bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fractal Pores or a Distribution of Pore sizes: Alternative Interpretations of Power-Law Small-Angle Scattering
Authors: Schmidt Paul W. 
Published: March 2011

ABSTRACTThe intensity I(q) of the small-angle x-ray or neutron scattering has been calculated for a system of randomly oriented, independently scatter-ing pores with a number distribution of pore diameters which has the form of a power law. As has already been shown, [P. W. Schmidt, J. Appl. Cryst. 15, 567–569 (1982)], when the number distribution of the maximum diameters a of the pores is proportional to a−γ, I(q) is proportional to q−(7−γ), where q = 4πλ−1sin(θ/2), θ is the scattering angle, and λ is the wavelength. The coefficient of the power-law intensity has been expressed in terms of some of the constants which determine the diameter distribu-tion. Equations have been obtained for the scattered intensity I(q) at q values larger and smaller than those at which power-law scattering occurs. The intensity scattered by this system is compared with the intensity from a system of pores with fractal pore-boundary surfaces which have a fractal dimension D.
The Pyrolysis of a Tungsten Alkyne Complex as a Low Temperature Route to Tungsten Carbide
Authors: Laine Richard N. , Hirschon Albert S. 
Published: March 2011

ABSTRACTThe synthesis of designed organometallic compounds and their selective activation and transformation into materials of high purity (for electronic applications), high strength and/or high temperature stability (for refrac-tory or structural applications), represents a potential area of extreme growth in organometallic chemistry. Research in this area could provide entirely new, inexpensive, fabrication methods for common and exotic materials.In this paper, we develop design principles for the preparation of organometallic precursors, “premetallics” that can be selectively con-verted, in high yields, to a desired refractory metal. We also describe our preliminary efforts to prepare tungsten carbides (WCx) from a pre-metallic. Pyrolysis studies using Cp2W2(CO)4(DMAD) [DMAD = Dimethyl-acetylene dicarboxylate], 5, as the premetallic demonstrate that 5 will decompose at temperatures of ∼ 700°C to give good yields of W2C. 5 is soluble and decomposes fully in 10–20 minutes, without the need of another reactant.
Precursors of Titanium Carbonitride
Authors: Maya L. 
Published: March 2011

ABSTRACTA series of novel compounds was isolated in the course of exploratory work on the chemistry of titanium halides in liquid ammonia. This work was undertaken to study synthetic approaches to titanium-containing precursors of ceramic materials. Representative of these compounds is a mixed valence Ti(III)-Ti(IV) tetramer, [NH4+·NH3]2[Ti4Br4 (NH2)12]−2, which was produced by the reaction of potassium borohydride and titanium IV bromide in liquid ammonia at room temperature. Similar ammonium salts of either Ti(IV) or Ti(III) were also prepared. The reaction of the ammonium salts with sodium acetylide in liquid ammonia evolves acetylene in an amount equivalent to the ammonium ion present. This provided the charge of the complex and yielded novel titanium acetylide derivatives. The acetylides convert into titanium carbonitrides upon thermal treatment to 800°C.The reaction of titanium halides of their ammonolytic products with sodium acetylide in liquid ammonia to yield halogen-free acetylide precur-sors having a relatively high titanium content appears to be a convenient synthetic approach. This is made possible by the fact that the alkali metal halide by-products are soluble and easily separated in that reaction medium. This approach appears to be a generalized route applicable to a number of transition metal elements of interest.
Conversion of Chemically-Derived Polymeric Precursors to High performance Ceramic Fibers
Authors: Haider M. Ishaq , Clark Terence J. 
Published: March 2011

ABSTRACTIn recent years, there has been steadily increasing research activity directed towards preparation of ceramic materials via polymer pyrolysis. Among the most thermomechanically stable structural ceramics are SiC, Si3N4, and their solid solutions. These materials are widely used as ceramic fiber reinforcements in composites owing to their high mechanical strength, stiffness, and oxidative stability. Processes have now been developed to make these fibers by utilizing melt spinning. Fine diameter continuous filaments are formed, and further processing involves the steps of mild reactive cure and high-temperature pyrolysis. The approach in this review is to summarize the fiber making process with emphasis on improving fired properties by utilizing known mechanisms of fiber failure and process modification procedures. Fiber characteristics, applications of high performance fiber, and perceived trends will also be discussed.
A Theoretical Study of Silanol Polymerization
Authors: Burggraf Larry W. , Davis Larry P. 
Published: March 2011

