Nanomanipulation and fabrication by ion beam molding

Nanoscale manipulation is a basic ability needed to realize many of the nanotechnology applications. We demonstrate an ion bean molding technique to shape the configuration of nanostructures. As an example, the native curvature of a carbon nanotube in an atomic force microscope tip and its undesirable angle with respect to the surface are removed by this technique to render the nanotube straight. The straightened nanotube is effectively used in a semiconductor profilometry application. The ion beam molding technique is also shown to be effective in creating a desirable net shape of nanotubes. As mechanical deformation determines electrical and other properties of nanotubes, such manipulation may be of use in nanodevice fabrication.     

低压注射成型工艺的研究进展

低压注射成型(LPIM)是高效、经济的近净形成型工艺.综述了LPIM工艺的特点及其优势,总结了LPIM的发展研究状况,并对其发展前景作了展望.     

Design and fabrication of gypsum mold for injection molding

Traditionally, a mold made of gypsum can only be used in a low-pressure molding, e.g. casting, due to the weak strength of gypsum material. This study addresses the potential of gypsum as a candidate for rapid tooling used in injection molding. The ingredients for the gypsum mold were decided upon, and an additional compression with a vibration process was introduced to enhance the mechanical strength of the gypsum mold. Scanning electron microscope (SEM) results show that the amount of void inside the gypsum mold is reduced, and more interlocking of the microstructure of gypsum is formed by increasing the intensity of the compression with a vibration process. A higher degree of interlocking produces a significant enhancement of the compressive strength of the gypsum. Two samples were selected as master designs for testing the replication performance and lifetime of the gypsum mold. The dimensional replication accuracy of the molded part was over 99.9%. The maximum lifetime of the gypsum mold is about 210 cycles of injection shots. This work provides an alternative tooling for injection molding that can allow manufacturers to produce a small quantity of prototypes in an efficient and cost-effective way in the early stages of product development.     

脉动压力诱导注射成型下的模腔压力响应

自行研制的脉动压力诱导注射成型装置成功地通过聚合物熔体将脉动变化的压力引入到注射成型的充模与保压过程.在该装置上进行实验,实验结果表明:模腔压力的波动频率与活塞杆的振动频率相一致;模腔压力的波动幅值随着活塞杆振幅的增大而增大;活塞杆的振动频率对模腔压力的波动幅值影响较小.     

Wafer-scale fabrication of polymer-based microdevices via injection molding and photolithographic micropatterning protocols

Because of their broad applications in biomedical analysis, integrated, polymer-based microdevices incorporating micropatterned metallic and insulating layers are significant in contemporary research. In this study, micropatterns for temperature sensing and microelectrode sets for electroanalysis have been implemented on an injection-molded thin polymer membrane by employing conventional semiconductor processing techniques (i.e., standard photolithographic methods). Cyclic olefin copolymer (COC) is chosen as the polymer substrate because of its high chemical and thermal stability. A COC 5-in. wafer (1-mm thickness) is manufactured using an injection molding method, in which polymer membranes (approximately 130 microm thick and 3 mm x 6 mm in area) are implemented simultaneously in order to reduce local thermal mass around micropatterned heaters and temperature sensors. The highly polished surface (approximately 4 nm within 40 microm x 40 microm area) of the fabricated COC wafer as well as its good resistance to typical process chemicals makes it possible to use the standard photolithographic and etching protocols on the COC wafer. Gold micropatterns with a minimum 5-microm line width are fabricated for making microheaters, temperature sensors, and microelectrodes. An insulating layer of aluminum oxide (Al2O3) is prepared at a COC-endurable low temperature (approximately 120 degrees C) by using atomic layer deposition and micropatterning for the electrode contacts. The fabricated microdevice for heating and temperature sensing shows improved performance of thermal isolation, and microelectrodes display good electrochemical performances for electrochemical sensors. Thus, this novel 5-in. wafer-level microfabrication method is a simple and cost-effective protocol to prepare polymer substrate and demonstrates good potential for application to highly integrated and miniaturized biomedical devices.     

Study of micropart fabrication via 17-4 PH stainless nanopowder injection molding

Micropart fabrication via 17-4 PH stainless nanopowder injection molding was investigated. The nanopowder was mixed with a binder that was based on wax to produce a feedstock composed of 45% powder and binder (the powder load). Initially, the fit and proper test was done before the micropart was made by making some bars of green samples, which the properties were examined after the sintering process. The examination involved the mechanical properties such as the porosity, hardness, and some of metallurgical aspects, such as the second-phase formation and the final compound after the sintering. The results showed that utilizing 17-4 PH stainless nanopowder is promising for micropart fabrication since it can form a nearly full-density sintered sample with a low porosity and good toughness, and can provide a smooth surface finish. After this, the investigations followed with the injection of the feedstock into the PDMS micromold that was formed by the nickel pattern from the X-Ray LIGA process. The green samples successfully produced a high-aspect-ratio sample with a thickness of up to 1 mm and an aspect ratio of 15 in the microchannel part. Then the green samples were sintered at 1,300 degrees C for 2 h, since from the initial test, they showed optimum parameters with nearly full density, low porosity, and a high degree of hardness. The research shows the excellent results of the application of the 17-4 PH stainless nanopowder to micropart fabrication.     

