As we are moving rapidly towards the twenty first century, the development within the world of science and technology is moving even faster. Just think of the everyday situation, where you go to a store to buy yourself a computer, and as you leave the store, noticing the door closing behind you, it occurs to you that the value of your loving computer already has decreased. This is caused by the tremendous research in the microelectronics, which has changed a lot of things in the last twenty years or so. It has opened up a great range of new possibilities, as the size of the electrical devices has diminished. About every second year, the amount of transistors placed on a micro chip doubles, but it is limited and soon a new technique has to be developed to carry on building faster computers. The silicon is the very heart of the microelectronics and will probably still be of great importance as we pass the change of millennium. However, experiments indicate a growing field for a new technique based on molecules. This is due to the scientists, who try to bring us from the micro scale to the nano scale, though it is another matter in the periodic table that is used, Carbon. This leads us to the main issue of this project. Carbon nanotubes describes a specific topic within solid state physics, but is also of interest in other sciences like chemistry or biology, actually the topic has coating boundaries, because we are on the molecule level. The carbon nanotubes have in the recent years become more and more popular to the scientists. Initially, it was the spectacularly electronic properties, that were the basis for the great interest, but eventually other remarkable properties were discovered too.
2.1 SUMMARY OF CARBON NANOTUBES
Carbon nanotubes are wires of pure carbon with nanometer diameters and lengths of many microns. A single-walled carbon nanotube (SWNT) may be thought of as a single atomic layer thick sheet of graphite (called graphene) rolled into a seamless cylinder. Multi -walled carbon nanotubes (MWNT) consist of several concentric nanotube shells. Understanding the electronic properties of the graphene sheet helps to understand the electronic properties of carbon nanotubes. Graphene is a zero-gap semiconductor; for most directions in the graphene sheet, there is a bandgap, and electrons are not free to flow along those directions unless they are given extra energy. However, in certain special directions graphene is metallic, and electrons flow easily along those directions. This property is not obvious in bulk graphite, since there is always a conducting metallic path which can connect any two points, and hence graphite conducts electricity. However, when graphene is rolled up to make the nanotube, a special direction is selected, the direction along the axis of the nanotube. Sometimes this is a metallic direction, and sometimes it is semiconducting, so some nanotubes are metals, and others are semiconductors. Since both metals and semiconductors can be made from the same all-carbon system, nanotubes are ideal candidates for molecular electronics technologies. In addition to their interesting electronic structure, nanotubes have a number of other useful properties. Nanotubes are incredibly stiff and tough mechanically - the world's strongest fibers. Nanotubes conduct heat as well as diamond at room temperature. Nanotubes are very sharp, and thus can be used as probe tips for scanning-probe microscopes, and field-emission electron sources for lamps and displays. 1.2
ADVANTAGES OF CARBON NANOTUBES
1. Carbon nanotubes are useful in the area of electronic products including nano transistors, nano diodes, plasma displays, quantum computers and many more. 2. The development of more effective energy-producing, energy-absorbing, and energy storage products in smaller and more efficient devices is possible with carbon nanotubes e.g. batteries, fuel cells, and solar cells....
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