Magnetic particles stabilized by chemically adsorbed monolayers for use in functional fluids

Chemically adsorbed monolayers were applied to magnetic particle surfaces for preparing functional fluids. Fluorocarbon silanes were used to form the monolayers, as the methoxysilyl groups of fluorocarbon silanes can form a strong chemical bond with the surface of a magnetic particle without degrading its properties. Fluorocarbon oils were used as the carrier liquid because of their high affinity with the fluorocarbon group of the monolayers, enabling the particles to disperse easily in it. Also, fluorocarbon oils can sustain high temperature and low pressure. The functional fluids prepared using these materials showed magnetorheological characteristics and can be used under high-vacuum and/or high-temperature conditions like those encountered in space.     

Diffusion of nonstoichiometric defects in n-GaP crystals

Diffusion of nonstoichiometry-related point defects from a LEC-grown GaP substrate to a Te-doped GaP n-type epitaxial layer was investigated by means of photocapacitance. It was revealed that deep donor level at E_C−2.1 eV was introduced into GaP substrate with annealing under phosphorus vapor pressure. Thus, the 2.1 eV deep level is thought to be involved with excess P atoms such as interstitial phosphorus atoms. In Te-doped crystal, 2.1 eV level was detected and the density increased as the time of substrate annealing increased. By measuring PHCAP spectra of samples with different thickness of epitaxial layer, diffusion profile of the defects from the substrate interface was obtained. From this, the diffusion coefficient at 850°C is estimated to be 8×10^–11 cm²/s.     

Monolithically integrated photonic switching device using an MSMPD, MESFETs, and a VCSEL

We have fabricated a photonic switching device that monolithically integrates a metal-semiconductor-metal photodetector, metal-semiconductor field-effect transistors, and a vertical-cavity surface-emitting laser. This device can perform both NOR- and OR-types of operation with thresholding input-output characteristics. The contrast ratio is more than 30 dB with optical gain. The device also shows a 3-dB bandwidth of 220 MHz and switching energy of 700 fJ at a 100-MHz frequency     

Low-Temperature Synthesis of High-Adhesion Cu(Mg) Alloy Films on Glass Substrates

Cu(0.5 at.%Mg) alloy films were deposited on glass substrates, and annealed at 200–400 °C in vacuum. The resistivity of the Cu(Mg) films was reduced to about 3.0 μΩcm after annealing at 200 °C for 30 min, and the tensile strength of adhesion of the Cu(Mg) films to the glass substrates was increased to 30–40 and 35–55 MPa after annealing at 250 and 300 °C, respectively. The reduction in resistivity can be explained as reduced impurity scattering and grain-boundary scattering, since Mg segregation to the film surface and Cu(Mg)/glass interface, and consequent Cu grain growth, were observed. Increased adhesion of the Cu(Mg) films to glass substrates after annealing was also explained by the strong segregation of Mg atoms, and the formation of a reaction layer at the interface. Mg atoms were observed to have reacted with the glass substrates and formed a thin crystalline MgO layer at the interface in the samples annealed at 300 °C, while Mg atoms were highly concentrated above the Cu(Mg)/glass interface without oxide formation at the interface in the samples annealed at 250 °C. Thus, the process temperature and time to obtain low-resistivity and high-adhesion Cu alloy films on glass substrates could be reduced to 250 °C and 30 min using Cu(Mg) films.     

Rutherford Backscattering Spectrometry Analysis of Self-Formed Ti-Rich Interface Layer Growth in Cu(Ti)/Low-<Emphasis Type="Italic">k</Emphasis> Samples

