Nanoparticulate PdZn as a Novel Catalyst for ZnO Nanowire Growth

ZnO nanowires have been grown by chemical vapour deposition (CVD) using PdZn bimetallic nanoparticles to catalyse the process. Nanocatalyst particles with mean particle diameters of 2.6 ± 0.3 nm were shown to catalyse the growth process, displaying activities that compare well with those reported for sputtered systems. Since nanowire diameters are linked to catalyst morphology, the size-control we are able to exhibit during particle preparation represents an advantage over existing approaches in terms of controlling nanowire dimensions, which is necessary in order to utilize the nanowires for catalytic or electrical applications.     

Synthesis of photoluminescent SiC-SiOx nanowires using coal tar pitch as carbon source

SiC-SiOx nanowires (NWs) with core-shell and chain-bead structures were synthesized via a catalyst-free chemical vapor deposition (CVD) route without Ar gas, using silicon and coal tar pitch powders as raw materials. The SiC-SiOx NWs with sharp tips formed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g) growth process along the [111] direction. The NWs were several millimeters in length, and the average diameters of the chains and beads were 40–90 nm and 325 nm, respectively. The obtained NWs had good blue-green photoluminescence property owing to the stacking faults and amorphous SiOx. This novel CVD route is simple, low cost and suitable for large-scale production.     

Low-Temperature Chemical Vapor Deposition Tungsten Carbide Coatings for Wear/Erosion Resistance

A new chemical vapor deposition (CVD) process has been developed to deposit hard coatings, containing tungsten carbide, at temperatures below 500°C. These coatings, which have been applied to both ferrous and nonferrous alloys, exhibit excellent resistance to wear and erosion. The coatings comprise a mixture of tungsten and the tungsten carbide, the latter being present as W₂C, W₂C + W₃C, or W₃C. The coatings' composition and properties can be controlled by varying the CVD process parameters. The unique lamellar, fine-grained microstructures of these coatings contribute to their good tribological properties.     

多晶硅气相沉积反应器的研发与应用

基于多晶硅的化学气相沉积技术与工艺,运用计算流体力学（cFD）的气体运动的组分运输和表面反应动力学模型,NAnsys—F1uent对多晶硅的生长过程进行模拟计算,运用有限元应力分析（FEA）方法,对复杂设备结构进行热应力计算和强度安全性校核,研发并设计一系列大型高产能、低能耗的多晶硅反应器。该系列的反应器广泛应用于国内外多晶硅生产线,产能达500t／a,能耗低至45kW／kg。     

Diamond nucleation suppression in chemical vapor deposition process

A systematic study of the effect of different pre-treatments of the Si substrate surface in suppressing diamond nucleation was performed to investigate the nature of the nucleation centers in chemical vapor deposition (CVD) of diamond. The Si substrates were initially scratched with diamond powder and then submitted to one of the following pre-treatments: thermal annealing in high vacuum and in air, deposition of an amorphous silicon film, and ⁸⁴Kr⁺ ion implantation. The pre-treated substrates were used in a hot filament CVD diamond process, and the diamond films obtained were analyzed by different techniques. The results suggest that the observed nucleation reduction under certain pre-treatment conditions is related to modifications induced on the original topographical features of the scratched substrate surface, which would be responsible for the CVD diamond nucleation. The dimensions of these surface features are estimated to be of the order of 5 nm.     

Fabrication of one-dimensional Ag/multiwalled carbon nanotube nano-composite

ABSTRACT: Composite made of multiwalled carbon nanotubes coated with silver was fabricated by an electroless deposition process. The thickness of silver layer is about 40 to 60 nm, characterized as nano-crystalline with (111) crystal orientation along the nanotube's axial direction. The characterization of silver/carbon nanotube [Ag/CNT] nanowire has shown the large current carrying capability, and the electric conductivity is similar to the pure silver nanowires that Ag/CNT would be promising as building blocks for integrated circuits.PACS: 81.05.uj, carbon nanotubes, carbon-based materials, diamond/nanocarbon composites.     

