Table of contents

This paper briefly reviews our approach to render active functions to micro porous crystal 12CaO·7Al₂O₃ (C12A7), which is known as a constituent of alumina cement, utilizing nano-space and topology of sub-nanometer-sized cages inherent to the crystal structure. Each cage with a positive charge is coordinated by 12 cages to form a three-dimensional structure. This structure is a similar to a close packing of sphere except that each opening wall of a cage is shared with a neighboring cage. Free oxygen ion O²⁻ accommodates in 1/6 of the cages to reserve electro neutrality in the stoichiometric state. We replaced this free oxygen ion by other active anions such as O⁻, H⁻, and electron, aiming at emergence of novel function. C12A7:O⁻ exhibited strong oxidation power enough to oxide Pt, and field-assisted thermionic O⁻ emission to several μA levels, while conversion of insulator to persistent electronic conductor by illumination with ultraviolet radiation was discovered in C12A7:H⁻ sample. Further, almost all of the free O²⁻ ions in the cages were successfully replaced by electrons by a chemical treatment using metallic Ca. The resulting material, which has a composition [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻) and a high conductivity, ∼100 S cm⁻¹ at 300 K, is a first room-temperature stable electride, in which electrons work as anions. The present approach to novel function emergence by solely employing abundant oxide materials and fully utilizing nanostructure provides a way for material research for future to be done under severe circumstance of environment and resource.

The oxygen isotope exchange of ¹⁶O by ¹⁸O in SrTiO₃ causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of the huge domain wall response were evaluated by dielectric, magnetic (NMR), and optical measurements (SHG, light scattering). The results obtained corroborate (1) smeared ferroelectric transition at T_c due to quenched random field, (2) a quite large dielectric contribution from domain walls, (3) incomplete softening of the transverse optic mode, and (4) a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO₃ were also introduced.

Perovskite-type BaTiO₃/SrTiO₃ (BTO/STO) artificial superlattices were fabricated by molecular beam epitaxy process and their dielectric properties and refractive indices were measured. A large leakage current was observed in the films on Nb-doped STO substrate. Dielectric permittivity was therefore measured using planer interdigital electrodes. Fine planer electrodes were necessary to reduce the penetration of electric flux into the substrate. Interdigital electrodes were formed by electron-beam lithography. Dielectric permittivity of superlattices along the film surface was determined using electromagnetic field analysis. It was found that the dielectric permittivity of the BTO/STO superlattice with the period of 10 unit cells showed a maximum value above 30,000, which was almost independent from frequency up to 110 MHz. The refractive index of superlattices measured with a spectroscopic ellipsometer also showed the highest value when the period was 10 unit cells. This indicated that the structure of superlattices affected not only the ionic polarization but also the electric polarization. The origin of anomalous properties observed in superlattices may be interpreted by the strains induced into the film.

{100} One-axis-oriented PZT films with a thickness of 2 μm were obtained on (111)Pt/TiO₂/SiO₂/(100)Si substrates by metal organic chemical vapor deposition (MOCVD). These were obtained irrespective of the film thickness up to 2 μm and with a Zr/(Zr+Ti) ratio from 0.20 to 0.75. This was found to be due to the higher growth rate of these orientation grains than {110} and {111)} orientation grains. These films had columnar grains 50–100 nm in width. Moreover, they were found to include 90° nano-domains 10–20 nm in width. Dielectric constant, _r and the field induced-strain were maximum around a Zr/(Zr+Ti) ratio of 0.5, which was in good agreement with previous reports on sintered bodies with 100 times larger domains. This means that the domain size had any effect on _r or field-induced strain.

We have studied the lasing characteristics of a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (CLC) films as photonic band gap (PBG) materials. The nematic layer acts as a defect layer, the anisotropy of which brings about the following remarkable optical characteristics: (1) reflectance in the PBG region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film; (2) efficient lasing occurs either at the defect mode wavelength or at the photonic band edge; and (3) the lasing emission due to both the defect mode and the photonic band edge mode contains both right- and left-circular polarizations, while the lasing emission from a dye-doped single CLC layer with a left-handed helix is left-circularly polarized.

