bluuebunny/crossref_metadata_2025 huggingface dataset:
Conductometric Sensors for Detection of Elemental Mercury Vapor
Authors: Ryan M. A. , Homer M. L. , Shevade Abhijit V. , Lara L. M. , Yen S.P.S. , Kisor A. K. , Manatt K. S.
Published: October 2008

Several organic and inorganic materials have been tested for possible incorporation into a sensing array in order to add elemental mercury vapor to the suite of chemical species detected. Materials have included gold films, treated gold films, polymer-carbon composite films, gold-polymer-carbon composite films and palladium chloride sintered films.
Hafnium Silicate Gate Insulators in Field Effect Sensors Used to Detect DNA Hybridization
Authors: Jiang Weihong , Landheer Dolf , Lopinski Gregory , McKinnon W.Ross , Rankin Alasdair , Ghias-Begloo Ehsan , Griffin Ryan , Tarr N. Garry , Tait Niall , Liu Jian , Lennard William
Published: October 2008

Field-effect sensors with hafnium silicate gate insulators were fabricated following standard CMOS processes and compatible post-processes. The floating gates were functionalized with glycidoxypropyltrimethoxy silane and amine-terminated oligonucleotide probes. The pH sensitivity of the silicate surface decreased from 31.4 mV/pH to 24.6 mV/pH after functionalization due to passivation of a significant fraction of the amphoteric proton binding sites. A threshold voltage shift of 33 mV was observed as the buffer solution concentration changed from 0.015 M to 0.3 M after DNA probe molecule attachment. The hybridization caused a net increase in this shift of 3mV. With the help of a model which includes the solution of the Poisson-Boltzmann and proton site-binding at the gate, methods of achieving higher sensitivity are discussed.
Nanoparticles for Enhanced Sensitivity in Electrochemical Immunoassays
Authors: Lin Yuehe , Wang Jun , Wang Hua , Wu Hong , Tang Zhiwen
Published: October 2008

In this manuscript, we report on electrochemical biosensors based on various nanoparticles (NPs) as labels for sensitive detection of protein biomarkers. We used silica nanoparticle as a carrier to loading a large amount of electroactive species such as poly(guanine) for sensitive immunoassay of tumor necrosis factor-alpha (TNF-α). We took the advantages of the unique hollow structure and reconstruction properties of apoferritin to prepare Cd3(PO4)2 nanoparticles as labels for sensitive assay of TNF-α. A novel immunochromatographic/electro-chemical biosensor based on quantum dots as labels has also been developed for rapid and sensitive detection of prostate-specific antigen (PSA) in human serum. These biosensors are quite sensitive with the detection limit at pM level and these approaches based on nanoparticle labels offer a new avenue for sensitive detection of protein biomarkers.
Pegylated Polyurethane Nanoparticles as Support for a Biosensor Construction based on Peroxidase Extracted from Pine Kernel (Araucaria Angustifolia)
Authors: Oliveira Ines R. , Fritzen-Garcia Mauricia B. , Zanetti-Ramos Betina G. , Fatibello-Filho Orlando , Pasa Andre A. A. , Creczynski-Pasa Tania B.
Published: October 2008

In the present work, we have used polyurethane nanoparticles to support a biological material to construct a biosensor. The device is based on pine kernel (Araucaria angustifolia) tissue homogenate as a source of peroxidase, developed for the determination of dopamine in pharmaceutical products. The biosensor was constructed by the immobilization of peroxidase on pegylated polyurethane nanoparticles and square-wave and cyclic voltammetry experiments were performed. The best analytical response was obtained for a 75:15:10 % (w/w/w) composition of graphite powder: Nujol: polyurethane nanoparticles containing 2.5 units of peroxidase/mg of carbon paste, 0.1 mol L−1 phosphate buffer solution (pH 6.5), 2.0×10−3 mol L−1 hydrogen peroxide, 80 mV pulse height and 60 Hz frequency. The analytical curve was linear for dopamine concentrations from 3.33×10−5 to 6.60×10-4 mol L−1 (r = 0.9994) and the regression equation was found to be ≜I = 14.38 + 27.47×103 [dopamine] with limit detection.
Effect of Surface Morphology of a SiO2/Si Reference Electrode Modified by ODMS on the Responses to pH and Ionic Strength
Authors: Wang Jinping , Sasano Junji , Osaka Tetsuya
Published: October 2008

The purpose of this work was to study the effect of surface morphology on the responses to pH and ionic strength of a SiO2/Si reference electrode (RE) modified by octadecyltrimethoxysilane (ODMS). Representative REs with contact angles (CA) of 60o, 80o and 106o were studied in various solutions: those with combined effects of pH and ionic strength, those with ionic strength variation and constant pH, and those with pH variation and constant ionic strength. REs with the flat surface shows response to ionic strength, while REs with the rough surface shows response to pH. The reason may be that total ionic strength determines the charge and potential distribution in the electrolyte-insulator-semiconductor structure for REs with flat surfaces, but that the combined effects of uncovered binding sites, penetration of H+ into pinholes, and the special adsorption of H+ dictate the charge and potential distribution for REs with rough surfaces.
Thermodynamic Characterization of Reference Electrode Systems for Galvanic Cells Comprising Alkali Ion Conducting Solid Electrolytes
Authors: Nafe Helfried
Published: October 2008

By means of solid state electrochemical techniques the thermodynamic stability of potential reference electrodes for galvanic cells comprising ternary alkali oxide compounds have been characterized without distortion of the data by electronic transference.
Conductivities of Lithium Doped Lanthanoid Silicates as Gas Sensing Materials
Authors: Itagaki Yoshiteru , Takeda Naoki , Sadaoka Yoshihiko
Published: October 2008

