bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid state reactions between Pd and Si induced by high energy ball milling
Authors: Zhang D.L. , Massalski T.B.
Published: September 2007

Solid state reactions induced by high energy ball milling between Pd and Si have been studied. X-ray diffractometry and differential scanning calorimetry have been used to characterize the resulting phases. During milling, Pd and Si react by diffusion to form different phases depending on the Si content in the starting mixture. With a low Si content of 19 at. %, an amorphous phase forms of the same composition. On continued milling, this amorphous phase partially crystallizes into Pd9Si2 and Pd2Si compounds. With the Si content equal to or higher than 33 at. %, no amorphous phases were observed. Instead, the Pd2Si phase is produced. For powder composition corresponding to the stoichiometric compound Pd2Si (33 at. % Si), the Pd2Si forms and remains stable during further milling. With Si content equal to or higher than 50 at. %, the initially produced Pd2Si is destabilized by a reaction with the remaining Si to form PdSi, which is a metastable phase at the temperature of ball milling. It is very unlikely that an amorphous phase of a composition equal to or higher than 33 at. % Si could be produced by ball milling in the Pd-Si system. This is because the Pd2Si phase forms very easily through the reaction between Pd and Si, and this reaction competes effectively with glass formation.
Optical and electronic properties of nitrogen-implanted diamond-like carbon films
Authors: Doll G.L. , Heremans J.P. , Perry T.A. , Mantese J.V.
Published: September 2007

Optical and electrical measurements on nitrogen ion-implanted diamond-like carbon films are presented. Raman scattering measurements, which probe the crystallinity of the film surface, indicate that nitrogen implantation reduces the finite crystallographic order in the pristine carbon films. The absence of molecular vibrations in the infrared absorption spectra of the films argues against a polymeric structure of the ion-implanted films. Spectroscopic ellipsometry experiments determine the change in the optical constants of the carbon film due to nitrogen implantation. Electrical de conductivity measurements are interpreted within the framework of a schematic density of states picture of graphitic τ-electrons in an amorphous carbon system. Taken collectively, the optical and electrical measurements suggest that nitrogen implantation increases the density of localized states within the 1.5 eV bandgap of the quasi-amorphous carbon film, thereby reducing the bandgap and increasing the conductivity of the nitrogen-implanted films.
Hardness and Young's modulus of amorphous a-SiC thin films determined by nanoindentation and bulge tests
Authors: El Khakani M.A. , Chaker M. , Jean A. , Boily S. , Kieffer J.C. , O'Hern M.E. , Ravet M.F. , Rousseaux F.
Published: September 2007

Due to its interesting mechanical properties, silicon carbide is an excellent material for many applications. In this paper, we report on the mechanical properties of amorphous hydrogenated or hydrogen-free silicon carbide thin films deposited by using different deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a-SixC1−x: H PECVD, a-SiC LAD, and a-SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoindentation and bulge techniques, respectively. Hardness (H), Young's modulus (E), and Poisson's ratio (v) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a-SixC1−x: H PECVD films, both hardness and Young's modulus are dependent on the film composition. The nearly stoichiometric a-SiC: H films present higher H and E values than the Si-rich a-SixC1−x: H films. For hydrogen-free a-SiC films, the hardness and Young's modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a-SiC films present both hardness and Young's modulus values higher by about 50% than those of hydrogenated a-SiC: H PECVD films. By using the FTIR absorption spectroscopy, we estimated the Si-C bond densities (NSiC) from the Si-C stretching absorption band (centered around 780 cm−1), and were thus able to correlate the observed mechanical behavior of a-SiC films to their microstructure. We indeed point out a constant-plus-linear variation of the hardness and Young's modulus upon the Si-C bond density, over the NSiC investigated range [(4–18) × 1022 bond · cm−3], regardless of the film composition or the deposition technique.
Kinetic study of silicon carbide deposited from methyltrichlorosilane precursor
Authors: Tsai Ching Yi , Desu Seshu B. , Chiu Chien C.
Published: September 2007

The kinetics of silicon carbide (SiC) deposition, in a hot-wall chemical vapor deposition (CVD) reactor, were modeled by analyzing our own deposition rate data as well as reported results. In contrast to the previous attempts which used only the first order lumped reaction scheme, the present model incorporates both homogeneous gas phase and heterogeneous surface reactions. The SiC deposition process was modeled using the following reactions: (i) gas phase decomposition of methyltrichlorosilane (MTS) molecules into two major intermediates, one containing silicon and the other containing carbon, (ii) adsorption of the intermediates onto the surface sites of the growing film, and (iii) reaction of the adsorbed intermediates to form silicon carbide. The equilibrium constant for the gas phase decomposition process was divided into the forward and backward reaction constants as 2.0 × 1025 exp[(448.2 kJ/mol)/RT] and 1.1 × 1032 exp[(-416.2 kJ/mol)/RT], respectively. Equilibrium constants for the surface adsorption reactions of silicon-carrying and carbon-carrying intermediates are 0.5 × 1011 exp[(-21.6 kJ/mol)/RT] and 7.1 × 109 exp[(-33.1 kJ/mol)/RT], while the rate constant for the surface reaction of the intermediates is 4.6 × 105 exp[(-265.1 kJ/mol)/RT].
Emanation thermal analysis in the characterization of zinc sulfide thin films prepared from different precursors
Authors: Balek V. , Fusek J. , Kříž O. , Leskelä M. , Niinistö L. , Nykänen E. , Rautanen J. , Soininen P.
Published: September 2007

