A compact ellipsoidal cavity type microwave plasma reactor for diamond film deposition

Electric field distribution in ellipsoidal microwave cavities with different sizes was modeled by the finite difference time-domain method (FDTD). The influence of varying size on the performance of the ellipsoidal cavities was studied. Through the simulations, eight series of resonant patterns were found. Based on this simulation result, a compact ellipsoidal cavity type microwave plasma chemical vapor deposition reactor has been proposed and its performance was predicted. It is shown that such a compact ellipsoidal cavity type reactor retains the same ability to concentrate microwave energy into its focus, facilitating both production of high density plasmas and deposition of diamond films.     

Design of novel plasma reactor for diamond film deposition

Development of microwave plasma reactors is a key factor for improving microwave plasma chemical vapor deposition (MPCVD) techniques for producing high quality diamond films. In this paper, a new microwave plasma reactor operated at 2.45 GHz was proposed on the basis of numerical simulation. The Finite Element Method (FEM) was used to optimize the geometry, and the Finite Difference Time Domain (FDTD) method was employed to calculate the electric field and the plasma density. The proposed reactor works mainly at the TM₀₂₁ mode, and it has an excellent power handing capability. Preliminary experiment showed that high density hemispherical plasma could be ignited inside the reactor, and uniform diamond film could be deposited on substrates at high input microwave power.     

Design of a new TM021 mode cavity type MPCVD reactor for diamond film deposition

A new TM₀₂₁ mode cavity type microwave plasma chemical vapor deposition (MPCVD) reactor for diamond film deposition was derived by analyzing the TM₀₂₁ resonant pattern of microwave electric field in an idealized TM₀₂₁ mode reactor. Important characteristics of the reactor, including microwave electric field, electron density, gas temperature as well as absorbed microwave power density were obtained by using a phenomenological model of hydrogen plasma. On the basis of the simulation, a new TM₀₂₁ mode cavity type MPCVD reactor was built and 2-inch diameter freestanding diamond films were synthesized at 6 kW input microwave power. Raman and optical transmission spectroscopy analyses indicate that the diamond films prepared by using the new TM₀₂₁ mode cavity type reactor are of high quality.     

Multiwalled carbon nanotube deposition profiles within a CVD reactor: An experimental study

A number of proposed applications of carbon nanotube (CNT) arrays require that uniform deposition of well-aligned CNTs is achieved. The CNT deposition profiles inside a chemical vapor deposition (CVD) reactor are strongly dependant on the reaction temperatures, feed gas flow rates, carrier gas flow rates and reactor geometry. In addition, objects placed in the path of the flow of feed material could affect the deposition patterns. In this paper, an experimental study aimed at achieving better control of the deposition patterns of CNTs is presented. Multiwalled CNTs were grown on a long substrate by the catalytic CVD of a xylene/ferrocene solution. The deposition patterns on the substrate were examined for different furnace temperatures, xylene/ferrocene feed rates and carrier gas flow rates. Small objects representative of electronic devices were placed at different locations on the substrate and their effect on the deposition patterns was explored. The effect of changing the height and the gap distance between these objects was also studied.     

High rate of diamond deposition through graphite etching in a hot filament CVD reactor

Although a hot filament diamond CVD reactor has many advantages over other processes, the relatively low growth rate of the films has been a crucial drawback. We developed a new hot filament process that uses no hydrocarbon gas for diamond deposition. The graphite plate was placed below the silicon substrate and only hydrogen was supplied during the process. We could achieve the growth rate of 9 μm/h, which is approximately 9 times higher than that of conventional hot filament CVD using a gas mixture of methane and hydrogen. In spite of the high growth rate, the quality of diamond films was not degraded. Besides, the diamond films consisted of small crystallites with a smooth surface while the conventional diamond films of the same thickness tend to have a columnar structure with a rough surface.     

Laser plasma CVD diamond reactor

The results of multi-parametric investigations of laser plasmatron in application to CVD of diamond are presented. Different reaction chamber configurations were studied. CH₄/H₂/Xe(Ar) and CH₄/CO₂/H₂/Ar gas mixtures at total pressure 1.0–4.5 atm were used. Both convection and directed gas flows with velocity up to 50 cm/s delivered reactants to the substrate surface. Diamond film deposition rates up to 40–50 μm/h were reached. CW CO₂ laser beam power and intensity needed for a stationary plasma maintenance under various experimental conditions were found. Laser radiation absorption in plasma was measured. The possibility to combine laser plasma with an auxiliary electrical discharge is demonstrated. A comparison between laser and other plasma CVD techniques is made.     

