bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive liquid phase sintering of solution-derived YBa2Cu3O7−x superconducting thin films: Part I. Ambient and precursor effects on BaO–CuO liquid phase formation
Authors: Chu Peir-Yung , Buchanan Relva C.
Published: September 2007

Processing atmosphere and precursor effects on liquid phase formation were investigated in the BaO–CuO thin film system. Liquid phase was observed at a significantly lower temperature (∼620 °C) under N2 atmosphere with carboxylate solution precursors. In the processing of the YBCO oxide superconductors, formation of the liquid phase facilitated the decomposition of BaCO3 and crystallization of the YBCO grains. Larger grains and greater (00l) preferred orientation were also observed in the YBCO films prepared with the presence of the liquid phase.
The effect of post-annealing on laser-deposited superconducting Bi–Sr–Ca–Cu–O thin films
Authors: Kung P.J. , Wu X.D. , Muenchausen R.E. , Salazar K.V. , Foltyn S.R. , Peterson D.E. , Garcia A.R.
Published: September 2007

Superconducting Bi–Sr–Ca–Cu–O thin films were obtained from post-annealing partially crystallized and amorphous films grown on MgO(100) by pulsed laser deposition. The substrate temperature investigated was in the range of 350–750 °C, over a range of pressure 0.1 to 100 mTorr. The as-deposited films were annealed in 7.5 vol.% O2/Ar or in air at 800–865 °C from several minutes to a few hours. Unlike the pure Bi2Sr2CaCu2O8+δ (2212) phase (Tc = 80 K) which is easily formed after a long continuous period of post-annealing at a temperature below 830 °C, the formation of (Bi, Pb)2Sr2Ca2Cu3O10+δ (2223) phase from the as-deposited amorphous films requires repetitive annealing cycles of short duration in air at 850 °C to simultaneously achieve good crystal quality, small surface roughness, and sharp diamagnetic transition (Tc = 110 K). After annealing, the temperature is lowered down to ∼650 °C by quenching in air and then a slow-cooling step is employed. This procedure was found to enhance the volume fraction of the 2223 phase as compared with a direct slow-cooling process. The trade-off between annealing temperature and time was observed to affect the phase formation and the smoothness of the annealed films. To optimize the post-annealing conditions, Rutherford backscattering spectrometry, x-ray diffraction, and scanning electron microscopy were systematically used to examine the composition, structure, and morphology of the films, respectively.
Composition/structure/property relations of multi-ion-beam reactive sputtered lead lanthanum titanate thin films: Part II. Textured microstructure development
Authors: Fox G.R. , Krupanidhi S.B. , More K.L.
Published: September 2007

This paper, the second of three parts, presents a detailed analysis of the crystallographic texture observed in lead lanthanum titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering. Since films were deposited at a substrate temperature of 100 °C, they exhibit an amorphous structure that can be described by the structure zone model. The as-deposited microstructure is transformed via crystallization of the perovskite phase and PbO evaporation during postdeposition annealing. Transmission electron microscopy was used to determine that phase pure PLT films develop textured clusters (as large as 700 nm in diameter) consisting of 〈100〉 aligned 10 nm nanocrystals. As excess PbO is added to the PLT film, the textured cluster size decreases until only isolated PLT nanocrystals exist. Below a critical quantity of excess PbO in the as-deposited film (approximately 15 mole%), the textured cluster structure produces a 〈100〉 texture through the film thickness, which generates x-ray diffraction patterns typical of textured microstructures. At high PbO contents, the excess PbO causes the formation of clusters that are smaller than the film thickness, resulting in a polycrystalline-type x-ray diffraction pattern. A qualitative model describing microstructure development is presented.
Composition/structure/property relations of multi-ion-beam reactive sputtered lead lanthanum titanate thin films: Part III. Electrical properties
Authors: Fox G.R. , Krupanidhi S.B.
Published: September 2007

This paper, the third and final of a three part series, presents the electrical properties of postdeposition annealed, lead lanthanum titanate (PLT) thin films deposited by multi-ion-beam reactive sputtering (MIBERS). Also, a model is presented that explains the relations among composition, crystallographic structure, microstructure, and electrical properties of the PLT thin films. Thin films of PLT consisting of the perovskite phase exhibit 〈100〉 textured microstructures. Addition of a critical quantity of excess PbO results in the loss of this 〈100〉 texture, and continuity of the perovskite phase is disrupted while both excess PbO and porosity phases become continuous due to a percolation effect. Films with textured microstructures consisting of a continuous perovskite phase exhibit relatively high dc resistivities, high dielectric permittivities, and high remanent polarizations. At the transition between textured and nontextured microstructures, a discontinuous drop in the electrical properties occurs due to the ensuing continuity of the excess PbO and porosity. These composition-induced changes in the electrical properties were quantitatively modeled by applying a simple mixing rule model to the microstructure model developed in Part II of this series.
Nondestructive detection of fatigue cracks in PM 304 stainless steel by internal friction and elasticity
Authors: McGuire S.M. , Fine M.E. , Buck O. , Achenbach J.D.
Published: September 2007

