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Author: Menzel, Robert ×

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    Lumped Parameter Model for Silicon Crystal Growth from Granulate Crucible
    (Weinheim : Wiley-VCH, 2020) Lorenz-Meyer, M. Nicolai L.; Menzel, Robert; Dadzis, Kaspars; Nikiforova, Angelina; Riemann, Helge
    In the present paper, a lumped parameter model for the novel Silicon Granulate Crucible (SiGC) method is proposed, which is the basis for a future model-based control system for the process. The model is analytically deduced based on the hydromechanical, geometrical, and thermal conditions of the process. Experiments are conducted to identify unknown model parameters and to validate the model. The physical consistency of the model is verified using simulation studies and a prediction error of below 2% is reached. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Numerical Simulation of Species Segregation and 2D Distribution in the Floating Zone Silicon Crystals
    (Basel : MDPI, 2022) Surovovs, Kirils; Surovovs, Maksims; Sabanskis, Andrejs; Virbulis, Jānis; Dadzis, Kaspars; Menzel, Robert; Abrosimov, Nikolay
    The distribution of dopants and impurities in silicon grown with the floating zone method determines the electrical resistivity and other important properties of the crystals. A crucial process that defines the transport of these species is the segregation at the crystallization interface. To investigate the influence of the melt flow on the effective segregation coefficient as well as on the global species transport and the resulting distribution in the grown crystal, we developed a new coupled numerical model. Our simulation results include the shape of phase boundaries, melt flow velocity and temperature, species distribution in the melt and, finally, the radial and axial distributions in the grown crystal. We concluded that the effective segregation coefficient is not constant during the growth process but rather increases for larger melt diameters due to less intensive melt mixing.
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    Origins of high catalyst loading in copper(i)-catalysed Ullmann-Goldberg C-N coupling reactions
    (Cambridge : RSC, 2017) Sherborne, Grant J.; Adomeit, Sven; Menzel, Robert; Rabeah, Jabor; Brückner, Angelika; Fielding, Mark R.; Willans, Charlotte E.; Nguyen, Bao N.
    A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity. These results have significant implications on future ligand development for the Ullmann-Goldberg reaction and on the solid form of the inorganic base as an important variable with mechanistic ramifications in many catalytic reactions.