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University of South Carolina

2001

Articles 1 - 30 of 32

Full-Text Articles in Engineering

Localization Of Carriers And Polarization Effects In Quaternary Alingan Multiple Quantum Wells, E. Kuokstis, J. Zhang, M.-Y. Ryu, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur Dec 2001

Localization Of Carriers And Polarization Effects In Quaternary Alingan Multiple Quantum Wells, E. Kuokstis, J. Zhang, M.-Y. Ryu, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

We report on observing a long-wavelength band in low-temperature photoluminescence(PL)spectrum of quaternary Al0.22In0.02Ga0.76N/Al0.38In0.01Ga0.61N multiple quantum wells(MQWs), which were grown over sapphire substrates by a pulsed atomic-layer epitaxy technique. By comparing the excitation-power density and temperature dependence of the PLspectra of MQWs and bulk quaternary AlInGaN layers, we show this emission band to arise from the carrier and/or exciton localization at the quantum well interface disorders. PL data for other radiative transitions in MQWs indicate that excitation-dependent spectra position is determined by screening of the built-in electric field.

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Ultraviolet Light-Emitting Diodes At 340 Nm Using Quaternary Alingan Multiple Quantum Wells, V. Adivarahan, A. Chitnis, J. P. Zhang, M. Shatalov, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur Dec 2001

Ultraviolet Light-Emitting Diodes At 340 Nm Using Quaternary Alingan Multiple Quantum Wells, V. Adivarahan, A. Chitnis, J. P. Zhang, M. Shatalov, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

An ultraviolet light-emitting diode with peak emission wavelength at 340 nm is reported. The active layers of the device were comprised of quaternary AlInGaN/AlInGaN multiple quantum wells, which were deposited over sapphire substrates using a pulsed atomic-layer epitaxy process that allows precise control of the composition and thickness. A comparative study of devices over sapphire and SiC substrates was done to determine the influence of the epilayer design on the performance parameters and the role of substrate absorption.

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A Dipolar Coupling Based Strategy For Simultaneous Resonance Assignment And Structure Determination Of Protein Backbones, Fang Tian, Homayoun Valafar, James H. Prestegard Nov 2001

A Dipolar Coupling Based Strategy For Simultaneous Resonance Assignment And Structure Determination Of Protein Backbones, Fang Tian, Homayoun Valafar, James H. Prestegard

Faculty Publications

A new approach for simultaneous protein backbone resonance assignment and structure determination by NMR is introduced. This approach relies on recent advances in high-resolution NMR spectroscopy that allow observation of anisotropic interactions, such as dipolar couplings, from proteins partially aligned in field ordered media. Residual dipolar couplings are used for both geometric information and a filter in the assembly of residues in a sequential manner. Experimental data were collected in less than one week on a small redox protein, rubredoxin, that was 15N enriched but not enriched above 1% natural abundance in 13C. Given the acceleration possible with partial 13C …

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Si3N4/Algan/Gan-Metal-Insulator-Semiconductor Heterostructure Field-Effect Transistors, X. Hu, A. Koudymov, Grigory Simin, J. Yang, M. Asif Khan, A. Tarakji, M. S. Shur, R. Gaska Oct 2001

Si3N4/Algan/Gan-Metal-Insulator-Semiconductor Heterostructure Field-Effect Transistors, X. Hu, A. Koudymov, Grigory Simin, J. Yang, M. Asif Khan, A. Tarakji, M. S. Shur, R. Gaska

Faculty Publications

We report on a metal–insulator–semiconductor heterostructurefield-effect transistor (MISHFET) using Si3N4 film simultaneously for channel passivation and as a gate insulator. This design results in increased radio-frequency (rf) powers by reduction of the current collapse and it reduces the gate leakage currents by four orders of magnitude. A MISHFET room temperature gate current of about 90 pA/mm increases to only 1000 pA/mm at ambient temperature as high as 300 °C. Pulsed measurements show that unlike metal–oxide–semiconductor HFETs and regular HFETs, in a Si3N4 MISHFET, the gate voltage amplitude required for current collapse is much higher …

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Induced Strain Mechanism Of Current Collapse In Algan/Gan Heterostructure Field-Effect Transistors, Grigory Simin, A. Koudymov, A. Tarakji, X. Hu, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska Oct 2001

