bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric Pressure Plasma Enhanced CVD of Fe Nanoparticles
Authors: Alexandrov Sergei , Kretusheva Irina , Mishin Maxim V.
Published: September 2009

The results from an experimental study of a new process based on the use of low temperature atmospheric pressure RF (13,56 MHz) plasma generated between coaxial electrodes for synthesis of Fe nanoparticles from pentacarbonyl in He are reported. Two different forms of discharge and conditions of transferring from one to another are considered. The average size of particle is decreased from 20 nm down to 5 nm with an increase of electrical power absorbed between the electrodes in the range of 40-60 W. Influence of plasma parameters and precursor concentration on the rate of particle formation and their size are discussed.
Fabrication of ZnO thin film transistor by MO-CVD using Bis(acetylacetonato)zinc (II) Fiber and Ozone
Authors: Sakuma Mio , Seki Shigeyuki , Haga Koichi
Published: September 2009

C-axis oriented high resistance ZnO(100) thin films were prepared on Pyrex glass and SiO2/p-type Si (Si(p)) substrate by MO-CVD method using fibrous bis(acetylacetonato) zinc (II) (Zn(C5H7O2)2) formed by a novel process, and ozone (O3) gas. Compared to the introduction of oxygen (O2) gas, the introduction of high-active O3 gas mixed in O2 gas reduced oxygen defect in ZnO thin film and realized high resistance ZnO thin film of 1×103 Ω·cm resistivity. Bottom-gate-type zinc oxide thin film transistor (ZnO-TFT) was fabricated on the SiO2/Si(p) substrate with the 8 nm-thick ZnO film as an active layer. The electron field-effect mobility was 53 cm2·V−1·s−1, and TFT characteristic of 106 on/off ratio was obtained.
VUV-Stimulated MO CVD Processes of Copper Layer Deposition
Authors: Igumenov Igor K. , Kuchumov Boris M. , Kozlova Svetlana , Koretskaya Tat'yana P. , Trubin Sergey V. , Sokuev Roman , Lyakh Vladimir , Kruchinin Vladimir
Published: September 2009

VUV-stimulated processes of copper layer deposition were investigated. A conventional compound, copper bis-hexafluoroacetylacetonate, was used as a precursor. Excimer lamps emitting light within the wavelength range 116-172 nm were used as the sources of VUV radiation. The results of quantum-chemical calculations were compared with the electronic spectra of copper bis-hexafluoroacetylacetonate in the gas phase. Calculations were carried out using the quantum chemical method of the density functional theory with Slater type of atomic wave functions (DFT/TZP). On the basis of thus determined electronic structure, allowed dipole-dipole electron transitions within the wavelength region 100-1200 nm were calculated; they were compared with the experimental spectra. Investigation of copper deposition processes was carried out under variation of substrate temperature and precursor, process time, presence of reactant gas, spectral characteristics of the excimer lamps. The resulting layers were characterized by means of SEM, ESCA, ellipsometry.
Hierarchical Nanostructure Produced by Growing Carbon Nanotubes on Silicon Oxide Nanowires
Authors: Woo Hee Jin , Kim Jung H. , Choi Duck Kyun , Yoon Chong S.
Published: September 2009

It was demonstrated that an array of carbon nanotubes (CNT) can be grown using plasma-enhanced chemical vapor deposition on silicon oxide nanowires (SiOxNWs) to construct one-dimensional hierarchical heterostructure. In order to grow the CNTs on the SiOxNWs, the nanowire surface was decorated with Ni seed particles by direct physical deposition without any surface pretreatment. Nano-sized Ni seed particles allowed the CNTs to nucleate on the nanowire surface. Scanning and transmission electron microscopy verified the branches of CNTs projecting from the SiOxNWs. All CNTs were multi-walled and have an average diameter of 20 nm. These CNTs cover the entire length of the individual SiOxNWs. The CNT-coated SiOxNWs can be potentially used as a nanowire-supported catalyst with high active surface area.
Dynamic Study of Gas-Phase Species during Single-Walled Carbon Nanotubes Production by Chemical Vapor Deposition of Ethanol
Authors: Kouravelou Katerina , Verykios Xenophon
Published: September 2009

The gas-phase species of the reactions that take place during Carbon Nanotubes (CNTs) production by Chemical Vapor Deposition (CVD) of ethanol vapors has been investigated in the temperature range of 650 - 900oC. More specifically, the effluent gases were analyzed by mass spectrometry in correlation to time as a way to determine the reactions that occur during the process and their influence on the rate of carbon deposition, total yield and kind of CNTs produced. The experiments were carried out in a thermogravimetric CVD hot-wall reactor over a Fe2O3/Al2O3 catalyst and the final product was characterized with Scanning Electron Microscopy (SEM) and Raman spectroscopy. It was found that the optimal temperature towards the highest yield of Single-Walled Carbon Nanotubes (SWCNTs) was achieved at 800oC leading to SWCNTs of 0.8 to 1.0 nm diameter. It was also determined that the presence of catalyst is crucial not only for the formation of CNTs, but also for the decomposition of ethanol vapors.
Strain Evaluation in SiC MEMS Test Structures
Authors: Bosi Matteo , Attolini Giovanni , Watts Bernard E. , Frigeri Cesare , Rossi Francesca , Poggi Antonella , Roncaglia Alberto , Mancarella Fulvio , Martinez Oscar , Hortelano Vanesa
Published: September 2009

