bluuebunny/crossref_metadata_2025 huggingface dataset:
Hardness and adhesive properties of (Cr, Mo) oxycarbide films on stainless steel via vapor deposition
Authors: Lo Ming-Hung , Wei Wen-Cheng J.
Published: March 2008

A hexacarbonyl of chromium and molybdenum [(Cr, Mo) (CO)6] was used as an oxycarbide source for the coating on stainless steel 304 (SS304) at temperatures from 175 °C to 450 °C. Hardness of the films was determined from a microindentation technique through a similar calculation after Thomas (1987). Intrinsic hardnesses of the films formed at low and medium temperatures were determined to be 8.61 and 2.75 GPa, respectively. Both of them are larger than that of SS304 substrate, 1.75 GPa. Adhesive strength of the films was measured by the scratching test. The results reveal that the adhesive strengths of the films formed at low, medium, and high temperatures are 2.8 N, 37.6 N, and 36.0 N, respectively. Two different fracture modes after scratching were found for the films obtained at various temperature regions. A spalling-off type or a deformation failure with many cracks and deformation bands beside the striation was found.
Hardness and toughness of exoskeleton material in the stone crab, Menippe mercenaria
Authors: Melnick C. A. , Chen Z. , Mecholsky J. J.
Published: March 2008

Techniques from the field of materials science and engineering were utilized to examine the mechanical effects of dark pigment in exoskeleton material on the distal portion of stone crab, Menippe mercenaria, chelae. We made specimens from dark-and light-colored exoskeleton material to measure hardness and fracture toughness. The results from these tests showed the dark material to be much harder and tougher than light-colored material from the same crab chela. Scanning electron microscope photographs are presented to document the microstructure and level of porosity. We think that the structural difference in material properties is due to the lower level of porosity and phenolic tanning in dark material and that this tanning caused the dark color and filling of porosity. The exoskeleton structure is a laminated organic-inorganic structure which can serve as a model for self-healing structures.
Characterization of hydrated silicate glass microballoons
Authors: Isobe Hiroshi , Tokunaga Ichiro , Nagai Noriyoshi , Kaneko Katsumi
Published: March 2008

Glass microballoons (GB) of about 1 μm in diameter were prepared by ultrasonic spray pyrolysis from sodium silicate solution. A silica-rich type of glass microballoons (SB) was prepared by acid treatment of GB. The structural changes of both microballoons with thermal treatment up to 973 K were examined. Both GB and SB showed properties similar to hydrated sodium silicate glass, to some extent. SB was more thermally stable than GB, but the spherical structures of both microballoons were collapsed by heating at 973 K; cristobalite was observed in samples heated at 973 K. The loosely and tightly incorporated water molecules evolved up to 573 K and near 850 K, respectively. The crystallization of cristobalite caused tightly incorporated water molecules to develop. The ultramicropores accessible only to H2O molecules in SB gradually decreased by heating and disappeared by heating at 773 K.
Crystal growth and textured microstructures of 1,6-di(N-carbazolyl)-2,4 hexadiyne diacetylene
Authors: Liao Jun , Martin David C.
Published: March 2008

We are developing techniques to isolate and characterize grain boundary defects with controlled geometries in 1,6-di(N-carbazolyl)-2,4 hexadiyne (DCHD) diacetylene polymer bicrystals. To be successful in this endeavor, it is important to determine the influence of processing variables such as evaporation rate, solution concentration, and environment on DCHD diacetylene crystal morphology. We have found that large, high quality DCHD diacetylene single crystals can be grown from solution under a controlled atmosphere. The quality of the DCHD crystals can be evaluated by optical microscopy and quantitative digital image analysis. Defect structures in DCHD diacetylene crystals have been studied by transmission electron microscopy (TEM). Two single-crystal textured structures have been found in porous DCHD crystals precipitated from solution: (1) a microfibrillar structure and (2) a “cross-hatched” structure. The porous DCHD crystals show localized shear deformation zones (twins and kinks), but only in those regions where the density is greater than 95% that of the perfect crystal. Lateral chain invariant (LCI) small-angle grain boundaries have been identified in DCHD by HREM.
Ar+ ion irradiation in oxygen environment for improving wettability of polymethylmethacrylate
Authors: Koh Seok-Keun , Choi Won-Kook , Cho Jun-Sik , Song Seok-Kyun , Kim Young-Man , Jung Hyung-Jin
Published: March 2008

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.
High efficiency deposition of diamond film by hot filament chemical vapor deposition
Authors: Chen Yan , Chen Qijin , Lin Zhangda
Published: March 2008

A new designed reaction chamber with new relative distribution of filament and substrates has been adopted in order to increase the deposition area of diamond films and thus increase the deposition efficiency in conventional hot filament chemical vapor deposition (HFCVD) systems. The relatively small reaction chamber was cuboid shaped (50 × 25 × 25 mm3) and composed of molybdenum wafers. It was established in the vacuum chamber. A tungsten filament was hung up vertically in the center of the small chamber and parallel to the gas flow path. At the four inner sides of the reaction chamber, four Si(100) substrates (30 × 10 × 0.5 mm3) were installed to grow diamond films. The deposition results indicate that uniform diamond films can be obtained on the four substrates, and the film growth rate is the same at both ends of the substrates. The diamond film growth rate was about 1−2 μm/h, which is similar to those of the conventional HFCVD method. Thus, the deposition area and efficiency can be increased four times in the case without the filament number, gas flow rate, and power consumption.
Band gaps in diamond-graphite hybrids
Authors: Sen Rahul , Sumathy R. , Rao C. N. R.
Published: March 2008

