bluuebunny/crossref_metadata_2025_split huggingface dataset:
Supported Molybdenum Carbide Catalysts: Structure-Function Relationships for Hydrodenitrogenation
Authors: Dolce Gregory M. , Thompson Levi T. 
Published: April 2011

ABSTRACTEarly transition metal carbides and nitrides have been shown to be active for the hydrotreatment of model compounds and petroleum crudes. In this paper we describe our investigations of the structural and compositional properties of γ-Al2O3-supported molybdenum carbides and efforts to correlate these properties with their pyridine and quinoline hydrodenitrogenation (HDN) activities. The HDN activities of the materials scaled linearly with the loading and oxygen chemisorptive uptake. Oxygen chemisorption results also suggested that the molybdenum carbide particles were highly dispersed and perhaps raft-like. Using temperature programmed desorption and infrared spectroscopy of carbon monoxide, we were able to identify two types of sites on the carbides; sites “on top” of the particle and sites at the perimeter. We have tentatively concluded that the most active sites for HDN were “on top” of the supported carbide particles.
Synthesis and Characterization of Hydrotalcites: [Zn1−xAlx(OH)2](CO3)x/2·mH2O; x=0.25−0.66
Authors: Valenzuela M. A. , López-Salinas E. , Zapata B. , Montoya J. A. 
Published: April 2011

ABSTRACTIn this work a series of [Zn1−xAlx(OH)2](CO3)x/2·mH2O; x=0.25−0.66 were prepared at constant pH in order to study the effect of the thermal treatment on their crystalline srtucture. It was found that is possible to obtain pure Zn-Al hydrotalcite materials within a x = 0.25−0.50 range in comparison with Mg-Al hydrotalcites which yield pure phases in more restricted x ranges (0.25−0.33). All Zn-Al hydrotalcites lost their layered structure at temperatures above 473 K being less stable than their parental Mg-Al hydotalcite (623 K). Specific surface areas of these materials depended strongly on the Zn/Al ratio and calcination temperature, ranging from 280 to 20 m2/g. ZnO and ZnAl2O4 compounds were detected as the calcination products at temperatures higher than 873 K.
Separation of Diffusive Jump Motion and Trapped Motion of Atoms in a Glass Forming Process Via Molecular Dynamics Simulation
Authors: Matsui J. , Fujisaki M. , Odagaki T. 
Published: April 2011

ABSTRACTWe have carried out the molecular dynamics (MD) simulation for a binary soft-sphere system and calculated the self part of the generalized susceptibility χs(q, ω) at various temperatures. At higher temperatures in liquid state, only one peak appears in the imaginary part of Xa, which tends to split into two peaks, the so-called α- and β- peaks, as the temperature is reduced. The temperature dependence of the peak frequency is well described by the Vogel-Fulcher law for the α- peak, and the peak frequency does not change much for the α- peak. We have also measured the trajectory volume of a tagged atom V(t), which is related to the dynamical order parameter, the “generalized capacity”, in structural glass transitions recently proposed by J. F. Douglas. These results show the transition temperature which is in good agreement with that determined by the trapping diffusion model.
Glass Formation and Local Topological Instability of Atomic Structure
Authors: Egami T. 
Published: April 2011

ABSTRACTA direct connection between the local topology of the atomic structure of liquids and glasses and thermodynamic quantities through the atomic level stresses is suggested for metallic alloys. In particular the role of local topological instability in the phase transformations involving liquid and glass will be discussed. It is pointed out that a single local geometrical criterion can explain various phase transformations, such as melting, glass transition, and glass formation by solid state reaction and liquid quenching.
The Influence of Fiber/Matrix Interface on the Mechanical Behavior of Nicalon SiC Fiber Reinforced Glass-Ceramic Composites
Authors: Liu Y. M. , Mitchell T. E. , Wadley H. N. G. 
Published: April 2011

ABSTRACTThe mechanical properties of unidirectional Nicalon SiC fiber reinforced calcium aluminosilicate (CAS/SiC) and magnesium aluminosilicate (MAS/SiC) glass-ceramic composites have been investigated by tensile testing and a nondestructive laser-ultrasound technique. The barium-stuffed MAS was either undoped or doped with 5% borosilicate glass. The degradation of the elastic stiffness constant Cu in the transverse direction due to interface damage was monitored in-situ by measuring the laser-generated ultrasound wave velocity. The three composite materials show distinctly different macroscopic deformation characteristics, which are correlated strongly to the interface degradation. A stronger reduction trend of the elastic constant ?? is associated with a larger degree of inelastic deformation. Observations of the fracture surfaces also reveal the close relation between fiber pullout length and interfacial characteristics. Interfaces of these composites have been studied by TEM, and their influence on inhibiting and deflecting matrix cracks is discussed.
Characterization of Diffusion Barrier Interlayers Between Copper and Plasma Sprayed Beryluum
Authors: Bartlett A. H. , Castro R. G. 
Published: April 2011

