19%‐efficient and 43 µm‐thick crystalline Si solar cell from layer transfer using porous silicon

We present a both‐sides‐contacted thin‐film crystalline silicon (c‐Si) solar cell with a confirmed AM1.5 efficiency of 19.1% using the porous silicon layer transfer process. The aperture area of the cell is 3.98 cm². This is the highest efficiency ever reported for transferred Si cells. The efficiency improvement over the prior state of the art (16.9%) is achieved by implementing recent developments for Si wafer cells such as surface passivation with aluminum oxide and laser ablation for contacting. The cell has a short‐circuit current density of 37.8 mA cm⁻², an open‐circuit voltage of 650 mV, and a fill factor of 77.6%. Copyright © 2011 John Wiley & Sons, Ltd.     

Modeling solar cells with the dopant‐diffused layers treated as conductive boundaries

Modeling of transport and recombination of charge carriers in solar cells is useful for understanding and improving the device performance. We implement the fully coupled transport equations for electrons and holes into the finite‐element partial differential equation solver COMSOL . The dopant‐diffused surface regions such as junctions, floating junctions, or back surface field layers are treated as conductive boundaries of the volume in which the semiconductor equations are solved. This so‐called conductive boundary (CoBo) model characterizes diffused layers by their sheet resistances and diode saturation current densities. Both are directly experimentally accessible. The CoBo model exhibits excellent numerical stability and enables two‐dimensional simulations on a laptop. We find agreement when testing the two‐dimensional COMSOL implementation of the CoBo model for one‐dimensional devices against simulations using the code PC1D. We apply the CoBo model to elucidate how the sheet resistance of diffused vias impacts the power conversion efficiency of emitter wrap through solar cells. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrically Programmable Bistable Capacitor for High‐Frequency Applications Based on Charge Storage at the (Ba,Sr)TiO3/Al2O3 Interface

Hysteresis is induced in paraelectric (Ba,Sr)TiO₃ (BST) thin‐film capacitors by inserting an Al₂O₃ barrier layer of a few nanometers in thickness between the BST layer and the electrode. The observed hysteresis is explained by ambipolar charge carrier injection through the Al₂O₃ layer and charge storage at the BST/Al₂O₃ interface. The magnitude of the hysteresis can be directly adjusted by manipulating the thickness ratio between BST and Al₂O₃. Taking into account the low loss of (Ba,Sr)TiO₃ capacitors, the observed switching and retention characteristics are suitable for application as non‐volatile programmable high‐frequency devices, e.g., in radio‐frequency identification.     

Nano- and micrometre additions of SiO2, ZrO2 and TiO2 in fine grained alumina refractory ceramics for improved thermal shock performance

The present contribution investigates the influence of micro-metre- as well as nano-metre-additions of zirconia (ZrO₂), titania (TiO₂), silica (SiO₂) and magnesia (MgO) into alumina-rich fine grained ceramic materials for refractory applications. Slip casted samples in the system alumina–zirconia–titania (AZT), alumina–zirconia–titania–silica (AZTS) and alumina–zirconia–titania–magnesia (AZTM) were sintered and the physical as well as mechanical properties were investigated as fired and after thermal shock treatments. The generation of a micro-crack network after sintering due to the formation of phases with different thermal expansion coefficients and the formation and decomposition of aluminium titanate (Al₂TiO₅) before and after thermal shock exposure leads to higher strengths after thermal shock attack.     

RoHS regulated substances in mixed plastics from waste electrical and electronic equipment

The disposal and recovery of plastics from waste electrical and electronic equipment (WEEE) are of considerable importance, both from an environmental and an economic perspective. This paper presents the results of a study investigating current concentrations of hazardous substances in mixed plastics from WEEE and their implications for an environmentally sound recovery. The study included 53 sampling campaigns for mixed plastics from WEEE. The samples were analyzed with regard to heavy metals (cadmium, chromium, mercury, and lead) and flame retardants (PentaBDE, OctaBDE, DecaBDE, DecaBB) regulated in the RoHS Directive. Besides these substances, other brominated flame retardants known to occur in electronics (HBCD, TBBPA) as well as the total bromine and phosphorus contents were considered. Results show that no mixed plastics fraction from WEEE is completely free from substances regulated in the RoHS Directive. The lowest number and average concentrations were found in flat screen monitors. The highest concentrations were found in mixed plastics from CRT monitors and TVs. Mixed plastics fractions with high average concentrations of heavy metals originate from the treatment of small household appliances (cadmium), ICT equipment (lead), and consumer equipment (lead). Mixed plastics fractions with high average concentrations of brominated flame retardants mainly originate from the treatment of small household appliances for high temperature applications (DecaBDE), CRT monitors (OctaBDE and DecaBDE) and consumer equipment (DecaBDE), in particular CRT TVs (DecaBDE). To avoid a dissipation of hazardous substances into plastics and the environment, it is recommended that mixed plastics from WEEE are subject to a strict quality management.     