Zinc sulfide thin films were prepared by the Atomic Layer Epitaxy (ALE) process from zinc acetate and zinc chloride and studied by emanation thermal analysis (ETA). The effects of different precursors and growth temperatures were evident in the ETA curves. In the films grown from zinc acetate, thermally induced changes were detected below 95 °C and above 400 °C which can plausibly be attributed to a higher amount of volatiles and to a polymorphic transition, respectively. The cubic to hexagonal transition was confirmed by DSC. Doping with terbium distorts the crystal structure and causes the peaks to become poorly discernible.
Thermochemistry in the system Cu–In–S at 723 K
Authors: Migge H. , Grzanna J.
Published: September 2007

A thermochemical analysis is performed in the system Cu-In-S at 723 K. Free energies of In6,S7, In417S583, “In2S3”, Cu951In49, and CuIn5S8 have been estimated, the numerical values (kJ/mol) of which are −1285, −97 780, −481.1, −31 680, and −1444. The free energy (kJ/mol) of CuInS2 is calculated from the relation G° = (-306.1 ± 54.4) + 0.5092T −1.397 10−5T2 −0.09468T In T + 268.2T−1, which is obtained from published assessed standard formation enthalpy and specific heat and entropy data. The free energy of the Cu-In melt is taken from very new literature. A consistent set of data is used for the calculation of a tentative Gibbs triangle as well as of the corresponding predominance area diagram. The Gibbs triangle is calculated with the program thermo, the algorithm of which is given. The results are in agreement with the results of published measurements, also for the equilibria which involve the melt. The compound CuInS2, one of the possible base materials for thin film solar cells, is shown to equilibrate with most of the compounds of the system. Predictions are made how to prepare CuInS2 from Cu-In alloys and H2S/H2 gas mixtures. However, more experiments are necessary to establish the data, the experiments, and/or the results of the calculations.
Microstructure of Cr2O3 coatings on steel and the effect of silicon
Authors: den Burg M. Van , De Hosson J.Th.M.
Published: September 2007

This paper concentrates on the microstructural features of steel containing 22 wt. % Cr, coated with Cr2O3 by laser processing. It turned out that after laser coating the Cr2O3 powder has completely transformed to Fe0.3Cr2.7O4 having the tetragonal distorted spinel structure. Dispersed in the coating are metallic particles with composition FeCr and a bcc structure. The phases in the coating can be explained from the Fe-Cr-O equilibrium phase diagram with the assumption that complete phase equilibrium is reached in the liquid state but not during solidification. The two equilibrium phases, L0 and Lm, that exist in the molten state solidify as two independent liquids. Addition of Si to the ceramic material, either from the steel matrix or from the ceramic powder, results in a dendritic solidification structure of Cr3O4 dendrites and a Si-containing glassy phase. The dendrites are oriented vertically in the coating, resembling the columnar microstructure that is also observed in ZrO2 thermal barrier coatings. This structure contains fewer microcracks parallel to the interface resulting in a mechanically more stable ceramic coating.
Compositional and thermal effects on chemically processed AlN–BN nanocomposite powders
Authors: Chow G.M. , Xiao T.D. , Chen X. , Gonsalves K.E.
Published: September 2007

Powders of nanocrystalline aluminum nitride (AlN) and boron nitride (BN) were prepared via a chemical route. Precomposite gels, which were obtained from ammonolysis of aqueous solutions of boric acid, urea, and aluminum chloride hexahydrate, were thermally processed to produce AlN-BN nanocomposite powders with a wide range of compositions. These powders were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The structure, morphology, and crystallite size of the powders are correlated with the compositions and processing temperature. Normal and abnormal grain growth are discussed.
Microstructure, strength, and reaction products of ground granulated blast-furnace slag activated by highly concentrated NaOH solution
Authors: Schilling Paul J. , Roy Amitava , Eaton H.C. , Malone Philip G. , Brabston Newell W.
Published: September 2007

Ground granulated blast-furnace slag was reacted in 5 M (pH 14.7) and 1.5 M (pH 14.2) NaOH solutions at a water/slag ratio of ∼0.4, and characterized by unconfined compressive strength testing, scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The reacted material consisted of a dense layered matrix interspersed with unreacted glass particles and regions of reaction products with higher porosity. CSH(I) and (C, M)4AH13 were identified by x-ray diffraction. The C-S-H (calcium silicate hydrate) phase is proposed to consist mainly of structurally imperfect layers of tobermorite, interleaved with layers of (C, M)4AH13. Other cations, most significantly Na+, are incorporated into the structure. Use of the highly concentrated solution (5 M) produced a higher degree of reaction and, consequently, higher compressive strength (38 MPa after 28 days for 5 M solution vs 21 MPa for 1.5 M).
Microstructure and superconducting properties of attrition-milled Bi2Sr2CaCu2Ox
Authors: Luo J.S. , Lee H.G. , Sinha S.N.
Published: September 2007

