bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Formation and Characterization of Silicon-Quantum-Dots/Metal-Silicide-Nanodots Hybrid Stack and its Application to Floating Gate Functional Devices
Authors: Miyazaki Seiichi
Published: October 2011

Hybrid nanodots (NDs) structures have been designed and fabricated as a noble functional floating gate, in which Si quantum dots (QDs) as charge counting nodes and either Ni- or Pt-silicide NDs as charge storage nodes are stacked with an ultrathin SiO2 interlayer, to satisfy both large memory windows and multi-valued capability. MOS capacitors and nMOSFETs with a hybrid FG show clear characteristics caused by stable storage of many charges in the deep potential well of each silicide ND and stepwise charge injection to and emission from NDs through discrete energy states in Si-QDs. In addition, a distinct optical response to 1310nm light irradiation was detected in the C-V characteristics, being interpreted in terms of the shift of charge centroid in the hybrid FG stack due to transfer of photoexcited electrons from silicide NDs to the Si-QDs.
(Invited) Issues and Challenges of High-k Dielectrics on High-Mobility Substrates
Authors: Misra Durga
Published: October 2011

With the current trend in device scaling, for high speed and low power applications materials with high-k dielectric constant such as Hf-based dielectrics are being integrated into standard CMOS technologies. Hihg mobility substrates such as germanium (Ge) and gallium arsenide (GaAs) are being considered for their high electron mobility. The interface between the high-k dielectrics and the high mobility substrates are not well understood. A strong interface passivation technique is, therefore, necessary to optimize the device performance. As it is clear from the electrical performance in these devices depends on the deposition process, precise selection of deposition parameters, predeposition surface treatments and subsequent annealing temperatures. This work reviews the recent developments of high-k/Ge interface and its characterization. To form an electrically passive interface, interface treatments such as surface nitridation of HfO2/Ge interface will be evaluated. In addition, electrical characteristics of high-k on III-V substrates are also outlined.
Enhancement of a Channel Strain via Dry Oxidation of Recessed Source/Drain Si1−xGex Structures
Authors: Kim Sun-Wook , Yoo Jung-Ho , Koo Sang-mo , Ko Dae-Hong , Lee Hoo-Jeong
Published: October 2011

We investigated the effects of oxidation on recessed source/drain Si1-xGex structures. Epitaxial Si1-xGex films were deposited on recessed source/drain structures using a selective epitaxial growth process combined with ultrahigh-vacuum chemical vapor deposition and oxidized in dry oxygen ambient. Based on nano beam diffraction analyses, the channel strain was effectively enhanced at specific oxidation conditions. The increase in channel strain results from the formation of Ge-rich layers on the top surface of the Si1-xGex regions upon oxidation.
(Invited) Effect of Al2O3/InGaAs Interface on Channel Mobility
Authors: Yang Li , Cheng Cheng-Wei , Bulsara Mayank T. , Fitzgerald Eugene A.
Published: October 2011

In this paper, we discuss the effect of Al2O3/InGaAs interface on In0.53Ga0.47As quantum-well MOSFET channel mobility. We fabricated Al2O3 (gate dielectric)/In0.53Ga0.47As-In0.52Al0.48As (barrier)/In0.53Ga0.47As (channel) structures to study effects of gate dielectric thickness and barrier thickness on channel carrier mobility. Hall measurements were used to examine the mobility. The mobility was invariant with varying gate dielectric thickness, suggesting that charges trapped within the Al2O3 do not affect mobility significantly. The mobility varies with varying barrier thickness suggesting that Al2O3/In0.53Ga0.47As interfacial charges affect mobility. In our case, when the barrier thickness <5 nm, the mobility is dominated by coulomb scattering from interfacial charges; when the barrier thickness >5 nm, the mobility is dominated by internal phonon scattering. A model was developed to fit the experimental data and this model could be used to sample MOSFET designs that are limited by phonon scattering and gate dielectric/barrier layer interfacial charge density.
(Invited) GeSn Technology: Impact of Sn on Ge CMOS Applications
Authors: Zaima Shigeaki , Nakatsuka Osamu , Shimura Yosuke , Adachi Masaki , Nakamura Marika , Takeuchi Shotaro , Vincent Benjamin , Gencarelli Federica , Clarysse Trudy , Demeulemeester Jelle , Temst Kristiaan , Vantomme Andre , Caymax Matty , Loo Roger
Published: October 2011

In this paper, we reports our recent studies of the electrical and crystalline properties of heteroepitaxial Ge1-xSnx layers with various Sn content of 0~25%. We examined Ga-doping in strained Ge1-xSnx layers for developing source/drain stressor in CMOS applications and investigated the effect of Sn on the doping profile. The impact of Sn on carrier properties has been also studied with the Hall measurement of Ge1-xSnx/SOI structures. Also, we achieved the epitaxial growth of Ge1-xSnx layers with a Sn content as high as 25% on InP considering misfit between the epitaxial layer and substrate.
(Invited) Challenges of Si Photonics for Photonics Integration on Si LSIs
Authors: Wada Kazumi , Ishikawa Yasuhiko
Published: October 2011

The first generation of Si photonics is about over by breakthrough of n+Ge laser as a on-chip monolithic light source. The grand challenge for the next generation is to implement on-chip wavelength division multiplexing (WDM); how to lock the wavelength on an uncooled chip. The present paper proposes the key to the locking in terms of strain to control refractive and absorption indices.
Dependence of Interface-State Density on Three Dimensional Silicon Structure Measured by Charge-Pumping Method
Authors: Nakajima Kazuhiro , Sato Soshi , Kakushima Kuniyuki , Ahmet Parhat , Tsutsui Kazuo , Nishiyama Akira , Sugii Nobuyuki , Natori Kenji , Hattori Takeo , Iwai Hiroshi
Published: October 2011