This work presents the growth of b SiC on silicon by VPE performed in a home built, horizontal, cold wall reactor. Test structures used to assess the stresses in the film were obtained either by an etch through the wafer from the bottom side of the wafer to produce membranes or an attack from the front to reveal cantilevers. Membranes and cantilevers presented both compressive and tensile strain, depending on film thickness. Raman spectroscopy was used to study strain and defects.
Silver Films Deposited by Liquid-Delivery MOCVD using (Tertbutylcarboxylate)(Triethylphosphine)Silver with Toluene as the Solvent
Authors: Lisca Marian , Kalkofen Bodo , Lisker Marco , Burte Edmund , Szymańska Iwona , Szłyk Edward
Published: September 2009

Silver metallic films are prepared by liquid-delivery metal organic chemical vapor deposition (MOCVD) using (tertbutylcarboxylate) (triethylphosphine)silver ((Ag(OOCCH2tBu)(PEt3))n) solved 1M in toluene. The deposition of Ag thin films was carried out on different substrates at different pressures and temperatures within 300-550oC range. The reaction kinetics, film composition, film morphology and electrical properties of deposited Ag films were investigated. All the films were polycrystalline metallic silver as analyzed by X-ray diffraction with a preferred crystalline orientation (111). The surface structure investigation indicated that silver island formation takes place when Si and Si/SiO2 substrates were used, leading to a resistivity of the films from few MΩ/□ to infinity. In case of the silver films deposited on Si/SiO2/TiO2 substrates the films are rough but continuous showing a low resistivity (down to 3 mΩ/□) and offering potential applications in storage-capacitor or for solar cells technology.
Vertical Aligned Carbon Nanotube Deposition on Metallic Substrates by CVD
Authors: Doerfler Susanne , Meyer Andreas , Althues Holger , Dani Ines , Kaskel Stefan
Published: September 2009

Vertical aligned carbon nanotube (CNT) films are promising candidates for electrode surfaces in super capacitors suitable for electric energy storage. The CNT films provide a matrix with low internal resistance and a directed pore system for fast ion diffusion, both being crucial for high power supercap devices. The contribution describes the deposition process and properties of multiwall and single wall CNTs on various metallic substrates by thermal CVD. Up to 100 micron thick, well-aligned CNT films were obtained on Ni-substrates. For polished steel substrates flower-like and columnar structures are observed indicating side reactions of the substrate with the catalyst particles.
Shape Optimization of a Showerhead System for the Control of Growth Uniformity in a MOCVD Reactor Using CFD-based Evolutionary Algorithms
Authors: Xenidou Theodora C. , Prud'Homme Nathalie , Aloui Lyacine , Vahlas Constantin , Markatos Nicholas C. , Boudouvis Andreas G.
Published: September 2009

A steady state, laminar flow coupled with heat transfer, gas-phase and surface chemistry, is numerically solved for the optimal design of a showerhead gas delivery system in an axis-symmetrical MOCVD reactor. The design method involves an evolutionary algorithm based on CFD simulations. A finite-volume CFD code for aluminum growth provides the numerical predictions of the growth rate and its spatial variation over the substrate. A multilevel evolutionary algorithm is used to continuously adjust the shape of the shower plate so as to minimize the spatial variation of the growth rate. A 5-variable parameterization of the shower plate is investigated and a near-optimal solution is proposed and compared to the original configuration of the shower plate.
Preparation of High Permittivity GdScO3 Films by Liquid Injection MOCVD
Authors: Huseková Kristina , Jurkovič Michal , Cico Karol , Machajdik Daniel , Dobročka Edmund , Lupták Roman , Mackova Anna , Fröhlich Karol
Published: September 2009

We describe preparation and properties of GdScO3 thin films. The films were prepared by liquid injection metal-organic chemical vapor deposition, MOCVD at 600 ºC on (100) Si substrate. The as-deposited films were amorphous with a smooth surface and sharp GdScO3/Si interface. X-ray diffraction showed that the amorphous phase is well preserved upon rapid thermal annealing up to 1000 ºC. However, modification of the X-ray reflectivity pattern after annealing at 1000 ºC indicates increasing of the film thickness, presumably due to diffusion of silicon from the substrate into the whole volume of the film. Capacitance-voltage measurement resulted in dielectric constant of 22. It is shown, that exact stoichiometry of GdScO3 is not necessary to achieve dielectric constant above 20.
Plasma Composition and Kinetic Reaction Rates in a LEPECVD Ar-SiH4-H2 Plasma During nc-Si Films Deposition for Photovoltaic Applicationss
Authors: Moiseev Tamara , Chrastina Danny , Isella Giovanni , Cavallotti Carlo
Published: September 2009

The optimal plasma composition for the deposition of nano-crystalline silicon (nc-Si) films is investigated in connection to electron-impact and gas-phase reaction rates for the generation of useful radicals in a low energy plasma-enhanced chemical vapor deposition (LEPECVD) process. Mass spectrometry for the analysis of plasma composition and Langmuir probe space-resolved plasma parameters and electron energy distribution functions (eedf) are evaluated and discussed for Ar-H2 and Ar-SiH4-H2 plasma in the LEPECVD reactor. The observed ion and radical trends during nc-Si deposition can be explained by the dominance of gas-phase rates over electron-impact rates for silane reactions, leading to depletion of SiH3 and SiH2 towards SiH and Si that become precursors of the nc-Si layers.
Combination of Electron or Laser Beam Irradiation with High Vacuum Chemical Vapor Deposition (HV-CVD) of Al2O3 for in-situ Local Structuring on Wafer Scale Substrate
Authors: Kuzminykh Yury , Multone Xavier , Hoffmann Patrik
Published: September 2009

