bluuebunny/crossref_metadata_2025 huggingface dataset:
Sol-gel preparation of TiO2 ceramic coating films from aqueous solutions of titanium sulfate (IV) containing polyvinylpyrrolidone
Authors: Kishimoto Tomoko , Kozuka Hiromitsu
Published: March 2008

TiO2 ceramic coating films were deposited on silica glass substrates by the sol- gel method using aqueous solutions of Ti(SO4)2 containing polyvinylpyrrolidone (PVP) as the coating solutions. Unless PVP was added to the solution, the wettability of the substrate was poor, leading to failure in gel film formation. When PVP was added to the solution, on the other hand, homogeneous gel films could be deposited on the substrate, which could be converted to crack- free, transparent TiO2 ceramic thin films about 0.1 μm in thickness. The TiO2 films thus obtained had refractive index, porosity, and surface roughness Ra (the arithmetic average deviation of the assessed profile) of 2.68, 2.1%, and 0.94 nm, respectively. For comparison, a TiO2 film was also prepared from an alcoholic solution of Ti(OC3H7i)4, showing refractive index, porosity, and Ra of 2.65, 3.0%, and 0.98 nm, respectively. These values indicate that the TiO2 films prepared from the Ti(SO4)2 aqueous solutions containing PVP are as smooth and dense as those prepared from conventional alkoxide solutions. The solutions were found to be stable in viscosity for more than five months at room temperature in sealed containers. Thermal analysis, infrared absorption spectra measurement, and x- ray diffraction analysis indicated that the gel films are converted to ceramic films on firing via (i) vaporization of H2O; (ii) decomposition of H2SO4 and/or vaporization of H2SO4 · H2O; (iii) decomposition of SO42− coordinating Ti atoms and oxidation and decomposition of PVP, the latter of which leads to formation of residual carbons; (iv) oxidation of the carbonaceous residues; and (v) crystallization of the titania phase. During the gel- to- ceramic film conversion, the thickness decreased by 90%.
Subsurface cracking during indentation on hybrid coatings on polycarbonate
Authors: A Soloukhin Victor , Brokken-Zijp José C.M. , With Gijsbertus de
Published: March 2008

Subsurface cracking after nano- and Vickers indentation on transparent silica–(meth)acrylate hybrid coatings deposited on a polycarbonate substrate was observed for the first time. It appeared that after initiation at the interface, these cracks propagated toward the surface and in radial directions as the indentation load increased. It was found that, for chemically identical coatings, the thicker the coating, the higher load necessary to initiate these cracks. Subsurface cracks formed during nanoindentation occur at lower loads than the normally observed surface cracks and are accompanied by a very small change in the slope of the loading curve.
Compositional homogeneity of ferroelectric (Pb,La)(Ti,Zr)O3thick films
Authors: Bernik S. , Marinenko R.B. , Holc J. , Samardžija Z. , Čeh M. , Kosec M.
Published: March 2008

Quantified wavelength dispersive spectroscopy (WDS) x-ray element maps were used to characterize active (Pb,La)(Ti,Zr)O3(PLZT) layers on Pt/PLZT/Al2O3substrates, one fired at 1050 °C and the other at 1150 °C. In the layer fired at 1050 °C, randomly distributed micrometer-sized compositional irregularities were observed as La-rich regions that were in most cases enriched also with Ti and deficient in Pb and Zr compared to the matrix. Such compositional imperfections were not observed in the PLZT layer fired for the same duration at 1150 °C. The level of microheterogeneity for all elements in the specimen fired at 1150 °C and for Pb, Ti, and Zr in the specimen fired at 1050 °C was below 1% relative at confidence level of 99% while for La it was as much as 2.5% relative. In point-beam line profiles across the active layer starting from the Pt electrode toward the outer surface of the cross-section of the PLZT film, the Pb concentration decreased continuously in both samples, confirming the importance of providing a properly equilibrated partial pressure of Pb around the sample during the entire firing process. Better dielectric and ferroelectric characteristics of the specimen fired at 1150 °C compared to the sample fired at 1050 °C were attributed to the differences in compositional heterogeneity between these samples. The study of the micro-compositional characteristics of these ceramic materials with quantitative WDS mapping has contributed to the optimization of processing parameters and hence to the understanding of the properties of ferroelectric PLZT materials.
Synthesis of mesostructured lamellar lead sulfide in acidic media
Authors: Zhou Shuxi , Ke Yanxiong , Li Jianmin , Lu Shemin , Zhou Guien , Zhang Shuyuan
Published: March 2008

Mesostructured lamellar lead sulfide has been synthesized for the first time at room temperature in acidic media, employing sodium dodecyl sulfonate (SDS) as template and soluble lead salts, and hydrated sodium sulfide as the inorganic sources. The material was chiefly characterized by x-ray powder diffraction, high-resolution transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and thermogravimetric analysis. In the material, the Pb:S molar ratio for the inorganic phase is about 1:1.2, with a distance of about 2.7 nm between the inorganic layers.
Evolution of microstructure during the thermal processing of titania and vanadium-modified titania gels
Authors: Allison Francis J. , Grant David M. , McKinlay Karen , Bailey Craig , Harrison Philip G.
Published: March 2008

