Showing papers by "Hiroki Kondo published in 2010"

Measurement of Hydrogen Radical Density and Its Impact on Reduction of Copper Oxide in Atmospheric-Pressure Remote Plasma Using H2 and Ar Mixture Gases

Abstract: A 60 Hz alternating current excited atmospheric-pressure plasma with an ultrahigh electron density of over 1016 cm-3 employing H2/Ar [ p(H2)/p(H2+Ar) 1–3%] gases was used to reduce copper oxides on copper. The remote plasma reduced CuO and Cu2O at room temperature. The ground-state hydrogen (H) radical density in the atmospheric-pressure plasma was measured by vacuum ultraviolet absorption spectroscopy using a micro hollow cathode lamp. The ratio of reduction of amount of CuO flux to the H radical flux was determined from the measured H radical density and gas temperature.

Mapping of Heterogeneous Chemical States of Lithium in a LiNiO2-Based Active Material by Electron Energy-Loss Spectroscopy

Abstract: It is difficult to analyze the local concentrations and chemical states of lithium in lithium-ion secondary battery electrodes by microanalysis techniques based on transmission electron microscopy because the core excitation spectra of transition metals invariably overlap with the absorption/emission spectra of Li-K. We propose a promising analysis method that enables the spatial distribution of lithium with different chemical states from the original phase in a LiNiO 2 -based positive electrode to be visualized. It employs a suite of spectrum imaging techniques including scanning transmission electron microscopy, electron energy-loss spectroscopy, and multivariate curve resolution. This method is successfully applied to a cross-sectioned positive electrode.

Critical Factors for Nucleation and Vertical Growth of Two Dimensional Nano-Graphene Sheets Employing a Novel Ar+ Beam with Hydrogen and Fluorocarbon Radical Injection

Abstract: Two-dimensional nano-graphene sheets, standing vertically on carbon nanowalls (CNWs) substrates, were synthesized by multi-beam chemical vapor deposition employing three types of irradiation, Ar+ beam with tunable fluxes and energies, hydrogen (H) and fluorocarbon radicals, which could be independently controlled The CNWs growth processes were investigated by changing the Ar+ irradiation conditions Irradiation of Ar+ ions with appropriate fluxes and energies on fluorocarbon layers evolved nanoislands for growth of the CNWs By tuning the fluxes and energies of the incident Ar+ on amorphous carbon nanoislands, critical factors for controlling nucleation and growth of CNWs were determined

Optical Properties of Evolutionary Grown Layers of Carbon Nanowalls Analyzed by Spectroscopic Ellipsometry

Abstract: Carbon nanowalls (CNWs), vertically standing graphene sheets, grown by the radical injection plasma-enhanced chemical vapor deposition system were analyzed by spectroscopic ellipsometry. The refractive indexes (n), extinction coefficients (k), and optical band gaps (Eg) of evolutionary growth layers were evaluated using the Tauc–Lorentz model with the effective medium approximation. It was observed that an amorphous carbon interfacial layer with n of 1.9–2.0 was formed prior to the growth of CNWs with n of 1.2–1.5. Moreover, the imaginary parts of complex dielectric functions analyzed using the Tauc–Lorentz model indicate the possibility that the CNWs have semiconducting features.

Aqueous secondary battery

Abstract: An aqueous secondary battery 10 according to the present invention includes a positive electrode containing a NASICON-type positive-electrode active material that can insert and extract sodium as a positive-electrode active material 12, a negative electrode containing a negative-electrode active material 17 that can insert and extract sodium, and an electrolyte solution 20 disposed between the positive electrode and the negative electrode, the electrolyte solution 20 being an aqueous solution in which sodium is dissolved. The NASICON-type positive-electrode active material is, for example, Na3V2(PO4)3, and the electrolyte solution 20 is an aqueous solution in which sodium is dissolved. The negative-electrode active material 17 is preferably a NASICON-type negative-electrode active material (for example, LiTi2(PO4)3 or NaTi2(PO4)3).

