Nanotechnology and Carbon Nanotube Promises

Nanotechnology is a technology that owes its basis on the prefix nano, a Greek word, which means (dwarf) billionth (1 x 10-9) meter dimensions. It is a relatively new technology that deals, studies or possesses the ability to systematically organise and manipulate properties and behaviour of matter and even builds matter at the atomic and molecular levels. It may be seen as the next technological rush since the Silicon Valley outburst in electronic miniaturisation, and the emerging cutting-edge technology. It is certainly setting the pace for the creation of functional devices, manufacturing and fabrication, materials and systems at the molecular level, atom by atom, to create large structures with fundamentally precise and specific molecular organisation. Two interrelated specialities in the manufacturing industry that point at nanotechnology as a common focus in their trend of developments are miniaturisation and ultra-precision processing, because both are moving towards dimensions that lie in several nanometer range. According to Rocco, three basic attributes of nanotechnology are: (1) at least one dimension of 1-100 nm is present, (2) there are processes that exhibit fundamental control over the physical and chemical characteristics of structures at molecular scales, and (3) the molecular structures otherwise known as nanostructured materials can be combined into larger structures, that are appreciable to the ordinary human vision. A promising group of nanostructured materials is the nanotubes, which are currently fabricated from various materials such as boron nitride, molybdenum, carbon (carbon nanotube), etc. However, at the moment, carbon nanotubes seem to be superior and most important due to their unique nanostructures with interesting properties, which suit them to a tremendously diverse range of applications in micro- or nanoscale electronics, biomedical devices, nanocomposites, gas storage media, scanning probe tips, etc.

Carbon nanotubes can be described as graphene sheets rolled into seamless cylindrical shapes as presented in Fig. 10.1 (Ebbesen 1994; Poole and Owens 2003) with such a small diameter that the aspect ratio (length/diameter) is large enough to become a one-dimensional structure in terms of electronic transmission. Since its discovery in 1991 by Iijima while experimenting on fullerene and looking into soot residues, two types of nanotubes have been made, which are single walled carbon nanotubes (SWNTs) and multi walled carbon nanotubes (MWNTs). SWNT consists only of a single graphene sheet with one atomic layer in thickness, while MWNT is formed from 2 to several tens of graphene sheets arranged concentrically into tube structures. The SWNTs have three basic geometries, armchair, zigzag and chiral forms as presented in Fig. 10.1.

Fig. 10.1. Graphics showing types of carbon nanotubes (a) SWNT: from top is the armchair, zigzag and bottom, chiral form; (b) double wall helicoidal form typifying MWNT (Ebbesen 1997; Poole 2003)

Fig. 10.1. Graphics showing types of carbon nanotubes (a) SWNT: from top is the armchair, zigzag and bottom, chiral form; (b) double wall helicoidal form typifying MWNT (Ebbesen 1997; Poole 2003)

They are promising one-dimensional (1D) periodic structure along the axis of the tube, where dispersion relations predict interesting electronic characteristics. Electronic transport confinement in radial direction is maintained by the monolayer thickness of the nanotubes, while circumferentially, periodic boundary conditions are imposed leading into 1-D dispersion relations for electrons and photons in SWNTs. Various experiments and simulations have estimated that about one-third of the nanotubes are metallic and two-third semiconducting as a result of the tube diameter and the chiral angle between its axis and the zigzag direction. Quite a number of resistivity measurements on MWNTs had revealed that some are metallic as much as graphite, and others are semiconducting having resistivity value in the order of 5 greater than the former. Experiments had affirmed that armchair carbon nanotubes are metallic (Ebbesen 1997). Multi walled nanotubes on the other hand, not only have shown metallic and semiconducting properties, they are also being used for fuel storage such as hydrogen and methane (Iyuke 2001, 2004). It is therefore interesting to infer that carbon nanotube is emerging as a building block for nanotechnology, nanoelectronics, nanomanufacturing and nanofabrication, etc.

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Brain Blaster

Brain Blaster

Have you ever been envious of people who seem to have no end of clever ideas, who are able to think quickly in any situation, or who seem to have flawless memories? Could it be that they're just born smarter or quicker than the rest of us? Or are there some secrets that they might know that we don't?

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