ABSTRACTPlasma spraying is being investigated as a method to fabricate first wall Be armor for the International Thermonuclear Experimental Reactor. Diffusion barriers of Ti, V, and W were deposited between the Be and the Cu substrate, also by plasma spray, to prevent formation of brittle Be-Cu intermetallics. Interface fracture toughness tests revealed loading mode-dependent crack behaviors and interface fracture toughnesses.
Hard and Soft Composition Lead Zirconate Titanate Thin Films Deposited by Pulsed Laser Deposition
Authors: Lacey Johanna L. , Trolier-McKinstry Susan 
Published: April 2011

ABSTRACTLead zirconate titanate thin films offer considerably larger piezoelectric coefficients than do ZnO, and so are attractive for microelectromechanical sensors and actuators. To date, much of the research in this field has concentrated on undoped PZT. In this work, PZT films grown from both hard and soft PZT targets have been deposited on platinum coated silicon wafers by pulsed laser deposition so that the effect of doping on the properties can be determined. Dielectric constants of 1000–1500 are regularly achieved in both types of films, with loss values varying from 0.01 for soft films to 0.03 for hard films. Remanent polarizations are typically 30 μC/cm2 for both types of films with no observable difference in coercive fields. When subjected to ∼140 MPa of biaxial tension and compression, only small (∼5%) reversible changes were observed, indicating a lack of substantial domain reorientation in the films.
Effect of Nitrogen on Shape Memory Behaviour of FE-MN-SI-CR-NI Alloys
Authors: Ariapour A. , Perovic D. D. , Mclean A. 
Published: April 2011

ABSTRACTThe composition of an Fe-Mn-Si-Cr-Ni stainless steel with shape memory effect was altered in this work in order to increase the strength of the alloy. The alloy possessed a low yield strength which is a major draw back for structural applications.Nitrogen alloying, using nitrogen pressurized melting (P=l–10 atm), was employed to introduce a nitrogen concentration of up to 0.36 wt%. The effect of nitrogen alloying on shape memory effect was studied through mechanical testing. It was found that nitrogen alloying increased the hardness; however, nitrogen as an interstitial alloying element suppressed the γ⇒ε transformation and therefore decreased the shape memory effect.Introducing small amount of Nb (e. g., 0.36 wt%) to the nitrogen containing alloys caused formation of NbN. The NbN compound was in the form of globular dispersed particles (200 nm) which increased the strength of the alloy without significantly changing the shape memory effect.
Smart Composite Biomaterials TiAIV/AI2O3/TiNi
Authors: Filip Peter , Musialek Jaroslav , Kneissl Albert C. , Mazanec Karel 
Published: April 2011

ABSTRACTThe TiNi shape memory alloy wires were plasma coated by α-Al2O3 ceramics and afterwards they were cast into Ti6Al4V or Ti6Al1.5V2.5Nb (Ti-alloy) matrix. The wire fibers melt and the alumina ceramics reacts with both TiNi and Ti-alloy if cooling rate is small. The interphases which are formed are Ti2(Al, Ni) and Ti3AL-type phases, respectively. The structure of TiNi wires changes to dendritic one, Ti-alloys contain 10 to 15% of primary α and transformed β phase. The optimal conditions for rolling are 900°C with reductions of 5%. At this conditions all the constituents of composite material can be deformed plastically. The adhesive strength of TiNi/Al2O3 is 60 MPa.
Characterization and Electrical Properties of WO3 Sensing Thin Films
Authors: Cantalini C. , Di Nardo S. , Lozzi L. , Passacantando M. , Pelino M. , Phani A. R. , Santucci S. 
Published: April 2011

