bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Dynamics Simulations of Contact Line Motion
Authors: Robbins Mark O. , Thompson Peter A. 
Published: March 2011

ABSTRACTWe report on molecular dynamics simulations of incompressible Lennard-Jones fluids sheared between two solid walls. Boundary conditions and flow fields were studied for both single fluid and immiscible two-fluid systems. For single fluid systems, equal wall and fluid densities or strong wall-fluid couplings crystallized the first layers of fluid atoms. Different wall densities and weaker coupling led to normal Couette flow with a no-slip boundary condition. Our simulations of two fluid systems indicate that there is always slip within ∼ 2 atomic spacings from the contact line. This slip appears to be associated with the breakdown of hydrodynamics at atomic scales. Changes with capillary number in the interface shape and dynamic contact angle were consistent with previous analytic results.
A Computer Model for the Average “Cluster” Size in Polymer Aggregates
Authors: Balazs Anna C. , Hu Jenny C. , Lentvorski Andrew P. , Lewandowski Steven , Lantman Christopher W. 
Published: March 2011

ABSTRACTA reversible diffusion-limited aggregation model for self-assembling polymers has been developed with the aid of computer simulations. The calculations have been performed in three dimensions and apply to linear chains bearing an associating site at each terminus. The results reveal that the associating sites form finite-sized clusters that, in turn, lead to the assemblage of a supermolecular network. The average cluster size is found to vary with the degree of reversibility of site binding.
What can we Learn from Molecular Dynamics Simulations of Macromolecular Liquids?
Authors: Grest Gary S. , Kremer Kurt , Murat Michael 
Published: March 2011

ABSTRACTWe describe how molecular dynamics simulations for a relatively simple coarse grained model can be very useful for investigating the static and dynamic properties of polymers and other macromolecular liquids. We show that it is important to use a simplified coarse grained model instead of a detailed microscopic model if one is interested in studying on modern supercomputers large systems which also relax slowly. As examples we present results for isolated star polymers with f-arms and diluted gelation/percolation clusters. We find in agreement with recent neutron scattering experiments that diluted percolation clusters swell and that their fractal dimension is reduced from 2.5 to 2. We also discuss our results for a dense melt of entangled linear polymers to show that the method is effective at high density. Our results for the entangled melt cover the crossover from Rouse to reptation and strongly support the concept of reptation.
Ion-Beam-Induced Silicide Formation in Nickel Thin Films on Silicon
Authors: Chen L. J. , Hou C. Y. 
Published: March 2011

As+-ion-induced silicide formation in nickel thin films on silicon was investigated by Rutherford backscattering spectrometry and transmission electron microscopy. The emphasis was on the study of ion-beam-induced microstructural changes.For 160 keV As+ implantation, amorphization of the interface occurred at a dose of 5 × 1014 cm−2. Ni2Si was found together with an amorphous layer after a 1 × 1015 cm−2 bombardment. For Ni/Si(100) the surface layer became completely amorphous after implantation to 5×1015 cm−2. Silicides were found after a 1×1016 cm−2 irradiation. The amorphous layer was not stable enough to withstand the enormous chemical driving force causing the formation of crystalline silicides as the composition ratio Nsi/NNi reached a critical value. A similar trend for ion-beam-induced reactions was found for 190 keV As+ implantation on Ni/Si(111) as for 160 keV implantation.The results of post-implantation annealing showed major differences from those obtained for directly annealed samples.
Effects of Two-Step Annealing on the Epitaxialgrowth of CoSi2 on Silicon
Authors: Chen L. J. , Chang T. T. 
Published: March 2011

The formation of epitaxial CoSi2 on silicon by both conventional and two-step annealing of cobalt thin films on silicon was studied by transmission electron microscopy.For two-step annealing, samples were first annealed at 350°C for 1 h, followed by high temperature annealing at 650–950°C for 1 h. The scheme was found to bevery effective in promoting the epitaxial growth of CoSi2 on silicon as well aseliminating faceted structures on Si(111). The results are discussed in terms of the driving away of impurities from the interfaces.
Materials Research Frontiers In Semiconductor Heterojunctions
Authors: Bauer Robert S. 
Published: March 2011

