bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of Large Single-grain Y–Ba–Cu–O Through Infiltration and Seeded Growth Processing
Authors: Hari Babu N. , Kambara M. , Smith P. J. , Cardwell D. A. , Shi Y.
Published: March 2008

Large, single-grain Y–Ba–Cu–O (YBCO) was fabricated via the infiltration of Ba–Cu–O liquid into a precursor body composed of solid, porous Y2BaCuO5 (Y-211) and observed to trap a magnetic field of 0.15 T at 77 K. In this process a NdBCO seed crystal was used to promote heterogeneous nucleation, which allows the fabrication of single-grain YBCO containing a uniform and very fine distribution of Y-211 inclusions in the YBa2Cu3O7−δ(Y-123) matrix without the addition of Pt. These superior microstructural features and significant field trapping ability compared with samples processed by conventional top-seeded melt growth suggest this technique could be a practical alternative for processing large, single-grain superconductors for engineering applications.
Preparation of TiO2-coated Hydroxyapatite Single Crystals
Authors: Teraoka K. , Nonami T. , Yokogawa Y. , Taoda H. , Kameyama T.
Published: March 2008

TiO2-coated hydroxyapatite single crystals were prepared by hydrolysis of Ti-bearing dicalcium phosphate powder. On the surface of the TiO2-coated hydroxyapatite single crystals, TiO2 regions and hydroxyapatite regions can function as photocatalysts and adsorbents for organic contaminants, respectively, allowing simultaneous decomposition of organic contaminants by the photocatalysis of TiO2 under irradiation. Therefore, the TiO2-coated hydroxyapatite single crystals can favorably be applied for antibacterial applications and environmental purification.
Favored Structure of Ag Nanoparticles Embedded in SiO2 by Implantation: Single Crystal with Contracted (111) Lattice
Authors: Liu Zhengxin , Li Hao , Wang Honghong , Shen Dingyu , Wang Xuemei , Alkemade Paul F. A.
Published: March 2008

The structure of Ag nanoparticles, embedded in crystalline SiO2 by high-dose implantation, was investigated. It was found that single crystal is favored over multiple-twinned particles. In addition, the contracted (111) lattice spacing of the Ag nanocrystals was measured by x-ray diffraction.
Effect of Gold Addition on the Nanostructure of Amorphous Fe–Zr–B Alloy
Authors: Zhang Y. , Czubayko U. , Wanderka N. , Zhu F. , Wollenberger H.
Published: March 2008

The behavior of Au in the course of the primary crystallization process of Fe87Zr7B5Au1 amorphous alloy was examined by use of atom probe field ion microscopy and transmission electron microscopy. In the early stage of crystallization, Au atoms were still distributed uniformly in the amorphous matrix. Au atoms form clusters at a later stage when more α–Fe particles are present. The Au clusters were observed to be separated from α–Fe particles, indicating that Au clusters do not stimulate nucleation of α–Fe particles. During the growth of α–Fe grains, cosegregation of Au and Zr occurred without any influence on the α–Fe grain growth. We conclude that Au addition has no effect on nanocrystallization of Fe–Zr–B amorphous alloys.
Preparation and Characterization of Pb(Zr, Ti)O3Thin Films by Metalorganic Chemical vapor Deposition Using a Solid Delivery System
Authors: Hong Eunki , Shin Ju Cheol , Choi Jaeho , Hwang Cheol Seong , Kim Hyeong Joon
Published: March 2008

Pb(Zr, Ti)O3(PZT) thin films were deposited on Pt/SiO2/Si substrates by metalorganic chemical vapor deposition using solid delivery system. The effects of deposition parameters such as the substrate temperature, the concentration of Pb precursor in the precursor mixtures, and the reactor pressure on the structural and electrical properties of PZT thin films were investigated. To obtain single-phase PZT thin films, the optimal range of the substrate temperature should be between 600 and 650 °C. The PbO content in PZT thin films was proportional to the fraction of Pb in the precursor mixture below 550 °C, but it was independent of the fraction of Pb in the mixture above 600 °C. With the increment of the reactor pressure, Zr contents in PZT thin films were increased, and the Pb/(Zr + Ti) ratio became more stoichiometric so that the ferroelectric properties were improved.
Preparation, Property, and Mechanism Studies of Amorphous Ferroelectric (Ba, Sr)TiO3 Thin Films for Novel Metal–ferroelectric–metal Type Hydrogen Gas Sensors
Authors: Zhu W. , Tan O. K. , Deng J. , Oh J. T.
Published: March 2008

Ferroelectric(Ba0.67Sr0.33)TixO3 (BST) thin films with x = 0.98, 1.00, 1.02, and 1.04 were prepared by the sol-gel technology, and their thermal, structural, dielectric, and gas sensing properties were systematically characterized. The amorphous (Ba0.67Sr0.33)TixO3 thin film capacitive devices were made on Si substrate to detect hydrogen gas and to study hydrogen-induced interfacial polarization potential.Experimental results showed that the Schottky I–V behavior appears in these Pd/amorphous BST thin film/metal capacitive devices and that enhanced interfacial dipole potentials as large as 4.5 V at 1000 ppm hydrogen gas in air were newly observed, which is about 7 times larger than the best value reported under similar testing conditions. It was clearly shown that the hydrogen-induced interfacial polarization potential is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this interfacial polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. A simple hydrogen interface-blocking model is also presented to explain this interesting phenomenon.
Phase Relations and Microwave Dielectric Properties of ZnNb2O6–TiO2
Authors: Kim Dong-Wan , Kim Deok-Yang , Hong Kug Sun
Published: March 2008

