bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphization and metastable polymorphs of ordered intermetallics Zr3Al and Ni3Al
Authors: Ma E.
Published: September 2007

Observations of various metastable crystalline and amorphous polymorphs of Ll2-type intermetallics Zr3Al and Ni3Al are summarized. The difference in the tendency of these two alloys to become amorphous is obvious. Regardless of the nonequilibrium routes employed for synthesis and processing, amorphous Zr3Al is obtained easily, while amorphization of Ni3Al is rare. An analysis of thermodynamic and kinetic factors responsible for the observed polymorph selection and amorphization behavior is presented. The inadequacy of a simplified model proposed earlier is also discussed.
Pyrolytic properties of di-n-butyltin(IV) diacetate as a precursor for sprayed SnO2 thin films
Authors: Yagi Isao , Ikeda Eiichiro , Kuniya Yasuo
Published: September 2007

The saturated vapor pressure and pyrolytic properties of di-n-butyltin(IV) diacetate have been investigated with and without oxygen in order to understand the orientational growth of SnO2 thin films by spray pyrolysis. The dependence of the saturated vapor pressure on temperature was determined: log P(evap.)Torr = −2.827 × 103/T + 7.687. It has been found that the pyrolysis of this compound consisted of two stages: elimination of the n-butyl groups in a temperature range between about 280°and 310 °C, and of the acetoxy groups above 320 °C. Such decompositions were shifted toward lower temperatures under oxygen. It was also found that oxygen in air in addition to intramolecular oxygen contributed to the formation of SnO2 crystal phase. Moreover, it was suggested that pyrolized chemical species preserving the Sn-O bond probably related the orientational growth of the (200) plane of sprayed SnO2 thin films.
Influence of donor density in ZnO on ZnO–PrCoOx thin-film junctions: Role of O2 and Al dopant in varistors
Authors: Yano Yoshihiko , Shirakawa Yukihiko , Morooka Hisao
Published: September 2007

ZnO/PrCoOx and ZnO/PrCoOx/ZnO junctions have been fabricated by sputtering as a model of a single grain boundary in a ceramic ZnO varistor. The relations between barrier parameters and varistor characteristics were investigated using voltage-current (V-I) capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The varistor voltage of the junctions increases as the donor density (ND) of the ZnO film decreases. The interface states vary according to the method of ZnO sputtering. A clear correlation has been established between the α value and the interface states. The highest α value is obtained when ND is ≃ 1018 cm−3, the interface level is 0.70 eV, and the breakdown voltage is 3–4 V. Oxygen is effective on control of ND in ZnO and the interface states. Al added as a dopant is also effective in terms of its ability to increase ND in ZnO. However, Al doping was found to degrade the interface states and increase the leakage current.
Heteroepitaxy of cubic zirconia on basal and prismatic planes of sapphire
Authors: Cain M.G. , Lange F.F.
Published: September 2007

The epitaxial growth of yttria stabilized cubic zirconia produced via the solution precursor route deposited onto the basal and prismatic planes of sapphire was characterized. The evolution of the polycrystalline thin film was described with reference to two concurrent physical processes: abnormal grain growth due to the growth of grains with preferred orientations and a morphological instability which resulted in an uncovering of the substrate. X-ray diffraction, electron backscattering patterns (EBSP), and transmission electron microscopy (TEM) (plan- and cross-sectional view) were used to determine the epitaxial relation (normal and in-plane). The observed epitaxial orientations for the two substrate planes are listed in Table I. A computer search was used to determine the planar, near coincident site lattices (NCSL) for the observed normal epitaxial relations (c-plane: [001]ZrO2ll[0001]Al2O3; a-plane: [001]ZrO2‖[1210[Al2O3). The determined NCSL's did include all the observed epitaxial relations, but also included others not observed within the same range of misfit and coincident site density.
The radiation-induced crystalline-to-amorphous transition in zircon
Authors: Weber William J. , Ewing Rodney C. , Wang Lu-Min
Published: September 2007

A comprehensive understanding of radiation effects in zircon, ZrSiO4, over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural zircon, Pu-doped zircon, and ion-beam irradiated zircon. Radiation damage in zircon results in the simultaneous accumulation of both point defects and amorphous regions. The amorphization process is consistent with models based on the multiple overlap of particle tracks, suggesting that amorphization occurs as a result of a critical defect concentration. The amorphization dose increases with temperature in two stages (below 300 K and above 473 K) and is nearly independent of the damage source (α-decay events or heavy-ion beams) at 300 K. Recrystallization of completely amorphous zircon occurs above 1300 K and is a two-step process that involves the initial formation of pseudo-cubic ZrO2.
Synthesis of barium hexaferrite by pyrolysis of an aerosol
Authors: Cabañas M.V. , González-Calbet J.M. , Vallet-Regí M.
Published: September 2007

Polycrystalline BaFe12O19 has been synthesized by pyrolysis of an aerosol produced by ultrahigh frequency spraying of a solution. Two precursor solutions have been used in order to study its influence on the formation temperature of the barium hexaferrite and on the microstructural and magnetic properties. The relationship between in situ temperature, pyrolysis precursor, and textural and magnetic properties of the products obtained is discussed.
Heat treatment of spun-on acid-catalyzed sol-gel silica films
Authors: Parrill T.M.
Published: September 2007

