bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of BaSn(OH)6 and BaSnO3 acicular particles
Authors: Buscaglia M. T. , Leoni M. , Viviani M. , Buscaglia V. , Martinelli A. , Testino A. , Nanni P.
Published: March 2008

The synthesis of BaSn(OH)6 acicular crystals by precipitation at 100 °C from aqueous solutions and their transformation in the perovskitelike compound BaSnO3 was investigated. Single acicular crystals 100–200 μm in length were obtained from a 0.05M solution, whereas bundlelike aggregates of 20–40 μm were precipitated from 0.2–0.6 M solutions. The x-ray diffraction pattern of barium hexahydroxostannate was indexed according to monoclinic symmetry with cell parameters a = 11.029 ± 0.002 Å, b = 6.340 ± 0.001 Å, c = 10.563 ± 0.001 Å = 128.51 ± 0.01°, α = γ = 90°. The BaSn(OH)6 particles decomposed to BaSnO3 and water at approximately 270 °C and the original morphology was retained. The resulting product had specific surface area up to 30–40 m2/g and consisted of 10–20 nm crystallites. The larger unit cell edge in comparison to the reference value and the continuous weight loss up to 1200 °C indicate that water is not completely released during decomposition and a substantial amount of proton defects (up to 0.4 mol per mole of BaSnO3) is incorporated in the perovskite lattice as OH− groups. Normal crystallographic properties of BaSnO3 are restored only after calcination at 1300 °C.
Dependence of fracture toughness on annealing temperature in Pb(Zr0.52Ti0.48)O3 thin films produced by metal organic decomposition
Authors: Zheng X. J. , Zhou Y. C. , Zhong H.
Published: March 2008

Lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) thin films were grown on Pt/Ti/Si(001) by metal organic decomposition (MOD). The effects of the annealing procedure on the crystalline microstructure, hysteresis loops, and fracture toughness of PZT thin films were investigated by x-ray diffraction, RT66A analyzer, and Vickers indentation method, respectively. It was found that the fracture toughness, crystalline microstructure, and ferroelectric properties depend on the annealing procedure. When the annealing temperature is in the range of 600–750 °C, the higher the annealing temperature, the better the crystalline quality. The fracture pattern diagram, as a function of indentation load and annealing temperature, was introduced to describe the fracture characteristics of PZT thin film induced by indentation load. With the increase of annealing temperature from 600 °C to 750 °C, the fracture toughness of PZT thin films decreased from 0.492 MPa m1/2 to 0.478 MPa m1/2.
Uniformly distributed nickel nanoparticles created by heating the carbon nanotube
Authors: Zhang Zaoli , Gao Min
Published: March 2008

Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discharge were studied by electron diffraction, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and x-ray energy dispersive spectrometer (EDS). The nanoparticles have diameters in the range of 3–15 nm. Electron diffraction pattern and HRTEM images analysis both show that the nanoparticles can be nickel or diamond. EELS and EDS analysis in a dedicated scanning transmission electron microscope showed that the nanoparticles are face-centered-cubic nickel particles rather than diamond nanocrystals. The mechanism of formation of nickel nanoparticles below its melting point is discussed.
Long-lasting phosphorescence and photostimulated long-lasting phosphorescence in Mn2+-doped alumino-phosphofluoride glasses irradiated by a femtosecond laser
Authors: Jiang Xiongwei , Qiu Jianrong , Fan Youyu , Hu Hefang , Zhu Congshan
Published: March 2008

We report on long-lasting phosphorescence and photostimulated long-lasting phosphorescence phenomena in femtosecond laser-irradiated Mn2+-doped alumino-phosphofluoride glasses. Long-lasting phosphorescence was observed in the glass samples after the irradiation of the focused femtosecond laser. Photostimulated long-lasting phosphorescence was observed in the femtosecond laser pre-irradiated region by excitation of an ultraviolet light of 365 nm, after the femtosecond laser-induced long-lasting phosphorescence decayed completely. The mechanisms of these phenomena have been discussed. These phenomena have potential uses in three-dimensional ultra-high-density optical recording.
Composition and temperature dependence of optical energy gaps of TlGa1−xSbxS2 single crystals
Authors: Jin Moon-Seog , Kim Jae-Yeol , Kim Koung-Suk , Choe Sung-Hyu , Song Ho-Jun
Published: March 2008

TlGa1−xSbxS2 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) single crystals were grown using the Bridgman–Stockbarger method. The direct energy gaps of the single crystals were found to be 2.586, 2.459, 2.344, 2.228, 2.119, and 1.987 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The indirect energy gaps were found to be 2.479, 2.357, 2.232, 2.118, 1.983, and 1.871 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The optical energy gaps decreased linearly with increasing composition x. The temperature dependence of the optical energy gaps for each of the single crystals was well fitted with the Varshni equation.
Small-angle neutron scattering study of the role of feedstock particle size on the microstructural behavior of plasma-sprayed yttria-stabilized zirconia deposits
Authors: Boukari Hacène , Allen Andrew J. , Long Gabrielle G. , Ilavsky Jan , Wallace Jay S. , Berndt Christopher C. , Herman Herbert
Published: March 2008

