bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of interfacial reaction on tensile and creep behaviors of aluminum-borate-whisker-reinforced AA6061 composite
Authors: Ma Z. Y. , Tjong S. C. , Geng L. , Wang Z. G.
Published: March 2008

Aluminum-borate (AlBO) whisker-reinforced AA6061 composite fabricated by squeeze casting was subjected to both tensile and creep investigations. The whisker exhibited a significant reinforcing effect on as-extruded AA6061, but not for T6-treated specimen. The yield strength of the composite decreased slightly after T6 treatment. This was caused by the degradation of the whiskers and the microcrack initiation. The incorporation of the AlBO whisker into the AA6061 improved the creep resistance of the alloy by several orders of magnitude. Moreover, the composite exhibited higher values of apparent stress exponent and apparent activation energy for both the static and cyclic creep. Finally, cyclic creep retardation behavior was observed for both reinforced and unreinforced AA6061.
Processing of epitaxial LiMn2O4 thin film on MgO(110) through metalorganic precursor
Authors: Ikuhara Yumi H. , Iwamoto Yuji , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

Epitaxial LiMn2O4 was successfully synthesized by coating a [Li–Mn–O] metalorganic precursor solution onto MgO (110) substrates at temperatures as low as 350 °C. Cross-sectional transmission electron microscopy observation revealed that the orientation relationship between LiMn2O4 and MgO was (111) LiMn2O4 //(111) MgO, (110) LiMn2O4 //(110) MgO, and [112] LiMn2O4 //[112] MgO, which resulted in the (111) LiMn2O4 planes growing perpendicular to the surface plane of MgO. The interface structure consisted of (111) layers of Mn atoms in the LiMn2O4 crystal aligned with the Mg atoms in the (111) planes of the MgO substrate when viewed along the [112] direction.
Thermoelectric properties of the incommensurate layered semiconductor GexNbTe2
Authors: Snyder G. Jeffrey , Caillat T. , Fleurial J-P.
Published: March 2008

The compounds GexNbTe2 (0.39 ≤ x ≤ 0.53) have been studied for their thermoelectric properties. By changing x, the carrier concentration can be adjusted so that the material changes from a p-type metal to a p-type semiconductor. The maximum germanium concentration at about Ge0.5NbTe2 is also the most semiconducting composition. High- and low-temperature electrical resistivity, Hall effect, Seebeck coefficient, and thermal conductivity were measured. Evidence of electronic ordering was found in some samples. The thermal conductivity is reasonably low and glasslike with room temperature values around 20–25 mW/cm K. However, the power factor is too low to compete with state-of-the-art materials. The maximum thermoelectric figure of merit, ZT found in these compounds is about 0.12. The low ZT can be traced to the low carrier mobility of about 10 cm2 /Vs. The related compounds Si0.5NbTe2 and Ge0.5TaTe2 were also studied.
Effect of target processing on CoCrPtTa thin-film media
Authors: Harkness S. D. , Lewis W. , Bartholomeusz M. , Tsai M.
Published: March 2008

The ensuing paper summarizes an investigation on the effect of target microstructural morphology on resultant sputter deposited media magnetic performance. Significant differences in media magnetic coercivity were obtained from Co–Cr–Pt–Ta targets possessing the same chemistry, sputtered under identical conditions, but possessing different microstructural phase and crystallographic texture characteristics. This result was most likely caused by the difference in sputter yields for the Ta-containing phases in the two distinct target microstructures. Results support enhanced chromium segregation yielding a decrease in the intergranuler exchange energy field for the deposited thin films.
Techniques of observation and characterization of the domain structure in periodically poled lithium niobate
Authors: Bermúdez V. , Gil A. , Arizmendi L. , Colchero J. , Baró A. M. , Diéguez E.
Published: March 2008

The domain structure of bulk periodically poled lithium niobate crystals were analyzed by different techniques. Images of topography, electrostatic force, and piezoelectric response were studied by scanning force microscopy. All these images showed the domain structure of the samples. The electrostatic force was always attractive pointing to a dielectric origin. The diffraction of a laser beam by the periodic structures was also observed, denoting a periodic change of refractive index. From the angle of diffraction the domain spatial frequency was directly obtained. The topographic profile of etched samples was studied by both scanning force and scanning electron microscopy.
Intermetal dielectric process using spin-on glass for ferroelectric memory devices having SrBi2Ta2O9 capacitors
Authors: Hong Suk-Kyoung , Yoon Yang Han , Baek Yong Ku , Lee Chang Goo , Suh Chung Won , Lee Seok Won , Kang Young Min , Kang Nam Soo , Hwang Cheol Seong , Kwon Oh Seong
Published: March 2008

The degradation behavior of integrated Pt/SrBi2Ta2O9/Pt capacitors caused by hydrogen impregnation during the spin-on glass (SOG)-based intermetal dielectric (IMD) process was investigated. SOG was tested as an IMD since it offers better planarity for multilevel metallization processes compared to other SiO2 deposition methods. It was found that the SOG itself does not degrade the ferroelectric performance. Deposition of an under-layer of SiOxNy by plasma-enhanced chemical vapor deposition (PECVD) using SiH4 + N2O + N2 source gases and a SiO2?x capping layer by another PECVD process using SiH4 + N2O source gases produced hydrogen as a reaction by-product. The hydrogen diffused into the SBT layer and degraded the ferroelectric performance during subsequent annealing cycles. A very thin (10 nm) Al2O3 layer grown by atomic layer deposition before the IMD process successfully blocked the impregnation of the hydrogen. Therefore, excellent ferroelectric performance of the SBT capacitors were maintained after the multilevel metallization process as well as passivation. The adoption of SOG in the IMD process greatly improved the surface flatness of the wafer resulting in a higher capacitor yield with very good uniformity in ferroelectric properties over the 8-in.-diameter wafer.
Cement as a thermoelectric material
Authors: Wen Sihai , Chung D. D. L.
Published: March 2008

