bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Electron Hopping in Eu3S4 by Combined Electrical Conductivity and Thermal EMF Measurements
Authors: Bransky I. , Tallan N. M. , Hed A. Z.
Published: February 2004

Combined electrical conductivity and thermoelectric power measurements have been made on Eu3S4 at temperatures from 100° to 1000°K. These measurements show that the charge carrier concentration in this temperature range is essentially constant. The activation energy for electrical conduction arises, therefore, from the temperature dependence of the drift mobility, and is interpreted as an energy required for the hopping motion of the electronic charge carriers. An abrupt change in resistivity, characteristic of a transition, occurs at about 175°K. The activation energy for conduction above and below the transition is 0.163±0.004 eV and 0.21±0.01 eV, respectively. The Seebeck coefficient data obtained are interpreted in terms of the contribution of the kinetic energy term and the influence of the high charge carrier density on the concentration of available sites.
Plasmas Injected into Solids: Analytic Study of the Diffusion Corrections
Authors: Schilling R. B. , Lampert M. A.
Published: February 2004

The properties of a plasma injected into an insulator or semiconductor are analytically describable if diffusive current flow is neglected. However it is known from experimental and theoretical (computer) studies that the corrections imposed by the dominance of diffusive current flow near the contacts are quite large for L/La<10 and significant even for larger L/La, where L is the distance between the injecting contacts and La the ambipolar diffusion length. The regional approximation method is employed to obtain an approximate, but complete analytical description of the injected plasma for the two problems. Satisfactory agreement is obtained with previous computer results of Baron.
Numerical Solution to Laplace's Equation in Spherical Coordinates with Axial Symmetry
Authors: Hoeper P. S. , Wenstrup Robert S.
Published: February 2004

A numerical method for solving Laplace's equation in spherical coordinates for an axially symmetric geometry has been developed. Dirichlet boundary conditions on a closed surface yield a set of difference equations. The method of successive overrelaxation has been employed to find solutions to those equations. Application of the method is illustrated by finding the field configuration in a new type of electron gun used in a spherical electron monochromator.
Tunneling Conductance of Asymmetrical Barriers
Authors: Brinkman W. F. , Dynes R. C. , Rowell J. M.
Published: February 2004

The voltage-dependent tunneling conductance of trapezoidal potential barriers has been calculated using two extreme models of (1) the WKB approximation and (2) perfectly sharp boundaries between the metal electrode and the insulator. We show that for both models the conductance-voltage plot is roughly parabolic at low voltages (≲0.4 V). The minimum conductance is not at zero bias unless the barrier is symmetrical and identical Fermi energies are chosen for the two metal electrodes. The inclusion of image forces does not radically alter the shape of the conductance-voltage dependence. Using reasonable barrier shapes, the asymmetry of the calculated conductance about V=0 is not as large as we frequently observe experimentally. We point out that this extreme asymmetry appears to be associated with the presence of organic impurities in the oxide layer of the junction.
Diffusion of Aluminum in the ZnSe–ZnTe System
Authors: Aven M. , Kreiger E. L.
Published: February 2004

The diffusivity of Al in ZnSe, ZnSe0.5Te0.5, and ZnTe has been determined in the temperature range of 700°–1000°C. At 1000°C the diffusivities, calculated from the experimental data assuming the Fick's diffusion law to be valid, are (0.66±0.11) × 10−9 cm2/sec for ZnSe; (1.2±0.3) × 10−9 cm2/sec for ZnSe0.5Te0.5; and (1.3±0.5) × 10−9 cm2/sec for ZnTe. The activation energy for diffusion is approximately 2 eV for all three. It is suggested that the diffusion of Al proceeds substitutionally via the Zn sublattice.
Charge Transport Through an Aerosol Cloud
Authors: Hoppel W. A. , Gathman S. G.
Published: February 2004

