Three-layer Structures Research Articles

Residual stresses generated during joining of dissimilar alumina–zirconia composites by plastic deformation and its implications on mechanical properties

Ceramic bars of zirconia toughened–alumina composites were fabricated by pressureless sintering in air at 1450 °C for 4 h. Composite samples were fabricated with two different compositions: zirconia with 60 vol.% alumina (ZT60A) and zirconia with 40 vol.% alumina (ZT40A). Average four-point-bend strengths for the ZT40A and ZT60A were 480 ± 45 MPa and 410 ± 120 MPa, respectively. Three-layered sandwich structures were fabricated by joining two bars of sintered ZT60A with a sintered ZT40A bar. High-temperature plastic joining was accomplished at 1350 °C at a strain rate of 5 × 10 −6 s −1 and a compressive stress ranging from 30–40 MPa. Bend tests conducted on the layered structure exhibited average strengths of 707 ± 81 MPa. Strength enhancements for the multilayered structure were higher than those predicted by stress analysis. Stress enhancements were compared with the residual stresses measured in the layered sample using X-ray micro-diffraction at the Advance Photon Source (APS). Scanning electron microscopy (SEM) was also conducted to identify the location of failure causing flaws.

Critical temperature of a ferromagnet/superconductor structures in a parallel magnetic field

Two- and three-layered structures consisting of ferromagnetic metal (F) film and superconductor (S) film are considered in the magnetic field H applied parallel to the plane of the F/S interface. Magnetic-penetration depth is presumed much greater than thicknesses of layers. Assuming that both S and F layers are dirty the boundary problem for the Usadel function is solved taking account of so called "Umklapp processes" for momenta of superconducting pairs on the F/S interface. It is shown that the field H can significantly alter a functional form of the dependence of critical temperature Tc versus thickness of the F layer df. Keeping in mind the possible applications like the superonducting spin-valve the behavior of Tc(df) for the F/S/F trilayer in the magnetic field is investigated.

Effects of optical variables in immersion lens-based near-field optics

We analyze the effects of optical variables, such as illumination state, focal position variation, near-field air-gap height, and refractive index mismatch, in immersion lens-based near-field optics on the resultant field propagation characteristics, including spot size, focal depth, and aberrations. First, to investigate the general behaviors of various incident polarization states, focused fields near the focal planes in simple two- or three-layered media structures are calculated under considerations of refractive index mismatch, geometric focal position variations, and air-gap height in a multi-layered medium. Notably, for solid immersion near-field optics, although purely TM polarized illumination generates a stronger and 15% smaller beam spot size in the focal region than in the case of circularly polarized incident light, the intensity of the focused field decreases sharply from the interface between air and the third medium. For the same optical configurations, we show that changes in geometric focal position to the recording or detecting medium increases focal depth. Finally, through focused field analysis on a ROM (read-only memory) and a RW (rewritable) medium, compound effects of considered variables are discussed. The resultant field propagation behaviors described in this study may be applicable to the design of either highly efficient reflection or transmission near-field optics for immersion lens based information storage, microscopy and lithographic devices.

A highly symmetric two-handed metamaterial spontaneously matching the wave impedance

We demonstrate a two-handed metamaterial (THM), composed of highly symmetric three-layered structures operated at normal incidence. Not only does the THM exhibit two distinct allowed bands with right-handed and left-handed electromagnetic responses, but posses a further advantage of being independent to the polarizations of external excitations. In addition, the THM automatically matches the wave impedance in free space, leading to maximum transmittances about 0.8 dB in the left-handed band and almost 0 dB in the right-handed band, respectively. Such a THM can be employed for diverse electromagnetic devices including dual-band bandpass filters, ultra-wide bandpass filters and superlenses.

Single-pulse excimer laser nanostructuring of silicon: A heat transfer problem and surface morphology

We present computer modeling along with experimental data on the formation of sharp conical tips on silicon-based three-layer structures that consist of a single-crystal Si layer on a 1 μm layer of silica on a bulk Si substrate. The upper Si layers with thicknesses in the range of 0.8−4.1 μm were irradiated by single pulses from a KrF excimer laser focused onto a spot several micrometers in diameter. The computer simulation includes two-dimensional time-dependent heat transfer and phase transformations in Si films that result from the laser irradiation (the Stefan problem). After the laser pulse, the molten material self-cools and resolidifies, forming a sharp conical structure, the height of which can exceed 1 μm depending on the irradiation conditions. We also performed computer simulations for experiments involving single-pulse irradiation of bulk silicon, reported by other groups. We discuss conditions under which different types of structures (cones versus hollows) emerge. We confirm a correlation between the presence of the lateral resolidification condition after the laser pulse and the presence of conical structures on a solidified surface.

