Er,O-codoped GaAs is a promising candidate for application to light sources including lasers and single photon emitters in fiber-optic communication, due to sharp luminescence from Er³⁺ ions at 1.54 μm and temperature insensitivity of their luminescence wavelength. In this contribution, we review our recent research activities regarding the formation and optical characteristics of two types of photonic crystal (PhC) nanocavities, L3-type two-dimensional (2D) and bridge-type PhC nanocavities. The computational method to design the PhC nanocavities is established to couple the cavity modes to the Er luminescence at 1.538 μm by using the finite-difference time-domain method. By optimizing several parameters including the lattice constant and radii of the holes, the simulated cavity Quality(Q)-factor of 10⁵ is obtained from the L3-type PhC nanocavities. Such designed cavity Q-factor can be further improved to 1.2 × 10⁶ from the bridge-type PhC nanocavities. Based on these numerical simulations, several bridge-type PhC cavities with different lattice constant are fabricated, in order to couple the cavity mode to the Er luminescence, and optical characterization at room temperature is performed utilizing micro-photoluminescence (μ-PL) measurements. Enhancement of Er luminescence due to coupling to the cavity mode of the 2D-PC nanocavities is observed. The observed experimental cavity Q-factors of L3- and bridge-type PhC nanocavities are 5.0 × 10³ and 1.2 × 10⁴, respectively. Furthermore, incident pump power dependence of Er luminescence in the bridge-type PhC nanocavity with higher cavity Q-factor exhibits superlinearity with excitation power, suggesting Er luminescence amplification. This result would pave the way towards the realization of lasers and highly efficient single-photon emitters based on rare-earth-doped compound semiconductors.

The prototype of creatinine sensor using differential extended-gate FETs was fabricated for the application of continuously measurement in point-of-care diagnosis of chronic kidney disease. The voltage drift of this sensor caused by temperature changes in the test solution and by fluorescent light irradiation was significantly reduced by introducing a differential circuit. The sensor showed a reversible voltage response to increases or decreases in creatinine concentration in phosphate buffer solution. The detectable range of creatinine concentration is 0.01 - 0.3 mg/mL, covering the high end of the serum creatinine concentration range in healthy adults to the threshold for starting dialysis.

Cu-based metal halides, such as Cs₃Cu₂I₅ and CsCu₂I₃, are promising materials for light-emitting diodes, photodetectors, and scintillators because of their excellent optical properties, non toxicity, and high air stability. In this study, we deposited thin films of the Cs-Cu-I system using Mist deposition varying the precursor composition of CsI and CuI and investigated their optical properties. X-ray diffraction 2θ-ω revealed that the Cs-Cu-I system thin films deposited by Mist deposition showed peaks corresponding to Cs₃Cu₂I₅ and CsCu₂I₃ phases, with both phases existing in the composition of the concentration of Cu higher than Cs. Energy Dispersive X-ray Spectroscopy measurements presented the decreasing of Cs concentration in thin films compared to the precursor solution. The Cs-Cu-I system thin films exhibited blue and yellow emissions under UV radiation, originating from Cs₃Cu₂I₅ and CsCu₂I₃, respectively. Especially, by adjusting the composition properly, Cs₃Cu₂I₅ thin films achieved a photoluminescence quantum yield of 92.4% in thin films. This study paves the way for the thin film deposition and the application of Cu-based metal halide.

Optical properties of wide band-gap semiconductor ZnMgSTe have been investigated. ZnMgSTe thin film crystals were grown on GaAs substrates by molecular beam epitaxy. It was found that ZnMgSTe thin films exhibit relatively strong photoluminescence as compared to ZnSTe thin films. It was also found that the luminescence mechanism in ZnMgSTe is similar to that in ZnSTe and related to Te iso-electronic traps. The enhanced luminescence with Mg incorporation may be due to the fluctuation in microscopic composition of Zn and Mg.

Gallium oxide (Ga₂O₃), which is known as an ultra-widegap oxide semiconductor, is a promising material for applications of deep ultraviolet region photodetectors with high sensitivity. Mist chemical vapor deposition (mist-CVD) is a growth method with strong epitaxial properties and is suitable for the growth of Ga₂O₃. In this study, Ga₂O₃ thin films are grown on quartz (0001) substrates using mist-CVD at different growth temperatures to evaluate their crystal quality and photoconductivity. The gallium oxide thin films grown at 450°C were amorphous films with sparse structure, while the gallium oxide films grown at 550°C were mixture thin films of β-Ga₂O₃ and amorphous phase. MSM photodetectors with a platinum comb-type electrodes were fabricated to evaluate their photoconductivity and visible-rejection-ratio (VRR) values. As a result, Ga₂O₃ thin films grown at 550°C exhibited large photoconductivity and high VRR value of 10^5.1 at 12 V and 10^5.4 at 24 V. As well, the dark current and photocurrent under halogen lamp illumination was under the detection limit (<100 pA). These results indicate that Ga₂O₃ thin films grown using mist-CVD can be a good candidate for deep-ultraviolet photodetectors.