Sol-gel materials of TiO2 and vanadium-modified TiO2 of nominal composition 4, 8, and 16 wt.% vanadium were prepared by evaporation of aqueous colloidal sols obtained by the hydrolysis of aqueous solutions of titanium(IV) chloride with the appropriate amount of vanadyl oxalate using aqueous ammonia followed by peptization of the resulting hydrated solids using nitric acid. The nature of the sol-gel materials and their behavior on calcinations at temperatures up to 1273 K were investigated using x-ray fluorescence, powder x-ray diffraction, transmission electron microscopy, and electron diffraction and FT-Raman spectroscopy. At 333 K, all the gels comprised small (about 5 ± 1 nm) particles of anatase together with traces of brookite. The particle size changed little on thermal treatment at 573 K, but increased significantly at higher temperatures and was accompanied by transformation to rutile. Incorporation of vanadium in the gels reduced the temperature at which rutile began to appear from 923 K in pure TiO2 to 773 K in the V/TiO2 gels. Only rutile was present at high temperatures, except for the 16 V/TiO2 gel, when small amounts of phase-separated vanadia were also observed. A 2–3% substitutional incorporation of V4+ ions in the tetragonal rutile lattice occurred at high temperatures, but the majority of the vanadium was present in an amorphous, highly dispersed fashion.
Casting properties of the high-strength AlZnMgCuNiSi alloys
Authors: Vojtěch Dalibor , Tagiev Elšad , Barta Čstmír , Barta Čestmír , Šerák Jan , Janda Petr , Eckert Ondřej
Published: March 2008

In this paper, the improvement of casting properties of the high-strength AlZnMgCu alloys is described. This improvement was achieved by additions of Ni, Mg, and Si, which formed eutectic phases, thus reducing the crystallization interval of the alloy. The comparison of the castability and hot-tearing tendency was made for three alloys: nearly single-phase AlZn6Mg2 alloy, quasi-ternary eutectic AlZn7Mg7Cu1Ni3Si3 alloy, and common casting AlSi10 alloy. It was shown that the castability and hot-tearing tendency of the quasi-ternary eutectic alloy are similar to those of the AlSi alloy.
Glass-forming ability of Pr–(Cu,Ni)–Al alloys in eutectic system
Authors: Zhang Y. , Tan H. , Kong H. Z. , Yao B. , Li Y.
Published: March 2008

A eutectic point in Pr-rich Pr-(Cu,Ni)-Al alloys was experimentally determined by measuring the solidus temperature (Tm) and liquidus temperature (T1). It was found that Pr68(Cu0.5Ni0.5)25Al7 (at.%) is at the eutectic composition in the pseudoternary Pr–(Cu0.5Ni0.5)–Al alloys. The alloy Pr68(Cu0.5Ni0.5)25Al7 exhibits better glass-forming ability (GFA) than the ternary eutectic alloy Pr68Cu25Al7. However, the best GFA was obtained at an off-eutectic composition (Pr54[Cu0.5Ni0.5]30Al16) in the Pr–(Cu0.5Ni0.5)–Al alloys, which can be formed in fully amorphous rods with diameter of 1.5 mm by copper mold casting. Moreover, the glass-transition temperature Tg increases quickly (from 367 to 522 K) with the increasing of the Al content (from 3 to 27 at.%). The deviation of the best GFA composition from the eutectic point [Pr68(Cu0.5Ni0.5)25Al7] was explained in terms of the asymmetric coupled eutectic zone, the competition between growth of crystalline phase and formation of amorphous, and the higher glass-transition temperature Tg on the hypereutectic side.
Formation of composite gel fiber from cellulose acetate and zirconium tetra-n-butoxide and entrap-immobilization of β-galactosidase on the fiber
Authors: Nakane K. , Ogihara T. , Ogata N. , Kurokawa Y.
Published: March 2008

The formation of a composite gel fiber from cellulose acetate and zirconium tetra-n-butoxide was examined. The gel was thought to have formed by the coordination of OH and CO groups of cellulose to zirconium, taking six coordination numbers around the zirconium. The gel fiber had good stability in common solvents, phosphate solution, and electrolyte solution. Then, under mild conditions, a β-galactosidase was entrap-immobilized on it. The apparent Michaelis constant of the Immobilized β-galactosidase was larger than that of native β-galactosidase, whereas the opposite tendency was observed for the maximum reaction velocity. The activity of the immobilized β-galactosidase increased as the fiber diameter decreased. These findings indicated that lactose hydrolysis took place in the vicinity of the fiber surface. The immobilized β-galactosidase had a higher thermal stability than the native type.
Effect of crystallinity on the dielectric loss of sputter-deposited (Ba,Sr)TiO3 thin films in the microwave range
Authors: Kim Tae-Gon , Oh Jeongmin , Moon Taeho , Kim Yongjo , Park Byungwoo , Lee Young-Taek , Nam Sangwook
Published: March 2008

The crystallinity dependence of the microwave dielectric losses in (Ba,Sr)TiO3 thin films was investigated. The sputter-deposition temperatures were altered to vary the level of thin-film crystallinity on a Pt/Si substrate. The dielectric losses (tan δ) were measured up to 6 GHz without parasitic (stray) effects by using a circular-patch capacitor geometry and an equivalent-circuit model. The microwave dielectric losses increased from 0.0024 ± 0.0018 to 0.0102 ± 0.0017 with increasing crystallinity. These deteriorated dielectric losses showed a good correlation with the symmetry-breaking defects, as confirmed by Raman spectra at approximately 760 cm−1, inducing microscopic polar regions above the Curie temperature of the bulk (Ba0.43Sr0.57)TiO3.
Heat-treatment retention time dependence of polyvinylidenechloride-based carbons on their application to electric double-layer capacitors
Authors: Endo M. , Kim Y. J. , Ishii K. , Inoue T. , Nomura T. , Miyashita N. , Dresselhaus M. S.
Published: March 2008

