bluuebunny/crossref_metadata_2025 huggingface dataset:
Templated growth of a complex nitride island dispersion through an internal nitridation reaction
Authors: Brady M. P. , Hoelzer D. T. , Payzant E. A. , Tortorelli P. F. , Horton J. A. , Anderson I. M. , Walker L. R. , Wrobel S. K.
Published: March 2008

A new synthesis route, based on internal oxidation reactions in multiphase alloys, is proposed for the controlled production of near-surface, complex ceramic-ceramic or ceramic-metallic composite structures. Using this approach, a microdispersion of a complex nitride perovskite, Cr3PtN, was formed in Cr2N or Cr(Pt) by internal nitridation of a two-phase Cr(Pt) + Cr3Pt precursor alloy. A framework for use of this phenomenon to synthesize island micro- (and potentially meso- or nano-) composite functional surface structures is presented.
Mass density of glassy Pd80Si20 during low-temperature light ion irradiation
Authors: Schumacher G. , Birtcher R. C. , Rehn L. E.
Published: March 2008

Changes in mass density of amorphous Pd80Si20 were monitored in situ during irradiation with He2+ and H+ ions at temperatures below 100 K and during subsequent thermal treatment. The mass density decreased with increasing ion fluence and exponentially approached a saturation value of −1.2%, corresponding to a recombination volume of 190 atomic volumes. The initial swelling rate was 2.3 atomic volumes/displaced atom. The mass density of the irradiated material increased during subsequent thermal treatment, and the irradiation-induced decrease of the mass density recovered completely at room temperature.
Microprobe fluorescence spectroscopy evaluation of stress fields developed along a propagating crack in an Al2O3/CaO 6Al2O3ceramic composite
Authors: Sbaizero O. , Maschio S. , Pezzotti G. , Davies I. J.
Published: March 2008

The fracture behavior upon stable crack propagation in bending was investigated for a ceramic matrix composite comprising 15 vol% of calcium hexaluminate (CaAl12O19 or “CA6”) in an Al2.O3 matrix and compared to the crack bridging stresses as measured by microprobe fluorescence spectroscopy. In addition, piezospectroscopy coefficients of -4.57 and -3.79 cm-1 GPa-1 were determined for the peaks located at 14488 and 14528 cm-1, respectively, for monolithic CA6. It was concluded that the macroscopic R-curve behavior of the composite could be predicted from microscopic bridging stress data and indicated microprobe fluorescence spectroscopy to be a significant experimental tool for the investigation of fracture micromechanisms in ceramic materials.
Preparation, structure, and magnetic properties of cobalt nanoparticles in carbon fibers
Authors: Bashmakov I. , Dorosinez V. , Lukashevich M. , Mazanik A. , Tihonova T. , Zabel T. , Wiedenhorst B. , Micklitz H.
Published: March 2008

Samples of Co clusters embedded in a carbon fiber matrix have been prepared using a heat-treatment method of cellulose fibers with ion-absorbed cobalt cations. Depending on the heat-treatment temperature used, different cluster sizes have been obtained, ranging from superparamagnetic clusters (average size 10 nm) to ferromagnetic nanoparticles (size between 30 and 200 nm). The formation of graphite planes surrounding the nanoparticles has been observed.
Formation and mechanical properties of Cu–Hf–Ti bulk glassy alloys [Article Retracted]
Authors: Inoue Akihisa , Zhang Wei , Zhang Tao , Kurosaka Kei
Published: March 2008

High-strength Cu-based bulk glassy alloys were formed in the Cu–Hf–Ti system by the copper mold casting and melt clamp forging methods. The maximum diameter is 4 mm for the Cu60Hf25Ti15 alloy. The substitution of Hf in the Cu60Hf40 alloy by Ti causes an increase in the glass-forming ability (GFA). As the Ti content increases, the glass transition temperature (Tg) decreases, while the crystallization temperature (Tx) shows a maximum at 5% Ti and then decreases, resulting in a maximum supercooled liquid region ΔTx (= Tx − Tg) of 78 K at 5% Ti. The liquidus temperature (T1) has a minimum of 1172 K around 20% Ti, and hence, a maximum Tg//T1 of 0.62 is obtained at 20% Ti. The high GFA was obtained at the compositions with high Tg/T1. The bulk glassy alloy exhibits tensile fracture strength of 2130 MPa, compressive fracture strength of 2160 MPa, and compressive plastic elongation of 0.8 to 1.6%. The new Cu-based bulk glassy alloys with high Tg/T1 above 0.60, high fracture strength above 2100 MPa, and distinct plastic elongation are encouraging for future development as a new type of bulk glassy alloy that can be used for structural materials.
Microwave sintering of ZnO at ultra high heating rates
Authors: Xu Geng-fu , Lloyd Isabel K. , Carmel Yuval , Olorunyolemi Tayo , Wilson Otto C.
Published: March 2008

In this paper, a unique processing approach for producing a tailored, externally controlled microstructure in zinc oxide using very high heating rates (to 4900 °C/min) in a microwave environment is discussed. Detailed data on the densification, grain growth, and grain size uniformity as a function of heating rate are presented. With increasing heating rate, the grain size decreased while grain size uniformity increased. At extremely high heating rates, high density can be achieved with almost complete suppression of grain growth. Ultrarapid microwave heating of ZnO also enhanced densification rates by up to 4 orders of magnitude compared to slow microwave heating. The results indicate that the densification mechanisms are different for slow and rapid heating rates. Since the mechanical, thermal, dielectric, and optical properties of ceramics depend on microstructure, ultrarapid heating may lead to advanced ceramics with tailored microstructure and enhanced properties.
Initial growth mechanism of Yba2Cu3Oycrystal on MgO substrate by liquid-phase epitaxy
Authors: Nomura Katsumi , Hoshi Saburo , Nakamura Yuichi , Izumi Teruo , Shiohara Yuh
Published: March 2008

