bluuebunny/crossref_metadata_2025 huggingface dataset:
An analysis of high temperature (1150 °C) furnace annealing of buried oxide wafers formed by ion implantation
Authors: Wilson S. R. , Burnham M. E. , Kottke M. , Lorigan R. P. , Krause S. J. , Jung C. O. , Leavitt J. A. , McIntyre L. C. , Seerveld J. , Stoss P.
Published: September 2007

Silicon-on-insulator films were formed by ion implantation of oxygen and were treated with various annealing cycles at peak temperatures of 1150 °C, 1200 °C, and 1250 °C in a conventional diffusion furnace. The objective of this study was to examine the structural effects on samples with similar oxygen diffusion lengths (from 17 to 33 μm) achieved by annealing at different times and temperatures. The oxygen and silicon distributions, as well as the residual damage and precipitate size and distribution, were measured by Auger electron microscopy, Rutherford backscattering spectroscopy, and transmission electron microscopy. In agreement with previous findings, higher temperatures produced a larger and less defective, “precipitate-free” superficial Si region. The buried oxide layer thickened from 0.33 μm to a maximum of 0.43 μm as some precipitates were incorporated into the buried oxide while others adjacent to the buried oxide grew in size (up to 47 nm) and decreased in relative number. A new result of this systematic study of annealing conditions was that the peak temperature has a greater effect on the morphology and crystal quality of the superficial Si structure than does time at temperature. Structural changes for longer anneals at 1150 °C are not equivalent to shorter anneals at 1250 °C even though the diffusion length of oxygen for these treatments is the same.
Transformation steps of microstructures in photodeposited films of a-Se
Authors: Peled Aaron
Published: September 2007

Amorphous selenium (a-Se) colloid particles have been directly photodeposited onto insulating substrates. Scanning Electron Microscopy (SEM) supported by kinetic adsorption measurements reveals the origin of the photodeposition process. The studies show that film formation occurs through a sequence of particle precipitation, growth, and photoadsorption. A plastic flow and coalescence process creates a continuous monolayer before a fast deposition rate of Se on the deposited materials commences. Surface forces seem to have an important role in the creation of the morphological structures of the adsorbed particles.
Growth rate, surface morphology, and defect microstructures of β–SiC films chemically vapor deposited on 6H–SiC substrates
Authors: Kong H. S. , Glass J. T. , Davis R. F.
Published: September 2007

Beta–SiC thin films have been epitaxially grown on 6H–SiC {0001} substrates via chemical vapor deposition (CVD). The growth rate increased linearly with the source/carrier gas flow rate ratio. The activation energy for the growth of β–SiC grown on the Si face of the 6H–SiC substrate was 12 Kcal/mole. These observations are consistent with a surface reaction-controlled process. The as-grown surface morphology is dependent on the terminal layer of the substrate, the growth temperature, and the source/carrier gas flow rate ratio. The C face of a 6H–SiC {0001} substrate caused a higher growth rate and thus poorer surface morphology than the Si face under the same growth conditions. The optimum temperature range for growth of a flat, mirror-like β–SiC surface was determined to be 1773–1823 K in the present CVD system. The microstructure and nucleation of double positioning boundaries were investigated via transmission and scanning electron microscopies. Triangular defects and their modifications were also observed, and their origins have been discussed.
Deep-level transient spectroscopy studies of thermal donor annihilation in silicon by rapid thermal annealing
Authors: Tokuda Yutaka , Kobayashi Nobuji , Inoue Yajiro , Usami Akira , Imura Makoto
Published: September 2007

The annihilation of thermal donors in silicon by rapid thermal annealing (RTA) has been studied with deep-level transient spectroscopy. The electron trap AO (Ec – 0.13 eV) observed after heat treatment at 450 °C for 10 h, which is identified with the thermal donor, disappears by RTA at 800 °C for 10 s. However, four electron traps, A1 (Ec 0.18 eV), A2 (Ec – 0.25 eV), A3 (Ec – 0.36 eV), and A4 (Ec – 0.52 eV), with the concentration of ∼1012 cm−3 are produced after annihilation of thermal donors by RTA. These traps are also observed in silicon which receives only RTA at 800 °C. This indicates that traps A1–A4 are thermal stress induced or quenched-in defects by RTA, not secondary defects resulting from annealing of thermal donors.
Aurivillius-Popper mixed superconductors in BiO–CuO–(Sr0.5, Ca0.5)O system
Authors: Fukuhara Mikio , Bhalla Amar S. , Mulay Laxman N. , Newnham Robert E.
Published: September 2007

We report the effect of inhomogeneities on the electrical resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO–CuO–(Sr0.5,Ca0.5)O system and propose a crystal structure of the major phase having highest Tc. Nominal Aurivillius compositions with molar ratios of BiO/(Sr0.5,Ca0.5)O = 1/2 are superconductors with Tc ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. Tc increases with decreasing of the c lattice parameter. An oxide BiSrCaCu2Ox (n = 2) shows a maximum Tc value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi2Sr2CaCu2Ox consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain.
Microstructure of atomized Ni3Al–B powder
Authors: Huang S. C. , Ritter A. M.
Published: September 2007