Bis(ethylenedithio)tetrathiafulvalene (ET) molecules with one alkyl chain, C_nET (n=1–6) are synthesiszed. The solubility in usual organic solvents is remarkably improved without changing the electron donating ability, and good thin films are formed by the solution cast method. C₁ET has the same dimer structure as ET, while the structures of the n=2–4 molecules are composed of zig-zag columns.

This paper reports our recent progress on a microbial system for efficient production of biodegradable copolyester of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate], P(3HB-co-3HHx), with desirable copolymer compositions using genetically engineered bacteria. We have developed a fermentation technique to achieve high cell density cultivation of a recombinant Ralstonia eutropha using inexpensive soybean oil as a sole carbon source. In addition, we demonstrate that the use of polyhydroxyalkanoate (PHA) synthase (PhaC) mutants having an amino acid substitutions is able to vary the copolymer composition of P(3HB-co-3HHx) synthesized from soybean oil by the recombinant bacteria. On the other hand, it is also important to understand the enzymatic degradation process of PHA materials for establishing a method to regulate the rate of biodegradation. The enzymatic degradation process of P(3HB-co-3HHx) thin film using an extracellular PHB depolymerase has been studied by in situ atomic force microscopy in buffer solution. We demonstrate that the PHA depolymerase predominantly degrades the less-ordered molecular chain-packing regions along the crystallographic a-axis.

The preparation process and proton transport properties of zirconium tricarboxybutylphosphonate Zr(O₃PC(CH₂)₃(COOH)₃)₂(Zr(PBTC))/polybenzimidazole (PBI) composite membranes have been investigated with a view to developing a novel electrolyte for direct methanol fuel cells. A compacted Zr(PBTC) powder sample and a Zr(PBTC)/PBI composite membrane with 50 wt.% Zr(PBTC) content show conductivities of 6.74×10⁻² S cm⁻¹ and 3.82×10⁻³ S cm⁻¹ at 200 °C under a fully humid condition, respectively. Post-sulfonation thermal treatment, which has a great effect on the ligand structure of PBI, gives a marked increase in the conductivity of the membrane by a factor of 2 in the same condition. This effect is mainly attributed to the proton transport via sulfonic acid groups bonded to the PBI unit.

In this study, the effective charge density of a sulfonated polymer membrane was investigated under low-water-content condition in order to develop novel polyelectrolyte membrane for the fuel cell which can be operated without humidification. At first, the sulfonated polymer membranes, which have various water contents and an inhomogeneous fixed-charge distribution, were prepared, and then the membrane potentials across them were measured. The experimental results were analyzed on the basis of the Donnan equilibrium theory and the Nernst–Planck transport equation considering the fixed-charge inhomogeneities in the membrane. It was revealed that the charge effectiveness depended on the water content, the ionic radii of the counterions and the valence of the counterion. In order to interpret the variation of the charge effectiveness depending on those values, the ion-pair theory based on the Fuoss formula was introduced. This approach showed that the ion-pairing effect causes the difference between the effective charge density and the fixed-charge density especially for low-water-content condition.

We have developed a novel methodology using polymer anions specially designed to comprise either of the three same or different polymer segments for the synthesis of well-defined regular and asymmetric star-shaped polymers. The polymer anion was prepared by the addition reaction of living anionic polymer to in-chain-functionalized polymer with 1,1-diphenylethylene (DPE) moiety and in situ coupled with chain-end-functionalized polystyrene with two or four benzyl bromide moieties. Although the anions located at the cores of 3-armed star polymers were believed to be highly sterically hindered, the coupling reactions proceeded virtually quantitatively under the conditions in THF at −78 °C for 24 h. Regular 7-armed A₇ and 13-armed A₁₃ star-shaped polystyrenes as well as quite new asymmetric 7-armed A₂B₂C₂D and 13-armed A₄B₄C₄D star-shaped polymers were synthesized in ca. 100% yields. Four polymer segments, A, B, C, and D, were, poly(4-trimethylsilylstyrene), poly(4-methoxystyrene), poly(4-methylstyrene), and polystyrene prepared by sec-BuLi-initiated living anionic polymerization. Thus, three same or different polymer chains could be simultaneously introduced into either two or four benzyl bromide reaction sites only by one-step coupling reaction with the above-prepared polymer anion. The resulting star-shaped polymers all were well-defined in architecture and precisely controlled in-chain length and composition. Accordingly, they have a high molecular weight and structural homogeneity. Among them, asymmetric star-shaped polymers synthesized herein are the first successful examples comprised of four plural different polymer segments. As expected, new morphologies with nanoscopic ordered structures applicable to nanotechnology have been expressed.

