bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible behavior of a diamond (111) surface in methane/hydrogen systems
Authors: Valone Steven M. , Trkula Mitchell , Laia Joseph R.
Published: September 2007

A combined numerical and experimental investigation into the behavior of diamond (111) surfaces in plasma CVD reactors is presented. Numerically, semiempirical molecular orbital methods are used as a model of diamond (111) surfaces represented by a 20-atom carbon cluster plus surface species. The abstraction of hydrogen atoms by gas-phase hydrogen atoms, the coverage dependence of the heat of formation for submonolayers of CH3 and C2H groups coadsorbed with H, and the energy change for abstraction of H atoms from the surface by various radicals in the gas phase are examined. No barrier to abstraction is found, steric effects in achieving clusters of CH3 groups are large, and C2H and atomic oxygen are found to be the most energetically favored for removal of adsorbed H. Experimentally, relative concentrations of atomic H in the near-surface region as a function of added O2 mole fraction were measured. A weak dependence on O2 concentration is observed, but does not appear to be significant enough to account for observed changes in growth rate. This suggests that other radical species be investigated for their contribution to diamond film growth.
Growth of textured diamond films on Si(100) by C2H2/O2 flame method
Authors: Hwang J. , Zhang K. , Kwak B. S. , Erbil A. , Feng Z. C.
Published: September 2007

Highly textured diamond thin films with (111) orientation have been successfully grown on the single crystal silicon (100) substrates by the flame method using the premixed acctylene and oxygen gas. Scanning electron microscopy (SEM), x-ray diffraction, and Raman spectroscopy studies have shown the formation of uniform diamond films with the full coverage of the deposition area on the Si substrates. An approach which leads to growing diamond films with very low graphite and/or amorphous carbon contaminations is described.
The effects of UV laser irradiation on the filament-assisted deposition of diamond
Authors: Celii F. G. , Nelson H. H. , Pehrsson P. E.
Published: September 2007

The effects of 193 and 308 nm excimer laser radiation on the filament-assisted chemical vapor deposition (CVD) of diamond were investigated, in attempts to reproduce and quantify the reported mechanism of laser-enhanced diamond deposition. The deposited materials were analyzed using optical microscopy, SEM, scanning Auger microprobe, and micro-Raman scattering. With fluence levels of >50 mJ · cm−2, UV laser irradiation was found to suppress rather than enhance the quantity of diamond deposition. The size, morphology, and Raman spectra of crystallites in the irradiated regions were nearly identical to those in adjacent unirradiated regions of the same sample. An additional laser-induced effect was a region of enhanced etching on the Si substrate, which appeared as a “shadowing” of the diamond crystallites. The results are interpreted in terms of a laser-induced depletion of diamond nucleation sites, and suggest a new method for patterning of CVD films.
Infrared optical properties of CVD diamond films
Authors: Wang X. H. , Pilione L. , Zhu W. , Yarbrough W. , Drawl W. , Messier R.
Published: September 2007

Diamond films of 15–20 μm thicknesses were prepared by microwave plasma enhanced chemical vapor deposition onto crystalline silicon substrates. The growth surfaces of the films were rough with polycrystalline crystallographic habits, while the substrate sides of these films were smooth and featureless as viewed by optical microscopy. A heated cast iron scaife was used to polish the rough growth surfaces, and free-standing films were removed from the silicon substrates by dissolving the silicon in an aqueous HF. Both infrared optical transmission and reflection spectra were measured over the range of 600–4000 cm−1. For polished films, near 70% transmittance was obtained over the whole range, while the transmittance for nonpolished films was much lower and varied strongly with the wave number. Absorptions due to carbon-hydrogen stretching bands as well as a silicon carbide phase were observed in the transmission spectra. The optical absorption coefficient and the refractive index were found to vary from as high as 150 to as low as 7 cm−1 and 2.41 to 2.49, respectively (depending on the film quality and the wave number). A weak signature of the two-phonon absorption band of diamond was observed. The relationship between deposition conditions and infrared optical properties of diamond films before as well as after polishing is discussed.
Measurement of crystalline strain and orientation in diamond films grown by chemical vapor deposition
Authors: Specht E. D. , Clausing R. E. , Heatherly L.
Published: September 2007

We have used x-ray diffraction to characterize diamond films grown in three characteristic morphologies by chemical vapor deposition. Each morphology has a fiber texture about the growth direction; we report the crystal axis aligned in this direction for each morphology. In all cases the average lattice constant agrees with that of bulk diamond; we report the range of strain in each sample.
Electron microscopic characterization of diamond films grown on Si by bias-controlled chemical vapor deposition
Authors: Ma G-H.M. , Lee Y. H. , Glass J. T.
Published: September 2007

Diamond films grown by Bias-Controlled Hot Filament Chemical Vapor Deposition (BCCVD) on silicon (Si) substrates were characterized by Transmission Electron Microscopy (TEM). Both plan-view and cross-sectional TEM samples were made from diamond films grown under different biasing conditions. It was found that defect densities in the films were substantially reduced under zero and reverse bias (substrate negative relative to the filament) as compared to forward bias. Furthermore, the diamond/Si interface of the reverse and zero bias films consisted of a single thin interfacial layer whereas multiple interfacial layers existed at the diamond/Si interface of films grown under forward (positive) bias. Tungsten (W) contamination was also found in the interfacial layers of forward bias films. It is concluded that forward biasing in the present condition is not favorable for growing high quality, low defect density, diamond films. The possible mechanisms which induced the microstructural differences under different biasing conditions are discussed.
Structural analysis of hydrogenated diamond-like carbon films from electron energy loss spectroscopy
Authors: Wang Yaxin , Chen Hsiung , Hoffman R. W. , Angus John C.
Published: September 2007

