Experiments were conducted in order to obtain the relation between surface tension of molten and oxygen partial pressure. Clarifyiyng the relation holds a key for understanding the Marangoni convection of molten silicon in a Czochralski (CZ) system.Measurements of surface tension and density of molten silicon were performed by the sessile drop method using BN substrate under argon atmosphere at 1693 K. Oxygen partial pressure Po_2 of argon gas was controlled below the equilibrium Po_2, that was, Po_2,_<sat>, of S1O_2 by the aid of argon gas purifier and tightly sealed furnace made of double alumina tubes. Po_2 was determined with oxygen sensor of solid electrolytes, ZrO_2・CaO. Surface tension of molten silicon was 813 mN/m at 1693 K under a condition of Po_2=2.58×l0^<-22> MPa. The surface tension remarkably decreases with increasing Po_2 up to Po_2,_<sat> of SiO_2 at 1693 K. However, above Po_2,_<sat>, the surface tension keeps almost constant with incrcasing Po_2.
Preferred orientation of AlN film is changed from (0001) to (101^^-0) by preparation conditions. The reason is explaincd based on extended PBC theory. Any (hkl) planes are made by hypothetical primitive prism units with the height d_<hkl> and the basal plane S_<hkl>. There are some growth units in the prism unit. These growth units have a different attachment energy E_<att> defined as the number of broken bonds of itself. We assume the growth rate (V_<hkl>) is proportional to E_<att>/S_<hkl> of the growth unit having a minimum value or E_<att>, and decreases with in creasing evaporation rate or dissociation rate of the growth unit (dissociation energy: E_<dis>). In AlN crystal, we consider two kinds of growth units: atoms (Al, N) and dimer (Al-N). The preferred orientation of (0001) plane occurs at V_<hkl> ∝E_<att>/n, where n is the number of growth unit with the minimum valuc of E_<att>. The (101^^-0) orientation appears at V_<hkl> ∝E_<dis>, and with the growth unit of Al-N dimer.
Aiming at the fabrication of SIS tunnel. Josephson junctions, complexity of c-/a-axis oriented YBa_2Cu_3O_x (YBCO) thin film growth with T_c=90 K is discussed from epitaxy points of view. The preferred orientation of YBCO thin films is strongly depending on growth parameters, namely growth temperature and oxygen partial pressure, independent of substrate materials. a-axis oriented films on perovskite-related substrates shows usually T_c as low as 30 K, which may be caused by 90°-domains where each c-axis intersects at right angles to each other. "Pure" a-axis oriented (c-axis in-plane aligned, a-axis oriented) films with a T_c of 90 K, which is though to be favorable to realize SIS struclure, are successfully grown on tetragonal K_2NiF_4-typed (100) substrates such as SrLaGaO_4 and Nd_2CuO_4. This epitaxy can be explained by a novel mechanism called Atomic Graphoepitaxy, which provides a coherent ( structural continuity and elctronical disconitinuity) interfaces nescessary to SIS tunnel junction fabrications. Thus grown "purc" a-axis oriented films on (l00) SrLaGaO_4 substrates consist of epiaxial grains surrounded by anti-phase and stacking-fault defects boundaries. The formation of such defect boundaries id closely connected with cobbled substrate surface during film depositio, and the atomic graphoepitaxy model gives a consistent full explanation of their formations. Efforts on the search of new K_2NiF_4-type substrate materials like SrLaGaO_4 are still needed. They are also usuiful to select insulating I-layer materials in SIS tunnel junctions, because K_2NiF_4-type materials allow coherent interfaces with structural continuity and electronical discontinuity.
Growth mechanism of hydroxyapatite crystal under the psudo-physiological conditions was investigated by in situ atomic force microscopy using hydrothermally synthesized single crystal as the seed. It was revealed that the rate determining process of a growth was not in the diffusion process but in the incorporation of a growth unit into the crystal. The relative resistance of incorporation showed a similar value as that of macromolecular protein and virus crystals suggesting that the growth unit of hydroxyapatite was a duster. This cluster may correspond to the "Posner cluster" which was defined in the structure of amorphous calcium phosphate.
The bottle neck of a three-dimensional structural analysis of protein molecules is the crystallization of large (>0.1μm) and suitable high quality crystals. To overcome this difficulty, the growth process of protein crystals, such as the mass transfer of the molecules and the growth kinetics of the crystals, must be quantitatively analyzed. Two-beam interferometry is a powerful technique for an in situ observation of the concentration distribution around a growing crystal. By using interferometer of Michelson type, we have been successfully observed the concentration distribution around a hen egg-white lysozyme crystal. Here, we outline the principle of two-beam interferometry, and explain how the growth mode and the diffusion coefficient of lysozyme molecules can be obtained. We also show a rapid solubility measurement of protein crystals by using the same interferometric technique, which can determine the solubility of lysozyme crystals at one point in a phase diagram within 1-2 hrs. This technique is about ten times quicker than other ordinary methods so far used for a solubility measurement.
This article reviews recent studies on the crystallization phenomena and operation for the preparation of pharmaceuticals and functional foods. Main interests are focused on selective crystallizotion of polymorphs and solvent mediated phase transition, clathrative crystallization of green tea polyphenol with cyclodextrin, crystallization of maltose accompanying anomerization process, crystallinity and functionalities of drug, and the modification ofcrystal habits by controlling agitation condition for improvement of sparation by filtration.
The effects of impurities present in crystallizeds. solution on the change in the crystal habit of aspartic acid crystals were investigated. Aspartic acid is produced by an enzymatic method using fumaric acid as raw matcrials in an industrial scale. The characteristics of this method are to produce very limited amounts of sub-products such as other amino acids, compared with conventional fermentation methods. When aspartic acids were crystallized by a continuous crystallization at 50℃ with neutrallization by 98% sulfuric acid, the changes in the crystal habit from plate to pillar forms were observed with the operation times elapsed, maintaining the α form crystal structure.The plate form crystallized under the higher supersaturation in the vicinity of 5g/dl, irrespective of the existence of impurities. On the other hand, the impurities in the solution, mainly fumaric acid and malic acid, inhibited the growth rate along b-axis direction and the crystal habit changes to the pillar form crystals, when the supersaturation decreased as low as 2g/dl.