bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural evolution in lead substituted Bi–Sr–Ca–Cu–O superconductors
Authors: Ramesh R. , Remschnig K. , Tarascon J.M. , Green S.M.
Published: September 2007

The structural evolution and cationic stoichiometry of Bi(Pb)–Sr–Ca–Cu–O superconductors have been studied using transmission electron microscopy and x-ray microanalysis. The nature of the incommensurate modulation changes systematically as increasing amounts of lead are added. X-ray microanalysis studies reveal that lead replaces Bi in the structure. Pb addition improves the microstructural homogeneity leading to the formation of a nearly homogeneous sample consisting of the “2223” phase. Based upon all the experimental results, it is inferred that the role of Pb substitution is related to the thermodynamics and kinetics of the formation of the n = 3 phase.
First principles calculation of the elastic constants of intermetallic compounds: metastable Al3Li
Authors: Guo X-Q. , Podloucky R. , Freeman A.J.
Published: September 2007

We report first principles local density calculations for the metastable Al3Li intermetallic compound with cubic L12 crystal structure using the full-potential linearized augmented plane wave method. From the second derivative of the total energy as a function of volume, and generated tetragonal and trigonal lattice distortions, the elastic constants C11, C12, and C44 were derived yielding C11 = 158 GPa, C12 = 29.4 GPa, and C44 = 57.7 GPa. Because of the very high Young's modulus (E = 141 GPa) compared, for example, to pure Al (E = 66 GPa), it is suggested that Al3Li plays an important role in strengthening the Al–Li alloys. The calculated Young's modulus appears in good agreement with experimental estimates when the experimental values are extrapolated to 0 K. Although the Young's modulus of Al3Li is increased in comparison to Al, the calculated bulk modulus is decreased to a value of 72 GPa as compared to pure Al (82 GPa), in agreement with experiment. As a result, the Poisson ratio is reduced to ŝ = 0.173 as compared to the value 1/3 for an isotropic medium. Because of this and the high Young's modulus, the calculated Debye temperature ΘD at 0 K amounts to 672 K, which is substantially larger than ΘD for Al, which is about 400 K.
51V and 93Nb high resolution NMR study of NbVO5
Authors: Davis J. , Tinet D. , Fripiat J.J. , Amarilla J.M. , Casal B. , Ruiz-Hitzky E.
Published: September 2007

NbVO5 is characterized by 51V and 93Nb NMR resonance frequencies strongly upfield shifted when compared to those in model compounds V2O5 and LiNbO3. The chemical shift anisotropy dominates the 51V observed spectrum in a magnetic field of 11.7 T. The asymmetry parameter ηc is 0.2 and the quadrupole coupling constant is relatively small (1 MHz). The quadrupolar Hamiltonian overwhelmingly dominates the 93Nb spectrum (ηQ = 0.9) and the quadrupole coupling constant is huge (16.5 MHz). In agreement with the structure obtained from the x-ray powder diagram the isotropic chemical shift of 51V suggests that NbVO5 is indeed an orthovanadate. Interestingly, in NbVO5 the isotropic chemical shift of 93Nb reveals a better shielding of the 93Nb nucleus and a lower electric field gradient than in LiNbO3. Nb octahedra in NbVO5 are sharing corners whereas they share edges in LiNbO3.
Synthesis, characterization, and potential application of highly chemically durable glasses based on AlF3
Authors: Iqbal Tariq , Shahriari Mahmoud R. , Merberg Glenn , Sigel George H.
Published: September 2007

Fluorozirconate glasses are stable with respect to devitrification but have poor chemical durability and only fair mechanical strength. AlF3-based glasses with improved chemical durability and enhanced mechanical strength are reported here. The optical, mechanical, and thermal properties of these glasses are contrasted to the more familiar ZBLAN composition. The infrared edge of these glasses lies at shorter wavelengths than ZrF4-based glasses, but aluminum fluoride glasses offer some interesting opportunities for short-range IR fiber applications such as sensing, remote spectroscopy, and laser power propagation.
Influence of a rapid annealing on the surface oxide film of a tinned copper wire
Authors: Gillet Isabelle , Boyer Lionel , Bodin Camille , Binder Germaine
Published: September 2007

A continuous annealing, using the Joule effect, is performed during the fabrication of a tinned copper wire. During this operation, which lasts between 1/10 and 1/100 of a second, the wire is brought in air to a temperature which exceeds the melting point of tin. The influence of the continuous annealing on the nature of the surface layer of the tin coating is studied using XPS. The thickness of the tin oxide film covering the metallic tin is shown to be reduced after the annealing. This result is confirmed by measurements of the electrical contact resistance using the crossed rods method.
Pulse laser processing of a SiC/Al-alloy metal matrix composite
Authors: Dahotre Narendra B. , McCay Mary Helen , McCay T. Dwayne , Gopinathan Santosh , Allard Lawrence F.
Published: September 2007

