bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation of Shape-Memory Materials
Authors: James Richard D.
Published: March 2011

We present an overview of a theory of martensitic transformations developed by J. M. Ball and the author, and additional related results by Bhattacharya, Chu and Collins and Luskin and Kinderlehrer. This theory is in a form that is amenable to detailed numerical computations of microstructure. We describe the energy minimizing microstructures of a single crystal under applied displacements and under detailed dead loading. The relation of the theory to the crystallographic theory of martensite is presented.

A consequence of the theory is the sensitivity of the patterns of microstructure to the precise lattice parameters. In the case of the wedge-like microstructure studied by Bhattacharya, it is found that this microstructure is only possible as a coherent, energy minimizing microstructure if very restrictive conditions on the lattice parameters are satisfied. Materials that exhibit the wedge satisfy this relation closely. The analysis suggests that optimal shape-memory behavior may be related to relations of this type.

The theory has a relation to the work of Khachaturyan, Roitburd and Shatalov. We compare and contrast the two approaches. We present results that suggest that any approach based on the kinematics of linear elasticity will make serious quantitative errors in the prediction of microstructure.
Time-Resolved X-Ray Diffraction from Liquid Crystalliine Systems: Thermotropic Phase Transitions and the Effect of Applied Electric Fields
Authors: Mcnamee Scott G. , Galli G. , Ober C. K.
Published: March 2011

Time resolved X-ray diffraction from thermotropic liquid crystalline (LC) materials has been studied in conjunction with standard LC characterization techniques to investigate phase transitions and alignment due to applied electric fields. A more detailed understanding of the kinetics of the interaction between LC systems and applied fields is being sought. Both the effect of electric fields on the inter-molecular structure and the orientation parameter have been evaluated as a function of temperature for LC model compounds. These results are compared to observations of these mesogens in applied electric fields using optical microscopy. Materials of interest include low molar mass distyrylbenzene mesogens which exhibit both nematic and smectic mesophases. Results of investigations of thermotropic polymers will be discussed.
Predictions of Static and Dynamic Properties of Liquid Crystalline and Polymeric Systems in Electric Fields
Authors: Dowell F.
Published: March 2011

Predictions of static and dynamic properties from a unified molecular statistical mechanics theory for complex fluids in static electric fields are summarized. Included are thermodynamic, molecular ordering, and transport properties. In this new theory, the effects of an electric field Ee on the dipole moments and bond polarizabilities of tile molecules have been added to an eaxlier successful theory for complex organic molecules in condensed phases. Included are liquid crystalline (LC) and polymeric systems (including the first interlocking polymers).
Simiple Shear Flow of a Non-Aligning Nematic
Authors: Han W. H. , Rey A. D.
Published: March 2011

This paper presents a nonlinear numerical analysis of the orientational instabilites, textures, and flow patterns of a characteristic rod-like nematic liquid crystal in steady simple shear flow. The parameter vector V=(λ,E) is given by the reactive parameter (λ) and the Ericksen number (E). There are two stationary solutions: in-plane(IP) and out-of-shear-plane(OP), according to whether the average orientation lies in or out of the plane of shear. For a given λ the in-plane stationary solutions may undergo a continuous transition (second order) to two dissipatively equivalent OP solutions when E=Eo or a discontinuous transition (first order) to a highly distorted IP solution when E=Ei. The continuous transition at E=Eo is a supercritical (pitchfork) bifurcation and the discontinuous transition at E=Ei is a limit point instability. Nonlinear numerical analysis shows that for the studied liquid crystal Eo < Ei. The orientation phase diagram for stable stationary solutions therefore consist of a region of OP solutions separated from a region of IP solutions by the curve Vo = (λ,Eo), describing a set of continuous supercritical bifurcations. These stable OP solutions are characterzied by the absence of sharp splay and bend deformations and by the presence of complex secondary flows arising from the three dimensional orientation. Presented results also include the dependence of the three dimensional texture, primary and secondary velocity fields on E.
Kinetics of Shear Induced Micellar Association
Authors: Dewalt L. E. , Ou-Yang H. D. , Kim M. W. , Liu S-N , Pine D. , Dixon P. , Peiffer D. G.
Published: March 2011

Rheological measurements have been used to study the kinetics of shear induced association for rod-shape micelles formed by mixtures of ADHAB and salicylic-sodium salt. Pronounced hysteresis and large fluctuations were found in the stress-shear rate diagram. We investigate the association and dissociation mechanism through stress quench experiments where viscosity measurements study the system relaxation. The association process was found to be a single exponential with a relaxation time of about 1 minute, whereas the dissociation process was much slower and was non-exponential. In the semidilute regime, the critical shear rates increase with concentration, contradictory with existing theories.
Characterization of Pmma Gel Spheres and Shear Induced Microstructure
Authors: Paulin S. E. , Ackersons Bruce J. , Wolfe M. S.
Published: March 2011

Polymethylmethacrylate (PMMA) particles are suspended without additional free polymer in benzyl alcohol, where they swell to nearly three times their dry radius. The single particle properties are examined by static and dynamic light scattering measurements, as well as by intrinsic viscosity measurements. A colloidal liquid/crystal phase diagram is determined as a function of effective volume fraction determined from the intrinsic viscosity. The samples are subjected to oscillatory shear flows to determine the influence of flow on the particle microstructure. A nonequilibrium phase diagram is constructed indicating a correlation between spontaneous ordering at equilibrium and shear induced ordering. These results are compared with previous work done for hard PMMA sphere suspensions.
Theory of Defects in Condensed Phases of Langmuir Monolayers
Authors: Selinger Jonathan V.
Published: March 2011

