Armando H. Shinohara

Effect of Impurity Segregation on Crystal Morphology of Y-Bar Synthetic Quartz

The effects of Al and H impurities on the crystal morphology of Y-bar synthetic quartz were studied. The growth velocities perpendicular to the Y-axis were evaluated in relation to the Al and H impurity segregations on the growth interfaces. It was found that the -X-growth region has the highest H content and shows the lowest growth velocity, due to the effect of H2O adsorbed on the growth interface in hydrothermal solution. Therefore, the -X-face, (20), always becomes larger in size. Al has a selective effect on the (112) and (2) faces to suppress the growth velocities and thus is important for crystal morphology. The growth velocities perpendicular to these faces, however, are controllable by the Al impurity content in the nutrient.

X-ray topographic characterization of epitaxially grown diamond film

Abstract X-ray double crystal diffraction topography of homoepitaxial diamond film grown by microwave plasma chemical vapor deposition has been conducted to-study the residual stress generated by the lattice mismatch and defects at the film-substrate interface. Even though the stress-relaxation mechanism occurs by uniform film cracking, and there is no bending effect, a relatively large strain ( Δd d = 8.7 × 10 −4 ) still remains. Based on the X-ray topographic observation, a strain distribution model with alternate unstrained and tensioned regions is suggested.

Study of S- and /spl xi/-bar synthetic quartz by X-ray topography

Synthetic quartz crystals were grown on S- and /spl xi/-bar seeds and characterized by X-ray topography. For comparison, synthetic quartz crystals grown on intermediary cutting between S- and /spl xi/-planes (/spl phi/=24-42/spl deg/) seeds were also investigated. As a result, several new growth regions usually not present in the Y-cut of Y- and Z-bars synthetic quartz crystals have been observed, in a number of four in the /spl xi/-bar and two in the S-bar. For convenience, these new growth regions were called /spl xi/-regions. The texture of /spl xi/-regions of /spl xi/- and S-bars synthetic quartz crystals are quite similar, with strong distortions in the crystal lattice structure due to a high segregation of impurities. This fact was also verified by the degree of darkness after a /spl gamma/-ray irradiation. The impurity analysis by atomic absorption spectroscopy revealed high content of Al in the /spl xi/-regions with a concentration of about 30 ppm. Furthermore, the growth velocities of /spl xi/-regions are higher in comparison with other regions. In the present research the occurrence of the new regions is directly related to the orientation of seed, which can induce an aggregation of high concentration of Al impurity.

Growth and characterization of optical grade synthetic quartz

A method to position the seed and Z-region of growth out of the circulating micro-particle flux in commercial autoclave has been used to grow optical grade synthetic quartz. The number of solid inclusions is in the range of 0.02-0.03 particles/cm/sup 3/, depending on the bar. The observation of X-ray topographic contrast of (0003) reflection shows a much smaller Z-region lattice spacing (strain) in comparison with the seed. The dislocation lines are in their totality originated by the seed etch-channels, that means, they can be eliminated by using a better quality seed.

In Situ Extended X-Ray Absorption Fine Structure Study on the Local Structure around Gallium in Liquid Silicon

The local structure around gallium of 0.5, 1 and 5 at.% in liquid silicon at 1440° C has been investigated by the extended X-ray absorption fine structure (EXAFS). The amplitude of EXAFS oscillations is distinct for the very dilute case of 0.5 at.% gallium. The EXAFS analysis shows that the structural parameters of Ga–Si pairs change from 2.8 atoms at a distance of 2.36 A to 2.1 atoms at a distance of 2.43 A with increasing gallium content in liquid silicon. These results suggest that a certain local structure around gallium in liquid silicon is formed at low gallium content and that this structural feature disappears with increasing gallium content.

Effect of Heat Treatment on the High-Purity Silica Glass Prepared from Amorphous and Crystalline Powders by Small Angle X-Ray Scattering

High-purity silica glass prepared from high-purity amorphous and crystalline powders by flame fusion and sintering at high temperatures in vacuum, was heat-treated at 1250°C for several periods of time and its structure was studied using the small-angle X-ray scattering technique. As a result, the structure of silica glass was dependent on its thermal history. The structure of as-fused silica glass samples prepared by flame fusion appeared to be quite similar, even though raw materials with different degrees of homogeneity were used. However, the structure of silica glass behaved differently after heat treatment. This different response of the structure of silica glass to heat treatment was analyzed in terms of impurity content and viscosity.

Characterization of low-dislocation synthetic quartz grown on highly distorted seed by X-ray topography

In the present study, the feasibility to grow a dislocation-free synthetic quartz with large Z-region from a seed containing high density of dislocation is reported. For such purpose, a seed with new geometric design was prepared. A seed long in Y-direction and containing V-shaped cuts with cutting angle of 90/spl deg/ made on Z-face {0001} was prepared and grown in the hydrothermal process. As a result, new growth regions usually not found in the conventional Y- and Z-bars synthetic quartz crystals have been imaged by the X-ray topography. The new growth region grown from the V-shaped cut was composed with two sub-regions of distinct textures. Due to their high growth velocity perpendicularly to cut faces, they disappeared and were replaced by the so-called Z-region. However these newly grown sub-regions played an important role to change the direction of dislocation propagation present in the seed trapping them and minimizing their propagation into the grown Z-region.

Micron order structural inhomogeneities in vitreous silica observed by etching technique

Abstract Etching of various vitreous silica samples over a long period (∼ 200 min) with hydrofluoric acid revealed a high contrast configuration of micron to sub-millimeter order boundaries similar to the grain boundaries of crystalline materials. In order to better understand this new result, various parameters, such as the vitreous silica preparation processes, the type of basic insume, the grain size of silica powder, the surface roughness, and the OH-content, were studied. They should no correlation with the configuration of “amorphous-grain”. A possibility of an anistropic micro-strain configuration induced by heterogeneous distribution of defects and impurities in the vitreous silica structure is suggested to explain the appearance of such grain boundary-like contrast.

A uniformly cleaved epitaxically grown diamond crystal for synchrotron radiation

A homoepitaxic single-crystal diamond (111) film grown by microwave-assisted chemical vapour deposition (CVD) and fractured along the [110] directions to form small triangles was investigated by X-ray double-crystal topography. The X-ray topographic image showed that all parts of the cleaved CVD diamond film sections uniformly reflected X-rays at the peak position of the rocking curve, which was measured in the Bragg case. Furthermore, no bending effect was observed and the CVD diamond film appeared to be more perfect than and showed higher integrated intensity than the natural diamond substrate.

Small-angle X-ray scattering of heat-treated flame-fused silica glass from amorphous and crystalline powders

High-quality as-fused silica glass, heat treated at 1523 K and prepared by the flame-fusion process using natural crystalline quartz and high-purity amorphous silica glass powders, was investigated by small-angle X-ray scattering (SAXS). The X-ray scattering intensity amplitude from the amorphous structure after heat treatment was analysed in terms of viscosity, density and metallic impurity content. It is shown that SAXS scattering of the amorphous sample is sensitive to the structural change induced by annealing.