bluuebunny/crossref_metadata_2025 huggingface dataset:
The growth of strained Si1−xGex alloys on 〈001〉 silicon using solid phase epitaxy
Authors: Paine D.C. , Howard D.J. , Stoffel N.G. , Horton J.A.
Published: September 2007

In this paper we report on the growth of pseudomorphically strained Si1−xGex alloys on 〈001〉 Si by solid phase epitaxy. One set of amorphous alloys was formed by high dose ion implantation 74Gc implanted at an energy of 200 kcV to a fluence of 9.6 ⊠ 1020/m2). Our TEM observations show that regrowth of these Si1−xGex(xmax = 0.14) films at ≍590°C results in a high density of planar defects and that these defects are associated with faceting of the amorphous/crystalline interface during annealing. These results were compared with the solid phase regrowth of MBE-grown Si0.7Ge0.3 amorphized with 170 keV 28Si ions which exhibited identical defects and faceting during regrowth. Attendant with this faceting was a decrease in the regrowth velocity, a result of a change from a planar {001} growth morphology to a multi-faceted growth surface containing many <50 nm deep pyramidal impressions. The regrowth rate was quantified, at a particular temperature, by the use of Si homoepitaxy for calibration of in situ TEM experiments. It was shown that the regrowth rate at 594°C in pure Si was 51 nm/min, whereas in the Si0.7Ge0.3 the regrowth rate decreased, as a result of {111} faceting, to 21 nm/min. RBS was used to characterize Ge concentrations and lattice resolution TEM was used to study the development of the faceted interface and associated planar defects during regrowth.
Characterization of GaAs solar cells made by ion implantation and rapid thermal annealing using selective photoetching
Authors: van Sark W.G.J.H.M. , Weyher J.L. , Giling L.J. , de Potter M. , van Rossum M.
Published: September 2007

Shallow n-p GaAs solar cells have been made by implantation of Si into Zn-doped (p-type) GaAs substrates followed by rapid thermal annealing. The structure of the GaAs crystal has been determined by the DSL photoetching method (Diluted Sirtl-like etchants used with Light). It was found that implantation-induced-damage (revealed by DSL as microroughness and craters) was not removed after annealing for energies exceeding 60 keV. This leads to substrates that contain many precipitates, which appears to be disastrous for the fabrication of good solar cells. In addition, good cell performance is hampered by compensation effects in the n-p transition region and in the n-type layer itself.
Sol-gel preparation of amorphous ZBLA heavy metal fluoride powders
Authors: Melling Peter J. , Thomson Mary A.
Published: September 2007

Amorphous fluoride powder in the ZrF4-BaF2-LaF3-AlF3 (ZBLA) system has been prepared by a direct chemical route from metal alkoxides by reaction with bromine trifluoride. The potential of bromine trifluoride as a solvent for use in sol-gel synthesis of fluoride glass is discussed.
Sol-gel processing of cordierite: Effect of seeding and optimization of heat treatment
Authors: Kazakos Ann M. , Komarneni Sridhar , Roy Rustum
Published: September 2007

Three series of cordierite powders were prepared by the sol-gel route: a single phase (monophasic) gel prepared from alkoxides, a nominally triphasic nanocomposite gel made with two nanosized powders and one solution phase, and a truly compositionally triphasic nanocomposite gel prepared from three nanosized powders. Crystalline α-cordierite seeds were also incorporated with the gels and their effectiveness as nucleating agents was investigated and found to lower the crystallization temperature of α-cordierite by 125–150°C. The densification behavior of powder compacts was examined and alterations made to the heat treatment until optimum conditions were found. The truly triphasic compact sintered at 1300°C for 2 h resulted in 100% of theoretical density whereas the nominally triphasic and monophasis pellets densified to 96% and 80%, respectively. The enhanced densification achieved with powder compacct prepared for triphasic nanocomposite gels is due to part to the excess free energy of the three components.
Measuring the interfacial shear strength of thin polymer coatings on glass
Authors: Lin M.R. , Ritter J.E. , Rosenfeld L. , Lardner T.J.
Published: September 2007

The interfacial adhesive shear strengths of four commercial polymer coatings on soda-lime glass were measured by the microindentation and single lap shear tests. The indentation interfacial shear strengths were over an order of magnitude greater and exhibited significantly less variability than those measured by lap shear. It is believed that the indentation test measures the “intrinsic” interfacial shear strength of the bonded coatings, whereas the lap shear strengths are controlled by large processing flaws (pores in this study) in the region of stress concentration near the overlap edge.
Carbon retention in YBa2Cu3O7–δ and its effect on the superconducting transition
Authors: Shaw T. M. , Dimos D. , Batson P. E. , Schrott A. G. , Clarke D. R. , Duncombe P. R.
Published: September 2007

Magnetic susceptibility measurements are used to show that the superconducting transition temperature of yttrium barium cuprate is lowered by carbon trapped in the microstructure of dense polycrystalline materials during sintering. We show that carbon is retained in the material as a result of the porosity closing off during the sintering process. X-ray photoelectron spectroscopy and electron energy loss spectroscopy are used to show that the retained carbon forms a solid solution with YBa2Cu3O7–δ and resides in a barium carbonate-like configuration in the crystal structure. The origin of the lowering of the superconducting transition temperature and processing strategies for preventing carbon retention are discussed.
Microstructures and mechanical properties of NiAl–Ni2AlHf alloys
Authors: Takeyama M. , Liu C. T.
Published: September 2007

