A unipolar pulsed plasma generator in combination with a laser as a plasma jet source

A pulsed plasma generator ignited by plasma produced by laser radiation is described. The plasma generator can provide a relatively high-velocity plasma jet of specific chemical composition. The principal parameters of the plasma jet (its velocity, charged particle concentration, and temperature) have been measured and the properties of the plasma jet have been found to be independent of the polarity of the plasma generator ring electrode.The authors are grateful to M. A. El'yashevich for discussing the present paper.     

超声辅助电镀的仿真与实验*

为了提高镀层的表面质量,提出了一种超声辅助电镀的方法。超声的空化与搅拌作用可以影响电镀的电沉积过程。设计了合理的换能器结构,并搭建了超声辅助电镀装置。通过对模型进行压电声学场与电镀场耦合仿真分析,结果表明：在硫酸铜电解液,镀铜时间60s,电压300V条件下,进行超声辅助电镀,镀层厚度分布均匀,镀层中部电流密度分布均匀,边缘最大电流密度是未加超声的2倍左右 。基于仿真结果,进行相同的实验测试,结果表明：超声辅助电镀可以提高镀层的均匀性,减少铜颗粒表面的杂质,提高表面的光洁度。阴极样品距离换能器头部位置在60mm左右,镀层质量良好。     

Investigation of a novel hybrid process of laser drilling assisted with jet electrochemical machining

Recast layer and spatter are two inherent defects commonly associated with holes produced with laser drilling. This paper reports a novel hybrid process of laser drilling assisted with jet electrochemical machining (JECM-LD) that aims to minimize such defects and improve the quality of laser-drilled holes. The process based on the application of a jet electrolyte, being aligned coaxially with the focused laser beam, on the workpiece surface during laser drilling. The effect of the jet electrolyte mainly is an electrochemical reaction with materials. The jet electrolyte also cools the workpiece and transports debris during the process. On the basis of a measurement of laser attenuation in electrolyte, an experimental apparatus system is made and JECM-LD experiments have been performed on 0.5-mm-thick 321S20 stainless steel with two lasers at wavelength of 1064 and 532 nm. It is shown that recast layer and spatter have been effectively reduced during the JECM-LD compared with laser drilling in ambient atmosphere conditions.     

Laser-Induced Particle Jet and Its Ignition Application in Premixed Combustible Gases

A hot particle jet is induced as a laser pulse from a free oscillated Nd：YAG laser focused on a coal target. The particle jet successfully initiates combustion in a premixed combustible gas consisting of hydrogen, oxygen, and air. The experiment reveals that the ionization of the particle jet is enhanced during the laser pulse. This characteristic is attributed to the electron cascade process and the ionization of the particles or molecules of the target. The initial free electrons, which are ablated from the coal target, are accelerated by the laser pulse through the inverse Bremsstrahfung process and then collide with the neutrals in the jet, causing the latter to be ionized.     

Visualization of particle trajectories in the laser shock cleaning process

The laser shock cleaning (LSC) method has recently attracted substantial attention since it can remove micro/nano-scale contaminant particles from a solid surface without direct exposure of the surface to laser irradiation. However, despite the importance of the particle detachment and redeposition mechanisms in the LSC process, the behavior of the particles during the cleaning process has never been analyzed experimentally. In this work, the motion of the micrometer-scale particles detached by a laser-induced plasma/shock wave is visualized by a photoluminescence imaging technique. The technique yields time-resolved particle trajectories under typical conditions of the LSC process, with and without a gas jet blowing. Discussions are made on the behavior of the detached particles and redeposition mechanisms.     

自悬浮定向流技术中铜纳米微粒的粒度控制研究

 采用自悬浮定向流技术制备了金属铜纳米微粒，根据TEM的行貌像对样品平均粒度进行标定，并结合样品制备的条件对制备工艺进行了研究。结果表明，自悬浮定向流技术可以方便地制备出不同粒度的金属铜纳米微粒，微粒平均粒径随熔球温度的降低而减小，随冷却气体流速的增大而减小；在1 200℃下微粒平均粒径随惰性气体压强的增大而减小，而在1 300℃时惰性气体压强对微粒平均粒径的影响不再具有规律性。     

Study of surface treatment processes for improvement in the wettability of silicon-based materials used in high aspect ratio through-via copper electroplating

We report the improvements in wetting characteristics of silicon-based materials with copper electrolyte by various surface treatments to achieve uniform and void free copper deposition in high aspect ratio through-via electroplating. The contact angles of samples such as native silicon, thermally oxidized silicon, silicon nitride, deep reactive ion etched silicon etc, with copper electrolyte, were measured before and after the surface treatments. The wetting of copper electrolyte with silicon nitride coated silicon samples was found to be more than that with thermally oxidized samples. Due to its better wettability, silicon nitride was later used as an insulating layer instead of commonly used silicon oxide in the electroplating experiments. After the SC1 wet surface treatment, the contact angles of all the samples were found to be significantly lower, thus making the surface more suitable for electroplating applications. X-ray photoelectron spectroscopy results verified the presence of polar functional groups on the samples surface, which has helped to improve wetting with copper electrolyte. The conclusions drawn by the experimental results were employed in the high aspect ratio through-via copper electroplating; and void free copper interconnects, having aspect ratio as high as 20, were fabricated.     

