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Alzenau, Germany

Kiessling F.-M.,Leibniz Institute for Crystal Growth | Bullesfeld F.,Schott AG | Dropka N.,Leibniz Institute for Crystal Growth | Frank-Rotsch C.,Leibniz Institute for Crystal Growth | And 2 more authors.
Journal of Crystal Growth | Year: 2012

Solar-grade boron doped silicon has been directionally solidified in a vertical gradient freeze-type furnace equipped with KRISTMAG ®- heaters to study the influence of travelling magnetic fields (TMFs) on the ingot quality. As-grown silicon ingots of 22×22×13 cm 3 in volume were cut vertically and analysed. Information was obtained on the curvature of the melt-solid interface, the grain size distribution, the content of SiC and Si 3N 4 particles and the electrical activity of defects. TMFs were used to enhance melt stirring and to control the growth interface shape. Primarily inclusion-free ingots were solidified with grains of several centimetres in size. Minority carrier lifetimes of τ=20-30 μs were measured on polished surfaces of cuts from as-grown ingots. The concentrations of carbon, oxygen and nitrogen were determined by FTIR spectroscopy to (3-4)×10 17 atoms/cm 3, (2-3)×10 17 atoms/cm 3 and (0.6-2)×10 15 atoms/cm 3, respectively. Mean etch pit densities were evaluated on vertical cuts as low as (2-3)×10 3 cm -2. © 2012 Elsevier B.V.

Feldhoff J.F.,German Aerospace Center | Schmitz K.,Flagsol GmbH | Eck M.,German Aerospace Center | Schnatbaum-Laumann L.,Solar Millennium AG | And 3 more authors.
Solar Energy | Year: 2012

Parabolic trough power plants are currently the most commercially applied systems for CSP power generation. To improve their cost-effectiveness, one focus of industry and research is the development of processes with other heat transfer fluids than the currently used synthetic oil. One option is the utilization of water/steam in the solar field, the so-called direct steam generation (DSG). Several previous studies promoted the economic potential of DSG technology (Eck et al., 2008b; Price et al., 2002; Zarza, 2002). Analyses' results showed that live steam parameters of up to 500. °C and 120. bars are most promising and could lead to a reduction of the levelized electricity cost (LEC) of about 11% (Feldhoff et al., 2010). However, all of these studies only considered plants without thermal energy storage (TES). Therefore, a system analysis including integrated TES was performed by Flagsol GmbH and DLR together with Solar Millennium AG, Schott CSP GmbH and Senior Berghöfer GmbH, all Germany. Two types of plants are analyzed and compared in detail: a power plant with synthetic oil and a DSG power plant. The design of the synthetic oil plant is very similar to the Spanish Andasol plants (Solar Millennium, 2009) and includes a molten salt two-tank storage system. The DSG plant has main steam parameters of 500. °C and 112. bars and uses phase change material (PCM) for the latent and molten salt for the sensible part of the TES system. To enable comparability, both plants share the same gross electric turbine capacity of 100. MWel, the same TES capacity of 9. h of full load equivalent and the same solar multiple of the collector field of about two. This paper describes and compares both plants' design, performance and investment. Based on these results, the LEC are calculated and the DSG plant's potential is evaluated. One key finding is that with currently proposed DSG storage costs, the LEC of a DSG plant could be higher than those of a synthetic oil plant. When considering a plant without TES on the other hand, the DSG system could reduce the LEC. This underlines the large influence of TES and the still needed effort in the development of a commercial storage system for DSG. © 2011 Elsevier Ltd.

Torres E.,Max Planck Institute Fur Eisenforschung | Torres E.,Technological University of Bolivar | Blumenau A.T.,Max Planck Institute Fur Eisenforschung | Blumenau A.T.,Schott Solar AG | Biedermann P.U.,Max Planck Institute Fur Eisenforschung
ChemPhysChem | Year: 2011

The translational and orientational potential energy surfaces (PESs) of n-alkanethiols with up to four carbon atoms are studied for (√(3) × √(3))R30° self-assembled monolayers (SAMs). The PESs indicate that methanethiol may form SAM structures that are not accessible for long-chain thiols. The tilt of the thiol molecules is determined by a compromise between the preferred binding geometry at the sulfur atom and the steric requirements of the alkane chains. The Au-S bond lengths, offset from the bridge position (brg), and the Au-S-C bond angles result in tilt angles of the S-C bond in the range of 55-60°. As DFT/generalized gradient approximation systematically underestimates chain-chain interactions, the binding energies are corrected by comparison to MP2 interaction energies of alkane dimers in SAM-like configurations. The resulting thiol binding energies increase by approximately 1 kcal mol -1 per CH 2 group, which results in a substantial stabilization of long-chain SAMs due to chain-chain interactions. Furthermore, as the chain length increases, the accessible range of backbone tilt angles is constrained due to steric effects. The combination of these two effects may explain why SAM structures with long-chain thiols exhibit higher order in experiments. For each thiol two favorable SAM structures are found with the sulfur head group at the fcc-brg and hcp-brg positions, respectively. These domains may coexist in thermal equilibrium. In combination with the symmetry of the gold (111) surface, this raises the possibility of up to six different domains on single-crystal terraces. Reconstructions by an adatom or vacancy of ethanethiol SAMs with (√(3) × √(3))R30° lattice are also studied using PES scans. The results indicate that adsorption of thiols next to a vacancy is favorable and may lead to point defects inside SAMs. Showing potential: The translational and orientational potential energy surfaces of n-alkanethiols with up to four carbon atoms are studied for (√(3) × √(3))R30° self-assembled monolayers (SAMs, see picture). The binding energies with the van der Waals interactions corrected using MP2 calculations increase by about 1 kcal mol -1 per CH 2 group. This trend and the increasingly confined accessible range of the tilt angles may contribute to the higher order observed in long-chain thiol SAMs on gold. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

For forming the separating lines, (

Process for producing strip-shaped and/or point-shaped electrically conducting contacts on a semiconductor component like a solar cell, includes the steps of applying a moist material forming the contacts in a desired striplike and/or point-like arrangement on at least one exterior surface of the semiconductor component; drying the moist material by heating the semiconductor component to a temperature T

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