bluuebunny/crossref_metadata_2025 huggingface dataset:
The observation of various grain boundary atomic structures in Au by high-resolution electron microscopy
Authors: Krakow William , Smith David A.
Published: September 2007

A number of grain boudary structures prepared from evaporated Au thin films have been investigated using very high-resolution electron microscopy. Particular emphasis has been placed on analyzing [110] tilt boundaries with both low- and high-angle misorientations. Observations of the atomic positions at dislocation cores and close-packed polyhedral shapes at the interface have been made. Symmetric boundaries have been observed as well as interfacial regions where the grain orientations deviate from perfect coincidence and hence the boundary structure exhibits perturbations to the regular polyhedron stacking. The special case of “plane coalescence” has also been observed, as well as the boundary splitting near a hole. The fabrication and observation of a generalized boundary, which cannot be classified as a tilt structure, will also be demonstrated.
Carbon effects in rapidly solidified Ni3Al
Authors: Huang S. C. , Briant C. L. , Chang K.-M. , Taub A. I. , Hall E. L.
Published: September 2007

The effect of carbon on the mechanical properties of ordered, face-center-cubic Ni3Al has been studied. It has been found that carbon provides no ductihzation to the intermetallic compound, but exerts a large solid solution strengthening effect. The strengthening rate measured is Δσy/ΔC∼0.5G per atom percent carbon, where G is the Ni3Al shear modulus. Auger analysis and lattice parameter measurements were also carried out. The results are discussed with respect to the nature of carbon in grain boundary regions and in the bulk.
Dynamic cleavage in ductile materials
Authors: Lin I.-H. , Thomson R. M.
Published: September 2007

Ductile materials are found to sustain brittle fracture when the crack moves at high speed. This fact poses a paradox under current theories of dislocation emission, because even at high velocities, these theories predict ductile behavior. A theoretical treatment of time-dependent emission and cleavage is given which predicts a critical velocity above which cleavage can occur without emission. Estimates suggest that this velocity is in the neighborhood of the sound velocity. The paper also discusses the cleavage condition under mixed mode loading, and concludes that the cleavage condition involves solely the mode I loading, with possible sonic emission under such loadings
Oxidation of SiC powder by high-temperature, high-pressure H2O
Authors: Yoshimura Masahiro , Kase Jun-ichiro , Sōmiya Shigeyuki
Published: September 2007

The reaction between SiC powder and H2O has been studied at 400°–800 °C under 10 and 100 MPa. Silicon carbide reacted with H2O to yield amorphous SiO2 and CH4 by the reaction SiC + 2H2O→SiO2 + CH4 above 500 °C. Cristobalite and tridymite crystallized from amorphous silica after the almost complete oxidation of SiC above 700 °C. The oxidation rate, as calculated from the weight gain, increased with temperature and pressure. The Arrhenius plotting of the reaction rate based on a Jander-type model gave apparent activation energies of 167–194 kJ/mol. Contrasted with oxidation in oxidative atmosphere, oxidation in H2O is characterized by the diffusion of H2O and CH4 in an amorphous silica layer where the diffusion seemed to be rate determining. Present results suggest that the oxidation of SiC includes the diffusion process of H2O in silica layers when atmospheres contain water vapor.
Influence of toughness on Weibull modulus of ceramic bending strength
Authors: Kendall K. , Alford N. McN. , Tan S. R. , Birchall J. D.
Published: September 2007

It is demonstrated both theoretically and experimentally that fracture toughness does not directly influence the Weibull modulus of ceramic bending strength for materials that obey the Griffith criterion for crack propagation. Weibull modulus remains unchanged as toughness is increased. However, toughness variations with crack length do affect the Weibull modulus. Thus materials that display R-curve behavior or Dugdale character give an increased Weibull modulus and appear more reliable.
Dynamic strain aging and serrated flow in MnO
Authors: Goretta K. C. , Routbort J. L. , Bloom T. A.
Published: September 2007

The effects of aging on the upper yield stress τupand serrated flow have been studied in MnO single crystals at 900 °C for oxygen partial pressuresρO2of 10−11and 10−7Pa. Aging initially increases τupas a consequence of segregation of aliovalent impurities to dislocations for bothρO2values. For long aging times andρO2= 10-11Pa, serrated flow accompanied by solute softening is observed. The data fit predictions of a Portevin-Le Chatelier model for serrations, but with impurity atmospheres causing softening instead of hardening. This is believed to result from changes in local defect equilibria caused by segregation of impurities with valences greater than two to dislocations.
Nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation
Authors: Larson B. C. , Tischler J. Z. , Mills D. M.
Published: September 2007

We have used the pulsed time structure of the Cornell High-Energy Synchrotron Source (CHESS) to carry out a nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation. Time-resolved temperature distributions and interfacial overheating and undercooling were measured on 〈111〉 and 〈100〉 silicon during 25 ns UV laser pulses through the analysis of thermal expansion induced strain. The temperature gradients were found to be > 107 K/cm at the liquid-solid interface and the temperature distributions have been shown to be in agreement with numerical heat flow calculations for these laser conditions. The combined overheating and undercooling (during ∼ 10 m/s melting and ∼ 6 m/s regrowth) was measured to be 110 ± 30 K on 〈111〉 oriented silicon and 50 ± 25 K on 〈100〉 silicon. These values have been interpreted in terms of velocity coefficients of overheating and undercooling.
Knoop hardness anisotropy on {001} faces of germanium and gallium arsenide
Authors: Roberts S. G. , Warren P. D. , Hirsch P. B.
Published: September 2007

