bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural glass modifications in as-fired and high-voltage-surged RuO2-based thick film resistors
Authors: Adachi Kenji , Iida Sadahiro , Ishigame Juji , Sekihara Shyu
Published: September 2007

Electrical conduction in thick film resistors has been studied, and microstructures, especially around conducting RuO2 phases in a lead-borosilicate glass matrix in as-fired and high-voltage-surged thick film resistors, have been observed in detail using transmission electron microscopy. Lattice images of as-fired thick film resistors have suggested the presence of subtle structural modifications in the very thin area across the RuO2/glass interface, whereas in the glass matrix very small dot-like contrasts on the order of 1 nm were occasionally observed and were interpreted as being small crystallites or Ru clusters. Heavy electrical loadings of thick film resistors were found to induce the local formation of plate-like crystals in glass, which were identified by electron diffraction to be a slightly modified anorthite. The significance of these observations in terms of the conduction network and the degradation due to the electrical overloading of thick film resistors are discussed.
Characterization and control of phase segregation in the fine particles of BaTiO3 and SrTiO3 synthesized by the spray pyrolysis method
Authors: Nonaka K. , Hayashi S. , Okada K. , Otsuka N. , Yano T.
Published: September 2007

Fine particles of BaTiO3 and SrTiO3 have been synthesized by the spray pyrolysis technique, and the chemical homogeneity of their particles was analyzed by x-ray diffraction (XRD) and analytical electron microscopy (AEM). The stock solutions were prepared by dissolving Ti(OC3H7)4 and Ba(NO3)2 or Sr(NO3)2 in diluted nitric acid solution. They were atomized into a reaction chamber held at 1000 °C through a two-fluids atomizer with N2 gas. Mostly hollow spherical particles 3 μm in diameter were obtained, composed of very fine grains of 40 nm. As-prepared powders were crystallized to BaTiO3 or SrTiO3 with a small amount of by-product such as Ba2TiO4, Sr2TiO4, and TiO2. The AEM study revealed that the bulk composition of each particle was chemically homogeneous, but a local chemical composition segregation was observed within each particle. This chemical inhomogeneity was considered to be caused by the difference in the precipitating speed of each component from the precursor salts; that is, the precipitation of Ti4+ ion as TiO2 · xH2O was faster than those of Ba2+ and Sr2+ ions. To control this segregation, (a) replacing a part of the solvent of stock solutions with methanol or ethanol, (b) adding H2O2 to the solutions, and (c) increasing the concentration of the solution, are found to be effective. The reasons for these effects are discussed.
Structural model for nitrogen incorporation in phosphate glasses
Authors: Reidmeyer Mary R. , Day Delbert E.
Published: September 2007

In this paper a model is presented for predicting the structural changes that occur in a metaphosphate glass during nitriding in anhydrous ammonia. Predicted values for the nitrogen content, the mole fraction of phosphate groups, the bridging to nonbridging oxygen ratio, and the ratio of the structural types for nitrogen are compared to the values obtained in earlier experimental work. A plausible correlation is found between the values predicted from this structural model and those observed experimentally. In addition, a maximum nitrogen content (N/P = 0.9) is predicted and the lower nitrogen content normally observed is explained.
Hillocks on half-micron aluminum lines
Authors: Pico Carey A. , Bonifield Tom D.
Published: September 2007

A new regime of hillock growth has been observed in patterned Al98.5 W.%Si1.0 Wt.%-Cuo0.5 wt.%films. The “surface” hillock and “side” hillock, which have been seen previously, form on patterned metal lines having linewidths greater than the larger Al alloy grain sizes (∼3 μm). None is seen on the fabricated lines having linewidths between 0.9 and 2 μm where long-range grain boundary diffusion cannot occur because of its bamboo structure. However, a new type of hillock, the “line hillock”, occurs in structures having linewidths of 0.6 μm. The presence of this last type of hillock is inconsistent with the current understanding of hillock formation and may present severe restrictions on the down-sizing of ultra–large–scale integrated devices.
Electron beam effects on Bi–Sr–Ca–Cu–O superconductors
Authors: Cota-Araiza L. , Galvan D.H. , Farías M.H.
Published: September 2007

We present measurements on the superconductor compound Bi–Sr–Ca–Cu–O, obtained using a scanning Auger microscope (SAM), which indicate that this material is extremely unstable under an electron beam with energy of several KeV, Using relatively high current densities for the SAM, it is possible to melt small regions of the material and to form spheres several micrometers in diameter in a few seconds. We characterize the changes in the elemental concentration of the surface of these spheres as a function of time after the beam exposure.
An investigation of the crystalline and electronic structures of a 4:3:3:4 layered Bi–Ca–Sr–Cu oxide
Authors: Giardin M.D. , Feduzi R. , Manara A. , Spirlet J.C. , Zocchi M. , Depero L.E. , Mobilio S.
Published: September 2007

