bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid-phase epitaxy of Ti-implanted LiNbO3
Authors: Poker D. B. , Thomas D. K.
Published: September 2007

The solid-phase epitaxy of LiNbO3 following ion implantation of Ti dopant for the purpose of producing optical waveguides has been studied. Implanting 360-keV Ti at liquid nitrogen temperature produces a highly damaged region extending to a depth of about 400 nm. This essentially amorphous region can be recrystallized epitaxially by annealing in a water-saturated oxygen atmosphere at temperatures near 400 °C. though complete removal of all irradiation-induced damage requires temperatures in excess of 600 °C. The activation energy of the regrowth is 2.0 eV for implanted fluences below 3 ⊠ 1016 Ti/cm2. At higher fluences the regrowth proceeds more slowly, and Ti dopant segregates at the regrowth interface. Complete recrystallization following high-dose implantation requires annealing temperatures in excess of 800 °C.
Generalized Bogue calculations for determining phase compatibility/equilibria: Assessing potential use of inorganic industrial by-products
Authors: Majling J. , Jesenák V. , Roy Della M. , Roy Rustum
Published: September 2007

A method has been developed for determining the equilibrium phase composition of multicomponent systems at subsolidus conditions and atmospheric pressure, based on the knowledge of binary phase compatibilities and on information concerning the existence and stoichiometry of ternary and higher order compounds. The method, combined with material balance, enables computation of the changes of equilibrium phase compositions of fired products dependent on the proportions of multicomponent raw materials; the procedure is useful for assessing the exploitability of industrial wastes for production of binding materials and ceramics. It is also possible to find the raw material mixture composition needed for the desired phase composition of the fired product.
Electron microscopy of a Gd–Ba–Cu–O superconductor
Authors: Ramesh R. , Thomas G. , Meng R. L. , Hor P. H. , Chu C. W.
Published: September 2007

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd–Ba–Cu–O superconductor alloy. The GdBa2Cu3O7−x phase in the oxygen annealed sample is orthorhombic while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the [001] zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.
The 1430 cm−1 Raman line in single crystals of La2CuO4−y
Authors: Ohana I. , Dresselhaus M. S. , Heiman D. , Dresselhaus G. , Picone P. J.
Published: September 2007

The Raman line at 1430 cm−1 (M-line) in single crystal La2CuO4−y was studied as a function of doping, temperature, magnetic field, and excitation wavelength. Upon Li doping the line becomes broader, and it vanishes rapidly with Sr-doping. The line also broadens with increasing temperature and increasing applied magnetic field. Resonance enhancement was found for decreasing laser excitation energies but was not as pronounced as the enhancement of several alleged two-phonon lines. Many of these features are correlated with the 2D antiferromagnetic ordering measured in this system by neutron scattering. The possible identification of this line as a one-spin excitation is favored by the data though a two-phonon excitation is also considered.
Molecular dynamics simulation of displacement cascades in Cu and Ni: Thermal spike behavior
Authors: de la Rubia T. Diaz , Averback R. S. , Hsieh Horngming , Benedek R.
Published: September 2007

Molecular dynamics simulations of energetic displacement cascades in Cu and Ni were performed with primary-knock-on-atom (PKA) energies up to 5 keV. The interatomic forces were represented by the Gibson II (Cu) and the Johnson-Erginsoy (Ni) potentials. Our results indicate that the primary state of damage produced by displacement cascades is controlled basically by two phenomena: replacement collision sequences during the ballistic phase, and melting and resolidification during the thermal spike. The thermal-spike phase is of longer duration and has a more marked effect in Cu than in Ni. Results for atomic mixing, defect production, and defect clustering are presented and compared with experiment. Simulations of “heat spikes” in these metals suggest a model for “cascade collapse” based on the regrowth kinetics of the molten cascade core.
Nature of the disordered state of hydrogenated amorphous silicon as revealed by the study of anelastic relaxation behavior
Authors: Lal Ram , Kulkarni A. V. , Dusane R. O. , Bhide V. G. , Ogale S. B.
Published: September 2007

The nature of the disordered state of hydrogenated amorphous silicon is examined for the first time by measurement of anelastic relaxation behavior. It is demonstrated that local structural units and their modifications control the relaxations in these films under different conditions of deposition, aging, and light exposure. Specifically, the light-induced state in this material is shown to be characterized by four distinct relaxations.
Metastable supersaturated solutions of nitrogen in rapidly-solidified silicon
Authors: Stein H. J. , Peercy P. S. , Hills C. R.
Published: September 2007

The depth distribution, chemical bonding, and electrical behavior of N quenched into Si by pulsed laser-induced melting have been investigated by secondary ion mass spectroscopy, infrared (ir) absorption, transmission electron microscopy (TEM), and electrical conductivity. The results demonstrate that laser-induced melting of N-implanted layers provides access to a useful range of otherwise inaccessible conditions for the study of N in Si. Nitrogen concentrations four orders of magnitude above equilibrium solid solubility are retained in implanted layers with limited diffusion during laser-induced melt and rapid solidification. The N is incorporated predominantly as N–N pairs bonded to Si, similar to the bonding configuration for equilibrium concentrations introduced during ingot growth. Formation of SixNy clusters is suggested to explain ir absorption bands, features in TEM, and shallow donor activity observed after furnace annealing near 750 °C. These cluster effects are removed by a melt/solidification sequence which restores the N to N–N pair centers together with a small fraction of off-center substitutional N.
Thin film backside gettering in n-type (100) Czochralski silicon during simulated CMOS process cycles
Authors: Partanen J. , Tuomi T. , Tilli M. , Hahn S. , Wong C-C. D. , Ponce F. A.
Published: September 2007

