A Review of Advanced Composite and Nanostructured Coatings by Solid-State Cold Spraying Process

Cold spraying (CS) has been widely explored over the last decade due to its low process temperature and limited thermal effect on spray materials. As a solid-state process, the inherent deficiencies of traditional thermal spraying such as oxidation, decomposition, and grain growth are avoided. This article summarizes the research work on the fabrication of composites and nanostructured coatings by the promising CS process. After a brief introduction to CS and its deposition mechanisms, the preparation methods of spray powders are classified. Different methods are appropriate for particles of various properties, and the tendency is to design composite powders by combined methods in order to create coatings with specified properties. Then, the co-deposition mechanism of composite particles as well as research findings on metal–metal, metal–ceramic, and metal–intermetallic composite coatings are reviewed concerning the deposition characteristics, microstructure and its relation to properties. Moreover, CS has been used to deposit a variety of nanostructured materials, including metals, metal–ceramic composites, and even ceramics, retaining their nanocrystalline nature in the coating without grain growth or phase transformation. Finally, the potential applications of CS and issues to be addressed in coating deposition are discussed.     

沉积工艺对二氧化锆薄膜生长特性影响的研究

利用反应离子束溅射、反应磁控溅射和电子束蒸发在K9基底上沉积ZrO2薄膜，并用原子力显微镜对薄膜表面形貌进行测量。通过数值相关运算，对不同工艺条件下薄膜生长界面进行定量描述，得到了薄膜表面的粗糙度指数、横向相关长度、标准偏差粗糙度等参量。由于沉积条件的不同，薄膜生长具有不同的动力学过程。在反应离子束溅射和反应磁控溅射沉积薄膜过程中，薄膜生长动力学行为均可用Kuramoto-Sivashinsky方程来描述，电子束蒸发制备薄膜的过程可以用Mullins扩散模型来描述，并发现在沉积薄膜过程中基底温度和沉积过程的稳定性对薄膜表面特征影响很大。     

耗散粒子动力学模拟方法在软物质体系研究中的一些进展与应用

软物质是指处于固体和理想流体之间的复杂态物质,主要包括聚合物、表面活性剂、液晶、胶体悬浮液、以及生物大分子等。软物质能够对外界微小的作用产生强烈的非线性响应,并展现出丰富的有序自组装相态。作为一种新颖的模拟技术,耗散粒子动力学方法非常适合在介观尺度上对软物质体系的复杂行为进行合理的描述。本文对耗散粒子动力学模拟方法的发展及一些应用进行了系统评述。耗散粒子动力学模拟方法体现了分子动力学与格子Boltzmann模型的优点,通过与其它理论模型（如Flory-Huggins理论、Smoothed particle hydrodynamics模型等）相结合,该方法能够在介观尺度上有效地研究聚合物熔体和溶液体系、生物膜及囊泡体系以及胶体悬浮液等体系的行为。这些研究结果,对新材料的研发、特殊材料的制备、以及材料加工条件的选择具有十分重要的科学意义和实际应用价值。     

Dissipative Particle Dynamics Simulation of Microscopic Properties in Diblock Copolymer Films

利用耗散粒子动力学模拟方法研究了两嵌段共聚高分子薄膜中的一些微观性质. 结果表明：薄膜中共聚高分子链的均方根末端距2_e>^1/2、均方根回旋半径2_g>^1/2与薄膜厚度l、不同粒子间的相互作用强度a_ij、粒子与薄膜边界间的排斥作用强度a_pb均呈线性关系,而均方键长与a_ij、a_pb呈线性关系,随l增加则呈现出波浪形趋势. 2_e>^1/2与2_g>^1/2的变化趋势可以相互对应. 任一组分在薄膜中的密度分布可以通过其与薄膜边界间的相互作用来有效控制与调节.     

