bluuebunny/crossref_metadata_2025 huggingface dataset:
Barrier-Thickness Dependence of the dc Quantum Interference Effect in Thin-Film Lead Josephson Junctions
Authors: Schwidtal Klaus , Finnegan Robert D.
Published: February 2004

The barrier-layer thickness of cross-type square Pb–PbO–Pb thin-film Josephson junctions has been varied systematically and reproducibly by employing a mask-substrate changer and a low-pressure-glow-discharge oxidation technique. A series of junctions has been fabricated in which the ratio of film width w to the Josephson penetration depth λJ is varied from λJ≫w to λJ≪w while the width of both films is kept constant at 0.3 mm. The magnetic-field dependence of the maximum zero-voltage current in these junctions has been measured as a function of the barrier-layer thickness. For non-negligible self-fields of the tunneling currents, the field dependence follows a Fresnel diffraction pattern rather than a Fraunhofer diffraction pattern. For very thin barrier layers, the maximum zero-voltage current is eventually limited by the critical current of the Pb films. Relatively thick barrier layers, on the other hand, tend to be shorted at the edges, as can be seen from the magnetic-field dependence. The stability of Pb–PbO–Pb Josephson junctions is compared with that of Nb–NbOx–Pb Josephson junctions.
Quantum Phase Noise in Superconductors: Temperature Dependence Measured by Quantum Interference Techniques with Point-Contact Josephson Junctions
Authors: Ulrich B. T.
Published: February 2004

Thermodynamic fluctuations limit the ultimate performance of superconducting devices of practical interest, devices such as the quantum interference magnetometer and the Josephson junction radiation detector. We report direct observations of thermodynamically driven quantum phase fluctuations near the superconducting critical temperature. The experiments used point-contact quantum interference techniques with niobium points on a single-crystal tin substrate. Near the superconducting transition of tin, TC=3.72°K, the niobium points served as probes to measure fluctuations in the phase of the superconducting order parameter within the tin crystal. The temperature was slowly increased, beginning well below TC for tin, where the quantum phase was stable. Quantum phase fluctuations were first observed approximately 5 mdeg below TC. As the temperature continued to increase through this 5 mdeg range near TC, the characteristic frequency of the phase fluctuations increased 6 orders of magnitude. At TC a discontinuous transition to a resistive state gave rise to a finite voltage difference in the tin with the associated driven quantum phase precession. Thermodynamic Johnson noise voltages developed across this resistance of order 10−10Ω observably broadened the precession line. We will present the detailed temperature dependence of the frequency power spectrum of quantum phase fluctuations below and above TC.
Flux Displacers for Pulse Generation with Superconducting Multipole Magnets
Authors: Thome R. J. , Gaulé G. K.
Published: February 2004

Short, steep pulses of high electrical energy are required to drive systems such as pulsed transmitters, light sources and plasma discharges. A low impedance stationary coil will generate such pulses when the magnetic flux threading the coil undergoes large and rapid changes. The rapid change can be achieved by a ``flux displacer,'' a conductor driven at high speed past the stationary coil. The applied field is provided in the present work by a superconducting magnet in order to produce a magnetic flux of the necessary magnitude and density with small operating loss, bulk and weight. The stationary coil together with the load and the flux displacer were not superconducting and were placed outside the Dewar. Two series of experiments with flux displacers driven by a rotary prime mover are discussed. The first series used relatively small, isolated specimens. These experiments served to determine the effect of displacer shape, speed and conductivity on output. The second series used relatively large displacers formed by pairs of cylindrical shell segments which are electrically and mechanically connected by end plates. These experiments give information on the influence of various system parameters on the energy, and on the duration and shape of the pulses. The results are presented in dimensionless form, so that the performance of higher-energy systems can be predicted. Ultimately, the rotary prime mover may be a lightweight explosive drive or gas turbine or, in a vehicle or aircraft, one of the propulsion engines.
Use of Superconductors as Thermometric Fixed Points
Authors: Colwell Jack H. , Schooley James F. , Soulen Robert J.
Published: February 2004

The possibility of using superconductors with sharp transition temperatures as fixed points on a thermometer scale was examined. Annealed polycrystalline specimens 3.2 cm long by 0.157 cm in diameter were placed in a cryostat which would operate from 0.3 to 10.0 K; the superconductive transitions were measured with a Hartshorn bridge operating at 270 Hz. One specimen each was made from the purest available Pb, In, Ga, Zn, and Cd—the latter two elements are obtainable from the Office of Standard Reference Materials. In all cases but Cd, the width of the transitions were less than 0.001 K; for Cd it was 0.002 K. The specimens were cycled once to room temperature and remeasured to check their reproducibility vs two germanium resistance thermometers. The reproducibility was better than 0.001 K. These preliminary results indicate the strong possibilities for this approach to fixed point thermometry.
Hall Effect in an Amorphous Ferromagnetic Alloy
Authors: Lin S. C. H.
Published: February 2004

The ordinary Hall coefficient of the amorphous ferromagnetic alloy Fe80P13C7 is 3.0×10−11 V·cm/A·G. Its spontaneous Hall coefficient is 0.6×10−9 V·cm/A·G and is independent of temperature from 4.2°K to its Curie temperature at 586°K if the ordinary Hall coefficient does not change much over the temperature range. The free electron assumption calculated by Samoilovich and Kon'Kov explains the temperature independent behavior of the spontaneous Hall coefficient.
Effect of Coherency Strains on Diffusion in Copper-Palladium Alloys
Authors: Philofsky E. M. , Hilliard J. E.
Published: February 2004