Initial growth features of Yba2Cu3Oy (YBCO) crystal on an MgO substrate by a liquid-phase epitaxy (LPE) process were investigated and compared with homoepitaxial growth on a YBCO substrate. The partial dissolution of the seed grains in the initial stage of the LPE growth was influenced by the crystallinity of in-plane alignment of the seed grains, which could be explained by the preferential dissolution and growth mechanism. Concurrently, the slope angle of the growth grain varied with growth time. The opposite tendency of the slope angle change between the hetero- and the homoepitaxial growth was observed and could be explained by considering the difference in the step-advancing rates on each interface. It could be understood that the formation of entrapped liquid inclusions was the combination phenomena of both the small step-advancing rate of YBCO crystal on the MgO surface and the roughening of the MgO surface due to the partial dissolution of MgO to the solution.
Anode-supported planar solid oxide fuel cells by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) and electrostatic spray deposition (ESD): Fabrication of dense thin layers of yttria-stabilized zirconia by PE-MOCVD
Authors: Giuseppe Gianfranco Di , Selman J. Robert
Published: March 2008

This paper reports a study of plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) as a suitable technique for depositing dense, crack-free thin layers of yttria-stabilized zirconia onto porous substrates, as a step in the fabrication of anode-supported planar solid oxide fuel cells (SOFC). Our objective is to present an alternative method by which an SOFC assembly may be fabricated at lower temperature than by conventional methods. PE-MOCVD using zirconium tertbutoxide (ZrTB) -and yttrium hexafluoroacetylacetonate dihydrate (Y6FA) is capable of producing the electrolyte in thin dense layers on smooth surfaces, as demonstrated for Si(110) wafers. If a porous substrate is used, the average surface pore size should not exceed 1–2 μm to obtain a dense film. The crystalline phase of the film was related to the Y6FA concentration in the gas phase using x-ray diffraction. Depth profiling, using x-ray photoelectron spectroscopy, showed that Y is present (fairly uniform) at all depths of the film. Growth rates are dependent on the applied power but independent of substrate temperature. Film density, however, shows a significant dependence on substrate temperature.
Thermal stress in a polymer-coated optical glass fiber with a low-modulus coating at the ends
Authors: Suhir E.
Published: March 2008

A polymer-coated glass fiber with a low-modulus coating at the ends is considered. The objective of the analysis is to find out if there is sufficient incentive to use such a dual coating system for lower interfacial thermally induced stresses. These are due to the different coefficients of thermal expansion (contraction) of the dissimilar materials in the trimaterial structure. The study is restricted to the evaluation of the shearing stresses only and is based on a simplified strength-of-materials model, rather than on a rigorous theory-of-elasticity method. Such a approach seems to be justified, since the most accurate predictions of the magnitude and the distribution of the induced stresses are beyond the scope of this analysis. On the basis of the calculated data, we conclude that there is a definite incentive for employing a bimaterial coating system, in which “conventional” (high modulus) polymeric material is used in the midportion of the fiber, while a low-modulus material (typically, with a higher coefficient of expansion) is applied at its ends. Such a system could be recommended, when there is a need to bring down the interfacial stresses, and the possible increase in the manufacturing cost is not viewed as an obstacle.
Evaluation of the impactive-surface-fracture behavior of glass plates using a back-surface strain measurement
Authors: Kim Hyoung-Gu , Choi Nak-Sam , Cho Nahmgyoo
Published: March 2008

This paper proposes an evaluation method for the surface fracture behavior of coated glass or ceramic plates subjected to an impact with a small particle. The increase of the maximum stress and absorbed fracture energy measured from the back surface indicated the extent of the surface fracture that occurred in the simple soda lime glass and composite-lamina attached glass plates tested in a range of particle velocities up to 119 m/s. Impact surface-fracture indices expressed in terms of the maximum stress and absorbed energy are suggested as an effective evaluation parameter.
Change in local atomic structure during formation of the icosahedral quasicrystalline phase in Zr70Pd30glassy alloy
Authors: Imafuku Muneyuki , Saida Junji , Inoue Akihisa
Published: March 2008

The local atomic structures in glassy, supercooled liquid and quasicrystalline phases for a Zr70Pd30binary alloy have been examined by the x-ray diffraction method. It was found that the local atomic structure in the glassy phase can be identified as the distorted icosahedral-like structure around Zr and remains almost unchanged by the phase transformation into the supercooled liquid. In the formation process of the icosahedral phase, approximately one Zr atom substitutes with one Pd atom in this local structure. This kind of atomic rearrangement may improve the perfectibility of the as-quenched icosahedral-like cluster, leading to the phase evolution of the icosahedral phase.
Silicalite/poly(dimethylsiloxane) nanocomposite pervaporation membranes for acetic acid/water separation
Authors: Lu Shih-Yuan , Huang Hsiang-Yuan , Wu Kwen-Hua
Published: March 2008

Composite separation membranes of poly(dimethylsiloxane) (PDMS) containing well-dispersed silicalite particles of 50 nm were successfully prepared and applied to the preferential pervaporation of acetic acid over water. The nanocomposite membranes showed improvement on both separation factor and permeation flux for the pervaporation process, as compared to plain PDMS membranes and composite membranes containing silicalite particles of 5 μm. The improvement can be attributed to higher readily accessible specific surface area and higher sorption selectivity toward acetic acid of the nano-size silicalite particles. Improvement on membrane thermal stability was also acquired through incorporation of nano-size silicalite particles.
Formation and characteristics of highly c-axis-oriented Bi3.25La0.75Ti3O12 thin films on SiO2/Si(100) and Pt/Ti/SiO2/Si(100) substrates
Authors: Chon Uong , Jang Hyun M. , Lee Sun-Hwa , Yi Gyu-Chul
Published: March 2008

