bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of surface structures upon ultrathin film interference fringes
Authors: Taijing Lu , Ogawa Tomoya , Toyoda Koichi , Wang Zhenguo
Published: September 2007

Effect of surface structures upon ultrathin film interference fringes generated from extremely thin films or epitaxial layers grown on semiconductor wafers has been studied. Since dark regions of fringes correspond to the places where the thin films are destroyed or absent, the fringes are investigated to detect uneven surfaces with undesired structures. Therefore, surface microstructures can be detected and characterized effectively by the modification of the fringes.
Control of strength and toughness of ceramic/metal laminates using interface design
Authors: Chen Z. , Mecholsky J.J.
Published: September 2007

The fracture strength and toughness of alumina can be increased by lamination with strategically placed nickel layers and by controlling the geometry of the interfaces. This paper describes the interface design of a ceramic/metal bonded system produced by changing the surface topography of the interface between the metal and ceramic layers in order to vary the strength of bonding. The tortuosity of the interface is described quantitatively using fractal geometry. Experiments and models of single ductile layer laminates show that the work of fracture of ductile layers which contribute to the increment of toughness of ceramic/metal laminates is dependent on the tortuosity of the interface. The more tortuous the interface, the stronger the laminate; the smoother the interface, the tougher the laminate. The results are used to design a ceramic/metal multilayer composite. The strength and toughness of the laminates can be controlled by the tortuosity of the interface and characterized using the fractal dimension.
Effect of partial vacuum on YBCO thick films on Y2BaCuO5 and ZrO2 substrates
Authors: Dhingra Indu , Tripathi R.B. , Das B.K.
Published: September 2007

High Tc superconducting YBCO films have been prepared on Y2BaCuO5 (211) and ZrO2 substrates by screen printing and by the partial vacuum sintering method. The influence of reduced pressure and temperature in correlation with adherence, microstructure, and superconducting properties has been observed. This study was carried out under two different partial pressures, 1 and 45 mm. Films on Y2BaCuO5 substrates were found to have better superconducting properties as compared to the ZrO2 substrate.
Diffusion of Sr in Bi2Sr2Can–1CunO2n+4
Authors: Chen Nan , Rothman S.J. , Routbort J.L.
Published: September 2007

Tracer diffusion of 85Sr in polycrystalline Bi2Sr2Can-1CunO2n+4 has been investigated for n = 1, 2, and 3 in an oxygen atmosphere between 775 and 850 °C. A radiotracer serial-sectioning technique was used to measure the concentration profiles, which were fit to a solution of the diffusion equation to calculate the diffusivities. The activation energies were 403, 553, and 519 kJ/mole, for n = 1, 2, and 3, respectively. However, the absolute values of D for the various layered superconductors did not differ by more than an order of magnitude over the measured temperature range. The diffusivity of Sr at 800 °C for n = 1 or 2 over an oxygen partial pressure range of 103 to 105 Pa increased as the pressure decreased.
Tribological properties of quasicrystalline coatings
Authors: Kang S.S. , Dubois J.M. , von Stebut J.
Published: September 2007

Coatings of three different compositions (Al65Cu20Fe15, Al64Cu18Fe8Cr8, and Al67Cu9Fe10.5Cr10.5Si3) were realized by various thermal deposition techniques. They were studied in the as-deposited state and after annealing. In view of potential applications, these quasicrystalline coatings were examined from the point of view of tribology: friction and wear. Some basic components of friction such as roughness, plowing, and adhesion have been studied in scratch testing. The friction resistance of the coating is strongly dependent on its inherent porosity, hardness, and thickness. The damage of the coatings is essentially brittle though some ductile behavior is observed. Static indentation hardness is in the range 500–600 HV0.03 (5–6 GPa), whereas the scratch hardness varies from 1.4 to 2.4 GPa depending on the percentage of porosity. Friction coefficients (measured at constant load of 20 N) were found to be typically 0.07 and 0.20 for diamond (tip radius R = 0.79 mm) and AISI 52100 (radius R = 0.79 mm) indenters, respectively.
Transformation of Al–Ni–(Si) decagonal quasicrystals to 1–D quasicrystal and crystalline approximants
Authors: Li X.Z. , Kuo K.H.
Published: September 2007

Rapidly quenched Al86-xNi14Six (x = 0, 2, 6, and 10) alloys have been studied by means of transmission electron microscopy. Two-dimensional (2-D) decagonal quasicrystal with a periodicity of 1.6 nm along its tenfold axis was found in the rapidly quenched Al86Ni14 binary alloy. With the addition of some silicon, such as AlgoNi14Si6, the 2-D decagonal quasicrystal first transforms to a one-dimensional (1-D) quasicrystal that inherits the periodicity along the tenfold axis and has, in addition, translation periodicity in one of the twofold axes of the decagonal phase, and finally transforms to a new orthorhombic crystalline phase (a = 0.78, b = 1.62, and c = 1.48 nm). In the Al76Ni14Si10 ternary alloy, a 2-D decagonal quasicrystal with a periodicity of 0.4 nm and a coexisting crystalline phase with the “Al3Ni2” structure were found, and their orientational relationship has been determined.
Experimental and theoretical investigation of the order-disorder transformation in Ni3Al
Authors: Cardellini Francesco , Cleri Fabrizio , Mazzone Giorgio , Montone Amelia , Rosato Vittorio
Published: September 2007