Electron energy loss spectral analysis of the π and (π + σ) electron plasma resonances are used to analyze the structure of hydrogenated diamond-like carbon (a-C:H) films. Energy loss peaks associated with the resonances of the π and (π + σ) plasmons in a-C:H are identified by comparison with reference spectra taken on natural diamond and on highly oriented pyrolytic graphite. The decrease in energy of the π plasmon with increasing hydrogen atom fraction provides direct experimental evidence that addition of hydrogen serves to reduce the density of π bonds in a-C:H. Under several important assumptions, the mass density, the sp3/sp2 site ratio, and the average coordination number are related to the resonance energies of the π and (π + σ) plasmons. The mass density of a-C:H samples inferred from the energy of (π + σ) electron plasma resonance is in the range from 1.46 to 1.69 g/cm3, which is in general agreement with an independent sink-float measurement. The ratio of sp3 (tetrahedral) to sp2 (trigonal) carbon sites increases from 0.29 to 0.75 and the average coordination number of each atomic site decreases from 2.6 to 2.3 as the hydrogen increases from 28 to 44 at.%. The fully constrained covalent network model is used to discuss the experimental results. The measured ratio of sp3/sp2 carbon sites and the average coordination numbers are in agreement with the predictions of the model, particularly at high hydrogen concentration.
Laser plasma diamond
Authors: Davanloo F. , Juengerman E. M. , Jander D. R. , Lee T. J. , Collins C. B.
Published: September 2007

Diamond-like films containing no hydrogen can be deposited from laser plasmas that are highly ionized. Growth rates of 0.5 μm/h over 100 cm2 areas have been realized on untreated substrates of a variety of materials including Si, Ge, ZnS, glass, and plastics. Measurements of optical properties and mass densities support the identification of this laser plasma diamond as a conglomerate of very fine grains of diamond polytypes in a matrix of other carbon forms.
Growth of diamond films and characterization by Raman, scanning electron microscopy, and x-ray photoelectron spectroscopy
Authors: Sharma S. C. , Green M. , Hyer R. C. , Dark C. A. , Black T. D. , Chourasia A. R. , Chopra D. R. , Mishra K. K.
Published: September 2007

We have deposited diamond films on Si〈111〉 using hot filament assisted chemical vapor deposition at low pressures ∼25 Torr. Diamond films deposited at different relative concentrations of methane (ranging from 0.25% to 2.0%) in methane-hydrogen mixtures have been characterized by Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. With varying methane concentration, Raman spectra show features characteristic of crystalline diamond, diamond-like carbon, and polycrystalline graphite. Scanning electron micrographs show densely packed diamond crystallites. SEM measurements made on diamond films grown as a function of time show that the median grain size of the diamond crystallites increases linearly with time during the initial phase of the growth. X-ray photoelectron spectroscopy reveals differences between the diamond sp3 covalent bonding and sp2 graphitic bonding as well as the extent of s-p hybridization as a function of methane concentration. The plasmon loss shoulder, characteristic of graphite, is absent from the spectrum of 0.25% methane concentration film. But it appears in the XPS spectra of films grown at higher concentrations.
Role of microstructure on the oxidation behavior of microwave plasma synthesized diamond and diamond-like carbon films
Authors: Nimmagadda Rao R. , Joshi A. , Hsu W. L.
Published: September 2007

Oxidation kinetics of microwave plasma assisted CVD diamond and diamond-like carbon (DLC) films in flowing oxygen were evaluated in the temperature range of 500 to 750 °C and were compared with those of graphite and natural diamond. The diamond and DLC films were prepared using CH4/H2 ratios of 0.1, 0.25, 0.5, 1.0, and 2.0%. The films deposited at 0.1% ratio had a faceted crystalline structure with high sp3 content and as the ratio increased toward 2%, the films contained more and more fine crystalline sp2 bonded carbon. The oxidation rates were determined by thermal gravimetric analysis (TGA), which shows that the films deposited at ratios of 2, 1, and 0.5% oxidized at high rates and lie between the rates of natural diamond and graphite. The oxidation rate decreased with lower CH4/H2 ratio and the films deposited at 0.25 and 0.1% exhibited the lowest oxidation rates associated with the highest activation energies in the range of 293–285 kJ/mol · K. The oxidation behavior of microwave plasma assisted diamond films was similar to that of DC plasma assisted CVD diamond films. The results suggest that the same mechanism of oxidation is operational in both DC and microwave plasma assisted diamond films and is probably related to the microstructure and preferred orientation of the crystallites.
Isotopic effects in a–C:(H/D) films deposited from methane/hydrogen RF plasmas
Authors: Boutard D. , Möller W.
Published: September 2007

Hard amorphous hydrocarbon films have been deposited by RF glow discharges in methane/hydrogen mixtures with different hydrogen isotopes. For CH4 + D2 and CD4 + H2 gas mixtures, the film growth rate, the density, the refractive index, and the isotopic hydrogen content are obtained as functions of the process gas composition. Further, the hydrogen loss induced by 15 keV helium ions is studied. The results are qualitatively interpreted in terms of different effects of ion bombardment during film deposition which influence the properties of the resulting films.
(110)-oriented diamond films synthesized by microwave chemical-vapor deposition
Authors: Kobashi Koji , Nishimura Kozo , Miyata Koichi , Kumagai Kazuo , Nakaue Akimitsu
Published: September 2007

