Deposition of carbon films by electrolysis of a water-ethylene glycol solution

An attempt was made to deposit carbon films by electrolysis of a water-ethylene glycol solution. Carbon plate and an n-type silicon substrate were dipped in the solution and a high d.c. potential was negatively applied on the silicon substrate. Some deposits were observed in the region between the boiling point curve and the line approximately 50 °C below and parallel to the boiling point, when electrolysis was carried out at 1 kV for 6 h. For higher potentials of 1.4–2.0 kV and longer electrolysis of 12 h, some samples showed a broad X-ray diffraction peak and Raman peaks, corresponding to graphitic carbon.     

Deposition of diamond coating on pure titanium using micro-wave plasma assisted chemical vapor deposition

The nucleation and growth of diamond coatings on pure Ti substrate were investigated using microwave plasma assisted chemical vapor deposition (MW-PACVD) method. The effects of hydrogen plasma, plasma power, gas pressure and gas ratio of CH₄ and H₂ on the microstructure and mechanical properties of the deposited diamond coatings were evaluated. Results indicated that the nucleation and growth of diamond crystals on Ti substrate could be separated into different stages: (1) surface etching by hydrogen plasma and the formation of hydride; (2) competition between the formation of carbide, diffusion of carbon atoms and diamond nucleation; (3) growth of diamond crystals and coatings on TiC layer. During the deposition of diamond coatings, hydrogen diffused into Ti substrate forming titanium hydride and led to a profound microstructure change and a severe loss in impact strength. Results also showed that pre-etching of titanium substrate with hydrogen plasma for a short time significantly increased the nuclei density of diamond crystals. Plasma power had a significant effect on the surface morphology and the mechanical properties of the deposited diamond coatings. The effects of gas pressure and gas ratio of CH₄ and H₂ on the nucleation, growth and properties of diamond coatings were also studied. A higher ratio of CH₄ during deposition increased the nuclei density of diamond crystals but resulted in a poor and cauliflower coating morphology. A lower ratio of CH₄ in the gas mixture produced a high quality diamond crystals, however, the nuclei density and the growth rate decreased dramatically.     

直流氩等离子体硅粉纯化工艺的研究

针对立式反应室、直流氩等离子体情况,建立硅粉的运动学模型,绘出粉粒沉降时间与粉粒粒度和进气速率的关系曲线,并通过该模型选择进气速率为4～10L/s,粉粒的粒度范围为70～100μm.为了提高粉粒沉降过程中纯化效果,建立并分析鞘层模型中与鞘层厚度、鞘层区离子浓度以及鞘层离子平均动能有关的工艺参数的变化关系并提出一套优化选择放电参数的方法.通过该方法优化工艺参数为反应室总压力为4～6Pa,阴极电压为2000V或是更高,鞘层厚度为1.2～2cm.提纯实验结果表明,硅粉的纯度可由99.6%提高到99.95%.     

Nano-crystalline CVD diamond films deposited on cemented carbide using high current extended DC arc plasma process

Nano-crystalline diamond (NCD) films have been grown on cemented carbide substrates by high current extended DC arc plasma process using Ar/H₂/CH₄ gas mixture at low gas pressure. The plain view and cross section of films are characterized with scanning electron microscopy. A uniform and smooth surface morphology of NCD thin films is observed. Raman spectroscopy has been used to investigate purity of the NCD films. Experimental results on the synthesis and characterization of the NCD films on cemented carbide substrates are discussed in this article.     

金刚石膜中黑色缺陷形成过程的计算机模拟

多晶金刚石膜中的黑色缺陷是影响材料光学、电学性能的一种重要缺陷。利用水平集方法对黑色缺陷的形成过程进行了模拟。模拟的基本假设为:黑色缺陷形成的基本条件为相邻晶粒间的晶界环境使活性气体扩散的过程难以进行,形成了一种形如"峡谷"状的、相邻晶面夹角30°的局部环境。金刚石膜的生长参数α2d值由1.3改变为1.5,在其晶粒表面{11}面上形成孪晶。孪晶的长大促进了黑色缺陷的形成。     

Preparation of zinc oxide nanorods by microwave assisted technique using ethylene glycol as a stabilizing agent

Zinc oxide nanorods have been synthesized by microwave assisted method using zinc nitrate, ethylene glycol and sodium hydroxide as a precursors. The material was characterized by XRD, SEM, EDAX and UV–Visible techniques. XRD analysis revealed all the relevant Bragg’s reflections for wurtzite (hexagonal phase) structure of zinc oxide. The average particle size was obtained 34 nm from the Williamson–Hall plot. The value of particle size determined from XRD was in good agreement with the SEM and TEM results. The direct optical band gap was found to be 3.13 eV.     

