Sachiko Matsushita

Defective Black TiO2 Synthesized via Anodization for Visible-Light Photocatalysis

Defective TiO(2-x) was synthesized via a facile anodization technique. Electron paramagnetic resonance spectra confirmed the presence of oxygen vacancy, which extended the photon-absorbance deeply into the visible-light region. By stripping off the nanotubes on top, a hexagonally dimpled layer of black TiO(2-x) was exposed and exhibited remarkable photocatalytic activity.

Coupling of wrinkle patterns to microsphere-array lithographic patterns

We report a method to modulate spontaneously formed microwrinkle patterns on a metal-capped elastomer surface by introducing lithographic patterns (structures) on the original surface as spatial triggers for directed wrinkling. The lithographic patterns are designed to have approximately the same lateral length scales as the characteristic wavelength of the microwrinkles by utilizing self-assembled two-dimensional microsphere arrays with hexagonal packing as a lithographic mask. When the lateral periodicity of the lithographic pattern is close to the wavelength of wrinkles, a novel directional order originating from the hexagonal packing of microspheres is induced. Otherwise, the wrinkle crests tend to form along the small ridges of the lithographic structure. The compression direction-dependent and reversible ordering of wrinkle patterns by compressive strain is also found for patterns with directional order.

Sliding of Water Droplets on Hydrophobic Surfaces with Various Hydrophilic Region Sizes

Four patterned surfaces with hydrophilic areas of different sizes were prepared using photolithography with a smooth octadecyltrimethoxysilane (ODS) hydrophobic coating. The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. The sliding angle and contact angle hysteresis of the water droplets increased concomitantly with increasing pattern size. The increase of the contact line distortion between defects at the receding side plays an important role in this trend. The droplet sliding velocity also increased concomitantly with increasing pattern size. This trend was simulated by a simple flow model. The contribution of the interface between the ODS region and the hydrophilic area was deduced from this trend. This study demonstrated the different size dependency of the chemical surface defects for sliding behavior between the critical moment at which a droplet slides down and the period when a droplet is sliding.

Sliding of Water Droplets on Smooth Hydrophobic Silane Coatings with Regular Triangle Hydrophilic Regions

The effect of the triangular pinning region on the sliding of water droplets on the smooth hydrophobic surface was investigated. Smooth hydrophobic silane coatings with various regular triangle hydrophilic regions were prepared using photolithography and octadecyltrimethoxysilane (ODS). The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. Thereby water contact angles of the coatings were almost equivalent. The water droplet sliding velocity increased continuously with increasing pattern size. Anisotropic sliding velocity was observed on the surface, suggesting different pinning effects. The sliding motion of water droplets on the gradient surface with changing hydrophilic region size deflects against the downward direction. The deflection length depends on the direction of triangle hydrophilic regions and the initial sliding position. These results demonstrate that control of the sliding velocity while sustaining the static contact angle is feasible by designing the shape and alignment of chemical heterogeneity.

Preparation and gas permeability of the surface-modified porous Al2O3 ceramic filter for CO2 gas separation

Abstract Al2O3 filters for CO2 gas separation were prepared by slip casting method. Average pore size and porosity of the obtained Al2O3 filters were about 74 nm and 40%, respectively. To evaluate the pore size effect, the Al2O3 filters having average pore size of 760 nm were also prepared. FE-SEM micrographs show fine new crystals on the pore surface. They were synthesized by hydrothermal treatment, and were identified to AlOOH by XRD and XPS. Both gas selectivity of the filter having larger pore size were about 1, which indicated that this filter has no gas separation capability. In contrast, the gas selectivity of the Al2O3 filter with 74 nm pores became about 1.47 at 0.01 MPa. The N2/CO2 gas selectivity was improved by controlling the pore size and the chemical properties of a pore surface precisely and by setting an appropriate gas permeation pressure.

