Yoshizo Takai

Catalysis of Nickel Ferrite for Photocatalytic Water Oxidation Using [Ru(bpy)3]2+ and S2O82–

Single or mixed oxides of iron and nickel have been examined as catalysts in photocatalytic water oxidation using [Ru(bpy)(3)](2+) as a photosensitizer and S(2)O(8)(2-) as a sacrificial oxidant. The catalytic activity of nickel ferrite (NiFe(2)O(4)) is comparable to that of a catalyst containing Ir, Ru, or Co in terms of O(2) yield and O(2) evolution rate under ambient reaction conditions. NiFe(2)O(4) also possesses robustness and ferromagnetic properties, which are beneficial for easy recovery from the solution after reaction. Water oxidation catalysis achieved by a composite of earth-abundant elements will contribute to a new approach to the design of catalysts for artificial photosynthesis.

Quantitative measurement of surface potential and amount of charging on insulator surface under electron beam irradiation

Surface potential and the amount of charging on an insulator surface under electron beam irradiation have been quantitatively measured. For these measurements, a special sample holder was developed. The surface potential was measured using a secondary electron method. The measurement of the surface potential revealed that the sample behaves as a resistor, enabling the present technique to be applied for mapping microarea resistance. The results of measuring the amount of charging revealed that the amounts of charging obtained with different beam currents are the same in spite of different surface potentials. This strongly suggests that the charging phenomenon depends on the distribution of the charge trapping sites.

Direct Observations of the Arrangement of Atoms around Stacking Faults and Twins in Gold Crystals and the Movement of Atoms Accompanying Their Formation and Disappearance

Two types of imaging methods in high resolution transmission electron microscopy, which give the images of atoms at the atomic positions in crystals containing defects, are presented. Using one of the methods, atomic arrangements of partial dislocations, intrinsic and extrinsic stacking faults, sessile dislocations formed by the interaction of two partial dislocations, and coherent and incoherent twin boundaries in gold thin crystals have been observed. Dynamic observations using TV systems have been carried out on the movement of atoms accompanying the formation, the movement and disappearance of stacking faults and twins, and their interaction.

Characterization of Silicon Native Oxide Formed in SC-1, H2O2 and Wet Ozone Processes

The structures of silicon native oxides formed in the SC-1, H2O2 and wet ozone processes were characterized using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Spectral simulation was performed to clarify the FT-IR spectra, assuming that the native oxide was pure silicon dioxide. Effective medium theories were applied to understand deviations of the observed spectra from the calculated ones. The deviations between the native oxide thickness evaluated by XPS and the absolute thickness obtained by TEM were also discussed. These deviations can be explained if the void is incorporated in the native oxides and the interface between the native oxide and the basal silicon obtained by the wet ozone process has a relatively smooth surface and a structure more similar to that of pure silicon dioxide, compared with that obtained by SC-1 or H2O2 treatment.

Wave field restoration using three-dimensional Fourier filtering method.

A wave field restoration method in transmission electron microscopy (TEM) was mathematically derived based on a three-dimensional (3D) image formation theory. Wave field restoration using this method together with spherical aberration correction was experimentally confirmed in through-focus images of amorphous tungsten thin film, and the resolution of the reconstructed phase image was successfully improved from the Scherzer resolution limit to the information limit. In an application of this method to a crystalline sample, the surface structure of Au(110) was observed in a profile-imaging mode. The processed phase image showed quantitatively the atomic relaxation of the topmost layer.

Application of the Focused-Ion-Beam Technique for Preparing the Cross-Sectional Sample of Chemical Vapor Deposition Diamond Thin Film for High-Resolution Transmission Electron Microscope Observation

Atomic-scale observation of chemical vapor deposition (CVD)-diamond/silicon interface structures was successfully performed by applying a focused-ion-beam (FIB) technique for preparing the cross-sectional samples. Several severe conditions such as weak adhesion and extreme difference in sputtering yield have virtually prevented the proper processing of the interface cross sections by only the conventional method. A sample preparation procedure is proposed with some specific devices for extreme thinning, sufficient for high-resolution transmission electron microscope (HRTEM) observation, emphasizing the good potential for wider practical use.

Characterization of Sc?O/W(100) Surface as Schottky Emitter: Work Function Change for Activation Processing

To elucidate the electron emissivity of the Sc–O/W(100) Schottky emitter, the Sc–O/W(100) surface, prepared by scandium deposition onto the W(100) surface followed by oxygen exposure and heating at an operating temperature of ~1400 K, was studied by ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES) and measurement of the relative work function change. The results have revealed that heating of the oxygen adsorbed Sc/W(100) surface leads to the diffusion of the oxygen atoms into the substrate to locate very probably beneath the topmost scandium atoms. This relocation of the oxygen atoms forms an electric double layer, resulting in a significant decrease of the work function. The topmost surface composition of the Sc–O/W(100) system observed by ISS did not change during cooling the sample from ~1400 K to room temperature under the present conditions. The results of the present work strongly suggest that the surface properties of the Sc–O/W(100) system are very similar to those of the Zr–O/W(100) system at the operating temperature.

Surface Structure of Sc-O/W(100) System used as Schottky Emitter at High Temperature

The surface characterization of the Sc–O/W(100) system was performed by low-energy electron diffraction, Auger electron spectroscopy and work function measurement at 1500 K, the operating temperature of the Sc–O/W(100) emitter. For this, a sample holder with a heater was newly developed. In addition, the differential measurement method was applied to low-energy electron diffraction. The present results reveal that the p(1×1)-Sc–O/W(100) surface having a work function of 3.2 eV is formed by heating at 1700 K.

Distorted surface and interface structures of catalytic gold nanoparticles observed by spherical aberration-free phase electron microscopy

The surface and interface atomic structure of catalytic gold nanoparticles was studied by analyzing a spherical aberration-free phase image. Typically, a catalytic gold particle forms a single crystal having a cuboctahedral shape. The atomic structure of the surface and interface is largely deformed from the bulk structure by stress produced by the atom missing row structure, the reconstructed surface structure, and strong interaction with the substrate. In addition, the structure inside the particle is also deformed by distortion of the surface and the interface.

Effects of Wall Charge on Firing Voltage and Statistical Delay Time in Alternating-Current Plasma Display Panels

The effects of wall charge on firing voltage, Vf, and the statistical delay time of discharge, ts, in plasma display panels were investigated. Vf, i.e., the ion-induced secondary electron emission, is independent of both the polarity and amount of wall charge. In contrast, ts, i.e., the exoelectron emission, strongly depends on the wall charge and is smaller for a high positive wall charge, revealing the coexistence of trapped electrons and holes in the surface region. Positive charging of the MgO surface of the cathode side is effective to improve the response of the address discharge.