bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermomechanical response of bare and Al2O3-nanocoated Au/Si bilayer beams for microelectromechanical systems
Authors: Gall Ken , Hulse Michael , Dunn Martin L. , Finch Dudley , George Steven M. , Corff Brian A.
Published: March 2008

We present results on the thermomechanical behavior of bare and nanocoated gold/polysilicon (Au/Si) bilayer cantilever beams for microelectromechanical system applications. The cantilever beams have comparable thicknesses of the Au and Si layers and thus experience significant out-of-plane curvature due to a temperature change. The experiments focus on the inelastic behavior of the bilayer beams due to thermal holding and thermal cycling. In uncoated Au/Si beams, thermal holding directly after release or thermal cycling both lead to a curvature decrease as a function of time or cycle number, respectively. The drop in curvature during thermal cycling or thermal holding in uncoated beams was not accompanied by a change in the slope of the thermoelastic curvature–temperature relationship. The absolute change in curvature depends on the temperature and the holding time. When holding or cycling to a temperature of 175 °C, the curvature change in uncoated beams is minimal for hold times up to 4500 min or 15,000 cycles. When holding or cycling to temperatures of 200 or 225 °C, the curvature in uncoated beams drops by a factor of three for hold times up to 4500 min or 15,000 cycles. The surface structure induced by long-term holding of uncoated beams shows grooving at the grain boundaries while the surface structure induced by cycling of uncoated beams shows consolidation of the grain boundaries. The Au/Si beams with a conformal 40-nm atomic layer deposition Al2O3 coating show a considerably different response compared to identical Au/Si bare beams subjected to the same thermal histories. The coating completely suppresses decreases in curvature when the beams are held at 225 °C for 4500 min. On the contrary, the coating does not always suppress thermal ratcheting when the beam is cycled from a low temperature to 225 °C. In the coated beams, the drop in curvature due to thermal cycling was accompanied by a change in the thermoelastic slope of the curvature–temperature relationship. Negligible microstructural changes were detected on the Al2O3-coated Au surface after holding or cycling. The results are discussed in light of potential deformation mechanisms and a simple analysis linking the mismatch strain between the layers to the curvature in the beams.
Amorphous alloy composition with high glass-formation ability in the pseudoternary Zr-[IQC-Al62Cu25.5Fe12.5]-[DQC-Al70Co15Ni15] alloy system
Authors: Lei Yi , Calvo-Dahlborg M. , Dubois J.M. , Hei Zukun , Weisbecker P. , Dong Chuang
Published: March 2008

A pseudoternary alloy system was constructed by combining icosahedral quasicrystal (IQC), decagonal quasicrystal (DQC), and Zr into one alloy system. Different proportions of Zr were added into pseudobinary alloy IQC80DQC20 (in wt.%). The structural evolution in these alloys is discussed. An amorphous alloy composition was found in this system. Melt-spinning amorphous alloy was produced in this composition. Through differential scanning calorimetry experiments, the amorphous alloy exhibited a high glass-forming ability comparable to that of the Inoue alloy Zr65Al7.5Cu17.5Ni10.
Strengthening mechanisms in nanostructured copper/304 stainless steel multilayers
Authors: Zhang X. , Misra A. , Wang H. , Shen T.D. , Swadener J.G. , Embury J.D. , Kung H. , Hoagland R.G. , Nastasi M.
Published: March 2008

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering. 304SS has a face-centered-cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the 304SS layers exhibit the fcc structure for layer thickness of ≤5 nm in epitaxy with the neighboring fcc Cu. For 304SS layer thickness larger than 5 nm, body-centered-cubic (bcc) 304SS grains grow on top of the initial 5 nm fcc SS with the Kurdjumov-Sachs orientation relationship between bcc and fcc SS grains. The maximum hardness of Cu/304SS multilayers is about 5.5 GPa (factor of two enhancement compared to rule-of-mixtures hardness) at a layer thickness of 5 nm. Below 5 nm, hardness decreases with decreasing layer thickness. The peak hardness of fcc/fcc Cu/304SS multilayer is greater than that of Cu/Ni, even though the lattice-parameter mismatch between Cu and Ni is five times greater than that between Cu and 304SS. This result may primarily be attributed to the higher interface barrier stress for single-dislocation transmission across the {111} twinned interfaces in Cu/304SS as compared to the {100} interfaces in Cu/Ni.
Energetics of oxidation of RE–Si–Al–O–N glasses
Authors: Zhang Yahong , Navrotsky Alexandra , Matusch Dirk , Seifert Hans Jürgen
Published: March 2008

Enthalpies of drop solution in molten 52 wt.% LiBO2-48 wt.% NaBO2 at 1078 K were measured for RE1.1Si1.7Al0.6O6-1.5xNx (x = 0, 0.2, 0.4, 0.6, 0.8) glasses for RE = Nd, Gd, Dy, Er, and Y. Linear relations between enthalpies of formation from elements and nitrogen content indicate that, within the experimental composition range, sites occupied by nitrogen ions are approximately equivalent in energy for a given substitutional series. The energetics of different rare-earth SiAlON glasses appears to be dominated by differences in the acid/base character of the cations. The onset glass-transition temperature increases linearly with increasing nitrogen content for the same rare earth and with decreasing rare-earth ionic radius for the same nitrogen content.
Cosolvent-assisted spray pyrolysis for the generation of metal particles
Authors: Kim Jung Hyeun , Babushok Valeri I. , Germer Thomas A. , Mulholland George W. , Ehrman Sheryl H.
Published: March 2008

