bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of secondary phase particles on postrecrystallization grain growth in reactive spray deposited 5083 Al alloys
Authors: Dai S. L. , Delplanque J-P. , Lavernia E. J.
Published: March 2008

Grain growth behavior in reactive spray deposited Al–Mg–Mn alloy 5083 and 5083 + Zr was quantitatively studied at 500, 530, and 560 °C. Results show that reactive spray deposited 5083 processed using N2–5% O2, in which no significant volume fraction of oxide particles was found, experienced significant grain growth when annealed at 500, 530, and 560 °C following recrystallization. On the other hand, reactive spray deposited 5083 atomized with N2–10% O2 and 5083 + Zr atomized with N2–5% O2 exhibited very slow grain growth below 530 °C and limited grain growth at 560 °C. This behavior is attributed to the retardation effect of the secondary phase particles that were formed in these alloys.
High-strain-rate response of hot-explosively consolidated W–Ti alloys
Authors: Kecskes Laszlo J. , Hall Ian W.
Published: March 2008

Disk-shaped, two-phase, full-density W–Ti alloy billets have been fabricated by a new, hot-explosive-compaction technique. As part of a characterization effort, the compressive behavior of the alloy was investigated. Quasistatic and split Hopkinson pressure bar (SHPB) tests of cylindrical samples, taken from a 83W–17Ti at.% alloy billet, demonstrate the propensity of this material to fail via shear localization at high strain rates. The effects of strain rate, orientation of the matrix phase with respect to the direction of the SHPB compression, and spatial location within the billet (i.e., periphery or core) were evaluated. At quasistatic strain rates, the alloy deformed in a ductile mode and exhibited a definite spatial location sensitivity. At high strain rates, spatial location sensitivity was absent. Shear localization was unaffected by density variations, matrix orientation in the alloy, or the presence of coarsened substructural features in the matrix. These experiments and the microstructural characteristics of the resultant localized regions are discussed.
Mechanical properties of vapor-grown carbon fiber composites with thermoplastic matrices
Authors: Tibbetts Gary G. , McHugh John J.
Published: March 2008

This article discusses the mechanical properties of vapor-grown carbon fiber (VGCF)/nylon and VGCF/polypropylene composites. Fibers in the as-produced condition yielded composites with marginally improved mechanical properties. Microscopic examination of these composites clearly showed regions of uninfiltrated fibers, which could account for the unsatisfactory mechanical properties. The infiltration of the fibers by both polymers was improved by carefully ball milling the raw fiber so as to reduce the diameter of the fiber clumps to less than 300 μm. Properties of composites made with ball-milled material were improved in every respect. VGCF reinforcement in nylon slightly improved the tensile strength and doubled the modulus, while VGCF in polypropylene doubled the tensile strength and quadrupled the modulus compared to unreinforced material. Moreover, the composites were sufficiently improved that differences in fiber surface preparation became important. For example, air-etched fibers and fibers covered with low concentrations of aromatics produced polypropylene composites with significantly better mechanical properties than did fibers whose surfaces were heavily coated with aromatics. Both the tensile strength and the modulus of the composites fabricated with clean fibers exceeded theoretical values for composites made with fibers randomly oriented in three dimensions, indicating that the injection-molding process oriented the fibers to some extent.
Investigation of interfacial phenomena in Ag–Si multilayers during the annealing process
Authors: Zhao J. H. , Zhang M. , Liu R. P. , Zhang X. Y. , Cao L. M. , Dai D. Y. , Chen H. , Xu Y. F. , Wang W. K.
Published: March 2008

Interfacial phenomena and microstructure in Ag–Si multilayers with a modulation period of 7.64 nm during annealing from 323 to 573 K were investigated by in situ x-ray diffraction and high-resolution transmission electron microscopy. Uphill and downhill diffusion were observed on annealing. The temperature dependence of the effective diffusion coefficient from 373 K (as to downhill diffusion regime) to 523 K was De = 2.02 × 10−20 exp(−0.24 eV/kBT) m2/s. Diffusion of silicon atoms along silver grain boundaries was proposed as the main diffusion mechanism. After annealing, continuous silver sublayers changed to nanometer-sized silver particles (about 4.5 nm) coated completely by amorphous silicon.
Polymer-bonded magnets: Part I. Analytic thermogravimetry to determine the effect of surface modification on dispersion of Nd–Fe–B fillers
Authors: Xiao Jun , Otaigbe Joshua U.
Published: March 2008

The degree of mixing is a critical factor in controlling the magnetic properties and mechanical properties of polymer-bonded magnets. Pretreatment of the NdFeB fillers with a silane coupling agent improved the degree of mixing of the fillers in the polymer matrix. The observed improvement in the degree of mixing of the silanetreated fillers was ascribed to good wetting as evidenced by viscosity reduction of the coupled polymer-bonded magnets. However, traditional materials characterization methods could not be used to quantitatively determine the degree of mixing of the polymer-bonded magnets. This paper describes use of thermogravimetric analysis to quantify the degree of mixing of polymer-bonded magnets. The intensity of segregation of the fillers was calculated from the measured weight change of the magnetic filler in the samples. The results of this work showed that the thermogravimetric analysis method was useful in determining the degree of mixing of NdFeB fillers in polymer-bonded magnets.
Structural characterization of laser ablated epitaxial (Ba0.5Sr0.5)TiO3 thin films on MgO(001) by synchrotron x-ray scattering
Authors: Kim Sangsub , Kang Tae Soo , Je Jung Ho
Published: March 2008

