Armchair CNTs

Fig. 3. Raman intensities as a function of the sample orientation for the (10, 10) armchair CNT. As shown on the right, 0 and 62 are angles of the CNT axis from the z axis to the x axis and the y axis, respectively. 63 is the angle of the CNT axis around the z axis from the x axis to the y axis. The left and right hand figures correspond to the VV and VH polarisations [12].

In the paper we continue the researches started in [1] where the possibility of existence of T-junctions of (6,6) CNT with graphite monolayer was shown. Here some samples of T-junctions of carbon zigzag and armchair CNTs are investigated. Experimental and theoretical aspects of perspectives of using of CNT T-junctions as elements of future nanoscale electronic devices are considered earlier in [4-10]. 

Fig. 4. Unit cell of the (5,5)-armchair CNT. The 2N = 20 atoms are used to construct the tight-binding Bloch states. = IT2I is the unit cell length.

Fig. 5. The Il-orbital (tight-binding approximation) EB spectrum of the (5,5)-armchair CNT. Note the independent symmetries of the EBs with respect to —k and Ei -Ef.

Fig. 6. The Il-orbital (tight-binding approximation) QEB spectrum of the (5,5)-armchair CNT. o) = 0.037 a.u. ( 1.0 eV, A 1.2 p.m) and Eq = 0.05 a.u. ( 9 X 10 W/cm ). Note the independent symmetries of the QEBs with respect to k<- —k and (compare to Fig. 5), which appear due to the dipole and tight-binding approximations employed in the calculation.

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]. 

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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