ABSTRACTThe microstructure and the electrical properties of thermallyevaporated WO3 thin films have been investigated by glancing angle XRD, atomic force microscopy AFM, X-ray photoelectron spectroscopy XPS and dc techniques. Thin films of 1500 Å thickness have been obtained by evaporating high purity WO3 powders by an electricallyheated crucible at 5 × 10−4 Pa on sapphire substrates. Theas-deposited films have resulted to be amorphous. After annealing at 500°C in dry air for 6, 12 and 24 hours the films have shown well crystallized structures with preferential orientations of WO3 in the (200)direction. The increase of the annealing time has shown marked influence onthe microstructural features of the films surface, as highlighted by AFM investigations. The binding energies of W 4f7/2 have been close to that of WO3, the 24 h annealed yielded an O/W ratio close to 2.9 which is in good agreement with the theoretical one. The gas sensitivity, selectivity and stability of the annealed films in presence of NO2 gas (between 0.7 and 5 ppm) have been evaluated by measuring the electrical change of the film resistance in dry air and in gasatmosphere conditions. The influence of NO and Humidity interfering gases to the NO2 electrical response has been also evaluated. The 500 °C annealed at 24 h has shown better electrical properties in terms of NO2 sensitivity, stability and cross sensitivity effects.
Cracking a Tough Nut with a big Computer
Authors: Abraham Farid F. , Schneider D. , Land B. , Lifka D. , Skovira J. , Gerner J. , Rosenkrantzt M. 
Published: April 2011

ABSTRACTWe have simulated the dynamical failure of three-dimensional notched solids under tension using molecular dynamics and up to 100 million atoms. We discovered a dynamical brittle-to-ductile transition in the rapid cleavage of rare-gas solids when the crack velocity approaches one-third of the Rayleigh sound speed. At this transition, the crack tip has already begun to roughen on the atomic scale. This suggests that the brittle crack undergoes a dynamic instability which immediately leads to the initiation of plastic failure by the spontaneous emission and proliferation of dislocations and crack arrest.
Dynamics and Stability of Surfactant Coated thin Spreading Films
Authors: Matar Omar K. , Troian Sandra M. 
Published: April 2011

ABSTRACTWithin lubrication theory, we investigate the hydrodynamic stability of a thin surfactant coated liquid film spreading strictly by Marangoni stresses. These stresses are generated along the air-liquid interface because of local variations in surfactant concentration. The evolution equations governing the unperturbed film thickness and surface surfactant concentration admit simple self-similar solutions for rectilinear geometry and global conservation of insoluble surfactant. A linear stability analysis of these self-similar flows within a quasi steady-state approximation (QSSA) yields an eigenvalue problem for a single third-order nonlinear differential equation. The analysis indicates that a thin film driven purely by Marangoni stresses is linearly stable to small perturbations of all wavenumbers. The insights gained from this calculation suggest a flow mechanism that can potentially destabilize the spreading process.
Structure of Polymer Chains Confined in Vycor
Authors: Lal Jyotsana , Sinha Sunil K. , Auvray Loic 
Published: April 2011

ABSTRACTWe observe by Small Angle Neutron Scattering (SANS) the structure of polystyrene chains in semi-dilute solutions confined in model porous medium, Vycor. The size of the free polymer chains in solution is always larger than the pore diameter, 70 Å. The use of a suitable mixture of hydrogenated and deuterated solvents and polymers enables us to directly measure the form factor of one single chain among the others. The penetration of the chain in the porous media is almost complete for the concentration (Φ = 20%) and the range of molecular weights (35000 <M< 800000) used. The measured radius of gyration of confined chains is always smaller than the radius of gyration of free chains in the equivalent bulk solution.
Imaging and Resistivity Studies of Saturation Gradients in Two-Phase Flow in 3-D Porous Media
Authors: Kawamoto E. H. , Wong Po-Zen 
Published: April 2011

ABSTRACTWe have carried out x-ray radiography and computed tomography (CT) to study two-phase flow in 3-D porous media. Air-brine displacement was imaged for drainage and imbibition experiments in a vertical column of glass beads. By correlating water saturation Sw with resistance R, we find that there is a threshold saturation S* ≈ 0.2, above which R(SW) ∼ Sw−2, in agreement with the empirical Archie relation. This holds true for both drainage and imbibition with littlehysteresis, provided that Sw remains above S*. Should Sw drop below S* during drainage, R(Sw) rises above the Archie prediction, exhibiting strong hysteresis upon reimbibition. This behavior suggests a transition in the connectivity of the water phase near S*, possibly due to percolation effects.
Simulations of Lubricants in Confined Geometries
Authors: Stevens Mark J. , Mondello Maurizio , Grest Gary S. 
Published: April 2011

