bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen content, microstructure, and superconductivity of YBa2Cu3O7−x
Authors: Viegers M. P. A. , de Leeuw D. M. , Mutsaers C. A. H. A. , van Hal H. A. M. , Smoorenburg H. C. A. , Hengst J. H. T. , de Vries J. W. C. , Zalm P. C.
Published: September 2007

The influence of preparation conditions and microstructure on the superconductive properties of single-phase poly-crystalline YBa2Cu3O7−x was investigated by electron probe microanalysis, transmission electron microscopy (TEM), and x-ray powder diffraction as a function of temperature in various ambients supplemented by resistivity and susceptibility measurements. Leaching of Ba was observed when samples were brought in contact with water. The TEM imaging revealed that individual grains have an extremely defect-rich outer shell and an inner core with a domain structure with a and b axes interchanged. The transition temperature Tc was found to decrease with increasing quench temperature in the range 400–900°C. The Tc was observed to be linearly proportional to the difference in the orthorhombic cell parameters (b-a). Further implications are discussed.
Magnetization studies of the high-Tc compound Y 1Ba2Cu3Oz
Authors: Thompson J. R. , Christen D. K. , Sekula S. T. , Brynestad J. , Kim Y. C.
Published: September 2007

The superconductive state magnetization of the high-Tc compound Y1Ba2Cu3Oz has been investigated. Single-phase, polycrystalline samples of this archetype were prepared by solidstate reaction. The onset of the superconductive transition, measured magnetically, was 90.7 K. In addition to low-field dc magnetization results, measurements of the magnetic critical current density Jc (H,T) are presented as a function of magnetic field and temperature. The low values of Jc, especially at high temperature, are discussed in terms of intergranular supercurrents that flow within individual grains in superconductive layers of reduced dimensionality.
Shear-modulus change belowTcin YBa2Cu3O7−x
Authors: Ledbetter H. M. , Austin M. W. , Kim S. A. , Datta T. , Violet C. E.
Published: September 2007

The ultrasonic transverse-wave velocity in the high-Tcmetal-oxide superconductor YBa2Cu3O7−xbetween 275 and 4 K was measured. AboveTcthe velocity shows normal behavior: during cooling, it displays a monotonic increase with decreasing slope. During cooling belowTcthe shear modulus departs from normal behavior, increasing as ΔG /G=b[1 − (T/Tc)n, wheren= 3. These results depart dramatically from those expected for a simple second-order normal-superconducting phase transition.
The solidification of aluminum-manganese powders
Authors: Mueller B. A. , Schaefer R. J. , Perepezko J. H.
Published: September 2007

The solidification behavior of Al–Mn alloy powders was studied as a function of cooling rate and manganese content. The phases present in the powders differed from those expecied at equilibrium due to competetive nucleation and growth kinetics. The equilibrium Al6Mn phase was absent due to its relatively sluggish nucleation kinetics, and in the more concentrated and rapidly cooled alloy powders, the metastable quasicrystalline phases were present. Nucleation temperatures measured in alloys cooled at 25°C/s are interpreted to represent formation of the icosahedral phase, which subsequently transforms to the decagonal phase and provides a lower bound estimate of 870°C for the melting point of the icosahedral phase in an Al-30 wt. % Mn alloy.
Hydration phase transitions and magnetic properties of vermiculite intercalation compounds
Authors: Wada N. , Suzuki Masatsugu , Hines D. R. , Koga K. , Nishihara H.
Published: September 2007

Experimental results from x-ray scattering, Raman scattering, neutron scattering, and magnetic susceptibility measurements are presented to discuss hydration states and magnetic orderings in vermiculite intercalation compounds. In Na-vermiculite, the hydration transitions between 2- and I-water layer hydration states (WLHS), and 1- and 0-WLHS were studied as a function of temperature from 22–200°C. The transitions are of first order, exhibiting phase coexistence and large hysteresis. In Ni-vermiculite, de susceptibility measurements showed both magnetic-field directions and hydration dependencies. Also, ac susceptibility and small-angle neutron scattering experiments revealed evidence for magnetic phase transitions in a temperature range between 1.5 and 4 K.
Excimer laser-assisted etching of polysilicon at 193 nm
Authors: Armacost M. D. , Babu S. V. , Nguyen S. V. , Rembetski J. F.
Published: September 2007

Excimer laser-assisted etching of polysilicon at 193 nm was studied in the presence of CF3Br, CF2Cl2, and NF3. In the presence of 193 nm radiation, CF3Br showed some propensity to etch polysilicon, while CF2Cl2did not show any appreciable etching. In the presence of NF3, maximum etch rates of 0.6 Å/pulse were obtained for pressures greater than 500 Torr and fluences exceeding 200 mJ/(cm2pulse). The etch rate increased with both fluences and pressure to a limiting value of 0.6 Å/pulse. An adsorptive etch mechanism was proposed, where NF3molecules diffuse to the surface, adsorb, and then react after absorbing laser radiation. Thermal effects enhance this process and appear to dominate at lower pressures (<400 Torr) and higher fluences. Etching caused by the gas phase formation of F atoms is minimal due to the low absorption cross section of NF3at 193 nm. Etching of submicron profiles in polysilicon was also examined. Polysilicon samples masked by patterned SiO2were exposed to NF3and 193 nm ArF radiation. Subsequent scanning electron microscopy (SEM) analysis demonstrated directional etching with some surface roughening.
In situ transformation behavior of icosahedral and decagonal quasicrystalline phases
Authors: Suryanarayana C. , Chandra Subash , Menon Jyothi
Published: September 2007

