An almost uncountable number of papers have been written concerning the fullerenes in organic chemistry journals, physical chemistry journals, and other journals in other areas of science, as well as many articles in magazines for the layperson, such as Popular Science. Even more have been written on the Internet. Fullerene galleries, fullerene research groups, and hundreds of U.S. patents concerning inventions using fullerenes have since joined the parade on the Information Superhighway, which now is a common medium by which information is exchanged. One may, and often does, wonder "Why is so much attention given to fullerenes"? In order to answer this and many related questions, one must look at and examine the discovery of, as well as the potential applications of, buckminsterfullerene, the simplest of the fullerenes, buckyball's "big brothers," C70, C76, C78, C82 on up to as high as C1,000,000, as well as entities known as nanotubes or buckytubes, all of which are the fullerenes directly related to buckminsterfullerene, and fullerene derivatives and their useful properties.
The facet of buckminsterfullerene and the related fullerenes that one first must look at is their discovery. Buckminsterfullerene and the rest of the fullerenes, except for buckytubes, had three co-discoverers, while buckytubes themselves were discovered by Sumio Iijima, a scientist working at NEC Corporation's Fundamental Research Laboratories in Japan.
The story of the discovery of buckminsterfullerene is a long and complex one, and before one can look at the big historical moment of discovery by Smalley, Kroto, and Curl, one must look further back in time to the summer of 1967, which just happened to be Canada's centennial. In celebration of the anniversary, Canada threw a huge party, and invited millions of guests from around the world, and called it the Montreal EXPO. At this EXPO, each country that came each set up its own interesting brightly colored pavilion, giving their exposition of what technology their country had come up with and how they were going to use it within the next few years. Little did Richard Smalley and Harry Kroto realize at the time they had separately visited the EXPO, if it weren't for that big party that Canada threw in celebration of 100 years, the molecule today that is known to have sixty carbon atoms, all locked in a soccer ball-like form, might not have the name Buckminsterfullerene.
The party that Canada threw was a huge success, but one of the most memorable exhibits was the American exhibit, designed by a maverick architect by the name of Richard Buckminster Fuller. The exhibit was what people would now know as a geodestic dome, one of Fuller's inventions, but up until 1967, hardly anyone had seen one. The dome itself was one of Fuller's more grand plans to make "more with less," to make the geodestic dome the home of the future. It greatly lowered manufacturing costs, because, being in the shape of a sphere, it enclosed the most volume with the least amount of material used. The dome at the Montreal EXPO was 76 meters tall and was three-quarters of a sphere, and, to many people there, looked quite strange, but still very beautiful. It was comprised of a repetitive triangular steel network, which, if one ignored the triangles, comprised a soccer ball shape. This is the image that stayed with Kroto and Smalley, being recollected many years later, in 1985.
By the 1970's, Harry Kroto was primarily a spectroscopist at Sussex University in Britain looking for different molecules in interstellar space to explain different anomalous wavelengths found in interstellar spectra, known as diffuse interstellar bands. Astronomers were attempting to explain these and other strange phenomena that occurred in spectra from different regions of space. An example is known as the ultraviolet extinction, which is a result of a portion of ultraviolet radiation being both absorbed and scattered, which are respectively quantum mechanical and classical phenomena. Absorbsion is explained by atoms absorbing energy, making the electrons move into higher orbitals. Scattering is the spreading of light by macroscopic bits of matter, such as light from a prism. However, in the case of the ultraviolet extinction, both processes are happening simultaneously, so bits of matter whose size borders on that of the macroscopic world and the world of the quantum. So, in order to explain what was happening on this level, one would have to look at objects large enough to scatter light, but, on the other hand, were small enough to absorb light as well. In 1977, the suggestion was put forward by a scientist by the name of Alec Douglas that very long carbon chains might explain the diffuse interstellar bands that were so anomalous. So, most of the scientists studying this phenomena were trying to look at smaller and smaller particles, like cosmic dust particles and smaller. An example of such scientists were two physicists by the name of Donald Huffman and Wolfgang Krätschmer, who, in attempting to explain the ultraviolet extinction, sought to make soot particles as small as possible, recording their spectra. They did several experiments off and on for about six years, initially failing at the attempt to make carbon particles that had the absorbsion close to 220 nanometers, the ultraviolet extinction, but they got close. They figured it had something to do with the coalescing of particles from the gas phase, so they tried trapping the first formed carbon particles in a frozen noble gas, attempting to slow and control the reaction. This proved to be unsuccessful. They came together finally in 1982 in Germany and produced their best results, having basically the same spectrum, near 220 nanometers, but instead of having one hump, the better spectrum for the 1982 sample had two humps, which the two physicists called "the camel spectrum." This "camel spectrum," they figured was a manifestation of a regular molecule causing the absorption, instead of the previously thought irregularly shaped particle.
