bluuebunny/crossref_metadata_2025 huggingface dataset:
Pt Hillock Formation and Decay
Authors: Summerfelt Scott R. , Kotecki Dave , Kingon Angus , Al-Shareef H.N.
Published: April 2011

The formation of Pt hillocks during high temperature processing is a problem when using Pt as a bottom electrode for high dielectric constant materials. The hillock height is frequently larger than the dielectric thickness, degrading the leakage current of the device. In this work, Pt was deposited by electron beam evaporation on in-situ formed 40 nm ZrO2 coated SiO2 / Si substrates. The samples were then annealed at temperatures between 400°C and 700°C for times ranging from 2 min to 40 min. The surface roughness was measured by atomic force microscopy (AFM). The surface was characterized using Ra, RMS and Zmax over 5 μm × 5μm regions. Zmax is sensitive to hillock formation and Ra is sensitive to changes in general surface roughness. Analysis of Zmax indicates that 100 nm Pt / ZrO2 deposited at 315°C forms hillocks above 450°C during initial heatup. Subsequently, the hillocks decay for temperatures of 600°C and above such that they are almost gone after a 30 min air anneal. In-situ wafer stress measurements of Pt / ZrO2 were performed in O2 at temperatures up to 650°C. The Pt relaxes above 500°C in O2.
Liquid Delivery CVD of Ferroelectric (Pb,La)(Zr,Ti)O3 Thin Films
Authors: Tao W. , Desu S.B. , Peng C.H. , Dickerson B. , Li T.K. , Thio C.L. , Lee J.J. , Hendricks W.
Published: April 2011

High quality lanthanum doped PZT films were deposited on platinum coated silicon wafers by direct liquid injection MOCVD using lead bis-tetramethylheptadione, lanthanum tri-tetramethylheptadione, zirconium tetramethylheptadione, and titanium ethoxide as precursors. The films were deposited at 650°C and a reduced pressure of 5 Torr. The deposition rates were higher than 10 nm/min. The liquid delivery system led to highly reproducible deposition rate, composition, and ferroelectric properties in the PLZT films. The remanent polarization of the films decreased from about 25 μC/cm2 for PLZT(0/55/45) to about 12 μC/cm2 for PLZT(8/55/45). The coercive field of the films seemed to be independent on the La doping concentration up to 8% La doping.
Growth of Epitaxial BaTiO3 Thin Films at 600°C by Metalorganic Chemical Vapor Deposition
Authors: Kaiser D.L. , Vaudin M.D. , Rotter L.D. , Wang Z.L. , Cline J.P. , Hwang C.S. , Marinenko R.B. , Gillen J.G.
Published: April 2011

Metalorganic chemical vapor deposition (MOCVD) was used to deposit epitaxial BaTiO3 thin films on (100) MgO substrates at 600°C. The metalorganic precursors employed in the deposition experiments were hydrated Ba(thd)2 (thd = C11H19O2) and titanium isopropoxide. The films were analyzed by means of transmittance spectroscopy, wavelength dispersive x-ray spectrometry, secondary ion mass spectrometry depth profiling, x-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, nanoscale energy dispersive x-ray spectrometry and second harmonic generation measurements. There was no evidence for interdiffusion between the film and substrate. The x-ray and electron diffraction studies showed that the films were oriented with the a-axis normal to the substrate surface, whereas second harmonic generation measurements showed that the films had some c-axis character.
Influence of the Sol-Gel Synthesis Conditions on the Properties of Thin PbTiO3Films
Authors: Retuert P.J. , Velilla T.P. , Martin V. Del C. , Avila R.E.
Published: April 2011

Tetragonal, perovskite type, powders and thin films of PbTiO3have been synthesized by the sol-gel method, using trihydrate lead acetate and titanium tetraisopropoxide as starting alkoxides. The thermal treatment has been established from differential thermal and thermogravimetric analysis. An interpretation is presented for the various processes occurring during the gel to dense oxide conversion. The optimal process towards thin films includes annealing stages at 180, 400 and 650°C. Thin films were prepared by spinning on Si and Pt-covered Si. By SEM analysis the films appear cracked, porous, or homogeneous, with 0.5 to 1 um per solution coating. Current-voltage characteristics of Al/PT/Pt/Si capacitors exhibit a resistivity of 0.5 to 20·108Ωm, nondestructive breakdown in the range of 4 to over 20V, and relative dielectric permittivity of 100.
Preparation and Electrical Characteristics of (100), (111), and Randomly Oriented PZT Thin Films
Authors: Kim Chang Jung , Yoon Dae Sung , Lee Joon Sung , Choi Chaun Gi , Lee Won Jong , No Kwangsoo
Published: April 2011

The (100), (111) and randomly oriented PZT thin films were fabricated on Pt/Ti/Coming 7059 glass using sol-gel method. The thin films having different orientation were fabricated by different drying conditions for pyrolysis. The preferred orientations of the PZT thin films were observed using XRD, rocking curves, and pole figures. The microstructures were investigated using SEM. The hysteresis loops and capacitance-voltage characteristics of the films were investigated using a standardized ferroelectric test system. The dielectric constant and current-voltage characteristics of the films were investigated using an impedance analyzer and pA meter, respectively. The films oriented in a particular direction showed superior electrical characteristics to the randomly oriented films.
In Situ Monitoring in the Pulsed Laser Deposition of Ferroelectric Thin Films
Authors: Schenck Peter K. , Vaudin Mark D. , Lee Byeong W. , Bonnell David W. , Hastie John W. , Paul Albert J.
Published: April 2011

