bluuebunny/crossref_metadata_2025 huggingface dataset:
On the fluctuation field in multidomain barium hexaferrite particles
Authors: González J. M. , Giri Anit K. , de Julián C. , Vélez M. , Vicent J. L.
Published: March 2008

A complete study of the thermally activated demagnetization phenomenology taking place in multidomain barium hexaferrite sample is presented. From the irreversible magnetization dependence of the fluctuation field, it is concluded that a demagnetization mechanism independent of the magnetization value rules the reversal in samples having large enough particles. Differently from this, in a sample having a broad particle diameter distribution (and including a minority percentage of small, single domain particles), our results clearly indicate the occurrence of two different demagnetization processes. Also, it was observed that the activation volume, in all the samples, was of the same order of magnitude and clearly smaller than the particle volume.
Giant magnetoresistance in bulk La0.6Mg0.4MnO3
Authors: Li Yadong , Duan X. F. , Zhang J. H. , Wang H. R. , Qian Y. T. , Huang Z. , Zhou J. , Yuan S. L. , Liu W. , Zhu C. F.
Published: March 2008

A bulk sample of La0.6Mg0.4MnO3 has been prepared from coprecipitated carbonate precursor for the first time in this study. Structure analysis conducted by powder x-ray diffraction indicates that the sample is in the cubic perovskite phase. It shows a metal-insulator transition at 115 K (Tp) When applied to an external field, GMR effects are observed in the whole measured temperature range. The maximum negative MR value reaches as large as 480% at 105 K and 5 T. There may be two different mechanisms governing the GMR effects in the sample for the temperatures below and above Tp.
Decomposition behavior of Ln2Mn4/3W2/3O7 (Ln = Eu and Er) in reducing atmosphere and their thermodynamic properties
Authors: Atsumi Taroh , Kamegashira Naoki
Published: March 2008

Decomposition behavior of Ln2Mn4/3W2/3O7 (Ln = Eu and Er) in reducing atmosphere at 1273 K was determined. These compounds decomposed to LnMnO3 and Ln2MnWO7 at PO2 = 10−8.46 atm for Ln = Eu and 10−7.46 atmosphere for Ln = Er, respectively. Decomposition product Eu2MnWO7 decomposed to Eu2MnWO6 at PO2 = 10−15.67 atm, while Er2MnWO7 decomposed to Er2O3, MnO, and W less than 10−17 atm. The standard Gibbs free energy changes of decomposition for Eu2Mn4/3W2/3O7, Eu2MnWO7, and Er2Mn4/3W2/3O7 at 1273 K were determined to be 34.4 kJ · mol−1, 191.9 kJ · mol−1, and 44.8 kJ · mol−1, respectively. The standard Gibbs free energy changes of formation of Er2Mn4/3W2/3O7 and Er2MnWO7 were also determined to be −2429.5 and −2463.2 kJ · mol−1 at 1273 K, respectively.
Reaction path in the magnesium thermite reaction to synthesize titanium diboride
Authors: Sundaram V. , Logan K. V. , Speyer R. F.
Published: March 2008

TiB2, along with MgO and Mg3B2O6, was formed by a thermite reaction between Mg, amorphous B2O3, and TiO2 powders in argon. The mixture 5Mg–TiO2–B2O3 along with binary mixtures and single components were analyzed using differential thermal analysis (DTA) and x-ray diffraction (XRD). Large (25 g) specimens were also ignited in bulk using a resistance-heated nichrome wire. The reaction path in forming TiB2 in the three component mixture was deduced. Mg reduces TiO2 and B2O3 to form Ti and MgB2, respectively, which in turn react to form TiB2. In an oxidizing atmosphere, the significant speed of the reaction permitted solid state reaction to form TiB2 before atmospheric oxygen could diffuse into the powder mass and react to form oxide phases. Thermite reactions in air have the advantage (over furnace heating in air) of not providing time at elevated temperatures for Mg and intermediate products to become consumed in the formation of oxides, nor time for oxidation degradation of TiB2.
A sequential Raman analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical vapor deposition reactor
Authors: Fayette L. , Marcus B. , Mermoux M. , Rosman N. , Abello L. , Lucazeau G.
Published: March 2008

A sequential analysis of the growth of diamond films on silicon substrates in a microwave plasma assisted chemical vapor deposition (CVD) reactor has been performed by Raman spectroscopy. The plasma was switched off during measurements, but the substrate heating was maintained to minimize thermoelastic stresses. The detectivity of the present experimental setup has been estimated to be about a few tens of μmg/cm2. From such a technique, one expects to analyze different aspects of diamond growth on a non-diamond substrate. The evolution of the signals arising from the substrate shows that the scratching treatment used to increase the nucleation density induces an amorphization of the silicon surface. This surface is annealed during the first step of deposition. The evolution of the line shape of the spectra indicates that the non-diamond phases are mainly located in the grain boundaries. The variation of the integrated intensity of the Raman signals has been interpreted using a simple absorption model. A special emphasis was given to the evolution of internal stresses during deposition. It was verified that compressive stresses were generated when coalescence of crystals took place.
Nanoindentation measurements of amorphous carbon coatings
Authors: Kulkarni Ashok V. , Bhushan Bharat
Published: March 2008

