A Three-Dimensional Two-Phase Model for Thermal Plasma Chemical Vapor Deposition with Liquid Feedstock Injection

In this paper, a comprehensive model for thermal plasma chemical vapor deposition (TPCVD) with liquid feedstock injection is documented. The gas flow is assumed to be steady, of a single temperature. Radiation and charged species contributions are excluded, but extensive homogeneous and heterogeneous chemistry is included. The liquid phase is traced by considering individual droplets. Discussion on the model's application to diamond production from acetone in a hydrogen–argon plasma is included. The major conclusions are: (1) Liquid injection possesses a capability to deliver the hydrocarbon precursor directly onto the deposition target. (2) For the case of complete evaporation of the droplet before reaching the substrate, the deposition rate is similar to that obtained with gaseous precursors. (3) The computational results compare well with experimental data. The modeling results can be used to optimize the injection parameters with regard to the deposition rate.     

激光CVD法合成SiC-Si3N4复合纳米颗粒

用激光化学蒸汽沉积(CVD)法合成了SiC-Si₃N₄复合纳米颗粒,并用X射线衍射(XRD),透射电子显微镜(TEM)和电子自旋共振磁力计(ESR)分析了试料的晶体结构,颗粒形状以及悬空键的状况。合成的试料粒度分布集中,平均粒径为32nm,颗粒由直径为5～30nm的单晶或多晶组成。试料纯度高,颗粒为近似球形,十分适合于粉体的加工和烧结。另外试料有很高的热稳定性,在加热的过程中的变化首先是悬空键减少,然后是相分解和颗粒长大。     

Pulsed-Spray Radiofrequency Plasma Enhanced Chemical Vapor Deposition of CuInS2 Thin Films

Thin films of CuInS₂ were grown on various substrates at a temperature of 523 K from two metal-organic precursors using radiofrequency plasma enhanced chemical vapor deposition (PECVD). Two precursor molecules, with different solubility properties, were dissolved in appropriate solvents and sprayed into the plasma region in the PECVD chamber. The resulting films were examined for atomic composition, growth rate, crystalline orientation, and uniformity. Films made from each precursor differed in thickness, atomic composition, and crystallinity. The uniformity of the film was fairly good from near the edge to the center of the substrate, and evidence for a chalcopyrite-like structure was found in several samples deposited from one of the precursor molecules.     

Growth Modes of SiO x Films Deposited by Evaporation and Plasma-Enhanced Chemical Vapor Deposition on Polymeric Substrates

In order to study the very first stages of plasma-enhanced chemical vapor deposition (PECVD) of SiO₂ on polymer substrates, we used a distributed electron cyclotron resonance (DECR) reactor, with the substrate placed (I) in the active glow zone, (II) downstream therefrom, and (III) downstream, but shielded from photon emission (e.g., VUV) from the plasma. For comparison, we also study films deposited by physical vapor ddposition (PVD, thermal evaporation). To characterize the ultra-thin deposits, we used oxygen plasma etching combined with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectroscopy (RBS). We elucidate the roles of various energetic species (VUV photons, ions, atomic oxygen, and other radicals) in the plasma during the earliest growth phase, and the origin of the interphase which is present between the deposited SiO₂ and the polymer substrate.     

Characterization of silicon nitride particles synthesized in an atmospheric-pressure convection-stabilized arc

Silicon nitride powders were synthesized in an atmospheric-pressure convection-stabilized arc using silicon and ammonia as reactants. The morphology and particle size distributions of the silicon nitride particles were characterized by SEM, TEM, and electron diffraction analyses. The silicon nitride particles collected in the plasma reactor were formed by either gas-condensed phase reactions or chemical vapor reactions. The morphologies of the particles formed by gas-condensed phase reactions consisted of -Si₃N₄ prisms, -Si₃N₄ matte, -Si₃N₄ needles, and spaghetti-like whiskers. For the homogeneously nucleated particles, the morphologies included dendrites, needles, platelets, and amorphous particles. Most of the particles formed were aggregates with particle size distributions ranging from 500 to 1500 Å depending on the location of injection of the reactants.     

