Masahiko Ishii

Toyota Central R & D Labs., Inc., Nagoya, Aichi, Japan

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Publications (17)50.53 Total impact

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    ABSTRACT: It is important to check distortion in an opaline photonic crystal, since it may affect the photonic band structure and optical properties of the crystal. In this paper, we demonstrate that the existence of distortion can be checked by measuring both angle-resolved reflection spectra produced by two-dimensional (2D) diffraction and mirror reflection spectra. The lattice constant (a2D) determined by 2D diffraction is derived from the periodicity in the surface plane of the opaline crystal. In contrast, the lattice constant (am) determined from the mirror reflection spectra results from the periodicity in the direction perpendicular to the surface. Therefore, the existence of distortion can be checked by comparing these two lattice constants (a2D and am). The measurements revealed that the structure of an opaline photonic crystal composed of polystyrene (PS) spheres had the structure shrunken approximately 4% in the direction perpendicular to the surface. The origin of this distortion is discussed in terms of shrinkage of the PS spheres.
    Journal of Optics A Pure and Applied Optics 08/2007; 9(9):S372. · 1.92 Impact Factor
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    ABSTRACT: We acquired angle- and polarization-resolved reflection spectra from a colloidal crystal made of polystyrene spheres along the two perpendicular directions corresponding to the LU and LW directions in the first Brillouin zone of an fcc lattice. Dispersion relations between the reflection peak positions and the wave vectors of the incident light were obtained from the measured spectra and compared with calculated photonic band structures. For the first stop band region in the spectra, the behavior of the reflection peak due to Bragg diffraction agreed with the calculated band structure and revealed some differences induced by the polarization and crystalline orientations. The spectral features observed in the higher energy regions also revealed these differences. In addition, dispersion relationships between the peak positions and the wave vectors were obtained from the results of fitting each spectrum with several Gaussian curves, compared with the calculated photonic band structures. The relationships obtained for the LU direction almost matched the calculated band structure, while the relationships obtained for the LW direction revealed the features of the mixed band structure calculated for the two perpendicular directions. These results indicate that angle- and polarization-resolved reflection spectroscopy has the potential to experimentally analyze the photonic band structures of actual photonic crystals.
    Colloids and surfaces B: Biointerfaces 05/2007; 56(1-2):224-30. · 4.28 Impact Factor
  • Masashi Harada, Masahiko Ishii, Hiroshi Nakamura
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    ABSTRACT: Colloidal crystals melt by applying focused light of optical tweezers and recrystallize after removing it. The disturbed zone by the light grows radially from the focus point and the ordering starts from the interface with the crystal. Although the larger disturbed zone is observed for the higher power optical tweezers, a master curve is extracted by normalization of the disturbed zone. The temporal changes of the normalized disturbed zone are well described with exponential functions, indicating that the melting and recrystallization process is governed by a simple relaxation mechanism.
    Colloids and surfaces B: Biointerfaces 05/2007; 56(1-2):220-3. · 4.28 Impact Factor
  • Hiroshi Nakamura, Masahiko Ishii
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    ABSTRACT: Non-close-packed silica colloidal crystalline array was immobilized by polymer, and effects of stretching on the change of the optical properties and microstructure of the colloidal crystalline arrays have been demonstrated. The immobilization was a two-step polymerization process: the first step was with hydrophilic polyethylene glycol acrylate (PEGA) polymer gel, and the second step was with 2-hydroxyethyl acrylate polymer matrix. The structure of the three-dimensional array was maintained during the immobilizing process with lock in periodic order. The peak wavelength of Bragg diffraction of the polymer-immobilized colloidal crystalline array shifted to shorter wavelength with stretching. The peak shift was caused by the compression of the polymer proportional to the stretching ratio, and the compression was homogeneous throughout the polymer-immobilized colloidal crystalline arrays. These results show that by using polymer-immobilized non-close-packed colloidal crystalline array, mechanically tunable photonic crystals can be realized, and they open the possibility of tuning the microstructure of colloidal crystalline array for photonic crystal.
    Colloid and Polymer Science 02/2007; 285(6):693-697. · 2.16 Impact Factor
  • Hiroshi Nakamura, Masahiko Ishii
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    ABSTRACT: The effects of medium composition on the optical properties and microstructures of non-close-packed silica colloidal crystalline arrays have been demonstrated. Water–alcohol mixtures were used as dispersion media for these arrays. Optical properties and microstructures were examined using angle-resolved reflection spectra measurements. The Bragg diffraction peaks of the colloidal crystalline arrays shifted with changing of concentration or hydrocarbon number of alcohol. With an increase in concentration or hydrocarbon number of alcohol, the effective refractive index of the dispersion increased and the interplanar spacing of the colloidal crystalline array decreased. The increase in effective refractive index was caused by an increase in the refractive index of the mixed medium with the change in solvent. The decrease in interplanar spacing of the array was caused by decreased electrostatic repulsions between the silica spheres with decreasing dielectric constant. The current work suggests new possibilities for the control of optical properties and microstructures of colloidal crystalline arrays.
