Electronic properties of double-layer carbon nanotubes

The electronic spectra for double-wall zigzag and armchair nanotubes are found. The influence of nanotube curvatures on the electronic spectra is also calculated. Our finding that the outer shell is hole doped by the inner shell is in the difference between Fermi levels of individual shells which originate from the different hybridization of π orbital. The shift and rotation of the inner nanotube with respect to the outer nanotube are investigated. We found stable semimetal characteristics of the armchair DWNTs in regard of the shift and rotation of the inner nanotube. We predict the shift of k_F towards the bigger wave vectors with decreasing of the radius of the armchair nanotube.     

Electronic properties of oxidized carbon nanotubes

The effect of oxygenation on the electronic properties of semiconducting carbon nanotubes is studied from first principles. The O2 is found to bind to a single-walled nanotube with an adsorption energy of about 0.25 eV and to dope semiconducting nanotubes with hole carriers. Weak hybridization between carbon and oxygen is predicted for the valence-band edge states. The calculated density of states shows that weak coupling leads to conducting states near the band gap. The oxygen-induced gap closing for large-diameter semiconducting tubes is discussed as well. The influence of oxygen on the magnetic property is also addressed through a spin-polarized calculation and compared to experiment.     

Electronic properties of multi-defected zigzag carbon nanotubes

Electronic properties of multi-defected zigzag single-walled carbon nanotubes are investigated by use of the tight-binding Green's function method. The Stone-Wales defects and the vacancies are considered. We find that the conductance sensitively depends on the realistic defect configurations for the metallic zigzag carbon nanotubes. Interestingly, the electronic transport properties of the nanotubes with three vacancies can be considered as the sum effect of two double-vacancies, while those with Stone-Wal...     

Electronic structures and magnetic properties in Cu-doped two-dimensional dichalcogenides

We explore the electronic structures and magnetic properties in Cu-doped MX₂ (=MoS₂, MoSe₂, MoTe₂, and WS₂) based on density functional theory. A Cu dopant leads to a net moment of 5.0 or 1.0 μ_B in MX₂, which mainly depend on the size of crystal-field splitting relative to that of the spin splitting. No magnetism is observed in Cu-doped MoTe₂. The local distortion around the Cu atom reduces the total magnetic moment in two-Cu-doped MX₂. The magnetic coupling between the nearest neighboring Cu atoms is ferromagnetic for all the cases, but they demonstrate various magnetic ground states with the increasing distance between Cu atoms: the Cu-doped MoS₂ and WS₂ exhibit anti-ferromagnetic and nonmagnetic ground state, respectively. A long-range ferromagnetic or ferrimagnetic coupling is attributed to double-exchange interaction in Cu-doped MoSe₂. Half-metallic ferromagnetism with Curie temperature above room temperature in Cu-doped MoSe₂ provides a useful guidance to engineer the magnetic properties of MoSe₂ in experiments.     

Electronic transport properties of metallic single-walled carbon nanotubes

We have calculated the differential conductance of metallic carbon nanotubes by the scatter matrix methon.It is found that the differential conductance of metallic nanotube-based devices oscillates as a function of the bias voltage between the two leads and the gate voltage.Oscillation period T is directly proportional to the reciprocal of nanotube length.In addition,we found that electronic transport properties are sensitive to variation of the length of the nanotube.     

Electronic properties of carbon nanotube/fabric composites

Single walled carbon nanotube (SWNT)/fabric composite materials were manufactured using two simple manufacturing processes. The first method is direct deposition of SWNTs by either a spray method or by incubation; the other is a Quasi-Langmuir–Blodgett (QLB) transfer technique. The composite retains high mechanical strength (governed by the fabric), and good electrical properties (determined by the nanotubes). We measure the DC electrical conductivity of the composite fabric to be 5.33 S/cm for the sprayed tubes, 13.8 S/cm for the incubated SWNTs, and 8 S/cm for the QLB transferred tubes; these values are limited not by the nanotube network, but by the surface roughness of the fabric itself. Measurements of the conductivity up to 1 MHz reveal a transport process that proceeds along a random network, with barriers separating the various nanotubes. The material is resistive both to changes in temperature (range of 0–80 °C) and mechanical deformations. The conductivity of the composite decreases by less than 10% when bent around a cylinder of 1 cm diameter.     

