Structure of Lennard-Jones nanowires encapsulated by carbon nanotubesStructure of Lennard-Jones nanowires encapsulated by carbon nanotubesStructure of Lennard-Jones nanowires encapsulated by carbon nanotubesStructure of Lennard-Jones nanowires encapsulated by carbon nanotubesStructure of Lennard-Jones nanowires encapsulated by carbon nanotubes

Molecular dynamics simulations have been performed to investigate the structures of Lennard-Jones （LJ） nanowires （NWs） encapsulated in carbon nanotubes （CNTs）. We find that the structures of NWs in a small CNT only adopt multi-shell motifs, while the structures of NWs in a larger CNT tend to adopt various motifs. Among these structures, three of them have not been reported previously. The phase boundaries among these structures are obtained regarding filling fractions, as well as the interaction between NWs and CNTs.     

Potentials of classical force fields for interactions between Na~+ and carbon nanotubes

Carbon nanotubes(CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here,using density functional theory calculations, we provide classical force field potentials for the interactions of Na+/hydrated Na+with(7,7),(8,8),(9,9), and(10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics(NAMD) by employing the tcl BC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.     

Applications of carbon nanotubes in high performance lithium ion batteries

The development of lit;triton ion batteries （LIBs） relies on the improvement in the performance of electrode materials with higher capacity, higher rate capability, and longer cycle lift;. In this review article, the recent advances in carbon nanotube （CNT） anodes, CNT-based composite electrodes, and CNT current collectors for high performance LIBs are concerned. CNT has received considerable attentions as a candidate material for the LIB applications. In addition to a possible choice for anode, CNT has been recognized as a solution in improving the performance of the state-of-the-art electrode materials. The CNT-based composite electrodes can be fabricated by mechanical or chem- ical approaches. Owing to the large aspect ratio and the high electrical conductivity, CNTs at very low loading can lead to an efficient conductive network. The excellent mechanical strength suggests the great potential in forming a structure scaffold to accommodate nano-sized electrode materials. Accordingly, the incorporation of CNTs will enhance the conductivity of the composite electrodes, mitigatc the agglomeration problem, decrease the dependence on inactive binders, and improve the clcctrochenfical properties of both anode and cathode materials remarkably. Freestanding CNT network can be used as lightweight current collectors to increase the overall energy density of LIBs. Finally, research perspectives for exploiting CNTs in high-performance LIBs are discussed.     

Thermal conductivity of nanowires

Thermal conductivity of nanowires(NWs) is a crucial criterion to assess the operating performance of NWs-based device applications, such as in the field of heat dissipation, thermal management, and thermoelectrics. Therefore, numerous research interests have been focused on controlling and manipulating thermal conductivity of one-dimensional materials in the past decade. In this review, we summarize the state-of-the-art research status on thermal conductivity of NWs from both experimental and theoretical studies. Various NWs are included, such as Si, Ge, Bi, Ti, Cu, Ag, Bi_2Te_3, ZnO, AgTe,and their hybrids. First, several important size effects on thermal conductivity of NWs are discussed, such as the length,diameter, orientation, and cross-section. Then, we introduce diverse nanostructuring pathways to control the phonons and thermal transport in NWs, such as alloy, superlattices, core–shell structure, porous structure, resonant structure, and kinked structure. Distinct thermal transport behaviors and the associated underlying physical mechanisms are presented.Finally, we outline the important potential applications of NWs in the fields of thermoelectrics and thermal management,and provide an outlook.     

Analysis,design and simulation of MIM plasmonic filters with different geometries for technical parameters improvement

In this paper, four optical filter topologies based on metal–insulator–metal waveguides are proposed and the designed structures are investigated numerically using finite-difference timedomain method. Triangular-shaped adjunctions have been added to the filter structures to improve their transmission spectrum. These improved structures consist of air as the insulator and silver as the metal. The relative permittivity of metal has been described via the Drude,Drude–Lorentz, and Palik models. The first filter's transmission spectrum shows an acceptable transmittance. In the second optimized filter, the transmission spectrum has been improved. The transmittance spectrum can be tuned through adjusting the edge of the triangle in these four optimized filters. As a result, the bandwidths of resonance spectra can be adjusted. The theory of such tapered structures will be investigated by the tapered transmission line and will be solved with the transfer matrix method. This method shows a better performance and higher transmission efficiency in comparison with the basic structures. On the other hand, the final filter has been chosen as the best one because of its hexagonal resonator. The main reason for having a better result is due to a longer interaction length in comparison with the circular resonator. This in turn creates much better energy coupling and results in higher transmission.     

