bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymers on a Random Liquid Surface
Authors: Duplantier Bertrand 
Published: March 2011

ABSTRACTWe report a recent theoretical study of polymers moving on a random two-dimensional fluid surface. The metric of the liquid membrane is free to fluctuate and these new degrees of freedom couple to those of the polymers - as a result, the critical exponents describing the polymers are changed, but are nevertheless related to those in two dimensions. The relation to possible experimental studies on membranes with vanishing surface tension, which should search for new universal values of exponents u and 7, is discussed.
Mechanical Properties of Crosslinked Semidilute Polymer Solutions Near and Far from the Gelation Threshold
Authors: Allain C. , Limat L. , Salome L. 
Published: March 2011

Recently, many works have been devoted to the study of the critical properties of the sol-gel transition. Only a few of them have dealt with the description of the properties observed on the whole range of the values of the gelation control parameter. In the present paper, we discuss the steady-state rheological properties observed near and far from the gelation threshold and we show that the effective medium theory in conjunction with the percolation model allows to understand entirely the variations of the viscosity and of the elastic modulus.In the first part, we present the gelling polymer system under study and the experimental methods with the help of which we measured the variations of the rheological quantities versus the concentration in crosslink points. In the second part, we discuss the critical behaviors observed near the gelation threshold. Finally, in the third part, we propose an effective medium theory applied to the description of the gelling polymer and we compare the variation of the viscosity measured outside of the critical domain to the results of these effective medium calculations.
Low Ohmicity Contacts to Mono- and Polycrystalline Silicon
Authors: Harrison H. B. , Williams J. S. , Reeves G. K. 
Published: March 2011

With the continued rapid development of integrated circuits and the evolution towards higher chip component densities brought about by down–scaling of device dimensions, it is useful to assess the limits of performance of presently known device structures using current fabrication technology. The silicon gate field effect transistor is of obvious importance, since at the present limit of decreasing dimensions these devices are expected to give comparable speed and lower powerdelay products than their bipolar counterparts. The rapid developments in fabrication methods such as increases in wafer dimensions coupled with the reduction in device dimensions has led to a reduction in maximum processing temperatures. In particular, this downward trend is incompatible with the necessity to lower contact resistance given appropriate device down–scaling.In this paper we present techniques using ion implantation and tailored impurity profiles that are compatible with low temperature ohmic contact formation. The application of these techniques to mono- and polycrystalline silicon are presented. Our results suggest that these techniques show considerable promise for semiconductor device applications. As a consequence, a production technology that optimizes the contact resistance to both gate-poly and drain and source regions is being investigated and current results will be presented.
New Chemical Routes to Metal Nitrides
Authors: Gladfelter Wayne L. , Hwang Jen-Wei , Evans John F. , Hanson Scott A. , Jensen Klavs F. , Ho Kwok-Lun 
Published: March 2011

ABSTRACTAfter a brief introduction on how the differing properties of H2O and NH3may effect the strategies used to synthesize metal nitrides, an overview of our use of azides to produce aluminum nitride thin films will be presented. The effect of changing the nitrogen source to one which contains at least one N - C bond is to increase dramatically the carbon content of the films. Replacing the alkyl groups attached to the aluminum with hydride ligands removes the final carbon source and forms what appears to be a promising new class of precursors. This is demonstrated by the study of the reaction of Me3NGaH3with NH3to produce the novel trimer, [H2GaNH2]3. This fully characterized molecule converts at 150°C into gallium nitride. Surprisingly, it yields GaN having the sphalerite structure instead of the known wurtzite phase. A discussion of the reasons for this unusual route to a new crystalline phase of GaN is included.
Laser Densification of Sol-Gel Coatings
Authors: Taylor D.J. , Fabes B.D. , Steinthal M.G. 
Published: March 2011

ABSTRACTAlkoxide-derived silica coatings were deposited on fused silica by dip coating. The samples were covered with a metal film to absorb the infrared radiation from an Nd:YAG laser. Coupling the laser power to the coating produced localized surface heating on the samples. By scanning the sample across the beam's path, channels in the coating were formed. The channels varied from 150 μm to 600 μm wide and from 200Å to 1000Å deep depending on the laser power and the translation speed. The size and shape of the channels also depended on the composition of the sol-gel coating. Optical microscopy showed that there were no cracks in either the substrate or in the coating on the micron scale. SEM revealed cracks on the nanometer scale in the laser fired coatings and no cracks in the unfired coatings. Ellipsometry showed that the index of refraction increased with increasing depth of the channels.
Fractal Structure and Fractal Time in Silica Sol-Gels
Authors: Martin James E. , Wilcoxon Jess 
Published: March 2011

