bluuebunny/crossref_metadata_2025 huggingface dataset:
High-k Materials in Flash Memories
Authors: Alessandri Mauro , Piagge Rossella , Alberici Stefano , Bellandi Enrico , Caniatti Massimo , Ghidini Gabriella , Modelli Alberto , Pavia Giuseppe , Ravizza Enrica , Sebastiani Alessandro , Wiemer Claudia , Spiga Sabina , Fanciulli Marco , Fiorentini Vincenzo , Cadelano Emiliano , Lopez Giorgia Maria
Published: November 2006

The scaling down of Flash memories can be pursued using the conventional stacked gate architecture only with major changes of the active dielectrics, mainly the inter-poly dielectric (IPD).The required 4-6 nm EOT thickness for the IPD cannot be achieved by the conventional ONO (Oxide-Nitride-Oxide) technology which starts failing in the 10-12 nm range in terms of charge retention properties. Therefore high-k materials are currently investigated for IPD formation in future Flash memories. It is worth noticing that the requirements for IPD are very different from those of the gate dielectrics used in logics. Alumina and alumina based materials (like hafnium aluminates) are among the possible candidates. Promising and tunable electrical and structural properties are achieved for these materials by varying the high-k stack chemical compositions and post- deposition thermal treatments. Different material combinations have been selected as potential solutions for the replacement of the conventional ONO (Oxide-Nitride-Oxide) stack.
Rare-Earth Metal Scandate High-k Layers
Authors: Zhao Chao , Heeg Tassilo , Wagner Martin , Schubert Jurgen , Witters Thomas , Brijs Bert , Bender Hugo , Richard Olivier , Afanas'ev Valeri , Houssa Michel , Caymax Matty , De Gendt Stefan
Published: November 2006

Ternary rare-earth metal scandate layers deposited using pulsed laser deposition (PLD) were studied as dielectrics for high-k applications. GdScO3, DyScO3 and LaScO3 blanket layers with different nominal thicknesses were deposited directly on 2-inch Si (100) substrates for physical characterizations and 2-inch substrates with a lateral SiO2 isolation structure, for capacitor formation with wet-etched electrodes. High- temperature X-ray diffraction (HT-XRD) and TEM reveal that DyScO3 and GdScO3 remain amorphous up to 1000C. The as- deposited DyScO3 layer on both 1nm chemical SiO2 and HF-last surface of Si shows good interface properties as revealed by C- V curves. The leakage current through the layers is comparable to or even lower than that through HfO2 layers of the same EOT. Material properties show sensitivity to annealing conditions.
Y-Doped HfO2 Thin Films Grown by Injection MOCVD
Authors: Rauwel Buzin Erwan , Ducroquet Frederique , Rossell Marta , Verbeeck Jo , Van Tendeloo Gustaaf , Hollaender Bernd , Rushworth Simon , Dubourdieu Catherine
Published: November 2006

HfO2 based compounds are extensively studied as possible gate oxides to replace SiO2 for future advanced microelectronic applications. In this paper we investigated the addition of Y in HfO2 and subsequently the possible stabilization of the cubic structure of HfO2. The films were grown on (001)Si/SiO2 by liquid injection Metal Organic Chemical Vapor Deposition. They were characterized by X-ray diffraction, X-ray reflectometry, attenuated total reflection infrared spectroscopy and Rutherford backscattering spectrometry. Electrical measurements (C-V and I-V) were carried out on MOS structures after evaporation of gold electrodes. For yttrium content starting at ~ 6 % the cubic structure of HfO2 is formed and the monoclinic phase is no longer observed by X-ray diffraction and infrared spectroscopy. An effective permittivity of 14-17 is obtained for Y content in the range 6- 10 %.
Prospect of Hf-Based Gate Dielectric by PVD with FUSI Gate for LSTP Application
Authors: Niwa Masaaki , Mitsuhashi Riichirou , Hayashi Shigenori , Yamamoto Kazuhiko , Harada Yoshinao , Kubota Masafumi , Rothchild Aude , Hoffmann Thomas , Kubicek Stefan , De Gendt S. , Heyns Marc , Lauwers Anne , Biesemans Serge , Kittle Jorge
Published: November 2006

Study of Hf based high-k gate stack, HfO2 and its silicate, prepared by PVD-high k dielectric and Ni-Fully Silicide(FUSI) gate focusing on interfacial reaction between high-k and Ni- FUSI electrode is overviewed. Effects of SiN capping between Ni-FUSI gate and high-k dielectric and post deposition anneal (PDA) to suppress the reaction during FUSI process were investigated. The SiN cap could increase transistor yield and PDA could suppress instability of the drive current due to defects/roughness caused by interfacial reaction during NiSi formation. It is noteworthy that not only elimination of poly- depletion but also EOT reduction was observed by replacing the poly Si with the Ni-FUSI, which was remarkable for Ni- FUSI/SiON than HfO2 case. Hereof, by optimizing the PDA condition with SiN cap, decent electrical characteristics were obtained, Ion(n/p) > 600/200 uA/um at Ioff = 20 pA/um at Vdd = 1.1V. This drivability meets low stand-by power specification of the MOSFET for 45nm node.
Structural Effects in the Dielectric Constant of Rare-Earth Oxides: Nd2O3
Authors: Busani Tito , Devine Roderick , Gonon Patrice
Published: November 2006

Thin films of Nd2O3 have been studied. For the amorphous phase the dielectric constant is ~ 11 whilst the refractive index is 1.76 {plus minus} 0.02, in the cubic form these values are ~ 13.6 - 15.4 and 1.93 {plus minus} 0.02. Hexagonal films have dielectric constants in the range 17 - 21 and estimates based upon the cubic values lead to k ~ 27, we were unable to determine a reliable refractive index value. The normally high temperature hexagonal phase could be nucleated on a Si substrate by deposition at relatively low temperature ~ 280 {degree sign}C.
Quality Improvement and Electrical Characteristics of High-k Films after Receiving Direct Superimposed with Alternative Current Anodic Oxidation Compensation
Authors: Hwu Jenn-Gwo , Chang Chia-Hua , Wang Tsung-Miau
Published: November 2006