Laser scattering by metallic particles in two-phase nozzle flow into a vacuum

For several years the Max-Planck-Institute for Extraterrestrial Physics has performed experiments with artificial barium clouds in space by means of research rockets and satellites in order to investigate electric fields and currents in the ionosphere and in the magnetosphere. The processes which lead to the formation of these artificial clouds were simulated in laboratory in order to optimize the barium vapor yield and to obtain a better insight into the initial phase of the clouds. In these experiments the combustion of excess barium with copper oxide, the two-phase flow of the combustion products through a nozzle and their expansion into a 20 m³ vacuum chamber were investigated in detail. Purpose of this work is to measure through detection techniques of scattered laser light and thermal radiation: 1) the density of small metall particles on the particle jet axis, 2) the particle velocity, 3) the thermal radiation of larger particles, and 4) the position of the Mach disk which limits the free nozzle jet downstream. This work was carried out at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany.     

电解质中添加氧化物颗粒对染料敏化太阳电池性能的增强

"在液态电解质中加入纳米TiO2、微米TiO2、Al2O3和ZrO2颗粒后,在一定的氧化物含量下,都不同程度地提高了DSC的光电特性,而以加入12.5%的纳米TiO2 (P25)得到最高的提高,达到5.5%,比没有加入氧化物颗粒的DSC效率提高达到51%以上．利用电化学阻抗谱和循环伏安法研究了在染料敏化太阳电池液态电解质中加入各种氧化物颗粒对电池电解质特性的影响,结果发现,加入氧化物颗粒后,由于界面效应,提供了I3-的快速扩散通道,从而I3-扩散系数得到较大提高,电解质/Pt电极间的电荷传输电阻下降,改善     

Influence of metal powder shape on drag coefficient in a spray jet

In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 μm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed.     

Infrared particle detection for battery electrode foils

Failures of electrochemical cells caused by internal shorts still are an important issue to be faced by the cell manufacturers and their customers. A major cause for internal shorts are contaminated electrode foils. These contaminations have to be detected securely via a non-destructive inspection technique integrated into the electrode manufacturing process. While optical detection already is state of the art, infrared detection of particles finds a new field of application in the battery electrode manufacturing process. This work presents two approaches focusing on electrode inspection by electromagnetic radiation (visible and infrared). Copper foils with a carbon based coating were intentionally contaminated by slivers of aluminum and copper as well as by abraded coating particles. Optical excitation by a flash and a luminescent lamp was applied at different angles in order to detect the reflected visible radiation. A laser impulse was used to heat up the specimen for infrared inspection. Both approaches resulted in setups providing a high contrast between contaminations and the coated electrode foil. It is shown that infrared detection offers a higher security thanks to its reliance on absorbance and emissivity instead of reflectivity as it is used for optical detection. Infrared Detection offers a potential since it is hardly influenced by the particle’s shape and orientation and the electrode’s waviness.     

Selective laser processing of ink-jet printed nano-scaled tin-clad copper particles

The deposition of tin-clad nano-size copper particles was carried out by means of ink-jet printing. Curing the particles on Polyimide (PI) turned them into soldered structures using an Nd-YAG laser. Area coverage of 55% was achieved for a single-layer print. Subsequent laser sintering increased this value to 95%. A Butanol-based copper ink and an aqueous tin (Sn)-clad Copper (Cu) ink were produced and were ink-jetted in this work. These nano-metallic inks showed excellent suspension stability with particle weight concentrations as high as 5%. The ink components were examined by measuring the particle size distribution in a dispersed condition, and the melting temperature. A piezo ink-jet print head was used to deposit the inks onto a moveable substrate. The thermal effect of the laser irradiation allowed approaching and connecting adjacent particles by melting the particle’s tin coating. The results were examined with regard to structure and soldering properties using EDX, SEM and optical microscopy.     

