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Carbon nanotubes (CNTs) are of great interest
because of their outstanding mechanical, electrical and optical
properties. Intense research has been undertaken to synthesize long
aligned CNTs because of their potential applications in nanomedicine,
aerospace, electronics and many other areas.
Especially important is that long CNT arrays can be
spun into fibers that are - in theory - significantly stronger and
lighter than any existing fibers and are electrically conductive.
Nanotube fibers are expected to engender revolutionary advances in the
development of lightweight, high-strength materials and could
potentially replace copper wire.
Carbon nanotube arrays can also be grown in
intricate patterns using metal masks.
Years of effort by UC researchers Vesselin Shanov
and Mark Schulz, co-directors of the University of Cincinnati Smart
Materials Nanotechnology Laboratory, along with Yun YeoHeung and
students, led to the invention of the method for growing long nanotube
arrays. Employing this invention, the UC researchers (in conjunction
with First Nano, a division of CVD Equipment Corporation of Ronkonkoma,
New York) have produced extremely long CNT arrays (18 mm) on their
EasyTube System using a Chemical Vapor Deposition (CVD) process.
Moreover, in a re-growth experiment on a separate
substrate, they produced an 11-mm long CNT array. This array was then
successfully peeled completely off the substrate. Without additional
processing, the same substrate was reused for a successive growth that
yielded an 8-mm-long CNT array.
The photographs in figures "c" and "d," above, are
scanning electron microscopy (SEM) and high-resolution transmission
electron microscopy (HRTEM) images of the multi-wall CNT arrays.
Shanov notes that their research has had four major
milestones this year already.
The figure above shows a CNT array image of UC|21,
representing UC's strategic mission statement.
"First, we were able to grow the arrays up to 18
mm," he says, ticking off the achievements. "Second, we produced a
uniform carpet of 12-mm carbon nanotube arrays on a 4-inch wafer,
which moves the invention into the field of scaled-up manufacturing
for industrial application. Third, we filed a patent application on
the inventions at the US Patent and Trademark Office and, fourth, we
were invited to participate in a very prestigious workshop (invitation-only)
organized by NASA and Rice University, where we presented our latest
results. The workshop focused on "Single Wall Carbon Nanotube
Nucleation and Growth Mechanisms." This event was attended by the best
scientists in the world working on synthesis carbon nanotubes, from
Japan, China, Europe and the United States. Our presentation was
accepted very well and confirmed that with the current record of
18-mm-long carbon nanotube arrays, and also with the big area growth
on 4-inch wafers, we are leading in manufacturing extremely long CNT
arrays."
The Fine Print and Nano Details
The UC substrate for growing CNT arrays is a
multilayered structure with a sophisticated design in which a metal
based catalyst alloy is formed on top of an oxidized silicon wafer.
Its manufacturing requires a "clean room" environment and thin-film
deposition techniques that can be scaled up to produce commercial
quantities. CNT synthesis is carried out in a hydrogen/hydrocarbon/water/argon
environment at 750 degrees Celsius. The achievement of growing
centimeter-long nanotube arrays provides hope that continuous growth
of CNTs in the meter length range is possible. Leonard Rosenbaum,
president and CEO of CVD Equipment Corporation, is looking forward to
continuing the partnership with UC to bring this technology from the
laboratory into full-scale production. UC is also partnering with
another company to develop production of long CNT arrays that can be
spun into fibers. |