A novel, cost-effective compensation method with low thermal budget is proposed to improve the quality of high-k HfO2 films. Anodic oxidation using direct superimposed with alternating current (DAC-ANO) in deionized water was carried out on as-grown high-k films to compensate the defects in the dielectrics. The main contribution of the technique proposed in this work comes from the idea that the reaction between OH- anions and imperfect Hf-O bonds is useful for the improvement of the electrical characteristics. Investigations of leakage current densities, breakdown fields, interface states, and constant dielectric field reliability, demonstrate that the devices that receive anodic oxidation compensation exhibit better characteristics than ones that do not. The anodic compensation technique is a novel, cost-effective and promising process to improve the characteristics of high-k gate dielectrics.
Theoretical Studies on the Physical Properties of Poly-Si and Metal Gates/HfO2 Related High-k Dielectrics Interfaces
Authors: Shiraishi Kenji , Torii Kazuyoshi , Akasaka Yasushi , Nakayama Takashi , Nakaoka Takashi , Miyazaki Seiichi , Chikyow Toyohiro , Yamada Keisaku , Nara Yasuo
Published: November 2006

We have theoretically investigated poly-Si and metal gates on Hf-related high-k gate dielectrics. First, we have investigated the cause of the substantial threshold voltage (Vth) shifts observed in Hf-related high-k gate stacks with p+poly-Si gates. The oxygen vacancy (Vo) level in ionic HfO2 is located in a relatively higher part of the band gap. If the p+poly-Si-gate is in contact with HfO2, Vo formation in the HfO2 induces a subsequent electron transfer across the interface because of the higher energy level position of Vo, causing a substantial Vth shifts in p+poly-Si gate MISFETs. Next, we also investigate the microscopic electronic structures at metal gates/HfO2 interfaces. We have found that the wave functions of metal induced gap states (MIGS) have large amplitudes both around Hf and O atoms, which may be the cause of unusual work function behaviors of p-like metals.
HfSiON Gate Dielectrics for hp45 Node and Beyond
Authors: Nara Yasuo , Inumiya Seiji , Torii Kazuyoshi , Nakamura Kunio
Published: November 2006

In order to fabricate sub-0.9nm EOT HfSiON gate dielectrics, we have investigated post-high-k-deposition processes. We found that plasma nitridation and post-nitridation annealing are the key processes for realizing low leakage currents and high carrier mobility with reduced EOT. By using low-pressure plasma nitridation and high temperature post-nitridation annealing, we have successfully fabricated a 0.81nm-EOT HfSiON gate dielectric with a gate leakage current of 0.74A/cm2 at 0.7V and an electron mobility of 235cm2/Vs at 0.8MV/cm, which can be applied to low operating power devices at the hp45 and hp32 technology nodes.
Electrical Breakdown and Reliability of Metal Gate - La2O3 Thin Films after Post Deposition Annealing in N2
Authors: Molina Joel , Tsutsui Kazuo , Iwai H. , Kakushima Kuniyuki , Sugii Nobuyuki , Ahmet Parhat
Published: November 2006

We report the electrical characteristics and reliability of Metal-La2O3 stacks on silicon after Post Deposition Annealing (PDA) of La2O3 in N2. MIS capacitors were fabricated and their C-V and I-V characteristics before and after applying a Constant Voltage Stress (CVS) in the substrate injection condition were evaluated. By using 2 different physical thickness for La2O3, the same Equivalent Oxide Thickness EOT ~ 1.5nm is obtained for Al-gated and W-gated La2O3 stacks. This is explained by the presence of an already existent Al2O3 interfacial layer IL at the Al-La2O3 interface which results in a lower k for the total oxide stack. It is speculated that the physical thickness of this IL slightly increases after stress, which can be seen as degradation in the C-V characteristics of the Al-La2O3-nSi structure. This can be explained by the use of a modified Reaction-Diffusion (R-D) model, which is based on the Electric Stress-Induced Defect Generation (ESIDG) mechanism (1). Finally, longer lifetimes before breakdown were obtained for W-gated La2O3 MIS capacitors and a 10 years operation is guaranteed by using both the linear or reciprocal Vg models.
Evidence of Deep Energy States from Low Temperature Measurements and Its Role in Charge Trapping in Metal Gate/Hf-Silicate Gate Stacks
Authors: Chowdhury Naser A. , Srinivasan Purushothaman , Misra D.
Published: November 2006

Pre-existing electron and hole trap energy levels, lying deep within the bulk high-k bandgap, are experimentally observed from low temperature measurements for the first time in metal organic chemical vapor deposited (MOCVD) TiN/HfSixOy based gate stacks. Their role in trapping under constant voltage and substrate hot hole stress conditions is investigated. Mixed degradation due to both electron and hole trapping in the deep pre-existing bulk traps, which induces a turn-around effect in flatband voltage shift (DVFB), is observed for n-channel MOS capacitors under gate injection. Bulk hole trap generation, which causes DVFB to follow tn power law dependence, is observed for p+-ringed p-channel MOS capacitors under substrate hot hole injection. Activation energies of the stress induced traps and pre-existing deep defects are experimentally found to be different.
Asymmetric Distribution of Charge Trap in HfO2-Based High-k Gate Dielectrics
Authors: Higuchi Keiichi , Naito Tatuya , Uedono Akira , Shiraishi Kenji , Torii Kazuyoshi , Boero Mauro , Chikyow Toyohiro , Yamasaki Satoshi , Yamada Keisaku , Hasumuma Ryu , Yamabe Kikuo
Published: November 2006

