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University of South Carolina

Series

2002

Articles 1 - 30 of 38

Full-Text Articles in Engineering

Milliwatt Power Deep Ultraviolet Light-Emitting Diodes Over Sapphire With Emission At 278 Nm, J. P. Zhang, A. Chitnis, V. Adivarahan, S. Wu, V. Mandavilli, R. Pachipulusu, M. Shatalov, Grigory Simin, J. W. Yang, M. Asif Khan Dec 2002

Milliwatt Power Deep Ultraviolet Light-Emitting Diodes Over Sapphire With Emission At 278 Nm, J. P. Zhang, A. Chitnis, V. Adivarahan, S. Wu, V. Mandavilli, R. Pachipulusu, M. Shatalov, Grigory Simin, J. W. Yang, M. Asif Khan

Faculty Publications

We report on AlGaN multiple-quantum-well (MQW)-based deep ultraviolet light-emitting diodes over sapphire with peak emission at 278 nm. A new buffer layer growth process was used to reduce the number of defects and hence the nonradiative recombination. The improved material quality and carrier confinement resulted in pulsed powers as high as 3 mW at 278 nm and a significantly reduced deep-level-assisted long-wavelength emission.

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Polarization Effects In Photoluminescence Of C- And M-Plane Gan/Algan Multiple Quantum Wells, E. Kuokstis, C. Q. Chen, M. E. Gaevski, W. H. Sun, J. W. Yang, Grigory Simin, M. Asif Khan, H. P. Maruska, D. W. Hill, M. C. Chou, J. J. Gallagher, B. Chai Nov 2002

Polarization Effects In Photoluminescence Of C- And M-Plane Gan/Algan Multiple Quantum Wells, E. Kuokstis, C. Q. Chen, M. E. Gaevski, W. H. Sun, J. W. Yang, Grigory Simin, M. Asif Khan, H. P. Maruska, D. W. Hill, M. C. Chou, J. J. Gallagher, B. Chai

Faculty Publications

Polarizationeffects have been studied in GaN/AlGaN multiple quantum wells(MQWs) with different c-axis orientation by means of excitation-dependent photoluminescence(PL) analysis. Quantum structures were grown on [0001]-oriented sapphire substrates (C plane) and single-crystalline [11̄00]-oriented freestanding GaN (M plane) using the metalorganic chemical vapor deposition technique. Strong PL spectrum line blueshifts (up to 140 meV) which are correlated with the excitation intensity have been obtained for C-plane MQWs, whereas no shift has been observed for M-plane MQWs.Theoretical calculations and comparison with the PL data confirm that the built-in electric field for C-plane structures is much stronger than the field present for M-plane MQWs. …

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Distributions Of Noble Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu Oct 2002

Distributions Of Noble Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous silica nanostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalytic properties for CO–CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

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Distributions Of Nobel Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu Oct 2002

Distributions Of Nobel Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous silicananostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalyticproperties for CO–CH4CO–CH4CO–CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

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Gan Homoepitaxy On Freestanding (11̄00) Oriented Gan Substrates, C. Q. Chen, M. E. Gaevski, W. H. Sun, E. Kuokstis, J. P. Zhang, R. S. Q. Fareed, H. M. Wang, J. W. Yang, Grigory Simin, M. A. Khan, Herbert-Paul Maruska, David W. Hill, Mitch M. C. Chou, Bruce Chai Oct 2002

Gan Homoepitaxy On Freestanding (11̄00) Oriented Gan Substrates, C. Q. Chen, M. E. Gaevski, W. H. Sun, E. Kuokstis, J. P. Zhang, R. S. Q. Fareed, H. M. Wang, J. W. Yang, Grigory Simin, M. A. Khan, Herbert-Paul Maruska, David W. Hill, Mitch M. C. Chou, Bruce Chai

Faculty Publications

We report homoepitaxialGaNgrowth on freestanding (11̄00) oriented (M-plane GaN) substrates using low-pressure metalorganic chemical vapor deposition.Scanning electron microscopy,atomic-force microscopy, and photoluminescence were used to study the influence of growth conditions such as the V/III molar ratio and temperature on the surface morphology and optical properties of the epilayers. Optimized growth conditions led to high quality (11̄00) oriented GaN epilayers with a smooth surface morphology and strong band-edge emission. These layers also exhibited strong room temperature stimulated emission under high intensity pulsed optical pumping. Since for III-N materials the (11̄00) crystal orientation is free from piezoelectric or spontaneous polarization electric fields, …

