Papers by Author: Kazuo Shinozaki

Abstract: The effects of processing conditions on the morphologies of Mn-doped BiFeO₃ thin films have been investigated. BiFeO₃ thin films were prepared on a SrTiO₃ (001) substrate by CSD method. BiFeO₃ grew epitaxially on SrTiO₃ and Bi₂Fe₄O₉ has also orientation relationships with BiFeO₃. It was found that the formation of Bi₂Fe₄O₉ was promoted in an O₂ atmosphere. Island morphologies were observed in the BiFeO₃ thin films after post-annealing at 1023K both in N₂ and O₂ atmospheres. The formation of the islands is promoted in an O₂ atmosphere.

Abstract: This study examined effects of applying a magnetic field (up to 2 kG) on the magnetic properties of epitaxial NiFe₂O₄ (NF) thin films during deposition. The NF films were deposited on Y_0.15Zr_0.85O1.93 (YSZ) buffered Si (001) substrates using pulsed laser deposition (PLD). Although application of magnetic field during deposition affected neither the crystal structure nor orientation of the NF thin films, it improved magnetic properties. The saturation magnetization (Ms) of NF thin films deposited at 500°C and 600°C without application of a magnetic field was as low as 40 emu/g. However, that of NF deposited under magnetic field of 2 kG got to bulk Ms (50.3 emu/g). The TEM observation results revealed that the anti-phase boundary (APB) density decreased by application of the magnetic field during deposition. Results show that magnetic properties of NF thin films are controllable using the magnetic field during deposition.

Abstract: Highly oriented and polycrystalline Gd₂O₃ doped CeO₂ thin films were prepared on α-Al₂O₃(0001) substrates by chemical vapor deposition, using Ce(C₅H₄C₂H₅)₃ and Gd(C₅H₄C₂H₅)₃ as precursors. The compositions of the films were controlled by optimizing the vaporization pressure of Gd precursor under the constant vaporization condition of Ce precursor. In-plane electrical conductivities of the films at various temperatures and oxygen partial pressures were evaluated by electrochemical impedance spectroscopy measurements. The activation energy of the film was determined as 0.94 eV, which is comparable with that of pulsed laser deposited films.

Abstract: The effect of in-situ magnetic field during deposition (dynamic aurora PLD) was examined for SrTiO₃ thin film deposited on (La_0.5Sr_0.5)CoO₃/CeO₂ buffered YSZ(001) substrates. It was found that both in-plane and out-of-plane lattice parameters were changed by the in-situ magnetic field. Reciprocal space map measurement revealed that the in-plane and out-of-plane lattice parameters are 0.3817 and 0.3953 nm without magnetic field, meanwhile those are 0.3906 and 0.3974 nm with magnetic fields of 2 kG. This indicates that biaxial strain induced by the magnetic field. The effect of magnetic fields on the ferroelectric properties was examined.

Abstract: Thermal stability of bottom electrode thin films (La0.5Sr0.5)CoO3 (LSCO) and (La0.6Sr0.4)MnO3 (LSMO) were investigated. The crystallization and surface morphology of the heterostructure were characterized using x-ray diffraction and atomic force microscopy. Resistivity of the LSCO thin film was 25 cm. However, the resistivity of LSCO thin film increases sharply with annealing temperature. The LSMO thin film has high resistivity (100 mcm). The film does not decompose after thermal processing at 900 °C. To confirm thermal stability, we examined the effect of post annealing at various temperatures on the morphology and resistivity. Results showed that LSMO has higher thermal stability than that of LSCO.

Abstract: We investigated electrical properties of epitaxial Mn doped bismuth ferrite BiFe0.97Mn0.03O3 (BFMO) thin films with different crystal orientations deposited on Si substrates with appropriate buffer layers. Epitaxial SrRuO3 (SRO) thin films with (001), (101), and (111) orientations were grown on CeO2/yttria-stabilized zirconia (YSZ)/Si(001) substrates and YSZ/Si(001), respectively, by the insertion of MgO and TiO2 atomic layers using pulsed-laser deposition (PLD). Using spin coating, we deposited BFMO thin films onto orientated SRO thin films. The BFMO orientation followed the SRO orientation. The Pr values of the BFMO were ordered as follows {111}>{110}>{100}, which is the same as that predicted by crystallographic considerations. The largest Pr value of the {111} orientation is 76 μC/cm2 at 100 kHz, 25°C.

Abstract: Porous scaffolds, consisted of hydroxyapatite (HAp), chondroitinsulfate (ChS) and collagen, were prepared by freeze-drying technique. HAp/ChS composite particles were incorporated into a collagen matrix. Scanning electron microscope (SEM) observations showed that the porous scaffolds involved interconnected pores whose size was 80~200 µm in diameter. The HAp/ChS particles were homogeneously distributed in the collagen matrix. Surface area of the scaffolds was increased by the incorporation of the particles. Compression tests in phosphate buffer saline indicated that the porous scaffolds had elastic property and had larger compressive modulus than the pure collagen scaffold. The porous scaffolds obtained in this study could be useful for a cartilage tissue engineering.

Abstract: Insulin delivery carriers using low crystalline porous zinc hydroxyapatite (ZnHAp) microparticles with different crystal sizes and novel formulation method of poly (lactic acid) (PLA) have been developed to achieve the sustained-release of insulin. The adsorption isotherm curves of insulin dissolved into acetic acid of pH4.5 onto ZnHAp nanocrystals show non-Langmuir type due to the dissolution of the ZnHAp microparticles; the adsorption amounts were increased with the increase of crystalline sizes. The PLA formulation, coating the outer layer of microparticles, showed the apparent reduction of initial burst for insulin. The amounts of initial release of insulin decreased with the increase of crystalline sizes of ZnHAp, which could be attributed to the different meso-porous structure depending on its crystal sizes.

Abstract: Lithium niobate (LiNbO3) thin films were deposited on Al2O3(001) substrates using metal-organic chemical vapor deposition (MOCVD), with Li(dpm) and Nb(C2H5)5 as precursors. By optimizing the conditions of thin film deposition, the c-axis oriented and epitaxially grown LiNbO3 thin films with stoichiometric composition were deposited on an Al2O3(001) substrate. The refractive index of the stoichiometric LiNbO3 thin film was 2.24 at = 632.8 nm, which is close to that of bulk crystal.

Abstract: Thin films of HfO2 were fabricated on a p-Si(001) substrate using double pulse excitation (DPE) pulsed laser deposition (PLD) with KrF excimer and Nd:YAG lasers, and using conventional Nd:YAG laser PLD under two typical oxygen pressures (7.3 × 10-2 and 7.3 × 10-1 Pa). At 400°C or higher temperatures, the films are crystalline; at less than 400°C, they are amorphous. At higher oxygen pressures, DPE-PLD was effective against droplets. Then the surface morphology and electrical insulation properties of thin films were improved. At lower pressure, DPE-PLD was ineffective.