Molecular dynamics studies on the thermal conductivity of single-walled carbon nanotubes

We have studied the thermal conductivity of single-walled carbon nanotubes (SWCNTs) using the NEMD method. The results indicate that the thermal conductivity values are not profoundly influenced by the specific simulation-technique used in the MD simulations. Some possible reasons, which could be responsible for the discrepancy on thermal conductivity values of SWCNTs in the literatures, are discussed.      

功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法,模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小,当有一列碳原子被氢化后（功能化程度为5%）,碳管的热导率减小了大约1/3,为了进一步解释这种功能化对碳纳米管热导率的影响,计算了不同功能化程度下碳纳米管的声子谱.     

功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法,模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小,当有一列碳原子被氢化后（功能化程度为5%）,碳管的热导率减小了大约1/3,为了进一步解释这种功能化对碳纳米管热导率的影响,计算了不同功能化程度下碳纳米管的声子谱.     

Thermal conductivity of carbon nanoring linked graphene sheets:A molecular dynamics investigation

Improving the thermal conduction across graphene sheets is of great importance for their applications in thermal management. In this paper, thermal transport across a hybrid structure formed by two graphene nanoribbons and carbon nanorings(CNRs) was investigated by molecular dynamics simulations. The effects of linker diameter, number, and height on thermal conductivity of the CNRs–graphene hybrid structures were studied respectively, and the CNRs were found effective in transmitting the phonon modes of GNRs. The hybrid structure with 2 linkers showed the highest thermal conductivity of 68.8 W·m~(-1)·K~(-1). Our work presents important insight into fundamental principles governing the thermal conduction across CNR junctions and provides useful guideline for designing CNR–graphene structure with superior thermal conductivity.     

碳纳米管和碳化硅纳米管热导率的分子动力学研究

采用Tersoff势测试和研究了反向非平衡分子动力学中的Müller-Plathe法和Jund法在一维纳米管热传导中的应用.在相同的模拟步数中,Müller-Plathe法可以得到很好的结果,热导率在交换频率大于50时对参数的选择并不敏感.然而,Jund法并不能得到良好的线性温度梯度,其热导率在一定程度上依赖于选择的热流大小.在此基础上,运用Müller-Plathe法进一步研究了碳纳米管和碳化硅纳米管的长度、直径和温度对热导率的影响.结果表明,无论是碳纳米管还是碳化硅纳米管,其长度、直径和温度对热导率的影响是一致的.只要长度增加,纳米管的热导率相应增大,但增长速率不断降低.直径对热导率的影响很大程度上还取决于温度,在高温时,直径对热导率几乎没有影响.除此之外,纳米管的热导率随着温度的增加总体上也是不断降低的,但峰值现象的出现还受纳米管长度的影响.     

Molecular dynamics simulation of an argon cluster filled inside carbon nanotubes

The effects of the diameters of single-walled carbon nanotubes （SWCNTs） （7.83A to 27.40A） and temperature （20 K-45 K） on the equilibrium structure of an argon cluster are systematically studied by molecular dynamics simulation with consideration of the SWCNTs to be fixed. Since the diameters of SWCNTs with different chiralities increase when temperature is fixed at 20 K, the equilibrium structures of the argon cluster transform from monoatomic chains to helical and then to multishell coaxial cylinders. Chirality has almost no noticeable influence on these cylindrosymmetric structures. The effects of temperature and a non-equilibrium sudden heating process on the structures of argon clusters in SWCNTs are also studied by molecular dynamics simulation.     

Effects of doping, Stone Wales and vacancy defects on thermal conductivity of single-wall carbon nanotubes

The thermal conductivity of carbon nanotubes with certain defects (doping, Stone-Wales, and vacancy) is investigated by using the non-equilibrium molecular dynamics method. The defective carbon nanotubes (CNTs) are compared with perfect tubes. The influences of type and concentration of the defect, length, diameter, and chirality of the tube, and the ambient temperature are taken into consideration. It is demonstrated that defects result in a dramatic reduction of thermal conductivity. Doping and Stone-Wales (SW) defects have greater effect on armchair tubes, while vacancy affects the zigzag ones more. Thermal conductivity of the nanotubes increases, reaches a peak, and then decreases with increasing temperature. The temperature at which the thermal conductivity peak occurs is dependent on the defect type. Different from SW or vacancy tubes, doped tubes are similar to the perfect ones with a sharp peak at the same temperature. Thermal conductivity goes up when the tube length grows or diameter declines. It seems that the length of thermal conductivity convergence for SW tubes is much shorter than perfect or vacancy ones. The SW or vacancy tubes are less sensitive to the diameter change, compared with perfect ones.     

