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We report on the growth of nanowires and unusual hollow microducts of tungsten oxide by thermal treatment of tungsten films in a radio frequency H2/Ar plasma at temperatures between 550 and 620 °C. Nanowires with diameters of 10–30 nm and lengths between 50 and 300 nm were formed directly from the tungsten film, while under certain specific operating conditions hollow microducts having edge lengths∼0.5 μm and lengths between 10 and 200 μm were observed. Presence of a reducing gas such as H2 was crucial in growing these nanostructures as were trace quantities of oxygen, which was necessary to form a volatile tungsten species. Preferential restructuring of the film surface into nanowires or microducts appeared to be influenced significantly by the rate of mass transfer of gas-phase species to the surface. Nanowires were also observed to grow on tungsten wires under similar conditions. A surface containing nanowires, annealed at 500 °C in air, exhibited the capability of sensing trace quantities of nitrous oxides (NOx).
After creep failure at 1300 °C, silica-based nanofibers with diameters of ∼250 nm and lengths of up to a few tens of microns were observed on the fracture surfaces of Ti3SiC2. A possible mechanism for the formation of these fibers is proposed.
The effects of residual stress induced during the annealing process on the microstructural evolution and electrical properties of Pb(Zr,Ti)O3 (PZT) films were investigated. PZT films were deposited on platinized silicon substrates by the radio frequency magnetron sputtering method using a single oxide target. Compressive stress was induced in the film by bending the silicon substrate during sputtering using a specially designed substrate holder and subsequently annealing the film without the holder. Without the residual stress, the PZT film was severely cracked when it was thicker than 2 μm due to the thermal expansion mismatch between the PZT and the Si substrate. On the other hand, when the residual stress was applied, no cracks were detected in the film for thicknesses of up to 4 μm. The suppression of crack formation was attributed to the residual compressive stress that compensated for the tensile stress generated during and/or after the annealing process. The electrical properties of the PZT film with the residual stress were improved compared to those of the PZT film without the residual stress.
Chorioamnion, the membrane surrounding a fetus during gestation, is a structural soft tissue critical for maintaining a successful pregnancy and delivery. However, the mechanical behavior of this tissue membrane is poorly understood. The structural component of chorioamnion is the amnion sublayer, which provides the membrane’s mechanical integrity via a dense collagen network and is the focus of this investigation. Amnion uniaxial and planar equi-biaxial tension testing was performed using cyclic loading and stress-relaxation. Cyclic testing demonstrated dramatic energy dissipation in the first cycle followed by less hysteresis on subsequent cycles. Fractional energy dissipation per cycle was strain dependent, with greatest dissipation at small strain levels. Stress-relaxation testing demonstrated a level-dependent response and continued relaxation after long relaxation times. A nonlinear viscoelastic (separable) hereditary integral approach was inadequate to model the amnion response due to intrinsic coupling of the strain- and time-dependent responses.
Mechanically alloyed Mo44Si26Ta5Zr5Fe3Co12Y5 multicomponent glassy alloy exhibits an exceptionally high glass transition temperature of 1202 K and a crystallization temperature of 1324 K, as well as an ultrahigh hardness of 18 GPa. This example is used to demonstrate metallic glasses that possess extraordinary thermal stability and ultrahigh strength and, at the same time, a wide supercooled liquid region (122 K) that is needed for processing into bulk forms through powder metallurgy routes.
The degree of undercooling of Sn in near eutectic, SnAgCu solder balls upon cooling at a rate of 1 °C/s from the melt was examined and found to increase linearly with inverse nominal sample diameter (for balls of radius between 100 and 1000 μm). The mean undercooling for SnAgCu solder balls in a flip chip assembly was 62 °C. The microstructures of these different samples were examined by means of scanning electron microscopy. The Sn dendrite arm width was observed to monotonically increase with ball diameter, indicating a possible dependence of the mechanical response of such solder balls upon size.