Interdiffusion coefficients have been measured in Cu–Pd alloys containing 70–90 at.% Pd at temperatures from 355° to 440°C using films containing short wavelength composition modulations produced by evaporation. From the relative intensities of the high- and low-angle satellites about the 111 Bragg peak, it was established that the composition modulations were coherent for λ<28 Å (where λ is the wavelength of the modulation) and were incoherent for λ>38 Å. Over the range 28 to 38 Å, there was a progressive loss in coherency and this was accompanied by a twofold decrease in the diffusivity. This decrease confirms quantitatively the effect of coherency strains on diffusion predicted by Cahn. The dependence of the effective diffusion coefficient on wavelength in the coherent modulations yielded K=−10.3×10−6 erg·cm−1 for the gradient-energy coefficient.
Pressure Calibration to 60 kbar Based on the Resistance Change of a Manganin Coil under Hydrostatic Pressure
Authors: Zeto Robert J. , Vanfleet H. B.
Published: February 2004

The relative resistance change of a properly seasoned manganin coil was measured at the center of the region of indifference for the bismuth II-III, thallium II-III, and barium I-II phase transformations in a hydrostatic system. The equilibrium pressures for these transformations were obtained from the relative resistance change of manganin which was calibrated with pressure by means of the mercury L-I and bismuth I-II transition pressures. Equilibrium pressures corrected to 25°C of 26.861±0.042, 36.569±0.153, and 56.273±0.521 kbar were determined for the bismuth II-III, thallium II-III, and barium I-II phase transformations, respectively. Only the barium I-II point deviated from the presently accepted high pressure scale. On the basis of the manganin pressure gauge, either the presently accepted value of the barium I-II point is too high by about 2.5 kbar or the pressure coefficient of manganin resistance changes sharply between 37 and 59 kbar. A two-point quadratic calibration curve was satisfactory for pressures to 37 kbar.
Principles of Stability in Cooled Superconducting Magnets
Authors: Stekly Z. J. J. , Thome R. , Strauss B.
Published: February 2004

The equations for the terminal characteristics of a composite superconductor are formulated taking into account heat transfer to a coolant, interface thermal contact resistance, and the size of the superconductor itself. The nonlinear heat-transfer characteristics of liquid helium are also taken into account in an approximate manner. The general relationship for stability is derived in terms of dimensionless parameters involving the size and characteristics of the substrate and the superconductor and the heat-transfer coefficients at the interfaces between the superconductor and the substrate, and between the substrate and the coolant. It is also concluded that if the superconducting strands are smaller than a characteristic size, one would espect that flux jumps should disappear.
Annealing Behavior of Induced Anisotropy and Related Magnetic Properties in Permalloy Films
Authors: Iwata Takao , Hagedorn F. B.
Published: February 2004

Anisotropy aging and stabilization effects have been investigated in vapor-deposited zero-magnetostrictive Permalloy films by annealing either in a rotating magnetic field or in an easy direction field. Two major components in the anisotropy relaxation were observed. Amounts of the two components are comparable in fresh films. By stabilization annealing at 300°C for 35 h, the fraction of the anisotropy affected by the faster component can be made less than 17 of the total initial anisotropy, during which time the relaxation frequency of the slower component gradually decreases from about 10−4 sec−1 to about 10−6 sec−1. The fast component is suggested to be related to high-diffusivity paths in films while reorientation of the ordered atomic pairs as a result of the bulk diffusion process can account for the slow component. However, the vacancy concentration is found to be far in excess of the thermal equilibrium value in fresh films, leading to marked increases in the initial diffusion rates compared with bulk Permalloy values. It is found that the vacancy rate-of-change process follows the chemical rate equation of order 2, which suggests the formation of divacancies. The change-of-slope method is introduced for determination of the activation energy for atomic movement involved in the reorientation process of atom pairs, giving a value of 1.6 eV which is in reasonable agreement with estimates of this quantity from bulk data.
Transition from Ferromagnetism to Paramagnetism in Ni–Cu Alloys
Authors: Robbins C. G. , Claus Helmut , Beck Paul A.
Published: February 2004

The low-temperature (1.4° to 4.2°K) specific heat, the ferromagnetic Curie temperature, and the magnetic moment of Ni–Cu solid solutions were measured near the composition where ferromagnetism terminates. The anomaly in the specific heat cannot be accounted for by the bT3 ln T term expected from electron-paramagnon interaction, but it can be interpreted as a magnetic cluster contribution independent of temperature from 1.4° to 4.2°K. Another magnetic contribution is included in the term of the specific heat linear in temperature. Whether the maximum in the linear term at 50–54 at.% Cu should be attributed to this magnetic contribution or to the (enhanced) electronic specific heat is uncertain. For alloys near the critical composition the Curie temperature, as determined by methods based on high field data, is distinctly higher than that measured at low fields.
Precision Measurements of the F19 NMR in FeF2 from 4.2°K to the Critical Region
Authors: Kulpa Stanley M.
Published: February 2004