Knoop hardness measurements have been carried out as a function of azimuthal angle and temperature (in the range 20°–440°C) on {001} faces of n-type, p-type, and intrinsic Ge and GaAs. The degree of hardness anisotropy shown increases with increasing temperature and for Ge is undetectable below a certain temperature which depends on doping. In GaAs, asymmetry in hardness between [110] and [110] directions was found at high temperatures. A new model of hardness anisotropy has been developed, based on detailed modeling of the plastic zone. This relates the hardness to the degree of workhardening in different regions of the plastic zone. Using this model, detailed explanations are given of the hardness anisotropy behavior and of the plastic recovery around indentations.
Twinning and crystal slip in black monoclinic ZnP2
Authors: Fleet Michael E. , White Joseph C.
Published: September 2007

MonoclinicβZnP2(black ZnP2) single crystals, synthesized in the presence of excess P, contain regions of polysynthetic lamellar-twinned structure, with dislocations and stacking fault-like features. The twin law is a* twin axis, (100) composition plane: (100) is also the slip plane. The twin composition plane migrates across (100) lattice fringes. In the revisedβZnP2crystal structure, Zn(1) and P(4) positions are related across a (100) twin composition plane at x = 0.84 by two twin operations, with axes throughis also a possible slip plane, with three partial dislocations, ½[001], ½[001], and ½[001]. A third possible twin operation relates Zn(2) and P(1) positions across a (100) twin plane atx= 0.5, with twin axis throughAll twin and slip operations result in very little distortion in nearest- and nextnearest-neighbor coordination geometries. Twin and stacking fault mistakes may be facilitated by approach of the monoclinic cell parameter ratioc[α sin(β—π/2)] to 4 (which yields a pseudo-orthorhombic unit cell) and by Zn1-xP2nonstoichiometry.
Temperature dependence of tracer diffusion coefficients in polystyrene
Authors: Green Peter F. , Kramer Edward J.
Published: September 2007

The temperature dependence of the tracer diffusion coefficient D* of long deuterated polystyrene (d-PS) chains of molecular weight M>Mc, where Mc is the critical molecular weight for entanglement, diffusing into highly entangled PS matrices, each of molecular weight P = 2×107, is studied using forward recoil spectrometry. It is found that the temperature dependence of D*/T, reflected primarily in the monomeric friction coefficient, is accurately described by a Vogel equation. The constants that are used to fit these results are independent of M and are the same as those used to fit the temperature dependence of the zero shear rate viscosity of polystyrene.
Metal film deposition by laser breakdown chemical vapor deposition
Authors: Jervis T.R. , Newkirk L.R.
Published: September 2007

Dielectric breakdown of gas mixtures can be used to deposit thin films by chemical vapor deposition with appropriate control of flow and pressure conditions to suppress gas-phase nucleation and particle formation. Using a pulsed CO2 laser operating at 10.6 μ where there is no significant resonant absorption in any of the source gases, homogeneous films from several gas-phase precursors have been sucessfully deposited by gas-phase laser pyrolysis. Nickel and molybdenum from the respective carbonyls representing decomposition chemistry and tungsten from the hexafluoride representing reduction chemistry have been demonstrated. In each case the gas precursor is buffered with argon to reduce the partial pressure of the reactants and to induce breakdown. Films have been characterized by Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, pull tests, and resistivity measurements. The highest quality films have resulted from the nickel depositions. Detailed x-ray diffraction analysis of these films yields a very small domain size consistent with the low temperature of the substrate and the formation of metastable nickel carbide. Transmission electron microscopy supports this analysis.
Mechanisms of the electron irradiation-induced amorphous transition in intermetallic compounds
Authors: Pedraza D.F.
Published: September 2007

A buildup of radiation-induced lattice defects is proposed as the cause for lattice instability that can give rise to a crystalline-to-amorphous transition. An analysis of published experiments on intermetallic compounds suggests that, when amorphization takes place, no microstructural evolution based on the aggregation of like-point defects occurs. This observation leads us to suggest that buildup of a different type of defect, which will destabilize the crystal, should occur. We thus propose that an interstitial and a vacancy may form a complex, giving rise to a relaxed configuration exhibiting a sort of short-range order. Two mechanisms of complex formation are analyzed, one diffusionless (limited by the point defect production rate) and the other temperature dependent. The amorphization kinetics as a function of temperature, dose, and point defect sink strength are studied. Theoretical predictions on the amorphization dose as a function of temperature are made for the equiatomic TiNi alloy and compared with available experimental results.
Electronic transport and microstructure in MoSi2 thin films
Authors: Martin T.L. , Mahan J.E.
Published: September 2007

