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Carbon Nanotube
What are carbon nanotubes?
A "Carbon Nanotube" is a tube-shaped material, made of carbon, that has a diameter measuring on the nanometer scale. A nanometer is one one-billionth of a meter, or about one ten-thousandth of the thickness of a human hair. The graphite layer appears somewhat like a rolled-up chicken wire with a continuous unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons. In some cases, the hexagons are arranged in a spiral form. The pattern is reminiscent of the Japanese art of bamboo basket weaving ("Takekago").
Solid state carbon has been known to appear in four basic forms: "diamond structures,""graphite structures,""non-crystalline structures" (such as charcoal), and "fullerene molecules" such as C60, which is comprised of 60 carbon molecules clustered in a soccer ball shape. Fullerene molecules were discovered in 1985. The carbon nanotubes that I discovered thus became the fifth type of solid state carbon.
The carbon nanotubes that I found in 1991 had multiple walls, but in 1993 I discovered single-wall carbon nanotubes that were one nanometer thick and several tens of nanometers long. (These were discovered separately at IBM around the same time.) Later, our group promoted research into material characterization and computational physics, and this became the forerunner of carbon nanotube research. In 1996, Thomas Ebbesen's group at the Princeton NEC Research Institute succeeded in measuring the electrical characteristics of carbon nanotubes.
Then, in 1998, during the Japan Science and Technology Corporation (JST) International Cooperative Research Project "Nanotubulites," I discovered single-layer graphite shaped like a tube with a closed end, which was later to be given the name "Carbon Nanohorn." These carbon nanohorns were comprised of carbon collected in the shape of an bull's horn covered over with a hood.
Carbon nanotubes have many structures, differing in length, thickness, type of spiral, and number of layers. Although they are formed from essentially the same graphite sheet, their electrical characteristics differ depending on these variations, acting either as metals or semiconductors.