A laser or electron beam assisted deposition in HV-CVD conditions was used in order to achieve structured amorphous alumina (Al2O3) deposits. Selective deposition of Al2O3 in the irradiated regions has been demonstrated. We investigate the influence of irradiation parameters on the deposition rate and composition of the deposits. The technique is aimed to be used on full wafer substrates.
Combustion-Driven Synthesis of Non-Oxide Nanoparticles in a High Temperature Reducing Jet
Authors: Scharmach William J. , Papavassiliou Vasilis , Pacouloute Perry , Buchner Ray , Swihart M. T.
Published: September 2009

Copper nanoparticles were synthesized using a new technique that combines thermal decomposition and hydrogen reduction. The technique uses a flame as a source of low-cost energy to initiate particle synthesis. Molar concentration of the aqueous precursor solution, reactor pressure and temperature, and flow rate of combustion gases (hydrogen, oxygen, and nitrogen), were varied to control particle size, size distribution, and morphology. Copper serves here as a prototype for non-oxide materials that are generally difficult to produced in flame-based reactors. This work demonstrates that such materials can be produced in substantial quantities with particle diameters below 50 nm in this process.
Local Area Deposition of SiOC Films by using a Very-high-frequency Atmospheric Pressure Microplasma Jet from Tetraethoxysilane
Authors: Ding Yi , Kobayashi Tomohiro , Jia Haijun , Shirai Hajime
Published: September 2009

SiOC films have been fabricated by using an atmospheric pressure microplasma jet (APPJ) from a tetreethoxysilane (TEOS) and argon mixture. By adjusting the plasma parameters, film morphology changes from the particle to the unifiorm film state with parabolic or dome profile. The correlation among the deposition profile, film fine structure,and white photoluminescence is demonstrated in terms of the gas flow dynamics.
ZrO2 Thin Films Grown on 2D and 3D Silicon Surfaces by DLI-MOCVD for Electronic Devices
Authors: Galicka-Fau Karolina , Andrieux Michel , Legros Corinne , Herbst-Ghysel Michaële , Gallet Isabelle , Brunet Magali , Scheid Emmanuel , Schamm Sylvie
Published: September 2009

Zirconia films are already used as thermal barrier, sensors and fuel cells and have great potential for electronic applications in particular as a dielectric in high density filter capacitors in future micro DC-DC converters. In this context, the SiO2/Si3N4 standard dielectric was replaced by ZrO2 (ε = 25-40) in 2D and 3D MIS (Metal-Isolator-Semiconductor) structures. Zirconia thin layers (100nm) were deposited between 550{degree sign}C and 700{degree sign}C on Si(100) planar substrates and inside pores etched in Si(100) by direct liquid injection MOCVD from Zr2(OiPr)6(thd)2 precursor and annealed at 900{degree sign}C to check phase stability. As-deposited films exhibit a cubic/tetragonal structure that was identified by DRX and FT-IR. The electric properties on specific samples were measured and discussed. After annealing, phase transformation occurs in the film, from cubic/tetragonal structure to a tetragonal/monoclinic one, depending on the deposition parameters.
Phase Change Memory using InSbTe Chalcogenide Materials Deposited by Metal-organic Chemical Vapor Deposition
Authors: Ahn Jun-Ku , Park Kyung-Woo , Jung Hyun-June , Pammi Sri-Venkata , Hur Sung-Gi , Yoon Soon Gil
Published: September 2009

The feasibility of InSbTe (IST) chalcogenide new materials by metalorganic chemical vapor deposition (MOCVD) was demonstrated for PRAM applications. The IST films grown below 225oC exhibit an amorphous structure and the films grown at 300oC include various crystalline phases of IST, In-Sb, and In-Te. Samples grown at 225oC for various working pressures have a stoichiometric composition (In3Sb1Te2). The IST films grown at 225oC exhibit smooth morphologies having an rms (root mean square) roughness below 1nm and the step-coverage on trench structure with 5:1 aspect ratio was approximately above 90%. An increase of the deposition time increases the filling rate keeping the conformal step-coverage. IST-MOCVD is a powerful candidate method for reliable PRAM device applications.
Growth Mechanisms and Size-Dependent Characteristics of Si and Si1-xGex Nanowires
Authors: Redwing Joan M. , Nimmatoori Pramod , Lew K.K. , Zhang Xi , Zhang Qi , Clark Trevor , Pan Ling , Dickey Elizabeth
Published: September 2009

Si and Si1-xGex nanowires are of interest for nanoscale electronics, sensors and photovoltaics. These structures are commonly formed by chemical vapor deposition via a metal-mediated vapor-liquid-solid mechanism using SiH4 and GeH4 sources. The effect of growth conditions on the growth rate and composition of Si1-xGex was investigated. This work reveals a difference in the mechanism of incorporation of Si into Si1-xGex nanowires compared to Si nanowire growth which is believed to arise as a result of gas phase interactions between SiH4 and GeH4. The growth of Si1-xGex/Si axial heterostructured nanowires was also investigated. Compositional analysis indicates that the Ge profile exhibits turn-on and turn-off transients which are associated with the time required to saturate and deplete Ge from the Au-Si-Ge catalyst. This leads to an increase in the interfacial width with increasing nanowire diameter.
Preparation and Functional Characterizations of Ta2O5 Deposits Organized at the Micro- and Nano-scale
Authors: Terranova Maria Letizia , Guglielmotti Valeria , Orlanducci Silvia , Sessa Vito , Tamburri Emanuela , Rossi Marco
Published: September 2009

