Microstructure of multilayer interface in an Al matrix composite reinforced by TiNi fiber

A multilayer interface was formed in the Al matrix composite which was reinforced by 30% volume fraction of TiNi fiber. The composite was fabricated by pressure infiltration process and the interface between the TiNi fiber and Al matrix was investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). When the TiNi fiber was pre-oxidized in the air at 773 K for 1 h, three layers have been found and characterized in the interface: TiNi–B₂ layer near the TiNi fiber, Ti–Al compound layer with Ti and granular TiO₂ near the Al matrix, and Ti–Ni compound layer between TiNi–B₂ and Ti–Al compound layers. The effect of the multilayer interface on the mechanical properties of the composite was also discussed. The result showed that the uniaxial tensile strength of the composite at room temperature was 318 MPa, which was very close to the theoretical calculation value of 326 MPa. Moreover, the composite with good ductility exhibited a typical ductile-fracture pattern.     

Numerical modeling of the reflection coefficients for the plane sound wave reflection from a layered elastic bottom

The matrix method and its numerical realization are considered in calculating the complex reflection coefficients and refraction indices of plane sound waves for geoacoustic models of the ocean bottom in the form of homogeneous elastic (liquid) absorbing layers overlying an elastic halfspace. In calculating the reflection coefficients at high frequencies or in the presence of a large numbers of sedimentary layers, a passage from the Thomson-Haskell matrix approach to the Dunkin-Thrower computational scheme is performed. The results of test calculations are presented. With the aim of developing resonance methods for the reconstruction of the parameters of layered elastic media, the behavior of the frequency-angular dependences of the reflection coefficient are studied for various geoacoustic bottom models. The structure of the angular and frequency resonances of the reflection coefficients is revealed. The dependence of the structure (the position, width, and amplitude) of two types of resonances on the parameters of the layered bottom is considered.     

Study of the microstructure and mechanical properties of white clam shell

The microstructure and mechanical properties of white clam shell were investigated, respectively. It can be divided into horny layer, prismatic layer and nacreous layer. Crossed-lamellar structure was the microstructural characteristic. The extension direction of lamellae in prismatic layer was different from that in nacreous layer, which formed an angle on the interface between prismatic layer and nacreous layer. The phase component of three layers was CaCO₃ with crystallization morphology of aragonite, which confirmed the crossed-lamellar structural characteristic. White calm shell exhibited perfect mechanical properties. The microhardness values of three layers were 273 HV, 240 HV and 300 HV, respectively. The average values of flexure and compression strength were 110.2 MPa and 80.1 MPa, respectively. The macroscopical cracks crossed the lamellae and finally terminated within the length range of about 80 μm. It was the microstructure characteristics, the angle on the interface between prismatic and nacreous layer and the hardness diversity among the different layers that enhanced mechanical properties of white calm shell.     

Oxygen transport in La2NiO4 + δ: Assessment of surface limitations and multilayer membrane architectures

The steady-state oxygen permeation through dense La₂NiO_4 + δ ceramics, limited by both surface exchange and bulk ambipolar conduction, can be increased by deposition of porous layers onto the membrane surfaces. This makes it possible, in particular, to analyze the interfacial exchange kinetics by numerical modelling using experimental data on the oxygen fluxes and equilibrium relationships between the oxygen chemical potential, nonstoichiometry and total conductivity. The simulations showed that the role of exchange limitations increases on reducing oxygen pressure, and becomes critical at relatively large chemical potential gradients important for practical applications. The calculated oxygen diffusion coefficients in La₂NiO_4 + δ are in a good agreement with literature. In order to enhance membrane performance, the multilayer ceramics with different architecture combining dense and porous components were prepared via tape-casting and tested. The maximum oxygen fluxes were observed in the case when one dense layer, ~ 60 μm in thickness, is sandwiched between relatively thin (< 150 μm) porous layers. Whilst the permeability of such membranes is still affected by surface-exchange kinetics, increasing thickness of the porous supporting components leads to gas diffusion limitations.     

