Silicon enhanced carbon nanotube growth on nickel films by chemical vapor deposition

Silicon enhances carbon nanotube growth on nickel films by chemical vapor deposition using methane and hydrogen. Nanotube growth characteristic is significantly improved on nickel films patterned by argon plasma etching on silicon oxide layers. Auger electron spectroscopy shows that a reduced silicon phase forms in the surface silicon oxide layer by Ar ion bombardment used for patterning. The enhanced growth of carbon nanotubes could be ascribed to an oxygen removal effect by silicon in the process of synthesis.     

Simple methods for site-controlled carbon nanotube growth using radio-frequency plasma-enhanced chemical vapor deposition

We demonstrate the validity of very simple methods for site-controlled carbon nanotube growth using a radio-frequency magnetron-type plasma-enhanced chemical vapor deposition technique. Enhanced plasma density and optimized ion-bombardment energy achieved by magnetic field introduction are found to be responsible for the uniform and well-aligned carbon nanotube growth. Based on these results, we attempted to perform experiments on site-controlled carbon nanotube growth using very convenient methods such as scratching or simply masking a substrate surface where carbonaceous materials deposit. PACS 61.46.+w; 52.80.Pi; 81.15.Gh     

Hydrogen-free spray pyrolysis chemical vapor deposition method for the carbon nanotube growth: Parametric studies

Spray pyrolysis chemical vapor deposition (CVD) in the absence of hydrogen at low carrier gas flow rates has been used for the growth of carbon nanotubes (CNTs). A parametric study of the carbon nanotube growth has been conducted by optimizing various parameters such as temperature, injection speed, precursor volume, and catalyst concentration. Experimental observations and characterizations reveal that the growth rate, size and quality of the carbon nanotubes are significantly dependent on the reaction parameters. Scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy techniques were employed to characterize the morphology, structure and crystallinity of the carbon nanotubes. The synthesis process can be applied to both semiconducting silicon wafer and conducting substrates such as carbon microfibers and stainless steel plates. This approach promises great potential in building various nanodevices with different electron conducting requirements. In addition, the absence of hydrogen as a carrier gas and the relatively low synthesis temperature (typically 750 °C) qualify the spray pyrolysis CVD method as a safe and easy way to scale up the CNT growth, which is applicable in industrial production.     

Chemistry and kinetics of chemical vapor deposition of pyrolytic carbon from ethanol

Synthesis of pyrolytic carbon as a matrix for carbon fiber reinforced carbon composites by chemical vapor infiltration (CVI) is studied experimentally and numerically using the oxygen-containing precursor ethanol. The effects of residence time on microstructure and deposition rate of pyrolytic carbon are investigated. A short residence time is found to favor the formation of high-textured pyrolytic carbon. The evolutions of microstructure and deposition rate of pyrolytic carbon are compared with those of carbon deposited from methane. Compared to methane, ethanol exhibits a much higher deposition rate of pyrolytic carbon with similar microstructures. Pyrolysis of ethanol is modeled using a two-dimensional flow model coupled with a detailed gas-phase reaction mechanism involving 261 species taking part in 1177 reversible reactions. Reaction rate analysis reveals that C₃-hydrocarbons are the most important intermediate species contributing to the maturation of gas-phase composition. A comparison of the kinetic predictions with equilibrium calculations demonstrates that the CVD reactor applied is operated far away from equilibrium.     

In situ observation of carbon nanotube yarn during voltage application

Carbon nanotube (CNT) yarns are fabricated by drawing (combined with spinning) from CNT forests and grown on a substrate. Three types of phenomena occur in these CNT yarns with increasing amounts of current: yarn rotation, catalyst evaporation, and breakage of the yarn. These phenomena result from the resistive heating occurring during the current flow, and have been observed in situ under vacuum by transmission electron microscopy. If these CNT yarns are applied to electronic circuits, the rotation and breakage may lead to circuit failure. However, catalyst evaporation is a useful method for purifying CNT yarns without additional treatments prior to yarn fabrication.     