SiO2 films, formed by spin coating acid-catalyzed TEOS-based sol-gel on Si substrates, were annealed at 300–1000 °C and analyzed using ellipsometry, FTIR, and in situ stress measurements. Film porosity ranged from an average of 28% before annealing to 7% after annealing 3 h at 1000 °C. Below ≍800 °C, water and silanol removal caused a decrease in refractive index and increase in the in-plane tensile stress. Infrared spectra indicated compressive strain normal to the plane, however. Above ≍800 °C, further densification and structural relaxation occurred. Exposure to H2O also caused relaxation after annealing, as the most compressed Si–O–Si units reacted preferentially with moisture.
Thermal properties of organic and inorganic aerogels
Authors: Hrubesh Lawrence W. , Pekala Richard W.
Published: September 2007

Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. This paper examines the three major contributions to thermal transport through porous materials, solid, gaseous, and radiative, to identify how to reduce the thermal conductivity of air-filled aerogels. We found that significant improvements in the thermal insulation property of aerogels are possible by (i) employing materials with a low intrinsic solid conductivity, (ii) reducing the average pore size within aerogels, and (iii) affecting an increase of the infrared extinction in aerogels. Theoretically, polystyrene is the best of the organic materials and zirconia is the best inorganic material to use for the lowest achievable conductivity. Significant reduction of the thermal conductivity for all aerogel varieties is predicted with only a modest decrease of the average pore size. This might be achieved by modifying the sol-gel chemistry leading to aerogels. For example, a thermal resistance value of R = 20 per inch would be possible for an air-filled resorcinol-formaldehyde aerogel at a density of 156 kg/m3, if the average pore size was less than 35 nm. An equation is included which facilitates the calculation of the optimum density for the minimum total thermal conductivity, for all varieties of aerogels.
Deformation and fracture of mica-containing glass-ceramics in Hertzian contacts
Authors: Cai Hongda , Kalceff Stevens Marion A. , Lawn Brian R.
Published: September 2007

The Hertzian indentation response of a machinable mica-containing glass-ceramic is studied. Relative to the highly brittle base glass from which it is formed, the glass-ceramic shows evidence of considerable “ductility” in its indentation stress-strain response. Section views through the indentation sites reveal a transition from classical cone fracture outside the contact area in the base glass to accumulated subsurface deformation-microfracture in the glass-ceramic. The deformation is attributed to shear-driven sliding at the weak interfaces between the mica flakes and glass matrix. Extensile microcracks initiate at the shear-fault interfaces and propagate into the matrix, ultimately coalescing with neighbors at adjacent mica flakes to effect easy material removal. The faults are subject to strong compressive stresses in the Hertzian field, suggesting that frictional tractions are an important element in the micromechanics. Bend-test measurements on indented specimens show that the glass-ceramic, although weaker than its base glass counterpart, has superior resistance to strength degradation at high contact loads. Implications of the results in relation to microstructural design of glass-ceramics for optimal toughness, strength, and wear and fatigue properties are discussed.
Atomistic structure and lattice effects of vacancies in Ni-Al intermetallics
Authors: Xie Zhao-Yang , Farkas Diana
Published: September 2007

Atomistic computer simulation with embedded atom method potentials has been performed to study the energetics and structures of point defects in L12Ni3A1 and B2 NiAl. The large size of Al atoms plays a dominant role in the relaxed atomic configurations of vacancies and antisite defects in the system. In both Ni3Al and NiAl, it was found that excess Ni can be accommodated by Ni in Al sites. Accommodation of excess Al by locating Al in Ni sites is not energetically favorable in NiAl. The most stable di-vacancy configuration is two vacancies as first nearest neighbors in Ni sublattices for Ni3Al and as second nearest neighbors in Al sublattices for NiAl. General attraction of two vacancies in Ni3Al was found. On the contrary, vacancies in NiAl show repulsive interaction in several cases. This accounts for the existence of structural vacancies in B2 NiAl. The effects of different degrees of random disorder on the lattice parameters were evaluated, and it was found that these effects can be correlated with the local distortion around antisite defects using a simple model.
Synthesis and superstructural characterization of Fe1.89Mo4.11O7
Authors: Schimek George L. , McCarley Robert E. , Scott Chumbley L.
Published: September 2007

Superstructuring in the new compound Fe1.89Mo4.11O7 has been elucidated by transmission electron microscopy. This compound is a member of the family M2MO4O7 and has both iron and molybdenum atoms occupying octahedrally coordinated sites in the structure, represented by Fet(Fe0.89M0.11)0Mo4O7. The superstructuring, detected only by electron diffraction, involved tripling of all three lattice parameters of the subcell. The subcell was structured by single crystal x-ray diffraction [Imma, no. 74, a = 5.9793(5) Å, b = 5.7704(4) Å, and c = 17.036(1) Å]. This structure type contains a close-packed arrangement of Mo4O7 units, which are infinite chains of trans edge-shared molybdenum octahedra running parallel to b*. Two different coordination environments are observed for the cations. Parallel to the a* direction, infinite edge-sharing MO6 (M = 89% Fe or 11% Mo) octahedra are observed. The second cation site, with nearly tetrahedral coordination by oxygen, is filled solely by iron. The superstructure can be rationalized by a regular arrangement of iron and molybdenum atoms in the octahedrally coordinated cation sites.
Initial stages of SiOx deposition on graphite
Authors: Hoveland M. M. , Danner J. B. , Vohs J. M. , Bonnell D. A.
Published: September 2007