Cement pastes containing short steel fibers, which contribute to electron conduction, exhibit positive values (up to 68 μV/°C) of the absolute thermoelectric power. Cement pastes containing short carbon fibers, which contribute to hole conduction while the cement matrix contributes to electron conduction, exhibit negative or slightly positive values of the absolute thermoelectric power. The hole and electron contributions in carbon fiber reinforced cement paste are equal at the percolation threshold. Addition of either steel or carbon fibers to cement paste yields more reversibility and linearity in the variation of the Seebeck voltage with temperature difference (up to 65 °C).
Influence of vapor-phase reaction on the reduction of OH?and S–H absorption bands in GeS2-based glasses for infrared optics
Authors: Liu Xiaobo , Tikhomirov V. , Jha A.
Published: March 2008

The reduction of OH- and S–H absorption bands in unary and ternary germanium sulphide glasses with oxides and hydroxides present in the raw materials and in impure glasses was studied via the chemical reaction of H2and HCl gases at high temperatures. Multicomponent phase equilibria calculations in the Ge–S–H–O–X (X = Cl, I) system were performed to determine the equilibrium partial pressures of gaseous species for removing oxygen and hydrogen from the glasses used for infrared (IR) applications. The effect of carbon on the reduction in oxide and hydroxide absorption bands was also investigated. The absorption characterization was carried out using a Fourier transform infrared reflection spectrophotometer. The IR absorption bands between 1000 and 3700 cm-1 were identified and analyzed. The Boson peaks (BP) in glass samples with two different OH- concentrations were also analyzed. It was found that the presence of OH- enhanced the intensity of Boson peaks. The sites for OH- and shared oxygen with the main [GeS4] 4- tetrahedron structural units in the glass are discussed with respect to the BP and IR absorption analyses. The structure model also identifies the origin of the reduced Rare-earth (RE+3 ) ion solubility (in particular Pr 3+ ions) and its dependence on OH- ion concentrations in GeS2 glasses
Raman spectroscopic determination of phase evolutions in LiAlxCo1−xO2 battery materials
Authors: Dobal P. S. , Katiyar R. S. , Tomar M. S. , Hidalgo A.
Published: March 2008

Superior battery materials LiAlxCo1−xO2 (x = 0.0, 0.1, 0.3, 0.5, and 0.7) were synthesized using a solution-based route at various sintering temperatures (450–800 °C). In this communication, we report on the use of Raman spectroscopy to study effect of composition and sintering temperature on the resulting material. The phase evolutions in LiAlxCo1−xO2 compositions were studied using micro-Raman spectroscopy and a phase diagram is proposed based on the observations. For less Al content, the low-temperature phases of LiAlxCo1−xO2 showed Raman spectra corresponding to a monoclinic (space group C2/m) structure, while a low-temperature spinel (space group Fd3m) phase was observed for 50% or more Al in these compounds. All these compositions exhibited a layered hexagonal (space group R3m) structure when sintered above 700 °C. Raman spectra also revealed residual Co3O4 in the low-temperature forms of LiCoO2 and LiA10.01Co0.9O2.
Metal/ceramic interface in an in situsynthesized Ti/TiCP composite coating by laser processing
Authors: Yu R. , Zhang S. , He L. L. , Wu W. T. , Ye H. Q.
Published: March 2008

The metal/ceramic interface in an in situ synthesized Ti/TiCP composite coating by laser processing was analyzed using high-resolution transmission electron microscopy. The TiC particles were distributed uniformly in the matrix and were highly faceted. The interfaces between the TiC particles and the β matrix were abrupt and free of any other reaction phases. It was the Ti-terminated TiC surface that bonded to the β matrix, resulting in the metallic bonding between the TiC particles and the matrix.
High Jc YBa2Cu3O7-δ films via rapid, low pO2 pyrolysis
Authors: Dawley J. T. , Clem P. G. , Siegal M. P. , Overmyer D. L.
Published: March 2008

In this investigation YBa2Cu3O7-δ (YBCO) films were fabricated via a metal acetate, trifluoroacetic acid based sol-gel route and spin-coat deposited on (100) LaAlO3 with a focus on maximizing Jc, while minimizing processing time. We demonstrate that the use of a low-pO2 atmosphere during the pyrolysis stage can lead to at least a tenfold reduction in pyrolysis time, compared to a 1 atm O2 ambient. High-quality YBCO films on LaAlO3, with Jc values up to 3 MA/cm2 at 77 K, can be routinely crystallized from these rapidly pyrolyzed films.
The healing of quenched crack in 1045 steel under electropulsing
Authors: Yizhou Zhou , You Zeng , Guanhu He , Benlian Zhou
Published: March 2008

Specimens of 1045 steel with quenched crack were treated under electropulsing. Scanning electron microscopy was employed to examine the change of specimens before and after the treatment. The results showed that the crack can be healed under electropulsing without melting, and the healing could be produced within a very short time. The original microstructure of specimens was not changed during the healing. It is thought that the temperature and the transient thermal compressive stress caused by high-rate heating are the main factors causing the healing of the crack.
Formation of intermetallic compounds at eutectic Sn–Zn–Al solder/Cu interface
Authors: Yu Shan-Pu , Wang Moo-Chin , Hon Min-Hsiung
Published: March 2008