Current Density-Dependent Thermal Stability of ZnSe Nanowire in M-S-M NanostructureD

Due to semiconductor nanowire （NW） having a very tiny diameter, the electronic devices based on metal-semiconductor NW-metal （M-S-M） nanostruc- ture can carry a very large current density com- pared to electronics based on bulk semiconductors. A small mass of a NW also means a small heat capacitance. In this case, any small energy trans- fer from the current-carry electrons to local ionic or/and lattice vibrations in NWs may cause a sub- stantial self-heating of the NWs. Thus thermal insta- bility of NWs in M-S-M nanostructure due to Joule heating has become a fundamentally and technolog- ically important issue concerning the performance of semiconductor NW-based nanoelectronics and has at- tracted a lot of attention. The failure behaviors of various semiconductor and metallic NWs inves- tigated by in situ transmission electron microscopy （TEM） and confocal micro-Raman spectroscopy re- spectively have confirmed semiconductor NWs includ- ing Si, Ge, GaN, ZnO, Sn02, Ti02, ZnSe and ZnTe NWs electrically broken by thermal evaporation due to Joule heating and metallic NWs electrically de- stroyed by electromigration. Electron-phonon in- teraction that transfers energy from conduction elec- trons to the ions in the material causes Joule heating. Electromigration due to the transfer of the momentum of conduction electrons to the ions causes migration of atoms in the material when high current density flows through a circuit. The different failure mechanisms of these NWs are significantly materials-dependent due to the difference of their chemical and physical prop- erties and have a very close relation with the param- eters governing the electron transport mechanism at the metal-semiconductor （M-S） nanocontact such as Schottky barrier and bias polarity .     

Nodular Carbon Nanotubes and Their Field Emission Characteristics

A new configuration of carbon namotubes(CNTs) has been discovered in our laboratory and their surfaces are fully covered with nano-sized node-like structures.The node structures have almost the same size of 40-50nm.We refer to this material as the nodular carbon nanotube (NCNT).Field emission scanning electron microscopy shows that after a hydrogen plasma process in our homemade plasma equipment,the common carbon nanotubes were changed into NCNTs.The experimental result demonstrates that this material has good field emission characteristics,low threshold field,stable and suitable emitting surrent,especdially for the emission site density up to the order of 10^6cm^-2.     

Topological origin of global attractors in gene regulatory networks

Fixed-point attractors with global stability manifest themselves in a number of gene regulatory networks. This property indicates the stability of regulatory networks against small state perturbations and is closely related to other complex dynamics. In this paper, we aim to reveal the core modules in regulatory networks that determine their global attractors and the relationship between these core modules and other motifs. This work has been done via three steps. Firstly, inspired by the signal transmission in the regulation process, we extract the model of chain-like network from regulation networks. We propose a module of “ideal transmission chain(ITC)”, which is proved sufficient and necessary(under certain condition) to form a global fixed-point in the context of chain-like network. Secondly, by examining two well-studied regulatory networks(i.e., the cell-cycle regulatory networks of Budding yeast and Fission yeast), we identify the ideal modules in true regulation networks and demonstrate that the modules have a superior contribution to network stability(quantified by the relative size of the biggest attraction basin). Thirdly, in these two regulation networks, we find that the double negative feedback loops, which are the key motifs of forming bistability in regulation, are connected to these core modules with high network stability. These results have shed new light on the connection between the topological feature and the dynamic property of regulatory networks.     

Electronic structures and optical properties of TiO₂:Improved density-functional-theory investigation

TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha’s modified Becke-Johnson(TB-mBJ) exchange potential(plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation(LDA) and generalized gradient approximation(GGA),in contrast with substantially overestimated values from many-body perturbation(GW) calculations.As for optical dielectric functions(both real and imaginary parts),refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.     