The microstructural changes and the tensile behavior of laser processed A356-Al alloy matrix composites reinforced with 10 and 20 vol.% SiC particulates are characterized. The autogenous bead-on-plate welds were made using a pulsed CO2 laser operating at a peak power level of 3.2 kW. The pulse on-time was constant at 20 ms and the off-time was varied from 20 to 2 ms (duty cycles of 50–91%). The microstructure of the laser melted region was investigated by optical, scanning, and transmission electron microscopy, and x-ray microchemical analysis techniques. The extent of microstructural changes varied directly with duty cycle, i.e., being a maximum for the longest (91%) duty cycles. Pulsed laser processing produced partial to complete dissolution of SiC particles and sometimes resulted in the formation of aluminum carbide. The associated rapid cooling also produced a fine distribution of nonequilibrium complex precipitates. In addition, the laser energy modified the SiC surface both physically and chemically. The results of tensile tests indicated that the modified SiC and the distribution of fine nonequilibrium precipitates enhance the mechanical properties of the laser processed composites. Optimum changes in microstructure and mechanical properties were obtained in the composites processed with intermediate (67 and 74%) duty cycles; therefore pulsed processing appears to be a strong candidate for successful joining of these MMCs.
Fiber bridging of a carbon fiber-reinforced carbon matrix lamina composite
Authors: Miyajima Tatsuya , Sakai Mototsugu
Published: September 2007

Fracture mechanics and mechanisms of a carbon fiber reinforced carbon matrix lamina composite are studied. The importance of microfracture processes of first matrix cracking, fiber bridging, and fiber pullout processes for toughening C/C-composites is emphasized, and then, the fiber bridging process of the composite is mainly focused through the measurement of the R-curve. The fiber bridging tractions are estimated by the Dugdale approach from which the superb stress shielding and excellent notch tolerance of the composite are demonstrated.
Stress in evaporated films used in GaAs processing
Authors: Strifler W.A. , Bates C.W.
Published: September 2007

A simple and practical method is described for determining the residual stress in vapor deposited thin films that are less than 1000 Å in thickness. The method relies on the evaporation of thin films onto prefabricated micro-cantilever beams of SiO2. The vertical deflection at the end of the beam is measured using an optical microscope to determine the average film stress with a resolution of 25 MPa. Calculations show that the vapor deposition of metal films onto these beams does not induce significant heating, so the thermal component of residual film stress is minimal. The micro-cantilever technique is used to measure the film stress in 500 Å films of Al, Ti, Pt, Au, Ni, and Ge. These measured values are compared to similar measurements reported in the literature.
Microstructural analysis of Pd-based ohmic contacts to p-type GaAs
Authors: Schmitz K.M. , Jiao K.L. , Sharma R. , Anderson W.A. , Rajeswaran G. , Zheng L.R. , Cole M.W. , Lareau R.T.
Published: September 2007

As part of the investigation of the use of Pd-based ohmic contacts to p-type GaAs, cross-sectional transmission electron microscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy were used to explore the uniformity at the metal/GaAs interface and its composition profile after ohmic contact formation. Comparisons were made among Au:Be, Au:Be/Pd, and Au/Pd contacts. Regions of p+ were formed in n-type GaAs by a spin-on source which was rapid diffused at 950 °C for 6 s or by ion implantation at a dose of 3 × 1014 atoms/cm2 at 150 keV for 15 min. Metallizations were accomplished by evaporation with a base pressure of 3 × 10−6 Torr. Sintering of the metallizations was done in a furnace at 350 °C for 15 min. Cross-sectional transmission electron microscope studies revealed an absence of spiking when Be is present in the metallization scheme but a broad band diffused into GaAs. An improper metal/GaAs adhesion was observed when Pd is absent. Be assists in confining the reaction of Pd with GaAs and acts as a diffusion barrier to the p+ dopant. Electrical measurements, taken from transmission line and cross bridge Kelvin resistors, were best for the Pd/Au:Be, which yielded a contact resistance of 0.3 μΩ-cm2.
Synthesis of dense β, β″–alumina ceramics by reaction sintering of Na2O-containing alumina compact
Authors: Hirata Yoshihiro , Izaiku Takeshi , Ishihara Yoshimi
Published: September 2007

Reaction sintering in the Na2O–MgO–Al2O3system was studied with α–alumina green compacts containing Na2O and MgO in the pores of a controlled structure to produce β, β″–alumina polycrystalline at low temperatures. HCOONa and (CH3COO)2Mg were infiltrated into the alumina powder compacts (average particle size 0.2 μm) with relative densities of 51 to 66% at the compositions of Na2O/MgO/Al2O3= 1/0.10/4.0–7.6. The alumina powder compacts were formed by filtration of the aqueous colloidal suspensions through gypsum molds. Phase change from α to β, β″–alumina proceeded fast at low temperatures in the samples with high Na2O/Al2O3ratios. However, no significant densification occurred below 1500 °C owing to the volume increase of powder compacts associated with the phase change of α to β, β″–alumina. At 1600 °C, the green compacts were rapidly densified to relative densities above 99%. This densification was related to the liquid phase sintering based on the partial decomposition of β″–alumina. The dense β, β″–alumina polycrystalline consisted of needle-like grains of 2–5 μm in length and 1–2 μm in width.
A comparative study of side chain liquid crystalline polymers and their monomers designed for nonlinear optical applications
Authors: Findlay R.B. , Lemmon T.J. , Windle A.H.
Published: September 2007

Characterizations of side chain liquid crystalline polymers and their monomers point toward chemical structures and processing techniques which optimize their suitability for nonlinear optical applications. Polymers with methacrylate backbones and nitrostilbene or nitrobiphenyl side groups are studied; they tend to form smectic phases, but no solid crystallinity. By copolymerizing with nonmesogenic backbone units, the smectic-isotropic transition temperature can be controlled and may fall below the glass transition temperature. There is evidence for a significant degree of pretransitional alignment due to the surface fields, and mesogen ordering perpendicular to flow-induced backbone alignment. Very rapid cooling can suppress the highly scattering polydomain smectic phase.
Dislocation emission at ledges on cracks
Authors: Zhou S.J. , Thomson Robb
Published: September 2007

