bluuebunny/crossref_metadata_2025 huggingface dataset:
On the energetics of dislocation emission from a crack tip in nickel containing hydrogen
Authors: Hoagland Richard G.
Published: September 2007

A method that determines the work done in shearing atom pairs straddling the slip plane, Φ, during emission of dislocations from a crack tip in an atomic model is presented. The model is based on an EAM-type potential for nickel. The dislocations are emitted as partials, and the disregistry, Δ, across the slip plane is found to be fit accurately by a simple arctan function of position for each partial. The width of the partials is also found to remain essentially constant as they are emitted and move away from the crack tip. Rice's unstable stacking energy is extracted from the Φ - Δ curves for the atom pairs along the slip plane and is observed to vary somewhat, particularly near the crack tip. In addition to the Φ (Δ) at points on the slip plane, the total work done on the entire slip plane is determined as a function of the dislocation position in the spirit of the Peierls approach. The derivative of this total work with respect to dislocation position leads to the lattice resistance, ŝr. The first partial dislocation to be emitted experiences a maximum in ŝr at about 0.2 nm from the crack tip, and several contributions to the overall resistance can be identified including the creation of a new surface at the tip as emission occurs, the creation of stacking fault as the dislocation glides away from the tip, and a small but discernible periodic component with a period related to the lattice. A string of hydrogen interstitials is introduced at various locations in the lattice and its effect on Δ, Φ - Δ curves along the slip plane, and the lattice resistance is examined. A substantial effect on the unstable stacking energy results as the dislocation passes an interstitial on the slip plane, but the effect of an interstitial on the resistance to dislocation emission expressed in terms of the maximum ŝr is small and then only if it is confined to a region very near the crack tip. The significance of these results is discussed together with some additional observations including dislocation pinning on the interstitials.
Deposition process and characterization of chromium-carbon coatings produced by direct sputtering of a magnetron chromium carbide target
Authors: Maréchal N. , Quesnel E. , Pauleau Y.
Published: September 2007

Chromium-carbon coatings have been deposited on various substrates by direct sputtering of a chromium carbide, Cr3C2, target in pure argon atmosphere. The composition of coatings determined by Rutherford backscattering spectroscopy and the deposition rate were investigated as functions of the sputtering gas pressure and self-bias voltage applied to substrates. The atom number ratio C/Cr in the coatings was equal to 0.7 regardless of the deposition conditions investigated. Oxygen and argon atoms were the major impurities incorporated in the amorphous coatings. Oxygen-free Cr-C coatings were prepared at low argon pressures or on substrates biased to a voltage in the range −100 to −320 V. The Cr-C coatings deposited on biased substrates contained less than 2 at. % of argon. The morphological features of Cr-C coatings examined by scanning electron microscopy were also dependent on the sputtering gas pressure and bias voltage of substrates. Fully dense structures were observed for coatings deposited at low argon pressures or on biased substrates. The electrical resistivity of Cr-C coatings was extremely dependent on the concentration of oxygen atoms incorporated in the coatings. Oxygen-free Cr-C coatings exhibited electrical resistivity values as low as 120 μΩ cm, i.e., less than twice the bulk resistivity of Cr3C2. The residual stresses in the coatings and microhardness of the deposited material were also investigated as functions of the deposition parameters. Tensile residual stresses were lower than 0.8 GPa, and the maximum microhardness of coatings was about 13000 MPa, i.e., similar to that of the bulk material.
Electrical properties of plastic composites using Br2-intercalated vapor-grown carbon fibers as a conductive filler
Authors: Katsumata M. , Endo M. , Yamanashi H. , Ushijima H.
Published: September 2007

Graphite fiber intercalation compounds were prepared by immersing graphitized thin vapor-grown carbon fibers (VGCF's) with diameters less than 0.5 μm into liquid bromine. The composition of Br2-intercalated VGCF was C70Br-C90Br. The powder resistivity of Br2-intercalated VGCF was estimated as 1/3 of pristine VGCF. An electroconductive plastic composite was prepared by mixing phenol resin with that of bromine intercalated VGCF as a conductive filler, and its electrical properties were investigated. The resistivity of a Br2-intercalated VGCF composite was 1.1 × 10−2 Ω · cm at room temperature, which is about 50% of pristine VGCF composite. Br2-intercalated VGCF-based composite had a high degree of stability against exposure at 150 °C in air and at 85 °C with 90% humidity for 500 h. Br2-intercalated VGCF-based plastic composites could be used as highly electroconductive materials.
A photoluminescence study of the effect of well thickness in strained InGaAs/AlGaAs heterostructures grown by molecular beam epitaxy
Authors: Yoon S.F. , Radhakrishnan K. , Li H.M. , Zhang D.H.
Published: September 2007

Low temperature photoluminescence measurements were carried out on pseudomorphically strained InxGa1−xAs-Al0.28Ga0.72As ternary-on-ternary heterostructures grown by molecular beam epitaxy to investigate the change in the transition energy, linewidth, and intensity as a function of InGaAs well thickness at two different indium compositions, x = 0.10 and x = 0.15, respectively. Sharp exciton peaks as narrow as 4-6 meV were observed from the InGaAs wells grown at 530 °C with 1 min of growth interruption at the top and bottom heterointerfaces. The linewidth decreases as the well thickness is increased up to 300 Å. In addition, there are signs of linewidth broadening and sharp decrease in the photoluminescence intensity at higher well thicknesses that may indicate the onset of plastic relaxation. Relatively small variations in the transition energy were observed at well thicknesses that are up to ≍3 times the theoretical critical layer thickness calculated by the Matthews-Blakeslee model,10 suggesting that the small density of dislocations that may be present may not have a significant effect on the band structure of the well.
On the role of penetration twins in the morphological development of vapor-grown diamond films
Authors: Tamor M.A. , Everson M.P.
Published: September 2007

