bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric Properties of Stable and Metastable Phase-III KNO3
Authors: Taylor G. W. , Lechner B. J.
Published: February 2004

The ferroelectric properties of stable phase-III polycrystalline and single-crystal KNO3 have been studied at temperatures up to 150°C and hydrostatic pressures up to 20 000 psi. Results obtained show phase III has two Curie points, the upper increasing and the lower decreasing with pressure. At constant temperature near the center of phase III, the polarization increases linearily with pressure at 0.007 μC/cm2/atm. Within the stable phase-III region, KNO3 suffers no shelf or excitation decay, has a significant t* effect with a power-law E dependence, and has its switching speed decrease exponentially (τ≃10 sec) as the time between reversals increases. Disturb-pulse measurements show that the exponential high-E dependence of the switching time continues down to low E with an eventual reduction of α. Switching times as long as 10 min have been observed at low E. For typical matrix memory operation, only about 103 disturb pulses can be tolerated. The indications of a threshold field seen in metastable phase-III KNO3 appear to be due to field-induced ferroelectricity.
The Character of Modes in Small Axially Magnetized Ferrite-Filled Waveguides
Authors: Vasile Carmine F. , La Rosa Richard
Published: February 2004

The modes of small, lossless, axially magnetized, ferrite-filled waveguides of various cross sections are described. The transverse dimensions are taken to be small compared to the dielectric wavelength in order to permit an accurate approximation. The approximation along with a new method of analysis greatly simplifies the description of the fields. Sketches of the transverse b, e, and h patterns are given for cylindrical, coaxial, and square cross sections. Formulas for the field components of each case considered are tabulated. The modes of rectangular waveguide, which cannot be described in a closed form solution, are discussed.
Input Admittance of a Cylindrical Antenna in a Magneto-Ionic Medium
Authors: Seshadri S. R.
Published: February 2004

The input admittance of a cylindrical antenna immersed in a magneto-ionic medium with the magnetostatic field parallel to the axis of the antenna is investigated and is found to become infinite for an idealized delta-function voltage generator. Depending on the frequency and the plasma parameters, either the susceptance, which can be inductive or capactive, or the conductance, which is always positive, is infinite. For the practical case of highly localized generators, these infinites become finite, but remain relatively large. The occurrence of such large values of the input admittance of an antenna in a magneto-ionic medium can be used to obtain information on the relative values of the magneto-ionic parameters.
Characteristics of Thermal Annealing of Radiation Damage in MOSFET's
Authors: Danchenko Vitaly , Desai Upendra D. , Brashears Sidney S.
Published: February 2004

The thermal annealing characteristics of radiation damage in p-channel MOSFETS due to irradiation by 1.5 MeV electrons as a function of time and temperature are presented. Both isothermal and isochronal annealing curves are analyzed and it is found that the activation energy of the annealing processes has a distribution in a range of 1 eV with the peak at about 1 eV. The mechanism of radiation damage and the model of thermal annealing in the MOSFETS are discussed.
Auger Electron Spectroscopy of fcc Metal Surfaces
Authors: Palmberg P. W. , Rhodin T. N.
Published: February 2004

The energy spectra of Auger electrons from clean Au, Ag, Cu, Pd, and Ni surfaces have been determined. Uniform deposition of a second metal onto clean metal surfaces has made it possible to assess the depth of the surface region which contributes to the Auger peaks in the secondary electron energy distribution characteristic. These results indicate that the mean escape depth for Auger electrons in Ag (without significant loss of energy) varies between 4 and 8 Å for energies of 72 and 362 eV, respectively. It has been shown (using Auger electron spectroscopy for detection of surface imuprities and low-energy electron diffraction for determining surface structure) that a clean Au (100) surface is reconstructed into a (1×5) structure, while clean Ag (100), Cu (100), and Pd (100) surfaces are characterized by bulk atomic arrangement. The combination of these two techniques has also been effectively applied to the interpretation of the structure and composition of CuAu surface alloys.
A High-Temperature, Low-Magnetic-Field Theta Pinch
Authors: DeSilva A. W. , Kunze H.-J.
Published: February 2004

A theta-pinch device of low stored energy, constructed to provide a convenient spectroscopic source, has produced an interesting and useful plasma. The discharge tube has an i.d. of 15 cm and the coil is 32 cm long. The main bank energy is 9 kJ at 40 kV, and the current rings with a 7.5 μsec period. Plasma conditions have been investigated for a filling gas pressure of 12 mTorr H2 or D2 and an antiparallel bias field of 500 G using light scattering, time- and space-resolved emission spectroscopy, streak photography, and neutron emission. These reveal that following the initial compression, the plasma forms a stable cylinder about 4.5 cm in diameter which persists for about 1.5 μsec. The maximum electron temperature, determined by light scattering, is about 260 eV. Absolute continuum emission and light-scattering measurements show the average electron density to be between 3 and 4×1015 cm−3. The temperature of carbon impurity ions is determined to be 1.3 keV from Doppler broadening, and neutron emission with a deuterium filling indicates an ion temperature of about 700 eV.
Device Applications of Superconductive Tunneling
Authors: Taylor B. N.
Published: February 2004