New Astrophysical Reaction Rates for ^18F（P,α）^15O and ^18F（P,γ）^19Ne

The rates of the thermonuclear ^18F(P,α)^15O and ^18F(P,γ)^19Ne reactions in hot astrophysical environments are needed to understand gamma-ray emission from nova explosions. The rates for these reactions have been uncertain due to discrepancies in recent measurements, as well as to a lack of a comprehensive examination of the available structure information in the compound nucleus ^19Ne. We have examined the latest experimental measurements with radioactive and stable beams, and made estimates of the unmeasured ^19Ne nuclear level parameters, to generate new rates with uncertainties for these reactions. The rates are expressed as numerical values over the temperature range relevant for stellar explosions, as well as analytical expressions as functions of temperature in a format suitable for use in astrophysical simulations. Comparisons with the previous rate calculations are carried out, and the astrophysical implications are briefly discussed.     

Contact welding study of carbon nanotube with ZnO nanowire

Study of proton beam induced welding of multiwall carbon nanotubes (MWCNTs) with ZnO nanowires (NWs) has been carried out by proton (H⁺) beam irradiation. The samples were irradiated by 70-keV proton (H⁺) ion beams at different substrate temperatures. The irradiation-induced defects in CNTs and ZnO NWs were greatly reduced at elevated temperature. The crystalline structure of ZnO NWs and MWCNTs were found to remain stable after the irradiation at 700 K. As a preparation step, a coupling of two parallel ZnO NWs with irradiation has also been demonstrated. The welding mechanisms of MWCNTs and ZnO NWs were also been suggested. These two welding processes between same and distinct nanostructures to form homo- and hetero-junctions have provided an opportunity to mass produce interconnecting one-dimensional structures used for the manufacturing of future nanowire-based electronic circuits and devices.     

Aligned Ni nanoparticle arrays encapsulated in carbon nanotubes

Using the carbon nanotube (CNT) arrays embedded in anodic aluminum oxide (AAO) template as an electrode, large amounts of Ni nanoparticles have been encapsulated into the CNTs by an alternating current (AC) electrodepostion technique. As deposited Ni nanoparticles with a typical size of 50–60 nm randomly nucleated on the CNT walls, thus inhomogeneously distributed in the CNTs. After annealing at 600 ^°C, the nanoparticles transformed into quasi-spherical structures with the diameter increasing to 60–80 nm. The quasi-spherical nanoparticles were aligned in orderly rows along the axis of the CNT channels. Magnetic hysteresis measured at 5 K showed that the coercivity was 450 Oe for the as-deposited sample and 385 Oe for annealed sample, with the applied magnetic field parallel with the CNT’s axis. The structures and magnetic properties were discussed for both as-deposited and annealed samples.     

Physics and applications of aligned carbon nanotubes

Ever since the discovery of carbon nanotubes (CNTs) by Iijima in 1991, there have been extensive research efforts on their synthesis, physics, electronics, chemistry, and applications due to the fact that CNTs were predicted to have extraordinary physical, mechanical, chemical, optical, and electronic properties. Among the various forms of CNTs, single-walled and multi-walled, random and aligned, semiconducting and metallic, aligned CNTs are especially important since fundamental physics studies and many important applications will not be possible without alignment. Even though there have been significant endeavors on growing CNTs in an aligned configuration since their discovery, little success had been realized before our first report on growing individually aligned CNTs on various substrates by plasma-enhanced chemical vapor deposition (PECVD) [Science 282 (1998) 1105–1108]. Our report spearheaded a new field on growth, characterization, physics, and applications of aligned CNTs. Up to now, there have been thousands of scientific publications on synthesizing, studying, and utilizing aligned CNTs in various aspects. In this communication, we review the current status of aligned CNTs, the physics for their alignment, their applications in field emission, optical antennas, subwavelength light transmission in CNT-based nanocoax structures, nanocoax arrays for novel solar cell structures, etc.