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Low-Temperature Operation Of Alfan Single-Quantum-Well Light-Emitting Diodes With Deep Ultraviolet Emission At 285 Nm, A. Chitnis, R. Pachipulusu, V. Mandavilli, M. Shatalov, E. Kuokstis, J. P. Zhang, V. Adivarahan, S. Wu, Grigory Simin, M. Asif Khan Oct 2002

Low-Temperature Operation Of Alfan Single-Quantum-Well Light-Emitting Diodes With Deep Ultraviolet Emission At 285 Nm, A. Chitnis, R. Pachipulusu, V. Mandavilli, M. Shatalov, E. Kuokstis, J. P. Zhang, V. Adivarahan, S. Wu, Grigory Simin, M. Asif Khan

Faculty Publications

We present a study of the electrical and optical characteristics of 285 nm emission deep ultraviolet light-emitting diodes(LED) at temperatures from 10 to 300 K. At low bias, our data show the tunneling carrier transport to be the dominant conduction mechanism. The room-temperature performance is shown to be limited mostly by poor electron confinement in the active region and a pronounced deep level assisted recombination but not by the hole injection into the active region. At temperatures below 100 K, the electroluminescence peak intensity increases by more than one order of magnitude indicating that with a proper device design and …

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Near-Band-Edge Photoluminescence Of Wurtzite-Type Aln, E. Kuokstis, J. Zhang, Q. Fareed, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. Shur, C. Rojo, L. Schowalter Sep 2002

Near-Band-Edge Photoluminescence Of Wurtzite-Type Aln, E. Kuokstis, J. Zhang, Q. Fareed, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. Shur, C. Rojo, L. Schowalter

Faculty Publications

Temperature-dependentphotoluminescence(PL)measurements were performed for A-plane and C-plane bulk AlN single crystals and epitaxial layers on sapphire. A strong near-band-edge (NBE) emission and deep-level luminescence were observed. At low excitations, the emission spectra are dominated by free and bound excitonic transitions and their LO-phonon replicas. At high excitations, the broadening and redshift of the NBE band is attributed to dense electron–hole plasma formation. The PL spectra differences of bulk single crystals and epilayers is explained by the electron–hole plasma expansion peculiarities.

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Low-Loss High Power Rf Switching Using Multifinger Algan/Gan Moshfets, Alexei Koudymov, Xuhong Hu, Kirill Simin, Grigory Simin, Mohammod Ali, Jinwei Yang, M. Asif Khan Aug 2002

Low-Loss High Power Rf Switching Using Multifinger Algan/Gan Moshfets, Alexei Koudymov, Xuhong Hu, Kirill Simin, Grigory Simin, Mohammod Ali, Jinwei Yang, M. Asif Khan

Faculty Publications

We demonstrate a novel RF switch based on a multifinger AlGan/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1a/mm 100 mum wide device exceeds 40 W for a 1-mm wide 2-a/mm …

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On Localized Control In Qos Routing, Srihari Nelakuditi, Srivatsan Varadarajan, Zhi-Li Zhang Jun 2002

On Localized Control In Qos Routing, Srihari Nelakuditi, Srivatsan Varadarajan, Zhi-Li Zhang

Faculty Publications

In this note, we study several issues in the design of localized quality-of-service (QoS) routing schemes that make routing decisions based on locally collected QoS state information (i.e., there is no network-wide information exchange among routers). In particular, we investigate the granularity of local QoS state information and its impact on the design of localized QoS routing schemes from a theoretical perspective. We develop two theoretical models for studying localized proportional routing: one using the link-level information and the other using path-level information. We compare the performance of these localized proportional routing models with that of a global optimal proportional …

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Dynamic Multiphysics Model For Solar Array, Shengyi Liu, Roger A. Dougal Jun 2002

Dynamic Multiphysics Model For Solar Array, Shengyi Liu, Roger A. Dougal

Faculty Publications

An approach to model the solar cell system with coupled multiphysics equations (photovoltaic, electro-thermal, direct heating and cooling processes) within the context of the resistive-companion method in the Virtual Test Bed computational environment is presented. Appropriate across and through variables are defined for the thermal terminal of the system so that temperature is properly represented as a state variable, rather than as a parameter of the system. This allows enforcement of the system power conservation through all terminals, and allows simultaneous solutions for both the electrical potentials and the system temperature. The thermal port built accordingly can be used for …

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Nonresonant Detection Of Terahertz Radiation In Field Effect Transistors, W. Knap, V. Kachorovskii, Y. Deng, S. Rumyantsev, J.-Q. Lü, R. Gaska, M. S. Shur, Grigory Simin, X. Hu, M. Asif Khan, C. A. Saylor, L. C. Brunel Jun 2002