Metal-organic chemical vapor deposition of high-dielectric-constant praseodymium oxide films using a cyclopentadienyl precursor

Abstract: Praseodymium (Pr) oxide films were grown by metal-organic chemical-vapor-deposition (CVD) using Pr(EtCp)3. Using H2O as an oxidant, Pr2O3 films with columnar structures are formed and its C concentration can be reduced to about one-tenth compared with the case using O2. Activation energy of 0.37 eV is derived for this CVD using H2O. This CVD-Pr oxide film deposited at 300 °C has a dielectric constant of 26±3. Furthermore, conduction band offset of 1.0±0.1 eV and trap levels of 0.40±0.02 and 0.22±0.02 eV in the CVD-Pr2O3/Si structure were also determined by current conduction characteristics.

Formation of Pr Oxide Films by Atomic Layer Deposition Using Pr(EtCp) 3 Precursor

Abstract: The formation of Pr oxide films by an atomic layer deposition (ALD) technique using Pr(EtCp)3 and H2O was investigated in this study. The ALD-mode growth of Pr oxide films at a rate of 0.07 nm/cycle and a thickness variation of less than 2% on 3-in. Si wafers was achieved. Transmission electron microscopy (TEM) images and transmission electron diffraction (TED) patterns revealed that polycrystalline cubic Pr2O3 films were grown on Si(001) substrates. On the other hand, epitaxial growth of the cubic Pr2O3 film was clearly observed on a Si(111) substrate. According to X-ray photoelectron spectroscopy (XPS) analyses, the C content of the ALD-Pr oxide film grown at 130 °C is 1.6%. Relatively fine capacitance–voltage curves were observed for the Al/ALD-Pr oxide/Si(001) capacitors. The interface state density between the 130 °C-grown ALD-Pr oxide film and the Si(001) substrate is about 1×1011 cm-2 eV-1. The dielectric constant of the ALD-Pr oxide film grown at 250 °C was determined to be about 18, assuming that the dielectric constant of the interlayers is similar to that of SiO2.

Crystalline Structures and Electrical Properties of High-Nitrogen-Content Hf-Si-N Films

Abstract: The crystalline structures and electrical properties of high-nitrogen (N)-content Hf–Si–N films were investigated. When the N2 concentration of a sputtering ambient increases from 9.0 to 13.0%, Hf–Si–N resistivity increases by a factor of more than 105 despite the almost constant N content of the film. According to X-ray diffraction profiles and X-ray photoelectron spectra, such high-N-content Hf–Si–N films consist of Hf3N4 and Si3N4, and have energy band gaps. These results indicate that Hf3N4 and high-N-content Hf–Si–N including Hf3N4 have semiconducting features. In Pt/Hf–Si–N/Pt structures with high-N-content Hf–Si–N, nonlinear current–voltage characteristics and hysteresis behaviors are also observed, which markedly change depending on N2 concentration and postdeposition annealing temperature. Although the elemental composition and crystalline structure hardly change, the phase separation and segregation of nanocrystallites clearly develop. Therefore, these unique electrical characteristics are attributed to current conduction at grain boundaries or Pt/Hf–Si–N interfaces.

Control of crystalline and electronic structures of carbon nanowalls for their device applications

Abstract: Controlling factors of crystalline and electronic structures of carbon nanowalls were investigated in this study. Precise measurements and controls of radicals and ions in the plasma make the controlled syntheses of CNWs possible. For example, density ratios of hydrogen (H) and carbon atoms are essential to determine the density and height of CNWs. Ar+ ion irradiation is also important for vertical-growth of graphene sheets. Vertical-growth of graphene sheets could occur only under Ar+ ion irradiation with suitable energy and flux for each process. On the other hand, by N 2 gas addition to C 2 F 6 /H 2 /Ar mixture ambient, the CNWs with n-type conducting properties can be formed. These results obtained in this study suggest that the CNWs are promising as new functional device materials in various applications.

Governmental Transfers Can Reduce a Moral Hazard Problem

Abstract: An altruistic agent who may aid a person with a low income may cause that person to exert little effort to increase his income. Such behavior generates a Dilemma, in which welfare is lower than when no one is altruistic. We show how governmental transfers, which do not allow for reallocation from a person who saves much to one who saves little, reduces the effect, and can lead to an outcome which is Pareto-superior to the outcome under a Nash equilibrium with no government taxation and transfers.