The microstructures of thick plasma-sprayed yttria-stabilized zirconia (8% mass fraction yttria) deposits were studied in a series of Porod small-angle neutron scattering (SANS) and multiple small-angle neutron scattering (MSANS) experiments. Three main void components were identified in the deposits: intrasplat cracks, interlamellar planar pores, and globular pores. The SANS and MSANS measurements were analyzed using the traditional theory for Porod scattering and a recently developed three-component model for MSANS evaluation. The average size, volume fraction, internal surface area, and orientation distribution for each void component within the deposits were determined. This study focused on gaining a better understanding of the effects of initial feedstock particle size and annealing temperatures on the microstructure of deposits sprayed under equivalent particle-impact conditions. Quantitative results are presented for each of four deposit samples: one prepared using the as-received feedstock particle wide-size distribution and three prepared from feedstock powder of different and relatively narrow particle size ranges with average sizes of 32, 47, and 88 μm. Except for the coarse (88 μm) feedstock powder, only mild monotonic variations were found in the microstructural anisotropies, the porosities (13 ± 1%), and the internal surface areas in the as-sprayed deposits. The internal surface area was independent of the feedstock particle size, even with the coarse feedstock. When the deposits were annealed at high temperatures (1100 and 1400 °C), the microstructures were altered with a reduction of the total internal surface area and a mild coarsening of the voids. These changes in the microstructural evolution were well-captured and described by the three-component model. The results were compared and related with those obtained from scanning electron microscopy images and elastic moduli measurements.
Composition rule of bulk metallic glasses and quasicrystals using electron concentration criterion
Authors: Wang Y. M. , Qiang J. B. , Wong C. H. , Shek C. H. , Dong C.
Published: March 2008

This paper aims at establishing a number of electrons/atom (e/a)-based criterion for searching bulk metallic glasses (BMGs) and quasicrystals with large forming abilities in the Zr-based multicomponent alloy systems. After discussions on the diffraction characteristics corresponding to the Fermi surfaces-Brillouin zone interaction in the Zr-based Hume-Rothery phases, the Hume-Rothery matching rule is well explained when the effective e/a value of the matrix element Zr is taken as 1.5. The BMG- and quasicrystal-related phases are pointed out to be a family of nearly e/a-constant phases in a given alloy system. An e/a-constant criterion is then used to predict the ideal composition of the quasicrystals and BMGs in the Zr-Ti-Ni, Zr-Al-Ni, and Zr-Al-Ni-Cu systems, respectively. Nearly pure bulk Zr-Ti-Ni quasicrystals and a series of BMGs with glass-forming abilities greater than that of the known Zr65Al7.5Ni10Cu17.5 alloy are found.
Preparation of monodisperse silica particles with controllable size and shape
Authors: Zhang J. H. , Zhan P. , Wang Z. L. , Zhang W. Y. , Ming N. B.
Published: March 2008

The effects of dilution of tetraethyl orthosilicate (TEOS) with ethanol on the shape and monodispersity of silica particles were investigated. The results indicated that the dilution of TEOS with ethanol can depress the formation of new nuclei and the aggregation or adhesion of particles and make the distillation of TEOS unnecessary to achieve monodispersed silica spheres. A seeded growth technique using continuous drop addition of TEOS diluted with 4× volume of ethanol was developed to improve monodispersity and spheric shape and increase the size of silica particles. The monodisperse silica particles (150 nm ± 5%−1.2 μm ± 1%) with fine spheric shape were successfully synthesized by the seeded growth technique. Using the homemade 280 nm ± 2.8% silica spheres, we prepared opals of high quality which showed periodically ordered packing and a photonic band-gap effect.
Structural phase evolution of strontium-doped lead titanate thin films prepared by the soft chemical technique
Authors: Pontes F. M. , Leal S. H. , Pizani P. S. , Santos M. R. M. C. , Leite E. R. , Longo E. , Lanciotti F. , Boschi T. M. , Varela J. A.
Published: March 2008

Strontium-modified lead titanate thin films with composition Pb1−xSrxTiO3 were grown on Pt/Ti/SiO2/Si substrates using the polymeric precursor method. The structural phase evolution as a function of the Sr contents was studied using micro-Raman scattering, specular reflectance infrared Fourier transform spectroscopy, and x-ray diffraction. The results showed a gradual change from tetragonal to cubic structure, the transition occurring at about x = 0.58. The infrared reflectance spectra showed that the frequency of several peaks decreases as the strontium concentration increases. These features are correlated with a decrease in the tetragonal distortion of the TiO6 octahedra as the strontium concentration increases.
Synthesis of solid and spirally cracked TiO2 fibers by a liquid mix process
Authors: Fan Chen-Lung , Ciardullo Daniel , Huebner Wayne
Published: March 2008

Titania fibers were synthesized by a liquid mix process, starting by complexing titanium isopropoxide with a chelating agent solution to form a precursor resin for further fiber drawing. The as-drawn continuous precursor fibers underwent a weight change of 80% and a volume change of 75% after heat treatment at 800 °C in nitrogen followed by an additional treatment at 600 °C in air. The fibers consisted mainly of rutile with 5–10% anatase. Further treatment at 700 °C transformed the anatase completely into rutile. Fibers with finished diameter less than about 15 μm were solid with smooth surfaces. Fibers with finished diameter greater than about 15 μm were hollow and spirally cracked in a uniform manner. Fibers treated at 600 °C showed no visible grains. Additional annealing at 800 °C grew grains to an average size of 0.3–0.4 μm. The fibers appeared solid and dense.
Low-temperature growth of ZnO nanowires
Authors: Tseng Yung-Kuan , Lin I-Nan , Liu Kuo-Shung , Lin Tzer-Shen , Chen I-Cherng
Published: March 2008