Induced Strain Mechanism Of Current Collapse In Algan/Gan Heterostructure Field-Effect Transistors, Grigory Simin, A. Koudymov, A. Tarakji, X. Hu, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska

Faculty Publications

Gated transmission line model pattern measurements of the transient current–voltage characteristics of AlGaN/GaN heterostructurefield-effect transistors(HFETs) and metal–oxide–semiconductor HFETs were made to develop a phenomenological model for current collapse. Our measurements show that, under pulsed gate bias, the current collapse results from increased source–gate and gate–drain resistances but not from the channel resistance under the gate. We propose a model linking this increase in series resistances (and, therefore, the current collapse) to a decrease in piezoelectriccharge resulting from the gate bias-induced nonuniform strain in the AlGaN barrier layer.

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Indium-Silicon Co-Doping Of High-Aluminum-Content Algan For Solar Blind Photodetectors, V. Adivarahan, Grigory Simin, G. Tamulaitis, R. Srinivasan, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska Sep 2001

Indium-Silicon Co-Doping Of High-Aluminum-Content Algan For Solar Blind Photodetectors, V. Adivarahan, Grigory Simin, G. Tamulaitis, R. Srinivasan, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska

Faculty Publications

We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrierphotodetectors with the cut-off wavelength of 278 nm.

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Pulsed Atomic Layer Epitaxy Of Quaternary Alingan Layers, J. Zhang, E. Kuokstis, Q. Fareed, H. Wang, J. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. Shur Aug 2001

Pulsed Atomic Layer Epitaxy Of Quaternary Alingan Layers, J. Zhang, E. Kuokstis, Q. Fareed, H. Wang, J. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. Shur

Faculty Publications

In this letter, we report on a material deposition scheme for quaternary AlxInyGa1−x–yN layers using a pulsed atomic layer epitaxy (PALE) technique. The PALE approach allows accurate control of the quaternary layer composition and thickness by simply changing the number of aluminum,indium, and gallium pulses in a unit cell and the number of unit cell repeats. Using PALE, AlInGaN layers with Al mole fractions in excess of 40% and strong room-temperature photoluminescence peaks at 280 nm can easily be grown even at temperatures lower than 800 °C.

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Passivity-Based Control Of Saturated Induction Motors, Levent U. Gökdere, Marwan A. Simaan, Charles W. Brice Aug 2001

Passivity-Based Control Of Saturated Induction Motors, Levent U. Gökdere, Marwan A. Simaan, Charles W. Brice

Faculty Publications

A passivity-based controller, which takes into account saturation of the magnetic material in the main flux path of the induction motor, is developed to provide close tracking of time-varying speed and flux trajectories in the high magnetic saturation regions. The proposed passivity based controller is experimentally verified. Also, a comparison between the controllers based on the saturated and nonsaturated magnetics is presented to demonstrate the benefit of the controller based on the saturated magnetics

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Green Electrochemistry. Examples And Challenges, Michael A. Matthews Aug 2001

Green Electrochemistry. Examples And Challenges, Michael A. Matthews

Faculty Publications

Electrochemical methods have been proposed for synthesis of organic compounds, including conversion of CO2. Such methods may provide a basis for environmentally friendly and sustainable methods for chemical production. Nevertheless, electrochemical syntheses are not widely utilized. Several examples of ongoing research are presented that illustrate both the opportunities as well as the challenges associated with the utilization of electrochemistry for green chemical manufacturing.

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Low Frequency Noise In Gan Metal Semiconductor And Metal Oxide Semiconductor Field Effect Transistors, S. L. Rumyantsev, N. Pala, M. S. Shur, R. Gaska, M. E. Levinshtein, M. Asif Khan, Grigory Simin, X. Hu, J. Yang Jul 2001

Low Frequency Noise In Gan Metal Semiconductor And Metal Oxide Semiconductor Field Effect Transistors, S. L. Rumyantsev, N. Pala, M. S. Shur, R. Gaska, M. E. Levinshtein, M. Asif Khan, Grigory Simin, X. Hu, J. Yang

Faculty Publications

The low frequency noise in GaNfield effect transistors has been studied as function of drain and gate biases. The noise dependence on the gate bias points out to the bulk origin of the low frequency noise. The Hooge parameter is found to be around 2×10−3 to 3×10−3.Temperature dependence of the noise reveals a weak contribution of generation–recombination noise at elevated temperatures.