Electronic properties of telescoping carbon nanotubes under external fields

In this work, we use the tight-binding model to study the low-energy electronic properties of telescoping double-walled carbon nanotubes subject to the influences of a transverse electric field and a parallel magnetic field. The state energy and energy spacings are found to oscillate significantly with the overlapping length. External fields would modify the state energies, alter the energy gaps, and destroy the state degeneracy. Complete energy gap modulations can be accomplished either by varying the overlapping length, or by applying an electric field or a magnetic field. The variations of state energies with the external fields will be directly reflected in the density of states. The numbers, heights, and frequencies of the density of states peaks are strongly dependent on the external fields.     

Electronic structures and transport properties of sulfurized carbon nanotubes

The electronic and transport properties of side-walled sulfurized (8, 0) zigzag carbon nanotube were investigated by using density functional theory coupled with a non-equilibrium Green function approach. It is found that the adsorption of the sulfur chains largely reduces the bandgap of the semiconducting (8, 0) carbon nanotube, even changing it into a metallic one. More importantly, the transmission eigenstates around the Fermi level are contributed by not only the sulfur chains but also the complex system made of the sulfur chains and the single-walled carbon nanotube. Our results provide a method to improve the conductivity and utilization rate of the surface in the electrodes of supercapacitor which are made of the carbon nanotubes.     

Electronic properties of alkali-metal intercalated single walled carbon nanotubes

We present a comparative study of the electronic properties of sodium and lithium intercalated single walled carbon nanotubes in a bucky paper sample by electron energy loss spectroscopy and photoemission spectroscopy. We have found that at room temperature both sodium and lithium rapidly diffuse into the bulk of the sample while different magnitudes of charge transfer from Na and Li to the nanotube bundles have been observed. The maximum observed displacement of the Fermi level is almost the same for both alkali although Na and Li induce quite different changes in the carbon nanotube electronic structure. We interpret our results as a more covalent character of the Li-carbon nanotube interaction with respect to the ionic character of the Na-carbon nanotube interaction; the localization of the charge density along the Li-C bond is responsible for an intertube interaction within the carbon nanotube ropes.     

Electronic and elastic properties of expanded radialenes carbon nanotubes

The series of expanded radialenes of molecular formulae C_2n H _n and C_3n H _n are obtained by inserting acetylene or diacetylene groups between each pair of methylene units of radialenes C _n H _n . This paper reports on the new theoretical investigation of electronic and elastic properties of some carbon nanotubes based on expanded radialenes with different diameters and with the armchair and zigzag edges Using the ABINIT software package, which is based on the density functional theory (DFT), we found that all studied carbon nanotubes based on expanded radialenes possess metallic behavior. Also, the calculations show that the elastic properties of the nanotubes depend on the form of the rolling up (armchair (m,m) or zigzag (m,0)). The Young’s modulus is slightly smaller for the (m,0) nanotubes and a bit larger for (m,m) nanotubes.     

Electronic properties of a two-dimensional quasicrystal model based on octagonal covering structure

A two-dimensional quasilattice with eight-fold rotational symmetry is formed by covering of identical octagonal clusters; a tight-binding Hamiltonian is presented based on it. We study the electronic properties by analyzing the energy spectrum and wave functions. The main energy levels are obtained and the gaps are labeled. The wave functions with different localization features are found and the self-similar distribution is shown.     