Deposition of Diamondlike Carbon Film and Mass Spectrometry Measurement in CH4/N2 RF Plasma

The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH₄/N₂ RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH₄/N₂ composition ratio and RF power input. It was decreased monotonically as CH₄ content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH₄ content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH₄ plasma. The predominant ionic products in CH₄/N₂ plasma were NH⁺ ₄ and CH₄N⁺ ions, which were produced by reactions of hydrocarbon ions, such as CH⁺ ₃, CH⁺ ₂, CH⁺ ₅, and C₂H⁺ ₅ with NH₃ molecules in the plasma. It was speculated that the production of NH⁺ ₄ ion induced the decrease of C₂H⁺ ₅ ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N⁺ ₂ ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions.     

大气压射频等离子体化学气相沉积TiO2体系的发射光谱诊断

开展了大气压射频(RF)等离子体化学气相沉积(PCVD)TiO₂放电体系的发射光谱诊断研究, 分别考察了氧气分压、钛酸四异丙酯(TTIP)分压和输入功率对氧原子谱线相对强度、氩原子激发温度、OH振动温度以及转动温度的影响. 结果表明: 随着氧气分压的增加, 氧原子谱线相对强度先迅速增加至峰值后缓慢下降, OH振动温度缓慢增加, 而氩原子激发温度和OH转动温度基本不变. 随着TTIP 分压的增加, 氧原子谱线相对强度下降, 氩原子激发温度没有明显变化, 而OH振动温度和转动温度增加. 随着输入功率的增加, 氧原子谱线相对强度下降, 氩原子激发温度、OH振动温度和转动温度升高.     

Piranha改性玻璃基板液相沉积制备SrTiO3功能陶瓷薄膜

以Piranha溶液处理玻璃基板,采用液相沉积技术,制备了钛酸锶晶态薄膜。改性基板的亲水性测定与偏光显微镜测试表明,Piranha溶液能够有效改善玻璃基板的亲水性,并且基板表面的硅烷醇对钛酸锶薄膜的沉积具有积极指导作用;X射线衍射(XRD)与扫描电镜(SEM)表征显示,制备成功的钛酸锶薄膜纯度高,结晶良好,样品表面均匀,在垂直基板表面方向上呈纤维花簇状生长。文章同时对基板表面硅烷醇形成过程进行了研究。     

Silicon nitride synthesis in an atmospheric pressure convection—Stabilized arc

Submicron -, -, and amorphous-phase silicon nitride particles have been synthesized in an experimental plasma reactor, using metallic silicon and ammonia as reactants. Injection of ammonia at different locations of the reactor results in different yields. A maximum yield of 85 wt% has been achieved by injecting NH₃ at both downstream and upstream locations of the reactor. The powders synthesized in this way contained approximately 60 wt% silicon nitride in crystal form with equal amounts of and phases. The remainder consisted of the amorphous phase. The average size of the particles ranged from 50 to 90 nm, with a standard deviation of 1.47–1.87 depending on the location of ammonia injection. Seeding with 1 and 10 wt% of preexisting silicon nitride particles for fostering heterogeneous nucleation did not improve the yield, but it changed the particle size distribution.     

Deposition of Gallium Nitride Thin Films by MOCVD in Microwave Plasma

The deposition of GaN thin films in a nitrogen–hydrogen microwave plasma using Ga(CH ₃ ) ₃ as a gallium precursor was investigated. The deposit was identified as stoichiometric GaN by XPS and XRD. The substrate was dielectrically heated in the microwave discharge and the substrate temperature was lower than that in usual thermal MOCVD. The NH radicals, which were the primary N-atoms precursors, and fragments of Ga(CH ₃ ) ₃ were identified in the plasma by OES. The NH radical formation and the decomposition of Ga(CH ₃ ) ₃ in the plasma may be one of the reasons for the lower deposition temperature of GaN. The position dependence of the substrate temperature showed similar tendency as the position dependence of the electron temperature. The plasma state contributes to the deposition of GaN thin films. The deposited GaN exhibited a wide optical band gap of 3.4eV. Material highly oriented along the c axis was detected in the deposit, and a PL spectrum which has the band head at about 450 mm was obtained.     

