Micro-structure and frictional characteristics of beetle’s joint

Geometric and micro-structure design, tribology properties of beetle joints were experimentally studied, which aimed to enlighten ideas for the joint design of MEMS. The observation by using SEM and microscopy suggested that beetle’s joints consist of a concave surface matched with a convex surface. The heads of the beetles, rubbing with flat glass, were tested in fresh and dried statuses and compared with sapphire ball with flat glass. Frictional coefficient of the joint material on glass was significantly lower than that of the sapphire sphere on glass. The material of the joint cuticle for convex surface is rather stiff (the elastic modulus 4.5 Gpa) and smooth. The surface is hydrophobic (the contact angle of distilled water was 88.3°). It is suggested here that the high stiffness of the joint material and hydrophobicity of the joint surface are parts of the mechanism minimizing friction in insect joints.     

Biocompatibilities of sapphire and borosilicate glass as cortical neuroprostheses

The in vivo biocompatibility of pure sapphire and borosilicate glass (BSG) implanted onto the cerebral cortex was studied via magnetic resonance imaging (MRI) and histopathology. Each implant was embedded onto the cortical surface of an adult rat brain for a total of 28 days. Rats underwent surgery with and without implants, and rats with purposely damaged cortical implant sites were also studied. Each animal was imaged via MRI before surgery as well as 10 and 28 days after the surgery. Histopathological results of animals were obtained on the 28th day to determine the specific effect on neurons. Despite the fact that sapphire has been widely used in a variety of medical implants, both MRI and histopathological results indicate that pure sapphire is not biocompatible with the cerebral cortex. On the contrary, BSG implants appear to be biocompatible with the cortical surface.     

Rubbing effect on surface morphology and thermoelectric properties of TTF-TCNQ thin films

Thin films of tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ), a typical organic material of charge transfer salts, were prepared on glass substrates by evaporation using TTF-TCNQ powder. The rubbing effect on the surface morphology and thermoelectric properties was studied. TTF-TCNQ films exhibited a bush-like disordered growth on the as-received glass substrate, whereas those on the rubbed glass substrate had extremely flat surfaces tiled with small rectangular TTF-TCNQ single crystals. Due to the ordered alignment of TTF-TCNQ tiles, improvement in the electrical conductivity and enhancement of the Seebeck coefficient were achieved.     

Aluminum thin film enhanced IR nanosecond laser-induced frontside etching of transparent materials

Laser processing of glass is of significant commercial interest for microfabrication of precision optical engineering devices. In this work, a laser ablation enhancement mechanism for microstructuring of glass materials is presented. The method consists of depositing a thin film of aluminum on the front surface of the glass material to be etched. The laser beam modifies the glass material by being incident on this front-side. The influence of ablation fluence in the nanosecond regime, in combination with the deposition of the aluminum layer of various thicknesses, is investigated by determining the ablation threshold for different glass materials including soda-lime, borosilicate, fused silica and sapphire. Experiments are performed using single laser pulse per shot in an air environment. The best enhancement in terms of threshold fluence reduction is obtained for a 16 nm thick aluminum layer where a reduction of two orders of magnitude in the ablation threshold fluence is observed for all the glass samples investigated in this work.     

Raman spectroscopy based on a single-crystal sapphire fiber

We demonstrate the advantages of using a single-crystal sapphire fiber to perform Raman spectroscopy over using a standard glass fiber. The narrow Raman peaks and the low background signal of a single-crystal sapphire fiber allow for the detection of weaker Raman signals or Raman signals much closer to the incident laser wavelength than with a standard glass fiber, which has a strong broadband Raman spectrum of its own. The Raman spectra of calcite, single-walled carbon nanotubes, and aqueous sodium carbonate solution were collected using a 50 cm long, 200 μm diameter sapphire fiber, and then they were compared with the results using a 50 cm long, 100 μm diameter glass fiber. The Raman spectrum of each tested material becomes indistinguishable due to the background Raman signal of the glass fiber but can easily be seen using the sapphire fiber, which has only a few narrow Raman peaks of its own.     