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Increasing Power Density Of Lsgm-Based Solid Oxide Fuel Cells Using New Anode Materials, Kevin Huang, Jen-Hau Wan, John B. Goodenough Jun 2001

Increasing Power Density Of Lsgm-Based Solid Oxide Fuel Cells Using New Anode Materials, Kevin Huang, Jen-Hau Wan, John B. Goodenough

Faculty Publications

Chemical reactions between the superior perovskite oxide-ion conductor Sr- and Mg-doped LaGaO3 (LSGM), CeO2, and NiO have been studied by powder X-ray diffraction. The results showed that an extensive reactivity occurs as a result of La migration driven by a gradient of La chemical activity. La migration across the LSGM/electrode interfaces in a fuel cell leads to the formation of resistive phases at the interface, either LaSrGa3O7 or LaSrGaO4. Use of 40 mol % La2O3 -doped CeO2 as an interlayer between anode and electrolyte as well as in …

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Oxygen Permeation Through Cobalt-Containing Perovskites: Surface Oxygen Exchange Vs. Lattice Oxygen Diffusion, Kevin Huang, John B. Goodenough May 2001

Oxygen Permeation Through Cobalt-Containing Perovskites: Surface Oxygen Exchange Vs. Lattice Oxygen Diffusion, Kevin Huang, John B. Goodenough

Faculty Publications

The oxygen permeation fluxes from p′O2 to pnO2 (p′O2>pnO2) across cobalt-containing perovskite ceramic membranes La1−xSrxCoO3−δ and SrCo0.8Fe0.2O3−δ were measured by gas chromatography as functions of oxygen chemical potential gradient, temperature, thickness, and catalytic activity on the surface. Power indexes 0.5>n>0 for uncatalyzed La1−xSrxCoO3−δ and 1>n>0.5 for SrCo0.8Fe0.2O3−δ were obtained when JO2 vs. p′nO2−p'′nO2 …

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Very-Low-Specific-Resistance Pd/Ag/Au/Ti/Au Alloyed Ohmic Contact To P Gan For High-Current Devices, V. Adivarahan, A. Lunev, M. Asif Khan, J. Yang, Grigory Simin, M. S. Shur, R. Gaska Apr 2001

Very-Low-Specific-Resistance Pd/Ag/Au/Ti/Au Alloyed Ohmic Contact To P Gan For High-Current Devices, V. Adivarahan, A. Lunev, M. Asif Khan, J. Yang, Grigory Simin, M. S. Shur, R. Gaska

Faculty Publications

We report on Pd/Ag/Au/Ti/Au alloyed metallic contact to pGaN. An 800 °C anneal for 1 min in flowing nitrogen ambient produces an excellent ohmic contact with a specific contact resistivity close to 1×10−6 Ω cm2 and with good stability under high current operation conditions. This high-temperature anneal forms an alloy between Ag,Au, and pGaN resulting in a highly p-doped region at the interface. Using x-ray photoelectron spectroscopy and x-ray diffractionanalysis, we confirm that the contact formation mechanism is the metal intermixing and alloying with the semiconductor.

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Mechanism Of Radio-Frequency Current Collapse In Gan-Algan Field-Effect Transistors, A. Tarakji, Grigory Simin, N. Ilinskaya, X. Hu, A. Kumar, A. Koudymov, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska Apr 2001

Mechanism Of Radio-Frequency Current Collapse In Gan-Algan Field-Effect Transistors, A. Tarakji, Grigory Simin, N. Ilinskaya, X. Hu, A. Kumar, A. Koudymov, J. Yang, M. Asif Khan, M. S. Shur, R. Gaska

Faculty Publications

The mechanism of radio-frequency current collapse in GaN–AlGaN heterojunctionfield-effect transistors(HFETs) was investigated using a comparative study of HFET and metal–oxide–semiconductor HFET current–voltage (I–V) and transfer characteristics under dc and short-pulsed voltage biasing. Significant current collapse occurs when the gate voltage is pulsed, whereas under drain pulsing the I–V curves are close to those in steady-state conditions. Contrary to previous reports, we conclude that the transverse electric field across the wide-band-gap barrier layer separating the gate and the channel rather than the gate or surface leakage currents or high-field effects in the gate–drain spacing is responsible for the current collapse. We …