ABSTRACTNear the gel point, light scattering studies of silica sol-gels reveal fractal clusters whose size diverges as a power law, in accord with the predictions of percolation theory. More surprising is the appearance of a fractal time description of the dynamics of these clusters. This novel dynamics has recently been revealed by quasielastic light scattering from the density fluctuations that occur at the sol-gel transition. Since the relaxation of fluctuations in these branched polymer systems is self-similar, decay processes occur on all time scales (fractal time), and average decay times diverge. An interpretation of this observation will be presented that relies on a length-scale-dependent viscosity and the geometrical self-similarity of the sol-gel transition. The scattering theory is extended to the calculation of time- and frequency-dependent viscoelastic properties, as well as mechanical properties such as the shear modulus, steady state creep compliance, and viscosity. The viscoelastic predictions are found to be in good agreement with experimental data.
Low Wavenumber Raman Scattering in Silica and Silicophosphate Aerogels
Authors: Walden Barbara L. , Breval Else , White William B. 
Published: March 2011

ABSTRACTRaman spectra, measured on silica and silicophosphate aerogels in the range of 5 to 70 cm−1 , revealed a “particle band” that arises from the discrete particulate character of the gels at very small size scales. TEM measurements of the nanoscale structure in the gels correlate with the location of the particle band maximum.
The Influence of Cations on Growth Kinetics of Silica Aggregates
Authors: Beelen Theo P.M. , Wijnen Peter W.J.G. , Rummens Kees P.J. , Van Santen Rutger A. 
Published: March 2011

ABSTRACTSilica gels are prepared by acidification (pH = 2 − 4) of water glass. SAXS measurements show that the gel consists of fractal aggregates (D = 2.2). Although the fractal dimension is not influenced by addition of cations, Al3+ and Mg2+ retard the growth of the fractal aggregates, while TMA+ has a promoting effect.
Fractal Concepts And Aggregation Of Iron Oxides
Authors: Amal R. , Raper J.A. , Waite T.D. 
Published: March 2011

ABSTRACTThe modelling of the aggregation kinetics of iron oxides has been succesful in predicting the increase in aggregate size as determined by dynamic light scattering measurements. The aggregates were found to exhibit fractal behaviour with fractal dimensions obtained from the scattering exponent in static light scattering studies dependent on the aggregation mechanism and ranging from 2.3 for rapid (diffusion limited) to 2.8 for slow (reaction limited) aggregation. Polydispersity and restructuring of aggregates were found not to affect the relationship between scattering exponent and aggregate fractal dimension. Excellent correspondence over a range of temperatures and ionic strengths has been obtained between results of sizing experiments using dynamic light scattering and sizes predicted using a modified Smoluchowski model incorporating fractal dimensions.
Positronium Decay in Silica Sol-Gels
Authors: Hopkins B. , Quarles C. A. , Zerda T. W. 
Published: March 2011

ABSTRACTPositronium lifetimes inside porous silica are measured and discussed in terms of surface interactions, oxygen and nitrogen induced quenching and pore sizes. Surface interactions are studied for silica gels having surfaces covered solely with hydroxyl or methoxy groups. A rapid decay of positronium inside the pores filled with gaseous or liquid oxygen is reported and explained in terms of quenching mechanisms. An increase in the measured lifetimes for pores filled with nitrogen is attributed to the change in the pore distribution function.
Titania/Silica Sol-Gel Films: Comparison of Techniques for Thin Film Thickness Measurement
Authors: Melpolder S. M. , West A. W. , Cunningham M. P. , Sharma R. 
Published: March 2011

