Bucky Balls

Andy Gion

It is the roundest and most symmetrical large molecule known to man. Buckministerfullerine continues to astonish with one amazing property after another. Named after American architect R. Buckminister Fuller who designed a geodesic dome with the same fundamental symmetry, C60 is the third major form of pure carbon; graphite and diamond are the other two. Buckyballs were discovered in 1985 - the product of an experiment on carbon molecules in space. However, it was not until 1991 that buckyball science came into its own. Just how do buckyballs manage their chemical and physical feats? In C60, hexagons and pentagons of carbon link together in a coordinated fashion to form a hollow, geodesic dome with bonding strains equdistributed among 60 carbon atoms. Some of the electrons are delocalized over the entire molecule--a feature even more pronounced in that workhorse of organic chemistry, benzene. Benzene is flat and many of its derivatives also tend to stack in flatsheets. Spherical buckyballs literally add a new dimension to the chemistry of such aromatic compounds. Buckministerfullerine has been named the Molecule of the Year. In addition to openingup new fields on chemistry, C60 also shows interesting physical properties. It is resistant to shock and it has been suggested that as a lubricant, there is even evidence of superconductivity and it may provide the added ingredient that makes diamond films more practical.

A NEW CHEMISTRY FOR CARBON

Until a few years ago, there were two known forms of pure carbon, graphite and diamond. Then an improbable-seeming third form of carbon was discovered: a hollow cluster of 60 carbon atoms shaped like a soccer ball. Buckminsterfullerene or "buckyballs"--named for the American architect R. Buckminster Fuller, whose geodesic domes had a similar structure--is the roundest, most symmetrical large molecule known. It is exceedingly rugged and very stable, capable of surviving the temperature extremes of outer space. At first, however, the molecule was a mystery wrapped in an enigma. But when a convenient way of making this molecule, also known as C60, was discovered, it set off an explosion of research among chemists, physicists, and materials scientists to uncover the molecule's secrets. Investigators soon discovered a whole family of related molecules, including C70, C84 and other "fullerenes"--clusters as small as C28 and as large as a postulated C240.These unusual molecules turn out to have extraordinary chemical and physical properties.They react with elements from across the periodic table and with the chemical species known as free radicals--key to the polymerization processes widely used in industry--thus opening up the fullerenes to the manipulative magic of organic chemists. When a fullerene is "doped" by inserting just the right amount of potassium or cesium into empty spaces within the crystal, it becomes a superconductor--the best organic superconductor known. More important, because C60 is a relatively simple system, it may help physicists master the still mysterious theory of high-temperature superconductivity. Speculation and some hard work on potential applications began almost immediately after the discovery of buckyballs. Possible applications of interest to industry include optical devices; chemical sensors and chemical separation devices; production of diamonds and carbides as cutting tools or hardening agents; batteries and other electrochemical applications, including hydrogen storage media; drug delivery systems and other medical applications; polymers, such as new plastics; and catalysts. Catalysts, in fact, appear to be a natural application for fullerenes, given their combination of rugged structure and high reactivity. Experiments suggest that fullerenes which incorporate alkali metals possess catalytic properties resembling those of platinum. The C60 molecule can also absorb large numbers of hydrogen atoms--almost one hydrogen for each carbon--without disrupting the buckyball structure. This property suggests that fullerenes may be a better storage medium for hydrogen than metal hydrides, the best current material, and hence possibly a key factor in the development of new batteries and even of non-polluting automobiles based on fuel cells. A thin layer of the C70 fullerene, when deposited on a silicon chip, seems to provide a vastly improved template for growing thin films of diamond. It is too early to make reliable forecasts of commercial potential, although the early indications are that buckyballs may represent a technological bonanza when their properties are fully understood. Yet it is important to note that the discovery of this curious molecule and its cousins was serendipitous, made in the course of fundamental experiments aimed at understanding how long-chain molecules are formed in outer space. It is a strong reminder that fundamental science is often the wellspring of advanced technology in ways that are completely unpredictable.

