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transper_1pic.gif The Carbon Nanotube,
a Product of Nanotechnology

These days, following the surge of interest in information technology and biotechnology, the talk of the town is nanotechnology. Scientists around the world are excitedly discussing the possibilities inherent within this frontier field. The "carbon nanotube," a mesh of carbon atoms arranged in atubular shape, is said to be likely to produce the first practical applications of nanotechnology. The person who discovered and named this object, found in a tiny realm with dimensions measured in millionths ofmillimeters, is one of today's leading scientists, and he is in Aichi Prefecture.

Computer-drawn image of a carbon nanotube. This double-walled nanotube hasone cylinder of carbon atoms within another. Carbon nanotubes with variousforms have been found, but it was this sort of multiwalled structure that Iijima came across in 1991.

The fifth form of carbon
Through the eyes of the electron microscope
Aichi's place in carbon nanotubes

A nano is a one-billionth part of a specified unit. A nanometer is one-billionth of a meter, or one millionth of a millimeter. Just how short such a length is can be readily grasped when one considers that a typical hairfrom the head stretches some 10,000 nanometers across. Nanotechnology is the overall term used to designate an assortment of technologies that operate on this extraordinarily tiny scale.

The nanometer is the level on which atoms and molecules are built.Technologies making use of the properties and behavior of substances inthis microcosm have a very wide range of potential applications. It is hoped that they can be utilized in all sorts of existing technologies infields starting from computers and telecommunications and extending farbeyond, including biotechnology, chemistry, medicine, engineering, energy,and environmental science.

Institutions around the world have started up basic research in this field. Many countries, regarding it as a twenty-first-centurytechnology of the likes of the IT and biotech fields, are competing in its development. No single technology has yet reached the applications stage, but the first off the bloc, many people think, will be the carbon nanotube.

The fifth form of carbon

A carbon nanotube is an atomic array of carbon atoms in acylindrical shape. Diamonds and graphite and charcoal are three common substances made entirely of carbon atoms. Carbon can also take the form ofthe "fullerene," a molecule of carbon atoms with the shape of a soccerball. The first of these was discovered in 19851 by three American andBritish scientists, and it has 60 carbon atoms. Fullerenes with 70 or 82 atoms and more turned up later.

The only other known form pure carbon may take is the carbon nanotube. Although others may be discovered in the future, it can be calledthe fifth form of carbon. It was discovered in 1991 by Sumio Iijima, asenior research fellow in the NEC Laboratories of NEC Corp. and professorat Nagoya's Meijo University. And it has a number of unique characteristics that may make it a very useful substance, Iijima says.

In terms of properties, the carbon nanotube is chemically and thermally stable. It is highly absorptive, which may make it a good storage device for substances. It can be either a conductor or an insulator depending on the direction of the electric field applied to it. "We have also found," Iijima reports, "that it interacts with certain substances selectively and aids electricity generation in a hydrogen-oxygen reaction,which opens the door to its use in the fuel cell.

Experimental equipment in the Department of Materials Science and Engineering for making carbon nanotubes using laser plasma.Carbon melts and evaporates in the plasma from a pulse laser, leaving behind deposits containing carbon nanotubes.
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The fuel cell is one of the places where Iijima is most hopeful of applications. This is a battery that reverses the normal process of electrolysis, in which hydrogen and oxygen are separated from water by passing a current through it. A fuel cell combines hydrogen and oxygen,thereby producing electricity. As is commonly known, automakers are currently engaged in intensive R&D programs to commercialize fuel cellelectric vehicles, which hold the promise of being next-generation,environment-friendly vehicles. If carbon nanotubes can be successfully incorporated into them, fuel cells will be significantly reduced in efficiency and cost, giving them a much broader range of applications.

Various other uses for carbon nanotubes may also turn up. Iijima observes that within a couple of years, we will see a large size flat panel display for television, that they may supply a superior substitute for thesilicon in the computer chip, that they may serve biotechnology in a variety of ways, and that they may even find use as reservoirs for storing hydrogen. "But the biggest challenge before us today is to overcome energy problems," he adds, "and people are looking to technology for help. Just possibly carbon nanotubes may give us the materials we need for solving these problems and thereby conserving the global environment."

