bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Electron Beam Irradiation on PZT/PLZT Thin Film Capacitors
Authors: Jiang Bo , Kim Jiyoung , Khamankar Rajesh , Lee Insup , Lee Jack C. 
Published: April 2011

ABSTRACTThe effects of electron beam irradiation on the electrical characteristics of Pt-PZT-Pt and Pt-PLZT-Pt (with La concentration of 5% and 10%) thin film capacitors were studied. The top electrode of each capacitor was bombarded by localized energetic electrons with incident energies varying from 5 keV to 25 ke.V. Large distortions in the hysteresis loops were observed when the incident electrons had enough energy to penetrate the 1000Å Pt top electrode. The damage effects are strongly dependent on the original domain orientation when the film is irradiated, and an applied a.c. field after the irradiation seems to induce some recovery effects. The damage mechanism is explained by a simple model which considers the effect of space charge fields generated by the charge carriers trapped at the domain boundaries.
The Effect of Low-Angle and High-Angle Grain Boundaries on Elevated Temperature Strength
Authors: Kassner M. E. 
Published: April 2011

AbstractThe influence of small (subgrain) misorientation interfaces on the mechanical behavior of metals and alloys deforming within the creep regime has been intensively studied over the past several decades. Controversies have existed, but some new experiments suggest, contrary to the general opinion, that low-angle boundaries are not associated with the rate controlling process for plasticity and do not affect strength. The new evidence will be discussed in terms of other established experimental trends. Large-angle boundaries may have a smaller effect on elevated temperature strength than at ambient temperatures and do not appear to dramatically affect elevated temperature strength. Superplastic effects are not addressed.
Microstructural Effects on the Cyclic Deformation of Polycrystalline FCC Materials
Authors: Peralta P. , Llanes L. , Czapka A. , Laird C. 
Published: April 2011

AbstractThe effect of crystallographic texture and grain size on the cyclic hardening of FCC polycrystals was studied using copper as a model material. Samples with textures approximately random and two grain sizes were tested under cyclic loading. The cyclic response for high values of the plastic strain amplitude of the random-textured material was softer than that of polycrystals with strong <111>-<100> texture reported in [1], and almost the same at low plastic strains, when similar testing conditions were used. The cyclic behavior of specimens with different grain sizes and similar texture was almost the same as well. This result shows that texture had a much more important effect on the cyclic behavior of polycrystalline copper than the grain size. The effect of ramp loading as a pretreatment was also studied. The results show that large grained samples had a softer cyclic response after the ramp than small grained ones, but the effect was still smaller than that of texture.
The Structure and Properties of Centrifugally Spray Formed Ti6AI4V
Authors: Duggan M. A. , Loreito M. H. , Smallman R. E. 
Published: April 2011

AbstractTi6AI4V rings have been centrifugally spray deposited with the long term aim of producing sheet which can be superplastically formed. Spray deposition has been carried out under vacuum and under an argon atmosphere in order to assess the significance of gas entrapment during spray forming. Some samples have been HIPped and others have been used for hot rolling trials after spray deposition and the microstructures of these differently treated samples compared. Some preliminary measurements of the room temperature tensile properties have also been made.The results are briefly discussed in terms of the advantages of using a vacuum spray forming route and in terms of the properties of the spray-formed and HIPped samples.
Mechanical Hardness as a Probe of Nanocrystalline Materials
Authors: Koch C. C. , Shen T. D. , Malow T. , Spaldon O. 
Published: April 2011

AbstractThe use of mechanical hardness as a probe of nanocrystalline materials is reviewed. The fact that the grain size dependence of hardness is very different for nanocrystalline materials compared to conventional (≥1 μm diameter) polycrystals suggests a different deformation mechanism may be operative in nanocrystalline materials. Hardness is useful for following the sintering, densification reactions of nanoparticles. Solid solution hardening in nanocrystalline alloys is found to be overwhelmed by the grain boundary hardening. If alloying decreases the grain boundary hardening, i.e. increases grain size, an apparent solid solution softening effect is observed.
Simulation of Grain Growth During Directional Annealing
Authors: Zacharopoulos N. , Holm E. A. , Srolovitz D. J. 
Published: April 2011

