碳纳米管杨氏模量的模拟计算

使用分子动力学和 Tersoff-brenner 多体势,模拟计算单壁碳纳米管的杨氏模量。所计算的单壁碳纳米管的杨氏模量的平均值为704.5 GPa,计算结果与实验值吻合。     

扶手椅型单壁碳纳米管的扭转和弯曲变形

实验提出了一种针对单壁碳纳米管的原子尺度有限元模型.利用该模型对(5,5)型扶手椅型单壁碳纳米管的扭转和弯曲变形过程进行了模拟,发现其屈曲的临界扭转和纯弯曲角度分别约为40°和20°,与扭转屈曲相比,该碳管更容易发生弯曲屈曲.当弯扭复合变形时发生屈曲后,卸载时壁面褶皱的回复比较缓慢.在某些情况下,碳管的局部势能的变化与经典连续介质力学理论不一致,对此本文结合原子势理论给出了模拟结果的原子尺度的解释.     

新型一维材料--单壁碳纳米管的制备和应用研究

本文简要综述了单壁碳纳米管的最新进展.主要介绍了最近两年单壁碳纳米管的制备技术发展情况,包括电弧放电,化学气相沉淀,激光蒸发和太阳能方法.展望了其在储氢材料,纳米电子器件等领域的应用前景.讨论了影响单壁碳纳米管制备及实际应用的几个关键因素.提出了单壁碳纳米管的发展方向.     

单壁碳纳米管制备的最新进展

碳纳米管是纳米材料研究的一个新领域。本文综述了单壁碳纳米管制备方面的最新进展,并对各种制备方法进行比较。     

Ho/Ni作为催化剂合成单壁碳纳米管

利用直流电弧等离子体方法，以Ho／Ni作为催化剂合成了单壁碳纳米管，借助扫描电子显微镜、拉曼光谱和热重分析方法对所合成的单壁碳纳米管的形貌、结构以及含量进行了表征。电镜观察以及热重分析表明，收集到的大量网状物中单壁碳纳米管含量较高；不同激发波长拉曼测量表明碳纳米管直径分布比较集中，在1．35nm～1．69nm范围，且直径为1．5nm的碳纳米管占多数；与Ce／Ni等作为催化剂合成的单壁碳纳米管的直径分布不同。研究结果表明，Ho／Ni对于合成单壁碳纳米管具有很好的催化效果且影响管径分布，元素Ho对单壁碳纳米管的形成起到了重要的作用。     

影响单壁碳纳米管氢气传感器的因素（英文）

单壁碳纳米管用于制造氢气传感器已有几十年的历史。由于单壁碳纳米管与氢气的相互作用很小，因此需采用了多种改性来辅助，改性物包括金属、金属氧化物与聚合物等。一些研究指出，当与碳纳米管上的官能团结合时，改性物可以使响应提高几个数量级。在目前的研究中，已开发了许多新的结构。此外，单壁碳纳米管的直径和手性等结构也会影响氢气探测器的性能。本文对单壁碳纳米管的改性进行了分类，并对其影响因素进行了讨论，旨在为制造高响应度和低检测限的探测器提供支撑。     

单壁碳纳米管量子点的传导电流与电流噪声谱

近来，碳纳米管尤其是单壁碳纳米管越来越引起人们的注意，并已经广泛应用于实践中。本文采用开放量子系统的研究方法，利用量子主方程给出了与扫描隧道显微镜耦合的单壁碳纳米管量子点的输运电流与电流噪声谱的一般性计算方法，并研究了强弛豫条件下输运电流的性质。     

利用振动研究单壁碳纳米管力学性能

单壁碳纳米管的力学性能是碳纳米管增强复合材料和碳纳米管器械的基本问题之一。文中根据分子结构力学方法建立单壁碳纳米管的有限元模型,通过振动频率计算单壁碳纳米管的弹性模量和剪切模量。详细讨论了用不同阶数弯曲振动固有频率和扭转振动固有频率求得的弹性模量和剪切模量结果的准确性,并分析了单壁碳纳米管的直径对弹性模量及剪切模量的影响。     

氨基磺酸铵修饰的单壁碳纳米管

通过过二硫酸铵氧化和氨基磺酸铵化学修饰两个步骤,制备了在水中有较大溶解度的单壁碳纳米管.Raman光谱和UV-vis-NIR吸收光谱表明,上述处理过程没有改变单壁碳纳米管的电子结构;此外,红外光谱的研究说明氨基磺酸铵与碳纳米管是通过酰胺键连接起来的.这种水溶性单壁碳纳米管将会在生物化学和生物医药领域有着重要的应用前景.     