Optical multichannel emission spectroscopie studies and ICCD (intensified charge coupled device) imaging have been applied to real-time, in situ gas phase species identification and plume structure analysis during the pulsed excimer laser deposition (PLD) of various ferroelectric thin films. Additional information on the non-excited plume species has been obtained using molecular beam-sampling mass spectrometry. The materials studied included targets of PbZr0.53Ti0.47O3 (PZT) and BaTiO3. For the BaTiO3 films, the partial pressure of oxygen in the buffer gas and the atomic oxygen emission within the plume both correlated with the observed lattice parameter, as determined by X-ray analysis. Reduced plume oxygen content resulted in an increased lattice parameter that, in turn, could be related to a reduced oxygen content in the film. ICCD imaging of plumes from PZT targets identified the presence of ejected particulates in the plume after multiple laser shots had worked the target surface. Scanning electron microscopy (SEM) studies of the PZT target surface and film morphology, revealed cone-like formations on the target and éjecta on the films which correlated well with the ICCD observation of plume particulates.
Y-Ba-Cu-O/PZT Current Controllable Distributed RC-Element
Authors: Hagberg J. , Levoska J. , Leppävuori S. , Murtoniemi T.
Published: April 2011

A superconducting, current controllable, distributed RC-component was designed and fabricated. The component consisted of YBa2Cu3O7 (YBCO) thin film resistor, which was covered with a dielectric layer and an electrode to form a capacitor. The YBCO thin film was deposited by pulsed laser ablation on a SiTiO3 (100) substrate. It was patterned by photolithography and wet etched to form a tapered strip. This YBCO strip was covered with a lead zirconate titanate layer made by laser ablation and, finally, the dielectric layer was covered with a gold electrode by vacuum evaporation. The electrical characteristics of the superconducting YBCO film and the -element were measured.

Using the constructed component, high-pass and notch filter circuits were demonstrated. It was possible to control the electrical properties of these filters by a dc-current applied through the YBCO strip which causes the superconducting film to be come partly resistive.
Pile-Up Based Hall-Petch Considerations at Ultra-Fine Grain Sizes
Authors: Smith T. R. , Armstrong R. W. , Hazzledinew P. M. , Masumura R. A. , Pande C. S.
Published: April 2011

The dislocation pile-up explanation for the Hall-Petch (H-P) relation is re-examined for ultrafine grain sizes when only a few dislocations are involved in the pile-up, formed necessarily at applied stress levels near to the theoretical limit. Each dislocation added to the pile-up produces a step reduction in the H-P stress. Consequently, differences in dislocation configurations and types of pile-ups are easily recognized in the limit of small dislocation numbers. A significant reduction occurs in the H-P slope value (i.e., microstructural stress intensity) for the extreme case of only one dislocation loop being expanded against the grain boundary obstacle stress.
Spatio-Temporal Evolution of Dislocation Patterns in Fatigued Metals: Fundamental Limitations Imposed by Grain Size
Authors: Glazov Michael V. , Laird Campbell
Published: April 2011

An attempt to employ the self-organization theory has been made in order to describe different types of dislocation patterning in fatigued metals. We demonstrate that the formation of certain patterns can be understood as a result of competition between the intrinsic length scales of the “reaction+diffusion” model, on the one hand, and grain size, L on the other hand. Our results indicate that a critical grain size, Lcr, exists such that below Lcr the formation of dislocation structures of any type in fatigued metals becomes impossible.
Producing and Controlling Substrate Temperature Uniformity from 600°C to 1100°C in CVC Rotating Disk Reactors
Authors: Gurary A. I. , Tompa G. S. , Stall R. A. , Kroll W. J. , Zawadzki P. , Schumaker N. E.
Published: April 2011

Rotating Disk Reactors used for Chemical Vapor Deposition have evolved into a leading manufacturing technology for several materials, including metals, compound semiconductors, oxides, silicides, and nitrides. One of the hurdles to be surmounted in bringing this technology into routine high yield manufacturing has been to produce and maintain a highly uniform temperature distribution over the deposition area. With our recent introduction of the real-time Rotating Wafer Thermal Imaging (RWTI) technique, we have made dramatic improvements in the implementation of multi-zone heating systems and producing a uniform deposition temperature. Using multi-zone heaters we have demonstrated wafer temperature uniformity of less than 2°C in the temperature range from 600°C to 1100°C for 50 mm substrates located on wafer carriers with diameters from 125 to 300 mm. The wafer temperature uniformity dependence upon process parameters such as reactor pressure, reactant flows, and wafer carrier rotation speed was investigated. We have shown that multi-zone heating systems can provide high wafer temperature uniformity over a wide range of the process parameters, whereas single zone heating can provide a high degree of wafer temperature uniformity only for a limited set of process parameters. The experimental data allowed us to establish requirements for the application of single and multi-zone heating systems in vertical MOCVD Rotating Disk Reactors.
The Modeling Routes for the Chemical Vapor Deposition Process
Authors: Pons M. , Bernard C. , Rouch H. , Madar R.
Published: April 2011

