Electronic structure of carbon nanoparticles

The electronic structure of graphitic nanoparticles is investigated within a gauge field-theory model. The local and total densities of states (DOS) near the pentagonal defects (disclinations) are calculated for three geometries: sphere, cone, and hyperboloid. It is found that the low-energy electron states have a rather specific dependence on both the energy and the distance from a disclination line. In particular, the low-energy total DOS has a cusp that drops to zero at the Fermi energy for disclinations with the Frank index v<1/2, while a region of a nonzero DOS across the Fermi level is formed for v=1/2. The true zero-mode fermion state is found for the graphitic hyperboloid. The appearance of an enhanced charge density near the Fermi level for nanocones with a 60° opening angle (180° disclination) is predicted.     

Electronic structure of FCC carbon

We report first-principles calculations of the electronic structure for carbon in the fcc structure with the experimentally observed lattice parameter. The calculated orbital population shows that the chemical bond in fcc carbon is close to the s²p² bonding with a small s-p hybridization. We find that, in contrast to graphite and diamond, fcc carbon exhibits metallic behavior with an electronic density of states at the Fermi level of 0.5 states/(eV atom).     

Electronic structure of deformed carbon nanotubes

Electronic structure of deformed carbon nanotubes varies widely depending on their chirality and deformation mode. We present a framework to analyze these variations by quantifying the dispersion relation and density of states. The theory is based on the Huckel tight-binding model and confirmed by four orbital tight-binding simulations of nanotubes under stretching, compression, torsion, and bending. It unriddles and unifies previous band gap studies and predicts the shifting, merging, and splitting of Van Hove singularities in the density of state, and the zigzag pattern of band gap change with strains. Possible applications to nanotube devices and spectroscopy research are also presented.     

Electronic structure at carbon nanotube tips

Received: 27 November 1998 / Accepted: 5 January 1999     

Electronic structure of Pd nanoparticles on carbon nanotubes

The effect of the oxygen plasma treatment on the electronic states of multi-wall carbon nanotubes (MWCNTs) is analyzed by X-ray photoemission measurements (XPS) and UPS, both using synchrotron radiation. It is found that the plasma treatment effectively grafts oxygen at the CNT-surface. Thereafter, the interaction between evaporated Pd and pristine or oxygen plasma-treated MWCNTs is investigated. Pd is found to nucleate at defective sites, whether initially present or introduced by oxygen plasma treatment. The plasma treatment induced a uniform dispersion of Pd clusters at the CNT-surface. The absence of additional features in the Pd 3d and C 1s core levels spectra testifies that no Pd-C bond is formed. The shift of the Pd 3d core level towards high-binding energy for the smallest clusters is attributed to the Coulomb energy of the charged final state.     

Electronic structure model of a metal-filled carbon nanotube

Carbon monolayer nanotubes filled with K, Rb, and Cs atoms, in which every ten carbon atoms captures an electron from the doping atoms, are considered. It is assumed that a positive charge in the bulk of the nanotube and a negative charge on its surface are distributed uniformly so that the potential energy of a conduction electron inside the nanotube is proportional to the square of the distance to its center. The dependences of the Fermi quasi-momentum for conduction electrons inside the nanotube on their volume density and the tube radius are obtained in the one-electron approximation for an arbitrary number of subbands of transverse motion. The Landauer formula is used for calculating the dependence of the conductivity of the metallic subsystem of the nanotube on its radius.     

Electronic structure and quantum transport in carbon nanotubes

Received: 3 April 1998     

Electronic structure in finite-length deformed metallic carbon nanotubes

Using the -band tight-binding (TB) model and the quantum box boundary condition, we have discussed how both of the applied strain and finite-length affect the energy bands of metallic carbon nanotubes (CNTs). It is found that, for finite-length CNTs, energy gap for the armchair tube under uniaxial strain and metallic zigzag tube under torsional strain will oscillate with increasing strain, which do not exist in the case of infinite-length CNTs, and will be able to be observed by experiments in future.     

