bluuebunny/crossref_metadata_2025 huggingface dataset:
Vacuum Electrical Breakdown between Plane-Parallel Copper Electrodes
Authors: Davies D. Kenneth , Biondi Manfred A.
Published: April 2005

Measurements have been made of prebreakdown currents between thoroughly outgassed plane-parallel copper electrodes in ultrahigh vacuum, for electrode separations in the range 0.03 cm to 0.2 cm. These currents are found to be in good agreement with the Fowler-Nordheim theory of field emission from the pure metal surface. From combined measurements of prebreakdown current and breakdown voltage at different electrode separations it is deduced that the cathode microscopic field at breakdown is constant and of magnitude (6±1)×107 V/cm.

Spectroscopic measurements of both resonance line absorption and line fluorescence have revealed that the density of neutral copper vapor present in the interelectrode space during the application of electric fields only fractionally (<1%) less than the breakdown field is considerably less than that necessary for volume ionization to occur. For the same experimental conditions, infrared radiation observations have revealed no hot spots on the anode surface.

From the measurements it is concluded that mechanisms involving the amplification of field-emission current in electrode vapor produced by steady evaporation from either the anode or the cathode do not explain the electrical breakdown of vacuum between extended copper surfaces. Further, the production of electrode vapor by the detachment of heated anode material under the influence of the force of the applied electric field is unlikely.
Vacancy and Interstitial Cluster Production in Neutron-Irradiated α Iron
Authors: Beeler J. R.
Published: April 2005

Vacancy cluster and interstitial cluster production in α iron was computed by simulating atomic collision cascades on a computer. Each collision was determined by the Erginsoy-Vineyard interatomic potential for α iron. The computed densities of displacement spikes produced by primary knock-on atoms with energies above 3 keV correlated qualitatively with the degrees of irradiation hardening observed by Harries et al. in ferritic steel specimens for five different neutron energy spectra. The computed total displaced atom densities did not correlate with the degrees of irradiation hardening observed by Harries et al. Annealing simulations indicated that displacement spikes produced by primary knock-on atoms with energies below 2.5 keV should not contribute importantly to irradiation hardening in specimens irradiated at the temperature (∼60°C) adopted by Harries et al. The volume of collided atoms involved in a collision cascade usually exhibited a marked orientation along 〈110〉 directions as did the associated displacement spike. Spikes are therefore oriented in the primary slip planes of α iron and each could serve in toto as a barrier to dislocation motion.
Current—Voltage Characteristics by Image Photometry in a Field-Ion Microscope
Authors: Tsong Tien Tzou , Müller Erwin W.
Published: April 2005

Current—voltage characteristics of a FIM were determined indirectly through total image photometry in order to avoid known difficulties with ion current measurements. Relative phosphor screen efficiencies as a function of ion energy were calibrated separately. The total ion current under isothermal conditions is found to depend more sensitively upon the temperature than the T−1 power predicted by the present theory. The total ion current remarkably depends also on the tip temperature when the gas temperature is kept constant. Both temperature effects indicate that only a fraction of the gas molecules attracted to the tip by polarization contributes to the ion current. From the emitter cone-angle dependence of the slope in the imaging range of the log I—log V plot and from the time-lag effect after changing the emitter temperature it is concluded that the initial arrival of molecules at the emitter shank contributes significantly to the image gas supply. Image photometry can be used as a simple means to monitor the tip temperature with sufficient accuracy for most practical purposes.
Pyroelectricity and Spontaneous Polarization in LiNbO3
Authors: Savage A.
Published: April 2005

Measurements have been made concerning the magnitude of the pyroelectric coefficient dPs/dT in LiNbO3 over the temperature range from 25° to 450°C. The pyroelectric coefficient was found to be −4×10−9 C/cm2/°C at 25°C. The spontaneous polarization was determined to be a decreasing function of temperature in the crystals measured which were pulled from the melt. Over the temperature range measured Ps was found to decrease by 3.7 μC/cm2. From these pyroelectric measurements and preliminary data on the temperature dependence of the nonlinear optical coefficient d33 in LiNbO3, for d33 ∝ Ps, the magnitude of Ps at room temperature is estimated to be at least of the order of 50 μC/cm2.
Quench Defects Formed in a Low-Stacking-Fault-Energy Silver—Tin Alloy
Authors: Ruff A. W. , Ives L. K.
Published: April 2005

A transmission electron microscopy study of defects was conducted in quenched and plastically deformed samples of a silver—8 at. % tin alloy. After quenching from 750°C and aging at 200°–300°C, dislocation loops and small faulted defects were found distributed randomly in low numbers. Many examples of aligned rows of clustered defects were also observed in addition to the growth of stacking faults on existing screw-oriented dislocations. Helical-like dislocations were found containing visibly extended segments. It is believed that the formation of 〈110〉 rows of stacking-fault tetrahedra may involve such helices. A specific mechanism is proposed to explain those observations. Extensive plastic deformation was observed to produce similar features.
Reflection and Transmission of Electromagnetic Waves by a Moving Plasma Medium
Authors: Yeh C.
Published: April 2005