Direct writing of carbon nanotube patterns by laser-induced chemical vapor deposition on a transparent substrate

Dot array and line patterns of multi-walled carbon nanotubes (MWCNTs) were successfully grown by laser-induced chemical vapor deposition (LCVD) on a transparent substrate at room temperature. In the proposed technique, a Nd:YVO₄ laser with a wavelength of 532 nm irradiates the backside of multiple catalyst layers (Ni/Al/Cr) through a transparent substrate to induce a local temperature rise, thereby allowing the direct writing of dense dot and line patterns of MWCNTs below 10 μm in size to be produced with uniform density on the controlled positions. In this LCVD method, a multiple-catalyst-layer with a Cr thermal layer is the central component for enabling the growth of dense MWCNTs with good spatial resolution.     

Real-time volumetric growth rate measurements and feedback control of three-dimensional laser chemical vapor deposition

Received: 4 June 1997/Accepted: 12 June 1997     

Bistable growth in laser chemical vapor deposition

This is the first report on the observation of a bistability in laser-CVD. The effect is demonstrated for silicon deposition from silane by means of Ar⁺-laser radiation.     

Effect of temperature on growth and structure of carbon nanotubes by chemical vapor deposition

The effect of temperature on growth and structure of carbon nanotubes (NTs) using chemical vapor deposition (CVD) has been investigated. Iron embedded silica was used to grow NTs in large quantity at various temperatures from 600 to 1050 °C with gas pressure fixed at 0.6 and 760 Torr, respectively. The growth and structure of the NTs are strongly affected by the temperature. At low gas pressure, the NTs are completely hollow at low temperature and bamboo-like structure at high temperature. While at high gas pressure, all the NTs are bamboo-like structure regardless of temperature. The diameter of NTs increases significantly with temperature. At low gas pressure the diameter gets bigger by mainly increasing the number of graphene layers of the wall of NTs, whereas at high gas pressure the diameter gets bigger by increasing both the number of graphene layers of the wall and the inner diameter of the NTs. This result indicates that the growth temperature is crucial in synthesizing NTs with different structures. The findings here are important for realizing controlled growth of NTs for their applications in different fields. Received: 20 November 2001 / Accepted: 21 November 2001 / Published online: 4 March 2002     

Computational modeling of forced flow laser chemical vapor deposition

Laser chemical vapor deposition (LCVD) utilizes a laser to localize a CVD reaction. The process involves complex physical interactions within a very small spatial region. Experimental investigations into the dynamics of the LCVD process are limited by spatial and resolution capabilities of instrumentation. Models are developed herein using the computational fluid dynamics (CFD) code, FLUENT, that incorporate heat transfer, fluid flow, and species transport in a single integrated modeling environment. The models are used to study the carbon deposition process. Insight is gained into the relationships among the process parameters and the deposition rates and deposition rate profiles. Phenomena such as thermal diffusion and the relative importance of mass convection and mass diffusion are explored. A designed set of model cases is executed and the results are used to develop a simple polynomial expression for relating experiment conditions to deposit attributes. PACS 81.10.Bk; 81.05.Uw; 81.15.Gh; 47.50.Cd; 81.16.Mk     

Controllable growth of individual, uniform carbon nanotubes by thermal chemical vapor deposition

We report on the controllable growth of individual, uniform carbon nanotubes using thermal chemical vapor deposition (CVD). We performed a detailed study of the various factors influencing the growth of single nanotubes. In particular, we investigated the role played by catalyst layer thickness, catalyst dot size, deposition temperature, and gas source pressure on the growth process of straight, single nanotubes. Straight, individual nanotubes with uniform diameter can be obtained by decomposition of 0.1 mbar of acetylene at a temperature of 800 °C over a 5 nm thick nickel film that is patterned into square dots with dimensions below 500 nm. We compare the performance of thermal CVD and of plasma enhanced CVD for growing individual nanotubes.     

