bluuebunny/crossref_metadata_2025 huggingface dataset:
The measurement and analysis of epitaxial recrystallization kinetics in ion-beam-amorphized SrTiO3
Authors: Rankin J. , Sheldon B.W. , Boatner L.A.
Published: September 2007

The solid-state epitaxial-regrowth kinetics of ion-beam-amorphized SrTiO3 surfaces annealed in water-vapor-rich atmospheres have been studied using time-resolved reflectivity (TRR). For this material, the conversion of the reflectivity-versus-time data obtained from the TRR measurements to recrystallized depth-versus-time data is more complicated than in systems such as silicon, where the reflectivity can be fit by assuming that the refractive index N (N = n + ik) in the amorphous layer is constant. In SrTiO3, agreement between measurements made directly with Rutherford backscattering spectroscopy (RBS) and those made using TRR can be obtained only when N is permitted to vary within the amorphous layer, with nonzero values for both the real and imaginary components. In some cases, the roughness of the amorphous/crystalline interface must also be considered. Additionally, a model for H2O-enhanced epitaxial regrowth is presented, which is in good agreement with the shape of the depth-versus-time profiles that are obtained from the TRR data.
Ultrasonic study of liquid-quenched sulfur from room temperature to 200 °C
Authors: Doi Akira , Kariya Satoru , Kamioka Hiroaki
Published: September 2007

When liquid S is heated above 159 °C, the S8 rings (which are the dominant structural units below this temperature) break open and polymerize into helical chains (S∞). Therefore, samples quenched from liquids at temperatures above or below 159 °C would be different in various properties by the difference in the amount of S∞. The present ultrasonic study of liquid-quenched S in the temperature range from room temperature to 200 °C has revealed this difference. It has been demonstrated that ultrasonics is as powerful as a conventional thermal analysis in dealing with the variation of a material with increasing temperature, even though both techniques were found to be relatively insensitive to the polymerization process.
The surface reactivity of hollandite in aqueous solution
Authors: Pham D.K. , Myhra S. , Turner P.S.
Published: September 2007

Hollandite, [BaxCSy][Ti, Al)3+2x+y Ti4+8−2x+y]O16, has been subjected to aqueous chemical attack at 75 and 150 °C. The resultant surface alterations have been monitored by solution analysis, SEM/TEM investigations, and surface analysis. The evolution of the solid/solution system can be described by the following mechanisms: There is a near-instantaneous release of Cs and Ba from reactive surface sites, followed by relatively rapid dissolution of the first few monolayers. The release of Al drives the pH to low values as a result of Al-OH hydroxylation and precipitation of AIO(OH) and/or AI(OH)3 species. The rate of dissolution is reduced by an order of magnitude or more by the formation of a thin and continuous Al(Ti)-rich surface layer. The layer remains stable and protective even under extreme hydrothermal conditions. This description has implications for the use of hollandite as a ceramic phase for disposal of high level nuclear wastes.
Graphitization and particle size analysis of pyrolyzed cobalt phthalocyanine/carbon catalysts for oxygen reduction in fuel cells
Authors: Dignard-Bailey L. , Trudeau M.L. , Joly A. , Schulz R. , Lalande G. , Guay D. , Dodelet J.P.
Published: September 2007

Cobalt phthalocyanine (CoPc) adsorbed on a carbon black support (Vulcan XC-72) and pyrolyzed at various temperatures is a potential catalyst for the reduction of oxygen in solid polymer electrolyte fuel cells. This paper reports the results of the microstructural characterization of β-Co particles that are formed after pyrolysis at temperatures of 700, 900, and 1050 °C. Transmission electron microscopy (TEM) indicated that (i) for a pyrolysis temperature of 700 °C, the size distribution of the Co particles is bell-shaped with an average value of 4 nm and mean deviation of 1 nm; (ii) for a pyrolysis temperature of 900 °C, the Co particle size distribution skews toward larger particle sizes. The most probable particle size is about 6 nm, and the average particle size is 13 nm. By comparison with the TEM results, the particle size estimated from a spectroscopic method like x-ray absorption is underestimated, while from x-ray diffraction is overestimated. The TEM images show that Co particles act as heterogeneous nucleation sites for the graphitization of amorphous carbon. It is shown that (i), at least for pyrolysis temperature of 900 °C and above, most of the β-Co particles are surrounded by a shell of graphitic carbon layers that appears to protect the particles from corrosion in acidic media; (ii) for pyrolysis temperature of 1050 °C, graphite strings also appear throughout the amorphous carbon support in areas where Co particles are not detected. This behavior was not observed after pyrolysis of as-received carbon support at 1050 °C. These results allow for a better understanding of the behavior of the pyrolyzed catalysts immersed in an acidic solution or in a solid polymer fuel cell.
Chemistry, microstructure, and electrical properties at interfaces between thin films of cobalt and alpha (6H) silicon carbide (0001)
Authors: Porter L.M. , Davis R.F. , Bow J.S. , Kim M.J. , Carpenter R.W.
Published: September 2007

