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High Current Density (high + current_density)
Selected AbstractsStable, Glassy, and Versatile Binaphthalene Derivatives Capable of Efficient Hole Transport, Hosting, and Deep-Blue Light EmissionADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Bin Wei Abstract Organic light-emitting diodes (OLEDs) have great potential applications in display and solid-state lighting. Stability, cost, and blue emission are key issues governing the future of OLEDs. The synthesis and photoelectronics of a series of three kinds of binaphthyl (BN) derivatives are reported. BN1,3 are "melting-point-less" and highly stable materials, forming very good, amorphous, glass-like films. They decompose at temperatures as high as 485,545,°C. At a constant current density of 25,mA,cm,2, an ITO/BN3/Al single-layer device has a much-longer lifetime (>80,h) than that of an ITO/NPB/Al single-layer device (8,h). Also, the lifetime of a multilayer device based on BN1 is longer than a similar device based on NPB. BNs are efficient and versatile OLED materials: they can be used as a hole-transport layer (HTL), a host, and a deep-blue-light-emitting material. This versatility may cut the cost of large-scale material manufacture. More importantly, the deep-blue electroluminescence (emission peak at 444 nm with CIE coordinates (0.16, 0.11), 3.23 cd A,1 at 0.21,mA cm,2, and 25200,cd,m,2 at 9,V) remains very stable at very high current densities up to 1000,mA,cm,2. [source] A kinetic perspective on extracellular electron transfer by anode-respiring bacteriaFEMS MICROBIOLOGY REVIEWS, Issue 1 2010César I. Torres Abstract In microbial fuel cells and electrolysis cells (MXCs), anode-respiring bacteria (ARB) oxidize organic substrates to produce electrical current. In order to develop an electrical current, ARB must transfer electrons to a solid anode through extracellular electron transfer (EET). ARB use various EET mechanisms to transfer electrons to the anode, including direct contact through outer-membrane proteins, diffusion of soluble electron shuttles, and electron transport through solid components of the extracellular biofilm matrix. In this review, we perform a novel kinetic analysis of each EET mechanism by analyzing the results available in the literature. Our goal is to evaluate how well each EET mechanism can produce a high current density (>10 A m,2) without a large anode potential loss (less than a few hundred millivolts), which are feasibility goals of MXCs. Direct contact of ARB to the anode cannot achieve high current densities due to the limited number of cells that can come in direct contact with the anode. Slow diffusive flux of electron shuttles at commonly observed concentrations limits current generation and results in high potential losses, as has been observed experimentally. Only electron transport through a solid conductive matrix can explain observations of high current densities and low anode potential losses. Thus, a study of the biological components that create a solid conductive matrix is of critical importance for understanding the function of ARB. [source] Modelling CO poisoning and O2 bleeding in a PEM fuel cell anodeINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2003J.J. Baschuk Abstract Fuel gas containing carbon monoxide severely degrades the performance of a polymer electrolyte membrane (PEM) fuel cell. However, CO poisoning can be mitigated by introducing oxygen into the fuel (oxygen bleeding). A mathematical PEM fuel cell model is developed that simulates both CO poisoning and oxygen bleeding, and obtains excellent agreement with published, experimental data. Modelling efforts indicate that CO adsorption and desorption follow a Temkin model. Increasing operating pressure or temperature mitigates CO poisoning, while use of reformate fuel increases the severity of the poisoning effect. Although oxygen bleeding mitigates CO poisoning, an unrecoverable performance loss exists at high current densities due to competition for reaction sites between hydrogen adsorption and the heterogeneous catalysis of CO. Copyright © 2003 John Wiley & Sons, Ltd. [source] Current filamentation and negative differential resistance in C60 diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Philipp Stadler Abstract Current-Voltage (IV) measurements of C60 thin film diodes in the temperature range of 300,4.2 K are presented. The fullerene diodes exhibit space charge limited currents as well as reversible voltage instabilities (S-shape IV characteristics) at temperatures below 200 K and at high current densities. The instabilities are similar to certain charge transport effects in amorphous inorganic semiconductors, which are explained by injection of holes and electrons at the same time and charge trapping near the electrodes. Beyond certain current densities conductive filaments in the fullerene bulk phase are formed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sodium channel distribution on uninnervated and