Excellent solid lubrication of electrodeposited nickel-multiwalled carbon nanotube composite films

Nickel-multiwalled carbon nanotube (MWCNT) composite films were fabricated by an electrodeposition technique, and their frictional properties were investigated by ball-on-plate type friction testing using an Al₂O₃ ball as a counter surface without lubricant. Ni-MWCNT composite films showed superior frictional properties compared to nickel films. The friction coefficient of Ni-MWCNT composite films decreased with increasing MWCNT content. The Ni-0.5 mass% MWCNT composite film showed the minimum friction coefficient value of 0.13.     

Synthesis and characterization of large area well-aligned carbon nanotubes by ECR-CVD without substrate bias

Large area, well-aligned carbon nanotubes (CNTs) were synthesized on porous silicon by electron cyclotron resonance chemical vapor deposition (ECR-CVD). No bias was applied on the substrate in this experiment. CH₄ and H₂ were used as source gases and Fe₃O₄ nanoparticles as the catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Raman spectrum were used to evaluate the structure and composition. The results show that these CNTs have varying outer diameters from 10 to 90 nm and uniform length over 10 μm. They display hollow tubular and chain structures. The possible formation mechanism of aligned CNTs is discussed.     

First-principles study of electronic structure of deformed carbon nanotubes

On the basis of density functional theory, we study the electronic structures of five types of carbon nanotubes: the non-deformed (6,6) tube, the uniformly stretched tube along the tube axis, the uniformly compressed tube, the partially stretched tube and the partially compressed tube. The electron charge density increases at the compressed C-C bond of the partially stretched tube, while the density decreases at the stretched C-C bond of the partially stretched tube. In addition, the a₁ and e₁ states of the (6,6) tube contribute to the bonding along the tube axis and the a₂ and e₂ states are the bonds connecting the atoms in the same layers. Thus, the energy bands of the a₁ and e₁ states are sensitively affected by the deformation of the tubes along the tube axis.     

碳纳米管溶解性及其化学修饰

详细评述了增加碳纳米管在水和有机溶剂中溶解性的途径，包括单一溶剂直接分散、电子供一受体电荷转移、可溶性聚合物或表面活性剂筒状胶束包裹等非共价键相互作用和顶端开口、化学衍生以及侧壁化学修饰等共价化学修饰。指出今后一段时期碳纳米管化学的主要任务为通过非共价的或共价的化学修饰，改善碳纳米管本身的性能和用途，并耦合其他如化学的、生物的或物理的功能扩展其应用范围。进一步深入理解碳纳米管化学(尤其是其溶液化学)反应理论。     

Coating of carbon nanotubes with amorphous carbon nitride thin films and characterization of long-term emission stability

The effects of amorphous carbon nitride (CN) thin films that were coated on carbon nanotubes (CNTs) and their thermal treatment were investigated, in terms of the chemical bonding and morphologies of the CNTs and their field emission properties. CNTs were directly grown on conical tip-type tungsten substrates via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and the CNTs were coated with CN films using the RF magnetron sputtering system. The CN-coated CNTs were thermally treated using the rapid thermal annealing (RTA) system by varying the temperature (300-700 °C). The morphologies, microstructures, and chemical compositions of the CN-coated CNTs were analyzed as a function of the thickness of the CN layers and the RTA temperatures. The field emission properties of the CN/CNT hetero-structured emitters, and the fluctuation and long-term stability of the emission currents were measured and compared with those of the conventional non-coated CNT-emitter. The results showed that the electron emission capability of CNT was noticeably improved by coating a thin CN layer on the surface of the CNT. This was attributed to the low work function and negative electron affinity nature of the CN film. The CN-coated CNT-emitter had a more stable emission characteristic than that of the non-coated one. In addition, the long-term emission stability of the CN-coated emitter was further enhanced by thermal treatment, which was verified by x-ray photoelectron spectroscopy (XPS) analysis.     

碳纳米管的性能及应用

本文在概括碳纳米管的制备基础上,着重对其性能和应用做出了阐述,并对应用前景和存在的问题进行了介绍.     

自组装和分散可逆的碳纳米管圆片

通过加热碳纳米管和强酸的混合物,使碳纳米管的憎水表面发生氧化.加热含经处理的碳纳米管的悬浮液,使之脱水,得到自组装的碳纳米管圆片,该圆片可直接分散.扫描电镜图显示该圆片由局部规则排列的碳纳米管构成;红外光谱和光电子谱分析表明在化学处理过程中,碳纳米管的表面产生了含氧官能团;虽然拉曼谱测出处理过程增加了缺陷,但是X射线衍射结果表明碳纳米管类似石墨的层状结构得到保留;同时研究了经处理的碳纳米管的热稳定性.这种自组装且可分散的碳纳米管圆片为研究碳纳米管结构材料和碳纳米管复合材料提供了有效途径.     