新型一维材料—单壁碳纳米管的制备和应用研究

本文简要综述了单壁碳纳米管的最新进展。主要介绍了最近两年单壁碳纳米管的制备技术发展情况,包括电弧放电,化学气相沉淀,激光蒸发和太阳能方法。展望了其在储氢材料,纳米电子器件等领域的应用前景。讨论了影响单壁碳纳米管制备及实际应用的几个关键因素。提出了单壁碳纳米管的发展方向。     

Effect of ending surface on energy and Young's modulus of an armchair single-walled carbon nanotubes

The energy and Young's modulus as a function of tube length for (10, 10) armchair single-walled carbon nanotubes (SWCNTs) are investigated by using a linear scaling self-consistent-charge density functional tight binding (SCC-DFTB) method. It is found that the formula derived from total energy for a zigzag SWCNT [Physica B404, 3930 (2009)] can be also used to explain these calculated length-dependent properties. Moreover, a transition occurs from fast change of length-dependent properties of the SWCNT to their slow change. This transition corresponds to the SWCNT's length of about 5 nm. The length for the armchair SWCNT is about one half of that of the corresponding Zigzag SWCNTs. In addition, a definition of volume for a short SWCNT is discussed.     

Suspended carbon nanotube nanocomposite beams with a high mechanical strength via layer-by-layer nano-self-assembly

The fabrication and characterization of single-walled carbon nanotube (SWCNT) composite thin film micropatterns and suspended beams prepared by lithography-compatible layer-by-layer (LbL) nano-self-assembly are demonstrated. Negatively charged SWCNTs are assembled with a positively charged polydiallyldimethylammonium chloride, and the composite thin film is patterned by oxygen plasma etching with a masking layer of photoresist, resulting in a feature size of 2 μm. Furthermore, the SWCNT nanocomposite stripe pattern with a metal clamp on both ends is released by etching a sacrificial layer of silicon dioxide in the hydrofluoric acid vapor. I-V measurement reveals that the resistance of SWCNT nanocomposite film decreases by 23% upon release, presumably due to the effect of reorientation of CNTs caused by the deflection of about 50 nm. A high Young's modulus is found in a range of 500-800 GPa based on the characterization of a fixed-fixed beam using nanoindentation. This value is much higher than those of the other CNT-polymer composites reported due to organization of structures by self-assembly and higher loading of CNTs. The stiff CNT-polymer composite thin film micropattern and suspended beam have potential applications to novel physical sensors, nanoelectromechanical switches, other M/NEMS devices, etc.     

Computational study of the effect of carbon vacancy defects on the Young's modulus of (6, 6) single wall carbon nanotube

Most molecular dynamics (MD) simulations for single wall carbon nanotubes (SWCNT) are based on a perfect molecular material structure. The presence of vacancy defects in SWCNTs could lead to deviations from this perfect structure thus affecting the predicted properties. The present paper investigates the effect of carbon vacancy defects in the molecular structure of SWCNT on the Young's modulus of the SWCNT using MD simulations performed via Accelrys and Materials Studio. The effect of the position of the defects in the nanotube ring and the effect of the number of defects on the Young's modulus are studied. The studies indicate that for an enclosed defect with the same shape in a SWCNT structure, its position did not cause any change in the Young's modulus. However, as the number of defects increased, the predicted Young's modulus was found to decrease. For a 10 ring (6, 6) SWCNT, six vacancy defects (corresponding to a defect percentage of 2.5%) reduced the Young's modulus by 13.7%.     

Molecular dynamics study of the effect of chemical functionalization on the elastic properties of graphene sheets

In this study, the effects of chemical functionalization on the elastic properties of graphene sheets are investigated by using molecular dynamics (MD) and molecular mechanics (MM) simulations. The influences of the degree of functionalization, which is defined as the ratio of the number of the total sp3-hybridized atoms to the number of the total carbon atoms of the graphene sheet, the chirality of graphene sheets, the molecular structure and molecular weight of functional groups on Young's modulus are studied. The dependence of shear modulus and wrinkling properties on the functional groups are also investigated. The simulation results indicate that Young's modulus depends strongly on the degree of functionalization and the molecular structure of the functional groups, while the effects of chirality of the graphene sheets and the molecular weight of the functional groups are negligible. The chemical functionalization also reduces the shear modulus and critical strain, beyond which the wrinkling instability occurs.     

