bluuebunny/crossref_metadata_2025 huggingface dataset:
Multielement ultratrace analysis of molybdenum with high performance secondary ion mass spectrometry
Authors: Virag A. , Friedbacher G. , Grasserbauer M. , Ortner H. M. , Wilhartitz P.
Published: September 2007

Electron beam melting has been used to obtain ultrapure refractory metals that are gaining importance in metal oxide semiconductor-very large scale integration (MOS-VLSI) processing technology, fusion reactor technology, or as superconducting materials. Although the technology of electron beam melting is well established in the field of production of very clean refractory metals, little is known about the limitations of the method because the impurity level of the final products is frequently below the detection power of common methods for trace analysis. Characterization of these materials can be accomplished primarily by in situ methods like neutron activation analysis and mass spectrometric methods [glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS)]. A suitable method for quantitative multielement ultratrace bulk analysis of molybdenum with SIMS has been developed. Detection limits of the analyzed elements from 10−7g/gdown to 10−12g/g have been found. Additional information about the distribution of the trace elements has been accumulated.
Measurement of small elastic strains in silicon using electron channeling patterns
Authors: Kozubowski J. A. , Gerberich W. W. , Stefanski T.
Published: September 2007

A silicon single-crystal slab 0.15 mm in thickness was bent to produce small, nonuniform surface strains of the order of 0.2%. The electron channeling patterns were observed in a JSM 840 SEM (scanning electron microscope) at an accelerating voltage close to 25 kV. Proper choice of the triangles formed by intersecting channeling lines of zero-order and of higher-order Laue zones allows one to measure the changes in their dimensions caused by imposed strain. It was estimated that the lower limit of detectable elastic strain is close to 0.1%. The possibilities of using this method for estimation of the average elastic strains in thin epitaxial layers are discussed.
The effect of hydrogen plasma on the properties of indium-tin oxide films
Authors: Major S. , Bhatnagar M. C. , Kumar S. , Chopra K. L.
Published: September 2007

The effect of hydrogen plasma exposure on the properties of transparent conducting indium-tin oxide films has been studied. The exposure reduces the film surface to elemental indium. The thickness of the reduced layer increases with increasing exposure and finally saturates to a thickness of about 100 nm. The reduced surface is rough and decreases the visible transmittance of these films drastically due to increased absorptance and reflectance. The reduced metal layer decreases the sheet resistance of the films. Annealing of the plasma-exposed film in oxygen recovers the visible transmittance except in the case of the severely damaged films.
Reaction of NF3and SF6with some oxides connected with heavy-metal fluoride glass processing
Authors: Broer M. M. , Atkins R. M.
Published: September 2007

The fluorinating properties of NF3and SF6in heavy-metal fluoride glass processing were investigated between 200 and 1100 °C. Using infrared (IR) absorption spectroscopy the reactions of NF3with ZrO2and Al2O3and the reactions of SF6with ZrO2, SiO2, and Ni were studied. The reaction of NF3with zirconia and alumina starts at 300 and 650 °C, respectively (yielding nitrogen oxides, nitrogen oxyfluoride, and presumably the metal fluorides). The reaction of SF6and zirconia starts at 600 °C, yielding SO2F2. Sulfur hexafluoride and silica yield (above 900 °C) SiF4, SO2F2, and SOF2. Nickel and SF6react above 700 °C yielding SF4(and presumably NiF4). The results indicate that both gases are effective in oxide conversion at typical fluoride glass melting temperatures (800–900 °C). In addition NF3can be used as a low-temperature fluorinating source for both oxide containing fluoride and pure oxide precursors. This offers great advantages over the use of solid NH4HF2, which is typically used and which forms an additional source of contamination.
Dislocations in shock-loaded titanium diboride
Authors: Vanderwalker D. M. , Croft W. J.
Published: September 2007

The structure of shock-loaded polycrystalline titanium diboride was examined with transmission electron microscopy. The shock wave from ballistic impact produces prismatic and basal slip in grains favorably oriented with respect to the shock wave. It can be deduced from annealing experiments with the formation of stacking fault hexagons that there is a high concentration of point defects in deformed regions from the motion of dislocation jogs. Weak-beam microscopy shows that the dislocations in TiB2 are dissociated into partial dislocations. The stacking fault energy measured from a screw dislocation in the basal plane was found to be 120 mJ/m2. Widely dissociated dislocations in the shocked sample suggest that residual stresses are present in some regions.
Some observations of microstructural changes in alumina induced by Ti inhomogeneities
Authors: Jayaram V. , Dalgleish B. J. , Evans A. G.
Published: September 2007

Analysis of Ti-containing heterogeneities in a hot-pressed Al2O3 has revealed changes in microstructure caused by oxidation that provide some insight regarding the effects of Ti on local grain growth. The most consistent hypothesis is that Ti4+ in solution compensates the Mg2+ ion taken into solution from the MgO additive, probably by forming dipoles, and negates the effect of Mg2+ on grain boundary drag.
Investigation of hydration phases in the system CaO–SiO2-P2O5-H2O
Authors: Hu Jiashan , Agrawal D. K. , Roy R.
Published: September 2007

