bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonequilibrium X-Ray Study of the Nematic to Smectic-a Transition Under Shear Flow
Authors: Safinya C. R. , Sirota E. B. , Piano R. , Lei N.
Published: March 2011

We report on synchrotron x-ray scattering studies of the microscopic structure of the nematic (N) and the smectic-A (SmA) phases in the liquid crystal 8CB under dynamic “steady state” shear flow conditions carried out in an x-ray Couette cell. These measurements directly probe length scales less than 100 Å and as large as 104 Å in the vicinity of the N-SmA phase transition away from equilibrium. The N-SmA transition corresponds to the onset of a one-dimensional mass density wave. In the nematic phase close to the smectic-A phase, there are very large pretransitional smectic-A fluctuations because the transition is almost second order. Under shear flow, we find that the nematic director undergoes a series of abrupt transitions between different orientational states of the director. We discuss the stability regimes of these orientational states by considering the fluctuation induced renormalization of one of the nematic shear viscosities and the fluctuation induced torque on the nematic director.
Formulation and Processing of Colloidal Dispersions
Authors: Russel William B.
Published: March 2011

Colloidal dispersions are encountered during the processing of chemicals and materials in a number of contexts, generally requiring control of macroscopic properties such as the phase behavior and rheology through the manipulation of the chemistry. This paper surveys several applications, including the fabrication of advanced ceramics and the formulation of coatings, and attempts to identify the limiting science in each case.
The Mechanical Properties of Thixotropic Gels and their Effect on Attenuation in Optical Fiber Communication Cables
Authors: Taylor Carl R. , Overton Bob J. , Tu Ching Fang
Published: March 2011

Fumed silica/oil gels exhibiting rheological properties characterized by a yield stress followed by shear thinning behavior have been studied for application as waterblocking filling compounds for fiber optic cable. It is found that added signal attenuation in optical fibers after processing into a filled fiber optic ribbon cable is a function of the yield stress of the filling gel. We derive experimentally and apply a model of the relationship to formulate an optimum fumed silica/oil filling gel for fiber optic ribbon cables.
Dehydration of Protein Polymers in Concentrated Nematic Solutions
Authors: Hentschke Reinhard , Herzfeld Judith
Published: March 2011

Protein fibers (e.g., actin filaments, microtubules, and sickle cell hemoglobin polymers), formed by reversible association of quasispherical protein monomers, contain substantial solvent. At high concentrations, solutions of these fibers become non-ideal due to interactions between the elongated particles. One manifestation of this non-ideality is the spontaneous alignment of the fibers. Model calculations, involving simple intra- and inter aggregate interactions leading to polymerization and alignment, agree well with osmotic pressure measurements of sickle cell hemoglobin solutions in the region of the phase transition. However, at higher concentrations the theory cannot fit the experimental data unless solvent is gradually squeezed out of the fiber under osmotic stress. We find that a linear potential for the fiber dehydration gives osmotic pressure results consistent with the experimental data. Under these conditions, substantial fiber dehydration occurs with increasing protein concentrations beyond the alignment transition. This indicates that particle interactions sufficient to cause alignment are also sufficient to squeeze significant amounts of solvent out of the sickle cell hemoglobin fibers.
Statistical Thermodynamics of Phase Transitions in Surfactant Monolayer Films
Authors: Cantor Robert S.
Published: March 2011

A lattice statistical mechanical method has recently been developed and used to predict structural and thermodynamic properties of fluid phases of surfactant monolayer films of uniform chain length. This mean-field approach is extended here to examine films of mixed chain length. As in the earlier work, a fluid-fluid (LC-LE) phase transition is predicted to occur at high surface densities. This transition is found to exhibit non-ideal mixing behavior, ranging from positive azeotropy to phase separation (in the LC phase) as the difference in chain lengths increases. In contrast, the phase diagram in the liquid-gas (LEG) transition region is predicted to exhibit almost ideal behavior, with a nearly linear bubble-point curve.
X-Ray Studies of the Liquid/Vapor Interface: Water and Polymer and Fatty Acid Monolayers on Water
Authors: Schlossman M. L. , Schwartz D. K. , Kawamoto E. H. , Kellogg G. J. , Pershan P. S. , Ocko B. M. , Kim M. W. , Chung T. C.
Published: March 2011

X-ray specular reflectivity is used to study the liquid-vapor interface of pure water and of fatty acid and polymer monolayers at that interface. For the pure water surface the reflectivity was measured for three different spectrometer resolutions and simultaneous fits with only one free parameter to all of the data are in excellent agreement with the prediction of capillary wave theory for the RMS surface roughness. Diffuse scattering away from the specular condition, at wavevectors corresponding to those of the capillary waves, yields intensities and line shapes in agreement with theory with no significant adjustable parameters. Reflectivity from separate monolayers of co-poly 1,2-butadiene/butyl alcohol (50% random substitution) and lignoceric acid (CH3(CH2)22COOH) at the water/vapor interface are interpreted to obtain profiles of the average electron density ρ(z) as a function of distance z along the surface normal. For the polymer monolayer we find the following: 1) a local maximum in the electron density approximately 10% larger than that of the bulk polymer and 2) the RMS roughness of the vapor/polymer interface agrees with capillary wave theory predictions for the lower surface pressures. For the highest surface pressure the RMS roughness exceeds the value predicted by the capillary wave model. Measurements of reflectivity from a lignoceric acid monolayer, as a function of surface pressure throughout an isotherm (near room temperature), reveal the following behavior: 1) the overall thickness of the monolayer increases with increasing pressure and 2) the head groups occupy a progressively larger region along the surface normal as the pressure increases, indicating that they rearrange normal to the interface.
Dynamics of Flexible Polyions in Solution: Ionic Strength Effects
Authors: Mattoussi Hedi , Langley Kenneth H. , Karasz Frank E.
Published: March 2011