In this study, amorphous carbon coatings were deposited with thicknesses ranging from 20 nm to 100 nm on single-crystal silicon substrates by sputtering, ion beam, and cathodic arc deposition techniques. An indentation system with a three-plate transducer with electrostatic actuation and capacitive sensor has been used to make load displacement measurements and subsequently carry out in situ imaging of the indents. Indentation experiments were carried out using a three-sided pyramidal (Berkovich) diamond tip. Measurements include load-displacement curves and calculation of hardness and Young's modulus of elasticity at various indentation depths, studies of hysteresis behavior, creep behavior, and strain rate effect of various carbon coatings. The cathodic arc coating exhibited the highest hardness and elastic modulus followed by the sputtered and ion beam coatings.
Preparation of nanocrystalline copper by electrodeposition
Authors: Bandyopadhyay S. , Chakravorty D.
Published: March 2008

Copper particles of sizes in the range 3.1 to 11.4 nm have been grown within gel compositions of the system CuO–SiO2 by an electrodeposition process applying voltages varying from 5 to 15 V. Composite films of these metal particles dispersed in a polystyrene matrix have been prepared on Corning No. 7059 glass slides by a dip-coating technique and their optical absorption characteristics have been delineated. The spectra show maxima at wavelengths in the range 380 to 470 nm, depending on the particle size. The results have been analyzed using the Mie theory. The electrical conductivity as extracted from this analysis is found to have reasonable correspondence with data reported earlier for copper nanoparticles in glass-ceramic systems.
Photo-oxidatively self-cleaning transparent titanium dioxide films on soda lime glass: The deleterious effect of sodium contamination and its prevention
Authors: Paz Y. , Heller A.
Published: March 2008

In the context of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, thin (60 ± 10 nm) photocatalytic films of TiO2 were formed by a sol-gel process on (a) soda lime glass, (b) the proton-exchanged surface of soda lime glass, and (c) fused silica. The hypothesis that diffusion of sodium oxide from the soda lime glass into the titanium dioxide layer during the calcination step causes the lower photoefficiency in films on glass was tested and proven. At high concentration sodium prevented formation of the photoactive anatase phase and, at low concentration, introduced surface and bulk recombination centers. Sodium transport was efficiently blocked by a thin layer at the interface of proton-exchanged (“hydrogen”) glass and nascent TiO2, formed at 400 °C of a poly(titanyl acetylacetonate) TiO2 precursor. The sodium transport blocking layer did not form and the highly photocatalytic film was not obtained when the TiO2-precursor film was applied to glass that was not proton exchanged. Furthermore, only a much less effective sodium transport blocking layer was formed on glass that was proton-exchanged, but was calcined at 400 °C prior to application of the TiO2 precursor layer, showing that the sodium depleted glass surface, by itself, was a less effective barrier against sodium transport than the interfacial product of hydrogen glass and the TiO2 precursor.
Preparation and characterization of Nd3+ and Er3+-doped silica sol-gel coatings by Rutherford backscattering spectroscopy and spectroscopic ellipsometry
Authors: Bruynooghe S. , Chabli A. , Bertin F. , Pierre F. , Leflem G.
Published: March 2008

Neodymium- or erbium-doped silica films are deposited on single crystal silicon substrates using a sol-gel process and a spin-coating technique. These glasses are doped with neodymium or erbium in various Nd/Si or Er/Si atomic ratios up to 8% using neodymium nitrate or erbium nitrate as precursor. A preparation method of such films is described. Film rare earth concentration measured by Rutherford Backscattering Spectroscopy (RBS) is the same as in the initial liquid solution. Film thickness and refractive index are obtained by variable angle spectroscopic ellipsometry. We have shown that both RBS analysis and spectroscopic ellipsometry are powerful tools to control rare earth doping level and optical properties of the silica films.
The nature of residues following the ashing of arsenic implanted photoresist
Authors: Draper Clifton W. , Pearce Chuck W. , Glick Jere T. , Gordon Mike , Olness Gwen E. , Bernasek Steven L.
Published: March 2008

Extensive analytical characterization indicates that the most significant contaminant following dry processing of As-implanted photoresist is not a carbon-based residue, but is in fact arsenic itself. The arsenic residue is an amorphous form of elemental arsenic, relatively free of oxygen or carbon, that is stable for long periods of time. Since arsenic is not particularly soluble in sulfuric acid, hydrogen peroxide, or their mixtures, it makes sense to pose questions regarding the optimum choice for post-dry processing wet chemical cleans.
Impression recovery of PMMA
Authors: Yang Fuqian , Li J. C. M.
Published: March 2008

Impression recovery in which the deformation temperature is the same as recovery temperature is studied for the first time. PMMA is deformed by impression above the glass transition temperature to a depth of less than 0.3 mm and recovered at the same temperature. Almost complete recovery of dimension is observed every time. The dimensional changes obey second order kinetics and the temperature dependence of the rate constant shows two consecutive processes with activation energies 440 kJ/mole (between 104 and 113 °C) and 95 kJ/mole (between 113 and 140 °C). Two pairs of defects of opposite signs are believed to be involved in the dimensional recovery processes.
Subsolidus phase equilibria of coexisting high-Tc Pb-2223 and 2212 superconductors in the (Bi, Pb)–Sr–Ca–Cu–O system under 7.5% O2
Authors: Wong-Ng W. , Cook L. P. , Jiang F. , Greenwood W. , Balachandran U. , Lanagan M.
Published: March 2008

The subsolidus phase relationships of the high-Tc 2223 superconductor in the (Bi, Pb)–Sr–Ca–Cu–O (BSCCO) system have been examined at 810–820 °C. All experiments were carried out at ambient pressure in a 7.5% O2 (92.5% Ar) atmosphere. Eleven phases were found to exist in equilibrium with the 2223 phase. These 11 phases include CuO and 10 oxide solid solutions. From among these phases, a total of 48 five-phase combinations including the 2223 and 2212 phases were investigated experimentally, and 16 equilibrium assemblages were found which define a multicomponent compositional space corresponding to the 2223 + 2212 solid-state compatibility region. The subsolidus data form a partial basis for future investigation of the Pb-2223 primary phase field.
Diffusion model for the crystal growth of Pr1+xBa2−xCu3O7–δ by the top seeded crystal pulling method
Authors: Tagami Minoru , Umeda Takateru , Shiohara Yuh
Published: March 2008

