bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Scalable Modeling of SiGe HBT DC Currents Down to 43K
Authors: Feng Zhiming , Niu Guofu , Zhu Chendong , Najaﬁzadeh Laleh , Cressler J. D.
Published: November 2006

A group of improved temperature mapping models for modeling of DC currents down to 43 K are presented. Excellent Gummel and output ﬁtting across a wide temperature range from 300 K down to 43 K are achieved on a 50 GHz SiGe HBT technology.
From Thin Relaxed SiGe Buffer Layers to Strained Silicon Directly on Oxide
Authors: Mantl Siegfried , Buca Dan , Holländer Bernd , Lenk St , Hueging Norbert , Luysberg Martina , Carius Rainer , Loo Roger , Caymax Matty R. , Schäfer Herbert , Radu Ionut , Reiche Manfred , Christiansen Silke , Goesele Ulrich
Published: November 2006

Thin relaxed SiGe buffer layers with Ge contents of 23at% and 26at% and thicknesses between 150 to 180 nm on Si(100) terminated with 6 nm Si were made by He ion implantation and annealing. Subsequent overgrowth of the thin buffers with thin strained Si cap layers with SiGe and strained Si reduced the threading dislocation and pile-up densities significantly. Best results were achieved for high temperature SiGe overgrowth with a thickness of 200nm and Ge contents lower than the effective Ge content of the buffer. Threading dislocation densities as low as 1x105 cm-2 and dislocation pile-up densities of 10 cm-1 were determined. Strained silicon on insulator wafers were produced by wafer bonding. Wafer splitting was done by H ion implantation and annealing. The strain of the layers was measured by Raman spectroscopy revealing a strain of 0.66% in the tensile strained Si on the partially relaxed Si0.77Ge0.23 buffers.
Dislocation Pile-Up Quantification Using Automated Room Temperature Photoluminescence Mapping
Authors: Buczkowski Andrzej , Laurent Nicolas , Shachaf Amit , Walker Tom , Hummel Steven , Berne Cécile , Kennard Mark
Published: November 2006

A room temperature photoluminescence (RT-PL) inspection and quantification method has been successfully applied for contactless and nondestructive discrimination of dislocation pile-ups generated via relaxation of SiGe materials grown on Si substrates. Advances in image acquisition and processing enabled DPU mapping over the entire wafer area, which contributed to significant reductions in process development cycle times required to produce high quality SiGe-based materials.
Thermal Redistribution of Oxygen and Carbon in Sub-50 NM Strained Layers of Boron Doped SiGeC
Authors: Enicks Darwin , Oleszek Gerald
Published: November 2006

This work is the second report on a localized elevated oxygen concentration (or pileup), which occurs with thermal anneals of strained, boron doped SiGeC layers. The thermally activated oxygen updiffusion into thin strained layers of SiGeC is correlated to the preferential outdiffusion of carbon from the SiGe setback or spacer layers. A strong dependency on both prebake temperature and post-growth anneal is demonstrated, which correlates to available oxygen at the surface of the p-type silicon substrate. Additionally, evidence is provided with SIMS (secondary ion mass spectrometry) data that carbon diffusivity in SiGeC:B is significantly reduced as compared to SiGeC without boron.
Ge Diffusion in Strained Si / Relaxed SiGe Heterostrucutures
Authors: Bogumilowicz Yann , Barnes Jean-Paul , Holliger Phillipe , Rouchon Denis , Daval Nicolas , Hartmann Jean-Michel , Abbadie Alexandra , Lallemand Fabrice , Guiot Eric , Akatsu Takeshi , Deguet Chrystel , Kernevez Nelly
Published: November 2006

We have studied the Ge diffusion in tensile-strained Si on relaxed SiGe. Two Ge concentrations have been used, 30 and 40%, in order to induce two different strain levels in the Si layer. Thermal budgets in-between 750 and 1000ºC for four hours have been tested. Higher thermal budgets lead as expected to a higher diffusion of Ge in sSi. The diffusion length is superior to 20 nm at 1000ºC, 4 hours. We have observed a slight increase of the diffusion coefficient of Ge in tensile strained silicon when the strain was increased.
Germanium Surface Cleaning with Hydrochloric Acid
Authors: Kim Jungyup , McVittie Jim , Saraswat Krishna , Nishi Yoshio , Liu S. , Tan S.
Published: November 2006

Germanium cleaning is crucial in successful integration of high mobility germanium substrates. HF and HCl do not consume the Ge substrate and do not deteriorate the Ge surface roughness. HF and HCl both show greater than 80% metal recovery rates for most metals. But concentrated HCl solution is more effective in removing the contaminant containing oxide/sub-oxide layers than HF. Therefore HCl is a good candidate for metal contamination removal from Ge surface but other factors such as organic and particle removal and passivation need to be considered simultaneously for an efficient and integrated Ge cleaning process.
Scanning Tunneling Microscopy Study on the Reaction of Oxygen with Clean Ge(001) Surfaces
Authors: Sakai Akira , Wakazono Yasunobu , Nakatsuka Osamu , Zaima Shigeaki , Ogawa Masaki
Published: November 2006

Chemical reaction of oxygen to the clean Ge surfaces has been investigated by in situ scanning tunneling microscopy. The Ge surface structure varied sensitively to the oxygen partial pressure and the substrate temperature during the reaction. The observed phenomena can be categorized typically into the modes of either etching or oxidation, and the transient mode including both processes, by analyzing the surface structures on an atomic scale. The etching (oxidation) tends to proceed at higher (lower) temperature and lower (higher) oxygen pressure. The surface step was found to act as a preferential reaction site for the etching whereas no remarkable changes were detected at the step site during the oxidation. The oxygen reactivity on Ge will be discussed compared to the Si case.
Atomic-Order Thermal Nitridation of Si1-xGex(100) at Low Temperatures by NH3
Authors: Akiyama Nao , Sakuraba Masao , Murota J.
Published: November 2006