The present communication deals with the coating of bundles of single wall carbon nanotube (SWCNTs) by nanocrystalline tantalum pentoxide (Ta2O5) deposits. Arrays of SWCNTs bundles are produced on Si, and AlN plates by means of a Hot Filament CVD apparatus, using as reactants carbon nanopowders and in-situ produced atomic hydrogen. A subsequent process, carried out in an O2-rich atmosphere, enables to cover the bundles by a uniform deposit of Ta2O5 nanograins. The coating process does not modify the organization of the pristine nanotube deposits. A series of SWCNT/Ta2O5 samples, characterized from both the morphological and structural point of view, have been tested as cathodes in Field Emission experiments (F.E.). The F.E. experiments proved that these hybrid SWCNT/dielectric systems are good field emitters and that their properties make them suitable for the realization of cold cathodes.
Multi-Functional Copper Oxide Nanosystems for H2 Sustainable Production and Sensing
Authors: Gasparotto Alberto , Barreca Davide , Fornasiero Paolo , Gombac Valentina , Lebedev Oleg , Maccato Chiara , Montini Tiziano , Tondello Eugenio , Van Tendeloo Gustaaf , Comini Elisabetta , Sberveglieri Giorgio
Published: September 2009

This work focuses on the use of tailored copper oxide nanoarchitectures as multi-functional materials for the sustainable production of hydrogen and its on-line detection. An innovative copper(II) precursor, Cu(hfa)2•TMEDA, was adopted in the CVD of CuxO (x=1,2) nanosystems under both O2 and O2+H2O atmospheres on Si(100) and Al2O3 substrates. A multi-technique characterization indicates that both the phase composition (from Cu2O to CuO) and morphology (from continuous films to entangled quasi-1D nanosystems) can be tailored by varying the growth temperature and reaction atmosphere. The obtained CuxO nanodeposits are active in the photocatalytic H2 production from aqueous solutions under UV-Vis irradiation and display interesting gas sensing performances towards hydrogen detection even at moderate temperatures.
CVD Synthesis of Shape and Size Controlled ZnO Nanoparticles for Application as UV Filters
Authors: Bacsa Revathi R. , Sienkiewicz Andrzej , Pierzchala Katarzyna , Dexpert-Ghys Jeannette , Forró Laszlo , Serp Philippe
Published: September 2009

For the application of nanocrystalline ZnO in pharmaceuticals and cosmetics, in addition to high purity, a precise control of particle size, shape and agglomeration is necessary so that transparent films with high absorption coefficients can be obtained. In this communication we report the synthesis and structure-property correlation of ZnO nanospheres and tetrapods prepared by the gas phase oxidation of zinc metal precursor. We have evaluated the ecotoxicity of the ZnO tetrapods and spheres by studying the rate of formation of reactive oxygen species using EPR spectroscopy. We find that ZnO tetrapods form reactive oxygen species, but at a rate much lower than nanocrystalline TiO2 when irradiated with UV-A
MOCVD Grown Thin Film Nanocomposites Based on YBCO with Columnar Defects Comprised of Self-Assembled Inclusions
Authors: Boytsova Olga V. , Samoilenkov Sergej , Vasiliev Alexander , Kaul Andrey , Kalinov Alexey , Voloshin Igor
Published: September 2009

MOCVD growth of epitaxial YBa2Cu3O7 high Tc superconducting films containing BaZrO3 and BaCeO3 nanosized inclusions is described. It is shown that inclusions grow epitaxially within the matrix of YBCO superconductor. The introduction of optimal quantity of BaZrO3 and BaCeO3 inclusions improves the transport critical current density of superconducting films in external magnetic field up to 1T
Combinatorial Chemical Vapor Deposition of Lithium Niobate Thin Films
Authors: Dabirian Ali , Kuzminykh Yury , Sandu Silviu Cosmin , Wagner Estelle , Benvenuti Giacomo , Parsons Catherine , Rushworth Simon , Hoffmann Patrik
Published: September 2009

Combinatorial lithium niobate deposition on 150 mm naturally oxidized silicon (100) wafers in a high-vacuum chemical vapor deposition reactor using Li(OBut) and Nb(OEt)4(dmae) is presented. The novel precursor supply system allows individual spatial control of precursors impinging rates on the substrate. This results in variations of the film properties in a single experiment at a certain substrate temperature due to the influence of different precursors flow rates and ratios. It efficiently leads to deposition conditions to achieve highly <001> oriented polycrystalline lithium niobate films.
Initiated Chemical Vapor Deposition (iCVD) of Hydrogel Polymers
Authors: Bose Ranjita , Nejati Siamak , Lau Kenneth K.
Published: September 2009

Initiated chemical vapor deposition (iCVD) represents a novel CVD method for synthesizing polymer thin films in a single-step bottom-up polymerization-co-deposition process. Specifically, iCVD has been utilized to create poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. FTIR and NMR evidenced the stoichiometric composition of PHEMA with full retention of chemical functionality. By controlling iCVD reaction kinetics, PHEMA deposition rate and molecular weight were successfully tuned, achieving rates as high as 1.5 microns/min, yielding high molecular weight polymers as observed through DSC. Because PHEMA hydrogels are polymers capable of absorbing substantial amounts of water and other liquid media, iCVD PHEMA has been studied and is demonstrated as a potential biomaterial to support living cell growth and as a potential polymer electrolyte material for dye sensitized solar cells.
Liquid Droplet Evaporation in Simulations of the Flow in Pulsed-Pressure MOCVD
Authors: Lim Chin Wai , Cave Hadley , Jermy Mark , Krumdieck Susan
Published: September 2009

