Nitride-based laser diodes using thick n-AlGaN layers

We obtained 1 μm crack-free AlGaN layers up to an AlN molar fraction of 0.4 by growing directly on low-temperature-deposited buffer layers. The buffer layer is effective for growing AlGaN layers without the stress caused by the lattice mismatch. We also demonstrated nitride-based laser diodes with such a 1 μm crack-free n-AlGaN cladding layer/n-AlGaN contact layer/low-temperature-deposited buffer layer/sapphire structure, which showed a clear single spot in a far field pattern. The AlGaN-based structure can suppress optical leakage from the waveguide region to the underlying layer. The threshold current of the laser diode is about 230 mA, which is comparable to or better than that of our laser diodes with the conventional GaN-based structure.     

Design formula for involute profile shifted gears applied to a skew shaft gear-box

By the intermeshing of a pair of helical gears having different absolute helix angles, we can design a gear-box for non-parallel shafts. This paper presents an analytical formulation and a geometrically approximated formulation concerned with the minimum shaft distance and the skew shaft angle when involute profile shifting is applied in design. In order to approximate the calculated result of the analytically correct formulae, when using the practical formulae, the correction factors, especially important in the case of high skew shaft angle, are also provided.     

Future challenges and directions for nitride materials and lightemitters

A review is presented of future issues on wide-bandgap group-III nitride materials and device technology for optoelectronic and high-temperature devices such as LEDs     

Development of high-resolution single-ion PSD using random access memories

Using heavy-ion microbeam, we have examined the feasibility of a Static Random Memory (SRAM) as an in situ Position Sensitive Detector (PSD) with bit-cell size resolution for extremely low current ion beams. It is found that SRAMs are promising candidates for high-resolution PSD to diagnose an extremely low current ion microbeam.     

Synthetic chiral chromophoric bilayer membranes as chemical transducers: effect of alcohols on enhanced circular dichroism

A bilayer-forming synthetic lipid containing a chiral centre and a chromophoric group was investigated as a spectroscopic transducer, based on its enhanced circular dichroism (CD). The CD intensity of chiral bilayers was reduced with addition of alcohol. For ten additives tested, a linear correlation was observed between the CD spectral response to the alcohols and their partition coefficient (logP) in octanol/water system. By use of an immobilization technique, the bilayer film was obtained on a quartz plate, and a possible application as a solid-phase assay of methanol was demonstrated.     

Preparation of high-modulus and high-strength nylon-6 fibre by the zone-annealing method

In order to produce ultra-high strength fibre, a new method which was developed in our laboratory, called the zone-annealing method', has been applied to nylon-6. In spite of very simple apparatus and easy procedure, the dynamic modulus of the zone-annealed fibre was 10.8 × 10¹⁰ dyne cm^?2, which corresponds to 2.2–4.0 times that of the high-tenacity fibre available commercially. To elucidate the effectiveness of the zone-annealing process, the relationship between mechanical properties and superstructure of the fibre obtained has been investigated. It was found that the structure of the amorphous regions, especially the orientation of amorphous chains, played an important role in improving the mechanical properties. The principle and the characteristics of this method are also described in this paper.     

Thermal analysis of polyethylene prepared by γ-ray-induced polymerization in various solvents

Thermal properties of polyethylenes prepared by γ-ray-induced polymerization in various solvents were examined by differential scanning calorimetry. The solvents used were ethyl and n-butyl alcohols, tert-butyl alcohol containing 25 vol% of water, 2,2,4-trimethylpentane, 2,2,5-trimethylhexane, and cyclohexane. The dependence of the profiles of the heating curves for the produced polymers on polymerization temperature varies with the solvent type. This difference was discussed in terms of the degree of undercooling in various solvents during polymerization. In all solvent systems, the melting point and heat of fusion of the polymers decrease continuously with polymerization temperature. This decrease is caused by an increase in branches with reaction temperature. The melting point and heat of fusion are 100–124°C and 30–44 cal/g, respectively, and no superheating is observed. These facts suggest that folded chain crystals are commonly formed in these systems.     

The deterioration of mechanical properties of chloroprene rubber in various conditions

The changes of mechanical properties of chloroprene rubber, used as a jacket material for electric cables in nuclear power generating stations, were investigated under various deterioration environments. The heat resistant properties of the rubber material were measured at various temperatures using a stress relaxation method. From the view point of stress-strain behaviour and chemorheology, the addition of antioxidant and/or antirad reagent to the rubber improves the resistance to heat and/or radiation, respectively. The effects of dose-rate and surrounding atmosphere on the mechanical properties of rubber under radiation were also studied. The radiation damage of rubber was accelerated remarkably under a pressure of 90 atm of air. A vibration fatigue test under heat and radiation was also performed.     

Microstructure Development of Mechanical-Deformation-Induced Sn Whiskers

The development of the microstructure of mechanical-deformation-induced Sn whiskers on electroplated films has been examined using a focused ion beam system (FIB). The 6-μm-thick matte Sn films were compressed by using a ZrO₂ ball indenter under ambient conditions. After compression, tin whiskers and small nodules were found adjacent to, and several grains further away from, the indents. The cross-sectional microstructures of the indents and whiskers indicate that the lateral boundaries of the newly created grains caused by recrystallization are the main routes for stress relaxation.