A cosolvent-assisted spray pyrolysis process was developed for the formation of phase-pure metal particles from metal salt precursors without the direct addition of hydrogen or other reducing gas. Generation of phase-pure copper and nickel particles from aqueous solutions of copper acetate, copper nitrate, and nickel nitrate over the temperature range of 450 to 1000 °C was demonstrated. Addition of ethanol as a cosolvent plays a crucial role in producing phase-pure metal powders. Results of a modeling study of ethanol decomposition kinetics suggest that cosolvent decomposition creates a strong reducing atmosphere during spray pyrolysis via in situ production of hydrogen and carbon monoxide.
Formation, corrosion behavior, and mechanical properties of bulk glassy Zr–Al–Co–Nb alloys
Authors: Pang Shujie , Zhang Tao , Asami Katsuhiko , Inoue Akihisa
Published: March 2008

Bulk glassy Zr55Al20–xCo25Nbx (x = 0 to 5 at.%) alloys with critical diameters of 2.5–5 mm and supercooled liquid region of 48–75 K were produced by copper-mold casting. These alloys were spontaneously passivated in 3 mass% NaCl and 1 N H2SO4 solutions. The addition of Nb to the alloy enhanced the pitting corrosion resistance in the NaCl solution and enabled the open-circuit potential in the H2SO4 solution. Zr- and Al-enriched passive films formed on the bulk glassy Zr–Al–Co–Nb alloys exposed to air and on those immersed in the solutions. The increase in Nb content of the alloys resulted in an increase in Zr and Nb concentrations and a decrease in Al concentration of the passive film. The Vickers hardness, Young's modulus, compressive fracture strength, fracture strain, and plastic strain of the bulk glassy Zr–Al–Co–Nb alloys were 550, 98 GPa, 2100 MPa, 2.9%, and 0.9%, respectively.
Ordering in (La,Sr)(Al,Ta)O3 substrates
Authors: Li H. , Salamanca-Riba L. , Ramesh R. , Scott J. H.
Published: March 2008

(La, Sr)(Al, Ta)O3 (LSAT) has recently received increased attention as a substrate for the deposition of various oxide films. LSAT is usually considered as having a perovskite structure. However, the exact atomic structure of LSAT is not yet well known and has received little attention up to now. In this paper, a series of studies using x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometry were conducted to determine the atomic structure of LSAT. It was found that LSAT consists of two types of domains: one with a simple cubic perovskite structure (disordered with a = 0.3868 nm) and the other with a face-centered-cubic structure (ordered with a = 0.773 nm). Computer image simulation of high-resolution lattice images suggests that the ordered structure is due to ordering of the Al and Ta ions.
On the grain-size-dependent elastic modulus of nanocrystalline materials with and without grain-boundary sliding
Authors: Sharma P. , Ganti S.
Published: March 2008

A closed-form model was proposed to evaluate the elastic properties of nanocrystalline materials as a function of grain size. Grain-boundary sliding, present in nanocrystalline materials even at relatively low temperatures, was included in the formulation. The proposed analytical model agrees reasonably well with the experimental results for nanocrystalline copper and palladium.
Structure and properties of Al–Mg mechanical alloys
Authors: Schoenitz Mirko , Dreizin Edward L.
Published: March 2008

Mechanically alloys in the Al–Mg binary system in the range of 5–50 at.% Mg were produced for prospective use as metallic additives for propellants and explosives. Structure and composition of the alloys were characterized by x-ray diffraction microscopy (XRD) and scanning electron microscopy. The mechanical alloys consisted of a supersaturated solid solution of Mg in the α aluminum phase, γ phase (Al12Mg17), and additional amorphous material. The strongest supersaturation of Mg in the α phase (20.8%) was observed for bulk Mg concentrations up to 40%. At 30% Mg, the γ phase formed in quantities detectable by XRD; it became the dominating phase for higher Mg concentrations. No β phase (Al3Mg2) was detected in the mechanical alloys. The observed Al solid solution generally had a lower Mg concentration than the bulk composition. Thermal stability and structural transitions were investigated by differential scanning calorimetry. Several exothermic transitions, attributed to the crystallization of β and γ phases were observed. The present work provides the experimental basis for the development of detailed combustion and ignition models for these novel energetic materials.
Mechanical properties of blended single-wall carbon nanotube composites
Authors: Penumadu D. , Dutta A. , Pharr G. M. , Files B.
Published: March 2008

The improvement in mechanical properties of blended nanocomposites prepared using a low-viscosity, liquid epoxy resin and purified single-wall carbon nanotubes (SWCNTs) was evaluated. The macroscopic tensile stress–strain behavior for hybrid materials made with varying amounts of SWCNT was determined and showed little improvement in the breaking tensile strength. The corresponding variations in modulus and hardness were obtained using nanoindentation considering time effects and showed quantifiable but modest improvements. The small changes in the observed stiffness and breaking strength of carbon nanotube composites is due to the formation of bundles and their curvy morphology.
Atomic-scale simulations of cascade overlap and damage evolution in silicon carbide
Authors: Gao F. , Weber W. J.
Published: March 2008

In a previous computer-simulation experiment, the accumulation of damage in silicon carbide (SiC) from the overlap of 10 keV Si displacement cascades at 200 K was investigated, and the damage states produced following each cascade were archived for further analysis. In the current study, interstitial clustering, system energy, and volume changes are investigated as the damage states evolve due to cascade overlap. An amorphous state is achieved at a damage energy density of 27.5 eV/atom (0.28 displacements per atom). At low-dose levels, most defects are produced as isolated Frenkel pairs, with a small number of defect clusters involving only four to six atoms; however, after the overlap of five cascades (0.0125 displacements per atom), the size and number of interstitial clusters increases with increasing dose. The average energy per atom increases linearly with increasing short-range (or chemical) disorder. The volume change exhibits two regimes of linear dependence on system energy and increases more rapidly with dose than either the energy or the disorder, which indicates a significant contribution to swelling of isolated interstitials and antisite defects. The saturation volume change for the cascade-amorphized state in these simulations is 8.2%, which is in reasonable agreement with the experimental value of 10.8% in neutron-irradiated SiC.
Radiative properties of Eu(DBM)3Phen-doped poly(methyl methacrylate)
Authors: Liang Hao , Zheng Zhiqiang , Zhang Qijin , Ming Hai , Chen Biao , Xu Jie , Zhao Hui
Published: March 2008

