bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silicon Oxycarbide Glasses from Sol-Gel Precursors
Authors: Babonneau F. , Soraru G. D. , D'Andrea G. , Dire S. , Bois L. 
Published: March 2011

ABSTRACTSilicon oxycarbide glasses have been prepared from sol-gel precursors containing not only Si-CH3, but also Si-H bonds. Three systems have been chosen containing various Si units but the same C/Si ratio. Their pyrolysis process has been mainly followed by 29Si MAS-NMR and the composition of the final glass extracted. This study shows that a suitable choice of Si-CH3 and Si-H functionnalized silicon alkoxides can lead to a strong decrease in the free carbon content and to an almost pure silicon oxycarbide phase.
Characterization of High Surface Area Silicon Oxynitrides
Authors: Lednor Peter W. , Ruiter Rene De , Emeis Kees A. 
Published: March 2011

ABSTRACTHigh surface area silicon oxynitrides have been prepared by nitrida- tion of silica with ammonia. Characterization by Fourier-transform infrared spectroscopy has allowed quantitative determination of hydroxyl, amido and imido groups. Data obtained by X-ray photoelectron spectroscopy show that the nitrogen is well distributed in the surface of the materials.
Electronic Properties of OMVPE Grown films of YBa2Cu3O7-δ on 1” LaAlO3 Substrates
Authors: Rees William S. , Hascicek Yusuf S. , Testardi Louis R. 
Published: March 2011

ABSTRACTFilms of YBa2CU3O7-δ have been grown on 1” LaAlO3 by OMVPE utilizing M(tmhd)n (M = Ba, Cu: n = 2; M = Y: n = 3; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) as the source materials in a cold wall, vertical rotating disk reactor. The resultant films were characterized by SEM, XRD, Tc, Jc, and surface profilometry measurements. Relative to laser ablated thin films, the surface morphology was determined to be virtually featureless. In-situ depositions at substrate temperatures of <700°C, employing nitrous oxide as the oxidizing reagent, produced annular irregularities in the electronic properties of these films. The highest quality was observed near the film's center, with a marked decay evident toward the exterior 7 mm perimeter of the coated wafer.
Omcvd Elaboration and Characterization of Silicon Carbide and Carbon-Silicon Carbide Films from Organosilicon Compounds
Authors: Morancho R. , Reynes A. , Amjoud M'b. , Carles R. 
Published: March 2011

ABSTRACTTwo organosilicon molecules tetraethysilane (TESi) and tetravinylsilane (TVSi) were used to prepare thin films of silicon carbide by chemical vapor deposition (C. V. D.). In each of the molecule, the ratio C/Si = 8, the only difference between TESi and TVSi is the structure of the radicals ethyl (.CH2-CH3) and vinyl (.CH=CH2). This feature induces different thermal behavior and leads to the formation of different materials depending on the nature of the carrier gas He or H2· The decomposition gases are correlated with the material deposited which is investigated by I.R. and Raman spectroscopy. The structure of the starting molecule influences the mechanisms of decomposition and consequently the structure of the material obtained.
Deposition of Ceramic Films by A Novel Pulsed-Gas Mocvd Technique
Authors: Aitchison Kenneth A. , Barrie James D. , Ciofalo Joseph 
Published: March 2011

ABSTRACTMetal-Organic Chemical Vapor Deposition (MOCVD) is a versatile technique for the deposition of thin films of metals, semiconductors and ceramics. Commonly used hot wall flow-reactor designs suffer from a number of limitations. Chemical processes occurring in these reactors typically include a combination of homogeneous (gas-phase) and heterogeneous (gas-surface) reactions. These complex conditions are difficult to model and are poorly understood. In addition, flow reactors use large quantities of expensive precursor materials and are not well suited to the formation of abrupt interfaces. We report here a novel MOCVD technique which addresses these problems and enables a more thorough mechanistic understanding of the heterogeneous decomposition pathways of metal-organic compounds. This technique, the low-pressure pulsed gas method, has been demonstrated to provide high deposition rates with excellent control over film thickness. The deposition conditions effectively eliminate homogeneous processes allowing surface-mediated reactions to dominate. This decoupling of gas-phase chemistry from film deposition allows a better understanding of reaction mechanisms and provides better control over film growth. Both single metal oxides and binary oxide systems have been investigated on a variety of substrate materials. Effects of precursor chemistry, substrate surface, temperature and pressure on film composition and morphology will be discussed.
Synthesis and Properties of Molecular Fragments of Metal Chalcogenides
Authors: Steigerwald Michael L. 
Published: March 2011