The eutectic Sn–Zn–Al solder alloy was used [composition: 91Sn–9(5Al–Zn)] to investigate the intermetallic compounds (IMCs) formed between solder and a Cu substrate. Scanning electron microscope, transmission electron microscope, and electron diffraction analysis were used to study the IMCs between solder and a Cu substrate. The γ–Cu5Zn8 and γ–Cu9Al4 IMCs were found at the Sn–Zn–Al/Cu interface. Thermodynamic calculation can explain the formation of γ–Cu5Zn8 and γ–Cu9Al4 IMCs instead of Cu–Sn compounds. The formation and growth of γ–Cu9Al4 IMC at 423 K resulted in the decrease of adhesion strength at the interface of solder and a Cu substrate, where the Kirkendall voids were severely formed. As the heating time increased up to 1000 h at 423 K, the adhesion strength between the eutectic Sn–Zn–Al solder and a Cu substrate decreased from 7.6 ± 0.7 MPa to 4.4 ± 0.8 MPa.
Relaxation of ultraviolet-radiation-induced structure and long-lasting phosphorescence in Eu2+-doped strontium aluminosilicate glasses
Authors: Qiu Jianrong , Shimizugawa Y. , Kojima K. , Tanaka K. , Hirao K.
Published: March 2008

We report on the relaxation of ultraviolet-radiation-induced structure and long-lasting phosphorescence in Eu2+-doped glass samples with compositions of xAl2O3 · 40SrO · (60 − x)SiO2· 0.05Eu2O2 · 0.05Dy2O3 (x = 0, 10, 30) (mol%). After irradiation by an ultraviolet lamp (λmax = 254nm) with a power density of 5 mW/cm2 for 30 min, a visible light (peaking at 510 nm) could be seen with the unaided eye in the dark even 24 h after the removal of the activating light. Thermostimulated luminescence glow curves, x-ray absorption, and electron-spin-resonance spectra were measured. We suggest that the long-lasting phosphorescence in the Eu2+-doped glass samples resulted from the recombination of electrons and holes at shallow traps in the glass matrix that can be thermally released at room temperature, and energy transfer between the recombination centers and Eu2+ ions.
Improvement in oxidation resistance of TiB2 by formation of protective SiO2 layer on surface
Authors: Koh Young-Hag , Kim Hae-Won , Kim Hyoun-Ee
Published: March 2008

To improve the oxidation resistance of TiB2 material, dense silica (SiO2) layer was caused to form on the surface. The coating layer was formed on the surface by exposing the specimens next to a bed of SiC powder in a flowing H2 containing 0.1% H2O at 1450 °C. Part of SiO2 “smoke”, generated by a reaction between the SiC powder and H2O in the H2 gas stream, was deposited on the sample surface to form a dense and uniform SiO2 layer. Beneath the SiO2 layer, an interfacial layer composed of Ti2O3 and B2O3was formed. Oxidation resistance of the specimen was improved markedly by the coating layers. The coating layers enhanced the oxidation resistance through the retardation of oxygen transport and also through the consumption of oxygen by a reaction with Ti2O3 to form TiO2.
Oxygen self-diffusion in cerium oxide doped with Nd
Authors: Kamiya Michiyo , Shimada Eriko , Ikuma Yasuro , Komatsu Manabu , Haneda Hajime , Sameshima Soichiro , Hirata Yoshihiro
Published: March 2008

Polycrystalline Ce0.77Nd0.23O1.885having a relative density in excess of 98% was prepared. Oxygen diffusion experiments were performed for the temperature range from 750 to 1100 °C, in an oxygen partial pressure of 6.6 kPa. The concentration profile of18O in the specimens following diffusion annealing was measured by secondary ion mass spectroscopy (SIMS). The oxygen self-diffusion coefficient obtained using secondary ion mass spectrometry was expressed by D = 6.31 × 10−9exp(−53 kJ mol−1/RT) m2s−1and was in the extrinsic region. The oxygen diffusion coefficient of Ce0.77Nd0.23O1.885was larger than that of Ce0.8Y0.2O1.90; it was close to those of Ce0.6Y0.4O1.80and Ce0.69Gd0.31O2−δ. The oxygen diffusion coefficient obtained by the tracer method at 700 °C agreed with that calculated from the electrical conductivity in Ce0.77Nd0.23O1.885. The activation energy of the surface exchange coefficient was 94 kJ mol−1, and the values of the surface exchange coefficient were similar to those of stoichiometric CeO2and ThO2.
Diffusion of oxygen and silicon in silicon: Silicon monoxide model
Authors: Doremus Robert H.
Published: March 2008

The diffusion of oxygen in silicon was modeled to result from the diffusion of dissolved silicon monoxide. The SiO molecule dissolved in the largest space in the diamond lattice of silicon, oriented in a 〈111〉 direction, with the oxygen lightly bonded to a network silicon atom. This configuration is consistent with infrared spectra, dichroism of infrared spectral lines, and internal friction of oxygen in silicon. The anomalous rapid diffusion of oxygen below 700 °C could result from the diffusion of molecular water or oxygen in silicon, but more evidence is needed to test these possibilities. Diffusion and exchange of silicon tracer in SiO with lattice silicon can possibly explain tracer diffusion of silicon in silicon.
Combined out-of-plane and in-plane texture control in thin films using ion beam assisted deposition
Authors: Dong L. , Srolovitz D. J. , Was G. S. , Zhao Q. , Rollett A. D.
Published: March 2008