The HOMO-LUMO gaps have been estimated in a graphite-like sp2 carbon network with a progressive increase in the fraction of sp3 carbons, taking into account several possible structural alternatives for each composition. The gap is shown to increase exponentially with the fraction of sp3 carbons. Accordingly, the gap in a diamond-like sp3 network decreases with the increase in the fraction of sp2 carbons.
Single-crystal structure refinement of four compounds in the Y1−xPrxBa2Cu3−yAlyO7−δ system
Authors: Meden A. , Holzinger-Schweiger E. , Leising G. , Pejovnik S. , Golič L.
Published: March 2008

X-ray single crystal diffraction data were used for structural refinement of the title compounds with different x (0.15, 0.27, 0.49, and 0.89). Crystals were grown in alumina crucibles using the self-flux method. Aluminum, which originates from the crucibles, substitutes only Cu(1), and thus induces tetragonal symmetry which was observed in all four crystals. The main structural effect of praseodymium is an increased separation of superconducting layers. Substituent concentrations (x and y in the formula) have been refined and compared with the values obtained by EDX (energy dispersive x-ray analysis) in an electron microscope. It was indicated that the refined values of Y: Pr ratio and the oxygen content are more reliable than those obtained by EDX while the refinement is less sensitive for Cu(1): Al ratio, and this value is more uncertain. This is in accordance with the result of wet chemical analysis.
Preparation and characterization of several group 12 element (Zn, Cd)-bis(thiolate) complexes and evaluation of their potential as precursors for 12–16 semiconducting materials
Authors: Rees William S. , Kräuter Gertrud
Published: March 2008

Compounds of the general formula M(SR)2(M = Zn, Cd; R =i-Pr,t-Bu, Bz) have been prepared and explored as potential unimolecular starting materials for the preparation of binary group 12 metal sulfides. These new compounds have been characterized by IR spectroscopy and thermogravimetric analysis. Chemical derivatization of these insoluble metal-bis(thiolate) compounds by complexation withN-CH3-imidazole renders them more soluble. These adducts were investigated by elemental analysis. Thermolytic decompositions of both the parent and derivatized compounds have been carried out both in the solid state and by heating a suspension of the appropriate metal-bis(thiolate) compound in an inert high boiling hydrocarbon medium. The thermolysis products have been studied by GC/MS (liquids) and x-ray powder diffraction (XRPD), scanning electron microscopy (SEM), and particle size determination (solids).
X-ray diffraction and Raman scattering studies of FeCl3–SbCl5-graphite bi-intercalation compounds
Authors: Abe Takeshi , Yokota Yasukazu , Mizutani Yasuo , Asano Mitsuru , Harada Toshio , Inaba Minoru , Ogumi Zempachi
Published: March 2008

X-ray diffraction (XRD) and Raman spectroscopy have been used for the study of the bi-intercalation of SbCl5 into a stage 5 FeCl3-graphite intercalation compound (GIC). The stage 5 FeCl3-GIC is prepared by an ordinary two-bulb method with the temperature of graphite at 788 K and that of FeCl3 at 573 K. The FeCl3-SbCl5-graphite bi-intercalation compound (GBC) with one SbCl5 layer is obtained when the temperature of the stage 5 FeCl3-GIC is held at 443 K and the temperature of SbCl5 at 373 K in the two-zone system. The stacking sequence of the GBC is found to be an admixture of G(FeCl3)GG(SbCl5)GGG(FeCl3)G and G(FeCl3)GGG(SbCl5)GG(FeCl3)G by XRD, where G, (FeCl3), and (SbCl5) are the graphite, FeCl3, and SbCl5 layers, respectively. The Raman spectrum of the GBC shows two peaks associated with the and modes at 1588 cm−1 and 1610 cm−1, respectively. For the temperatures of stage 5 FeCl3-GIC at 443 K and SbCl5 at 403 K in the two-zone system, the FeCl3-SbCl5-GBC with two SbCl5 layers is obtained. The stacking sequence of the GBC is determined to be an admixture of G(FeCl3)GG(SbCl5)GG(SbCl5)G(FeCl3)G and G(FeCl3)G(SbCl5)GG(SbCl5)GG(FeCl3)G In the Raman spectrum of this GBC, two peaks associated with the mode are observed at 1616 and 1624 cm−1.
Barium titanate-added lead nickel niobate ferroelectrics: Accelerated perovskite formation and dielectric properties
Authors: Lu Chung-Hsin , Wu Jai-Fang
Published: March 2008