Dependence of interface-state density (Dit) on three dimensional (3D) Si channels with a rectangular cross section of various width and shape was measured by charge-pumping method with gated PIN-diode configuration formed on silicon-on-insulator (SOI) wafer. The increase in Dit was observed with decreasing the width of the fin structure.
A Deep-Level Transient Spectroscopy Study of Implanted Ge p+n and n+p Junctions by Pt-Induced Crystallization
Authors: Simoen Eddy , Lauwaert Johan , Vrielinck Henk , Ioannou-Sougleridis V , Dimoulas A.
Published: October 2011

This paper reports on a Deep-Level Transient Spectroscopy (DLTS) study of ion-implanted Ge n+p and p+n junctions, subjected to a 350 oC anneal after Pt-metallization. It is shown that good quality diodes with acceptable reverse current levels can be achieved, pointing to a successful activation and defect removal, especially for the p+n junctions. Nevertheless, DLTS reveals the presence of small concentrations of deep levels, which can be associated with residual ion implantation damage and possibly Pt in-diffusion. In the case of the p+n diodes, the thermal activation energy of the leakage current increases from 0.38 eV to 0.45 eV, which could be in line with the annealing of the deep-level traps, observed in DLTS. The situation is more complex for the n+p junctions, where the low activation energy points to field-assisted leakage current mechanisms, which can be mediated by the residual implantation damage.
(Invited) Pulsed UV-Laser Processing of Amorphous and Crystalline Group IV Semiconductors
Authors: Chiussi Stefano , Gontad Francisco , Stefanov Stefan , Conde Jorge Carlos , López Estefanía , Serra Carmen , Benedetti Alessandro , Serra Julia , León Betty , González Pio
Published: October 2011

In the last decade, UV-Excimer laser systems have been dramatically improved in terms of beam quality, power stability and gas lifetime. The benefits of using them for group IV semiconductor processing have, up to now, principally been recognized for some few processes like laser marking, UV-lithography and Excimer Laser Crystallization (ELC). Although several other techniques like Laser induced Chemical Vapor Deposition (LCVD), Excimer Laser Annealing (ELA) and Pulsed Laser Induced Epitaxy (PLIE) have been extensively studied 30 years ago for producing silicon coatings, little is known about the prospects of up-scaling those processes to other group IV semiconductors. This contribution presents UV-Laser processes combining LCVD of amorphous Si and of SiGeC alloys with their subsequent laser, in particular PLIE, treatment for modifying their composition and structure in order to engineer lattice parameters.
Low-Frequency Noise Assessment of CMOS Transistors with a Through-Silicon Via
Authors: Simoen Eddy , Mercha Abdelkarim , Van der Plas Geert , Claeys Cor
Published: October 2011

Low-frequency (LF) noise has been used to study the impact of a nearby copper through-silicon via (TSV) on the gate oxide quality of p- and n-channel MOSFETs. It is shown that the spectra in all cases studied are governed by 1/f-like noise, associated with trapping of carriers in the gate dielectric. While the impact of the TSV on the noise magnitude and behavior of n-channel transistors is marginal, some increase of the spectral density can be found for the pMOSFETs, although there is no systematic trend with distance. This is discussed in terms of the impact of strain on the LF noise.
The Effects of Mechanical and Tribological Properties of Coatings on Scratch Generation in Chemical-Mechanical Polishing
Authors: Kim Sanha , Saka Nannaji , Chun Jung-Hoon
Published: October 2011

In chemical mechanical polishing, even the soft pad asperities may, under certain conditions, generate scratches on relatively hard surfaces. The present study, accordingly, focuses on the effects of coating and pad hardnesses and of interfacial friction on scratch generation. The hardness of various thin films (Al, Cu, SiO2, Si3N4, TiN and three low-k dielectrics) and of a CMP pad were determined by a Hysitron Triboindenter. Additionally, the coefficients of friction between the pad and the coatings were determined by sliding friction experiments. Scratches were produced only on the Al and Cu coatings, whose hardness and friction conditions fall in the scratching regime of the scratch-regime map. No scratches were produced, not surprisingly, on hard coatings even at high friction.
(Invited) Low Temperature Atomic Layer Deposition of Ru Thin Films with Enhanced Nucleation Using Various Ru(0) Metallorganic Precursors and Molecular O2
Authors: Kim Soo-Hyun
Published: October 2011

Ruthenium (Ru) thin films were grown on thermally-grown SiO2 substrates by atomic layer deposition (ALD) using a sequential supply of three kinds of novel zero valence Ru precursors, isopropyl-methylbenzenecyclohexadiene Ru(0) (IMBCHRu, C16H22Ru), ethylbenzen-cyclohexadiene Ru(0) (EBCHRu, C14H18Ru), and ethylbenzen-ethyl-cyclohexadiene Ru(0) (EBECHRu, C16H22Ru) and molecular oxygen (O2) as a reactant at substrate temperatures ranging from 140 to 350 oC. It was shown that little incubation cycle was observed at ALD temperature window, indicating of the improved nucleation as compared to the use of typical higher valence Ru precursors such as cyclopendadienyl-based Ru (II) or β-diketonate Ru (III) metallorganic precursors. The step coverage of ALD-Ru was excellent, around 100 % at ultra-small trench with an aspect ratio of ~ 4.5 (top-opening diameter: ~ 25 nm). The developed ALD-Ru films was successfully used as a seed layer for Cu electroplating.
Copper-ALD Seed Layer as an Enabler for Device Scaling
Authors: Mao Jiajun , Eisenbraun Eric , Omarjee Vincent , Korolev Andrey , Dussarrat Christian
Published: October 2011