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Reduced-Temperature Solid Oxide Fuel Cells Fabricated By Screen Printing, Changrong Xia, Fanglin Chen, Meilin Liu Mar 2001

Reduced-Temperature Solid Oxide Fuel Cells Fabricated By Screen Printing, Changrong Xia, Fanglin Chen, Meilin Liu

Faculty Publications

Electrolyte films of samaria-doped ceria (SDC, Sm0.2Ce0.8O1.9) are fabricated onto porous NiO-SDC substrates by a screen printing technique. A cathode layer, consisting of Sm0.5Sr0.5CoO3 and 10 wt % SDC, is subsequently screen printed on the electrolyte to form a single cell, which is tested at temperatures from 400 to 600°C. When humidified (3% H2O) hydrogen or methane is used as fuel and stationary air as oxidant, the maximum power densities are 188 (or 78) and 397 (or 304) mW/cm2 at 500 and 600°C, respectively. Impedance analysis …

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Bistable Operation Of A Two-Section 1.3-Mm Inas Quantum Dot Laser—Absorption Saturation And The Quantum Confined Stark Effect, Xiaodong Huang, A. Stintz, Hua Li, Audra Rice, G. T. Liu, L.F. Lester, Julian Cheng, K.J. Malloy Mar 2001

Bistable Operation Of A Two-Section 1.3-Mm Inas Quantum Dot Laser—Absorption Saturation And The Quantum Confined Stark Effect, Xiaodong Huang, A. Stintz, Hua Li, Audra Rice, G. T. Liu, L.F. Lester, Julian Cheng, K.J. Malloy

Faculty Publications

Room temperature, continuous-wave bistability was observed in oxide-confined, two-section, 1.3- m quantum-dot (QD) lasers with an integrated intracavity quantum-dot saturable absorber. The origin of the hysteresis and bistability were shown to be due to the nonlinear saturation of the QD absorption and the electroabsorption induced by the quantum confined Stark effect.

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Highly Doped Thin-Channel Gan-Metal-Semiconductor Field-Effect Transistors, R. Gaska, M. S. Shur, X. Hu, J. W. Yang, A. Tarakji, Grigory Simin, A. Khan, J. Deng, T. Werner, S. Rumyantsev, N. Pala Feb 2001

Highly Doped Thin-Channel Gan-Metal-Semiconductor Field-Effect Transistors, R. Gaska, M. S. Shur, X. Hu, J. W. Yang, A. Tarakji, Grigory Simin, A. Khan, J. Deng, T. Werner, S. Rumyantsev, N. Pala

Faculty Publications

We report on the influence of the channel doping on dc, high frequency, and noise performance of GaN metal–semiconductor field-effect transistors (MESFETs) grown on sapphire substrates. The devices with the channel thicknesses from 50 to 70 nm and doping levels up to 1.5×1018 cm−3 were investigated. An increase in the channel doping results in the improved dc characteristics, higher cutoff, and maximum oscillation frequencies, and reduced low frequency and microwave noise. The obtained results demonstrate that the dc and microwave performance characteristics of short-channel GaN MESFETs may be comparable to those for conventional AlGaN/GaN heterostructure FETs.

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Band-Edge Luminesce In Quaternary Alingan Light-Emitting Diodes, M. Shatalov, A. Chitnis, V. Adivarahan, A. Lunev, J. Zhang, J. W. Yang, Q. Fareed, Grigory Simin, A. Zakheim, M. Asif Khan, R. Gaska, M. S. Shur Feb 2001

Band-Edge Luminesce In Quaternary Alingan Light-Emitting Diodes, M. Shatalov, A. Chitnis, V. Adivarahan, A. Lunev, J. Zhang, J. W. Yang, Q. Fareed, Grigory Simin, A. Zakheim, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

Operation of InGaNmultiple-quantum-well(MQW)light-emitting diodes(LEDs) with quaternary AlInGaN barriers at room and elevated temperatures is reported. The devices outperform conventional GaN/InGaN MQWLEDs, especially at high pump currents. From the measurements of quantum efficiency and total emitted power under dc and pulsed pumping, we show the emission mechanism for quaternary barrier MQWs to be predominantly linked to band-to-band transitions. This is in contrast to localized state emission observed for conventional InGaN/InGaN and GaN/InGaN LEDs. The band-to-band recombination with an increased quantum-well depth improves the high-current performance of the quaternary barrier MQWLEDs, making them attractive for high-power solid-state lighting applications.