The heat-treatment retention time effect of carbonized polyvinylidenechloride (PVDC) was investigated. Homogeneous PVDC with a crystallite size of 267 Å was used as a precursor material for an electric double-layer capacitor electrode. The P-120m material, which was heat treated for 120 min at 700 °C, shows a larger specific capacitance than any other material in this study. It shows the largest values reported up to now, reaching values as high as 100.2 F/g for a two-electrode system, which is equivalent to 400.8 F/g in a conventional three-compartment electrode system. It is difficult to distinguish the difference in the pore-size distribution by way of gas adsorption as the retention time is varied. However, the difference can be clarified using a novel method based on the analysis of transmission electron microscopy images. As the retention time for heat treatment increases, the pore size grows through the coalescence of small pores. Furthermore, a new concept for the electric double-layer capacitance is suggested on the basis of analysis of the transmission electron microscopy observations.
Optical absorption of Co2+ in MgIn2S4, CdIn2S4, and HgIn2S4 spinel crystals
Authors: Lee Seok-Joo , Kim Jae-Eun , Park Hae Yong
Published: March 2008

The optical absorption spectra of cobalt-doped MgIn2S4, CdIn2S4, and HgIn2S4 single crystals grown by a chemical transport reaction were investigated at 7 K. The values of Dq and B calculated from the observed spectra show that the d electrons are more delocalized in the order of MgIn2S4, CdIn2S4, and HgIn2S4. Because this order corresponds to the decreasing order of the electronegativity differences between the metal and sulfur atoms of the host crystals, we conclude that as the metal-sulfur bonds in the host crystals are more covalent, the d electrons of the cobalt impurities are more spread out and the cobalt-sulfur bonds are also more covalent.
Effects of poly(ethylene glycol) additive molecular weight on the microstructure and properties of sol-gel-derived lead zirconate titanate thin films
Authors: Yu Shuhui , Yao Kui , Shannigrahi Santiranjan , Hock Francis Tay Eng
Published: March 2008

Poly(ethylene glycol) (PEG) additives with different molecular weights were used to modify sol-gel precursor solutions for preparing lead zirconate titanate (PZT) thin films. The morphology, crystalline structure, and mechanical and electrical properties of the films were characterized. The relationship between the characteristics of the films and the molecular weight of PEG was investigated. It was observed that the PEG eliminated cracking of the films during multiple pyrolysis treatments. However, with the increase of the PEG molecular weight, the films became less dense, which led to decreased Young's modulus and dielectric constant and increased coercive field. Our experiments showed that films prepared from sols modified by PEG with a molecular weight of 200 exhibited a dense morphology and excellent mechanical and electric properties without cracking.
Synthesis of rutile and anatase TiO2 nanoparticles from Ti-peroxy compound aqueous solution with polyols
Authors: Uekawa Naofumi , Suzuki Miki , Ohmiya Takahiro , Mori Fumihiko , Wu Yong Jun , Kakegawa Kazuyuki
Published: March 2008

Ti-peroxy compound was synthesized from Ti(O-iPr)4 and H2O2. Anatase and rutile TiO2 nanoparticles were prepared by heating the Ti-peroxy compound diluted with a polyol aqueous solution at 368 K for 24 h. In this research, ethylene glycol, glycerin, erythritol, and D-mannitol were used as polyols in the diluting solution. The ratio of anatase/rutile of the TiO2 obtained depended on the polyol concentration in the diluting solution. Furthermore, the polyol concentration at which single-phase anatase could be obtained was lowest when the number of OH groups in the polyol molecule was the highest. With increasing polyol concentration, the obtained TiO2 nanoparticles showed increasing specific surface area and decreasing particle size.
Giant magnetoimpedance and stress-impedance effects in multilayered FeSiB/Cu/FeSiB films with a meander structure
Authors: Mao Xin-Hui , Zhou Yong , Chen Ji-An , Yu Jin-Qiang , Cai Bing-Chu
Published: March 2008

Giant magnetoimpedance (GMI) and giant stress-impedence (GSI) effects were realized in multilayered FeSiB/Cu/FeSiB films with a meander structure by magnetron sputtering on thin glass substrates. The GMI and GSI effects were studied in the frequency range of 1–40 MHz for the multilayered FeSiB/Cu/FeSiB films. Experimental results show that a large negative GMI ratio of –23% is obtained at Ha=12 kA/m for a frequency of 20 MHz. The GSI ratio is –20% for a frequency of 1 MHz with the deflection of 150μm of the multilayered FeSiBsCu/FeSiB films. The GSI effect is attractive for stress or pressure sensor applications.
X-ray absorption fine structure study on the formation of Cu–Br bonds in (Br + Cu) ion implanted silica glass
Authors: Fukumi Kohei , Chayahara Akiyoshi , Kinomura Atsushi , Kageyama Hiroyuki , Kadono Kohei , Kitamura Naoyuki , Nishii Junji , Horino Yuji
Published: March 2008

The valence and coordination structure of implanted Cu and Br ions were investigated by x-ray absorption fine structure spectroscopy in (2.4 MeV 6 × 1016 Br2+ ions cm−2+ 2 MeV 6 × 1016 Cu+ ions cm−2)-implanted silica glass. It was found that the implanted Cu and Br atoms were coordinated by oxygen atoms and silicon atoms, respectively, in as-implanted glass. After heating at 600 °C, at least two-thirds of the Cu atoms were coordinated by Br atoms without the formation of crystals. The γCuBr crystal was formed after heating to 1100 °C. It was deduced that the coordination structure of Cu and Br atoms depends on defects as well as thermochemical stability and mass transport processes.
Improved crystallinity and optical properties of AlOx thin films by a ZnO interlayer
Authors: Lin Su-Shia , Huang Jow-Lay
Published: March 2008