The gettering effectiveness of various backside gettered polysilicon, silicon nitride, or poly + nitride film structures on n-type (100) Czochralski silicon wafers from a single ingot during simulated complementary-metal-oxide-semiconductor process cycles has been investigated by synchrotron section topography, breakdown voltage of 25-nm gate oxide, and minority carrier lifetime measurements. Interfacial structure was studied by cross-section transmission electron microscopy. Our studies show that for successful implementation of thin film backside gettering, good control of interactions between intrinsic gettering and thin film backside gettering during device processing cycles is critical. Thin film deposition generally increases oxygen precipitation. No extended defects propagate toward the bulk silicon. The structural and electrical quality of a denuded zone is found important. The best device yield (90%) is observed from the middle section wafers (with a 2 μm thick polysilicon backsurface coverage) which develop no recognizable bulk precipitates and stacking faults after the complete thermal cycles.
Reactions of silicon tetrachloride and germanium tetrachloride with oxygen and oxides of nitrogen
Authors: Atkins R. M. , Hohan V. A.
Published: September 2007

The reactions of SiCl4 and GeCl4 with oxygen and oxides of nitrogen have been studied in a continuous flow system. SiCl4 is found to react with nitrous oxide at a considerably lower temperature (700 °C vs 1050 °C) than with oxygen. In both cases the formation of silicon oxychlorides (hexachlorodisiloxane and octachlorocyclo-tetrasiloxane) was observed for the first 300 °C after reaction initiates. Activation energies of 115 kcal/mole and 40 kcal/mole were determined for the reactions with oxygen and nitrous oxide, respectively (under conditions of 100-fold excess oxidizer). GeCl4 is also found to react with nitrous oxide at a lower temperature than with oxygen; however, in this case no oxychloride species were observed. Activation energies of 53 kcal/mole and 48.6 kcal/mole were determined for the reactions with oxygen and nitrous oxide, respectively (under conditions of 70-fold excess oxidizer). Reactions of GeCl4 with nitric oxide and nitrogen dioxide are also reported. The use of N2O as an oxidant in optical fiber fabrication processes is discussed.
Structural imperfections in CVD diamond films
Authors: Zhu W. , Badzian A. R. , Messier R.
Published: September 2007

Microwave plasma assisted CVD diamond films have been studied by transmission electron microscopy. Cross-section TEM as well as plan-view TEM methods were used to investigate various structural defects formed in the films. It was found that diamond films contain a large number of stacking faults and twins which lie on the {111} planes in diamond. With an increase in methane concentration during the deposition process, the density of these defects increases and their dimensions become smaller. The tendency for forming these structural defects is of concern in developing tailored structures and properties of diamond films.
Alkali metal ion exchange selectivity of Al-substituted tobermorite
Authors: Tsuji Masamichi , Komarneni Sridhar
Published: September 2007

Alkali metal ion exchange isotherms at a total ionic strength of 0.001 M were determined at 25 °C on a 1.13 nm anomalous [Al3+ + Na+]-substituted tobermorite with the formula, Ca5Na0.75Al0.9Si5.1O16(OH)2 · 6.03H2O. The Kielland plots of Na+/K+, Na+/Rb+, and Na+/Cs+ exchange reactions showed straight lines. The slopes were steeper for Cs+ and Rb+ exchange reactions, as compared to K+ exchange. The cation-exchange selectivity for alkali metals was found to increase as follows: Cs+>Rb+>K+>Na+. A new evaluation method of the separation factor (αMN/KMd/KNd,Kd: distribution coefficient) for a combination of two cations at infinite dilution was proposed in terms of the selectivity coefficient (KMNa) which can be easily determined from the Kielland plot. An extremely large separation factor for Cs (αCsNa = 112) was found at infinite dilution. These basic studies of cation exchange selectivity are of relevance in cation separation and purification and nuclear waste disposal.
Environmental effects on luminescence yield of superconducting YBa2Cu3Ox
Authors: Jahan M. S. , Cooke D. W. , Sheinberg H. , Smith J. L. , Lianos D. P.
Published: September 2007

Gamma-ray-induced surface defects in YBa2Cu3Ox (x ≈ 7) have been investigated by thermally stimulated luminescence (TSL) following storage of the samples in dry (vacuum), oxygen, and 98% relative humidity environments. Irradiation of samples stored in either vacuum or oxygen environments shows that no insulating chemical species are formed on the surface of the superconductor. In contrast, exposure to the humid environment produces various chemical components on the surface, and, consequently, enhances the TSL yield. Comparison of the YBa2Cu3Ox, TSL glow curve and emission spectra with those of BaCO3 suggests that one of the components contributing to the purported YBa2Cu3Ox luminescence is BaCO3. Evidence for formation of other chemical species and the suitability of the TSL technique for their determination are discussed.
Superconducting YBa2Cu3O7−x fibers from the thermoplastic gel method
Authors: Uchikawa Fusaoki , Mackenzie John D.
Published: September 2007