The microstructure of boron-doped Ni3Al powder has been characterized by optical and transmission electron microscopy. Remarkable variations in the solidification morphology and phase reaction were observed as a function of powder size. The degree of boron segregation appeared to be reduced significantly, as the formation of M23B6 boride was suppressed in powder below ∼30 μm diameter. The primary solidification phase was disordered γ–Ni, which underwent a solid-state ordering transition to produce fine γ′–Ni3Al antiphase domains. A bi-modal distribution of domain sizes was observed due to Al segregation. The solidification morphology was dendritic for particles above ∼20 μm, and it changed to cellular below. In powder less than 40 μm diameter, second-phase particles of β–NiAl were found in intergranular regions, likely due to a metastable eutectic reaction of L ⇉ γ + β. The β phase was suppressed only for powder sizes below ∼2 μm. Judging from the tendency of second-phase formation, the Ni3Al–B powder appeared to cool slower than arc-hammer foil and melt-spun ribbon.
Effect of grain shape on environmental embrittlement in Ni3Al tested at elevated temperatures
Authors: Liu C. T. , Oliver B. F.
Published: September 2007

This paper describes the effect of grain shape on environmental embrittlement in boron-doped Ni3Al (24 at. % Al). The alloy showed severe embrittlement when tested at 600 and 760 °C in air. The embrittlement can be alleviated by control of grain shape, and the material with a columnar-grained structure produced by directional levitation zone remelting shows good tensile ductilities when tested in oxidizing environments. The columnar-grained structure with vertical grain boundaries minimizes the normal stress and consequently suppresses nucleation and propagation of cracks along the boundaries.
Lattice statics Green's function method for calculation of atomistic structure of grain boundary interfaces in solids: Part I. Harmonic theory
Authors: Tewary V. K. , Fuller E. R. , Thomson R. M.
Published: September 2007

A lattice statics Green's function method is described for calculating the atomistic structure of a solid near a grain boundary interface. First, a reference state is defined which is ‘near’ the equilibrium state. The Green's function for the reference state is obtained in terms of the perfect lattice Green's function by mapping the lattice sites of the reference state to the perfect lattice sites and solving the Dyson's equation within a supercell. This Green's function gives the response of the reference state which determines the atomic relaxations under the net forces which would be present in the reference state. The specific case of a ∑5 tilt boundary in a fec lattice has been considered, assuming the validity of the harmonic approximation.
Compound formation and kinetics in Al–Pd2Si reactions
Authors: Liu Joyce C. , Mayer J. W.
Published: September 2007

Lateral diffusion couples containing Al islands on Pd–Si multiple layers are used to study Al–Pd2Si reactions. The Pd2Si phase was first formed in the Pd–Si multiple-layer region after furnace annealing at 225 °C. Then, the Al–Pd2Si lateral couples were in situ annealed in a transmission electron microscope at temperatures ranging from 377–438 °C. The laterally growing region is composed of the Al3Pd2 compound and Si precipitates, as identified by selected area diffraction (SAD). During the in situ anneals, transmission electron microscopy (TEM) images were recorded by a video cassette recorder allowing thereafter a kinetic study. The lateral growth is parabolically dependent on the annealing time. An activation energy of 1.7 eV is found for this diffusion process.
Partially ionized beam deposition of oriented films
Authors: Yapsir A. S. , You L. , Lu T. -M. , Madden M.
Published: September 2007

The microstructure of Al films deposited on SiO2 using the partially ionized beam (PIB) deposition technique is studied. It is shown that by employing less than 1% ions (ion-to-atom ratio) derived from the evaporated material and about 1–2 kV bias voltage at the substrate during deposition, one can grow highly (111) oriented Al films at room temperature. For a fixed bias potential, the value of the ion-to-atom ratio to achieve the optimum orientation effect is determined. At the optimum condition for the (111) preferred orientation growth, no significant enhancement in the grain size is observed. It is also found that a drastic reduction in the degree of the preferred orientation occurs when the films are deposited at a substrate temperature greater than 150 °C.
Mechanical properties and dislocation dynamics of GaP
Authors: Yonenaga Ichiro , Sumino Koji
Published: September 2007

Mechanical properties of GaP crystals are investigated in the temperature range 600–900 °C by means of compression tests. Stress-strain characteristics of a GaP crystal in the temperature range 600–800 °C are very similar to those of a GaAs crystal in the temperature range 450–600 °C. The dynamic state of dislocations during deformation is determined by means of the strain-rate cycling technique. The deformation of GaP is found to be controlled by the dislocation processes the same as those in other kinds of semiconductors such as Si, Ge, and GaAs. The velocity v of dislocations that control deformation is deduced to be v = v0 τ exp(–2.2 eV/kT) as a function of the stress τ and the temperature T, where v0 is a constant and k the Boltzmann constant. The Portevin-LeChatelier effect is observed in the stress-strain behavior in the deformation at high temperatures and under low strain rates, which may be attributed to the locking of dislocations by impurities or impurity-defect complexes.
Mechanical property and dislocation dynamics of GaAsP alloy semiconductor
Authors: Yonenaga Ichiro , Sumino Koji , Izawa Gunzo , Watanabe Hisao , Matsui Junji
Published: September 2007