Recent fluorescence-microscopy experiments have observed two types of defects—star defects and striped textures-in the liquid—condensed phases of Langmuir monolayers. These defects can be understood through a continuum elastic theory. This theory predicts both splay stripes, which are driven by the asymmetry between molecular heads and tails, and bend stripes, which are driven by a spontaneous breaking of chiral symmetry in the monolayer. These predictions are compared with experimental observations.
Butterfly Patterns: an Anomaly Common to the Neutron Scattering Spectra of Elongated Rubbers, Melts and Gels:
Authors: Bastide J. , Boue F. , Oeser R. , Mendes E. , Zielinski F. , Buzier M. , Lartigue C. , Lindner P.
Published: March 2011

A totally unexpected phenomenon has been observed for the first time a few years ago when studying, by small angle neutron scattering, rubbery networks containing a small proportion of uncrosslinked labelled (deuterated) chains [1].When such a system is elongated, the scattered intensity strongly increases with the extension ratio λ for q vectors parallel to the stretching direction (and for low q values). Conversely, in the direction perpendicular to the elongation axis, the scattered intensity slightly decreases at low q for small extension ratios and then remains approximately constant when λ is further increased. The changes which are observed occur therefore in a direction opposite to the “conventional” one, i.e. that corresponding to chains effectively linked by at least two chemical junctions to the network and thus oriented on an average along the direction of stretching.
Physical-Chemistry Parameters of SiO2 Monoliths Processed Via Sol - Gel
Authors: Elias A. M. , Elias M. E. , Nunes M. M
Published: March 2011

High quality glasses may be prepared from liquid precursors, via sol - geL Starting materials and variable control determine the final characteristics of silica monoliths for optical fiber preforms, prepared via sol - gel, as we have found in previous studies. The rate of hydrolysis. and condensation reactions, as wcU as the time required for densification of a gel, is dependent on water/alkoxide ratio, pH and the presence of drying control chemical additives. The physical and optical properties of the preforms are also determined by the specific conditions of the sol - gel processing.

In this study we present an additional analysis of pH effects on the kdnetics, before and during the material syneresis. The effect of CO2 as a contaminant, is also considered. Samples are prepared from hydrolysis of tetrametoxysane in methanol - water mixtures, in the presence of a - picoline. At 20°C, the initial values of pH range between 8 and 6 and show an exponential decrease as the hydrolytic polymensation proceeds, tending to acidic or more acidic values. These steps also are followed by TEM and SEM and are correlated with the sort of aggregates formed in the material along the percolation process. Optical properties of the preforms are interpreted in terms of the clusters formed from those aggregates.

Details on instrumental monitoring of [H+] along the alcogelation process are discussed.
Two-Dimensional Melting of Magnetic Bubble Arrays: A Continuous Hexatic-To-Liquid Transition
Authors: Seshadri R. , Westervelt R. M.
Published: March 2011

Arrays of two-dimensional magnetic bubbles in thin garnet films undergo a hexatic-toliquid transition as a function of bubble density controlled by an applied spatially uniform dc bias magnetic field that opposes the magnetization in the bubbles. The phase transition is driven by topological point defects. The bubbles are observed directly using optical microscopy and digital imaging techniques. In the presence of a linear gradient in the dc bias magnetic field the hexatic-to-liquid transition occurs spatially in the direction of the gradient. As the system goes from hexatic to liquid, a continuous decrease in bubble density accompanied by a continuous disordering of the array is observed along the gradient direction. This continuous disordering persists even after the system is allowed to equilibrate for very long periods of time, indicating that the hexatic-to-liquid transition is continuous at equilibrium. Dynamics of topological defects observed in the gradient field correspond to those observed in the uniform field.
Surface Evolution of Copolymer thin Films as Revealed by Atomic Force Microscopy
Authors: Coulon G. , Collin B. , Chatenay D. , Ausserre D.
Published: March 2011

Atomic Force Microscopy has been used to study the early stage evolution of the free surface of annealed symmetric poly(styrene-b-n-butylmethacrylate) diblock copolymer thin films. As the lamellar ordering propagates through the film thickness, Islands or holes are formed on the free surface. It Is shown that, depending on the Initial film thickness, I.e. on the fraction of the film surface occupied by the islands (or holes) In the ordered state, the existence or non-existence of spatial correlations characterizes the ordering kinetics of both islands and holes. However, the limit between these two regimes is not the same in the two cases : in the case of holes, spatial correlations occur for a higher value of the surface coverage than In the case of islands.
The Volume Fraction Profile of Terminally Adsorbed Polymers
Authors: Composto R. J. , Mansfield T. , Beaucage G. , Stein R. S. , Iyengar D. R. , Carthy T. J. Mc , Satija S. K. , Ankner J. F. , Majkrzak C. F.
Published: March 2011