Highly c-axis-oriented Bi3.25La0.75Ti3O12 (BLT) films with a homogeneous in-plane orientation were successfully grown on SiO2/Si(100) and Pt/Ti/SiO2/Si(100) substrates by a sol-coating route. The substitution of lanthanum ions for bismuth ions in the layered perovskite suppressed the formation of pyrochlore phase and enhanced the c-axis-oriented growth. The c-axis-oriented BLT film fabricated on a Pt/Ti/SiO2/Si(100) substrate showed fatigue-free characteristics with a large remanent polarization of 26–28 μC/cm2 and the coercive field of 50–75 kV/cm. These features significantly enhance the potential value of the BLT film for the applications to high-density ferroelectric random-access memories devices. In addition, the c-axis-oriented BLT film, with a homogeneous in-plane orientation on an amorphous surface, can be used as a suitable template material for applications to various electro-magneto-optic devices.
Parameter effect on the crystallization of Nd:yttrium aluminum garnet laser-ablated TiO2 thin film
Authors: Pal Mrinal , Narazaki Aiko , Sasaki Takeshi , Koshizaki Naoto
Published: March 2008

Process parameter dependency on the phase transition from anatase to rutile phase of laser-ablated TiO2 films was investigated. Lower ambient argon pressure, longer deposition time, higher laser fluence, and smaller target–substrate separation give rutile phase from anatase phase at comparatively lower temperature. The relationship between thickness and onset temperature of anatase–rutile transformation can be comprehensively explained in terms of film thickness. Thinner films have higher phase transition temperature. The presence of helium gas during deposition favors the anatase–rutile transition at a temperature lower than that expected from the above relationship.
Derivation of plastic stress–strain relationship from ball indentations: Examination of strain definition and pileup effect
Authors: Ahn Jeong-Hoon , Kwon Dongil
Published: March 2008

The ball indentation technique has the potential to be an excellent substitute for a standard tensile test, especially in the case of small specimens or property-gradient materials such as welds. In our study, the true stress–true strain relationships of steels with different work-hardening exponents (0.1–0.3) were derived from ball indentations. Four kinds of strain definitions in indentation were attempted: 0.2sinγ, 0.4hc/a, ln[2/(1 + cosγ)], and 0.1tanγ. Here, γ is the contact angle between the indenter and the specimen, hc is the contact depth, and a is the contact radius. Through comparison with the standard data measured by uniaxial tensile testing, the best strain definition was determined to be 0.1tanγ. This new definition of strain, in which tanγ means the shear strain at contact edge, reflected effectively the work-hardening characteristics. In addition, the effects of pileup or sink-in were considered in determining the real contact between the indenter and the specimen from the indentation load–depth curve. The work-hardening exponent was found to be a main factor affecting the pileup/sink-in phenomena of various steels. These phenomena influenced markedly the absolute values of strain and stress in indentation by making the simple traditional relationship Pm/σR ≈ ≈ 3 valid for the fully plastic regime.
Thermal stability of carbon nitride thin films
Authors: Hellgren Niklas , Lin Nian , Broitman Esteban , Serin Virginie , Grillo Stefano E. , Twesten Ray , Petrov Ivan , Colliex Christian , Hultman Lars , Sundgren Jan-Eric
Published: March 2008

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N2 discharge, was studied for postdeposition annealing temperatures TA up to 1000 °C. Films were grown at temperatures of 100 °C (amorphous structure) and 350 and 550 °C (fullerenelike structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure, and mechanical properties as a function of TA and annealing time. All properties investigated were found to be stable for annealing up to 300 °C for long times (>48 h). For higher TA, nitrogen is lost from the films and graphitization takes place. At TA = 500 °C the graphitization process takes up to 48 h while at TA = 900 °C it takes less than 2 min. A comparison on the evolution of x-ray photoelectron spectroscopy, electron energy loss spectroscopy and Raman spectra during annealing shows that for TA > 800 °C, preferentially pyridinelike N and –C≡N is lost from the films, mainly in the form of molecular N2 and C2N2, while N substituted in graphite is preserved the longest in the structure. Films deposited at the higher temperature exhibit better thermal stability, but annealing at temperatures a few hundred degrees Celsius above the deposition temperature for long times is always detrimental for the mechanical properties of the films.
Solid solubility and transport properties of Ce1−xNdxO2−δ nanocrystalline solid solutions by a sol-gel route
Authors: Li Liping , Lin Xiaomin , Li Guangshe , Inomata Hiroshi
Published: March 2008