A solidification model for Pr1+xBa2−xCu3O7−δ ternary oxides by the top seeded crystal pulling (SRL–CP: Solute Rich Liquid–Crystal Pulling) method is presented in which the composition of the grown single crystals is estimated from the starting composition in the crucible. This model involves the diffusion flux balance of each element at the growth interface in the liquid considering equilibrium tie-lines in the PrOy–BaO–CuO ternary phase diagram which have been obtained experimentally. The self-diffusion coefficient for Pr and the interdiffusivities for Ba and Cu in the liquid are used in this model because this liquid is a dilute solution for Pr. The calculated results are in good agreement with the experimental ones.
Influence of deposition rate on the properties of thick YBa2Cu3O7–δ films
Authors: Foltyn S. R. , Peterson E. J. , Coulter J. Y. , Arendt P. N. , Jia Q. X. , Dowden P. C. , Maley M. P. , Wu X. D. , Peterson D. E.
Published: March 2008

To investigate potential limits to the rate at which high-quality YBa2Cu3O7–δ can be deposited, we have produced a series of 1 μm thick films by pulsed laser deposition on single-crystal SrTiO3 substrates at average rates ranging from 2 Å/s to 240 Å/s. The critical current density of low-rate films was over 2 MA/cm2 at 75 K, self field, but dropped linearly with rate to about 1 MA/cm2 at the upper end of the range. In addition, the superconducting transition temperature, resistivity above the transition, and performance in an applied magnetic field were all degraded by increasing the deposition rate. A change in c-axis lattice parameter suggests that possible causes for this degradation are oxygen deficiency or cation disorder with the latter being the more likely. Annealing high-rate films at 790 °C for as little as 20 min improved critical current density to within 20% of low-rate values, and resulted in dramatic improvements in other film properties as well.
Y1Ba2Cu3O7–xmultilayer structures with a thick SiO2interlayer for multichip modules
Authors: Afonso S. , Chen K. Y. , Xiong Q. , Tang Y. Q. , Salamo G. J. , Chan F. T. , Cooksey J. , Scott S. , Shi Y. J. , Ang S. , Brown W. D. , Schaper L. W.
Published: March 2008

For high temperature superconducting multichip modules and other related electronic applications, it is necessary to be able to fabricate several Y1Ba2Cu3O7–x(YBCO) layers separated by thick low dielectric constant dielectric layers. In this work, we report the successful fabrication of YBCO/YSZ/SiO2(1–2 μm)/YSZ/YBCO multilayer structures on single crystal yttria stabilized zirconia (YSZ) substrates. In contrast to previously reported work, the top YBCO layer did not show any cracking. This is due to a technique that allows for stress relief in the SiO2layer before the second YBCO layer is deposited. The top YBCO layer in our multilayer structure hadTc= 87 K andJc= 105A/cm2(at 77 K), whereas the bottom YBCO layer hadTc= 90 K andJc= 1.2 × 106A/cm2(at 77 K). We also showed that the quality of the bottom YBCO layer was preserved during the fabrication of the multilayer due to the annealing process during which O2diffused into the YBCO, replacing the O2lost during the deposition of the top YBCO layer.
REBa2ZrO5.5 (RE = La, Ce, Eu, and Yb): Synthesis, characterization, and their potential use as substrates for YBa2Cu3O7–δ superconductors
Authors: Jose R. , John Asha M. , Kurian J. , Sajith P. K. , Koshy J.
Published: March 2008

A new class of complex perovskites REBa2ZrO5.5 (where RE = La, Ce, Eu, and Yb) have been synthesized and sintered as single phase materials by the solid state reaction method. The structure of these materials was studied by x-ray diffraction, and all of them were found to be isostructural, having a cubic perovskite structure. X-ray diffraction and resistivity measurements have shown that there is no detectable chemical reaction between YBa2Cu3O7–delta; and REBa2ZrO5.5 even under severe heat treatment at 950 °C, and that the addition of REBa2ZrO5.5 up to 20 vol.% in YBa2Cu3O7–δ shows no detrimental effect on the superconducting properties of YBa2Cu3O7-δ. Dielectric constants and loss factors are in the range suitable for their use as substrates for microwave applications. Thick films of YBa2Cu3O7–δ fabricated on polycrystalline REBa2ZrO5.5 substrates gave a zero resistance transition temperature Tc(0) ∼ 92 K, indicating the suitability of these materials as substrates for YBa2Cu3O7–δ.
Structure of grain boundaries: Correlation to supercurrent transport in textured Bi2Sr2Can−1CunOx bulk material
Authors: Yan Y. , Kirk M. A. , Evetts J. E.
Published: March 2008

Two kinds of characteristic grain boundaries were observed in textured Bi2Sr2Can−1CunOx (n = 2 and 3) bulk material: one (P-type) is nearly parallel to the (001) plane, and the other (N-type) is approximately normal to the (001) plane. Low-angle tilt N-type boundaries are composed of arrays of dislocations. However, for a small c-axis misorientation, the regions between the dislocation cores are still well connected, providing “pathways” for supercurrents crossing the boundary plane. The P-type boundaries exhibit compositionally and structurally modulated faceting. Although we see local regions of the low Tc (2201) phase at low-angle tilt (<10°) P-type boundaries, there are also “pathways” crossing the boundary plane made up of the high Tc (2212) and (2223) phases. The characteristics of such low-angle tilt grain boundary structures can therefore be modeled to provide general insight into the correlation between high critical current densities and low-texture breadths. On the other hand, a weak link could be formed at high-angle (> 10°) boundaries where there are the low Tc (2201) or insulating phases.
The effects of variable oxygen partial pressures during Bi-2223 tape processing
Authors: Holesinger T. G. , Bingert J. F. , Willis J. O. , Maroni V. A. , Fischer A. K. , Wu K. T.
Published: March 2008