    Colloid and Polymer Science 01/2007; 285(7):833-837. · 2.16 Impact Factor
  • Masahiko Ishii, Masashi Harada, Hiroshi Nakamura
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    ABSTRACT: Growth processes of colloidal crystalline arrays in a fluidic glass cell were observed in situ by confocal laser scanning microscopy. The results showed that the growth direction varied with the growth rate. At an extremely low growth rate, the array grew toward the 〈112〉 direction of the face-centered-cubic lattice. At a moderate growth rate, it grew toward the 〈110〉 direction. However, an extremely high growth rate induced random arrays of the spheres. Moreover, we were able to visualize the generation and/or annihilation processes of several kinds of defects. The variation of the growth direction with the growth rate is discussed in terms of the difference in water-flow resistance in the crystalline arrays.
    Soft Matter 01/2007; 3(7). · 4.15 Impact Factor
  • KOBUNSHI RONBUNSHU 01/2007; 64(1):29-34.
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    ABSTRACT: Inverse opal having mesoporous silica walls has been synthesized using close-packed polystyrene beads and octadecyltrimethylammonium chloride as a templates, and tetramethoxysilane as a silica precursor. The synthesized bimodal porous silica was characterized by XRD, N2 sorption, SEM and TEM. Hollow silica with inverted opaline structure had a macroporous diameter of 390 nm and a wall thickness of approximately 30 nm, and the mesoporous silica walls had a specific surface area of 367 m2/g, a mesopore diameter of 2.9 nm and a wall thickness of 1.8 nm. The refractive index (n) of this material was found be 1.05, which is lower than that of silica (n = 1.44) and also close to that of the air.
    Microporous and Mesoporous Materials 11/2006; · 3.37 Impact Factor
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    ABSTRACT: Titania coated monodisperse silica spheres have been synthesized and fabricated as a close-packed colloidal crystalline array. We have demonstrated that the coated colloidal sphere can be used to control the peak position of the optical stop band through variation of the coating thickness. The titania coated silica spheres were prepared by the layer-by-layer assembly coating process, which reciprocally laminates the cationic polyelectrolyte and the anionic titania nanosheets on a monodisperse silica spheres, and were sintered to change the titania nanosheets to anatase. The Bragg diffraction peak of the colloidal crystalline array shifted to the long wavelength region with an increase of thickness of the titania layer. Angle-resolved reflection spectra measurements clarified that the red shift was caused by increasing of the refractive index with increase of the thickness of the layer. The current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties from tailored colloidal spheres.
    Langmuir 02/2006; 22(3):1268-72. · 4.38 Impact Factor
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    ABSTRACT: Colloidal crystalline arrays are three dimensionally periodic lattices of self-assembled monodisperse colloidal spheres. These periodic structures have been actively explored as functional components in fabricating new types of diffractive devices such as optical filters and chemical sensors, mechanical sensors, and photonic bandgap structures. We have demonstrated the synthesis of silica or polystyrene spheres uniformly coated with titania nanosheets and the fabrication of these spheres into close-packed colloidal crystalline arrays. We have also reported on the optical properties and microstructures of the colloidal crystalline array estimated by angle-resolved reflection spectra measurements. The titania nanosheets were synthesized by delamination of layered titanate crystallites. The titania nanosheets coated spheres were prepared by the LBL (Layer-By-Layer) assembly coating process, which consisted of alternately laminating cationic polyelectrolyte and anionic titania nanosheets on monodisperse silica or polystyrene spheres. The close-packed colloidal crystalline array was fabricated in the glass cell by drying process of the aqueous dispersion of the spheres. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with increasing thickness of titania nanosheets layers. Angle-resolved reflection spectra measurements showed that this red shift was caused by increasing the mean effective refractive index neff of this crystalline lattice without changing interplanar spacing d111 with increasing thickness of titania nanosheets layers. Since a wide range of coated colloids of different size, composition, and optical properties can be prepared via the LBL coating, the current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties.
    Proc SPIE 01/2006;
  • Masashi Harada, Masahiko Ishii, Hiroshi Nakamura
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    ABSTRACT: The reflection from colloidal crystals of core-shell particles is evaluated by the calculation of photonic band structures, and is compared with the prediction of the Bragg condition. Although the results of the calculation of the photonic band structures are consistent with those of the Bragg condition, generally, the photonic band structures predict another reflection which has no origin in the Bragg condition, when the shell of the particle is sufficiently thin and the difference in refractive index between the core and the shell is relatively large. Moreover, no reflection is expected in the case of moderate shell thickness and moderate refractive index difference.
