Papers by Keyword: Crystal Growth

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Authors: Christoph Seitz, Z.G. Herro, Boris M. Epelbaum, Albrecht Winnacker, Rainer Hock, Andreas Magerl
Abstract: A structural characterisation of the first [01-15] grown 6H SiC crystals is presented. They show a different micro domain structure outside the facetted region as compared to conventionally [0001] grown crystals. It is imposed by the reduced rotational symmetry for this direction which favours the activation of a low number of glide systems.
Authors: C.C. Tang, M.C. Miller, Robert J. Cernik, S.M. Clark, C.A. Koh, R.E. Motie, R.I. Nooney, R. Westacott, R. Wisbey, J.L. Savidge
Authors: Matthias Stockmeier, Rainer Hock, Octavian Filip, Boris M. Epelbaum, Albrecht Winnacker, Andreas Magerl
Authors: Liang Yu, Liu Shun Wu, Liao Sha Li, Yuan Chi Dong
Abstract: Dendrite structure in solidification process has been studied by many researchers for it’s widely existence. In present work, a cellular automata model was proposed according to the basic physical chemistry concepts, which was helpful for a better understanding of the dendrite crystal growth and its physical chemistry mechanism. Two kinds of structures were considered in the model: hexagonal and rectangle. The status of every site was set as 0 and 1 which represent non-solidified and solidified state. Temperature field was simulated using finite difference method on the same mesh. The states of sites were changed according to the overcooling condition only. The computer simulation results showed that dendrite structure could be obtained under overcooling condition and temperature field calculation only, the structure of the dendrite was decided by the geometry of the model. The simulation resulted similar pattern as that obtained by experimental observation. The present model suggested that there exist a very simple basic for the typical complex phenomena, dendrite structure.
Authors: P. Råback, Risto M. Nieminen, Rositza Yakimova, M. Tuominen, Erik Janzén
Authors: Dang Ni Gao, Z.J. Li, H.W. Guo, X.F. Wang
Abstract: Pure eulytite Bi4(SiO4)3 crystals were prepared by high temperature melt cooling method using Bi2O3 and SiO2 as starting materials. In this study, the properties of the samples were characterized by thermo gravimetric (TG),differential scanning calorimeter (DSC), field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed that eulytite Bi4(SiO4)3 was crystallized when high temperature glass-melt were cooled to 943°C and obvious exothermal peak is shown on the DSC curve; and pure eulytite Bi4(SiO4)3 crystals were synthesized by keeping the processing temperature for 8 hours. Bi4(SiO4)3 grains grew larger and the amount of vacancy increased along with the extension of holding time, while Bi4(SiO4)3 grains still presented a structure of partial ordering. Eulytite Bi4(SiO4)3 prepared through melt-cooling method is of high purity and good stability, and can be applied as starting materials of preparation of Bi4(SiO4)3 thin film and high quality Bi4(SiO4)3 macrocrystal.
Authors: Yan Sui, Dong Sheng Liu, Rong Hua Hu
Abstract: In this paper, maleopimaric acid anhydride (MPA) has been synthesized by the Diels-Alder addition reaction between abietic acid and maleic anhydride. Single crystal X-ray diffraction analysis reveals that MPA crystallizes in the polar space group P21 and contains one MPA and one DMF (Dimethylformamide) molecule in the asymmetric unit. MPA is firstly found to be a new type of low-molecular-mass organic ferroelectric with the saturation spontaneous polarization (Ps) about 60.0-61.6 μC·cm-2 for single crystal samples, which is close to that of typical inorganic ferroelectric materials. MPA·DMF also shows second-order NLO property, with the second harmonic generation (SHG) responses approximately 0.5 times that of urea.
Authors: Eugene Y. Tupitsyn, Arul Arjunan, Robert T. Bondokov, Robert M. Kennedy, Tangali S. Sudarshan
Abstract: 4H-SiC crystals were grown using the seeded sublimation technique (modified Lely technique) in the temperature range of 1950-2200°C. The nucleation of 4H-SiC on 6HSiC has been optimized and 4H-SiC crystals of 1cm thickness were grown using 6H-SiC seeds. a-face and c-face wafers obtained from the grown boules were characterized by KOH etching, X-ray diffraction, and Raman scattering studies. Complete polytypic homogeneity of 4H SiC was obtained during growth and it was found that the 6H to 4H transition occurs in three ways: 1) without a transition layer, 2) with thick 6H-SiC layer growth, and 3) with traces of 3C SiC inclusions. The crown regions of the grown crystals exhibit an X-ray rocking curve width of 21 arcsecs.
Authors: W.T. Young, L.K.L. Falk, H. Lemercier, Stuart Hampshire
Authors: Hiroki Yamaguchi, Yukinori Sakiyama, Emi Makino, Shoichi Onda, Yoichiro Matsumoto
Abstract: The origin of the polytypes of SiC has been investigated from the viewpoint of surface reactions by the density functional theory (DFT) within the Projector Augmented Wave-Generalized Gradient Approximation. Three radicals were considered here as the major species in the crystal growth process: Si, Si2C and SiC2. We supposed that these radicals contribute to the crystal growth directly through the adsorption on the 4H-SiC (000-1) C-face surface. The DFT calculations showed that the Si2C, which relatively has a similar structure with the SiC crystal, had no activation barrier to be adsorbed chemically to the 4H-SiC C-face surface. On the other hand, SiC2 with Si showed an activation barrier of 0.79eV to form the 4H-SiC crystal. In order to investigate the arrangements to decide polytypism in SiC, we compared the adsorption energies between the different sites, which correspond to the 4H-SiC crystal and a disordered arrangement. The activation energies had almost no difference. Our calculations indicated that these radicals do not contribute to the origin of the polytypes of SiC.
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