In the exploding field of nano science and nanotechnology, carbon nano tubes have attracted considerable attention owing to their unique mechanical and electronic properties for a broad field of potential applications.
Carbon nano tubes (CNTs) belong to the family of synthetic carbon allotropes and are characterized by a network of sp2 hybridized carbon atoms. The one dimensional (1D) carbon nanotubes can thus be queued between their zero dimensional relatives fullerenes and the two dimensional (2D) relative graphene. The structure of nanotubes has first been described as helical microtubules of graphitic carbon in 1991 by Iijima, who generated the novel material by an arc discharge evaporation process originally designed for the production of fullerenes.1 CNTs are theoretically constructed by rolling up
a graphene sheet into a cylinder with the hexagonal rings joining seamlessly.
Depending on the way the graphene sheet is rolled up
(classified by their chirality and the so-called (n,m)-indices, see Figure 2), a huge diversity of single-walled carbon nanotube (SWCNT) structures can be constructed differing in length, diameter and roll-up angle, which defines the orientation of the hexagonal carbon rings in the honeycomb lattice relative to the axis of the nanotube. In addition, carbon nanotubes possess unique electronic properties, as they exhibit either metallic or semiconducting behavior – depending on the (n,m)-indices.
In carbon nanotube science, significant hurdles — such as controlled production and purification, the intrinsically low solubility and polydispersity with respect to electronic type,
length and diameter — had and still have to be overcome in order to tap their potential in industrial applications. Nonetheless, a broad spectrum of proof of principle devices
has been developed, as carbon nanotube functionalization enabled their dispersion, processing and separation. For example, metallic SWCNTs are particularly interesting as conductive coatings useful for applications such as touch screens, flexible displays, printable electronics, thin film photovoltaics, transparent electrodes, supercapacitors, and nanowires due to their outstanding current-carrying capacities and the ballistic conductivity along the CNT axis. The semiconducting SWCNTs have found applications in field effect transistors, switching, sensing.