Although superconductive tunneling has proved to be a very useful tool for investigating the phenomenon of superconductivity, it also has many potential device applications worth further development. Examples of such devices based on the tunneling of normal electrons might include an rf oscillator and amplifier, a low-temperature thermometer, and a generator and detector of microwave phonons. Examples of devices based on the tunneling of paired electrons, that is, the dc and ac Josephson effects, might include a magnetometer, computer elements, a generator and detector of microwave radiation, and a voltage standard. It is the purpose of this paper to briefly review normal electron tunneling as well as the dc and ac Josephson effects, how these different tunneling phenomena manifest themselves, and how these manifestations can be used for these several device applications.
Tunneling and Weak-Link Superconductor Phenomena Having Potential Device Applications
Authors: McCumber D. E.
Published: February 2004

A general physical picture of superconductor weak-link junctions is outlined with emphasis on phenomena relevant to device applications. The total junction current contains a dissipative quasiparticle component nearly analogous to the current in a normal-state junction plus an electron-pair component responsible for superconducting effects such as the Josephson effects. Stochastic relaxation processes such as have been commonly associated with vortex motion and flux flow sometimes perturb the pair current and must also be taken into account.
Superconductive Phenomena in Ultrathin Films
Authors: Strongin M. , Kammerer O. F.
Published: February 2004

Experiments on very thin films and systems composed of small particles have shown transition temperatures significantly higher than the bulk Tc. Of the numerous ideas advanced to explain the high Tc's in these films, one of the most exciting is the suggestion of Cohen and Douglass that superconductive pairing can occur across dielectric barriers, and thereby lead to high Tc's. Recent results on the Tc of thin superconductors in contact with dielectric barriers, evaporated on cryogenic substrates, are presented. Some representative Tc's obtained in these experiments are Al∼5.7°K, Zn∼1.9°K, Sn∼6°K, In∼4.5°K, and Pb∼7.1°K. In the case of Al, Sn, and Zn these Tc's are much higher than the values found by Buckel and Hilsch for films deposited on quartz at liquid-helium temperatures. Explanations other than the dielectric barrier idea, such as ``amorphorus structure'' and the suggestion of Ginzburg that surface interactions may modify Tc, are also discussed. In the course of these experiments to investigate high Tc's in films it was found that very thin continuous films (∼20 Å or less) could be prepared at cryogenic temperatures. An investigation of superconductivity in these ultrathin films showed that Tc was much lower than the Tc of the thicker films. This occurred in all the metals measured, which included Pb, Al, Sn, and Bi. An explanation of these results in terms of the destruction of long-range order in two-dimensional systems due to fluctuations in the Ginzburg-Landau order parameter will be discussed. By using this idea and numerical values from the data, estimates can be made of the possibility of obtaining very high Tc's in films approaching a few atomic layers.
Pair-Breaking Mechanisms in Superconductors
Authors: Parks R. D.
Published: February 2004

A review is given of the theoretical and experimental situation concerning the problem of superconductivity in the presence of pair-breaking perturbations. The problem was first considered by Abrikosov and Gorkov, who advanced a theory which explained the results of the experiments by Matthias and co-workers on the lowering of Tc of superconductors containing small concentrations of magnetic impurities. The theory predicted further that the presence of magnetic scattering centers severely distorts the excitation spectrum of a superconductor and that for sufficiently large spin concentrations the energy gap disappears from the spectrum, even at T=0°K. It has since been found that the AG theory can be extended to treat other pair-breaking situations which lead to second-order superconducting-normal phase transitions. Examples of these are the vortex state, the surface sheath state, the proximity effect, small superconductors in large magnetic fields, superconductivity in the presence of high currents, and superconductivity in the presence of strong Pauli paramagnetism. In the dirty limit (where the mean free path is much smaller than the zero-temperature coherence length) the different pair-breaking regimes are equivalent in that their behavior is specified by a unified single parameter theory. In transforming from one pair-breaking regime to another, one needs only to change the pair-breaking parameter. Experimental results from the different depairing regimes are presented and compared with the predictions of the unified theory.
Superconducting Magnets for High-Energy Physics
Authors: Brechna H.
Published: February 2004

Superconducting magnets have established themselves as useful tools in solid-state physics, magneto-optical experiments, NMR, MHD, plasma, and other areas of physics. In high-energy physics only the bubble-chamber physicist has shown ample interest in using superconducting magnets. Reasons why there is a reluctance against large superconducting magnets in combination with high-energy physics experiments and accelerators are discussed. However, in various areas of high-energy physics superconducting magnets may be utilized, such as accelerator, beam-transport, and experimental magnets. This paper summarizes physical properties of superconducting systems for experimental and beam transport magnets in quantitative form. Charging time, field uniformity, resolution, acceptance, solid angle, improvement in optical measurements accuracy, and first- and second-order optics for superconducting magnets, with and without ferromagnetic return paths, will be compared to room and cryogenic magnets. Summary of experiences with superconducting magnets (energies > 106 J) will be given, as well as irradiation properties of superconducting type II materials and systems. Expected irradiation doses in accelerators and their effect on superconducting systems will be discussed. Lifetime expectancy, economy of operation, and effect of power failures are treated. A short section is devoted to possible design of superconducting magnets with and without ferromagnetic return paths.
Fast Neutron Irradiation Effects in Superconducting Niobium
Authors: Sekula S. T. , Kernohan R. H.
Published: February 2004

The superconducting magnetization behavior and transition temperatures of single crystals of Nb were investigated prior to and after a series of fast neutron irradiations (E>1 MeV) in the Oak Ridge Research Reactor at a temperature of 40°C.1 In addition to increases in the upper critical field Hc2 and small changes in the transition temperature after irradiation, it has been found that defects have been created with the ability to pin magnetic flux as evidenced by an increase in the nonequilibrium behavior of the magnetization.