The mechanical behavior of GaAsP alloy semiconductor was investigated by means of compressive deformation and compared with those of GaAs and GaP. The nature of collective motion of dislocations during deformation was determined by strain-rate cycling tests. The dynamic characteristics of dislocations in GaAsP were found to be similar to those in elemental and compound semiconductors such as Si, Ge, GaAs, and GaP. An alloy semiconductor has a component of the flow stress that is temperature-insensitive and is absent in compound semiconductors.
Fourier transform infrared analysis of ceramic powders: Quantitative determination of alpha, beta, and amorphous phases of silicon nitride
Authors: Trout T. K. , Bellama J. M. , Brinckman F. E. , Faltynek R. A.
Published: September 2007

Fourier transform infrared spectroscopy (FT–IR) forms the basis for determining the morphological composition of mixtures containing alpha, beta, and amorphous phases of silicon nitride. The analytical technique, involving multiple linear regression treatment of Kubelka-Munk absorbance values from diffuse reflectance measurements, yields specific percent composition data for the amorphous phase as well as the crystalline phases in ternary mixtures of 0–1% by weight Si3N4 in potassium bromide.
A silicon-29 NMR study of the structural intermediates in low pH sol-gel reactions
Authors: Kelts L. W. , Armstrong N. J.
Published: September 2007

Silicon-29 NMR is used to study the structural intermediates in tetramethyl and tetraethyl orthosilicate (TMOS and TEOS) low pH sol-gel reactions. Differences in the number of compact ring structures are related to differences in gel times. Reactions are followed at various silicon: water: acid molar ratios.
A work-hardening model of the lower yield strength of discontinuously yielding alloys: Ni3Al and mild steel
Authors: Schulson E. M.
Published: September 2007

The lower yield strengths of Ni3Al and mild steel and their respective relationships to (grain size)−0.8 and (grain size)−0.5 are explained in terms of work hardening within Lüders bands.
Structural information concerning the glass network in Bi–Zn–Fe–B–O glasses
Authors: Montenero A. , Condrate R. A. , Guo Y. M.
Published: September 2007

Fourier transform infrared (FTIR) absorption spectra were measured for various glasses in the Bi–Zn–Fe–B–O system, and interpreted upon the basis of glass structure. Spectral changes were noted with variations in the composition for these glasses that were related to changes in the atomic arrangement of the boron oxide portion of the glass network. The changes in glass transformation temperature with changes in glass composition were discussed in terms of structural data.
Freestanding thick films of YBa2Cu3O6.9 by screenprinting techniques
Authors: Ginley D. S. , Mitchell M. A. , Kwak J. F. , Venturini E. L. , Baughman R. J. , Fu W.
Published: September 2007

Thick (20–300 μm) freestanding polycrystalline films of ceramic YBa2Cu3O6.9 have been obtained by resintering YBa2Cu3O6.9 powder in air after screen printing onto fused silica substrates. An interfacial reaction occurs between the powder and the silica substrate which efficiently detaches the resintered film upon cooling. The magnetization and transport properties of these films are comparable to those for high quality bulk ceramic samples.
Fractographic fingerprinting of proton-irradiation-induced disordering and amorphization of intermetallic compounds
Authors: Cheng J. , Yuan M. , Wagner C. N. J. , Ardell A. J.
Published: September 2007

The intermetallic compounds NiTi, NiTi2, CuZr, CuTi2, and Zr3Al were irradiated by 2 McV protons at various temperatures between –175 °C and –44 °C to a fluence of 1.9 × 1022 H+/m2. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi2) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surfaces of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfaces of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is considerable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr3Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.
Strain hardening during superplastic deformation of A1-7475 alloy
Authors: Adabbo H. E. , González-Doncel G. , Ruano O. A. , Belzunce J. M. , Sherby O. D.
Published: September 2007

Strain hardening dominates the deformation process in fine-grained A1-7475 alloy in the temperature range 400 to 515 °C. It is shown that anomalously low stress exponents are obtained as a result of strain hardening in strain-rate-change tests. In order to measure stress exponents in a quasi-steady state condition, the samples must be initially deformed at a relatively high stress (≍ 10 MPa) to a relatively high strain (∊ ≍ 0.5) before initiating a strain-rate-change test. Such a procedure revealed that a stress exponent about equal to two and an activation energy (141 kJ/mole) nearly equal to the activation energy for lattice diffusion are obtained. The results are interpreted in terms of a model involving grain boundary sliding accommodated by slip following the Gifkins' “core and mantle” concept. It is proposed that strain hardening is associated with the development of a boundary-dislocation structure in the mantle region in a manner similar to the development of subgrains in the core of a grain when slip is the principal deformation mode.
Some correlations for diffusion in amorphous alloys
Authors: Sharma S. K. , Banerjee S. , Kuldeep  , Jain Animesh K.
Published: September 2007

Diffusion of several impurity atoms (Cu, Al, Au, and Sb) has been studied in Zr61Ni39 and Fe82B18 amorphous alloys. A definite correlation between the diffusion coefficient (D) and the atomic size of the diffusant is seen for the metal-metal (M–M) alloy, while it is not clear for the metal-metalloid (M–Me) alloy. Based on the present data, as well as other published data in binary amorphous alloys, empirical correlations have been found between (i) the activation energy (Q) and the energy required to form a hole of the size of the diffusing atom in the host alloy, and (ii) the pre-exponential factor (D0) and Q. While the former correlation is seen only for binary M–M type of amorphous alloys, the latter correlation is more general and holds for all types of amorphous alloys. Based on the correlation between D0 and Q, it is proposed that there are two distinct mechanisms of diffusion in amorphous alloys.
The mechanism of laser-assisted CVD of germanium
Authors: Gow T. R. , Coronell D. G. , Masel R. I.
Published: September 2007

