Fabrication tolerance of asymmetric silicon-on-insulator polarization rotators

We investigate the fabrication tolerance of novel slanted-angle silicon-on-insulator polarization rotators with asymmetric external waveguiding regions. We also minimize the input and output coupling loss between the polarization rotator and the rib waveguides through a lateral shift in the relative waveguide positions.     

图形化SOI衬底上侧向外延生长GaN研究

采用MOCVD系统,在图形化的绝缘体上硅(SOI:silicon-on-insulator)衬底上侧向外延生长了GaN薄膜。利用SEM、TEM和Raman光谱对生长的GaN薄膜的质量进行了分析研究。研究发现,在GaN的侧向外延生长区域,侧向生长的GaN能够完全合并,GaN薄膜内的残余应力减小,穿透位错密度大幅度降低。     

Fabrication and measurement of low-stress membrane mirrors for adaptive optics

We have fabricated low-stress membranes from single-crystal silicon for use as deformable mirrors in adaptive optics. These membranes have lower stress than membranes made from silicon nitride or other materials and therefore are capable of greater deformation than previously used membrane mirrors. Membranes were assembled into devices by flip chip bonding to electrode chips with either 256 or 1024 electrodes. We have characterized devices with static and dynamic tests and compared their performance with an analytical model. We tracked the evolution of strain in the membrane during the device's fabrication and assembly and identified sources of stress and strain in this process. We identified boron dopant concentration as a critical determinant of intrinsic stress in the membrane.     

Fabrication of a compact storage inductor for railguns

A liquid nitrogen-cooled, coaxial, energy storage inductor has been designed and built to be used in conjunction with a compact homopolar generator to form a high-energy-density power supply for use with electro-magnetic accelerators. The low-resistance, lightweight aluminum inductor stores 3.1 MJ at a peak current of 1.0 MA. Minimizing weight rather than size was emphasized in the design, resulting in a 1.23-m (48.5-in.) diameter by 0.91 m (36 in.) long inductor weighing 14.7 kN (3,300 lb). A coaxial design was chosen to eliminate high external magnetic fields without the necessity for shielding. External magnetic fields are undesirable because of effects on nearby components and the possibility of detection. Also, attention has been given to minimizing the partial flux linkages or internal inductance of the coil, thereby maximizing the overall transfer efficiency into a railgun. Details of the design, fabrication, and predicted performance will be presented.     

Thermal expansion uniformity of materials for large telescope mirrors

Uniformity of thermal expansion has been measured for fused quartz (Heraeus-Amersil TO8E) and borosilicate glass (Schott Duran and Ohara E6). The variation of expansion coefficient for three melts of TO8E was 5 x 10(-9)/K over a temperature range of 300 to 100 K and was found to vary linearly with position in the melt. This spatial gradient averaged 3.5 x 10(-11)/K cm. The room-temperature thermal expansivity variation of Duran (Tempax) glass was approximately 27 x 10(-9)/K, while that of E6 glass was approximately 52 x 10(-9)/K.     

Fabrication and testing of large steering mirrors for a scanning lidar

Large. inexpensive scanning mirrors for a lidar have been designed and built out of common float glass mirrors and aluminum honeycomb.The flatness of the scanning mirrors has been characterized with a modified Foucault knife-edge test.The peak-to-peak surface slope error over the entire surface of the mirrors was found to be less than 1 mrad, with slope errors of 0.15 mrad over small areas. This performance was sufficient for use of the mirrors in a scanning CO(2) lidar system that uses direct detection.     

Wave theory of high-speed cutting regimes in turning of materials

A theory of high-speed cutting regimes involved in turning of materials has been developed. According to this theory, the cut layer and the blade are considered as acoustic resonators coupled via a nonlinear contact stiffness and excited by the lowest antisymmetric Lamb mode. The turning process is described in terms of a parametric oscillatory system. Using the proposed theory, it is possible to determine optimum turning regimes.     

Study of the reflectivity of ceramic materials for laser-cavity mirrors

High power lasers for industrial applications necessitate easy handling and ability to be subjected to fast movements. Thus, small volume and weight for these devices without prejudicing their accuracy of beam-fire and their integrity during the time is required. Solid state crystal Nd: YAG lasers were consequently considered. An important aspect under high power irradiation, is the system of mirrors of the cavity that must reflect back towards the laser active crystal source a sufficient radiant energy to activate laser pumping. At the same time the material of these mirrors must not degrade in short times (in the sense of industrial applications) and be sufficiently able to dissipate the produced heat. Ceramics are obvious candidates in particular alumina ceramic. After the test concerning the reflectivity of a wide range of white materials, it was realized that alumina ceramic is up to now the better and about which current technology allows easy manufacture of these mirrors. Certain rules must be followed to prepare white alumina mirrors able to maintain for sufficiently long times their reflectivity such as sintering at suitably high temperature in reducing atmosphere using very pure corundum-like spheroidal grains, correct granulometry of the utilized powders and treatment of the surface with a specific porcelain-like glaze before firing.     

