Keio University · Materials Science
Professor Hiroaki Imai's research lab specializes in the synthesis and characterization of functional inorganic materials through controlled crystal growth and defect engineering. The lab focuses on developing biomimetic and solution-based approaches to fabricate hierarchical nanostructures, such as ZnO and titania films, using self-organization processes in gel matrices and polymer templates. A key research direction involves understanding and manipulating point defects in fused silica glass under extreme conditions, particularly using excimer laser irradiation, to explore defect dynamics and their implications for optical materials. The lab also investigates the role of complexing agents, substrates, and gel media in directing crystal morphology and nucleation kinetics for advanced functional materials.
Figures are computed from collected data and may differ slightly.
A pH above 9.0 was essential for the formation of wurtzite zinc oxide (ZnO) in aqueous solution systems. The addition of complexing agents to decrease the deposition rate was required for the direct growth of ZnO on the surface of substrates through heterogeneous nucleation. The nucleation of the crystals was promoted by undercoats derived from zinc acetate. Wurtzite ZnO films consisting of hexagonal columns with diameters of 20–100 nm were successfully prepared on various substrates under suita
Monodisperse hollow nanocylinders consisting of crystalline titania particles have been directly prepared in a porous alumina membrane by a deposition technique using an aqueous solution system of titanium tetrafluoride.
The effects of ArF excimer laser irradiation on dehydrated high-purity silica glass were investigated on both the optical-absorption bands due to oxygen-deficient centers (ODC) and the formation of ${E}^{\ensuremath{'}}$ centers. With an intense uv flux from an excimer laser, an ${E}^{\ensuremath{'}}$-center density of the order of ${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ was created. The 7.6-eV absorption band remains at the original level, while the 5.0-eV absorption band having the 4.3-e
The morphological evolution of the inorganic crystals (Ba(NO3)2, NH4Cl, H3BO3, and K2Cr2O7) was demonstrated in various kinds of organic gel media (agar, gelatin, pectin, and poly (vinyl alcohol)). As the gel density increased, the morphology grown in the gel matrix remarkably changed from polyhedral single crystals exhibiting specific habits into dendritic forms consisting of irregularly branched polycrystalline aggregates regardless of the sorts of inorganic compounds and gelling agents. The e
Abstract Here, we describe a biomimetic pathway for the synthesis of hierarchically structured inorganic crystals. In artificial systems mimicking biomineralization, versatile morphogenesis was achieved with the construction of bridged nanocrystals through self-organization by controlling growth with polymeric molecules such as a gel matrix and soluble anionic polymers. The self-organized formation of bridged crystals in hierarchical architectures is a possible new paradigm for advanced material
Effects of intrinsic defects on defect formation by excimer-laser irradiation were examined in synthetic silica glasses prepared by different methods. In samples containing oxygen-deficient centers (ODC's), laser-induced E' centers were stable at room temperature. In contrast, in samples heat treated in ${\mathrm{H}}_{2}$ atmosphere, in which almost all ODC's changed into Si-H bonds, the induced-E'-center concentration increased by about two orders of magnitude, and the resulting E' centers were
Abstract We report a novel hierarchically organized superstructure emerging from an exquisite association of inorganic crystals, organic polymers, and dyes. The resultant K 2 SO 4 /poly(acrylic acid) composite includes five different tiers from the nanoscopic to the macroscopic. An additional new tier leading to functionality is formed by the incorporation of organic dyes that are organized in a nanospace. The emergent superstructure and properties are designed through changes in polymer concent
Ceramic textiles and wools consisting of micrometer-sized TiO2 hollow fibers with porous walls were prepared by a chemical solution deposition technique using TiF4 aqueous solutions.
The band-gap energy tuning of WO3 quantum dots was realized in the range of 2.6 eV (bulk) to 3.7 eV (sub-nano) by precise size control around one nanometer. Newly synthesized sub-nanoporous silicas act as excellent templates. In addition, single-electron reduction of oxygen under UV irradiation is now achievable with WO3.
Generation of typical paramagnetic centers by \ensuremath{\gamma} irradiation was studied for various kinds of synthetic silica glasses. Growth behavior of E' centers and nonbridging oxygen hole centers (NBOHC's) with \ensuremath{\gamma}-ray dose depends on contained preexisting point defects. By irradiation at room temperature, E' centers grow linearly and show a saturating tendency in silicas that contain precursors for E' centers, such as oxygen-deficient centers (ODC's), Si-H bonds or Si-Cl
Open papers in the app to read, cite, and organize with AI.
