bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of Carbon Nanotubes from CO and in situ Formed Nano-sized Pd Particles
Authors: Andersson M. , Alberius-Henning P. , Jansson K. , Nygren M.
Published: March 2008

Carbon nanotubes, typically of 0.5-μm length and 20-nm diameter, were prepared with good selectivity by disproportionation of CO in He over a Pd/La2O3 catalyst. The catalyst was formed in situ by reduction of a La4PdO7 precursor. The obtained nanotubes had the so-called fishbone structure with the graphitic planes inclined at an angle to the long axis of the nanotube. The effect of CO concentration was studied at 673 °C, and it was found that, among the concentrations studied, 20 vol% CO in the gas was suitable for nanotube growth. The obtained nanotube/La2O3/Pd composite contained typically only 3 wt% nanotubes after 8 h of CO treatment. A process for selective dissolution of La2O3 and Pd was applied, and a product containing 85 wt% nanotubes was obtained. The nanotubes were characterized by high-resolution, transmission, and scanning electron microscope studies, combined with element analyses using energy dispersive spectrometers, x-ray powder diffraction studies, and thermogravimetric analysis.
Effect of Processing Temperature on the Morphology of Hydrothermally Derived Barium Titanate/polymer Thin Films
Authors: Collins David E. , Slamovich Elliott B.
Published: March 2008

Thin-film composites of BaTiO3particles in a polymeric matrix were processed by reacting films of a titanium alkoxide, mixed with a polybutadiene-polystyrene triblock copolymer, in aqueous solutions of 1.0 M Ba(OH)2at temperatures ranging from 60 to 90 °. After reaction, the composite films displayed distinct surface and subsurface morphologies. The film surface consisted of a continuous layer of BaTiO3grains, the film grain size decreasing from 180 to 60 nm as the reaction temperature increased from 60 to 90 °. The subsurface growth of BaTiO3depended on the presence of a percolating network of hydrolyzed titanium alkoxide, which enabled the reaction solution to permeate throughout the thin film. The resulting subsurface film morphology was composed of segregated regions of BaTiO3particles dispersed throughout the polymeric matrix. The growth of subsurface BaTiO3particles appeared to be constrained by the polymer matrix, resulting in a subsurface particle size of approximately 5 to 10 nm that was independent of the hydrothermal processing temperature. The reacted films displayed a dielectric constant ranging from 10 to 15 at room temperature and a frequency of 10 kHz.
Self-organization in porous 6H–SiC
Authors: Zangooie S. , Woollam J. A. , Arwin H.
Published: March 2008

Pores in porous 6H–SiC were found to propagate first nearly parallel with the basal plane and gradually change direction and align with the c axis. As a consequence, well-defined columnar pores were formed. It was shown that the rate of change of propagation directions was influenced by the etching parameters, such as hydrofluoric acid concentration and current density. Larger currents resulted in formation of larger pores. Pore sizes were found to increase with depth due to a decrease of the acid concentration. In addition, due to chemical etching effects, larger pore sizes were obtained close to the sample surface.
Anomalous strain rate dependence of tensile ductility in moisture-embrittled Co3Ti alloys
Authors: Takasugi T. , Tsuyumu T. , Kaneno Y. , Inoue H.
Published: March 2008

The effect of strain rate on tensile ductility of moisture-induced embrittlement of Co3Ti alloys was investigated at ambient temperatures (298–353 K) by tensile test and scanning electron microscope fractography. The anomalous increase of tensile elongation and ultimate tensile stress was observed in a very low strain rate region and also at high temperatures, accompanied by an increase of area fraction in ductile transgranular fracture pattern. The anomalous strain rate dependence of tensile ductility was shown to become more evident with decreasing grain size and also with deviation from alloy stoichiometry. Oxidation on the alloy surface was suggested as a process counteractive to the hydrogen decomposition process from moisture in air.
Effect of Nb content on the strength of Cu–Nb filamentary microcomposites
Authors: Hong Sun Ig
Published: March 2008

The yield strength of Cu–Nb filamentary microcomposites was predicted as a function of Nb content by modifying the barrier strengthening model. To predict the variation of the yield strength with Nb content, the interfilamentary spacing was calculated as a function of Nb content on the basis of the assumption that Nb filaments are distributed regularly along the sides of triangular unit cells. The yield stress can be described as the sum of the substructural strengthening component and the filament boundary strengthening term. The good agreement between the prediction and the experimental data suggests that the strength increase in Cu–Nb filamentary microcomposites with increasing Nb content results mostly from increasing the volume fraction of Nb filaments, which act as barriers to plastic flow.
Quasicrystalline coatings: Thermal evolution of structure and properties
Authors: Lang C. I. , Sordelet D. J. , Besser M. F. , Shechtman D. , Biancaniello F. S. , Gonzalez E. J.
Published: March 2008

Quasicrystals (QCs) are known to exhibit unique properties as a result of their unique quasiperiodic structure. Real quasicrystalline (QC) materials, however, may exhibit complex phase structures, and as a consequence, their properties may differ from expectations. In the present work, QC coatings of the Al–Cu–Fe, Al–Cu–Fe–Cr, and Al–Pd–Mn systems were prepared by a plasma spray process, followed by heat treatments in the range 500–800 °C. The phase structure and evolution of the coatings were evaluated, and thermal diffusivity, hardness, and friction coefficient were measured. The presence of quasicrystalline and crystalline phases and their influence on these properties is systematically considered for the first time. Broadly, the coatings exhibit the properties expected of QC materials, low thermal diffusivity, high hardness, and low coefficients of friction, but it is also shown that these properties can be sensitive to the phase structure of the coatings. This suggests that phase structure may be manipulated by heat treatment to optimize the properties of QC coatings.
In situAl3Ti–Al2O3 intermetallic matrix composite: Synthesis, microstructure, and compressive behavior
Authors: Peng H. X. , Fan Z. , Wang D. Z.
Published: March 2008