The crystalline disordered phase obtained by mechanical alloying of elemental 75 at. % Ni and 25 at. % Al powders has been investigated. The stability of this phase with respect to the thermal reordering process leading to the L12 structure has been analyzed by means of x-ray diffractometry, scanning electron microscopy, and differential scanning calorimetry. Atomistic simulations on an Ni3Al model, reproduced via molecular dynamics using a many-body potential, have been used to interpret experimental data. The ordering transformation takes place in an extended range of temperature (from 320 to 600 °C) and occurs simultaneously with the release of internal strain. Numerical simulations performed under different conditions show that the activation energy of the Ni-vacancy migration mechanism responsible for the ordering process depends on the local state of strain, thus suggesting an explanation for the considerable lowering of this energy in samples obtained by ball milling.
Environmental embrittlement of boron-doped Ni3(Al, Ti) single crystals at room temperature
Authors: Takasugi T. , Hanada S.
Published: September 2007

Environmental embrittlement of L12-type Ni3(Al, Ti) single crystals doped with 0.05 mass % boron was investigated at room temperature as functions of environmental media and strain rate. Environmental embrittlement occurs in air, water, and hydrogen gas, and is also very sensitive to strain rate with a decrease of elongation with decreasing strain rate. Environmental embrittlement is little influenced by boron doping, indicating no strong interaction with hydrogen in lattice. In embrittled condition, tensile elongation and fracture stress are reduced, and fracture mode is primarily {001} cracking with a river pattern. Based on these results, it is proposed that hydrogen affects lattice bonding and thereby reduces the cohesion strength on {001} atomic plane. Also, it is suggested that the major cause of environmental embrittlement of boron-doped Ni3(Al, Ti) single crystals is due to the reaction of water (i.e., H2O) in environment with the reactive element of Al (and/or Ti) and of H2 in environment with the surface reactive element of Ni.
Combined surface characterization and tribological (friction and wear) studies of CVD diamond films
Authors: Perry Scott S. , Ager Joel W. , Somorjai Gabor A.
Published: September 2007

The tribological properties of polycrystalline chemically vapor deposited (CVD) diamond films grown on silicon substrates and containing varying amounts of amorphous carbon impurities were investigated. Films were characterized by secondary electron microscopy (SEM) and atomic force microscopy (AFM) for surface morphology and roughness and by spatially resolved Raman spectroscopy for amorphous carbon (a-C) content. Friction measurements were performed with a Rockwell C hemispherical diamond tip in ultrahigh vacuum (UHV) and in ambient air. In vacuum, the friction coefficient rises monotonically from 0.6 in a region with substantial a-C to 0.85 in a region with pure diamond. Under ambient conditions, the friction coefficient is substantially lower than that in vacuum and deceases slightly (from ∼0.19 to ∼0.16) with the decreasing a-C content. Under both vacuum and ambient conditions, the friction coefficient was observed to be independent of load over the range of 0.1–0.5 N. The friction values are discussed in terms of adhesion between the diamond tip and the film. Qualitative scratch hardness measurements were performed in UHV by measuring the minimum load at which plastic deformation occurs for a single traversal of the tip. Scratch hardness is found to increase with increasing diamond content of the films. The wear mechanism of the pure diamond regions was evaluated by examining wear tracks with SEM and AFM. The wear tracks showed evidence of spalling, buckling, and grain pull-out indicative of a cohesive mode of failure (failure at grain boundaries). A decrease in surface roughness in the wear tracks indicates asperity wear. Adhesive failure at the Si substrate interface or of a phase transformation of the diamond film was not observed in this load regime.
The dielectric constant of TCNQ single crystals as deduced by reflection electron energy loss spectroscopy
Authors: Mondio G. , Neri F. , Curró G. , Patané S. , Compagnini G.
Published: September 2007

The dielectric constant of tetracyanoquinodimethane (TCNQ) single crystals has been obtained by reflection electron energy loss spectroscopy (REELS) over the 0–60 eV energy range, using primary electron energies ranging from 0.5 to 1.5 keV at an incidence angle of about 40°. A self-consistent method is discussed concerning the evaluation of the surface and bulk contributions to the loss spectra. As a result, for the first time, the Im(−1/∊) function and the dielectric constant of TCNQ have been deduced in such a wide energy range. According to the results obtained by other authors, the low-energy loss spectral profile is characterized by two main structures ascribed to the π → π∗ dipole-allowed transitions located at about 3.5 and 6.5 eV while, at higher energy loss, the π + σ plasmon, centered at about 21.5 eV, dominates the spectrum. The differences among the spectra taken at different primary energies are interpreted as due only to surface effects, more evident in the low-energy-loss spectral region. The results are in good agreement with those obtained by recent transmission-mode (TEELS) experiments.
Spherical iron oxide particles synthesized by an aerosol technique
Authors: Cabañas M.V. , Vallet-Regí M. , Labeau M. , González-Calbet J.M.
Published: September 2007

Spherical particles of several iron oxides have been obtained by pyrolysis of an aerosol generated by ultrahigh frequency spraying of a solution. Two different precursor solutions were used to produce the aerosol: Fe(NO3)3 · 9H2O and FeC6H5O7 · 4H2O. The iron nitrate decomposition leads to the formation of α-Fe2O3, while the organic precursor pyrolysis leads to magnetic particles of either γ–Fe2O3 or Fe3O4. Structural phase, particle size, texture, and homogeneity of the products so obtained can be controlled as a function of some synthesis conditions such as precursor solution, temperature, solution concentration, and surrounding atmosphere.
Erratum
Authors: Baker I.
Published: September 2007