The microstructure and mechanical properties of several Ni–Al–Hf alloys in the composition range between NiAl (β) and Ni2AlHf (Heusler phase) have been studied. The volume fraction of Heusler phase, Vf, in these alloys varies from about 15 to 96%. The lattice misfit between the β and Heusler phases in two-phase alloys is larger than 5%, indicating no coherency between them. The yield strength increases with increasing Vf at all temperatures to 1000°C. Compressive ductilities of 4 and 7% were obtained for the alloy with Vf of 15% at room temperature and 500°C, respectively, but they decreased to 0% with increasing Vf to 96%. The corresponding fracture mode is basically transgranular cleavage. However, all the alloys can be deformed extensively without fracture at 1000°C. The hardness of the Heusler alloy is very high (8.3 GPa) at room temperature, and it decreases gently with temperature to 600°C, followed by a rapid decrease to 1000°C. The brittleness and high hardness of the Ni2AlHf Heusler phase at low temperatures are interpreted in terms of internal lattice distortion resulting from its crystal structure. The thermally activated process of deformation takes place above 600°C, which is responsible for the rapid drop of the hardness of the alloys.
Stability of tantalum nitride thin film resistors
Authors: Au C. L. , Anderson W. A. , Schmitz D. A. , Flassayer J. C. , Collins F. M.
Published: September 2007

Post-deposition rapid vacuum annealing of tantalum nitride (Ta2N) thin film resistors (TFR) was successful in improving the temperature coefficient of resistance (TCR) to ±5 ppm/°C with starting TCR at about −140 ppm/°C. A subsequent aging study revealed degradation of the nichrome (NiCr) contact interlayer. Two improved contact layers, TiW and Tamelox (Ta/NiCr), were compared. The structural grain growth induced by the annealing effect resulted in Ta2N films having 100–1000 Å polycrystals in an amorphous matrix. The corresponding current conduction mechanisms were identified with a substrate-assisted tunneling model. The frequency response predicted potential applications to 100 GHz.
Weak localization and coulomb interaction in graphite intercalation compounds and related materials
Authors: Piraux L.
Published: September 2007

The effects of weak-localization and electron-electron interaction have to be invoked to explain anomalies in the resistivity and the magnetoresistance of quasi two-dimensional electron systems formed in acceptor graphite intercalation compounds and in prcgraphitic carbon materials. After introducing the basic concepts involved in the physics of these phenomena, a review is given of recent data for the low temperature electronic transport properties in these materials.
Near-surface stoichiometry of high temperature superconducting YBaCuO thin films
Authors: Drehman A. J. , Dumais M. W. , Horrigan J. A. , Wang G-C. , Liew Y-F.
Published: September 2007

The surface morphology and near-surface chemical composition of high temperature superconducting Y–Ba–Cu–O thin films have been studied by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. These films were fabricated on SrTiO3 substrates by RF diode sputter deposition and subsequent furnace annealing in oxygen. The chemical composition at and near the surface of thin films was found to differ from the bulk composition. At about 500 Å below the surface the Y, Ba, and Cu stoichiometry, as determined by AES, gradually approach that of the film interior. These results suggest that, for furnace annealed films, there may exist a minimum deposited Y–Ba–Cu–O film thickness in which superconductivity is possible. It was also found that the calculated copper concentration determined by AES during depth profiling is significantly lower than its actual value.
Equilibrium phase diagrams for the systems PbO–SrO–CuO and PbO–CaO–SrO
Authors: Kitaguchi Hitoshi , Takada Jun , Oda Kiichi , Miura Yoshinari
Published: September 2007

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb–Sr–Ca–Cu–O system, subsolidus phase equilibrium in the systems PbO(PbO2)–SrO–CuO and PbO(PbO2)–CaO–SrO has been studied, mainly by XRD analysis. A pseudoternary Pb–Sr–Cu–O solid solution was newly found. This solid solution has a wide solubility range including its typical composition Pb2.03Sr3Cu0.73O7.70. It has a hexagonal structure with lattice parameters a = 10.11 and c = 7.11 in AU. Composition dependences of the lattice parameters and the decomposition (incongruent melting) temperature of (Ca1−xSrx)2PbO4 solid solution are also reported.
Equilibrium phase relations in the Bi–Ca–Sr–Cu–O system at 850 and 900°C
Authors: Lee C-L. , Chen J-J. , Wen W-J. , Perng T-P. , Wu J-M. , Wu T-B. , Chin T-S. , Liu R-S. , Wu P-T.
Published: September 2007

The phase relations of equilibrium compounds in the pseudoternary system Bi2O3–(Ca,Sr)O–CuO at 850 and 900°C were studied. The ratio of Ca : Sr was fixed at 1:2. Starting materials of Bi2O3, CaCO3, SrCO3, and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900°C for different durations to ensure that equilibrium had been reached. The products were cooled in air or quenched in liquid nitrogen and then identified by x-ray powder diffraction. At 850°C, only the superconducting phase, Bi2CaSr2Cu2Ox (2122), was observed inside the triangle. The other stable phases were all positioned on the boundary lines, and included CuO·⅗MO, CuO·MO, CuO·2MO, 1.½Bi2O3·0.9MO, Bi2O3·4MO, Bi2O3·9MO, and a solid solution, Bi2O3·xMO, where 0.16  x  0.82 and MO represents ⅓(CaO·2SrO). At 900°C, the above boundary line phases remained stable but the 2122 phase was not observed. The tie lines among the stable phases in the two isotherms were established.
Crystal-to-amorphous transformation of NiTi induced by cold rolling
Authors: Koike J. , Parkin D. M. , Nastasi M.
Published: September 2007