New materials preparation techniques such as molecular beam epitaxy (MBE) provide dramatically improved possibilities for interface control and novel device structures. However, compared with our knowledge of Schottky barriers or semiconductor-insulator interfaces, our microscopic information on the basic science underlying semiconductor heterojunctions is very limited. Insight into the growth, extent and composition of such interfaces is needed to illuminate the origins of the electronic and optoelectronic behavior. Most recent experimental studies have not properly monitored the detailed structural characteristics of the heterojunctions being measured.In this paper we discuss the scientific exploration of the interrelationship between growth and electronic properties of hetero-interfaces prepared by MBE. In situ low energy electron diffraction and synchrotron radiation photoemission were performed on germanium interfaces with GaAs and AlAs polar and non-polar surfaces. The individual surface and subsurface bonding interactions (rather than bulk thermodynamic properties of the semiconductors) are shown to control the formation and electrical properties of hetero-interfaces of either germanium on the compound or the inverse deposition sequence. Simple arguments based on bulk semiconductor heats of formation incorrectly predict the relative stability of interfaces in the lattice-matched Ge/GaAs/AlAs system. Rather the formation of a GeAsx surface layer provides a lower energy free surface during MBE growth and causes arsenic diffusion from the interface layer to lower the free energy when a pure germanium surface begins to form. Significant variations in the band edge offsets of heterostructures are observed when the semiconductor-semiconductor interface microstructure changes with substrate orientation and overlayer crystallinity. Neither the common electron affinity difference “rule” nor recent tight-binding models for determining heterojunction barriers allows for effects of interface microstructure. Measurement and analysis of such “materials-related” aspects of semiconductor interfaces are central to the understanding and control of device characteristics.These studies are partially funded by the U.S. Office of Naval Research (L. R. Cooper), Contract N00014-81-C-0696. Part of this work was performed at SSRL and Stanford Linear Accelerator Center, supported by National Science Foundation Grant DMR 77–27489 and the U.S. Department of Energy.
Lattice Structure and Electrical Properties of Epitaxial Aluminum on GaAs
Authors: Fernando  , Ponce A. , Eglash Stephen J. 
Published: March 2011

The crystal structure of aluminum layers grown by molecular beam epitaxy (MBE) on GaAs(100) was studied using high resolution transmission electron microscopy. We obtained cross-sectional images with nearly atomic resolution of the lattice structure at Al-GaAs interfaces. GaAs epitaxial layers were grown at 585 °C and cooled in the ultrahigh vacuum MBE growth chamber prior to aluminum deposition. After the desired substrate temperature had been achieved, aluminum was immediately deposited onto arsenic-rich surfaces at a rate of 1000 Å h−1.Aluminum layers deposited onto substrates at 80 °C exhibit an Al(110)/GaAs(100) epitaxial relationship along an abrupt interface. In some regions of the interface we observed isolated arsenic crystallites which were epitaxial with the GaAs substrate. The current-voltage (I-V) and capacitance-voltage (C–V) characteristics of this material are well behaved. Barrier heights of 0.79 eV and ideality factors of 1.04 were determined from room temperature I–V measurements.For aluminum deposited onto GaAs substrates at 400 °C, evidence of twodimensional nucleation and growth was observed. The resulting pyramid-shaped aluminum crystallites had facets along crystallographic planes. Two epitaxial relationships were observed: Al(100)/GaAs(100) and Al(110)/GaAs(100). We observed 12 Å steps along the Al(100)–GaAs(100) interface. C–V and scanning electron microscopy measurements indicate that the individual aluminum crystallites are electrically and physically separated.
GaAs Microcircuit Contact and Interconnect Technology
Authors: Welch Bryant .M 
Published: March 2011