The microwave dielectric properties of ceramics based on Ba[(Mg1/3Ta2/3)1−xTix]O3 (BMT-BT) and Ba[(Mg1−xZnx)1/3Ta2/3]O3 (BMT-BZT) were investigated as a function of composition x. In BMT-BT solid solution, the dielectric properties deteriorated with increasing concentration of Ti substitution at the B-site of BMT. A correlation was established between the quality factors of the solid solution phases and their tolerance factor. In BMT-BZT solid solution, where both the end compounds are ordered perovskites, the unit cell expands with increasing mole fraction of the Zn in Mg site of BMT while the dielectric constant increases monotonously from 24.8 (for BMT) to 29.7 (BZT). In BMT-BZT solid solution, the quality factor reaches a maximum (Qu·f = 109,900 GHz) for 60 mol/ of BZT.
The crystallization behavior of melt-spun amorphous Al92−xNi8Lax (x = 4 to 6) alloys was investigated by means of differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Crystallization kinetics were analyzed by Kissinger and Johnson–Mehl–Avrami approaches. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding structural evolution. The results show that the variation of La content from Al88Ni8La4 to Al86Ni8La6 has significant influence on the crystallization pathways from amorphous to stable crystalline phases and on the evolution of microhardness with temperature. The two stages of crystallization in Al88Ni8La4 and Al87Ni8La5 alloys correspond to formation of fcc-Al and Al11La3, Al3Ni, Al3La. In Al86Ni8La6, three stages of crystallization are observed which correspond to formation of a metastable phase, fcc-Al, Al11La3, Al3Ni, and Al11La3, Al3Ni, Al3La, and decomposition of a metastable phases to stable crystalline phases.
A simple solution combustion synthesis technique was explored to produce Tb3+-doped Lu3Al5O12 (LuAG:Tb) phosphor with particle size in the range from about 25 to 900 nm by using glycine, urea, and the mixture of them as fuels. The effects of processing parameters such as type of fuel, fuel-to-oxidizer ratio and the composition of the complex fuel were studied. An increase in phosphor brightness and a decrease in crystallization temperature with increasing urea content in the fuel were observed. The integrated emission intensity ratio of the 5D3–7Fj transition to the 5D4–7Fj transition as a function of Tb concentration in LuAG was also investigated. It is very interesting that the growth process of the particles exhibited two steps when the content of urea in the complex fuel increased from 0 to 1.0. By tailoring the glycine-to-urea ratio in the fuel, an excellent fuel was found and high performance phosphors were obtained.
A systematic investigation and comparison of the photoluminescence (PL) quantum yields of six erbium(III) organic complexes are reported. We demonstrated that the PL quantum yield could be significantly improved by getting rid of OH and CH groups in the complexes. Moreover, perfluooctanoic acid with neither OH nor CH groups was used as a ligand to form complex with Er3+. The quantum yield of the newly synthesized erbium(III) complex was found to be as high as 2%, 100 times higher than ever reported.
The cationic surfactant cetyltrimetylammonium bromide was used to synthesize mesostructured γ–Al2O3. The effects of the surfactant concentration and of the sol aging (at 95 °C for 24 h) were studied by x-ray powder diffraction, nuclear magnetic resonance, transmission electron microscopy, and analysis of the low-temperature nitrogen adsorption-desorption isotherms. Mesostructured alumina with wormhole morphology and amorphous walls was obtained through the precipitation by ammonium hydroxide of a 0.1 M aluminum nitrate aqueous solution in presence of 0.1 M surfactant. The pore size was smaller than 5 nm. After digesting the milky suspension under atmospheric pressure at 95 °C, a crystallized boehmite-surfactant phase, with fiber morphology, is formed which at 550 and 700 °C is transformed into a highly porous γ−Al2O3. A similar evolution was observed using 0.01 M CTAB solution and aging. Pore volume up to 1.1 cm3/g and pore size up to 16 nm were obtained. Without surfactant, the same aging treatment led to aggregated fibers: the pore size is less than 8 nm and the pore volume is smaller than 0.6 cm3/g. The γ-alumina surface area is determined mainly by the organization generated by the surfactant and to a lesser extent by the boehmite precursor particle size. From the point of view of catalyst preparation, the surfactant at the concentration of 0.01 M in 0.1 M aluminum nitrate and the aging treatment in solution play a beneficial role.