A fully dense in situ Al3Ti–Al2O3 intermetallic matrix composite containing about 30 vol% Al2O3 particles was prepared by combining squeeze casting with combustion synthesis using the chemical reaction between TiO2 and Al. The microstructure of the in situ composite was examined using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Compressive behavior of the composite was investigated in the temperature range of 25–600 °C and compared with that of the as-cast Al3Ti alloy. The in situ formed spherical α–Al2O3 particles with a size of 0.2–1 μm were uniformly distributed in the Al3Ti matrix. The grain size of the Al3Ti matrix containing a small amount of Al2Ti precipitate was 2–10 μm. The compressive strength of the in situ composite was about 6–9 times that of the as-cast monolithic Al3Ti alloy and could be maintained at temperatures up to 600 °C. This was mainly attributed to the fine grain size of Al3Ti matrix and the rule of mixture strengthening of Al2O3 particles. The existence of Al2Ti phase and high dislocation density in the matrix also contributed positively to the composite strength.
Slow recrystallization in the polymer electrolyte system poly(ethylene oxide)n–LiN(CF3SO2)2
Authors: Edman Ludvig , Ferry Anders , Doeff Marca M.
Published: March 2008

Thermal and ion-transport properties of the salt-in-polymer system poly(ethylene oxide)n–LiN(CF3SO2)2 [P(EO)nLiTFSI] were investigated for compositions ranging from n = 5 to n = 50. Particular attention was paid to the region n = 8 to 10 where a crystallinity gap previously had been reported. We concluded that the absence of distinct melting transitions for salt-rich compositions (n = 5 to 12) was attributable to the extremely slow kinetics of recrystallization of this system following a heat treatment. The results further indicated that it was primarily the nucleation process that was inhibited by the [(bis)trifluoromethanesulfonate imide] (TFSI) anion. As a corollary, the ionic conductivity was strongly dependent on the thermal history of samples, and an enhancement of up to 300% was observed in the ambient temperature ionic conductivity for pre-heated salt-rich samples.
Thermal analysis studies of oxygen chemisorption on nanocrystalline SnO2
Authors: Shek C. H. , Lin G. M.
Published: March 2008

The oxygen chemisorption on nanocrystalline SnO2 at temperature range between 100 and 450 °C was studied with differential thermal analysis (DTA) and electrical conductivity measurement. The O2−, O−, and O2m ionosorptions were observed and could be distinguished from each other only on nanocrystalline SnO2 with grain size less than 5 nm. Assuming steady-state adsorption, the heats of adsorption for O2− and O− (or O2−) on nanocrystalline SnO2 are 1.09 and 1.50 eV respectively from the results of DTA.
Zinc environment in aluminoborosilicate glasses by Zn K-edge extended x-ray absorption fine structure spectroscopy
Authors: Grand M. Le , Ramos A. Y. , Calas G. , Galoisy L. , Ghaleb D. , Pacaud F.
Published: March 2008

The structural surrounding of Zn in inactive nuclear glasses was determined using extended x-ray absorption fine structure spectroscopy. Zn was found in tetrahedralcoordination ([4]Zn) with [4]Zn–O distances of 1.95 Å. ZnO4 tetrahedra shared corners with SiO4 tetrahedra [d(Zn–Si) around 3.20 Å]. The oxygens of the Zn–O–Si bonds were charge compensated by Na+ and, to a minor extent, by Cs+. The influence of [4]Zn on the formation of charge-compensating cations at the expense of network modifiers may explain the stabilizing effect of Zn in these glasses.
Compositional variation of microstructure in ion-implanted AlxGa1−xAs
Authors: Lagow B. W. , Robertson I. M. , Rehn L. E. , Baldo P. M. , Coleman J. J. , Yeoh T. S.
Published: March 2008

The ion damage produced in alloys of AlxGa1−xAs (x = 0.6, 0.7, 0.8, and 0.85) by implantation at 77 K with Kr ions (500, 700, and 1500 keV) was studied by using Rutherford backscattering channeling and transmission electron microscopy. In addition, the accumulation of ion damage at 50 K was studied by performing the ion implantations in situ in the transmission electron microscope. In Al0.8Ga0.2As, damage accumulation at 77 K was independent of dose rate, indicating that dynamic annealing is not occurring at 77 K. The in situ studies demonstrated that planar defects are produced on warm-up from 50 K to room temperature, indicating that they are not the nucleation site for amorphization. The lower energy implantations revealed that amorphization initiated within the AlxGa1−xAs layer, showing that heterointerfaces are not required for amorphization. These results, along with the similarity of the room-temperature microstructures in the different alloys, imply that the amorphization mechanism is independent of Al content. It is proposed that the observed dependence of the amorphization dose on Al content is related to an increase in the number of cascade overlaps needed to initiate and to produce a continuous amorphous layer. A mechanism explaining the microstructural changes with composition, based on the thermal and physical properties of the alloy and on the distribution of energetic cascade events, is presented.
Formation of nanophases in a Cu–Zn alloy under high current density electropulsing
Authors: Zhang W. , Sui M. L. , Hu K. Y. , Li D. X. , Guo X. N. , He G. H. , Zhou B. L.
Published: March 2008