The phase relations and microwave dielectric properties of (1−x)ZnNb2O6–xTiO2 were investigated using x-ray powder diffraction and a network analyzer. Four phase regions were studied with increasing TiO2 mol% (x): columbite solid solution, ixiolite (ZnTiNb2O8) solid solution, mixture of ixiolite and rutile solid solutions, and rutile solid solution. It was suggested that the microwave properties depend on crystal structure rather than chemical composition. In the columbite solid solution region, an order–disorder transition was found with an increasing amount of TiO2, and the quality factor decreased sharply. ZnTiNb2O8 (x = 0.5), has a fully disordered structure and possesses a quality factor of 42,500, relative dielectric constant (εr) of 34.3, and temperature coefficient of resonant frequency (τf) of −52 ppm/°C. In the mixture region of ixiolite and rutile structure, τf was modified to around 0 ppm/°C.
Non-steady-state Photovoltaic Current in (Pb0.85La0.15)TiO3 and BaTiO3 Ceramics
Authors: Kim S. R. , Choi S. K. , Lee H. M.
Published: March 2008

The effect of poling field on the photocurrent was investigated in (Pb0.85La0.15)TiO3 and BaTiO3 ceramics. Non-steady-state photovoltaic current and no pyrocurrent on cooling were observed in both poled ceramics. The maximum behaviors were obtained at the poling field of 1.5 kV/mm. They were explained in terms of the photoinduced reversible and irreversible increases in the remanent polarization resulting from the space charge field, which was established by electrons trapped at grain boundary during illumination. No pyrocurrent on cooling was responsible for the reversible increase of the remanent polarization. The photoinduced irreversible increase of the remanent polarization, i.e., photodomain effect, was confirmed using the acoustic emission technique.
Influence of Mechanical Pressure and Temperature on the Chemical Interaction Between Steel and Silicon Nitride Ceramics
Authors: Kalin M. , Vižintin J. , Vleugels J. , Van Der Biest O.
Published: March 2008

The chemical interaction between a Si3N4ceramic, with Al2O3and MgO sintering additives, and DIN 100Cr6 steel was studied by means of static interaction couple experiments between 500 and 1200 °C. At 500 °C, the ceramic was chemically stable in contact with the steel. In the temperature range between 700 and 1100 °C, the silicon nitride dissociated in contact with the steel. The Si dissolved and diffused into the steel, whereas a nitrogen pressure built up in the micropores at the interface, limiting and inhibiting the reaction rate. The strength of the obtained interfacial bond was too low to withstand the residual stresses formed during cooling, and therefore, the interaction couples fell apart during cooling. Above 1100 °C, the nitrogen also dissolved and diffused into the steel, enhancing the overall rate of interaction. A strong interface was formed, resulting in a well-defined interaction layer on the ceramic side of the interaction couple. The mechanical pressures on the interaction couples were adjusted to study the influence of plastic deformation of the steel on the chemical interaction. Higher contact pressures resulted in more homogeneous and uniform interaction layers. The reactivity of plastically and elastically deforming steel, however, was found to be the same.
Adsorption and Kinetic Effects on Crack Growth in MnZn Ferrites
Authors: Donners M. A. H. , Dortmans L. J. M. G. , de With G.
Published: March 2008

The variation of the fracture toughness of MnZn ferrite ceramics with varying loading rate and humidity was determined with the aid of the single edge notched beam (SENB) test. A strong decrease with increasing humidity and decreasing loading rate was observed. A model for subcritical crack growth incorporating kinetic and adsorption effects was formulated to analyze the data. The value of the adsorptioncontrolled fracture toughness was determined independently by double torsion experiments and agreed favorably with the values as determined from the SENB data using the model. The strength of the material was determined, and analysis showed a strength behavior similar to the fracture toughness behavior, as predicted by the model. The analysis presented can be used to assess the subcritical crack growth behavior using a limited number of SENB specimens.
Structural Studies of Pulsed-laser-deposited Ba4Fe4Ti3O16 Oxide Films
Authors: Bendersky L. A. , Maier R. , Cohn J. L. , Neumeier J. J.
Published: March 2008

For this paper the pulsed laser deposition on single-crystal MgO substrates of Ba4Fe4Ti3O16 target was studied by transmission electron microscopy and x-ray diffraction. The initial stage of the deposition resulted in the formation of the perovskite Ba(Fe, Ti)O3 phase in an epitaxial, cube-on-cube orientation relationship with a substrate. Further growth of the pseudo-cubic phase was interrupted by the formation of oriented grains with a disordered structure. This disordered structure had a mixture of lamellae of the cubic and hexagonal Ba(Fe, Ti)O3 phases. No formation of the Ba4Fe4Ti3O16 (E) phase was observed. Formation of the disordered phase was explained by the higher stability of hexagonal Ba(Fe, Ti)O3 where accommodation of Fe3+ occurred on a twinning plane. The development of the V-shape morphology and a limited number of orientations of the D structure were explained by the faceting and columnar morphology of the perovskite phase.
Synthesis and Structure of BxC1−x Intercalation Compounds with Heavy Alkali Metals (K, Rb, and Cs)
Authors: Duclaux L. , Béguin F. , Ottaviani B. , Flandrois S.
Published: March 2008