MudPIT analysis of alkaline tolerance by Listeria monocytogenes strains recovered as persistent food factory contaminants

Alkaline solutions are used to clean food production environments but the role of alkaline resistance in persistent food factory contamination by Listeria monocytogenes is unknown. We used shotgun proteomics to characterise alkaline adapted L. monocytogenes recovered as persistent and transient food factory contaminants. Three unrelated strains were studied including two persistent and a transient food factory contaminant determined using multilocus sequence typing (MLST). The strains were adapted to growth at pH 8.5 and harvested in exponential phase. Protein extracts were analysed using multidimensional protein identification technology (MudPIT) and protein abundance compared by spectra counting. The strains elicited core responses to alkaline growth including modulation of intracellular pH, stabilisation of cellular processes and reduced cell-division, independent to lineage, MLST or whether the strains were transient or persistent contaminants. Alkaline adaptation by all strains corresponded to that expected in stringent-response induced cells, with protein expression supporting metabolic shifts concordant with elevated alarmone production and indicating that the alkaline-stringent response results from energy rather than nutrient limitation. We believe this is the first report describing induction of a stringent response in different L. monocytogenes strains by alkaline pH under non-limiting growth conditions. The work emphasises the need for early intervention to avoid persistent food factory contamination by L. monocytogenes.     

Graphene Nanocomposites Prepared From Blends of Polymer Latex with Chemically Reduced Graphite Oxide Dispersions

Graphene nanocomposites are prepared by chemical reduction of graphite oxide (GO) dispersion with vitamin C in the presence of SAN latex followed by melt compounding. In this process, GO is well dispersed in an aqueous SAN emulsion before reduction. During reduction the SAN latex is adsorbed on the graphene sheets of the chemically reduced GO (CRGO). After melt compounding of such hybrid particles with SAN, the nanocomposites show uniform dispersion of CRGO in SAN resulting in improved stiffness with respect to SAN/graphite. The reduction of GO in the presence of polymer latex represents a versatile route to graphene masterbatches and does not require either drying of GO or thermal GO expansion at high temperatures.

     

Novel acrylic nanocomposites containing in-situ formed calcium phosphate/layered silicate hybrid nanoparticles for photochemical rapid prototyping, rapid tooling and rapid manufacturing processes

Novel acrylic nanocomposites containing calcium phosphate/layered silicate hybrid nanoparticles have been developed for use in photochemical Rapid Prototyping processes like Structural Light Modulation (SLM) and Stereolithography (SL). When tertiary alkyl amines, protonated with phosphoric acid, were added to an acrylic suspension of calcium bentonite, the cation exchange of Ca²⁺ rendered bentonite organophilic, caused swelling, intercalation and dispersion of silicate nanoplatelets in the monomer. The simultaneous precipitation of calcium phosphate onto the silicate nanoplatelets accounted for the in-situ formation of hybrid nanoparticles. The uniform dispersions of such hybrid nanoparticles afforded a high degree of shear thinning, reflecting the presence of anisotropic filler particles, and increased photosensitivity in SLM with respect to the unfilled resin. Young’s modulus of green and postcured parts increased by 30% at a filler content of 15 wt.% with respect to that of the unfilled benchmark material. This enhanced stiffness was paralleled by 30% increased fracture toughness. As evidenced by fracture surface analysis using Environmental Electron Microscopy (ESEM) and optical microscopy, the improved energy dissipation at the crack tip correlated with roughness of the fracture surfaces, increasing with increasing filler content. Moreover, the examination of the volumetric polymerization shrinkage and the fabrication of H-shaped diagnostic specimens revealed that the nanocomposites were processed with high accuracy, increasing with increasing filler content. Nanocomposite morphologies, examined by means of Transmission Electron Microscopy (TEM), demonstrated that the large primary bentonite particles with average diameters >10 μm fragmented into much smaller particles with average diameters in the range of 1 μm. According to TEM and Wide Angle X-Ray Scattering (WAXS), such in-situ formed nanoparticles were composed of both stacks of organoclay nanoplatelets and also isolated nanoplatelets typical for fully exfoliated organoclays.     