The microstructure of samples before and after a high current density electropulsing treatment was characterized by using high-resolution transmission electron microscopy. It has been found that in the coarse-grained Cu–Zn alloy subjected to the electropulsing treatment, two nanophases were formed, α–Cu(Zn) and β′–(CuZn), the average grain size of which is about 11 nm. A possible mechanism for the formation of nanophases was proposed. The experimental results indicated that electropulsing, as an instantaneous high-energy input, plays an important role in the nonequilibrium microstructural changes in materials and serves as a potential processing approach to synthesize nanostructured materials.
Optical and electrical properties of solid photocatalyst Bi2InNbO7
Authors: Zou Zhigang , Ye Jinhua , Arakawa Hironori
Published: March 2008

A polycrystalline sample of Bi2InNbO7 was synthesized by a solid-state reaction and characterized by powder x-ray diffraction and Rietveld structure refinement. The optical absorption and electrical properties of Bi2InNbO7 were investigated. It was found that the Bi2InNbO7 compound exhibited a direct gap semiconducting behavior. Conductivity measurement showed the compound had an activation energy of 2.62(5) eV. Ultraviolet–visible diffuse reflectance spectroscopy measurement revealed that the band gap of Bi2InNbO7 is about 2.7(4) eV.
Nanostructured carbon generated by chemical vapor deposition from acetylene on surfaces pretreated by a combination of physical and chemical methods
Authors: Siska Andrea , Kónya Zoltán , Hernádi Klára , Kiricsi Imre , Kordás Krisztián , Vajtai Róbert
Published: March 2008

Chemical vapor deposition of carbon nanotubes by catalytic decomposition of acetylene on V2O5microtube crystals is presented. The catalyst was prepared by laser irradiation of vanadium sheets and treated with cobalt acetate solution. The carbon deposits generated on this novel type of catalyst were characterized by transmission electron microscopy measurements. Both carbon nanofibers and carbon nanotubes were found to be formed. This catalyst system, generated by the combined laser irradiation and chemical impregnation methods, is a new and promising way to study the differences in the mechanism of the generation of nanostructures.
Deformation-induced α2 ↔ γ phase transformation in a Ti–48Al–2Cr alloy
Authors: Zhang J. X. , Ye H. Q.
Published: March 2008

The structure of γ–α2 interfaces in deformed Ti–48Al–2Cr alloy was analyzed by high-resolution transmission electron microscopy (HREM) and image simulations. Growth of γ–TiAl plate in α2–Ti3Al phase was found to be a result of a ledge mechanism consisting of Shockley partial dislocations on alternate (0001)α2 planes. The height of the ledges was always a multiple of two (0001)α2 planes. The γ → α2 phase transformation was also an interface-related process. Large ledges of six close packed planes (111)γ high were often observed at the γ–α2 interface. Every large ledge consisted of six Shockley partial dislocations that originated from the γ–a2 interfacial lattice misfit. The movement of these partial dislocations accomplished the transformation of γ → α2 phase. Comparing the experimental and simulated HREM image, it was found that atomic reordering appears during the deformation-induced γ↔α2 transformation.
Energetics and electronic structure of point defects associated with oxygen excess at a tilt boundary of ZnO
Authors: Oba Fumiyasu , Adachi Hirohiko , Tanaka Isao
Published: March 2008

The formation energies and electronic structure of zinc vacancies and oxygen interstitials at a tilt boundary of ZnO were investigated by a combination of static lattice and first-principles molecular orbital methods. For both of the defect species, the formation energies were lower than those of the bulk defects at certain sites in the grain boundary. The defects with low formation energies formed electronic states close to the top of the valence band. The interfacial electronic states observed experimentally in ZnO varistors cannot be explained solely by the point defects associated with the oxygen excess: the effects of impurities should be significant for the states.
Amorphous iron oxide prepared by microwave heating
Authors: Palchik Oleg , Felner Israel , Kataby Gina , Gedanken Aharon
Published: March 2008

Amorphous iron oxide (Fe2O3) was prepared by the pyrolysis of iron pentacarbonyl [Fe(CO)5] in a modified domestic microwave oven in refluxing chlorobenzene as a solvent under air. The reaction time was 20 min. Partially separated particles of iron oxide, 2–3 nm in diameter, were obtained. The other part showed aggregated spheres with a diameter of 25–40 nm. Differential scanning calorimetry measurements showed an amorphous/crystalline phase transition at about 250 °C.
Microstructure of (Y + Sm)–α-sialon with a-sialon seeds
Authors: Chen Wei-wu , Sun Wei-ying , Li Ya-wen , Yan Dong-sheng
Published: March 2008

(Y + Sm)–α-sialon compositions with and without α-sialon seeds were hot-pressed at 1800 °C for 1 h and then heat treated at 1800 °C for 4 h. The effect of α-sialon seeds on the microstructures of (Y + Sm)–α-sialon ceramics was studied by scanning electron microscopy. The results showed that hot-pressed α-sialon ceramics with elongated grains can be fabricated by adding 10 wt% seeds. Through heat treatment, the seed-free composition could also develop into a similar microstructure with big elongated grains dispersed in a fine matrix.
Novel route to alumina and aluminate interlayer coatings for SiC, carbon, and Kevlart® fiber-reinforced ceramic matrix composites using carboxylate–alumoxane nanoparticles
Authors: Callender Rhonda L. , Barron Andrew R.
Published: March 2008