A greater degree of flux pinning in single-crystal Nb can be attained by fast-neutron irradiation than has heretofore been reported for pinning introduced by mechanical deformation, and for fast-neutron doses of approximately 2×1019 neutrons/cm2 the magnetization approaches that of a completely irreversible type II superconductor. The initial magnetization cycle and subsequent hysteresis loop for an irradiated sample are shown in Fig. 1 as well as the magnetization cycle prior to irradiation. Successive reductions in cross-sectional area of the highly irradiated sample and subsequent magnetization measurements reveal only a small size dependence of the hysteresis, indicating that rather steep flux gradients can be established even at applied fields close to the upper critical field. From size-dependent studies of the remanent moment it is concluded that a flux gradient has been established in a macroscopic surface sheath approximately 0.1 mm thick with the corresponding shielding current density calculated to be approximately 2×105 A/cm2.
Superconductivity Critical Current Densities in Ti–V Alloys
Authors: Vetrano J. B. , Guthrie G. L. , Kissinger H. E. , Brimhall J. L. , Mastel B.
Published: February 2004

Specimens of Ti-20% V alloy were heat treated to a β-solid-solution condition and then aged for several fixed times and temperatures below the β transus. X-ray and electron diffraction were used to determine the composition and distribution of the metallurgical phases produced by the aging treatments. These data were correlated with measurements of the superconducting transition temperature and critical current density. In order for these materials to carry resonable supercurrent densities at 4.2°K, it is necessary that the matrix be rich enough in V for the transition temperature to be greater than 4.2°K and that there be present an array of flux-pinning sites. It was found that aging temperatures of 400°, 500°, or 600°C were required to insure the first condition. The flux pinners produced were ω particles in the case of the 400°C treatment and α precipitates in the case of the 500° and 600°C treatments. In many specimens, the superconducting-to-normal transition at a given value of applied field was spread out over a wide range of transport current rather than being abrupt as is usually the case.
Angular Dependence of Critical Currents in Plasma-Plated Nb3Sn Strip Superconductors
Authors: Fietz W. A.
Published: February 2004

In many instances it appears that the limiting performance of a superconductive device is determined by low-field instabilities rather than by the high-field current density. If the device is made of flat-strip superconductors, a further complication may arise from the fact that in the low-field regions the magnetic field usually is oriented at some nonzero angle to the surface of the strip. To see how these conditions affect the performance of plasma-plated superconductors, we have measured critical currents in flat strips of Nb3Sn in transverse applied field, varying the angle θ between the surface of the strip and the magnetic field. When transport current is applied first and the field increased until the specimen undergoes a normal transition, the relationship Hc(IT) = H0(IT)+H1(IT) cos2θ is roughly obeyed, where IT is the transport current and H0 and H1 are found to be of comparable magnitude. When the magnetic field is applied first and the transport current increased to its critical value, virtually no angular dependence is observed. We tentatively explain this result by describing the plasma-plated material as a matrix of miniature hollow cylinders aligned with the magnetic field. Because of the anisotropy of the plating process the effective wall thickness of the ``cylinders'' varies with the specimen orientation. When the field is applied first, the transport current can find paths around these ``cylinders'' which will not result in locally exceeding the critical current density of the material until nearly all the specimen is critical. However, when the transport current is applied first, the additional shielding currents induced by the magnetic field are forced to travel in paths which are already carrying transport current, and locally the critical current density may be exceeded, precipitating a normal transition before the entire specimen is critical. Further tests are being carried out to determine the effect of heat treatment and strip dimensions on this angular dependence of the critical current. These results should discriminate between our proposed explanation and the possibility that the effect is simply a demagnetization phenomenon.
Parallel and Perpendicular Magnetic Transitions of Films and Foils of Pb and Sn
Authors: Cody G. D. , Miller R. W.
Published: February 2004

A summary will be presented of extensive measurements of the parallel and perpendicular magnetic transitions of Pb and Sn as a function of temperature (1°K to Tc for Sn; 1°K to 4.2°K for Pb) and thickness (500 Å to 16 μ). The results, apart from their intrinsic interest, can be utilized to extract many of the superconducting parameters of the metals, including their thickness and temperature dependence.
Granular Superconductors
Authors: Cohen R. W. , Abeles B.
Published: February 2004