Thin films (4–1000 Å) of Co were deposited onto n-type 6H-SiC(0001) wafers by UHV electron beam evaporation. The chemistry, microstructure, and electrical properties were determined using x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and I-V and C-V measurements, respectively. The as-deposited contacts exhibited excellent rectifying behavior with low ideality factors and leakage currents of n < 1.06 and 2.0 × 10−8 A/cm2 at −10 V, respectively. During annealing at 1000 °C for 2 min, significant reaction occurred resulting in the formation of CoSi and graphite. These annealed contacts exhibited ohmic-like character, which is believed to be due to defects created in the interface region.
Determining the mechanical properties of small volumes of material from submicrometer spherical indentations
Authors: Field J.S. , Swain M.V.
Published: September 2007

The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression; however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of “piling up” and “sinking in”.
B2 and B32 ordering transformations of equiatomic bcc alloys with ballistic and thermal atom movements
Authors: Hong L.B. , Anthony L. , Fultz B.
Published: September 2007

We used Monte Carlo simulations to study the kinetics and steady states of B2 and B32 ordering in an equiatomic binary bcc alloy having both thermal and ballistic atom movements. Atom movements occurred by a vacancy mechanism, where first-neighbor atoms exchanged sites with the vacancy. In the thermodynamic case, where this jump probability was set by a Boltzmann factor alone, we found the formation of large amounts of transient B2 (B32) during disorder → B32 (B2) order transformations. The transient order developed in distinct regions, but vanished completely when equilibrium was attained. Ballistic jumps were included as random interchanges of the vacancy with one of its neighboring atoms. Even with small fractions of ballistic jumps, there were large changes in the transient states and steady states of order in the alloy. A kinetic explanation is proposed, in which the presence of ballistic jumps contributed a greater amount of internal energy to the B2 phase than to the B32 phase when there was a strong asymmetry in the second-nearest neighbor pair potentials (VAA2 ↗ VBB2). A two-phase coexistence in the steady state was explained by fluctuations in the local density of ballistic jumps.
The structure and property characteristics of amorphous/nanocrystalline silicon produced by ball milling
Authors: Shen T.D. , Koch C.C. , McCormick T.L. , Nemanich R.J. , Huang J.Y. , Huang J.G.
Published: September 2007

The structural transformation of polycrystalline Si induced by high energy ball milling has been studied. The structure and property characteristics of the milled powder have been investigated by x-ray diffraction, scanning electron microscopy, high-resolution electron microscopy, differential scanning calorimetry, Raman scattering, and infrared absorption spectroscopy. Two phase amorphous and nanocrystalline Si has been produced by ball milling of polycrystalline elemental Si. The nanocrystalline components contain some defects such as dislocations, twins, and stacking faults which are typical of defects existing in conventional coarse-grained polycrystalline materials. The volume fraction of amorphous Si is about 15% while the average size of nanocrystalline grains is about 8 nm. Amorphous elemental Si without combined oxygen can be obtained by ball milling. The distribution of amorphous Si and the size of nanocrystalline Si crystallites is not homogeneous in the milled powder. The amorphous Si formed is concentrated near the surface of milled particles while the grain size of nanocrystalline Si ranges from 3 to 20 nm. Structurally, the amorphous silicon component prepared by ball milling is similar to that obtained by ion implantation or chemical vapor deposition. The amorphous Si formed exhibits a crystallization temperature of about 660 °C at a heating rate of 40 K/min and crystallization activation energy of about 268 kJ/mol. Two possible amorphization mechanisms, i.e., pressure-induced amorphization and crystallite-refinement-induced amorphization, are proposed for the amorphization of Si induced by ball milling.
Improved wear properties of high energy ion-implanted polycarbonate
Authors: Rao G.R. , Lee E.H. , Bhattacharya R. , McCormick A.W.
Published: September 2007

Polycarbonate (LexanTM) (PC) was implanted with 2 MeV B+ and O+ ions separately to fluences of 5 × 1017, 1 × 1018, and 5 × 1018 ions/m2, and characterized for changes in surface hardness and tribological properties. Results of tests showed that hardness values of all implanted specimens increased over those of the unirradiated material, and the O+ implantation was more effective in improving hardness for a given fluence than the B+ implantation. Reciprocating sliding wear tests using a nylon ball counterface yielded significant improvements for all implanted specimens except for the 5 × 1017 ions/m2 B+-implanted PC. Wear tests conducted with a 52100 steel ball yielded significant improvements for the highest fluence of 5 × 1018 ions/m2 for both ions, but not for the two lower fluences. The improvements in properties were related to Linear Energy Transfer (LET) mechanisms, where it was shown that the O+ implantation caused greater ionization, thereby greater cross-linking at the surface corresponding to much better improvements in properties. The results were also compared with a previous study on PC using 200 keV B+ ions. The present study indicates that high energy ion irradiation produces thicker, more cross-linked, harder, and more wear-resistant surfaces on polymers and thereby improves properties to a greater extent and more efficiently than lower energy ion implantation.
Investigation of the effect of host composition on the photoluminescent properties of SrxBa1−xS doped with Eu and Sm
Authors: Brower Daniel T. , Lloyd Isabel K.
Published: September 2007

