Screening of long-wavelength laser at high temperature and high current levels

It is found that electroluminescent mode aging at high-temperature and high-current levels is useful for selecting long-lived InGaAsP 1.3 ?m lasers. Lasers selected by this screening have little change in threshold current or forward voltage through the aging test at an elevated temperature with constant light-output power.     

Diffusion of silicon in aluminum

Interdiffusion coefficients in Al-Si alloys were determined by Matano’s method in the tem-perature range from 753 to 893 K with the couple consisting of pure aluminum and an Al-Si alloy. Temperature dependence of the impurity diffusion coefficients of Si in Al, obtained by extrapolation of the concentration dependence of the interdiffusion coeffi-cient to zero mole fraction of Si, is given by the following equation: DSi/Al = (2.02^+0.97 _-0.66 × 10^-4 exp [-(136 ±3) kJ mol^-1/RT] m²/s. p ] The Kirkendall marker was found to move toward the Si-rich side, indicating that the Si atom diffuses faster than the Al atom in Al-Si alloys. From the interdiffusion coeffi-cient and the marker shift, the intrinsic diffusion coefficients were calculated. The difference in the activation energies (ΔQ) between the impurity diffusion of Si in Al and the self-diffusion of Al was estimated by means of the asymptotic oscillating po-tential and the Le Claire theory. The calculated value of ΔQ is in fair agreement with the experimental value. The vacancy-solute binding energy for Si in Al was also dis-cussed based on the diffusion data. formerly Undergraduate Student, Tohoku University     

Production of arachidonic acid by filamentous fungus, Mortierella alliacea strain YN-15

A filamentous fungus producing significant levels of arachidonic acid (AA, C20∶4n−6) was isolated from a freshwater pond sample and assigned to the species Mortierella alliacea. This strain, YN-15, accumulated AA mainly in the form of triglyceride in its mycelia. An optimized culture in 25 L of medium containing 12% glucose and 3% yeast extract yielded 46.1 g/L dry cell weight, 19.5 g/L total fatty acid, and 7.1 g/L AA by 7-d cultivation in a 50-L jar fermenter. Assimilation of soluble starch by YN-15 was notably enhanced by the addition of oleic acid, soybean oil, ammonium sulfate, or potassium phosphate to a starch-based medium. Using starch as a main carbon source in the pre-pilot scale cultivation improved the production of AA by up to 5.0 g/L. Mortierella alliacea strain YN-15 is therefore a promising fungal isolate for industrial production of AA and other polyunsaturated fatty acids.     

A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

The difference in reflow characteristics between electroplated and sputtered Cu films during high-temperature high-pressure treatment was confirmed, and the basis for this difference was analyzed. Using test element groups containing a number of via holes, it was found that electroplated Cu films had much superior embedding characteristics compared with sputtered Cu films. This was confirmed by measurements of the stress–strain curves of these Cu films, which indicated that the strength at high temperature of the electroplated films was lower than that of sputtered films. Identification of lattice defects and analysis of the microstructure of these films were carried out by positron lifetime measurements and transmission electron microscopy, respectively. The results showed that a large quantity of vacancy clusters was present in the electroplated Cu films, and this increased to a maximum after isochronal annealing at 300°C. From the results, it was shown that Cu atoms in electroplated films with a large number of vacancy clusters diffuse rapidly at around 300°C, and this rapid diffusion contributes greatly to softening of the film and a promotion in reflow behavior. This study revealed that the reflow behavior of Cu films strongly depends on the presence of vacancy clusters within it.     

Hydrogen storage and thermal conductivity properties of Mg-based materials with different structures

Mg-based hydrogen storage materials can be very promising candidates for stationary energy storage application due to the high energy density and low cost of Mg. Hydrogen storage kinetics and thermal conductivity are two important factors for the material development for this kind of application. Here we studied several types of Mg-based materials with different structure-micrometer scale Mg powders, Mg nanoparticles, single crystal Mg, nanocrystalline Mg₅₀Co₅₀ BCC alloy and Mg thin film samples. It seems the Mg materials with good kinetics usually are the ones with nanostructure and tend to show poor thermal conductivity due to electron/phonon scattering resulting from more interfaces and boundaries in nanomaterials. Based on this work, good crystallinity Mg phase incorporated in carbon nano framework could be one promising option for energy storage.     

Studies of characteristics and design of superconducting fault current limiter with adjustable trigger current level in current limiting operation

Superconducting fault current limiters (SCFCLs) are expected to improve not only reliability but also stability of power systems. To introduce an SCFCL in a power system, various specifications such as trigger current level, impedance in current limiting operation, recovery time, and so on are necessary. Fault analyses point out that accuracy of the trigger current level is necessary. Therefore, an SCFCL of a transformer type with adjustable trigger current level was proposed and manufactured. Using the trial SCFCL, adjustability of the trigger current level was confirmed. It is found that the SCFCL has good limiting and recovery characteristics. In this paper, characteristics of the SCFCL are considered from a design point of view. Most of the specifications necessary for design depend on the characteristics in current limiting operation. Therefore, the characteristics of the SCFCL in current limiting operation are discussed. It is shown that this kind of SCFCL has good property for easy design, and its design principle is summarized. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 30–38, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10054