To ascertain how the substrate influences the quality of AlOx films, AlOx films were grown on a bare glass and a ZnO-deposited glass in this study. By applying a ZnO interlayer before the AlOx deposition, AlOx films exhibited polycrystalline structure rather than amorphous as obtained by sputtering on a bare glass. For AlOx film on the ZnO-deposited glass, the transmission electron microscopy observation showed the coexistence of amorphous and polycrystalline structure, which reveals that the (122) plane in AlOx film is parallel to the surface of the substrate. The grains of the AlOx film grown on a ZnO-deposited glass comprising many small crystallites aggregated with sizes varying between 38 and 54 nm with irregular grain shapes. Besides, the ZnO interlayer with different deposition parameters had a significant effect in the diffusion interface between AlOx and ZnO. The ZnO interlayer could improve the optical transmission of AlOx films, especially when ZnO films are prepared with a high power of 200 W. Therefore, the glass/ZnO may be a good alternative substrate for producing high-quality AlOx films by controlling the epitaxial grain growth. The AlOx films grown on ZnO-deposited glasses have very good qualities in terms of crystallinity and optical properties.
Current concentration at defects in ZnO varistor material
Authors: Anderson R. A. , Pike G. E.
Published: March 2008

We numerically simulated the current density distribution in electrically nonlinear varistor material containing geometrically simple inclusion defects. Nonconductive spheres and disks, which resemble inclusion shapes observed in chemically prepared varistor material, were investigated. Current densities near perfectly conductive spheres and rods were also computed to gain insight into observed electrical degradation phenomena. These defects were assumed to be much larger than the characteristic size of the zinc oxide (ZnO) grain structure, and our computational method treated the varistor material as electrically isotropic. Results showed strong, localized concentrations of current with either perfectly conductive or nonconductive inclusions, and a dependence on the density of the conductive defects. The small spatial extent of strong current intensification may help to explain the stepwise electrical degradation we have observed when a failing ZnO varistor is subjected to high-power electrical pulses.
Conversion of uniform colloidal Cu2O spheres to copper in polyols
Authors: Orel Zorica Crnjak , Matijević Egon , Goia Dan V.
Published: March 2008

Colloidal copper particles with a high degree of crystallinity were obtained by heating solutions of copper(II) acetate in ethylene glycol (EG) and tetraethylene glycol (TEG). The formation mechanism of copper particles involved first the formation of sparingly soluble nano-sized copper(I) oxide, which aggregated into uniform spheres. On prolonged heating the Cu2O particles were reduced to nano-sized copper crystallites followed by their sintering to colloidal metal. The conversion of the copper(I) oxide to metallic copper proceeds uniformly within the body of each particle.
Photoinduced hydrophilicity and photocatalytic decomposition of endocrine-disrupting chemical pentachlorophenol on hollandite
Authors: Mori Toshiyuki , Watanabe Mamoru , Nakajima Hiromitsu , Harada Masaru , Fujimoto Kenjiro , Awatsu Satoshi , Hasegawa Yoshio
Published: March 2008

Surface properties and photocatalytic oxidation reactions on the hollandite-type compound K2Ga2Sn6O16 (KGSO) were examined for photoinduced hydrophilicity and oxidative decomposition of an endocrine-disrupting chemical, pentachlorophenol (C6Cl5OH, PCP), under ultraviolet (UV) illumination. The thin films and mesoporous powders of hollandite were used for examination of surface properties and photocatalysis, respectively. The photoinduced surface property was examined by measurement of the contact angle of water, ortho-chlorophenol (o-C6H4ClOH), and toluene on the surface of KGSO. The contact angle of H2O and o-C6H4ClOH decreased to 0° under UV illumination. The toluene showed little change in contact angle under UV irradiation. It is concluded that the surface of KGSO shows photoinduced hydrophilicity for H2O and aromatic compounds with hydroxyl groups (−OH). In addition, KGSO clearly showed a photo-oxidative decomposition of PCP under weak UV illumination at room temperature. The decomposition speed of C6Cl5OH on KGSO was much faster than that on previous reported nano-sized SnO2 photocatalysts. It is expected that photo-oxidative decomposition of aromatic compound will be controlled by a combination of optimum composition of the hollandite phase and control of the morphology of the hollandite particles. This suggests that hollandite would be a promising photocatalyst for decomposition of aromatic compounds in endocrine-disrupting chemicals.
Structure and microwave dielectric properties of (Zn1−xNix)TiO3 ceramics
Authors: Kim Hyo Tae , Hwang Joon-Cheol , Nam Joong-Hee , Choi Byung Hyun , Lanagan Michael T.
Published: March 2008

Dielectric ceramics in the system (Zn1−xNix)TiO3, x = 0 to 1 were synthesized by the solid-state reaction route. The phase distribution, microstructure, and dielectric properties were characterized using powder x-ray diffraction analysis, electron microscopy, and microwave measurement techniques. Three phase composition regions were identified in the specimens sintered at 1150 °C: [spinel + rutile] at 0 ≤ x ≤ 0.5, [spinel + ilmenite + rutile] at 0.5 < x ≤ 0.8, and [ilmenite] phase at 0.8 < x ≤ 1. For the 0 ≤ x ≤ 0.5 region, the amount of Ti-rich precipitates incorporated into the spinel phase decreased with the Ni content at 0 ≤ x ≤ 0.5, with a concomitant increase of the rutile phase. The microwave dielectric properties depended on the phase composition and volume according to the three typical phase regions, where the relative amount of rutile to the spinel or ilmenite determined the dielectric properties. The dielectric constant as a function of Ni addition was modeled with a Maxwell mixing rule. An optimum phase distribution was determined in this system with dielectric constant of 22, a Q × f of 60,000, and a low temperature coefficient of the resonant frequency.
Transition from brittle fracture to ductile behavior in 4H–SiC
Authors: Zhang Ming , Hobgood H. M. , Demenet J. L. , Pirouz P.
Published: March 2008

