bluuebunny/crossref_metadata_2025 huggingface dataset:
High-purity thermal treatment of silicon
Authors: Borchardt G. , Weber E. , Wiehl N.
Published: February 2003

A specially designed, radio-frequency heated oven made out of polycrystalline silicon has been used for high-purity thermal treatments of silicon at 1200 °C. Neutron activation analysis and electron paramagnetic resonance proved that the content of iron and other transition metals could be kept well below 1014 cm−3.
Loading effects on Josephson junction fluxon oscillators
Authors: Erné S. N. , Parmentier R. D.
Published: February 2003

Resonant fluxon propagation on an overlap-geometry Josephson tunnel junction of length 5lJ having a McCumber bc = 5r and a variable resistive load at one end is studied by numerical integration of the circuit equations of a 50-section lumped RSJ-type model. The optimum load resistance for maximum power transfer is 4–10 times the (linear) characteristic impedance of the junction. With optimum loading, such a junction should be able to furnish at least 1 nW of microwave power.
Spin density waves in the uniform electron gas
Authors: Brener N. E. , Fry J. L.
Published: February 2003

We have made a study of the effect of exchange and correlation on spin density waves in the uniform electron gas. In order to take these effects into account, we have used two new magnetic susceptibility formulas which we have recently derived. The first of these is the time-dependent Hartree-Fock (TDHF) formula which contains exchange but no correlation, while the second one is the generalized random phase approximation (GRPA) formula which contains both exchange and correlation. Both of these formulas were evaluated for the uniform electron gas. The TDHF susceptibility was found to have an absolute maximum at a nonzero value of q, while the GRPA susceptibility was found to have an absolute maximum at q = 0. This indicates that when exchange effects are included in the susceptibility, the ground state of the uniform electron gas contains a spin density wave, but when correlation effects are also included, then the spin density wave is no longer present in the ground state of the uniform electron gas.
Band structure measurements and multi-electron effects (satellites) for nearly-filled d-band metals: Fe, Co, Ni, Cu, Ru, and Pd (invited)
Authors: Himpsel F. J. , Heimann P. , Eastman D. E.
Published: February 2003

Angle-resolved photoelectron spectroscopy has been used to determine energy band dispersions E(k↘) along symmetry lines. A complete description of the ferromagnetic energy bands of Ni at the X-point has been obtained. We observed that the ferromagnetic exchange splitting δEex for the d-like valence bands of Fe, Co, and Ni depends on the symmetry character of the wave functions. In particular, states derived from t2g tight binding orbitals (e.g., Γ25′, X5) exhibit a larger exchange splitting than eg-derived orbitals (e.g., Γ12, X2). This agrees with theoretical estimates based on self-energy calculations. The d-band widths as observed in photoemission are smaller than those determined by ab initio ground state calculations. This effect increases from Fe to Co to Ni, and is small for Cu, Ru and Pd. We correlate this apparent d-band narrowing to the position and strength of two-electron excitations which are seen as satellite structures to the valence band emission.
Enhanced magnetism in metal film sandwiches (invited)
Authors: Brodsky M. B.
Published: February 2003

The magnetic susceptibilities, χ, of Pd and Cr have been found to show very large enhancements in metal-film sandwiches of Au/Pd/Au and Au/Cr/Au. The enhancement arises from a combination of two factors: a narrowing of the density of states due to the thinness (∼1.5 nm) of the Pd and Cr films, and a stretching of the lattice by the Au. Stretching has been verified for the Au/Pd/Au films. Although the low density of states for Cr should limit such an enhancement, resistivity and susceptibility data are consistent with an antiferromagnetic transition at 2.4 K. Between 3 and 10 K, the temperature dependences of χ are approximately Curie-Weiss like for both Au/Pd/Au and Au/Cr/Au. The Au/Pd/Au and Au/Cr/Au data yield exchange enhancements of 400–28000 and ∼200, respectively. This makes Au/Pd/Au a possible candidate for p-wave-pairing superconductivity. Measurements seeking superconductivity at 0.010 K for Au/Pd/Au are described. No measurable χ is observed with Au/V/Au sandwiches, although surface spin fluctuations have been predicted.
Spin-glass/ferromagnetic transitions and multicritical points in amorphous transition metal alloys (invited)
Authors: Salamon M. B. , Rao K. V. , Yeshurun Y.
Published: February 2003

Experimental results on a number of amorphous alloys with compositions (M1−xM′x)75P16B6Al3, with M either Fe or Co and M′ either Mn or Ni are summarized for compositions in the vicinity of the boundary between ferromagnetic and spin-glass behavior. The qualitative nature of the phase boundary is very similar to that of the Sherrington-Kirkpatrick model, but with non-classical values for the critical exponents. Critical behavior along the ferromagnetic-paramagnetic, ferromagnetic-spin glass, and spin glass-paramagnetic lines are discussed. Some evidence for a qualitative change within the ferromagnetic phase near the spin-glass transition is also given. These represent the first detailed critical-point studies of such a phase diagram.
Faraday rotation measurements of time dependent magnetic phenomena in insulating spin glasses (invited)
Authors: Ferré J. , Rajchenbach J. , Maletta H.
Published: February 2003

