Yasuyuki Akita

Construction of Highly Oriented Crystalline Surface Coordination Polymers Composed of Copper Dithiooxamide Complexes

Layer-by-layer bottom-up crystal engineering of metal-organic crystals at the surface of sapphire or glass from organic (rubeanic acid and derivatives) and inorganic (Cu(2+)) components which when mixed in solution form instantly an amorphous solid with high proton conduction.

Atomically Stepped Glass Surface Formed by Nanoimprint

We investigated atomic-scale surface modifications of silicate glass by nanoimprint using an atomically stepped sapphire (α-Al2O3 single crystal) plate as nanopattern mold. The sapphire mold had regularly arranged straight atomic steps, with uniform height and terrace width of about 0.2 and 80 nm, respectively. During pressing, vertical positions of the sapphire mold and glass plate significantly affected the morphology of the imprinted glass surface. The nanopattern was transferred to the glass surface when the mold was set on the glass plate, while the nanowave pattern was formed on the glass surface when the glass plate was set on the mold.

Anisotropic electric conduction derived from self-organized nanogroove array on Li-doped NiO epitaxial film

The self-assembly formation of straight and periodic nanogroove arrays was carried out on the surface of Li-doped NiO thin films by use of atomic steps on the substrate. The nanostructure was formed by annealing Li-doped NiO (111) epitaxial thin film prepared on an atomically stepped α-Al2O3 (0001) substrate via pulsed laser deposition at room temperature. V-shaped nanogrooves, with a depth of ∼20nm and an open-end width of ∼50nm, were observed over the entire substrate and characterized by cross-sectional transmission-electron microscopy. The separation of the aligned nanogrooves was from 80to100nm, comparable to the size of the atomic steps on the substrate. Anisotropic electric conduction was definitely attained for the Li-doped NiO thin film with the nanogroove array. A resistance ratio up to about 100 was obtained for both directions parallel and perpendicular to the nanogrooves. The resultant anisotropy was considered to be mainly caused by anisotropic grain growth due to self-organized reconstructi...

Evolution of Atomically Stepped Surface of Indium Tin Oxide Thin Films Grown on Nanoimprinted Glass Substrates

Indium tin oxide (ITO) thin films were deposited on atomically stepped glass substrates (step height of ~0.2 nm and separation of ~80 nm) by pulsed laser deposition. The atomically stepped glass was prepared via thermal nanoimprint using an atomically stepped sapphire mold. The surface morphology of the ITO thin film definitely reflected the atomically stepped pattern of the glass substrate surface. The step height and the separation of the ITO film surface were close to those of the nanoimprinted glass surface. The fast Fourier transform analysis of the atomic force microscopy image also confirmed the periodicity of the atomic-step pattern.

Nanoimprint Fabrication and Thermal Behavior of Atomically Ultrasmooth Glass Substrates with 0.2-nm-Height Steps

We examined the conditions for the development of atomically stepped ultrasmooth surfaces on commercial silicate glass substrates by the thermal nanoimprint technique using sapphire (α-Al2O3 single crystal) molds with 0.2-nm-height atomic steps. Under the pressing conditions of 3 MPa, 300 s, and 610 °C for imprinting, a 0.2-nm-high stepped and atomically ultrasmooth terraced surface could be formed on soda-lime silicate glass substrates having the glass transition temperature of 521 °C. We found that the 0.2-nm-height step structure of the imprinted glass surface disappeared after annealing at 490 °C, and the smoothness of the terrace increased.

Toward step-by-step nuclear growth of surface two-dimensional porphyrin nanonetworks

We report the development of a solution-based step-by-step technique, which utilizes the coordination bond between metalloporphyrin molecular units and metal linkages and results in the nuclear growth of nano-networks on solid substrates. The growth of the surface structures is strongly influenced by the choice of substrate materials and solvents: the molecule-substrate interaction and the solubility of the molecular units are important parameters in tuning the size and growth of the domains.

Low-Temperature Heteroepitaxial Growth of α-Al2O3 Thin Films on NiO Layers by Pulsed Laser Deposition

We investigated the growth of epitaxial α-Al2O3 thin films on NiO layers at a low-temperature of 400 °C by pulsed laser deposition (PLD). Fabricated films were characterized by X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED). During deposition, a plasma plume was analyzed by optical emission spectrometry. We found that the crystal growth behavior depends greatly on the laser fluence applied during deposition. α-Al2O3 layers were grown epitaxially with high laser fluence (4 J/cm2). In contrast, mixed-phase γ- and α-Al2O3 films and amorphous Al2O3 films were obtained with lower laser fluences (3 and 2 J/cm2, respectively).

Fabrication and Characterization of Electrically Functional Lanthanum Hexaboride Thin Films on Ultrasmooth Sapphire Substrates

The crystal growth of lanthanum hexaboride (LaB 6) thin films was examined by applying the laser molecular beam epitaxy (laser MBE) process. C-axis (100) highly-oriented LaB 6 thin films could be fabricated on ultrasmooth sapphire ( α-Al 2O3 single crystal) (0001) substrates with atomic steps of 0.2 nm in height and atomically flat terraces. The obtained film exhibited a smooth surface with root mean square roughness of 0.15 nm. The lattice parameter of the LaB 6 thin film was close to the bulk value reported previously. In the case of deposition on commercial mirror-polished sapphire substrates, the grown film was amorphous. The resistivity of the prepared crystalline LaB 6 thin films was as low as 2.2 × 10 �4 � cm and almost constant in the temperature range of 10–300 K.

Transformation from an atomically stepped NiO thin film to a nanotape structure: A kinetic study using x-ray diffraction

Transformation from an atomically stepped epitaxial thin film of NiO to a self-assemble nanotape structure at the step edge was observed in situ using synchrotron x-ray diffraction. The pristine NiO thin film was epitaxially grown on an ultrasmooth sapphire (0001) substrate with a regular step of 0.2nm in height using laser molecular beam epitaxy. Transformation from the thin film to the nanotape structure was facilitated by postannealing in air from room temperature to 620K. From the Arrhenius plot of ln(in-plane domain sizes) versus 1∕T, an atomic-scale transformation energy of ∼0.0135eV/atom was derived.

Fabrication of nanostructured ITO thin films on nanoimprinted glasses by pulsed laser deposition

We fabricated indium tin oxide (ITO) thin films on nanoimprinted glass substrates using pulsed laser deposition (PLD). The nanoimprinted glass substrate was prepared by thermal nanoimprint using an atomically stepped sapphire (α-Al2O3 single crystal) mold. Two kinds of sapphire molds were employed, one with a single step about 0.2 nm high and the other with a bunched step about 2 nm high. The surface morphology of the stepped sapphire mold was successfully transferred to the glass surface in an atomic scale. The nanoimprinted glass had a regular nanostepped pattern; one had a step height of about 0.2 nm and step separation of about 100 nm, the other had a step height of about 2 nm and step separation of about 1 μm. The ITO films were deposited at room-temperature (RT) or 200°C on the nanoimprinted glass substrates and on the non-patterned commercial glass for comparison. The ITO films deposited at RT were post-annealed for further crystallization. The surface of the ITO thin films deposited on the nanoimprinted glass well reflected the nanopattern of the glass substrate surface. Preferential crystalline orientation of the ITO thin films was achieved on the nanoimprinted glass substrates. The resistivity of ITO thin films deposited on the nanoimprinted glass was lower than that on the commercial glass, which was probably due to the higher crystal orientation of the films grown on the nanoimprinted glass surfaces.