Nanoindentation technique was used to measure the strain rate sensitivity (m) of a nanocrystalline Cu-Ni-P alloy prepared by means of electrodeposition. The m value decreases from 0.034 to 0.018 when the nominal grain size increases from 7 nm to 33 nm. Both m values of the alloy are obviously lower than those of the pure Cu with similar grain size, implying that P segregation at grain boundaries might play a key role in retarding grain boundary activities as compared to pure Cu samples.
Y2O3:Eu nanophosphors were prepared by flame synthesis using ethanol or water as precursor solutions. The effects of precursor solvents and flame temperature on particle size, morphology, and photoluminescence intensity were investigated. The results showed that flame synthesis using ethanol solution could produce nanoparticles with better homogeneity, smoother surface structure, and stronger photoluminescence intensity than using water. It was found that the concentration quenching limit of the as-prepared nanophosphors from both ethanol and water solution was 18 mol% Eu, which is higher than the reported limit at similar particle size. The x-ray diffraction (XRD) spectra showed that the ethanol precursor solvent produced monoclinic phase Y2O3:Eu nanoparticles at a lower flame temperature than previously reported. It was also shown that the particle size could be controlled by varying the precursor concentration and flame temperature.
PbxBa1−xTiO3 (0.2 ⩽ x ⩽ 1) thin films were deposited on single-crystal MgO as well as amorphous Si3N4/Si substrates using biaxially textured MgO buffer templates, grown by ion beam-assisted deposition (IBAD). The ferroelectric films were stoichiometric and highly oriented, with only (001) and (100) orientations evident in x-ray diffraction (XRD) scans. Films on biaxially textured templates had smaller grains (60 nm average) than those deposited on single-crystal MgO (300 nm average). Electron backscatter diffraction (EBSD) has been used to study the microtexture on both types of substrates and the results were consistent with x-ray pole figures and transmission electron microscopy (TEM) micrographs that indicated the presence of 90° domain boundaries, twins, in films deposited on single-crystal MgO substrates. In contrast, films on biaxially textured substrates consisted of small single-domain grains that were either c or a oriented. The surface-sensitive EBSD technique was used to measure the tetragonal tilt angle as well as in-plane and out-of-plane texture. High-temperature x-ray diffraction (HTXRD) of films with 90° domain walls indicated large changes, as much as 60%, in the c and a domain fractions with temperature, while such changes were not observed for PbxBa1−xTiO3 (PBT) films on biaxially textured MgO/Si3N4/Si substrates, which lacked 90° domain boundaries.
In the current work, a novel combustion method is demonstrated for the direct synthesis of nanocomposite materials. Specifically doped tin dioxide (SnO2) powders were selected for the demonstration studies due to the key role SnO2 plays in semiconductor gas sensors and the strong sensitivity of doped SnO2 to nanocomposite properties. The synthesis approach combines solid and gas-phase precursors to stage the decomposition and particle nucleation processes. A range of synthesis conditions and four material systems were examined in the study: gold–tin dioxide, palladium–tin dioxide, copper–tin dioxide, and aluminum–tin dioxide. Several additive precursors were considered including four metal acetates and two pure metals. The nanocomposite materials produced were examined for morphology, phase, composition, and lattice spacing using transmission and scanning electron microscopy, x-ray diffractometry, and energy-dispersive spectroscopy. The results using the combustion synthesis approach indicate good control of the nanocomposite properties, such as the average SnO2 crystallite size, which ranged from 5.8 to 17 nm.
Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposition (MOD) precursor routes have been studied on textured Ni-based tape substrates. Even though films processed by both techniques showed similar property characteristics, the MOD-derived samples developed a high degree of texture alignment at significantly lower temperatures. Both precursor chemistries resulted in exceptionally dense, pore-free, and smooth microstructures, reflected in the cross-sectional and plan-view high-resolution scanning and transmission electron microscopy studies. On the MOD GZO buffered Ni–3at.% W (Ni–W) substrates with additional CeO2/YSZ sputtered over layers, a 0.8-μm-thick YBa2Cu3O7−δ (YBCO) film, grown by an ex situ metalorganic trifluoroacetate precursor method, yielded critical current, Ic (77 K, self-field), of 100 A/cm width. Furthermore, using pulsed-laser deposited YBCO films, a zero-field superconducting critical current density, Jc (77 K), of 1 × 106 A/cm2 was demonstrated on an all-solution, simplified CeO2(MOD)/GZO(MOD)/Ni–W architecture. The present study establishes GZO buffers as a candidate material for low-cost, all-solution coated conductor fabrication.