H,F修饰单层GeTe的电子结构与光催化性质

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了单层GeTe、表面氢化及氟化单层GeTe的晶体结构、稳定性、电子结构和光学性质.计算结果表明,经过修饰后, GeTe的晶格常数、键角、键长增大,且均具有较好的稳定性.电子结构分析表明,单层GeTe为间接带隙半导体,全氢化修饰、全氟化修饰以及氢氟共修饰(F, Ge同侧;H, Te同侧)则转变为直接带隙半导体,且修饰后的能隙均不同程度减小.载流子有效质量表明,全氢化、全氟化以及氢氟共修饰GeTe (F, Ge同侧;H, Te同侧)的有效质量减小,其载流子迁移率增强.带边势分析结果显示,单层GeTe能够光裂解水制氢和析氧,而修饰后的GeTe的价带带边势明显下移,其氧化性明显增强,能够光裂解水析O2, H2O2, O3以及OH·等产物.光学性质表明,修饰后的GeTe对可见光区和红、紫外区的光谱吸收效果明显增强,表明其在光催化领域有着广阔的应用前景.     

Electronic structure and nonlinear optical properties of a two-dimensional hexagonal quantum dot

In this work electronic structure, the linear and the third-order nonlinear refractive index changes as well as optical absorption coefficients of a two-dimensional hexagonal quantum dot are investigated. Energy eigenvalues and eigenfunctions of the system are calculated by the matrix diagonalization technique, and optical properties are also obtained using the compact density matrix approach. As our results indicate, both the dot size and the confinement potential have a great influence on the intersubband energy intervals, the transition probability and consequently, the linear and the third-order nonlinear refractive index changes and optical absorption coefficients.     

二维InSe/SnSe2范德华异质结的电子结构和光学特性研究

本文构建了三种不同堆叠形式下的二维InSe/SnSe₂范德华异质结模型,利用基于密度泛函理论的第一性原理方法综合考察了二维InSe/SnSe₂三种不同堆叠情况下的几何构型及稳定性,在此基础上选取具有最稳定性能的构型.该异质结呈现出Ⅱ型能带对齐特征,带隙值为1.118 eV,可以实现电子-空穴的有效分离.另外,相比与单层二维InSe/SnSe₂范德华异质结的光吸收能力达到明显提升,在紫外光范围内吸收系数达到10~6 cm^-1.研究结果将为相关物理实验及机理研究提供理论基础,对二维InSe/SnSe₂范德华异质结在光电器件中的应用具有重要的物理意义.     

含有五边形—七边形缺陷的单壁纳米碳管的输运性质研究

运用第一性原理的密度泛函理论结合非平衡格林函数研究了含有五边形—七边形拓扑缺陷的纳米碳管异质结的输运性质.结果发现：拓扑缺陷对碳管的输运性质有很大影响；另外，不同类型的碳管形成的异质结的输运性质也有明显的差异. 关键词： 纳米碳管 输运性质 异质结 透射系数     

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 transport properties of junctions between carbon nanotubes and graphene nanoribbons

Using the tight-binding model and Green’s function method, we studied the electronic transport of four kinds of nanotube-graphene junctions. The results show the transport properties depend on both types of the carbon nanotube and graphene nanoribbon, metal or semiconducting. Moreover, the defect at the nanotube-graphene interface did not affect the conductance of the whole system at the Fermi level. In the double junction of nanotube/nanoribbon/nanotube, quasibound states are found, which cause antiresonance and result in conductance dips.     

低偏压下单层碳纳米管的输运特征

系统地计算了各种手性碳纳米管最低导带的电子速度和有效质量的变化规律,在此基础上推断手性碳纳米管低偏压下的输运特征,计算表明:在低偏压电子输运时,同一系列(手性角相同)的各种手性金属碳纳米管的输运性质相同,与管径无关,但不同系列的手性金属碳纳米管的输运性质有明显区别;而同一系列的各种手性半导体型碳纳米管的输运性质有一定差异,但不同系列的手性半导体型碳纳米管的输运性质有着显著差异.这一结果说明:碳纳米管在低偏压下的输运特征与系列有着密切的关系,手性角是决定各种碳纳米管在低偏压下具有不同输运性质的最关键的几何参 关键词： 碳纳米管 手性角 电子速度 有效质量