Hydration reactions and their rates have been studied qualitatively in CaO-and P2O5-rich compositional regions of the system CaO–SiO2-P2O5-H2O. Using aqueous solutions of Ca (NO3)2–4H2O, Ludox, and H3PO4 as starting materials, amorphous powders made by the sol-gel process were reacted with water. Some “curing” reactions were carried out at several temperatures: room temperature, 90 °C, and under hydrothermal conditions. Some glasses in the phosphate-rich region of the system were also made and hydrated. The hydration products are OH–Ap [OH–Ap = Ca10(PO4)6-(OH)2], Ca(OH)2 [CH = Ca(OH)2],C–S–H crystalline, C–S–P–H (C = CaO,S = SiO2,P = P2O5,H = H2O) crystalline, C–S–H gel, C–S–P–H gel, Ca(H2PO4)2·H2O, and CaHPO4. All phases have been identified and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDAX). The reactivities of the precursor materials and the compositional-structural nature of the hydration products formed are discussed. Some new compositions for “cementlike behavior” have been discovered.
Characterization and dehydration of zirconium tetrafluoride for fluoride glass preparation
Authors: Atkins R. M. , Broer M. M. , Bruce A. J.
Published: September 2007

Zirconium tetrafluoride (ZrF4) is the major constituent of many heavy metal fluoride glasses of technological interest. Five samples of commercially available “zirconium fluoride” were analyzed to determine their exact nature. Two samples were found to be anhydrous β-ZrF4, one was found to be α-ZrF4, one was zirconium tetrafluoride monohydrate (ZrF4 · H2O), and the final sample was identified as a hydrated amorphous phase of ZrF4. The behavior of these samples on heating was investigated with particular interest in the removal of water and the loss of fluorine from the hydrated materials. Infrared spectroscopy, x-ray diffractometry, thermogravimetric analysis, and differential scanning calorimetry were used in this investigation.
Sol–gel synthesis of fine-particle superconducting oxide, YBa2Cu3O7−x
Authors: Ravindranathan P. , Komarneni S. , Bhalla A. , Roy R. , Cross L. E.
Published: September 2007

A sol-gel method of preparing fine-particle superconducting oxide YBa2Cu3O7−x was developed. Single-phase superconducting oxide YBa2Cu3O7−x formed at temperatures as low as 750°. The particle size obtained by this method was found to be ≤0.2μm. Pellets sintered from these sol-gel powders exhibited very sharp resistivity drops at Tc = 90 °C with a Δc of ∼3°K.
Effect of ion bombardment during the low-mobility growth of metallic superlattices
Authors: Window B. , Sharples F.
Published: September 2007

The structure of sputtered Mo/Fe superlattices of periodicities 9 to 30 Å grown at a substrate temperature of 300 K at various pressures and levels of low-energy ion bombardment have been studied using x-ray diffraction. The samples show the growth of an amorphous phase below 17 Å periodicity and a crystalline phase above 21 Å, with mixed phases in between. Limited ion bombardment reduces the coherency in the growth direction in the crystalline phase, while heavy bombardment sufficient to promote significant mixing acts to improve the coherency, but not to the level observed in films with no bombardment. The relative intensities of the average lattice spacing reflection and its most intense satellite give the composition profile change due to the ion mixing. Some ion bombardment of the iron layer markedly improves the reflectance for x-rays at both low and high angles near the Bragg peak due to the average lattice spacing.
On the influence of iron on the reaction between silicon and nitrogen
Authors: Jennings Hamlin M.
Published: September 2007

The ways in which iron may affect the reaction between silicon and nitrogen are summarized and considered both in terms of possible mechanisms of the nitridation process and also in terms of the phases produced by the reaction. Some new results are reported that indicate that, in addition to removing an oxide layer from the silicon, or forming an alloy with the silicon, iron can activate the gaseous nitrogen. Other impurities, such as hydrogen in the gas, may also modify the behavior of nitrogen.
Solid-phase regrowth of compound semiconductors by reaction-driven decomposition of intermediate phases
Authors: Sands T. , Marshall E. D. , Wang L. C.
Published: September 2007

The solid-phase epitaxial regrowth of a III–V compound semiconductor by a two-stage reaction between a two-layer metallization and a compound semiconductor substrate is described. The regrowth process begins with a low-temperature reaction between a metal M (e.g. Ni, Pd, or Pt) and a compound semiconductor substrate, AB, to produce an intermediate M, AB or MB, phase. A subsequent reaction at a higher temperature between an overlayer of Si, Ge, Al, or In and the intermediate phase results in the decomposition of the intermediate phase and the epitaxial regrowth of a layer of the compound semiconductor. This regrowth mechanism is verified experimentally for the specific case of the Si/Ni/GaAs system. Rutherford backscattering spectrometry and transmission electron microscopy data show that the ternary phase Nix GaAs, formed during the initial stage of the reaction, decomposes toNiSi and GaAs by reaction with the Si overlayer. The incorporation of the overlayer element into the regrown semiconductor layer is proposed as a mechanism to explain the formation of Ohmic contacts in Si/Pd/n-GaAs, In/Pd/n-GaAs, In/Pt/n-GaAs, and similar two-layer metallization systems on n-GaAs.
An investigation of a nonspiking Ohmic contact to n-GaAs using the Si/Pd system
Authors: Wang L. C. , Zhang B. , Fang F. , Marshall E. D. , Lau S. S. , Sands T. , Kuech T. F.
Published: September 2007

A low-resistance nonspiking Ohmic contact to n-GaAs is formed via solid-state reactions utilizing the Si/Pd/GaAs system. Samples with Si to Pd atomic ratios greater than 0.65 result in specific contact resistivity of the order of 10−6 Ω cm2, whereas samples with atomic ratios less than 0.65 yield higher specific contact resistivities or rectifying contacts. Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, and electron diffraction patterns show that a Pd, Si layer is in contact with GaAs with excess Si on the surface after the Ohmic formation annealing. This observation contrasts with that on a previously studied Ge/Pd/GaAs contact where Ohmic behavior is detected after transport of Ge through PdGe to the interface with GaAs. Comparing the Ge/Pd/GaAs system with the present Si/Pd/GaAs system suggests that a low barrier heterojunction between Ge and GaAs is not the primary reason for Ohmic contact behavior. Low-temperature measurements suggest that Ohmic behavior results from tunneling current transport mechanisms. A regrowth mechanism involving the formation of an n+ GaAs surface layer is proposed to explain the Ohmic contact formation.
Raman spectra during the electropolymerization of polypyrrole
Authors: Olk C. H. , Beetz C. P. , Heremans J.
Published: September 2007

