Showing papers by "Susumu Saito published in 2002"

Interwall interaction and electronic structure of double-walled BN nanotubes

Abstract: We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, $(n,0)$@(15,0) and $(m,0)$@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall distances are about $3 \AA{}.$ The electronic energy bands around the Fermi energy depend interestingly on the tube radii due to the hybridization between $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ states. We also find that the nearly-free-electron states of the nanotubes induce peculiar charge redistribution in the interwall region.

Geometries, Electronic Properties, and Energetics of Isolated Single Walled Carbon Nanotubes

Abstract: Using the density-functional electronic-structure calculations, we study so-called zig-zag carbon nanotubes. From the complete geometry optimization, it is found that two kinds of bond lengths are ...

Electronic structure of potassium-doped carbon nanotubes

Abstract: We present a density functional study of zigzag carbon nanotubes containing potassium atoms inside. We find that the effect of potassium doping is not simple charge transfer. The nearly free electron state of nanotube couples with the $\mathrm{K} 4s$ orbital. The state comes downward as the tube is thicker and crosses the Fermi level when the diameter is as large as $0.8--1\mathrm{nm}$. It is distributed near the center of the tube and extends to the tube direction, which suggests high conductivity via this state.

Geometric and Electronic Structure of New Carbon-Network Materials: Nanotube Array on Graphite Sheet

Abstract: We design a new class of carbon-network materials with a periodically modified graphite sheet. The modified part corresponds to (6,6) carbon-nanotube geometry. Their tube parts form triangular lattice on graphite sheet. On these systems each tube has six heptagons at the bottom, giving rise to a seamless s p 2 -C network with a negative curvature. We consider these nanotube arrays on graphite sheet with three kinds of tube-end geometries and various sizes for both graphite and tube parts. We report their electronic structures obtained by using a realistic tight-binding model, and for selected systems the density-functional theory. Interestingly, results show that most of them are semiconductors although both (6,6) tube and graphite are metallic. The difference in their tube-end geometries and the sizes of graphite and tube parts affect their electronic structures. Some have nearly flat band states around the Fermi level, showing a possibility of ferromagnetic behavior if hole or electron is doped. Some ar...

Prediction of electronic properties of carbon-based nanostructures

Abstract: We present first-principles total-energy calculations that allow us to predict two new properties of carbon-based nanostructures. First,it is shown that carbon nanotubes (CNTs) encapsulating C 60; now commonly called carbon peapods,are one-dimensional conductors with different types of carriers. Second,CNTs and carbon nanoflakes with zigzag edges are predicted to have ferromagnetic ordering. It is also shown that hetero-nanotubes and hetero-sheets consisting of boron and nitrogen in addition to C are also nano-scale ferromagnets. r 2002 Elsevier Science B.V. All rights reserved.

Electronic and geometric structures of multi-walled BN nanotubes

Abstract: Using the density functional theory, we report energetics and electronic structure of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes are (7,0)@(15,0) and (12,0)@(20,0) in which the inter-wall distance is about 3 A . We observe that the energy gap of double-walled BN nanotubes narrows due to the hybridization between σ and π states. We also find that the nearly free-electron state of the nanotubes induces peculiar charge transfer from the π states to the inter-wall region.

Electronic structure of potassium-doped carbon nanotubes

Abstract: The electronic structure of potassium-doped (12,0) carbon nanotube bundle is studied by using density-functional theory. The material contains one potassium atom inside the unit cell, and the stoichiometry is KC 48 . It is found that the effect of doping is not simple charge-transfer. The nearly free electron state couples with the potassium 4s state, and the hybridized state is pulled down to the Fermi level. The state is distributed inside the tube rather than near the carbon wall. The doped system is thus a multi-carrier conductor in which carriers transfer inside the tube as well as on the tube wall.

Hierarchical assembly of nanostructured carbon foam

Abstract: This contribution addresses the unusual structural and electronic properties of carbon foam, a hypothetical new system that may form by a hierarchical self-assembly process from nanostructured graphite. Due its topological relationship to bulk forms of carbon, the postulated foam covers the structural phase space extending from hexagonal diamond to graphite. Ab initio results for the optimized structure indicate that carbon foam should be stable, structurally rigid, and metallic.