Direct observation of magnetic domains in phase separated Nd0.7Ca0.3MnO3 single crystals

The magnetic properties of single-crystalline Nd0.7Ca0.3MnO3 were studied with both macroscopic and microscopic probes. The magnetization shows large irreversibility behavior between zero-field-cooled and field-cooled data at low field, suggesting a phase separation driven by competition between ferromagnetic and antiferromagnetic phases. The scanning superconducting quantum interference device microscope observations under zero field gave clear evidence that the compound includes ferromagnetic regions as the ground state below Tc. It was also found that two different phase-separated states appear, depending on temperature. At T∼125 K, weak but finite spontaneous magnetization develops, while the magnetization is abruptly enhanced below 95 K, possibly reflecting an increase of the volume fraction of the ferromagnetic region. The present results support the phase separation scenario that fine ferromagnetic particles embedded in an antiferromagnetic matrix are magnetostatically coupled to each other to form a network of macroscopic sizes

Construction and Superfunction of Metal-oxide Nanostructures and Interfaces(Interfaces by various techniques)

Metal oxides show such versatile properties as high T_C superconductivity, ferroelectricity, colossal magnetoresistance and non-linear optical properties. By developing laser molecular beam epitaxy, we have been working on atomic scale control for the heteroepitaxy of these materials in order to explore a novel field of "oxide electronics", in which monolithically integrated devices composed of epitaxially grown oxide nanostructures show outstanding performances that Si-based semiconducting devices would not be able to give. Among many topics we have, we concentrate on Josephson tunnel junction made out of high T_C superconductors and ultra-violet laser emission from ZnO nanocrystal films

Molecular dynamics simulation on a layer-by-layer homoepitaxial growth process of SrTiO3(001)

科研費報告書収録論文(課題番号:09355030・基盤研究(A)(2)・H9～H11/研究代表者:宮本, 明/次世代エレクトロニクス材料としての酸化物人口超格子の原子レベル設計と開発

Layer-by-layer heteroepitaxial growth process of a BaO layer on SrTiO3(001) as investigated by molecular dynamics

科研費報告書収録論文(課題番号:09355030・基盤研究(A)(2)・H9～H11/研究代表者:宮本, 明/次世代エレクトロニクス材料としての酸化物人口超格子の原子レベル設計と開発

Layer-by-layer homoepitaxial growth process of MgO(001)as investigated by molecular dynamics, density functional theory,and computer graphics

科研費報告書収録論文(課題番号:09355030・基盤研究(A)(2)・H9～H11/研究代表者:宮本, 明/次世代エレクトロニクス材料としての酸化物人口超格子の原子レベル設計と開発

Combinatorial screening of halide perovskite thin films and solar cells by mask-defined IR laser molecular beam epitaxy

As an extension of combinatorial molecular layer epitaxy via ablation of perovskite oxides by a pulsed excimer laser, we have developed a laser molecular beam epitaxy (MBE) system for parallel integration of nano-scaled thin films of organic–inorganic hybrid materials. A pulsed infrared (IR) semiconductor laser was adopted for thermal evaporation of organic halide (A-site:CH3NH3I) and inorganic halide (B-site: PbI2) powder targets to deposit repeated A/B bilayer films where the thickness of each layer was controlled on molecular layer scale by programming the evaporation IR laser pulse number, length, or power. The layer thickness was monitored with an in situ quartz crystal microbalance and calibrated against ex situ stylus profilometer easurements. A computer-controlled movable mask system enabled the deposition of combinatorial thin film libraries, where each library contains a vertically homogeneous film with spatially programmable A- and B-layer thicknesses. On the composition gradient film, a hole transport Spiro-OMeTADlayer was spin-coated and dried followed by the vacuum evaporation of Ag electrodes to form the solar cell. The preliminary cell performance was evaluated by measuring I-V characteristics at seven different positions on the 12.5 mm × 12.5 mm combinatorial library sample with seven 2 mm × 4 mm slits under a solar simulator irradiation. The combinatorial solar cell library clearly demonstrated that the energy conversion efficiency sharply changes from nearly zero to 10.2% as a function of the illumination area in the library. The exploration of deposition parameters for obtaining optimum performance could thus be greatly accelerated. Since the thickness ratio of PbI2 and CH3NH3I can be freely chosen along the shadow mask movement, these experiments show the potential of this system for high-throughput screening of optimum chemical composition in the binary film library and application to halide perovskite solar cell

Strong ferromagnetism in Pt-coated ZnCoO: The role of interstitial hydrogen

We observed strong ferromagnetism in ZnCoO as a result of high concentration hydrogen absorption. Coating ZnCoO with Pt layer, and ensuing hydrogen treatment with a high isostatic pressure resulted in a highly increased carrier concentration of 10(21)/cm(3). This hydrogen treatment induced a strong ferromagnetism at low temperature that turned to superparamagnetism at about 140 K. We performed density functional method computations and found that the interstitial H dopants promote the ferromagnetic ordering between scattered Co dopants. On the other hand, interstitial hydrogen can decrease the magnetic exchange energy of Co-H-Co complexes, leading to a reduction in the blocking temperature.open7

Binary composition spread approach for parallel pulsed laser deposition synthesis and highthroughput characterization of transparent and semiconducting oxide thin films

62-65Conventional ‘one by one’ synthesis approach has been a major rate limiting step in the systematic exploration of increasingly complex materials for the demanding new technologies. Derived from the new concepts of combinatorial chemistry, recently introduced continuous binary composition spread technique based on the non-uniformity of the deposition rate typically observed in pulsed laser deposition (PLD) is applied to the parallel growth of transparent and semiconducting oxides LixNi₁₋xO. A large variation of x in LixNi₁₋xO was achieved on a single MgO(100) substrate. Details of the synthesis technique are discussed. Microstructural, transport and optical studies were done to optimize the Li concentration in the film. XRD and AFM confirmed an epitaxial growth and smooth surface for all the Li contents. SIMS data revealed a non-linear Li variation along the film with a minimum of 0.01% of Li content. High conductivity of 1.42 ohm⁻¹ cm⁻¹ was obtained in sufficiently high Li concentration regions. Optical transparency beyond 80% was obtained in the 40 nm thick films. The combinatorial binary composition spread technique results in significant time and energy savings for rapidly optimizing the thin film growth parameters to explore new TCOs for future optoelectronic applications