Charge pumping in carbon nanotubes

We demonstrate charge pumping in semiconducting carbon nanotubes by a traveling potential wave. From the observation of pumping in the nanotube insulating state we deduce that transport occurs by packets of charge being carried along by the wave. By tuning the potential of a side gate, transport of either electron or hole packets can be realized. Prospects for the realization of nanotube based single-electron pumps are discussed.     

Biexciton stability in carbon nanotubes

We have applied the quantum Monte Carlo method and tight-binding modeling to calculate the binding energy of biexcitons in semiconductor carbon nanotubes for a wide range of diameters and chiralities. For typical nanotube diameters we find that biexciton binding energies are much larger than previously predicted from variational methods, which easily brings the biexciton binding energy above the room temperature threshold.     

Potential energy,force distribution and oscillatory motion of chloride ion inside electrically charged carbon nanotubes

In this research, a continuum-based model is presented to explore potential energy, force distribution and oscillatory motion of ions, and in particular chloride ion, inside carbon nanotubes (CNTs) decorated by functional groups at two ends. To perform this, van der Waals (vdW) interactions between ion and nanotube are modeled by the 6-12 Lennard-Jones (LJ) potential, whereas the electrostatic interactions between ion and functional groups are modeled by the Coulomb potential and the total interactions are analytically derived by summing the vdW and electrostatic interactions. Making the assumption that carbon atoms and charge of functional groups are all uniformly distributed over the nanotube surface and the two ends of nanotube, respectively, a continuum approach is utilized to evaluate the related interactions. Based on the actual force distribution, the equation of motion is also solved numerically to arrive at the time history of displacement and velocity of inner core. With respect to the proposed formulations, comprehensive studies on the variations of potential energy and force distribution are carried out by varying functional group charge and nanotube length. Moreover, the effects of these parameters together with initial conditions on the oscillatory behavior of system are studied and discussed in detail. It is found out that chloride ion escapes more easily from negatively charged CNTs which is followed by uncharged and positively charged ones. It is further shown that the presence of functional groups leads to enhancing the operating frequency of such oscillatory systems especially when the electric charges of ion and functional groups have different signs.     

Energetics and stability of vacancies in carbon nanotubes

In this work we present ab initio calculations of the formation energies and stability of different types of multi-vacancies in carbon nanotubes. We demonstrate that, as in the case of graphene, the reconstruction of the defects has drastic effects on the energetics of the tubes. In particular, the formation of pentagons eliminates the dangling bonds thus lowering the formation energy. This competition leads to vacancies having an even number of carbon atoms removed to be more stable. Finally the appearance of magic numbers indicating more stable defects can be represented by a model for the formation energies that is based on the number of dangling bonds of the unreconstructed system, the pentagons and the relaxation of the final form of the defect formed after the relaxation.     

碳纳米管的稳定性研究

石墨晶体结构遭到破坏时，总是碎化为微小尺寸的片状粉末.孤立的石墨烯片在其边缘存在大量的悬挂键，使得石墨烯片的能量较高，状态也不稳定.石墨烯片卷曲形成碳纳米管后，悬挂键减少，系统能量相应降低.另一方面，石墨烯片卷曲形成碳纳米管将产生相应的形变势能，形变势能的产生将抵消由于减少石墨烯片边缘上的悬挂键所带来的能量降低，使碳纳米管的能量可能高于石墨烯片的能量，导致碳纳米管结构的不稳定.在建立碳纳米管生成的力学模型并进行深入理论分析的基础上得出了碳纳米管可以稳定存在的最小直径约为0.32nm的结论.     

碳纳米管的稳定性研究

石墨晶体结构遭到破坏时,总是碎化为微小尺寸的片状粉末.孤立的石墨烯片在其边缘存在大量的悬挂键,使得石墨烯片的能量较高,状态也不稳定.石墨烯片卷曲形成碳纳米管后,悬挂键减少,系统能量相应降低.另一方面,石墨烯片卷曲形成碳纳米管将产生相应的形变势能,形变势能的产生将抵消由于减少石墨烯片边缘上的悬挂键所带来的能量降低,使碳纳米管的能量可能高于石墨烯片的能量,导致碳纳米管结构的不稳定.在建立碳纳米管生成的力学模型并进行深入理论分析的基础上得出了碳纳米管可以稳定存在的最小直径约为0.32nm的结论. 关键词： 碳纳米管 稳定性 形变势能 键能     

Chirality distribution and transition energies of carbon nanotubes

From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, the radial breathing mode frequency, and the Raman intensity of both metallic and semiconducting tubes. We unambiguously assigned the chiral index (n(1),n(2)) of approximately 50 nanotubes based solely on a third-neighbor tight-binding Kataura plot and find omega(RBM)=(214.4+/-2) cm(-1) nm/d+(18.7+/-2) cm(-1). In contrast to luminescence experiments we observe all chiralities including zigzag tubes. The Raman intensities have a systematic chiral-angle dependence confirming recent ab initio calculations.     

