Anomalously soft dynamics of water in a nanotube: a revelation of nanoscale confinement

Quasi-one-dimensional water encapsulated inside single-walled carbon nanotubes, here referred to as nanotube water, was studied by neutron scattering. The results reveal an anomalously soft dynamics characterized by pliable hydrogen bonds, anharmonic intermolecular potentials, and large-amplitude motions in nanotube water. Molecular dynamics simulations consistently describe the observed phenomena and propose the structure of nanotube water, which comprises a square-ice sheet wrapped into a cylinder inside the carbon nanotube and interior molecules in a chainlike configuration.     

Proton conductivity of single-walled carbon nanotubes: A semiempirical study

The possibility of using single-walled carbon nanotubes as materials with proton conductivity is investigated. Two possible mechanisms of migration of a proton over the surface of single-walled carbon nanotubes are proposed. The proton transfer over the outer surface of carbon nanotubes is calculated at the semiempirical quantum-mechanical level. The surface profiles of the potential energy are constructed and used to calculate the activation energy of proton hopping from one carbon atom to another carbon atom. This activation energy can be useful for determining a temperature dependence of the relative hopping conductivity of a nanotube.     

170keV质子辐照对多壁碳纳米管薄膜微观结构与导电性能的影响

碳纳米管具有优异的导电性, 是未来电子元器件的理想候选材料, 应用前景广阔. 针对碳纳米管在空间电子元器件的应用需求, 本文研究了170 keV质子辐照对多壁碳纳米管薄膜微观结构与导电性能的影响. 采用扫描电子显微镜(SEM)、拉曼光谱仪(Raman)、X射线光电子能谱仪(XPS)及电子顺磁共振谱仪(EPR)对辐照前后碳纳米管试样的表面形貌和微观结构进行分析; 利用四探针测试仪对碳纳米管薄膜进行导电性能分析. SEM分析表明, 170 keV质子辐照条件下, 当辐照注量高于5×10¹⁵ p/cm² (protons/cm²)时, 碳纳米管薄膜表面变得粗糙疏松, 纳米管发生明显弯曲、收缩及相互缠结现象. 目前, 质子辐照纳米管发生的收缩现象被首次发现. 基于Raman和XPS分析表明, 170 keV质子辐照后碳纳米管的有序结构得到改善, 且随辐照注量增加, 碳纳米管的有序结构改善明显. 结构的改善主要是由于170 keV质子辐照碳纳米管所产生的位移效应导致缺陷重组. EPR分析表明, 随着辐照注量的增加, 碳纳米管薄膜内的非局域化电子减少. 利用四探针测试分析表明, 碳纳米管薄膜的导电性能变差, 这是由于170 keV质子辐照导致碳纳米管薄膜中的电子特性及形态发生改变. 本文研究结果有助于利用质子辐照对碳纳米管膜结构和性能进行调整, 从而制备出抗辐射的纳米电子器件.     

多壁碳纳米管固相微萃取测定水中的三唑酮和噻嗪酮

将多壁碳纳米管涂在不锈钢丝上制作了固相微萃取探头,利用固相微萃取-气相色谱-质谱联用技术测定湖水中的三唑酮和噻嗪酮。对萃取温度、萃取时间及离子强度等影响萃取效率的因素进行了优化。在优化的条件下,通过加标水样的分析对方法进行了评估。结果表明,方法的线性范围为25—150μg/L,相关系数为0.9922—0.9982,三唑酮和噻嗪酮的检出限（LOD,S/N=3）分别为2.21ng/L和0.18ng/L。湖水的加标回收率在84%—110%之间,相对标准偏差小于10.8%。     

Long fine single-wall carbon nanotube growth by Nano-spin-threading: model schematics and simulations

We have investigated model schematics for a long fine single-wall carbon nanotube growth inside a larger diameter nanotube. Our proposed schematics are as follows: fullerenes are encapsulated into the nano-channel connected with fullerene storage tank; and then a inner nanotube grows via fullerene coalescence under 1200 °C in the nano-channel. Then the grown carbon nanotube is extracted from the nano-channel by mechanical control. We have investigated fullerene mergence inside single-wall carbon nanotube using classical molecular dynamics simulations based on the Tersoff–Brenner potential and the Lennard–Jones potential. During fullerene-encapsulating, since the fullerenes naturally have the kinetic energies due to the suction force and can be also accelerated by external force fields to improve the fullerene encapsulation rate, they can be migrated toward the other side of the nano-channel with kinetic energies. Our molecular dynamics simulations showed that the structural relaxation of dynamically free atoms affected on the growth of inner carbon nanotube rather than the Stone-Wales transformations. Since the broken bonds make the structural relaxation during merging to be easily achieved from the migration of carbon atoms or carbon chains, the inner nanotube grows via the re-bonding-reactions of dynamically free carbon atoms or chains as well as the Stone-Wales transformations. We could conclude that the growth rate of the inner CNT could be increased when bond-breakings between carbon atoms of fullerenes were easily achieved.     