Polycrystalline diamond films may be produced by chemical vapor deposition (CVD) with morphologies ranging from multimicron crystallites with well-defined facets and texture to nanocrystalline “cauliflower” nodules. While previous efforts to connect diamond film “quality” to growth conditions focus on competitive growth of non-diamond phases, we propose that twinning is a major controlling factor. We use geometric arguments to define the conditions under which a given twin can outgrow and bury the “parent” face on which it originated. We then show how the full spectrum of diamond crystallite shapes and film morphologies can be explained in terms of penetration twins without reference to the actual mechanistics of diamond growth.
Ruthenium clusters in lead-borosilicate glass in thick film resistors
Authors: Adachi Kenji , lida Sadahiro , Hayashi Kazuhide
Published: September 2007

An interparticle glass matrix in ruthenium dioxide-based thick film resistors has been studied intensively by means of analytical and high resolution transmission electron microscopy. The ruthenium dioxide phase interacts with lead-borosilicate glass at high temperature by dissolving ruthenium ions and incorporating a small number of lead and aluminum ions on the surface. Ruthenium ions diffuse through the glass network at least over a distance of 1 μm during firing, but are accommodated in the glass structure by an amount only less than 7 at. % at room temperature. High resolution electron microscopy reveals numerous ruthenium-pyrochlore crystallites in high-lead glasses, but hardly any Ru-based clusters/crystallites in low-lead glasses, where lead-rich glass clusters due to glass immiscibility and reduced lead metal clusters are more commonly observed instead of ruthenium clusters. Lead oxide is prone to reduction both in high- and low-lead glasses upon irradiating with a high-energy incident electron beam. Comparison with gold-based resistor and estimation of average dispersion length of ruthenium clusters, 2 to 4 nm, prefer the model of electron hopping via ruthenium clusters/crystallites as a dominant conduction mechanism in thick film resistors.
Formation of BaCeO3 and its influence on microstructure of sintered/melt-textured Y-Ba-Cu-O oxides with CeO2 addition
Authors: Kim Chan-Joong , Kim Ki-Baik , Won Dong-Yeon , Moon Hong-Chul , Suhr Dong-Soo , Lai S.H. , McGinn P.J.
Published: September 2007

The formation of BaCeO3 and its effects on microstructure were studied in sintered/melt-textured Y-Ba-Cu-O oxides containing 5 wt. % CeO2 and various amounts of Y2Ba1Cu1O5. The added CeO2 was converted to fine particles of BaCeO3 near 930 °C, which is the conventional sintering temperature for Y-Ba–Cu-O. Y2Ba1Cu1O5 and CuO are formed as by-products of the reaction between CeO2 and Y1Ba2Cu3O7−y phase. The CeO2 addition reduced the particle size of Y2Ba1Cu1O5 which was trapped in the Y1Ba2Cu3O7−y matrix after the melt-texture growth. During the peritectic decomposition stage of Y1Ba2Cu3O7−y phase into Y2Ba1Cu1O5 and liquid phase, the morphology of the decomposed Y2Ba1Cu1O5 was changed from a blocky shape in the undoped sample to an acicular shape of high anisotropy in the CeO2-added sample. The formation of the highly anisotropic Y2Ba1Cu1O5 particles appears to be responsible for the refinement of Y2Ba1Cu1O5 particle after the melt-texture processing.
Thin film coatings of (Ca0.6, Mg0.4)Zr4(PO4)6 on Si3N4 and SiC
Authors: Li T.K. , Hirschfeld D.A. , Brown J.J.
Published: September 2007

Thin film coatings of (Ca0.6, Mg0.4)Zr4(PO4)6 (CMZP) on Si3N4, and SiC substrates, including porous SiC used in ceramic filters, were investigated using sol-gel and dip coating techniques. The coating thickness, ranging from 1 to 5 μm, was found to vary with the selected precursors and their concentrations in the solution. When applied to Si3N4 and SiC, CMZP coatings exhibit good thermal shock resistance and greatly improved alkali corrosion resistance. For porous silicon carbide, homogeneous, crack-free coatings were formed on both the outer surface and the interior sections of the pore walls. The CMZP coatings on Si3N4 and SiC exhibit good thermal shock resistance. The CMZP coating greatly improved the alkali corrosion resistance of Si3N4 and SiC.
Evolution of phases and microstructure in optical waveguides of lithium niobate
Authors: McCoy M.A. , Dregia S.A. , Lee W.E.
Published: September 2007

