G. Mathiak

Bio: G. Mathiak is an academic researcher from Technical University of Berlin. The author has contributed to research in topics: Convection & Magnetic field. The author has an hindex of 1, co-authored 1 publications receiving 24 citations.

Interdiffusion and Convection in High Magnetic Fields

Abstract: In liquid diffusion measurements, the main problem is the additional mass transport by convection. In the system indium-tin, convection caused by density gradients in horizontal and vertical capillaries was characterised, and the magnetohydrodynamic damping was investigated experimentally. While the magnetic field effect on diffusion experiments in vertical capillaries was relatively minor, the damping effect of the magnetic field could be clearly demonstrated in horizontal capillaries. Comparing these experiments with experiments in microgravity it can be seen that in the investigated system convection was practically completely suppressed by transversal magnetic fields higher than 3T. In electrically conducting crucibles, the sample was mixed by Lorentz forces on account of thermoelectric currents.

New Determinations of Diffusion Coefficients for Various Dopants in Liquid Silicon

Abstract: The objective of this article is to propose new determinations of the diffusion coefficients of various dopants in liquid silicon. The approach of this work is based on an analysis of the effective segregation coefficients obtained by Kodera in Czochralski growth of silicon-based alloys. However, it will be shown that the solidification model used by Kodera presents some serious deficiencies as it does not account for (i) the dependence of the solute boundary layer thickness on the interface velocity and (ii) the effect of density change upon freezing. In addition, the values of the thermophysical parameters used by Kodera can be questioned in view of recently published data. The approach proposed in the present work can be used to provide a much sounder physical basis for the analysis of the data, but it should be stated that the uncertainty on the partition coefficients is such that a measurement technique based on solidification experiments cannot be expected to be very accurate. In this respect, the scatter of the data, hardly avoidable in Czochralski growth experiments, is also discussed. To put things on a quantitative basis, an error analysis is carried out to quantify the error bar attainable by such a measurement technique.

Ferromagnetic Cu-doped AlN nanorods

Abstract: Copper-doped AlN (AlN:Cu) nanorods were grown on catalyst-free Si substrates by chemical vapour deposition. The AlN:Cu nanorods exhibited the wurtzite structure with a growth direction along the c-axis. Ferromagnetic ordering of the AlN:Cu nanorods was observed at room temperature by an alternating gradient magnetometer. The spontaneous magnetization and the coercivity of the AlN:Cu nanorods are about 0.38?emu?cm?3 and 100?Oe, respectively. The results reveal that Cu is a potential nonmagnetic dopant for AlN.

Reference Microgravity Measurements of Liquid Phase Solute Diffusivities in Tin- and Aluminum-Based Alloys

Abstract: This paper presents results of the measurement of solute diffusivities in the Al–Ni and Sn–Bi–In systems. These experiments were conducted in microgravity and may therefore be assigned as reference values. A dedicated facility, which can be used for processing of four identical samples in parallel, was developed for the experiments under consideration. In addition, a rather thorough analysis of possible error sources in shear cell type experiments is carried out. Comparison with work carried out using magnetic fields to control convective flows, and with previous indirect measurements results, is also provided. A coherent picture emerges from the overall agreement between various measurements, and the data from the current work can thus be considered as reference benchmarks for future experiments. Another conclusion of the present study is that the shear cell technique is well suited for the measurement of solute diffusivities.