Size of Bucky Balls

All the hauling, lugging and lifting to construct the ancient pyramids one block at a time was, no doubt, tedious work. But forming an object one molecule at a time can be even more intricate. Now two groups exploring nanotechnology have recently incorporated buckminsterfullerene and related structures into their repertoire, thereby bringing buckyballs--those spherical molecules made of carbon--a step closer to genuine applications. One group's work may improve an existing specialized tool of nanoengineering--the scanning-force microscope (SFM), which relies on fine tips to detect and nudge molecules. Until now, tips were rather large, up to 2,000 nanometers thick. Hongjie Dai of Rice University, working with buckyball co-discoverer and Nobelist Richard E. Smalley, fashioned some fullerenes into a pipe, or "nanotube," to replace some SFM tips. Shaped like concentric cylinders of chicken wire, these multiwall tubes can range between five and 20 nanometers thick, thus facilitating more accurate atomic manipulation. When capped at one end with a hemispheric fullerene, the tip can serve as a chemical probe. What makes them even more appealing is their durability. Fellow researcher Daniel Colbert explains that although they tried to "crash," or damage, the tubes, the inherent flexibility enabled them to return to their original shape. To make nanotubes, the team vaporized carbon with an electric current. The vapor condenses to form a sooty gob, rich in nanotubes. The workers mine the clump with cellophane tape, and then, holding a glue-dipped conventional tip, they lightly touch it to the wad of nanotube bundles and gingerly pull one out. A continent away, scientists at the IBM Zurich Research Laboratory incorporated buckyballs for a less practical purpose: a smaller-than-Lilliputian-size abacus. Researcher James Gimzewski and his colleagues lined up buckyballs on a multigrooved copper plate, mimicking beads on a string, and proceeded to manipulate the beads with a scanning tunneling microscope (STM), using them to calculate. The authors write in Applied Physics Letters that because hundreds of buckyballs can fit in the width of a processor chip, they could be exploited in building a better computer chip. That vision, though, may be a while in coming, considering how slow the computation is. Gimzewski notes that moving the buckyballs with an STM probe is the equivalent of operating a standard abacus with the Eiffel Tower. But by showing what is possible, buckyballs are starting to score big in the small field of nanotechnology.

Bucky Ball Win Nobel Prize

The 1996 Nobel Prize in Chemistry has been awarded to three chemists for their discovery of fullerenes, a family of highly symmetrical carbon-cage molecules whose prototypical member is C60, known as buckminsterfullerene, or "buckyball" for short. A bond-line structure of buckyball is shown below:

Richard E. Smalley, the Gene and Norman Hackerman Professor of Chemistry and Physics at Rice University; Robert F. Curl, Jr., Professor of Chemistry at Rice; and Harold Kroto, Professor of Chemistry at the University of Sussex, in Brighton, England, will share this year's prize, which is worth about $1.1 million - as well as an incalculable amount of prestige. "This is the dream of every kid who's every owned a chemistry set," Curl said. Kroto, Curl, and Smalley came together to study carbon clusters because Kroto, a microwave spectroscopist, was interested in carbon-rich red giant stars. Curl, a microwave and infrared spectroscopist, was a firend of Kroto's who often collaborated with Smalley. Smalley had designed and built a device for creating and characterizing clusters of almost any element. A series of experiments was carried out in September, 1985, by the three and a number of Rice collaborators. They generated carbon clusters by laser vaporization of graphite into a pulsed stream of helium, and analyzed the clusters by mass spectrometry. A variety of polyacetylenes and other carbon clusters were formed, but under various conditions, the mass peak corresponding to C60 totally dominated the spectrum. Their then controversial explanation was that C60 was a spherical molecule with the geometry of a truncated icosahedron - a polygon with 60 vertices and 32 faces, 12 of which are pentagons and 20 of which are hexagons. The geometry is the same as the pattern of seams on a soccer ball, or of the geodesic domes developed by architect Buckminster Fuller. Hence, the name buckminsterfullerene, or buckyball.

Here are a couple more representations of buckyball in ball-and-stick form, one encircled by a projection of its electron density on the equatorial plane.

More Bucky balls

R. Buckminster Fuller