The Effect of Substrate Temperature on the Properties of Nanostructured Silicon Carbide Films Deposited by Hypersonic Plasma Particle Deposition

Nanostructured silicon carbide films have been deposited on molybdenum substrates by hypersonic plasma particle deposition. In this process a thermal plasma with injected reactants (SiCl₄ and CH₄) is expanded through a nozzle leading to the nucleation of ultrafine particles. Particles entrained in the supersonic flow are then inertially deposited in vacuum onto a temperature-controlled substrate, leading to the formation of a consolidated film. In the experiments reported, the deposition substrate temperature T_s has ranged from 250°C to 700°C, and the effect of T_s on film morphology, composition, and mechanical properties has been studied. Examination of the films by scanning electron microscopy has shown that the grain sizes in the films did not vary significantly with T_s. Micro-X-ray diffraction analysis of the deposits has shown that amorphous films are deposited at low T_s, while crystalline films are formed at high T_s. Rutherford backscattering spectrometry has indicated that the films are largely stoichiometric silicon carbide with small amounts of chlorine. The chlorine content decreases from 8% to 1.5% when the deposition temperature is raised from 450°C to 700°C. Nanoindentation and microindentation tests have been performed on as-deposited films to measure hardness, Young's modulus and to evaluate adhesion strength. The tests show that film adhesion, hardness and Young's modulus increase with increasing T_s. These results taken together demonstrate that in HPPD, as in vapor deposition processes, the substrate temperature may be used to control film properties, and that better quality films are obtained at higher substrate temperatures, i.e. T_s700°C.     

Ar离子辅助沉积对含氢类金刚石薄膜结构影响的计算机模拟

选C₂分子和一定量的H原子作为沉积源,Ar离子作为辅助沉积粒子,采用分子动力学(MD)方法模拟研究离子束辅助沉积(IBAD)生长类金刚石(DLC)膜的物理过程.给定Ar的入射能量并改变Ar的到达比(Ar/C),研究辅助沉积对DLC膜结构的影响;重点讨论Ar辅助沉积引起表面原子的瞬间活性变化对薄膜结构产生的影响.结果表明,由于Ar离子轰击引起的能量和动量的传递,增加了合成薄膜的SP³键含量,增大了合成薄膜的密度,加宽了沉积粒子和衬底的结合宽度,研究结果和实验观察一致,并从合成机理上给出一些定量解释.     

Sintering of titanium dioxide nanoparticles: a comparison between molecular dynamics and phenomenological modeling

Molecular dynamics simulations were used to determine the melting points of anatase and rutile nanoparticles. The melting points decrease with decrease in particle diameter and are in reasonable agreement with the empirical formula derived by Buffat and Borel. The phenomenological model of Koch and Friedlander is unable to predict the temperature rise during initial stages of sintering with acceptable accuracy. It is argued that the Koch and Friedlander assumption of linear surface reduction rate upon sintering may be inadequate for the time scales under consideration. A theoretical model using direct area measurement from molecular dynamics simulations and a single adjustable parameter is able to predict temperature rise during initial stages of sintering within acceptable error limits.     

Surface Stabilization of Nano-sized Titanium Dioxide: Improving the Colloidal Stability and the Sintering Morphology

We have developed a simple surface modification technique to avoid irreversible agglomeration of titanium dioxide nanoparticles. The technique is based on hydrolysis-precipitation procedure, using TiOSO₄ as a precursor and water as a hydrolyser and a preparation medium. Diethylene glycol monomethyl ether is used as a surface modifier. Using a variety of characterization techniques, including XRD, SEM, TEM, TGA, DTA, AES, XPS, ELS and DLS, the resulting powders and the mechanism of surface stabilization were investigated. According to the proposed mechanism, hydroxyl-terminated ether molecules react with the surface of nanoparticles and then chemically adsorbed there. The layer of adsorbed molecules prevents the strong irreversible agglomeration during precipitation from the sol. The obtained anatase powder remains within the nanometric scale under heat-treatment up to 760 °C. The powders can be re-dispersed in water by ultrasound treatment, resulting in relatively stable aqueous dispersions. In addition, the morphology of sintered bodies made of these powders is significantly improved as compared to non-stabilized powders, due to less agglomeration in the initial sintering stage.     