Aligned growth and alignment mechanism of carbon nanotubes by hot filament chemical vapor deposition

Carbon nanotubes (CNTs) growth on Inconel sheets was carried out using hot filament chemical vapor deposition (HFCVD) in a gas mixture of methane and hydrogen. Scanning electron microscopy, transmission electron microscopy and field electron emission (FEE) measurement were applied to study the structure and FEE properties of the deposited CNTs. The effect of bias voltage and substrate surface roughness on the growth of vertically aligned carbon nanotubes was investigated. Well-aligned CNTs were synthesized by bias enhanced HFCVD. The results show that a bias of −500 V generates the best alignment. It has been observed that at the early growth stage, aligned and non-aligned CNTs are growing simultaneously on the unscratched sheets, whereas only aligned CNTs are growing on the scratched sheets. The results indicate that tip growth is not necessary for the electric field to align the CNTs, and larger catalyst particles created by scratching before the heat treatment can induce alignment of CNTs at the early growth stage. In addition, tree-like CNTs bundles grown on the scratched substrates exhibit better FEE performances than dense carbon nanotube forest grown on the unscratched substrates due to the reduced screen effect.     

Aligned carbon nanotube from catalytic chemical vapor deposition technique for energy storage device: a review

Carbon nanomaterial especially carbon nanotube (CNT) possesses remarkably significant achievements towards the development of sustainable energy storage applications. This article reviews aligned CNTs grown from chemical vapor deposition (CVD) technique as electrode material in batteries and electrochemical capacitors. As compared to the entangled CNTs, aligned or well-organized CNTs have advantages in specific surface area and ion accessibility in which more electrolyte ions can access to CNT surfaces for better charge storage performance. CVD known as the most popular technique to produce CNTs enables the use of various substrates and CNT can grow in a variety of forms, such as powder, films, aligned or entangled. Also, CVD is a simple and economic technique, and has good controllability of direction and CNT dimension. High purity of as-grown CNTs is also another beauty of the CVD technique. The current trend and performance of devices utilizing CNTs as electrode material is also extensively discussed.     

Coupled process of plastics pyrolysis and chemical vapor deposition for controllable synthesis of vertically aligned carbon nanotube arrays

Efficient conversion of waste plastics into advanced materials is of conspicuous environmental, social and economic benefits. A coupled process of plastic pyrolysis and chemical vapor deposition for vertically aligned carbon nanotube (CNT) array growth was proposed. Various kinds of plastics, such as polypropylene, polyethylene, and polyvinyl chloride, were used as carbon sources for the controllable growth of CNT arrays. The relationship between the length of CNT arrays and the growth time was investigated. It was found that the length of aligned CNTs increased with prolonged growth time. CNT arrays with a length of 500 μm were obtained for a 40-min growth and the average growth rate was estimated to be 12 μm/min. The diameter of CNTs in the arrays can be modulated by controlling the growth temperature and the feeding rate of ferrocene. In addition, substrates with larger specific surface area such as ceramic spheres, quartz fibers, and quartz particles, were adopted to support the growth of CNT arrays. Those results provide strong evidence for the feasibility of conversion from waste plastics into CNT arrays via this reported sustainable materials processing.     

Morphology transition during low-pressure chemical vapor deposition

Assuming a reemission model, we have studied, in detail, the effect of sticking coefficient on the morphology evolution in low-pressure chemical vapor deposition processes. We have shown that the surface morphology changes from a self-affine fractal to a columnarlike morphology with increasing sticking coefficient, which agrees qualitatively with experimental observations.     