The effect of modifying the host composition on the photoluminescent properties of the ir stimulable phosphor system SrBaS : (Eu, Sm) was investigated. Spectral measurements (stimulated emission, fluorescent emission, excitation, and IR stimulation) were made on nine separate host compositions. The lattice constant, ionicity, and lattice strain affect Stark splitting of the rare earth excited states. While large shifts in the ir stimulated emission and fluorescence wavelengths were observed, no shift was observed for the peak excitation and ir stimulation wavelengths.
Growth kinetics, phase transitions, and cracking in cholesterol gallstones
Authors: Kumar Sujeet , Burns S.J. , Blanton T.N.
Published: September 2007

The growth kinetics of cholesterol gallstones have been studied by growing crystals from melted gallstones. The resulting microstructures are spherulitic which is essentially the same as the structures seen in natural gallstones prior to melting. The cholesterol crystals when observed in hot stage microscopy emerge from a unique nucleation center growing radially in the [001] direction with constant rate. The DSC thermograph of a natural gallstone is initially similar to that of cholesterol monohydrate. Upon melting, cholesterol monohydrate changes to anhydrous cholesterol; both forms are crystalline and exhibit polymorphic transformations. Synthetic stones grown from cholesterol were anhydrous and have a phase change at temperatures close to human body temperature. Optical microscopy established that this phase transformation cracks the spherulitic crystals perpendicular to the fast growth direction. Thermal expansion measurements demonstrate that upon heating, the low density, low temperature phase is transformed to a high density phase. This phase transformation and repeated cracking may prove to be useful in destroying natural gallstones, while suppressing this transformation and its associated cracking might aid in securing other solid cholesterol deposits within the human body.
Zircon: A host-phase for the disposal of weapons plutonium
Authors: Ewing R.C. , Lutze Werner , Weber William J.
Published: September 2007

Zircon, ZrSiO4, is a well-characterized, naturally occurring phase that is extremely durable. Zircon has been synthesized with Pu-concentrations up to 10 wt. % and radiation-damage effects studied to saturation doses of nearly 0.8 displacements per atom. We propose that zircon be used as a waste form for the disposal of the more than 100 metric tons of plutonium that will result from the dismantling of nuclear weapons. There are already several demonstrated processing technologies, of which hot pressing offers the most potential. This highly durable material, even under hydrothermal conditions, with its high waste loading and smaller volume allows deep, permanent disposal of the weapons plutonium in geologic environments in which the borosilicate waste-form glass would not be stable.
Preparation of textured alumina films by the sol-gel route
Authors: Campaniello J. , Berthet P. , d'Yvoire F. , Revcolevschi A.
Published: September 2007

Alumina films were fabricated by the sol-gel route under various preparation conditions. The peptization rate and the structure of colloidal particles depend on these conditions. In particular, the peptization of a dried boehmite precipitate prepared from aluminum alkoxide was achieved within a few seconds without heating. The resulting sol is made of highly dispersed crystallites; this allows the formation of well-textured xerogel films as evidenced by the Weissenberg x-ray method.
The oxidation of an aluminum nitride powder studied by bremsstrahlung-excited Auger electron spectroscopy and x-ray photoelectron spectroscopy
Authors: Wang Pu Sen , Malghan Subhas G. , Hsu Stephen M. , Wittberg Thomas N.
Published: September 2007

Bremsstrahlung-excited Auger electron spectroscopy (AES) was used to study the oxidation kinetics of an aluminum nitride powder oxidized in air at 750, 800, 850, and 900 °C. An equation was derived to calculate the average surface oxide film thickness from the aluminum AES spectra. The oxidation of this powder was found to follow a parabolic rate law within this temperature range. The measured activation energy was 230 ± 17 kJ/mol (55 ± 4 kcal/mol). Analysis with x-ray photoelectron spectroscopy (XPS) showed that in addition to the nitride N 1s peak, there was a second N 1s peak. This peak has been observed in previous studies and can be attributed to N-O bonding either within the growing oxide film or at the Al2O3/AlN interface.
EXAFS and RDF studies of TeO2–Li2O glasses
Authors: Shimizugawa Y. , Maeseto T. , Suehara S. , Inoue S. , Nukui A.
Published: September 2007

Local arrangements around Te atoms in TeO2-Li2O glasses with four different Li2O contents (15, 20, 25, and 30 mol %) are observed by Te K EXAFS spectroscopy and x-ray diffraction by making use of synchrotron radiation. EXAFS results based on the two-shell fitting method indicate that interatomic distances of Te-O in axial (ax) sites decrease from 0.208 to 0.197 nm with increasing Li2O contents, while distances between tellurium atom and oxygen atoms in equatorial (eq) sites change slightly from 0.190 to 0.188 nm. Total coordination numbers seem to decrease slightly with increasing Li2O contents. These results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO3+1 polyhedra and TeO3 trigonal pyramids. RDF results also suggest the change of coordination states of tellurium atoms. TeO3+1 polyhedra in glasses are considered to be connected at the vertices with Te-eq Oax-Te or Te-ax Oax-Te linkage as seen in crystalline α-Li2Te2O5.
New opportunities for metals extraction and waste treatment by electrochemical processing in molten salts
Authors: Sadoway Donald R.
Published: September 2007

