Masaaki Ohmasa

Development of a System to Analyse the Structure of a Submicrometre-Sized Single Crystal by Synchrotron X-ray Diffraction

A system has been developed for the analysis of the structure of a submicrometer-sized single crystal using synchrotron radiation (SR) at the Photon Factory (PF), KEK. The Laue method combined with an imaging plate was employed for the collection of diffracted intensities. To reduce background, the experiment was carried out in a vacuum and with a very thinly collimated incident X-ray beam. The system has been shown to reach a level where a molybdenum sphere with diameter as small as 0.8 Ixm was found to be twinned and the volume ratio of the twin domains was determined, together with an isotropic temperature factor, which was comparable with the value determined in the same experiment on another single-crystal sphere of almost the same size. It was in good agreement with that determined by a powder diffraction study. The present study showed that any single crystal detectable under an optical microscope can be analysed and, further, that the diffraction intensities from a crystal with volume of 0.02 Ix m 3, which is composed of 10 9 atoms, can be detected.

Te atom splitting and modulated structure in calaverite

By a crystal structure refinement of calaverite, (Au, Ag) Te2, it was found that Te atom is split symmetrically to the both‐side of mirror plane where Te atoms are supposed to exist. We assumed a regular wavy displacement of Te atom in the calaverite structure and tried to explain the superstructure observed in this mineral.

Development of a microarea diffraction system by polychromatic synchrotron radiation with the Laue method

Microarea diffraction equipment has been developed with a micropinhole and an imaging plate using the Laue method combined with polychromatic synchrotron radiation. The crystal structure of 8 μm diam area of olivine [(Mg,Fe)2SiO4] grain included in a thin section of meteorite was successfully refined based on the intensities of Laue spots.

Characterization of 5‐μm‐sized icosahedral chemical vapor deposited diamond by synchrotron x‐ray diffraction with Laue method

A system for analyzing and refining the crystal structure of a submicrometer‐sized specimen has been developed at the Photon Factory, KEK, employing a Laue method with an imaging plate. The system was evaluated using two molybdenum spheres with diameters of 0.8 μm and 0.27 μm3 in volume. The result showed that the isotropic temperature factors of both spheres were successfully refined, and that one of the samples was found to be twinned. The smaller domain of the twin was determined to be 0.02 μm3 in volume, which means that the smaller domain is composed of only 109 Mo atoms. The system was applied to a 5‐μm‐sized icosahedral CVD diamond as a first application. Analysis of several Laue patterns revealed that the sample is composed of more than 17 domains. Among them, 16 domains are twinned with each other, and the mode of twinning is of the spinel twin type.

The modulated structure of Cu3Bi5S9

The X‐ray diffraction patterns of Cu3Bi5S9 show subsidiary reflections. From these characteristics a model of the modulated structure was uniquely derived. The structure consists of two kinds of slabs: a galena‐like structure and Bi2S4 double chains. The subsidiary reflections are due to a ’’synchronized’’ replacement of Bi atoms within the slab of a galena‐like structure with Cu atoms.

Characterization of CVD micrometer‐size diamond (abstract)

In the field of material sciences, it has long been desired to develope the equipment to obtain crystallographic information of micrometer‐size crystalline substances. Synchrotron radiation (SR) could be a candidate to deal with such a small specimen other than electron microscope. It seems more advantageous to utilize SR from the viewpoint that the processing of the diffraction data that has already been established for identification of the materials, structure analysis, and refinement. Even in the case of SR, special care should be taken for the measurement of very weak diffracted intensities. In the case not using SR, the size of 50 μm might be the limit for the specimen to be examined by the diffraction method. The diffracted intensity is proportional to the volume of the specimen, and that of micrometer‐size crystal is estimated as 10−5 times of that of the limit mentioned above. The noise level of the experiment, therefore, should be as low as possible. If the noise level becomes negligibly small, ...

Studies on the process of reaction in crystals by synchrotron radiation: Dehydration of α‐AlOOH (abstract)

In order to study the process of reaction in crystals, it is necessary to observe decomposition of precursor and formation of the product during the transformation. Since such change is related to the structures of both the phases, x‐ray diffraction is the most powerful method for this purpose. However, not only Bragg reflections but diffuse scattering or satellite reflections are observed occasionally in the early stage of the process and intensities of those scattering are extremely weak although they are important to analyze the process. Therefore, use of synchrotron radiation is desirable to study those problems. There are many compounds which show topotaxy during phase transformation. Since the product of such transformation is formed in an oriented manner under the influence of the structure of the precursor, diffraction patterns of the product are similar to those of a single crystal and anomaly of the diffraction can be easily detected. We have consequently studied the process of dehydration in α‐...