SiC, carbon, and Kevlart® fibers were coated with carboxylate–alumoxane nanoparticles and their calcium-, lanthanum-, and yttrium-doped analogs; firing to 1400 °C formed uniform aluminate coatings. Optimum processing sequences were determined. Both carboxylate–alumoxane- and ceramic-coated fibers were examined by field emission scanning electron microscopy, microprobe analysis, and optical microscopy. Coatings produced were stable to thermal cycling under air at 1400 °C. Fiber-reinforced ceramic matrix composites were prepared and results from 3-point bend tests for carbon/Kevlar®-fabric-reinforced ceramic matrix composites (CMCs) and carbon-fiber-reinforced CMCs were determined. Flexure strength for carbon-fiber- and carbon/Kevlart®-fiber-reinforced alumina CMCs was determined.
Microstructural observation of a composite film of c-BN and h-BN phases
Authors: Park Young-Joon , Baik Young-Joon , Choi Jae Hyoung , Lee Jeong Yong , Hahn Jun-Hee
Published: March 2008

BN films consisting of c-BN and h-BN phases were synthesized using an ion-beam-assisted deposition process. In contrast to conventional observations, the c-BN and h-BN phases did not form separate layers, but were distributed in the form of nano-sized grains throughout the film thickness. No distinctly aligned h-BN layer was observed before the c-BN phase. Such a mixed character of the film was attributed to a localized ion bombardment effect instead of the macro-stress. Possibly because of the presence of scattered h-BN phases, the thin film described here possessed a low hardness of about 20 GPa and a low stress of about 5 GPa, compared with other reported c-BN-containing films.
Liquid metal extraction of Nd from NdFeB magnet scrap
Authors: Xu Y. , Chumbley L. S. , Laabs F. C.
Published: March 2008

This research involves using molten magnesium (Mg) to remove neodymium (Nd) from NdFeB magnet scrap by diffusion. Mg was melted over pieces of NdFeB scrap and held at temperatures in the range 675–705 °C for 2–8 h. The Mg was allowed to solidify, and the castings were then sectioned and characterized using scanning electron microscopy, x-ray diffraction, and chemical analysis. Nd was found to have diffused out of the solid scrap into the molten Mg. The thickness of the diffusion layer was measured, the diffusion of Nd through the NdFeB scrap into liquid Mg was described, and the diffusion coefficient of Nd in liquid Mg was estimated.
Synthesis of bimodally porous titania powders by hydrolysis of titanium tetraisopropoxide
Authors: Song Ki Chang , Pratsinis Sotiris E.
Published: March 2008

Bimodally porous titania powders with controlled phase composition and porosity were made by hydrolysis of titanium tetraisopropoxide (TTIP) and calcination. The extent of calcination was followed by thermogravimetric differential thermal analysis and Fourier transform infrared spectroscopy. The specific surface area (SSA) of the powders ranged from 10 to 500 m2/g as determined by nitrogen adsorption. The SSA increased by decreasing either the water concentration during hydrolysis or the calcination temperature. The pore size distribution was bimodal with fine intraparticle pore diameters at 1–6 nm and larger interparticle pore diameters at 30–120 nm as determined by nitrogen adsorption isotherms. The particle phase composition as determined by x-ray diffraction ranged from amorphous to crystalline anatase and rutile largely proportional to the calcination temperature and to a lesser extent on the initial H2O/TTIP molar ratio.
Study of diamond adhesion behavior on chromium and titanium for obtaining adherent diamond coatings on steel
Authors: Fan Q. H. , Grácio J. , Pereira E. , Ali N. , Ahmed W.
Published: March 2008

It is known that diamond films display poor adhesion on metals such as copper and steel. One solution to overcome the poor adhesion is to use interlayer materials. In this study we report results of an investigation of the adhesion behavior of diamond on pure chromium (Cr) and titanium (Ti) substrates. Cr and Ti are promising interlayer materials for adhering diamond to stainless steel. The coating adhesion was studied using indentation tests combined with acoustic emission signals during loading. It was found that a 105-N load indentation caused the film to delaminate from the Cr substrate, while the diamond film remained attached to the titanium even after the indentation at 180 N. Micro-Raman spectroscopy was used to monitor the film stress. The diamond films grown on Ti substrates were found to be less stressed than the films grown on Cr substrates. Therefore, Ti was used in thin-film form to obtain adherent diamond coatings on steel.
Optimization of seeding conditions for the fabrication of c-axis-oriented large NdBCO–Ag grains
Authors: Lo Wai , Salama Kamel
Published: March 2008

NdBCO large-grain materials can improve the performance of engineering devices based on superconducting bulk materials if c-axis-oriented large grains can be produced in large quantities under simple processing conditions. This study concentrates on exploring the factors dictating the seeding behavior and the subsequent growth morphology of Ag-doped NdBCO grains under relatively high oxygen partial pressure using NdBCO seeds and a simple processing system. It was found that seeding temperature, aspect ratio of seed, and amount of Ag were all important factors affecting the success rate of inducing c-axis-oriented growths. With the optimized seeding conditions and in view of the simplicity of the processing system, the processing conditions derived from this study could lead to the up-scaling of NdBCO–Ag large-grain materials production.
Properties of zirconia films dispersed with PbS nanoparticles
Authors: Huang Weimin , Shi Jianlin
Published: March 2008

PbS/ZrO2 optical films were prepared by the dip-coating method from a mixed sol containing two precursors, Zr(OC3H7)4 and Pb(CH3COO)2. The phase structure and size of PbS nanoparticles were characterized by x-ray diffraction and transmission electron microscopy, respectively. Optical absorption and fluorescence spectra were taken on the PbS/ZrO2 films. Larger blue shifts of band edge and weak fluorescence emission of PbS were observed. The third-order nonlinear properties of PbS/ZrO2 films were studied. The calculated values of nonlinear refractive indexes n2 varied between 10−8 and 10−9 cm2/W.
A comparative fatigue study of solder/electroless-nickel and solder/copper interfaces
Authors: Liu Pi Lin , Shang Jian Ku
Published: March 2008

