BUCKYBALL: THE MAGIC MOLECULE

This past weekend, British chemist Sir Harry Kroto passed away at the age of 76. He is the co-discoverer of buckyballs, a form of carbon that is made up of 60 atoms and shaped like "a hollow soccer ball." The discovery won Kroto and his team the Noble Prize in chemistry. This cover story, written by Edward Edelson and originally published in the August 1991 issue ofPopular Science, explores how buckyballs were accidentally discovered and the future of possibilities to those scientists in 1991.

A revolution in chemistry is taking place in a small room in a converted mining building in Tucson, Ariz., where a woman wearing a soiled smock and a face mask is painstakingly scraping soot off a metal container.

Although it's not too exciting to look at, this is the world's first production facility for a newly discovered, exotic material, dubbed "buckyball," that has such extraordinary potential that chemists and physicists around the country are lining up to pay $1,200 a gram for the stuff, roughly one hundred times the price of gold.

"This is the biggest news in chemistry I could have imagined," exclaims Robert Whetten of the University of California at Los Angeles.

The reason? Together with the plain-Jane carbon particles that make up most of the soot is a carbon molecule with a unique structure, totally different from that of the two previously known forms of carbon.

The discovery of a new kind of carbon came as a stunning surprise to most scientists. Carbon is the most intensely studied of all the elements because it is the basis for most ofthe molecules of life—the organic molecules. Look in any chemistry textbook and youll read that for centuries research showed carbon came in just two basic structures: hard, sparkling diamond, whose carbon atoms are arranged in little pyramids; and dull, soft, slippery graphite, which consists of sheets of carbon-atom hexagons.

Those chemistry textbooks are now obsolete. There's a new basic form of carbon with an almost unbelievable structure: Its 60 carbon atoms form something that looks like a hollow soccer ball. It is the only molecule of a single element to form a spherical cage.

The molecule's official name is buckminsterfullerene, because it is shaped like the geodesic dome invented by that American original, Buckminster Fuller. Informally, chemists call it buckyball, or C-60. Its atoms are arrayed in a collection of regular pentagons and hexagons—12 pentagons and 20 hexagons to be precise. It's one of a newly discovered family of similar molecules that has a related geometry, but different multiples of carbon atoms. Scientists have called this whole family the fullerenes; scores of chemists and physicists are working full blast to unravel their properties.

It's not just the intellectual kick of a major advance that is energizing the scientific community as much as the discovery of high-temperature superconductors did a few years ago. It's the prospect that buckyball's properties will make possible a cornucopia of valuable applications.

"To a chemist it's like Christmas," exults Richard Smalley of Rice University in Houston, one of the key players in the buckyball game. To explain, he harkens back to the discovery of benzene in 1825. The benzene molecule is a relatively simple six-carbon ring, yet it's the parent of countless compounds, from aspirin to nasal decongestants to paints, dyes, and plastics—all made by working with that six-carbon ring. Now chemists hope to perform the same magic with this family of new carbon molecules that is at least 10 times bigger than benzene, with, therefore, even greater possibilities.

"This isn't 1825," Smalley says. "It's like discovering benzene, only now you have all the techniques and the scientific instruments of the 1990s available."

It is now clear to researchers that the C-60 molecule is exceptionally stable and resistant to radioactivity and chemical corrosion. It also greedily accepts electrons, but is not reluctant to release them. These and other attributes have scientists and engineers already speculating about microscopic ball bearings, new cancer treatments, lightweight batteries, powerful rocket fuels, and the infinite possibilities in plastics and other organic compounds that have carbon atoms as their backbones.

One proposal for anti-tumor therapy in cancer patients is to enclose radioactive atoms inside buckyballs. The carbon barrier would help maintain the integrity of the radioisotopes after injection. Smalley has already replaced some carbon atoms in the ball with other elements to create semiconducting "dopeyballs." Doping silicon with foreign atoms is what turns silicon into the semiconductors found in transistors.