The four-point bend test was used to measure the brittle-to-ductile transition (BDT) temperature in precracked samples of semi-insulating 4H—SiC at four different strain rates. As in other semiconductors, the BDT temperature TBDT was found to be very sharp, within ±15 °C, and to shift to higher temperatures with increasing rates of the applied load (or strain rate). The results appear to be consistent with a transition temperature Tc recently observed in the yield stress of the same material as measured by compression experiments. However, strain-rate measurements in four-point bend tests are not strictly equivalent to those in compression experiments, and therefore it is difficult to directly compare the measured BDT temperatures with the yield stress transitions. Nevertheless, it is believed that the reasonable agreement between TBDT and Tc supports the model recently proposed to explain these transition temperatures.
Characterization of columns grown during KrF laser micromachining of Al2O3–TiC ceramics
Authors: Oliveira V. , Vilar R.
Published: March 2008

This paper aims to contribute to the understanding of column formation mechanisms in Al2O3–TiC ceramics micromachined using excimer lasers. Chemical and structural characterization of columns grown in Al2O3–TiC composite processed with 200 KrF laser pulses at 10 J/cm2 was carried out by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction analysis. Fully developed columns consist of a core of unprocessed material surrounded by an outer layer of Al2TiO5, formed in oxidizing conditions, and an inner layer, formed in reducing conditions, composed of TiC and Al3Ti or an AlTi solid solution. Possible mechanisms of column formation are discussed.
Effect of furfuryl alcohol on the properties of hydrated cement mortar
Authors: Singh V. K. , Singh R. K. , Khatri S. D.
Published: March 2008

The effect of furfuryl alcohol addition to ordinary cement on its properties, such as heat of hydration, setting time, compressive strength, and tensile strength was studied by adding 0.5–3.0% by weight of cement. Hardness was tested using the Vickers indentation method. Fracture toughness of cementitious bond and bending strength were determined using the three-point bending system. Corrosion resistance of resulting products was tested against 0.1 and 1.0 N HCI and H2SO4 and seawater, respectively. Water absorption/open porosity and microstructure were also determined. It was observed that strength, hardness, toughness, and corrosion resistance increase up to 3.0% addition of furfuryl alcohol in ordinary Portland cement. Polymeric phase was interspersed in cement, causing a decrease in water absorption/open porosity, and its interaction with hydrating cement caused additional bond formation, leading to the increase in strength.
Micron diamond composites with nanocrystalline silicon carbide bonding
Authors: Qian J. , Zerda T. W. , He D. , Daemen L. , Zhao Y.
Published: March 2008

Diamond composites with nanocrystalline cubic silicon carbide bonding were sintered from diamond/amorphous silicon mixtures under high pressure and high temperature (p = 5 GPa and temperatures up to 1673 K). Differential scanning calorimetry, ex situ x-ray, and Raman spectroscopy investigations showed that amorphous silicon partially transformed into nanocrystalline silicon at 873 K under 5 GPa. This was followed by the formation of nanocrystalline silicon carbide from the reaction between the silicon and diamond after silicon melting. Refinement of the x-ray diffraction patterns of composites with the Rietveld method revealed that considerable microstrain (0.3–0.5%) remained within the nanocrystalline silicon carbide grains. Small strain (0.1–0.2%) was observed in the compacted diamonds, but after the reaction they became almost strain free (<0.1%). Enhanced fracture toughness was obtained for hybrid composites compared to liquid-infiltrated composites.
Dielectric properties of plasma-spray-deposited BaTiO3 and Ba0.68Sr0.32TiO3 thick films
Authors: Ahn K. , Wessels B. W. , Sampath S.
Published: March 2008

The dielectric properties of high-k dielectric BaTiO3 and Ba0.68Sr0.32TiO3 thick films deposited on alumina substrates using a plasma-spray process were investigated. The as-deposited films were predominantly crystalline but contained an amorphous second phase, the amount of which depended on spray conditions. The effect of the spray conditions on crystallinity was studied and related to the dielectric properties of the films. The presence of a low dielectric constant interfacial layer in plasma-spray-deposited films was determined from the dependence of the dielectric constant on film thickness. After annealing at 500 °C for 20 h in air, the crystallinity and dielectric constant increased. Annealing was also found to affect the interfacial layer properties.
Photoluminescence intensity of GaN films with widely varying dislocation density
Authors: Sun Yue Jun , Brandt Oliver , Ploog Klaus H.
Published: March 2008

We investigated the impact of the presence of dislocations on room-temperature photoluminescence intensity in GaN films grown by molecular beam epitaxy. To determine both screw and edge dislocation densities, we employed x-ray diffraction in conjunction with a geometrical model, which relate the width of the respective reflections to the polar and azimuthal orientational spread. There is no direct dependence of the emission efficiency on the density of either type of dislocation in the samples under investigation. We conclude that dislocations are not the dominant nonradiative recombination centers for GaN grown by molecular beam epitaxy.
Identification of the constituents of double-walled carbon nanotubes using Raman spectra taken with different laser-excitation energies
Authors: Li Feng , Chou S. G. , Ren Wencai , Gardecki J. A. , Swan A. K. , Ünlü M. S. , Goldberg B. B. , Cheng Hui-Ming , Dresselhaus M. S.
Published: March 2008