Semiconducting samples of a Bi–Ca–Sr–Cu oxide, having a nominal composition 4:3:3:4, were prepared by melting high purity oxides of the various elements. Superconducting samples were obtained by annealing the semiconducting samples at a temperature close to the melting temperature. Electrical resistivity measurements indicated the presence of two superconducting phases, one with the onset temperature at about 110 K, the other with a significantly lower onset temperature. The presence of this second phase is proven by the x-ray powder diffraction patterns. The crystalline structures of both the semiconductor and superconductor samples have almost equal lattice parameters and are orthorhombic, but belong to different space groups: Fmmm and Bbmm, respectively. No significant amount of the 110 K superconducting phase was present in the diffraction pattern of the superconducting compound. XPS and XANES data on the Ca atom indicate that a different electronic state of Ca is present in the superconducting compound, which still contains an appreciable amount of the semiconducting phase.
Interdiffusion reaction, phase sequence, and glass formation in Ni-Zr composites
Authors: Eckert J. , Schultz L. , Urban K.
Published: September 2007

The progress of solid-state reaction in Ni–Zr composite wires with different elemental layer thicknesses has been studied in detail. Besides x-ray diffraction and differential scanning calorimetry, dilatometric measurements, magnetization and resistivity measurements, and cross–sectional transmission electron microscopy were used to monitor the reaction during constant-rate heating and to characterize the various reaction products. An amorphous phase initially forms at the interface between the elemental layers. As soon as the layer thickness exceeds a critical value, the intermetallic NiZr phase appears at the interface between the amorphous phase and pure Zr, as shown by TEM investigations. This is due to a reduced velocity of the reaction front caused by the longer diffusion path enabling the intermetallic phase to become stable. As shown in experiments at a constant heating rate, a second intermetallic phase forms at higher temperatures at the interface between Zr and crystalline NiZr. The amorphous phase remains unchanged up to crystallization at about 520 °C. To obtain fully amorphous material, the interdiffusion reaction must be completed (or especially the Zr layers must be completely reacted) before the intermetallic NiZr phase starts to form. A criterion for achieving completely amorphous bulk material is derived.
Microstructure of hardened and softened zirconia after xenon implantation
Authors: Fleischer Elizabeth L. , Norton M. Grant , Zaleski Mark A. , Hertl William , Carter C. Barry , Mayer James W.
Published: September 2007

Ion-channeling and transmission electron microscopy (TEM) techniques were used to examine the microstructure of single-crystal Y2O3 stabilized cubic zirconia (YSZ) after implantation with 240 keV Xe+ ions. The observed microstructure was related to Knoop indentation hardness measurements. These measurements showed an increase in hardness for low ion-doses, reaching some maximum value, then a decrease in hardness at higher doses. In the hardening regime, below 7.5 × 1015 Xe+/cm2, point defects and dislocation networks were observed by TEM. Ion-channeling showed a corresponding increase in damage as a function of ion-dose. For doses between 7.5 × 1015 and 3 × 1016 Xe+/cm2 the hardness falls, and the amount of damage, measured with ion-channeling, reaches a limiting value at less than complete damage. In this dose range the Xe concentration continues to increase beyond the dose where the amount of damage saturates. For high doses, greater than 3 × 1016 Xe+/cm2, where softening of the zirconia occurs, additional reflections appear in the electron diffraction pattern that are consistent with the lattice parameter of solid Xe. A diffuse ring is also visible; this is believed to be due to the presence of fluid Xe. Both ion-channeling and TEM show that a significant amount of monocrystalline zirconia remains even up to doses of 1 × 1017 Xe+/cm2. There is also evidence for the presence of recrystallized zirconia at the high doses. Since so much crystalline material remains, it seems that amorphization of the zirconia is not the dominant cause of the softening at high doses.
High temperature creep of SiC densified using a transient liquid phase
Authors: Jou Zuei C. , Virkar Anil V. , Cutler Raymond A.
Published: September 2007

Silicon carbide-based ceramics can be rapidly densified above approximately 1850 °C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 °C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 °C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 °C were between 10−9/s and 10−7/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of ≍1.7.
Measurement of the fracture toughness of CVD-grown ZnS using a miniaturized disk-bend test
Authors: Zhang Jimin , Ardell Alan J.
Published: September 2007

Novel apparatus and methodology have been developed for measuring the fracture toughness of ceramics using small disk-shaped samples 3 mm in diameter. The method involves the Vickers indentation of specimens ranging in thickness from 300 to 700 μm, and testing them in a ring-on-ring bending mode. Experiments on ZnS grown by chemical vapor deposition (CVD) have been used to evaluate the technique. The apparent fracture toughness of this material increases with crack length (R-curve behavior). This behavior is analyzed using established equations in conjunction with a new graphical method that obviates the need for measuring the apparent toughness of samples containing very large cracks. The fracture toughness at “infinite” crack length, 0.86 ± 0.08 MPa · m1/2, is in very good agreement with the values obtained by conventional methods. The effect of sample size on the accuracy of the results is thoroughly discussed. The thickness, t, of the sample should exceed by a factor of ten the initial crack length produced by the indentation. Also, since samples are tested at various indentation loads, P, the ratio of their thicknesses should be chosen to satisfy the condition t ∝ P2/3. The importance of several parameters in the design of the apparatus is also discussed.
Outgassing behavior of spin-on-glass (SOG)
Authors: Romero J.D. , Khan M. , Fatemi H. , Turlo J.
Published: September 2007