Results of in situ hot-stage electron microscopic investigations on the transformation behavior of icosahedral Mg32 (Al,Zn)49 and decagonal Al–Co quasicrystalline phases are presented. It is shown that in both the cases the transformation begins with the formation of fine holes. This has been interpreted on the basis of the lower density of the quasicrystalline phase. Differences in the transformation behavior between the icosahedral and decagonal phases are highlighted.
Magnetic hardening mechanism in sintered R–Fe–B permanent magnets
Authors: Sagawa M. , Hirosawa S.
Published: September 2007

After a short review on temperature dependence of the intrinsic coercivity in sintered Nd–Fe–B-type magnets is given, recent experimental results concerning the coercivity-anisotropy (HC–HA) correlation in B-rich Pr–Fe–B and Nd–Fe–B sintered magnets and the influence of the surface conditions of the sintered Nd–Fe–B magnets on the coercivity are reported. The results are interpreted in terms of the μoHc vs cμoHA – NIs plot, where Is is the spontaneous magnetization of R2Fe14B (R = Pr or Nd) and N is the effective demagnetization field coefficient.
Tracer diffusion of 60Co and 63Ni in amorphous NiZr alloy
Authors: Hoshino K. , Averback R. S. , Hahn H. , Rothman S. J.
Published: September 2007

Tracer diffusion of 60Co and 63Ni in the amorphous alloy NiZr near the equiatomic composition has been measured in the temperature range between 486 and 641 K using the ion-beam sputter-sectioning technique for serial sectioning. The temperature dependence for the diffusivities of Co and Ni in a-NiZr exhibit Arrhenius behavior; these can be expressed as follows: D∗co = 3.6 × 10−7 exp [− (135 ± 14) kJ mol−1 /RT] m2/s and D∗Ni = 1.7 × 10−7 exp [− (140 ± 9) kJ mol−1 /RT] m2/s. The values of D∗Ni are in good agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion.
Reactions between palladium and gallium arsenide: Bulk versus thin-film studies
Authors: Lin J. -C. , Hsieh K. -C. , Schulz K. J. , Chang Y. A.
Published: September 2007

Reactions between Pd and GaAs have been studied using bulk-diffusion couples of Pd (∼0.6 mm thick) /GaAs and thin-film Pd (50 and 160 nm)/GaAs samples. The sequence of phase formation at 600°C between bulk Pd and GaAs was established. Initial formation of the solution phase μ and the ternary phase T does not represent the stable configuration. The stable configuration is GaAs |∊|Λ|γ|ν|Pd and is termed the diffusion path between GaAs and Pd. The sequence of phase formation for the bulk-diffusion couples is similar at 500°C. Phase formation for the thin-film Pd/GaAs specimens was studied at 180,220,250,300,350,400,450,600, and 1000°C for various annealing times. The sequence of phase formation obtained from the thin-film experiments is rationalized readily from the known ternary phase equilibria of Ga–Pd–As and the results from the bulk-diffusion couples of Pd/GaAs. The thin-film results reported in the literature are likewise rationalized. The diffusion path concept provides a useful guide in understanding the phase formation in Pd–GaAs interface or any other M-GaAs interface. This information is important in designing a uniform, stable contact for the metallization of GaAs.
Effects of the band offset on interfacial deep levels
Authors: Beres Richard P. , Allen Roland E. , Dow John D.
Published: September 2007

The energy levels of antisite defects at a GaAs/Ge (110) interface are calculated and shown to be essentially unaltered with respect to the GaAs valence band maximum by different choices of the valence band offset.
Layered in situ copper/polyimide composite films
Authors: Porta G. M. , Taylor L. T.
Published: September 2007

Incorporation of bis (trifluoroacetylacetonato) copper (II), Cu (TFA)2 into poly (amide acid) prior to imidization produces bi-and trilayered composite films upon curing. Choice of curing atmosphere and concentration of dopant control the formation of a particular layered structure. Dry air and 100% relative humidity are the curing atmospheres used. The trilayered films are typified by a zero-valent copper layer sandwiched between a thin polyimide overlayer and the bulk polyimide. Curing in 100% relative humidity produces the thinnest overlayer. By doubling the dopant concentration used to prepare the trilayered films, bilayered films will result upon curing. In this instance the lack of a polyimide overlayer affords the oxidation of copper at the surface to copper (II) oxide. In each case the formation of the copper layer results from the migration of all Cu (TFA)2 from a depth of approximately 2000 Å to the surface where subsequent reactions take place. Several [Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM)] analytical techniques are used to characterize the physical and chemical nature of the films.
Formation of intermetallic compounds during the sintering of zirconium–iron powders compact
Authors: Stupel M. M. , Weiss B. Z. , Bamberger M.
Published: September 2007

The sintering process at 840°C and at 925°C, of Zr-7.2 wt. % Fe was studied by room-temperature Mössbauer spectroscopy, x-ray diffractometry, and scanning electron microscopy. According to phase analysis, most of the αFe phase disappeared after 20 h of sintering at 840°C and after 4 h at 925°C. During the sintering, small quantities of the intermetallic compound ZrFe2 as an intermediate phase were observed clearly by the Mössbauer technique and very weakly by x-ray diffractometry. The relationship among the relative quantities of αFe, ZrFe2, and Zr3Fe phases was determined. The change in density as a function of sintering time was measured, and the results were explained on the basis of the different sintering stages and phase transformations.
Nucleation, growth, and glass formation in an electron-beam surface-processed Cu47Zr53 alloy
Authors: Huang J. S. , Kaufmann R. N.
Published: September 2007

