用于制备优质单壁碳纳米管管束的MgO负载Fe3O4纳米粒子的合成

采用沉淀方法制备了直径分布狭窄的均匀Fe3O4纳米颗粒.Fe3O4纳粒形体几近一致,平均粒径为10.33 nm±2.99 nm(平均粒径±标准偏差).在超声作用下将MgO纳米颗粒分散在一定量Fe3O4纳米颗粒的水溶液中获得MgO负载Fe3O4的纳米颗粒.以甲烷为碳源,Fe3O4/MgO为催化剂,经化学气相沉积,在Fe3O4纳粒上制得了大量直径近乎均匀的单壁碳纳米管(SWCNTs)束.TEM显示:SWCNTs的平均直径1.22rm.热重分析显示:样品在400℃～600℃温度区间失重量约19％.拉曼光谱显示:SWCNTs的ID/IG的强度比为0.03,表明采用Fe3O4/MgO催化剂可制得高石墨化程度的单壁碳纳米管.     

Designing a strategy for fabrication of single-walled carbon nanotube via CH4/N2 gas by the chemical vapor deposition method

Fe/Mo catalysts supported on alumina are suggested for the growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD) in methane (CH₄). One obvious synergistic advantage identified by molybdenum (Mo) is that by controlling the reaction temperature, it eliminates the need to activate the catalyst in hydrogen gas (H₂). So as activation of the growth catalyst in H₂ is a costly and extra step in the CVD method, this is a significant result of the present study. Herein, the sample quality and the dependence of carbon mass yield on CVD growth conditions are disserted. The activity of the catalyst is perused in the form of oxide under CH₄ flow (160 sccm) and in the temperature range of 680 to 1000 °C. We came to the conclusion that the Fe/Mo/Al₂O₃ oxide catalyst is activated at temperatures as low as 800 °C. Under these conditions (800 °C, 160 sccm of CH₄), the temperature is not enough for the tube to grow, but by increasing it, the desired conditions can be achieved (900 –1000 °C).     

Odako growth of dense arrays of single-walled carbon nanotubes attached to carbon surfaces

A novel process is demonstrated whereby dense arrays of single-walled carbon nanotubes (SWNT) are grown directly at the interface of a carbon material or carbon fiber. This growth process combines the concepts of SWNT tip growth and alumina-supported SWNT base growth to yield what we refer to as “odako” growth. In odako growth, an alumina flake detaches from the carbon surface and supports catalytic growth of dense SWNT arrays at the tip, leaving a direct interface between the carbon surface and the dense SWNT arrays. In addition to being a new and novel form of SWNT array growth, this technique provides a route toward future development of many important applications for dense aligned SWNT arrays. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Critical oxide thickness for efficient single-walled carbon nanotube growth on silicon using thin SiO2 diffusion barriers

The ability to integrate carbon nanotubes, especially single-walled carbon nanotubes, seamlessly onto silicon would expand their range of applications considerably. Though direct integration using chemical vapor deposition is the simplest method, the growth of single-walled carbon nanotubes on bare silicon and on ultrathin oxides is greatly inhibited due to the formation of a noncatalytic silicide. Using X-ray photoelectron spectroscopy, we show that silicide formation occurs on ultrathin oxides due to thermally activated metal diffusion through the oxide. Silicides affect the growth of single-walled nanotubes more than multi-walled nanotubes due to the increased kinetics at the higher single-walled nanotube growth temperature. We demonstrate that nickel and iron catalysts, when deposited on clean silicon or ultrathin silicon dioxide layers, begin to form silicides at relatively low temperatures, and that by 900 degrees C, all of the catalyst has been incorporated into the silicide, rendering it inactive for subsequent single-walled nanotube growth. We further show that a 4-nm silicon dioxide layer is the minimum diffusion barrier thickness that allows for efficient single-walled nanotube growth.     

碳纳米管阵列/热解炭复合材料的制备和表征（英文）

以甲烷为碳源,通过化学气相沉积和化学蒸汽渗透两步法将热解炭填充至碳纳米管阵列间的空隙而制备出碳纳米管阵列/热解炭复合材料。采用扫描电镜和拉曼光谱仪对样品的结构进行表征。结果表明,碳纳米管被热解炭填充和覆盖形成均相的复合膜,其密度增加4倍,同时热解炭已石墨化。     

CVD-grown horizontally aligned single-walled carbon nanotubes: synthesis routes and growth mechanisms

Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided.     

炭纤维表面生长碳纳米管

采用化学气相沉积工艺在炭纤维表面生长了碳纳米管,并观察了它的微观形貌,且对其影响因素进行了初步研究.结果表明:纤维表面的纵向沟槽可以负载催化剂粒子,是生长碳纳米管的物理基础;催化剂的浓度太高,金属粒子容易团聚长大,所得碳纳米管的管径较大;而催化剂浓度太低,则不能在炭纤维整个表面均匀生长碳纳米管;最佳的催化剂溶液的浓度是0.05mol/L的硝酸钴.比较了铁、钴、镍三种过渡金属催化剂,从形成的碳纳米管的质量来看,钴催化剂最佳.     