The microstructural development of Ti: LiNbO3 optical waveguides, as a function of annealing time and temperature, was studied by x-ray diffraction, scanning and transmission electron microscopy, and Auger electron spectroscopy. The microstructure evolves in three major stages: oxidation, precipitation and abnormal grain growth, and interdiffusion. The deposited Ti film is oxidized at low temperatures through a series of intermediate TiOx phases until complete oxidation to rutile TiO2 occurs at ∼500 °C. At intermediate temperatures, 500-800 °C, epitaxial precipitates of LiNb3O8 are formed at the rutile/LiNbO3 interface. At this stage abnormal grain growth occurs in the rutile film, causing multivariant epitaxy where all of the grains have a single orientation relationship to the substrate. Subsequent interdiffusion between TiO2 and LiNb3O8 produces a solid solution with the rutile structure which, at these temperatures, appears to coexist in equilibrium with the underlying lithium niobate substrate. This rutile solid solution serves as the source of Ti in the final stage of interdiffusion, which occurs only at higher temperatures (≳ 1000 °C), and leads to consumption of the rutile layer by the substrate. Structural models are discussed for epitaxial grain growth and interdiffusion.
Stress-induced formation of structural defects on the {311} planes of silicon
Authors: Weng-Sieh Z. , Krulevitch P. , Gronsky R. , Johnson G.C.
Published: September 2007

Structural defects occurring on the {311} planes of single crystal silicon have been observed near the bottom oxide corner in silicon-on-insulator structures formed by selective epitaxial growth. These {311} defects exhibit a preferential orientation and are clustered near the silicon/silicon dioxide interface. This new observation provides an opportunity to study the mechanism of {311} defect generation in a system with discernible microstructure and stress state. High resolution electron microscopy combined with analytical and numerical three-dimensional stress modeling are used to show the dependence of these {311} defects on the local stress field, and to establish their origin in terms of a homogeneous dislocation nucleation model.
Local equilibrium phase diagrams: SiC deposition in a hot wall LPCVD reactor
Authors: Chiu Chien C. , Desu Seshu B. , Chen Zhi J. , Tsai Ching Yi
Published: September 2007

Traditional CVD phase diagrams, which neglect the depletion effects in a hot wall reactor and assume the gaseous species concentrations at the substrate are the same as input concentrations, are at best valid for a cold wall reactor. Due to the constant change of gaseous species concentration along the length of the reactor, traditional CVD phase diagrams do not accurately predict the phases in the deposit on the substrate in a hot wall CVD system. In this paper, a new approach to calculate the local equilibrium CVD phase diagrams at the substrate is presented by coupling the depletion effects in a hot wall reactor to the equilibrium thermodynamic computer codes solgasmix-pv. The deposition of SiC using the gas system of methyltrichlorosilane (MTS)-hydrogen (H2) under low pressure was chosen for this study. Differences between the new CVD phase diagrams and the traditional phase diagrams for this gas system are discussed. The calculated CVD phase diagrams are also compared with the experimental data both from our own experiment and from the literature. The local equilibrium phase diagrams predicted the deposition of a single phase of SiC much better than those without the consideration of the depletion effects. The experimental regions for depositing single phase SiC are larger than the calculated local phase diagrams. This is attributed to the higher linear velocity of the gas flux under low pressure and the polarity of the Si carrying intermediate species.
Micromechanical characterization of chemically vapor deposited ceramic films
Authors: Grow J.M. , Levy R.A.
Published: September 2007

In this study, nanoindentation is used to determine Young's modulus of chemically vapor deposited films consisting of silicon carbide, silicon nitride, boron carbide, boron nitride, and silicon dioxide. Diethylsilane and ditertiarybutylsilane were used as precursors in the synthesis of the silicon-based material, while triethylamine borane complex was used for the boron-based material. The modulus of these films was observed to be dependent on the processing conditions and resulting composition of the deposits. For the silicon carbide, silicon nitride, boron carbide, and boron nitride films, the carbon content in the films was observed to increase significantly with higher deposition temperatures, resulting in a corresponding decrease in values of Young's modulus. The composition of the silicon dioxide films was near stoichiometry over the investigated deposition temperature range (375–475 °C) with correspondingly small variations in the micromechanical properties. Subsequent annealing of these oxide films resulted in a significant increase in the values of Young's modulus due to hydrogen and moisture removal.
Contribution of electrolysis current to growth of SrTiO3 thin film by the hydrothermal-electrochemical method
Authors: Kajiyoshi Koji , Tomono Kunisaburo , Hamaji Yukio , Kasanami Toru , Yoshimura Masahiro
Published: September 2007

The electrolysis treatment of the hydrothermal-electrochemical method has been modified so that it permits SrTiO3 thin films to be grown on Ti electrodes being oxidized anodically in Sr(OH)2 solutions far beyond a thickness limit of several tens of nanometers hitherto attained. The relation between the total current passed through the Ti anode and the amount of the resulting SrTiO3 film was analyzed on the basis of a reaction model that interprets the anodic current to be compensated with electrons generated partly by oxidation of Ti and partly by decomposition of H2O. Current efficiency for the film growth was estimated to be in the range from 0.8 to 3% depending on the Ti electrode potential.
Structural variations in strained crystalline multilayers
Authors: Hoekstra J. , Yan H. , Kalonji G. , Jónsson H.
Published: September 2007

We present a computer simulation study of thin crystalline multilayers constructed from two fcc solids with differing lattice constants and binding energies. Initially the two solids have the same orientation, and the interface is perpendicular to the common [100] direction. We then minimize the energy of the system at zero temperature or equilibrate it at a finite temperature. Both materials are described by Lennard-Jones interatomic potentials. A novel technique for analyzing local atomic ordering, common neighbor analysis, is used to identify structural characteristics in these systems. As we gradually vary the lattice mismatch between the two solids, several structural changes are observed in the layers of smaller atoms after energy minimization. At a mismatch larger than 14%, the layers transform into the hep structure, while at smaller mismatches extended structural defects are generated. At elevated temperatures, the hcp structure is transformed back to fcc, and the structure defects disappear.
Microstructure of epitaxial VO2 thin films deposited on (1120) sapphire by MOCVD
Authors: Zhang H. , Chang H.L.M. , Guo J. , Zhang T.J.
Published: September 2007