Molybdenum disilicide thin films having the tetragonal crystal structure were prepared by furnace reaction of ion-beam-sputtered molybdenum layers with silicon substrates. The room temperature intrinsic resistivity is ∼20 μΩ cm. The Hall effect indicates predominantly hole conduction. Geometrical magnetoresistance measurements provide a carrier mobility estimate of 90 cm2 /V.s at room temperature. The Hall mobility is much less than this; the large difference between the two mobility values suggests multiband conduction. An isotropic, degenerate, twoband model may be fitted to the data with a comparatively low majority carrier concentration (holes) of ∼ 1.5 × 1021 cm−3 Regarding the effects of microstructure on transport, the residual resistivity for films formed on 1-0-0 silicon wafers is much greater than for those formed on an (LPCVD) polysilicon layer: 92 vs 29 μΩ cm, respectively. A correlation with average grain size for the two sample types suggests that grain boundary scattering is the principal cause of the residual resistivity. electronic materials; electrical properties; thin film
On the kinetics of thermal donor formation in silicon
Authors: Borenstein Jeffrey T. , Peak David , Corbett James W.
Published: September 2007

A model for the kinetic growth of oxygen-related thermal donors in Czochralski silicon at about 450°C is presented. The model, which is based on the work of Suezawa and Sumino, derives forward reaction rates for the electrically active species by comparing analytic expressions for the early-time annealing kinetics with the infrared electronic absorption data. The analytic expressions, which are independent of the chemical structure of each species, result from three assumptions: (1) the donor defects beyond the first donor species (TD-1) are chemically stable at the donor formation temperature, (2) the reactions for the TD-1 and those electrically inactive clusters smaller than TD-1 are in equilibrium, and (3) the oxygen interstitial concentration remains constant for short annealing times. The parametrized values of the rate constants indicate that the forward rates of reaction vary widely between species, with a sharp peak at the reaction which takes the first electrically active species to the second. If the rate constants are taken to be of the form K = 4πRD, where R is the capture radius for the given forward reaction and D represents the effective diffusion coefficient, then the variation between reaction constants may be associated with differences in capture radii between species, with the diffusion coefficient assumed to be the value determined by Stavola et al. [Appl. Phys. Lett. 42, 73 (1983)] for “as-provided” material, which has an activation energy of 1.95 eV. The model is successfully applied to the two available sets of infrared absorption data (the Oeder-Wagner and Suezawa-Sumino data) when differences in the annealing temperatures and initial oxygen concentrations are taken into account. The best-fit parameters found by fitting the analytic expressions are then applied to a set of chemical reaction equations which characterize the formation rates of specific oxygen aggregates. The use of such a set of coupled, nonlinear differential equations, which must be solved numerically, introduces free parameters for the oxygen clusters smaller than the first thermal donor. It is shown that the assignments of a thermal donor core containing two, three, four, or five oxygen atoms are all capable of fitting the experimental data. This result indicates that a best fit to the kinetic data cannot be used to argue for a specific thermal donor core. Finally, the authors discuss possible mechanisms for the enhanced values of the capture radii.
The growth of AuGa2 thin films on GaAs(001) to form chemically unreactive interfaces
Authors: Lince Jeffrey R. , Thomas Tsai C. , Stanley Williams R.
Published: September 2007

Thin AuGa2 films were grown by codeposition from separate Au and Ga evaporation sources on clean GaAs(001) substrates in ultrahigh vacuum, and were studied by Auger electron spectroscopy, electron energy-loss spectroscopy, low-energy electron diffraction, scanning electron microscopy, and x-ray diffractometry. The morphology and crystallinity of the AuGa2 were highly dependent upon the film deposition and annealing history. Films grown on room-temperature substrates were continuous, specular, and polycrystalline, but the dominant orientation was with the (001) planes of the crystallites parallel to the substrate surface. Annealing to temperatures between 300°and 480°C caused the film to break up and coalesce into rectangular crystallites, which were all oriented with (001) parallel to the surface. An anneal to 500°C, which is above the AuGa2 melting point, resulted in the formation of irregular polycrystalline islands of AuGa2 on the GaAs(001) substrate. No interface roughening or chemical reactions between the film and substrate or interface were observed for even the highest-temperature anneals.
Growth and photoluminescence characterization of ZnSe layers grown on (100)Ge by molecular beam epitaxy
Authors: Park R.M. , Mar H.A.
Published: September 2007

ZnSe layers have been grown on (100)-oriented Ge substrates by molecular beam epitaxy for the first time. The optimum in-situ Ge substrate preparation technique was found to consist of argon-ion sputtering at room temperature followed by annealing at ∼400°C. This cleaning technique provided Ge surfaces which exhibited (2X2) surface reconstruction as observed by reflection high-energy electron diffraction and which had O and C contamination levels below the detection limit of the Auger electron spectroscopy system. ZnSe layers grown on argon-ion sputtered and annealed (100)Ge substrates using a variety of substrate temperatures and Zn to Se beam pressure ratios were characterized by 4.2 K photoluminescence (PL) measurements. The highest quality layers as judged by PL analysis were grown in the substrate temperature range, 310–350°C, with a Zn to Se beam pressure ratio around unity. ZnSe layers grown under these conditions exhibited a dominant donor-bound exciton peak at 2.7976 eV having a minimum linewidth of ∼1.1 meV.
Preparation and crystal properties of thin InSb films for highly sensitive magnetoresistance elements
Authors: Isai Masaaki , Fukunaka Toshiaki , Ohshita Masahide
Published: September 2007

