A Positron Named Priscilla Scientific Discovery at the Frontier (1994) / Chapter Skim
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9 Bouncing Balls of Carbon: The Discovery and Promise of Fullerences
9 Bouncing Balls of Carbon: The Discovery and Promise of Fullerences
Pages 258-289
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From page 258... ...
Some might call it an obsession. Neatly packaged by Mother Nature into never-before-seen hollow molecules that resemble infinitesimally small soccer balls or geodesic domes, buckyballs now have celebrity status.
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From page 259... ...
buckyball) is only one although the roundest, most abundant, and most popular of a whole family of similar molecules generally referred to as "fullerenes." The second most common fullerene is C70, whose 70 carbon atoms bond into what some say looks like a rugby ball (see Figure 9.1~.
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From page 260... ...
UCLA's Whetten has been on the trail of a particularly enticing fullerene property: superconductivity, perhaps the hottest subject in materials science today. And researchers such as Bethune and his colleagues at IBM have already succeeded in performing one of the neatest fullerene tricks so far locking up one or more metal atoms inside individual carbon cages, creating what are called metallofullerenes whose properties are just beginning to be explored.
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From page 261... ...
Before the fullerene discovery, it was gospel among chemists that pure carbon had only two distinct crystalline forms: diamond and graphite. (Other carbon material such as charcoal and coke, has an amorphous quality but appears to consist primarily of tiny graphite crystals.)
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From page 262... ...
made some strikingly accurate predictions about hollow spherical molecules, predating the discovery of the fullerenes by nearly two decades. Some of that column is excerpted here: There is a curious discontinuity between the densities of gases around 0.001 relative to water, and liquid and solids from 0.5 to 25 or so; this week Daedalus has been contemplating ways of bridging this gap and has conceived the hollow molecule, a closed spherical shell of a sheet-polymer like graphite, whose molecules are flat sheets of benzene-hexagons.
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From page 263... ...
Once formed, it cannot add additional atoms and grow. It was this property that made buckyballs stick out like sore thumbs in mass spectra of carbon vapor and opened a new chapter on carbon chemistry.
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From page 264... ...
O'Brien. This U.S.-British team reported finding convincing evidence for the existence of a new form of pure carbon a hollow round molecule, which they named "buckminsterfullerene." At the Houston campus of Rice University, Smalley had been doing experiments, similar to those at Exxon, using a supersonic cluster-beam device he had developed.
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From page 265... ...
The researchers theorized that as the carbon clusters were growing in the condensing vapor they rearranged their bonding to produce pentagonal as well as hexagonal rings of atoms that closed the clusters into soccer-ball-like spheres. Suddenly, the C60 peak made sense.
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From page 266... ...
The second most stable arrangement is that of C70, whose signal always appears along with C60 in mass spectra of vaporized carbon, although to a lesser degree. The researchers calculated that the other fullerenes are not as stable because the pentagons in their structures are located in strained positions that make them vulnerable to chemical attack.
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From page 267... ...
While the IBM group was working on collecting more fullerenecontaining soot with its laser deposition method, a U.S.-German team of physicists reported evidence that they had produced soot containing a relatively large amount, roughly 1 percent, of C60 using an even simpler technique. Their fullerene generator, said Bethune, was little more than "a pencil lead and battery." A graphite rod was attached to the terminals of a battery or other power supply, and 100 amps of current was sent through the sample until it smoked and deposited soot on the inside of the helium-filled chamber.
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From page 268... ...
"When we learned of this result," said Bethune, "we immediately tried their recipe for making soot." The IBM team set up a similar "pencil-lead and battery" device and let the current run until the graph
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From page 269... ...
They immediately tried obtaining a Raman spectrum, and began work on photographing the molecules using a scanning tunneling microscope (STM)
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From page 270... ...
The remaining tests were increasingly more sophisticated, but they would inch researchers closer and closer to the final answer. The Raman Spectrum The IBM team was the first to get a key molecular fingerprint, called a Raman spectrum, from the thin films of C60 they had sublimed from soot prepared with the "camel" recipe.
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From page 271... ...
The Raman spectrum, which also complemented the infrared absorption spectrum obtained earlier, was strong support but not conclusive evidence for a soccer-ball structure. That would come from the results of NMR studies of buckyballs.
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From page 272... ...
This identified which carbon atoms are bonded to each other and, when combined with the NMR spectrum obtained by the British team, completely confirmed the rugby-ball structure for C70- To do this more exacting test, however, Bethune and Meijer first had to enrich the natural i3C isotope content of their fullerene sample. They did this by packing off-the-shelf 13C into a hole bored into a graphite rod before burning it into soot and subliming out C70 Unexpectedly, this little chemistry trick performed for the 2D NMR analysis also turned up new insight into how fullerenes form in a condensing carbon vapor.
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From page 273... ...
And, in fact, solid-state NMR analysis carried out independently by Costantino Yannoni of the IBM group and Robert Tycko at AT&T Bell Labs in Murray Hill, New Jersey, revealed a surprising fact: even when solidified into a crystal (when atoms and molecules normally are locked into place by their neighbors) , buckyballs are about as sedate as a five year old in a dentist's chair; they're jittery molecules that don't like to sit still.