The reaction of tetraethoxysilane (TEOS) and the subsequent deposition of SiOx on the basal plane and edges of highly oriented pyrolytic graphite (HOPG) were studied. Interfacial bonding and surface morphologies resulting from different reaction conditions were probed using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), Rutherford backscattering spectroscopy (RBS), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS). The initial reaction of TEOS was found to occur at surface defects. STM images indicated that SiCx films do not grow layer-by-layer, confirming earlier indirect observations to that effect.
Structural and optical characterization of BaTiO3 thin films prepared by metal-organic deposition from barium 2-ethylhexanoate and titanium dimethoxy dineodecanoate
Authors: Ousi-Benomar W. , Xue S.S. , Lessard R.A. , Singh A. , Wu Z. L. , Kuo P. K.
Published: September 2007

Single phase BaTi03 thin films were prepared by metal-organic deposition (MOD) using barium 2-ethylhexanoate and titanium dimethoxy dineodecanoate as the metal-organic precursors. A series of experiments was conducted on the metal-organic spin-coated films and their correspondingly annealed samples by employing experimental techniques ranging from thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), to various optical property characterization methods. A better understanding has been achieved regarding the metal-organic decomposition mechanism, the solid-state BaTi03 film formation and crystallization process, as well as the relationship between the structure and the optical properties of the prepared films. The conclusions of our experiments are as follows: Upon annealing the barium 2-ethylhexanoate spin-coated films, barium carbonate (BaC03) is formed at a relatively low temperature of 300 °C, and at an annealing temperature around 700 °C forms the barium peroxymonocarbonate (BaCO4). Upon annealing the titanium dimethoxy dineodecanoate spin-coated films, anatase is first formed at a low annealing temperature about 400 °C and transforms to rutile phase around an annealing temperature of 800 °C. Upon annealing the spin-coated films from the equimolar mixture of barium 2-ethylhexanoate and titanium dimethoxy dineodecanoate formulations, BaTi03 is formed around an annealing temperature of 600 °C via solid-state reaction between BaCO3 and TiO2 (anatase). The structure of MOD prepared BaTiO3 films has several specific features: instead of the columnar structure in physical vapor deposited (PVD) films, the crystal grains in granular shape are characteristic of MOD films, and the crystallites are much larger near the surface of the film than near the substrates. Optical properties of the prepared BaTi03 films have been reported. Optical characterization shows that the scattering losses contribute dominantly to the total optical losses. The relationship between the structure and the optical properties of the prepared films has also been discussed.
Nanowires formed in anodic oxide nanotemplates
Authors: Al-Mawlawi D. , Liu C. Z. , Moskovits Martin
Published: September 2007

A simple electrochemical method is described for producing metal or semiconductor nanowires with diameters in the continuous range 10 to 200 nm. The technique involves a three-step process that begins with the electrochemical generation of an aluminum oxide template with uniform nanometer-sized pores, followed by the deposition of metal or semiconductor in them. The nanowires are then exposed for study or device fabrication by etching back the oxide matrix. Examples of cadmium nanowires fabricated by this technique are shown.
The synthesis of TiAl intermetallic films by a rf magnetron sputtering and the mechanical properties of the microcomposites with SiC fibers
Authors: Suzuki Takakazu , Umehara Hiroyuki , Hayashi Ryuichi
Published: September 2007

The intermetallic matrix composites reinforced with heat-resistive fibers are expected to improve the ductility and the toughness of intermetallic compounds. Titanium aluminide, TiAl, shows a unique behavior that increases the mechanical strength with increasing temperature up to 1000 K. Vapor phase processings for manufacturing near-net-shaped composites or continuous fiber-reinforced composites will be hopeful methods. The synthesis of TiAl by a magnetron sputtering using a multiple target has been successfully established, and the microcomposites with SiC fibers have been prepared. The TiAl film was evaluated by Auger electron spectroscopy and the x-ray analysis and so on. The tensile strength properties of the SiC/TiAl microcomposites, of which the interface bonding was controlled with the powers of sputtering, were estimated. The results show that the strength properties of SiC/TiAl microcomposites are decreasing with increasing the power of the sputtering, and the irradiation-cured SiC fiber has better compatibility with TiAl than the oxidation-cured SiC fiber.
Fiber push-out testing apparatus for elevated temperatures
Authors: Eldridge Jeffrey I. , Ebihara Ben T.
Published: September 2007

A newly developed apparatus has been designed for performing fiber push-out testing on continuous fiber-reinforced composites at elevated temperatures. This test measures the force at which a fiber resists being pushed by a flat-bottomed indenter moving at a constant speed. The applied load versus time curve characterizes the fiber debonding and sliding behavior. Extending measurements to elevated temperatures required incorporating sample/indenter heating in a nonoxidizing environment. With this new apparatus, fiber push-out tests have been performed up to 1100 δC in a vacuum of 10-6 Torr. A line-of-sight to the sample is maintained during the test which allows video monitoring of the push-out process. Results are shown for SCS-6 SiC fiber-reinforced Ti-24Al-llNb (at. %) and Ti-15V-3Cr-3Sn-3Al (at. %) matrix composites. The results are discussed in terms of residual stresses, interfacial wear, matrix ductility, and changing modes of interfacial failure. The effect of temperature-dependent interfacial wear on the interfacial roughness contribution to frictional shear stresses during fiber sliding is examined.
Superconducting YBa2Cu3Ox films prepared on YSZ polycrystalline substrates by rf thermal plasma evaporation
Authors: Tsujino J. , Tatsumi N. , Shiohara Y.
Published: September 2007