The addition of BaTiO3 to Pb(Ni1/3Nb2/3)O3 has been confirmed to vary the formation kinetics of the perovskite solid solutions of Pb(Ni1/3Nb2/3)O3-BaTiO3, and to suppress the generation of the pyrochlore phase. A semiquantitatively calculated reaction conversion verified that increasing the BaTiO3 content significantly accelerated the formation of the perovskite solid solutions. The formed solid solutions of Pb(Ni1/3Nb2/3)O3-BaTiO3 (up to 90 mol% of BaTiO3) exhibited a cubic symmetry at room temperature. The lattice parameter monotonously decreased with an increase in the BaTiO3 content. The structural stability of the perovskite phase was found to be enhanced by the addition of BaTiO3 as well. The formed solid solutions were able to maintain the perovskite structure without decomposition when heated up to 1250 °C. The frequency dependence of the apparent Curie temperature and the diffuseness of the dielectric peak of sintered specimens were increased with increasing the BaTiO3 content up to 50 mol%. Whereas with further addition, the relaxor characteristics in the specimens became obscure, associated with lower frequency dependence and less broadening of the dielectric maximum. The largest broadening of the dielectric peak occurred at x = 0.5, implying that this composition exhibited the most disordered structure, which is probably related to the most random arrangement of B-site cations in oxygen octahedran.
Titania and silica powders produced in a counterflow diffusion flame
Authors: Rulison Aaron J. , Miquel Philippe F. , Katz Joseph L.
Published: March 2008

Earlier publications describe the counterflow diffusion flame burner and its unique capability to produce oxide particles having certain structures, such as spheres of one material coated with another, spheres of one composition with attached bulbs of another composition, and uniform multicomponent mixtures. Here we describe the production and properties of bulk quantities of powders produced using this burner. Measurements were made of specific surface area and, for titania, of phase composition. It was found that the controls over powder characteristics used in other forms of flame-synthesis are equally effective in the counterflow diffusion flame burner. We found that the specific surface area of both silica and titania powders decrease with increasing precursor concentrations. Transmission electron microscopy analysis of the titania powders indicates that the mean size of the particles that comprise these powders increases with increasing concentration. These trends are consistent with the collision-coalescence theory of particle growth. In addition, the crystalline phase of titania can be controlled by selecting the appropriate feed stream. For example, over the ranges TiCl4 precursor concentrations tested, feeding it only into the oxidizer stream yields mainly anatase TiO2 powders, while feeding only into the fuel stream yields mainly rutile TiO2 powders. These trends can be explained by the known atmosphere-dependent anatase-rutile transformation. The present data demonstrate that, in addition to its unique capability to produce certain particle shapes and morphologies, the counterflow diffusion flame burner can be manipulated to produce either of the major commercial titania phases, and also silica, with a wide range of specific surface areas.
Transmission electron microscopy observation and optical property of sol-gel derived LiNbO3 films
Authors: Terabe K. , Gruverman A. , Matsui Y. , Iyi N. , Kitamura K.
Published: March 2008

Crystallization behavior, defects, and interface structures of sol-gel derived LiNbO3 films on three kinds of substrates were examined. The nucleation was found to occur epitaxially at the interface between the film and the substrate. The continuous film is formed by coalescence of the island-like crystallites. When sapphire substrate is used, which has large lattice mismatch with the LiNbO3, the resulting film contains a large amount of micropores, twin structures, and misfit dislocations. On the other hand, while LiTaO3 and 5% MgO-doped LiNbO3 substrates with smaller mismatch are used as substrates, the films show no evidence of the formation of dislocations and twins. The film on 5% MgO-doped LiNbO3 substrate shows better optical waveguiding property.
The intercalation of Ar into C60 films
Authors: Gadd G. E. , Evans P. J. , Moricca S. , James M.
Published: March 2008

In this Communication we discuss how unimplanted and implanted films (Y and Au implanted) of C60, when hot isostatically pressed (HIPed) at a pressure of 170 MPa (1.7 kbar) of Ar and temperatures of 300 or 400 °C, show substantial uptake of Ar into the film. Rutherford backscattering (RBS) provides an effective method for elucidating film composition, showing the films to have ∼1.5 at.% of Ar, consistent with a stoichiometry close to Ar1 C60. The Ar was found to diffuse from the films when these were held in a vacuum at 300 °C. It could subsequently be reincorporated into the film by re-HIPing, with uptake of a similar amount of Ar. IR spectroscopy showed that the C60 IR absorptions remain unchanged throughout uptake of the Ar and its subsequent loss during heating at 300 °C. It appears that the Ar is trapped interstitially in the films outside the C60 cages.
Stabilization of lead lithium iron tungstate with adding barium titanate
Authors: Lu Chung-Hsin , Fang Buh-Kuan
Published: March 2008

The kinetics of formation, phase stabilities, and dielectric constants of Pb(Li1/4Fe1/4W1/2)O3 and BaTiO3-added Pb(Li1/4Fe1/4W1/2)O3 have been compared. The addition of 2 mol% BaTiO3 in Pb(Li1/4Fe1/4W1/2)O3 was confirmed to promote the complete formation of the perovskite phase at 700 °C. Also, the thermal stability of the perovskite phase was significantly enhanced, which resulted in an increase of the dielectric permittivity.
Influence of powder characteristics on the properties of green compacts of Bi-2212 powders
Authors: Yuan D.-W. , Aesoph M. D. , Kajuch J.
Published: March 2008

With the growing potential for use of Bi-2212 powders in high temperature superconducting applications, it is important to understand the processing characteristics of the material. To meet this need, the present work established the relationship between confining pressure and green density for powders of different particle sizes and morphologies. Mechanical properties, including elastic and plastic behavior, of the resulting green compacts were also measured as a function of relative density. Particle size and size distribution are shown to have a significant impact on the properties of interest. The implications of such findings are discussed with respect to the powder-in-tube process for making high temperature superconducting wire and tape.
X-ray diffraction line broadening effects in MBa2Cu3O7−δ (M = Y, Gd) thin films
Authors: Scardi P. , Matacotta F. C. , Dediu V. I. , Correra L.
Published: March 2008