A series of Li-doped lanthanoide silicates, LixLn1-x(SiO4)6O3-x (Ln=La, Nd), were prepared by the solid phase reaction and their ionic conductivities were evaluated. The Li-doping gave the apatite crystal structures (hexagonal, P63/m) analogous to Ln10(SiO4)6O3. The Li-doping was limited up to around x=2 for Ln=La and around x=3.5 for Ln=Nd. In the region of low Li-contents, oxide ion conduction characteristic for Ln10(SiO4)6O3 was still dominant. With an increase in the Li-content, the component of Li-ion conduction emerged due to the formation of lithium silicate glassy phase existing at the grain-boundaries. The O2 and CO2 sensor measurements using the sinters well supported the results of the conductivity analyses. Thus it was found that varying the Li-content could regulate an ionic conductivity and carrier. These properties of the Li-doped lanthanoid silicates might give a good compatibility into the two conduction layers junction, oxide ion conductor//alkali ion conductors fundamental to solid electrolyte gas sensors.
Synthesis and Characterization of Cobalt(III) Complexes with High Selectivity for NO Sensing
Authors: Ozawa Tomohiro , Yano Takuma , Zhang Zizheng , Inomata Tomohiko , Funahashi Yasuhiro , Mausda Hideki
Published: October 2008

Square planar Co(III) complexes,1 and 2, were synthesized and characterized. The structure kept in any other organic solution and even in an aqueous one, indicating that Lewis acidity of the metal center is rather small. Introduction of NO gas into CH3OH solutions of 1 and 2 caused a decrease of the absorption band in a visible region. This result indicates that NO molecule interacted to the Co(III) center. Reduction potential corresponding to Co(III)/(II) also shifted from -1.24 V to -1.65 V for 2 (vs. Ag/Ag+ in CH3CN) by addition of NO. On the other hand, addition of the other ions or molecules such as O2, Cl-, CO, and NO2- that is producible by reacting NO gas and O2 in an aqueous solution did not show any changes for the chemical properties.
Work Function and Effective Oxide Thickness Engineering via Alloying of Metal Gate Electrodes
Authors: Schaeffer Jamie , Raymond Mark , Gilmer David , Gregory Rich , Taylor Bill , Jiang Jack , Triyoso Dina , Hegde Rama , Samavedam Sri
Published: October 2008

Dielectric capping layer and electrode alloying approaches for tuning the effective work function and effective oxide thickness of metal oxide semiconductor transistors are compared. TaMgC and MoAlN electrodes are compared to MgO and Al2O3 capping layers for n-type and p-type transistors respectively. Results indicate that by incorporating the Mg or Al into the gate electrode instead of into the dielectric capping layer reductions in threshold voltage can be achieved, but with the added benefit of an effective oxide thickness reduction. SIMS results suggest that the threshold voltage shift is likely caused by the inward diffusion of Mg or Al though the gate dielectric towards the bottom interface layer. The limitations of each approach for work function engineering are discussed.
Engineering High Dielectric Constant Materials for Band-Edge CMOS Applications
Authors: Jagannathan Hemanth , Narayanan Vijay , Brown Stephen
Published: October 2008

This paper summarizes studies performed using capping layers in conjunction with high-K dielectrics to obtain band-edge CMOS devices. MgO and Al2O3 cap layers are evaluated for nFET and pFET devices respectively. By precisely positioning the cap materials in the gate stack and evaluating their effect as a function of process temperature and capping layer thickness, a deeper understanding of the mechanism of threshold voltage shift caused by the capping layers is obtained. MgO is observed to readily diffuse into the HfO2 stack at temperatures as low as 600 oC while Al2O3 diffuses through HfO2 at higher temperatures of 1000 oC. MgO caps located below the HfO2 and processed at 600 oC provide the best scaling and maximum voltage shift, while a trade-off between scaling and voltage shift has to be made when using Al2O3 caps.
Fundamental Aspects of Effective Work Function Instability of Metal/Hf-based High-k Gate Stacks
Authors: Watanabe Heiji , Yoshida Shinichi , Kita Yuki , Hosoi Takuji , Shimura Takayoshi , Shiraishi Kenji , Nara Yasuo , Yamada Keisaku
Published: October 2008

Instability of the effective work function (WF) of metal/Hf-based high-k gate stacks was investigated by means of the flat-band voltage (Vfb) shift in capacitance-voltage curves and interface dipole characterized by x-ray photoelectron spectroscopy. We observed a negative Vfb shift and corresponding interface dipole, which suggest formation of oxygen vacancy (Vo) in the Hf-based oxides. In contrast, we observed an opposite (positive) Vfb shift and interface dipole when Au electrodes were formed on cleaned Hf-based dielectrics. This indicates that Au-Hf bond hybridization at the Au/HfSiON interface also causes effective WF modulation, as theoretically predicted by Shiraishi et al. Moreover, the interface dipole causing positive Vfb shift was found to be stable under vacuum and dry ambient, but it was gradually released when the gate stacks were exposed to the air and wet ambient.
The Application of X-ray Metrology for Rapid Development of High-k Dielectrics
Authors: Hung Pui Yee , Böscke Tim , Wormington Matthew , Bowen D. K. , Lysaght Pat , Kirsch Paul , Tseng Hsing-Huang , Jammy Raj
Published: October 2008