The purpose of this article is to present the modeling routes for the chemical vapor deposition process with a special emphasis to mass transport models with near local thermochemical equilibrium imposed in the gas-phase and at the deposition surface. The theoretical problems arising from the linking of the two selected approaches, thermodynamics and mass transport, are shown and a solution procedure is proposed. As an illustration, selected results of thermodynamic and mass transport analysis and of the coupled approach showed that, for the deposition of Si1-x Gex solid solution at 1300 K (system Si-Ge-Cl-H-Ar), the thermodynamic heterogeneous stability of the reactive gases and the thermal diffusion led to the germanium depletion of the deposit.
Chemical Vapor Deposition of Ruthenium and Osmium Films from Mono- and bis-(Cyclopentadienyl) Complexes as Precursors
Authors: Smart Christopher J. , Gulhati Akshaya , Reynolds Scott K.
Published: April 2011

We have investigated cyclopentadienyl (Cp) complexes of Ru and Os as precursors for low temperature CVD of pure ruthenium and osmium films. Films were grown on a variety of substrates in a warm-walled CVD reactor, equipped with a resistively heated wafer chuck, massflow controllers for carrier gas regulation, and a mechanically-backed oil-vapor diffusion pump. Typical depositions were done under ca. 1 Torr total pressure. Use of air or oxygen as a carrier gas and Cp2M (M = Ru or Os) as precursors gave high purity, conformal films of ruthenium and osmium at temperatures as low as 275°C and 350°C, respectively. Under these conditions, the only observable by-products were CO2 and H2O, indicating that surface-catalyzed, complete oxidation of the ligands was involved in the decomposition process. Growth rates, film purities, resistivities and conformality were measured.
The Chemical Vapor Deposition of Dispersed Phase Composites in the B-Si-C-H-Cl-Ar System
Authors: Moss T. S. , Lackey W. J. , Freeman G. B.
Published: April 2011

The CVD of the coatings in the B-Si-C-H-C1-Ar system was accomplished using a statistically designed experiment. The experimental design used five factor half-fraction factorial with a central composite design that was both rotatable and orthogonal. Deposits were thick and dense and were composed of B13C2 and β-SiC with compositions ranging from 0 to 100%. Response surfaces were generated using multivariate regression for unit cell volumes of B13C2 and β-SiC, %B13C2/%SiC in the coating, and the Si to B ratio in the deposit. These equations could then be used to examine the significant variables in the reaction, as well as for tailoring and optimizing the deposition process.
CVD of Refractory Amorphous Metal Alloys
Authors: Tenhover M.
Published: April 2011

In this work, a novel process is described for the fabrication of multi-metallic amorphous metal alloy coatings using a chemical vapor deposition (CVD) technique. Of special interest in this work are amorphous metal alloys containing Mo and/or Cr which have high crystallization temperatures and readily available low decomposition temperature metal-bearing precursors. The conditions for amorphous alloy formation via CVD are described as well as the chemical properties of these materials. High temperature, aqueous corrosion tests have shown these materials (especially those containing Cr) are among the most corrosion resistant metal alloys known.
Aerosol-Assisted Chemical Vapor Deposition (AACVD) of Binary Alloy Films: Studies of Film Composition
Authors: Xu Chongying , Hampden-Smith Mark J. , Kodas Toivo T.
Published: April 2011

The chemical vapor deposition (CVD) of Cu-Ag and Cu-Pd alloys using aerosol precursor delivery over a range of preheating temperatures, 70∼80 °C and substrate temperatures, 250∼300 °C is described. The precursors used include Cu(hfac)2, (hfac)Ag(Set2) and Pd(hfac)2 dissolved in toluene and 10% H2 in Ar as carrier gas. The films were characterized by SEM, EDS and X-ray diffraction (XRD). The X-ray diffraction results showed the Cu/Ag films were composed of α-and β-phases of Cu-Ag alloys, the Cu/Pd films were Cu-Pd alloy, solid solutions, under these conditions. Compositional variation studies in Cu-Pd and Pd-Ag alloy systems were also conducted by mixing Cu(hfac)2/Pd(hfac)2 and (hfac)Ag(SEt2)/Pd(hfac)2 in toluene solution in different ratios. The films were characterized by X-ray diffraction and the results showed the composition of films was affected by the solution stoichiometry.
Rate of SiC Deposition from Methyltrichlorosilane and Influence of HCL Addition
Authors: Delhaes Christof , Neuschütz Dieter
Published: April 2011

Suitable feedgas compositions for monophase SiC deposition were determined starting from methyltrichlorosilane-hydrogen-argon mixtures at 1 bar total pressure and H2/MTS ratios between 50 and zero. At temperatures from 900 to 1400°C, only a ratio of 1 at PMTS = 18 mbar gave the desired result. The deposition rate of SiC was determined as a function of MTS and HCl partial pressures, of gas flow rate, and of temperature at a H2/MTS ratio of 1. Two different rate equations were found at [MTS]/[HCI] ≥ 5.8 (region I) and < 5.8 (region II), respectively:

where brackets denote gas concentrations. The apparent activation energy was 380 kJ/mol common to both rate equations. A mathematical model taking into account temperature fields at reactor wall and substrate, heat and mass transport in the flowing gas, and heterogeneous reaction rates jSiC(I) and (II) was developed and found to be in very good agreement with the experimental results.
Phase Transformations in Multilayered CVD Mullite Coatings
Authors: Doppalapudi D. , Muipuri R. , Basu S. N. , Sarin V. K.
Published: April 2011

