Crystal Growth

We have developed a modified physical vapor transport (M-PVT) growth technique for the preparation of SiC single crystals which makes use of an additional gas pipe in order to control the gas phase composition of the conventional physical vapor transport (PVT) configuration. We discuss ...

Snowflakes and silicate mushes are two examples of the terrestrial regimes that may be characterized as partially solidified systems. Change of phase in clouds and magma chambers as well as in the earth's mantle and core introduces a variety of phenomena to challenge both the mathematical modeler and the experimentalist intent upon understanding the nature of such processes. Paralleling the efforts of researchers in the natural sciences, metallurgists and materials scientists have extensively investigated solidification in alloy melts to discover the controlling mechanisms for undesirable behavior such as melt segregation, freckling (Figure 1), and crystal dislocation. Unfortunately, most of the studies, whether in the geosciences or in material sciences, have focused on highly specialized problems with little or no attempt at generalizing the results or methods to other physical systems. During May 12-16, 1986, at the Stanford University Conference Center at Fallen Leaf Lake, ...

The epitaxial growth and the structure of Cu on Si(111)7 × 7 deposited at high temperature (< 300–600°C) was investigated mainly by medium energy ion scattering (MEIS) and scanning tunneling microscopy (STM). The domain images whose periodicity is about 5.5 ± 0.2 times of the Si bulk unit were observed at high sample bias (VS = 2.5 V). The periodicity

A new theory of oscillatory zoning in naturally grown plagioclase crystals is presented. This describes explicitly the coupling between the interface kinetics and the diffusion of chemical species in the melt. The crystal growth rate R responds with a finite delay time to concentration ...

Amelogenin-mineral interactions were investigated using an in vitro binding approach. Rat incisor enamel matrix proteins (mainly amelogenins) were dissolved in synthetic enamel fluid and allowed to equilibrate with deproteinised developing enamel crystals. The results showed that amlogenin proteins of 21, 23, 24, 26 and 27-kDa (corresponding to nascent and partially degraded amelogenins) were associated with the crystals whilst the lower Mr amelogenins (< 21 KDa) remained free in the synthetic enamel fluid. These data suggest the nascent and partially degraded amelogenins may interact with developing enamel crystals and could influence their growth. Albumin-mineral interactions were investigated by extracting developing rat incisor enamel with synthetic enamel fluid. Insoluble material (including the enamel crystals) was then further extracted with 0.1 M phosphate buffer (pH 7.4) to desorb any mineral bound proteins. Western blotting using anti-albumin antibodies showed that almost all of the albumin from the secretory stage enamel and a significant proportion of the albumin present in early transition stage was extractable in the synthetic enamel fluid. However, synthetic enamel fluid did not extract albumin from late transition or maturation stage tissue, which could only be removed following further extraction with phosphate buffer. Albumin degradation was apparent during the transition and maturation stages, where it is degraded and ultimately removed. This binding pattern may be related to amelogenin degradation and removal during the transition stage, permitting albumin access to the previously obscured crystal surfaces. That the secretory stage matrix appears to "protect" secretory stage crystals from albumin may be an important consideration in the aetiology of enamel hypoplasias (i.e. incomplete crystal growth) and when using dissociative extraction procedures for the identification of mineral bound proteins.

Crystals of LTA zeolites were obtained in absence of organic templates using a crystallization temperature of 373 K. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-Transform Infrared (FTIR) spectroscopy. The aging time was found to be a crucial factor for the control of the crystal size. Samples aged between 72 and 144 h presented an

Transparent conducting ZnO:F was deposited as thin films on soda lime glass substrates by atmospheric pressure chemical vapor deposition (CVD) deposition at substrate temperatures of 480–500 °C. The precursors diethylzinc, tetramethylethylenediamine and benzoyl fluoride were dissolved in xylene. The solution was nebulized ultrasonically and then flash vaporized by a carrier gas of nitrogen preheated to 150 °C. Ethanol was vaporized separately, and these vapors were then mixed to form a homogeneous vapor mixture. Good reproducibility was achieved using this new CVD method. Uniform thicknesses were obtained by moving the heated glass substrates through the deposition zone. The best electrical and optical properties were obtained when the precursor solution was aged for more than a week before use. The films were polycrystalline and highly oriented with the c-axis perpendicular to the substrate. The electrical resistivity of the films was as low as 5 × 10−4 Ωcm. The mobility was about ...

The formation of minerals and mechanisms by which bacteria could control their formation in natural habitats is now of current interest for material scientists to have an insight of the mechanism of in vivo mineralization, as well as to seek industrial and technological applications. Crystalline uniform structures of calcium and barium minerals formed micron-sized building blocks when synthesized in the presence of an organic matrix consisting of secreted protein extracts from three different lactic acid bacteria (LAB) viz.: Lactobacillus plantarum MTCC 1325, Lactobacillus acidophilus NRRL B4495 and Pediococcus acidilactici CFR K7. LABs are not known to form organic matrix in biological materialization processes. The influence of these bacterial extracts on the crystallization behavior was investigated in details to test the basic coordination behavior of the acidic protein. In this report, varied architecture of the mineral crystals obtained in presence of high molecular weight protein extracts of three different LAB strains has been discussed. The role of native form of high molecular weight bacterial protein extracts in the generation of nucleation centers for crystal growth was clearly established. A model for the formation of organic matrix–cation complex and the subsequent events leading to crystal growth is proposed.