A precise determination of the temperature dependence of the zero external field F19 NMR frequency in the antiferromagnet FeF2 has been made over the temperature range from 4.2°K to 0.99966TN. Ferrous fluoride, unlike the previously studied antiferromagnet MnF2, has a large single ion magnetic anisotropy. The present data, which were taken on a high-quality single crystal with one millidegree temperature control and measurement techniques, were carefully least-squares fitted to the equation ν19(T)/ν19(0)=D(1−T/TN)βover ranges θ <T/TN<0.99966. For θ=0.995, it is found that β=0.333±0.009, D=1.428±0.067, TN=78.373±0.005, while for θ=0.971, β=0.320±0.001, D=1.341±0.005, TN=78.367±0.001. The present data, which demonstrate the need for precise measurements and analysis over small ranges near TN, are at variance with the wider-range power law fits reported recently by Wertheim et al. A Kouvel-Fisher plot of the present data shows that the apparent value of β drops rather rapidly for θ<0.95. This behavior is distinctly different from MnF2, where the apparent value of β varies more slowly. Although no analysis of the data below the critical region has yet been made, its accuracy should prove helpful for comparison with spin-wave interaction theories.
Elastic Constants of Single-Crystal Ni3Al from 10° to 850°C
Authors: Dickson R. W. , Wachtman J. B. , Copley S. M.
Published: February 2004

The single-crystal elastic constants of Ni3Al were determined by a rod resonance technique. Their values and standard deviations at 25°C in units of 10−12 m2/N are s11=9.27±0.15, s44=8.25±0.27, and s12=−3.19±0.50.
Preyield Plastic Deformation in Copper Polycrystals
Authors: Vellaikal Gopinathan , Washburn Jack
Published: February 2004

Preyield dislocation motion and multiplication were studied in large-grained polycrystalline OFHC copper by the etch-pit technique. Specimens were loaded in compression and dislocation arrangements were observed in both the stressed and unstressed conditions. The dislocation loops generated by the first few active sources on both primary and secondary slip systems generally traversed the entire cross section of the grain. The observations were consistent with the idea that jog density is an important factor in determining the mobility of a dislocation segment. The external surface was found to be a preferential site for dislocation multiplication even when grown in segments, where they cut the surface, were immobile, and stress concentrations were carefully avoided. It is suggested that the rapid increase in length per unit volume of moving dislocation line that is associated with macroscopic yield requires motion of dislocation segments of high jog density.
Diffusion Doped Organic p-n Junctions
Authors: Krikorian E. , Sneed R. J.
Published: February 2004

It is demonstrated that the conductivity type of organic semiconductors can be modfied by a mechanism analogous to impurity doping. That is, by suitable choice and control of additives, a given organic host may be rendered either n or p type. Moreover, it is shown that diffusion doping can be employed to form p-n junctions in a variety of organic host materials. Two examples are discussed in detail to demonstrate the feasibility of doping. First, p-type tetrathiotetracene (TTT) is shown to become n type on addition of orthochloronil (OC). The apparent cause is the formation of TTT/OC charge transfer complex molecules within the bulk of the TTT host. Secondly, the normally n-type TTT/OC charge transfer complex is shown to become either increasingly n type or p type on introduction of metal additives. n-type conduction is achieved with group I and IV metal additives and p-type conduction with group II and III metal additives. It is also shown that the additives have a significant effect on the conductivity and the activation energy of conduction. Moreover, the changes in the conductivity of TTT, induced by OC additives, are indicative of a tunneling type conduction mechanism. In contrast, the effects due to metal additives can be described by a simple band model. All experiments were performed with compressed powder pellets and the pellet preparation pressure is shown to have a systematic, residual effect on the material properties. The applicability of the doping technique for the preparation of organic p-n junction diodes is demonstrated by diffusion doping of TTT with OC, TTT/OC complex with Ag and Mg, Perylene with Br, and tetracyano-quinedymethanol-quinolinium (TCNQ/QUIN) complex with Ag. Rectification ratios of up to 200 were recorded using, in all cases, compressed powder diodes.
Microwave Permittivity of the InSb Lattice at 77°K
Authors: Glover Gary H. , Champlin Keith S.
Published: February 2004

This paper reports a direct determination of the relative, static permittivity of the atomic lattice of InSb at 77°K. The measurements were performed on relatively pure (ND≤1014 cm−3) n-type single-crystal samples at 70.1 GHz by utilizing a strong magnetic field (∼40 kG) to immobilize the charge carriers in a direction parallel to the applied TE01°-mode electric field. In this manner, the rf losses normally associated with ``drift'' motion of the charge carriers were made negligible, thus permitting the lattice component of the permittivity to be accurately resolved. The measured relative value, εs=17.78±0.15, compares favorably with several values previously calculated from measurements of the ir reststrahlen spectrum.
Photoluminescence Field Quenching and Breakdown of CdS at 4.2°K
Authors: Yee Jick H. , Condas George A.
Published: February 2004

A quenching of the exciton-related blue-edge photoluminescence was observed in high-purity single crystals of CdS at their electrical breakdown at 4.2°K. The ionization or destruction of the exciton structures by the carriers in breakdown appeared to be an adequate explanation of this quenching. A differential negative resistance was also seen at breakdown and in some crystals after breakdown as well. This negative resistance was also studied in an attempt to understand the origin of the carriers in breakdown.
Avalanche Breakdown in Epitaxial SiC p-n Junctions
Authors: van Opdorp C. , Vrakking J.
Published: February 2004