The fatigue resistance of the interface between electroless–nickel and the eutectic tin–lead solder alloy was examined in the as-reflowed and aged conditions and compared to fatigue behavior of the copper/solder interface under the same conditions. In the as-reflowed state, the fatigue resistance of the solder/electroless-nickel interface was slightly superior to that of the solder/copper interface. However, after long-term aging, the fatigue resistance of the solder/electroless-nickel interface became far worse in the high crack growth rate regime. Examinations of interfacial microstructures and crack growth mechanisms indicated that the differences in fatigue resistance between the two interfaces were not directly related to the thickness of the intermetallic phase at the interface, as commonly believed, but were due to differences in crack growth mechanisms.
Effect of annealing on fluorescence of Ce3+-doped silica prepared by sol-gel process
Authors: Bi H. J. , Cai W. P. , Shi H. Z. , Zhang L. D. , Yao B. D.
Published: March 2008

We prepared Ce3+-doped silica by the sol-gel method and studied the effect of annealing on fluorescence of these samples. Different fluorescence was observed for samples annealed at different temperatures, changing gradually from solution like fluorescence to fluorescence similar to that observed in the Ce3+-doped silica prepared by chemical vapor deposition. It was found that the emission intensity first decreased with increasing annealing temperature until 500 °C, and then increased with the temperature ranging from 500 to 950 °C. Meanwhile, the emission peak showed a large red shift and an obvious broadening. These changes were attributed to the annealing-induced structural evolution in silica: Ce3+ ions changed from coordinating with water and terminal OH-groups to embedding in silica network.
Characterization of yttrium aluminate garnet precursors synthesized via precipitation using ammonium bicarbonate as the precipitant
Authors: Li Ji-Guang , Ikegami Takayasu , Lee Jong-Heun , Mori Toshiyuki
Published: March 2008

Stoichiometric yttrium aluminate garnet (Y3Al5O12) precursors with a wide range of chemical compositions were precipitated by dripping a mixed solution of ammonium aluminum sulfate and yttrium nitrate into ammonium bicarbonate solutions. The resultant precursors were characterized by chemical analysis, infrared spectroscopy, differential thermal analysis/thermogravimetry, x-ray diffractometry, and scanning electron microscopy. The effects of reaction temperature, precipitant concentration, dripping speed of the salt solution, and the molar ratio of precipitant/total-cations on the composition, thermal behavior, and particle morphology of the resultant precursors were investigated. The precipitation conditions that yield carbonate precursors composed of ammonium dawsonite [NH4Al(OH)2CO3] and yttrium normal carbonate [Y2(CO3)3 · 3H2O] were determined.
Effect of current crowding on contact failure in heavily doped n+- and p+-silicon-on-insulator
Authors: Huang J. S. , Chen Chih , Yeh C. C. , Tu K. N. , Shofner T. L. , Drown J. L. , Irwin R. B. , Vartuli C. B.
Published: March 2008

Stability of submicron contacts under high current density has been an outstanding reliability issue in advanced Si devices. Polarity effect of failure was observed in Ni and Ni2Si contacts on n+-Si and p+-Si. In this report, we studied the failure due to high current density in contacts to n+- and p+-silicon-on-insulator (SOI). We found similar polarity effects below certain current: the p+-SOI failed preferentially at the cathode, while the n+-SOI failed preferentially at the anode. At higher current, damage occurred at both contacts. The effect of current crowding was evident in both cases.
Formation and characterization of germanium nanoparticles
Authors: Welham N. J.
Published: March 2008

Elemental germanium was mechanically milled with magnesium oxide with the intention of forming disperse nanoparticulate germanium in a soluble matrix. The crystallite size was determined by x-ray diffraction (XRD) and Raman spectroscopy using a phonon confinement model. The crystallite size was found to decrease exponentially with milling time; however, the size determined by XRD was typically five to ten times greater than that by Raman. This was attributed to the presence of two separate crystallite sizes, which were averaged when using the Scherrer equation for the XRD data. Sonication of the powder resulted in the breakup of >20 μm aggregates into individual particles of approximately 40 nm. These particles are thought to compose a single crystal core with a crystallite size of approximately 28 nm surrounded by a layer of smaller crystallites (approximately 5 nm), which showed quantization during Raman spectroscopy. Separation of the germanium from the magnesium oxide was readily achieved using a simple acid leach, although some oxidation of germanium was evident when using an aqueous leach.
Structure of polymer intercalated MnPS3 and CdPS3
Authors: Yang D. , Frindt R. F.
Published: March 2008

Layered MnPS3 and CdPS3 powders were used to prepare M1−xK2xPS3/poly(ethylene glycol) (PEG) and M1−xK2xPS3/poly(vinyl pyrrolidone) (PVP) (M = Cd, Mn) intercalation nanocomposites. The structure of these compounds was studied by x-ray diffraction. The host layers in Cd0.8K0.4PS3 (PEG)2.0 and Mn0.8K0.4PS3(PEG)2.0 nanocomposites were 3-dimensional crystals with a monoclinic unit cell. The in-plane spacings were slightly expanded from original monoclinic MPS3 (0.2% for CdPS3 and 0.5% for MnPS3), while the inter-layer spacing was expanded by 8.87 Å for Cd0.8K0.4PS3(PEG)2.0 and 8.86 Å for Mn0.8K0.4PS3(PEG)2.0. The Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites, on the other hand, had an expanded interlayer spacing of about 30 Å and the diffraction patterns contained only (00l) and (hk0) peaks, and no mixed (hkl) peaks were observed. The (hk0) peaks were 2-dimensional, with strongly asymmetric line shapes, and there was excellent agreement with pattern calculations for single molecular layers. This demonstrated that the host layers in Cd0.8K0.4PS3(PVP)1.1 and Mn0.8K0.4PS3(PVP)1.1 nanocomposites were tubostratically stacked layered systems.
Ni-based bulk amorphous alloys in the Ni–Ti–Zr–(Si, Sn) system
Authors: Yi S. , Park T. G. , Kim D. H.
Published: March 2008