The system of coupled equations which governs the electric field, ion densities, and aerosol charge in a quiescent cloud between semi-infinite charged plates is solved numerically for the case when ionization is confined to a layer near each plate and the case of volume ionization. The results predicted by the governing equations are verified experimentally. The electrical stress produced in the case of volume ionization tends to stabilize the fluid whereas surface ionization can produce hydrodynamic instability. The electroconvective instability produced by surface ionization is easily observable both visually and electrically. If turbulence is generated in the chamber by mechanical means, the turbulent transfer of charge will oppose the conduction current in the case of volume ionization and enhance the total current in the case of surface ionization.
Diffusion in Decaying Plasmas
Authors: Kregel Mark D.
Published: February 2004

An iterative numerical technique has been employed to model the decay of plasmas in an electronegative gas, nitric oxide, and in an electropositive gas, helium. The spatial and temporal behavior of the charged species are followed and compared with experiments through four regimes: (1) positive ion-electron ambipolar diffusion regime, (2) transition regime, (3) positive ion-negative ion ambipolar diffusion regime for an electronegative gas, and (4) free diffusion regime for an electropositive gas. Densities of all charged-particle species are calculated from Gauss' law. The structural features in the experimental measurements of decaying plasmas are reproduced in the results of the numerical calculation.
Electrical Fluctuations in Iodine
Authors: Caruthers Jerald W. , Ham Joe S.
Published: February 2004

Large-current-produced noise was observed in polycrystalline iodine samples in a range where the conduction is Ohmic. The voltage and frequency dependence between 5 and 500 Hz was V3/f2. At lower frequencies the spectrum seemed to approach a variation as V2 and to become independent of frequency indicating relaxation times of 200–600 msec. Large spatial correlations were observed with a lag time indicating positive charge carriers with a mobility about 1.3 cm2/V sec. These measurements are consistent with conduction taking place by the motion of clusters of charges where a cluster moves distances of the order of millimeters with a mobility of the order of 1 cm2/V sec. Difficulties with the sample reproducibility precludes more detailed analysis but the results indicate that noise measurements may be a useful method to study the mechanism of electrical conduction in low-mobility materials.
Ambipolar Drift Noise in a Semiconductor in the Presence of a Magnetic Field
Authors: Maldonado C. D. , Bhattacharjie A.
Published: February 2004

The noise spectrum due to fluctuations of electron-hole pairs in a semiconductor in the presence of uniform and time-independent electric and magnetic fields is presented in this paper. This spectrum is obtained via the Green's function for the macroscopic differential equation which governs the behavior of the conditional average for fluctuations in the electron-hole pair particle density when generation-recombination and ambipolar drift are the only important processes. For the general situation when the electric and magnetic fields are not collinear, the obtained spectrum is a complicated function of both frequency and magnetic field for a fixed value of electric field. From this spectrum the spectra corresponding to the special cases when the electric field is parallel and perpendicular to the magnetic field are obtained. Since the case when the electric field is perpendicular to the magnetic field is the most interesting from an experimental viewpoint, it is discussed in more detail and illustrative plots of the spectrum are presented.
Thermally Stimulated Currents in Mylar, High-Field Low-Temperature Case
Authors: Lilly A. C. , Henderson Rosemary M. , Sharp P. S.
Published: February 2004

The thermally stimulated current (TSC) technique has been used to study the release of charge injected into Mylar films with both short (μ sec) and long (10 sec) voltage pulses. The electric field applied across the Mylar is as high as 800 kV cm−1. The TSC spectrum is complex with the peaks at low temperature depending on the type of electrode used and the sign of the voltage pulse. A current reversal exists, which leads to peaks of both signs indicating the possibility that double-injection has occurred. The spectrum at low temperature is characterized by 1/f noise arising possibly from ``slow'' surface states. At high temperatures (410°–450°K) a peak from a deep trapping level occurs with a trap energy estimated to be 1.6–2.0 eV. The spectrum is discussed in terms of possible trap mechanisms.
Control of Optical Losses in p-n Junction Lasers by Use of a Heterojunction: Theory and Experiment
Authors: Kressel H. , Nelson H. , Hawrylo F. Z.
Published: February 2004

