Carbon Nanotubes

Carbon nanotubes were discovered in 1991 by Sumiyo Iijima, a Japanese scientist working at the NEC Corporation. A carbon nanotube (CNT) is a tubular form of carbon with a diameter as small as 0.4 nm and length from a few nanometers up to a millimeter.  The length-to-diameter ratio of a carbon nanotube can be as large as 28,000,000:1, which is unequalled by any other material.

Carbon exists in several allotropes (different physical forms) including graphite and diamond which are the most familiar. To imagine the structure of a carbon nanotube, think about taking a single layer of a graphite sheet, cutting it into a long rectangular piece, and curling it up so the long edges of the rectangle join one another.  The result is a single-wall carbon nanotube (SWCNT). If you take multiple layers of a graphite sheet, then you get a multiwall carbon nanotube (MWCNT).

Of course, no one is sitting out there rolling graphite sheets in order to make nanotubes. These are grown in laboratories often using a process called chemical vapor deposition.

This process can be carried out using instruments called reactors that can be quite sophisticated, but carbon nanotubes can be made in a standard chemistry laboratory relatively easily. A quartz tube about 2.5 cm in diameter serves as the reactor vessel and is inserted inside a furnace (a furnace is a standard heating device for synthesizing and treating materials). The nanotube is grown on a silicon wafer that is placed at a central location inside the quartz tube. A thin layer of iron or nickel or cobalt is applied to the silicon wafer to serve as a catalyst to grow the nanotubes. A hydrocarbon such as methane or ethane or acetylene is sent through the reactor tube which is heated to 750-900ºC by the furnace.

Continue to explore nanomaterials by reading about other examples of materials that exhibit interesting properties on the nanoscale: inorganic nanowires, dendrimers, nanoparticles, graphene, and quantum dots.