The microstructure and superconducting properties of Bi2Sr2CaCu2Ox (Bi-2212) during high-energy attrition milling were investigated in detail by a combination of x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and magnetization techniques. The starting superconducting powder was milled in a standard laboratory attritor using yttria-stabilized ZrO2 balls and a stainless steel tank. After selected time increments, the milling was interrupted and a small quantity of milled powder was removed for further analysis. It was found that the deformation process rapidly refines Bi-2212 into nanometer-size crystallites, increases atomic-level strains, and changes the plate-like morphology of Bi-2212 to granular submicron clusters. At short milling times, the deformation seems localized at weakly linked Bi-O double layers, leading to twist/cleavage fractures along the {001} planes. The Bi-2212 phase decomposes into several bismuth-based oxides and an amorphous phase after excessive deformation. The superconducting transition is depressed by about 10 K in the early stages of milling and completely vanishes upon prolonged deformation. A deformation mechanism is proposed and correlated with the evolution of superconducting properties. The practical implications of these results are presented and discussed.
Study of cluster-assembled nanophase copper using NMR
Authors: Suits B.H. , Meng M. , Siegel R.W. , Liao Y.X.
Published: September 2007

Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10 nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to −1/2 transition. The broadening of the central line is associated with a distribution of Knight shifts. A very broad background is observed on either side of that peak, associated with broadening due to internal electric field gradients. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger-grained copper samples. The strain within the grains is estimated to be 0.7%. Line shape measurements as a function of spin echo delay time show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant line narrowing after an anneal at 450 °C consistent with other nanophase metals which show grain growth above 40-50% of the absolute melting temperature. The dependence of NMR linewidth on average grain diameter is estimated.
Plastic deformation in icosahedral Al–Pd–Mn alloys
Authors: Shield J.E. , Kramer M.J. , McCallum R.W.
Published: September 2007

The deformation characteristics of icosahedral Al70Pd21.5Mn8.5 have been investigated by high temperature creep experiments, and the resultant microstructures have been examined by transmission electron microscopy (TEM). From 730 to 780 °C, microstructural analysis revealed that the deformation is controlled by dislocation glide, with an activation energy of 210 ± 30 kJ/mole and a stress exponent of 1.2 ± 0.2. From 780 to 810 °C, microstructures were characteristic of deformation controlled by dislocation glide and climb. The activation energy and stress exponent were determined to be 1700 ± 80 kJ/mole and 2.9 ± 0.3, respectively. Hardness measurements also reflected an increase in dislocation density, as the hardness of the deformed samples was approximately 10% higher than the as-cast sample.
Kinetics of B2, DO3, and B32 ordering: Results from pair approximation calculations and Monte Carlo simulations
Authors: Anthony L. , Fultz B.
Published: September 2007

A kinetic theory of ordering based on the path probability method was implemented in the pair (Bethe) approximation and used to study the kinetics of short- and long-range ordering in alloys with equilibrium states of B2, DO3, or B32 order. The theory was developed in a superposition approximation for a vacancy mechanism on a bcc lattice with first- (1nn) and second-nearest neighbor (2nn) pair interactions. Chained 1nn conditional probabilities were used to account for the entropy of 2nn pair configurations. Monte Carlo simulations of ordering were also performed and their results compared to predictions of the pair approximation. Comparisons are also made with predictions from an earlier kinetic theory implemented in the point (Bragg-Williams) approximation. For all three calculations (point, pair, and Monte Carlo), critical temperatures for B2 and DO3 ordering are reported for different 1nn and 2nn interaction strengths. The influence of annealing temperature on the kinetic paths through the space of B2, DO3, and B32 order parameters was found to be strong when the thermodynamic preferences for the ordered states were of similar strengths. Transient states of intermediate order were also studied. A transient formation of B32 order in an AB3 alloy was found when 2nn interactions were strong, even when B32 order was neither a Richards-Allen-Cahn ground state nor a stable equilibrium state at that temperature. The formation of this transient B32 order can be argued consistently from a thermodynamic perspective. However, a second example of transient B2 order in an AB alloy with equilibrium B32 order cannot be explained by the same thermodynamic argument, and we believe that its origin is primarily kinetic.
Preparation of FeCl3–IBr–H2SO4–graphite multi-intercalation compounds
Authors: Abe Takeshi , Mizutani Yasuo , Ihara Eiji , Asano Mitsuru , Harada Toshio
Published: September 2007

Stages 4-6 FeCl3-graphite intercalation compounds (GIC's) have been prepared by an ordinary two-bulb method, and FeCl3-IBr-graphite bi-intercalation compounds (GBC's) are synthesized by holding the FeCl3-GIC's in the saturated vapor of IBr. The x-ray diffraction patterns of the FeCl3-IBr-GBC's obtained from stages 4, 5, and 6 FeCl3-GIC's give the stacking sequences as G(FeCl3)GG(IBr)GG(FeCl3)G, G(FeCl3)GG(IBr)GGG(FeCl3)G, and G(FeCl3)GG(IBr)GG(IBr)GG(FeCl3)G, respectively, where G, (FeCl3), and (IBr) refer to the graphite, FeCl3, and IBr layers, respectively. The multi-intercalation of H2SO4 into the FeCl3-IBr-GBC's synthesized from stages 4 and 6 FeCl3-GIC's occurs at all the vacant galleries of the GBC's at the same time. In contrast, the multi-intercalation of H2SO4 into the FeCl3-IBr-GBC obtained from the stage 5 FeCl3-GIC takes place in two processes. The first multi-intercalation occurs at the gallery adjacent to the bi-intercalated IBr layer, and the stacking sequence of the resulting graphite multi-intercalation compound is determined to be G(FeCl3)GG(IBr)G(H2SO4)GG(FeCl3)G, where (H2SO4) refers to the H2SO4 layer. The second multi-intercalation occurs at all the rest of the vacant galleries.
Amorphous carbon antireflective coatings in the 10 to 50 μm region of the far-IR
Authors: Metin Serhat , Kaufman James H. , Saperstein David D. , Scott Campbell J. , Heyman James , Haller Eugene E.
Published: September 2007