Influence of Mo or Cu doping in Fe/MgO catalyst for synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of methane

A series of mono-, bi- or tri-metallic Fe–Mo-Cu/MgO catalysts with the same metal loading of 6 wt% were prepared by impregnation method and used as catalysts for synthesis single-walled carbon nanotubes (SWCNTs) via methane decomposition. XRD, H₂-TPR, and nitrogen physisorption techniques were used to characterize the freshly calcined catalysts, while HRTEM, Raman spectroscopy and TGA were employed to investigate the morphology and microstructure of the SWCNTs product. The obtained results indicated that the introduction of Mo or Cu in the Fe/MgO catalyst enhanced the catalytic growth activity. TEM images showed that both bundles and isolated SWCNTs were obtained over Mo containing catalysts, whereas only SWCNTs bundles were grown over the Fe-Cu/MgO catalyst. The obtained SWCNTs having a diameter of around 0.9–2.4 nm. Raman analysis illustrated that all promoted catalysts produced high quality of SWCNTs compared to the unpromoted Fe/MgO catalyst.     

Fabrication horizontal aligned MoO2/single-walled carbon nanotube nanowires for electrochemical supercapacitor

The horizontally aligned MoO₂/single-walled carbon nanotube (MoO₂/SWNT) composite has been prepared by electrochemically induced deposition method which utilizes the good electronic conductivity of SWNTs as supporting material to deposit MoO₂. The morphology and crystal structure of the composite were investigated by X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. The capacitive properties of the MoO₂/SWNT composites have been investigated by cyclic voltammetry (CV). A specific capacitance (based on MoO₂) as high as 597 F g^− 1 is obtained at a scan rate of 10 mV s^− 1 in 0.1 M Na₂SO₄ aqueous solution. Additionally, the MoO₂/SWNT composites electrode shows excellent long-term cycle stability (only 2.5% decrease of the specific capacitance is observed after 600 CV cycles).     

Multi-walled carbon nanotube growth on oxidized silicon substrates using cyclohexane precursor by chemical vapor deposition

Randomly oriented multi-walled nanotubes (MWNTs) are grown by a thermal chemical vapor deposition (CVD) process from cyclohexane precursor on a 20% copper-80% nickel (Cu-Ni) catalyst on oxidized silicon substrates. This combination of precursor and catalyst, to our knowledge, has been employed for the first time to demonstrate growth of multi-walled carbon nanotubes. The effects of annealing, gas ambient and catalyst layer thickness on the morphology of the grown carbon layers are discussed. The low resistivity values of the MWNTs grown on oxidized silicon substrates are attractive for their potential use in photonic devices and display applications.     

Optimization of processing parameters of the chemical vapor deposition process for synthesizing high-quality single-walled carbon nanotube fluff and roving

The use of the Taguchi method to optimize the processing parameters for the synthesis of high-quality single-walled carbon nanotubes (SWCNTs) in a vertical chemical vapor deposition reactor was demonstrated. An investigation containing 18 experiments featuring different parameters and levels was performed. SWCNTs with a low intensity D-band to G-band ratio of 0.027 of a Raman spectrum were obtained when the optimal processing conditions were adopted. The quantitative contribution of the processing parameters can be calculated using the analysis of variance. According to the analysis, the reactor temperature and the evaporation temperature of ferrocene significantly affect the graphitization of the synthesized SWCNTs, while the chamber pressure exerts an insignificant effect. The formation of carbon nanotube films with entangled networks during synthesis was recorded using a digital camera, and a synthesis mechanism was proposed. Using the optimal parameters, SWCNT fluff with a diameter of 7.0 cm and SWCNT roving with a diameter of approximately 1.0 cm and a length of over 30.0 cm can be attained. In this work, field-emission scanning electron microscopy and Raman spectroscopy and high-resolution transmission electron microscopy were adopted to examine the morphology and microstructure, respectively.     

An intermetallic Fe-Zr catalyst used for growing long carbon nanotube arrays

Metallic nanoparticles containing single and binary components have been known for their catalytic properties to grow carbon nanotube (CNT) arrays. In this paper, an intermetallic catalyst consisting of iron and zirconium was used to grow millimeter long, well aligned arrays. The Fe-Zr catalysts enabled the growth of 1.7 mm-long carbon nanotube arrays in 45 min. A comparison with pure iron catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. SEM images showed the different growth behaviors for Fe-Zr and Fe catalysts. The long, uniform CNT arrays grown here have potential applications in many advanced composites.     