ABSTRACTIn this manuscript we describe several approaches to the preparation of molecule-sized fragments of inorganic solids. The first is the arrested precipitation of metal selenides in reverse micelles; the second is the arrested pyrolysis of molecular precursors to II–VI compounds; and the third is the chemical moderation of molecules-to-solids reactions.
Analysis of Collective Resonances in Clusters: Metals and Carbon
Authors: Kresin Vitaly V. 
Published: March 2011

ABSTRACTDipole photoabsorption spectra of small clusters are analyzed. Two types of systems are considered: metal clusters and the carbon fullerenes. Both have been found to exhibit strong collective photoabsorption modes associated with the motion of delocalized electrons. We describe analytical results for the resonance frequencies in both spherical (closed-shell metallic, C60 ) and spheroidal (openshell metallic, C70) particles. The calculation is based on the techniques of many-body physics (random-phase approximation, sum rules), affords a unified view of the dynamical response of microscopic clusters, and leads to good agreement with experimental data.
Structural Analysis of Gold Clusters Using Exafs
Authors: Cluskey P.D. , Newport R.J. , Benfield R. E. , Gurman S.J. , Schmid G. 
Published: March 2011

ABSTRACTThree gold clusters, Au55 (PPh3 )12Cl6, Au55{PPh2(C6H4SO3Na)}12Cl6 and Au11{PPh2(p-ClC6H4)}7I3 (which we shall denote Au55, Au55, and Au11 for convenience) have been studied using EXAFS. Average near-neighbour bond lengths are contracted from the bulk by approximately 0.15Å (±0.02Å) for Au55, and 0.22Å (± 0.02Å) for Au11. Ligand contributions have been successfully modelled in the fitting. Debye-Waller factors for samples at room temperature and at 80K are compared to ascertain the relative degrees of thermal and static disorder present in the systems. Results clearly indicate that static structural disorder predominates over thermally induced vibrational disorder.
Inorganic-Organic Sol-Gel Processing of Semiconductor Quantum Dots and some Preliminary Self-Diffraction Studies on CdS-PbS
Authors: Spanhel L. , Schmidt H. , Uhrig A. , Klingshirn C. 
Published: March 2011

ABSTRACTFilms and monoliths, containing clusters (sizes < 5 nm) of the binary semiconductor CdS and sandwiched CdS-PbS, were prepared via multifunctional inorganic-organic sol-gel processing. As a sulfur source, hexamethyldisilylthiane was employed. In precursor sols, the metal sulfide clusters are carrying functionalized silanes acting as stabilizing centers as well as inorganic and organic network formers. Hydrolysis and condensation produces an inorganic network yielding viscous liquids useful to prepare optically transparent films or monoliths. The final organic cross-linking at T < 100°C results in materials of variable spectral response, thickness and optical density. In preliminar degenerate four-wave mixing experiments, self-diffraction from laser-induced gratings was observed on unsupported 200 μm thick CdS-PbS doped monoliths. The maximum first order grating efficiency, measured at different wavelengths between 490 and 520 nm, was 0.5 · 10−3 and the corresponding calculated effective third order susceptibility was of the order of 10−9 esu.
Chemistry and Optical Properties of Small Metal Particles in Aqueous Solution
Authors: Henglein Arnim 
Published: March 2011

ABSTRACTMetal particles in aqueous solution can be surface-modified by chemisorbed molecules and/or by a second deposited metal. The electron density in the metal particles is varied by controlled electron transfer from free radicals.’ These modifications lead to significant electronic changes in the metal particles, the result being changes in the optical properties and in chemical reactivity.The physicochemical properties also change during the transition from the atomic to the metallic state with increasing particle size. In the case of silver, oligomeric non-metallic clusters can be stabilized in solution for days, time enough to study many of their properties. In other cases (Au, Cu, Pb), the clusters are short-lived; they are investigated by fast kinetic methods such as pulse radiolysis.
Extrusion Textures in NiAl and Reaction Milled NiAl/AlN Composites
Authors: Bieler T. R. , Noebe R. D. , Whittenberger J. D. , Luton M. J. 
Published: March 2011