We report here on a detailed study of the relaxation of the magnetization in an external field and of the remanent magnetization for the insulating spin glass: Eu0.4Sr0.6S. The Faraday rotation has allowed us to extend previous experiments near and just above the spin glass temperature Tfo = 1.55 K on a large time scale (10−6<t<103 s) and to measure its susceptibility magneto-optically. The temperature of the susceptibility cusp Tf(ν) varies as log ν for ν≳10 Hz and tends to reach the static value Tfo at lower frequencies. The time dependence of the thermoremanent magnetization (TRM) can generally be described by a power law TRM = At−a. The exponent a depends both on the temperature and on the initially applied field H, as recently found by Monte Carlo simulations for a 2d-Ising spin glass. The unusual field dependence of the TRM, always found in SG systems, i.e., the maximum in TRM versus H, results from an increase of the demagnetization rate with H, which can compensate the large initial magnetization at high fields. The isothermal remanent magnetization is analyzed from our knowledge of the time and field dependence of the in-field magnetization. The Tf(ν) variation and the TRM (H) behavior cannot be explained by a model of non interacting clusters and suggest a cooperative behavior, as for ferromagnets.
A scaling method for low temperature behavior of random antiferromagnetic systems (invited)
Authors: Bhatt R. N. , Lee P. A.
Published: February 2003

Low temperature properties of random antiferromagnetic Heisenberg spin-1/2 systems with a wide distribution of exchange couplings are examined using a scaling technique. The method iteratively discards the irrelevant high energy excitations of strongly coupled clusters, while retaining the low lying states which are reproduced by an equivalent smaller cluster. The method is applied to n-doped semiconductors, a spatially random three dimensional system of spin-1/2 donors with Heisenberg exchange varying exponentially with separation. It shows how the system does not order down to temperatures well below the median nearest neighbor exchange. Comparison is made with the corresponding system in two dimensions and the one-dimensional random antiferromagnetic chain (applicable to certain organic charge transfer salts), as well as with the case of Ising spins in three dimensions.
Experiments on random-ordering field critical behavior in dilute antiferromagnets (invited)
Authors: Rohrer H.
Published: February 2003

We present experimental results bearing on the random-field problem near the bicritical point (BCP) of antiferromagnetic GdAlO3 with various degrees of dilution: 1) From the phase boundaries near the BCP, a random-field crossover exponent φrf≊1.75 is derived. 2) At random-exchange transitions, the susceptibility χ̄ exhibits a divergence-like peak as in the pure material. At random-field transitions, on the other hand, only a broad maximum of χ̄ is observed, suggesting a specific-heat exponent α<−1. 3) The transition from the antiferromagnetic state to the spinflop state below the bicritical point is qualitatively different from the pure case. 4) In the paramagnetic state above the bicritical point, an additional susceptibility peak is observed, whose intensity increases rapidly with the degree of dilution. These results are compared with current theory on the random-field problem.
Search for spin waves in (Eu,Sr)S spin glasses
Authors: Maletta H. , Zinn W. , Scheuer H. , Shapiro S. M.
Published: February 2003

Inelastic neutron scattering studies on the magnetic dilution system EuxSr1−xS with x = 1.00, 0.70, 0.52, and 0.50 reveal inelastic scattering even in the spin-glass phase, as measured for wave vectors between Q = 1.0 and 0.5 Å−1 in compounds with x = 0.52 and 0.50. These lines, however, are quite broad, and there is, in addition, considerable magnetic scattering intensity at small energies. The observations are in reasonable agreement with numerical model calculations for (Eu,Sr)S by Krey.
Spin glass-ferromagnetic phase transition in amorphous (FexNi1−x)0.75P0.16B0.06Al0.03
Authors: Lynn J. W. , Erwin R. W. , Rhyne J. J. , Chen H. S.
Published: February 2003

Inelastic neutron scattering studies have been carried out on the magnetically isotropic amorphous system (FexNi1−x)0.75P0.16B0.06Al0.03 in the concentration range (x≳0.17) where both ferromagnetic and spin-glass behavior are observed. For x = 0.4, well defined spin waves which obey the customary quadratic dispersion relation E = DQ2 are observed below the Curie temperature (Tc = 365K) and D is found to increase with decreasing temperature as usual. Below ∼80K, however, D begins to decrease with decreasing temperature as the spin-glass state is approached. Accompanied by this decrease in D is an increase in the spin wave linewidths. Preliminary results for x = 0.3 and x = 0.2 show qualitatively similar behavior.
Magnetic susceptibility studies of amorphous Ni-Mn-P-B-Al alloys
Authors: Goldfarb R. B. , Rao K. V. , Fickett F. R. , Chen H. S.
Published: February 2003

Magnetic susceptibility studies have been made on amorphous (Ni1−xMnx)75P16B6Al3 alloys in the temperature range 4–300 K. In the case of the x = 0 alloy, the mass susceptibility is quite small, ∼10−8 m3/kg at room temperature. With the addition of Mn to x = 0.2, the susceptibility increases to ∼5×10−7 m3/kg. The susceptibility does not change appreciably with the composition from x = 0.2 to x = 0.4. With the further addition of Mn to x = 0.6, the room temperature susceptibility increases to ∼3×10−6 m3/kg. The x = 0.2 alloy shows a broad peak in susceptibility at ∼28 K and a shifted hysteresis loop at 4 K upon field cooling, behavior associated with spin glasses and mictomagnets. The shifted hysteresis loops are unstable at 4 K and shift back toward the origin upon cycling the field. Time dependent effects are also seen at 4 K. These results are interpreted in terms of a continuous freezing of small paramagnetic clusters as the temperature is lowered.
Frequency dependence of Tf and short time remanence for Eu0.4Sr0.6S spin glass
Authors: Bontemps N. , Rivoal J. C. , Billardon M. , Rajchenbach J. , Ferre J.
Published: February 2003