Simple fabrication of an antireflective hemispherical surface structure using a self-assembly method for the terahertz frequency range

A hemispherical surface structure was fabricated on a sapphire substrate by utilizing a self-assembly and spin-coating process for a terahertz (THz) antireflection coating. The self-assembled glass spheres and spin-coated material led to a gradual change in the effective refractive index. The aspect ratio of the hemispherical surface structure was controlled easily by adjusting the thickness of the B-staged bisbenzocyclobutene used as a coating. The reflectance of the fabricated hemispherical surface structure, having a period of 140 μm, exhibited low reflectance and low Fabry-Perot resonance in a THz spectral range from 0.1 to 1.9 THz.     

腐蚀时间对蓝宝石衬底上外延生长GaN质量的影响

使用熔融的KOH在高温下对c面蓝宝石衬底进行不同时间的腐蚀,借助扫描电镜、原子力显微镜对衬底表面进行了表征,然后利用金属有机物化学气相沉积设备在不同腐蚀时间的衬底样品上进行了GaN材料的外延生长。通过X射线衍射结果比较了两组衬底上外延材料的质量,利用原子力显微镜结果对外延层表面形貌进行了分析,最后论述了腐蚀时间的调整对蓝宝石衬底上外延生长氮化镓质量的影响机理。     

利用等厚干涉法测量玻璃弹性模量简

提出了一种基于等厚干涉原理测量玻璃弹性模量的方法。在标准平板玻璃上表面和待测平板玻璃下表面形成空气薄膜劈尖,分别测量待测平板玻璃在自然和受力两种状态下等厚干涉条纹的分布情况,从而得出玻璃弹性模量。该方法有效消除了玻璃平板表面不平整、材料内部不均匀和自身重力等因素对测量结果的影响。干涉条纹的分布信息通过CCD图像采集及计算机处理获得。该方法原理简单,设备常见,测量精度高,适用于实验教学,也可用于科研测量。     

Silver Nanocube Aggregates in Cylindrical Pores for Higher Refractive Index Plasmonic Sensing

We report on silver nanocubes (AgNCs) infiltrated into cylindrical nanopores of porous alumina membranes (PAM) with an outstanding chemical sensitivity based on refractive index sensing (RIS) measurements. Numerical simulations performed using the finite‐difference time‐domain (FDTD) method suggested that the enhanced sensitivity is based mainly on the inter‐pore coupling plasmonic effect. This effect is related to plasmonic amplification based on localized surface plasmon resonance (LSPR) coupling between AgNCs located at the pore walls of neighboring cylindrical pores and separated by a nanoscale wall. Results are discussed for different aggregation scenarios ranging from individual nanocubes through pentamers on a flat glass surface, a flat alumina surface, and a concave local shape representing the experimental conditions. An experimental RIS sensitivity of about 770 nm per refractive index unit was found to be more than an order of magnitude higher for silver nanocube aggregates within cylindrical pores than that observed for ordinary planar substrates.     

循环载荷下粘接接头真空性能的实验研究

粘接接头在经历反复冷却、复温后能否保持良好的真空密封性,是决定无磁杜瓦耐用性的一个重要因素。该文实验研究了循环载荷对粘接接头气密性的影响。用MTS 810材料试验机对玻璃钢管状粘接试样施加循环载荷,并用动态真空法测量试样真空度的变化。结果一半试样的真空度随循环次数的增加而降低,而其余试样破坏前真空度变化不大。因此,无磁杜瓦在使用过程中反复冷却及复温所产生的循环应力载荷,是导致其真空性能下降的一个重要原因。     

