bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Electron Statistics of the Neutral Acceptor Level of Gold in Germanium
Authors: Ashley K. L. , Ham W. E. , Brown R. T.
Published: February 2004

Detailed correlation of Hall Effect and resistivity data with electron statistics relations have been performed for experimentally determining the degeneracy ratio for the lower acceptor level of gold in germanium. Information on the density of gold in the germanium crystals is deduced through growing indentical crystals except that the dominant shallow impurity is a donor in one case and an acceptor in the other. A value for the degeneracy ratio of four is obtained. The Hall effect data is supported by neutron activation analysis data.
Temperature Dependence of the Transport Properties of Gallium Arsenide Determined by a Monte Carlo Method
Authors: Ruch J. G. , Fawcett W.
Published: February 2004

Transport properties of gallium arsenide in an electric field have been calculated in the temperature range 77°–500°K using a Monte Carlo technique. In intrinsic material it is found that the threshold field for the onset of negative differential mobility changes only slightly over this temperature range increasing from 3.1 kV/cm at 77°K to 3.7 kV/cm at 500°K, while the negative differential mobility reduces from 4200 to 1000 cm2/V sec over the same temperature rise. The influence of impurity scattering on the velocity field characteristic has been considered at 77°K for impurity concentrations of 1015 and 1017 cm−3 and at 300°K for concentrations for 1013, 1015, and 1017cm−3. The threshold field for the onset of negative differential mobility is found to change only slightly while the peak-to-valley ratio decreases significantly with increasing impurity concentration. The temperature dependence of the low-field mobility has been calculated for impurity concentrations of 1015, 1016, and 1017 cm−3.
Laser-Induced Infrared Absorption in Silicon
Authors: Gauster W. B. , Bushnell J. C.
Published: February 2004

Absorption of intense light, of photon energy greater than the bandgap, produces changes in the optical properties of semiconductors. The induced absorption produced by 1.06-μ laser light in high-resistivity single-crystal silicon wafers was measured, by use of a monitor flash lamp, at monitor wavelengths λm = 1.2 to 2.7 μ. The Q-spoiled glass: Nd3+ laser produced pulses of typically 25-nsec duration. The induced absorption increased with monitor wavelength, as expected for a free carrier mechanism. As a function of laser-pulse-energy density, the transmission immediately following the laser pulse was of the form T(λ) = exp (−σλE), with σλ = 1.7×10−17 cm2 at λm = 2.6 μ for Si at room temperature. The exponential dependence is in agreement with an analysis of the induced absorption process, and the value of σλ is in approximate accord with that calculated from measurements of infrared absorption in doped silicon.
Photoluminescent Saturation in GaP (Zn, O)
Authors: Jayson J. S.
Published: February 2004

This paper describes a room-temperature study of the red emission from GaP (Zn, O) as a function of 4880- and 5145-Å photoexcitation intensity, and was initiated to determine the importance of nonradiative bulk recombination centers shunting the radiative path through the Zn–O complexes. The technique used is the investigation of the saturation behavior of the emitted red light as a function of excitation intensity. An analysis is given in which the functional dependence of the red-light emission on such parameters as the excitation absorption coefficient, diffusion length, surface recombination velocity, and excitation beam diameter is considered. The diffusion lengths and surface recombination velocities were obtained by means of low-intensity excitation spectral measurements. Diffusion lengths covering the range 0.5–5.0 μ were measured and surface recombination veloclties from 5 to 100 times the diffusion velocity were extracted. The samples saturated at intensities ranging from 3×1019 photons/sec cm2 to 2×1021 photons/sec cm2. This wide range was correlated with the correspondingly large ranges of diffusion lengths and minority carrier lifetimes. From the analysis and experimental results, it was concluded that (i) for photoexcitation with beam diameters many times greater than the diffusion length the emitted red light will saturate at high excitation intensities, independent of the presence of nonradiative bulk centers, because of nonradiative recombination at the surface. The analysis demonstrated that this conclusion is true even when the excitation penetration depth is ten times greater than the diffusion length. (ii) When beam diameters of the same order as the diffusion length are utilized, diffusion parallel to the surface is important, and it is possible to extract information on the relative importance of bulk nonradiative centers. (iii) Numerical values measuring the significance of the nonradiative bulk recombination centers could not be obtained from the saturation measurements, but the saturation measurements and diffusion length measurements yielded values for the capture cross section of conduction-band electrons into a Zn–O complex σc. The values fall in the range 1.5–4.5×10−16 cm2.
Temperature and Bias Dependence of Zero-Bias Tunneling Structure in GaAs Schottky Junctions
Authors: Carruthers Tom
Published: February 2004

The zero-bias conductance minimum in p-type GaAs–Au Schottky junctions was studied as a function of bias voltage and temperature. The minimum is not well described by the inelastic tunneling model of Duke, Bennett, and Silverstein but can be rather closely matched by the expression G = G0 ln{[(eV)2+ (nkT)2+Γ2]/E02}, where n = 2.4, Γ lies between 3 and 4.5 meV, and E0 lies between 13 and 15 meV.
Photoconduction, Trapping, and Chemisorption Effects in Sputtered Niobium Oxide Films
Authors: Ullman Frank G. , Deertz Carl L. , Smith Lucas W.
Published: February 2004