A Cu47Zr53 alloy was surface processed with a directed-energy electron beam. Optical microscopy, x-ray diffraction, and transmission electron microscopy were used to identify the resolidified phases obtained under systematically varied rapid solidification conditions. The results of the investigation indicate that the underlying bulk substrate always nucleates the growth of a crystalline phase that was identified as a metastable CuZr phase with an ordered bcc (B2) structure. The maximum growth velocity of this phase was determined to be between 0.05 ± 0.02 m/s. This limit was compared under different assumptions to the predictions of a reaction rate growth theory. As the solidification speed increased beyond this limit, the crystalline growth eventually ceased and glass formation occurred in the remaining undercooled liquid under rapid cooling conditions. Crystalline particles also nucleated and grew in the liquid at intermediate cooling rates. These particles had a dendritic morphology and were also a CuZr phase with the B 2 structure.
Calculation of diffuse scattering near Bragg reflections from coherent precipitates
Authors: Iida S. , Larson B. C. , Tischler J. Z.
Published: September 2007

Numerical calculations of the diffuse scattering near Bragg reflections from coherent solute precipitates in a dilute alloy have been made. Results are presented for spherical precipitates in an elastically isotropic continous medium where the calculations have been reduced to a one-dimensional numerical integral. The scattering is separated into direct scattering from the precipitates, the Huang scattering from the lattice distortions, and the higher-order distortion scattering; calculations are presented for 50 Å radius precipitates with an internal strain of – 1.5%, and the sensitivity of the scattering to changes of the size and the internal strain of the precipitates is demonstrated. The possibility of using such scattering for the determination of the concentration, size distribution, and internal strain of solute precipitates is discussed.
Precision measurements of the effect of implanted boron on silicon solid phase epitaxial regrowth
Authors: Park Won Woo , Becker M. F. , Walser R. M.
Published: September 2007

The epitaxial recrystallization rates of self-ion amorphitized layers in silicon wafers with 〈100〉 substrate orientation were measured by in situ, high precision, isothermal cw laser interferometry. With this one-sample technique the changes produced by implanted boron impurity concentrations (NB) in the activation energy Ea and preexponential V0 of solid phase epitaxy were measured for concentrations in the range 5 × 1018 cm−3 < NB < 3 × 1020 cm−3 and for temperatures from 450 to 550°C. The differential changes in Ea produced were measured to within ± 23 meV when systematic errors were eliminated. Changes in activation energy and entropy [Ea and log (V0)] were found to be linearly correlated for all concentrations. This observation is consistent with the idea that electronically active impurities alter regrowth velocities by reducing the critical temperature for disordering at some of the interfacial sites at which elementary reconstructive processes are driven by thermal fluctuations. For small Nn, the critical temperature of the impurity-modified reconstruction is estimated at 1200K, approximately 200 K below the melting temperature of amorphous silicon. The Ea decreased exponentially with NB to a concentration Ninfl, larger than the estimated equilibrium solubility limit, where there was an inflection point in the V vs NB curve. The Ea increased for values of NB larger than Ninfl, showing that the differential increase in V for higher concentrations was due to a differential increase in the activation entropy. A change in the correlation between Ea and log (V0) at Ninfl indicated that larger NB produced an additional reduction of the critical temperature of the reconstruction. For small NB, the data support a simple Fermi level shifting model for the “electronic effect” of impurities on SPE (solid phase epitaxial) regrowth.
The preparation and electrical properties of TiO2−xFx
Authors: Endo Tadashi , Morita Naoki , Sato Tsugio , Shimada Masahiko
Published: September 2007

The substitution of fluorine for oxygen in TiO2 was investigated by the reaction of Ti2O3, TiO2, and TiF3 under conditions of 4–6.5 GPa and 700–1400°C. The single phase of TiO2−x Fx solid solution was obtained in the region of 0≤x≤0.7. According to the x-ray diffraction data, the a and c axes of the rutile-type structure linearly increased with increasing fluorine content. The electrical resistivities of TiO2−x Fx were in the range from 10 Ω cm for x = 0.3 to 850 Ω cm for x = 0.7 at 300 K and the relationship between In ρ and 1000/T was linear. The activation energies were estimated to be from 0.17 eV at x = 0.3 to 0.28 eV at x = 0.7. Also, the thermoelectric powers at room temperature changed from 250μV/K to + 50 μV/K. The mechanism of electric conduction was discussed on the basis of the extended band model of rutile.
Direct observation of ordering in (GaIn) P
Authors: McKernan S. , De Cooman B. C. , Carter C. B. , Bour D. P. , Shealy J. R.
Published: September 2007

Gax In1 − x Pepilayers grown under a range of growth conditions by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates have been studied in the electron microscope. The results show the presence of an ordering of the group III sublattice parallel to some of the {111} planes. Dark-field images directly reveal ordered domains of different orientations that appear not to be perfect, but contain many planar defects parallel to the growth surface.
Preparation of heterosiloxanes containing Zr and Hf and their use as precursors to refractory materials
Authors: Hrncir Duane C. , Skiles Gary D.
Published: September 2007