In this paper, a numerical model of the liquid precursor droplet flash evaporation and transport is introduced. This droplet model is coupled with the Quiet Direct Simulation (QDS) scheme to model the unsteady flow development in a Pulsed Pressure MOCVD reactor. A preliminary simulation of the PP-MOCVD process including the injection and pump down phase is conducted. The simulation results are consistent with the measured pressure change in the PP-MOCVD process.
Influence of the Heating Mode and the Spray Introduction on Chemically Vapour Deposited Aluminium Doped Zinc Oxide Thin Films
Authors: Garnier Jérôme , Sreekumar Rajappan Achary , Bouteville Anne
Published: September 2009

Aluminium doped zinc oxide films were deposited by spray pyrolysis using zinc acetate and aluminium pentanedionate as precursor and doping agent respectively. The aim was to determine the best way for introducing the spray and for heating the glass substrate. As-deposited films are characterized according to their structural, electrical and optical properties for solar cell applications. The growth rate was also taking into account as the deposition process must be a low cost one. We used of a new liquid injection head allowing to introduce an aerosol of very small droplets horizontally into the reactor. We showed that infrared heating can be an interesting alternative to the common generally used hot plate. We obtained Al:ZnO films with a growth rate of 0.358 nm/s and a figure of merit of 1.7 10-3Ω-1.
Fibre-scale Modeling of C/C Processing by Chemical Vapour Infiltration using Xray CMT Images and Random Walkers
Authors: Vignoles Gerard L. , Germain Christian , Coindreau Olivia , Mulat Christianne , Ros William
Published: September 2009

We present a computational tool for the modeling of Chemical Vapor Infiltration of carbon/carbon composites, which is based on 3D images acquired by X-ray Computerized Micro-Tomography with a very fine resolution, such that the fibers are clearly distinguishable from each other. Preliminary image processing is necessary in order to perform segmentation between solid and void phases. Then, morphological and transport properties are computed in the images. Random walkers are used for the simulation of gas transport in continuum and rarefied regimes. The image modification under chemical deposition is handled by a specific surface discretization technique and a pseudo-VOF method. Results are presented and discussed: the notion of infiltrability is introduced as a design tool for the CVI engineer.
Fabrication of Micro- and Nano-electrodes by Selective Chemical Vapor Deposition of Cu on Si Substrates Patterned with AZ5214{trade mark, serif} and PMMA
Authors: Papadimitropoulos Giorgos , Cibella Sara , Leoni Roberto , Arapoyianni Aggeliki , Davazoglou Dimitris
Published: September 2009

Planar Cu electrodes with high length (starting from 1 mm down to 50 μm) and fine widths dimensions (starting from 20 μm and going down to 100 nm) were fabricated using selective chemical vapour deposition (SCVD) of the metal. For the fabrication, oxidized Si substrates were used on which a TiN layer was deposited and patterned either with AZ5214TM, for width dimensions of the order of microns, or by PMMA for lower dimensions. Then, Cu was deposited by SCVD on the exposed regions of the substrate only. Finally, the remaining polymers and the TiN were removed in acetone and by plasma etching, respectively. Due to the advanced CVD equipment used the above fabrication method proved to be robust, reproducible and with a high yield. The use of such equipment also assures a quite wide process window and inhibits the intrusion of other parameters which are known to destroy Cu SCVD.
Residual Stress Mechanisms in Aluminium Oxide Films Grown by MOCVD
Authors: Soni Sumit , Samelor Diane , Sheldon Brian W. , Vahlas Constantin , Gleizes Alain N.
Published: September 2009

Residual stresses in amorphous aluminium oxide films were investigated with in situ wafer curvature measurements. The films were deposited from aluminium tri-isopropoxide, on sapphire substrates. Large tensile stresses of 1-2 GPa occurred during growth. These values are well above the fracture stress in bulk materials, but they are sustainable in thin film form. Subsequent heat treatment of these films produced additional tensile stress, even at low temperatures prior to crystallization. The mechanisms responsible for all of these stress contributions are discussed. The variety of operative mechanisms at low to moderate temperatures in these amorphous films suggests that different processing routes can be used to engineer significant differences in the final stress state of these materials.
Interfacial Morphology and Contact Resistance Model for Polymer Electrolyte Fuel Cells
Authors: Swamy Tushar , Hizir F. Erinc , Khandelwal Manish , Kumbur Emin C. , Mench Matthew M.
Published: September 2009

The imperfect interface between the catalyst later (CL) and micro porous layer (MPL) in a polymer electrolyte fuel cell (PEFC) results in interfacial gaps which can be considerably larger than the pores in the bulk CL and MPL. This leads to an electronic resistance and a potential pooling location for liquid water resulting in mass transport losses. In this study, an analytical model representing the CL|MPL interface under compression is developed to estimate the electrical contact resistance and to elucidate the effect of the initial surface morphology on the contact resistance and interfacial void volume. The results show that the local compression pressure, elasticity of the diffusion media and surface morphology of the mating materials are the key factors controlling the CL|MPL interfacial contact. This micro-contact model not only strengthens our understanding of the CL|MPL interface, but once integrated with a macroscopic fuel cell model, can be used to more accurately predict fuel cell performance.
A Modeling Study of the Effects of the Properties of Anode Porous Layer on the Performance of a PEM Fuel Cell
Authors: Wang Xuhai , Nguyen Trung V.
Published: September 2009

In this study, a two-phase flow model focusing on anode side was developed to investigate the effect of the properties of the porous media in anode side on the performance of a proton exchange membrane (PEM) fuel cell. Two cases (with and without micro-porous layer (MPL) in anode side) were included to elucidate the proper water management strategy in the anode side. The results showed that an MPL in the anode side might lead to flooded anode catalyst layer (CL) as well as flooded cathode. The increased saturation levels in the PEM fuel cell may cover the active catalyst sites, occupy the reactant transport path, and eventually lead to bad fuel cell performance. For the case without an MPL in the anode side, the amount of liquid water pushed from the cathode side to the anode side was sufficient to saturate the dry fuel in the anode side.
Evaporation Modeling for Proton Exchange Membrane Fuel Cells
Authors: Fritz David L. , Allen Jeffrey S.
Published: September 2009