氧等离子体对金刚石膜的刻蚀研究

用微波放电法产生氧等离子体，通过改变系统中氧的浓度和金刚石膜的温度研究了氧等离子体对CVD多晶金刚石膜刻蚀的影响。实验结果表明：随着氧浓度的增加和金刚石膜温度的提高，刻蚀作用加剧；而在较低的氧浓度和金刚石膜温度条件下金刚石膜的晶界处首先被刻蚀，说明金刚石膜的境界处含有较多的非金刚石碳相。并且从等离子体对(100)和(111)面的刻蚀现象可知(100)面的生长是二维生长，(111)面的生长是岛状生长。     

HFCVD diamond deposition parameters optimized by a Taguchi Matrix

A Taguchi Matrix was used for the experimental design to study the CVD diamond deposition parameters in a cold-wall HFCVD reactor. Gas composition, total gas pressure, total mass flow and substrate temperature were considered as controllable factors, and three levels for each of these factors were selected, in an L9 orthogonal array. A new Figure-of-Merit (FOM) is proposed to assess the best combination of film properties: grain size, residual stress, structural quality and growth rate. Substrate temperature affects mostly grain size and diamond quality, while methane content mostly determines residual stresses and the growth rate. The latter is also mainly affected by the total pressure as well as is grain size, while total gas flow has a neutral effect. Under the limits of deposition conditions, the best FOM is obtained at the highest total gas pressure and mass flow, average CH₄ content, and lowest substrate temperature.     

Growth of polycrystalline and nanocrystalline diamond films on pure titanium by microwave plasma assisted CVD process

Well-faceted polycrystalline diamond (PCD) films were deposited along with nanocrystalline diamond (NCD) films on the pure titanium substrate by a microwave plasma assisted chemical vapor deposition (MWPCVD) system in the environment of CH₄ and H₂ gases at a moderate temperature. Diamond film deposition on pure titanium and Ti alloys is always extremely hard due to the high diffusion coefficient of carbon in Ti, the big mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty of attaining very high nucleation density. A well-faceted PCD film and a smooth NCD film were successfully deposited on pure Ti substrate by using a simple two-step deposition technique. Both films adhered well. Detailed experimental results on the preparation, characterization and successful deposition of the diamond coatings on pure Ti are discussed. Lastly, it is shown that smooth NCD film can be deposited at moderate temperature with sufficient diamond quality for mechanical and tribological applications.     

A promising solution using CVD diamond for efficient cooling of power devices

Diamond has several exceptional physical and chemical characteristics. This is the best material for both electrical insulators (10 MV cm⁻¹) and thermal conductors (2000 W m⁻¹ K⁻¹, five times more than copper at room temperature). In this study, we analyzed and quantified the advantages of the insertion of CVD diamond layer in the innovative thermal management assemblies. We also developed a specific model to simulate the working environment of the component. In the simulation, we compared the use of a traditional substrate (AlN) with that of the diamond CVD one in order to confirm that using the diamond substrate reduced thermal resistance.     

微波等离子体化学气相沉积法在硅片上同时生长碳化硅和金刚石

研究了衬底温度、核化密度、衬底表而预处理等工艺参数对微波等离子体化学气相沉积法在硅片上同时生长碳化硅和金刚石的影响.采用扫描电镜、X-射线衍射、喇曼光谱和红外光谱对样品进行了表征.结果表明:从高核化密度生长的金刚石膜中探测不到碳化硅;不论对硅衬底进行抛光预处理还是未抛光预处理,从低核化密度牛长的金刚石厚膜中总能探测到碳化硅.碳化硅生长在硅衬底上未被金刚石覆盖的地方,或者是在金刚石晶核之间的空洞处.碳化硅形成和金刚石生长是同时发生的两个竞争过程.此研究结果为制备金刚石和碳化砟复合材料提供了一种新的方法.     

Effects of PVP and KCl concentrations on the synthesis of gold nanoparticles using a solution plasma processing

Application of plasma in an aqueous environment, so called Solution Plasma Processing (SPP) is a recent development. Solution plasma processing for the synthesis of gold nanoparticles by reducing HAuCl₄ in the presence of Polyvinylpyrrolidone (PVP) and potassium chloride (KCl) was investigated in this work. Effects of PVP and KCl concentrations on the size and the shape of the gold nanoparticles in SPP were studied using a UV-vis nir spectrophotometer, and high resolution transmission electron microscopy (HRTEM). The results showed that the shape and size of the nanoparticles were affected by various KCl and PVP concentrations. The average particle size of the gold nanoparticles synthesized by SPP decreased with an increase in PVP concentration and the particle shape became more spherical with the addition of KCl. The HRTEM results indicated that gold nanoparticles with a diameter less than 10 nm were single crystals, while particles with a diameter greater than 15 nm were polycrystalline.     