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Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. S. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. E. Lofland, Jason R. Hattrick-Simpers, H. Chang Jan 2001

Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. S. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. E. Lofland, Jason R. Hattrick-Simpers, H. Chang

Faculty Publications

We have performed variable-temperature multimode quantitative microwavemicroscopy of in situepitaxial Ba1−xSrxTiO3 thin-film composition spreads fabricated on (100) LaA1O3 substrates. Dielectric properties were mapped as a function of continuously varying composition from BaTiO3 to SrTiO3. We have demonstrated nondestructive temperature-dependent dielectric characterization of local thin-film regions. Measurements are simultaneously taken at multiple resonant frequencies of the microscope cavity. The multimode measurements allow frequency dispersion studies. We observe strong composition-dependent dielectric relaxation in Ba1−xSrxTiO3 at microwave frequencies.

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Hysteresis During Cycling Of Nickel Hydroxide Active Material, Venkat Srinivasan, John W. Weidner, John Newman Jan 2001

Hysteresis During Cycling Of Nickel Hydroxide Active Material, Venkat Srinivasan, John W. Weidner, John Newman

Faculty Publications

The nickel hydroxide electrode is known to exhibit a stable hysteresis loop, with the potential on charge being higher than that on discharge at every state-of-charge (SOC). What we show here is that this loop created during a complete charge and discharge (i.e., boundary curves) is not sufficient to define the state of the system. Rather, internal paths within the boundary curves (i.e., scanning curves) can be generated that access potentials between the boundary curves. The potential obtained at any SOC, as well as how the material charges and discharges from that point, depends on the …

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Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White Jan 2001

Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White

Faculty Publications

No abstract provided.

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Preparation Of Ordered Macroporous Sr0.5sm0.5coo3 As Cathode For Solid Oxide Fuel Cells, Fanglin Chen, Changrong Xia, Meilin Liu Jan 2001

Preparation Of Ordered Macroporous Sr0.5sm0.5coo3 As Cathode For Solid Oxide Fuel Cells, Fanglin Chen, Changrong Xia, Meilin Liu

Faculty Publications

Ordered macroporous Sr0.5Sm0.5CoO3 structrures with an average pore size of 140 nm have been prepared using closepacked arrangement of monodispersed polystyrene spheres as templates. A fuel cell using ordered macroporous Sr0.5Sm0.5CoO3 as the cathode, gadolinia-doped ceria (GDC) film as the electrolyte, and GDC–NiO as the anode generated maximum power densities of 150, 196 and 267 mW/cm2 at 500, 550 and 600 °C, respectively.

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Inside An Agent, José M. Vidal, Paul A. Buhler, Michael N. Huhns Jan 2001

Inside An Agent, José M. Vidal, Paul A. Buhler, Michael N. Huhns

Faculty Publications

When we discuss agent-based system construction with software developers or ask students to implement common agent architectures using object-oriented techniques, we find that it is not trivial for them to create an elegant system design from the standard presentation of these architectures in textbooks or research papers. To better communicate our interpretation of popular agent architectures, we draw UML (Unified Modeling Language) diagrams to guide an implementer's design. However, before we describe these diagrams, we need to review some basic features of agents. The paper considers an architecture showing a simple agent interacting with an environment. The agent senses its …

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Consensus Ontologies: Reconciling The Semantics Of Web Pages And Agents, Larry M. Stevens, Michael N. Huhns Jan 2001

Consensus Ontologies: Reconciling The Semantics Of Web Pages And Agents, Larry M. Stevens, Michael N. Huhns

Faculty Publications

As you build a Web site, it is worthwhile asking, "Should I put my information where it belongs or where people are most likely to look for it?" Our recent research into improving searching through ontologies is providing some interesting results to answer this question. The techniques developed by our research bring organization to the information received and reconcile the semantics of each document. Our goal is to help users retrieve dynamically generated information that is tailored to their individual needs and preferences. We believe that it is easier for individuals or small groups to develop their own ontologies, regardless …