The successful fabrication of ceramic superconducting YBa2Cu3O7−x fibers has been investigated. A new method was proposed for synthesis of the fibers through a solution route. The thermoplastic gels were synthesized using Y, Ba, Cu, ethoxides, and diethylenetriamine. The fibers were drawn from the reheated gels. The fibers were characterized by x-ray diffraction, SEM, and shrinkage ratio measurements. The fired and then annealed fiber is shown to have a superconducting transition temperature of 91 K (onset) and zero resistance temperature of 84 K. With regard to the fired fibers, it is found that the surface area increased and superconducting transition temperature decreased with increasing organic content in the initial gel. The usefulness of this method is shown and the structure of the synthesized gel is discussed.
Superconducting (YBaCuO)–(CuO)–Ag composites
Authors: Song Yi , Cao Yue , Misra Anupam , Gaines J. R.
Published: September 2007

We have fabricated superconducting composites composed of Y1Ba2Cu3O7–δ, copper oxide, and metallic silver. Sharp superconducting transitions were observed well above the liquid nitrogen temperature. The normal state resistivity of these composites was much lower than that of the pure ceramic Y1Ba2Cu3O7–δ. The critical current density was measured and it was comparable to that of ceramic superconductors. A substantial improvement of the mechanical properties has been achieved over those of the ceramic Y1Ba2Cu3O7–δ material.
Analytical TEM study of Al-doped, “two-phase” Nd–Fe–B sintered magnets
Authors: Fidler J. , Knoch K. G. , Kronmüller H. , Schneider G.
Published: September 2007

The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x = 0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets we found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe, Al)2, phase between the hard magnetic grains. Our analytical TEM study revealed that in “Al2O3-doped” magnets the crystal structure of the Nd-rich intergranular phase partly changes from fcc (a = 0.52 nm) to hep (a = 0.39 nm, c = 0.61 nm), whereas the content of iron simultaneously decreases from 5–10 at.% to 1.5–4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2 (B, O)x, phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.
The influence of hydrogen on ion beam mixing of multilayer films
Authors: B⊘rgesen P. , Wistrom R. E. , Johnson H. H. , Lilienfeld D. A.
Published: September 2007

Previous qualitative studies of ion beam mixing of Ni–Ti and Fe–Ti multilayers at room temperature have shown the Ni–Ti samples to mix considerably faster than the Fe–Ti, in apparent contrast with theory. Furthermore, the Fe–Ti mixing was strongly inhibited by previous charging of the sample with hydrogen, whereas only a small effect was seen for Ni–Ti. We have quantified the mixing and extended the study to four more systems (Al–Ti. Co–Ti, Cu–Ti, and Pd–Ti) and lower temperatures. This allows some important conclusions to be drawn. Predictions based on a thermal spike model underestimate the larger room temperature mixing rates (Cu–Ti, Ni–Ti, and Pd–Ti), apparently because of contributions from a temperature dependent mechanism such as radiation enhanced diffusion. The lower mixing rates (Fe–Ti, Co–Ti, and Ni–Ti at ∼80 K) are overestimated by a factor of 2–3.5, possibly because of hydrogen contamination of the as-deposited samples. For the Al–Ti sample, the experimental mixing rate was in good agreement with predictions. Except for the Cu–Ti sample, results were seen to vary with heat of solution, rather than heat of mixing, suggesting significant contributions from the lower temperature after-spike regime. Hydrogen charging was found to reduce the Fe–Ti mixing rate by a factor of 7 at room temperature, whereas the Co–Ti and Ni–Ti rates were only reduced by a factor of 2, and the mixing of the Pd–Ti was influenced very little. Near liquid nitrogen temperature the Ni–Ti mixing rate was more strongly reduced (by a factor of 3–4). Our results suggest that the original hydrogen contamination in as-deposited samples may also cause significant reduction of mixing rates in some materials.
The formation mechanism of planar defects in compound semiconductors grown epitaxially on {100} silicon substrates
Authors: Ernst F. , Pirouz P.
Published: September 2007

Films of three compound semiconductors with the zincblende structure grown epitaxially on {100} silicon substrates by chemical vapor deposition or metal-organic chemical vapor deposition were investigated by transmission electron microscopy. The three systems have similar thermal mismatches but cover a wide range of lattice mismatch. From the comparison of the observed microstructures as well as from the investigation of early stages of film formation it is concluded that the lattice mismatch plays a minor role in the formation of stacking faults and twin boundaries. A formation mechanism is proposed for these defects which is based on deposition errors during the adsorption of atoms on {111} facets of film nuclei. The observed microstructural features are discussed in terms of this model.
Preparation and properties of PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 composition
Authors: Yan M. F. , Ling H. C. , Rhodes W. W.
Published: September 2007

We prepared and characterized PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 stoichiometric composition. We examined microstructures, sintering behavior, and phase compositions in this system and prepared several new compositions, which have a single phase perovskite structure and a high dielectric constant (28000), by low sintering temperature (950–1020 °C). These compositions have a high electrical resistivity (1013 ohm-cm), which is about 1000 times higher than those of Pb(Fe½Nb½)O3 and Pb(Fe⅔W⅓)O3 based ceramics. The new compositions can be readily prepared into a single phase perovskite without a detectable amount of pyrochlore second phase by a simple method of mixing and calcining the constituent oxide and carbonate powders. Our dielectric measurements and XRD data establish the correlation between the decrease in dielectric constant and the presence of pyrochlore second phase. The effects of PbTiO3 dopant were quantitatively measured and our data showed that at a low (10 mole %) PbTiO3 concentration, the Curie temperature increases 6.6 °C for every mole % PbTiO3 dopant in the new compositions. The dielectric constant increases from 18000 in the undoped composition to 27 100 and 29000 by a PbTiO3 dopant concentration of 5% and 10%, respectively. The maximum dissipation factor also decreases from 0.10 in the undoped composition to 0.055 in the 10% PbTiO3 doped composition. The electrical resistivity, ρ, decreases with the PbTiO3 dopant concentration, t, following the ρ = ρ0 exp (–t/t0) relation where ρ0 ≍ (9.6 ± 0.2) × 1012 Ωcm and t0 ≃ 0.044.
Epitaxial crystallization of polyphenylene sulfide on sodium chloride
Authors: Qian X. J. , Rickert S. E. , Lando J. B.
Published: September 2007