ZnO nanowires with diameters of 40–200 nm were grown with a gold catalyst in bulk quantities on alumina substrates and sapphire substrates. This synthesis procedure was achieved by heating a 1:1 mixture of ZnO and Zn powder to 500 °C with trace water vapor as an oxidizer. X-ray diffraction and transmission electron microscopy revealed that the nanowires were in the pure wurtzite phase. Photoluminescence spectroscopy showed two peaks: one was a strong ultraviolet emission at around 380 nm, which corresponds to the near-band-edge emission; the other was a weak near-infrared emission around 750 nm, which indicates a low concentration of oxygen vacancy. Moreover, we observed that the Zn/Au alloy droplets appeared on the tips of ZnO nanowires. As a consequence, we can select areas to grow ZnO nanowires by patterning the thin metal film on the substrates. These findings prove that the low-temperature growth mechanism is via vapor–liquid–solid rather than vapor transport deposition or vapor supersaturation (vapor–solid) mechanism. On the basis of the site-specific growth and the low-temperature requirement developed from this work, the synthesis of ZnO is compatible to microelectric machining system processing.
Nanoindentation study of plasticity length scale effects in LIGA Ni microelectromechanical systems structures
Authors: Lou J. , Shrotriya P. , Buchheit T. , Yang D. , Soboyejo W. O.
Published: March 2008

This paper presents the results of a nanoindentation study of the effects of strain gradient plasticity on the elastic–plastic deformation of lithographie, galvanoformung, abformung (LIGA) Ni microelectromechanical systems (MEMS) structures plated from sulfamate baths. Both Berkovich and North Star/cube corner indenter tips were used in the study to investigate possible effects of residual indentation depth on the hardness of LIGA Ni MEMS structures between the micro- and nanoscales. A microstructural length scale parameter, , was determined for LIGA nickel films. This is shown to be consistent with a stretch gradient length-scale parameter, ls, of approximately 0.9 μm.
Microwave-assisted polyol synthesis of Ag powders
Authors: Katsuki Hiroaki , Komarneni Sridhar
Published: March 2008

Silver metal powders were prepared through reduction of AgNO3 in ethylene glycol using microwave-polyol (M-P) and conventional-polyol (C-P) reactions at 100–200 °C. Powders of Ag were rapidly produced by microwave-assisted reaction at temperatures above 160 °C. The formation yield of Ag powders from AgNO3 reached 97.8% after treatment for 135 min at 140 °C and 98.6% after treatment for 23 min at 160 °C. Compared to the formation of Ag powders using a C-P reaction, a M-P reaction led to increased rate of formation by 6.5 times at 160 °C, 5.2 times at 140 °C, and 3 times at 130 °C. Silver particles of 0.3–2 μm in diameter were produced using M-P and C-P reactions at 100–120 °C. The particle size of Ag powders increased with increasing reaction temperatures and times, and particles strongly aggregated at 160 °C using C-P and M-P reactions.
Rate dependence of serrated flow in a metallic glass
Authors: Jiang W. H. , Atzmon M.
Published: March 2008

Plastic deformation of amorphous Al90Fe5Gd5 was investigated using nanoindentation and atomic force microscopy. While serrated flow was detected only at high loading rates, shear bands were observed for all loading rates, ranging from 1 to 100 nm/s. However, the details of shear-band formation depend on the loading rate.
Microstructure evolution in monocrystalline silicon in cyclic microindentations
Authors: Zarudi I. , Zhang L. C. , Swain M. V.
Published: March 2008

The study presents evidence of the microstructural evolution during cyclic indentation of monocrystalline silicon with a spherical indenter. Transmission electron microscopy examination of microindentation on cross-section view samples showed that the structure change in the transformation zone features a decomposition of the amorphous phase to R8/BC8 crystals. Outside the zone, cyclic loading gives rise to bending of pristine silicon, slip penetration, and radial cracking. The development of the load–displacement curves during consecutive indentations is justified in terms of the phase transformation events observed.
Wavelength-dependent Raman scattering of hydrogenated amorphous silicon carbon with red, green, and blue light excitation
Authors: Park Minseo , Sakhrani V. , Maria J-P. , Cuomo J. J. , Teng C. W. , Muth J. F. , Ware M. E. , Rodriguez B. J. , Nemanich R. J.
Published: March 2008

This study presents results of wavelength-dependent Raman scattering from amorphous silicon carbon (a-Si:C:H). The a-Si:C:H films were produced by radio-frequency plasma-enhanced chemical vapor deposition. Prior results with amorphous carbon indicate that laser excitation selectively probes clusters with differing sizes. Our measurements with a-Si:C:H indicate that when using red (632.8 nm), green (514.5 nm), and blue (488.0 nm) excitation, the Raman D and G peaks shift to higher wave numbers as the excitation energy increases. The higher frequency is associated with smaller clusters that are preferentially excited with higher photon energy. It appears that photoluminescence occurs due to radiative recombination from intracluster transitions in Si-alloyed sp2-bonded carbon clusters
Microstructural features of Al-implanted 4H–SiC
Authors: Wang C. M. , Zhang Y. , Weber W. J. , Jiang W. , Thomas L. E.
Published: March 2008

The microstructural features of highly damaged 4H–SiC implanted with Al22+ ions at 450 K were studied using transmission electron microscopy (TEM) and electron energy-loss spectroscopy. Conventional TEM images reveal that the crystalline SiC domains are highly strained/distorted when the relative disorder on the Si sublattice ranges between about 0.4 and 0.8, as determined by Rutherford backscattering spectrometry in channeling geometry. As the relative disorder approaches 1.0, the high strain contrast appears to be relieved, and localized amorphized domains are observed. Plasmon-loss energy shows a red shift following the implantation, and the magnitude of the red shift increases with increasing relative disorder. Based on the red shift, the estimated volume expansion is approximately 8% for highly damaged crystalline SiC and approximately 16% for the amorphous state. Energy-loss near-edge-structure of both the C and Si K edge reveals the existence of Si–Si and C–C bonding in the Al22+ implanted SiC.
Investigation on the arc erosion behavior of new silver matrix composites: Part II. Reinforced by short fibers
Authors: Hsu Chia-Jung , Chang Shou-Yi , Chou Liang-Yu , Lin Su-Jien
Published: March 2008