Previous workers have shown that germane does not decompose below 700 K on silica substrates. However, if the germane is irradiated with an ArF or KrF laser, germanium films will grow at temperatures down to 610 K. In the work reported here, the role of the laser in the growth process was explored. First, the species impinging on the substrate during ArF laser-assisted chemical vapor deposition (LCVD) were analyzed with a mass spectrometer. The analysis showed that when germane is irradiated with an ArF laser under growth conditions, digermane is formed in the gas phase. The digermane then impinges on the substrate and pyrolyses. Many other species have been reported previously to be formed transiently during the laser pulse. However, we were not able to detect any other species with a high enough flux onto the substrate to condense at an appreciable rate. Next, temperature programmed decomposition was used to see if photochemical decomposition of chemisorbed germane played an important role in film growth. It was found that a laser dose comparable to that needed for film growth did not produce an appreciable change in the decomposition spectra. Lastly, film growth studies were used to examine the role of the digermane formed by the laser in the film growth process. It was found that a mixture of germane and digermane will decompose on a silica substrate down to 580 K to produce a germanium film. The growth characteristics of the germane/digermane mixtures were virtually the same as those seen in LCVD. Thus, it appears that under the conditions used previously for LCVD, the main role of the ArF laser is to convert some of the germane source gas to digermane. It also has been found that under other conditions, one can grow germanium films down to at least 300 K via digermane photolysis.
Co+-ion implanted sapphire-annealing in oxidizing atmosphere
Authors: Noda Shoji , Doi Haruo , Kamigaito Osami
Published: September 2007

C-cut sapphire was implanted with 400 keV Co+ ions to doses of 3 × 1017/cm2 and 5 × 1017/cm2 and then annealed in air sequentially at 1273, 1373, and 1473 K. Before and after the annealing, the implanted surfaces were examined by RBS and XRD methods. A nearly homogeneous layer of 350 nm thickness was formed on the surface when sapphire was implanted to a dose of 5 × 1017/cm2 and then annealed at 1473 K. For sapphire implanted to a dose of 3 × 1017/cm2 and then annealed at 1473 K, the implanted layer had a complex structure: the top surface layer of 70 nm thickness was α-alumina with Co3+ ions at the substitutional sites and the near-surface layer (70 nm–300 nm) was a mixed phase of CoAl2O4 and α-alumina.
Coherent phase equilibria in systems possessing a consolute critical point
Authors: Chiang C. S. , Johnson William C.
Published: September 2007

The influence of coherency strains on phase equilibria in a two-phase microstructure is examined for a binary or pseudobinary alloy system possessing a consolute critical point (chemical miscibility gap). The qualitative features of phase equilibria, including the limits of metastability (chemical spinodal), are shown to depend critically on the mechanical loading conditions and the geometric arrangement of the phases in the microstructure. If the elastic state of a phase in a two-phase coherent system is independent of the presence of the other phase, then the equilibrium characteristics usually associated with fluid systems should be observed, even though the system is nonhydrostatically stressed. If the elastic state of a phase depends upon the presence of the other phase, then the equilibrium characteristics that have come to be associated with coherent systems should be observed; tie lines and field lines do not coincide, the common tangent construction is invalid, and Gibbs phase rule is not applicable.
The pore morphology of fluoride catalyzed xerogels
Authors: Chan J-B. , Hua D-W. , Winter R. , Jonas J.
Published: September 2007

The fluoride anion has been shown to be one of the most effective catalysts in accelerating the polycondensation of alkoxide-derived silica gels. A detailed pore analysis study has been employed to investigate the effect of NaF on the pore structure of the resulting xerogels and its evolution during thermal heat treatment up to 800 °C. Addition of NaF to tetramethylorthosilicate-sols leads to an increase in average pore size, and the pore size distribution becomes narrower. By changing the fluoride concentration and the heating temperature, the surface properties of the xerogels can be tuned over a wide range. The possible application of the F− anion catalyzed sol gel process to prepare porous host materials for the studies of fluids in restricted geometries is also discussed.
Characterization and superconducting properties of phases in the Bi–Sr–Cu–O system
Authors: Chakoumakos B. C. , Ebey P. S. , Sales B. C. , Sonder Edward
Published: September 2007