Understanding the loading dependence of self-diffusion in carbon nanotubes

The influence of flexible walls on the self-diffusion of CH4 in an isolated single walled carbon nanotube, as an example, is studied by molecular dynamics simulations. By simulating the carbon nanotube as a flexible framework we demonstrate that the flexibility has a crucial influence on self-diffusion at low loadings. We show how this influence can be incorporated in a simulation of a rigid nanotube by using a Lowe-Andersen thermostat which works on interface-fluid collisions. The reproduction of the results of a flexible carbon nanotube by a rigid nanotube simulation is excellent.     

Single-file transport of water molecules through a carbon nanotube

Recent molecular dynamics simulations of water transport through the interior channel of a carbon nanotube in contact with an aqueous reservoir showed that conduction occurred in bursts with collective water motion. A continuous-time random-walk model is used to describe concerted transport through channels densely filled with molecules in a single-file arrangement, as also found in zeolites, as well as ion channels and aquaporins in biological membranes. Theoretical predictions for different collective properties of the single-file transport agree with the simulation results.     

Stiffness of single-walled carbon nanotubes under large strain

Large-scale molecular dynamic simulations of the axial deformations in single-walled carbon nanotubes have been performed using an O(N) tight-binding method. Our simulations indicate that under large strain, 0 K stress is remarkably sensitive to helicity, and that a zigzag nanotube and an armchair nanotube are the stiffest, respectively, under elongation and compression regimes. Furthermore, the elastic properties of a graphite sheet have been investigated using a simple harmonic potential and an analytic bond-order potential. The results suggest that the unique elastic properties of carbon nanotubes originate from those of a six-membered ring.     

Frequency change by inter-walled length difference of double-wall carbon nanotube resonator

Ultrahigh frequency nanomechanical resonators based on double-walled carbon nanotubes with different wall lengths were investigated via classical molecular dynamics simulations. For a double-walled carbon nanotube resonator with a short outer wall, the free edge of the short outer wall plays an important role in the vibration of the long inner wall. For a double-walled carbon nanotube resonator with a short inner wall, the short inner wall can be considered as a flexible core, thus, the fundamental frequency is influenced by its length. By controlling the length of the inner or outer wall, various frequency devices can be realized by a single type of double-walled carbon nanotube with walls of equal length.     

Simple and accurate model for voltage-dependent resistance of metallic carbon nanotube interconnects: An ab initio study

In this work, development of a voltage dependent resistance model for metallic carbon nanotubes is aimed. Firstly, the resistance of metallic carbon nanotube interconnects are obtained from ab initio simulations and then the voltage dependence of the resistance is modeled through regression. Self-consistent non-equilibrium Green's function formalism combined with density functional theory is used for calculating the voltage dependent resistance of metallic carbon nanotubes. It is shown that voltage dependent resistances of carbon nanotubes can be accurately modeled as a polynomial function which enables rapid integration of carbon nanotube interconnect models into electronic design automation tools.     

Electrical conduction of carbon nanotubes due to the migration of protons over their surface

The results of the theoretical calculation of the proton conductivity tensor for single-walled carbon nanotubes are presented. The electronic structure of the objects under investigation is considered within the band model in the approximation of an ideal proton Fermi gas. The temperature dependence of the proton contribution to the static longitudinal conductivity σ of the carbon nanotube is obtained using the Green’s function method. The function σ(T) for all the carbon nanotubes under consideration exhibits a characteristic behavior that is inherent in conductors. The differences in the conductivity curves for zigzagtype carbon nanotubes with the chirality indices both multiple and not multiple of three are predicted.     

Molecular dynamic study on contact angle of water droplet on a single-wall carbon nanotube (SWCNT) plate

Molecular dynamics (MD) simulations are carried out to study the interaction between a carbon nanotube (CNT) plate and nano-sized water droplet. The cases with or without a quadrupole term acting on the charge sites of the water molecule, are directly compared. The wettability of the CNT plate with different separation distances is studied, and the contact angle on the plates with various separation distances is measured and analyzed. The simulation indicates that the contribution from quadrupole potential is negligible for wetting between twin CNTs and liquid water, while it is significant for holding a sphere-like water droplet and forming a reasonable contact angle.     