Epitaxial VO2 thin films grown on (1120) sapphire (α-Al2O3) substrates by MOCVD at 600 °C have been characterized by conventional electron microscopy and high resolution electron microscopy (HREM). Three different epitaxial relationships between the monoclinic VO2 films and sapphire substrates have been found at room temperature: I. (200) [010] monoclinic VO2 ‖ (1120) [0001] sapphire, II. (002) [010] monoclinic VO2 ‖ (1120) [0003] sapphire, and III. (020) [102] monoclinic VO2 ‖ (1120) [0001] sapphire. Expitaxial relationships II and III are equivalent to each other when the film possesses tetragonal structure at the deposition temperature; i.e., they can be described as (010) [100] tetragonal VO2 ‖ (1120) [0001] sapphire and (100) [010] tetragonal VO2 ‖ (1120) [0001] sapphire. HREM image shows that the initial nucleation of the film was dominated by the first orientation relationship, but the film then grew into the grains of the second and the third (equivalent to each other at the deposition temperature) epitaxial relationships. Successive 90°transformation rotational twins around the a-axis are commonly observed in the monoclinic films.
The effect of TiO2addition on the preparation and phase transformation for precursor β-spodumene powders
Authors: Wang Moo-Chin
Published: September 2007

Fine β-spodumene-type amorphous powders were obtained through sol-gel techniques using Si(OC2H5)4, Al (OC2H5)3, LiOCH3, and Ti(OC2H5)4as the starting metal alkoxides. Differential thermal analysis (DTA), x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction (ED) analysis were utilized to study the phase transformation behavior of the LAST gels. The viscosity of the LAST solution increased abruptly at longer time when the TiO2content was increased. As the TiO2content was increased, the peak position of β-spodumene phase formation in DTA curves was shifted to a lower temperature. For calcination of LAST gels at 800°-1200 °C, the crystallized phases are composed of the major phase of β-spodumene and a minor phase of rutile (TiO2). Unlike earlier studies, heating the dried LAST gels from 800 °C to 1200 °C did not show β-eucryptite, nor found γ-spodumene.
Microstructure, chemical aspects, and mechanical properties of TiB2/Si3N4 and TiN/Si3N4 composites
Authors: Huang Jow-Lay , Chen Shih-Yih , Lee Ming-Tung
Published: September 2007

The chemical stability of TiB2 and TiN in a silicon nitride matrix under various conditions of temperature and gaseous environments was investigated. The addition of TiB2 and TiN on the microstructure and mechanical properties was also studied. No trace of interactions between TiN and Si3N4 was noticed. The addition of TiB2 to Si3N4 enhanced conversion of the α to β phase of the Si3N4 matrix. Observations of BN and TiN indicated a possible reaction between TiB2 and Si3N4. The fracture toughness of Si3N4 was substantially enhanced with the addition of TiB2 or TiN, while the strength was decreased. Crack deflection was the major toughening mechanism in a Si3N4/TiB2 composite. Most of the microcracks passed through TiN particles and cleavaged along preferred orientations with large deflection angles.
Phase chemistry in the Ti-Si-N system: Thermochemical review with phase stability diagrams
Authors: Sambasivan S. , Petuskey W.T.
Published: September 2007

The phase chemistry and thermodynamics of the Ti-Si-N system are reviewed leading to a revision of the ternary phase diagram at 1273 K to include the extended compositional ranges of δ-TiNxand Ti5Si3(Ny) and the compounds Ti3Si, Ti5Si4, and α-Ti. This same information is presented in the form of phase stability diagrams which plot the stability criteria for each phase as a function of thermodynamic activity of one component and the relative composition of the other two components. Plots in terms of logasivs Ti/(Ti + N), logaN2vs Si/(Ti + Si), and logaTivs N/(Si + N) were constructed. All diagrams are consistent with current knowledge of phase compatibility and, therefore, are topologically correct. Further refinement will be possible as more accurate information on thermodynamics and compositional limits of solid solutions becomes available.
Synthesis and sintering of Ca0.5Sr0.5Zr4P6O24 powders by the decomposition/combustion of Ca-, Sr-, nitrate-ammonium dihydrogen phosphate-urea mixtures
Authors: Hong Chang S. , Ravindranathan P. , Agrawal Dinesh K. , Roy Rustum
Published: September 2007

Ca0.5Sr0.5Zr4P6O24 (CSZP) powders were prepared by the decomposition/combustion method using Ca(NO3)2 · 4H2O, Sr(NO3)2, ZrO(NO3)2 · xH2O, NH4H2PO4, urea, and NH4NO3 as starting materials. The homogenized slurries of the mixture were heated at 500 °C for 5 min to obtain CSZP powders. The as-synthesized powders were amorphous and crystallized after heating 800 °C for 2 h. The specific surface area of the powder was varied with the batch weight of starting materials or the amount of urea and ammonium nitrate. Powders with high specific surface area (150 m2/g) could be produced by this method. The sinterability of the powders was comparable to that of sol-gel derived powders. The sintered density of the compacts was 99% of theoretical after firing in air at 1350 °C for 6 h.
Uniform spherical colloidal palladium particles by reduction of solid complex precursors
Authors: Kratohvil Stanka , Matijević Egon
Published: September 2007