The efficiency of far-IR germanium photoconductive detectors can be markedly improved by antireflective coatings. Recently, there has been an effort to develop several micrometer thick, low stress, amorphous carbon films for this purpose. To date, films of no more than 1 to 2 μm have been reported in the literature. In this paper we report the deposition of low stress carbon films which are over 5 μm thick and are effective antireflective coatings at wavelengths of up to Λ = 43 μm. Minimal stress, a requirement for good adhesion, was achieved with a chemical vapor deposition process (CVD) by controlling the hydrocarbon partial pressure (2.2 mTorr) and by doping the carbon film with nitrogen.
On the microstructure, chemistry, and dielectric function of BaTiO3 MOCVD thin films
Authors: Dravid V.P. , Zhang H. , Wills L.A. , Wessels B.W.
Published: September 2007

Thin films of BaTiO3 deposited on (100)LaAlO3 substrate by metal-organic chemical vapor deposition (MOCVD) are investigated using several electron-optical techniques. Combined high resolution transmission electron microscopy (HRTEM), electron energy loss spectrometry (EELS), and convergent beam electron diffraction (CBED) indicate a substantial influence of lattice strain on the structural and optical characteristics of BaTiO3 films. Spatially resolved EELS and CBED studies indicate that the substrate influence persists up to about 40 nm away from the interface. The changes in the dielectric function of the films, as inferred from spatially resolved EELS, appear to correlate well with internal lattice strain in the films as deduced from convergent beam electron diffraction (CBED).
The mechanism of combustion synthesis of titanium carbonitride
Authors: Eslamloo-Grami M. , Munir Z.A.
Published: September 2007

Titanium carbonitride, TiC0.5N0.5, is synthesized directly by a self-propagating reaction between titanium and carbon in a nitrogen atmosphere. Complete conversion to the carbonitride phase is achieved with the addition of TiN as diluent and with a nitrogen pressure ≥0.6 MPa. Thermodynamic phase-stability calculations and experimental characterizations of quenched samples support a proposed mechanism in which the formation of the carbonitride is a two-step process. The first step involves the formation of the nonstoichiometric carbide, TiC0.5, and is followed by the formation of the product by the incorporation of nitrogen in the defect-structure carbide to form the carbonitride solid solution.
Decomposition of CO2 to carbon by H2-reduced Ni(II)- and Co(II)-bearing ferrites at 300 °C
Authors: Kodama T. , Kato H. , Chang S.G. , Hasegawa N. , Tsuji M. , Tamaura Y.
Published: September 2007

Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO2 decomposition. Ni2+ and Co2+ have been substituted for Fe2+ or Fe3+ in magnetite with the spinel type of crystal structure up to 14% and 26% for the mole ratio of Ni2+ and Co2+ to the total Fe contents, respectively. The metal substitution was corroborated by Mössbauer spectroscopy and XRD studies. They were activated in a flow of H2 gas to form oxygen-deficient ferrites with the spinel structure retained. The oxygen-deficient M(II)-bearing ferrites have been found to show high reactivity toward CO2 decomposition to carbon at 300 °C. The reactivity increased with the level of metal substitution and activation. The oxygens of CO2 were incorporated into the spinel structure and carbon was deposited on the surface of the ferrites. The deposited carbon was visible on dissolution of the ferrites used. The rate of decomposition on H2-activated Ni(II)-bearing ferrite with the mole ratio of 14% was 30 times as high as that of H2-activated magnetite.
Effects of thermal cycling in a reducing atmosphere on metal/polyimide interfaces
Authors: Rao Peddada S. , Robertson I.M. , Birnbaum H.K.
Published: September 2007

Effects of thermal cycling in a reducing (deuterium) atmosphere on the structure and chemistry of Cr/Cu/Cr/polyimide (PI)/Si and Au/Cu/Ti/polyimide (PI)/Si multilayer systems have been studied. In the Cr/PI system the interface between the Cr and PI was sharp and distinct in the as-deposited state, and after the anneal in the reducing atmosphere. Tensile cracks through the Cr/Cu/Cr layers were found after annealing and are the result of thermal stresses. No evidence for significant diffusion of Cr into the PI was found. In the Ti/PI system, the interface between the Ti and PI was sharp in the as-deposited state. After annealing in vacuum and in the reducing environment, regions of the interface between the Ti layer and the PI were converted to an oxide, Ti5O9. Annealing in the deuterium environment also caused delamination of the Ti film from the PI and blistering of the metal in the sample interior. No significant diffusion of the Ti into the PI was detected. In both systems, the metal in contact with the PI acted as a barrier to the diffusion of Cu into the PI.
Amorphous silicon nitride fibers grown from the vapor phase
Authors: Wallenberger Frederick T. , Nordine Paul C.
Published: September 2007