A resonant frequency mechanical vibration method was used to nondestructively detect fatigue crack initiation in notched 304 stainless steel samples prepared by powder metallurgy. This method allowed the determination of an effective elastic modulus and the direct measurement of internal friction. Changes in the modulus and internal friction were found to correlate well with the presence of 50 μm long fatigue cracks. The length of the through cracks initiated at the notch was measured using surface replicas, which were examined in a scanning electron microscope. Small crack growth rate data were also obtained and plotted versus the stress intensity factor. The crack growth rates were compared with long crack data performed on compact tension samples of this material. The short cracks grew at intensity factors below the long crack threshold stress intensity factor.
Influence of vibration on grain size and degree of grain refinement in mild steel weldments
Authors: Tewari S.P.
Published: September 2007

Mild steel plates were welded under stationary and dynamic (longitudinal and transverse vibration) conditions. The frequency and amplitude ranges selected were 0 Hz to 300 Hz and 0 μm to 30 μm, respectively. It has been observed on the basis of experimental findings that vibration, in general, reduces the grain size of the weldment, and this reduction is appreciable at a lower amplitude of vibration. This may be due to the lower energy required for nucleation of the solid phase. Fast removal of latent heat of solidification from the solid liquid interface plays a significant part in the grain refinement under vibration.
A novel stable solid formed by C60 + oxygen at high P(O2)
Authors: Morris D.E. , Singh K.K. , Sinha A.P.B.
Published: September 2007

We report the formation of a novel solid form of carbon + oxygen. Exposure of C60 to high oxygen pressure [P(O2) ≍ 100 MPa] for several days at slightly above ambient temperature results in absorption of significant amounts of oxygen (up to ∼48% by weight after 3 days). X-ray diffraction measurements showed that the C60 pellets had become amorphous. Although part of the added weight is slowly lost in flowing oxygen at ambient pressure and temperature, most remains up to at least 100 °C. Heating in flowing He at 200 °C brought the weight back to near the original value. The reaction appears to be specific to C60 since the amorphous outgassed material had lost the capacity to absorb oxygen at high P(O2), and the oxygen absorption effect was absent in powdered graphite and in commercial amorphous carbon. The Raman spectrum differs from those of C60, soot, amorphous carbon, graphite, and diamond.
Effect of FeCl4– intercalation on the transport properties of a graphitized polyimide film
Authors: Nysten B. , Issi J-P. , Shioyama H. , Crespin M. , Setton R. , Béguin F. , Inagaki M.
Published: September 2007

The temperature variation of the thermal conductivity, the electrical resistivity, and the thermoelectric power of a graphitized polyimide film have been measured in the temperature range 2 < T < 300 K. The effect of the electrochemical intercalation with FeCl4− ions has also been studied. The thermal conductivity measurements confirm the high degree of graphitization that may be obtained with polyimide films. They show how intercalation increases the structural disorder and how the intercalate substantially contributes to the thermal conductivity at low temperatures. The electrical-resistivity and thermoelectric-power measurements reveal that the density of free carriers is about three times lower in stage-2 FeCl4− solvated intercalation compounds obtained by an electrochemical way than in stage-2 FeCl3 compounds obtained by a classical synthesis method.
Damage-to-dose ratio after low energy silicon ion implantation into crystalline silicon
Authors: Levin Y. , Herbots N. , Dunham S.
Published: September 2007

In this work, we develop a model describing the diffusion of vacancies and self-interstitials and their recombination during ion implantation. The model includes the effect of the moving surface due to regrowth and the defect generation rate as a function of depth based on Monte Carlo simulations. The results are compared to experimental measurements of the damage-to-dose ratio (DDR) after low energy, 40 eV, silicon ion implantation into silicon at 300 and 685 K. We have derived an analytic approximation which agrees with the results of the computational model, implemented on a CM-2 parallel computer. We find that the calculated effective diffusivity, the main adjustable parameter in the simulations, is much lower than predicted based on extrapolation from experiments at higher temperatures. We attribute this difference to the aggregation of self-interstitials. We also find that the effect of interstitial-vacancy recombination on DDR is negligible under the experimental conditions considered; however, the crystal surface motion has a significant impact on the results.
Epitaxial growth of AlN by plasma-assisted, gas-source molecular beam epitaxy
Authors: Rowland L.B. , Kern R.S. , Tanak S. , Davis Robert F.
Published: September 2007

Monocrystalline AlN(0001) films with few defects were deposited on vicinal α(6H)–SiC(0001) wafers via plasma-assisted, gas-source molecular beam epitaxy within the temperature range of 1050–1200 °C. The Al was thermally evaporated from an effusion cell. An electron cyclotron resonance plasma source was used to produce activated nitrogen species. Growth on vicinal Si(100) at 900–1050 °C resulted in smooth, highly oriented AlN(0001) films.
Crystal growth and morphology of hydrothermally grown lithium borates
Authors: Byrappa K. , Shekar K.V.K. , Rodriguez-Clemente R.
Published: September 2007

The Li2O–B2O3–H2O system has been studied under hydrothermal conditions. Li4B7O12Cl, Li2B4O7, Li3B5O8(OH)2, Li2HBO3, and LiH2B5O9 are the phases crystallizing in this system at 250 °C and P < 100 bars. The growth of these phases has been discussed in brief. Also, the growth morphology of these phases has been studied with reference to the growth parameters.
Effect of gallium oxide in preventing cristobalite formation in binary borosilicate glass composite
Authors: Jean Jau-Ho , Gupta Tapan K.
Published: September 2007