We have used neutron reflectivity to measure the concentration profile of carboxylic acid-terminated polystyrene at the liquid/solid interface. Two isotopic systems were studied: (1) deuterated polystyrene (DPS) in cyclohexane and (2) polystyrene (PS) in deuterated cyclohexane. Although measured at 24°C (a poor solvent condition), the high grafting density of PS tethered chains causes the chains to weakly stretch to 3-5 times its unperturbed dimension. Although of similar molecular weight, the height of the DPS layer is about 50% higher than that of the PS. In both systems, the volume fraction of polymer near the wall is ∼ 0.60. For the DPS system, reflectivity profiles can be simulated using a parabolic profile with a depletion layer at the silicon-liquid interface. However, in the PS system, no depletion is observed. Here, the shape. of the PS concentration profile is parabolic with a rounded tail.
Static and Hydrodynamic Dimensions of Flexible Polyions in Solutions
Authors: Mattoussi Hedi , O'donohue Steve , Karasz Frank E.
Published: March 2011

The variation of the radius of gyration RG and the hydrodynamic size RH are followed as the ionic strength of the medium is monitored for a flexible polyelectrolyte compound in solutions. In addition, a comparison between the thermodynamical and hydrodynamical interaction parameters is given for the present system.
Structural Relaxations in the GHz Frequency Range in Glass Forming Silicate Melts
Authors: Masnik John E. , Kieffer J. , Bass J.D.
Published: March 2011

The Brillouin light scattering technique is used for the investigation of structural relaxations in glass-forming liquids at high temperatures. From the analysis of the line shapes of Rayleigh and Brillouin peaks, the friction coefficients, which are associated with the atomic scale mechanisms of the structural relaxations in these systems, are determined. Results for a series of K2O-SiO2 compositions, which were chosen as model substances, are reported. As a function of temperature, maxima in the Brillouin line widths were observed, which reflect resonant conditions of molecular scale structural motions, where the relaxation time is of the order of the reciprocal Brillouin frequency shift. Due to thermal activation of the component mobilities, different relaxation mechanisms couple at different temperatures. Typically, at least one strongly absorbing regime is observed in between the glass transition and the equilibrium melting temperatures. The prominence of this regime decreases with increasing silica concentration. The friction coefficients approach the hydrodynamic viscosity in the high temperature limit, when the relaxation times become short in comparison with the time scale of the Brillouin shift.
Structure and Dynamics of the Ferrosmectic Phase
Authors: Fabre Pascale
Published: March 2011

We have elaborated a system -that we call a ferrosmectic- which contains magnetic particles included in a lamellar phase. Because of the presence of the confined particles, this phase exhibits specific features that are revealed by submitting it to a magnetic field as well as by neutrons or quasi-elastic light scattering experiments. We present here a review of the different properties of this ferrosmectic phase.
The Rotator Phases of the Normal Alkanes
Authors: Sirota E. B. , King H.E. , Singer D.M. , Shao H.
Published: March 2011

We present results of an x-ray scattering study on the rotator phases of normal alkanes: CH2-(CH3)n-CH2 (20 ≤ ≤ 33). We have characterized a new tilted rotator phase and measured the distortion and tilt order parameters in all 5 rotator phases. We have shown that there is no strong even-odd chain effect within the rotator phases.
X-Ray Diffraction Studies of Tubules Formed from a Diacetylenic Phosphocholine Lipid
Authors: Thomas B. , Safinya C. R. , Plano R.J. , Clark N. A. , Ratna B.R. , Shashidar R.
Published: March 2011

The diacetylenic phosphocholine lipid 1,2-bis(10, 12-tricosadiyonol)-sn-glycerol- 3-phosphocholine forms, upon cooling below the chain melting temperature, hollow cylindrical structures known as ‘tubules’. These tubules are approximately one micron in diameter and may range from tens to hundreds of microns in length. We have carried out x-ray diffraction studies of tubules (1) in 75/25 ethanol/water by volume and (2) in a dessicated state. We present results which show marked differences in the nature of both the in-plane and inter-layer correlations associated with the wrapped multilayer structure of the tubules in the two states.
Ba2YCu3O7−x Thin Films with Jc>105 A/cm2 at 77 K Prepared by Metalorganic Deposition at Reduced Oxygen Pressure
Authors: Hallock Robert B. , Rhine W.E. , Jolly M.S. , Cima MIchael J.
Published: March 2011

Superconducting Ba2YCu3O7-x films 0.1-0.2 gim thick were prepared by spin coating a methanol solution of Ba, Y and Cu acrylates on (100)LaAlO3 and firing to 800°C in a total pressure of 1 mm O2. X-ray diffraction showed that these films were epitaxial with the c-axis normal to the substrate. Zero resistance was achieved above 90 K and transport DC critical current densities as high as 125,000 A/cm2 were measured at 77 K in zero applied field.
Sol Gel Derived Aluminum Nitride Thin Films Via the Nitridation of Alumina
Authors: Russell M.W. , Giannelis E.P.
Published: March 2011

Crystalline aluminum nitride thin films (∼ 1200 Å) were prepared via nitridation of amorphous aluminum oxide and characterized by XRD, SEM, TEM, oxygen resonance, Auger depth-profile analysis and ellipsometry. Precursor chemistry, heating rate, nitridation temperature and nitridation time were varied to explore the competition between densification, crystallization and nitridation. Oxygen content in the films decreased with increasing nitriding temperature or nitriding time. Heating rate was determined to have minimal effect on the oxygen content for the parameters evaluated. A modified Kissinger analysis of DTA data for the crystallization of α-Al2O3 yielded an effective activation energy of ∼104 kcal/mol.
A Novel Route to Silocon Based Ceramic Coatings on Carbon Substrates
Authors: Macinnes Andrew N. , Barron Andrew R.
Published: March 2011