    Japanese Journal of Applied Physics 01/2006; 45:7729-7731. · 1.07 Impact Factor
  • Masashi Harada, Masahiko Ishii, Hiroshi Nakamura
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    ABSTRACT: We present the photonic band schemes of colloidal crystals with rhombohedral structures that are compressed along the [111] direction of a close-packed face-centered structure while maintaining the shapes of the colloidal particles. The compressed colloidal crystals transform from an A10 structure to an Ai structure through a simple cubic structure. The photonic band schemes reveal that, as the colloidal crystals are compressed, the stop-band frequencies increase for A10 structures and decrease for Ai structures upon becoming simple cubic structures. This transition can be explained by the change of the lattice plane responsible for Bragg diffraction.
    Japanese Journal of Applied Physics 01/2006; 45. · 1.07 Impact Factor
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    ABSTRACT: We have demonstrated that polystyrene latex coated with titania nanosheets can be fabricated into a close-packed colloidal crystalline array, and that these coated colloidal spheres can be used to control the peak position of optical stop bands through the coating. The titania-nanosheets-coated polystyrene latex was prepared by the layer-by-layer (LBL) assembly coating process, involving alternating lamination of cationic polyelectrolytes and anionic titania nanosheets on monodisperse polystyrene latex particles. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with the coating of titania nanosheets. This red shift was caused by an increase in refractive index upon coating, as revealed by angle-resolved reflection spectra measurements. The current work suggests new possibilities for the creation of advanced colloidal crystals having tunable optical properties from tailored colloidal spheres.
    Langmuir 10/2005; 21(19):8918-22. · 4.38 Impact Factor
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    ABSTRACT: The growth of colloidal crystal films from a dispersion of monodispersed silica spheres using a simple cell with one opening was investigated. Colloidal crystal films with large domain sizes were successfully fabricated almost over the cell (approximately 10 cm2) without applying any external force at room temperature. During the drying process, three distinct conditions were observed, in each of which the films exhibited different optical properties. Films with high transmittance were formed in the first stage. Upon further solvent evaporation, the films entered a medium transmittance state via an extremely low transmittance state. Angle-resolved reflection spectroscopy, which was used to analyze the three conditions, revealed that close-packed arrays with water-filled spaces between were formed in the first stage. One-directional flow was generated in the cell because water evaporation occurred only at the opening. The flow caused the spheres to be arranged epitaxially, resulting in a large domain size.
    Langmuir 07/2005; 21(12):5367-71. · 4.38 Impact Factor
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    ABSTRACT: We demonstrate the two-dimensional silicon backbone structure of siloxene nanosheets, which produces relatively monodisperse nanosheets with a thickness of 0.7 nm and lengths in the range 100-200 nm; the thickness is an order of magnitude smaller than that of previously reported silicon nanoparticles prepared by a variety of other methods.
    Chemical Communications 07/2005; · 6.38 Impact Factor
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    ABSTRACT: Colloidal crystals formed by polymer-grafted silica particles were immobilized by a stepwise procedure consisting of gelation by radical copolymerization followed by solidification by ring-opening radical polymerization. In the first step, the poly(methyl methacrylate) (PMMA)-grafted silica colloidal crystal suspension was incorporated into the gel without altering the crystal structure by copolymerization of cross-linker, 1,2-dimethylacryloyloxyethane (DME) and methyl methacrylate (MMA). In the second step, ring-opening radical polymerization was performed after substituting the solvent with vinylidene-1,3-dioxolane. By this two-step procedure, the silica particle array of colloidal crystals was immobilized and made into durable material.
    Langmuir 06/2005; 21(10):4471-7. · 4.38 Impact Factor
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    ABSTRACT: The incorporation of monodisperse, polymer-modified silica into poly(methyl metharylate) to prepare polymer films containing particle array structure was investigated. The preparation was carried out by a two-step radical polymerization for gelation and solidification. The colloidal crystallization of poly(methyl metharylate)-modified silica, in 78 nm size, in acetonitrile and successive copolymerization of methyl methacrylate and 1,2-dimethacryloylethane by UV light irradiation gave the polymer gel containing the colloidal crystal structure. The exchange of acetonitrile in the gel with methyl methacrylate and further photo-radical polymerization gave the durable polymer film composed of silica particle array.
    Colloid and Polymer Science 12/2004; 283(3). · 2.16 Impact Factor