Metallasiloxanes of the type, M (OSiR3)4, which contain zirconium and hafnium can be prepared by the facile silanol-induced cleavage of organometallic compounds. The metallasiloxanes vary from mobile liquids to insoluble nonmelting powders depending upon the constituents bonded to the silicon. The compounds can be fired into inorganic refractory oxides at temperatures varying from 350–600 °C. The resulting materials have the general formula M Si4O10. Electron spectroscopy for chemical analysis (ESCA) data suggest that the M-O–Si linkage remains intact during this process. Thus the M Si4O10 material can be considered a mixed oxide alloy rather than a simple mixture of the oxides M O2 and SiO2.
Liquid supercoolings and droplet cooling rates of remelted argon-atomized Fe–30Ni powder particles
Authors: Libera Matthew R. , Bolsaitis Pedro P. , Erik Spjut R. , VanderSande John B.
Published: September 2007

Individual particles of argon-atomized Fe-30Ni powder are electrodynamically levitated and remelted by a CO2laser pulse. The thermal history of each droplet during remelting and solidification is monitored by single-color radiation pyrometry at each of three wavelengths (850, 750, and 550 nm). Experiments are done in an atmosphere of either air or nitrogen. The average supercooling of six experiments performed in nitrogen is 298 K with a standard deviation of 14 K. This value is of the same order as several others reported in the literature using bulk levitation and emulsification techniques. The average supercooling of seven experiments performed in air is 163 K with a standard deviation of 20 K. The difference suggests that oxides are forming in the air-remelting experiments and catalyzing nucleation at relatively low supercoolings. The average cooling rate of the liquid droplets prior to solidification in nitrogen is 1.5 × 105K/s. This measured cooling rate is somewhat higher than that predicted by Newtonian heat flow modeling, and the difference is attributed to radiative losses not considered in the Newtonian model. The measured cooling rate is used to estimate the total heat transfer coefficient characterizing cooling of a small metal droplet in a quiescent gas atmosphere. A lower bound of 1.5 × 106K/s on the droplet heating rate during recalescence and a minimum average liquid/solid interfacial velocity during recalescence of 0.1 m/s are estimated.
The thermal fission-induced crystalline-to-amorphous transformation in U6Fe
Authors: Parkin Don M. , Elliott Reed O.
Published: September 2007

The crystalline-to-amorphous transformation in U6Fe produced by thermal fission fragment damage was studied using resistivity and differential scanning calorimetry. The results are described in terms of a model of radiation-produced defect buildup in the crystalline matrix followed by transformation of small regions to an amorphous phase when a critical local defect concentration is reached. This can occur directly in a single cascade or from cascade overlap. The total resistivity is modeled assuming an inhomogeneous media consisting of a crystalline matrix containing a dose-dependent concentration of defects and amorphous zones. The crystallization behavior is initially, starting at Tc = 388 K, a kinetically limited process of shrinkage of amorphous zones that gradually transforms to nucleation and growth in fully amorphous material at Tc = 555 K.
Model of Si–SiO2 interfaces based on ARXPS measurements
Authors: Halbritter J.
Published: September 2007

Angle-resolved x-ray photoelectron spectroscopy (ARXPS) results in a very detailed analysis of minor amounts (≥0.3 nm) of interface compounds and their spatial distribution. First experimental results on the Si–SiO2 interface used in microelectronics, are presented. The ARXPS results on plane, single crystalline (100) Si, oxidized to about 5 nm SiO2, indicate a planar Si surface connected by about one monolayer Si∗ to a compressed SiO∗2 layer coated by SiO2. Separated from this interface region, Si clusters stabilized by a compressing SiO∗2 coating have been found in SiO2. Dehydrogenation is showing up in binding energy changes in SiO2 indicating that H or OH is not only saturating Si∗ but is also bonded to SiO2. The O deficiency of amorphous SiO2,x is increasing toward the outer SiO2 surface.
A high-resolution NMR and synchrotron x-ray powder diffraction study of zeolite ZSM-11
Authors: Toby B. H. , Eddy M. M. , Fyfe C. A. , Kokotailo G. T. , Strobl H. , Cox D. E.
Published: September 2007

High-resolution nuclear magnetic resonance (NMR) spectra and synchrotron x-ray powder diffraction data have been obtained from a well-crystallized highly dealuminated sample of the zeolite ZSM-11. The Rietveld profile technique has been applied to the synchrotron data to give the first detailed refinement of the idealized structure derived ten years ago by distance least-squares modeling methods [G. T. Kokotailo, P. Chu, S. L. Lawton, and W. M. Meier, Nature 275, 119 (1978)], which involves 54 variable atomic positional parameters. The structure is tetragonal (a = 20.065 Å, c = 13.408 Å at 25 °C) and consistent with the previously reported tetragonal space group I \overline 4 m2, but the NMR spectra indicate local deviations from this symmetry that disappear at 100 °C.
Mechanism of plastic deformation of Mn-added TiAl L 10 -type intermetallic compound
Authors: Hanamura T. , Uemori R. , Tanino M.
Published: September 2007

Titanium aluminum intermetallic compound is a possible candidate for a high-temperature structural material, except for a problem of lack of room-temperature ductility. Recently, this problem was found to be overcome possibly by the addition of Mn, but this mechanism has not been fully understood yet. In order to understand the fundamental mechanism of the ductility improvement by Mn addition, microanalyses have been carried out. The results are as follows. Twin structures in a TiAl intermetallic compound in the as-cast state can be climinated by high-temperature annealing, while those in Mn-added TiAl are thermally more stable and exist even after annealing for 86.4 ks at 1273 K. The reason for this thermal stabilization of twin structures is considered to be due to the pinning effect of twin dislocations by Mn addition. The enhancement of twin deformation in TiAl by Mn addition is regarded to be caused by two factors. One is the stabilization of twin partial dislocations, becoming the nucleation sites for twin formation. The other is the decrease in stacking fault energy, which makes twin deformation energetically easier.
Effect of grain size on yield strength of Ni3Al and other alloys
Authors: Takeyama M. , Liu C. T.
Published: September 2007