Molten salt electrolysis is a proven technology for the extraction of metals—all the world's primary aluminum is produced in this manner. The unique properties of molten salts also make them excellent media in which to treat a variety of forms of waste. Of special note in this regard is electrolysis in molten oxides, a concept put forward by the author, initially as a “clean technology” for producing primary metal. However, in the context of waste treatment, elcctrolysis in molten oxides is a process offering the prospect of changing the valence of dissolved heavy metals while making pure oxygen gas as the main by-product. Laboratory tests conducted at a temperature of 1550 °C on chromate sludge dissolved in melt composed of Al2O3, SiO2, CaO, and MgO have confirmed electrochemical production of oxygen on a carbon-free anode.
A silver-tin alternative to dental amalgams
Authors: Dariel M.P. , Admon U. , Lashmore D.S. , Ratzker M. , Giuseppetti A. , Eichmiller F.C.
Published: September 2007

This paper describes a novel technology for a mercury-free metallic direct filling material, a substitute to dental amalgams. The consolidation relies both on cold-welding that takes place under moderate pressure between suitably surface-treated silver particles and on silver-tin intermetallic compound formation at ambient temperature. A dilute acid is used for removing the silver surface oxide layers, thereby promoting the cold-welding process. The condensability, namely the ability of a loose powder to undergo consolidation within a short time duration, at body temperature and under moderate pressure has been investigated for a variety of mixtures of silver, tin, and prealloyed silver-coated intermetallic powders. The resulting metallic composite material displays transverse rupture strength values higher than those of amalgams and somewhat lower values of compressive strength and Knoop hardness.
A process engineering approach to remedy an environmental problem of fugitive lead emissions during lead refining
Authors: Wang Liming , Morris Arthur E.
Published: September 2007

The refining of lead blast furnace bullion involves the transfer and handling of hot impure lead bullion. Fugitive emissions of lead-containing fumes create a plant hygiene problem. The cause of the emissions is the high vapor pressure of lead and its compounds when lead blast furnace bullion is transferred in an open ladle at ∼1000 °C from the blast furnace and poured into the drossing kettle, and later during the manual skimming of powdery dross. A laboratory study was conducted on a new concept for lead refining that eliminates contact between hot lead and the cnvironment, and thus abates fugitive lead emissions. The new process takes place in two steps: controlled solidification of bullion as it flows from the blast furnace, followed by remelting in a closed centrifuge to separate lead and dross. Refined lead was produced with <0.05% copper and <0.01% of all other impurities. Suggestions are outlined for implementing the process.
Development of copper-on-alumina catalytic materials for the cleanup of flue gas and the disposal of diluted ammonium sulfate solutions
Authors: Centi G. , Hodnett B.K. , Jaeger P. , Macken C. , Marella M. , Tomaselli M. , Paparatto G. , Perathoner S.
Published: September 2007

Some aspects of the industrial development of copper-on-alumina catalytic materials for the combined removal of SO2 (DeSOx and NOx (DeNOx) from flue gas of power plants are discussed. Applications of these catalytic materials for the recovery of sulfuric acid from diluted aqueous solutions of ammonium sulfate are also outlined. In particular, the following specific topics are analyzed: (i) the relationship between textural and reactivity properties. (ii) the problem of the design of samples with improved DeSOx properties in relation to the stability of the samples over extended operations, and (iii) the optimization of the regeneration characteristics of the samples. Details on the flow sheet of the technology are also given.
Activated carbon for control of nitrogen oxide emissions
Authors: Rubel A.M. , Stewart M.L. , Stencel J.M.
Published: September 2007

Activated carbons were used to selectively remove NOx from simulated flue gas at temperatures between 25 and 125 °C. Processing conditions and physical/chemical characteristics of the carbons which affected NOx adsorption, storage, and release were investigated. Oxygen as a coreactant was necessary to maximize the conversion of NO to NO2 and condensation of NO2 within the pores of the carbons. A NO-to-NO2 conversion mechanism is presented and discussed relative to previous research. A process for selectively removing NOx and concentrating it as NO2 in an alternate process stream is outlined. The purified NO2 stream could be used for chemicals manufacturing.
Indentation-induced deformation and microcracking of highly textured superconducting (Bi,Pb)2Sr2Ca2Cu3Ox ceramic
Authors: Lo Wai , Campbell A.M. , Luo Jie , Stevens R.
Published: September 2007

A high Tc ceramic superconductor has been prepared having a high degree of preferred orientation, this having been generated by means of a large magnetic field during the early stages of processing. The texture of the material has been characterized using XRD textural analysis and the microstructure by high resolution electron microscopy. Pyramidal indentation (Vickers indent), deformation, and cracking have been investigated using high resolution SEM. Semispherical deformation zones were formed under indents, a result of slipping of adjacent ab/ab (basal) plane grain boundaries and some microcrack development, together with lattice deformation on the basal plane. Densification of the green compact was also observed in the deformation zones, where lateral cracking has been seen to take place along the ab/ab plane grain boundaries. Radial cracking has been seen to take place along the low angle grain boundaries of the lattice ab/ab plane when indentations were made on the surface perpendicular to the preferred texture surface of the materials and also at the highly deformed corners of indent diagonals. The stresses generated resulted in the fracture of the flake-shaped grains and initiated small radial cracks. The Vickers microhardness of the textured ceramics was found to decrease with increasing load.
Chemistry, microstructure, and electrical properties at interfaces between thin films of titanium and alpha (6H) silicon carbide (0001)
Authors: Porter L.M. , Davis R.F. , Bow J.S. , Kim M.J. , Carpenter R.W. , Glass R.C.
Published: September 2007

