Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride.

Cathodoluminescence (CL) spectroscopy is a suitable technique for studying the luminescent properties of optoelectronic materials because CL has no limitation on the excitable bandgap energy and eliminates ambiguous signals due to simple light scattering and resonant Raman scattering potentially involved in the photoluminescence spectra. However, direct CL measurements of atomically thin two-dimensional materials have been difficult due to the small excitation volume that interacts with high-energy electron beams. Herein, distinct CL signals from a monolayer hexagonal BN (hBN), namely mBN, epitaxial film grown on a graphite substrate are shown by using a CL system capable of large-area and surface-sensitive excitation.

Temperature Field, Flow Field, and Temporal Fluctuations Thereof in Ammonothermal Growth of Bulk GaN-Transition from Dissolution Stage to Growth Stage Conditions.

With the ammonothermal method, one of the most promising technologies for scalable, cost-effective production of bulk single crystals of the wide bandgap semiconductor GaN is investigated. Specifically, etch-back and growth conditions, as well as the transition from the former to the latter, are studied using a 2D axis symmetrical numerical model. In addition, experimental crystal growth results are analyzed in terms of etch-back and crystal growth rates as a function of vertical seed position.

High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors-A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN.

For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure.

Dopant activation process in Mg-implanted GaN studied by monoenergetic positron beam.

A process for activating Mg and its relationship with vacancy-type defects in Mg-implanted GaN were studied by positron annihilation spectroscopy. Mg ions were implanted with an energy of 10 keV, and the Mg concentration in the subsurface region (≤ 50 nm) was on the order of 10 cm. After the Mg-implantation, N ions were implanted to provide a 300-nm-deep box profile with a N concentration of 6 × 10 cm.

Self-formed compositional superlattices triggered by cation orderings in m-plane AlInN on GaN.

Immiscible semiconductors are of premier importance since the source of lighting has been replaced by white light-emitting-diodes (LEDs) composed of thermodynamically immiscible InGaN blue LEDs and yellow phosphors. For realizing versatile deep-ultraviolet to near-infrared light-emitters, AlInN alloys are one of the desirable candidates. Here we exemplify the appearance and self-formation sequence of compositional superlattices in compressively strained m-plane AlInN films.

Effects of ultra-high-pressure annealing on characteristics of vacancies in Mg-implanted GaN studied using a monoenergetic positron beam.

Vacancy-type defects in Mg-implanted GaN were probed by using a monoenergetic positron beam. Mg ions were implanted into GaN to obtain 0.3-μm-deep box profiles with Mg concentrations of 1 × 10 cm.

Photocatalytic NO removal over calcium-bridged siloxenes under ultraviolet and visible light irradiation.

Ca-Bridged siloxenes (Ca-siloxenes) composed of two-dimensional siloxene planes with Ca bridging were prepared and their photocatalytic properties for nitrogen oxide (NO) removal were investigated. Ca-Siloxenes were synthesized via a solid-state metathesis reaction using TaCl5 to extract Ca from CaSi2 with different Cl2/Ca molar ratios of 0.25, 1.

Local structure around In atoms in coherently grown m-plane InGaN film.

The local structure around In atoms in an m-plane InGaN film coherently grown on a freestanding m-plane GaN substrate was investigated by polarization-dependent X-ray absorption fine-structure. A step-by-step fitting procedure was proposed for the m-plane wurtzite structure. The interatomic distance for the first nearest neighbour In-N atomic pairs was almost isotropic.

Photocatalytic activity of silicon-based nanoflakes for the decomposition of nitrogen monoxide.

The photocatalytic decomposition of nitrogen monoxide (NO) was achieved for the first time using Si-based nanomaterials. Nanocomposite powders composed of Si nanoflakes and metallic particles (Ni and NiSi) were synthesized using a simple one-pot reaction of layered CaSi and NiCl. The synthesized nanocomposites have a wide optical absorption band from the visible to the ultraviolet.

Defect-Resistant Radiative Performance of m-Plane Immiscible Al In N Epitaxial Nanostructures for Deep-Ultraviolet and Visible Polarized Light Emitters.

Planar vacuum-fluorescent-display devices emitting polarized UV-C, blue, and green light are demonstrated using immiscible Al In N nanostructures grown in nonpolar m-directions. Despite the presence of high concentration of nonradiative recombination centers, the Al In N nanostructures emit polarized light with the luminescence lifetimes of 22-32 ps at 300 K. This defect-resistant radiative performance suggests supernormal localized characteristics of electron-hole pairs.

Signatures of Γ1-Γ5 mixed-mode polaritons in polarized reflectance spectra of ZnO.

Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Γ(1) and Γ(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k is perpendicular to a and E is parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Γ(1) transverse mode and two Γ(5) longitudinal modes.

Femtosecond-laser-driven photoelectron-gun for time-resolved cathodoluminescence measurement of GaN.

A rear-excitation femtosecond-laser-driven photoelectron gun (PE-gun) is developed for measuring time-resolved cathodoluminescence (TRCL) spectrum of wide bandgap materials and structures such as semiconductors and phosphors. The maximum quantum efficiency of a 20-nm-thick Au photocathode excited using a frequency-tripled Al(2)O(3):Ti laser under a rear-excitation configuration is 3.6×10(-6), which is a reasonable value for a PE-gun.

Optical polarization properties of m-plane AlxGa1-xN epitaxial films grown on m-plane freestanding GaN substrates toward nonpolar ultraviolet LEDs.