When an appropriate mixture of low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG and is controlled by the transport of alkali ions (e.g., K, Na, and Li) from BSG to HSG.1 In this paper we report that when a small amount of gallium oxide is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Ga+3 from gallium oxide particle and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to gallium oxide, thus forming a K+ and Ga+3-rich reaction layer adjacent to gallium oxide particles far too rapidly compared with that of cristobalite formation.
Ca(1−x)NixO catalytic thin films prepared by pulsed laser deposition
Authors: Mao X.L. , Perry D.L. , Russo R.E.
Published: September 2007

Ca(1−x)NixO solid-solution films with varying stoichiometry have been prepared by pulsed laser deposition from sintered targets of NiO and CaO. X-ray diffraction data indicate that the films have the structure of sodium chloride. The lattice constants for different stoichiometries vary with film composition. Using the Madelung energy as the binding energy between anions and cations and assuming that nickel and calcium ions are distributed randomly in lattice sites, the lattice constants were calculated and found to compare with experimental results. This study investigated the compositional changes that occur during the target sintering process and the pulsed laser deposition of films. Using these data, a target composition can be prepared to produce Ca(1−x)NixO thin films with any desired lattice constant.
Erratum
Authors: Sheldon Brian W. , Besmann Theodore M. , More Karren L. , Moss Thomas S.
Published: September 2007

“Epitaxical nucleation of polycrystalline silicon carbide during chemical vapor deposition” [J. Mater. Res. 8, 1086 (1993)]
Aligned gadolinium barium copper oxide thick films formed by in situ crystallization in a magnetic field
Authors: McKittrick Joanna , Contreras Ramiro , Clougherty Dennis
Published: September 2007

Gd-1:2:3 films were synthesized from acetate precursors and spun-on to polycrystalline substrates of yttria-stabilized zirconia. The substrates were fired in air at 500 °C in between each applied coat. After applying 10–30 coats, they were crystallized by heating to 900 °C in Ar or O2 with or without the application of a 1 T magnetic field. The applied magnetic field was found to produce c-axis alignment for films <4 μm. Annealing in argon produced alignment, but the effect was less pronounced than annealing in oxygen. Substrates with films > 20 μm were not aligned for either environment.
Role of Ag additions in the microstructural development, strain tolerance, and critical current density of Ag-sheathed BSCCO superconducting tapes
Authors: Singh J.P. , Joo J. , Vasanthamohan N. , Poeppel R.B.
Published: September 2007

Ag-sheathed tapes of Bi–Sr–Ca–Cu–O (BSCCO) and BSCCO–Ag superconducting cores were made by a powder-in-tube technique and subjected to repeated cycles of pressing and heat treatments. These thermomechanical treatments resulted in enhanced texturing and grain growth that improved the critical current density (Jc). Additions of Ag to the BSCCO core further increased texturing and brought an additional improvement in Jc. Strain tolerance of the tapes was evaluated by measuring Jc before and after application of a predetermined level of tensile strain in a uniaxial mode. The fraction of Jc retained after the strain application was higher in the BSCCO–Ag composite tapes than in the monolithic BSCCO. For a 1.2% applied strain, 90% of the initial Jc was retained in the BSCCO–Ag composite tape, compared to only 40% in the monolithic BSCCO tapes. The higher strain tolerance of the BSCCO–Ag tapes may be related to improved mechanical properties (strength, flexibility, and fracture toughness) and grain connectivity due to Ag addition.
Mechanical properties and metallography of aluminum matrix composites reinforced by the Cu- or Ni-plating carbon multifilament
Authors: Suzuki Takakazu , Umehara Hiroyuki , Hayashi Ryuichi , Watanabc Shuichiro
Published: September 2007

The feasibility study of electroless plating as carbon fiber modification for aluminum matrix composites was carried out. The comparison of Cu plating and Ni plating of carbon fiber by the electroless method was investigated. The Cu- or Ni-coated carbon fiber reinforced aluminum was fabricated with a centrifugal pressure infiltration method. The mechanical property was metallographically discussed. Electroless plating is able to improve the throwing power of the precipitant into the multifilament and uniformly coat Cu or Ni onto the carbon fiber. The technique using centrifugal casting seems to be an innovative method for fabrication of composite materials. The eutectic reaction between aluminum and Cu or Ni on the fiber appears to improve the affinity of the carbon fiber and aluminum. The Cu-plated carbon fiber reinforced aluminum is two times higher in bending strength than Ni-plated carbon fiber reinforced aluminum.
High temperature creep transitions in single crystalline Ni3Al(Ta, B)
Authors: Wolfenstine J. , Kim H.K. , Earthman J.C.
Published: September 2007

The high temperature (T= 1083–1388 K, 0.65–0.84Tm) creep behavior of single crystalline Ni3Al(Ta, B) was investigated. A change in the creep characteristics as a function of applied stress was observed at the uppermost testing temperatures of 1288 and 1388 K. At low applied stress levels the Norton law stress exponent is equal to 4.3; for higher stresses the stress exponent is equal to 3.2. Different creep curves were observed, depending on the value of the stress exponent. The change in stress exponent and nature of the creep curve correspond to a change in the controlling deformation mechanism from dislocation climb to viscous dislocation glide for Ni3Al(Ta, B). The experimentally observed transition stress values between climb and viscous glide are in good agreement with values predicted from theory, assuming that the major force retarding viscous dislocation glide in Ni3Al(Ta, B) is the antiphase boundary interaction.
Interfaces in β–SiC whiskers/6061 aluminum composites
Authors: Suganuma Katsuaki
Published: September 2007

