Effect of annealing conditions on the optical properties and surface morphologies of (201)-oriented β-Ga2O3 crystals

The bulk properties of β-Ga2O3 are sensitive to temperature and atmosphere; therefore, suitable annealing conditions are required. This study was performed to investigate the effects of annealing conditions on the (201) surface of β-Ga2O3 crystal using atomic force microscopy, optical transmission/ luminescence spectroscopy, and X-ray photoelectron spectroscopy. Annealing was performed in air and in evacuated glass capsules at different temperatures. After annealing at 900 ◦C in air, the sample became a colorless insulator, and faceting was observed. On the other hand, sample decomposition was observed after annealing in the evacuated capsules. While, after annealing at 300 ◦C in air, step-terrace formation was observed. With increase of the annealing temperature, faceting was observed after annealing at 600 ◦C exposing the (100) and (001) surfaces. These results demonstrate the need for optimized annealing conditions for different surface orientations to obtain desirable β-Ga2O3 surfaces for heterointerfaces.Fil: Okada, Arifumi. Kyoto Institute of Technology; JapónFil: Nakatani, Masahiro. Kyoto Institute of Technology; JapónFil: Chen, Lei. Kyoto Institute of Technology; JapónFil: Ferreyra, Romualdo Alejandro. Kyoto Institute of Technology; Japón. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias Físicas. - Universidad Nacional de San Martín. Instituto de Ciencias Físicas; ArgentinaFil: Kadono, Kohei. Kyoto Institute of Technology; Japó

DFT Study of the Stereoselective Formation of <i>cis</i>-W(CO)₄(η²‑C₂H₄)₂ in the Gas-Phase Consecutive Coordination of C₂H₄ onto Doubly Coordinatively Unsaturated W(CO)₄

B3LYP-based density functional theory (DFT) calculations are reported that provide insight into the stereoselective formation of <i>cis</i>-W­(CO)₄(η²-C₂H₄)₂ observed in the pulsed 266 nm laser photolysis of tungsten hexacarbonyl (W­(CO)₆) in the presence of C₂H₄ in the gas phase at room temperature (<i>J. Phys. Chem.</i> <b>1995</b>, <i>99</i>, 4558). W­(CO)₄(η²-C₂H₄) formed through the coordination of C₂H₄ onto coordinatively unsaturated W­(CO)₄ was found to have a pseudo-<i>C</i>_2<i>v</i> symmetry (distorted trigonal bipyramid with an angle of ca. 90° between the two equatorial COs) with a bond dissociation enthalpy (BDE) of W–C₂H₄ of 125 kJ mol^–1. In the subsequent coordination of C₂H₄ onto the W­(CO)₄(η²-C₂H₄), having one vacant coordinatively unsaturated site, no barrier was found in the reaction path to <i>cis</i>-complex formation, while there was a barrier of about 89 kJ mol^–1 to the <i>trans</i>-complex. The calculations show that the stereoselective formation of <i>cis</i>-W­(CO)₄(η²-C₂H₄)₂ is due to kinetic rather than thermodynamic control. The <i>trans</i>-W­(CO)₄(η²-C₂H₄)₂ was calculated to be more stable than <i>cis</i>-W­(CO)₄(η²-C₂H₄)₂ by about 10 kJ mol^–1. The BDE of W–C₂H₄ in <i>cis</i>-W­(CO)₄(η²-C₂H₄)₂ was estimated to be 61 kJ mol^–1

Magnesiothermic reduction of silica glass substrate—Chemical states of silicon in the generated layers

<p>We applied magnesiothermic reduction to silica glass substrates at various conditions including solid state or solid-Mg liquid reaction, and solid-Mg vapor reaction. Magnesium silicide with highly oriented to the 〈110〉 direction against the substrate surface was obtained in the solid state reaction at temperatures from 600 °C to 700 °C using Mg grains while Si crystallites were obtained in the reaction with Mg film deposited on the glass substrate at 560 °C. On the other hand, in the reduction with Mg vapor at 575 °C, brown and amorphous layer was formed on the surface of the silica glass substrate. The layer was transparent in the visible and near-infrared regions, and showed an interference pattern in the transmission spectra, indicating the homogeneity of the layer. The thickness and refractive index were estimated as 770 nm and 1.94, respectively. As the reaction with Mg vapor proceeded further, Mg₂Si and MgO crystallites were formed. Oxidation states and their depth profiles of silicon atoms in the layers were investigated by X-ray photoelectron spectroscopy. The silicon atoms in the brown and amorphous layer existed in intermediate oxidation states, −2 and +3. The reaction proceeding, the formal charge of the silicon atoms varied to −4 corresponding to Mg₂Si and +2.</p

Establishment of Induced Pluripotent Stem Cells from Centenarians for Neurodegenerative Disease Research

<div><p>Induced pluripotent stem cell (iPSC) technology can be used to model human disorders, create cell-based models of human diseases, including neurodegenerative diseases, and in establishing therapeutic strategies. To detect subtle cellular abnormalities associated with common late-onset disease in iPSCs, valid control iPSCs derived from healthy donors free of serious late-onset diseases are necessary. Here, we report the generation of iPSCs from fibroblasts obtained immediately postmortem from centenarian donors (106- and 109-years-old) who were extremely healthy until an advanced age. The iPSCs were generated using a conventional method involving OCT4, SOX2, KLF4, and c-MYC, and then differentiated into neuronal cells using a neurosphere method. The expression of molecules that play critical roles in late-onset neurodegenerative diseases by neurons differentiated from the centenarian-iPSCs was compared to that of neurons differentiated from iPSCs derived from familial Alzheimer's disease and familial Parkinson's disease (PARK4: triplication of the α synuclein gene) patients. The results indicated that our series of iPSCs would be useful in neurodegeneration research. The iPSCs we describe, which were derived from donors with exceptional longevity who were presumed to have no serious disease risk factors, would be useful in longevity research and as valid super-controls for use in studies of various late-onset diseases.</p> </div

Expression of α-synuclein and tau by neurons differentiated from iPSCs 100–1 #8 and 100–1 #16, and the neurodegenerative disease-specific iPSCs.

<p>(A) Western blotting of α-synuclein and tau protein in the seven lines of neurons differentiated from iPSCs. Note that the level of α-synuclein expression by neurons differentiated from the PARK4-4 iPSCs is markedly increased. (B and C) Immunoblots were scanned and analyzed using densitometry. The level of α-synuclein (B) and tau (C) expression was normalized to the internal control α-tubulin. The histograms show expression relative to expression by 201B7. Data are from three independent experiments and are expressed as the mean ± standard deviation. Asterisks indicate a significant difference versus wild type as determined by one-way analysis of variance followed by Tukey-Kramer's post hoc test (<i>P</i> = 0.05).</p

Differentiation of centenarian-iPSCs into neurons.

<p>(A) Neural differentiation of iPSCs 100–1 #8 and 100–1 #16. Representative images of immunocytochemical staining for the early neuronal marker βIII-tubulin following neural differentiation. (B) Confocal images of co-staining with the mature neuron marker MAP-2 and the dopaminergic and noradrenergic neuronal marker tyrosine hydroxylase (TH). Inserts show high magnifications of dotted white squares. Bar  = 20 μm. Cells were counterstained with DAPI (blue).</p