New Ni-based bulk amorphous alloys in the alloy system Ni–Ti–Zr–(Si,Sn) were developed through systematic alloy design based upon the empirical rules for high glass forming alloys. Small additions of Si and/or Sn significantly improved the glass forming ability (GFA) of the alloys Ni57Ti23−xZr20 (Si,Sn)x leading to a Ni-based bulk amorphous alloy. The amorphous ribbons of the alloys Ni57Ti23−xZr20 (Si,Sn)x exhibited very high glass transition temperatures (Tg > 823 K), crystallization temperatures (Tx > 883 K), and large undercooled liquid regions (δTx > 50 K) implying the high GFA of the alloys. Fully amorphous rods with the diameter of up to 2 mm can be fabricated by a copper mold casting method. Development of the new Ni-based bulk amorphous alloys having high Tg,Tx, and δTx expands the practical applications of amorphous alloys as structural materials.
Epitaxially grown LiNbO3 thin films by polymeric precursor method
Authors: Bouquet V. , Bernardi M. I. B. , Zanetti S. M. , Leite E. R. , Longo E. , Varela J. A. , Viry M. Guilloux , Perrin A.
Published: March 2008

LiNbO3 thin films were grown on (0001) sapphire substrates by a chemical route, using the polymeric precursor method. The overall process consists of preparing a coating solution from the Pechini process, based on metallic citrate polymerization. The precursor films, deposited by dip coating, are then heat treated to eliminate the organic material and to synthesize the phase. In this work, we studied the influence of the heat treatment on the structural and optical properties of single-layered films. Two routes were also investigated to increase the film thickness: increasing the viscosity of the coating solution and/or increasing the number of successively deposited layers. The x-ray diffraction θ-2θ scans revealed the c-axis orientation of the single- and multilayered films and showed that efficient crystallization can be obtained at temperatures as low as 400 °C. The phi-scan diffraction evidenced the epitaxial growth with two in-plane variants. A microstructural study revealed that the films were crack free, homogeneous, and relatively dense. Finally, the investigation of the optical properties (optical transmittance and refractive index) confirmed the good quality of the films. These results indicate that the polymeric precursor method is a promising process to develop lithium niobate waveguides.
Atom location by channeling enhanced microanalysis study of site distributions of alloying elements in titanium aluminides
Authors: Hao Y. L. , Yang R. , Cui Y. Y. , Li D.
Published: March 2008

The original equation of Spence and Taftø for quantitative determination of site occupancy using atom location by channeling enhanced microanalysis method has been extended to take into account both delocalization effect and the influence of point defects (antisite atomic distribution and vacancies). The outcome of this treatment suggests that, for crystals free of antisite defects, the accuracy of site occupancy is influenced by delocalization effect but is independent of both thermal and structural vacancies. For crystals free of structural vacancies, the accuracy of site occupancy is influenced by both delocalization effect and antisite defects, but is independent of thermal vacancies. The delocalization effect was shown to vary with channeling strength at a given channeling condition. For a binary ordered phase in which at least one of the host elements exhibits weak delocalization effect (as is the case for many transition-metal aluminides), a tangent-line method for obtaining the value of k (a parameter necessary for the calculation of site occupancy) was proposed, allowing the determination of the delocalization correction factor for the other host element. Application of this method to estimating the delocalization effect of Al in Ti3Al and TiAl under axial and planar channeling conditions, respectively, was demonstrated.
Semi-coherent zirconia inclusions in a ceramic matrix
Authors: Guinebretière R. , Oudjedi Z. , Soulestin B. , Dauger A.
Published: March 2008

Nanocomposite ceramic materials were fabricated by conventional sintering of composite powders obtained by sol-gel coating of submicron powders. The microstructure of these MgAl2O4–ZrO2 materials was studied by transmission electron microscopy. All zirconia grains were in the tetragonal phase. In addition, the intragranular zirconia crystals exhibited heteroepitaxial orientation relationships with the surrounding spinel grains, (hkl)zirconia//(hkl)spinel. Semi-coherent interfaces along {111} planes were observed by high-resolution microscopy. The transformation toward the orthorhombic or the monoclinic phase retained the epitaxial relationships as far as possible. The presence of such heteroepitaxial intragranular crystals in sintered ceramic materials, which did not involve a melting stage, was attributed to the specificity of the material preparation process.
A new route for the synthesis of calcium-deficient hydroxyapatites with low Ca/P ratio: Both spectroscopic and electric characterization
Authors: Andrés-Vergés M. , Fern´andez-González C. , Martínez-Gallego M. , Solier J. D. , Cachadiña I. , Matijević E.
Published: March 2008