BxC1−x (x = 0.1 and 0.25) oriented platelets were intercalated with alkali metal vapor (M = K, Rb, Cs), giving first-stage M(B0.1C0.9)8 and M(B0.25C0.75)10. The presence of M(BxC1−x)5 dense domains interstratified in the first-stage structure were brought out from the 00.ℓ simulations. The presence of these domains is attributed to the acceptor electron effect of boron, which slightly enhances the intercalation rate as compared to pure carbon. Intercalation of Cs in liquid ammonia is improved using 1600 °C heat-treated B0.25C0.75 as a host material, and the composition Cs(B0.25C0.75)12 is reached after intercalation. In intercalation compounds of Cs in liquid ammonia obtained from heat-treated B0.25C0.75, as the heat-treatment temperature (HTT) was increased from 1600 to 2000 °C, the segregation of first stage was observed in two structures Cs(BxC1−x)8 and Cs(BxC1−x)10 with the respective 2 × 2 0° and 2.23 × 2.23 two-dimensional lattices of the cesium atoms. The presence of these two structures is assigned to the heterogeneity of the host material induced by the formation of B4C boron carbide domains and the consecutive boron elimination of the BxC1−x lamellar phase with increasing HTT.
Face-centered-cubic to Hexagonal-close-packed Transformation in Nanocrystalline Ni(Si) by Mechanical Alloying
Authors: Datta M. K. , Pabi S. K. , Murty B. S.
Published: March 2008

An allotropic transition from face-centered-cubic (fcc) to hexagonal-close-packed (hcp) Ni(Si) solid solution in Ni95Si5 and Ni90Si10 during nanocrystallization by mechanical alloying is reported. The transformation was identified as a defect-induced melting accompanied by a volume expansion of 8.6% and was observed when fcc Ni(Si) reached a critical crystallite size of 10 nm. Calculation based on equation of state showed that a 37% reduction in tetragonal shear modulus and a negative pressure of about 8.7 GPa were generated at the onset of transformation.
Electrosynthesis and Microstructural Characterization of Anodic VOx Films
Authors: Schreckenbach J. P. , Butte D. , Marx G. , Johnson B. R. , Kriven W. M.
Published: March 2008

Anodic conversion films of vanadium oxides on vanadium were potentiodynamically generated at high voltages in an acetate electrolyte system. The microstructure of the anodic VOx coatings was characterized by surface and solid-state techniques such as scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. An amorphous structure is proposed in which network-forming [VO4] tetrahedra in various degrees of condensation are connected by distorted [VO5] and [VO6] units. Such polyhedra lead to the formation of nanocrystalline phases of stoichiometric and substoichiometric vanadium oxides, which were observed in the amorphous phase.
Sol-gel Synthesis of Li–ZrSiO4
Authors: Pfeiffer Heriberto , Bosch Pedro , Odriozola Jose A. , Lopez Alberto , Ascencio Jorge A. , Bulbulian Silvia
Published: March 2008

Li–ZrSiO4 was synthesized by the sol-gel method. Reactions were performed with different Li:Zr molar ratios: 1, 3, 5, and 6. Cell parameters changed as follows: a0 decreased and c0 increased as the Li:Zr molar ratio increased. The x-ray photoelectron spectroscopy analysis showed two kinds of oxygen atoms. The first one was attributed to ZrSiO4 oxygens. The second one was attributed to Li–O bonds. All these results were supported by a theoretical analysis. It was concluded that lithium atoms were held in interstitial positions of the ZrSiO4 structure.
Well-sinterable Y3Al5O12 Powder from Carbonate Precursor
Authors: Li Ji-Guang , Ikegami Takayasu , Lee Jong-Heun , Mori Toshiyuki
Published: March 2008

Carbonate precursors of Y3Al5O12 (YAG) were synthesized from a mixed solution of alum and yttrium nitrate using ammonium hydrogen carbonate as precipitant. Precipitation method (normal-strike or reverse-strike) and aging were found to have dramatic effects on cation homogeneity of the precursor, which in turn influenced the formation temperature of the YAG phase. Reactive YAG powders were produced from the reverse-strike-derived, as-synthesized precursors at temperatures ≤1200 °C. These powders densified to >98.0% of the theoretical density up to 1500 %C at a constant heating rate of 8 %C/min or to transparency by vacuum sintering at 1700 %C for 1 h without additives.
Formation of the (La0.67Sr0.33)2MnO4 Phase in La–Sr–Mn–O Thin Films by Pulsed Laser Deposition
Authors: Li Y. H. , Salamanca-Riba L. , Zhao Y. , Ogale S. B. , Ramesh R. , Venkatesan T.
Published: March 2008

La0.67Sr0.33MnO3 thin films were grown on LaAlO3 substrate in vacuum using pulsed laser deposition to investigate the effect of changing oxygen content. Transmission electron microscopy studies showed that the epitaxial (La0.67Sr0.33)2MnO4 phase with K2NiF4 structure formed unexpectedly as a matrix with a square-shaped nanometer-sized MnO phase distributed in a regular pattern throughout the whole film like self-assembled quantum dots. The MnO phase grew epitaxially from the LaAlO3 substrate to the top of the film with no outgrowth. High-resolution image simulation indicated that Sr ions take up only positions in every other La layer in the (La0.67Sr0.33)2MnO4 structure. Basing our theory on the composition and structure of the matrix phase, we propose that it is possibly electron-doped with a mixed valence of Mn2+/Mn3+ instead of the Mn3+/Mn4+ as in the hole-doped case.
Investigation on Structure Transition of Fullerene During Mechanical Alloying and Subsequent Treatments
Authors: Liu Z. G. , Ohi H. , Masuyama K. , Tsuchiya K. , Umemoto M.
Published: March 2008