The time-dependences of leakage currents by electrons and holes flowing through HfO2-based high-k gate dielectric films under constant voltage stresses are investigated by a carrier separation method using field-effect transistor structures. The ratio of the electron current to the hole current depended on gate voltage and the type of transistors. In the case of unbalanced charge injection, the trapping of the major leakage current carriers controlled the time dependence of both leakage currents. However, in the case of balanced injection, some of the injected electrons were trapped near the gate, while some of the injected holes were trapped near the substrate, giving rise to the both current reduction. As a result, both leakage currents reduced. Capacitance change during the relaxation after the removal of the gate voltage stress was consistent with the leakage current change. The relationship between the electron-/hole-trapping centers and oxygen-related defects in high-k dielectric films is discussed.
ALD for Data Storage Applications
Authors: Mao Ming , Bubber Randhir , Schneider Thomas
Published: November 2006

A variety of ALD applications were explored for manufacturing magnetic recording heads, concentrating on AlOx. ALD AlOx films were prepared in a broad thickness range from 5 to 4500 Aå at temperatures from 80 to 300 {degree sign}C and at a maximum growth rate of ~120 Aå/min to meet the specific needs for various read and write head related processes. ALD has shown great potential to become an indispensable part of integrated magnetic recording head manufacturing.
Scale-up of the BaTiO3 ALD Process onto 200 mm Wafer
Authors: Matero Raija , Rahtu Antti , Haukka Suvi , Tuominen Marko , Vehkamäki Marko , Hatanpää Timo , Ritala Mikko , Leskelä Markku
Published: November 2006

BaTiO3 films were deposited onto 200 mm silicon wafers by Atomic Layer Deposition (ALD) from barium bis(tris(tert-butyl) cyclopentadienyl) Ba(tBu3CpH2)2, titanium methoxide Ti(OMe)4 and water H2O. The films were characterized for thickness uniformity, stoichiometry and crystallinity. The thickness non- uniformity varied from 2.7 to 6.0% with different Ba(tBu3CpH2) 2 - H2O / Ti(OMe)4 - H2O cycle ratios. The most stoichiometric films were obtained with the 5:3 and 2:1 BaO:TiO2 cycling ratios. The as-deposited films were amorphous but were crystalline after thermal annealing. The study showed that this process can be transferred from small experimental scale to large production scale wafers.
A Stable Ultra Low Flow Reference Electrode Using a Nanochannel Glass Array Junction
Authors: Gao Frank , Broadley Scott , Chen Ta-Yung , Payne Pamela M. , Silverman Herbert
Published: November 2006

This paper describes the development of a novel pressure-driven nanofluidic- flowing liquid junction (NFLJ) reference electrode with an invariant liquid junction potential, for use in potentiometric sensors. These NFLJ reference electrodes have been shown to have a stable and reproducible potential with electrolyte flow under 5 ml per year. Use of the NFLJ reference electrode will result in sensors with outstanding precision that are maintenance free for periods of one year or more. This research is based on an innovative combination of nanochannel glass (NCG) and the nanofluidic liquid junction structure. The typical NCG array used for NFLJ reference electrodes has fewer than 200 channels with IDs smaller than 500 nm. Sensors using the NFLJ reference electrode demonstrate better potential stability, faster response time, and longer operational life than conventional commercial gel filled reference electrodes and are competitive with laboratory quartz fiber electrodes.
Semi-transparent UV-Detecting ZnO-TFTs with Polymer Gate Dielectric
Authors: Im Seongil , Bae Heesun , Choi Jeongmin , Hwang Do Kyung , Kim Jae Hoon , Lee Kimoon
Published: November 2006

We report on the fabrication of ZnO-based ultraviolet (UV)- detecting thin-film transistors (TFTs) with a semitransparent conducting NiOx top-gate electrode window and 450 nm-thick poly-4-vinylphenol (PVP) gate dielectric layer that has been formed on n-ZnO by spin-casting. The field effect electron mobility of our device was only about 0.0032 cm^2/Vs at the saturation regime of gate bias showing a low saturation current level in the dark because the PVP dielectric has a relatively low dielectric capacitance (7.4 nF/cm^2). The on/off current ratio of the device was about 10^3. However, the current increased up by more than 30 times with UV illumination of 325 nm wavelength (power density ~0.05mW/cm^2) while the initial current level was not varied with visible green illumination. We conclude that our ZnO-TFT with organic gate dielectric can be a promising transparent UV-detecting device.
The Electronic Properties of Chemically Delithiated LiFePO4
Authors: Julien C. M. , Dodd Joanna L. , Ait Salah Atmane , Mauger Alain , Gendron Francois , Fultz Bret , Yazami Rachid
Published: November 2006

We report on the structure and the electronic features of LiFePO4 and the delithiated mixture (1-x)Li1FePO4+x Li0FePO4 powder obtained by chemical delithiation. X-ray diffraction, Fourier transform infrared spectroscopy, and magnetic experiments are analyzed for x=0.0, 0.5, and 1.0. The magnetic properties give evidence of a super-paramagnetism associated to iron-based ferromagnetic nanoparticles, superposed to the intrinsic magnetic contribution of LiFePO4 which undergoes an antiferromagnetic ordering at TN(x=1)=50 K and TN(x=0)=125 K. Magnetization curves show superparamagnetism due to nanometer- sized magnetic particles. The magnetic clustering (amount of iron in the ferromagnetic nanoparticles, mean size distribution) is independent of the lithium concentration.
Si-Graphite Composite as a New Anode Material for Lithium Secondary Batteries
Authors: Lee Ki-Young , Kwon Ou Jung , Lee Yong Ju , Chang Won Seok , Kim Ki-Tae , Lee Seo-Jae
Published: November 2006