Thermally stimulated conductivity (TSC) measurements on reactively sputtered niobium oxide films on polished silica substrates have revealed a single set of traps with a depth of 0.26±0.05 eV, similar to those found in tantalum oxide in previous work. The resistance of the niobium oxide films decreases by a few orders-of-magnitude when the film surface is depleted of oxygen and returns to its original value with oxygen readsorption. The TSC measurements indicate the surface oxygen also serves as a trap with a depth of 1.03±0.09 eV. A model is proposed in which singly occupied oxygen-vacancy traps in the bulk compete with singly ionized oxygen traps at the surface for conduction electrons. The surface traps also act as hole traps and to provide charge compensation for the positively charged vacancies.
Shock Initiation of XTX-8003 and Pressed PETN
Authors: Stirpe Dante , Johnson James O. , Wackerle Jerry
Published: February 2004

Explosively driven, plane shock waves were used to study initiation characteristics of wedge- and pellet-shaped samples of PETN (pentaerythritoltetranitrate) pressed to densities of 1.60 and 1.72 g/cc, and the extrudable explosive XTX-8003, a mixture of PETN and an inert material. In each shot experiment the free-surface motion of the final attenuator element and the buildup to detonation of the reactive shock front through the explosive wedge were observed with a streak camera. Initial shock states of the explosives were determined by using the mirror-image approximation and the impedance-matching technique. Quantitative results include the Hugoniots of the unreacted explosives and curves relating the distance to detonation to the input shock pressure. Buildup to detonation in the lower density PETN samples appears to be controlled by a reaction occurring at or near the shock front, as is usually observed in shock initiation studies of heterogeneous explosives. However, buildup to detonation in the higher density PETN appears to be dominated by a reactive pressure pulse that forms well behind the leading shock, and which accelerates until it overtakes the leading shock, after which detonation occurs. Such an initiation behavior is more characteristic of homogeneous explosives.
Characteristics of a Magnetic Energy Storage System Using Exploding Foils
Authors: DiMarco J. N. , Burkhardt L. C.
Published: February 2004

A capacitor bank operating at 15 kV and 34 kJ is used to energize an inductive system of 40 nH. Interrupting the current of ∼800 kA, by means of an exploding copper foil fuse, produces voltages across the fuse of the order of 80 kV. The opening time of the fuse, as well as the characteristics of the voltage developed across the fuse are examined as a function of the fuse dimensions. If transfer of the current into a matching inductive load is to take place at the time of peak voltage, energy transfer efficiency is of the order of 8% with İ's of the order of 2×1012 A/sec.
Diffusional Flow in Polycrystalline Materials
Authors: Green H. W.
Published: February 2004

The thermodynamic theory of equilibrium under nonhydrostatic stress developed by Gibbs and Kamb is applied to obtain the general solution for stress-directed diffusion in an elastically isotropic solid. It is shown that the form of the strain-rate tensor is the same for lattice and grain-boundary diffusion mechanisms and that the relation derived in the classic paper by Herring is a special case of the general theory. Diffusional creep acting by itself cannot lead to steady-state flow; strain rates always decline at high strains.
Magnetization and Susceptibility Measurements of Polycrystalline Niobium
Authors: Brechna H. , Allen M. A. , Cobb J. K.
Published: February 2004

Magnetization and susceptibility data are presented for niobium rod samples in the temperature range of 1.2°–8.9°K. The niobium samples tested had a range of tantalum content from 700 to 4000 ppm. The samples were annealed and degassed in high vacuum at temperatures between 2100° and 2300°C. Values of κ1, κ2, Hc1, Hc2, and Hc are presented as a function of tantalum impurity, and these values are compared with theoretical predictions.
Superconducting Microwave Mixers Utilizing Josephson Junctions
Authors: DiNardo A. J. , Sard E.
Published: February 2004

Microwave superconducting mixers operating at 10–13 GHz utilizing Josephson junctions have been investigated analytically and experimentally. Measurements on mixer sensitivity were carried out at 13 GHz using waveguide-mounted experimental point-contact Josephson junctions at 4.2 K. Results showed sensitivities of −90 dBm/MHz (10−18 W/Hz) which included mismatch losses encountered in the waveguide structure. The Josephson junction mixing mechanism was analyzed on the basis of small-signal modulation of the staircase like dc I-V characteristics. It was shown that a small-signal microwave excitation results in an ac lateral shift of the regions between steps, such that: (a) Optimum Josephson mixing occurs halfway between steps. (b) Mixing occurs between all steps with maximum conversion efficiency between the zero and first step. (c) Predicted low conversion loss and possibly internal gain for a matched mixer. The analytical model was simulated by a digital computer and the behavior of the Josephson mixer predicted for various conditions of excitation. The model chosen for the analysis and the computer simulation is based on the simplest assumptions concerning bulk-formed Josephson junctions. In the laboratory an external local oscillator set 60 MHz below the signal frequency was used to induce the well-known step structure in the dc I-V characteristic of the point-contact Josephson junction. Mixing of the Lo and signal was found to occur between constant voltage steps in agreement with both analysis and computer simulation. The correctness of the model is demonstrated by the agreement between the theory and experiment.
Mechanisms Determining the Critical Current in Hard Superconductors
Authors: Webb W. W.
Published: February 2004

