bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Resonance as a Structural Probe of a Uranium (Vi) Sol-Gel Process
Authors: King Charles M. , Bruce King R. , Ronald Garber A. , Thompson Major C. , Buchanan Bruce R.
Published: March 2011

Nuclear Magnetic Resonance (NMR) investigations on the Oak Ridge National Laboratory process for sol-gel synthesis of microspherical nuclear fuel (UO2), has been extremely useful in sorting out the chemical mechanism in the sol-gel steps. 13C, 15N, and 1H NMR studies on the HMTA gelation agent (hexamethylenetetramine, C6H12N4) has revealed near quantitative stability of this adamantane-like compound in the sol-gel process, contrary to its historical role as an ammonia source for gelation from the worldwide technical literature. 17O NMR of uranyl (UO2++) hydrolysis fragments produced in colloidal sols has revealed the selective formation of a uranyl trimer, [(UO2)3 (μ3-O)(μ2-OH)3]+, induced by basic hydrolysis with the HMTA gelation agent. Spectroscopic results will be presented to illustrate that trimer condensation occurs during sol-gel processing leading to layered polyanionic hydrous uranium oxides in which HMTAH+ is occluded as an ‘intercalation’ cation. Subsequent sol-gel processing of microspheres by ammonia washing results in in-situ ion exchange and formation of a layered hydrous ammonium uranate with a proposed structural formula of (NH4)2 [(UO2)8 O4 (OH)10]- 8H2)O. This compound is the precursor to sintered UO2 ceramic fuel.
Oxygen-17 Nmr Studies of Uranium (VI) Hydrolysis and Gelation
Authors: Bruce King R. , King Charles M. , Ronald Garber A.
Published: March 2011

Hydrolysis and gelation processes in uranyl solutions are observed using the strong sharp uranyl oxygen-17 resonance.
Mechanical Properties of Silica Alcogels and Aerogels.
Authors: Woignier T. , Phalippou J. , Hdach H. , Scherer G.W.
Published: March 2011

The mechanical properties of silica gels (alcogels and aerogels) are measured by three point bending. The elastic moduli (E,G) and the fracture strength (σ) are investigated as functions of the concentration of silicon precursor, the catalysing conditions, and the aging time.

Elastic moduli and strength follow scaling laws as a function of the bulk density of the solid. The scaling exponents are discussed in terms of percolation theory.

The evolution of the mechanical properties is also followed during the steps of the gel to glass transformation:

- hypercritical drying

- oxidation of the organic groups

-densification heat treatment

At each step of the process the increases of the elastic moduli and σ are related to the gel structure. During the hypercritical drying flexible “dead ends” in the network can condense and form new links. The connectivity is also enhanced by the removal of the organic groups creating siloxane bonds. Finally densification leads to a material having mechanical properties identical to those of conventional vitreous silica.
Simple Models for Particle Aggregation, Deposition and Segregation
Authors: Meakin Paul
Published: March 2011

Most conventional and experimental methods for the formation of ceramic objects involve the manipulation of small particles and/or structures comprised of these particles. Consequently, a better understanding of the physics and chemistry of small particles could contribute to the development of better ceramics. Here the results of some recent computer simulation studies of processes such as particle aggregation, deposition and segregation are surveyed. More realistic models are needed to represent accurately the behavior of most real systems.
Mechanisms of Silica and Titania Colloidal Particle Formation from Metal Alkoxides
Authors: Bailey Joseph K. , Mecartney Martha L.
Published: March 2011

Control of the preparation of monodisperse particles for green body formation can be achieved by understanding the growth mechanism. Growth processes for colloidal silica and titania were followed by cryo-TEM, which allows direct observation of the particles in the liquid state. Structural development was tracked by quenching samples at successive reaction times. The preparation of silica particles involved the formation of ramified species which subsequently collapsed after reaching a certain size. In the titania system, initially small dense nuclei are observed which eventually form uniformly textured homogeneous particles.
Rheological and Related Colloidal Aspects of Aqueous Processing that affect the Development of Microstructure
Authors: Bleier Alan , Gary Westmoreland C.
Published: March 2011

Shear flow in α-A12O3 suspensions having a volume fraction of solids (φ) in the range between 0.17 and 0.50 was investigated between pH 4 and 12. It is Newtonian if the magnitude of the zeta potential exceeds a critical value which depends on φ;its value is 39 mV if φ= 0.40 and 74 mV if φ= 0.50. If this potential is less than the critical value, shear flow is pseudoplastic; its yield value markedly changes (e.g., 0 to >100 Pa) in a slightly φ-dependent, narrow pH range (<0.5 units). If a second oxide, t-ZrO2 , is present, its pH-dependent colloidal behavior governs the overall rheology, though its concentration may be only 11 % that of α-A12O3. Scanning electron microscopy of composite pieces indicates that a detrimental, rheologically detectable interaction between α-Al2O3 and t-ZrO2 can be avoided and the distribution of t-ZrO2 can be optimized during pressure casting by control of pH. Best conditions correspond to either Newtonian flow or pseudoplastic flow with a very low yield value.
Preparation of Multicomponent Ceramic Powders by Sol-Gel Processing
Authors: Bartlett J.R. , Woolfrey J.L.
Published: March 2011