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Automating Supply Chains, Michael N. Huhns, Larry M. Stevens Jan 2001

Automating Supply Chains, Michael N. Huhns, Larry M. Stevens

Faculty Publications

A recent study found that supply-chain problems cost companies between 9 and 20 percent of their value over a six-month period (T.J. Becker, 2000). The problems range from part shortages to poorly utilized plant capacity. When you place this in the context of the overall business-to-business (B2B) market expected to reach US$7 trillion by 2004 (37 percent of which is projected to be e-commerce sales), it is easy to see that effective supply-chain management (SCM) tools could save companies billions of dollars. Attempts to automate solutions to these problems are complicated by the need for the different companies in a …

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Trust And Persistence, Paul A. Buhler, Michael N. Huhns Jan 2001

Trust And Persistence, Paul A. Buhler, Michael N. Huhns

Faculty Publications

We rely on computers to control our power plants and water supplies, our automobiles and transportation systems, and soon our economic and political systems. Increasingly, software agents are enmeshed in these systems, serving as the glue that connects distributed components. Clearly, we need mechanisms to determine whether these agents are trustworthy. What do we need to establish trust? Agents are often characterized by features such as autonomy, sociability, proactiveness, and persistent identity. This latter feature is key in determining trust. When agents operate over an extended period, they can earn a reputation for competence, timeliness, ease of use, and trustworthiness, …

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Electrochemical Generation Of Superoxide In Room-Temperature Ionic Liquids, Inas M. Alnashef, Matthew L. Leonard, Matthew C. Kittle, Michael A. Matthews, John W. Weidner Jan 2001

Electrochemical Generation Of Superoxide In Room-Temperature Ionic Liquids, Inas M. Alnashef, Matthew L. Leonard, Matthew C. Kittle, Michael A. Matthews, John W. Weidner

Faculty Publications

We have demonstrated that superoxide ion can be generated electrochemically in room-temperature ionic-liquid solvents. In the absence of impurities, cyclic voltammetry showed that the super oxide ion is stable in these solvents. Similar superoxide ion chemistry has previously been demonstrated in volatile and environmentally suspect aprotic solvents such as dimethyl formamide and acetonitrile. However, ionic liquids are nonvolatile and should minimize the problems of secondary solvent waste. It is proposed that the resultant superoxide ion can be used to perform low temperature oxidation of wastes. Low-temperature oxidation of waste solvents can provide a much needed alternative to high-temperature waste incinerators, …

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Synthesis And Characterization Of Hydrous Ruthenium Oxide-Carbon Supercapacitors, Manikandan Ramani, Bala S. Haran, Ralph E. White, Branko N. Popov Jan 2001

Synthesis And Characterization Of Hydrous Ruthenium Oxide-Carbon Supercapacitors, Manikandan Ramani, Bala S. Haran, Ralph E. White, Branko N. Popov

Faculty Publications

It is shown that composite Ru oxide-carbon based supercapacitors possess superior energy and power densities as compared to bare carbon. An electroless deposition process was used to synthesize the ruthenium oxide-carbon composites. Ru is dispersed on the carbon matrix as small particles. The effect of electrochemical oxidation and temperature treatment on the material performance has been studied extensively. Increasing the oxidation temperature reduces the proton transport rate and also increases the degree of crystallinity of the deposits. This adversely affects the performance of the composite. Loading a small amount of Ru oxide (9 wt %) on carbon increases the capacitance …

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Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White Jan 2001

Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White

Faculty Publications

No abstract provided.

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Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White Jan 2001

Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White

Faculty Publications

Approximate models are developed, based on second, fourth, and sixth order polynomials, that describe the concentration profile of an electrochemically active species in a spherical electrode particle. Analytical expressions are obtained that describe the way the concentration profiles, surface concentrations, and electrode utilization change during the galvanostatic discharge of an electrode particle. Based on a comparison with an exact analytical model over a wide range of dimensionless current densities, all three approximate models performed extremely well in predicting these quantities. Quantitative criterion for the validity of these models is also developed and shows that the sixth order, four parameter approximate …

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