bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface structure of face-centered-cubic-Ti thin film grown on 6H–SiC substrate
Authors: Sugawara Y. , Shibata N. , Hara S. , Ikuhara Y.
Published: March 2008

A titanium thin film was deposited on the flat (0001) face of a 6H–SiC by electron beam evaporation at room temperature in a vacuum of 5.1 × 10−8 Pa. The Ti film was epitaxially grown on the surface, and the interface between Ti and SiC was characterized by high-resolution electron microscopy. It was found that the structure of the deposited titanium is face-centered cubic (fcc), although bulk titanium metal usually has a hexagonal close-packed or body-centered cubic crystal structure. We believe that the unusual fcc structure of Ti thin film is due to the high adhesion of the film to the substrate and the high degree of coherency between them. The orientation relationship of the fcc-Ti/6H–SiC interface was (111)fcc-Ti//(0001)6H–SiC and [110]fcc-Ti//[1120]6H−SiC. Preliminary calculations indicate that this orientation relationship maximizes the lattice coherency across the interface.
Synthesis and characterization of nanoparticles of Ba2EuZrO5.5: A new complex perovskite ceramic oxide
Authors: Jose R. , James J. , John Asha M. , Divakar R. , Koshy J.
Published: March 2008

Nanoparticles of barium europium zirconate, a complex perovskite oxide, were synthesized using a modified self-propagating combustion synthesis. The solid combustion products thus obtained were characterized by x-ray and electron diffraction, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, particle-size analysis, surface area determination, gas adsorption studies, and high-resolution transmission electron microscopy. According to the results of the x-ray and electron diffraction, as-prepared powder showed the single phase of barium europium zirconate (Ba2EuZrO5.5) without another phase and had a complex cubic perovskite (A2BB′O6) structure. The transmission electron microscopic investigation showed a mean grain size of 38 nm with a standard deviation of 12 nm. High-resolution lattice imaging of the nanoparticles indicated the possibility of finer crystallite in the particle having the same orientation. The nanoparticles of Ba2EuZrO5.5 obtained by the present method could be sintered to 97% theoretical density at a relatively low temperature of 1525 °C.
Formation of Ruddlesden–Popper faults and polytype phases in SrO-doped SrTiO3
Authors: Šturm S. , Rečnik A. , Scheu C. , Čeh M.
Published: March 2008

The formation of so-called Ruddlesden–Popper planar faults was studied in SrO-doped SrTiO3 for different quantities of SrO additions and sintering conditions. For small SrO additions we observed a microstructure with a uniform grain size distribution and the enrichment of SrO at the grain boundaries. Larger additions of SrO produced a microstructure of elongated grains containing random planar faults, polytypic lamellae of more or less ordered faults, and polytype loops within SrTiO3 grains. We showed that these SrTiO3 grains were elongated as a result of preferential growth of the polytypic lamellae. In addition, we discuss a correlation between the formation of planar faults embedded in the perovskite matrix at low firing temperatures and Ruddlesden–Popper phases that are stable at higher temperatures.
The synthesis and characteristics of SiC nanopowder produced by chemical vapor reaction of SiH4–C2H4–H2 system
Authors: Yang Xiu-chun , Ding Zi-shang
Published: March 2008

SiC nanometer powders were synthesized by the chemical vapor reaction of the SiH4–C2H4–H2 system in the temperature range between 1423 K and 1673 K. The effects of processing conditions such as reactive temperature, gas composition ratio, and total flow rate on powder characteristics were studied using transmission electron microscopy, x-ray diffraction, infrared, Brunauer–Emmett–Teller, and chemical analyses. A forming mechanism has been proposed for solid and hollow particles in different processing conditions. The experimental results concerning particle growth are discussed according to the model of G.D. Ulrich et al., which considers both collision and coalescence phenomena.
Nickel oxide–silica and nickel–silica aerogel and xerogel nanocomposite materials
Authors: Casula M. F. , Corrias A. , Paschina G.
Published: March 2008

The sol-gel method was used to prepare nickel oxide–silica and nickel–silica nanocomposite materials and the corresponding silica matrices. Different drying conditions were used to obtain aerogel and xerogel materials. The samples were characterized by thermal analysis, x-ray diffraction, N2–physisorption, transmission electron microscopy techniques, and infrared spectroscopy. Aerogel samples had a much higher surface area than the xerogel samples; moreover, different supercritical drying conditions gave rise to a different porous structure, which influenced the size and distribution of the nanoparticles in the matrix.
RETRACTED – Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility
Authors: Inoue A. , Zhang T. , Chen M. W. , Sakurai T. , Saida J. , Matsushita M.
Published: March 2008

The crystallization mode of the Zr–Al–Ni–Cu amorphous alloys changed from a single stage to become two stages by the addition of Ag or Pd, and the first-stage exothermic reaction was found to result from the precipitation of nanoscale icosahedral particles with a size of 20 to 50 nm. The precipitation took place by high nucleation and low growth rates in a polymorphous mode for the Ag-containing alloys, and a diffusioncontrolled mode for the Pd-containing alloys. The nanoscale mixed structure alloys exhibited improved strength and ductility as compared with the corresponding amorphous single-phase alloys. The findings of the dispersion strengthening as well as the dispersion ductilization gave a future opportunity to fabricate a new bulk nonequilibrium phase alloy by use of the new phenomenon.
Creep behavior of a cryomilled ultrafine-grained Al–4% Mg alloy
Authors: Hayes R. W. , Tellkamp V. , Lavernia E. J.
Published: March 2008

