Catalytic CVD Growth of Carbon Nanotubes by Electric Heating Method

Carbon nanotubes（CNTs） were synthesized by the electric heating catalytic chemical deposition method（CCVD） using acetylene（C2H2） as the carbon source and nitrogen（N2） as carrier gas,and nickel catalyst was loaded by electroplating.The electric heating method,as a new method,electrifies the carbon fiber directly by using its conductivity.The morphology and structure of CNTs were characterized by SEM and TEM,and the surface properties of carbon fibers before and after the growth of CNT were characterized by Raman spectroscopy.The experimental results show that the electric heating method is a new method to produce CNT,and can grow a large number of CNTs in a short time,the crystallization degree and surface average crystallite size of carbon fiber increased after the growth of CNT on it.In addition,electroplating loading catalyst can also be used as an ideal loading way,which can control the number,shape,and distribution of nickel particles by controlling the plating time.

Influence of plasma condition on carbon nanotube growth by rf-PECVD

Carbon nanotubes(CNTs)have been synthesized from Ar-CH_4 mixtures using rf-plasma enhanced chemical vapor deposition(rf-PECVD)at 500oC.Reduction gases such as H_2 and NH_3 were found unnecessary for carbon nanotube formation compared to thermal CVD.The relationship between the growth of CNTs and the plasma condition in PECVD has been investigated by in situ self bias measurement.Plasma conditions were controlled by changing the interelectrode distance,rf power and the applied substrate negative bias.By increasing the interelectrode distance and rf power,the spatial density of CNTs was on a rise as a result of the increase in ions density and self bias.As the applied substrate negative bias increased,the spatial density of CNTs decreased possibly due to the positive ions over bombarding effect.

Purification of Single-walled Carbon Nanotubes Grown by a Chemical Vapour Deposition(CVD) Method

A procedure for purification of single walled carbon nanotubes(SWNTs) grown by the chemical vapour deposition(CVD) of carbon monooxide has been developed. Based on the result from TGA/DTA of as prepared sample, the oxidation temperature was determined. The process included sonication, oxidation and acid washing steps. The purity and yield after purification were determined and estimated by TEM. Moreover, for the first time, a loop structure for CVD SWNTs has been observed.

Growth of carbon nanotubes on the novel FeCo-Al_2O_3 catalyst prepared by ultrasonic coprecipitation

FeCo-Al2O3 catalyst was prepared by an ultrasonic coprecipitation （UC） method for the growth of carbon nanotubes （CNTs） from catalytic decomposition of methane.Its catalytic performance was compared with that of the FeCo-Al2O3 catalyst counterparts prepared by stepwise impregnation （I） and conventional coprecipitation （C） methods,respectively.The structure and properties of the catalysts and the CNTs as produced thereon were investigated by means of XRD,XPS,TEM and N2 adsorption techniques.It was found that the catalyst prepared by the ultrasonic coprecipitation method was more active,and the yield and purity of the synthesized CNTs were promoted evidently.The XPS results revealed that there were more active components on the surface of the catalyst prepared by the ultrasonic coprecipitation method.On the other hand,N2 adsorption demonstrated that the catalyst prepared by the ultrasonic coprecipitation method conferred larger specific surface area,which was beneficial to dispersion of active components.TEM images further confirmed its higher dispersion.These factors could be responsible for its higher activity for the growth of CNTs from catalytic decomposition of methane.

Carbon Nanotubes Grown on Sepiolite as Catalyst Carrier

Multi-walled carbon nanotubes were synthesized by the catalytic decomposition of acetylene at 750oC over sepiolite powder, which was treated with aqueous cobalt nitrate. It is expected that the composite with high specific area will have high capacity of hydrogen storage.

Experimental evidence for the formation mechanism of metallic catalyst-free carbon nanotubes

Our work reported that the so-called pure carbon nanotubes(CNTs)can be synthesized without metallic catalyst by chemical vapor deposition(CVD).The as-prepared CNTs have average diameter of 50 nm and length over several microns.Analysis of intermediate objects in the products indicates that their formation mechanism follows the wire-to-tube model.Besides,according to thermodynamic analysis of the driving force combing with experimental results,we find that the thermal gradient can effectively favor the formation of CNTs in our metallic catalyst-free CVD.