Epitaxial (Ba0.5Sr0.5) TiO3 thin films of two different thickness (∼25 and ∼134 nm) on MgO(001) prepared by a pulsed laser deposition method were studied by synchrotron x-ray scattering measurements. The film grew initially with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became significantly rougher, but the interface between the film and the substrate did not. In the early stage of growth, the film was highly strained in a tetragonal structure (c/a = 1.04) with the longer axis parallel to the surface normal direction. As the growth proceeded further, it relaxed to a cubic structure with the lattice parameter near the bulk value, and the mosaic distribution improved significantly in both in- and out-of-plane directions. The thinner film (∼25 nm) showed only one domain limited mainly by the film thickness, but the thicker film (∼134 nm) exhibited three domains along the surface normal direction.
Crack tip 90° domain switching in tetragonal lanthanum-modified lead zirconate titanate under an electric field
Authors: Fang Fei , Yang Wei , Zhu Ting
Published: March 2008

Lanthanum-modified lead zirconate titanate ferroelectric ceramics (Pb0.96La0.04)(Zr0.40Ti0.60)0.99O3 were synthesized by the conventional powder processing technique. X-ray diffraction experiments revealed that the samples belong to the tetragonal phase with a = b = 0.4055 nm, c = 0.4109 nm, and c/a = 1.013. After being poled, the samples were indented with a 5-kg Vickers indenter, and lateral electric fields of 0.4 Ec, 0.5 Ec, and 0.6 Ec (Ec = 1100 V/mm) were applied, respectively. Field-emission scanning electron microscopy showed that 90° domain switching appeared near the tip of the indentation crack under a lateral electric field of 0.6 Ec. A mechanism of 90° domain switching near the crack tip under an electric field is discussed.
Bismuth composition control of SrBi2TaNbO9 thin films by heat treating Bi2O3-inserted heterostructure
Authors: Park Yoon-Baek , Lee Jeon-Kook , Jung Hyung-Jin , Park Jong-Wan
Published: March 2008

Ferroelectric properties of SrBi2TaNbO9 (SBTN) thin films were changed by the amount of Bi content in SBTN. We proposed that the addition of excess Bi to the SBTN thin films could be accomplished by heat treating the SBTN/Bi2O3/SBTN heterostructure fabricated by the radio frequency magnetron sputtering method. The Bi composition was controlled by changing the thickness of the inserted Bi2O3 from 50 to 400Å in the SBTN/Bi2O3/SBTN heterostructure. As the thickness of Bi2O3 films was increased from 0 to 100 Å, the grain grew faster and the ferroelectric properties improved. On the other hand, when the thickness, of Bi2O3 films was thicker than 150 Å, the ferroelectric properties deteriorated. In particular, when a 400 Å Bi2O3 layer was inserted between SBTN films, a Bi2Pt phase appeared and the Bi2O3 films remained between SBTN films, resulting in poor ferroelectric properties. A Bi2Pt phase was formed by the reaction between the platinum bottom electrode and Bi2O3 films. On the other hand, the leakage current density of SBTN thin films decreased with the increase of inserted Bi2O3 film thickness. As the thickness of inserted Bi2O3 films was increased from 0 to 50 Å, leakage current density abruptly decreased because Bi content of the SBTN thin films was increased from 8 mol% deficient to stoichiometric composition. As the thickness of inserted Bi2O3 films increased from 100 to 400 Å, leakage current density gradually decreased because the remaining Bi2O3 layer in SBTN thin films increased.
Design for high-performance functional composite thermistor materials by glass/ceramic composing
Authors: Wang D. J. , Qiu J. , Gui Z. L. , Li L. T.
Published: March 2008

A negative temperature coefficient–positive temperature coefficient (NTC-PTC) composite thermistor with high performance was designed by glass/ceramic composing. The material exhibited low resistivity and a large negative temperature coefficient of resistivity. The minimum resistivity was the magnitude of 102 Ω cm, and the negative temperature coefficient of resistivity was better than −3% °C−1. The results showed that the large negative temperature coefficient of resistivity was closely related to the glass phase, and the NTC-PTC functional composite material was a kind of grain-boundary–controlled material.
Influence of additives on the properties of spherical nickel particles prepared by ultrasonic spray pyrolysis
Authors: Stopić S. , Nedeljković J. , Rakočević Z. , Uskoković D.
Published: March 2008

Ideal spherical nonagglomerated Ni particles (mean diameter 0.62–1.12 μm) were prepared by ultrasonic spray pyrolysis of NiCl2 aqueous solution in the presence of 0.1 mass% of Pd, Cu, or Ni in an H2–N2 atmosphere at 900 °C. Incomplete reduction of the NiCl2 aqueous solution in the absence of additives was observed under the same conditions. Differential thermal and thermal-gravimetric analyses revealed a decrease in initial reduction temperature of NiCl2 from 375 to 275 °C by the addition of Pd, Cu, or Ni. The morphology of Ni particles was analyzed using scanning tunneling microscopy. The surface roughness of Ni particles was found to be controllable by addition of appropriate additives.
Preparation of phase homogeneous Mn–Zn ferrite powder by spray pyrolysis
Authors: Zhao Xinyu , Zheng Baicun , Gu Hongchen , Li Chunzhong , Zhang Shi Chang , Ownby P. Darrell
Published: March 2008

