Band structures of carbon nanotube with spin-orbit coupling interaction

We explore the band structures of single-walled carbon nanotubes (SWCNTs) with two types of spin-orbit couplings. The obtained results indicate that weak Rashba spin-orbit coupling interaction can lead to the breaking of four-fold degeneracy in all tubes even though without the intrinsic SO coupling. The asymmetric splitting between conduction bands and valence bands is caused by both SO couplings at the same time. When the ratio of Rashba spin-orbit coupling to the intrinsic spin-orbit coupling is larger than 3, metallic zigzag nanotube is always metallic conductor, on the contrary it becomes semiconducting properties. However, only when this ratio is equal to about 3 or the intrinsic spin-orbit coupling is much weak, the metallic armchair nanotube still holds the metallic behavior in transport.     

Size effect of spin-polarized transport in FM/Single-walled carbon nanotube/FM junctions

We investigated theoretically in detail the size effect of spin-polarized transport in FM/Single-walled carbon nanotube/FM junctions (FM/SWCNT/FM) consisting of the achiral types of tubes: armchair tubes and zigzag tubes. The results show that the spin-polarized transport has different oscillation behaviors with the junction?s size in these two junctions. And the effect of tunnel magnetoresistance (TMR) in zigzag tube is stronger than that in armchair tubes. For all zigzag tubes when the size exceeds a limit the size effect on TMR disappears and TMR value reaches one maximum 20%. Furthermore, for each family of zigzag tubes, this limit of size increases with increasing tube?s radius. For short zigzag tubes the TMR can be negative at some special sizes. And the negative TMR value can reach −12%$-12\text{\%}$ at the angle π. Finally, except for the zero angel, the obtained results show that for all zigzag tubes the extremum of TMR is at the angle π  . For all armchair tubes, the TMR value has one oscillation of small amplitude with the increase of angle and it has two extrema: the maximum at π/2$\pi /2$ and the minimum at π, respectively.     

碳纳米管阵列水渗透性质的研究

碳纳米管阵列组成的碳纳米管分子膜在生物学分子器件等方面有重要应用. 本文利用分子动力学方法计算研究水分子对(11, 11)碳纳米管阵列的渗透过程. 结果发现, 只有当阵列间隙面积大于57.91 Ų时, 水分子才能进入阵列间隙中, 并揭示了碳管内部、阵列间隙内水分子结构随相邻碳管间距变化的演化趋势以及管内外水分子电偶极矩的分布特性.     

Development of hydrogel microstructures on single-walled carbon nanotube films

In this study, the development of polyethylene glycol (PEG) hydrogel microstructures led to the micropatterning of single-walled carbon nanotube (SWCNT) films. Polyethylene glycol was patterned in a process analogous to photolithography in order to manufacture high-density arrays of micrometer-scale hydrogel wells on SWCNT film surfaces. These microwells were composed of hydrophobic SWCNT films surrounded by hydrophilic PEG hydrogel walls. Effects of PEG hydrogel microstructures on the micropatterning of SWCNT films were systematically investigated under different substrates prepared with 3-(trichlorosilyl)propyl methacrylate or octadecyltrichlorosilane solution. A characterization of protein adsorption and an electrochemiluminescence (ECL) reaction were performed to evaluate the biocompatible and electrical efficiency of the patterned SWCNT films in various applications. The proteins selectively adhered to the SWCNT surface inside the microwells, while adherent proteins were absent from the hydrogel walls. In the ECL reaction, the SWCNT films patterned with PEG hydrogel exhibited good, stable ECL behavior, a sign that patterned SWCNT films can be used as flexible and transparent electrodes.     

通量可控的双壁碳纳米管水分子泵

以双壁碳纳米管作为基本单元设计了一种新型纳米机械水泵, 其内管固定作为水分子通道, 外管做活塞式轴向运动. 分子动力学计算表明, 水分子净通量及管内水分子电偶极矩分布均与外管运动速率有强烈耦合效应. 该设计可以实现水分子的高效单向运输, 且输运效率可以通过外管活塞运动的速率进行调控. 这些发现可为未来实用纳米分子泵器件的设计提供新的思路.     

Different localized states of travelling-wave convection in a rectangular container

We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendicular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and supercritical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable. The weak structures in the conducting region are demonstrated too.     