Using high reactor pressures (>1 bar) and a unique rate control mechanism, three fibers were recently obtained by laser assisted chemical vapor deposition (LCVD) having elemental (i.e., boron, carbon, and silicon) compositions, small diameters (>9 μm), and surprisingly high growth rates (0.3–1.1 mm/s). By reacting silane and ammonia at high pressures (>1 bar) near the focus of a Nd-YAG laser beam, we have now obtained the first LCVD fibers with binary (i.e., silicon-nitrogen and silicon nitride) compositions having small diameters and high growth rates (0.34–0.74 mm/s). These fibers were amorphous.
Structural and magnetic characterization of granular Y1Ba2Cu3O7−δ nanocrystalline powders
Authors: Simoneau M. , L'Espérance G. , Trudeau M.L. , Schulz R.
Published: September 2007

High energy ball milling has been used to produce nanocrystalline Y1Ba2Cu3O7-δ powders. These powders are being used as starting materials for manufacturing superconducting textured wires by a solid state recrystallization process. Magnetic and microstructural characterizations were performed as a function of milling time. The milling reduces the average crystal size and creates low and high-angle grain boundaries which increase the granularity of the superconductor. As a result, the long-range order on the oxygen sublattice and on the yttrium and barium sites is destroyed. A transition from orthorhombic to tetragonal and finally to a cubic metastable phase is observed. Total loss of superconductivity occurs after about 1 h of milling. Prior to this time, superconductivity can partially be restored by room-temperature aging. High-temperature heat treatment of the nanocrystalline phase produces a tetragonal structure with c = 3a.
High-temperature deformation and fracture of Bi–Sr–Ca–Cu–O superconductors
Authors: Goretta K.C. , Zamirowski E.J. , Calderoñ-Moreno J.M. , Miller D.J. , Chen Nan , Holesinger T.G. , Routbort J.L.
Published: September 2007

Dense polycrystalline Bi2Sr2Cu2Ox (2201), Bi2Sr2CaCu2Ox (2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (2223) specimens were compressed in air at 730–835 °C. All of the materials exhibited an apparent steady-state creep response. Strain rate was proportional to stress to the 3.1–3.8 power. Apparent activation energies for the deformation processes were 520 ± 50 kJ/mole for the 2201, 630 ± 210 kJ/mole for the 2212, and 960 ± 210 kJ/mole for the 2223. Transmission electron microscopy revealed substantial generation and propagation of basal-plane dislocations during deformation. Few nonbasal-plane dislocations were observed. Intergranular fracture was evident in all deformed samples, and intragianular fracture was evident along the basal planes of some grains. It is suggested that the kinetics of fracture were determined by dislocation motion within the grains.
The finite electromigration boundary value problem
Authors: Lloyd J.R. , Kitchin J.
Published: September 2007

The electromigration boundary value problem is investigated for the three physically reasonable boundary conditions, assuming a perfectly blocking boundary on one side. The solution to this problem is believed to be that for nucleation dominated electromigration lifetime. The three boundary conditions investigated are the semi-infinite constant vacancy source of Shatzkes and Lloyd,9 the closed system of De Groot13 and Kirchheim and Käber,19 and the heretofore unsolved constant vacancy source at a finite distance from the blocking boundary. It is argued that the first is unrealistic in that there is no length effect possible, which has been repeatedly observed experimentally. The second is argued to be too restrictive to account for failure, leaving the last as the most physically reasonable under most circumstances. The deceptively simple appearance of the boundary conditions belies a complex, double infinite series solution arrived at by a unique approach to inverting the Laplace transform of the solution. The solution correctly predicts the experimental observations of a length effect and, combined with the understanding provided by the solutions under the other two boundary conditions, the effect of a thick passivation layer on electromigration lifetime.
Reconstruction of grain boundaries in copper and gold by simulation
Authors: Phillpot S.R.
Published: September 2007

The reconstructions of high-angle twist grain boundaries on the four densest atomic planes in fcc copper, as described by a Lennard-Jones potential, and gold, as described by an embedded-atom-method potential, are investigated using the recently developed method of grand-canonical simulated quenching. It is found that the grain boundaries on the widely spaced (111) and (100) planes do not reconstruct, while those on the less widely spaced (110) and (113) planes do reconstruct. The effect that reconstruction can have on the physical properties of an interfacial system is illustrated by comparing the elastic properties and ideal cleavage energies of reconstructed grain boundaries with those of corresponding unreconstructed grain boundaries.
Thermodynamics and kinetics of stable and metastable phases in the Ni–Zr system
Authors: Ghosh G.
Published: September 2007

The thermodynamic parameters of all stable phases in the Ni-Zr system are reported in this paper. The available experimental data are taken into account in deriving the interaction parameters of various phases. The Ni7Zr2, Ni21Zr8, Ni11Zr9, NiZr, and NiZr2 phases are treated as stoichiometric. The solid solubility of the Ni5Zr, Ni3Zr, and Ni10Zr7 phases are described using a two sublattice model. The calculated thermodynamic properties and the phase diagram are in good agreement with the experimental ones. The thermodynamic parameters, along with the classical nucleation and crystal growth theory, have been used to explain the formation of metastable noncrystalline and crystalline phases upon rapid quenching of the liquid alloys. It has been demonstrated that even without any prior knowledge of the physical property, such as glass transition or crystallization temperature and thermodynamic property, such as the enthalpy of amorphous → crystal transformation of the amorphous alloy, it is possible to make a reasonably good “first order prediction” of the glass-forming range in a binary system. The experimentally determined glass-forming range in the Ni-Zr system is found to be in good agreement with the predicted one.
Morphological variations in flame-deposited diamond
Authors: Frey E.A. , Tamhane A. , Rebello J.H.D. , Dregia S.A. , Subramaniam V.V.
Published: September 2007