The creep behavior of a cryomilled ultrafine-grained Al–Mg alloy was examined. The grain size ranged from 300 to 400 nm. The stress exponents ranged from 7.2 to 7.4. The apparent activation energy for creep, 83.7 kJ/mol at 27.5 MPa and 77 kJ/mol at 38 MPa, agreed well with the activation energy for grain boundary diffusion in aluminum. Transmission electron microscope analysis following creep at 300 °C to approximately 0.2% strain in 1411 h revealed the grain size was unchanged from its as-extruded size indicating significant thermal stability of this material at relatively high fractions of the melting temperature. The creep resistance of the Al–Mg alloy was rationalized in terms of an attractive interaction between grain boundary dislocations and incoherent particles within the boundary region, which suppressed grain boundary deformation. The grain boundary particles also led to high thermal stability by exerting a Zener pinning force on the grain boundaries, thus inhibiting grain growth at high temperatures.
Fracture behavior and reliability of brazed alumina joints via Mo–Mn process and active metal brazing
Authors: Yang S. H. , Kang S.
Published: March 2008

Alumina/alumina and alumina/kovar/alumina joints were produced via two joining techniques: (i) a moly-manganese process and (ii) active metal brazing. These joints were heat treated at 400 °C for 100 h to evaluate their fracture strength, fracture behavior, and high-temperature reliability. Depending on the joining methods employed, the optimum microstructure of ceramics for joining is different. It was found in most cases, that the active metal brazing resulted in superior joint strength and reliability over the moly-manganese process. The fracture strength and reliability of alumina/kovar/alumina joints were lower than those of alumina/alumina joints and showed different fracture behaviors. After heat treatment, fracture strength and reliability decreased due to the formation of brittle phases at the joint interface. The fraction of brittle debonding at the interface increased with heat treatment, while that of fracture within the alumina decreased.
Difficulties in measuring electrical conductivities in highly insulating materials: Radiation-induced electrical degradation is an artifact
Authors: Kesternich W.
Published: March 2008

Measurement of the electrical conductivity in high-resistance insulators is made difficult by previously unrecognized limits in the electric guarding technique. Electron irradiation experiments on single-crystalline Al2O3, performed for studying the effects of irradiation on the electrical conductivity, revealed that radiation-induced electrical degradation effects in ceramic insulators, previously reported to occur after electron, ion, and neutron irradiation, are an artifact.
The effect of Pb stiochiometry on switching behavior of Pt/lead zirconate titanate/Pt ferroelectric capacitors
Authors: Norga G. J. , Maes J. , Coppye E. , Fè Laura , Wouters D. , Biest O. Van der
Published: March 2008

A promising approach to control Pb stoichiometry during crystallization of sol-gel-derived lead zirconate titanate (PZT) layers is presented. Pyrolyzed layers were encapsulated in a quartz ampoule containing PbZrO3 powder and crystallized in a lamp furnace. For moderate heating rates, the PbO ambient created by the powder resulted in a pronounced sharpening of the preferential (111) texture, while the remanent polarisation Pr increased by 50% compared to nonencapsulated samples. A significant reduction of the coercive field was seen for layers crystallized under PbO ambient, reflected in a lowering of the switching voltage by 0.5 V compared to standard hotplate crystallized films. The results highlighted the key role of Pb stoichiometry control for further lowering the switching voltage of PZT films.
Fabrication and mechanical properties of Al/Al2O3 composite bodies by reactive infiltration of molten Al into SiO2 preform
Authors: Yoshikawa Noboru , Funahashi Singo , Taniguchi Shoji , Kikuchi Atsushi
Published: March 2008

Al/Al2O3 composites were fabricated by a displacement reaction between SiO2 and molten Al. In this study, fabrication of Al/Al2O3 composites was attempted by means of reactive infiltration to provide variation of their mechanical properties. SiO2 preforms having various porosities and pore size distributions were prepared by sintering the powder at different temperatures between 1273 and 1723 K. Molten Al was infiltrated at 1373 K without application of pressure. Infiltration kinetics were studied and the microstructures of the composite bodies were observed by means of scanning electron microscopy (with energy dispersive x-ray microanalysis), wave dispersive x-ray microanalysis, and x-ray diffractions. The infiltrated specimens were mainly composed of Al and α–Al2O3 phases, and the Si content was less than 5 at.%. Volume fraction of Al phase in the composite bodies was not altered very much with the porosities of the SiO2 preforms because of the difficulty in filling out the entire pore space. Properties and microstructures of Al/Al2O3 composites, however, were dependent on the sintering temperature of the SiO2 preforms. In the case of low sintering temperature, a thick Al channel existed, which deformed upon compression. In the case of high sintering temperature, the microstructure became homogeneous and had thinner Al channels. The composite bodies became brittle. The deformation behavior was shown to be changed from ductile to brittle as an increase of the sintering temperature of the preforms.
Hollow metal cylinders produced from diacetylenic lipid
Authors: Zabetakis Dan
Published: March 2008

A method was presented for the formation and metallization of cylindrical tubules from a diacetylenic lipid. This improved technique allowed for the production of metal microcylinders without the need for preliminary lipid purification and in large quantities. The physical and electrical properties of the material were investigated, and composites were used to form parallel plate capacitors. A comparison of the conductivity of the bulk material with the derived conductivity of a composite showing electromagnetic percolation showed the proportionality of the specific packing density and the critical volume fraction characteristic of percolating systems.
Chemical vapor deposition of titanium nitride thin films from tetrakis(dimethylamido)titanium and hydrazine as a coreactant
Authors: Amato-Wierda Carmela , Wierda Derk A.
Published: March 2008