DC Arc Plasma Jet CVD金刚石自支撑膜的质量对物理性能的影响

本研究对Raman谱进行高斯（Gauss）和洛仑兹（Lorenz）分峰拟合，将金刚石自支撑膜Raman谱分成纯金刚石峰和非金刚石峰，对比两种方法的精度，结果显示高斯拟合的精度高些。运用经验公式计算出金刚石自支撑膜的质量因子，发现质量因子主要受纯金刚石峰强度和无定型碳峰强度的影响，非金刚石峰强度与质量因子成反比，纯金刚石峰强与质量因子成正比，同时还受到内应力的影响。质量因子与热导率、断裂强度和红外透过率的关系表明，金刚石自支撑膜的以上物理性能与其质量成正比关系。     

系统压强对微波等离子体化学气相沉积金刚石成核的影响

为了在氧化铝上制备（100）定向织构的金刚石薄膜,必须先提高金刚石的成核密度,在微波等离子体化学气相沉积（MPCVD）系统中,采用低压成核的方法,在氧化铝陶瓷上沉积出高成核密度的金刚石薄膜,扫描电镜显示其成核密度可达10^8cm^-2。在此基础上,沉积出（100）织构的金刚石薄膜。     

Nanohydroxyapatite synthesis using optimized process parameters for load-bearing implant

In this study, nanohydroxyapatite (NHA) was synthesized using calcium nitrate tetrahydrate and diammonium hydrogen phosphate via the precipitation method assisted with ultrasonication. Three independent process parameters: temperature (T) (70, 80 and 90°C), ultrasonication time (t) (20, 25 and 30 min), and amplitude (A) (60, 65 and 70%) were studied and optimized using response surface methodology based on 3 factors and 5 level central composite design. The responses of the model were analysed with the help of the particle size measured from field-emission scanning electron microscopy and Brunauer–Emmett–Teller (BET). The surface area of particle was measured with BET and the thermal stability of the powder was measured using thermogravimetric analysis. Finally, with the optimized process parameters obtained from the model, the NHA powder was synthesised and validated against the predicted value. The results show a good agreement with an average error 8% between the actual and predicted values. Moreover, the thermal stability and porosity of synthesized NHA was further improved after calcination. This improvement could be due to the removal of impurities from the NHA powder after calcination as indicated by the Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy.     

Comparative study of the electrical properties of diamond films grown by microwave plasma assisted and hot-filament chemical vapor deposition

Schottky diodes were built on different polycrystalline diamond films grown by Microwave Plasma and Hot Filament Chemical Vapor Deposition and their electrical properties were studied. The barrier height increased with the diamond film quality and the corresponding ideality factor decreased. Even though the lower-quality HFCVD film displayed poor rectifying properties, it was found to be much less sensitive to variations in the operating conditions (air vs. vacuum). The activation energies of the films depend on morphological parameters, as preferable grain size or orientation. The bulk conduction also depends on the quality of the deposited films, changing from ohmic to trap-free or shallow trap SCLC and SCLC with an exponential distribution of traps. The hypothesis of using the electrical measurements as an indicator for film quality has been discussed.     

On investigation of the parameters of a low density nonequilibrium plasma by using a thermoanemometer-langmuir probe

Formulas are obtained to determine the fundamental local parameters of a partially ionized low density gas. Results are presented of experimental investigations of a nonisothermal rarefied plasma of a high-frequency discharge in helium at pressures of 0.07, 0.12, and 0.20 mm Hg in the absence of a magnetic field.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 6, pp. 1050–1057, December, 1969.     

Synthesis novel multi-petals ZnO nano-structure by a cyclodextrin assisted solution route

Multi-petals ZnO nano-structure has been directly prepared through a facile solution route with β-cyclodextrin (β-CD) assistance. The product was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicate that this ZnO nano-structure consists of several petals, and each petal is composed of many little rods. The rods prefer to grow along the [0001] direction (+c axis) and lay parallel, and β-CD plays a crucial role in forming such novel structure. If not using β-CD in the preparation process, only larger rods could be obtained. Furthermore, the possible formation mechanism for this multi-petals nano-structure is also discussed.     

Preparation and characterization of ultra-fine diamond powders obtained by using a d.c. arc plasma jet

Ultra-fine diamond powders were prepared from C₂H₂ and H₂ by quenching a d.c arc plasma jet on a metal disc cooled with water. The powders obtained were agglomerated with very small particles about 20 nm in diameter, with an average size of about 80 nm. Raman spectra, X-ray diffraction, and transmission electron micrographs of them showed that each particle consisted of very small diamond crystals and a small amount of amorphous carbon, and that a single crystal particle had a twin plane. The formation mechanism of the powders has been briefly discussed from the viewpoint of the supersaturation ratio based on the classical theory of homogeneous nucleation.     

Solid-state synthesis of cubic ZnTe nanocrystals using a microwave plasma

Cubic ZnTe nanocrystals were produced from 1:1 and 1.8:1 molar ratios of Zn:Te by a 900 W microwave plasma. The phase was detected using X-ray diffraction (XRD), which are in accordance with those of the simulations, and selected area electron diffraction (SAED). Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the products were nanocrystals with different orientations, including three longitudinal optical (LO) vibrations at 205, 410 and 620 cm^? 1 and a transverse optical (TO) vibration at 166 cm^? 1. Their green emissions were detected at 562 nm (2.21 eV) using luminescence spectrophotometry.