bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics of Laser Ablation and Vaporization of Lead Zirconate Titanate: Target Effects
Authors: Leuchtner R.E. , Horwitz J.S. , Chrisey D.B. 
Published: March 2011

ABSTRACTUsing the pulsed laser deposition (PLD) technique to prepare PbZrxTi(1−x)03 (PZT) films from stoichiometric targets, it has been found that the Pb content of the films is very sensitive to, among other parameters, the phase of the ablation target. In an effort to better understand PZT film growth, a time-of-flight quadrupole mass spectrometer (TOF/QMS) was used to obtain the temporal and mass profiles of material ejected from two different solid targets with a nominal composition of PbZr0.54Ti0.46O3over a laser fluence range of 0.2 to 2.0 J/cm2. The ablation targets were made from either a compressed mixture of oxides or a fully reacted PZT solid. The composition of the plume varied significantly depending upon the phase of the target and the laser fluence. In general, two distinct ejection processes were identified and the TOF profiles observed could be characterized as either thermal vaporization (fluence ≤ 0.3 J/cm2), ablation, with a highly forward directed ejection pattern normal to the target surface, or a combination of the two processes (fluences ≥ 0.3 J/cm2). The thermal vaporization (or low energy) component of the ejected species were modeled using a Maxwell-Boltzmann distribution. The fully reacted target yielded atomic species which had higher translational temperatures (about 100–700K) than the corresponding components of the pressed oxide target. The translational temperatures ranged from about 1000–6500K, depending upon the species and the laser fluence. Both targets showed distinctly different behavior as a function of laser fluence with regard to the production of PbO: the PbO/Pb ratio from the pressed oxide target was roughly constant while the PbO/Pb ratio from the fully reacted target decreased significantly with increased laser fluence. It is postulated that PbO plays an important role in the incorporation of Pb into the film during film growth.
Ultra Fine Particle Films by Gas Deposition Method
Authors: Oda Masaaki , Katsu Isao , Tsuneizumi Michitaka , Fuchita Eiji , Kashu Seiichiro , Hayashi Chikara 
Published: March 2011

ABSTRACTUltra fine particles(UFP) of organic and inorganic materials can be formed by the gas evaporation method(gas condensation method). In the gas deposition method, particles formed by the gas evaporation method in an evaporation chamber are carried to another chamber (a deposition chamber) through a pipe. Particles are accelerated in the pipe with a gas flow and come out of a nozzle located in the deposition chamber which is being evacuated down to less than 10 torr and deposited on a substrate to form UFP films. The final speed of the particles depends on the pressure difference between the evaporation chamber and the deposition chamber. The particles speed exceeds 500m/s and adhesion strengths of the films reach 50OKgf/cm2 as well as vacuum deposition films in the condition that the pressure of the evaporation chamber is at 4 atms. Patterns of spots and lines with 50μm size and also wider films can be formed on a substrate without a masking system. The process is effective for repairing electric connecting lines or producing electrodes and condensers on an industrial scale.
Production of Silicon Powder by Square-Wave Modulated Rf Silane Plasma
Authors: Costa J. , Sardin G. , Campmany J. , AndÚjar J.L. , Canillas A. , Bertran E. 
Published: March 2011

ABSTRACTSilicon powder has been produced by means of square-wave modulated rf silane plasma. The plasma conditions were: 30°C of reaction chamber temperature, 70 Pa of pressure, 80 W of rf power and 0. 1 Hz of square-wave modulation frequency. The gas flow rate was varied from 5 to 90 sccm.The distribution and size of the powder grains were determined by transmission electron microscopy. The compositional and microstructural analysis of the powder was performed by FTIR spectroscopy. This analysis has revealed the dominant presence of SiH2 groups (2100 cm−1), in a highly polymeric form (850 and 890 cm−1), as well as the existence of an absorption band (1000-1100 cm−1) associated with oxidation of the powder.These results have shown the great influence of the flow rate, through the gas residence time, on the composition and microstructure of silicon powder.
Atom-Probe Microanalysis of Metallic Nanostructured Materials
Authors: Mackenzie Ross A.D. , Cerezo Alfred , Conyers James S. , Petford-Long Amanda K. , Subrandu Sybren J. , Smith George D. W. 
Published: March 2011