Another idea Smalley talks about is creating a superpowerful battery by wrapping lithium and fluorine atoms, which create energy when they combine, inside a buckyball cage to protect them from being attacked by oxygen in the air. Other researchers imagine batteries that can be made by stripping away some electrons from the new molecule.

Scientists speculate about stringing buckyballs together to form the basis of new types of plastics. They dream of altering the molecule in a million ways by hanging different atoms or chemical groups from the 60 carbons. "It's the starting material for making a whole new family of organic compounds," says organic chemist Fred Wudl of the University of California at Santa Barbara.

The story behind the discovery of the buckyball is as bizarre as its structure. It's a story of an inspired guess that seemed to lead to a dead end, of creative midnight hours, of years of methodical hard work that finally led to the unexpected breakthrough. It's a story that stretches across two continents over more than five years of applied effort.

Go back to 1984 to Rice University, where a team headed by Smalley was investigating the properties of atomic clusters, groups of atoms larger than molecules but smaller than visible solids. The Smalley team was using an unusual device they had invented, called the laser-supersonic cluster beam apparatus. It's a steel vacuum chamber that holds a hollowed-out steel block. A sample placed inside the block is zapped by a very intense, short pulse of laser energy that vaporizes it. At the moment of zapping, a whiff of inert helium gas carries the vaporized material toward another laser, which ionizes the clusters by stripping away electrons. The clusters are then pushed into an analytical instrument called a mass spectrometer, which gives a reading of their size. Smalley was using the machine on a variety of elements, including silicon.

At that time, Harry Kroto of the University of Sussex in England was visiting Rice and suggested that carbon be added to the list of elements Smalley's team had been zapping. Kroto was interested in this because he was working on the possible origins of long-chain carbon molecules in interstellar space; he had found evidence of a nine-carbon molecule in the dust between stars. He theorized that carbon molecules might be forged in the atmospheric furnaces of red giant stars that are rich in carbon. (When a star has burned about 10 percent of its hydrogen fuel, it swells to a much greater size and becomes redder and much brighter. When our sun becomes a red star in a few billion years, it will gobble up Mercury and Venus.) Kroto thought that Smalley's apparatus, which generated temperatures of tens of thousands of degrees—hotter than the surface of a red giant—was a way to replicate that furnace in the laboratory.

Smalley's bunch got around to investigating carbon a year later, a delay due partly to the work a team at the Exxon Research and Engineering Corp. was already doing on carbon using a Rice-built machine; Smalley wanted to avoid overlap.

When Smalley's group, joined by Kroto, zapped carbon, the results were astonishing. They had expected a similarly random, and uninteresting, assortment of carbon clusters like that found by the Exxon people. Most of those contained from 2 to 30 carbon atoms, with some much larger clusters of even-numbered atoms. There were also increased amounts at 10-carbon intervals: 50-, 60-, 70-carbon clusters.

But there was something strange about the 60-carbon cluster that drew their attention. Much more of it appeared in their samples than could be explained by random formation—three times more than any other even-numbered cluster. Intrigued by that finding, Jim Heath, one of Smalley's graduate students, worked over a weekend to develop a way to increase the yield of C-60 clusters; he found that he could tinker with the experiment so that the amount of C-60 yielded was 40 times as great as any other even-numbered cluster.

As the Rice chemists kicked these results around, they asked two questions: Why even-numbered clusters and why so much carbon-60? One explanation was that they were making carbon "sandwiches," flat sheets of material that contained large numbers of atoms, made up of graphitelike hexagonal groups. But, Smalley recalls, such a flat molecule would have unattached dangling chemical bonds at its ends with no apparent way to tie them up.

Besides, why should such an open-ended cluster have exactly 60 carbon atoms, no more and no less?

One of the Rice group members—no one remembers who—suggested that the carbon-60 cluster wasn't actually a cluster, but a molecule, and a molecule in the shape of a hollow ball. Maybe those flat sheets they talked about actually curled around to form a sphere and would turn out looking something like a geodesic dome. That would take care of the dangling-bond problem. Smalley had seen a photo of one of Buckminster Fuller's geodesic domes, with its hexagonal units, and thought the geometry worth trying.