AbstractA Monte Carlo simulation procedure is applied to simulate non-uniform grain growth during directional annealing. The assumed temperature profile consists of a small, finite size hot zone which blends smoothly into cold zones ahead and behind the hot zone. The hot zone is assumed to move with a constant velocity. The influence of the ratio of hot zone to cold zone temperatures and the velocity of the temperature field are investigated. The grain size is analyzed as a function of these variables. We find that very high aspect ratio grains (long axis parallel to the thermal field velocity vector) are possible within a restricted velocity window. These results are analyzed in terms of an analytic model based upon conventional grain growth laws.
Deformation and Comminution of Shock Loaded α-Al2O3 in the Mescall Zone of Ceramic Armor
Authors: Mcginn J. T. , Klopp R. W. , Shockey D. A. 
Published: April 2011

AbstractIncursion of high density penetrators into ceramic armor is preceded by the formation of a finely comminuted rubble bed at the penetrator tip, the Mescall zone. The deformation and failure processes that result in the Mescall zone are critical to understanding penetration resistance and to modeling penetration behavior. Transmission electron microscopy (TEM) was used to examine shock loaded material in the vicinity of an explosive detonation in α-Al2O3 and to infer the phenomenology of plasticity and fracture occurring at the tip of an advancing penetrator in ceramic armor. Comminution proceeds by intergranular fracture until the fragment size approaches the grain size. Further fragmentation proceeds by transgranular cracks, which nucleate at preexisting microvoids and at intersections of basal twins and primary and secondary slip bands.
Interfacial Strengthening in Semi-Coherent Metallic Multilayers
Authors: Rao S. I. , Hazzledine P. M. , Dimiduk D. M. 
Published: April 2011

AbstractExperimental results show that a nanolayered composite structure made of two kinds of metals strengthens dramatically as the layer thickness is reduced. In epitaxial systems, this strengthening has been attributed classically, to the modulus and lattice parameter mismatches between adjacent layers. The modulus mismatch introduces a force between a dislocation and its image in the interface. The lattice parameter mismatch generates stresses and mismatch dislocations which interact with mobile dislocations. In addition to these two interactions, there is the difficulty of operating a Frank-Read source in any very thin layer. However, the calculations suffer from the drawback that elasticity theory is being used at such short range from the dislocations that it is not strictly valid. In this paper the issues in strengthening of multilayer systems are defined within a simple analytical model. Additionally, a parametric approach using the atomistic embedded atom method (EAM), is developed to study, dislocation-interface interactions in metallic multilayers. Preliminary results of the atomistic calculations verify that Koehler strengthening is significant especially when the lamellae are very thin. For thicker lamellae the lattice parameter mismatch effects, which have been modelled within continuum theory, contribute increasingly to the strength. In Cu-Ni, the peak in the yield stress occurs when single dislocations must overcome both barriers. The yield stress drops in thicker lamellae as pile ups of increasing length form in the lamellae, finally conforming to the Hall-Petch equation.
Crack Dynamics and Grain Size
Authors: Gilman John J. 
Published: April 2011

AbstractTwo aspects of fast cracks are considered: 1. the terminal velocity, and corresponding relative kinetic energy; 2. the grain size dependence of the fracture. It is argued that this is determined by the kinetic energies of cracks when they have expanded enough to reach the boundaries of the grains in which they lie. This is more consistent with the observed facts than the more usual quasi-static models.By considering the limiting conditions at the very tip of a moving crack, many complications are avoided in calculating the terminal velocity. The maximum transverse acceleration of material is limited by the maximum stress (cohesive) that can be applied. The resulting terminal velocity is: 0.4 vs, where vs is the longitudinal sound speed; compared with measured values which average about: 0.31 vs.In polycrystals, microcracks are found when the applied stress exceeds the yield stress. However, the microcracks do not propagate in fine-grained specimens because they do not have enough kinetic energy to cross a typical grain boundary. This leads to the observed dependence of the fracture stress on the grain size.
Nucleation and Growth Processes During the Chemical Vapor Deposition of Diamond
Authors: Wang Yaxin , Evans Edward A. , Kovach Christopher S. , Landau Uziel , Angus John C. 
Published: April 2011