Two kinds of aqueous precursor solutions are used to synthesize Mn–Zn ferrite powders: (i) nitrate (NO) precursor—derived from solutions of Mn(NO3)2, Zn(NO3)2, and Fe(NO3)3; and (ii) acetate (AC) precursor—derived from solutions of Mn(CH3COO)2, Zn(CH3COO)2, and Fe(NO3)3. The composition of the powders synthesized from the precursor AC is very uniform, whereas powders derived from the precursor NO have Mn and Zn segregated on the particle surfaces. In addition, the powders synthesized from precursor AC are solid spherical particles with fine porosity, whereas many hollow and fragmented particles are observed in the powder derived from precursor NO. Overall, the properties of Mn–Zn ferrite cores prepared from the precursor AC are superior to those prepared from the precursor NO. The reasons for the differences are explained and described in detail. The AC precursor powders synthesized by spray pyrolysis produced Mn–Zn ferrite cores with good magnetic properties.
Preparation of epitaxial SrBi2Nb2O9 and SrBi2Ta2O9 thin films by the coating-pyrolysis process
Authors: Nagahama T. , Manabe T. , Yamaguchi I. , Kumagai T. , Mizuta S. , Tsuchiya T.
Published: March 2008

Epitaxial and polycrystalline thin films of bismuth layer-structured ferroelectrics, SrBi2Nb2O9 (SBN) and SrBi2Ta2O9 (SBT), were prepared on single-crystal SrTiO3(001) and polycrystalline yttria-stabilized zirconia substrates, respectively, by the coating-pyrolysis process. The epitaxial relationship of the films and substrates was SBN, SBT (001)//SrTiO3(001) and SBN, SBT [100]//SrTiO3[100],[010], where pseudotetragonal indices were adopted for SBN and SBT. The lattices of the epitaxial films were found to be slightly strained owing to stress from the substrate. Atomic force microscopy observations showed that the epitaxial films as well as polycrystalline films consisted of round-shaped, islandlike grains of submicrometer size.
Scanning electron acoustic microscopy of electric domains in ferroelectric materials
Authors: Qian MengLu , Wu XianMei , Yin QingRui , Zhang BingYing , Cantrell John H.
Published: March 2008

Electric domains in single-crystal and polycrystalline barium titanate (BaTiO3) have been observed by use of scanning electron acoustic microscopy (SEAM). A model is presented of the SEAM signal generation, spatial resolution, and contrast mechanism associated with the imaging of electric domains in ferroelectric materials. The SEAM signal is found to depend directly on the sum of the piezoelectric coupling coefficient and spontaneous polarization of the domain, on the charge density of the electron beam interaction volume, and inversely on both the permittivity and the elastic constants of the material. Application of the model to BaTiO3 yields a contrast of roughly 3.5% from 90° domain structures and 6.8% from 180° domain structures.
Synthesis, electrochemical, and microstructural study of precursor-derived LiMn2O4 powders
Authors: Ikuhara Yumi H. , Iwamoto Yuji , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

Stable and homogeneous alkoxide precursor solutions of lithium ethoxyethoxide and manganese ethoxyethoxide in 2-ethoxyethanol were synthesized by ligand exchange reaction of lithium isopropoxide and manganese 2-ethoxide, respectively, with 2-ethoxyethanol. [Li–Mn–O] precursor solution was prepared by mixing these modified alkoxide precursor solutions. LiMn2O4 powders were successfully synthesized by pyrolysis of the [Li–Mn–O] precursor powder in O2 temperature as low as 200 °C. The nanocrystalline LiMn2O4 powders 20–50 mm in diameter after heat treatment up to 700 °C consisted of the ordered (111) plane and performed with good cyclability as the cathode materials for Li secondary batteries.
Planar waveguides prepared by K+–Na+ field-assisted ion exchange in different types of silicate glass
Authors: Kosíková Jitka , Schröfel Josef
Published: March 2008

The goal of this work was to address the technological problems associated with waveguide preparation by thermal- and electric-field–assisted K+–Na+ ion exchange in two types of soda-lime glass: common FTD and special pure GIL49. The number of modes, depth, profile, and the change in refractive index were measured for waveguides prepared at temperatures between 250 and 410 °C and electric-field values between 0 and 50 V/mm. Although the influence of some admixture content inside the glass was relatively high, all of these parameters were controlled accurately and repeatedly by the electric field.
Growth of a-axis-oriented HgBa2CaCu2Oxthin films by rapid quenching
Authors: Yun S. H. , Karlsson U. O. , Jönsson B. J. , Rao K. V. , Madsen L. D.
Published: March 2008

High-quality a-axis-oriented HgBa2CaCu2Ox superconducting thin films have been grown on (100) LaAlO3 substrates using a modified conventional method that contains a short annealing time of 5 min, rapid-quenching process, and an alternative encapsulated approach. We found that the preferred orientations of HgBa2CaCu2Ox thin films can be controlled by rapid quenching at specific temperatures: 800, 700, 600, and 500 °C. The films rapidly quenched in water from 700 °C during a cooling cycle showed predominantly a-axis orientation perpendicular to the film surface. Phase was confirmed by x-ray diffraction pole figures. The a-axis films exhibited a zero-resistance transition temperature >120 K, which is comparable to epitaxial c-axis-oriented films.
Surface oxidation of a quasicrystalline Al–Cu–Fe alloy:No effect of surface orientation and grain boundaries onthe final state
Authors: Pinhero P. J. , Anderegg J. W. , Sordelet D. J. , Lograsso T. A. , Delaney D. W. , Thiel P. A.
Published: March 2008