Epitaxial crystallization of polyphenylene sulfide (PPS) from 1-chloronaphthalene solution on NaCl (001) surface has been studied using electron microscopy and electron diffraction techniques. Three different epitaxial morphologies were observed: (1) conventional rodlike structures (fold plane epitaxy); (2) platelet structures (fold surface epitaxy); and (3) roselike structures whose growth mechanism and molecular packing are not completely understood at present. Of primary importance is the fact that a possible new crystal structure β-phase) of PPS was formed in the fold surface epitaxy through a true two-dimensional lattice matching by lateral lattice dimensional adjustment of PPS. Lattice match criterion again shows its merit in explaining the formation of fold surface epitaxy and the new crystal structure of PPS. Solution concentration, crystallization temperature, and time have significant influence on crystal growths, orientations, molecular packing, and morphological arrangements.
Epitaxial crystallization of polyphenylene sulfide: Lattice effects on structures
Authors: Qian X. J. , Rickert S. E. , Lando J. B.
Published: September 2007

The investigation of dilute solution epitaxy of polyphenylene sulfide (PPS) has been carried out on a series of inorganic substrates, which cover a wide range of interatomic spacings, surface energies, and geometries. A variety of morphological arrangements of PPS on various substrates were observed. Both 〈100〉 and 〈110〉 epitaxial orientations were observed on monovalent alkali halides. While the 〈100〉 epitaxy is generally thought to grow upon nucleation on surface steps along the 〈100〉 direction, 〈110〉 epitaxy may also be nucleated on these surface steps. Changes in ionic lattice dimensions and ionic nature of the substrate have a substantial effect on the molecular packing of PPS and the resulting crystal orientations. Four new crystalline phases of PPS have resulted from the fold surface epitaxies on NaCl, KCl, KBr, and mica with favorable one- or two-dimensional lattice matching. This is a direct indication of the important role of lattice matching in inducing and defining the epitaxies and polymorphism of PPS.
Pitch-based carbon fibers as studied by transmission electron microscopy
Authors: Hamada T. , Sajiki Y. , Furuyama M. , Tomioka T. , Endo M.
Published: September 2007

The microstructures of carbon fibers prepared from coal tar mesophase pitch and heat-treated at 2500 °C were studied by transmission electron microscopy (TEM). The degree of preferred orientation of the carbon fibers along the fiber axis was not significantly changed: by spinning, while stirring the pitch above the capillary; by changing the viscosity of the pitch in spinning from 60 poise to 250 poise, keeping the diameter of the pitch precursor fiber about 11.5 μm, which is that of the as-spun fiber; and by controlling the diameter of the pitch fiber from 8 μm to 18 μm, keeping the viscosity of the pitch at about 250 poise. Such a weak dependency of the degree of preferred orientation of the carbon fibers on the spinning conditions is qualitatively consistent with the relationships between the degree of preferred orientation of a pitch precursor fiber and the spinning conditions. The graphite layers of the carbon fibers heat-treated at 2500 °C showed shrinkage in the transverse fiber cross section. The degree of shrinkage was significantly increased by stirring the pitch above the capillary while spinning, and the shrinkage also increased when the viscosity of the pitch was increased for spinning, and when the diameter of the fibers was decreased. Roughly speaking, the degree of shrinkage was proportional to the mean size of the mesophase domains in the transverse section of pitch precursor fibers.
Relative stability of LI2, DO22, and DO23 structures in MAl3 compounds
Authors: Carlsson A. E. , Meschter P. J.
Published: September 2007

The structural energy differences between cubic LI2 and tetragonal DO22 crystal structures are calculated for MAl3 compounds, where M is a group III, IV, or V transition metal. The stability of the DO22 structure relative to L12 increases rapidly as the transition-metal d-electron count increases. Typical values of E(DO22) – E(L12) are 0.1–0.15 eV/atom (9600–14500 J/g-atom) for group III,  0.05 eV/atom ( 4800 J/g-atom) for group IV, and ∼ –0.2 eV/atom (∼ –19000 J/g-atom) for group V trialuminides. Similar trends are calculated for the DO23/L12 energy difference. The calculated electronic densities of states (DOS) show that each structure has a minimum in the DOS distribution at a characteristic d-electron count. The preferred crystal structure for a given compound is the one in which the Fermi level lies in the minimum.
Microstructure and superconducting properties of Y–Ba–Cu–O and Yb–Ba–Cu–O thin films formed by metalorganic deposition
Authors: Chen Y. L. , Mantese J. V. , Hamdi A. H. , Micheli A. L.
Published: September 2007