Fabrication of porous low crystalline calcite block by carbonation of calcium hydroxide compact

Calcium carbonate (CaCO₃) has been widely used as a bone substitute material because of its excellent tissue response and good resorbability. In this experimental study, we propose a new method obtaining porous CaCO₃ monolith for an artificial bone substitute. In the method, calcium hydroxide compacts were exposed to carbon dioxide saturated with water vapor at room temperature. Carbonation completed within 3 days and calcite was the only product. The mechanical strength of CaCO₃ monolith increased with carbonation period and molding pressure. Development of mechanical strength proceeded through two steps; the first rapid increase by bonding with calcite layer formed at the surface of calcium hydroxide particles and the latter increase by the full conversion of calcium hydroxide to calcite. The latter process was thought to be controlled by the diffusion of CO₂ through micropores in the surface calcite layer. Porosity of calcite blocks thus prepared had 36.8–48.1% depending on molding pressure between 1 MPa and 5 MPa. We concluded that the present method may be useful for the preparation of bone substitutes or the preparation of source material for bone substitutes since this method succeeded in fabricating a low-crystalline, and thus a highly reactive, porous calcite block.     

Application of metal injection molding process to fabrication of bulk parts of TiAl intermetallics

In the present study, a metal injection molding (MIM) process was applied to the fabrication of bulk parts of TiAl intermetallics, and effects of sintering parameters on densification of fabricated parts were investigated. The specimens sintered at 1350 °C showed about the same densification as the ones sintered at 1400 °C, while grains and pores were finer, and thus 1350 °C was chosen as the sintering temperature. In the sintered specimens after debinded in an H₂ atmosphere, Al₂O₃ precipitates were observed around pores. The densification decreased with increasing heating rate up to the sintering temperature. It was also found that the sintering time increased the densification without grain coarsening. The optimal heating rate was found to be 3 °C/min, and the densification reached a near-full level of 98.8% when sintered at 1350 °C for 30 h. These findings suggested a useful idea to successfully fabricate TiAl intermetallic parts by the MIM process.     

Visualization of counter pressure mechanism in gas-assisted injection molding process

Abstract

Gas-assisted injection molding (GAIM) refers to injecting gas into the short shot melt during the filling stage. Compressed gas is used as the medium to push the melt and to provide the packing pressure. In GAIM, the hollow area and penetration length are the main factors that will affect the quality of molded parts. This study has applied a Gas Counter Pressure (GCP) mechanism and has discussed the effect of GCP in the GAIM process with in-mold visualization of this complex molding flow. This study introduces a counter pressure mechanism in a thick paper-clip-shaped cavity design. The flow field under different counter pressure conditions is observed by high-speed photography, the fiber orientations are analyzed with SEM, and the affected penetration length and hollow area are measured relatively. The experimental results show that when the GCP is applied to GAIM, although the hollow area is reduced, the penetration length will be increased, so as to make the quality of molded part more uniform and reduce the shrinkage. And a quantitative measuring method of two-stage penetration time span is proposed to get more in-depth discussion about the interactions between GCP and GAIM.     

粘结剂对注射成型钕铁硼粘结磁体性能的影响

为了制备出高性价比的注射成型粘结钕铁硼永磁材料,系统地研究了粘结剂对注射成型磁体的加工性能、磁性能和力学性能等的影响。用国产的快淬钕铁硼磁粉和尼龙6粘结剂制备出了磁性能为Br:0．5158T,Hcb：321kA／m,Hcj：730kA／m,(BH)m：40kJ／m^3的注射钕铁硼磁体。     

基于微结构的柔性压力传感器设计、制备及性能

随着科技的快速发展,电子皮肤和柔性可穿戴设备由于在人体运动、健康监测、智能机器人等领域具有重要应用而引起了人们广泛的关注。传统的基于贵金属或金属氧化物半导体的压力传感器成本高、柔韧性差,而新型的基于微结构的柔性压力传感器具有灵敏度高、应变范围宽、低成本、低功耗、响应速度快等优势,在电子皮肤和柔性可穿戴设备等方面发挥重要作用,成为当前柔性电子材料与器件主要研究热点之一。本文系统总结了近年来颇受关注的基于金字塔形、微球形、微柱形、仿生结构、褶皱等不同柔性基底微结构和多孔导电聚合物材料的柔性压力传感器在材料选择、结构设计、制备方法、传感性能等方面取得的重要进展,并对柔性压力传感器的未来发展进行了展望。     