Atomic order thermal nitridation of Si1-xGex(100) (x=0, 0.4, 1) by NH3 gas environment at low temperature of 400ºC has been investigated using an ultraclean low-pressure chemical vapor deposition system. After NH3 exposure (NH3 partial pressure of 550 Pa for 30 min), it is found that Si(100), Si0.6Ge0.4(100) and Ge(100) are nitrided in atomic-order. In the case of Ar purging at cooling period after the nitridation, N atom amounts on Si(100) and Ge(100) are 8.0x1014 and 5.5x1014 cm-2, and the amount on Si0.6Ge0.4(100) is 12.5x1014cm-2. In the case of H2 purging at the cooling period, it is found that slight reduction of the N atom amount on Si(100) down to 5.6x1014 cm-2(70 %) is observed, although the N atom amount on Ge(100) is significantly reduced to 1.2x1014 cm-2 (22 %).
Characterization of Strained Si/SiGe with Raman, Pulsed MOS Capacitor, and Gate Oxide Integrity Measurements
Authors: Liao Jiun-Hsin , Canonico Michael , Robinson Mcdonald , Schroder Dieter
Published: November 2006

We use several characterization techniques including Raman spectroscopy, pulsed metal-oxide-semiconductor (MOS) capacitor capacitance-time, and gate oxide integrity measurements to characterize strained silicon/relaxed SiGe/graded SiGe/Si samples. The effective generation lifetime depends on the defect density in the various layers varying from 10-4 s near the surface to 10-7 s in the graded and highly defective SiGe. GOI statistical analysis shows worsening oxide breakdown as the Ge concentration in the SiGe increases.
Dielectric Relaxation and Defect Generation Under Pulsed and Constant Voltage Stressing of Ultrathin TiO2 Films on Strained-Si/Si0.8Ge0.2
Authors: Bera Milan K. , Saha Satyajit , Maiti Chinmay K.
Published: November 2006

Ultra-thin high-k TiO2 (~11 nm) films have been deposited on strained-Si/relaxed-SiGe heterolayers using microwave plasma below 200ºC using organo-metallic precursor titanium isopropoxide (TTIP). Dielectric relaxation and oxide reliability studies have been performed with constant voltage stressing. During constant voltage stressing of MIS capacitors, an increase in time-dependent gate current is observed followed by occurrence of current fluctuations. The amplitude of fluctuations increases with increasing stress voltage. A comparative study on the time dependent defect density variation, ΔNhigh-k is performed within a dispersive transport model, assuming that the defects are produced during random hopping transport of defects in the insulating layer. Effects of transient response and dielectric relaxation have been studied under high pulse voltage stress. Stress induced trap charge density and its spatial distribution have also been investigated.
Oxygen Reduction Electrocatalysis at Chalcogen-Modified Ruthenium Cathodes
Authors: Zelenay Piotr , Choi Jong-Ho , Johnston Christina , Cao Dianxue , Babu Panakkattu , Wieckowski A. , Alonso-Vante Nicolas
Published: November 2006

We have recently developed a method for obtaining chalcogenide catalysts, which is based on surface modification of ruthenium black particles rather than the synthesis of a bulk metal-chalcogen compound [1]. Electrochemical, non- electrochemical and fuel cell testing have revealed high ORR activity and very good methanol tolerance of such surface chalcogenide catalysts [2,3]. Uniquely for Pt-free cathode catalysts, such surface chalcogenides also exhibit very good performance durability under fuel cell operating conditions at 70{degree sign}C. In this paper, we focus on hydrogen-air and direct methanol fuel cell performance of chalcogen-modified Ru blacks as well as on the mechanism of oxygen reduction on such catalysts, as determined in rotating ring disk-electrode (RRDE) studies.
Electroactive Alcohol-Tolerant Pt-Alloys
Authors: Rodriguez-Varela Francisco Javier , Savadogo Oumarou
Published: November 2006

The electro catalytic activity of PtCr/C and PtCo/C catalysts for the ORR in an ethanol-containing medium was studied. It was found that these materials present a high tolerance to the alcohol in an acid solution as well as in a Direct Ethanol Fuel Cell (DEFC) configuration. Particularly the PtCo/C catalyst showed very important electrocatalytic characteristics, i.e., a small increase in onset potential of the ORR in the presence of ethanol, a very small variation in current density at 400 mV vs. DHE and a very important performance as cathode material in a DEFC. The current densities from the DEFC equipped with a 10% PtCo/C cathode were similar to those obtained when a 20% PtCr/C cathode was used. However, an improved performance in terms of mass specific current density was shown by the PtCo-based cathode in the DEFC. These results indicate the advantage of using PtCo-alloys as oxygen electrodes in DEFCs.
XAFS Study of Heat-Treated Cobalt Tetraphenylporphyrin Supported on Active Carbon
Authors: Hiroshima Kazutaka , Nonaka Takamasa , Asaoka Takahiko , Morimoto Yu
Published: November 2006

Co K-edge XANES measurements were conducted for heat-treated cobalt tetraphenylporphyrins supported on activated carbon (CoTPP/C) which was under use as the cathode electrode of a PEFC to investigate the effect of applied potential on the local structure and the electronic property of cobalt of CoTPP/Cs. N K-edge NEXAFS measurements of CoTPP/Cs were also conducted to examine the effect of heat treatment temperature on the local structure around the nitrogen atoms. As a result, the structure of the cobalt atom surrounded by the nitrogen atoms (Co-N4 structure) was preserved during the fuel cell operation when the heat treatment temperature was 600{degree sign}C. The preservation of the Co-N4 structure is likely the reason for the highest catalytic activity for oxygen reduction reaction of this catalyst.
Non-Platinum Cathode Based on Tantalum for PEFC
Authors: Kim Jin-Hwan , Ishihara Akimitsu , Mitsushima Shigenori , Kamiya Nobuyuki , Ota Kenichiro
Published: November 2006

