Local chemical vapor deposition of carbon nanofibers from photoresist

The addition of nanofeatures to carbon microelectromechanical system (C-MEMS) structures would greatly increase surface area and enhance their performance in miniature batteries, super-capacitors, electrochemical and biological sensors. Negative photoresist posts were patterned on a Au/Ti contact layer by photolithography. After pyrolyzing the photoresist patterns to carbon patterns, graphitic nanofibers were observed near the contact layer. The incorporation of carbon nanofibers in C-MEMS structures via a simple pyrolysis of modified photoresist was investigated. Both experimental results considered to consist of a local chemical vapor deposition mechanism. The method represents a novel, elegant and inexpensive way to equip carbon microfeatures with nanostructures, in a process that could possibly be scaled up to the mass production of many electronic and biological devices.     

One-step growth process of carbon nanofiber bundle-ended nanocone structure by microwave plasma chemical vapor deposition

In this work, we report a simple one-step growth process to synthesize a novel and distinct carbon nanostructure, called a carbon nanofiber bundle-ended nanocone (CNFNC) structure, by using microwave plasma chemical vapor deposition (MPCVD) method with CH₄ and H₂ as source gases and Fe catalyst. The nanostructures and their properties after each processing step were characterized by FESEM, HRTEM, ED, AES, and Raman spectroscopy. The preliminary results have demonstrated that the CNFNC structures exhibit excellent field emission properties. The results also show that the favored conditions to form the CNFNC structures include a combination of lower CH₄/H₂ flow ratio, higher substrate negative bias, and proper working pressure and deposition time. The possible growth mechanism of the CNFNC structures is proposed.     

Growth of carbon nanofibers on activated carbon fiber fabrics

Activated carbon fiber fabrics, an excellent adsorbent, were used as catalyst supports to grow carbon nanofibers. Because of the microporous structure of the activated carbon fibers, the catalysts could be distributed uniformly on the carbon surface. Based on this concept, the carbon nanofibers can be grown directly on the activated carbon fiber fabrics. We demonstrate that carbon nanofibers with a diameter between 20 and 50 nm for most of the fibers can be synthesized uniformly and densely on activated carbon fiber fabrics, impregnated by nickel nitrate catalyst precursor, using catalytic chemical vapor deposition. Although the carbon nanofibers are not straight with a crooked morphology, they form a three-dimensional network structure. Structure characterizations by TEM and XRD indicate that the carbon nanofibers have a turbostratic graphite structure and the graphite layers are stacked with a herringbone structure.     

化学气相催化热解法制备螺旋纳米碳纤维

采用酒石酸铜前驱体热分解得到纳米铜粒子作为催化剂,分别对250℃、280℃、310℃分解产生的纳米铜粒子进行测试分析,在3个温度下用化学气相沉积法生长螺旋纳米碳纤维并进行综合热分析。采用X-射线衍射(XRD)分析其物相组成,晶粒大小;用扫描电子显微镜(SEM)观察螺旋纳米纤维的外观形貌。结果表明,310℃生长出的螺旋纳米碳纤维纯度高、外观形貌清晰,热分析质量损失少。     

Differences between carbon nanofibers produced using Fe and Ni catalysts in a floating catalyst reactor

Carbon nanofibers were produced by the catalytic CVD process by the floating catalyst method, in semi-industrial systems at temperatures above 1350 K. Iron-derived carbon nanofibers were produced from natural gas and xylene, using ferrocene as catalyst source, yielding a thickened submicron vapor grown carbon fibers with a core of multi-wall nanotubes. For the production of Ni derived nanofibers, natural gas was used as the carbon feedstock, and the Ni was added in a nickel compound solution. When no sulfur is used, only soot was obtained, but when sulfur is added to the reactive feedstock, a highly graphitic and very nice stacked-cup-type nanofibers with no free-CVD thickened layer were produced. TEM-EDS analysis confirms that this type of stacked-cup carbon nanofiber is produced only with a partially molten catalyst and methane as hydrocarbon source. In fact, very few fibers have either a particle tip at the end or trapped metal particle inside the wide hollow core of this type of produced carbon material.     

Mechanism of carbon nanotube growth from camphor and camphor analogs by chemical vapor deposition

Single walled nanotubes have been synthesized by chemical vapor deposition from camphor, camphor analogs (camphorquinone, norcamphor, norbornane, camphene, fenchone), and various other precursors (menthone, 2-decanone, benzene, methane). The high temperature conditions (865 °C) and Fe/Mo alumina catalyst used in the syntheses are archetypal conditions for the production of single walled carbon nanotubes. It has been shown that the mechanism of tube growth is unlikely to depend upon the production of reactive five- and six-member rings, as has been previously suggested. The results suggest that the presence of oxygen in the precursor does not significantly improve the quality of tubes by etching amorphous carbon: it is suggested that the control of the flux of the precursor to the catalyst is more important in the production of high quality tubes. There is, however, evidence for different distributions of tube diameter being produced from different precursors.     

