喷雾清洗中微颗粒受到流体作用力的研究

对喷雾清洗过程中微颗粒所受到的流体力进行了研究.由于液滴撞击在平面上产生的不稳定流, 无法用现有的层流作用力公式来预测颗粒所受到的作用力,本文采用了计算流体力学模拟的方法对流场分布进行了模拟,并且汁算颗粒上相应受到的作用力.通过计算结果,讨论了影响颗粒清除效果的关键因素.研究表明,在微米尺度内,平面的可湿性质对液滴展开的初始阶段流场分布有显著影响,从而也大大影响了平面上颗粒所受到的作用力.此外,撞击在下燥表面时,颗粒受到的拖拽力会比撞击到湿表面上时大三个数量级以上.而在湿表面上时,提高撞击速度会比增大液滴大小来得更有效,主导颗粒去除的力为拖拽力.     

在微机上进行的离子源中离子发射和运动的Monte—Carlo模拟计算

用Monte—Carlo模拟法研究了液态金属离子源中的离子发射过程,离子有Poi-sson分布的发射噪音,有Maxwell分布的初始速度,有随机的初始位置.离子运动时不只受场力的作用,还受到其他离子的库仑作用力.文章给出考虑和不考虑库仑作用力的轨迹各十条,可见其影响.计算用了分时进行法,即把整个计算分成若干次进行,故能在IBM微机上进行运算.     

稳态磁场辅助激光熔注制备梯度涂层

利用稳态磁场辅助激光熔注,在316L不锈钢基体上成功制备了碳化钨(WC)颗粒分布可调的WC/316L金属基梯度复合材料涂层。讨论了激光熔注时稳态磁场对复合材料涂层中硬质颗粒的分布和组织的影响。研究结果表明,稳态磁场可以抑制熔池流动,降低颗粒在熔池中受到的拖曳力,且随着磁场强度的增大,WC颗粒集中分布在复合材料表层的趋势增大;稳态磁场未改变复合材料层表面的物相种类,但表面的W相含量明显增多,且可使复合材料层表面的共晶组织数量增多、尺寸变大。     

激光干扰CCD规则亮点分布原理研究

激光干扰CCD时光的传输过程的研究,对激光干扰CCD干扰图像的仿真、干扰效果的分析等具有重要意义。理论分析了考虑探测器表面反射时的激光干扰CCD时光的传输过程。由于透镜的作用,首先激光会聚焦到探测器表面。聚焦光会被探测器表面反射。由于CCD探测面是网格状分布,反射光的分布会被这一结构调制。反射后的光经过透镜,会成像在某些平面上。根据透镜中光的传输计算发现,因为透镜的傅里叶变换作用,光阑平面上会出现周期性的亮点分布。由于光阑平面上不透光的部分的反射,亮点会再次成像在探测器表面上。仿真了亮点被光阑平面上不透光部分的反射后,经过光阑后面的透镜又成像在探测器上的过程,得到了规则的周期性的亮点分布。实验结果验证了这一理论。     

激光微织构表面水滴撞击动力学行为特性研究

为了探究低韦伯条件下,微织构超疏水表面的液滴撞击动力学行为特性,利用激光微织构技术在航空用材Ti 6Al4V试样表面用不同扫描速度的纳秒激光制备出三角纹理微纳织构,借助高速摄像实验平台研究水滴撞击水平表面和倾斜表面动力学行为特性。实验结果表明,水滴冲击平表面高度越高,空气越不容易进入片层,使最大铺展系数增加;与平表面相比,相同高度的斜表面滑移时更多空气进入片层,最大铺展系数最小;其中在扫描速度为100mm/s的工况下,表面凸起占比达到64611,表面纳米颗粒最大,微米颗粒最多,表面的静态接触特性与动态接触特性最优。受表面结构和表面能协同作用共同影响水滴弹离表面的状态。本实验可为航空领域制备超疏水、主动防除冰表面提供一定参考。     