ABSTRACTAtom-probe techniques have been used to characterise nanostructured metallic materials prepared by thermal evaporation and by sputtering. Multilayer samples of Fe-Cr have been prepared by sputter deposition and analysed using the Oxford position-sensitive atom probe. This has made it possible to observe the quality of interfaces in the material, and also accurately determine local compositions at each layer within the multilayer stack. Preliminary experiments aimed at producing dual phase nanocrystalline films by thermal evaporator deposition are also reported.
Nanocrystalline Ni-Mo Alloys Prepared by Mechanical Alloying for Applications in Catalysis
Authors: Schulz R. , Dignard-Bailey L , Trudeau M.L , Huot J.Y. , Yan Z.H. 
Published: March 2011

ABSTRACTAmorphous and nanocrystalline Nil-xMox alloys have been prepared by mechanical alloying of pure Ni and Mo elemental powders in an atmosphere containing various amounts of oxygen. Metastable fcc solid solutions are formed when the Mo content is less than 30 at.%. The amorphization of the supersaturated solid solution occurs when the Mo concentration exceeds 30 at.%. The electrocatalytic properties of the nanocrystalline alloys for the hydrogen evolution reaction in alkaline solutions have been investigated. High electrocatalytic activity is found when the average crystal size is below 10 nm and when the supersaturated solid solution contains some oxygen.
Nanocomposites: Retrospecr and Prospect
Authors: Roy Rustum 
Published: March 2011

ABSTRACTIn this paper we make clear distinctions from the terms nanophase, nanocrystalline and deal only with nanocomposites defined as an interacting mixture of two phases, one of which is in the nanometer size range in at least one dimension. The author's origins of development of the idea that nanocomposites are a virtually infinite class of new materials are described.Then we refer to the results of our extensive studies of nanocomposites derived by solution-solgel techniques to illustrate the properties of such materials in the area of chemical and thermal reactivity.Finally it is pointed out that in the last few years nanocomposite materials have become a major part of new materials synthesis all over the world for applications ranging from mechanical to optical, to magnetic to dielectric.
Sintering of Coated Powders. I. Silica-Ytfria System
Authors: Giesche Herbert 
Published: March 2011

ABSTRACTSilica particles were produced by the well known “Stbber” process. The silica core size as well as the coating thickness could be varied by the reaction conditions. Respectively, yttria core particles or coatings on silica nuclei were synthesized by the ureadecomposition method, previously described in general by Matijevic or Akinc et al.The (silica or yttria) core size (86 to 400 nm) as well as the coating thickness (monolayer to 100 nm) was varied systematically. Green compacts of about 50 to over 60 % thD. were produced either by sedimentation, centrifugation, or pressure filtration of well dispersed slurries.The results demonstrated the enhanced densification of coated powders. A two step shrinkage process was observed for some of the samples. TEM micrographs and X-ray analysis exemplify the microstucture and phase development during sintering.
Structural Investigation of Sol-Gel-Derived Hybrid Siloxane-Oxide Materials Using 29Si MAS-NMR Spectroscopy
Authors: Babonneau F. , Bois L. , Livage J. , Dire S. 
Published: March 2011

ABSTRACTHybrid siloxane-oxide systems were prepared by sol-gel techniques. Siloxane precursors are either monomeric species, dimethyldiethoxysilane, or OH-terminated polydimethylsiloxanes. The oxide component is introduced via metallic alkoxides, M(OR)n (M=Si, Ti, Zr). Transparent materials from flexible to brittle gels, can be obtained over a large M/siloxane range. The structure of the various systems was investigated by 29Si MAS-NMR. The signals due to the difunctional Si units, (CH3)2SiO, depend strongly on the nature of M and on the M/siloxane ratio. Structural models are proposed, ranging from single phase systems with highly interconnected siloxane and oxide units, to nanocomposites made of polysiloxane chains crosslinked with oxide-based particles.
Textured Coatings from Colloidal Suspensions of Faceted Oxide Microcrystals
Authors: Steadman Gregg.W. , Brewster J. R. , Budai J. D. , Boatner L. A. 
Published: March 2011

ABSTRACTThe morphological properties of cubic, faceted MgO microcrystals have been exploited in the formation of textured coatings. Coatings exhibiting a <100> “fiber” texture were formed by centrifugal sedimentation of colloidal suspensions onto a flat substrate. A decrease in the degree of preferred orientation in the coatings with increasing areal coverage of the particles was quantified for several particle-size distributions by using x-ray diffraction. Novel methods for the deposition of particles exhibiting an in-plane preferred orientation in addition to fiber texture have been investigated.
Layered Inorganic-Organic Nanocomposites: Application to Photofunctional Materials and Conversion to Inorganic Microporous Materials
Authors: Kuroda Kazuyuki , Ogawa Makoto , Yanagisawa Tsuneo , Kato Chuzo 
Published: March 2011