6061 alloy matrix composites reinforced with β–SiC whiskers were fabricated both by squeeze casting and by hot-pressing and were heat-treated in the temperature range between 600 °C and 800 °C. The changes in interface microstructure were observed by transmission electron microscopy. In all treatment conditions, no special reaction product, e.g., Al4C3, were observed except for fine γ–Al2O3 particles adhering to the whiskers. A direct lattice connection at the whiskers/matrix interfaces was observed in all composites. β–SiC whiskers were proved to be quite stable in the 6061 matrix.
Role of grain boundaries in the epitaxial realignment of undoped and As-doped polycrystalline silicon films
Authors: Spinella C. , Benyaïch F. , Cacciato A. , Rimini E. , Fallico G. , Ward P.
Published: September 2007

The early stages of the thermally induced epitaxial realignment of undoped and As-doped polycrystalline Si films deposited onto crystalline Si substrates were monitored by transmission electron microscopy. Under the effect of the heat treatment, the native oxide film at the poly-Si/c-Si interface begins to agglomerate into spherical beads. The grain boundary terminations at the interface are the preferred sites for the triggering of the realignment transformation which starts by the formation of epitaxial protuberances at these sites. This feature, in conjunction with the microstructure of the films during the first instants of the heat treatment, explains the occurrence of two different realignment modes. In undoped films the epitaxial protuberances, due to the fine grain structure, are closely distributed and grow together forming a rough interface moving toward the film's surface. For As-doped films, the larger grain size leaves a reduced density of realignment sites. Due to As doping some of these sites grow fast and form epitaxial columns that further grow laterally at the expense of the surrounding polycrystalline grains.
Low pressure chemical vapor deposition (LPCVD) of β–SiC on Si(100) using MTS in a hot wall reactor
Authors: Chiu Chien C. , Desu Seshu B. , Tsai Ching Yi
Published: September 2007

Stoichiometric β–SiC thin films with a high preferred orientation of (111) planes were successfully deposited on Si(100) substrates at a relatively low temperature of 1050 °C from the mixture of methyltrichlorosilane (CH3SiCl3 or MTS) and H2 in a hot wall LPCVD reactor. No etching of the Si substrate and smooth topography of the deposit were observed at high H2/MTS ratios and/or low deposition pressures. The presences of excess silicon, excess carbon, or incorporated hydrogen atoms in the films were not detected. Poor topography, degradation in preferred orientation, and etching of the Si substrate were observed at high values of deposition pressure, MTS concentration, and temperature. The etching on the Si substrate was due to the out-diffusion of Si atoms from the substrate and the presence of Cl-containing radicals resulting from the decomposition of MTS molecules while transporting to the Si substrates. A deposition mechanism was proposed to model the deposition of SiC in a hot wall reactor by using (1) gas phase decomposition of MTS molecules, (2) adsorption of the intermediates on the surface, and (3) reaction of the adsorbed intermediates to form SiC. The deposition rates were predicted very well for various deposition conditions in a hot wall LPCVD reactor.
The influence of microstructure on the electrochromic properties of LixWO3 thin films: Part I. Ion diffusion and electrochromic properties
Authors: Zhang Ji-Guang , Tracy Edwin C. , Benson David K. , Deb Satyen K.
Published: September 2007

The chemical diffusion coefficients of lithium ions in LixWO3 films were investigated as a function of lithium concentration and film porosity. Thin films were deposited with different porosities by thermal evaporation of WO3 powder in various partial water pressures. Our results indicate that diffusion coefficients increase with film porosity and decrease with increasing lithium concentration. Large diffusion coefficients that were found for small lithium concentrations appear to be due to the contribution of protons generated from ion exchange reactions between lithium and water incorporated in the film. Simultaneous electrical and in situ optical measurements were carried out to study the effect of porosity on the electrochromic properties of LixWO3. The coloring efficiency of porous WO3 films increases by approximately 70% when deposited in partial water pressure of 10−4 Torr, but decreases with further increments in water pressure.
Metal coatings on semiconductor particles in glass
Authors: Sukumar Vijay , Kao Shou-Chen , Rao Pratima G.N. , Doremus Robert H.
Published: September 2007

Glasses containing semiconductor particles coated with metal were synthesized and studied. Glasses containing CdS and silver were heated to grow the CdS particles first, followed by the growth of metal on them. The solubility of silver in the CdS glass was increased by changing the base glass composition. Optical absorption and transmission electron microscopy results showed that silver coated the CdS particles in these glasses. The CdS particles had to be a critical size before silver grew on them. This critical size was calculated from nucleation theory and was found to be in good agreement with the experimental results. Glasses containing CuCl particles were partially reduced in hydrogen to obtain copper-coated CuCl particles. Absorption spectroscopy and TEM indicated a copper coating on the particles.
Gas-source molecular beam epitaxy of monocrystalline β–SiC on vicinal α(6H)–SiC
Authors: Rowland L.B. , Kern R.S. , Tanaka S. , Davis Robert F.
Published: September 2007

