ABSTRACT
Carbon nanotubes, first discovered by Sumio Iijima in 1991,18are a subset of the family of fullerene structures and are the most exciting and researched nanotube structures due to their exceptional physical properties and application prospects. The physical properties of CNTs depend on the atomic architecture, tube diameter, and length. From the structural perspective, CNTs are composed of seamless covalent C-C hexagonal networks and are formed through rolling graphene sheets into cylinders, as shown in Fig. 5.1a. The rolling direction of the graphene nanosheet is denoted by the chirality vector (n, m). The indexes n and m of the chirality vector denote the number of unit vectors along the two directions in the honeycomb lattice of graphene nanosheet. The nanotubes are called “zig-zag” if m = 0, or “arm-chair” if m = n. CNTs can crystallize in both single-walled and multi-walled nanophases. Multi-walled carbon nanotubes (MWCNTs) are simply composed of multiple concentric single-walled carbon nanotubes (SWCNTs), as illustrated in Fig. 5.1b. The spacing between the neighboring graphite layers in MWCNTs is ~0.335 nm. Two adjacent layers interact with each other via van der Waals interactions. Figure 5.1c shows two representative high-resolution transmission electron microscopy (HRTEM) images of SWCNTs (left) and MWCNTs (right), respectively.19 The methods to synthesize CNTs include electric arc-discharge,20,21laser ablation,22 and catalytic chemical vapor deposition (CVD)
methods.23 It is noted that the CVD method is capable of producing directionally aligned CNTs by applying external electric fields.24
