| They were discovered in 1991 by the Japanese | | | | their functionality as electrical conductors. |
| electron microscopist Simio Iijima who was | | | | One problem that plagues researchers looking to |
| studying the material deposited on the cathode | | | | fashion circuit components from nanotubes is |
| during the arc-evaporation synthesis of fullerenes. | | | | separating metallic tubes from the ones that are |
| Carbon nanotubes are fullerene-related structures | | | | semi-conducting. Common synthesis procedures |
| which consist of graphene[1] cylinders closed at | | | | produce spaghetti-like mixtures of nanotube ropes |
| either end with caps containing pentagonal rings. | | | | that are unusable for semiconductor applications |
| Examples of Nanotubes are Single-layer nanotubes | | | | because they contain both types of tubes. |
| and nanotube "ropes" and nanohorns. Carbon | | | | Nanotubes can be metals or semiconductors, and |
| nanotubes, therefore, are rolled-up sheets of | | | | because of their strong chemical bonds and |
| graphite - i.e. the same material that is used in | | | | satisfied valences[2], the materials boast high |
| pencils. A sheet of graphite is composed of | | | | thermal, mechanical, and chemical stability. In |
| carbon atoms arranged in a flat hexagonal pattern | | | | addition, carbon nanotubes can be efficient |
| similar to chicken wire mesh. | | | | conductors as a result of their tiny diameters, |
| Nanoelectronic has witnessed a shift towards | | | | long lengths, and defect-free structures that |
| molecular systems in recent years. Though the | | | | make them ideal one-dimensional systems. |
| term molecular electronic is rather an old one, it is | | | | Theoretical models have predicted that nanotubes |
| only recently that single molecules have become | | | | could behave as ideal one-dimensional "quantum |
| the focus of interest, as nanoelectronic start to | | | | wires" with either semi conducting or metallic |
| surface. This was triggered by research on | | | | behaviours. Study of Transmission Electron |
| carbon nanotubes. But before the carbon | | | | Micrograph (TEM) images, however, has indicated |
| nanotubes entered the scene, molecular electronic | | | | that the nanotubes also incorporate kinks and |
| was the science of organic polymers, their | | | | defects into their walls |
| synthesis, processing and doping. With carbon | | | | Progress in nanotubes synthesis has now yielded |
| nanotubes, we finally have a model system at | | | | single-walled nanotubes (SWNTs) with well-defined |
| hand that is equally of interest for chemists, | | | | diameters, bringing the experimental situation |
| material scientists and physicists. However, carbon | | | | much closer to that of the theoretical models. |
| nanotubes are supramolecular objects for a | | | | Recent measurements indicate that these |
| chemist; they are one-dimensional solids for a | | | | materials do behave like one-dimensional wires. |
| physicist. In the future, more of this | | | | The SWNTs should also be more sensitive to |
| supramolecular structure will be studied on a single | | | | defects, to the extent that defects may |
| molecule level. | | | | dominate the transport characteristics. In this |
| Theorists have shown that nanotubes can be | | | | work, an STM tip was used as a sliding electrical |
| conducting or insulating depending on their | | | | contact to probe the length-dependence of |
| structure. Therefore, this may lead to applications | | | | SWNT conductance. Although atomic defects |
| in nanoelectronic. | | | | were not directly imaged, sharp conductance |
| Wires are not possible for use in nanoelectronic, | | | | transitions and hetero-junction behaviours in the |
| because they are susceptible to thinning and | | | | nanotube conductance are suggestive of the |
| breakage. Despite recent interest in carbon | | | | signatures of nanotube defects. |
| nanotubes, they have variable electronic | | | | Altawell. |
| properties, depending on their orientation, reducing | | | | |