bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of reactions between gaseous organo-silicon compounds and metal surfaces
Authors: Yates D. J. C. , Behal S. K. , Kear B. H.
Published: September 2007

A procedure for modifying the surface composition of catalytically active metals with silicon-containing gaseous reactants has been developed. This new gas-solid reaction method is unique in that it can be used for the in situ synthesis of catalytically interesting materials, which cannot be done by conventional solid-solid reaction techniques. Using an oxygen-free silicon compound (e.g., hexamethyldisilazane, HMDS), the metals studied fall into two categories: those that involve reaction followed by diffusion, and those that exhibit surface reaction only. The first group, consisting of the metals Ni, V, Rh, Pt and Pd, formed thick (up to 0.6μ) Si diffusion layers, after reaction at 430 °C for a few hours, with either H2/HMDS or Ar/HMDS mixtures. Under the same conditions, the second group of metals, Fe and Co, showed thin (∼ 500 Å) overlayers containing silicon, but with no diffusion. The only nonmetal (graphite) studied so far showed no reaction, within the detectability limits of Auger spectroscopy. This observation shows that these reactions are catalytically induced by certain metal surfaces; in other words, they selectively take place on metals. These findings clearly have important implications for catalysis. For example, the metal surfaces of oxide-supported metal catalysts can, in principle, be selectively modified by gas-phase reactants. This treatment can readily be accomplished in situ in the catalytic reactor. The above reactions may well result in a new class of metallic catalysts, with one of the components being silicon. Furthermore, gas-phase compounds containing the elements aluminum, boron, and germanium are known to react with metals in an analogous manner, which further extends the range of possibilities for the synthesis of new catalytic materials.
Improved stability of the ZnO varistor via donor and acceptor doping at the grain boundary
Authors: Gupta T. K. , Miller A. C.
Published: September 2007

The ZnO varistor degradation has been attributed to the field-assisted, temperature-activated diffusion of interstitial zinc in the depletion layer. To improve stability, one approach is to reduce the formation of interstitials, and then further, to prevent their migration through empty interstitial sites. Based on this concept, an amphoteric dopant, such as Na or K, has been incorporated in the ZnO varistor grain boundary wherein a dopant is substituted both in the lattice and in the interstitial sites. A grain boundary defect model has been developed for this dual mode of substitution, with the dopant acting as an acceptor at the lattice site and as a donor at the interstitial site. Under these conditions, and given a desired neutrality range, the concentration of zinc interstitial is indeed shown to be reduced and stability greatly improved. The experimental data presented here validate the grain boundary defect model presented in this and in an earlier paper [J. Mater. Sci. 20, 3487 (1985)].
Zirconium oxide crystal phase: The role of the pH and time to attain the final pH for precipitation of the hydrous oxide
Authors: Srinivasan Ram , Harris Mary B. , Simpson Stanley F. , De Angelis Robert J. , Davis Burtron H.
Published: September 2007

Precipitated hydrous zirconium oxide can be calcined to produce either a monoclinic or tetragonal product. It has been observed that the time taken to attain the final pH of the solution in contact with the precipitate plays a dominant role in determining the crystal structure of the zirconium oxide after calcination at 500 °C. The dependence of crystal structure on the rate of precipitation is observed only in the pH range 7–11. Rapid precipitation in this pH range yields predominately monoclinic zirconia, whereas slow (8 h) precipitation produces the tetragonal phase. At pH of approximately 13.0, only the tetragonal phase is formed from both slowly and rapidly precipitated hydrous oxide. The present results, together with earlier results, show that both the pH of the supernatant liquid and the time taken to attain this pH play dominant roles in determining the crystal structure of zirconia that is formed after calcination of the hydrous oxide. The factors that determine the crystal phase are therefore imparted in a mechanism of precipitation that depends upon the pH, and it is inferred that it is the hydroxyl concentration that is the dominant factor.
Fluorination of the high-Tc superconductors YBa2Cu3O7−δ and GdBa2Cu3O7−δ
Authors: Sauer Nancy N. , Garcia Eduardo , Martin Joe A. , Ryan Robert R. , Gary Eller P. , Tesmer Joseph R. , Maggiore Carl J.
Published: September 2007

Powdered samples of the high-temperature superconductors A Ba2Cu3O7−δ (A = Gd,Y) were treated with fluorine gas (100 Torr) at room temperature and 400 °C for varying times (12–64 h). Magnetic shielding measurements on fluorinated products showed that the superconducting volume fraction in treated samples was greatly reduced or even completely eradicated. All samples were structurally characterized by x-ray powder diffraction. Two yttrium samples, one fluorinated at 25 °C and one at 400 °, were also examined by neutron powder diffraction. For samples treated at room temperature, no change in the structure or composition of the products was apparent by either technique. However, samples fluorinated at 400 °C are tetragonal, with a = 3.8641 (3), c = 11.704(1) Å, and bulk composition corresponding to the formula YBa2Cu3F3.5O4.5. Nuclear activation analysis, nuclear reaction analysis, and Auger spectroscopy were used to determine fluorine concentration and distribution in the fluorinated materials. For samples treated at room temperature, fluorine was found primarily within approximately 1 μm of the surface of the product particles. No evidence for a fluorinecontaining superconducting phase was found in any sample; fluorine was found to be detrimental to superconductivity in all cases. These results suggest that the 123 oxides are sensitive to surface effects.
Neutron powder diffraction study of the products from fluorinating YBa2Cu3O7−s at room temperature and at 400 °C
Authors: Garcia E. , Sauer N. N. , Ryan R. R. , Williams A. , Eller P. G.
Published: September 2007