Vapor deposition polymerization of synthetic rubber thin film in a plasma enhanced chemical vapor deposition reactor

Rubber is one of the most commonly used industrial materials worldwide. However, there is a gap in the literature on the production of rubber thin films in nanoscale. When the rubber thin films are produced in nanoscale, they can be used in high-tech applications where bulk rubbers have never been used before. This study is one of the first investigations to focus on the vapor-based production of the polyisoprene (PI), which is an important member of the synthetic rubber class. For this purpose, a single-step, rapid and environmentally friendly method based on plasma enhanced chemical vapor deposition (PECVD) was employed to produce PI thin films using 2-methyl-1,3-butadiene (isoprene). The high-vapor pressure of isoprene makes it a promising monomer for the production of chemical vapor deposition polymers. The effect of plasma processing parameters on the PI deposition rate was investigated. The deposition rate of PI thin film as high as 40 nm/min was achieved and the contact angle of PI coated bamboo surface was found to be 146.8°. The mechanical durability and laundering tests of PI thin films were performed. Based on this study results, PI thin films produced by PECVD can be used in a number of potential applications.     

A new elegant technique for polishing CVD diamond films

It is well known that the columnar growth nature of CVD diamond results in a very rough growth surface and the surface roughness steeply increases with film thickness, especially for thick CVD diamond films. In this paper, we report the successful implementation of a new elegant technique for polishing thick polycrystalline CVD diamond films at high polishing rate of up to 10 μm/h. This technique involves polishing the as-grown polycrystalline diamond films with another thick as-grown polycrystalline diamond film, which acts as a polishing abrasive. Two types of diamond films were prepared using microwave plasma CVD and then polished for 2 h using the new polishing technique. A stylus profilometer, scanning electron microscopy and Fourier transform infrared spectroscopy were used to measure the surface roughness, characterize morphology and optical transmission of the samples before and after polishing, respectively. By polishing, thickness of 20–30 μm was removed from the top surface, and the mean surface roughness R_a of the films reduced significantly, e.g. for one film R_a reduced initially from 5.2 to 1.35 μm and the other from 3.2 to 0.55 μm. The principal advantages of this new polishing technique are simplicity, flexibility and time saving. This simple method can serve as ‘rough chipping’ to quickly remove the rough top surface and then combine with conventional polishing methods for precision machining to further reduce the surface roughness to a specific desired degree.     

CFD modeling and optimal design of SiC deposition on the fuel combustion nozzle in a commercial CVD reactor

This work presents a new CFD model developed to investigate the SiC film growth over a fuel combustion nozzle in the commercial hot-wall CVD reactor. A detailed 3D model consisting of the compressive transport models and the reaction mechanism to account for the chemistry of the gas-phase and surface reactions are developed. The velocity, temperature, and concentration profiles inside the reactor are predicted numerically. The multispecies transport and its interplay with the gas and surface reactions are understood to operate the reactor effectively. The natural convection and hydrodynamics stability of the flow is investigated using various dimensionless groups (Re, Pr. Pe, and Gr/Re²). It has been observed that the buoyancy-driven flow is dominant at a large Reynolds number (Re) and Gr/Re² ratio. This results in flow recirculation, which ultimately deteriorates the film uniformity. A sensitivity analysis is performed to identify how critical parameters affect the deposition process. Besides, the optimisation of the CVD reactor is also served by combining the support vector machine, a versatile supervised machine learning method, and the Nelder-Mead algorithm to improve the film quality. Our results demonstrate that the present methodology effectively obtains optimal process conditions, significantly enhancing the film performance.     

Effects of CCl4 concentration on nanocrystalline diamond film deposition in a hot-filament chemical vapor deposition reactor

The effect of CCl₄ concentration on the nanocrystalline diamond (NCD) films deposition has been investigated in a hot-filament chemical vapor deposition (HFCVD) reactor. NCD films with a thickness of few-hundred nanometers have been synthesized on Si substrates from 2.0% and 2.5% CCl₄/H₂ at a substrate temperature of 610 °C. Polycrystalline diamond films and nanowall-like films with higher formation rates than those of the NCD films were deposited from lower and higher CCl₄ concentrations, respectively. The grain sizes of the diamond film grown using 2.0% CCl₄ increased with film thickness while a diamond film with uniform nanocrystalline structure all over a thickness of 1 μm can be deposited in the case of 2.5% CCl₄. We suggest that both the primary nucleation and the secondary nucleation processes are crucial for the growth of the NCD films on Si substrates.     

Numerical modeling of a microwave plasma CVD reactor

This paper presents the results of numerical simulation of a microwave CVD reactor operating in CW and pulsed regimes. Dependencies of discharge parameters on the hydrogen pressure and microwave power have been studied. The possibility to use the pulse–periodic regime of discharge for deposition of diamond films has been analyzed. It is shown that a pulsed discharge may be used to improve the quality and increase the growth rate of the films.     

A novel concept reactor design for preventing salt deposition in supercritical water

Reactor plugging and corrosion are the key problems which hinder commercial applications of supercritical water oxidation and gasification, and can be efficiently overcome by preventing salt deposition on internal surface of reactor. In this work the problems caused by salt deposition and the correspondingly main solutions are further reviewed objectively. A novel reactor is designed and manufactured with a feed rate of about 100 L/h for sewage sludge treatment. The reactor combines the characteristics of Modar reactor and transpiring wall reactor for the first time, which is expected to prevent reactor plugging and corrosion as well as to decrease catalyst deactivation rate. The reactor is the core equipment of the first pilot-scale plant for supercritical water oxidation in China. Further optimizations of reactor configuration and operational parameters need plenty of experiments and/or a long-time test with sewage sludge in the subsequent work.     