It is well established that critical current densities in hard superconductors depend on pinning of the fluxoid lattice by microstructural inhomogeneities against electromagnetic forces. However, the connection between the measured critical current densities which are continuum quantities and the interactions between the pinning objects and the fluxoid lattice which are virtual point interactions has presented a rather complex problem that is the focus of this review. An experimental approach to diagnosis of the mechanisms and a rather general phenomenological theory are described and illustrated by a summary of some studies of hard superconductors containing high lattice-dislocation densities that provide a high density of rather weak pinning objects. Conclusions of general applicability are summarized.
Characteristics of Photodielectric Optical Detectors Using Superconducting Cavities
Authors: Hartwig W. H. , Hinds J. J.
Published: February 2004

Superconducting cavities loaded with various semiconductor crystals form a unique class of digital optical transducers. There are several low-temperature photodielectric effects in semiconductors. They are used to tune superconducting cavity resonators and have been demonstrated as laser detectors and for optical feedback control of the resonant frequency. The free-carrier PDE is due to inertia forces on mobile carriers and the trapped carrier PDE is due to polarizability changes on entering a trap. Recent work by Hartwig, Hinds, and Khambaty (unpublished) shows most semiconductors display mixtures of the two effects. The present state of knowledge supports a preliminary design rationale for radiation detectors. This paper establishes the link between the several photodielectric mechanisms, the properties of the superconducting cavity, and accepted standards of qualifying a radiation detector.
Sputtered Thin-Film Superconductor-Semiconductor Tunnel Junctions
Authors: Keller W. H. , Nordman J. E.
Published: February 2004

Thin-film tunnel junctions using a semiconductor rather than an oxide barrier have been fabricated. Niobium, used for the bottom layer, and the semiconducting center layer were deposited using rf sputtering techniques, while the top layer was evaporated lead. Sputtering was done from high-purity single-crystal slices of Ge, Si, and GaAs and from polycrystalline InSb. Superconductive tunneling was observed in most samples. The semiconductor tunnel junctions were somewhat light/heat sensitive and also exhibited a nonlinear I-V characteristic at voltages greater than the superconducting energy gap to a greater extent than comparable oxide devices. Excess current was noted in the devices at voltages below the superconducting gap and the measured gap of the niobium film was found to be reduced from that of pure material. Although initial devices were inferior to good oxide junctions, present results show that techniques of rf-bias sputtering and sputter etching have strong possibilities for the production of deposited insulator junctions.
Observation of Single Fluxon Drift through a Superconductor
Authors: Burnette K. T. , Newhouse V. L.
Published: February 2004

This paper reports what is believed to be the first direct observation of the drift of single fluxons through a superconductor. This has been achieved by using an ultrasensitive cryotron amplifier to sense the changes in persistent current which occur in a superconducting film loop when a fluxon is drifting into or out of the loop. The loop is deposited on an insulated superconducting ground plane; this decreases the inductance sufficiently so that the current changes induced by single fluxons entering or leaving the loop can be sensed. It has been found possible to nucleate single fluxons by current pulsing narrow films which are superimposed over but insulated from the loop. The fluxons are found to be nucleated at the intersections of the edges of the film loop with the superimposed films, and then swept into or out of the loop by the Lorentz force exerted by the loop current. The fluxon velocity component normal to this current has been measured for tin and is found to be less than a factor of two different from the values predicted by certain of the present theories of fluxon motion.
High-Current ac Losses in Large Superconducting Niobium Tubes
Authors: Meyerhoff R. W. , Beall W. T.
Published: February 2004

Loss measurements were made at 60 Hz on 6-m lengths of 1- and 3-cm-diam superconducting niobium tubes used as the inner conductor of a coaxial line. These tubes carried transport currents up to 1700 and 5300 A, respectively. The losses were found to fit the relation P=fAEc1(H/Hc1)n,where f is the frequency, A is the surface area, Ec1 is the energy loss per unit surface area per cycle at Hc1, the lower critical magnetic field, and H is the peak magnetic field at the surface of the superconductor. The exponent n equals 3 for H≤Hc1 and n≥4 for H≥Hc1. The ac losses showed a 25% linear increase with temperature from 4.2 to 5 K. For the case of an eccentric coaxial line, where the current and magnetic field vary about the circumference of the superconductor, the ac losses were found to agree with those predicted from calculated values of the current and magnetic field distributions. In particular, when the peak surface field is less than Hc1 and R is the ratio of the maximum to minimum surface magnetic fields about the circumference of the superconductor, the losses were a factor (3R2+2R+3)/4R greater than those found at an equivalent current for a concentric configuration.
Comparison of Superconducting and Semiconducting Bolometers
Authors: Bertin C. L. , Rose K.
Published: February 2004

Superconducting tin bolometers are now reasonably well understood, and the results of calculations of performance are given over a large range of sheet resistances (0.01–1000 Ω/□ at 4.2°K). Comparison of superconducting bolometers with semiconducting ones show that tin and germanium are equivalent in performance. The superconducting devices have the additional advantage of simplicity of sample preparation and lower impedance levels permitting higher operating speeds if desired.
Nuclear Radiation Detection Using a Superconducting Resonant Cavity
Authors: Alworth C. W. , Haden C. R.
Published: February 2004