Sol-gel methods have been applied to the production of the multicomponent ceramic, Synroc B. These techniques involved the hydrolysis of a mixture of Ti and Zr, alkoxides peptising to form a sol and subsequent sorption of Al3+, Ba2+ and Ca2+ cations under acidic conditions. Powder properties were examined by a variety of techniques, including electron microscopy, x-ray diffraction, N2 sorption, and differential thermal analysis. The effects of processing conditions on the physical properties of the powders are discussed.
Base-Catalyzed Silica Gels: Structure and Chemistry
Authors: Garvey Garry J. , Smith Bruce E.
Published: March 2011

The chemical and physical properties of two base-catalyzed silica gels systems were characterized. The sol-gel transition was studied by titration, rheometry, and NMR. Pyrolysis behavior was monitored by TGA and mass spectroscopy. Many characteristics were strikingly similar for the two base-catalyzed systems. However ammonium hydroxide additions resulted in heterogeneities at lower concentrations than ammonium carbonate. Ammonium carbonate enhanced oxidation on pyrolysis.
Catalytic Control of SiO2 Sol-Gel Kinetics - a Mechanistic Study of Bases
Authors: Sanchez Jorge , Reese Mary , Mccormick Alon
Published: March 2011

The aim of this research was to determine the relative effects of three different base catalysts (NaOH, NH4OH, and RbOH) on the rate of gelation of SiO2 from reactive silicon ethoxide solutions in alcohol (the sol/gel method). The time to gelation was determined using a reaction protocol which assured that condensation was the rate controlling step. NMR spectroscopy was used to verify that the nature of the reacting polymers remained similar as the base catalyst was varied. It was determined that under these conditions the condensation reactions avoid diffusional limitations. Furthermore, the base catalyst serves to modulate both the activation energy and also the Arrhenius preexponential factor. This leads to the proposal of a new condensation mechanism.
Organic Catalysts in the Silica Sol-Gel System
Authors: Gallo T.A. , Simms B.L. , Brice V.T.
Published: March 2011

Ethyl silicate-derived silica gels were synthesized with organic acid and base hydrolysis catalysts. The nature of the organic catalyst was found to strongly affect dry gel structure and carbon content. No consistent relationship between dry gel structure and water content of the calcined gels was identified.
Solvent Selection and the Control of Sol-Gel Reactions
Authors: Jones K , Boulton J M , Emblem H G
Published: March 2011

The hydrolysis and gelation sequence occurring in the formation of a filament or a rigid coherent gel from an organic silicate requires a mutual solvent for the organicsilicate and water if it is to proceed successfully. The solvent is usually a water-miscible alcohol. This alcohol can also be a reaction product, which makes the sequence very solvent dependent. The best control of both hydrolysis and gelation is obtained when the alcohol solvent and the organic silicate each contain the same alkoxy group. The gel resulting is also the best binder for refractory grain. Suitable systems are ethyl silicate and ethanol also isopropyl silicate and isopropanol. The formation of rigid coherent gels, or filaments which on firing convert to ceramic fibres, from hydrolysates of ethyl silicate and aluminium chlorhydrate species is also very solvent dependent. With glycol solvents, aluminium chlorhydrates do not form filaments nor ceramic fibres. With ethanol as solvent, aluminium chlorhydrate-polyol complexes readily form rigid coherent gels and filaments, hence ceramic fibres, because the polyol complex is formed by displacing coordinated water in the aluminium chlorhydrate. This reduces the amount of water available for reaction, which optimises filament and fibre formation.
Preparation of the Porous Supports With SiO2-ZrO2-Na2O Composition.
Authors: Tsurita Y. , Wada K.
Published: March 2011

A new method for preparation of porous mixed oxide with SiO2 -ZrO2 -Na2O composition was investigated by heating the sol-gel derived SiO2 microsphere gel in the presence of ZrOCl2 and NaCI. Surface of the -products was composed of sponge-like structure, similar to the porous glasses manufactured by the phase separation method. Their pore volumes ranged from 1.0 to 1.5 cc/g(pore radius 100–lO00Å) and their pore distributions were sharp, with peak tops of about 450–600Å in radius.
Sol-Gel Synthesis of thin Films for use as Planar Waveguides
Authors: Dale G.W. , Fox H.H. , Zelinski Brian J.J. , Weller-Brophy Laura
Published: March 2011

SiO2-TiO2 sol-gel solutions and synthesis techniques have been developed to produce thin films of proper index, thickness and quality for use as planar waveguides. The composition of the synthesized films ranged from 50 to 68 mole % TiO2 and produced layers with indices ranging from 1.7 to 1.8. Final film thicknesses ranged from 1000 to 3000 A and varied as a function of the coating chemistry and conditions. Also, changes in film shrinkage and index with heat treatment were determined and compared to literature data on similar films used as antireflective coatings. Finally, confirmation of the waveguiding qualities of these films was made through prism coupler measurements conducted by the University of Arizona Optical Sciences Center.
Sol-Gel Thin Film Electronic Properties
Authors: Warren W. L. , Lenahan P. M. , Brinker C. J. , Shaffer G. R. , Ashley C. S. , Reed S. T.
Published: March 2011

We have explored the effects of various processing parameters on the dielectric and
electronic integrity of sol-gel derived silicate thin films and have identified several factors that strongly affect the thin film electronic properties. We find that sol-gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown SiO2 film on Si.
Sol-Gel Deposition of Electronic Ceramic Films.
Authors: Bell J.M. , Ben-Nissan B. , Anast M. , West B.O. , Spiccia L. , Cullen J. , Watkins I. , Devilliers D. , Johnston G.
Published: March 2011

