We report the growth and optical characteristics of Tm,Yb-codoped ZnO (ZnO:Tm,Yb) films on ZnO nanowires (NWs). The growth conditions of the NWs are optimized by changing the growth duration as well as growth temperature and VI/II ratio, which are grown on sapphire (0001) substrates. Photoluminescence (PL) characterization of the ZnO:Tm,Yb films on optimum ZnO NWs is performed with excitation by different lasers to investigate the mechanism of the energy transfer between the Tm³⁺ and Yb³⁺ ions in the films. Above-bandgap excitation of the films on optimum ZnO NWs yields several sharp peaks from Tm³⁺ and Yb³⁺ ions as well as a broad luminescence band from the oxygen vacancies in the ZnO. The PL intensity of each peak can be controlled by changing the concentration ratio of Tm³⁺ and Yb³⁺ ions. This result is due to the energy transfer between Tm³⁺ and Yb³⁺ ions where the energy transfer from Tm³⁺ to Yb³⁺ ions takes place in the sample with the high Yb mixing ratio and the reversed energy transfer process occurs with the lower Yb mixing ratio. Direct excitation of Tm³⁺ ions at 488 nm results in luminescence from the Yb³⁺ ions with specific luminescence centers. Furthermore, time-resolved PL characterization of the NWs with different concentrations of Tm³⁺ and Yb³⁺ ions reveals a change in the lifetime of luminescence from Tb³⁺ ions in the films. These results suggest the possible energy transfer between Tm³⁺ to Yb³⁺ ions in the ZnO:Tm,Yb films on ZnO NWs.

We fabricated and characterized Au/Ni Schottky contacts on cleaved m-plane free-standing n-GaN surfaces (i) without any surface treatment, (ii) with H₂O₂ treatment, or (iii) with HCl treatment by current-voltage (I-V), capacitance-voltage (C-V), and photoresponse (PR) measurements. 50-nm-thick Ni films and 50-nm-thick Au films were deposited in turn on the m-plane surface by electron-beam evaporation to form Schottky contacts. All of the Schottky contacts were circular and 100µm in diameter. The highest step determined by the laser microscope was 5 nm, but in some dots, steps were not observed. The as-cleaved samples showed I-V characteristics with small n-values and less diode-to-diode variation. However, the H₂O₂ samples had much smaller Schottky barrier height (qϕ_B). Whereas the HCl samples exhibited significantly large diode-to-diode variation. The qϕ_B and n-values obtained from the I-V, C-V, and PR results are nearly constant, independent of the step height. This is probably because the steps also consist of m-plane facets, which have no effect on the electrical characteristics of the Schottky diodes. It is confirmed that cleaving without any surface treatment can provide a cleaner surface to form Schottky diodes on m-plane n-GaN surfaces than that with conventional HCl treatment.

The in situ surface modification of InN films by nitrogen (N) radical beam irradiation was investigated using different substrate temperatures, plasma powers, and irradiation times. The changes in the surface morphology and electrical properties of the irradiated InN templates were studied. It was confirmed that N radical beam irradiation could modify the InN template's surface morphology. Furthermore, a comparison with annealing without N radical beam irradiation revealed that the N radical beam irradiation on the InN template could modify the surface morphology of the template and suppress InN thermal decomposition.

Corundum structured α-Ga₂O₃ is a promising semiconductor material for power switching devices due to its large bandgap (5.3 eV). The high dislocation density of α-Ga₂O₃ caused by a large lattice mismatch between the α-Ga₂O₃ and a sapphire substrate is a significant issue to a high-reliability operation. We featured LiTaO₃ substrates exhibiting a near corundum structure as growth substrates to decrease the lattice mismatch. Our previous study revealed that the growth of α-Ga₂O₃ on LiTaO₃ substrates required α-Fe₂O₃ buffer layers. In this study, the impact of α-Fe₂O₃ buffer layer growth time on the growth of α-Ga₂O₃ was investigated. X-ray diffraction 2θ-ω analysis revealed that α-Ga₂O₃ was successfully grown by inserting α-Fe₂O₃ buffer layer regardless of the buffer layer growth time. The growth time of the α-Fe₂O₃ buffer layer affected the number of edge dislocations examined by XRD rocking curve (XRC) measurements. The smallest full width at half maximum of XRC measurements at (0006) plane of the α-Ga₂O₃ with the buffer layer growth time of 1min was 60 arcsec. The α-Ga₂O₃ with the buffer layer growth time of 1 min had a smooth surface. This study contributes power switching device application of α-Ga₂O₃ grown on LiTaO₃ substrates.