Carbon fiber tows have been impregnated by ethanolic solutions of organo-silicon chlorides, and fired at temperatures up to 900°C to form silicon based coatings. Fired tows were subsequently examined by X-ray photoelectron spectroscopy and scanning electron microscopy to characterize the coated material. A uniform silicon oxycarbide is formed at temperatures upwards of 400°C, which provides an oxidation barrier in carbon fiber reinforced metals.
Reaction Injection Molding of Silica-Alumina Mixtures Using Heterocoagulation
Authors: Pujar Vijay V. , Cawley James D. , Hu Ping , Lee L. James
Published: March 2011

A colloidal processing technique based on the heterocoagulation of selected ceramic oxide systems, and analogous to reaction injection molding of polymers, is described. Commercial colloidal silica and boehmite sols, which have oppositely charged particles in the pH range 2.0-9.0, and mixtures of these suspensions with micron sized oxide powders, have been used to determine whether a liquid to solid transformation could be induced when the two materials are simultaneously injected at high velocities into a mold cavity. Rheological changes have been measured as a function of relative flow rates of the two suspensions, solids loading and oscillatory frequency. Viscosity is observed to increase by as much as six orders of magnitude under optimized conditions.
Binder Design for Fabricating Internal Crack-Free Injection-Molded Si3N4-Based Ceramics
Authors: Su Sophia R.
Published: March 2011

Binder design is an important issue in ceramic injection molding technology. The binder decomposition mechanism, which involves thermodynamics, kinetics, as well as heat and mass transfer, controls the binder removal process. This process, in turn, is governed by the thermal and physical characteristics of the organic waxes used, and is the most critical step in injection molding ceramics. In this paper, we present the binder design philosophy and the method of binder selection. A systematic binder removal study focusing on heating rate, setter powder, and sublimable materials was carried out with the selected compositions. As a result of this study, we concluded that the fluid wicking controls the binder removal at the molten temperature of the binder, and the diffusion and permeation-controlled mechanism dominate at the decomposition temperature range of the binder. With the right binder selection, it is feasible to produce internal and external crack-free large cross-section injection-molded ceramic parts.
Combined Stage Sintering Model: Review and Applications
Authors: Rusin R.P. , Hansen J.D. , Teng M.-H. , Johnson D. Lynn
Published: March 2011

In the combined stage sintering model previously introduced[l], a single equation was derived that quantifies sintering as a continuous phenomenon from beginning to end. The microstructure is characterized by two separate parameters representing the geometry (Γ) and the scale (G). Calculations of Γ from experimental data show the effect of surface diffusion and microstructural geometry on Γ. The model is reviewed and discussed with respect to the sintering of alumina and spherical nickel powder.
Cellular Automaton Simulations of Surface Mass Transport Due to Curvature Gradients: Simulations of Sintering in 3-D.
Authors: Bentz D.P. , Pimienta P.J.P. , Garboczi E.J. , Carter W.C.
Published: March 2011

A cellular automaton algorithm is described that simulates the evolution of a surface driven by the reduction of chemical potential differences on the surface. When the surface tension is isotropic, the chemical potential is proportional to the curvature at the surface. This process is important in the development of microstructure during the sintering of powders. The algorithm is implemented in two and three dimensions in a digital image mode, using discrete pixels to represent continuum objects. The heart of the algorithm is a pixel-counting-based method for computing the potential at a pixel located in a digital surface. This method gives an approximate measure of the curvature at the given surface pixel. The continuum version of this method is analytically shown to give the true curvature at a point on a continuum surface. The digital version of the curvature computation method is shown to obey the scaling laws derived for the continuum version. The evolution of the surface of a three dimensional loosely packed powder, along with the percolation characteristics of its pore space, are computed as an example of the algorithm.
Liquid Phase Sintering in the Glass-Cordierite System - Effect of Melt Infiltration Distance
Authors: Jean Jau-Ho , Gupta Tapan K.
Published: March 2011

Effect of glass infiltration distance, controlled by particle sizes of glass and ceramic filler, and green density, on densification kinetics of glass-filled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing cordierite size, reducing glass size and increasing green density. The above results are attributed to both increased driving force of densification by reducing glass particle size, and decreased glass redistribution distance by either increasing green density of compacts or increasing the particle size ratio between cordierite and glass powders.
Additive Sintering Process in Aluminum Nitride Ceramics
Authors: Makihara H. , Kamehara N.
Published: March 2011

Calcium compounds and yttrium compounds are frequently used as additives to densify AlN ceramics[l,2]. They react with oxygen impurities, such as A1203 in the raw AlN powder and in aluminate forms. A phase diagram is helpful in deciding the amount of additives to add, but the AlN sintering process doesn't come to equilibrium. We investigated the differences between sintering AlN with CaCO3 and with Y2O3.

