Junichi Nakano

MOVPE growth of strained InAsP/InGaAsP quantum-well structures for low-threshold 1.3-/spl mu/m lasers

Device-quality strained InAsP/InGaAsP multiple-quantum-well (MQW) structures are successfully grown using the low-pressure metalorganic vapor phase epitaxy method. The grown MQW structures are characterized using X-ray, photoluminescence, and photocurrent measurements that confirm that their structural and optical qualities are high enough for practical device applications, as well as that the InAsP/InGaAsP heterostructures have a large conduction-band offset. The grown wafers are processed into 40-/spl mu/m-wide stripe-ridge waveguide lasers. Threshold current densities as low as 88 A/cm/sup 2/ are achieved for a graded-index separate-confinement heterostructure (GRIN-SCH) single-quantum-well laser diode. Buried heterostructure laser diodes fabricated from GRIN-SCH 4-well strained MQW wafers have threshold currents as low as 1.05 mA at 26/spl deg/C and 7.2 mA at 106/spl deg/C. >

Top-seeded flux growth of LiNdP4O12 single crystals

LiNdP4O12 single crystals were grown by top-seeded pulling technique using LiPO3 as flux. Using a compact pulling apparatus, growth conditions for preparing large and high quality LiNdP4O12 single crystals were examined. Among the three crystallographic principal axes, the [001]-axis was most favorable as the pulling direction. It was found that the flat growing solid-liquid interface of the (001) endface was important for growing crystals free from inclusions. Optically transparent crystals up to 20 mm in diameter and 40 mm in length were obtained. Crystal quality was investigated by polarizing microscopy, X-ray topography and etching. These studies showed that the crystallographic and optical qualities of the pulled crystals were excellent.

Improvement of the oxidation resistance of a graphite material by compositionally gradient SiC/C layer

Abstract For the improvement of the oxidation resistance of a graphite material, a preparation study of compositionally gradient SiC/C layer was performed. The compositionally gradient material of SiC/C, which is a graphite material with compositionally gradient SiC/C layer, was produced by a combination of the reaction between gaseous SiO and graphite and chemical vapour deposited SiC coating. The compositionally gradient material showed the same excellent oxidation resistance as the SiC coated graphite material at high temperatures in air. Against severe thermal cycle, furthermore, the compositionally gradient material exhibited more stable characteristic compared with the SiC coated graphite.

Strained-layer InGaAs/InGaAsP MQW structures and their application to 1.67 μm lasers grown by metalorganic vapor phase epitaxy

Abstract Strained multiple quantum well (MQW) structures are grown by low pressure metalorganic vapor phase epitaxy. The strained MQWs are characterized by double-crystal X-ray diffraction and photoluminescence measurements. Close agreement with theoretical calculations clearly indicates the perfection of the strained MQWs. Buried-heterostructure laser diodes are fabricated to evaluate the strained MQW structures in a practical application. High-power, high-efficiency operation up to 61 mW is achieved at a lasing wavelength of 1.67 μm.

Flux growth of LiNdP4O12 single crystals

Abstract LiNdP 4 O 12 single crystals were grown by slow-cooling a Li 2 OP 2 O 5 flux. Crystal morphology and macroscopic crystal quality depend on the solution composition in the ternary system Li 2 ONd 2 O 3 P 2 O 5 . Under the favorable growth conditions, platy crystals of 15 × 10 × 1 mm 3 were obtained.

Characterization of 316L(N)-IG SS joint produced by hot isostatic pressing technique

Abstract Type 316L(N) stainless steel of the international thermonuclear experimental reactor grade (316L(N)-IG SS) is being considered for the first wall/blanket module. Hot isostatic pressing (HIP) technique is expected for the fabrication of the module. To evaluate the integrity and susceptibility to stress corrosion cracking (SCC) of HIPed 316L(N)-IG SS, tensile tests in vacuum and slow strain rate tests in high temperature water were performed. Specimen with the HIPed joint had similar tensile properties to specimens of 316L(N)-IG SS, and did not show susceptibility to SCC in oxygenated water at 423 K. Thermally sensitized specimen was low susceptible to SCC even in the creviced condition. It is concluded that the tensile properties of HIPed SS are as high as those of the base alloy and the HIP process caused no deleterious effects.

Evaluation of in-pile and out-of-pile stress relaxation in 316L stainless steel under uniaxial loading

Abstract Stress relaxation of tensile type specimens under fast neutron irradiation at 288 °C has been studied for 316L stainless steel (SS) in the Japan Materials Testing Reactor. In-pile stress-relaxation tests were carried out at fast neutron fluence levels of 1.3×10 24 , 5.5×10 24 and 1.5×10 25 n/m 2 ( E >1 MeV). These tests were carried out at the applied total strain levels of 0.06%, 0.1%, 0.3% and 0.75%. In order to evaluate the thermal stress-relaxation behavior and to distinguish it from the irradiation induced stress-relaxation behavior, out-of-pile stress-relaxation tests were also performed at 288 °C in air using an electric furnace. This paper describes results of in-pile and out-of-pile stress-relaxation tests on 316L SS tensile specimens. These results are compared with the literature data by Foster et al. [J. Nucl. Mater. 252 (1998) 89] which were mainly obtained from bend beam specimens. Moreover, these experimental results are compared with analytical results obtained using Nagakawas model [J. Nucl. Mater. 212–215 (1994) 541].

Evaluation of cyclic oxidation behavior of SiC/C compositionally gradient graphite materials

Abstract For the characteristic evaluation of developed compositionally gradient graphite materials, which are composed of a surface SiC coating layer, an intermediate SiC/C layer and a graphite matrix, a thermal cyclic oxidation test in air environment was carried out together with two kinds of the SiC coated graphite materials. It was clarified that the developed materials exhibited high performance under severe thermal cyclic conditions independent of the SiC contents in the intermediate SiC/C layers and had a longer cycle margin from crack initiation to failure of the surface SiC coating layer compared with both SiC coated graphite materials.

Ablation of work hardening layers against stress corrosion cracking of stainless steel by repetitive femtosecond laser pulses

Femtosecond laser pulses successfully ablated the work hardening layers on SUS316L used in boiling water reactors. The measurement of hardness inside the material clarified this new technique to reduce the risk of Stress Corrosion Cracking.

Thermal diffusivity measurement for SiC/C compositionally graded graphite materials

Thermal diffusivity of oxidation-resistant SiC/C compositionally graded graphite materials has been measured by using the laser flash method. In order to study the effect of the SiC/C graded layer on the diffusivity, the thickness of the graded layer and the SiC content were changed. In addition, the specific surface areas of the SiC/C materials have been measured. It is shown that the effect of the SiC/C graded layer on thermal diffusivity was small within SiC contents (0.27-8.52 mass%) used in this study.