High electron mobility thin InSb films were prepared on mica substrates by conventional vacuum evaporation of InSb to obtain highly sensitive magnetoresistance (MR) elements. The 0.15–0.5 μm thick InSb films were prepared in the present work. An optimum evaporation programming pattern was obtained. The crystal properties of these InSb films of 0.2–0.3 μm were investigated using a transmission electron microscope. It was shown that films thinner than 0.2 μm were semitransparent and consisted of [111] oriented single-crystal films. The 0.15–0.3 μm thick InSb films are therefore most useful for low-cost MR elements because of their high element resistance, small temperature coefficient of electron mobility, and high sensitivity.
Radiation-induced implantation of polymeric films in metallic substrates
Authors: Ferralli M.W. , Luntz M.
Published: September 2007

Implanted, polymeric films have been produced by accelerator-ion-beam irradiation of metallic substrates immersed in hydrocarbon gases. Typical substrates include silver, aluminum, and steel; hydrocarbon gases include 1,3 butadiene and ethylene at 6.6 Pa pressure; ion beams employed include singly ionized H, He, and Ar at 30 keV. Experimental procedures and corrosion-resistance properties of the films are reviewed (each discussed elsewhere). A theory of the film-formation process is presented. It is concluded that the films form as the result of a two-stage process: glow-discharge adhesion and polymerization followed by radiation-induced implantation resulting from collisional recoil and substrate sputtering.
The effect of lateral crack growth on the strength of contact flaws in brittle materials
Authors: Cook Robert F. , Roach David H.
Published: September 2007

The effect of lateral cracks on strength controlling contact flaws in brittle materials is examined. Inert strength studies using controlled indentation flaws on a range of ceramic, glass, and single crystal materials reveal significant increases in strength at large contact loads, above the predicted load dependence extrapolated from strength measurements at low indentation loads. The increases are explained by the growth of lateral cracks decohesing the plastic deformation zone associated with the contact from the elastically restraining matrix, thereby reducing the residual stress field driving the strength controlling radial cracks. A strength formulation is developed from indentation fracture mechanics which permits inert strengths to be described over the full range of contact loads. The formulation takes account of the decreased constraint of the plastic deformation zone by lateral crack growth as well as post-contact nonequilibrium growth of the radial cracks. Simple extensions permit the strengths of specimens controlled by impact flaws to be described, as well as those failing under nonequilibrium (fatigue) conditions. The implications for materials evaluation using indentation techniques are discussed and the dangers of unqualified use of strength measurements at large indentation loads pointed out. The work reinforces the conclusion that a full understanding of the residual stress field at dominant contact flaws is necessary to describe the strength of brittle materials.
High-resolution electron microscopy of amorphization of Cu4 Ti3
Authors: Luzzi D.E. , Meshii M.
Published: September 2007

The electron irradiation-induced, crystalline-to-amorphous transition was studied in the intermetallic compound Cu4Ti3 by high-resolution electron microscopy. Using highresolution maps from the crystalline region into the amorphized region, the amorphization process and the amorphous structure were examined. The extent of chemical order in crystalline regions just prior to amorphization was studied by simultaneously imaging superlattice and fundamental lattice fringe contrast. The chemical order continuously decreased in these regions but faint superlattice contrast was recognized as long as the crystalline feature remained on the image, supporting the theory that chemical disordering is the major driving force for amorphization. The amorphization process appears to be evolutionary, leading to a nanocrystalline type of amorphous structure. A model of the amorphization process is proposed based on the present results and those from previous studies.
Surface segregation in a dilute copper–silver alloy
Authors: Bronner S.W. , Wynblatt P.
Published: September 2007

The equilibrium surface composition of a Cu-0.83 at. % Ag alloy has been studied over the range from 600°–400°C. Above 450°C the alloy consists of a single phase, whereas below that temperature the material separates into copper-rich and silver-rich phases. The kinetics of equilibration appear to be controlled by grain boundary diffusion, leading to more rapid equilibration than expected on the basis of lattice diffusion-controlled kinetics. In the single-phase regime, silver segregates to the surface with an average enthalpy of segregation of −24 kJ/mol and an entropy of segregation of 0.94 J/mol K, and displays a trend of increasing equilibrium silver surface concentration with decreasing temperature. Theoretical estimates of the enthalpy of segregation yield the somewhat more negative values of −60 and −47 kJ/mol, respectively. In the two-phase regime, the surface continues to be enriched in silver, but the silver surface concentration decreases with decreasing temperature as a result of the rapidly decreasing equilibrium solubility of silver in copper.
Microstructure and mechanical properties of synthetic opal: A chemically bonded ceramic
Authors: Simonton Thomas C. , Roy Rustum , Komarneni Sridhar , Breval Else
Published: September 2007

Among chemically bonded ceramics (i.e., those not utilizing thermally activated diffusion for bonding) the French synthetic opal gilsonite provides an excellent existence theorem. By using optical, scanning, and electron microscopy techniques and x-ray, chemical, and differential thermal analyses, it is shown for the first time that the synthetic opal is composed of two separate phases: noncrystalline silica and crystalline (tetragonal) zirconia balls. The zirconia balls with sizes ranging from 7-50 nm appear to be present in an extraordinary regular “lattice” in the void spaces of the silica “balls” of mean size 200 nm. A comparison of the fracture toughness, Kic, data for the gilsonite and natural opal shows that the former is significantly tougher than the latter. The KIC values for gilsonite fall between those of the Corning 0337 Glass Ceramic and Wesgo Al-500 alumina, showing that surprisingly tough ceramics can be made near room temperature by resorting to chemical bonding.
Cesium and bromine doping into hexagonal boron nitride
Authors: Sakamoto M. , Speck J.S. , Dresselhaus M.S.
Published: September 2007