A new route for obtaining calcium-deficient apatites with a Ca/P ratio lower than 1.5 is described, in order to study their proton conduction at temperatures lower than 400 °C. The process is based on the hydrolysis of a mixed solution of Ca(NO3)2 and NH4H2PO4 in the presence of hexamethylenetetramine at a pH of approximately 5 and temperatures of 85–90 °C. The resulting spherical particles of 14 μm in average diameter were aggregates of smaller needles with approximate composition Ca8.5(HPO4)2(PO4)4OH · H2O. The effects of the reagent concentrations, pH, aging time, and temperature were studied, and the solids were characterized by x-ray diffraction, infrared absorption spectroscopy, and electron microscopy. The ionic conduction measured by alternating-current impedance spectroscopy yielded a value of 3 μSm−1 at 200 °C.
Influence of scandium on superplastic ductilities in an Al–Mg–Sc alloy
Authors: Komura Shogo , Horita Zenji , Furukawa Minoru , Nemoto Minoru , Langdon Terence G.
Published: March 2008

Ultrafine grain sizes, of the order of approximately 0.2 μm, may be introduced into Al–Mg–Sc alloys by subjecting the material to severe plastic deformation through the process of equal-channel angular pressing (ECAP). Experiments were conducted to evaluate the influence of the solution treatment temperature on the ductility of an Al–3% Mg–0.2% Sc alloy after ECAP. The results show the highest ductilities are achieved when the solution treatment temperature is within the narrow range of approximately 878 to about 883 K, immediately below the temperature associated with the onset of partial melting. These high temperatures serve to maximize the amount of scandium in solid solution and this leads, on subsequent heating, to an extensive precipitation of fine secondary Al3Sc particles which inhibit grain growth at the higher temperatures. Conversely, solution treatments at temperatures below approximately 878 K give less Sc in solid solution within the matrix and the precipitation of the Al3Sc particles is then insufficient to retain a uniform ultrafine microstructure.
Novel epitaxial growth of barium titanate thin films by electrodeposition
Authors: Tamaki Jun , Goh Gregory K. L. , Lange Fred F.
Published: March 2008

Electrodeposition was used to grow epitaxially BaTiO3 thin films on SrTiO3 single-crystal substrates with La0.7Sr0.3MnO3 (LSMO) conducting buffer layers. The epitaxial films appeared to consist of very small (ø10 nm) particles. The film completely covered the substrate when the reaction was performed at temperatures between 60 and 90 °C with LSMO potentials of –0.5 to –1.0 V against a Pt counter-electrode. It appeared that an electrophoretic force, acting on BaTiO3 nuclei within the solution, facilitated the deposition of the film.
Preparation of SiO2-pillared layered titanate thin films
Authors: Sumida Takeshi , Abe Ryu , Hara Michikazu , Kondo Junko N. , Domen Kazunari
Published: March 2008

The interlayer space of a thin film of layered titanate, Cs0.68Ti1.83‪0.17O4, was successfully expanded by SiO2 pillaring. Ion exchange of the Cs ions in the interlayer to alkylammoniuim cations, n-CnH2n+1NH3+ (n = 8, 12, 18), expanded the interlayer space, and enabled intercalation of tetraethylorthosilicate. X-ray diffraction and the cross section of transmission electron microscopy images revealed that tetraethylorthosilicate-treated thin film maintained the expansion of interlayer space by SiO2 pillaring after calcination at 773 K. X-ray photoelectron spectroscopy after etching the thin film about 100 nm from the surface further confirmed the existence of SiO2 in the interlayer space.
Hard multilayered thin films of metal–intermetallic Ni/Ni3Al
Authors: Meng X. K. , Vehoff H. , Ngan A. H. W.
Published: March 2008

Metal–intermetallic Ni/Ni3Al multilayered thin films were synthesized by the magnetron sputtering technique. The synthesized films possessed high hardness that could be compared with intermetallic Ni3Al films. The constituent layers of Ni and Ni3Al were fully adherent to one another at the multilayered boundaries. The fracture surface of the multilayered films on bending showed the characteristics of local ductile fracture. This novel type of multilayered thin films is expected to be used as hard coatings and miniaturized parts of apparatus in micro-electromechanical systems.
Oxygen diffusion along the short-circuit paths in bicrystal SrTiO3
Authors: Sakaguchi Isao , Komastu Manabu , Watanabe Akio , Haneda Hajime
Published: March 2008

Oxygen diffusion in bicrystal SrTiO3 was investigated with the aid of resistive anode encoder of secondary-ion mass spectrometry. The diffusion profiles of 18O on volume, grain boundary (joining interface), and dislocation were separately determined from the three-dimensional distribution of 18O in the bicrystal SrTiO3. The volume diffusion of oxygen is found to be dependent on (i) Nb doping concentration, (ii) crystallographic orientation, and (iii) nonequilibrium oxygen defects that are annihilated by thermal annealing. The feature of 18O diffusion image along the dislocation in (100) and (110) bicrystals can be explained by the dislocation array introduced by the mechanical polishing.
Improvement of the crystallinity of GaN epitaxial layers grown on porous Si (100) layers by using a two-step method
Authors: Kang T. W. , Park S. H. , Kim T. W.
Published: March 2008

A new approach was used for combining GaN and porous Si with the goal of producing high-quality GaN epitaxial layers for optoelectronic integrated circuit devices based on Si substrates. Reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), photoluminescence (PL), and Van der Pauw–Hall effect measurements were performed to investigate the structural, optical, and electrical properties of the GaN epitaxial films grown on porous Si(100) by plasma-assisted molecular-beam epitaxy with a two-step method. The RHEED patterns were streaky with clear Kikuchi lines, which was direct evidence for layer-by-layer two-dimensional growth of GaN epitaxial layers on porous Si layers. The XRD curves showed that the grown layers were GaN(0001) epitaxial films. The results of the XRD and the PL measurements showed that the crystallinities of the GaN epilayers grown on porous Si by using a two-step growth were remarkably improved because the porous Si layer reduced the strains in the GaN epilayers by sharing them with the Si substrates. Hall-effect measurements showed that the mobility of the GaN active layer was higher than that of the GaN initial layer. These results indicate that high-quality GaN epitaxial films grown on porous Si(100) by using two-step growth hold promise for potential applications in new kinds of optoelectronic monolithic and ultralarge integrated circuits.
Real-time x-ray scattering study of growth behavior of sputter-deposited LaNiO3 thin films on Si substrates
Authors: Lee Hsin-Yi , Liang K. S. , Lee Chih-Hao , Wu Tai-Bor
Published: March 2008

