Tomoaki Kamiyama

Morphological and magnetic characteristics of monodispersed Co-cluster assemblies

Co-cluster-assembled films have been prepared using a size-controllable cluster beam deposition system, by which monodispersed Co clusters with a mean diameter, d=6–13 nm are available. Their morphology and magnetic properties have been studied by scanning electron microscopy (SEM), small-angle x-ray scattering (SAXS) and magnetization measurements. The SEM images show that the film has a porous structure consisting of fine grains without a columnar texture and its density is about 25% of the bulk Co. The SAXS measurements indicate that monodispersivity of the incident clusters is maintained through their assembling process only for d=13 nm. All the specimens exhibit ferromagnetic behavior at room temperature and the magnetic coercive field Hc rapidly increases with decreasing temperature: Hc=168 kA/m (2.1 kOe) at 5 K. Such an enhancement in Hc is ascribed to the exchange anisotropy which arises from the antiferromagnetic Co–oxide layers covering the Co clusters, and to the assemblies of single-domain fer...

Structural and electrical properties of AgI dispersed As-chalcogenide glasses

Abstract X-ray diffraction, EXAFS and Raman spectroscopic studies, together with transport phenomena measurements, have been carried out for (AgI) x (As 2 Se 3 ) 1− x glasses in order to investigate the ionic conduction mechanism in AgI doped non-oxide glasses. The addition of AgI into As 2 Se 3 glass is responsible for a pronounced increase in the electrical conductivity. Particularly, the ionic component of the electrical conductivity is dominant in highly doped glasses. Results of Raman spectra, EXAFS measurements and least squares fitting analysis for observed X-ray structural functions suggest that the local structure of the present glasses can be described as a pseudo-binary mixture of As–Se networks and fourfold coordinated AgI clusters.

A SAXS study of V2O5·nH2O sols and gels

Abstract Small-angle X-ray scattering (SAXS) measurements on V2O5·nH2O sols and gels, prepared by dissolving V2O5 glass into water at room temperature, show that there are V2O5 polymeric fibers entangled like random coils in the sol of n ≦ 5000, while the deviation from the random coil behavior occurs in the dilute sol of n ≧ 6000 . A Bragg peak appears at the scattering vector h ∼ 0.02 A −1 to be superimposed on an asymptotic h−2-course in the SAXS curve of the concentrated sol of n ≦ 680. This means that the spatial correlation between V2O5 polymeric fibers takes place even in the fluid state. V2O5·nH2O sols completely lose fluidity at n ∼ 250 to transfer to the gel state, where V2O5 polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n ∼ 4. However, V2O5 polymeric fibers are randomly oriented within each layer.

EXAFS study on amorphous and nanocrystalline M–W (M=Fe,Ni) alloys produced by electrodeposition

Abstract Ductile amorphous and nanocrystalline M–W (M=Fe,Ni) alloys were produced by electrodeposition. Structural studies of these alloys were made by using EXAFS and SAXS methods. The crystal structure of the electrodeposited Ni–W alloy was similar to that of the Ni4W crystal phase. The nearest Ni–Ni distance was determined to be 2.49 A; the Ni–W distance was determined to be 2.50 A. The atomic distances in the nanocrystalline Ni–W alloys increases with the tungsten concentration. The average crystal grain size of the Ni–W alloy was estimated at about 2.5 nm from a Guinier plot of the SAXS spectra. The electrodeposited amorphous Fe–21.6 at.% W alloy has only short range order, and no medium range order.

Variation of microfibril angles and chemical composition: Implication for functional properties

Wood cell walls are a composite material consisting of cellulose, hemicellulose, lignin and other minor components, such as pectin and extractives. Two main factors, cellulose microfibril angle (MFA) in S2 layer (thickest layer) and chemical composition, govern functional properties of the cell wall such as Young’s modulus and growth-stress. Recently it was suggested that a change of MFAs resulted in the change of required mechanical properties such as stiffness or flexibility [1–3]. The relationship between growth-stress and MFA and chemical composition has also been discussed [4, 5]. Reaction wood is one of the adaptations required for mechanical balance in wood, which forms in leaning stems or branches. The reaction wood in softwood, compression wood, is found on the lower side of leaning stems or branches. It has a higher MFA and more abundant lignin than normal wood. On the other hand in hardwood, tension wood forms on the upper side. Typical tension wood has cellulose-rich G-layer, which consists of highly longitudinally orientated microfibrils. A branch is often displaced downward by its own weight or snow and ice. The function of the reaction wood in the branch is to maintain it in its proper orientation. In this study, change of MFA and chemical composition were investigated by small angle X-ray scattering (SAXS) and FT-IR. Samples used for SAXS and FT-IR were taken from a branch of Cryptomeria japonica (softwood) and Liriodendron tulipifera (hardwood) growing at the Wood Research Institute, Kyoto University. The softwood branch was cut into four disks, 30–60 cm distance from each other. The largest softwood sample had 10 annual rings, the second 8, the third 4 and the smallest 3. A hardwood branch was cut into 8 disks 40–60 cm from each other. 14 annual rings were found in largest disk. From the second to the eighth one, the number of annual ring was 12, 10, 9, 7, 4, 3, 2, 2, respectively. In both cases areas less affected by knots were chosen. 1 mm thick plates in the radial direction were prepared from