innervated embryonic skeletal myotubesDEVELOPMENTAL NEUROBIOLOGY, Issue 1 2001Blake D. Anson Abstract Acetylcholine receptor (AChR) and sodium (Na+) channel distributions within the membrane of mature vertebrate skeletal muscle fibers maximize the probability of successful neuromuscular transmission and subsequent action potential propagation. AChRs have been studied intensively as a model for understanding the development and regulation of ion channel distribution within the postsynaptic membrane. Na+ channel distributions have received less attention, although there is evidence that the temporal accumulation of Na+ channels at developing neuromuscular junctions (NMJs) may differ between species. Even less is known about the development of extrajunctional Na+ channel distributions. To further our understanding of Na+ channel distributions within junctional and extrajunctional membranes, we used a novel voltage-clamp method and fluorescent probes to map Na+ channels on embryonic chick muscle fibers as they developed in vitro and in vivo. Na+ current densities on uninnervated myotubes were approximately one-tenth the density found within extrajunctional regions of mature fibers, and showed several-fold variations that could not be explained by a random scattering of single channels. Regions of high current density were not correlated with cellular landmarks such as AChR clusters or myonuclei. Under coculture conditions, AChRs rapidly concentrated at developing synapses, while Na+ channels did not show a significant increase over the 7 day coculture period. In vivo investigations supported a significant temporal separation between Na+ channel and AChR aggregation at the developing NMJ. These data suggest that extrajunctional Na+ channels cluster together in a neuronally independent manner and concentrate at the developing avian NMJ much later than AChRs. © 2001 John Wiley & Sons, Inc. J Neurobiol 48: 42,57, 2001 [source] A kinetic perspective on extracellular electron transfer by anode-respiring bacteriaFEMS MICROBIOLOGY REVIEWS, Issue 1 2010César I. Torres Abstract In microbial fuel cells and electrolysis cells (MXCs), anode-respiring bacteria (ARB) oxidize organic substrates to produce electrical current. In order to develop an electrical current, ARB must transfer electrons to a solid anode through extracellular electron transfer (EET). ARB use various EET mechanisms to transfer electrons to the anode, including direct contact through outer-membrane proteins, diffusion of soluble electron shuttles, and electron transport through solid components of the extracellular biofilm matrix. In this review, we perform a novel kinetic analysis of each EET mechanism by analyzing the results available in the literature. Our goal is to evaluate how well each EET mechanism can produce a high current density (>10 A m,2) without a large anode potential loss (less than a few hundred millivolts), which are feasibility goals of MXCs. Direct contact of ARB to the anode cannot achieve high current densities due to the limited number of cells that can come in direct contact with the anode. Slow diffusive flux of electron shuttles at commonly observed concentrations limits current generation and results in high potential losses, as has been observed experimentally. Only electron transport through a solid conductive matrix can explain observations of high current densities and low anode potential losses. Thus, a study of the biological components that create a solid conductive matrix is of critical importance for understanding the function of ARB. [source] Analysis of Direct Methanol Fuel Cell (DMFC)-Performance via FTIR Spectroscopy of Cathode ExhaustFUEL CELLS, Issue 4 2003F. Meier Abstract Water and methanol flux through NafionÔ and polyaryl-blend membranes prepared at ICVT were studied under DMFC operation. The water, methanol, and CO2 content in the cathode exhaust were measured by FTIR spectroscopy. Both the water and methanol flux turned out to be strongly dependent on the operating temperature and thus on membrane swelling. Apart from this, water flux through the membrane is primarily affected by the gas volume flux on the cathode side. A coupling between water flux and methanol flux was observed, which leads to the conclusion that methanol is transported both by diffusion and by convection caused by the superimposed water flux. Polyaryl-blend membranes showed a reduced diffusive methanol transport when compared to NafionÔ due to their different internal microstructure. The impact of methanol cross-over on cathode losses at high current density needs further clarification with respect to the prevailing mechanism of methanol oxidation at the cathode. [source] Fabrication of Large-Scale Single-Crystalline PrB6 Nanorods and Their Temperature-Dependent Electron Field EmissionADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Qin Yuan Zhang Abstract A simple catalysis-free approach that utilises a gas,solid reaction for the synthesis of large-scale single-crystalline PrB6 