Real-time x-ray reflectivity and diffraction measurements under in situ sputtering conditions were employed to study the growth behavior of LaNiO3 thin films on a Si substrate. Our results clearly show there is a transition layer of 60 Å, which grew in the first 6 min of deposition. The in situ x-ray-diffraction patterns indicated that this transition layer is amorphous. Subsequently, a polycrystalline overlayer grew as observed from the in situ x-ray reflectivity curves and diffraction patterns. Nucleation and growth took place on this transition layer with random orientation and then the polycrystalline columnar textures of (100) and (110) grew on the top of this random orientation layer. By comparing the integrated intensities of two Bragg peaks in the plane normal of x-ray diffraction, it was found that a crossover of the growth orientation from the ⟨110⟩ to the ⟨100ߩ direction occurred and the ability of (100) texturization enhanced with increasing film thickness beyond a certain critical value.
Production of Al–Ti–C grain refiner alloys by reactive synthesis of elemental powders: Part I. Reactive synthesis and characterization of alloys
Authors: Brinkman H. J. , Zupanič F. , Duszczyk J. , Katgerman L.
Published: March 2008

The first part of this article reports on the reactive synthesis and characterization of Al–Ti–C alloys intended as master alloys for aluminum grain refining. The alloys were produced from elemental powders by the thermal explosion mode and analyzed with x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Parameters were the titanium concentration (15 and 30 wt%) and the Ti/C ratio (9/1, 20/1, and 120/1) in the reactant powder mixture and the cooling rate after the reactive synthesis (1 and 120 °C/min). Full conversion of titanium and carbon into Al3Ti and TiC was achieved for the 30 wt% Ti mixtures but not for the 15 wt% Ti mixtures where the reaction was not exothermic enough. The Ti/C ratio did not affect the phase composition after reactive synthesis in the 30 wt% Ti alloys and could be used to tailor the microstructure of the alloy. The formation of Al4C3 was suppressed with a high cooling rate after the exothermic formation reactions.
Filling of single-walled carbon nanotubes with silver
Authors: Zhang Z. L. , Li B. , Shi Z. J. , Gu Z. N. , Xue Z. Q. , Peng L-M.
Published: March 2008

We showed, by high-resolution transmission electron microscopy and spatially resolved electron energy-loss spectroscopy, that silver atoms have been introduced into single- walled carbon nanotubes (SWCNTs) produced by the arc-discharge method with solution phase chemistry by capillary filling, and a high efficiency of filling may be realized. Both partially filled and completely filled SWCNTs were observed, and the metal inside the tube may be regarded as one-dimensional silver nanowires with high length-to-diameter ratios. The length of filling ranged from several to tens of nanometers. Under strong electron beam irradiation the filling metal condensed to a particle, while the silver-containing SWCNT shrank and disintegrated.
Influence of experiment parameters on the growth of cBN films by bias-assisted direct current jet plasma chemical vapor deposition
Authors: Zhang W. J. , Matsumoto S.
Published: March 2008

Boron nitride films were synthesized on silicon substrates by radio frequency-bias- assisted direct current jet chemical vapor deposition in Ar–N2–BF3–H2 system. The formation and content of cBN phase were investigated by means of Fourier transform infrared spectroscopy, glancing-angle x-ray diffraction, and scanning electron microscopy. The influences of the experimental parameters, i.e., bias voltage, substrate temperature, and gas composition, on the cBN content in the deposited films were systematically studied, and an experimentally optimum window for the deposition of cBN films was observed. Under optimized conditions, a boron nitride film with cBN content higher than 85% was deposited and a growth rate of about 70 nm/min was achieved.
Photoluminescence spectra of Zn1−xCdxAl2Se4-4xS4x single crystals
Authors: Choe Sung-Hyu , Yoon Chang-Sun , Jin Moon-Seog , Hyun Seung-Cheol , Kim Chang Dae , Lee Choong-Il , Goh Jae-Mo , Oh Seok-Kyun , Song Ho-Jun , Kim Wha-Tek
Published: March 2008

We investigated the photoluminescence as well as the crystal structure and optical energy gaps of the Zn1-xCdxAl2Se4-4xS4x solid solution system based on the Al-related compounds of ZnAl2Se4, ZnAl2S4, CdAl2Se4, and CdAl2S4. The single crystals of the system with 0.0 ≤ x ≤ 1.0 were grown by the chemical transport reaction technique. The Zn1-xCdxAl2Se4-4xS4x crystallizes in a defect chalcopyrite structure for a whole composition and has an optical energy gap ranging from 3.525 to 3.577 eV at 13 K. The photoluminescence spectra at 13 K showed a strong emission band in the blue spectral region and a weak broad emission band in the visible region due to donor–acceptor pair recombination. The composition and temperature dependence of these bands were examined in the investigated regions. The simple energy band scheme for the radiative mechanisms of the Zn1-xCdxAl2Se4-4xS4x is proposed on the basis of our experimental results along with photo-induced current transient spectroscopy measurements.