The reflection and transmission of electromagnetic waves by a moving dispersive dielectric half-space or slab are investigated theoretically. The dispersive dielectric medium is assumed to be a cold plasma medium. Two cases of the movement are considered: (a) The plasma medium moves parallel to the interface. (b) The plasma medium moves perpendicular to the interface. It is interesting to note that, for case (a), the reflected and transmitted fields for an incident plane E wave are independent to the movement of the plasma medium. For case (b), the reflected wave and the transmitted wave are functions of the velocity of the moving plasma medium. Detailed results on the reflection and transmission coefficients for case (b) are given and discussed. In the present analysis, the electric vector of the incident wave is assumed to be polarized in a direction that is normal to the plane of incidence.
Optical Quenching of Photoconductivity in Single-Crystal Stannic Oxide
Authors: Houston Jack E. , Kohnke E. E.
Published: April 2005

The optical quenching of photoconductivity in single-crystal specimens of stannic oxide has been investigated as a function of extrinsic wavelength and of temperature in the region where sensitization occurs. Quenching is found in a single band extending from the fundamental optical gap at 4.0 eV down to a cutoff indicative of a 1.3-eV activation energy for the sensitizing centers. The discrepancy between this value and the 0.33-eV value obtained earlier from thermal-quenching measurements suggests that the sensitizing states themselves do not play an active role in the process of thermal quenching, but rather that the thermal quenching arises through the action of the shallow electron trapping states.
Photoelectroluminescence of Single Crystals of Manganese-Activated Zinc Sulfide
Authors: Taagepera Rein , Williams Ferd
Published: April 2005

Photoelectroluminescence, which involves the control of electroluminescence by electromagnetic radiation, is reported for single crystals of manganese-activated zinc sulfide. Both plane-parallel and point-contact electrode structures were used. The latter resulted in greater homogeneity of luminescent emission with the applied voltage mainly across the spreading resistance regions. The field distribution was probed. The observations are explained with essentially the same basic theory as was earlier used to explain observations on vapor-deposited films. However, from the analysis of the data on single crystals we deduce that carrier multiplication is occurring in the cathode region and to a lesser extent in the anode region, and also obtain values for the local fields for acceleration of carriers and for collision excitation.
Velocity-Profile Measurement in Plasma Flows using Tracers Produced by a Laser Beam
Authors: Chen Che Jen
Published: April 2005

A giant pulse laser is focused in a gas flow by a lens. The plasma drop produced by the gas breakdown is used as a tracer for the flow velocity measurement. The motion of the plasma drop is detected by both electrostatic probe and drum-camera techniques. The estimated experimental error in the present setup is about 3%. The new features of this method are (1) very high spatial resolution, (2) minimum disturbance in the flow due to the instrumentation, and (3) applicability both to un-ionized and ionized flows.
Electrical and Structural Properties of Epitaxial bcc Tantalum Films
Authors: Marcus R. B.
Published: April 2005

Tantalum films have been epitaxially deposited on cleaved MgO (001) surfaces at temperatures above 700°C under high-vacuum conditions. The interstitial impurity content is below 0.5 at.% for thicknesses greater than 1000 Å; the impurity concentration increases with decreasing film thickness, and severe lattice dilation occurs in the very thin film region (250–350 Å). Films of thicknesses greater than 1000 Å have specific resistivities and critical temperatures (16.0 μΩ·cm and 4.30°K, respectively) close to bulk values. Two impurity-stabilized phase transitions produced by electron microscope beam heating are described.
Electron and Ion Emission from Polycrystalline Surfaces of Be, Ti, Cr, Ni, Cu, Pt, and Type-304 Stainless Steel in Cesium Vapor
Authors: Wilson R. G.
Published: April 2005

Full-temperature-range electron and ion emission data from the eight cesiated nonrefractory metals are reported in the range of cesium arrival flux from 1012 to 1018 atoms/cm2·sec, as determined from measurements between 1013 and 1017 atoms/cm2·sec. Cesiated electron emission S curves and cesium surface-ionization critical-temperature envelopes are shown. The experimental techniques, which include automatic data recording and computer analysis and reduction, are described.
Vacuum Thermionic Work Functions of Polycrystalline Nb, Mo, Ta, W, Re, Os, and Ir
Authors: Wilson R. G.
Published: April 2005

Experimentally measured effective vacuum thermionic work functions are reported for well-outgassed polycrystalline (but thermally preferentially oriented in many cases) surfaces of 70% (100)+20% (211)-oriented niobium (4.19 eV), 70% (100)+20% (211)-oriented molybdenum (4.0–4.3 eV), 70% (211)-oriented tantalum (4.25 eV), 96% (100)+4% (111)-oriented tungsten (4.52 eV), fairly randomly oriented rhenium (4.96 eV), randomly oriented osmium (4.83 eV), and 80% (111)+15% (100)-oriented iridium (5.27 eV) in a clean, 10−9 Torr background vacuum. Special techniques were employed to ensure accurate current, area, and temperature values. Purities, heat treatment histories, and x-ray crystallography measurements on the surfaces are included.
Pressure Calibration to 100 kbar Based on the Compression of NaCl
Authors: Jeffery R. N. , Barnett J. D. , Vanfleet H. B. , Hall H. T.
Published: April 2005