X-ray diffraction line profile analysis (LPA) has been carried out on a set of superconducting thin films of MBa2Cu3O7−δ (MBCO, M = Y, Gd), deposited by pulsed and continuous physical vapor deposition (PVD) techniques on different single-crystal substrates. The choice of appropriate deposition conditions, substrates, and buffer layers promoted a high degree of [00l] preferred orientation, leading to a well-defined columnar grain morphology in the MBCO films. Under such conditions, the LPA of diffraction patterns, collected with the widely spread Bragg–Brentano geometry, gives detailed information on the distributions of coherent scattering domain (crystallite) size and microstrain along the [00l] growth direction; considering the particular MBCO film microstructure, the mean crystallite size () can be regarded as the mean distance between extended planar defects parallel to the film surface. The significance of goes beyond a merely statistical value. As long as the morphology of the films is similar, is found to be strictly connected with the average microstrain by a simple proportionality relation. Moreover, the correlation extends to important superconducting transport parameters, like the transition width ΔTc. These regular behaviors are irrespective of deposition techniques, substrate, and film materials, and are a clear indication of some fundamental relation between the defects and the overall properties of the films.
Precipitate size refinement by CeO2 and Y2BaCuO5 additions in directionally solidified YBa2Cu3O7
Authors: Vilalta N. , Sandiumenge F. , Piñol S. , Obradors X.
Published: March 2008

Directional solidification of YBa2Cu3O7 has been carried out through a Bridgman technique, and the influence of Y2BaCuO5 and CeO2 additives on the size of Y2BaCuO5 precipitates has been investigated. It is demonstrated in this work that the most efficient procedure to reduce the size of the Y2BaCuO5 precipitates is to increase the concentration of nucleation centers present in the peritectic decomposition of YBa2Cu3O7−x. A small concentration (0.3−1 wt. %) of CeO2 has a strong influence on the solidification process and on the size of Y2BaCuO5 precipitates. It is shown that when CeO2 is added, further refinement of the size of precipitates results from the formation of nanometric Y2O3 particles which further enhance the multinucleation effect. We have also observed that coarsening effects are avoided with CeO2 additives.
Oxygen content and inhomogeneity effects on the electrical properties of YBa2Cu3Oy thin films
Authors: Aguiar R. , Sánchez F. , Varela M.
Published: March 2008

Oxygen content is a very important factor influencing the electrical properties of YBa2Cu3Oy. In this work the electrical properties of laser deposited YBa2Cu3Oy thin films on LaAlO3(100), in the whole range 6 ≤ y ≤ 7, are studied. An electrical network model, which randomly assigns oxygen contents and R(T) characteristics to the different elements in the circuit according to an arbitrary distribution, is used to analyze several features in the measured R(T) characteristics as a function of oxygen homogeneity. The model takes into account both short-range and long-range oxygen inhomogeneities. Good agreement between estimated oxygen contents from x-ray diffraction data in our samples and the average oxygen contents used to reproduce their R(T) characteristics is found.The model points out that oxygen homogeneity is very important in order to get the best and reproducible properties, and for conduction and superconductivity analysis through the shape or derivatives of R(T) characteristics.
Comparison of C2F6 and FASi-4 as fluorine dopant sources in plasma enhanced chemical vapor deposited fluorinated silica glass films
Authors: Yoo Woo Sik , Swope Richard , Sparks Barbara , Mordo David
Published: March 2008

Fluorine doping of silicon dioxide films in tetraethylorthosilicate (TEOS)-based plasma enhanced chemical vapor deposition (PECVD) processes was investigated using two fluorine dopant sources, C2F6 and 1,2 bis[methyldifluorosilyl]ethane (FASi-4). Much as TEOS-based undoped silica glass (USG) films display improved step coverage over silane-based USG films, it was suspected that fluorinated silica glass (FSG) films deposited using the relatively new TEOS-based fluorine source FASi-4 might have improved gap fill capabilities as compared to FSG films deposited using gas-based C2F6 fluorine sources. The physical properties and intermetal gap filling capabilities of FSG films deposited using FASi-4 as a fluorine dopant source were compared with the properties of FSG films deposited using C2F6 as a fluorine source. Fluorine dopant levels in the films were found to be linear functions of C2F6TEOS and FASi-4yTEOS ratios. The RI, film stress, and gap fill capability were found to be strongly dependent on the Si–F content in the film regardless of dopant source reagents. Improved gap fill characteristics were observed in films doped with FASi-4 at a given Si–F/Si–O% as compared to C2F6-based FSG films. Dopant source dependence of doping characteristics, physical properties, and gap filling capability of FSG films is reported.
Embedded atom calculations of unstable stacking fault energies and surface energies in intermetallics
Authors: Farkas D. , Zhou S. J. , Vailhé C. , Mutasa B. , Panova J.
Published: March 2008

We performed embedded atom method calculations of surface energies and unstable stacking fault energies for a series of intermetallics for which interatomic potentials of the embedded atom type have recently been developed. These results were analyzed and applied to the prediction of relative ductility of these materials using the various current theories. Series of alloys with the B2 ordered structure were studied, and the results were compared to those in pure body-centered cubic (bcc) Fe. Ordered compounds with L12 and L10 structures based on the face-centered cubic (fcc) lattice were also studied. It was found that there is a correlation between the values of the antiphase boundary (APB) energies in B2 alloys and their unstable stacking fault energies. Materials with higher APB energies tend to have higher unstable stacking fault energies, leading to an increased tendency to brittle fracture.
Fatigue in hydrazone-based xerographic photoreceptors: Effect of ultraviolet irradiation
Authors: Wong C. K. H. , Chan Y. C. , Pfleger J. , Lam Y. W. , Leung K. M. , Chiu D. S.
Published: March 2008