影响化学气相沉积多晶硅致密料比例的因素

改良西门子法生产多晶硅还原工艺是高纯的三氯氢硅和氢气在还原炉内发生化学气相沉积反应,得到固态多晶硅,多晶硅根据表观质量,分为致密料、玉米料、珊瑚料。目前,国内多晶硅生产以大型还原炉为主,对成本控制具有明显优势,但存在的问题是多晶硅致密料比例较低。本文通过对还原炉反应温度控制、进料喷嘴布置、反应配比等因素的分析研究,得出了提高还原炉化学气相沉积多晶硅致密料比例的方法、思路。     

Growth of vertically aligned ZnO nanorods using textured ZnO films

A hydrothermal method to grow vertical-aligned ZnO nanorod arrays on ZnO films obtained by atomic layer deposition (ALD) is presented. The growth of ZnO nanorods is studied as function of the crystallographic orientation of the ZnO films deposited on silicon (100) substrates. Different thicknesses of ZnO films around 40 to 180 nm were obtained and characterized before carrying out the growth process by hydrothermal methods. A textured ZnO layer with preferential direction in the normal c-axes is formed on substrates by the decomposition of diethylzinc to provide nucleation sites for vertical nanorod growth. Crystallographic orientation of the ZnO nanorods and ZnO-ALD films was determined by X-ray diffraction analysis. Composition, morphologies, length, size, and diameter of the nanorods were studied using a scanning electron microscope and energy dispersed x-ray spectroscopy analyses. In this work, it is demonstrated that crystallinity of the ZnO-ALD films plays an important role in the vertical-aligned ZnO nanorod growth. The nanorod arrays synthesized in solution had a diameter, length, density, and orientation desirable for a potential application as photosensitive materials in the manufacture of semiconductor-polymer solar cells.

PACS

61.46.Hk, Nanocrystals; 61.46.Km, Structure of nanowires and nanorods; 81.07.Gf, Nanowires; 81.15.Gh, Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)     

Copper nanowires within the central channel of tobacco mosaic virus particles

Simple electrochemical deposition techniques can produce highly defined metal nanostructures in templates. Electroless deposition (ELD) can be effectively used for depositing metals on insulators such as biological or plastic surfaces. With biomolecular templates, metallization methods are often restricted to mild reductions, and the deposition of copper at pH values above 12 is usually not applicable. We produced copper nanowires of 3 nm in diameter and up to 150 nm in length by electroless deposition within the 4 nm wide channel of tobacco mosaic virus (TMV) particles. We employed a low pH (7.5) copper electroless deposition solution that is compatible with biomolecules. The fabrication process of the nanowires is based on sensitization of tobacco mosaic virus with Pd(II) prior to the electroless deposition. We analyzed the chemical composition of the nanowires by energy-filtering transmission electron microscopy, and used the method also for nickel and cobalt nanowires deposited within the viral channel.     

Direct synthesis of vertically aligned ZnO nanowires on FTO substrates using a CVD method and the improvement of photovoltaic performance

In this work, we report a direct synthesis of vertically aligned ZnO nanowires on fluorine-doped tin oxide-coated substrates using the chemical vapor deposition (CVD) method. ZnO nanowires with a length of more than 30 μm were synthesized, and dye-sensitized solar cells (DSSCs) based on the as-grown nanowires were fabricated, which showed improvement of the device performance compared to those fabricated using transferred ZnO nanowires. Dependence of the cell performance on nanowire length and annealing temperature was also examined. This synthesis method provided a straightforward, one-step CVD process to grow relatively long ZnO nanowires and avoided subsequent nanowire transfer process, which simplified DSSC fabrication and improved cell performance.     