A procedure is described that yields uniform spherical colloidal palladium particles of modal diameters ranging between 0.1 and 0.7 μm. The process consists of two stages. First a monodispersed solid composite precursor is precipitated in solutions containing PdCl2, urea, and a nonionic surfactant. The resulting particles are then reduced in aqueous media, either by hydrazine or ascorbic acid in the presence of a protective agent. No change in particle shape occurred during the transformation to pure metals.
Competition between strain and interface energy during epitaxial grain growth in Ag films on Ni(001)
Authors: Floro J.A. , Thompson C.V. , Carel R. , Bristowe P.D.
Published: September 2007

Epitaxial Grain Growth (EGG) is an orientation-selective process that can occur in polycrystalline thin films on single crystal substrates. EGG is driven by minimization of crystallographically anisotropic free energies. One common driving force for EGG is the reduction of the film/substrate interfacial energy. We have carried out experiments on polycrystalline Ag films on Ni(001) substrates. The orientation dependence of the Ag/Ni interfacial energy has been previously calculated using the embedded atom method. Under some conditions, EGG experiments lead to the (111) orientations calculated to be interface- and surface-energy-minimizing. However, when Ag films are deposited on Ni(001) at low temperature, EGG experiments consistently find that (111) oriented grains are consumed by grains with (001) orientations predicted to have much higher interface and surface energy. The large elastic anisotropy of Ag can account for this discrepancy. Strain energy minimization favors growth of (001) grains and can supersede minimization of interfacial energy if sufficient strain is present and if the film is initially unable to relieve the strain by plastic deformation.
Effect of crystalline phase on the nanoparticle growth in glass-ceramics
Authors: Kundu T.K. , Chakravorty D.
Published: September 2007

Nanometer-sized silver particles with diameters in the range 4.3 to 11.5 nm have been grown within a glass-ceramic containing BaTiO3 by just subjecting the former to an alkali/silver ion exchange reaction. A reduction treatment in hydrogen is, however, shown to be necessary for such growth in glass-ceramics having crystalline phases such as BaTiSiO5, Zn2SiO4, and Li4P2O7, respectively. The possible presence of Ti3+ ions in the BaTiO3 phase is believed to cause such a difference in the reduction behavior of these composites.
Formation of pits on ceramic surfaces coated with gold
Authors: Yang X.F. , Xi X.M.
Published: September 2007

It was shown through two experiments that submicron-size pits formed on the surfaces of a dense fused quartz substrate and a Y2O3-ZrO2 ceramic thin film that were coated with gold and then heat-treated in air at 1200 °C. The formation of the pits is believed to be caused by the positive capillary pressure (approximately 22 MPa) generated in the molten gold droplets (<1 μm in diameter) that were formed as the gold coating melted.
Investigation of the low angle grain boundaries in highly oriented diamond films via transmission electron microscopy
Authors: Sivazlian F.R. , Glass J.T. , Stoner B.R.
Published: September 2007

Highly oriented diamond thin films grown on silicon via microwave plasma chemical vapor deposition were examined by transmission electron microscopy. In the plan view, defects appearing at the grain boundary were easily observed. (100) faceted grains that appeared to have coalesced were connected at their interfaces by dislocations characteristic of a low angle grain boundary. From Burgers vector calculations and electron diffraction patterns, the azimuthal rotation between grains was measured to be between 0 and 6°. The defect densities of these films are compared to reports from (100) textured randomly oriented films, and the relative improvement due to the reduction of misorientation and grain boundary angles is discussed.
Spray pyrolysis of YBCO precursors
Authors: Grader Gideon S. , Machado Darío R. , Semiat Raphael
Published: September 2007

Acetate, nitrate, and oxalate precursors for YBCO have been spray pyrolyzed under different conditions. Shelled and nonhollow microparticles were obtained from acetate and nitrate precursors, while nonhollow agglomerates were obtained from the oxalate suspension. At low furnace temperatures, the temperature and residence time of the particles were insufficient for complete decomposition of the precursors leading to Cu2O and Cu metal in the product. At 900 °C and above, reduced forms of CuO were not detected by x-ray measurements, and up to ∼60 wt.% YBCO was obtained. An approximate model predicting the particle and gas temperatures along the reactor under different operating conditions was developed. The model demonstrates that under the experimental conditions used here, the absorbed radiation heat by the particles from the furnace walls is significant in heating the gas. The gas and the particle temperatures are fairly close due to the effective heat transfer to the particles. At furnace temperatures of 700 °C, the maximum predicted particle temperature is about 500 °C (for ∼1 s). This explains the incomplete reactions obtained under these conditions. Above 900 °C the reactions are predicted to be complete within the first half of the furnace, leaving sufficient residence time for partial conversion into YBCO. Finally, an approximate expression predicting the relative contribution to the gas heating by the walls and the aerosol has been developed.
Division of the hardness of molybdenum into rate-dependent and rate-independent components
Authors: Stone D.S. , Yoder K.B.
Published: September 2007