Vacuum-deposited, nonpolymeric flexible organic light-emitting devices

We demonstrate mechanically flexible, organic light-emitting devices (OLED's) based on the nonpolymetric thin-film materials tris-(8-hydroxyquinoline) aluminum (Alq(3)) and N, N(?) -diphenyl- N, N(?) -bis(3-methylphenyl)1- 1(?) biphenyl-4, 4(?) diamine (TPD). The single heterostructure is vacuum deposited upon a transparent, lightweight, thin plastic substrate precoated with a transparent, conducting indium tin oxide thin film. The flexible OLED performance is comparable with that of conventional OLED's deposited upon glass substrates and does not deteriorate after repeated bending. The large-area (~1 - cm>(2)) devices can be bent without failure even after a permanent fold occurs if they are on the convex substrate surface or over a bend radius of ~0.5>cm if they are on the concave surface. Such devices are useful for ultralightweight, flexible, and comfortable full-color flat panel displays.     

航天器表面环境散射返回流TPMC模拟

介绍试验粒子Monte Carlo(test particle Monte Carlo,TPMC)方法,并采用该方法对4种航天器表面出气分子形成的环境散射返回流进行数值模拟.其中,圆球出气表面的计算结果与已有的DSMC(direct simulation Monte Carlo)结果一致,验证了方法的正确性.此外,对不同出气和来流条件下圆形平板、凸半球和凹半球3种航天器简化表面出气分子形成的环境散射返回流进行计算,结果表明:出气表面外形是影响返回通量比的一个重要因素;圆形平板和凹半球出气表面的返回通量比远大于凸半球表面的;凹半球表面的出气分子会直接和出气表面碰撞形成直接流污染,且其量级远大于返回流污染.因此,在航天器设计中尽可能使用凸形表面作为敏感的出气表面可以有效降低出气分子污染.     

A three-level non-deterministic modeling methodology for the NVH behavior of rubber connections

Complex built-up structures such as vehicles have a variety of joint types, such as spot-welds, bolted joints, rubber joints, etc. Rubber joints highly contribute to the nonlinear level of the structure and are a major source of uncertainties and variability. In the general framework of developing engineering tools for virtual prototyping and product refinement, the modeling of the NVH behavior of rubber joints involve the computational burden of including a detailed nonlinear model of the joint and the uncertainties and variability typical of that joint in a full-scale system model. However, in an engineering design phase the knowledge on the joint rubber material properties is typically poor, and the working conditions a rubber joint will experience are generally not known in detail. This lack of knowledge often do not justify the computational burden and the modeling effort of including detailed nonlinear models of the joint in a full-scale system model.Driven by these issues a non-deterministic numerical methodology based on a three-level modeling approach is being developed. The methodology aims at evaluating directly in the frequency domain the sensitivity of the NVH behavior of a full-scale system model to the rubber joint material properties when nonlinear visco-elastic rubber material behavior is considered. Rather than including directly in the model a representation of the rubber nonlinear visco-elastic behavior, the methodology proposes to model the material nonlinear visco-elastic behavior by using a linear visco-elastic material model defined in an interval sense, from which the scatter on the full-scale system NVH response is evaluated. Furthermore the development of a multi-level solution scheme allows to reduce the computational burden introduced by the non-deterministic approach by allowing the definition of an equivalent linear interval parametric rubber joint model, ready to be assembled in a full-scale system model at a reasonable computational cost.By using a commercial finite element code the developed methodology is illustrated through a numerical case-study: the low-frequency dynamic analysis of automotive door weather-strip seals.     

Electrical conductivity of glass and sapphire cells exposed to dry cesium vapor

We demonstrate that the walls of glass cells become electrically conductive when exposed to a dry cesium vapor, glasses of different compositions leading to similar effects. We find dramatically different results for monocrystalline sapphire cells, which exhibit typical resistances of a few GΩ, nearly five orders of magnitude larger than glass cells in similar conditions. In spectroscopy experiments requiring the application of an electric field, low cell resistances imply leakage currents generating stray magnetic fields. The latter, at the origin of harmful effects in precise tests of the fundamental laws of physics performed in cesium cells, will thus be suppressed in sapphire cells. Moreover, with such cells it becomes possible to place the electrodes outside. A tentative interpretation of the surface electrical conductivity of glass cells is propounded by establishing a connection with the surface coverage by cesium atoms physically adsorbed on the glass surface. This results from the observed dependences of the cell conductance versus Cs vapor density in the mtorr range and versus the wall temperature up to 200 °C, which indicates an activation energy of 0.66±0.05 eV. In the sapphire cell, where there is no hint of surface effects, the conductivity looks instead attributable to collisional processes occuring inside the vapor for Cs number densities ≳10¹⁴ at/ cm³. Received: 4 November 1998 / Published online: 7 April 1999     

Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.     