Double-walled carbon nanotubes (DWNTs), synthesized by the catalytic decomposition of methane, were explored by resonance Raman spectroscopy using different energies for laser excitation. Based on the radial breathing mode frequencies, the indices of the two layers of a DWNT were approximately assigned, depending on the interlayer separation of the two coaxial layers of the DWNT, which ranged from 0.34 to 0.40 nm. From the tentatively assigned results, it was found that the two walls of the DWNT are not strongly selected by chirality and diameter. The results, however, suggest that, for the tubes that are resonant with the available laser excitation energies, most of the outer layers of the observed DWNTs in our samples are semiconducting, while the inner layers of the observed DWNTs are either semiconducting or metallic based on the assembled DWNTs. The characteristics of the G, D, and G′ band of the DWNTs are discussed, and a double peak feature in the D and G′ band, originating from the inner and outer layers of the DWNTs, is reported.
Micropatterned lead zirconium titanate thin films
Authors: Vartuli J. S. , Özenbaş M. , Chun C-M. , Trau M. , Aksay I. A.
Published: March 2008

Micropatterning of Pb(Zr0.52Ti0.48)O3 (PZT) thin films with line features as small as 350 nm was demonstrated through capillary molding of organometallic solutions within the continuous channels of an elastomeric mold. Despite the large stresses that develop during the evaporation of the solvent, pyrolysis of the organics, and the densification and crystallization of the inorganic gel, the patterned crystalline PZT films were crack-free and mechanically robust. Flawless regions as large as 1 cm2 were obtained. The cross-sectional shape of the patterned PZT lines was trapezoidlike. Single perovskite PZT grains that formed during annealing at 600–700 °C completely filled the cross-sectional area of the patterned lines. Lead acetate, zirconium propoxide, and titanium isopropoxide were used as the starting materials. Substrates used included silver tape, stainless steel plate, silicon wafer, and platinum-coated silicon wafer.
Modeling of contact-induced radial cracking in ceramic bilayer coatings on compliant substrates
Authors: Hsueh Chun-Hway , Miranda Pedro
Published: March 2008

Contact-induced radial cracking in ceramic coatings on compliant substrates was analyzed recently. Radial cracks initiate at the coating/substrate interface beneath the contact where maximum flexural tension occurs, and an analytical expression for the onset of radial cracking in monolayer coatings was formulated on the basis of the classical solution for flexing plates on elastic foundation. In the present study, the analytical expression was derived for the case of ceramic bilayer coatings on compliant substrates, which have significant applications in the structure of dental crowns. It was found that the analytical solution for bilayer-coating/substrate systems can be obtained from that of monolayer-coating/substrate systems by replacing the neutral surface position and the flexural rigidity of monolayer coating with those of bilayer coating. The predicted critical loads for initiating radial cracking were found to be in good agreement with existing measurements and finite element results for glass/alumina, glass/glass-ceramic, and glass/Y2O3-stabilized ZrO2polycrystal bilayers on polycarbonate substrates. Limitations of the present analysis are discussed.
Electromigration effects upon the low-temperature Sn/Ni interfacial reactions
Authors: Chen Chih-ming , Chen Sinn-wen
Published: March 2008

Sn/Ni interfacial reactions at 100 °C with and without the passage of electric currents were studied by using the Sn/Ni/Sn sandwich-type reaction couples. The Ni3Sn4 and metastable NiSn3 phases were formed at both the Sn/Ni and Ni/Sn interfaces in the couples reacted at 100 °C without the passing through of electric currents. Metallographical analyses revealed that the metastable NiSn3 phase nucleated and grew at the grain boundary, and the growth rate of the NiSn3 phase was much faster than that of the Ni3Sn4 phase. For the couples with the passage of electric currents of 4 × 103 A/cm2 density, the Ni3Sn4 reaction layers were found at both interfaces as well. However, the NiSn3 phase was found only at the Ni/Sn interface where the directions of electron flow and Ni diffusion were the same, and the NiSn3 phase was not found at the Sn/Ni interface. The NiSn3 phase formed at the Ni/Sn interface was found to nucleate and grow much faster than those without the passage of electric currents. It is likely that the electromigration effect enhances the movement of Ni atoms and accelerates the nucleation and growth of the NiSn3 phase while at the Sn/Ni interface, where the directions of electron flow and Ni diffusion are opposite, electromigration effects retard the movement of Ni atoms and inhibit the nucleation of the NiSn3 phase.
Preparation of BaZrO3 powders by a spray-drying process
Authors: Robertz B. , Boschini F. , Rulmont A. , Cloots R. , Vandriessche I. , Hoste S. , Lecomte-Beckers J.
Published: March 2008

The potential use of barium zirconate for the manufacture of corrosion-resistant substrates emphasizes the need for a simple, inexpensive, and easily scalable process to produce high-quality powders with well-controlled composition and properties. However, the classical solid-state preparation of barium zirconate leads to an inhomogeneous powder unsuitable for applications in highly corrosive environment. For this paper, the possibility to use the spray-drying technique for the preparation of BaZrO3 powders with a controlled size distribution and morphology was investigated. The influence of the nature and concentration of the precursor solution and the influence of the spray-drying step are discussed on the basis of x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and dilatometric measurements.
Effects of substrate metallizations on solder/underbump metallization interfacial reactions in flip-chip packages during thermal aging
Authors: Zhang F. , Li M. , Chum C. C. , Tung C-H.
Published: March 2008