In this paper, we propose that, depending on their height, ledges on cracks can be efficient sources of dislocations at loadings well below the critical loading for homogeneous emission. Detailed 3-D elastic calculations are presented supporting this proposition. There are two configurations for emission: one which blunts the crack, and one we call a jogging configuration. By our calculations, the blunting configuration should be the more efficient source; however, jogging dislocations are more frequently observed, experimentally. We find that the ledge is only a finite source of dislocations, in the sense that the ledge height decreases as the dislocations are emitted. The atomic configuration at the ledge is composed of finite lengths of real dislocations, which is the reason why such dislocations can be emitted easier than homogeneously produced dislocations. The stresses at the ledge tip produce a cloud of bound dislocations near the ledge, pinned at the ledge ends, so that the ledge crack configuration becomes delocalized. Delocalization of the pileup dislocations in the jogging direction may explain why the jogging dislocations are more frequently seen. Implications for dislocation free zones and ductile transitions are discussed.
Corrosion of polycrystalline ZnSe by alternating high voltage in a saline solution
Authors: King Joseph
Published: September 2007

Prolonged exposure of chemical vapor deposited, polycrystalline ZnSe to high ac voltages in the presence of a 1 molal NaCl solution induces severe mechanical damage. The damage takes the form of defects which originate at the surface and grow intergranularly into the bulk with a bush-like morphology. Neither exposure to the salt solution in the absence of the high voltage nor low voltage dc electrolytic exposure produces the defects. The damage may be associated with an intergranular hydride phase or grain boundary impurity segregations present or formed during the environmental exposure.
Synthesis of superconductors from metal neodecanoates
Authors: Bowmer T.N. , Shokoohi F.K.
Published: September 2007

Metal-organic precursors can facilitate the production of superconducting thin films on large area substrates for microelectronic device applications. This paper describes the chemistry that occurs during the thermal processing of yttrium-, barium-, and copper-neodecanoate mixtures into a superconducting material, YBa2Cu3O7−x. Intermediates such as metal carbonates and oxides are identified by combining thermogravimetry with infrared spectral and x-ray diffraction analysis. Changing from argon to oxygen atmospheres increased decomposition rates and metal oxide formation. We found that (1) a low temperature (500–600 °C) decomposition in an oxygen-poor atmosphere, (2) a high temperature (>925 °C) annealing step in an oxygen-rich atmosphere, and (3) slow cooling to 50 °C are all required to produce uniform superconducting films.
Sputtering synthesis and properties of molybdenum nanocrystals and Al/Mo layered nanocomposites
Authors: Chow G.M. , Pattnaik A. , Schlesinger T.E. , Cammarata R.C. , Twigg M.E. , Edelstein A.S.
Published: September 2007

Molybdenum nanocrystals (4 nm < particle size < 12 nm) were synthesized in the vapor by sputtering in a thermal gradient at argon pressures between 0.2 and 0.6 Torr. The gradient was achieved by cooling the substrate table with liquid nitrogen in order to enhance the deposition rate of the nanocrystals. The size of these nanocrystals depended on the sputtering argon gas pressure. Using appropriate deposition parameters, these nanocrystals were incorporated, either as a dispersed phase in a major phase produced by normal sputtering or as a layer in a layered structure to produce nanocomposite films. Results of Auger electron spectroscopy (AES) study of the Al/Mo layered nanocomposite films are presented. The Knoop microhardness of these films was increased by as much as a factor of four compared with the hardness of homogeneous Al films. A correlation of the microhardness to the microstructures as revealed by transmission electron microscopy (TEM) is discussed.
Diffraction studies on Ni–Co and Ni–Cr alloy thin films
Authors: Sethuraman A.R. , De Angelis R.J. , Reucroft P.J.
Published: September 2007

Alloy films of Ni–Co and Ni–Cr of compositional ratios 1:1, 1:3, and 3:1 deposited by vapor deposition were studied by Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Results of TEM analysis on the Ni–Co alloy films indicated that the films were face-centered cubic (fcc) in structure. XRD results confirmed the TEM observations. TEM analysis of Ni–Cr alloy films showed that the films were body-centered cubic (bcc) in structure. With increase in the Cr content more than 25%, the material contained a higher fraction of an amorphous phase. XRD studies provide limited information owing to the quasi-amorphous structure of the films of high Cr content.
The transport properties of activated carbon fibers
Authors: di Vittorio S.L. , Dresselhaus M.S. , Endo M. , Issi J-P. , Piraux L. , Bayot V.
Published: September 2007

The transport properties of isotropic pitch-based carbon fibers with surface area 1000 m2/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity, and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons.
Surface planarity and microstructure of low temperature silicon SEG and ELO
Authors: Arst M.C. , Ritz K.N. , Redkar S. , Borland J.O. , Hann J. , Chen J.T.
Published: September 2007

