Norio Tanaka

Epitaxial Growth of Zinc Oxide Whiskers by Chemical-Vapor Deposition under Atmospheric Pressure.

ZnO whiskers were epitaxially grown by a chemical-vapor deposition technique employed at atmospheric pressure. Highly oriented ZnO whiskers grew at a substrate temperature of 550°C on (0001)α-Al2O3 substrates with a growth rate of 3.7 nm/s. X-ray diffractometry revealed that the epitaxial relationship between the whiskers and the substrate was determined as ZnO[1010](0001)//Al2O3[1210](0001) or ZnO[1210](0001)//Al2O3[1010](0001). In addition, the full-width at half maximum value of the (0002) reflection was as low as 0.43°. Images obtained using a scanning electron microscope were analyzed and it was found that the whisker tip likely has a radius of curvature of approximately 20 nm. The typical number density of the whiskers has reached 1.3×105mm-2.

Homogeneous Growth of Zinc Oxide Whiskers

Several common modes of crystal growth provide particularly simple and elegant examples of spontaneous pattern formation not only in nature but also under artificial circumstances. We have already reported that well-organized ZnO whiskers are epitaxially grown using a chemical vapor deposition technique [Satoh et al..: Jpn. J. of Appl. Phys. 38 (1999) L586]. One aim of this study is to determine the optimum growth conditions for obtaining the structure containing homogeneous whiskers grown with a relatively high growth rate. A substrate temperature of 550°C and a vaporizing temperature of 125°C are the most appropriate for obtaining homogeneous whiskers. Whiskers are highly oriented in the a-and c-axes directions of the hexagonal structure. The growth rate reached a maximum value as high as 7.5 nm/s.

High-Rate Epitaxy of Anatase Films by Atmospheric Chemical Vapor Deposition

Crystalline orientation often provides particularly the anisotropy of chemical and physical properties. Since the epitaxial films are composed of highly oriented crystals, it is expected that chemical and physical advantages are predominantly in one specific direction. In this study, high-rate epitaxy of anatase films was attempted using a chemical-vapor-deposition technique. Four types of epitaxial anatase films were obtained, i. e. , , , and oriented normal to the substrate surface. These films reduced methylene blue under ultraviolet irradiation. The reduction rate of methylene blue was largely affected in the direction of crystalline orientation.

Fabrication of Dye-Dispersed Optical-Quality Polymer Films by Coprecipitation of Cyanine Dye with Polymers

3,3-Diethyloxadicarbocyanine iodide (DODCI)-dissolved polymer powders were formed by coprecipitation of DODCI with polymers [poly(methyl methacrylate) (PMMA), poly(2-hydroxypropyl methacrylate) (PHPMA), etc.]. An acetone solution of DODCI in which a purified polymer was also dissolved was injected into a large amount of n-hexane. The precipitated powder in n-hexane was filtered and then dried under ultrahigh vacuum (UHV), and formed into a thin film by a hot-press method [Hiraga et al.: Chem. Lett. (1990) 2255]. Another method for preparing a powder by coprecipitation has successfully been developed using a vacuum process. The acetone solution of DODCI and polymer was directly injected into UHV from the liquid phase through a modified needle valve. Deposits were formed on a heat-controlled substrate through quick evaporation of a carrier solvent and they were hot-pressed to produce a thin transparent film. Condensed states of DODCI associates in these films have been analyzed by optical absorption and emission, small-angle X-ray scattering (SAXS), and NMR spectroscopy. A new technique to control the arrangement of dye associates in three-dimensional space has been proposed.

A novel formation method of thin polymer film with densely dispersed organic dye by using vacuum technique

Abstract A novel method of thin film formation of organic materials using a vacuum technique is proposed. An organic dye with a high sublimation pressure is loaded in a crucible along with a thin polymer film. After pumping down, the crucible is sealed, then placed in a constant temperature oven. The vapor of dye dissolves into the polymer film, thus forming a thin dye-containing layer.