Hydrazine was used as a coreactant with tetrakis(dimethylamido)titanium for the low-temperature chemical vapor deposition of TiN between 50 and 200 °C. The TiN film-growth rates ranged from 5 to 45 nm/min. Ti:N ratios of approximately 1:1 were achieved. The films contain between 2 and 25 at.% carbon, as well as up to 36 at.% oxygen resulting from diffusion after air exposure. The resistivity of these films is approximately 104 μΩ cm. Annealing the films in ammonia enhances their crystallinity. The best TiN films were produced at 200 °C from a 2.7% hydrazine–ammonia mixture. The Ti:N ratio of these films is approximately 1:1, and they contain no carbon or oxygen. These films exhibit the highest growth rates observed.
Reactively sputtered WOxNy films
Authors: Shen Y. G. , Mai Y. W.
Published: March 2008

A combined investigation of stress relaxation in WOxNy thin films sputter deposited on silicon wafers in an Ar–N2–O2 gas mixture by in situ substrate curvature measurements and of structural properties by ex situ x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), electron energy loss spectroscopy, and transmission electron diffraction is reported. It was found that the W2N films deposited under oxygen-free conditions had a high compressive stress of 1.45 GPa. As the oxygen concentration was increased, the stress became smaller and reached almost zero for films near 10–15 at.% oxygen. These results can be understood in terms of the decrease in the lattice parameter caused by substituting nitrogen atoms with oxygen in the lattice sites and the development of an amorphous network in the WOxNy films as the incorporation of oxygen was increased. Plan view and cross-sectional TEM analyses showed that 150-nm-thick oxygen-free crystalline W2N films had a columnar microstructure with an average column width of 15–20 nm near the film surface, whereas oxygen imbedded in the films provided a finer grain structure. The effect of oxygen in stabilizing the W2N structure was also elucidated and explained on the basis of structural and thermodynamic stability.
Layered microdomains and columnar grains in epitaxial La0.7Ca0.3MnO3 films and Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3 multilayers
Authors: Lu C. J. , Wang Z. L. , Xiong G. C. , Lian G. J.
Published: March 2008

Epitaxial La0.7Ca0.3MnO3 thin film and [Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3]10 multilayers of about 140 nm in thickness were grown by pulsed laser deposition on (001)LaAlO3. Their microstructures were investigated by transmission electron microscopy and associated techniques. It was found that both the film and the multilayers contain an almost defect-free layer near the substrate, followed by columnar grain grown. The columns were separated by strained regions in the top layer. No interfacial dislocations were observed at either of the La0.7Ca0.3MnO3/LaAlO3 or the Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3 interfaces. Interestingly, both the epitaxial film and the multilayers exhibited layered crystallographic domains. The formation mechanisms of the layered domain structures observed are discussed.
Solid-state nuclear magnetic resonance study of the structure of lanthanum phosphate crystals and glasses
Authors: Rashid Nancy E. , Phillips Brian L. , Risbud Subhash H.
Published: March 2008

Lanthanum phosphate glasses were synthesized by melt quenching and characterized by x-ray diffraction, electron microprobe analysis, and solid-state nuclear magnetic resonance spectroscopy. A range of compositions near the metaphosphate composition (75 mol% P2O5) was examined. Comparison of 31P chemical shifts and shielding anisotropies of glasses with those of the crystalline phases of La(PO3)3 (metaphosphate) and LaP5O14 (pentaphosphate) were consistent with the presence of primarily chainlike Q2 phosphate groups.
Magnetization, micro-x-ray fluorescence, and transmission electron microscopy studies of low concentrations of nanoscale Fe3O4 particles in epoxy resin
Authors: Thorpe A. N. , Senftle F. E. , Holt M. , Grant J. , Lowe W. , Anderson H. , Williams E. , Monkres C. , Barkatt A.
Published: March 2008

Magnetization measurements, transmission electron microscopy (TEM), and high-resolution micro-x-ray fluorescence (μ-XRF) using a synchrotron radiation source (Advanced Photon Source) were used to examine Fe3O4 particle agglomerates of nominally 10-nm particles at low concentrations (down to 0.03%) in thick epoxy resin samples. The magnetization measurements showed that at low concentrations (<0.5%) the magnetite particles, although closely packed in the agglomerates, did not interact magnetically. Predicated on a 2-μm sample step scan, the μ-XRF results were compatible with the presence of spherical agglomerates due to magnetostatic attraction, and these ranged in size from 100 to several thousand nanometers, as observed in TEM measurements. At smaller step scans the resolution could be significantly improved. Thus, the synchroton μ-XRF method was very useful in detecting very small concentrations of particles in thick samples and could probably be used to detect particles in amounts as low as 10−16 g.
Sintering studies on ultrafine ZrB2 powder produced by a self-propagating high-temperature synthesis process
Authors: Mishra (Pathak) S. K. , Das S. , Das S. K. , Ramachandrarao P.
Published: March 2008

A detailed study on the sintering behavior of zirconium diboride powder produced by the self-propagating high-temperature synthesis (SHS) process was carried out in the temperature range of 1500–1800 °C. The fine powder prepared by the SHS process exhibited excellent sinterability and could be sintered at 1800 °C for 1 h to approximately 94% of the theoretical density. The apparent activation energy of densification in the range of 1500–1800 °C was estimated to be 248 ± 4 kJ mol−1. A zirconium dioxide layer formed on the surface of the sintered body and was attributed to boron oxide formation during sintering and concurrent surface oxidation by the oxygen generated from the reduction of boron oxide in the carbonaceous atmosphere. Sintering aids like Fe and Cr appeared to help in densification of ZrB2 powder.
Correlation between Ni3Sn4 intermetallics and Ni3P due to solder reaction-assisted crystallization of electroless Ni–P metallization in advanced packages
Authors: Hung K. C. , Chan Y. C. , Tang C. W. , Ong H. C.
Published: March 2008