Nuclear radiation is detected using a superconducting resonant circuit operated at 380 MHz. The technique uses a doped semiconductor crystal placed on the stub of a reentrant cavity. The cavity is lead plated and cooled to 4.2°K, such that it becomes superconducting. The cavity then becomes the frequency controlling element for a voltage variable oscillator. Nuclear radiation impinging on the crystal causes a change in the relative dielectric constant, which in turn causes the resonant frequency of the cavity to change. The crystal exhibits a peculiar trap property at 70°K or below, which allows any electron-hole pairs generated in the crystal to be indefinitely trapped. The output frequency of the resonant circuit is then proportional to the total dose received by the crystal. Frequency shifts of the order of 4.051 kHz/min are observed in CdS, for a 14C source of 1 μ Ci.
High-Frequency Limit of the Josephson Effect
Authors: McDonald D. G. , Evenson K. M. , Wells J. S. , Cupp J. D.
Published: February 2004

Coherent detection of applied radiation via a Josephson current step has been achieved with an applied frequency approximately a factor of 3 higher than heretofore reported. The detected signal is at 2.5 THz (118 μ). The inadequacy of existing theory to predict the frequency dependence of the Josephson effect is discussed.
Characteristics of NbN Dayem Bridges
Authors: Janocko M. A. , Gavaler J. R. , Jones C. K. , Blaugher R. D.
Published: February 2004

Dayem-bridge weak links have been fabricated by sputter etching niobium nitride thin films having Tc's of ∼15 K. These junctions exhibit a negative resistance region extending to 45 mV at 3.2 K, in which are seen self-induced subharmonic current steps and structure near the energy gap voltage. Temperature dependence of these features and effects of applied microwave radiation are discussed, and possible explanations of the negative resistance region and of the self-induced step structure are given.
Incubation Time Versus Applied Electric Field and Lattice Loss Coefficient for Acoustic Waves in Low-Resistivity CdS
Authors: Preier Horst
Published: February 2004

The lattice loss coefficient αl for acoustic waves in low-resistivity (0.6 Ω cm) CdS was determined from the electric-field-dependent incubation time. At the frequency of the maximum gain, the value for αl lies between the extrapolated experimental curves as measured by Bateman and McFee [J. Appl. Phys. 39, 4471 (1968)] and by Zucker, Zemon, and Wasko [Proc. Int. Conf. Phys. Semicond. 9th Moscow, 1968 2, 904 (1968)]. Two simple theories for the field dependence of the incubation time were compared and critically analyzed.
Longitudinal Magnetoresistance Anomalies
Authors: Fickett F. R. , Clark A. F.
Published: February 2004

We have observed the anomalous longitudinal magnetoresistance conditions R(H) = 0 and 0<R(H) < R(0) on a [111]-oriented copper crystal specimen. The magnetoresistance voltages measured by two probe sets on mutually perpendicular faces of the specimen are observed to have a significant difference. Both of these effects are shown to be due to very slight misorientations of the specimen with respect to the magnetic field. In light of the observations, we present some precautions which should be observed in making longitudinal magnetoresistance measurements on high-purity materials.
Dielectric Relaxation of ZnF2:LiF and Its Crystallographic Orientation Dependence
Authors: Roth Thomas A.
Published: February 2004

The thermally activated release of the dielectric polarization of ZnF2:LiF crystals has been studied using the ionic thermoconductivity method. Measurements of the current discharge are made in single crystal samples oriented for polarization in the [001], [100], and [110] directions in order to study the crystallographic orientation dependence of the dielectric relaxation process. Strong discharge currents are observed only for [001]-oriented crystals. The important parameters (including the activation energy, relaxation time, and number of dipoles) for the process are determined; the change in dipole orientation causing the discharge is examined in relation to possible anion vacancy movements in the lithium-doped zinc fluoride crystal structure. The results confirm that the dielectric relaxation of lithium-doped ZnF2 is dependent upon the crystallographic orientation of the dielectric material.
Optical and Ferroelectric Properties of KxNa1−xBa2Nb5O15
Authors: Smith Archibald W. , Burns Gerald , O'Kane D. F.
Published: February 2004

The ferroelectric tungsten—bronze system KxNa1−xBa2Nb5O15 is studied particularly in the region x=0.7–0.9 where the crystals remain tetragonal down to at least 77°K. These crystals should have many applications in the quantum electronics field. The temperature and wavelength dependence of the two indices of refraction are reported as well as the temperature dependence of the linear electro-optic constant and the nonlinear optical effect (second-harmonic generation). These quantities are discussed in terms of a model that treats these ferroelectrics as biased paraelectrics, the biasing field being supplied by the spontaneous polarization. The agreement is fairly good. To demonstrate the usefulness of these materials an x=0.8 crystal was used for the efficient intracavity harmonic generation of 0.53-μ light using a 1.06 μ Nd–YAG laser. The same crystal was used to phase lock the laser, thus increasing the harmonic power.
Oscillations of a Gas Bubble in Viscoelastic Liquids Subject to Acoustic and Impulsive Pressure Variations
Authors: Fogler H. S. , Goddard J. D.
Published: February 2004

An analysis is presented of the forced oscillations of a gas-filled bubble at rest in a large body of a linear viscoelastic fluid. Two types of forcing are considered. In the first, oscillations are induced by a pressure surge on the system. For the three-parameter fluid model employed, numerical computations show that for a given ratio of the fluid's elastic modulus to the pressure surge, the damping of the bubble motion exhibits a maximum as a function of the fluid relaxation time at a value of this parameter equal approximately to one-fifth the natural period of oscillation. At very high or very low relaxation times, the damping becomes insignificant. As the second type of forced oscillation, we consider the motion induced by the application of ultrasonic waves to the system. Here, damping is found to depend strongly on the product of impressed frequency and fluid relaxation time.
Thermal Diffusivity of Heterogeneous Materials
Authors: Kerrisk Jerry F.
Published: February 2004