Simulation and analysis of group-hole nozzle sprays using a gas jet superposition model

A gas jet superposition model has been recently developed for computing group-hole nozzle sprays in computational fluid dynamics (CFD) simulations. The objectives of this study are: (1) to perform a systematic validation of the comprehensive spray model for group-hole nozzles using a broad range of experimental data; (2) to analyze the dynamics and physical insight of group-hole nozzle sprays based on the simulation results; and (3) to further clarify the impact of included-angle on spray/mixture properties of group-hole nozzle sprays. An updated version of the KIVA-3V Release 2 code, which employs the Lagrangian-Drop Eulerian-Fluid (LDEF) methodology for numerical calculation of two-phase flows, was used in the simulations. Diverging group-hole nozzles with various included-angles were considered. The test conditions included non-evaporating and evaporating ambient conditions, free sprays and sprays impinging on a flat wall. Detailed comparisons were made between the experiments and computations in terms of spray/mixture characteristics. The results show that numerical parameter dependencies are significantly reduced with the new models, and good levels of agreement are obtained in terms of spray structure, liquid/vapor penetration, overall SMD and cumulative vaporized fuel mass. Both experimental measurements and simulations reveal the importance of included-angle in group-hole nozzle sprays. In particular, some important features of group-hole nozzle spray are captured in the computations by the present models: compared to the equivalent single-hole nozzle, smaller local droplet size can be achieved in the near nozzle field, indicating an enhanced fuel primary atomization; the ambient gas entrainment rate is increased during the injection period, implying the better mixing; the spray axis deflection is identified in the case of group-hole nozzles with smaller angles, which is caused by a negative relative pressure region that exists between the sprays; in addition, the asymmetric structure of wall-impinging group-hole nozzle spray is well predicted by the present models through applying the gas jet superposition model in the entire computational domain.     

Superconductivity in 4-Angstrom carbon nanotubes--a short review

We give an up-to-date review of the superconducting phenomena in 4-Angstrom carbon nanotubes embedded in aligned linear pores of the AlPO(4)-5 (AFI) zeolite, first discovered in 2001 as a fluctuation Meissner effect. With the introduction of a new approach to sample synthesis around 2007, new data confirming the superconductivity have been obtained. These comprise electrical, specific heat, and magnetic measurements which together yield a consistent yet complex physical picture of the superconducting state, largely owing to the one-dimensional (1D) nature of the 4-Angstrom carbon nanotubes. For the electrical transport characteristics, two types of superconducting resistive behaviors were reproducibly observed in different samples. The first type is the quasi 1D fluctuation superconductivity that exhibits a smooth resistance drop with decreasing temperature, initiating at 15 K. At low temperatures the differential resistance also shows a smooth increase with increasing bias current (voltage). Both are unaffected by an applied magnetic field up to 11 Tesla. These manifestations are shown to be consistent with those of a quasi 1D superconductor with thermally activated phase slips as predicted by the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory. The second type is the quasi 1D to 3D superconducting crossover transition, which was observed to initiate at 15 K with a slow resistance decrease switching to a sharp order of magnitude drop at ～7.5 K. The latter exhibits anisotropic magnetic field dependence and is attributed to a Berezinskii-Kosterlitz-Thouless (BKT)-like transition that establishes quasi-long-range order in the plane transverse to the c-axis of the aligned nanotubes, thereby mediating a 1D to 3D crossover. The electrical data are complemented by magnetic and thermal specific heat bulk measurements. By using both the SQUID VSM and the magnetic torque technique, the onset of diamagnetism was observed to occur at ～15 K, with a rapid increase of the diamagnetic moment below ～7 K. The zero-field-cooled and field-cooled branches deviated from each other below 7 K, indicating the establishment of a 3D Meissner state with macroscopic phase coherence. The superconductivity is further supported by the specific heat measurements, which show an anomaly with onset at 15 K and a peak at 11-12 K. In the 3D superconducting state, the nanotube arrays constitute a type-II anisotropic superconductor with H(c1)≈ 60 to 150 Oe, coherence length ξ≈ 5 to 15 nm, London penetration length λ≈ 1.5 μm, and Ginzburg-Landau κ≈ 100. We give a physical interpretation to the observed phenomena and note the challenges and prospects ahead.