多晶硅生产技术发展方向探讨

还原高频电源技术、硅烷流化床法和气液沉积法,可与改良西门子法工艺技术有机结合生产多晶硅,对解决目前国内多晶硅所面临的生产成本高、产品质量低下等问题具有非常重要的意义。本文总结了改良西门子法、硅烷流化床法和气液沉积法生产多晶硅的工艺技术,分析了各自的优缺点和发展方向。指出了目前的改良西门子法核心设备的改进方向和应用还原高频电源技术、硅烷流化床技术需在加热方式上做进一步开发研究,气液沉积法可与现有的多种工艺技术相结合形成多种工艺路线,其中二氧化硅经碳热氯化法制备四氯化硅后,与氢气还原四氯化硅法相结合制备多晶硅,是值得研究开发的一种新工艺路线。该工艺路线不仅工艺流程大大缩减,而且四氯化硅的提纯比其他氯硅烷更容易,生产的多晶硅产品质量更高、成本更低。     

Une nouvelle technologie d'appareils de dépôt chimique en phase vapeur. Partie 2 : Modélisation du dépôt de silicium pur à partir de silane et de silicium dopé in situ au phosphore

A better understanding of Chemical Vapour Deposition (CVD) process can be obtained by modelling the phenomena involved in CVD reactors. The established model is then a useful tool for industrial equipment design and for the optimization of operating conditions. The research for optimal operating conditions is done by a more rational and efficient way using a model. The specific case of the polycristalline silicon deposition from silane in a new technology of LPCVD reactor is used to illustrate the approach. Hypotheses and methods necessary for the development of the model are presented and discussed first, then results are described and compared to experimental data. Finally, the more complex case of in situ phophorus doped polysilicon is discussed.     

化学气相沉积六方氮化硼涂层的制备及应用

六方氮化硼(h-BN)涂层是一种性能优异的功能陶瓷材料,介绍了化学气相沉积( CVD)六方氮化硼涂层的制备工艺,综述了h-BN涂层的优异性能和应用现状,并对其研究发展趋势进行了展望.认为先驱体性能存在缺陷、沉积机理复杂、工艺可控性差、生产成本高是目前CVD制备h-BN涂层存在的主要工艺问题,指出今后还需在新型先驱体的研发和使用、沉积机理的深入探究、工艺优化和放大等方面开展深入研究,以实现h-BN涂层的大规模工业化生产和应用.     

The effect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating in hot filament chemical vapor deposition

Effect of substrate temperature on microstructural evolution and hardenability of tungsten carbide coating produced by hot filament chemical vapor deposition (HFCVD) process was studied. Annealed sheets of 316L stainless steels were used as the substrate. HFCVD technique, with substrate temperatures of 400 and 500°C, was used to deposit tungsten carbide coating on these sheets. Field Emission Scanning Electron Microscope (FE‐SEM) was used to study the evolution of microstructure. X‐Ray Diffraction spectroscopy was used to analyze the phases formed and Raman spectroscopy was employed to differentiate molecular composition of the coatings. The amount of the porosity of the coatings was measured and Vickers hardness measurement was used for hardness assessment. Results show that the tungsten carbide coatings have a honeycomb structure and increasing the temperature of the substrate increases the amount of porosity of the coating. XRD results showed that 3 different crystalline structures containing W, WC, and W₂C were formed in the coating deposited on the 316L stainless steel. Increasing the temperature of the deposition has increased the intensity of the peaks in the XRD results. Raman spectroscopy results indicated the presence of a carbon in the tungsten carbide coatings. Finally, microhardness of the tungsten carbide coating increases with increasing the temperature of the substrate.     

氧化铝模板中Ag纳米线阵列的选择性生长

利用Ag离子与Br离子之间的化学沉积作用在孔隙中充满明胶的阳极氧化铝（AAO）模板中制备了AgBr/AAO纳米介孔复合材料.材料选择性曝光后,利用原位显影液对其进行化学显影,在AAO模板中选择性得到Ag纳米线阵列.实验结果表明：Ag纳米线是连续的、致密的,且具有多晶结构,充满了曝光部分的模板孔隙.本文还对影响Ag纳米线选择性生长的因素进行了简单讨论.     