The effect of changes in the oxygen partial pressure during the heat treatment of Bi-2223 tapes has been investigated. Distinct differences were observed in the phase assemblages, compositions, and critical current densities. Of particular importance in the correlation of transport properties and microstructure was the redistribution of lead in both the secondary phases and the Bi-2223 matrix. The highest Jc values were associated with tapes that contained Ca2PbO4 as part of the phase assemblage coupled with lower concentrations of lead in the superconducting phase. The high Jc of 30.4 kA/cm2 was obtained in tapes processed at 820 °C where the oxygen partial pressure was increased from 10% O2/Ar to 20% O2/Ar after 25 h of each 50-h sinter cycle. Samples processed only in 10% O2/Ar at 820 °C did not contain Ca2PbO4, had slightly higher concentrations of lead in the superconducting phase, and had significantly lower Jc values.
Losses in ac of BSCCO-2223 superconducting monofilament and multifilament tapes at power frequencies
Authors: Mench S. , Lelovic M. , Deis T. , Eror N. G. , Balachandran U. , Haldar P.
Published: March 2008

The ac magnetic losses at power frequencies (60 Hz) were investigated for mono- and multifilament Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Oy (BSCCO-2223) tapes with similar Ic values at 77 K. The multifilament sample exhibited higher losses than the monofilament under the same conditions. Loss peaks are discussed in terms of intergranular, intragranular, and eddy current losses. Because of BSCCO's anisotropy, field orientation has a large effect on the magnitude of these peaks, even at relatively small angles. Losses for fields applied parallel to the c-axis of the textured BSCCO grains are larger by over an order of magnitude than those applied perpendicular.
Epitaxial growth of β–SiC thin films on a 6H–SiC substrate using the chemical solution deposition method
Authors: Heimann D. , Wagner T. , Bill J. , Aldinger F. , Lange F. F.
Published: March 2008

A polyvinylmethylsilane precursor has been used for the epitaxial growth of SiC thin films on 6H–SiC single crystal substrates. The films were prepared by dipping the single crystal 6H–SiC substrates into the precursor polymer solution with subsequent thermal treatments at different temperatures. Transmission electron microscopy (TEM) was used to characterize the microstructure and chemistry of the different SiC films. At 1100 °C, the film was amorphous and contained substantial oxygen. At 1600 °C, an epitaxial, single crystalline β–SiC film was observed.
Equation of state of polycrystalline Ni50Al50
Authors: Otto J. W. , Vassiliou J. K. , Frommeyer G.
Published: March 2008

Polycrystalline Ni50Al50 suitable for high pressure studies was prepared by grinding and subsequent annealing of an inert-gas atomized alloy. The equation of state was determined by energy-dispersive x-ray diffraction in a diamond anvil cell to 25 GPa. The bulk modulus Bo and the pressure derivative of the bulk modulus B′o were found to be Bo = 156 ± 3 GPa and B′o = 4.0 ± 0.5.
Supercritical fluid infusion of silver into polyimide films of varying chemical composition
Authors: Rosolovsky J. , Boggess R. K. , Rubira A. F. , Taylor L. T. , Stoakley D. M. , St. Clair A. K.
Published: March 2008

Polyimides can be infused with silver complexes by the use of supercritical fluids. Highly reflective polyimide films were formed by infusing (1,5-cyclooctadiene-1,1,1,5,5,5-hexafluoroacetylacetonato)silver(I) [Ag(COD) (HFA)] into a number of polyimides and then thermally curing those films at 300 °C for time intervals between 30 min and 3 h. Reflectivities of the films exhibited strong dependence on the infusion and cure conditions as well as on the type of polyimide used. The highest reflectivity of 67.1% was achieved with a silvered film prepared from 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride (BTDA) and oxydianiline (ODA) infused at 5000 psi, 100 °C, for 30 min and cured for 1 h at 300 °C. Reflectivities of silvered surfaces of other polyimides investigated varied from 39% to 61%. A strong correlation between the presence of a ketonic group in the polyimide structure and the formation of mirror surfaces was detected.
Simulation of nacre with TiN/Pt multilayers and a study of their hardness
Authors: He J. L. , Li W. Z. , Li H. D.
Published: March 2008

TiN/Pt multilayers with individual thicknesses between 1 and 8 nm were prepared by ion beam sputtering deposition to simulate the micro-laminated architecture of nacre. Multilayer hardness and the laminated structure were investigated. It was found that sharp but incoherent interfaces were formed between individual layers. The multilayer hardness had strong dependence on layer arrangement. The range of layer thickness appropriate for high hardness was experimentally determined. Hardness enhancement of 30–70% was generally observed. With the layer thickness properly adjusted, the multilayer can even be harder than the hard component (TiN). Annealing experiments indicated that the hardness enhancement was an intrinsic property of the TiN/Pt multilayers.
Colloidal processing and mechanical properties of silicon carbide with alumina
Authors: Hirata Yoshihiro , Hidaka Kouji , Matsumura Hiroaki , Fukushige Yasuo , Sameshima Soichiro
Published: March 2008