The focus of this review is to examine various aligned CNT systems, either as an individual or as an array, either the orientation is vertical, parallel, or at other angles to the substrate horizon, either the CNT core structures are mostly hollow channels or are composed of complex compartments. Major fabrication methods are illustrated in detail, particularly the most widely used PECVD growth technique on which various device integration schemes are based, followed by applications whereas current limitations and challenges will also be discussed to lay down the foundation for future developments.     

The interaction between unique hyperbranched polyaniline and carbon nanotubes,and its influence on the dielectric behavior of hyperbranched polyaniline/carbon nanotube/epoxy resin composites

Novel hybridized multi-walled carbon nanotubes (CNTs), consisting of a unique hyperbranched polyaniline (HSiPA) and CNTs, were prepared. The interaction between HSiPA and CNTs was investigated by many techniques, and results show that there are strong π–π and electrostatic interactions between HSiPA and CNTs, so HSiPA can stack firmly onto the surface of CNTs to form a coating. Based on this, a new kind of ternary composites made up of hybridized CNTs and epoxy (EP) resin was prepared, the influence of the ratio of HSiPA to CNTs on the structure and properties of the HSiPA/CNT/EP composites was intensively studied. The percolation threshold of HSiPA/CNT/EP composites is very low (1.26 wt%); besides, with a suitable ratio of HSiPA to CNTs, the HSiPA/CNT/EP composite has much higher dielectric constant and lower dielectric loss than the CNT/EP composite with the same loading of CNTs. When the ratio of HSiPA to CNTs is 0.5:1, the dielectric constant and loss at 100 Hz of the resultant HSiPA/CNT0.5/EP composite are 711 and 1.53, about 7.1 and 4.3 × 10^?3 times the corresponding value of CNT0.5/EP composite, respectively. In addition, compared with traditional CNT/EP composites, the HSiPA/CNT0.5/EP composites have different equivalent circuit models. These attractive results are attributed to unique structure of hybridized CNTs, and thus leading to greatly different structures between the CNT0.5/EP and HSiPA/CNT0.5/EP composites. This investigation reported herein suggests a new approach to prepare new CNTs and related composites with controllable dielectric properties.     

碳纳米管阵列、捆束的三步升温工艺制备及其形貌与结构

使用结构简单的单温炉设备，通过三步升温热解二茂铁、三聚氰氨混合物方法，在二氧化硅、多晶陶瓷基底上分别合成了碳纳米管阵列、碳纳米管捆束.使用扫描电子显微镜、透射电子显微镜、电子能量损失谱和x射线光电子能谱对合成样品进行了结构和成分分析.结果显示：两种基底上合成的纳米管均为多壁纯碳管；生长于光滑二氧化硅表面的碳纳米管具有高度取向性和一致的外径，长度为10—40μm.碳纳米管采取催化剂顶端生长模式并展示出类杯状形貌；生长于粗糙多晶陶瓷表面的碳纳米管捆束随机取向，碳纳米管直径为15—80nm，长度在几百微米，展示 关键词： 碳纳米管 热解法 三步升温工艺     

Studies on structural defects in carbon nanotubes

Structural defects in carbon nanotubes (CNTs) have been paid much attention, because they influence the properties of the CNTs to some extent. Among various defects in CNTs, both single vacancies and Stone-Wales (SW) defects are the simple and common ones. In this paper, we review the progress of research in these two kinds of defects in CNTs. For single vacancies, we first address their different structural features in both zigzag and armchair CNTs, and their stabilities in CNTs with different sizes and different symmetries systematically. The presence of the single vacancies in CNTs not only influences the electronic structures of the systems, but also affects the vibrational properties of the tubes. Nevertheless, being active chemically, the single vacancies in the tubes prefer to interact with adsorbates nearby, of which the interaction of the defects with hydrogen atom, hydrogen molecule and some small hydrocarbon radicals (-CH, -CH₂ and -CH₃) are discussed. The former is associated with H storage and the latter is of merit to improve the local structure of the defect in a CNT. For the Stone-Wales defect, we mainly focus on its stability in various CNTs. The influence of the SW defects on the conductance of CNTs and the identification of such a defect in CNT is described in brief.      