Fluorination of YBa2Cu3O7−s at room temperature results in no change of the critical temperature but a drastic reduction of superconducting volume fraction as determined by magnetic flux exclusion measurements. Rietveld refinement of neutron powder diffraction data indicates that the bulk structure has not changed in any significant way despite the loss of superconductivity. In marked contrast, when the superconducting oxide is fluorinated at 400 °C, a structural transformation from orthorhombic to tetragonal symmetry occurs that is accompanied by essentially complete filling of eight of the nine perovskite anion sites and total loss of superconductivity above 7 K. Interpretation of neutron activation analysis and neutron diffraction results render the formula of the fluorinated product as YBa2Cu3F3.5O4.5, but fluoride ions in the unit cell were not distinguished from oxide ions.
Effect of prestress on tensile yield strength of a Ni3Al alloy
Authors: Yoo M. H. , Liu C. T.
Published: September 2007

An experimental technique of prestressing and quenching was employed in order to elucidate the nature of pinning points responsible for the anomalous yield strength of Ni3Al. The apparent number density of pinning points at room temperature was found to be unaffected by the prestressing and quenching from elevated temperatures. This result is consistent with the crossslip-pinning (CSP) model in that cross-slipped segments act as pinning points on the leading superpartial dislocations.
Slip, twinning, and fracture at a grain boundary in the L12 ordered structure—AΣ = 9 tilt boundary
Authors: Yoo M. H. , King A. H.
Published: September 2007

The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to occur, not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni3 Al and its improvement by boron segregation are discussed.
Sputter deposition of a corrosion-resistant amorphous metallic coating
Authors: Lee Natalia L. , Fisher Galen B. , Schulz Robert
Published: September 2007

Starting with corrosion-resistant amorphous Fe32Ni36Cr14P12B6 alloy material, rf sputter deposition has been successfully used to deposit amorphous thin films very similar in composition onto low-carbon (i.e., 1008) steel. The effects that varying sputter deposition parameters has on a film's corrosion resistance, microstructure, and chemical composition have been examined. Optical, scanning, and transmission electron microscopy, Auger depth profiling, and x-ray diffraction were used to characterize the microstructure and composition of the films, while the corrosion resistance was determined by anodic polarization in basic and acidic solutions. A ∼4000 Å thick amorphous film sputtered at ambient temperature onto a 0.05 μm polished 1008 steel substrate improved the corrosion resistance of the steel in a buffered borate solution by lowering the steel's critical current density by two orders of magnitude and by raising its corrosion potential by ∼0.4 V. Bias voltage sputtering was required to produce a film with properties that could withstand a sulfuric acid solution. For example, a film sputtered at – 70 V at ambient temperature onto a steel substrate passivated in sulfuric acid solution, whereas the steel was completely active in this solution without the sputtered film. Passive current densities in this case were ∼2x102μA/cm2. In both solutions the improved corrosion resistance was exhibited by films with lower oxygen content and a denser microstructure. Thus a direct correlation between corrosion resistance, microstructure, and composition is shown.
Hydrogen storage characteristics of mechanically alloyed amorphous metals
Authors: Harris J. H. , Curtin W. A. , Schultz L.
Published: September 2007

The hydrogen storage properties of a series of mechanically alloyed (MA) amorphous Ni1xZrx alloys are studied, using both gas phase and electrochemical techniques, and are compared to H storage of rapidly quenched (RQ) amorphous Ni1−xZrx. In the MA alloys, hydrogen resides in the Ni4−nZrn (n = 4,3,2) tetrahedral interstitial sites, with a maximum hydrogen-to-metal ratio of 1.9(4 n)xn(1 − x)4 − n. These features are identical to those of the RQ alloys and indicate that the topological and chemical order of the MA and RQ materials are essentially the same. However, the typical binding energy of hydrogen in a Ni4−nZrn site, En, is shifted in the MA alloys relative to the RQ alloys and the distribution of binding energies centered on En is significantly broader in the MA samples. Thus, the MA and RQ alloys are not identical and sample annealing does not alter this subtle distinction. The sensitivity of H storage to the presence of chemical order in binary alloys are analyzed theoretically and the data are found to be most consistent with little or no chemical order (random alloys).
Solid-state amorphization in Al–Pt thin films
Authors: Legresy J. M. , Blanpain B. , Mayer J. W.
Published: September 2007

Solid-state amorphization is reported to occur in aluminum-platinum thin films. A uniform amorphous alloy layer was observed at the interface between aluminum and platinum layers for electron beam evaporated samples in an as-deposited state. For a pure aluminum overlayer deposited on top of a coevaporated Al–Pt amorphous alloy, the aluminum dissolves into the amorphous phase leading to a fully amorphous sample. In this last case the amorphization is nonuniform upon low-temperature anneals (T < ≃2 200 °C) and gives rise to hole formation in the aluminum overlayer. Direct observations of this phenomenon during in situ annealing of the thin films in a transmission electron microscope were carried out.
Oxidation of Si implanted with nondopant, metallic ions
Authors: Holland O. W. , White C. W. , Pennycook S. J.
Published: September 2007