AbstractIn situmicrobalance measurements of diamond growth rates are described. These results can be used to test proposed mechanisms for diamond growth and suggest mechanisms for sp2impurity incorporation. The Thiele modulus is a simple criterion for growth uniformity and is used to compare hot-filament and combustion-assisted growth.
Molecular Beam Epitaxy of Boron Nitride Thin Films and Their Analytical Characterization
Authors: Davis Robert F. , Kester Daniel J. , Ailey K. Shawn 
Published: April 2011

AbstractBoron nitride (BN) thin films have been grown on the (100) surfaces of Si, diamond, Ni and Cu via ion beam assisted deposition (IBAD) using electron beam evaporation of B in tandem with N and Ar ion bombardment within the ranges of substrate temperature and ion flux of 200–700°C and 0.20–0.30 mA/Cm2, respectively, Fourier-transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) revealed a growth sequence of amorphous (a-BN), hexagonal (h-BN) and cubic (c-BN) layers on Si and diamond under most conditions. This sequence is attributed primarily to increasing biaxial compressive stress with film thickness due to interstitial Ar incorporation observed via Rutherford backscattering spectroscopy (RBS). The effect of deposition conditions, specifically substrate temperature and bombardment intensity, on the film growth was studied. Increasing the substrate temperature above 400°C led to the onset of the cubic phase at a greater film thickness, while increased ion flux led to earlier growth of this phase. These results may be explained by the relaxation of intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment, respectively. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300°C) is required for nucleation and growth of single phase c-BN by this technique. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.
Improvement of Adhesion of Diamond Coatings to WC(CO) Tool Substrates
Authors: Fan W. D. , Jagannadham K. , Narayan J. 
Published: April 2011

AbstractAdhesion of diamond coatings to cutting tool substrates is an important property that is needed to replace the polycrystalline diamond tools (PCD) in machine tool applications. The improvement in adhesion of diamond on WC(Co) tool substrates is brought about by formation of a composite layer. Composite layers made up of TiC or TiN and diamond were formed by laser physical vapor deposition of ceramic coatings and hot filament chemical vapor deposition of diamond films. A first layer of discontinuous diamond film on WC is embedded in the ceramic coatings followed by growth of a continuous diamond film that maintains continuity with the first diamond layer. The composite coatings were characterized by SEM and Raman spectroscopy. Adhesion and wear resistance of the diamond coatings were measured using a polishing wear test. The mechanisms of improvement in adhesion were analyzed by finite element modeling. Results show that TiC composite layers improve the adhesion of diamond coatings significantly. This improvement is considered to arise from the modification of the thermal stress at the interface between the diamond film and the WC(Co) tool substrate.
CVD Precursors Containing Hydropyridine Ligands
Authors: Gordon Roy G. , Thornton John , Chen Feng 
Published: April 2011

AbstractHydropyridine is introduced as a new ligand for use in constructing precursors for chemical vapor deposition. Detachment of hydropyridine occurs by a low-temperature reaction leaving hydrogen in place of the hydropyridine, and a very stable byproduct, pyridine vapor. Hydropyridine ligands can be attached to a variety of elements, including main group metals, such as aluminum and antimony, transition metals, such as titanium and tantalum, semiconductors such as silicon, and nonmetals such as phosphorus and arsenic.
AlN Grown by Metalorganic Molecular Beam Epitaxy
Authors: Mackenzie J. D. , Abernathy C. R. , Pearton S. J. , Wilson R. G. 
Published: April 2011

AbstractThin film AlN has been grown on Al2O3 and GaAs substrates by metalorganic molecular beam epitaxy (MOMBE) using amine bonded alane precursors, tertiarybutylamine, and nitrogen from a compact electron cyclotron resonance (ECR) plasma source operating at 2.45 GHz. Typical growth pressures were in the 0.5 − 1 × 10−4 Torr range. The growth rates, impurity backgrounds and surface morphologies were examined for both nitrogen sources and both the solid and liquid alanes. In general, growth efficiencies were good for both alane precursors, allowing for deposition of the low temperature, ∼ 400°C, AlN buffers needed for subsequent growth of GaN and InGaAlN alloys. Low growth temperatures could not be obtained using tertiarybutylamine, presumably due to poor decomposition efficiency of the source at low temperatures. The structural quality of material grown at high temperatures from the ECR plasma was measured by atomic force microscopy (AFM) and high resolution x-ray diffraction (HRXRD), indicating a surface roughness of ∼ 8 Å and an x-ray width half maximum (FWHM) of 430 arcsec.
Synthesis and Selected Micro-Mechanical Properties of Titanium Nitride Thin Films by the Pyrolysis of Tetrakis Titanium in Ammonia.
Authors: Bae Y. W. , Lee W. Y. , Besmann T. M. , Blau P. J. , Riester L. 
Published: April 2011