Surface planarity and epi/SiO2 interface characteristics of selective epitaxial growth (SEG) and epitaxial lateral overgrowth (ELO), deposited at 800–950 °C/10 or 25 Torr, have been studied for micron-sized structures. SEG at 860 °C showed superior planarity and reduced ratio of facet width to epi thickness, compared to higher deposition temperatures. Data showed that epi/SiO2 interface defects are greatly reduced for structures parallel to (100) and/or by adding HCl to the source gas, compared to interfaces positioned at standard orientation (110) on a (100) substrate. The transition from SEG to ELO in view of the facet orientations will be discussed. To correlate structural with electrical data, n+/p diodes were fabricated on as-grown and polish planarized SEG. Leakage current values of approximately 100 nA/cm2 could be measured. These are comparable to similar n+/p junctions fabricated on conventional epi.
Structure of twinned {113} defects in high-dose oxygen implanted silicon-on-insulator material
Authors: Visitserngtrakul Supapan , Krause Stephen J. , Barry John C.
Published: September 2007

Conventional and high resolution electron microscopy (HREM) were used to study the structure of {113} defects in high-dose oxygen implanted silicon. The defects are created with a density of 1011 cm−2 below the buried oxide layer in the substrate region. The HREM images of the {113} defects are similar to the ribbon-like defects in bulk silicon. It is proposed that there is a third possible structure of the defects, in addition to coesite and/or hexagonal structures. Portions of some defects exhibit the original cubic diamond structure which is twinned across {115} planes. The atomic model shows that the {115} interface is a coherent interface with alternating five- and seven-membered rings and no dangling bonds.
Solid state reactions of SiC with Co, Ni, and Pt
Authors: Chou T.C. , Joshi A. , Wadsworth J.
Published: September 2007

Solid state reactions between SiC ceramics and Co, Ni, and Pt metals have been studied at temperatures between 800 and 1200 °C for various times under He or vacuum conditions. Reactions between the metals and SiC were extensive above 900 °C. Various metal silicides and carbon precipitates were formed in layered reaction zones. Interfacial melting was also observed at certain temperatures; teardrop-shaped reaction zones, porosity, and dendritic microstructure resulting from melting/solidification were evident. The metal/ceramic interfaces exhibited either planar or nonplanar morphologies, depending upon the nature of the metal/ceramic reactions. Concave interfacial contours were observed when interfacial melting occurred. By contrast, planar interfaces were observed in the absence of interfacial melting. In all cases, the decomposition of SiC was sluggish and may serve as a rate limiting step for metal/ceramic reactions. Free unreacted carbon precipitates were formed in all the reaction zones and the precipitation behavior was dependent upon the metal system as well as the location with respect to the SiC reaction interface. Modulated carbon bands, randomly scattered carbon precipitates, and/or carbon-denuded bands were formed in many of the reaction zones, and the carbon existed in a mixed state containing both amorphous and graphitic forms.
Tetragonal to orthorhombic transformation during mullite formation
Authors: Li Dong X. , Thomson William J.
Published: September 2007

The mullite formation process in both single phase and diphasic sol-gel precursors to mullite was studied using dynamic x-ray diffraction (DXRD). A metastable, tetragonal-like mullite phase was observed in all the single gels at temperatures from 980 °C to 1200 °C, but not in any of the other precursors. The tetragonal to orthorhombic mullite transformation was very slow as the lattice parameters, a and b, split and moved gradually away from each other as a result of a gradual decrease of alumina content in the mullite solid solution with increasing temperature from 1100 °C to 1200 °C. The formation of tetragonal mullite coincides with that of the Al–Si spinel. The occurrence of tetragonal mullite or the spinel (or both) is determined mainly by the processing conditions of the sol-gel precursors.
Analysis of depth profiles of sol-gel derived multilayer coatings by Rutherford backscattering spectrometry and by cross-sectional transmission electron microscopy1
Authors: Schutte Carol L. , Smith Patrick M. , Whitesides George M.
Published: September 2007

This paper describes the preparation and compositional analysis of multilayer thin-film coatings prepared using sol-gel techniques. Alternate layers were labeled with an iron tag, derived from hydrolyzed 1,1'-bis(triethoxysilyl)ferrocene. Iron-free layers were composed of SiO2 derived from hydrolyzed tetraethylorthosilicate (TEOS). Analyses of these systems were based on Rutherford Backscattering Spectrometry (RBS) and Cross-Sectional Transmission Electron Microscopy (XTEM). The depth profile of iron, measured by RBS, yielded thicknesses (1000–1600 Å) for the individual layers that could be verified independently by XTEM.
Ionic transport in LiNbO3
Authors: Mehta Apurva , Chang Edward K. , Smyth Donald M.
Published: September 2007

The high temperature equilibrium conductivity (950 °C–1050 °C) of congruent LiNbO3 can be resolved into two components: an electronic portion that is dependent on the oxygen partial pressure and an ionic portion that is pressure independent. It is shown that the two components can be obtained from an analysis of the total equilibrium conductivity measured as a function of oxygen partial pressure. The ionic transport number (fractional ionic conductivity) thus obtained is compared with that obtained from an oxygen concentration cell measurement. The two techniques are found to be in excellent agreement, confirming the experimental validity of the defect chemistry method. From the temperature dependence of the ionic conductivity, the activation energy (138 kJ/mol [1.43 eV]) for the ionic transport is obtained. The results are in good agreement with the value previously obtained for the oxygen chemical diffusivity.
Plasma modification of polyvinyltoluene and polystyrene latices
Authors: Zimmermann C.J. , Ryde N. , Kallay N. , Partch R.E. , Matijević E.
Published: September 2007