An independent determination has been made of the transformation pressures assigned to the high-pressure transformations in Ba and Bi which are generally used for calibration points. The metals were imbedded in NaCl, and the transitions were detected by the resistance change of the metal while the NaCl lattice parameter was simultaneously measured by x-ray diffraction. The NaCl compression values determined at the fixed points were related to pressure by reference to the semiempirical compression curve of Decker. The Ba I–II and Bi III–V transformations at room temperature were assigned thermodynamic equilibrium values of 53.3±1.2 kbar and 73.8±1.3 kbar, respectively, corresponding to NaCl linear compression values of Δa/a0=0.0510 and 0.0637, respectively. Hysteresis in the transformation pressures was investigated and sample hysteresis was separated from apparatus hysteresis. The hysteresis measurements imply a stress energy which inhibits nucleation of the new phase and causes a sizable sample hysteresis in solid-media systems.
Gunn Domain Dynamics
Authors: Allen J. W. , Shockley W. , Pearson G. L.
Published: April 2005

A phenomenological equation for the motion of carriers in a Gunn diode is written in terms of an average drift velocity and an average diffusion coefficient, both of which are functions of the field only. The equation can be reduced to a simple form in the case of a steady-state dipole domain with a flat top. Various properties of the domain can be deduced using only elementary analytical methods. As an example, it is found that although the domain boundary shapes change with carrier concentration the domain velocity remains constant and equal to the drift velocity of the carriers in the uniform field regions, provided the mobility is independent of concentration.
Temperature Dependence of the Thermal Conductivity of Amorphous Polymers: Polymethyl Methacrylate
Authors: Reese William
Published: April 2005

An analysis of the thermal conductivity of polymethyl methacrylate is presented which fits the experimental data to better than 10% from 1°K to the glass temperature. The model employed is a slight modification of Klemens' theory of the thermal conductivity of amorphous substances in which explicit account of the fibrous nature of polymers is taken by assigning a portion of the specific heat to one-dimensional vibrations and assigning to these vibrations a mean-free path which is different from that for three-dimensional vibrations. It is found that the resulting mean-free path for vibrations along the polymer chains is of the order of 7 Å.
Magnetization and State of Order in MnNi3
Authors: Paoletti A. , Ricci F. P. , Passari L.
Published: April 2005

Magnetization-vs-temperature curves were determined in MnNi3 for different states of order in the temperature range −196° to 375°C and for fields up to 4000 Oe. Neutron-diffraction analysis has been performed on the same specimens in order to determine both the average-order parameter S and the size of ordered regions. The results are compared with the ones available in the literature and discussed in terms of details of the state of order.
Energy of One-Dimensional Domain Walls in Ferromagnetic Films
Authors: Aharoni Amikam
Published: April 2005

The energy of a one-dimensional 180° domain wall in a ferromagnetic film is minimized for all possible configurations of the magnetization distribution in the wall, using an approximate expression for the magnetostatic self-energy. It is shown analytically that there is no solution other than Néel or Bloch wall. There is, however, some degeneracy, which indicates a breakdown of the one-dimensional calculation, in the region of parameter values where cross-tie walls are observed experimentally. The Bloch wall energy for this approximation is shown to be rather close to the absolute minimum computed by Brown and LaBonte. Néel walls are found to have an infinitely long tail, the behavior being that of tanh. Using the functional form of this approximate minimization in the exact energy expressions, it is shown that the Néel wall energy is at most a few percent below previous estimations.
Production and Annealing of Defects in 6–88 MeV Electron-Irradiated n-Type Germanium
Authors: Fischer J. E. , Corelli J. C.
Published: April 2005

Two classes of defect acceptor levels, three classes of minority hole traps, and recombination centers are introduced by 48-MeV- electron bombardment of As- and Sb-doped (n-type) germanium at 85°K. The recovery of traps and acceptors occurs together in five stages, suggesting that the traps and acceptors are due to the same defects. The stages are centered at 150°, 200°, 360°, 460°, and about 540°K. The dominant acceptor energy levels are at or below the middle of the forbidden gap, and the dominant trapping energy levels are within 0.16 eV of the valence band. Less than 15% of the removed electrons are trapped by a level 0.20 eV below the conduction band. The recombination centers recover completely below 200°K. After 300°K irradiation with 6-, 47-, and 88-MeV electrons, only one trapping level, located at 0.10±0.01 eV above the valence band in all samples (As- or Sb-doped), is observed. The introduction rate and recovery behavior of this trapping level are independent of As and Sb concentration up to 2×1015 donors/cm3. The decay of excess carriers is analyzed in terms of the large-injection model due to Baicker. The applicability of this model is criticized in light of the present results. The effect of arsenic and antimony on the nature and recovery of the various defects is investigated. The results are compared with those obtained in low-energy-electron (≲1 MeV) and 60Co gamma irradiation.
X-Radiation Alignment of Quartz Crystals for Improved Hypersonic Propagation
Authors: Young John D. , Newkirk John B.
Published: April 2005

