Carbon nanotubes Diameter

Characterization of the MW-CNT by TEM and TG techniques indicated that the higher thermal stability and the smaller carbon nanotube diameter are obtained for the samples containing a Co/Co+Fe atomic ratio < 0.35 (Table 1). 

FIGURE 8.60 Scanning electron microscope (SEM) image of well-aligned carbon nanotubes (diameter, 50-70 nm length, 3-4 xm) grown on a titanium substrate by plasma-enhanced chemical vapor deposition. (From Chen, J.H., et al., Appl. Phys. A, 73, 129, 2001. With permission.)... 

SWNT Singlewall carbon nanotube (diameter 1 nm) CNF Carbon nanofiber (diameter 200 nm)... 

Nasibulin AG, Pikhitsa PV, Jiang H, Kauppinen EL Correlation between catalyst particle and single-walled carbon nanotube diameters. Carbon 2005 43 2251-7. 

SAMPLE CALCULATION Carbon Nanotube Diameter. We will estimate the diameter of the (3,3) carbon nanotube to be prepared in Fig. 11.7, assuming a carbon-carbon bond length of 1.42 A. The diameter works out to only... 

Siegal MP, Overmyer DL, Provencio PP, Precise control of multiwall carbon nanotube diameters using thermal chemical vapor deposition. Applied Physics Letters, 2002. 80(12) 2171-2173. 

The coimection between carbon nanotubes and other fullerenes has been defined by the observation that the nanotubes were closed by fullerene-like caps or hemispheres. It is interesting to observe that the smallest reported carbon nanotube diameter is the same as the diameter of C60. This is important in evaluating the minimum dimension of carbon nanostructures. It is necessary to identify all types of nanoparticles and nanostructures of the fullerene family (multiwall and/or single-wall nanotubes, carbon-encapsulated metal nanoparticles, fullerene black and soot, carbon onion, nanowhiskers, etc.). For each nanostructure it is possible to define a set of physical and chemical properties and subsequent applications. It is also interesting to explore the interrelationships between the various nanostructured carbon forms, as well as their relation to the traditional forms of ordered carbon atoms such as diamond and graphite. Carbon is a unique material and can be a good metallic... 

RBM (radial breathing mode at -130-300cm" ) represents, in the low-frequency region of the Raman spectra, the radial breathing mode of carbon nanotubes. The peak position of the RBM ( cm ) is related to the single-wall carbon nanotube diameter (d) by the following relation ... 

Kanzow, H, Lenski, C and Ding, A (2001), Single-wall carbon nanotube diameter distributions calculated from experimental parameters , Phys Rev B, 63, 125402-125407. 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

The earliest observations of carbon nanotubes with very small (nanometer) diameters [151, 158, 159] are shown in Fig. 14. Here we see results of high resolution transmission electron microscopy (TEM) measurements, providing evidence for m-long multi-layer carbon nanotubes, with cross-sections showing several concentric coaxial nanotubes and a hollow core. One nanotube has... 

Fig. 14. High resolution TEM observations of three multi-wall carbon nanotubes with N concentric carbon nanotubes with various outer diameters do (a) N = 5, do = 6.7 nm, (b) N = 2, do = 5.5 nm, and (c) N = 7, do = 6.5 nm. The inner diameter of (c) is d = 2.3 nm. Each cylindrical shell is described by its own diameter and chiral angle [151].

The diameter distribution of single-wall carbon nanotubes is of great interest for both theoretical and experimental reasons, since theoretical studies indicate that the physical properties of carbon nanotubes are strongly dependent on the nanotube diameter. Early results for the diameter distribution of Fe-catalyzed single-wall nanotubes (Fig. 15) show a diameter range between 0.7 nm and 1.6 nm, with the largest peak in the distribution at 1.05 nm, and with a smaller peak at 0.85 nm [154]. The smallest reported diameter for a single-wall carbon nanotube is 0.7 nm [154], the same as the diameter of the Ceo molecule (0.71 nm) [162]. 

Whereas multi-wall carbon nanotubes require no catalyst for their growth, either by the laser vaporization or carbon arc methods, catalyst species are necessary for the growth of the single-wall nanotubes [156], while two different catalyst species seem to be needed to efficiently synthesize arrays of single wall carbon nanotubes by either the laser vaporization or arc methods. The detailed mechanisms responsible for the growth of carbon nanotubes are not yet well understood. Variations in the most probable diameter and the width of the diameter distribution is sensitively controlled by the composition of the catalyst, the growth temperature and other growth conditions. 

Structurally, carbon nanotubes of small diameter are examples of a onedimensional periodic structure along the nanotube axis. In single wall carbon nanotubes, confinement of the stnreture in the radial direction is provided by the monolayer thickness of the nanotube in the radial direction. Circumferentially, the periodic boundary condition applies to the enlarged unit cell that is formed in real space. The application of this periodic boundary condition to the graphene electronic states leads to the prediction of a remarkable electronic structure for carbon nanotubes of small diameter. We first present... 

The ID electronic energy bands for carbon nanotubes [170, 171, 172, 173, 174] are related to bands calculated for the 2D graphene honeycomb sheet used to form the nanotube. These calculations show that about 1/3 of the nanotubes are metallic and 2/3 are semiconducting, depending on the nanotube diameter di and chiral angle 6. It can be shown that metallic conduction in a (n, m) carbon nanotube is achieved when... 

Fig. 19. The energy gap FJ, for a general chiral single-wall carbon nanotube as a function of 100 kidt, where dt is the nanotube diameter in A [179].

Early transport measurements on individual multi-wall nanotubes [187] were carried out on nanotubes with too large an outer diameter to be sensitive to ID quantum effects. Furthermore, contributions from the inner constituent shells which may not make electrical contact with the current source complicate the interpretation of the transport results, and in some cases the measurements were not made at low enough temperatures to be sensitive to 1D effects. Early transport measurements on multiple ropes (arrays) of single-wall armchair carbon nanotubes [188], addressed general issues such as the temperature dependence of the resistivity of nanotube bundles, each containing many single-wall nanotubes with a distribution of diameters d/ and chiral angles 6. Their results confirmed the theoretical prediction that many of the individual nanotubes are metallic. 

Fig. 23. Experimental room temperature Raman spectrum from a sample consisting primarily of bundles or ropes of single-wall nanotubes with diameters near that of the (10,10) nanotube. The excitation laser wavelength is 514.5 nm. The inset shows the lineshape analysis of the vibrational modes near 1580 cm . SWNT refers to singlewall carbon nanotubes [195].

Fig. 24. The armchair index n vs mode frequency for the Raman-active modes of single-wall armchair (n,n) carbon nanotubes [195]. From Eq. (2), the nanotube diameter is given by d = Ttac-cnj-K.

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