Using a two-zone method, the possible formation of an intercalation compound of hexagonal boron nitride (BN) with Cs and Br2 was investigated. Only a few percent weight increase was observed by doping BN with Cs and Br2. The electron paramagnetic resonance (EPR) signal was significantly modified by Cs doping, which is attributed to the reaction between the Cs atoms and spin resonance centers (N vacancies) in BN; no change in the EPR spectra was observed with Br2 doping. However, the deep blue colored Cs-BN complex reported by Mugiya and co-workers was not obtained with the two-zone method. Though no evidence of systematic intercalation reaction in BN was observed in contrast to graphite host materials, intercalation islands induced by the introduction of Cs atoms were suggested by the transmission electron microscopy (TEM) observations.
Internal gettering heat treatments and oxygen precipitation in epitaxial silicon wafers
Authors: Wijaranakula W. , Burke P.M. , Forbes L.
Published: September 2007

As-received P/P + (100) epitaxial silicon wafers were heat treated using the one-, two-, and three-step internal gettering heat treatment cycles in wet oxygen, dry oxygen, and nitrogen ambients. The results indicate that ambients have an effect on the growth of bulk defects and denuded zone formation in the epitaxial silicon wafers.
Effect of pre- and postepitaxial deposition annealing on oxygen precipitation in silicon
Authors: Wijaranakula W. , Burke P.M. , Forbes L. , Matlock J.H.
Published: September 2007

Substrate material used for fabrication of P/P + epitaxial silicon wafers was preannealed at 650 °C in nitrogen ambient prior to the epitaxial deposition process for various times up to 300 min. The substrate material originated from a characterized crystal ingot. The results show that annealing before epitaxial deposition can preserve oxide precipitate nuclei from dissolution during the epitaxial deposition process. Additional postepitaxial annealing at 750 °C further enhances the growth of bulk defects.
Strain measurement in heteroepitaxial layers—Silicon on sapphire
Authors: Vreeland Thad
Published: September 2007

An x-ray diffraction technique is presented for the determination of the strain tensor in an epitaxial layer grown on a crystallographically distinct substrate. The technique utilizes different diffracting planes in the layer and in a reference crystal fixed to the layer, and is illustrated by application to an ∼4000 Å (001) silicon layer grown on a (01$\overline 1$2 sapphire wafer. The principal strains were measured, and the measured strain normal to the layer was found to agree with the normal strain calculated from the measured in-plane strains within the experimental uncertainty of strain measurement. The principal stresses in the plane of the silicon film, calculated from the measured strains were −0.92 ± 0.16 GPa in the [100] direction and −0.98 ± 0.17 GPa in the [010] direction.
Review: The nucleation of disorder
Authors: Cahn R.W. , Johnson W.L.
Published: September 2007

Four types of phase transformation that involve the conversion of crystalline phases into more disordered forms are reviewed: melting, disordering of superlattices, amorphization by diffusion between crystalline phases, and irradation amorphization. In the review emphasis is placed on evidence for the heterogeneous nucleation of the product phases; in this connection, the role of surfaces, antiphase domain boundaries, dislocations, vacancies, and grain boundaries is specifically discussed. All of these features have been either observed, or hypothesized, to play a role as heterogeneous nucleation sites in one or more of the four transformations. An attempt is made to draw parallels between nucleation mechanisms in the various processes.
Thin-film reactions of Au with Ti, Zr, V, and Nb
Authors: Colgan E. G. , Mayer J. W.
Published: September 2007

The thin-film interactions of Au with Ti, Zr, V, and Nb have been investigated between 350C and 700°C with Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD). Initially the most Au-rich phase is formed, except. with V, and it is followed sequentially by the more metal-rich ones in an increasingly layer-by-layer fashion. For Au reactions on Ti and Nb, all the intermetallic phases on the phase diagrams were observed. In the formation of Au4Ti, Au is the dominant moving species.
Microstructure and behavior of laser-mixed Cr/Ni films on Cu alloys
Authors: Draper C. W. , Franey J. P. , Gibson J. M. , Graedel T. E. , Jacobson D. C. , Kammlott G. W. , Poate J. M.
Published: September 2007

Deposited thin films of Cr and Ni on Cu substrates have been melted and intermixed with a frequency-doubled Q-switched Nd:YAG laser. The laser pulses melt the thin films and a shallow portion of the substrate. Resolidification interface volocities are on the order of 1–10 m s−1. Rutherford backscattering, Auger spectroscopy, and energy dispersive x-ray mapping have been used to characterize the elemental distribution. Channeling and transmission electron microscopy were used to investigate the microstructure of the surfaces produced. In contrast to the binary Cr–Cu system, where extended solid solutions are produced, the Cr–Ni–Cu system results in a metallic glass surface. We have found that these metallic glass surfaces, which have been dubbed “stainless coppers,” exhibit excellent hydrogen sulfide corrosion resistance. Their contact resistance is low and stable over long periods of time and through tens of thousands of electronic dial switching cycles.
Reversible structural relaxation in Fe–B metallic glasses
Authors: Altounian Z. , Strom-Olsen J. O. , Olivier M.
Published: September 2007