With CaCO3 added, the calcium-aluminate liquid phase evaporates from the sintered AlN body at high sintering temperatures. The AlN thermal conductivity doesn't increase above a sintering temperature of 1700°C because residual oxygen substitutes into the AlN grains. With Y2O3 added, AlN sinters below 1850°C, as predicted by a phase diagram. With a large amount of Y2O3 added, 5 wt%, thermal conductivity doesn't depend on residual oxygen. This is because yttrium doesn't evaporate from the sintered AlN body and residual oxygen substitutes into AlN grains at an early stage of the AlN sintering.
Fundamental Issues in the Sintering of Ceramic Particulate Composites
Authors: Rahaman Mohamed N.
Published: March 2011

The sintering rate of a ceramic powder matrix can be reduced significantly by the presence of rigid inclusions. The factors that lead to this reduced sinterability have been the subject of much debate in the last 5–10 years. Recent work indicate that the reduction in the matrix sinterability is a processing-related problem. The main factors that control the sinterability of ceramic particulate composites include the packing of the matrix immediately surrounding the inclusions and interactions between the inclusions which constrain the matrix. A processing method which avoids the difficulties associated with these two factors is outlined. The method involves the synthesis of coated inclusion particles. Composites containing up to 40 volume percent inclusions can be freely sintered in the solid state to full density.
Modeling Refractory Material Production by Self-Propagating High Temperature Synthesis (SHS)
Authors: Crane Thomas F. , Gutierrez-Miravete Ernesto
Published: March 2011

Self-propagating high temperature synthesis (SHS) can be used to prepare near net refractory shapes which are difficult to produce by other methods. In SHS, green compacts capable of strong exothermal reaction are ignited at one end and transformed into the desired products by a self-propagating reaction. Physical processes involved in SHS include chemical kinetics, macroscopic transport phenomena and phase transformations. This paper describes a simplified mathematical model of the SHS process derived by combining the heat equation with the chemical reaction rate equation. The model equations are solved numerically to obtain representation of the SHS process. Parametric studies have been performed to investigate the relative importance of the physical parameters in the model.
From Minierals to Materlals: A Facile Synthetic Route to Preceraic Polymers for Aluminum Oxide
Authors: Apblett Allen W. , Landry Christopher C. , Mason Mark R. , Barron Andrew R.
Published: March 2011

Reaction of boehmite, [AI(O)(OH)]n, with an excess of carboxylic acid (HO2CR) results in the formation of the carboxy substituted alumoxanes, [AI(O)x(OH)y(O2CR)z)]n where 2x + y + z = 3 and R = alkyl substituents. The alumoxanes have been fully characterized by SEM, elemental analysis, IR and multinuclear NMR spectroscopy. The physical properties of the alumoxanes are highly dependent on the identity of R, and range from insoluble crystalline powders, e.g. R = CH3, to powders which readily form solutions or gels in hydrocarbon solvents, e.g. R = C5H11. All of the alumoxanes decompose under mild thermolysis to yield γ-alumina.
Advanced Hydrothermal ZrO2 Powder
Authors: Sōmiya Shigeyuki , Hishinuka Kazumitsu , Nakai Zenjiro , Abe Notoshi , Akiba Tokuji
Published: March 2011

Well-crystallized Y2O3 -ZrO2 powder of 12nm crystallite size was synthesized by RoAogenious precipitation under hydrothermal condition at 180°C for 1 hour. This powder consisted of tetragonal zirconia. After calcination and ball milling, the crystiilite size was 22 nm and the tetragonal phase was reduced to 55% by ball milling. The average grain size was 0.5 µm and specific: surface area was 20 m /g. Highly dense TZP(> 99%) with a homogeneous microstructure was obtained by sintering this powder at 1400°C for 2 hours.
Oxygen Effect and Redistribution in Cobalt Silicide Formation
Authors: Lien Chuen-Der , Nicolet Marc-A.
Published: March 2011

18O was implanted in the Si substrate or in the Co overlayer to study the effect of oxygen and its redistribution during Co silicides formation. Implanted and unimplanted samples were annealed in vacuum at 450°C for different durations. Over the investigated dose range of 0.5 to 2 × 101618O/cm2 in the Co film, the phases formed upon annealing are Co2Si and CoSi, as for the unimplanted samples. The kinetics of the silicide growth is changed little by the presence of oxygen in the Co film. Oxygen accumulates at the Co2Si/Co interface. When the oxygen is implanted in the Si substrate, the higher the oxygen dose is, the slower (fasteil the growth rate of CoSi(Co2Si) becomes. Below 1 × 1016 O/cm, both phases (i.e. CoSi and Co2Si) still form; above 2 × 1016 O/cm2 , only Co2Si formsWhen two phases form, the oxygen moves deep into the Si substrate; when only Co2Si forms, the oxygen moves toward the surface.
Kinetics of Phase Formation in Cu-Al Thin Films Couples Studied by In-Situ X-Ray and Rutherford Backscattering Analysis.
Authors: Hamm R. A. , Vandenberg J. M.
Published: March 2011

X-ray diffraction (XRD) and Rutherford backscattering analysis (RBS) have been used independently to study the interface reaction of copperaluminum thin film couples during in-situ annealing in the temperature range 157°–220°C. For the X-ray studies a high vacuum annealing system was constructed on a Huber-Guinier thin film goniometer base1. This system enabled us to monitor the thin film interface reaction via changes of integrated X-ray intensities during the annealing treatment. RBS analysis was carried out with an existing in-situ heating stage. Using both techniques isothermal annealing experiments were carried out for four different temperatures. For this study 900Å Cu/1600Å Al and 1800Å Cu/3200Å Al thin film couples were prepared by sequential evaporation onto water cooled oxidized <111> silicon and MgO substrates.
A Comparison of Electron Energy Loss Spectroscopy and Electron Diffraction for Polycrystalline and Xe+ Irradiated Nickel Silicides
Authors: Barbour J.C. , Grunes L.A. , Mayer J.W.
Published: March 2011