A new fabrication technique to prepare ultrathin barrier layers for nanoscale Cu wires was proposed in our previous studies. Ti-rich layers formed at Cu(Ti)/dielectric layer interfaces consisted of crystalline TiC or TiSi and amorphous Ti oxides. The primary control factor for the Ti-rich interface layer composition was C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds. To investigate Ti-rich interface layer growth in Cu(Ti)/dielectric layer samples annealed in ultrahigh vacuum, Rutherford backscattering spectrometry (RBS) was employed in the present study. Ti peaks were obtained only at the interfaces for all samples. Molar amounts of Ti atoms segregated to the interfaces (n) were estimated from Ti peak areas. Log n values were proportional to log t values. Slopes were similar for all samples, suggesting similar growth mechanisms. The activation energy (E) for Ti atoms reacting with the dielectric layers containing carbon (except SiO₂) tended to decrease with decreasing C concentration (decreasing k), while those for the SiO₂ layers were much higher. Reaction rate coefficients [Z · exp(−E/RT)] were insensitive to C concentration in the dielectric layers. These factors lead to the conclusion that growth of the Ti-rich interface layers is controlled by chemical reactions, represented by the Z and E values, of the Ti atoms with the dielectric layers, although there are a few diffusion processes possible.     

Numerical modeling on a reciprocating active magnetic regenerator refrigeration in room temperature

Considering the unignorable factors in practice, a new time independent, 2-dimensional porous media model of room-temperature Active Magnetic Regenerative Refrigeration (AMRR) has been proposed. The 2-D model improved the existing 1-dimensional model by introducing the influence of heat transfer effect though the regenerator wall and conduction for y-axis inside the regenerator. This study compared the previous 1-D model with the 2-D model and concluded that the system can lose 22% of cooling capacity caused by air convection and the conduction loss in y can reach to 10% of cooling capacity. It is concluded that the new model will be useful to predict the performance of room AMRR for more practical conditions.     

A multibranch exchange method for distribution loss minimization

This paper presents a multibranch exchange method for reconfiguration of distribution systems to reduce their line losses. In this method several switches are closed and opened simultaneously in each branch exchange operation to expand the search neighborhood. The switches to be closed are selected as the intermediate systems will be meshed configuration. Sequential branch opening method can be applied to open the switches to obtain the radial configuration efficiently. Test examples show the effectiveness of the proposed method in the case of double branch exchange. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 40–48, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21015     

Interfacial microstructure characterization and strength evaluation of Si3N4/Si3N4 joints with Si–Mg composite filler for high-temperature applications

Silicon-nitride (Si₃N₄) components were joined under vacuum at 1100 °C for 10 min using Si–Mg composite fillers with Mg contents (X_Mg) that ranged from 0 at.% to 59 at.%. The Si₃N₄/Si₃N₄ joints were fabricated via Si layer formation at the joint interface; the molten Si–Mg liquid was transformed into a solid Si layer after Mg-evaporation-induced isothermal solidification. The joint tensile strength at room temperature increased considerably when X_Mg exceeded the liquidus composition of 37 at.% because of the enhanced densification/thinning of the Si layer. In these cases, some Mg atoms reacted with Si₃N₄ to form a fine-grained MgSiN₂-based layer, whereas relatively large (>0.1 μm) and smaller MgO precipitates (<10 nm) were observed in the Si layer. At a high X_Mg, the MgO precipitates were arranged in a network-like structure, which improved the fracture strength of the Si layer. The joints with a high strength at room temperature were examined using a three-point bending test at 1200 °C in air and endured a maximum fracture stress of ~200 MPa, which confirmed their potential for use in oxidizing atmospheres at least 100 °C above the bonding temperature.     

A monolithically integrated smart pixel using an MSM-PD, MESFET's,and a VCSEL

We have developed a smart pixel that monolithically integrates a metal-semiconductor-metal (MSM) photodetector, metal-semiconductor field effect transistors (MESFET's), and a vertical-cavity surface-emitting laser (VCSEL). This device can perform both NOR- and OR-types of operation with a thresholding function. Optimal device parameters are obtained by using a SPICE simulation. Calculations show that the switching time is mainly limited by the CR time constant of the input stage, which consists of the MSM photodetector, the load-resistor, and the MESFET connected to the MSM photodetector. The fabricated device attained a contrast ratio of more than 30 dB with optical gain. The 3-dB bandwidth was 220 MHz and the switching energy was 700 fJ at an operation frequency of 100 MHz. We also discuss the power consumption and the packing density of the smart pixel including the VCSEL as a function of operation frequency. A MESFET that has high f_T with low bias voltage and a VCSEL that has a low threshold current while maintaining the wall-plug efficiency are necessary to obtain a higher performance device