Mechanical milling of fullerene (soot containing C60/C70fullerenes in a 8:2 molar ratio) was investigated through various characterization methods. It was found that mechanical milling would not destroy the molecular structure of fullerene C60(C70), while the long-range order of the face-centered-cubic crystalline structure was easily modified and transformed into amorphous phase, a mixture of fullerene C60(C70) polymers and monomers. Differential scanning calorimetry analysis revealed a recovery of polymers to pristine fullerene molecules at 678 K, which is much higher than the reported depolymerization temperature of fullerene polymers induced by photo irradiation and by high-pressure–temperature processes. It is suggested that the contaminated Fe acts as a catalyst in the polymerization process.
High-resolution Electron Microscopy Observation of Grain-boundary Films in Superplastically Deformed Silicon Nitride
Authors: Zhan Guo-Dong , Mitomo Mamoru , Ikuhara Yuichi , Sakuma Taketo
Published: March 2008

The thickness distribution of grain-boundary films during the superplastic deformation of fine-grained β–silicon nitride was investigated by high-resolution electron microscopy. In particular, grain-boundary thickness was considered with respect to the stress axis in two orientations; namely, parallel and perpendicular to the direction of applied stress. The results showed that the thickness distribution in boundaries perpendicular to the direction of applied stress was unimodal, whereas in parallel boundaries it was bimodal. Moreover, it was found that the majority of film-free boundaries were parallel to the direction of applied stress in the extremely deformed sample. The variation in spacing reflects distribution of stresses within the material due to irregular shape of the grains and the existence of percolating load-bearing paths through the microstructure.
Grain size, Grain Uniformity, and (111) Texture Enhancement by Solid-phase Crystallization of F- and C-implanted SiGe Films
Authors: Rodríguez A. , Olivares J. , González C. , Sangrador J. , Rodríguez T. , Ballesteros C. , Gwilliam R. M.
Published: March 2008

The crystallization kinetics and film microstructure of poly-SiGe layers obtained by solid-phase crystallization of unimplanted and C- and F-implanted 100-nm-thick amorphous SiGe films deposited by low-pressure chemical vapor deposition on thermally oxidized Si wafers were studied. After crystallization, the F- and C-implanted SiGe films showed larger grain sizes, both in-plane and perpendicular to the surface of the sample, than the unimplanted SiGe films. Also, the (111) texture was strongly enhanced when compared to the unimplanted SiGe or Si films. The crystallized F-implanted SiGe samples showed the dendrite-shaped grains characteristic of solid-phase crystallized pure Si. The structure of the unimplanted SiGe and C-implanted SiGe samples consisted of a mixture of grains with well-defined contour and a small number of quasi-dendritic grains. These samples also showed a very low grain-size dispersion.
Cracking of Brittle Coatings Adhesively Bonded to Substrates of Unlike Modulus
Authors: Lee Kee Sung , Rhee Young-Woo , Blackburn Douglas H. , Lawn Brian R. , Chai Herzl
Published: March 2008

The role of elastic mismatch in determining critical conditions for indentation fracture in brittle coatings on substrates of unlike modulus was investigated. A model transparent trilayer system, consisting of a glass coating layer bonded to a thick substrate of different glass or polymer by a thin layer of epoxy adhesive, facilitatedin situobservations of crack initiation and propagation. A tungsten carbide sphere was used to load the layer system. Abrasion flaws were introduced into the top and bottom glass coating surfaces to control the flaw populations and to predetermine the origins of fracture: cone cracks occurred at abraded top surfaces, radial cracks at abraded bottom surfaces. Analytical relations for the critical loads are presented for each crack system in terms of elastic modulus mismatch, indenter and coating dimensions, and material fracture parameters. Implications concerning materials selection for resistance to crack initiation are considered.
Silicon Carbonitride Ceramics Produced by Pyrolysis of Polymer Ceramic Precursor
Authors: Wan J. , Gasch M. J. , Mukherjee A. K.
Published: March 2008

Two processing routes were explored to produce crack-free amorphous Si–N–C ceramics by pyrolysis of polyureasilazane ceramic precursor. Using a warm-pressing/ pyrolysis route, a ceramic body with certain amount of open porosity was produced; densification behavior during pyrolysis was examined. A prepyrolysis/binding/pyrolysis route was also developed. Ceramics formed using this route were characterized by higher density, lower volume shrinkage during consolidation, and larger viable material size. Open porosity was essentially absent in consolidated amorphous materials produced by this second route. Recrystallization of the consolidated amorphous ceramics resulted in a Si3N4/SiC nanocomposite with both silicon nitride and silicon carbide grains in the nanometric size range.
A New Bi-substituted Rare-earth Iron Garnet for a Wideband and Temperature-stabilized Optical Isolator
Authors: Huang Min , Zhang Sho
Published: March 2008