The reverse current-voltage characteristics of epitaxial SiC p-n junctions were investigated. After electrolytic etching the junctions showed sharp breakdown. The largest value found for the maximum field at breakdown is 5×106 V/cm. Microplasma pulses were observed analogous to but three orders-of-magnitude smaller than those hitherto reported for other materials.
Radiative Recombination in Tin-Doped Germanium
Authors: Hergenrother K. M. , Feldman J. M.
Published: February 2004

Strong radiative recombination with 0.49 eV energy at 77°K is found in Ge containing Sn. It is proposed that this radiation is due to excitons bound to an isoelectronic Sn center.
Recrystallization of Thin Films of α Cu–Ge Alloys
Authors: Ahlers M. , Vassamillet L. F.
Published: February 2004

Ultramicrotomed foils of Cu and Cu-5 at.% Ge were annealed in the electron microscope. Nucleation and growth of recrystallized grains were observed and their orientations determined. It was found that the fastest growing grains had an orientation relationship with the deformed lattice, which could be described in terms of high-order {114} twins.
Effects of Oxidation on Electrical Characteristics of Silicon-on-Sapphire Films
Authors: Ross E. C. , Warfield G.
Published: February 2004

Hall-effect measurements are presented for oxidized and unoxidized p-type silicon-on-sapphire films in the temperature range 77° to 300°K. These measurements show that the dominant scattering mechanism in this temperature range is phonon scattering. The measurements on oxidized films have demonstrated that the mechanism responsible for the observed reduction in acceptor concentration with oxidation is diffusion and preferential redistribution of aluminum from the silicon into the silicon dioxide layer. An additional effect of the oxidation, mobility degradation, is identified as the introduction of scattering centers by the precipitation of neutral aluminum-oxygen complexes.
Measurements of Ionic Species Present in rf Discharges of Argon and Argon-Cesium
Authors: Gilkinson J. L. , Held Herman , Chanin L. M.
Published: February 2004

Mass spectrometric measurements have been made of the ions present in rf discharges of argon and argon containing small concentrations of cesium. Data were obtained for normalized argon and cesium pressures up to 3 and 4×10−3 Torr, respectively. The relative ion singals are functions not only of the argon and cesium concentrations but also of the plasma excitation power. For argon-cesium mixtures the primary ions that are observed are Ar+, Ar2+, and Cs+. Analysis of the data for Ar+ and Ar2+ suggests that Ar2+ is produced by both Hornbeck-Molnar and three-body conversion processes. Interpretation of the results leads to the conclusion that in the present study Cs+ is formed by both direct ionization and by collisions of argon metastables with neutral cesium.
Brillouin Scattering from Ultrasonic Microwave Pulses in LiNbO3
Authors: Farah Oscar G. , Wagner Peter E. , Cummins Herman Z.
Published: February 2004

The spatial intensity distribution of 8.9-GHz longitudinal ultrasonic pulses propagating along the trigonal axis of LiNbO3 has been measured between 80° and 475°K by means of Brillouin scattering. The absolute attenuation coefficient Γ varied from 8±1 dB/cm at 80°K to 31±2 dB/cm at 475°K. Above 150°K, the attenuation could be fitted by Γ=0.53T0.66 dB/cm. Examples are given of other applications of the scattering technique.
Investigation of Thermal Stresses in Silicon by Source Image Distortion
Authors: Carron Gene J. , Walford L. K. , Schoeffel James A.
Published: February 2004

The source image distortion (SID) technique has been used to measure the stresses produced by electron beam melting of small regions of single-crystal silicon wafers. Stress values thus calculated (∼108 Nm−2) agree with other worker's results for stress levels close to the fracture point for single-crystal silicon. For wafers which had fractured, no source image distortion was visible indicating the absence of stress in those wafers.
Some Experimental Observations of the Propagation of Streamers in ``Low Field'' Regions of an Asymmetrical Gap
Authors: Acker F. E. , Penney G. W.
Published: February 2004

Positive corona streamers are observed photographically and by a photomultiplier in a 3.17 cm point-to-plane gap which has a third electrode (a metal ring or disk with a center hole) placed 1.50 cm from the point between the point and plane. The experiments are conducted in room air at room temperature and pressure. Streamers are triggered by voltage pulses superimposed on the direct voltages (sufficiently large that visible steady corona occurs at the 40 μ radius point tip but too small to permit breakdown between any of the electrodes) applied to the gap. For the voltages considered, the experiments support the conclusions and model of Dawson and Winn as opposed to the model of Wright and the evidence of Nasser in that the streamers easily pass through the ring, showing that the streamers do not drastically distort the potential distribution in the gap as they propagate. However, the experiments also show that the value of the electric field far from the point (between the disk and plane) significantly affects the distance a streamer propagates, an effect ignored by Dawson and Winn, and that for a field value of 4.6 kV/cm between the disk and plane, many of the triggered streamers propagate completely across the gap.
Cesium Depletion in the Positive Column of Cs–Ar Discharges
Authors: Waszink J. H. , Polman J.
Published: February 2004

