Carbon nanotube and its possible applications

Carbon nanotubes are the closed tabular structures consisting of nested cylindrical graphitic layers capped by fullerene-like ends with a hollow internal cavity, which were first discovered by Iijima in 1991. It consists of either one cylindrical graphene sheet, i.e., single-wall nanotube (SWNT)) or of several nested cylinders with an interlayer spacing of 0.34-0.36. nm, i.e., multiwall nanotube (MWNT)). The lengths of SWNTs and MWNTs are usually well over 1 mu m and diameters range similar to 1 nm (for SWNTs) to similar to 50 nm (for MWNTs). SWNTs are usually closed at both ends by fullerene-like half spheres that contain both pentagons and hexagons. Carbon nanotubes show exceptional electronic and mechanical properties. They are flexible but very hard to stretch and have extremely low turn-on-fields and high current densities ranking them among,the best electron field emitters for future field emission displays. This article presents an overview of current state of research on carbon nanotubes. In this review, we have focused on different; synthesis routes for carbon-nanotubes growth, used during last 12 years and possible future applications of carbon nanotubes especially in fuel cell and. field emission displays. We have also discussed various parametric studies reported by several groups and extracted from their observations the common factors, which seem to be important towards a controlled production of carbon nanotubles. The limitations of these approaches, compatibility between an up-scaled production, the quality of the grown nanotube, materials as well as the question of an economic production, have also been addressed.