“Hard sphere modeling of the effect of slip on interstitial sites in the B2 structure” [J. Mater. Res. 8, 1203 (1993)]
Influence of Y2BaCuO5 particles on the growth morphology of peritectically solidified YBa2Cu3O7−x
Authors: Schmitz G.J. , Laakmann J. , Wolters Ch. , Rex S. , Gawalek W. , Habisreuther T. , Bruchlos G. , Görnert P.
Published: September 2007

Modifications of a recent model by Izumi et al.1 on diffusion controlled growth of YBa2Cu3O7−x (123) superconductors are proposed, taking into account especially the engulfment process of the Y2BaCuO5 (211) particles into the solidifying 123 interface. The proposed modifications are evidenced by experimental results and applied to explain microstructural features of the 123 superconducting material. In particular, the 1:1 correlation between 123 platelet thickness (planar defect spacing) and 211 particle size as described by Jin et al.2 is explained by an observed bridge growth resulting in a zipper-like mechanism. By this mechanism the platelets grow together in an oriented way leading to a quasi single crystalline material.
An investigation of ductility and microstructural evolution in an Al−3% Mg alloy with submicron grain size
Authors: Wang Jingtao , Horita Zenji , Furukawa Minoru , Nemoto Minoru , Tsenev Nikolai K. , Valiev Ruslan Z. , Ma Yan , Langdon Terence G.
Published: September 2007

A submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining. Experiments show that tensile specimens of the SMG alloy exhibit high elongations to failure at low testing strain rates at the relatively low temperature of 403 K. The stress exponent is high (∼7–8) and calculations show deformation is within the region of power-law breakdown. The initial microstructure of the alloy consists of diffuse boundaries between highly deformed grains. At strain rates of ∼10−4 s−1 and lower, plastic deformation leads to dynamic recrystallization and the formation of highly nonequilibrium grain boundaries that gradually evolve into a more equilibrated configuration.
Morphology of heavily B-doped diamond films
Authors: Miyata Koichi , Kumagai Kazuo , Nishimura Kozo , Kobashi Koji
Published: September 2007

B-doped diamond films were synthesized by microwave plasma chemical vapor deposition using a mixture of methane (0.5% or 1.2%) and diborane (B2H6) below 50 ppm on either Si substrates or undoped diamond films that had been synthesized using 0.5% or 1.2% methane. The surface morphologies of the synthesized films were observed by Secondary Electron Microscopy, and the infrared absorption and Raman spectra were measured. It was found that when diborane concentration was low, B-doped films preferred (111) facets. On the other hand, high diborane concentrations resulted in a deposition of needle-like material that was identified as graphite by x-ray diffraction.
The α → β polytypic transformation in high-temperature indented SiC
Authors: Yang J.W. , Pirouz P.
Published: September 2007

High-quality single crystals of 6H–SiC have been indented at 1170 °C in vacuum. A TEM study of the indented regions shows that a 6H → 3C polytypic transformation has occurred, further confirming that this phase transformation can be induced by an applied stress.
Synthesis and characterization of zinc ferrite particles prepared by hydrothermal decomposition of zinc chelate solutions
Authors: Andrés Vergés M. , Martinez M. , Matijevié E.
Published: September 2007

Crystalline zinc ferrite particles of the general formulation ZnxFe3−xO4 (O ≤ x ≤ 1) were prepared by aging at elevated temperature solutions containing Zn(NO3)2, Fe(NO3)3, and triethanolamine in the presence and in the absence of hydrazine. The powders were characterized by x-ray diffraction and infrared analyses.
The synthesis, sintering, and thermal properties of (Ca1−x, Mgx)Zr4(PO4)6 (CMZP) ceramics
Authors: Li T.K. , Hirschfeld D.A. , VanAken S. , Yang Y. , Brown J.J.
Published: September 2007

(Ca1−x, Mgx)Zr4(PO4)6 (CMZP) ceramics have been made by sol-gel and solid state reaction methods. Single phase (Ca1−x, Mgx)Zr4(PO4)6 (x = 0.4) has been obtained. The densification of CMZP depends on the powder synthesis method. Near theoretical density can be achieved by cold pressing and sintering with the addition of a sintering aid. Bulk thermal expansion of CMZP is shown to depend on the phase composition, grain size, and presence of microcracks. By choosing different sintering temperatures and times, the thermal expansion of CMZP can be controlled. CMZP (x = 0.4) ceramics exhibit near zero bulk thermal expansion, low thermal expansion anisotropy, low thermal conductivity, and thermal stability up to 1500 °C.
Ion beam sputter deposition of YBa2Cu3O7−δthin films
Authors: Kellett B.J. , James J.H.
Published: September 2007

This article addresses issues associated within situgrowth of superconducting YBa2Cu3O7−δthin films by ion beam sputtering. High oxygen partial pressure during ion beam deposition can cause significant beam broadening and oxidation of filaments and grids. Also, many of the targets used for processing YBCO are unstable when sputtered in a high oxygen partial pressure. It is shown that ion beam sputtering can produce YBCO films of comparable quality to those produced by laser ablation or dc magnetron sputtering. Typical film properties areTco= 91 K andJc(77 K) = 106A cm−2. It appears that the oxygen gas pressure during the postdeposition cooldown has a more important influence on film properties than the oxygen partial pressure during deposition.
Influence of rare earth element additions on phase transformations in the Zn−27% Al alloy
Authors: Zhu Yao Hua , Goodwin Frank E.
Published: September 2007