Relaxation effects in Fe–B metallic glasses have been studied through measurements of the Curie temperature (Tc) and changes of enthalpy. A monotonic increase inTcwith annealing temperature is observed for all compositions due to irreversible structural relaxation. This increase continues until the start of surface/bulk crystallization. The observed decrease inTc, upon further annealing is attributed to the strain introduced in the partially glassy system, which masks any evidence for reversible structural relaxation. Enthalpy measurements do show a small reversible structural relaxation. The magnitude of the effect is about a factor of 6 smaller than in ternary metalloid-containing glasses.
Protons and deuterons in stoichiometric and nonstoichiometric MgAl2O4
Authors: González R. , Chen Y. , Barhorst J. F. , Tsang K. L.
Published: September 2007

The OH− and OD− vibrational frequencies in stoichiometric and nonstoichiometric MgAl2O4 were measured. The nonstoichiometric material had a Al/Mg ratio of 7. The diffusion coefficient of deuterons in the nonstoichiometric material at 1600 K is about 6 ± 3 ⊠ 10−8 cm2/s. Deuterons can readily be swept out by applying an electric field at temperatures above 1000 K.
Semiconducting CsMo4−x O12(x≍0.13): Room temperature crystal structure and resistivity anisotropy of a new alkali molybdenum bronze
Authors: Abrahams S. C. , Marsh P. , Schneemeyer L. F. , Rice C. E. , Spengler S. E.
Published: September 2007

Cesium molybdenum bronze, CsMo4xO12, is a recently discovered highly anisotropic semiconductor that crystallizes in the monoclinic system with space group C2/m and four formulas in the unit cell. The lattice constants at 295 K are a = 19.063(5), b = 5.5827(23), c = 12.1147(23) Å, and β = 118.94(2)°. The integrated intensities of 13.529 reflections within a full sphere of reciprocal space with radius (sin θ)/λ≤0.75 Å−1 were measured on a CAD-4 diffractometer with MoKα radiation, resulting in 12 553 reflections above background. Correction and averaging in C2/m gave 1923 significant and independent structure factors, for an internal unweighted agreement factor of 0.0288. The crystal structure was solved from the Patterson function and Fourier series and refined by the method of least squares. The Cs atoms occupy two different sites; both, as well as the nine independent O atom sites, are fully occupied, but the four independent Mo atom sites contain significant Schottky defects, with x = 0.132(8) in the chemical formula. All metal atoms undergo significant anharmonic motion. The final agreement factor R = 0.0269, Two Mo atoms are tetrahedrally, the other two octahedrally, coordinated. The average tetrahedral Mo–O distance is 1.761 Å, the octahedral distance is 1.950 Å. Bond length–bond strength considerations suggest that Mo6+ ions (almost) completely occupy the tetrahedral sites whereas the octahedral sites are (almost) half occupied by Mo6+, half by Mo5+ ions, resulting in charge balance. Infinite polyhedral sheets of corner-sharing Mo–O octahedra and tetrahedra form normal to the a axis, separated by linear arrays of Cs+ ions. The resistivity in this and other low-dimensional alkali molybdenum bronzes is a minimum (10−1–10−2 Ω cm) in the direction along which both corner-sharing octahedra, and the shortest contacts between cations arranged in infinite chains, form. The resistivity normal to the polyhedral sheets is about 2 orders of magnitude greater, at ∼ 10 Ω cm.
Interfacial overheating during melting of Si at 190 m/s
Authors: Tsao J. Y. , Peercy P. S. , Thompson Michael O.
Published: September 2007

An upper limit is placed on the overheating at the liquid/solid interface during melting of (100) Si at high interface velocity. The limit is based on an energy-balance analysis of melt depths measured in real time during pulsed-laser melting of Si on sapphire. When combined with previous measurements of the freezing kinetics of Si, this limit indicates that the kinetics of melting and freezing are nonlinear, i.e., the undercooling required to freeze at modest (15 m/s) velocities is proportionately much greater than the overheating required to melt at high (190 m/s) velocities.
Multitechnique surface spectroscopic studies of plasma-modified polymers II: H2O/Ar plasma-modified polymethylmethacrylate/polymethacrylic acid copolymers
Authors: Hook Thomas J. , Gardella Joseph A. , Salvati Lawrence
Published: September 2007

Results from the x-ray photoelectron spectroscopy (XPS or ESCA), ion scattering spectroscopy (ISS or LEIS), and Fourier transform infrared spectrometry (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate)/poly (methacrylic acid) (PMMA/PMAA) copolymer films. Analyses of the unmodified PMMA/PMAA copolymer series, via ESCA, ISS, and FTIR, established the surface composition and functionality of the PMMA/PMAA copolymers before the H2O/Ar rf-plasma treatment was employed. The ESCA, ISS, and FTIR analysis of these modified PMMA/PMAA copolymers show that surface modification over a limited depth (50–200 Å) has occurred. The composition, bonding, and functionality changes of the surfaces are discussed. A two-step modification mechanism (surface reduction of the PMMA/PMAA copolymer followed by H2O adsorption) is proposed to interpret the spectroscopic results.
A study of the thermodynamics of the crystalline-to-amorphous transformation in Zr-based hydrides by means of thermal analysis
Authors: Yeh X. L. , Cotts E. J.
Published: September 2007