Harold Kroto, on the other hand, with another chemist named David Walton, went the other direction, from smaller particles and molecules, to larger ones. He tried to find bigger and bigger molecules in space. They started out looking for poly˙nes, acetylenes with concatenated triple-bonded carbon units that were increasingly unstable the longer the chain, so protecting groups had to be put at the end of the chains to prevent an often explosive cross linkage. Poloy˙nes are symmetrical, however, and they are known not to give rotational spectra, which is what Kroto wanted, so they looked at a class of compounds known as cyanopoly˙nes, which are unsymmetrical, thus yielding rotational spectra. Specifically, they synthesized cyanodiacetylene, which produced the results they wanted. Kroto then went out and collaborated with a former colleague of his, Takshi Oka, and some Canadian astronomers, and used a radio telescope to see if the long molecule existed in interstellar space. The next year, after much searching, they found what they were looking for. They also found cyanotriacetylene, the largest find up until then. Kroto and Oka extrapolated the spectrum of the next molecule, having a nine carbon chain. They searched for it, and found it as well. They were finding all of these molecules, but couldn't figure out where they came from or how they were formed. Obviously, the theory concerning interstellar molecular formation needed some revising. They needed to simulate the formation conditions necessary to produce large molecules. This is where Dr. Rick Smalley comes in.
At about the same time Kroto was finding his molecules in space, Smalley was building his machine, known as the AP2, or, more formally, the "laser-supersonic cluster beam apparatus," at Rice University. AP2 simply meant that it was the second apparatus that Smalley built at the University. The Exxon Corporation funded the manufacture of two apparatuses as well as provided the lasers that were to be used by them. One apparatus stayed at Rice, the other was shipped to the Exxon lab in New Jersey. There, at the Exxon lab, scientists used their apparatus to vaporize iron and carbon. They found that carbon and iron existed in clusters of even numbers of atoms, but thought they were chains cross-linked in some unspecified manner and thus failed to take significant notice of them. However, they did report their existence at the same conference that Donald Huffman and Wolfgang Krätschmer reported their failed attempt at the controlled condensation of their carbon clusters.
The apparatus itself was used to vaporize various elements, most notably, silicon and germanium and mostly transition metals, in the interest of commercial electronic applications. The apparatus was huge and sat on large tables to accommodate its weight. Underneath the table was a maze of wires, tubes, pumps, and everything else that worked "behind the scenes." At the heart of the entire operation was a steel drum about a meter in diameter. To this drum several plates were affixed which had quartz windows in them to let laser light pass through. A spinning disk was inside the drum and it spun the sample to be vaporized. Right beside this, there was a nozzle to release a stream of gas. On the other side of the disk from the gas outlet, was another tubular outlet that led into a vacuum chamber. On the far side of the vacuum chamber was a small borehole that led directly into a solid steel cube. The cube itself had its own quartz window, which allowed laser light from a second laser. From here there was a pipe leading vertically upward to a mass spectrometer. The apparatus worked as follows: Helium was first introduced into the vaporization chamber. A laser was used to vaporize a very small portion the spinning disk of sample to be vaporized. As the disk spun, fresh sample was exposed to each laser blast. This produced a very hot vaporized sample. The temperature of the resulting plasma was around ten thousand degrees Celsius, well above the temperature of the surface of stars. Immediately after the sample was vaporized, the helium stream immediately carried the vaporized particles away from the spinning sample disk to the other side. This event of the onrush of helium caused the sample, which was at an extremely high temperature, to cool with great rapidity, down to room temperature. The cluster-gas mixture then went through the outlet nozzle into the vacuum chamber where, in an attempt to fill the vacuous space, spread out, and, as a consequence, cooled further to a temperature just a few degrees above absolute zero. By far, most of this cold, vaporized sample hit the walls of the vacuum chamber. However, a small amount of vaporized sample went into the borehole at the opposite side of the vacuum chamber. After entering this borehole, the sample was inside the solid steel cube, where the second laser ripped the electrons from the vaporized sample, thus ionizing it. These ions then traveled through charged plates, which produced an electric field, which directed them up toward the mass spectrometer. The mass spectrometer recorded the size of each part that the sample was broken up into as well as recorded the flight time. From this the mass is calculatable. Large masses traveled slower than small masses, and thus took a longer time to reach the spectrometer.