Several methods exist in which evaporation is accounted for in fuel cell modeling. Whether at the system level, the cell level, or at the individual component level, understanding water management is paramount. In order to fully understand water management an understanding of the product water phase is necessary, as the liquid and vapor phase transport quite differently in the porous media and micro-channels. Most of the current literature follows a variation of a few main approaches. A common approach is to create a switch that tells the model whether water is evaporating or condensing. During a simulation the partial pressure of water vapor varies, and as it approaches the saturation pressure evaporation is subsequently turned on or off. Other approaches involve adjusting evaporation rates to keep thermodynamic equilibrium. Many models neglect calculating transient interfacial mass transport all together and only assume a constant evaporation and condensation rate for a transient process.
Complex Dynamics in a PEM Fuel Cell
Authors: Mota Andressa , Lopes Pietro , Ticianelli Edson A. , Gonzalez Ernesto R. , Varela Hamilton
Published: September 2009

Oscillatory kinetics in a polymer electrolyte membrane fuel cell (PEMFC) was studied at different applied currents and fluxes in the anodic compartment. The system consisted of a Pt/C cathode fed with oxygen and a PtRu(1:1)/C anode fed with H2 mixed with 108 ppm of CO, and was operated at 30 oC. Many different states including periodic and non-periodic series were observed as a function of the applied current (j) and the H2/CO flux. In general, aperiodic/chaotic states were favored at high currents and low flux. This allowed us to discuss the connection between the observed dynamics and the reaction mechanism.
Electrochemical Evidence of Two Types of Active Sites for Oxygen Reduction in Fe-based Catalysts
Authors: Herranz Juan , Jaouen Frederic , Dodelet Jean-Pol
Published: September 2009

Fe-based catalysts for the reduction of oxygen were synthesized by wet-impregnation of FeII acetate or FeIII-porphyrin on pristine carbon black followed by pyrolysis in ammonia or argon. The catalysts were characterized using RDE and RRDE voltammetry in both acid and alkaline electrolytes. The results support the presence of two types of active sites for oxygen reduction in these catalysts: (i) the Fe-N4/C type, with a structure resembling the central porphyrin moiety, and (ii) the Fe-N2+2/C type, hosted in the micropores of the carbon support. Fe-N4/C sites are poorly active in acid but highly active in alkaline, whereas Fe-N2+2/C sites are highly active in both electrolytes.
Zirconium Oxide-based Cathode without Platinum Group Metals for PEFC
Authors: Ohgi Yoshiro , Ishihara Akimitsu , Matsuzawa Koichi , Mitsushima Shigenori , Ota Ken-ichiro
Published: September 2009

Partially oxidized zirconium carbonitrides (Zr-CNO) powders were evaluated as a non-precious cathode for polymer electrolyte fuel cells (PEFCs). Zr-CNO powders were prepared from zirconium carbonitrides (Zr-CN) with heat-treatment under 0.25%O2/2%H2/N2 at 1000 - 1400oC. The slow scan voltammetry was performed to evaluate the catalytic activity for the oxygen reduction reaction (ORR) under nitrogen and oxygen in 0.1 mol dm-3 H2SO4 at 30oC. Although the onset potential of ORR for untreated Zr-CN is 0.55 V vs. reversible hydrogen electrode (RHE), the onset potential of the appropriate oxidized Zr-CNO reached 0.97 V vs. RHE. XRD and XPS data suggested that the surface of the Zr-CNO was oxidized to ZrO2 and Zr-CN remained in the inner part of the each particle. The existence of tetragonal and/or cubic ZrO2 in the XRD patterns of the Zr-CNO suggested that the vacancies on the surface of the Zr-CNO might affect the catalytic activity for the ORR.
Characterization of Nickel-Carbon Thin Film Electrocatalysts for Low-Temperature Acidic Fuel Cells
Authors: Chin Xiao Yao , Haslam Gareth , Rees Eric , Burstein Gordon T. , Barber Zoe
Published: September 2009

Nickel-carbon (Ni-C) film was investigated for use as anode in polymer exchange membrane fuel cells (PEMFCs) as well as other low-temperature acidic fuel cells. The Ni-C film which was synthesized using DC magnetron sputter deposition comprised about 50 at.% nickel. The film was polarized potentiostatically in 1.5 M H2SO4 at 70 ºC. The film demonstrated passivity against corrosion in hot sulphuric acid solution and electrocatalytic activity towards the anodic and cathodic hydrogen reactions, even after being polarized at high potential.
Tantalum Oxide-based Cathodes without Precious Metals for PEFC
Authors: Ishihara Akimitsu , Imai Hideto , Matsuzawa Koichi , Mitsushima Shigenori , Ota Ken-ichiro
Published: September 2009

A partially oxidized TaC0.58N0.42 has been investigated as a new cathode for polymer electrolyte fuel cells. The catalytic activity for oxygen reduction reaction (ORR) significantly depended on an oxidation state of the TaC0.58N0.42. TaC0.58N0.42 and Ta2O5 had a poor catalytic activity for the ORR. The onset potential on the partially oxidized TaC0.58N0.42 for the ORR had a maximum value of 0.9 V vs. RHE in 0.1 mol dm-3 H2SO4 at 30oC. Time-of-flight secondary ion mass spectroscopy suggested that carbon and/or nitrogen remaining on the surface might affect the catalytic activity for the ORR.
Non Noble Metal Electrocatalysts for High Temperature PEM Fuel Cells
Authors: Papakonstantinou George , Daletou Maria , Kotsifa Areti , Paloukis Fotios , Katerinopoulou Katerina , Ioannides Theophilos , Neophytides Stylianos G.
Published: September 2009

