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.


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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.


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.


Schmidbauer M.,Leibniz Institute for Crystal Growth | Kwasniewski A.,Leibniz Institute for Crystal Growth | Schwarzkopf J.,Leibniz Institute for Crystal Growth
Acta Crystallographica Section B: Structural Science | Year: 2012

The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature. An accuracy of the order of 10 -5 has been achieved by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method. The results on cubic SrTiO 3 [a = 3.905268 (98) Å], orthorhombic DyScO 3 [a = 5.442417 (54), b = 5.719357 (52) and c = 7.904326 (98) Å], and orthorhombic NdGaO 3 [a = 5.428410 (54), b = 5.498407 (55) and c = 7.708878 (95) Å] are discussed in view of possible systematic errors as well as non-stoichiometry in the crystals. © 2012 International Union of Crystallography Printed in Singapore - all rights reserved.


Cantu G.,Leibniz Institute for Crystal Growth | Popescu A.,West University of Timișoara | Miller W.,Leibniz Institute for Crystal Growth
Acta Materialia | Year: 2012

In this paper we report on 2-D phase-field simulations in order to study the influence of the growth kinetics and the surface energy on the growth behaviour of grains during solidification of silicon. We investigated in detail the growth of two grains. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Dropka N.,Leibniz Institute for Crystal Growth | Frank-Rotsch C.,Leibniz Institute for Crystal Growth
Journal of Crystal Growth | Year: 2013

Accelerated VGF-growth of 4 in. GaAs ingots by downwards traveling magnetic fields (TMFs) was investigated numerically. The focus was led on the feasibility of control of s/l interface shape by Lorentz forces in the range of crystal growth rates from 3 to 9 mm/h. Particularly, the aim of this study was to derive a method for a prediction of electro-magnetic parameters of TMF such as frequency, phase shift and AC amplitude that provide maximal improvement of interface deflection towards convex morphology during the fast growth. A typical VGF furnace equipped with a KRISTMAG® internal heater-magnet module was used for the simultaneous generation of heat and TMF. The revealed deflections were correlated with dimensionless numbers: Grashof Gr, Stephan Ste and Forcing number F. With an increase of F while holding Gr and Ste numbers constant, transition through the point of maximal positive deflection was marked by a lift of the stream function vortex from the region of triple point upwards. © 2013 Elsevier B.V. All rights reserved.


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.


Bottcher K.,Leibniz Institute for Crystal Growth
International Journal of Heat and Mass Transfer | Year: 2010

We propose a multi-component species transport benchmark which combines diffusion and fluid flow. By using identical species input volume rates per minute into a test geometry and in absence of chemical reactions, the species mass fractions are known analytically exact after complete mixing, which permits to evaluate the absolute numerical error of the diffusion computation. It is demonstrated that the absolute error of the mass fractions is reduced quadratically with decreasing the element size of the grid. The finite-element-method is applied for solving the system of equations. © 2009 Elsevier Ltd. All rights reserved.


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.


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.


Klimm D.,Leibniz Institute for Crystal Growth
Journal of Crystal Growth | Year: 2010

DTA measurements with mixtures of aluminum oxide and lutetium oxide around the 1 : 1 perovskite composition were performed up to 1970 {ring operator} C. A peak with onset 1901 {ring operator} C was due to the melting of the eutectic Lu4 Al2 O9 (monoclinic phase) and LuAlO3 (perovskite). Neither peritectic melting of the perovskite nor its decomposition in the solid phase could be resolved experimentally. The maximum of the eutectic peak size is near x = 0.44, on the Lu-rich side of the perovskite, which is consistent with the conclusion that LuAlO3 melts peritectically at ca. 1907 {ring operator} C as proposed by Wu, Pelton, J. Alloys Compd. 179 (1992) 259. Thermodynamic equilibrium calculation reveals that under strongly reducing conditions (oxygen partial pressure < 10- 13 bar) aluminum(III) oxide can be reduced to suboxides or even Al metal. It is shown that under such conditions a new phase field with liquid Al can appear. © 2009 Elsevier B.V. All rights reserved.

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