Carbon nanotubes (CNTs) tend to be manufactured in single-wall (SW) and multiwall (MW) versions, both of which contain thousands of carbon atoms (Fig. 1). SW CNTs feature one shell of hexagonal arrangement, whereas MW CNTs consist of multiple concentrically nested carbon tubes similar to the ring of a tree trunk.
Although MW CNTs are easier to manufacture than SW CNTs, their properties aren't as useful as SW types. That's why most nanotechnology work is going the SW CNT route. But as mentioned in the article, CNTs are difficult to handle and control.
To get around the difficulties of manipulating CNTs, designers are proposing another type of carbon-based material--fullerenes. Fullerenes are a more structured order of carbon atoms. They're a lot easier to manipulate than CNTs. Also, they're readily processable and have uniform properties, attributes not evident with CNTs. And like CNTs, they're readily available, stable, and affordable. The most abundant fullerene has 60 atoms (C60), followed by C70 and C80 in terms of abundance (Fig. 2). Each of these has unique properties.
Like CNTs, fullerenes are very hard. Unlike CNTs, which are insoluble and react modestly to other chemicals, fullerenes are soluble and are very reactive. Like CNTs, they can be made as insulators and conductors. Solid C60 can be readily doped with alkali metals to create conducting phases, and superconducting phases at low temperatures. Its transition temperatures of up to 40K are the highest for any organic superconducting phase.
Information for this sidebar was excerpted from the presentation "Nanomanufacturing with Fullerenes and Nanotubes," by Glen P. Miller of the University of New Hampshire, presented at the 3rd New England International Nanomanufacturing Workshop, June 21-22, 2005, at Northeastern University.
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