The outgassing behavior and mechanical properties of polysiloxane based and phosphorus doped silicate based films as planarization candidates for device processing were evaluated using various analytical techniques. After curing between 370 °C and 450 °C, a high temperature rebake above 410 °C caused twice the weight loss in polysiloxane based films as in silicate films. This means that further outgassing, which could occur to a greater degree from polysiloxane than from silicate, could lead to a more probable blistering within the interlayer of the sandwiched spin-on-glass (SOG) during subsequent thermal processing. However, a well-cured polysiloxane would be a better candidate for planarization applications because the film was found to absorb less moisture and had lower stress than the silicate. Due to high silanol content and high porosity in silicate, it was found to absorb six times more water than polysiloxane. When water evolved, significantly higher stress levels were observed in silicate than in polysiloxane during thermal cycle tests. Infrared spectroscopic analysis revealed that polysiloxane contained Si–O–CH3 moiety, which rendered the film flexible, while silicate contained near-stoichiometric SiO2 bonds, which made for a more rigid and dense structure. This difference in the film structures translated to three times higher stress in silicate than in polysiloxane. During device processing, it was seen that silicate films were more prone to cracking than polysiloxane films. The components of the outgassing materials were either volatile organic species from residual solvents not completely burned out during cure, or carbon dioxide and water vapor as by-products from further cure. Gas chromatography indicated that both types of films contained volatile organic residues when cured at 370 °C. However, at 410 °C, volatile organic species were present in the polysiloxane but not in the silicate. A 30 to 60 min cure at temperature greater than 410 °C was then found to adequately cure polysiloxane. It was concluded that a “well cured” polysiloxane based spin-on-glass (SOG) would be more suitable than a silicate based SOG for planarization application.
Microstructure of entrained air voids in concrete, Part I
Authors: Rashed Ahmed I. , Williamson Robert Brady
Published: September 2007

The microstructure of air voids in both air-entrained and non air-entrained paste, mortar, and concrete has been studied at different ages (5 min to 60 days) in order to understand how air-entrained voids form in portland-cement systems. Scanning electron micrographs of air voids are presented for different ages. The solidification process of portland-cement paste and mortar was frozen at different ages using a low temperature scanning electron microscope and freeze drying. At very early ages the air voids show thin shells made of very fine particles. The packing of the cement grains behind the air void varies, depending on the water-to-cement ratio. Air voids appear to have the same interface with the cement paste matrix as aggregates. No readily visible difference was found between entrapped and entrained air voids.
Chemically disordered Ni3Al synthesized by high vacuum evaporation
Authors: Harris S.R. , Pearson D.H. , Garland C.M. , Fultz B.
Published: September 2007

Films of chemically disordered fcc Ni3Al were synthesized by the vacuum evaporation of Ni3Al onto room temperature and liquid nitrogen temperature substrates. X-ray diffractometry and transmission electron microscopy showed the material to be single phase with an average grain size of about 4 nm. The formation of the equilibrium L12 ordered phase occurred simultaneously with grain growth at temperatures above 350°C. Differential scanning calorimetry provided ordering enthalpies of 7 kJ/mole and 9 kJ/mole for material evaporated onto room temperature and liquid nitrogen temperature substrates, respectively.
Microstructural features of the hydrogenation-dehydrogenation process in Ti alloys
Authors: Grimberg I. , Levin L. , Botstein O. , Froes F.H.
Published: September 2007

Temporary alloying of Ti alloys with hydrogen is used to modify microstructure and hence enhance mechanical properties. In the present work the influence of the thermal history of the Ti–6Al–4V alloy on the final microstructure was studied. Two different kinds of microstructures were investigated: (a) as-hot isostatic pressed (HIP) having an α + β microstructure; (b) β-solution-treated and subsequently quenched (α'-microstructure). After each stage of the hydrogenation-dehydrogenation (HDH) process the material was analyzed by optical, scanning electron and transmission electron microscopy, and by x-ray diffractometry. It was found that fcc (γ) hydrides precipitate in both the α and the α' matrix. The orientation relationships were found to be the same in both cases. Hydrides precipitate from the β-phase when the hydrogen content of the alloy is sufficiently high. The minimum concentration that still led to precipitation was 1.4 wt. % H. The β/γ orientation relationship was determined. The HDH process resulted in either of two structures: (1) a fine, broken-up microstructure containing a fine mixture of α' + (α + β) when the starting microstructure was α', or (2) a modified α + β microstructure containing fine α and β precipitates and a high density of microdefects within the primary α in the as-HIP α + β microstructure specimens.
Design and production of the Zr3Ti2Si3 intermetallic compound
Authors: Celis Pedro B. , Kagawa Eiji , Ishizaki Kozo
Published: September 2007

The new ternary intermetallic compound Zr3Ti2Si3, with a (Mn5Si3)16H crystal structure, was designed based on the information of the crystal structure of the related binary compounds Zr5Si3 and Ti5Si3 in order to be used in ultra-high temperature structural applications. By x-ray diffraction analysis, we demonstrate the possibility of substituting an entire layer of zirconium atoms with a layer of titanium atoms in the (Zr5Si3)16H. An analysis of atomic neighbor distances in each compound was done. It was found that the Zr–Si relative interatomic distance diminishes while the Ti–Si distance increases. This indicates that Zr–Si bond strength is maintained as in the binary Zr5Si3. The resulting ternary intermetallic compound has a 16H crystal structure and has a lower density than the original compound of zirconium silicide. This new compound, which is stronger than Ti5Si3 and lighter than Zr5Si3, is considered an excellent candidate of the next generation of intermetallic compounds for ultra-high temperature structural applications.
Transient kinetics of nucleation and crystallization: Part I. Nucleation
Authors: Shi G. , Seinfeld J.H.
Published: September 2007