ABSTRACTExtrusion textures in monolithic NiAl and an NiAl/AlN particle composite are compared. The NiAl has a generally increasing grain size with extrusion temperature, and a corresponding transition from <110> to <111> fiber texture. The results suggests that <110> is more closely related to the deformation texture, while the <111> is a recrystallization orientation formed by preferential growth. The composite exhibits <311> fiber texture, and this is consistent with slip in <100> directions. The effect of the AlN particles is to prevent the orientation changes observed in the monolithic NiAl during recrystallization.
In-Situ Synthesis of Particle Dispersed Nanocrystalline NiAl By Cryomilling
Authors: Huang Benlih , Vallone J. , Klein C. F. , Luton M. J. 
Published: March 2011

ABSTRACTThe present research was carried out to study the cryogenic synthesis NiAl from elemental powders with the view of forming particle dispersed NiAl. It was found that nanocrystalline NiAl with a crystallite size in the range 5nm to 10nm is produced during cryomilling. Additionally, the nanocrystalline NiAl maintains the fine crystallite size when annealed at high temperatures. It is thought that the resistance of the microstructure to coarsening is due to the presence of nano-scale particles of AIN formed by reaction between milling medium, liquid nitrogen, and aluminum. The transformation of Ni and Al to ordered NiAl was studied using x-ray diffraction. This showed that cryomilling not only produces a solid solution but also can induce in-situ ordering of stoichiometric NiAl. The B2 NiAl structure forms during milling after the elemental powder blend is cryomilled for about 40 hours. It also forms when the “mechanical” solid solution is annealed at room temperature for about twelve hours.
An Evaluation of the Creep Properties of an Al2O3/Ni3A1 Composite and the Effect of Disorder on Mechanical Properties
Authors: Brennan P. C. , Kao W. H. , Yang J.-M. 
Published: March 2011

ABSTRACTOrdered Ni3A1 alloys and their composites are attractive materials for elevated-temperature structural applications due to their many favorable properties. The addition of alloying elements can significantly lower the Ni3Al order-disorder transition temperature and also result in the formation of a Ni solid solution. As the percentage of Ni solid solution increases, the composite's room-temperature flexural strength increases. The effect of rocessing parameters on the material's microstructure is discussed. The complex matrix microstructure also has a significant effect on the composite's creep properties. Normal power-law creep was exhibited by the composite material when tested in compression.
Evaluation of Coatings for Sapphire Fibers in TiAl Using the Fiber Push-Out Test
Authors: Mackin T. J. , Yang J. 
Published: March 2011

ABSTRACTFiber push-out tests were used to evaluate several double coating systems for sapphire fibers in γ -TiAl. The double coatings consisted of an inner debond coating, followed by an outer coating of alumina that serves as a diffusion barrier. The inner coatings were of three types: carbon black, colloidal graphite and porous alumina. By comparing estimates of interface toughness computed from the push-out tests, each double coating is found to permit debonding and sliding of the sapphire fibers. Consequently, each of the double coatings would afford improved fracture toughness for sapphire reinforced γ -TiAl.
Particulate Intermetallic Matrix Composite Made by One-Step Pulsed Laser Deposition
Authors: Chen Li-Chyong , Hall Ernest L. , Lou Karen A. 
Published: March 2011

ABSTRACTA novel way of producing particulate intermetallic matrix composites based on Nb-Al in one step using pulsed laser deposition (PLD) has been investigated. One unique characteristic, inherent to laser ablation, is the generation of particulates. These particulates condense on the substrate and become part of the film. In some cases, such as in high Tc superconducting or optical films applications, it is believed that the presence of particulates diminishes the quality of the films. In this work, we demonstrate that it can be advantageous in some applications to incorporate these particulates into the films.Nb-Al films were prepared by laser ablation from a Nb3Al target using a 248nm KrF excimer laser at various fluences and substrate temperatures. Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Auger electron spectroscopy (AES) were used to characterize the samples. The resultant films consist of a homogeneous matrix with uniformly distributed inclusions. The size of the particles generated by PLD is in the range of a few tens of nanometers to a few microns. EDX shows that the matrix has a composition of Nb7A13 and the particulates contain barely detectable Al. The mechanism of the depletion of Al in the particulates will be discussed. The merit of having a ductile Nb phase embedded in the intermetallic matrix is evident as the cracks generated during TEM sample thinning process propagate in the brittle matrix and finally are arrested at the ductile inclusions.
Fatigue Crack Growth in a TiAl Alloy with Lamellar Microstructure
Authors: Davidson David L. 
Published: March 2011