Ta-based compounds for PEFC cathode were prepared by R.F. sputter using TaC target under Ar (Ta-C) or Ar+N2 gas mixture (Ta-C-N) by heating a substrate in the range from room temperature to 800oC. The Ta-C-N compounds were found to be stable in 0.1moldm-3 H2SO4. The catalytic activity of the Ta- C-N compounds for the oxygen reduction reaction (ORR) increased with the increase in the substrate temperature. The ORR current at 0.4V of the Ta-C-N compound deposited at 800oC was about 75mAcm-2 and 125 times larger than that at room temperature. The ORR of the Ta-C-N compound deposited at 800oC was observed at about 0.73V vs. RHE. The physical properties, such as a crystallinity, crystal structure and chemical composition, of the Ta-C-N compounds were investigated by XRD and RBS analysis. The relationship between the physical properties and the catalytic activity for the ORR was discussed.
Effect of Catalyst Support Morphology on the PEMFC Performance
Authors: Waje Mahesh M. , Li Wenzhen , Chen Zhongwei , Yan Yushan
Published: November 2006

The performance of a proton exchange membrane fuel cell is evaluated for Pt/carbon black and Pt supported on cup stacked carbon nanotubes (CSCNTs). The effect of spherical and tubular morphology of the catalyst support on the catalyst layer structure is evaluated. A detailed analysis of the contributions of different overpotentials on the performance is done. The improved performance of Pt/CSCNT catalyst in the high current density region is attributed to the improved catalyst structure because of tubular morphology of CSCNTs.
Improvement of PEMFC's Power Performance by Electrophoretic Deposition of Pt/MWNT Nanocatalysts
Authors: Louh Rong-Fuh , Tsai Felix
Published: November 2006

The multi-walled carbon nanotubes (MWNTs) were treated through a chemical oxidation by mixture of nitric acid and sulfuric acid. Nearly monodispersed nanosized platinum catalysts (2-3 nm) for PEM fuel cells were synthesized by the reduction of hexachloroplatinic acid precursor with ethylene glycol solvent, which were simultaneously distributed over the surface of MWNT carriers. In the preparation of Pt/MWNT nanocatalysts, ethylene glycol solvent, as compared to formaldehyde, was an ideal chemical to obtain improved dispersivity, narrower particle size distribution, and platinum loading capability on MWNT carriers (18.6 wt% Pt on MWNT). The evenly distributed loading of Pt/MWNT nanocatalysts on the carbon-based gas diffusion layers (GDLs) for the PEM fuel cells was carried out via the electrophoretic deposition (EPD). The cell performance of PEMFC with both synthesized Pt/MWNT and Pt/C (E-TEK, XC-72) nanocatalysts and the influence of hydrophobicity by using MWNTs and carbon black carriers for the Pt nanoparticles on GDLs were evaluated by cyclic voltammetry and contact angle measurement, respectively. The power density (mW/cm2) of PEMFC fabricated by electrophoretic deposition of Pt/MWNT nanocatalysts was increased by ~36% as compared to the same Pt loading (0.16 mg- Pt/cm2) of Pt/C nanocatalysts.
Pt - Ru Deposition on MWCNT for PEM Fuel Cell Electrodes
Authors: Verde Ysmael , Gómez-Vargas Ramon , Gonzalez Guillermo , Alonso Gabriel , Antunez Willberth
Published: November 2006

Development of nanoestrutured materials as catalyst in PEM fuel cells has been the target to reduce the energy systems costs. Pt-Ru on Multiwall Carbon Nanotubes (MWCNTs) were synthesized by aqueous solution synthesis from (NH4)2PtCl6 and (NH4)2RuCl6. The MWNT were synthesized by spray pyrolysis method. Before the metal impregnation, the MWNT were treated with H2O2 and HNO3 in reflux. The Pt-Ru/MWCNT electrocatalyst was evaluated by Scanning Electron Microscopy, Transmission Electron Microscopy (TEM) and X-Ray Diffraction. The nanotubes synthesized have diameters between 60 to 100 nm and approximately 300 μm of length. TEM analyses shows Pt and Ru nanoparticles uniformly distributed along the nanotube with particle size between 4 and 10 nm. The Pt-Ru ratio was approximately 1:1. The electrochemical characterization shows performances comparables with traditional catalyst.
Development of Catalyst and Gas Diffusing MEA Layers for PEFC using Taguchi's Method
Authors: Shigyo Kazuhiro , Nishiguchi Hiroto
Published: November 2006

Taguchi's method was applied to an MEA design, and identified the robust design conditions. The generic function was defined as the relationship between the fuel gas flow rate and the electric power. The four kinds of control factors for the catalyst layer formation and eight control factors for the geometrical and process parameters of gas diffusing layer (GDL) were selected to optimize the MEA design conditions. These parameters were allocated in the orthogonal arrays of L9 (for the catalyst layer) and L18 (for GDLs) based on the design of experiment (DOE). The robustness and performance were identified of MEA using the indexes called S/N ratio and sensitivity. The variability of the power operated at a large gas flow rate was diminished (within 20%), and the time required for optimum designing was also reduced.
Studies of the CO Tolerance for Anodes of PtFe/C in PEMFC
Authors: Ticianelli Edson A. , Pereira Luis G. , Paganin Valdecir A.
Published: November 2006