Copper-seed layer deposition by plasma enhanced atomic layer deposition (PEALD) has been developed and characterized using a recently introduced copper precursor, AbaCus. Film properties such as composition, grain size and resistivity have been studied. Electroplated structures were successfully filled, demonstrating a high potential of this process for use in advanced interconnect technologies.
Structural Characteristics of Electrically Scaled ALD HfO2 from Cyclical Deposition and Annealing Scheme
Authors: Consiglio Steven , Clark Robert D. , Bersch Eric , LaRose Joshua , Wells Ilyssa , Tapily Kandabara , Leusink Gert J. , Diebold Alain
Published: October 2011

We have recently reported electrical performance improvements in atomic layer deposited (ALD) HfO2 films grown by use of a cyclical deposition and annealing scheme (termed DADA) compared to a single deposition followed by a post-deposition anneal (PDA). We previously proposed a model for bottom-up crystallization in DADA films in contrast to random crystallization for PDA films. To elucidate the mechanisms for this structural modification, in this study we utilized grazing incidence in-plane X-ray diffraction and pole figure measurements using synchrotron radiation as well as transmission electron microscopy. Structural differences were investigated from different annealing conditions as well as from different thickness of films. We observed significant differences in structural properties of DADA films compared to films receiving PDA. We also report on the evolution of monoclinic HfO2 with a (-111) preferred orientation (fiber texture) for DADA films whereas PDA treatment resulted in a random grain alignment and mixed phase structure.
(Invited) Tailor-Made, Magnetic Nanotubes by Template-Directed Atomic Layer Deposition
Authors: Zierold Robert , Nielsch Kornelius
Published: October 2011

This article shows how a gas-phase deposition technique like atomic layer deposition can be utilized for the preparation of tailor-made, magnetic nanotubes by applying it to different template structures, as nanoporous alumina membranes or arrays of silica columns, respectively. On the one hand, such magnetic nanotubes can lead to new insights in basic physical fundamentals, like transitions in the magnetic reversal mechanisms as a function of the wall thickness or the angle of the applied field. On the other hand, novel magnetic, tubular structures might reveal new applications as ferrofluids in terms of liquid suspension or data storage devices comprised of two bit core-shell structure.
Metalcone and Metalcone/Metal Oxide Alloys Grown Using Atomic and Molecular Layer Deposition
Authors: Lee Byoung Hoon , Anderson Virginia R. , George Steven M.
Published: October 2011

Atomic and molecular layer deposition (ALD & MLD) techniques can be used to fabricate various hybrid organic-inorganic polymer films. One class of hybrid organic-inorganic films are metal alkoxide polymers that are formed from organometallic precursors and organic alcohols. These metal alkoxide polymers are called "metalcones". The metalcones can also be mixed with metal oxides to grow metalcone/metal oxide alloys. This paper will overview some of the new metalcones and metalcone/metal oxide alloys that can be grown and some of their properties. Zircone MLD films were grown using zirconium tert-butoxide (ZTB) and ethylene glycol (EG) at 145°C. Alucone alloy films were grown by combining Al2O3 ALD and alucone MLD at 135°C. Zircone alloy films also were fabricated by combining ZrO2 ALD and zircone MLD at 145°C. These new materials offer a tool set for engineering the functional properties of thin films.
Indium Oxide ALD Using Cyclopentadienyl Indium and Mixtures of H2O and O2
Authors: Elam Jeffrey W. , Libera Joseph A. , Hryn John N.
Published: October 2011

This study describes how In2O3 films can be prepared by ALD using alternating exposures to cyclopentadienyl indium (InCp) and combinations of H2O and O2, even though H2O and O2 are ineffective when used individually. When H2O and O2 are used together, either as a simultaneous exposure or in the sequence H2O-O2 or O2-H2O, very uniform, highly conducting In2O3 films are deposited at 1.0-1.6 Aå/cycle over large areas (12"x18") at temperatures as low as 100°C. In agreement with our published mechanism, in-situ Fourier transform infrared measurements revealed that the H2O and O2 work synergistically to facilitate the In2O3 ALD. Ex-situ measurements on films prepared over the deposition temperature range 100-250°C identified a remarkable correlation between the film structure and electrical properties around an amorphous-to-crystalline phase transition near 140°C.
Diffusion-Reaction Model of ALD in Nanostructured Substrates: Analytic Approximations to Dose Times as a Function of the Surface Reaction Probability
Authors: Yanguas-Gil Angel , Elam Jeffrey W.
Published: October 2011

We have developed a transport model for Atomic Layer Deposition (ALD) in nanostructured substrates. The model comprises a non-linear advection-diffusion-reaction equation coupled to a surface kinetic equation that incorporates the self-limiting nature of ALD. In their nondimensional forms, these equations show that coverage dynamics in ALD depend only on two parameters: the Damkoeler number and the precursor excess number. These parameters depend on the surface chemistry and experimental conditions and can be readily calculated for a wide range of substrate geometries including trenches and vias, anodized alumina, and powders.
(Invited) Reaction Mechanisms in ALD of Ternary Oxides
Authors: Elliott Simon D. , Nilsen Ola
Published: October 2011