Influence of the antireflection,window, and active layers on optical properties of exponential-doping transmission-mode GaAs photocathode modules

In order to well study the influence of the thickness and doping concentration on optical properties of transmission-mode GaAs photocathode, three exponential-doping and one uniform-doping photocathode modules were prepared by molecular beam epitaxy with a structure of glass/Si₃N₄/Ga_1 ? xAl_xAs/GaAs. By use of the spectrophotometer, the optical properties were separately measured including the reflectivity and transmissivity curves. Based on thin film optical principles, the optical properties and their integral values are calculated by matrix formula for the four-layer photocathode module. The result shows that the antireflection and window layers affect the peak and valley of the optical property curves and the active layer influences the absorptivity values of the transmission-mode cathode modules. The photocathode module has high absorptivity within the response waveband when the optimal module has the Si₃N₄ antireflection layer of 0.1 μm, the Ga_1 ? xAl_xAs window layer of more than 0.4 μm, and the GaAs active layer of 1.5 μm–2 μm and low average doping concentration.     

1.55 μm silicon-based reflection-type waveguide-integrated thermo-optic 2 × 2 switch

In this work a waveguide-integrated 2 × 2 switch operating at the infrared communication wavelength of 1550 nm is proposed and theoretically discussed. The device is based on the total internal reflection (TIR) phenomenon and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapour deposition (PECVD) techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be therefore achieved at the interface by acting on the temperature. The device is integrated in a 4 μm-wide and 3 μm-thick single-mode rib waveguide. The substrate is a silicon-on-insulator (SOI) wafer with an oxide thickness of 500 nm. We calculated an output crosstalk always better than 24 dB and insertion losses as low as 3.5 dB.     

Tunable characteristics of one dimensional magnetic photonic crystal composed with single-negative materials

In this paper, we present the study of dispersion and transmittance characteristics of one dimensional magnetic photonic crystal composed by single negative indexed materials. For this structure, we have considered magnetic negative (MNG) with ? = 1 and μ < 0 and electric negative (ENG) with ? < 0 and μ = 4. We used simple transfer matrix method and Bloch's theorem for its analytical explanations. Analyzing transmittance characteristics of the proposed structure, we obtain the tunneling of certain frequency range where as the dispersion characteristic shows total forbidden for the same range for TM mode. The tunable property is found inside the band structure due to zero-?, zero-μ and magnetic behavior of the material. To identify zero-? and zero-μ of the structure, we have calculated the dispersion and the transmittance of the magnetic structure of MNG–ENG on different angles of incidence and thickness of layers.     

Stabilization of high spin FCC Fe in (Fe/Pd)n multilayers

Polycrystalline (Fe/Pd)_n multilayers are grown onto sapphire substrates at room temperature in a UHV system. The number of periods n=40 and the thickness of Pd layers of t_Pd=4 nm are kept constant, whereas the thickness of the Fe layers is varied from 1.5 to 5 nm. Structural properties are studied by in situ reflection high energy diffraction (RHEED), scanning tunnelling microscopy (STM) and ex situ by X-ray diffraction at small angles and large angles. Analyzing the experimental data using the program SUPREX we obtain interplanar distances of d_Fe=2.03±0.01 Å for an Fe layer thickness larger than about 2.5 nm as expected for (1 1 0) planes of BCC Fe. For Fe layers with thicknesses less than about 2.5 nm the interplanar distance is d_Fe=2.1±0.01 Å, which is close to the distance between (1 1 1) planes of FCC Fe with a lattice parameter of a=3.64 Å. Magnetic susceptibility measurements at temperatures between 1.5 and 300 K for (Fe/Pd)_n multilayers with FCC Fe yield a magnetic moment per Fe atom of μ=2.7±0.1 μ_B, which is about 20% larger compared to μ=2.2 μ_B for BCC Fe. We show that the occurrence of the large magnetic moment originates from FCC Fe being in the high spin (HS) state rather than from polarization effects of Pd at Fe/Pd interfaces.     