3D printed concrete (3DPC) is rapidly developing and promisingly expected to contribute to free modeling of structural member, un-manned construction method and so forth. On the other hand, it is known that the anisotropic property of its layered structure is influenced by the existence of interface between the extruded materials. Since the heterogeneity of aggregate distribution affects the mechanical properties, it can have effects on the interfacial bonding and adhesion between layered filaments of the extruded materials of 3D printed object. This paper aims to clarify the mechanism of aggregate heterogeneity formation in the printing nozzle and the printed filament with evaluating the influence of material extrusion speed. The sequential cross-sectional images are acquired with X-ray CT method and analyzed three-dimensionally to quantify the distribution of aggregates. The result indicates that the aggregate heterogeneity shows the characteristic distribution of aggregate, which is influenced by material extrusion speed. Specially, it is found that the area with large size aggregate moves from the outside toward the center of the cross section, as the extrusion speed increases, inside the nozzle. Also, as the extrusion speed increases, large size aggregate inside the nozzle moves from the center of the cross section toward the bottom. Meanwhile, the lubrication layer between the internal surface of nozzle and the extruded material, which is formed by increment of pressure inside nozzle determined by extrusion speed, alters the flow velocity distribution inside the nozzle from laminate flow to plug flow and the aggregate distribution before and after extrusion.

To correctly evaluate the safety of mechanical components, considering manufacturing induced residual stresses is essential. In this study, the risk analysis of fatigue crack initiation and propagation in cylindrical rollers for large size carburized bearings subjected to the rolling contact stress in services was conducted with consideration of the heat treatment stresses. Firstly, the residual stresses were reproduced by inherent strains measured using extended contour method, which combined the conventional contour method and surface stress measurement methods such as the X-ray diffraction method. The total stress in bearings during services is the summation of residual stress and contact stress. The location of fatigue crack initiation was examined using the Dang Van criterion. As a source of stress concentration, cavities were assumed as a harmful type of defects like inclusions with poor adhesion to the base microstructure. The direction of crack initiation around the defect was also examined using the Dang van criterion. The stress intensity factor (SIF) around the vacancy was calculated considering both residual stress and contact stress with a hypothetical initial crack. The SIF for a three-dimensional crack was modified by applying the shape factor. The effect of residual stress, the vacancy diameter and the shape of the defect on the crack propagation were discussed and compared with the threshold effective stress intensity factor of the standard bearing steel. A step-by-step approach was proposed to evaluate the risk of crack initiation and propagation by considering the residual stress distribution.

There is no unified view on the strength development mechanism of chemically grouted sand, which has not been clarified yet. This study investigated the cohesion and friction angle, which are the shearing strength components of the chemical grouted sand, using a consolidated drained triaxial compression test. The microscopic molecular structure of the hydrogels in which the grout gelled itself was analyzed using a small angle x-ray scattering. In the experiment, we used a type of chemical grout that gelled in the non-alkaline region and caused macro volumetric shrinkage. As a result of the triaxial compression test until 300 days, the strength development of the grouted sand added cohesion and increased friction angle because of the fixed soil particles. And these values did not decrease. In the void of soil particles, neither volumetric shrinkage nor peeling of the hydrogel occurred. These suggest that the effect of fixing the soil particles continues. On the other hand, it was confirmed that the aggregation structure became smaller in microscopic molecular structure.

The humidity control capacity of Sugi end-grain wood installed in a sealed box is investigated using the Cb value for specimen thicknesses ranging from 1 mm to 30 mm. The Cb value is defined as the ratio of the humidity difference in a box lined with a specimen to that in an empty box when subjected to sinusoidal temperature variation. The temperature variation periods were set at four steps, ranging from 6 hours to 48 hours. Based on the results at a period of 24h, Cb values demonstrated good humidity control capacity for specimen with a thickness of 10 mm or more. From the variation in Cb values with specimen thickness, the thickness contributing to humidity control capacity, termed the 'effective thickness,' was determined. The Cb values decrease with an increase in the temperature variation period. The manner of this decrease is governed by two factors: effective thickness and specimen thickness. Furthermore, it was found that by specifying sample thickness and effective thickness for each variation period, Cb values can be estimated through calculation alone, without the need for experimental procedures.