nanorods using Pr and BCl3 as starting materials is demonstrated. The nanorods exhibit a low turn-on electric field (2.80,V µ-b;m,1 at 10,µ-b;A cm,2), a low threshold electric field (6.99,V µ-b;m,1 at 1,mA cm,2), and a high current density (1.2,mA cm,2 at 7.35,V µ-b;m,1) at room temperature (RT). The turn-on and threshold electric field are found to decrease clearly from 2.80 to 0.95 and 6.99 to 3.55,V µ-b;m,1, respectively, while the emission current density increases significantly from 1.2 to 13.8,mA cm,2 (at 7.35,V µ-b;m,1) with an increase in the ambient temperature from RT to 623,K. The field enhancement factor, emission current density, and the dependence of the effective work function with temperature are investigated. The possible mechanism of the temperature-dependent emission from PrB6 nanorods is discussed. [source] High-Current-Density CuO x/InZnOx Thin-Film Diodes for Cross-Point Memory Applications,ADVANCED MATERIALS, Issue 16 2008Bo Soo Kang Room-temperature-deposited CuOxInZnOx thin-film heterojunction diodes show a high current density of 3.5,×,104,A cm,2 and a high on/off current ratio of 106 (see figure). The oxide diode is a promising switch element for three-dimensional stackable memory devices, where high-temperature-prepared silicon diodes are difficult to apply. [source] Diamond plates on dome-like particles: preparation, characterization and field emission propertiesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2010Rajanish N. Tiwari Thin diamond microplates have been grown on dome-like/hemispherical carbon particles on titanium carbide by a microwave plasma chemical vapour deposition (MPCVD) method using a gas mixture of methane and hydrogen. The diamond microplates have a thickness of about 200,nm. A thin (300,nm) film of titanium carbide was formed during carburization of sputtered titanium on an Si(100) substrate in MPCVD. The hemispherical carbon particles were covered with diamond microplates. The diamond microplates are isolated electron-emitting spherules and exhibit a low threshold (50,V,µm,1) and high current density (0.92,mA,cm,2) in their field emission properties. A possible mechanism for the formation of the diamond microplates and hemispherical carbon particles is presented. [source] Assembly, structure, and performance of an ultra-thin film organic field-effect transistor (OFET) based on substituted oligothiophenesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008K. Haubner Abstract We report on the improved assembly and characterization of a small molecule organic field-effect transistor (OFET). Novel ,,,-dicyano substituted ,,,,-dibutylquaterthiophene molecules (DCNDBQT) were synthesized and characterized by UV,Vis spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and cyclic voltammetry. The ultra-thin organic film formation on TiO2 templates was effectively promoted through the specifically designed bifunctional self assembly molecules (SAM) 5-cyano-2-(butyl-4-phosphonic acid)-3-butylthiophene (CNBTPA). Excellent structural properties were found for up to 9 DCNDBQT molecule thick films prepared through UHV vacuum sublimation as investigated with UHV non-contact atomic force microscopy (nc-AFM) and X-ray diffraction. Both X-ray and nc-AFM data indicate that the DCNDBQT molecules form a well-ordered terraced structure exhibiting step heights of 1.5 nm to 2.0 nm layers. Hence, the DCNDBQTmolecules are linked to the functional SAM interface layer by H-bond interactions (see structure model) standing quasi perpendicular to the TiO2 template, and thus providing optimal orbital overlap neigh-bouring thiophene rings. The vacuum sublimated DCNDBQT molecules form a closed packed and dense molecular layer that was used to construct and operate a nanoscopic OFET-structure. The resulting field mobilities of 10,5 cm2 V,1 s,1 reflect a high current density in our ultrathin but highly ordered structure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Direct evidence for group III atoms migration in aged 980 nm InGaAs/AlGaAs pump lasersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003M. Bettiati Abstract Low Temperature,Spectrally Resolved Cathodo-Luminescence (LT-SRCL) and Cathodo-Luminescence Imaging (CLI) have been used to study the effects of high temperature and high current density aging on 980 nm InGaAs/AlGaAs pump lasers. The aged lasers show a characteristic evolution of the luminescence band related to a thin (, 25 nm) InGaP etch-stop layer: a blue-shift of several meV is observed, together with a rather strong increase in the luminescence intensity. The blue-shift is related to an increase in the disorder of the InGaP alloy while the strong increase of the intensity may result from a different localization of the injected carriers due to a modification of the potential profile. A possible microscopic mechanism for the disordering of the InGaP layer is discussed, based on the migration of either p-type impurities (Zn, in this case) or excess group III interstitials. [source] | |||||||||||||||||||