The superconducting transition temperatures Tc of some metals prepared in the form of small grains are appreciably higher than the ordinary values. The extremely small grain size gives rise to very short mean free paths and critical magnetic fields up to two orders of magnitudes larger than the thermodynamic critical fields. The critical fields and resistivities can be explained by a model which assumes tunneling between grains. Experiments indicate that the transmissivities of the tunneling barriers are large (≃10−1). Thus the grains are strongly coupled to each other, a finding which would appear to rule out enhancement of Tc due to quantization of electronic motion expected in small isolated systems. Other possible enhancement mechanisms discussed are: Josephson tunneling, surface enhancement of the electron-phonon interaction, and an increase in the electronic density of states due to atomic disorder. The relation between the somewhat unusual properties of granular superconductors and current application of thin films will be discussed.
Flux Flow and Thermal Stability of Stabilized Superconductors
Authors: Gauster W. F. , Hendricks J. B.
Published: February 2004

Test equipment has been designed in such a way that complete test cycles with bare or insulated compound conductor samples in unrestricted liquid-helium flow can be easily obtained. Sample currents up to 2000 A and fields to 80 kG can be used. An evaluation of the recovery points yields magnetoresistance data for the stabilizer material. Using these stabilizer resistance values, it is possible to split the total current into the superconductor and the stabilizer components. The tests show that, in general, the take-off points cannot be explained by the transition from nucleate to film boiling of the liquid helium. The V vs I curves in the flux-flow zone seem to indicate a heat-transfer law in the form Q=h*τn with n≃2 5 in the nucleate boiling regime. Tests with poorly stabilized samples (either bare or insulated) can be explained by assuming that parts of the sample are in the superconducting state, while other parts are in the normal state or in the flux-flow state.
A Multi-Aperture Cryogenic Storage Cell
Authors: Mundy J. L. , Newhouse V. L.
Published: February 2004

Two types of superconducting memory cells are now being considered: the continuous-film memory and cryotron-switched storage loops. The former suffer from low cell operating range compared to cell-to-cell variation. The cryotron cells, although having a wider operating range, must be switched very rapidly to have a detectable output signal. A recent development in cryogenic sensing called ``Current Stretch'' has allowed more freedom in the design of superconducting memory cells. With current stretching the information is transformed to a persistent input current in a cryotron amplifier. The signal produced when the cell is switched is then proportional to the magnetic flux change rather than the rate of change of flux. This feature eliminates the usual memory requirements of fast-access current risetime, pickup noise cancellation, fast cell switching, and the need for a separate sense line with cryotron-accessed memories. A new class of cell which takes advantage of this technique will be described. It consists of a cryotron shunted across a loop, one side of which has a lower inductance and critical current than the other. If the cryotron is activated while current is injected into the cell, a persistent current is created in the loop. Cell-flux changes are detected through one of the cryotron access trees using current stretching. The operating tolerance of these cells is only limited by their geometry. They have no metal-to-metal contacts, use only three metal layers including the ground plane, need no sense line, no noise cancellation, and can be switched arbitrarily slowly. Cells can be fabricated as small as 10 mil2 and operating ranges as large as 40% have been observed. The cell speed is on the order of 50 nsec with a single crossover access cryotron.
Electronic Grey Matter
Authors: Parmentier R. D. , Scott A. C.
Published: February 2004

One of the most exciting long term goals of Electrical Engineering is to construct an electronic machine with functional ability similar to that of the human brain. A brief inspection of the brain indicates the enormous difficulties involved. The brain is overlaid with a thick covering or cortex of grey matter comprising approximately 1010 neurons or active elements plus additional regulating circuitry in the cerebellum. The electrical engineer setting out to duplicate such a gadget is faced with three stark problems: (1) Wired in cost per active element. The cost of 1010 at a penny each (wired in) would be $100 million for hardware. (2) Power dissipation per active element. The power dissipation of 1010 neurons at 1 μW each would be 10 kW. (3) Design scheme. Some plan of construction is obviously necessary before one begins to build something with 1010 working parts. If the design requires every interconnection to be correctly made, it will be impossible to carry it through. The main purpose of this paper is to suggest that there is now the possibility of overcoming these difficulties using tunnel junctions between superconducting metals as the active elements.1,2 These devices are analyzed in detail and it is demonstrated both analytically and experimentally that neuristor pulse propagation is possible. The junctions have extremely low power dissipation per unit area (about 400 μW/cm2 in the resting state for normal electron tunneling and zero dissipation if the resting state for Josephson or superelectron tunneling) which solves problem 2. The use of modern photoresist fabrication techniques should satisfy problem 1. Finally, problem 3 has been discussed in detail by Beurle3 who has assumed a mass of randomly interconnected active trigger circuits with a learning capability (provided, for example, by an excitation threshold which decreases with use). He has shown that large scale wave and oscillatory behavior occur which can be arranged to provide both conditioned response and memory patterns of time sequences of events. In this paper we also describe a saturable ferromagnetic interconnection which is compatible with the superconducting neuristors and which will provide the necessary learning capability required for the construction of the systems considered by Beurle.
Dynamic Fault Tolerance in Cryoelectric Arrays
Authors: Pritchard J. Paul , Slay B. G.
Published: February 2004