ABSTRACTLayered inorganic-organic nanocomposites can be prepared by intercalation of organic compounds into various two dimensional inorganic compounds, such as clay minerals and layered polysilicates. Two different roles of organic guest species are described in the application of intercalation compounds to development of functional materials. The first case shows that organic substances with peculiar photochemical properties can be incorporated in the nanometer—scaled interlayer spaces. Luminescence behavior and photochemical hole burning (PHB) of layered inorganic—organic nanocomposites are investigated from the viewpoint of host-guest interactions. The luminescence maxima of intercalated Ru(bpy)32+ incorporated into fluor—tetrasilicic mica cointercalated with poly(vinylpyrrolidone) shifted gradually oward blue with the decrease in the loading of Ru(bpy)32+ Ru(bpy)32+ was effectively isolated to suppress self quenching due to aggregation even at its high concentration loading. 1,4-Dihydroxyanthraquinone which is known to show a PHB reaction was intercalated into a tetramethylammonium pillared clay mineral and persistent spectral zero—phonon hole was observed at liquid helium temperatures. In spite of the high concentration of 1,4-dihydroxyanthraquinone, a narrow hole was obtained with no distinct decrease in burning efficiency if compared with those doped in ordinary polar polymers or organic glasses. In the second case, intercalation of organic substances into a layered polysilicate induces the change of the layered structure to form a three—dimensional silicate network by condensation of silanol groups in adjacent layers. This phenomenon indicates that novel microporous materials with controlled pore sizes can be prepared through inorganic-organic nanocomposites.
Structure, Mechanical Properties, and Oxidation Behavior of Nanolayered MoSi2/SiC Coatings
Authors: Hirvonen J-P. , Lappalainen R , Kattelus H. , Likonen J. , Suni I. , Kung H. , Jervis T.R. , Nastasi M. 
Published: March 2011

ABSTRACTThe structure, hardness and elastic properties, and oxidation behavior of a nanolayered MoSi2/SiC structure were examined. DC magnetron and rf diode sputtering were used to deposit MoSi2 and SiC, respectively. The total number of sublayers of each kind was 90. The nominal thickness of the MoSi2 sublayers was 10 and that of the SiC 3 nm. The microstructure of the as-deposited samples was amorphous whereas annealing at 500 °C for I h resulted in the transformation of MoSi2 into C40 type hexagonal structure as determined using cross-section transmission electron microscopy (TEM). However, silicon carbide still remained amorphous. Hardness and Young's modulus were determined by using a nanoindentation technique. Hardness of 11.6 and 20.8 GPa were obtained for the asdeposited and annealed structure, respectively. Corresponding Young's moduli were 220 and 290 GPa, which yield values of 232 and 332 GPa for Young's moduli of amorphous and crystalline MoSi2. Oxidation tests were carried out in wet oxidation conditions at 400 and 500 °C. The degree of oxidation was determined by measuring oxygen concentration on the surface using a nuclear reaction 16O(d,p) 17O at a deuterium energy of 950 keV. The MoSi2/SiC coating gave good protection against oxidation for unalloyed steel. As compared to a single MoSi2 coating a slightly higher degree of oxidation and a significantly different mechanism of oxidation was observed. This was also supported by secondary ion mass spectroscopy (SIMS) measurements. Cracking of the coating caused by a thermal mismatch and transformation stresses was worse in the case of the single MoSi2 layer than in the case of the composite coating. Thus cracking of the coating can be significantly reduced by using a nanolayered structure.
Jet Vapor Deposition of Nanostructure Composite Materials
Authors: Zhang J.-Z. , Golz J.W. , Johnson D.L. , Mcavoy D.T. , Halpern B.L. , Schmitt J.J. 
Published: March 2011

ABSTRACTWe describe the use of Jet Vapor Deposition for efficient synthesis of nanoscale multilayer films, ceramic-organic films, cluster embedded films, and colloids.
Anisotropic Electron Transport in Cu/Al Multilayers
Authors: Fadnis A. N. , Baxter David V. 
Published: March 2011