Mullite (3Al2O3.2SiO2) is an ideal candidate for coatings on SiC due to its toughness, corrosion resistance and coefficient of thermal expansion (CTE) match. We have deposited alternating layers of Al2O3 and SiO2 followed by post deposition heat treatment to induce mullite formation at the interface. We found that the devitrification of silica to cristobalite led to spallation of the multilayered coatings due to the fracture within the crystalline silica layers. To understand this transformation better, we studied the effect of pressure and temperature on devitrification of silica in both bulk and in coating form. We have demonstrated that the difference in specific volumes of the two phases plays a key role in the vitreous to crystalline transformation in silica.
Asymmetric Drainage in Foam Films N4.1
Authors: Joye Jean-Luc , Hirasak George J. , Miller Clarence A.
Published: April 2011

Drainage of circular foam films is much more rapid when the drainage is asymmetric. The same basic mechanism is responsible for asymmetric drainage of thin circular films and marginal regeneration. A linear stability analysis showed that these phenomena are caused by a hydrodynamic instability that is produced by a surface-tension-driven flow and stabilized by surface viscosity, surface diffusivity and system length scale. A criterion for the onset of this instability was derived. Experiments performed on small circular films of aqueous solutions of SDS and SDS:l-dodecanol demonstrated the strong stabilizing effect of surface viscosity. Experimental results were found to be in good agreement with the predictions of the linear stability analysis. Finite difference simulations demonstrate the validity of the linear stability analysis for when the radius of curvature of the “barrier ring” is large compared to the transverse wave length of the instability. These simulations also show the circulation cells that relax the surface tension gradient and thus accelerate the drainage of the film.
Optimization of Diffusive Transport to Irregular Surfaces with Low Sticking Probability
Authors: Pfeifer Peter , Sapoval Bernard
Published: April 2011

We study steady-state diffusion to an irregular membrane or catalyst surface which “annihilates” arriving particles by transfer across the membrane or chemical reaction at the surface. For diffusion in two dimensions and an arbitrary given surface, we present a simple algorithm to compute the total flux across the surface (annihilation rate) when the permeability of the membrane or reaction probability at the surface is small. The resulting flux increases with increasing surfaceirregularity and depends nonlinearly on the transport parameters and on the surface area. It predicts an optimal temperature, dependent on the surface irregularity, at which the flux is maximal. We illustrate this for self-similar surfaces, in which case the flux is a power law of the transport parameters and is governed by the fractal dimension of the surface.
Low-Temperature Mobility of Thionine in a Faujasite Cage
Authors: Deeg F. W. , Ehrl M. , Bräuchle C.
Published: April 2011

We have used low-temperature optical spectroscopy to characterize the guest/host interaction of thiazine and oxazine dyes encapsulated in the three-dimensional pore structure of faujasite cages. The system thionine in dehydrated zeolite-Y exhibits a thermal and optical equilibrium between two spectroscopically distinguishable species. Temperature-dependent measurements allow the determination of the energy difference and barrier between these two forms as 170cm−1and 120cm−1, respectively. The two forms are associated with two different locations/conformations of the chromophore within the faujasite pore structure. The degree of freedom responsible for the interconversion of the two forms is extremely sensitive to the relationship between molecular size and form of the void.
Morphology & Exchange Kinetics in Polymer Brushes: The Physical Significance of Hydrodynamic Transitions and Stretched Exponential Evolutional Forms
Authors: Rodgers S. D. , Santore M. M.
Published: April 2011

This work reexamines equilibrium and kinetic features of polymer brushes end-adsorbed onto solid substrates from solution, providing a new interpretation of previously-published experimental results and insight into the comparison between experiments and existing kinetic models. The study centers on an end-modified polyethylene oxide (PEO) which may adsorb to form a polymer brush on a hydrophobic polystyrene latex, and whose main backbone also exhibits an attraction for the surface. In a previous work, Gao and Ou-Yang claim a sharp pancake-to-brush transition with increasing surface coverage of the samples with the strongest end group attraction to the substrate, and only a delicate increase in the hydrodynamic thickness of layers whose chain ends are weakly attracted to the surface. Our reevaluation of this data, however, collapses all molecular architectures to a single curve describing the hydrodynamic thickness at different surface loadings, and which shows a relatively sharp transition for all samples. Gao and Ou-Yang have also performed kinetic exchange experiments where low molecular weight species replace preadsorbed high molecular species (with the same endgroup-surface adsorption energy), and observed stretched exponential behavior in the evolution of the hydrodynamic thickness of the adsorbed layer. We employed Milner's treatment for brush exchange kinetics, to extract equivalent phenomenological parameters for more direct comparison between fundamental parameters and experiment.
Reaction-Diffusion Model for the A + A → O Reaction
Authors: Lindenberg Katja , Kopelman Raoul , Argyrakis Panos
Published: April 2011

We formulate an approach to the A + A → products reaction based on a reaction-diffusion model. We construct the first equations in a moment hierarchy whose first two members are the global density of A particles and the pair correlation function. We terminate the hierarchy by relating the three-particle correlation function to two-particle correlation functions and thereby obtain a set of coupled equations that turns out to be linear and hence analytically tractable.

This approach leads naturally to the proportionality of the rate of the reaction to the pair correlation function evaluated at r=a, where a is the diameter of the reacting particles. It also confirms the relation between anomalous kinetics and the deviation of the pair correlation function from that associated with a random distribution of particles.