Complete control of the texture of a film during growth requires the ability to determine the in-plane and out-of-plane texture simultaneously. We present both computer simulation and experimental evidence for the simultaneous establishment of out-of-plane and in-plane texture during ion beam assisted deposition of aluminum. Channeling along 〈110〉 directions (60° from the normal) creates a {220} out-of-plane orientation rather than the thermodynamically preferred {111} orientation. The ion beam also aligned 〈220〉 directions within the plane of the film. Measured x-ray pole figures confirmed the presence of a strong out-of-plane texture and the presence of two main, twin-related, in-plane texture components. We theoretically demonstrated that it is impossible to completely control both the in-plane and out-of-plane texture with a single ion beam in high-symmetry crystals and two ion beams must be employed to ensure complete texture control.
Optical evaluation of the flexural rigidity and residual stress in thin membranes: Picosecond tra nsient grating measurements of the dispersion of the lowest-order Lamb acoustic waveguide mode
Authors: Rogers John A. , Bogart Gregory R.
Published: March 2008

This article describes a convenient, noncontacting technique for determining the flexural rigidity and residual stress in thin membranes. The method was based on transient grating photoacoustics, also known as impulsive stimulated thermal scattering. Crossed laser pulses provided a coherent source of wavelength tunable acoustic modes in the membranes. Diffraction of a probe laser revealed the time dependence of these motions. The measured dispersion of the lowest-order Lamb mode at small acoustic wavevectors, coupled with classical plate theory, allowed the flexural rigidity and the residual stress to be determined. The technique, its accuracy, and spatial mapping capabilities were demonstrated through analysis of membranes designed for masks in next-generation lithography systems based on projected beams of electrons.
Surface effects in field-assisted sintering
Authors: Groza J. R. , Garcia M. , Schneider J. A.
Published: March 2008

The more-stringent requirements for densification of new out-of-equilibrium powders have created a growing demand for nonconventional rapid sintering processes. Among those, field-assisted sintering techniques (FASTs) have seen a recent renewed interest motivated by their ability to consolidate a large variety of powder materials into high densities in short times. Characterization of a range of FAST-consolidated materials displayed relevant associated surface effects, such as grain boundary cleaning with direct grain-to-grain contact and advanced densification without sintering aids. These effects may be attributed to phenomena ranging from dielectric breakdown to a possible nonconventional plasma generation. Such surface effects provided a better intergranular bonding of powder particles during subsequent sintering
Study of the effects of low-energy electron bombardment during the chemical vapor deposition of diamond
Authors: Gonzaález J. A. , Figueroa O. L. , Weiner B. R. , Morell G.
Published: March 2008

The effects of low-energy electron bombardment during the chemical vapor deposition of diamond were studied. The film growth was monitored in real time with in situ phase-modulated ellipsometry, in order to trigger the electron bombardment at different growth stages. Ex situ Raman spectroscopy and scanning electron microscopy were employed to evaluate the crystalline quality and the morphology of the grown films, respectively. The results indicated that triggering the electron bombardment after high-quality scattered diamond crystallites had formed results in finely grained smoother films of similar diamond yield and crystalline quality as those grown without bombardment. However, the electron bombardment deteriorates the film crystalline quality and the diamond yield when it was triggered from the start of deposition.
Evaluation of the modified edge lift-off test for adhesion characterization in microelectronic multifilm applications
Authors: Hay Jack C. , Liniger Eric G. , Liu Xiao Hu
Published: March 2008

The modified edge lift-off test (MELT) has gained enough acceptance in the community for evaluating interfacial adhesion that there is now commercial equipment for automating the test. However, there are several experimental and mechanics assumptions of the test that may provide unexpected outcomes. Experimental data suggested that for crack lengths greater than 5% of the film thickness the energy release rate was independent of crack length, contradicting the rule of thumb suggesting that the crack length should be greater than 10–20 times the film thickness to obtain a steady-state energy release rate in the edge crack problem. Finite element simulations not only corroborated the experimental observation but seemed to indicate that the crack length required for steady-state conditions was a function of the relative Young's moduli for the film and substrate. It was also shown via an analytical model that plate bending (commonly neglected) can significantly affect the energy release rate in the MELT and lead to incorrect conclusions regarding the reliability of an interface.
Microstructure of (Nd, Eu, Gd)-123 matrix with (Nd, Eu, Gd)-211 inclusions
Authors: Muralidhar M. , Jirsa M. , Iida K. , Sakai N. , Murakami M.
Published: March 2008

Microstructure of (Nd, Eu, Gd)Ba2Cu3O7−δ (NEG-123) samples with (Nd, Eu, Gd)2BaCuO5 (NEG-211) particles were observed by transmission electron microscopy. High-resolution electron microscopy observation demonstrated that the density of microstructural defects was small around the NEG-211 secondary phase particles. Furthermore, the 123/211 interfaces were found to be very clean and sharp. Chemical compositional analysis of the submicron secondary phase particles revealed that these fine particles are not composed of NEG-211 but Eu2BaCuO5 (Eu-211) or Gd2BaCuO5 (Gd-211).
Chemical vapor deposition of an aluminum nitride–diamond composite in a triple torch plasma reactor
Authors: Asmann Marcus , Cook Robert F. , Heberlein Joachim V. , Pfender Emil
Published: March 2008

An aluminum nitride–diamond composite has been produced by sequential deposition of AlN and diamond in a triple torch plasma reactor (TTPR). AlN was deposited from AlN powder by injection into the argon–nitrogen, converging plasma plume of a TTPR. Velocity and temperature profiles of the converging plasma plume, obtained by enthalpy probe measurements, were used to show that the powder decomposed prior to reaching the substrate. Diamond was deposited in an argon–hydrogen–methane system onto the existing AlN film. Characterization of an AlN–diamond–AlN composite indicated a Vickers hardness of 18.6 GPa and a modulus of elasticity of 245–282 GPa.
Characterization of bond formation in SiC and Si3N4 implanted with Ti, Fe, and Co
Authors: Zanghi Didier , Traverse Agnès , Gautrot Sébastien , Kaïtasov Odile
Published: March 2008

