Single walled nanotubes

The field of fullerene chemistry expanded in an unexpected direction in 1991 when Sumio lijima of the NEC Fundamental Research Laboratories in Japan discovered fibrous carbon clusters in one of his fullerene preparations This led within a short time to substances of the type portrayed in Figure 11 7 called single-walled nanotubes The best way to think about this material IS as a stretched fullerene Take a molecule of Ceo cut it in half and place a cylindrical tube of fused six membered carbon rings between the two halves... 

Fig. 8. A, Structure of a single wall nanotube B, schematic illustration of arm-chair, zigzag and spiral forms of single wall nanotubes the arrows denote the tubule axis.

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]. 

Fig. 15. Histogram of the single-wall nanotube diameter distribution for Fe-catalyzed nanotubes [154], A relatively small range of diameters are found, the smallest diameter corresponding to that for the fullerene Ceo.

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. 

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].

Much of the experimental observations on carbon nanotubes thus far have been made on multi-wall tu-bules[15-19]. This has inspired a number of theoretical calculations to extend the theoretical results initially obtained for single-wall nanotubes to observations in multilayer tubules. These calculations for multi-wall tubules have been informative for the interpretation of experiments, and influential for suggesting new re-... 

We have carried out a series of geometry optimizations on nanotubes with diameters less than 2 nm. We will present some results for a selected subset of the moderate band gap nanotubes, and then focus on results for an example chiral systems the chiral [9,2] nanotube with a diameter of 0.8 nm. This nanotube has been chosen because its diameter corresponds to those found in relatively large amounts by Iijima[7] after the synthesis of single-walled nanotubes. 

Experimental measurements to test these remarkable theoretical predictions of the electronic structure of carbon nanotubes are difficult to carry out because of the strong dependence of the predicted properties on tubule diameter and chirality. Ideally, electronic or optical measurements should be made on individual single-wall nanotubes that have been characterized with regard to diameter and chiral angle. Further ex-... 

Abstract—Experimental and theoretical studies of the vibrational modes of carbon nanotubes are reviewed. The closing of a 2D graphene sheet into a tubule is found to lead to several new infrared (IR)- and Raman-active modes. The number of these modes is found to depend on the tubule symmetry and not on the diameter. Their diameter-dependent frequencies are calculated using a zone-folding model. Results of Raman scattering studies on arc-derived carbons containing nested or single-wall nanotubes are discussed. They are compared to theory and to that observed for other sp carbons also present in the sample. 

Small diameter, single-wall nanotubes have been synthesized with metal catalysts by maintaining a dc arc (30 V, 95 A) between two electrodes in —300 Torr of He gas.[21,22] The metal catalyst (cobalt[22] or... 

In Fig. 11 we show the Raman speetrum of earbo-naeeous soot eontaining l-2 nm diameter, singlewall nanotubes produeed from Co/Ni-eatalyzed carbon plasma[28). These samples were prepared at MER, Inc. The sharp line components in the spectrum are quite similar to that from the Co-catalyzed carbons. Sharp, first-order peaks at 1568 cm and 1594 cm , and second-order peaks at -2680 cm" and -3180 cm are observed, and identified with single-wall nanotubes. Superimposed on this spectrum is the contribution from disordered sp carbon. A narrowed, disorder-induced D-band and an increased intensity in the second-order features of this sample indicate that these impurity carbons have been partially graphitized (i.e., compare the spectrum of carbon black prepared at 850°C, Fig. Id, to that which has been heat treated at 2820°C, Fig. Ic). 

Fig. 11. Raman spectrum (T = 300 K) of arc-derived carbons containing single-wall nanotubes generated in a Ni/Co-catalyzed dc arc (after ref. [42 ).

Finally, in second order, the Raman feature at — 3180 cm" observed in Co- and Ni/Co-catalyzed single-wall nanotube corresponds to a significantly downshifted 2 x fjg mode, where E g represents the mid-zone (see Figs, la and lb) frequency maximum of the uppermost optic branch seen in graphite at 3250 cm". ... 

M. and Lefrant, S., Bundles of single wall nanotubes produced by the electric arc technique. In Electron Microscopy ICEM-14, Vol. 3, ed. H. 

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