Epitaxial thin films (4–1000 Å) of Ti contacts have been deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type, alpha (6H)-SiC(0001). The interfacial chemistry and microstructure, and the electrical properties, were investigated at room temperature and after annealing at 700 °C up to 60 min. High resolution TEM analyses revealed the formation during annealing of reaction zones consisting of Ti5Si3 and TiC. The corresponding electrical properties exhibited considerable stability except after an initial 20 min anneal. Current-voltage (I-V) measurements showed that the Ti contacts were rectifying with low ideality factors (n < 1.09) and typical leakage currents of 5 × 10−7 A/cm2 at −10 V. The Schottky barrier heights calculated from x-ray photoelectron spectroscopy and I-V and V-V measurements were between 0.79 and 0.88 eV for the as-deposited contacts and between 0.86 and 1.04 eV for the annealed contacts.
Magnesium reduction of WO3 in a self-propagating high-temperature synthesis (SHS) process
Authors: Ko Seog Gueon , Won Chang Whan , Chun Byong Sun , Sohn H.Y.
Published: September 2007

High-purity tungsten was prepared by the self-propagating high-temperature synthesis (SHS) process from a mixture of WO3 and Mg. The MgO in the product was leached with an HCl solution. The complete reduction of WO3 required a 33% excess of magnesium over the stoichiometric molar ratio Mg/WO3 of 3. The product tungsten had a purity of 99.980% which was higher than that of the reactant WO3. This is because the impurities were either volatilized at the high temperatures generated during the rapid exothermic reaction or dissolved into the HCl solution during leaching.
YBa2Cu3O7−x films on off-axis Y-ZrO2 substrates using Y-ZrO2 or Y2O3 barrier layers
Authors: Mueller C.H. , Holloway P.H. , Budai J.D. , Miranda F.A. , Bhasin K.B.
Published: September 2007

YBa2Cu3O7−x (YBCO) and barrier layer films were deposited on single-crystal (Y2O3)0.09(ZrO2)0.91 substrates cut between 3.6 and 35.7°off-axis from the (001) planes. The barrier layers were (Y2O3)0.065(Y-ZrO2)0.935(Y-ZrO2), Y2O3, or multilayered structures of Y-ZrO2 and Y2O3. X-ray diffraction showed that the Y-ZrO2 and Y2O3 barrier layers generally grew epitaxially on the off-axis substrates, with the (001) barrier layer film planes being parallel to those of the substrate, and the (100) directions being parallel. YBCO films deposited on Y2O3 barrier layers also showed epitaxy with the YBCO (001) planes being nearly parallel to the substrate (001) planes, even for miscuts up to 35.7°. In contrast, the (001) planes of YBCO films deposited on Y-ZrO2 barrier layers were almost parallel to the substrate surface, not the (001) substrate planes. However, YBCO films on Y-ZrO2 films maintained particular in-plane epitaxial orientations with respect to the substrate. The YBCO full-width at half-maximum (FWHM) x-ray peaks were slightly narrower (0.8°) on Y2O3 barrier layers than on Y-ZrO2 layers (1.3°). The electrical resistivity versus temperature behavior of the YBCO/Y2O3 films was consistent with increased grain boundary scattering as the degree of substrate miscut increased, whereas YBCO/Y-ZrO2 films' resistivities showed less sensitivity to substrate miscut, consistent with the loss of epitaxy.
Thermal evaluation of zone-melting recrystallization of thin-film structures over a wide range of melting points
Authors: Robinson Richard D. , Wong Peter Y. , Miaoulis Ioannis N.
Published: September 2007

Zone-melting recrystallization (ZMR) is a lateral epitaxy technique used to recrystallize polycrystalline thin films on substrates. Large-area multilayer structures of thin films processed with ZMR are usable in microelectronics applications. During the processing, slight variations in thermal gradients can lead to different crystalline qualities. Thus, processing uniformity over the wafer is strongly affected by the sensitivity of both the melt width and the solid/liquid interface to changes in the thermal environment. Processing control must either be set initially in a stable operating range or adjusted dynamically to variations in processing. Numerical simulations of the ZMR process were conducted to evaluate the sensitivity of the process over a wide range of temperatures and materials. Results indicate that material with melting points below 900 °C are very sensitive to temperature disturbances. This is due to the increased influence of conductive heating and decreased influence of radiative heating. The increased reflectivity during phase change curbs the amount of absorbed radiation. As the absorbed radiation becomes less influential, the sensitivity of the slush width decreases. Conductive effects should be considered when processing materials with melting points at or below 900 °C.
Adhesion properties of a structural etch stop material for use in multilayer electronic wiring structures
Authors: Haring Ruud A. , Nunes Sharon L. , McGouey Richard P. , Galligan Eileen A. , Volksen Willi , Hedrick James L. , Labadie Jeff
Published: September 2007