Measurements of the collective diffusion coefficient, for polyelectrolyte solutions at high ionic strength and in the dilute regime, are reported. The data are discussed within the framework of a persistent chain with electrostatic contribution to account for the Coulomb interactions.
Class F Fine Fly Ash
Authors: Sheu T. C. , Quo L. W. , Kuo S. T.
Published: March 2011

The Taiwan Power Company's (TPC) coal combustion power plants produced approximately 1 million tons of class F fly ash in 1988 but only 25% of it was effectively utilized. Accordingly, this study investigated the use of separation techniques to improve the quality of the fly ash in order to increase its application. In the experiment, the fly ash was dry-sieved through sieves No. 200, 300 and 400 mesh respectively. The chemical, physical and some of the engineering properties of those classified class F fine fly ashes were ascertained.
The Use of Fly Ash in Concrete - A European View
Authors: Pratt P. L.
Published: March 2011

A European view of the use of fly ash in concrete, if there is one, is very confused. Mehta [1] produced figures for the production and utilisation of fly ash in the cement and concrete industries for 1984, ranging from 10% utilisation in the UK where the cement makers are not enthusiastic, to 80% in the Federal Republic of Germany and even 94% in the Netherlands according to Fraay, Bijen, de Haan and Larbi [2]. Looking a little deeper into these figures the CEGB Ash Marketing Board says that it sells over 40% of its production of fly ash of some 14 million tons/year, much of it for landfill, while the figures for Germany relate only to the 2.6–2.9 million tons of ash from black coal; 70% of the German ash comes from brown coal, and all of this is returned to the open-pit mine for dumping. This paper will review some of the European papers in the Third CANMET/ACI International Conference on Fly ash, Silica Fume, Slag and Natural Pozzolans in Concrete held in Trondheim in June 1989 and some more recent work funded by the Ash Marketing Division of CEGB at Imperial College and the Building Research Establishment, Garston. Four specific aspects of the effects of fly ash on concrete will be considered: rheology and workability; the pozzolanic reaction and the effects of curing; the development of microstructure; and the development of strength and some aspects of durability.
Hydraulic Properties of Fluidized Bed Combustion Ashes
Authors: Odler I. , Zysk K. -H.
Published: March 2011

Seven fluidized bed combustion ashes of different composition were studied as to their hydraulicity and pozzolanicity. Four of them exhibited hydraulic reactivity and hardened when mixed with water. All of them exhibited a positive effect on strength development if used as constituents of blended cements. However, the presence of significant amounts of Fe2+ and free lime in the ash, as well as excessive amounts of SO3 in the produced cement caused unsoundness associated with the decline of flexural strength after longer hydration times.
Stratlingite and Hydrogarnet from Calcium Aluminosilicate Glass Cements
Authors: MacDowell John F.
Published: March 2011

Calcium aluminosilicate glass cements that hydrate directly to stratlingite (2CaO·Al2 O3 SiO2 · 8H2 O) and/or hydrogamet solid solution (3CaO·Al2 O3·XsiO2 ·[16–2X]H2O) are described.

Hydrogamet develops rapidly during curing of pastes containing between 12 and 16 wt.% SiO2, while stratlingite grows more slowly in bladed radial spherulites in compositions containing 18 to 25% SiO2

Compressive strengths between 35 and 70 MPa, 20–35% porosity, and excellent thermal and chemical stability are characteristic of the cured hydrogamet cements, while the stratlingite pastes have strengths between 70 and 140 MPa and 1–10% porosity.

A preferred composition area is described that yields mixtures of the two hydrated phases, resulting in a useful combination of low porosity and high early strength.
Lattice Structure at ZnSe-GaAs Heterojunction Interfaces Prepared by Organometallic Chemical Vapor Deposition
Authors: Ponce F. A. , Stutius W. , Werthen J. G.
Published: March 2011

The lattice structure of ZnSe grown on GaAs by a low temperature low pressure organometallic chemical vapor deposition (CVD) process was studied using high resolution transmission electron microscopy. The defect structure of ZnSe epitaxial layers and of their interface with the GaAs substrate was directly imaged in cross section for GaAs substrate surfaces in the <100> and <111> orientations. It is shown that the ZnSe layers grow indeed epitaxially. The ZnSe layers grown on GaAs(100) contain a large density of faulted loops which are extrinsic in nature, whereas the prevailing defects in ZnSe layers grown on GaAs(111)B substrates are microtwins and stacking faults parallel to the filmsubstrate interface. A possible connection between the observed defect structure and the reported photoluminescence and electrical transport properties of ZnSe layers grown by organometallic CVD is also discussed.
Transmission Electron Microscopy Studies of the Polycrystalline Silicon–SiO2 Interface
Authors: Bravman J. C. , Sinclair R.
Published: March 2011