以光辅助MOCVD法在有取向Ni衬底及LAO单晶衬底上制备YBCO外延膜的比较研究

采用光辅助金属有机物化学气相沉积(MOCVD)法,在生长有CeO2/YSZ/Y2O3(YSZ为Y稳定的ZrO2)缓冲层的双轴取向Ni衬底上进行了YBa2Cu3O7-x(YBCO)外延膜生长,并与LaAlO3(100)[LAO(100)]单晶衬底上的YBCO外延膜生长进行了对比.发现在Ni衬底上c轴取向YBCO外延膜的生长温度比LAO衬底上的生长温度低约30℃,但生长速度更快.经分析认为,这种差别主要是由于Ni衬底的热导率比LAO衬底高造成的.Ni衬底及LAO衬底上生长的c轴取向YBCO外延膜的超导极限电流密度(Jc)分别约为0.5 MA/cm2及1.8 MA/cm2.     

In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiN_xC_y nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si₃N₄, TiN_xC_y (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.     

AES investigations on starting powders for high performance ceramics

AES depth profiles on ceramic powders (untreated/hydrolyzed/oxidized/ (Al, Y)₂O₃ coated Si₃N₄, [BaO, SiO₂] coated Al₂O₃) are feasible on thin, homogeneous layers or m sized agglomerations prepared on an Au foil. By means of the depth profiles one can qualitatively characterize the coating around the particles. Factor analysis of the depth profiles on the differently treated Si₃N₄ powders suggests the existence of an Si₂N₂O phase on the oxidized sample.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

New In-situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors using a Novel Wet Collection System in a rf Inductively Coupled Thermal Plasma Reactor. Part 1: Reactor System and Sampling Probe

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO₂ powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO₂ powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO₂ formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO₂ formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO₂ were found.     

Comparative Study of the Decomposition of CCl4 in Cold and Thermal Plasma

Decomposition of carbon tetrachloride was studied in an inductively coupled thermal plasma reactor and in a low temperature, non-equilibrium plasma reactor, in neutral and oxidative conditions, respectively. In neutral conditions formation of solid soot, aliphatic- and cyclodienes was observed in equilibrium, and products, such as Cl₂ and C₂Cl₆ were detected in non-equilibrium plasma. Feeding of oxygen into the thermal plasma reactor depressed both soot and dienes formation and induced the formation of oxygen containing intermediates and products. GC-MS analyses of the gaseous products and the extract of the soot referred to as complex decomposition and recombination mechanism at given conditions. Presence of oxygen in the low temperature plasma reactor results in the formation of carbonyl compounds as intermediers. CO₂ and Cl₂ revealed as final products of CCl₄ decomposition in cold plasma.     

Non-isothermal crystallization kinetics of recycled PET-Si3N4 nanocomposites

Poly(ethylene terephthalate) (PET) is an important industrial material and has been widely applied in consumer products. Due to its slow crystallization rate, nanoparticles are incorporated into PET to function as heterogeneous nucleating agents. In this study, the non-isothermal crystallization behavior of recycled PET-silicon nitride (Si₃N₄) nanocomposites was investigated by differential scanning calorimetry (DSC). In the general analysis of the non-isothermal crystallization curves, it was found that the Si₃N₄ nanoparticles could effectively accelerate the nucleation of PET, but the crystal growth rate was slowed down when the Si₃N₄ content was more than 1 wt%. This might be attributed to the interaction between the PET chains and the surface-treated Si₃N₄ nanoparticles. Results obtained from Avrami and Mo treatments agreed well with the general analysis. Application of the Kissinger method and isoconversional method of Flynn-Wall-Ozawa also showed that Si₃N₄ nanoparticles had a good nucleation effect on the crystallization of PET, and the crystal growth was hindered by Si₃N₄ when the particle loading is higher than 1 wt%.     