Polyvinyltoluene (PVT) latex particles were etched with O2 or CF4/O2 plasma and polystyrene (PS) latex by the O2 plasma. While the effect of these treatments on the surface topology and the specific surface area was minor, the electrokinetic measurements showed a significant change in the surface charge characteristics. The interpretation of the results in terms of a surface complexation model, taking the Stern–Gouy–Chapman structure of the interfacial layer into consideration, yielded the values of the corresponding equilibrium constants, which indicated that the chemical nature and the density of the surface charged groups were altered by plasma attacks.
Interfacial reactions in polyimide/metal systems
Authors: Iacona Fabio , Garilli Marco , Marletta Giovanni , Puglisi Orazio , Pignataro Salvatore
Published: September 2007

Ultra-thin films of polyamic acid (BTDA-ODA type) are prepared by spin coating a very dilute solution onto bare or metallized silicon wafers (estimated thickness 25 ± 5 Å). The XPS analysis of the various polymer/metal interfaces suggests the occurrence of acid-base type interaction between the carboxylic groups of the polymer and the oxides and hydroxides that cover the Ni and Cr surfaces. When these systems arein situcured, the XPS analysis shows the occurrence of a variety of chemical interfacial reactions. In particular: (i) when the substrate is a naturally passivated Ni layer, the complete destruction of the polymer is observed; (ii) when the substrate is a naturally passivated Si wafer, no relevant interaction occurs; (iii) for a naturally passivated Cr and an oxidized Ni surface, partial decomposition of the polymer is observed. The above effects are explained in terms of the acid or basic properties of the oxidized layers that cover the metal surfaces, and in terms of their stability toward heating.
Tribological properties of metals modified by ion-beam assisted deposition of silicone oil
Authors: Itoh Y. , Hibi S. , Hioki T. , Kawamoto J.
Published: September 2007

Silicone oil vapor deposition and Ar+ ion irradiation can form an adhesive carbonaceous film on a steel substrate. The friction coefficient μ of the coated substrate is found to be very low for sliding against a steel ball both in air (μ ∼ 0.04) and in N2 gas (μ < 0.02). The duration of the low friction state is comparatively long and is 5 × 103–1.5 × 104 cycles for a film 0.15 μm thick. X-ray photoemission spectroscopy, infrared reflection spectra, and Raman measurements indicate that the film mainly consists of amorphous carbon containing Si and O.
Glancing angle x-ray study of the effect of oxygen on interface reactions in Al/Ni bilayers
Authors: Heald S.M. , Barrera E.V.
Published: September 2007

Glancing angle x-ray reflectivity and EXAFS measurements have been made on a series of UHV prepared Al/Ni bilayers with varying amounts of oxygen impurities. These samples show an intrinsic reacted region prior to annealing, and for clean samples further reaction occurs at 250 °C. Oxygen is found to influence strongly the course of the reaction with an effect which depends on its location. A few percent O impurity within the Al film strongly suppresses the grain boundary diffusion path, which allows the growth of a smooth NiAl3 layer. Interfacial O exposures of 60 and 600 Langmuir both inhibit the initial reaction and raise the temperature at which further reaction occurs to as much as 300 °C with an effect which depends on exposure. The thickness of the intrinsic reaction zone is about 60 Å for clean samples, and is nearly eliminated for contaminated interfaces. The results indicate that surface/interface, grain boundary, and bulk diffusion all play important roles in the formation of these interfaces, and that each of these is influenced by O impurities.
Ternary atom site location in L12-structured intermetallic compounds
Authors: Munroe P.R. , Baker I.
Published: September 2007

Ternary sublattice site occupancy in two L12-structured intermetallic compounds were evaluated by a transmission electron microscope technique called ALCHEMI, or atom site location by channeling enhanced microanalysis, and by x-ray diffractometry, through measuring the relative integrated intensity of fundamental and superlattice x-ray diffraction peaks. The x-ray diffractometry showed that in nickel-rich Ni3Al + Hf hafnium was found to occupy preferentially the aluminum sublattice, and in a multiphase alloy an L12-structured phase with the composition Al74.2Ti19Ni6.8 nickel atoms showed a strong preference for the titanium sublattice. The ALCHEMI data broadly agreed with the x-ray results for Ni3Al but gave completely the opposite result, i.e., a preference of nickel for the titanium sublattice, for Al3Ti. The methods of ALCHEMI and x-ray diffractometry are compared, and it is concluded that ALCHEMI data may be easily convoluted by peak overlap and delocalization effects.
Plastic deformation and fracture behavior of a Fe-modified Al3Ti-base L12 intermetallic alloy
Authors: Gengxiang Hu , Shipu Chen , Xiaohua Wu , Xiaofu Chen
Published: September 2007

The microstructure of the ordered intermetallic alloy with a nominal composition of Al66Fe9Ti24 is nearly single-phase L12 structure, with a few second phase agglomerates at some grain corners. Room temperature compression tests showed that this material exhibits a plastic strain of about 11% at fracture. Final fracture of the compression specimens occurred by a shear-off process along a surface oriented about 45 degrees to the compression axis. Fractographic analysis revealed that the fracture is transcrystalline and the fracture mode is mainly quasicleavage plus tearing. Transmission electron microscopy (TEM) was used to explore its deformation mechanisms. The dislocation density was low after homogenization, but is greatly increased during deformation. The deformation mode was found to be 〈110〉 {111} slip instead of twinning as in Al3Ti. The a〈110〉 superdislocations dissociated into two partials of a/3〈211〉-type, bounding a superlattice intrinsic stacking fault (SISF) on the {111} slip plane.
Phase transformations in Ti3Al and Ti3Al + Mo aluminides
Authors: Djanarthany S. , Servant C. , Penelle R.
Published: September 2007