Si-Graphite composite was synthesized by the mechano-chemical process. HAADF analysis confirmed that silicon particles were uniformly distributed in the graphite matrix, and each silicon particle was completely covered by the multiple graphite layers. The discharge capacity of the silicon graphite composite material was as high as 1360 mAh/g and 74.4% of the initial capacity was retained after 300 cycles. Si-Graphite composite material could be utilized as a promising new anode material for the lithium ion secondary batteries due to the high capacity and outstanding cyclic performance.
Probing the Self-Discharge Current in LiMn2O4, LiCoO2 and Li(NiMnCo)1/3O2 Cathodes
Authors: Yazami Rachid , Ozawa Yasunori
Published: November 2006

We combined open-circuit voltage (OCV) measurements at equilibrium at the ambient temperatures and during thermal aging of Li/LiMO half-cells (M=transition metal) in 60-75ºC temperatures range and electrochemical entropymetry to indirectly determine the self-discharge current in the cells at the corresponding aging temperature. Comparison of normalized currents show highest self-discharge rates in LiMn2O4 and lowest in Li(NiMnCo1/3O2, LiCoO2 being intermediary. The results are discussed in terms of lithium re- intercalation induced phase transitions associated with electrolyte oxidation together with the phases intrinsic stability and their reactivity with the electrolyte.
High Temperature Oxidation of Cr-ZrO2-Al2O3 Composite
Authors: Martinez-Villafane Alberto , Arce-Colunga Ubaldo , Orozco-Carmona Victor Manuel , Almeraya-Calderon Facundo , Chacon-Nava Jose Guadalupe , Saucedo-Acuna Rosa Alicia , Diaz de la Torre Sebastian
Published: November 2006

The high temperature oxidation resistance of Cr-ZrO2-Al2O3 composites fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) has been studied. High temperature oxidation tests (900-11000C) under still air for 72 hours, have revealed good oxidation resistance (1.8, 2.6 and 15.3 mg/cm2 at 900, 1000 and 1100{degree sign}C respectively) since a protective Cr2O3 layer forms upon heating. EDAX analysis revealed that ionic Cr diffusion takes place at 1100oC from the bulk towards the composite's surface leading to a Cr-depletion at the near surface-zones. Chromium contained in the bulk tends to oxidize through oxygen diffusion apparently acting along the grain boundaries. The products of oxidation were studied by x-ray diffraction and scanning electron microscopy.
Photoluminescence Behavior of Ti-Doped Zn2SiO4 Thin Film Phosphors
Authors: Lin Chih-Mou , Lai Yi-Sheng , Chen Jen-Sue
Published: November 2006

This work investigates the luminescent properties and structure of Zn2SiO4:Ti thin-film phosphor, before and after annealing up to 1000oC. The Zn2SiO4:Ti films are fabricated by RF sputtering using ceramic target. After annealing at 800oC the beta-Zn2SiO4 phase is formed, but this phase is not suitable for the application in electroluminescence. The willemite structure (alpha-Zn2SiO4) is formed after annealing at 900oC or higher temperature. Concurrently, the Zn-O-Si bonding is observed by XPS analysis and it corresponds to the willemite structure. A broad PL peak locates at 386 nm is observed for the 700oC annealed Zn2SiO4:Ti film. However, three PL peaks, centered at 380 nm, 398 nm and 402 nm, can be observed in the 900oC annealed sample. All films exhibit a high transmission (>80%) in the visible spectrum, either before or after annealing.
Characterization of High Efficient Red Phosphorescent OLEDs Fabricated on Flexible Substrates
Authors: Kim Sunghyun , Lee Yoo Jin , Byun Ki Nam , Lee Bum-Sung , Jung Sang-Yun , Yoo Han Sung
Published: November 2006

In this study, we have applied a new iridium(Ir) complex as a red dopant and fabricated a red phosphorescent organic light emitting diodes(OLEDs) on a flexible polycarbonate(PC) substrate. Also, we have investigated the electrical and optical properties of the devices with a structure of Al/LiF/Alq3/(RD05 doped)BAlq/NPB/ 2-TNATA/ITO/PC substrate. Our device showed the lightening efficiency of > 30 cd/A at an initial brightness of 1000 cd/m2. The CIE(Commission Internationale de L'Eclairage) coordinates for the device were (0.62, 0.37) at a current density of 1 mA/cm2. In addition, although the sheet resistance of ITO films on PC substrate is higher than that on glass substrate, the flexible OLED showed much better lightening efficiency without much increase in operating voltage.
Fractal Carbon-MEMS Architectures for 3D Miniature Power and Sensor Applications
Authors: Madou Marc J. , Zaouk Rabih , Wang Chunlei , Park B. Y.
Published: November 2006

Biomimetic fractal electrode designs are proposed for electrochemical devices including miniature energy conversion devices and sensors. A zeroth order approximation fractal structure is analyzed and basic insights into the scaling laws of its electrical properties and surface to area ratio are derived. Fractal geometry is an optimal method of scaling electrochemical devices while minimizing internal resistance and maximizing surface to volume ratios. Recent advances in nanotechnology and C-MEMS that show great promise in facilitating the fabrication of fractal electrodes for electrochemical applications are detailed.
Three-Dimensional, Nanostructured Electrochemical Energy Storage Devices
Authors: In Hyun Jin , Kumar Sundeep , Shao-Horn Yang , Barbastathis George
Published: November 2006