AbstractThin films of titanium nitride were chemical vapor deposited on (100)-oriented single-crystal silicon substrates from tetrakis (dimethylamino) titanium, Ti((CH3)2N)4, and ammonia gas mixtures in a cold-wall reactor at 623 K and 655 Pa. The films were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron spectroscopy. The nano-scale hardness of the film, measured by nanoindentation, was 12.7±0.6 GPa. The average kinetic friction coefficient against unlubricated, type- 440C stainless steel was determined using a computer-controlled friction microprobe to be ∼0.43.
Ellipsometric Investigation of Metal-Organic Chemical Vapor Deposition of Niobium Oxide Films
Authors: Gerfin Tobias , Graetzel Michael 
Published: April 2011

AbstractNiobium oxide films have been prepared by metal-organic chemical vapor deposition (MOCVD) in two different systems via thermal decomposition of Nb(OEt)5.A detailed study by exsitu variable-angle spectroscopic ellipsometry indicates a wavelength dependence of the refractive index that could be described by a Cauchy type dispersion formula and typical values of 1.9 to 2.1 at 632.8nm. The band gap of these films were at about 3.5 and 4eV for the indirect and direct transition. Preliminary results of in-situ ellipsometry at four different wavelengths in the visible and UV will be discusssed. The films were amorphous, extremely smooth and pinhole free and therefore they are useful candidates for interdiffusion barrier layers.
Molecular Dynamics of Monomer, Oligomer, and Polymer Liquids in Porous Media: A Field-Cycling Nmr Relaxometry and NMR Field-Gradient Diffusometry Study
Authors: Kimmich R. , Stapf S. , Seitter R.-O. , Callaghan P. , Khozina E. 
Published: April 2011

ABSTRACTThe molecular dynamics of fluids in porous media has been studied using field-cycling NMR relaxometry and NMR field-gradient diffusometry. The frequency dependences of the 1H and 2H spin-lattice relaxation times T1 of various liquids in porous glass reveal weak and strong adsorption behaviour depending on the polarity of the adsorbates. Correlation times eight orders of magnitude longer than in bulk have been observed. The T1 dispersion moreover reflects geometrical details of the matrix in a length scale three orders of magnitude longer than the adsorbate molecules. The mean-square displacements of adsorbate molecules on the surface are only one order of magnitude less than in bulk. The global diffusivity is reduced by tortuosity and porosity effects. The observed phenomena may be explained by bulk-mediated surface diffusion, i.e., Lévy walks. The dynamics of polymer chains much longer than the pore size is characteristicly different from that in bulk melts. There is evidence that the reptation mechanism explains at least a part of the phenomena observed for the porous matrix in contrast to findings with bulk polymer melts.
A Vibrational Investigation of Crystal Nucleation and Growth from a Physically Confined and Supercooled Liquid
Authors: Mu R. , Henderson D. O. , Pan Z. , Xue Y. 
Published: April 2011

ABSTRACTTemperature dependent Raman measurements were conducted on bulk and the confined 2,4,6-trinitrotoluene (TNT) in 2.5, 5, 10, and 20 nm porous silica. Two bands at 23 and 190 cm−1 were chosen to evaluate the structure and the melting and freezing transitions of the confined TNT in pores. The results show that the solid phase TNT confined in larger pores (dp > 5 nm) forms conventional solid TNT structure, while the TNT restricted in small pores has no freezing and melting transition characteristics. The results also suggest that the freezing transition of the confined TNT starts at the pore center and the confined TNT maintains its interconnectivity during the freezing transition.
Reactant Correlation Effects Study of Hydrogen Isotope Exchange Reaction on Supported Metal Catalysts
Authors: Choi Inchan , Kopelman Raoul 
Published: April 2011

