New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Nanocrystals, especially with an anisotropic shape such as cubic, are candidates for building blocks for new bottom-up approaches to materials assembly, yielding a functional architecture. Such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here, we report synthesis and characteristics of BaTiO3 and SrTiO3 nanocubes and the ordered assemblies as ferroelectric supracrystals. BaTiO3 and SrTiO3 nanocubes with narrow size distributions were obtained in an aqueous process. BaTiO3 films made up of ordered nanocube assemblies were fabricated on various substrates by evaporation-induced self-assembly method. Regardless of the substrate, the nanocubes exhibited {100} orientations and a high degree of face-to-face ordering, which remained even after heat treatment at 850 °C. Piezoresponse force microscopy was carried out on the supracrsytal films to obtain plots of the d33 piezoelectric coefficient against the poling field, and ferroelectric hysteresis curves were shown.

In the sophisticated architectures of various biominerals, a multilevel hierarchy of lengths from nanometers to millimeters is commonly observed. In this article, superstructures composed of inorganic crystals associated with organic molecules from carbonate-based biominerals were identified and categorized as mesocrystals, which are composed of crystallographically oriented crystals. For the production of hierarchically structured mesocrystals, two strategies using self-organized growth with organic agents in aqueous solution systems were proposed. Arranged structures of micrometric and nanometric units were induced with an insoluble gel matrix and soluble adsorbable organic molecules, respectively. Consequently, bioinspired hierarchical crystals were successfully achieved by combining the matrix and soluble species.

Silica thin films containing organic groups were directly deposited from aqueous solutions of silicon alkoxides. Effects of functional groups of the alkoxides and the deposition conditions on the preparation of the films were investigated in order to clarify the deposition process. Silica films containing methyl and phenyl groups were deposited from aqueous solutions of methyl- and phenyltrialkoxysilanes, respectively, in the pH region lower than 3 or higher than 6. The composition and the property of the deposited films were influenced by pH and the temperature of the solutions and the starting materials. The adhesion of the deposited films on hydrophobic substrates was lower than that on hydrophilic ones, although the films were formed on both surfaces. The refractive index of the methyl-containing films, ca. 1.44, decreased with removal of methyl groups by heating up to 500 °C.

A new direct-deposition process for silica thin films was developed using silicon alkoxide solutions. Silica thin films incorporating organic groups, such as methyl (CH3) and phenyl (C6H5 ) groups, were deposited on substrates from aqueous and ethanol solutions of organyltrialkoxysilane. Silica films without organic groups were also formed using ethanol solution of tetraalkoxysilane with aqueous ammonia. Composition of the deposited silica films were influenced by temperature and pH of the solutions and the starting alkoxides. From aqueous solutions containing organyltrialkoxysilane and organic dyes, such as Disperse Red 1 and Rhodamine B, silica films including the dyes were directly prepared on substrates. The composition of silica-organic hybrid films prepared by the deposition method was successfully controlled by selecting the deposition condition and the starting materials.

Thin films of ZrO2 and lead zirconate-titanate, PZT, about 100 to 1000 nm in thickness, were prepared by electrophoretic deposition from transparent sols obtained by hydrolysis of metal alkoxides. Stainless steel plates and Pt-coated glass plates were used as substrates/electrodes. The applied field was up to 20 V/cm. The refractive indices of as dried films were higher than those of dip-coated films. High temperature oxidation of stainless steel plates was suppressed by the ZrO2 coatings. Uniformity of the chemical composition of the as-dried PZT films, determined by Auger electron spectroscopy, was better than the dip-coated PZT films.

In order to densify and to improve the physical properties, TiO2 sol-gel films, about 100 nm in thickness, on silica glass or silicon wafer were implanted with Ar+ or B+ ions. The refractive index of the as-dried films increased and the IR absorption band of OH disappeared after Ar+ implantation. Drying and densification of sol-gel films were enhanced by Ar+ implantation. On the other hand, the refractive index and the thickness of the films hardly changed with B+ implantation. However, IR absorption bands of B-O bond were observed after B+ implantation. This suggests that sol-gel films could be chemically modified by ion implantation with reactive ion species.

The interaction of synchrotron radiation (SR) emitted from a polarizing undulator with SiO2 gel films was investigated by ellipsometry and infrared spectroscopy. The photon energy in SR was varied in the range of 6.4−17.8 eV using an Onuki-type undulator in order to study the energy dependence of the interaction. We found that an increase of refractive index, a decrease of thickness of the films and a loss of OH groups were induced by photons with energies above ˜9 eV although any changes were not observed with photons below ˜7 eV. These results suggest that SiO2 gel films are densified through electronic processes stimulated by the energetic photons.