Marine environment compatible antireflection coating with nanotop layer on silicon optics

Antireflection coating on silicon optics have crucial importance in thermal device working in 3.6–4.9 μm wavelength region. When the thermal device is used in marine environment, the optics face harsh saline weather condition compared to normal field environment. This deteriorates coated optics and to improve mechanical strength of the coating, a nanotop layer on the antireflection coating has been developed. In this paper a study has been carried out to improve marine environment compatibility by employing a nanolayer on the top of antireflection coating on silicon optics. Optimac synthesis method was used to design the multilayer stack on the substrate with germanium and IR-F625 as high/low refractive index respectively and the layer number was restricted to four layers. The top nanolayer was 60 ± 2 nm thick hafnium dioxide layer developed with ion assisted deposition (End–Hall) on the optics during coating process. The deposition of multilayer coating was carried out inside the coating plant fitted with cryo pump and residual gas analyzer. The evaporation was carried out at high vacuum (2–6 × 10⁻⁶ mbar) using electron beam gun and layer thicknesses were measured with crystal monitor. The average transmission achieved was 97% in the spectral band of 3.6–4.9 μm with a hardness of 9.7 GPa on the coated optics.     

Electrical characteristics and efficiency of organic light-emitting diodes depending on hole-injection layer

In a device structure of ITO/hole-injection layer/N,N′-biphenyl-N,N′-bis-(1-naphenyl)-[1,1′-biphthyl]4,4′-diamine(NPB)/tris(8-hydroxyquinoline)aluminum(Alq₃)/Al, we investigated the effect of the hole-injection layer on the electrical characteristics and external quantum efficiency of organic light-emitting diodes. Thermal evaporation was performed to make a thickness of NPB layer with a rate of 0.5–1.0 Å/s at a base pressure of 5 × 10⁻⁶ Torr. We measured current–voltage characteristics and external quantum efficiency with a thickness variation of the hole-injection layer. CuPc and PVK buffer layers improve the performance of the device in several aspects, such as good mechanical junction, reducing the operating voltage, and energy band adjustment. Compared with devices without a hole-injection layer, we found that the optimal thickness of NPB was 20 nm in the device structure of ITO/NPB/Alq₃/Al. By using a CuPc or PVK buffer layer, the external quantum efficiencies of the devices were improved by 28.9% and 51.3%, respectively.     

Electronic structure and magnetism of Cr/Sn multilayer systems

The electronic structure and magnetism of Cr/Sn and Fe/Cr/Sn/Cr multilayer systems with monolayer Sn are studied by means of a first-principles method. The calculated hyperfine field at Sn site is significantly large (∼20 T) in Cr/Sn multilayers, while the value is remarkably diminished (∼4 T) in the case of Fe/Cr/Sn/Cr multilayers. This trend of the hyperfine field is consistent with recently reported experimental results. It is found that the hyperfine field at Sn site is determined by the spin magnetic moment at the interface Cr site. The most important feature in the electronic structure of the multilayer systems is the existence of an interface state at the Cr interface layer near the Fermi energy region.     

Multi-spectral antireflection coating on zinc sulphide simultaneously effective in visible,eye safe laser wave length and MWIR region

In recent years multi-spectral device is steadily growing popularity. Multi-spectral antireflection coating effective in visible region for sighting system, laser wavelength for ranging and MWIR region for thermal system can use common objective/receiver optics highly useful for state of art thermal instrumentation. In this paper, design and fabrication of antireflection coating simultaneously effective in visible region (450–650 nm), Eye safe laser wave length (1540 nm) and MWIR region (3.6–4.9 μm) has been reported. Comprehensive search method of design was used and the number of layers in the design was optimised with lowest evaluated merit function studied with respect to various layers. Finally eight-layer design stack was established using hafnium oxide as high index layer and silicon-di-oxide as low index coating material combination. The multilayer stack had been fabricated by using electron beam gun evaporation system in Symphony 9 vacuum coating unit. During layer deposition the substrate was irradiated with End-Hall ion gun. The evaporation was carried out in presence of oxygen and layer thicknesses were measured with crystal monitor. The result achieved for the antireflection coating was 85% average transmission from 450 to 650 nm in visible region, 95% transmission at 1540 nm and 96% average transmission from 3.6 to 4.9 μm in MWIR region.     

