Science & Technology
SCIENCE'S AMAZING NEW BUILDING BLOCKS
At first glance, chemist Richard E. Smalley's laboratory at Rice University in Houston looks more like a welding operation than a research center. In one corner, a Sears arc welder vaporizes a carbon rod. In the searing 2,500C heat of the machine, atoms of common carbon--as in pencil lead--cling together in a grimy soot. But that black powder contains a miracle of chemistry: carbon atoms that have combined in never-before-seen shapes--molecular soccer balls, tubes, and even a helical form.
In these strangely shaped molecules, called fullerenes, scientists have discovered a gold mine of tantalizing possibilities. This new form of carbon displays unique properties. Linking up these molecules or playing other chemical tricks, scientists say, could create new catalysts, superstrong plastics, superconductors that carry electricity without resistance, and even optical switches. "We are playing with the building blocks for totally new materials," says Smalley.
BREAKTHROUGH. Six years ago, it was Smalley and British researcher Harry W. Kroto of the University of Sussex who, while studying large molecules together, discovered structures composed of 60 carbon atoms arranged in soccer-ball-like spheres. They were dubbed "buckminster fullerenes" and "buckyballs" after the geodesic domes created by inventor R. Buckminster Fuller. But the substance--the first new form of carbon discovered since the 1800s--remained a curiosity until last year, when scientists at the University of Arizona and the University of Heidelberg, working independently, figured out how to produce millions of fullerenes in an electric arc.
Since then, like children modeling Play-Doh, researchers at Du Pont, NEC, AT&T, and universities such as UCLA, UC Santa Barbara, and Rice have been squeezing the material through chemical sieves, baking it in ovens, and lacing it with metals and plastics. On Dec. 5, they plan to explain their latest gains at the Materials Research Society in Boston. The research shows scientists are just beginning to decipher the nature of these amazing molecules -- and guess at their ultimate applications. "We haven't scratched the surface of what might come out of work on fullerenes," says Mark M. Ross, program manager at the Office of Naval Research, which funds some of the research.
Scientists are intrigued with fullerenes because carbon is so important in all aspects of life. It is the basis of carbohydrates, proteins, fats, and other components of cells. And it is at the heart of industrial economies--in carbon-based fossil fuels, petroleum-based plastics, and other chemicals. Carbon atoms also form strong bonds between one another, a characteristic that gives diamonds their strength.
Fullerenes are already helping researchers who are trying to produce single diamond crystals to make superfast computer chips. In October, RobertChang, head of the materials research center at Northwestern University, vaporized graphite and used the resulting fullerenes to make an ultrathin film. He was able to grow multiple diamond crystals on top of the film. The result was thousands of times better than similar efforts on silicon have been. The next trick: finding a way to use fullerene thin films to cultivate single diamond crystals that are needed for circuitry.
Because the shape of molecules plays a part in determining the properties of a substance, scientists believe the quirky fullerenes may open up new worlds. In September, University of California at Los Angeles chemist Francois N. Diederich reported that some fullerenes resemble the double-helix structure of human genes in DNA. What's more, helix-like fullerenes have right-handed and left-handed versions, similar to biological molecules. "That is a very profound property," says Diederich, who predicts the two versions may help chemists produce purer drugs with fewer side effects. Fullerenes can also change the wavelength of light, a property that might eventually be harnessed to produce optical switches for communication.
PINCHED AND PULLED. In October, Sumio Iijima, a research fellow at NEC Corp.'s Fundamental Research Lab near Tokyo, announced that he had found under a microscope yet another shape in the soot: tubular molecules consisting of as many as 20 cylinders of carbon inside one another. One day, these defect-free tubes might be developed as superstrong fibers in construction materials.
Although the research is just beginning, fullerenes are unusually promising chemical building blocks because they are "molecules that behave like an atom," says Katsumi Tanigaki, head of the NEC lab. If scientists insert noncarbon atoms into fullerenes or attach them, the resulting molecules have different chemical and physical characteristics. Eventually "we can make new molecules with properties never even predicted by science," Tanigaki says.
So researchers are zealously stringing atoms of everything from iodine to yttrium and lithium between fullerenes or on their surfaces as if they were popcorn on a Christmas tree. And the early results are riveting. At the University of California at Santa Barbara, Fred Wudl, a professor of chemistry, strung ammonia-like groups of molecules along the surface of a buckyball: It became magnetic. Wudl and others also squeezed atoms of potassium between buckyballs--they became superconductors. Last summer, NEC researchers slipped in atoms of cesium and rubidium. That raised the superconducting temperature of the fragile and unstable fullerenes to -400F, still far below the high-temperature superconducting materials. But if researchers insert a sodium atom in the gaps between the carbon spheres, the new fullerenes don't conduct electricity at all--they become insulators instead.
By adding other atoms and taking advantage of fullerenes' propensity to react with other substances, scientists hope to create new medical and industrial catalysts. To do their work of controlling chemical reactions, catalysts break and reform the bonds between atoms. As it turns out, the hollow-centered buckyballs sop up electrons from neighboring atoms, while the twisting lattices of helix-shaped fullerenes give up electrons. Du Pont Co. researchers have demonstrated they can make a fullerene catalyst by hitching a methyl group of atoms to a buckyball. The buckyball snatched three electrons from the group of carbon and hydrogen atoms. Molecules that absorb electrons like this are important catalysts in the production of paints that resist fading in light and clear plastics, such as Du Pont's lucite.
SERENDIPITY. Despite fascinating laboratory results, many obstacles remain before fullerenes emerge as workhorse materials, which is why some scientists and institutions aren't yet rushing to the patent office with their results. To take full advantage of the potential of fullerenes, scientists must be able to insert foreign atoms into the molecules. That will require them to open the bonds between carbon atoms and then reseal them. But they are having difficulty dissolving the tight bonds that hold carbon atoms together. So far, the standard techniques--chemical peels, laser blasts, and high temperatures that dissolve most other bonds between atoms -- haven't worked.
Scientists are also hampered because theory hasn't caught up with the rush of new laboratory discoveries. Existing theories, largely based on the behavior of smaller molecules, don't adequately explain how these curious new structures behave.
A better understanding of the behavior of fullerenes could have profound ramifications. Knowing precisely how fullerenes become superconductors, for instance, may lead to improvements in other types of superconductors. If research on fullerenes does that, "it will be important in itself," says Andrew Kaldor, director of fullerene research at Exxon Corp.'s Corporate Research Lab.
For his part, Smalley is leading the rush to test what happens to fullerenes when bits of metal are attached to the outside, the inside, or in between. He confidently envisions a day when fullerenes will be snapped together like Lego blocks to create miniature factories cranking out catalysts. Indeed, the potential for fullerenes is so fantastic that researchers expect to have soot on their hands for years to come.Gary McWilliams in Boston, with John Carey in Washington and Neil Gross in Tokyo