Chirality, single walled SWNTs

Carbon nanotubes can be single walled (SWNT) or multi-walled (MWNT). SWNTs can be metallic or semiconducting, depending on their chirality. MWNTs contain several walls, so in combination they will tend to be metallic. In addition, as the band gap of semiconducting tubes varies inversely with their diameter, the larger diameter of MWNTs means that effectively most walls are metallic. 

Carbon nanotubes prepared by several methods are mixed with nanoparticles, amorphous carbon, fullerenes, and other contaminants [1576]. Nanotubes isolated from the mixture contain single-walled (SWNT) as well as multiwalled (MWNT) nanotubes. In general, the diameter of a SWNT is on the order of several nanometers, but the length can be several microns. Thus far, spectroscopic (mainly Raman) studies have been focused on SWNTs of small diameters (<2nm) that become metallic or semiconducting depending on their diameter and chirality. Chemical and physical... 

Carbon nanotubes can have one, two, or many sidewalls and are referred to as single-, double-, or multi-walled nanotubes (SWNT, DWNT, or MWNT). Nanotubes can be metallic, or semi-conducting depending on the chirality of the tube. Single-walled nanotubes (SWNT) are about 1 nm in diameter, and hundreds of nanometers long, whereas multi-walled nanotubes (MWNT) are like nested... 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

Ceo = Fullerene SWNTs = Single-walled carbon nanotubes MWNTs = Multiwalled carbon nanotubes DWNTs = Double-walled carbon nanotubes CNTs = carbon nanotubes TEM = Transmission electron microscopy HRTEM = High-resolution transmission electron microscopy SEM = Scanning electron microscopy AFM = Atomic force microscopy Ch = Chiral vector CVD = Chemical vapor deposition HiPco process = High-pressure disproportionation of CO RBM = Radical breathing vibration modes DOS = Electronic density of states. 

Single-walled carbon nanotubes (SWNTs) can behave as semiconductors or metals, depending on their chirality. Therefore, vibrational spectroscopy is indispensable for characterizing chemical stmctures. Especially, resonance Raman spectroscopy is ccai-sidered to be one of most powerful tools, which provides us rich information about nanotube diameters or defect densities [10, 27, 39]. However, much more detailed characterization is required for further development of carbon-based nanotechnology. 

The imaging of single-walled carbon nanotubes (SWNTs) has become the most frequent application of TERS [23-25]. SWNTs have generated intense interest due to their potential applications in nanotechnology. Four types of Raman mode are usually observed in the TER spectra of SWNT the radial breathing modes (RBM), two graphitic bands (G, G ), and the disordered (D) band. The positions of these bands are vibrational signatures of the state of the SWNT, for example, its defect density, chirality, and so on. 

P20.36 Single-walled carbon nanolubes (SWNT) may be either conductors or semiconductors depending upon the tube diameter and the chiral angle of the fused benzene rings with respect to the lube axis. Van der Waals forces cause SWNT to slick together in clumps, which are normally mixtures of conductors and semiconductors. SWNT stick to many surfaces and they bend, or drape, around nano-sized features that are upon a surface. 

It has been shown that resonance Raman spectra can give complete structural information on an individual carbon (n, m) single-walled nanotube (SWNT). For example, a radial breathing mode at 156 cm for 785 nm laser excitation is assigned to a (13,10) metallic chiral nanotube on a silicon/Si02 surface. " The Raman spectra of individual carbon SWNTs in solution show radial mode frequencies about 10 cm higher than for tubes in a rope. " " ... 

Beside their well-known extra-high mechanical properties, single-walled carbon nanotubes (SWNTs) offer either metallic or semiconductor characteristics based on the chiral structure of fullerene. They possess superior thermal and electrical properties so SWNTs are regarded as the most promising reinforcement material for the next generation of high performance structural and multifunctional composites, and evoke great interest in polymer based composites research. The SWNTs/polymer composites are theoretically predicted to have both exceptional mechanical and functional properties, which carbon fibers cannot offer [105]. 

Carbon nanotubes are classified as single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). A SWNT can be visualized as a grapheme sheet that has been rolled into a hollow cylinder with ends caps. So the atomic structure of SWNT can be described by the chiral vector and the chiral angle 6 (see Fig. 23.5) given by Refs. [70-77] ... 

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