A NiTi intermetallic compound was cold rolled at room temperature by 30% and 60% thickness reductions, and microstructures were studied by means of transmission electron microscopy (TEM). In the cold-rolled samples we observed both a phase of nanometer-sized crystals and an amorphous phase. A substantially high dislocation density, 1013 to 1014/cm2, was evident in the transition region between crystalline and amorphous phases. A simple estimate of the elastic energy arising from this dislocation density is of the same order as the crystallization energy, suggesting that dislocation accumulation is a major driving force for amorphization in cold-rolled NiTi.
The effect of temperature on the chemistry and morphology of the interphase in an SCS6/Ti–6Al–4V metal matrix composite
Authors: Jones C. , Kiely C. J. , Wang S. S.
Published: September 2007

The changes in the chemistry and morphology within the interphase region of an SCS6/Ti–6A1–4V metal matrix composite upon exposing the samples to varying heat treatments have been studied using Auger electron spectroscopy, TEM and convergent beam diffraction techniques. These changes, such as the formation of small TiC particles at one interface and the narrowing of a protective pyrocarbon layer at another, induce fracture to occur at different places within the interphase upon heating. The reasons for this are explained. Evidence for a change in phase of a TixSiy(C) layer to the more thermodynamically stable Ti5Si3 is also given.
R-curve measurements in PSZ ceramics
Authors: Srinivasan S. , Scattergood R. O.
Published: September 2007

An indentation-bend failure-stress method was used for measurement of R-curves in a series of PSZ ceramics with varying peak toughness. Dilatational transformation-stress constraints are included in the residual-stress driving force contribution to the applied stress intensity factor. A power-law fit to the form of the R-curve simplifies the analysis. While the resulting curves show the expected form, measured toughness values are high relative to the expected peak toughness. Limitations and the range of applicability of the indentation-bend technique are discussed.
Improved uniformity of densification of ceramic composites through control of the initial preform porosity distribution
Authors: Middleman Stanley , Heble Brian , Cheng Herman C.T.
Published: September 2007

Densification arising from chemical vapor deposition within a porous preform is modeled as a problem in diffusion and reaction. The effect of reaction rate on the nonuniformity of the final densified composite is explored. The possibility of achieving uniform densification by starting with an initially nonuniform porosity distribution is demonstrated with a simulation model. This model permits one to design a densification process from first principles using a simulation tool that yields results on a timescale far less than that of the processing laboratory.
On lattice trapping of cracks
Authors: Curtin W. A.
Published: September 2007

A simple analytic theory to quantify the extent of “trapping” of cracks by a crystal lattice and its dependence on the range of the interatomic force law is presented. The theory requires a priori knowledge of only one or two lattice-dependent, but force law independent, parameters and can then reproduce nearly all previous (numerically demanding) theoretical results. Moreover, the extent of lattice trapping does not decrease monotonically with increasing range of the force law. For realistic interatomic potentials, however, lattice trapping is quite small. The analysis is then extended to the case of chemical corrosion by direct chemical attack of the crack tip bond. It is shown that similar slow crack growth thresholds can be predicted by the thermodynamic Griffith approach and a fracture criterion based on a local bond instability.
Electrical properties of natural and synthetic pyrite (FeS2) crystals
Authors: Schieck R. , Hartmann A. , Fiechter S. , Könenkamp R. , Wetzel H.
Published: September 2007

We have prepared a series of syntheticn-type pyrite (FeS2) crystals by chemical vapor transport and high temperature solution growth. These and natural crystals were characterized with respect to Hall mobility, carrier concentration, and conductivity, and chemically analyzed by mass spectroscopy and atomic emission spectroscopy. The results are compared in detail to previous work on natural crystals. Conductivity and carrier concentration in our measurements varied between 0.05 and 3.5 (Ω cm)−1and between 6.9·1015and 5.4·1017cm−3, respectively. The peak mobilities have values ranging from 100 to 2000 cm2/Vs. We find that sulfur deficiency and a number of impurity elements, such as Si, Cu, and Al, can qualitatively account for the trends in the electronic properties.
Low-pressure metalorganic chemical vapor deposition of photoluminescent Eu-doped Y2O3 films
Authors: West Gary A. , Beeson K. W.
Published: September 2007

We have produced thin photoluminescent films of Eu-doped Y2O3 (Y2O3: Eu) by low-pressure metalorganic chemical vapor deposition (MOCVD). Yttrium and europium β-diketonate precursors are thermally decomposed in a hot-walled MOCVD reactor in the presence of oxygen at a total reactor pressure of 1 Torr. The films are microcrystalline and photoluminescent as-deposited and contain <1 at.% of carbon contamination. Subsequent annealing at 1200°C in air enhances and stabilizes the luminescence. We have measured the photoluminescent lifetimes of the MOCVD films as a function of temperature for the Eu+35D1 ⇉ 7F1 and 5D0 ⇉ 7F2 transitions using excimer laser excitation at 248 nm. We present a kinetic model which can account for the observed emission lifetimes from 20–1000°C.
Crystalline perfection of chemical vapor deposited diamond films
Authors: Hetherington A. V. , Wort C. J. H. , Southworth P.
Published: September 2007

The crystalline perfection of microwave plasma assisted chemical vapor deposited (MPACVD) diamond films grown under various conditions has been examined by TEM. Most CVD diamond films thus far reported contain a high density of defects, predominantly twins and stacking faults on {111} planes. We show that under appropriate growth conditions, these planar defects are eliminated from the center of the crystallites, and occur only at grain boundaries where the growing crystallites meet.
An electron diffraction study of Bi2Sr2(GdxCa1−x)0.8Cu2O8+δ
Authors: Kulik J. , Xue Y. Y. , Sun Y. Y. , Bonvalot M.
Published: September 2007