Analytical results obtained for the transient kinetics of nucleation enable one to interpret N(gd,t), the accumulated number concentration of clusters at the instrumentally detectable size, gd. The new results enable one to extract kinetic and thermodynamic parameters of nucleation from experimentally measured cluster concentrations and to test nucleation theories experimentally. An approach to estimate the mean time to form the first nucleated cluster in a given sample is also presented.
Cavity formation and plastic flow ofa–Si: H during heavy ion bombardment
Authors: Klaumünzer S. , Rammensee M. , Löffler S. , Neitzert H.C. , Saemann-Ischenko G.
Published: September 2007

Irradiation of unsupported samples of hydrogenated amorphous silicon below 100 K with 360-MeV Xe ions results in macroscopically visible changes in sample dimensions. These changes have two different causes. Formation and growth of cavities lead to an isotropic increase of the specimen dimensions and to a drastic decrease of the mass density. Simultaneously plastic flow occurs, which produces additional but anisotropic changes of the specimen dimensions. The dimensions perpendicular to the beam grow whereas the dimension parallel to the ion beam shrinks. Neither effect saturates in the investigated fluence range (Φt< 1014Xe/cm2) and both are absent in crystalline silicon. The effects are most likely provoked by electronic excitations and/or ionizations in the wake of the fast ions. With respect to plastic flow,a–Si:H behaves like metallic and oxide glasses. Formation of cavities and their growth, however, seem to occur only in tetrahedrally coordinated solids.
Microstructural and chemical effects in Al2O3 implanted with iron at room temperature and annealed in oxidizing or reducing atmospheres
Authors: McHargue C.J. , Sklad P.S. , White C.W. , Farlow G.C. , Perez A. , Marest G.
Published: September 2007

Rutherford backscattering (RBS)-ion channeling, transmission electron microscopy (TEM), and conversion electron Mössbauer spectroscopy (CEMS) have been used to determine the structure of α–Al2O3 implanted with iron at room temperature. Changes produced by post-implantation annealing in oxidizing and reducing atmospheres were followed using the same techniques. Implantation of 160 keV Fe at room temperature produces a damaged but crystalline microstructure for fluences as high as 1 × 1017 Fe/cm2. The iron resides in a variety of local environments: three Fe2+ components, one Fe0 component, and two Fe4+ components. The relative amount of each component varies with implantation fluence. Only the Fe0 component seems to be associated with second-phase formation. In this case, 2 nm diameter α-iron particles were detected by TEM studies. Recovery of implantation-induced disorder in the Al- and oxygen-sublattices occurs in two stages for annealing in oxygen and in one continuous stage for hydrogen-annealing. The end state for iron is Fe3+ for oxygen anneals and Fe0 for hydrogen anneals. The precipitated phases observed are those to be expected from the equilibrium phase diagrams.
Microstructural and chemical effects in Al2O3 implanted with iron at 77 K and annealed in oxidizing or reducing atmospheres
Authors: McHargue C.J. , Sklad P.S. , White C.W. , McCallum J.C. , Perez A. , Marest G.
Published: September 2007

Implantation of Fe (160 keV) into α–Al2O3 at 77 K produces an amorphous surface layer for fluences in the range of 1016 to 1017 Fe/cm2. Measurements of short-range order were made by extended energy loss fine structure analysis (EXELFS). The structure of amorphous Al2O3 produced by implantation of iron at 77 K exhibits short-range order that differs from that produced by stoichiometric (Al + O) implants. This difference is manifested by changes in the Al–O near-neighbor bond length. The local environments of implanted iron were determined from conversion electron Mössbauer spectroscopy (CEMS). The iron resides in several different local environments consistent with the electronic states of Fe2+, Fe4+, and Fe0. The relative amount of each environment depends upon the concentration (fluence) of the implanted iron ions. Regrowth of the amorphous zone during annealing occurs in the sequence amorphous → γ–Al2O3 ↠ α–Al2O3. The kinetics of regrowth and phase separation vary with implanted fluence and with annealing atmosphere. The higher the concentration of implanted iron, the slower the formation of iron-aluminum oxide precipitate phases in oxidizing atmospheres and α–Fe precipitates in reducing atmospheres.
High dose neutron irradiation damage in alpha alumina
Authors: Youngman R.A. , Mitchell T.E. , Clinard F.W. , Hurley G.F.
Published: September 2007