Rare earth additions of 3 wt. % were added to the Zn−27% Al−2% Cu−0.02% Mg alloy, known as ZA-27. The as-cast microstructure of this alloy consisted of two phases of supersaturated face-centered cubic β′s and α′s together with a hexagonal close-packed rare-earth-containing zinc-rich phase termed E phase. The phase transformations in this alloy after aging at 100 °C and 200 °C were determined. The E phase was determined to have the lattice parameters a0 = 9.0348 Å and c0 = 13.2194 Å, giving c0/a0 = 1.4632. The chemical formula of the E phase was determined to be RE1Zn10.9Cu0.8. The addition of 3% rare earths into ZA-27 delayed the phase transformations of this alloy. This was caused by an increase in the aluminum content of the supersaturated β′s phase.
Planar fault energies and dislocation core spreading in B2 NiAl
Authors: Farkas Diana , Vailhe Christophe
Published: September 2007

We present computer simulation results for the planar faults involved in core spreading of 〈100〉 and 〈111〉 dislocations. Seven γ surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111}, and {122}). Stable APB's are observed in the {110} and {112} planes, but they are deviated from the exact 1/2a〈111〉 position. No other stable planar fault was observed. The fact that a stable minimum is observed deviated from the 1/2〈111〉 position suggests the possibility of different dissociation reactions for the 〈111〉 screw dislocation in the {110} and {112} planes. The fact that no other stable minima were observed in the γ surfaces indicates that no true core dissociation is expected for the 〈100〉 dislocations. We propose that dislocation core spreading in various planes can be understood in terms of the directions of lowest restoring forces observed for the corresponding γ surfaces.
An investigation of photoassisted diffusion of oxygen in solid C60 films using resonant alpha-scattering
Authors: Eloi Corinne C. , Robertson David J. , Rao A.M. , Zhou Ping , Wang K-A. , Eklund Peter C.
Published: September 2007

The interaction of molecular oxygen with thin C60 films was investigated using the 3.04 MeV resonance in the 16O(α, α)16O elastic scattering reaction to measure the concentration profile of oxygen in the fullerene films. A thin (d ≍ 20 nm) layer containing oxygen was observed on the surface of C60 films (d ≍ 200 nm) exposed to ∼1 atm of O2 for 1 h in the absence of light. In contrast, oxygen was uniformly distributed throughout the entire film when samples were irradiated for 1 h with either a 488 nm Ar ion laser or Xe lamp in the presence of ∼1 atm of O2. This O2 uptake was found to be both power dependent and reversible.
The effect of interruption during the growth of strained GaAs/InGaAs/GaAs quantum wells by molecular beam epitaxy
Authors: Yoon S.F. , Li H.M. , Radhakrishnan K. , Zhang D.H.
Published: September 2007

Low-temperature photoluminescence measurements have been taken to monitor the changes in the properties of strained GaAs/InGaAs/GaAs quantum wells grown by molecular beam epitaxy at different substrate (well) temperatures with and without a 90 s-growth-interruption at the heterointerfaces. Sharp exciton peaks with average linewidths as low as 1.7 meV were observed in all the spectra. The spectra from the samples grown employing interrupts were narrower than those without interrupts, indicating structurally improved interfaces. Further linewidth narrowing was also seen in samples employing an additional interrupt of the same duration at the bottom InGaAs/GaAs interface, or by increasing the interrupt time at the top GaAs/InGaAs interface to 180 s. A consistent reduction in the linewidth was also observed in wells grown at higher temperatures. This is most likely due to greater indium re-evaporation leading to a reduction in strain, well width, and interface fluctuations.
Electrical and optical characterization of Sb : SnO2
Authors: He Yue-Song , Campbell Joe C. , Murphy Robert C. , Arendt M.F. , Swinnea John S.
Published: September 2007

Films of Sb : SnO2 have been formed by vacuum e-beam evaporation. The structural, electrical, and optical properties of these films have been investigated with respect to annealing time and temperature. After heat treatment in an oxygen atmosphere, thin films with a peak transmittance of 98% and 4–9 × 10−3 Ωcm resistivity have been obtained. The barrier heights and energy band diagrams of Sb : SnO2/Si n-n and p-n heterojunctions have been determined by C-V measurements.
Dip coating of alumina films by the sol-gel method
Authors: Lee Jung-Won , Won Chang-Whan , Chun Byong-Sun , Sohn H.Y.
Published: September 2007

Thin alumina films were prepared on stainless steel and glass surfaces by dip coating from an aluminum alkoxide solution. Multiple coatings from a low-viscosity solution were necessary for high quality and sufficient thickness of the films. To determine the bonding mechanism and strength, wavelength dispersive x-ray was used. Aluminum was found to diffuse into the substrate in both cases. The possible bonding mechanism is a combination of diffusion and the formation of chemical compound between the alumina and the substrates. The surface properties of stainless steel, such as microhardness, electric resistance, and corrosion resistance, were substantially improved when coated with alumina.
Effects of α-silicon nitride powder processing on surface oxidation kinetics
Authors: Wang Pu Sen , Malghan Subhas G. , Hsu Stephen M. , Wittberg T.N.
Published: September 2007