Nanotips: Growth,Model, and Applications

The tip morphology in the nanoscale is discussed as a member of the one-dimensional nanostructure family. Different growth techniques used for the synthesis of the nanotips have been outlined and compared against each other including, etching, pyrolysis, physical, and chemical vapour deposition. Growth models for hollow and solid nanotips are compared and discussed in detail with a thrust on the ‘cone-helix’ model for the hollow tips and the ‘platelet stacking’ model for the solid tips. Application of the nanotips in field emission, scanning probe microscopy, sensing, anti-reflection, and nanoindentation is discussed.     

红荧烯薄膜生长及稳定性的研究

利用原子力显微镜研究了二氧化硅衬底上红荧烯薄膜的生长及稳定性。在较低沉积速率下,较低衬底温度时,红荧烯分子有充足的扩散时间,利于薄膜的横向生长,形成连续性、均匀性较好的薄膜。快速蒸镀及较高衬底温度使红荧烯薄膜转变为纵向生长模式,形成团粒状岛。横向生长的红荧烯薄膜在退火和空气中表现为亚稳特性,随着退火温度的升高和空气中放置时间的延长,红荧烯分子会自发地进行质量传输,发生纵向转移,转变为团粒状岛。获得了二氧化硅界面上红荧烯薄膜的生长及亚稳定机制模型。研究结果证明红荧烯分子与二氧化硅界面之间的作用力小于红荧烯分子间的作用力。     

Simulation on the Effect of Brownian Motion on Nanoparticle Trajectories in a Pulsed Microplasma Cluster Source

We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment.     

Monte Carlo Simulation of Sculptured Thin Films Growth of SiO2 on Si for Applications

A fully three-dimensional Monte Carlo model for simulation of sculptured thin-film growth is presented. After explaining the model, the simulation results are compared with the corresponding experiments, and encouraging consistency is proven. The morphology of sculptured thin films is then compared on periodical patterned and bare substrates. It is shown that there are more uniform structures and hence possible better optical properties by fabricating on patterned substrates. Finally, with the aid of computer simulation, we examine the sell-shadowing effect and our theoretical analysis of simulated morphology data deals with the accuracy of this model.     

选区激光烧结瞬态温度场模拟与测试方法研究

采用有限元方法,考虑实际的边界条件和热物性参量的变化,对Al2O3覆膜陶瓷粉末的选区激光烧结过程瞬态三维温度场进行动态模拟.通过比色测温法对红外热成像系统的发射系数进行修正后,对选区激光烧结过程瞬态温度场进行测试.数值模拟和实测结果显示,两者吻合较好.     

Review on Atomic Layer Deposition and Applications of Oxide Thin Films

Atomic layer deposition technique is able to grow conformal thin films over high aspect ratio structures. This article reviews the various aspects of oxides grown by this method including applications in photovoltaics and memristors. The main focus of this review is to concentrate on the oxides grown by atomic layer deposition and their growth mechanisms. The oxides deposited using atomic layer deposition are also likely to find application in memristor, an emerging field in the non volatile memories design with the ability to retain data and memory states even in power-off condition. The use of this technique to obtain oxides in surface modification of nanostructures gives the significance of these materials.     

ZnO:Fe薄膜制备、光学与电学性质研究

用双靶磁控溅射设备制备了ZnO:Fe薄膜。分析了铁靶溅射功率对薄膜的光学及电学性质的影响。X射线衍射(XRD)和原子力显微镜(AFM)图像表明:ZnO:Fe薄膜为六角纤锌矿结构,且具有非常好的沿垂直于衬底的c轴择优取向。当铁靶功率小于250W时,沉积速率随铁靶功率的增加而增加。随着铁靶功率的增加,透射光谱的吸收边有微弱蓝移,透过率在可见光区超过75%。掺铁后薄膜的电阻率只有10-2Ω.cm,远小于纯氧化锌的电阻率。通过实验得到ZnO:Fe薄膜的最佳制备条件。     