Bulk samples of single crystalline and polycrystalline alpha alumina have been neutron-irradiated in the Experimental Breeder Reactor-II (EBR-II) to doses of 1026 n/m2 at temperatures of 925 K and 1100 K. The samples were found to swell macroscopically between 3% and 6%, depending on the temperature of irradiation and the form of the material. The damaged microstructures were investigated via transmission electron microscopy in order to understand the origin of the macroscopic swelling. In both single crystals and polycrystals the damage consists of a high density of dislocations containing predominately b = 1/3<101> dislocation loops on the (0001) planes coexistent with a high density of voids, which are aligned along the c-axis in this rhombohedral material. The established theory of void formation in metals is utilized to explain the formation of voids in alumina. The polycrystalline samples were extensively microcracked, and this is thought to be due to anisotropic swelling of the grains which in turn leads to stresses and fracturing at the grain boundaries.
Microstructural development and electrical properties of sol-gel prepared lead zirconate-titanate thin films
Authors: Hsueh Cheng-Chen , Mecartney Martha L.
Published: September 2007

A systematic investigation of the microstructural evolution of fast fired, sol-gel derived Pb(Zr, Ti)O3 films (Zr/Ti = 54/46) was performed by analytical transmission electron microscopy (TEM). It was found that the nucleation and growth of the sol-gel PZT films were influenced by the precursor chemistry. The precursor solution was composed of Pb 2-ethylhexanoate, Ti isopropoxide, and Zr n-propoxide in n-propanol. Porous and spherulitic perovskite grains nucleated and grew from a pyrochlore matrix for NH4OH-modified films, but no chemical segregation was found. These thin films consisted completely of porous spherulitic PZT grains (∼2 μm) when the firing temperature was increased. Chemical phase separation with regions of Zr-rich pyrochlore particles separated by Zr-deficient perovskite grains was observed in the initial stages of nucleation and growth for CH3COOH-modified PZT films. This phase separation is attributed to the effect of acetate ligands on the modification of molecular structure of the PZT precursor. Firing the acid-modified films at higher temperatures for long times resulted in porous perovskite grain structures. The residual porosity in these films is suggested to be a result of differential evaporation/condensation rates during the deposition process and the gas evolution at high temperatures due to trapped organics in the films. Dielectric and ferroelectric properties were correlated to the microstructure of the films. Lower dielectric constants (∼500) and higher coercive fields (∼65 kV/cm) were found for the acid-modified PZT films with phase separation in comparison to those measured from the sol-gel films with a uniform microstructure (∽ > 600, Ec < 50 kV/cm). All films fired at 650 °C showed relatively good remanent polarization on the order of 20 μC/cm2.
Electron microscope study of Synroc before and after exposure to aqueous solutions
Authors: Lumpkin Gregory R. , Smith Katherine L. , Blackford Mark G.
Published: September 2007

A well-characterized Synroc was subjected to durability tests in de-ionized water at 70 °C and 150 °C, and silicate and bicarbonate solutions at 70 °C, to study the effect of temperature and solution composition on the mechanisms of aqueous alteration. SEM and TEM were used before and after durability experiments to characterize the primary and secondary phases in and on the Synroc samples, and to describe changes in morphology and chemistry. Leachant compositions after durability testing were analyzed using ICP/OES and ICP/MS and have been reported elsewhere.8 After durability testing, titaniferous surface layers were observed primarily on perovskite, the most soluble Synroc phase. Electron microscopy demonstrates that the surface layer formed at 70 °C is an amorphous Ti–O film and is fine grained anatase at 150 °C. Congruent dissolution is the major mechanism of perovskite alteration. However, at 150 °C, selective loss of Ca and Sr may occur locally. A number of additional secondary phases were identified, including Al–oxide/hydroxide, Fe–oxide, REE-bearing Ti–oxides, and several silicate phases. The abundance and composition of the secondary phases are related to solution composition and temperature.
The microstructure of SCS-6 SiC fiber
Authors: Ning X.J. , Pirouz P.
Published: September 2007

A thorough investigation of the microstructure of single SCS-6 SiC fibers widely used as reinforcements in metal-matrix and ceramic-matrix composites has been made. Various techniques of electron microscopy (EM) including scanning (SEM), conventional transmission (TEM), high resolution (HREM), parallel electron energy loss spectroscopy (PEELS), and scanning Auger microscopy (SAM) have been used to analyze and characterize the microstructure. The fiber is a complicated composite consisting of many different layers of SiC deposited on a carbon core and different carbonaceous coatings covering the SiC layers. The structural and chemical aspects of each layer are characterized and discussed.
Microstructure and microwave properties of YBCO thin films grown on MgO and SrTiO3 by CVD
Authors: Young K.H. , Robinson McD. , Negrete G.V. , Yamashita T. , Hirai T. , Suzuki H. , Kurosawa H. , Drabeck L. , Grüner G.
Published: September 2007

The microstructure and microwave properties of YBa2Cu3O7−δ thin films grown on SrTiO3 (100) and MgO (100) substrates by chemical vapor deposition have been studied. Both 100 GHz cavity measurement of surface resistance and ground plane substitution in a 5 GHz microstrip resonator show that films on SrTiO3 have better microwave properties than those on MgO. Although there are some a-axis grains and secondary phases on the surface, a large fraction of each film on SrTiO3 is epitaxial with its c axis normal to the substrate. The 100 GHz surface resistance of these films is less than copper for temperature ⋚ 82 K, and approaches the detection limit at 10–20 K. For the films on MgO, c-axis grains of different in-plane rotation are found together with some a-axis needle-like grains. The grain boundaries are detrimental to the microwave properties, and the resulting surface resistance at 100 GHz and 10–20 K is about 20 mΩ higher than that of films on SrTiO3.
The atomic structure of growth interfaces in Y–Ba–Cu–O thin films
Authors: Ramesh R. , Inam A. , Hwang D.M. , Ravi T.S. , Sands T. , Xi X.X. , Wu X.D. , Li Q. , Venkatesan T. , Kilaas R.
Published: September 2007