The oxidation of two α–Si3N4 powders has been studied using x-ray photoelectron spectroscopy (XPS) and Bremsstrahlung-excited Auger electron spectroscopy (AES). These two powders had comparable specific surface areas but were produced by different methods. The powders were oxidized by heating in air at temperatures between 850° and 1000 °C. The oxide thickness for each heating time and temperature was determined both from the relative O 1s and N 1s peak intensities and from the relative SiO2 and Si3N4 Si KLL peak intensities. In each case, the oxide thickness calculated from the XPS data was systematically higher than those determined from the AES data. This difference may be due to uncertainties in the data analysis procedures. The oxidation of each powder followed a linear rate law for these temperatures. On one of the powders, the XPS data showed evidence of oxynitride formation. Analysis with thermal decomposition mass spectroscopy also showed that much more hydrogen was evolved from this particular powder, particularly at temperatures >700 °C. These differences in bulk impurity levels are believed to be responsible for the differences in the activation energies for oxidation which were measured to be 104 ± 22 kJ/mol and 62 ± 4 kJ/mol for these two powders.
Effect of dose stoichiometry on the structure of vapor-deposited polyimide thin films
Authors: Pethe R.G. , Carlin C.M. , Patterson H.H. , Unertl W.N.
Published: September 2007

PMDA-ODA polyimide thin films can be formed by vapor co-deposition of the precursor molecules PMDA (pyromellitic dianhydride) and ODA (4, 4′-oxydianiline) if the resulting polyamic acid film is heated to a 473 to 573 K cure step. We have used laser Raman spectroscopy to study how dose composition, dose rate, and substrate temperature influence the properties of the resulting polyimide films. We find that only doses with excess PMDA produce high quality films. Doses with 1 : 1 stoichiometry or excess ODA produce thermally unstable films that contain imine bonds; these films decompose below 575 K. Dosing onto substrates below 315 K produces the polyamic acid precursor of polyimide. At higher substrate temperatures, films with high defect densities or decomposed films are produced. The equilibrium vapor pressures of ODA and PMDA are reported.
A note on the elastic contact stiffness of a layered medium
Authors: Gao Huajian , Wu Tsai-Wei
Published: September 2007

A perturbation method is used to confirm that the elastic contact stiffness associated with a flat-ended punch indenting a layered medium is insensitive to the cross-section shape of the punch as long as the shape does not differ too much from a circle. This result supports the practice of modeling nonaxisymmetric indenters such as Vickers or Berkovich indenters as an axisymmetric flat-ended cylindrical punch.
Erratum
Authors: Morell José I. , Economou Demetre J. , Amundson Neal R.
Published: September 2007

“Chemical vapor infiltration of SiC with microwave heating” [J. Mater. Res. 8, 1057 (1993)]
Formation of tetragonal YBa2Cu3O7−δ from an undercooled melt
Authors: Olive J.R. , Hofmeister W.H. , Bayuzick R.J. , Carro G. , McHugh J.P. , Hopkins R.H. , Vlasse M. , Weber J.K.R. , Nordine P.C. , McElfresh M.
Published: September 2007

Containerless processing of YBa2Cu3O7−δ was performed using an aero-acoustic levitation technique. Upon solidification from the liquid, spheres of size 2.5 mm diameter undercooled and recalesced, forming tetragonal YBa2Cu3O7−δ directly from the melt. Subsequent to solidification processing, these samples were annealed to single phase YBa2Cu3O7−δ with orthorhombic symmetry as indicated by powder XRD, SQUID magnetometer measurements indicate a sharp superconducting transition at approximately 85 K. Magnetic Jc values, calculated using the Bean critical state model, indicate that the spheres can carry critical current densities on the order of 104 A cm−2. Microstructural characterization has been performed on both the as-solidified and annealed spheres.
An x-ray method for direct determination of the strain state and strain relaxation in micron-scale passivated metallization lines during thermal cycling
Authors: Besser Paul R. , Brennan Sean , Bravman John C.
Published: September 2007

We describe a method for directly determining the strain state of passivated metal lines. Synchrotron radiation in the grazing incidence geometry is used to directly measure the in-plane interplanar spacing along the length and width of the lines, while the strain normal to the surface of the line is measured using conventional diffraction methods. The entire strain state is thereby defined. Previous work has measured out-of-plane reflections, fit them to a straight line as a trigonometric function of the angle of orientation, and extrapolated to determine the principal strains. The equivalence of the two x-ray methods on the same sample is demonstrated at room temperature before and after thermal cycling. For short time strain relaxation experiments during thermal cycling, measurement of the three principal strains leads to the direct calculation of the stress relaxation. We apply the strain determination technique to Al-0.5% Cu lines passivated with Si3N4 as the lines are thermally cycled from room temperature to 450 °C and back. The strain state, stress state, and strain relaxation of the lines are calculated at several temperatures during thermal cycling.
The elastic biaxial modulus of Ag–Pd multilayered thin films measured using the bulge test
Authors: Small Martha K. , Daniels Brian J. , Clemens Bruce M. , Nix William D.
Published: September 2007

Analysis and sample preparation techniques for the bulge test have been improved to the point where the test can provide reliable and accurate measurements of the mechanical properties of thin films. Ag-Pd multilayer films of variable bilayer period were prepared for this study and characterized by cross-section transmission electron microscopy and by x-ray methods. The films were tested in the bulge test to determine their biaxial moduli. The data show no peak in biaxial modulus at a critical composition wavelength and no nonlinear elastic behavior. They do show a slight trend toward increasing elastic modulus with increasing strength of (111) crystallographic texture. These findings refute a previous report of the “supermodulus” effect in this system and add to the evidence that the effect is caused by artifacts of the mechanical testing technique. Methods for eliminating such artifacts are discussed.
The early stages of phase formation during mechanical alloying of Ti–Al
Authors: Klassen T. , Oehring M. , Bormann R.
Published: September 2007