In situ Raman spectra were taken, between 800 and 1200 cm−1, on films of polypyrrole during both the electrochemical growth and the reduction reactions. During the reduction reaction we observed a frequency shift of approximately 10 cm−1 of two in-plane vibrational modes. We attribute these shifts to the bond conjugational defects induced by doping and undoping of the polypyrrole films. A quantitative model for this phenomenon based on normal mode calculations is presented. The electrical conductivity and thermopower of polypyrrole doped with tetrafluoroborate and iron chloride ions is also reported for temperatures between 10 and 350K.
Crystallization of BaF2–ZnF2–YbF3–ThF4 glass
Authors: Garcia Roberto , Doremus Robert H. , Bansal Narottarn P. , Ko Sen-Hou , Margraf Tracey
Published: September 2007

The crystallizing phases from a BaZn YbTh fluoride glass were a BaYbTh fluoride, ZnF2, and YbF3, as identified with x-ray diffraction and composition-enhanced scanning electron microscopy. Blocky BaYbTh fluoride crystallizes first, at about 450 °C, and ZnF2 excluded from this phase crystallizes at its surfaces. At higher temperatures the BaYbTh fluoride phase decomposes partially to BaThF6 and YbF3 phases. The kinetics and temperatures of crystallization were also followed with differential scanning calorimetry.
Effects of annealing on the structure and electrical conductivity of CVD alumina films
Authors: Wong A. S. , Michal G. M. , Locci I. E. , Cheung P. W.
Published: September 2007

Alumina films, 160 nm thick, were deposited on (100) -oriented silicon single-crystal substrates by pyrohydrolysis of aluminum chloride. Such films are candidate gate materials for an improved pH ion-sensitive field-effect transistor (pH-ISFET) for industrial and medical pH measurements. The current-voltage (I–V) characteristics of films annealed for 30 min at temperatures of 850, 1000, and 1175 °C were determined, Annealing at 850 °C produced the optimum I–V behavior for the aluminum oxide pH-sensitive films as evidenced by minimum leakage current and maximum breakdown voltage. The structures of the annealed films were examined using transmission electron microscopy. The anneals at 1000 and 1175 °C caused partial and complete transformation, respectively, of the as-deposited α-alumina to the α-alumina phase. Associated with a-alumina formation was the creation of voids along the grain boundaries and in the grain interiors that provided paths of increased electrical conduction through the alumina films and degraded their dielectric behavior.
Dynamic consolidation of cubic boron nitride and its admixtures
Authors: Tan Hua , Ahrens Thomas J.
Published: September 2007

Cubic boron nitride (C–BN)' powders admixed with graphite-structured boron nitride powder (g-DN), silicon carbide whisker (SCW), or silicon nitride whisker (SNW) were shock compacted to pressures up to 22 GPa. Unlike previous work with diamond and graphite [D. K. Potter and T. J. Ahrens, J. Appl. Phys. 63, 910 (1987) it was found that the addition of g-BN inhibited dynamic consolidation. Good consolidation was achieved with a 4–8 μm particle size C–BN powder admixed with 15 wt.% SNW or 20 wt.% SCW whereas a 37–44 μm particle size C–BN mixture was only poorly consolidated. Scanning electron microscopy (SEM) analysis demonstrates that SCW and SNW in the mixtures were highly deformed and indicated melt textures. A skin heating model was used to describe the physics of consolidation. Model calculations are consistent with SEM analysis images that indicate plastic deformation of SCW and SNW. Micro-Vickers hardness values as high as 50 GPa were obtained for consolidated C–BN and SNW mixtures. This compares to 21 GPa for single-crystal Al2O3 and 120 GPa for diamond.
The cracking and decohesion of thin films
Authors: Evans A. G. , Drory M. D. , Hu M. S.
Published: September 2007

The cracking and decohesion of thin films can be characterized by critical values of a nondimensional parameter governed by the residual stress, the film thickness, and a fracture resistance. This article reviews the status of understanding concerning the magnitude of this number for various types of adherent film on either brittle or ductile substrates. Important effects of elastic properties, substrate thickness, and yield strength are described.
Characterization of ion-beam mixed multilayers via grazing x-ray reflectometry
Authors: Le Boité M. G. , Traverse A. , Névot L. , Pardo B. , Corno J.
Published: September 2007

The grazing x-ray reflectrometry technique was used as a way to study modifications in metallic multilayers induced by ion-beam irradiation. Due to the high sensitivity of the technique, short-range atomic displacements of an atom A in a layer B can be detected so that the first stages of ion-beam mixing can be investigated. The rate of mixing is measured and the compound A1−xBxformed at the layers' interfaces is characterized.
Polishing wear resistance of ion-implanted 304 steel
Authors: Singer I. L. , Vardiman R. G. , Bolster R. N.
Published: September 2007

