Morihiro Okada

Interfacial Oxygen Stabilizes Composite Silicon Anodes

Silicon can store Li(+) at a capacity 10 times that of graphite anodes. However, to harness this remarkable potential for electrical energy storage, one has to address the multifaceted challenge of volume change inherent to high capacity electrode materials. Here, we show that, solely by chemical tailoring of Si-carbon interface with atomic oxygen, the cycle life of Si/carbon matrix-composite electrodes can be substantially improved, by 300%, even at high mass loadings. The interface tailored electrodes simultaneously attain high areal capacity (3.86 mAh/cm(2)), high specific capacity (922 mAh/g based on the mass of the entire electrode), and excellent cyclability (80% retention of capacity after 160 cycles), which are among the highest reported. Even at a high rate of 1C, the areal capacity approaches 1.61 mAh/cm(2) at the 500th cycle. This remarkable electrochemical performance is directly correlated with significantly improved structural and electrical interconnections throughout the entire electrode due to chemical tailoring of the Si-carbon interface with atomic oxygen. Our results demonstrate that interfacial bonding, a new dimension that has yet to be explored, can play an unexpectedly important role in addressing the multifaceted challenge of Si anodes.

Study of Carbon-Nanotube Web Thermoacoustic Loud Speakers

Thermoacoustic carbon nanotube (CNT) speakers were fabricated using CNT webs spun from a multiwalled carbon nanotube (MWNT) array of 0.8–1.6 mm height. The generated sound pressure level (SPL) showed a linear relationship with frequency over a wide range from 10 Hz to 40 kHz with a slope of 6 dB/octave. In addition to this, significantly broad and flat SPLs were obtained in the ultrasonic region, ranging from 40 to 100 kHz. The distance from the speaker to the microphone was 0.5 m. The high SPL is due to the good heat radiation property of the MWNT web. Herein, we showed an acoustical property for the MWNT web thermoacoustic speaker from the viewpoint of the structural web morphology. The role of heat radiation behavior and the effects of the length of individual MWNTs are discussed.

Synthesis of Bi(FexAl1-x)O3 thin films by pulsed laser deposition and its structural characterization

We have been attempting to synthesize perovskite BiAlO3 as a new lead-free piezoelectric material. No indication of the formation of the BiAlO3 phase by the bulk ceramic processing or thin film processing has been obtained. Therefore, we undertook to synthesize a solid solution of BiAlO3 and BiFeO3, which has a stable perovskite structure and contains Bi as a component element. Bi(FexAl1-x)O3 solid solution could not be obtained by bulk ceramic processing. However, we succeeded in the fabrication of single-phase Bi(FexAl1-x)O3 thin films on (001) SrTiO3 substrates by pulsed laser deposition. The crystal structure was revealed to be rhombohedral at x=1 and tetragonal at x=0.9.

Structural and emission characteristics of iron-oxide whiskers on a steel plate

Summary form only given. In this presentation, the results of the field emission characteristics of magnetite whiskers grow on one side of a steel plate are presented. Iron-oxide whiskers grown on an SUS304 steel plate were shown thru SEM and TEM.

Application of a Hall Accelerator to Diamondlike Carbon Film Coatings

A Hall accelerator-type ion source for low-voltage continuous operation (hereafter called HALOC) without any exhaustible filaments, designed for film coating purposes, has successfully produced a large-area low-energy continuous beam of methane or oxygen. The thin film of carbon uniformly coated on a steel plate by the HALOC has been found to be a typical amorphous hard carbon film with high Vickers hardness, strong adhesion, and strong anticorrosion properties. The causes of strong adhesion of the film have been studied.

Fabrication and characteristics of novel graphite field emitters for application to electron-beam-pumped light sources

Light emission based on the excitation of rare gases by a low energy dc electron beam is a promising approach for realizing deep- or vacuum-ultraviolet light sources or lasers that are compact and have high efficiency. Carbon nanotube (CNT) field emitters have been used as electron sources in replacement of thermal cathodes to construct a low energy-consumption, compact and low-cost system. However, CNT technologies experience problems relating to the adherence of the interface between the carbon layers and their substrate. To try to solve the problem, carbon nanoneedle field-emitters were fabricated by etching a graphite substrate with H2 gas using radio frequency (RF) magnetron sputtering equipment. Scanning electron microscopy, energy-dispersive X-ray fluorescence spectroscopy, and electron emission measurements were performed for the characterization of graphite field-emitters

Enhancement in electron emission from polycrystalline silicon field emitter arrays coated with diamondlike carbon

The gated polysilicon field emitter arrays coated with diamondlike carbon (DLC) were fabricated by a transfer mold method using anisotropic etching of Si and the deposition of DLC using methane ion beam. This paper describes significant enhancement in electron emission and considerable reduction in turn-on voltage for the emitter arrays by the DLC coating. In addition, the paper discusses the emission mechanism from the energy band diagram of a field emitter coated with a sufficiently thin dielectric material having a low electron affinity, and shows that an effective work function of the DLC coated polysilicon field emitter is about 2.9 eV.

Measurement of z-direction component of electron spins field-emitted from a single-crystal magnetite whisker.

A 90° sector type spin rotator was developed for measurement of the z-direction component of a spin polarization, which is parallel to the emitter axis. The rotator enables us to measure all components of electron spins field-emitted from a single crystalline magnetite. In-plane component of spin polarization dominated of field-emitted electrons from single crystalline magnetite whisker, thus it is suggested that the magnetization of the magnetite whisker results from the anisotropy of crystalline structure rather than its shape.

Nanosized hexagonal plateletlike ZnO for nanophosphor applications

ZnO hexagonal plateletlike materials have been synthesized by reacting of hexamethylenetetramine in an aqueous solution of Zn2+ in the presence of sodium bis (2-ethylhexyl) sulfosuccinate emulsions as a structure-directing agent. The authors used a variety of analytical techniques, such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction to show that this synthesis method yields ZnO nanocrystals with a well-defined morphology. By changing the synthesis conditions, crystal size could also be controlled, for example, both micron- and nanometer-sized crystals were fabricated. Photoluminescence measurements have been carried out at various temperatures under the excitation with a cw He–Cd laser and a pulsed Nd3+:YAG laser. At higher excitation energies, whispering gallery mode emission appears in the spectrum.

Fabrication of a Spin-Polarized Electron Source with a Single Magnetite Whisker

-oriented single crystal magnetite whiskers 30 to 200 nm in diameter were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. Microscopic analyses have revealed that the whiskers have some defects such as stacking faults and dislocations and also that manganese is the dominant impurity. A spin-polarized electron source with a single magnetite whisker was fabricated by using a micro-sampling instrument in a focused ion beam (FIB) system. The spin polarization of this sample was measured by using a Mott electron polarimeter and was found to be 15% at room temperature.