CNT CARBON NANOTUBE

Carbon nanotubes(CNTs) are allotropes of carbonwith a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, [ 1 ]significantly larger than for any other material. These cylindrical carbon moleculeshave unusual properties, which are valuable for nanotechnology, electronics, opticsand other fields of materials scienceand technology. In particular, owing to their extraordinary thermal conductivityand mechanical and electricalproperties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber) baseball bats, golf clubs, or car parts. [ 2 ] Nanotubes are members of the fullerenestructural family. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete (" chiral") angles, and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metalor semiconductor. Nanotubes are categorized as single-walled nanotubes(SWNTs) and multi-walled nanotubes(MWNTs). Individual nanotubes naturally align themselves into "ropes" held together by van der Waals forces, more specifically, pi-stacking. Applied quantum chemistry, specifically, orbital hybridizationbest describes chemical bonding in nanotubes. The chemical bondingof nanotubes is composed entirely of sp 2 bonds, similar to those of graphite. These bonds, which are stronger than the sp 3 bondsfound in alkanesand diamond, provide nanotubes with their unique strength. Types of carbon nanotubes and related structures Terminology There is no consensus on some terms describing carbon nanotubes in scientific literature: both "-wall" and "-walled" are being used in combination with "single", "double", "triple" or "multi", and the letter C is often omitted in the abbreviation; for example, multi-walled carbon nanotube (MWNT) Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices (n,m). The integersnandmdenote the number of unit vectorsalong two directions in the honeycomb crystal latticeof graphene. Ifm= 0, the nanotubes are called zigzag nanotubes, and ifn=m, the nanotubes are called armchair nanotubes. Otherwise, they are called chiral. The diameter of an ideal nanotube can be calculated from its (n,m) indices as follows wherea= 0.246 nm. SWNTs are an important variety of carbon nanotube because most of their properties change significantly with the (n,m) values, and this dependence is non-monotonic (see Kataura plot). In particular, their band gapcan vary from zero to about 2 eV and their electrical conductivity can show metallic or semiconducting behavior. Single-walled nanotubes are likely candidates for miniaturizing electronics. The most basic building block of these systems is the electric wire, and SWNTs with diameters of an order of a nanometer can be excellent conductors. [ 3 ] [ 4 ]One useful application of SWNTs is in the development of the first intermolecular field-effect transistors(FET). The first intermolecular logic gateusing SWCNT FETs was made in 2001. [ 5 ]A logic gate requires both a p-FET and an n-FET.