An electroless plating and hot-pressing process was developed to fabricate silver matrix composites reinforced with uniformly distributed graphite and Saffil short fibers (Graphitesf and Saffilsf). The hardness of the composites increases as the content of short fibers increase. Static-gap, single-spark erosion and repeated-collision, multiple-arc erosion tests were used to investigate the arc erosion behavior of the composites. The composites exhibited better arc erosion resistance when the contents of short fibers were increased in a static-gap, single-spark erosion test. However, the weight loss of the composites after 10,000 times repeated-collision, multiple-arc erosion operation shows that the composites with low volume percents of short fibers have a good arc erosion resistance. The Saffilsf/Ag composites show a better arc erosion resistance than Graphitesf/Ag because of the greater strengthening effect of the finer Saffil short fibers. The erosion behavior of the composites is dominated by the viscosity of composites in single-spark tests, while it depends on the competition of viscosity and thermal properties in multiple-arc tests.
Determining constitutive models from conical indentation: Sensitivity analysis
Authors: Capehart T. W. , Cheng Y-T.
Published: March 2008

Several procedures have previously been advanced for extracting constitutive relations from the force–displacement curves obtained from indentation. This work addresses the specific problem of determining the elastic modulus E, yield stress Y, and hardening exponent n, which define the isotropic strain-hardening model from a single force–displacement curve with a sharp conical tip. The sensitivity of the inversion process was tested through a series of finite element calculations using ABAQUS. Different magnitudes of normally distributed noise were superimposed on a calculated force–displacement curve to simulate hypothetical data sets for specific values of E, Y, and n. The sensitivity of the parameter confidence intervals to noise was determined using the χ2-curvature matrix, statistical Monte Carlo simulations, and a conjugate gradient algorithm that explicitly searches the global parameter space. All three approaches demonstrate that 1% noise levels preclude the accurate determination of the strain-hardening parameters based on a single force–displacement curve.
Micromechanical properties of a laser-induced iron oxide–aluminum matrix composite coating
Authors: Nayak S. , Riester Laura , Meyer Harry M. , Dahotre Narendra B.
Published: March 2008

A laser-based technique was used to deposit Fe3O4 on A319Al, producing an Fe3O4/Al reaction composite coating. Scanning Auger microscopy indicated a reaction between oxide particles and aluminum-forming Fe–Al intermetallic compounds, Al2O3, and various intermediate reaction products. Analysis of the coating region, fractured in vacuo, indicated substantial toughness of the material due to extremely refined microstructure with finely distributed oxide and intermetallic particles and strong interfacial bonding between particles and the matrix. Mechanical properties of the coating were evaluated by nanoindentation techniques employing both Berkovich and cube-corner indenters. Hardness and elastic modulus values were found to be uniform at 1.24 and 76 GPa, respectively. No radial cracking was observed for either the Berkovich or cube-corner indenters. These results indicate that the laser-induced rapidly solidified composite material is tough and fracture resistant.
Experiments and modeling study on growth behavior of Cr-nitrides formed on electroplated hard Cr during ion-nitriding
Authors: Eom J. Y. , Rao V. Shankar , Kwon H. S. , Nam K. S. , Kwon S. C.
Published: March 2008

The structure and composition of Cr-nitrides formed on an electroplated hard Cr layer during an ion-nitriding process were analyzed, and its growth kinetics was examined as a function of the ion-nitriding temperature and time to establish a computer simulation model for the prediction of growth behavior of the Cr-nitride layer. The Cr-nitrides formed during the ion-nitriding at 550–770 °C were composed of outer CrN and inner Cr2N layers. A nitrogen diffusion model in the multilayer, based on fixed-grid finite difference method, was applied to simulate the growth kinetics of Cr-nitride layers. By measuring the thickness of Cr-nitride layers as a function of ion-nitriding temperature and time, the activation energy (Q) and nitrogen diffusion constant (Do) were determined for growth of CrN and Cr2N; the result was applied to simulate the growth kinetics of Cr-nitride layers, and reasonable good agreement was obtained with the experimental results.
High critical current density YBa2Cu3O7–δ coatings on LaMnO3-buffered biaxially textured Cu tapes for coated conductor applications
Authors: Aytug T. , Goyal A. , Rutter N. , Paranthaman M. , Thompson J. R. , Zhai H. Y. , Christen D. K.
Published: March 2008

High critical current density (high-Jc) YBa2Cu3O7–δ (YBCO) films were obtained by pulsed laser ablation on biaxially textured Cu substrates. To achieve epitaxy of LaMnO3 (LMO) on Cu, thin epitaxial Ni overlayers were deposited on Cu tapes. The structure comprises the layer sequence of YBCO/LMO/Ni/Cu. For 200-nm-thick YBCO, self-field Jc values exceeding 1 × 106 A/cm2 at 77 K were achieved. Characterization of these short prototype conductors revealed good structural and morphological properties. Magnetic analysis suggested that hysteretic loss due to the ferromagnetic Ni overlayer is minimal.
Interface reactions and phase equilibrium between Ni/Cu under-bump metallization and eutectic SnPb flip-chip solder bumps
Authors: Huang Chien-Sheng , Duh Jenq-Gong
Published: March 2008