ABSTRACTWe have applied state-of-the-art semi-empirical molecular orbital methods to a study of the anionic polymerization of silanols to form silica. In particular, we have considered nucleophilic attack on silanols and subsequent reactions of the products. Hydroxide addition proceeds without activation to form five-coordinate silicate anions. Five-coordinate structures can also be formed by oligomerization following the attack of hydroxide on neutral silanols to abstract a proton. These five-coordinate structures are predicted to play a key role as intermediates in the polymerization process. Water can be eliminated from these anions, but with a substantial activation barrier. The activation barrier appears to be lower for the larger, more complex systems. These predictions are consistent with a rapid pre-equilibrium to form dimer anions followed by the slower reaction to form higher oligomers.
Polymer Growth and Gelation in Borate-Based Systems
Authors: Brinker C. J. , Ward K. J. , Keefer K. D. , Holupka E. , Bray P. J. 
Published: March 2011

ABSTRACTIn situ FTIR, NMR and SAXS were used to investigate the synthesis and molecular structure of xLi2O-(1−x)B2O3 gels derived from tri-n-butyl borate (TBB) and lithium methoxide. In solution the fraction of tetrahedrally coordinated borons (N4) increases linearly with x, and a critical value of N4 must be exceeded in order to form gels. The primary criterion affecting gel formation is the kinetic stability of borate bonds toward molecules which are able to undergo dissociative chemisorption.
Reactivity of Silicates 1. Kinetic Studies of the Hydrolysis of Linear and Cyclic Siloxanes as Models for Defect Structure in Silicates
Authors: Balfe Carol A. , Ward Kenneth J. , Tallant David R. , Martinez Sheryl L. 
Published: March 2011

ABSTRACTThe kinetics of hydrolysis of hexamethylcyclotrisiloxane and di-t-butyldimesitylcyclodisiloxane in tetrahydrofuran solution have been determined and compared to hydrolysis rates of silica defects. In the presence of sufficient excess witer, the first-order rate constant of the cyclotrisiloxine, k= 3.8 × 10−3 min is similar to the rate constant, k = 5.2 × 10−1 min, of the disappearance of the D2 Raman silica defect band it has been proposed to model. Limited hydrolysis rate data for the cyclodisiloxane suggests that it hydrolyzes at least four times faster than does the cyclotrisiloxane. These data are consistent with rate data available for silica crack growth and support the assignment of highly strained siloxane bonds at the crack tip to cyclodisiloxanes. Infrared spectra determined for the cyclodisiloxanes lend further support to this model.
SOL-GEL AR Films for Solar Applications
Authors: Ashley Carol S. , Reed Scott T. 
Published: March 2011

ABSTRACTSol-gel derived antireflective films have been prepared for a variety of solar applications. The optical properties of the films are optimized by microstructure tailoring in solution by aging and/or in the film by heating and etching. The resulting film provides a quarter-wave, single layer interference surface with a reflectance minimum of <1% at 600 nm. We have applied sol-gel derived AR films to glass and plastics for solar thermal and photovoltaic applications, e.g., parabolic trough collector envelopes, plastic Fresnel lenses, and glazing materials for flat plate collectors.
Nucleation and Growth of Uniform m-ZRO2
Authors: Bleier A. , Cannon R. M. 
Published: March 2011

ABSTRACTHydrothermal treatment of zirconyl salt solutions produces uniform m-ZrO2 powder on the order of 80 nm. This powder is porous, has a 3-nm crystallite size, and exhibits an unusually high degree of crystallographic alignment within particles. The generation of this powder occurs via a complex process involving nucleation, growth, and controlled agglomeration of primary particles. Particle formation, crystallographic alignment and particulate uniformity are explained in terms of solution reactions and colloidal behavior.
Preparation of Gradient-Index Glass Rods by the Sol-Gel Process
Authors: Yamane Masayuki , Caldwell J. Brian , Moore Duncan T. 
Published: March 2011

ABSTRACTThe fabrication of gradient-index material via the sol-gel technique is reported. The material is based on the PbO-B2O3-SiO2 system and a K2 O- PbO liquid phase interdiffusion is used to produce the necessary composition gradient.
Effect of in Situ Polymer Adsorption on the Synthesis of Monodisperse Tio2 Powders
Authors: Jean J. H. , Ring T. A. 
Published: March 2011