This study presents the application of X-ray metrology for phase engineering of high-k materials. In particular, grazing angle X-ray diffraction (GIXRD) is used to measure the phase and lattice constants of HfO2 doped with varying amounts of SiO2. Using the molar volume obtained from GIXRD as a guide, we narrow down the compositional range of SiO2 that exhibits a higher dielectric constant in device measurements. This scheme can be employed for screening dopants, optimizing composition, and reducing the typical development cycle from weeks to less than two hours.
Electrical and Chemical Properties of the HfO2/SiO2/Si Stack: Impact of HfO2 Thickness and Thermal Budget
Authors: Martinez Eugenie , Leroux Charles , Benedetto Nicolas , Gaumer Clement , Charbonnier Mathieu , Licitra Christophe , Guedj Cyril , Fillot Frédéric , Lhostis Sandrine
Published: October 2008

In this paper, we investigate the impact of thermal budget and HfO2 thickness on the chemical and electronic properties of the HfO2/SiO2/Si stack. In the first part, we have seen that high temperature anneal at 750{degree sign}C induces both the regrowth and the reoxidation of the SiO2 interfacial layer. O1s and C1s core level shifts indicate a bias drop along the whole stack of 1.1 eV. This bias drop is ascribed both to the interfacial dipole and to fixed charges in the dielectric. In the second part, ellipsometry and ultraviolet photoelectron spectroscopy are combined to deduce the HfO2 electron affinity (1.8{plus minus}0.2 eV). This value does not change with increasing thermal budget or dielectric thickness.
Annealing-temperature Dependence of Compositional Depth Profile and Chemical Structures of LaOx/ScOx/Si and ScOx/LaOx/Si Interfacial Transition Layer
Authors: Nohira Hiroshi , Takenaga Yoshinori , Kakushima Kuniyuki , Ahmet Parhat , Tsutsui Kazuo , Iwai H.
Published: October 2008

We have investigated the effects of post deposition annealing (PDA) on chemical structures of 4nm-LaOx, 4nm-ScOx/Si, 2nm-LaOx/2nm-ScOx/Si and 2nm-ScOx/2nm-LaOx/Si interfaces by angle-resolved X-ray photoemission spectroscopy. Analyses of Si 2s spectra show that the reactivity between ScOx and Si substrate is lower than that between LaOx and Si substrate. Analyses of O 1s spectra show that the absorption of moisture in the LaOx is suppressed by 2nm-ScOx/2nm-LaOx/Si structure. In addition, the electronic band structure of ScOx/Si(100) was decided.
Scanning Transmission Electron Microscopy Studies of Interface Stability and Point Defects in Gate Stacks with High-k Dielectrics
Authors: Stemmer Susanne , Agustin Melody P. , Klenov Dmitri O.
Published: October 2008

Advanced gate dielectric stacks are comprised of multiple layers of different materials, including high-k gate dielectrics, metal gate electrodes and interfacial layers with sub-nanometer thickness. The composition, point defect chemistry, interface atomic structure and interaction between the layers determine the properties of these gate stacks. This paper reviews recent applications of advanced scanning transmission electron microscopy techniques to determine the atomic structure and defects in advanced gate stacks.
Atomic Layer Deposition of High-κ/Metal Gate Stack MOSFET-Devices on Strained Silicon-on-Insulator Substrates
Authors: Henkel Christoph , Abermann Stephan , Bethge Ole , Reiche Manfred , Bertagnolli Emmerich
Published: October 2008

We investigate a new process scheme for the integration of Metal-Oxide-Semiconductor-Field-Effect transistor (MOSFET) devices on strained silicon-on-insulator (sSOI) substrates. As the gate dielectric we implement different Atomic Layer deposited high-k dielectrics, namely ZrO2 and Al2O3. For the formation of the source and drain regions an implantation free approach using a spin-on-dopant resist driven by a rapid thermal annealing step is employed. In this work we demonstrate the capabilities of this process scheme to be applied in future CMOS-technology.
Novel Highly Volatile MOCVD Precursors for Ta2O5 and Nb2O5 Thin Films
Authors: Yotsuya Tadahiro , Chiba Hirokazu , Furukawa Taishi , Yamamoto Toshiki , Inaba Koichiro , Tada Ken-ichi , Suzuki Takao , Fujimoto Koichi , Funakubo Hiroshi , Yamakawa Tetsu , Oshima Noriaki
Published: October 2008

Novel Ta and Nb compounds Ta(NtBu)(OtBu)3 (1) and Nb(NtBu)(OtBu)3 (2) were prepared as volatile liquid precursors for the MOCVD process. Ta2O5 and Nb2O5 films were obtained by using 1 and 2 in a lower temperature regime than pentaethoxy tantalum (PET) and pentaethoxy niobium (PEN). The deposition rates of 1 and 2 were higher more than 10 times than PET and PEN. Both precursors 1 and 2 gave conformal metal-oxide films, which exhibit excellent step coverage of over 90% on SiO2 holes with an aspect ratio of ca. 6.
In-Situ Studies of Interfacial Bonding of High-k Dielectrics for CMOS Beyond 22nm
Authors: Wallace Robert M.
Published: October 2008

Using in-situ synthesis and surface analysis, we examine the reactions of selected high-k dielectrics with candidate alternate channel materials, Ge and InGaAs, for CMOS applications beyond 22 nm. The study of the reaction of Hf-germanate on Ge and alumina on InGaAs are presented. The in-situ methods described enables the study of the bond formation at these interfaces, and enables a better understanding of the reaction mechanisms.
Improved Lower Electrode Oxidation of High-k TiCeO Metal-Insulator-Metal Capacitors by Using Dual Plasma Treatment
Authors: Cheng Chun-Hu , Hsu H. H. , Deng C. K. , Chin Albert , Chou C. P.
Published: October 2008