Heath spent that evening with his wife trying to assemble a C-60 molecule out of gum drops and toothpicks, a sticky and eventually unedifying enterprise.

Meanwhile, Smalley sat down at his computer and tried to generate a model structure for a 60-atom ball of carbon. After hours of work, he got nowhere. Frustrated, he began cutting regular hexagons out of legal paper, one inch on a side, and tried to make a sphere out of them. No dice. As he reached for an after-midnight beer, he remembered Kroto saying that he had once built a geodesic dome for his children, and that it might have contained regular pentagons as well as hexagons. So Smalley cut out a pentagon and began arranging hexagons around it, adding more pentagons and hexagons, taping the flimsy paper shapes together as he worked, and finally, halfway through, saw he had something.

"My heart leaped," Smalley recalls. "Unless I had counted wrong, the structure could close to form a sphere with the magic number of vertices: sixty."

In fact, the paper model formed a ball; it even bounced when dropped on the floor. It had 20 hexagons and 12 pentagons. Each of the 60 vertices, or corners, representing one carbon atom, was identical to the others; each occurred at the joining point of one pentagon and two hexagons.

The shape seemed so elegant that Smalley knew it had to be well known to geometricians. He called the head of Rice's mathematics department, William Veech, and described what he had built. Eventually Veech responded: "I could explain this to you in a number of ways," he said, "but what you've got there, boys, is a soccer ball."

The structure is technically called a truncated icosahedron, one of an infinite number of spheroidal cages that can be formed with hexagons and pentagons. Buckminster Fuller realized that many of these structures are endowed with unusual rigidity for their mass because of their geometry. Thus, the strong, light-weight geodesic dome was born.

The day after their epochal discovery, the Rice chemists thought of names like "soccerene" and "ballene" for the C-60 molecule, but finally decided on "buckminsterfullerene."

Today, it is also known as buckyball. The other even-numbered geodesic-dome-shaped carbon clusters are collectively known as "fullerenes." Smalley and his colleagues announced the discovery of C-60, the theory of its structure, and the structure of other fullerenes in a scientific paper published in 1985.

Many scientists were intrigued by the idea; some were disturbed by it. Disagreement came from the Exxon group, who stuck to the idea that the carbon clusters were most likely composed of uninteresting, cross-linked strands of atoms. Whetten of the University of California, then a graduate student working at Exxon, remembers talking about Smalley's discovery with Roald Hoffmann, his teacher at Cornell University, who had won the Nobel Prize in chemistry for his work on carbon. "He said there was nothing unusual about repeats of 10-carbon atoms," Whetten recalls. "So at Exxon, we stopped."

After announcing their exciting discovery, the Rice people were in a bind. They had only fractions of a milligram of C-60, not enough to confirm its existence.

How could they convince the doubters and substantiate their theory of C-60's structure? Obviously, they had to produce a whole lot of buckminsterfullerene, enough of the stuff so it could be thoroughly analyzed. Smalley assigned the job to Heath. Smalley called it "the search for the yellow vial" because theory indicated that the C-60 molecule would be yellowish. It seemed a simple job, but it turned into a nightmare—-a "no-joy experiment," he remembers.

The Rice researchers collected the black stuff that was coming out of the nozzle of the cluster beam apparatus. For two years, Heath mixed the material with benzene, hoping the solvent would concentrate appreciable amounts of C-60. The effort was a bust.

"After two years of looking at a clear benzene solution, with no evidence of fullerenes, our conclusion was that perhaps someone else would isolate a bit of this someday," Smalley said. "We rather expected that some chemist in a Third World country would get a milligram of this out of cow dung or something like that."

Instead, the answer came from Tucson and Heidelberg, Germany, in a way that demonstrates the sometimes inexplicable nature of scientific breakthroughs. The two men who found the way to make buckyballs by the bucketful were studying something else entirely.

Donald Huffman of the University of Arizona and Wolfgang Kratschmer of the Max Planck Institute for Nuclear Physics were working with carbon clusters, but with a totally different perspective and with different goals from Smalley.