Effects of Ni and Au from Ni/Au substrate metallizations on the interfacial reactions of solder joints in flip-chip packages during long-term thermal aging were systematically investigated. It was found that both Au and Ni influenced the solid-state interfacial reactions, underbump metallization (UBM), and intermetallic compound (IMC) evolution. Because large amounts of Ni could incorporate into IMC to form a multicomponent (Cu, Ni)6Sn5 phase during assembly reflow, while Au could only affect the reaction during thermal aging through the reconfiguration of AuSn4 phase, Ni had stronger effects on solid-solution type Ni–V UBM consumption than Au. It was found that the UBM consumption process was faster in the eutectic SnPb solder system than that in the SnAgCu solder system during aging. A porous structure was formed in the UBM layer after Ni in UBM was consumed. Electrical resistance of flip-chip packages increased significantly after the porous structure reached certain extents. The results showed that the diffusion process of Ni from UBM and Sn from solder in the presence of (Cu, Ni)6Sn5 or (Ni, Cu)3Sn4 phase at solder joint interfaces could be much faster than that in the case of binary Cu6Sn5 or Ni3Sn4 IMC.
Sintering polydispersed spherical glass particles
Authors: Prado Miguel O. , Zanotto Edgar D. , Fredericci Catia
Published: March 2008

We used the Clusters model to study the densification kinetics and resulting porosity of a compact of polydispersed soda-;lime-;silica glass spheres. In addition to the physical data (viscosity, surface tension, particle size distribution) required by the Clusters model, for the first time in glass-;sintering studies, we took extra variables into account: the average number of necks per sphere, the effects of pre-;existing crystals on the particle surfaces, and sample size. The model predicted both the densification kinetics and the resulting pore-;size distribution of sintered compacts. A cross section of a porous sample displayed a porosity pattern that agreed with computer-;simulated cross sections, whose pore-;size distributions was calculated via the Clusters model using a Monte Carlo technique. Its capacity to predict both density and pore-;size distribution makes the Clusters model a valuable tool for designing sintered glasses with any desired microstructure.
Fabrication of α-sialon sheets by tape castingand pressureless sintering
Authors: Xu Xin , Mei Sen , Ferreira José M. F.
Published: March 2008

Sheets of α-sialon were prepared by tape casting and pressureless sintering. Suspensions consisting of precursor α-sialon powders, dispersant, binder, plasticizer, and 60 MEK/40E as solvent were optimized for tape casting by rheological measurements. Crack-free green tapes with good flexibility and high strength were obtained from suspensions with suitable rheological properties (moderate viscosity, shear-thinning behavior, and negligible thixotropy). The obtained green tapes showed great homogeneity by means of scanning electron microscope observation and pore-size distribution, leading to homogeneous α-sialon sheets after pressureless sintering at 1750 °C for 2 h. The results showed that it was possible to fabricate homogeneous α-sialon sheets with smooth surfaces through tape casting and pressureless sintering.
Fabrication of nano-sized Si powders with a narrow size distribution by two-step milling
Authors: Kim Bong-Chull , Uono Hiroyuki , Fuse Tooru , Ishihara Tadashi , Senna Mamoru
Published: March 2008

By the combination of two successive dry milling processes (i.e., by using a multiring mill and subsequently a pin-type disintegrator), downsizing of Si powders was achieved to 30 nm crystallites and their aggregated mean volume diameter about 100 nm, with the top size less than 400 nm. Combination of the two dry milling processes proved to be effective to reduce the particle size and sharpen the size distribution of the aggregates without using any additives, tedious wet processes, or subsequent classification. Increase in the impurity due to milling was <0.1% for Fe and <0.4% for Zr, being well within a tolerable limit for most of the technological purposes.
Synthesis of hyperbranched poly(amine–ester)-protected noble metal nanoparticles in aqueous solution
Authors: Bao Chunyan , Jin Ming , Lu Ran , Xue Pengchong , Zhang Tierui , Tan Changhui , Zhao Yingying
Published: March 2008

The synthesis of Au and Ag metal nanoparticles stabilized by G4, G5, and G6 hyperbranched poly(amine–ester) (HPAE) is reported. The reduction of hydrogen tetrachloroaurate and silver nitrate in the presence of HPAE resulted in the formation of stable, uniform, water-soluble nanoparticles. The average particle sizes are (2.4 ±0.5)–(4.1 ±0.4) nm for Au and (2.5 ±4.9)–(10.3 ±1.7) nm for Ag, depending on the generation of HPAE and metal ion-to-end tertiary amine of HPAE (M:N) used. All of the obtained colloidal solutions are stable for a long period of time. The results from ultraviolet–visible absorption spectra and Fourier transform infrared absorption spectroscopic investigations confirm the interactions between metal and HPAE.
Determination of fracture toughness from the extra penetration produced by indentation-induced pop-in
Authors: Field J. S. , Swain M. V. , Dukino R. D.
Published: March 2008