Ni3Sn4 intermetallic was formed by the depletion of Ni from electroless Ni–P, and a Ni3P layer was formed simultaneously due to solder reaction-assisted crystallization during solder reflow. Both Ni3Sn4 and Ni3P grew rapidly due to the solder reaction-assisted crystallization and their growth was diffusion controlled during the first 15 min of annealing at 220 °C. After that, the growth rate of Ni3Sn4 was greatly reduced and the crystallization of electroless Ni–P to Ni3P was no longer induced. Based on kinetic data and scanning electron microscope morphology observations, underlying mechanisms causing this specific phenomenon are proposed. This finding is indeed very crucial since we may control the growth of Ni–Sn intermetallics by monitoring the solder reaction-assisted crystallization of electroless Ni–P.
Stress and microstructure evolution during initial growth of Pt on amorphous substrates
Authors: Phillips M. A. , Ramaswamy V. , Clemens B. M. , Nix W. D.
Published: March 2008

An understanding of the relationship between stress and the corresponding microstructure at various stages of thin film growth might allow prediction and control of both microstructure and film stress during thin film deposition. In the present study, a combination of in situ curvature measurement and ex situ microstructural characterization was used to make correlations between stress and microstructure for the growth of Pt on SiO2. Plan view transmission electron micrographs of Pt films with average thicknesses ranging from 3 to 35 Å show the evolution of microstructure from isolated islands to a coalesced film, in agreement with models for stress behavior during the early stages of film growth. Quantitative measurements of grain size, island size, and areal fraction covered are extracted from these micrographs and, in conjunction with an island coalescence model, used to calculate the magnitude of the tensile stresses generated during coalescence. The predicted curvature is shown to compare favorably with the measured stresses.
Mechanical and water barrier properties of corn-protein-based biodegradable plastics
Authors: Gioia Lodovico di , Cuq Bernard , Guilbert Stéphane
Published: March 2008

Experiments were performed to evaluate the mechanical and water barrier properties of corn-protein-based materials that were compression molded from thermoplastic resins. The influence of varying concentrations of water, glycerol, and octanoic acid was studied. At 0% relative humidity, the material exhibited a linear elastic deformation and a brittle fracture at any glycerol or octanoic acid content. Raising relative humidity from 0% to 97.3%, progressively decreased the tensile strength (from 24.1 to 2.2 MPa and 19.4 to 1.0 MPa), and the modulus of elasticity (from 1.67 to 0.03 GPa and 1.87 to 0.13 GPa), respectively, for the octanoic acid- or glycerol-plasticized materials. Increasing water content did not increase the tensile strain at break of the glycerol-plasticized material, whereas this parameter changed from 1.6 to 52.3% for octanoic-acid-plasticized material. This last material was waterproof during 21 h and its water transmission rate was then 0.05 mmolmm-2 s -1. Differences in water absorption were related to plasticizer solubility and material structure.
Photo–and cathodoluminescence in yttrium–aluminium–borate–based phosphors
Authors: Mordkovich V. Z. , Umnov A. G. , Inoshita T. , Yamaura Tatsuo , Itoh Shigeo , Toki Hitoshi
Published: March 2008

Ce3+ luminescence in Ce3+ –activated yttrium aluminium borates was studied. A substantial red shift in photoluminescence and low-voltage cathodoluminescence spectra was found to be induced by Ce concentration increase. Complicated concentration dependence of emission intensity and strong influence of cerium content on emission wavelength suggest strong activator–host interaction in rare-earth borates.
Bismuth titanium indium antimony oxide: A low-temperature-coefficient, high-K dielectric material
Authors: Cava R. J. , Krajewski J. J. , Qin Y. L. , Zandbergen H. W.
Published: March 2008

The 1 MHz dielectric properties for mixed-phase polycrystalline ceramics in the system Bi4Ti3O12–Bi(InxSb1x)O3 were reported. In the vicinity of ambient temperature, the dielectric constants for the Sb and In end-members were approximately 430 and 160, respectively, and the temperature coefficients of dielectric constant (TCKs) were approximately -7600 and +430 ppm/deg. At an overall composition of Bi4Ti3O12:Bi(In0.37Sb0.63)O3 a dielectric constant of 144 and a low TCK were found. Powder x-ray diffraction and electron microscopy analyses indicated that the optimal composition contained three major phases. Deviation of any of the elements from the above ratio leads to degradation of the properties.
Adsorption of H2O, H2S, and N2 on MnZn ferrite
Authors: Donners M. A. H. , Niemantsverdriet J. W. , With G. de
Published: March 2008

MnZn ferrites show extensive subcritical crack growth. In this process water plays an important role. The fracture surfaces of MnZn ferrites with three different stoichiometries were investigated with adsorption isotherm measurements, temperature-programmed desorption, diffusive reflection infrared Fourier transform spectroscopy (DRIFT), low-energy ion spectroscopy (LEIS), and x-ray photoelectron spectroscopy (XPS). The XPS results confirmed the presence of Mn, Zn, Fe, and O atoms in the surface region, but LEIS indicated that the outer layer of the fracture surfaces contained no Zn atoms. DRIFT confirmed that hydroxyl groups were present on the fracture surfaces. Experiments with H2S, for which the XPS is more sensitive, indicated that at low coverage pairs of S atoms bridge a pair of Fe atoms. With increasing coverage the S bridge shifts to one Fe atom while at the highest coverage each Fe atom is bonded to one S atom. In experiments with N2 the highest nitrogen absorption is found for the lowest oxygen concentration in the ferrite, which is probably related to the polarity of the surface. Both the adsorption and desorption tests indicated that N2 had a larger adsorption affinity to MnZn ferrite surfaces than H2O.
Al–Fe-based bulk quasicrystalline alloys with high elevated temperature strength
Authors: Kimura Hisamichi M. , Sasamori Kenichiro , Inoue Akihisa
Published: March 2008

