Takehiko Hihara

Intrinsic ferromagnetism and magnetic anisotropy in Gd-doped ZnO thin films synthesized by pulsed spray pyrolysis method

This paper reports an in-depth study on nanocrystalline Gd-doped ZnO thin films synthesized using versatile pulsed spray pyrolysis method and exhibit room temperature ferromagnetism. The detailed structural and microstructural studies confirm that the doped Gd ions occupy Zn sites and the peak shift can be elucidated by charge neutrality. Optical investigation shows that the Gd doping in ZnO lattice leads to a decrease in the near band edge position due to the introduction of new unoccupied states by Gdu20024f electrons. The electronic structure of the Zn1−xGdxO at the Ou2009K edge shows the evolution of pre-edge spectral features similar to cuprates and manganites, and also confirms the strong hybridization of Ou20022p–Gdu20024f/5d states. Furthermore, the Gdu2009M5 edge provides evidence that Gd ions are in the trivalent state. Hysteresis measurements demonstrate that the Gd-doped ZnO films are magnetically anisotropic and exhibit intrinsic ferromagnetic behavior at room temperature. Higher magnetization in 3 kOe values is...

Investigations on the structural, optical and electronic properties of Nd doped ZnO thin films

We report the synthesis and characterization of Nd doped ZnO thin films grown on Si (1 0 0) substrates by the spray pyrolysis method. The surface morphology of these thin films was investigated by scanning electron microscopy and shows the presence of randomly distributed structures of nanorods. Grazing angle x-ray diffraction studies confirm that the doped Nd ions occupied Zn sites and these samples exhibited a wurtzite hexagonal-like crystal structure similar to that of the parent compound, ZnO. The micro-photoluminescence measurement shows a decrease in the near band edge position with Nd doping in the ZnO matrix due to the impurity levels. The near-edge x-ray absorption fine structure (NEXAFS) measurements at the O K edge clearly exhibit a pre-edge spectral feature which evolves with Nd doping, suggesting incorporation of more charge carriers in the ZnO system and the presence of strong hybridization between O 2p‐Nd 5d orbitals. The Nd M5 edge NEXAFS spectra reveal that the Nd ions are in the trivalent state. (Some figures in this article are in colour only in the electronic version)

Electron transport properties in Nb and NbN cluster-assembled films produced by a plasma–gas–condensation cluster source

Nb and NbN cluster-assembled films were produced by a plasma–gas–condensation cluster deposition apparatus and examined by transmission electron microscopy, electrical resistivity, and ultraviolet photoemission spectroscopy. The electron diffraction patterns of the Nb and NbN clusters displayed body-centered-cubic and NaCl-type diffraction rings, respectively. The electrical sheet resistance, R□, of both Nb and NbN cluster-assembled films, however, showed no superconductivity down to 2 K. We found a linear relation in the log R□ versus T−1/4 plot for the Nb cluster assembly, suggesting an electron localization effect. For the NbN cluster-assembly, on the other hand, R□ showed a semiconductor type temperature dependence, which is consistent with the valence electron spectra.

Li+ ionic conduction properties on NaI doped with a small amount of LiBH4

In the present work, Li+ conductor is synthesized via small doping of LiBH4 into “Li-free” compound (or solid solvent), NaI. The formation of solid solution between NaI and LiBH4 is confirmed by XRD measurement, and the solubility limit of LiBH4 exists between 6 to 13xa0mol%. The value of σ for 15NaI·LiBH4 (6xa0mol% LiBH4) showed 1.7xa0×xa010−6xa0S/cm at room temperature, which is comparable to that for LiI. From the plot of log σT vs. 1000/T, an activation energy for Li+ conduction in NaI is estimated to be 0.68 and 0.32xa0eV for heating and cooling cycle, respectively. The results of AC impedance measurement and DC polarization test indicate that Li+ plays a major role in ionic conduction in NaI regardless of the slight molar fraction of Li+. The present results suggest that the expansion in the material choice for solid solvent and other alkali halides can also work as a base material for Li+ ion conductors.