Properties peculiar to superconductive phenomena and derived devices permit operation of cryoelectric arrays containing failed elements. This fault tolerance extends throughout the operational life of the array and is therefore referred to as dynamic fault tolerance. A cryotron-gated, superconductive loop possesses three stable states: two with circulating current of opposite polarity and a third without circulating current. The latter can be paired with either of the circulating states to form a binary logic device which will fail safe to the noncirculating current state under all failure modes except short-circuit formation. Analysis of failure origin and technology redefinition has eliminated short circuitry as a failure mode in completed arrays. The requirements for implementation of dynamic fault tolerance are developed and illustrated in terms of successful experiences with a 20 000 gate cryoelectric array objective.
Proposed Ammeter Using Flux Quantization
Authors: Meservey R.
Published: February 2004

The possibility is discussed of using flux quantization in superconductors as the basis of an ammeter and more generally as a fundamental standard of electromagnetic measurement. A particular design is proposed and in this context some of the fundamental design problems of this sort of instrument are considered. It is concluded that an instrument of this type could measure a current in terms of the flux quantum, length, and time to an accuracy approaching 1 part in 106. The limitations and advantages of the proposed instrument are discussed and comparisons are made with present current-measuring instruments and some conjectures are made of the future potential of flux quantization instruments of this kind.
Microwave Studies of Thin Superconducting Films
Authors: Soderman D. A. , Rose K.
Published: February 2004

The results of linear microwave transmission measurements on superconducting tin films are presented. The effects of residual reactances are noted and a comparison is made with calculations based on the BCS theory. Residual reactances are found to have a substantial effect on the nonlinear transmission measurements. They allow a clear separation of regions where superelectron depairing and ``domain growth'' dominate. Linear transmission measurements in the presence of a perpendicular magnetic field suggest the ``domain growth'' is the result of fluxon penetration.
The Superconducting Magnet for the ANL 12-ft Hydrogen Bubble Chamber
Authors: Purcell J. R.
Published: February 2004

The large Argonne magnet is scheduled for completion in late 1968. The bore of this magnet is 16 ft and the distance between pole faces is 10 ft. Iron is used for the magnetic return path. Major components and materials have been ordered and fabrication of the complete system is proceeding on schedule. Construction has started on the container. A 2-ft bore magnet has been wound from the conductor to be used in the large magnet and tested. This small magnet, which weighs about 2000 lb, performs very well. A model has been built to study problems associated with the coil structure, such as cooldown, maintenance of clamping forces, and general mechanical integrity.
Stabilized, Levitated Superconducting Rings
Authors: File J. , Martin G. D. , Mills R. G. , Upham J. L.
Published: February 2004

A levitated, stabilized superconducting ring is described. The ring, wound of 3310 turns of Nb-25% Zr 10-mil wire, has been operated with currents up to 16 A. It has been floated, with its associated Dewar, independent of all physical connections, for periods exceeding 7 h. Ring stabilization criteria and a system to maintain the ring position are presented.
The Design of an 88-kG, 20-in.-Bore Superconducting Magnet System
Authors: Lucas E. J. , de Winter T. , Laurence J. , Coles W.
Published: February 2004

The integrated design of a large superconducting magnet system includes mutually compatible solutions to mechanical, thermal, and electrical problems. This paper reports on the results of such a design and some of the analytical and experimental work that was carried out to provide data for these solutions. The system consists of a set of bour 51 cm bore 5 T solenoids, two of which, when operating as a close pair, will produce a central field of 8.8 T. Each of the four solenoids is divided into three concentric sections. The inner sections are composed of twenty pancakes wound with a stabilized Nb3Sn ribbon, while both the middle and outer sections are wound with a stabilized Nb–Ti square conductor. The over-all current densities in each of the sections are 5000 A/cm2 for the inner, 4540 A/cm2 for the middle, and 6450 A/cm2 for the outer.
Results of Tests on Models for an 88-kG, 51-cm-Bore-Diameter Solenoid
Authors: Stekly Z. J. J. , Lucas E. J. , de Winter T. , Strauss B. , Di Salvo F. , Laurence J. , Coles W.
Published: February 2004

As part of a program to build an 88 kG, 51-cm-bore solenoid, two model coils were built to test the conductor characteristics as well as the final coil-construction techniques. The first coil was wound with a square conductor 0.218 cm on a side, with many strands of Nb–Ti. The coil winding i.d. was 15.24 cm, the o.d. was 22.3 cm, and the length was 10.16 cm. This coil was built using small cooling passages, and its construction was such as to simulate the techniques to be used up to 80 kG in the full-size magnet. The second coil was wound with steel reinforced Nb3 Sn of over-all dimensions 1.27 cm by 0.0292 cm and had a winding i.d. of 12.2 cm and an o.d. of 31.1 cm, and consisted of two pancakes. Its purpose was to simulate the high-field windings of the full-size coil. Both coils were instrumented with heaters to determine their stability characteristics. The performance of each coil is discussed with regard to stability, charge rate, and quench characteristics.
Photodielectric Detector using a Superconducting Cavity
Authors: Arndt G. D. , Hartwig W. H. , Stone J. L.
Published: February 2004

