of graphene (from a few layers
to a few dozen) on top formed in a self-organizing way,
thereby forming a complex composite.
Carbon-based materials come in a variety of different forms
that depend on how their atoms link together, such as
zero-dimensional fullerenes[7], one-dimensional nanotubes,
two-dimensional (2-D) graphene, and three-dimensional (3-D)
diamonds. Complex structures consisting of zero-dimensional
and one-dimensional elements, known as "peapod[8]"
structures, have already been created. The new complex
composite developed by Fujitsu Laboratories is the world's
first composite featuring one-dimensional and
two-dimensional elements based on graphene layers and
nanotubes, which are perpendicularly connected. The
composite was synthesized at the relatively low temperature
of 510 C.
Results
Due to the fact that carbon nanotubes are linear,
one-dimensional structures, in the two-dimensional
directions perpendicular to the tube axis they have nearly
no thermal or electrical conductivity between tubes.
Graphene, on the other hand, possesses electrical and
thermal conductivity across two dimensions. The
newly-discovered carbon nanostructure is expected to have
electrical conduction and thermal dissipation in all
directions. Conventionally aligned-growth carbon nanotubes
have had relatively poor uniformity in length, thus being
inconsistent when joined in the upper areas and resulting in
increased thermal and electrical resistance. As the new
carbon nanostructures from Fujitsu Labs feature carbon
nanotubes that nearly all connect to the graphene with good
uniformity at their endpoints, and since the graphene
surface is planar, it is anticipated that the new carbon
nanostructures will enable excellent electrical and thermal
conductivity. This technology brings the application of
graphene for electronic devices one step closer to practical
use.
Future Developments
Fujitsu Laboratories will continue to explore the mechanisms
by which complex carbon nanostructures form and elucidate
their physical characteristics, in order to develop
electronic device application technologies that take
advantage of those characteristics. In addition, in the
field of material sciences Fujitsu Laboratories will pursue
the development of technologies to enable the formation of
high-quality carbon nanostructures at a lower temperature. |