Multi-barrier layer-mediated growth of carbon nanotubes

Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al₂O₃, Al/SiO₂, Al₂O₃/SiO₂ were prepared onto a n-type Si (100) substrate. The thickness of SiO₂ was ∼ 550 nm, where as, Al₂O₃ and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al₂O₃/SiO₂ barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.     

Synthesis of multiwalled carbon nanotubes by high-temperature vacuum annealing of amorphous carbon

Vacuum annealing of a mixture of amorphous carbon and cobalt nanoparticles supported on microporous zeolite at high-temperature results in the formation of multiwalled carbon nanotubes which are essentially filled with metal nanoparticles or nanowires as observed by transmission electron microscopy. The electronic properties of nanotubes by variable temperature ESR techniques shows that g values show little change with temperature from 77 to 327 K but the line width (ΔH_pp) of the ESR signal for nanotubes synthesized from amorphous carbon increases from 7.9 G at 77 K to 9.5 G at 327 K.     

Molecular dynamics simulation of polarizable carbon nanotubes

This paper is aimed to develop a modified force field for molecular dynamics (MD) simulations of polarizable carbon nanotubes (CNTs). The effects of electrical polarization and the associated electronic degrees of freedom are represented by a network of negative charged shell particles which move relative to the surrounding positively charged carbon atoms in response to an applied electric field. In this setting, the negative and positive charges are exactly balanced so that the total system remains electrically neutral, and the motion of the shell particles relative to their equilibrium positions leads to polarization within the nanotube. Potential applications of the proposed model include simulations of controlled translocation of ions, water and polymers through solid-state CNT membranes.     

Tunable amorphous carbon nanotubes prepared by a simple template

An easy versatile method is reported to synthesize tunable amorphous carbon nanotubes (a-CNTs) with different pore diameter, length and orientation of graphene layers at a low temperature of 450 °C in the absence of metal catalysts by using porous anodic aluminum oxide (AAO) as a template and citric acid as a precursor. Since citric acid was adsorbed by hydrogen bonds with the -OH groups at the walls of the AAO templates, which can be influenced by the concentration of H⁺ ions in the solution, the pH leads to the change of the orientation of graphene layers and the graphitization degree.     

不同压力下碳纳米管的电弧法合成及其表征

采用电弧放电法在氦气/乙炔混合气氛中,在不同压力下合成了碳纳米管.运用场发射扫描电镜、场发射透射电镜、X-射线衍射仪和拉曼光谱对碳纳米管的形貌进行了表征.采用可见发射光谱对碳纳米管的形成过程进行了原位诊断研究.场发射扫描电镜结果表明,在氦气/乙炔气氛中合成的碳纳米管的长度大于50微米,许多碳颗粒沉积在碳纳米管壁上.场发射透射电镜结果表明,在0.100MPa下合成的碳纳米管的壁厚明显大于0.035MPa下合成的碳纳米管的壁厚.可见发射光谱诊断结果表明,CH和C2物种可能作为碳纳米管形成的前驱体,其中,以H原子作为无定形炭的刻蚀物种.阳极消耗速率和产物在阴极的沉积速率随着反应器中压力的增加而增加.因此,可以通过加强阳极和乙炔的蒸发速率及CH和C2物种的沉积速率而增加碳纳米管的形成速率.     

Mechanical characterization of epoxy composite with multiscale reinforcements: Carbon nanotubes and short carbon fibers

Carbon nanotubes (CNT) and short carbon fibers were incorporated into an epoxy matrix to fabricate a high performance multiscale composite. To improve the stress transfer between epoxy and carbon fibers, CNT were also grown on fibers through chemical vapor deposition (CVD) method to produce CNT grown short carbon fibers (CSCF). Mechanical characterization of composites was performed to investigate the synergy effects of CNT and CSCF in the epoxy matrix. The multiscale composites revealed significant improvement in elastic and storage modulus, strength as well as impact resistance in comparison to CNT–epoxy or CSCF–epoxy composites. An optimum content of CNT was found which provided the maximum stiffness and strength. The synergic reinforcing effects of combined fillers were analyzed on the fracture surface of composites through optical and scanning electron microscopy (SEM).     

催化剂对爆炸法合成碳纳米管的影响

通过热引发方式使炸药-催化剂前驱体-碳氢化合物体系在密闭反应管中发生爆炸合成碳纳米管。采用TEM,HRTEM,XRD和TG等方法研究了以二茂铁、甲酸镍和乙酸钴作为催化剂前驱体对所合成碳纳米管产物的形貌、微观结构和纯度的影响。以乙酸钴为前驱体可以得到纯度较高(约80%～90%)、微观结构较好的管腔中空的碳纳米管。以二茂铁为前驱体,只有约10%～20%的碳管生成且多呈竹节状形貌。以甲酸镍为前驱体,得到的碳管纯度也不高(约10%～20%),碳管管壁富含结构缺陷,相当多的碳管端口膨胀成直径约为160nm的纳米泡。XRD分析表明这些催化剂前驱体在爆炸反应后均被分解、还原为金属单质。通过对生成的碳纳米管的质量和纯度进行比较,得出本方法中催化剂的催化活性依次为:钴>铁>镍,并对本方法中高碳源浓度环境下不同催化剂的活性差异作了简要分析。     