We have analyzed the phase relationships in two titanium aluminides containing 3.4 at. % Mo with different aluminum compositions. The alloys were first homogenized in the β field, then cooled continuously at different cooling rates from 80 °C/s to 0.1 °C/s. The continuous cooling transformation diagrams (CCT) show that phase transformations and resulting microstructures are highly dependent on cooling rate. The microstructure consists of ordered α2 (DO19), ordered β0 (B2), and athermal ω (hexagonal) phases. The “tweed microstructure” is observed. The evolution of microhardness was determined as well as the relative partitioning of Al and Mo in (α2', α2) and β0 phases as a function of cooling rate.
Mechanical behavior of nanocrystalline Cu and Pd
Authors: Nieman G.W. , Weertman J.R. , Siegel R.W.
Published: September 2007

This report gives results of a study of the bulk mechanical properties of samples of nanocrystalline Cu and Pd consolidated from powders prepared by inert gas condensation. Fourier analysis x-ray diffraction techniques, used to determine average grain size and mean lattice strains of the as-consolidated samples, show grain sizes in the range of 3–50 nm and lattice strains ranging from 0.02–3%. Sample densities range from 97–72% of the density of a coarse-grained standard. Microhardness of the nanocrystalline samples exceeds that of annealed, coarse-grained samples by a factor of 2–5, despite indications that sample porosity reduces hardness values below the ultimate value. Uniaxial tensile strength of the nanocrystalline samples is similarly elevated above the value of the coarse-grained standard samples. Restrictions on dislocation generation and mobility imposed by ultrafine grain size are believed to be the dominant factor in raising strength. Residual stress may also play a role. Room temperature diffusional creep, predicted to be appreciable in nanocrystalline samples, was not found. Instead, samples appear to show logarithmic creep that is much smaller than the predicted Coble creep.
Structural changes and physical properties of Fe–Ni-based metallic glasses rapidly heated by pulsed electrical currents
Authors: Zaluski L. , Zaluska A. , Kopcewicz M. , Schulz R.
Published: September 2007

Fe–Ni–Si–B metallic glasses have been annealed and crystallized using short electrical current pulses. Two types of electrical heat treatment have been used. The first one is an isothermal annealing treatment using a very high initial heating rate while the second one is a thermal spike applied on an amorphous sample held at various initial temperatures. The microstructure of the alloys after heat treatment has been characterized by x-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy. The thermal and magnetic properties of the samples measured by DSC and hysteresis loop tracer have been studied after the various heat treatments and correlated with the microstructure of the alloys. The crystallization at high temperatures produces the gamma phase only, while at low temperatures, a mixture of the gamma and alpha phases (the alpha phase being predominant) is usually observed. The samples initially held at liquid nitrogen temperature and heat treated with a thermal spike remain amorphous and show improved magnetic properties (lower coercive field and higher induction at saturation) without loss of ductility.
Amorphization of elemental and compound semiconductors upon ion implantation
Authors: Jones K.S. , Santana C.J.
Published: September 2007

Cross-sectional TEM studies of ion implantation induced amorphization in a large number of semiconductors have been performed. Samples of Si, AlAs, GaAs, GaP, GaSb, InP, InAs, and ZnSe were simultaneously implanted at 77 K with 20 keV Si+ at doses between 1 × 1014/cm2 and 1 × 1016/cm2. A dose of 1 × 1015/cm2 minimized the ion beam induced epitaxial crystallization and sputtering effects. The depth of the amorphous layer at this dose was compared with Monte Carlo damage density distribution calculations (TRIM'90). The threshold damage density (TDD) necessary for amorphization was determined for each compound. The values of the threshold damage density vary from as low as 2.4 × 1019 keV/cm3 for InAs up to 7.3 × 1020 keV/cm3 for AlAs. ZnSe never became amorphous and GaSb exhibited an unusual disordering after the highest dose. The values of the threshold damage density for the various compositions were compared with known thermochemical data and several bond energy estimates. No single calculation explained all of the trends observed.
Silicate bonded unsintered ceramics of Bayer process waste
Authors: Wagh Arun S. , Douse Victor E.
Published: September 2007

Sodium silicates are investigated to enhance the strengths of Bayer process muds and develop structural ceramics without sintering. With an impregnation of sodium silicate from 2% to 10% concentration in red mud, the fracture toughness is enhanced from 0.2 to 0.9 MPa. Compression strengths of 25.1 MPa (3628 psi) have been attained with red mud at 10% silicate concentration. Similar enhancements by a factor of 4 to 5 have been obtained for modulus of rupture and Brinell hardness number. It is shown that these properties do not deteriorate in acidic and neutral environment in water, implying stability to weathering conditions. SEM investigations reveal elongated crystal formation, possibly of aluminum and iron silicates in the aggregate. These crystals act like whiskers enhancing the strength. The process is applicable for development of low-cost construction components.
Preparation of the 110 K single phase superconductor Bi1.6Pb0.4Ca2Sr2Cu3Ox using a precursor matrix reaction method
Authors: Wang Z. , Statt B.W. , Lee M.J.G. , Bagheri S. , Rutter J.
Published: September 2007