Reaction mechanisms underlying the atomic layer deposition (ALD) of ternary oxide films are investigated via the dependence of film stoichiometry on the sequence of ALD pulses. Data on film composition are brought together from experiments on five ternary oxide systems containing La, Mn, Ca, Fe, Sr, or Co, all using beta-diketonate ligands (thd) in the metal precursor and ozone as the oxygen source. These data are compared with the predictions from two possible reaction models: one where all ligands are combusted by ozone, the other where extra ligands are eliminated during the metal precursor pulse due to the availability of surface hydroxyl. The latter reaction is seen to be strongly dependent on the strength of the metal-ligand bond. Differences in cation charge also affect the stoichiometry. In this way, factors dictating the composition of ternary oxides are elucidated, opening the way to improved control of ALD processes and material properties.
ALD for a Sustainable Future - Paving the Way to a Cleaner World from Sub-Nanometer Level
Authors: Toivola Minna , Pilvi Tero
Published: October 2011

Atomic layer deposition (ALD) is a chemical vapor processing method with which highly conformal, uniform, defect and pinhole free ultrathin films can be coated even on the most challenging nanoscale architectures such as high aspect ratio trenches, through silicon vias and highly tortuous through-porous networks. ALD is already widely in use in e.g. electronics, optics and sensor industries but it is rapidly gaining foothold also inside the renewable energy and clean and sustainable technology community. Picosun is Finnish, globally operating ALD equipment manufacturer whose exclusive, pioneering expertise in the field reaches back to the invention of the ALD technology itself and whose ALD systems are used by high profile industries and top level research organizations across four continents.
Development of Novel Silicon Precursors for Low-Temperature CVD/ALD Processes
Authors: Iwanaga Kohei , Tada Ken-ichi , Chiba Hirokazu , Yamamoto Toshiki , Maniwa Atsushi , Yotsuya Tadahiro , Oshima Noriaki
Published: October 2011

Novel silicon precursors, Si-TBES (2) and Si-TBAS (3), were prepared for CVD/ALD processes. Thermal analyses revealed that compound 2 and 3 were highly volatile, and their decomposition temperatures were lower than those of comparable silicon precursors, Si(OEt)4 (TEOS) and SiH(NMe2)3 (TDMAS). Deposition properties of SiO2 thin films were investigated by a thermal CVD apparatus. Deposition rates of precursor 2 and 3 were higher than that of TDMAS, and the growth rate using precursor 3 at 500 degrees Celsius was tens of times as high as that of TDMAS. Deposition rate dependency on oxygen partial pressure indicates the high reactivity of precursor 2 and 3 towards oxygen.
Atomic Layer Deposition of AlN with Tris(Dimethylamido)Aluminum and NH3
Authors: Liu Guo , Deguns Eric , Lecordier Laurent , Sundaram Ganesh , Becker Jill
Published: October 2011

Atomic layer deposition of aluminum nitride on Si wafers using tris(dimethylamido)aluminum and ammonia has been investigated in the temperature range from 180 to 400°C. Saturated growth behavior not observed with NH3 pulsed in continuous mode has been achieved in NH3 exposure mode. Thin AlN films have been analyzed by spectroscopic ellipsometry and SIMS for optical and chemical properties, X-ray diffraction for crystallinity, and mercury probe for electrical properties. Polycrystalline and high purity AlN films have been obtained at 300°C or higher. A high dielectric constant in the range of 7.4-7.7 and high breakdown field of 5.3-5.6 MV/cm with relatively low leakage current in the 10-7 to 10-8 A/cm2 range at 2MV/cm have been obtained for AlN films deposited between 300 and 400°C in NH3 exposure mode.
Deposition and Characterization of Atomic Layer Deposited ZnS Thin Films on p-type GaSb(100) Using Diethylzinc Precursor and Hydrogen Sulfide
Authors: Xu Runshen , Huang Jun , Ghosh Sid , Takoudis Christos G.
Published: October 2011

Diethylzinc precursor and hydrogen sulfide were used for the atomic layer deposition (ALD) of ZnS films on thioacetamide (TAM)-treated p-type GaSb substrates for the passivation of GaSb-based devices. The film growth rate was found to be 0.13±0.01 nm/cycle with an ALD window of 175 - 275 °C. X-ray photoelectron spectroscopy (XPS) analyses of as-deposited ZnS films showed that the resulting films were stoichiometric ZnS with no evidence of other sulfur species in the film. XPS indicated the surface of GaSb treated with TAM was a mixture of Ga-S and Sb-S without detectable oxides. After the ALD of 1 nm-thick ZnS on TAM-treated GaSb, the major component at the interface of ZnS/TAM-treated GaSb system was found to be gallium sulfide. Surface morphology and structure of as-deposited ZnS were studied with phase-shifting interferometry and grazing incidence X-ray diffraction.
Enabling High Performance Instruments for Astronomy and Space Exploration with ALD
Authors: Greer Frank , Hoenk M.E. , Jacquot B.C. , Jones T.J. , Dickie M.R. , Monacos S.P. , Nikzad S. , Hamden E. , Schmonivich D. , Day P. , Leduc H.
Published: October 2011