Ni-based under-bump metallization (UBM) for flip-chip application is widely used in today's electronics packaging. In this study, electroplated Ni UBM with different thickness was used to evaluate the interfacial reaction during multiple reflow between Ni/Cu UBM and eutectic Sn–Pb solders in the 63Sn–37Pb/Ni/Cu/Ti/Si3N4/Si multilayer structure. During the first cycle of reflow, Cu atoms diffused through electroplated Ni and formed the intermetallic compound (IMC) (Ni1−x, Cux)3Sn4. After more than three times of reflow, Cu atoms further diffused through the boundaries of (Ni1−x, Cux)3Sn4 IMC and reacted with Ni and Sn to form another IMC of (Cu1-y, Niy)6Sn5. After detailed quantitative analysis by electron probe microanalysis, the values of y were evaluated to remain around 0.4; however, the values of x varied from 0.02 to 0.35. The elemental distribution of IMC in the interface of the joint assembly could be correlated to the Ni–Cu–Sn ternary equilibrium. In addition, the mechanism of (Cu1−y, Niy)6Sn5 formation was also probed.
Grain-growth kinetics in a nanocrystalline 2 yttria-stabilized tetragonal zirconia polycrystals ceramic with a silica-based glassy phase
Authors: Markhsev O. , Chaim R.
Published: March 2008

Grain-growth kinetics of a nanocrystalline 2 yttria-stabilized tetragonal zirconia polycrystals ceramic containing a silica-based glassy phase was determined at 1200 to 1600 °C. At short durations below 1300 °C, the slow grain growth was associated with zirconia dissolution for composition equilibration. The significant increase in the grain size started only after 10 h at 1400 °C or at shorter durations at higher temperatures. Clusters of the cubic grains formed at the two-phase field confirm the inhibited tetragonal grain growth to be independent of the cubic grains. The microstructure evolution during the tetragonal grain growth was interpreted in terms of grain coalescence. Grain growth was initiated by contact flattening and followed by grain-boundary diffusion through the grain-boundary glassy phase. Some aspects of cation diffusion within the viscous glass were also discussed.
Segregation of aluminum in Si and SiO2 films deposited by plasma-enhanced chemical vapor deposition in fabrication of low-temperature poly Si thin-film transitor
Authors: Oh U. C. , Kim Kwang Nam , Kim Sung Chul , Kim Hye Dong , Chung Ho Kyoon
Published: March 2008

Metal contamination in Si and SiO2 films deposited by plasma-enhanced chemical vapor deposition (PECVD) in the fabrication of low-temperature poly Si thin-film transitor was investigated. Aluminum was the major metal impurity to have the highest concentration. Segregation of Al was always observed in the films deposited at temperatures above 400 °C. The impurity level in the segregated region was 1018 ∼ 1020 atoms/cm3 for Al, while the concentration in matrix was about 1016 atoms/cm3. From the transmission electron microscopy image, the Al segregated region contains small-size Al precipitates. Although the Al impurity level of 1016 atoms/cm3 did not cause any serious degradation of device performance, the level of 1018 atom/cm3 and higher can induce a fatal degradation of the threshold voltage. This study revealed that the Al originated from the PECVD chamber, carbon precipitates provided the preferred sites for Al precipitates, and the solubility and diffusivity of Al in Si accelerated the segregation of Al.
Silica-encapsulated magnetic nanoparticles formed by a combined arc evaporation/chemical vapor deposition technique
Authors: Klug Kevin L. , Dravid Vinayak P. , Johnson D. Lynn
Published: March 2008

A multistep technique has been developed for the generation of metallic/alloy nanoparticles coated with amorphous silica. As a proof of concept, an inert-gas blown-arc geometry was used to create nanoparticles from a bulk nickel source, and silica coating formation was accomplished via tetraethyloxysilane (TEOS) decomposition over the nanoparticles in an adjacent chemical vapor deposition chamber. The composite particles exhibit resistance to hydrochloric acid attack over extended times, thereby confirming the protective nature of the silica coating, and magnetic measurements indicate a superparamagnetic transition temperature of 41 K. TEOS flow rate was found to have a profound effect on particle morphology, and individually coated dispersed particles were observed for the intermediate flow rate studied. These results, combined with the well-established field of silica functionalization, offer the possibility that a variety of industrially significant coated magnetic nanostructures may be synthesized with this versatile approach.
Crystal structures of (Ba1−xLax)[Mg(1+x)/3Nb(2−x)/3]O3 with 0.9 ≤ x ≤ 1.0
Authors: Park Hyun Min , Lee Hwack Joo , Cho Yang Koo , Nahm Sahn
Published: March 2008

Based on a structure model of mixture of phases, the crystal structure analysis of (Ba1−xLax)[Mg(1+x)/3Nb(2−x)/3]O3 (BLMN) (x = 0.9 and 1.0) by Rietveld refinements was carried out. The pure La(Mg2/3Nb1/3)O3 (LMN) and BLMN (x=0.9) actually consist of a two-phase mixture rather a single phase. One is Fm-3m, which is cubic and 1:1 ordered and the other is P21/n, which is monoclinic and has both 1:1 ordering and the antiphase and inphase tilting of oxygen octahedra with a−a−c+. The weight fraction of the Fm-3m phase is 17.5% at x=0.9 and further decreases to 7.5% in pure LMN. Meanwhile, that of the P21/n phase is 82.5% at x =0.9 and further increases to 92.5% in pure LMN. The I4/m phase, which is present as a minor phase from x=0.3 to 0.7, disappeared when x≥0.9. The abrupt change of the x-ray diffraction pattern at x=0.9 is caused by a change of major phase from Fm-3m to P21/n phase in the matrix.
Wet oxidation kinetics of AlAs at elevated temperatures
Authors: Ko Sun-Chien , Lee Sanboh , Wang Hai-Lin , Chou Y. T.
Published: March 2008