Thin films of Y–Ba–Cu–O and Yb–Ba–Cu–O, 0.5–1.5 μm in thickness, were deposited onto (211) and (100) SrTiO3 single crystal substrates by metalorganic deposition (MOD). After deposition the samples were annealed either by conventional furnace annealing or rapid thermal annealing (RTA). The microstructures of these films were then characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectrometry (EDS). Grain size of the annealed films varied from 0.25 to 1.0 μm. Improved superconducting properties were found for the RTA samples, compared to furnace annealing, and were attributed to larger grain size, little strontium diffusion into the thin films from the substrate, and highly preferred orientation of the 1:2:3 phase.
Crystallography of YBa2Cu3O6+x thin film-substrate interfaces
Authors: Tietz Lisa A. , Barry Carter C. , Lathrop Daniel K. , Russek Stephen E. , Buhrman Robert A. , Michael Joseph R.
Published: September 2007

The epitactic nature of the growth of YBa2Cu3O6+x (YBCO) superconducting thin films on ceramic substrates has been studied using high-resolution electron microscopy (HREM) and selected-area diffraction (SAD) of cross-sectional specimens. The films were grown in situ on (001)-oriented MgO and (001)-oriented Y2O3-stabilized cubic ZrO2 (YSZ) single-crystal substrates by electron beam evaporation. Both of these materials have large lattice misfits with respect to YBCO. Different orientation relationships were observed for films grown on the two types of substrates. These orientation relationships are shown to provide the best matching of the oxygen sublattices across the substrate-film interfaces. A crystalline intermediate layer, 6 nm thick, between the YBCO film and YSZ substrate was observed by HREM and shown by EDS to be a Ba-enriched phase, possibly barium zirconate formed by a reaction. In contrast, the YBCO–MgO interface was found to be sharp and free of any intermediate layers.
Ion microprobe analysis of laser-deposited Y–Ba–Cu thin film: Effects of anneal temperature
Authors: Wang Y. L. , Levi-Setti R. , Chabala J. M. , Venkatesan T. , Wu X. D. , Inam A. , Dutta B.
Published: September 2007

We have employed high spatial resolution (<50 nm) SIMS to study thin film deposited on SrTiO3, produced by pulsed laser evaporation of bulk stoichiometric YBa2Cu3Ox pellets derived from either BaCO3 or Ba3N2. The grain growth, film-substrate interaction, and carbon contamination of the films were examined as a function of post-deposition anneal temperature ranging between 700 °C and 900 °C. On the surface of both types of film, we found overgrowth crystals, which are enriched in copper, that increased in size from a few tenths of a micron to several microns with increasing anneal temperature. Above 800 °C, the film forms a polycrystalline structure with grain size of ∼1 micron. With increasing anneal temperature, more strontium was observed on the surface of the film. Films prepared from YBa2Cu3Ox targets derived from BaCO3 and Ba3N2 were both contaminated with carbon: however, only the former showed segregated carbon along the grain boundaries of the polycrystalline film annealed at 900 °C.
Magnetic, electrical, and microstructural properties of YBa2Cu3O7: A comparison of sol-gel, co-precipitated, and solid state processing routes
Authors: Hayri E. A. , Greenblatt M. , Ramanujachary K. V. , Nagano M. , Oliver J. , Miceli M. J. , Gerhardt R.
Published: September 2007

Samples of YBa2Cu3O7 were prepared by sol-gel, co-precipitation, and solid state processes. Sol-gel samples were prepared from a solution of yttrium, barium, and copper nitrates dissolved in ethylene glycol, co-precipitated samples were made by the amorphous citrate method, and solid state samples were prepared by conventional high temperature reaction of the appropriate metal oxides and carbonates. The sol-gel process was shown to yield superconducting samples of superior Meissner effect, critical current, and critical field. The co-precipitated samples contain impurities that affect the critical properties. The sol-gel and co-precipitated processes yield materials with well-formed, plate-like particles with a fairly uniform size of about 10 μm. The grains in the solid state sample are smaller but have a much wider distribution of sizes than the samples prepared by solution methods.
Preparation and characterization of the superconducting system Bi1−xPbxSrCaCu2Oy
Authors: Agostinelli E. , Bohandy J. , Green W. J. , Phillips T. E. , Kim B. F. , Adrian F. J. , Moorjani K.
Published: September 2007

The superconducting properties of the system Bi1−xPbxSrCaCu2Oy have been studied as a function of lead concentration and preparation conditions. Energy dispersive x-ray analysis indicates the nominal stoichiometry is preserved up to x = 0.2 and for this concentration, zero resistance occurs at 97 K. Magnetically modulated microwave absorption measurements provide a global probe of the samples and show that resistance measurements alone can give a false impression of the quality of the materials.
Consecutive inert and oxygen atmosphere sintering in the synthesis of LaBa2Cu3Oy with T(R = 0)>90 K
Authors: Ghandehari M. H. , Brass S. G.
Published: September 2007

Combinations of inert atmosphere sintering and oxygen atmosphere sintering have previously been reported as necessary for the synthesis of LaBa2Cu3Oy superconductors which achieve zero resistance at temperatures above 90 K. Sintering under oxygen atmosphere only is known to produce La(1+x)Ba(2−x)Cu3Oy, in which La is substituted for Ba in the crystal lattice. The latter substituted compounds achieve zero resistance at temperatures well below the boiling point of liquid nitrogen. In this work, we show that during the initial inert atmosphere sintering step, LaBa2Cu3Oy powder decomposes, in part, into several intermediate compounds. These compounds are then recombined in the subsequent oxygen atmosphere sintering step to form LaBa2Cu3Oy, which achieves zero resistance at temperatures above 90 K. We propose that the net effect of these two processing steps is to inhibit the substitution of La for Ba in the lattice of the fully processed material.
Preparation and properties of uniform mixed colloidal particles; VI, copper(II)–yttrium(III), and copper(II)–lanthanum(III) compounds
Authors: Ribot François , Kratohvil Stanka , Matijevié Egon
Published: September 2007