Ti, Fe, and Co ions were implanted in two ceramics, SiC and Si3N4, to reach concentrations on the order of 10% over a depth of about 50–60 nm. X-ray absorption spectroscopy was performed at the K edge of the implanted ions to identify their local environment at the end of the implantation process. Ti was found to form Ti–C and Ti–N bonds whereas Co and Fe precipitated and formed clusters in Si3N4. CoSi was detected in SiC whereas, in the same matrix, Fe clusters coexist with FeSi. A coherent interpretation of these results is given in terms of the heat of reaction for all possible systems. We also successfully interpret in the same way some results found in literature in the case of implanted oxides.
Silica particle growth in metastable supersaturation solution
Authors: Kim Kyung-Soo , Kim Jun-Kyung , Kim Woo-Sik
Published: March 2008

In a metastable solution the particle growth rate of silicon dioxide increased with an increase in the initial supersaturation of the metastable solution and agitation speed in the ranges of 2.5 × 10−4 to 2.0 × 10−3 M and 300–1500 rpm, respectively. Based on a power law expression, the particle growth rate order was estimated as 2.0 independent of the initial supersaturation and agitation speed. Meanwhile, the particle growth rate coefficient was enhanced from 2.0 × 10−3 to 1.4 × 10−2 with increase in the agitation speed from 300 to 1500 rpm. From the experimental data, it would appear that the enhanced particle growth rate resulted from the promotion of molecular transport due to the agitation and driving force of the supersaturation in the particle growth process. A slight addition of sodium chloride into the metastable solution caused a marked reduction of the particle growth rate due to the inhibition of growth process by sodium chloride adsorbed on the particle. This effect of sodium chloride on the particle growth appeared in a significant drop of the particle growth rate coefficient from 4.5 × 10−3 to 8.0×10−4 with increase in the sodium chloride concentration from zero to 5.0×10−3 M, but not in the particle growth rate order. The influence of sodium chloride on the particle growth process of silicon dioxide predicted with a Langmuir isotherm matched with the experimental data.
Grain boundary structure in Al–Mg and Al–Mg–Sc alloys after equal-channel angular pressing
Authors: Oh-ishi Keiichiro , Horita Zenji , Smith David J. , Langdon Terence G.
Published: March 2008

Samples of an Al–3% Mg alloy and an Al–3% Mg–0.2% Sc alloy were subjected to equal-channel angular pressing (ECAP) to reduce the grain size to approximately 0.2–0.3 μm. Some samples of each alloy were also annealed for 1 h at temperatures of either 423 or 673 K, respectively. High-resolution electron microscopy was used to examine the microstructure both before and after annealing. The grain boundaries after ECAP were wavy and faceted and in high-energy nonequilibrium configurations. These results were consistent with earlier observations of materials subjected to severe plastic deformation using high-pressure torsion. In addition, some grain boundaries in the Al–Mg–Sc alloy had a zigzag appearance after annealing at 673 K, where the straight portions of the boundary were identified as low-energy {111} planes. It is suggested these are mobile boundaries lying in a lowest energy configuration where mobility may be restricted by the presence of incoherent Al3Sc particles.
Sol-gel-derived photosensitive TiO2 and Cu/TiO2 using homogeneous hydrolysis technique
Authors: Wu Jeffrey C.S. , Yeh Chih-Yang
Published: March 2008

Titania and copper-loaded titania were synthesized by an improved sol-gel method using a homogeneous hydrolysis technique. Unlike the conventional sol-gel procedure that added water directly, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of titania. Fourier transform infrared spectra confirmed the presence of bidental ligand. The sol was dried, then calcined at 500°C to remove organics and transformed to anatase titania. Transmission electron microscopy revealed that the titania particles were uniform, and the particle size ranged from 10 to 25 nm. The band gaps of TiO2 and Cu/TiO2 ranged from 3.01 to 3.17 eV based on the diffusive reflective ultraviolet-visible spectrometry. X-ray photoelectron spectroscopy analysis showed a positive shift of binding energy of Ti2p3/2 and a negative shift of Cu 2p3/2 in Cu/TiO2. The redistribution of electric charge is due to the Schottky barrier of Cu and TiO2.
Effect of bond valence on microwave dielectric properties of (Pb1−xCax)(Mg0.33Ta0.67)O3 ceramics
Authors: Park Heung Soo , Yoon Ki Hyun , Kim Eung Soo
Published: March 2008

The relationship between the dielectric properties of the complex perovskite (Pb1−xCax)(Mg0.33Ta0.67)O3 ceramics, where 0.45 ≤ × ≤ 0.60, and the dielectric polarizability, related to bond valences of A-site ions, was investigated at microwave frequencies. As the Ca content (x) increased, the deviation of the observed dielectric polarizabilities, calculated by the Clausius–Mosotti equation from the theoretical values calculated by the additivity rule of dielectric polarizability, decreased from −3% to −0.69%. It was found that this deviation was related to the bond valence of the A-site. Smaller negative deviation corresponded to the cations with lower bond valence, and larger negative deviation corresponded to the cations with higher bond valence. Also, the temperature coefficient of resonant frequency (TCF) was affected by the bond valence of the A-site, and then TCF decreased with decreasing bond valence of the A-site in ABO3 perovskite compounds.
Magnetotransport properties of La0.7Ca0.3MnO3 thick films prepared by spray pyrolysis
Authors: Damay F. , MacManus-Driscoll J. L. , Cohen L. F.
Published: March 2008