Ce1−xNdxO2−δ (x = 0.05 to 0.55) nanocrystalline solid solutions were prepared by a sol-gel route. X-ray diffraction analysis showed that Ce1−xNdxO2−δ crystallized in a cubic fluorite structure. The lattice parameter for the solid solutions increased linearly with the dopant content. The solid solubility of Nd3+ in ceria lattice was determined to be about x = 0.40 in terms of the nearly constant lattice parameters at a dopant level larger than x = 0.40. First-order Raman spectra for Ce1−xNdxO2−δ at a lower dopant content exhibited one band associated with the F2g mode. At higher dopant contents, F2g mode became broadened and asymmetric, and a new broad band appeared at the higher frequency side of the F2g mode. This new band was assigned to the oxygen vacancies. The electron paramagnetic resonance spectrum for x = 0.05 showed the presence of O2− adsorbed on sample surface at g = 2.02 and 2.00 and of Ce3+ with a lower symmetry at g = 1.97 and 1.94. Further increasing dopant content led to the disappearance of the signals for O2−. Impedance spectra showed the bulk and grain boundary conduction in the solid solutions. The bulk conduction exhibited a conductivity maximum and an activation energy minimum with increasing dopant content. Ce0.80Nd0.20O2−δ was determined to give promising conduction properties such as a relatively high conductivity of σ700 °C = 2.44 × 10−2 S cm−1 and moderate activation energy of Ea = 0.802 eV. The variations of conductivity and activation energy were explained in terms of relative content of oxygen vacancies Vö and defect associations {CeCe ′Vö}/{NdCe ′Vö}.
Direct writing of polymer thick film resistors using a novel laser transfer technique
Authors: Modi R. , Wu H. D. , Auyeung R. C. Y. , Gilmore C. M. , Chrisey D. B.
Published: March 2008

Polymer thick film (PTF) resistors were fabricated using a new laser-based transfer technique called matrix-assisted pulsed laser evaporation direct write (MAPLE-DW). MAPLE-DW is a versatile direct writing technique capable of writing a wide variety of materials on virtually any substrate in air and at room temperature. Epoxy-based PTF resistors spanning four decades of sheet resistances (10 Ω/sq. to 100 kΩ/sq.) were deposited on alumina substrates under ambient conditions. Electrical characteristics of these MAPLE-DW deposited resistors were studied at a wide frequency range (1 MHz to 1.8 GHz), and the results were explained through an equivalent circuit model and impedance spectroscopy. Temperature coefficient of resistance measurements for the PTF resistors were performed between 25 and 125 °C. The results based on the percolation theory were used to explain the temperature dependence of the resistance behavior of the PTF resistors.
Processing and characterization of hydroxyapatite coatings on titanium produced by magnetron sputtering
Authors: Nieh T. G. , Jankowski A. F. , Koike J.
Published: March 2008

Hydroxyapatite (HA) coatings with different thicknesses were produced on Ti and Si substrates using the radio frequency magnetron sputtering method. The mechanical properties, for example, modulus and hardness, of the coatings were measured using nanoindentation. The measured values of modulus and hardness were close to the upper limit of that reported for bulk HA, indicating a fully dense structure. Interfacial strengths between the HA coatings and substrates were also evaluated using a nanoscratch technique. The HA–Ti interface appeared to be stronger than the HA–Si interface. The microstructures of the HA coating and the HA–Ti interface were examined using high-resolution electron microscopy. Chemical compositions of the HA coating and the HA–Ti interface were also analyzed using x-ray energy dispersive spectrometer and electron energy loss spectroscopy. The results indicated that the strong HA–Ti bonding is associated with an outward diffusion of Ti into HA layer and concomitant formation of TiO2 at or near the interface.
Growth and characterization of aligned carbon nanotubes from patterned nickel nanodots and uniform thin films
Authors: Wen J. G. , Huang Z. P. , Wang D. Z. , Chen J. H. , Yang S. X. , Ren Z. F. , Wang J. H. , Calvet L. E. , Chen J. , Klemic J. F. , Reed M. A.
Published: March 2008

Microstructures of well-aligned multiwall carbon nanotubes grown on patterned nickel nanodots and uniform thin films by plasma-enhanced chemical vapor deposition have been studied by electron microscopy. It was found that growth of carbon nanotubes on patterned nickel nanodots and uniform thin films is different. During growth of carbon nanotubes, a nickel particle sits at the tip of each nanotube, and its [220] is preferentially oriented along the plasma direction, which can be explained by a channeling effect of ions coming into nickel particles in plasma. The alignment of nanotubes is induced by the electrical field direction relative to substrate surface.
Dependence of fracture stress on applied stress rate in a Yb2O3–SiO2-doped hot-pressed silicon nitride ceramic
Authors: Guo Shuqi , Hirosaki Naoto , Yamamoto Yoshinobu , Nishimura Toshiyuki , Mitomo Mamoru
Published: March 2008

High-temperature fracture behavior of a Yb2O3–SiO2–doped hot-pressed silicon nitride (Si3N4) ceramic was investigated in four-point flexure between 1000 and 1500 °C at five crosshead speeds, using the specimens precracked with three indentation loads. Above 1000 °C, a temperature and stressing rate dependence of fracture stress was seen. At 1200 °C the fracture stress of the precracked specimens increased with decreasing stressing rates due to a toughening effect, the absence of slow crack growth (SCG). However, at 1400 and 1500 °C the fracture stress decreased with decreasing stressing rate. In particular, this dependence was stronger at 1500 °C than at 1400 °C. The SCG was observed only in the specimens precracked with indentation loads of 98 and 196 N. This crack extended with increasing test temperature and/or decreasing stressing rate. The dependence of fracture stress on stressing rate was attributed to a SCG behavior at higher temperatures.
Consolidation and crystallization of Si3N4/SiC nanocomposites from a poly(urea–silazane) ceramic precursor
Authors: Wan Julin , Gasch Matt J. , Mukherjee Amiya K.
Published: March 2008