Uniform spherical colloidal particles of mixed internal composition were obtained by aging at 90 °C solutions containing Cu(NO3)2 + Y(NO3)3 and Cu(NO3)2 + La(NO3)3, respectively, in the presence of urea. The molar ratio of metal ions in the solids precipitated from a given solution varied with the reaction time. After sufficiently long aging, this ratio corresponded closely to that in solutions in which the particles were generated. The original precipitates consisted of basic carbonates, which on calcination converted to mixed oxides of defined composition.
The dose, temperature, and projectile-mass dependence for irradiation-induced amorphization of CuTi
Authors: Koike J. , Okamoto P. R. , Rehn L. E. , Meshii M.
Published: September 2007

CuTi was irradiated with 1-MeV Ne+, Kr+, and Xe+ in the temperature range from 150 to 563 K. The volume fraction of the amorphous phase produced during room temperature irradiation with Ne+ and Kr+ ions was determined as a function of ion dose from measurements of the integrated intensity of the diffuse ring in electron diffraction patterns. The results, analyzed by Gibbons' model, indicate that direct amorphization occurs along a single ion track with Kr+, but the overlapping of three ion tracks is necessary for amorphization with Ne+. The critical temperature for amorphization increases with increasing projectile mass from electron to Ne+ to Kr+. However, the critical temperatures for Kr+ and Xe+ irradiations were found to be identical, and very close to the thermal crystallization temperature of an amorphous zone embedded in the crystalline matrix. Using the present observations, relationships between the amorphization kinetics and the displacement density along the ion track, and between the critical temperature and the stability of the irradiation-induced damage, are discussed.
Laser-induced interface reactions of copper thin films on sapphire substrates
Authors: Godbole Mukund J. , Pedraza Anthony J. , Lowndes Douglas H. , Kenik Edward A.
Published: September 2007

The interface of a copper-sapphire couple that was irradiated with a nanosecond pulsed-exeimer laser was studied by transmission electron microscopy. Deposited layers of 30 or 100 nm thickness were laser treated with energy densities in the range of 0.5 to 0.75 J/cm2. Two different atmospheres were used during these treatments, viz., air or a mixture of argon-4 vol. % hydrogen. The copper film and a thin alumina layer were melted by the laser pulse. Two well differentiated regions could be observed in the modified layer. The region closer to the unmodified substrate consisted of epitaxially regrown alumina with crystallites misoriented up to 10° relative to the substrate sapphire orientation, while precipitate particles could be seen closer to the resolidified copper. The nature of the precipitates generated in the second region was dependent on the atmosphere present during the treatment. In air a trirutile-like compound was obtained which is either oxygen or copper deficient. In an argon atmosphere a compound having a hexagonal structure closely related to sapphire was observed, where copper substituted for some aluminum. These observations are in agreement with a previously developed mathematical model that predicts melting of a thin substrate layer.
The formation of amorphous Ni–B by solid state and ion-beam reaction
Authors: Campbell A. N. , Barbour J. C. , Hills C. R. , Nastasi M.
Published: September 2007

An amorphous Ni–B alloy was formed at the interfaces between layers of polycrystalline nickel and amorphous boron during electron-beam deposition of Ni/B/Ni trilayer structures. Formation of the amorphous alloy appears to be thermally-assisted and, in addition, the amorphous alloy regions can be extended by post-deposition ion-beam mixing. The existence of an upper limit to the thickness of the amorphous Ni–B alloy layer which forms (40 nm) indicates that the amorphous layer serves as a reaction or diffusion barrier. It has been shown for the first time that an amorphous metal-boron alloy is produced by thermal solid state amorphization reaction (SSAR).
Preparation of YBa2Cu3O7−x precursors from a fused eutectic of sodium and potassium hydroxides
Authors: Coppa Nicholas , Nichols Daniel H. , Schwegler John W. , Crow J. E. , Myer G. H. , Salomon R. E.
Published: September 2007

A method for preparing YBa2Cu3O7−x from the simultaneous thermal decomposition of the nitrates of yttrium, barium, and copper in an anhydrous fused eutectic of sodium and potassium hydroxide is described. This method eliminates the need for any mechanical grinding or the introduction of carbon containing anions. Products formed are fine powders (∼1 μm) having mole ratios 1.00Y:2.00Ba:3.06Cu.X-ray diffraction analyses reveal that the initial products are Y(OH)3, BaO2, and CuO, which when air calcinated/oxygen annealed at 900–950 °C form the superconducting YBa2Cu3O7−x A mechanism is postulated for product formation as a function of reaction conditions.
Multilayer high Tc thin film structures fabricated by pulsed laser deposition of Y–Ba–Cu–O
Authors: Chase E. W. , Venkatesan T. , Chang C. C. , Wilkens B. , Feldmann W. L. , Barboux P. , Tarascon J. M. , Hart D. L. , Wu X. , Inam A.
Published: September 2007