锥顶碳纳米管的结构稳定性与场致发射性能

运用密度泛函理论研究了锥顶碳纳米管的结构稳定性与电子场致发射性能.结果表明:在外电场作用下,该体系的结构稳定性明显优于碳纳米锥体、C₃₀半球封口的碳纳米管,且电子发射性能与锥角大小、锥顶构型密切相关,特别是锥角38.9°及棱脊型顶部的cone₁@(6,6)综合性能最优,用其作为场致发射源的阴极时可显著提高发射电流密度并延长器件的使用寿命. 关键词： 锥顶碳纳米管 电子场致发射 结构稳定性 密度泛函理论     

Optimisation of stability and charge transferability of ferrocene-encapsulated carbon nanotubes

Ferrocene-encapsulated carbon nanotubes (Fc@CNTs) became promising nanocomposite materials for a wide range of applications due to their superior catalytic, mechanical and electronic properties. To open up new windows of applications, the highly stable and charge transferable encapsulation complexes are required. In this work, we designed the new encapsulation complexes formed from ferrocene derivatives (FcR, where R = –CHO, –CH₂OH, –CON₃ and -PCl₂) and single-walled carbon nanotubes (SWCNTs). The influence of diameter and chirality of the nanotubes on the stability, charge transferability and electronic properties of such complexes has been investigated using density functional theory. The calculations suggest that the encapsulation stability and charge transferability of the encapsulation complexes depend on the size and chirality of the nanotubes. FcR@SWCNTs are more stable than Fc@SWCNTs at the optimum tube diameter. The greatest charge transfer was observed for FcCH₂OH@SWCNTs and Fc@SWCNTs since the Fe d levels of FcCH₂OH and Fc are nearly equal and close to the Fermi energy level of the nanotubes. The obtained results pave the way to the design of new encapsulated ferrocene derivatives which can give rise to higher stability and charge transferability of the encapsulation complexes.     

Observation of charged excitons in hole-doped carbon nanotubes using photoluminescence and absorption spectroscopy

We report the first observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped carbon nanotubes at room temperature. When p-type dopants are added to carbon nanotube solutions, the photoluminescence and absorption peaks of the trions appear far below the E11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy separation between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in carbon nanotubes.     

单壁碳纳米管端口结构的热稳定性

利用紧束缚势分子动力学模拟方法,研究了温度在1000 K-3000 K之间单壁碳纳米管端口结构的变化趋势.计算表明,温度对整个管端口结构有重要影响,温度升高容易使理想单壁碳管端口封闭.温度在3000 K下碳管端口达到封闭,而且端口封闭导致碳管系统能量的降低.碳纳米管长度越长,端口封闭越快,且扶手型碳纳米管比锯齿型碳纳米管更容易形成端口封闭的结构.     

Improved emission stability of HfC-coated carbon nanotubes field emitters

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to synthesize the Fe-catalyzed carbon nanotubes (CNTs). Hf films were deposited onto the synthesized CNTs, followed by heat treatment at 1200 °C which could form HfC. Field emission properties indicate that the HfC-coated CNTs have good emission current density due to low work function of HfC and also keep stable emission characteristics under poor vacuum owing to the chemical inertness of HfC. Consequently, field emission characteristics of the CNTs can be improved by the HfC-coated surface treatment compared with the synthesized CNTs.     

Improved emission uniformity and stability of printed carbon nanotubes in electrolyte

In this paper, we studied the effect of NaCl electrolyte as a surface treatment on improving the uniformity and stability of field emission of screen-printed carbon nanotubes (CNTs). A short period of the electrolyte treatment of CNT films remarkably increase emission uniformity and stability. Furthermore, the field emission characteristics of screen-printed carbon nanotubes (CNTs) such as low turn-on field, high emission current density and strong adhesion of the CNT film on the substrate were also reinforced after post-treated. SEM, TEM and Raman spectrum study revealed that uniformity and stability of field emission is enhanced by two factors. Firstly, the electrolyte treatment appeared to render the CNT surfaces more actively by exposing more CNTs form the CNT paste, which dominates initial uniformity and stability of field emission. Secondly, the number of opened CNTs and defects CNTs of CNT film were increased by electrical current energy.     