As-grown YBa2Cu3Ox films prepared on single crystal (100)MgO substrates by rf thermal plasma evaporation have the advantages of a high deposition rate of 730 nm/min, a large area deposition over 300 cm2, and a high Jc of 6.8 × 105 A/cm2 (77 K, O T), as reported in previous papers.1,2 We report in this paper about the preparation of YBa2Cu3Ox films on yttria-stabilized zirconia (YSZ) polycrystalline substrates for a practical application using this technique to synthesize these films on flexible (metal or flexible polycrystal) substrates. Films prepared on YSZ polycrystalline substrates grew with a c-axis orientation at a relatively high deposition rate and exhibited a zero resistance temperature (TcO) of 88 K and a critical current density Jc of 3500 A/cm2 (77 K, O T). Films prepared on flexible YSZ polycrystalline tapes with a length of 100 mm were also grown with a c-axis orientation and exhibited TcO) over 77 K.
Deformation mechanisms of Al films on oxidized Si wafers
Authors: Volkert C.A. , Alofs C.F. , Liefting J.R.
Published: September 2007

The mechanism for plastic deformation of 0.5 μm thick, 0.5 μm grain-size evaporated Al films on oxidized Si wafers has been studied using wafer curvature measurements over a temperature range from room temperature to 500 °C. Extensive evidence for both morphology changes and plastic deformation was obtained. Transmission electron microscopy confirmed the occurrence of grain growth, and stress changes attributed to recrystallization were observed. Deformation under tension could be explained by dislocation glide according to the kinetics observed in bulk Al at the same temperatures, stresses, and grain sizes. The kinetics of deformation under compression were investigated at 400 °C and were completely different from those under tension. This is either due to a difference in the deformation mechanism or to the occurrence of work softening.
Crack propagation and deformation behavior of Al2O3-24 vol. % ZrO2 composite studied by transmission electron microscopy
Authors: Lee Byong-Taek , Hiraga Kenji
Published: September 2007

Crack propagation and deformation behavior of a pressureless-sintered Al2O3-24 vol. % ZrO2 composite have been studied by transmission electron microscopy on Vickers-indented specimens from room temperature to 1200 °C. Hardness of the composite gradually decreases with increasing temperature, whereas the ratio of indent to crack lengths, which corresponds to the apparent toughness of materials, decreases up to about 1000 °C and then quickly increases with increasing temperature. In the samples indented at room temperature and 1000 °C, most of the cracks propagate along Al2O3/ZrO2 interfaces and Al2O3 grain boundaries, but a few monoclinic ZrO2 grains are transgranularly fractured. These fractured grains are heavily deformed and produce a marked reduction of the driving force for propagation of cracks at room temperature. In the sample indented at 1200 °C, cracks are hardly observed, but on the other hand, formation of subgrain boundaries, elongation of grains, and grain boundary sliding are observed both in the Al2O3 and ZrO2 grains located around the indentation site.
Morphology of TiSi2 and ZrSi2 on Si(100) and (111) surfaces
Authors: Sukow C.A. , Nemanich R.J.
Published: September 2007

The morphologies of ZrSi2 on Si(111) and TiSi2 on Si(111) and (100) have been investigated, and the results compared and contrasted. Films were prepared by UHV deposition of Ti or Zr onto clean, reconstructed Si(100) or (111) substrates, and reacted by in situ annealing. The sheet resistivity of the ZrSi2 was measured and found to be 33-42 μΩ-cm. The morphologies were examined by transmission and scanning electron microscopy. In particular, the islanding properties were studied; both the temperature of the onset of islanding and the island characteristics were measured. The surface and interface energies have been determined from the contact angles of the silicide islands, according to a solid-state capillarity model. The system of ZrSi2 on Si(111) was found to have surface and interface energies lower than those of the system of TiSi2 on Si(100), but higher than those of the system TiSi2 on Si(111). ZrSi2 on Si(111) was found to island at a higher temperature than TiSi2 on either substrate, a result attributed to kinetic effects. Areal coverage of the islands was measured, and the results were consistent with the solid-state capillarity model. For both TiSi2 and ZrSi2, increasing faceted structure was observed with increasing anneal temperature. Preferred faceting planes were found to be of Si(111) and (100) type for TiSi2 islands and of Si(111) type for ZrSi2. Faceted islands were apparently epitaxial. As the solid-state capillarity model does not directly apply to islands with a faceted structure, an observation of the percentage of faceted islands produced by different annealing temperatures was used to suggest the processing conditions in which the model is applicable.
Effect of intergranular glass films on the electrical conductivity of 3Y-TZP
Authors: Gödickemeier M. , Michel B. , Orliukas A. , Bohac P. , Sasaki K. , Gauckler L. , Heinrich H. , Schwander P. , Kostorz G. , Hofmann H. , Frei O.
Published: September 2007

The electrical conductivity of 3Y-TZP ceramics containing SiO2 and Al2O3 has been investigated by complex impedance spectroscopy between 500 and 1270 K. At low temperatures, the total electrical conductivity is suppressed by the grain boundary glass films. The equilibrium thickness of intergranular films is 1-2 nm, as derived using the “brick-layer” model and measured by HRTEM. A change in the slope of the conductivity Arrhenius plots occurs at the characteristic temperature Tb at which the macroscopic grain boundary resistivity has the same value as the resistivity of the grains. The temperature dependence of the conductivity is discussed in terms of a series combination of RC elements.
Vapor phase synthesis of Al-doped titania powders
Authors: Akhtar Kamal M. , Pratsinis Sotiris E. , Mastrangelo Sebastian V.R.
Published: September 2007