A thermally stable copolymer of a polyimide and a dianiline terminated polydimethylsiloxane has been developed for use as a structural oxygen etch barrier material in high performance multilayer electronic wiring structures. We report on the preparation of the etch barrier material and on investigations of the etch stop and adhesion properties of this material. Studies on the effects of adhesion-promoting plasma treatments are supported by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) data. Before plasma treatment, it is observed that the siloxane component segregates to the surface. After either an O2 reactive ion etch treatment or H2O plasma exposure, the unusual XPS charging effects are interpreted as a surface layer containing two distinct phases: the etched polyimide fraction and a partial overlayer of a carbon containing SiO2
Effect of Mn valence on crystal structure of La–Mn–O perovskite oxides
Authors: Yao Takeshi , Ito Toyoji , Kokubo Tadashi
Published: September 2007

La:Mn = 1:1 mixtures of lanthanum oxide and manganese carbonate were heat-treated under various oxygen partial pressures at 1400 °C or 1300 °C. The Mn valence of the samples was measured by a chemical analysis, and the crystal structures were refined by the powder x-ray diffraction and the Rietveld analysis. A novel orthorhombic perovskite phase, belonging to the space group Pbnm and containing - Mn2+ ions, was formed by heat-treatment under low oxygen partial pressures. The structure was very close to a cubic symmetry. It is supposed that the micro Jahn-Teller effects of Mn2+ ions were nearly canceled by one another.
Reduced YSZ deposition temperatures for YBa2Cu3Ox/YSZ thin films on sapphire
Authors: Kroese J.H. , Drehrman A.J. , Horrigan J.A.
Published: September 2007

Thin films of Y-stabilized ZrO2 (YSZ) were deposited by RF diode sputtering on R-plane sapphire as a buffer layer for the deposition of YBa2Cu3O3 (YBCO). By increasing the partial pressure of oxygen in the sputter gas mixture from 20% to 50%, it was found that the substrate temperature required to obtain (100) oriented YSZ deposition could be lowered to 630 °C from 800 °C. This change is attributed to heating or mixing effects at the film surface, due to an increase in negative ion bombardment, which supplements the effects of external heating. Increases in the partial pressure of oxygen beyond 50% were found to be counterproductive. YBCO films, deposited on the YSZ buffer layers via magnetron sputtering, showed c-axis orientation and transition temperatures of 82 K. Orientation of both the YSZ and YBCO films was confirmed by x-ray diffraction and SEM characterization.
Analysis of doped rodlike surface fibers in Al–Al3Ni eutectic alloys
Authors: Rosell-Laclau E. , Durand-Charre M. , Joud J-C.
Published: September 2007

Undoped and Cr doped rodlike Al-Al3Ni eutectics have been studied as initial alloys of Raney nickel catalysts. The aim was to localize the dopant at different stages of the catalyst life: in the initial alloy, after Al leaching out, and after hydrogenation reaction. We have followed this dopant by STEM analysis and high resolution Auger spectroscopy. The outcome is that during Al leaching out, the dopant is also extracted from its initial phase and then forms a deposit on the Ni crystallites of the catalyst. Moreover, during the hydrogenation, the quantity of Cr remains roughly constant.
Elevated temperature creep properties of NiAl eryomilled with and without Y2O3
Authors: Whittenberger J. Daniel , Luton Michael J.
Published: September 2007

The creep properties of lots of NiAl eryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol % yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar crecp strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n ≍ 10) mechanism, the low stress exponent regime n was ∼6 in tension and ∼2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of ∼600 kJ/mol for tensile testing were closer to the previously measured values (∼700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cyromilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.
Preparation of stages 2–4 ternary AlCl3–FeCl3-graphite intercalation compounds
Authors: Abe Takeshi , Mizutani Yasuo , Asano Mitsuru , Harada Toshio
Published: September 2007

Intercalation of AlCl3 into stage 2 FeCl3-graphite intercalation compound (GIC) using an ordinary two-bulb method has been studied by x-ray diffraction. Stages 2, 3, and 4 ternary AlCl3-FeCl3-GlC's are obtained when the temperatures of the stage 2 FeCl3-GIC were set at T (GIC) = 503, 523, and 553 K, respectively, for the AlCl3 intercalate material at T (AlCl3) = 473 K, that is, the vapor pressure of (AlCl3)2 (g) of the main vapor species to be held at p {(AlCl3)2} = 2.4 × 105 Pa. However, for the temperature of the stage 2 FeCl3-GIC at T (GIC) = 573 K, the (AlCl3)2 (g) vapor is found to promote the decomposition of the stage 2 FeCl3-GIC, resulting in the formation of graphite. The decomposition of the stage 2 FeCl3-GIC is considered to take place because the complex AlFeCl6 (g) in the gas phase, which is formed from both (AlCl3)2 (g) and FeCl3 existing at the edge of the FeCl3-GIC, is thermodynamically more stable than the FeCl3 and AlCl3 intercalates in their GIC at p {(AlCl3)2} = 2.4 × 105 Pa and T (GIC) = 573 K.
Elastoplastic deformation of multilayered materials during thermal cycling
Authors: Shen Y-L. , Suresh S.
Published: September 2007