A new approach towards the development of non- noble metal electrocatalysts for high temperature PEM fuel cells is reported herein. RFur-(MF)-Fe, electrocatalysts prepared by pyrolysis of organic resins (resoscinol-furaldehyde), were prepared. A thorough physicochemical characterization took place showing that the amount of solids and the drying method influence the electrochemical activity. The presence of Fe and most importantly the presence of high amount of nitrogen species in the catalyst is crucial for the electrochemical activity. RFur-(MF)-Fe are interesting candidates for use in high temperature fuel cells.
Electrocatalysis on Well-defined Surfaces
Authors: Garcia G. , Rodriguez P. , Frank S. , Koverga A. A. , Koper Marc
Published: September 2009

The paper summarizes recent work from our group on the mechanisms of CO electro-oxidation of well-defined Pt and Au surfaces, employing electrochemical, spectroscopic and computational techniques.
Research and Development of Fuel Cell Vehicles at Honda
Authors: Sando Yasuyuki
Published: September 2009

Rapid responses are demanded from the automotive industry towards global warming and the depletion of fossil fuel resources. Honda considers fuel cell vehicles, which produce no pollutants, including CO2, during operation to be the ultimate clean vehicles enabling resolution of these environmental and energy issues. The development of the FCX Clarity brought together outstanding environmental performance and the drive performance. The Clarity achieves a fuel efficiency approximately twice that of a small gasoline vehicle and approximately 1.5 times that of a small hybrid vehicle. The size of the vehicle's hydrogen tank has been increased, realizing a driving range of 280 miles in EPA combined mode, a figure which is comparable to the driving range of a gasoline vehicle. This paper will provide a technological introduction to the FCX Clarity, Honda's next-generation fuel cell vehicle, and will further touch on issues relevant to the future market diffusion of the vehicles.
Technique for Measuring Gas Transport Resistance in Application-Scale Aged Fuel Cell Gas Diffusion Media
Authors: Carter Robert N. , Greszler Thomas A. , Baker Daniel
Published: September 2009

A technique for measuring the gas transport resistance of fuel cells is described that enables this analysis to be performed on application-scale parts including those that have been aged in full scale stacks. The general procedure is to measure the limiting current of a portion of the active area using a current distribution tool at several different values of RH (relative humidity) and oxygen concentrations. Probing just a small portion of the cell's active area enables one to achieve highly differential flow conditions locally, thereby ensuring uniform conditions. This method is applied to a set of new and aged soft goods to illustrate the efficacy of the technique. By comparing the transport resistance of the new and aged parts at different operating conditions, it is shown that the ability of the soft goods to reject liquid water diminished, while the purely gas phase transport resistance is unchanged.
Portable Military Fuel Cell Power Systems
Authors: Martin Jerry L. , Osenar Paul
Published: September 2009

This paper summarizes recent developments in portable military fuel cell systems. Military fuel cells may provide an early market entry point for a number of portable fuel cell types. Recent progress in man-portable fuel cells, fuel cells for UAVs and field battery chargers are discussed, along with fuel cell/battery tradeoffs.
Surface Species and Product Distribution in the Electrooxidation of Small Organic Molecules
Authors: Heinen Martin , Jusys Zenonas , Behm R. Jürgen
Published: September 2009

The electrooxidation of small organic molecules proceeds via a complex reaction network, involving a number of stable, adsorbed or desorbed (volatile) reaction intermediates and side products in addition to the main product. These reaction networks will be discussed for a number of C1-C3 molecules, focusing on the electrooxidation of ethanol. The discussion is based on ATR-FTIRS/DEMS flow cell measurements, where in-situ IR spectroscopy in an ATR configuration is employed for the detection of adsorbed reaction intermediates and the product distribution is quantitatively determined via on-line DEMS. The implications on the mechanism of the electrooxidation of small organic molecules will be addressed.
Analysis of Water Transport in Catalyst Layers: The Effect of Carbon Supports
Authors: Sato Kazuyuki , Ohma Atsushi , Yamaguchi Koichi , Shinohara Kazuhiko
Published: September 2009

Water transport phenomena in catalyst layers (CLs) were investigated experimentally and analytically. Water transport resistance in CLs was regarded as being driven by the water activity gradient and examined using an equivalent circuit model consisting of two transport mechanisms in parallel. In this study, the effect of different carbon supports on water transport resistance was investigated. The experimental results showed that CLs with a carbon support of graphitized ketjen black displayed lower water transport resistance than CLs with a carbon support of ketjen black. One possible reason for that difference is that the tortuosity of the ionomer in the CLs differed depending on the carbon support shape. The water resistance values in the CLs calculated with the model were higher in both cases than the experimental results. This suggests the existence of another water transport path that is faster than the path in the ionomer.
An Updated Look at the Role of Micro-Porous Layer on Liquid Water Distribution in Polymer Electrolyte Fuel Cells
Authors: Preston Joshua S. , Fu Richard S. , Pasaogullari Ugur , Hussey Daniel S. , Jacobson David L.
Published: September 2009