It took only milliseconds from the gas pulse to the firing of the second laser that ionized the sample. A millisecond later one operating the apparatus obtained the mass spectrum for the given sample. The exact timing between the two laser blasts wasn't always the same because the pulse duration and times for each of the lasers were computer controlled. An experimenter could also alter the frequency of the ionization laser, making it possible to ionize a specific species if it was thought to be in the sample-gas mixture.
By the spring of 1985, Dr. Harry Kroto and another spectroscopist, Bob Curl, together attended a conference in Austin Texas. Bob asked Harry if he would like to visit Rice University, and Kroto replied he would. While at Rice, Curl showed Kroto the progress that Smalley had made with his cluster apparatus. The capabilities of the apparatus excited Kroto very much because what Kroto realized is that the apparatus could answer the question concerning where the large interstellar molecules he had been finding were coming from. The laser produced conditions that are similar to that near the surface of hot stars, the burst of helium and the vacuum chamber mimicked the interstellar region, where, in interstellar space, no interactions would occur between the molecules being formed. Smalley was already doing experiments attempting to produce silicon carbide, a chemical found in comets. Kroto was certain that if one were to put carbon into the machine, and create the right conditions, that the long molecules, the cyanopolyynes, would be created and Kroto would get his corresponding spectra, solving the problem of unaccountability of the larger interstellar molecules by the older collision theory. In August of 1985, Kroto went to Houston after deciding that doing the experiments jointly was the best thing to do, since he had to teach in October.
The week before Kroto's arrival, Smalley and his team of students that worked with him, doing research with the apparatus, tried carbon out in the apparatus and collected spectra. They claimed it to be the same result as the Exxon group. The students then performed what is known as resonant two-photon ionization, in which the molecule to be ionized is hit with two laser pulses, the first one gets the molecule into an excited state, which is said to be in resonance with the laser pulse, the second completes the process by totally removing an electron from the molecule. The results they obtained form these experiments suggested that the spectra that Bob Curl and Harry Kroto were interested in were at least something to look at and study.
When Kroto arrived, he told the students his agenda, and he did it in such a way as to arouse their interest. He told Smalley and his student research group about how he would use Smalley's cluster beam apparatus to simulate the conditions near a surface of a star thus explaining how large molecules in space that he discovered got there and how he sought to explain the diffuse interstellar spectrum in this manner by obtaining the spectrum of the synthesized long chain molecules. It appealed to one of Smalley's students, Jim Heath, as well as Smalley himself, so the team of students, Rick Smalley, Bob Curl, and Harry Kroto set out to synthesize long chain cyanopolyynes in the cluster apparatus.
Kroto befriended Jim almost immediately, conversing with him on a wide range of scientific subjects and Jim found Kroto's enthusiasm in his work quite contagious, and Jim caught the bug. On September 1, 1985, they went to the lab and Jim showed Harry exactly how the apparatus operated, showed him how the timing sequences were important, and, all the while, they recorded the pertinent spectra. They also used several add-ons to the apparatus that Jim had previously made himself, the most important of which they used was the integrating cup. The integrating cup lengthened the tube that led into the vacuum chamber but also added a sort of antechamber that the cluster beam was to pass through before entering the vacuum chamber. Adding this integrating cup and using moderate laser energies, as well as using helium as the carrier gas yielded the same results as the Exxon group obtained a few months prior. Just as in those spectra, the sixty carbon peak was much larger than the other peaks, as well as other, large even numbered carbon clusters, but it did not cause any concern because it was found in the Exxon spectra beforehand. Much more was to occur before the peak had any special significance, which were the experiments done in an attempt to synthesize Kroto's cyanopolyynes.
Kroto's molecules required that hydrogen and nitrogen were to be used, which would hydrogenate the clusters as well as stick nitrogen atoms on the end, producing cyanide groups, at least in theory. What actually happened is that when they used hydrogen to form clusters with hydrogen-capped ends, they obtained, not the neat increments of pure carbon clusters, but oil and tar fragments, products, they certainly didn't want. However, strangely enough, the large, even numbered clusters remained, impervious to hydrogen's attack. The C60 peak remained, and was arbitrated to be the peak to be looked at as a reference point from which to determine how much small clustering they were getting. Next, they replaced hydrogen with nitrogen, attempting to produce chains terminated with nitrogen, and once again, failed to get any good results. So then they reasoned to use pure helium and then mix in the new gases to see what results they would get. Again they started out with pure helium. However, because they now were monitoring the C60 distribution, they noticed that the C60 peak was off the scale they were using. Near the C60 peak, there was a large peak for C70 as well, but its peak was smaller. They then repeated the experiment, each time gradually increasing the nitrogen and hydrogen mix. Through it all, the large, even numbered clusters remained resistant to attack. It was then that Smalley, Kroto, and the working group of students realized they weren't dealing with any ordinary carbon cluster. They were dealing with something new.