We report on the frequency variation of the freezing temperature and on the time variation of the magnetization of the insulating spin-glass Eu0.4Sr0.6S. Faraday rotation was used to monitor optically the susceptibility or the magnetization and is well adapted to measurements in a large frequency range (10−2–107 Hz) or at various time scale (down to 25 ns). The temperature Tf(ν) associated with the maximum of the susceptibility peak exhibits a linear dependence with Log(ν) in the range 102–107 Hz. At lower frequencies (down to 10−2 Hz) it approaches a ’’static’’ limit equal to 1.55 K. This result cannot be explained by a model of superparamagnetic clouds. The frequency shift of the freezing temperature is experimentally shown to be related to the occurrence of a remanent magnetization during the time associated with the measuring frequency. Finally the time dependent behavior of the magnetization was investigated down to 25 ns after cutting a weak magnetic field (∼2 Oe). The main part of the magnetization is shown to relax more quickly than 25 ns even at 1.26 K. The only change when lowering the temperature below Tf is the emergence of the remanent magnetization; its time dependence is briefly discussed.
Remanent magnetization and thermal relaxation in a frustrated spin-glass: Eu1−xGdxS
Authors: Berton A. , Chaussy J. , Odin J. , Rammal R. , Souletie J. , Tholence J. L. , Tournier R. , Holtzberg F. , Von Molnar S.
Published: February 2003

The Eu1−xGdxS system evolves from ferromagnetism for small x to antiferromagnetism for x→1. We have studied the remanent magnetization and the thermal relaxation in the concentration range 40%≲x≲58% where a spin-glass state is observed (1). Both properties are found to decrease exponentially with T ℓn (t/τo) but with different coefficients (T is the temperature, t the measuring time and τo a characteristic relaxation time). This appears to be a general property of spin glasses at low temperature consistent with a description in terms of two levels systems.
The low temperature specific heat of amorphous alloys (invited)
Authors: Onn David G.
Published: February 2003

Increased availability of amorphous metal alloys, particularly the transition-metal-metalloid metallic glasses has permitted more studies of the low temperature specific heat (CP) in recent years. The contributions to CP due to phonons (CL), electrons (CE) and magnetic effects (CM) are discussed. In CL the contribution of low-energy phonons is sensitive to composition, structure and annealing state. In analyzing CE in the [FeNi] [PB] alloys a split-band model offers the best description of present data. Spin-glass contributions to CM provide entropy distribution near the spin-glass anomaly and show the spin-glass state persisting up to 20% iron in the [FeNi] [P14B6] series. Preliminary results on annealing effects in CP are presented and areas for future research through CP measurements summarized.
The low temperature specific heat of the metallic glasses (FexNi80−x)B20 heat of the metallic glasses
Authors: Onn David G. , Sundermier Amy , Krause J. K.
Published: February 2003

The specific heat, CP, between 0.6 K and 60 K has been determined for the metallic glasses (FexNi80−x)B20 for x = 80, 60, 40, 30 and 20 using melt-spun ribbon samples. The magnetic contribution (CM) is small, enabling analysis of (CP−CM) into electronic and phonon contributions, which are compared with those in related alloy series. The composition dependence of the electronic term provides further evidence for application of the split-band model to these alloys. The phonon contribution showed marked composition dependent deviations from the Debye model at temperatures above 10 K. No large spin-glass contribution to CM is observed for the x = 20 composition, in contrast to the previously studied alloy Fe20Ni60P14B6.
Hyperfine interactions and magnetization of (Fe1−xCox)80B20 amorphous alloys
Authors: Dey S. , Deppe P. , Rosenberg M. , Luborsky F. E. , Walter J. L.
Published: February 2003

Mössbauer spectra of ternary (Fe1−xCox)80B20 ferromagnetic amorphous alloys were taken at 300, 77, and 6 K. The relatively broad distributions of the Fe57 hyperfine field could be fitted to quasi-symmetrical Gauss profiles with a relative half-intensity line width of 8–10%. Whereas the average hyperfine field HF at 6 K decreases slowly with x for x≳0.1, the isomer shift increases with x stronger than in the case of (Fe1−xNix)80B20 amorphous alloys. The saturation magnetization Ms has been measured in the temperature range 4–300 K. A linear dependence of HF (at 6 K) on the average magnetic moment μ holds over the whole investigated compositional range according to the equation HF = aμFe+μb where μFe is the moment of Fe in Fe80B20, a≃134 kOe/μB and b≃10 kOe/μB. A small enhancement of HF takes place only in the range 0<x<0.2 as does the average magnetic moment, but for both HF and μ the changes are much smaller than the crystalline FeCo alloys. The dependence of Ms on T is in very good agreement with the Bloch law Ms(T) = Ms(0)×[1−BT3/2] with values of B ranging between 0.67 and 1.25×10−5K3/2 for 0.75≳x≳0.125 in good agreement with those obtained from the dependence of HF on T.
Magnetic properties of rare earth-gallium-iron glasses
Authors: Cornelison S. G. , Sellmyer D. J. , Hadjipanayis G.
Published: February 2003