ABSTRACTTwo techniques for thin film measurement were compared: an optical method combining ellipsometry and reflectance spectroscopy, and cross-sectional transmission electron microscopy. These techniques were used to measure the absolute thicknesses of titania/silica sol-gel films in the size range 0.1 to 0.8 microns. The relative advantages and disadvantages of these methods will be described in this study.
Synthetic and Structural Studies Bismuth/Copper Alkoxides
Authors: Evans William J. , Hain John H. 
Published: March 2011

ABSTRACTThe reaction of Bi[OC(CH3)3]3 with [Cu(μ-O2CCH3)2]2 has been investigated as a possible route to mixed-metal materials containing bismuth and copper. The product distribution obtained from this reaction depends not only upon the stoichiometry, but also upon the method of product isolation. Products containing bismuth and copper are obtainable as well as an unusual, soluble hexametallic copper(II) alkoxide acetate complex, Cu6[OC(CH3)3]6(O2CCH3)6. The mixed-metal products were examined by differential scanning calorimetry, and thermolyzed and hydrolyzed samples of these products were compared by scanning electron microscopy.
Heterometallic Alkoxides as Precursors to Multicomponent Oxides
Authors: Hubert-Pfalzgraf Liliane G. , Papiernik Renee , Massiani Marie-Cecile , Septe Bernard 
Published: March 2011

ABSTRACTLead(II) oxides are involved in various advanced materials. Their high volatility as compared to that of other elements makes chemical routes to such materials especially attractive. Various synthetic routes to lead(II) alkoxides have therefore been estimated. They display a strong tendency to undergo spontaneous condensation reactions, giving oxoalkoxides Pb4O(OR)6 (R = tBu, iPr, Et). Reaction between Pb4O(OEt)6 and [Nb(OEt)5l2 does not proceed by simple addition of the alkoxides, but the lead tetranuclear oxoalkoxide is transformed to a hexanuclear one, Pb6O4 (OEt)4 , whose oxo ligands bear Nb(OEt)5 moieties, the overall formula being Pb6O4 (OEt)4 [Nb(OEt)5]4 1. The stoichiometry between the two metals corresponds to that of the PNM ceramic, and 207Pb NMR has been used as a tool to study the reactivity of 1 in the presence of various modifiers and magnesium ethoxide.
Stabilization, Characterization and Optical Applications of Niobium and Tantalum Oxide Sols Prepared Via Alkoxide Routes
Authors: Parraud Stephen , Hubert-Pfalzgraf Liliane G. , Floch Herve 
Published: March 2011

ABSTRACTHydrolysis of niobium and tantalum pentaethoxides in ethanol and in the presence of basic (ammonia, tetramethylammonium hydroxide, di and triethylamine) or acidic (nitric or hydrochloric acids) additives was investigated. Triethylamine gives monodispersed, small particles of amorphous M2O5,nH2O (M = Nb, Ta). These colloidal suspensions were used to obtain thin films by spin-coating techniques. The coatings display a thickness of 100–300 nm and a refractive index around 1.7. Laser damage tests at 1064 nm wavelength with a pulse length of 3 ns were carried out on the single layer systems. The threshold values (one-onone) are in favor of the Ta2O5 coatings with an average of 14.5 ± 2.1 J/cm2 , by comparison with 8.3 ± 1.6 J/cm2 for the Nb2O5 films.
Particle Growth and Development During the In-Situ Precipitation of Silica in a Polymeric Matrix
Authors: Xu Ping , Wang Shuhong , Mark James E. 
Published: March 2011

ABSTRACTThe hydrolysis of tetraethoxysilane much used in the sol-gel approach to ceramics can be studied in a matrix isolation technique in which the silica thus formed precipitates within a polymeric material. This technique was applied here in the in-situ precipitation of silica particles in an elastomeric matrix of poly(dimethylsiloxane). Transmission electron microscopy and mechanical property measurements were carried out as a function of time over a period of 60 days. The equilibrium amount of silica precipitated was obtained relatively quickly, after approximately one day, but reorganization of the particles continued for several days thereafter. This “aging” process resulted in particles that are better defined and more uniform in size, but their ability to reinforce the elastomeric materials was only marginally increased. Scattering techniques are also being used to obtain additional information on this interesting process.
The Formation of thin Films and Fibers of TiC from a Polymeric Titanate Precursor
Authors: Ting S-J. , Chu C-J. , Limatta E. , Mackenzie J. D. , Getman T. , Hawthorne M. F. 
Published: March 2011