Femtosecond luminescence decay due to exciton energy transfer in single-walled carbon nanotube bundles

We investigated luminescence decay kinetics in single-walled carbon nanotubes in large bundles excited by femtosecond pulses. The time constant of luminescence decay becomes longer with decrease in photon energy: 40 fs at 1.2 eV and 380 fs at 0.6 eV. This behavior is explained by exciton energy transfer from an excited to neighboring tubes.     

Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled carbon nanotube (SWNT) is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H₂, however it can chemisorb three H₂ at most, with the average binding energy per H₂ suitable for the hydrogen storage at the room temperature. More H₂ would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H₂ approaches the Ni--Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.     

Well-defined single-walled carbon nanotube fibers as quantum wires: Ballistic conduction over micrometer-length scales

We report quasi-ballistic conduction in single-walled carbon nanotube (SWNT) fibers at room temperature, with a measured mean free path of 1.0–2.6 μm. The dynamic submersion of vertical SWNT fibers into liquid mercury (Hg) electrode shows plateaus and steps indicative of quasi-ballistic electron transport. This response is described with a newly developed network model that uses surface impurities to simplify the parallel conducting channels. The quasi-ballistic SWNT fibers exhibit a resistance per unit length of 2.5–6.5 kΩ/μm and a mean free path exceeding 1 μm, a length longer than typical via dimensions in existing Si-chip technologies. These results highlight that SWNT fiber conductivity can be enhanced by increasing the metallic to semiconducting SWNT ratio and reducing the surface impurities.     

First-principles study of the switching characteristics of the 15,16-dinitrile DDP/CPD-based optical molecular switch with carbon nanotube electrodes

We have studied the switching characteristics of an optical molecular switch based on the 15,16-dinitrile dihydropyrene/cyclophanediene (DDP/CPD) molecule with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the DDP shows an overall higher conductance than the CPD at low bias which is independently of the SWCNT chirality. Meantime, the conductance of the molecular switch can be tuned by the chirality of the SWCNT.     

Distribution and thermophysical properties of n-heptacosane molecules confined in carbon nanotube

Molecular dynamics (MD) simulations were performed to provide an insight about the molecule distribution and thermophysical properties of n-heptacosane confined in the (25, 25) single-walled carbon nanotube (CNT). The results show that an orderly distribution of n-heptacosane molecules along the CNT inner wall is clearly observed. Meanwhile, n-heptacosane confined in CNT exhibits an increased self-diffusion coefficient, a decreased melting point and an enhanced thermal conductivity, compared to the bulk. The simulations reveal that MD is an effective and convenient method to understand the variation characteristics of alkane-based phase change materials confined in CNT on molecular and atomic scale.     

单壁碳纳米管声子谱及比热计算

利用卷曲法计算了有限长单壁碳纳米管的声子色散关系．讨论了单壁碳纳米管的比热随管径、温度的变化趋势．结果表明碳管的比热随温度、管径的增大而增大,并逐渐趋于一恒定数值．根据色散关系的计算结果,给出了有限长（5,5）型单壁碳纳米管的振动模式以及部分振动模式的频率随长度的变化关系． 关键词： 碳纳米管 声子 比热     

基于碳纳米管场效应管构建的纳电子逻辑电路

展示了由碳纳米管场效应管构成的三种逻辑电路，分别为单个p型碳纳米管场效应管的开关电路、由集成在同一片硅片上的单个p型碳纳米管场效应管和单个n型掺氮碳纳米管场效应管构成的互补型反相器，以及两个独立的p型碳纳米管场效应管构成的或非门. 其中p型碳纳米管场效应管以单壁碳纳米管作为沟道，而n型碳纳米管场效应管则以掺氮的多壁碳纳米管作为沟道，器件的源漏电极均为铂电极. 关键词： 碳纳米管 场效应管 逻辑电路     

磁场下含结构缺陷多组分超晶格中的局域电子态和电子输运

在有效质量近似理论下，利用转移矩阵和有效垒高方法研究了有限磁场下含结构缺陷的多组分超晶格中局域电子态的性质.在考虑各组分层有效质量的失配时，外加磁场会导致磁耦合效应的出现.磁耦合效应不仅引起局域电子能级的量子化，并且随着朗道指数或磁场强弱的变化，局域能级及其局域程度都会发生显著移动，特别是对高能区域的局域电子态影响更大.此外，还计算了电子输运系数，讨论了含结构缺陷的三组分超晶格中局域电子能级与输运谱透射禁区中的共振透射峰的关系，发现两者之间有着很好的对应关系，为相应的实验研究提供了依据. 关键词： 超晶格 局域电子态 磁场     