The optical losses of homojunction and heterojunction ``close-confinement'' GaAs injection lasers fabricated by liquid phase epitaxy have been described in terms of a simple waveguide model. By introducing an (AlGa) As–GaAs p+-p heterojunction (ΔEg∼0.1 eV) within ∼2 μ of the p-n junction, the room-temperature absorption loss is substantially reduced and the laser efficiency increased. This reduced absorption is due to combination of improved optical waveguiding and reduced absorption in the p+ material adjoining the active region. In addition, the laser gain coefficient can be increased in some cases by the addition of a heterojunction with the degree of improvement depending on the electron diffusion length, width, and doping level of the active region. The increased gain coefficient can contribute substantially to the reduced threshold current density of ``close-confinement'' lasers at room temperature. However, the relative contributions of reduced laser loss and increased gain coefficient to the improved performance depends critically on the details of the laser construction, and no generally valid conclusions can be made applicable to all heterojunction lasers. Values of the exterior differential quantum efficiency of 43% are obtained at 300°K, which means that much of the light internally generated is emitted. Because of the reduced internal loss, the spontaneous exterior efficiency is also greatly increased (a factor of 2–3). State-of-the art values of the threshold current density for the optimum structures are 10 000 A/cm2 for a cavity length of 20 mils, with values of 8000 A/cm2 in exceptional units. A power conversion efficiency at 300°K of 10% has been measured, which agrees with the theoretically predicted value. It is noteworthy that the diode series resistance is comparable in the solution-grown lasers with and without the heterojunction. The laser behavior has been studied as a function of varying acceptor concentration, donor concentration and bandgap energy discontinuity at the p+-p interface. Semiquantitative agreement for the laser loss between theory and experiment at 300° and 77°K is obtained for an active region width of ∼2 μ, using reasonable values of the index-of-refraction differences between the various laser regions and free-carrier absorption.
X-Ray Temperatures from Laser-Induced Breakdown Plasmas in Air
Authors: Daiber J. W. , Thompson H. M.
Published: February 2004

The soft x-ray flux from laser sparks in air at a pressure near 330 Torr has been measured with a three-channel absorption spectrometer. From these measurements plasma temperatures were inferred. For laser peak-power levels from 300 to 600 MW and pulse durations from 10 to 25 nsec, the temperatures varied from 40 to 160 eV. Streak camera records were taken of the axial plasma growth. For the shortest laser pulses, the plasma temperatures and luminous front velocities were in near agreement with the predictions of the radiatively supported detonation wave model. As the laser pulse width increased so did the plasma velocity, but not the temperature. These higher-velocity streak records also showed several slower-moving luminous fronts behind the faster front. These slower fronts are believed to be detonation waves. Space- and time-resolved x-ray flux measurements were also made, from which the x rays were found to be associated with the highly luminous plasma and only occurred during laser heating of the plasma.
Inductive Coupling of Josephson Junctions to External Circuits
Authors: Owen C. S. , Scalapino D. J.
Published: February 2004

The inductive coupling between a Josephson junction and a superconducting stripline is calculated. In the overlapping region they share a superconducting film, the structure having superconducting (S) and insulating layers (I) sandwiched S—I—S—I—S. The coupling arises from the magnetic field penetration through the common superconductor. An equivalent circuit representation is exhibited which has the same modes and coupling as the original system. Using the circuit analog, the power transfer is calculated for several cases of interest: (a) power is radiated outward in the stripline from a biased junction and (b) power is absorbed by the junction from a source coupled to the stripline. The criterion for matching the tunnel junction to the stripline is discussed.
Critical Field in the Ti–Nb–V System
Authors: Bellin P. H. , Gatos H. C. , Sadagopan V.
Published: February 2004