The purpose of this paper is to review the current status of and to discuss key technological issues relative to GaAs integrated circuit contact and interconnect technology. Rapid progress and performance advantages exhibited by GaAs MSI circuits in both ultrahigh speed and low power dissipation has recently provided the motivation for the development of GaAs large-and very-large-scale integration (LSI and VLSI). The complexity, density and small feature size requirements of high speed LSI and VLSI places severe demands on GaAs contact and interconnect technology with respect to yield, reliability and performance.The key device used today in GaAs integrated circuits is the depletion-mode Schottky barrier field effect transistor. Results on the optimization of GaAs field effect transistor Schottky barriers and ohmic contacts using X-ray photoelectron spectroscopy and Auger electron spectroscopy surface analysis techniques in conjunction with thermal reliability studies of various metal systems on GaAs will be presented. The established reliability for GaAs integrated circuits with a goldbased metallization system has been shown to have a mean time to failure of more than 109 h at room temperature.The microcircuit lithography requirements of GaAs LSI and VLSI rely heavily on lift-off and dry etch replication techniques. Several high yield techniques, which have been specifically developed for GaAs, will be described. Finally, recent trends in GaAs device research relative to new non-alloyed contacts and high temperature Schottky barriers will be presented.
Rapid Thermal Processing Of High Temperature Superconducting Fiber
Authors: Halloran J.W. , Neal M.J. , Ginley D.S. , Venturini E.L. , Kwak J.F. , Baughman R.J. , Mitchell M.A. , Morosin B. , Basu S.N. , Mitchell T.E. 
Published: March 2011

ABSTRACTWe report on the rapid thermal processing (RTP) of YBa2Cu3O7 (Y-123) fibers. Unsintered fibers are densified by RTP. We show that fibers which were originally semiconducting and tetragonal before RTP form normal twinned orthorhombic material after processing for 2–4 seconds above 1000°C with a 3 min. cool down in oxygen. They subsequently show Tc to 90K and magnetization indicative of substantially shielding. We present the effects of varying the RTP parameters on the morphology, phase, and superconducting properties of a number of tetragonal and orthorhombic Y-123 fibers.
Preparation of Porous Oxide Beads Using Polymeric Beads to Control Bead Size and Shape
Authors: Hardy Anne B. , Rhine Wendell E. , Bowen H. Kent 
Published: March 2011

ABSTRACTA method was developed for preparing silica gels by silicon alkoxide hydrolysis using
water-swellable polymers to control the shape. A variety of polymer beads with different water absorbencies and different bead sizes were used. Silica beads in a wide range of sizes were prepared from polymer beads. The final bead size was dependent on the size and water absorbency of the beads, on the extent of reaction, and on the final density. It was shown that porosity could be formed in two regions. The silica beads contained pores of 3–4 nm that were attributed to the intrinsic gel structure. In addition, when large amounts of polymer were removed, additional porosity on the scale of 20–50 nm was formed. It was also shown that surface areas varied dramatically with calcining. For beads containing only small pores, surface areas varied from 400 m2/g to less than 0.2 m2/g as the calcining temperature was increased from 600°C to 1000°C. Beads containing porosity formed by removal of the polymer remained porous even after calcining at 1000°C.
Boron Nitride and Composite Aerogels from Borazine Based Polymers
Authors: Lindquist David A. , Smith Douglas M. , Datye Abhaya K. , Johnston Gregory P. , Borek Theodore T. , Schaeffer Riley , Paine Robert T. 
Published: March 2011

ABSTRACTPoly(borazinylamines) have been processed in THF and toluene solvents and aerogel forms produced by supercritical drying methods. The polymer aerogels have been pyrolyzed and porous amorphous and crystalline BN monoliths have been produced. These have been characterized and effects of processing factors on surface area and pore structure are described.
Small Angle X-ray Scattering Studies of Polymeric Zirconium Species in Aqueous Solution
Authors: Jutson J.A. , Richardson R.M. , Jones S.L. , Norman C. 
Published: March 2011

ABSTRACTSmall angle X-ray scattering techniques have been used to investigate the shape and size distribution of Zr(IV) species in aqueous solution. This study has shown that when zirconyl chloride solutions, containing the zirconyl tetramer, are subjected to various treatments polymerisation occurs. While ageing and addition of base produces an increase in particle size the shape remains globular. Refluxing the solutions produces “rod” like particles of varying length but constant cross sectional radius.
High Pressure Raman Study of the Hydrolysis Reaction of Tmos and Teos
Authors: Hoang G. , Watson J. , Zerda T. W. 
Published: March 2011

ABSTRACTHigh pressure Raman spectroscopy is used to monitor the hydrolysis reaction of TMOS in solutions with methanol, acetonitrile, acetone, dioxane and formamide, and of TEOS as a function of pH and the catalyst used. The rate constants for various solvents, temperatures and pressures are experimentally determined from the time dependence of Raman band intensities. It is shown that the reaction is slow in dioxane and fast in methanol or formamide. The volume of activation is found from the pressure dependence of the rate constant. The volume of activation, the dielectric constant, dipole moments and hydrogen bonding properties and their role in the hydrolysis reaction are discussed. It is shown that solvents which can form hydrogen bonding with Si-OR groups can increase the rate of the reaction.
Rheology and Microstructure of Concentrated Suspensions
Authors: Mondy Lisa A. , Graham Alan L. 
Published: March 2011