Nonresonant Detection Of Terahertz Radiation In Field Effect Transistors, W. Knap, V. Kachorovskii, Y. Deng, S. Rumyantsev, J.-Q. Lü, R. Gaska, M. S. Shur, Grigory Simin, X. Hu, M. Asif Khan, C. A. Saylor, L. C. Brunel

Faculty Publications

We present an experimental and theoretical study of nonresonant detection of subterahertz radiation in GaAs/AlGaAs and GaN/AlGaN heterostructurefield effect transistors. The experiments were performed in a wide range of temperatures (8–300 K) and for frequencies ranging from 100 to 600 GHz. The photoresponse measured as a function of the gate voltage exhibited a maximum near the threshold voltage. The results were interpreted using a theoretical model that shows that the maximum in photoresponse can be explained by the combined effect of exponential decrease of the electron density and the gate leakage current.

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A Localized Adaptive Proportioning Approach To Qos Routing, Srihari Nelakuditi, Zhi-Li Zhang Jun 2002

A Localized Adaptive Proportioning Approach To Qos Routing, Srihari Nelakuditi, Zhi-Li Zhang

Faculty Publications

In QoS routing, paths for flows are selected based on knowledge of resource availability at network nodes and the QoS requirements of flows. Several QoS routing schemes have been proposed that differ in the way they gather information about the network state and select paths based on this information. We broadly categorize these schemes into best path routing and proportional routing. The best path routing schemes gather global network state information and always select the best path for an incoming I-low,based on this global view. It has been shown that best path routing schemes require frequent exchange of network state, …

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Time-Resolved Photoluminescence Of Quaternary Alingan-Based Multiple Quantum Wells, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan, G. G. Sim, P. W. Yu May 2002

Time-Resolved Photoluminescence Of Quaternary Alingan-Based Multiple Quantum Wells, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan, G. G. Sim, P. W. Yu

Faculty Publications

Time-resolvedphotoluminescence(PL)dynamics has been studied in AlInGaN/AlInGaN multiple quantum wells(MQWs) grown by a pulsed metalorganic chemical vapor deposition (PMOCVD) procedure. The PL decay kinetics was found to be sensitive to the emission energy and temperature. The PL decay time increases with decreasing emission energy, which is a characteristic of localized carrier/exciton recombination due to alloy fluctuations. Its temperature dependence shows radiative recombination to be the dominant process at low temperatures, indicating a high quality of PMOCVD grown quaternary AlInGaN MQWs and establishing them as promising structures for the active region of deep ultraviolet light emitting diodes.

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Luminescence Mechanisms In Quaternary AlXInYGa1-X-YN Materials, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan May 2002

Luminescence Mechanisms In Quaternary AlXInYGa1-X-YN Materials, Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan

Faculty Publications

Low-temperature photoluminescence investigations have been carried out in the quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by pulsedmetalorganic chemical-vapor deposition (PMOCVD). With increasing excitation power density, the emission peaks in both AlInGaN epilayers and MQWs show a strong blueshift and theirlinewidths increase. The luminescence of the samples grown by PMOCVD is attributed to recombination of carriers/excitons localized at band-tail states. We also demonstrate theluminescence properties of AlInGaN and AlGaN materials grown by a pulsed atomic-layerepitaxy and conventional MOCVD, respectively.

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Nanofatigue Studies Of Ultrathin Hard Carbon Overcoats Used In Magnetic Storage Devices, Xiaodong Li, Bharat Bhushan May 2002

Nanofatigue Studies Of Ultrathin Hard Carbon Overcoats Used In Magnetic Storage Devices, Xiaodong Li, Bharat Bhushan

Faculty Publications

A technique to perform nanofatigue experiments was developed. This technique utilizes a depth-sensing nanoindenter with harmonic force. The nanofatigue behavior of 20 nm thick amorphous carbon coatings was studied. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. It was found that the filtered cathodic arc coating exhibits longer fatigue life than a direct ion beam coating. Failure mechanisms of the coatings during fatigue are also discussed in conjunction with the hardness,elastic modulus, and fracture toughness, …

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Crack-Free Thick Algan Grown On Sapphire Using Aln/Algan Superlattices For Strain Management, J. P. Zhang, H. M. Wang, M. E. Gaevski, C. Q. Chen, Q. Fareed, J. W. Yang, Grigory Simin, M. Asif Khan May 2002