Bilayer diamond films were deposited on Si substrates by microwave-plasma chemical-vapor deposition (CVD) using a methane-hydrogen gas mixture. The first layer was deposited for 3 h using a reaction gas which was composed of 2.5 vol. % methane and 97.5 vol.% hydrogen. The deposited film consisted of very weakly (110)-oriented microcrystalline diamonds as well as amorphous carbon and graphite. In order to remove non-diamond carbons from the film surface, the specimen was treated in hydrogen plasma for 1 h. Finally, a second layer was deposited on the first layer for 14 h using a methane concentration of between 0.2 and 1.6 vol.%. It was found that the x-ray intensity of the (220) diffraction of the bilayer films was much greater than that of the (111) diffraction, indicating that the diamond grains in the second layer were strongly oriented with their crystallographic (110) planes parallel to the substrate surface. X-ray diffraction spectra of bilayer films in which the second layer was deposited for 7, 14, 21, and 35 h using two different methane concentrations, 0.3 and 1.2 vol.%, showed that within periods of up to 21 h, the (220) intensity increased with the deposition time much more quickly than the (111) intensity, indicating that the degree of (110) orientation was further enhanced as the second layer thickness increased. However, the (220) intensity decreased after 21 h, presumably due to thermal randomization. Results of scanning electron microscopy, electron diffraction, and Raman spectroscopy of the bilayer films are also presented.
Oxidation of diamond films synthesized by hot filament assisted chemical vapor deposition
Authors: Tankala K. , DebRoy T. , Alam M.
Published: September 2007

Oxidation of polycrystalline diamond films on (111) Si wafers in air at temperatures up to 1073 K was investigated by thermogravimetry. The diamond films before and after partial oxidation were characterized by optical and scanning electron microscopy, x-ray, infrared, and Raman spectroscopy. The oxidation of synthetic diamond films started at a lower temperature than that for natural diamond. The rates of oxidation of the diamond films synthesized by the hot filament and the microwave plasma methods were intermediate between the rates of oxidation of the 111 and 100 planes of natural diamond crystals. The apparent activation energy for the oxidation of the synthetic diamond films agreed well with that for the oxidation of natural diamond via diamond to graphite transition at low oxygen pressures.
Rectification and internal photoemission in metal/CVD diamond and metal/CVD diamond/silicon structures
Authors: Grot S. A. , Lee S. , Gildenblat G.Sh. , Hatfield C. W. , Wronski C. R. , Badzian A. R. , Badzian T. , Messier R.
Published: September 2007

Schottky diodes were formed with free-standing polycrystalline thin film diamond base as well as with polycrystalline diamond films grown on crystalline silicon. Current-voltage and internal photoemission measurements were used to characterize the Schottky diodes and the diamond film. Internal photoemission measurements yielded a barrier height of 1.15 eV. A comparison of experimental data for metal contacts to free-standing diamond films and those on silicon substrates indicates that both rectification and internal photoemission originate at the metal/diamond interface.
Adhesion and tribological properties of diamond films on various substrates
Authors: Kuo Cheng-Tzu , Yen Tyan-Ywan , Huang Ting-Ho , Hsu S. E.
Published: September 2007

The adhesion of diamond films deposited by microwave plasma-enhanced CVD on various substrates can be quantitatively determined by an indentation method. The friction behaviors of diamond-coated cemented carbides sliding against a brass ring were studied. The wear resistance of the diamond-coated cemented carbide inserts and the commercial inserts with the other ceramic coatings were compared and directly evaluated by turning tests. Effects of the coating conditions, the substrate materials, and the surface pretreatments of the substrate on adhesion, friction, and wear properties are discussed.
Tribological characteristics of diamond-like films deposited with an are-discharge method
Authors: Hirvonen J-P. , Lappalainen R. , Koskinen J. , Anttila A. , Jervis T. R. , Trkula M.
Published: September 2007

Using an are-discharge method, we deposited a diamond-like carbon film 600 nm thick on hardened steel. Characterization of the film was carried out with Raman spectroscopy. In dry sliding wear and friction tests, with a hardened steel pin as a counterpart, we obtained a friction coefficient between 10000 and 20000 cycles, with the maximum value of 0.18. The value decreased to 0.12 after about 100000 cycles. We obtained a wear coefficient of 7 × 10−17 m3/mN. A transfer layer formed on the pin during sliding and probably had the dominating effect on the tribological behavior. We observed in nanoindentation measurements that the film softened in a wear track during the first 20000 cycles. Although fracture pits on the wear track occurred, fracture is not the dominant failure mechanism of these films. Degradation of good tribological properties was caused mainly by partial wear-through of the film after 370000 cycles and by a subsequent redeposition of the transfer film on the wear track during prolonged sliding.
Optical and mechanical properties of dc sputtered carbon films
Authors: Rubin M. , Hopper C. B. , Cho N-H. , Bhushan B.
Published: September 2007