A transmission electron microscopy analysis has been made of the wet oxidation of polycrystalline silicon (poly–Si) films heavily doped with phosphorus in which the poly–Si–SiO2 interface has been given primary consideration. Using conventional and cross section transmission electron microscopy two distinct morphologies have been identified. Firstly, there is a region of enhanced oxidation at the poly–Si grain boundaries, with the concurrent formation of a new crystalline phase. Secondly, a significant roughening of the interface occurs, also associated with a crystalline phase. It is postulated that the formation of these features requires an inhomogenous distribution of the phosphorus dopant, which resulted from low temperature processing.
The Effects of Interfacial SiO2 on Pd2Si Formation
Authors: Scott D. M. , Lau S. S. , Pfeffer R. L. , Lux R. A. , Mikkelson J. , WieluŃIski L. , Nicolet M.-A.
Published: March 2011

We investigated the effects of thin Si16O2 and Si18O2 interfacial layers on Pd2Si formation using He+ backscattering spectrometry and the16O(d,α)14N and 18O(p,α)15N nuclear reactions. SiO2 films from 10 to 50 Å thick were formed on Si<100> substrates by 16O2 or 18O2 plasma oxidation. Nickel, palladium or platinum films from 1000 to 1400 Å thick were then evaporated onto this SiO2 layer and the samples were annealed in vacuum at temperatures ranging from 250 to 750 °C. The minimum temperature necessary for Pd2Si formation is approximately 400 °C for about 24 Å of SiO2 compared with 600 °C for Pt2Si and 650 °C for Ni2Si formation. The ability of Pd2Si to form in the presence of an SiO2 interfacial layer is compared with that of Ni2Si and Pt2Si and is interpreted using the relative mobilities of the metals in SiO2 and the redistribution of the 18O during silicide formation.
Temperature Effects on Internal Stress in Molybdenum Thin Films on Single-Crystal Silicon Substrates
Authors: Chen Jiann-Ruey , Ho Ching-Hung
Published: March 2011

Molybdenum thin films were deposited with an electron beam gun onto (100)- oriented silicon substrates. The samples were then annealed in vacuum, and the internal stresses in the molybdenum thin films were studied as functions both of the annealing temperature and of the substrate temperature during deposition. Silicide formation and the film thickness after annealing were monitored by the Rutherford backscattering spectrometry technique, and the stress was determined from the substrate curvature which was measured from Newton's ring interference fringes. It was found that, when the substrate temperature was kept at 400°C during deposition, MoSi2 was formed after annealing at temperatures above 500 °C. This MoSi2 exhibited large tensile stresses of about 2 × 1010 dyn cm−2 for annealing above 700 °C, whereas at the lower annealing temperature of 500 °C the stresses were compressive. No detectable silicides were observed when the substrates were kept at temperatures below 150 °C. The Mo-Si film stresses were tensile for substrates kept at room temperature during deposition and compressive for substrates kept at 150 °C.
Quantum Effects At Gaas/AlxGa1−xJunctions
Authors: Gossard A. C.
Published: March 2011

Quantum effects occurring at interfaces between GaAs and AlxGa1−x As are reviewed. Electrons and holes can be confined to two-dimensional quantum states in thin semiconductor layers or at semiconductor heterointerfaces. The twodimensional states in GaAs/AlxGa1−xAs structures show strongly modified electrical and optical behavior relative to unconfined material, with the properties strongly dependent on the structural design.

Electrons confined in high mobility structures at selectively doped GaAs-AlxGa1−xAs heterointerfaces show a quantized Hall effect with an associated vanishing parallel resistance and, in high magnetic fields, an apparent electron crystallization.

Optical transitions between confined electron and hole states in quantum well thin layers form the basis of quantum well luminescence and for new non-linear optical logic structures.

All the quantum effects are sensitive to interfacial properties which are closely dependent on the conditions of epitaxial growth.
Chemical Profiling and Structural Studies of Ionbeam-Mixed Aluminum on Silicon
Authors: Namavar F. , Budnick J. I. , Otter F. A.
Published: March 2011

The ion beam mixing technique has been applied to the production of Al–Si thin alloy layers as an alternative method to thermal annealing. Both unimplanted deposited aluminum thin films on silicon substrates and films implanted with energetic xenon ions were studied by Rutherford backscattering, channeling, secondary ion mass spectroscopy, nuclear resonance profiling and scanning electron microscopy techniques. The results of these experiments indicate that (i) intermixing between aluminum and silicon became observable when the implantation dose of energetic xenon through the interface surpassed 2 × 1016 ions cm−2; (ii) intermixing is dependent on the dose but not on the dose rate of implantation; (iii) damage to the silicon substrate extended only to the region penetrated by implanted ions; (iv) the Al-Si alloy layer region is uniform in texture and no segregation can be observed. Moreover, the integrity of the alloy layer is retained for a long period of room temperature annealing.
Soft X-Ray Photoemission Measurement of Schottky Barrier Formation at The Pd-si Interface
Authors: Purtell R. , Ho P. S. , Rubloff G. W. , Holinger G.
Published: March 2011

The binding energy of the bulk Si 2p levels observed with soft X-ray photoemission can be used to monitor the band bending in the silicon space charge region when a metal is deposited onto the silicon surface. Changes in the 2p binding energy with metal coverage can then be used to determine the change in the Schottky barrier height as the metal-silicon contact is formed. By tuning the photon energy and therefore the photoemitted electron escape depth, chemical shifts (atomic environment effects) at the interface can be separated from the bulk band bending effects. When combined with annealing to produce in-depth atomic intermixing, the result may reveal information on the distribution of metal atoms at the interface and its effect on the barrier height.