Synthesis of Y–Ba–Cu–O films with ethylene diamine tetra-acetic acid complexes assisted by excimer laser ablation

Y–Ba–Cu–O films were prepared on yttria-stabilized zirconia polycrystalline substrate using KrF excimer laser irradiation with ethylene diamine tetra-acetic acid (EDTA) complexes as a target material. The results of the x-ray θ-2θ scan showed that the films grown above 750 °C were preferentially oriented with a c -axis normal to the substrate. The value of full-width at half-maximum of (005) reflection reduced from 4.4° to 2.1° by increasing the laser power density in a range between 0.8 and 3.8 J/cm 2 . The transcription of the compositional ratio was improved by approaching the target-substrate distance from 45 to 20 mm. The films obtained at 800 °C consisted of many islands showing well-developed spiral growth, suggesting that the droplets of metal-EDTA complexes do not form random oriented crystalline particles on the surface of the substrate.

Noncrystalline Condensation of Densely Dissolved Optically Nonlinear Organic Compound in Polymer Matrices

Optical properties and condensed states of the densely dissolved optically nonlinear organic compound in polymer matrices were investigated by means of optical measurements, structural analysis and pressure tuning spectroscopy. In the investigation of the absorption peak wavelength, 2-methyl-4-nitroaniline (MNA) in poly(methyl methacrylate) (PMMA) exhibited characteristics intermediate between the crystal and the MNA dissolved in solvents, i.e., noncrystalline condensation. This result was consistent with those of X-ray diffraction analysis, second- and third-harmonics generation, IR absorption and 13C-NMR spectroscopies. It has also been revealed that such a system provides the most suitable measuring method of the third optical nonlinear constant for a variety of compounds.

Biaxial Rapid Epitaxy of Titanium Dioxide Crystals

(100)-oriented titanium dioxide films were rapidly grown on a (100) single crystalline MgO substrate using an air-opened CVD apparatus. The possibility of advanced morphological design, such as titanium dioxide whiskers and crystalline wells, obtained by the rapid epitaxy technique is described and discussed. The single surface promotes a preferential growth type. When the single surface grows along in the direction of the (100) axis, titanium dioxide whiskers are formed on the MgO substrate. On the other hand, two such surfaces form a crystalline well structure consisting of crystallites.

Initial Growth Process of Epitaxially Chemical-vapor-deposited Titanium Dioxide Crystallites

Publisher Summary In recent years, there has been considerable interest in rapid film formation techniques of metal oxides. This interest derives from the outstanding optical and electric properties of these films that consisted of randomly oriented nano-or micro-crystallites. An air-opened reactor operated under an atmospheric pressure was designed for the rapid deposition of polycrystalline titanium dioxide films. The chapter explains that titanium dioxide films were chemically prepared on single crystalline SrTiO 3 by a vapor deposition apparatus operated under atmospheric pressure with titanium tetraisopropoxide. At a substrate temperature of 400oC, titanium dioxide grows epitaxially with a manner of lateral growth of the steps as well as multi-nucleation during initial growth process. Finally, multi-nucleation growth becomes dominant and promotes to grow a number of highly oriented crystallites having well developed facets. X-ray diffractmetry revealed that these crystallites consisted of -oriented anatase type structure.

Condensed States and Optical Properties of the Densely Dissolved Organic Compounds in Polymer Matrices by Coprecipitation

Abstract Association of 3,3′-Diethyloxadicarbocyanine Iodide (DODCI) molecules has been revealed in polymer matrices [poly(methyl methacrylate), poly(benzyl methacrylate), etc.], comparing it with association states in appropriate solvents ranging from a dilute concentration (∼10−5 mol/1) to a saturated one, and in a crystal grown in methanol. The association state was investigate by means of optical-absorption and emission spectroscopy, emission lifetime analysis, 13C-NMR spectroscopy and small angle X-ray scattering. Properties of DODCI molecules in polymer matrices were controlled by varying side-chain substituents of the polymers, and DODCI contents.