Katsuhisa Usami

Infrared absorption spectra and compositions of evaporated silicon oxides (SiOx)

Abstract Clear and simple relationships among oxygen content, peak position in the 9–10 μm region and intensity of infrared absorption were obtained for a wide range of x value in evaporated silicon oxides (SiOx). Using these relationships, the origin of 875 cm−1 peak was proposed to be due to a vibrational mode from a structural combination of Si(OySi4-y) (y = 2, 3 and 4).

Chemical bonding states in the amorphous SixC1–x: H system studied by X-ray photoemission spectroscopy and infrared absorption spectra

Abstract XPS studies and infrared absorption measurements of the reactively sputtered (RS) amorphous SixC1–x: H alloy system have been made. The binding energy of the Si 2p core electrons decreases monotonically as the alloy composition x increases while the corresponding line-width remains almost constant. On the other hand, a curve of the C 1s core electron binding energy versus x has a kink at around x = 0·5∼0·6. Infrared absorption spectra reveal the existence of C–H, Si–H, Si–C bonds in the films. These results are discussed in terms of chemical bonding states.

IN SITU X-RAY CT UNDER TENSILE LOADING USING SYNCHROTRON RADIATION

Internal damage in metal matrix composite (MMC) under static tensile loading was observed by in situ x-ray computed tomography based on synchrotron radiation (SR-CT). A tensile testing sample stage was developed to investigate the fracture process during the tensile test. Aluminum alloy matrix composites reinforced by long or short SiC fibers were used. The projection images obtained under tensile loading showed good performance of the sample stage, and matrix deformation and breaks of the long SiC fibers could be observed. In the CT images taken at the maximum stress just before failure, debondings of the short SiC fibers to the matrix, many pullouts of the fibers, and matrix cracking could be clearly observed. The in situ SR-CT allowed the observation of generation and growth of such defects under different tensile stress levels. The results from the nondestructive observation revealed that the MMC was broken by propagation of the matrix cracks which might be caused by stress concentration at the ends of the short fibers. A three-dimensional CT image reconstructed from many CT images provided easy understanding of the fiber arrangement, crack shape, and form of the void caused by fiber pullout. In situ SR-CT is a useful method for understanding failure mechanisms in advanced materials.

Rietveld Refinement of the Structure of TlSr2CaCu2O7 by X-Ray Powder Diffraction Data

Single phase TlSr2CaCu2O7 was synthesized, and the crystal structure was refined from X-ray powder diffraction data using Rietveld analysis. The structure has single Tl-O sheets and tetragonal symmetry (a=3.7859 A, c=12.104 A) with space group P4/mmm, and is similar to TlBa2CaCu2O7 and Tl0.5Pb0.5Sr2CaCu2O7 (1212 type). Possible substitution of about 14% of Ca-sites with Tl ions was suggested.

Observation of Compositional Separation in CoCrTa Thin Film Using Transmission Electron Microscope with Imaging Filter

The elemental mapping of a CoCrTa thin film deposited at 270° C has been performed using a transmission electron microscope equipped with an imaging filter. A compositional separation, which consists of Co-enriched areas and a Cr-enriched phase around them, is quantitatively observed. The Co-enriched areas are about 20 nm in diameter and the Cr-enriched phase extends with a two-dimensional network, which corresponds to grain boundaries. Intragrain Cr-enriched areas, which are less enriched than at the grain boundaries, are also observed.

Relationship between crystal structures and solid solution of Tl-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O superconductors

We report on the superconductivity and crystal structures in Tl-(Ba, Sr)-Ca-Cu-O (TBSCC) system. In the case of TBSCC system, the 2223 phase was obtained as a single phase more easily compared with the Tl-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems. As a result, we achieved a high superconducting volume fraction, 95% above 100 K. The crystallographic transformation was caused by changing the ratio of Ba to Sr. By the X-ray diffraction and TEM analysis, the crystal structure was determined as a 2223 structure consisting of Tl-O bilayers in the Ba-rich side, and a 1223 structure consisting of Tl-O monolayer in the Sr-rich side.

Control of Optical Gap in a-SixC1-x: H Alloy Films Produced by Reactive Sputtering Method

Hydrogenated amorphous silicon-carbon alloy (a-SixC1-x: H) films are prepared by simultaneous if reactive sputtering of silicon and graphite in a H2–Ar gas mixture. The optical gap E0 of a-SixC1-x: H depends on alloy composition x and preparation conditions. The optical gap E0 of a-SixC1-x: H prepared under a same condition is ~1.7 eV at x=1.0 (a-Si: H), increases with the decrease in x, reaches a maximum value of 2.2 eV at x=0.6 and then decreases with decrease in x, reaching ~1.4 eV at x=0 (a-C: H). For films prepared at lower substrate temperature, the optical gap becomes larger. This behavior of the optical gap is discussed referring to the results of X-ray photoemission spectroscopy, infrared absorption measurements, etc., on a-SixC1-x: H.

X-ray computerized tomography using monochromated synchrotron radiation

An X-ray computerized tomographic (CT) imaging system using monochromated synchrotron radiation has been constructed and its performance has been evaluated. Spatial resolution is about 125 µm. Several CT images have been taken. Element mapping in a test sample has also been obtained using the difference between two CT images at different X-ray energies just above and below the absorption edge of the element.

Improvement of Spatial Resolution of Monochromatic X-ray CT Using Synchrotron Radiation

X-ray computed tomography using synchrotron radiation (SR) as X-ray source potentially provides CT images of improved quality, since SR produces tunable, monochromatized and collimated X-ray beams of high flux density. We can obtain CT images of small samples rapidly with better spatial resolution and contrast; we can also obtain the spatial distribution of a specific element using the absorption edge. In this paper, a method for improving the spatial resolution of such a system is presented, involving the magnification of projection images using asymmetric diffraction. First, the modulation transfer function (MTF) of projection images of an X-ray test chart is measured in order to evaluate the spatial resolution. Next, using this method, we show CT images of several industrial materials with spatial resolution of 15~30 µm and demonstrate the usefulness of SR-CT with a high spatial resolution.

Measurement of Strain in Locally Oxidized Silicon using Convergent-Beam Electron Diffraction

Possibility has been studied for analysis using convergent-beam electron diffraction (CBED) of strain in large-scale integrated circuits (LSIs). In the present study, a strain of 1×10-4 can be detected, which is sufficient to analyze strain in LSIs. This technique is applied to the measurement of strain in locally oxidized silicon (LOCOS). The silicon substrate is found to have a maximum compressive strain of 4×10-4 at a point 1.5 µm from the SiO2 edge. Although the influence of specimen thinning preparation on stress is not negligible, the stress distribution was found to suffer from a uniform shift of tensile stress by about 30 MPa.