Eu(DBM)3Phen-doped poly(methyl methacrylate) (PMMA) with different doping concentrations was prepared. Judd–Ofelt parameters Ω2 and Ω4 and the fluorescence intensity ratio R were computed from the fluorescence emission spectra and were analyzed. The radiative properties, such as transition probabilities, emission cross section (46.47 × 10−22 cm2), fluorescence branching ratios (90.34%), and radiative lifetime (1.704 ms), reveal that Eu(DBM)3 Phen-doped PMMA has potential use as a laser material.
Thin-film compound phase formation at Fe–Ge and Cr–Ge interfaces
Authors: Ndwandwe O. M. , Theron C. C. , Marais T. K. , Pretorius R.
Published: March 2008

Phase formation was studied in the Fe–Ge and Cr–Ge thin-film systems by means of Rutherford backscattering spectrometry and x-ray diffraction. In the Fe–Ge system, FeGe was the first phase to form while in the Cr–Ge system, Cr11Ge8 was found to form first. The results are compared with the predictions of the effective heat of formation model. Heats of formation were calculated using the Miedema model. The effect of the transformation enthalpy term ΔHtr, used to convert a semiconducting element into a hypothetical metallic one in the Miedema model, is also discussed.
Nanostructures in Ti processed by severe plastic deformation
Authors: Zhu Y. T. , Huang J. Y. , Gubicza J. , Ungár T. , Wang Y. M. , Ma E. , Valiev R. Z.
Published: March 2008

Metals and alloys processed by severe plastic deformation (SPD) can demonstrate superior mechanical properties, which are rendered by their unique defect structures. In this investigation, transmission electron microscopy and x-ray analysis were used to systematically study the defect structures, including grain and subgrain structures, dislocation cells, dislocation distributions, grain boundaries, and the hierarchy of these structural features, in nanostructured Ti produced by a two-step SPD procedure—warm equal channel angular pressing followed by cold rolling. The effects of these defect structures on the mechanical behaviors of nanostructured Ti are discussed.
Effect of hydrogen dilution on electronic properties of a-SiHx films deposited by low-frequency plasma
Authors: Kosarev A. I. , Torres A. J. , Zuniga C. , Abramov A. S. , Rosales P. , Sibaja A.
Published: March 2008

The effect of hydrogen dilution during plasma deposition on hydrogen incorporation and the optical and electrical properties of a-SiHx films were studied. The films were grown in capacitive low-frequency (f = 10 and 110 kHz) discharge in SiH4 diluted with H2, varying the ratio RH of the gases H2/SiH4 from RH = 0 to 40. The optical absorption coefficient and optical bandgap were changed with RH. Si–H bonding, studied by infrared spectroscopy, depended on RH. Hydrogen concentration in the films estimated from infrared spectra was in the range 20–30%. We observed the significant effect of RH on the temperature dependence of conductivity σ(T) and on the subgap absorption spectra measured by the constant photocurrent method. The reduction of subgap absorption up to 1.5 order of magnitude was observed with increasing RH.
Recovery of platinum using magnesium vapor
Authors: Okabe Toru H. , Yamamoto Sachiko , Kayanuma Yoshihiro , Maedaaff Masafumi
Published: March 2008

To develop an effective process for the recovery of precious metals from scrap, we investigated a new platinum extraction process using alloy formation by magnesium vapor and successive leaching with an aqueous solution. Pure platinum plates were reacted with magnesium vapor at constant temperatures ranging between 873 and 1173 K for 3 h, and Mg–Pt alloy samples were synthesized. The obtained Mg–Pt alloy was then dissolved in aqua regia or in an aqueous HCl solution at room temperature. Platinum was recovered from the leaching solution by conventional precipitation technique, and the platinum obtained by each process was analyzed chemically. It was found that 94% of the platinum was recovered by this process. After Mg vapor treatment, 100% of the platinum was dissolved when kept in aqua regia for 1 h, whereas only 25% of untreated pure platinum was dissolved when kept in aqua regia for 4 h.
Evaluation of nanoscale inhomogeneity in as-quenched state of Cu–Hf–Ti alloys
Authors: Saida J. , Osuna T. , Inoue A. , Onuma M.
Published: March 2008

The microstructure of the melt-spun Cu60Hf30Ti10 and Cu50Hf40Ti10 alloys was investigated. The high-resolution transmission electron microscopy (HRTEM) image in the Cu60Hf30Ti10 alloy reveals the existence of nanoscale inhomogeneity, which appears to originate from nanocrystalline particles. The compositional segregation with a diameter of approximately 5 nm was detected, and its size agrees with the scale of nanocrystalline particle. Small-angle x-ray scattering measurement of the melt-spun Cu60Hf30Ti10 alloy also indicates the development of nanoscale inhomogeneity with the same size as that of nanocrystalline particles. It is found that the Cu element is enriched in and Hf element is rejected from the nanocrystalline particles. Since the melt-spun Cu50Hf40Ti10 alloy, which has a similar alloy composition to that of the glassy region of melt-spun Cu60Hf30Ti10 alloy, has a homogeneous glassy structure without fringe contrast in the HRTEM image, it is suggested that the excess of Cu causes the nanoscale inhomogeneity with crystalline structure in the rapidly quenched Cu–Hf–Ti alloys.
Behavior of intermetallics in liquid Sn–Zn–Ag solder alloys
Authors: Song Jenn Ming , Lin Kwang Lung
Published: March 2008