Attenuation of interfacial pinning enhancement in YBCO using a PrBCO buffer layer

Numerous experimental results have suggested that the J_c of YBa₂Cu₃O₇ (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa₂Cu₃O_7?δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower J_c of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (～0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface.     

Design of the chirped Mo/Si multilayer mirror with SiC capping layer in extreme ultraviolet region

The design procedures were discussed in detail for a normal incident chirped Mo/Si multilayer mirror with Group Delay Dispersion (GDD) of ?3600 as² in the wavelength region of 13–17 nm. The GDD was calculated using an analytical approach by fitting the optical constants of the coating materials in the wavelength range of 12.8–17.2 nm, respectively. The final structure of the chirped mirror was obtained by using the simplex algorithm from the initial structure obtained by the genetic algorithm based on structure generated by a random generator. After considering the interfacial roughness and layers thickness deviation, the effects on the reflectivity and the GDD were discussed. It was found that the average reflectivity decreases from 5.98% to 4.22% and the average GDD decreases from ?3561.86 as² to ?3462.03 as², the vibration of GDD were larger than that of the reflectivity. The reflectivity was affected greatly by the 9th layer and the GDD was affected greatly by the 25th layer when each layer thickness changes ±0.2 nm. Compared with the GDD, the reflectivity was affected greatly by the layer thickness error.     

Use of film thickness and Cu additive to improve (0 0 1) texture in MgO/FePtCu(C) bilayers

A multilayer structure has been proposed that demonstrates improved (0 0 1) texture for FePt-based L1₀ perpendicular media. Achieving a strong perpendicular magnetic anisotropy requires aligning the L1₀ crystallographic c-axis along the film normal. The ordered L1₀ FePt structure is tetragonal with a c/a ratio close to 0.965. This makes discriminating between the three crystallographic variants ([1 0 0], [0 1 0], and the desired [0 0 1]) difficult. Alloying FePt with Cu to reduce the c/a ratio and using a multilayer approach to keep the magnetic layers thin results in a structure with an adjustable M_rt and a strong (0 0 1) texture (rocking curve widths around 2°). This is a remarkable improvement in texture from pure FePt multilayered films or monolithic FePt(X) films. The proposed [MgO(2 nm)/Fe_50−xPt₅₀Cu_x(5 nm)]_×n structure limits grain size in the vertical (perpendicular) direction albeit not in the plane of the film. Carbon can be added to the FePtCu layer to reduce the grain size with minimal degradation of the (0 0 1) orientation.     

Interface photoluminescence of the SnO2:F/CdS:In/CdTe thin film solar cells prepared partially by the spray pyrolysis technique

CdS/CdTe solar cells were built by depositing a 200 nm layer of SnO₂:F on glass substrates by the spray pyrolysis (SP) technique, a 500 nm CdS:In layer by the same technique and a 1–1.5 μm CdTe layer by vacuum evaporation. The cells were CdCl₂ heat-treated in nitrogen atmosphere for 30 min at 350 °C. The photoluminescence (PL) spectra were measured at the CdS/CdTe interface for two cells with different values of the CdTe layer's thickness at the temperature T=60 K. A deconvolution peak fit was performed from which it is found that the peaks are characteristic of the solid solution CdS_xTe_1?x. The parabolic relation that relates the bandgap energy with the composition was used to estimate x, where x is [S]/([Te]+[S]) and [Te], [S] are the concentrations of Te and S atoms, respectively. The results show that the interface is smooth and the change of the bandgap occurs gradually. The solar cell of the thicker CdTe layer showed more interdiffusion at the CdS/CdTe interface and better photovoltaic characteristics.     