Modeling on ion rejection using membranes comprising ultra-small radii carbon nanotubes

In this paper, we investigate the complete ion rejection using carbon nanotube membranes comprising ultra-small radii nanotubes. Three acceptance radii for a water molecule, a sodium ion and a chloride ion are determined assuming the continuous approximation. Given the acceptance radii, we may confine the scope of the nanotube radius so that only water molecules can pass through but the heavier sodium and chloride ions are repulsed from the nanotube ends. We assume that the collective motion of water molecules inside a sufficiently long nanotube is driven by atomic vibrations so that classical phonon theory might be used to deduce the average water transit time inside the nanotube for ion rejection. We predict that for carbon nanotube membranes comprising nanotubes of radii lying between 3.4 and 3.9 ?, only water molecules will pass through, and sodium and chloride ions will not, which together using phonon theory, we deduce that the smaller the nanotube radius, the lower the average water transit time and the higher the efficiency of the membrane for ion rejection purposes. The present theoretical approach has the merit of rapid computational times and indicates those nanotube radii where future experimental work might be focussed.     

Mechanical property of carbon nanotubes with intramolecular junctions: Molecular dynamics simulations

Intramolecular junctions (IMJs) of carbon nanotubes hold a promise of potential applications in nano-electromechanical systems. However, their structure-property relation is still unclear. Using the revised second-generation Tersoff-Brenner potential, molecular dynamics simulations were performed to study the mechanical properties of single-walled to four-walled carbon nanotubes with IMJs under uniaxial tension. The dependence of deformation and failure behaviors of IMJs on the geometric parameters was examined. It was found that the rupture strength of a junction is close to that of its thinner carbon nanotube segment, and the rupture strain and Young's modulus show a significant dependence on its geometry. The simulations also revealed that the damage and rupture of multi-walled carbon nanotube junctions take place first in the innermost layer and then propagate consecutively to the outer layers. This study is helpful for optimal design and safety evaluation of IMJ-based nanoelectronics.     

Gating of Water Flow Induced by Bending of a Carbon Nanotube

The ON-OFF state transition of the water transport induced by the structural bending of a carbon nanotube is studied by molecule dynamics simulation. The water permeation through a bent carbon nanotube shows excellent gating property with a threshold bending angle of about 14.6°. We also investigate the water density distribution inside the nanochannel to illustrate the mechanism.     

Initial growth of single-walled carbon nanotubes on supported iron clusters: a molecular dynamics study

Molecular dynamics simulations were used to study the initial growth of single-walled carbon nanotubes (SWNTs) on a supported iron cluster (Fe₅₀). Statistical analysis shows that the growth direction of SWNTs becomes more perpendicular to the substrate over time due to the weak interaction between carbon nanotube and the substrate. The diameter of the nanotube also increases with the simulation time and approaches the size of the supported iron cluster.     

界面羟基对碳纳米管摩擦行为和能量耗散的影响

本文采用分子动力学模拟研究了羟基对碳纳米管摩擦和能量耗散方式的影响.研究结果表明:由于界面间氢键的形成,碳纳米管所受的平均摩擦力明显增大;随着羟基比例的改变,界面间氢键的数量与摩擦力的变化趋势一致;碳纳米管的手性角对摩擦力有一定的影响,扶手椅型碳纳米管所受的摩擦力比其他类型的碳纳米管的大;直径对摩擦力的影响较大,直径越大界面间的摩擦力越大,其原因是大直径的碳纳米管底部变平导致界面接触面积增大;界面接枝羟基后,体系的声子态密度中出现羟基的振动峰;随羟基比例的增加,羟基的振动在能量耗散中起到更为重要的作用,当碳纳米管和硅基底的羟基比例为10%/20%时,体系能量耗散的主要途径由碳纳米管和硅基底的振动转变为羟基的振动.     

Fabrication of cross-linked multi-walled carbon nanotube coatings with improved adhesion and intrinsic strength by a two-step synthesis: electrochemical deposition and hyperthermal proton bombardment

A two-step synthesis for multi-walled carbon nanotube (MWCNT) coating was reported that includes an electrochemical deposition followed by 10 eV hyperthermal proton bombardment at a dose as low as 1×10¹⁶ H⁺/cm². Electrochemical deposition ensures an improved adhesion of MWCNT coating on metal substrates, while hyperthermal proton bombardment effectively induces inter-chain cross-linkages among MWCNTs, leading to a coating with both higher stiffness and mechanical strength. It was found experimentally that the MWCNT film made by the proposed two-step synthesis can better resist spinning and ultrasonic rinsing in both organic (hexane) and aqueous (water) media. PACS 61.46.+w; 68.35.Np; 68.37.Ps; 81.15.Pq     

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.