Steel (AISI-304) disks, polished to a 3 μm diamond finish, were implanted to doses of about 2 × 1017/cm2 with N+, Ni+ or, Ne+, ions. Polishing wear rates, measured to a depth resolution of about 20 nm, showed that each of the implanted disks wore 20% to 40% faster than nonimplanted layers. Auger analysis showed (1) Gaussian-like profiles of the N-implanted layer, but with somewhat enhanced oxidation of the surface, and (2) a sputter-limited implantation profile in the Ni-implantcd layer, with some vacuum carburization. Transmission electron microscope analysis indicated that polishing produced an α′-martensite layer in the mainly austenitic 304 surface, but that implantation of N transformed the martensite to austenite at the outermost layers and produced iron nitrides below. In addition. Nimplantation stabilized the austenite against martensite transformation during subsequent wear. Martensite vanished after Ni implantation because of sputter removal, not phase transformation, during Ni bombardment. The Ne-implanted layer remained predominantly martensite. Changes in wear rates and microstructures were confined to depths commensurate with the range of ions in the implanted layer. Several hypotheses on the effects of ion implantation on microstructureand wear are discussed.
Ultraviolet photon-induced heteroepitaxy of CdTe on GaAs
Authors: Cody N. W. , Sudarsan U. , Solanki R.
Published: September 2007

Ultraviolet photon-induced metalorganic vapor phase epitaxy of CdTe films on GaAs substrates has been investigated using diethyltelluride and dimethylcadmium as the precursor gases. The relationship between the deposition parameters and the properties of the epilayers have been examined using transmission electron microscopy and x-ray rocking curves. Epilayers grown at 6μm/h show an x-ray double-crystal rocking curve full width at half-maximum (FWHM) of 250 arcsec.
Ion-beam-assisted growth of doped Si layers
Authors: Priolo F. , La Ferla A. , Rimini E.
Published: September 2007

The growth of preamorphized silicon layers doped by multiple energy implants of boron, phosphorus, and boron plus phosphorus ions was investigated under irradiation with a 600 keV Kr+ + beam. The target temperature was set in the range 250–450 °C. During irradiation the growth was measured in situ by transient reflectivity. Boron and phosphorus at a concentration of 1 × 1020/cm3 enhance the rate by a factor of 3 and 2, respectively, whilst in compensated samples the rate is still more than a factor of 2 higher than in intrinsic or Ge-doped samples. This growth rate is characterized by an activation energy of 0.32 ± 0.05 eV which is, within the experimental uncertainties, independent of the dopant. The results are tentatively explained in terms of an interaction between generated point defects and impurities that increases the lifetime of defects at the crystal–amorphous interface.
Selective growth of B 1-NbN in Nb thin film by high-dose nitrogen molecular ion implantation
Authors: Tanabe Nobuo , Iwaki Masaya
Published: September 2007

Nitrogen molecular ion implantations have been performed in niobium thin films to form B 1-NbN layers with an accelerating voltage of 150 kV up to a dose of 5 × 1017 N2+ ions/cm2 at room temperature. Measurements of superconducting transition temperature (Tc), Auger electron spectroscopy analyses (AES), and x-ray diffraction analyses (XRD) have been carried out as a function of nitrogen dose in order to characterize the implanted layer. It has been found that there are two regions in the dose dependence of Tc; in the low-dose case, Tc decreases from the initial value of 8 K to less than 4.2 K with increasing dose, and in case of the high dose (more than 2.5 × 1017 ions/cm2) it increases rapidly to 11 K and becomes independent of the implantation dose. The XRD patterns indicate the generation of lattice disorder at the low dose, the formation of Nb2N and ∊NbN at the intermediate dose, and the formation of δNbN (B 1 structure) at the high dose; the selective growth of δNbN occurs at the highest dose, in spite of the fact that thermodynamically Nb2N and ∊NbN are equilibrium phases at room temperature and they are formed at the intermediate dose. In conclusion, high-dose nitrogen implantation at room temperature causes the formation of δNbN to increase Tc.
Ion-beam-induced aggregation in polystyrene: The influence of the molecular parameters
Authors: Puglisi Orazio , Licciardello Antonino , Calcagno Lucia , Foti Gaetano
Published: September 2007

The formation of an insoluble gel under ion-beam bombardment is governed by ion-beam parameters and target parameters. Here reported is a study of the influence of the target molecular parameters on the sol–gel transition of ion-bombarded polystyrene with particular emphasis for the number-average molecular weight $\overline M$n. It is shown that the main parameter is the number of macromolecules of the film so that by adopting a “corrected” fluence F/n (ions per macromolecule), the different curves of the various polymers collapse in only one universal curve. The importance of the “corrected” fluence is shown also at molecular level and the MWD of the various polymers is similar at equal F/n values. An experimental model is outlined which explains the sol–gel transition on the basis of transition from an isolated-track regime to an overlap regime where the formation of insoluble giant macromolecules occurs.
Soft vacuum, pulsed electron-beam hardening of lithographic polymers
Authors: Krishnaswamy J. , Li L. , Collins G. J. , Hiraoka H. , Caolo M. A.
Published: September 2007

A 25 kV pulsed electron beam was used to harden 0.5−3.0μm thick AZ-type, MacDermid, and polyamic acid (PMDA + ODA) resist patterns. The resist profiles are stable against high-temperature treatment that ranges between 200−350 °C. The short pulse ∼ 100 ns, electron beams employed in resist hardening are produced from a cold cathode in 30−50 m Torr air by discharging energy stored in a 7.5 nF capacitor producing a dose/pulse ∼ 1μC/cm2 at the processed surface. Comparisons with conventional hardening methods using ultraviolet emission from a high-pressure mercury lamp, a windowless, vacuum ultraviolet (VUV) lamp, and low-energy electron emission from a cw source are also made.
Theoretical investigation of possible low-lying electronic excitations in YBa2Cu3O7−x
Authors: Curtiss L. A. , Tam S. W.
Published: September 2007