Flame propagation of nano/micron-sized aluminum particles and ice (ALICE) mixtures

Flame propagation of aluminum–ice (ALICE) mixtures is studied theoretically and experimentally. Both a mono distribution of nano aluminum particles and a bimodal distribution of nano- and micron-sized aluminum particles are considered over a pressure range of 1–10 MPa. A multi-zone theoretical framework is established to predict the burning rate and temperature distribution by solving the energy equation in each zone and matching the temperature and heat flux at the interfacial boundaries. The burning rates are measured experimentally by burning aluminum–ice strands in a constant-volume vessel. For stoichiometric ALICE mixtures with 80 nm particles, the burning rate shows a pressure dependence of r_b = aPⁿ, with an exponent of 0.33. If a portion of 80 nm particles is replaced with 5 and 20 μm particles, the burning rate is not significantly affected for a loading density up to 15–25% and decreases significantly beyond this value. The flame thickness of a bimodal-particle mixture is greater than its counterpart of a mono-dispersed particle mixture. The theoretical and experimental results support the hypothesis that the combustion of aluminum–ice mixtures is controlled by diffusion processes across the oxide layers of particles.     

Novel TMM for analyzing evanescent waves and optimized subwavelength imaging in a multilayer structure

Here, we report the best configuration for metal-dielectric multilayer structure that recently has been used for sub-wavelength imaging beyond the diffraction limit. We have used Genetic Algorithm (GA) to achieve the best optical transfer function (OTF) calculated by a novel Transfer Matrix Method (TMM) for evanescent waves, to find optimized configuration of the structure for sub-wavelength imaging. Our optimized configuration composed of Ag–GaP with 10 nm thickness for both layers and air as the surrounding medium, shows 0.05 λ imaging resolution with 83.82% contrast at 545 nm wavelength. Also, we show that in photolithographic applications if imaging and object layers are replaced by a photoresist and quartz respectively instead of air, 0.03 λ resolution can be obtained. In contrast to the other works, we have mathematically obtained a structure that exhibits better resolution in a visible wavelength in spite of thinner layers thickness by regarding fabrication difficulties.     

Layer optimization in wight organic light emitting diodes (WOLEDs) to reduce the portion of guided waves in ITO/Glass interface

In this paper, our main attempt was to reduce Total Internal Reflection (TIR) happening at Indium Tin Oxide (ITO, n_ito = 1.8 + 0.01i) and Glass (n_glass = 1.51) interface, which is due to ITO's higher index in comparison with Glass's, that makes light guided in ITO layer, 50% of generated light in Wight Organic Light Emitting Diodes (WOLED) are trapped in ITO layer; here we tried to reduce this portion of trapped light by implying 12-fold quasi-photonic crystal to the mentioned interface. With some gentle changes in 12-fold's structure we could reduce TIR in this interface to less than 9%. Also, far field results before and after adding the structure to WOLED were studied, which represents suitability of using this structure for lighting applications.     

Optimization of microcrystalline silicon thin film solar cell isolation processing parameters using ultraviolet laser

This study used ultraviolet laser to perform the microcrystalline silicon thin film solar cell isolation scribing process, and applied the Taguchi method and an L₁₈ orthogonal array to plan the experiment. The isolation scribing materials included ZnO:Al, AZO transparent conductive film with a thickness of 200 nm, microcrystalline silicon thin film at 38% crystallinity and of thickness of 500 nm, and the aluminum back contact layer with a thickness of 300 nm. The main objective was to ensure the success of isolation scribing. After laser scribing isolation, using the minimum scribing line width, the flattest trough bottom, and the minimum processing edge surface bumps as the quality characteristics, this study performed main effect analysis and applied the ANOVA (analysis of variance) theory of the Taguchi method to identify the single quality optimal parameter. It then employed the hierarchical structure of the AHP (analytic hierarchy process) theory to establish the positive contrast matrix. After consistency verification, global weight calculation, and priority sequencing, the optimal multi-attribute parameters were obtained. Finally, the experimental results were verified by a Taguchi confirmation experiment and confidence interval calculation. The minimum scribing line width of AZO (200 nm) was 45.6 μm, the minimum scribing line width of the microcrystalline silicon (at 38% crystallinity) was 50.63 μm and the minimum line width of the aluminum thin film (300 nm) was 30.96 μm. The confirmation experiment results were within the 95% confidence interval, verifying that using ultraviolet laser in the isolation scribing process for microcrystalline silicon thin film solar cell has high reproducibility.