We describe a dip-coating method of depositing thin electronic ceramic coatings on various substrates from sol-gel solutions. The solutions we use are alkoxide-based, although the specific formulations depend on the system being deposited. We are working with two electronic ceramic systems: barium titanate on glass, and alumina, and yttrium barium copper oxide on alumina. We discuss methods used to reduce and remove processing defects such as crazing, cracking and pin-holing. We are also studying the effects of varying the processing conditions (dipping, hydrolysis and firing) on the electronic properties of the films. Initial results on BaTiO3 indicate that it is better to deposit thin films (∼0.1 – 0.2μm) and build up the coating thickness by repeated dipping.
Glasses and Multi-Component Sol-Gels for Use as High-Temperature Protective Coatings
Authors: Devore Lauri J. , Osborne Nora R.
Published: March 2011

Two multi-component sol-gel compositions were developed and compared to several commercially available high-temperature glasses. All were then used and characterized as protective coatings for intermetallic titanium aluminide.

The sol-gels were studied as thin film coatings and the commercial glasses were studied as enameled coatings. Attention was given to (1) the effect of the application temperature on the original microstructure of the metal, and (2) the role of interfacial conditions between the glass and metal in cyclic and isothermal thermal cycles between ambient temperature and 760°C (1400°F).
The Process of Gel Fiber Formation
Authors: Taneda N. , Kawaguchi T. , Arai D. , Matsuzaki K.
Published: March 2011

The gel fiber formation was studied for the spinnable silica sols prepared from a mixture of TEOS, H2O, EtOH and HNO3 ( 1 : 2 : 2 : 0.01, in mole ratio). The effect of polysiloxane molecular size in the spinning sol on spinnability indicated that the tough skeleton of gel, which is preferable for fabrication of high-strength fiber without breakage, was formed by the selective connection of large size polymers (about 106 in M.W.) during the spinning. It was also found that the smaller size polymers in gel fiber continued to react with water in the atmosphere after the spinning, and attached to the skeleton to strengthen the fiber.
Inhomogeneities In Sol-Gel Coatings
Authors: Fabes. B. D. , Klein. D. L. , Raymond L. J.
Published: March 2011

The structure of sol-gel derived silica coatings was investigated using nanoindentation. chemical etching. and cross-sectional TEM. For coatings heated at 100°C. the surfaces were harder, etched slower, and appeared less porous than the interior of the coatings. For samples fired at higher temperatures (400–800°C). the surfaces remained harder and etched slower than the interior. even though the porosity appeared to be evenly distributed throughout the thickness of the coating. It is proposed that this difference is due to inhomogeneities on two scales in the coatings: bulk porosity and skeletal strain.
Grin Rod of Large Diameter and Large Delta-N
Authors: Yamane Masayuki , Yasumori Atsuo , Iwasaki Mitsunobu , Hayashi Kazutaka
Published: March 2011

A gradient-index glass rod of about 13 mm in diameter and 20 mm in length with the refractive index difference of about 0.05 between center and perimeter has been prepared by the solgel process from a precursor solution consisted of tetramethoxysilane, tetraethoxysilane, boron ethoxide and aqueous solution of lead acetate. A bubble free wet gel of about 35 mm in diameter and 50 mm in length was obtained by adding acetic acid to the precursor solution as a buffering agent. The liquid in the micropores of the wet gel was totally replaced with acetone. Then the compositional gradient of lead was formed in radial direction of the gel by soaking in an ethanolic solution of potassium acetate. A transparent r-GRIN rod of about 10 mm in diameter was obtained by the sintering of the gel at 580°C.
Studies on the Reproducible Production of Grin (Gradient Index) Glass Rods By A Sol-Gel Process
Authors: Brian Caldwell J. , Che Tessie M. , Cruse Richard W. , Mininni Robert M. , Nikles Randall E. , Warden Victor N. , Banash Mark A.
Published: March 2011

Optical quality radial gradient-index (GRIN) glass can be made by first leaching a TiO2-Al2O3-SiO2 gel in aqueous sulfuric acid solution, then drying and firing the gel. In this paper, we present details of a study on the reproducible production of GRIN glasses by this sol-gel process. Physical and optical data on the intermediate gels and resulting gradient-index glass will be discussed.
Optical Switches Based on Vanadium Dioxide Films Grown By The Sol-Gel Process
Authors: Potember Richard S. , Speck Kenneth R.
Published: March 2011

Vanadium dioxide thin films have been grown from vanadium tetrakis (t-butoxide) by the sol-gel process. A new method for the synthesis of the vanadium precursor was also developed. Films were deposited by dipcoating glass slides from an isopropanol solution, followed by post-deposition annealing of the films at 600°C under nitrogen. The properties of these films, to a high degree, were a function of crystalline boundaries and crystalline grain size. These gel-derived VO2 films undergo a reversible semiconductor-to-metal phase transition near 72°C, exhibiting characteristic resistive and spectral switching comparable with near stoichiometric VO2 films prepared on non-crystalline substrates by other techniques. Films were doped with hexavalent transition metal oxides to demonstrate lowering of the transition of the transition temperature.
Preparation of Phenylsiloxane Films VIA Solution Deposition Techniques
Authors: Burkhardt E.W. , Burford R.R. , Deatcher J.H.
Published: March 2011

