Tamaki Shibayama

Photocatalytic activity of octahedral single-crystalline mesoparticles of anatase titanium(IV) oxide

Octahedral titanium(IV) oxide (TiO(2)) crystallites with exposed anatase [101] facets exhibited relatively high photocatalytic activity for oxidative decomposition of organic compounds and low activity for hydrogen evolution in the absence of molecular oxygen, probably due to the characteristics of the anatase [101] surface.

Preparation and photoelectrochemical properties of densely immobilized Cu2ZnSnS4 nanoparticle films

Colloidal Cu2ZnSnS4 (CZTS) nanoparticles with sizes of 5–6 nm that contain no highly toxic elements were successfully synthesized through thermal reactions of metal acetate and sulfur in high-temperature oleylamine solution. The reaction temperature was a key factor for the synthesis of CZTS nanoparticles: synthesis at temperatures higher than 240 °C gave a pure CZTS crystal phase, whereas a secondary phase of CuS was formed at reaction temperatures lower than 180 °C. Nanoparticles were successfully accumulated on ITO-coated or quartz glass substrates via layer-by-layer deposition using 1,2-ethanedithiol as a cross-linking agent. The resulting CZTS particle films exhibited a photoresponse similar to that of p-type semiconductor photoelectrodes in an aqueous solution containing Eu(NO3)3 as an electron scavenger. Potentials of the valence band edge and conduction band edge were determined from the onset potential of the cathodic photocurrent to be +0.3 and −1.2 V vs. Ag/AgCl, respectively.

Controlled formation of metallic nanoballs during plasma electrolysis

Formation of spherical nanoparticles (hereafter “nanoballs”) in a gas/liquid mixed dual phase system during plasma electrolysis is reported. A gas/vapor sheath is formed at the electrode/electrolyte interface when the applied voltage is high enough to induce discharge plasma. Through this nonequilibrium process, the authors have produced Ni, Ti, Ag, and Au metallic nanoballs from the cathode mother materials with a certain size controllability. The electrode surface is partially melted by the local current concentration induced by electrothermal instability followed by an immediate cooldown, yielding nanoballs without contamination from electrolyte.

Joining of silicon carbide composites for fusion energy applications

Abstract Joining of silicon carbide based materials has been recognized as one of the enabling technologies for the successful utilization of ceramic components in fusion energy systems. Sintered silicon carbide (Hexoloy SA) and silicon carbide (Hi-Nicalon™) fiber reinforced silicon carbide matrix composites have been joined using reaction forming/bonding based joining technologies. The room- and high-temperature mechanical properties and fractography of ceramic joints have been reported.

Tip artifact in atomic force microscopy observations of InAs quantum dots grown in Stranski–Krastanow mode

The tip artifact in atomic force microscopy (AFM) observations of InAs islands was evaluated quantitatively. The islands were grown in the Stranski–Krastanow mode of molecular beam epitaxy. The width and height of the islands were determined using transmission electron microscopy (TEM) and AFM. The average [1¯10] in-plane width and height determined using TEM excluding native oxide were 22 and 7nm, respectively; those determined using AFM including the oxide were 35 and 8nm, respectively. The difference in width was due to the oxide and the tip artifact. The sizes including the oxide were deduced from TEM observations to be a width of 27nm and a height of 6nm with correction for the thickness of the oxide. The residual difference of 8nm between the width determined using AFM and that determined using TEM including the oxide was ascribed to the tip artifact. The results enable us to determine the actual size of the islands from their AFM images.