The compound Bi2Sr2(GdxCa1−x)0.8Cu2O8+δ is examined by electron diffraction for several values of x. The incommensurate modulation which has been reported for x - 0 persists for all values of x with the wave vector increasing as x increases. A secondary modulation with a wave vector equal to one-half that of the primary is observed for x  0.85. This modulation manifests itself through satellite reflections that are highly streaked normal to the (001) planes and that flank certain select positions in reciprocal space. The appearance of this secondary modulation is accompanied by a change in the average crystal structure from B-centered to F-centered orthorhombic.
Ultra rapid heating by spontaneous mixing reactions in metal-metal multilayer composites
Authors: Bordeaux F. , Yavari A. R.
Published: September 2007

The mixing of multilayers of two pure metals or alloys A and B with strong negative heat of mixing ΔHm can result in rapid heat release provided that the mixing time is short compared to the time to dissipate ΔHm in the environment, which is the case for sufficiently thin layers. The mixing reaction sets off the heat release when the composite is heated up to temperatures near or equal to the melting temperature of the metal layer with the lower melting point. Experimental results are given for the mechanisms and for the kinetics of the exothermic reaction. Possible applications of these materials are given.
Surface mechanical properties of aluminum implanted nickel and co-evaporated Ni–Al on nickel
Authors: Was Gary S.
Published: September 2007

Implantation of Al into nickel and co-evaporation of Ni–Al films onto nickel substrates followed by ion irradiation was conducted in order to investigate the mechanical properties of ion beam surface modifications and their relation to the composition and microstructure of the surface. Implantations were made using 400 keV Al+ to doses from 1 × 1015 to 6 × 1017 cm−2 at room temperature. Nickel films with 0–25% Al were co-evaporated onto nickel substrates and mixed using the same irradiation conditions but to a lower maximum dose. Hardness was measured using ultra-low load indentation, and residual stress was measured by the bending beam method. Results indicate that the primary contributor to the hardness increase of as-implanted surfaces is the irradiation-induced defects. The effect of Al in solution (γ phase) or Al in γ′ (Ni3Al) in either implanted or co-evaporated and mixed surfaces is evident only upon thermal treating to remove radiation damage. The high inherent hardness of the co-evaporated films is due to the small grain size of the film. The magnitude of the hardness in Al implanted nickel is very sensitive to the surface condition of the substrate. The observed hardness effects are all directly relatable to microstructure or phases present. Residual stresses change from tensile to compressive as a result of damage from low dose irradiation and heat treatment.
Microstructure and mechanical behavior of Al–Mg/Ni–P composites
Authors: Raman V.
Published: September 2007

The microstructure and mechanical behavior of electroless deposited Ni–P on Al–Mg substrates were investigated. The microstructures of the as-deposited and annealed samples were characterized through optical and scanning electron microscopy. Hardness measurements were made both on the Al–Mg substrate and the Ni–P coating using a depth sensing hardness machine. The plastic deformation behavior of the composites was studied and the results show that the initial deformation is accompanied by the appearance of serrations on load-displacement curves. Decohesion of the hard Ni–P takes place at large strains. An estimate of the ultimate shear strength of the Al–Mg/Ni–P interface was made and the strength of the interface was determined to be −0.45 GPa. The tribological properties of the amorphous Ni–P were studied using ball-on-disk and slider-on-disk tests. In particular, the influences of humidity, surface roughness, and heat treatment on friction and durability of the coatings were investigated.
Polyacetylene as heterogeneous catalyst for electroless deposition of bulk amorphous metals
Authors: Kamrava S. J. , Söderholm S.
Published: September 2007

Polyacetylene shows catalytic activity in an aqueous solution for electroless deposition of amorphous alloys. The catalytic activity of polyacetylene is comparable to the activity of some highly catalytic metals, i.e., Cu, steel, and Pt. Modifications of the Shirakawa technique led to the formation of a foam-like polyacetylene, which is highly porous and has a low degree of crystallinity. This material can be used as a catalytic substrate for the preparation of amorphous metals in bulk form. The amorphous Ni–Co–B and Ni–Co–P alloys deposited on a PAc substrate were investigated by magneto-thermogravimetry and x-ray diffraction. These investigations gave a Curie temperature of about 413 K and a crystallization temperature of about 600 K for the metal-metalloid component of the system.
Evaluation of a silicon-containing benzocyclobutene thermoset resin as a plasma etch stop
Authors: Cain Stephen R. , Matienzo Luis J. , Wang David W.
Published: September 2007

An experimental silicon-containing benzocyclobutene thermosetting resin from DOW has been evaluated for use as a plasma etch stop in packaging applications. The thermal and etch properties of this particular resin (DOW UX-13005.02L) make it suitable for use as an etch stop. Further, a model for in situ laser interferometry is proposed. By applying the model to the laser interferogram, the initial etch rate and amount of material removed before etching ceases may be determined.
Fracture toughness of macro-defect-free cement using small crack techniques
Authors: Chou Y-S. , Mecholsky J. J. , Silsbee M.
Published: September 2007

The fracture toughness of a macro-defect-free (MDF) cement was calculated from two measurement techniques: (1) indentation-strength method and (2) fracture surface analysis (FSA). It was found that the indentation-strength method, which showed good agreement with FSA, was applicable for estimating the fracture toughness of MDF cement. The ultimate toughness was found to be 1.25 MPa m1/2 for this MDF cement, which contained 3 wt. % polymer. An R-curve (crack-growth-resistance) bchavior was also observed. Scanning electron micrographs showed extensive microcracking on the fracture surface. Microstructural effects are discussed.
Ion beam analysis of laser-deposited high Tc YBa2Cu3O7 superconducting thin films
Authors: Singh Rajiv K. , Narayan J.
Published: September 2007