Longitudinal vibration and stability analysis of carbon nanotubes conveying viscous fluid

Nowadays, carbon nanotubes (CNT) play an important role in practical applications in fluidic devices. To this end, researchers have studied various aspects of vibration analysis of a behavior of CNT conveying fluid. In this paper, based on nonlocal elasticity theory, single-walled carbon nanotube (SWCNT) is simulated. To investigate and analyze the effect of internal fluid flow on the longitudinal vibration and stability of SWCNT, the equation of motion for longitudinal vibration is obtained by using Navier-Stokes equations. In the governing equation of motion, the interaction of fluid-structure, dynamic and fluid flow velocity along the axial coordinate of the nanotube and the nano-scale effect of the structure are considered. To solve the nonlocal longitudinal vibration equation, the approximate Galerkin method is employed and appropriate simply supported boundary conditions are applied. The results show that the axial vibrations of the nanotubesstrongly depend on the small-size effect. In addition, the fluid flowing in nanotube causes a decrease in the natural frequency of the system. It is obvious that the system natural frequencies reach zero at lower critical flow velocities as the wave number increases. Moreover, the critical flow velocity decreases as the nonlocal parameter increases.     

Effect of charge on the stability of single-walled carbon nanotubes

Carbon nanotubes can be viewed as a complete tube structure formed from graphitelayers and they have long been a research focus since the discovery in 1991[1,2]. Due totheir distinct atomic and electronic structures, carbon nanotubes, especially single-walled carbon nanotubes (SWNTs), have got into the frontier of the nanoelectronics andthe molecular electronics[3], in addition to their applications in the field of material sci-ence. After successfully manufacturing model electronic devices[4…     

模拟研究碳纳米管的热稳定性质

运用分子动力学方法具体模拟研究单个碳纳米管（CNTs）在加热过程中的结构变化．选择多组不同结构的单壁碳纳米管（SWCNTs）和双壁碳纳米管（DWCNTs）作为研究对象,加热温度从室温开始到4000 K,压强保持为1 atm．结果表明单壁碳管中手性型结构热稳定性最好,其次是扶手椅型和锯齿型,当手性角相同时,直径大的热稳定性更高;对于双壁碳管,研究表明当双壁中至少之一为手性结构时其热稳定好,而内外壁均为锯齿结构的稳定性最差,该结果进一步支持了有关单壁碳管的结论;还从理论上探索了描述结构热稳定性的方式,并在键层 关键词： 单壁碳纳米管 双壁碳纳米管 分子动力学方法 热稳定性能     

Structure, stability, and motion of dislocations in double-wall carbon nanotubes

In this paper,a novel double-wall carbon nanotube(DWCNT) with both edge and screw dislocations is studied by using the molecular dynamics(MD) method.The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9,respectively,by taking into account the symmetry,integrality,and thermal stability of the composite structures.It is found that melting first occurs near the dislocations,and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K-2700 K.At the premelting temperatures,the shrink of the dislocation loop,which is comprised of edge and screw dislocations,implies that the composite dislocation in DWCNTs has self-healing ability.The dislocated DWCNTs first fracture at the edge dislocations,which induces the entire break in axial tensile test.The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs.Our results not only match with the dislocation glide of carbon nanotubes(CNTs) in experiments,but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope(HRTEM),which is deemed to cause the motion of dislocation loop.     

Relative isomer abundance of fullerenes and carbon nanotubes correlates with kinetic stability

A methodology to evaluate the kinetic stability of carbon nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations. The kinetic stability is directly correlated to the cleavage probability for the weakest bond of a given nanostructure. The application of the presented method to fullerenes and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. The general and simple formulation of the method ensures its applicability to other nanostructures for which formation is controlled by kinetic factors.     

Interaction of charged particles with nanotubes

We have studied the interaction of charged particles with single-walled metallic nanotubes by solving Poisson’s equation with appropriate boundary conditions. Numerical results for the energy dispersion relations as a function of the wave vector are presented when the charged particle is inside or outside the nanotube.