TITLE: Symmetry breaking in single walled and multi-walled carbon nanotubes

SPEAKER: Professor David L. Carroll,

TIME: Thursday Sept. 26, 2002 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Symmetry breaking can occur in several distinct ways for carbon nanotubes. Deformation of the nanotube, perpendicular to its axis, leads to the opening of the associated band-gap (or the formation of a pseudo-gap in the case of metallic tubes) for low strains. For intermediate strain values, the formation of defects is observed, while for large strains (inelastic deformation) re-hybridization occurs. A second process of symmetry breaking occurs when impurity atoms are added to the nanotube lattice. We have doped the nanotube lattice with boron and nitrogen to show the formation of defect related states. However, using tunneling spectroscopy coupled with bulk thermo-power measurements, we demonstrate that the formation of such states is not analogous to bulk materials. In fact, in both cases of symmetry breaking discussed here, the nanotube doesnt act as a bulk material or a one-dimensional material but rather expresses a more complex topology. These results will be discussed in the context of organic devices based on nanotubes and their composites.