Amorphous carbon films were deposited on glass by dc magnetron sputtering from a graphite target in mixtures of argon and hydrogen. Hydrogen flow and other parameters affected the optical and mechanical properties of these films. Increasing hydrogen content caused the average visible transmittance to vary from 16% to 86% for 500-Å thick films. Maximum compressive stress and hardness occur between 0 and 1% hydrogen flow, resulting in rapid delamination. Low sputtering power moderately increases transmittance and hardness while relieving stress. Transparency is induced in both the high-hydrogen and low-power films by formation of sp3 C–C bonds. In the case of the hydrogenated films, however, a softer polymeric structure is formed.
Comparative fractography of chemical vapor and combustion deposited diamond films
Authors: Hoff H. A. , Morrish A. A. , Butler J. E. , Rath B. B.
Published: September 2007

Polycrystalline diamond films of several thicknesses have been fractured by manual bending and examined by scanning electron microscopy. These films have been deposited in controlled environments at low pressures by chemical vapor deposition and in ambient atmosphere with an oxygen-acetylene torch. Fracture surfaces in the low pressure depositions exhibit cleavage steps across the grains. These surfaces, independent of thickness, are primarily transgranular, attesting to the inherent strength of the deposits. However, the ambient deposited diamond has primarily intergranular fracture indicative of weak grain boundaries. Internal defects, observed with transmission electron microscopy, such as twins, stacking faults, and dislocations, occur generally in both types of deposition with no apparent preference for location or type of deposition.
Analytical and mechanical evaluation of diamond films on silicon
Authors: Peebles D. E. , Pope L. E.
Published: September 2007

A diamond film commercially deposited on a 10 cm diameter silicon wafer has been evaluated by a variety of analytical and mechanical procedures. The film is nominally 2.5 μm thick and is very smooth with a surface roughness of only 28.1 nm, as measured by atomic force microscopy. The grain size is very small, with grains from 10 nm to about 100 nm in diameter. A sharp diamond diffraction pattern is obtained across at least 98% of the surface area, as measured by transmission electron diffraction. Raman spectra show a strong diamond band at 1330 cm−1, as well as a strong graphite band at 1580 cm−1. Additional bands are seen near 1500 cm−1 and 1200 cm−1 and are attributed to non-diamond, non-graphite carbon and to macrocrystalline diamond, respectively. Intensity in the graphite band decreases toward the outer edge of the wafer. Elastic recoil detection shows the bulk hydrogen content of the film to range from 1 at.% near the edge of the wafer to 3 at.% near the center. The film is considerably harder than the silicon substrate and is highly adherent. During acoustic emission scratch adhesion testing, the film exhibits a critical load for failure of 11.2 N. At this load the film spalls from the substrate, at the film interface. Almost 50% of the scratch tests also show limited local failure (partial film loss) at a critical load of 2.6 N. Both failure modes may be similar to cohesive failure modes in the underlying silicon substrate which shows critical loads of 4.1 and 10.0 N. The separate failure loads may be related to processes with different friction coefficients.
Fractal analysis of erosion surfaces
Authors: Srinivasan Sreeram , Russ John C. , Scattergood Ronald O.
Published: September 2007

Fractal analysis of steady-state erosion surfaces generated by erodents of widely different hardnesses on single crystal sapphire shows surprising similarities in spite of a large difference in erosion rates and single impact morphology. This study quantifies the surfaces in terms of the surface texture measurements using recently developed image analysis techniques. The interpretation for such similarities is that a single mechanism of material removal is operative for all erodents. The differences are explained in terms of the efficiency of crack initiation in the target by the two erodents.
Microstructure of YBa2Cu3O7−x thin films deposited by laser evaporation
Authors: Eibl O. , Roas B.
Published: September 2007

YBa2Cu3O7−x thin films deposited by laser evaporation were studied by transmission electron microscopy. The crystal structure and microstructure of the films depend sensitively on the oxygen partial pressure during deposition. Cooling conditions affect primarily the oxygen sublattice and thus determine electrical properties in the superconducting state. Deposition of technologically relevant thin films requires an oxygen partial pressure of 0.3 mbar during deposition and slow cooling in an oxygen atmosphere. Such films have a Tc of 90 K and a transition width of 0.6 K. Electron diffraction patterns yielded a relative lattice parameter difference (b − a)/b of 1.6%, from which the oxygen content can be determined with considerable accuracy. Extended crystal defects and second phases were analyzed by analytical and high-resolution electron microscopy. Films deposited at lower oxygen partial pressures (≍10−2 mbar) exhibit a strongly strained crystal structure with lattice planes heavily bent on an atomic scale. In these films evidence for a decomposition reaction of YBa2Cu3O7−x was found by the simultaneous presence of BaCu2O2 grains and Y2O3 precipitates. The films deposited at low oxygen partial pressure become superconducting when cooled slowly in an oxygen atmosphere. The onset of the broad transitions lies at 50 K.
Atomic structure of a Σ = 21 grain boundary
Authors: Krakow William
Published: September 2007

An electron microscope structure image of a σ = 21/[111] tilt grain boundary in Au was obtained and atomic column positions identified to yield a structural unit model of the interface consisting of repeating polyhedron shapes. This result represents the smallest projected spacings at a grain boundary containing defect structures imaged by an electron microscope and interpreted atomistically.
Single-phase aluminum nitride films by dc-magnetron sputtering
Authors: Morgan J. S. , Bryden W. A. , Kistenmacher T. J. , Ecelberger S. A. , Poehler T. O.
Published: September 2007