A spray pyrolysis deposition technique has been used to prepare thick films of half-metallic ferromagnet La0.7Ca0.3MnO3 on LaAlO3 (001) and yttria-stabilized zirconia Y–ZrO2 (100) single-crystal substrates. The films deposited on LaAlO3 (001) exhibited a high degree of crystallinity with both in-plane and out-of-plane texture and a very sharp insulator to metal transition at TIM = 270 K. The intrinsic magnetoresistance (MR) reaches 70% at TIM in 3 T, a similar value as in the bulk material of the same composition. The extrinsic intergrain MR, however, is only 0.5% at 40 K in 3 T, 50 times smaller than for the bulk. By contrast, films grown on YSZ single crystals have a broad insulator to metal transition at a lower TIM of approximately 220 K and poor intrinsic MR. They show however an extrinsic MR as large as in the bulk. The extrinsic MR is interpreted as arising from crystalline and magnetic disorder at the grain boundaries.
Deposition of epitaxial transition metal carbide films and superlattices by simultaneous direct current metal magnetron sputtering and C60 evaporation
Authors: Högberg H. , Birch J. , Johansson M. P. , Hultman L. , Jansson U.
Published: March 2008

Thin epitaxial TiC and VC films and superlattices have been deposited on MgO(001) by simultaneous sputtering of the metals and evaporation of C60. It was found that epitaxial growth conditions for TiC could be maintained down to a temperature of 100 °C, while the epitaxial growth of VC required 200 °C. Epitaxial VC films were completely relaxed at all growth temperatures, while a change from a relaxed to a strained growth behavior was observed for TiC films. The structural quality of the TiC films was better than for the VC films. A general observation was that a plasma-assisted deposition process yields films with a higher quality and allows epitaxial growth at lower temperatures than for a pure coevaporation process.
Magnetic properties, domain structure, and microstructure of anisotropic SmCo6.5Zr0.5 ribbons with C addition
Authors: Yan A-Ru , Sun Zhi-Gang , Zhang Wen-Yong , Zhang Hong-Wei , Shen Bao-Gen
Published: March 2008

The magnetic properties and the domain structure of anisotropic melt-spun SmCo6.5Zr0.5 alloys with C addition was investigated by means of x-ray diffraction (XRD), magnetic measurement, and magnetic force microscopy. The XRD analyses showed that the addition of a few percent of C led to a significant increase in the coercivity and simultaneously affected the characterization of crystalline texture of the ribbons. The easy magnetization c axis changed from parallel to the ribbon plane for SmCo6.5Zr0.5 ribbons to normal to the ribbon plane for SmCo6.5Zr0.5C0.25−0.75 ribbons. An optimal coercivity of 0.92 T was obtained for the SmCo6.5Zr0.5C0.5 ribbon spun at 5 m/s. The corresponding remanence measured normal or parallel to the ribbon plane was 7.1 kGs or 3.1 kGs, respectively. The domain structure was studied by magnetic force microscopey. A strip-shaped domain was observed on the surface of the SmCo6.5Zr0.5 ribbons and the walls lay straight and parallel. For C-doped ribbons, the domain walls formed a maze domain pattern of grains with c axis normal to the ribbon plane. Scanning electron micrographs showed that a dendrite structure was present in the SmCoZr ribbon surface, and C addition caused the above-mentioned dendrite to diminish.
Analysis of a ceramic/metal laminate under thermal shock
Authors: Sherman D. , Schlumm D.
Published: March 2008

A ceramic/metal laminated system has lately been proposed by the authors. It is capable of maintaining high mechanical strength and structural integrity after high-temperature thermal shock. In this investigation, a multilayered, multimaterial system with strong interface, subjected to thermal shock loading, was analyzed. The analysis was based on a 1-D finite difference scheme and considers the thermal residual stresses. Using a failure criterion based on crack initiation, the number of broken layers due to thermal shock and the residual mechanical strength at room temperature was determined. A comparison with experimental results of three different lay-ups was made, demonstrating the ability of the program to predict the experimental results. The program was thus shown to be a significant tool for designing multimaterial multilayered systems for thermal shock applications.
Dielectric properties anomaly of (1−x)Pb(Ni1/3Nb2/3)O3−xPbTiO3 ceramics near the morphotropic phase boundary
Authors: Li Zhenrong , Zhang Liangying , Yao Xi
Published: March 2008

Dielectric properties and the phase compositions of (1−x)Pb(Ni1/3Nb2/3)O3−xPbTiO3 ceramics were investigated. A morphotropic phase boundary (MPB) in the system between pseudocubic and tetragonal phase regions has been identified to lie in the composition range x = 0.34–0.38 by means of x-ray diffraction and dielectric measurements. The samples of composition lying near the MPB have good dielectric properties, but at the same time, exhibit two dielectric peaks. The possible reasons for the occurrence of dielectric bipeaks are discussed. One dielectric peak is phase transition peak, and the other peak lying in 130–150 °C temperature range is suggested to result from structure defects in the ceramics.
Statistical behavior and misfit stresses in ceramic and metal laminated system
Authors: Sherman D. , Gong X.
Published: March 2008

The statistical behavior of ceramic and metal laminates was studied, and in particular the relationship between the failure distribution of the laminate and that of the ceramic layers that it comprises. An important result of this investigation is the ability to predict the misfit stresses due to thermal processing of the laminates. A finite different scheme that was capable of calculating the local stresses at each constituent and of considering the thermal residual stresses was developed. The laminated system was constructed from 380-μm-thick alumina alternating with nickel foil 25- or 50-μm thick.
Characterization of the induction period in tricalcium silicate hydration by nuclear resonance reaction analysis
Authors: Livingston R. A. , Schweitzer J. S. , Rolfs C. , Becker H-W. , Kubsky S.
Published: March 2008