Huffman and Kratschmer were studying how all kinds of small particles absorbed light: biological particles, soot particles, any very small particle. They had been studying carbon for many years because astronomers think that the minute carbon particles floating between the stars absorb starlight in interesting ways that could help them understand the universe.

After trying a number of methods, Huffman and Kratschmer had developed an ingeniously simple device for making lots of small carbon particles. Their machine consisted of two graphite rods connected to a high electric-current circuit surrounded by a helium atmosphere. A hacksaw blade acted as a spring to push the rods together. Where they touched, carbon vaporized, forming lots of carbon clusters—soot to you.

It's a dirty business, working with soot, but this time it paid off. The reward came from methodical work that measured how carbon clusters absorb visible light.

"We were the first to measure directly the optical absorption spectrum of very small carbon particles," Huffman said. "And when we did, we saw this feature."

The feature was a peak indicating that light at the wavelength of 2,200 angstroms was being absorbed by the carbon—almost, but not quite, like the peak astronomers were seeing in interstellar dust.

Huffman and Kratschmer didn't understand the finding. "So we went back to the lab and started making more carbon clusters," Huffman says. "It was then that we started seeing new and funny things in this peak. In fact, we saw three little wiggles in it." Kratschmer immediately called it the kamel sample (for the German word for camel).

That was in March of 1983, and Kratschmer and Huffman began arguing about what it might be: "Maybe it's a new form of carbon. That's ridiculous. Maybe it's some sort of cluster of carbon atoms. Maybe it's just junk. Mostly we thought it was some kind of junk," Huffman says.

When Huffman read the 1985 Kroto-Smalley paper that discussed a new 60-carbon molecule, a light flashed on. This strange new stuff could explain all the funny things he and Kratschmer had been seeing. Quickly, the focus of their research on carbon changed radically. Huffman and Kratschmer weren't at all convinced they had made buckminsterfullerene, but they began to point their work toward that direction. To be on the safe side, in 1987 Huffman put in a patent disclosure memo through his university for "a proposed way of making macroscopic amounts of C-60."

When the patent attorney called back, in February 1988, Huffman found he could no longer make samples with the camel feature. To increase the yield of C-60, his graduate student, Lowell Lamb, began tinkering with the experiment, changing combinations of conditions, mostly the helium pressure. The result was large amounts of C-60—milligrams of it, more than anyone else had ever made.

They couldn't yet take a picture to prove they had carbon-60, but they could work on the basis of its predicted properties. Organic chemists had become interested enough in Smalley's proposal to figure out how buckminsterfullerene would absorb infrared light. They conjectured that most of the infrared light would go right through the carbon molecule, except for four wavelengths that would be absorbed. Plotted on a graph, the absorption spectrum was a mostly smooth curve, with only four strong peaks. When Huffman and Kratschmer beamed infrared energy through their sample, they saw the predicted four peaks. Bingo!

Well, almost. Vacuum pump oil, used to lubricate their experimental apparatus, has two peaks of its own—almost dead on the ones predicted for buckyball. Kratschmer performed an experiment that eliminated the possibility that two of the peaks had come from the oil. He made buckyballs out of carbon-13, which is slightly heavier than the dominant isotope, carbon-12. The heavier atom is predicted to shift the infrared peaks by a predictable amount; it won't shift any peaks attributable to contamination. The predicted shift appeared. Buckyball lived.

For a meeting, Huffman and Kratschmer wrote up a small paper modestly titled, "The Possibility of Carbon-60 in Laboratory-produced Interstellar Dust Analogues." It was published in a fairly obscure journal in September 1989. By early 1990, Kratschmer and Huffman had relatively pure samples, not only of C-60, but of another fullerene, C-70. Now at last they could reveal to the scientific world what they had been doing.

They did it in full-fledged style in the journal Nature, in September 1990. Painstakingly, Huffman and Kratschmer described their method for making buckminsterfullerenes and showed photos of the actual crystals.

Word that something big was happening had already leaked out. The real surprise was that buckyballs were so easy to make. But they were still not being made in large enough quantities to enable scientists to pin down their structure. That task fell to others among the by-now droves of investigators who were playing buckyball.