平凸型氮化硅球面微透镜的研究

介绍了用激光化学汽相沉积球面微透镜的技术，首先对激光化学汽相沉积法获得球面微透镜进行了理论分析，并用计算机分析了在一定沉积技术下的微透镜厚度剖面形状及光学聚集特性。其后介绍了激光化学汽相沉积的实验装置，用该装置在平面石英玻璃衬底上，制出了平凸型氮化硅球面微透镜，并对其参量进行了测量。     

Single Telephoto Lens for Focus Error Detection with Astigmatic Method

An astigmatic method for focus error detection has been integrated into a singlet. The first convex and the second concave surfaces compose a telephoto system with a telephoto ratio of about 0.4. The first surface of the lens is rotationally symmetrical asphere and the second surface is a toric shape whose aspherical profiles correct spherical aberration. We implemented our optical design using a molded glass process. Its performance was confirmed using the optical head of a magneto-optical disk system.     

Substrate-assisted laser patterning of indium tin oxide thin films

Maskless laser patterning of indium tin oxide (ITO) thin films was studied by the use of a diode-pumped Q-switched Nd:YLF laser. The ITO films were sputter-deposited either on lime glass, the standard substrate material for flat panel display applications, or fused quartz so that the efficiency of laser patterning as a function of substrate absorption could be studied. The laser wavelength was varied among infrared (5=1047 nm), visible (5=523 nm), and ultraviolet (5=349 nm and 5=262 nm). It is observed that strong light absorption by the substrate is a crucial requirement for a residue-free patterning of the ITO film. Observations and numerical calculations of the laser-induced surface temperature indicate that material removal occurs via thermal vaporization and that other mechanisms such as photochemical decomposition or spallation can be neglected.     

Sapphire surface patterning using femtosecond laser micromachining

This study presents an alternative method for micron-resolution patterning of a sapphire surface utilizing the characteristic of an ultra-short pulse (10^?15 s) from ytterbium (Yb) femtosecond laser (FS-laser) irradiation. Conventional processes often involve several steps, such as wet chemical or dry etching, for surface structuring of sapphire. In this study, two-dimensional array patterns on the sapphire surface with an area of 5×5 mm² and a depth of 1.2±0.1 μm can be directly and easily fabricated by a single step of the FS-laser process, which involves 350-fs laser pulses with a wavelength of 517 nm at a repetition rate of 100 kHz. The measured ablation depths on the sapphire surface display that the proposed process can be under well-controlled conditions. Based on the design changes for being quickly implemented in the micromachining process, a FS laser can be a promising and competitive tool for patterning sapphire with an acceptable quality for industrial usage.     

Photoluminescence of ZnO films prepared by r.f. sputtering on different substrates

Polycrystalline ZnO films with good orientation were deposited on sapphire, quartz, Si and 7059 glass substrates by r.f. magnetron sputtering. A strong UV photoluminescence (PL) peak (located at 356 nm) and a weak blue emission peak (located at 446 nm) were observed at room temperature (RT) for the films deposited on sapphire, quartz and Si substrates when excited with 270 nm light. For the films prepared on Corning 7059 glass, only a strong 446 nm blue emission peak was found, and the PL intensity decreased with increasing oxygen pressure during films deposition. The intensity of the UV emission increased 7 and 14 times, respectively, for the films on sapphire and quartz substrates after high temperature annealing in vacuum. The UV emission originates from the inter-band transition of electrons and the blue emission is due to transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.