Carbon nanotubes are attractive candidates for use as the active
elements in the next generation of electronic devices. However, it has
proven incredibly difficult to align nanotubes within device
architectures. Most of the approaches for lining up carbon nanotubes
reported until now are only applicable to discrete devices and are not
readily scalable to the levels required for the mass production of
nanotube-based chips. Now, this seemingly intractable problem has been
overcome by a collaborative team of researchers from Seoul National
University and Sungkyunkwan in South Korea. Kahp Suh and his colleagues
have developed a technique for aligning nanotubes over large areas based
on the flow of a nanotube-containing solution through nanochannels. This
technique is especially attractive because of its simplicity; no
external stimuli such as the application of an electric field or syringe
pumping are required to align the nanotubes.
This novel approach for aligning carbon nanotubes is based on the
simple flow of a nanotube solution through a nanochannel fabricated
from a charged polymeric mold. The nanotubes are ordered within the
channels by the influence of the capillary force existing within the
confines of the channel. When the channels are of the correct geometry,
aqueous solutions containing nanotubes enter from both ends, and upon
evaporation leave behind dense and highly oriented arrays of nanotubes.
Suh cautions that the mechanical properties and surface chemistry of
the polymeric mold used for making the nanochannels are of paramount
importance. �The stiffness of the polymer has to be just right�, says
Suh, �it has to be rigid enough to keep the nanochannels from
collapsing but flexible enough to bond well with the substrate over a
large area�. Good adhesion is required between the nanochannel and the
substrate to prevent the polymer nanochannels from coming unstuck upon
the introduction of the aqueous nanotube solution. The researchers
have found that polyethylene glycol diacrylate has the right
combination of properties for use as the polymer mold. It is
negatively charged and facilitates conformal contact with the
substrate. Moreover, it is hydrophilic and thus the nanotube solution
is able to enter and flow through the channels without need for
additional pumping.
Suh further added that this approach represents a promising advance
for the integration of nanotubes in microscale devices. The use of
fluidics to bring typically unruly bundles of nanotubes into line may
help to solve prevailing bottlenecks for scaling up the production of
nanotube devices.
Further Information
and Source:
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Pilnam Kim, Seunghyun Baik, Prof., Kahp Y. Suh, Prof.: Capillarity-Driven Fluidic Alignment of Single-Walled Carbon
Nanotubes in Reversibly Bonded Nanochannels.
In: Small; Volume 4, 2008, Issue 1 , Pages 92 - 95; doi
10.1002/smll.200700300.
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Homepage of
Kahp Y. Suh, Seoul National University (South Korea)