Parametric study for the growth of carbon nanotubes by catalytic chemical vapor deposition in a fluidized bed reactor

Multiwalled carbon nanotubes have been produced from H₂-C₂H₄ mixtures on Fe-SiO₂ catalysts by a fluidized bed catalytic chemical vapor deposition process. Various parameters such as the catalyst preparation, the residence time, the run duration, the temperature, the H₂:C₂H₄ ratio, the amount of metal deposited on the support have been examined. The influence of these parameters on the deposited carbon yield is reported, together with observations of the produced material. This process allows an homogeneously distributed deposition of nanotubes (10-20 nm diameter), that remain anchored to the support.     

化学气相沉积法制备碳纳米管的研究进展

从催化剂、碳源气体及反应器的选择等方面综述了化学气相沉积法制备碳纳米管的研究进展 ,讨论了碳纳米管的合成机理。指出催化合成碳纳米管的研究难点在于管径的有效调控和大批量生产 ,今后的研究方向应为单层碳纳米管的有效合成     

Laser assisted chemical vapor deposition synthesis of carbon nanotubes and their characterization

The deposition of carbon nanotubes using the laser assisted chemical vapor deposition process was studied to determine the effects of processing conditions on the quantity and quality of the tubes. A structured experimental design was utilized to test the effects of laser power, and concentration of the two precursors, acetylene and iron pentacarbonyl. Processing conditions were optimized with the assistance of heat and mass transport modeling. The synthesis of lines of carbon nanotubes as well as deposits formed under the influence of an electric field were also investigated.     

Continuous deposition of carbon nanotubes on a moving substrate by open-air laser-induced chemical vapor deposition

Continuous deposition of carbon nanotubes under open-air conditions on a moving fused quartz substrate is achieved by pyrolytic laser-induced chemical vapor deposition. A CO₂ laser is used to heat a traversing fused quartz rod covered with bimetallic nanoparticles. Pyrolysis of hydrocarbon precursor gas occurs and subsequently gives rise to rapid growth of a multi-wall carbon nanotube forest on the substrate surface. A “mushroom-like” nanotube pillar is observed, where a random orientation of carbon nanotubes is located at the top of the pillars while the growth is more aligned near the base. The typical carbon nanotube deposition rate achieved in this study is approximately 50 μm/s. At high power laser irradiation, various carbon microstructures are formed as a result of excessive formation of amorphous carbon on the substrate. High-resolution transmission and scanning electron microscopy, and X-ray energy-dispersive spectrometry are used to investigate the deposition rate, microstructure, and chemical composition of the deposited carbon nanotubes.     

Mechanistic study of cobalt catalyzed growth of carbon nanofibers in a confined space by plasma-assisted chemical vapor deposition

Carbon nanofibers (CNFs) were grown in the porous anodic aluminum oxide (AAO) thin film grown on the Si wafer by electron cyclotron resonance chemical vapor deposition using cobalt as the catalyst. A larger Co particle electrodeposited in the AAO pore channel produced vertically aligned CNFs with a tube diameter in compliance with the pore size of the AAO template. On the other hand, a smaller Co particle resulted in CNF growth with a nonuniform distribution of the tube diameter and a sparse tube density. Amorphous carbon residue produced under the plasma-assisted CNF growth condition seemed to play an essential role leading to the observation. A growth mechanism is proposed to delineate the volume effect of the electrodeposited Co catalyst on the CNF growth confined in pore channels of the AAO template.     

Fluidized bed catalytic chemical vapor deposition synthesis of carbon nanotubes—A review

Carbon nanotubes (CNTs) are pure carbon in nanostructures with unique physico-chemical properties. They have brought significant breakthroughs in different fields such as materials, electronic devices, energy storage, separation, sensors, etc. If the CNTs are ever to fulfill their promise as an engineering material, commercial production will be required. Catalytic chemical vapor deposition (CCVD) technique coupled with a suitable reactor is considered as a scalable and relatively low-cost process enabling to produce high yield CNTs. Recent advances on CCVD of CNTs have shown that fluidized-bed reactors have a great potential for commercial production of this valuable material. However, the dominating process parameters which impact upon the CNT nucleation and growth need to be understood to control product morphology, optimize process productivity and scale up the process. This paper discusses a general overview of the key parameters in the CVD formation of CNT. The focus will be then shifted to the fluidized bed reactors as an alternative for commercial production of CNTs.     

