Modeling of incorporation of oxygen and carbon impurities into multicrystalline silicon ingot during one-directional growth

We propose a simple numerical model for incorporation of oxygen and carbon impurities into multicrystalline Si during one-directional crystal growth in comparison with experimental results. The model includes parameters that are oxygen and carbon concentrations in the melt in the beginning of the growth, carbon flux form the atmosphere, oxygen fluxes from the crucible and to the atmosphere. Variation of oxygen and carbon concentrations in multicrystalline Si ingots with a diameter of 30 cm and a height of 7.5 cm solidified one-directionally was measured by infra red absorption spectroscopy at room temperature. By fitting the numerical results on the experimental results, the parameters were evaluated. In the modeling we found fruitful suggestions for suppressing and controlling the oxygen and carbon concentrations in multicrystalline Si for solar cells.     

Pattern formation mechanism of a periodically faceted interface during crystallization ofSi

We investigated the pattern formation mechanism of a periodically faceted crystal–melt interface during the crystallization of Si by in situ observation. It was directly proved that spacing between the reentrants of adjacent zigzag facets increases with the unification of adjacent facets when a facet with a higher growth velocity catches up with the one with a lower growth velocity. The spacing becomes stable after unification, and the stable spacing was found to increase with increase in growth velocity. The experimental results was discussed by taking the negative temperature gradient in front of the growth interface into account.     

Growth of multicrystalline Si with controlled grain boundary configuration by the floating zone technique

The floating zone technique was employed to grow multicrystalline Si with controlled grain boundary configuration. Purposely designed bi-crystals were utilized as seed crystals to investigate the effect of the tilt angle from the perfect twin boundary on the growth behavior. When the growth was initiated from a bi-crystal with a Σ3 twin boundary, no particular change took place on the grain boundary configuration during growth. On the other hand, the decrease of the tilt angle during growth was observed when the growth was initiated from a bi-crystal with a tilted boundary from Σ3. This was accompanied by the appearance of new crystal grains. The reduction of the total interface energy would be a possible driving mechanism for this phenomenon.     

Development and application of an eco-hydrodynamic model for radionuclides in a brackish lake: Case study of Lake Obuchi, Japan, bordered by nuclear fuel cycling facilities</p> </p>

Summary In order to evaluate the transport of ³H and ¹³⁷Cs radionuclides in semi-closed brackish Lake Obuchi, Japan, bordered by nuclear fuel cycling facilities, a 3D-lower-trophic eco-hydrodynamic model has been developed and validated. In a short-term prediction, ³H and ¹³⁷Cs activity levels in water should be in an agreement with field measurements. It became clear that the results depended on the mixing of fresh water and seawater in the model. Moreover, a short-term simulation estimated that most ³H and ¹³⁷Cs flowed to the ocean rather than remaining in the lake. Based on calculations over the past 50 years, a peak of ¹³⁷Cs in sediment was in 1963, when the maximum ¹³⁷Cs fallout was observed. The calculation showed a rapid decrease after that peak, however, the field measurement data gradually declined. This suggested that the process by which ¹³⁷Cs accumulated from the watershed to the lake was actually slower in the field than in the model calculations. The model may be successfully applied to a variety of different environmental situations as a generic tool for evaluating the concentration and migration of ³H and ¹³⁷Cs in a brackish lake.</p> </p>