Molecular dynamics study of bamboo-like carbon nanotube nucleation

Molecular dynamics (MD) simulations based on an empirical potential energy surface were used to study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations reveal that inner walls of the bamboo structure start to nucleate at the junction between the outer nanotube wall and the catalyst particle. In agreement with experimental results, the simulations show that BCNTs nucleate at higher dissolved carbon concentrations (i.e., feedstock pressures) than those where nonbamboo-like carbon nanotubes are nucleated.     

Y-型纳米碳管的HRTEM研究

本文对Y-型纳米碳管的形貌和微观结构进行了HRTElVl表征,并探讨了其形成机理。结果表明：形成的Y-型纳米碳管内包裹Fe纳米微粒,管径分布在50—60nm之间;在反应中由于催化剂Fe纳米微粒粒径、形状和表面曲率不同,使纳米碳管在生长过程中产生分支,形成Y-型纳米碳管。     

大电流密度碳纳米管阴极的生长及场发射性能研究

研究了碳纳米管作为大电流密度场发射阴极的CVD生长情况与场发射性能。结果表明,通过CVD生长的碳纳米臂的直径与催化剂颗粒的直径相近,其生长方向是随机的。根据薄膜厚度与催化剂颗粒的关系,认为通过控制催化剂薄膜的厚度可能会达到调节碳纳米管直径的目的。在实验中获得的碳纳米管具备了良好的场发射性能,在直径为0．13mm的圆形面积上获得的碳纳米管场发射平均电流密度达到1．28A／cm^2。     

Comparative study of the influence of the solvent on the catalytic growth of carbon nanotubes

The catalytic growth by chemical vapor deposition is a well-established route to single-wall carbon nanotubes (SWNTs). In this process, the choice and preparation of the metal catalyst determines the nanotube growth. The system Fe/Mo is known to yield a large percentage of SWNTs. In order to make use of SWNTs in electronic or electromechanical devices, the patterned growth relies on lithography techniques like photolithography or electron beam lithography. Many standard lithographic processes, i.e. the combination of photoresist and lift-off procedure, are not compatible with Fe/Mo catalyst solutions, resulting in low SWNT yield. We present a systematic study of the influence of the catalyst solvent on the patterned SWNT growth. Most remarkably, the use of water as a solvent is the basis for integrating SWNT with the established processing techniques due to its compatibility with any lithographic process and the simultaneous high SWNT yield.     

利用化学气相沉积法在SiO2小球基底上制备纳米碳管的研究

利用匀胶机将经过超声混合的二氧化硅小球的酒精溶液旋涂在洗净的硅片上,获得了具有曲面的纳米碳管生长基底.利用以二茂铁和二甲苯作为反应前驱体的化学气相沉积法在该基底上实现了碳管在二氧化硅与硅之间的选择性生长,并在不同的沉积温度条件下,可以分别获得球状和束状碳管产物.通过扫描电镜观察分析经过退火处理的原始基底的表面形貌,讨论了碳管产物与反应温度之间的关系.     

碳纳米管制备及其生长机制研究

采用乙醇催化燃烧法，以钴盐作为催化剂先体、薄铜片作为基底制备碳纳米管。分别以氯化钴、硝酸钴和硫酸钴作为催化剂先体，研究了不同催化剂先体对碳纳米管生长的影响；利用扫描电镜，透射电镜对碳纳米材料的形貌和结构进行了表征，研究了不同钴盐的催化剂先体对碳纳米管形态与结构的影响，讨论了碳纳米管的生长机制。实验发现，其他制备条件相同，当催化剂先体为氯化钴时，碳纳米管与大量絮状杂质缠绕在一起；当催化剂先体为硝酸钴时，碳纳米管容易形成弯曲、不规则的波浪形结构；而当催化剂先体为硫酸钴时，实验所得的碳纳米材料几乎全为取向规则、直径均一的碳纳米纤维，只观察到少量碳纳米管。     

碳纳米管制备及其生长机制研究

采用乙醇催化燃烧法,以钴盐作为催化剂先体、薄铜片作为基底制备碳纳米管。分别以氯化钴、硝酸钴和硫酸钴作为催化剂先体,研究了不同催化剂先体对碳纳米管生长的影响;利用扫描电镜,透射电镜对碳纳米材料的形貌和结构进行了表征,研究了不同钴盐的催化剂先体对碳纳米管形态与结构的影响,讨论了碳纳米管的生长机制。实验发现,其他制备条件相同,当催化剂先体为氯化钴时,碳纳米管与大量絮状杂质缠绕在一起;当催化剂先体为硝酸钴时,碳纳米管容易形成弯曲、不规则的波浪形结构;而当催化剂先体为硫酸钴时,实验所得的碳纳米材料几乎全为取向规则、直径均一的碳纳米纤维,只观察到少量碳纳米管。     