The superconducting resistive critical field Hr of the bcc region of the Ti–Nb–V ternary system has been studied. Measurements at 4.2°K on cold-rolled alloys at 10 at.% composition intervals determined that Hr varied smoothly with composition. A maximum in Hr occurred at a valence electron to atom ratio n of 4.4 for pseudobinaries of the system. The ratio of critical field to transition temperature was found to be a function of n alone in qualitative accord with the theory for type II superconductors. A criterion for predicting the behavior of similar systems is presented.
Simple and Sensitive Magnetic Resonance Spectrometer Using Thermal Detection and Square Wave Frequency Modulation
Authors: Janssens L. , Witters J.
Published: February 2004

The special features of this spectrometer are square wave frequency modulation and thermal detection. The modulation results from switching the microwave source between two eigenfrequencies of the cavity, obtaining pulsed frequency modulation without amplitude modulation in the microwave field. This technique is in many respects superior to the conventional static field modulation and has comparable noise suppression. The thermal detection is based on resistance modulation of a silicon monocrystal plate in contact with the sample and constitutes a very sensitive detection method at low temperatures.
Forces on Moving Magnets due to Eddy Currents
Authors: Reitz John R.
Published: February 2004

A magnet or a current-carrying coil, moving with constant velocity above a conducting plate, will experience magnetic lift and drag forces from the eddy currents induced in the plate. The lift and drag forces are calculated for various coil geometries on the assumption that the conducting plate is thin. For this model, the lift at high speeds approaches the force between the coil and its ``image'' located directly below it, and the drag force falls off as (velocity)−1. The ratio of lift to drag is found to be independent of coil geometry, but the velocity dependence of the lift is greatly affected by the geometry. The ratio of lift to coil weight can be as high as 2000 for a superconducting coil moving at 300 mph at 0.1 m above a conducting plate. The relevance of the calculation to magnetically supported high-speed vehicles is discussed.
Metal Membranes with Uniform Submicron-Size Pores
Authors: Desorbo W. , Cline H. E.
Published: February 2004

Porous metal wafers and thin films were produced by selectively etching the rod phase of the directionally solidified eutectics NiAl–Cr and NiAl–Mo and by a two-state replication process, respectively. The 0.5-μ-diam holes were uniform in size and distribution with densities as high as 8.5×107 holes/cm2. The flow properties of these porous membranes were tested using three liquids of different viscosity and were found to be in agreement with Poisseuille's law.
Xeroradiographic Properties of Amorphous Selenium
Authors: Donovan John L.
Published: February 2004

The xeroradiographic properties of selenium have been investigated using a typical medical x-ray spectrum. The influence of applied field was found to be very important in determining the surface potential discharge rate for both positively and negatively charged selenium. The x-ray energy absorbed per surface charge neutralized varied from 39 to 2.2 eV as the applied field increased from 104 to 2.4×105 V/cm. No effect of thickness on the discharge properties of evaporated selenium layers up to 530-μm thick was observed.
Time-Controllable Continuum Photon Emission from a Pulsed Vacuum Spark and Application to Absorption Spectroscopy in the Vacuum Ultraviolet
Authors: Mehlman-Balloffet G.
Published: February 2004

A high-voltage vacuum spark emitting a continuum in the vacuum ultraviolet was triggered by the particles originating from a dense plasma produced by a laser beam focused onto a nearby solid target. The emitted radiation was used to observe absorption processes in the same laser plasma. Because of the fast transient phenomena occurring in this plasma, the delay-time before spark breakdown had to be minimized. With the particular device used, the minimum delay-time between laser pulse and continuum emission was found to be about 200 nsec with a jitter time of the order of 20 nsec. This delay-time is too long to allow numerous observations of absorption by singly charged ions, but the applicability of the method to absorption studies on neutral species was demonstrated. Examples of absorption spectra from atoms of beryllium and magnesium are discussed.
Unified Transport Theory of Partially Ionized Nonisothermal Plasmas
Authors: Daybelge Umur
Published: February 2004

