Enhanced performance in the deteriorated area of multicrystalline silicon wafers by internal gettering

The deteriorated area of the multicrystalline silicon (mc‐Si) ingots grown by directional solidification, commonly known as the Red Zone, is usually removed before wafering. This area, characterized by poor minority carrier lifetime, is located on the sides, at the top, and the bottom of the mc‐Si ingots. In this study, the effect of internal gettering by oxygen precipitates and structural defects has been investigated on the bottom zone of a mc‐Si ingot. Nucleation and growth of oxygen precipitates as well as low temperature annealing were studied. Photoluminescence imaging, lifetime mapping, and interstitial iron measurements performed by μ‐PCD reveal a considerable reduction of the bottom Red Zone. An improvement of lifetime from below 1 µs to about 20 µs and a reduction of interstitial iron concentration from 1.32 × 10¹³ at/cm³ to 8.4 × 10¹⁰ at/cm³ are demonstrated in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

Distribution of Nitrogen in the Cationized Potato Starch Granule

The distribution of a cationic reagent in the potato starch granule derivatized by reaction with 1,2-epoxypropyl trimethylammonium chloride was studied by ESCA spectroscopy. It was possible to detect and quantify the contents of nitrogen derived from proteinous material and nitrogen derived from the cationizing reagent on the surfaces of starch preparations. The results show that the differences in nitrogen distribution between cationic starches prepared by different (dry or wet) methods are negligible. According to the result it seems that the cationization takes place more easily in the amorphous material of the inner parts of the granule than in the crystalline amylopectin layer of the surface.     

Imaging of two-dimensional unsaturated moisture flows in uncracked and cracked cement-based materials using electrical capacitance tomography

The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks.     

Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

Carbene‐metal‐amides (CMAs) are a promising family of donor–bridge–acceptor molecular charge‐transfer (CT) emitters for organic light‐emitting diodes. A universal approach is demonstrated to tune the energy of their CT emission. A blueshift of up to 210 meV is achievable in solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally‐activated triplet diffusion, and electrostatic interactions between guest and polar host. This allows the emission of mid‐green CMA archetypes to be tuned to sky blue without chemical modifications. Monte‐Carlo simulations based on a Marcus‐type transfer integral successfully reproduce the concentration‐ and temperature‐dependent triplet diffusion process, revealing a substantial shift in the ensemble density of states in polar hosts. In gold‐bridged CMAs, this shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganization energy, or intersystem crossing rate. These discoveries offer new insight into coupling between the singlet and triplet manifolds in CMA materials, revealing a dominant interaction between states of CT character. The same approach is employed using materials which have been chemically modified to alter the energy of their CT state directly, shifting the emission of sky‐blue chromophores into the practical blue range.     

Intrapersonal and interpersonal risk factors for peer victimization in immigrant youth in Finland.

This study (a) compared native Finns and immigrant children with respect to different forms of peer victimization and (b) tested whether intrapersonal (e.g., depression) and interpersonal (e.g., peer rejection) risk factors help to explain the association between immigrant status and peer victimization. The sample was drawn from the first phase of a large intervention evaluation project, KiVa, in Finland, composed of 4,957 native Finns (51% girls), 146 first-generation immigrants (48% girls), and 310 second-generation immigrants (53% girls) 9 to 12 years of age. The concurrent data included self- and peer reports collected via Internet-based questionnaires. Compared with native youth, first- and second-generation immigrants were more often targets of both peer- and self-reported victimization. Both immigrant groups experienced higher levels of physical, racist, and sexual victimization than natives. Furthermore, second-generation immigrants reported higher levels of property damage, threats, and cybervictimization than native Finns. Significant indirect effects were found between immigrant status and victimization. Interpersonal but not intrapersonal risk factors helped to explain these associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determination of specific heat of phenol formaldehyde resol resins by differential scanning calorimetry

The specific heat, Cp, was determined by DSC on a series of resol-type phenol formaldehyde resins with varying phenol formaldehyde molar ratio. The extrapolated Cp values at 25°C vary between 1.181-1.206 kJ · kg^?1 K^?1 and the dCp/dT ratio was found to be 0.0042kJ · kg^?1K^?2 in the temperature range of 70–125°C.     

On-Line Characterization of Morphology and Water Adsorption on Fumed Silica Nanoparticles

The first wetting layer on solid nanoparticles has direct implications on the roles these particles play in industrial processes and technological applications as well as in the atmosphere. We present a technique for online measurements of the adsorption of the first few water layers onto insoluble aerosol nanoparticles. Atomized fumed silica nanoparticles were dispersed from aqueous suspension and their hygroscopic growth factors (HGF) and number of the adsorbed water layers at subsaturated conditions were measured using a nanometer hygroscopic tandem differential mobility analyzer (HTDMA). Particle morphology was characterized by electron microscopy and particle density was determined by mobility analysis. The HGFs of the size-selected particles at mobility diameters from 10 to 50 nm at 90% relative humidity (RH) varied from 1.05 to 1.24, corresponding to 2–6 layers of adsorbed water. The morphology of the generated fumed silica nanoparticles varied from spheres at 8–10 nm to agglomerates at larger diameters with effective density from 1.7 to 0.8 g/cm³ and fractal dimension of 2.6. The smallest spheres and agglomerates had the highest HGFs. The smallest particles with diameters of 8 and 10 nm adsorbed two to three water layers in subsaturated conditions, which agreed well with the Frenkel, Halsey, and Hill (FHH) isotherm fitting. In comparison to the small spheres or large agglomerates, the compact agglomerate structure containing a few primary particles increased the number of adsorbed water layers by a factor of ～1.5. This was probably caused by the capillary effect on the small cavities between the primary particles in the agglomerate.     

Study of the PM Gas-Phase Filter Artifact Using a Setup for Mixing Diesel-Like Soot and Hydrocarbons

The filter artifact is a significant source of error in gravimetric measurements of particulate matter (PM) exhaust. However, only a few studies on the subject exist. Results from these studies show a large discrepancy mainly because the experiments were performed using real diesel vehicle exhaust with varying exhaust composition. In this study, a setup for mixing diesel-like soot and hydrocarbon vapor was constructed for generating a stable exhaust aerosol with adjustable composition. The particle size distribution of the diesel-fueled soot generator (GMD [geometric mean diameter] adjustable between 27 and 164 nm) was found to represent “real” exhaust particulate emission. This setup was applied for studying the filter artifact on Teflon-coated glass fiber filters using pentadecane as the hydrocarbon vapor. Experiments were performed using particle and hydrocarbon concentrations of 130–700 μg/m³ and 10–12 ppm, respectively. It was found that the particle concentration of the aerosol affects the filter artifact. At lower particle concentrations, more hydrocarbon adsorption was detected. In the absence of particles, the adsorption was highest. Furthermore, filter soot load, corresponding to 0.13%–0.66% of the clean filter mass, was found to affect adsorption. Sooty filters adsorbed less vapor than clean filters. However, increasing the soot load resulted in more adsorption. Moreover, it was found that the backup filter serves as a reasonable estimate of the filter artifact only for low particle concentrations and filter soot loads. These results indicate that the filter soot load is an important parameter influencing the filter artifact, and therefore, it should be considered when performing gravimetric sampling. The setup was proven to be a unique tool for quantitative studies of the filter artifact.

Copyright 2012 American Association for Aerosol Research