Variations in the valence and core level electron energy loss spectroscopy (EELS) peaks are studied as a function of nickel silicide composition.Analysis of the EELS spectra in comparison with the electron diffraction patterns show the plasmon energies fingerprint the silicide phases. The EELS core level spectra reflect the Si bonding and the electronic density of states in each phase.Irradiated Ni 2Si becomes amorphous causing a change in the plasmon peak energy and the Si L23peaks.
The Morphology of the Polysilicon - SiO2 Interface
Authors: Bravman J.C. , Sinclair R.
Published: March 2011

A systematic TEM study of the morphology of the polysilicon - SiO2 interface has been performed. LPCVD films were deposited on thermally oxidized silicon substrates, doped via diffusion or ion implantation, and oxidized in pyrogenic steam. Several aspects of the interface have been investigated as a function of dopant species, dopant concentration, oxidation time and oxidation temperature.
Thermal behavior of Metal-Metal-Silicon or Metal-Silicide-Silicon Structures for Pt, Ni, and Cr
Authors: Barcz A. J. , Bartur M.
Published: March 2011

We report on a study of thermal interactions between pairs of Ni, Cr, and Pt films and their silicides on a Si substrate. For each pair of metals M1, M2, four systems were investigated: Si−M1 −2, Si−M2 −M2, Si−M1 Si−M2 and Si−M2Si−M1 giving altogether twelve initial combinations. Samples were annealed in the temperature range of 300−700°C and the analysis was made by Backscattering Spectrometry (BS). It is found that double layers of uniform silicides can be grown when the Cr silicide is the top layer. The rate of CrSi2 formation in this case is less then that reported for CrSi2 growth on Si substrate. In all other cases we find some intermixing. Impurities are found to effect the growth kinetics and the layer morphology.
The Early Stages of Silicide Formation on Metal and Silicon Surfaces, Time-of-Flight Atom-Probe Studies of Atomic Structures and Compositions
Authors: Tsong T. T.
Published: March 2011

The early stages of silicide formation on metal and silicon surfaces have been studied in the atom-probe FIM. Precursors to silicide formation are low temperature diffusion of single Si atoms, their interactions, and adsorption layer superstructure formation. These phenomena have been studied quantitatively. At high temperatures, silicide films can be formed. Four distinctive stages of silicide formation on tungsten surfaces have been observed from the atomically resolved FIM images. Formation of silicide layers on platinum, nickel, and silicon surfaces have also been studied. From both the atom-probe compositional depth profiling and the FIM observation one can conclude that the interface formed at low temperature is sharp. At high temperature, Si atoms can diffuse deep into a Pt matrix and Ni atoms into a Si matrix. Conclusions drawn from these atom-probe studies are summarized, and future directions suggested.
Structural Effects in the Initial Stages of Epitaxy
Authors: Pimbley J. M. , Lu T.-M.
Published: March 2011

Structural effects of sub-monolayer epitaxial films are described by the pair correlation function of surface atoms. We have developed a new scheme to evaluate this atomic pair correlation function analytically and exactly for the combined overlayer and substrate system during the first stages of epitaxy. We employ this correlation function to calculate electron diffraction profiles from model surfaces and compare these calculations to recent LEED measurements of Si/Si(111) and W/W(110) epitaxy.
Resonance between Channeled Particle Wavelengths and Periodicity of Strained-Layer Superlattices
Authors: Chu W. K. , Picraux S. T. , Biefeld R. M. , Osbourn G. C. , Ellison J. A.
Published: March 2011

Recent studies of the resonance effect between the wavelength of planar channeled ions and the periodicity of strained-layer superlattices are summarized for MeV 4He ions backscattering from GaAsxP1-X/GaP superlattices. When the incident beam energy is adjusted so the half-wavelength matches the thickness of the layers, a catastrophic dechanneling effect is observed. A simple phase rotation analysis has been developed to calculate the dechanneling in each layer and good agreement is obtained with the observed dechanneling per interface. This resonance effect is used to measure the amount of strain in the GaAsxP1-x/GaP strained-layer superlattice.
Electromigration in Al And Al-Alloy Thin-Film Conductors
Authors: Pasco R.W. , Felton L.E. , Schwarz J.A.
Published: March 2011

Temperature-ramp Resistance Analysis to Characterize Electromigration (TRACE) has been applied to thin-film Al and Al-alloy conductors. Results have yielded activation energies in agreement with literature values. The TRACE technique has been used to determine the effect of H2on the kinetics of electromigration damage (EMD) for both Al and Al-2%Cu thin-film conductors.
Barrier Properties of Tasi2 in Contact With Al-Metallization
Authors: Neppl F. , Schwabe U.
Published: March 2011

The reaction between cosputtered amorphous and polycrystalline tantalum silicide with Al-Si-metallization was investigated by means of Schottky and ohmic contacts on Si. Diffusson of Al and Si across the silicide was impeded up to 475 °C, as long as the silicide films contained excess Ta with respect to the TaSi2 stoichiometry. The results show that Al-Si with a thin Ta-rich tantalum silicide underlayer provides a VLSI-metallization with considerably reduced contact resistance, particularly for small contacts, and low Schottky barrier to n-Si without significant Si consumption from the substrate
Formation of Titanium Disilicide by Electron Beam Irradiation Under Non Steady State Conditions
Authors: Maydell-Ondrusz E A , Harper R E , Abid A , Hemment P L F , Stephens K G
Published: March 2011

Titanium disilicide was formed by multiply-scanned electron beam irradiation of titanium films of nominal thickness 1200Å on silicon substrates. Samples were annealed at power densities of 2 to 52.5Wcm−2 using times in the range of 1 to a few hundreds seconds. Rutherford backscattering analysis was used to study the metal redistribution and to estimate the approximate compositions and thicknesses of the films. Compounds were identified by X-ray and electron diffraction. Sheet resistance was measured by the four probe technique and surface topography inspected by scanning electron microscopy.