ABSTRACTNon-classical results due to reactant correlation effects have been observed in the study of Monte Carlo simulations of the A2 + B2 → 2AB reaction. These simulation results, interpreted by the Pair Density Analysis method and the experimental kinetic studies, may provide an explanation of the early time anomalous kinetic behavior of the catalytic hydrogen isotope exchange reaction exhibited for surface-diffusion limited conditions on alumina supported platinum islands.
Scaling of Reaction Fronts in the Presence of Disorder
Authors: Araujo Mariela 
Published: April 2011

ABSTRACTA study of the dynamics of the reaction front that appears in diffusion-reaction systems of the form A + B → C with initially separated reactants in the presence of quenched disorder is presented. The scaling of the width of the front w is analyzed as a function of the “disorder strength” and the dimensionality of the system. It is shown that disorder strongly affects the width exponent α, ω tα even for d ≥ 2, where the mean field approximation is known to be valid. The scaling of the nearest neighbor distance, midpoint fluctuations and concentration profiles near the center of the front, are also studied.
A Population Balance Analysis of Substrate Distribution Effects on Enzymatic Reaction Rates in Reversed Micelles
Authors: Hatton T. Alan , Bommarius Andreas S. 
Published: April 2011

ABSTRACTA population balance analysis of the statistical distribution of substrates over reversed micelles indicates the importance of accounting for concentration fluctuations within the micelles in interpreting observed enhancements in enzymatically-catalysed reactions in reversed micellar media. When the reactions are slow relative to the rates of solubilizate exchange via micellar coalescence and redispersion processes, analytical solutions to the detailed population balance equations are obtained, and the connection between Michaelis-Menten kinetics in reversed micellar media and bulk aqueous solution is made. It is shown that the finite occupancy number of the micelles at low water content leads to a statistical distribution of substrates over the micelle population, and that this can give rise to changes in the apparent reaction kinetics, even in the absence of changes in the intrinsic reaction parameters themselves. The model predictions are in good qualitative agreement with reported experimental results.
Preparation and Pretreatment Effects on Co/SiO2 Catalysts for Fischer-Tropsch Synthesis
Authors: Coulter Kent E. , Sault Allen G. 
Published: April 2011

ABSTRACTCatalyst drying procedures are often given little attention in the experimental section of papers on supported metal catalysts. In general, drying appears to be regarded as a method to remove water and other volatile components prior to calcining or reduction, but not as a method to affect the surface properties of the catalyst. This study uses x-ray photoelectron spectroscopy (XPS) to examine the surface properties of silica supported cobalt catalysts, prepared using incipient wetness impregnation of cobalt nitrate hexahydrate, and finds a wide range of cobalt distributions, extent of nitrate decomposition, and reducibility for various drying procedures. After UHV annealing and subsequent reduction, the final cobalt surface properties are found to depend on the length of heating and the environment during the drying process. Maximum cobalt metal surface area is obtained for samples exposed to limited amounts of air and dried under conditions where gas phase species generated during the precursor decomposition are rapidly removed from the surface of the sample.
Surface Models of Alumina Supported Copper Oxide Prepared by Laser Ablation: Dispersion and Electron Structure Changes Following Reduction and Oxidation Cycles
Authors: Hirschauer B. , Paul J. 
Published: April 2011

ABSTRACTWe have explored and developed laser ablation as a tool to synthesize realistic planar models of high surface area catalysts as well as novel materials, not accessible with wet chemical methods. The process is illustrated by data for dispersion and electron structure modifications following thermal treatments of alumina supported copper oxide. Planar models of different wet and dry carrier/overlayer combinations were prepared and exposed to oxidizing and reducing atmosphere at 500°C. Characterization was made by XPS/ESCA. The data reveal the importance of surface hydroxyl groups in the two initial components to control coalescence and interdiffusion. The ablation route is part of our ongoing DENOX project and comparisons are made with other materials, tested for their materials properties and catalytic behavior in HC/NO reactions.