Essential Electronic Properties of Zigzag Carbon and Silicon Nanotubes

Abstract

In this chapter, we introduced the essential geometric and electronic properties of zigzag nanotubes including of carbon and silicon. The geometric types of nanotubes are divided into achiral and chiral nanotubes. Here we focus on achiral nanotubes, which exhibit a spiral symmetry of mirror image. Since carbon nanotubes (CNTs) have been discovered in 1991, they arouse every one’s interests due to the tubular structure and distinctive electronic properties. Carbon nanotubes have great potential in various fields, such as field emission sources, lithium ion batteries super capacitors and actuators due to its special mechanical, electronic, and optical features. The electronic properties of nanotubes can be either metallic or semiconducting characteristics. The zigzag carbon nanotubes present zero-gap semi-metallic and semiconducting characters, and so do the silicon of armchair nanotubes. Both generate the energy gap and exhibit the transition state of indirect to direct when the tube size is increased. A single wall zigzag carbon nanotube can be metallic and semiconducting behaviors dependent on its chiral vectors. Silicon nanotubes are metallic at small tube size and are semiconducting when both of the diameters are increased. It is very significant to realize the spin-orbit coupling in nanotubes due to their curved surfaces. The curved tubular carbon structure compared with graphene is unsymmetrical, enhances the intrinsic spin-orbit coupling in carbon nanotubes and silicon nanotubes as well. The results of spatial charge density provide the multi-/single-orbital hybridizations because of various chemical bonds. The orbital-projected density of states (PDOSs) present the orbital-decomposed contributions, especially for the pz-orbital at low energy.