The longitudinal electric field and the electron density and temperature have been measured in the positive column of low-pressure dc arc discharges in mixtures of cesium and argon at densities around 5×1018 and 5×1022 m−3, respectively. The measurements have been made with electrostatic probes and with a microwave interferometer. At a low discharge current cesium alone is ionized. When the discharge current is increased the cesium atom density is reduced by ionization and radial diffusion, and at a critical current a discontinuous transition to a state having a high electron temperature is observed. This discontinuity is explained as the result of a multivaluedness of the electric field as a function of the current density. Even at the present low degree of ionization the electron mobility is found to be strongly influenced by Coulomb collisions.
Exact Solution of Poisson's Equation for Space-Charge-Limited Flow in a Relativistic Planar Diode
Authors: Boers J. E. , Kelleher Dermod
Published: February 2004

Poisson's equation, governing space-charge-limited flow in a relativistic planar diode, is solved assuming the initial velocities of the accelerated particles are zero, through the use of two power series convergent in the potential range 0≤V≤2m0c2/Ze and 2m0c2/Ze≤V < ∞. In the region of lower potential the solution is expressed in a power series in U, a normalized potential. As U becomes small the solution reduces to the well-known Child's Law. In the region of higher potential, a power series in inverse powers of U is employed. As U becomes large the solution reduces to the ultra-relativistic form obtained if v, the particle velocity, can be considered equal to the speed of light. Convergence of both series is rapid, and it is only necessary to retain a few terms to realize a high degree of accuracy.
Heat Conduction in Linear Amorphous High Polymers: Orientation Anisotropy
Authors: Washo Basil D. , Hansen David
Published: February 2004

The anisotropy of heat conductivity that develops on uniaxial stretching of amorphous high polymers has been examined theoretically and experimentally. Experimental measurements on oriented polystyrenes and polymethylmethacrylates show a linear increase in conductivity (parallel to stretching) with increasing elongation. The slope of the relationship is sensitive to the molecular weight distribution of the polymer and the stretching conditions (temperature). The observations are discussed in relation to current theories of heat conduction in polymers.
Magnetization Studies in Nb 3Sn and Ti–Nb Alloys
Authors: McInturff A. D. , Paskin Arthur
Published: February 2004

Magnetization measurements were performed on commercial Nb3Sn and Ti–Nb alloy samples to determine hysteretic loss (magnetization vs magnetic field) and flux-jump stability at 4.2°K in magnetic fields up to 9.3 Wb/m2. The aforementioned superconducting properties were also observed and recorded with various geometries, field sweep rates and thermal environments. The samples consisted of ribbons and/or wires ranging in size from 1.0 to 0.1 cm wide and 0.1 to 0.0001 cm thick. The transport currents ranged from a few amperes to greater than a thousand amperes. These data were obtained utilizing an experimental setup similar to that described by Fietz. The shape and magnitude of the magnetization curves with and without the presence of transport current was not a function of frequency in the range employed, 0.012 to 3.0 Wb/m2·min, except for the multifilament composites. The magnetization and flux-jump stability was found to be a function of the sample dimensions, as would be expected with the earlier expressions given by Wipf, Hancox, Chester, and Stekly. The transport current density was not a function of the dimensions. These data on magnetization and transport current effects are in accord with earlier work by LeBlanc and co-workers on Nb–Zr. There is a first principle derivation of the flux-pinning effects that uses a Josephson junction tunneling model and results in the Kim-Anderson expression. The internal field distribution could be characterized by Hint(x)=(Ha−Hs exp(−x/λ)+Hs,  λ=(Hs−Ha)/Jc(Ha).

The exponential expression for Jc(Ha) vs Ha of Fietz et al. fits the sample data; however, the Kim-Anderson expression that would be the first term in the expansion of the exponential would also fit the observed data within the experimental error. The data concerning transport current and magnetization can be accurately accounted for (in the infinite sheet configuration) by expressions derived by Yasukochi. The thin plate geometry, with the proper demagnetization factor, is in agreement as well.
Currents and Coil Forces as Contour Integrals in Two-Dimensional Magnetic Fields
Authors: Beth Richard A.
Published: February 2004

A general method is given for evaluating currents and coil forces in two-dimensional magnetic fields. When the field components HX and HY are known along a closed contour C in the field plane Z=X+iY and we define H≡HY+iHX, the total current within C is ∮ C HdZ/4πiand the total field force per unit length, F≡FY+iFX, acting on all the currents within C is − ∮ C H2dZ/8π. As an example, the current and coil force are worked out for the uniform field magnet formed by intersecting parallel cylindrical conductors and compared with prior results.
Switching Threshold of Uniaxial Ferromagnets
Authors: Muller M. W. , Goldstein R. M.
Published: February 2004

We calculate the threshold values of applied magnetic field for magnetization reversal or domain formation in uniaxial ferromagnets. The calculation is carried out for ellipsoidal specimens whose dimensions are large compared with typical domain dimensions. The threshold curve reduces to the familiar astroid for thin films whose plane contains the easy axis.
Influence of Spin-Orbit Interaction on the Anisotropy of the Extraordinary Hall Effect in Ferromagnetic Single Crystals
Authors: Thomas G. , Marsocci V. A.
Published: February 2004

In this paper it is demonstrated that the anisotropy, as measured by Hiraoka et al., in the extraordinary Hall constant R1 of nickel can be theoretically predicted but cannot be explained in terms of the anisotropy in the resistivity alone. A quantum calculation, using both the tight-binding approximation and the Karplus-Luttinger theory of the extraordinary Hall effect, is performed to show the existence and estimate the magnitude of the anisotropy in R1. The phenomenological equations for the anisotropy in the resistivity, as derived by Döring, are employed to indicate that Hiraoka's experimental results cannot be explained only in terms of the anisotropy in the resistivity measured in the direction of the Hall voltage.
Dynamic Kerr Observations of High-Speed Flux Reversal and Relaxation Processes in Permalloy Thin Films
Authors: Kryder M. H. , Humphrey F. B.
Published: February 2004