Mixed carbon nanotube bundles for interconnect applications

The increasing resistivity of copper with scaling and demands for higher current density are the driving forces behind the ongoing investigation for new wiring solutions for deep nanometer scale VLSI technologies. Metallic carbon nanotubes (CNTs) are promising candidates that can potentially address the challenges faced by copper, and thereby extend the lifetime of electrical interconnects. This article examines the state of the art in CNT applications with focus on CNT interconnect research. It is observed that individually, single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) exhibit characteristics that can be better exploited when a combination of the two is used – in the form of a CNT bundle that plays a vital role in interconnect applications. The focus here is that the usage of a combination of SWCNT (at the centre area of the bundle) and MWCNT (on the outside) provides great performance boost with lower interaction and crosstalk between neighbouring CNT bundles. Simulation results show that the resistance, capacitance, and inductance of a CNT depend on the probability of metallic CNTs present in the bundle and the length of the nanotube. Because Cu is metallic, it indicates that using a higher number of metallic nanotubes in the bundle would aid the CNT bundle performance. In addition, using MWCNT on the outer periphery of the bundle and SWCNT in the centre of the bundle would be the ideal way to maximise the performance of the bundle. Based on the observations we provide an analysis of why a mixed CNT bundle would be highly suitable as interconnections.     

Characterization and estimation of tunnel barrier height in metallic single-wall carbon nanotube quantum dots

A tunnel barrier height has been estimated in quantum dots (QDs) formed in metallic single-wall carbon nanotubes (SWNTs), where QDs can be fabricated simply by depositing metallic contacts on top of the nanotube. Transport measurements have been carried out in a temperature range between 1.5 and 300 K, and revealed single and multi-QD behaviors in different samples at low temperatures. The Arrhenius plot gave an activation energy of ∼6 meV for the barrier formed very likely at the metal-SWNT interface for the single QDs, and two activation energies for seemingly double dots. The latter case comes from the unintentional tunnel barrier due to defects. Discussions on the QD formation and suggestions for a higher temperature operation are given.     

Controlling Electrical Transport through Bundles of Single-Wall Carbon Nanotubes

A technique is developed of the deposition and electrode-bonding of single-wall carbon nanotubes. The causes are investigated of breakdown observed at the nanotube–electrode interface. A method is proposed for the conduction alteration of as-prepared bundles, using electrical breakdown. A mock-up of p-channel FET is produced from a nanotube bundle. Its static performance is measured.     

Oxidised carbon nanotubes as solution processable,high work function hole-extraction layers for organic solar cells

For efficient hole-extraction in solution processed organic solar cells the transparent indium-tin oxide (ITO) electrode is invariably pre-coated with a thin layer of the high work function conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate). Herein we show that thin films of partially oxidised multi-wall and single-wall carbon nanotubes are equally effective at facilitating hole-extraction in efficient (～2.7%) bulk-heterojunction organic solar cells based on poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) blends. Crucially, in contrast to PEDOT:PSS, deposition is from aqueous solutions of low acidity (pH 6–7) ensuring compatibility with ITO and other emerging conducting oxides. Furthermore, thin oxidised carbon nanotube films offer greater transparency in the near-infrared as compared to PEDOT:PSS films of comparable thickness. The functionality of these nano-structured films is demonstrated in relatively large area devices (～0.35 cm²) and the performance rationalised based on measurements of the electronic structure and morphology.     

纳米碳管的电子衍射及其螺旋度测量

本文对电弧放电和催化剂热解碳氢气法制备的多层直形纳米碳管的倒空间及其螺旋度，采用电子衍射进行了研究。结果表明：尽管制备方法不同，两类多层管的结构相似，皆由螺旋和非螺旋的单层石墨管组成；对其倒空间的分析以及系列倾转电子衍射实验证明，衍射图中测得的表观螺旋度值随和射条件而改变，只有在垂直入射条件下该值才代表碳管的真实螺旋度；     

Inductance of mixed carbon nanotube bundles

The carbon nanotube (CNT) bundle is a promising candidate for next-generation interconnect/via applications. A realistic CNT bundle is a mixture of single-wall and multi-wall CNTs and its performance analysis needs to consider both kinds of CNTs. The inductances of the mixed CNT bundles are estimated, which are in agreement with the recent experimental results. Impacts of different parameters such as tube density, tube distribution, metallic tube ratio and bundle dimensions are discussed, providing an important guideline to design and fabricate a CNT bundle with a desirable inductance performance.     