ABSTRACTWe have measured the anisotropy of the electron diffusivity in a series of Cu/Al multilayers. The Samples were made by magnetron sputtering and characterized by X-Ray diffraction. The low temperature transverse magnetoresistance of each sample was measured for two different orientations of the magnetic field—parallel and perpendicular to the plane of the sample film. The Weak Localization(WL) contribution to the magnetoresistance is sensitive to the component of the electron diffusivity in a plane perpendicular to the magnetic field. We use this fact to calculate the ratio of different components of the diffusivity from the observed dependence of magnetoresistance on the orientation of magnetic field. For our samples, the ratio of the in and out of plane components of the diffusivity, (Dxy/Dz), is seen to range between 1 and 2.2, and the anisotropy is largest for the sample with the highest conductivity.
Raman and X-Ray Scattering From Dense Semiconductor-Dielectric Nanocomposites
Authors: Yang W.H. , Huber T.E. , Lubin J.A. , Walrafen G.E. , Huber C.A. 
Published: March 2011

ABSTRACTRaman scattering measurements have been performed on semiconductor-insulator nanocomposites in which the semiconducting phase occupies a significant (30%) volume fraction. The composites have been synthesized by high pressure injection of the conducting melt into the nanochannels of commercially available insulating matrices. The optical phonon spectra of GaSb- and Te-SiO2 composites exhibit shifts, broadenings, and asymmetries when compared to those of the semiconducting bulk. These are interpreted in terms of strains and phonon confinement in the microcrystalline semiconducting phase. Xray diffraction measurements allow us to correlate the effects of crystallite size and strains on the optical modes of the composites.
Synthesis, Processing and Phase Evolution of TiN/TiB2 Composites From Polymeric Precursors
Authors: Nowakowski M. , Su K. , Sneddon L. , Bonnell D. 
Published: March 2011

ABSTRACTA high yield synthetic route to TiN/TiB2 nanocomposites based upon polymeric precursors has been developed. The phase evolution and microstructural development have been characterized and related to preliminary measurements of properties, i.e. hardness. The observations indicate the existence of TiN-TiB2, TiN-BN, and TiB2-BN subsolidus compatibilities.
Template Synthesis and Optical Properties of Small Metal Particle Composite Materials: Effects of Particle Shape and Orientation On Plasmon Resonance Maxima.
Authors: Foss Colby A. , Hornyak Gabor L. , Stockert Jon A. , Martin Charles R. 
Published: March 2011

ABSTRACTAn electrochemical method for the preparation of nanoscopic gold particles which allows for the control of particle size, shape and orientation is described. The UV/visible/near-IR spectra of Au/alumina and Au/polyethylene composites are described and shown to be in accord with the predictions of Maxwell-Garnett theory. The applications of such composites to surface enhanced spectroscopy are also discussed.
Connected Cadmium Selenide Nanocrystallite Networks
Authors: Majetich Sara A. , Carter Adriaan C. , Mccullough Richard D. 
Published: March 2011

ABSTRACTThe optical properties of semiconductor nanocrystallites, or small quantum dots, are well understood, but little is known about nanocrystallite networks. Here we report preliminary results on a glassy network of CdSe nanocrystallites connected by molecular bridges. This network has been analyzed by transmission electron microscopy (TEM) and small angle X-ray scattering to determine its structure, and to see if long range order is present. The effect of nanocrystallite interactions on electron-hole recombination is inferred from characterization by UV-VIS absorption and photoluminescence.
Sinter-Forging of Nanocrystalline TiO2
Authors: HÖfler H.J. , Averback R.S. 
Published: March 2011

ABSTRACTSinter-forging experiments were performed on cylindrical samples of n-TiO2 at various stresses and temperatures and with varying initial densities. The results are described on the basis of a constitutive law similar to creep deformation of dense bodies. The activation enthalpy measured is consisted with a grain boundary diffusion limited process, whereas the stress exponent found excludes simple diffusional creep. Furthermore, a threshold stress was found to exist. The results are discussed in terms of existing models and it is shown that the threshold stress can be explained in terms of the creation of additional surface area due to grain boundary sliding.
Sialon Ceramics Sintered with Yttria and Rare Earth Oxides
Authors: EkstrÖm Thommy 
Published: March 2011