The effect of ultraviolet irradiation on the xerographic sensitometry of organic photoreceptors was studied. Absorbed ultraviolet light decreased both the dark decay and the photoinduced discharge rates, and an increased buildup of the residual potential was observed. Above a threshold dose of ultraviolet irradiation, the residual potential was seen to decrease, and at the same time a slight increase of the hardness of the photoreceptor surface was detected. These behaviors originate from a decrease in the density of charge transport sites which is caused by the photochemical changes in the charge transport layer system.
Epitaxial dependence of the melting behavior of In nanoparticles embedded in Al matrices
Authors: Sheng H. W. , Ren G. , Peng L. M. , Hu Z. Q. , Lu K.
Published: March 2008

Nanometer-sized In particles (5−45 nm) embedded in the Al matrix were prepared by using melt-spinning and ball-milling techniques. Different crystallographic orientationships between In nanoparticles and the Al matrix were constructed by these two approaches. Melting behavior of the In particles were investigated by means of differential scanning calorimetry (DSC). It was found that the epitaxially oriented In nanoparticles (with the Al matrix) in the melt-spun sample were superheated to about 0−38 °C, whereas the randomly oriented In particles in the ball-milled sample melted below its equilibrium melting point by about 0−22 °C. We suggest that the melting temperature of In nanoparticles can be either enhanced or depressed, depending on the epitaxy between In and the Al matrix.
Response of silicon carbide to high-intensity laser irradiation in a high-pressure inert gas atmosphere
Authors: Sadler L. Y. , Shamsuzzoha M.
Published: March 2008

α–SiC (hexagonal) pressed powder targets were heated with a highly focused beam of CO2 laser radiation to temperatures in excess of 3200 °C in an oxygen- and water-free argon atmosphere. The argon pressure was maintained at greater than 100 atm to prevent vaporization of any liquid formed. This pressure was estimated to be several times greater than the total vapor pressure above a liquid solution of carbon and silicon. After a 30 s period at temperature, the heating was abruptly terminated. The 1 mm diameter region most affected on the surface of the SiC targets consisted of a central crater from which all SiC had been vaporized. The crater walls consisted of an amorphous carbon phase which acted as a matrix for fibrous graphite and granular silicon. Beyond the crater wall, the microstructure changed to that of various polytypes of hexagonal SiC, with the grains being equiaxed and smaller than those of the starting SiC powder, an indication that melting, followed by formation of a finer grain structure on abrupt cooling, may have occurred. Still farther from the crater, the microstructure was characterized by β-silicon (cubic) particles of spherical morphology and of larger size than the starting SiC powder, a response typical of solid state sintering. Even further from the crater, the structure was α-SiC, and the grain size was nearly the same as that of the starting material. The particles were lightly bonded together at points of contact between them, indicating only light sintering.
High temperature strength of silicon nitride ceramics with ytterbium silicon oxynitride
Authors: Nishimura Toshiyuki , Mitomo Mamoru , Suematsu Hisayuki
Published: March 2008

Silicon nitride ceramics with ytterbium silicon oxynitride (Yb4Si2O7N2) as secondary phase were fabricated by hot-pressing the powder mixtures, including 50.0 to 97.0 mol% of silicon nitride with a mixture of Yb2O3 and SiO2 (Yb2O3/SiO2 = 4). Sinterability of the materials with Yb2O3 was higher than that with Y2O3 in the same composition of raw powder mixtures. High density materials were obtained under the condition of 50.0 to 89.1 mol% of silicon nitride in raw powder mixtures. Mechanical properties of silicon nitride containing 97.6 mol% of Si3N4 and 2.4 mol% of Yb4Si2O7N2 were measured. Fracture toughness measured by the indentation technique was 5.9 MPam1/2. Bending strength at room temperature and at 1500 °C was 977 MPa and 484 MPa, respectively. The silicon nitride grains consisted of highly elongated rod-like grains and thin needle-like grains. The Yb4Si2O7N2 grains were crystallized at multigrain junctions and bonded close to Si3N4 grains. High strength at high temperature is supposed to be based on the presence of crystalline Yb4Si2O7N2 having a high melting point.
Excimer laser ablation of aluminum nitride
Authors: Lumpp Janet K. , Allen Susan D.
Published: March 2008

Excimer laser wavelengths ablate aluminum nitride at rates up to 0.2 μm/pulse where the rate increases with decreasing background pressure and increasing fluence. The ablation threshold for AlN at 248 nm is approximately 2 J/cm2. Blind vias are produced with flat bottoms, straight walls, and a decomposed metallic layer remaining on the surface. Ablation rate dependence on fluence saturates at high fluences due to absorption by the ablation plume. The influence of processing variables on ablation rate and ablation mechanisms are discussed. Statistical design of experiments is used to compare data sets.
The characterization of strain, impurity content, and crush strength of synthetic diamond crystals
Authors: McCormick Terri L. , Jackson W. E. , Nemanich R. J.
Published: March 2008