Multiband Mobility in Semiconducting Carbon Nanotubes

We present new data and a compact mobility model for semiconducting single-wall carbon nanotubes, with only two adjustable parameters, the elastic and inelastic collision mean free paths at 300 K. The mobility increases with diameter, decreases with temperature, and has a more complex dependence on charge density. The model and data suggest that the room temperature mobility does not exceed 10 000 cm²/Vmiddots at high carrier density (n > 0.5 nm^-1) for typical single-wall nanotube diameters, due to the strong scattering effect of the second subband.     

铁/碳纳米管催化剂CVD法制备碳纳米管

以乙烯为碳源,碳纳米管负载铁基为催化剂,于790℃制备了平均直径约为30 nm的多壁碳纳米管。研究了700~850℃范围内碳纳米管产物的形貌特征和纯度,并与以Al2O3负载铁基作为催化剂的产物进行了比较。利用SEM、TEM、拉曼光谱,对催化剂和产物进行了表征。发现在最佳反应温度下,两种催化剂制备的碳纳米管形貌、直径分布范围及平均直径相当,但以碳纳米管负载铁基为催化剂,产量明显提高100%,且不具有难处理的氧化物载体,纯度很高。     

Effect of an AC electric field on the conductance of single-wall semiconductor-type carbon nanotubes

The effect of an ac electric field on the conductance of a system of single-wall semiconductor-type carbon nanotubes placed in a dc electric field is considered. The strength vectors of dc and ac electric fields are directed along the nanotube axis. The electronic system of carbon nanotubes is considered in the context of the Boltzmann kinetic equation in the relaxation-time approximation. The dependence of the current density in the system on the characteristics of applied fields is studied. The effect of absolute negative conductance is detected.     

碳纳米管微电极的直流介质阻挡放电特性

研究了一种基于碳纳米管尖端的直流介质阻挡放电(DBD)微结构,使用MEMS加工工艺制作出深宽比0.5的侧壁相对的叉指状金属电极,在电极上电泳多壁碳纳米管,采用真空磁控溅射沉积二氧化硅介质层。在大气压下测试了所制备的DBD微结构样品的直流放电基本特性。实验结果表明,在几伏特的直流加载电压下即可检测到纳安量级的放电电流,并且放电电流对人体呼吸和环境气体变化有明显响应。放电起始电压小于10V并显现出明显的抑制电流自由增长的DBD放电特征,但电流下降持续时间达102～103s量级,大于常规常压DBD时间,显示出碳纳米管尖端的特异效应。     

Carbon‐Nanotube‐Templated Microfabrication of Porous Silicon‐Carbon Materials with Application to Chemical Separations

Carbon‐nanotube‐templated microfabrication (CNT‐M) of porous materials is demonstrated. Partial chemical infiltration of 3D carbon‐nanotube structures with silicon results in a mechanically robust material, structured from the 10 nm scale to the 100 μm scale. The nanoscale dimensions are determined by the diameter and spacing of the resulting silicon/carbon nanotubes, while the microscale dimensions are controlled by the lithographic patterning of the CNT growth catalyst. We demonstrate the utility of this hierarchical structuring approach by using CNT‐M to fabricate thin‐layer‐chromatography (TLC) separations media with precise microscale channels for fluid‐flow control and nanoscale porosity for high analyte capacity. Chemical separations done on the CNT‐M‐structured media outperform commercial high‐performance TLC media.     

Monolayer metallic nanotube interconnects: promising candidates for short local interconnects

Mono- or bi-layer metallic single-wall carbon nanotube interconnects have lateral capacitances more than four times smaller than those of copper interconnects. The resistance and time-of-flight of these monolayer nanotubes would be larger than that of copper interconnects. For short lengths, however, driver resistance is quite dominant, and latency is determined by interconnect capacitance. Monolayer nanotube interconnects are therefore promising candidates for local interconnects. The average capacitance per unit length of these nanotube interconnects can be 50% smaller than that of copper interconnects and that leads to significant saving in power dissipation.     

Toward the integration of a single carbon nanofibre as via interconnect

The use of carbon nanotube/nanofibres as via interconnects is widely studied. As the vias dimensions decrease below 50 nm, the number of carbon nanotubes could be close to the unity in each via hole. In the present study we show the integration processes to obtain interconnects made of one single vertically free standing carbon nanofibre. Two different catalyst integrations are detailed and tested.