The generation and detection of a large number of reverberating acoustic echoes in crystalline quartz at liquid-hel um temperatures and at frequencies above 1 Gc/sec require and end-face parallelism alignment less than 0.4 sec of arc for 3-mm-diam rods. Parallelism angles of this magnitude are beyond the present commercial capability of optical companies to process quartz rods. This paper describes an x-radiation technique which induces a permanent bend in quartz crystals and, when applied in a specific azimuth direction, makes the end faces more nearly parallel. The acoustic response of quartz crystals at 10 Gc/sec and 4.2°K is used as an indicator of end-face parallelism. Our experimental acoustic results show the effects of thermal annealing of quartz crystals, the effects of x radiation applied to the specimens in various directions, the effects of increasing dosage of x irradiation, and the effects of rotating the crystal while irradiating it with x rays. We have been able to improve the 10-Gc/sec acoustic response of quartz rods from 3 to 7 times by the x-ray correction of the end-face parallelism.
Photolytic and Reduction Coloring of Na-Compensated CaWO4:Nd
Authors: Cronemeyer D. C. , Beaubien M. W.
Published: April 2005

Two sets of CaWO4:Nd:Na crystals have been grown having Nd concentrations of 0.5 and 1.0 at.%, and various concentrations of Na. The photolytic coloring is somewhat enhanced by the presence of Na, whereas reduction coloring is made much more difficult by full compensation of the Nd with Na. The 2.9-eV absorption for the extraordinary ray becomes more prominent with increasing Na content, in the case of reduction coloring. The atomic model applicable is discussed. Practical applications of these findings are also mentioned.
Electronic Properties of Titanium Monoxide
Authors: Denker Stephen Paul
Published: April 2005

Electric, magnetic, and optical properties of the rocksalt form of titanium monoxide (TiO0.80 to TiO1.25) have been studied. TiO is metallic, exhibiting weak paramagnetism. Properties of TiO-phase samples are determined primarily by the relative concentration of titanium and oxygen atoms and to a lesser extent by sample preparation. The resistivity of TiO1 can be represented as the sum of an extremely large residual resistivity and a temperature-dependent part having positive slope. Although off-stoichiometric samples exhibit resistivity vs temperature variation not typical of metals, the entire phase can be characterized as metallic. Specular reflectance data suggest that the yellow color of TiO-phase samples is due to a plasma edge relaxation in the yellow region of the visible spectrum.
X-Ray Analysis of Diffusion-Induced Defects in Gallium Arsenide
Authors: Schwuttke G. H. , Rupprecht H.
Published: April 2005

X-ray diffraction microscopy measurements were made on zinc-diffused surface layers. The diffraction contrast produced through diffusion-induced defects was investigated. Fault structures were deduced from changes in diffraction contrast that occur in large-area topographs recorded through different Bragg reflections. Dislocations having 〈110〉 axis have been identified and associated with the Lomer-Cottrell reaction. X-ray junction profiles have been obtained and correlated with zinc-concentration profiles. It is concluded that diffusion-induced defects in gallium arsenide are generated by a stress-relief mechanism.
A New Modification of the Semiconducting Compound K3Sb
Authors: Sommer A. H. , McCarroll W. H.
Published: April 2005

It is possible to prepare a cubic modification of K3Sb in the form of a thin film by the superficial oxidation of an antimony layer prior to the addition of potassium. Annealing of the film thus formed in an excess of potassium at 160°–170°C results in an apparently irreversible transformation to the purple hexagonal form. An analysis of the optical absorption and photoemission data shows that cubic K3Sb is a p-type semiconductor with a bandgap estimated to be 1.4 eV and an electron affinity between 0.6 and 1.3 eV. The cubic nature of brown K3Sb was determined by x-ray and electron diffraction analyses. These studies show that K3Sb has the DO3 structure, typical of cubic alkali antimonides and bismuthides. The data indicate that the material is essentially ordered.
Low-Frequency Impedance Characteristics of a Langmuir Probe in a Plasma
Authors: Crawford F. W. , Grard R.
Published: April 2005

Measurement of the low-frequency impedance of a Langmuir probe in a plasma can give the local electron density and temperature. Such diagnostic methods have been employed in ionospheric probing, but the interpretation of the results based on simplified theory has not been entirely satisfactory. This paper describes laboratory plasma studies designed to investigate the validity of the simplified theory. Good agreement is obtained between results obtained by two different impedance techniques, and conventional Langmuir probe data reduction. It is concluded that the methods could provide additional methods of measurement in laboratory plasmas, with some inherent advantages, but that a more detailed theory and extensive experimental verification are required before they can be applied with confidence to more complicated conditions in the ionosphere.
Ferromagnetic Resonance in Nickel and Iron
Authors: Bhagat S. M. , Hirst L. L. , Anderson J. R.
Published: April 2005

The ferromagnetic resonance linewidth has been measured at frequencies from 9–57 kMc/sec at room temperature in bulk single-crystal samples of nickel and in thick single-crystal whiskers of iron. The results for nickel can be accounted for by relaxation damping described by a frequency-independent Landau-Lifshitz coefficient λ=2.3×108 sec−1 plus a smaller contribution from the exchange-conductivity mechanism. The widths in iron are found to vary as the square root of the frequency and are due mainly to exchange-conductivity broadening. They can be fit with exchange stiffness 1.9×10−6 erg/cm (known from other experiments), magnetic surface-anisotropy energy 0.4 erg/cm2, and Landau-Lifshitz relaxation parameter ≲0.7×108 sec−1.
Guardring Probes in Hot-Cathode Hg-Vapor Discharges
Authors: Medicus G.
Published: April 2005

