Comparison of thin epitaxial film silicon photovoltaics fabricated on monocrystalline and polycrystalline seed layers on glass

We fabricate thin epitaxial crystal silicon solar cells on display glass and fused silica substrates overcoated with a silicon seed layer. To confirm the quality of hot‐wire chemical vapor deposition epitaxy, we grow a 2‐µm‐thick absorber on a (100) monocrystalline Si layer transfer seed on display glass and achieve 6.5% efficiency with an open circuit voltage (V_OC) of 586 mV without light‐trapping features. This device enables the evaluation of seed layers on display glass. Using polycrystalline seeds formed from amorphous silicon by laser‐induced mixed phase solidification (MPS) and electron beam crystallization, we demonstrate 2.9%, 476 mV (MPS) and 4.1%, 551 mV (electron beam crystallization) solar cells. Grain boundaries likely limit the solar cell grown on the MPS seed layer, and we establish an upper bound for the grain boundary recombination velocity (S_GB) of 1.6x10⁴ cm/s. Copyright © 2014 John Wiley & Sons, Ltd.     

Flexural behaviour and strength of cold-formed steel L-headers

Cold-formed steel headers are structural components used over wall openings in cold-formed steel residential and light commercial construction. Recently, there has been an increased interest in cold-formed L-headers among homebuilders primarily due to their ease of installation and low material cost. The findings from an extensive laboratory testing program, of full-scale single and double cold-formed steel L-headers are presented in this paper. The objective of the research was to investigate the flexural behaviour and strength of L-headers under both gravity and uplift loads. Based on the results improved ultimate strength design expressions and new deflection expressions for a wide range of L-header assemblies have been proposed.     

Influence of the quinoline-insoluble matter in pitch on carbonization behaviour and structure of pitch coke

The influence of the quinoline-insoluble matter in pitch on the carbonization behaviour and especially on the pitch-coke properties is of basic interest both for the production of pitch coke and the manufacture of carbon electrodes. A more isotropic coke is produced by increasing the amount of quinoline-insolubles. The coefficient of thermal expansion (CTE) by volume measured directly at the coke particle is strongly influenced by the type of quinoline-insoluble. A larger amount of the primary type of quinoline-insolubles causes a large increase of the CTE (volume) from 3.2 to 17.4 × 10^?6K^?1, whereas the secondary type influences the CTE only slightly. This strong influence of quinoline-insolubles on the structure of pitch-binder coke results in a remarkable increase of mechanical strength of carbon artefacts.     

Book Reviews

By Dr. Alexander J. Patton, P.E.. and Dr. John C. Russell, M.D. Available from Garland Law Publishing, 136 Madison Avenue, New York, NY 10016. The cost is $95.00.     

Calculating evacuation times for tall buildings

This paper includes a summary of the history of investigations into calculating evacuation times. Included are the basic concepts along with selected calculation methods. Limitations of such efforts are reviewed to illustrate the limited applicability of some of the methods for actual conditions.     

In situ gas-phase hydrosilylation of plasma-synthesized silicon nanocrystals

Surface passivation of semiconductor nanocrystals (NCs) is critical in enabling their utilization in novel optoelectronic devices, solar cells, and biological and chemical sensors. Compared to the extensively used liquid-phase NC synthesis and passivation techniques, gas-phase routes provide the unique opportunity for in situ passivation of semiconductor NCs. Herein, we present a method for in situ gas-phase organic functionalization of plasma-synthesized, H-terminated silicon (Si) NCs. Using real-time in situ attenuated total reflection Fourier transform IR spectroscopy, we have studied the surface reactions during hydrosilylation of Si NCs at 160 °C. First, we show that, during gas-phase hydrosilylation of Si NCs using styrene (1-alkene) and acetylene (alkyne), the reaction pathways of the alkenes and alkynes chemisorbing onto surface SiH(x) (x = 1-3) species are different. Second, utilizing this difference in reactivity, we demonstrate a novel pathway to enhance the surface ligand passivation of Si NCs via in situ gas-phase hydrosilylation using the combination of a short-chain alkyne (acetylene) and a long-chain 1-alkene (styrene). The quality of surface passivation is further validated through IR and photoluminescence measurements of Si NCs exposed to air.     

Visual–motor integration functioning in children with Tourette syndrome.

A neuropsychological model of visual–motor integration skill was proposed and tested in 50 children with Tourette syndrome (TS) and 23 unaffected control children matched for age. Children with TS performed significantly worse than control children on the Beery Visual–Motor Integration (VMI) Test. Consistent with the proposed model, visuoperceptual and fine-motor coordination subprocesses were significant predictors of VMI scores. However, the subprocesses did not fully account for the diagnostic group difference on the VMI. These results suggest that the integration of visual inputs and organized motor output is a specific area of neuropsychological weakness among individuals with TS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)