This paper analyzes the effect of grain size on yield stress of ordered Ni3Al and Zr3Al, and mild steels that show Lüders band propagation after yielding, using the Hall-Petch relation, σy= σ0+ kyd−½, and the new relation proposed by Schulsonet al., σy= σ0+ kd−(p − 1)/2[Schulsonet al., Acta Metall.33, 1587 (1985)]. The major emphasis is placed on the analysis of Ni3Al data obtained from published and new results, with a careful consideration of the alloy stoichiometry effect. All data, except for binary stoichiometric Ni3Al prepared by powder extrusion, fit the Hall-Petch relation, whereas the data from boron-doped Ni3Al and mild steels do not follow the Schulson relation. However, no conclusion can be made simply from the curve fitting using either relation. The results are also discussed in terms of Lüders strain and alloy preparation methods. On the basis of the Hall-Petch analysis, the small slope kyis obtained only for hypostoichiometric Ni3Al with boron, which would be related to a stronger segregation of boron in nickel-rich Ni3Al. In addition, the potency for the solid solution strengthening effect of boron is found to be much higher for stoichiometric Ni3Al than for hypostoichiometric alloys.
The effect of electron irradiation in high-Tc oxide superconductors
Authors: Adem E. , Martínez L. , Richards J. , Orozco E. , Fuentes-Maya J. , Albarrán J. L. , Mendoza A. , Carrillo E. , Cota L. , Reyes-Gasga J. , Boldú J. L. , Pérez R. , Pérez-Ramirez J. G. , José-Yacamán J.
Published: September 2007

A superconductor ceramic oxide with the Y1Ba2Cu3O7−x phase and exhibiting a transition temperature at Tc ≍92K, was irradiated at room temperature with 1 MeV electrons. It was found that the irradiation produces a sharp drop in the Tc value from 92 K down to ∼40K. The irradiated sample suffered a change from metallike character to semiconductorlike behavior at T > Tc. It is also shown that after irradiation the twin boundaries on the material become irregular.
Excimer laser-induced sputtering of YBa2Cu3O7−x
Authors: Sudarsan U. , Cody N. W. , Bozack M. J. , Solanki R.
Published: September 2007

Excimer laser-induced sputtering of YBa2Cu3O7−x targets has been investigated. Two aspects of this process are reported here: the spectral content of the emission and sputtering of the target. Postsputtering analysis of the sputtered area of the target shows a nonstoichiometric composition: rich in Cu but depleted of Ba and Y.
Nucleation and amorphization of radiation-produced phases in a modified austenitic stainless steel during Ni-ion irradiation
Authors: Lee E. H. , Kenik E. A.
Published: September 2007

The nucleation and amorphization of radiation-induced (G) and radiation-enhanced (η) phases in a silicon- and titanium-modified austenitic stainless steel have been studied under nickel-ion irradiation. These silicon- and nickel-enriched phases form under high-temperature (950 K) irradiation as the result of radiation-induced segregation to radiation-produced interstitial dislocation loops. Availability of carbon promotes the formation of η phase relative to G phase. Under lower temperature (450 K) irradiation, G and η phases are amorphized without significant change in composition of metallic elements. Two carbide phases (MC, M23C6) remain crystalline for the same irradiation conditions. The amorphization of the silicides may result from (1) radiation damage increasing their free energy above that of the amorphous state or (2) direct formation of the amorphous phase in the damage cascade.
Electrical resistivity of fluorinated carbon black
Authors: Luly Matthew H.
Published: September 2007

The electrical resistivity of fluorinated carbon black particles, CFx, is reported as a function of fluorine content, pressure, and temperature. Fluorination does not destroy the aggregate structure of carbon black, but does change its physical properties. The resistivity changes from 10−2 to 10+12 Ω cm as x increases from 0 to 1.2, with a very rapid change occurring in the range 0.08≤x≤0.27. Samples with x = 0 and x = 0.07 exhibit a pressure dependence described by p∝ P−s with s>0. Fully fluorinated samples (x = 1.2) have s≃0. Intermediate compositions have low-pressure regimes where the resistivity is independent of pressure, and high-pressure regimes with s>0. For all samples exhibiting pressure-dependent resistivity, s increases as x increases. For samples with low-fluorine content, the resisitivity increases with decreasing temperature. These observations are interpreted in terms of structure, especially surface structure.
Elimination of slip lines in capless rapid thermal annealing of GaAs
Authors: Goff Michael J. , Wang Sujane C. , Yu Tan-Hua
Published: September 2007

A new rapid thermal annealing (RTA) procedure has been developed that eliminates the problem of crystallographic slip in 2 in, ion-implanted GaAs wafers. This annealing arrangement is easy to implement and is reliable. A precision machined graphite support structure and guard ring are used to insure uniform cooling across the entire wafer, thus eliminating slip line production. Characteristics of silicon ion implants have been determined using van der Pauw Hall, Polaron C–V profiling, and eddy current resistivity measurements. Characterization showed excellent dopant activation and uniformity can be achieved using this new technique. Low-temperature photoluminescence measurements were performed on samples annealed with and without graphite in the system, and no detectable difference in surface carbon contamination was found.
Mechanical deflection of cantilever microbeams: A new technique for testing the mechanical properties of thin films
Authors: Weihs T. P. , Hong S. , Bravman J. C. , Nix W. D.
Published: September 2007