This study investigated the characteristics of the intermetallics that appear in Sn–Zn–Ag solder alloys, particularly their behavior in molten solder during cooling and remelting. The results indicated that the intermetallics, which deplete the Zn-rich phase, were present in the form of inhomogeneous dendrites and consisted of two intermetallic phases, ε–AgZn3 and γ–Ag5Zn8. These Ag–Zn intermetallics formed as the primary dendrites upon cooling from temperatures slightly below 300 °C. These intermetallics transformed into coarse nodules with a stable, high Ag-content phase when isothermally heated at 250 °C. These massive intermetallic particles tended to settle at the bottom of the melt due to low buoyancy. Isothermal heating at slightly above 300 °C resulted in the rapid melting of these intermetallics. Subsequent quenching caused numerous fine dendritic intermetallics to form throughout the solder.
Influence of structure and chemistry on piezoelectric properties of lead zirconate titanate in a microelectromechanical systems power generation application
Authors: Eakins L. M. R. , Olson B. W. , Richards C. D. , Richards R. F. , Bahr D. F.
Published: March 2008

Lead zirconate titanate (PZT) films between 1 and 3 μm thick were grown using solution deposition techniques to study the effects of crystal structure and orientation on the direct piezoelectric output of these films on platinized Si membranes. By varying the chemistry of the film from Zr-rich to Ti-rich, the {100}/(111) relative intensity increased for films grown on randomly oriented Pt films. The 40:60 PZT had a tetragonal crystal structure and produced greater electrical output at a given strain than the rhombohedral film (Zr:Ti concentrations less than 50:50), while having a similar e31 constant, between 4.8 and 6.3 C/m2. Orientation and voltage output at a given strain were not strongly influenced by thickness in the ranges investigated. Defects in internal PZT/PZT crystallization interfaces were identified and include porosity on the order of tens of nm, with a corresponding depletion in Pb and accumulation of O at these interfaces. The {100} texture of rhombohedral films deposited upon (111) textured Pt films is significantly greater than the {100} texture of tetragonal films, which show both a {100} and {111} orientation on the same Pt film.
Laser-controlled precipitation of gold nanoparticles in silicate glasses
Authors: Jiang Xiongwei , Qiu Jianrong , Zeng Huidan , Zhu Congshan
Published: March 2008

We report on the observation of space-selective precipitation of gold nanoparticles in Au2O-doped silicate glass by a method of irradiation with an 800-nm femtosecond laser and further heat treatment. The irradiated region of the glass first became gray in color after irradiation with the femtosecond laser and then turned red after further heat treatment at around 520 °C, indicating that gold nanoparticles have precipitated in the irradiated region of the glass. A possible mechanism has been suggested that the Au+ ions in the region irradiated are reduced to Au0 atoms by the femtosecond laser, and then the Au0 atoms accumulate to form gold nanoparticles with the glass sample heat treated. The observed phenomenon should have potential applications in the fabrication of ultrafast all-optical switches.
Incongruent reduction of tungsten carbide by a zirconium-copper melt
Authors: Grzesik Zbigniew , Dickerson Matthew B. , Sandhage Ken H.
Published: March 2008

The reduction of tungsten carbide (WC) to elemental tungsten by reaction with a Zr–Cu melt was examined. Dense WC disks were immersed in a vertical orientation in molten Zr2Cu at 1150–1400 °C for 1.5–24 h. Continuous, adherent layers of W and ZrC formed at WC/melt interfaces. The rates of thickening of the W and ZrC product layers were examined as a function of reaction time and temperature and position along the vertical WC surface. Such kinetic data, along with microstructural analyses, indicate that the incongruent reduction of tungsten carbide is likely to be controlled by carbon diffusion through one or both of the product layers.
Glass formation in a (Ti, Zr, Hf)–(Cu, Ni, Ag)–Al high-order alloy system by mechanical alloying
Authors: Zhang L. C. , Shen Z. Q. , Xu J.
Published: March 2008

In this work, glass formation under high-energy ball milling was investigated for a (Ti0.33Zr0.33Hf0.33)50(Ni0.33Cu0.33Ag0.33)40Al10 high-order alloy system with equiatomic substitution for early and late transition-metal contents. For comparison, an amorphous alloy ribbon with the same composition was prepared using the melt-spinning method as well. Structural features of the samples were characterized using x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Mechanical alloying resulted in a glassy alloy similar to that obtained by melt spinning. However, the glass formation was incomplete, and a small amount of unreacted crystallites smaller than 30 nm in size still remained in the final ball-milled product. Like the melt-spun glass, the ball-milled glassy alloy also exhibited a distinct glass transition and a wide supercooled liquid region of about 80 K. Crystallization of this high-order glassy alloy proceeded through two main stages. After the primary nanocrystallization was completed, the remaining amorphous phase also behaved as a glass, showing a detectable glass transition and a large supercooled liquid region of about 100 K.
Microstructural evolution of low-dose separation by implanted oxygen materials implanted at 65 and 100 keV
Authors: Jeoung Jun Sik , Anderson Philip , Seraphin Supapan
Published: March 2008