The effect of implantation of low-solubility, metallic impurities into Si on the oxidation kineties in steam was studied. The list of impurities that were studied include Ti, Co, Ni, Fe, Yb, Pb, Sn, and Ag. Kinetic data from Pb+ -implanted Si is correlated with the impurity behavior during the oxidation. It will be shown that the oxidation rate is dependent both on the impurity segregation phenomena at the oxide/Si interface and on the nature of the ion-induced damage that is stable at the oxidation temperature. Also, it is shown that novel morphologies can develop in the Si substrate during oxidation. Transmission electron microscopy and Rutherford backscattering/channeling spectroscopy were used to characterize these structures. Mechanisms responsible for the morphological changes in the substrate during oxidation are discussed.
An ultra high vacuum system for thin dielectric film deposition at low temperatures
Authors: Chang R. P. H. , Griffiths G.
Published: September 2007

An ultra high vacuum system has been designed and constructed for the purpose of depositing high-quality oxide films on well-characterized crystal surfaces at low temperatures. In particular, aluminum phosphorus oxide films have been deposited on both In P and Ge surfaces for the purpose of device application. Electrical measurements of metal-oxide-semiconductor structures show much improved interfacial properties with little or no hysteresis.
Phase selection in electrohydrodynamic atomization of alumina
Authors: Levi C. G. , Jayaram V. , Valencia J. J. , Mehrabian R.
Published: September 2007

Electrohydrodynamic atomization'has been adapted to produce Al2O3 powders ranging in size from 10 nm to 300 μm. Microstructural characterization using x-ray diffraction, scanning, and transmission electron microscopy reveals changes in phase selection as a function of particle size, hence supercooling. Amorphous powders are common below 100 nm in diameter. Cubic spinel γ is found in single phase form between 100 nm and 2μm, and partially transformed to δ between 2 and 20 μm. There is also evidence of σ and θ or a precursor of θ forming directly from the liquid above 5 μm. The stable corundum structure is consistently found above 20 μm but exhibits three different morphologies: faceted, dendritic, and cellular. Phase selection is examined on the basis of fundamental thermodynamic and kinetic considerations and results from computer models predicting the thermal history of the powders. It is concluded that metastable phases require the elimination of catalytic sites for the nucleation of a and are thus more likely to form in the smaller powders. Furthermore, submicron powders achieve sufficiently high cooling rates to preserve the metastable phases formed (γ), but those higher than ∼ 1 μm experience a thermal excursion long enough to transform γ to more stable forms of Al2O3.
Correlation of steady-state creep and changing microstructure in polycrystalline SiC sintered with powder derived via gaseous reactants in an are plasma
Authors: Nixon R. D. , Posthill J. B. , Davis R. F. , Baumgartner H. R. , Rossing B. R.
Published: September 2007

The mechanisms of steady-slate creep in compression in a sintered SiC produced via sintering of β-SiC powders derived from gaseous reactants in a plasma are have been determined from (1) kinetic data within the ranges of temperature and constant stress of 1770–2020 K and 17–208 MPa, respectively, and (2) the results of transmission electron microscopy (TEM) and other microbeam characterization techniques. The stress exponent was 2.06 ± 0.04; the values of activation energy were 913 ± 13 and 630 ± 14 kJ/mol above and below, respectively, a knee of ∼∼ 1920 K. Gliding dislocations and B4C precipitates, which developed within the grains during creep, and their interaction were the dominant microstructural features of the crept material. Apparent nonmechanical pinning of the dislocations at the precipitates indicated that the latter attracted the dislocations rather than acting as classical obstacles to dislocation movement. A synthesis of this information leads to the conclusion that the controlling creep mechanisms in this SiC were grain boundary sliding accommodated by grain boundary diffusion at T < 1920 K and lattice diffusion at T > 1920 K. The parallel mechanism of dislocation glide also contributed to the total strain.
Growth of semiconductors by the close-spaced vapor transport technique: A review
Authors: Perrier G. , Philippe R. , Dodelet J. P.
Published: September 2007

The close-spaced vapor transport (CSVT) is an efficient and cost-effective technique that allows the growth of polycrystalline as well as epitaxial thin layers of semiconductors. The close spacing between a source and a substrate, introduced in 1963 as a special feature in the vapor phase method, has been applied to about 18 semiconductors with a special focus on CdTe and GaAs. This paper reviews the close-spaced technique, the models presented to explain the film growth rates, the transport reactions, and film characteristics for all the semiconductors that have been obtained by CSVT. All-thin-film structures for solar cells or other applications are certainly feasible with the use of the CSVT technique when a good lattice matching exists between the successive layers.
Ion-beam mixing of Ni/Pd layers: I. Cascade mixing regime (low temperature)
Authors: Akano U. G. , Thompson D. A. , Davies J. A. , Smeltzer W. W.
Published: September 2007