The mechanical deflection of cantilever microbeams is presented as a new technique for testing the mechanical properties of thin films. Single-layer microbeams of Au and SiO2have been fabricated using conventional silicon micromachining techniques. Typical thickness, width, and length dimensions of the beams are 1.0,20, and 30 μm, respectively. The beams are mechanically deflected by a Nanoindenter, a submicron indentation instrument that continuously monitors load and deflection. Using simple beam theory and the load-deflection data, the Young's moduli and the yield strengths of thin-film materials that comprise the beams are determined. The measured mechanical properties are compared to those obtained by indenting similar thin films supported by their substrate.
29Si nuclear magnetic resonance spectra of transition metal silicides
Authors: Duncan T. M. , Hamilton D. M.
Published: September 2007

The 29Si chemical shielding parameters derived from 29Si nuclear magnetic resonance (NMR) spectra of 25 silicides of Group IVB, VB, VIB, VIIB, and VIII metals are presented. The isotropic shifts of these silicides span the range from −1650 to + 925 ppm, relative to TMS, and have shielding anisotropies −250 to + 335 ppm; these extremes are approximately ten times as large as those of organosilicon and silicon oxide compounds. For silicides of Ti, Zr, Nb, Ta, Cr, Mo, W, Rh, Ni, Pd, Pt, and Cu, the chemical shielding interaction is sufficiently larger than the extraneous spectral broadening to allow detection of multiple phases owing to different crystal structures and local differences in stoichiometry. The potential to detect multiple phases in silicides of Hf, V, Mn, Fe, Ru, and Co is less owing to smaller differences in isotropic shifts and/or broadening that overwhelms the chemical shielding information. However, it is possible that the broadening is not an inherent property of these silicides, but rather, suggests the presence of structural defects in these particular samples.
On the stabilization of diamond relative to graphite by surfaces
Authors: Machlin E. S.
Published: September 2007

Bond counting, and calculations of entropy, bond, and bond angle strain have been used to evaluate the relative stability of diamond and graphite on various substrates for conditions that normally stabilize the graphite structure in bulk. Pseudomorphic and many metallic substrates that bond to carbon when clean are found to stabilize the diamond phase; others stabilize the graphite phase. If the relative thermodynamic stability governs the kinetics of growth under film deposition conditions, then an interesting prediction of the present research is that growth of diamond on {100} surfaces should proceed by formation of surface monolayers that alternately have graphite and diamond bonding configurations, and with the graphite monolayer converting to a diamond configuration when it becomes subsurface. The latter mode of growth should not occur in an atomic hydrogen atmosphere, nor should it occur on {111} surfaces.
Polyimide/metal composite films via in situ decomposition of inorganic additives: Soluble polyimide versus polyimide precursor
Authors: Rancourt J. D. , Porta G. M. , Moyer E. S. , Madeleine D. G. , Taylor L. T.
Published: September 2007

Polyimide-metal oxide (Co3O4 or CuO) composite films have been prepared via in situ thermal decomposition of cobalt (II) chloride or bis (trifluoroacetylacetonato) copper (II). A soluble polyimide (XU-218) and its corresponding prepolymer (polyamideacid) were individually employed as the reaction matrix. The resulting composites exhibited a greater metal oxide concentration at the air interface with polyamideacid as the reaction matrix. The water of imidization that is released during the concurrent polyamide acid cure and additive decomposition is believed to promote metal migration and oxide formation. In contrast, XU-218 doped with either HAuCl4 · 3H2O or AgNO3 yields surface gold or silver when themolyzed (300 °C).
Ion-beam mixing of Ni/Pd layers: II. Thermally assisted regime (>500K)
Authors: Akano U. G. , Thompson D. A. , Smeltzer W. W. , Davies J. A.
Published: September 2007

Atomic mixing in Ni/Pd bilayer films due to 120 keV Ar+ irradiation in the thermally assisted regime (523−673 K) has been measured, in situ, using Rutherford backscattering with 2.0 MeV 4He+ ions. The mean diameter of grains in these polycrystallinc films increased from 10 to 60 nm, following Ar+ bombardment at 573 K. Initial mixing was rapid due to grain boundary diffusion and incorporation of the metal solute into the solvent metal matrix by grain growth; this mixing stage was essentially complete within 10 min for annealed films or after an Ar+ dose of 4 × 1015 cm−2 in irradiated films (10 min irradiation). No further measurable mixing occurred in the annealed, unirradiated films. For the irradiated samples the initial rapid mixing (6−35 atoms/ion) was followed by a slower mixing stage of 0.7–1.8 atoms/ion for irradiation doses of up to 2.5 × 1016 Ar+ cm−2. The Ar+ bombardment gave rise to much smaller mixing levels when the Pd films were deposited on large-grain or single-crystal Ni. A diffusion analysis demonstrates that the effective diffusivity, Deff, for ion-irradiation-enhanced mixing in the thermally assisted regime satisfied the relation Dl < Deff < DB, where the ratio of the grain boundary to lattice diffusivity was DB/Dl > 106.
Atomic transport in Xe-irradiated Ni/SiO2 bilayers
Authors: Banwell T. , Nicolet M-A.
Published: September 2007