Thin films (1–10μ thick) can be spin coated on a variety of substrates from formulations containing polyphenylsiloxanes and alkylsilicates. These films may be cured either thermally or photochemically, yielding films with good adherence to the substrate. The combination of photolysis and thermolysis results in changes in the film hardness characteristics. The use of a mask during photocuring results in films which may be developed in either a positive or negative fashion. The preparation of various formulations along with film curing processes will be discussed.
Polymerizations of Alkenylsilanes Using Early Transition Metal Catalysts
Authors: Masnovi John , Bu Xin Y. , Conroy Paula , Harry Andrist A. , Hurwitz Frances I. , Miller Doug
Published: March 2011

Oxidative coupling of primary alkylsilanes catalyzed by Group IVB metallocene complexes leads predominantly to linear polysilanes, as first reported by Harrod. We have investigated the polymerization of ethylsilane and vinylsilane using dimethyltitanocene in order to determine the suitability of such polymers as precursors to Si-C based ceramics for application as coatings or composite matrices. A photochemical procedure for initiation of polymerization is described. Ethylsilane forms polysilanes (which contain a -Si-Si-Si-Si- backbone) by a step growth mechanism. Vinylsilane shows some Si-Si formation; however, polymerization by several different routes, including formation of polycarbosilanes (which contain a -Si-C-SI-C- backbone) by hydrosilation reactions and crosslinking via metathesis, predominate. The carbosilane polymer has high char yield (60-75%) and appears advantageous for conversion into silicon carbide, as determined by X-ray diffraction.
The use of Soluble Metal-Polyselenide Complexes as Precursors to Binary and Ternary Solid Metal Selenides
Authors: Dhingra S. , Kanatzidis M. G.
Published: March 2011

The use of several soluble metal polychalcogenides to prepare solid state materials is presented. Thermal gravimetric analysis (TGA) data, under inert atmosphere, of the molecular compounds (Ph4P)2[Cd(Se4)2], (Ph4P)4[Cu2Se14], (Ph4P)2[Cu4Se12], (Ph4P)4[In2Se21] and (Et4N)3[M3Se15], (M=In, TI), show that the corresponding binary solid state compounds are formed as single phases at temperatures as low as 530°C. We have grown films of CdSe, Cu2-xSe, β-In2Se3, TISe and CuInSe2 using these complexes as precursors. The films were prepared by pyrolysis of green precursor films, cast from DMF solutions. CuInSe2 was prepared by co-thermolysis of Cu/Sex and In/Sex complexes. The chemical, X-ray, spectroscopic and electron microscopic characterization of these molecular precursor-derived films as well as their charge transport characterization is reported.
Plasma Synthesis of Fine Ceramic Powders by a Novel Counter-Flow Liquid Injection Method.
Authors: Kong P. , Or T.W. , Stachowicz L. , Pfender E.
Published: March 2011

Ceramic powders of carbides, oxides, solid solutions of oxides, magnetic and non-magnetic spinels, superconductors and composites have been successfully synthesized in a thermal plasma jet reactor using a novel counter-flow liquid injection plasma synthesis (CF LIPS) method developed to overcome the problems associated with solid injection and to realize the benefits of gas phase reactions and counter-flow injection. Standard material characterization techniques have been used for powder analysis.
Superconducting Fibers from Anhydrous Metal Carboxylates
Authors: Laine Richard M. , Youngdahl Kay A. , Kennish Richard A. , Hoppe Martin L. , Zhang Zhi-Fan , Jean Ray D.
Published: March 2011

A variety of anhydrous Y, Ba and Cu carboxylates were synthesized and screened for utility as spinnable precursors to 123 superconducting fibers. Simple extrusion studies demonstrate that THF solutions of mixtures of Y, Ba and Cu isobutyrates with some Ba 2-ethyl- hexanoate can be used to form 70 μm dia. precursor fibers. Following a curing at 150°C for 24–48 h, pyrolysis of these fibers in air to 900°C, with controlled heating rates, gives dense, flexible ceramic fibers 15–20 μm in dia. These fibers have the appropriate orthorhombic phase. Flux exclusion measurements indicate the fibers are superconducting; but ΔTc is not optimal.
Polyfunctional Carboxylic Acids as Coprecipitating Agents For Barium, Yttrium, and Copper
Authors: Hallock Robert B. , Rexer P.O. , Jolly M.S. , Rhine W.E. , Cima M.J.
Published: March 2011

The suitability of several polyfunctional carboxylic acids as coprecipitating agents for Ba, Y, and Cu was investigated. Essentially complete precipitation from alcoholic solutions was achieved for all three metals when tartaric acid was employed as the precipitating agent. The amorphous precipitate formed under these conditions was composed of uniform particles about 50 nm in diameter, and was converted readily to high purity Ba2YCu3O7−x.
Ten Minute Preparation Of Yba2Cu3O7−x Using Barium Hydroxide
Authors: Coppa N. , Kebede A. , Schwegler J. W. , Perez I. , Salomon R. E. , Myer G. H. , Crow J. E.
Published: March 2011

High quality bulk YBa2CuOx−7 was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide, in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated, (900 C, 18–24 h, in air, followed by 500 C, 5 h., in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnetic response (field cooled), 76% (zero field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly
Rubbery Ormosils
Authors: Chung Young J. , Ting Su-Jen , Mackenzie John D.
Published: March 2011