Results of magnetic susceptibility, high-field magnetization, and Mössbauer effect are reported for several R-Ga and R-Ga-Fe metallic glasses, where R = Pr and Tb. Magnetic ordering temperatures, effective moments, and coercive forces were determined. In certain cases the data indicate that the low temperature states of magnetic order are asperomagnetic or spin-glass-like. For (Pr80Ga20)80Fe20, several anomalies were observed including a large coercive field (45 kOe) at 100 K.
Multistage linear electron acceleration using pulsed transmission lines
Authors: Miller R. B. , Prestwich K. R. , Poukey J. W. , Epstein B. G. , Freeman J. R. , Sharpe A. W. , Tucker W. K. , Shope S. L.
Published: February 2003

A four-stage linear electron accelerator is described which uses pulsed radial transmission lines as the basic accelerating units. An annular electron beam produced by a foilless diode is guided through the accelerator by a strong axial magnetic field. Synchronous firing of the injector and the acccelerating modules is accomplished with self-breaking oil switches. The device has accelerated beam currents of 25 kA to kinetic energies of 9 MV, with 90% current transport efficiency. The average accelerating gradient is 3 MV/m.
Laser emission cross section of Nd:YAG at 1064 nm
Authors: Birnbaum Milton , Tucker Armin W. , Fincher Curtis L.
Published: February 2003

The stimulated emission cross section of Nd:YAG (yttrium aluminum garnet) (4F3/2→4I11/2) was compared to the known cross section of Nd:ED-2 glass at 1060 nm. Small samples of Nd:YAG and ED-2 glass were end pumped with a chopped cw 514.5-nm argon-ion laser in an identical geometrical arrangement. The stimulated emission cross section obtained for Nd:YAG at 1064 nm was found to be 7.6 ×10−19 cm.
Excited-state absorption in Eu+2: CaF2 and Ce+3: YAG single crystals at 298 and 77 K
Authors: Owen James F. , Dorain Paul B. , Kobayasi Takao
Published: February 2003

Excited-state absorption has been studied in Eu+2-doped CaF2 and in Ce+3-doped Y3Al5O12 at room temperature and 77 K. It is shown that the conduction band of the host crystal is responsible for absorption in both systems. In Eu+2: CaF2 the excited-state absorption is caused by a transition from the fluorescence level, the 4f6(7F)5d(2eg)G8 state, to the conduction band of CaF2. In Ce+3: YAG two processes are responsible for the absorption: (1) excitation from the lowest Ce+3 5d energy level to the conduction band of YAG and (2) transitions from the ground state of a trap to its excited states and to the conduction band of YAG. The results provide general guidelines in the search for new uv solid-state laser materials.
Collisional radiative recombination in high-pressure noble gas mixtures
Authors: Whitten Barbara L. , Downes Lawrence W. , Wells William E.
Published: February 2003

Rate coefficients are calculated for neutral-assisted collisional radiative recombination in dense, weakly ionized rare-gas mixtures using the quasiequilibrium model developed by Bates. It is shown that the recombination rate can be significantly altered by the presence of a buffer gas. In particular, the presence of helium can enhance the collisional radiative recombination rate coefficient of heavy rare gases by a factor of 5.
Magnetically insulated plasma sheath in coaxial transmission lines with an external magnetic field
Authors: Mostrom Michael A. , Jones Michael E. , Thode Lester E.
Published: February 2003

A relativistic Brillouin flow equilibrium model is assumed for the plasma sheath and a cylindrical analytic solution including a uniform external magnetic field is obtained. A free parameter appearing in all previous magnetic insulation theories is shown to be accurately determined by maximizing the transmitted power flow. The theory is supported by particle-in-cell simulations.
A theoretical model of laser ionization of alkali vapors based on resonance saturation
Authors: Measures R. M. , Cardinal P. G. , Schinn G. W.
Published: February 2003

We have developed a theoretical model of the ionization that results from extended laser saturation of an atomic resonance transition within a dense alkali vapor. Although this model includes all of the essential collisional-radiative interactions, nevertheless, it leads to relatively simple analytical relations that predict the ionization time history to within 20% of that calculated by our extensive laser ionization based on resonance saturation (LIBORS) computer code in the case of sodium. When allowance is made for the temporal and spatial nature of a realistic laser pulse, the apparent ionization time has been shown to be approximately double that of the value predicted on the basis of a steplike, flat laser pulse.
Plasma erosion switches with imploding plasma loads on a multiterawatt pulsed power generator
Authors: Stringfield R. , Schneider R. , Genuario R. D. , Roth I. , Childers K. , Stallings C. , Dakin D.
Published: February 2003

Plasma erosion switches have been fielded on the PITHON generator during imploding plasma experiments. Theta pinch plasma guns were used to inject carbon plasmas of densities in the range of 1012–1014 cm3 between the electrodes of the vacuum power feed region, upstream from an imploding plasma load. Current monitors indicated that the erosion switches carried substantial current early in time, diverting it from the load. Late in the pulse the erosion switches opened, transferring the current to an imploding plasma with the effect of sharpening the current rise time at the load. Associated withthe sharper rise time was an improvement in the quality of the plasma implosions. The results of varying the density and total number of particles in the plasma of the switches are presented with regard to the effect on the current along the vacuum feed and on the behavior of vacuum flowing electrons.
Origin of emitting species in the plasma deposition of a-Si:H alloys
Authors: Kampas F. J. , Griffith R. W.
Published: February 2003