The concept of the thermal diffusivity as a characteristic constant of a heterogeneous material is examined. By considering the derivation of the heat conduction equation, and the concept of the thermal wavelength associated with a particular problem, a general criterion for the homogeneity of a material under transient conditions is obtained. This criterion limits the scale of heterogeneity of the material (expressed as a lattice spacing) to be much smaller than the minimum thermal wavelength associated with the problem. The flash method of measuring the thermal diffusivity is considered in detail. The criterion developed limits the particle size of a particulate phase to be much smaller than the sample thickness for the sample to be considered homogeneous, and for the usual relation between the thermal diffusivity and thermal conductivity to hold.
Versatile Superconducting Femtovolt Amplifier and Multimeter
Authors: Lukens J. E. , Warburton R. J. , Webb W. W.
Published: February 2004

We describe the adaption and use of superconducting quantum interference magnetometers for the measurement of voltage, resistance, and inductance. The instrument which we discuss achieves the Nyquist noise limit, about 10−22 W of noise power in a 1-Hz bandwidth, over a wide range of conditions. This permits resistance measurements down to this power level and a voltage sensitivity of a few femtovolts for low impedance sources. Using a 10-μA measuring current, inductance changes of 0.1 pH have been measured. We discuss in detail the noise limitations of the device and the design criteria for optimum performance. Circuit and construction designs are presented which allow the device to be used, with minimal changes, for measurements over a wide range of parameters.
Thermal Properties of Synthetic Fluorapatite Crystals
Authors: Hopkins R. H. , Damon D. H. , Piotrowski P. , Walker M. S. , Uphoff J. H.
Published: February 2004

Measurements of the heat capacity, thermal expansion, and thermal conductivity on synthetic crystals of undoped and neodymium-doped fluorapatite are reported. Fitting the low-temperature specific heat data to a Debye model yields a Debye temperature of 550°K. At 25°C the thermal expansion coefficients are 10.0×10−6 °K−1 and 9.4×10−6 °K−1, respectively, along the [0001] and [101̄0] directions. The thermal-expansion measurements yield a Debye temperature of 500°K. A typical value of the thermal conductivity is 0.020 W cm−1 °K−1 at room temperature. The thermal conductivity is only feebly temperature dependent and, similar to the thermal-expansion coefficient, shows very little crystallographic anisotropy.
Laser Action and Spectroscopic Properties of Er3+ in YAlO3
Authors: Weber M. J. , Bass M. , deMars G. A.
Published: February 2004

Stimulated emission at 1.663 μ due to a 4S3/2→4I9/2 transition has been observed from Er3+ ions in a crystal of YAlO3. The threshold for pulsed laser action at room temperature was 52 J. Crystalline Stark levels determined from absorption and fluorescence spectra and fluorescence lifetimes of YAlO3:Er3+ are reported.
CO2 Laser Heterodyne Plasma Diagnostics in an Adverse Environment
Authors: Zucker O. S.
Published: February 2004

A CO2 laser heterodyne system was successfully used to measure plasma density-length product (DLP) in the 1013–1014-cm−2 range, with μsec response. This was done in the extremely adverse environment of the Astron-controlled fusion experimental area at the Lawrence Radiation Laboratory, Livermore. The results indicate that the system is capable of covering a plasma DLP range of 1012–1016 cm−2 with 20-nsec response.
Study of a Self-Pulsing GaAs Laser by Intensity Correlation in Lithium Iodate
Authors: Gloge D. , Lee T. P.
Published: February 2004

Nonuniform excitation of tandem-bisected GaAs lasers produces light pulses whose width is not resolved by presently available photodiodes. We have used an intensity correlation technique involving phase matched second harmonic generation in LiIO3 to investigate the output of such a laser. From this measurement we inferred a pulse width of 100 psec.
Laser-Driven Waves in a Freely Expanding Gas Jet
Authors: Thompson H. M. , Rehm R. G. , Daiber J. W.
Published: February 2004

The focused output of a ruby laser has been used to drive waves which travel in the same direction as the laser beam. The density gradient produced by expanding high-pressure air or hydrogen into a vacuum was irradiated by the laser from the vacuum side of the jet. A luminous plasma was observed to propagate up the jet, through the orifice, and into the gas reservoir. Observations of this type have application to the study of comparable waves generated at the surface of a solid. Measurements of the luminous front velocity are reported over the gas density range of 1–7 amagats and laser power range of 100–500 MW. The scaling relations for this front velocity with laser intensity and gas density are derived for many of the interaction models proposed in the literature. Only the gasdynamic model with fluid motions induced during laser heating compares favorably with the data.
Pull-In Phenomena of Josephson Oscillators
Authors: Fack H. , Kose V.
Published: February 2004

Constant voltage steps in dc current-voltage characteristics occur by assuming pull-in phenomena. Based on this concept, steps above the gap voltage and frequency dependence of the step amplitudes are found.
Maximal Output PowEr of Point-Contact Josephson Junctions
Authors: Fack H. , Kose V.
Published: February 2004

A simple model is considered in order to describe point-contact Josephson junctions as oscillators. The maximal output power of these generators into a matched load is determined as a function of frequency.
Effect of Noise on the Current-Voltage Characteristics of a Josephson Junction
Authors: Lee Patrick A.
Published: February 2004