A new technique which permits the successful preparation of ORMOSILS (Organically Modified Silicates) with rubbery elasticity has been developed. Common alkoxides were reacted with polydimethyl siloxane (PDMS) and the microstructures were carefully controlled. Large monoliths of the porous rubbery ORMOSILS have been prepared. Gelation process was studied by 29Si liquid NMR spectroscopy. A structural model for rubber elasticity of ORMOSILS was proposed.
Applications of Solid Phase Doping in Manufacturing MOS Devices
Authors: Gong S. F. , Hentzell H. T. G. , Robertsson A.
Published: March 2011

Solid phase doping from Sb heavily-doped Si films has been studied by using transmission electron microscopy and secondary ion mass spectroscopy. Based on the results of the material study, metal-oxidesemiconductor field effect transistors (MOSFETs) made on a (100) Si wafer, and thin film transistors have been implemented. The technique for the MOSFETs suggests the possibility for making small dimensional and high speed integrated circuits by using the method of solid phase doping.
Effect of Grain Boundary Segregation on the Transbarrier Conductivity of Polycrystalline Silicon
Authors: Pizzini S. , Acciarri M.
Published: March 2011

The conductivity of single grain boundaries of electronic grade, Bridgman grown polycrystalline silicon samples was measured using the dc polarization technique with the aim of detecting any influence on the carrier transport regime resulting from the segregation of oxygen and carbon, which, by themselves, should behave as electrically inactive impurities. To this scope as grown samples and samples heat treated at 1123 and 1223 K, differing in their initial oxygen and carbon content, were used and the conductivity measured in the 298-100 K range.

The results indicate that for both the carbon rich and for the oxygen rich samples the conductivity across the grain boundaries is of the thermally activated type and that it could be discussed in terms of carriers which are thermally emitted over the barrier and cross the barrier in the limit of the short mean free path.

Samples which do not present a net excess of oxygen or carbon, apparently behave as single crystal specimens, instead.

The deconvolution of the I-V curves is then used for obtaining the densitl of the interface states responsible of the set-up of the grain boundaries barrier, whose shape supports a completely new hypothesis about the configuration of the impurity cloud at the grain boundaries.
In Situ Hrem Observations of Crystallization in LPCVD Amorphous Silicon
Authors: Morgiel J. , Wu I.W. , Chiang A. , Sinclair R.
Published: March 2011

This article describes the application of in situ, high-resolution electron microscopy to the study of crystal nucleation and growth in amorphous silicon. It is shown that dynamic events at elevated temperatures (e.g. 600-750°C) can be recorded at the atomic level by such an approach. It is anticipated that fundamental information, important for the technological development of polysilicon thin films, can be generated by work of this type.
Characterization of Polycrystalline Silicon Thin Films by Photoluminescence
Authors: Pandya R. , Shahzad K.
Published: March 2011

Photoluminescence (PL) measurements have been carried out in hydrogenated and as deposited polycrystalline silicon thin films deposited on quartz substrates. Behavior of the PL spectrum as a function of temperature and intensity in the hydrogenated samples is reported. A mechanism that provides a qualitative explanation for the observed PL results is described. In the unhydrogenated sample the signal was much weaker and we were unable to observe any signals over an appreciable range of intensity and temperatures. The cause for much lower signals in the unhydrogenated sample is most likely due to higher surface recombination velocity.
Electrical and Structural Characterization of Polysilicon Deposited in a Rapid Thermal Processor
Authors: Ren X. , Öztüirk M.C. , Wortman J.J. , Batchelor D. , Maher D. , Blat C. , Niccolian E.
Published: March 2011

Low pressure chemical vapor deposition of polysilicon in a lamp heated rapid thermal processor (RTCVD) has been studied. Polysilicon films were deposited using SiH4 diluted in Ar. Structural characterization of the films was accomplished by transmissionelectron microscopy (TEM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), auger electron spectroscopy (AES) and ultraviolet surface reflectance measurements. Smooth polysilicon films were obtained at deposition temperatures above 700ºC with rms roughness values better than 100 Å. Both p- and n- polysilicon gated MOS capacitors were fabricated using 80 - 200 Å thick gate oxides grown by dry oxidation in a conventional furnace. Polysilicon doping was achieved by ion-implantation and rapid thermal annealing (RTA). Our results show that the electrical properties ofthe capacitors fabricated using RTCVD polysilicon are comparable to those of conventional polysilicon. Dopant diffusion through the gate is a problem for both types of polysilicon and can lead to a degradation of the electrical properties.
Polysilicon Thin Film Transistors
Authors: Yudasaka Ichio , Ohshima Hiroyuki
Published: March 2011

Polysilicon thin film transistors are now in mass production. Key factors of the success are thinner polysilicon film and thermal oxidation. Practical applications of polysilicon thin film transistors have been limited, however, because of high temperature processing. Alternative technologies to thermal oxidation are very low pressure deposition, solid-phase crystallization, laser-annealing and hydrogenation. These technologies are compatible with low temperature processing and will contribute to the advance of polysilicon thin film transistors in the future.
Measurements of Grain Boundary Trap Density and Hydrogen Diffusivity in Polycrystalline Silicon Fet's
Authors: Moore Chad B. , Ast Dieter G.
Published: March 2011

