bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Chemical Reactions During the Thermal Processing of Borazene Polymers
Authors: Rye R. , Borek T. T. , Lindquist D. A. , Paine R. T. 
Published: March 2011

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTThis 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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTSilica 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

ABSTRACTMicroelectrophoresis 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

ABSTRACTThe 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

ABSTRACTTitania-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

ABSTRACTHydrolysis, 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

ABSTRACTZirconium 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTBackscattering 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

ABSTRACTLead 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

ABSTRACTTransparent 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

ABSTRACTA 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

ABSTRACTSingle-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

ABSTRACTThe 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

ABSTRACTPolysilazanes 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

ABSTRACTWhen 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

ABSTRACTSamples 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

ABSTRACTSoluble 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

ABSTRACTBy 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

ABSTRACTAlkoxide 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.