Electronic structure of carbon nanohorns near the Fermi level

The effect of pentagonal defects on the electronic structure at the tip of carbon nanohorns is investigated within the continuum gauge field-theory model. It is found that the existence of a localized electron state at the Fermi level (a true zero-mode state) results in enhanced charge density near the tip. Using a self-consistent perturbation scheme, the eigenfunctions and the local density of states near the pentagonal defects are numerically calculated.     

镁/镀镍碳纳米管界面特性电子理论研究

建立了复合材料中（镀镍）碳纳米管/镁界面原子集团模型,采用递归法计算了界面电子结构.计算表明：镀镍碳纳米管与镁形成的界面结构能、原子结合能较低,镍能够加大纳米管/基体界面结构的稳定性,促进界面结合强度的提高;在界面镍镀层中镁原子的相互作用能为正,说明镍镀层中的镁原子相互排斥,不能形成原子团簇,具有有序化倾向,形成起到强化界面作用的有序相;碳、镁原子在未镀镍碳纳米管与镁的界面格位能较高,降低界面稳定性,因而界面比较脆弱.碳纳米管镀镍后,镍使界面处镁、碳的格位能大幅降低,界面稳定性增强. 关键词： 复合材料 纳米管 电子结构 界面     

Electronic structure and dynamics of optically excited single-wall carbon nanotubes

We have studied the electronic structure and charge-carrier dynamics of individual single-wall carbon nanotubes (SWNTs) and nanotube ropes using optical and electron–spectroscopic techniques. The electronic structure of semiconducting SWNTs in the band-gap region is analyzed using near-infrared absorption spectroscopy. A semi-empirical expression for E₁₁^S transition energies, based on tight-binding calculations is found to give striking agreement with experimental data. Time-resolved PL from dispersed SWNT-micelles shows a decay with a time constant of about 15 ps. Using time-resolved photoemission we also find that the electron–phonon (e–ph) coupling in metallic tubes is characterized by a very small e–ph mass-enhancement of 0.0004. Ultrafast electron–electron scattering of photo-excited carriers in nanotube ropes is finally found to lead to internal thermalization of the electronic system within about 200 fs. PACS 78.47.+p; 81.07.De; 78.67.Ch; 87.64.Ni     

碳掺杂ZnO的电子结构和光学性质

采用基于密度泛函理论框架下的第一性原理计算研究碳掺杂ZnO的电子结构和光学性质.计算结果表明：C原子替代O原子和C原子替代Zn原子两种掺杂体系的电子结构存在明显差异,这主要是由于C原子的电子分布及对周围原子的影响不同;碳掺杂ZnO光学性质的变化集中在低能量区,而高能量区的光学性质没有明显变化.结合电子结构定性解释了光学性质的变化. 关键词： ZnO 碳掺杂 电子结构 光学性质     

Electronic structure of carbon nanotubes modified by alkali metal atoms

The electronic structure and parameters of the energy band structure of (n, 0)-type nanotubes modified by alkali metal atoms (Li, Na) and intercalated by potassium atoms are studied. The quantum-chemical semiempirical MNDO method and a model of the covalent cyclic cluster built in via ionic bonding are used to model infinitely long nanotubes. The electronic density of states of modified nanotubes is found. It is shown that semiconductor-metal transitions can occur in semiconductor nanotubes and that semimetal nanotubes can undergo metal-metal transitions.     

Electronic structure and field-emission characteristics of open-ended single-walled carbon nanotubes

The field-emission mechanism of open-ended single-walled carbon nanotubes (SWNTs) is studied. Owing to electronic effects that directly alter the bonding mode and remarkably influence the work function, an open-ended SWNT has much better field-emission properties than a closed SWNT; owing to geometrical effects that slightly influence the work function and the amplification factor, an open-ended SWNT with relaxation has higher threshold voltage and higher current density compared to one without relaxation. It is suggested that adjusting the localized electronic states of the emitting regions, by electronic and geometrical means, could improve the field-emission properties of carbon nanotubes.