Nanometre-size tubes of carbon

Abstract

We review the present state of understanding of the structure, growth and properties of nanometre-size tubes of carbon. Two different types of carbon nanotubes, namely single-shell nanotubes made of single layers of graphene cylinders and multishell nanotubes made of concentric cylinders of graphene layers have now become available. The subtle structure parameters such as helicity in the carbon network and the nanometre diameters give the nanotubes a rich variety in physical properties. Recent experimental progress on the measurements of properties using electron-energy loss spectroscopy, Raman spectroscopy, electron-spin resonance, electrical conductance, mechanical stiffness and theoretical predictions on electronic and mechanical properties of nanotubes will be discussed. In addition to synthesis techniques, methods to purify and make aligned arrays of nanotubes will be described. Different approaches for fabricating composite structures using nanotubes as moulds and templates and their future implications in materials science will be evaluated. Finally, promising areas of future applications, for example as tiny field-emitting devices, micro-electrodes, nanoprobes and hydrogen storage material will be outlined.