A tomic mixing resulting from heavy-ion bombardment of thin-film Ni/Pd bilayers and thin Pd markers sandwiched between Ni layers has been investigated. Mixing experiments were performed over a temperature range 40–473 K, using 120 keV Ar+ and 145 keV Kr+ ions at a constant dose rate of 5.5 × 1012 ions cm −2s−1 for doses up to 4 × 1016cm−2. The resulting interdiffusion was measured, in situ, using Rutherford backscattering with 2−2.8 MeV 4He+ ions. The results showed that, for both markers and bilayers, the amount of mixing is similar for both configurations and varies linearly with the square root of the ion dose. Comparison of the induced mixing per ion, following irradiation at 40 K, shows that the mixing is dependent on the damage energy FD deposited at the interface region. The mixing is essentially athermal.
Ion-beam mixing and thermal annealing of Al–Nb and Al–Ta thin films
Authors: Rai A. K. , Bhattacharya R. S. , Mendiratta M. G. , Subramanian P. R. , Dimiduk D. M.
Published: September 2007

Ion-beam mixing and thermal annealing of thin, alternating layers of Al and Nb, as well as Al and Ta, were investigated by selected area diffraction and Rutherford backscattcring. The individual layer thicknesses were adjusted to obtain the overall compositions as Al3Nb and Al3Ta. The films were ion mixed with 1 MeV Au+ ions at a dose of 1 × 1016 ions cm−2. Uniform mixing and amorphization were achieved for both Al−Nb and Al−Ta systems. Equilibrium crystalline A13Nb and Al13Ta phases were formed after annealing of ion mixed amorphous films at 400 °C for 1 h. Unmixed films, however, remained unreacted at 400 °C for 1 h. Partial reaction was observed in the unmixed film of Al–Nb at 400 °C for 6 h. After annealing at 500 °C for 1 h, a complete reaction and formation of Al3Nb and Al3Ta phases in the respective films were observed. The influence of thermodynamics on the phase formation by ion mixing and thermal annealing is discussed.
Epitaxy and defects in laser-irradiated, single-crystal bismuth
Authors: Helms Aubrey L. , Draper Clifton W. , Jacobson Dale C. , Poate John M. , Bernasek Steven L.
Published: September 2007

The (0001), (1010), and (2110) faces of Bi have been pulsed laser irradiated at 0.5–0.8 J/cm2 with a Q-switched ruby laser. Nomarski interference contrast microscopy, channeling, and selective chemical etching have been used to investigate the response of the material to the laser irradiation. The response of Bi is shown to be strongly orientation dependent. The χmin and half-angle for the Bi (0001) surface have been measured and compared to theoretical values. The Bi(0001) surface has been shown to regrow epitaxially without an increase in the disorder. In contrast, the epitaxial regrowth of the Bi(1010) and Bi(2110) surfaces show a marked increase in disorder after irradiation. The levels of damage show a strong correlation to the critical resolved shear stress characteristics in the particular crystallographic orientation studied.
Laser surface modification of metal-coated ceramics
Authors: Singh R. K. , Jagannadham K. , Narayan J.
Published: September 2007

Pulsed excimer laser radiation has been successfully employed in the improvement (> 50%) of fracture strength of metal-coated ceramics. Thin metallic layers (∼500 Å) of nickel were deposited on silicon nitride and silicon carbide substrates and further irradiated with pulsed excimer (xenon chloride, krypton fluoride) laser pulses. The laser energy density was varied from 0.4 to 2.0 J cm −2 to optimize the formation of mixed interfacial layers. The formation of interfacial layers was studied by transmission electron microscopy and Rutherford backscattering spectrometry techniques. Detailed heat flow calculations using implicit finite difference methods were performed to simulate the effects of intense laser irradiation on metal-coated ceramic structures. Three different mechanisms were found to play an important role in the improvement in the fracture strength of these ceramics. Theoretical calculations showed that the displacement of the crack tip away from the free surface by laser surface modification can lead to a 100% improvement in the fracture strength of the ceramic.
Photochemical deposition and characterization of Al2O3 and TiO2
Authors: Hudson M. D. , Trundle C. , Brierley C. J.
Published: September 2007

Thin films of aluminum oxide and titanium dioxide have been deposited onto gallium arsenide at low temperatures (<200 °C). A high-pressure xenon–mercury are lamp (1 kW) and a frequency doubled argon ion laser (100 mW at 257 nm) have been used as illumination sources Suitable volatile metallo-organic precursors have been synthesized with strong absorptions at the wavelengths of the light sources. The Al2O3 or TiO2 layers grown at 200 °C or less are amorphous although the anatase phase of TiO2 is deposited at temperatures over 350 °C. Ellipsometry has been used to measure the thickness and refractive index of the films. Films have been deposited onto gold on silicon in order to make simple electrical measurements. Resistivity, dielectric constant, loss factor, and breakdown voltage have been measured. The results shows values in good agreement with the results published on films grown by other CVD techniques using much higher temperatures.
Production of 0.1–3 eV reactive molecules by laser vaporization of condensed molecular films: A potential source for beam-surface interactions
Authors: Cousins Lisa M. , Leone Stephen R.
Published: September 2007