ABSTRACTWe examine the shear flow of hexadecane and squalane confined between plates with nm separation using molecular dynamics simulations. For both molecules substantial slip occurs at the walls and the density profile exhibits strong oscillations. In contrast to surface force apparatus measurements, our calculated effective viscosities are not much greater than bulk viscosities, but the simulations shear rates are much larger than the experimental ones. The actual viscosity calculated using the shear rate measured from the observed velocity profile is almost equal to the bulk viscosity within uncertainty.
Single Wafer Amorphous Silicon Process Evaluation
Authors: O'Meara David , Chang Chow Ling , Blumenthal Roc , Hegde Rama I. , Prabhu Lata , Kaushik Vidya 
Published: April 2011

ABSTRACTSingle wafer amorphous silicon deposition was characterized through process modeling and film characterization for application in semiconductor production. DOE methodology was used to determine the main deposition parameters, and the responses were limited to device production requirement properties of surface roughness, deposition rate and degree of crystallinity of the as-deposited film. The data trends and models show that deposition temperature and silane flow are the main factors. Increasing either or both factor increases the deposition rate and the surface roughness. The surface morphology, evaluated by AFM, SEM and TEM, was found to be rougher at extreme growth conditions than the poly crystalline film formed after anneal. The as-deposited surface morphology was not a result of pre-anneal crystal formations as determined by TEM cross sections of samples before and after anneal. Lack of crystalinity is important for impurity diffusion considerations. Device application of the single wafer a-Si process will be a compromise between growth rate (and associated throughput) and surface roughness that can be tolerated.
Electronic and Optical Properties of Bulk GaN and GaN/AlGaN Quantum Well Structures
Authors: Suzuki M. , Uenoyama T. 
Published: April 2011

ABSTRACTElectronic structures and optical gains of bulk GaN and GaN/AlGaN quantum wells (QWs) are theoretically investigated for the wurtzite and the zincblende structures, using the k-p theory. It is found that the lower crystal symmetry, that is the wurtzite, is preferable for the lower threshold carrier density in the bulk. Although the QW structure leads to symmetry lowering only in the zincblende, we can not find a significant benefit of the zincblende QWs. As for the reduction of the threshold carrier density, biaxial strains are more effective in the zincblende. However, the threshold carrier density is still higher than in the wurtzite. It is proposed that the uniaxial strain in the c-plane of the wurtzite is more useful for reducing it.
Implantation Activation Annealing of Si-Implanted Gallium Nitride at Temperatures > 1100 °C
Authors: Zolper J. C. , Han J. , Biefeld R. M. , Van Deusen S. B. , Wampler W. R. , Pearton S. J. , Williams J. S. , Tan H. H. , Karlicek R. J. , Stall R. A. 
Published: April 2011

ABSTRACTThe activation annealing of Si-implanted GaN is reported for temperatures from 1100 to 1400 °C. Although previous work has shown that Si-implanted GaN can be activated by a rapid thermal annealing at ∼1100 °C, it was also shown that significant damage remained in the crystal. Therefore, both AlN-encapsulated and uncapped Si-implanted GaN samples were annealed in a metal organic chemical vapor deposition system in a N2/NH3 ambient to further assess the annealing process. Electrical Hall characterization shows increases in carrier density and mobility for annealing up to 1300 °C before degrading at 1400 °C due to decomposition of the GaN epilayer. Rutherford backscattering spectra show that the high annealing temperatures reduce the implantation induced damage profile but do not completely restore the as-grown crystallinity.
Molecular Dynamics Simulation of Transport in Diamond and GaN: Role of Collective Excitations
Authors: Miskovsky N. M. , Lerner P. B. , Cutler P. H. 
Published: April 2011

ABSTRACTIn this paper we consider the role of collective excitations in transport of charge carriers in the conduction band of diamond and GaN. The present molecular dynamics simulation uses a Monte Carlo algorithm to determine the time between collisions with scattering rates calculated quantum mechanically using the Fermi Golden Rule. For very thin films (L=0.01 μm) and for low fields (F<10 V/μm), the energy spectra of both diamond and GaN contain a series of peaks which are attributed to the absorption and emission of discrete plasmons. In diamond. the intervalley LA, LO and TO scattering becomes increasingly more important at higher fields while electron-plasmon interactions decrease. For thicker diamond films (L=0.1 μm), there is hot electron transport for F∼10 V/μm and quasi-ballistic transport for F-100 V/μm. In GaN with L=0.01 μm and fields F∼10 V/μm, there is a discrete series of peaks in the energy spectrum corresponding to excitations associated with polar optical scattering.
Integrated Vapor Phase Cleaning and Pure no Nitridation for Gate Stack Formation
Authors: Glowacki F. , Froeschle B. , Deutschmann L. , Sagnes I. , Laviale D. , Bensahel D. , Halimaoui A. , Martin F. , Bauer A. J. 
Published: April 2011