The effect of noise on the current-voltage characteristic of a Josephson junction is investigated (1) when the temperature is near the transition temperature of the superconductors and (2) when the junction is driven by an external signal. In case (1) the noise source is the quasiparticle tunneling current but in case (2) there is in addition the noise arising from the finite linewidth of the external signal. This latter noise source is shown to dominate when the junction is operating at high harmonics. We treat the problem in the limits of small and large capacitance and obtain a criterion to determine under what circumstances each limit applies. A solution that includes a first-order correction due to a finite capacitance is given. In the limit of large capacitance the existence and lifetime of hysteresis curves are discussed.
Magnetic Perpendicular Anisotropy Due to Substrate Constraint in Ni–Fe and Ni–Co Thin Films
Authors: Johnson G. O. , Wilts C. H.
Published: February 2004

The contribution to the magnetic uniaxial perpendicular anisotropy which arises from substrate constraint through magnetostrictive effects has been measured in Ni–Fe and Ni–Co thin films evaporated on substrates at room temperature. This was accomplished by measuring the perpendicular anisotropy before and after removal of the film from the substrate. Data are given for the predominantly fcc crystal structure regions of both alloy systems. The constraint contribution to the perpendicular anisotropy correlates well with the value of the bulk magnetostriction constant using the equation ΔK⊥=32λsσ. Measured values of isotropic stress for films thicker than 600 Å were 1.6×1010 dyn/cm2. In films less than 600-Å thick the isotropic stress decreased with decreasing thickness.
Temperature and Field Dependence of Magnetization of Amorphous (Fe, Mn)-P-C Alloys
Authors: Sinha Ashok K.
Published: February 2004

Amorphous quasibinary alloys having the composition (Fe1−xMnx)0.75P0.15C0.10, where 0.0≤x≤1.0, were synthesized by rapid quenching from the liquid state. Their magnetic behavior was characterized by measurements of the magnetization as a function of temperature in the range 4.2°–300°K, and in fields ranging from 1 to 8.5 kOe. The iron-rich alloys with 0.0≤x≤0.4 are ferromagnetic: the magnetic moment at 0°K decreases linearly from 2.07 μB/Fe atom in Fe0.75P0.15C0.10 to 0.22 μB/(Fe, Mn) atom in (Fe0.6-Mn0.4)0.75P0.15C0.10. Judging from the large values of the parameter qc/qs, where qc and qs are the number per mole of magnetic carriers in the paramagnetic and ferromagnetic states, respectively, and also from the nonsaturating behavior of magnetization with field at 4.2°K, it appears that the ferromagnetism in these alloys may be of the itinerant kind. Alloys having 0.5≤x≤1.0 possess considerably more complex magnetic structures. They are characterized by a peak in the magnetization curve at temperatures between 15° and 40°K, and a ferrimagnetic-type curvature in the Curie-Weiss plots. This kind of magnetic behavior may be ascribed to ferrimagnetism existing in conjunction with parastic antiferromagnetism over some local regions in the amorphous structure.
Parallel Pumping of Phonons in Yttrium Iron Garnet at 114 MHz
Authors: Sage J. P.
Published: February 2004

The process of magnetic parallel pumping of phonons in magnetostrictive materials has been investigated experimentally using a single-crystal sphere of yttrium iron garnet at a pump frequency of 114 MHz. Theoretical results presented elsewhere have been verified in detail. The frequency dependence of the threshold field shows characteristic phonon resonances whose frequencies shift with temperature and static field and whose Q values and line shapes can be measured and compared with theory. In addition, the dependence of the average threshold on bias field and crystal orientation can be studied. By using an rf signal with rapid amplitude and phase modulation, one can learn about the dynamics of the pumping process. Double mode pumping, in which two rf signals at nearby frequencies are applied, has also been performed both to test the suitability of the process to frequency selective limiting and to observe a frequency shift found to be induced in all the phonon resonances when a phonon is driven unstable. The latter effect is not adequately understood.
Superparamagnetism and Exchange Anisotropy in Microparticles of Magnetite Embedded in an Inert Carbonaceous Matrix
Authors: Aharoni Shaul M. , Litt Morton H.
Published: February 2004

By the controlled thermal degradation of ferricinium nitrate a material composed of iron oxide particles embedded in an inert carbonaceous matrix was obtained. The iron oxide particles were found to be mostly magnetite, and their average diameter about 35 Å. This value was obtained from both x-ray diffraction line broadening and from static magnetic measurements. The small particle size caused the material to be superparamagnetic down to and below liquid-nitrogen temperature. At liquid-helium temperature the material was ferromagnetic and exhibited exchange anisotropy in the form of a shifted hysteresis loop. A coupling energy of 2.28×105 erg/cm3 was calculated from the shifted hysteresis loop. EPR and Mössbauer-effect spectra showed electron hopping at room temperature within the Fe3O4. In the ferromagnetic state, local disorder around the magnetic ions manifests itself as broadening of the Mössbauer spectra and displacement of the hysteresis loop.
Experimental Verification of the ``Blocking Curve'' in Thin Permalloy Films
Authors: Hoffmann Horst
Published: February 2004