温度梯度驱动下水银在石墨烯表面的运动特性北大核心

采用分子动力学模拟的方法,探究温度梯度驱动下水银在石墨烯表面的流动特性。重点研究了石墨烯的全局热振荡对石墨烯表面水银运动的影响。研究表明:在稳定的温度梯度下,单层石墨烯模型与刚体石墨烯模型的表面温度均呈近似线性分布,但刚体石墨烯模型表面温度分布的线性特征更加明显;同时,石墨烯表面水银液滴在温度梯度驱动下从高温区域向低温区域运动,且水银液滴在石墨烯表面流动的速度、加速度均随温度梯度的增大而增大。提出了刚体石墨烯模型。研究结果表明,石墨烯的全局热振荡所产生的驱动力方向与水银液滴在石墨烯表面的运动方向相同,均由高温区域指向低温区域。     

光通信中天线表面颗粒沾染与激光波长的关系

空间光通信系统天线表面的颗粒沾染能够导致光通信系统光学性能的变化.利用时域有限差分法(FDTD)建立了空间光通信系统天线表面沾染模型,考虑到空间光通信远场发射、远场接收的特点,在直接利用FDTD法得到近场光强分布的基础上,进行了近场一远场变换.实例计算表明,对于一定直径的微粒,当颗粒间距达到某一值时,近场光强分布为具有一定数值的直线.然后以此光强分布为参考,计算了微粒直径相同、入射波长不同时所对应的颗粒间距最大值.结果表明,r>时,波长越长,对应的颗粒间距越大.在进行空间光通信系统的防护设计时,如果载波波长较长,应尽量减少光学表面大颗粒的形成.     

基于蒙特卡罗方法的波动水面对激光水下目标探测的影响

机载海洋激光雷达在探测水下目标时,水面波动会影响向下传输的激光光束质量。基于蒙特卡罗方法定量分析了光子在目标平面上的空间分布,以及光子返回海气界面的空间分布和时间分布。模拟结果表明,随着风速的增加,光子在目标平面上的空间分布越来越偏离高斯分布;而光子返回海气界面的空间分布则严重偏离高斯分布,且风速的影响已经不再占主导地位。根据计算获得的光子返回海气界面的时间分布,发现当风速较大时,激光雷达的探测深度降低。     

微米颗粒粘附力的光学测量法

分析了吸附于介质表面的微米颗粒所受的力 ,并通过理论模型估计了直径为 1 5 μm的小球在表面所受到的粘附力为 10 - 6 N量级。同时利用脉冲激光的光压对吸附于蓝宝石玻璃表面的玻璃小球进行了粘附力的测量。测量结果和理论计算值吻合。在给定实验条件下 ,粘附力的大小主要是由毛细力决定的     

填充不流动胶的倒装焊封装中芯片的断裂问题

用断裂力学方法和有限元模拟分析了填充不流动胶芯片断裂问题 .模拟时在芯片上表面中心预置一裂缝 ,计算芯片的应力强度因子和能量释放率 .模拟表明 ,由固化温度冷却到室温时 ,所研究的倒装焊封装在填充不流动胶时芯片断裂临界裂纹长度为 12 μm,而填充传统底充胶时为 2 0 μm.模拟结果显示芯片断裂与胶的杨氏模量和热膨胀系数相关 ,与胶的铺展关系不大 .焊点阵列排布以及焊点位置也会影响封装整体翘曲和芯片断裂 .     

A lubrication model between the soft porous brush and rigid flat substrate for post-CMP cleaning

A 3D lubrication model between a soft porous brush and rigid flat surface in the post-CMP (chemical mechanical polishing) cleaning process for wafer or hard-disc surface is set up in this article. The mesh porous structure of the brush and the kinematic relations between the brush and the surface are taken into account. The flow governing equations for cleaning process are deduced with Newtonian fluids between the brush nodule and the substrate. The distributions of fluid pressure and hydrodynamic removal moment are calculated. The simulation results show that the fluid pressure has negative regions in inlet area. The removal force is depended on system parameter, location, time and particle size. The load and hydrodynamic moment increase with the increase of brush velocity and deflection of brush nodule, which is effective for cleaning. A low wafer rotation speed is recommended to keep the cleaning uniformity. The removal moment is increasing during the cleaning process. The hydrodynamic drag force decreases rapidly with decreasing of particle size. The models are coincident with the actual process and can be used as reference for designing a higher level cleaning process and the analysis of the formation of particle defect.     

