C. T. White

Carbon nanotubes as long ballistic conductors

Early theoretical work on single-walled carbon nanotubes predicted that a special achiral subset of these structures known as armchair nanotubes should be metallic. Tans et al. have recently confirmed these predictions experimentally and also showed directly that coherent electron transport can be maintained through these nanowires up to distances of at least 140 nm. But single-walled armchair nanotubes are one-dimensional conductors with only two open conduction channels (energy subbands in a laterally confined system that cross the Fermi level). Hence, with increasing length, their conduction electrons ultimately become localized owing to residual disorder in the tube which is inevitably produced by interactions between the tube and its environment. We present here calculations which show, however, that unlike normal metallic wires, conduction electrons in armchair nanotubes experience an effective disorder averaged over the tubes circumference, leading to electron mean free paths that increase with nanotube diameter. This increase should result in exceptional ballistic transport properties and localization lengths of 10 µm or more for tubes with the diameters that are typically produced experimentally.

Electronic and structural properties of carbon nanotubes

Abstract Recent developments using synthetic methods typical of fullerene production have been used to generate graphitic nanotubes with diameters on the order of fullerene diameters: “carbon nanotubes.” The individual hollow concentric graphitic nanotubes that comprise these fibers can be visualized as constructed from rolled-up single sheets of graphite. We discuss the use of helical symmetry for the electronic structure of these nanotubes, and the resulting trends we observe in both band gap and strain energy versus nanotube radius, using both empirical and first-principles techniques. With potential electronic and structural applications, these materials appear to be appropriate synthetic targets for the current decade.

Graphene Valley Filter Using a Line Defect

With its two degenerate valleys at the Fermi level, the band structure of graphene provides the opportunity to develop unconventional electronic applications. Herein, we show that electron and hole quasiparticles in graphene can be filtered according to which valley they occupy without the need to introduce confinement. The proposed valley filter is based on scattering off a recently observed line defect in graphene. Quantum transport calculations show that the line defect is semitransparent and that quasiparticles arriving at the line defect with a high angle of incidence are transmitted with a valley polarization near 100%.

Mechanical properties of nanotubule fibers and composites determined from theoretical calculations and simulations

Theoretical Youngs moduli have been estimated for carbon fibers composed of single-walled fullerene nanotubules aligned in the direction of the tubule axis. In the limit of infinitely long tubules, the fibers can have a Youngs modulus comparable to that of diamond. Exploiting this property of nanotubule fibers, we investigate a new carbon composite composed of layered nanotubule fibers and diamond. Such a composite is found to be a high-modulus, low-density material that is quite stable to shear and other distortions.

Molecular dynamics simulations of the nanometer-scale mechanical properties of compressed Buckminsterfullerene

Molecular dynamics simulation techniques and an analytic many-body potential function have been used to study a spherical C60 cluster (“Buckminsterfullerene”) compressed between graphite planes. We find that the cluster can reversibly deform under anisotropic compression to a radius (in the direction of compression) that is 13 that of the uncompressed cluster. On compression the restoring pressure first rises and then exhibits a distinct drop beginning at a pressure of about 3 GPa. This drop in pressure is a result of a reversible change which occurs when the cluster transforms to a disc-like structure. Further compression results in a rise in pressure with a slope different from the initial compression.

Room-temperature ballistic transport in narrow graphene strips

We investigate electron-phonon couplings, scattering rates, and mean free paths in zigzag-edge graphene strips with widths of the order of

Semiconducting graphene nanostrips with edge disorder

10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Density of states reflects diameter in nanotubes

. Our calculations for these graphene nanostrips show both the expected similarity with single-wall carbon nanotubes (SWNTs) and the suppression of the electron-phonon scattering due to a Dirichlet boundary condition that prohibits one major backscattering channel present in SWNTs. Low-energy acoustic phonon scattering is exponentially small at room temperature due to the large phonon wave vector required for backscattering. We find within our model that the electron-phonon mean free path is proportional to the width of the nanostrip and is approximately

Altering low-bias transport in zigzag-edge graphene nanostrips with edge chemistry

70\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}

Properties of fullerene nanotubules

for an