The silicide thickness achieved depends only on annealing time for power densities in the range of 20 to 50Wcm−2 and hence is independent of heating rate and peak temperature during the heating cycle.
3d C/C Processing with High Gas Pressure
Authors: Hsu S. E. , Chen C. I. , Chou S. T.
Published: March 2011

Carbon/Carbon composite is densified by Hipping infiltrated pitch. The pore size in matrix decreased as processing pressure increases. The porosity decreasing rate is defined as (Vi−Vi+ 1)/Vi, and is proportional to the applied gas pressure, where Vi and Vi+1 are the pore volume before and after hipping respectively. The bonding strength also increases with the applied gas pressure and with densification cycle. The density of a 67% porosity fiber preform can reach up to 1.9 g/cm3 in less than 6 hipping cycles with maximum gas pressure of 103 Mpa.
Elastic Deformation in Hardness Test and Young's Modulus of Hipped Si3N4
Authors: Hamasaki Toyohiro , Ishizaki K.
Published: March 2011

The relationship between sintering conditions and mechanical properties were examined for fully densified Si3N4 with different, β phase fractions (0.2 to 1). The samples were sintered by a capsule-HIP method with Y2O3 and Al2O3 additives (6 mol% in total) at temperatures between 1823 to 2023 K, under 60 MPa for 1 hour. The elastic deformation was calculated by Vickers indentation recovery. The Vickers hardness reached the maximum value for a β phase fraction of about 0.5, while fracture toughness, elastic deformation, and Young's modulus increased as the β phase content augmented.
Direct Evidence on the Elimination of Pore by the Applied Pressure in Hot Isostatic Pressing of Alumina
Authors: Fukai Seiki , Uchida Nozomu , Kato Zenji , Uematsu Keizo
Published: March 2011

Removal of natural pore during capsule hot isostatic pressing (HIP) and normal sintering were examined directly with the novel liquid immersion technique, which can reveal details of micro-structure and characterize flaw-forming defects of microns-size in lightly densified specimens. The results were supplemented by the pore size measurement with the mercury porosimetry, microstructural examination with SEM as well as microstructural examination of specimens after final densification. The behaviors in both pore size and shape changes were different in HIP and normal sintering. Removal of large pores of microns-size started from the beginning of densification in HIP. Whereas large pores grow with densification in normal sintering. Large pores changes their shape drastically in HIP, but hardly changes in normal sintering. The behavior of pore in the early stage of densification is closely related to the microstructure of densified specimen; without HIP, large defects of processing origin are present in near-fully dense specimen. These observations were discussed in terms of current sintering theory.
Hot Isostatic Forging of Materials at Pressures up to 60,000 Psi
Authors: Tavenner Robert F. , Hodge Edwin S.
Published: March 2011

This paper will discuss the role of Hot Isostatic Forging (HIF) of partially dense powder preforms to full density at greatly reduced temperatures at pressures to 60,000 psi. The floor to floor cycle times are minutes compared to hours for more conventional Hot Isostatic Processing (HIP) of materials. The process greatly reduces energy consumption and labor costs. Materials that would normally require temperatures of 1225°C to achieve full densification by HIP canbe densified at temperatures as low as 800 to 850°C. Composite materials can be processed rapidly enough at much lower temperatures by HIF to greatly reduce the potential for reaction between the matrix and the reinforcement material. In addition, composites can also be fabricated by a combination of SHS (Self- Propagating High Temperature Synthesis) and HIF to further reduce the reaction between the matrix and the reinforcement material. This permits going from a CIP'ed (Cold Isostatic Pressing) blend of Nickel, Aluminum, and Aluminum Oxide whiskers to final density in about 5 to 10 minutes. The process is amenable to the fabrication of near-net finished shapes by this rapid integrated cycle.
Materials Processing through Levitation in High Gas Pressure
Authors: Nanko Makoto , Ishizaki K.
Published: March 2011

New levitation materials processing on the ground was developed using high gas pressure. Conventional levitation materials processes are carried out in microgravity fields, such as in space or in free-falling, or by applying aerodynamic force, electromagnetic force etc.. This innovated method is based on buoyancy by very high density of high pressure gas. Advantages of this new method are not only as a containerless processing which is able to prepare high purity materials, to produce perfect spheres, but also the possibility to use normal HIP techniques. It is expected that the new processing is applicable in many fields and easy to commercialize.
Oxidation of Si1−xGex Alloys at Elevated Pressure
Authors: Caragianis Christine , Paine David C. , Schwartzman Alan F. , Shigesato Yuzo
Published: March 2011

