Chirality, single walled carbon nanotubes

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].

Rikken proposed that the EMCA effect could also result from the simultaneous application of a magnetic field and a current to a crystal with an enantiomorphous space group, and that it is a universal property. He showed the existence of this effect in the case of chiral single-walled carbon nanotubes.For most of the investigated tubes, a dependence of the resistance is observed that is odd in both the magnetic field and the current. These observations confirm the existence of EMCA not only for a macroscopic chiral conductor but also for a molecular conductor with chirality on the microscopic level. 

Chang, T. (2007). Torsional Behavior of Chiral Single-Walled Carbon Nanotubes is Loading Direction Dependent. Appl. Phys. Lett., 90, 201910. 

Bandow S, Asaka S, Saito Y, Rao AM, Grigorian L, Richter E, Eklund PC (1998) Effect of the growth temperature on the diameter distribution and chirality of single-wall carbon nanotubes. Physical Review Letters 80 3779-3782. 

Sundaram RM, Koziol KKK, Windle AH. Continuous direct spinning of fibers of single-walled carbon nanotubes with metallic chirality. AdvMater. 2011 Nov 16 23(43) 5064-8. 

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

G. L. J. A. Rikken, Magneto-chiral Anisotropy in Charge Transport through Single-walled Carbon Nanotubes, J. Chem. Phys. 2002, 117, 11315-11319. 

In single-wall carbon nanotubes, various chiralities are realized from arm-chair type through zigzag type to chiral type (Figure 2.35), which are known to govern their properties [15]. 

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-... 

Single-walled carbon nanotubes comprise rolled sheets of sp graphene carbon, which form well-defined cylinders with diameters in the range 1 to 2 run. The diameter depends on the synthesis conditions as does the orientation of the six-membered carbon rings with respect to the nanotube axis. Achiral zigzag, achiral armchair, or chiral nanotubes can be obtained as illustrated in Figure 16. ... 

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. 

A series of supported chiral VO(salen) complexes anchored on silica, single-wall carbon nanotube, achvated carbon or ionic liquids have been prepared through the simple methods based on the addition of mercapto groups to terminal C=C double bonds (Scheme 7.17) [58]. The four recoverable catalysts and the standard VO(salen) complex 37 were tested for the enantioselechve cyanosilylation of benzaldehyde using trimethylsilyl cyanide (Table 7.9). It should be noted that the ionic liquid-supported IL-VO(salen) showed the highest catalyhc achvity, though the ee-value was considerably reduced compared to the soluble 37 in [bmim][PF6] (entries 4 and 5). 

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. 

For single-walled carbon nanotubes, it is also possible to predict the stracture of their infrared spectra. It turns out that depending on the structure of the tube under consideration, a different number of bands should be IR-active. Zig-zag nanotubes possess IR-active A2 - and two Eiu-modes for armchair tubes there are three Eia-modes, and chiral species exhibit one A2- and five Ej-modes. The signals can be expected to lie chiefly in one of two spectral regions about 870 and 1590 cm" . The first of these is always Raman-inactive, whereas for the latter this is only true... 

G. Mpourmpakis, G.E. Froudakis, G.P. Lithoxoos and J. Samios, Effect of curvature and chirality for hydrogen storage in single-walled carbon nanotubes a combined ab initio and Monte Carlo investigation . The Journal of Chemical Physics, 126, 144704 (2007). 

Let us fix the parameter 2A = 0.34 nm which is equal to the graphite inter-layer separation. The chirality and the radius of single-wall carbon nanotube are uniquely specified by the chiral vector C/, = iai +112 2 - ( i. 2)> where ni,ri2 are integers and ai, a2 are the unit cell basis vectors of graphite [1]. The chiral vector C is a circumferential lattice vector defined on nanotube surface, and C is perpendicular to the tube axis. For armchair nanotubes n =ri2 = n, and the tube radius r is defined by r = C/, /2ti = a f3n/2n, where a = 0.249 nm is the lattice constant for graphite. These values of r are used in our calculations. 

Single-walled carbon nanotubes (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. 

---