Submicrometer-sized SiC coated with SiO2 of 0.4–1.8 wt.% and α–Al2O3 powder of median size 0.2 μm were mixed in aqueous solutions in the pH range 3.0–10.0. The SiC/Al2O3 (4.3–6.9 wt. %) powders were consolidated by filtration through gypsum molds and hot-pressed at 1600°–2040 °C under a pressure of 39 MPa. These compacts were densified to near the theoretical density at 1700°–1800 °C. The sintering mechanisms are discussed based on the analysis of shrinkage curves of SiC/Al2O3 compacts during hot-pressing. The equiaxed SiC grains grew with low aspect ratios below 1800 °C and changed to plate-like grains at 1900 °C. The fracture toughness of SiC as a function of average grain size reached a maximum of 5 Mpa · m0.5 at 2.5 μm grains of low aspect ratios of 1–2. The flexural strengths at room temperature were 230–430 MPa in the SiC above 98% of the theoretical density and showed a similar grain size dependence.
Structural characterization of sputter-deposited LaNiO3 thin films on Si substrate by x-ray reflectivity and diffraction
Authors: Lee Hsin-Yi , Wu Tai-Bor
Published: March 2008

X-ray reflectivity and diffraction were applied to characterize the highly (100)-textured thin films of LaNiO3, which were deposited on Si substrate via radio frequency magnetron sputtering at temperatures ranging from 250 to 450 °C. Two interference fringes of different period were observed from the reflectivity curves, and the fitting result indicates that in addition to the normal lanthanum-nickel oxide layer, a transition layer, which has a larger mass density than the previous one, exists in the sputter-deposited films. A comparison of the measured x-ray diffraction intensity with that calculated from layer thickness and mass density obtained from reflectivity data indicates that the transition layer is noncrystalline. The x-ray diffraction result also shows that there is a significant decrease of (100) diffraction intensity relative to that of (200) as increasing the deposition temperature. Using the reflectivity and diffraction data along with results of electron diffraction and film composition analysis from our other studies, such a change of relative intensity between the two diffraction peaks is attributed to the increasing content of two also highly textured La-rich phases, i.e., (110)-textured La4Ni3O10 and (100)-textured La2NiO4, in addition to the LaNiO3.
A study of microstructure and ductility of directionally solidified Ni50Al20Fe30
Authors: Chen J. , Lee J. H. , Lee Y. T. , Zheng Q. , Yu Y. , Li Y. A. , Tang Y. J. , Hu Z. Q.
Published: March 2008

The microstructure and ductility of directionally solidified Ni50Al20Fe30 were studied. Calculation and experiment show that the elastic modulus of the sample with completely eutectic lamellar structure is higher than that of the sample with dendritic structure. During deformation, in the samples with dendritic structure, some load is transferred from the proeutectic area to the γ-rich eutectic area and enhances the ductility of the sample.The existence of thick interdendritic γ phase and thick lamellar γ phase in the eutectic area of the dendritic sample is very effective in suppressing the microcrack propagation and also contributes to the ductility enhancement.
Fully dense Al–Pb nanocomposite bulk samples consolidated from mechanically milled powders
Authors: Zhou F. , Sheng H. W. , Lu K.
Published: March 2008

Powders with a nanostructured mixture of pure Al and Pb phase were produced by mechanical milling of elemental blends of Al and Pb with a composition of Al90Pb10 (wt. %). Under a pressure of 1.5 GPa at 280 °C, the as-milled powders were successfully consolidated into bulk, full-density samples (>99.5% theoretical density) while the average grain sizes of Al and Pb in the compacted samples remain unchanged with respect to those in the as-milled powders. The achievement of the full density without grain coarsening in the consolidation process could be reasonably attributed to melting of the nanometer-sized Pb particles of which the melting point is considerably depressed.
Method for producing large, stable concentrations of Sc2+in optically clear CaF2 crystals
Authors: Marquardt C. L. , Pinto J. F. , Allen R. E. , Esterowitz L. , Dergachev A. Yu , Ke S. , Mirov S. B.
Published: March 2008

This communication describes a new method for producing stable, high concentrations of Sc2+ in optically clear CaF2 crystals. We have achieved Sc2+ concentrations as high as 3 × 1018 cm−3 without degradation of optical quality. We have converted as much as 5% of the scandium dopant to the divalent state. The concentration of divalent scandium is stable during room temperature storage for periods of at least one year.
Supercritical antisolvent precipitation: A new technique for preparing submicronic yttrium powders to improve YBCO superconductors
Authors: Reverchon E. , Celano C. , Della Porta G. , Di Trolio A. , Pace S.
Published: March 2008

The solvent, supercritical antisolvent technique (SAS) has been used to produce submicronic particles of yttrium acetate for the synthesis of YBCO superconductors. For this purpose, in a continuous SAS apparatus dimethylsulfoxide (DMSO) as yttrium acetate solvent and supercritical carbon dioxide as antisolvent have been adopted. Experiments have been performed in the pressure range between 70 and 160 bar and for temperatures between 40 and 70 °C. Different concentrations of yttrium acetate in DMSO have also been tested. Various morphologies of yttrium acetate particles have been obtained, having mean particle diameters from 0.1 to 7 μm. At 40 °C and pressures larger than 120 bar, submicronic spherical particles of yttrium acetate of about 0.1 μm diameter and with a narrow particle size distribution have been achieved.
Hydrothermal preparation of the mixed titanium (IV) phosphate-phenylphosphonates and characterization of their properties
Authors: Jaimez Enrique , Bortun Anatoly I. , Khainakov Sergei A. , Voitko Igor' I. , García José R. , Rodríguez Julio
Published: March 2008