Nuclear resonance reaction analysis has been applied for the first time to measure the development of the hydrogen depth profile in the early stages of hydration of tricalcium silicate using the 1H(15N,αγ)12C reaction. The surface layer had an H concentration and thickness consistent with a few unit cells (1.1 nm) of tobermorite-like material. The inner regions exhibited diffusion-controlled growth with time until the hydrogen concentration approaches that of the surface layer at 4.25 ± 0.07 h. This event marked the end of the induction period and the onset of the rapid hydration reaction period.
Planar oxidation of strained silicon substrates
Authors: Lin M-T. , Jaccodine R. J. , Delph T. J.
Published: March 2008

We report here on a series of experiments in which relatively low levels of in-plane bending strain were applied to oxidizing silicon substrates. These were found to result in significant decreases in oxide thickness in the ultrathin oxide regime. Both tensile and compressive bending resulted in roughly the same degree of thickness retardation, although compressive bending typically led to somewhat thinner oxides than did tensile bending. An examination of the experimental data indicate that the principal effect seems to occur in the very early stages of oxidation, with only minor effects on subsequent oxide growth. We hypothesize that the observed oxide thickness retardation is related to straining of the underlying silicon lattice at the oxidation front.
Tensile fracture during transformation superplasticity of Ti–6Al–4V
Authors: Schuh C. , Dunand D. C.
Published: March 2008

During thermal cycling through the α–β phase transformation under the action of a small external biasing stress, Ti alloys exhibit an average deformation stress exponent of unity and achieve superplastic strains. We report tensile experiments on Ti–6Al–4V with an applied stress of 4.5 MPa, aimed at understanding the failure processes during transformation superplasticity. The development of cavities was assessed as a function of superplastic elongation, and macroscopic neck formation was quantified at several levels of elongation by digital imaging techniques. The effects of thermal inhomogeneity on neck initiation and propagation were also elucidated experimentally. Tensile ductility during transformation superplasticity is compared with that during isothermal creep at the average, effective cycling temperature, and a numerical model is used to show the effect of thermal gradients in limiting superplastic elongation.
Multifunctional microtruss laminates: Textile synthesis and properties
Authors: Sypeck D. J. , Wadley H. N. G.
Published: March 2008

Open cell periodic metal truss structures can exhibit significantly higher stiffnesses and strengths than stochastic cellular metal structures of the same relative density while still providing high mechanical energy absorption and efficient heat exchange opportunities. Here, a potentially inexpensive textile-based approach to the synthesis of periodic metal microtruss laminates is reported. The process consists of selecting a wire weave, laying up the mesh and joining using a transient liquid phase. Example structures constructed from nichrome (Ni–24Fe–16Cr) wire cloth were made and tested. These exhibited a linear dependence of stiffness and strength upon relative density, absorbed large amounts of mechanical energy, and showed good potential for efficient heat exchange.
Synthesis and properties of BxCyNz coatings
Authors: Oliveira M. N. , Conde O.
Published: March 2008

Some of the most interesting compounds from both technological and a scientific viewpoint can be found within the B–C–N composition triangle. Despite all the attention that some phases on the vertices and sides of the triangle have attracted, few works have focused inside the triangle itself. A laser-assisted chemical vapor deposition system was used to deposit B–C–N phases over fused quartz substrates. Two sets of gaseous precursors were used, namely B2H6 + NH3 + C2H4 and B2H6 + (CH3)2NH. The coatings were characterized regarding chemical composition, structure, and morphology. Hardness measurements were also carried out with a depth-sensing indentation instrument. It was found that depending on the gas phase, different regions of the BCN solid composition triangle are accessed. Coatings ranging from pure h-BN to pure B4C were obtained, as well as mixtures of these with BxCyNz compounds.
Subsolidus phase relations in the La2O3–Fe2O3–Al2O3 system
Authors: Kuščer Danjela , Bernik Slavko , Hrovat Marko , Holc Janez
Published: March 2008

The subsolidus phase relations in the La–Fe–Al–O system were investigated for solid oxide fuel cell (SOFC) applications. Five compounds, LaAlO3, LaAl11O18, LaFe12O19, AlFeO3, and LaFeO3, coexist in the La–Fe–Al–O system at 1380 °C in air. The microstructure and composition of the samples were studied by x-ray diffractometry and scanning electron microscopy. Based on experimental evidence, a phase diagram of the La2O3–Al2O3–Fe2O3 system has been proposed.
Electrical transport properties of single-crystalline Mn–Zn ferrous ferrite
Authors: Chung Yong-Chae , Yoo Han-Ill
Published: March 2008

Electrical transport properties, electrical conductivity, and thermoelectric power of a single-crystalline Mn0.45Zn0.43Fe2.12O4 were measured as functions of temperature in the range of 25 to 1000 °C. According to the small polaron hopping model, the values of the activation energy for small polaron hopping (EH) were obtained from the conductivity data in three different temperature regions: 0.032 eV for T < TC, 0.12 eV for TC < T < 600 °C, and 0.25 eV for 600 °C < T < 1000 °C. The behavior of conductivity and thermoelectric power data above TC is discussed in connection with cation redistribution.
Photocatalytic activity of TiO2prepared at low temperature by a photo-assisted sol-gel method
Authors: Guan Zi-Sheng , Zhang Xin-Tong , Ma Ying , Cao Ya-An , Yao Jian-Nian
Published: March 2008