Gradient Quasi-Liquid Surface Enabled Self-Propulsion of Highly Wetting Liquids

Self-propulsion of highly wetting liquids is important in heat exchanger, air conditioning, and refrigeration systems. However, it is challenging to achieve such a spontaneous motion as these liquids tend to wet all the surfaces due to their ultralow surface tensions. Despite that extensive asymmetric surface structures and gradient chemical coatings are developed for directional droplet transport, they will be flooded and covered by these liquids. Here, this challenge is addressed by creating a gradient quasi-liquid surface to achieve the self-propulsion of droplets with surface tensions down to 10.0 mN m⁻¹. Such a surface engineered by tethering flexible polymers with gradient grafting density shows ultralow contact angle hysteresis (<1^o) to highly wetting liquids. Thus, the surface can simultaneously provide sufficient driving forces through the gradient wettability and negligible retention forces through the slippery boundary lubrication for spontaneous droplet movement. Moreover, continual self-propulsion of tiny droplets is achieved by spraying highly wetting liquids in simulated condensation conditions and demonstrates that adding temperature gradient can further accelerate the self-propulsion. The study provides a new paradigm to promote passive removal of highly wetting droplets, leading to potential impacts in enhancing condensation heat transfer regardless of surface orientations.     

Reduction of a micro-object's adhesion using chemical functionalisation

The adhesion and interaction properties of functionalised surfaces (substrate or cantilever) were investigated by means of atomic force microscope (AFM)-related force measurements. The surfaces were functionalised with a polyelectrolyte - poly(allylamine hydrochloride) (PAH) - or with silanes - 3-(ethoxydimethylsilyl) propyl amine (APTES) or (3-aminopropyl) triethoxysilane (APDMES). Measurements of forces acting between a bare glass sphere (functionalised or not) and a functionalised surface indicated repulsive or attractive forces, depending on functionalisation and medium (wet or dry). Adhesion forces (pull-off) can be observed in dry medium, whereas in wet medium this phenomenon can be cancelled. Now, the pull-off forces represent an important problem in the automation of micro-object manipulations. The cancellation of this force by chemical functionalisation is thus a promising way of improving micro-assembly in the future.     

Highly Permeable Skin Patch with Conductive Hierarchical Architectures Inspired by Amphibians and Octopi for Omnidirectionally Enhanced Wet Adhesion

Amphibian adhesion systems can enhance adhesion forces on wet or rough surfaces via hexagonal architectures, enabling omnidirectional peel resistance and drainage against wet and rough surfaces, often under flowing water. In addition, an octopus has versatile suction cups with convex cup structures located inside the suction chambers for strong adhesion in various dry and wet conditions. Highly air‐permeable, water‐drainable, and reusable skin patches with enhanced pulling adhesion and omnidirectional peel resistance, inspired by the microchannel network in the toe pads of tree frogs and convex cups in the suckers of octopi, are presented. By investigating various geometric parameters of microchannels on the adhesive surface, a simple model to maximize peeling strength via a time‐dependent zig‐zag profile and an arresting effect against crack propagation is first developed. Octopus‐like convex cups are employed on the top surfaces of the hexagonal structures to improve adhesion on skin in sweaty and even flowing water conditions. The amount of reduced graphene oxide nanoplatelets coated on the frog and octopus‐inspired hierarchical architectures is controlled to utilize the patches as flexible electrodes which can monitor electrocardiography signals without delamination from wet skin under motion.     