CVD法可控制备碳包覆金属纳米复合材料

以Fe质量分数分别为0.3%、1.6%、3.3%和5.2%的氯化钠担载铁为催化剂,化学气相沉积法催化裂解乙炔400℃下进行反应,系统探讨了碳包覆金属纳米颗粒的可控制备。通过扫描电子显微镜和高分辨透射电子显微镜对产物进行了表征,结果表明,w(Fe)=0.3%的催化剂制备的样品粒径在20～50 nm,平均直径约为30 nm;w(Fe)=1.6%的催化剂制备的样品粒径在35～60 nm,平均直径约为49 nm;而w(Fe)=3.3%和5.2%的催化剂制备的样品粒径差别不大,在40～100 nm,平均粒径约为65 nm。所制备的碳包覆金属纳米颗粒具有清晰的同心石墨壳层结构,并存在一定的结构缺陷。     

Coiled carbon nanotubes growth via reduced-pressure catalytic chemical vapor deposition

Coiled carbon nanotubes were prepared by catalytic chemical vapor deposition (CCVD) on finely divided Co nano-particles supported on silica gel under reduced pressure and relatively low gas flow rates. The morphology and the graphitization of the coil tube, coil bend, and coil node of the coiled carbon nanotubes were examined by transmission electron microscope (TEM). The influence of pH value, reaction pressure, and flow rate of C₂H₂ on the growth of the coiled carbon nanotubes were also discussed. With the drastic reduction in the consumption of C₂H₂ and lower required pressure with the modified CCVD approach, the amount of amorphous carbon coated on the carbon nanotubes was shown to be greatly reduced. Most importantly, this method offers a preferable alternative for the efficient, environment-friendly and safer growth of coiled carbon nanotubes.     

Intermetallic catalyst for carbon nanotubes (CNTs) growth by thermal chemical vapor deposition method

The methane conversion and carbon yield of the chemical vapor deposition (CVD) reaction suggests that the optimum reaction conditions of the formation of multi-wall carbon nanotubes (MWCNTs) can be obtained by using a 50 mg of nano-MgNi alloy under pyrolysis of the pure CH₄ gas with the flow rate about 100-120 cm³/min at 650 °C for 30 min. Raman results indicate the CNTs are in multi-wall structure, since no single-wall characteristic features appearing in the 200-400 cm⁻¹ region. This is consistent with those of the XRD and TGA findings. Under selected condition, the carbon yield and the CNTs purity can reach up to 1231% and 92% in the presence of hydrogen. It is presumable that the presence of hydrogen in the pyrolysis of CH₄ prevents the deactivation of catalysts and enhances the graphitization degree of CNTs. In addition, the presence of Mg metal in the alloy can prevent the aggregation of the Ni metal and forms the active Mg₂Ni phase to enhance the CH₄ pyrolysis to form CNTs. After the purification procedures with both air oxidation at 550 °C and HCl treatments, the final purified yield and purity of CNT reach to 73.2% and (98.04 ± 0.2)% respectively.     

SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films

Amorphous carbon films, characterized by XRD, AFM, SEM and Raman, were deposited from SiCl₃CCl₃ on quartz substrates at 773-1273 K by low pressure chemical vapor deposition using a hot-wall reactor. XPS studies showed that the films grown at 773 K contained 90% C and 10% Cl, while the films grown at 1273 K contained 100% C. SiCl₄, CCl₄ and Cl₂CCCl₂ were detected by on-line FT-IR studies. The extrusion of dichlorocarbene, :CCl₂, from SiCl₃CCl₃ should provide the source of carbon in the reaction. On Si substrates, an etching process at the film-substrate interface assisted the lift-off of the films from the substrates. The C films curled and formed rolls.     

Narrow multi-walled carbon nanotubes produced by chemical vapor deposition using graphene layer encapsulated catalytic metal particles

The use of graphene layer encapsulated catalytic metal particles for the growth of narrower multi-walled carbon nanotubes (MWCNTs) has been studied using plasma-enhanced chemical vapor deposition and conventional thermal CVD. Ni–C or Fe–C composite nanoclusters were fabricated using the dc arc discharge technique with metal–graphite composite electrodes carrying a current of 100–200 A in a stainless-steel chamber filled with He and CH₄ mixture gas at 27 kPa. Nano-sized grains with diameters less than 10 nm were fabricated and deposited on a Si substrate, and were used as a catalyst for MWCNT growth. Structural analyses of the composite nanoclusters and MWCNTs were carried out using transmission electron microscopy. The results show that the diameters of the MWCNTs were reduced from 50–100 nm for a conventional Ni thin film-evaporated Si substrate to a minimum of roughly 2–4 nm in the present study.