Ab initio molecular orbital calculations of oxygen 2p hole states of small CuO clusters representing the chains and planes in YBa2Cu3O7−x are reported. The results suggest that the absorption observed at 0.37 eV in reflectivity studies of YBa2Cu3O7−x may be due to excitation of these holes between inequivalent oxygen sites.
Microstructure and fracture toughness of powder-processed Al3Nb
Authors: Schneibel J. H. , Becher P. F. , Horton J. A.
Published: September 2007

Intermetallic alloys with the nominal compositions Al–24.5Nb, Al–25Nb, and Al–25.5Nb (at.%) were fabricated by hot-pressing of pre-alloyed powders in graphite dies in vacuum. The hot-pressed disks contained substantial porosity even at processing temperatures of 0.95 Tm, where Tm is the absolute melting point. In addition to some copper and silicon contamination, significant concentrations of oxygen and carbon were measured in Al–25.5Nb. Alpha alumina precipitates as well as niobium-enriched precipitates were identified. The fracture toughness of pre-cracked bend specimens with the nominal composition Al–25.5Nb was found to be 2.5 ± 0.5 MPa m1/2. Possibilities for improving this value are discussed.
Fast diffusion and nucleation of the amorphous phase in Ni–Zr films
Authors: Ehrhart P. , Averback R. S. , Hahn H. , Yadavalli S. , Flynn C. P.
Published: September 2007

The nucleation of the amorphous phase by solid-state reactions has been investigated on single-crystal Zr films grown by molecular beam epitaxy and covered in situ with either polycrystalline Ni, amorphous (a-) NiZr, or single-crystalline Zr99N01 films. Interfacial reactions were investigated by backscattering analysis or secondary ion mass spectroscopy. The amorphizing reaction occurred only in the specimen with the a-NiZr over layer, although fast Ni diffusion through the single-crystalline Zr layer was observed in all three specimens. The nucleation behavior of a-NiZr is attributed to the combination of high-Ni and low-Zr mobility in crystalline Zr.
Critical current density of Ba2Y1Cu3O7−x superconducting filaments produced by various suspension spinning conditions
Authors: Goto Tomoko , Kada Masahiro
Published: September 2007

The suspension spinning of a Ba2Y1Cu3Ox superconductor under various conditions was studied to prepare a long filament with high Jc. The oxide powder was suspended in a PVA solution containing a dispersant. The viscous suspension was extruded as a filament into a precipitating medium and coiled on a winding drum. The obtained filament was heated to remove volatile components and to generate the layered perovskite phase. The spinning was examined in an aqueous system and a nonaqueous system. The filament with higher Jc was obtained for the nonaqueous solution. The Jc was dependent on the fineness of the starting oxide powder, solvent, precipitating medium, degree of polymerization of PVA, the kind of dispersant used, and the oxide powder contents of the spinning dope, as well as the heating condition. The highest Jc value obtained by resistivity measurement at 77 K and zero field, 680 A/cm2, was attained for the filament spun under optimum spinning conditions. The magnetization curve of the filament showed that the material was a type II superconductor. The hysteresis of thin filaments was relatively small compared with that for the thick filaments. The Jc at 79 K, estimated from the magnetization curve, was one order of magnitude higher than the Jc measured by the resistivity method and decreased drastically with increasing field.
Superconducting properties of mixtures of Y1Ba2Cu3O9−xand Y1.8Ba0.2Cu1O5−y
Authors: Wang X. W. , Kwok H. S. , Shi L. , Zheng J. P. , Mattocks P. , Shaw D. T.
Published: September 2007

The superconducting properties of heat-treated mixtures of Y1Ba2Cu3O9−x(A) and Y1.8Ba0.2Cu1O5−y(B) have been studied. As the concentration of B increases, the Meissner effect decreases, while the resistance jump near the superconducting transition increases. When the fraction of B approaches about 0.5, the superconducting transition disappears. Four different phases are identified in the mixture from the x-ray spectra, i.e., Y1Ba2Cu3O9−x, Y2Ba1Cu1O5–z, Y2Cu2O5, and Y2O3. The results agree well with the published phase diagram of this system.
Microstructure study of Y–Ba–Cu oxide superconducting thin films
Authors: Hamdi A. H. , Mantese J. V. , Micheli A. L. , Waldo R. A. , Chen Y. L. , Wong C. A. , Karmarkar M. M. , Padmanabhan K. R.
Published: September 2007

Grain growth as a function of annealing temperature in Y–Ba–Cu oxide superconducting thin films is presented. Effects of excess Cu on the temperature dependence of the resistance, grain growth, and sheet resistivity are discussed. This is the first systematic study of the microstructure of thin films formed by the nonvacuum technique of metallo organic deposition. The Cu-rich films show an anomalous behavior in the resistivity at 220–240 K. The presence of excess Cu was found to enhance grain growth for films annealed below the melting point of the 1–2–3 phase. Films deposited on 〈100〉 SrTiO3 and rapid thermal annealed showed partial epitaxial growth of the 1–2–3 phase. The analytical techniques of Rutherford backscattering spectrometry, ion channeling, x-ray diffraction, scanning electron microscopy, electron microprobe analysis, sheet resistivity, and temperature versus resistance measurements have been used in this study.
Structure and composition in the superconductive Bi–Sr–Ca–Cu–O system
Authors: Carim A. H. , Kentgens A. P. M. , Hengst J. H. T. , de Leeuw D. M. , Mutsaers C. A. H. A.
Published: September 2007