Controlled pyrolysis of polymer ceramic precursors provides a new way of obtaining silicon nitride ceramics with high creep resistance. In this study, crack-free bulk amorphous Si–N–C materials were produced by warm-pressing followed by pyrolysis or alternatively by prepyrolysis and binding followed by pyrolysis. Amorphous compacts were then heat-treated at different temperatures to promote crystallization. High-resolution electron microscopy revealed that, at about 1650 °C, silicon nitride/silicon carbide nanocomposites with a high degree crystallinity can be achieved with grain sizes of about 30 nm. Aside from heterogeneous crystallization, which is closely related to gaseous phase reactions that happen along outer or inner surfaces, homogenous crystallization is responsible for crystallization of the bulk material. Although a certain amount of amorphous Si–N–C usually remains in intergranular regions, clean boundaries free of amorphous interlayers can be observed between grains when they come into contact.
Analysis of interdiffusion of Dy, Nd, and Pr in Mg
Authors: Xu Y. , Chumbley L. S. , Weigelt G. A. , Laabs F. C.
Published: March 2008

The diffusion characteristics of Mg–rare-earth diffusion couples were studied. Cylinders of pure Mg and rare earth (Dy, Nd, and Pr) were abutted and annealed at 500 °C for 100 h or 300 h. Point-by-point composition profiles were collected starting in pure Mg, across the diffusion zone, and ending in the pure rare earth, using energy dispersive x-ray spectroscopy with a scanning electron microscope. The intermetallic phases that resulted due to diffusion were identified and compared to existing phase diagrams, for which the data is limited. For each diffusion couple, a plot of concentration versus distance perpendicular to the original plane of contact was obtained and analyzed using the Boltzman–Matano method. The interdiffusion coefficients for each set of phases were then calculated. The results show that diffusion through the intermetallic phases is much slower than is expected in a solid solution.
Microstructure of laser-ablated superconducting La2CuO4Fx thin films on SrTiO3
Authors: Kong G. , Jones M. O. , Abell J. S. , Edwards P. P. , Lees S. T. , Gibbons K. E. , Gameson I. , Aindow M.
Published: March 2008

Thin films of lanthanum cuprate were grown on SrTiO3 substrates by pulsed laser deposition and made superconducting (Tc ∼ 38 K) through the process of post-deposition fluorination using elemental fluorine. A microstructural analysis showed that the [110] zone of the film grows parallel to the [100] zone of the SrTiO3 substrate, reducing the lattice mismatch from 37.5% to 2.4%. At the film–substrate interface there is an intermediate layer 3–4 nm thick and twin-related grains emanate from this region. Stacking faults are present in the bulk of the film, with misoriented subgrains present at the deposit surface.
Photovoltaic effect of Sn2P2S6 ferroelectric crystal and ceramics
Authors: Cho Y. W. , Choi S. K. , Vysochanskii Yu. M.
Published: March 2008

To investigate the photovoltaic effect in Sn2P2S6 ferroelectrics, Sn2P2S6 crystal and ceramic sample that had a high relative density of 95% and a grain size of below 1 μm were fabricated. The steady-state photovoltaic currents under infrared light illumination on both Sn2P2S6 crystal and ceramic sample were observed for the first time. The photovoltaic currents ipv on Sn2P2S6 ceramic sample and crystal were 5 and 25 nA/cm, respectively. The difference in the magnitude of the photovoltaic current resulted from the difference in the remanent polarization Pr between the crystal and the ceramic sample. The values of the photovoltaic field Epv determined from I–V curve for Sn2P2S6 ceramic sample and crystal were 0.2 and 6 V/cm, respectively; these values were several orders lower than that observed on the perovskite-type ferroelectric ceramics. The photovoltaic fields observed in this study were discussed with the conductivity of the crystal and the ceramic sample, in consideration of the figure of merit for the photostriction.
Deformation under nanoindents in Si, Ge, and GaAs examined through transmission electron microscopy
Authors: Lloyd S. J. , Molina-Aldareguia J. M. , Clegg W. J.
Published: March 2008

Cross sections through nanoindents on Si, Ge, and GaAs {001} were examined through transmission electron microscopy. A focused ion beam workstation was used to machine electron transparent windows through the indents. In both Si and Ge there was a transformed zone immediately under the indent composed of amorphous material and a mixture of face-centered-cubic and body-centered cubic crystals. Cracking and dislocation generation were also observed around the transformed zone. In GaAs the dominant deformation mechanism was twinning on the {11} planes. The hardness of these materials is discussed in light of these observations and their macroscopic material properties such as phase transformation pressure.
Highly oriented diamond growth on positively biased Si substrates
Authors: Chang Te-Fu , Chang Li
Published: March 2008

Deposition of highly textured diamond films on Si(001) has been achieved by using positively bias-enhanced nucleation in microwave plasma chemical vapor deposition. During the biasing period, an additional glow discharge due to the dc plasma effect appeared between the electrode and the substrate. The discharge is necessary for enhanced nucleation of diamond. X-ray diffraction, scanning electron microscopy, and cross-sectional transmission electron microscopy (XTEM) were used to characterize the microstructure of the diamond films on Si. The results show the morphology of diamond grains in square shape with strong diamond (001) texture. XTEM reveals that an amorphous interlayer formed on the smooth Si surface before diamond nucleation.
Microstructural and mechanical characterization of carbon coatings on SiC fibers
Authors: Kendig K. L. , Gibala R. , Miracle D. B.
Published: March 2008