The pulsed laser deposition technique was used to deposit stoichiometric thin films from multi-component targets. By changing the target during deposition, multilayer thin film structures were fabricated. We have prepared multilayer structures consisting of alternating superconducting layers with different compositions and elements separated by thin insulating layers. The sharpness of the interfaces was studied by Auger spectroscopy depth profiling. Comparison of films deposited at room temperature and at 680 °C showed that a 10 nm yttrium stabilized zirconium oxide film can completely prevent gross interdiffusion between Y–Ba–Cu–O films and between Y–Ba–Cu–O and Si.
Carbon fiber reinforced tin-superconductor composites
Authors: Ho C. T. , Chung D. D. L.
Published: September 2007

Unidirectional and continuous carbon fiber tin-matrix composites were used for the packaging of the high-temperature superconductor YBa2Cu3O7–δ by diffusion bonding at 170 °C and 500 psi. Tin served as the adhesive and to increase the ductility, the normal-state electrical conductivity, and the thermal conductivity. Carbon fibers served to increase the strength and the modulus, both in tension along the fiber direction and in compression perpendicular to the fiber layers, though they decreased the strength in compression along the fiber direction. Carbon fibers also served to increase the thermal conductivity and the thermal fatigue resistance. At 24 vol. % fibers, the tensile strength was approximately equal to the compressive strength perpendicular to the fiber layers. With further increase of the fiber content, the tensile strength exceeded the compressive strength perpendicular to the fiber layers, reaching 134 MPa at 31 vol. % fibers. For fiber contents less than 30 vol. %, the compressive ductility perpendicular to the fiber layers exceeded that of the plain superconductor. At 30 vol. % fibers, the tensile modulus reached 15 GPa at room temperature and 27 GPa at 77 K. The tensile load was essentially sustained by the carbon fibers and the superconducting behavior was maintained after tension almost to the point of tensile fracture. Neither Tc nor Jc was affected by the composite processing.
Mechanical properties of nickel beryllides
Authors: Nieh T. G. , Wadsworth J. , Liu C. T.
Published: September 2007

The elastic properties of nickel beryllide have been evaluated from room temperature to 1000 °C. The room temperature modulus is measured to be 186 GPa, which is relatively low by comparison with other B2 aluminides such as NiAl and CoAl. Hardness measurements were carried out on specimens that had compositions over the range from 49 to 54 at. % Be, using both a Vickers microhardness tester and a nanoindentor. It was found that the hardness of NiBe exhibits a minimum at the equiatomic composition. This behavior is similar to that of aluminides of the same crystal structure, e.g., NiAl and CoAl. The effect of interstitial oxygen on the hardness of NiBe has also been studied and the results show that the presence of oxygen in NiBe can cause a significant increase in hardness. It is demonstrated that the hardness increase for the off-stoichiometric compositions is primarily caused by interstitial oxygen and can only be attributed partially to anti-site defects generated in off-stoichiometric compositions. Nickel beryllides appear to have some intrinsic room temperature ductility, as evidenced by the absence of cracking near hardness indentations.
Influencing the shape of creep cavities in nickel aluminides by stress changes
Authors: Martinez L. , Schneibel J. H.
Published: September 2007

A nickel aluminide of composition Ni–23.5Al–0.5Hf–0.2B (at. %) is found to develop intergranular cavities with a quasi-equilibrium shape when it is creep deformed at high temperatures and low stresses. When the temperature is lowered and the stress significantly increased (by a factor of 10), crack-like noses form at the tips of the original quasi-equilibrium cavities. Although this observation is in general agreement with previously published computer simulations, certain complications are found as well. The experimental and theoretical relationships between growth rates and sizes of the crack-like noses are inconsistent, and growth rates vary from nose to nose. Possible reasons for these effects are discussed.
Rapid e-beam heating for studying metastable transitions in Mn
Authors: Knapp J. A. , Follstaedt D. M.
Published: September 2007

We have used rapid e-beam heating and quenching to study metastable transitions between allotropic phases in Mn and to determine relative rates of transformation between the allotropes. The equilibrium α ⇉ β transition at 720 °C is bypassed and the metastable α ⇉ γ transition is observed to occur at a temperature (880 ± 30 °C) near that predicted thermodynamically (864 °C).
Mechanical alloying of Fe and V powders: Intermixing and amorphous phase formation
Authors: Fultz B. , Le Caür G. , Matteazzi P.
Published: September 2007

Mössbauer spectrometry and x-ray diffractometry were used to characterize the microstructural changes that occurred during the mechanical alloying of Fe and V powders, After 3 h of essentially no interatomic intermixing, an Fe–V alloy began to form. At first the chemical composition of this alloy was highly inhomogeneous, having large variations over distance scales of less than 100 Å. After about 24 h of ball milling, the alloy homogenized and then became at least partly amorphous.
Identification and characterization of (Ti, Cu, A1)6N, a new η nitride phase
Authors: Carim A. H.
Published: September 2007

In the interfacial reaction zone between AlN and a Ag Cu–Ti braze alloy, a previously unreported phase belonging to the η family (M6X) has been found by transmission electron microscopy. The compound has an approximate stoichiometry of (Ti3−x Cu3−xAl2x)N and space group symmetry of Fd3m, with a cubic lattice parameter of a0 = 1.13 ± 0.02 nm. Large (>1 μm diameter), defect-free grains are present with occasional {111} twinning. Grain boundaries are free of second phases and amorphous interlayers. The formation of continuous layers that grow with reaction time indicate possible stability of the η nitride at 900 °C. The presence of this phase is integral to the chemical and structural development of the ceramic-metal interface.
Explosive crystallization phenomena in SOI structures
Authors: Geiler H. D. , Wagner M. , Glaser E. , Andrä G. , Wolff D. , Götz G.
Published: September 2007