The early stages of phase formation during mechanical alloying of Ti/Al powder blends were investigated using x-ray diffraction and transmission electron microscopy. After the initial formation of an hep solid solution by the diffusion of Al into Ti, the first phase nucleated at the Ti/Al interface is a (partially) Ll2-ordered fcc phase with a crystallite size of about 10–30 nm. This observation is ascribed to the kinetics of phase formation and the energetic destabilization of the equilibrium intermetallic compounds during milling due to chemical and structural disordering. A mechanism of phase formation during mechanical alloying is proposed, and comparisons are made with the thermal annealing behavior of Ti/Al multilayered thin films.
Diamond nucleation on surfaces using carbon clusters
Authors: Meilunas R.J. , Chang R.P.H.
Published: September 2007

Thin solid films of C60and C70have been used as nucleating layers for the growth of diamond thin films on a variety of substrate surfaces, including metal, insulator, and semiconductors. Compared to other forms of carbon, such as graphite, amorphous carbon, soot, etc., it is found that the nucleation density on a C70film is equivalent to that of diamond seeds themselves. On the other hand, diamond nucleation on a C60film is less favorable. We argue from our experiments that the reason for C70film to have such favorable nucleating properties is its chemical stability and geometry. A working model is proposed to explain the nucleation of diamond on solid C70films. Application of this work extending to the growth of diamond on a wide range of substrates is also discussed.
Influences of ambient atmosphere on diamond synthesis using an oxygen-acetylene torch
Authors: Aldredge R.C. , Goodwin D.G.
Published: September 2007

The influence of the ambient atmosphere on the synthesis of diamond by chemical vapor deposition using an oxygen-acetylene torch is investigated experimentally. Diamond synthesis in an air atmosphere is compared to that in an inert atmosphere. It is found that the quality of diamond deposited on substrates positioned in the burnt gases near the premixed flame of the torch (within 1 mm) is independent of the composition of the ambient gas. Farther downstream from the premixed flame in the feather region, however, diamond deposition is controlled by the combustion of incomplete products from the premixed flame with oxygen from the atmosphere. In this region diamond grows in an annulus on the substrate with an air atmosphere, but no film is grown with an inert atmosphere.
Microwave sintering of hydroxyapatite ceramics
Authors: Fang Yi , Agrawal Dinesh K. , Roy Della M. , Roy Rustum
Published: September 2007

Hydroxyapatite ceramics have been fabricated by microwave sintering in a 500 W microwave oven. Circular-plate specimens of various green densities were sintered in the oven at 1200 and 1300 °C, for 5, 10, and 20 min, respectively. Ceramics with density up to 97% of the theoretical were obtained. Density, grain size, microstructure, and strength of the ceramics sintered by microwave and by conventional methods were compared. The results show that microwave sintering of hydroxyapatite is not only highly efficient in saving time and energy, but can also improve the microstructure and thus enhance mechanical strength of the ceramics.
Fe–Cr/Al2O3 metal-ceramic composites: Nature and size of the metal particles formed during hydrogen reduction
Authors: Laurent Ch. , Demai J.J. , Rousset A. , Kannan K.R. , Rao C.N.R.
Published: September 2007

Fe-Cr/Al2O3 metal-ceramic composites prepared by hydrogen reduction at different temperatures and for different periods have been investigated by a combined use of Mössbauer spectroscopy, x-ray diffraction, transmission electron microscopy, and energy-dispersive x-ray spectroscopy in order to obtain information on the nature of the metallic species formed. Total reduction of Fe3+ does not occur by increasing the reduction time at 1320 K from 1 to 30 h, and the amount of superparamagnetic metallic species is essentially constant (about 10%). Temperatures higher than 1470 K are needed to achieve nearly total reduction of substitutional Fe3+. Interestingly, iron favors the reduction of chromium. The composition of the Fe-Cr particles is strongly dependent on their size, the Cr content being higher in particles smaller than 10 nm.
Structure/property observations for Al–Ti–Cr intermetallic alloys
Authors: Klansky J.L. , Nic J.P. , Mikkola D.E.
Published: September 2007

The microstructures and mechanical properties of single phase and multiphase alloys are reported for Al-rich intermetallic alloys containing up to 45 at. % Ti and as much as 68 at. % Cr. Among the individual phases formed in these alloys, TiAl and tau (Al67Cr8Ti25) had both the lowest hardnesses and the greatest resistance to cracking. Additionally, the presence of these two phases in multiphase alloys improved mechanical properties.
Scanning tunneling spectroscopy of carbon nanotubes
Authors: Olk Charles H. , Heremans Joseph P.
Published: September 2007

Calculations predict that carbon nanotubes may exist as either semimetals or semiconductors, depending on diameter and degree of helicity. This communication presents experimental evidence supporting the calculations. Scanning tunneling microscopy and spectroscopy (STM-S) data taken in air on nanotubes with outer diameters from 17 to 90 Å show evidence of one-dimensional behavior; the current-voltage (I-V) characteristics are consistent with a density of states containing Van Hove type singularities for which the energies vary linearly with inverse nanotube diameter.
Comparison of the critical current anisotropy in epitaxial YBa2Cu3O7−x films on (100) LaAlO3 and (100) yttria stabilized zirconia
Authors: Harshavardhan K.S. , Rajeswari M. , Hwang D.M. , Chen C.Y. , Sands T. , Venkatesan T.
Published: September 2007