We have fabricated high-k Ir/TiCeO/TaN metal-insulator-metal (MIM) capacitors using a dual plasma treatment on bottom electrode. The novel plasma treatment suppresses the growth of bottom interface layer to reduce the degradation of capacitor performance under 400oC PDA. A low leakage current of 1.7x10-7 A/cm2 at -1 V and capacitance density of ~18 fF/μm2 at 1 MHz were obtained at 21nm TiCeO MIM devices; moreover, a 37 nm-thick TiCeO film has a capacitance density of 11 fF/um2, which gives a k value of 45. Consequently, the excellent device performance is due to the combined effects of the dual plasma treatment, high-k. TiCeO dielectric and a high work-function Ir metal
Plasma Nitridation of HfO2 Gate Dielectric on p-GaAs Substrates
Authors: Dalapati G K. , Sridhara Aditya , Wong Andrew S. , Chia C , Chi Dongzhi
Published: October 2008

Plasma nitridation (PN) method has been used for nitrogen incorporation in HfO2 based gate dielectrics for future GaAs-based CMOS devices. It has been demonstrated that the introduction of nitrogen in HfO2 on p-GaAs improves the interface quality and bulk oxide properties. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the plasmanitridation of HfO2 effectively suppresses the interfacial oxide formation and elemental out diffusion of As during thermal treatment. Such suppression of out-diffusion led to a substantial enhancement in the overall dielectric properties of the HfO2 film. It has been found that the metal-oxide-semiconductor device characteristics such as interface-state-density, accumulationcapacitance, hysteresis, and leakage current improve for nitrided HfO2 films on p-GaAs. An equivalent-oxide-thickness of 3.5 nm and leakage current density of 10-6 Acm-2 has been achieved at VFB -1 V, for nitrided-HfO2 films. In addition, the effects of nitrogen in HfO2 on band alignments have also been studied.
Interface Characterization of CeO2-Gated MOSFETs Using Gated Diode Method and Charge Pumping Technique
Authors: Chiu F. C. , Chen H. W. , Chen C. H. , Liu C. H. , Chen S. Y. , Huang B. S. , Hsieh Z. Y. , Huang H. S. , Hwang H. L.
Published: October 2008

Metal-oxide-semiconductor field-effect transistors (MOSFETs) incorporating CeO2 dielectrics were fabricated and investigated. In this work, the interfacial and electrical properties of CeO2/Si were characterized by gated-diode method and charge pumping technique. The lowest density of interface traps per area and energy (Dit) of CeO2/Si interface in comparison with other high-k material is about 7.3×1010 cm-2-eV-1 due to the very low lattice mismatch at CeO2/Si interface. The density of interface trap per area (Nit) determined using gated diode method is 6×109 cm-2. The minority carrier lifetime (tFIJ), the effective capture cross section of surface state (αs) and surface recombination velocity (so) extracted using gated-diode method are 4.09×10-8 s, 7.14×10-14 cm2 and 4310 cm/s, respectively. Furthermore, a comparison with MOSFETs using the other high-k materials as gate dielectrics was also made.
Modelling of Layers and Traps in High-Κ Gate Stacks and Energy Band and Equivalent Circuit Representations
Authors: Kar Samares , Rawat S.
Published: October 2008

Five layers - two bulk and three chemically graded layers - have been identified to constitute the high-K gate stack; the bulk layers being the intermediate oxide and the high-K layers; the three chemically graded layers being the silicon/intermediate-oxide, the intermediate-oxide/high-K, and the high-K/metal-oxide interfacial layers. Energy band diagrams across the silicon space-charge, the five gate stack, and the metal layers, have been modeled, in which graded band-gap in the chemically graded layer, and the effects of the electric fields and image force barrier lowering have been considered. Response of traps in all the five layers of the gate stack to an applied small signal has been modeled, including the profile of the quasi-Fermi function in the gate stack. Relations for the potentials across the five gate stack layers have been formulated. Finally, small-signal equivalent circuit representations have been developed for the entire gate stack and the silicon space-charge layer.
Electrical Characterization of Metal Gate/High-k Dielectrics on GaAs Substrate
Authors: Budhraja Vinay , Misra D.
Published: October 2008

This paper investigates the electrical characteristics of HfO2 on GaAs substrate through C-V and I-V measurements to understand the interface trap density characteristics of Ti-Au/HfO2/p-GaAs gate stack. Interface state density, Dit, estimated for as-deposited Ti-Au/HfO2/GaAs capacitors was found to be 3.68x1011cm-2eV-1. Low temperature measurement suggests that only fast interface states contribute to the conduction process. Further degradations were observed for devices subjected to a post-deposition annealing (PDA) at 900C. When the characteristics of two different metal gates were compared, the capacitance density observed to be 1.4 fF/μm2 and 8.98 fF/μm2 for Be-Au/HfO2/GaAs and Ti-Au/HfO2/GaAs respectively in accumulation region at 1 MHz. After annealing, the value of capacitance density decreased significantly mainly because of reduction in dielectric constant.
Real Space Surface Reconstructions of Decapped As-rich In0.53Ga0.47As(001)-(2×4)
Authors: Shen Jian , Winn Darby L. , Melitz Wilhelm , Clemens Jonathon B. , Kummel Andrew C.
Published: October 2008