Parametric experiments are described that characterize the process of atomic relocation in Ni/SiO2 bilayers induced by Xe irradiation. The parameters varied are the irradiation temperature (− 196 to + 500 °C) and the Xe irradiation dose (0.01−15 × 1015cm−2). Backscattering spectrometry of the irradiated samples after removal of the unreacted Ni film is the main analytical tool. A phenomenological model is given that describes the results quantitatively. It is deduced that secondary recoil implantation followed by subsequent redistribution within the cascade's lifetime produces the dominant transport mechanism responsible for incorporating Ni into the SiO2.
Effect of excimer laser alloying of Ti on the sliding friction of AISI 304 stainless steel
Authors: Jervis T. R. , Hirvonen J. -P. , Nastasi M.
Published: September 2007

Dry sliding friction measurements made on titanium layers evaporated on AISI 304 stainless steel in the as-deposited and excimer laser mixed form show a dependence on the film thickness and the amount of mixing. The effect of laser mixing is dependent on the incident fluence with high fluences and/or large numbers of pulses producing surfaces with poor frictional properties. The optimum total fluence depends on the thickness of the surface layer, a result consistent with thorough mixing of the alloyed layer without the surface damage that results from large numbers of pulses.
Effect of laser beam irradiation on AISI 1045 steel
Authors: Riabkina-Fishman M. , Zahavi J. , Zevin L. S.
Published: September 2007

The effect of the parameters of laser irradiation (beam power and travel velocity) as well as of various surface coatings and protecting atmospheres on the size, structure, and hardness of the laser-affected region was studied in the case of commercial 1045 steel and a continuous CO2 laser. The action of the laser beam depends more strongly on its traverse velocity than on its power. When the power density exceeds a certain threshold level, a drastic decrease in the size of the laser-affected region takes place. The action can be enhanced by surface treatment in orthophosphoric acid as well as by some painted surface coatings. Unlike the latter, electroplated Cr and Ni layers were found to cause substantial alloying of the laser-treated layer. The laser-affected region formed by a single pass consists of two distinct zones: a melt zone, surrounded by an austenitization zone with a duplex structure representing former pearlite and ferrite regions. The hardness of the melt zone (about HV 750) exceeds that of conventionally hardened 1045 steel; even higher values (up to HV 900) are observed in the former pearlite regions of the austeniti zation zone, that of the former ferrite regions being about HV 250. In the case of an extended surface processed by a series of equidistant passes, a relatively wide region of tempered martensite is formed (with minimum hardness values down to HV 400) due to the heating generated by each pass in the previously hardened layer. As a result, a periodic hardness distribution is observed, whose fcatures depend on the degree of overlapping. High tensile residual stresses were found by x-ray diffraction in surface layers both in the cases of overlapping and separated passes.
Friction and wear studies in N-implanted Al2O3, SiC, TiB2, and B4C ceramics
Authors: Nastasi M. , Kossowsky R. , Hirvonen J. -P. , Elliott N.
Published: September 2007

Bulk polycrystalline samples of sintered Al2O3, and hot-pressed Al2O3, SiC, TiB2, and B4C ceramics were ion implanted at 77 K with 190 keV N+ to a dose of 3 × 1017 N/cm2. Nitrogen implantation resulted in reduced friction coefficients for SiC, TiB2, and B4C samples and a reduction in wear for TiB2. Both Al2O3 samples showed a significant increase in friction coefficients after nitrogen implantation. Nitrogen-implantation-induced changes in these properties appear to be correlated with the thermodynamic tendency of the sample to form “nitridelike” bonds.
Divacancy control of the balance between ion-beam-induced epitaxial cyrstallization and amorphization in silicon
Authors: Linnros J. , Elliman R. G. , Brown W. L.
Published: September 2007

The ion-bombardment-induced reversible movement of a planar amorphous/crystalline interface in silicon has been studied between 100 and 400 °C. The temperature dependence of the ion dose rate at which there is zero interface movement has an activation energy of 1.2 eV, the dissociation energy of divacancies. Scaling of this dose rate for different ion species exhibits a quadratic dependence on the density of displaced atoms in the collision cascade of individual ions, giving further evidence for divacancy control of the interface movement.
A defect model for ion-induced crystallization and amorphization
Authors: Jackson K. A.
Published: September 2007

Extensive experimental investigations have been reported on the ion-induced motion of the interface between the crystalline and amorphous phases of silicon. The crystal grows into the amorphous phase at low ion fluxes and high temperatures. The amorphous phase grows into the crystal at high ion fluxes and low temperatures. The experimental observations are shown to fit a model based on a single defect. The concentration of this defect decays by binary recombination, this is, two of the defects annihilate one another. The model accounts for the linear relationship between interface motion and reciprocal temperature, for the Arrhenius temperature dependence of the flux at which no interface motion occurs, and for the temperature independence of the crossover frequency observed in beam pulsing experiments. The defect on which this model is based has a motion energy of 1.2 eV. Assuming that the same defect is also responsible for thermal recrystallization of the amorphous phase gives a formation energy of 1.5 eV for the defect. The defect is believed to be a dangling bond in the amorphous phase.
Structural characterization of La2−xMxCuO4 (M = Sr,Ba) samples by synchrotron x-ray and neutron powder diffraction techniques
Authors: Cox D. E. , Moss S. C. , Meng R. L. , Hor P. H. , Chu C. W.
Published: September 2007