Amorphous Zr–Rh and Zr–Pd hydrides are prepared both by hydriding metallic glasses and by hydriding metastable, polycrystalline fcc alloys. The thermal stabilities of the amorphous hydrides produced by these two distinct methods are examined by means of differential scanning calorimetry and are found to be similar. The enthalpy difference between the fcc phase and the amorphous phase of Zr81Rh19 is determined to be 0.6 kcal/mol. The thermal stability of Zr–Rh hydrides as a function of hydrogen concentration is investigated.
Glass corrosion in ambient temperature lithium battery headers
Authors: Bunker Bruce C. , Douglas Sally C. , Quinn Rod K.
Published: September 2007

During high-temperature storage, glass corrosion in glass-to-metal feedthroughs can limit the lifetimes of lithium batteries designed to operate at ambient temperatures. Ampule tests have been conducted to simulate glass corrosion for Li/So2, Li/SOCl2, and Li/SOCl2 + BrCl batteries. In all lithium battery systems tested, lithium metal has been identified as the source of glass corrosion. On the basis of thermodynamic and kinetic stability, glass compositions have been developed that minimize the corrosion problem in all lithium battery systems tested.
Solid-phase epitaxy of ion-implanted LiNbO3 for optical waveguide fabrication
Authors: Buchal Ch. , Ashley P. R. , Appleton B. R.
Published: September 2007

A new technique for successfully fabricating high-quality optical waveguides in LiNbO3 is reported. A high concentration of Ti is implanted with the substrate at liquid nitrogen temperature and an amorphous, Ti-rich, nonequilibrium phase is produced in the implanted, near-surface region. Subsequent thermal annealing in water-saturated oxygen atmosphere at up to 1000°C initiates solid-phase epitaxial regrowth onto the crystalline substrate. A highquality single crystalline layer results that is rich in Ti and has excellent waveguiding properties.
Magnetic susceptibility study of Te-rich Mnx Te1−x
Authors: Zou X. M. , Gardner John A.
Published: September 2007

The magnetic susceptibility of Te, MnTe2, and three dilute TeMn alloys was measured from room temperature to 800°C. The effective magnetic moment of dilute Mn in liquid Te is 5.0(2) μB and appears to be slightly temperature dependent. The effective moment for Mn in MnTe2 is 6.05 μB, approximately equal to that of a free 5/2 spin. The Weiss temperature of MnTe2 is 610(20) K. These data are used to determine an accurate phase diagram for Terich Mnx Te1−x. The eutectic is found at 0.6(1) at. % Mn with a eutectic temperature within 2°C of the tellurium melting temperature. Because liquid tellurium remains in metastable equilibrium with solid MnTe2 as much as 80°C below the eutectic, a metastable lowtemperature extension of the liquidus is also determined.
Laser photosublimation of compound semiconductors
Authors: Rothschild M. , Arnone C. , Ehrlich D. J.
Published: September 2007

The visible-laser sublimation of CdTe, HgCdTe, CdS, and GaAs has been studied. A dynamic light guiding has been identified with an active feedback mechanism and is connected to the observation of 0.4 μm wide single-mode guiding structures during deep etching. The incipient stages of sublimation have been studied by mass spectrometry and are discussed in relation to diffusion mechanisms in the solid state.
Ion-beam-induced formation of a stable phase at the expense of an otherwise dominant metastable phase
Authors: Lee E. H. , Mansur L. K.
Published: September 2007

Thermal aging and irradiation experiments were carried out in Fe–Ni–Cr base alloys containing Ti or Nb as well as low levels of oxygen, nitrogen, and carbon. After aging, fine dispersions of TiC and NbC were formed. However, after irradiation the Ti-containing alloy precipitated Ti(N,O) rather than TiC, while the Nb-containing alloy precipitated NbC. Analysis of the energetics of these reactions reveals that the Ti(N,O) phase is thermodynamically more stable than the TiC phase, while the NbC phase is more stable than the NbO phase. These results are therefore consistent with observed behavior. While it is well known that irradiation can drive a system away from equilibrium, the present results show that irradiation also can catalyze the formation of a more stable phase at the expense of a persistent metastable phase.
Single-crystal x-ray diffraction from an icosahedral quasicrystal
Authors: Kortan A. R. , Chen H. S. , Waszczak J. V.
Published: September 2007

Single-crystal x-ray diffraction measurements made on a millimeter-size single icosahedral quasicrystal of an Al–Li–Cu alloy are reported. The point symmetries observed directly by real-time transmission Laue x-ray diffraction and the measured angles between the major symmetry axis are consistent with an icosahedral quasicrystal, and the peaks observed in the single-crystal diffraction scans are found to be indexable with six indices that belong to a primitive icosahedral Bravais quasilattice.
Intercalation of M F−6 ions (M = Nb, Ta, As, and Sb) into pyrolytic graphite using Hg2+ and Hg2+2 salts
Authors: Ummat P. K. , Zaleski H. , Datars W. R.
Published: September 2007

The mercury cation Hg2+ is used to intercalate NbF−6 and TaF−6 anions into pyrolytic graphite (HOPG). The Hg2+ cation in Hg (NbF6)2 and Hg(TaF6)2 oxidizes HOPG to form stage-3 compounds. The Hg2+2 cation is also used as an oxidant to intercalate AsF−6 and SbF−6 ions into graphite. The reduced products of the reactions are identified by Raman spectra. The intercalation compounds are characterized by (00l) x-ray diffraction, and the intercalants are identified with mass spectrometer analysis.
Growth of BiYIG films from MoO3–containing fluxes
Authors: Luther L. C. , Norelli M. P.
Published: September 2007