Analytical models are presented for the elastoplastic deformation of multilayered materials subjected to fluctuating temperatures. The layered structure comprises an elastic-perfectly plastic ductile material sandwiched between two elastic brittle materials. With creep, heat transfer, and edge effects excluded, closed-form solutions for different characteristic temperatures for thermal cycling are presented as a function of the layer geometries and the thermomechanical properties of the constituent phases. The evolution of curvature, the generation of thermal residual stresses within each layer, and the onset and spread of plasticity in the ductile layer are also examined. It is theoretically shown that reversals of curvature in the layered solid can occur during monotonic changes in temperature, even when the thermomechanical properties of the layer do not vary significantly with temperature. The predictions of the analytical model are seen to compare favorably with experimental observations of curvatures during thermal cycling in the limiting case of bilayer composite with Al–Al2O3 layers and Al–Si layers and in a Si–Al–SiO2 trilayer system. Case studies of the effects of the relative variations in the geometry, elastic properties, and plastic response of the constituent phases on the overall deformation are examined for two practically significant layered systems: a Si–Al–SiO2 layered solid with extensive applications in the electronics industry and a Cr2O3-coated steel with an interlayer of a Ni–Al alloy which is used in structural applications.
The low temperature hexagonal to orthorhombic transformation in Si3N4 reinforced BAS matrix composites
Authors: Bandyopadhyay A. , Aswath P.B. , Porter W.D. , Cavin O.B.
Published: September 2007

The amount of Si3N4 in a Si3N4-BaO · Al2O3 · 2SiO2 (BAS) composite and the time of sintering was examined in the context of the low temperature hexagonal to orthorhombic transformation in BAS. It was found that with increasing amounts of Si3N4 in the composite, the temperature of the hexagonal to orthorhombic transformation was decreased. As the sintering time was increased for a given composite composition, a drop in the temperature of the hexagonal to orthorhombic transformation was observed. which was linked to an increase in the β-Si3N4 content in the composite. In addition, as the Si3N4 content in the composite was increased, a resultant drop in the coefficient of thermal expansion of the composite occurred. The extent of the linear dimensional change of the composite during the BAS hexagonal to orthorhombic transformation is reported.
Elastic constants and internal friction of polycrystalline copper
Authors: Ledbetter Hassel , Fortunko Christopher , Heyliger Paul
Published: September 2007

Using ultrasonic-resonance spectroscopy (URS), we measured the elastic constant C and companion internal friction Q−1 of isotropic polycrystalline copper. The annealed material was 0.9999 pure with equiaxed heavily twinned grains averaging about 75 μm diameter. The URS method offers the principal advantage of point contact or loose coupling, thus there was no contribution from a transducer-specimen bond and only small contributions from transducers and fixture. A second advantage is one measurement for all elastic constants and all associated internal frictions. The C's agree with established values. The Q−1's are much lower than pulse-echo-method values. Comparison of measured Q−1 with the Koehler-Granato-Lücke model permits estimating an effective dislocation-loop length. Q−1 (shear) exceeds Q−1 (longitudinal) by a factor of about 1.5.
Alumina aerogel catalysts prepared by two supercritical drying methods used in methane combustion
Authors: Mizushima Yasuyuki , Hori Makoto
Published: September 2007

Palladium-supported alumina aerogels were prepared by two different supercritical drying methods. In one method, an alumina wet gel was dried under supercritical conditions of ethanol in an autoclave. In the other, the aerogel was supercritically dried by extracting ethanol using carbon dioxide in an extractor. The Pd-supported alumina aerogel prepared in the autoclave exhibited a high specific surface area of 112.8 m2/g after firing at 1200 °C for 5 h, while the other had a specific surface area of only 5.2 m2/g due to α-alumina transformation. Their catalytic properties for methane combustion were measured. The Pd-supported alumina aerogel prepared in the autoclave combusts methane perfectly at 50–60 °C lower temperature than the other. Palladium particles on the alumina aerogel prepared in the autoclave contained palladium oxide, while those prepared in the CO2 extractor contained only palladium metal.
Effects of implantation temperature on the structure, composition, and oxidation resistance of aluminum-implanted SiC
Authors: Yang Zunde , Du Honghua , Libera Matthew , Singer Irwin L.
Published: September 2007

α-SiC crystals were implanted with aluminum to a high dose at room temperature or 800 °C. Transmission electron microscopy showed that SiC was amorphized by room temperature implantation but remained crystalline after 800 °C implantation. Crystalline aluminum carbide was formed and aluminum redistribution took place in SiC implanted at 800 °C. Implanted and unimplanted crystals were oxidized in 1 atm flowing oxygen at 1300 °C. Amorphization led to accelerated oxidation of SiC. The oxidation resistance of SiC implanted at 800 °C was comparable with that of pure SiC. The oxidation layers formed on SiC implanted at both temperatures consisted of silica embedded with mullite precipitates. The phase formation during implantation and oxidation is consistent with thermodynamic predictions. The results from our current and earlier studies suggest that there exists an optimum range of implantation temperature, probably above 500 °C but below 800 °C, which preserves the substrate crystallinity and retains the high aluminum dosage, for the enhancement of oxidation resistance of SiC.
Diamond nucleation and growth on reactive transition-metal substrates
Authors: Zhu W. , Yang P.C. , Glass J.T. , Arezzo F.
Published: September 2007