Studies of Size Effects on Carbon Nanotubes' Mechanical Properties by Using Different Potential Functions

We use molecular mechanics calculations to study size effects on mechanical properties of carbon nanotubes. Both single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) are considered. The size-dependent Young's modulus decreases with the increasing tube diameter for a reactive empirical bond order (REBO) potential function. However, we observe a contrary trend if we use other potential functions such as the modified Morse potential function and the universal force field (UFF). Such confliction is only obtained for small tubes within cutoff diameters (3 nm for REBO and 1.5 nm for others). In light of these predictions, Young's moduli of large nanotubes concur with experimental results for all the potential functions. No matter which potential function is used, the Poisson's ratio decreases with the increasing tube diameter. We also study the chirality effects on mechanical properties of SWNTs. We find that the Young's moduli are insensitive to the chirality of nanotubes. The chirality effect on the Poisson's ratio is significant for the UFF but not the REBO or modified Morse potential functions.     

Catalytically grown carbon nanotubes of small diameter have a high Young's modulus

Experimental studies of carbon nanotubes (CNTs) obtained through different synthesis routes show considerable variability in their mechanical properties. The strongest CNTs obtained so far had a high Young's modulus of 1 TPa but could only be produced in gram scale quantities. The synthesis by catalytic chemical vapor deposition, a method that holds the greatest potential for large-scale production, gives CNTs with a high defect density. This leads to low Young's modulus values below 100 GPa for multiwall CNTs. Here we performed direct measurements of the mechanical properties of catalytically grown CNTs with only a few walls and find a Young's modulus of 1 TPa. This high value is confirmed for CNTs grown under two different growth conditions where the synthesis parameters such as the hydrocarbon source, catalyst material, and the synthesis temperature were varied. The results indicate that the observed difference in the Young's modulus for the catalytically grown CNTs with high and low numbers of walls is probably related to the growth mechanism of CNT.     

Atomistic study of structures and elastic properties of single crystalline ZnO nanotubes

The structural stability and Young's modulus of single crystalline ZnO nanotubes are investigated using atomistic simulations. Unlike the case for conventional layered nanotubes, the energetic stability of single crystalline ZnO nanotubes is related to the wall thickness. The potential energy of ZnO nanotubes with fixed outer and inner diameters decreases with increasing wall thickness, while the nanotubes with the same wall thickness are independent of the outer and inner diameters. The transformation of single crystalline ZnO nanotubes with a double layer from wurtzite phase to graphitic phase suggests the possibility of wall-typed ZnO nanotubes. The size-dependent Young's modulus of ZnO nanotubes is also investigated. The wall thickness plays a significant role in the Young's modulus of single crystalline ZnO nanotubes, whereas the variation of outer and inner diameters slightly affects the Young's modulus of nanotubes with same wall thickness.     

Molecular dynamics study on size-dependent elastic properties of silicon nanoplates

Using molecular dynamics simulations, the size-dependent Young's moduli of silicon nanoplates due to surface effects are investigated at intrinsic scale. The transformations of surface reconstructions are discussed in terms of the difference between the total strain energy densities (u_T) of the system from the MD and the specified strain energy densities (u_C). An analytical prediction for the effective Young's modulus is derived for the intrinsic scale specimens, and it agrees well with MD simulations.     

Molecular dynamics simulation studies of structural and mechanical properties of single-walled carbon nanotubes

Structural and mechanical properties of armchair, zig-zag and chiral single-walled carbon nanotubes are computed by employing Molecular Dynamics simulation technique using Discover code with Compass force field via Materials Studio program developed by the Accelrys. Consistent with the literature, we find that the armchair SWCNT is energetically favored over zig-zag and chiral nanotubes. Predicted structural parameters agree well with experimental observations. Observed radial distribution functions show that the single-walled carbon nanotubes remain crystalline after exposing them to 300 K. The predicted Young's and the Shear moduli were in reasonable agreement with other reports. Our predictions show that the Young's modulus of the tubes increases as the diameter of the tube decreases.     

Mechanical behavior and interphase structure in a silica-polystyrene nanocomposite under uniaxial deformation

The mechanical behavior of polystyrene and a silica-polystyrene nanocomposite under uniaxial elongation has been studied using a coarse-grained molecular dynamics technique. The Young's modulus, the Poisson ratio and the stress-strain curve of polystyrene have been computed for a range of temperatures, below and above the glass transition temperature. The predicted temperature dependence of the Young's modulus of polystyrene is compared to experimental data and predictions from atomistic simulations. The observed mechanical behavior of the nanocomposite is related to the local structure of the polymer matrix around the nanoparticles. Local segmental orientational and structural parameters of the deforming matrix have been calculated as a function of distance from nanoparticle's surface. A thorough analysis of these parameters reveals that the segments close to the silica nanoparticle's surface are stiffer than those in the bulk. The thickness of the nanoparticle-matrix interphase layer is estimated. The Young's modulus of the nanocomposite has been obtained for several nanoparticle volume fractions. The addition of nanoparticles results in an enhanced Young's modulus. A linear relation describes adequately the dependence of Young's modulus on the nanoparticle volume fraction.