A series of carbon coatings was deposited on a 1040 SiC monofilament using chemical vapor deposition, and failure of the fiber-matrix interfacial region under transverse tension was studied. Deposition substrate temperatures were approximately 920, 1000, and 1080 °C, and all other deposition parameters were held constant. The microstructures of these carbon-coated fibers were examined using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). TEM observations were made using bright-field imaging, dark-field imaging, selected-area diffraction, and high-resolution lattice imaging. Tensile testing of single-fiber composite samples was performed transverse to the fiber axis to determine the stress required to cause debonding of the fiber from the titanium alloy matrix. Adhesion experiments were used to examine differences in bond strength of the SiC–C interfaces of the three coatings. A systematic increase in the grain size of the SiC substrate fiber within 3 μm of the SiC–C interface with increasing deposition temperature was observed. The crystallographic texturing of the basic structural units of carbon within the coatings was also found to increase with increasing deposition temperature. The SiC–C interface strength increased with increasing deposition temperature and correlates with the microstructural changes in both the SiC and carbon at the interface. The overall composite transverse strength was not affected by the change in deposition temperature, although the fracture location was affected. The carbon coating with the lowest SiC–C interface strength failed at this interface, and the coatings with more highly textured carbon failed within the coating, where the proportion of weak van der Waals bonds parallel to the tensile direction was correspondingly higher.
Preparation of superfine Fe-base alloy by liquidus casting
Authors: Pan X. F. , Zhang H. F. , Wang A. M. , Ding B. Z. , Hu Z. Q.
Published: March 2008

The superfine Fe–B–Si–Mo and Fe–B–Zr–Nb alloys were prepared by liquidus casting in which the levitation melting combining with the rapid solidification was used. The melt was poured into a copper mold at various temperatures, and a superfine granular microstructure was obtained at liquidus temperature. The behavior of Cu and Ag addition to Fe–B–Si–Mo and Fe–B–Zr–Nb alloys was studied. Both adding Cu and Ag to Fe–B–Si–Mo and Fe–B–Zr–Nb alloys had influence on refining the alloys. The refinement effect of adding Cu is stronger than that of adding Ag in Fe–B–Zr–Nb alloy.
Preparation of γ–Fe2O3 nanoparticles from a nonaqueous precursor
Authors: Deb P. , Basumallick A.
Published: March 2008

Nanosized particles of γ–Fe2O3 were prepared by heat treatment of the precipitates, obtained from a homogeneous solution of stearic acid and hydrated iron(III) nitrate. The compositional and thermal characteristics of the precipitates were studied with the aid of infrared spectroscopy and differential scanning calorimetry. The x-ray diffraction and small-angle x-ray scattering investigation shows that γ–Fe2O3 nanoparticles with narrow size distribution can be prepared successfully by this route.
Impacts of postannealing ambient atmospheres on Pt/SrBi2.2Ta2O9/Pt capacitors
Authors: Li Ai-Dong , Yu Tao , Ling Hui-Qin , Wu Di , Liu Zhi-Guo , Ming Nai-Ben
Published: March 2008

SrBi2Ta2O9 (SBT) films were prepared on Pt/TiO2/SiO2/Si substrates at 750 °C in oxygen by the metalorganic decomposition method. SBT film capacitors were postannealed in Ar (N2) at 350–750 °C and then reannealed in O2 at 750 °C. Effects of annealing atmosphere on the structure, morphology, and ferroelectric properties have been investigated systematically. The composition analyses indicate Ar- or N2-annealing at 750 °C leads to Bi evaporation and oxygen loss. Above 550 °C 100% Ar or N2 postannealing, the remnant polarization decreases and the coercive field increases significantly. The subsequent O2 recovery can hardly rejuvenate the electrical properties. The result is different from that with the effective O2 recovery in forming gas processing (annealing in an atmosphere containing 5% hydrogen). The possible origin and mechanism is discussed and proposed.
Cure depth in photopolymerization: Experiments and theory
Authors: Lee Jim H. , Prud'homme Robert K. , Aksay Ilhan A.
Published: March 2008

The depth of photocuring for a model resin system was investigated as a function of photoinitiator concentration. Direct measurements of gel thickness were made from thin films of cross-linked multifunctional methacrylate monomer. The monomer,2,2-bis{4-[2-hydroxy-3-(methacryloxy)propoxy]phenyl}propane, was polymerized in a solution of trichloroethylene with an ultraviolet laser light source at 325 nm. The monomer solutions were photocured using varying levels of both photonic energy and photoinitiator concentration. An optimal photoinitiator concentration that maximized the gel cure depth was observed. Additionally, two regimes were shown to exist in which the shrinkage (upon solvent removal) was minimized or maximized. A model was developed to probe the physics of the system. Good agreement with experiment was obtained, and the model may be employed to predict both the existence and location of the optimal photoinitiator concentration and the corresponding cure depth. The study showed that photoinitiator plays a significant role in controlling the quality and performance of the formed gel network, with special regard to thickness of cured layers. This has potential application to fields as diverse as industrially cured coatings and dental fillings, and more generally, 3-dimensional rapid prototyping techniques.
Determination of optical constants of Si/ZnO polycrystalline nanocomposites by spectroscopic ellipsometry
Authors: García-Serrano J. , Koshizaki N. , Sasaki T. , Martínez-Montes G. , Pal U.
Published: March 2008

The optical constants of Si/ZnO composite films grown on quartz glass substrates were determined in the spectral range 1.5–5.0 eV by spectroscopic ellipsometry using a rotating-analyzer ellipsometer. The structure of the samples was modeled by a two-phase (substrate–film) model, and the optical functions of the film were parameterized through different effective medium approximations. The results allowed us to estimate the microstructural film parameters, such as film thickness, the volume fractions of each of the constituents, and optical constants.
Preparation and characterization of nanocrystalline potassium lithium niobate powders and films
Authors: Zhang H. X. , Kam C. H. , Zhou Y. , Han X. Q. , Cheng S. D. , Chan C. Y. , Lam Y. L.
Published: March 2008