We have performed Rutherford backscattering spectrometry, non-Rutherford proton elastic scattering, and axial ion channeling analysis to determine the composition, the crystallinity, and the epitaxial quality of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 and (100) yttria stabilized zirconia (YSZ) substrates. YBa2Cu3O7 superconducting thin films were fabricated both by high and low temperature laser ablation techniques. The former method requires high temperature annealing in oxygen to recover the superconducting properties, whereas in the latter method as-deposited in situ superconducting thin films are formed at low processing temperatures (500 °C–650 °C). Helium ions in the energy range of 2.0–2.5 MeV were used to determine the relative stoichiometries of the heavier atomic number elements (Y, Ba, Cu) in the film, but are not sensitive enough to determine the relative amount of oxygen in the superconducting phase. The detection sensitivities to oxygen can be greatly enhanced by using the proton elastic scattering [16O(p,p) 16O] reaction, which was found to increase the scattering cross section by a factor of 3 to 5 relative to the Rutherford scattering cross section. The ion-channeling of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 substrates showed excellent minimum channeling yields corresponding to epitaxial growth, but the presence of defects increased the channeling yields for films deposited on (100) YSZ substrates. The ion channeling yields are compared with the microstructure of the films determined by transmission electron microscopy.
A search for a low temperature phase transition prior to superconducting behavior in the YBa2Cu3O7 compound
Authors: Rodriguez M. A. , Matheis D. P. , Bayya S. S. , Simmins J. J. , Snyder R. L. , Cox D. E.
Published: September 2007

We report the results of a systematic examination of the lattice parameters for the YBa2Cu3O7 compound in the 100 K to 110 K temperature range by means of high resolution synchrotron x-ray powder diffraction techniques. The data indicate a linear decrease in the lattice parameters with decreasing temperature over this temperature range. An observed asymmetric broadening of the diffraction peaks is explained by the presence of residual stress in the lattice.
Influence of growth parameters on the microstructure of directionally solidified Bi2Sr2CaCu2Oy
Authors: Cima M. J. , Jiang X. P. , Chow H. M. , Haggerty J. S. , Flemings M. C. , Brody H. D. , Laudise R. A. , Johnson D. W.
Published: September 2007

Laser-heated float zone growth was used to study the directional solidification behavior of Bi–Sr–Ca–Cu–O superconductors. The phases that solidify from the melt, their morphology, and their composition are altered by growth rate. Highly textured microstructures are achieved by directional solidification at all growth rates. The superconducting phase is found always to have the composition Bi2.5Sr2CaCu2.2Oy when grown from boules with composition 2:2:1:2 (BiO1.5:SrO:CaO:CuO). Planar growth fronts of Bi2.5Sr2CaCu2.2Oy are observed when the temperature gradient divided by the growth rate (G/R) is larger than 3 ⊠ 1011 K-s/m2 in 2.75 atm oxygen. Thus, the 2212 compound was observed to solidify directly from the melt at the slowest growth rates used in this study. Measurement of the steady-state liquid zone composition indicates that it becomes bismuth-rich as the growth rate decreases. Dendrites of the primary solidification phase, (Sr1−xCax)14Cu24Oy, form in a matrix of Bi2.5Sr2CaCu2.2Oy when G/R is somewhat less than 3 ⊠ 1011 K-s/m2. Observed microstructures are consistent with a peritectic relationship among Bi2.5Sr2CaCu2.2Oy, (Sr1−xCax)14Cu24Oy (x = 0.4), and a liquid rich in bismuth at elevated oxygen pressure. At lower values of G/R, Sr3Ca2Cu5Oy is the primary solidification phase and negligible Bi2.5Sr2CaCu2.2Oy forms in the matrix.
A structural and calorimetric study of the transformations in sputtered Al–Mn and Al–Mn–Si films
Authors: Chen L. C. , Spaepen F. , Robertson J. L. , Moss S. C. , Hiraga K.
Published: September 2007

Scanning and isothermal calorimetry, together with x-ray diffraction and high resolution transmission electron microscopy (TEM), have been used to characterize Al–Mn and Al–Mn–Si films sputtered onto substrates at 60 °C, 45 °C, and −100 °C. In the case of Al0.83Mn0.17, the monotonically decreasing isothermal calorimetric signal, characteristic of a grain growth process, has proved decisive in identifying the as-sputtered “amorphous” state as microquasicrystalline, with an average grain size of ∼ 20 Å, in agreement with an estimate of correlation range from the x-ray pattern. The TEM at 400 keV reveals well-defined atomic or lattice images in annealed films but only barely resolved grains (ordered clusters) in the as-sputtered films. The relation between the metallic glass and the microquasicrystalline state in these alloys is discussed.
Characterization of metallurgical grade silicon
Authors: Anglézio J. C. , Servant C. , Dubrous F.
Published: September 2007