Single-crystal epitaxial films of cubic β(3C)–SiC(111) have been deposited on hexagonal α(6H)–SiC(0001) substrates oriented 3–4° toward [1120] at 1050–1250 °C via gas-source molecular beam epitaxy using disilane (Si2H6) and ethylene (C2H4). High-resolution transmission electron microscopy revealed that the nucleation and growth of the β(3C)–SiC regions occurred primarily on terraces between closely spaced steps because of reduced rates of surface migration at the low growth temperatures. Double positioning boundaries were observed at the intersections of these regions.
Synthesis of YBa2Cu3O7−x powder by autoignition of citrate-nitrate gel
Authors: Roy Sukumar , Sharma Das A. , Roy S.N. , Maiti H.S.
Published: September 2007

A simple and convenient method for the synthesis of YBa2Cu3O7−x powder is described. The technique involves autoignition of a citrate-nitrate gel resulting from a thermally induced oxidation-reduction reaction to yield an ash that upon calcination produces the desired compound. The resulting powder is pure, homogeneous, and possesses a reasonably fine particle size. The autoignition is restricted to a particular range of citrate-nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good potential for large-scale production.
Interfacial reaction products and film orientation in YBa2Cu3O7−x on zirconia substrates with and without CeO2 buffer layers
Authors: Skofronick G.L. , Carim A.H. , Foltyn S.R. , Muenchausen R.E.
Published: September 2007

Thick film (1.2 μm) YBCO superconductors grown by pulsed laser deposition on unbuffered and CeO2-buffered single crystal (001)-oriented yttria-stabilized zirconia (YSZ) substrates have been investigated. YBCO and YSZ react to form BaZrO3 (BZO), whereas YBCO and CeO2 react to form BaCeO3. Reaction phases were examined by θ-2θ and four-circle x-ray diffraction and high resolution electron microscopy. Three orientation relationships identified for the unbuffered films were (i) (001)YBCO ‖ (011)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, (ii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, and (iii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [100]YBCO ‖ [100]BZO ‖ [100]YSZ. The results suggest that for films grown at typical deposition temperatures, YBCO epitaxy is established before the interfacial reaction occurs. The presence of BaCeO3 in buffered films grown at high temperatures (790 °C) was confirmed by θ-2θ scans and selected area diffraction patterns.
Investigation of Ni3Al-matrix composites strengthened by TiC
Authors: Mei Bingchu , Yuan Runzhang , Duan Xinlong
Published: September 2007

In this paper, the possibilities of preparing TiC-reinforced Ni3Al-matrix composites by SM (self-propagating high temperature synthesis and melting process) were examined. Two kinds of composites, namely, commercial TiC-reinforcement and synthesized TiC-reinforcement Ni3Al-matrix composites, were fabricated. The effects of particle size of the commercial TiC on the mechanical properties of the Ni3Al-matrix composites were studied. The results show that the mechanical properties of the composites decrease with increasing particle size of the commercial TiC. The microstructures of 35 wt. % TiC + 65 wt. % Ni3Al composites produced by SM technology from the four elements Ti, C, Ni, and Al were examined. The results show that in these composites, the particle size of TiC synthesized in situ is fine and that the materials have considerable high-temperature bending strength and fracture toughness.
Space groups of the diamond polytypes
Authors: Phelps A.W. , Howard W. , Smith D.K.
Published: September 2007

Space groups and atomic coordinates for the 4H, 6H, 8H, 10H, 15R, and 21R polytypes of diamond are presented. The systematic method used to determine the highest symmetry space group for diamond polytypes is described.
The kinetics of chemical vapor deposited diamond-oxygen reaction
Authors: Alam M. , Sun Q.
Published: September 2007

The kinetics of reaction between chemical vapor deposited diamond films (prepared by the hot filament method) and oxygen gas was studied by thermogravimetry. The reactions were carried out at atmospheric pressure in gas mixtures containing between 25 and 100 vol. % oxygen (balance argon), and in the temperature range of 973–1073 K. The apparent order of the reaction is close to 0.6, and the apparent activation energy is 232 kJ/mole. The kinetic data are explained by assuming no mass transfer limitations, direct reaction between CVD diamond and oxygen to form CO and CO2, and thermodynamic equilibrium between CVD diamond, CO, and CO2. The dominant chemical reaction involves the formation of CO, while the formation of CO2 is not significant. Three stage mechanistic schemes are developed involving adsorption of oxygen on CVD diamond surface, surface chemical reaction, and desorption of adsorbed species to CO or CO2. The experimental rate data conform to the reaction rate expressions developed for the mechanistic schemes leading to the formation of CO and CO2, assuming adsorption as the rate-controlling step. The adsorption rate constants for the formation of CO and CO2 are determined. The activation energy of the adsorption step leading to the formation of CO is 213 kJ/mole.
Nucleation and growth of oxide precipitates in CZ–Si wafers
Authors: Ataka Mitsuo , Ogawa Tomoya
Published: September 2007