PVDF冲击压力传感器的制备和应用

PVDF（聚偏氟乙烯）及其共聚物压电计具有响应快、灵敏度高、测压范围宽等特点，是一种理想的冲击压力传感器。用它制作超高压力传感器的关键是必须解决传感器的一致性问题。本文对近年来国内外在此方面的工作进行了总结，给出了该类传感器的爆炸、高速撞击、高能脉冲激光辐照等压力测试方面的应用，并对该类传感器中存在的问题进行了归纳。     

Temperature and pressure evolution in fast heat cycle injection molding

An accurate mold temperature control during injection molding processes allows obtaining objects with better surface finishing, more accurate surface replication, and reduced frozen-in orientation. The control of these properties is particularly important when the thickness of the molded part is very small as in the case of microinjection. In this work, thin multilayer heaters are adopted to obtain a very fast mold surface temperature evolution during the process of an isotactic polypropylene (iPP). The effect of mold temperature history on the pressure developed inside the cavity is analyzed and correlated to both gate solidification and mold deformation. Results confirmed that, with a fast control of the cavity surface temperature, a reduction of the injection pressure is achieved, without affecting the cycle time. The understanding of the phenomena that occur during the fast temperature evolution on the cavity surface can allow the microstructural calibration of the molded parts.     

"Inversed" surface micelle array fabrication of an amphiphilic block copolymer on water surface

A mixed film of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with 6-{4-[(4-hexylphenyl)azo]phenoxy}hexanoic acid (6Az5COOH) were prepared on water by co-spreading method. The resulting films were transferred onto mica at various surface pressures. Atomic force microscopy (AFM) and pi-A isotherm measurements revealed that both PS and p4VP blocks in PS-b-P4VP forms spread monolayer on water with the assist of 6Az5COOH at low surface pressures. Upon compression on water, we observed that the P4VP/6Az5COOH parts in the hybrid film are collapsed selectively at an early stage and form dot array morphology. In addition, gold cluster dots were deposited selectively on the dots in the dot array film by metallization based on deposition of HAuCl4 to the P4VP chain and reduction with dimethylamino borane. These results strongly support the fact that the "inversed" surface micelles are formed on water via hybridization of PS-b-P4VP with 6Az5COOH.     

Low Li ion diffusion barrier on low-crystalline FeOOH nanosheets and high performance of energy storage

Nano Research - To obtain symmetric supercapacitors (SCs) with high energy density, it is critical to fabricate an electrode with wide potential window and excellent capacitive performance. Herein,...     

工艺特性对二维微加速度传感器性能的影响

工艺特性在很大程度上决定了MEMS器件最终的功能特性.本文针对自主设计的二维微加速度传感器,在概念设计阶段定量分析了工艺特性对传感器性能的影响,主要包括质量偏心、梁加工误差、结构对称性、非平行效应等.结果表明:质量偏心会引起角位移变化,但对主轴刚度无影响,传感器不会有输出;在现有工艺条件下,可忽略梁厚误差的影响,但需严格控制梁宽误差;各种不对称方案对传感器主轴刚度和横向灵敏度的影响程度不同,不对称方案对横向灵敏度的影响随着不对称性的加剧而增大;非平行效应使得在相同外载荷作用下敏感轴向位移减小,但静态灵敏度却有所增加.     

Preparation of low-crystalline apatite nanoparticles and their coating onto quartz substrates

We prepared low-crystalline apatite nanoparticles and coated them onto a surface of a Au/Cr-plated quartz substrate by the electrophoretic deposition (EPD) method or by using a self-assembled monolayer of 11-mercaptoundecanoic acid (SAM method). Low-crystalline apatite nanoparticles around 10?nm in size with extremely low contents of undesirable residual products were obtained by adding (NH(4))(2)HPO(4) aqueous droplets into a modified synthetic body fluid solution that contained Ca(CH(3)COO)(2). The apatite nanoparticles were successfully coated by either the EPD method or the SAM method; the nanoparticle coating achieved by the SAM method was more uniform than that achieved by the EPD method. The present SAM method is expected to be a promising technique for obtaining a quartz substrate coated with apatite nanoparticles, which can be used as a quartz crystal microbalance device.     

Effect of molding temperature on the properties of nanocomposite films based on low-density polyethylene

The influence of the molding temperature on the density and porosity of nanocomposite films based on low-density polyethylene (LDPE) filled with CdS and MnO nanoparticles has been studied. It is established that molding at temperatures of about 110°C ensures the formation of nanocomposite films with a minimum porosity, (i.e., maximum density). The results open ways to the modification of some other macroscopic parameters of LDPE-based nanocomposite films by varying the molding temperature, since the properties dependent on the material porosity include dielectric permittivity, refractive index, elastic modulus, and some other.