A versatile, repetitively pulsed source of translationally fast, reactive molecules is described that is suitable for materials processing experiments. The pulsed beams are generated by excimer laser vaporization of cryogenic molecular films that are continuously condensed on transparent substrates. The generation of fast, energy variable pulsed molecular sources of Cl2 and NO is demonstrated. The most probable translational energies of Cl2 and NO molecules can be reproducibly varied monotonically by adjusting the laser fluence or film thickness. Here, the most probable translational energy is quoted as the energy corresponding to the maximum of the time-of-flight trace. Using laser fluences of 2–25 mJ cm−2 from a 193 nm excimer laser, the most probable translational energies of Cl2 are 0.4–2 eV. Significant fractions of molecules with translational energies greater than 3 eV are observed at the leading edges of the distributions. Very similar results are obtained by vaporizing Cl2 with 248 and 351 nm radiation. Pulses of translationally fast NO molecules are generated in a similar manner; most probable energies from 0.1–0.4 eV, with the fastest molecules up to 0.8 eV, are obtained using laser fluences of 1–11 mJ cm−2 at 193 nm. Approximately 1013−1014 molecules per cm2 of the film are vaporized per laser pulse, depending on film thickness and laser fluence.
Pulsed laser deposition of thin superconducting films of Ho1Ba2Cu3O7 − x and Y1Ba2Cu3O7 − x
Authors: Geohegan D. B. , Mashburn D. N. , Culbertson R. J. , Pennycook S. J. , Budai J. D. , Valiga R. E. , Sales B. C. , Lowndes D. H. , Boatner L. A. , Sonder E. , Eres D. , Christen D. K. , Christie W. H.
Published: September 2007

Thin films of Ho1Ba2Cu3O7 − x and Y1Ba2Cu3O7 − x were deposited on SrTiO3 and Al2O3, substrates by pulsed laser deposition of high-Tc bulk superconductor pellets in vacuum. Following annealing in O2 at 800–900 °C the films were superconducting with typical Tc (50%) = 89 K and transition widths of 10 K. Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) were utilized to study the stoichiometry of the as-deposited films for laser energy, densities between 0.11 and 4.5 J cm−2. The films were deficient in holmium and yttrium for energy densities below 0.6 and 0.4 J cm −2, respectively. The films were stoichiometric for fluences above 0.6 J cm−2. In addition, preliminary time dependence and spectroscopic observations of the laser-produced plasma are presented. The results indicate an ablation mechanism that at high energy densities preserves stoichiometry. TEM and x-ray characterization of annealed, superconducting Ho1Ba2Cu3O7 − x films on (100) SrTiO3 showed mixed regions of epitaxially oriented 1:2:3 material with either the c axis or a axis oriented along the surface normal. The a-axis-oriented material grew preferentially in the films with b, c, twinning.
Deposition of tin oxide films by pulsed laser evaporation
Authors: Vispute R. D. , Godbole V. P. , Chaudhari S. M. , Kanetkar S. M. , Ogale S. B.
Published: September 2007

Thin films of SnO2−x (0<x<1) were deposited on Corning glass and alumina substrates by employing a pulsed laser evaporation (PLE) technique. The microstructural features of the films were probed with Sn119 conversion electron Mössbaucr spectroscopy (CEMS) whereas the structural characteristics were identified by using low-angle x-ray diffraction measurements. The electrical and optical properties have also been studied. It is shown that films with conductivity of 3 × 102 (ohm·cm)−1 and transmission of 90% can be obtained by appropriate postannealing of the as-deposited films in air and vacuum. The energy gap of this nearly stoichiometric single-phase SnO2 film was found to be 3.5 eV and spectroscopic ellipsometry measurements indicated the refractive index lobe typically between 1.8–1.9 over the wavelength range of 400–800 nm.
A study of laser marking of thin films
Authors: Gupta Mool C.
Published: September 2007

Some observations of laser marking of thin films are presented. Time-resolved reflectivity measurements performed during laser marking of thin organic films indicate that the pit-formation processes start in less than 10 ns after the onset of the laser pulse and that some reversal of the process occurs following exposure termination. Temperature calculations for laser heating of thin films with focused scanning beams explain some of the mark (pit) morphology and material flow behavior that is observed. Scanning electron microscopy (SEM) studies of the marks indicate that at high laser powers, pit formation occurs by ablation and at low laser powers, pits can be formed without ablation. Pits were also formed in a 100nm thin film by resistive heating where the maximum temperature was less than 300 °C.
Mechanisms for crystallographic orientation in the crystallization of thin silicon films from the melt
Authors: Atwater Harry A. , Thompson Carl V. , Smith Henry I.
Published: September 2007

The dependence of the growth velocity on crystal orientation has been studied during crystallization of thin polycrystalline silicon films from the melt. Two types of growth velocity anisotropy have been observed. In the first, competitive growth between (100) textured seeds and seeds with (110) and (111) textures indicates that the relative growth velocities are ν(100) > ν(110)ν(111). It is postulated that this textural growth velocity anisotropy is a result of the differences in the interal energy of grains with different textures. This assumption, combined with the data, yields estimates of the interfacial energy anisotropy for the Si–SiO2 interface: γ(111) − γ(100) = 0.069 J/m2 and γ(110) − γ(100) = 0.012 J/m2. Another type of growth velocity anisotropy is responsible for the development of in-plane orientation in competitive growth between (100)-textured seeds. Simple models, which describe development of these two types of crystallographic orientation via anisotropies in growth velocity, agree well with the experimental results.
Synthesis of NiSi2by 6 MeV Ni implantation into silicon
Authors: Lindner J. K. N. , te Kaat E. H.
Published: September 2007