A wideband and temperature-stabilized optical isolator for 1.55-μm wavelength was developed using a new Bi-substituted holmium–ytterbium ion garnet (HoYbBiIG) single crystal as a Faraday rotator. The optical isolator features 0.34-μm bandwidth, less 0.6 dB insertion loss and over 37 dB backward loss at a wavelength of (1.55 ± 0.17) μm throughout the temperature range from −10 to 60 °C. The Faraday rotation and optical absorption loss of HoYbBiIG were investigated in the near-infrared wavelength region (λ = 0.9 to 1.7 μm). The specific Faraday rotation of Ho0.85Yb1.02Bi1.13Fe5O12 is about −767°/cm at λ = 1.55 μm. The Faraday rotation wavelength and temperature characteristics of HoYbBiIG crystals are also discussed. These results indicate that the Bi-substituted holmium–ytterbium iron garnet single crystals realize a high Faraday rotation stability against temperature and wavelength in the near-infrared region.
Interfacial Morphology and Shear Deformation of Flip Chip Solder Joints
Authors: Jang J. W. , Liu C. Y. , Kim P. G. , Tu K. N. , Mal A. K. , Frear D. R.
Published: March 2008

We examined the interfacial morphology and shear deformation of flip chip solder joints on an organic substrate (chip-on-board). The large differences in the coefficients of thermal expansion between the board and the chip resulted in bending of the 1-cm2 chip with a curvature of 57 ± 12 cm. The corner bump pads on the chip registered a relative misalignment of 10 μm with respect to those on the board, resulting in shear deformation of the solder joints. The mechanical properties of these solder joints were tested on samples made by sandwiching two Si chips with electroless Ni(P) as the under-bump metallization and 25 solder interconnects. Joints were sheared to failure. Fracture was found to occur along the solder/Ni3Sn4 interface. In addition, cracking and peeling damages of the SiO2 dielectric layer were observed in the layer around the solder balls, indicating that damage to the dielectric layer may have occurred prior to the fracture of the solder joints due to a large normal stress. The failure behavior of the solder joints is characterized by an approximate stress analysis.
Chemical Vapor Deposition of Sr1−xBaxNb2O6 Thin Films Using Metal Alkoxide Precursors
Authors: Zhang Ruichao , Xu Ren
Published: March 2008

A novel two-step metalorganic chemical vapor deposition process was used in this study to prepare Sr1−xBaxNb2O6 (SBN) thin films. Two thin layers of single-phase SrNb2O6 and BaNb2O6 were deposited alternately on a silicon substrate, and the solid solution of SBN was obtained by high-temperature annealing. The stoichiometry control of the SrNb2O6 and the BaNb2O6 thin films was achieved through deposition process control, according to the evaporation characteristics of double metal alkoxide. The evaporation behavior of double metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 was studied, and the results were compared with the evaporation of single alkoxide Nb(1-OC4H9)5.
Incorporation of Pb into the Crystal Structure of Ba6−3xNd8+2xTi18O54 Solid Solution
Authors: Podlipnik Mojca , Suvorov Danilo , Valant Matjaz , Kolar Drago
Published: March 2008

Investigations of a substitutional mechanism of Pb incorporation into the crystal structure of Ba6−3xNd8+2xTi18O54 performed by x-ray diffraction analysis, scanning electron microscopy, and energy dispersive and wavelength dispersive x-ray spectroscopy revealed that Pb2+ substitutes for Ba2+ according to the formula (Ba1−zPbz)6−3xNd8+2xTi18O54. The solid solubility limit for 0.5 = x = 0.6 compositions was determined to be at 0.35 ≤ z < 0.4 (nominal composition) which, according to measurements of PbO loss occurring during the heat treatment, gives 0.30 ≤ z < 0.35 (analyses of matrix phase). Increasing the Pb2+ concentration in (Ba1−zPbz)4.5Nd9Ti18O54, results in tf decreasing from an initial positive value (80 ppm/K) to a negative value at the solid solubility limit (−25 ppm/K at z = 0.35). In the same concentration range the Q-value decreases from an initial 2000 to 1250 (z. = 0.35), measured at 4 GHz, while permittivity remains almost constant (k = 87 ± 1.5). After exceeding the solid solubility limit of Pb2+ in (Ba1−zPbz)4.5Nd9Ti18O54 the appearance of secondary phases (Nd4Ti9O24 and Pb-rich phase at grain boundaries) changes the trends of the microwave dielectric properties; permittivity decreases, Q-value remains almost constant, and Tf increases.
Size-dependent Phase Transformations During Point Loading of Silicon
Authors: Mann A. B. , van Heerden D. , Pethica J. B. , Weihs T. P.
Published: March 2008

Using a unique combination of in situ electrical and acoustical measurements and ex situ transmission electron microscopy, the phase transformations of silicon during point loading were shown to exhibit a strong dependence on the size of the deformed volume. For nanometer-size volumes of silicon, the final phase was the body centered cubic structure BC8, but for larger volumes it was amorphous. The size dependence was explained by considering how shear stress fields vary with contact size and how interfacial effects between the silicon substrate and the BC8 phase determine its stability. For both small and large contacts the presence of a nonmetallic phase (assumed to be the Rhombohedral structure R8) was observed.
Influence of Substrate Hardness on the Response of W–C–Co-coated Samples to Depth-sensing Indentation
Authors: Fernandes J. V. , Trindade A. C. , Menezes L. F. , Cavaleiro A.
Published: March 2008

Depth-sensing indentation tests were used to determine the hardness of amorphous W–C–Co coatings deposited on different steel and copper substrates. The hardness of the film, Hf, was chosen to be always greater than the hardness of the substrate Hs and within the range Hf/Hs = 2 to 18.5. The influence of the ratio Hf/Hs on the ratio (t/hD)C between the film thickness t and the critical value of the indentation depth (hD)C, for which the substrate starts to deform plastically, was studied. Two independent methods were used to determine (hD)C values. One utilized the differential analysis of the loading part of the indentation curve, and the other was based on the plot of (Hc – Hs)/(Hf − Hs) versus t/(hD), Hc being the measured hardness of the film/substrate composite at a given indentation depth (hD). A good correlation between both methods was found.
The Effects of the Mechanical Properties of the Confinement Material on Electromigration in Metallic Interconnects
Authors: Hau-Riege Stefan P. , Thompson Carl V.
Published: March 2008