Measurements of the Schottky barrier height change as a function of palladium deposition were made on (2 × 1) p-type and (7 × 7) n-type Si(111) surfaces by monitoring Si 2p core level shifts in a bulk sensitive mode. The barrier height change reached 1/e of its final value at a palladium coverage of 2.9 Å. Several experiments have made it possible to relate the measured Si 2p core level monitor of band bending to absolute Schottky barrier heights in a fully consistent fashion. Therefore, these results provide a means to measure the barrier height in the initial stages of Schottky barrier formation (i.e. at low metal coverage) and to compare these observations with the chemical behavior of the interface at low coverage and with electrical measurements on bulk contacts. Since the Pd/Si Schottky barrier height is established at the bulk value within a coverage of 3–5 Å (even before the overlayer is metallic), the role of interface chemical bonds in determining the barrier height is paramount.

This work was supported in part by the U.S. Office of Naval Research.
Material Compatibility and Degradation Problems in Microelectronics
Authors: Tu K. N.
Published: March 2011

To build a large integration of circuits on a semiconductor chip, a composite of thin film materials of extremely small dimensions is used. For example, metallic films serve as interconnectors, gates, contacts, diffusion barriers, interfacial bonds, passivation coatings and adhesive layers, and so they are making interfaces between themselves as well as to semiconductors and insulators. The compatibility between neighboring layers and the degradation of these films and their interfaces are crucial to device yield and reliability. These problems may become more serious when we reduce the device dimensions. A review of a simple silicon device will be presented in order to illustrate some of the material compatibility and degradation problems such as contact stability and electromigration. The review will not emphasize the device performance but rather the connection between the driving force and the corresponding kinetic changes in thin films.
Temperature-Dependent X-Ray Study of Alloyed Gold Metallization Contacts On In1–xGaxAsyP1–y/Inp Layers
Authors: Vandenberg J. , Temkin H. , Hamm R. A. , Diguiseppe M. A.
Published: March 2011

Gold metallization for ohmic contacts is extensively used for the fabrication of InP/In1−xGaxAsyPn1−y light-emitting and microwave devices. While the electrical properties of Au/InP and Au/In1−xGaxAsyPn1−y have been the subject of many investigations, relatively little is known about the metallurgy of contact formation and solid state reactions occurring during high temperature alloying and the subsequent device processing steps. Therefore a temperature-dependent X-ray diffraction study on Au–Inn1−xGaxAsyPn1−y interface reactions was made as a function of composition x, y.
Microcharacterization of Interfaces
Authors: PETROFF P. M.
Published: March 2011

The atomic structure of semiconductor heterostructure interfaces and metalsemiconductor interfaces are best characterized by transmission electron microscopy (TEM). Both phase contrast TEM and structure factor contrast TEM are able to distinguish very small structural (two monolayers) or compositional (less than 0.2%) fluctuations at interfaces. Applications of these techniques to the study of the roughening transition temperature at the Gal−xAlxAs–GaAs and Ga1−xAlxAs–Ge interfaces grown by molecular beam epitaxy are presented. Minority carrier recombination at interfaces is characterized on a microscopic scale by low temperature cathodoluminescence. This technique is used to demonstrate the role of interfaces in gettering defects in Gal1−xAlxAs/GaAs heterostructures. Finally, the effects of interfacial strain in producing a localization of the luminescence in GaAs quantum well wire structures will be discussed.
Chemical Reactions During the Thermal Processing of Borazene Polymers
Authors: Rye R. , Borek T. T. , Lindquist D. A. , Paine R. T.
Published: March 2011

A class of borazene polymers has been developed which consist of a twodimensional array of six-membered borazene rings with the borons of adjacent borazene rings separated by -NH- groups. Pyrolysis of these polymers above ≈1000 C leads to crystalline graphite-like boron nitride (h-BN). The thermal chemistry of thin films of one polymer deposited on KOH etched Al has been examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA), and the gas evolution chemistry is found to be essentially complete by temperatures of less than 400 C. All products desorb with the same temperature profile and the major desorbing species are NH3 and N2 consistent with a loss of excess nitrogen and hydrogen in the polymer, ang HCI from decomposition of by-products of the synthesis step. Isotope labeling shows that complete exchange occurs below 400 C between the ring and amino bridge nitrogens. Since the formation of ordered crystalline h-BN films requires heating to temperatures of the order of 1000 C, whereas the gas evolution and ring opening chemistry is complete by roughly 400 C, it is concluded that gas evolution chemical Processes are not rate limiting in BN ceramic production.
The Chemical Processing of Silicates for Biological Applications - A Review
Authors: Hench L. L. , Wilson June
Published: March 2011

A new application area for sol-gel processing biomaterials and implant devices, is presented. The concepts of bioactive fixation of implants is reviewed. Conventional processing methods for bioactive materials are compared with low temperature chemical processing. Advantages of sol-gel processing include new bioactive compositional ranges of ultraporous CaO-P2O5-SiO2biogel-glass powders. Clinical applications of bioactive implants are discussed.
Current Issues in Sol-Gel Reaction Kinetics
Authors: Assink Roger A. , Kay Bruce D.
Published: March 2011