A mobile information management system used in textile enterprises

The mobile information management system (MIMS) for textile enterprises is based on Microsoft Visual Studios. NET2003 Server, Microsoft SQL Server 2000, C++ language and wireless application protocol (WAP) and wireless markup language (WML) technology. The portable MIMS is composed of three-layer structures, i.e. showing layer; operating layer; and data visiting layer corresponding to the port-link module; processing module; and database module. By using the MIMS, not only the information exchanges become more convenient and easier, but also the compatible between the giant information capacity and a micro-cell phone and functional expansion nature in operating and designing can be realized by means of build-in units. The development of MIMS is suitable for the utilization in textile enterprises.

Spectroscopic investigation of homoepitaxial CVD diamond for detection applications

Three-layer structures consisting of intrinsic/B-doped homoepitaxial CVD diamond grown onto commercial HPHT Ib substrates have been studied by means of Raman spectroscopy and photoluminescence (PL). The intrinsic layers have been deposited, at fixed methane to hydrogen ratio (1%), by systematically changing the substrate temperature (620–820 °C). Raman measurements point out the excellent crystalline quality and phase purity of the samples. Moreover, flat PL spectra in a wide energy range (1.7 eV–2.7 eV) indicate also their great purity. As the free-exciton recombination can be used to further probe the quality of synthetic diamond, measurements of free-exciton emission at room temperature have been also performed. The excitation was produced by a 5 ns pulsed tunable laser irradiation. The results have been compared with the detection characteristics of simple alpha-particle detector prototypes based on the analyzed samples. A clear correlation between excitonic emission and detector sensitivity is demonstrated. On the basis of these results, low methane concentrations (approx. 1% CH 4/H 2) in the deposition gas mixture and intermediate substrate temperatures (approx. 720 °C–770 °C) have been identified as the best working conditions of our growth reactor.

三层不对称人工电磁材料界面处表面等离子体激元的理论研究

三层不对称人工电磁材料界面处表面等离子体激元的理论研究

Modeling and Simulation of Thermal NDT of Three-layered Structures by Finite Element Method

Modeling and computer simulation of thermal nondestructive testing (TNDT) of three-layered structures are studied based on the finite element method (FEM).The TNDT mathematical model of three-layered structures is constructed in cylindrical coordinates,and the application of FEM to solving transient heat conduction problems in the cylindrical geometry is discussed.The evolutions of TNDT informative parameters versus defect size and depth are simulated by using the FEM analysis software ANSYS. The basic relationships between defect parameters,such as radius and depth,and chosen informative parameters,such as maximum differential temperature and maximum running contrast,are thoroughly explored to obtain some simple regression expressions.It is shown that,at a fixed defect depth,maximum differential temperature is directly proportional to defect radius,and maximum running contrast is linear to defect radius.However,if defect radius is fixed,both informative parameters become non-linear functions of defect depth.It is believed that obtained results may help engineers in developing a TNDT strategy for aviation bonded aluminum panels.

Design of Three-layer Circular Mushroom-like EBG Structures

In this paper two types of three-layer mushroom-like electromagnetic band-gap (EBG) surfaces with circular patches are investigated. One of them consists of a square array of circular patches and the other one consists of a triangular array of circular patches in upper and lower layers. Guidelines for designing a ground plane for low proflle antenna applications are presented using the re∞ection phase characteristics. The efiect of some parameters of the three-layer structures on the re∞ection phase characteristic is studied. The frequency band in which a wire antenna adjacent to the three-layer EBG surface has good matching is determined by investigating the re∞ection phase characteristics of the EBG ground plane.