Ultraviolet laser removal of small metallic particles from silicon wafers

Laser removal of small 1 μm sized copper, gold and tungsten particles from silicon wafer surfaces was carried out using ultraviolet radiation at 266 nm generated by Nd:YAG harmonic generation. Successful removal of both copper and gold particles from the surface was achieved whereas tungsten particles proved to be difficult to remove. The cleaning efficiency was increased with an increase of laser fluence. The optimum processing window for safe cleaning of the surface without any substrate damage was determined by measuring the damage threshold laser fluence on the silicon substrate and the required fluence for complete removal of the particles. The different cleaning efficiencies with particle type are discussed by considering the adhesion force of the particle on the surface and the laser-induced cleaning force for the three different particles.     

Jet produced by collapse of conical free surface of a metal by plane shock wave

Theoretical and experimental investigations of metal-jets, produced by interaction of a plane shock wave with a conical cavity at free surface of metals like aluminium, copper and mild steel, have been carried out and an attempt has been made to correlate the jet velocity with shock parameters. The velocity of the jet, obtained from the cavity of different half angles have been mostly measured with oscillographic technique. The experimental results agree with theory within experimental variations. The velocity of the jet increases monotonically with the particle velocity but decreases with increase in the angle of the cavity.     

超强激光与固体气体复合靶作用产生高能氦离子

激光氦离子源产生的MeV能量的氦离子因有望用于聚变反应堆材料辐照损伤的模拟研究而得到关注.目前激光驱动氦离子源的主要方案是采用相对论激光与氦气射流作用加速高能氦离子,但这种方案在实验上难以产生具有前向性和准单能性、数MeV能量、高产额的氦离子束,而这些氦离子束特性是材料辐照损伤研究中十分关注的.不同于上述激光氦离子产生方法,我们提出了一种利用超强激光与固体-气体复合靶作用产生氦离子的新方法.利用这种方法,在实验上,采用功率密度5×10~(18)W/cm~2的皮秒脉宽的激光脉冲与铜-氦气复合靶作用,产生了前向发射的2.7 MeV的准单能氦离子束,能量超过0.5 MeV的氦离子产额约为10~(13)/sr.二维粒子模拟显示,氦离子在靶背鞘场加速和类无碰撞冲击波加速两种加速机理共同作用下得到加速.同时粒子模拟还显示氦离子截止能量与超热电子温度成正比.     

Temperature analysis of the powder streams in coaxial laser cladding

The powder stream temperature of a newly developed coaxial laser cladding technique have been calculated and measured in this study. A simplified one-dimensional model of the particle heating problem under laser irradiation was solved with various conditions of laser intensity, particle size and flow velocity. The experimental results have been successfully detected by a pin-hole infrared sensor with the temperature calibration for hot particles. The thermal profiles of the coaxial nozzle give an optimum operation range of the stand-off distance for coaxial laser cladding.     

三维层流等离子体射流中陶瓷颗粒的运动与加热

本文对带载气-颗粒侧向喷射的三维层流等离子体长射流中陶瓷颗粒的运动与加热进行了模拟研究,并与忽略载气喷射影响时的结果进行了比较。模拟结果表明,侧向载气喷射所引起的三维效应对颗粒行为有明显影响,陶瓷颗粒在等离子体射流中加热时颗粒内部可能出现相当大的温差,取决于环境参数,陶瓷颗粒表面温度可以高于也可以低于中心温度。     

XPS studies of short pulse laser interaction with copper

The effect of laser ablation on copper foil irradiated by a short 30 ns laser pulse was investigated by X-ray photoelectron spectroscopy. The laser fluence was varied from 8 to 16.5 J/cm² and the velocity of the laser beam from 10 to 100 mm/s. This range of laser fluence is characterized by a different intensity of laser ablation. The experiments were done in two kinds of ambient atmosphere: air and argon jet gas.The chemical state and composition of the irradiated copper surface were determined using the modified Auger parameter (α′) and O/Cu intensity ratio. The ablation atmosphere was found to influence the size and chemical state of the copper particles deposited from the vapor plume. During irradiation in air atmosphere the copper nanoparticles react with oxygen and water vapor from the air and are deposited in the form of a CuO and Cu(OH)₂ thin film. In argon atmosphere the processed copper surface is oxidized after exposure to air.     

GaN基垂直结构LED的n型电极结构设计及芯片制备

首先利用电流路径模型分析n型电极尺寸及间距等对垂直结构发光二极管(VS-LEDs)电流分布均匀性的影响,依此设计出一种螺旋状环形结构电极。其次,通过建立有限元分析软件Comsol仿真模型模拟VSLEDs有源层的电流密度分布,发现螺旋状环形结构电极的环间距越小,电流密度分布越均匀。最后,利用VS-LEDs芯片制备技术实现具有螺旋状环形电极的垂直结构LED芯片。实验结果显示,在350 m A电流驱动下,电极环间距为146.25μm的芯片具有最大的功能转换效率,达到26.8%。