催化剂结构与形态对碳纳米管生长的影响

采用溶胶-凝胶超临界流体干燥技术制备了含铁、钴的纳米SiO2复合气凝胶催化剂,用于碳纳米管和纳米碳包覆磁性纳米粒子的合成。利用N2物理吸附、XRD、TEM、HRTEM、EDS、SAED等手段对催化剂在不同温度下处理后晶型的转变、形态的变化进行了分析,并考察了催化剂对碳纳米管形貌、结构和碳增重率的变化。结果表明:随着处理温度从600℃升高到1000℃,催化剂比表面积从312.4m2 g降低到79.6m2 g,催化剂粒子从非晶态向晶态转变,粒径从5nm增大至60nm左右,碳的增重率从254.8%下降41.5%。采用低温处理的催化剂,碳产物中以碳纳米管为主,而采用较高温度处理后的催化剂,碳产物中则以碳包覆粒子为主,且随处理温度的升高碳包覆粒子的含量逐渐增加。     

Nanostructured tantalum nitride films as buffer-layer for carbon nanotube growth

Tantalum nitride (TaN_x) films are usually used as barriers to the diffusion of copper in the substrate for electronic devices. In the present work, the TaN_x coating plays an extra role in the iron catalyzed chemical vapor deposition production of carbon nanotubes (CNT). The CNTs were grown at 850 °C on TaN_x films prepared by radio frequency magnetron sputtering. The correlation between the CNT morphology and growth rate, and the pristine TaN_x film nature, is investigated by comparing the evolution of the nano-composition, roughness and nano-crystallinity of the TaN_x films both after annealing and CVD at 850 °C.     

Wafer scale synthesis of dense aligned arrays of single-walled carbon nanotubes

Here we present an easy one-step approach to pattern uniform catalyst lines for the growth of dense, aligned parallel arrays of single-walled carbon nanotubes (SWNTs) on quartz wafers by using photolithography or polydimethylsiloxane (PDMS) stamp microcontact printing (μCP). By directly doping an FeCl₃/methanol solution into Shipley 1827 photoresist or polyvinylpyrrolidone (PVP), various catalyst lines can be well-patterned on a wafer scale. In addition, during the chemical vapor deposition (CVD) growth of SWNTs the polymer layers play a very important role in the formation of mono-dispersed nanoparticles. This universal and efficient method for the patterning growth of SWNTs arrays on a surface is compatible with the microelectronics industry, thus enabling of the fabrication highly integrated circuits of SWNTs.     

In situ growth carbon nanotube reinforced SiCf/SiC composite

Carbon nanotube (CNT) reinforced SiC_f/SiC composite was prepared by in situ chemical vapor deposition (CVD) growth of CNTs on SiC fibers then following polymer impregnation pyrolysis (PIP) process. The nature of CNTs and the microstructure of the as prepared CNT-SiC_f/SiC composite were investigated. The mechanical properties of the as prepared CNT-SiC_f/SiC composite were measured. The results reveal that the in situ CVD growth of CNTs on SiC fibers remarkably promotes the mechanical properties of SiC_f/SiC composite. The secondly pull-out of CNTs from matrix during the pull-out of the SiC fibers from matrix consumes the deformation energies, resulting in promotion of the mechanical properties for composite.     

Role of catalysts in the surface synthesis of single-walled carbon nanotubes

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.      

化学气相沉积法制备定向碳纳米管及其生长机理的研究

以环己烷为碳源,二茂铁作催化剂,采用浮动催化化学气相沉积法制备了定向碳纳米管,并用SEM、TEM及Raman光谱对样品进行了鉴定和表征.并从不同的角度,提出了定向碳纳米管遵循底部生长的机理.     

Fluctuation-induced tunneling dominated electrical transport in multi-layered single-walled carbon nanotube films

Low temperature measurements may give some insight into the transport mechanism of single-walled carbon nanotube (SWCNT) films, which could lead to an optimal SWCNT film with designed photoelectric properties. Despite intense research efforts on the low temperature transport in SWCNT films, it is still an open question for the low temperature transport in multi-layered SWCNT films. In this work, the multi-layered SWCNT films were prepared with a layer by layer vacuum filtration. It suggests that the space between different layers of the multi-layered SWCNT can be ignored. For deposition of different-layered SWCNT films using the same total amount of SWCNT suspension, the increase of the layer numbers can reduce the density of the resulting films, which may account for the low temperature transport. The effect of thermal annealing and subsequent nitric acid treatment on the electrical properties of the SWCNT films has also been investigated. At the temperature range of 80-300 K, the transport of the multi-layered SWCNT films can be explained by a fluctuation-induced tunneling model. Our results could build a bridge connecting measured temperature coefficient of resistance and the microscopic tunneling barrier.     

Controlled growth and characterization of two-dimensional single-walled carbon-nanotube networks for electrical applications

We demonstrate the reproducible fabrication of single-walled carbon nanotube (SWNT) networks, via catalyzed chemical vapor deposition (cCVD). Fe nanoparticles are employed as the catalyst, with methane as the carbon-containing gas. cCVD growth under these conditions results in the formation of multiply interconnected, random, two-dimensional networks of SWNTs. Investigation of the effect of parameters such as methane flow rate and temperature on the growth process enables control over the density of the network, which controls the network conductivity. Low-density networks demonstrate p-type semiconductor behavior, whilst high-density networks exhibit semimetallic behavior. In both cases conductance is demonstrated over macroscopic length scales, up to millimeters, much longer than the individual SWNTs, despite the surface coverage being <1 %. The networks can be defined in regions of a surface by photolithography before or after growth. Controlled growth of SWNT networks thus enables the application of SWNTs as macroscale conductors with controllable, predictable, and reproducible characteristics.