Mixed crystalline titanium (IV) phosphate-phenylphosphonates were synthesized under hydrothermal conditions using tetramethylammonium hydroxide as a templating reagent. It was found that at a relatively low molar ratio H3PO4 : PhPO3H2 in the reaction mixture (<1) only a pure α-titanium phenylphosphonate is formed. At the molar ratio H3PO4 : PhPO3H2 = (3–5): 1 the formation of a novel mixed compound titanium (IV) dihydrogenphosphate-hydrogenphosphate-phenylphosphonate takes place. Further increase of the ratio H3PO4 : PhPO3H2 gives mechanical mixtures of different phases. Preliminary results on the characterization of the novel compound of formula Ti(H2PO4)1.25(HPO4)0.12(C6H5PO3)1.25 · 0.3H2O are presented.
Microstructural development of Si3N4–SiC–Y2O3 ceramics derived from polymeric precursors
Authors: Iwamoto Yuji , Kikuta Ko-ichi , Hirano Shin-ichi
Published: March 2008

[Si–Y–O–C–N] amorphous powders were synthesized by the pyrolysis at 1000 °C in N2 of chemically modified perhydropolysilazane using n-decyl alcohol and yttrium tri-methoxide. [Si–Y–O–C–N] amorphous powders yielded a unique fibrous microstructure by heat treatment in N2 at 1800 °C. The fibrous microstructure was composed of β–Si3N4 whiskers of submicron in diameter and more than 10 μm in length. Fully dense Si3N4 –SiC–Y2O3 ceramics were also fabricated by heat treatment at 1800 °C followed by powder-vehicle hot pressing at 1700 °C. After these two-step processings, [Si–Y–O–C–N] amorphous powders yielded a unique fine-grained microstructure composed of submicron grains with high aspect ratio.
Reactive ion etching damage to the electrical properties of ferroelectric thin films
Authors: Pan W. , Thio C. L. , Desu S. B.
Published: March 2008

Reactive ion etching damage to Pt/Pb(Zr, Ti)O3/Pt ferroelectric capacitors was evaluated under Ar bombardment and CHClFCF3 etch plasmas. The hysteresis and degradation properties, including fatigue and leakage current, were examined systematically to study the mechanism of damage. The damage was measured quantitatively by comparing the relative voltage shift with respect to the initial hysteresis loops. The damage effects were found to be dependent on etching time and mainly due to the physical effect of ion bombardment. The electrical properties of the etched Pt/Pb(Zr, Ti)O3/Pt capacitors were substantially recovered by annealing at 400 °C for 30 min.
Composition and chemical width of ultrathin amorphous films at grain boundaries in silicon nitride
Authors: Gu H. , Cannon R. M. , Rühle M.
Published: March 2008

Two different electron energy loss spectroscopy (EELS) quantitative analytical methods for obtaining complete compositions from interface regions are applied to ultrathin oxide-based amorphous grain boundary (GB) films of ∼ 1 nm thickness in high-purity HIPed Si3N4 ceramics. The first method, 1, is a quantification of the segregation excess at interfaces for all the elements, including the bulk constituents such as silicon and nitrogen; this yields a GB film composition of SiN0.49±1.4O1.02±0.42 when combined with the average film thickness from high resolution electron microscopy (HREM). The second method, II, is based on an EELS near-edge structure (ELNES) analysis of the Si–L2,3 edge of thin GB films which permits a subtraction procedure that yields a completeEELS spectrum, e.g., that also includes the O–K and N–K edges, explicitly for the GB film. From analysis of these spectra, the film composition is directly obtained as SiN0.63±0.19O1.44±0.33, close to the one obtained by the first method but with much better statistical quality. The improved quality results from the fewer assumptions made in method II; while in method I uniform thickness and illumination condition have to beassumed, and correction of such effects yields an extra systematic error. Method II is convenient as it does not depend on the film thickness detected by HREM, nor suffer from material lost by preferential thinning at the GB. In addition, a chemical width for these films can be deduced as 1.33 ± 0.25 nm, that depends on an estimation of film density based on its composition. Such a chemical width is in good agreement with the structural thickness determined by HREM, with a small difference that is probably due to the different way in which these techniques probe the GB film. The GB film compositions are both nonstoichiometric, but in an opposite sense, this discrepancy is probably due to different ways of treating the surface oxidation layers in both methods.
The dependence of structural and mechanical properties on film thickness in sol-gel zirconia films
Authors: Paterson Melissa J. , Paterson Peter J. K. , Ben-Nissan Besim
Published: March 2008

The structure, morphology, and mechanical properties of sol-gel zirconia films have been examined using XRD, AES depth profiling, AFM, and ultramicro indentation. There is a systematic variation in the structure and morphology of the zirconia films with increasing thickness. These changes include increases in the amount of monoclinic phase, substrate oxides, and a decrease in grain size. Ultramicro indentation measurements indicate measured hardness increases with film thickness. The highest hardness value was 6.12 GPa for a 900 nm thick film. However, these values may be influenced by the substrate oxide layer at the film/substrate interface which increases with film thickness. The modulus of the films appears to be thickness independent. As the films are made up of a number of separately fired layers, it appears that the property changes observed are also related to the number of thermal cycles experienced by the sample.
Observations of grain boundary structure in submicrometer-grained Cu and Ni using high-resolution electron microscopy
Authors: Horita Zenji , Smith David J. , Nemoto Minoru , Valiev Ruslan Z. , Langdon Terence G.
Published: March 2008