The angular magnetic field dependence of the critical current density JC(θ) of epitaxial YBa2Cu3O7 thin films is presented in the temperature regime close to Tc. The high temperature behavior of Jc(θ) shows features that are significantly different from the earlier observations at lower temperatures. A comparison between the films on (100) LaAlO3 and (100) yttria stabilized zirconia (YSZ) indicates significant differences that may be attributed to the differences in the microstructure of the films on the two substrates. In particular, the observation of enhanced pinning in the films on YSZ may be due to the pinning effects of the low angle grain boundaries present in these films.
Grain growth and sintering in Bi–(Pb)—Sr—Ca—Cu—O superconductors made by sol-gel
Authors: Ma Kunsong , Pierre Alain C.
Published: September 2007

Bi—(Pb)—Sr—Ca—Cu—O superconductors were synthesized by sol-gel processing from nitrates by complexation with citric acid. Their grain growth and sintering above 800 °C were studied by Scanning Electron Microscopy (SEM) and Brunauer, Emmett, Teller (BET) porosimetry. The sintering was limited by anisotropic grain growth, and microcracks in 2212 phase grains were created due to the formation of 2223 phase.
Relation of starting precursors to the resulting high-Tc phases in the Pb and Sb doped Bi—Sr—Ca—Cu—O system
Authors: Constantinescu F. , Holiastou R. , Niarchos D. , Nicolaides G.K. , Vasiliu F. , Bunescu C. , Aldica G.
Published: September 2007

The introduction of more reactive precursors for Pb and Sr (oxalates), as well as Ca (citrate) and the use of a Bi nitrate decomposition route, has increased the percentage of the high-Tc (2223) phase in the Bi—Sr—Ca—Cu—O (BSCCO) system. Partial substitution of Bi(Pb) with Sb gives an almost single (2223) phase sample. In addition, a single (2212) phase sample is obtained when high purity Bi2O3 is used as a precursor, whereas Bi acetate leads to semiconducting behavior. The morphology of the samples is studied with a scanning electron microscope (SEM), the stoichiometry with energy-dispersive x-ray analysis (EDAX), and the structure with x-ray diffraction (XRD), while the superconducting properties are investigated by dc-resistivity, ac-susceptibility, and SQUID magnetometry techniques.
Structural comparison of Ba1−xKxBiO3 superconducting thin films
Authors: Ciofi C. , Platt C.E. , Eades J.A. , Amano Jun , Hu R.
Published: September 2007

The microstructure of Ba1−xKxBiO3 (BKBO) thin films from three different sources has been extensively compared by transmission electron microscopy studies. The three films were prepared independently in three different laboratories on three different substrates of (100) orientation and displayed excellent superconducting properties. The observed microstructure is remarkably similar in the three films. They are epitaxial with (100) orientation through all their extension and no cracks have been observed. Their defect density is similar and the resulting extension of defect-free regions is of the order of 50–80 nm.
Electrochemical and high pressure superoxygenation of YCuO2+x and LaCuO2+x delafossites
Authors: Cava R.J. , Peck W.F. , Krajewski J.J. , Cheong S-W. , Hwang H.Y.
Published: September 2007

Electrochemical and high pressure oxygenation experiments are described which extend the range of intercalated oxygen content beyond that accessible in 1 atm O2 treatments for the triangular planar cuprate delafossites YCuO2+x and LaCuO2+x, with the intention of increasing the hole doping, and filling vacancies in the intercalated oxygen lattice to decrease electrical resistivities. Stabilization of the 2H polytype of YCuO2 through 1% Ca substitution for Y and oxidation conditions for obtaining the pure orthorhombic intercalated oxygen superlattice form of YCuO2.50 are also described. Temperature dependent resistivities for some of the superoxygenated compositions are reported; metallic behavior was not observed.
Reverse martensitic phase transformation induced in Nb–Co multilayers by ion irradiation
Authors: Liu B.X. , Zhang Z.J.
Published: September 2007

A reverse martensitic phase transformation was observed in Nb-enriched Nb-Co multilayers induced by room temperature 200 ke V xenon ion mixing. Further experiments revealed that this bcc-fcc transition proceeds in two steps, i.e., bcc-hcp and hcp-fcc. A crystallographic model is proposed to explain the two-step transition through shearing and sliding, which are mediated by irradiation-induced defects and strain in the films. In addition, the existence of the hcp and fcc metastable states in the Nb-Co system was confirmed by high-temperature solid state interdiffusion of the corresponding multilayers.
Heteroepitaxy of rare-earth hexa-aluminates on sapphire
Authors: Vaidya K.J. , Yang C.Y. , DeGraef M. , Lange F.F.
Published: September 2007

We have grown epitaxial thin films of rare-earth hexa-aluminates on basal plane sapphire from liquid precursors. LnAl11O18 (Ln = Gd3+, Nd3+) films form via the reaction of a perovskite intermediate phase and the sapphire substrate according to LnAlO3 + 5Al2O3 = LnAl11O18. Hexa-aluminate thin films with magnetoplumbite (MP) structure grow epitaxially with (0001)mp ‖(0001)s, 〈1120mp‖〈1010〉s orientation relationship. The a-axis of the film is rotated 30°with respect to the substrate. This rotation results in a smaller mismatch (∼1%) between the two oxygen sublattices. Thermodynamic and kinetic arguments pertaining to magnetoplumbite formation for the smaller Gd3+ cation are presented. These epitaxial thin films are likely to have application in higher temperature ion conduction, catalysis, fluorescence, and as laser host.
Scanning tunneling microscope observations of the mirror region of silicate glass fracture surfaces
Authors: Kulawansa D.M. , Jensen L.C. , Langford S.C. , Dickinson J.T. , Watanabe Yoshihisa
Published: September 2007