Room temperature sensor based on carbon nanotubes and nanofibres for methane detection

Carbon nanotubes and nanofibres deposited by an electrodeposition technique were utilized to fabricate sensor material for the detection of methane. Carbon nanotubes (CNT) and nanofibres were grown on Si(0 0 1) substrate using acetonitrile (1% v/v) and water as electrolyte at an applied d.c. potential ∼20 V. Sensing properties were studied with as-deposited CNT films. It was found that the films showed good sensing properties at room temperature.     

Analysis of localized failure of single-wall carbon nanotubes

A method is developed to determine the conditions for the onset of localized failure of carbon nanotubes. Examples of failure modes include ductile necking under tension or localized crushing under compression. A nanoscale continuum theory for carbon nanotube is adapted. The onset of localized failure is identified by the singularity point of the acoustic tensor derived from continuum energy function based on Tersoff–Brenner potential. The analysis predicts 35–44% of breaking strains for tension and 18–25% compressive strain for plastic collapse. The results are in agreement with molecular dynamics simulations and experimental estimations reported in the literature.     

碳源对碳纳米管形态的影响

以苯和甲苯为碳源,二茂铁为催化剂,含硫化合物为助催化剂,采用浮游催化裂解法制备了碳纳米管,并采用TEM对不同条件下所得碳纳米管进行了形态分析。结果发现,碳源中苯和甲苯的配比对碳纳米管的形态有着重要的影响。以纯苯为碳源时,产物主要为直线型碳纳米管,并存在极少量短的弯曲型碳纳米管。随着碳源中甲苯比例的增加,产物中折线型碳纳米管增加。以纯甲苯为碳源,产物中仍有少量直线型碳纳米管,而不完全是折线型碳纳米管;此外,产物中还发现了极少量分支型碳纳米管。根据所得结果讨论分析了甲苯的加入对碳纳米管形态的影响以及各种碳纳米管的形成机理,认为可能是由于甲苯在催化热解过程中产生的碳种不同于苯催化热解所产生的碳种,造成碳在催化剂颗粒各处浓度不同,从而在碳纳米管的不同部位引入五元环和七元环而形成各种形态的碳纳米管。     

In situ synthesis of ceria decorated carbon nanotubes by chemical vapor deposition

Ceria decorated carbon nanotubes (CNTs) were in-situ synthesized by chemical vapor deposition using a Ni/Ce/Cu catalyst. Ceria nanoparticles, with a diameter of about 3-8 nm, were highly dispersed on the CNTs, and it is believed that they are formed at the same time as the CNTs.     

Enhancement of field emission property from hills-like carbon nanotubes film

Improved field emission property of carbon nanotubes (CNTs) is achieved by using NiTi alloy film as catalyst under optimized condition. The NiTi alloy films are prepared by magnetron co-sputtering process and the CNTs films are synthesized by thermal chemical vapor deposition. With the increase of the Ni/Ti ratio from 19 at.% to 95 at.%, the CNTs density increases from discrete cluster to dense network, and the optimized field emission property of CNTs film is found at the medium density. However, the field emission property is significantly enhanced when the Ni/Ti ratio is about 76 at.%, and it is supposed to attribute to the combined effect of the hills-like surface enhancement and the intrinsic emission properties of CNTs.     

利用电沉积Ni纳米晶制备无缠绕阵列碳纳米管

以金属Cu基板上脉冲电沉积Ni纳米晶薄膜作为催化剂,在乙醇火焰中制备了直立、无缠绕阵列碳纳米管.利用原子力显微镜(AFM)、扫描电子显微镜(SEM)、透射电镜(TEM)和激光拉曼谱仪(Raman)对不同工艺制备的Ni纳米晶薄膜和阵列碳纳米管的形貌进行了表征.结果表明:通过综合控制脉冲电沉积参数、电沉积时间和火焰中的合成时间,可以获得大面积、密集、均匀、直立、无缠绕、形态良好、重复性高的阵列碳纳米管.脉冲电沉积Ni纳米晶和合成无缠绕阵列碳纳米管的最佳工艺条件是:脉冲电沉积正、负脉冲的工作频率为154Hz、占空比为38.5%、电沉积时间为1min、基板预热至600℃、火焰中停留1min.通过对生长机理的研究发现:当电沉积时间较短时,获得的Ni纳米晶薄膜较薄,具有较高的局域粗糙程度和催化活性,有利于碳纳米管的同时大面积"拥挤生长"形成阵列结构;另外,通过调整脉冲电沉积参数,可以控制Ni纳米晶的大小,从而控制碳纳米管的长径比,当长径比较小时即可获得无缠绕的阵列碳纳米管.