Titration of copper acetate solution with a dilute NaOH solution to pH 6.5 and subsequent aging at 313 K yielded copper hydroxide acetate with an analytical composition of Cu2(OH)3.1(OCOCH3)0.9nH2O (n ∼ 0.7) and layered discoid crystals. The chemical composition, structure, and holistic trend in thermal behavior are similar to those of the previously known Cu2(OH)3(OCOCH3)H2O phase with layered rectangular crystals. The most obvious difference between the two compounds is morphology of the crystals. The other major differences are found in stability of bonding of the interlayer acetate ions to solid phase and behavior in anion-containing solutions. The interlayer acetate ions in the present compound begin to be dissociated from the solid phase at ∼343 K while those in the previous compound are not dissociated below 383 K. The reaction of the present compound is topotactic in Cl− and NO3− aqueous solutions but reconstructive in a SO42− aqueous solution while the reaction of the previous compound in those solutions is topotactic.
Boron sub-arsenide, B12As2, is based on twelve-atom clusters of boron atoms and two-atom As–As chains. By contrast, SiC is a tetrahedrally bonded covalent semiconductor. Despite these fundamental differences, the basal plane hexagonal lattice constant of boron sub-arsenide is twice that of SiC. This coincidence suggests the possibility of heteroepitaxial growth of boron sub-arsenide films on properly aligned SiC. However, there are a variety of incommensurate alignments by which heteroepitaxial growth of B12As2 on (0001) 6H–SiC can occur. In this study, we first used geometrical crystallographic considerations to describe the possible arrangements of B12As2 on (0001) 6H–SiC. We identified four translational and two rotational variants. We then analyzed electron backscattered diffraction and transmission electron microscopy images for evidence of distinct domains of such structural variants. Micron-scale regions with each of the two possible rotational alignments of B12As2 icosahedra with the SiC surface were seen. On a finer length scale (100–300 nm) within these regions, boron-rich boundaries were found, consistent with those between pairs of the four equivalent translational variants associated with a two-to-one lattice match. Boron-carbide reaction layers were also observed at interfaces between SiC and B12As2.
Nitrogen-doped titanium oxides nanostructures were synthesized by a new method proposed here from titanium oxysulfate precursor in a NH4OH solution under hydrothermal conditions without any extra templates as structure driving agents. The material synthesized with NH4OH was an ammonium titanate and showed curled nanosheets, nanofibers or nanorods morphologies depending on the molar ratio of NH4OH to titanium precursor and the hydrothermal temperature. The nanofibrous titanates had a high surface area over 500 m2 g−1 and a pore volume of 0.72 cm3 g−1. The calcination of as-synthesized material at 673 K produced a titanium oxynitride TiO2−xNx with anatase phase, which absorbed visible light. Ion exchange of ammonium ion of the titanate with sodium Na2Ti3O7−xNx enhanced the thermal stability of the titanate phase.
Production of gold nanoparticles with the specific goal of particle size control has been investigated by systematic variation of chamber pressure and substrate temperature. Gold nanoparticles have been synthesized on SiO2 nanowires by plasma-enhanced chemical vapor deposition. Determination of particle size and particle size distribution was done using transmission electron microscopy. Average nanoparticle diameters were between 4 and 12 nm, with particle size increasing as substrate temperature increased from 573 to 873 K. A bimodal size distribution was observed at temperatures ≥723 K indicating Ostwald ripening dominated by surface diffusion. The activation energy for surface diffusion of gold on SiO2 was determined to be 10.4 kJ/mol. Particle sizes were found to go through a maximum with increases in chamber pressure. Competition between diffusion within the vapor and dissociation of the precursor caused the pressure effect.