Phase formation in the system Bi–Sr–Cu–O has been examined as a function of composition, temperature, ambient atmosphere, cooling history, and annealing time. Ceramic processing and melt crystallization techniques were used. For the ceramic materials (using Bi2O3, SrCO3, and CuO) processed at 700 °C in air the Bi2Sr2CuO6composition (221) crystallizes to a mixture of CuO, SrCO3, and the rhombohedral Bi2O3·xSrO solid solution. At 800–830 °C in air for short durations (5 min to 2 h) the reacted products consist principally of the ideal 221 phase with minor amounts of CuO. For longer reaction times (2–400 h) the reacted products consist of the ideal 221-type structure withc= 24.64 Å anda= 3.804 Å, a “collapsed” 221 structure withc= 23.6 Å, and CuO. With increasing reaction time the “collapsed” 221 phase grows gradually at the expense of the ideal 221 phase. The “collapsed” 221 phase is not an oxycarbonate and appears to be a distinct ternary compound near the 221 composition, with a layered structure having a 1 Å smaller stacking repeat. The ideal 221 phase is a solid solution with variable Sr content. With decreasing Sr in the starting mixture [2 to 1.25 atoms per formula unit (afu)] we observe the following: (1) the formation of the “collapsed” 221 structure is inhibited; (2) for the ideal 221 phase thec-cell dimension decreases significantly (0.2 Å) and thea-cell dimension increases slightly (0.02 Å); (3) the low temperature resistivity behavior changes from superconducting withTconset of 6 K for Sr>1.5 afu to semiconducting for Sr > 1.5 afu; (4) the positions of the superlattice peaks around the (001) reflections become more incommensurate with respect to the parent structure. Rapid quenching (<5 s) from temperatures near the melting point (900 °C) can raise the superconductingTconset to 9 K. Independent of the cell variation with Sr content, quenching causes thec-cell dimension to expand by 0.03 Å on average while thea-cell dimension remains invariant. A small number of oxygen vacancies are quenched in from high temperature, and presumably originate in the Bi2O2layer. As grown from the melt, crystals of the ideal 221 phase exhibit semiconducting behavior at low temperature; but with an additional high-temperature anneal in oxygen, metallic resistivity is restored with a superconducting onset near 5 K. Ca doping does not increaseTcin the ideal 221 phase. La and Y substitution occurs for Sr in the ideal 221 phase and ruins superconductivity.
New chemical solutions for the etching of (011) oriented V-grooves in InP(001) for CSBH laser diodes
Authors: Huo D. T. C. , Van M. F. , Wynn J. D.
Published: September 2007

We have developed two new etchant systems by adding H2O2 and HBr into the conventional HCI–H3PO4 etchant for the fabrication of InP-based channeled substrate heterostructure (CSBH) lasers. These etchants do not erode photoresists and they provide high quality etched side walls. The etch factors for the new etchant systems based on HBr and H2O7 are 17% and 12% higher than that of the: conventional 5HCI–H3PO4 etchant, respectively. These high etch factors give a narrow V-groove in InP and they lead to a lower magnitude and a better control of the threshold current of CSBH lasers.
Monolayers of 11-trichlorosilylundecyl thioacetate: A system that promotes adhesion between silicon dioxide and evaporated gold
Authors: Wasserman Stephen R. , Biebuyck Hans , Whitesides George M.
Published: September 2007

The use of sulfur-containing organic monolayer films improves adhesion between gold and silicon dioxide. The structures of these monolayers were analyzed using contact angle, ellipsometry, and XPS. The zone of adhesive failure was at or near the gold-monolayer interface.
Electrochemical and photoelectrochemical deposition of thallium(III) oxide thin films
Authors: Phillips Richard J. , Shane Michael J. , Switzer Jay A.
Published: September 2007

Thallium (III) oxide is a degenerate n-type semiconductor with high optical transparency and electrical conductivity. Films of thallium(III) oxide can be electrochemically deposited onto conducting and p-type semiconducting substrates, and photoelectrochemically deposited onto n-type semiconducting substrates. Films deposited at currents below the mass transport limit onto platinum or stainless steel were columnar, and the current efficiency on stainless steel was 103 ±2%. Dendritic films were deposited at mass-transport-limited currents. Films were deposited with thicknesses ranging from 0.1 μm on n-silicon, to 170 μm on stainless steel. The photoelectrochemically deposited films were “direct-written” onto n-silicon, since the material was deposited only at irradiated portions of the electrode. Thin films were grown by irradiating the n-silicon with 450 nm monochromatic light, since the light was strongly absorbed by the thallium(III) oxide. The most uniform thin films were deposited when the n-silicon was initially irradiated with a short pulse of high intensity light. The pulse apparently promoted instantaneous nucleation of a high density of thallium(III) oxide nuclei.
1200 to 1400 K slow strain rate compressive behavior of small grain size NiAl/Ni2AlTi alloys and NiAl/Ni2AlTi–TiB2 composites
Authors: Daniel Whittenberger J. , Viswanadham R. K. , Mannan S. K. , Kumar K. S.
Published: September 2007

Since 1976 NiAl–Ni2AlTi alloys have been known to possess elevated temperature mechanical properties approaching those of Ni-base superalloys; however, due to their apparent brittleness, little additional work has been undertaken to exploit this strength. In an attempt to instill ductility in these materials, small grain size single (Ni–45Al–5Ti) and two (Ni–40Al–10Ti) phase intermetallics were fabricated by XDTM technology and tested (XDTM is a trademark of Martin Marietta Corporation). As these compositions have the potential for being the matrix material in high temperature composites, Ni–40Al–10Ti and Ni–45Al–5Ti with 20 vol.% TiB2 in the form of ∼1 μm diameter particles were also investigated. The as-fabricated materials were fully dense and polycrystalline. The grain sizes measured ∼8 μm for Ti-poor and about 15 μm for the Ti-rich unreinforced materials but could not be determined for either TiB2 containing composite. Elevated temperature compression testing was conducted to about 8% deformation between 1200 and 1400 K with strain rates varying from ∼10−4 to ∼10−7 s−1. The majority of the tests exhibited diffuse yielding over approximately 1% strain followed by negative strain hardening. However, a few experiments resulted in steady state behavior where deformation continued under a constant stress. The flow strengths on yielding of both forms of Ni–40Al–10Ti were higher than those for the Ni–45Al–5Ti versions. For each matrix composition the addition of 20 vol.% TiB2 decreased the strength at the higher strain rates in comparison to the TiB2-free forms. During slow deformation conditions, however, the particles do provide reinforcement. Light optical microscopy of tested specimens revealed that these materials are generally quite brittle as numerous longitudinal and transverse cracks were found irrespective of the type of stress-strain behavior.
Nucleation and propagation of cracks at grain boundaries in zinc bicrystals
Authors: Schmitz H. A. , Dew-Hughes D. , Bilello J. C.
Published: September 2007