Optical metallography, scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy were used to characterize metallurgical grade silicon, produced in an electric are furnace. Coincidence fraction determinations were assumed to be Σ7 and Σ9 when grain boundaries are underlined by precipitated phases and Σ3 when they are not. The study of intergranular compounds was emphasized; ten compounds were found, the main ones being Si2Ca, Si8Al6Fe4Ca, Si2Al2Ca, Si2FeTi, and Si2.4Fe (α leboitc). The precipitation of these compounds was discussed according to the principal impurity concentrations in silicon. The crystalline structure of Si8Al6Fe4Ca was determined to be triclinic with a = 1.3923 nm, b = 1.3896 nm, c = 1.3900 nm and α = 92.4°, β = 110.3°, γ = 119.9°.
Optical propagation loss reduction in ZnO thin films under CO2 laser treatment
Authors: Bertolotti M. , Laschena M. V. , Rossi M. , Ferrari A. , Qian L. S. , Quaranta F. , Valcntini A.
Published: September 2007

The reduction of propagation losses in ZnO thin film waveguides for integrated optics after CO2 laser treatment is studied. RHEED patterns show that the measured decrease of optical losses is accompanied by an increase of ordering after the laser treatment. The reordering depends on the initial film state and the laser irradiation conditions.
Stabilization and hyperfine characterization of metastable tetragonal ZrO2
Authors: Caracoche M. C. , Dova M. T. , López García A. R.
Published: September 2007

Hydrolyzed ZrCl4 and ZrO2 · nH2O have been used as starting compounds in a time-differential perturbed-angular correlation (TDPAC) investigation on the stabilization and thermal evolution of the metastable tetragonal form of ZrO2. This phase, of quadrupole parameters very similar to those reported for the high temperature tetragonal form, emerges at moderate temperatures previous to the monoclinic phase, when starting from hydrolyzed ZrCl4 and from ZrO2 · 2H2O treated previously at 673 K. Though in all cases zirconia appears initially as an amorphous compound characterized by unique hyperfine parameters, two different precursors have been observed to exist immediately previous to the occurrence of either the monoclinic or the metastable tetragonal crystal phases. Each of them exhibits a quadrupole frequency identical with and an asymmetry parameter higher than the ones characterizing the forthcoming corresponding crystal phases. A crystallization enthalpy of (33 ± 5) kJ/mol has been determined for the formation of the metastable tetragonal phase out of its precursor.
The preparation and processing of bulk superconducting ceramic Nd1.85Ce0.15CuO4−y
Authors: López-Morales M. E. , Savoy R. J. , Grant P. M.
Published: September 2007

We report the development of a reaction technique which yields ceramic Nd1.85Ce0.15CuO4−y with macroscopically uniform concentrations of Ce and O. Under appropriate argon annealing conditions, samples exhibiting bulk superconductivity as gauged by resistive transition width and diamagnetic shielding are obtained. In addition. metallic behavior, indicated by positive dp/dT above Tc, is obtained for the normal state.
Kinetic study and modeling of the solid-state reaction Y2BaCuO5 + 3BaCuO2 + 2CuO ⇉ 2YBa2Cu3O6.5−x + xO2
Authors: Wu Nae-Lih , Wei Ta-Chin , Hou Shau-Y , Wong S-Yen
Published: September 2007

The kinetics of the solid-state reaction Y2BaCuO5 + 3BaCuO2 + 2CuO ⇉ 2YBa2Cu3O6.5−x + xO2 was studied by using x-ray diffractometric and thermogravimetric analyses. Both analyses established that the reaction was well described by the kinetic equation: 1 − 3(1 − F)2/3 + 2(1 − F) = k0 exp(− E/RT)t, where F is the fractional conversion of a calcined powder, E is 520 kcal/molc and, for a rcactant mixture with an average particle size of 3 μm, k0 is 2.03 ⊠ 1092 min−1. An unreacted-core shrinking model was proposed to obtain the particle-size dependence of the reaction, and predicted that the pre-exponential constant k0 changed with reactant particle size by k0 = 2.03 ⊠ 1092(3/d)2 exp(4/d − 4/3), where d is the average reactant particle size in μm.
Reduced splashing effect in laser ablated superconducting thin films formed from a melt-quenched nonsuperconducting amorphous target
Authors: Agostinelli E. , Bohandy J. , Green W. J. , Kim B. F. , Adrian F. J. , Moorjani K.
Published: September 2007

Comparison of superconducting thin films of Bi–Sr–Ca–Cu–O deposited by laser ablation from a melt-quenched, amorphous, nonsuperconducting target and a polycrystalline sintered superconducting target shows that they have similar superconducting properties, but the melt-quenched target yields a much smoother film. Additionally, the melt-quenched target is much easier to prepare with target preparation time reduced by a factor of twenty-five.
Indentation load relaxation experiments with indentation depth in the submicron range
Authors: LaFontaine W. R. , Yost B. , Black R. D. , Li C-Y.
Published: September 2007

Indentation load relaxation (ILR) experiments with indentation depths in the submicron range are described. Under appropriate conditions, the ILR data are found to yield flow curves of the same shape as those based on conventional load relaxation data. Variations in flow properties as a function of depth in submicron metal films deposited on a hard substrate are detected by the experiments described.
An x-ray Fourier line shape analysis in cold-worked hexagonal magnesium base alloys
Authors: Chattopadhyay S. K. , Chatterjee S. K. , Sen Gupta S. P.
Published: September 2007