The probe curves J(V)=Je(V)+Ji(V) for planar guardring probes (GP) are found to approximate ``ideal plane probe'' (IPP) behavior only in Je≈const.≈Je0 [=zero-field electron (e-) current] for e-attraction; for ion (i-) attraction Ji≈const.≳5Ji0, in columnless Hg-vapor discharges with hot cathode. The sharp knee of the IPP is prevented mainly by perturbations of the plasma by the large G whose radius rG≫ Debye length, and rG≫rP. The perturbations are proportional to the surface area of G+P.

The planar GP reacts strongly to a weak fast group of electrons of perpendicular incidence, while small spherical probes (SP) react only weakly.

The probe curves for planar and spherical GP's and for small SP's and their second derivatives (SD) are automatically plotted and discussed. Peculiar distortions of the SD's of the GP's (double hump shape) are found to be caused by the perturbations of the plasma by the GP's.
Shape Demagnetizing Effects in Permalloy Films
Authors: Coren R. L.
Published: April 2005

An experimental and theoretical study was made of the shape-dependent demagnetizing fields in thick (∼1 μ) uniaxial Permalloy films. Measured values of the wall motion coercive field Hc and of the rotational anisotropy field Hk change by factors of 20 and 3, respectively, as the lateral sample dimensions vary from 20:1 through 1:20. The values of Hc agree with a theory in which magnetization switching occurs when the total internal field (applied field plus demagnetizing field) exceeds an intrinsic coercive field which is independent of sample shape. In films for which the demagnetizing effects are significant this leads to a well-defined range of effective switching fields and to highly skewed hysteresis loops. The total internal field also gives agreement with the measured values of Hk, reflecting the fact that the remanent state of a hard direction hysteresis cycle is multidomain, with a consequent reduction of the easy axis demagnetization. The theoretical analysis approximates the rectangular film by a very flat ellipsoid; the good agreement with the experiments indicates that stray fields from corners and edges can be ignored when studying magnetic films.
Anisotropy of the Snoek Phenomenon in Niobium
Authors: Hoffman R. A. , Wert C. A.
Published: April 2005

The anisotropy of the strength of the Snoek relaxation has been measured for both oxygen and nitrogen in niobium. Single crystals of niobium of extreme orientations, [100] and [111], as well as several intermediate orientations were grown in an electron beam melter. The height of the Snoek peaks of the residual oxygen and nitrogen was measured at 80 kcps using a quartz transducer. The orientation for which the peak height is maximum is [100]; the orientation for which it is minimum is [111] —it is actually zero for this orientation. This result shows that the interstitial site is symmetrical about [111], but it alone does not differentiate between occupancy by the interstitial of the octahedral and tetrahedral sites.
Measurement of the Sticking Coefficients of Silver and Gold in an Ultrahigh Vacuum
Authors: Bachmann L. , Shin J. J.
Published: April 2005

The sticking coefficients of silver and gold evaporated on a SiO substrate under ultrahigh-vacuum conditions have been measured as a function of the thickness of the metal deposit. The mass of the deposit was determined by a quartz crystal oscillator. The incident rate of the metal was measured by observing the metal vapor flux through an ionization gauge. Observations were made at an incident flux between 3 and 4×1013 atoms/cm2/sec and substrate temperatures of 300° and 450°K. A sticking coefficient of unity was found for silver when the mean thickness of the deposit was greater than 10 Å and for gold when the deposit was thicker than 20 Å. The mean sticking coefficient measured for silver is 0.81±0.05 in the thickness range of 0–10 Å. Gold was found to have a mean coefficient of 0.89±0.05 in the thickness range 0–20 Å. These values are higher than those previously reported in the literature. The experiments indicate that the discrepancies are due to a higher substrate contamination in previous studies.
Nucleation of Solid in an Undercooled Liquid by Cavitation
Authors: Hunt J. D. , Jackson K. A.
Published: April 2005

Cavitation in an undercooled liquid can nucleate solid. We have demonstrated, by a new experimental technique, that nucleation occurs when a cavity collapses, rather than when it expands. Extremely large pressures, ∼105 atm, are generated by the collapse of a cavity. The change in pressure lowers the freezing temperature of the liquid, and thereby results in nucleation.