New low-dielectric-constant interlevel dielectrics are being investigated as alternatives to SiO2 for future integrated circuits. In general, these materials have very different mechanical properties from SiO2. In the standard model, electromigration-induced stress evolution caused by changes in the number of available lattice sites in interconnects is described by an effective elastic modulus, B. Finite element calculations were carried out to obtain B as a function of differences in the modulus, E, of interlevel dielectrics, for several stress-free homogeneous dilational strain configurations, for several line aspect ratios, and for different metallization schemes. In contradiction to earlier models, we found that for Cu-based metallization schemes with liners, a decrease in E by nearly two orders of magnitude has a relatively small effect on B, changing it by less than a factor of 2. However, B, and therefore the reliability of Cu interconnects, can be strongly dependent on the modulus and thickness of the liner material.
Effect of the Pretreatment Step Condition in the Growth Process of the Si Melt Method on the Size of β–Si3N4 Single Crystals
Authors: Ye Jiping , Furuya Kenji , Matsuo Kazuo , Okamura Takeo , Munakata Fumio , Akimune Yoshio
Published: March 2008

Two kinds of obviously different-sized –Si3N4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si Kβ bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si3N4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si3N4 whiskers were grown from the surface of Si3N4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si3N4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si3N4 single crystals.
Structural and Electronic Properties of (CdTe)1−x(In2Te3)x Films Grown by Close-spaced vapor Transport Combined with Free Evaporation
Authors: Zapata-Torres M. , Mascarenhas Y. P. , Santana-Aranda M. A. , Luyo-Alvarado J. , Melé-Lirandez M. , Zapata-Navarro A. , Jimé-Sandovalnez S. , Castro-Rodriguez R. , Peña J. L.
Published: March 2008

The structural and electronic properties of (CdTe)1−x(In2Te3)x thin films as a function of substrate temperature were studied using x-ray diffraction, energy dispersive x-ray analysis, and Raman, transmission, and modulated transmission spectroscopies. The films were grown by the close-spaced vapor transport technique combined with free evaporation; CdTe and In2Te3 were used as sources. From x-ray diffraction the presence of mixed phases and differences in composition were detected, and good correlation with Raman spectroscopy was found. Transmission spectroscopy suggested the possibility of a modulation of the band gap of the alloy from a value as low as 0.5 eV up to 1.5 eV. Single-phase films presented a direct band gap of around 1.15 eV, as obtained from modulated transmission measurements.
Facile Sol-gel Synthesis of Porous Silicas Using Poly(propylene)imine Dendrimers as Templates
Authors: Larsen Gustavo , Lotero Edgar , Marquez Manuel
Published: March 2008

Commercially available poly(propylene)imine (DAB-Am-32 and DAB-Am-64) dendrimers were used as single-molecule templates to tailor the porosity of silicas via a nonacidic sol-gel method. X-ray diffraction on both the as-prepared (oven-dried at 373 K) and the calcined (833 K) materials revealed that modest contraction took place on template removal and that the cavities created did not achieve three-dimensional ordering under the current synthesis conditions. Transmission electron microscopy of “Pt-stained” samples supported this picture. A modified Horvath–Kawazoe analysis of the argon adsorption isotherms indicated that DAB-Am-64 is a much more effective template than DAB-Am-32. Pyrolysis and oxidation protocols for template removal are also presented.
Synthesis and characterization of carbon filaments grown from Pd3P colloids
Authors: Cesar F. , Bovin J-O. , Wallenberg L. R. , Karlsson G. , Falk L. K. L. , Oku T.
Published: March 2008

Amorphous carbon filaments were synthesized by catalytic pyrolysis of propene over Pd3P colloids. The channel close to the center of the filaments usually contained particles, which were analyzed by analytical electron microscopy to be palladium. The palladium particles could be found anywhere along the filament. The carbon filaments were of two types and of different diameters, about 8–15 nm and about 40–80 nm. The thinner type of filament shows a channel diameter of about 5 nm. The type of filament produced depends on the reaction conditions. Increased reaction time results in a large number of filaments, whereas an increased propene gas flow results in more of the thicker type of filaments.
Reactive yttrium aluminate garnet powder via coprecipitation using ammonium hydrogen carbonate as the precipitant
Authors: Li Ji Guang , Ikegami Takayasu , Lee Jong-Heun , Mori Toshiyuki , Yajima Yoshiyuki
Published: March 2008

Ammonium hydrogen carbonate was used as the precipitant to synthesize yttrium aluminate garnet (YAG) precursors from a mixed solution of aluminum and yttrium nitrates via coprecipitation. The carbonate precursor, with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2 · 0.8H2O, transformed to pure YAG at 900 °C without the formation of intermediate phases. Reactive YAG powder was produced by calcining the precursor at 1100 °C. The YAG powder densified to 99.8% of the theoretical density by vacuum sintering at 1500 °C for 2 h, and the sintered body showed transparency. Less agglomeration of the precursor and good dispersity of the resultant YAG powder were responsible for the excellent sinterability.
Effect of substrate deformation on the microcantilever beam-bending test
Authors: Zhang Tong-Yi , Zhao Ming-Hao , Qian Cai-Fu
Published: March 2008