The fracture toughness of small volumes of brittle materials may be investigated by using pyramidal indenters to initiate radial cracks. The length of these cracks, together with indenting load and the hardness to modulus ratio of the material, were combined to calculate the critical stress intensity factor Kc pertinent to fracture toughness. Modulus and hardness may be obtained from the literature or may be measured using nanoindentation techniques. If the material volume is very small, such as single grains in a conglomerate, a reduction of scale may be obtained by reducing the internal face angles of the indenter. This encourages crack initiation at lower loads, but cracks produced at very low loads are short and difficult to measure. Experiments on fused silica and glassy carbon suggested that radial cracks are initiated during loading and that when indenters with sufficiently small angles are used these cracks immediately pop-in, to become fully developed median/radial crack systems. Following pop-in, the rate of penetration of the indenter increases and at higher loads there is an extra increment of penetration over that which would otherwise have occurred. In this study a method is described whereby this extra penetration may be determined. Then for two dissimilar brittle materials, crack length is shown to be correlated with extra penetration leading to a relationship that may possibly avoid the necessity for crack-length measurement.
Adhesion, passivation, and resistivity of a Ag(Mg) gate electrode for an amorphous silicon thin-film transistor
Authors: Lee Jaegab , Yang Heejung , Lee Jinhyung , Shin Hyunjung , Kim Jiyoung , Jeong Changoh , Cho Beomseok , Chung Kyuha , Lee Eungu
Published: March 2008

The effect of Mg in Ag(Mg)/SiO2/Si multilayers on the adhesion, passivation, and resistivity following vacuum annealing at 200–500 °C has been investigated. The annealing of Ag(Mg)/SiO2/Si multilayers produced surface and interfacial MgO layers, resulting in a MgO/Ag/MgO/SiO2/Si structure. The formation of a surface MgO/Ag bilayer structure provided excellent passivation against air and CF4 plasma chemistry. In addition, the adhesion of Ag to SiO2 was improved due to the formation of an interfacial MgO layer resulting from the reaction of segregated Mg with SiO2. However, the negligible solubility of Si in Ag prevented the dissolution of free silicon into the Ag(Mg) film produced from the reaction Mg + SiO2 = MgO + free Si, which in turn limited the reaction between Mg and SiO2, which led to a decrease in the adhesion of Ag to SiO2 at the higher temperature. The use of an O2 plasma prior to Ag(Mg) alloy deposition on SiO2 produced an oxygen-rich surface on the SiO2, which allowed for the enhanced reaction of the segregated Mg and SiO2 at the surface, thus resulting in markedly increased adhesion properties.
Synthesis of rutile titania powders: Agglomeration, dissolution, and reprecipitation phenomena
Authors: Klein Sascha M. , Choi Joon Hwan , Pine David J. , Lange Fred F.
Published: March 2008

Rutile titania powders were synthesized via a sol-gel/hydrothermal process using nitric acid as the catalyst. A molar acid to alkoxide ratio of 10 and a water to alkoxide molar ratio of 250 produced 100% rutile powders when precipitated below 45 °C. Higher temperatures yielded initially either anatase or mixtures of anatase and rutile. Spherulitic growth produced cauliflower-shaped agglomerates with a mean size of 760 nm. The agglomerates could be broken apart into approximately 100-nm large broomlike agglomerates via a dissolution and reprecipitation process when reacted with approximately 2.4 molar nitric acid. Transmission electron microscopy observations showed that the broomlike agglomerate consisted of linear clusters of rodlike agglomerates composed of crystallographically aligned, primary particles approximately 4 nm in size.
Development of laboratory x-ray fluorescence holography equipment
Authors: Takahashi Yukio , Hayashi Kouichi , Wakoh Kimio , Nishiki Naomi , Matsubara Eiichiro
Published: March 2008

Laboratory x-ray fluorescence holography equipment was developed. A single-bent graphite monochromator with a large curvature and a high-count-rate x-ray detection system were applied in this equipment. To evaluate the performance of this equipment, a hologram pattern of a gold single crystal was measured. It took two days, which was about one-third the time required for the previous measurements using the conventional x-ray source and several times that using the synchrotron source. The quality of the hologram pattern is as good as that obtained using the synchrotrons. Clear atomic images on (002) are reconstructed.
Fabrication of ternary Mg–Cu–Gd bulk metallic glass with high glass-forming ability under air atmosphere
Authors: Men H. , Kim D. H.
Published: March 2008

A new Mg65Cu25Gd10 alloy having significantly improved glass-forming ability (GFA) has been developed. In this article, we show that the ternary Mg65Cu25Gd10 bulk metallic glass with diameter of at least 8 mm can successfully be fabricated by a conventional Cu-mold casting method in air atmosphere. The critical cooling rate for glass formation was estimated on the order of magnitude of approximately 1 K/s. When compared with the GFA of Mg65Cu25Y10 alloy, the significantly improved GFA of Mg65Cu25Gd10 alloy cannot be explained by ΔTx and Trg values.
Characterization of electroplated Ni/SiC and Ni/Al2O3 composite coatings bearing nanoparticles
Authors: Wang Sheng-Chang , Wei Wen-Cheng J.
Published: March 2008

Ultrafine SiC and Al2O3 particles with 30–50 nm sizes were used to codeposit with Ni in a sulfamate bath to form composite coatings. The microstructure and mechanical properties of the layers were investigated by x-ray diffractometry, scanning and transmission electron microscopy, high-resolution transmission electron microscopy, microindentation, and wear testing. The microstructural results revealed that 7 vol% of SiC or Al2O3 particles dispersed randomly in the Ni matrix. The addition of the ultrafine SiC or Al2O3powder into the Ni matrix apparently reduced the size of Ni grains during the electroplating and inhibited the grain growth during heat treatment. The microhardness and wear resistance were improved by the addition of SiC and Al2O3 particles, especially for SiC/Ni samples after heat treatment at 400 °C for 24 h. The mechanisms of hardening and wearing of Ni-based electroplated layers are discussed.