Influence of chirality on the thermal conductivity of single-walled carbon nanotubes

The influence of chirality on the thermal conductivity of single-walled carbon nanotubes(SWNTs) is discussed in this paper, using a non-equilibrium molecular dynamics(NEMD) method. The tube lengths of the SWNTs studied here are 20, 50, and 100 nm, respectively, and at each length the relationship between chiral angle and thermal conductivity of a SWNT is revealed. We find that if the tube length is relatively short, the influence of chirality on the thermal conductivity of a SWNT is more obvious and that a SWNT with a larger chiral angle has a greater thermal conductivity. Moreover, the thermal conductivity of a zigzag SWNT is smaller than that of an armchair one. As the tube length becomes longer, the thermal conductivity increases while the influence of chirality on the thermal conductivity decreases.     

多壁碳纳米管光限幅特性的研究

用化学气相沉积法制备了多壁碳纳米管,并将其溶解在甲苯溶液中.用波长为1064nm的皮秒脉冲激光测量该样品的透过率,发现了非常明显的光限幅特性.当入射光强较小时,透射光强度随入射光强度的增大而增大,输出与输入为线性关系;随着入射光强的增大,透射光强增长的速度明显变慢,并逐渐趋于饱和.当入射光强度较小时,样品的透过率接近100%;而当入射光强为8GW/cm²时,非线性透过率达到30%.根据三光子吸收理论计算,理论拟合与实验结果非常符合,说明多壁碳纳米管的三光子吸收产生了光限幅效应.实验测 关键词： 多壁碳纳米管 光限幅 三光子吸收     

多壁碳纳米管阵列场发射研究

研究了Ar离子束轰击及温度对多壁碳纳米管阵列场发射性能的影响.经Ar离子轰击35min后，发现阵列顶端的Fe催化剂颗粒明显减少，弯曲的顶部被轰击掉，使碳纳米管的场发射电流明显减小而场发射像无明显改变.温度的增加引起碳纳米管的场发射电流也随之增加.还研 究了在透明阳极技术中涂在阳极的荧光粉对场发射电流的影响.对同一碳纳米管阵列样品，发现涂有荧光粉的透明阳极使测量到的场发射电流大幅度减小，只是未涂荧光粉阳极电流的 1/30左右.直接用二氧化锡导电膜作阳极时，测得样品的开启场强为1.0V/μm.沉积了荧光粉的二 关键词： 多壁碳纳米管 场发射     

双壁碳纳米管电浸润现象的分子动力学模拟

在单壁碳纳米管电浸润现象原子模拟的基础上,对双壁碳纳米管的电浸润现象进行了计算机模拟.运用经典分子动力学方法结合一个宏观的电毛细管模型模拟了双壁碳纳米管在水银中的电浸润过程,对不同内管尺寸情况下的浸润现象作了研究和比较.计算结果表明双壁碳管和单壁碳管的电浸润过程存在很大的不同,双壁碳管的内管在电浸润过程中起到重要的作用：当改变双壁碳管中内管的尺寸时,浸润现象会产生很大的改变. 关键词： 双壁碳纳米管 电浸润 分子动力学     

Thermal conductive performance of deposited amorphous carbon materials by molecular dynamics simulation

A series of diamond-like carbon (DLC) films with different microstructure were prepared by depositing carbon atoms on diamond surface with incident energy ranging from 1 to 100 eV. The thermal conductivity of the deposited films and the Kapitza resistance between the film and the diamond substrate were investigated. Results show that the average density, the average fraction of sp³ bonding and the thermal conductivity of the DLC films increase first, reaching a maximum around 20–40 eV before decreasing, while the Kapitza resistance decreases gradually with increased deposition energy. The analysis suggests that the thermal resistance of the interface layer is in the order of 10^?10 m²K/W, which is not ignorable when measuring the thermal conductivity of the deposited film especially when the thickness of the DLC film is not large enough. The fraction of sp³ bonding in the DLC film decreases gradually normal to the diamond surface. However, the thermal conductivity of the film in normal direction is not affected obviously by this kind of structural variation but depends linearly on the average fraction of sp³ bonding in the entire film. The dependence of the thermal conductivity on the fraction of sp³ bonding was analysed by the phonon theory.     