Six MeV high-dose Ni implantation into silicon has been applied to synthesize deep-buried metallic layers. These layers have been analyzed by optical reflectivity and spreading resistance depth profiling as well as transmission electron microscopy and cross-section transmission electron microscopy. Already in the as-implanted state, at target temperatures of 450 K and doses above 1017Ni/cm2, epitaxial precipitates of NiSi2are formed. They grow in type-A and type-B orientations. In addition to these polyhedral crystallites, thin NiSi2platelets on {111} lattice planes exist. At a dose of 1.3 × 1018Ni/cm2, a continuous but highly defective layer of epitaxial NiSi2is formed by coalescence of mainly type-A precipitates at the maximum of the Ni profile. Investigations indicate that damage gettering of nickel atoms as well as the atomic density increase during implantation influence the depth distribution of implanted metal atoms. Moreover, a suppression of silicon amorphization by nickel is evident.
Ion-induced conductivity in poly (phenylene sulfide)
Authors: Ruddy F. H. , Bartko J. , Schoch K. F.
Published: September 2007

New data on the production of electrical conductivity in poly (phenylene sulfide), PPS, by ion irradiation are presented. These and previously reported PPS data are investigated in the framework of a theoretical semiempirical model that relates observed conductivity to parameters associated with the deposition of energy in the polymer by the bombarding ions. It is shown that the onset of conductivity with increasing ion dose is dependent on overlap of individual ion damage regions. A straight line relationship is obtained between log of the ion stopping power and log of the effective overlap radius of the ion damage regions. Furthermore, the magnitude of the values of effective overlap radii are consistent with physical observations and theoretical predictions. At higher ion doses, the rapid increase in conductivity appears to be consistent with a multistage reaction mechanism for the production of conducting species in the polymer. A universal curve of conductivity as a function of dose above threshold dose is seen to fit all of the PPS data up to a dose of a factor of 50 above threshold. This curve and the predictable behavior of the threshold dose allow the selection of ion/dose combinations to produce a desired conductivity.
Liquidus relations in Y–Ba–Cu oxides
Authors: Aselage Terry , Keefer Keith
Published: September 2007

The liquidus relations in the system YO1.5–BaO–CuOx in air in the compositional region near the superconducting oxide YBa2Cu3Ox were studied by differential thermal analysis, x-ray diffraction, electron microprobe analysis, and visual observation. The temperatures of 11 invariant points and the corresponding reactions were determined. YBa2Cu3Ox was found to melt incogruently at 1015 °C to Y2BaCuO5, which in turn melts incongruently to Y2O3 at 1270 °C. These reactions mean that preparing the superconducting phase by melting and rapid cooling will result in the presence of these two phases as well. The peritectic reaction YBa2Cu3Ox + CuO⇉Y2BaCuO5 + liquid at 940 °C accounts for the observation of partial melting, improved synthesis purity, and grain growth at temperatures of 950 °C. The determination of these invariant temperatures and reactions provide insight into optimal processing conditions.
Effect of processing parameters on the characteristics of high-Tc superconductor YBa2Cu3Oy
Authors: Bansal Narottam P.
Published: September 2007

The influence of sintering temperature, sintering and annealing atmospheres, and quench rate on the properties of the high-temperature superconductor YBa2Cu3Oy has been investigated by electrical resistivity and magnetic susceptibility measurements, thermogravimetric analysis, powder x-ray diffraction, and scanning electron microscopy. Room-temperature resistivity and the transition width decreased, and the fraction of the superconducting material and the bulk density increased with increase in the sintering temperature, but had no effect on the transition temperature (Tc) for samples fired in flowing oxygen. A sample that was rapidly quenched from 930 °C to room temperature after sintering in air had a perovskite structure and Tc (onset) ∼90 K but its resistance did not become zero even at 77 K. A sample sintered in air at 930 °C and furnace cooled had Tc (midpoint) of ∼89.6 K and transition width (10%–90%) of ∼2.6 K. The loss and gain of oxygen occurs reversibly in YBa2Cu3Oy.
Study of point defects in alkaline-earth sulfides
Authors: Pandey Ravindra , Kunz A. Barry , Vail John M.
Published: September 2007

The results of a computer simulation study of point defects including vacancy, interstitial, and F+ center in alkaline-earth sulfides are presented. The study is based on ICECAP/HADES simulation procedures and uses empirical interionic potentials obtained from the analysis of macroscopic data for these materials. The results predict the dominance of Schottky disorder and suggest that vacancy migration predominates in alkaline-earth sulfides. Furthermore, the calculated F+ center absorption energy is in good agreement with the experimental data deduced from the optical stimulated studies in these materials.
Synthesis, characterization, and properties of nanophase TiO2
Authors: Siegel R. W. , Ramasamy S. , Hahn H. , Zongquan L. , Ting L. , Gronsky R.
Published: September 2007