The surface reconstructions of decapped In0.53Ga0.47As(001) have been studied using scanning tunneling microscopy (STM). It is shown that the As-rich α2(2×4) and β2(2×4) reconstructions, predicted by density function theory (DFT) (1-3) for GaAs(001)-(2×4), InAs(001)-(2×4) and InGaAs(001)-(2×4) surfaces, were observed to coexist on In0.53Ga0.47As (001). In contrast to molecular beam epitaxy (MBE) grown In0.53Ga0.47As(001), the STM results on decapped In0.53Ga0.47As(001) do not show the existence of the heterodimer In0.53Ga0.47As(001)-(4×3) structure (4-5). At the intermediate annealing temperature ranges of 400 - 440oC, a (2×4)-(4×2) mixed surface reconstruction was observed. When In0.53Ga0.47As(001)/InP sample was annealed between 440oC and 470{degree sign}C, a pure In/Ga-rich (4×2) surface reconstruction was observed.
Tuning of Material and Electrical Properties of Strontium Titanates using Process Chemistry and Composition
Authors: Katamreddy Rajesh , Omarjee Vincent , Feist Benjamin , Dussarrat Christian , Singh Manish , Takoudis Christos
Published: October 2008

In this work, we study the compatibility of a highly volatile strontium precursor, HyperSr, which has a low melting point, good thermal stability and good reactivity, with various Ti precursors for atomic layer deposition (ALD) of strontium titanates (STO). Novel Ti precursors studied for STO deposition include PrimeTi & StarTi. We will then discuss the interesting trends in material properties observed in STO films deposited with various compositions. X-ray photoelectron spectroscopic analysis of ALD SrO films showed the presence of carbonate groups in the film. There is the potential that this carbonate species is inherent to the ALD process; however, it has been reported that SrCO3 forms when SrO films are exposed to atmospheric CO2. To isolate the effects of atmospheric exposure on the carbonate formation in the film, a TiO2 capping layer is used on the surface of ALD SrO films and the resulting film structures are analyzed.
Effect of Rare-Earth Doping and Nitrogen Passivation Treatments on the Properties of Ultra-thin Hafnia Films
Authors: Ramanathan Shriram , Karthikeyan Annamalai , Govindarajan Shrinivas , Kirsch Paul
Published: October 2008

Rare-earth doped hafnia films are of great interest as higher-k dielectrics that could potentially function as alternate gate dielectrics on Si and other high-mobility semiconductor channels. We present results on the effect of nitridation on electrical and dielectric properties of hafnia films prepared by physical vapor deposition. Particular emphasis is placed on passivation of point defects by nitrogen studied through high temperature electrochemical conductivity measurements.
Effect of Annealing on Electronic Characteristics of HfSiON Films fabricated by Damascene Gate Process
Authors: Yamabe Kikuo , Murata Kouichi , Hayashi Tomohiro , Tamura T C. , Sato Motoyuki , Uedono Akira , Shiraishi Kenji , Umezawa Naoto , Chikyow Toyohiro , Watanabe Heiji , Nara Yasuo , Ohji Yuzuru , Miyazaki S. , Yamada Keisaku , Hasunuma Ryu
Published: October 2008

The conduction mechanism of HfSiON stacked-gate dielectric films after a spike annealing is investigated. FETs fabricated using the Damascene process is used to evaluate the electronic characteristics of a stacked-gate dielectric film. The effect of an additional spike annealing after the TiN gate electrode fabrication on the conductivity is analyzed. The electron current over the entire range of gate voltage is increased, while the hole current remains unchanged. The TAT and Schottky analyses derive a consistent energy level of the intermediate trap centers contributing to the electron conduction. The average lifetime is improved by annealing. However, the spike annealing does not change the slope of the TDDB Weibull plots. The average lifetime is improved by annealing. From NBTI analyses, the threshold voltages displayed linearly shifts with increasing injection charge concentration, both with and without the spike annealing. The slope of the threshold voltage shift is defined as a degradation rate.
PEMFC Model Development for Designing MEA: Model Validation and a Parameter Study for Low Humidity Operations
Authors: Nonoyama Nobuaki , Ikogi Yoshihiro
Published: October 2008

We have developed mathematical models of PEMFC to design MEA. For quantitative simulations, a model is required to reflect the effects of the physical properties of each component and the operating conditions of a cell accurately. Therefore, the model was constructed with as many principal physical equations as possible and was validated with experimental data from a wide range of conditions. Here, we examined the effect of some physical parameters of membrane for low-humidity operation. The importance of water diffusion as well as proton conductivity was shown. The orders of performance for small-size cells with high gas stoichiometry are often different from that of large-size cells with the same parameters. The reason for this discrepancy is explained.
A Three-dimensional, Two-fluid Model of PEM Fuel Cell Cathodes
Authors: Berning Torsten
Published: October 2008

This research focuses on the analysis of multi-phase flow through the porous media of the cathode side of a PEM Fuel Cell using a three-dimensional, multi-fluid model based on computational fluid dynamics (CFD). In a first step, it is assumed that all product water exists and leaves the cell in the liquid phase, and its flow through the catalyst layer, micro-porous layer, and gas diffusion medium is investigated as function of in- and through plane hydraulic permeability, effective contact angles, and irreducible saturation of each layer. The effect of under-the-land compression on the predicted water saturation level will be discussed. Finally, the important role of the pore size distribution of the porous media on the liquid water transport and predicted saturation level ("flooding") is highlighted, and a qualitative approach to obtain the capillary pressure curve as function of liquid saturation for different types of porous media will be outlined.
Steady-State Fuel Cell Performance Model for Unadhered MEAs
Authors: Desouza Andrew J. , Bradean Radu , Branzea Virginia , Hamada Stephen , Kleemann Joerg , Haas Herwig , Roberts Joy , Gallagher Emerson
Published: October 2008

