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University of Cincinnati engineering researchers have developed a novel composite catalyst and optimal synthesis conditions for oriented growth of multi-wall CNT arrays.
The attached image shows a 12-mm-thick carpet of aligned CNTs grown on a 4-inch wafer. These samples prove that scaling up of the growth process of super-long carbon nanotube arrays on large area substrates is possible.
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 fibres that are, in theory, significantly stronger and lighter than any existing fibres and are electrically conductive. Nanotube fibres are expected to engender revolutionary advances in the development of lightweight, high-strength materials.
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.
Shanov notes that their research has had four major milestones this year already. “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.”
The UC substrate for growing CNT arrays is a multilayered structure with a sophisticated design in which a composite catalyst 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 centimetre-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 fibres.
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