Researchers from the University of Southern California (USC) and the National Institute of Standards and Technology (NIST) have demonstrated a technique for growing virtually pure samples of single-wall carbon nanotubes (SWCNTs) with identical structures, a process they liken to "cloning" the nanotubes.* If it can be suitably scaled up, their approach could solve an important materials problem in nanoelectronics: producing carbon nanotubes of a specific structure to order.
Single-wall carbon nanotubes are hollow cylinders of carbon atoms bound together in a hexagonal pattern, usually about a nanometer in diameter. One fascinating feature of nanotubes is that there are many ways to wrap the hexagon sheet into a cylinder, from perfectly even rows of hexagons that wrap around in a ring, to rows that wrap in spirals at various angles"chiralities," to be technical. Even more interesting, chirality is critical to the electronic properties of carbon nanotubes. Some structures are electrical conductorsessentially a nanoscale wireothers are semiconductors.
"Experts in the electronics industry believe that single-wall carbon nanotubes are a promising option for nanoelectronicssemiconductor devices beyond today's CMOS technology," says NIST materials scientist Ming Zheng, "But for that particular application, the structure is critically important. A fundamental issue in that field is how to make single-wall nanotubes with a defined structure."
The problem is that methods for manufacturing carbon nanotubes, which often use a metal catalyst to initiate growth, usually produce a mixture of many different chiralities or twistsalong with a lot of junk that's just soot. A lot of research has concentrated on schemes for "purifying" the batch to extract one particular kind of nanotube. And also you have to get rid of the catalyst.
The team led by Zheng and Professor Chongwu Zhou of USC took a different tack. NIST researchers had developed a t
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National Institute of Standards and Technology (NIST)