单壁碳纳米管在石墨基底上运动的分子动力学模拟

采用分子动力学模拟方法研究单壁碳纳米管在石墨基底上的运动.首先碳纳米管在基底弛豫至平衡状态，然后对其施加一固定外力，撤去外力后，碳纳米管在基底上逐渐减速至停止.为了研究管径、手性角对运动方式的影响，本文选择了C(10,10)，C(10,9)，C(10,8)，C(10,5)，C(10,0)，C(8,8)六种单壁碳纳米管进行模拟.结果表明，碳纳米管在石墨基底上的运动方式由手性角决定，与管径无关.手性角等于30°时，碳纳米管与石墨基底之间为公度结构，碳纳米管的运动出现周期性的滑动和翻滚现象；手性角大于28.3°小于30°时，碳纳米管一边向前滑动一边滚动；手性角小于26.3°时，碳纳米管在基底上滑动.碳纳米管的手性角决定了它与石墨基底接触界面的微观构型，从而决定了碳纳米管的运动方式. 关键词： 分子动力学模拟 碳纳米管 动能 结构公度性     

Thermal conductivity and thermal rectification in carbon nanotubes with geometric variations of doped nitrogen: Non-equilibrium molecular dynamics simulations

The thermal conductivity of carbon nanotubes with geometric variations of doped nitrogen is investigated. The phenomenon of thermal rectification shows that the heat transport is preferably in one direction. The asymmetric heat transport of the triangular single-nitrogen-doped carbon nanotubes (SNDCNTs) is larger than that of the parallel various-nitrogen-doped carbon nanotubes (VNDCNTs).     

碳纳米管的可控长度拾取及导电性分析

拾取指定长度的半导体性碳纳米管对大规模制造碳纳米管场效应管具有重要意义.本文提出了一种利用原子力显微镜探针和钨针对碳纳米管进行可控长度拾取的方法并进行了碳纳米管导电性分析.在扫描电子显微镜下搭建微纳操作系统,针对切割操作过程中原子力显微镜探针、钨针和碳纳米管的接触情况进行了力学建模和拾取长度误差分析.建立了单根金属性碳纳米管、单根半导体性碳纳米管及碳纳米管束与钨针接触的电路模型,推导了接入不同性质碳纳米管后电路的电流电压特性方程.使用原子力显微镜探针对碳纳米管的空间位姿进行调整,控制钨针对碳纳米管上目标位置进行通电切割,同时获取切割电路中的电流电压数据.实验结果表明,本文提出的方法能够有效控制所拾取碳纳米管的长度,增加碳纳米管与原子力显微镜探针的水平接触长度能够减小碳纳米管形变导致的拾取长度误差,建立的电流电压特性方程能够用于分析碳纳米管的导电性.     

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.     

硅纳米颗粒在碳纳米管表面生长的分子动力学模拟

采用分子动力学模拟方法研究了硅纳米颗粒在碳纳米管上的生长，并分析了这种复合材料的基本结构.研究表明，由于硅原子和碳纳米管之间的相互作用以及碳纳米管的巨大的表面曲率，硅原子在碳纳米管表面不是形成覆盖碳纳米管的二维薄膜，而是生成具有三维结构的硅纳米颗粒.小纳米颗粒的结构和无基底条件下生成的颗粒结构基本一致.对于大纳米颗粒，不同于无基底条件下形成的球状纳米晶体硅结构，硅纳米颗粒沿管轴方向伸长，其结构为类似于硅晶体的无定形网络结构. 关键词： 纳米颗粒 碳纳米管 硅 分子动力学模拟     

Enhancing the hydrogen storage capacity of Pd-functionalized multi-walled carbon nanotubes

We demonstrate that the hydrogen storage capacity of multi-walled carbon nanotubes can be enhanced by polyvinylpyrrolidone functionalization. The polyvinylpyrrolidone acts as a stabilizing agent for Pd-nanoparticles, reduces their size and facilitates their uniform and enhanced loading onto multi-walled carbon nanotubes. According to sorption studies, the polyvinylpyrrolidone capping and consequent nanostructural modification enables 2.3 times more hydrogen adsorption than mere Pd-functionalization of multi-walled carbon nanotubes. Corresponding morphological changes before and after polyvinylpyrrolidone capping, characterized using Raman Spectroscopy, X-ray diffraction, TEM and thermal analysis techniques, are also presented. The results contribute towards increasing the efficiency of hydrogen based sustainable energy sources.     

不同参数多壁碳纳米管太赫兹谱特性

探索不同管径和长度的多壁碳纳米管（MWCNT）的太赫兹（THz）谱特性,采用透射型太赫兹时域光谱系统研究了5个不同管径和长度的MWCNT样品的太赫兹吸收谱和折射率谱,并对比和分析了它们的差异。结果表明：在0.2～2.0 THz内,多壁碳纳米管太赫兹吸收没有特征吸收峰,吸收强度随着频率的增加而增加,并可以拟合为不同斜率的直线,且MWCNT在THz波段的吸收强度与管径和长度成正比。折射率随着频率的增加呈指数衰减,同时,管径是影响其折射率的一个重要因素,而长度对其影响不大。