Remarkable carbon dioxide catalytic capture (CDCC) leading to solid-form carbon material via a new CVD integrated process (CVD-IP): An alternative route for CO_2 sequestration

Through our newly-developed ＂chemical vapor deposition integrated process （ISVD-IP）＇＂ using carbon OlOXlae （t..u2） as me raw matenal and only carbon source introduced, CO2 could be catalytically activated and converted to a new solid-form product, i.e., carbon nanotubes （CO2-derived） at a quite high yield （the single-pass carbon yield in the solid-form carbon-product produced from CO2 catalytic capture and conversion was more than 30% at a single-pass carbon-base）. For comparison, when only pure carbon dioxide was introduced using the conventional CVD method without integrated process, no solid-form carbon-material product could be formed. In the addition of saturated steam at room temperature in the feed for CVD, there were much more end-opening carbon nano-tubes produced, at a slightly higher carbon yield. These inspiring works opened a remarkable and alternative new approach for carbon dioxide catalytic capture to solid-form product, comparing with that of CO2 sequestration （CCS） or CO2 mineralization （solidification）, etc. As a result, there was much less body volume and almost no greenhouse effect for this solid-form carbon-material than those of primitive carbon dioxide.

Investigation on the Formation Mechanism of Double-Layer Vertically Aligned Carbon Nanotube Arrays via Single-Step Chemical Vapour Deposition

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays(VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy(SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM.During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.

The production of carbon nanotubes from carbon dioxide:challenges and opportunities

Recent advances in the production of carbon nanotubes （CNTs） are reviewed with an emphasis on the use of carbon dioxide （CO2） as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be ex- plored further. A theoretical and analytical comparison of the cur- rently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters （i.e., temperature, pres- sure, catalyst, etc.） that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology： （1） the CNT-CO2 synthesis and formation mechanism, （2） catalytic effects of transitional metals and mechanisms, （3） uti- lization of metallocenes in the CNT-CO2 reactions, （4） applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and （5） the effects of process parameters such as temperature, etc.

Effect of Electron Drag on Performances of Carbon Nanotubes as Flow Sensors

Experimentally, the electron drag effect on carbon nanotube surface in flowing liquids was investigated. It was found that electric current could be generated in metallic carbon nanotubes immersed in the liquids. Carbon nanotubes were synthesized on Si substrate by hot filament chemical vapor deposition. The experimental results showed that the flow-induced current on the surface of carbon nanotube films was closely depended on the flow rate, concentration, properties and temperature of liquids. The flow-induced current was increased with the increasing of flow rate, concentration and temperature of liquids. The obtained results were discussed in detail.

Production of Carbon Nanotubes by Different Routes-A Review

Carbon Nanotubes are one the most important materials of future. Discovered in 1991, they have reached a stage of attracting the interests of many companies world wide for their large scale production. They possess remarkable electrical, mechanical, optical, thermal and chemical properties, which make them a perfect “fit” for many engineering applications. In this paper various methods of production of carbon nanotubes are discussed outlining their capabilities, efficiencies and possible exploitation as economic large scale production methods. Chemical vapor disposition (CVD) is proposed as a potential method for economic large scale production of carbon nanotubes due to its relative simplicity of operation, process control, energy efficiency, raw materials used, capability to scale up as large unit operation, high yield and purity.

Electro-Optical Properties of Carbon Nanotubes Obtained by High Density Plasma Chemical Vapor Deposition

In this work, we studied the electro-optical properties of high-aligned carbon nanotubes deposited at room temperature. For this, we used the High Density Plasma Chemical Vapor Deposition system. This system uses a new concept of plasma generation: a planar coil is coupled to an RF system for plasma generation. This was used together with an electrostatic shield, for plasma densification, thereby obtaining high-density plasmas. The carbon nanotubes were deposited using pure methane plasmas. Three methods were used for the surface modification of the sample: reference substrate (silicon wafer only submitted to a chemical cleaning), silicon wafer with surface roughness generated by plasma etching, silicon wafer with a thin iron film and silicon wafer with diamond nano powder used as precursor materials. For each kind of silicon wafer surface, the carbon nanotubes were deposited with two different deposition times (two and three hours). The carbon nanotubes structural characteristics were analyzed by Atomic Force Microscope and Scanning Electronic Microscope. The carbon nanotubes electrical characteristics were observed by Raman Spectroscopy and the carbon nanotubes electro-optical properties were analyzed by current vs voltage electrical measurements and photo-luminescence spectroscopy measurements. The photoelectric effect in the carbon nanotubes were determined by photo-induced current measurements. In this work, we obtained carbon nanotubes with semiconductor properties and carbon nanotubes with metallic properties. The electro-optical effects depend strongly on the substrate preparation and the deposition parameters of the carbon nanotubes. The carbon nanotubes are high aligned and show singular properties that can be used for many applications.