An experimental verification of the theoretically predicted blocking curve in thin uniaxial ferromagnetic films is given. Hysteresis, associated with blocking, was investigated by means of a high-sensitivity torquemeter (rotational hysteresis). The blocking curve could be determined in two different ways: (i) by investigating the rotational hysteresis and (ii) by evaluating the structure constant S by means of transverse susceptibility measurements and calculating the blocking curve from the resulting value of S. Both results agree and show the existence of the blocking curve. It follows that the single-domain theory cannot be used to discuss critical effects such as magnetization switching.
Monte Carlo Calculations of the Electron-Sample Interactions in the Scanning Electron Microscope
Authors: Shimizu Ryuichi , Murata Kenji
Published: February 2004

The Monte Carlo technique was applied to the fundamentals of the Electron Probe Microanalyzer (EPMA) and the Scanning Electron Microscope (SEM). A model based on the multiple scattering formula of Lewis was applied to simulate the scattering processes of the primary electrons in the specimen and was exemplified by comparison with the experimental results on the escape electrons, the backscattered electrons, and the secondary-electron yield, and good agreements were obtained. As simple approaches to further study, the lateral distributions of the backscattered electrons and the secondary electrons on the specimen surface were calculated from the Monte Carlo procedure which has brought about very useful knowledge on the resolving power of both the scanning image of the backscattered electrons in EPMA and SEM.
Graphical Analysis of Time-Dependent Spectra
Authors: Adam G. , Katriel J.
Published: February 2004

Graphical component analysis is suggested for any quantity which arises from the contribution of several differently time dependent components. The method is widely applicable and easily programmable. Its use to the analysis of mixed radioactive sources is demonstrated.
Light Scattering by a Rotating Disk
Authors: Crosignani Bruno , Daino Benedetto , Di Porto Paolo
Published: February 2004

The theoretical expression of the power spectrum of laser light scattered by a ground-glass rotating disk is investigated. In particular, it is shown that the coherence time is not always determined by the transit time of the disk through the illuminated area. The results of several measurements of the conditional probability of scattered light, which exhibit a good agreement with the theory, are presented.
Stimulated Raman Effect in Ortho-Phosphoric Acid
Authors: Parkash Ved , Jaseja T. S.
Published: February 2004

Stimulated Raman emissions from phosphoric acid solutions of varying concentrations were studied. A 99% concentrated solution produced one Raman line (910 cm−1). However, the solution of concentration ≤85% produced three more sharp lines close to the Raman line (910 cm−1) which were not observed earlier in the corresponding spontaneous Raman effect. It was also found that no Raman line shifted its position when the concentration of the solution was varied, contrary to the earlier observations on the corresponding spontaneous Raman emission (914 cm−1). The stimulated Raman emissions were found sharp even under multimode excitations.
Resonantly Sustained Discharges by dc Current and High-Frequency Power
Authors: Leprince P. , Matthieussent G. , Allis W. P.
Published: February 2004

New results are obtained on plasma column resonances subjected to a high-frequency field for the case of high incident power. The resonance shift and hysteresis are measured with good accuracy. A theoretical model based on the energy balance of the electron gas is established. It is shown that the plasma is maintained in a resonant state by the high-frequency (HF) power with or without dc current. A graphical method to determine the electron density variation due to the HF field is described. This method predicts correctly the resonance shift and the hysteresis.
Correlation of Hydrogen Evolution with Surface Blistering in Proton-Irradiated Aluminum
Authors: Daniels Raymond D.
Published: February 2004

The outgassing behavior of aluminum samples irradiated with 100-keV protons was studied during annealing to determine the relationship between hydrogen evolution and observations on blister formation during annealing. The outgassing process appears to be diffusion controlled and competes with the process of blister formation for the available hydrogen.
Crystals and Epitaxial Layers of Boron Phosphide
Authors: Chu T. L. , Jackson J. M. , Hyslop A. E. , Chu S. C.
Published: February 2004

The thermal decomposition of diborane-phosphine mixtures in a hydrogen atmosphere and the thermal reduction of boron tribromide-phosphorus trichloride mixtures with hydrogen have been used for the deposition of boron phosphide on the basal plane of hexagonal silicon carbide substrates. In the thermal decomposition process, the substrate must be maintained at temperatures below 900°C to minimize the contribution of gas-phase reactions, and the boron phosphide layers showed only preferred orientations. The thermal reduction process was carried out over a wide temperature range, and the boron phosphide layers deposited on the silicon face of silicon carbide substrates at 1050°–1150°C were found, by optical microscopy and reflection electron diffraction examinations, to be single crystalline and epitaxial with respect to the substrate. Epitaxial boron phosphide layers prepared by the halide reduction reaction without intentional doping are p type with a room-temperature carrier concentration of approximately 1019 cm−3. Resistivity measurements in the temperature range 300°–1000°K indicated the presence of two impurity states with activation energies of approximately 0.22 and 0.66 eV, respectively. Needle-shaped boron phosphide crystals have also been obtained by the halide reduction reaction. They are single crystals with the elongated axis along a 〈111〉 direction and are p type with a room-temperature resistivity of approximately 20 Ω cm.
Distribution Coefficient of Germanium in Gallium Arsenide Crystals Grown from Gallium Solutions
Authors: Rosztoczy F. E. , Wolfstirn K. B.
Published: February 2004