For liquid phase epitaxial (LPE) growth of BiYIG films, MoO3 is shown to be a flux modifier that increases Bi content xBi, and growth-induced anisotropy Ku8, for MoO3 flux concentrations up to 12 mol %. The addition of MoO3 to PbO–Bi2O3 fluxed garnet melts caused the saturation temperature to increase at a rate of 7 deg/mol % while growth rates decreased. For a given amount of supercooling, ΔTs, xBi increased with MoO3 flux content up to 12 mol %. A linear dependence of xBi on ΔTs, was observed for all MoO3 concentration levels. The anisotropy increased both with supercooling and with MoO3 flux concentration. The Kgu can be represented by a two-variable model, Kgu = A +BxBi + C4IIMs, where B increases from 143–213 kerg/cm3 per Bi atom per formula unit as the MoO3 content of the flux increases from 0–12 mol %. The density of the melt decreases with increased MoO3 content. A melt based on a 15 mol % MoO3 flux is less dense than gadolinium gallium garnet.
Crystal chemical incorporation of high level waste species in aluminotitanate-based ceramics: Valence, location, radiation damage, and hydrothermal durability
Authors: Fielding P. E. , White T. J.
Published: September 2007

A compilation is made of the crystallographic mechanisms whereby (simulated) radwaste species are incorporated in the “synroc” phases zirconolite, perovskite, hibonite, and “hollandite.” From these data and consideration of the crystal chemical criteria of valence and effective ionic radii, the most probable host phases for transuranic isotopes are identified. The distinction is drawn between incorporation of radwaste species as dilute homogeneous, continuous solid solutions and as heterogeneous, noncontinuous solid solutions. It is shown that compositional variations at the nanometer level are frequently accompanied by the generation of new interstices within extended defects, which are suitable for the location of radwaste. Nuclides that are unstable towards beta and gamma decay lead to transmutation-induced changes in stoichiometry. Crystallochemical mechanisms that minimize structural disruption during the formation of radiogenic species are discussed. Thermally promoted recovery of metamict phases, which were rendered aperiodic by direct atomic displacements of alpha-recoil nuclei, are examined in terms of recrystallization via the hierarchial arrangement of space groups. An evaluation is made of the hydrothermal durability of synroc phases under conditions likely to be experienced by the wasteform should the repository be breached by groundwaters shortly after disposal.
The crystal structure of YBa2Cu3O6, the x = 1 phase of the superconductor YBa2Cu3O7−x
Authors: Swinnea J. S. , Steinfink H.
Published: September 2007

Black crystals, displaying a micaccous habit, result from heating the 90 K superconducting phase YBa2Cu3O7−x above 1050°C. The crystals are tetragonal, P4/mmm, a = 3.863 (2) Å, c = 11.830 (4) Å, Z = 1, ρcal = 6.115 g/cm3. The 184 independent single-crystal reflections were used to refine the structure by least squares to R = 0.0374, wR = 0.0347. The structure contains Cu+ in twofold coordination and corrugated layers of Cu2+–O. The Ba2+ is in eightfold coordination between the Cu+ and Cu2+ layers and Y is in eightfold coordination between the Cu2+ layers.
Effect of boron on the mechanism of strain transfer across grain boundaries in Ni3Al
Authors: Bond G. M. , Robertson I. M. , Birnbaum H. K.
Published: September 2007

The effect of boron on the mechanism of strain transfer across grain boundaries in Ni3Al has been investigated by dynamic recording of events occurring during in-situ straining in the transmission electron microscope. Boundaries in both doped and undoped material can act as effective barriers to dislocation motion, large numbers of dislocations being incorporated into the boundary without any plastic strain occurring in the adjacent grain. In the undoped material, the grain-boundary strain is relieved by the sudden failure of the grain boundary. In the doped material the strain is relieved by the sudden generation and emission of large numbers of dislocations from the grain boundary. This effect may be understood by boron either increasing the grain-boundary cohesion or reducing the stress required to operate grain-boundary dislocation sources, rather than easing the passage of slip dislocations through the grain boundary.
Ambient dependence of the interactions in Pt/Ni/Cu and Au/Ni/Cu structures
Authors: Chang Chin-An
Published: September 2007

The interactions of the Pt/Ni/Cu and Au/Ni/Cu structures and their ambient dependence are studied. Comparison of the Pt–Cu interdiffusion with that of Au–Cu across the Ni layer shows an interesting relation between the interactions and their ambient dependence. According to the surface potential model, which has been shown to correlate the ambient effects for many systems, diffusion of both Pt and Au into the Cu layer via the Ni layer should be enhanced by oxygen. This is observed for Au but not for Pt. On the other hand, the anticipated oxygen-enhanced diffusion of Cu into Pt and Au layers via the Ni layer is observed in both structures. The difference between the Pt and Au diffusion via Ni is attributed to the presence of competing interdiffusion between Pt and Ni in the Pt/Ni/Cu structure, which is reduced by oxygen, whereas little diffusion of Ni into the Au layer is observed for the Au/Ni/Cu structure. The ambient effects on the trilayer structures are compared with those on the binary Au/Ni, Au/Cu, Ni/Cu, Pt/Ni, and Pt/Cu structures. The diffusion mechanisms are discussed, and relations among various systems are suggested.