Numerical simulations in one and two dimensions that support our theory are presented in a companion paper in this session.
Dynamics of Phase Separation of Binary Fluid Mixtures in the Presence of Surfactants
Authors: Laradji Mohamed , Mouritsen Ole G. , Toxvaerd Søren , Zuckermann Martin J.
Published: April 2011

The dynamics of phase separation of binary fluid mixtures in the presence of surfactants is studied via molecular dynamics simulations. In contrast to phase separation in pure binary fluid mixtures, which is characterized by an algebraic time dependence of the average domain size, mixtures containing surfactants exhibit nonalgebraic slow dynamics. At very late times, the average domain size saturates at a value inversely proportional to the surfactant concentration. Despite the fact that these systems only microphase separate, a dynamical scaling was observed at late times.
Thermal Conditions Favoring Buckytube Growth on the Anode
Authors: Koprinarov Nikola , Marinov Miko , Pchelarov George , Konstantinova Mariana , Stefanov Radoslav
Published: April 2011

The most widespread methoid for buckytube synthesis is by arc discharge in an inert gas ambient. At arc discharge the major kind of charge carriers are the electrons generated from the cathode by thermal emission. For this reason up until now the deposit was always obtained on the cathode. By supplementary electrode heating and cooling we studied the effects of the anode-cathode temperature difference and found that it plays a major role in defining the quality and quantity of the deposit obtained. Given appropriate heat-up or cool-down of the electrodes, a state can be reached such that the temperature at the cathode is higher than the temperature at the anode. A deposit was obtained on the anode, observed by a TEM. In our view employing this method yields the most favorable conditions for buckytube growth. Our results show that except buckytubes with a high ratio of their length with respect to their width, a multitude of small size polyhedral carbon systems closed in by spatial carbon nets and thin flat interfering carbon plates were also obtained. When using electrodes of different cross-section, with the deposition of an ever thicker deposit on the anode, its temperature regime changes. The lower initial temperature at the anode begins to grow steadily with time tending towards the temperature at the cathode. Thus, buckytube growth proceeds at the lowest possible rate, at a small temperature difference between the vapor source and growing structure. In our view employing this method yields the most favorable conditions for buckytube growth.
Infrared Spectroscopic Characterization of Sulfide Cluster-Derived Ensembles
Authors: Brenner James R. , Thompson Levi T.
Published: April 2011

The transition metal sulfide clusters (MeCp)2Mo2(μ-SH)2(μ-S)2, (MeCp)2Mo2Co2(μ3-S)2(μ4-S)(CO)4 [MoCoS], and (MeCp)2Mo2 Fe2 (μ3-S)2(CO)8, (MeCp = methylcyclopentadienyl) were used to prepare γ-Al2O3-supported catalysts. For comparison, a series of supported materials was also prepared using conventional incipient wetness impregnation. Infrared spectroscopy of adsorbed species was used to characterize the sites in the clusterderived and conventionally prepared catalysts. Nitric oxide chemisorbed onto the MoCoS/A catalyst was associated initially only with Co sites and then upon gentle heating shifted to the Mo sites, indicating that Co and Mo were in close proximity. In contrast, NO adsorbed onto both Co and Mo sites in the conventionally prepared materials and desorbed independently from these two types of sites. Infrared spectra of adsorbed thiophene and pyridine were similar for the clusterderived and conventionally prepared catalysts. Thiophene reacted at 100 °C to produce both olefinic species. The most abundant products from thiophene HDS were 1-butene, cis-2-butene, and trans-2-butene. Displacement studies showed that thiophene, pyridine, and NO adsorbed to the same site. The most active sites for HDS and HDN contained both Mo and a late transition metal. The HDN product distributions suggested that Mo was selective for C=N bond cleavage while the late transition metals were more active for C=C hydrogenolysis.
Heteropoly Compounds: Efficient Superacid Catalysts
Authors: Misono Makoto , Okuhara Toshio
Published: April 2011

Our recent studies on the acidity and acid catalysis of heteropoly compounds are described, together with a brief introduction of the background. High catalytic activities were observed due to the combination of their superacidity, pseudoliquid behavior, acid-base bifunctionality and/or high surface concentration of proton. It was also shown how the acid strength and the number of acid sites as well as their tertiary structure were controlled by the constituent elements (heteroand addenda-atoms and counter cations), and how those properties were correlated with the catalytic activities
Catalytic Implications for Keggin and Dawson Ions: A Theoretical Study of Stability Factors of Heteropolyoxoanions
Authors: Wang Shu-Hsien , Jansen Susan A.
Published: April 2011

Hetreropolyoxoanions(HPAs) have received wide spread attention due to their unique oxidation-reduction properties in catalysis. Two main structural motifs groups of HPAs have been described by Keggin and Dawson. The first is composed of twelve distorted, octahedrallycoordinated metal atoms forming trimeric and tetrameric subunits connected such that a closed shell results. The second is formed by fusing two Keggin units. The most common Keggin ions(XM12O40n−,) with Td symmetry and the Dawson ions(X2M18O62n−) with D3h symmetry are the α-isomers; while the β-isomers are generated by rotating one trimer 60° along its C3 axis, thus producing the Cs, symmetry for β-Keggin ions and D34 symmetry for β-Dawson ions. Here, M is the framework metal atom, usually Mo, W, and X is the central heteroatom which can be the metal or nonmetal. From our previous studies, the instability of β-isomers caused by the “rotated” trimer can not be compensated by other coordination effects within the cluster and therefore defect states are retained between the HOMO-LUMO gap relative to the α-isomer. This enhances catalytic properties and causes thermal/photo lability. The catalytic function of a-Keggin ions are well studied; however, related research reports about Dawson ions are rare. The α-Dawson ion possesses stronger oxidizing ability and higher activities in oxidative dehydrogenation and oxygen addition reactions than the α-Keggin ions; the β-isomers have a greater tendency to be reduced than the α-isomers. Most of the characterization methods applied have not yielded the electronic or the structural requisites for the catalytic properties of the HPAs. In this work, the theoretical analysis is done through the application of crystal/tight binding theory coupled with the extended HMckel methodology. The stability trends and the redox behaviors provided by this work reliably trace the experimental data. In addition, the intrinsic instability and the redox effects in the β-isomers with respect to the α-isomers is assessed and a rationale for the observed catalytic and electronic develpoment of structrual function is also offered.
New Nanophase Iron-Based Catalysts for Hydrocracking Applications
Authors: Matson Dean W. , Linehan John C. , Darab John G. , Camaioni Donald M. , Autrey S. Thomas , Lui Eddie G.
Published: April 2011