Potassium lithium niobate (KLN) powders and thin films were prepared from metalorganic compounds through the sol-gel process. A homogeneous and stable KLN precursor was synthesized by mixing the metal ethoxides. Powder gels were obtained through the hydrolysis of the solution by exposing it to the ambient atmosphere. Thin films were deposited on Si, SiO2/Si, and fused quartz by a spin coating technique. The pyrolysis and crystallization of KLN powders and films were investigated through the methods of differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and Raman scattering spectroscopy. The results revealed that both KLN powders and films could crystallize into a tetragonal tungsten–bronze-type phase with appropriate annealing. Optical studies indicated that the films were highly transparent in the visible–near-infrared wavelength range and could support optical modes.
Preparation of nanocrystalline nickel oxide–yttria-stabilized zirconia composite powder by solution combustion with ignition of glycine fuel
Authors: Kim Sun-Jae , Lee Wonhee , Lee Won-Jun , Park Soon Dong , Song Jae Sung , Lee Eun Gu
Published: March 2008

Nanocrystalline nickel oxide–yttrium-stabilized zirconia (NiO/YSZ) composite powder for the solid oxide fuel cells was prepared by solution combustion through control of pH values and contents of glycine fuel in precursor solution. A strongly acidic precursor solution with appropriate amounts of glycine fuel added increased the specific surface area of the synthesized composite powders. This results from the increased binding of metal ions and glycine under strongly acidic solution (pH = 0.5) conditions. After sintering and reducing treatment of nanocrystalline NiO/YSZ composite, the Ni/YSZ pellet showed an ideal microstructure: fine Ni particles of 3 to 5 μm were distributed uniformly, and fine micropores around Ni metal particles were formed, thus leading to an increase in the triple phase boundary area among gas, Ni and YSZ.
Rapid Growth of Nd2−xCexCuO4 Thick Films as a Buffer for the Growth of Rare-earth Barium Cuprate–coated Conductors
Authors: Qi Xiaoding , Soorie Masood , Lockman Zainovia , MacManus-Driscoll Judith L.
Published: March 2008

Nd2−xCexCuO4 (x = 0 to 0.15) thick films were grown directly on LaAlO3 substrates and surface-oxidized Ni tapes by fast liquid-phase processing methods. The films had a smooth surface and a very good biaxial texture, with the full width at halfmaximum equal to 0.8° and 5° on LaAlO3 substrates and surface-oxidized Ni tapes, respectively. Films of thickness of 5–15 μmm were grown at rates in excess of 2 μm/min. Nd2−xCexCuO4 has a good lattice and thermal-expansion match to rare-earth Ba2Cu3O7−δ (REBCO), minimum reaction with the high-temperature CuO:BaO solutions, and is nonpoisoning to superconductivity. It is an ideal buffer for liquidphase expitaxy processing of REBCO thick films.
Low-temperature Crystallization of SrBi2Ta2O9 Thin Filmswith Bi2O3 Interfacial Layers by Liquid-delivery Metalorganicchemical Vapor Deposition
Authors: Shin Woong-Chul , Choi Kyu-Jeong , Yoon Soon-Gil
Published: March 2008

Ferroelectric SrBi2Ta2O9 (SBT) thin films and Bi2O3 interfacial layers were depositedonto the Pt/Ti/SiO2/Si substrates via liquid-delivery metalorganic chemical vapordeposition. The SBT films with a 5-nm-thick Bi2O3 interfacial layer were well crystallized without c-axis orientation, even at deposition temperature of 540 °C and showed a stronger (115) orientation than those without a Bi2O3 layer with increasing annealing temperature. The remanent polarizations of SBT films with Bi2O3 interfacial layer were significantly improved in comparison with those without Bi2O3 layer. The remanent polarization (2Pr) and coercive field (Ec) of SBT films without and with aBi2O3 interfacial layer annealed at 750 °C were 12 and 21 μC/cm2 and 60 and38 kV/cm, respectively, at an applied voltage of 5 V.
Tb L3-edge X-ray Absorption Near-edge Structure Spectroscopic Analysis of Terbium-doped Phosphor Compoundsfor Plasma Display Panel Applications
Authors: Choi Yong Gyu , Sohn Kee-Sun , Kim Kyong Hon , Park Hee Dong
Published: March 2008

We have analyzed Tb L3-edge x-ray absorption near-edge structure spectra of Tb-doped phosphor compounds for plasma display panel applications. Intensity and lifetime of the green emission from the Tb3+:5D4→7F5 transition were measured with respect to nominal terbium concentration in the host compounds, i.e., YBO3, YPO4,and Y4Al2O9, all of which were made through the solid-state reaction. Typical concentration quenching was evident on the fluorescence intensity and the fluorescing level lifetime in our samples. From the analyses of white line absorption peaks at TbL3-edge, it was verified that terbium is essentially trivalent in all the samples, even invery highly concentrated ones. Thus, this implies that the concentration quenching was not caused by presence of mixed-valent states of terbium. Instead, it is believed that anonradiative energy transfer route among Tb3+ ions might be responsible for thebehavior.
Interfacial Microstructure and Joint Strength of Sn–3.5Ag–X (X = Cu, In, Ni) Solder Joint
Authors: Choi Won Kyoung , Kim Jong Hoon , Jeong Sang Won , Lee Hyuck Mo
Published: March 2008