The hardness, H, and rate sensitivity of the hardness, m = ∂ ln H/∂ ln ∊eff|xp, where ∊eff is an effective strain rate and xp the plastic depth, are measured in molybdenum at room and low temperature (160 and 170 K) using as-received and annealed specimens. Based on these measurements it is found that H separates into two components: one depending on indentation rate and temperature, and the other depending on the starting state of the material. An activation volume is defined, v∗ = 9kT/mH, which falls within the range of values derived from other experimental techniques. The values of m obtained from indentation creep, indentation load relaxation, and indentation rate-change experiments agree closely with each other provided a consistent analysis is used. The results of these experiments suggest that the rate- and temperature-dependence of the hardness can be used to discriminate between strengthening mechanisms at low temperature.
Study of stability of ultrathin Au films on Cu(100) using positron annihilation-induced Auger electron spectroscopy (PAES)
Authors: Yang G. , Kim J.H. , Lee K.H. , Yang S. , Koymen A.R. , Weiss A.H.
Published: September 2007

PAES (Positron Annihilation induced Auger Electron Spectroscopy) intensities from ultrathin Au films deposited at 198 K on Cu(100) were measured as a function of temperature (from 198 K to 348 K) for three different Au coverages. Intermixing of Au and Cu atoms with the increase of temperature was directly monitored. The measurements indicated that the intermixing was not reversible as a function of temperature. EAES (Electron induced Auger Electron Spectroscopy) results were compared with PAES results for each experiment, and the comparison showed the feasibility of PAES over EAES for the study of surface alloy formation as a function of temperature.
Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates
Authors: Brooks Keith G. , Reaney Ian M. , Klissurska Radosveta , Huang Y. , Bursill L. , Setter N.
Published: September 2007

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.
Surface and interface properties of ferroelectric BaTiO3 thin films on Si using RuO2 as an electrode
Authors: Jia Q.X. , Chang L.H. , Anderson W.A.
Published: September 2007

Ferroelectric BaTiO3 thin films were deposited on Si by rf magnetron sputtering. A conductive oxide, RuO2, was used as the bottom electrode of the capacitors. The performance of the thin film capacitors was found to be a strong function of the surface and interface properties between ferroelectric BaTiO3 and the bottom electrode. A suitable capacitor configuration must be used to preserve the bottom electrode, to enhance the dielectric constant, and to reduce the leakage current density of the films. BaTiO3 thin film on the RuO2/Si substrate, where the BaTiO3 thin film has a bilayer structure of polycrystalline on microcrystalline, showed a dielectric constant of 125 at a frequency of 1 MHz, leakage current density of 10−6 A/cm2 at a field intensity of 2.5 × 105 V/cm, and a breakdown voltage above 106 V/cm.
Atomic scale oxide superlattices grown by RHEED controlled pulsed laser deposition
Authors: Shaw T.M. , Gupta A. , Chern M.Y. , Batson P.E. , Laibowitz R.B. , Scott B.A.
Published: September 2007

By depositing thin films under conditions where intensity oscillations are observed in RHEED (reflection high-energy electron diffraction) spots, unit cell level multilayers of SrTiO3/BaTiO3 structures have been grown by pulsed laser ablation. High resolution TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) observations of the deposits show that epitaxial multilayers with layer thicknesses of 1, 2, 4, 8, and 16 unit cells can be grown on [100] orientation SrTiO3 substrates. The superlattices show partial intermixing of the Sr and Ba for layer thicknesses less than 8 unit cells, but incomplete intermixing occurs even when the layers are only a single unit cell thick. From observations of the degree of intermixing at different depths in the deposit, it was determined that most of the intermixing takes place during deposition and not during subsequent annealing of the deposit. The 16 and 8 unit cell thick BaTiO3 layers were found to be tetragonal with the c-axis of the layers oriented normal to the substrate but with the a-axis strained to coherently match the SrTiO3 layers.
Stabilization of perovskite phase and dielectric properties of Pb(Zn, Mg)1/3Nb2/3O3-PbTiO3 ceramics prepared by excess constituent oxides
Authors: Jang Hyun M. , Lee Kyu-Mann , Lee Moon-Ho
Published: September 2007

The perovskite phase in PZN-PMN-PT (PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbTiO3) pseudoternary ceramics was stabilized by the addition of excess constituent divalent oxides (PbO, MgO, and ZnO). 5 mol% excess MgO or 7.5 mol% excess PbO was sufficient to eliminate the remnant cubic pyrochlore phase after sintering at 1100 °C for 1 h. The enhanced diffuse phase transition (DPT) and the decrease in the electrical resistivity were observed in the presence of excess ZnO or MgO. These were interpreted in terms of the additional formation of negatively charged, short-range ordered 1: 1 domains with a concomitant generation of charge carriers (holes). The behavior of excess MgO or ZnO at concentrations above 5 mol% was studied by examining complex impedance patterns.
Cyclic fatigue of a mica-containing glass-ceramic at Hertzian contacts
Authors: Cai Hongda , Kalceff Stevens Marion A. , Hooks Bryan M. , Lawn Brian R. , Chyung Kenneth
Published: September 2007