We report scanning tunneling microscope images of gold-coated fracture surfaces of soda lime glass and fused silica in the mirror region. The scans show a variety of nanometer scale features that are attributed to fracture phenomena at this scale. We find considerable similarity to the structures observed in regions of extensive crack branching (e.g., “mist”). The density of these features increases as one progresses away from the crack origin toward the mirror-mist boundary. Comparisons are made between soda lime glass and fused silica, revealing differences in the local deformation behavior of these two materials. Self-similarity of the observed structures is probed by measurements of the fractal dimension, Df, of the surfaces created in soda lime glass near the mirror-mist boundary, where we observe 2.17 > Df > 2.40.
Statistics of low-density microcellular materials
Authors: Noever David A.
Published: September 2007

The statistics of random cellular patterns are analyzed in cross sections of low-density microcellular materials. Agreement is found with a variety of topological relations previously found for other networks, namely Lewis's law and Aboav's law. To investigate three-dimensional packing effects, experiments are performed on compressed polystyrene shot material, the resulting networks of which are subsequently analyzed in cross section. Implications for material properties and stability are discussed.
Study of copper on graphite with titanium or chromium bond layer
Authors: Abel Phillip B. , Korenyi-Both Andras L. , Honecy Frank S. , Pepper Stephen V.
Published: September 2007

Improvement of copper to graphite adhesion by thin interfacial films of titanium and chromium was investigated. Graphite fibers and highly oriented pyrolytic graphite flats were sputter-coated first with 10 nm of titanium or chromium and then with 50 nm of copper. After annealing to 970 °C in argon/5%-hydrogen at atmospheric pressure for 5 min, copper without an interfacial bond layer agglomerated into nearly spherical particles, copper with the chromium bond layer agglomerated into particles with a contact angle less than 90°, indicating improvement in adhesion, and copper with the titanium bond layer exhibited a continuous metal film. In the latter case, most of the interfacial titanium was observed to have migrated into the copper and to the free surface, where the titanium reacted with contaminants in the annealing ambient.
Dependence of perovskite/pyrochlore phase formation on oxygen stoichiometry in PLT thin films
Authors: Fox G.R. , Krupanidhi S.B.
Published: September 2007

Thin films in the Pb-La-Ti-O (PLT) system were prepared under two different oxygen partial pressure (Po2) conditions by multi-ion-beam reactive sputtering (MIBERS). The oxidation of the depositing species was determined from the deposition rate dependence on Po2 and the Po2 dependence of the positive secondary ion emission from the sputtering targets. Films deposited at high Po2 (Po2 greater than the critical partial pressure for oxidation of the Pb target surface) were fully oxidized, and they formed the pyrochlore phase during annealing. The low Po2 conditions (Po2 less than or equal to the critical partial pressure for oxidation of the Pb target surface) caused sputtering of incompletely oxidized Pb species, and the resulting oxygen deficient films produced phase-pure perovskite. The formation of the pyrochlore phase at high Po2 and the perovskite phase at low Po2 is independent of Pb content within the film; the phase formation is dependent on the oxidation state of the Pb, which is sensitive to both the Po2 and the sputtering rate of the Pb. A perovskite/pyrochlore phase formation model (PPFM) that incorporates annealing time, temperature, and heating rate, and thin film oxygen deficiency was developed to explain the formation of the perovskite and pyrochlore phase during postdeposition annealing of PLT thin films.
Reactive liquid phase sintering of YBa2Cu3O7-xsuperconducting thin films: Part II. Sintering mechanism and film properties
Authors: Chu Peir-Yung , Buchanan Relva C.
Published: September 2007

Reactive liquid phase sintering of the YBCO films prepared from carboxylate solution precursors was investigated. A liquid phase was formed by the BaO—CuO binary compound at 620 °C, which facilitated the crystallization and growth of the YBCO grains. Strong capillary forces associated with the liquid phase sintering resulted in a dense, highly oriented microstructure. The YBCO films processed by this reactive liquid phase process showed Tc(zero)= 90.2 K and Jc= 1.3 × 105 A/cm2at 77 K. The (006) rocking curve measurement indicated excellent grain orientation with a FWHM better than 0.2°. A secondary ion mass spectroscopy (SIMS) study showed uniform film composition, and the film/substrate interaction zone was limited to ≈0.1 μm. Average film roughness was about 32 nm.
Oxidation of epitaxial Fe films monitored by x-ray reflectivity
Authors: Stierle A. , Mühge T. , Zabel H.
Published: September 2007

We have studied the oxidation of thin epitaxial Fe(100) films on MgO(100) with and without an Au(100) protecting cap by x-ray reflectivity measurements. The oxidation was carried out under atmospheric conditions between 20 δC and 200 δC. The results are compared to the oxidation of Fe(110) oriented films on Al2O3(1120) substrates with an Au(111) cap. Auger electron spectroscopy before and after oxidation was carried out for sublimentary chemical information of the surface. For the uncovered Fe films we observe smoothly growing oxide films at the surface during oxidation at elevated temperatures. As expected, the Au(100) cap serves as an effective shield against oxidation, while the Au(111) cap, surprisingly, does not. In the case of Au/Fe/Al203, we find Fe2O3 formation at the surface of the Au layer at 200 δC. The different behavior of Au(100) and Au(111) is discussed in terms of stacking faults and/or domain structure occurring in the latter case during epitaxial growth.