It is suggested that nucleation by scratching also takes place through the medium of cavitation.
Anomalous Critical Currents in Superconducting Noninductive Coils of Nb-25% Zr Wire
Authors: Lubell M. S.
Published: April 2005

The critical current vs preset magnetic field has been measured for a number of multilayer bifilar noninductive coils wound with cold-worked 0.025-cm-diam Nb-25% Zr wire. In an applied field greater than 8 kG and less than 24 kG the superconducting to normal transitions are not single-valued and show an effect analogous to ``antitraining.'' It is shown that the anomalous critical currents are due to cooling in a constant applied field. The conditions for obtaining, avoiding, and eliminating the different values of critical current have been investigated and the results are compared with short-sample and magnet data. The experimental results suggest the unorthodox view that high transport currents are obtained when induced magnetization currents are initially present and low transport currents are measured when only the reversible magnetization is present in part of the noninductive coil.
Fracture Phenomena in Amorphous Selenium
Authors: Andersen A. Lindegaard , Dahle Birgit
Published: April 2005

Fracture surfaces of amorphous selenium broken in flexure at room temperature have been studied. The fracture velocity was found to vary in different regions of the fracture surface. Peculiar features were observed in a transition zone between fast and slower fracture. In this zone cleavage steps with a nearly constant spacing of approximately 1 μ were found. Occasionally long cleavage whiskers—up to some millimeters long—were observed. Within certain regions the cleavage steps were crossed and interrupted by two line systems. The maximum fracture velocity has been measured to 350 m/sec. Further the velocities of ultrasonic longitudinal and shear waves were measured to 1820 m/sec and 930 m/sec, respectively. Based on these results the two line systems in the transition zone can be interpreted as ``Wallner lines'' with sources within the zone.
Comparison of a Numerical Method and the WKB Approximation in the Determination of Transmission Coefficients for Thin Insulating Films
Authors: Politzer Beverly A.
Published: April 2005

A direct numerical solution of the Schrödinger equation for the case of electron tunneling through thin-film metal—insulator—metal sandwiches is described. Curves of transmission coefficient vs energy are obtained for an image-force barrier model by this method and are then compared, for applied fields ranging from 103 to 109 V/m, to analogous curves obtained by application of the WKB approximation. For a constant applied field, the WKB treatment predicts transmission coefficients which are smoothly varying functions of energy and monotonically decreasing functions of insulator thickness at all energies. On the other hand, the corresponding numerically computed quantities show definite periodic oscillations in energy and also thickness ``resonances.'' The dependence of these oscillations on energy and thickness is shown to be the result of the partial reflection and interference of electron waves as the electron beam penetrates the barrier region representing the insulator film. The numerically computed transmission curves indicate that these reflection effects are significant at very low energies and at energies approaching the barrier maximum and that the resulting interference becomes significant at high energies and fields where the electron wavelength becomes comparable to the dimensions of the barrier. At the low energies, the major portion of the reflection is shown to originate from the regions adjacent to the metal—insulator interfaces; at the high energies, the reflection is attributed mostly to regions contiguous to the first metal—insulator interface and the top of the potential barrier. In all cases, however, the conditions for validity of the WKB treatment are seen to rule out these effects. Finally, the numerical results confirm the expected breakdown of the WKB connection formulas at those energies where a major portion of the barrier region is reflecting.
Sputtering of Gold by Low-Energy Inert Gas Ions—II
Authors: Scott H. G.
Published: April 2005

The sputtering of gold by neon and xenon ions with energies from 40 to 100 eV has been measured by determining the change in electrical resistance of thin gold films. With xenon ions the yield is proportional to ion energy, and the value at 100 eV (0.14 atoms/ion) is lower than that found previously with argon. It is therefore concluded that factors other than the mass ratio of ion to target atom are important in determining low-energy sputtering yields. The variation of yield with ion current for 40-eV neon ions (cf. Scott, 1962) is confirmed, and pulsed currents have been used to investigate the hypothesis that this is due to excitation of an atom followed by ejection: the lifetime of the excited state is estimated to be less than 10−6 sec, which is inconsistent with the magnitude of the yield.
Role of Spirals in the Growth of Prism Faces of Cultured Quartz
Authors: Joshi M. S. , Vagh A. S.
Published: April 2005

A detailed study is made of surface structures of over four-hundred prism faces of cultured quartz. Growth spirals observed are illustrated. They have been examined with the help of a phase contrast microscope. Density of screw dislocations is found to vary between wide limits, being of the order of 104 cm−2 in most of the crowded regions. The role of spirals in the development of prism faces is discussed. Different types of interactions of spirals are illustrated. The origin of the formation of the spirals is also discussed. It is shown that the edges of the growth layers on the steeper sides of spiral growth pyramids constitute striations inclined at 45° to the edge between m(101̄0) and R(101̄1) faces.
Growth and Properties of β-SiC Single Crystals
Authors: Nelson W. E. , Halden F. A. , Rosengreen A.
Published: April 2005

Chemical, electrical, and optical measurements were performed on n- and p-type β-silicon carbide crystals grown from pure or doped carbon-saturated silicon melts. Pure, transparent yellow crystals showed no detectable impurities and had carrier concentrations in the range of 1016 cm−3. Extensive twinning was observed. Uncorrected electron mobilities of 700–1000 cm2/V·sec were measured at room temperature. Intense injection electroluminescence, peaking at 2.28 eV and 2.0 eV, was observed in many diodes. Strong photoluminescence was observed in aluminum-doped crystals at 77°K and at room temperature when irradiated with uv light.
Investigation of the Geometrical-Optical Theory of Magnetic Structure Imaging in the Electron Microscope
Authors: Wade R. H.
Published: April 2005