ABSTRACTThe purpose of this publication is to give an insight into process development performed in two modules which belong to a cluster tool designed for the gate stack process sequence of cleaning, gate oxidation, and polysilicon chemical vapor deposition. For the first time, following the hardware and software MESC-based standards, two suppliers have integrated complementary modules to build a cluster tool. This equipment answers the demands of the 1C Manufacturers and follows the “best of breed” approach. Four single wafer rapid thermal process chambers, a Vapor Phase Cleaning (VPC) and a Rapid Thermal Oxidation/Nitridation (RTO/N) module from STEAG-AST Elektronik, a polysilicon and a nitride chemical vapor deposition module from ASM International are currently connected together to prove the feasibility of the single wafer processing gate stack cluster tool.
Surface Charging of Phosphors and its Effects on Cathodoluminescence at Low Electron Energies
Authors: Seager C. H. , Warren W. L. , Tallant D. R. 
Published: April 2011

ABSTRACTMeasurements of the threshold for secondary electron emission and shifts of the carbon Auger line position have been used to deduce the surface potential of several common phosphors during irradiation by electrons in the 0.5 – 5.0 keV range. All of the insulating phosphors display similar behavior: the surface potential is within ±1 V of zero at low electron energies. However, above 2–3 kV it becomes increasingly negative, reaching hundreds of volts within 1 keV of the turn-on energy. The electron energy at which this charging begins decreases dramatically after Coulomb aging at 17 μA/cm2 for 30–60 min‥ Measurements using coincident electron beams at low and high electron energies to control the surface potential were made to investigate the dependence of the cathodoluminescence (CL) process on charging. Initially, the CL from the two beams is identical to the sum of the separate beam responses, but after Coulomb aging large deviations from this additivity are observed. These results indicate that charging has important, detrimental effects on CL efficiency after prolonged e-beam irradiation. Measurements of the electron energy dependence of the CL efficiency before and after Coulomb aging will also be presented, and the implications of these data on the physics of the low-voltage CL process will be discussed.
Deposition and Characterization of Eu:Y2O3 Red Phosphor Thin Films
Authors: Jones S. L. , Kumar D. , Singh Rajiv K. , Holloway P. H. 
Published: April 2011

ABSTRACTThin film phosphors are very promising for the fabrication of flat panel field emission displays (FEDs). In the present paper we have reported the growth and characterization of Eu:Y2O3 phosphor thin films. The effect of surface roughness and crystallinity on the brightness of phosphor films have been studied. A post annealing treatment of the films have been found to result in the realization of Eu:Y2O3 films with 70% brightness compared to powder materials.
Effects of Interfacial States on Asymmetric Polarization Switchings of Epitaxial Bi4Ti3012 Thin Films
Authors: Park Bae-Ho , Hyun Sang-Jin , Mun S. H. , Noh T. W. , Lee J. , Lee See-Hyung , Jo W. 
Published: April 2011

ABSTRACTEpitaxial Bi4Ti3012 (BTO) films with Lao0.5Sr0.5Co03 (LSCO) or Pt bottom electrodes were grown on MgO(OOl) substrates by pulsed laser deposition. Surprisingly, a symmetric Pt/BTO/Pt capacitor showed a highly asymmetric polarization switching and an asymmetric Pt/BTO/LSCO capacitor revealed a nearly symmetric polarization switching. To understand these intriguing phenomena, Auger electron spectroscopy and x-ray photoemission spectroscopy depth-profiles were used. The evidences for interdiffusions at the bottom BTO/Pt interface were found. To get further understanding on the interfacial states, a capacitance-voltage (C-V) measurement was performed on the Pt/BTO/Pt capacitor. By fitting the C-V data with a back-to-back Schottky diode model, built-in voltages at the top and the bottom interfaces were determined to be 1.1 V and 3.2 V, respectively. From the obtained built-in voltages, an asymmetric band diagram for the Pt/BTO/Pt structure was suggested. Therefore, the imprint failure can be explained by existence of asymmetric interracial states.