Single-phase aluminum nitride films were deposited onto fused quartz and single-crystal sapphire by current-controlled, reactive, de magnetron sputtering from an aluminum metal target. Optical and structural properties were observed to correlate systematically with the composition of the sputter gas over a wide range of nitrogen partial pressures. A transition in the electrical conductivity of the deposited films occurred as a function of N2 partial pressure. This transition is driven by the condition of the target surface. When the N2 partial pressure was high and the target surface was substantially covered with AlNx, the deposited film was insulating, stoichiometric AlN. When the N2 partial pressure was low and the target surface was substantially Al°, the deposited film was conducting, substoichiometric AlNx.
Inviscid melt spinning: As-spun crystalline alumina fibers
Authors: Wallenberger F. T. , Weston N. E. , Dunn S. A.
Published: September 2007

Inviscid melt spinning yielded the first crystalline alumina fibers directly from the melts. In this experimental process, a liquid jet having a melt viscosity of <101 poise (vs>104 for fiberglass) is extruded into propane and is thus chemically stabilized (vs rapidly quenched) before it forms Rayleigh waves and breaks up into droplets. This letter describes a 65.5% alumina-zirconia fiber, an 81.5% and a 90.6% alumina-calcia fiber, a 98.6% alumina-magnesia fiber, and a 100% alumina fiber. The δ-allomorph was identified as the crystalline phase of the melt spun 100% alumina fibers, compared to the α-allomorph reported for FIBER FP, a slurry spun and sintered 100% alumina fiber.
Radiation-induced defects and amorphization in zircon
Authors: Weber W. J.
Published: September 2007

The effects of self-radiation damage as a function of cumulative alpha-decay events in synthetic zircon doped with 238Pu and natural zircons damaged over geologic time are compared and interpreted in terms of the accumulation of both defects and amorphousness. The radiation-induced unit-cell expansion and amorphization result in macroscopic swelling that increases sigmoidally with cumulative decay events and saturates at a fully amorphous state. The derived amorphous fraction as a function of cumulative dose is consistent with models based on the multiple overlap of displacement cascades, indicating that amorphization in zircon occurs as a result of the local accumulation of high defect concentrations rather than directly within a displacement cascade. Annealing of point defects in the natural zircons suppresses initial swelling and delays the onset of amorphization. Full recrystallization of the zircon structure from the amorphous state occurs in two stages, with kinetics and activation energies consistent with the reported thermal stability of the amorphous state. This study further confirms that actinide doping is a viable accelerated technique to study or simulate radiation effects from alpha decay on geologic time scales.
Synthesis and characterization of layered bismuth vanadates
Authors: Varma K. B. R. , Subbanna G. N. , Guru T. N. , Rao C. N. R.
Published: September 2007

Bi2VO5.5 (Bi4O11), which is the vanadium analog of the first member of the Aurivillius family of oxides of the general formula Bi2An−1BnO3n+3, has been prepared and characterized. The vanadate has the expected layered structure and is ferroelectric with a Curie temperature of 720 K. While we have not been able to synthesize the vanadium analog of the n = 2 member of the Aurivillius family, we have examined the structure and properties of a vanadate of the composition Bi2V3O9.
Observation of the early stages of heteroepitactic growth of BaTiO3 thin-films
Authors: Grant Norton M. , Barry Carter C.
Published: September 2007

Thin-films of barium titanate (BaTiO3) have been deposited onto single-crystal MgO substrates using pulsed-laser ablation. The early stages of film growth have been examined using transmission electron microscopy by deposition of very thin films onto specially prepared electron transparent thin-foil substrates. The films, which were crystalline as deposited and close to stoichiometric composition, were formed by the nucleation and growth of small islands.
Texture development in Ba2YCu3O7−x films from trifluoroacetate precursors
Authors: McIntyre Paul C. , Cima Michael J. , Fai Ng Man , Chiu Raymond C. , Rhine Wendell E.
Published: September 2007

The effect of heat treatment on microstructure development in Ba2YCu3O7−x films prepared from metal trifluoroacetate precursors is investigated. The growth of textured Ba2YCu3O7−x on BaZrO3 substrates is shown to be strongly influenced by the furnace atmosphere used during calcination. Differential thermal analysis was used to show that conditions that promote c-axis texture are also those which cause partial melting of Ba–Y–Cu–O compositions that are depleted in barium relative to Ba2YCu3O7−x.
A Raman investigation of isotope exchange in YBa2Cu3O7−x
Authors: Irwin J. C. , Chrzanowski J. , Altendorf E. , Franck J. P. , Jung J.
Published: September 2007

Raman scattering experiments have been carried out on sintered pellets of YBa2Cu3−16O7−x and YBa2Cu318O7−x. The latter samples were obtained both by gas exchange and by growth with substituted oxides. Three of the observed Raman modes arise from motion of the oxygen atoms only and have nominal frequencies of 500, 435, and 340 cm−1 at room temperature in the 16O compound with x = 0. The frequencies of these modes shift significantly with oxygen isotope exchange, and these frequency shifts have been measured for several sets of samples. The results indicate that in samples prepared primarily by gas exchange the degree of exchange on the O(2) and O(3) planar sites is greater than the degree of exchange on the bridging O(4) site. Linewidth measurements have revealed that the O(4) phonon (500 cm−1) is significantly broadened by 18O exchange, and this is attributed to a random occupation of the O(4) site by 18O and 16O. The results are discussed in the context of recent measurements of oxygen diffusion in YBa2Cu3O7−x and a proposed mode for the oxygen exchange mechanism. Measurements have also been carried out on YBa263Cu316O7−x and YBa265Cu316O7−x. The results confirm that the Raman mode at 150 cm−1 arises from motion of the Cu(2) planar copper atoms.
A pathway for the decomposition of YBa2Cu3O7−x in water
Authors: Yokota Katsuhiro , Kura Takeshi , Ochi Mitsukazu , Katayama Saichi
Published: September 2007