The oxidation of hydrogen containing carbon monoxide was studied on Pt-Fe electrocatalysts supported on a high surface area carbon powder. A good electrocatalytic activity was observed for anodes formed by this catalyst and supplied with H2 containing 100 ppm of CO, which presented overpotential loss of 250 mV at 1 A cm-2, compared to pure hydrogen. The on line differential electrochemical mass spectrometry has shown that the production of CO2 started at low potentials for PtFe/C, confirming that the CO tolerance is at least partially achieved by the bifunctional mechanism. However, X-ray absorption experiments showed an enhancement of the Pt 23/2-5d white line, compared to the Pt/C, indicating that the Pt atoms present more vacant 5d electronic states in the PtFe/C catalyst. This may lead to a change of the Pt-CO bond energy in this catalyst as compared to Pt/C.
Probing Effects of GDL Microstructure on Liquid Water Transport by Pore Network Modeling
Authors: Wang Chao-Yang , Sinha Puneet
Published: November 2006

A pore-network model is developed to study the liquid water movement and flooding of gas diffusion layer (GDL) with GDL morphology taken into account. We have computed capillary pressure and relative permeability as function of liquid water saturation. The dynamics of liquid water transport and evolution of the saturation profile in GDL under realistic fuel cell operating conditions is examined for the first time. It is found that capillary forces control the liquid water movement in the GDL and liquid water moves in connected clusters with finger-shaped liquid water fronts. Relative permeability of liquid water is found to be very small at high saturation due to poor connectivity among liquid water clusters. The effect of mixed wettability (contact angle varying from 60o-120o) on capillary pressure and relative permeability functions is also investigated.
Measurements of Two-Phase Flow Properties of the Porous Media Used in PEM Fuel Cells
Authors: Nguyen T. V. , Lin Guangyu , Ohn Heebong , Hussey Dan , Jacobson David , Arif Muhammad
Published: November 2006

In a hydrogen PEM fuel cell (PEMFC), liquid water is generated as a by-product (O2 + 4 H+ + 4 e- ↔ 2H2O) at the cathode during operation. The presence of liquid water results in a two-phase (gas/liquid) condition in the porous media, such as, the gas diffusion and catalyst layers. In a direct methanol PEM fuel cell (DMFC), in addition to the two-phase condition in the cathode similar to that of a hydrogen PEMFC, another two-phase condition also exists in the anode when gaseous carbon dioxide is generated as a by-product (CH3OH + H2O ↔ CO2 + 6 H+ + 6 e-) during operation. These two-phase conditions affect the transport rates of the reactants (oxygen and methanol/water) to the reactive sites in the electrodes. Knowledge of two-phase transport properties of the porous media used in PEMFCs and DMFCs is required to develop materials that will result in optimal fuel cell performance. This paper discusses the techniques that we have developed for measuring two-phase transport properties of porous media used in PEMFCs and DMFCs and the results obtained for some commercially available materials.
Metal Carbide-Based Hydrodesulfurization Catalysts as Sulfur-Tolerant Electrocatalysts for PEMFC Anodes
Authors: Pietron Jeremy , Laberty Christel , Swider-Lyons Karen
Published: November 2006

Nanostructured nickel tungsten carbide (Ni6W6C) and nickel molybdenum carbide (Ni6Mo6C) are well known hydrodesulfurization catalysts, that have been speculated to be useful as sulfur-tolerant proton exchange membrane fuel cell anode catalysts. We synthesized these compounds and evaluated their electrocatalytic activities for the hydrogen oxidation reaction (HOR) in sulfur-free electrolyte as well as electrolyte contaminated with 31 μM mercaptosuccinic acid (1 ppm sulfur) using a rotating disk electrode. The HOR activity of the carbides is higher than that reported elsewhere, but still is low when compared to platinum catalysts. The nanostructured catalysts corrode and show poor sulfur tolerance. Further development is needed to understand why these catalysts perform poorly in fuel cell environments.
Fabrication of Silicon Based Fuel Cell Electrodes by Selective Plasma Etching
Authors: Brito-Neto Jose Geraldo A. , Araki Shintaro , Shirako Soichi , Hayase Masanori
Published: November 2006

In this work, the fabrication of electrodes for silicon based fuel cells by plasma etching is reported. The fuel channels were opened by SF6 plasma etching through a copper mask after a porous platinum catalyst layer had been synthesized on the opposite side of the silicon wafer. Prototype cells were assembled by hot pressing two such electrodes with a polymer electrolyte membrane between them. Polarization curves for such cells were measured and a peak power density of 35 mW/cm2 was obtained when dry H2 and O2 were fed to the anode and cathode sides respectively.
New Evaluation Method for Degradation Rate of Polymer Electrolytes
Authors: Uchida Hiroyuki , Aoki Makoto , Watanabe Masahiro
Published: November 2006

Decomposition behavior of perfluorosulfonic acid (PFSA) electrolytes caused by the crossover of H2 or O2 in PEFCs was evaluated at 80 oC with a new method. Two gas-diffusion electrodes (Nafion-coated Pt/CB catalysts printed on carbon paper) were mounted in a fuel cell housing with and without Nafion membrane. Mixed gas of H2 and air with a constant composition was supplied to the cell, simulating the crossover at the anode and the cathode. The F− emission rates (FER) increased with increasing the relative humidity in both H2-rich and O2-rich conditions, probably due to the enhanced penetration of H2O2 in swollen electrolyte. It was found that an appreciable fraction of H2O2 or OH radical was easily scavenged at Pt particles in the catalyst layer or in the Pt-dispersed Nafion, resulting in the suppressed FER. Degradation mechanism of PFSA electrolytes was discussed.
Phenomenon Analysis of PEFC for Automotive Use(1) Membrane Degradation Behavior During OCV Hold Test
Authors: Ohma Atsushi , Suga Sohei , Yamamoto Shinji , Shinohara Kazuhiko
Published: November 2006

