C<Subscript>60</Subscript> fullerene decoration of carbon nanotubes

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C₆₀ molecule to a defect on the nanotube surface.     

Electronic transport spectroscopy of carbon nanotubes in a magnetic field

We report magnetic field spectroscopy measurements in carbon nanotube quantum dots exhibiting fourfold shell structure in the energy level spectrum. The magnetic field induces a large splitting between the two orbital states of each shell, demonstrating their opposite magnetic moment and determining transitions in the spin and orbital configuration of the quantum dot ground state. We use inelastic cotunneling spectroscopy to accurately resolve the spin and orbital contributions to the magnetic moment. A small coupling is found between orbitals with opposite magnetic moment leading to anticrossing behavior at zero field.     

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.     

Shell filling in closed single-wall carbon nanotube quantum dots

We observe twofold shell filling in the spectra of closed one-dimensional quantum dots formed in single-wall carbon nanotubes. Its signatures include a bimodal distribution of addition energies, correlations in the excitation spectra for different electron number, and alternation of the spins of the added electrons. This provides a contrast with quantum dots in higher dimensions, where such spin pairing is absent. We also see indications of an additional fourfold periodicity indicative of K-K' subband shells. Our results suggest that the absence of shell filling in most isolated nanotube dots results from disorder or nonuniformity.     

椭圆截面金纳米管的局域表面等离激元共振特性研究

基于时域有限差分方法研究了几何形状、入射电场偏振方向、管壁厚度及内核和包埋介质的变化对椭圆截面金纳米管局域表面等离激元共振特性的影响.研究发现,当长轴固定时,短轴的减小将导致纳米管消光峰红移;入射电场偏振方向与椭圆长轴夹角的增大将导致消光峰红移;当颗粒整体尺寸不变时,管壁厚度减小同样会使得消光峰红移.此外,内核及包埋介质介电常数的增大均导致消光峰红移.利用等离激元杂化理论及自由电子和振荡电子竞争机理对上述现象进行了理论分析. 关键词： 消光光谱 局域表面等离激元共振 金纳米管 时域有限差分方法     

热力耦合作用下双层碳纳米管的扭转屈曲

考虑碳纳米管周边弹性介质和层间范德瓦耳斯力的作用,利用连续介质力学的壳体理论,建立了热力耦合作用下碳纳米管屈曲问题的控制方程,给出了相应的临界屈曲扭矩的解析解.数值模拟结果表明,在低温和室温环境下,碳纳米管的临界屈曲载荷随着温度变化量的增加而提高;在高温环境下,碳纳米管的临界屈曲载荷随着温度变化量的增加而降低. 关键词： 碳纳米管 屈曲 热力耦合     

Some characteristic phenomena in a transverse Ising nanotube

The phase diagram and magnetizations of a cylindrical nanotube described by the transverse Ising model are investigated by the use of the effective field theory with correlations. Some comparisons between the nanotube and the nanowire have been given for the phase diagrams. In particular, the temperature dependences of longitudinal magnetization in the system with a negative shell–core interaction are investigated. Some characteristic phenomena (new types in ferrimagnetism) which have not been observed in the nanowire as well as similar phenomena are found in the thermal variations, depending on the ratio of the physical parameters in the surface shell and the core. The possibilities of two compensation points and a field induced compensation point in the nanotube are also discussed.     

基于非局部弹性理论的单壁碳纳米管轴向受压屈曲研究

基于非局部弹性理论，在考虑小尺度效应影响的情况下，建立了单壁碳纳米管在均匀轴向外 部压力下的壳体模型. 得到了单壁碳纳米管的轴向受压屈曲的临界条件，验证了小尺度效应 对纳米管轴向受压屈曲的影响. 经典的壳体模型理论由于没有考虑小尺度效应影响而导致碳 纳米管轴向屈曲临界压力值偏高. 关键词： 非局部弹性理论 碳钠米管 小尺度效应 轴向受压     

Eightfold shell filling in a double-wall carbon nanotube quantum dot

We fabricated a quantum-dot device consisting of an individual double-wall carbon nanotube and studied its electrical transport properties at low temperatures. In the negative bias region, the gate modulation curve exhibited quasiperiodic current oscillations, attributed to the Coulomb blockade of single-electron tunneling. We observed both four- and eightfold shell filling in the Coulomb diamond structures. The observation implies an eightfold degeneracy in the single-particle energy levels, which is higher than the fourfold degeneracy of a single-wall carbon nanotube. We show that the observed eightfold shell filling is a unique characteristic of a double-wall carbon nanotube quantum-dot device.     