Membrane electrode assemblies (MEAs) that were initially adhered at the cathode-catalyst-layer/cathode-porous-electrode (CCL/CPE) interface can become unadhered at this interface because of operational stressors. Unadhered MEAs may have an additional electrical contact resistance between the CCL and the CPE that was not present for adhered MEAs. This paper investigates the impact of an electrical contact resistance between the CCL and the CPE on fuel cell performance. Model predictions and experimental results are compared for adhered and un-adhered MEA designs operating in plates with different gas distribution channel geometries for a wide range of operating conditions. Model and experiment indicate that the effect of an electrical contact resistance between the CCL and the CPE can lead to significant performance loss.
A Multiphase, Two-Fluid Model for Water Transport in a PEM Fuel Cell
Authors: Jain Kunal , Cole James Vernon , Kumar Sanjiv , Gidwani Ashok , Vaidya N.
Published: October 2008

A finite volume based computational method for predicting two-phase flows in fuel cells is presented. The model formulation and numerical algorithms are selected to provide robustness and accuracy, while allowing the treatment of important phenomena relevant to fuel cell water management such as segregation of the phases to form films and slugs in gas channels. Variations in the algorithms for computing pressure corrections and phase fractions are assessed using water-air flows in fuel cell channel geometries. The accuracy of the model is evaluated by comparison to benchmark simulations, measured pressure drop data for air-water flows, and analytical solutions for capillary pressure in porous media. The results indicate that the selected formulation is sufficiently stable and accurate to serve as the basis for a detailed model of water transport in fuel cells.
Multi-scale Simulation Approach for Polymer Electrolyte Fuel Cell Cathode Design
Authors: Koyama Michihisa , Kim Donghyun , Kim Boyeong , Hattori Tatsuya , Suzuki Ai , Sahnoun Riadh , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Del Carpio Carlos , Deka Ramesh , Kubo Momoji , Miyamoto Akira
Published: October 2008

Toawrd rational design of polymer electrolyte fuel cell (PEFC), understandings of both atomistic scale and systems characteristics are important. Multi-scale simulation can contribute to bridging microscopic and macroscopic understandings effectively. In this manuscript, we described a multi-scale simulation approach based on an original porous structure simulator and computational chemistry methods. Proton conductivity was estimated by molecular dynamics method and structures of porous catalyst layer were modeled by the porous structure simulator. Multi-scale simulations for macroscopic current-voltage characteristics of PEFC were performed considering both atomistic-scale properties and porous microstructure. Influences of atomistic properties and microstructure of porous catalyst layer on macroscopic current-voltage characteristics were successfully studied. Effectiveness of the developed multi-scale simulation approach was confirmed from the simulation results.
IrCo Metal-alloy As a Novel Anode Catalyst for PEFCs
Authors: Qiao Jinli , Zheng Jun Sheng , Li Bing , Ma Jianxin
Published: October 2008

Binary IrCo alloy as a novel substitute for platinum has been viewed as the anode catalyst in hydrogen-air fuel cells. The resulting IrCo/C of 50/50 ratio, heat treated at 800{degree sign}C in argon atmosphere, shows promising catalytic performance in terms of hydrogen oxidation reaction. Results of electrochemical characterization, which was performed using a rotating disc electrode (RDE) by cyclic voltammetry (CV) and liner sweep voltammetry (LSV), with emphasis on the activity of the catalyst are presented.
No-platinic and Low Platinic Electrocatalysts for Fuel Cell Application
Authors: Sebastian Pahiyamattom J. , Valenzuela Edgar , Joseph Shine , Moreira Joel
Published: October 2008

The authors studied no-platinic and low-platinum containing electrocatalysts for fuel cell application. The electrocatalysts were based on Pt, Ru, Mo, W, Pd and Au. In some cases Pt was alloyed with these elements and in others without Pt and also alloyed among the non-platinic catalysts. The Pt-M (M represents the non-platinic element) and no-platinic catalysts exhibited better characteristics for oxidation of fuels other than hydrogen. All the catalysts showed suitable characteristics for oxygen reduction reaction. The catalysts were synthesized by a thermal pyrolysis of the carbonyl compounds or by a chemical reduction of the chlorides of the corresponding elements. The catalyst performance depended on the particle size, distribution on the gas diffusion electrode, type of catalyst support, the alloy composition etc. The nanostructured catalysts were characterized by high resolution transmission electron microscope (TEM), x-ray diffraction (XRD) and the electrochemical techniques.
Platinum-free Carbon Nitride Electrocatalysts for PEMFCs Based on Pd, Co and Ni: Effect of Nitrogen on the Structure and Electrochemical Performance
Authors: Di Noto Vito , Negro Enrico , Lavina Sandra , Boaretto Nicola , Piga Matteo
Published: October 2008

This report describes two new synthesis protocols for the preparation of "core-shell" platinum-free electrocatalysts consisting of graphite cores covered by carbon nitride shells embedding the active sites. The resulting systems are characterized by a well-controlled chemical composition with different wt% of nitrogen in their supports. The protocols rely on the thermal decomposition of precursors obtained by networking suitable metal coordination complexes with an organic binder over active carbon nanoparticles. The resulting electrocatalysts showed a higher thermal stability in oxidizing conditions with respect to a reference system. The materials provided a remarkable performance in the oxygen reduction reaction (ORR), even if a lower selectivity towards the desired 4-electron pathway is observed. Membrane electrode assemblies (MEAs) tested in operative conditions with the proposed materials applied at the cathode required a lower mass of noble metal (up to 0.46 g/kW) to achieve the same electrical power as the platinum-based reference (1.1 g/kW).
Polyaniline-derived Non-Precious Catalyst for the Polymer Electrolyte Fuel Cell Cathode
Authors: Wu Gang , Chen Zhongwei , Artyushkova Kateryna , Garzon Fernando H. , Zelenay Piotr
Published: October 2008

