Masato Ohnuma

Cu clustering stage before the crystallization in FeSiBNbCu amorphous alloys

The Cu clustering stage before the crystallization of FeSiBNbCu amorphous alloys have been studied by three dimensional atom probe (3DAP), small-angle neutron scattering (SANS) and high sensitive differential calorimetry (DSC). Cu clustering occurs prior to the onset of the primary crystallization reaction. The number of the clusters estimated by 3DAP is large enough to provide heterogeneous nucleation sites to all bcc/DO3 FeSi crystals which appear at higher temperatures. This fact indicates that the distribution of nanocrystalline FeSi is strongly affected by that of the Cu-enriched clusters. The average diameter and interparticle distance of the Cu-enriched clusters have also been estimated by SANS. An exothermic reaction is observed above the Curie Temperature in the DSC curves of the FeSiBNbCu alloys. The onset temperature of the exothermic reaction is shifted to lower temperature with increasing Cu content.

Mesoporous silica nanotubes hybrid membranes for functional nanofiltration

The development of nanofiltration systems would greatly assist in the production of well-defined particles and biomolecules with unique properties. We report a direct, simple synthesis of hexagonal silica nanotubes (NTs), which vertically aligned inside anodic alumina membranes (AAM) by means of a direct templating method of microemulsion phases with cationic surfactants. The direct approach was used as soft templates for predicting ordered assemblies of surfactant/silica composites through strong interactions within AAM pockets. Thus, densely packed NTs were successfully formed in the entirety of the AAM channels. These silica NTs were coated with layers of organic moieties to create a powerful technique for the ultrafine filtration. The resulting modified-silica NTs were chemically robust and showed affinity toward the transport of small molecular particles. The rigid silica NTs inside AAM channels had a pore diameter of <or= 4 nm and were used as ultrafine filtration systems for noble metal nanoparticles (NM NPs) and semiconductor nanocrystals (SC NCs) fabricated with a wide range of sizes (1.0-50 nm) and spherical/pyramidal morphologies. Moreover, the silica NTs hybrid membranes were also found to be suitable for separation of biomolecules such as cytochrome c (CytC). Importantly, this nanofilter design retains high nanofiltration efficiency of NM NPs, SC NCs and biomolecules after a number of reuse cycles. Such retention is crucial in industrial applications.

Low-temperature fabrication of high-coercivity L10 ordered FePt magnetic thin films by sputtering

We report that fully ordered L10 FePt magnetic thin films with high coercivity can be fabricated by a simple sputtering method at a substrate temperature of 300°C. Although fcc→L10 ordering proceeds only above 600°C in ex situ annealing of disordered FePt films, the ordering occurs spontaneously by surface diffusion during the sputtering process of FePt alloy upon heating the substrate at 300°C. High coercivity larger than 7 kOe was achieved from the as-sputtered state.

Bulk amorphous (Mg0.98Al0.02)60Cu30Y10 alloy

Recently, Inoue and Masumoto have found that Mg-Cu-Y alloys show high glass-forming ability (GFA), hence making it possible to produce bulk amorphous samples of such alloys. The aim of the present work was to characterize in some detail one of these new bulk amorphous alloys, (Mg{sub 0.98}Al{sub 0.02}){sub 60}Cu{sub 30}Y{sub 10}. Its stability and crystallization process was examined by using x-ray diffraction (XRD), differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS). One finding was the formation of nanocrystalline particles on annealing. It was also found that the addition of Al increases the hardness.

Extraction of blocking temperature distribution from zero-field-cooled and field-cooled magnetization curves

Superparamagnetic fluctuation of magnetic nanoparticles is studied. We examine the validity of the simplified approach using the difference between zero-field-cooled magnetization and field-cooled one. The results show that it is valuable for estimating the blocking temperature distribution of polydispersive particles even in magnetic fields, if both surface effects and inter-particle interactions are negligible.