The unified charged-particle interaction operators of Kihara and Aono have been used in the system of kinetic equations for a partially ionized, nonisothermal gas in a magnetic field. It has been assumed that the coupling between the kinetic equation of the electrons and those of the heavy species is weak, as it is always the case in MHD-generator plasmas. It has been demonstrated that the new theory introduces essential corrections to the values of transport coefficients calculated by other theories of nonisothermal plasmas. Simplified calculation methods for electron transport coefficients have been proposed, which are based on the exact results given by this theory.
Liquid Epitaxial Growth of GaAsSb and Its Use as a High-Efficiency, Long-Wavelength Threshold Photoemitter
Authors: Antypas G. A. , James L. W.
Published: February 2004

The ternary-phase diagram of GaAsSb has been calculated using Darken's quadratic formalism for a ternary liquid and assuming a regular solid solution. Liquid epitaxial layers of GaAsxSb1−x have been grown in the range 0.75>x>1 on {100} and {111} GaAs substrates. Results are in excellent agreement with the calculated phase diagram. Variation of bandgap with composition of the layer has been determined by transmission, photoemission, and x-ray fluorescence experiments. The data were fitted to a curve of the form EG=A+Bx+Cx2, where A=0.725 eV, B=−0.32 eV, and C=1.02 eV. Graded bandgap layers have been obtained, with gradients of 700 eV/cm near the substrate interface and 25 eV/cm for thick layers. For use as high-efficiency photoemitters, the samples were doped p type by the addition of elemental Zn to the melt. Cesium and oxygen surface layers were used to lower the work function. Quantum yields of 0.1%–0.2% at 1.06 μ were obtained. Field assisted photoemission in a graded bandgap sample has been calculated and demonstrated experimentally.
Hugoniot Equation of State and the Effect of Shock Stress Amplitude and Duration on the Hardness of Hadfield Steel
Authors: Champion A. R. , Rohde R. W.
Published: February 2004

The effect of shock stress amplitude and duration on the hardness and microstructure of Hadfield steel has been investigated over the pressure range of 5–480 kbar. Electron microscopy techniques were used to examine the microstructure and measure the dislocation density of shock loaded specimens. Stacking fault and twin fault probabilities were estimated from x-ray diffeaction experiments. For a given peak shock stress the time duration of the stress pulse greatly affected the hardness and microstructure of the shocked material. The Hugoniot equation of state of Hadfield steel is reported for shock stresses of 5–500 kbar.
Use of fcc Metals as Internal Temperature Standards in X-Ray Diffraction
Authors: Simmons R. O.
Published: February 2004

A clear pattern of systematic error is found in thermal expansion values for Al, Ag, and Au commonly recommended and used as internal references for temperature determination in x-ray diffraction. Evidence comes from a critical analysis of the literature, including several studies of temperature measurement errors in powder cameras, and from new calibration of a thermometer used previously in precise lattice and length expansion studies. Necessary changes in the commonly accepted values for expansion of Pt and MgO are implied.
Thermoelectric Effect of Hot Carriers in Semiconductors with Nonparabolic Energy Bands
Authors: Kamal Jyoti , Sharma Satish , Kaw Predhiman
Published: February 2004

An analytical investigation of the thermoelectric effect of hot carriers in semiconductors with non-parabolic energy bands and spherical energy surfaces has been carried out. The analysis is good for moderately high intensities of the applied electric field. Some numerical results, particularly applicable to indium arsenide and indium antimonide, are presented at the end.
Temperature Dependence of Elastic, Dielectric, and Piezoelectric Constants in TeO2 Single Crystals
Authors: Ohmachi Yoshiro , Uchida Naoya
Published: February 2004