We have used x-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxides on two types of quasicrystalline Al–Cu–Fe samples. One type was formed by consolidation of powders, resulting in multiple grains with random surface orientations. The other was a single grain, oriented to expose a fivefold surface. Both were oxidized to saturation in a variety of environments at room temperature. We measured the elemental constituents that oxidized, the extent of oxygen-induced Al segregation, and the depth of the oxide. Under the conditions of our experiments, there was little, if any, significant difference between the two types of samples. Hence, surface orientation and bulk microstructure played little or no role on the final state of the oxide under these conditions.
Correlation between effective activation energy and pre-exponential factor for diffusion in bulk metallic glasses
Authors: Sharma S. K. , Faupel F.
Published: March 2008

The values of effective activation energy (Q) and pre-exponential factor (D0) reported in the literature for diffusion in the novel bulk metallic glasses, both in the glassy and the deeply supercooled liquid regions, are found to follow the same correlation as reported earlier in conventional metallic glasses, namely D0 = A exp(Q/B), where A and B are fitting parameters with values A = 4.8 × 10−19 m2 s−1 and B = 0.056 eV atom−1. A possible explanation for the observed values of A and B is given by combining an activation energy and a free volume term. The interpretation favors a cooperative mechanism for diffusion in the glassy and deeply supercooled liquid states.
Studies of electron energy loss near edge structure at the interface between Si and amorphous carbon films deposited by direct carbon ion beams
Authors: Sohn M. H. , Kim S. I. , Siangchaew K.
Published: March 2008

Using direct carbon ion beam deposition, in situ surface modification was performed by an energetic C- beam (400 and 500 eV) prior to amorphous carbon film growth to enhance adhesion of the film. It has been found from high-resolution electron microscopy that the C and Si mixing layer at the interface causes strong adhesion of the film. Electron energy loss spectroscopy was used to investigate chemical states of the C and Si mixing layer at the interface. The carbon composition profile in silicon showed that the thickness of the mixing layer was about 30 nm for 500 eV modification (at 200 °C). Silicon L-edge study at the C/Si interface found C–Si bond formation only at the surface of silicon over 2–3-nm-thick layers. The C–Si bond formation is a function of C- ion impingement energy. The thickness of the bonding layer decreased to less than 1 nm for 400 eV surface modification. When the substrate was modified by a 500-eV C- beam at 800 °C, the thickness of the SiC layer was about 10 nm. C–Si bond formation was enhanced by the supplemental thermal energy.
Deposition of zinc sulfide quantum dots from a single-source molecular precursor
Authors: Revaprasadu N. , Malik M. Azad , O'Brien P. , Wakefield G.
Published: March 2008

Nanoparticles of ZnS capped with tri-n-octylphosphineoxide (TOPO) and close to monodispersed have been prepared by a single-source route using ethyl(di-ethyldithiocarbamato)zinc(II) as a precursor. The nanoparticles obtained showed quantum size effects in their optical spectra, and the photoluminescence spectrum showed a broad emission that could be attributed to the surface traps. A blue shift of 0.31 eV in relation to the bulk material was observed. The selected area electron diffraction, x-ray diffraction pattern and transmission electron microscopy showed the material to be of the zinc blend structure. The crystallinity of the material was also evident from high-resolution transmission electron microscopy, which gave well-defined images of nano-sized particles with clear lattice fringes and a spacing of approximately 3 Å, corresponding to the (111) planes of the cubic crystalline ZnS phase and in the size range of 3.9–4.9 nm. The presence of strong phosphorus peak in the energy dispersion analytical x-ray pattern, together with a shift in infrared band for P = O of TOPO showed that the particles were TOPO capped.
A new surface-alloying technique for pure copper
Authors: Zhang M-X. , Reilly K. , Kelly P. M.
Published: March 2008

A totally new technique of surface modification—thermal surface-alloying treatment for pure copper—was developed. A 0.2–1.8 mm copper alloy layer, which has a hardness 4 to 5 times higher than the pure copper substrate, was formed after the treatment. The significance of this technique is that the surface of pure copper can be efficiently hardened without significant reduction of the overall thermal and electrical conductivity. Variations of composition and microstructure in the alloy layer were studied after pure copper was surface alloy treated with aluminum.
Segregation in the MgO–MgAl2O4 system processed from nitrate precursors
Authors: Bhatia Tania , Chattopadhyay K. , Jayaram Vikram
Published: March 2008

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in MgO–MgAl2O4 powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free MgO–MgAl2O4 powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 μm at temperatures as low as 973 K. By comparison, the segregation-free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5–30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973–1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation.
Positive temperature coefficient resistance effect in Ba1-xSrxTiO3 ceramics modified with Bi2O3 and PbO by a vapor-doping method
Authors: Qi Jianquan , Gui Zhilun , Li Longtu , Wu Yajing
Published: March 2008

Ba1−xSrxTiO3-based positive temperature coefficient resistance (PTCR) ceramics were prepared by use of a vapor-doping method. When doped with Bi, the PTCR effect is improved; when doped with lead, however, the effect is weakened. The different influences of Bi and Pb doping on the ceramic properties are discussed in terms of the defect chemistry.
Characterization of processing pores and their relevance to the strength in alumina ceramics
Authors: Zhang Yao , Inoue Mineyuki , Uchida Nozomu , Uematsu Keizo
Published: March 2008