Interfacial phase and microstructure, solder hardness, and joint strength of Sn–3.5Ag–X (X = Cu, In, Ni; compositions are all in wt% unless specified otherwise) solder alloys were investigated. Considering the melting behavior and the mechanical properties, five compositions of Sn–3.5Ag–X solder alloys were selected. To examine the joint characteristics, they were soldered on under bump metallurgy isothermally at 250 °C for 60 s. Aging and thermal cycling (T/C) were also performed on the solder joint. The interfacial microstructure of the joint was observed by scanning electron microscopy. X-ray diffraction and energy dispersive x-ray analyses were made toidentify the type of solder phase and to measure compositions. Excessive growth of an interfacial intermetallic layer in the Sn–3.5Ag–6.5 In solder joint led to a brittle fracture. In the other four solder joints, ductile fractures occurred through the solder region and the solder hardness was closely related with the joint strength.
C60 Nanowhiskers Formed by the Liquid–liquid Interfacial Precipitation Method
Authors: Miyazawa K. , Kuwasaki Y. , Obayashi A. , Kuwabara M.
Published: March 2008

Fine needlelike crystals of C60 have been formed by a liquid–liquid interfacial precipitation method which uses an interface of the concentrated toluene solution of C60/isopropyl alcohol. The needlelike crystals of C60 with a diameter of submicrons (“C60 nanowhiskers”) were found to be single crystalline and composed of thin slabswith a thickness of about 10 nm. The intermolecular distance of the C60 nanowhiskerswas found to be shortened along the growth axis as compared with the pristine C60crystals, indicating a formation of strong bonding between C60 molecules. TheC60 nanowhiskers are assumed to be polymerized via the “2 + 2” cycloaddition inthe close-packed [110]c direction.
Novel Hybrid Inorganic–organic Film Based on the Tungstophosphate Acid–polyacrylamide System: Photochromic Behavior and Mechanism
Authors: Feng Wei , Zhang Tie Rui , Liu Yan , Wei Li , Lu Ran , Li Tie Jin , Zha Ying Ying , Yao Jian Nian
Published: March 2008

A novel photochromic complex composed of Keggin-type tungstophosphate acid (PW12) and polyacrylamide (PAM) was prepared. Atomic force microscopy (AFM), thermogravimetric study, Fourier transform infrared spectra (FTIR), ultraviolet–visiblea bsorption spectra (UV-VIS), and electron resonance spectra (ESR) were used to investigate the surface topography, composition, and photochromic behavior and mechanism of the film. Under UV irradiation, the film was reduced photochemically to yield a blue species. AFM images indicated that surface topography of the polymer matrix changed after adding PW12. FTIR results showed that the Keggin geometry of PW12 was still preserved inside the matrix, and a charge-transfer bridge was built between PW12 and PAM by hydrogen bonding. The characteristic signal of W (V) and the formation of a radical signal in ESR spectra indicated that PAM was a hydrogen donor and the photoreduced process was in accordance with the radical mechanism.The diffusion of oxygen in the polymeric network plays an important role in the reversibility of photochromism.
Optimal and Manufacturable Two-dimensional, Kagomé-like Cellular Solids
Authors: Hyun S. , Torquato S.
Published: March 2008

We used the topology optimization technique to obtain two-dimensional, isotropic cellular solids with optimal effective elastic moduli and effective conductivity. The overall aim was to obtain the best (simplest) manufacturable structures for these effective properties, i.e., single-length-scale structures. Three different but simple periodic structures arose due to the imposed geometric mirror symmetries: lattices with triangular-like cells, hexagonal-like cells, or Kagomé-like cells. As a general rule, the structures with the Kagomé-like cells provided the best performance over a wide range of densities, i.e., for 0 ≰ ф <0.6, where ф is the solid volume fraction (density). At high densities (ф > 0.6), Kagome-like structures were no longer possible, and lattices with hexagonal-like or triangular-like cells provide virtually the same optimal performance. The Kagomé-like structures were found to be a new class of cellular solids with many useful features, including desirable transport and elastic properties, heat-dissipation characteristics, improved mechanical strength, and ease of fabrication.
Growth and Density Control of Carbon Tubule Nanocoils Using Catalyst of Iron Compounds
Authors: Pan Lujun , Hayashida Taichi , Nakayama Yoshikazu
Published: March 2008

We synthesized carbon tubule nanocoils by catalytic thermal chemical vapor deposition. The iron catalyst necessary in the growth of carbon nanocoils was prepared only by coating the iron compound solution on indium tin oxide–coated glass substrate. It was found that the iron compounds have the same catalytic function as iron thin film prepared by evaporation or electroplating. Furthermore, the density of the prepared carbon nanocoils could be easily controlled by changing the density of the solution of iron compounds. In addition, the poly(methylphenylsilane) proved to be an excellent dispersive medium for the iron compound in preparation of the carbon nanocoils in desired densities.
Numerical Analyses of Fluid Dynamics of an Atomization Configuration
Authors: Xu Q. , Cheng D. , Trapaga G. , Yang N. , Lavernia E.J.
Published: March 2008

Computational fluid dynamic techniques were used to analyze the gas flow behavior of a typical atomization configuration. The calculated results are summarized as follows. The atomization gas flow at the atomizer's exit may be either subsonic at ambient pressure or sonic at an underexpanded condition, depending on the magnitude of the inlet gas pressure. When the atomization gas separates to become a free annular gas jet, a closed recirculating vortex region is formed between the liquid delivery tube and the annular jet's inner boundary. Upon entering the atomization chamber, an underexpanded sonic gas flow is further accelerated to supersonic velocity during expansion. This pressure adjustment establishes itself in repetitive expansion and compression waves. A certain protrusion of the liquid delivery tube is crucial to obtain a stable subatmospheric pressure region at its exit. The vortex flow under the liquid delivery tube tends to transport liquid metal to the high kinetic energy gas located outside the liquid delivery tube, thereby leading to an efficient atomization.