外壳层最近邻交换相互作用对Blume-Capel模型相变行为的影响

利用有效场理论研究了纳米管上双模随机晶场中混合自旋Blume-Capel模型的相变行为。结果表明，系统相变行为与取值概率、晶场强度比值、晶场参数、温度以及外壳层最近邻交换相互作用密切相关。取值概率、晶场强度比值、晶场参数和外壳层最近邻交换相互作用等诸多因素相互竞争，影响系统的一级和二级相变以及临界点。     

Shell filling and exchange coupling in metallic single-walled carbon nanotubes

We report the characterization of electronic shell filling in metallic single-walled carbon nanotubes by low-temperature transport measurements. Nanotube quantum dots with average conductance approximately (1-2)e(2)/h exhibit a distinct four-electron periodicity for electron addition as well as signatures of Kondo and inelastic cotunneling. The Hartree-Fock parameters that govern the electronic structure of metallic nanotubes are determined from the analysis of transport data using a shell-filling model that incorporates the nanotube band structure and Coulomb and exchange interactions.     

Ferrimagnetic behaviors in a double-wall cubic metal nanotube

A double-wall cubic metal nanotube consists of the ferromagnetic spin-1 inner shell and spin-3/2 surface shell. It is of the ferrimagnetic exchange coupling between two shells. Considering the single-ion anisotropy and transverse field exist together, the magnetization, the initial susceptibility, the internal energy and the specific heat have been investigated by using the effective-field theory with correlations. Some interesting phenomena have been found in the thermal variations of the system. Magnetization appears two or three compensation points in certain parameters. It is an unconventional ferrimagnetic behavior in the nanotube. The shapes of total magnetization and the initial susceptibility are great influenced by the surface exchange coupling, surface single-ion anisotropy and surface transverse field. Some results of nanotube may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.     

Flame synthesis of single-walled carbon nanotubes

Flames offer potential for synthesis of carbon nanotubes in large quantities at considerably lower costs than that of other methods currently available. This study aims to examine conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single-walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/15 mol% argon flame operated at 6.7 kPa with Fe(CO)₅ vapor used as a source of metallic catalyst necessary for nanotube growth. Thermophoretic sampling and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving a resolution of formation dynamics within the flame system. Catalyst particle formation and growth is observed to dominate the immediate post-flame region (10–40 mm HAB). Nanotubes were observed to be present after 40 mm HAB with nanotube inception occurring as early as 30 mm HAB. Between 40 and 70 mm HAB, nanotubes are observed to coalesce into clusters. A nanotube formation ‘window’ is evident with formation limited to fuel equivalence ratios between 1.5 and 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between these lower and upper limits. High-resolution TEM and Raman spectroscopy revealed nanotube bundles with each nanotube being single-walled with diameters between 0.9 and 1.5 nm.     

A novel method for studying the buckling of nanotubes considering geometrical imperfections

Buckling of nanotubes has been studied using many methods such as molecular dynamics (MD), molecular mechanics, and continuum-based shell theories. In MD, motion of the individual atoms is tracked under applied temperature and pressure, ensuring a reliable estimate of the material response. The response thus simulated varies for individual nanotubes and is only as accurate as the force field used to model the atomic interactions. On the other hand, there exists a rich literature on the understanding of continuum mechanics-based shell theories. Based on the observations on the behavior of nanotubes, there have been a number of shell theory-based approaches to study the buckling of nanotubes. Although some of these methods yield a reasonable estimate of the buckling stress, investigation and comparison of buckled mode shapes obtained from continuum analysis and MD are sparse. Previous studies show that the direct application of shell theories to study nanotube buckling often leads to erroneous results. The present study reveals that a major source of this error can be attributed to the departure of the shape of the nanotube from a perfect cylindrical shell. Analogous to the shell buckling in the macro-scale, in this work, the nanotube is modeled as a thin-shell with initial imperfection. Then, a nonlinear buckling analysis is carried out using the Riks method. It is observed that this proposed approach yields significantly improved estimate of the buckling stress and mode shapes. It is also shown that the present method can account for the variation of buckling stress as a function of the temperature considered. Hence, this can prove to be a robust method for a continuum analysis of nanosystems taking in the effect of variation of temperature as well.     