Hydrogen diffusion in as-deposited and in oxidation-annealed polycrystalline silicon films was investigated using n-type accumulation-mode MOSFET's. The diffusion was studied by measuring the reduction in the grain boundary trap density with hydrogenation time. The number of traps in fully hydrogenated as-deposited films fell to about 45% of the initial trap state density and fell to about 20% in the oxidized-annealed films. Concurrently, the mobility increased about 95 % to 5cm2/Vs in the as-deposited films and by about 55 % to 25 cm2/Vs in the oxidized polysilicon devices. The effective preexponential diffusion coefficient and activation energy for hydrogen diffusion in the two different films were Do= 5.4×10−10 cm2/s and EA= 0.37 eV for the as-deposited polysilicon and Do=2.1×10−10 cm2/s and EA= 0.36 eV for the oxidized polysilicon.
Effect of Gate Dielectric on Performance of Polysilicon thin Film Transistors
Authors: Hatalis Miltiadis K. , Kung Ji-Ho , Kanicki Jerzy , Bright Arthur A.
Published: March 2011

The effect of gate dielectric on the electrical characteristics of n-channel polysilicon thin film transistors was investigated. The following insulators were studied: silicon dioxide grown by wet oxidation, silicon dioxide deposited by plasma enhanced chemical vapor deposition (PECVD) and nitrogen-rich silicon nitride deposited by PECVD. It was observed that the effective electron mobility in TFTs having a deposited dielectric, either silicon nitride or silicon dioxide was higher than that measured in devices with grown silicon dioxide. The TFT leakage current was found to be lowest in devices with PECVD silicon nitride. Devices with deposited dielectrics did not degrade after a positive gate bias stress. However, reduction of the threshold voltage was observed in devices with PECVD silicon nitride, when they were subjected to a negative gate bias stress.
Properties of in Situ Doped Polycrystalline Silicon Films Deposited from Phosphine and Disilane
Authors: Madsen Lynnetie D. , Weaver Louise
Published: March 2011

The deposition of in situ phosphorus doped silicon films was performed using disilane (Si2H6) instead of monosilane (SiH4) as the silicon source gas. The negative aspects of in situ doping with phosphine, namely low deposition rates and poor across wafer uniformity, were to a large extent eliminated. Haze-free polycrystalline films were deposited at ∼60 Å-min1 with less than 5% radial thickness variation over a 100 mm wafer. However, the temperature suitable for depositing films using Si2H6 was shifted downward from that used for SiH4 and similarly, the conditions for good quality (haze-free)films were adjusted. Within specific temperature ranges, varying the gas pressure, flow,and Si2H6 to PH3 ratio resulted in the formation of oneof three types of haze. The films produced had unusually low resistivities of ∼770 μohm-cm after furnace annealing at 850ºC for 1800s. A 20 nm thick surface layer of amorphous silicon oxide was revealed during transmission electron microscopy (TEM) examination of annealed films. Although this oxide layer was undoped, the phosphorus gradient, measured by energy dispersive x-ray analysis (EDX) and secondary ion mass spectroscopy (SIMS), increased towards the surface of the polycrystalline film, suggesting that dopant was diffusing to the surface. A matrix involving different annealing and capping layers was conducted to investigate this phenomenon further. Extremely large grains resulted when a capping layer of SiO2 was deposited prior to rapid thermalannealing (RTA). An autodoping effect was observed when another capping layer, such as undoped polycrystalline silicon, was used.
Thermal Stability of CoSi2 on Single Crystal and Polycrystalline Silicon
Authors: Phillips J. R. , Revesz P. , Olowolafe J. O. , Mayer J. W.
Published: March 2011

The thermal stability of Co silicide on single crystal and polycrystalline Si has been investigated. Co films were evaporated onto (100) Si and undoped polycrystalline Si and annealed in vacuum. Resulting silicide films were examined using Rutherford backscattering spectroscopy, scanning electron microscopy, electron—induced x—ray spectroscopy, and sheet resistivity measurements. We find that CoSi2 on single crystal (100) Si remains stable through 1000ºC. In contact with undoped polycrystalline Si, intermixing begins at temperatures as low as 650ºC for 30min annealing. The Co silicide and Si layers are intermixed after 750ºC 30min annealing, giving islands of Si surrounded by silicide material, with both components extending from the surface down to the underlying oxide layer. The behavior of CoSi2 contrasts with results reported for TiSi2 which agglomerates on single crystal Si around 900ºC but is stable on polycrystalline silicon as high as 800ºC. Resistivity measurements show that the Co silicide remained interconnected despite massive incursion by Si into the silicide layer.
Cobalt Silicide Formation on Polysilicon: Dopant Effects on Reaction Kinetics and Silicide Properties
Authors: Sitaram A.R. , Murarka S.P.
Published: March 2011

The concept of using cobalt disilicide as a self-aligned metallization scheme for gate/interconnection and contact formation is gaining wide acceptance. The silicide formation on the gate will require a Co-metal film interaction with the underlying polysilicon that may be doped heavily. We have investigated the silicide formation kinetics during this reaction. The effect of different dopants (B,P, and As) and their concentration on the Co-Si interaction and the dopant redistribution during such reactions were investigated. The results from these studies will be presented and discussed.
Microanalysis of Tungsten Silicide/Polysilicon Interface: Effectiveness of in Situ Rie Clean on Removal of Native Oxide
Authors: Nowicki Ronald S. , Geraghty Patrice , Harris David W. , Lux Gayle
Published: March 2011

