Physical Properties of Carbon Nanotubes

Abstract

A carbon nanotube is a honeycomb lattice rolled into a cylinder. The diameter of a carbon nanotube is of nanometer size and the length of the nanotube can be more than lpm. The nanotube diameter is much smaller in size than the most advanced semiconductor devices obtained so far. Thus the availability of carbon nanotubes may have a large impact on semiconductor physics because of its very small size and the special electronic properties that are unique to carbon nanotubes. Because of the large variety of possible helical geometries known as chirality, carbon nanotubes provide a family of structures with different diam- eters and chiralities. One of the most significant physical properties of carbon nanotubes is their electronic structure which depends only on their geometry, and is unique to solid state physics. Specifically, the electronic structure of a single-wall carbon nanotube is either metallic or semiconducting, depending on its diameter and chirality, and does not requiring any doping. Thus we can imag- ine that the smallest possible semiconductor devices are likely to be based on carbon nanotubes. Further, the energy gap of semiconducting carbon nanotubes can be varied continuously from 1 eV to 0 eV, by varying the nanotube diame- ter. Thus, in principle, it may be possible to specify the desired semiconducting properties using only carbon atoms with a specified geometric structure. The purpose of this book is to define the structure of carbon nanotubes as clearly as possible, starting from basic physics and chemistry. Since the uniqueness in the electronic structure comes directly from the uniqueness of the electronic structure of graphite, this volume provides background information about the structure and properties of graphite and related carbon materials. From our definition of the structure of carbon nanotubes, we can explain the electronic structure and phonon dispersion relations based on simple physical models, which the reader can follow with a pen and paper. Thus the contents of the book are rather theoretically oriented, and experimental results are used primarily to provide evidence for the validity of the theory.