Wet oxidation in the AlAs layer sandwiched between two GaAs plates was investigated for the temperature range of 400 to 480 °C. The oxidation rate increased with increasing thickness of the AlAs layer. Theoretical analysis based on the boundary layer diffusion was performed to account for the thickness effect. The theory is in excellent agreement with the experimental measurement.
Photoluminescence of mesoporous silica films impregnated with an erbium complex
Authors: Park Oun-Ho , Seo Se-Young , Jung Ji-In , Bae Jae Young , Bae Byeong-Soo
Published: March 2008

Transparent mesoporous silica films were prepared by sol-gel spin coating on silicon wafers at room temperature. An erbium complex, erbium tris 8-hydroxyquinoline (ErQ), was homogeneously impregnated into the pores of the mesoporous silica films, and its concentration was easily controlled by using a solution immersing technique. The ErQ-impregnated mesoporous silica films show a room-temperature photoluminescence at 1.5 µm.
Magnetic and microstructure study of bulk (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy with submicron Gd2BaCuO5 second-phase particles
Authors: Muralidhar M. , Jirsa M. , Sakai N. , Wu Y. , Murakami M.
Published: March 2008

We fabricated melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy superconductors with fine Gd2BaCuO5 (Gd-211) particles and studied microstructure and magnetic properties as a function of the Gd-211 content and the initial particle size. Microstructure observation by scanning electron microscopy and transmission electron microscopy confirmed the presence of submicron secondary-phase particles and nanometer-sized RE1+xBa2-xCu3Oy (x ≫ 0) clusters. At 77 K, the critical current densities of 107 and 83 kA/cm2 were achieved at 0 T (self-field) and 2.2 T, respectively (superconducting quantum interference device data).
Structural investigation of the C60/C70 whiskers fabricated by forming liquid–liquid interfaces of toluene with dissolved C60/C70 and isopropyl alcohol
Authors: Miyazawa Kun'ichi , Hamamoto Koichi , Nagata Satoru , Suga Tadatomo
Published: March 2008

The structure of C60 and C70 whiskers with diameters between submicrometers and micrometers were analyzed by scanning electron microscopy and transmission electron microscopy. The fullerene whiskers were produced by forming liquid–liquid interfaces between toluene solutions of fullerenes and isopropyl alcohol. The growth fronts of C70 whiskers were observed to be crystalline. The C70 whiskers were assumed to be in a state of order–disorder transition. The whiskers of C60 are very flexible, and C60 whiskers bent strongly were torn into finer C60 whiskers. The C70 whiskers showed a higher crystallinity, though a high density of dislocations was observed in the C60 whiskers.
Thickness dependence of microstructure and critical current density of Yba2Cu3O7−δ on rolling-assisted biaxially textured substrates
Authors: Leonard K. J. , Goyal A. , Kroeger D. M. , Jones J. W. , Kang S. , Rutter N. , Paranthaman M. , Lee D. F. , Kang B. W.
Published: March 2008

The change in microstructure associated with the decrease in critical current density (Jc) of Yba2Cu3O7−δ (YBCO) films with increasing thickness was examined. Samples of pulse laser deposited YBCO films varying in thickness from 0.19 to 3.0 μm on rolling-assisted biaxially textured substrates with an architecture of CeO2/YSZ/CeO2/Ni were prepared by tripod polishing for cross-sectional electron microscopy. More randomly oriented grains in the upper portion of the YBCO film surface were observed with increasing film thickness, resulting in less cube texture. In addition, increases in mismatch across the boundaries of the c-axis grains with increasing time during deposition, along with the development of BaCeO3 and Y2BaCuO5 phases at the YBCO/CeO2 interface, contributed to the degradation of film properties. Surface outgrowths of the YBCO film were examined as well as the defect structures and second-phase formations within the films.
Accurate measurement of tip–sample contact size during nanoindentation of viscoelastic materials
Authors: Tang B. , Ngan A. H. W.
Published: March 2008

Polypropylene (PP) and amorphous selenium (a-Se) were used as prototype materials at room temperature to explore the problems that may exist in the accurate measurement of the reduced modulus of viscoelastic materials using depth-sensing nanoindentation. As has been reported previously by others, we observed that a “nose” in the load-displacement curve may occur during unloading, indicating significant creep effects at the onset of unloading. To accurately measure the elastic modulus in viscoelastic materials like PP or a-Se, both the contact stiffness and the contact area at the onset of unloading must be determined accurately. The issue of removing the influence of creep on the measurement of the contact stiffness using the Oliver-Pharr method has been addressed in a previous paper by Feng and Ngan. In this work, the effect of creep on contact-depth measurement is considered. Removal of creep effects in both contact stiffness and contact-area measurement leads to satisfactory prediction of the reduced moduli in PP and a-Se.
Wet erosion damage of Cr3C2/Al2O3composite
Authors: Jeng Ching-An , Huang Jow-Lay
Published: March 2008

This study focused on investigating the role of interfacial microcracking of injection-molded Cr3C2/Al2O3composite on the erosion mechanism under an impingement erosion test rig. The surface residual strain (stresses) as well as damage were compared in both airborne and wet erosion. The delays in crack propagation at interfacial or triple points and the crack direction changes were frequently observed in the composite. Spontaneous microcracking induced from sintering process, due to thermal expansion mismatch between alumina and chromium carbide, played a key role in erosion mechanism.
Effects of additives on the microstructure and dielectric properties of Ba2Ti9O20microwave ceramic
Authors: Wang Sea-Fue , Hsu Yung-Fu , Ueng Tzuu-Hsing , Chiang Chung-Chuang , Chu Jinn P. , Huang Chi-Yuen
Published: March 2008