This paper focuses on a new polyaniline-derived non-precious cathode catalyst with high oxygen-reduction activity, verified in electrochemical and fuel cell testing. The rotating disk (RDE) onset and half-wave potential of oxygen reduction were measured at 0.90 V and 0.77 V, respectively. Rotating ring-disk electrode (RRDE) study revealed very good selectivity in the four-electron reduction, with peroxide yields below 1% (0.4% at 0.4 V). Similarly, the catalyst showed good performance in the hydrogen-air fuel cell, even at high cell operating voltages, yielding 0.04 A cm-2 at 0.80 V and 0.21 A cm-2 at 0.6 V. Fuel cell life test at a constant voltage of 0.4 V demonstrated promising stability up to 450 hours, generating a current density of approximately 0.32 A cm-2, a respectable performance for a non-precious cathode catalysts operated on air rather than oxygen. Ex situ characterization pointed to pyridine- and pyrrole-like metal species as likely active ORR sites.
Fuel Cell Vehicle and Infrastructure Learning Demonstration Status and Results
Authors: Wipke Keith B. , Sprik Sam , Kurtz Jennifer , Garbak John
Published: October 2008

The "Controlled Hydrogen Fleet and Infrastructure Demonstration and Validation Project," is a five-year U.S. Department of Energy (DOE) project started in 2004. The purpose of this project is to conduct an integrated field validation that examines the performance of fuel cell vehicles and the supporting hydrogen infrastructure. NREL has analyzed data from almost three years of the five-year project. During this time, 92 vehicles have been deployed, 15 project refueling stations were placed in use, and no fundamental safety issues have been identified. We've analyzed data from over 200,000 individual vehicle trips covering 1,100,000 miles traveled and over 40,000 kg hydrogen produced or dispensed. Public analytical results for this project are in the form of composite data products, which aggregate individual performance into a range that protects the intellectual property and the identity of each company, while still publishing overall status and progress.
Development of Fuel Cell Hybrid Vehicle in Toyota
Authors: Kojima Koichi , Morita Toru
Published: October 2008

Concerns surrounding the timing of peak oil for conventional fossil fuels (i.e., the point at which the maximum global production rate will be reached) and the growing need to reduce CO2 emissions are increasing the importance of energy source diversification. For vehicles, this can be accomplished by more efficient internal combustion engines (ICE), the use of bioethanol, more widespread application of ICE-hybrid systems, and the development of technologies that use electricity and hydrogen, such as plug-in hybrid vehicles (PHV) and fuel cell hybrid vehicles (FCHV). Since Toyota started limited lease of the Toyota FCHV, the world's first market-ready fuel cell vehicle, in 2002, Toyota has steadily improved the technology, and has succeeded in significantly extending the vehicle's cruising range in actual driving conditions and enhancing its cold start capabilities. For the next step, Toyota aims to work toward the commercialization and popularization of fuel cell vehicles by focusing on reducing costs and improving durability, and by cooperating with governments and energy companies to establish hydrogen infrastructure.
First-principles Investigations of Electrocatalysis and Corrosion
Authors: Greeley Jeffrey
Published: October 2008

Three case studies of the use of Density Functional Theory calculations to model electrochemical phenomena are presented. These studies range from fundamental investigations of electrocatalytic reaction mechanisms to detailed atomistic analyses of dissolution and dealloying phenomena. The studies are intended to illustrate how first principles calculations are beginning to complement and enhance well-established experimental results in electrochemistry.
Current Progress of Electrocatalyst R&D in TKK
Authors: Tada Tomoyuki , Yamamoto Yumi , Matsutani Koichi , Hayakawa Katsuichiro , Namai Tatsunori
Published: October 2008

After optimization of the preparation procedure and the alloy composition of a PtCo catalyst, we found that MEA of the PtCo catalyst could show better I-V performance than that of a Pt catalyst. To improve the stability of a carbon support, we have evaluated various types of carbon, and we found a graphitized carbon could show better stability than a normal carbon. We also evaluated the PtCo catalyst on the graphitized carbon to achieve both better ORR activity and better stability of carbon, but the PtCo catalyst on the graphitized carbon could not show any ORR activity improvement due to the larger particle size of PtCo. After exploring new carbons, we could find a unique carbon which has higher surface area and better stability than a normal carbon. We prepared the PtCo catalyst on the carbon, and this catalyst could show good balance between the ORR activity and the carbon stability.
Electrocatalyst Durability under Simulated Automotive Drive Cycles
Authors: Uchimura Masanobu , Sugawara Seiho , Suzuki Yosuke , Zhang Jianbo , Kocha Shyam S.
Published: October 2008

Proton Exchange membrane fuel cells (PEMFCs) for automotive applications are subject to hundreds of thousands of potential or load cycles during normal operation of the vehicle. Pt dissolves under such cycling and is a major contributing factor to the lowered durability of PEMFCs. This paper details the effect of various simplified potential-cycle profiles, the effect of operating conditions such as temperature, relative humidity, reactant gases etc., as well as different catalyst materials under normal fuel cell operating voltage ranges (0.95-0.60V) in fuel cells. Results on Pt dissolution utilizing complementary ex-situ methods are also presented. The fundamental and practical implications of varying the operating parameters as well as a possible hypothesis for Pt dissolution are reported.
Anion Exchange Membrane and Ionomer for Alkaline Membrane Fuel Cells (AMFCs)
Authors: Yanagi Hiroyuki , Fukuta Kenji
Published: October 2008

We newly developed the anion exchange membranes and ionomers for alkaline membrane fuel cell system. The AEMs consist of hydrocarbon type main chain and quaternary ammonium groups as ion exchanging site, and they show sufficient OH- conductivity and thermal durability. The ionomer also consists of hydrocarbon type main chain and quaternary ammonium groups. It shows applicable OH- conductivity for the catalyst layer of fuel cells. We evaluated the cell performance based on the developed membrane and ionomer . It shows sufficient cell output even if the ambient air was used as the oxidant.
Electro-osmosis and Water Uptake in Polymer Electrolytes in Equilibrium with Water Vapor at Low Temperatures
Authors: Gallagher Kevin G. , Pivovar Bryan S. , Fuller Thomas F.
Published: October 2008