Characterization of superconducting Bi–Sr–Ca–Cu oxides has been carried out by electrical measurements, x-ray diffraction, conventional and high-resolution electron microscopy, and electron microprobe analysis. Nominal starting compositions with cation ratios of 1:1:1:2 and 2:2:1:2 show considerably different superconducting behavior. In both cases multiphase materials are formed. The predominant superconducting phase occurs as thin platelets with an orthorhombic, modulated structure. These particles often have edges aligned along [110], [100], and [010] directions and contain subgrain boundaries. Electron diffraction patterns and high-resolution micrographs taken along several zone axes are consistent with an incommensurate centered modulation along the b axis with a magnitude of 4.7 ± 0.1 times b. Unexpectedly, two distinct chemical compositions were found in platelets with the same apparent structure: Bi4Sr3Ca3Cu4O16±δ for the lower Tc phase in the 1:1:1:2 material, and Bi2Sr2CaCu2O8±δ for the isomorphic higher Tc phase present in the 2:2:1:2 samples.
The annealing behavior of sputter-deposited Al–Mn and Al–Mn–Si films
Authors: Kaufman M. J. , Biancaniello F. S. , Kreider K. G.
Published: September 2007

The annealing behavior of amorphous and icosahedral Al–17Mn and Al–20Mn–4Si films, prepared by sputter deposition, have been studied. Both hot stage transmission electron microscopy of thin (20–200 nm) films and furnace annealing plus x-ray diffration of thicker (1–10μm) films were utilized to study the various transformations resulting from elevated temperature exposures. The results are presented and correlated with the reactions anticipated from the phase diagrams and the results reported in previous studies.
An amorphous-to-amorphous transition in Ni–Zr–B alloys as probed by hydrogen storage
Authors: Harris J. H. , Curtin W. A.
Published: September 2007

The hydrogen occupation characteristics of the ternary amorphous alloy system Ni–Zr–B are investigated using gas-phase and electrochemical hydrogen-absorption techniques. Boron concentrations of as little as 1% are observed to cause large changes in the hydrogen storage properties relative to the binary Ni–Zr. Generalizations of a site statistical model, which accurately accounted for H storage in thebinary Ni–Zr and is based on tetrahedral interstitial hydrogen sites, cannot account for the hydrogen absorption properties of the boron-containing alloys, suggesting a structural transition between two amorphous phases induced by only 1% boron. A simple model in which the new amorphous phase stores H in higher-coordinated interstitial sites is shown to be consistent with the electrochemical and gas-phase data.
An electron microscopy study of the atomic structure of a mullite in a reaction-sintered composite
Authors: Schryvers D. , Srikrishna K. , O'Keefe M. A. , Thomas G.
Published: September 2007

The mullite matrix of a reaction-sintered mullite/zirconia composite has been characterized by various electron microscopy techniques. The mullite was determined to be stoichiometrically Al4.76Si1.23O9.61 (1.7:1 mullite) with a disordered vacancy structure and Pbam symmetry. The atomic structure of the mullite has been described in terms of an average unit cell.
Oxygen transport through high-purity, large-grain Ag
Authors: Outlaw R. A. , Sankaran S. N. , Hoflund G. B. , Davidson M. R.
Published: September 2007

The permeation of oxygen through high-purity, large-grain Ag membranes has been studied over the temperature range of 400–800 °C. The permeability was found to be linear and repeatable, but the magnitude was 3.2 times smaller than that determined by past research. This factor may be due to negligible grain boundary diffusion that exists in this work. Auger electron spectroscopy (AES) does, however, suggest the importance of grain boundaries since intragranular oxygen was virtually undetectable and since AES line scans show substantial oxygen signals around the grain boundaries. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 °C. The high-temperature data have an activation energy (11.1 kcal mol−1) similar to that reported by others, but the low-temperature data have a comparatively larger activation energy (15.3 kcal mol−1). Vacuum desorption of the oxygen-saturated Ag was found to occur at the critical temperature of 630 °C, which is consistent with the increased mobility of oxygen atoms in the higher temperature regime. The higher activation energy observed in the lower temperature regime is probably due to the higher efficiency of traps.
Growth of diamond by rf plasma-assisted chemical vapor deposition
Authors: Meyer Duane E. , Ianno Natale J. , Woollam John A. , Swartzlander A. B. , Nelson A. J.
Published: September 2007

A system has been designed and constructed to produce diamond particles by inductively coupled radio-frequency, plasma-assisted chemical vapor deposition. This is a low-pressure, low-temperature process used in an attempt to deposit diamond on substrates of glass, quartz, silicon, nickel, and boron nitride. Several deposition parameters have been varied including substrate temperature, gas concentration, gas pressure, total gas flow rate, rf input power, and deposition time. Analytical methods employed to determine composition and structure of the deposits include scanning electron microscopy, absorption spectroscopy, scanning Auger microprobe spectroscopy, and Raman spectroscopy. Analysis indicates that particles having a thin graphite surface, as well as diamond particles with no surface coatings, have been deposited. Deposits on quartz have exhibited optical bandgaps as high as 4 5 eV. Scanning electron microscopy analysis shows that particles are deposited on a pedestal which Auger spectroscopy indicates to be graphite. This is a phenomenon that has not been previously reported in the literature.
High temperature transport properties of the high Tc superconductor, Y1Ba2Cu3Ox
Authors: Yoo Han-Ill
Published: September 2007