Carbon-carbon bond cleavage catalysts produced in situ at reaction conditions from nanocrystalline hydrated iron oxides, show high activity and selectivity in model compound studies. Two highly active catalyst precursors, ferric oxyhydroxysulfate (OHS) and 6-line ferrihydrite, can be produced by a flow-through hydrothermal powder synthesis method, the Rapid Thermal Decomposition of precursors in Solution (RTDS) process. Model compound studies indicate that both catalyst precursors are active at a 400°C reaction temperature, but that there are significant differences in their catalytic characteristics. The activity of 6-line ferrihydrite is highly dependent on the particle (aggregate) size whereas the activity of the OHS is essentially independent of particle size. These differences are attributed to variations in the crystallite aggregation and particle surface characteristics of the two catalyst precursor materials. Catalytic activity is retained to lower reaction temperatures in tests using OHS than in similar tests using 6-line ferrihydrite.
Mixed Metal Oxide Interfaces: An Experimental and Theoretical Assessment of Secondary Metal Influences in Metal Impregnated Aluminas
Authors: Malaty M. , Singh D. , Schaeffer R. , Jansen S. , Lawrence S.
Published: April 2011

Studies of the mixed-metal interface in metal impregnated alumina have indicated the possibility of much metal-metal and metal-substrate interaction. Studies were carried out on NiCu/Al2O3 system which was evaluated to develop a better understanding of the forces that drive modification of the catalytic selectivity of Ni in the presence of Cu. Electron Paramagnetic Resonance (EPR), Powder X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD) and theoretical calculations were carried out on this bimetallic system, using Ni,Ag/Al2O3 as a reference as Ni shows negligible electron perturbation on co-adsorbance with Ag onto alumina. XRD results indicate that gross modification of the electronic fields of Ni and Cu are due to direct coupling and intercalation into the alumina matrix. As a result of this phenomena, these materials may form a good base for the development of novel ceramics based on mixed-metal interactions where the intermetallic perturbations are driven by the substrate effects.
Perovskite Catalysts: High-Surface Area Powders Synthesis, Monoliths Shaping and High-Temperature Applications
Authors: Sadykov Vladislav A. , Isupova L.A. , Tikhov S.F. , Kimkhai. O.N.
Published: April 2011

Monolith perovskite catalysts of honeycomb structure for high-temperature applications are elaborated. Problems of powdered perovskites synthesis by efficient plasmochemical and mechanochemical methods as related to real structure and reactivity of these compounds are discussed. Pilot testing in reactions of fuels combustion, ammonia oxidation, methane conversion and sulphur dioxide reduction proved high activity and stability of these catalysts.
Advances in the Design of Pillared Clay Catalysts by Surfactant and Polymer Modification
Authors: Pinnavaia T. J. , Butruille Jean-Rémi , Michot Laurent J. , Guan Jingie
Published: April 2011

The catalytic properties of pillared clays for organic chemical conversions, especially those occurring in liquid media, can be substantially improved by surfactant modification of the pore structure during the pillaring reaction. For instance, the incorporation of a non-ionic surfactant, such as the alkylated polyethylene oxide C12–14H25–29O(CH2CH2O)5H, in the synthesis of alumina pillared montmorillonite results in a dramatic increase in the interparticle (textural) mesoporosity of the final calcined products. These surfactant-modified mesoporous pillared clays are exceptionally active as catalysts for the diffusion controlled liquid phase alkylation of biphenyl. The enhanced mesoporosity facilitates access of the reactants to the active acid sites in the interlayer nanopores of the pillared clay tactoids. Organic polymeric molecules also can be used to mediate the pore structure of pillared clay materials. The reaction of aluminum chlorohydrate oligomers with Na+ rectorite in the presence of polyvinyl alcohol as a pillaring precursor affords a supergallery alumina pillared rectorite with a basal spacings of 52 Å and a corresponding gallery height of 33 Å under air- dried conditions. A stable gallery height of 23 Å is observed even after treatment with 100% steam at 800°C for 17 hour. The new supergallery intercalate is characterized by a surface area, pore volume, and catalytic cracking activity superior to conventional alumina pillared rectorite and related smectites with 9 Å gallery heights.
Reactivity of Interstitial Cl− Anions in Synthetic Hydrotalcite-Like Materials in the Halide Exchange Reaction with Alkyl Halides
Authors: López-Salinas Esteban , Ono Yoshio , Suzuki Eiichi
Published: April 2011