Photoinduced free-carrier processes in Si and Ge have been studied in superconducting cavities to exploit their excellent frequency stability and negligible dissipation. Using the narrow bandwidth and very high unloaded Q, it is possible to detect changes in the complex dielectric constant by observing the shift in resonant frequency. Simultaneous measurement of relative power absorption gives additional and confirming data. An increase in frequency of several kHz/mW and a linear power absorption is observed for low values of light. At higher intensity both responses become nonlinear due to the growth of the plasma frequency and nonuniform carrier density distribution. For a 525 Ω·cm sample of n-type Si in a cavity with resonances at 290 and 810 MHz, data analysis showed the thermal carrier density at 4.2°K was 109 cm−3, relaxation time was 1.44×10−10 sec, the Fermi level was 0.00305 eV above the donor level, and the unilluminated plasma frequency was 148 MHz. The product of conversion efficiency and free-carrier lifetime was approximately 10−10 sec, indicating the effect could be used for a wide-bandwidth optical detector. By repeating the experiment at different frequencies, temperatures, and wavelengths, the theoretical agreement holds and considerable insight can be gotten into recombination and trapping processes, lattice collision and mobility effects, and the changes in these phenomena with radiation and stress of many kinds.
Relaxation Oscillations in Josephson Junctions
Authors: Vernon F. L. , Pedersen R. J.
Published: February 2004

Investigation of the characteristics of Josephson tunneling in tin-tin-oxide-tin junctions showed that pulse voltages with sharp risetimes were being generated. Pulse amplitude across the junction remained constant and equal to the energy gap voltage Vg, but pulse frequency could be changed over a 25:1 range by a change in bias voltage from 0 to an upper limit approximately equal to Vg/2. The oscillation mechanism is that of switching between the pair-current state of the junction at V=0 and the quasiparticle-current state at V=Vg. The external circuit maintains the switching cycle and determines the output frequency characteristics. Using the L/R time constant of the external circuit and the assumed basic dc I(V) curve of the junction in the absence of relaxation oscillations, calculations were made that accurately describe the observed dc I(V) curves, frequency, and waveforms, including their dependence on bias voltage and magnetic field.
Physics of Preparation of Josephson Barriers
Authors: Schroen Walter
Published: February 2004

Josephson barriers of the tunneling type are usually prepared by oxidation in room environment, but they degrade after storage at room temperature for a few days. This paper describes a preparation technique based on an oxygen glow discharge which renders stable, reproducible superconductive tunneling devices (STDs). The barrier may also consist of organic molecules (KPR, monocarbonic acids); lead serves as the superconducting metal. Simplified models are used to discuss the main features and advantages of the glow-discharge technique. Extensive investigation has shown that arrays of STDs can be fabricated using the photoresist technique developed by Pritchard et al. The current-voltage and magnetic-field characteristics of these arrays are examined; it was found that they did not change during array storage at room temperature for more than 240 days and repeated temperature cycling from room temperature to 4.2°K.
Frequency Conversion Using Weak Multiply Connected Josephson Junctions
Authors: Rothwarf F. , Krisch H. M. , Ford D.
Published: February 2004

A Josephson tunneling device essentially consisting of a lead-tin solder bead encircling a 5-mil niobium wire has been used to produce some frequency conversion effects. Thin spots in the oxide coating of the niobium wire give rise to two or more parallel weak-contact regions between the solder and the niobium. A typical voltage vs junction current plot displays an antisymmetric tunneling curve with zero voltage across the junction until a certain critical current Ijc is supplied. A field current IH flowing through the niobium wire produces a magnetic flux which links the multiply connected region(s) formed by the penetration depths of the solder and the niobium and the distance(s) between the parallel weak contacts. The critical current Ijc is a periodic function of the magnetic flux threading the multiply connected region(s), the modulation period being proportional to one flux quantum. When the device is biased with a junction current Ij in the interval Ijc≤Ij≤3Ijc, a modulated dc voltage appears across the junction as IH is varied. The period of the oscillations is independent of the junction bias Ij. The number of cycles ΔN produced for a given absolute change | ΔIH | defines the junction constant Kj of the device. Kj depends upon the geometry of the device and the penetration depths of the superconductors used in its construction. If a time varying IH is applied to the niobium wire an output frequency f0 can be obtained, given by the relation f0=Kj | dIH/dt |. For a triangular IH the device acts as a frequency multiplier giving f0=4KjIHm fin, where IHm is the current amplitude of the triangular waveform and fin its frequency. A sinusoidal IH gives rise to a frequency-modulated output: f0=2πKjIHm fin | cos2πfint |. Other input waveforms yield other frequency-modulated outputs.
Wall Potential in Crossed-Field Devices
Authors: Bacal Martha
Published: February 2004