"We always regarded its shape as the most likely and it was so attractive that everybody talked about it as though it was proven," says Whetten, who by then had his own lab at UCLA.

When Whetten and a colleague, Francois Dederich, read the Nature paper, they shifted gears and began working on the Huffman-Kratschmer method.

Something similar was going on with Don Bethune at the IBM Almaden Research Center in San Jose, Calif. Inspired by the Kroto-Smalley paper, he had begun work on carbon clusters using a machine developed by another IBM scientist, Heinrich Hunziker, to study contamination of disk-drive heads. That machine used laser pulses to lift organic molecules off a clean surface and put them into an analytical instrument called a spectrometer to study their masses.

But Bethune was having the same sort of trouble as Smalley: He couldn't get enough of the carbon-60 clusters to do a useful experiment. So he cast about for another method.

One evening, Bethune and a colleague were talking about his problem with someone who was using a Smalley apparatus at Lawrence Livermore Laboratory in California. Maybe, Bethune suggested, if you held some small object in front of the laser and tried pulsed beams, that might work. The response was, "That can't really be done. You might as well just light a match and put some soot on a metal plate. That's as stupid as what you're asking me to do here."

The IBM scientists hung up the phone, exchanged glances of recognition, and looked around for something to burn. The first thing they tried was methanol, wood alcohol, which burns with a nice, clean soot-free flame. Then they tried a piece of paper. No soot again. Then Bethune spotted a polyethylene lid from an empty can of peanuts. That gave him the soot he wanted. The mass spectrometer showed the desired peaks in the region of the 60-carbon atom.

Bethune and his colleagues cleaned up the experiment, burning pure carbon, and saw a major peak of carbon-60 clusters. Just about that time, they saw the Huffman-Kratschmer paper and knew what they had.

They then began an intensive set of studies on their carbon-60 samples: nuclear magnetic resonance, Raman spectroscopy, infrared spectroscopy. They cooled the samples to liquid nitrogen temperatures to slow down the buckyballs, which spin madly at room temperature, and made scanning tunneling microscope pictures showing the overall shapes of both C-60 and C-70 molecules, but not the arrangements of their atoms. The IBM group quickly published a paper confirming the Huffman-Kratschmer finding.

The world's first buckyball production facility came onlinThe world's first buckyball production facility came online early in 1991 at the Materials and Electrochemical Research Corp. in Tucson, assigned the patent to produce research-quantity amounts. The process is hardly elaborate. The heart of the operation is a metal chamber the size of an ordinary bucket. The current that runs through the graphite electrodes inside the chamber is provided by a Sears Craftsman arc welder. After the graphite vaporizes (in what looks like diesel exhaust), the soot is dissolved in toluene, and the solution is spun down to get relatively pure fullerenes. Sounds simple, but the extraction process is tricky, Huffman says.

"At the moment, the problem is that they can't keep up with the demand," he adds. "They're making more than a gram a day, but it's time-consuming." Down the hall, though, is the equipment for a tenfold scale-up, with bigger plans on the horizon. "If there's a really big demand," Huffman adds, "C-60 ultimately could be produced for pennies a gram. I really think that ten or twenty years down the road there will be large factories producing this material."

The absolute, complete confirmation of the soccer-ball geometry of C-60 came in April 1991, when chemist Joel Hawkins and colleagues at the University of California at Berkeley published the first X-ray pictures of the molecule's crystal structure.

Meanwhile, researchers have found even more curious and potentially valuable properties of buckyballs. In April, scientists at Bell Laboratories in New Jersey planted potassium in buckyballs and found that they became superconductors at a temperature of minus 427 degrees F. That's the highest superconducting temperature of any organic compound, and it opens a whole new field of buckyball research.

In California, Whetten fired buckyball molecules into a stainless steel wall at 15,000 miles an hour. They bounced back unharmed. "It's resilient beyond any particle that's been known," Whetten says—resilient enough, maybe, to be used as rocket fuel, which must with stand enormous pressures.

