| PREPARATION |
Team developed a catalyst-free procedure for preparing single-walled carbon nanotubes. Conventional methods for preparing single-walled tubes, such as discharge and vapor deposition techniques, rely on particles of nickel and cobalt or other catalytic transition metals. A problem with those procedures is that the metal particles left behind in the products disturb the nanotubes' electrical properties, forcing scientists to take complex purification measures. Authors have shown that single-walled nanotubes can be prepared from SiC in the absence of metal catalysts at temperatures above 1,500 °C. The method produces nanotubes that are 1.2 to 1.6 nm wide and are aligned along the face of the support. Other researchers have reported techniques for growing vertically aligned products, which they dub nanotube forests. But nanotubes that grow horizontally are amenable to standard vapor deposition methods and may be connected in parallel to lower their electrical resistance. Author asserts that nanotube FETs remain "far from optimized." Improvements could be made by using thinner insulators with higher dielectric constants, he suggests. "But what's really needed is a better understanding of the mechanism of electrical switching in nanotube FETs."
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