What are Carbon Nanotubes?
Carbon nanotubes are large molecules of pure carbon that are long and thin and shaped like tubes, about 1-3 nanometers (1 nm = 1 billionth of a meter) in diameter, and hundreds to thousands of nanometers long. As individual molecules, nanotubes are 100 times stronger-than-steel and one-sixth its weight. Some carbon nanotubes can be extremely efficient conductors of electricity and heat; depending on their configuration, some act as semi-conductors. Why are they important? Some people believe that nanotubes are one of nanotechs most promising molecular building blocks because they exhibit unique properties with a wide range of potential commercial applications. Industry enthusiasts believe that carbon nanotubes will radically improve the performance of tiny sensors, electronic and optical devices, catalysts, batteries, fuel cells, solar cells and drug delivery vehicles. Currently 50% of all lithium batteries incorporate carbon nanofibers (wires spun from carbon nanotubes), which double
Carbon nanotubes are hexagonally shaped arrangements of carbon atoms that have been rolled into tubes. These tiny straw-like cylinders of pure carbon have useful electrical properties. They have already been used to make tiny transistors and one-dimensional copper wire. They were developed by using nanotechnology, a relatively new field that involves building electronic circuits and devices from single atoms and molecules. Nano means one thousand millionth of a unit. A nanometer is therefore one thousand millionth of a meter. The first nanofabrication experiments occurred in 1990 when individual xenon atoms were placed on a nickel substrate and used to spell out a company logo. One primary goal of nanotechnology is to build computer chips and other devices that are thousands of times smaller than they are now. Carbon nanotubes have enormous theoretical possibilities but have not lived up to the hype surrounding their development. Researchers have continued to look for ways to use them,
Dr. Meyyappan: Carbon nanotubes look like nanoscale cylinders, about 1 nm or so in diameter and a few microns long. Imagine rolling up a sheet of graphite into a tube; that is what we are talking about. There are a few procedures in the lab we are using to grow these structures. One method is called Chemical Vapor Deposition (CVD), which uses some hydrocarbon gases such as methane with a catalyst material like iron. In the second method, called plasma enhanced CVD, we use low temperature plasmas to grow nanotubes. NTB: What is it about the structure of nanotubes that makes them so versatile and functional to all of these diverse industries? Dr. Meyyappan: Carbon nanotubes are very unique in the sense that they have extraordinary mechanical properties. For example, compared to steel, nanotubes have a strength-to-weight ratio of 500. At the same time, nanotubes can be used to make a computer chip, because in addition to these wonderful mechanical properties they also have very exciting e
Carbon nanotubes are regarded as one of the prime examples of nanotechnology. Scientists are really excited by their properties and potential applications. Carbon nanotubes (CNTs) consist of rolled up sheets of graphite. Depending of the number of sheets and their structure, size and properties may vary. Structures consisting of one sheet of graphite (called graphene) are single wall carbon nanotubes (SWCNT), those consisting of two sheets double wall carbon nanotubes (DWCNT) and those consisting of multiple sheets are generally known as multi wall carbon nanotubes (MWCNT). These different structures show different properties (conductivity / semi conductivity / thermal conductivity, mechanical strength) and morphology (length, diameters, shape, …). Typically they measure a few nanometers in diameter and several microns in length. Parameters such as processability and handling, exposure potential as well as toxicological and ecotoxicological profile may also differ widely.
Carbon nanotubes (CNT’s) are single molecules, hollow and elongated like a fiber that incorporate the perfect atomic arrangement made famous by their predecessor, the buckyball – the remarkable closed cage of 60 symmetrically arranged carbon atoms that was recognized as a new form of carbon when it was discovered more than a decade ago. Carbon nanotubes are, effectively, buckyball structures played out as long strands rather than spheres. There length can be millions of times greater than their diameter. The periodic pattern has the periodicity of a helix (see Figures 1 and 2), though not as complex as the double helix responsible for life itself! A chemist might think of a carbon nanotube as a monoelemental polymer, a physicist might describe it as a one-dimensional single crystal with a unit cell that keeps on propagating and repeating while a mathematician would be interested in the symmetry and rigor of these structures and how nicely they obey Euler’s rule of polyhedra. These unus