The role of aluminum as dopant in gas phase synthesis of titania powders was experimentally investigated in an aerosol flow reactor between 1300 and 1700 K. Titania was produced by vapor phase oxidation of titanium tetrachloride in the presence of dopant aluminum trichloride vapor. The presence of aluminum altered the particle morphology from polyhedral to irregular crystals. Energy dispersive analysis and transmission electron microscopy indicated that the powders were mixtures of crystalline titania and amorphous alumina. Analysis by XPS indicated significant enrichment of aluminum on the particle surface. Some aluminum titanate (up to 17% by volume) was formed at 1700 K when a high concentration of AlCl3 was used (AlCl3/TiCl4 ≥ 0.07). Measurements of lattice parameters by x-ray diffraction indicated that aluminum formed a solid solution in titania. While titania synthesized in the absence of aluminum was about 90% anatase, the introduction of aluminum resulted in pure rutile at AlCl3/TiCl4 = 0.07. The effects of aluminum on titania phase composition and morphology are explained by the creation of oxygen vacancies in the titania crystallites and by the enhancement of the sintring rate of titania grains.
Electro-optic potassium-tantalate-niobate films prepared by pulsed laser deposition from segmented pellets
Authors: Yilmaz S. , Gerhard-Multhaupt R. , Bonner W.A. , Hwang D.M. , Inam A. , Martinez J.A. , Ravi T.S. , Sands T. , Wilkens B.J. , Wu X.D. , Venkatesan T.
Published: September 2007

Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser deposition and investigated with a number of analytical techniques, including electrical and electro-optical measurements. For applications in longitudinal electro-optic modulators, a transparent electrode is required between substrate and electro-optic layers. Suitable electrode materials, which at the same time permit epitaxial growth of KTN, were identified and prepared. The resulting layered samples were not only of good epitaxial and optical quality, but also exhibited the expected maximum of the longitudinal electro-optic effect at temperatures between the phase transitions from cubic to tetragonal and from tetragonal to orthorhombic. However, the maximum achievable electro-optic phase shift was found to be limited to roughly τ/100 for KTN films in the thickness range around 1 μm. Therefore, much thicker films are probably necessary for most practical applications, which requires significant improvements in the long-term stability and homogeneity of the deposition process.
Effects of oxygen ion energy on the growth of CuO films by molecular beam epitaxy using mass-separated low-energy O+ beams
Authors: Kita Ryusuke , Kawaguchi Kenichi , Hase Takashi , Koga Takeshi , Itti Rittaporn , Morishita Tadataka
Published: September 2007

We have studied the effects of the kinetic energy of mass-separated O+ beams on the growth of CuO thin films deposited on unheated MgO(001) and at 510 °C, in energy ranging from 10 to 200 eV by x-ray photoemission spectroscopy, x-ray diffraction, reflection high-energy electron diffraction, and scanning electron microscopy. The films deposited at 510 °C show a full width at the half maximum (FWHM) of 0.06°for the rocking curve through the (111) peak, regardless of the kinetic energy of oxygen ions. CuO has been epitaxially grown on MgO(001) without heating it in a vacuum of 4 × 10−7 Pa. The x-ray diffraction intensity of the CuO(111) increases with an increase in the kinetic energy of O+, and its FWHM approaches that of the CuO film grown at 510 °C. The surface morphology is improved for the films deposited on unheated substrates.
Synthesis of single phase YBa2Cu3O7−x thin films from a Y-Ba-Cu metallic precursor by a low-temperature annealing
Authors: Hase Takashi , Kita Ryusuke , Kawaguchi Kenichi , Koga Takeshi , Morishita Tadataka
Published: September 2007

YBa2Cu3O7−x (YBCO) superconducting thin films that show no x-ray diffraction peaks due to any other non-superconducting phases have been synthesized by annealing Y-Ba-Cu-O amorphous precursors at 750 °C. The Y-Ba-Cu-O precursors have been fabricated by oxidizing Y-Ba-Cu metallic precursors coevaporated from Y, Ba, and Cu metallic sources under ultrahigh vacuum conditions. Crystallization behavior from the Y-Ba-Cu-O precursor to YBCO films drastically depends on an oxidation temperature for the Y-Ba-Cu metallic precursor. YBCO thin film synthesized from the precursor oxidized at an optimum temperature shows a zero resistance temperature of over 80 K and a very smooth surface.
Mechanical behavior of fine-grained Mg-6.5Li at elevated temperature
Authors: Taleff Eric M. , Sherby Oleg D.
Published: September 2007

A Mg-6.5 wt. % Li alloy containing 80% hep alpha phase and 20% bcc beta phase was processed to achieve an average grain size of 5.9 μm. Strain-rate-change tests were performed in the temperature range from 398 K to 573 K. Two types of creep behavior were observed. A stress exponent of five, obtained at low temperatures and high stresses, is attributed to a diffusion-controlled dislocation creep process in the alpha matrix. A stress exponent of three, obtained at high temperatures and low stresses, is attributed to a solute-drag controlled dislocation creep process in the alpha matrix.
X-ray structural studies of epitaxial yttrium silicide on Si(111)
Authors: Martínez-Miranda L.J. , Santiago-Avilés J.J. , Graham W.R. , Heiney P.A. , Siegal M.P.
Published: September 2007