Critical field of two-dimensional superconducting Sn1−x/Six bimetallic composite cluster assembled films with energetic cluster impact deposition

Sn1−x/Six cluster assembled films have been prepared by an energetic cluster impact deposition using a plasma-gas-condensation cluster beam deposition apparatus. Transmission electron microscope images indicated that individual clusters have composite morphologies, where Sn and Si were separated from each other. The superconducting critical magnetic fields, Hc, of Sn1−x/Six cluster assembled films were measured and found to be much higher than the critical magnetic field of the bulk Sn. We estimated the Hc values by using a theory of the superconducting thin film. The estimated values are in good agreement with the experiments, indicating that the Sn1−x/Six cluster assembled films can be regarded as a two-dimensional system although thickness, t, of Sn1−x/Six cluster assembled films (t ≈ 1000u2009nm) is thicker than conventional superconducting thin film (tu2009<u2009100u2009nm).

Raman Spectra and Magnetic Property Analysis of Nd-Doped ZnO Thin Films

The present investigation is a detailed study aiming to understand the origin of the ferromagnetism of the well-characterized Nd-doped ZnO films. Raman scattering shows that the E2high phonon line of Zn1-xNdxO (x = 0, 0.05, 0.10, and 0.15) is broadened asymmetrically and shifts to a lower frequency, suggesting microscopic structural disorder induced by Nd3+ substitutions. Zn1-xNdxO films exhibit room-temperature ferromagnetism with a Curie temperature higher than 350 K. In addition, the films revealed magnetic anisotropy with higher magnetization in 3 kOe when the field was applied in the perpendicular direction to the sample surface than when applied in an in-plane direction.

PEFC catalytic properties of Pt – Ni nanoparticles prepared by a plasma-gas-condensation

Pt – Ni nanoparticles were fabricated via the gas phase method. Their performance as anode catalysts for the proton exchange membrane fuel cell was investigated as a function of Ni concentration. The microscopic configurations of the nanoparticles were rather heterogeneous; Pt-rich alloys existed in the core region of particles while a part of the surface layer was composed of the Ni-rich layer. Despite the Ni-rich layer in the shell region, the anode catalyst performance of the Pt – Ni nanoparticles was never deteriorated compared with that of the Pt ones. When the anode catalyst was composed of the Pt nanoparticles, a maximum power density of 112 mW/cm2 was obtained. However, 90% of the power density was still kept even when 40 at. % of Pt was replaced with Ni. The results suggest that a further decrease of Pt composition with maintaining its catalyst performance can be feasible by effective particle dispersing.

Metal coated glasses by sputtering and their microfouling properties

Some elements as contaminant tend to be concentrated in biofilm. In order to prevent the fogging of glass, it is very important to control biofilm formation by metal dissolution. In this study, Metals were deposited on glass substrate by Helicon-wave-excited-plasma sputtering process. Sample was very thin metals layer like as half mirror, it could transmit light. The results of biofilm formation test, biofilm formation were inhibited on Cu, Sn and Cr, and light transmission of these samples was not degradation. It could be said that inhibition of biofilm formation was effective to suppressing cloudiness.

Possibility of Exciton Mediated Superconductivity in Nano-Sized Sn/Si Core–Shell Clusters: A Process Technology towards Heterogeneous Material in Nano-Scale

We have produced Sn/Si core–shell cluster assemblies by a plasma-gas-condensation cluster beam deposition apparatus. For the sample with Si content = 12 at. %, the temperature dependence of electrical resistivity exhibits a metallic behavior above 10 K and the onset of superconducting transition below 6.1 K. With decreasing temperature, the thermomagnetic curve for the sample with Si content = 8 at. % begins to decrease steadily toward negative value below 7.7 K, indicating the Meissner effect. An increase in the transition temperature, TC is attributable to exciton-type superconductivity.