A new two-impinging-streams heterogeneous reactor

The characteristics of a new heterogeneous reactor of the “two impinging streams” type, suitable for gas-solid heat and mass-transfer operations, were investigated. The operating limits of the reactor, with respect to gas and solid particles mass flow rate and pressure drop, were determined; scale-up criteria with respect to the hydrodynamics of the reactor were also established. It has been found that, under certain conditions, the introduction of solid particles into the gas stream lowers the pressure drop on the reactor. In addition, the maximal pumping energy per kg of solids transported through the reactor by the air is much lower than in a fluidized-bed-type reactor. A stochastic model based on Markov processes was developed which closely describes the behavior of the solid particles in the reactor. A technique based on this model was employed for determining the residence time distribution of the particles in the reactor.     

CVD金刚石膜投资财务分析

文章从经济的角度,通过专业的财务分析,对CVD金刚石膜这一新型材料的投资价值进行研究。研究认为,CVD金刚石膜将成为金刚石材料未来发展的主流,其材料和制品具有广阔的市场前景。因此,投资CVD金刚石膜将获得丰厚的经济回报。     

分子吸收光谱在半导体薄膜化学气相沉积中的应用

在化学气相沉积(CVD)生长半导体薄膜过程中,反应前体的浓度测量对于了解反应机理至关重要。紫外-可见吸收光谱和红外光谱是测量半导体薄膜CVD生长中分子浓度的主要工具,特别是可以实现气体浓度的原位测量。本文介绍了CVD中紫外-可见吸收光谱的测量系统,以及它们在测量Ⅲ～Ⅴ族气体浓度和确定在不同条件下化学反应路径中的应用。包括常见金属有机物等气体的吸收特征,紫外-可见吸收光谱在不同温度和压力下CVD过程中InN、GaN薄膜生长中的应用。本文也介绍了红外光谱分析方法在CVD中的应用,包括不同条件下TMG和NH₃气相反应机理的分析、SiC薄膜的元素成分分析以及GaN薄膜的气相反应速率的确定。     

A new model for a hollow fibre enzyme reactor

A new model based on the concept of axial dispersion has been developed for predicting the performance of a hollow fibre enzyme reactor. It is shown that a simple closed form analytical solution for the prediction of the reactor performance results. The model parameters are obtained a priori from the welldefined hydrodynamic conditions. The agreement between the model predictions and the numerical solutions is excellent over a wide range of variables. The comparison of the model predictions with the experimental data shows good agreement. The model can be easily extended to include further complications. The extension to non-Newtonian substrates is discussed and results for reactor performance under these conditions are given.     

Use of carbonitride film as buffer layer for CVD diamond nucleation

Enhanced nucleation of polycrystalline diamond has been achieved on Si(100) with an intermediate layer of carbonitride. The carbonitride film was formed by an ion beam assisted deposition method and was characterized by Rutherford backscattering, X-ray photoelectron and laser Raman spectroscopies. The diamond deposition was accomplished using a hot filament chemical vapor deposition technique. Diamond film quality was examined with the help of laser Raman spectroscopy and scanning electron microscopy.     

Secondary electron amplification using single-crystal CVD diamond film

The current amplification characteristics of an unbiased 8.3-μm-thick single-crystal CVD diamond film are examined using secondary-electron-emission measurements. In particular, the intensity and energy distribution of transmitted and reflected secondary electrons are measured and used to examine the transport and emission properties that govern the current amplification process. Overall, the measurements confirm the excellent transport and emission properties of single-crystal CVD diamond, as compared to polycrystalline CVD diamond films studied previously. Specifically, the transmitted and reflected energy distributions measured from the single-crystal diamond are nearly identical, with a sharp, narrow (FWHM = 0.35 eV) emission peak dominating the spectra. However, the transmitted distributions are more fully thermalized as a result of the longer transport distances. In fact, transmitted electrons are detected even after traveling more than 8 μm through the film, which demonstrates the potential for excellent transport efficiency. Maximum transmission gains of 3–4 are obtained, which is encouraging under such field-free conditions. However, the results of the study indicate that the transmission process is being limited by diffusive transport in the unbiased diamond film.     

Parametric study of EAA polymer thin film deposition on carbon substrates in a fluidized electrode bed reactor

Electrodeposition of ethylene-co-acrylic acid (EAA) polymer, as thin films on carbon particle substrates, was carried out in a fluidized electrode bed reactor. Feeder current, time of deposition, and flow rate of anolyte (i.e., bed expansion or bed porosity) were the key parameters investigated. The film characteristics were evaluated through SEM and FTIR analyses and the amounts determined by weighing. The effect of these parameters on the electrodeposition process is discussed, and optimum conditions for deposition are proposed. Also, a possible mechanism for electrodeposition, particularly for the EAA–carbon system, is discussed.