Preparation of dense and phase-pure Ba2Ti9O20is generally difficult to achieve using a solid-state reaction, due to the presence of several thermodynamically stable compounds in the vicinity of the desired composition. This work investigated the effects of various additives (TiO2, MnO, and ZrO2) on the densification, microstructural evolution, phase stability, and dielectric properties of Ba2Ti9O20. Ceramics with theoretical density of ≥95% were achieved in all cases after sintering at 1300 °C. A pure Ba2Ti9O20phase was obtained by treating the material with TiO2additions (≤5.6 wt.%) and sintering at temperatures ranging between 1200 and 1350 °C. Ba2Ti9O20is a nonstoichiometric compound that can accommodate an excess amount of TiO2. As the temperature was increased, pure Ba2Ti9O20partially decomposed and formed a mixture of BaTi4O9and Ba2Ti9O20. The ceramic with excess TiO2sintered at 1390 °C possessed a higher permittivity and a lower quality factor due to the larger grain size and lower density. For ceramic with the addition of ZrO2(≤6 wt.%), pure Ba2Ti9O20phase was obtained after sintering between 1200 and 1390 °C, and the quality factor was improved. The decomposition temperature of the Ba2Ti9O20phase was greater than 1390 °C. For sintering temperatures ≥1350 °C, the extent of Ba2Ti9O20phase decreased with MnO additions. As the MnO content reached 0.5 wt.%, only BaTi4O9and TiO2phases existed, suggesting a decrease in the decomposition temperature of Ba2Ti9O20with the addition of MnO. The microwave properties of the ceramics degraded significantly at the sintering temperature of 1390 °C.
Sonochemical synthesis of large-scale single-crystal PbS nanorods
Authors: Zhou S. M. , Feng Y. S. , Zhang L. D.
Published: March 2008

Large-scale single-crystal cubic PbS nanorods were successfully achieved by using ultrasound irradiation in certain ethylenediamine tetraacetic acid (EDTA) solutions, particularly in the solution of Pb:EDTA = 1:1. The obtained PbS nanorods were characterized using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersed x-ray spectrometry, selected area electronic diffraction, and high-resolution transmission electron microscopy. The results reveal that the PbS nanorods with straight and uniform structure have a diameter of about 70–80 nm and length of about 1000 nm, where the growth mechanism is tentatively discussed. The successful synthesis of these cubic structure semiconductor PbS nanorods may open up new possibilities for using these materials as building blocks to create functional two-dimensional or three-dimensional nanostructured materials.
Effect of indentation unloading conditions on phase transformation induced events in silicon
Authors: Juliano Tom , Gogotsi Yury , Domnich Vladislav
Published: March 2008

More than 2500 indentations were made on a silicon wafer surface using a range of different unloading rates and maximum applied loads. The unloading curves were examined for characteristic events (pop-out, kink pop-out, elbow followed by pop-out, and elbow) that were assigned to different phase transitions within the affected material based on Raman microspectroscopy analysis of residual imprints. The effect of unloading rate and maximum applied load on the average contact pressure at the beginning of the event was found. A permissible range for each event to occur was established.
Interface microstructure between Fe-42Ni alloy and pure Sn
Authors: Hwang Chi-Won , Suganuma K. , Lee Jung-Goo , Mori H.
Published: March 2008

The interfacial reaction and microstructure of Sn with an Fe-42Ni substrate soldered at 250 °C were studied primarily using transmission electron microscopy. Apparent double reaction layers formed between Fe-42Ni and Sn of the same phase of FeSn2 containing Ni from 2 to 6 at.% as a substitution impurity for Fe. The first layer, which faced an Fe-42Ni substrate, was thin and grew with a flat interface. The second layer, which adhered to Sn solder, showed needle/square pillar-shaped small crystalline structures. Between these two layers, voids were frequently observed. The morphological difference between these two layers and voids could be attributed to the slow-fast diffusion mechanism during soldering. The fast diffusion occurring along the surfaces or the grain boundary of FeSn2 in the second layer led to the growth of FeSn2 products into Sn melt. Simultaneously, the slow diffusion penetrating the Fe-42Ni and FeSn2 grain contributed to the formation of the first layer and voids. Ni from Fe-42Ni can dissolve into Sn melt at the reaction temperature. The dissolved Ni formed platelets of Ni3Sn4 intermetallic compound inside a β-Sn matrix on solidification or on cooling. In contrast, Fe formed FeSn2 crystallines directly along the interface, because its activity was higher than that of Ni in a Sn liquid at reaction temperature. The joint of Fe-42Ni/Sn/Fe-42Ni, reacted for 2 min, had a joint strength of about 65 MPa, and maintained this high strength regardless of the reaction time.
Addition of Nb2O5 on the electrical properties of buried resistors in low-temperature cofired ceramics
Authors: Cheng Ching-Tai , Lin Jiang-Tsair , Lin Hong-Ching
Published: March 2008

Nb2O5 was added to buried resistors for low-temperature cofired ceramics, and the electrical properties of the resultant resistors were examined. Remarkable increases in electrical resistivity and attractive decreases in the temperature coefficient of resistance (TCR) were observed by the addition of Nb2O5, which was attributed to the high solubility of Nb2O5 into the PbO-SiO2-Al2O3 matrix glass. With higher dissolved contents of Nb2O5 into the glass, the resistivity of buried resistors increased by approximately six-fold magnitude, while TCR decreased substantially toward zero. It was indicated that the conductance for these buried resistors was limited by tunneling of charge carriers through the thin glass layer penetrating into the ruthenium-oxide agglomerates. A larger separation observed between RuO2 particles due to high solubility of Nb2O5 in the glass increased the charging energy (E) and lump term (Rbo), which in turn gave rise to a higher resistivity and a lower TCR value.
Role of fluorite phase formation in the texture selection of sol-gel-prepared Pb(Zr1−x, Tix)O3 films on Pt electrode layers
Authors: Norga G. J. , Vasiliu F. , Fè L. , Wouters D. J. , Van der Biest O.
Published: March 2008