This paper surveys a few of the current issues in sol-gel reaction kinetics. Many times seemingly modest changes in reactants or reaction conditions can lead to substantial differences in the overall reaction rates and pathways. For example, qualitative features of the reaction kinetics can depend on catalyst concentration. At very high acid-catalyst concentrations, reverse reactions are significant for TMOS solgels, while for moderate acid-catalyst concentrations, reverse reactions are substantially reduced. The reaction kinetics of two similar tetraalkoxysilanes: tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS), can be markedly different under identical reaction conditions. Under acid-catalyzed reaction conditions, a TMOS sol-gel undergoes both water- and alcoholproducing condensation reactions while a TEOS sol-gel undergoes only water-producing condensation. The early time hydrolysis and condensation reactions of a TMOS sol-gel are statistical in nature and can be quantitatively described by a few simple reaction rate constants while the reaction behavior of a TEOS sol-gel is markedly nonstatistical. A comprehensive theory of sol-gel kinetics must address these diverse experimental findings.
Solution Chemistry in the A12O3-Sio2 System
Authors: Fahrenholtz W.G. , Hietala S.L. , Smith D.M. , Hurd A.J. , Brinker C.J. , Earl W.L.
Published: March 2011

In the alumina-silica system, the surface area of gels exhibit dependence upon both composition and the fluid in the pores during drying. Under controlled conditions, an anomalous drop in both the surface area and skeletal density of identically prepared gels occurs at a composition of 47% alumina. An effort has been made to understand the reasons for this phenomenon. The effect of various solution precursor systems has been investigated. Precursors that contain boehmite, or other colloidal species, do not exhibit low surface area/density at 47% alumina. Data from light scattering, infrared spectroscopy, and solution NMR will be discussed for the precursor system used to prepare low surface area gels. Data will be interpreted to determine the effect of solution structure on gel characteristics.
In-Situ Pore Structure Analysis During Aging and Drying of Gels
Authors: Smith Douglas M. , Davis Pamela J. , Brinker C. Jeffrey
Published: March 2011

The use of NMR relaxation measurements for the in-situ study of pore structure evolution during gel aging and drying is illustrated. The change in the pore size distribution and surface area of both wet and dried gels is examined as a function of aging conditions including temporal aging, thermal aging, changing pH, and changing pore fluid. The effect of pore fluid pH on dissolution/reprecipitation in ordered packings of monodisperse silica spheres is also examined as a model system for particulate gels. As expected, the pore size distribution narrows with increasing time of treatment in high pH pore fluids. Interpretation of high pH results for the wet state is complicated by a microporous layer which forms on colloidal silica resulting in significantly larger wet surface area as compared to the final dried material. Narrowing of the pore size distribution, which is of interest for maximizing drying rates, is maximized in the least time by using either high pH or repeated ethanol washes for the base-catalyzed gel (B2) used.
Relationship Between Strained Silicon-Oxygen Bonds and Radiation Induced Paramagnetic Point Defects in Silicon Dioxide
Authors: Warren W.L. , Lenahan P.M. , Brinker C.J. , Ashley C.S.
Published: March 2011

We have investigated the radiation induced generation of paramagnetic point defects in high surface area sol-gel silicates containing various concentrations of the Raman active 608 cm−1 D2 “defect” band attributed to cyclic trisiloxanes (3 membered rings). Our results indicate that strained silicon-oxygen bonds due to three membered rings are the dominant E΄ (trivalent silicon center) and paramagnetic oxygen center precursors at high irradiation doses for silicates containing large concentrations of the D2 species. These results directly demonstrate that atomic level stress does play a role in the radiation damage process of silicon dioxide.
Investigation Of The Silica Network During The Sol To Gel Transition And Final Xerogel Properties
Authors: Soskey Paul R. , Nikles Randall E. , Fattman George F. , Mininni Robert M. , Gerenza Deborah A.
Published: March 2011

Silica sols were produced with various catalysts (NaOH and HF). Dynamic small strain rheometry was used to probe the formation of the silica network from the sol state through the gelation point into the region of high modulus. These results were related to the dried xerogel properties of surface area and porosity.
Reliable Electrokinetic Characterization Procedures For Ceramic Powders
Authors: Wang Jiun-Fang , Riman Richard E. , Shanefield Daniel J.
Published: March 2011

Microelectrophoresis Is An Important method for measuring surface properties of colloidal materials. In order to obtain reliable measurements, a good reference colloid must be chosen first, and both the behavior of the reference under a variety of measurement conditions and instrumental factors must be established. Polystyrene latex has proven to be a good reference material. Time-dependent, solids-loading, and electrolyte concentration effects are determined below in order to establish reproducible referencing conditions. Using these referencing conditions, surface properties of silicon nitride as a function of aging time and atmosphere are studied.
Sol-Gel Chemistry of Hydrogenosiliconates: The Role of Hypervalent Silicon Species
Authors: Belot V. , Corriu R. , Guerin C. , Henner B. , Leclercq D. , Mutin H. , Vioux A. , Wang Q.
Published: March 2011

The hydrolysis of organic silicates ( mainly Si(OEt)4: [TEOS] and Si(OMe)4: [TMOS]) is the key reaction in sol gel process for preparation of silica. The mechanism of this reaction is not well known because of the competition taking place between hydrolysis itself and condensation reactions (homo or heterocondensations) but also because of redistribution reactions which take place competitively. Furthermore the competition between these steps depends also on the catalysis (acid,basic or nucleophilic) [1, 3].
A Comparison of Tio2-Sio2 Aerogels and Xerogels
Authors: Cogliati G. , Guglielmi M. , Che T.M. , Clark T.J.
Published: March 2011

Titania-silica gels containing up to 30% titania have been obtained from silicon and titanium alkoxides and from silicon alkoxides and TiCl4. These gels were then processed by normal drying and by hypercritical methods. The thermal evolution of these gel/glass systems, specifically with respect to crystallization behavior has been followed using x-ray diffraction and Raman spectroscopy. From these studies, it was found that not only the different chemistries, but also the different processing methods significantly affect the microstructure of these titania-silica systems.
Effects Of Trioxane On Silica Gel
Authors: Li Xiaoming , Johnson P.F.
Published: March 2011