An icosahedral (I) phase in coexistence with Al phase was found to precipitate in atomized Al93Fe3Cr2Ti2 and Al93Fe3Cr2V2 powders. The mixed structure was formed in the size fraction range up to 125 μm for the Al–Fe–Cr–V alloy, while the increase of the particle size to 125 μm for the Al–Fe–Cr–Ti powder led to the precipitation of Al23Ti9. The replacement of Cr by Mn for the Al93Fe3Cr2Ti2 powder caused a mixed structure of Al+I+Al23Ti9 +Al6Mn even for the ?26 mm powder. The formation tendency of the I-phase increased in the order of Al–Fe–Cr–V > Al–Fe–Cr–Ti > Al–Fe–Mn–Ti system. The decomposition temperature of the I-phase was about 790 K. The I particles were analyzed to have approximate compositions of Al84.2Fe7.0Cr6.3Ti2.5 and Al82.9Fe9.0Mn6.4Ti1.7, and the use of the analytical compositions enabled the formation of a mostly single I phase with an average grain size of 90 to 130 nm in the melt-spun state. Bulk I alloys in a cylindrical rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys exhibited good mechanical properties; i.e., σ 0.2 of 550 MPa, σ UTS of 660 MPa, and ε P of 4.5% at room temperature, and σ 0.2 of 330 MPa, σ UTS of 350 MPa, and ε P of 1.5% at 573 K. The high σ UTS exceeding 350 MPa at 573 K was superior to the final target of the United States Air Force and hence the I-based Al93Fe3Cr2Fe2 alloy is expected to be extended as a new type of high elevated temperature strength material.
Dielectric properties of Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 system in the rhombohedral region near the morphotropic phase boundary
Authors: Jiang X. P. , Fang J. W. , Zeng H. R. , Li G. R. , Chen D. R. , Yin Q. R.
Published: March 2008

A diffuse phase transition for Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 (PZN-PZ-PT) system in the rhombohedral region near the rhombohedral/tetragonal morphotropic phase boundary (MPB) is reported in this paper. A thermal-driven macrodomain– microdomain switching was revealed and confirmed for compositions close to the MPB in the rhombohedral region after poling. Morever, the transition from rhombohedral phase to tetragonal phase was first revealed in the curves of dielectric permittivity (or dissipation factor) versus temperature. This rhombohedral–tetragonal phase transition resulted from the MPB bending toward the rhombohedral phase region and was confirmed by high-temperature x-ray diffraction.
Elastic flexure of bilayered beams subject to strain differentials
Authors: Chuang T-J. , Lee S.
Published: March 2008

The residual stresses present in a thin film and the curvature formed at its substrate during deposition have been a great concern to electrochemists and process engineers. Here a new hybrid analytical method is presented to reanalyze the flexural problem subjected to a strain differential in the general case. It was shown that the present solutions for ultrathin films agree with Stoney's equation. Moreover, single or dual neutral axes resulted, depending on materials and thickness ratios between the film and the substrate. Quantitative differences with others in the solutions of deformed curvature and residual stress are discussed in a representative case of GaAs top coat/Si substrate wafers.
Tantalum diffusion barrier grown by inorganic plasma-promoted chemical vapor deposition: Performance in copper metallization
Authors: Kaloyeros Alain E. , Chen Xiomeng , Lane Sarah , Frisch Harry L. , Arkles Barry
Published: March 2008

As-deposited and annealed tantalum films, grown by plasma-promoted chemical vapor deposition (PPCVD) using pentabromotantalum and hydrogen as coreactants, were evaluated as diffusion barriers in copper metallization. Stacks consisting of 500-nm-thick sputtered Cu/55-nm-thick untreated PPCVD Ta/Si were annealed in argon in the range 450 to 650 °C, in 50 °C intervals, along with sputtered Cu/preannealed PPCVD Ta/Si and sputtered Cu/sputtered Ta/Si stacks of identical thickness. Pre- and postannealed stacks were characterized by x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, hydrogen profiling, x-ray diffraction, atomic force microscopy, sheet resistance measurements, and Secco chemical treatment and etch-pit observation by scanning electron microscopy. The sputtered and preannealed PPCVD Ta films acted as viable diffusion barriers up to 550 °C, while the as-deposited PPCVD Ta films failed above 500 °C. In all cases, breakdown occurred through the migration of Cu into Si, rather than an interfacial reaction between Ta and Si, in agreement with previously reported results for sputtered Ta films. The accelerated barrier failure for as-deposited PPCVD Ta might have been caused by the presence of approximately 20 at.% hydrogen in the as-deposited PPCVD Ta, an observation which was supported by the enhanced performance of the same PPCVD Ta films after annealing-induced hydrogen removal.
Measurement of Gibbs energy of formation of LaGaO3 using a composition-graded solid electrolyte
Authors: Jacob K. Thomas , Dasgupta Niladri , Näfe Helfried , Aldinger Fritz
Published: March 2008