Pore size dependence of self-assembled type photonic crystal on dye-sensitized solar cells efficiency utilising Chlorine e6

There are few reports on photoelectric conversion efficiency using naturally-occurring dyes for dye-sensitized solar cells (DSSC). This is because the matching with an excited electronic level of naturally-occurring dye to the conduction band of semiconductor is problematic; the excited electrons are easily relaxed to the steady state with fluorescence or heat emission. We examined the fluorescence inhibition effect of a self-assembled photonic crystal using Chlorine e6 dye. Chlorine e6 is derived from chlorophyll and has a long excited electron lifetime. We prepared TiO2 inverse opals with various particle sizes by liquid phase deposition and described their effect on DSSCs with regard to structural, optical and electrochemical properties. In addition, we explored the implications of fluorescence lifetime measurements relative to the photonic band diagram and the amount of adsorbed dye. Although the main factor affecting the external photoelectric conversion efficiency was the diffusion resistance of the electrolyte and the contact resistance between TiO2 interfaces, the possibility that the dye fluorescence lifetime, i.e. the photonic band structure, can affect the internal quantum efficiency per one dye molecule was also investigated.

Angled etching of (001) rutile Nb–TiO2 substrate using SF6-based capacitively coupled plasma reactive ion etching

We demonstrated the plasma etching of a (001) rutile Nb–TiO2 substrate using SF6 plasma. A vertical etching profile and a smooth etched surface were obtained. In addition, the angled etching of a (001) rutile Nb–TiO2 substrate was achieved in a conventional SF6 reactive ion etching system for the first time. The etching angle was determined by the angle of the groove of the holder. We believe that our simple dry etching technique is suitable for the formation of a three-dimensional photonic crystal with complete photonic bandgap (CPBG) and optical waveguides.

Preparation and photocatalytic activity of porous spherical TiO2 particles comprised of H3PW12O40 in hydrophobic nanopores

Porous TiO2 sphere particles were prepared by impregnating titanium (IV) oxysulfate solutions into organic monolith particles, with subsequent calcination in air. The powder possessed pores of meso-order. Its crystalline phase was anatase. Then, 12 Tungsto(VI) phosphoric acid (PW12) was present in the mesopores. The entire surface was modified to be hydrophobic by octadecylphosphonic acid (ODP). Subsequent UV illumination in water removed the PW12 and ODP adsorbed onto the outer sphere surface. The obtained spherical TiO2 particles with hydrophobic acidic nanopores exhibited high photocatalytic performance against the removal of 1,4-dioxane in water. Detailed analysis revealed that this material removed both 1,4-dioxane and ethylene glycol diformate (EGDF), the main intermediate of the photocatalysis of 1,4-dioxane. Results suggest that hydrophobic acidic nanopores enhance adsorption of EGDF in water and play an important role in the overall photocatalytic performance of this system.

SF6-Based Deep Reactive Ion Etching of (001) Rutile TiO2 Substrate for Photonic Crystal Structure with Wide Complete Photonic Band Gap

We demonstrated the fabrication of a photonic crystal structure of a (001) rutile TiO2 substrate by deep reactive ion etching (RIE) using SF6 plasma. A vertical etching profile and a smooth etched surface, which satisfy the requirements for optical device application, were obtained. We think that this proposed process is useful for the microfabrication of TiO2-crystal-based optical devices, such as photonic crystals with a complete photonic band gap (CPBG) and optical waveguides.

Enhanced light diffraction from self-assembled double-layer colloidal crystals

We demonstrate that double-layer colloidal photonic crystals function as wavelength- and polarization-insensitive blazed transmission gratings with efficiencies as high as 63% in the high-energy spectral region. This phenomenon, which is known as specular-resonance-enhanced diffraction, has been reported for a small-scale cluster of microspheres with a limited size parameter. By performing accurate characterization employing large-area colloidal crystal films self-assembled by an inclined dip-coating method with a controlled number of layers, this peculiar and efficient diffraction was demonstrated to be a universal property of double-layer colloidal crystal films.