The imaging of domain walls in thin ferromagnetic films by off-focus transmission electron microscopy is generally considered in terms of a simple geometrical-optical theory in which the electron beam is deviated by the Lorentz force exerted by the internal magnetic flux of the film. Calculated intensity profiles of the wall images are rectangular in form for large off-focus distances where the geometrical-optical approach is valid. The width of the images is simply related to the thickness and internal magnetic flux of the film and to the off-focus distance of the observation plane and the electron beam accelerating potential. An experimental investigation of these relationships for vacuum-condensed films of iron, nickel, and their alloys shows general agreement with the theoretical relationships derived for 180° Néel walls. The observed electron beam deflections within the films are about half of the calculated values. This is largely due to the wall angles being less than 180° and to the film density being below that of the bulk material. Domain wall widths in 80–20 Ni–Fe films about 200 Å thick were found to be approximately 2000 Å, leading to a value for the exchange constant of this material of around 8×10−7 erg·cm−1.
Ion Beam Analysis by an Electrostatic Technique
Authors: Martin D. H. , Wakefield R. H.
Published: April 2005

A method of spatially analyzing a positive ion beam by electrostatic means is presented. In this method, a small portion of a given ion beam passes through a low-density gas-filled chamber, where ionization and charge exchange products are collected and analyzed so as to reveal the original positive and neutral beam components. Results of a detailed spatial analysis of a 10-keV argon ion beam from a Von Ardenne duoplasmatron ion source are given and discussed. Comparison of integrated beam components with theoretical beam ``blowup'' indicates that microscopic and macroscopic neutralizations are the same within limits of the measurements.
Strain-Rate Effects in Metals
Authors: Butcher B. M. , Karnes C. H.
Published: April 2005

A series of computations has been completed which investigates strain-rate effects on stress-wave propagation in metals. The principal difficulty in calculations of this type is the choice of a functional relationship between stress, strain, and strain rate. Experimental results have shown that the stress-strain relation of a material experimentally determined under quasistatic conditions may not be extended to dynamic conditions, i.e., the rate of loading is important. Therefore, a relation between stress, strain, and strain rate was constructed that is consistent with the experimental observations of plastic wave propagation in high-purity aluminum rods (one-dimensional stress) and adapted to the behavior of 6061-T6 aluminum. This function was then used to calculate the propagation characteristics of a stress pulse propagating in a state of one-dimensional strain. The calculations compare favorably with the experimentally observed dynamic behavior of 6061-T6 aluminum impacted at 322 m/sec.
Thermal Conductivities of MgO, Al2O3, and ZrO2 Powders to 850°C. II. Theoretical
Authors: Godbee Herschel W. , Ziegler Waldemar T.
Published: April 2005

A theoretical expression is presented to relate the effective thermal conductivity of statistically describable two-phase systems to the conductivities of the pure phases, the volume concentrations of the phases, and a shape factor. Auxiliary equations to relate bulk gas conductivity and small interparticle distance and to predict a radiation heat transfer contribution to effective thermal conductivity are also presented. The shape factor is a property of the discontinuous phase and is related to the two-phase system only through the volume balance of the phases. In the derivation of the expression no assumptions are made concerning particle shape, size, or spatial arrangement. However, the derivation is based on a simplified model in that the isotherms in the model are assumed to be planes perpendicular to the heat flow. In exact solutions of the heat flow equation, no assumptions are made regarding the heat flow or temperature pattern. On the other hand, exact solutions have been carried out only for simple shapes in fixed arrangements that seem to fall short of describing actual powder-gas systems.
Superconductivity of a Composite of Fine Niobium Wires in Copper
Authors: Cline H. E. , Strauss B. P. , Rose R. M. , Wulff J.
Published: April 2005

Composites consisting of fine Nb filaments in a copper matrix were fabricated, and the following superconducting properties measured: the critical temperature, critical transverse magnetic field as a function of temperature, critical current density at 4.2°K as a function of transverse magnetic field, and magnetization at 4.2°K. The reduction in Nb filament size was checked by optical and electron micrography. Filament diameters ranged down to 100 Å. As the diameter decreased, Tc, Hc(T), and Jc all decreased. This behavior was attributed to the proximity effects of the copper matrix on the Nb. The results are closely comparable to those of investigations of superimposed thin films. It is therefore not expected that high critical fields can be attained by composites involving a type II superconductor in a matrix of a nonsuperconductor.
Potential Barrier Parameters in Thin-Film Al–Al2O3-Metal Diodes
Authors: Nelson O. L. , Anderson D. E.
Published: April 2005

Internal photoelectric thresholds for collection of electrons through a thin Al2O3 layer formed by anodization in an aqueous nonsolvent electrolyte were measured as a function of photon energy, applied bias, oxide thickness, temperature, and overlayer metal. These data were analyzed in terms of photoexcitation mechanisms and optical absorption calculations to determine the potential barrier profile presented by anodized Al2O3 between metal films. The barrier profile was found to be given by the work function of the metal minus the electron affinity of the oxide, modified by the image effect for an electron between conductors and by the applied bias and the work function difference between the metals. For this agreement the electron affinity of the oxide was chosen to be approximately 2.0 eV and the high-frequency dielectric constant was used. A slight asymmetry was observed for Al–Al2O3–Al devices, possibly resulting from the metal-oxide transition regions. The potential barrier was found to increase with decreasing temperature, consistent with I-V characteristics.
Magnetohydrodynamic Flows in Closed Regions with Complete Symmetry about an Axis
Authors: Eraslan Arsev H.
Published: April 2005