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From page 274... ...
Formal portraits were made by both the IBM team and a group led by the University of Arizona's Huffman using a scanning tunneling microscope (STM)
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From page 275... ...
Buck:ybalIs by the Bushel Both the IBM team and Harry Kroto's Sussex group continued to concentrate their research efforts on analyzing the fullerene structure. During this time, the U.S.-German collaboration of Kratschmer and Huffman, now joined by University of Arizona physicist Lowell D
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From page 276... ...
RCT has also filed international patents on a process developed at Northwestern University that uses C70 to greatly enhance the growth of diamond films used in a variety of commercial applications.
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From page 277... ...
In late 1991 Japanese researchers reported the discovery of what have been dubbed "buckytubes," hollow microscopic tubules that appear to be layers of graphite rolled into cylinders. The Japanese scientists, with the NEC Corporation, had been vaporizing carbon by attaching one graphite rod to the positive electrode of a power supply and a second rod to the negative electrode.
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From page 278... ...
Bethune wonders if Isaac Silvera, Nancy Chen, and Fred Moshary of Harvard, working in collaboration with the IBM team, may have made similar structures when they compressed tiny samples of C60 under the extraordinarily high pressures created by a diamond
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From page 279... ...
Fullerene scientists are hoping for at least as much, if not more, practical impact from their newly found carbon. "The physical stability and relative inertness of the fullerenes allow them to be assembled into very unusual solids," notes Bethune, "thus opening up a new branch of materials science." A particularly exciting aspect of fullerenes is that, since they are hollow spheres, chemistry can be done both on the molecule's exterior surface ("exohedral chemistry")
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From page 280... ...
Materials that become superconducting at higher and higher temperatures have long been sought. What the Bell Labs scientists did was turn C60 into an artificial metal by slipping potassium atoms into the spaces between buckyballs that had been crystallized into a solid thin film (see Figure 9.6~.
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From page 281... ...
In the meantime, the Bell Labs and UCLA researchers were also trying to slip other atoms into the buckyball crystals to see the effect on FIGURE 9.6 Computer graphic showing how potassium atoms {smaller balIsJ fit in between larger buckyballs to make an artificial metal that becomes superconducting when chilled to 18 degrees Kelvin. {Courtesy of University of California, los Angeles/State University of New York.J 281
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From page 282... ...
"Such species would be an interesting new class of molecules," said Bethune, "with tunable electronic, optical, vibrational, and chemical properties depending on what atoms you put inside." What seems like a wild idea has turned out to be as easy to do as making plain vanilla fullerenes. Right after the U.S.-British team first detected the peak for C60 in the mass spectrum of carbon vapor and realized what they had, they tried an experiment to see if they could get a guest atom to take up residence inside some of the carbon cages by
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From page 283... ...
For example, one lanthanum atom inside a buckyball would be designated "La@C60," while "Sc3@C~2" would mean three scandium atoms inside Cal, a metallofullerene recently made by the IBM group and by Shinohara and his colleagues in Japan. Initial experiments on stuffing atoms into carbon cages produced a variety of metallofullerenes but in such minute quantities that the only indication of their presence were signals in mass spectra taken of the samples.
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From page 284... ...
Nevertheless, the possibilities that these novel species offer, both for scientific study and for practical applications, are very exciting and still largely unexplored." For example, isolating clusters or molecules of different atoms inside fullerene cages or even tubes may make it possible to fabricate exotic new structures at the nanometer scale, said Bethune. A nanometer is one-billionth of a meter, a size so small that "nanotechnologists" work with building blocks that are only a few atoms in size to make the tiniest components physically possible.
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From page 285... ...
Worldwide demand for diamond films and coatings is projected to reach $260 million in 1995 and nearly $2 billion by the year 2000, according to Research Corporation Technologies. This Tucson-based technology transfer company has filed international patents on the C70 treatment method, developed at Northwestern University, and is leading efforts to commercialize it.
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From page 286... ...
It is, says buckyball's British codiscoverer Harold W Kroto of the University of Sussex, "a prime example of the way in which an interest in fundamental problems for their own intrinsic sake, irrespective of their predicted use, can yield results of applied significance." Before getting caught up in fullerene fame, Kroto had been conducting a long-term research project to understand the origins of linear carbon chains detected in space.
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From page 287... ...
He speculated that the spontaneous formation of fullerenes out of a chaotic carbon vapor may be related to the mechanism that formed the first particles in space. "Indeed, that vital link in planet formation, the primordial solid particle, may well have been carbonaceous ...." In addition to linear carbon chains and related molecules, said Kroto, "a new character, C60, has emerged, whose shadowy role, like that of the Third Man, has only now come to light." In their now-famous Nature report announcing the discovery of buckminsterfullerene, Kroto and his colleagues wrote: "Because of its stability when formed under the most violent conditions, it [C60]
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From page 288... ...
1990. Laser deposition of carbon clusters on surfaces: a new approach to the study of fullerenes.
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From page 289... ...
1990. Imagine Cog clusters on a ~ ~ vie surface using a scanning tunneling microscope.
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