The power dependence of the emission intensities for the species Si, SiH, H, H2, and added N2 in the rf glow discharge decomposition of silane (SiH4) was studied. It was found that H and the emitting excited states of Si and SiH are primary products of the silane decomposition.
Interface instability and cell formation in ion-implanted and laser-annealed silicon
Authors: Narayan J.
Published: February 2003

The phenomenon of solid-liquid interface instability during directional solidification has been studied in In+, Ga+, Fe+, and Sb+ implanted silicon after pulsed laser annealing. Interface instability results in lateral segregation which leads to the formation of cellular structures. The cellular structures have been studied using transmission electron microscopy. The critical bulk solute concentration above which instability develops, and the wavelength of instability (cell size) as a function of velocity of solidification have been calculated following the perturbation theory originally developed by Mullins and Sekerka. A good agreement between the experimental results and the calculations is obtained when the dependence of the interfacial distribution coefficient on the velocity of solidification is taken into account in the calculations.
Grain boundary potential determination in polycrystalline silicon by the scanning light spot technique
Authors: Martinez J. , Criado A. , Piqueras J.
Published: February 2003

Local grain boundary potential has been determined by scanning light spot technique. Photocurrent peaks vary from boundary to boundary giving a strong peak for large-angle grain boundaries and becoming negligible for the smallest-angle grain boundaries observed. The largest potentials had typical values of around 0.3 eV and the corresponding interface state densities were in the 1013 cm−2 range.
Measurements of deep penetration of low-energy electrons into metal-oxide-semiconductor structure
Authors: Nakamae Koji , Fujioka Hiromu , Ura Katsumi
Published: February 2003

A polycrystalline Si-SiO2-Si metal-oxide-semiconductor (MOS) transistor covered with thick insulation and passivation layers of SiO2 was examined to measure the threshold voltage shifts as a function of electron energy over the range of from 5 to 18 keV. The electron-beam fluence was varied over six orders of magnitude from 2×10−9 to 2×10−3 C/cm2. From the experimental data, the fraction of the incident electron energy deposited in the gate oxide was determined. The result shows a deep penetration of low-energy electrons beyond the electron range.
Thermal stability of Pb-alloy Josephson junction electrode materials. I. Effects of film thickness and grain size of Pb-In-Au base electrodes
Authors: Murakami Masanori
Published: February 2003

Pb-alloy Josephson devices are attractive for potential use as active elements in high-speed computers. Failures occur in some Pb-alloy junctions during repeated thermal cycling between 300 and 4.2 K. The failures are believed to be primarily caused by rupture of the ultrathin tunnel barrier oxide between base and counter electrodes when strain in the electrode films induced by thermal-expansion-coefficient mismatch between film and substrate is relaxed. The strain relaxation can cause microstructure changes such as grain rotation and hillock formation that can lead to device failure. The effects of film thickness h and grain size g on the strain behavior and microstructure of Pb-12 wt. % In-4wt. % Au films similar to those used for a Josephson junction base electrode were studied by x-ray diffraction, and by transmission and scanning electron microscopy. Films with various combinations of h and g were prepared by evaporation onto oxidized Si substrates at room or liquid-nitrogen temperature. In the present Pb-alloy films, grain size and film thickness were found to be the key factors that control strain relaxation upon cooling from 300 to 4.2 K, as previously observed in pure Pb films. By reducing the average grain size or the film thickness down to ∼0.1 mm, the strain relaxation during cooling to 4.2 K was reduced to near zero. The stress at 4.2 K was calculated from the measured strain, and it was found that the stress level supported in fine-grained Pb-alloy films was close to the theoretical shear strength of Pb. It is believed that this stress level is the highest value obtained in soft materials with a film thickness of ∼1 mm. After repeated cycling between 300 and 4.2 K of fine-grained Pb-In-Au films, no evidence of microstructure changes which could cause device failure was found. The use of such fine-grained Pb-alloy base-electrode films has allowed a 100-times improvement in the ability of Pb-alloy Josephson devices to withstand repeated thermal cycling to 4.2 K.
Thermal stability of Pb-alloy Josephson junction electrode materials. II. Effects of SiO coating on Pb-In-Au base electrode
Authors: Murakami Masanori
Published: February 2003

The preceding paper pertains to studies which were carried out for Pb-In-Au films without overlying SiO layers. Because use is made of configurations in Josephson junction integrated circuits presently under investigation in which Pb-In-Au base-electrode films are coated by overlying layers of SiO, a study was undertaken of the effects of such layers on the strain behavior of Pb-In-Au films using an x-ray diffraction technique. Pb-12 wt. % In-4 wt. % Au films were prepared at 298 or 77 K to obtain large or fine grains, respectively, and then thermally cycled between 300 and 4.2 K and between 300 and 350 K. In large-grained Pb-In-Au films, the strain relaxation, upon thermal cycling, by dislocation glide or by grain-boundary diffusion creep, was observed to be significantly inhibited by overlying SiO layers. However, in fine-grained films, that was not observed. For junctions in which the tunnel oxide is formed within an opening in an overlying SiO layer, it is believed, e.g., that upon heating, a compressive strain gradient develops in the large-grained base-electrode films between the junction area and its surrounding, leading to base-electrode deformation inside the opening that could rupture the tunnel oxide. This study indicates that the strain gradient should be reduced by reducing the average grain size of the base-electrode films. These results agree well with the previous experimental results in which no hillocks were detected by scanning electron microscopy inside similar SiO-layer openings above fine-grained Pb-In-Au films during repeated thermal cycling between 300 and 4.2 K or upon heating from 300 to 343 K.
Detection of impurities on silicon surfaces
Authors: DiMaria D. J. , Reuter W. , Young D. R. , Pesavento F. L. , Calise J. A.
Published: February 2003

