The influence of grain size and density of yttria-tetragonal zirconia polycrystals (Y-TZPs) ceramics on mechanical properties and on low-temperature aging degradation (LTD) in air and in hot water was investigated. A TZP powder containing 3 mol% Y2O3 was consolidated by slip casting and densified by the sintering/hot isostatic pressing (HIP) method. Only the presintered samples that contained less than 0.15% open porosity reached near full density after HIP. The best conditions to reach full density were found to be attained by presintering and HIP both at 1400 °C. At these conditions, some of the best mechanical properties such as modulus of rupture and Weibull modulus reached 1397 ± 153 MPa and, 10.6, respectively. These values were clearly higher than those obtained from sintered bodies and samples hot isostatically pressed at 1600 °C. Aging degradation of 3Y-TZP materials can be avoided through microstructural design. Fully dense materials with a critical grain size <0.36 μm did not show any evidence of degradation after extreme aging conditions at pressurized autoclaving in hot water at 100, 200, and 260 °C for 8 h. We propose a criterion to predict degradation in air as well as in hot water for the characterized materials based on the microstructure and density control of the samples.

We have estimated the characteristic temperature T0 of GaN-based vertical-cavity surface-emitting lasers. The density matrix theory including intraband relaxation broadening has been taken into account. The estimated T0 is about 300 K, which suggests a good temperature characteristic in GaN-based lasers.

We have made CO mapping observations of nearby barred spiral galaxies (NGC253, NGC3504, NGC4303, NGC4321, NGC6951, M83) with the Nobeyama 45-m telescope using the 2×2 SIS focal-plane array receiver. The purpose of this project is to investigate distribution and kinematics of molecular gas in barred spiral galaxies and the relation between star formation and them. We present some of the results (NGC3504 and NGC6951).

We have estimated the characteristic temperature T0 of GaN-based vertical-cavity surface-emitting lasers. The density matrix theory including intraband relaxation broadening has been taken into account. The estimated T0 is about 300 K, which suggests a good temperature characteristic in GaN-based lasers.

ZnO layers have been deposited by electron beam (EB) evaporation and laser ablation molecular beam epitaxy (MBE) as buffer layers to grow GaN by metal organic vapor phase epitaxy (MOVPE). The photoluminescence spectrum of the ZnO layer deposited by an EB evaporator shows an emission peaks of 367 nm. GaN was grown on ZnO/Si, Si and sapphire substrates under the same growth condition employing low-temperature-grown AIN buffers to prevent the dissociation of ZnO during the high GaN growth. The GaN on ZnO/Si shows sharp photoluminescence spectra at room temperature and 10 K. These results indicate a potential use of ZnO/Si substrates for GaN based blue-UV optical devices such as vertical-cavity surface-emitting lasers (VCSELs).

The threshold current density of GaN-based vertical cavity surface emitting lasers (VCSELs) has been estimated. It is clarified that the introduction of a quantum well structure as an active layer is very effective for a low threshold operation and that high reflective mirrors are required for low threshold GaN-based VCSELs. Also, attempts on micro-fabrication process of GaN is presented.

A dry etch technique using Cl2 based reactive ion beam etching (RIBE) has been developd for GaN-based semiconductor lasers. The etching rate of 350 − 1000 Å/min was obtained. This is applicable for micro fabrication of GaN based materials in the same way as used for other III-V group semiconductors. Furthermore, it is found that the surface damage of GaN layers induced by the RIBE-etch can be removed using ultra-violet assisted wet-etching using alkali solution. The PL intensity of damaged GaN layers is increased after the post-process wet-etching.