The reactants produced at the start of the reaction of YBC with water include Y2O3, Ba(OH)2, BaCu(OH)3, and Cu2O. The compound Ba(OH)2 changes to form BaCO3, BaC2O4, and Ya(COOH)2 by reacting with CO2 present in the water. Compounds such as BaCuO2, CuO, and Y2BaCuO5 were then produced by reactions among such reactants as Y2O3, Ba(OH)2, BaCu(OH)3, and Cu2O.
Flux bundle interactions
Authors: Stephens Richard B.
Published: September 2007

We show that magnetic flux lattice interactions are important at fields above a few thousand gauss. These interactions interfere with thermally activated current-induced flux bundle hopping and reduce the superconductor's flux creep resistance below that estimated from the standard flux creep models (which assume completely independent hopping). We find that the flux bundles can hop independently at the low fields at which, e.g., antennas and SQUID detection coils would be used, but interact very strongly at fields typical of magnet applications.
Preparation of fine Ni particles by the spray-pyrolysis technique and their film forming properties in the thick film method
Authors: Nagashima Kazuro , Wada Masayoshi , Kato Akio
Published: September 2007

Fine Ni particles were directly prepared from Ni(NO3)2 and NiCl2 aqueous solutions by the spray-pyrolysis technique under an H2-N2 atmosphere. Hollow Ni particles with rough surfaces were obtained at a low reaction temperature (700–900 °C). With increasing reaction temperatures from 900 °C to 1500 °C, the particles varied gradually to solid ones with a smooth surface, and the particles obtained at 1600 °C were perfectly spherical ones whose average size was ∼0.6 μm. From the point of view that aggregation free powders are considered to be good for thick film applications, Ni(NO3)2 was preferred to NiCl2 as a starting material. The perfectly spherical particles derived from Ni(NO3)2 gave a Ni film about 3 μm in thickness having sheet resistance of 37.7 mΩ · square−1.
Improvement of resistance to corrosion of stainless steel 304 in acid solutions by simultaneous deposition with doping of Si using KrF excimer laser
Authors: Sugioka Koji , Tashiro Hideo , Toyoda Koichi , Murakami Hideyuki , Takai Hiroshi
Published: September 2007

The chemical stability of the surface of stainless steel (SUS) 304 in acid immersion tests is greatly improved by the laser implant-deposition (LID) process, i.e., the simultaneous deposition and incorporation of silicon by KrF excimer laser irradiation. The etching depths of the treated samples in 1.32 N HCl solution are substantially zero at the laser irradiation conditions of more than 40 pulses and of more than 400 mJ/cm2 at the surface. By the quantitative verification of cathodic polarization in 1 N H2SO4, the highest polarization resistance is estimated to be 26.7 times that of the nontreated sample.
Titanium disulfide thin film prepared by plasma CVD
Authors: Kikkawa S. , Miyazaki M. , Koizumi M.
Published: September 2007

Titanium disulfide films were prepared by plasma CVD. Crystalline orientation of layered TiS2 was investigated in relation to deposition rate, film thickness, and kinds of substrate. The preferred orientation of TiS2 basal plane perpendicular to substrates was obtained on the films with their thickness of more than ca. 10 μm at the deposition rate of ca. 4 ⊠ 10−3 g/cm2·h on all kinds of substrate. This orientation resulted in a large discharge capacity in a lithium battery cathode application.
Synthesis of YBa2Cu3O7−x by chemical precursors
Authors: Peterson D. E. , Kubat-Martin K. A. , George T. G. , Zocco T. G. , Thompson J. D.
Published: September 2007

An alternative synthetic route for obtaining bulk forms of the high temperature superconductor YBa2Cu3O7−x has been investigated. The approach is based on first preparing the phases Y2Cu2O5 and BaCuO2, followed by a single sintering of an appropriate mixture of these intermediate compounds to produce the superconducting phase. The resulting materials are largely single-phase as shown by x-ray diffraction, and have densities as high as 86% of the theoretical value, and superconducting onset temperatures of 93 K with magnetic shielding factors ranging from 0.85 to 1.02 (±0.05). Metallography and scanning electron microscopy data were also obtained on the best (high Tc, high shielding factors) of the samples. This synthesis approach is believed to be simpler, more reproducible, and has the potential of producing better materials than previously used bulk synthesis methods.
Critical currents after thermal neutron irradiation of uranium doped superconductors
Authors: Luborsky F. E. , Arendt R. H. , Fleischer R. L. , Hart H. R. , Lay K. W. , Tkaczyk J. E. , Orsini D.
Published: September 2007

Fission fragment damage was introduced into aligned sintered samples of various superconductors containing small additions of UO2 by irradiation with thermal neutrons. Samples of aligned, sintered YBa2Cu3Ox, powdered Bi2Sr2Ca1Cu2Oy, powdered Bi1.7Pb0.3Sr2Ca2Cu3Oz, and epitaxial films of YBa2Cu3Ox on (100)SrTiO3 were used. Magnetic hysteresis, with the critical state model, was used to evaluate changes in the intragranular critical current. In the case of the Bi1.7Pb0.3Sr2Ca2Cu3Oz powders an increase in intragranular Jc at 0.8 T of greater than 70 times was produced by the radiation. The epitaxial film showed no change in Jc on irradiation. This behavior upon irradiation is attributed to the pinning caused by damage produced by the fission products of uranium.
On the kinetics of the δ′ (Al3Li) phase precipitation in a rapidly solidified Al–Mn–Li–Zr alloy
Authors: Baram J. , Sembira A. N.
Published: September 2007

