Single armchair

Fig. 17. Schematic models for a single-wall carbon nanotubes with the nanotube axis normal to (a) the 6 = 30° direction (an armchair (n, n) nanotube), (b) the 0 = 0°...

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. 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.

Fig. 2. By rolling up a graphene sheet (a single layer of ear-bon atoms from a 3D graphite erystal) as a cylinder and capping each end of the eyiinder with half of a fullerene molecule, a fullerene-derived tubule, one layer in thickness, is formed. Shown here is a schematic theoretical model for a single-wall carbon tubule with the tubule axis OB (see Fig. 1) normal to (a) the 6 = 30° direction (an armchair tubule), (b) the 6 = 0° direction (a zigzag tubule), and (c) a general direction B with 0 < 6 < 30° (a chiral tubule). The actual tubules shown in the figure correspond to (n,m) values of (a) (5,5), (b) (9,0), and (c) (10,5).

The electronic properties of single-walled carbon nanotubes have been studied theoretically using different methods[4-12. It is found that if n — wr is a multiple of 3, the nanotube will be metallic otherwise, it wiU exhibit a semiconducting behavior. Calculations on a 2D array of identical armchair nanotubes with parallel tube axes within the local density approximation framework indicate that a crystal with a hexagonal packing of the tubes is most stable, and that intertubule interactions render the system semiconducting with a zero energy gap[35]. 

There remains the question why activated carbons differ from carbons heat-treated at 1200° with respect to the relative position of the carboxyl groups. Perhaps this difference is based on the structure of the edges of the carbon layers. Hennig (87, 88) found, by observations with single crystals of graphite, that after oxidation with dry oxygen the armchair configuration of the periphery resulted ... 

Figure 2. Calculations of the radial breathing mode frequency of (10,10) armchair single-walled nanotubes a) isolated tubes b) bundle of 7 tubes and c) bundle with an infinity of tubes.

Fig. 14.3 Representative structures of (a) armchair, (b) zigzag, and (c) chiral type single-walled carbon nanotubes...

Fig. 14.9 The variation of H-chemisorption energies at the B3LYP/6-31G(d) level for the chemisorption of one and two hydrogen atoms on the external surface of (3, 3), (4, 4), (5, 5) and (6, 6) armchair single-walled carbon nanotubes (SWNTs) of 9 and 15 carbon layers...

T.C. Dinadayalane et al., Chemisorption of hydrogen atoms on the sidewalls of armchair single-walled carbon nanotubes. J. Phys. Chem. C 111, 7376 (2007)... 

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