We have examined the atomic structure of growth interfaces in thin films of Y–Ba–Cu–O grown on [001] perovskite or cubic substrates. At substrate heater temperatures in the range of 780–820 °C c-axis oriented growth is observed on these substrates. On SrTiO3, the first layer appears to be either a BaO or a CuO2 plane while on LaAlO3 the first layer appears to be a CuO chain layer. The mismatch on the a-b plane is accommodated by the formation of interface dislocations. Defects on the substrate surface propagate as defects in the film. These defects are primarily translational boundaries and in some cases second phases. At lower substrate heater temperatures, i.e., 650–700 °C, a, b-axis growth dominates. Defects and steps on the substrate surface are more detrimental in the growth of a, b-axis oriented films, since they tend to favor the nucleation of c-axis oriented domains. This is ascribed to the ledge mechanism of c-axis film growth, for which the surface steps are good nucleation sites.
Influence of silver on critical current of the Y–Ba–Cu–O superconductor
Authors: Itoh Mineo , Ishigaki Hiroyuki , Ohyama Takashi , Minemoto Takumi , Nojiri Hiroyuki , Motokawa Mitsuhiro
Published: September 2007

Electrical properties of Y–Ba–Cu–O superconductors, such as the critical current density and the zero-resistance temperature, are systematically improved by changing the compression pressure during the formation process of the specimens. Also, by changing the silver powder content of the superconducting Y–Ba–Cu–O powder, the critical current density and the zero-resistance temperature are remarkably improved. The resistance-drop temperature is insensitive to changes in the compression pressure, silver content, and magnetic field, if the field is applied perpendicular to the specimens. The critical current density of the specimens with and without silver decreases exponentially with the perpendicular magnetic field. The critical current densities of specimens without silver showed much lower sensitivity to perpendicularly applied magnetic fields than those of the specimens having a silver content. Along with the above improvements, the present paper also examines several factors that affect the superconducting characteristics. These factors include impurities in the air and strong magnetic fields.
Boron and antimony codiffusion in silicon
Authors: Margesin B. , Canteri R. , Solmi S. , Armigliato A. , Baruffaldi F.
Published: September 2007

The codiffusion of B and Sb implanted in Si with a dose of 2 × 1016 cm−2, corresponding to concentration far above the solid solubility, is investigated at 900 and 1000 °C on the basis of SIMS and carrier profile measurements and TEM observations. The comparison of the codiffusion data with the corresponding ones obtained by the diffusion of each element alone revealed several anomalous effects due to dopant interaction. In particular, our experimental results support the hypothesis of the formation of mobile donor-acceptor pairs and of the increase of the Sb solubility in the region where a high concentration of acceptors is present. On the basis of this feature, a diffusion model that takes pairing and precipitation into account is presented. A simulation program including this model allows us to foresee most of the anomalous phenomena occurring in the high concentration codiffusion experiments and shows in general a satisfactory agreement with experimental profiles.
Thin silicon dioxide and nitrided oxide using rapid thermal processing for trench capacitors
Authors: Yoneda Kenji , Todokoro Yoshihiro , Inoue Morio
Published: September 2007

Electrical characteristics of trench capacitors using RTO (Rapid Thermal Oxidation) oxides, nitroxides, and reoxidized nitroxides as the gate insulators are discussed. High temperature RTO is effective in preventing oxide thinning at the trench corner, and so the dielectric strength of trench capacitors is improved drastically. The mean time to failure (MTTF) of trench capacitors using RTO is more than ten times longer than that of trench capacitors using conventional furnaces. Using reoxidized nitroxides as the gate insulator, superior charge to breakdown (QBD) is obtained. RTP (Rapid Thermal Processing) is superior to the process using the conventional furnace for the gate insulators of trench capacitors. Improvements in temperature uniformity, repeatability, and lessening of slip line formation are essential for RTP equipment to be practical.
Highly oriented thin films of cubic zirconia on sapphire through grain growth seeding
Authors: Miller K.T. , Lange F.F.
Published: September 2007

A two-step process has been developed to form highly oriented thin films in material systems with dissimilar crystal structures and interatomic spacings. This processing method utilizes current polycrystalline thin film deposition techniques. In this method, a polycrystalline thin film is first deposited and heat treated to promote its breakup into isolated grains. The breakup process favors those grains that have a low substrate interfacial energy and so produces a film of highly oriented but isolated grains. In the second process step, another polycrystalline thin film is deposited. The remnant grains act as seeds for the growth of a highly oriented thin film. The process is demonstrated through the growth of highly (100) oriented thin films of cubic ZrO2 (25 mol % Y2O3) on (0001) Al2O3 single crystal substrates, a material system in which film and substrate have dissimilar structures and interatomic spacings. Implications for the growth of epitaxial films using this method are discussed.
Chemical vapor deposition of boron nitride using premixed borontrichloride and ammonia
Authors: Pavlović Vladimir , Kötter Horst-Rainer , Meixner Christoph
Published: September 2007