Zeolite thin films were prepared on cordierite (Mg₂Al₄Si₅O₁₈) honeycomb substrates by in situ crystallization using soft hydrothermal conditions. The synthesized zeolite films (zeolite A and ZSM-5) were characterized by XRD, FTIR, SEM, NH₃-TPD, and Ns₂ and propane gas adsorption. Zeolite-A films were prepared by dip-coating on a cordierite substrate in a precursor of molar composition of Na₂O:Al₂O_3: SiO_2: H₂O=4:1:2:100 and heating in an autoclave at 80 °C for 6–10 h. The resultant zeolite-A films consisted of cubic crystals about 2–3 μm in size, achieving a thickness of 20 μm after re-coating. ZSM-5 films were similarly formed using a microporous silica precursor obtained by selective leaching of metakaolinite with tetrapropylammonium hydroxide (TPAOH) as the templating agent. The molar composition of the precursor was NaOH:microporous silica:TPAOH:H₂O=1:10:1:200. The dipped substrate covered with the wet precursor gel was heated in an autoclave at 150 °C for 24 h. The resultant films were composed of short prismatic <1 μm crystals achieving thickness of several to 10 μm after re-coating. The microstructure and porous properties of the ZSM-5 films were found to change according to the chemical composition and surface treatment of the cordierite substrates. The presence of a SiO₂-rich interfacial layer between the substrate and zeolite film increased the amount of zeolite formed and the physical adsorption but decreased the solid acidity and amount of chemisorption.

Phonon glass and electron crystal (PGEC) thermoelectric materials have been expected to be a new class of thermoelectric materials for high temperature applications. Among the efforts to optimize the high temperature thermoelectric properties of various PGEC thermoelectric materials, recent experimental works on the Skutterudite IrSb₃ and half-Heusler TiNiSb intermetallic compounds are presented herein by which the material design concept for high energy conversion efficiency, i.e. a high figure of merit, is suggested. It is revealed that the thermoelectric efficiency of IrSb₃ can be increased by the decrease of lattice thermal conductivity due to the rattling effect of La atoms filled in the structural vacancies of the Skutterudite crystal structure. In the half-Heusler TiNiSn, high temperature thermoelectric properties are improved by Hf substitution to the Ti sites by reducing lattice thermal conductivity and also by Sb doping to increase power factor. It is concluded that the proper alloy designing for controlling crystal structure and carrier concentration could enable these intermetallic compounds to exhibit a high potential for elevated temperature thermoelectric applications.

To correlate quantitatively the mechanical properties of precipitate free zones (PFZ) with the corresponding microstructural and compositional characteristics, TEM observation, EDX analysis and nanoindentation measurement have been performed in the vicinity of grain boundaries in Al–4.9 mass%Zn–1.8 mass%Mg (−0.28 mass%Ag) alloys. The remarkable decreases in hardness and solute concentrations were observed towards grain boundaries even in the regions just outside PFZ. With increasing aging time, it is firstly revealed that the hardness inside PFZ monotonously decreases although the hardness inside grains increases in the earlier stage of aging. Three distinct regions of "PFZ", "Transition-area" and "Grain-region" were therefore proposed to explain the origins of such age-hardening behavior observed in this work. In the Ag-added alloy, on the other hand, the hardness could be maintained up to closer regions to grain boundaries at the same level as that inside grains.