One-dimensional method of investigating the localized states in armchair graphene-like nanoribbons with defects

In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphenelike nanoribbons. The method is based on the tight-binding model and with a standing wave assumption. The system of armchair graphene-like nanoribbons includes the armchair supercells with arbitrary elongation-type line defects and the semi-infinite nanoribbons. With this method, we analyze many interesting localized states near the line defects in the graphene and boron-nitride nanoribbons. We also derive the analytical expressions and the criteria for the localized states in the semi-infinite nanoribbons.     

Fabrication and electrical properties of a carbon nanotube quantum dot

Single-walled carbon nanotubes (SWNTs) were synthesized by pyrolyzing methane (CH₄) at a temperature of 900℃ on SiO₂ substrates pre-coated with iron nano-particles. Electrical contacts were fabricated onto one of the SWNTs by using an electron beam lithography process. Coulomb blockade and single-electron tunnelling characters were found at low temperatures, indicating that the SWNT in-between the electrodes forms a quantum dot. It is found that the Coulomb gap of the quantum dot is about 8.57 meV, and the factor \alpha , which converts the gate voltage to the true electrostatic potential shift, is around 200 for this device.     

Coherent field emission from a multi-walled carbon nanotube with two open-ended branches

Interference fringes are obtained in a field-emission microscopy (FEM) study of a multi-walled carbon nanotube (MWCNT) with two open-ended branches. The FEM pattern, which is composed of three parallel streaks, can be interpreted by using classical Young's double-slit interference with the ends of the two MWCNT branches treated as two secondary sources of the electron wave. The origin of the coherency of the electron beams from the two branches is discussed on the basis of the quantitative analysis of the FEM pattern. The result suggests a new approach to obtaining a coherent electron source.     

Energetics and electronic structure of a single copper atomic chain wrapped in a carbon nanotube: a first-principles study

In the generalized gradient approximation, the energy and electronic structure are investigated for a single copper atomic chain wrapped in (4, 4), (5, 5) and (6, 6) armchair carbon nanotubes by using the first-principles projector-augmented wave potential within the framework of density functional theory. The results show that the (4, 4) and (5, 5) tubes are too narrow to wrap a Cu chain, but the (6, 6) tube is nearly ideal to wrap a Cu chain on its centre axis. Wider tubes are anticipated to wrap more than one Cu chain spontaneously with forces amounting to a fraction of a nanonewton. Although the tube--chain interaction decreases with the increase of the tube diameter of (4, 4), (5, 5) and (6, 6) successively, the charge density of the Cu@(6, 6) combined system still does not show complete superposition of that of the pristine (6, 6) tube and Cu chain. Successively reducing the restrictions of (4, 4), (5, 5) and (6, 6) tubes on the Cu chain leads to a reduction in shift of the highest peak of the Cu chain towards lower energies, that is from -0.5177~eV of the isolated Cu chain to -1.36785~eV, -0.668~eV and -0.588~eV for the Cu@(4, 4), Cu@(5, 5) and Cu@(6, 6) systems, respectively. In reverse, the strong metallic character of the Cu chain also enhances the metallic character of the combined systems so that the broader pseudogaps of the pristine carbon nanotubes around the Fermi level change into the narrow pseudogaps of the combined systems.     

Particle-hole bound states of dipolar molecules in an optical lattice

We investigate the particle-hole pair excitations of dipolar molecules in an optical lattice, which can be described with an extended Bose-Hubbard model. For strong enough dipole-dipole interaction, the particle-hole pair excitations can form bound states in one and two dimensions. With decreasing dipole-dipole interaction, the energies of the bound states increase and merge into the particle-hole continuous spectrum gradually. The existence regions, the energy spectra and the wave functions of the bound states are carefully studied and the symmetries of the bound states are analyzed with group theory. For a given dipole-dipole interaction, the number of bound states varies in momentum space and a number distribution of the bound states is illustrated. We also discuss how to observe these bound states in future experiments.