Evidence of a region of gradual property change between the microporous layer and macroporous layer of bi-layer diffusion media is presented, and a mathematical model describing the effects of this gradual interfacial region is developed. The model results in a continuous water distribution across the diffusion media, whereas the sudden interface model results in a sharp discontinuity in the liquid phase saturation. High resolution neutron radiography is used to measure the water content profile across the diffusion media, and the results are compared with the model predictions.
Ice Formation in PEM Fuel Cells Operated Isothermally at Sub-Freezing Temperatures
Authors: Mukundan Rangachary , Lujan Roger , Davey John R. , Spendelow Jacob S. , Hussey Daniel S. , Jacobson David L. , Arif Muhammad , Borup Rodney
Published: September 2009

The effect of MEA and GDL structure and composition on the performance of single-PEM fuel cells operated isothermally at sub-freezing temperatures is presented. The cell performance and durability are not only dependent on the MEA/GDL materials used but also on their interfaces. An increase in high frequency resistance was observed in certain MEAs where there is a possibility of ice formation between the catalyst layer and GDL leading to a loss in contact area. The total water/ice holding capacity for any MEA was lower at lower temperatures and higher current densities. The durability of MEAs subjected to multiple isothermal starts was better for cloth GDLs when compared to paper GDLs. The ice formation was monitored using high-resolution neutron radiography and was found to be concentrated near the cathode catalyst layer. Finally, there was significant ice formation in the GDLs especially at the higher temperature and lower current density operations.
Characterization of GDL for Water Transport in PEMFC Cathode
Authors: Martinez Michael , Shimpalee Sirivatch , Tong Cui , Ohashi Masato , Van Zee John W.
Published: September 2009

Several techniques were used to characterize carbon cloth and carbon paper gas diffusion media (GDM). A technique for measuring the MacMullin number is described. This number provides the missing data to test the applicability of the commonly used Bruggeman equation. Analysis of the data show that only carbon cloth GDM follow the Bruggeman equation and that carbon paper GDM have a different relationship with porosity. Data obtained by using intrusion porosimetry (IP) and the method of standard porosimetry (MSP) for the hydrophilic and hydrophobic pore size distributions (PSD) is presented. The use of multiple working fluids to access hydrophilic and hydrophobic pores is discussed as well as limitations associated with structural changes of the GDM during the tests. Scanning electron microscopic (SEM) images are also presented to illustrate differences in structures. Finally, characteristics of the GDM are incorporated into a mass transport model in order to describe water phase distribution.
Nanoscale Investigation of Nafion Membranes after Artificial Degradation
Authors: Friedrich K. A. , Schulze Mathias , Bauder Alexander , Hiesgen Renate , Wehl Ines , Yuan Xiao-Zi , Wang Haijiang
Published: September 2009

In this contribution we report on the nanostructure and conductivity of freshly prepared as well as artificially degraded Nafion membranes investigated by contact atomic force microscopy (AFM), conductive AFM, and pulsed force-mode (PFM)-AFM. The different techniques can provide complementary information on structure and conductivity. Conductive AFM is used to investigate the conductivity of Nafion membrane surfaces. The images show a quite inhomogeneous distribution of current at the surface. The percentage of conductive surface increases with humi¬dity, but regions without any current are still present up to 80% relative humidity [1,2]. Comparison with PFM-AFM images, where differences in adhesion forces are measu¬red, indicates that hydrophobic regions, which are attribu¬ted to PTFE-like polymer back bone without conductivity, are present at the surface with comparable dimensions. Conductive AFM gives information about the internal structure of ionic clusters during current flow. High resolution current images of the membrane were used to directly compare the measured nanostructure of the single conductive channels with model predictions from the literature (Fig. 3). The influence of H2O2 treatment as a method for artificial degradation is investigated. The analysis of adhesion forces demonstrates a significant change of the surface properties with different membrane treatment. Topography and adhesion measurements clearly show materials changes with high resolution and correlate with changes in conductivity distributions. In particular, small protrusions in the topography correlating with strongly diminished conductivity in the current images are observed. These areas are interpreted as crystalline polymer backbone which higher stability against radical decomposition.
Small-Angle X-ray Scattering and Proton Conductivity of Anhydrous Nafion-Blend Membranes for High Temperature PEFCs
Authors: Kim Je-Deok , Ohnuma Masato , Nishimura Chikashi , Mori Toshiyuki
Published: September 2009

Various nafion-blend membranes were investigated as an anhydrous proton conducting electrolytes. Among them, nafion-bz and -triazole blend membranes showed high proton conductivity properties under non-humidified (anhydrous) conditions. The SAXS data showed that the bases as a proton source was successfully incorporated in the nafion nanostructure, and also the bz base in the nanostructure was stable under both wet and dry conditions at room temperature. The nanostructural stability of the nafion-bz blend membrane was also investigated at various temperatures, and was compared to the XRD and proton conductivity data.
Poly(arylene ether) Block Copolymer Membranes: Synthesis, Properties and Durability
Authors: Bae Byungchan , Miyatake Kenji , Watanabe Masahiro
Published: September 2009

Poly(arylene ether sulfone)s (SPEs) block copolymers containing fluorenyl groups were synthesized for fuel cell applications. Postsulfonation of the polymers by chlorosulfonic acid gave sulfonated block copolymers having highly sulfonated hydrophilic block. SPE block copolymer membrane with the ion exchange capacity (IEC) = 2.20 meq/g showed proton conductivity, 0.14 S/cm (80% RH) and 0.02 S/cm (40% RH) at 80°C, which is higher or comparable to that of perfluorinated ionomer (Nafion®) membrane. STEM observation of Ag-stained membranes revealed that phase separation of the SPE block copolymers was more developed than that of the SPE random copolymers. Long-term hydrolytic stability of these membranes has been confirmed.