The Bucky Story
In 1980 while studying different types of carbon with the high-resolution electron microscope he had developed, Sumio Iijima of Arizona State University noticed rolled-up balls of carbon he called spherical graphite. His published paper generated little interest.
Five years later, when Harold Kroto, Richard Smalley and Robert Curl announced the discovery of buckyballs, Iijima realized it was the same structure he had seen earlier but had not fully appreciated. (Kroto, Smalley and Curl received the 1996 Nobel Prize in Chemistry. Kroto is now a professor in FSU’s department of chemistry and biochemistry.)
A meeting with Kroto at a conference in 1990 inspired Iijima, now with NEC Laboratories in Japan, to revisit his earlier experiment. He created buckyballs in the arc discharge between two carbon electrodes and examined the resulting particles under his electron microscope. He found the buckyballs he expected, but he also noticed needles of carbon. Further study showed that the needles were in fact made of hollow tubes of carbon, a new type of molecule that Smalley had earlier predicted as theoretically possible. Iijima published his discovery in 1991.
But just as Iijima had seen buckyballs before Kroto, Smalley and Curl, others had seen carbon nanotubes (as Iijima named them) before Iijima. As far back as the late 1950s, Roger Bacon of Union Carbide had reported hollow tubes of carbon, and they were observed again by Morinobu Endo in the 1970s.
In nanotubes, the carbon atoms are arranged in a lattice of hexagons. The lattice is curled up and joined seamlessly to itself, creating a long, hollow tube. The structure looks like nothing so much as a length of rolled-up chicken wire. Each individual nanotube is about a nanometer—a billionth of a meter—in diameter. That’s about half the diameter of a DNA molecule, or about 100,000 times thinner than a human hair. But each tube is about a thousand times longer than its diameter, so the molecule as a whole resembles a strand of cooked spaghetti.
This unusual molecule is one of the fullerenes, a class of molecules in which hexagons and pentagons of carbon form hollow, structures. They are named in honor of Buckminster Fuller because spherical fullerenes resemble the designer’s famous geodesic dome. Spherical fullerenes came to be called buckyballs, and carbon nanotubes are sometimes called buckytubes. So paper made from buckytubes is called, well, you get the idea.
Because of their structure, carbon nanotubes exhibit a number of remarkable properties. On a weight-for-weight basis, they are 500 times stronger than steel, yet weigh just a tenth as much. In fact, they form the strongest and toughest fiber known. In addition, the nanotubes can conduct electricity as well as copper (they make the most conductive fiber known) and also can function as semiconductors. They conduct heat, too, even better than diamond, the previous world record holder.
Carbon nanotubes come in a wide variety of forms. They can be single-walled or multi-walled. They can be made in different lengths and thicknesses and with different spirals in their structure. The different forms have differing properties, so the type of nanotube can be matched to the potential application.