The correlation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open circuit voltage (OCV) hold test was studied. It was found that the location of the Pt band correlated with the magnitude of the FERRs. The Pt band was observed close to where the mixed potential in the membrane, which was determined by the gas compositions, changed dramatically.
Effective Testing Matrix for Studying Membrane Durability in PEM Fuel Cells: Part I. Chemical Durability
Authors: Liu Wen , Crum Matt
Published: November 2006

In order to advance membrane technologies for PEM fuel cells, it is critical to establish an effective testing matrix, which includes tests that target specific mechanisms of chemical and mechanical durability, as well as tests that can challenge the membrane with combined failure mechanisms. Furthermore, the tests should be both accelerated and realistic. In studies of membrane chemical durability, it was discovered that using regular test cells resulted in highly non-uniform membrane degradation in the active area. This compromised the quantitative value of the data and prevented the use of average fluoride release rate over the entire cell as an accurate measure of the chemical degradation rate of the membrane. Therefore, a homogeneous environment was needed for more quantitative studies of membrane chemical durability. Among various options, operation at OCV using standard test cells and operation under a load using high gas stoichiometries with a uniform test cell were chosen. Test results indicate that combinations of these test protocols enable the dependable selection of more chemically durable membranes and also provide quantitative data to assist understanding of degradation mechanisms in fuel cells under various operation conditions.
Increased Stability of PFSA Proton Exchange Membranes Under Fuel Cell Operation by the Decomposition of Peroxide Catalyzed by Heteropoly Acids.
Authors: Herring Andrew M. , Gregory Haugen M. , Fanqin Meng , Aieta Niccolo V. , Horan James L. , Frey Mathew H. , Hamrock Steven J. , Kuo Mei Chen
Published: November 2006

Proton exchange membranes were cast from mixtures of the 3M perfluorinated sulfonic acid ionomer, with side chain -O-(CF2) 4-SO3H, and various heteropoly acids (HPAs) at a 10 or 20 wt% doping level. The membrane electrode assemblies (MEAs) prepared from these membranes were subjected to a fuel cell testing protocols involving incubation to steady state, temperature challenge, accelerated testing, and post mortem analysis. The cell temperature was varied from 70 - 100 ºC under relatively dry conditions, 70 ºC dewpoint, to avoid leaching of the HPA. The most important finding from this study was that the more stable HPAs, H4SiW12O40, α-H3P2W18O62, and H6P2W21O71 reduce the rate of F- release threefold and improve the performance of the MEA dramatically under these conditions. For HPAs that possibly rearrange in peroxide or at elevated temperatures, H3PW12O40, H6CoW12O40, H5SiAlW11O39, H6As2W21O69, and H21B3W39O162, the results were mixed as fragments of these molecules possibly interfere with the fuel cell electrochemistry.
Durability of Nafion-Teflon-Phosphotungstic Acid Composite Membranes in PEM Fuel Cells at 100{degree sign}C and 25%RH
Authors: Xu Hui , Wu Man , Liu Yuxiu , Mittal Vishal , Kassim Faisal , Vieth Bob , Bonville Len , Kunz Harold R. , Fenton James M.
Published: November 2006

Composite membranes consisting of Nafion-Teflon- phosphotungstic acid (NTPA) were developed for high temperature/low RH operation and demonstrate a 20% higher conductivity than that of Nafion. A fuel cell using an NPTA membrane was tested at 100{degree sign}C, 25% RH, and 150kPa total pressure for 1000 hours. The membrane resistance and hydrogen crossover were very stable over the 1000 hours. After 1000 hours, at 400mA/cm2, there was a 90mV voltage drop (initial cell voltage ~500 mV), which was due to catalyst degradation
Extended PEMFC Durability From MEAs Based On A New Reinforced Membrane
Authors: Ralph Thomas R. , Barnwell David
Published: November 2006

A key requirement for the adoption of PEMFCs is demonstration of improved durability from the MEA. Most MEA failures have been ascribed to rupture of the membrane as a result of mechanical stress and chemical attack. Johnson Matthey Fuel Cells has developed a reinforced membrane impregnated with PFSA ionomer solution. In 30-cell stack tests the membrane has a high performance and shows a 6-fold improvement in durability compared to commercially available unreinforced membranes, under demanding automotive operating conditions. The improved durability is ascribed to an increased tear resistance and to an improved response to the change in dimensions during the hydration/dehydration cycles present during vehicle durability testing. Initial testing in large-scale single cells highlighted that MEA durability can be compromised by poor gasket design. Edge protection films were designed to overcome the impact of the gasket on durability with thinner films providing prolonged durability.
Accelerated Degradation Tests for Pt/C Catalysts in Sulfuric Acid
Authors: Ornelas Ruben , Stassi Alessandro , Modica Ester , Arico Antonino S. , Antonucci Vincenzo
Published: November 2006

Durability and cost reduction are the more important aspect for a large scale commercialization of PEM FC systems. This work presents a set of experiments ex situ for the selection of carbon catalyst supports in polymer electrolyte membrane (PEMFC).
Degradation Resistant Cathodes in Polymer Electrolyte Membrane Fuel Cells
Authors: Ye Siyu , Hall Miho , Cao Hong , He Ping
Published: November 2006