With regard to substrate deformation, this work analyzed the microcantilever beam-bending test and provided a closed formula of deflection versus load. The substrate deformation was formulated using two coupled springs; the spring compliances were related to the elastic compliances of the substrate, the support angle between the substrate and the microcantilever beam, and the beam thickness. Finite element analysis was conducted to calculate the spring compliances and verify the analytic formula. The results showed that the proportionality factor of the load to the deflection was a third-order polynomial of the length from the loading point to the fixed beam end. Examples are also given to indicate the relative error of Young's modulus when evaluated with the beam-bending theory without considering the substrate deformation.
Direct writing of electronic and sensor materials using a laser transfer technique
Authors: Piqué A. , Chrisey D. B. , Fitz-Gerald J. M. , McGill R. A. , Auyeung R. C. Y. , Wu H. D. , Lakeou S. , Nguyen Viet , Chung R. , Duignan M.
Published: March 2008

We present a laser-based direct write technique termed matrix-assisted pulsed-laser evaporation direct write (MAPLE DW). This technique utilizes a laser transparent fused silica disc coated on one side with a composite matrix consisting of the material to be deposited mixed with a laser absorbing polymer. Absorption of laser radiation results in the decomposition of the polymer, which aids in transferring the solute to an acceptor substrate placed parallel to the matrix surface. Using MAPLE DW, complex patterns consisting of metal powders, ceramic powders, and polymer composites were transferred onto the surfaces of various types of substrates with <10 micron resolution at room temperature and at atmospheric pressure without the use of masks.
A finite difference model for the combustion of zirconium in oxygen
Authors: Ewald K. H. , Anselmi-Tamburini U. , Munir Z. A.
Published: March 2008

The combustion of zirconium in oxygen was simulated using a two-dimensional finite difference model. The model accounts for heat generation by the oxidation reaction and heat loss due to convective and radiative processes. Using geometric considerations along with the heat transfer conditions, the model was utilized to determine the effect of dilution and particle size on the combustion process. Dilution was examined in regular and random geometries and the results showed a marked influence on the nonlinearity of the wave. The effect of particle size was also examined as a function of the geometry of diluent dispersion.
Microstructure and properties of PbZr0.6Ti0.4O3 and PbZrO3 thin films deposited on template layers
Authors: Koritala R. E. , Lanagan M. T. , Chen N. , Bai G. R. , Huang Y. , Streiffer S. K.
Published: March 2008

Polycrystalline Pb(ZrxTi1−x)O3 thin films with x = 0.6 and 1.0 were deposited at low temperatures (450–525 °C) on (111)Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition. The films were characterized by x-ray diffraction, electron microscopy, and electrical measurements. The texture of the films could be improved by using one of two template layers: PbTiO3 or TiO2. Electrical properties, including dielectric constants, loss tangents, polarization, coercive field, and breakdown field, were also examined. PbZrO3 films on Pt/Ti/SiO2/Si with a pseudocubic (110) orientation exhibited an electric-field-induced transformation from the antiferroelectric phase to the ferroelectric phase. The effect of varying processing conditions on the microstructure and electrical properties of the films is discussed.
Effective elastic and transport properties of regular honeycombs for all densities
Authors: Hyun S. , Torquato S.
Published: March 2008

The effective planar elastic moduli and planar conductivity (or dielectric constant) of regular hexagonal and triangular honeycombs were investigated for the entire range of volume fractions. Only the extreme limits of the volume fraction have been studied in the past. We studied the effective properties both numerically, via finite elements, and analytically, via rigorous three-point bounds, three-point approximations, and cross-property bounds. We show here that the three-point bounds and approximations are generally in excellent agreement with the simulation data and are superior to the two-point Hashin–Shtrikman bounds. Therefore, the three-point estimates provide accurate analytical predictions of the effective properties for all densities. Both the effective bulk modulus and effective conductivity are nearly extremal in the case of hexagonal honeycombs for the entire volume-fraction range, in contrast to the effective shear modulus. In the case of triangular honeycombs, all of the property values are relatively close to being optimal. Thus, the triangular honeycomb has desirable multifunctional performance for all densities in so far as the elastic moduli, conductivity, and dielectric constant are concerned.
Model for mechanical properties nanoprobes
Authors: Burnham N. A. , Baker S. P. , Pollock H. M.
Published: March 2008

Researchers may use several different instruments to determine chemical and mechanical properties of materials with nanometer-scale vertical, and occasionally, lateral, resolution. Three such instruments are the depth-sensing indenter, the atomic force microscope, and the surface forces apparatus. Until now, these methods were individually modeled, and an analysis of their mechanical response was never done in a general way. In this article, we show that these instruments can be treated as a class—a class that we call mechanical properties nanoprobes (MPNs)—that can be described by a single universal linear model. Using this model, we solved both the quasistatic and dynamic response as a function of excitation frequency and complex compliance using an electrical analog for the mechanical system. Earlier work did not find correct solutions for the amplitude and phase, did not examine the influence of finite stiffness in the head of the MPN, and overlooked the difference between a partial and full derivative and its influence on quasistatically acquired force curves. The equations here will allow scientists to correctly interpret their results concerning elastic and anelastic materials response, especially for low-modulus, high-damping samples such as polymers.
Effects of solution temperature on mechanical properties of 319.0 aluminum casting alloys containing trace beryllium
Authors: Wang Paih-Shiarng , Lee Sheng-Long , Lin Jing-Chie , Jahn Min-Ten
Published: March 2008