An oxy-acetylene flame, impinging vertically upward on an Si(001) substrate, is systematically examined for morphological variations in the resulting diamond deposits. The flame is operated under near neutral (O2/C2H2 ratio near 1.0) conditions in the unconfined, open atmosphere. Singly twinned crystal morphologies in addition to the usual (001) faceted structures are observed and reported for the first time. Similar morphological variations are observed along the radial as well as the axial (vertical) coordinate directions in the flame. Large changes in morphology are observed for changes in vertical position as small as 50 μm.
13C NMR investigation of CVD diamond: Correlation of NMR and Raman spectral linewidths
Authors: Merwin Lawrence H. , Johnson Curtis E. , Weimer Wayne A.
Published: September 2007

Six CVD diamond thin films were examined by magic angle spinning (MAS) 13C nuclear magnetic resonance (NMR), Raman, and electron spin resonance spectroscopy. The use of film samples cut to the diameter of the magic-angle spinning rotor provided ease of spinning and the opportunity to obtain good signal-to-noise spectra in 4 to 16 h. MAS NMR linewidths exhibit a linear correlation with Raman linewidths and reflect the optical quality of the material. Residual MAS NMR linewidths most likely arise from a combination of crystal defect sites and paramagnetic effects.
Diamond-coated carbon fiber
Authors: Ting J. , Lake M.L.
Published: September 2007

Diamond deposition was attempted on polyacrylonitrile (PAN) fiber and vapor grown carbon fiber (VGCF). PAN fibers were severely etched in a microwave plasma, whereas diamond was successfully deposited on VGCF. A diamond growth rate of 0.1 μm/h on VGCF was determined at a gas mixture of 99.9 sccm H2/0.1 sccm CH4 and a pressure of 30 Torr. It is proposed that diamond formation on VGCF occurs on not only the prism planes, but also the basal planes owing to the unique structure of VGCF. An explanation is proposed to explain diamond nucleation on the basal planes.
Electrical resistivity of carbon black loaded polyethylene modified by ion implantation
Authors: Švorčik Václav , Rybka Vladimír , Jankovskij Oleg , Hnatowicz Vladimír , Kvítek Jiří
Published: September 2007

Different properties of the mixtures of polyethylene with carbon black modified by the implantation of Sb+ ions were studied. Chemical changes of polymer were examined by IR- and UV-visible spectroscopy. Sheet resistivity as a function of sample temperature was studied. Depth profiles of implanted Sb atoms and incorporated oxygen were determined by the Rutherford backscattering technique. The percolation threshold of unimplanted mixtures is found at 4.5 and 5 wt. % of carbon black. As a result of ion implantation, the polymer is oxidized and conjugated double bonds are produced. The mixtures with carbon black concentration above percolation threshold exhibit metal-like conductivity. For the mixtures below percolation threshold, the measurements of resistivity versus temperature dependence indicate semiconductor type conductivity and charge transport via a variable range-hopping mechanism.
Solid-state reaction of Pt thin film with single-crystal (001) β–SiC
Authors: Chen J.S. , Kolawa E. , Nicolet M-A. , Ruiz R.P. , Baud L. , Jaussaud C. , Madar R.
Published: September 2007

Thermally induced solid-state reactions between a 70 nm Pt film and a single-crystal (001) β-SiC substrate at temperatures from 300 °C to 1000 °C for various time durations are investigated by 2 MeV He backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, scanning electron microscopy, and cross-sectional transmission electron microscopy. Backscattering spectrometry shows that Pt reacts with SiC at 500 °C. The product phase identified by x-ray diffraction is Pt3Si. At 600–900 °C, the main reaction product is Pt2Si, but the depth distribution of the Pt atoms changes with annealing temperature. When the sample is annealed at 1000 °C, the surface morphology deteriorates with the formation of some dendrite-like hillocks; both Pt2Si and PtSi are detected by x-ray diffraction. Samples annealed at 500–900 °C have a double-layer structure with a silicide surface layer and a carbon-silicide mixed layer below in contact with the substrate. The SiC—Pt interaction is resolved at an atomic scale with high-resolution electron microscopy. It is found that the grains of the sputtered Pt film first align themselves preferentially along an orientation of {111}Pt//{001}SiC without reaction between Pt and SiC. A thin amorphous interlayer then forms at 400 °C. At 450 °C, a new crystalline phase nucleates discretely at the Pt-interlayer interface and projects into or across the amorphous interlayer toward the SiC, while the undisturbed amorphous interlayer between the newly formed crystallites maintains its thickness. These nuclei grow extensively down into the substrate region at 500 °C, and the rest of the Pt film is converted to Pt3Si. Comparison between the thermal reaction of SiC-Pt and that of Si–Pt is discussed.
Surface characteristics of high-strength MgO–CaO–SiO2−P2O5 glass-ceramics
Authors: Shyu Jiin-Jyh , Wu Jenn-Ming
Published: September 2007