ABSTRACTMonodisperse and spherical titania powders were prepared by the hydrolysis of titanium tetraethoxide in ethanol with hydroxy-propyl cellulose(HPC) present during particle precipitation. The mean particle size decreased as the concentration of tLPC increased. The critical concentration of HPC for the in situ stabilization of titania powder suspensions was determined by a photographic method, and found to be independent of the molecular weight of HPC within the molecular range of 60,000 to 300,000. The amount of HPC adsorbed on the particle surface, determined by a colorimetric method using a UV-visible spectrophotometer, decreased with the increasing molecular weight of HPC. Suspension stability was confirmed by theoretical calculations based on experimental results.
Excimer Laser Induced Oxidation of Silicon: Characterization of the Oxide Stoichiometry in the Interface Region
Authors: Mantell D. A. , Orlowski T. E. 
Published: March 2011

AbstractNew results on the ultrafast laser-induced formation of high-quality patterned silicon dioxide (SiO2) layers on silicon substrates at room temperature are presented. Using a pulsed ArF excimer laser (λ = 193 nm) operating at pulse energies near the melting threshold of silicon, SiO2 layers can be grown at a rate of 3–4 Å/pulse with an oxygen pressure of 500 torr. This growth rate exceeds by a factor of 5 the rate found using a XeCI excimer laser (λ = 308 nm) indicating that oxygen atoms produced by the direct photodissociation of oxygen by the ArF excimer laser play a role in achieving this extremely fast oxidation rate. Careful analysis of the laser exposed regions following each laser shot was performed using angle-resolved XPS with 150 micron spatial resolution. After one laser shot, a nonstoichiometric SiOx interface layer (<5Å) is clearly visible. Subsequent laser shots show the oxide peak shifting to higher energy as the oxide thickness increases until the characteristic ∼4.5 eV chemical shift for SiO2 (relative to the bulk Si 2p peak) is realized at a thickness of ∼20Å. The nonstoichiometric SiOx layer is still present at this oxide thickness but is confined to the interface region (<10Å) as observed in thermally grown oxides. Oxide thicknesses obtained by angle-resolved XPS were confirmed using sputter depth-profiling. XPS measurements on samples irradiated at low oxygen pressure (5 torr) show evidence for oxidation of the silicon substrate outside the focused laser beam (2X). At this pressure the recombination time for oxygen atoms is long enough to allow diffusion and apparent reaction with the silicon substrate at reduced temperatures.
Influence of Environment on Excimer Laser Irradiation of Metals
Authors: Partridge Julian P. , Pellegrino Joseph , Murphy Craig , Strutt Peter R. 
Published: March 2011

AbstractIrradiation of metals in gaseous and liquid nitrogen by KrF excimer laser pulses shows the way in which vapor or plasma pressure fields determine the nature of the rapidly solidified surface topography. Wave patterns formed on aluminum by irradiation in N2 gas arise from recoil pressure differences produced by highly localised differential surface evaporation. The solidification time, calculated from the observed ripple wavelength, is in good agreement with that deduced from a heat flow calculation. For irradiation in liquid N2, the homogeneous pressure within the center of the dense plasma zone results in a smooth surface. Beyond this region the progressively diminishing pressure induces surface ripples, fragmentation and droplet formation. Intriguingly, immersion of Ni, Ti, Zn, and Al in liquid N2 (to a depth of 2 to 4 mm) considerably increases the area and depth of irradiation-modified regions.
Excimer Laser Processing of Crystalline Iron-Boron Alloys
Authors: McCamy J. W. , Pedraza A. J. , Lowndes D. H. 
Published: March 2011

AbstractCrystalline Fe-B alloys in the concentration range of 5–25 at. pct. boron were processed by slightly (∼5%) overlapping single pulse XeCl excimer laser. The influence of the initial microstructure and phases upon the structure that results after laser processing (LP) were studied. The specimens were made by a rapid solidification procedure that permits readily glass-forming alloys to be obtained with structures ranging from fully amorphous to fully crystalline. The technique is briefly described. Two crystalline specimens of Fe-20 pct. boron, one in the as-cast condition and the other annealed, were laser treated. While the melted layer of the former was amorphous, the latter remained crystalline, exhibiting a similar phase content as before irradiation. Observations of both samples by scanning electron microscopy (SEM) prior to LP revealed a difference in particle size of one order of magnitude. A mathematical model of diffusion is developed for studying the homogenization process. It is concluded that the time for diffusion in the liquid state in the sample containing the larger particles is insufficient for homogenization to occur. Similar results regarding the influence of particle size were obtained with all the other samples.
Metastable Phase Formation in Laser Processed Al-Ge Thin Films
Authors: Catalina F. , Afonso C. N. , Ortiz C. 
Published: March 2011