We performed a series of glancing angle and reflection x-ray diffraction experiments to study both the in-plane and out-of-plane structure of epitaxial YSi2−x films grown on Si(111), with thicknesses ranging from 85 Å to 510 Å. These measurements allowed us to characterize the mean film lattice constants, the position correlation lengths of the film, and the presence and extent of strain as a function of film thickness. We find that the strain along the basal plane increases as a function of increasing thickness to approximately 1% in the 510 Å film; the corresponding out-of-plane strain is such that the film unit cell volume increases as a function of thickness. The corresponding in-plane microscopic strain varies from 0.5% for the 85 Å film to 0.3% for the 510 Å film. We relate our results to the mode of film growth and the presence of pinholes in the films.
Low frequency damping and ultrasonic attenuation in Ti3Sn-based alloys
Authors: Wong Catherine R. , Fleischer Robert L.
Published: September 2007

Studies of high-temperature alloys in the Ti-Sn system based on the intermetallic compound Ti3Sn have identified alloys that damp strongly both at low frequencies (0.1 to 10 Hz) and high frequencies (5 to 20 MHz). The low frequency damping behavior shows loss factors as high as 0.04 at room temperature and Young's moduli that rise with temperature from 40 °C to 100 °C for two alloys. Although the basic mechanism or mechanisms of energy dissipation are presently unknown, the alloys are notable for unusual shapes of microhardness indentations. The deformations imply that large reversible strains can occur at temperatures from 23 °C to 1150 °C.
Structure and mechanical properties of epitaxial TiN/V0.3Nb0.7N(100) superlattices
Authors: Mirkarimi P.B. , Barnett S.A. , Hubbard K.M. , Jervis T.R. , Hultman L.
Published: September 2007

Epitaxial TiN/V0.3Nb0.7N superlattices with a 1.7% lattice mismatch between the layers were grown by reactive magnetron sputtering on MgO(001) substrates. Superlattice structure, crystalline perfection, composition modulation amplitudes, and coherency strains were studied using transmission electron microscopy and x-ray diffraction. Hardness H and elastic modulus were measured by nanoindentation. H increased rapidly with increasing Λ, peaking at H values ≍75% greater than rule-of-mixtures values at Λ ≍ 6 nm, before decreasing slightly with further increases in Λ. A comparison with previously studied lattice-matched TiN/V0.6Nb0.4N superlattices, which had nearly identical composition modulation amplitudes, showed a similar H variation, but a smaller H enhancement of ≍50%. The results suggest that coherency strains, which were larger for the mismatched TiN/V0.3Nb0.7N superlattices, were responsible for the larger hardness enhancement. The results are discussed in terms of coherency strain theories developed for spinodally decomposed materials. Nanoindenter elastic modulus results showed no significant anomalies.
Thermochemical stability of BaFe12O19and BaFe2O4and phase relations in the Ba-Fe-O ternary system
Authors: Li Jinshan , Gür Turgut M. , Sinclair Robert , Rosenblum Stephen S. , Hayashi Hidetaka
Published: September 2007

The stability of BaFe12O19and BaFe2O4was studied by the oxygen coulometric titration technique between 700 °C and 1000 °C using a solid-state electrochemical cell. This temperature range is technologically important for the deposition of BaFe2O19magnetic thin films. The thermodynamic information obtained from the titration measurements was corroborated with structural identification of phases prepared under electrochemically controlled conditions. Accordingly, a section of the Ba–Fe–O ternary phase diagram around the BaFe12O19composition was constructed in this temperature range. The standard Gibbs free energy change for the decomposition of BaFe12O19into BaFe2O4, Fe3O4, and O2is given by the expression ΔG°[J/mol] = 7.23 × 105−480T. In the oxygen pressure-temperature domain, the thermodynamic stability limits of BaFe12O19and BaFe2O4are given by the expressions In[Po2(atm)] = 69.37 −1.04 × 105T−1and In[Po2(atm)] = 27.68 −7.12 × 104T−1, respectively. The stability limits determined here help define the process conditions for the successful synthesis of these phases.
Fracture surface analysis of free-standing diamond films
Authors: Hehn L.P. , Chen Z. , Mecholsky J.J. , Klocek P. , Hoggins J.T. , Trombetta J.M.
Published: September 2007

Free-standing CVD diamond disk-shaped films of varying thicknesses between ∼40 and 1000 μm were fractured in ball-on-ring flexure using a high-precision hydraulic testing machine. Some of the films were smooth on the side formerly in contact with the substrate and rough (large crystallites) on the reverse side and some of the films were polished. Raman spectroscopic examination showed some of the films to be of high quality and others to be of lower quality (higher levels of non-diamond carbon mixed with diamond phase). All fracture surfaces were examined to identify the origin of failure. Strength varied between 650 and 971 MPa, and the fracture toughness was determined from fracture surface analysis to average 8 ± 1 MPam1/2.
Direct correlation of microtwin distribution with growth face morphology of CVD diamond films by a novel TEM technique
Authors: Wang Z.L. , Bentley J. , Clausing R.E. , Heatherly L. , Horton L.L.
Published: September 2007