Characterization of bulk defects was successfully accomplished in alumina with a transmission optical microscope. The characterization technique used is based on the fact that many ceramics are essentially transparent. Most defects in this particular ceramic were found to be pore. Their size distribution was found to follow a simple power function. With these characteristics of defects, the strength distribution of the ceramics was calculated with Baratta's model and compared to the measured strength of the ceramics. A good agreement was found between them when the pore was assumed to be accompanied with cracks 4 times the length of the grain size.
Temperature-stable dielectric ceramics in Ba4Nd2Ti4Ta6O30/(La0.1Bi0.9)2Ti2O7 biphase system
Authors: Wang J. , Chen X. M. , Yang J. S.
Published: March 2008

Biphase dielectric ceramics in the system of (1 − x)Ba4Nd2Ti4Ta6O30/ x(La0.1Bi0.9) 2Ti2O7 were investigated to obtain a near-zero temperature coefficient of dielectric constant. With the increase in x, the dielectric constant increased slightly, and the temperature coefficient changed from negative to positive. High dielectric constant of ε = 143 and good temperature stabibility (τ ε = −48 ppm/ °C) were achieved in a composition of x = 0.45, and the increased dielectric loss became the new problem.
Synthesis of calcium silicate hydrate/polymer complexes: Part I. Anionic and nonionic polymers
Authors: Matsuyama Hiroyoshi , Young J. Francis
Published: March 2008

High molecular weight anionic polymers have been incorporated into the calcium silicate hydrate (C–S–H) structure during precipitation of quasicrystalline C–S–H from aqueous solution. The anionic polymers studied were poly(methacrylic acid), poly(acrylic acid), and the sodium salt of poly(vinyl sulfonic acid). Expansion of the interlayer spacing coupled with high-carbon contents confirmed that the polymers intercalated between the layers. D-gluconic acid behaves similarly. Intercalation characteristics strongly depended on both the type of polymer and Ca/Si molar ratio of C–S–H; intercalation reached a maximum at an initial Ca/Si = 1.3 in all cases. Poly(vinyl alcohol) was the only nonionic polymer among those studied that was incorporated into C–S–H. Evidence for interlayer intercalation is less definite. The C–S–H/polymer complexes were examined by Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance magic angle spinning, and 13C cross-polarization, magic angle spinning nuclear magnetic resonance spectroscopy.
Synthesis of calcium silicate hydrate/polymer complexes: Part II. Cationic polymers and complex formation with different polymers
Authors: Matsuyama Hiroyoshi , Young J. Francis
Published: March 2008

Some high molecular weight cationic polymers, poly(diallyldimethylammonium chloride) (PDC) and poly(4-vinylbenzyltrimethylammonium chloride) (PVC), have been incorporated into the calcium silicate hydrate (C–S–H) structure during precipitation of quasicrystalline C–S–H from aqueous solution. Expansion of the interlayer spacing [0.9 nm (PDC), 1.5 nm (PVC)] and a high-carbon content provided evidence that these polymers were intercalated between layers of C–S–H when Ca/Si <1.0. Intercalation characteristic properties strongly depended on both of the type of polymer and Ca/Si ratio in C–S–H. Poly(4-vinyl-1-methylpyridinium bromide) and methyl glycol chitosan (iodide) also interacted with C–S–H, probably by surface adsorption. The C–S–H/polymer complexes were examined by Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance magic angle spinning, and 13C cross-polarization, magic angle spinning nuclear magnetic resonance spectroscopy. Mechanisms of intercalation of different kinds of polymers between the C–S–H layers are discussed.
Interfacial reactions of Co/Si0.76Ge0.24 and Co(Si0.76Ge0.24)/Si0.76Ge0.24 by pulsed KrF laser annealing
Authors: Luo Jian-Shing , Hang Yu-Lin , Lin Wen-Tai , Chang C. Y. , Shih P. S.
Published: March 2008

Interfacial reactions of Co/Si0.76Ge0.24 and Co(Si0.76Ge0.24)/Si0.76Ge0.24 by pulsed KrF laser annealing as a function of energy density and pulse number were studied. For the Co/Si0.76Ge0.24 samples annealed at an energy density of 0.2–0.6 J/cm2, three germanosilicide layers, i.e., amorphous structure and/or nanocrystal, Co(Si1−xGex), and Co(Si1−xGex)2, were successively formed along the film-depth direction. At 0.3 J/cm2 Ge segregated to the underlying Si0.76Ge0.24 film, inducing strain relaxation in the residual Si0.76Ge0.24 film. At 0.8 J/cm2 the reacted region was mostly transformed to a single layer of Co(Si1−xGex)2, whereas Ge further diffused to the Si substrate. At 1.0 J/cm2, constitutional supercooling appeared. Even the Co(Si0.76Ge0.24) film used as the starting material for laser annealing could not prevent the occurrence of constitutional supercooling at energy densities >1.6 J/cm2. The energy densities at which Co(Si1−xGex) transformation to Co(Si1−xGex)2, Ge segregation to the underlying Si, and constitutional supercooling occurred were higher for the Co(Si0.76Ge0.24)/ Si0.76Ge0.24 system than for the Co/Si0.76Ge0.24 system. Higher energy density and/or pulse number enhanced the growth of Co(Si1−xGex)2 film. In the present study, the Co/Si0.76Ge0.24 samples subjected to annealing at 0.2 J/cm2 for 20 pulses produced a smooth Co(Si0.76Ge0.24)2 film without inducing Ge segregation out of the germanosilicide and strain relaxation in the unreacted Si0.76Ge0.24 film.
Point defect incorporation during diamond chemical vapor deposition
Authors: Battaile C. C. , Srolovitz D. J. , Butler J. E.
Published: March 2008