Microstructure and integrity of multilayer ceramic coating with alumina top coat on silicon carbide by laser chemical vapor deposition

Thin double-layer coatings comprising an alumina top coat and mullite bond coat were deposited on SiC substrates by laser chemical vapor deposition (CVD). The effect of the presence of mullite bond coat and the phases of alumina top coat on the structural integrity against the thermal residual stress loaded by the high-temperature CVD process was examined by microstructural characterization and simulative consideration. A laminated layered structure having a dense γ-alumina top surface with a cone-like morphology are grown at a deposition temperature of 1323 K, whereas an α-alumina top layer comprising densely packed faceted grains was grown at 1473 K. The interfaces between the SiC and mullite layers were coherent owing to the formation of a thin transition layer. The γ-alumina layer formed an adhesive interface bordering the mullite layer, whereas small residual defects were formed in the α-alumina layer bordering the mullite layer. Spacings of surface cracking induced by the high-temperature deposition process in the double-layer coatings were approximately half of those in the coatings without mullite layers. As simulative results by finite element method suggested, the double-layer coatings were experimentally verified to be more tolerant to the formation of surface cracks and interfacial delamination, compared to single-layer coatings without the mullite bond layers.     

流化床生产多晶硅的研究

在流态化CVD法生产多晶硅的过程中发生了无数的均相反应和异相反应,均相反应十分的复杂,生成的无定形硅粉中含有氢键,是硅粉发生爆炸的关键因素。主要介绍了均相反应和异相反应的反应机理和主要影响因素(反应温度、入口硅烷浓度、进料气速、颗粒的平均直径、反应压力、床层高度等)对多晶硅和硅粉的影响规律。     

Dysprosium-Catalyzed Growth of Single-Walled Carbon Nanotube Arrays on Substrates

In this letter, we report that dysprosium is an effective catalyst for single-walled carbon nanotubes (SWNTs) growth via a chemical vapor deposition (CVD) process for the first time. Horizontally superlong well-oriented SWNT arrays on SiO₂/Si wafer can be fabricated by EtOH-CVD under suitable conditions. The structure and properties are characterized by scanning electron microscopy, transition electron microscopy, Raman spectroscopy and atomic force microscopy. The results show that the SWNTs from dysprosium have better structural uniformity and better conductivity with fewer defects. This rare earth metal provides not only an alternative catalyst for SWNTs growth, but also a possible method to generate high percentage of superlong semiconducting SWNT arrays for various applications of nanoelectronic device.     

Fabrication of Ni-silicide/Si heterostructured nanowire arrays by glancing angle deposition and solid state reaction

This work develops a method for growing Ni-silicide/Si heterostructured nanowire arrays by glancing angle Ni deposition and solid state reaction on ordered Si nanowire arrays. Samples of ordered Si nanowire arrays were fabricated by nanosphere lithography and metal-induced catalytic etching. Glancing angle Ni deposition deposited Ni only on the top of Si nanowires. When the annealing temperature was 500°C, a Ni₃Si₂ phase was formed at the apex of the nanowires. The phase of silicide at the Ni-silicide/Si interface depended on the diameter of the Si nanowires, such that epitaxial NiSi₂ with a {111} facet was formed at the Ni-silicide/Si interface in Si nanowires with large diameter, and NiSi was formed in Si nanowires with small diameter. A mechanism that is based on flux divergence and a nucleation-limited reaction is proposed to explain this phenomenon of size-dependent phase formation.     

利用市售不锈钢箔制备氮化硼纳米线

Chemical vapor deposition growth of one-dimensional nanomaterials usually demands substrates that have been coated with a layer of catalyst film. In this study, a green process to synthesize boron nitfide （BN） nanowires directly on commercial stainless steel foils was proposed by heating boron and zinc oxide powders under a mixture gas flow of N2 arid 15% H2 at 1100℃, and a large quantities of pure h-BN nanowires have been produced directly on commercial stainless steel foil. The stainless steel foils not only acted as the substrate but also the catalyst for the nanowire growth. The synthesized BN nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopes, X-ray energy dispersive spectrometer and photoluminescence spectroscopy, The nanowires also possess strong PL emission bands at 515, 535, and 728 nm.