Hydrolysis, condensation and thermal reactions of silica gels derived from TEOS with and without 1,3,5-trioxane (C3H6O3) were studied. Effects of trioxane on viscosity and gelation time of solutions were determined. Specific surface, density, porosity and microhardness of gels were measured. The behavior of gels at elevated temperature was clarified using DTA, TGA, and dilatometry. The properties and structure of trioxane containing sol/gels may be explained by the role trioxane played in the sol-gel transition. The results of this investigation concerning sol-gel/gel-glass transitions, structure and properties of gels are presented.
Effect Of Dopants on the Crystallization of Zircon From Zirconium Silicate Gels
Authors: Barrie J.D. , Meshishnek M.J.
Published: March 2011

Zirconium silicate gels containing small amounts of foreign cations were found to exhibit different crystallization behavior as compared to undoped gels. The reaction to form the zircon phase was enhanced by the presence of these dopants, with zinc oxide additions causing the largest decrease in crystallization temperature. The crystallization behavior of these gels is compared to that of zircon prepared from alternative processing techniques.
Effect Of SnO2 on the Mechanical Properties of SiO2/SnO2 Gel-Derived Composites
Authors: Dal Maschio R. , Dire S. , Campostrini R. , Soraru G.D. , Carturan G.
Published: March 2011

The morphological evolution and SnO2 crystallization of various gel-derived materials, composed of SiO2-SnO2 in the range from 34 to 5 wt % SnO2, are studied in function of the thermal treatment in the interval 200-800°C. SnO2 phase separation occurring above 400°C affects the density, the apparent porosity and mechanical properties like hardness and Young's modulus. At the lowest SnO2% a continuous density increase is observed on heating at variance with high tin dioxide contents for which the apparent density is almost constant. The results are discussed on the basis of SnO2 crystallization, which occurs by two different mechanisms, evidenciated by X-ray analyses. The data will be compared with those of pure SiO2.
Processing of SiO2-TiO2 Thin Film Waveguides
Authors: Weisenbach L. , Davis T.L. , Zelinski B.J.J. , Roncone R.L. , weller-Brophy L.A.
Published: March 2011

The shrinkage behavior and changes in refractive index of sol-gel derived SiO2 -TiO2 thin films, with a composition of 50 mole %, were investigated. Two regions of shrinkage rate were observed, a rapid initial stage and a slower second stage. The refractive index of the film was found to be dependent upon the heat treatment. Samples prebaked to 100°C and processed at temperatures below 500°C were found to have lower indices than films processed without prebaking. Films heated to 700°C contained small crystallites of anatase uniformly distributed throughout the film.
Microstructural Evolution of TiO2 Sol-Gel Thin Films
Authors: Keddie J.L. , Giannelis E.P.
Published: March 2011

Backscattering spectrometry has been used to determine the density of TiO2 sol-gel films. The density of the as-deposited films relative to that of anatase varies slightly with respect to deposition conditions and is approximately 0.5. Annealing at temperatures as high as 750°C increases the relative density to 0.7 with concomitant decreases in the O:Ti ratio and H content but it does not result in complete densification. Film densities are consistently higher for films annealed under dynamic vacuum compared to those in air.
Sol-Gel Processing of PbTiO3 Fibers
Authors: Aoki S.I. , Choi S. C. , Payne D.A. , Yanagida H.
Published: March 2011

Lead titanate fibers were formed from lead acetate and titanium isopropoxide by sol-gel methods. Additions of acids and chelating agents were used to influence hydrolysis and condensation reactions. A variety of solvents were examined, and the effect of conditioning treatments at elevated temperatures were investigated. Data are reported for the rheological behavior of viscous sols, fiber drawing ability, pyrolysis and crystallization of gels and fibers. Features of the ceramic microstructure are reported. A pyroelectric effect was measured for PbTiO3 fibers.
Phase Transformations in ZrO2-SiO2 Gels
Authors: Campaniello J. , Rabinovich E. M. , Berthet P. , Revcolevschi A. , Kopylov Nonna A.
Published: March 2011

Transparent sols and gels in the ZrO2-SiO2 system containing 25, 50 and 75 mole % ZrO2 were prepared using tetraethyl orthosilicate (TEOS) and Zr n-propoxide solution in the presence of acids. Heating the gels to 600°C yielded an amorphous product which at higher temperature crystallized with formation of tetragonal and monoclinic ZrO2 . Zircon crystallized slowly at 1600°C. The results are explained by metastable liquid-liquid phase separation in the studied system.
Molecular Routes to Tin Oxides
Authors: Wark T.A. , Gulliver E.A. , Jones L.C. , Hampden-Smith M.J. , Rheingold A.L. , Huffman J.C.
Published: March 2011

A general route to low temperature synthesis of ternary metal tin oxides with controlled stoichiometries from single component molecular metal alkoxide precursors is described. The solid state and solution structures of homoleptic tin(IV) alkoxide compounds have been investigated to establish criteria for the determination of their solution structure. Tin alkoxide compounds suitable for metathesis reactions have been synthesized and used to prepare the mixed metal alkoxide compounds [ZnSn(OEt)6] and [((COD)Rh)2Sn(OEt)6] (where Et = ethyl and COD = 1,5-cyclooctadiene). Hydrolysis of [ZnSn(OEt)6] at neutral pH results in the formation of a high surface area, mainly amorphous hydrous oxide powder which forms Zn2SnO4 and SnO2 on heating to 600°C and ZnSnO3 on heating to 1000°C.Thermolysis of [((COD)Rh}2Sn(OEt)6] results in formation of rhodium and tin(IV) oxide (cassiterite phase).
Preparation Of Single-Phase Knbo3, Using Bimetallc Alkoxides
Authors: Amini Mostafa M. , Sacks Michael D.
Published: March 2011