Gallium oxide is receiving increased attention as a next-generation material for power devices having both low switching loss and high breakdown voltage. In this paper, we described the growth of Ga₂O₃ on Si substrates using mist chemical vapor deposition (CVD) technique. Firstly, amorphous Ga₂O₃ and polycrystalline Ga₂O₃ thin films were obtained on Si(111) substrates accompanying with rough surface conditions and low crystallinity. Secondly, <001> oriented κ-Ga₂O₃ thin films were grown on n-type Si(100) and Si(111) substrates by introducing ZnO buffer layers to avoid influence from surface oxide layers of Si substrates. The RMS value of κ-Ga₂O₃ was smaller than the values of amorphous Ga₂O₃ and polycrystalline Ga₂O₃ on Si(111). These results suggested that the ZnO buffer layer on Si played significant roles in crystallinity and improved planarity of κ-Ga₂O₃.

The fatigue characteristics of carbon fiber reinforced plastics (CFRPs) in the very high cycle fatigue (VHCF) regime have not been well understood. Moreover, it is necessary to research the fatigue behavior of L-shaped CFRP laminates in VHCF regime, which is often seen in structures. To investigate the fatigue behavior of L-shaped CFRP laminates in the VHCF regime, an ultrasonic fatigue test method was constructed in this study. An ultrasonic fatigue test was conducted in the range of 10⁷ - 10⁹ cycles. The working frequency was 20 kHz, and the geometry of the specimen was designed by the results of finite element analysis to resonate in the same frequency. Displacement, temperature, and fatigue damage of specimen were observed. As a result, it was confirmed that specimens resonated at 20 kHz during the test. The high temperature was measured, and delamination was observed at the curved section of specimens. The results showed ultrasonic fatigue tests can perform with L-shaped CFRP laminates. The observation suggests that stress concentration occurs at curved section during the test, and the interlayer stresses between 90°ply and 45°ply near the center of the 16 layers are dominant in fatigue damage initiation.

The obtained quality data of coal gasification slag fine aggregate (CGS) produced by the integrated coal gasification combined cycle (IGCC) and its characteristics are summarized. The effects of the quality characteristics of CGS on mechanical properties such as the compressive strength of concrete were investigated. From these results, it was considered that CGS is expected to have pozzolanic reactivity because it had almost amorphous and has a chemical composition close to that of coal fly ash. It was also suggested that the degree of strength development of concrete using CGS is affected by chemical components such as the ratio of the modified oxide amount to SiO₂ of CGS and the degree of polymerization of amorphous phase (NBO/T). Furthermore, it was confirmed that the modulus of elasticity tends to increase gradually corresponding to the CGS mix ratio, and that the tensile strength can be shown by the correlation with the compressive strength regardless of the CGS mix ratio.

It is important to predict thermal crack width in mass concrete accurately in order to satisfy the performance requirements of the structure in a reliable and reasonable manner. However, the authors found that the prediction accuracy of the currently used prediction expression is not sufficient for structures with large member thickness. Therefore, the purpose of this study is to propose a new crack width prediction expression in order to predict the thermal crack width accurately for various structures. First, the relationship between the relative humidity and the drying shrinkage strain was derived from the specimen experiment, and then it was input to the detailed analytical model of the actual structure with discrete crack, which shows that the crack width analysis can accurately predict the actual measurement. Second, a parametric study was conducted on the predicted crack width obtained by the detailed model and the thermal cracking index of the surface layer derived from the ordinary model, and it was shown that it is reasonable to focus on the stress to strength ratio (reciprocal of the thermal cracking index) of the surface layer when making a simple crack width prediction expression. Based on the knowledge a simple crack width prediction expression is proposed with organizing the measured crack width, the stress to strength ratio of the surface layer and the reinforcement ratio.

This paper experimentally investigates the application of an X-ray stress measurement called “cos α method” to analyze the electrical pitting generated on rolling bearings. First, a small size ball bearing rotation test was conducted in which an electric current passed continuously through the test bearings under various rotating conditions such as current density and electrical conductivities of lubricating greases. Then, the residual stress and full width at half maximum (FWHM) on the electrically damaged bearing raceway were measured. From the correlation between the residual stress and FWHM and the shape of the damage on the raceway surface, it was found that when the bearing was lubricated by the non-conductive grease, the surface was softened by the electric current and the characteristic shape of surface damage occurred. It was also found that lubrication by the conductive grease could reduce the thermal energy during discharge and suppress the surface softening. These findings demonstrate the validity of applying the X-ray stress measurement for electrical pitting analysis.

The 3rd generation wrought TiAl alloys are expected to be applied to high-temperature equipment because those have higher specific strength than Ni-based superalloys and toughness due to β phase. In this study, creep properties of Ti-43Al-5V-4Nb with improved forgeability by adding V and Nb were investigated. The relationship between the minimum creep rate and the rupture time could be approximated according to the Monkman-Grant law. This means the rupture time can be estimated from the behavior up to the secondary creep. The cracking modes changed from inter-lamellar to trans-lamellar and duplex cracking with crack growth. The generation of micro cracks on the surface did not depend on the microstructure.