The effect of a magnetic field on the two stable potentials of the glass wall in high-vacuum devices is investigated; it is shown that a transition is possible from one stable potential to another under the effect of a magnetic field. The physical conditions are formulated for the stabilization of the wall potential at either of two values. The applicability of the expression given by James and Carter for the lower stable potential is discussed. The influence on the higher stable potential of the ion and electron currents reaching the wall and of the secondary-emission multiplication process is also investigated. The experimental results on the variation of the wall potential as a function of the magnetic field in a plane-parallel crossed-field device with glass walls are compared with those obtained in similar devices with walls provided with a conducting coating.
Internal Field Distribution in Keepered and Nonkeepered Permalloy Film Memories
Authors: Mo Roger S. , Rabinovici B. M.
Published: February 2004

The magnetic field distribution inside an 80–20 Ni–Fe Permalloy layer is a major contributing factor to the adjacent bit interference effect limiting the maximum permissible packing density of a high-speed main memory. The internal field distribution Hi (z) is calculated using the concept of magnetic charge distribution and Stoner-Wohlfarth switching model. The results are plotted for various driving field distribution and magnetic film magnetization parameters. The data are obtained with the aid of an iterative computer-program solution for small volumes [(δM/Hk) <10−5m] and with an inverse matrix computer solution for large values of (δM/Hk) (δ=film thickness). These techniques are further extended to the treatment of magnetic keepers and their effect on adjacent bit interference. The calculated data are compared with experimental results and the agreement is found to be very close.
Standing-Spin-Wave Modulation of the Reflected Microwave Power in YIG
Authors: Wang S. , Thomas G. , Hsu Ta-lin
Published: February 2004

Low-frequency oscillations which occur above the threshold for spin-wave instability are examined in detail. The frequency of these coherent oscillations is found to vary with the applied dc magnetic field. A simple theory based on the assumption of standing spin waves is given and it is shown that this assumption can explain well the experimental observations.
Dislocation Core Structures
Authors: Shaw Bevil J. , Jaswon M. A.
Published: February 2004

A technique is described to construct the atomic configuration of a dislocation core in any crystal lattice. Examples of dislocation cores in primitive cubic, bcc, and diamond lattices are depicted. Problems associated with the ``dangling bond'' and the movement of a dislocation line through the lattice, or the Peierls-Nabarro force, are also discussed.
Some Observations on the Effect of Surface Roughness upon Diffusion
Authors: Borg R. J. , Lai D. Y. F.
Published: February 2004

The effect of surface roughness has been investigated experimentally and found to lead to spuriously high values of the diffusion coefficient. The magnitude of the error has been estimated as a function of Dt and the degree of roughness. The results indicate that surface roughness may contribute the major source of error in the determination of very small diffusion coefficients. The presence of an uneven source surface may also account for the anomalous tracer penetration profiles which are observed in the vicinity of the surface and, corresponding to which, anomalous values of D have been frequently reported.
Effects of Dislocation Motion on the Ultrasonic Attenuation in Potassium and Gold at Low Temperatures
Authors: Natale Giovan G. , Rudnick Isadore
Published: February 2004

Measurements of ultrasonic attenuation in thin bars of potassium were made with a resonant decay technique from 2.5°K to 77°K in the frequency range of 200 to 400 kHz. A broad absorption peak was found in the region between 25°K and 40°K. The relation between the temperature at which the absorption is peaked and the ultrasonic frequency seems to indicate, together with other considerations, the presence of a thermally activated relaxation process (activation energy: 0.01 eV). The dependence of the peak amplitude on the purity and the state of anneal indicates that the effect may be due to dislocation motion. A strain-amplitude dependence of the attenuation was found at 4.2°K in both potassium and gold. The data follow the Granato-Lücke relation for strains above 10−6 in K and above 10−8 in Au; values of the Granato-Lücke constants were obtained in these regions.
Preparation of Efficient Electroluminescent Diodes from p-on-n Liquid-Phase Epitaxial Layers of GaP
Authors: Shih K. K. , Lorenz M. R. , Foster L. M.
Published: February 2004

Efficient red-emitting GaP diodes have been fabricated from p-on-n layers formed by liquid epitaxy in a closed-tube system. The external quantum efficiency may increase by a factor of two to three after the diodes are heat-treated.
Low-Energy Electron Interaction with Coadsorbates on Tungsten
Authors: Bennette Carol J. , Swanson Lynwood W.
Published: February 2004

The effect of low-energy electrons (20–300 eV) impinging on cesium, mercury, and oxygen adsorbed on clean and oxygenated tungsten has been studied by field-emission techniques. Desorption cross sections were determined from the work-function changes and the known relationships between work function and coverage for the various systems studied. For cesium on clean tungsten and for mercury on both clean and oxygenated tungsten, the cross sections are less than 10−21 cm2, the minimum level of sensitivity for these experiments. Cesium is desorbed from an oxygenated tungsten surface by the impact of 250 eV electrons without disturbing the underlying chemisorbed oxygen layer. Cross sections for the desorption of cesium from oxygenated tungsten increase with increasing cesium coverage to a maximum of 8×10−20 cm2, and are insensitive to the amount of underlying oxygen. These results suggest that an important change in the character of the surface bond is effected by the underlying oxygen layer, in particular, a greater localization of the bonding electrons in the cesium-oxygen bond as compared to the cesium-tungsten bond.
The Application of Electron-Mirror Microscopy to the Examination of Biological Material
Authors: McLeod G. C. , Oman R. M.
Published: February 2004