Measurements of the electro-osmotic drag coefficient for Nafion® and both random and multi-block co-polymer sulfonated poly(arylene ether sulfone) (BPSH) chemistries are reported for vapor equilibrated samples below 0 {degree sign}C. No significant change in the drag coefficient behavior for Nafion from that reported above 0 {degree sign}C is found. However BPSH is found to have a drag coefficient of 0.4. The implication of a drag coefficient less than unity in the interpretation of conduction mechanisms is discussed. Measurements of water sorption isotherms below 0 {degree sign}C are also presented. A significant reduction in the capacity of polymer electrolytes to store water below 0 {degree sign}C is found. This reduced water content is a result of the lower vapor pressure of ice compared to supercooled liquid.
Water Dynamics in a PEM Fuel Cell: Effect of Current and Humidity Transients
Authors: Davey John , Mukundan R. , Spendelow Jacob , Hussey Daniel S. , Jacobson David , Arif Muhammad , Borup Rodney L.
Published: October 2008

The water dynamics of the membrane electrode assembly (MEA) of a 50 cm2 polymer electrolyte membrane (PEM) fuel cell was studied in response to current and humidity step transients as a function of inlet relative humidity (RH) and cell operating temperature. MEA water content change was monitored by high frequency resistance (HFR) and in situ neutron imaging. The MEA "wetting" response was significantly faster (10-30 seconds) than the reciprocal "drying" response (several minutes). The wetting response to increasing current appears faster than that to increasing gas inlet RH. Wetting and drying responses to gas inlet RH transients are greater at low current densities showing the dominating effect of current wetting over gas inlet humidity effects. Operating the fuel cell at 40oC with no inlet gas humidification, a current wetting response was observed and 34 amps of current sustained. This showed that reaction water produced at the cathode is sufficient to support high current density if the drying effect of inlet gases is low. It also suggests that back diffusion of reaction water to the MEA is sufficient to account for the fast drop in HFR. In situ neutron imaging results show that GDL wetting is also faster than drying but on a slower time scale than that for the MEA. However, MEA and GDL drying are on a similar slow time scale and are coupled because water diffusing out of the MEA must move through the GDLs.
An Analysis of The Water Transport Properties of Polymer Electrolyte Membrane
Authors: Aotani Koichiro , Miyazaki Shin-ichi , Kubo Norio , Katsuta Masafumi
Published: October 2008

Water transport resistance through the polymer electrolyte membrane was evaluated by measuring the water permeability of it. From the results of a thickness sensitivity evaluation, two types of water transport resistance were found. One was "internal diffusion resistance," which was proportional to the membrane thickness, and the other was "interfacial transport resistance," which was independent of thickness. This interfacial resistance was found not to be negligible. Furthermore, both resistances showed sensitivity to temperature and relative humidity. The internal diffusion coefficient estimated from the results of water permeation experiments correlated well with the results obtained by the pulse field gradient nuclear magnetic resonance (PFG-NMR) method. And, the electro-osmotic drag coefficient was also measured by the proton pump balance method based on the water permeation test system. It was concluded that water permeation experiments are helpful for obtaining a better fundamental understanding of water transport mechanism through the membrane.
Aging Studies of Pt/Glassy Carbon Model Electrocatalysts
Authors: Gu Yunlong , St-Pierre Jean , Goeke Ronald S. , Datye Abhaya , Atanassov P.
Published: October 2008

A model Pt catalyst nano-array on planar glassy carbon was synthesized and subjected to a potential cycle aging procedure. Preliminary experimental data suggest a similar degradation behavior as gas diffusion electrodes with an observed decrease in surface area (decrease in H2 and CO oxidation peak areas as determined by cyclic voltammetry). Atomic force microscopy topography images support this conclusion.
Analysis of Pt Catalyst Degradation of a PEFC Cathode by TEM Observation and Macro Model Simulation
Authors: Takeshita Tomohiro , Murata Hajime , Hatanaka Tatsuya , Morimoto Yu
Published: October 2008

Pt particle size distributions at various positions in a cathode catalyst layer were evaluated by transmission electron microscopy (TEM) observation before and after a potential cycling test and by simple 1D macro model simulation to describe the degradation phenomena. Both the results showed similar tendencies: at the position near the membrane, the number of Pt particles for all sizes decreased with time; in contrast, at the position near the gas diffusion layer (GDL), the number of large Pt particles increased. The validity of this model is not verified yet because the precision of parameters is not confirmed. This model, however, can be used as a tool for deeper understanding of Pt degradation.
A Non-Precious Electrocatalyst for Oxygen Reduction Based on Simple Heat-Treated Precursors
Authors: Chung Hoon T. , Johnston Christina M. , Garzon Fernando H. , Zelenay Piotr
Published: October 2008

An active, non-precious catalyst for electrochemical oxygen reduction was made by heat-treating simple precursors. The current density obtained in an H2/O2 PEM fuel cell was as high as 0.34 A/cm2MEA at 0.65 V. The oxygen-reduction activities of catalysts prepared at different temperatures over the range 800-1050{degree sign}C were shown to be equivalent by the Rotating Ring Disk Electrode (RRDE) method. The nitrogen content, however, was observed by XPS to be highly variable with preparation temperature. Thus, in contrast to some reports in the literature, the surface nitrogen content was not strongly correlated to performance. The nature of the active site(s) is currently under investigation.