Forces on a Rayleigh particle in the cover region of a planarwaveguide

We report on the optimization of a waveguide structure for the maximization of the radiation forces exerted on a Rayleigh particle in the cover region. The two main radiation forces involved are the transverse gradient force which attracts a particle into the waveguide and the combined scattering and dissipative forces which drive the particle forward along the channel. The dependence of these forces on parameters including the incident wavelength, the surrounding medium embedding the particles, and the polarizability of the particles is discussed. Both dielectric and metallic gold spheres of radius 10 nm are considered in the model. Special emphasis is devoted to the maximization of the transverse gradient force due to the optical intensity gradient at the waveguide surface, and the wavelength dependence of the polarizability of gold nanoparticles     

无图形损伤的选择性去除微小尘粒的湿法清洗技术

The drastic shrinking of semiconductor linewidths has led to a need for new wafer cleaning strategies in the FEOL. For past technology generations, particle removal has been accomplished typically using the SC 1 (NH4OH/H2O2/H2O) solution in conjunction with megasonic energy in a wet bench, or by DI water with a high pressure jet or megasonic nozzle in a wafer scrubber. However, such techniques have been found to damage patterns, particularly narrow polysilicon gate lines. Furthermore, the etching of oxide associated with SC 1, which facilitates particle removal by an undercutting mechanism, has recently become a concern due to increasingly strict oxide budgets. An alternative technique using an atomized liquid spray nozzle on a single wafer platform is proposed. Small droplets are able to effect particle removal without damage to sensitive patterns, by control of their carrier gas (N2) flow rate. Mechanisms for particle removal will be discussed.Results using this technique show particle removal comparable to megasonics can be achieved. Furthermore, 90 nm and 65 nm polysilicon gate structures were processed with high particle removal efficiency and no damage, as were A1 lines. Effects of the N2 flow rate on particle removal and damage performance will be presented. The physical mechanism of atomized spray enables chemical etching of oxides to be minimized without sacrificing particle removal efficiency. Results using this technique in conjunction with chemistry, to further improve particle removal, will be presented. Results over a large range of particle sizes will be shown. Specific applications will be discussed.     

半导体IC清洗技术

介绍了半导体IC制程中存在的各种污染物类型及其对IC制程的影响和各种污染物的去除方法,并对湿法和干法清洗的特点及去除效果进行了分析比较。     

溶胶-凝胶膜光学表面激光清洗工艺研究

为了解决光学元件表面的颗粒污染问题，在单发次激光干式清洗的基础上，提出了气流置换系统辅助的激光清洗方法，使用波长为355nm的Nd:YAG激光器，针对镀溶胶-凝胶SiO₂薄膜熔石英光学表面粒径为1μm~50μm的典型SiO₂颗粒污染物，进行了理论分析和清洗实验，取得了可用于激光清洗的工艺参量。结果表明，对于镀溶胶-凝胶膜熔石英样品的单发激光干式清洗，最佳激光能量密度为2.29J/cm2，与未镀膜石英的激光清洗工艺参量存在一定差异；在最佳工艺参量下，单发次激光清洗对于粒径1μm以上的SiO₂颗粒清洗效果明显，移除率可达82.96%；当污染密度过高时会导致清洗效果的减弱及对基底的损伤，而气流置换系统辅助的激光清洗方法可进一步增强对光学表面颗粒污染的去除效果。该研究对大型高功率固体激光装置中的光学元件在线清洗及清洗装备的设计具有重要的研究意义与实用价值。     

掺杂GaN的湿法刻蚀研究

对掺杂GaN的湿法刻蚀研究进行了总结,回顾了不同的湿法刻蚀技术,包括传统的酸碱化学刻蚀和电化学刻蚀。从掺杂GaN的生长过程、表面化学组分和光电性质出发,深入地分析了湿法刻蚀的特性,对比了不同刻蚀方法的原理和效果。考虑到p-GaN的表面氧化层比较厚,接触电阻较大,能带向下弯曲不能进行光增强湿法刻蚀,重点阐述了p-GaN的传统湿法刻蚀和n-GaN的紫外光增强湿法刻蚀技术。与传统化学刻蚀相比,光增强湿法刻蚀具有更为广阔的前景。结合GaN基半导体器件的制作,对湿法刻蚀的主要应用进行了较为详细的归纳。目前,湿法刻蚀和干法刻蚀可以有效结合。将来湿法刻蚀有希望代替干法刻蚀。