The incorporation of vacancies, H atoms, and sp2 bond defects into single-crystal homoepitaxial (100) (2 × 1)–and (111)-oriented chemical-vapor-deposited diamond was simulated by atomic-scale kinetic Monte Carlo. Simulations were performed for substrate temperatures from 600 to 1200 °C with 0.4% CH4 in the feed gas, and for 0.4–7% CH4 feeds with a substrate temperature of 800 °C. The concentrations of incorporated H atoms increased with increasing substrate temperature and feed gas composition, and sp2 bond trapping increased with increasing feed gas composition. Vacancy concentrations were low under all conditions. The ratio of growth rate to H atom concentration was highest around 800–900°C, and the growth rate to sp2 ratio was maximum around 1% CH4, suggesting that these conditions are ideal for economical diamond growth under simulated conditions.
Study of the overtones and combination bands in the Raman spectra of polyparaphenylene-based carbons
Authors: Marucci A. , Pimenta M. A. , Brown S. D. M. , Matthews M. J. , Dresselhaus M. S. , Endo M.
Published: March 2008

A detailed study of the second-order Raman spectrum of the polymer polyparaphenylene (PPP) prepared according to the Kovacic method and heat treated at temperatures THT between 650 and 750 °C is presented. The Raman experiments have been performed with five different laser excitation energies in the visible range between 1.92 and 3.05 eV. Several Raman bands in the region between 2400 and 3400 cm−1 have been detected and assigned to the overtones and combination bands of the two conformations of the PPP polymer (benzenoid and quinoid) that co-exist in our samples. Due to the carbonization process, these bands broaden and decrease in intensity with increasing heat treatment temperature, as is also observed for the corresponding first-order Raman features. The complete absence of these high-frequency Raman bands for PPP with heat treatment temperatures in excess of 750 °C indicates complete transformation of the polymer into a disordered carbon material.
The boron oxide–boric acid system: Nanoscale mechanical and wear properties
Authors: Ma Xiangdong , Unertl W. N. , Erdemir A.
Published: March 2008

The film that forms spontaneously when boron oxide (B2O3) is exposed to humid air is a solid lubricant. This film is usually assumed to be boric acid (H3BO3), the stable bulk phase. We describe the nanometer-scale surface morphology, mechanical properties, and tribological properties of these films and compare them with crystals precipitated from saturated solutions of boric acid. Scanning force microscopy (SFM) and low-load indentation were the primary experimental tools. Mechanical properties and their variation with depth are reported. In all cases, the surfaces were covered with a layer that has different mechanical properties than the underlying bulk. The films formed on boron oxide showed no evidence of crystalline structure. A thin surface layer was rapidly removed, followed by slower wear of the underlying film. The thickness of this initial layer was sensitive to sample preparation conditions, including humidity. Friction on the worn surface was lower than on the as-formed surface in all cases. In contrast, the SFM tip was unable to cause any wear to the surface film on the precipitated crystals. Indentation pop-in features were common for precipitated crystals but did not occur on the films formed on boron oxide. The surface structures were more complex than assumed in models put forth previously to explain the mechanism of lubricity in the boron oxide–boric acid–water system.
Mechanisms of structural anomaly and orthorhombic–tetragonal transition of YBa2Cu3Oy
Authors: Wu Ma-Shine , Fang Tsang-Tse
Published: March 2008

Powdered samples of oxygen-deficient YBa2Cu3Oy were annealed in various atmospheres at 880 and 300 °C to study the relations of structural anomaly, phase transition, and oxygen content. It was found that the structural anomaly in the c axis is reversible during oxygenation and deoxygenation. The change of the c axis arose from the electrical repulsion among Ba and Cu cations as oxygen was removed or refilled. The anomaly in the c axis occurred when the oxygen was further removed or refilled to a critical value, at which structural relaxation and electrical repulsion changed greatly. The phase transition is attributed to the anomalous change in the c axis, and the mechanism is proposed and discussed in this paper.
Homoepitaxial (111) diamond grown by temperature-controlled chemical vapor deposition
Authors: Nishitani-Gamo Mikka , Sakaguchi Isao , Takami Tomohide , Suzuki Katsunori , Kusunoki Isao , Ando Toshihiro
Published: March 2008

We investigated the growth of high-quality homoepitaxial diamond on the (111) face in a microwave-assisted plasma chemical-vapor-deposition system incorporating an individual substrate heating/cooling device. The grown diamond films were characterized by scanning electron microscopy, reflection high-energy electron diffraction, atomic force microscopy, confocal micro-Raman spectroscopy, and secondary ion mass spectrometry. The (111) diamond films show a tendency to incorporate a significant amount of hydrogen during chemical-vapor-deposition growth. Hydrogen incorporation degrades the crystal quality and surface smoothness. The amount of incorporated hydrogen decreases with the decrease in deposition temperature. We have shown that the crystal quality and surface smoothness of homoepitaxial diamond strongly depend on the substrate temperature. Independent control of the substrate temperature and incident microwave power is essential for high-quality diamond homoepitaxy.
Nucleation, growth, and aggregation of gold on polyimide surfaces
Authors: Travaly Y. , Zhang L. , Zhao Y. , Pfeffer R. , Uhrich K. , Cosandey F. , Garfunkel E. , Madey T. E.
Published: March 2008

