Papers by Author: Kazumi Kato

Abstract: Single crystalline BaTiO₃ nanocubes, which were synthesized by hydrothermal reaction with organic surfactants and additives, were assembled in order and directly on the substrates by dip-coating method using the dispersed solution. After evaporation of solvent, the orderly assembly of the nanocubes was developed over the large region in about several tens of micrometers square. It can cover whole surface of the substrate. The microstructures of the nanocube assemblies were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrical property of the nanocube-assembled film was characterized by piezoresponse force microscopy (PFM). The d₃₃-V curve showed ferroelectric hysteresis and saturation behaviors under high applied voltage.

Abstract: Numerical simulations of the oriented aggregation of BaTiO₃ nanocrystals using the dipole-dipole interaction model have been performed under conditions corresponding to those used in ultrasound-assisted synthesis. The results suggest that BaTiO₃ nanocrystals with a diameter of 5 nm have a spontaneous polarization that is not more than one order of magnitude lower than the value of ~0.15 C/m² for a macroscopic BaTiO₃ single crystal.

Abstract: Barium titanate (BT) and strontium titanate (ST) nanocubes which have been synthesized by hydrothermal method with surfactants were assembled in order directly on the substrates by using capillary-force-assisted self-assembly method. The ordered structures, crystallinity and orientation of the nanocubes were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning probe microscopy (SPM) and X-ray diffraction (XRD). The piezoresponse properties of the nanocubes ordering structures characterized by Piezoresponse Force Microscopy (PFM) seemed to depend on the constituents and their interface.

Abstract: The HfO2 films were prepared on the ITO/polyimide substrate using alkoxy-derived precursor solutions at low temperature. The HfO2 films prepared by UV-assisted process using the precursor solution modified with diethanolamine had smooth surface and RMS roughness values of HfO2 film were 1.2nm. The electrical properties of HfO2 films were improved by optimization of preparation condition. The leakage current density at 1V was below 10-5A/cm2. The dielectric constant was about 20. The loss tangent was below 0.1.

Abstract: Porous nano-scale ZnO particle film was rapidly synthesized from a mixing solution of zinc acetate dihydrate – acetone at about 90 °C. The crystal structure and morphology　were clarified by the X-ray diffraction and a field emission scanning electron microscope. The evaporation of higher vapor pressure acetone resulted in the hydrolysis of zinc salt in itself crystalline water. Three morphologies of ZnO (dispersed nanoparticles, dispersed bread chip-shaped particles and flower-like bread chip-shaped assemblies) were observed.

Abstract: The HfO2 films prepared from alkoxy-derived precursor solution chemically modified with diethanolamine. The effects of UV irradiation on the HfO2 films were investigated. The UV irradiation using low pressure mercury lamp (LPML) was effective for the organics decomposition in the film and densification. The uniform and smooth HfO2 films were obtained. The refractive index of HfO2 films was enhanced.

Abstract: Anhydrous zinc acetate pre-coated on the FTO substrate was served as a template layer, and ZnO nanowhisker arrays were simply and successfully fabricated by its forced-hydrolysis-initiated-nucleation of the layer in an aqueous solution at low temperature below 100 °C. The technique doesn’t need any expensive metal catalyst and high-temperature treatment. The density, diameter and length of whiskers were controllable by changing the deposition time. As-grown ZnO nanoarrays showed photo-induced electrical property. Enhanced photo-induced current (2.0~3.0  10-5 A) was detected under laser irradiation after DNA molecules labeled with dye molecules were loaded on the ZnO nanowhisker arrays.

Abstract: Length-tailored, monodisperse, highly orientated, single-crystalline hexagonal and aligned ZnO nanowhiskers were grown onto F-doped SnO2 conductive glass (FTO) substrate at 88 °C using an aqueous solution. The aqueous solution for growth of ZnO nanowhiskers included zinc nitrate hexahydrate, hexamethylenetetramine and polyethylenimine. The addition of branched polyethylenimine, which may be adsorbed on the nonpolar surface of ZnO crystals, improved the growth of ZnO nanowhiskers along the c-axis.

Abstract: Various BaTiO3 thin films were fabricated at 650oC by using different conditions such as the heating rate and alkoxy-derived gel-film thickness. In this study, the spin-coating and calcination step were repeated several times to control the gel-films thickness. And then the one-sintering was carried out with various heating rates. BaTiO3 films with perovskite phase were obtained by using the heating rate of 100oC/sec and the surface morphology became rough with increase of gel-film thickness. We considered that the change of root mean square (rms) roughness and cross-sectional profiles by various heating rates was caused by densification.

Abstract: Semi-crystalline mesoporous titania films were prepared by the reactions of titanium isopropoxide (TTIP) in acidic aqueous solutions containing EO106PO70EO106 triblock copolymer (F127) and 1,3,5-triisopropylbenzene (TIPBz). Adsorption experiments of dye molecules over the mesoporous films calcined at different temperatures and prepared with different TTIP/F127 molar ratios showed that adsorption property of the dye molecules would be related to the crystallinity of the frameworks and the macroporosity at the surfaces.