Thin separation by implanted oxygen substrates are attractive candidates for low-power, low-voltage electronic devices and can be obtained by low-dose, low-energy oxygen–ion implantation. We report in this study a variation of the process parameters that have never been investigated before, particularly for implantation with a high current density implanter. Characterization of the sample sets by transmission electron microscopy, secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS) shows an optimum dose of 3.0 to 3.5 × 1017 O+/cm2 at 100 keV for forming a continuous buried oxide (BOX) layer compared to 2.5 × 1017 O+/cm2 at 65 keV. At this optimum condition for 100 keV, the thickness of Si top layers and BOX layers is in the range of 175–185 nm and 70–80 nm, respectively. Analysis of the breakdown voltage of small area capacitors shows a breakdown field in the range of 6.0–7.0 MV/cm, which is adequate for low-power, low-voltage devices. SIMS analysis shows that the maximum oxygen concentration of as-implanted samples is located at depths of 160 and 240 nm for the implantation energy of 65 and 100 keV, respectively. A significant redistribution of oxygen occurs at temperatures above 1300 °C during the ramping process. RBS analysis showed that a high-quality crystalline Si layer was produced after annealing at 1350 °C for 4 h. The defect density determined by the chemical etching method was found to be very low (<300 defects per cm2) for all samples with a dose range of 3.0 × 1017 O+/cm2 to 6.0 × 1017 O+/cm2 implanted at 100 keV. However, a 65 keV sample with a dose of 4.5 × 1017 O+/cm2 contains about 109 defects per cm2. The larger defect density in the 65-keV sample may be due to the shift of oxygen depth distribution toward the surface, resulting in easier defect extension during the annealing process. The oxide precipitates in the Si overlayer play a key role in defect reduction by blocking the extension of dislocations to the surface.
Interfacial and twin boundary structures of nanostructured Cu–Ag filamentary composites
Authors: Lee K. H. , Hong S. I.
Published: March 2008

A high-resolution transmission electron microscope was used to study the interfacial and twin boundary structure of nanostructured Cu–Ag filamentary composites. Copper matrix and silver filaments have the orientation relationship {111}Cu∥{111}Agand 〈111〉Cu∥〈111〉Ag. In some regions, twin bands propagated through the silver filaments with some boundary steps at the matrix/filament interface, and the silver filament appeared to be kinked in the twin band in the same direction as the twinning shear. This suggests that twins propagated after the formation of silver filament, and twin bands were deformation twins. At the matrix/filament interface, misfit interface dislocations were introduced periodically to relieve the misfit strain. The distance between interfacial misfit dislocations along the matrix/filament interface in the longitudinal section was measured to be 1.88 nm, which is in good agreement with that (1.81 nm) calculated based on lattice misfit. In Cu–Ag nanocomposites, the spacing between Moire fringes was found to be quite close to that between interfacial misfit dislocations.
Electrodeposition of eutectic Sn–Zn alloy by pulse plating
Authors: Lin Kwang-Lung , Sun Li-Min
Published: March 2008

A uniform deposition of a Sn–Zn alloy deposit was achieved by pulse plating. Apparently, the relative composition of Sn and Zn in the deposit was affected by the bath compositions and pulse condition. A pulse-plating condition of 99.9 ms on-time and 1.0 ms off-time gave rise to a eutectic Sn–Zn deposit, with a eutectic temperature of 198.8 °C (as analyzed by differential scanning calorimetry) and a uniform composition distribution across the deposit. A mechanism for explaining the pulse-deposition behavior of the Sn–Zn eutectic deposit was proposed. A longer off-time period, 99.9 ms versus 0.1 ms, resulted in a nodular, yet thinner deposit.
Microcolumn development on titanium by multipulse laser irradiation in nitrogen
Authors: György E. , del Pino A. Pérez , Serra P. , Morenza J. L.
Published: March 2008

We report the growth of titanium nitride microcolumns under multipulse Nd:yttrium aluminum garnet (λ = 1.064 μm, τ ∼ 300 ns, ν = 30 kHz) laser irradiation of titanium targets in nitrogen atmosphere. The laser intensity value was chosen below the single-pulse melting threshold of titanium. The evolution with the number of laser pulses of the target morphology, crystalline state, and chemical composition at the surface as well as in depth were investigated by scanning electron microscopy, x-ray diffractometry, Raman spectroscopy, and wavelength dispersive x-ray spectroscopy. Under the action of the laser pulses, during progressive surface nitridation, an initial rippled morphology developed, which evolved with further irradiation to TiN microcolumns. In-depth investigations showed a granular zone beneath the surface consisting of rutile and anatase phase TiO2, followed by a compact needlelike layer of titanium until the interface with the unaffected target material.
Addition of TiO2 on the electrical properties of buried resistors in low-temperature cofired ceramics
Authors: Cheng Ching-Tai , Lin Jiang-Tsair , Hung Ying-Chang
Published: March 2008

Effects of TiO2 addition on the conduction mechanism of buried resistors in low temperature cofired ceramics were investigated. Remarkable increases in electrical resistivity and attractive decreases in the temperature coefficient of resistance were observed by the addition of TiO2 for all ratios of RuO2/glass investigated. Such significant effects can be attributed to a larger separation observed between RuO2 particles. The results were compared with the calculated data from theoretical model of tunneling barrier, showing that good agreement could be obtained. In addition, while the distance separation was taken into account as a fixed constant, it was found that the resistivity of buried resistor decreased with increasing TiO2 contents in the glass at higher weight ratios of TiO2/glass. This result implies that a substitution takes place due to the Si+4 displacement by Ti+4 in the glass, resulting in a looser network structure and a lower resistivity value.
Novel silver/mica multilayer compressive seals for solid-oxide fuel cells: The effect of thermal cycling and material degradation on leak behavior
Authors: Chou Yeong-Shyung , Stevenson Jeffry W.
Published: March 2008