All of the elastic stiffness constants except c13 have been found to decrease almost linearly with temperature between −120° and 120°C. The constant c13 reaches the maximum in the vicinity of 0°C, above which it also decreases with temperature. On the other hand, the effective elastic constant (c11–c12)/2, which corresponds to the exceptionally slow shear wave propagating along [110], increases with temperature. The shear wave propagating in the (001) plane making angle of 35.9° with the X axis has zero temperature coefficient of velocity. Acoustic absorptions for several sound modes vary within 1 dB/cm for both the longitudinal wave (measured at 36 MHz) and shear wave (48 MHz) in the measured temperature range. Both real and imaginary parts of the dielectric constants increase monotonically with temperature, while the piezoelectric constant d14 decreases in the temperature range between −150° and 180°C.
Dislocation Dynamics and Single-Crystal Constitutive Relations: Shock-Wave Propagation and Precursor Decay
Authors: Johnson J. N. , Jones O. E. , Michaels T. E.
Published: February 2004

Rate-dependent constitutive relations for single crystals are derived in terms of dislocation dynamics. Contributions from slip on the individual glide planes are assumed to superpose linearly to give the total plastic strain. As an application of the theory, equations describing elastic precursor decay are developed for longitudinal plane-wave propagation in fcc, bcc, and rocksalt structures with wave propagation in the [100], [110], and [111] directions. In addition, expressions for precursor decay in zinc (hcp structure) are derived for wave propagation both parallel and perpendicular to the c-axis. Calculated theoretical results are compared with experimental data on precursor amplitudes for single-crystal copper (fcc), tungsten (bcc), NaCl (rocksalt), and LiF (rocksalt). Dislocation mobilities determined from direct observation of dislocations are used in these calculations. In general the theory predicts the proper relative order of the precursor amplitudes for different propagation directions. The comparisons show that in order for theoretically determined amplitudes to agree with experimental data, initial mobile dislocation densities must be two or three orders-of-magnitude greater than initial total densities which are measured in the material prior to shock loading. Possible explanations for this discrepancy are discussed.
Preparation of Thin BaTiO3 Films by dc Diode Sputtering
Authors: Shintani Yoshihiro , Tada Osamu
Published: February 2004

Direct current diode sputtering of reduced BaTiO3 ceramic has been applied to the preparation of thin BaTiO3 films. Sputtering was carried out over a range of apparent sputtering rates of ∼500–1200 mg/Ah in atmospheres of argon and air. As the substrate, Pt sheet and fused quartz were principally used. Grain size of the deposited film was ∼1000 Å for the Pt substrate at 400°C. The lattice constants were in good agreement with those of ordinary BaTiO3 when the Pt substrate was kept at a temperature above 1000°C, although they were slightly larger for substrates below 900°C. Measurements of optical density and observations of electron micrographs indicated that the sputter-deposited films have more favorable properties of transparency, uniformity, and crystallization than vacuum-evaporated films. The film prepared on a Pt substrate at 1000°C in an air atmosphere had a dielectric constant of 1700 and dissipation factor of 1.8% without post-deposition treatment. However, the remanent polarization was very small and the temperature dependence of the dielectric constant was slight.
Electromigration Damage in Aluminum Film Conductors
Authors: Attardo M. J. , Rosenberg R.
Published: February 2004

Electromigration studies of large- and fine-grain aluminum films showed that fine-grain films were characterized by a mixed orientation and a grain size of ≈2 μ, and that large-grain films had a highly preferred 98% 〈111〉 orientation and a grain size of ≈8 μ. Stripes fabricated from the large-grained films had a consistently longer life, higher activation energy, and lower standard deviation of the life distribution than stripes fabricated from fine-grained films. These results are interpreted in terms of the nature of flux divergences in the two films. Calculations give the magnitude of vacancy supersaturations at various structural divergences present in the films studied.
Dynamic Potentials in Gyrotropic Plasma
Authors: Bevc Vladislav
Published: February 2004