The Nanostructured Origami{trade mark, serif} process is a novel fabrication and assembly method that is ideal for creating nanostructured devices with a three-dimensional (3D) geometry. In this paper, we describe the application of this new technique to the fabrication of an electrochemical energy storage device, namely a supercapacitor. The supercapacitor is ideal for origami fabrication because the incorporation of nanostructures and 3D geometry into its design will help improve its electrochemical performance. A first-generation supercapacitor with activated carbon electrodes has been successfully fabricated and tested. A capacitance of ~1 microfarad has been obtained from a device with dimensions of approximately 1 mm × 1 mm × 0.1 mm.
Oxygen Reduction at the Pt/Recast-Nafion Film Interface at Different Temperatures and Relative Humidities
Authors: Chlistunoff Jerzy , Uribe Francisco , Pivovar Bryan
Published: November 2006

The effects of temperature (20-80{degree sign}C) and relative humidity (~0- 100%) on the oxygen reduction reaction (ORR) on a Nafion®- covered platinum ultramicroelectrode were investigated using cyclic voltammetry and chronoamperometry. The cyclic voltammograms exhibited a significant hysteresis between the forward and reverse scans, which increased with either humidity or temperature increases. No hysteresis was observed for the fully hydrated film equilibrated with liquid water. It is postulated that the oxygen transport may be obstructed by water produced by oxygen reduction, which accumulates at the interface due to its hindered diffusion in the partially hydrated films. The charge transfer kinetics of ORR at both clean and oxide-covered platinum were found to slow down with increases in relative humidity. The effect was stronger for the oxide-covered platinum and was correlated with differences in platinum oxide coverage associated with changes in film hydration.
Palladium-Alloy Catalysts as Ethanol Tolerant Cathodes for Direct Alcohol Fuel Cell (DEFC) Applications
Authors: Savadogo O. , Valera F.J. Rodriguez
Published: November 2006

Palladium and palladium-alloy catalysts cathode have shown a high degree of tolerance to ethanol during the ORR in an acid medium. In particular, it was shown that the onset potential for the ORR in the presence of 0.5M C2H5OH decreases by only 33 mV and 18 mV on palladium and palladium-cobalt catalysts, respectively. This decrease in the onset potential due to the presence of ethanol on the Pd-based catalysts is more than ten times lower than those observed on Pt electrodes (513 mV). On the other hand, the palladium-based catalysts do not show any peak current attributed to the electro-oxidation of ethanol, whereas the Pt-based catalyst exhibited a high peak current related to the oxidation of ethanol. The high activity of Pd and Pd-Co catalysts for the ORR, as well as their high level of tolerance to the ethanol make them suitable candidates for Direct Ethanol Fuel Cell applications.
Modeling and Simulation Approach for Standardized Testing and Analysis of PEMFC CHP Systems
Authors: Konig Patrick , Weber André , Ivers-Tiffee Ellen
Published: November 2006

Fuel cell combined heat and power (FC CHP) systems propose a high-efficient, low emission and decentralized power and heat supply for buildings. An exact comparison between the different fuel cell CHP systems as well as detailed conclusions about efficiencies and optimization potential is hardly possible. Therefore, based on system tests, a model- aided system analysis tool using Matlab/Simulink{trade mark, serif} was developed to model and simulate different types of fuel cell systems. In the experimental modeling and simulation approach the general and flexible system model structure was parameterized and validated on the basis of measured data of a natural gas operated PEMFC CHP system. The results of the simulation agree well with the measured values.
Molecular Dynamic Simulation of Transport Processes in Nafion Polymer Electrolyte and Experimental Validation
Authors: Zhou Xiangyang , Chen Zhen , Delgado Francisco , Brenner Danny , Srivastava Rajiv
Published: November 2006

Molecular dynamic simulation models have been developed to investigate microscopic transport processes in Nafion polymer electrolyte. The diffusivity of methanol, water, hydronium, and proton in Nafion and the conductivity of Nafion were evaluated in a wide range of temperatures from 20 to 120 {degree sign}C for various water contents (lambda=3.0, 13.0, and 22.0). In order to validate the simulation results, the conductivity of Nafion was evaluated using a four-probe conductivity measurement apparatus at temperatures from 20 to 120{degree sign}C and at relative humidity from 30 to 100%. The permeability of methanol in Nafion was evaluated using a high temperature membrane diffusion cell. The differences between calculated conductivity results and measurement results were within 10% at room temperature but gradually increased with temperature. Computational permeability results were in good agreement with the experimental results within the confidence intervals.
Current Distribution along a Quad-Serpentine Flow Field: GDL Evaluation
Authors: Hicks Michael , Kropp Karl , Schmoeckel Alison , Atanasoski Radoslav
Published: November 2006

This paper presents a new, segmented cell concept for in-situ monitoring of current distribution and demonstrates its performance during PEM fuel cell operation. The segmented cell design utilizes printed circuit board technology to create a 121-segment cell from a 50-cm2 quad serpentine flow field. For this study, only the cathode flow field is segmented. The effect of air flow rate, load setting and gas-diffusion layer type on current distribution uniformity is studied. Although the load setting and the gas-diffusion layer type have an effect on current distribution, these appear to be secondary effects. The dominant factor for the uniformity of the current distribution is air stoichiometry.
Studies on Rib and Channel Characteristic of Flow Field on PEMFC Performance
Authors: Shimpalee Sirivatch , Van Zee John W. , Greenway Scott D.
Published: November 2006

Distributions in reactant species concentration in a PEMFC cause distributions in local current density, temperature and water over the area of a PEMFC. These can lead to effects such as flooding and cause stresses in different regions of the fuel cell. Changing flow field configuration including channel path length, width, or height to distribute the gas more evenly is one method of minimizing these stresses. This work investigates how 200 cm2 serpentine flow field with different number of gas path and channel/rib's cross section area affect performance and species distributions.
Development of Highly Durable MEA for PEMFC under High Temperature Operations (2)
Authors: Endoh Eiji , Kawazoe Hisao , Nakagawa Hideki
Published: November 2006