A novel Ag/mica compressive seal was thermally cycled between 100 °C and 800 °C in air to evaluate its stability. The novel Ag/mica compressive seal was composed of a naturally cleaved Muscovite mica sheet and two thin silver layers, and was reported in a previous study to have very low leak rates at 800 °C. In the present study, we examined the thermal cycle stability of the Ag/mica-based compressive seals pressed between mating couples with large and small mismatch in thermal expansion. For comparison, thermal cycling also was conducted on plain mica as well as plain silver only. In addition, the results were compared with published data of a similar mica seal using glass instead of Ag as the interlayers. For mating materials of large mismatch in thermal expansion coefficient (CTE; Inconel/alumina), the Ag/mica seal showed lower leak rates than the plain mica. For mating materials of small mismatch in CTE (SS430/alumina), the leak rates were similar for both the Ag/mica and the plain mica seal. Scanning electron microscopy was used to characterize the microstructure of the mica after thermal cycling. Microcracks, fragmentation, and wear-particle formation were observed on the mica and were correlated to the leak behavior. Overall, the novel Ag/mica seals present good thermal cycle stability for solid-oxide fuel cells, although the leak rates were greater than the corresponding mica seals with glass interlayers.
In situ deposition of iron nanoparticles on transmission electron microscopy grid in furnace aerosol reactor
Authors: Park Kyun Young , Park Jong Kwan , Lim Sang Hwa
Published: March 2008

In the current work, a device was proposed for the first time to deposit the particles in situ on a transmission electron micrography grid within furnace aerosol reactors. The device was successfully tested on iron particles produced by thermal decomposition of Fe(CO)5 at 600 °C in a quartz tube heated by an electric heater. The particle depositions were made at four different spatial locations in the axial direction and investigated by transmission electron microscopy. At the reactor inlet, chain agglomerates of 2–3-nm particles were observed. At 19 cm from the inlet, the particles within the agglomerate structures fully coalesced by sintering, and at 32 cm (reactor outlet), polyhedral particles of about 100 nm in diameter emerged from the sintered body.
A new Mg65Cu7.5Ni7.5Zn5Ag5Y10 bulk metallic glass with strong glass-forming ability
Authors: Ma H. , Ma E. , Xu J.
Published: March 2008

We report a new Mg-based bulk metallic glass-forming alloy: Mg65Cu7.5Ni7.5Zn5 Ag5Y10. The alloy exhibits a glass-forming ability significantly stronger than all previously discovered Mg-based glass formers. Fully glassy rods 9 mm in diameter can be obtained by using copper mold casting. The critical cooling rate for glass formation was estimated to be <50 Ks−1. The reduced glass-transition temperature (Trg) of the glass was determined to be 0.59.
Ultralow dielectric constant nickel–zinc ferrites using microwave sintering
Authors: Peelamedu Ramesh , Grimes Craig , Agrawal Dinesh , Roy Rustum , Yadoji Purushotham
Published: March 2008

Ultralow dielectric constant values were measured on Ni–Zn ferrites prepared using Fe2O3 as a starting material and sintered in a microwave field. Significant differences in microstructure, magnetic, and dielectric properties were observed between microwave-sintered Ni–Zn ferrites prepared using Fe3O4 (T34) and those starting with Fe2O3 (T23) ingredients. Higher magnetization values observed in T23 ferrite are attributed to large grain size, possibly containing abundant domain walls and the presence of fewer Fe2+ ions. The ultralow dielectric constant values observed on T23 ferrites show that this procedure is highly suitable to prepare Ni–Zn ferrites for high-frequency switching applications.
Fabrication of nanoporous tungsten oxide by galvanostatic anodization
Authors: Mukherjee Niloy , Paulose Maggie , Varghese Oomman K. , Mor G. K. , Grimes Craig A.
Published: March 2008

Nanoporous tungsten oxide (WO3), with pores of 50 to 100 nm in diameter, has been obtained by galvanostatic (constant-current) anodization of tungsten in a 0.25 M oxalic acid electrolyte. At room temperature, the optimum current density for nanoporous formation is approximately 6.5 to 8 mA/cm2. Monitoring of the anodization voltage during the fabrication process reveals a close match with the theoretical model of Parkhutik et al. [V.P. Parkhutik and V.I. Shershulsky, J. Phys. D 25, 1258 (1992)] for growth of nanoporous Al2O3. The as-anodized films are amorphous and crystallize upon annealing at 350 °C in an oxygen atmosphere.
Effects of mixed abrasives in chemical mechanical polishing of oxide films
Authors: Lu Zhenyu , Lee Seung-Ho , Gorantla Venkata R. K. , Babu S. V. , Matijević Egon
Published: March 2008

Thermal oxide covered silicon wafers were polished with slurries containing (i) only nano-sized particles of ceria, monodispersed colloidal spherical silica, or hematite of different shapes, (ii) a binary mixture of the same nano-sized and uniform colloidal particles, and (iii) the same colloids coated with nano-sized ceria. The procedures for the preparation of the coated particles are described in this article. The polish rates and surface qualities were in all cases higher with mixed slurries, and even more so with coated particles. The performance of composite systems also depended on the shape of the particles, cubic ones being the most and spheres least efficient. Experimental results indicated that ceria in mixtures was responsible for the enhanced polish process, while core materials enhanced a closer contact of nano-sized particles with the wafer. In general, the polish rates were higher with the larger contact area between the abrasives and the wafer. This mechanism was further verified by polishing oxide wafers on 3-M fixed abrasive pads, which have cylindrical structures with flat surfaces.
Synthesis of nanocrystalline aluminum–gallium nitride (AlxGa1−xN; x = 0.1 to 0.5) with oxide precursors via ammonolysis
Authors: Faulhaber Sabine , Loeffler Lars , Hu Jerry , Kroke Edwin , Riedel Ralf , Lange Fred F.
Published: March 2008