A composition-graded solid electrolyte (LaF3)y · (CaF2)1-y was used for the measurement of the standard Gibbs energy of formation of LaGaO3 from its component oxides. An equimolar mixture of CaO and CaF2 was employed as the reference electrode. The composition of the working electrode depended on temperature. A three-phase mixture of LaGaO3 + Ga2O3 + LaF3 was used in the temperature range from 910 to 1010 K, while a mixture of LaGaO3 + Ga2O3 + LaO1-xF1+2x was employed from 1010 to 1170 K. Both the reference and working electrodes were placed under pure oxygen gas. Because of the high activity of LaF3 at the working electrode, there was significant diffusion of LaF3 into CaF2. The composition-graded electrolyte was designed to minimize the electrode–electrolyte interaction. The concentration of LaF3 varied across the solid electrolyte; from y = 0 near the reference electrode to a maximum value y = 0.32 at the working electrode. For the correct interpretation of the electromotive force at T > 1010 K, it was necessary to use thermodynamic properties of the lanthanum oxyfluoride solid solution. The standard Gibbs energy of formation of LaGaO3 from its component oxides according to the reaction, ½La2O3 (A-rare earth) + ½Ga2O3 (b) → LaGaO3 (rhombohedral) can be represented by the equation: δGo f,(ox) /J mol -1 = –46 230 + 7.75 T/K (±1500).
Adhesion strength of cordierite glass-ceramic coatings on molybdenum substrates
Authors: Lu Guo-Quan , Calata Jesus Noel
Published: March 2008

Cordierite glass-ceramic coatings do not bond to molybdenum directly because of the absence of a suitable transition layer. Dual metallic interlayers of copper/chromium and nickel/chromium were electroplated on the substrates to enhance adhesion. The adhesion of the glass-ceramic coatings was evaluated by indentation testing and a modified analytical method based on interfacial fracture toughness. Quantitative chemical analyses of the interfaces were used to explain differences in fracture toughness among samples with different interlayers. Of those tested, the best interface for adhering glass-ceramic coatings to molybdenum was found to be a 4 μm chromium over 2 μm copper on molybdenum.
Chemical-vapor-deposition growth and characterization of epitaxial 3C–SiC films on SOI substrates with thin silicon top layers
Authors: Moon C. K. , Song H. J. , Kim J. K. , Park J. H. , Jang S. J. , Yoo J-B. , Park H-R. , Lee Byung-Teak
Published: March 2008

Epitaxial 3C–SiC films were grown by chemical vapor deposition on the silicon-on-insulator (SOI) substrates with 20–75-nm-thick Si top layers. A relatively low growth temperature of 1150 °C and a reduced hydrogen flow rate of 1 lpm during the precarbonization process was necessary to preserve the SOI structure and thereby obtain high-quality SiC films. The transmission electron microscopy observation of the SiC/SOI structures revealed high density of misfit dislocations in the SiC film, but no dislocation within the top Si layer. The x-ray-diffraction results did not show any significant shift of the (400) SiC peak position among the SiC/Si and the SiC/SOI samples. This strongly suggests that the Si top layer is not deformed during the SiC/SOI growth and the strain within the 3C–SiC layer is not critically affected by substituting the Si substrate with the SOI substrate, even when the Si top layer is as thin as 20 nm.
Redistribution behavior of constitutional elements at an initial crystallization stage in the Zr65Al7.5Ni10Cu17.5 glassy alloy
Authors: Saida J. , Matsushita M. , Inoue A.
Published: March 2008

We investigated the transformation behavior from glassy to Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with a low oxygen content below 400 ppm mass%. The mostly single face centered cubic Zr2Ni phase precipitated as a primary phase at the initial crystallization stage. The Zr2Ni particles had a cubical morphology in the diameter range of 300 to 500 nm and were in an isolated state for the sample annealed at the temperature near crystallization temperature. A significant redistribution leading to the enrichment of Zr and Ni into the Zr2Ni phase is confirmed. Moreover, it is recognized that Cu and Al are rejected from the Zr2Ni phase. The compositional differences of Zr, Al, Ni, and Cu between the Zr2Ni and remaining glassy phases are in the range of 1.5 to 5 at.%. It is strongly suggested that such a significant redistribution of the constitutional elements restrains the nucleation and growth of crystalline phases. It is one of the important factors for the stabilization of the glassy state in Zr–Al–Ni–Cu alloy.
High-strength porous silicon nitride fabricated by the sinter-forging technique
Authors: Kondo Naoki , Suzuki Yoshikazu , Ohji Tatsuki
Published: March 2008

Porous silicon nitride with aligned fibrous grains was fabricated by sinter-forging technique, where uniaxial pressure was applied to achieve a specific density after soaking at elevated temperatures. Fibrous silicon nitride grains were formed during the soaking, and the grains were aligned by the subsequent forging. As the result, a specimen with strongly aligned fibrous silicon nitride grains was successfully fabricated. The specimen with a relative density of 76% exhibited high bending strength of 778 MPa.
Macroporous morphology of titania films prepared by sol-gel dip-coating method from a system containing poly(ethylene glycol) and poly(vinylpyrrolidone)
Authors: Kajihara Koichi , Nakanishi Kazuki
Published: March 2008

Macroporous titania (TiO2) films were prepared by a sol-gel dip coating method from a system containing poly(ethylene glycol) (PEG) and poly(vinylpyrrolidone) (PVP). The thickness of the macroporous films increased with an increase in PVP concentration, but the excess incorporation of PVP suppressed the macroscopic phase separation and enhanced the formation of macroscopic cracks. The porosity and the domain size were simply determined by PEG concentration. Although both PEG and PVP are hydrogen-bonding polymers having proton-accepting ability, preparation of macroporous TiO2 films was unsuccessful in systems containing only PVP as a polymer. Macroporous TiO2 films having interconnected pore structure as thick as 1 mm were successfully prepared by repeating the deposition several times.
Structure and dielectric properties of pyrochlore–fluorite biphase ceramics in the Bi2O3–ZnO–Nb2O5 system
Authors: Wang Hong , Yao Xi
Published: March 2008