Chemical vapor deposition (CVD) of boron nitride (BN) is most readily performed using BCl3 and NH3, which are brought into the deposition zone through two separate tubes. This causes some problems: inadequate mixing leading to a nonuniform deposit, formation of solid intermediates, etc. To avoid these problems, the process was performed by mixing BCl3 and NH3 at elevated temperatures (120–220 °C) prior to entering the deposition zone. The reaction between them took place by the forming of volatile stoichiometric B–N compounds (trichloroborazine and iminochloroborane), which were then transported through a single tube into a deposition zone. The resulting deposit was found to be hexagonal boron nitride.
High pressure combustion synthesis of aluminum nitride
Authors: Costantino Marc , Firpo Carlo
Published: September 2007

We report initial results on the synthesis of monolithic aluminum nitride by burning Al–AlN mixtures in high pressure nitrogen. The objective is to synthesize economically large, near-theoretical density AlN parts. In this work, we begin with compacted mixtures of 10 μm Al and 3 μm AlN powder formed into 7.62 cm diameter by 3.81 cm thick disks having densities up to 60% of theoretical. Then, at N2 pressures up to 180 MPa (26 000 psi), we ignite the disk on one face. The fraction of Al converted to AlN, density, and severity of macroscopic cracking vary with N2 pressure and heat transfer from the sample. Presently, products are inhomogeneous, showing regions of relatively high porosity, regions with no porosity but with AlN in a matrix of Al, and regions of nearly theoretical density AlN.
Composite ceramic powders obtained by laser induced reactions of silane and amines
Authors: Alexandrescu R. , Morjan I. , Borsella E. , Botti S. , Fantoni R. , Dikonimos-Makris T. , Giorgi R. , Enzo S.
Published: September 2007

Ultrafine, ternary (Si/C/N) ceramic powders have been produced after CO2 laser initiated reactions between silane and mono- or dimethylamine. Various spectroscopic diagnostics and chemical analyses, including ir spectrophotometry, x-ray photoelectron spectroscopy, and x-ray diffraction analysis have been employed to correlate the parameters involved in gas-phase reactions and the powder final composition.
Synthesis and characterization of polyacrylic acid–zinc oxide composites
Authors: Padilla A. , Vázquez A. , Castaño V.M.
Published: September 2007

Zinc oxide (ZnO) powders were mixed with Polyacrylic Acid (PAA) to form waterless cements. The optimal ZnO/PAA ratio in terms of mechanical strength was found. Also, the role of the relation ZnO to PAA, the curing time, and the strain rate on the final properties of the composites was studied.
Effect of composition and grain size on electrical discharge machining of BN–TiB2 composites
Authors: Gadalla A.M. , Bedi H.S.
Published: September 2007

TiB2 conducts the current and forms a liquid phase at the interface with BN. Neighboring crystals of BN and some TiB2 spall due to thermal shock. During pause periods parts of the liquid and fragments are flushed out by the dielectric. Composites rich in TiB2 or with fine TiB2 grains gave high material removal rates. Increasing the amount of the conducting phase by 10% is as effective as decreasing the grain size from 11 to 7 μm. Coarse TiB2 could withstand high pulse durations before wire breaks. Material removal rate increases with pulse duration, frequency, and current. For the same composition and grain size, increasing the pulse duration or current increased the crater depth (the roughness) up to a certain value, beyond which increasing these parameters yielded a smoother surface. The conductivity of the dielectric was effective only for compositions rich in TiB2 content. In such cases, higher water conductivity lowered the energy required for material removal.
Micromechanical theory and uniaxial tensile tests of fiber reinforced cement composites
Authors: Yang C.C. , Mura T. , Shah S.P.
Published: September 2007

The mechanism of fracture arrest in brittle-matrix composites with strong, long fibers is analyzed by using the inclusion method. The maximum stress contribution of the matrix in composites is discussed in this paper. A critical volume fraction of fibersfcis theoretically derived. If the volume fractionfis less thanfc, then debonding between fibers and matrix occurs before the crack propagates through the whole section. Iffis greater thanfc, then no debonding occurs before the crack propagates through the whole section. The value offcdepends on the matrix and fiber properties and the bond character of the interface. To verify the analytical predictions, experiments on fiber reinforced cement composites subjected to uniaxial tension were conducted. The results of the theoretical predictions were also compared satisfactorily with other published experimental data.
Synthesis of KSbOSiO4 by the sol-gel route
Authors: Kanno Y. , Pagnoux C. , Piffard Y. , Touraoux M.
Published: September 2007

Fine powders with high sinterability of KSbOSiO4, an isomorphous derivative of KTiOPO4, have been prepared by a sol-gel route starting from stoichiometric mixtures of KSb(OH)6 and Si(OC2H5)4 with two types of polymerization catalysts: HNO3 and aqueous ammonia. KSbOSiO4 is formed upon calcination of the gels at 1373 K, and the XRPD studies show that HNO3 improves the crystallinity. However, the crystallite size is smaller with aqueous ammonia, which should then improve the sinterability.
Plastic flow between Bridgman anvils under high pressures
Authors: Kuhlmann-Wilsdorf D. , Cai B.C. , Nelson R.B.
Published: September 2007