With regards to perfluorinated polymer based MEAs for PEMFC, the world's first highly durable MEA under high temperature and low humidity operations has been developed. The newly developed MEA, which uses a new perfluorinated ion-exchange polymer composite (NPC), reduces the degradation rate by 1/100 - 1/1000 compared to the conventional MEA. The NPC MEA can be operated for more than 4,000 hours at 120 ºC and 50% relative humidity. This paper reports on the performance of the NPC MEA under high temperature and low humidity conditions.
Accelerated Testing and Lifetime Modeling for the Development of Durable Fuel Cell MEAs
Authors: Hicks Michael , Pierpont Dan , Turner Pete , Watschke Theresa
Published: November 2006

Accelerated testing and lifetime modeling are important tools for the development of durable membrane electrode assemblies (MEAs) to meet U.S. Department of Energy's (DOE) 2010 lifetime target of 40,000 hours for stationary systems. Several methods were used to model MEA lifetime and make predictions for MEA lifetime at end use conditions. Statistical modeling and initial fluoride release modeling offer the best opportunity for reliably predicting MEA lifetime. Accelerated testing results found that a near OCV load setting has a strong negative impact on fuel cell life and that new 3M membranes improve durability significantly over industry standard membranes. The data suggest a pathway for MEAs to last in excess of 20,000 hours.
High Durability of Asahi Kasei Aciplex Membrane
Authors: Miyake Naoto , Wakizoe Masanobu , Honda Eiji , Ohta Tetsuro
Published: November 2006

In our last paper it had been implied that the presence of Pt on the cathode was more essential for membrane degradation. In this paper both effluent analysis and X-ray CT study have been done for the further understanding of membrane degradation. These studies support that the presence of Pt on the cathode is more essential for membrane degradation. Second purpose of this paper is to report the influence of electrocatalyst, GDL and types of membranes on membrane durability at open circuit voltage, i.e. OCV. It was confirmed that membrane was much less degraded on OCV test when using Asahi Kasei Advanced Membrane or using Pt:Co alloy as electrocatalyst. These results imply that the problem of membrane degradation during higher cell temperature operation under low humidification can be overcome by the further improvement of both membrane and electrocatalys
Hydrogen Peroxide Formation as a Degradation Factor of Polymer Electrolyte Fuel Cells
Authors: Inaba Minoru , Yamada Hirohisa , Tokunaga Junko , Matsuzawa Koichi , Hatanaka Aoi , Tasaka Akimasa
Published: November 2006

20wt.% Pt/C catalyst was loaded at different densities (0.28- 56.7 mgcarbon cm-2) on glassy carbon (GC) disk electrode, and the effect of its agglomeration on hydrogen peroxide formation in oxygen reduction reaction (ORR) was investigated by the rotating ring-disk electrode technique. The formation of H2O2 was enhanced with a reduction in agglomeration of Pt/C. Even in the operating potential range of PEFC cathodes (0.6-0.8 V), 20% of hydrogen peroxide was formed on Pt/C loaded at densities lower than 1.41 mgcarbon cm-2 on GC. These results revealed that series 2-electron reduction pathway, which is negligible on clean bulk Pt surface, exists on Pt nanoparticles supported on carbon. A large amount of H2O2 formation was observed on Pt nanoparticles deposited not only on GC, but also on Au, which indicated that H2O2 formation is not specific to Pt nanoparticles on carbon support.
PEMFC Stack Field Experiences
Authors: Maekawa Akira , Aoki Tsutomu
Published: November 2006

Some key subjects for PEMFC cell stack stability and durability in the field are reviewed with power plant shut down statistics, cell stack performance after field operation up to 10k hours, and cell stack failure case studies. Mitigation strategy including system-oriented approach is discussed based on lessons learnt.
Influence of Anodic Polarizations on the Electrodeposition of Metals on BDD Films
Authors: Ribeiro Mauro C. , de Oliveira Priscilla , Sumodjo Paulo
Published: November 2006

This paper accounts for the effect of anodic polarizations of BDD films in the electrodeposition of Pt an Cu. Deposition of those metals on anodized BDD surfaces gives deposits with larger specific areas. Such effect is discussed in terms of possible interactions between the Pt complex ion and the partially oxidized surface of the BDD.
GMR in Multilayered CoNi(Fe)Cu/Cu Nanotubes and Nanowires
Authors: Podlaha Elizabeth J. , Moldovan Monica , Young Dave , Davis Despina
Published: November 2006

Electrodeposited multilayer CoNiFeCu/Cu nanowires and nanotubes were fabricated with pulsed applied potential and their giant magnetoresistance (GMR) behavior characterized. The effect of electrolyte concentration on the GMR was investigated. The FeSO4 and CoSO4 concentrations were varied and altered the value of the GMR and the saturation field of the multilayered nanowires. Multilayered nanotubes also exhibited GMR at room temperature, and were influenced by the iron ions in the electrolyte. To the best of our knowledge this is the first demonstration of GMR in a nanotube.
Coordination Chemistry in the Electrodeposition of IG-V, W, and Mo Alloys from Aqueous Carboxylate Solutions
Authors: Schwartz Morton , Nobe Ken
Published: November 2006

Coordination chemistry of the transition metals, as the iron group (IG), and rare earths, V, W or Mo in aqueous media containing various carboxylate complexes play a crucial role in the electrodeposition of these alloys. Experimental results of the electrodeposition of IG-X(RE, V, W and Mo) alloys from aqueous solutions are discussed in light of recent results identifying the existence and structures of IG-X- carboxylate-complexes for biological and physiological applications. Mechanisms for alloy electrodeposition from hetero-dinuclear complexes are proposed in aqueous solutions.
Improving the Morphology of Copper Electrodeposits from Halide Media Using Additives and Mass Transport Control
Authors: Free Michael , Bhide Ravindra , Rodchanarowan Aphichart
Published: November 2006