Impurities initially present on a Si surface can be detected using the photo I-V technique. An Al impurity deposited to a thickness less than 8 Å on a silicon substrate which was subsequently oxidized, capped by a chemically vapor deposited (CVD) SiO2 layer, and incorporated into a capacitor structure with an Al gate electrode was found mostly near the interface between the thermal and CVD oxides using the photo I-V technique. This impurity layer which was probably converted to Al2O3 showed greatly enhanced electron trapping compared to either oxide layer.
Magnetoresistance of Fe-B-P glasses
Authors: Naka M. , Kern R. , Gonser U.
Published: February 2003

The magnetoresistance of Fe100−xBx, Fe100−xPx, and Fe80B20−xPx glasses was measured at room temperature. The anisotropic magnetoresistance ratio Dp/p = (p∥−p⊥)/p of Fe100−xBx and Fe100−xPx decreases monotonically with increasing boron or phosphorus content. In the Fe80B20−xPx alloys the replacement of boron by phosphorus indicates the competing influence of the metalloids. The changes of the magnetoresistance ratio with metalloid composition are compared with the saturation moment per iron atom nb at 0 K. It is found that the experimental values can be fitted by the relation Dp/p = Anmb, with m = 7.9 and A = 1.13×10−5.
Dependence of magnetoelastic effects in Ni samples on temperature
Authors: Hernando A. , Madurga V. , Vázquez M.
Published: February 2003

Torsional magnetoelastic effects measurements in tubular polycrystalline samples have been carried out. Their variation with applied torque and temperature allows us to find a distribution function for the values of the residual stresses.
Electrostrictive effects in antiferroelectric perovskites
Authors: Uchino K. , Cross L. E. , Newnham R. E. , Nomura S.
Published: February 2003

Electrostrictive terms have been introduced into the simple Kittel free-energy function for antiferroelectrics. An additional coefficient W is found to be required to take account of the interaction with the sublattice polarizations, and Q and W values have been calculated from experimental data for typical antiferroelectric perovskites PbZrO3 and Pb(Mg1/2W1/2)O3. Consideration of several ferro- and antiferroelectric perovskites suggests that the magnitude of Q is not affected strongly by ferro- or antiferroelectricity, but that it does depend quite strongly upon any disorder in the cation arrangement. An empirical rule that the product of the electrostrictive Q coefficient and the Curie Weiss constant C is almost the same for all ferro- and antiferroelectric perovskites is proposed (QhC = 3.1±0.4×103 m4 C−2 K). A very simple ’’rattling ion’’ model is shown to give a simple intuitive explanation of the observed results.
Infrared absorption in highly transparent fluorozirconate glass
Authors: Bendow Bernard , Drexhage Martin G. , Lipson Herbert G.
Published: February 2003

Detailed measurements of the frequency and temperature dependence of absorption are reported for the highly transparent frequency regime of a promising new infrared glass based on zirconium fluoride. The results are interpreted in terms of intrinsic multiphonon processes.
Theory of photoacoustic signal generation for optimized photoacoustic cells
Authors: McDonald F. Alan
Published: February 2003

Recent advances in the theory of the photoacoustic effect are applied to the problem of cell optimization. Three-dimensional heat flow, including conduction to the cell window and walls, is considered. A relatively simple theoretical expression for the signal is obtained, provided certain experimental conditions are satisfied.
Electrochemical adsorption of metals on amorphous Se-Ge films
Authors: Singh Bhanwar , Chopra K. L.
Published: February 2003

Electrochemical adsorption of Ag and Cu on a−Se1−xGex films has been studied as a function of the composition of the films, angle of deposition (obliqueness), film thickness, pre-illumination of the films and temperature of the electrolytic solution. Metal adsorption is due to th eoxidation of germanium atoms by the metal ions present in the electrolyte. Its enhancement with obliwueness (angle of deposition f the film) arises due to increased surface defect sites/dangling bonds associated with the Ge atoms. Adsoprtion decreases for pre-illuminated a−Se1−xGex films, presumably as a result of changes in the surface topography arising from structural rearrangements of the defect centers.
Laser induced transient excitation of conducting targets by thermionic emission
Authors: Meadors John G. , Poirier Michael A.
Published: February 2003

A new technique for the transient excitation of conducting targets which introduces no electromagnetic interference is described. A fast rise-time laser pulse with a 1.06-μm wavelength is focused to a power density exceeding approximately 4×109 W/cm2 on the surface of a conducting target. The local heating of the surface by the laser energy produces thermionic emission which is electromagnetically equivalent to a transient current monopole normal to the target surface at the irradiated spot. This localized current pulse then couples to the modal surface currents on the target. This paper descibes an experimental investigation of this technique for target excitation. The results of several independent experiments and an explanation of the large difference in excitation strengths between targets in air and in vacuum are consistent with a physical model of the excitation mechanism based on surface heating by the optical energy to produce thermionic emission.
Hydrides of ternary TiFex
M1−x(M=Cr, Mn, Co, Ni) intermetallics
Authors: Mintz M.H. , Vaknin S. , Biderman S. , Hadari Z.
Published: February 2003