Crack-Free Thick Algan Grown On Sapphire Using Aln/Algan Superlattices For Strain Management, J. P. Zhang, H. M. Wang, M. E. Gaevski, C. Q. Chen, Q. Fareed, J. W. Yang, Grigory Simin, M. Asif Khan

Faculty Publications

We report on an AlN/AlGaN superlattice approach to grow high-Al-content thick n+-AlGaNlayers over c-plane sapphire substrates. Insertion of a set of AlN/AlGaN superlattices is shown to significantly reduce the biaxial tensile strain, thereby resulting in 3-μm-thick, crack-free Al0.2Ga0.8N layers. These high-quality, low-sheet-resistive layers are of key importance to avoid current crowding in quaternary AlInGaN multiple-quantum-well deep-ultraviolet light-emitting diodes over sapphire substrates.

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Maximum Current In Nitride-Based Heterostructure Field-Effect Transistors, A. Koudymov, H. Fatima, Grigory Simin, J. Yang, M. Asif Khan, A. Tarakji, X. Hu, M. S. Shur, R. Gaska Apr 2002

Maximum Current In Nitride-Based Heterostructure Field-Effect Transistors, A. Koudymov, H. Fatima, Grigory Simin, J. Yang, M. Asif Khan, A. Tarakji, X. Hu, M. S. Shur, R. Gaska

Faculty Publications

We present experimental and modeling results on the gate-length dependence of the maximum current that can be achieved in GaN-based heterostructurefield-effect transistors(HFETs) and metal–oxide–semiconductor HFETs (MOSHFETs). Our results show that the factor limiting the maximum current in the HFETs is the forward gate leakage current. In the MOSHFETs, the gate leakage current is suppressed and the overflow of the two dimensional electron gas into the AlGaN barrier region becomes the most important factor limiting the maximum current. Therefore, the maximum current is substantially higher in MOSHFETs than in HFETs. The measured maximum current increases with a decrease in the gate …

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Two Mechanisms Of Blueshift Of Edge Emission In Ingan-Based Epilayers And Multiple Quantum Wells, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur Feb 2002

Two Mechanisms Of Blueshift Of Edge Emission In Ingan-Based Epilayers And Multiple Quantum Wells, E. Kuokstis, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

We present the results of a comparative photoluminescence(PL) study of GaN and InGaN-based epilayers, and InGaN/GaN multiple quantum wells(MQWs). Room-temperature PL spectra were measured for a very broad range of optical excitation from 10 mW/cm2 up to 1 MW/cm2. In contrast to GaN epilayers, all In-containing samples exhibited an excitation-induced blueshift of the peak emission. In addition, the blueshift of the emission in the InGaN epilayers with the same composition as the quantum well was significantly smaller. The comparison of the blueshift in the “bulk” InGaN and in the MQWs allowed us to separate two different mechanisms …

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Trusted Autonomy, Michael N. Huhns, Duncan A. Buell Jan 2002

Trusted Autonomy, Michael N. Huhns, Duncan A. Buell

Faculty Publications

We describe how agents are the right building blocks for constructing trustworthy systems. Robust software and trusted autonomy represent the future for agent technology and software engineering.

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Robust Software, Michael N. Huhns, Vance T. Holderfield Jan 2002

Robust Software, Michael N. Huhns, Vance T. Holderfield

Faculty Publications

Agents offer a convenient level of granularity at which to add redundancy a key factor in developing robust software. Blindly adding code introduces more errors, makes the system more complex, and renders it harder to understand. However, adding more code can make software better, if it is added in the right way. As this article describes, the key concepts appear to be redundancy and the appropriate granularity.

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Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti Jan 2002

Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti

Faculty Publications

Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, …

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Simulating Shape Changes During Electrodeposition: Primary And Secondary Current Distribution, Venkat R. Subramanian, Ralph E. White Jan 2002

Simulating Shape Changes During Electrodeposition: Primary And Secondary Current Distribution, Venkat R. Subramanian, Ralph E. White

Faculty Publications

A technique based on the analytical method of lines is presented for predicting shape changes during electrodeposition. The technique is presented for both primary and secondary current distributions. The method presented does not require iterations for nonlinear Butler-Volmer boundary conditions or changing electrode shapes. The technique is based on a semianalytical method developed earlier for predicting current distributions in electrochemical cells. This technique is attractive because it provides a symbolic solution for the Laplace equation, and hence requires less computation time to perform case studies.