Sequences of photographs with 10 μ resolution have been taken during high-speed flux reversal and as the magnetization relaxes upon termination of the drive field. Equipment used consisted of a sampling Kerr magneto-optic camera with a Q-switched ruby laser for a light source. The 10 nsec exposure time was synchronized with a variable time delay between application of the magnetic field and actuation of the camera stable to within 3 nsec. The results show that, with zero transverse field, longitudinal propagation of diffuse transverse boundaries and nucleation of partially reversed regions are processes that are involved in intermediate and high-speed switching, respectively. The velocity of the diffuse boundary varies approximately as H5, and the mobility is as large as 1.4 cm/Oe·μsec. With a transverse field, the low-speed reversal is similar to diffuse boundary propagation and the higher-speed processes are rotational in nature. The transition from propagational to rotational phenomenon is abrupt. Blocking is easily observable. If the reversing field is terminated prior to saturation, the flux either continues to reverse or relaxes to a less switched condition, in times of the order of 1 μsec, casting considerable doubt on conclusions drawn from interrupted pulse experiments.
Period of a Torsion Pendulum as Affected by Adding Weights
Authors: Saxl Erwin J. , Allen Mildred
Published: February 2004

A precision torsion pendulum with electronic resetting mechanism is described. Prior to each swing, it is held electromagnetically against a stop where it stays for several seconds, held by an automatic time delay. Upon each release, the rotating disk thus has exactly the same starting potential. After a free rotation of several degrees, a beam of light reflected from a mirror on the disk sweeps over a photocell starting a crystal-controlled electronic digital counter. The pendulum then continues clockwise to its maximum excursion and reverses. Upon its counterclockwise return motion it stops the counter as the beam of light sweeps over the photocell in the reverse direction. The recorded times are printed out automatically. They are observed with and without concentric weights added to the rotating disk. In adding weights, there are four factors which act to lengthen the period of the pendulum: the increase in the moment of inertia due to the masses of the added weights, the change in dimensions of the suspending wire, the decreased torsional stiffness of this wire, and the energy used in raising and lowering the disk because of the Poynting effect. The latter three depend on the weights added. When account is taken of these four factors, there is excellent agreement between the observed and computed changes in period with the added loads. Proof is thus furnished that the period of a torsion pendulum is weight sensitive.
Some Characteristics of the Extreme Ultraviolet Spectrum Emitted by the Plasma Produced by Laser Impact on an Aluminium Target
Authors: Dhez P. , Jaegle P. , Leach S. , Velghe M.
Published: February 2004

Spectral emission from plasmas produced by ruby or Nd laser impact on an Al target was studied in the 100–200-Å region using both flow proportional counter and photographic techniques. The maximum intensities of continuous and Al IV line emissions were found to occur in quite different spatial zones of the plasma. The results are compared with those for Al V and Al VI spectra. From the appearance times of the 160.073-Å Al IV line a value of 107 cm sec−1 was obtained for the expansion velocity of the plasma.
Stopping by Elastic Collisions of Kilovolt Ions in Gaseous Mixtures and Amorphous Compounds
Authors: Baroody E. M.
Published: February 2004

Calculations are made of spatial moments 〈zn〉 for particles from a plane source brought to rest in an infinite medium of randomly located target atoms of several kinds. The relationships obtained are illustrated by the determination of the mean penetration 〈z〉 and the straggling parameter Ω= (〈z2〉 − 〈z〉2)1/2/〈z〉 for kilovolt 125Xe ions in WO3. Results compare favorably with published experimental data.
Electroabsorption by Substitutional Copper Impurities in GaAs
Authors: Burgiel J. C. , Braun H. J.
Published: February 2004

Previously, Hall effect and other thermal activation measurements have suggested that a copper atom substituted on a gallium site in GaAs is a double acceptor with its first ionization level at 0.145 eV and its second between 0.44 and 0.49 eV above the valence band. Also, previous photoluminescence measurements have revealed broad lines attributable to copper at the Stokes-shifted positions 0.155 eV and between 0.49 and 0.53 eV. Using an electroabsorption technique, we have studied the spectrum of substitutional copper in GaAs. We find an absorption line associated with a level at 0.463 eV above the valence band for temperatures of 103° and 300°K. We conclude from the selection rules that the wavefunction associated with this level transforms as the Γ6 representation of the double group Td. Except for a weaker additional absorption line (which we do not yet understand) occurring at 0.454 eV in a single p-type sample, we were able to find no other lines. These results supplement earlier work on the 0.145 eV state. We propose a simple model which we feel describes the substitutional copper impurity and apply it to our measurements on the 0.463 eV state and our earlier work on the 0.145 eV state. While this model is not adequate for a first-principles calculation, it does provide a framework in which to understand and discuss our results.
Vibrational Modes of Defects in GaP
Authors: Spitzer W. G. , Allred W. , Blum S. E. , Chicotka R. J.
Published: February 2004