When NB is moles of oxygen atoms dissolved into an Si wafer of NA moles, the concentration of oxygen atoms in the Si wafer is given by mole fraction as XB = NB/(NA + NB), and the degree of supersaturation is defined by σ = (XB/XBS,T) – 1 where XBS,T is the mole fraction of the saturated state at temperature T. We have proved that σ is equal to the chemical potential difference of oxygen atoms in between saturated and supersaturated states if σ ≪ 1. Here the spontaneous generation rate is proportional to σγ, where γ is the number of the oxygen atoms in the critical oxide particles in the Si wafers. Duration time of a low temperature heating (at about 700 °C) will determine the number of nuclei for oxide precipitates, and a treatment near 950 °C is very effective on growth of oxide particles, because growth of the oxide particles is determined by diffusion of the atoms. Before the low temperature treatments, preheating at a temperature higher than 1000 °C is effective in dissolving Si–O pairs and making interstitial oxygen atoms, where the Si–O pairs have been generated by the cooling stage after the crystal growth.
Morphological changes of poly(tetrafluoroethylene) by heat treatment on NaCl
Authors: Yamaguchi Sadaatsu , Tsuji Masaki
Published: September 2007

Fine granules of poly(tetrafluoroethylene) (PTFE) were heat-treated/annealed on NaCl near its melting temperature(Tm)and/or at a temperature(Tc)between upper and lower feet of the exothermic peak in the DSC cooling process fromTm. Morphological changes of the granules were examined in the bright- and dark-field modes by transmission electron microscopy. When the granules were heat-treated nearTm, microfibrils of 20–30 nm in width and fibrils of 70–120 nm in width came out of the granules. The microfibrils were also observed in the fibrils. The microfibrils formed by heat treatment nearTmseemed to be identified as microfibrils of 20–30 nm in width which were recognized outside the granules annealed atTc. It is expected that such a microfibril will grow to be a band in the band structure observed on the surface of bulk PTFE. Since the 0015 dark-field images showed that the PTFE chains in such microfibrils and fibrils are set perpendicular to their fibril axis, the chains should fold back and forth repeatedly at both lateral side-surfaces of the microfibrils and fibrils.
TEM study of synthetic hillebrandite (Ca2SiO4 · H2O)
Authors: Kim Youn Joong , Kriven Waltraud M. , Mitsuda Takeshi
Published: September 2007

Hillebrandite (dicalcium silicate hydrate) was produced by a hydrothermal process. Its crystal structure and microstructures were investigated by conventional TEM and HREM. Most hillebrandite fibers showed their elongation to be parallel to the b axis and tended to lie on the {001} cleavage planes. Selected area diffraction patterns frequently displayed continuous streaking, and corresponding dark-field images revealed stacking disorders perpendicular to the fiber axis. The morphology, stacking disorders, and extinction conditions of {hkO} reflections and hillebrandite resembled those of the minerals wollastonite (CaSiO3) and pectolite (Ca2NaH[SiO3]3). Periodic (100) faulting with a displacement vector 1/2 b is suggested to be the major origin of the streaking and the systematic absences in hillebrandite.
Barium titanate/noble metal laminates prepared by the oxidation of solid metallic precursors
Authors: Antony M.M. , Sandhage K.H.
Published: September 2007

A novel and attractive method for preparing multicomponent electronic ceramics and ceramic-metal composites is the oxidation of solid metallic precursors (SMP). This metallurgical processing route consists of the following steps: (i) preparation of a solid metallic precursor containing the proper ratio of elements for the final ceramic or ceramic-metal composite, (ii) compaction and forming of the metallic precursor into a desired shape, and (iii) oxidation to produce a monolithic ceramic or ceramic-metal composite. While the SMP method has been used to prepare wires and tapes containing a variety of superconducting oxides, this method has not been widely used to synthesize other electronic ceramics. In this paper, the synthesis of dielectric BaTiO3/noble metal laminates from solid metallic precursors is discussed. Ba–Ti precursor powders have been produced by solid-state mechanical alloying. The precursor powder was sealed inside noble metal tubes and rolled to form thin Ba–Ti/noble metal laminates. Exposure of the Ba–Ti core in such tapes to temperatures ≥ 300 °C in pure oxygen resulted in rapid oxidation. Post-oxidation annealing at elevated temperatures (≥900 °C) yielded dielectric BaTiO3/Ag or BaTiO3/Pd laminates.
Structural transformations of alumina by high energy ball milling
Authors: ZielińAski P.A. , Schulz R. , Kaliaguine S. , Van Neste A.
Published: September 2007

Room temperature, high energy ball milling was applied to various transition aluminas (γ, K, χ), producing thermodynamically stable α-alumina–a phenomenon that could otherwise be achieved only by high temperature (1100–1200 °C) heat treatment. The transformation proceeds in two steps. The first one consists of rapid microstructural rearrangements with continuously increasing α-transformation rate. In the second step (1–2 h from the start), only relatively small changes in morphology are observed with a constant α-transformation rate. The rate is influenced only by the milling intensity. The presence or the absence of oxygen in the milling atmosphere has a large influence on the final surface area of α-alumina.
Decomposition temperatures of Cu2Ln2O5 (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Lu) compounds
Authors: Mathews Tom , Jacob K.T.
Published: September 2007

The equilibrium decomposition temperatures of Cu2Ln2O5 (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Lu) compounds have been measured using a combined DTA-TGA apparatus under a flowing Ar + O2 gas mixture, in which the partial pressure of oxygen was controlled at 5.0 × 103 Pa. The Cu2Ln2O5 compounds yield Ln2O3 and Cu2O on decomposition. The decomposition temperature increases monotonically with the atomic number of the lanthanide element. This suggests that the stability of the Cu2Ln2O5 compounds with respect to the component binary oxides increases with decreasing radius of the Ln3+ ion.
Nanoindentation studies of sublimed fullerene films using atomic force microscopy
Authors: Ruan Juai , Bhushan Bharat
Published: September 2007