A formal perturbational technique was developed to obtain solutions for magnetohydrodynamic flow problems in closed regions with symmetric properties of flow and boundary conditions about an axis. The system of highly nonlinear partial differential equations, governing the problems of this class, was found to reduce to systems of simultaneous linear partial differential equations, thus creating a possibility of obtaining solutions by classical mathematical methods. The technique used was based on a well-known power series type of perturbational expansion in terms of a small parameter, which in the limit was assumed to become the solution of the original system. The general technique was applied to the magnetohydrodynamic flow in a toroid under the influence of a uniform applied magnetic field along the direction of the main axis of the toroid. It was found that the secondary flow caused by the centrifugal body force on the fluid element due to the curvature created induced electromagnetic components and a pressure variation along the radial direction.

The solutions were carried out to include completely the second perturbational equations and the electromagnetic and flow fields were discussed for different values of characteristic parameters appearing in the solutions.
Determination of Mobility in Nonstoichiometric Low-Mobility Semiconductors
Authors: Bruck A. , Tannhauser D. S.
Published: April 2005

The method of determining charge-carrier mobility by combining conductance with thermogravimetric measurements is discussed. The conditions of validity of the method are analyzed for one example. It is shown that the analysis of such measurements may permit estimation of an upper limit for the width of the conduction band. Application to CoO shows that the bandwidth in CoO is ≤kT at T=1500°K.
Deposition of Tantalum, Tantalum Oxide, and Tantalum Nitride with Controlled Electrical Characteristics
Authors: Krikorian E. , Sneed R. J.
Published: April 2005

Results are presented which indicate that the effects of sputtering voltage and current on the resistivity of films sputtered from pure tantalum appear to be traceable to the pressures and growth rates associated with each sputtering condition. From these data it can be deduced that the observed resistance variations are largely accountable in terms of film impurity content. Tantalum sputtered reactively in the presence of oxygen produces films which are shown to exhibit a sharp transition from relatively low to very high resistivities as the oxygen concentration in the working gas is raised. Changes of greater than 12 orders of magnitude are observed. It is demonstrated that sputtering voltages and anode potentials effect a significant change in the transition point. Similarly well-defined results are presented on films reactively sputtered in the presence of N2. The results tend to indicate that the anode potential retards (or enhances) electrostatically both the reactive and nonreactive interaction of tantalum with oxygen or nitrogen at the film surface. Results on the effect of substrate temperature on growth rate demonstrate that in reactive sputtering, the reaction occurs at the substrate surface.
Step Motion on Crystal Surfaces
Authors: Schwoebel Richard L. , Shipsey Edward J.
Published: April 2005

It is postulated that steps on crystal surfaces capture atoms diffusing on the surface with certain probabilities and, in addition, that the capture probability depends on the direction from which adsorbed atoms approach the step. A general solution for the time-dependent step distribution is obtained in terms of these probabilities and an arbitrary initial distribution of an infinite sequence of parallel steps. It is shown that coalescence of steps or stabilization of step spacings can occur as a consequence of assuming that capture probabilities are directionally dependent. Some of the implications of the theoretical model are related to the growth of real crystal surfaces.
Low-Frequency Oscillations in a Thermal Cesium Plasma
Authors: Decker John A.
Published: April 2005

The oscillation modes present in the ``TOPSY'' thermally generated cesium plasma device have been investigated experimentally; oscillation frequency spectra and three-axis (r,θ,z) maps of relative phase have been studied as functions of axial magnetic field strength, electron density, axial drift current, plasma column length, and ionizer sheath polarity. Both conducting and nonconducting cold end plates were used. Two distinct modes were observed: a low-frequency oscillation (∼1 kHz) which was identified as an ion acoustic wave excited by axial circulating currents in the periphery of the plasma column, and a higher-frequency oscillation (7 to 50 kHz) whose frequency behavior showed close agreement with the theory of the ``universal'' resistive drift-wave instability, but which failed to show the azimuthal propagation predicted by this theory. The lack of observed azimuthal phase shift could not be explained in terms of the transit-time-controlled potential-relaxation oscillations predicted for thermally generated plasmas, by sheath oscillations, or by the reflection of the drift waves at the plasma/end plate sheaths. Both modes were spontaneously present in the ``quiescent'' plasma (i.e., with no net drift current) and were neither further excited nor significantly altered in the presence of strong drift currents.
Nanosecond Breakdown in Liquid Dielectrics
Authors: Felsenthal Peter
Published: April 2005

Measurements of nanosecond formative times in various liquids are summarized. The experiments utilized applied fields of up to 3.3×106 V/cm while equipment time resolution was on the order of 0.3 nsec. Detailed results are given for n-hexane including aging time histories and formative times with and without an applied bias field. The data obtained in this study are compared with earlier work. Using a simplified breakdown model the mobility of charge carriers at 2×106 V/cm is calculated to be 8.7×10−2 cm2/V·sec. The nanosecond high-voltage insulating qualities of various liquids are discussed.