Localized vibrational modes of impurities in gallium phosphide are observed in infrared absorption. Tentative assignments for the observed absorption bands are as follows: ωL=453 cm−1 is due to SiGa, 464 cm−1 to NP or OP 569 cm−1 to 11BGa, and 592 to 10BGa. Other defect bands are observed at 443, 527, and 606 cm−1. However, present experimental results are not sufficient to permit identification of the impurities.
Phase Diagram of the Ternary System Pb–Sn–Te
Authors: Linden K. J. , Kennedy C. A.
Published: February 2004

The phase diagram of the ternary system Pb–Sn–Te has been investigated by experimentally determining the liquidus surface and verifying that certain solidus compositions fall on the pseudobinary PbxSn1-xTe line. This information is useful for growing the pseudobinary compound lead-tin telluride from nonstoichiometric melt compositions.
Studies of Electron Bombardment Damage in GaAs by Thermally Stimulated Conductivity Measurements
Authors: Schade H.
Published: February 2004

Semi-insulating, melt-grown n-type GaAs was irradiated with 1 MeV electrons of densities of 1016−1017 electrons/cm2, thereby introducing 1017−1018 cm−3 defects. The irradiation decreased the dark conductivity and the photosensitivity by about an order of magnitude, indicating that additional acceptor-like recombination centers were generated. However, no additional trapping centers were detected by thermally stimulated conductivity measurements for energies in the range 0.15–0.7 eV from either band edge. This suggests that the centers introduced had larger ionization energies than any other main trap present, namely, >0.5 eV. This is consistent with the effects of electron bombardment on luminescence in GaAs. Moreover, the calculated concentrations of the traps previously present were decreased, especially after the introduction of as many as 1018 cm−3 defects. This apparent decrease at these very high defect densities can be explained by assuming that the carriers tend to recombine via an intercenter process, rather than entering the bands. Annealing was found to remove most, but not all, of the effects of electron bombardment.
Solid Solutions in the Pseudobinary (III-V)-(II-VI) Systems and Their Optical Energy Gaps
Authors: Yim W. Michael
Published: February 2004

Solid solubilities and optical bandgaps on a large number of pseudobinary (III-V)-(II-VI) systems have been studied. Four systems, GaAs–ZnO, GaAs–CdS, InP–ZnO, and InP–CdS, were found to be completely immiscible. Five systems, GaAs–ZnS, GaAs–ZnTe, InP–ZnS, InP–ZnSe, and AlSb–ZnTe, exhibited partial miscibility. Only three alloy systems, GaAs–ZnSe, GaP–ZnSe, and GaP–ZnS, were found to form solid solutions throughout the entire system. The dependence of lattice parameter on composition for the GaAs–ZnSe system is sublinear, while for the GaP–ZnSe and GaP–ZnS systems, it is approximately linear. The dependence on composition of optical bandgap for the first system is sublinear, and the dependence both in the second and third systems is anomalously sublinear, with the greatest changes occurring near the II-VI end component. Preliminary analyses of optical absorption data in all the three miscible systems indicated the existence of direct bandgap material. Preliminary doping results indicated that some GaAs–ZnSe and GaP–ZnSe compositions can be doped both n- and p-type.
Elastic and Anelastic Behavior of V2O5·P2O5 Glasses
Authors: Field M. B.
Published: February 2004

The internal friction of several compositions of V2O5·P2O5 glasses has been measured in the kHz region from 100° to 400°K. A relaxation peak strongly dependent upon composition exists below room temperature in these glasses. The activation energies of the peaks lie between 0.1 and 0.2 eV. The isotropic elastic moduli and densities were measured for some compositions. These glasses are n-type semiconductors. Direct current electrical conductivities ranged from 6×10−2 to 4×10−6 Ω·cm−1 at 100°C over the composition region studied. The connection between the internal friction and the dc electrical conductivity is discussed.
Reordering Diffusion Processes in Amorphous Thin Films
Authors: Longini R. L. , Pansino S. R.
Published: February 2004

Germanium and Mg3Sb2 were vapor codeposited on a low-temperature substrate. The resulting films were amorphous. Subsequent heating to temperatures above room temperature resulted in an ultrafine-grained structure. Conductance measurements, used to follow the annealing process, indicated two distinct annealing modes. At low temperatures, the conductance decreased on annealing. Somewhat above room temperature, a sudden, almost discontinuous, increase in conductance occurred over a very narrow transition temperature interval. Annealing above this temperature resulted in a gradual increase in conductance. Electron microscope studies indicate that the annealing behavior above the transition temperature interval is associated with extensive grain growth, though below it no structure is observable at all. A study of the annealing behavior below the transition temperature interval by means of conduction measurements indicates an activation energy, for what must be a structural change, of about 0.1 eV. An ordinary diffusion process requires an activation energy an order of magnitude higher. A new mechanism is suggested to account for these observations.
Optical Properties of Bismuth-Tellurium Oxide Films
Authors: Lieberman Morton L.
Published: February 2004

Amorphous bismuth-tellurium oxide films have been prepared over a wide composition range by means of multicathodic reactive sputtering. Optical properties of the mixed-oxide films are not algebraic combinations of the optical properties of the single-oxide films. Relatively large quantities of bismuth oxide can be incorporated in virtually colorless mixed-oxide films, because the bismuth oxide undergoes an unidentified transformation. In the high atomic ratio (Bi/Te) region, optical absorption is visible and attributed to the formation of the impurity-stabilized δ-Bi2O3 structure.
Microwave Ultrasonic Attenuation in LiTaO3
Authors: Smith A. B. , Kedzie R. W. , McMahon D. H. , Kestigian M.
Published: February 2004