A thick as-grown diamond film was examined directly by conventional transmission electron microscopy (TEM) without thinning, and the important microstructures near the growth surface were characterized. Specimen preparation for TEM involved simply fracturing the film; some of the diamond grains located on the specimen edge were thin enough to be directly examined by TEM. The 3-D topography of the diamond grains located at the intersection of the growth and the fracture surfaces was obtained using secondary electron images, so that the 2-D projected grain geometry could be derived easily to help interpret the TEM images. A diamond film grown with a 〈001〉 texture and having grains 2–3 μm diameter with {001} facets parallel to the substrate and four inclined {111} facets was examined. Grains with fracture surfaces that intersected the top (001) facet, grains with fractures that intersected only {111} facets, and unfractured grains were studied. It was found that the core volume bounded by the (001) top facet and its projected column defined by orthogonal internal {110} were free from microtwins, but contained a few dislocations. The remaining volume around this core, bounded by {111} facets (or grain boundaries) and the internal {110}, was filled with microtwins. The microtwins were not merely at the {111} surfaces. Our results reveal a growth mechanism in which microtwins are formed as material is added to {111} but not {001}. The formation of microtwins in CVD diamond is thus clearly associated with growth on {111} surface facets.
Oxidation protective barrier coatings for high-temperature polymer matrix composites
Authors: Harding David R. , Sutter James K. , Schuerman Marla A. , Crane Elizabeth A.
Published: September 2007

Three coating techniques (metal-organic chemical vapor deposition, magnetron sputtering, and plasma-enhanced chemical vapor deposition) were employed to deposit different coating materials (alumina, a superalloy, and silicon nitride) on graphite-fiber-reinforced polyimide composites to protect against oxidation at elevated temperatures. Adhesion and integrity of the coatings were evaluated by isothermal aging (371 °C for 500 h) and thermal cycling (25 to 232 °C for 1000 cycles and −18 to 232 °C for 300 cycles). Best results were achieved with a plasma-deposited, amorphous silicon nitride (a-SiN: H) coating, which withstood stresses from 0.18 to −1.6 GPa. The major factors affecting the suitability of a-SiN: H as an oxidation protective coating are the surface finish of the polymer composite and the presence of a sizable hydrogen content in the coating.
Radiolytic effects in organic compounds induced and analyzed by a 15N beam
Authors: Jans S. , Kalbitzer S. , Oberschachtsiek P. , Behar M.
Published: September 2007

Cd-arachidat in the form of Langmuir-Blodgett films and thick photoresist layers of AZ5412H have been exposed to 15N-ion beams. The physico-chemical state of these targets as a function of the 15N fluence has been monitored by the 15N nuclear reaction with the respective H component. In this way, radiolytic changes in H distribution and bonding have been measured. In particular, diffusion and desorption processes have quantitatively been followed up to fluences of about 1 × 1016 N/cm2 at temperatures as low as 40 K. The correlated changes in H bonding, obtained by analyzing the concomitant Doppler widths as a function of the 15N fluence, consist of both decomposition and restoration of C-H and H-H molecular groups.
Ion beam modification of fullerene films and their frictional behavior
Authors: Bhattacharya Rabi S. , Rai A.K. , Zabinski J.S. , McDevitt Neil T.
Published: September 2007

C60 films were deposited on a variety of substrates by thermal evaporation. The presence of C60 in the films was confirmed by Transmission Electron Microscopy and Raman spectroscopic analysis. The C60 films exhibited an average friction coefficient of 0.4–0.5. The films were irradiated with 2 MeV Ag+ and B+ ions at various doses. High energy ion bombardment created damage that resulted in partly crystalline to amorphous films, dependent on the mass and dose of ions. The amorphous films showed a friction coefficient of <0.1. Partly crystalline films showed a friction coefficient at the same level as that of unirradiated films.
Diamond nucleation by carbon fibers on unscratched substrate by hot-filament chemical vapor deposition
Authors: Nakamura Yoshikazu , Tamaki Kazunori , Watanabe Yoshihisa , Hirayama Shigekazu
Published: September 2007

In order to overcome the difficulty of nucleation of diamond particles on unscratched substrates by the chemical vapor deposition (CVD) method, carbon fibers are introduced on unscratched substrates as a nucleation site of diamond particles. With assistance of carbon fibers, diamond particles can be synthesized on unscratched silicon substrate from a gas mixture of methane and hydrogen by the hot-filament CVD method. From SEM observations, nucleation of diamond particles has been confirmed on fibers at the beginning of deposition. Fine particles have formed initially on the rugged surface of fibers, and then they grow up to be diamond particles. Detailed SEM observations reveal nucleation has occurred on irregular surfaces such as boundaries on carbon fibers. We propose that nucleation of diamond particles can be controlled by arranging carbon fibers on the substrate without applying any mechanical pretreatment.
Deposition of molybdenum carbonitride thin films from Mo(NBut)2(NHBut)2
Authors: Chiu Hsin-Tien , Ho Wen-Yu , Chuang Shiow-Huey
Published: September 2007

Mo(NBut)2(NHBu1)2 is used as a single-source precursor to deposit thin films of cubic phase molybdenum carbonitride, MoCxNy (x: 0.2-0.55, y: 0.1-0.47), by chemical vapor deposition on silicon substrates. In general, the C/Mo ratios increased from 0.2 to 0.55 and the N/Mo ratios decreased from 0.47 to 0.1 with increasing the temperature of deposition from 773 to 923 K. Based on the elemental composition and the composition of the gas phase products, it is proposed that the carbon atoms were incorporated through β-methyl activation of the ligands.
A systematic study of the synthesis of useful Tl2Ba2Ca2Cu3O10−δ bulk superconductor
Authors: Xin Y. , Xu B.R. , Nasrazadani S. , He W.S. , Lu D.F. , Sun G.F. , Wong K.W. , Knapp D.
Published: September 2007