Through the eyes of the electron microscope

After his discovery of the fifth form of carbon in 1991, Iijima soon gained recognition around the world as one of the foremost authorities in this field of research. But this has not caused him to swagger about. After all,he says, he happened to come across carbon nanotubes "just by pure luck."

"Discoveries can be into two broad groups," he suggests. "In some cases the discovery comes about as a result of having set a goal and applied knowledge and theory to attain it. In other cases the discovery unexpectedly turns up one day in the course of a trial-and-error process,or perhaps thanks to knowledge and experience gained in an entirely separate field. The latter are gifts of fortune, but they actually account for the bulk of the discoveries that have triggered major scientific advances."

Iijima graduated from the University of Electro-Communications in1963 and went on to pursue graduate studies at Tohoku University. There he became acquainted with the electron microscope, which at the time was stilla rare instrument. After earning his doctorate he picked up experience in anumber of places, serving as a research associate at Arizona StateUniversity and working for the Research Development Corporation of Japan(now the Japan Science and Technology Corporation). Since 1987 he has been a research fellow in the NEC Laboratories. Since 1999 he has also served as a professor at Meijo University, where he works in the Department of Materials Science and Engineering, but throughout his career he has specialized in electron microscopy.

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Sumio Iijima, discoverer of the carbon nanotube. A senior research fellowin the NEC Laboratories and professor at Nagoya's Meijo University, he is known around the world as a leading authority in his field. "Carbonnanotubes," he says, "may become a key material for fundamentally resolving energy problems."
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"I found carbon nanotubes while using an electron microscope to investigate fullerenes, the fourth carbon form," he tells us. "I was looking at carbon deposits on electrodes, and my eye was caught by some whiskers I could see. Right away I sensed I was on to something. I happened to know about such tubular crystal structures because when I was in graduate school, I'd studied under one of the leading authorities on asbestos. That experience enabled me to grasp the essence of the nanotubes quickly. In fact, I probably wouldn't even have noticed them if I hadn't spent so many years working with electron microscopes."

This is a classic example of the serendipity people in the world of science often talk about. Many epochal advances, we are told, come from researchers with a gift for making serendipitous discoveries. Indeed, itwas a botched experiment that set Hideki Shirakawa on the road to his receipt of the 2000 Nobel Prize in Chemistry.

There is also another episode of happenstance leading to happy results in Iijima's story. The American and British scientists who discovered fullerenes, for which they received a Nobel Prize in 1996, made their discovery in 1985. Before that, in the 1970s, Iijima had in fact already seen fullerenes and taken photos of them. What he had come up with,though, was not real proof of their existence but only an indication that they existed. His interest thereafter moved off in other directions, but then he returned to the subject and embarked on research into fullerenes,with encouragement from their discoverers." And it was this research thatturned up carbon nanotubes.

"Actually there were already attempts to make carbon nanotubes backin the 1950s," Iijima elaborates. But in those days it was impossible to see these things, since electron microscopy hadn't yet reached the level for seeing atoms. There's a world of difference between 'apparently exists' and 'exists.' Something that 'apparently exists' is still in the realm ofscience fiction. It enters the realm of science only when its existence is objectively demonstrated."

Iijima introduced carbon nanotubes to the world using just such an objective demonstration. It may have been serendipity that put him in this position, but this was serendipity backed by a certain inevitability, one that could have produced happy results only for him.

Aichi's place in carbon nanotubes

The mechanisms involved in the creation of carbon nanotubes are now being elucidated, and the research at Meijo University has shifted to how the production process can be controlled. Mass production is still difficult,but Iijima is confident it will be achieved in time. Already a number of companies have come up with plate panel displays making use of carbon nanotubes, so the first practical applications can be said to be within shooting range.

The samples Iijima used in his discovery of carbon nanotubes came from Aichi, supplied by the laboratory of Professor Yoshinori Ando at Meijo University. And now steady progress is being made within the prefecture toward the application of this fifth form of carbon, which has potential within it for reshaping the society of the twenty-first century. (Masahiro Ota)

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