Nano structure of rapidly quenched Cu–(Zr or Hf)–Ti alloys and their devitrification process

Abstract The structure and primary devitrification process of the melt-spun Cu60(Zr or Hf)30Ti10 alloys were investigated. It was confirmed that the compositional segregation in the diameter range of 5–10 nm exists in the as-quenched state. The nanocrystalline particles with cubic structure are observed in the glassy matrix in thehigh-resolution transmission electron microscopy images, of which size is corresponding to the scale of compositional segregation. Small-angle X-ray scattering measurement also indicates the development of nanoscale inhomogeneity with the same size as that of nanocrystalline particles. The nanocrystalline region has high Cu content. In contrast, Zr or Hf and Ti elements are enriched in the glassy region. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of bcc CuZr phase as a primary crystallization phase proceeds in the glassy phase remaining the nanocrystalline phase in the Cu–Zr–Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu8Hf3 phase at the initial crystallization stage in the Cu–Hf–Ti alloy. These differences of crystallization process are consistent with the results of thermodynamic and kinetic analyses of the transformation mode.

Anatase-Dominant Matrix in Ge/TiO2 Thin Films Prepared by RF Sputtering Method

This paper investigates the crystal structure and optical absorption of Ge/TiO2 composite thin films for next-generation solar cells. X-ray diffraction patterns reveal that an anatase-dominant structure of TiO2 matrix is successfully obtained by compositional optimization. The optical absorption spectra are obviously shifted to visible- and near-infrared-regions due to the presence of Ge nanogranules, suggesting that Ge/TiO2 composite thin films are therefore capable of converting solar radiation to electrical power. Accordingly, the two valuable properties of anatase-dominant structure and favorable absorption are found to be retained simultaneously in the Ge/TiO2 composite thin films.

Probing Ar ion induced nanocavities/bubbles in silicon by small-angle x-ray scattering

Small-angle x-ray scattering (SAXS) measurements have been performed to investigate the nanocavities/bubbles and the amorphous silicon surrounding the cavities/bubbles generated after high fluence medium-energy (60 keV) Ar ion implantation in single crystalline Si as a function of incidence angle (with respect to the surface normal of the sample). The measurements were carried out using a high flux/high transmission laboratory scale SAXS set up with Mo-Kα radiation in transmission geometry. The scattering data have been used to calculate the average size (Dave), number density (dN), and volume fraction (Vf) of cavities/bubbles in ion induced amorphous layer of the crystalline Si substrate. The novelty of the SAXS technique applied in the present case lies on its ability to detect ultrafine defect features of size even less than 1 nm, which is otherwise impossible from the transmission electron microscopy measurements usually employed for inert gas ion induced cavities/bubbles in amorphous silicon.

Small-Angle X-Ray Scattering and Proton Conductivity of Anhydrous Nafion–Benzimidazole Blend Membranes

The small-angle X-ray scattering (SAXS) and proton conductivity of Nafion-benzimidazole (na―bz) blend membranes were investigated at various annealing temperatures. The SAXS data showed that the bz base as a proton source was successfully incorporated in the Nafion nanostructure, and the bz in the nanostructure was stable under both wet and dry conditions at room temperature. The nanostructural stability of the na―bz blend membrane was also investigated at various temperatures and was compared to the X-ray diffraction and proton conductivity data. In the na―bz blend membrane, both the nanostructure and the bz were stable up to 150°C under anhydrous (nonhumidified) conditions. The proton conductivity was also stable over this temperature range. The na―bz blend membrane may be useful as an anhydrous membrane for high temperature polymer electrolyte fuel cells.

Microstructure of soft magnetic FeCo–O(–Zr) films with high saturation magnetization

In this paper, we present our detailed work of the microstructural characterization, using transmission electron microscopy (TEM), high resolution TEM and small angle X-ray scattering (SAXS). The effect of oxygen on the microstructure and the relationship between the microstructure and magnetic properties are clarified. The effect of annealing on the magnetic properties and microstructure has also been studied.