This study addresses the correlation of the macroscopic and microscopic characteristics of synthetic diamond crystals produced by high pressure, high temperature conditions. Microscopic properties were characterized using Raman spectroscopy, birefringence, and photoluminescence (PL). Macroscopic properties characterized included inclusion content and crush force. Raman measurements detected measurable stress shifts in only two samples. The PL measurements indicated an increased presence of the H3 center in areas of high strain. The absence of the H3 center and the presence of the N-V PL center was correlated to lower average crush force. A hierarchy has been developed that relates microscopic properties to average crush force.
Effect of oxygen gas on polycarbonate surface in keV energy Ar+ ion irradiation
Authors: Cho Jun-Sik , Choi Won-Kook , Jung Hyung-Jin , Koh Seok-Keun , Yoon Ki Hyun
Published: March 2008

Ar+1 ion irradiation on a polycarbonate (PC) surface was carried out in an oxygen environment in order to investigate the effects of surface chemical reaction, surface morphology, and surface energy on wettability of PC. Doses of Ar+ ion were changed from 5 × 1014 to 5 × 1016 at 1 keV ion beam energy by a broad ion beam source. Contact angle of PC was not reduced much by Ar+ ion irradiation without flowing oxygen gas, but decreased significantly as Ar+ ion was irradiated with flowing 4 sccm (ml/min) oxygen gas and showed a minimum of 12° to water and 5° to formamide. A newly formed polar group was observed on the modified PC surface by Ar+ ion irradiation with flowing oxygen gas, and it increased the PC surface energy. On the basis of x-ray photoelectron spectroscopy analysis, the formed polar group was identified as a hydrophilic bond (carbonyl group). In atomic force microscopy (AFM) study, the root mean square of surface roughness was changed from 14 Å to 22–27 Å by Ar+ ion irradiation without flowing oxygen gas and 26–30 Å by Ar+ ion irradiation with flowing 4 sccm oxygen gas. It was found that wettability of the modified PC surface was not greatly dependent on the surface morphology, but on an amount of hydrophilic group formed on the surface in the ion beam process.
Laser-assisted formation of metallic oxide microtubes
Authors: Nánai László , George Thomas F.
Published: March 2008

The fabrication of metallic oxide microtubes is possible directly, without any support structure, by continuous wave infrared laser-assisted oxidation of the metal in air. The particular case presented is the growth of tube-like vanadium pentoxide microcrystals grown in our laboratories.
Internal friction and Mössbauer study of C–Cr associates in MANET steel
Authors: Gondi P. , Gupta R. , Montanari R. , Principi G. , Tata M. E.
Published: March 2008

Internal friction and Mössbauer techniques have been used to investigate the structure of C–Cr associates and the arrangement of Fe atoms near them in the Cr martensitic steel MANET subjected to different thermal treatments. After slow rate cooling from the austenitic field, the Mössbauer spectra exhibit, besides the complex magnetic pattern of martensite, a low intensity singlet attributed to the presence of a Cr-rich bcc phase. In correspondence, the internal friction curves, show, among others, a Snoek-type peak due to anelastic processes involving C–Cr associates with 6 Cr atoms. To explain the experimental results, a simple structural model is suggested.
Bi–Sr–Ca–Cu–O superconducting thin plates prepared by glass-ceramic processing: Dependence of Tc on the thickness
Authors: Kasuga Toshihiro , Nakamura Koichi , Hattori Tetsuji , Abe Yoshihiro
Published: March 2008

The melt of Bi–Sr–Ca–Cu–O (BSCCO) was quenched by splatting using iron plates, resulting in formation of the glassy plates (0.3–0.7 mm thickness). The plates were converted into superconductors by reheating in air. The critical temperature, Tc, depends on the thickness. The change in Tc is discussed in terms of the difference in the amount of oxygen absorption and in crystallization behavior of the glassy plate during the reheating process between the glassy phase in the interior and that around the surface. It was found that high-Tc glass-ceramic thin plates can be prepared by controlling the amount or the rate of oxygen supply.
Chemical stability of CuInS2 in oxygen at 298 K
Authors: Grzanna J. , Migge H.
Published: March 2008

A thermochemical analysis is performed in the quaternary system Cu–In–S–O at 298 K, including the respective four ternaries. The Cu–In phase diagram is updated with respect to the new experimental as well as to the new thermochemical results in the literature. Free energies of In6S7, In2.8S4, CuIn2, and Cu2In2O5 have been estimated. Consistent sets of data are used for the calculations of the ternary systems with the program thermo, and the results are used to calculate the quaternary tetrahedron Cu–In–S–O with the program thermoq; the algorithm is given. Twelve quaternary two-phase equilibria have been found. They are used to calculate predominance area diagrams of the quaternary system with the program stadiaq for different oxygen partial pressures. The algorithm of this program is given. From these diagrams it becomes obvious that CuInS2 is unstable in air and even in UHV systems and should react to form In2(SO4)3 and Cu2S at oxygen pressures larger than log p (pascal) = −51.5. The results are useful for research in fields such as oxidation and crystal growth of CuInS2 and for development of processes for producing this compound.
Uniformity and interfaces in ion-beam deposited Al/Ni multilayers
Authors: Edelstein A. S. , Everett R. K. , Perepezko J. H. , da Silva Bassani M. H.
Published: March 2008