The structure and dielectric properties of Bi2O3–ZnO–Nb2O5-based ceramics with pyrochlore–fluorite biphase structure were investigated. Mixed-sintered ceramics were prepared by two precalcined constituents in the system of x[Bi1.5Zn0.5(Zn0.5Nb1.5)O7]−(1 − x)Bi3/4Nb1/4O7/4 (0.05 ≤ x ≤ 0.35), where Bi1.5Zn0.5(Zn0.5Nb1.5)O7 is a cubic pyrochlore (α) and Bi3/4Nb1/4O7/4 is a defect cubic fluorite (F). The phase composition of the mixed-sintered ceramics were characterized as a biphasic structure with a distorted pyrochlore (β) and a fluorite (F) coexisting. The phase ratio of β pyrochlore and F fluorite is related to the chemical composition x. The dielectric properties of the ceramics gradually change with their structure.
Modeling of wave configuration during electrically ignited combustion synthesis
Authors: Graeve O. A. , Carrillo-Heian E. M. , Feng A. , Munir Z. A.
Published: March 2008

A model was developed to study the process of current-ignited combustion synthesis. In this process, Joule heating raises the temperature to the ignition point, at which the sample reacts to form a product. Two material systems were modeled: the synthesis of SiC and MoSi2. It was found that the mode of combustion is a function of the size (radius) of the sample. The anticipated volume combustion mode was only evident in small samples. At higher values of the radius, the mode becomes wavelike (selfpropagating high-temperature synthesis) in nature. The transition from volume to wave combustion mode also depended on the properties of the material. The results are interpreted in terms of thermal conductivity and heat-transfer conditions.
Contact fracture of brittle bilayer coatings on soft substrates
Authors: Miranda Pedro , Pajares Antonia , Guiberteau Fernando , Cumbrera Francisco L. , Lawn Brian R.
Published: March 2008

Contact-induced fracture modes in trilayers consisting of a brittle bilayer coating on a soft substrate were investigated. Experiments were performed on model transparent glass/sapphire/polycarbonate structures bonded with epoxy adhesive, to enablein situobservation during the contact. Individual layer surfaces were preferentially abraded to introduce uniform flaw states and so allowed each crack type to be studied separately and controllably. Fracture occurred by cone cracking at the glass top surface or by radial cracking at the glass or sapphire bottom surfaces. Critical loads for each crack type were measured, for fixed glass thickness and several specified sapphire thicknesses. Finite element modeling (FEM) was used to evaluate the critical load data for radial cracking, using as essential input material parameters evaluated from characterization tests on constituent materials and supplemental glass/polymer and sapphirse/polymer bilayer structures. The FEM calculations demonstrated pronounced stress transfer from the applied contact to the underlying sapphire layer, explaining a tendency for preferred fracture of this relatively stiff component. Factors affecting the design of optimal trilayer structures for maximum fracture resistance of practical layer systems were considered.
Coordination structures of implanted Fe, Co, and Ni ions in silica glass by x-ray absorption fine structure spectroscopy
Authors: Fukumi Kohei , Chayahara Akiyoshi , Kadono Kohei , Kageyama Hiroyuki , Akai Tomoko , Mizoguchi Hiroshi , Kitamura Naoyuki , Makihara Masaki , Horino Yuji , Fujii Kanenaga
Published: March 2008

Coordination structures of implanted Fe, Co, and Ni ions were studied in 1.78–2.00-MeV 5 × 1016 ions/cm2-implanted silica glasses by x-ray absorption and optical absorption spectroscopies. It was found from x-ray absorption spectra that the implanted Fe, Co, and Ni ions are coordinated by ca.3 oxygen atoms. The implanted ions dispersed in glass matrix and did not form crystals. The valence of the implanted ions was about 1.5. The Fe–O, Co–O, and Ni–O interatomic distances were 190, 191, and 192 pm, respectively. In addition, it was found from optical absorption spectra that one-fifth of implanted Co ions were present as Co2+ ions in tetrahedral symmetry.
Analysis of defect formation in Nb-doped SrTiO3 by impedance spectroscopy
Authors: Kim Seong-Ho , Moon Jung-Ho , Park Jae-Hwan , Park Jae-Gwan , Kim Yoonho
Published: March 2008

The thermal activation energies for conduction of Nb-doped SrTiO3 grains and grain boundaries have been investigated by impedance spectroscopy. First, to observe the effect of electrode/SrTiO3 bulk interface, the varied impedances of SrTiO3 single crystal were measured with temperatures. The activation energy of an electrode/bulk interface was determined to be 1.3 eV, whereas that of bulk was 0.8 eV. When the impedances of Nb-doped SrTiO3 ceramics were measured, it was suggested that the more precise impedance values of a single grain and a single grain to grain junction be obtained using a microelectrode method. The activation energies for a grain, a grain boundary, and an electrode/bulk interface were determined to be about 0.8, 1.3, and 1.5 eV, respectively. From these measured results, it was suggested that the activation energy, 0.8 eV, measured in grain was originated from oxygen vacancies and the activation energy, 1.3 eV, in grain boundary was from strontium vacancies.
BaTiO3 formation by thermal decomposition of a (BaTi)-citrate polyester resin in air
Authors: Durán P. , Capel F. , Tartaj J. , Moure C.
Published: March 2008