The influence of partial substitutions of iron in TiFe by some other 3-d transition metals on the hydrogenation characteristics of the corresponding ternary (pseudo-binary) TiFexM1−x(M=Cr, Mn, Co, Ni; 0.5≲x≲1) compounds was systematically investigated. Such substitutions result in two main effects:(i) stabilization of the monohydride β phases and (ii) reduction of hysteresis in the absorption-desorption isotherms. A linear dependence of the enthalpies of the monohydride formation on the iron concentration (i.e.x) has been obtained and accounted for by a model assuming local interactions of hydrogen with nearest-neighbor metal atoms.
Improvements of the electro-optic properties of (Al,Ga)As lasers by means of reduced reflection dielectric facet coatings
Authors: Nash F. R. , Paoli T. L. , Hartman R. L.
Published: February 2003

We demonstrate that reduced reflectivity facet coatings of Al2O3 on both mirrors can increase the output power levels at which ’’kinks’’ in the light-current characteristics of proton-delineated 12-μm stripe-geometry (Al,Ga)As lasers occur without causing a significant softening of the ’’turn-on.’’ The dielectric coating is intermediate between half- and quarter-wavelength thicknesses. The advantage of this solution to the kink problem is that it can restore to usefulness lasers which had been previously rejected solely because their kinks occurred just at the power output desired for optical communication application. Although the spontaneous emission output just below threshold is increased somewhat, operation with an extinction ratio equal to 15:1 and reasonable limits on the amplitude of the modulating current is still quite possible. It is also found that reduced reflection coatings can decrease the depth of modulation of self-induced pulsations and decrease the effects of ’’light jumps.’’ The benefits previously connected with half-wavelength coatings should remain unaffected if reduced reflection coatings are deposited instead; such benefits are increased catastrophic-damage thresholds, suppression of light-jump development, suppression of an initially occurring temporally saturable mode of degradation, blocking in-diffusion of degradation-promoting copper, stabilization of self-induced pulsations, and retardation of facet erosion.
Junction migration in PbTe-PbSnTe heterostructures
Authors: Eger D. , Zemel A. , Rotter S. , Tamari N. , Oron M. , Zussman A.
Published: February 2003

A systemtic study of spectral responsivity, quantum efficiency, carrier concentration, zero-bias resistance, and capacitance-voltage characteristics of LPE-grown PbTe-Pb0.8Sn0.2Te heterosturcture diodes is presented as a function of the PbTe growth temperature, 420 °C<T<650 °C. The results provide clear evidence for the migration of the p-n junction into thePbTe layer owing to interdiffusion of native defects across the interface during PbTe growth at T≳480 °C. The main effects of the junction migration on the diode characteristics are a reduction in the wuantum efficiency at wavelengths above the 6 μm and an increase in the junction zero-bias resistance. These results are interpreted on the basis of the energy-band diagrams of the heterostructure diodes obtained from the capacitance-voltage characteristics and the measured carrier concentration of the epilayers. It is shown that an energy barrier for the excited electrons in the Pb0.8Sn0.2Te layer, formed at the PbTe-Pb0.8Sn0.2Te interface, is responsible for the reduction of the photosignal above 6 μm. The junction migration is prevented by growing the PbTe layers below 480 °C. In this case, peak (∼10 μm) current responsivity in the range 1.7–2.3 A/W, quantum efficiency in the range 22–30% (both without an antireflection coating), and R0A≳1 Ω cm2 are reproducibly obtained.
The poling field and draw dependence of the piezoelectric and pyroelectric response of pressure-quenched, phase I poly(vinylidene fluoride) films
Authors: Scheinbeim J. I. , Chung K. T.
Published: February 2003

Recent investigations have shown that unoriented phase I poly(vinylidene fluoride) films can be produced by pressure quenching. The poling field dependence of the pyroelectric coefficient Py, the piezoelectric coefficients dp, d31 and e31, and the dielectric response is investigated for poling fields up to Ep = 2.75×106 V/cm. These quantities exhibit a plateau region where the initial rapid increase with increasing Ep decreases. This behavior is similar to that observed for unoriented and biaxially oriented phase II poly(vinylidene fluoride) films. The effect of draw ratio on dp and Py for draw ratios up to 6:1 is also examined. dp increases from 6.5 to 19 pC/N as the draw ratio goes from 1:1 to 6:1 (at constant Ep). Py increases from 1×10−9 to 5×10−9 C/cm2 K.
Some considerations of crazing of polymers: Two-dimensional quasifracture of polymers
Authors: Chern S. S. , Hsiao C. C.
Published: February 2003

In a tensile stress field, certain polymeric solids deform and develop quasifracture formations. Each such formation is termed a craze. Previous analyses by Knight and Lauterwasser and Kramer have treated a craze by introducing either an assumed or a measured displacement field for the calculation of the stress distribution around the craze profile. In this paper the new phase of oriented polymer molecular bundles within the craze profile has been considered through the use of a linear modulus function for those bundles. Both displacement and stress fields have been calculated. This model developed for studying planar crack has its limitations when it is used for craze investigations. The basic model treatment depends upon classical linear fracture mechanics which is not valid for materials with a zone of craze occurrence. In addition, anisotropic and nonlinear as well as time dependent considerations are difficult to be incorporated into the model analysis.
Effects of chain orientation of Raman and Brillouin scattering spectra of hydrostatically extruded polypropylene
Authors: Wang C. H. , Cavanaugh David B.
Published: February 2003