The growth of ultrathin gold films on polyimide (PI) surfaces and the stability of the films upon thermal annealing have been studied using a combination of various techniques. With scanning electron microscopy (SEM) we observe that, at room temperature, the Au film initially grows by nucleation of compact Au islands. With increasing metal coverage, the clusters partially agglomerate to produce a wormlike structure. Finally, percolation, hole-filling, and continuous thin-film growth are observed. To evaluate the thermal stability of the Au/PI system, annealing at various temperatures was performed on films that displayed the wormlike structure. SEM results indicate strong temperature-dependent changes in film morphology. Finally, from our SEM data we determine contact angles, allowing us to estimate interfacial and adhesion energies.
Ultraviolet laser-induced liquid-phase palladium seeding on polymers
Authors: Kordás K. , Békési J. , Bali K. , Vajtai R. , Nánai L. , George Thomas F. , Leppävuori S.
Published: March 2008

Excimer laser pulses with wavelength of 308 nm, repetition rates of 1–10 Hz, pulse energies of 300–400 mJ, and pulse width of 20 ns are used to selectively seed palladium aggregates from a liquid-phase solution on polymer (polyimide) surfaces. The precursors used are PdCl2 in hydrochloric acid and Pd(CH3CO2)2 in acetic acid. The coverage of the polyimide with palladium aggregates is determined by the analysis of scanning electron microscopy measurements. Qualitative and quantitative analyses of seeded particles on polyimide (PI) are investigated by x-ray diffraction and transmission measurements. The amount of deposited palladium showed a quadratic dependence on the laser fluence reaching the surface. On the other hand, the coverage versus number of laser shots shows a square-root-like dependence. The palladium deposits also appear as amorphous and Pd[111] crystallites forms depending on the number of laser pulses. The roughness of a PI surface prior to seeding is modified mechanically and characterized by its fractal dimension. The fractal dimension of the samples varies between 2.3 and 2.7 for all the parameters applied, and the palladium deposition is found to be dependent on this dimension of the PI film.
Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms
Authors: Stein David J. , Cecchi Joseph L. , Hetherington Dale L.
Published: March 2008

We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO3 concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO3 concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP.
Room-temperature synthesis of submicron platinum and palladium powders in glycols
Authors: Tekaia-Elhsissen K. , Bonet F. , Grugeon S. , Lambert S. , Herrera-Urbina R.
Published: March 2008

Platinum and palladium powders with average particle sizes in the submicron range have been synthesized at room temperature by hydrazine reduction ofand, respectively, in glycols. Platinum powders contain spherical particles with a bimodal size distribution. Palladium powders also contain spherical particles, but the size distribution is narrow. The effect of both ammonia and hydrazine concentration on the size distribution and average size of palladium particles was investigated.
Real-time synchrotron x-ray scattering study of an epitaxial BaTiO3 thin film during heating
Authors: Kim Sang Sub , Je Jung Ho
Published: March 2008

An epitaxial BaTiO3 film with 290-nm thickness was prepared on a MgO(001) single-crystal substrate by radio-frequency magnetron sputter deposition. The structural characteristics of the film were studied as a function of temperature in in situ, real-time synchroton x-ray scattering experiments. We found that the as-grown film was strained at room temperature and tetragonally distorted with the c axis normal to the film surface. Interestingly, its lattice parameters were found to be expanded 1.28% and 0.64% in both the in-plane and the out-of-plane directions, respectively (i.e., biaxially), comparing to those of a bulk BaTiO3. More importantly, as it was heated to 600 °C, the tetragonal structure was kept up without the phase transition, which is usually observed in other epitaxial ferroelectric thin films.
Persistent spectral hole burning and local structure of Eu3+ ions doped in BaO–PbO–P2O5 glasses
Authors: Ito Shunsuke , Hayakawa Tomokatsu , Kasuga Toshihiro , Nogami Masayuki
Published: March 2008

Persistent spectral hole burning was observed in Eu3+-doped BaO–PbO–P2O5 glasses, and the dependence of hole properties on the glass composition was investigated in relation to the local structure surrounding the Eu3+ ions. The hole was burned on the 7F0 → 5D0 transition of the Eu3+ ions, the depth of which decreased with increasing PbO content, whereas the hole width increased. The hole was burned at 6 K, filled on increase in temperature, and erased above 120 K. Judd–Ofelt parameters and fluorescence line-narrowing spectra indicated that the symmetry of the Eu3+ site increases and the covalency of the Eu–O bond decreases with increasing PbO content.
Deformation-induced microstructural changes in Fe40Ni40P14B6 metallic glass
Authors: Fan G.J. , Quan M. X. , Hu Z. Q. , Löser W. , Eckert J.
Published: March 2008