A study has been made of fatigue and fracture in zinc bicrystals. It is shown that cleavage cracks are nucleated, both under tension and as a result of fatigue, in regions of multiple slip adjacent to grain boundaries at stresses below those for crack nucleation in single crystals. The nature of crack penetration through the boundary is observed as a function of orientation across the boundary. Low angle tilt boundaries are barriers to crack propagation, increasing effective surface energies for crack propagation by 1.6–2 times. Twist boundaries, due to the tearing that accompanies penetration, can result in a twelvefold increase in effective surface energy. Nonbasal cleavage is associated with a twinning mechanism, and an even higher surface energy is required to propagate a crack into a crystal oriented for this type of cleavage. The results carry the implication that, in the absence of surface defects, fatigue, failure in polycrystalline zinc is nucleated at the first internal grain boundary and not at the surface.
Apparatus for low-temperature growth of diamond-containing films
Authors: Fang P. H. , Kinnier J. H.
Published: September 2007

In current processes of diamond growth, the substrate temperature is in general around 600–900 °C. In the case of diamond-like carbon, the substrate temperature is lower, around 25–200 °C. There are many superior properties of diamond compared with diamond-like carbon; however, the high temperature requirement to grow diamond precludes many technologically important substrate materials such as zinc sulfide for an infrared window or electronic devices on which protective diamond layers are to be coated. The present approach is a hot filament DC glow discharge of hydrocarbon gases. A graphite hot filament cathode is inserted in a discharge cylinder tube anode. The discharge voltage is in the range of 50 to 250 volts at a methane gas pressure of about 100 microns. A negative biased voltage of 100 volts is applied between the cathode and the substrate. A magnetic field of 1 kG is applied near the cathode-anode assembly. At a substrate temperature of 200–400 °C, the deposited film on silicon crystal is confirmed by an electron diffraction pattern to consist of microcrystalline diamond.
Mg–Ti–spinel formation by interfacial solid-state reaction at the TiN/MgO interface
Authors: Hultman L. , Sundgren J-E. , Hesse D.
Published: September 2007

Mg–Ti–spinel formation has been observed by cross-sectional transmission electron microscopy at the interface of TiN(100) films and MgO(100) substrates for films grown at substrate temperatures higher than 800 °C and for samples post-annealed at 850 °C. The TiN films were deposited by reactive magnetron sputtering onto cleaved (100)-oriented MgO substrates. The spinel formed 5 nm epitaxial layers along the interface with occasional (111) wedges growing into the MgO. The orientational relationships were found to be TiN(100)|spinel(100)|MgO(100) and TiN[001]|spinel[001]|MgO[001]. The spinel composition is suggested to be Mg2TiO4.
On the stability of Ni3Ge
Authors: Jena A. K. , Chaturvedi M. C.
Published: September 2007

Ni3Ge-containing nickel-germanium alloys with 12.10 to 16.8 at. % Ge were investigated. Nickel-saturated Ni3Ge had a lattice parameter of 3.57015 × 10−10 m and contained 22.5 at. % Ge over the temperature range 650 to 1100 °C. However, the precipitates in the initial stages contained 24.44 at. % Ge and were almost cubic in shape. The strengthening effects of Ni3Ge were appreciable. In alloys containing higher percentages of germanium, precipitates were observed in as-quenched specimens. The hardness after quenching was high and did not change appreciably with time. Hardness was reduced in the presence of aluminum.
Interfacial reactions in the Nb/GaAs system
Authors: Schulz Kevin J. , Zheng Xiang-Yun , Chang Y. Austin
Published: September 2007

Solid-state reactions between niobium and gallium arsenide in both thin film and bulk forms were studied in the temperature range 400 to 1000 °C using transmission electron microscopy (TEM), metallography, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Initially Nb4As3 and Nb5Ga3 formed at the interface and grew very slowly. Following an incubation period, NbAs and NbGa, nucleated and grew at rates several orders of magnitude faster than the initial phases. The resulting metastable diffusion path, Nb/NbGa3/NbAs/GaAs, was observed even after relatively long-term annealing and is believed to be kinetically stabilized. Formation of the other Nb–Ga binary compounds as predicted by the phase diagram was inhibited by nucleation and kinetic barriers. The observed reaction sequence is discussed considering the thermodynamics, kinetics, and possible growth mechanisms involved in the reaction.
Excimer laser cleaning, annealing, and ablation of β–SiC
Authors: Pehrsson Pehr E. , Kaplan Ray
Published: September 2007