Surface-related characteristics (growth of surface layer and crystal preferred orientation) and the resulting mechanical strength of apatite-containing glass-ceramics in the system MgO–CaO–SiO2−P2O5 were investigated. The variations of surface-layer thickness and crystal preferred orientation were explained by a criterion considering both the surface and bulk nucleation of apatite phase. Glass-ceramics with a fairly high strength of 250–410 MPa could be obtained by an appropriate two-step heat treatment. The high strength in the present study is closely related to the growth of the surface layer, which might result in surface compressive-stress.
Thermodynamic modeling of chemical interactions between CaO–TiO2 ceramics and molten salts
Authors: Johnson I. , Maiya P.S.
Published: September 2007

The mixed-oxide compounds of CaO with TiO2 are of interest in the development of container vessels for actinide recycling processes in which Ca (dissolved in molten salt) is used to reduce the actinide oxide to actinide metal. The chemical interactions between the mixed-oxide compounds and molten salt saturated with Ca have been analyzed by applying thermodynamic principles. Although the solubility of CaO in molten salt is suppressed by the formation of mixed oxide with TiO2, thermodynamic calculations show that corrosion of CaO-TiO2 ceramics by molten CaCl2 or CaCl2-20 mole % CaF2 that contains metallic Ca in solution occurs by dissolution of the CaO component of the mixed-oxide compounds in the molten salt and reduction of the TiO2 component by the metallic Ca. The thermodynamic predictions are consistent with the experimental observations. The corrosion products produced and the sequence of the various phases depend upon the activity of the CaO produced in the molten salt by reduction reactions. The results of this study show that ceramic materials in the CaO-TiO2 system are not suitable container materials for actinide recycling.
Formation and characterization of nanostructured V—P—O particles in flames: A new route for the formation of catalysts
Authors: Miquel Philippe F. , Katz Joseph L.
Published: September 2007

A counterflow diffusion flame burner was used to produce nanophase vanadium-phosphorus oxide powders in a hydrogen-oxygen flame. Liquid precursors, i.e., VOCl3 and PCl3, were used as source materials in a 1:1 ratio. In situ formation processes were investigated at two temperatures by laser light scattering, by emission and absorption spectroscopy, and by collecting particles directly onto carbon-coated TEM grids. At the higher temperature, the collected powders are spherical particles about 30 to 50 nm in diameter. At the lower temperature, the powders collected are chain-like structures composed of particles 5 to 10 nm in diameter. Particles formed in the burner were collected also from the burner's flanges and from two auxiliary strips. Their crystalline phases and surface area were determined by x-ray diffractometry, FT-IR spectroscopy, and BET analysis by nitrogen desorption. These results indicate a strong influence of temperature on the crystalline phases of the powders. At the higher temperature, the powder collected is a mixture of VOPO4 · 2H2O and δ-VOPO4. This mixture forms Λ-VOPO4 upon subsequent reheating at 750 °C. At the lower temperature, the powders collected are a VOHxPO4 · yH2O phase and VO(H2PO4)2, and form β-VOPO4 and V(PO3)3, respectively, upon subsequent reheating at 750 °C.
Porous glass-ceramics cation exchangers: Cation exchange properties of porous glass-ceramics with skeleton of fast Li ion-conducting LiTi2(PO4)3 crystal
Authors: Hosono Hideo , Tsuchitani Fumihiko , Imai Kazunari , Abe Yoshihiro , Maeda Masunobu
Published: September 2007

Lithium titanium orthophosphate LiTi2(PO4)3 (LTP) has attracted attention as a chemically stable fast Li+-conductor in ambient atmosphere. It was reported in our previous paper7 that monolithic microporous glass-ceramics with a skeleton of this crystal were successfully prepared from glasses in the pseudobinary system of LTP and Ca3(PO4)2. Here we report that these porous glass-ceramics (mean pore diameter: ∼40 nm; total specific surface area: ∼30 m2; porosity: ∼45 vol.%) show excellent cation exchange properties. Approximately 50% of Li+ ions in the materials are exchanged with monovalent ions with ionic radii smaller than 130 ppm in 1 h at room temperature. In particular, Li+ ions are selectively exchanged with Ag+ ions even in the presence of Na+ ions. The exchange rate in the porous glass-ceramics is larger by two orders of magnitude than that of sintered LTP. The ratio of these exchange rates is close to that of the total surface areas, indicating that most of the pores in porous LTP glass-ceramics are available for ion exchange reactions. These are the first porous glass-ceramics having excellent cation exchange properties.
An investigation of the assembly conditions of dielectric particles in uncured thermoset polymers
Authors: Bowen C.P. , Bhalla A.S. , Newnham R.E. , Randall C.A.
Published: September 2007

It has been found that electric field induced fibrolysis of suspended dielectric powder in a variety of uncured thermoset polymeric materials is a potential fabrication means to assemble ceramic-polymer composites. The resulting composite material consists of a quasi 1–3 connectivity pattern due to the formation of fibrils by the ceramic powder. For a given thermoset polymer, the degree to which these fibrils form is strongly dependent on both the magnitude and frequency of the applied field. Fibril formation is maximized at certain ac frequencies independent of the volume fraction of filler utilized. Outside these frequency ranges, electroviscous behavior and the associated fibrolysis are drastically diminished or even nonexistent. The critical frequency values and their relation to the ideal assembly conditions for this class of composite materials are the focus of this paper.
Thermal stress analysis for coated fibers
Authors: Ellenburg M.G. , Hanigofsky J.A. , Lackey W.J.
Published: September 2007

