Zigzag CNTs

Figure 14.5 Allowed wavevector lines leading to semiconducting and metallic CNTs and examples of band structures for semiconducting and metallic zigzag CNTs. (Adapted with permission from ref. 21 Copyright 2006 Institute of Physics.)...

Fig. 1 demonstrates the slow-down coefficient fi = k/Re(h) of the bundle surface wave in the terahertz (v = 2.5 THz) and infrared (v = 27 THz) ranges for different numbers of CNTs in the bundle. The calculations have been performed for the densely packed (21,0) zigzag CNTs. The coefficient increases 26 times with the N =900 and tends in thick bundles (with Rb > 25 nm) to 1 which is a characteristic for macroscopic metallic wires. The dependence of the slowdown coefficient on the bundle radius is linear up to Rb = 25 nm (see insert in Fig. 1). 

Fig. 7. The Il-orbital (tight-binding approximation) EB spectrum of the (9,0)-zigzag CNT. Note the independent symmetries of the EBs with respect to —k and Ei —E .

Fig. 8. The Il-orbital (tight-binding approximation) QEB spectrum of the (9,0)-zigzag CNT. o) = 0.037 a.u. ( 1.0 eV, A 1.2 p.m) and E = 0.05 a.u. ( 9 X 10 W/cm ). Note the independent symmetries of the QEBs with respect to —k and a (compare to Eig. 7), which appear due to the dipole and tight-binding approximations employed in the calculation.

Analytical analysis by exerting nonhnear Morse potential 0.94 for armchair (10,10) Mechanical properties of armchair and zigzag CNT ate investigated. The results show the atomic structure of CNT has a remarkable effect on stress- strain behavior... 

Sears and Batra [45] 2006 MM3 class n pair wise potential, FEM, equivalent continuum structures using Euler buckling theory Various zigzag CNTs 5 0 -350A — Buckling of axially compressed multiwaUed carbon nanotubes by using molecular mechanics simulations and developing continuum structures equivalent to the nanotubes... 

Consider the effect of the adsorption of atomic hydrogen on the response of single-walled zigzag CNTs to an external electric field applied along the x axis is directed along the axis of the CNT (Fig. 1.1). 

The electron diffusion coefficient D E) from the electric field in the single-walled zigzag CNT with adsorbed hydrogen atoms has a pronounced nonlinear character (Fig. 1.5). Increase of the field leads to an increase in first rate, and then to his descending to a stationary value. This phenomenon is observed for all systems with intermittent and limited electron dispersion law [17]. Electron diffusion coefficient can be considered constant in the order field amplitudes E 5x10 V/m. The maximum value of the diffusion coefficient for semiconductor CNTs observed at field strengths of the order ofE- 4.8x10 V/m. 

The method for theoretical calcrdation of the semiconducting zigzag CNT transport properties with adsorbed hydrogen atoms developed. Analytical expressions for the conductivity and the electron diffusion coefficient in zigzag CNT with hydrogen adatoms in the presence of an electric field. 

SWCNTs can be considered as rectangular strips of hexagonal graphite monolayers rolling up to cylinder tubes. Two types of SWCNTs with high symmetry are normally selected by researchers, which are zigzag SWCNTs and armchair SWCNTs. When some of the atomic bonds are parallel to the tube axis, the CNT is called a zigzag CNT, while if the bonds are perpendicular to the axis, it is called an armchair CNT, and for any other structures, they are called chiral CNTs, as shown in Fig. 16.6 [72]. 

Also analyzed the dependence of the conductivity o(E) on the intensity of the external electric E for CNT (10,0) type, containing different concentrations of hydrogen adatoms (Fig. 1.3). The increasing of the number of adsorbed atoms reduces the conductivity of zigzag CNT proportional to the number of localized adsorption bonds formed. When you add one hydrogen adatom... 

A hybrid atomistie/eontinuum mechanics method is established in the Feng et al. [70] study the deformation and fracture behaviors of CNTs in composites. The unit eell eontaining a CNT embedded in a matrix is divided in three regions, whieh are simulated by the atomic-potential method, the continumn method based on the modified Cauchy-Bom rule, and the classical continuum mechanics, respectively. The effect of CNT interaction is taken into account via the Mori-Tanaka effective field method of micromechanics. This method not only can predict the formation of Stone-Wales (5-7-7-5) defects, but also simulate the subsequent deformation and fracture process of CNTs. It is found that the critical strain of defect nucleation in a CNT is sensitive to its chiral angle but not to its diameter. The critical strain of Stone-Wales defect formation of zigzag CNTs is nearly twice that of armchair CNTs. Due to the constraint effect of matrix, the CNTs embedded in a composite are easier to fracture in comparison with those not embedded. With the increase in the Young s modulus of the matrix, the critical breaking strain of CNTs decreases. 

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