Introduction to Inorganic and Metallic Nanotubes

Nanotubular materials are classified into three types, single- and multi-walled ones, which correspond to one or more rectangular sheets rolled into their single or concentric cylindrical forms with no edge atoms and a scrolled one generated from a single straight sheet with keeping both free ends. In these nanotubular systems, the excess energy due to the sheet rolling or scrolling-induced strain and/or sheet surface and edge atoms is fully compensated by the energy decrease due to the loss of the sheet edges and/or the van der Waals interaction between neighboring cylindrical tubes. The pathway to nanotubes is based essentially on either the self-organization of constituent atoms or molecules or their tubular growth by the assistance of solid or molecular templates. The former processes are characteristic of the family of materials that are constructed by interatomic covalent bonding to stably form a 2D-layered structure as their typical phase, whereas the latter ones are applied to those with much less anisotropy in bonding character. This chapter also summarizes the structural and dimensional characteristics of inorganic and metallic nanotubes and finally refers to some representative applications and future applicabilities of the nanotubular materials.