Light polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1-xN epilayers suffering from anisotropic stresses are quantitatively explained. The epilayers were grown on an m-plane freestanding GaN substrate by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods. The light polarization direction altered from E [symbol see text]c to E//c at the AlN mole fraction, x, between 0.

Morphology of thyroid vascular casts of hypertensive rats.

Thyroid vascular casts were made by injecting a resin, Mercox, into 3 types of hypertensive rats (spontaneously hypertensive rats, SHR, stroke-prone SHR, SHRSP, malignant SHRSP, M-SHRSP), and the vascular casts were observed by scanning electron microscopy (SEM). There was no difference in the general morphology of the vascular casts between SHR and the control (Wistar Kyoto rats, WKY). However, the density and the diameter of blood vessels in SHRSP and M-SHRSP were significantly different from those in WKY, and abnormal vasculatures that formed protrusions with free endings were observed in M-SHRSP.

Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors.

Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al,In,Ga)N bulk films exhibit a defect-insensitive emission probability.

Characteristics of muscular contraction caused by magnetic stimulation.

Characteristics of muscular contraction induced by magnetic stimulation were studied using isolated gastrocnemius muscles of a frog. The figure-eight coil position was regarded as 0 degrees when the direction of induced current was parallel to the muscle fiber axis, and 90 degrees when the induced current was perpendicular to the muscle fiber axis. Muscular contraction readily occurred with lower outputs of magnetic stimulation at 0 degrees and 180 degrees, but it was weak at 90 degrees and 270 degrees.

Magnetically induced motor evoked potentials and H-reflex during nembutal and ketamine anesthesia administration in rats.

The effects of nembutal and ketamine anesthesia on motor evoked potentials (MEPs) and spinal segment reflex (H-response, F and M waves) were investigated in rats by magnetic stimulation. These potentials were generated by magnetic stimulation of the motor cortex and the spinal cord (L4-L5). After application of nembutal, MEP and H-response decreased in amplitude, eventually disappearing.

Changes in the gastric vascular network of malignant stroke-prone spontaneously hypertensive rats (M-SHRSP) after administration of the calcium antagonist manidipine.

In malignant SHRSP (M-SHRSP), a strain of stroke-prone spontaneously hypertensive rat (SHRSP), blood pressure rapidly increases during early development (5 weeks of age). Changes in the gastric vascular architecture of WKY and M-SHRSP were investigated using scanning electron microscope images of vascular casts focusing on the morphological differences in the three-dimensional arrangement of the capillaries. In WKY, the density, tortuosity and regular honeycomb formation of the gastric vessels were studied.

Gastric vascular network in stroke-prone spontaneously hypertensive rats.

The gastric vascular architecture in stroke-prone spontaneously hypertensive rats (SHRSP) was studied three-dimensionally by vascular casting; controls were Wistar Kyoto rats (WKY). The vascular network of the gastric mucosa of WKY showed a cylindrical shape with regular morphology (honeycomb-like capillary network) along the vascular course. In contrast, in SHRSP, an irregular vascular network was formed, and arterioles in the gastric mucosa and serous membrane were difficult to detect.

Thermal and antiradical properties of indirect moxibustion.

The thermal and antiradical properties of indirect moxibustion stimulation were investigated by thermal qualitative and spectroscopic methods. The thermal effect of indirect moxibustion was mainly dependent on the spacing distance between the moxa and skin, and not on the moxa weight. The radical scavenging activities of moxa and moxa-tar were measured by a photometric absorbance method, chemical reaction with 1,1-diphenyl-2-picrylhydrazyl.

Effect of indirect moxibustion on mouse skin.

Effect of indirect moxibustion stimulation on mouse skin was studied by thermal qualitative, biochemical, and histological methods. The maximum temperature change by indirect moxibustion was about 65 degrees C on the skin, and 45 degrees C in the subcutaneous layer. The treatment of indirect moxibustion was found to be associated with the decrease of lipid peroxidation and increase of superoxide dismutase (SOD) in the skin.

Electrophysiological changes in substantia nigra after striatal infarction.

The GABAergic efferent pathway from the striatum exerts inhibitory control on the substantia nigra pars reticulata (SNR) neurones. We studied sequential changes in spontaneous single-unit activities in the ipsilateral SNR 1 h, 1 day, 7 days and 14 days after striatal infarction induced by middle cerebral artery occlusion (MCAO) in rats. Compared with a sham-operated group, there was no change in the firing rate 1 h after MCAO, and one day after MCAO the mean firing rate decreased.

Electroencephalographic evaluation of the therapeutic efficiency of antihypertensive agents on M-SHRSP.

1. In order to evaluate the therapeutic effects of antihypertensive agents on malignant hypertension in M-SHRSP, EEG were performed as a non-invasive, therapeutic index. 2.

Temporal and spatial properties of slow waves in the electroencephalogram of spontaneously hypertensive rats.

1. Electroencephalogram (EEG) of stroke-prone spontaneously hypertensive rats (SHRSP) and M(malignant)-SHRSP were analysed for excitability changes in the cerebral neuronal circuit using power spectral comparisons. 2.

Phosphate metabolism during muscular contraction in starved frogs (Rana catesbeiana).

1. The muscle tension and the state of high-energy phosphate metabolism during contraction of the sartorius muscle in frogs (Rana catesbeiana) starved for 1-5 months was studied by in vivo 31P-NMR spectrometry. 2.