A systematic study on the effect of a transverse electric field on the optical properties of carbon nanotubes has been performed using density-functional calculations. The band gaps of the zigzag tubes decrease significantly as the electric field is increased. In the case of armchair tubes, the metallic band energy dispersion relation develops multivalleys at the Fermi level at high fields. The electric-field-induced changes in band dispersions lead to changes in optical properties as manifested in the dielectric functions. Some of the changes are not obvious. For example, a significant field-induced change in band gap can lead to small changes in dielectric functions in some special cases. Our results show that the armchair carbon nanotubes can be a promising material for electro-optical modulation device applications.

We propose a useful metallic field effect element based on the electric field control of armchair single-wall carbon nanotube. The electron conduction channels are enhanced by imposing a transverse gate voltage. Multiple Dirac points have been revealed theoretically by our density functional and tight binding calculations. Our electron transport results show that the performance of such unique transistors depends mainly on the diameter of nanotube exploited. The critical field strength required decreases rapidly with the tube diameter.

We report a first principles analysis of electronic transport characteristics for (n,n) carbon nanotube bundles. When n is not a multiple of 3, inter-tube coupling causes universal conductance suppression near Fermi level regardless of the rotational arrangement of individual tubes. However, when n is a multiple of 3, the bundles exhibit a diversified conductance dependence on the orientation details of the constituent tubes. The total energy of the bundle is also sensitive to the orientation arrangement only when n is a multiple of 3. All the transport properties and band structures can be well understood from the symmetry consideration of whether the rotational symmetry of the individual tubes is commensurate with that of the bundle.