Nearly single phase sintered samples of the lead-doped high-Tc oxide superconductor of nominal composition Bi1.6Pb0.4Ca2Sr2Cu3Ox have been prepared using a precursor matrix reaction method. The experimental results indicate that in samples annealed under optimum conditions (200 h at 855 °C) the volume fraction of impurity phases is only about 3%. If the optimum annealing time is exceeded, the high-Tc phase begins to decompose into the low-Tc phase and nonsuperconducting phases. It is found that the precursor reaction matrix method minimizes loss of lead during processing.
Ion beam mixing of U-based bilayers
Authors: Rossi François , Nastasi M. , Cohen M. , Olsen C. , Tesmer J.R. , Egert Chuck
Published: September 2007

Bilayer samples of U/Al, U/Ti, U/Si, and U/C have been ion beam mixed with 400 keV Ar and U/Al with Xe ions at doses from 2 × 1015 to 1 × 1017 ions/cm2. Mixing experiments were performed at various temperatures between 77 and 420 K. The amount of interfacial mixing, 4Dt, follows a linear dose dependence below a critical temperature, depending on the system studied. Below this temperature, the mixing efficiency, defined as ∂(4Dt)Φ where 4Dt is the mixing and Φ is the dose, is temperature independent. Its value, as well as the value of the transition temperature, agrees well with the thermodynamical model of chemically biased diffusion in a thermal spike for the four systems tested. The transition between the thermal spike regime and the temperature enhanced mixing regime was interpreted on the basis of an intracascade mechanism. The formation of an intermetallic compound in the U/Al system was detected and interpreted on a qualitative basis by crystallographic considerations.
Titanium silicide and titanium nitride formation by titanium-ion implantation for MOS LSI applications
Authors: Omura Yasuhisa , Inokawa Hiroshi , Izumi Katsutoshi
Published: September 2007

A 70-nm-thick, 19-μΩ · cm TiSi2 layer is formed using a Ti-ion implantation technique. TiN/TiSi2 double layers, whose surface morphology is superior to that obtained with conventional deposition and reaction techniques, can also be simultaneously formed by Ti-ion implantation into monocrystalline Si screened with the Si3N4 film. Discrete pn-junction diodes with a shallow TiSi2 layer and Ti-polycide-gate MOS capacitors are fabricated to determine the influences of Ti-ion implantation on electrical characteristics. The leakage current of the B-doped p+n junction and As/P-doped n+p junction with Ti-ion implanted silicide layer is low enough for device applications. Silicide formation on the gate polycrystalline-Si does not affect the breakdown electric field strength of a 20-nm-thick gate oxide. MOS capacitors showed normal C-V characteristics.
Alkali emission accompanying fracture of sodium silicate glasses
Authors: Langford S.C. , Jensen L.C. , Dickinson J.T. , Pederson L.R.
Published: September 2007

Measurements of atomic Na emission accompanying the fracture of sodium trisilicate glass and a soda lime glass in vacuum were made by quadrupole mass spectroscopy and surface ionization techniques. Peak Na° emission intensities occur some 3–6 ms after the fracture event and decay over tens of milliseconds. This behavior is attributed to the diffusion of Na+ ions into a layer of damaged material at the surface where the ions are subsequently neutralized and thermally emitted as Na°. Charge carriers generated during fracture and subsequently trapped at defect sites apparently play important roles in charge compensating Na+ diffusion and in neutralizing Na+. During the first 300 ms following fracture, we also observe intense, short lived (400 μs) bursts in Na° emission which may be associated with catastrophic relaxation of residual stresses. The kinetics of Na emission suggest that the relaxation of newly formed glass surfaces involves rather complex surface physical and chemical processes.
A new approach to fracture toughness analysis and its application to ABS polymers
Authors: Ni Beta Yuhong , Zhang Tong-Yi , Li J.C.M.
Published: September 2007

A new approach is proposed to analyze the fracture behavior with crack tip plasticity by the use of three independent measurements: E0 is the energy required per unit length of crack front to prepare the crack just before propagation; the Ef-curve is a plot of the energy required to produce a unit area of fractured surface versus the crack length; and the Ka-curve is a plot of the applied stress intensity factor KIapp versus the crack length. For ABS polymers, the prefracture energy E0 is 33 Jm−1; the Ef-curve is a horizontal line of 5.2 × 104 Jm−2; and the Ka curve has three different regions which depend on the development of the plastic zone during fracture.
Solvent-induced damage in polyimide thin films
Authors: Hu M.S. , He M.Y. , Evans A.G.
Published: September 2007

Solvent induced crazes formed in strained polyimide thin films on different substrates have been studied. A fracture mechanics approach has been used to simulate craze evolution. The experiments and simulations have identified a critical prestrain below which craze formation does not occur. This strain decreases with increase in solvent exposure time, but also exhibits a threshold. Diffusion of the solvent into the film is considered to be responsible for the time-dependent nature of damage formation.
Oxygenation characteristics in high-density YBa2Cu3Ox ceramics
Authors: Kuwabara M. , Shimooka H. , Katayama I. , Inada T.
Published: September 2007

Oxygenation characteristics in high-density YBa2Cu3Ox ceramics with a relative sintered density ≥97%, which were produced by hot-pressing to have various oxygen contents as-hot-pressed, have been investigated. The results indicate that the oxygenation characteristic in the materials was strongly affected by their oxygen content before oxygenation; that is, the attainable oxygen content (directly connected with the superconducting temperature Tc) of the materials after oxygenation increases with a decrease in their oxygen content before oxygenation. Oxygen annealing at 500 °C for 24 h dramatically increased the oxygen content of an YBa2Cu3Ox with x = 6.08 before the oxygen annealing up to 6.90, while the oxygen content of an YBa2Cu3Ox ceramic with x = 6.32 before oxygenation rose only to a value of 6.61 after the same oxygen annealing. This newly observed phenomenon on the oxygenation characteristic in the present materials may provide an idea for improving the superconducting properties in high-density YBa2Cu3Ox ceramics.
Vacancy properties in Cu3Au-type ordered fcc alloys
Authors: Kim S.M.
Published: September 2007