Fatigue damage in a mica-containing glass-ceramic is examined using Hertzian contact tests. For the material in its base glass state, such tests indicate that fatigue occurs solely by chemically enhanced cone crack extension. In the glass-ceramic, fatigue is evident as an expansion of a macroscopic subsurface microfracture zone. Comparative observations of the subsurface damage in static and cyclic loading, and tests in different environments, indicate that the fatigue in the glass-ceramic is mechanical in origin, although it is enhanced by moisture. This result is reinforced by load-point-displacement data, which reveal significant hysteresis in the glass-ceramic but not in the base glass. Flexure tests on Hertz-indented glass-ceramic specimens show only a slight loss of strength, <5%, over 105cycles. This contrasts with the base glass which, although of higher laboratory strength, is subject to abrupt and severe strength degradation from cone crack pop-in. High magnification examination of the subsurface damage in the glass-ceramic suggests the underlying cause of the mechanical fatigue mechanism to be attrition of frictional tractions at closed microcrack interfaces.
ZnO microtubes
Authors: Fox G.R. , Danai P.A.
Published: September 2007

Microtubes of ZnO have been produced using sputter coating and a fugitive phase technique. ZnO was sputtered onto polyester fibers by dc magnetron sputtering, and the polyester fiber fugitive phase was subsequently burned out by annealing in air or oxygen. Tubes with an inside diameter of 23 μm and a length of 3 cm were obtained. The 3 to 6 μm thick walls of the tubes exhibited a [002] radial texture.
Ion-beam sputter deposition process for Y1Ba2Cu3O7-δ thin-film structures
Authors: Krumme J-P. , Doormann V. , Welz F. , Dösssel O. , van Hal H.
Published: September 2007

Ion-beam sputter deposition (IBS) has been developed to a fully oxygen-compatible technology for growth of complex oxides, such as Y1Ba2Cu3O7−δ (YBCO) thin films. The IBS system consists of an rf-plasma ion source with molybdenum grids for sputtering, a dc-plasma electron source for space charge compensation, stoichiometric YBCO and NGO targets, a beam chopper with BaO2, Cu, and Nd blades for stoichiometry control, and an ECR-oxygen-plasma source for in situ film oxidation and photoresist removal. Due to its complexity the IBS process is fully computer-controlled. A salient feature of IBS is the excellent crystallographic and morphological properties of thin (100)/(010)- and (103)-oriented YBCO films on SrTiO3 (STO) and NdGaO3 (NGO) substrates. Sharp interfaces and good superconducting properties render this technology feasible for the fabrication of SIS-ramp-junction SQUID's.
Microstructural features and superconducting properties of Mn-doped YBa2Cu3O7−δ
Authors: Dhingra Indu , Kashyap S.C. , Das B.K.
Published: September 2007

Small additions of MnO2 up to 15 at. % in YBa2Cu3O7−δ in place of Cu have been carried out to study their influence on the superconducting properties. It has been found that transition temperature and microstructure of Mn-doped samples are highly sensitive to the sintering temperature and Mn content. The normal state resistance increases with Mn content. Microstructure shows plate-like grain growth for low Mn contents (up to x = 0.05) at higher sintering temperature. XRD and microstructure reveals the presence of additional Y2BaCuO5 and Ba3Mn2O8 phases with an increase in Mn content. Also, reduction in the diamagnetic signal and broadening of transition is observed beyond certain Mn content. A detailed discussion of microstructure, XRD, normalized resistance, and magnetic properties has been carried out in correlation with sintering temperature and Mn content.
CdS-silica xerogel nanocomposites: Processing-induced textural changes
Authors: Blanco E. , Litrán R. , Ramírez-del-Solar M. , de la Rosa-Fox N. , Esquivias L.
Published: September 2007

CdS-silica xerogel composites were prepared from tetramethoxysilane, acidic water, and formamide mixtures homogenized by high power ultrasounds. Different concentrations of Cd(NO3)2 were added. CdS semiconductor nanoparticles were precipitated by H2S gas diffusion through the sonogel porous structure. Composite mechanical properties were enhanced by an impregnation process by the gel soaking in the same sol as-prepared. Textural parameters evolution is compared to the salt content in order to find the best performance to CdS nanocrystal growth. The impregnation process allows a better composite protection.
The microstructure and dealloying kinetics of a Cu-Mn alloy
Authors: Min Un-Sig , Li James C.M.
Published: September 2007

Porous copper was produced by electrolytic dealloying of a Cu-Mn alloy (Incramute: Cu, 40-48 wt. % Mn, 1.4-2.3 wt. % Al) conducted in a 0.3 N-NaCl solution at a potential of −0.2 V (SCE). The dealloying time needed for the as-received cold-rolled specimen (50 h) is shorter than that of the annealed specimen (850 °C for 2 h). The pore size, about 1 μm, of the dealloyed cold-rolled specimen is bigger than that, about 0.1 μm, of the dealloyed specimen after annealing. This is probably because annealing reduced the phase inhomogeneity and removed the rolling effects.
The damping properties of dealloyed porous copper and its PMMA composite
Authors: Min Un-Sig , Li James C.M.
Published: September 2007

Incramute Cu-Mn alloys were dealloyed to remove Mn by selective electrolytic separation. The porous dealloyed specimens were compressed at 0.17-14 GPa, resulting in densities of 55-88% of the density of pure copper. Some porous copper specimens before compression were soaked in a mixture of monomer (MMA) and the initiator (AIBN), compressed, and then polymerized by heating. Young's moduli of both the dealloyed porous copper and its PMMA composite were found to decrease exponentially with porosity and volume fraction of PMMA, respectively. The apparent activation energy for damping of Cu-PMMA composite near the glass transition temperature of PMMA was found to increase with decreasing volume fraction of PMMA.
The formation mechanism of barium titanate thin film under hydrothermal conditions
Authors: Shi E. , Cho C.R. , Jang M.S. , Jeong S.Y. , Kim H.J.
Published: September 2007