Aligned carbon nanotube from catalytic chemical vapor deposition technique for energy storage device: a review

Carbon nanomaterial especially carbon nanotube (CNT) possesses remarkably significant achievements towards the development of sustainable energy storage applications. This article reviews aligned CNTs grown from chemical vapor deposition (CVD) technique as electrode material in batteries and electrochemical capacitors. As compared to the entangled CNTs, aligned or well-organized CNTs have advantages in specific surface area and ion accessibility in which more electrolyte ions can access to CNT surfaces for better charge storage performance. CVD known as the most popular technique to produce CNTs enables the use of various substrates and CNT can grow in a variety of forms, such as powder, films, aligned or entangled. Also, CVD is a simple and economic technique, and has good controllability of direction and CNT dimension. High purity of as-grown CNTs is also another beauty of the CVD technique. The current trend and performance of devices utilizing CNTs as electrode material is also extensively discussed.     

Molecular dynamics of reactions between (4,0) zigzag carbon nanotube and hydrogen peroxide under extreme conditions

ABSTRACT

Single-wall carbon nanotubes (CNTs) have been suggested as potential materials for use in next-generation gas sensors. The sidewall functionalisation of CNTs facilitates gas molecule adsorption. In this study, density functional theory (DFT)-based ab initio molecular dynamics simulations are performed for a periodic zigzag single-wall (4,0) CNT surrounded by a monolayer of hydrogen peroxide molecules in an attempt to find conditions that favour sidewall functionalisation. The dependency of dynamics on charge states of the system is examined. It is found negative charges favour reactions that result in the functionalisation of the CNT. First principles molecular dynamics of defect formation yields chemically reasonable structure of stable defects, which can be reproduced in CNTs of any diameter and chirality. The explored hydroxyl and hydroperoxyl defects increase conductivity in a large diameter (10,0) CNT, while decrease conductivities in a small diameter (4,0) CNT.     

The difficulties in establishing an occupational exposure limit for carbon nanotubes

Concern over the health effects from the inhalation of carbon nanotubes (CNTs) has been building for some time, and adverse health effects found in animal studies include acute and chronic respiratory damage, cardiac inflammation, and cancer including mesothelioma, heretofore only associated with asbestos exposure. The strong animal evidence of toxicity requires that the occupational hygiene community develops strategies for reducing or eliminating worker exposures to CNTs; part of this strategy involves the setting of occupational exposure limits (OELs) for CNTs. A number of government agencies and private entities have established OELs for CNTs; some are mass-based, while others rely on number concentration. We review these various proposed standards and discuss the pros and cons of each approach. We recommend that specific action be taken, including intensified outreach to employers and employees concerning the potential adverse health effects from CNT inhalation, the development of more nuanced OELs that reflect the complex nature of CNT exposure, a broader discussion of these issues among all interested parties, and further research into important unanswered questions including optimum methods to evaluate CNT exposures. We conclude that current animal toxicity evidence suggests that strong action needs to be taken to minimize exposures to CNTs, and that any CNT OEL should be consistent with the need to minimize exposures.     

Nanowire formation by coalescence of small gold clusters inside carbon nanotubes

The coalescence of Au₁₃, Au₅₅ and Au₁₄₇ icosahedral clusters encapsulated inside single walled carbon nanotubes (CNTs) of different diameters are investigated using molecular dynamics simulation with semi-empirical potentials. Three steps needed for the formation of encapsulated nanowires are followed in detail, namely, the penetration of clusters in CNTs, the coalescence between two clusters inside CNTs and their accumulation to form wires. It is suggested that no significant energy barrier is encountered during the penetration of free clusters into CNTs provided the CNT radius is large enough, that is, about 0.3 nm larger than the cluster radius. The relative orientation of clusters imposed by the CNT favors their spontaneous coalescence. After coalescence of two clusters, the Au atoms are rearranged to form new structures of cylindrical symmetry that may be seven fold, six fold, five fold, helical or fcc depending on the CNT diameter. The thermal stability of these structures is discussed and the structural properties of nanowires formed by accumulation of many clusters in CNTs are analyzed in detail. A geometrical method is presented which allows the prediction of the structure of multi-shell helical wires, when knowing only the CNT radius. These modeling results suggest the possibility of synthesizing metallic nanowires with controlled diameter and structure by embedding clusters into nanotubes with suitable diameters.