A theory of vacancy formation in Cu3Au-type ordered fcc alloys is presented. The present theory, which is based on the pairwise bonding model, is found to be in good agreement with the experimentally observed vacancy properties in ordered Cu3Au and Ni3Al. Various shortcomings in the previous theoretical calculations have also been identified.
Thermal stability of TiSi2 films on single crystal and polycrystalline silicon
Authors: Shenai Krishna
Published: September 2007

The stability of selectively formed TiSi2 films on single crystal and polycrystalline silicon layers at elevated process temperatures is reported. Extensive electrical and analytical studies were performed to understand the high-temperature stability of TiSi2 films as a function of (i) substrate dopant concentration, (ii) titanium silicide thickness, (iii) silicide formation sequence, and (iv) silicide post-processing steps. It is shown that all four process variations have a profound influence on the thermal stability of TiSi2 films. It is observed that titanium silicide films formed on single crystal silicon are stable at higher processing temperatures compared to those formed on polysilicon substrates under similar conditions. The degradation of high-temperature stability of TiSi2 films on polycrystalline silicon can be related to increased number of defects and grain boundaries. It is shown that TiSi2 films can be successfully used in silicon integrated circuit applications where the post-silicide processing temperatures do not exceed 1000 °C.
Fabrication of superconducting YBa2Cu3O7−x fibers by the sol-gel method using metal alkoxides
Authors: Katayama Shingo , Sekine Masahiro
Published: September 2007

Superconducting YBa2Cu3O7−x fibers were fabricated by the sol-gel method using modified metal alkoxides. To prepare a heterometallic alkoxide as a precursor of a homogeneous and viscous sol, Y and Cu alkoxides were modified with ethyl acetoacetate (EAA) and ethylenediamine (en), respectively. Their structures were determined by FT-IR and EXAFS. The heterometallic alkoxide was synthesized by partial hydrolysis of the modified alkoxides and was further hydrolyzed and concentrated to obtain a viscous sol. This sol had good spinability and was spun into gel fibers by a spinning apparatus. The gel fibers had a high oxide content of 61 wt.%. The fiber, fired at 950 °C for 10 h in O2, had only closed pores and a dense structure. Tc (onset) of this fiber was 94 K.
Stability of the YBa2Cu3O7−x−Si interface
Authors: Li Bin , Williams Ellen D.
Published: September 2007

Electron spectroscopies were used to study the reaction of Si and SiO2 layers with high-Tc superconductors at room temperature and under annealing conditions. The superconductor samples include YBa2Cu3O7 ceramic and thin film samples as well as GdBa2Cu3O7 ceramic samples. The results show that the Si overlayers withdraw oxygen from the superconductor and form an interfacial layer of Si oxide at room temperature. Annealing increases the reaction rate so that films as thick as 30 Å become completely oxidized following annealing above approximately 100 °C. Ba segregates to the surface from the bulk after Si oxidation when annealed at temperatures higher than 200 °C, while the rare earth element (Gd) does not segregate.
Reaction of beta-phase Ni–Al alloys with CrB2
Authors: Misra Ajay K.
Published: September 2007

Reaction of Ni–Al alloys within the β-NiAl phase with CrB2 was studied at 1473 K as a function of Al concentration in the alloy. Reaction of 49–50 at. % Al alloys with CrB2 occurred by interdiffusion of Ni into CrB2 and Cr into the alloy without forming a new product phase. On the other hand, a new product phase, rich in Ni and B, formed by the reaction of alloys having Al concentrations 48 at. % or lower with CrB2. The reaction product was observed both at the CrB2/alloy interface and along the alloy grain boundaries.
Infrared reflectance spectroscopy of electrochromic NiOxHy films made by reactive dc sputtering
Authors: Estrada W. , Andersson A.M. , Granqvist C.G. , Gorenstein A. , Decker F.
Published: September 2007

Films of NiOxHy were made by reactive dc magnetron sputtering of Ni followed by electrochemical treatment in KOH. Infrared reflectance spectroscopy with obliquely incident p-polarized light documented a unique topochemical reaction with the bleached state being β–Ni(OH)2 and the colored state being β–NiOOH. The same technique yielded clear, though not yet fully understood, data on the evolution of electrochromism during potentiodynamic cycling.
Microstructure-property relations in tungsten bronze lead barium niobate, Pb1−xBaxNb2O6
Authors: Randall C.A. , Guo R. , Bhalla A.S. , Cross L.E.
Published: September 2007

Transmission electron microscopy (TEM) has been used to explore details of the structural phase transitions and corresponding microstructural features in the solid solution of Pb1−xBaxNb2O6 (PBN) tungsten bronze ferroelectrics at compositions embracing the morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases. In addition to the ferroelectric domain structures that were consistent with the expected symmetries, incommensurate ferroelastic phases were observed. The “onset” and “lock-in” transition temperatures are a function of the Pb/Ba ratio, and for lead-rich compositions it appears that the incommensurate distortion may occur above the ferroelectric Curie temperature in the paraelectric phase.