Barium titanate thin films were produced under the hydrothermal conditions, and their formation mechanism was investigated. The phase structure and surface morphology of the resultant films were directly dependent on the reaction conditions. The films that have a reaction time shorter than 8 h below the processing temperature of 150 °C in the 0.8 N Ba(OH)2 solution were composed of compounds with the component ratio m(Ba)/ m(Ti) < 1, and a flower-like surface morphology. With extended reaction time under the higher temperature, the films showed a multiphase structure and a mosaic or island-like surface morphology. In the case of 1.0 N, 1.5 N Ba(OH)2 solution, well-crystallized, monoperovskite BaTiO3 thin films having uniform, mirror-like, and visible-defectless surfaces were produced at a processing temperature of 180 °C after 24 h. The experimental results were explained by hypothesizing that the formation mechanism consists of a “dissolutions-crystallization process”.
On the role of ions in the formation of cubic boron nitride films by ion-assisted deposition
Authors: Mirkarimi P.B. , McCarty K.F. , Medlin D.L. , Wolfer W.G. , Friedmann T.A. , Klaus E.J. , Cardinale G.F. , Howitt D.G.
Published: September 2007

We have investigated how ion irradiation can selectively promote the formation of dense sp3-bonded cubic boron nitride (cBN) over the graphite-like sp2-bonded phases. We have conducted a series of experiments using ion-assisted pulsed laser deposition in which either the ion mass (mion) or ion energy (E) was varied in conjunction with the ratio of ion flux to depositing atom flux (J/a). For a fixed ion energy and mass, there is a critical J/a above which cBN formation is initiated, a window of J/a values in which large cBN percentages are obtained, and a point at which J/a is so large that the resputter and deposition rates balance and there is no net film deposition, in agreement with Kester and Messier. As do Kester and Messier, we find that cBN formation is controlled by a combination of experimental parameters that scale with the momentum of the ions. However, unlike Kester and Messier, we do not find that cBN formation scales with the maximum momentum that can be transferred in a single binary collision, as either incorrectly formulated by Targove and Macleod and used by Kester and Messier, or as correctly formulated. Instead we observe that cBN formation best scales with the total momentum of the incident ions, (mionE)1/2. We also consider the mechanistic origins of this (mionE)1/2 dependence. Computer simulations of the interaction of ions with BN show that cBN formation cannot be simply scaled to parameters such as the number of atomic displacements or the number of vacancies produced by the ion irradiation. A critical examination of the literature shows that none of the proposed models satisfactorily accounts for the observed (mionE)1/2 dependence. We present a quantitative model that describes the generation of stress during ion-assisted film growth. The model invokes a kinetic approach to defect production and loss. We apply a simplified version of the model to cBN synthesis, and find that it predicts an approximate (mionE)1/2 dependence for cBN formation.
Hot-press sintering and the properties of lanthanum-rich calcium lanthanum sulfide ceramic
Authors: Tsai Ming Shyong , Hon Min Hsiung
Published: September 2007

The lanthanum-rich calcium lanthanum sulfide (CLS) was formed by a carbonate coprecipitating method followed by sulfurizing in a CS2 atmosphere at 950 °C for 3 h sulfurization. This powder then was densified by hot-press sintering at the temperature range from 1050 to 1150 °C for 0.5-2 h. The sintered pellets were resulfurized in a CS2 atmosphere at 950 °C for 1 h to restore the sulfur loss. The pellet sintered at 1050 °C for 0.5 h with 1.3 mm thickness had about 46% transmission at 13 μm.
Effects of PLT-buffer layer on microstructures of sputtered PLZT thin films epitaxially grown on sapphire
Authors: Wasa Kiyotaka , Satoh Toshifumi , Tabata Kenji , Adachi Hideaki , Yabuuchi Yasumufi , Setune Kentaro
Published: September 2007

The microstructures of sputtered thin films of lead-lanthanum zirconate-titanate (PLZT) on (0001) sapphire substrate have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thin films of polycrystalline PLZT (9/65/35), Pb0.91La0.09Zr0.65Ti0.35O3, were prepared on a (0001) sapphire substrate by reactive sputtering, using the dc-magnetron system with a multitarget, Pb, La, Zr, and Ti at the substrate temperature of 700 °C. The PLZT thin films comprised (111) oriented small crystallites of PLZT. Although the average direction of the crystal orientation corresponded to the ideal epitaxial relationship (111) PLZT ‖ (0001) sapphire, the individual crystallites showed misalignment in both the growth direction and the film plane. The thin films could not be considered epitaxially grown films. From analysis of the TEM images, there exists an interfacial region between the PLZT thin film and the substrate. The interfacial region comprises ordered clusters of (111), disordered (101), and/or (110) PLZT crystallites. The presence of the interfacial region will suppress ideal epitaxial growth with uniform crystal orientation. It is confirmed that the addition of the buffer layer of graded composition of PLT-PLZT, between the substrate and the PLZT thin film, will suppress the formation of the disordered interfacial region and will enhance the epitaxial growth of the (111) PLZT on (0001) sapphire with three-dimensional crystal orientations.