Fabrication of novel cellular-like aluminophosphate materials

The crystalline microlamellar aluminophosphates (LAP) with cellular frameworks has been fabricated through the reaction of phosphoric acid/surfactant/pseudo-boehmite in a matrix of triethylene glycol and water; biomineralization reactions occurred in the interconnecting water droplet channels; and resulting materials represented replicas of the microemulsion architecture.     

Fabrication of hard-shell microcapsules containing inorganic materials

The fabrication method of silica hard shell microcapsules containing disodium hydrogen phosphate dodecahydrate (Na₂HPO₄⋅12H₂O) has been developed. The effects of the mixing rates for the emulsification, of the volume ratios of solutions and of surfactant concentrations on the size of hollow microcapsules have been also studied. From the results, it was confirmed that silica hard shell microcapsules can contains Na₂HPO₄⋅12H₂O with the present method using hollow microcapsules. The present micro-encapsulated Na₂HPO₄⋅12H₂O was also found to cause the supercooling depression effect. As the fabricated microcapsules have no flammability, the present microcapsule was concluded to be a promising item not only for latent heat transportation media but also for the static thermal storage materials for architectural structures. From the studies on the fabrication parameters, it was concluded that the control of the surfactant concentration is effective for controlling the size of microcapsule.     

Optimization of multilayer mirrors at 13.4 nm with more than two materials

The design of multilayer mirrors with more than two materials is one of the key technologies for investigating lithography. We study a new procedure for optimizing multilayer mirrors of different combinations of materials at a wavelength of 13.4 nm. By adding Be and C layers in different orders to a Si/Mo stack, we have observed enhancement of the reflectivity and a reduction in the number of layers. The Luus-Jaakola optimization procedure has been implemented for the global optimization of the multilayer mirrors. With this algorithm it is not necessary to specify initially the number of layers present in a given design.     

Fabrication of mitigation pits for improving laser damage resistance in dielectric mirrors by femtosecond laser machining

Femtosecond laser machining is used to create mitigation pits to stabilize nanosecond laser-induced damage in multilayer dielectric mirror coatings on BK7 substrates. In this paper, we characterize features and the artifacts associated with mitigation pits and further investigate the impact of pulse energy and pulse duration on pit quality and damage resistance. Our results show that these mitigation features can double the fluence-handling capability of large-aperture optical multilayer mirror coatings and further demonstrate that femtosecond laser macromachining is a promising means for fabricating mitigation geometry in multilayer coatings to increase mirror performance under high-power laser irradiation.     

An automated compact vibromagnetometer for investigating soft magnetic materials

An automated vibration magnetometer for measuring the magnetization and hysteresis curves of soft magnetic materials at room temperature is described. The vibromagnetometer has a magnetic moment sensitivity of 5∙10^–6 Gs∙cm³, a measurement error of less than 3% and a magnetizing field strength range of up to ±200 Oe, which can be extended to ±10000 Oe using more powerful magnetic systems. Hysteresis characteristics of amorphous ferromagnetic microwire and of a printed text sign are presented.     

Fabrication of homogeneous titania/MWNT composite materials

MWNT/titania nanocomposites were prepared by an impregnation method and subsequent heat treatment at 400 °C. Precursor compounds such as titanium (IV) propoxide and titanium (IV) ethoxide were used to cover the surface of CNTs under solution conditions. Electron microscopy and X-ray diffraction techniques were carried out to characterize the as-prepared titania layers.     

压电材料的制备应用及其研究现状

从压电材料的压电效应入手,介绍了压电材料的分类及结构组成。针对不同压电材料在生产实践中的应用情况,列出现阶段压电材料的制备技术。综述了近年来压电材料的研究现状,并系统介绍了压电材料在各个领域的应用和发展。     

高纯致密的长余辉块体材料的制备方法的研究

在高温固相法的基础上,通过在900℃对原料进行预处理,成功制备出一种高纯、致密的长余辉块体材料。通过扫描电镜对其表面形态进行表征,结果表明该块体材料致密、均匀、无裂纹;并通过XRD 测试分析发现预处理后SrAl2O4 相已基本形成。     

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.     

Fabrication and characterization of rare earth hexaboride single-crystal materials

Oriented single crystals of LaB₆, CeB₆ and PrB₆ have been prepared by the arc float-zone refining technique, which is described. A critique of the various possible preparation techniques is given. Wet chemical methods were used to determine bulk stoichiometries of samples prepared from starting materials of various R/B compositions (where R = rare earth). It was found that LaB_6,09, a desired composition, could be grown in single-crystal form from LaB_6.2 starting material, the excess boron compensating for preferential boron vaporization. Starting materials with B/La < 6.2 produce a B/La gradient in two-pass zone-refined specimens. The level of metallic impurities in arc zone-refined LaB₆ is lower than that reported elsewhere for laser zone-refined LaB₆. Residual oxygen present in the zone-refined specimens was found to produce second-phase inclusions, which were studied in detail. The effect of contamination of LaB₆ surfaces by evaporated refractory metals has also been investigated.