The atomic potential of γFe has been constructed on the basis of the second-moment approximation of the tight-binding scheme potential. To apply this potential to molecular dynamics simulations at high temperatures up to about 1700 K, the cut-off distance has been set to the sixth neighbours and other parameters have been determined from fitting to physical properties of γFe such as the cohesive energy, vacancy formation energy, lattice constant, elastic constants and bulk modulus. This potential can also describe the temperature dependencies of the lattice constant and the specific heat at constant pressure and can simulate hypothetical melting of γFe.

Ferromagnetic shape memory alloys (FSMAs) such as NiMnGa are expected to be new practical actuator materials with high driving frequency by magnetic field and large strain due to the shape memory effect (SME). However, the brittleness and poor workability of FSMAs, especially at a polycrystalline state, are serious problems and should be improved for a practical use. From this viewpoint a smart composite has been designed by a combination of a polymer matrix and FSMA particles (FSMAP), and a systematic investigation has been done for a NiMnGa-FSMAP/epoxy smart composite. This paper summarizes the design concept and some experimental results of the smart composite. It is pointed out that the single-crystal NiMnGa-FSMAP are easily made by mechanical crush due to the brittleness of FSMAs, and microstructural control is also possible by applying magnetic field during curing. Experimental study revealed that the NiMnGa-FSMAP/epoxy smart composites exhibit both tensile ductility and SME, and that shape memory properties become improved by decreasing particle size of FSMAP. It is concluded that the FSMAP/polymer smart composite has a large potential to be a new practical actuator material.

A nanosecond pressure pulse is generated by focusing a nanosecond-pulsed laser onto an aluminum target with plasma confined geometry. A spatially uniform pressure pulse is generated by focusing laser beams with a flat-top spatial energy distribution. High-pressure pulse loading and recovery experiments were performed on yttria-doped (3 mol%) tetragonal zirconia polycrystals at 11 GPa. In the pressure-loaded region, the monoclinic phase was uniformely formed. The transition ratio was approximately 30%. Nanosecond time-resolved Raman spectroscopy was performed on polytetrafluoroethylene under high-pressure pulse loading at 1 GPa, and rapid structural phase transition within 10 ns was revealed.

During the initial growth, Si(001) surfaces were covered by thin Ge wetting layers. At the wetting layer surfaces, Ge atoms were reconstructed into dimers, which were aligned along the [110] direction to form one-dimensional (1D) 'dimer rows'. In addition, the dimer rows were partitioned by dimer vacancy lines at the Ge/Si(001) surfaces. As a result, the surfaces were covered spontaneously by an array of 1D dimer row segments. Scanning tunneling microscope images demonstrated that the 1D free-electrons in the dimer rows are confined in each segment and form an ultra-high density array of 1D quantum wells at the surfaces.

The sintering force was originally defined for an equilibrium state, in which the sintering contraction is balanced by an external force. The concept of sintering force can be expanded to non-equilibrium process of sintering by using Beere's definition of sintering force. The sintering of two spherical particles was simulated by using the Surface Evolver program. The shrinkage rate was approximately proportional to the sintering force in a non-equilibrium process. The sintering force in a non-equilibrium process was smaller than the force necessary to stop the shrinkage at equilibrium.

The nanoscale growth control of oxide thin films, such as ferroelectric and magnetic materials, were explored by a novel technique based on nanoscale substrate engineering as well as atomic layer control via laser molecular beam epitaxy (laser-MBE). Atomic-scale analysis of the terminating layer of perovskite oxide films was performed by in situ coaxial impact-collision ion scattering spectroscopy. The novel heteroepitaxies that could be attained were: (1) the termination-regulated molecular layer-by-layer epitaxy of BaTiO₃ and La_0.7Sr_0.3MnO₃ thin films and (2) the step-decoration epitaxy resulting in the nanowire or nanodot structures of magnetic oxides such as (Mn, Zn) ferrite on ultrasmooth sapphire substrates with straight atomic steps.