The electrical conductivity and thermopower of the cuprate, Y1Ba2Cu3Ox, have been measured as functions of temperature and oxygen partial pressure over the ranges of 400 °C–700 °C and 10−4 atm—1 atm, respectively. It has been confirmed that, as temperature increases, conduction mechanism changes from metallic to p-type to n-type semiconducting. It has been found that the p-n transition occurs at a specific value for oxygen content (x = 6.35) irrespective of temperature and that the thermopower in the p-type region is insensitive to temperature. The latter leads to a charge transfer mechanism of correlated hopping of holes. Mechanisms of hole generation due to oxygen nonstoichiometry are found to be different in the tetragonal and the orthorhombic phase of the cuprate.
Computer simulation on surfaces and [001] symmetric tilt grain boundaries in Ni, Al, and Ni3Al
Authors: Chen S. P. , Srolovitz D. J. , Voter A. F.
Published: September 2007

We have used “local volume” (embedded atom) type potentials to study the surfaces and grain boundaries of Ni, Al, and Ni3Al. The simulations show that with appropriately fit potentials, the surface and grain boundary structure can be realistically calculated. The surface rippling and relaxation show good agreement with experiments. The energies of most surfaces and grain boundaries also agree with existing data. The structural unit model for grain boundaries in Ni3Al shows the same generic units as in pure metals, but with large variations due to distortions and multiplicity. The utility of the structural unit model is thus more limited for alloys. The grain boundary energies were found to be the highest for Al-rich Ni3Al grain boundaries, and depend significantly on the local composition of the grain boundary. The cusps in the grain boundary energy as a function of misorientation angle are different for different grain boundary stoichiometries. The Ni3Al grain boundaries have approximately the same grain boundary energy and cohesive energy as that of Ni.
Dependence of the structural and electrical properties of ultrathin cobalt silicide films on formation conditions
Authors: Phillips Julia M. , Batstone J. L. , Hensel J. C. , Cerullo M. , Unterwald F. C.
Published: September 2007

We have studied the dependence of the electrical and structural properties of ultrathin cobalt silicide films on the annealing temperature and deposited Co thickness. If less than 10 Å of Co is deposited, epitaxial type B CoSi2 forms immediately. As the deposited thickness approaches 10 Å, small amounts of Co2Si are observed. If greater than 10 Å of Co is deposited, epitaxial Co2Si forms at room temperature, which proceeds either via the reaction Co2Si ⇉ CoSi ⇉ CoSi2 or via Co2Si ⇉ CoSi2 during annealing. In these thicker films our results suggest that the formation of type A CoSi2 is correlated with the presence of Co2Si; the presence of CoSi as an intermediate phase is correlated with the occurrence of type B CoSi2. Both film thickness and reaction temperature strongly influence the electrical transport in these films such that very high resistivities are encountered when films either become very thin or are reacted at low temperatures. In the former case the size effect is responsible whereas in the latter the transport properties are dominated by extensive atomic-scale disorder.
Strain measurements and thermal stability of Si1−xGex/Si strained layers
Authors: Holländer B. , Mantl S. , Stritzker B. , Jorke H. , Kasper E.
Published: September 2007

He ion channeling and backscattering experiments have been performed on MBE-grown Si1−xGex/Si strained layers to investigate the tetragonal lattice distortion and the Ge diffusion after thermal annealing. The tetragonal strain of the epitaxial layers has been determined by measuring the angular deviations of inclined 〈110〉 orientations of the adjacent layers. The measured angular shifts indicate a nearly pseudomorphic layer growth of the virgin sample. The angular yield scans of the Ge signal show a pronounced asymmetry, caused by beam steering in the tetragonally distorted lattices of the different layers. Thermal annealing above 800 °C results in strain relaxation and in layer mixing due to the diffusion of germanium. The observed Ge diffusion is strongly enhanced by the elastic strain in the layered structure.
Optical and valence band studies of ZnP2 thin films
Authors: Samuel V. , Rao V. J.
Published: September 2007

Conditions have been developed for the preparation of ZnP2 and deposition of its stoichiometric thin films, using the flash evaporation technique. Structural properties of the ZnP2 obtained have been studied using x-ray diffraction, and chemical composition has been established by the polarography technique. Optical absorption of thin films of β–ZnP2 has been investigated over the range 1.2–3.2 eV. Analysis of thin film data showed that β–ZnP2 is a direct band gap material. The XPS and UPS of β–ZnP2 show a shift in binding energy (BE), which is due to transfer of electrons from zinc to phosphorus.
Influence of chemical composition and inorganic admixtures on the electrical conductivity of hydrating cement pastes
Authors: Perez-Pena M. , Roy D. M. , Tamás F. D.
Published: September 2007

Electrical conductivity of cementitious materials with a wide range of chemical compositions has been studied during the first 24 h of hydration. Relationships between heat of hydration and electrical conductivity curves are discussed. Results are tentatively explained in terms of some physical and chemical parameters. Further evidence that the electrical conductivity of hydrating cement pastes is related to the hydration mechanisms operating in these systems was obtained. The order in which the cations of inorganic admixtures (chlorides and hydroxides) were found to increase the peak and rate of development of the electrical conductivity is the same order that they have been found to increase the heat liberated upon hydration of systems containing these admixtures.
Infrared absorption spectroscopy of hydrogen and deuterium in CaO and SrO crystals
Authors: Park J. L. , González R.
Published: September 2007

Infrared absorption spectra have been used to characterize OH− and OD− ions at the surface and the bulk of undoped CaO, lithium doped CaO, and SrO crystals. Diffusion of deuterons from D2O vapor into these crystals was performed at elevated temperatures. Diffusion coefficients were obtained to be D (CaO) = 3 ⊠ 10−6 cm2/sec at 1773 K and D (SrO) = 4 ⊠ 10−7 cm2/sec at 1523 K. For the doped CaO crystal with lithium concentration of 310 ppm, the diffusion coefficient was measured to be D (CaO:Li) = 4 ⊠ 10−7 cm2/sec at 1473 K and the activation energy in the Arrhenius equation was estimated to be 1.7 eV.
Microstructure and properties of superconducting sputter deposited Y–Ba–Cu–O films
Authors: Kwasnick R. F. , Luborsky F. E. , Hall E. L. , Garbauskas M. F. , Borst K. , Curran M. J.
Published: September 2007