The presence of a thin (10-30Å) oxide (“native oxide”) layer on a silicon surface prior to the deposition of another film on that surface can contribute todifficulties with subsequent device processing steps, e.g. contact metallization and hightemperature annealing or oxidation. Thus, the in situ process capability of “native oxide” removal affords an advantage over the conventional method of aqueous hydrofluoric acid cleaning prior to a film deposition step. This study describes such a technique, in which an in situ pre-deposition clean with C2F6 gas, using reactive ion etching (RIE) prior to tungsten silicide deposition, is employed. This technique allows post-silicide deposition high-temperature heat treatment and wet oxidation without loss of film adhesion or other obvious degradative effects. We also report the useof Secondary Ion Mass Spectrometry (SIMS) to show that this procedure has een effective in the removal of the oxide layer prior to silicide deposition. This study includes definition of the RIE etch parameters which provide acceptable etch selectivity of the oxideto silicon, and avoidance of excessive fluoropolymer formation on the silicon surface.
Rapid Thermal Annealed TIW/TI Contact Metallization for Advanced VLSI Si Circuits
Authors: Chung Henry W. , Yao Agnes T.
Published: March 2011

Rapid thermal annealed (RTA) bilayers of TiW/Ti were evaluated for contact metallization in advanced VLSI Si circuits. It was found that RTA and a minimum thickness of Ti are necessary to achieve consistently low + contact resistance. RTA has little effect on n+ and polysilicon contact resistances. With RTA, TiSi2 is formed at the Ti/Si interface and a thin nitrogen—containing layer is formed on the TiW surface. By controlling RTA temperature and time, the interaction between Si and TiW during RTA could be minimized while the gain factor of p—channel MOSFETs was not degraded. Moreover, the leakage currents of n+ and p+ contact chains did not increase after 30 minute anneals up to 525C.
Hrem of Defects in Silicon at Twin Intersections
Authors: Hetherington C. J. D.
Published: March 2011

Defects found in and around intersections of deformation twins have been examined by high resolution electron microscopy. Experimental difficulties, especially local buckling of the crystal and radiation damage under the electron beam, lead to a need to interpret images of lattices tilted by almost a degree from the zone axis. This paper demonstrates the ability of image simulation programs to model successfully the scattering from a tilted crystal. It is shown how the generation of moir6 patterns between a lattice image and a reference array of dots offers a convenient method for extracting information about distortions of the lattice around defects.
Misfit Dislocations at II-VI/GaAs Interfaces
Authors: Schwartzman A. F.
Published: March 2011

High-resolution electron microscopy -is used to characterize the defect structure of CdTe/GaAs and ZnTe/GaAs heterojunctions before and after annealing. For as-deposited films, a variety of defects exist both in the form of perfect misfit dislocations at the interface and extended defects into the thin film. The extended defects result from dissociation of 60° dislocations and reactions between perfect and partial dislocations lying on intersecting slip planes. The annealed interfaces consist of a periodic array of perfect edge Lomer dislocations, the most efficient type of misfit dislocation for accomodating the lattice mismatch, 14.6 % for CdTe/GaAs and 8 % for ZnTe/GaAs. In both cases, the spacing between dislocations corresponds to the value predicted for completely strain-free thin fims, 31 and 54 Å for CdTe and ZnTe respectively. This paper concentrates on the different dislocation reactions which transform the interfacial structure from the as-deposited case to the annealed case.
High Resolution Imaging of Twin and Antiphase Domain Boundaries in Perovskite KNbO3 Thin Films.
Authors: Rou Shang H. , Hren Philip D. , Hren John J. , Graettinger Thomas M. , Ameen Michael S. , Auciello Orlando H. , Kingon Angus I.
Published: March 2011

Perovskite KNbO 3 thin films were heteroepitaxially deposited onto (100) MgO substrates. Twin domains with tetrahedral shape were typically observed. These tetrahedrons were bounded by three {211} twin planes. High resolution transmission electron microscopy (HRTEM) was employed to examine these {211} twin boundaries. Surface steps of {110}<110> type generated by dislocation slip were present on the MgO substrate. The tetrahedral twin domains originate on surface steps, then grow with a stacking fault relationship to the matrix. The strain fields of dislocations near the stacking faults slightly rotate the tetrahedral twin nuclei. This small degree of misalignment between the matrix and the twin domain result in some of the twin boundaries having amorphous boundary regions rather than coherent interfaces.

Order-disorder antiphase domains (APD's) were directly imaged with HRTEM. Ultra small APD's ranging from 10 to 30 atomic spacings were observed. The origin of these APD's was either the surface steps of {100} <1 10> type on MgO substrates or the random nucleation of anions at either of two equivalent sites on the MgO substrate.
The Interpretation of HRTEM Images of Partially Amorphized Pyrochlore Structure Types.
Authors: Miller Mark L. , Ewing R. C.
Published: March 2011

The results of image simulations on partially amorphous microlite (Ca2Ta2O7, pyrochlore structure) are presented. Results indicate that HRTEM images are not sensitive to the position of amorphous layers within a crystalline matrix. In addition, it is observed that the limit of detection of amorphous material within a crystalline matrix is dependent upon the total thickness of the sample. In thin crystals (<150 Å), up to 75 volume percent crystalline material can give rise to aperiodic images, yet the addition of a small amount of crystalline material (80 volume percent crystalline) produces a periodic image. Images calculated for isolated spheres of amorphous material distributed within crystalline microlite suggest that isolated domains of amorphization are observable at sample thicknesses less than three times the diameter of the feature. The image contrast of amorphized domains is enhanced by imaging at defocus settings significantly different than Scherzer focus. These results indicate that interpretation of HRTEM images of partially amorphized crystalline materials should be undertaken with caution, and estimates of the volume of damage considered only qualitative.
Metallic Particles Supported in Several Synthetic Zeolitic Materials
Authors: Acosta Dwight R. , Yacaman Miguel J.
Published: March 2011

