Effective utilization of long wavelength light for photocatalytic and photoelectrochemical water splitting is an important challenge for practical realization of solar energy harvesting in the form of chemical energy, i.e., artificial photosynthesis. Meanwhile, narrowing the band gap of the semiconductor accompanied with the negative or positive shift of the valence band maximum or conduction band minimum, respectively, can cause the decline of the driving force of the photoexcited carriers. To break through this trade-off, innovative approaches to efficiently utilize the photoexcited carries generated inside the semiconductor for the chemical reaction performed outside the material should be necessary. In this study, novel concepts to control several processes with varying time scales involved in photocatalysis: 1) physical process inside the semiconductor, 2) chemical process at the photocatalyst surface, and 3) mass transfer of reactants in the bulk aqueous solution, are proposed with using particulate photocatalytic materials responsive up to near-infrared light.
Recently mixed anion compounds are paid attention due to their variety of crystal structures as well as functionalities. Especially, layered mixed-anion perovskites have several merits such as controllability of local structures and dimensionality, formation of natural superlattice, specific energy levels due to anisotropic coordination of anions and so on. In this paper, we will introduce feature of this system and summarize our recent research. In the Sr-Sc-Cu-Se-O system we have discovered two phases; Sr3Sc2Cu2Se2O5 and Sr2ScCuSeO3. Due to its longer blocking layer, Sr2ScCuSeO3 has larger confinement effect. We have also established the method to estimate the stable phases by DFT calculations. Sr2ScAgSeO3 phase is energetically favorable than Sr3Sc2Ag2Se2O5, and the phase formed by optimization of synthesis conditions. Characteristic luminescence with high efficiency is also observed in the compound of this system. These results suggest that layered mixed anion compounds are promising to develop new functional materials.
The Burton-Cabrera-Frank (BCF) theory has been applied to metalorganic vapor-phase epitaxy (MOVPE) of N-polar (0001) GaN. Owing to the hydrogen-rich atmosphere during MOVPE, surface N atoms of the N-polar (000-1) surface are mostly covered with H atoms. Extremely small coverage of the Ga adatoms competing with the H adatoms on the terraces can be calculated using the Langmuir adsorption isotherm. The equilibrium coverage of the Ga adatoms at steps and the equilibrium pressure of the NH3 gas at step kinks can be calculated from the conditions of Gibbs energy balance between the sources (Ga adatom and NH3 gas molecule) and the products (GaN and 3/2 H2 gas molecules) and of speed balance between Ga and N incorporation into the step kinks. Growth rates of GaN on vicinal surfaces and hexagonal spiral pyramids has been calculated as a function of the trimethylgallium flow rate and compared with experimental results.
Deep ultraviolet (DUV) light that span the wavelength range from 200 to 300 nm have numerous scientific and technological applications including spectroscopy, environmental monitoring, surface micromachining, and sterilization. Fluoride crystals have high transparency in DUV region because of their wide bandgap. In this report, we calculated the achromatic aberration of the couples of convex and concave lenses consist of fluoride crystals. Based on the calculated results, the prototype of achromatic objective lens in the wavelength range from 200 to 300 nm is fabricated. The prototype lens of a LiCaAlF6 and SiO2 has a focal length of 10 mm, working distance of 2mm, and numerical aperture of 0.2 with a chromatic aberration of about 2.8 %.
This article presents the development of the tube shape-controlled oxide scintillator directly grown from a melt via the micro-pulling-down method. We grew tube shape-controlled Ce doped Y3Al5O12 (tube-Ce:YAG) single-crystal scintillators with shape control using the µ-PD method, which we have reported in previous paper. We also developed and evaluated the diced Eu:SrI2 scintillator arrays and their scintillation properties for radiation imaging application. Using a novel dicing technique specific to halide scintillation crystals, a high-energy resolution scintillator array is developed that is cost-effective and widely applicable. Finally, these techniques and development were applied for the novel imaging method we proposed, called scintillation active collimator (SAC). These results demonstrated that the SAC could be promising imaging method for the future medical imaging application.