The effects of ArF excimer laser irradiation on β–SiC in UHV were examined for a variety of laser intensities and pulse densities. The samples were analyzed in situ with Auger and electron loss spectroscopies, and ex situ with x-ray photoelectron spectroscopy. With progressively higher laser intensities, the SiC surface was initially cleaned of carbon and oxygen surface contaminants, and the Si–LVV Auger lineshape changed from the oxide to the carbide. Still higher laser intensities then partially reordered the surface. A carbon surface layer developed, and the C-KLL lineshape transformed from carbidic to graphitic. Finally, the surface segregated into an almost pure Si layer and an underlying carbon-rich layer, followed by ablation and pitting. Bulk heating during laser exposure may enhance reordering of sputtered or implanted material.
X-ray diffraction and vibrational-spectroscopy study of the structure of La2Ti2O7
Authors: Balachandran U. , Eror N. G.
Published: September 2007

The compound La2Ti2O7 was prepared by a liquid mix technique and examined at room temperature by x-ray diffraction, infrared absorption, and Raman spectroscopy. The examinations confirm and supplement the earlier observation by x-ray diffraction that La2Ti2O7 crystallizes in the monoclinic structure without an inversion symmetry. The energy-shifts (cm−1) that were observed in the vibrational spectra may be explained by a sixfold coordination for the titanium and a ninefold coordination for the lanthanum in the structure. This type of coordination satisfies Pauling's electrostatic valence rule regarding the electrostatic bond strengths at the shared anions.
Room-temperature deformation in a Laves phase
Authors: Livingston J. D. , Hall E. L.
Published: September 2007

Transmission electron microscopy of two-phase V-Hf-Nb and V-Hf-Nb-Ti alloys plastically deformed at room temperature shows that {111} (112) twinning is a major deformation mode for the HfV2-based Laves phase. Bands of concentrated shear are also observed. Possible approaches to enhance low-temperature deformability in other Laves phases are discussed.
Electron microscopy studies of high Tc phase development in melt-quenched Bi-Ca-Sr-Cu oxides
Authors: Xu Z. , Han P. D. , Chang L. , Asthana A. , Payne D. A.
Published: September 2007

A Bi-Ca-Sr-Cu oxide composition (2:4:2:5) was rapidly solidified from the melt, and the crystallization behavior examined on heat-treatment. Annealing conditions were 865°C for up to 11 days. The high Tc 2223 phase (105 K) evolved from the 2122 phase (80 K), which in turn developed from the 2021 phase (12 K). The high Tc phase developed only in the presence of a liquid phase at 865 °C. Lattice imaging was used to follow the conversion of 2122 phase to 2223. Data are reported for syntactic intergrowths, which became less frequent with time at temperature. EDS results are consistent with the conversion of 2122 to 2223. Crystals of 2223 could not be grown from the melt, nor crystallized from the solid at temperatures below 820 °C. The presence of a Cu- and Ca-rich liquid was essential for the development of 2223 at 865 °C. A tentative model for the formation of 2223 via a liquid mediated reaction is proposed. EDS confirmed the liquid was rich in Ca and Cu near the solid-liquid interface, and precipitates of secondary phases were identified by SEM, TEM, and XRD methods. The presence of CuO and (Ca,Sr)2CuO3 verified the enrichment of Cu and Ca at the solid-liquid interface. The results are consistent with the evolution of structure of a 2223 from a 2425 starting composition.
A new method for analyzing data from continuous depth-sensing microindentation tests
Authors: Joslin D. L. , Oliver W. C.
Published: September 2007

A new parameter, hardness/modulus2 (H/E2), has been derived from the equations used to calculate the hardness and elastic modulus from data taken during continuous depth-sensing microindentation tests. This paper discusses the use of this parameter to treat the data obtained from a sample whose surface roughness was of the same scale as the size of the indents. The resulting data were widely scattered. This scatter was reduced when the data were plotted in terms of H/E2 versus stiffness. The effect of surface roughness on the hardness and elastic modulus results is removed via stiffness measurements, provided single contacts are made between the indenter and the specimen. The function relating the cross-sectional area of the indenter versus the distance from its point is not required for calculation of H/E2, but the hardness and modulus cannot be determined separately. The parameter H/E2 indicates resistance to plastic penetration in this case.
Compressive behavior and deformation-mode map of an open cell alumina
Authors: Dam Chuong Q. , Brezny Rasto , Green David J.
Published: September 2007

Compressive behavior of an open cell, porous ceramic has been examined and compared to a prior theoretical model. The study involved (i) microstructural characterization, (ii) crushing strength and Young's modulus measurements, and (iii) construction of a deformation-mode map. Initially, the crushing behavior was found to be different than predicted theoretically. Weaker struts throughout the material fractured during the loading and this damage was accumulated until a macroscopic crack or cracks propagated through the material at the crushing stress. Further work showed the discrepancy was related to the uniformity of loading in these porous materials. The use of compliant faces on the loading rams improved the loading uniformity, leading to a substantial reduction in the experimental scatter and increasing the likelihood of unstable crack propagation events rather than damage accumulation. Both crushing strength and Young's modulus were found to be dependent on cell size, but this was considered to be a result of strut cracking at the smallest cell size. A deformation-mode map was constructed using the average stress/strain values at critical points such as the onset of crushing, the minimum crushing stress, and the densification stress. Although some of the details of the deformation map were different from that expected theoretically, the map did appear to be a useful guide to the compressive behavior.
Thermal analysis of rare earth gallates and aluminates
Authors: O'Bryan H. M. , Gallagher P. K. , Berkstresser G. W. , Brandle C. D.
Published: September 2007

