[en] The authors studied the critical state field profile using magneto-optical technique in YBa₂Cu₃O_7-δ with columnar defects (CDs) when the field is tilted away from CDs. They observed an asymmetric critical state field profile with the current discontinuity line (d-line) considerably away from the center of the sample. The shift of the d-line from the center (Δy) has symmetric hysteresis loop with respect to H = 0. When the field sweep direction is changed, the previous d-line disappears and a new d-line is generated at the opposite side. The shift of the d-line is parallel to the tilting plane of H and toward the direction of the misalignment of H from CDs. They interpret this asymmetry as caused by the in-plane magnetization, which is originated from the alignment of vortices to CDs. The field dependence of Δy is discussed in relation with the correlation length of vortices along CDs

[en] Vanadium oxides possess various interesting properties due to multivalence of a vanadium atom and attract our interest as a target material for the exploration of new applications. We investigated vanadates (La_1-xCa_x)VO₃ with a perovskite structure as thermoelectric (TE) materials because heavy electrons in vanadates are expected to generate large thermopower. To proceed the investigation of thermoelectric properties of the composition spread library more efficiently, we devised a new instrument of multi-channel measurement of their thermoelectric properties. The polarity of Seebeck coefficients changed from positive (0≤x≤0.2) to negative (0.2< x<1.0), and the composition where the film shows the highest power factor in our investigated range is around pure LaVO₃ (x∼0)

[en] There have been two methods of observing melting transition; the method using Hall element and the magneto-optical differential method. In the Hall element method, which can detect the change of magnetic flux density ΔB=0.3 G, it is difficult to observe two-dimensional distribution in vast area. In the magneto-optical method, where the two-dimensional distribution can be easily observed, however, the magnetic field resolution is not sufficient. Recently, the improvement of the magnetic field resolution has been achieved and the in-situ measurement of vortex-lattice melting transition became possible. The brief description of the experimental method, the observed melting transition in Bi₂Sr₂CaCu₂O_8+y (BSCCO), and the characteristics of the BSCCO lattice is presented. (A. Yamamoto)

[en] Quick growth optimization of complex oxide, Y-type magnetoplumbite (Ba₂Co₂Fe₁₂O₂₂ (Co₂Y)) thin films is demonstrated by using combinatorial thin film technology. Planning a CoO buffer layer on MgAl₂O₄(1 1 1) substrate was found to be very effective for preventing the phase separation of Co deficient impurity (BaFe₂O₄) and forming the desired Co₂Y phase. The combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction facilitate the production of Y-type magnetoplumbite thin film in a single phase

[en] Magnetic properties of nanostructured epitaxial thin layers of a series of Co and Li co-doped NiO on MgO(1 0 0) substrate with NiO buffer layer have been investigated. Thin films were synthesized by combinatorial laser molecular beam epitaxy (CLMBE) in the continuous binary composition spread approach. Large and linear variation of x was achieved in the growth of Co_xLi_0.2Ni_0.8-xO_, onto 9 mm of single substrate. Homoepitaxial growth with smooth surface morphology was confirmed by grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). Linear decrease in the band gap and optical transparency was observed with increasing cobalt concentration. The magneto-optical Kerr effect revealed a strong photon energy dependency with negative Kerr rotation for all the Co-concentrations in the film, suggesting intra-valence charge transfer (IVCT) between low spin state Co²⁺ with host Ni²⁺. Ferromagnetic (FM)-like ordering was observed at low temperatures, while antiferromagnetism predominates at room temperature in the Co and Li co-doped nickel oxide epitaxial films.

[en] We have fabricated Al₂O₃, LaAlO₃ (LAO), CaHfO₃ (CHO) and CaZrO₃ (CZO) thin films for the dielectric layers of field-effect transistors (FETs) by pulsed laser deposition (PLD). The films exhibited very smooth surfaces with root-mean-squares (rms) roughnesses of ∼1.3 A as evaluated by using atomic force microscopy (AFM). The breakdown electric fields of Al₂O₃, LAO, CHO and CZO films were 7, 6, 10 and 2 MV/cm, respectively. The magnitude of the leak current in each film was low enough to operate FET. We performed a comparative study of pentacene FET fabricated using these oxide dielectrics as gate insulators. High field-effect mobility of 1.4 cm²/V s and on/off current ratio of 10⁷ were obtained in the pentacene FET using LAO gate insulating film. Use of the LAO films as gate dielectrics has been found to suppress the hysteresis of pentacene FET operations. The LAO films are relevant to the dielectric layer of organic FETs

[en] We have designed a compact combinatorial pulsed laser deposition (PLD) chamber as a building block of a desktop laboratory for advanced materials research. Development of small-size systems for the growth and characterization of films would greatly help in interconnecting a variety of analytical tools for rapid screening of advanced materials. This PLD chamber has four special features: (1) a drum-shaped growth chamber (2) a waterwheel-like combinatorial masking system (3) a multi-target system having one feedthrough, and (4) a small reflection high-energy electron diffraction (RHEED) system. The performance of this system is demonstrated by the RHEED intensity oscillation during homoepitaxial growth of SrTiO₃ as well as by simultaneous fabrication of a ternary phase diagram of rare earth-doped Y₂O₃ phosphors

[en] We have fabricated a combinatorial nm-planar electrode array by using photolithography and chemical mechanical polishing processes for high throughput electrical evaluation of organic devices. Sub-nm precision was achieved with respect to the average level difference between each pair of electrodes and a dielectric layer. The insulating property between the electrodes is high enough to measure I-V characteristics of organic semiconductors. Bottom-contact field-effect-transistors (FETs) of pentacene were fabricated on this electrode array by use of molecular beam epitaxy. It was demonstrated that the array could be used as a pre-patterned device substrate for high throughput screening of the electrical properties of organic semiconductors

[en] Planar type metal/insulator/metal structures composed of an epitaxial perovskite manganese oxide layer and various metal electrodes were prepared for electric-field-induced resistance switching. Only the electrode pairs including Al show good resistance switching and the switching ratio reaches its maximum of 1000. This resistance switching occurs around the interface between Al electrodes and epitaxial perovskite manganese oxide thin films