The Bounce of Buckyballs
Spend time with chemists nowadays, and you might think they've gone wild for a new sport. They're nearly all talking about buckyballs.
The chemists' enthusiasm comes not from a new game but a new form of carbon. When this configuration of the common element was discovered in 1985, as a serendipitous by-product of an experiment in space, the structured but spherical form of the 60-atom carbon molecule reminded researchers so much of Buckminster Fuller's geodesic domes that they promptly named it after him. Buckminsterfullerene, the original buckyball, now has become first in a family of extraordinary carbon molecules known as the fullerenes.
That early history plus just about everything else a nonspecialist might want to know about buckyballs appeared in a recent issue of Science, the journal published by the American Association for the Advancement of Science. The journal's editors have dubbed fullerenes Molecule of the Year.
The title came in honor of the broad array of features identified in fullerenes during 1991. The sweeping research was possible thanks to the discovery in fall 1990 of a way to produce the stuff comparatively simply and inexpensively, by heating a graphite rod in a helium atmosphere. During summer 1991, buckyballs were found in the sooty flames of burning benzene, offering an even easier way of generating fullerenes.
With an adequate supply of buckyballs, researchers tried all manner of experiments to discover just what fullerenes could do. In a buckyball molecule, the atoms link into pentagons and hexagons of carbon that form a hollow, geodesic sphere with bonding strains equally disrlibuted among the 60 atoms. Some of the attendant electrons treat the whole molecule as if it were an atom---to chemists, the electrons are"delocalized." This combination of cagelike structure and delocalized electrons help give the buckyball unusual abilities.
For example, a buckyball cage accepts electrons, so it can be doped with other elements to form a stable compound. Add three atoms of potassium, and the buckyball is a superconductor: add three more, and it's an insulator. Fullerenes doped with alkali metals such as potassium are called fullerides. Add an organic reducing agent to a fulleride, throw in an electric field, and the result is a ferromagnet---as long as the temperature is extremely low, up to 16 degrees Kelvin.
To some ambitious chemists, the buckyball cage looks like a promise waiting to be filled. They can envision stuffed buckyballs serving as molecular containers, offering potential drug-delivery systems or even shields for radioactive substances. This past year, experimenters filled buckyball cages with lanthanum atoms---an application of no known use, but at least a start toward fulfilling the dream of molecule-sized capsules.
Chemists are not the only scientists investigating fullerenes. Materials scientists making diamond films found that coating a silicon substrate with a layer of fullerene increased the growth of diamond film tenfold. Other buckyball-based materials show promise in optics; the frequency of laser light doubles when it passes through a fullerene film, while other fullerene materials seem to work as optical limiters, keeping intense light to nondamaging levels. Some day, the best welder's goggles may come with buckyball coatings.
Perhaps even better for researchers, in the odd world of fullerenes, buckyballs are only a start. In soot on apparatus used to make these oversized carbon molecules, scientists recently found buckytubes, incredibly thin hollow carbon fibers. According to Science, these fullerene tubes may be the strongest fibers known. Theoreticians are predicting that some versions ot these all-carbon tubules might behave like electrically conductive metals.
All in all, it's little wonder that buckyballs have some researchers bouncing off the walls. But fullerenes are not yet the stuff of kitchen chemistry. Even with the improved manufacturing techniques, a single gram (0.035 ounce) of buckyballs costs at least $2000. Delivzry's extra.