Transmission electron microscopy-selected area electron diffraction studies were performed on as-pyrolyzed sol-gel-derived Pb(Zr1-x, Tix)O3 films deposited on Pt electrode layers to elucidate the structural cause behind the large effects of pyrolysis conditions on orientation selection [L. Fè, G.J. Norga, H.E. Maes, and G. Maes, J. Mater. Res. 16, 2499 (2001)]. The crystallinity of the intermediate pyrochlore phase, which forms during pyrolysis, was found to strongly depend on pyrolysis conditions. Specifically, pyrolysis for 10 s at 350 °C was seen to result in conversion of the film to a well-crystallized, oxygen-deficient pyrochlore phase with the fluorite crystal structure (disordered pyrochlore). We speculate that formation of the metastable fluorite phase is favored by the reduced oxygen partial pressure, caused by burnoff of residual acetates. Longer pyrolysis times and/or higher pyrolysis temperatures result in a quasi-amorphous intermediate phase. The presence of the well-crystallized fluorite phase in the pyrolyzed film is seen to result in (111)-oriented films after crystallization, while pyrolyzed films consisting of a quasi-amorphous intermediate phase turn out (100) or mixed (100)/(111) oriented after crystallization. An explanation for the observed orientation effects, on the basis of the different surface energetics of fluorite versus perovskite structure oxides, is proposed.
Low-temperature preparation of dense 10 mol%-Y2O3-doped CeO2 ceramics using powders synthesized via carbonate coprecipitation
Authors: Wang Yarong , Mori Toshiyuki , Li Ji-Guang , Ikegami Takayasu , Yajima Yoshiyuki
Published: March 2008

A carbonate coprecipitation method was used for the facile synthesis of highly reactive 10 mol%-Y2O3-doped CeO2 (20YDC) nanopowders, employing nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. The AHC/RE3+ (RE = Ce + Y) molar ratio (R) and the reaction temperature (T) significantly affect the final yield and precursor properties, including chemical composition and particle morphology. Suitable processing conditions are T = 60 °C and R = 2.5 to 10, under which precipitation is complete, and the resultant precursors show ultrafine particle size, spherical particle shape, and good dispersion. The thus-processed precursors are basic carbonates with an approximate formula of Ce0.8Y0.2(OH)CO3 · 2H2O, which directly yield oxide solid solutions upon thermal decomposition at a very low temperature of approximately 400 °C. The 20YDC solid-solution powders calcined at 700 °C show excellent reactivity and were densified to >99% of theoretical via pressureless sintering at a very low temperature of 950 °C for 6 h.
Synthesis and structural characterization of rutile SnO2 nanocrystals
Authors: Chen Zhiwen , Lai J. K. L. , Shek C. H. , Chen Haydn
Published: March 2008

Nanocrystalline tin dioxide (SnO2) thin films were prepared on glass substrate by pulse laser deposition for the first time. The thin films were characterized for their composition, morphology, and crystalline structure by x-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. It was found that the thin films consisted only of the tetragonal phase SnO2 with no structural change, and they were well crystallized during deposition. In most cases, SnO2 particles were overlapped, predominantly grown on preferred (101) plane, and connected with two or three neighbors through necks. The average grain size of the as-prepared thin films was about 12 nm. These facts are of great importance for sensor characteristics, since smaller grains and preferred orientation properties provide higher gas sensitivity to the whole thin films. Our findings indicate that the n-type wide-band-gas semiconductor nanocrystalline thin films can be manipulated by using pulse laser deposition techniques, offering new opportunities to control material fabrication.
Subsolidus phase equilibria in the RuO2–Bi2O3–CeO2 system
Authors: Hrovat Marko , Benčan Andreja , Holc Janez , Rojac Tadej , Kosec Marija
Published: March 2008

Subsolidus equilibria in air in the RuO2–Bi2O3–CeO2 systems were studied with the aim of obtaining information on possible interactions between a Bi2Ru2O7-based cathode and a CeO2-based solid electrolyte in solid-oxide fuel cells. Bi2O3 is soluble in CeO2, and forms a cubic fluorite solid solution Bi1-xCexO2-x/2 up to Bi1/3Ce2/3O1.83, while no solid solubility of the CeO2 in Bi2O3 was detected. No ternary compound was found in the system. The tie line is between Bi2Ru2O7 and the CeO2 solid solution.
Thermal endurance evaluation of poly(butylene terephthalate) by conventional and analytical methods
Authors: Giannoni S. , Montanari G. C. , Motori A. , Saccani A.
Published: March 2008

The thermal endurance of poly(butylene terephthalate) was evaluated by both consolidated long-term conventional life tests and a short-term analytical procedure. The latter is based on oxidative stability measurements by isothermal differential calorimetry in a pure oxygen flow. The capability of the analytical technique to provide an activation energy for the thermo-oxidation process was verified. The results obtained by the two methods were compared and discussed. It is shown that the temperature index derived by the analytical procedure can be close to that obtained by the conventional tests, provided that a suitable selection of the test temperatures and failure criteria is made; however, benefits in term of test time shortening are lower than those previously obtained for polyolefin-based materials.