Ultrafine-grained, nanophase samples of TiO2 (rutile) were synthesized by the gas-condensation method and subsequent in situ compaction. The samples were studied by a number of techniques, including transmission electron microscopy, Vickers microharness measurements, and positron annihilation spectroscopy, as a function of sintering temperature. The nanophase compacts with average initial grain sizes of 12 nm were found to densify rapidly above 500 °C, with only a small increase in grain size. The hardness values obtained by this method are comparable to or greater than those for coarser-grained compacts, but are achieved at temperatures 400 to 600 °C lower than conventional sintering temperatures and without the need for sintering aids.
RESA—A wholly new process for fine oxide powder preparation
Authors: Kumar Amitabh , Roy Rustum
Published: September 2007

A new process for making fine (10–1000 nm) oxide powders has been devised. It is based on striking an are between two metallic electrodes submerged in a dielectric liquid, typically water. By controlling the process parameters (voltage, amperage, and composition of liquid), one can obtain fine sols of the anhydrous oxides of Al, Ti, Zr, etc., and exercise some control over the particular phase in variable valence metals such as Cr.
Lateral diffusion in Ni–GaAs couples investigated by transmission electron microscopy
Authors: Chen S. H. , Carter C. B. , PalmstrΦm C. J.
Published: September 2007

A method has been devised for preparing lateral Ni–GaAs diffusion couples for transmission electron microscopy investigations. By annealing diffusion couples in situ in a hot stage, the growth of a ternary phase has been observed in the microscope, and shows parabolic time dependence of the growth. In the temperature range of 200–300 °C, Ni is the predominant diffusing species in the ternary phase while Ga and As are essentially immobile. The experimental results are compared with previous investigations of the reactions of Ni thin films with bulk GaAs.
Studies on the plastic deformation of Tl3AsSe3 single crystals by hardness indentation
Authors: Yoo K. C. , Spitznagel J. A. , Hopkins R. H.
Published: September 2007

The deformation behavior of Tl3AsSe3 (TAS) single crystals has been studied by hardness tests in four different crystal surfaces, the (10$\overline 1$0), (1$\overline 2$10), (0001), and the plane where the normal is tilted 19° off the hexagonal c axis in the b–c plane. The dominant slip planes are of the (10$\overline 1$1) type; the possibility of (10$\overline 1$0) and (0001) slip was also observed. The observed dependence of force on the length of diamond pyramid indentations implies that TAS behaves to some degree like a ductile metal. Measurements of hardness anisotropy are very useful for defining crystal growth and handling conditions that minimize the effect of stresses. X-ray topographs of Knoop hardness indentations indicate that the measured x-ray diffraction contrast is closely related to the rotational component of each individual slip system activated by the hardness indentation.
Molecular statics of polymer configurations
Authors: Quesnel David J. , Mazlout Lazhar
Published: September 2007

Molecular behaviors of single isolated chains of various lengths are simulated using four energy potentials: the twisting, bending, stretching, and Van der Waals potentials. The origin and analytical form of these potentials is discussed and easy-to-evaluate quantitative expressions are given. A physically based algorithm for energy minimization is developed and used to determine the static configurations of single chains in their lowest energy states. Not surprisingly, the majority of the energy minima found are local minima implying metastability, which is, of course, a central phenomena in noncrystalline material behavior. A progressive distortion approach is then used to suppress conformational variations that depend on initial conditions from developing, thus making possible study of the force displacement characteristics of single chains of various lengths. The single chain force-displacement curve found in this way has a form comparable with the gentle yield point observed in many bulk polymers but with an initial apparent elastic stiffness higher than that of bulk material. Some aspects of the fracture phenomena of single chains are also discussed.
Depth profiles of Li ions implanted in the photoresist AZ111
Authors: Guimarães R. B. , Amaral L. , Behar M. , Fink D. , Zawislak F. C.
Published: September 2007

Depth profiles of 30–150 keV6Li implanted into the photoresist AZ111 have been analyzed through the 6Li(n,a)t nuclear reaction using thermal neutrons. As was found recently for 10B and 19F implanted into the same material, at certain threshold implantation energy the Li ions also split up into a regular and a nonregular distribution. This energy differs from the energies found for 10B and 19F, but at the threshold the electronic stopping power has the same value of about 20 eV/Å in the three cases. The nonregular Li fraction, typically around 10% of the implanted atoms, redistributes according to the TRIM code predicted profile of electronic energy transfer. The regular component exhibits a range profile that is well described by the TRIM code particle distribution predictions. The analysis of the B, F, and Li data shows that there is an approximately linear relation between the nonregular fraction of ions and the density of total deposited energy.
Superconductor-substrate interactions of the Y–Ba–Cu oxide
Authors: Cheung C. T. , Ruckenstein E.
Published: September 2007