ABSTRACTThe synthesis and characterization of several polymeric titanates and their conversion to carbon deficient TiC is described. The physical properties of one of these titanates allows it to be drawn into fibers and applied to substrates as thin films. Pyrolysis of these fibers and films to carbon deficient TiC is described.
Characterization of Ceria Stabilized Zirconia Coatings on Metal Substrates
Authors: Maggio Rosa Di , Scardi Paolo , Tomasi Andrea 
Published: March 2011

ABSTRACTIn this study ceria stabilized zirconia was used to obtain an uniform and adherent film on iron and 304 S.S.. Coatings were prepared by dipping in solutions of organometallic precursors of zirconium and cerium. Structure and morphology of samples were investigated using SEM and XRD techniques before and after thermal treatments. The oxidation behaviour in air of coated samples was followed through thermogravimetrical analysis in a range of temperature from 773 K to 1123 K. The preliminary results show, for the samples coated and pretreated in high vacuum at 923 K, a good decrease in oxidation rate.
Evolution of Surface area During the Controlled Growth of Silica Spheres
Authors: Bogush Gregory H. , Brinker C. J. , Majors P. D. , Smith D. M. 
Published: March 2011

ABSTRACTSeveral mechanisms have been proposed for the growth of silica spheres by the controlled hydrolysis of silicon alkoxides, the limiting cases of which are the conventional and aggregative growth models. The evolution of surface area predicted from the two models is substantially different at early times into the reaction. In order to probe the change in surface area during growth, 1H NMR measurements of the solvent were made during the growth process. It has been demonstrated that the spin-spin relaxation time.(T2) for an absorbed phase is less than that of the bulk solvent. Using this principal, the change in surface area can be followed in situ during the reaction. The experimental results were compared to the predictions of the conventional model and found not to be in agreement.
The Cracking of Sol-Gel Films During Drying
Authors: Garino Terry J. 
Published: March 2011

ABSTRACTThe cracking behavior of acidic silica sol-gel films during drying and low temperature heat treatment was studied. Films that cracked during drying exhibited a variety of unusual crack morphologies including sinusoidal cracks and parallel crack pairs. The effects of the water content of the sol and temperature on the critical thickness above which cracking of the films occurred were determined. The critical thickness decreased with increasing water content, most likely because the surface tension of the liquid in the pores of the gel increases with water content and because sols with low water concentrations did not gel until the solvent had evaporated. To determine why the critical thickness decreased with temperature, thermal analysis and shrinkage measurements of both constrained and unconstrained films were performed. Thermogravimetric analysis indicated that rapid weight loss occurred in the temperature region where the rapid decrease in critical thickness occurred. A small amount of shrinkage of the films also occurred in this region. Finally, shrinkage measurements of films debonded from the substrate indicated that shrinkage was very anisotropic with nearly all of the shrinkage occurring in the plane of the film and very little in the thickness direction.
Hybrid Gels Designed for Mullite Nucleation and Crystallization Control
Authors: Huling Jeffrey C. , Messing Gary L. 
Published: March 2011

ABSTRACTThe controlled nucleation of phase transformations by seeding is an established technique for influencing transformation kinetics and sintered microstructures in ceramics. Previous studies have focused on seeding with ultrafine, solid particles having the requisite crystal characteristics for either homo- or heteroepitactic nucleation of the desired phase. Size separation of particulate seed crystals is not an efficient process and thus more recent efforts have concentrated on chemical approaches to nucleating solid phase transformations. Hybrid gels, in which two or more gels are combined to capitalize on the benefits of each, have been reported for the homoepitactic nucleation of mullite. In principle, the molecularly-mixed gel crystallizes to mullite at ∼1000°C and, in turn, acts to nucleate the colloidal gel component's transformation to mullite at higher temperatures. However, the transformation sequence and kinetics are profoundly affected by the interfacial reaction between the two gels comprising the hybrid. This paper discusses how the physical distribution and chemistry of the gel components can be manipulated for the control of mullite nucleation, crystallization and microstructure development.
Rheology for Better Sol-Gel Fiber and Film Formation
Authors: Macosko C. W. , Mecartney M. L. , Scriven L. E. 
Published: March 2011