The effect of mechanical deformation via high-energy ball milling on the structure of the Fe40Ni40P14B6 metallic glass was studied by means of x-ray diffactometry, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). After 5 h of milling, TEM observations indicated that some nanocrystallites with a diameter of about 6 nm precipitated from surface layers of the amorphous ribbons, whereas the bulk remained amorphous. When milling time was increased to 11 h, bulk crystallization occurred. The amorphous Fe40Ni40P14B6 alloy crystallized into a mixture of γ–(Fe, Ni) and (Fe, Ni)3(P, B). To understand the microstructural changes occurring in the amorphous ribbons before the onset of bulk crystallization, the isothermal crystallization behavior of as-deformed amorphous ribbons was studied. Compared with as-quenched amorphous ribbons, the local value of the Avrami exponent, derived from isothermal DSC data, increased from 3.5 to 4.1 for bulk crystallization. The thermal crystallization mechanism of deformed amorphous Fe40Ni40P14B6 ribbons changed from an eutectic-type reaction with simultaneous precipitation of γ–(Fe, Ni) and (Fe, Ni)3(P,B) from the amorphous matrix to a primary-type reaction with precipitation of α–Fe(P,B) preceding the formation of γ–(Fe,Ni) and (Fe,Ni)3(P,B). Our results suggest that several hours of mechanical milling cause surface crystallization and some atomic rearrangements in the amorphous alloy. The latter effect may be responsible for the observed primary-type reaction for crystallization of the deformed amorphous alloy
Synthesis and blood compatibilities of novel segmented polyurethanes containing phosphatidylcholine analogous moieties in the main chains and long-chain alkyl groups in the side chains
Authors: Korematsu Arata , Li Yu-Jun , Murakami Takayuki , Nakaya Tadao
Published: March 2008

New segmented polyurethanes containing phospholipid moieties in the main chains and long-chain alkyl groups in the side chains were synthesized. The soft segments used in this study were poly(butadiene), poly(isoprene), hydrogenated poly(isoprene), and poly(1,6-hexyl-1,2-ethylcarbonate) diol. The hard segments of these polyurethanes were 4,4′-methylenediphenyl diisocyanate, bis[2-(2-hydroxyethyldimethylammonio)ethyl]2-cetyl- 1,3-propanediphosphate, and 1,4-butanediol. The blood compatibilities of the new polymers were evaluated by platelet-rich plasma contact studies and viewed by scanning electron microscopy using medical grade BioSpan® and nonphospholipid polyurethane as references. These new materials have good surfaces in terms of platelet adhesion, and the morphology of adhered platelets undergoes a relatively low degree of variation.
Internal friction of artificially multilayered Cu–Ni(100) membranes produced by electrodeposition
Authors: Oberle R. R. , Cammarata R. C. , Su C. M. , Wuttig M.
Published: March 2008

The internal stress and internal friction of electrodeposited multilayered Cu–Ni(100) thin films were investigated as a function of temperature by a sensitive vibrating membrane technique. Each membrane was in a state of biaxial stress (approaching the yield strength) resulting from contributions of the growth stress in the as-deposited film and from the thermal stress as the membrane was heated. The measured internal friction of these stressed multilayered films was enhanced by over an order of magnitude compared to the predicted value of classic damping related to the modulus defect when the effect of the internal stress was taken into account.
A solvothermal reaction route for the synthesis of CuFeS2ultrafine powder
Authors: Hu Junqing , Lu Qingyi , Tang Kaibin , Qian Yitai , Zhou Guien , Liu Xianming
Published: March 2008

A 100-nm CuFeS2ultrafine powder was prepared through a solvothermal reaction at 200–250 °C. X-ray powder diffraction and transmission electron microscopy results revealed that chalcopyrite-phase CuFeS2was crystallized with single-crystalline nature and preferential orientation growth. Mössbauer spectrum exhibited a six-peak hyperfine magnetic spectrum and a single nonmagnetic peak. Elemental analysis gave the atomic ratio of Cu:Fe:S of 1:1.02:2.10. The influence factors on the formation of CuFeS2ultrafine powder are discussed.
Anomalous wetting of Ti–48 at.% Al–2 at.% Cr–2 at.% Nb substrates by liquid copper
Authors: Gale W. F. , Shen Y. , Fergus J. W. , Wen X.
Published: March 2008

Conventionally, the wetting of metallic substrates by liquid metals involves undermining of the substrate–oxide layer by the liquid. Evidence is presented here for an alternative wetting process involving spreading of liquid copper along the exterior of the oxide layer on Ti–48 at.% Al–2 at.% Cr–2 at.% Nb substrates. A mechanism is presented that involves compositional changes in the liquid, which in turn allow a wetting-promoting reaction between the (initially unreactive) liquid and the exterior layer of the substrate oxide.
Interface modification for increased fracture toughness in reaction-formed yttrium aluminum garnet/alumina eutectic composites
Authors: Brewer Luke N. , Endler Derrick P. , Austin Shani , Dravid Vinayak P. , Collins Joseph M.
Published: March 2008

The validity of controlling interfacial toughness in reaction-formed composites was explored using solid-state reaction processing and microanalysis techniques. A variety of rare-earth oxides was added to a yttrium aluminum garnet (YAG)/alumina powder mixture and then melted in air. Some melts retained the crystallography and microstructure of the pure, binary YAG–alumina eutectic. Using scanning transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy, rare-earth ions were observed both to segregate to the YAG/alumina interface and to form a third phase. Some evidence of increased crack deflection at these interfaces was observed via indentation fracture.