Oxygen-containing precursor systems for the synthesis of mixed aluminum–gallium nitride (AlxGa1−xN with x = 0.1 to 0.5) through ammonolysis (heat treatment under ammonia) were evaluated. Three different precursor systems were studied: (i) aluminum isopropoxide (aluminum sec-butoxide)/gallium isopropoxide hydrolyzed with excess water and cross-linked with 1,6-hexanediol, (ii) aluminum–gallium hydroxide coprecipitated from aluminum–gallium nitrate solution, and (iii) spray-dried aluminum–gallium nitrate solutions. The specimens were heat-treated between 700 °C and 1100 °C and were characterized mainly by x-ray diffraction, nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). NMR was used to follow the conversion of oxygen to nitrogen bonds. TEM in combination with energy-dispersive x-ray spectroscopy was used to determine the solid-solution composition for separated particles. It is possible to synthesize a mixed hexagonal (Al,Ga)N with crystallite sizes in the range of ∼10 nm from all three precursor systems, but all products contained larger GaN crystals ranging from 20 nm (alkoxide-derived) to 200 nm (hydroxide-derived) and a fraction of untransformed Al–O bonds; e.g., (amorphous or γ-phase) Al2O3.
Shape and energies of a dynamically propagating crack under bending
Authors: Sherman Dov , Be'ery Ilan
Published: March 2008

We report on the exact shape of a propagating crack in a plate with a high width/thickness ratio and subjected to bending deformation. Fracture tests were carried out with brittle solids—single crystal, polycrystalline, and amorphous. The shape of the propagating crack was determined from direct temporal crack length measurements and from the surface perturbations generated during rapid crack propagation. The shape of the crack profile was shown to be quarter-elliptical with a straight, long tail; the governing parameter of the ellipse axes is the specimen's thickness at most length of crack propagation. Universality of the crack front shape is demonstrated. The continuum mechanics approach applicable to two-dimensional problems was used in this three-dimensional problem to calculate the quasistatic strain energy release rate of the propagating crack using the formulations of the dynamic energy release rate along the crack loci. Knowledge of the crack front shape in the current geometry and loading configuration is important for practical and scientific aspects.
Mechanical properties and low-temperature aging of tetragonal zirconia polycrystals processed by hot isostatic pressing
Authors: Muñoz-Saldaña J. , Balmori-Ramírez H. , Jaramillo-Vigueras D. , Iga T. , Schneider G. A.
Published: March 2008

The influence of grain size and density of yttria-tetragonal zirconia polycrystals (Y-TZPs) ceramics on mechanical properties and on low-temperature aging degradation (LTD) in air and in hot water was investigated. A TZP powder containing 3 mol% Y2O3 was consolidated by slip casting and densified by the sintering/hot isostatic pressing (HIP) method. Only the presintered samples that contained less than 0.15% open porosity reached near full density after HIP. The best conditions to reach full density were found to be attained by presintering and HIP both at 1400 °C. At these conditions, some of the best mechanical properties such as modulus of rupture and Weibull modulus reached 1397 ± 153 MPa and, 10.6, respectively. These values were clearly higher than those obtained from sintered bodies and samples hot isostatically pressed at 1600 °C. Aging degradation of 3Y-TZP materials can be avoided through microstructural design. Fully dense materials with a critical grain size <0.36 μm did not show any evidence of degradation after extreme aging conditions at pressurized autoclaving in hot water at 100, 200, and 260 °C for 8 h. We propose a criterion to predict degradation in air as well as in hot water for the characterized materials based on the microstructure and density control of the samples.
Self-reinforced Y-α-sialon ceramics with barium.aluminosilicate as an additive
Authors: Ye Feng , Iwasa Mikio , Su Caili , Chen Sheng
Published: March 2008

Y-α-sialons (Y0.333Si10Al2ON15) were prepared by hot pressing using 5 wt.% BaAl2Si2O8 as an additive. The results showed that barium aluminosilicate not only.served as a liquid-phase sintering aid to promote densification, but also facilitated the.development of elongated α-sialon grains. The obtained self-toughened α-sialon was.both hard and tough. The Vickers hardness, flexural strength, and fracture toughness.are 18.9 GPa, 802 MPa, and 6.0 Mpam1/2, respectively. Post heat treatment could.promote the growth of elongated α-sialon grains, hence further increasing its.toughness.
Compound growth and microstructure of carbon nanotube
Authors: Zhang Zaoli , Ouyang Lian , Shi Zujin , Gu Zhennan
Published: March 2008

The compound growth of single-walled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT), which formed a nanotube cable, was achieved by the chemical vapor deposition of natural gas on an Fe catalyst supported on SiO2–Al2O3 hybrid materials at 950 °C. The microstructure of nanotubes was characterized by high-resolution transmission electron microscopy (HRTEM). The SWCNTs encapsulated inside MWCNTs can be two, three, or even more in quantity with a diameter range from 1.0 nm to 2.0 nm. The diameter of SWCNT is controlled by the size of the catalyst nanoparticles. Some bundles of SWCNT and double-walled nanotubes were also found. The possible mechanism of compound growth is briefly discussed.
Distribution of chlorine in quartz determined by neutron beam focusing prompt gamma activation analysis and micro-x-ray fluorescence
Authors: Chen-Mayer H. Heather , Heward William J. , Paul Rick L. , Klug Frederic J. , Gao Yan
Published: March 2008