一步TCVD法制备大面积碳纳米管冷阴极及其场致发射性能研究

本文提出一步热化学气相沉积法(TCVD)热解二茂铁,并直接在硅衬底上制备大面积(1 cm^(2))、高质量碳纳米管(CNTs)场致发射冷阴极阵列的制备工艺.通过调控二茂铁的热解温度(650~1000℃),获得了最佳的二茂铁的碳转化效率以及高结晶度的碳纳米管阵列.研究了不同热解温度下制备的碳纳米管微观形貌及其对场致发射性能的影响机制.场致发射实验测试表明在热解温度850℃条件下制备的碳纳米管冷阴极其开启电场(10μA/cm^(2))和阈值电场(1 mA/cm^(2))分别为1.32 V/μm和2.64 V/μm,最大电流密度为14.51 mA/cm^(2),对应的场增强因子为13267,表现出良好的场发射性能.本文提出的一步制备碳纳米管冷阴极阵列的制备方法无需任何蚀刻气体或光刻图案工艺,该方法安全、经济、可重复性好,在碳纳米管场发射冷阴极领域具有广阔的应用前景.

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 effi cient method for the patterning growth of SWNTs arrays on a surface is compatible with the micro-electronics industry,thus enabling of the fabrication highly integrated circuits of SWNTs.

Direct Observation of the Strong Interaction Between Carbon Nanotubes and Quartz Substrate

We present a chemical vapor deposition(CVD)method for the growth of uniform single-walled carbon nanotube(SWNT)arrays on a stable temperature(ST)-cut single crystal quartz substrate using a mixture of methanol and ethanol as carbon source.It is found that introducing methanol during the growth can improve the density and the length of the well-aligned SWNTs in the arrays as well as increase the SWNT/quartz interaction.Obvious“up-shifts”of G-band frequencies in the Raman spectra have been found for the aligned SWNTs.A well-designed control experiment shows that the G-band“up-shifts”originate from the strong interaction between SWNTs and the quartz substrate.It is believed that exploring this interaction will help to elucidate the growth mechanism;ultimately,this will help realize the promise of controlling the chirality of SWNTs.

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.

From Carbon Nanotube Crystals to Carbon Nanotube Flowers

We have investigated the very initial deposition stages of chemical vapor deposition （CVD） with ferrocene （Fe（CsH5）2） and xylene （C8H10） for growing carbon nanotubes, and made clear that the mechanism for the self-organization behaviors of nanotubes at different growth stages by this approach. For instance, the organization of nanotubes into flower-like structures at prolonged deposition is developed from the crystal-like structures formed at early growth stages, both of which are closely related to and determined by the very initial deposition stages of this CVD approach. Based on this approach, ways have been established to build up different architectures of carbon nanotubes, by controlling the initial deposition stages of the CVD process, with which we have realized the selective growth of self-organized carbon nanotube structures. This study provides a new idea for growing carbon nanotube architectures by CVD.

CVD法制备多壁碳纳米管的研究进展

碳纳米管在力、热、光、电等方面均表现出独特的性质,因此受到众多领域专家的广泛关注。但碳纳米管价格较高,制作过程复杂,严重限制了大规模推广。因而探索高产量、低成本的碳纳米管制作方法备受关注。碳纳米管采用化学气相沉积(chemical vapor deposition,CVD)法制备,可实现连续批量化生产。综述了CVD法制备碳纳米管的生长机理,不同工艺参数对碳纳米管生产的影响,以及在定向碳纳米管的研究现状,并对CVD法制备的多壁碳纳米管在石油化工领域的应用前景做出了展望,为学者在CVD法制备多壁碳纳米方面的研究提供了一定参考。

Plasma-enhanced Deposition of Nano-Structured Carbon Films

By pre-treating substrate with different methods and patterning the catalyst, selective and patterned growth of diamond and graphitic nano-structured carbon films have been realized through DC Plasma-Enhanced Hot Filament Chemical Vapor Deposition (PE-HFCVD). Through two-step processing in an HFCVD reactor, novel nano-structured composite diamond films containing a nanocrystalline diamond layer on the top of a nanocone diamond layer have been synthesized. Well-aligned carbon nanotubes, diamond and graphitic carbon nanocones with controllable alignment orientations have been synthesized by using PE-HFCVD. The orientation of the nanostructures can be controlled by adjusting the working pressure. In a Microwave Plasma Enhanced Chemical Vapor Deposition (MW-PECVD) reactor, high-quality diamond films have been synthesized at low temperatures (310℃-550℃) without adding oxygen or halogen gas in a newly developed processing technique. In this process, carbon source originates from graphite etching, instead of hydrocarbon. The lowest growth temperature for the growth of nanocrystalline diamond films with a reasonable growth rate without addition of oxygen or halogen is 260℃.