High resolution electron microscopy observations were carried out in several zeolitic systems with different supported metallic phases in order to determine besides distributions of metallic particles, possible preferential orientations of metallic phases during impregnation processes and to detect some crystallographic relations between metallic particles and support.
High Resolution Transmission Electron Microscopy of Partial States of Oxygen Order in YBa2Cu3Oz
Authors: Burmester C. P. , Quong S. , Wille L. T. , Gronsky R. , Ahn B. T. , Lee V. Y. , Beyers R. , Gür T. M. , Huggins R. A.
Published: March 2011

High resolution electron microscopy is used to investigate the effect of electron irradiation induced oxygen loss on the states of partial order in YBa2Cu3Oz. Contrast effects visible in the [001] zone image as a result of the degree of the out-of-plane correlation of these ordered states are investigated. Using statistical simulations to aid in the analysis of the HREM images, an interpretation based on a kinetically limited evolution of the variation of long range [001] ordering is proposed.
An HREM Investigation into the Atomic Structure of an Aluminum Grain Boundary
Authors: Hetherington C. J. D. , Dahmen U. , O'Keefe M. A. , Kilaas R. , Turner J. , Westmacott K. H. , Mills M. J. , Vitek V.
Published: March 2011

An experimental high resolution image of a grain boundary has been compared with images simulated from atomic structures calculated by two theoretical methods. Some of the techniques used in the analysis of the images are presented. A good agreement is found between each theory and the experiment, confirming the validity of calculations of such a boundary.
Hrtem of the Cu/Mno Interface in an Internally Oxidized Cumn Alloy
Authors: Ernst F.
Published: March 2011

The structure of the Cu/MnO interface has been studied using high resolution electron microscopy (HRTEM). Interfaces were formed by internal oxidation of a CuMn alloy. In the course of the reaction, MnO particles precipitate in several special orientations relative to the Cu lattice: “parallel” topotaxy, “twin” topotaxy, and a 55°[110] rotation yielding (111)Cu∥(002)MnO. Each of the three Cu/MnO orientation relationships has a characteristic particle morphology reflecting thermodynamically favourable interface structures. In parallel topotaxy MnO particles preferentially form flat {111}Cu/{111} MnO interfaces with a lattice mismatch of 21%. Although this mismatch is large, the existence of coherence strains in the Cu cannot be excluded. MnO particles in the 55°[110] orientation form regions of semi-coherent Interface where {200}MnO planes face a set of parallel {111} Cu planes with a mismatch of only 6%. This interface variant exhibits equally spaced steps, every 16 to 18 Cu {111} planes. Parallel to every step there is a misfit dislocation in the Cu at a stand-off distance of about 2 Cu {111} spacings. The relationship between structure and energy of the Cu/MnO interface is discussed.
Aplications of Image Processing Techniques on the Structural Characterization of Decagonal Phases
Authors: Reyes-Gasga J. , Perez R. , Jose-Yacaman M.
Published: March 2011

Image processing techniques applied to HREM images of decagonal quasicrystalline phases are carried out. A comparison between these processed images, simulated images based on the multislice method and density wave techniques and also experimental STM images of the decagonal phase [9] suggest some insights on their structure.
Interface Structure and Layer Synthesis Modes in Mesotaxial Si/CoSi2/Si Structures
Authors: Hull R. , Hsieh Y. F. , Short K. T. , White A. E. , Cherns D.
Published: March 2011

We report observations of interfacial structure and consequences for layer synthesis modes in mesotaxial Si/CoSi2/Si structures, as deduced from high resolution transmission electron microscopy (HRTEM). It is argued that relative crystal misalignments arising from the lattice parameter mismatch between the Si and CoSi2 may render classic rigid shift measurements of interfacial structure inaccurate. An alternative method for determining interfacial structure at threedimensional precipitates by analyzing crystal stacking sequences is demonstrated.
Low - Temperature Defect - Induced Aging of GaAs Grown by Molecular Beam Epitaxy
Authors: Szafranek I. , Stockman S. A. , Szafranek M. , McCollum M. J. , Plano M. A. , Miller W. R. , Stillman G. E.
Published: March 2011

Degradation in optical and electrical properties has been observed for high-purity and high-mobility p-type GaAs layers which contain significant concentrations of an unidentified shallow acceptor-like defect, labeled “A”, that is frequently incorporated in crystals grown by molecular beam epitaxy. Low-temperature photoluminescence and variable temperature Hall-effect measurements were employed to monitor the aging process in samples stored for about one year at room temperature. Profound changes in the exciton recombination spectra, indicative of increasing concentration of the “A” defect, have been accompanied by a decrease in hole mobility and an increase in carrier concentration. These results are discussed in the context of the acceptor-pair defect model, originally proposed by Eaves and Halliday [J. Phys. C: Solid State Phys. 17, L705 (1984)].
Degradation Mechanism in GaAs Led
Authors: Jicheng Zhou , Zhiping Fu , Qianbao Zhan , Shuifu Feng
Published: March 2011

A series of experiments have been performed to verify the nature of hole trap A and B in GaAs proposed by Zou and revised by Zhou (one of the present authors). The relative concentration of these two Craps is responsible for the degradation behavior of the diodes. Accordingly, the degradation mechanism in GaAs LED can be reasonably deduced based on thermodynamic consideration.