Arthur Ruoff, who works in high-pressure materials science at Cornell University, has made theoretical calculations that show buckyballs to be far stiffer than diamonds at moderate pressures, although they are "mushy" at atmospheric pressure. He believes this property could be a way to extend the range of high-pressure research. So-called "diamond anvils" are now used to create pressures of four million atmospheres. Ruoff is thinking about putting the material to be tested inside buckyballs to achieve even higher pressures.

Aboriginal particles?

That's just the beginning, says IBM's Bethune. "This molecule looks like something some genius engineer sat down and designed....There's the possibility of making molecular Christmas trees. We can decorate them with all sorts of functional groups. It's a Swiss army knife of a molecule."

This flexibility may have given the C-60 molecule a primal role in the formation of matter as we know it. Smalley speculates that buckyballs may not only be among the most common molecules in the universe, but among some of the oldest, if they were indeed created in the seething heat of red giant stars 10 to 20 billion years ago. And because they are large enough to collect smaller particles in collisions, perhaps they served as the primordial nuclei around which the first solid objects coalesced: interstellar dust particles, then rocks, asteroids, comets, and the planets themselves.e early in 1991 at the Materials and Electrochemical Research Corp. in Tucson, assigned the patent to produce research-quantity amounts. The process is hardly elaborate. The heart of the operation is a metal chamber the size of an ordinary bucket. The current that runs through the graphite electrodes inside the chamber is provided by a Sears Craftsman arc welder. After the graphite vaporizes (in what looks like diesel exhaust), the soot is dissolved in toluene, and the solution is spun down to get relatively pure fullerenes. Sounds simple, but the extraction process is tricky, Huffman says.

"At the moment, the problem is that they can't keep up with the demand," he adds. "They're making more than a gram a day, but it's time-consuming." Down the hall, though, is the equipment for a tenfold scale-up, with bigger plans on the horizon. "If there's a really big demand," Huffman adds, "C-60 ultimately could be produced for pennies a gram. I really think that ten or twenty years down the road there will be large factories producing this material."

The absolute, complete confirmation of the soccer-ball geometry of C-60 came in April 1991, when chemist Joel Hawkins and colleagues at the University of California at Berkeley published the first X-ray pictures of the molecule's crystal structure

Meanwhile, researchers have found even more curious and potentially valuable properties of buckyballs. In April, scientists at Bell Laboratories in New Jersey planted potassium in buckyballs and found that they became superconductors at a temperature of minus 427 degrees F. That's the highest superconducting temperature of any organic compound, and it opens a whole new field of buckyball research.

In California, Whetten fired buckyball molecules into a stainless steel wall at 15,000 miles an hour. They bounced back unharmed. "It's resilient beyond any particle that's been known," Whetten says—resilient enough, maybe, to be used as rocket fuel, which must with stand enormous pressures.

Arthur Ruoff, who works in high-pressure materials science at Cornell University, has made theoretical calculations that show buckyballs to be far stiffer than diamonds at moderate pressures, although they are "mushy" at atmospheric pressure. He believes this property could be a way to extend the range of high-pressure research. So-called "diamond anvils" are now used to create pressures of four million atmospheres. Ruoff is thinking about putting the material to be tested inside buckyballs to achieve even higher pressures.

Aboriginal particles?

That's just the beginning, says IBM's Bethune. "This molecule looks like something some genius engineer sat down and designed....There's the possibility of making molecular Christmas trees. We can decorate them with all sorts of functional groups. It's a Swiss army knife of a molecule."

This flexibility may have given the C-60 molecule a primal role in the formation of matter as we know it. Smalley speculates that buckyballs may not only be among the most common molecules in the universe, but among some of the oldest, if they were indeed created in the seething heat of red giant stars 10 to 20 billion years ago. And because they are large enough to collect smaller particles in collisions, perhaps they served as the primordial nuclei around which the first solid objects coalesced: interstellar dust particles, then rocks, asteroids, comets, and the planets themselves.

 

http://www.popsci.com/buckyball-magic-molecule