The shear strength of materials after extensive plastic flow under a superimposed high hydrostatic stress component is most conveniently studied by means of Bridgman opposed anvils between which thin disk-shaped samples are sheared through relative rotation. A newly designed apparatus of this type permits, for the first time ever, the monitoring of sample thickness during shearing and thus the obtaining of averaged shear stress/shear strain curves. Such relations are needed for the better understanding of geological processes, behavior under shock or explosive impact, and of the surface layers during friction and wear, among others. A semiquantitative analysis shows that nonuniform pressure distribution in the samples cannot significantly falsify the results. It is concluded that distributed shearing is always accompanied by sample thinning and that, conversely, slippage between anvils and specimens is indicated whenever the sample stops thinning during rotation. Such slippage can be greatly reduced by raising the friction coefficient through etching of samples and/or anvils, but it apparently occurred undiscovered in previous studies, partly after initial distributed shearing. Further, in previous results slippage between directly contacting anvils was frequently mistaken for sample shearing. Additionally, the previously neglected sample material being extruded during shearing can falsify results, as can “turbulent flow” initiated at sample perforation. Correspondingly all prior data gained with Bridgman apparatuses are suspect. Present best results indicate (i) that in metals ordinary dislocation glide but apparently with strongly increased Peierls–Nabarro stresses continues to the highest pressures studied, (ii) that independent of thermal activation workhardening may cease at high strains, and (iii) that “turbulent flow” resulting through sample perforation or when the sample thickness decreases below a critical value, can give rise to mechanical alloying. The majority if not all of the data by Bridgman as well as Vereshchagin et al. probably involved such mechanical alloying. When plotted versus pressure in units of shear moduli, the apparent coefficients of friction of the five cubic metals examined so far follow nearly the same curve but they are lower for metals of lower symmetry.
Some aspects of forces and fields in atomic models of crack tips
Authors: Hoagland R.G. , Daw M.S. , Hirth J.P.
Published: September 2007

This paper examines the stresses and displacement gradients in atomistic models of cracks based on an EAM potential devised for aluminum. Methods for computing these quantities are described. Results are presented for two models differing in terms of the orientations of the crack relative to the crystal, a [100] (010) orientation that behaves in a brittle fashion and a [111] (110) orientation that emits partial dislocations prior to extending. Both models display lattice trapping. The stresses in the brittle crack model are compared with the linear elastic prediction and found to be in remarkably good agreement to within distances of about one lattice parameter of the crack tip and at the free surface where contributions from sources other than strain energy (e.g., surface tension) influence the results. Similar results are observed for the ductile model until dislocation emission occurs. The largest stresses that develop just prior to crack extension or dislocation emission are used to estimate the ratio of theoretical tensile strength to shear strength in this material. Eshelby's conservation integrals, F and M, are also computed. F is found to be essentially contour independent and in agreement with the linear elastic prediction in both models until dislocation emission occurs, at which point a large screening contribution arises from the emitted partials. The contour size dependence of M reveals some interesting features of the crack tip including a slight wobble of the crack tip inside its potential well with changing applied K and the existence of forces acting to move the crack faces apart as blunting occurs.
Interaction of a screw dislocation with a crack in an anisotropic body
Authors: Zhang Tong-Yi , Hack J.E.
Published: September 2007

The stress field, image force, and shielding effect of a screw dislocation in the vicinity of a Mode III crack were formulated for both semi-infinite and finite length cracks. The results show that there is an abnormal stress component, ŝ31, on the crack plane. This leads to a nonzero image force along the axis perpendicular to the crack plane when the dislocation is located on the crack plane. However, the abnormal stress component and image force disappear for orthotropic and isotropic media. The image force along a slip plane has the same expression as in isotropic media with an effective shear modulus. Generally the shielding effects are the same as in isotropic media. The anisotropy changes only the magnitude of the shielding effects. The case of multiple dislocations is also discussed.
Effect of tip radius on nanoindentation
Authors: Shih C.W. , Yang M. , Li J.C.M.
Published: September 2007

The blunt tip geometry of the so-called nanoindenter is modeled by a spherical cap of various radii. The relation between area and penetration depth of the indenter is comparable with experimental results if the radius of the tip is about 1.0 μm. Simulation of indentation tests was carried out using the finite element method by incremental loading and unloading based on a continuum model. Good agreement with the experimental results for nickel is obtained also for a tip radius of 1.0 μm.
Solidification of Al65Cu20Co15 and Al65Cu15Co20 alloys
Authors: Grushko B. , Urban K.
Published: September 2007

The solidification behavior of Al65Cu20Co15 and Al65Cu15Co20 alloys was studied by means of scanning electron microscopy, energy-dispersive x-ray analysis, powder x-ray diffraction, and differential thermal analysis. Slowly cooled as well as rapidly cooled ingots of both alloys contained a decagonal quasicrystalline phase as dominant phase with additions of several minor normal-crystalline phases. The decagonal phase was found to solidify in a temperature range limited by two peritectic reactions involving phases of CsCl-type structure. Formation of AlCu and Al2Cu phases was also observed.