The extraction and recovery of copper from the most common copper resource mineral, chalcopyrite (CuFeS2), can be performed using halide extraction and electrowinning chemistry in place of the traditional smelting and electrorefining. Electrowinning copper from halide media requires approximately 50 % of the energy needed using sulfate media. However, one challenge to the implementation of halide chemistry is the deposit morphology relative to that produced using sulfate chemistry. This study presents the effects of mass transport and organic additives on copper deposit morphology associated with halide electrowinning. The results show that appropriate control of mass transport through increased convective fluid flow or pulsing and the addition of some organic compounds can improve the morphology of the deposit significantly.
The Recovery of Metals from Waste Streams by Electrochemical Methods
Authors: Buckle Rachel C. , Roy S.
Published: November 2006

Tin stripping solution arises from a stage in the manufacture of printed circuit boards. This waste contains copper and tin that could be recovered for reuse. By focussing on this waste stream, a systematic approach has been developed to determine how the metals can be recovered. Pourbaix diagrams have been constructed for the metals and compared to find the pH or potential where the metals can be separated according to their state. Experiments were carried out to verify the theoretical findings.
Novel Silica Based Coatings as a Substitute for Chrome Passivates
Authors: Popov Branko N. , Kumaraguru Swaminatha
Published: November 2006

A novel electroless method was developed to deposit corrosion resistant silica coatings. Process parameters such as bath temperature, concentration of sodium silicate and sodium borohydride were optimized based on the uniformity and corrosion resistance of the final deposit obtained. Accelerated corrosion tests as per ASTM B117 standards show corrosion performance comparable to that of chrome passivates.
Numerical Simulation of Pitting Corrosion: Interactions Between Pits in Potentiostatic Conditions
Authors: Laycock Nick , White Stephen , Krouse Donal
Published: November 2006

Finite element simulations of single pit propagation have previously been combined with stochastic models of pit nucleation. In this paper, we use this model to focus on the possible interactions between pits by first considering the effect of a propagating pit (the primary pit) on the probability of pit initiation at a nearby site (the secondary site). We also describe a multiple-pit version of the simulation algorithm in which propagation of each pit is assigned to a separate process and these processes can be distributed over several computers. Initial results from many- pit simulations using this method are presented.
Modeling Gas-Phase Transport in Polymer-Electrolyte Fuel Cells
Authors: Weber Adam Z. , Newman John
Published: November 2006

In this transaction, the equations and methodology for modeling convection and ordinary, Knudsen, and pressure diffusion of gases in a fuel-cell gas-diffusion layer are described. Some results examining the magnitudes of the various terms are also made. This derivation results in a self-consistent description of the various transport mechanisms and is robust for numerical solutions, especially for conditions involving different flow regimes or where the regime is not known a priori.
A Comparison of the Corrosion Behavior of Several Nanocrystalline and Conventional Coarse Grain Al 5083 Samples
Authors: Mansfeld Florian , Kus Esra , Nutt Steve
Published: November 2006

The corrosion behavior of nanocrystalline and conventional Al 5083 was compared in solutions of different chloride concentrations. Bimodal samples which were made from a blend of nanocrystalline and coarse grain powders were also tested. Pitting scan (PS) and electrochemical impedance spectroscopy (EIS) have been used to evaluate the susceptibility of the samples to pitting. The nitric acid mass loss test (NAMLT) has been used to assess their intergranular corrosion susceptibility. All samples pitted at their corrosion potential (Ecorr) when exposed to 0.5 N NaCl; as the Cl- concentration decreased, higher pitting potentials (Epit) and passivation behavior were observed. The analysis of EIS data obtained in 0.5 N NaCl showed that the samples had similar tendencies in terms of pit growth rates. The results of the NAMLT showed that nanocrystalline and bimodal samples were not susceptible to intergranular corrosion, while grain boundary attack was observed for the conventional Al 5083.
Deposition of Polypyrrole on Porous Aluminum Oxide
Authors: Levine Kirill L. , Tallman Dennis , Bierwagen Gordon
Published: November 2006

We report the successful attempt of electrodeposition of polypyrrole (PPy) on the electrochemically developed porous oxide surface of aluminium alloy. Corrosion protection properties were assessed by potentiodynamic measurements and electrochemical impedance spectroscopy. It is shown that PPy on porous oxide significantly increases the corrosion potential making the surface more noble.
Electrochemical Behavior of Boron Carbide and Galvanic Corrosion of Boron Carbide Reinforced 6092 Aluminum Composites
Authors: Ding Hongbo , Hihara Lloyd
Published: November 2006

Electrochemical behavior of boron carbide (B4C) in 0.5 M Na2SO4 solution was studied using potentiodynamic polarization, cyclic voltammetry, and impedance spectroscopy. Polarization diagrams revealed three anodic current peaks and a gradual increase of anodic currents with increasing applied potential. Cyclic voltammograms revealed that the three anodic current peaks appeared only during the first positive potential scan. During the subsequent potential scans, the electrode behaved like an inert electrode within a wide potential window. Impedance spectra taken at various applied potentials revealed a potential-independent electrode/electrolyte interface double layer capacitance value approximately of 10 μf/cm2, a typical value of the electrolyte double layer capacitance of concentrated electrolyte solution, indicating that boron carbide is a degenerated semiconductor. The galvanic corrosion of particulate B4C reinforced 6092-T6 Al metal matrix composite (MMC) induced by the B4C reinforcement was examined with a zero resistance ammeter (ZRA) technique and a platinization method.
Corrosion Study of an AZ91 Magnesium alloy by EIS and LEIS
Authors: Tribollet Bernard , Galicia Gonzalo , Pebere Nadine , Vivier Vincent
Published: November 2006