AbstractThis paper presents a comparative study of the microstructures formed in Al.59Ge.41and Al.70Ge.30 (eutectic composition) free standing films under laser irradiation. An hexagonal metastable phase located between Allamella, can be formed depending on the film composition and the laser pulse length.
Plugging of Al Films Into Submicron Diameter Via Holes by Excimer Laser Irradiation
Authors: Mukai R. , Sasaki N. , Nakano M. 
Published: March 2011

AbstractVia-hole filling technique by momentarily melting an aluminum film has been developed, whereby planarization of aluminum films for multilevel interconnects on integrated circuits can be achieved. The melting is performed with an optical pulse irradiation from an ArF excimer laser without the problem of junction spiking. This technique is applicable to filling submicron-diameter vias having a diameter of 0.6μm with 0.7μm depth(aspect ratio:∼1.2). Very high aspect ratio(2.0) via-hole filling is achieved by heating the sample. During the laser irradiation, the sample substrate was kept at 300°C.
Write-Erase Mechanism of Indium-Antimony Optical Disk Medium
Authors: Goto Y. , Utsumi K. , Ushioda A. , Tsugawa I. , Koshino N. 
Published: March 2011

AbstractWritten and erased bits of the In-Sb phase change type optical disk medium were studied using transmission electron microscopy (TEN) and electron probe microanalysis (EPMA). Both the bits were separated into inner and outer areas and were composed of only rhombohedral Sb crystals and zinc blende In50Sb50 crystals. The difference between the two bits were in crystal size and atomic distribution of the inner area. Models of the writing and erasing processes were derived from these observations and the In-Sb phase diagram. With these models, the thicknesses, grain sizes and optical contrasts of the both bits were consistently explained.
Beam-Solid Interactions of Pyrolytic Graphite as a Function of Angle of Cut Surface
Authors: Yip Pearl W. , Jaklitsch Donald J. , Perkins Janet S. 
Published: March 2011

AbstractA study to examine beam-solid interaction as a function of the cut surfaces of pyrolytic graphite samples (0, 30, 60, and 90 degrees relative to the basal plane) was made using a high intensity, carbon dioxide laser beam operating at a wavelength of 10.6 μm.Crystal growth of redeposited carbon and impurities in the burn area as well as a melt on the burn edge were observed and examined using Scanning Electron (SEM) and Scanning Auger Microscopy (SAM). Similarities and differences relating to the structure of the material were further investigated using X-ray diffraction. Thermal transport properties as a function of angle were also examined.
Synthesis Induced by Laser Irradiation at Liquid/Solid Interfaces
Authors: Chan Siu-Wai , Dijkkamp D. , Wu X. D. , Venkatesan T. , Chang C. C. 
Published: March 2011

AbstractSynthesis of transition metal nitrides induced by excimer laser irradiation of metal foils immersed in liquid nitrogen was studied. Nitrogen incorporation was found by sputtering Auger Electron Spectroscopy in all six investigated metals (Ti, Zr, Hf, V, Nb and Ta). X-ray diffraction was used to determine the compounds formed. The morphologies of the irradiated surfaces often indicated that the surfaces had gone through a molten state. Micronthick mononitrides were grown on Ti, Zr and Hf, whereas Ta and Nb formed Ta2N and Nb2N respectively. The nitrides on V were not satisfactorily identified. The extent of nitridation correlates with the thermodynamic driving force, i.e. the Gibbs free energy for nitride formation.
Recrystallisation of Cadmium Sulphide Powder Films with a CO2 Laser
Authors: Barden P. E. , Cumberbatch T. J. 
Published: March 2011

AbstractThin films (1–2μm) of cadmium sulphide, deposited by electrophoresis, consist of a close packed layer of randomly oriented cubic-phase microcrystalline particles with an average diameter of 30nm. A CW CO2 laser, operating at 10.6μm has been used to convert this into a polycrystalline structure with columnar crystals, of hexagonal phase, which extend through the thickness of the film and whose c-axis is perpendicular to the substrate. The recrystallised regions comprise aligned grains up to 300nm in diameter whose cathodoluminescence spectrum exhibits a narrow peak centred at 2.42eV with a half width identical to that for evaporated CdS (0.1eV).
Combined Hrem and Eels Studies of the Electron Beam Induced Reduction of Maximal-Valence Transition-Metal Oxides.
Authors: Long Neil J. , Petford-Long Amanda K. 
Published: March 2011