Electrical and topological features of the giant unicellular alga Acetabularia crenulata were studied by electron-mirror microscopy. This technique which allows presentation of the voltage profiles at the sample surface without damage to the sample was used to show dynamic electrical effects. These effects are due to charging centers in the chloroplast.
Carrier Transport in Thin Silicon Films
Authors: Dumin D. J. , Robinson P. H.
Published: February 2004

Films of p-type and n-type silicon 1–2 μ thick have been epitaxially grown on single-crystal sapphire. The Hall mobilities of films with carrier concentrations varying between 1013/cc to mid-1020/cc have been measured. For carrier concentrations above 1017/cc the mobility decreased with increasing carrier concentration similar to the drop in mobility observed in bulk silicon, indicating the dominance of impurity scattering at higher carrier concentrations. At lower carrier concentrations the scattering from crystalline defects limited the mobility to values approaching 30% of the mobility of bulk silicon. The presence of crystalline defects acting as electron traps was demonstrated by measuring the electron concentration in films of constant donor density but varying dislocation density and noting that the electron concentration dropped as the defect density rose. This has lead to an estimate of the electronically active defect density in thin silicon films grown epitaxially on sapphire of about 1015/cc-1017/cc. Optical absorption data have indicated that there is considerable absorption at energies below 1.1 eV.
Thermally Induced Strains in Cubic Metal Films
Authors: Witt F. , Vook R. W.
Published: February 2004

Thin films bonded to substrates of different thermal expansion coefficients will experience ``thermal strains'' when their temperature is changed. Calculations of these thermal strains and the corresponding strain energies for crystals having various crystallographic orientations relative to the surface of the film were made for a number of fcc and bcc metals. Results are given for the (111), (200), (220), (311), (331), (420), (422), (511), (531), (442), (620), and (533) orientations of the fcc metals Cu, Au, Ag, Al, Ni, Pb, and Pd. They are basically similar for all fcc metals studied with the (100) orientation having the lowest strain energy and the (111) orientation the highest. For the bcc metals Cr, Fe, Nb, Mo, Ta, V, and W, calculations were made for the (110), (200), (211), (310), (222), (321), (411), (420), (332), (510), (431), (521), (530), (433), and (442) orientations. Neglecting W, which is isotropic, it was possible to classify the bcc metals into two groups depending upon whether the (100) orientation had a higher or lower strain energy than the (111) orientation. The strain energies for the other orientations lay between these extreme values in all cases.
The Voigt-Reuss-Hill (VRH) Approximation and the Elastic Moduli of Polycrystalline ZnO, TiO2 (Rutile), and α-Al2O3
Authors: Chung D. H. , Buessem W. R.
Published: February 2004

The Voigt-Reuss-Hill (VRH) approximation, a useful scheme by which one calculates isotropic polycrystalline elastic moduli in terms of the anisotropic single-crystal elastic constants, is shown to be accurately applicable for ZnO, TiO2 (rutile), and α-Al2O3, which are the simplest examples of oxide materials with the hexagonal, tetragonal, and trigonal symmetries, respectively. An experimental proof is established by measuring isotropic elastic moduli on dense-formed polycrystalline specimens. The recommended values of the polycrystalline isotropic elastic moduli of these oxides at room temperature are as follows: for ZnO, G=4.56(±0.04) and E=12.35(±0.09); for TiO2, G=11.15(±0.09) and E=28.42(±0.14); and for α-Al2O3, G=16.35(±0.12) and E=40.39(±0.31), where G and E are the isotropic shear and Young's moduli, respectively, and they are in units of 1011 dyn/cm2.
Dislocations and their Relation to Irregularities in Zinc-Diffused GaAsP p-n Junctions
Authors: Grenning Daniel A. , Herzog A. H.
Published: February 2004

The geometry of the p-n junctions formed from Zn diffusion into epitaxially grown n-type [100] GaAsP wafers is studied. In conjunction with this the dislocation structure has been investigated. For epitaxial crystals with a (100) growth plane it is shown that the predominant dislocation in the bulk is a grown-in dislocation whose axis lies in the [100] direction, perpendicular to the growth plane. By a special growth technique the bulk dislocation density may be markedly reduced in favor of an array of [110] dislocations lying adjacent to the epitaxial-substrate interface. The range of dislocation densities studied is about 0.5×106 cm−2 to 50×106 cm−2. The spiked irregularities in the Zn-diffused junctions are shown to be due to diffusion along the axes of the dislocations.
Affected Volume and Temperature Rise During Discontinuous Slip at Low Temperatures
Authors: Erdmann Joachim C. , Jahoda James A.
Published: February 2004

The temperature transients arising from discontinuous slip in copper-nickel alloys at helium temperature have been observed with thermometers of defined inertia properties. It is found that this type of slip can propagate through the specimen similar to a Luders band. In the discussed case, the temperature rises from approximately 5°K to approximately 35°K, and the mean value of the volume affected by each slip is 1.4×10−3 cm3. This volume corresponds very closely to the range of thermal diffusion during the time interval of slip. Thus, it is consistent with the assumption that discontinuous slip at low temperatures results from thermal feedback.