The electrochemical impedance diagrams obtained at the corrosion potential for pure Mg or for AZ91 alloy presented the same shape after an immersion time of few days. It was thus assumed that the magnesium matrix of the AZ91 alloy corrodes first. The diagrams are characterized by two capacitive loops and an inductive one. It was shown that the diagrams measured in different electrolytes (Na2SO4 or NaCl) and on a large pH range (from 2 to 12) also presented the same shape and can be reduced to one diagram if the impedance is normalized by the maximum value of the modulus. Considering the experimental data and taking also into account the Negative Difference Effect (NDE), a kinetic model was proposed. Local Electrochemical Impedance Spectroscopy (LEIS) was carried out with the bi-electrode technique. Both anodic and cathodic sites were evidenced when mapping the sample in the low frequency domain. These sites could be linked to the microstructure of the AZ91 alloy. With a larger bi-electrode, a local average of the impedances corresponding to the anodic and cathodic sites was obtained. Thus, local impedance diagrams were similar to those measured for the global impedance on the overall AZ91 electrode (1 cm2). The analysis of LEIS data obtained along the radius of the electrode gave some new information on the origin of the CPE behavior of the global impedance in the high frequency range.
Corrosion Resistance of AZ31B Magnesium Alloy Sheets Prepared by Extruding and Rolling
Authors: Zhang Bo-Ping , Li Peng-Xi , Chen Jing-Yi , Zhang H. L. , Kang Y.L. , Cai Q.W. , Suzuki Hirowo G.
Published: November 2006

AZ31B Magnesium alloy sheets with about 1 mm in thickness were rolled by one pass and several passes from the extruded ingots with different thickness. The effects of processing variables on microstructure and mechanical properties of AZ31B Mg alloy sheets were investigated. XRD indicated that AZ31B magnesium alloy sheets have a dominant texture with (000l) orientated plane. The large deformation results in the formation of fine and homogeneous microstructure due to the recrystallization during extruding and hot-rolling. The thinnest sheet rolled by several passes showed equiaxed grains with 5-10μm in diameter. The fine recrystallization grains contribute to the increase in the corrosion resistance. The corrosion rate of the sheets rolled by several passes was 1.9 mm/year in 3.5% NaCl solution.
Scanning Probe Studies of Water at the Aluminum Surface
Authors: Missert Nancy A. , Copeland Robert
Published: November 2006

Water adsorption on the passive aluminum surface was investigated as a function of relative humidity (RH) using atomic force microscopy (AFM). Aluminum surfaces exposed to the ambient environment for times longer than one month showed that water adsorbed by the formation of droplets ranging in lateral size from 20 nm - 1 µm at RH above 70%. A surface residue at the droplet sites was observed by scanning electron microsocopy and AFM following evaporation of these droplets as the RH was reduced. Aluminum surfaces with minimal exposure to the ambient environment did not show droplet formation at high RH, but rather a more uniform water layer as inferred from pull-off force measurements. Macroscopic contact angle measurements showed that hydrocarbon adsorption on the passive aluminum surface from ambient environment changes the surface from hydrophilic to hydrophobic in less than 24 hours.
EIS Corrosion Study of Co, Ni, CoNi, and CoNiMo Electrodeposited Thin Films
Authors: Esteves Marcos C. , Sumodjo Paulo
Published: November 2006

Co, Ni, Co78Ni22 and Co75Ni22Mo3 magnetic thin films (5 micron) were electrodeposited galvanostatically from chloride baths containing sodium citrate as additive. These films were kept during 24 hours in a 5 wt. % NaCl solution (pH 6.4). During this period, OCP measurements and EIS were used to tail the corrosion of each film. The films were also analyzed by SEM before and after the corrosion experiments. The OCP of Ni, Co and CoNi decreased during the first seven hours of immersion, whilst for CoNiMo, it increased during the first eight hours due to the presence of a MoO2 layer below the film. In both cases, OCP remained constant thereafter. Different equivalent circuits were adjusted to the EIS data. From these circuits, charge transfer resistance and double layer capacitance of each film could be evaluated.
The Effect of Cathodic Treatment and Annealing of the Fe76Nb3Cu1Si13.8B6.2 Alloy on Its Electrochemical Behavior
Authors: Pimenova Natalia , Skryabina Natalie
Published: November 2006

The effect of annealing and cathodic treatment on properties of oxide layer of the solid non-crystalline alloy Fe76Nb3Cu1 Si13.8B6.2 has been studied. Using secondary ion mass spectroscopy and X-ray photoelectron spectroscopy the chemical composition of the surface and subsurface layers was investigated. Redistribution of elements in subsurface layer significantly affects the electrochemical corrosion of the alloy. High amount of oxygen in subsurface layer was detected.
Effects of Oxygen Vacancy Concentration on Mechanical Properties of Cerium Oxide
Authors: Wang Yanli , Duncan Keith , Wachsman E. D. , Ebrahimi Fereshteh
Published: November 2006

Nonstoichiometric compositions of ceria were created by heat treatment at 800 C at various oxygen partial pressures. The different oxygen vacancy concentrations created by this heat treatment were conserved to room temperature by fast cooling. Nanoindentation technique was used to study the elastic modulus and hardness of samples. The room temperature results indicate that the elastic modulus of ceria decreases at very low partial pressures of oxygen, but the hardness shows a maximum as a function of oxygen partial pressure. The fracture toughness was evaluated using Brazilian disk samples under mode I loading condition. The preliminary results reveal that surprisingly fracture toughness is increased at very low oxygen partial pressure. In this paper, the change in toughness is discussed in terms of pore-crack interaction, internal stresses, microcracks and phase transformation.