ABSTRACTWe give an overview of some of the experiments currently underway to study the coupling of the microstructure and rheology of concentrated suspensions. Nuclear magnetic resonance imaging, real-time x-ray radiography, and refractive index matching allow the viewing of particles in concentrated suspensions. Both shear flow experiments and falling ball rheometry are reviewed. In the slow flow of these suspensions of large, hard, particles in a viscous Newtonian fluid, colloidal forces are negligible and hydrodynamic forces dominate.Large local concentration changes are shown to occur rapidly in suspensions of uniform spheres subjected to flow between concentric rotating cylinders. Suspensions of spheres with a bimodal size distribution not only show similar phenomena, but also exhibit particle separation according to size. In addition, the large particles in the bimodal suspension migrate into ordered, concentric, cylindrical sheets, parallel to the axis of the cylinders. These sheets of particles rotate relative to each other. The particle migration and structure formation induced by this inhomogeneous shear flow is believed to be responsible for torque reductions and other anomalous behavior witnessed during the rheological testing of concentrated suspensions reported in the literature. Thus, suspensions may not always be characterized by a viscosity that is a scalar material property.Suspensions of fibers also show markedly different rheological properties when the particles are aligned by flow. Falling ball rheometry is shown to be an effective tool to determine the bulk viscosity of a suspension while only slightly influencing the microstructure. This is illustrated by showing that falling ball rheometry can isolate the effect of orientation on the viscosity of a suspension of fibers.
Molecular Architecture and its role in Silica Sol-Gel Polymerization
Authors: Cagle P. C. , Klemperer W. G. , Simmons C. A. 
Published: March 2011

ABSTRACTSol-gel polymerization of [Si8O12](OCH3)8 in CH3CN under neutral conditions yields very high surface area (SBET > 900 m2/g) xerogels. This property is seen to result from the structure of the gel on the molecular level. According to N2 adsorption studies, model studies, and TEM studies, the large size and rigidity of the cubic [Si8O12] core structure leads to polymers whose rigidity inhibits extensive crosslinking of the type observed in orthosilicate derived xerogels.
S.A.N.S. Study Of Fractal Alumino-Silicate Aerogels
Authors: Chaput F. , Boilot J.P. , Dauger A. , Devreux F. , De Geyer A. 
Published: March 2011

ABSTRACTSmall angle scattering clearly shows that aluminosilicate aerogels, prepared from Si-Al double precursor, form mutually self-similar volume fractals at least in the range of densities 40-160kg/m3. The structure, insensitive to the pH of the added water, consists of primary homogeneous rough units attached into volume fractal clusters (D=2.1) .Heating at 800°C oxidizes residual organic groups and decreases the roughness of the unit particles. Densification above 900°C both implies increasing of the size of units and decreasing of the fractal domain.
Characterization Of Partially Condensed Silica Formed From The Partial Hydrolysis Of Tmos
Authors: Tillotson T.M. , Hrubesh L.W. 
Published: March 2011

ABSTRACTA stable mixture of partially condensed polysilicates is formed from the substoichiometric, acid catalysed hydrolysis of tetramethoxysilane [Si(OCH3)4] and the removal of the reaction- generated methanol by distillation. This mixture has been used as a precursor to make silica aerogels that show microstructural differences from base catalysed TMOS aerogels. In this paper, we report the analysis of this mixture for a determination of the type and distribution of the polysilicate species formed, and we include measurements of some physical properties of this fluid.
Crystallization and Phase Transformation of ZrO2-SiO2Gels
Authors: Li Xiaoming , Johnson P.F. 
Published: March 2011