Future UV, X-ray, and sub-millimeter telescopes and spectrometers have the potential to revolutionize our understanding of the formation and habitability of the modern universe.[1-4] Star formation, dark energy, and the composition of the intergalactic medium are only some of the key scientific topics that can be addressed by UV astronomy and astrophysics. Sub-millimeter astronomy can probe the fine structure of the cosmic microwave background, giving glimpses into the early universe immediately following the Big Bang.[5] Various surface engineering techniques including molecular beam epitaxy and atomic layer deposition have been utilized here to significantly boost the performance of key components of instruments for astronomy and astrophysics investigation, taking advantage of the atomic level precision that these techniques provide.
Novel Hybrid Organic/Inorganic Photovoltaic Device Configuration Utilizing ALD Technology and Template Based Nanoelectrode Arrays
Authors: Gu Diefeng , Baumgart Helmut , Namkoong Gon
Published: October 2011

The combination of composite insulating oxide layers alternating with semiconducting layers and metals can provide various types of novel applications and eventually provide unique and advanced levels of nanoscale photovoltaic devices. Semiconducting TiO2 nanotubes have potential applications in photovoltaic devices and have been incorporated into organic-inorganic solar cells using highly arrayed nanostructures that promise new levels of performance and efficiency. The 3-dimensional parameters such as thickness, spacing, and height of the nanostructures are controlled non-lithographically by Atomic Layer Deposition (ALD) technology. The crucial process for sacrificial spacer layers to be filled with organic blends for photo-absorption is discussed. The semiconducting ZnO has been used as electrode to connect electrically isolated TiO2 nanotubes.
(Invited) ALD of Thin Films for Lithium-Ion Batteries
Authors: Aaltonen Titta , Miikkulainen Ville , Gandrud Knut Bjarne , Pettersen Anders , Nilsen Ola , Fjellvaåg Helmer
Published: October 2011

Atomic layer deposition (ALD) technique is a thin film deposition method that provides highly conformal films on 3D structured supports, including powder materials. The technique relies on sequential self-limiting gas-to-surface reactions which enable control of thin film depositions even down to the atomic level on complex surface geometries. Even if ALD technique has been used in the semiconductor industry in production scale for several years now, there are rather few reports on ALD of battery materials. However, the recent development in processes for lithium containing films clearly opens up new possibilities. Promising applications of ALD include 3D structured all-solid-state batteries and surface modification of electrode powders. The present paper presents an overview of the present status in application of ALD in the field of lithium ion batteries.
Development Trends and Popularization Scenario for Fuel Cell Vehicle
Authors: Yoshida Toshihiko , Kojima Koichi , Yokoyama Tatsuaki , Sekine Shinobu
Published: October 2011

The Toyota FCHV-adv that was released in 2008 has a cruising range in actual driving conditions of more than 500 km and can be started in temperatures as low as -30°, thereby overcoming two of the major obstacles to the practical adoption of FCVs. Toyota is continuing to resolve technical issues to popularize FCVs. For example, Toyota aims to reduce the cost to about 1/20 by further development work. In addition to improving commercial appeal, the widespread adoption of FCVs depends on the establishment of basic hydrogen infrastructure. Toward 2015, Car manufactures including Toyota are continuing to cooperate with governments and energy businesses to establish infrastructure and make the necessary modifications to laws and regulations. This article summarizes the technical progress for FCVs
Electrons to Go: Electrochemistry and the Future of the Automobile
Authors: Wagner Frederick T. , Lakshmanan Balsu , Gu Wenbin , Greszler Thomas , Mathias Mark F.
Published: October 2011

Electrification of the automobile provides pathways to sustaining freedom of personal mobility in the face of environmental imperatives, increasing demand for cars in the developing world, and limitations in the supply of easily-recoverable petroleum. This paper weighs the pros and cons of hydrogen fuel cell electric vehicles (FCEVs) vs. lithium-based battery electric vehicles (BEVs) as sustainable long-term solutions. BEVs can make efficient use of renewably-sourced electricity but face persistent shortfalls in range, speed of recharge, infrastructure for rapid recharge, and operability over climatic extremes. FCEVs can provide the full function expected of automobiles and light trucks today. They can meet range requirements, can be rapidly refueled, and can operate well at cold temperatures. However, they make relatively inefficient use of renewably-sourced electricity and require the implementation of a hydrogen infrastructure. Both systems still face cost challenges. Research directions and prospects for these two technologies are outlined.
Modeling Ion Transport in Fuel Cell Electrodes including Water|Electrolyte Interfaces and Electric Double Layers
Authors: Zenyuk Iryna , Lee Jooyeob , Litster Shawn
Published: October 2011

We present a computational model for studying ionic transport within water-filled pores inside polymer electrolyte fuel cell (PEFC) catalyst layers. The model features the interface between a water-filled pore and polymer electrolyte, and the electric double layers (EDLs) that form at the water|polymer electrolyte interface and at the charged walls of the pores. This model is applicable to several catalyst layer scenarios, including ionic transport within ionomer-free nanostructured thin-film (NSTF) electrodes, ionomer-free pores within catalyst particle agglomerates, and the micropores within catalyst support particles. We investigate the coupling of the distributed electrochemical reactions and the EDL physics, and their effect on the overall catalyst layer performance through both the kinetics and transport. An important finding is the significant impact that the polyelectrolyte film's Donnan potential has on the reaction distribution along the pore.
Cold-Start Modeling of a Polymer-Electrolyte Fuel Cell Containing an Ultrathin Cathode
Authors: Balliet Ryan , Newman John
Published: October 2011