ABSTRACTFlow behavior of a liquid or suspension depends on how stress varies with strain rate, strainrate rotation, and strain history, as well as the progress of evaporation, extent of reaction, and degree of aggregation in sol-gel systems. Rheological methods suitable for measuring flow behavior are summarized. Examples of measurements and microstructural observations by transmission electron microscopy made during gelation of four sol-gel systems are presented. The relation of rheological response to microstructure is discussed.
Densification and Crystallization Of Thin Transition Metal Oxide Coatings From Metal Alkoxides
Authors: Hirashima H. , Muratake R. , Yamashita T. , Chiba T. 
Published: March 2011

ABSTRACTMonolithic gels of V2O5, Ta2O5 , and Nb2O5 have been prepared from VO(C2H5O)3 , Ta(C2H5O)5 , and Nb(C2H5 O)5 througg hydrolysis in ethanol Solutions. The conditions for gel formation have been determined. Thin coatings of these gels, less than 100 nm in thickness, have been prepared by dip coating. Changes in the thickness, d, and refractive indices, n, have been measured by ellipsometry during drying. In the first stage of drying, d decreases and n increases rapidly. Densification of the coatings takes place due to evaporation of solvent. In the following stage, increase in d and decrease in n have been observed for thin V2O5 gel coatings, about 30 nm or less in thickness. These results suggest that coarsening of pores and/or increase in surface roughness take place due to release of the capillary pressure during drying. Both d and n have increased with increasing number of dipping. After heat treating, decrease in d and increase in n have been observed.
Synthesis of Nanoceramic Particles by Intravesicular Precipitation
Authors: Bhandarkar Suhas , Yaacob Iskandar , Bose Arijit 
Published: March 2011

ABSTRACTNanometer sized magnetic particles have been fabricated by aqueous phase coprecipitation inside single compartment vesicles. These vesicles were generated by sonicating egg yolk phosphatidylcholine molecules in an appropriate ionic solution containing the reactant cations. Using cobalt and ferric nitrate as the starting solution, the reaction product was the desired cobalt ferrite; direct formation of the oxide is potentially a very important step. For the barium and ferric nitrate systems, the reaction product could not be identified easily. However, we have not been able to produce barium ferrite directly. In an attempt to compare the effect of drastic changes in the microenvironment, we have also completed aqueous phase precipitation in multilamellar vesicles. For the aluminum nitrate system, precipitation takes place only in the outermost “annular” space. Multiple particles are formed, and the resultant diffraction pattern shows a close match with an aluminum hydroxide chloride complex. This differs significantly from the product in single compartment vesicles, where β-Al2O3 was formed, and in free precipitation which resulted in Al(OH)3.
Wet Chemical Derived Films For Electrical Applications
Authors: Uhlmann D.R. , Teowee G. , Boulton J.M. , Zelinski B.J.J. 
Published: March 2011

ABSTRACTWet chemical methods have been used with success to synthesize films for a variety of electrical applications. After first reviewing the important microstructural features of films, the present paper focuses attention on ferroelectric (FE) films. The present state of and critical issues facing wet chemically derived FE films are considered. The needs for more extensive microstructural characterization and for more systematic exploration of electrical behavior are emphasized.
Evolution Of Molecular Structure In Alkoxide-Derived Lithium Niobate
Authors: Eichorst Dennis J. , Payne D. A. 
Published: March 2011

ABSTRACTStructural rearrangements during the sol-gel processing of lithium niobate were investigated by FTlR and Raman spectroscopic methods. The reaction of lithium ethoxide with niobium ethoxide resulted in the formation of a bimetallic alkoxide, LiNb(OEt)6 , which could be crystallized from solution. Single crystals were comprised of helical polymeric units consisting of niobium octahedra linked by lithium in tetrahedral (distorted) coordination. Successive crystallizations from solution allowed for the enhanced purification of the alkoxide precursor. Hydrolysis of the bimetallic alkoxide resulted in the formation of an amorphous network structure, which contained niobium-oxygen octahedral units modified by lithium. Heat-treatment facilitated structural rearrangements for the niobium environment, which allowed for the formation of the lithium niobate crystal structure. Further heat-treatment above 700°C resulted in structural changes associated with lithium oxide volatility.