Gallium arsenide crystals doped with germanium were grown from gallium solutions at 900°–875°C. The Ge concentration in the liquid was varied from 0.004 to 56 at.%, and the Ge concentration in the GaAs crystals determined using radiotracer and other techniques. The Ge concentration in the solid varied linearly with increasing Ge concentration in the liquid up to 5 at.% and kGe = (Ges)/(Gel)=0.0083±0.001. Above 5-at.% Ge in the growth solution, kGe increased. At low doping levels Ge acts predominantly as a simple acceptor substituting on arsenic sites. At high doping levels, in the extrinsic range, the Ge concentration in the solid is considerably greater than the free carrier concentration. The form in which the excess Ge exists is not known.
Electrical Conduction in Amorphous and Semicrystalline Ni–Cr–SiO Films
Authors: McMaster Alexander D. , Fuschillo Nicholas
Published: February 2004

A resistance maximum with respect to temperature has been observed in 40 Ni-10 Cr-50 SiO v/0 films of thickness 500–2200-Å vacuum coevaporated onto amorphous SiO2 substrates maintained at room temperature. The maximum occurs at a temperature TM between 275° and 325°C. On successive thermal cycling to 500°C the resistivity of the film decreases and the resistivity peak shifts to somewhat higher temperatures. The phenomena are attributed to short-range ordering processes occurring in the temperature range 200°–350°C due to the absence of significant oxidation. When the films of resistivity 200–1000Ω per square were deposited onto substrates maintained at 300°C, the resistivity maximum disappears and the films showed a near zero temperature coefficient of resistivity and excellent cyclic stability from 25° to 350°C. All films were apparently amorphous as determined by transmission electron microscopy and electron diffraction. Depositions and annealing of films at temperatures up to 600°C led to crystalline films and to the general rule that films of up to a thousand ohms per square deposited or annealed at a temperature TM exceeding 300°C are cyclically stable at least up to TM and exhibit near zero temperature coefficient of resistance.
Emission of Microwave Noise Radiation From InSb
Authors: Fleming W. J. , Rowe J. E.
Published: February 2004

Low-field 10-GHz noise radiation and attendant rf current oscillations are generated in 10-mm-long specimens of n-type InSb at 77°K. Using a special experimental arrangement, both the azimuthal and the polar orientation of the applied magnetic field can be varied and the spatial distribution of the radiation along the length of the InSb specimen can also be measured. Two distinct modes of low-field radiation are found in InSb specimens. One mode of radiation (B∥ mode) prevails when the magnetic field is aligned parallel to the direction of current flow and the other mode of radiation (B∥ mode) prevails when the magnetic field is aligned transverse to the direction of current flow. The B⊥ mode of radiation is investigated in considerable detail and it is determined that a reproducible anisotropic radiation pattern of twofold periodicity is obtained when a transverse magnetic field is rotated in the azimuthal plane around the InSb specimen. A computer analysis using a theory which incorporates an acoustoelectric interaction, involving off-axis acoustic waves, shows good agreement with the experimental azimuthal radiation patterns of the present experiment and other related experiments. It is concluded that an acoustoelectric-type interaction is involved in both the B⊥ and B∥ modes of low-field noise radiation.
Evaluation of Silicon Nitride Layers of Various Composition by Backscattering and Channeling-Effect Measurements
Authors: Gyulai J. , Meyer O. , Mayer J. W. , Rodriguez V.
Published: February 2004

Composition and density of silicon nitride layers deposited on silicon by the NH3–SiH4 reaction at 850°C were measured as a function of the reaction components. Backscattering and channeling-effect measurements with MeV 4He ions were used to determine the depth dependence of the concentration ratio of nitrogen to silicon and density. The compositions of the silicon nitride layers were stoichiometric with densities approximately 3.0 g/cm3 for NH3/SiH4 deposition ratios greater than 10. For lower ratios, the concentration of nitrogen decreased and that of silicon increased. The variation of the concentration ratio of nitrogen to silicon follows the variation in the physical and electrical properties of the layers.
Properties of Very Thin Aluminum Films
Authors: Meservey R. , Tedrow P. M.
Published: February 2004

Thin films of aluminum have been produced in the thickness range of 1000–30 Å in small area samples with photoetched edges. The superconducting transition temperature Tc, the critical magnetic field Hc, and the room-temperature conductivity have been measured as a function of thickness d. The results indicate that films as thin as 30 Å act essentially as uniform layers in which the crystal size is approximately equal to the film thickness. The transition temperature was found to vary linearly with d−1. Hc (T) was measured from Tc to 0.4°K. For thickness from 1000 to 200 Å, Hc∼d−3/2, as expected from the Ginzburg-Landau theory. For d <200 Å, Hc is paramagnetically limited to about 49 kOe = 19.6Tc, slightly above the Clogston limit.
Comparison of NbTi and Nb3Sn Material Tests with the Actual Performance of Coils
Authors: Coffey D. L. , Gauster W. F. , Lubell M. S.
Published: February 2004

A 100-kG, 8.26-cm-bore, 40-kJ Nb3Sn magnet and a 75-kG, 10.2-cm-bore, 95-kJ twisted filament NbTi magnet have been constructed and tested. A number of other magnets of smaller size using both the Nb3Sn and twisted filament NbTi conductors will also be described. Material evaluation tests leading to these magnet designs will be reported. They include short sample tests with controlled surface cooling conditions and cusp coil tests in which an external field is applied perpendicular to the cusp coil axis. Finally, two successful stabilization techniques for Nb3Sn ribbon will be presented with coil performance data before and after the stabilization has been employed.