High-resolution synchrotron x-ray powder diffraction studies on samples of La2−xMxCuO4 (M = Sr,Ba) prepared by standard ceramic techniques show that macroscopic compositional inhomogeneities may exist that are unlikely to be revealed by conventional x-ray diffraction methods. Rietveld refinement of neutron data collected at 200, 50, and 11 K from one such sample, nominally La1.8Sr0.2CuO4, gave satisfactory fits to a tetragonal structure of K2NiF4 type at all three temperatures. However, careful individual peak fits revealed that part of the sample transforms to orthorhombic between 200 and 50 K. It is suggested that this multiphase character has an important influence on the superconducting properties.
Identification of an η boride phase as a crystallization product of a NiMoFeB amorphous alloy
Authors: Kim Y. W. , Rabenberg L. , Bourell D. L.
Published: September 2007

A new, apparently metastable, Mo–Ni boride phase has been observed in transmission electron microscope samples of rapidly consolidated MoNiFeB metallic glass powders. The phase is cubic with lattice parameter 1.083 nm. Its space group as determined by electron diffraction is Fd $\overline 3$m and its approximate composition is Mo3Ni3B. Because its structure, its composition, and its role as a transition phase are analogous to those of η carbide (M6C) in steels and cemented carbides, this phase has tentatively been named “η boride.”
A comparative study of sintered and melt-grown recrystallized YBa2Cu3Ox
Authors: Hojaji Hamid , Michael Karen A. , Barkatt Aaron , Thorpe Arthur N. , Ware Matthew F. , Talmy Inna G. , Haught Debbie A. , Alterescu Sidney
Published: September 2007

This paper compares the properties of yttrium barium cuprate bulk specimens prepared by means of solid-state sintering on one hand and of growth from a largely molten state on the other. The current paper focuses on magnetization measurements at 77 K which show specimens made by the latter method to have high remanence magnetization values.
Defect structures in cold worked and small grain pure and boron-doped Ni3Al alloys
Authors: Usmar S. G. , Lynn K. G.
Published: September 2007

Positron lifetime spectroscopy was used to study the isochronal annealing of cold worked Ni3Al samples. In pure Ni76Al24, Ni74Al26, and boron-doped Ni74Al26 three annealing stages were observed. Boron-doped Ni76Al24 showed only two annealing stages. Vacancy annealing (stage III) was identified in all cases to start at ∼250 °C, somewhat higher than previously reported. The discrepancy is suggested to be due to carbon-vacancy interactions, because carbon (impurities) was observed to diffuse out of all samples at or above ∼350 °C. The high-temperature annealing stage in boron-doped Ni76Al24 (which is ductile) starts at 700–750 °C and is complete at 1000 °C. This stage was attributed to migration of dislocations to various sinks. In pure Ni76Al24, Ni74Al26, and boron-doped Ni74Al26 (which are brittle) the intermediate and high-temperature annealing stages occur at ∼750–800 and 1000 °C, respectively. These stages were attributed to the migration of dislocations (750–800 °C) and recrystallization (∼1000 °C) with incomplete annealing of dislocations at 1000 °C. This being the case, it is clear that dislocations interact with grain boundaries far more strongly in brittle than in ductile Ni3Al alloys. Thus, these data strongly suggest that the ductilization of Ni76Al24 by boron is largely due to a change in grain boundary structure which inhibits the pinning of dislocations at grain boundaries that occurs in pure Ni76Al24 (i.e., boron increases the susceptibility of grain boundaries to slip). Similar results for small-grain samples support this interpretation.
Fractal geometry of collision cascades
Authors: Rossi François , Parkin Don M. , Nastasi Michael
Published: September 2007

The fractal nature of self-ion collision cascades is first described using an inverse power potential and then by the more realistic potential of Biersack–Ziegler. Based on the model of Cheng et al. and TRIM Monte Carlo simulations, the average cascade fractal dimension is a function of both atomic mass and initial energy. The instantaneous fractal dimension increases as the cascade evolves. A critical energy Ec for producing a dense subcascade is derived and it is shown that Ec agrees well with the onset energy for constant damage efficiency.
Silicide formation in metal/Si structures and diffusion barrier properties of CVD tungsten films
Authors: Pauleau Y. , Dassapa F. C. , Lami Ph. , Oberlin J. C. , Romagna F.
Published: September 2007

Tungsten films were deposited on Si substrates by the H2 or Si reduction of WF6 under various experimental conditions. The composition and structure of as-deposited samples as well as the interfacial reactions and interdiffusion of elements in annealed samples were characterized by nuclear reaction analyses, sheet resistance measurements, x-ray diffraction technique, and Rutherford backscattering spectroscopy. The amount of oxygen at W–Si interfaces was found to be dependent on the cleaning treatment of the Si surface used before WF6–Si interaction. The interfacial oxygen concentration was less than 1 ⊠ 1014 at./cm2 (detection limit of the nuclear reaction analysis) and (2–7) ⊠ 1016 at./cm2 using an HF cleaning and the RCA treatment, respectively. For W/Si samples, the formation temperature of WSi2 was dependent on the dopant level in the Si substrates and the oxygen concentration at W–Si interfaces. The silicidation reaction occurred at 625 °C in “oxygen free” W/Si structures while for structures containing interfacial oxygen atoms, this reaction occurred above 800 °C. In Al/W/Si structures, the intermetallic compound, WAl12, was formed by annealing at 450 °C for 90 min. Furthermore, the formation of WSi2 was observed in structures annealed at a temperature in the range of 550 °C–600 °C regardless of the oxygen concentration at the W–Si interface. A model to explain the effect of interfacial oxygen atoms on the silicidation reaction and the influence of the Al overlayer on the thermal stability of Al/W/Si structures is proposed and discussed in this paper.