The uniformity and reaction kinetics of ion-beam deposited Al/Ni multilayer samples with the same composition, Al81.8Ni18.2, and modulation wavelength, Λ = 20 nm, but with different total film thicknesses were investigated by x-ray diffraction and differential scanning calorimetry measurements. The total film thicknesses varied between approximately 0.5 and 2.0 μm. It was found that the interface widths were approximately 1 nm and the Ni layers are much more disordered than the Al layers. The thicker samples show an increase in disorder on a length scale comparable to Λ. In other experiments, a change was observed with increasing modulation wavelength from semicoherent interfaces with a low density of misfit dislocations to semicoherent interfaces with a high density of misfit dislocations. The reaction kinetics for forming the Al9Ni2 phase is independent of the sample thickness.
Nanoparticles of Ag, Au, Pd, and Cu produced by alcohol reduction of the salts
Authors: Ayyappan S. , Gopalan R. Srinivasa , Subbanna G. N. , Rao C. N. R.
Published: March 2008

Nanoparticles of Ag, Au, Pd, and Cu have been prepared by the reduction of their salts by ethyl alcohol under refluxing conditions in the presence of polyvinylpyrrolidone (PVP). In the case of Au and Cu, it was necessary to use magnesium metal as a catalyst during the reduction. The nanoparticles are in the 5–35 nm range in the case of Ag, Au, and Pd, but there is considerable agglomeration in the case of Cu even in the presence of PVP.
The oxygen deficiency effect of VO2 thin films prepared by laser ablation
Authors: Nagashima M. , Wada H.
Published: March 2008

Vanadium dioxide thin films (VO2) have been deposited by laser ablation. The temperature dependence of resistivity and temperature coefficient of resistance (TCR) for each deposition condition were investigated. It was clarified that the TCR at room temperature (RT) can be optimized by controlling the oxygen pressure introduced during deposition as the deposition parameter. In the result, larger TCR's at RT were observed for the oxygen deficient condition of VO2 than for oxygen-richer samples. Obtained TCR values were 0.072/K and 0.045/K at 25°C for VO2 thin films deposited onto R-cut sapphire and SiO2/Si, respectively.
Modification of the phase transition temperatures in titania doped with various cations
Authors: Rodríguez-Talavera R. , Vargas S. , Arroyo-Murillo R. , Montiel-Campos R. , Haro-Poniatowski E.
Published: March 2008

Titania matrices prepared by a sol-gel technique were doped with several cations (La, Zn, Al, K, Na, Ca, Ba, and Co). The effect of the dopants on the thermal and structural properties of the materials is analyzed. The dopant concentration was 2% mol with respect to titanium, and in all cases the same anion (nitrate) was used. The transition temperatures from amorphous to anatase and from anatase to rutile were measured using x-ray diffraction. The amorphous-anatase transition is independent, for almost all samples, of the type of dopant used; however, the anatase-to-rutile phase transition depends strongly on the kind of cation. This means that the temperature range where the anatase phase exists can be controlled by choosing the appropriate dopant. We have found a correlation between the anatase-rutile phase transition temperature and the radius of the cations and their electric charge.
Determination of displacement vector on 180° domain boundary and polarization arrangements in lead titanate crystals
Authors: Chou Chen-Chia , Wayman C. Marvin
Published: March 2008

180° domain boundaries in flux-grown lead titanate single crystals show intriguing domain boundary extreme fringe contrast using transmission electron microscopy. Symmetrically distributed domain boundaries with alternate contrast have been observed, indicating that opposite displacement vectors exist one by one at boundaries. If appropriate reflection vectors were employed, an inclined domain boundary shows reversed fringe contrast. An analysis based upon the two-beam dynamical theory and a rule similar to stacking-fault contrast analysis was employed to predict the geometric configuration of a 180° domain boundary using the extreme fringe contrast (EFC) behavior. Appropriately choosing reflection vectors and utilizing the EFC reversal, a displacement vector as well as the polarization vector arrangement across a 180° domain boundary can be unambiguously identified. Employing the information derived from diffraction patterns and a tilting experiment across a nearby 90° boundary, the whole polarization configuration can be uniquely determined.
Superplastic forming of an α-phase rich silicon nitride
Authors: Rouxel Tanguy , Rossignol Fabrice , Besson Jean-Louis , Goursat Paul
Published: March 2008

The deformation behavior of fine-grained, α-phase rich silicon nitride materials has been studied between 1823 and 1923 K, both in compression and in tension. It is first shown that the higher the α-phase content, the better the superplastic forming ability. A large tension-compression flow asymmetry was evidenced. For instance, shear-thickening flow shows up in compression whereas shear-thinning is observed in tension. Furthermore, much higher flow stresses and hardening rates are reported in compression than in tension. Elongations of more than 80% were achieved for strain rates between 2.5 and 5 × 10−5 s−1. In the light of our results and of the abundant literature dealing with the high temperature deformation in silicon nitride, a sketch of the different deformation stages is proposed, which emphasizes the tension-compression asymmetry. Starting from the promising results obtained at the laboratory scale, the feasibility for net-shaping of a real part was demonstrated by hot-forging of a parabolic shell.
New microstructural model of polymer-ceramic nanocomposite materials
Authors: Becze C. E. , Xu G.
Published: March 2008