Barium titanate nanosized powders were prepared by a slightly modified Pechini method. The obtained polymerized resin was used as the precursor for BaTiO3 powder production. DTA TG thermal analysis indicated that thermal decomposition of the precursors proceeds through four major step processes: (i) dehydration reaction; (ii) combustion reactions; (iii) intermediate phases formation; (iv) decarbonation of the intermediate to give BaTiO3. X-ray diffractometry (XRD) and Raman spectroscopy results indicated that, depending on the heating rate, the BaTiO3 formation took place via a predominant solid-state reaction between nanosized BaCO3 and amorphous TiO2 (TiO2−x) when crystallized by a low-heating rate (1.5 °C/min), although a small amount of a quasi-amorphous intermediate phase was also present. BaTiO3 crystallization by rapid heating rate (5 °C/min) took place through a quasi-amorphous intermediate phase formation as the main rate-controlling factor for the crystallization process. The fact that the low heating rate minimizes the intermediate phase content indicates the strong influence of the thermal heating on the kinetics of the involved transformation or in the mechanism. Although XRD results seem to indicate the formation of pseudocubic BaTiO3 as the final reaction product, the Raman spectra indicated as more probable the formation of a mixture of an oxygen-deficient hexagonal and tetragonal BaTiO3 phases below 700 °C. Above that temperature the tetragonal BaTiO3 was the only phase present. As-prepared BaTiO3 strongly agglomerated powders were relatively sinter active, leading to dense ceramic bodies (≥95% of the theoretical value). Microstructural (grain size approximately 1 mm) and room-temperature dielectric properties (ετ ≈ 2000 and tan δ ≤ 2%) at 10 kHz indicated that the obtained powders have to be optimized.
Strength prediction of partially aligned discontinuous fiber-reinforced composites
Authors: Kuriger Rex J. , Alam M. Khairul , Anderson David P.
Published: March 2008

An experimental and theoretical approach has been described for the determination of the strength of partially aligned discontinuous fiber-reinforced composites. The fiber alignment information was obtained as a Gaussian or normal distribution function by using an x-ray-diffraction technique. The distribution function was then used in the composite strength equation to calculate the theoretical strength. This approach was applied to a composite of vapor grown carbon fiber (VGCF) in a polypropylene matrix, and the experimental and theoretical results were compared. As expected, the composite strength increased with increase in fiber volume fraction and the degree of fiber alignment. It was also observed that the composite strength was sensitive to variation in fiber length when the average fiber length was less than the critical fiber length. At higher fiber volume fractions the composite strength was much lower than predicted by theory. This is most likely due to incomplete wetting and infiltration of the VGCF.
Residual stress in fiber-textured thin films of cubic materials
Authors: Scardi P. , Dong Y. H.
Published: March 2008

The effect of fiber texture on the x-ray residual stress analysis in thin films of cubic materials is discussed according to different mechanical models. The x-ray elastic constants (XECs) were calculated from single-crystal elastic constants for Cu, cubic ZrO2, and TiN, in the case of a typical [111] fiber texture with different spread of orientations [expressed by the half-width at half-maximum of the (111) pole figure]. Calculations were performed according to Reuss, Voigt, and Hill models, considering different crystallographic directions in cubic structures, in order to underline the effect of the mechanical anisotropy and fiber texture. The results clearly indicated the dependence of the XECs on the sample tilting angle, with the notable exception of [111] and [200], which were texture oscillation-free directions. Profiting from this condition the residual stress gradient in a fiber-textured TiN thin film deposited on stainless steel was determined by the simultaneous analysis of texture and residual strain for the (111) and (200) reflections. Advantages and limits of the procedure are discussed together with the experimental results.
Chemical reaction at the interface between (Hg0.9Re0.1)Ba2CaCu2Oy thin film and SrTiO3 substrate
Authors: Wu Xiao-Jing , Inoue N. , Sugano T. , Morishita T. , Tanabe K.
Published: March 2008

c-Axis-oriented (Hg0.9Re0.1)Ba2CaCu2Oy thin films were grown on the (100) plane of SrTiO3 substrates by a so-called two-step process. Transmission electron microscopic observation revealed that, in the film annealed under a higher temperature, some steplike regions appeared at the top layer of SrTiO3 substrate. High-resolution transmission electron microscopic images showed that the lattice parameters in these regions are about 4.05–4.15 Å, being longer than the lattice parameter of SrTiO3. It is supposed that a chemical reaction occurred in these regions, and a phase of (Bax,Sr1−x)(Cuy,Ti1−y)O3δs was formed by partially substituted Ba for Sr and Cu for Ti.
Characterization of GaN grown on sapphire by laser-induced molecular beam epitaxy
Authors: Zhou H. , Rühm A. , Jin-Phillipp N. Y. , Phillipp F. , Gross M. , Schröder H.
Published: March 2008

GaN grown on sapphire (α–Al2O3) was characterized by laser-induced molecular beam epitaxy. Threading dislocations with Burgers vectors of 1/3〈1120〉, 1/3〈1123〉 and [0001] were observed with a predominance of the first type. Additionally, inversion domains with Ga-polarity existed with respect to the adjacent matrix, which was of N-polarity. The dislocation densities and coherence lengths were deduced from x-ray diffraction and found to be in accordance with those measured by transmission electron microscopy. Both displacement fringe contrast analysis and high-resolution transmission electron microscopy results indicated that the inversion domain boundaries had Ga–N bonds between domains and the adjacent matrix.