Diamond deposition on group VIII transition metals of Cr, Mn, Fe, Co, and Ni has been achieved by a multi-step chemical vapor deposition process consisting of (i) seeding the substrate with diamond powders, (ii) annealing the seeded substrate in hydrogen at high temperatures, and (iii) diamond nucleation and growth. It was found that high quality diamond can be grown on these substrates, and the often accompanied graphite formation, which has been the main obstacle in the deposition of diamond on these metal surfaces, can be largely suppressed by the above step-deposition procedure. This technique was further extended to the processes of depositing diamond on steels and Co-bonded WC materials.
A self-constraint strengthening mechanism and its application to seashells
Authors: Yang X.F.
Published: September 2007

A self-constraint strengthening mechanism for multilayered brittle materials is proposed. The strengthening is a result of the self-constraint of the individual layers on each other, and no additional reinforcements are needed. The proposed model predicts that when individual brittle layers are stacked and properly “glued” together with a weak interphase, each layer will be ensured a minimum tensile strength, regardless of the flaw size in the individual layers. Estimation of the minimum strength using this model yields an apparently close agreement with the measured values for one type of nacreous structure reported in the literature. It is also predicted that low-strength ceramic sheets, which might be produced by some low-cost fabrication techniques, can be used to construct high strength man-made nacreous ceramics.
Errors associated with depth-sensing microindentation tests
Authors: Menčík J. , Swain M.V.
Published: September 2007

In the determination of mechanical properties by ultra-microindentation, various errors can appear. This paper analyzes various sources of errors in estimation of elastic modulus and hardness. These errors arise from uncertainties of the indenter geometry and properties, as well as measuring instrument limitations and errors, such as the minimum detectable load, compliance, and noise of the system. Other sources of errors are thermal drift, shape of the impression, and scatter of properties of the tested material. Characteristic features and the magnitude of individual kinds of errors are discussed, together with formulas and recommended methods for their reduction.
Variant structure in metal-organic-chemical-vapor-deposition-derived SnO2 thin films on sapphire (0001)
Authors: Liu Donhang , Wang Q. , Chang H.L.M. , Chen Haydn
Published: September 2007

Tin oxide (SnO2) thin films were deposited on sapphire (0001) substrate by metal-organic chemical vapor deposition (MOCVD) at temperatures of 600 and 700 °C. The microstructure of the deposited films was characterized by x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). At the growth conditions studied, films were single-phase rutile and epitaxial, but showed variant structures. Three distinct in-plane epitaxial relationships were observed between the films and the substrate. A crystallographic model is proposed to explain the film morphology. This model can successfully predict the ratio of the width to the length of an averaged grain size based upon the lattice mismatch of the film-substrate interface.
Stable thin film resistors using double layer structure
Authors: Jia Q.X. , Lee H.J. , Ma E. , Anderson W.A. , Collins F.M.
Published: September 2007

Highly stable bilayer thin film resistors, which consist of an underlying layer of tantalum nitride and of a capping layer of ruthenium oxide, were developed by taking advantage of the desired characteristics of two different materials in a single system. The resistors fabricated in such a way were highly stable under power loading or thermal cycling. Resistors with one digit temperature coefficient of resistance (TCR) could be easily controlled by the layer thickness ratio of the tantalum nitride to the ruthenium oxide and the ex situ annealing temperature or duration. Auger electron spectroscopy depth profile on the thin films indicates that the ruthenium oxide layer is well defined for the as-deposited form. Nevertheless, interdiffusion takes place after thermal treatment of the bilayer which is used to tune the temperature coefficient of resistance and to stabilize the resistance of the resistors.
The characterization of high-performance PAN-based carbon fibers developed by continuous carbonization and air oxidation
Authors: Ko Tse-Hao , Li Chien-Hung , Hu Chung-Hua
Published: September 2007

The properties of four kinds of Type II carbon fibers, which had been precarbonized at 300 °C, 400 °C, 500 °C, and 600 °C, respectively, during two-stage continuous carbonization, were measured after being air oxidized for periods of 1 to 6 min at 550 °C. The effects of precarbonization temperature on mechanical properties, density, morphology, elemental composition, and microstructure of the carbon fibers during the air oxidation are discussed in this article. The precarbonization process strongly affected the surface properties and mechanical properties of the final oxidized carbon fibers. The carbon fibers developed from the different precarbonization temperatures all had different structures. The carbon fibers that had been precarbonized at 300 °C had a more ordered structure than other fibers after air oxidation. These carbon fibers also had a higher performance than the other fibers. Carbon fibers also showed different oxidation behaviors caused by differences in surface morphology resulting from each different precarbonization temperature. Optimum conditions not only improved the tensile strength and modulus, but also increased the density and oxygen content. Experimental results showed that the tensile strength of the carbon fibers precarbonized at 300 °C increased from 2.4 GPa to 4.3 GPa (80%) after 6 min oxidation at 550 °C.