Nanoindentation studies of sublimed fullerene films have been conducted using an atomic force microscope (AFM). Transfer of fullerene molecules from the as-deposited films to the AFM tip was observed during the indentation of AFM tip into some of the samples, whereas such a transfer was not observed for ion-bombarded films. The fullerene molecules transferred to the AFM tip were subsequently transported to a diamond surface when the diamond sample was scanned with the contaminated tip. This demonstrates the capability of material manipulation on a molecular scale using AFM. Atomic-scale friction of the fullerene films was measured to be low. Ability of fullerene films to form transfer film on the mating AFM tip surface may be partly responsible for low friction.
Protective films of nanophase diamond deposited directly on zinc sulfide infrared optics
Authors: Davanloo F. , Lee T.J. , Park H. , You J.H. , Collins C.B.
Published: September 2007

Nanophase diamond films can be grown at room temperature with a laser plasma discharge source without the use of any catalyst. This technique produces films that adhere readily to materials for which there are important applications as protective coatings. Described here is a study of the bonding and properties realized with the direct deposition of nanophase diamond on the II-VI compound of zinc sulfide. It was shown that adhesion and mechanical properties of the films can be correlated with the amounts of defects and impurities in the zinc sulfide substrates. In all cases significant interfacial layers caused by the deep penetration of carbon atoms into the substrates were observed. Resistance to wear was estimated with a modified sand blaster, and results indicated that only 1 μm coating of nanophase diamond can increase lifetimes of the zinc sulfide samples by a factor better than 5. Protection afforded by the nanophase diamond under harsh environmental conditions of rain impacts was also described.
Gas permeability of carbon aerogels
Authors: Kong F-M. , LeMay J.D. , Hulsey S.S. , Alviso C.T. , Pekala R.W.
Published: September 2007

Carbon aerogels are synthesized via the aqueous polycondensation of resorcinol with formaldehyde, followed by supercritical drying and subsequent pyrolysis at 1050 °C. As a result of their interconnected porosity, ultrafine cell/pore size, and high surface area, carbon aerogels have many potential applications such as supercapacitors, battery electrodes, catalyst supports, and gas filters. The performance of carbon aerogels in the latter two applications depends on the permeability or gas flow conductance in these materials. By measuring the pressure differential across a thin specimen and the nitrogen gas flow rate in the viscous regime, the permeability of carbon aerogels was calculated from equations based upon Darcy's law. Our measurements show that carbon aerogels have permeabilities on the order of 10−12 to 10−10 cm2 over the density range from 0.05–0.44 g/cm3. Like many other aerogel properties, the permeability of carbon aerogels follows a power law relationship with density, reflecting differences in the average mesopore size. Comparing the results from this study with the permeability of silica aerogels reported by other workers, we found that the permeability of aerogels is governed by a simple universal flow equation. This paper discusses the relationship among permeability, pore size, and density in carbon aerogels.
Formation of ultrathin CoSi2 films using a two-step limited reaction process
Authors: Schreutelkamp R.J. , Coppye W. , De Bosscher W. , van Meirhaeghe R. , van Meirhaeghe L. , Vanhellemont J. , Deweerdt B. , Lauwers A. , Maex K.
Published: September 2007

The formation of ultrathin (≤20 nm) and smooth CoSi2 layers on c–Si substrates has been studied by using a one- and a two-step RTP silicidation method. Pinhole-free silicide layers with a thickness down to ∼10–12 nm were formed on n−, n+, and p+ crystalline Si substrates in the one-step RTP process by sputtering of Co films as thin as 4 nm and subsequent silicidation at 750 °C for 5 or 30 s. The two-step RTP silicidation method is based on the consumption of only a small fraction of a thick sputtered Co film to form Co2Si or CoSi during a first RTP step at 400–500 °C. A selective etch follows to remove the unreacted Co film. During a second, higher temperature, RTP step CoSi2 is formed. Pinhole-free and smooth CoSi2 films with a thickness down to 20 nm were formed in this way on both n+ and p+ monocrystalline Si substrates.
Change of thermal expansion coefficient and electrical conductivity of LaCo1–xMxO3 (M = Fe, Ni)
Authors: Nagamoto H. , Mochida I. , Kagotani K. , Inoue H. , Negishi A.
Published: September 2007

The thermal expansion coefficient of LaCo1−xFexO3 averaging between 25 and 1000 °C decreased linearly with the Fe content, x. The thermal expansion of LaCo1−xNixO3 decreased with increasing the Ni content, but those for x = 0.67 and 1.0 were almost identical at 1000 °C due to the transition of the crystal system of LaNiO3. The behavior of thermal expansion was interpreted in terms of the formation enthalpy of the perovskites and the bond length between a B-site cation and an oxide anion. LaCo0.67Ni0.33O3, which has the electrical conductivity of 4 × 102 S/cm, could be a good candidate for the air electrode material.
Nanocomposite aerogels: The SiO2–Al2O3 system
Authors: Komarneni Sridhar , Roy Rustum , Selvaraj Ulagaraj , Malla Prakash B. , Breval Else
Published: September 2007