The acoustic attenuation of shear and longitudinal waves propagating along the c axis in LiTaO3 has been measured from 1 to 9 GHz. Measurements were made from 4° to 300°K using the microwave pulse-echo technique and at 300°K using optical Bragg diffraction. The shear- and longitudinal-wave attenuation in LiTaO3 at 300°K was found to be similar to that of LiNbO3. However, the change in shear-wave attenuation between 4° and 300°K is much smaller in LiTaO3 than in LiNbO3.
In Situ Electron-Microscopic Study of the Growth of Iron Whiskers by Chemical Vapor Deposition
Authors: Gabor Thomas , Blocher John M.
Published: February 2004

α-Iron whiskers were grown under observation in situ in an electron microscope by the thermal decomposition of iron carbonyl in a stream of hydrogen at 710°–820°C. As many as three growth periods with distinct growth rates were observed. An initial slow growth was postulated to be due to growth at the base, caused by localized stresses in the three-dimensional iron deposit on the screen on which the whiskers were growing. Subsequent growth at the tip appeared to be limited by both the impingement rate of iron carbonyl and the surface flux of iron on the shaft of the whisker. The diffusion coefficient, calculated to account for the observed maximum growth rate, is in good agreement with the value given in the literature. Subsequent slower growth was accounted for by the incorporation of the iron contained in the Fe (CO)5 which impinged on the tip alone. The morphological features observed and interpreted were tilting, bridge growth, lateral growth, curving, kinking, junction formation, and neck formation. It was shown that a whisker may grow by plastic deformation under tensile stress and simultaneous deposition on its shaft from a supersaturated gaseous atmosphere.
Curie Temperatures and Residual Resistivities of Nickel-Carbon Solid Solutions
Authors: Schwerer F. C.
Published: February 2004

The Curie temperatures and the electrical resistivity at 4.2°, 78°, and 300°K have been measured for nickel-carbon solid solutions containing up to 1.5 at.% carbon. The resistivity at 4.2°K increases at the rate 3.48±0.06 μΩ cm/at.% carbon; whereas the Curie temperature decreases by ∼30 C°/at.% carbon. The electrical resistivity shows positive apparent deviations from Matthiessen's rule. The variation of the Curie temperature is consistent with donor theories in which carbon donates both its p electrons to the d band of the metal. The susceptibility shows an unusually large field dependence near the Curie temperature presumably because of as yet unclassified modifications of the nickel moment due to the presence of carbon.
Extinction Changes During Annealing of Copper
Authors: Larson John A. , Corey Clark L.
Published: February 2004

``Particle'' or domain sizes and angular misorientations between domains change during the annealing of cold-worked crystals, leading to primary and secondary extinction changes in the x-ray diffraction lines. It has been found that domain sizes are too small in cold-rolled copper to produce significant primary extinction. An attempt was made to avaluate the secondary extinction changes in terms of Darwin's equation. The invalidity of the commonly used form of this equation was shown. With a dislocation model for the substructure it was possible to evaluate the integrated intensity ratio I/Is, with-to-without extinction, in terms of domain sizes which were determined by Fourier analysis of line shapes. It was found that microstrains annealed out prior to recrystallization but that secondary extinction began to change significantly only after the domain size had increased to about 700 Å. Thus there must be a considerable decrease in dislocation density prior to the misorientation changes which accompany secondary extinction increases in copper. It was found possible to predict the strength changes during annealing of copper from the secondary extinction changes associated with x-ray integrated intensity; this is of considerable practical importance for thin sheets.
Extrinsic Photoconductivity from Edge Dislocations in Germanium
Authors: Miles M. Howard
Published: February 2004

Extrinsic photoconductivity on plastically deformed germanium containing predominantly pure edge dislocation arrays were investigated. Conductivity and transient and steady-state photoconductivity were measured on Hall-type samples for current flow parallel and perpendicular to the dislocations. Dislocation photoresponse was observed to be strongly anisotropic with slow nonexponential decay requiring many minutes to achieve steady state at nitrogen temperature. The results are consistent with grain boundary-type potential barriers forming on active slip planes as edge dislocations accept electrons. The spectral response indicates a band of dislocation acceptor states with the majority of trapped electrons located 0.4 to 0.6 eV below the conduction band.
Response of a Triglycine Sulphate Pyroelectric Detector to High Frequencies (300 kHz)
Authors: Hadni Armand , Thomas Robert , Perrin Jean
Published: February 2004

The theory and performance of two types of pyroelectric TGS detectors working at room temperature, one type having electrodes on the front and back surfaces of the crystal plate and the other type with electrodes on the two-side surfaces, have been investigated. They have the same signal-to-noise (S/N) ratio at high frequencies, but the second type detectors, when used with a high-bias resistor, give a higher signal if they have a long edge parallel to the pyroelectric axis. One TGS detector, modified to give a bandwidth of 100 kHz was compared to a gold-doped germanium detector using a CO2 laser as the source. The S/N ratio of the TGS detector is nearly ⅕ of the germanium detector. The type II detector has also been used to study a HCN laser pulse. The possibilities of pyroelectric detectors working at room temperature appears promising in spite of their intrinsic character of thermal detectors.