Two types of synthetic hydrotalcite-like [Mg6Al2(OH)16 ][An−%D;2/n (HT) were prepared where A = Cl− anions (Cl-HT), and NiC42− complex anions (NiCl-HT), in order to examine: (1) the reactivity of Cl− anion (or ligand) towards alkyl halides and (2) their catalytic behavior in the Finkelstein reaction. For instance, 0.4 g of NiCl-HT (Cl−: 1.41 mmol) suspended in 20 cm3 of toluene with 14.1 mmol of butyl bromide at 373 K yielded 42 % butyl chloride after 15 min of reaction. In comparison, NiCl4(Et4N)2 (precursor to prepare NiCl-HT) yielded at the same conditions only 2.4 % of butyl chloride. This indicates a great mobility of Cl− in the interlayer region of HTs. The reaction rate is greatly accelerated using DMF instead of toluene and butanol totally suppressed it. This is consistent with a SN2 mechanism. The halide-exchange reaction between benzyl chloride and butyl bromide is catalyzed by both Cl-HT and NiCl-HT.
Molecular Sieve Synthesis using Metallocenes as Structure Directing Agents
Authors: Balkus Kenneth J. , Gabrielov Alexei G. , Sandler Netanya
Published: April 2011

We have been exploring molecular sieve synthesis using metal complexes as templates. Our objectives were to affect the crystallization of new structures as well as prepare bifunctional catalysts via the encapsulation of metal complexes during synthesis. In this paper the results for the synthesis of SiO2, AlPO4and SAPO molecular sieves in the presence of metallocenes will be presented. In particular, Cobalticinium ion, Cp2Co+, was found to be a template for Nonasil, AlPO4−5, AlPO4−16, SAPO−16 and CoAPO−16 which are known phases but require templates. The larger decamethyl derivative, CP*2Co+has produced a novel high silica zeolite molecular sieve, UTD-1 as well as a new SAPO phase UTD-2 which appear to be large pore materials. In all cases, the metal complex is occluded intact and cannot be extracted. Aspects of the synthesis and characterization of these microporous materials are presented below.
Carbon Fibrils Mechanism of Growth and Utilization as a Catalyst Support
Authors: Geus John W. , Van Dillen A. J. , Hoogenraad Marco S.
Published: April 2011

Especially with the production of fine chemicals catalytic reactions are being performed in which solid catalysts suspended in liquids are used. Carbon is stable in both acid and alkaline liquids and is not preferentially wetted by water. Carbon is therefore an attractive support for catalysts to be used in liquid-phase reactions. The relatively low diffusion coefficients in liquids call for catalyst bodies having wide pores and dimensions between 1 and 10 μm. Since particles smaller than 1 μm cannot be readily separated from liquids, attrition of carbon support bodies must be avoided. However, it is difficult to produce active carbon bodies of 1 to 10 μm of a high mechanical strength. Also with gas-phase reactions, the low mechanical strength of active carbon bodies limits the applicability of active carbon.

From supported metal particles carbon filaments of a diameter between 10 and 300 nm can be grown rapidly. The diameter is generally of the same order of magnitude as the size of the metal particles. The graphite layers within the fibrils, that have a circular cross-section, are oriented either parallel to the fibril axis or at an angle, which leads to cone-shaped graphite layers. The mechanism of growth of carbon fibrils from supported metal particles will be dealt with. The parallel orientation of the graphite layers leads to a very high mechanical strength, while the porous structure is extremely open. A representative value for the surface area is 225 m2/g and for the pore volume 1.6 ml/g, which leads to an average pore dimension of 28 nm.

To apply active precursors, such as, palladium salts, the surface of the carbon fibrils must be oxidized, e.g., by treatment with nitric acid. A very high dispersion of palladium can thus be achieved. The dispersion of components active in hydrogenation can be assessed by the ability to react the support with hydrogen to methane. The activity of catalyst on carbon fibrils in the hydrogenation of nitrobenzene as well as the filterability of carbon fibril catalysts will be compared with that of commercial catalysts.
Properties of a Carbon Negative Electrode in Completely Inorganic Thin Film Li-Ion Batteries with a LiCoO2 Positive Electrode
Authors: Goldner R.B. , Slaven S. , Liu T.Y. , Haas T.E. , Arnt F.O. , Zerigian P.
Published: April 2011

Completely inorganic thin film lithium ion battery cells have been prepared by vapor deposition processes (vacuum evaporation and sputtering). The negative and positive electrodes were films of disordered carbon and lithium cobalt oxide, respectively. The results of battery charging/discharging and other measurements (e.g., in-situ lithium chemical diffusion constant measurements for the carbon films) indicate that disordered carbon films have a relatively high reversible charge capacity, (> 160 mC/μmand possibly higher than 360 mC/cm2-μm, or > 296 and possibly 667 mAh/g, respectively, assuming the measured film density of 1.5g/cm3), and a lithium chemical diffusion constant at room temperature ≈10-9 cm2/s. These results suggest that disordered carbon films should be good substitutes for metallic lithium in thin film rechargeable batteries.
Vanadium Pentoxide Gels from Liquid Crystals to Lithium Batteries
Authors: Livage J. , Baffier N. , Pereira-Ramos J.P. , Davidson P.
Published: April 2011