Microstructural evolution of Hi-NicalonTM SiC fibers annealed and crept in various oxygen partial pressure atmospheres

It is expected that in the future SiC fiber-reinforced ceramic-matrix composites (CMCs) will be used in high temperature and hostile environments. In this study, Hi-NicalonTM SiC fibers were annealed and crept at 1500 °C for 1 hour in air, an argon flow and an ultra high-purity argon flow in order to investigate the effects of atmospheres and load conditions on the decomposition behavior and microstructural evolution of the fibers. After the fibers were annealed and crept in air, a silica layer with cracks was formed on the fiber surface. Under the creep load, the silica layer became thicker and porous due to the oxidation mechanism change from diffusion of ionic oxygen to transportation of oxygen molecules. An oxygen-enriched amorphous layer was formed at the fiber surface in the case of annealing in an argon flow, whereas SiC crystals were produced by the gas-phase reaction on the fiber surface when the fiber was crept in an argon flow. In an ultra high-purity argon flow, SiC crystals grew on the surface of both annealed and crept fibers. Growth of β-SiC grain was enhanced under low oxygen partial pressure atmospheres and creep load.

Ultrathin oxide shell coating of metal nanoparticles using ionic liquid/metal sputtering†

The surface coating of metal nanoparticles resulting into core–shell structures is expected to improve the physicochemical properties of the nanoparticle cores without changing their size and shape. Here, we developed a novel strategy to coat Au, AuPd or Pt catalyst cores having average sizes smaller than 2.5 nm, which were pre-synthesized in ionic liquids by corresponding metal sputtering, with an extremely thin In2O3 layer (ca. <1.5 nm) by sputter deposition of indium in a room-temperature ionic liquid. The metal cores of Au or AuPd in core–shell particles exhibited superior stability against heat treatments or during electrocatalytic reactions compared to the corresponding bare metal particles. The In2O3 shell coating considerably enhanced the durability of electrocatalytically active Pt particles (1.2 nm). This sequential metal sputter deposition of different metals in ionic liquids will considerably contribute to the exploitation of key nanostructured components for next-generation energy-conversion systems.

Tuning Optoelectrical Properties of ZnO Nanorods with Excitonic Defects via Submerged Illumination

When applied in optoelectronic devices, a ZnO semiconductor dominantly absorbs or emits ultraviolet light because of its direct electron transition through a wide energy bandgap. On the contrary, crystal defects and nanostructure morphology are the chief key factors for indirect, interband transitions of ZnO optoelectronic devices in the visible light range. By ultraviolet illumination in ultrapure water, we demonstrate here a conceptually unique approach to tune the shape of ZnO nanorods from tapered to capped-end via apical surface morphology control. We show that oxygen vacancy point defects activated by excitonic effects near the tip-edge of a nanorod serve as an optoelectrical hotspot for the light-driven formation and tunability of the optoelectrical properties. A double increase of electron energy absorption on near band edge energy of ZnO was observed near the tip-edge of the tapered nanorod. The optoelectrical hotspot explanation rivals that of conventional electrostatics, impurity control, and alkaline pH control-associated mechanisms. Thus, it highlights a new perspective to understanding light-driven nanorod formation in pure neutral water.

Site‐Selective Trimetallic Heterogeneous Nanostructures for Enhanced Electrocatalytic Performance

Trimetallic Au/Ag/Pt hetero-nanostructures (AAPHNs) with distinctive, designed morphology are synthesized by galvanic replacement reaction and a site-selective strategy. The three metals present on the surface are shown to act synergistically to enhance the electro-catalytic performance and durability for methanol oxidation. The described structural modification of the nanocomposites increases the range of potential applications to include both the oxygen reduction reaction in fuel cells and photocatalysis of the hydrogen evolution reaction.

Interface Properties of Copper/Aluminum/Stainless Steel Clad Materials

Copper/aluminum/stainless steel (Cu/Al/STS) clad materials were made by rolling and heat treatment process. These specimens were evaluated the formability and bonding strength of Cu/Al/STS clad materials. Thin disc specimens for TEM observation were prepared from the interfaces of Cu/Al and Al/STS by using the Focused Ion Beam (FIB) utility. Brittle oxide film formed on copper surface during heat treatment at 673K~773K. Diffusion bonding was observed at the interface of Cu/Al. Reacted region was formed in the interface of Al/STS with width about 10nm, while in the case of Cu/Al was formed about 1,600nm width. It was also observed nanosized crevice in reacted region of Al/STS interfaces.