Abstract

One and two dimentional (1D and 2D) forms of nano-carbon, Carbon nanotube (CNT) and graphene, have attracted researchers’ attention because of their unique electrical and photonic properties. Electrons propagating through 2D graphene have a linear dispersion relation between energy and momentum (band structure) crossing at the “Dirac point”, and thus behave as massless Dirac fermions [1]. Graphene exhibits a variety of transport phenomena that are characteristic of 2D Dirac fermions, such as extremely high mobility and anomalous quantum Hall effects. Despite being only one atom thick, graphene is found to absorb a significant fraction of incident light ~2.3%, and the absorption is wavelength independent due to the linear band structure. Single-wall CNT is an enrolled graphene, whose typical tube diameter is ~1nm, and length is ~1 m, thus it is a long 1D material [2]. Its structure is determined by a single parameter, chirality. Due to periodic boundary conditions along the circumferential direction of the tube, the allowed wave vectors are quantized. Thus the band structure of a CNT is given by superposition of the slices of graphene energy band along the corresponding allowed k lines (cutting lines). In case one of the slices contains Dirac point, the CNT is metallic, otherwise the CNT has bandgap thus is semiconductiong. Semiconducting CNT has energy bandgaps, and photons having corresponding wavelength are absorbed. The bandgap energy is inversely proportional to the tube diameter

© 2011 Optical Society of America