A new doctoral course, Project Managing Course, has been established as of April, 2003 for the graduate students in the four Departments involved in the 21st Century COE program supported by Japanese Government. The aim of the course is to let selected doctoral students learn the basic knowledge and skill necessary to bring the technology seeds into the business. Besides the requirement for the thesis work for their doctoral degree of Materials Science, they have to fulfill the unit requirements on the lectures offered by guest professors who are currently active at the front of financing, market analysis, venture capitals and technology management consulting. The attempt is unique in Management of Technology (MOT) education in Japan, probably even world-wide, in a sense that the course is offered to the doctoral students.

Recently, we proposed a two-step heating schedule involving pulse electric current sintering (PECS), a kind of pressure assisted vacuum sintering, and subsequent post-heat treatment in air to fabricate porous alumina support, using commercially available alumina and carbon powders [J. Mater. Res. 18 (2003) 751]. During pressure assisted vacuum sintering, Al₂O₃–C system of low porosity was obtained and in second stage, i.e. during post-heat treatment in air, carbon particles present in the Al₂O₃–C system burnt out to form highly porous Al₂O₃ support. Following our previous brief study, the effects of sintering parameters such as temperature, pressure, and heating rate on the properties of the porous alumina were investigated. The porosity varied between 28 and 38% depending on the sintering parameters. As desired, the pore size distribution did not change with post-heat treatment temperature and hence the mechanical properties as well. It was concurred from this present study that the sintering parameters of PECS greatly influenced pore characteristics and other properties of porous compacts. We admit that the initial composition ratio of powder mixture (Al₂O₃:C) also plays important role on properties such as porosity, pore size, etc. which is beyond the scope of this present study.

Monodispersed Eu-doped BaTiO₃ nanocrystallites with a pseudo-cubic perovskite phase were successfully prepared using highly concentrated alkoxide solution under hydrothermal conditions at temperatures <100 °C. The obtained nanoparticles had a very narrow particle size distribution and the average value was about 10 nm. By dispersing a piece of BaTiO₃ bulk gel into mixed solvent of 2-methoxyethonal and acetylacetone, we obtained well-dispersed and stable suspensions of Eu-doped BaTiO₃ nanocrystallites with a high transmittance. Using these suspensions, nanostructured thin films with a low porosity and a smooth surface were synthesized on Pt/Ti/SiO₂/Si substrate by electrophoretic deposition. The obtained Eu-doped BaTiO₃ thin films showed strong, visible room temperature photoluminescence (PL) associated with Eu ions. The PL spectra had typical ones for Eu³⁺ band corresponding to ⁵D_o–⁷F_j electronic transitions with a maximum intensity at 613 nm.

Flow modulation chemical vapor deposition (FMCVD) with titanium tetrachloride (TiCl₄) and ammonia (NH₃) is effective for depositing titanium nitride (TiN) films with conformal morphology, good step coverage, low electrical resistivity, and low chlorine residual contamination. It means that FMCVD TiN film is a good candidate of diffusion barriers for copper interconnection technology in ULSI. But the diffusion barrier property of FMCVD TiN film against Cu diffusion has not been confirmed. So, firstly, we deposited Cu (100 nm)/FMCVD TiN (25 nm)/Si multilayer films and investigated the thermal stability of Cu/TiN/Si structure. Vacuum annealing was done at 400, 500, 550 and 600 °C. For films annealed for 30 min at 400 °C, Cu diffused through the TiN layer and formed copper silicides on the surface of Si substrates. Therefore, FMCVD films formed under such conditions are unsatisfactory diffusion barriers. To enhance the diffusion barrier property of FMCVD TiN films, we used sequential deposition to introduce a monolayer of Al atoms between two TiN films. Etch-pit tests showed that for TiN films with Al interlayer, Cu diffusion through the barrier occurred at 500 °C and that is 100 °C higher than TiN film without Al interlayer. Al atoms formed AlO_x with oxygen atoms present in the TiN films as impurities, and fill up the grain boundaries of TiN film, thereby blocking the diffusion of Cu atoms.