Improved durability and reduced precious-metal loading are objectives of current polymer-electrolyte fuel-cell research. One path toward these objectives that shows promise is the use of ultrathin catalyst layers, which have thicknesses of less than 0.5 micrometer. In contrast, conventional platinum-on- carbon porous electrodes are generally between 10 and 20 micrometer thick. A disadvantage of ultrathin cathodes is their tendency to flood at low temperature, which could increase the time required to start the cell after an extended shutdown. In the present work, the cold-start performance of a polymer-electrolyte fuel cell with an ultrathin cathode is investigated by modifying a cold-start model (presented previously) such that the cathode is taken to be an infinitesimally thin surface. Performance is predicted over a temperature range of -40 to -5 °C. Comparisons are made to an equivalent conventional cell, parametric studies are performed, and mitigation strategies are investigated.
Effective Transport Properties Accounting for Electrochemical Reactions of Proton-Exchange Membrane Fuel Cell Catalyst Layers
Authors: Pharoah Jon , Choi Hae-Won , Chueh Chih-Che , Harvey David B.
Published: October 2011

There has been a rapidly growing interest in three-dimensional micro-structural reconstruction of fuel cell electrodes so as to derive more accurate descriptors of the pertinent geometric and effective transport properties. Due to the limited accessibility of experiments based reconstruction techniques, such as dual-beam focused ion beam-scanning electro microscopy or micro X-Ray computed tomography, within sample micro-structures of the catalyst layers in polymer electrolyte membrane fuel cells (PEMFCs), a particle based numerical model is used in this study to reconstruct sample microstructure of the catalyst layers in PEMFCs. Then the reconstructed sample structure is converted into the computational grid using body-fitted/cut-cell based unstructured meshing technique. Finally, finite volume methods (FVM) are applied to calculate effective properties on computational sample domains.
Exploration of Ultra-High Current Operation in PEFC Using a Validated Model
Authors: Zheng Lijuan , Srouji Abdul-Kader , Gambini Filippo , Mench Matthew
Published: October 2011

A comprehensive 2D+1 mathematical model has been developed to explore the operation of a polymer electrolyte fuel cell (PEFC)in the ultra-high current density regime (>2A/cm2). The accuracy of this model has been partially validated with simultaneous in-situ experimental testing in terms of performance, high frequency resistance (HFR) and net water drag coefficient. The experimental and modeling investigation found that for the unique open flow field architecture used, gas phase mass transport is not the limiting factor even in ultra-high current regime.
Validation of PEMFC Computer Models Using Segmented Current and Temperature Data
Authors: Carnes Brian , Chen Ken S. , Spernjak Dusan , Luo Gang
Published: October 2011

We present recent work on quantifying the impact of local temperature data in polymer electrolyte membrane fuel cells (PEMFC) model predictions. In particular, we compare differences in prediction of cell voltage and local current distribution when using either i) uniform cathode collector temperature and ii) spatially variable cathode collector temperature obtained from experimental data. We find that changes in temperature of +5/-2 C can result in +/-3 percent change in local current distribution. We conclude that local temperature data should be incorporated into PEMFC models in validation procedures when available.
Dynamic Performance of Automotive Fuel Cell Systems with Low Platinum Loadings
Authors: Ahluwalia Rajesh , Wang Xiaohua
Published: October 2011

A hierarchical algorithm is formulated to control and analyze the dynamic performance of an automotive polymer electrolyte fuel cell system with low platinum loading. Drive cycle simulations on combined urban (UDDS) and highway (HWFET) schedules indicate that the system performance and stack polarization curves deviate significantly from the steady-state results especially while the stack is initially cold. The dynamic response of the air management subsystem during deceleration can be improved by operating the motor as a motor-generator but the cathode stoichiometry remains high at low loads. A differential pressure sensor and control valves are used to regulate the flow of hydrogen on dynamic loads and to control the buildup of inert impurities in the anode gas channels. With a membrane humidifier, the relative humidity of the cathode air at the stack inlet depends on the power demand and the stack temperature. Anode gas recycle and in-cell water transport across the membrane are sufficient to humidify the feed hydrogen. The heat rejection system can maintain the stack at 75oC on the UDDS and HWFET cycles, but the stack temperature must be allowed to rise under some high power demand driving conditions.
Interaction of Heat Generation, MPL, and Water Retention in Corroded PEMFCs
Authors: Fairweather Joseph D. , Spernjak Dusan , Mukundan Rangachary , Spendelow Jacob , Artyushkova Kateryna , Atanassov Plamen , Hussey Daniel S. , Jacobson David L. , Borup Rodney
Published: October 2011

Carbon corrosion in PEM fuel cells was induced by a potential-hold accelerated stress test in 2.5 cm2 active area cells. Polarization curves and electrochemical impedance spectra quantified performance degradation from a combination of kinetic and mass transport losses. High-resolution neutron imaging of the operating cells showed a dramatic decrease in water retention at the same current density in the corroded cells, attributed to increasing internal heat generation. Omission of a cathode-side microporous layer resulted in significant differences in both water profiles and performance degradation. Post-mortem characterization of cell components was carried out by x-ray photoelectron spectroscopy to quantify changes in surface functionality.
Neutron Imaging of Isothermal Sub-Zero Degree Celsius Cold-Starts of a Polymer Electrolyte Fuel Cell (PEFC)
Authors: Oberholzer Pierre , Boillat Pierre , Siegrist Raphael , Perego Raffaella , Kaestner Anders , Lehmann Eberhard H. , Scherer Günther G. , Wokaun Alexander
Published: October 2011