The precipitation kinetics of the δ′ (Al3Li) phase in two rapidly solidified samples and one conventionally cast sample of an Al–2.3Li–6.5Mn–0.65Zr (in wt. %) alloy are compared. Following high cooling rates, manganese is retained in solid solution in the aluminum matrix (αAl) up to 6.0 wt.%, far beyond the thermodynamic equilibrium value (0.36 wt.% at 500 °C). Extended solid solution of manganese in aluminum induces strain gradients, similar to those produced by dislocations. The effect of such gradients, the size of which is proportional to the solute atomic fraction, is to enhance lithium precipitation by lowering the activation energy, as observed, and also by affecting the rate parameter. Kinetic thermal analysis has been performed in a series of nonisothermal experiments in the heat flux differential scanning calorimetry (DSC) mode. The precipitation of the δ′ (Al3Li) phase is evidenced by an exothermic peak whose characteristics were analyzed. The rate of transformation (precipitation) is assumed to obey the Johnson–Mehl–Avrami equation. The activation energy for the precipitation process as well as the kinetic rate parameter have been evaluated for the rapidly solidified and the conventionally cast specimens. The activation energy for precipitation is lowered, from 107.0 kJ mol−1 for the conventionally cast material, down to 81.8 kJ mol−1 and 77.0 kJ mol−1 for samples that exhibit manganese solid solubility extensions of 2.10 and 6.00 wt.%, respectively. The rate parameter for the precipitation reaction, which has the generally admitted value of 1.50, for a transformation involving diffusion controlled growth, is affected by the strain gradients, too. Its value is reduced from 1.40 for the slowly cast sample to 1.32 and 1.20, respectively, for the two rapidly solidified samples, as a result of competing mechanisms, namely: growth controlled by diffusion and strain-assisted precipitation.
Correlation among Si, Ge, and B deposition rates in low-pressure CVD with SiH4−GeH4−B2H6-He mixtures
Authors: Murase Katsumi
Published: September 2007

The deposition process at 500 °C with SiH4–GeH4–B2H6–He mixtures, which yields the amorphous Si–Ge–B alloy, was studied. Although in crystalline Si and Ge the maximum B content is limited to the solid solubility, any amount of B can uniformly be contained in amorphous Si–Ge–B. Thus, films with a B content up to 64 at.% have been prepared. The deposition rate of atoms, defined as the number of atoms deposited in a unit time interval, is obtained for each element by analyzing the growth rate together with the composition and the mass density of the film. When the SiH4 and the B2H6 partial pressures are constant, the Si and the B deposition rates are almost independent of the GeH4 partial pressure. In contrast, the Si deposition rate increases remarkably as the B2H6 partial pressure increases, even when the SiH4 partial pressure is maintained constant. A simple model is proposed for explaining the relationship between the Si and the B deposition rates.
Tribology and mechanical properties of excimer laser mixed Ti–Si–C surface alloys
Authors: Jervis T.R. , Hirvonen J-P. , Nastasi M.
Published: September 2007

We have examined the wear and friction and surface hardness of the mixed phase Ti–Si–C alloy formed by excimer laser surface processing of Ti layers on SiC substrates. The friction between a ruby pin and the mixed surface shows a complex behavior depending on relative humidity, a behavior clearly moderated by the chemistry of the interface between the sliding pin and the surface. The friction is sometimes much lower and sometimes comparable to that between the ruby pin and the unalloyed substrate. Wear in the unalloyed case is characterized by fatigue fracture and flaking of the SiC surface which leads to abrasive wear of the ruby pin. In the alloyed case, a transfer film forms and even in the worst case, a smooth wear track results in the alloy and the pin is undamaged. The surface hardness is intermediate between that of the SiC and the unalloyed Ti surface layer. The wear results are understood in terms of changes in the grain boundary structure of the surface induced by the laser alloying process.
Preparation of silica glass microspheres by sol-gel processing
Authors: Ding J.Y. , Day D.E.
Published: September 2007

A method for making glass microspheres by the sol-gel process has been developed. Porous silica microspheres were produced at temperatures as low as 500 °C and densified silica microspheres were prepared at 800 °C. The size of the microspheres was controlled by adjusting the feed rate of the raw materials and the frequency of the droplet generator so that uniform spheres were obtained. Glass microspheres prepared by this method were characterized by Nuclear Magnetic Resonance (NMR), Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), and optical microscopy.
Gel-derived amorphous cesium-aluminosilicate powders useful for formation of pollucite glass-ceramics
Authors: Hogan Mari A. , Risbud Subhash H.
Published: September 2007

Amorphous powders in the Cs2O–Al2O3−SiO2 system were prepared by sol-gel processing. Gels made from TEOS, Al-chelate, and Cs-acetate were dried and calcined to obtain molecularly mixed powders of analyzed compositions in the range useful for conversion to pollucite (CsAlSi2O6) glass-ceramics. X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetry (TG), and scanning electron microscopy (SEM) were used to characterize the powders. A typical amorphous powder of analyzed chemical composition (in wt.%) = 28.05Cs2O, 37.77SiO2, and 37.96Al2O3 was found to have a glass transition temperature of 945 °C and a glass crystallization temperature of 1026 °C. Preliminary experimental results of densification and crystallization of the amorphous powders show pollucite/mullite phases to be present.
The evolution of damage in tritium exposed copper
Authors: Goods S.H.
Published: September 2007