For a Polymer electrolyte membrane fuel cell (PEMFC) to be used commercially in stationary or transportation applications, cost and durability are the major challenges. Accordingly, there remains a need in the art to understand the degradation of fuel cell components and to develop design improvements to mitigate or eliminate such degradation. At Ballard, an accelerated stress test (AST) has been developed and used to evaluate the degradation resistance of different cathode catalyst materials and structures. Some cathode catalyst layer designs shown here demonstrated increased resistance to performance degradation due to carbon corrosion and Pt agglomeration/dissolution/migration without compromising performance.
The Impact of Carbon Stability on PEM Fuel Cell Startup and Shutdown Voltage Degradation
Authors: Yu Paul T. , Gu Wenbin , Makharia Rohit , Wagner Frederick T. , Gasteiger H. A.
Published: November 2006

Conventional carbon MEAs and graphitized carbon MEAs were evaluated for the resistance to carbon corrosion and startup/shutdown durability in this paper. Graphitized carbon MEAs show higher resistance to carbon corrosion than conventional carbon MEAs by a factor of 35 at a point where 5% weight loss had occurred. A graphitized carbon MEA yielded lower degradation rate than that of a conventional carbon MEA by a factor of 5 after 1,000 startup/shutdown cycles. The kinetics of carbon corrosion over both conventional carbon MEAs and graphitized carbon MEAs were measured, and carbon corrosion during startup/shutdown was explained and modeled. The model results correlate to what we have measured from our startup/shutdown durability test. Overall, MEAs with corrosion resistant carbon supports are one of major materials approaches to mitigate cell voltage degradation due to fuel cell startup/shutdown. We believe that a combination of corrosion resistant materials and system operating mitigation strategies is the path to attain the strict automotive durability targets.
Effect of Shutoff Sequence of Hydrogen and Air on Performance Degradation in PEFC
Authors: Takagi Yasuo , Takakuwa Yasutomo
Published: November 2006

The objective of this research is to characterize the performance degradation attributable to the shutdown operations of polymer electrolyte fuel cells and to explore possible methods of reducing such degradation. As a result, it was made clear that a sequence of shutting off the air supply prior to stopping the hydrogen supply was effective in mitigating such performance degradation. Diagnostic technology revealed that the performance degradation was mainly observed at the cathode catalyst and that it was caused by so-called reversal current, which was triggered by air that crossed leak from the cathode to the anode.
Behavior of Water below the Freezing Point in PEFCs
Authors: Ishikawa Yuji , Morita Tohru , Shiozawa Masahiro
Published: November 2006

This study investigates the phenomenon of water freezing below the freezing point in polymer electrolyte fuel cells (PEFCs). To perform in-situ observation of the fuel cell, a system capable of simultaneously observing inside the fuel cell with visible and infrared images was developed. Liquid water transportation was confirmed at -10 ºC when remaining water was dried enough inside the fuel cell before cold starting. The water generated on the gas diffusion layer expanded inside the gas flow channel with the water temperature at approximately - 10 ºC. Upon freezing, the water temperature rose significantly. This result indicates that the water is in a super-cooled state. Based on these results, it is confirmed that it is possible to generate a fuel cell maintaining water in a super- cooled state and fuel cell performance was dramatically improved by keeping the super-cooled state of water.
Fuel Cell Evaluation for Dynamic Applications
Authors: Moore Robert , Hauer K. H. , Randolf G. , Virji M.
Published: November 2006

The application of Hardware-in-Loop (HiL) methodology is well established in the automotive industry for control algorithm development and rapid prototyping. This paper presents and discusses the use of a new HiL methodology using a fuel cell as the HiL component that is experimentally evaluated within the context of a fuel cell system design, a specific application (e.g., a fuel cell vehicle), and a typical use pattern (i.e., a standard drive cycle). This new Fuel Cell HiL methodology has the goal of enabling the experimental evaluation of the performance, efficiency and durability of a fuel cell within a dynamic application. Experimental results are presented as a proof-of-concept and to illustrate actual fuel cell performance using this new technique.
Detection of Critical Operating Conditions for Fuel Cell Applications via Distortion Analysis
Authors: Schaffer Thomas , Schaffer Thomas , Baumgartner Wolfgang R. R. , Wallnöfer Eva , Hacker Viktor , Ramschak Erich , Peinecke Volker , Prenninger Peter
Published: November 2006

This new fuel cell stack diagnostics technology utilizes a signal distortion analysis to determine the actual status of a fuel cell / fuel cell stack in terms of critical operation conditions. Oxygen and hydrogen starvation, cell floodings are detectable with this method. In this paper the results of a flooding situation and an air starvation case are discussed. Also a semi empirical model is described which enables the prediction of the cell behavior in such critical operation modes.
Proton Transport Membranes for Fuel Cells: Polymeric versus Dense Ceramic
Authors: Prinz Fritz B. , Shim Joon Hyung , Cha Suk Won , Ohayre Ryan , Gur Turgut M.
Published: November 2006

Polymer based proton conducting membranes are currently employed as electrolytes in PEMFCs and DMFCs, but they present engineering challenges. Alternatively, we have explored dense ceramic membranes as proton conducting electrolytes for fuel cells. These dense membranes are effective electrolytes when fabricated in sufficiently thin layers, and eliminate some of the limitations of polymer-based membranes.
Combined Heat and Mass Transfer Model of a Passive Air Breathing Fuel Cell Cathode
Authors: O'Hayre Ryan , Fabian Tibor , Litster Shawn , Prinz Fritz B. , Santiago Juan G. G.
Published: November 2006