Vanadium pentoxide gels V205.nH20 are formed via the condensation of vanadic acid in aqueous solutions. They exhibit both ionic and electronic conductivity and could therefore be used as cathode materials in lithium batteries or electrochromic display devices. The polymerization process leads to ribbon-like vanadium pentoxide particles. In a given range of concentration, sols and gels exhibit a homogeneous lyotropic nematic phase in which the ribbons align in the same direction. Ordered fluid phases are thus obtained leading to oriented films when deposited onto flat substrates. Moreover, mixed oxides MxV205 (M = Na+, K+,Ba2+, Al3+, Fe3+,Fe3+,...) exhibiting some preferred orientation are obtained via ion exchange.These compounds exhibit improved lectrochemical properties (specific capacity, cycling properties) compared to usual mixed oxides prepared via solid state reactions.
Mass Transport and DC Electromotive Force Induced in Ionic Crystals by High-Frequency Electric Field
Authors: Rybakov K. I. , Semenov V. E.
Published: April 2011

Results of the theoretical study of the effects produced on ionic crystals by highfrequency electric fields of moderate intensity are presented. The ponderomotive action of the electric field on the space charge induced by it in a thin layer within the crystal near its surface causes directional mass transport that leads to plastic deformation and induces a stationary distribution of electric potential. The analysis shows that the proposed effect (that appears to be equivalent to the action of mechanical stresses which exceed the electromagnetic pressure by many orders of magnitude) can influence the results of processing of ionic crystalline materials significantly.
Processing and Electrochemical Properties of Mixed Conducting Lat-xAxCo1-yFeyO3-δ (A=Sr, Ca)
Authors: Weber W. J. , Stevenson J. W. , Armstrong T. R. , Pederson L. R. , Kingsley J. J.
Published: April 2011

Powder compositions in the series Lat-xAxCo1-yFeyO3-δ (A=Sr, Ca) have been prepared by a combustion synthesis method. Sintering of pressed powders produced high-density test specimens with the perovskite structure. The specimens exhibited high electrical conductivities with appreciable oxygen-ion conductivity that increased with Co content for the compositions studied. Oxygen permeation studies showed a significant flux of oxygen that increased with temperature for specimens in a P(O2) gradient with no applied field. Thermogravimetric studies of the Lat-xCo0.2Fe0.8O3-δ system indicated a reversible mass loss with increasing temperature that increased with Sr content.
Water Uptake and Conduction in Strontium Ytterbium Cerate
Authors: Coffey G. W. , Pederson L. R. , Weber W. J.
Published: April 2011

Water uptake and conduction have been studied in SrYb0.05Ce0.95O3-δ, a composition known to conduct protons, oxygen ions, and electrons, depending on temperature and environment. Water uptake kinetics evaluated by thermogravimetry occurred in two distinct stages: a rapid, initial weight gain (0.39±0.09 eV, attributed to grain boundary and near surface hydration) followed by a much slower uptake (2.8±0.4 eV, attributed to hydration of the bulk grains). From cyclic voltammetry and mass spectrometry measurements for a cell exposed to asymmetric conditions, currents and activation energies for electronic, oxygen ion, and proton conduction were determined. The activation energy for electronic conduction, 0.90±0.09 eV, is believed to be artificially high due to the increase in electron carrier concentration with increased temperature. The activation energy for oxygen ion conduction (0.97±0.10 eV) agrees well with other oxygen conductors. Proton conduction appeared to follow two different mechanisms: a low temperature process characterized by an activation energy of 0.42±0.04 eV, and a high temperature process, characterized by an activation energy of 1.38±0.13 eV. A possible explanation is that proton conduction at low temperatures is dominated by grain boundaries and is dominated by bulk conduction at higher temperatures.
Strain Driven Two-Dimensional Phase Transition in PbSnF4 Superionic Conductor
Authors: Denes Georges , Madamba M.C. , Parris J.M.
Published: April 2011

When a minor amount of HF is added to the SnF2 reacted with lead nitrate in aqueous solutions to prepare PbSnF4, a phase transition from tetragonal α-PbSnF4 to orthorhombíc o-PbSnF4 takes place. The transition is essentially bidimensional and takes place in the (a,b) plane of the unit-cell. The compactness of the structure increases at the transition. No essential structural change occurs: the transition is most likely displacive and it is driven by bidimensional nonuniform strain acting along the aand baxes of the unit-cell. This transition is similar to ferroic transitions (in this case, paraelastic → ferroelastic). No detectable change of chemical composition occurs at the transition, and the reason why the presence of HF in the reaction mixture causes the transition remains unknown.
Monitoring of Process of Ion Transport in Nonstoichiometric Fluorides with the LaF3 Structure
Authors: Sorokin Nikolay I. , Sobolev Boris P.
Published: April 2011

Fluoride compounds with the tysonite (LaF3- type) crystal structure form an important class of materials which find diverse technological applications as fast ionic conductors. The results of investigations of the ionic conductivity process within tysonite structured R1-xMxF3-x single crystals (R=rare earths and M=alkali-rare earths) are presented using various techniques of electrical response spectroscopy. Influence of isomorphic substitutions of iso- and heterovalent cations on ion transport parameters was studied. By monitoring the composition of nonstoichiometric R1-xMxF3-x. crystals we can vary fluorine-ion conductivity within the range 10−7 - 10−4 S/cm at 293 K and 10−4 - 10−2 S/cm at 500 K. The studied nonstoichiometric crystals with the LaF3-structure are promising solid electrolytes which can be used in chemical sensors and fluorine generators.
New Concepts in Primary and Rechargeable Solid State Lithium Polymer Batteries
Authors: Appetecchi Gianni , Croce Fausto , Gerace Furio , Panero Stefania , Passerini Stefano , Spila Eraldo , Scrosati Bruno
Published: April 2011

The properties of some examples of new classes of highly conducting ionic membranes are described and evoluated in terms of applications in new-design electrochemical devices.