Thermal stresses induced during cooling from temperatures used for coating deposition were calculated for various fiber-coating systems. Systems under study include several types of carbon, alumina, and zirconia fibers. Coatings considered were TiB2, Si3N4, and SiC. Typical calculated stresses were on the order of 0 to 2 GPa. The results were used to analyze the effects of variable physical parameters such as coating thickness and crystallographic orientation on the stress levels. Each fiber-coating system was then compared using a nominal coating thickness of 5 μm in order to rank the various fiber-coating combinations. Among the results obtained, it was shown that orientation of deposited coatings usually leads to higher tensile stresses.
Micro-impact technique and its applications
Authors: Wu T.W. , Lee C-K.
Published: September 2007

A micro-impact tester has been designed and built by using a piezoelectric impact hammer as an impactor driver. During the course of an impact process, force interactions between the impactor and target surfaces were monitored continuously by a miniaturized piezoelectric loadcell embedded in the flying head assembly. A 3-sided pyramidal diamond indenter (Berkovich indenter) was used as an impactor. After having fully characterized such an impact system, the trajectory of the impactor can be calculated by using the corresponding prerecorded impact force interaction in a simulation program. The contact and returning velocities, kinetic energy loss of the impactor, and the impact penetration curve are the key pieces of information obtained from the simulation. Furthermore, the impact morphology can reveal failure mechanisms of materials by providing details such as indent shapes, coating fragment, chipping, crack type and size, and other information which are useful in assessing the fracture toughness of testing materials. The micro-impact testing was carried out in the contact velocity ranging from 0.3 to 2.0 m/s. Three types of materials such as metal, glass, and amorphous carbon were used in studying their distinct mechanical behavior under high rate indentations. The correlations among the impact conditions, energy losses, impact morphologies, and material responses are illustrated and discussed.
The micro-wear technique and its application to ultrathin film systems
Authors: Wu T.W. , Lee C-K.
Published: September 2007

A micro-wear testing technique has been developed by incorporating a piezoelectric pusher into an existing microindenter system. The pusher and its associated servo-control circuitry were designed to generate a precise reciprocating horizontal motion at the indenter tip for implementing a microscaled wear test. The information acquired from the test includes the wear loading curve, i.e., the normal applied load versus wear penetration depth, the friction force, and in turn, the apparent wear friction coefficient. Measuring the electrical resistance across the coating thickness is also possible if an electrical conducting indenter is utilized. Furthermore, in conjunction with the surface characterization tools, the wear morphology revealed useful information regarding the coating failure mechanism(s) and shed some light toward understanding coating tribology. The tester design concepts, operating procedure, data acquisition, and analysis will be examined. Experimental results on ultrathin carbon coatings with various thicknesses will be employed to illustrate the capabilities of the micro-wear tester.
Nonlocal effects of existing dislocations on crack-tip emission and cleavage
Authors: Shastry Vijay , Anderson Peter M. , Thomson Robb
Published: September 2007

This paper investigates the criterion for a ductile-to-brittle transition in materials, due to nonlocal shielding effects at the crack tip when the dislocation free zone (DFZ) size is small. It is found that both cleavage and emission criteria are altered by nonlocal shielding, but that the emission shift is dominant, and is always in the direction to increase the local critical stress intensity for emission, kIIe. The nonlocal shift varies with the sum, Σ(γusdj)−3/2, over each dislocation (j), where γus is the unstable stacking fault energy, and dj is the distance from each dislocation to the crack tip. When there is a pileup of many shielding dislocations against a barrier near the crack tip, the total shift for the pileup varies as (γusd)−1. The most likely candidates for a brittle transition induced by the nonlocal shift are materials where barriers to dislocation motion exist within 10–100 nanometers of the crack tip, such as in thin films, multilayers, or ultrafine grain materials.
Preferred orientation of BSCCO via centrifugal slip casting
Authors: Steinlage Greg , Roeder Ryan , Trumble Kevin , Bowman Keith , Li Shi , McElfresh Mike
Published: September 2007

Due to the highly anisotropic properties of BSCCO superconductors, the bulk properties of these materials can be greatly affected by preferential orientation. Substantial c-axis orientation normal to the desired direction of current flow has been demonstrated by centrifugally slip casting lead-doped BSCCO-2223. The strong preferred orientation developed in the centrifugally slip-cast material demonstrates high critical current potential.
Texture formation on the melt-growth process of solution-spun Y1Ba2Cu3Ox filament
Authors: Goto Tomoko , Takahashi Tsuyoshi
Published: September 2007

Texture formation of the partially melted process of solution-spun Y1Ba2Cu3Ox, was examined to enhance the reproducibility of the high Jc of the filament. The effect of Rh addition on the texture formation was also investigated. Controlling the cooling rate through peritectic temperature to produce 123 is the key for obtaining the reproducible high Jc. A well-aligned texture in the present filament needs a relatively high cooling rate for the following 123 crystal growth, such as 40 °C/h. Addition of Rh promotes the preparation of the 123 phase and enhances the Jc.