Raman and Brillouin scattering techniques have been used to study the effect of chain orientation in uniaxially extruded isotactic polypropylene. The orientation parameters 〈P2〉 and 〈P4〉 are obtained by measuring several Raman scattering intensities associated with the CH2 rocking mode at 841 cm−1. Both 〈P2〉 and 〈P4〉 parameters represent the average of the local orientational distribution of the polypropylene backbone. The Raman scattering result for 〈P2〉 is found in good agreement with the previous study using another vibrational band. The high-frequency elastic constants C11, C33, C44, and C13 of extruded isotactic polypropylene are determined by Brillouin scattering. The elastic constants of deformed polymers have been related to the orientation parameters determined by Brillouin scattering. The result obtained for 〈P2〉 at high extension using Brillouin scattering is found to be smaller than that of Raman. The result suggests that the pair orientation correlation between segments is important in affecting the hypersonic velocity.
Direct detection of momentum flux in atomic and molecular beams
Authors: Choi J. G. , Hayden J. S. , O’Connor M. T. , Diebold G. J.
Published: February 2003

We describe the use of a microphone for detection of atomic and molecular beams in a high-vacuum environment. Two experiments were carried out to demonstrate this detection method. Pulsed beams of argon were detected using a conventional electret microphone where the output of the microphone was displayed directly on an oscilloscope or processed with a boxcar averager to remove the transient oscillations of the microphone diaphragm. Amplitude modulated, continuous beams of atomic argon were also detected using a lock-in amplifier. The microphone possesses a response to the pressure or momentum flux in the beam that appears to be unique among beam detectors. We use the classical equipartition theorem to calculate the magnitude of the random fluctuations in the output voltage of the microphone that is used to give an expression for the minimum detectable momentum flux in the beam. For a typical microphone we find this to be 3×10−8 Pa, (in a 1-Hz bandwidth), which corresponds to a minimum number density of 1×106 cm−3 for an effusive argon beam at 300 K.
Sub-sub T
g structural relaxation in glassy polymers
Authors: Chen H. S. , Wang T. T.
Published: February 2003

Structural relaxation in a temperature range from 32 to 62° K glass transition has been investigated, for the first time, for a nearly monodisperse polystyrene using a differential scanning calorimeter and a thermal mechanical analyzer. Low temperature anneals in the vicinity of 320 K stabilize the glassy structure and lead to volume contraction. Upon heating, the annealed samples show an excess endothermic peak and exhibit a gradual expansion associated with structural recovery above the annealing temperature. Significantly, the samples recover the initial heat content and volume without reheating through the glass transition temperature. This sub-Tg structural relaxation behavior is in many respects distinct from that commonly observed near the glass transition. Kinetics of relaxation processes are also discussed.
The annealing of solution grown crystals of alpha and gamma poly(vinylidene fluoride)
Authors: Grubb D. T. , Choi K. W.
Published: February 2003

Single crystals of poly(vinylidene fluoride) PVF2 have been grown from dilute solution and sedimented to form oriented mats. The product was α-PVF2 or a mixture of α- and γ-PVF2 and different morphologies were observed for the two phases. Annealed mats exhibited complex melting behavior, due in part to melting and recrystallization. Plots of melting temperature against reciprocal lamellar spacing indicate equilibrium melting points of 443.5 and 457.3 K for rapidly crystallized α- and γ-PVF2 after 1-h anneal, and fold surface free energies of 15.6 and 27.2 mJm−2 for α-PVF2 from different solvents, 24.8 mJm−2 for γ-PVF2. Long annealing times or high annealing temperatures tend to increase the melting point without changing the lamellar thickness probably due to rejection of head-to-head defects.
Depolarization-current study of low-density polyethylene containing an antioxidant
Authors: Ronarc’h D. , Haridoss S.
Published: February 2003

Thermally stimulated depolarization currents in low-density polyethylene containing Irganox 1076 are investigated. The thermal sampling technique has been used to study the elementary processes constituting β and γ relaxations. Irganox 1076 is found to increase the intensity of β and γ peaks and not to change the activation parameters. The participation of the antioxidant in the molecular relaxation processes is discussed.
Optimal heating of the working fluid in a cylinder equipped with a moving piston
Authors: Band Yehuda B. , Kafri Oded , Salamon Peter
Published: February 2003

We determine the optical heating of an ideal gas, which is contained in a cylinder equipped with a piston having a given arbitrary motion and which is coupled to a heat bath, so that the work produced is maximal given a total pumping energy. We show that the optimal heating is impulsive and we determine the location of the impulse. Efficiency and thermodynamic analyses are obtained for sinusoidal piston motion.
Pressure measurement at high temperatures in the diamond anvil cell
Authors: Wunder Stephanie L. , Schoen Paul E.
Published: February 2003

The frequency shift of the R1 ruby fluorescence peak has been measured in the diamond anvil cell along the ice/water melting curve in the temperature interval 25–200 °C and pressure interval 0–40 kbars. The temperature and pressure coefficients of the frequency shift were found to be independent in this region. Using a least-squares-fitting program to find the fluorescence peak positions, we could reproducibly measure pressures to ±0.2 kbar at 25 °C and to ±0.5 kbar at 300 °C. The temperature coefficient of the frequency shift of R1 in the interval 25–300 °C was determined to be −0.149 cm−1/°K. Large systematic errors in the pressure determination were found to arise when nonuniformity of temperature in the diamond anvil cell caused uncertainty in the ruby temperature.