Severe microstructural damage has been observed in polycrystalline OFHC copper specimens thermally exposed to high pressure tritium gas at temperatures ⋚200 °C, but not at 300 °C. No such damage occurs in single crystal specimens exposed under identical conditions, regardless of temperature. In the polycrystals, the damage takes the form of very flat, crack-like intergranular cavities. It is found that the cavitation evolves slowly with time. For short exposure times, cavities as small as 0.1 μm are observed. In specimens subjected to the longest aging times, the cavities grow and link until entire grain boundary facets fail. The driving force for the growth of these cavities is attributed to the internal gas pressure of helium-3 generated by the decay of tritium. The growth kinetics of the cavity microstructure are described by a coupled grain boundary, surface self-diffusion process. The tritium exposure profoundly affects the mechanical properties of the polycrystalline material, inducing a severe loss in ductility. In concert with the observed ductility loss is a change in fracture morphology from transgranular ductile rupture to intergranular fracture. Examination of the resulting grain boundary facets reveals a dimple structure. The spacing of these dimples can be correlated with the spacing of the exposure-induced grain boundary cavities.
The interaction between dislocations and intergranular cracks
Authors: Zhang H. , King A.H. , Thomson R.
Published: September 2007

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in situ TEM observations of intergranular cracks in molybdenum. Alternating brittle crack propagation and dislocation emission is observed. The number of emitted dislocations corresponding to each crack propagation is in good agreement with the calculated values.
Dislocation density reduction in heteroepitaxial III-V compound films on Si substrates for optical devices
Authors: Yamaguchi Masafumi
Published: September 2007

The reduction of dislocation density in heteroepitaxial III-V compound films on Si substrates has been studied using MOCVD (Metal-Organic Chemical Vapor Deposition). High-quality GaAs films on Si, with a dislocation density of about 106 cm−2, have been obtained by combining strained-layer superlattice insertion and thermal cycle annealing. Reduction of dislocation density in the III-V compounds on Si is discussed based on a simple model, where dislocation annihilation is assumed to be caused by dislocation movement under thermal and misfit stress. As a result of dislocation density reduction, high-efficiency GaAs-on-Si solar cells with total-area efficiencies of 18.3% (AM0) and 20% (AM1.5), and red and yellow emissions from InGaP-on-Si light-emitting diodes have been realized. Moreover, future prospects of heteroepitaxy of III-V compounds on Si are also discussed.
Bridged macrocyclic transition metal complexes, a new type of semiconducting materials
Authors: Hanack Michael , Hirsch A. , Lange A. , Rein M. , Renz G. , Vermehren P.
Published: September 2007

Bridged quasi–one-dimensional macrocyclic transition metal complexes [MacM(L)]nusing phthalocyanine (Pc), tetrabenzoporphyrine (TBP), 1,2- and 2,3-naphthalocyanines (1,2-Nc; 2,3-Nc) as macrocycles (Mac) with M = e.g., Fe, Ru, Co and L = e.g., pyrazine (pyz), 1,4-diisocyanobenzene (dib), tetrazine (tz) exhibit interesting electrical properties. Regardless of the size of the bridging ligand after either chemical or electrochemical doping stable semiconducting compounds [MacM(L)Xy]n(X = e.g., I2BF4−, ClO4−…) are formed. For the first time the complete characterization of soluble oligomers [MacM(L)]n(Mac =t-Bu4Pc, M = Ru, L = dib, me4dib) by1H-NMR spectroscopy is reported. Some of these shish kebab complexes, e.g., [PcM(tz)]n, (M = Fe, Ru) or [MacMCN]n; (Mac = Pc, TBP; M = Co, Fe) exhibit good semiconducting properties without additional external doping. Whether or not these compounds are intrinsic semiconductors will be discussed. The synthesis of oligomeric bridged mixed valence compounds [PcM(III)LPcM(II)L]n, (M = e.g., Fe) is another target of our work. We report here on first results of these oligomers.
Microscratch and load relaxation tests for ultra-thin films
Authors: Wu T.W.
Published: September 2007

The microindenter has proven to be a powerful device in the characterization of the mechanical properties of thin films. The machine has both high resolution in the applied load and penetration depth measurements, as well as the versatility to perform different types of testing. The former provides the capability to deal with extremely thin films, while the latter allows for other mechanical properties, in addition to hardness, to be acquired. Four types of tests, namely indentation, scratch, load relaxation, and indentation fatigue tests can currently be conducted using the microindenter via different operating procedures. Only the scratch and load relaxation techniques will be covered in this paper. In a microscratch test, the normal load, tangential load, scratch length, and acoustic emission are monitored simultaneously during an entire scratch process for the purposes of measuring the critical load and studying the failure mechanisms of the deposited films. The adhesion strength, scratch hardness, fracture toughness, and friction are the mechanical properties which are possible to obtain by using this technique. Results from aluminum, carbon, and zirconia coatings will be discussed. The load relaxation test provides information on the creep properties of the films and results in an empirical constitutive relation between the applied stress and plastic strain rate. The creep properties of DC sputtered Al films will be used as an illustration of this.