ABSTRACTThe mechanisms of fatigue crack advance are examined for a lamellar α2 + γ alloy. Crack growth rates are highly dependent on the orientation of the loading axis to the lamellae direction. Thus, the material has some of the characteristics of a composite. For crack growth perpendicular to the lamellae, the mechanisms of crack advance are similar to those of other titanium alloys, while crack growth parallel to lamellae has other characteristics.
Reinforcement from In-Situ Precipitated Silica in Polysiloxane Elastomers under Various Types of Deformation
Authors: Mark James E. , Wang Shuhong , Xu Ping , Wen Jianye 
Published: March 2011

ABSTRACTElastomeric networks prepared by tetrafunctionally end linking hydroxyl-terminated poly(dimethylsiloxane) chains (PDMS) were filled by the in-situ precipitation of silica. The resulting networks were investigated under uniaxial elongation, biaxial extension, shear, and torsion in order to characterize the resulting changes in mechanical properties. Compared with the unfilled networks, the silica-filled materials showed large reinforcing effects. Specifically, their values of the modulus, ultimate strength, and rupture energy increased significantly. The results thus indicate that the PDMS networks filled by the in-situ precipitation of silica have very good mechanical properties in several, rather different deformations. Examples of other deformations of interest are equilibrium swelling, and dynamic cycling for characterization of compression set.
Tc-δ Relations in YB2Cu3O7-δ Thin Films: Effects of Oxygen Pressure During Growth
Authors: Feenstra R. , Norton D. P. , Budai J. D. , Christen D. K. , Lowndes D. H. , Matijasevic V. C. , Eom C. B. , Geballe T. H. , Hellman E. S. , Hartford E. H. 
Published: March 2011

ABSTRACTThe Tc dependence on oxygen content was measured for YBa2Cu3O7-δ films grown with a variety of techniques (solid phase epitaxy, laser ablation, off-axis sputtering, co-evaporation) at oxygen pressures p(O2) ranging from 1.0 atm to 0.1 mTorr. Dissimilar dependences resulted for each film type, with Tc either increasing or decreasing for small increments in δ from maximum oxygen occupancy. Varying systematically with p(O2) during growth, the deviations are attributed to competing effects from hole-doping lattice defects (most likely on the Y-site) on the carrier density of the CuO2 planes and basal plane oxygen capacity, respectively, giving rise to overdoping or underdoping after low temperature oxidation in 1.0 atm of oxygen.
Extreme Sensitivity of Tc to Cool-Down Rate and Substrate Temperature for Epitaxial Fe-DOPED Ybco Films
Authors: Bridges Frank , Boyce J. B. , Johnson R. I. 
Published: March 2011

ABSTRACTEpitaxial Fe-substituted YBCO films on LaAIO3 substrates prepared by pulsed laser deposition exhibit a large variation in Tc with the substrate temperature and the cool-down rate of the films in an O2 environment, immediately after deposition. For 9% Fe films deposited at 700°C, a rapid cool-down yields a Tc of 60 K while a slow cool-down of 10°C/minute gives 18 K; Tc goes to 0 at 11% Fe for the slow cool-down films. For 9% Fe films deposited at 770°C, Tc > 80K and is much less sensitive to the cool-down rate or additional anneals.
Flux Pinning and Creep in High Temperature Superconductors
Authors: Kes P. H. , Van Der Beek C. J. 
Published: March 2011

ABSTRACTVarious questions concerning pinning and flux creep in high- temperature superconductors are addressed. First the pinning force by point defects in CuO2-layers in Bi:2212 and Y:123 single crystals is computed. Then some possibilities for the pin mechanism of the recently discovered screw dislocations in sputtered Y:123 films are discussed. Finally, we turn to the issue of flux creep in these materials and the relation between activation barrier and current density. The relevance of different creep models is further elucidated by the numerical solution of the non-linear creep equation for infinite slab and cylinder geometries and various initial field and current distributions.
Neutron Depolarisation by YBa2Cu5O6.85, Superconductors
Authors: Wang J. , Kennedy S. J. , N. R. K. 
Published: March 2011