The effects of beryllium (Be) and solution temperature on the morphologies of iron intermetallics, silicon particles, and copper intermetallics, relative to the mechanical properties of 319.0 alloys, were investigated. The experimental results indicated that adding Be to the alloy can raise the Al–Al2Cu eutectic melting temperature, change some plateletlike shape (βndash;Al5FeSi) of iron intermetallics to comparatively harmless Chinese-script morphologies (α–Al8Fe2Si), and reduce the amount and average length of βndash;Al5FeSi platelets. During high-temperature solution treatment (>500 °C), the thinner and smaller the β–Al5FeSi platelets were, the faster they dissolved and fragmented. However, where the solution temperature exceeded the Al–Al2Cu eutectic melting point, the Al–Al2Cu eutectic melted and resulted in an ultrafine eutectic phase on quenching, which deteriorated mechanical properties. The fracture behavior of 319 alloy was affected by the morphologies of the iron intermetallics, silicon particles, and copper intermetallics. Fractographic analysis of tested compact tension specimens revealed that the fracture processes were mainly initiated by void nucleation at β–Al5FeSi platelets as a result of their cracking and decohesion from the matrix. Adding Be to the 319.0 alloy and optimizing the solution temperature could significantly decrease the number of fracture-initiation sites of β–Al5FeSi platelets and improve the tensile properties and fracture toughness.
Nonlinear ultrasonic assessment of precipitation hardening in ASTM A710 steel
Authors: Hurley D. C. , Balzar D. , Purtscher P. T.
Published: March 2008

We investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity vL and attenuation αL. Although vL and aL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-inned dislocations.
First-principles estimate of the order–disorder transition in Ba(ZnxNb1−x)O3microwave dielectrics
Authors: Takahashi Takeshi , Wu Eric J. , Ceder Gerbrand
Published: March 2008

The B-site cation ordering in Ba(Zn1/3Nb2/3)O3was studied using a combination of first-principles energy calculations, a cluster expansion technique, and Monte Carlo simulations. Our calculations indicate that the ground state is a 1:2 ordered hexagonal structure, in contrast to x-ray diffraction observations, but consistent with recent Raman work by Kimet al.The order–disorder transition between the 1:2 ordered phase and the cubic perovskite phase is predicted to occur at approximately 2480 K. This prediction indicates that Ba(Zn1/3Nb2/3)O3in equilibrium should be fully ordered at all practical temperatures. These results indicate that Ba(Zn1/3Nb2/3)O3, previously considered to be disordered, may be ordered on a local scale, consistent with its good microwave characteristics.
Synthesis and characterization of homogeneous lead-substituted tin oxide with the (110) face of rutile structure
Authors: Nozaki Chika , Yamada Takashi , Tabata Kenji , Suzuki Eiji
Published: March 2008

Synthesis of a rutile-type lead-substituted tin oxide with (110) face was investigated. The characterization was performed by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, infrared spectroscopy, x-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller surface area measurements. The homogeneous rutile-type lead-substituted tin oxide was obtained until 4.1 mol% of tin was substituted with lead. The surface of obtained oxide had a homogeneously lead-substituted (110) face.
An alternative chemical route for synthesis of SrBi2Ta2O9 thin films
Authors: Zanetti S. M. , Leite E. R. , Longo E. , Araújo E. B. , Chiquito A. J. , Eiras J. A. , Varela J. A.
Published: March 2008

SrBi2Ta2O9 was synthesized by the modified polymeric precursor method using precursor reagents such as carbonate, nitrate, or oxide. The films were deposited onto Pt/Ti/SiO2/Si(100) substrates by spin coating and crystallized at temperatures ranging from 700 to 800 °C in air. Microstructural and phase evaluation were followed by grazing incidence x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The films displayed rounded grain structures with a superficial roughness of approximately 10 nm. The dielectric constant values were 362 and 617 for films treated at 700 and 800 °C, respectively. The remanent polarization and coercive field were 12.3 μC/cm2 and 61 kV/cm and 18.48 μC/cm2 and 47 kV/cm for the film treated at 700 and 800 °C, respectively. This method generally allows for the use of readily available reagents such as oxides, carbonates, or nitrate as cation sources, with the added advantage that it requires no special apparatus or atmosphere control.
Novel electrode materials for electrochemical capacitors: Part II. Material characterization of sol-gel-derived and electrodeposited manganese dioxide thin films
Authors: Pang Suh-Cem , Anderson Marc A
Published: March 2008

Material characterization of sol-gel-derived and electrodeposited MnO2 thin films showed that their microstructures are highly porous in nature. While sol-gel-derived films are nanoparticulate, electrodeposited films showed macropores of random and irregular platelike structures, comprising much denser surface layers and highly porous underlying layers. On the basis of calculated and theoretical density values of 1 and 4.99 g/cm3, respectively, the porosity of sol-gel-derived MnO2 films was determined to be as high as 80%, which is substantially higher than electrodeposited films at 67%. Apart from their higher specific capacitance, sol-gel-derived MnO2 films appeared to exhibit higher cycling stability and reversibility than electrodeposited MnO2 films. In the case of sol-gel films, thinner films appeared to exhibit higher cycling stability than thicker films. There was less alteration in surface morphology and microstructure, and the rate of loss in charge-storage capacity upon voltammetric cycling was not as significant for sol-gel MnO2 thin films