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Increasing Proton Exchange Membrane Fuel Cell Catalyst Effectiveness Through Sputter Deposition, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Timothy Stoner, Narender Rana Jan 2002

Increasing Proton Exchange Membrane Fuel Cell Catalyst Effectiveness Through Sputter Deposition, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Timothy Stoner, Narender Rana

Faculty Publications

Sputter deposition has been investigated as a tool for manufacturing proton-exchange membrane fuel cell (PEMFC) electrodes with improved performance and catalyst utilization vs. ink-based electrodes. Sputter-depositing a single layer of Pt on the gas diffusion layer provided better performance (0.28 A/cm2 at 0.6 V) than sputtering the Pt directly onto a Nafion membrane (0.065 A/cm2 at 0.6 V) and equaled the performance of the baseline for an equivalent Pt loading. Sputter-depositing alternating layers of Pt and Nafion-carbon ink (NCI) onto the membrane did not increase the performance over the baseline as measured in amperes per centimeter squared due …

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Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White Jan 2002

Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White

Faculty Publications

The validity of estimating the solid phase diffusion coefficient, Ds, of a lithium intercalation electrode from impedance measurement by a modified electrochemical impedance spectroscopy (EIS) method is studied. A macroscopic porous electrode model and concentrated electrolyte theory are used to simulate the synthetic impedance data. The modified EIS method is applied for estimating Ds. The influence of parameters such as the exchange current density, radius of active material particle, solid phase conductivity, porosity, volume fraction of inert material, and thickness of the porous carbon intercalation electrode, the solution phase diffusion coefficient, and transference number, on the …

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Water Transport In Polymer Electrolyte Membrane Electrolyzers Used To Recycle Anhydrous Hcl: I. Characterization Of Diffusion And Electro-Osmotic Drag, Sathya Motupally, Aaron J. Becker, John W. Weidner Jan 2002

Water Transport In Polymer Electrolyte Membrane Electrolyzers Used To Recycle Anhydrous Hcl: I. Characterization Of Diffusion And Electro-Osmotic Drag, Sathya Motupally, Aaron J. Becker, John W. Weidner

Faculty Publications

In this paper, diffusion and electro-osmotic drag of water across Nafion® membranes in the presence of HCl are characterized. For all the measurements, one side of the Nafion membrane was in contact with liquid water and the other side with gaseous anhydrous HCl. To characterize diffusion of water, the open-circuit flux of water across a catalyst-coated Nafion 115 membrane was measured as a function of HCl flow rate and temperature at a constant cell pressure of 1 atm. Due to the nature of varying driving force for diffusion as a function of HCl flow rate, the experimental data was analyzed …

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Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang Jan 2002

Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang

Faculty Publications

Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt:Ru alloy anodes, allowing a greater percentage of O2 to oxidize adsorbed CO to CO2. With an anode feed …

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Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros Jan 2002

Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros

Faculty Publications

Placing a layer of Ru atop a Pt anode increases the carbon monoxide tolerance of proton-exchange membrane fuel cells when oxygen is added to the fuel stream. Sputter-deposited Ru filter anodes composed of a single Ru layer and three Ru layers separated by Nafion-carbon ink, respectively, were compared to Pt, Pt:Ru alloy, and an ink-based Ru filter anodes. The amount of Pt in each anode was 0.15 mg/cm2 and the amount of Ru in each Ru-containing anode was 0.080 mg/cm2. For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O2 (in the form …

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Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov Jan 2002

Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov

Faculty Publications

The performance of Cell-Batt® Li-ion cells using nonstoichiometric spinel as the positive electrode material has been studied at different charging rates. The capacity of the cell was optimized based on varying the charging current and the end potential. Subsequent to this, the capacity fade of these batteries was studied at different charge currents. During cycling, cells were opened at intermittent cycles and extensive material and electrochemical characterization was done on the active material at both electrodes. For all charge currents, the resistance of both the electrodes does not vary significantly with cycling. This result is in contrast with cells …

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Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn Jan 2002

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn

Faculty Publications

This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …

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Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov Jan 2002

Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov

Faculty Publications

Anodic formation of oxide films on titanium surfaces, in various concentrations of aqueous KOH solutions, have been studied using ellipsometry and micro-Raman spectroscopy. By in situ ellipsometric measurements the coefficient of film thickness growth and indexes of refraction of anodic oxide films have been determined. The voltage at which the oxide film breaks down is strongly dependent on the KOH concentration. Further, the solution concentration strongly influences the potential at which the oxide film is transformed from the amorphous state to crystalline form. Using micro-Raman spectroscopy four crystalline forms of titanium oxides, namely, anatase, brookite, corundum, and rutile, have been …

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