Submicrometer-grained (SMG) structures were produced in Cu and Ni using an intense plastic straining technique, and the grain boundaries and their vicinities were observed by high-resolution electron microscopy. The grain boundaries exhibited zigzag configurations with irregular arrangements of facets and steps, and thus they were found to be in a high-energy nonequilibrium state. A similar conclusion was reached earlier for SMG Al–Mg solid solution alloys which have much lower melting points than Cu and Ni, suggesting that nonequilibrium grain boundaries are a typical feature of metals processed by intense plastic straining.
Development of preferred orientation in annealing of Fe–3.25%Si in a high magnetic field
Authors: Masahashi N. , Matsuo M. , Watanabe K.
Published: March 2008

Annealing of a cold-rolled Fe–3.25%Si sheet having {111} 〈112〉 preferred orientation is performed in a high magnetic field in order to control microstructure orientation. Magnetic field (10 T) was applied in a direction parallel to the rolling direction. Distributions of orientation and misorientation of primary recrystallization grains in the magnetically annealed specimens are characterized with electron backscattering pattern analysis. Magnetic annealing is found to enhance the selection of ?001? axis alignment parallel to the rolling direction in the {hk0} 〈001〉 recrystallization texture and to favor the occurrence of low energy grain boundaries in the recrystallized microstructure. The high frequency of low angle grain boundaries results in the appearance of coarse grains with traces of faint prior grain boundaries, suggesting extensive operation of the mechanism of grain coalescence. As a cause of selective formation of 〈100〉 grains in recrystallization, magnetostriction induced by applying a magnetic field is suggested.
Noble metal silicide formation in metal/Si structures during oxygen annealing: Implications for perovskite-based memory devices
Authors: Saenger K. L. , Grill A. , Cabral C.
Published: March 2008

This paper investigates the potentially undesirable noble metal silicide formation reactions that may occur in noble metal electrodes deposited directly on silicon without an intervening diffusion barrier. Metal (90–100 nm)/Si structures of Pt/Si, Rh/Si, Ir/Si, and Ir/Ti/Si were annealed in oxygen or nitrogen ambients at temperatures of 640–700 °C. Metalysilicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, x-ray diffraction, and electrical resistance measurements. While complete silicidation was observed in the Rh/Si, Pt/Si, and Ir/Si samples after 640 °C/6 min anneals in nitrogen, some Pt and most of the Ir remained after equivalent anneals in oxygen. More detailed studies of the Ir/Si samples indicated that some Ir is left unsilicided even after a 700 °C/6 min anneal in O2, and that the iridium silicide formed is the semiconducting IrSi1.75. The formation of this silicide can be delayed, but not prevented, with the use of a 5 nm Ti adhesion layer between the Ir and Si.
Preparation and optical properties of nanocrystallites of RE2Sn2−xB′xO7 (RE = Sm, Ce; B′ = Fe, Co, Ni; 0.0 ≤ x ≤ 1.0)
Authors: Gong Xiong , Wu Pengfei , Chen Wenju , Yang Hongxiu
Published: March 2008

New pyrochlore-type rare-earth-complex oxides of nanometer size and with B-site dopants, RE2Sn2−xB′xO7 (RE = Sm, Ce; B′= Fe, Co, Ni; 0.0 ≤ x ≤ 1.0), have been prepared by the nonalcoholate sol-gel method. The range of average particle size is from 25 to 30 nm. It is found that this method can lower the reaction temperature (about 500 K) and shorten the reaction time. The crystal structures of these nanocrystallites belong to the cubic system, and their lattice parameters are linearly related to the content of the dopant ions. The IR spectra of these nanocrystallites were investigated, and the excitation and emission spectra for these systems show that the luminescent intensities of RE3+ become weaker with the iron-group dopant in the order of Fe, Co, and Ni.
Metal oxide powder synthesis by the “emulsion combustion” method
Authors: Tani Takao , Takatori Kazumasa , Watanabe Naoyoshi , Kamiya Nobuo
Published: March 2008

Alumina powders were synthesized by the emulsion combustion method, using w/o (water in oil) type emulsions with different aqueous microsphere sizes. The effects of microsphere size on the size and shape of the synthesized powder were evaluated. The powders were spherical and hollow in shape with a very thin shell (from 10 to 20 nm in thickness) when synthesized from large aqueous microspheres (from 200 nm to 1 μm). The sizes and specific surface areas of the powders were consistent with those calculated. Large particles, which did not correspond to the microsphere size, were obtained from small aqueous microspheres (6 nm). The short distance (7 nm) between microspheres causes the adhesion of particles during the firing process.
Synthesis of thin films of polycrystalline ferroelectric BiNbO4 on Si by pulsed laser ablation
Authors: Chattopadhyay Soma , Ayyub Pushan , Pinto R. , Multani M. S.
Published: March 2008

The stibiotantalite (ABO4) family includes a number of ferroelectrics and antiferroelectrics with excellent potential for applications. We report the deposition of phase-pure, polycrystalline thin films of BiNbO4 on Si(100) substrates using pulsed laser ablation. The deposition conditions were optimized with respect to substrate temperature, laser parameters, and the ambient oxygen pressure. The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, and Raman spectroscopy, while their microstructure was studied by atomic force microscopy and scanning electron microscopy. Dielectric hysteresis studies indicated that films with a thickness below ≈250 nm are ferroelectric, while thicker ones are antiferroelectric.
Coalesced oriented diamond films on nickel
Authors: Yang P. C. , Wolden C. A. , Liu W. , Schlesser R. , Davis R. F. , Prater J. T. , Sitar Z.
Published: March 2008