Monolithic nanocomposite aerogels of two aluminosilicate compositions have been prepared and characterized by different techniques. The results show that high surface area and mesoporosity can be preserved in the above nanocomposite aerogels by heating at 1000 °C, unlike the single component aerogels. The presence of alumina as a second phase prevented their densification which resulted in surface areas on the order of 500–600 m2/g and mesopores of about 5–6 nm in diameter after heat treatment at 1000 °C. These novel nanocomposite aerogels are expected to find applications at high-temperatures in separations, insulation, catalysis, etc.
Densification behaviors and piezoelectric properties of MnO2, SiO2-doped Pb(Ni1/3Nb2/3)O3–PbTiO3–PbZrO3 ceramics
Authors: Moon Jong H. , Jang Hyun M. , You Beoung D.
Published: September 2007

The roles of additives (MnO2, SiO2, and CdO) in controlling microstructural development and piezoelectric properties of Pb(Ni1/3Nb2/3)O3– PbTiO3–PbZrO3(PNN–PT–PZ) ceramics were systematically examined. The addition of SiO2 (<1 wt. %) to the pseudoternary PNN–PT-PZ system enhances densification, but suppresses grain growth significantly. On the other hand, the presence of MnO2 expedites the rate of grain growth without increasing the rate of densification appreciably. The observed difference in the grain-growth behavior was discussed in terms of the viscosity of liquid phase formed during sintering and the diffusion-controlled process for the solute-atoms transport. The rapid increase in the mechanical quality factor (Qm) and the decrease in the relative dielectric permittivity (∊r) and d33 for the MnO2-doped specimens indicate the formation of oxygen vacancies by the dissolution of Mn-atoms into the B-sites of perovskite structure. On the contrary, the presence of CdO (2 mol %) remarkably increases ∊r and d33 of PNN–PT–PZ ceramics.
Effect of iron and cobalt addition on TiC combustion synthesis
Authors: Choi Yoon , Rhee Shi-Woo
Published: September 2007

Fe and Co metals were incorporated into a Ti and C mixture with a molar ratio of 1.0 over the range of 0 to 40 wt. % to study their effect on TiC combustion synthesis. The addition brought about the grain size decrease, change of grain shape (angular to spherical), and different distribution (agglomerated to isolated) of TiC grains. Both Fe and Co additives were distributed around TiC grains and served as a binder. It was observed that reaction between Ti and C was kinetically more favorable than any other reactions in the Ti–C–Fe or Ti–C–Co system. Based on the activation energy from an Arrhenius plot of In[(1−w)1/2u/Tc] vs 1/Tc, which was obtained by combustion temperature and wave velocity measurements, the reaction mechanism in combustion synthesis of TiC with the addition of 20 wt. % Fe and Co was suggested.
Fracture toughness of PMMA as measured with indentation cracks
Authors: Choi S.R. , Salem J.A.
Published: September 2007

Fracture toughness of polymethyl methacrylate (PMMA) was evaluated with indentation cracks. The cracks were developed by indenting in a liquid acetone environment, as suggested by previous researchers. Due to the inconsistency in crack configurations with varying indentation loads and to the negligible residual stress from indentation, the application of the indentation strength method was limited in evaluating fracture toughness of PMMA. The semielliptical crack approximation, however, particularly at a low indentation load of 9.8 N, resulted in reasonable agreement with the value determined by three conventional fracture toughness testings using the compact tension (CT), double cantilever beam (DCB), and single edge notched beam (SENB) specimens. Measurements at other indentation load typically were in poor agreement with conventional methods due to poorly developed crack configurations.
A review of catalytically grown carbon nanofibers
Authors: Rodriguez N.M.
Published: September 2007

Carbon nanofibers (sometimes known as carbon filaments) can be produced in a relative large scale by the catalytic decomposition of certain hydrocarbons on small metal particles. The diameter of the nanofibers is governed by that of the catalyst particles responsible for their growth. By careful manipulation of various parameters it is possible to generate carbon nanofibers in assorted conformations and at the same time also control the degree of their crystalline order. This paper is a review of the recent advances made in the development of these nanostructures, with emphasis both on the fundamental aspects surrounding the growth of the material and a discussion of the key factors which enable one to control their chemical and physical properties. Attention is also given to some of the possible applications of the nanostructures which center around the unique blend of properties exhibited by the material.
Amorphization of the TiV system by mechanical alloying and mechanical grinding in a hydrogen and nitrogen atmosphere
Authors: Aoki K. , Memezawa A. , Masumoto T.
Published: September 2007

A TiV system, which does not amorphize in an inert gas atmosphere, has been mechanically alloyed (MA) and mechanically ground (MG) using a planetary ball mill in a hydrogen and nitrogen atmosphere. The products were characterized by x-ray diffractometry, transmission electron microscopy, differential scanning calorimetry, and chemical analysis as a function of milling time and the gas pressure. Amorphization occurs by MA and MG in a hydrogen atmosphere and by MG in a nitrogen atmosphere. Amorphization by MA proceeds by the reaction between TiH2 and pure V in a hydrogen atmosphere, while it proceeds by MG by hydrogen and nitrogen absorption into the metastable β-TiV alloy and subsequent milling. The difference in the phase formation by MA and MG of the TiV system is discussed based on the gas absorption rate and the solubility of gases.