Detailed Fourier line shape analyses considering x-ray diffraction profiles from fault unaffected 10.0, 00.2, 11.0, 20.0, 11.2, and 00.4 reflections and fault affected 10.1, 10.2, 10.3, 20.1, 20.2, 10.4, and 20.3 reflections have been performed on three magnesium base hexagonal alloys used extensively in the aircraft industry. The first of the three alloys (Mg–Al–Mn, Alloy I) had the nominal composition in wt.% of Al-8.3, Mn-0.35, Si-0.2, Cu-0.12, Fe-0.2, and other 0.01; the second alloy (Mg–Zn–Mn, Alloy II) had the nominal composition in wt.% of Zn-4.0, Mn-0.15, Si-0.01, Cu-0.03, Fe-0.01, Zr-0.70, and rare earth elements-1.50; and the last of the alloys (Mg–Zn–Al, Alloy III) had the nominal composition in wt.% of Zn-4.3, Al-0.15, Mn-0.01, Si-0.03, Cu-0.01, Ni-0.005, Zr-0.6, and rare earth-1.4. The microstructural parameters determined in these analyses indicated the average domain size in alloys I, II, and III as 208 Å, 314 Å, and 400 Å, respectively. The deformation fault densities, α, in these alloy systems (∼54 ⊠ 10−3, 35 ⊠ 10−3, and 28 ⊠ 10−3, respectively, in alloys I, II, and III) were found to be appreciably high compared to the earlier work on pure magnesium (0.63 ⊠ 10−3). The deformation twin fault density, β, which was found to be negligible in pure magnesium (∼0.21 ⊠ 10−3), was found to be negative here, also indicating the negligible presence of twin faults in these alloys. These results establish that on cold work the solutes introduce deformation stacking faults in an appreciable quantity in magnesium which is not normally susceptible to faulting when in pure form. Of these three alloys, however, Alloy I (Mg–Al–Mn) was found to be the most prone to deformation faulting.
Low temperature phase separation in CeSi1.86
Authors: Madar R. , Houssay E. , Rouault A. , Senateur J. P. , Lambert B. , Meneau d'Anterroches C. , Pierre J. , Laborde O. , Soubeyroux J. L. , Pelissier J.
Published: September 2007

Samples of CeSi1.86 which exhibit Kondo behavior are shown by neutron powder diffraction and transmission electron microscopy to consist of two closely related tetragonal phases. The primary phase is of the ThSi2 structure type with some vacancies in the silicon sublattice. The second phase presents an ordering of these vacancies. These two phases coexist at low temperature, but the abundance of the second phase increases with decreasing temperature. Neutron diffraction measurements and TEM experiments show that the phase separation occurs reversibly around 260 K, in close relation with an anomaly in the transport properties. The presence of a hysteresis indicates that we are dealing with a first order transition.
Structural and chemical stability of thin films of Pt–Ga intermetallic compounds of GaAs(001)
Authors: Kim Young K. , Baugh Delroy A. , Shuh David K. , Stanley Williams R. , Sadwick Larry P. , Wang Kang L.
Published: September 2007

Nearly single-phase thin films of three different Pt–Ga intermetallic compounds have been grown on GaAs(001) by co-deposition of Pt and Ga. The resultant films have been annealed at various temperatures and then characterized using x-ray two-theta diffractometry (XRD), Auger electron spectroscopy (AES), and x-ray photoemission spectroscopy (XPS). The XRD results showed that PtGa2 and PtGa thin films are chemically stable on GaAs under one atmosphere of N2 up to 800 °C and 600 °C, respectively, but thin films of Pt2Ga react with GaAs at temperatures as low as 200 °C to form phases with higher Ga concentration PtAs2. The XRD patterns also revealed that the crystallite orientation and texture of the films were dependent on annealing temperature. Segregation of Ga to the surfaces of the films upon annealing was also observed by both AES and XPS. The results demonstrated that the as-deposited films of PtGa2 and PtGa were kinetically stabilized with respect to possible chemical reactions with the GaAs substrates that evolve gaseous As species during open system annealing.
Phase equilibria and structural chemistry in the ternary systems M–Si–N and M–B–N (M = Al, Cu, Zn, Ag, Cd, In, Sn, Sb, Au, Tl, Pb, Bi)
Authors: Weitzer F. , Remschnig K. , Schuster J. C. , Rogl P.
Published: September 2007

Phase equilibria in the ternary systems M–Si–N and M–B–N (M = Cu, Ag, Au, Zn, Cd, Al, In, Tl, Sn, Pb, Sb, and Bi) at temperatures 50–100 °C below the melting point of the metal components were investigated by means of x-ray powder analysis and are represented in the form of isothermal sections. No ternary compound formation was observed in any of the combinations M–Si–N and M–B–N. Silicon nitride and boron nitride, respectively, coexist with all metals investigated and with all binary compounds stable at the chosen temperatures. From unit cell dimensions negligible mutual solid solubilities are indicated between Si3N4 or BN and the metal components.
Preparation of perovskite oxides for high Tc superconductor substrates
Authors: Brandle C. D. , Fratello V. J.
Published: September 2007

A variety of materials of the general type A2BB′O6 that have an ordered perovskite structure have been prepared and examined as possible substrate candidates for high Tc superconducting films. Materials containing either Ca or Sr as the A cation and either Ga or Al in combination with Nb or Ta as the B and B′ cations have been shown to be congruent melting compounds. These compounds have melting points easily accessible using conventional rf heating techniques and are therefore materials that could possibly be grown in bulk form using the Czochralski growth technique.
High temperature extrusion behavior of fine-grain ZrO2
Authors: Kellett B. J.
Published: September 2007

High temperature forming of a fine-grain ceramic is demonstrated by a series of extrusion experiments with fine-grain ZrO2, 3 mole% Y2O3. Piston velocities, ranging up to 5 mm/min (for a die with an initial diameter of 30 mm and a final diameter of 10 mm), can be achieved at 1500 °C with piston stresses of 70 MPa and graphite paper lubrication. These piston velocities are consistent with a calculation based on the creep behavior of this ceramic. The calculation is based on a model of material flow through the die, consistent with experiments involving internal markers of graphite foil.
The infrared transmission spectra of four silicate glasses before and after exposure to water
Authors: Husung Roy D. , Doremus Robert H.
Published: September 2007