Rh Inclusion in Sol-Gel SiO2. Effects of Rh Precursors on Metal Dispersion and SiO2-Rh Thermal Behavior

RhCl₃·nH₂O and [RhCl(C₂H₄)₂]₂ are used as precursors for the preparation of 1%Rh in sol-gel derived SiO₂. The gelling process of Si(OEt)₄ is carried out in the absence of solvent and under strong acid catalysis. The thermal behavior of Rh precursors, of SiO₂ gel and Rh-SiO₂ composites is independently studied by analysing organic species released at definite temperature intervals and concomitantly collecting infrared, XPS, TEM, XRD and porosity data. Results indicate that nanometric Rh particles may be obtained from [RhCl(C₂H₄)₂]₂, their dispersion being homogeneous, dense and stable up to 250°C, whereas RhCl₃·nH₂O affords less metallic dispersion with other crystalline Rh-species; in both cases, well-shaped Rh metal crystallites are obtained at 650°C. The different synthetic approaches used for the preparation of RhCl₃- and [RhCl(C₂H₄)₂]₂-derived samples, are invoked to account for the features of Rh dispersion obtained by mild temperature treatment. Moreover, the particular procedures for sol-gel SiO₂ synthesis are related to the high-temperature maintenance of great porosity and elevated specific surface area.     

添加剂对化学沉积速率的影响

基于化学镀Ni-W-P和Ni-P体系中,添加剂LaCl3、乳酸、Fe2(SO4)3、硫脲和2,2’-联吡啶的浓度对沉积速率的影响表现出较为一致的变化规律,即随添加剂浓度的增加,出现最大沉积速率的实验事实,建立了一种吸附模型并导出添加剂加速化学沉积的公式.根据该公式和实验结果进行曲线拟合,得到相当吻合的结果.由拟合结果可得到一些参数值,如吸附平衡常数等.添加剂在基体上的吸附平衡常数(K1)大于已吸附了还原剂的表面上的吸附平衡常数(K2). K1值大表明添加剂在基体表面吸附能力更强. LaCl3、硫脲和2,2’-联吡啶的K1、K2值远大于乳酸、Fe2(SO4)3的K1、K2值,这表明LaCl3、硫脲和2,2’-联吡啶的吸附能力远强于乳酸、Fe2(SO4)3的, 因此,LaCl3、硫脲和2,2’-联吡啶所引起的沉积速率峰值的浓度远小于乳酸、Fe2(SO4)3的.     

New In-Situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors in a rf Thermal Plasma Reactor. Part 2: Analysis of CeO<Subscript>2</Subscript> Powders,Fuel Addition,and Image Analysis

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO₂ particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO₂ particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO₂ formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.     

氢气对正丁烷/空气混合物催化着火的热作用和化学作用

通过对正丁烷/氢气/空气混合物在Pt 催化表面的详细反应机理分析, 研究了氢气添加对正丁烷/空气混合物催化着火过程的影响. 研究发现, 在正丁烷/空气混合中添加氢气有助于正丁烷在更低的温度下实现催化着火, 而且不同的氢气添加量对混合物的着火温度和着火过程呈现不同的影响: 当氢气添加量较小时, 氢气的作用主要呈现为热影响; 而当氢气添加量较大时, 氢气的作用主要呈现为化学影响. 这些结果与实验结果是一致的. 本文进一步确定了发挥不同作用的氢气添加量的范围, 并分别对热作用和化学作用情况下的着火启动反应进行了动力学分析.