Cold-starts of a polymer electrolyte fuel cell (PEFC), isothermally maintained at various subfreezing temperatures, were visualized by dynamic in-plane neutron imaging. The results obtained strongly suggest that super-cooled water is present in the system and that its sudden freezing is the initiator of the final voltage drop occurring at the and of the cold-start.
Nano to Micro Scale Characterization of Water Uptake in The Catalyst Coated Membrane Measured by Soft X-ray Scanning Transmission X-ray Microscopy
Authors: Berejnov Viatcheslav , Susac Darija , Stumper Jürgen , Hitchcock Adam P.
Published: October 2011

We describe a method of quantitative mapping the water content in the catalyst coated membranes (CCM) of proton exchange membrane (PEM) fuel cells with high spatial resolution (~30 nm) using soft X-ray Scanning Transmission X-ray Microscopy. Detailed component chemical maps of CCMs at different environmental conditions (relative humidity (RH)) were generated from O 1s optical density measurements by fitting to the soft X-ray absorption reference spectra for liquid and gaseous water and those of the electrode and membrane materials. Under high RH conditions, different distributions of water (vapor and liquid) were found for the cathode layer and the membrane. These results are related to differences in hydrophilicity / hydrophobicity of different regions.
Catalyst Layer Analysis: Nanoscale X-ray CT, Spatially-Resolved In Situ Microscale Diagnostics, and Modeling
Authors: Litster Shawn , Hess Katherine , Epting William , Gelb Jeff
Published: October 2011

Transport limitations are a significant impediment to effective utilization of the costly Pt catalyst in polymer electrolyte fuel cells (PEFCs). We present a catalyst layer analysis framework to investigate the coupled catalyst layer properties that dictate performance, including the electrochemical reactions, electrode morphology, and transport phenomena. This framework combines 50 nm resolution X-ray computed tomography (nano-CT), spatially-resolved in-situ measurements with microstructured catalyst layer scaffold (MES) diagnostics, and porous electrode modeling. Together, these tools serve to identify limiting transport mechanisms and their relationship to catalyst layer architecture. In addition, this framework serves to identify limitations in PEFC catalyst layer models and to validate these models. Here, we apply the framework to ionic transport in the cathode catalyst layer. The results indicate the ionic conductivity is much higher than anticipated and typically specified in PEFC models.
Role of Micro-Porous Layer for Water Transfer Phenomena in PEFC
Authors: Kadowaki Kazumasa , Tabe Yutaka , Chikahisa Takemi
Published: October 2011

Micro-porous layers (MPLs) play an important role in the water management of polymer electrolyte membrane fuel cells (PEFCs), but details of the mechanism to suppress water flooding has not been fully understood. In this study, we investigated water distribution at the interface between MPL and catalyst layer (CL)  at the cathode side to clarify the effect of MPL on discharge of produced water. Freezing method was applied to observe the distribution of the condensed water, and the distribution of ice on the CL surface was quantified by a binary image processing. In addition, comparing normal operation with start-up temperature -10○C, there is large amount of condensed water on the CL surface after operation at -10○C. Based on these results, the MPL has a role to prevent accumulation of water on the surface of CL, and suppresses water flooding.
Influence of Anode GDL on PEMFC Ultra-Thin Electrode Water Management at Low Temperatures
Authors: Steinbach Andrew J. , Debe Mark K. , Pejsa Matthew J. , Peppin Daniel M. , Haug Andrew T. , Kurkowski Mike J. , Maier-Hendricks Susan M.
Published: October 2011

In this paper, we provide results of new anode gas diffusion layer materials which dramatically improved the performance of ultra-thin electrode polymer electrolyte membrane fuel cells under highly water-condensing operating conditions, realized via optimization of the anode gas diffusion layer backing and microporous layer coatings.
Novel Current Distribution Board for PEM Devices
Authors: Mittelsteadt Cortney K. , Cortes Pedro , Lilavivat Visarn , Shimpalee Sirivatch , Van Zee J. W.
Published: October 2011

Non-uniform current distribution in polymer electrolyte membrane fuel cells results in local over-heating, accelerated ageing, and lower power output than expected. This issue is very critical when fuel cell experiences water flooding1. Currently, many methods for current distribution significantly affect flow path and break up diffusion media and are usually very expensive. A cost-effective method of mapping the current distribution in a cell was developed without disrupting flow.
In Situ Measurement of Flow Velocity in Gas Channel in a PEMFC by Laser Ablation Tagging Visualization
Authors: Fukabori Daichi , Hirai Shuichiro , Tsushima Shohji , Nishida Kosuke
Published: October 2011

We developed a visualization system of gas flow behavior called laser ablation tagging visualization (LATV), which showed a potential to examine flow behaviors in gas channel in an operating proton exchange membrane fuel cells (PEMFC). We constructed LATV system with two pulsed lasers: one is for laser ablation tagging and the other is for excitation of the tag material for visualization. The system was validated and was also applied to an operating PEMFC. Flow velocity in channel at operating conditions was examined with variation of current density. Under low current density condition, gas flow velocity was consistent with theoretical values calculated from supplied volume flow rate at the inlet. On the other hand, result under high current density condition shows that flow velocity in the channel accelerated toward the downstream, possibly due to generation of vapor and enhancement of water transport across the MEA from the anode to the cathode.
The Influence of the Liquid Water Behavior at the GDL-Channel Interface on Cell Performance
Authors: Fukuyama Yosuke , Shiomi Takeshi , Aoki Osamu , Kubo Norio , Tabuchi Yuichiro
Published: October 2011