ABSTRACTDense single-phase α-, β- and O′-sialon cermics or mixed sialon ceramics without a glassy grain-boundary phase can be prepared at high temperatures and pressures, and these materials are well suited for high-temperature use, but they are usually brittle. Additional quantities of oxides of group IIIB metals in the periodic table are often added as sintering aids to achieve pressureless sintering and thereby to allow more complicated shapes to be manufactured directly and at lower costs. The most common additive is yttria, but the rare earth oxides are also of interest. All these oxides will promote the growth of elongated β crystals in the microstructure, and the fracture toughness will be improved considerably. Low-cost oxides like Nd2O3, La2O3or CeO2may replace Y2O3without significantly impairing the mechanical properties at room temperature. The expensive rare-earth oxides like Sm2O3, Dy2O3or Yb2O3have been found to be as good additives as yttria, or even better, but improvements in mechanical properties are generally small and do not justify the use of these additives in large-scale production. The residual intergranular glassy phase usually found in the microstructure of metal-oxide-doped sialons will deteriorate the properties at very high temperatures, and this type of material is best suited for use at operation temperatures below 900-1000°C.
Synthesis of Si3N4 Powder by Thermal Decomposition of SI(NH)2
Authors: Ampuero Silvia , Bowen Paul , Ring Terry A. 
Published: March 2011

ABSTRACTA fine white α-Si3N4 powder has been produced by the thermal decomposition of the coprecipitation product of the reaction between SiC14 and NH3. The Cl content, due to a reaction between Si(NH)2 and the NH4Cl by-product during the thermal treatment of the coprecipitate, has been reduced by using an isothermal step at ≈ 250°C in the heat treatment cycle.
Spectroscopic Characterization of the Nitridation Process of Polymeric Precursors to SI-M-N-O Systems (M=Ti, Zr, Al)
Authors: Babonneau F. , Soraru G. D. 
Published: March 2011

ABSTRACTA commercial polycarbosilane was modified with various metallic alkoxides to get mixed ceramic precursors in the Si-M-C-O systems (M=Ti, Zr Al). Pyrolysis under ammonia leads to the formation of various ceramic materials depending on the nature of M : Si3N4/TiN, Si3N4/ZrO2 or β′-SiAlON phases.The polymer-to-ceramics conversion have been studied by MAS-NMR (29 Si, 27Al) and X-ray absorption (Ti K-edge). This paper will show how these two complementary spectroscopic techniques can be used to follow the nitridation process by probing local environments of different elements. In addition, it will be pointed out how X-ray absorption can be a powerful tool for the detection of the crystallization of nitride cubic phases.
Tape Casting of Silicon Nitride
Authors: Kim Young-Wook , Lee June-Gunn 
Published: March 2011

ABSTRACTTape casting behavior of submicron silicon nitride powder(UBE SN–E1O) with Al2O3and Y2O3as sintering additives was studied. It was found that Hypermer KD1(polymeric dispersant) is effective dispersant for submicron silicon nitride in organic solvent system.Optimization of the rheological properties of the slurries allows the homogeneous green tapes with green densities of 45–50% theoretical. The cast tapes could be sintered to closed porosity with densities of higher than 96% theoretical.
Rheological Behavior of Silicon Nitride Whiskers
Authors: Toro Patricio , Wittke Oscar 
Published: March 2011

ABSTRACTSi3N4 whiskers are found through SEM analysis of powder obtained by carbothermal reduction of calcined Chilean rice husks. X-ray and FTIR analysis showed that the ceramic material was mainly α-Si3N4. A stable aqueous suspension with 30 or 40 wt% Si3N4 was obtained at pH = 8.5. A maximum viscosity at pH = 4.0 and low rpm was also observed and this rheological behavior is consistent with the zeta potential data. An irregular flow behavior near pH 4.0 shows a decrease in viscosity that is related to active impurities as detected by potentiometric titrations.These rheological studies conducted allowed production of a Si3N4 green ceramic body measuring 170 × 25 × 5 mm formed by slip casting. The optimal aqueous suspension of powder contained the following: 17.0 g Si3N4, 1.0 g Cu2O, 1.3 g bentonite, and 20.0 g water.
Strength Optimization Through Powder Modification
Authors: Pasto Arvid E. , Avella F. , Natansohn S. , Rourke W. J. 
Published: March 2011

ABSTRACTThe effect of oxygen content of silicon nitride powders on the properties of resulting ceramics was studied by physically and chemically treating the powder to modify its surface oxygen content. These powders were compounded with yttria and hot-pressed into dense ceramics. Strength and oxidation resistance of these ceramics were measured and correlated with the powder and ceramic compositions as well as the resulting intergranular phases. Results showed that the phases varied with slight differences in the initial powder oxygen content as predicted, and that strength could be correlated to initial oxygen concentration. Best results were obtained when the oxygen content was increased by thermal oxidation. A Taguchi Methods experimental study designed to optimize the thermal treatment resulted in silicon nitride ceramics with strength improvements of 22 and 37% at ambient temperature and 1370°C, respectively. Oxidation resistance was also improved.