The infrared transmission spectra of four silicate glasses were investigated. By using blown glass films, 1–2 μm thick, detailed infrared transmission spectra were generated over the 4000–180 cm−1 range, both before and after the films were exposed to water. The water had little effect on the spectra of the 70SiO2–20Na2O–10Al2O3 (mol %) and Pyrex compositions, but had a large effect on the spectra of the 70SiO2–30Na2O (mol %) and Corning 015 compositions. The Si–O nonbridged stretching band at ∼950 cm−1 and a largely overlooked bending band at ∼600 cm−1 were the bands most sensitive to hydration in the 70/30 and 015 compositions. Changes were also seen in the Si–O–Si bridged stretching bands at ∼1050 cm−1 and ∼770 cm−1. The water, however, had no effect on the dominant Si–O–Si bending band at 460 cm−1. It was also discovered that the 70/30 and 015 films reacted with the atmosphere to form a carbonate layer on their surface. This carbonate accounted for the 1450 cm−1 and 230 cm−1 bands seen in their infrared transmission spectra.
Adhesion and short-range forces between surfaces. Part II: Effects of surface lattice mismatch
Authors: McGuiggan Patricia M. , Israelachvili Jacob N.
Published: September 2007

The adhesion forces and interaction potentials between two mica surfaces as a function of the orientation (twist angle) of their surface lattices are reported. The forces were measured in air, in water, and in an aqueous KCl solution where oscillatory structural forces are present. In air, the adhesion is relatively independent of the twist angle θ in the range −10° < θ < +10° due to a 0.4 nm thick amorphous layer at the interface. In water, apart from a relatively angle-independent baseline adhesion, a sharp adhesion peak (energy minimum) occurs at θ = 0°, corresponding to maximum alignment of the surface lattices. As little as ±1° away from this peak the energy decreases by 50%. In aqueous KCl solution, due to potassium ion adsorption the water between the surfaces becomes ordered, resulting in an oscillatory structural force where the adhesive minima occur at discrete separations corresponding to an integral number of water layers. The adhesion energies corresponding to the first three potential minima were angle dependent near θ = 0° (again decreasing by 50% at ±1° away from θ = 0°). The repulsive maxima were also affected near θ = 0°. The results show that the whole interaction potential between two surfaces in liquids depends on the orientation of the surface lattices, and that these effects can extend at least four molecular layers. We discuss the consequences of these findings for material properties such as grain boundary energies, cracks, and friction.
Quantitative topographic analysis of fractal surfaces by scanning tunneling microscopy
Authors: Mitchell Morgan W. , Bonnell Dawn A.
Published: September 2007

The applicability of models based on fractal geometry to length scales of nanometers is confirmed by Fourier analysis of scanning tunneling microscopy images of a sputter deposited gold film, a copper fatigue fracture surface, and a single crystal silicon fracture surface. Surfaces are characterized in terms of fractal geometry with a Fourier profile analysis, the calculations yielding fractal dimensions with high precision. Fractal models are shown to apply at length scales to 12 Å, at which point the STM tip geometry influences the information. Directionality and spatial variation of the topographic structures are measured. For the directions investigated, the gold and silicon appeared isotropic, while the copper fracture surface exhibited large differences in structure. The influences of noise in the images and of intrinsic mathematical scatter in the calculations are tested with profiles generated from fractal Brownian motion and the Weierstrass-Mandelbrot function. Accurate estimates of the fractal dimension of surfaces from STM data result only when images consist of at least 1000–2000 points per line and 1/f-type noise has amplitudes two orders of magnitude lower than the image signal. Analysis of computer generated ideal profiles from the Weierstrass-Mandelbrot function and fractional Brownian motion also illustrates that the Fourier analysis is useful only in determining the local fractal dimension. This requirement of high spatial resolution (vertical information density) is met by STM data. The fact that fractal models can be used at lengths as small as nanometers implies that continued topographic structural analyses may be used to study atomistic processes such as those occurring during fracture of elastic solids.
Diamond polytypes and their vibrational spectra
Authors: Spear K. E. , Phelps A. W. , White W. B.
Published: September 2007

A series of diamond polytype structures are described and their IR and Raman vibrational modes predicted. The diamond polytypes are analogous to the well-known silicon carbide polytypes. The intermediate 6H diamond polytype was recently identified by single crystal electron diffraction of vapor precipitated diamond powder. In addition, end member polytypes of 3C (cubic diamond) and 2H diamond (hexagonal lonsdaleite) have been previously established, and polytypes such as 4H, 8H, 15R, and 21R diamond are predicted, but may be difficult to isolate and identify. The various diamond polytype structures differ only in the stacking sequences of identical puckered hexagonal carbon layers. These identical carbon layers lie parallel to the cubic 3C {111} and the hexagonal 2H {001} planes. A new method for uniquely labeling the structural layers in the polytype stacking sequences is presented. Factor group analysis was used to determine the IR and Raman selection rules for five diamond polytypes with structures intermediate between those of end members diamond and lonsdaleite. Brillouin zone folding techniques were used to determine band positions, in analogy with analyses of SiC polytypes discussed in the literature. The results predict that (i) all diamond polytypes are Raman active, (ii) limiting polytypes 3C and 2H are not IR active, and (iii) polytypes 4H, 6H, 8H, 15R, and 21R have IR active modes.