Liquid water in the gas channels is known to have a significant impact on cell performance. In this study, the role of the surface properties of the GDL and separator on the liquid water transport were investigated through combined experimental and numerical analyses. Hydrophilic separator showed better cell performance than hydrophobic separator under high current density condition when hydrophobic GDL was used. Due to the different capillary pressure between separator and GDL, the liquid water in the gas channel easily spread along the wall of the hydrophilic separator, while it became large on the surface of the GDL in case of hydrophobic separator. These results suggested that the difference of the liquid water behavior in the gas channel caused the cell voltage loss under high current density conditions since oxygen transport was hindered because of the reduced surface area of the GDL coverd with liquid water.
Hydrophilic and Hydrophobic Double MPL Coated GDL to Enhance PEFC Performance under Low and High Humidity Conditions
Authors: Kitahara Tatsumi , Nakajima Hironori , Mori Kyohei
Published: October 2011

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance under both low and high humidity conditions. For the double MPL coated GDLs, the hydrophilic layers using either PVA (polyvinyl alcohol) or TiO2 were coated on the hydrophobic MPL coated GDL. Under low humidity, the double MPLs with the hydrophilic layers using both PVA and TiO2 are effective for conserving humidity at the catalyst layer, thereby enhancing PEFC performance. Under high humidity, because hydrophilicity of the hydrophilic layer using PVA is too high, PEFC performance is deteriorated due to flooding. However, the appropriate hydrophilic layer using TiO2 is effective for reducing flooding, thereby enhancing PEFC performance.
Impact of Gas Diffusion Layers (GDLs) on MEA Performance
Authors: Tanuma Toshihiro , Kinoshita Shinji
Published: October 2011

The impact of anode GDLs and the hydrophobic/hydrophilic nature of GDLs were studied in order to determine the effect of water transport on MEA performance. Anode GDLs, regardless of their hydrophobic or hydrophilic nature, are of minimal bearing on the MEA performance, as long as they are thick enough to prevent flooding at the anode side. MEA performance largely depends on the combination of hydrophobic and hydrophilic anode and cathode GDLs. The best performance was obtained for the MEA using a hydrophilic GDL for both anode and cathode. In the case of an MEA with a hydrophilic anode GDL, use of a hydrophobic cathode GDL instead of a hydrophilic cathode GDL increased flooding of the cathode at 80 ºC and 100%RH, suggesting that water produced in the cathode catalyst layer was pushed across the membrane to the anode side by a pressure barrier created by the hydrophobic cathode MPL.
STXM Study of the Ionomer Distribution in the PEM Fuel Cell Catalyst Layers
Authors: Susac Darija , Berejnov Viatcheslav , Hitchcock Adam P. , Stumper Jürgen
Published: October 2011

A method of imaging ionomer in the catalyst layer (CL) of the catalyst coated membrane (CCM) in the proton exchange membrane (PEM) fuel cell was developed using scanning transmission X-ray microscopy (STXM). Component maps for ionomer in CL relative to the catalyst/carbon-support were obtained from STXM images at a few specifically pre-defined energies in the C 1s (on/off a peak characteristic for carbon support in the catalyst layer) and F 1s edges (on/off a peak characteristic for the fluorine in the ionomer). Comparing the different approaches, an optimized strategy to study the spatial distributions of chemical components in the catalyst layer was determined. C 1s multi-energy imaging was most informative for mapping all components of the carbon catalyst support. The F 1s maps offer a rapid and powerful way for visualization of ionomer in the catalyst layer.
Water Uptake in PEMFC Catalyst Layers
Authors: Gunterman Haluna P. , Kwong Anthony , Gostick Jeff T. , Kusoglu Ahmet , Weber Adam Z.
Published: October 2011

Water uptake profiles of proton-exchange-membrane fuel-cell catalyst layers are characterized in the form of capillary-pressure saturation (Pc-S) curves. The curves indicate that the catalyst layers tested are highly hydrophilic and require capillary pressures as low as -80 kPa to eject imbibed water. Comparison of materials made with and without Pt indicates a difference in water ejection and uptake phenomena due to the presence of Pt. Dynamic vapor sorption (DVS) is used to characterize the water-vapor sorption onto Nafion, Pt/C, and C surfaces. The DVS results align with the trends found from the Pc-S curves and show an increased propensity for water uptake in the presence of Pt. The effect of the ion in Nafion, sodium or proton, is also compared. Although the protonation of the Nafion in the catalyst layer also increases hydrophilicity, the effect is not as great as that caused by Pt.
Pulse Voltammetry: In Situ Measurements of Oxide Coverage on Platinum in Proton Exchange Membrane Fuel Cells
Authors: Stuckey Philip A. , Zawodzinski Thomas A.
Published: October 2011

An experimental method is introduced to measure platinum oxide coverage in situ on proton exchange membrane fuel cell electrodes using pulse voltammetry. The in situ nature of this technique allows us to investigate temperature and relative humidity effects at 120 C and 80 C with 50% and 25% relative humidity with the use of real fuel cell electrodes. Higher relative humidity conditions appeared to increase the platinum oxide coverage as evidenced by the oxide stripping current in the chronoamperometric response. This observation confirms that water is involved in the platinum oxide formation mechanism. For oxide conditioning times longer than 1 second, a linear logarithmic rate for oxide formation on platinum is observed. These findings suggest that higher water content in the PEMFC cathode at open circuit or low current density demand will lead to higher rates of electrode degradation.