Organoceramics are a new class of polymer/ceramic nanocomposite materials where polymer chains are molecularly mixed with the ceramics. A structural model for poly(vinyl alcohol) organoceramic nanocomposite materials proposed by Messersmith and Stupp [J. Mater. Res. 7, 2599–2611 (1992)] claims that polymer chains disperse in the interlayers of the ceramic precursor, causing a broadening of the basal plane spacing. The present research revealed this basal plane broadening does not exist. A new model was constructed where the polymer acts as a template for the ceramic microcrystals to nucleate and grow to reach a size of 20 Å. The ceramic microcrystals (hydrogen bonded to the polymer) further agglomerate and grow to the resulting rosette morphology, whereby the polymer is molecularly dispersed on the nanoscale throughout the ceramic.
Characterization of the disproportionated NdFeCoZrB alloy by means of electron microscopy
Authors: Gao Jian-rong , Song Xiao-ping , Wang Xiao-tian
Published: March 2008

The microstructure of the disproportionated NdFeCoZrB alloy during the solid-HDDR (hydrogenation-disproportionation-desorption-recombination) process was investigated by means of scanning electron microscope (SEM) and transmission electron microscope (TEM). Except for a similar colony-type structure to ternary alloy, fine particles including spherical (Fe, Co)2B phase and undecomposed rim-like Nd2(Fe, Co)14B compound were found dispersed within the α–(Fe, Co) matrix of the microstructure of the disproportionated NdFeCoZrB alloy. An unknown Fe-rich phase with a comparable size to that of the matrix grain was also detected by electron diffraction. These results strongly suggest that the undecomposed rim-like Nd2(Fe, Co)14B particles are probably the memory sites for the origin of anisotropy of the received NdFeCoZrB materials.
Biaxially textured yttria stabilized zirconia buffer layers on rotating cylindrical surfaces
Authors: Hoffmann J. , Dzick J. , Wiesmann J. , Heinemann K. , Garcia-Moreno F. , Freyhardt H. C.
Published: March 2008

Biaxially textured yttria stabilized zirconia (YSZ) buffer layers are prepared on rotating cylindrical surfaces by an ion-beam-assisted deposition (IBAD) process. A large fraction of the cylinder surface can be coated at the same time, resulting in an effective deposition rate of 40 nm/h for the whole tube circumference (diameter of the tube 12 mm). The in-plane alignment depends on the total film thickness and the rotation velocity. The best in-plane textures achieved so far with a full width half maximum (FWHM) value of 27° are sufficient for the preparation of YbaCuO films with critical current densities above 105 A cm−2 at 77 K and self-fields.
Oxide nanotubes prepared using carbon nanotubes as templates
Authors: Satishkumar B. C. , Govindaraj A. , Vogl Erasmus M. , Basumallick Lipika , Rao C. N. R.
Published: March 2008

Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.
Microstructural characterization of quenched melt-textured YBa2Cu3O7−δ materials
Authors: Alarco J. A. , Olsson E. , Golden S. J. , Bhargava A. , Yamashita T. , Barry J. , Mackinnon I. D. R.
Published: March 2008

The microstructure of YBa2Cu3O7−δ (YBCO) materials, melt-textured in air and quenched from the temperature range 900–;990 °C, has been characterized using a combination of x-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry. BaCu2O2 and BaCuO2 were found to coexist in samples quenched from the temperature range 920–960 °C. The formation of BaCu2O2 preceded the formation of YBCO. Once the YBCO had formed, BaCu2O2 was present at the solidification front filling the space between nearly parallel platelets of YBCO. Large Y2BaCuO2 particles at the solidification front appeared divided into smaller ones as a result of their dissolution in the liquid that quenched as BaCu2O2.
Metal-nonmetal transition and resistivity of silicon implanted with bismuth
Authors: Abramof E. , Silva A. Ferreira da , Sernelius Bo E. , Souza J. P. de , Boudinov H.
Published: March 2008

Bismuth was implanted at room temperature in (100)-Si wafers with controlled energy and doses to result in a plateau-like implantation profile. The van der Pauw Si : Bi samples were characterized by the Hall effect and resistivity measurements from room temperature down to 13 K. The electron concentration of the prepared samples at 290 K varied from 3.0 × 1017 to 1.4 × 1020 cm−3. The resistivity of the Si : Bi samples presents a larger enhancement, compared to other dopants, when decreasing the Bi concentration. The metal-nonmetal transition was determined to be around 2 × 1019 cm−3. The calculated values obtained from the Generalized Drude Approach and an equation derived from Kubo formalism agree very well with the experimental data. The results confirm also the behavior ρc (Bi) < ρc(As) < ρc(P) < ρc(Sb) at 290 K.
Characterization of mechanical nanocrystallization process of amorphous Fe–Mo–Si–B alloy by transmission Mössbauer spectroscopy
Authors: Liu X. D. , Guo F. Q. , Lu K. , Umemoto M.
Published: March 2008

The nanocrystallization process of the amorphous Fe–Mo–Si–B alloy under ball milling is characterized by means of transmission Mössbauer emission spectroscopy (TMES) in the present paper. It was found that a single α–Fe phase with the bcc structure is formed under ball-milling the amorphous Fe–Mo–Si–B alloy. A significant increase in the relative area of the subspectra of 8Fenn and 7Fenn and a remarkable decrease in isomer shift and half linewidth of the subspectra of various Fe configurations, especially in the case of 6Fenn, were observed during the ball-milling process. The diffusion of metalloid atoms from the bcc α–Fe phase to the remaining amorphous phase and α–Fe/α–Fe grain boundaries is suggested to occur during the mechanical crystallization of the current amorphous alloy based on the above TMES investigations.