The speculation of what kind of molecule they had started the next day. Kroto speculated that it could be a quadruple decker sandwich of planes of graphite, but there were unsatisfied bonds, which of course didn't correspond to the molecule's inertness to hydrogen and nitrogen attack. Meanwhile, the students were still performing experiments.
Jim switched out the laser to make sure that the peak wasn't reminiscent of the beam's resonance with the peak by coincidence. It wasn't. They had to figure out what was going on. Jim took out the integration cup and found that the C60 didn't survive when this extension was removed. It was also found that the process didn't involve left over carbon fragments form previous laser blasts. Following this data, his intuition suggested there was a cooking process going on. If the extension is taken off, the cluster does not have enough time to "cook."
The next day, Jim brought up his cooking idea, and Harry almost immediately adhered to it. The group of scientists with the team of students now knew that it was photochemically stable, was virtually inert to chemical attack, and it could not undergo photolysis with laser light. Harry was very interested with this data, because a few or even one species were thought to be the cause of the diffuse interstellar spectral lines. The yearning to explain all this data was now at its peak. They then set out to find out just what this mystery molecule actually was and what it looked like.
They realized that it takes time for the molecule to form and, when formed is impervious to many chemical and luminal interactions, such as photolysis by laser light. It is not known who thought of it first, but either Harry or Rick finally came to the correct conclusion that the carbon curls up into a geodestic dome. They had forgotten just how a geodestic dome was put together, if it used only hexagons or if it used both hexagons and pentagons. Rick went to Rice University's library, where he found a book on Buckminster Fuller and some of his works, namely The Dymaxion World of Buckminster Fuller. One night at a local Mexican restaurant, Harry, Rick, Bob, Jim, and Jim's wife, Carmen, all got together for dinner. They discussed and pondered how this molecule could be a geodestic dome and whether the dome could have sixty vertices or not. Even after dinner, they resolved not to let the questions go unanswered.
That night, Jim and his wife went back to the lab to turn off the apparatus that had been cooling down after a long day's run. On the way over there, they bought gummy bears and toothpicks to make a kind of ball and stick model. They got to the lab and tried several frustrating times to make a geodestic dome, but failed to produce a complete model.
At the same time, Smalley was at his house trying to coax the answer out of his IBM home computer, using the latest computer graphics available at the time. After a few hours of programming, Rick became extremely frustrated and finally decided to use scissors, paper, and tape to produce a model. He began just as Jim and Carmen did, attempting to make domes with just hexagons. It was about midnight when he again became frustrated. So, in desperation, he began another dome, this time with pentagons. The structure took shape quite easily, and when he obtained a half-shell he counted the vertices, each representing a carbon atom. He obtained a count of thirty vertices, making the total vertices in the complete molecule would be the magic number, sixty. When Smalley realized this, his heart leaped. He had an almost unshakable urge to call Kroto, who was at Curl's house, wake him up, and tell him the good news. However, he didn't, but had to force himself to sleep. The structure of C60 was finally uncovered, but it was still a nameless molecule.
Smalley brought his paper model to the meeting the next day. Bob Curl took a look at it and said the stability for the molecule could only be accounted for by alternating single and double bonds within the molecule. Smalley called the math chairman at Rice, Bob Veech, trying to ascertain what the shape was called. Veech called back, saying, "I could explain this to you in a number of ways, but what you got there, boys, is a soccer ball." Assuming these bond lengths were those normally for carbon, they calculated that the cavity inside would be 0.7 nanometers in diameter. This would mean that one could stick an atom of any element in the periodic table inside this molecule, which thus would lend itself to denizens of applications. They now had to come up with a name for this molecule.
It is also unknown just which of the scientists came up with the name, but several names were brought up, such as soccerene and ballene, but finally came up with the name Buckminsterfullerene.
They immedietly and hurriedly wrote a paper on the exciting discovery and published it in Nature, a scientific as well as layperson journal that hit a very wide and varied audience, which was the audience they wanted to reach.
The scientists all took a picture together with a soccer ball before Harry Kroto had to return to Britain. While the paper was being edited, the team managed to put lanthanium inside buckminsterfullerene, essentially being the first known chemistry of the molecule.