The chemical interactions between the YBa2Cu3O7−x high Tc superconductor and various substrates (Si, Al2O3, ZrO2, SrTiO3, MgO, Ag, Cu, and Nb) were studied. Powders of the orthorhombic YBa2Cu3O7−x (123) phase and each of the various substrates were mixed, pressed into pellets, and subjected to either one of the following heat treatments in flowing oxygen: 600 °C for 11 h, 800 °C for 10 h, 945 °C for 5 h, and 945 °C for 17 h. The reacted samples were characterized by qualitative and quantitative x-ray diffraction, scanning electron microscopy with EDAX, electrical resistivity, and magnetic susceptibility measurements. For all substrates studied, the extent of reaction is much more significant at 945 °C than at 800 °C and 600 °C. The reaction products, in general, are some Ba compounds, CuO (and Cu2O), and the Y2BaCuO5 (211) phase. The reaction with Si results in a morphology of layers of 123/211/Ba2SiO4/CuO/Si. Reactions with Al2O3 and ZrO2 result in similar products and morphologies. Reaction with SrTiO3 results in the replacement of Ba by Sr and the formation of a Ba–Ti–Y–Cu unknown phase. With MgO, the chemical reaction results in the enrichment of MgO with Cu and the formation of an apparently glassy Ba–Cu phase. With the metallic substrates Ag, Cu, and Nb, Ag shows no interaction at all, Cu results in the formation of CuO (and Cu2O), whereas the Nb samples completely disintegrated. By comparing the percentage of remaining 123 phase in samples reacted at 945 ° for 17 h, a reactivity scale in decreasing order was obtained as Nb > Si > ZrO2  Al2O3 > SrTiO3 > MgO  Cu > Ag. It is suggested that the chemical reactivity of the Y–Ba–Cu oxide superconductor is mostly controlled by the highly electropositive Ba2+ ions.
Physical processing effects on polycrystalline YBa2Cu3Ox
Authors: Ford W. K. , Anderson J. , Rubenacker G. V. , Drumheller John E. , Chen C. T. , Hong M. , Kwo J. , Liou S. H.
Published: September 2007

The effect of heating YBa2Cu3Oxin vacuum to 600 °C has been studied using photoelectron spectroscopy and diamagnetic susceptibility measurements. Evidence of two chemically distinct copper and barium species is found in single phase samples at room temperature cleaned by gentle heating at 450 °C. Such annealing also increases the volume diamagnetic susceptibility of the samples which suggests that the preferred stoichiometry of growth does not lead to an optimum superconducting phase. Samples cleaned by vacuum scraping or ion bombardment reveal more amorphous XPS structure and are less indicative of bulk properties.
Thermodynamics of the superconducting phase transformation in highTcceramics with magnetoelectric effects
Authors: Burns S. J.
Published: September 2007

A second order phase transformation in a dielectric ceramic superconductor is shown to relate jumps in physical properties to the ratio of state variables, i.e., to the phase boundary, near the critical point. The major jumps in specific heat, compressibility, permittivity, permeability, and spinodal composition curvature, between the normal and superconducting phases, are found from the continuity of the entropy, volume, electromagnetic fields (with zero fields), and chemical equilibrium. The thermal expansion, pyroelectric effects, and the piezoelectromagnetic effects are important differences between ceramic and metallic superconductors. The most important conclusions from experimental measurements are that the lattice plays a minor role in the superconductor transformation while the magnetoelectric jump may be related to the jump in permeability, i.e., the Meissner effect, and the jump in permittivity. The oxygen miscibility gap which controls order/disorder transformations thermodynamically mandate that only metastable compositions are obtained in the metal oxide, so absolute stability of the system may never be achieved. An explicit criterion to suggest other superconductor systems is given from magnetoelectric materials, i.e., some of the pervoskites.
The effect of composition and cooling rate on the structure of rapidly solidified (Fe, Ni)3Al–C alloys
Authors: Myers S. A. , Koch C. C.
Published: September 2007

There is controversy in the literature regarding the existence of the metastable γ′ phase with an ordered Ll2 structure in rapidly solidified Fe–Ni–Al–C alloys. In this study, the quench rate–metastable structure dependence was examined in the Fe–20Ni–8Al–2C (weight percent) alloy. The effect of silicon on the kinetics of phase formation was studied by adding two weight percent silicon to a base alloy of Fe–20Ni–8Al–2C. Samples were rapidly solidified in an arc hammer apparatus and examined by transmission electron microscopy. In the Fe–20Ni–8Al–2C alloy, the nonequilibrium γ′ and γ phases were found in foils 65 to 100 μm thick. At higher quench rates, i.e., thinner samples, the matrix was observed to be disordered fcc γ with K-carbide precipitates. Samples containing silicon were found to have a matrix composed of γ′ and γ structures when the foils were thicker than 40 μm. At higher quench rates, the matrix was disordered fcc γ with K-carbide precipitates. The nonequilibrium γ′ and γ structures are present in samples with or without silicon, but are observed at higher cooling rates with the addition of silicon. This sensitivity to cooling rate and composition in resulting metastable structures may explain the differences reported in the literature for these rapidly solidified materials.
Deformation twinning in superlattice structures
Authors: Yoo M. H.
Published: September 2007

The role of twinning in deformation and fracture behavior of ordered intermetallic compounds has been investigated from a viewpoint based on the crystallography of twinning. The conjugate relationship between the order twinning and the active slip system at elevated temperatures is identified in all the ordered structures considered. Implications of this conjugate relationship on the strength and ductility of ordered alloys are discussed.