A method to synthesize high density Tl2Ba2Ca2Cu3O10−δ bulk superconductor with uniformity from presintered powder of the 2223 phase material was developed. With a proper annealing process, the transport critical current density and the material density of such a synthesized superconductor are much improved over those of the starting material. The critical temperature and phase purity of this material are also enhanced. In this paper, we report our systematic study on some basic parameters of this material, including the normal state resistivity, Tc, Jc, phase purity, and morphology produced under different annealing conditions. An optimum preparation technique is then derived.
High quality a-Si/Nb and a-SiN/NbN artificial multilayers for Josephson applications
Authors: Chen J. , Rippert E.D. , Song S.N. , Ulmer M.P. , Ketterson J.B.
Published: September 2007

A high resolution transmission electron microscopy study of multilayer films prepared by magnetron sputtering shows that the morphology of the growing interface in a-Si/Nb and a-SiN/NbN multilayers is remarkably uniform and smooth; this is in contrast to the polycrystalline AlN/NbN multilayers grown under similar conditions, which exhibit columnar grain structure with rough interfaces. For proper sputtering parameters, the amorphous layers seem to periodically restore a relatively smooth initial interface condition for the successive Nb (or NbN) layer growth, consequently interrupting the tendency toward increased roughness due to mechanisms such as columnar growth. Artificial multilayers having very flat interfaces could stimulate applications based on multilayer Josephson junctions.
Reactive melt infiltration of silicon-niobium alloys in microporous carbons
Authors: Singh M. , Behrendt D.R.
Published: September 2007

Studies of the reactive melt infiltration of silicon-niobium alloys in microporous carbon preforms prepared by the pyrolysis of a polymer precursor have been carried out using modeling, DTA, and melt infiltration. Mercury porosimetry results indicate a very narrow pore size distribution with virtually all the porosity within the carbon preforms open to infiltrants. The morphology and amount of the residual phases (niobium disilicide and silicon) in the infiltrated material can be tailored according to requirements by careful control of the properties (pore size and pore volume) of the porous carbon preforms and alloy composition. The average room temperature four-point fiexural strength of a reaction-formed silicon carbide material (made by the infiltration of medium pore size carbon preform with Si–5 at. % Nb alloy) is 290 ± 40 MPa (42 ± 6 ksi) and the fracture toughness is 3.7 ± 0.3 . The fiexural strength decreases at high temperatures due to relaxation of residual thermal stresses and the presence of free silicon in the material.
A 27Al MAS nmr study of Synroc crystallization from alkoxide precursors
Authors: Hartman J.S. , Vance E.R.
Published: September 2007

27Al MAS nmr spectra from alkoxide-derived Al2O3-BaO-CaO-TiO2-ZrO2 Synroc precursors were studied after isochronal annealing in air for 1 h at temperatures between 200 and 1300 °C. At temperatures below 1000 °C, some tetrahedral and a trace of 5-coordinated Al were observed together with a majority of octahedral Al. The amount of nonoctahedral Al reached a maximum at 400–700 °C, beyond which it diminished and disappeared; essentially, complete conversion to octahedral Al took place on full crystallization at 1200–1300 °C, with the Al being contained in barium hollandite and minor α-alumina. The hollandite nmr signal was absent in Synroc which was hot-pressed at 1200 °C/20 MPa, presumably because of coincorporation of paramagnetic Ti3+ in the hollandite phase, but a signal from α-alumina was observed. Samples containing simulated waste fission products gave results similar to their waste-free counterparts when calcined at 750 °C in 3.5% H2/N2 and when hot-pressed.
Formation kinetics of PbZrxTi1−xO3 thin films
Authors: Kwok Chi Kong , Desu Seshu B.
Published: September 2007

The pyrochlore to perovskite transition in sputtered PZT thin films has been studied using SEM and XRD. The films were annealed in the temperature range between 350 °C and 750 °C, and the transition temperature for pyrochlore to perovskite transition was found to be around 525 °C. Isothermal annealing was used to study the nucleation and growth kinetics of the perovskite phase. The results showed a linear growth rate for the perovskite phase, thereby indicating an interface controlled process. Also, the growth was found to be isotropic in two dimensions parallel to the plane of the substrate. The nucleation of the perovskite phase was found to be random. The effective activation energy of the perovskite transition was found to be 494 kJ/mol using Avrami's approach.
A new procedure for measuring the decohesion energy for thin ductile films on substrates
Authors: Bagchi A. , Lucas G.E. , Suo Z. , Evans A.G.
Published: September 2007

A novel testing technique has been developed capable of measuring the interfacial fracture resistance, Γi, of thin ductile films on substrates. In this technique, the thin film on the substrate is stressed by depositing onto the film a second superlayer of material, having a large intrinsic stress, such as Cr. Subsequent processing defines a precrack at the interface between the film and the substrate. The strain energy available for driving the debond crack is modulated by varying the thickness of the Cr superlayer. Spontaneous decohesion occurs for superlayers exceeding a critical thickness. The latter is used to obtain Γi from elasticity solutions for residually stressed thin films. The technique has been demonstrated for Cu thin films on silica substrates.