Geometrical dependence of high-bias current in multiwalled carbon nanotubes

We have studied the high-bias transport properties of the different shells that constitute a multiwalled carbon nanotube. The current is shown to be reduced as the shell diameter is decreased or the length is increased. We assign this geometrical dependence to the competition between the electron-phonon scattering process and Zener tunneling.     

Preparation of Halloysite Nanotubes/Polystyrene (HNTs/PS) Core‐shell Particles via Soap‐less Microemulsion Polymerization

Halloysite nanotubes/polystyrene (HNTs/PS) inorganic/organic core‐shell particles were prepared via a convenient soap‐less microemulsion polymerization. The inorganic cores were pre‐treated with allyl alcohol (AA) and the polymer shells were prepared successfully by the facile soap‐less microemulsion polymerization of styrene (St) with the allyl alcohol‐modified halloysite nanotube (AA‐HNT) nanoparticles as seeds, and potassium persulfate (KPS) as initiator in water. The products were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The morphologies of the HNTs/PS core‐shell particles were characterized by transmission electron microscopy (TEM). The mechanism of the nucleation is also mentioned.     

Energetics and electronic structures of encapsulated C60 in a carbon nanotube

We report total-energy electronic structure calculations that provide energetics of encapsulation of C60 in the carbon nanotube and electronic structures of the resulting carbon peapods. We find that the encapsulating process is exothermic for the (10,10) nanotube, whereas the processes are endothermic for the (8,8) and (9,9) nanotubes, indicative that the minimum radius of the nanotube for the encapsulation is 6.4 A. We also find that the C(60)@(10,10) is a metal with multicarriers each of which distributes either along the nanotube or on the C60 chain. This unusual feature is due to the nearly free electron state that is inherent to hierarchical solids with sufficient space inside.     

基于碳纳米管分子封装的一维电子波函数扫描

利用第一性原理,设计并研究了一类基于单臂碳纳米管的分子封装的分子体系．计算表明,半环葫芦脲类化合物可有效封装碳纳米管,引入微弱的分子间相互作用,对碳纳米管的电子态能级结构分布 仅带来微弱影响．半环葫芦脲分子与碳纳米管在管径方向的一维电子态波函数充分耦合,进而有效改变了一些前沿分子轨道的波函数在管径两头的分布以及相应的电子布居浓度．基于电子输运的模拟,发现半环葫芦脲分子在碳纳米管一维方向滑动时的某个电压下的电导变化可准确反映电子态波函数在相应分子导电通道上的一维分布信息．     

Discrete and continuum models for calculating the phonon spectra of carbon nanotubes

The vibration spectrum of perfect carbon nanotubes is studied using a two-parametric potential which includes pairwise and three-particle interatomic interactions. This potential was proposed by Keating and allows one to take into account the elasticity of pairwise interatomic bonds and the elasticity associated with a change in the angle between directional interatomic bonds in covalent crystals. Using the Keating potential, the vibration spectrum of a graphite monolayer is calculated and fitted to the vibration spectrum of crystalline graphite, thereby determining the parameters of the potential. With these parameters, the phonon spectra of perfect monolayer graphite nanotubes are calculated. A continuum model, in which a monolayer nanotube is represented as an elastic cylindrical shell of a finite thickness, is also discussed. Within this model, the vibration spectrum of a nanotube is calculated numerically in the long-wavelength limit as a function of the radius and thickness of the nanotube.     

Microscopic model of superconductivity in carbon nanotubes

We propose the model of a manifold of one-dimensional interacting electron systems to account for the superconductivity observed in ropes of nanotubes. We rely on the strong suppression of single-particle hopping between neighboring nanotubes in a disordered rope and conclude that the tunneling takes place in pairs of electrons, which are formed within each nanotube due to the existence of large superconducting correlations. Our estimate of the transition temperature is consistent with the values that have been measured experimentally in ropes with about 100 metallic nanotubes.