Mechanisms and kinetics of the initial stages of growth of films grown by chemical vapor deposition

The initial stages of growth of films and coatings by chemical vapor deposition are investigated. A system of equations is derived which describes the evolution of an island film at the stage of Ostwald ripening under conditions characteristic of vapor deposition. Solving this system of equations yields the dependence of all of the main characteristics of island films (the size distribution function of the islands, the dependence of the mean radius and density of the islands) as functions of time and the spatial coordinate. Suggestions are given for the preparation of films with prescribed properties. Zh. Tekh. Fiz. 68, 111–117 (July 1998)     

A chemical kinetic model for chemical vapor deposition of carbon nanotubes

Carbon nanotubes (CNTs) are classified among the most promising novel materials due to their exceptional physical properties. Still, optimal fabrication of carbon nanotubes involves a number of challenges. Whatever be the fabrication method, a process optimization can be evolved only on the basis of a good theoretical model to predict the parametric influences on the final product. The work reported here investigates the dependence of the deposition parameters on the controllable parameters for carbon nanotube growth during Chemical vapor deposition (CVD), through a chemical kinetic model. The theoretical model consisted of the design equations and the energy balance equations, based on the reaction kinetics, for the plug flow and the batch reactor, which simulate the CVD system. The numerical simulation code was developed in-house in a g++ environment. The results predicted the growth conditions for CNT: the deposition temperature, pressure and number of atoms, which were found to be influenced substantially by the initial controllable parameters namely the temperature, volumetric flow rate of the carbon precursor, and the reaction time. An experimental study was also conducted on a CVD system developed in the laboratory, to benchmark the computational results. The experimental results were found to agree well with the theoretical predictions obtained from the model.     

Effect of sulfur on the growth of carbon nanotubes by detonation-assisted chemical vapor deposition

Thiophene was introduced as an additive in detonation-assisted chemical vapor deposition to investigate the effect of sulfur on the growth of carbon nanotubes. The results reveal that sulfur promoted the growth of hollow tubes, instead of bamboo-like carbon nanotubes without sulfur addition. Structural characterization of products indicates that the dynamic reshaping of the catalyst assisted bamboo-like carbon nanotube growth and the bamboo knots preferentially nucleated on the Ni-graphite step edges. It is suggested that sulfur suppressed the bamboo knot growth through blocking the step sites. The findings are important for understanding of nanotube growth mechanism and the role of sulfur often involved in catalytic reactions.     

Fabrication of carbon nanoflowers by plasma-enhanced chemical vapor deposition

Two and three-dimensional (2D and 3D) carbon nanoflowers have been prepared on silicon (1 1 1) substrates by plasma-enhanced chemical vapor deposition, using CH₄, H₂ and Ar as reactive gases in the presence of Fe catalyst. The flower patterns are controlled by the flux ratio of the carrier gas, the reaction pressure and the growth temperature. Through observation by scanning electron microscopy, we find that the 2D carbon nanoflowers are formed by various nanoleaves while the 3D flowers are composed of hundreds of nanofibers. The former is related closely to the flux ratio of gas and the reaction pressure, while the latter depended mainly on the growth temperature. The nucleation and growth process of the nanoflowers seem to be a vapor/liquid/solid mechanism.     

锗硅/硅异质结材料的化学气相淀积生长动力学模型

基于化学气相淀积(CVD)的Grove理论和Fick第一定律,提出并建立了锗硅(SiGe)/硅(Si)异质结材料减压化学气相淀积(RPCVD)生长动力学模型.与以前锗硅/硅异质结材料生长动力学模型仅考虑表面反应控制不同,本模型同时考虑了表面反应和气相传输两种控制机理,并给出了两种控制机理极限情况下的模型.本模型不仅适用于低温锗硅/硅应变异质结材料生长的表征,也适用于表征高温锗硅/硅弛豫异质结材料生长的表征.将模型计算值与实验结果进行了对比,无论是625℃低温下的应变SiGe的生长,还是900℃高温下的弛豫 关键词： SiGe/Si异质结材料 化学气相淀积生长动力学模型 Grove理论 Fick第一定律