ABSTRACTWe report a study of magnetic flux penetration into a single crystal superconductor, using the technique of 1-dimensional neutron depolarisation. In these experiments we have applied magnetic fields of up to 1.7 kOe to the crystal, perpendicular to the polarisation direction of the neutron beam. By analysing the polarisation of the transmitted neutron beam, after removal of the applied field, we are able to determine the remanent magnetisation in the crystal as well as its decay over periods from 10 to 105 seconds. This technique allows us to study both field and time dependent behaviour.We are developing a model to explain these observations, using the Bean critical state model to calculate the bulk trapped flux with the assumption of simple spin precession in a uniaxial magnetic environment. We have been able to relate the field dependence of the remanent magnetisation to the lower critical field Hcl and the field at which magnetisation saturation is reached 2H*-Hcl. We also relate the time dependence to the flux pinning energy U which determines the rate of flux relaxation. Measurements of this type could be used to plot the magnetic phase diagram of high temperature superconductors, to study anisotropy and flux creep in such crystals.
Scaling Behavior Near Superconducting Transition in the YBa2Cu3O7 System
Authors: Wu M. K. , Wang M. J. , Chen Y. C. , Chien T. R. , Chi C. C. , Holtzberg F. 
Published: March 2011

ABSTRACTWe have carried out a systematic study of the detailed I-V characteristic in magnetic fields of the YBa2Cu3O7 (YBCO) single crystals and c-axis oriented thin films. For all the samples studied, there exists a temperature at which the I-V satisfies simple power law. The I-V characteristic also follows the scaling behavior predicted by the phase transition model based on the random disorder. The derived critical exponents suggest the occurrence of 3D to 2D crossover of the flux motion. The critical field at which the crossover occurs depends on the sample thickness.
Ac Permeability Measurements in 770 MeV 129Xe17+ and 560 MeV 16O6+ Irradiated YBa2Cu3O7
Authors: Bechtold J. , Jin X. C. , Xue Y. Y. , Rusakova I. A. , Hungerford E. V. , Feng H. , Hor P. H. , Chu C. W. 
Published: March 2011

ABSTRACTHigh-energy heavy-ion irradiation has been shown to be effective in introducing flux-pinning defects in Y123 single crystals. Contrary to electron, low energy proton, and fast neutron irradiation, high-energy heavy-ion irradiation produces defects beneficial to flux pinning through the electronic (rather than nuclear) stopping mechanism. This type of stopping results in tubular defects many microns long that can increase the range of irreversible magnetic behavior to higher fields. In contrast, dense arrays of small defects (size < 100 Ang.) produce enhanced critical currents at low fields but do not extend the range of irreversible behavior significantly. We have used two ion-energy combinations in which the electronic stopping powers vary by nearly two orders of magnitude. The difference in stopping powers results in very different defect types, ranging from well oriented and dense (Xe) to much less well oriented and shorter (O) tubular defects. A novel analysis of the ac μ data indicates that the strong pinning introduced by the Xe irradiation breaks the vortex glass picture in favor of an individual pinning model, while O irradiation does not.
The Influence of Transport Currents on the Harmonic Generation in High Tc Superconductors
Authors: Wang J. , Yue Y. , Taylor K. N. R. , Russell G. J. , Matthews D. N. , Dou S. X. 
Published: March 2011

ABSTRACTThis paper details the experimental results for the influence of transport currents on the ac magnetisation of high-Tc superconductors. It has been found that the variation of the third harmonic amplitude V3 with an ac field can still be described by square and cubic laws for low and high ac fields, respectively, the same relationships as observed in the absence of transport currents. The only significant difference is that the magnitude of V3 in the low field region increases linearly with transport current. Consequently, the crossover point (from square law to cubic law) moves to higher ac fields and the variation of V3 with transport current is less pronounced in the high field region. The results are explained in terms of an effective increase in Hg, which is a parameter in Kim critical state model, with increase of transport current.
Properties of the Melt Processed 2212 Bscco in Silver
Authors: Yang Ming , Belenli I. , Grovenor C. M. R. , Goringe M. J. , Jenkins R. , Jones H. 
Published: March 2011

Introduction:This study is a part of an on-going research programme in Oxford to produce Bi-based ceramic superconductor wires. It aims at optimising processing parameters in order to achieve desired properties of the material. It has been shown that the 2212 BSCCO material can be successfully produced using the melt processing technique. High critical current density has been obtained in the form of wire and thin film/1,2/. Although several studies have been recently reported regarding the crystallisation of the 2212 phase/3/ and the effect of the oxygen stoichiometry on the properties of the material/4,5/, there is limited knowledge in the literature about the details of the processing of the 2212 material enclosed in silver. The present study is undertaken to elaborate the microstructural evolution mechanism of the 2212 phase in silver when it is cooled from the melted state, and to establish the effect of the cooling rate from the annealing temperature on the electric properties.