Shape-induced simple cubic arrangement in three-dimensional nanocube self-assemblies

The simple cubic packing rarely appears in nature primarily due to its low packing density. Here, we present that the cubic particle shape induces a preferred formation of three-dimensional arrays of simple cubic arrangement, confirmed by transmission electron microscopy and small-angle x-ray scattering. The calculation of van der Waals interaction energy between the particle cores showed that the highly coordinated, simple cubic packing is energetically the most stable, being consistent with the present experimental result.

A SAXS study of the gelation process of silicon and titanium alkoxides

The gelation process of silicon ethoxide and titanium iso-propoxide solutions was studied as a function of water content and reaction time by small-angle X-ray scattering (SAXS). Approaching the gelation points, the SAXS intensities for titanium tetra-iso-propoxide solutions start to follow a power-law decay in the Porod region, except for a H2O/Ti ratio greater than 4. For silicon ethoxide solutions, the fractal dimension, df, measured for aggregated clusters increases continually with the H2O/Si ratio and can be related to the spinnability of the solutions. For solutions of both silicon and titanium alkoxides, a solution of fractal dimension df 1.79 and no fractal structures do not show spinnability.

Medium-Range Order of Amorphous Silicon Germanium Alloys: Small-Angle X-Ray Scattering Study

A medium-range order of hydrogenated amorphous silicon germanium (a-Si1-xGex:H) alloys is investigated using small-angle X-ray scattering. It is found that the scattering intensities I(h) of a-Si:H and a-Ge:H decrease with scattering vector h as represented by I(h)~h-3. However, in the case of a-Si1-xGex:H alloys, the scattering intensity decreases with h as represented by I(h)~h-P (P<3). This shows that the alloys take on a mass fractal structure. At around x=0.5, the fractal dimension tends to approach the value of 2.

Characterization of the medium-range structure of Si-Al-C-O, Si-Zr-C-O and Si-Al-C Tyranno fibers by small angle X-ray scattering

The medium-range structures of Si-Al-C-O, Si-Zr-C-O and Si-Al-C Tyranno fibers, which were prepared by pyrolysing polymetalocarbosilane organic fibers, were observed by means of small angle X-ray scattering using a point-collimated Cu Kα incident beam and a two-dimensional imaging plate detector. Single Si-Al-C-O and Si-Zr-C-O Tyranno fibers of a few μm in diameter have an anisotropic structure comprising thousands of fine filaments of about 10 nm in diameter bundled together along with the long axis of the fibers. The anisotropic structure is not sensitive to the pyrolysing temperature during the organic-to-inorganic conversion process. However, the anisotropic structure of the Si-Al-C-O fibers is totally modified to an isotropic one in Si-Al-C fibers prepared by heating the Si-Al-C-O fibers above 1700°C in an argon gas stream, because of the formation of an aluminum oxide-rich phase at the grain boundaries of β-SiC nanoclusters.

A SAXS study of the ceramization process of Si–C organic precursor

Abstract Amorphous Si–Ti–O–C ceramic fibers are prepared from organic precursor fibers by heat treatment above 1000°C. Small-angle X-ray scattering (SAXS) measurements have detected a structural change accompanying an increase in mechanical strength of the fibers arising from an increase in heat-treatment temperature. The scattering profiles of Si–Ti–O–C fibers heat treated at temperatures below 800°C differ from those heat-treated at higher temperatures above 1000°C. The former profiles are fit by Gaussian functions, while the latter profiles can be fitted using the Percus–Yevick model of particle scattering including the concept of a depleted zone. The SAXS measurements showed that structural changes occur over a length scale greater than 1.5 nm for fibers heat-treated at temperatures between 500°C and 1000°C.