The behavior of an air breathing fuel cell (ABFC) operated on dry-hydrogen in dead ended mode is studied through theoretical analysis. A one-dimensional, non-isothermal, combined heat and mass transport model is developed that captures the coupling between water generation, oxygen consumption, self-heating, and natural convection at the cathode. The model is validated against ABFC experimental measurements over a range of ambient temperatures. The model confirms the strong effect of self- heating on the water balance within passive ABFCs. Model analysis provides several conclusions: 1) Thermal runaway caused by inadequate heat rejection predominantly limits performance. 2) The natural convection boundary layer represents a significant barrier to cathode mass and heat transfer. 3) Because the mass and heat transport numbers associated with natural convection are small, even slight forced convection dramatically affects behavior. 4) Performance optimization requires maximizing heat rejection while minimizing flooding. Decoupling these two phenomena is challenging due to the exponential relationship between water vapor saturation and temperature.
Water Management by Material Design and Engineering for PEM Fuel Cells
Authors: Nguyen T. V.
Published: November 2006

PEMFCs depend on proper water management to obtain high power density and energy efficiency. Traditionally, water management has been addressed by system design and engineering. That is, by adding processes to the basic PEMFC system to provide humidification to the anode and to remove water from the cathode. This approach adds significant complexities and costs and reduces the overall efficiency of the PEMFC system. Development of new materials and better understanding of the functions of these materials have led to a paradigm shift as to how water management can be implemented in a PEMFC system. In this new paradigm, materials with the right properties will be used in the membrane and electrode assemblies such that zero net water transport across the membrane is achieved. Once this goal is attained the next goal will be to achieve optimal anode and cathode gas humidification and membrane hydration with zero-external- system-water requirement.
Direct Methanol Fuel Cell with Extended Reaction Zone Anode
Authors: Bauer Alexander G. , Gyenge Elod , Oloman Colin
Published: November 2006

Three-dimensional DMFC anodes were prepared by galvanostatic electrodeposition of PtRu(Mo) catalytic particles onto compressed graphite felt in the presence of the nonionic surfactant Triton X-100. The Mo containing catalyst yielded higher power densities at 343 K and 353 K compared to PtRu, while utilizing about 50 % lower Pt and total catalyst loadings. The 3D anode design with PtRu catalyst yielded improved performance compared to a commercially available gas diffusion electrode with approximately equal Pt loading (~26 g m-2); i.e. at 3000 A m-2 and 333 K the power density was increased by ~38 %.
Free Convection Direct Methanol Fuel Cells Powered by Electroosmotic Pumps
Authors: Buie Cullen , Kim Daejoong , Litster Shawn , Santiago Juan G. G.
Published: November 2006

This work reports on the design and performance evaluation of a miniature direct methanol fuel cell (DMFC) integrated with an electroosmotic pump for methanol delivery. Electroosmotic pumps require minimal parasitic power while boasting no moving parts and simple fuel cell integration. Here, electroosmotic pumps are realized from commercially available porous glass frits. Experimental results show that electroosmotic pumps deliver 4M, and 8M methanol/water mixtures to DMFCs (at 50oC) while utilizing 1% and 4% of the fuel cells power, respectively. Furthermore, we discuss pertinent design considerations when using electroosmotic pumps with DMFCs and areas of future study.
Ethanol Oxidation on Pt-Sn Electrocatalysts Supported on Carbon Prepared by Reduction with Formic Acid
Authors: Gonzalez Ernesto R. , Colmati Flavio , Antolini Ermete
Published: November 2006

Carbon supported Pt-Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterised by X-ray diffraction, high resolution transmission electron microscopy and X-ray absorption near- edge structure analyses. Their electrocatalytic activity for ethanol oxidation was compared with commercial Pt/C and Pt3Sn/C electrocatalysts. The synthetized PtSn catalysts presented a low degree of alloy formation and high contents of Sn oxides. The electrocatalytic activity for ethanol oxidation in linear sweep voltammetry experiments at room temperature is greatly enhanced, mainly at low potentials, on Pt3Sn and Pt2Sn catalysts prepared by reduction with formic acid, while only a slight improvement is observed on Pt9Sn prepared with formic acid. On the other hand, a commercial Pt3Sn catalyst with a high degree of alloying showed the highest current performance as anode material in a direct ethanol fuel cell (DEFC) operating at 90 and 110 oC.
Palladium-Platinum Alloy Anode Catalysts for Direct Formic Acid Fuel Cells
Authors: Blair Sharon , Lycke Derek , Iordache Coca A.
Published: November 2006

The relationship between the composition of palladium-platinum alloy nanoparticles and their performance as electrocatalysts for formic acid electro-oxidation has been studied. Unsupported nanoparticle palladium-platinum alloys have been prepared by the co-reduction of palladium and platinum salts with ethylene glycol and characterized by X-ray diffraction (XRD). The electrocatalytic activities of the alloys were compared to that of pure platinum and palladium nanoparticle catalysts using cyclic voltammetry, chronopotentiometry, and chronoamperometry. The results reveal a synergetic effect of platinum and palladium as well as independent behaviour of the two metals for formic acid oxidation.
Suppressing Layout-Induced Threshold Variations by Halo Engineering
Authors: Moroz Victor , Smith Lee
Published: November 2006

When creating source/drain regions of a MOSFET transistor, the implants introduce crystal damage. During subsequent activation annealing, the implant damage serves as a source of silicon interstitials that create dopant transient-enhanced diffusion (TED). The amount of TED is determined by the source/drain area and by the proximity of STI boundary, where interstitials recombine. Different amount of TED, experienced by transistors with different shapes and sizes of their source/drain area, lead to the difference in dopant diffusion in the channel/halo, and the corresponding variation of the threshold voltage. Depending on specific combination of layout and process flow, the MOSFET threshold voltages can either increase or stay flat or decrease with the distance from the channel to the STI. For each set of design rules/technology node, it is possible to design the halo implants such that the threshold sensitivity is close to flat and therefore eliminate layout sensitivity of the threshold voltage.
Sheet Resistance Increase of Shallow Doped Silicon during Native Oxidation in Air
Authors: Kalkofen Bodo , Burte Edmund P.
Published: November 2006