The growth of coalesced, highly oriented diamond films has been achieved on nickel substrates using a multistep process that consisted of (i) seeding the Ni surface with 0.5 μm diamond powder, (ii) annealing at 1100 °C in a hydrogen atmosphere, and (iii) growth at 900 °C in a mixture of hydrogen and 0.5% methane. Auger depth profile analysis of a sample quenched after the annealing stage showed the presence of significant amounts of carbon (6 at. %) close to the substrate surface and about 3 at.% deeper in the substrate. The loss of carbon into the substrate resulted in relatively low nucleation density. The addition of methane into the gas phase during the annealing stage proved very effective in compensating for the diffusion. An addition of 0.5% methane in the gas phase produced optimum results, as the nucleation density, orientation of diamond particles, and uniformity were substantially improved. Substrates nucleated under these conditions were grown out into coalesced, 30 μm thick films. Both (100) and (111) oriented films showed a high degree of orientation and Raman spectra obtained from these orientations showed intense and narrow diamond signature peaks with FWHM's of 5 and 8 cm-1, respectively.
Species resolved analysis of the expansion of hydroxyapatite laser ablation plumes
Authors: Serra P. , Morenza J. L.
Published: March 2008

The plume generated by ablation of hydroxyapatite targets under ArF excimer laser irradiation has been investigated by means of fast intensified charge coupled device (CCD) imaging and optical emission spectroscopy. Results have shown that the plume splits into two plasma clouds as it expands. Time and spatial resolved spectra have revealed that under the experiment conditions emission is mostly due to calcium neutral atoms and calcium oxide molecular radicals. Imaging of the plume with the aid of bandpass filters has demonstrated that the emissive species in the larger and faster plasma cloud are calcium neutral atoms whereas in the smaller and slower one are calcium oxide molecular radicals.
Kinetic control of order in the layered perovskite La2Ba2Cu2Ti2O11
Authors: Palacín Maria Rosa , Gómez-Romero Pedro , Krumeich Frank
Published: March 2008

Definitive evidence on the variable degrees of order/disorder in the layered perovskite La2Ba2Cu2Ti2O11 is presented. This oxide was prepared by the ceramic method with varying reaction times and cooling rates; the average and local structures of the resulting solids were studied by x-ray diffraction, electron diffraction, and transmission electron microscopy (low and high resolution). The data clearly show the presence of an ap × ap × 4ap layered perovskite superstructure with a high concentration of defects in samples prepared over 48 h but with increasing degree of order for samples with longer reaction times. For samples reacted over 17 days, the order is complete and identical to that found for other related derivatives such as Ln2Ba2Cu2Ti2O11 (Ln = Nd, Eu, Tb). This behavior clearly indicates the existence of a kinetic control of order in this phase.
Mechanical alloying studies in the Γ(Fe3Zn10) and Γ1(Fe5Zn21) single and mixed phase compositions
Authors: Jordan Aszetta , Liu Zhentong , Uwakweh Oswald N. C.
Published: March 2008

Homogeneous or uniform crystalline materials are obtained following the ball milling of pure elemental powders of Fe and Zn in proportions to yield single phases Γ(Fe3Zn10), Γ1(Fe5Zn21), and Γ + Γ1 mixed phase (Fe25Zn75). Differential scanning calorimetry (DSC) measurements of the as-milled materials show characteristic stages in the temperature range of 50–600 °C prior to establishing stable equilibrium. The activation energies determined from kinetic analyses range from 49 to 189 kJ/mole in these materials. A characteristic stage at 130 °C marking the distinct evolution of the Γ and Γ1 phases from the intermediate or mixed phase composition is identified from XRD measurements. The identification of a unique Fe site with a quadrupole splitting (QS) of 1.5 mm/s in corroboration with x-ray diffraction (XRD) shows that this stage marks the onset of an in situ transformation prior to the distinct evolution of the homogeneous phases. The Mössbauer effect measurement of the as-milled materials are resolved in terms of four unique Fe sites with QS of 1.1, 0.241, 0.073, and 0.0772 mm/s.
Nanocrystalline nickel and nickel-copper alloys: Synthesis, characterization, and thermal stability
Authors: Natter H. , Schmelzer M. , Hempelmann R.
Published: March 2008

Pulsed electrodeposition is a simple, yet versatile method for the production of nanostructured metals. Forn-nickel we determine the influence of the physical and chemical deposition parameters on the nanostructure of the deposits and demonstrate that the grain size can be tuned to values between 13 and 93 nm, with rather narrow grain size distribution. The thermal stability of ourn-nickel as studied by x-ray diffraction and differential thermal analysis exhibits no detectable grain growth up to temperatures of about 380 K and an initialbehavior at 503 K followed by a regime of anomalous grain growth. For nanocrystalline Ni1-xCux(Monel-metal™) we demonstrate that alloy formation occurs at room temperature and that both chemical composition and grain size can be controlled by the pulse parameters and by appropriate organic additives.
Quantitative analysis of strengthening mechanisms in thin Cu films: Effects of film thickness, grain size, and passivation
Authors: Keller R-M. , Baker S. P. , Arzt E.
Published: March 2008

Thermal stresses in thin Cu films on silicon substrates were examined as a function of film thickness and presence of a silicon nitride passivation layer. At room temperature, tensile stresses increased with decreasing film thickness in qualitative agreement with a dislocation constraint model. However, in order to predict the stress levels, grain-size strengthening, which is shown to follow a Hall–Petch relation, must be superimposed. An alternative explanation is strain-hardening due to the increase in dislocation density, which was measured by x-ray diffraction. At 600 °C, the passivation increases the stress by an order of magnitude; this leads to a substantially different shape of the stress-temperature curves, which now resemble those of aluminum with only a native oxide layer. The effect of passivation is shown to be very sensitive to the deposition and test conditions.