White luminescence from silica glass containing red/green/blue luminescent nanocrystalline silicon particles

Silica glasses containing blue/green/red luminescent nanocrystalline silicon (nc-Si) particles that consist of monolayer and/or three-layer structures were fabricated by a radio-frequency sputtering technique and postannealing treatment. These silica glasses showed very broad luminescence spectra with a peak at 460 nm (blue light), 550 nm (green light), and 800 nm (red light). When these samples were irradiated by using a xenon lamp with an optical bandpass filter of 313 nm, the luminescence colors from these silica glasses were a white light. The white luminescence of the sample with the three-layer structure exhibited the high luminance value of 1.5 cd/m2. This value was ascribed to the adjustment of sizes and densities of blue/green/red luminescent nc-Si particles, and the lowering of densities of Pb centers (nonradiative recombination centers) at the nc-Si particle/silica glass interface layer.

Thickness effect on the formation of SiC nanoparticles in sandwiched Si/C/Si and C/Si multilayers

The effect of carbon (C) and amorphous silicon (a–Si) thicknesses on the formation of SiC nanoparticles (np–SiC) in sandwiched Si/C/Si and C/Si multilayers on Si(100) substrates were investigated using ultra-high-vacuum ion beam sputtering system and vacuum thermal annealing at 500, 700, 900 °C for 1.0 h. Three-layer a–Si/C/a–Si structures with thicknesses of 50/200/50 nm and 75/150/75 nm and a two-layer C/a–Si structure of 200/50 nm were examined in this study. The size and density of np–SiC were strongly influenced by the annealing temperature, a–Si thickness and layer number. Many np–SiC appeared at 900 °C at a density order about 10 8 cm − 2 in both three-layer structures while no particles formed in the two-layer structure. The thick a–Si structure (75/150/75 nm) produces a particle density approximately 1.8 times higher than thin structure (50/200/50 nm). This implies that thick a–Si structure had a lower activation energy of SiC formation compared to the thin a–Si structure. Few particles were found at 700 °C and no particles at 500 °C in both three-layer structures. The np–SiC formation is a thermally activated reaction. The higher temperature leads to higher particle density. A mechanism of np–SiC formation in thermodynamic and kinetic viewpoints is proposed.

Resonance magnetoelectric effects in magnetostrictive-piezoelectric three-layer structures

A theory is discussed for magnetoelectric (ME) interactions at electromechanical resonance in a heterogeneous ferromagnetic-piezoelectric three-layer structure. An expression has been obtained for the transverse ME coefficients αE,T as a function of interface coupling β between the layers. For 0<β<1, the theory predicts resonance enhancement of αE,T at two interrelated radial modes. As β is increased from 0, the low-frequency resonance occurs at progressively increasing frequency until it merges with the high-frequency mode when β=1. These predictions are in general agreement with representative data for a permendur-PZT-permendur trilayer composite.

Growth of stacked heterostructures of SIS-type with S = YBCO orBSCCO and I = (Ba,Ca)CuO2 or (Sr,Ca)CuO2

We investigated MOCVD growth ofc-axis two-layer and three-layer stacked heterostructures on(100)SrTiO3 of SI, IS or SIS type. S denotes high temperature superconductor thin films ofYBa2Cu3O7 (Y-123),Bi2Sr2Ca2Cu3O10 (Bi-2223)or Bi2Sr2CaCu2O8 (Bi-2212), while I stands for insulating thin films of(Ba,Ca)CuO2 or(Sr,Ca)CuO2. X-ray diffraction, atomic force microscopy and measurements of resistivity versustemperature were performed after the deposition of each layer. The best results,suitable for further device fabrication, were obtained for the SIS structure(100)SrTiO3/Bi- 2223/(Sr,Ca)CuO2/Bi- 2212. Similarstructures with I = (Ba,Ca)CuO2 have shown higher impurity phases and lower superconducting quality of the topsuperconducting layer. For two-layer or three-layer structures, Bi-2223 as a top layercould not be obtained and, instead, a phase with Bi-2212 formed. Structures with(100)SrTiO3/Y- 123/(Sr,Ca)CuO2/Y- 123 or(100)SrTiO3/Y- 123/(Ba,Ca)CuO2/Y- 123 were also promising, but a current leak often occurred due to greater roughness. Structureswith Y-123 are less sensitive to growth temperature than those with BSCCO.