Thermal passivation of Si1−xGex (x=10 at.%) using dry high pressure (>700 atm) and hydrothermal (>500 atm) oxidation (HPO) was studied. Alloys of Si1−xGex approximately 200 nm thick were oxidized using three processes: (i) dry oxygen at 700 atm and at a temperature of 550°C, (ii) hydrothermal at 510 atm and 550°C, and (iii) conventional 1 atm at 800°C. Auger sputter depth profiling (AES), X-ray photoelectron spectroscopy (XPS), and Raman Spectroscopy were used to characterize the oxides. AES and Raman studies reveal that both dry high pressure and hydrothermal oxidizing conditions produce compositionally congruent oxides from Si90Ge10, multicomponent alloys. XPS studies were used to establish that the Ge in these oxides is chemically incorporated. Thermodynamic and kinetic considerations of the Si-Ge-O system are discussed for both HPO and conventional oxidation. The metastable nature of the HPO oxides is confirmed by examining the microstructure of annealed oxides.
Dual Constant Composition Kinetics Studies of the Demineralization of Ceramic Plasma Coated Apatite Surfaces
Authors: Paschalis E. P. , Nancollas G. H.
Published: March 2011

Calcium phosphate phases such as hydroxyapatite (HAP) and octacalcium phosphate (OCP) have long been considered as model systems for biological minerals. Moreover such phases are involved in ceramic and plasma coated titanium (HPCTI) prosthetic devices. Most of these mineral preparations are mixtures of calcium phosphate phases, as evidenced by X-ray analysis. However, many mineralizing systems involve the formation of metastable intermediates which may subsequently undergo phase transformations. There is therefore considerable interest in investigating the simultaneous growth and dissolution of multiple mineral phases. Based on the Constant Composition (CC) method, the new Dual Constant Composition (DCC) technique has been developed for kinetics studies of the dissolution of the mixed calcium phosphate phases frequently encountered in-ceramic and plasma coated apatite surfaces.
In VitroCell Adhesion and Detachment Behavior for Various Biomaterial Substrates
Authors: Schmidt Mary Beth , Brunski John B.
Published: March 2011

Cell-biomaterial interactions for different material compositions were evaluated through quantitative examination ofin vitrocell spreading behavior and shear-induced cell detachment. Biomaterial substrates consisted of identically prepared, well characterized bulk samples of implant grade cp Ti, Ti-6AI-4V, and Synamel. 3T3 fibroblasts were seeded on the substrate surfaces and incubated for 2 hours. Adherent cell morphology was then examined using scanning electron microscopy and digital image analysis. The cell detachment response was measured using a parallel plate flow chamber. When categorized according to observed cell morphology, projected cell areas were found to be lognormally distributed for all biomaterials and ln(cell area) was significantly greater for Synamel, while no difference existed between cp Ti and Ti-6AI-4V. In addition, the average post-shear fraction of adherent cells was significantly greater for Synamel substrates, as compared to cp Ti and Ti-6AI-4V substrates. The results from this study indicate thatin vitrocell adhesion and detachment behavior are measurably influenced by biomaterial substrate composition.
Bone Cell Response to Ion Implanted Silicon Wafers
Authors: Walsh W. R. , Zou L. , Lefkoe T. P. , Kelly J. C. , Howlett C. R.
Published: March 2011

Results of preliminary investigations on the electrokinetic characterization and osteoblast morphology of ion implanted silicon wafers are presented. The goal of this study is to modify the surface of a material via ion implantation to control cellular interactions at the prosthesis-body interface.
Electrical Stability of Biocompatible Electrodes
Authors: He L. , Anderson W. A.
Published: March 2011

Biocompatible electrodes were fabricated using ordinary semiconductor device processing techniques. For the purpose of identifying electrically stable electrode materials, which are biocompatible for long life, several kinds of contact metal were used. From a comparison of the metal elemental constants, it is suggested that the metal atom ionization energy, cohesive energy and the metal material conductivity may be the major factors to decide the material biocompatibility. Electrical testing shows Pd, with high atom ionization energy and low electrical conductivity, to have the best long life stability. In a test of 140 hours in saline solution with electrical power, the average maximum resistance deviation for a Pd electrode was 5%. The metal Ru, with high atom cohesive energy, has the best ability to withstand surface erosion for biocompatibility requirements. In a microscopic examination, the surface erosion for the Ru layer was invisible after 140 hours testing. The double-layer structures Pd/Ru and Mo/Ru were also tested. The maximum resistance deviations were found to be 7% and 9%, respectively.
Atomistic Study of the Clean and Hydroxylated TiO2 Surface
Authors: Podloucky R. , Steinemann S. G. , Freeman A. J.
Published: March 2011

The coverage of an oxidized Ti-surface by amphoteric OH groups seems to be the driving mechanism for the attachement of bone material to Ti-implants. To contribute to the quantitative and fundamental understanding of this phenomenon, an ab-inito surface method was applied to calculate the electronic structure and energetics of the clean and hydroxylated (110) TiO2 rutile surface. Some of the most important relaxation and reconstruction effects of surface geometries were derived from total energy minimization.
Polymer Surface Modification Causes Change in Phenotypic Expression of Primary Bone Cells
Authors: Peel Sean A. F. , Sodhi R. N. , Duc Tran Minh , Davies John E.
Published: March 2011

Primary rat bone marrow cells were cultured on bacteriological grade polystyrene dishes which had been treated in selected areas with concentrated sulphuric acid. X-ray photoelectron spectroscopy, angle-resolved and imaging modes, and atomic force microscopy showed that the acid treatment brought about both chemical and topographical changes in the substratum surface. While the bone marrow cells attached to both treated and untreated areas of the surfaces of the dishes, the distribution of early mineralized extracellular matrix in these areas was reproducibily different. Thus, using extracellular matrix deposition as a marker, modification of the polymer surface resulted in the cells adhering to treated and untreated areas exhibiting different phenotypes.