Films of Y–Ba–Cu–O have been reproducibly prepared with metal stoichiometry near 1-2-3 by sputter deposition from a single sintered target. Twenty-seven depositions resulted in films with a standard deviation in composition of 1%. For 30 samples deposited on (100) SrTiO3 and annealed, the mean and standard deviation of the critical temperature, Tc (10% above ρ = ο), was 86.2 ± 1.4 K with a transition width (10–90%) of 1.8 ± 1.1 K. The composition and Tc were independent of film thicknesses from 0.09 to 2.5 μm. Critical currents were calculated for samples as a function of thickness from transport and from magnetization measurements. Within the considerable scatter observed of ± half an order of magnitude, the two methods agreed with each other over the thickness range studied. They were both fit with an initial Jc independent of thickness, t, for films up to about 0.3 μm thick followed by a 1/t decrease in Jc for thicker films. Metallographic examination of these films indicated microstructural features consistent with this behavior. Planar TEM images of 0.10 μm thick films showed that high Jc correlated with a film which predominantly has its c-axis normal to the film plane. An alternative structure was also seen, in which regions of the firm had their c-axis along each of the three 〈100〉 SrTiO3 directions, two in the film plane, and one normal to it. This type of film has a much lower Jc.
Reaction pathways for the formation of the YBa2Cu3O7−x compound
Authors: Ruckenstein Eli , Narain Sanjeev , Wu Nae-Lih
Published: September 2007

The kinetics of the reactions that lead to the formation of YBa2Cu3O7−x was investigated starting from various powder mixtures containing different reactants as sources of Ba, Cu, and Y (BaCO3, BaO, CuO, Y2O3. Y2Cu3O5. and BaCuO2). These powders were calcined at 940 °C for various time intervals. Quantitative x-ray analysis was used to determine the relative amounts of the compounds present in the calcined powders. When BaCO3 was used as the source of barium, long calcination times were required to obtain the single phased YBa2Cu3O7−x because of the slow decomposition of BaCO3. This leads to large particles and broad particle size distributions and hence to a lower density of the sintered superconducting pellets. Procedures to attain high density superconducting material are identified on the basis of the kinetic studies. Each of them isolates the slow reaction in a first step and prepares the superconducting material via a rapid reaction in a second step. The kinetic studies reveal the reaction mechanisms that were followed in different cases.
Structure of amorphous Fe–Cr–P alloys prepared by electrodeposition
Authors: Ng Patrick K. , Mitchell T. E. , Locci Ivan E. , Ruiz Augusto A.
Published: September 2007

Iron-chromium-phosphorus (Fe–Cr–P) alloys were prepared by electrodeposition from an acidic citrate electrolyte using sodium hypophosphite as the source of phosphorus. These alloys form a passive oxide layer when exposed to air and are useful as protective coatings on steel. The current efficiency of the plating process reaches a maximum of 20% at a current density of 100 mA/cm2 where the alloy has 10% Cr and 19% P. X-ray diffraction patterns and TEM analysis show that the alloy is amorphous. TEM results also indicate that small oxide particles (5–20 nm) are dispersed in the amorphous structure. Besides Fe, Cr, and P, the alloys contain a low level of oxygen (4–7%) in the form of mixed iron and chromium oxides, as confirmed by AES analysis. When heated, the amorphous structure transforms into a mixture of Fe3P and Cr3P, along with α–Fe–Cr grains. This phase transformation occurs in the temperature range of 450–460 °C for alloys with 19% P.
Polycrystalline hexagonal boron nitride films on SiO2 for III–V semiconductor applications
Authors: Hurd J. L. , Perry D. L. , Lee B. T. , Yu K. M. , Bourret E. D. , Haller E. E.
Published: September 2007

Isotropic hexagonal BN (h-BN) films were deposited on SiO2 crucibles used for synthesis of GaAs. Deposited films were analyzed for composition, morphology, and growth rates using proton resonant scattering, optical absorption, x-ray and electron diffraction, and transmission electron microscopy. The silicon concentration of GaAs synthesized in BN coated crucibles was approximately one order of magnitude higher than that for GaAs synthesized in uncoated crucibles under identical synthesis conditions.
Plasma deposition of a–Si, Ge: H, F thin films from SiF4–GeH4–H2 mixtures
Authors: Bruno G. , Capezzuto P. , Cicala G. , Cramarossa F.
Published: September 2007

The deposition of hydrogenated and fluorinated silicon-germanium alloys (Si1−xGex:H.F) by glow discharge decomposition of silicon tetrafluoride (SiF4) and germane (GeH4) mixtures has been studied. Optical emission spectroscopy (OES), for the analysis of the emitting species in plasma phase, and mass spectroscopy (MS) for the analysis of the stable species, are used for the plasma diagnostics. In addition, in situ measurements of the deposition rate by laser interferometry are performed. A series of alloys with germanium content ranging from 0 to 55% has been prepared by varying the gas compositional ratio. Data on the optical gap (Ec), sub-gap absorption, and photo-to-dark conductivity ratio (δσ/σ) are used to evaluate the quality of the materials. An alloy a–Si0.75Ge0.25: H, F having Ec δ 1.5 eV and δσ/σ = 104 has been prepared by adding 1% of GeH4 to SiF4 in the feed.