Using the double pulse technique with two synchronized lasers, we studied the conditions of ignition and evolution of explosive crystallization. The structure of the resulting crystallized layers is analyzed by TEM. Results of calculations are reported describing the development of the two phase fronts: amorphous/molten and molten/crystalline. It is shown that the system takes more than 500 ns to reach the steady state. The experimental results support the model of creating first a melt nucleus in the amorphous layer followed by the formation of the crystalline nucleus in the molten sphere. Competitive solid phase nucleation and growth in the amorphous layer limit the temperature-time interval of melt nucleation. Defined explosively crystallized areas in laterally structured SOI layers are presented.
Passivation of β–SiC surface with native and nonnative oxides
Authors: Chaudhry M. Iqbal , Berry W. B.
Published: September 2007

The passivation characteristics of various insulators are evaluated for the β–SiC surface. It is found that wet thermal oxides yield minimum electrical defects at the oxide-SiC interface. Dry thermal oxide results in too much charge either at the oxide-SiC interface or in the bulk. It is also shown that anodic aluminum oxide seems to possess suitable electrical properties for the fabrication of MOS structures on SiC, whereas the CVD silicon nitride proved to be the worst.
Thermodynamic rationalization of molten-salt clectrodeposition in oxide-based systems
Authors: Crouch-Baker S. , Huggins R. A.
Published: September 2007

Electrodeposition from molten-salt systems has been studied extensively as a method of producing both polycrystalline and single-crystalline materials. In this work, the thermodynamic aspects of the electrodeposition process are examined in a number of cases in which the molten-salt system behaves effectively as an oxygen-transporting medium, with particular reference to the thermodynamic properties of the melt. It is demonstrated how information gained from the construction of the appropriate isothermal phase diagram may be used to control and/or rationalize the behavior found in a given melt system on electrolysis.
Stress-displacement relation of fiber for fiber-reinforced ceramic composites during (indentation) loading and unloading
Authors: Hsueh Chun-Hway , Ferber Mattison K. , Becher Paul F.
Published: September 2007

The stress-displacement relation of the fiber is analyzed for fiber-reinforced ceramic composites during axial compressive loading (indentation) and unloading on the exposed end of an embedded fiber. An unbonded fiber/matrix interface subject to Coulomb friction and residual radial clamping stresses is considered in the present study. The results show that the stress-displacement curves during loading and unloading can be used to evaluate the magnitude of the clamping stress, the coefficient of friction, and the frictional stress distribution at the interface. Specifically, in the absence of Poisson's effect (i.e., when Poisson's ratio of the fiber is zero), the interfacial shear stress is constant, the loading curve is parabolic, and, after complete unloading, the residual fiber displacement equals half of the maximum fiber displacement at the peak loading stress. In the presence of Poisson's effect, the interfacial shear stress is not constant, and, after complete unloading, the residual fiber displacement is less than half of the maximum fiber displacement at the peak loading stress.
Atom-probe field ion microscope analysis of surfaces of materials
Authors: Tsong Tien T. , Chen Chong-lin , Liu Jiang
Published: September 2007

Our recent applications of the atom-probe field ion microscope to the study of physics and chemistry of materials at the atomic level are summarized. The materials applicability of field ion microscopy has recently been extended to silicon, silicide, graphite, high Tc superconductors, and other materials. Atom-probe field ion microscopy has been used for atomic layer by atomic layer chemical analysis of surfaces in alloy and impurity segregations, for analyzing the compositional changes across metal-semiconductor interfaces, and for studying formation of cluster ions in laser stimulated field desorption. The energetics of atoms in solids and on surfaces can be studied by a direct kinetic energy analysis of field desorbed ions using a high resolution pulsed-laser time-of-flight atom-probe and by other field ion microscope measurements. The site specific binding energy of surface atoms can be measured at low temperature, where the atomic structure of the surface is still perfectly defined, to an accuracy of about 0.1 to 0.3 eV.
Applications of graphite intercalation compounds
Authors: Inagaki M.
Published: September 2007

The properties of graphite intercalation compounds (GIC's) are discussed with respect to possible applications. Five families of intercalates give high electrical conductivity to GIC's: pentafluorides leading to high conductivity, 108 S/m (higher than metallic copper); metal chlorides; fluorine and alkali metals with bismuth giving relatively high conductivity of the order of 107 S/m plus stability in air; and residual halogens showing extremely high stability under severe conditions, though the conductivity is only of the order of 106 S/m. Electrodes of different GIC's have been tried in primary and secondary batteries, where their characteristics are high electrical conductivity and easy diffusion of electrochemically active species between the graphite layers. Primary lithium batteries of a covalent graphite fluoride are now widely used commercially. Secondary batteries using different host graphites and intercalates give interesting results. Large amounts of hydrogen can be stored in the functional space in alkali metal-GIC's. The same GIC's show high coefficients of isotope separation of hydrogen at liquid nitrogen temperature. The structure and texture of the host graphite play a decisive role in the absorption and separation behaviors of GIC's. Exfoliated graphite prepared by rapid heating of GIC's or their residue compounds leads to flexible graphite sheets which have great industrial applications. Some problems connected with the production and use of these sheets are discussed.