Preparation and Properties of Antimicrobial Poly(butylene adipate-co-terephthalate)/TiO2 Nanocomposites Films

Abstract

Poly(butylene adipate-co-terephthalate) (PBAT) nanocomposite films with various contents of nano-titanium dioxide (TiO₂) and titanium dioxide doped silver (Ag-TiO₂) were prepared by a solvent casting method. The TiO₂ and Ag-TiO₂ nanoparticles were surface-modified with silane coupling agents to improve their compatibility and dispersibility in the PBAT matrix. They were denoted as mTiO₂ and mAg-TiO₂, and were characrterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The morphology of the PBAT nanocomposite films was studied by field emission scanning electron microscopy (FE-SEM). The crystallinity of the PBAT film increased upon the introduction of the nano-TiO₂/Ag-TiO₂. Its mechanical properties and gas barrier properties were also significantly improved. In addition, the PBAT/mTiO₂ and PBAT/mAg-TiO₂ nanocomposite films showed a strong antibacterial activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) food-borne pathogenic bacteria.     

生长温度对立方MgZnO薄膜生长取向和紫外光吸收特性的影响

利用脉冲激光沉积技术在非晶石英衬底上制备立方结构MgZnO薄膜,并研究MgZnO薄膜结晶特性、光学带隙随生长温度的变化情况。当生长温度从150℃升高到700℃时,MgZnO薄膜的生长取向由（200）向（111）转变。在600℃以下,MgZnO薄膜光学带隙的变化规律与晶格中Mg和Zn原子比例的变化趋势是一致的;而当温度升至700℃时,虽然MgZnO晶格中Mg和Zn原子比例降低,但由于平均晶粒尺寸变大,薄膜的光学带隙反而上升。在300℃和700℃晶格匹配的情况下,获得了单一（200）和（111）取向的立方MgZnO薄膜。     

星形两嵌段共聚高分子薄膜微相分离的耗散粒子动力学模拟

利用耗散粒子动力学模拟研究了两类典型的星形两嵌段共聚高分子薄膜的微相分离行为. 结果表明,(A_x)₄(B_y)₄体系的相图较(A_xB_y)₄体系具有明显的对称性,且前者比后者更易发生相分离,与体相中的情况相近,并可归因于两类星形高分子在结构上的差异;组成相同的星形共聚高分子体系在体相与薄膜中所形成的介观结构之间存在对应关系;减小薄膜厚度与加大A-B组分间排斥强度均有利于增强所形成结构的有序性. 同样是缘于分子结构差异,两类星形高分 子薄膜中的均方回旋半径随体系组分分率的变化规律几乎相反.     

Effect of Particle Size and Phase Composition of Titanium Dioxide Nanoparticles on the Photocatalytic Properties

Titanium dioxide (TiO₂) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl₄) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO₂ nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO₂ nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO₂ nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.     

Effect of iron doping on the hydrophobicity of titanium dioxide film: experiment and simulation

In this study, we carried out experiments and molecular dynamics simulations to identify the effect of Fe doping on the hydrophobicity of a titanium dioxide film. TiO₂ and Fe-doped TiO₂ films were fabricated in situ by atomic layer deposition without annealing. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterise the crystal structure and elemental composition. Iron doping resulted in the TiO₂ becoming more hydrophobic at a macroscopic level, as estimated by atomic force microscopy observations and static contact angle measurements. Furthermore, the effect of iron doping on the structure and kinetics of water molecules on the exterior of TiO₂ were studied by molecular dynamics simulations. On the basis of the XPS results, the Fe-TiO₂ surface matrix has a Ti:Fe ratio of 36:5. In addition, the density distribution of oxygen and hydrogen atoms indicate that interfacial water molecules enter the Fe-TiO₂ film more easily and hydrogen atoms in the water molecules are oriented upward at the interface. The self-diffusion coefficients indicate that iron doping makes the TiO₂ more hydrophobic, which is consistent with the macroscopic test results.