Crystallization behavior and origin of c-axis orientation in sol–gel-derived ZnO:Li thin films on glass substrates

Preferentially, c-axis-oriented lithium-doped zinc oxide (ZnO:Li) thin films were prepared on Pyrex borosilicate glass substrates by a sol–gel method starting from zinc acetate dihydrate, lithium chloride, 2-methoxyethanol and monoethanolamine. Decomposition and crystallization behavior of dip-coated amorphous precursor films during post-annealing treatments were investigated by thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical transmittance measurements, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). It was revealed that the films contained the organic compounds at temperatures up to 300°C, which was the key to the transformation from the amorphous to the crystalline state. Thermodynamical consideration of nucleation and crystal growth was made taking account of surface energies of the film and the glass substrate and an interfacial energy between them. Mechanisms underlying the c-axis orientation were proposed based upon the initial orientation due to nucleation and final growth orientation.     

Dynamic observation of an atom-sized gold wire by phase electron microscopy

A single-atom-sized gold wire was successfully observed in real time by a newly developed defocus-image modulation processing electron microscope. Because of phase retrieval processing with spherical aberration correction, the single-atom strand wire was observed with high contrast and without contrast blurring. By carefully looking at the atomic distance, the contrast, and the dynamic behavior of the wire, we recognized that there are two stages of the wire. In the first stage the wire maintained the atomic distance in the bulk crystal, but in the second stage the wire showed the atomic distance of the nearest-neighbor atoms with weaker contrast. The gold wire was rather stable for a few seconds under strong electron beam illumination.     

Superconducting property of Zr–Co and Zr–Co–Al alloys fabricated by rapid solidification

The superconducting property of Zr_(1−x)Co_x (x = 10–50 at.%) alloys and a Zr₅₅Co₃₀Al₁₅ bulk metallic glass fabricated using techniques of rapid solidification was investigated. The Zr₅₅Co₃₀Al₁₅ alloy crystallized by heat treatment in a vacuum atmosphere exhibited superconductivity of T_c,on = 2.4 K. This was attributable to the superconducting property of a crystalline Zr–Co alloy precipitated in the Zr₅₅Co₃₀Al₁₅ alloy. The T_c,on of the crystalline Zr_(1−x)Co_x alloy was sensitive to the Co content. The increase of Co content for the Zr_(1−x)Co_x alloy led to the decrease of T_c,on. The Zr_(1−x)Co_x alloy exhibited superconductivity of a maximum T_c,on = 3.9 K for the Zr₈₀Co₂₀ alloy with superconducting nanocrystal particles embedded in the amorphous matrix.     

Multiphoton double ionization of Ar in intense extreme ultraviolet laser fields studied by shot-by-shot photoelectron spectroscopy

Photoelectron spectroscopy has been performed to study the multiphoton double ionization of Ar in an intense extreme ultraviolet laser field (hν ～ 21 eV, ～ 5 TW/cm2), by using a free electron laser (FEL). Three distinct peaks identified in the observed photoelectron spectra clearly show that the double ionization proceeds sequentially via the formation of Ar(+): Ar+hν→Ar (+) + e? and Ar2(+) + 2hν→Ar(+) + e?. Shot-by-shot recording of the photoelectron spectra allows simultaneous monitoring of FEL spectrum and the multiphoton process for each FEL pulse, revealing that the two-photon ionization from Ar(+) is significantly enhanced by intermediate resonances in Ar(+).     

Dielectric-field effect correction on i.r. band shapes in the liquid phase

The dielectric-field correction on i.r. band shape in the liquid has been studied by using the Lorentz internal field. The deformation of the band shape is inappreciable for a weak absorption band that becomes measurable only at a sample thickness larger than 10μ. The shapes of the strong singlet and doublet bands of hexafluorobenzene at 1530 cm^?1 and near 1000 cm^?1, respectively, and also of the doublet band of carbon tetrachloride near 790 cm^?1 have been measured in dilute solutions and compared with those for the pure liquid.     

A successive quadratic programming algorithm with global and superlinear convergence properties

This paper presents a successive quadratic programming algorithm for solving general nonlinear programming problems. In order to avoid the Maratos effect, direction-finding subproblems are derived by modifying the second-order approximations to both objective and constraint functions of the problem. We prove that the algorithm possesses global and superlinear convergence properties.This work was supported in part by a Scientific Research Grant-in-Aid from the Ministry of Education, Science and Culture, Japan.     

Spin-dependent transport in a nanopillar non-local spin valve

We investigate the injection of a pure spin current into a non-magnetic Cu wire in a lateral spin valve. We detect the spin accumulation occurring at the interfaces between the magnetic nanopillars and the non-magnetic wire in the non-local geometry. We confirm that the accumulated spins diffuse equally in the Cu wire irrespective of the presence of a charge current. The inversion of the injector and detector magnetic nanopillars does not affect the spin signal, in agreement with analytical predictions for this system.     

Abnormal Li diffusion in β-LiGa by the formation of defect complex

The diffusion coefficients of Li in the NaTl-type Li intermetallic compound of β-LiGa have been measured by using a short-lived radioactive diffusion tracer. As the tracer, the α-emitting radioisotope of ⁸Li delivered as the energetic and pulsed beam from Tokai Radioactive Ion Accelerator Complex (TRIAC) was implanted into the β-LiGa compounds with the composition in the range of about 43 to 54 at.% Li. By analyzing the time-dependent yields of the α-particles measured according to the repetition cycle of the beam, the tracer diffusion coefficients were extracted over the wide range of Li composition. Abnormal composition-dependence of Li diffusion coefficients in β-LiGa was observed; the stoichiometric β-LiGa showed the highest diffusivity of Li. By referring to the composition-dependent diffusivity of Li in the iso-structural β-LiAl and β-LiIn, we could identify the abnormal diffusion of Li in very Li-poor composition of β-LiGa. The anomaly has been discussed qualitatively in terms of the formation of defect complex and the interaction between the constitutional defects.     

High-Field and Multifrequency ESR Studies at KYOKUGEN in Osaka University

We have developed high-field and multifrequency (HFMF) electron spin resonance (ESR) apparatus for the magnetic fields up to 65 T at frequencies up to about 6 THz. In addition to this pulsed field ESR apparatus, we are making a multifrequency ESR apparatus with very high sensitivity in a static field. We report the results of ESR studies on BaCoV₂O₈ and NiGa₂S₄, followed by recent developments and future plans of our HFMF ESR apparatus.     

Magnetic interactions in the geometrically frustrated triangular lattice antiferromagnet CuFeO2

The spin-wave excitations of the geometrically frustrated triangular lattice antiferromagnet CuFeO2 have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in the ab plane (J1, J2, J3, with J{2}/J{1} approximately 0.44 and J{3}/J{1} approximately 0.57), as well as out-of-plane coupling (J{z}, with J{z}/J{1} approximately 0.29) are required to describe the spin-wave dispersion relations, indicating a three-dimensional character of the magnetic interactions. Two energy dips in the spin-wave dispersion occur at the incommensurate wave vectors associated with multiferroic phase and can be interpreted as dynamic precursors to the magnetoelectric behavior in this system.