TiO2nanocrystals were prepared by a photo-assisted sol-gel process in which tetrabutoxide titanate was hydrolyzed in acidic medium under ultraviolet irradiation. X-ray diffraction and Raman spectra showed that the as-prepared TiO2particles without further annealing were well-crystallized anatase. Such TiO2particles were easily immobilized on dacron cloth and showed very high photocatalytic activity. In contrast, TiO2particles were ill crystallized and showed lower activity when no light was introduced under otherwise equal conditions.
Epitaxial stabilization of orthorhombic cuprous oxide films on MgO(110)
Authors: Markworth Paul R. , Chang R. P. H. , Sun Y. , Wong G. K. , Ketterson J. B.
Published: March 2008

Continuous epitaxial films of cuprous oxide (Cu2O) have been formed by the thermal oxidation of 1.5-μm-thick Cu metal films deposited on MgO(110) substrates. These films melted at 1118 °C in air, in agreement with equilibrium phase diagrams. Upon cooling from the liquid, a highly crystalline, epitaxial, 2.5-μm-thick Cu2O film was formed. X-ray diffraction spectroscopy revealed that the Cu2O film crystal structure was orthorhombically distorted from the bulk cubic crystal structure. High-resolution transmission electron microscopy showed that the film is coherent, and energy dispersive x-ray spectroscopy showed that interdiffusion is limited to the interface. These results suggest that a new epitaxially stabilized phase of Cu2O has been formed.
Grain growth behavior of a nanostructured 5083 Al–Mg alloy
Authors: Tellkamp V. L. , Dallek S. , Cheng D. , Lavernia E. J.
Published: March 2008

A nanostructured 5083 Al–Mg alloy powder was subjected to various thermal heat treatments in an attempt to understand the fundamental mechanisms of recovery, recrystallization and grain growth as they apply to nanostructured materials. A low-temperature stress relaxation process associated with reordering of the grain boundaries was found to occur at 158 °C. A bimodal restructuring of the grains occurred at 307 °C for the unconstrained grains and 381 °C for the constrained grains. An approximate activation energy of 5.6 kJ/mol was found for the metastable nanostructured grains, while an approximate activation energy of 142 kJ/mol was found above the restructuring temperature.
Ultrathin TiB2 protective films
Authors: Huang Feng , Barnard John A. , Weaver Mark L.
Published: March 2008

TiB2 thin films demonstrate considerable potential for use as protective overcoats in the magnetic recording industry due to their excellent mechanical and tribological properties and good chemical and thermal stability. In the many studies performed on TiB2 films, the relative effectiveness of ultrathin TiB2 films has not been systematically investigated for very thin TiB2 films. In the present investigation, film stress and microstructure in as-sputtered and annealed ultrathin TiB2 films were investigated as a function of thickness. Ultrathin TiB2 films, as thin as 5 nm, were observed to adequately protect an underlying magnetic layer from oxidation up to 400 °C.
Absorption spectra of Co2+ in AgInS2 orthorhombic single crystals
Authors: Kim Hidong , Lee Seok-Joo , Kim Jae-Eun , Park Hae Yong , Oh Seok-Kyun , Kim Wha-Tek
Published: March 2008

The optical absorption spectra of AgInS2:Co2+ single crystals grown by chemical transport reaction using iodine as a transporting medium have been studied at 6 K. The peaks can be explained by the transitions of Co2+ in the Td symmetry with the spin-orbit coupling, which means that the deviations of the atomic sites from those of the ideal wurtzite structure can be considered negligibly small. The consideration of both the crystal field parameters and the electronegativity difference between atoms may indicate that Co atoms substitute In atoms.
Synthesis of nano-AgI arrays and their optical properties
Authors: Wang Yinhai , Mo Jimei , Cai Weili , Yao Lianzeng , Zhang Lide
Published: March 2008

Nano-AgI arrays were synthesized by electrochemical double liquor deposition in ordered porous alumina membrane. On the basis of the analysis of x-ray diffraction patterns, the assembly of nano-AgI/Al2O3 is a mixture of a cubic zinc blende type γ–AgI and a hexagonal wurtzite type β–AgI. The visible–ultraviolet optical absorption measuring showed that the assembly only had an absorption edge at 2.82 eV and exhibited the optical features of a semiconductor with a direct band gap. The absorption edge of the assembly was shifted to a shorter wavelength compared with pure γ–AgI and a longer wavelength compared with pure β–AgI. We believed that the change of the absorption edge of the assembly is due to the mixture of γ–AgI and β–AgI.
Torsion and bending of micron-scaled structures
Authors: Chong A. C. M. , Yang F. , Lam D. C. C. , Tong P.
Published: March 2008

Typical microelectromechanical systems (MEMS) devices and packages are composed of micron-scaled structures. Experimental investigations on the effect of size on the deformation behavior of simple structures have shown that the deformation behavior of metals and polymers is size dependent. The size dependence in small structures is attributed to the contribution of nonnegligible strain gradients. In this work, torsion and bending of micron-sized rods and plates were analyzed by using a two-parameter model of strain-gradient plasticity. Microrod torsion and microplate bending experimental data were analyzed to determine the magnitude of the strain-gradient material parameters. The parametric analyses showed that conventional analysis is applicable only when the size of the structure is significantly larger than the material parameters, which are typically in the micron range. Strain-gradient analysis of micron-sized rod revealed that the presence of strain gradient increased the torque by three to nine times at the same twist. For MEMS structures with micron-sized features, conventional structural analysis without strain gradient is potentially inadequate, and strain-gradient analysis must be conducted to determine the elastoplastic behavior in the micron scale.