An increase in sheet resistance of shallow doped silicon during air exposure was investigated. Shallow phosphorus doping of silicon wafers was carried out by an atomic-layer doping process forming a pn-junction close to its surface. The sheet resistance Rs of the n+-doped layer was found not to be constant during its contact to air after the process, but showed a remarkable step-like increase with time. After the removal of native oxide by an HF-treatment a similar behavior could be observed during re-oxidation. This behavior may be associated with a layer-by-layer growth of native oxide in conjunction with a silicon consumption and deactivation of dopants in the shallow doped subsurface layer. The observation suggests studying appropriate time-dependent surface related processes by means of the simple four-point probe setup by measuring surface affected sheet resistance changes of shallow doped layers.
Leakage Current Characteristics of Ultra-Shallow Junctions Formed by B2H6 Plasma Doping
Authors: Sauddin Hendriansyah , Sasaki Yuichiro , Ito Hiroyuki , Mizuno Bunji , Ahmet Parhat , Kakushima Kuniyuki , Sugii Nobuyuki , Tsutsui Kazuo , Iwai Hiroshi
Published: November 2006

Leakage currents across the ultra-shallow junctions formed by plasma doping using B2H6/He plasma were analyzed. With J-V-T and C-V-T measurements, we discussed the leakage current behavior in order to reveal the origin of the leakage current of ultra-shallow junctions formed by the plasma doping. Midgap trap levels of 0.59 eV have been found for these junctions.
3D Pattern Effects in RTA Radiative vs Conductive Heating
Authors: Granneman Ernst H. , Terhorst Herbert , Falepin Annelies , Rosseel Erik , Verheyden Kurt , Vanormelingen Koen , Bourdon Helene , Halimaoui Aomar , Funk Klaus
Published: November 2006

The effect of 3D patterns on the heating of silicon substrates was investigated theoretically and experimentally. As energy sources RTA systems based on radiant heating (i.e. lamp-based) and on conduction heating (wafer placed in very close proximity to hot surfaces) were applied. The 3D patterns were trenches with dimensions 150-450nm wide, and 400nm deep. In case of lamp- based systems with heat-up rates of 75{degree sign}C/s within- die temperature variations of 10-20{degree sign}C were observed. In case of conduction-based systems with heat-up rates up to 900{degree sign}C/s the impact of the 3D structures was negligible. Both types of systems were modeled, and a reasonable correlation with the experimental data was found.
Study of Ni-Silicide Contacts to Si:C Source/Drain.
Authors: Mertens Sofie , Cho Yonah , Nouri Faran , Schreutelkamp Robert , Kim Yihwan , Verheyen Peter , Steenbergen Johnny , Vrancken Christa , Bender Hugo , Richard Olivier , Van Daele Benny , Vandervorst Wilfried , Absil Philip , Kubicek Stefan , Demeurisse Caroline , Tokei Zsolt , Lauwers Anne , Geenen Luc
Published: November 2006

Integration of recessed Si:C source/drain (S/D) for deep sub- micron nMOSFET devices results in substantial improvement of electron mobility and drive current due to introduction of tensile strain in the channel. The compatibility of Ni-silicide contacts with Si:C source/drain is investigated in this paper. The Ni-silicide morphology and phase formation were studied by means of sheet resistance measurements, X-Ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) inspection. The carbon concentration and profile in the NiSi:C film was studied by Secondary Ion Mass Spectrometry (SIMS) analysis. The strain in the Si:C substrate and NiSi:C film was studied by high resolution XRD (HRXRD). This paper demonstrates that Ni-silicide is compatible with Si:C. The tensile strain in Si:C is maintained after Ni-silicidation. The addition of carbon to silicon is found to stabilize the silicide morphology.
Ab Initio Investigations of Textured Ni2Si Films on Silicon
Authors: Alippi Paola , Alberti Alessandra
Published: November 2006

Transition metal silicides grown on Si substrates show peculiar structural behavior, due to their rich variety of phases with different stoichiometric compositions. Phases with low electrical resistivity and high thermal stability are needed as contact materials in advanced integrated circuits while nickel silicide is the main candidate as future material for interconnects. Recently, structural investigations on thin silicide films on Si(100) have characterized novel forms of silicide texturing: alignment of planes across the interface seems to be preferred over standard in-plane epitaxial alignment. We investigate by first-principle total energy calculations the role of interface and elastic energies in the stabilization of textured silicide film structures on Si(001). From the comparison of calculated interface energy values we address the role of energetics in texture selection.
Effect of Deposition Temperature on Chemical Structure of Lanthanum Oxide/Si Interface Structure
Authors: Nohira Hiroshi , Matsuda Toru , Tachi Kiichi , Shiino Yasuhiro , Song Jaeyeol , Kuroki Yusuke , Ng Jin Aun , Ahmet Parhat , Kakushima Kuniyuki , Tsutsui Kazuo , Ikenaga Eiji , Kobayashi Keisuke , Iwai H. , Hattori Takeo
Published: November 2006

The effect of substrate-temperature during the deposition of lanthanum oxide on the chemical structure of lanthanum oxide/Si(100) interfacial transition layer formed between lanthanum oxide and Si-substrate was studied from the measurements of angle-resolved Si 1s, O 1s and La 3d5/2 photoelectron spectra. In the case of the deposition at room temperature the amount of lanthanum silicate (La-silicate) was extremely small, and was not affected by the post deposition annealing (PDA) at 300{degree sign}C, and increased by PDA at temperature above 500{degree sign}C. On the other hand, in the case of the deposition at 300{degree sign}C the amount of La-silicate increased appreciably by PDA even at 300{degree sign}C. Therefore, the existence of La-silicate accelerates the formation of La-silicate by PDA.