Analysis of a model of minority charge-carrier distributions generated in a three-layer semiconductor structure by a wide electron beam

Based on the use of a model of independent sources, a method is described for the calculation of minority-charge-carrier distributions generated in three-layer planar semiconductor structures by a wide electron beam with energy typical of electron probe devices (5–30 keV). It is shown that, in limiting cases, equations describing these distributions agree with the data obtained previously for a two-layer semiconductor structure.

Determining adhesion and hermeticity of the interface between encapsulation polymer and insulating layer of micro-sensing chips via a capacitance–voltage technique

The successful application of micro-sensing chips based on ion-sensitive field effect transistor principles depends on preventing the penetration of electrolyte into the interface between the encapsulation polymer and the insulating layer. This study employs a capacitance–voltage (C–V) technique to evaluate the adhesion and hermeticity of the polymer-substrate interface in a liquid environment. Three-layered structures simulating micro-sensing chips were fabricated for the evaluation. Each three-layered structure comprises an upper epoxy layer (with or without a window opening), a middle dielectric layer, and a lower Si wafer substrate. Equivalent circuits were established to explain the C–V characteristics of the three-layered structures. The results show that by applying the C–V technique and using an appropriate equivalent circuit, the adhesion and hermeticity between the encapsulating epoxy layer and the insulating layer can be evaluated.

An RBF Network With OLS and EPSO Algorithms for Real-Time Power Dispatch

This paper proposes a novel technique that combines orthogonal least-squares (OLS) and enhanced particle swarm optimization (EPSO) algorithms to construct the radial basis function (RBF) network for real-time power dispatch (RTPD). The goals considered are fuel cost, power wheeling cost, and NOx/CO2 emissions. The RBF network is composed of three-layer structures, which contain the input, hidden, and output layer. To simplify the network, the OLS algorithm is used first to determine the number of centers in the hidden layer. With an appropriate network structure, the EPSO algorithm is then used to tune the parameters in the network, including the dilation and translation of RBF centers and the weights between the hidden and output layer. The proposed approach has been tested on the IEEE 30-bus six-generator and practical Taiwan Power Company (Taipower) systems. Testing results indicate that the proposed approach can make a quick response and yield accurate RTPD solutions as soon as the inputs are given. Comparisons of learning performance are made to the existing artificial neural network (ANN), conventional RBF network, and basic particle swarm optimization (PSO) methods

Response function calculation and sensitivity comparison analysis of various bimorph deformable mirrors

Analysis of the response function for various possible bimorph-type deformable mirrors is presented by numerical calculation. Using this response function, sensitivity comparison of a five-layer bimorph with two-and three-layer structures is carried out. It is shown that the displacement of a bimorph deformable mirror surface reduces when the number of layers increases, and the displacement is closely related to the distance of the control layer from the median plane. The farther electrode contributes the larger deformation on the surface. Furthermore, for a fixed position of the control layer, the displacement is directly proportional to the loading voltage and inversely proportional to the square of the thickness of the PZT layer, and it increases about 1.4 times when the area of the electrode doubles.

Filling Empty Seats: How Status and Organizational Hierarchies Affect Exploration Versus Exploitation in Team Design

Informal and formal mechanisms affect choices between exploitation and exploration in team design. We argue that the status differentiation of team members and differences in organizational structure limit exploration in the form of introducing newcomers to teams and creating new combinations of team members. High- and low-status team members and one- and three-layer organizational structures were expected to be positively related to exploration, and middle-status team members and two-layer structures were expected to be negatively related to it. We used data on 6,446 motion pictures produced by the Hollywood film industry in the period 1929-58 to test our hypotheses.

Thermal deflections in multilayer microstructures and athermalization

Exact and approximate analytical solutions are developed for calculating the thermally induced deformation of three-layer cantilever structures. The solution is derived from the closed-form solutions for multilayer films. Thermal deformation and athermalization conditions are derived using dimensionless parameters for film to substrate thickness ratios for three-layer structures. The analytical solution for a narrow beam is applied to a scan mirror plate suspended with two torsional flexures. The results agreed well with finite element method simulations and experiments. Tests are performed using a bulk-micromachined silicon microelectromechanical system scanner that has a thin gold (Au) coil layer on one side and an aluminum (Al) mirror layer on the other side. Useful figures using film-to-substrate thickness ratios and the material independent normalized parameters are introduced for easy thermal deformation computations and performance trades for three-layer structures.