Single-phase KNbO3 was prepared using bimetallic alkoxides. Potassium-niobium ethoxide, KNb(OC2H5)6, and potassium-niobium propoxide, KNb(OC3H7)6, were synthesized and subsequently hydrolyzed using several water concentrations. Potassium-deficient particles were rapidly precipitated when higher water concentrations were used and this resulted in the formation of a multiphase material after calcination. In contrast, single-phase KNbO3 powders could be prepared by two methods: (1) hydrolysis of KNb(OC3H7)6/propanol solutions using 1 mole water (per mole of propoxide) added as a water/propanol solution and (2) hydrolysis of KNb(OC2H5)6,/ethanol solutions using 1 mole of water (per mole of ethoxide) added as a water/methanol solution. The latter method was also used to form thin films of KNbO3.
Sol-Gel Processed Inorganic and Organically Modified Composites for Nonlinear Optics and Photonics
Authors: Prasad Paras N.
Published: March 2011

The newly emerging field of Nonlinear Optics and Photonics offers tremendous opportunities for material scientists. In this paper, chemical processing using the sol-gel method is described for the preparation of new composite materials of both a silica glass and a V2O5 gel with a wπ conjugated polymer poly-p-phenylene vinylene up to 5d% by weight. The composite films show highly improved optical quality with large third-order nonlinear optical coefficients, the latter from the conjugated polymer. Optical waveguiding through the film has been achieved. Nonlinear optical studies using femtosecond degenerate four wave mixing and power dependent waveguide coupling have been successfully performed. Also, to investigate the use of such films for optical recording, a two-dimensional grating structure has successfully been produced.
Crystallization of Pyrolyzed Polysilazanes
Authors: Matsumoto Roger L. K.
Published: March 2011

Polysilazanes are inorganic polymers which convert to a ceramic material when pyrolyzed. Initial pyrolysis results in a solid, amorphous material. Further heating transforms the amorphous structure to a crystalline material. In addition to the Si-N linkages in the polymer backbone, polysilazanes generally contain appreciable amounts of carbon in side groups. Consequently, pyrolysis can result in mixed Si3N4 - SiC crystalline materials. It will be shown that either Si3N4 or SiC could be selectively crystallized depending upon processing conditions.
Stability of Boron Nitride Coatings on Ceramic Substrates
Authors: Datye Abhaya K. , Qui Xiaomei , Borek Theodore T. , Paine Robert T. , Allard Lawrence F.
Published: March 2011

When BN is synthesized via polymeric precursors and applied to ceramic substrates, tough adherent coatings of hexagonal-BN (h-BN) are obtained after annealing at 1200°C in N2. The study of these coatings is facilitated by using nonporous oxide powders containing single crystal particles of submicron size (e.g. cubes of MgO) as model ceramic substrates. These oxide powders permit high resolution TEM examination of the BN coatings with no further sample preparation. In this study, samples of BN/MgO cubes containing 50 wt% BN were heated in air at elevated temperatures for 16 hours to study the oxidation resistance of BN coatings. The BN coating was found to be stable at 600°C, but the 700°C-treated sample showed evidence for partial amorphization of the coating and reaction with MgO. A significant fraction of the MgO in the 800°C-treated sample had transformed to Mg2B2O5. The reaction of MgO with the BN coating under oxidizing ambients leads to loss of the cubic morphology in the precursor powder.
Chemical Preparation of Superconducting Oxides Using Conventional Chelating Agents
Authors: Chiang Cyril , Shei C. Y.
Published: March 2011

Samples of Bi1.4Pb0.6Sr2 Ca2Cu3Oy were prepared by sol-gel technique. The formation of polymeric chelate was made possible by oxalic acid in which metal cations are homogeneously distributed. The functional groups in the chelating agent determine the cation absorption rate that pH value is no more critical. XRD and SQUID showed that the compound has a nearly pure 2223 phase and Tc was measured at 110 K. The synthesis is reproducible and the process is amenable for scaling up.
Metallo-Organics Derived Tractable Resins for Ybco Superconducting Fiber Fabrication
Authors: Chen K.C. , Chen A.Y. , Mazdiyasni K. S.
Published: March 2011

Soluble resins were prepared by controlled hydrolysis of yttrium isopropoxide, barium isopropoxide and copper ethylhexanoate. The resins were converted to cohesive, viscous, fluid and precipitated states by the addition of different combinations of binary polar and non-polar organic solvents. Viscosity and spinnability of the resins were critically dependent on the solvent constituents. Continuous pre-ceramic fibers were spun from these resins and single phase YBa2Cu3Oy superconducting fibers with Tc=91.5K and ΔT=1.5K have been obtained.
Kinetic Study Of High Tc Bi-Pb-Sr-Ca-Cu-O System
Authors: Hurng W.-M. , Huang Y. T. , Shei C. Y. , Chiang C. , Koo H. S. , Wu S. F. , Wu P. T.
Published: March 2011

By studying the Bi-Pb-Sr-Ca-Cu-O system, we have found that the sintering time to form high Tc Bi-Pb-Sr-Ca-Cu-O systems was quite different as the compositions of the starting materials varied. Especially, the ratio of Sr/Ca played an important role in determining the sintering time.