ABSTRACTPure SiO2, ZrO2and SiO2−ZrO2gels have been prepared by hydrolysis and gelation of tetraethylorthosilicate (TEOS) and zirconium acetate solution. The crystallization and phase transformation of SiO2and ZrO2in these gels have been followed up to 1450°C using differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRD). The crystallization and phase transformation behavior of SiO2or ZrO2is quite different in different gel systems. It was found that in pure SiO2gel, the cristobalite phase was precipitated out at about 1000°C. In the pure ZrO2system, tetragonal (t−) phase zirconia was crystallized at about 430°C, t-ZrO2crystals grew three dimensionally and the activation energy for growth was calculated as about 365 kJmol−1. But in the SiO2-ZrO2system, the presence of ZrO2suppressed the crystallization of SiO2, and SiO2increased the initial crystallization temperature and the stability of t-ZrO2.
Studies in the Ba-Ca-Al-O System Chemical Modification of Aluminum Alkoxide by Propionic Acid
Authors: Hebert V. , Vilminot S. , Brion D. 
Published: March 2011

ABSTRACTBarium and calcium aluminate powders have been elaborated using chemical methods like coprecipitation, alkoxide polymerization and metalloorganic decomposition. These powders have been successfully used for impregnation of porous tungsten cathodes for use in electronic tubes. Spectroscopic studies on the modification of aluminum s-butoxide reveal that carboxylic acid substitutes OR groups forming preferentially bidentate chelating complexes.
Optical Interference Filters By Sol-Gel Processing
Authors: Keddie J.L. , Giannelis E.P. 
Published: March 2011

ABSTRACTOptical interference filters have been synthesized by sol-gel. The selected filter is a multilayer of alternating TiO2 and SiO2 films. In transmission, the filter edge depends on the angle of incident light, which can be tailored through control of thickness and refractive index of the individual films. Theoretical modeling of the filter with film thicknesses obtained by Rutherford backscattering spectrometry is in good agreement with the experimental optical response.
Microwave Processing of Sol-Gel Derived Potassium Niobate
Authors: Fathi Z. , Ahmad I. , Clark D.E. 
Published: March 2011

ABSTRACTMicrowave energy has been used in a novel processing method. The relationship between processing, structure and properties of sol-gel-derived potassium niobate sol as well as thin films has been investigated. A comparison has been established between microwave and conventional heating for drying, calcining and crystallizing sol-gel-derived samples. Structural and phase changes were monitored by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and x-ray diffraction (XRD).
Dielectric Characterization of Polyceram Films
Authors: Teowee G. , Boulton J.M. , Fox H.H. , Koussa A. , Gudgel T. , Uhlmann D.R. 
Published: March 2011

ABSTRACTPolycerams are an emergent class of hybrid, multifunctional materials which combine the properties of organic and inorganic materials. Films have been prepared from silicon alkoxides and reactive, functionalized polymers such as triethoxysilyl modified polybutadiene (MPBD), (N-triethoxysilylpropyl)O polyethylene oxide urethane (MPEOU) and trimethoxysilylpropyl substituted polyethyleneimine (MPEI). Characterization of dielectric constant and tan δ of the films has been carried out over a range of frequency from 500 Hz to 100 kHz; and the results are used to consider the potential of Polycerams as dielectric materials.
Sol-Gel Synthesis of Lead Titanate Fibres for Use in the Fabrication of Piezoceramic-Polymer Composites
Authors: Janusson H. , Millar C.E. , Milne S.J. 
Published: March 2011

ABSTRACTLead titanate fibres for use in piezoceramic-polymer composites have been prepared by extrusion of polymeric gels. The gels are formed from solutions of lead acetate, titanium isopropoxide and 2-methoxyethanol. The concentration of the solution, and amount of water and acid added, proved to have a strong influence on the suitability of the gel for extrusion purposes. The drying and firing conditions have been altered to obtain dense, fully crystalline PbTiO3 fibres of 100 μm diameter.
Electron Diffraction Analysis of the Structure of SiO2 Gel-Film
Authors: Ohsaki Hisashi , Aegerter Michel A. , Shichiri Takaki 
Published: March 2011

ABSTRACTThe structure of self-supported SiO2 gel-films prepared from acid and basic TEOS solutions is analysed by high energy transmission electron diffraction method. The reduced radial distribution function (RDF) curves show that all the films are already well dense despite the low drying temperature (≤50°C) and short drying time (≤30 s). The Si-O bond length of the gelfilms prepared from highly acid and basic solutions is about 1.58 Å; it is smaller than that of bulk vitreous silica (1.61 Å) but similar to that of BO Å thick evaporated a-SiO2 film.