AbstractHigh resolution electron microscopy has been used in conjunction with electron energy loss spectroscopy to follow the beam-induced reduction of WO3, V2O5and CuO, all of which are maximal valence oxides. All three oxides underwent reduction, although there are differences in the reduction pathway: WO3is reduced directly to the metal by loss of oxygen from the surface layers; CuO is reduced to the metal via at least two intermediate oxides (Cu4O3and Cu2O); and V205forms a reduced oxide (possibly V6O13) and then remains stable. It was possible to drill holes in V2O5with an intense, small electron probe (using a field-emission electron gun) provided the sample had previously only been exposed to an electron dose below a critical value (<108e/nm2). Preliminary doses higher than this critical value rendered the oxide immune to hole drilling (but not to a subsequent reduction to the stable oxide mentioned above), suggesting that holes can only be drilled while the material retains the original V2O5structure.
Ion Beam Enhanced Grain Growth in Thin Films
Authors: Atwater Harry A. , Tiiompson Carl V. , Smith Henry I. 
Published: March 2011

AbstractIon beam enhanced grain growth has been investigated in thin films of Ge. Grain boundary mobilities are greatly enhanced over their thermal equilibrium values and exhibit a very weak temperature dependence. We propose that defects which are generated by the ion beam at or near the grain boundary are responsible for the boundary mobility enhancement. Films of Ge deposited under different conditions, either unsupported or on thermally oxidized Si, exhibit similar normal grain growth enhancement when implanted with 50 keV Ge+. Beam-enhanced grain growth in Ge was also demonstrated using Xe+, Kr+, and Ar+ ions. The variation in growth enhancement with projectile ion mass is in good agreement with the enhanced Frenkel defect population calculated using a modified Kinchin-Pease formula and Monte Carlo simulation of ion transport in thin films. Calculations based on experiments suggest that there is approximately one atomic jump across the grain boundary per defect generated. Also, the grain growth rate for a given beam-generated defect concentration near the boundary is approximately equal to the expected growth rate for the same defect concentration if thermally generated.
Characteristic Comparison Between Ge-on-Insulator (GOI) and SI-on-Insulator (SOI) Beam-Induced Crystallization Mechanism
Authors: Lee El-Hang , Awal M. Abdul 
Published: March 2011

AbstractCharacteristics of beam-recrystallized Si-on-insulator (SOT) and Ge-on-insulator (GOI) material systems are compared for the first time to gain complementary understanding of the crystallization mechanism that would benefit both systems. In general, GOI has been found to behave quite differently from SOI. In SOI, Si yields sub-boundaries; in GOI, Ge generates twinned or faceted crystals. In GOI, too, sub-boundary-like features were observed, but only occasionally in the midst of twinned crystals. Also observed in GOI was the phenomenon of seeded crystallization breakdown, where defect-free crystals from the seed abruptly turn into defect-laced crystals at a certain distance from the seed. This phenomenon is highly characteristic in SOI, but has never been reported for GOI. These findings are compared and discussed in light of the traditional understanding of crystal growth.
The Role of Low-Energy Ion/Surface Interactions During Crystal Growth From the Vapor Phase
Authors: Greene J. E. , Rockett A. , Sundgren J.-E. 
Published: March 2011

AbstractLow-energy (often < 100 eV) ion bombardment during thin film deposition is commonly used in such diverse application areas as microelectronics, optical coatings. magnetic recording layers. and hard wear resistant coatings to modify the microstructure and microchemistry of films deposited by a variety of techniques (e.g. sputtering, primary ion deposition, plasma-assisted CVD, and accelerated-beam MBE). Ion irradiation has been shown to affect every phase of deposition including nucleation and growth kinetics, crystal structure and phase stability, the average grain size and degree of preferred orientation of polycrystalline films, the epitaxial temperature of single-crystal films, defect concentrations, elemental incorporation probabilities, surface segregation, and, hence, film properties. As discussed in this brief review, a detailed understanding of many of these processes is beginning to emerge. Effects such as trapping, preferential sputtering, enhanced diffusion, and collisional mixing have been used to interpret and, in some cases, model experimental results. Nevertheless, there are still large gaps in our knowledge of the role of ion bombardment on fundamental processes such as nucleation kinetics.