DTA study already showed that partial melting occurred during the reaction. The temperature of the partial melting was also related to the ratio of Sr/Ca. Our results supported the existence of a reactive liquid phase in sintering process.
Characterization Of Amorphous Gel To Superconducting Oxide Conversion For Sol-Gel Produced Y1Ba2Cu3O7-x.
Authors: Moore G.A. , Kenzer D. , Teepe M. , Kordas G.
Published: March 2011

Alkoxide sol-gel processing of Y1Ba2Cu3O7-x was performed using copper(II) ethoxide, barium methoxyethoxide, and yttrium methoxyethoxide precursors in a methoxyethanol/methy ethyl ketone/toluene solvent system. In situ neutron diffraction experiments were performed on individual precursors and mixed component gels during heat treatment. Phase development and consumption was observed for both the calcination and annealing segments of the heat treatment. Formation of Y1Ba2Cu3O7-x was observed as early as 700°C. CuO, Cu2O, BaCuO, YCu2O5, BaCO3, BaCO4, and YlBa2Cu3O7-x were observed during the conversion/ consolidation reactions to 850°C.
Dopant Enhanced Grain Growth During Crystallization of Amorphous Silicon Using Rapid Thermal Anealing
Authors: Kakkad R. , Fonash S. J. , Howell P. R.
Published: March 2011

PECVD a-Si deposited at 250ºC on 7059 glass was used as precursor material to produce low resistivity large grain doped poly Si. The films doped in the range of 1020−1021 cm-3 with P during growth or by ion implantation wereannealed at 700ºC for times 2 to 5 minutes using RTA. A dopant enhanced grain growth was observed with grain sizes of the order of 3 μm for films of only 2000Å thickness. Resistivity as low as 6x10-4 Ω-cm and mobility as highas 34 cm2 /V-sec. were obtained using this low thermal budget process.These values are comparable to those obtained in the literature using significantly higher annealing temperatures.
Nanosecond Thermal Processing of Polysilicon thin Films
Authors: McCarthy A. M. , Weiner K. H. , Sigmon Tom. W.
Published: March 2011

Significant improvement in properties of polysilicon thin films for VLSI applications was achieved using nanosecond thermal processing causing laser-induced melting followed byrecrystallization. Sheet resistance was reduced by as much as a factor of five on polysilicon thin films and underlying oxide integrity was not detectably disturbed.
Origin of Grain Boundary Recombination Activity in Silicon Wafers
Authors: Amanrich H. , Martinuzzi S. , Pasquinelli M.
Published: March 2011

In silicon bicrystals grain boundaries (GBs) become recombining after they have been annealed in argon at temperatures higher than 800°C for tens of hours. In order to verify the eventual influence of metallic elements, interstitials gold atoms are introduced in the bicrystals by diffusion (T ≤ 8000 C) from gold dots deposited far from the GB (gold could be segregated by the GB but cannot give deep levels in the grains). It is found by DLTS, EBIC contrast and LBIC scan map that the recombination strength of GBs is not changed by gold in diffusion in as grown bicrystals, while it is reduced in annealed samples. Similar results are obtained with GBs of polycrystalline wafers.

It is concluded that the activation of GBs in CZ silicon bicrystals is certainly due to the segregation of a slow diffuser like oxygen, and that fast diffusers play a secondary role only.
Effects of the Grain Size on the Electrical Properties of Boron-Doped Polysilicon Films
Authors: Kobayashi A. , Baba S. , Kinbara A. , Akimori H. , Kawaji M. , Owada N.
Published: March 2011

The electrical properties have been investigated on boron-doped polycrystalline silicon films with the average grain size of 50 nm and of 370 nm. It is shown that Hall mobility is strongly dependent on the grain size, and the temperature dependence is changed by hydrogenplasma treatment (HPT).

After the treatment in the larger grain film, the mobility of about 40 cm2/V sec is obtained and it shows the boron acceptor level of 0.043 eV, which is almost the same as that of the level in monocrystalline silicon. A kink in the mobility vs temperature curve which is observed in the smaller grain film disappears by HPT.

These phenomena will be discussed in relation to the density of the trapping states at the grain boundary of the films.
Polysilicon Integration
Authors: Ellul J. , Calder I.D.
Published: March 2011

Polycrystalline silicon has found numerous applications in silicon integrated circuits, initially as a MOS gate material, and later for advanced isolation, capacitor electrodes, resistors, interconnect, bipolar emitters and bases, trench refill, doping sources, and the active material in thin film transistors. Integration of these techniques in a BiCMOS technology requires knowledge of the interactions between the processing steps, and their cumulative effect on the final device and circuit operation. New process techniques also present opportunities for process simplification, added functionality, or improved performance. Examples of polysilicon applications that interact with other process steps and influence device performance are P+ and N+ poly gates and silicidation of gate poly. Silicidation improves circuit speed and provides additional integration opportunities in the form of faster local interconnect, but it may create a problem for older designs with synchronous timing circuitry. More innovative integration of polysilicon includes improved deposition techniques, such as the use of amorphous silicon, “Lo-Hi” poly, in sinat doping, and deposition from disilane sources enable more flexible process design. Other innovations include polysilicon emitters, bases, and buried sinkers in bipolar design, polysilicon sidewall spacers in CMOS, and polysilicon based active transistors for display applications and three dimensional integration.