Dilatometry, high-temperature x-ray diffraction, differential thermal analysis, and differential scanning calorirmetry have been performed on LaGaO3, NdGaO3, PrGaO3, SmAlO3, and LaAlO3 single crystals grown by the Czochralski technique. First order phase transitions have been located at 145°C for LaGaO3 and 785°C for SmAlO3, and ΔH has been measured for the LaGaO3 transition. Second order transitions have been identified for LaGaO3, PrGaO3, NdGaO3, and LaAlO3. The usefulness of these compounds as substrates for high temperature superconducting films is discussed in terms of thermal expansion matching.
The formation and role of a phase with glassy appearance in the Tl-Ca-Ba-Cu system
Authors: Cheung C. T. , Ruckenstein E.
Published: September 2007

A phase with a glassy appearance has been detected in samples of the Tl–Ca–Ba–Cu system. The presence of such a phase is expected to have a negative effect on the critical current density in a bulk superconductor. Samples of 2-2–2-3 starting composition were prepared from Tl2O3, BaO2, and relatively large particles of CaO and CuO. These samples were then heat-treated at 867°C for various periods of time. The use of large particles of CaO and CuO facilitates the examination of the morphological changes associated with the formation of the superconducting phases. Using scanning electron microscopy, a layer of the 2122 phase was found to form on the surface of the large CaO particles whereas near the surface of the large CuO particles, large voids were observed. By varying some of the experimental conditions, a liquid phase with a composition close to 2-0–2-3 was inferred to form. The voids observed in the surroundings of the CuO particles may be due to the formation of such a melt. This liquid phase, after cooling, apparently leads to the “glassy” phase detected in the reacted samples. This glassy phase may play a role as an intermediate in the formation of the 2122 phase, which could result by a direct reaction between the liquid phase and CaO, A part may remain, however, among the superconducting grains, thus having a negative effect on the critical current density.
Aluminum and Ni–silicide lateral reactions
Authors: Liu Joyce C. , Mayer J. W.
Published: September 2007

The Al–Ni2Si reactions were studied in lateral diffusion couples containing Al islands on Ni–Si multiple layers. The samples were first in situ annealed in a transmission electron microscope at a temperature of 370°C for 5 min to form the Ni2Si phase in the multiple-layer area. Then they were in situ annealed at temperatures ranging from 498–545 °C. During the second-step anneal, a sequential formation of Al3Ni, Al3Ni2, and Ni3Si2 was observed. After the nucleation of the third phase (Ni3Si2), the three phases grew simultaneously with time. The lateral growth of Al3Ni and Al3Ni2 is a result of the Al diffusion and the Al–Ni silicide reactions; the lateral growth of Ni3Si2 is caused by the diffusion of Si atoms dissociated from the silicides.
The formation of discontinuous Al2O3 layers during high temperature oxidation of IrAl alloys
Authors: Chou T. C.
Published: September 2007

Oxidation of IrAl alloys (50-50 at.%) was conducted at 1300 and 1600°C in air for different times. Due to the outward diffusion of Al atoms and subsequent oxidation, the formation of Al2O3 is accompanied with the generation of an Ir-rich phase in the vicinity areas. The oxidation zone is separated from the bulk IrAl alloy by a phase boundary. In the oxidation zones, alternating layers of Al2O3 and Ir-rich phase are produced at 1300°C, while irregularly intertwined; Al2O3 and Ir-rich phase are produced at 1600 °C. The discontinuous formation of Al2O3 gives rise to internal oxidation of the IrAl alloys. The thickness of the Al2O3 layer is in the range of tens of micrometer, and it grows thicker as its location gets farther away from the free surface. The formation of an Al2O3/Ir-rich phase layered structure is discussed based on the diffusion kinetics of O, Al, and Ir, the chemical reactivities of Al and Ir with respect to O, and the nucleation and growth kinetics of Al2O3.
Microwave heating of ceramics and its application to joining
Authors: Fukushima H. , Yamanaka T. , Matsui M.
Published: September 2007

A new butt joining method for ceramics by microwave heating was developed. Ceramics were heated in a rectangular cavity, and a klystron of maximum 3 kW at 6 GHz was used as the power amplifier. The heating system can control an iris, a plunger, and the microwave power to maintain the power efficiency up to 90% and the accuracy within ±10°C at 1800 °C. This system was applied to alumina-alumina direct joining. The average strength of alumina rods (92% purity) joined for 3 min was 420 MPa, which was equal to the original strength. The joined boundary line at the interface was not observed, and there was little difference in microstructure between before and after joining. This suggests that sintering aids in the grain boundary phase were preferentially heated and melted, resulting in the sound joining of ceramics. Next, silicon nitride ceramics containing yttrium were indirectly joined with an intermediate, which was a sintered ceramic sheet having lower purity and larger dielectric loss factor than the base material. The microwave energy was concentrated on the ceramic sheet, so that only the joining area was locally heated. The strength of the joined rods was in excess of 70% of the base material, but a deficient layer of yttrium occurred in the area of the joined boundary.