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Berlin, Germany

The Leibniz-Institut für Kristallzüchtung, German for Leibniz Institute for Crystal Growth and abbreviated with IKZ, is a research institute within the Gottfried Wilhelm Leibniz Scientific Community and is a member of the Forschungsverbund Berlin . The institute is based in Berlin, Germany at the WISTA Science and Technology Park in the sub-district of Berlin-Adlershof. Its research activities concentrate on basic research on the fields of natural science and materials science. Wikipedia.

Wunder S.,Helmholtz Center Berlin | Lu Y.,Helmholtz Center Berlin | Albrecht M.,Humboldt University of Berlin | Ballauff M.,Helmholtz Center Berlin | Ballauff M.,Leibniz Institute for Crystal Growth
ACS Catalysis | Year: 2011

We present the analysis of the catalytic activity of gold nanoparticles in aqueous solution as a function of temperature. As a model reaction, the reduction of p-nitrophenol (Nip) by sodium borohydride (BH4 -) is used. The gold nanoparticles are immobilized on cationic spherical polyelectrolyte brushes that ensure their stability against aggregation. High-resolution transmission electron microscopy shows that the Au nanoparticles are faceted nanocrystals. The average size of the nanoparticles is 2.2 nm, and the total surface area of all nanoparticles could be determined precisely and was used in the subsequent kinetic analysis. Kinetic data have been obtained between 10 and 30 °C by monitoring the concentrations of Nip and BH4 - by UV-vis spectroscopy. The reaction starts after an induction time t0, and the subsequent stationary phase yields the apparent reaction rate, kapp. All kinetic data could be modeled in terms of the Langmuir-Hinshelwood model; that is, both reactants must be adsorbed onto the surface to react. The analysis of the temperature dependence of kapp leads to the heat of adsorption of both Nip and BH 4 - and the surface of the Au nanoparticles. Moreover, the true activation energy of the surface reaction is obtained. The analysis of t0 reveals clearly that the induction period is not related to the limitations due to diffusion but to the surface restructuring of the Au nanoparticles induced by the adsorbed Nip. The rate 1/t0 of this substrate-induced surface restructuring is found to be proportional to the square of the surface coverage, θNip, by Nip and therefore points to a cooperative process. © 2011 American Chemical Society. Source

The undercooling at the Si(1 1 1) facet is of great importance, e.g. in explaining effects during grain growth of multicrystalline Si. Data of experiments spread over a wide range and there is only one paper published on numerical simulations (by Beatty and Jackson). However, there are some discrepancies in this paper, which are discussed here. © 2011 Elsevier B.V. Source

Uecker R.,Leibniz Institute for Crystal Growth
Journal of Crystal Growth | Year: 2014

The Czochralski technique is currently the most developed method for growing bulk single crystals. The high technical level and degree of process automation make this technique the method of choice for growing and producing high-quality bulk single crystals, such as silicon, a variety of oxides, fluorides and multielement compounds. The historical development and spread of this method is shown from the time of its invention by Jan Czochralski in 1916 until the early 1970s when key modifications were made. © 2013 Elsevier B.V. Source

Miller W.,Leibniz Institute for Crystal Growth
Physica Status Solidi (B) Basic Research | Year: 2010

Numerical modelling has become an important tool for improving or introducing new processes in bulk crystal growth. For a complete description, scales ranging from atomistic ones up to those of industrial furnaces have to be considered. This article presents methods used on different scales for the Czochralski growth of silicon as well as of Ge1-xSix alloys and for ingot casting of silicon. It shows the recent developments for the different scales and the attempts at coupling the approaches. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Rudolph P.,Leibniz Institute for Crystal Growth
AIP Conference Proceedings | Year: 2010

Selected fundamentals of transport processes and their importance for crystal growth are given. First, principal parameters and equations of heat and mass transfer, like thermal flux, radiation and diffusion are introduced. The heat- and mass- balanced melt-solid and solution-solid interface velocities are derived, respectively. The today's significance of global numeric simulation for analysis of thermo-mechanical stress and related dislocation dynamics within the growing crystal is shown. The relation between diffusion and kinetic regime is discussed. Then, thermal and solutal buoyancy-driven and Marangoni convections are introduced. Their important interplay with the diffusion boundary layer, component and particle incorporation as well as morphological interface stability is demonstrated. Non-steady crystallization phenomena (striations) caused by convective fluctuations are considered. Selected results of global 3D numeric modeling are shown. Finally, advanced methods to control heat and mass transfer by external forces, such as accelerated container rotation, ultrasonic vibration and magnetic fields are discussed. © 2010 American Institute of Physics. Source

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