This paper describes two spatially resolved analytical techniques for chlorine distribution analysis in high-purity quartz glass. The first, prompt gamma activation analysis (PGAA), to which most of this paper is devoted, is emphasized because a new neutron focusing technique has made this study feasible. Despite the low concentration of chlorine, the neutron absorption cross section for Cl is about 200 times greater than for Si, making Cl in Si an ideal system for PGAA. The second technique described is micro-x-ray fluorescence using a laboratory-based spectrometer. The results from each technique and their ability to quantify low levels of chlorine (400–1800 μg Cl/g SiO2) are described.
Rapid structural and chemical characterization of ternary phase diagrams using synchrotron radiation
Authors: Specht E. D. , Rar A. , Pharr G. M. , George E. P. , Zschack P. , Hong H. , Ilavsky J.
Published: March 2008

A technique based on synchrotron radiation was developed that allows for rapid structural and chemical characterization of ternary alloys over a wide range of composition. The technique was applied to isothermal sections of the Cr–Fe–Ni system grown on Al2O3(0001) sapphire substrates by sequential deposition of layers of graded.thickness followed by annealing to interdiffuse the elements. A film spanning the Cr–Fe–Ni ternary system was measured in 4 h at a resolution of 2 at.% by rastering the sample under a focused beam of synchrotron radiation while simultaneously measuring the diffraction pattern with a charge-coupled device detector to determine crystallographic phases, texture, and lattice parameters and also measuring the x-ray fluorescence with an energy-dispersive detector to determine elemental composition. Maps of phase composition and lattice parameter as a function of composition for several annealing treatments were found to be consistent with equilibrium values. The technique will be useful in combinatorial materials design.
Hydrogen storage in Ti–V-based body-centered-cubic phase alloys
Authors: Yu Xuebin , Wu Zhu , Xia Baojia , Huang Taizhong , Chen Jinzhou , Wang Zaosong , Xu Naixin
Published: March 2008

The hydrogen storage performance of a single body-centered-cubic phase Ti-40V-10Cr-10Mn alloy was investigated. A hydrogen absorption capacity of 4.2 wt.% (H/M = 2.1), which is the highest value at room temperature reported so far, was achieved at 293 K under modest pressure (3 MPa) for this as-cast alloy. The effective hydrogen capacities of this alloy were 2.6, 2.8, and 3.2 wt.%, respectively, at 353, 393, and 523 K, which gave hope of bringing Ti-V-based alloys into the reach of practical application for onboard hydrogen storage systems in fuel cell-powered vehicles.
Strength enhancement of single crystal laser components
Authors: Shafer K.E. , Eakins D.E. , Bahr D.F. , Norton M.G. , Lynn K.G.
Published: March 2008

The effect of chemical etching on the surface roughness and fracture strength of Nd:yttrium-aluminum-garnet single crystals was investigated. Etching the laser host material in a 1:1 mixture of concentrated sulfuric and phosphoric acid at elevated temperatures enabled material removal from the surface of laser rods cored from single-crystal boules. The roughness on the rod surface increased from the as-drilled condition after etching, but after 17 μm of material was removed, the roughness remained approximately constant. The modulus of rupture increased from 133-530 MPa when 87 μm of material was removed by the chemical etching procedure.
Composition and Growth-Temperature Effect on the Microstructure of Epitaxial La1−x Srx MnO3 (x = 0, 0.2) Thin Films on (001) LaAlO3
Authors: Jiang J.C. , Meletis E.I. , Gnanasekar K.I.
Published: March 2008

La0.8Sr0.2MnO3 (LSMO) and LaMnO3 (LMO) thin films epitaxially grown on (001) LaAlO3 substrate at 700 and 800°C were studied using cross-section and plan-view transmission electron microscopy. In both LSMO and LMO films deposited at 700°C, a two-layered structure was observed: a continuous cubic perovskite layer epitaxially grown on the substrate followed by epitaxially grown orthorhombic column nanostructures. The orthogonal nano columns in LSMO were very well defined with a narrow size distribution. The LMO films exhibited a somewhat distorted orthogonal shape for the nanostructured columns and a wider size distribution. LSMO and LMO epitaxial films deposited at 800°C consisted of only a continuous single layer of cubic perovskite. These results reveal that formation of epitaxial column nanostructures in the La1-xSrxMnO3 thin films strongly depends on the growth temperature. Sr substitution on La sites in La1-xSrxMnO3 can improve uniformity of column size distribution and perfection of the orthogonal shape of nano columns.
High-yield synthesis of carbon coils on tungsten substrates and their behavior in the presence of an electric field
Authors: Jiao Jun , Einarsson Erik , Tuggle David W. , Love Logan , Prado Josie , Coia George M.
Published: March 2008

We report an effective procedure for fabricating carbon microcoils and nanocoils with three-dimensional spiral structures in high yield by nickel (Ni)-catalyzed thermal decomposition of acetylene. The Ni catalyst particles used in this preparation were electrochemically deposited onto tungsten substrates. Springlike coils having low pitch and micrometer-scale diameters and ropelike coils having higher pitch and nanometer-scale diameters were observed. Electrical and optical properties were investigated by employing a field-emission probe system equipped with an optical spectrometer. In an applied field above 1.5 V/μm, significant electron emission was observed from individual ropelike nanocoils. The approximately linear slope of the corresponding Fowler-Nordheim plot denotes predominately field-emission behavior. During measurement, individual carbon coils aligned themselves along the electric field, exhibiting a natural resonance on some occasions. As the field strength increased above 2.5 V/μm, the emission-current density for a single nanocoil was measured to be on the order of 104 A/cm2. This high-current density caused Joule heating, resulting in strong photon emission by incandescence.