Wave equations are derived for the scalar and vector potentials of guided electromagnetic waves propagating in a laterally bounded magnetized plasma along the axis of the static magnetic field. Solutions are given in the Coulomb and the Lorentz gauge. These solutions are used in a critical examination of the conceptual basis of the quasistatic theory because they allow convenient partitioning of the high-frequency electric field into a lamellar and a rotational part. In the quasistatic approximation the electric field is considered to be entirely lamellar, i.e., the gradient of a scalar potential that is not consistent with Maxwell's equations. To avoid inconsistencies the problem is formulated so that the dynamic scalar potential replaces the quasistatic potential. The rotational part of the electric field is readily obtained as the time derivative of the vector potential. Exact quantitative comparison of two parts of the electric field is made possible in this way and the relative importance of each part is evaluated for a few typical cases of interest. There exist some waves with dispersion characteristics that can not be obtained with the quasistatic formula although the condition that the phase velocity be smaller than the velocity of light presumed to be necessary for the applicability of the quasistatic approximation is satisfied. In these waves the rotational part of the electric field is comparable or greater than the lamellar part. Conversely, in modes with dispersion characteristics that can be well approximated with the quasistatic formula even when the phase velocity exceeds the velocity of light the lamellar part of the electric field is much larger than the rotational part. It can be inferred that the essential element of the quasistatic theory is the assumption that the high-frequency electric field is predominantly lamellar rather than the condition that the phase velocity be smaller than the velocity of light and related criteria.
Electromagnetic Fields in a Dissipative Half-Space: A Numerical Approach
Authors: Siegel Marvin , King Ronold W. P.
Published: February 2004

The electromagnetic fields of a source in a dissipative half-space are evaluated by a numerical technique. This report illustrates the application of the method to the case of the submerged horizontal electric dipole, but the method is applicable to horizontal or vertical dipoles located in either medium. The major advantage of this method is that it provides solutions for media and frequencies which were previously unavailable. In addition, this numerical solution can independently verify previously obtained asymptotic solutions and their regions of validity. Comparisons are included between numerical results and experimental measurements performed in the Atlantic Ocean.
Interface Barrier Energy Determination from Voltage Dependence of Photoinjected Currents
Authors: Powell R. J.
Published: February 2004

Interface barrier energies and their dependence on applied field may be obtained from the voltage dependence of currents produced by electron photoinjection from an electrode. Unlike the conventional Fowler plot method, direct measurement is possible and knowledge of the absorbed light intensity is not required. A theoretical analysis gives the dependence of photocurrent on voltage and photon energy, and it is shown that barrier heights are obtainable by examination of the V-I characteristics to determine the sign of the second derivative. Theoretical forms of the V-I characteristics are derived for specific electron energy distributions which should be generally applicable. Experimental results from MIS structures using thermally grown SiO2 on degenerate n-type silicon are found to be in good agreement with theoretical predictions. Thresholds for emission from the conduction band (3.2 eV) and from the valence band (4.16 eV) are clearly defined in the V-I characteristics. The fact that the difference between these values is significantly less than the Si bandgap is explained by phonon scattering effects in Si and it is concluded that the actual separation between the Si and SiO2 conduction bands is about 3.0 eV. The barrier energy for Au on SiO2 was found to be 4.1 eV, and a value of 2.2 was determined for the SiO2 image force dielectric constant.
Axial Pressure Gradients in dc Discharges with a Return or Bypass Connection
Authors: Tombers Reid B. , Chanin Lorne M.
Published: February 2004

Measurements have been made of the effect of a bypass on longitudinal pressure differences in dc discharges of helium and xenon and for a 10% mixture of neon in helium. Comparison of the data in helium and xenon confirms the validity of previously predicted theoretical expressions for the pressure reduction. Measurements of the reduction of cataphoretic effects using the bypass are also reported for the mixture.
Theoretical Approach to a Technique for Measuring Thermal Conductivity at High Temperature
Authors: Vardi Joseph , Lemlich Robert
Published: February 2004

A theoretical solution by finite difference methods is presented for the steady-state temperature field within a solid uniform right circular cylinder which is heated by a uniform source along its curved surface and which simultaneously loses heat by fourth-power radiation from all its surfaces to much cooler surroundings. The results of the solution are more accurate than the semi-empirical relationship of Hoch et al., and so can be applied with greater reliability to their new metal-envelope induction technique for determining thermal conductivities of nonmetals at high temperatures.
Collision Processes in a CO2 Laser Plasma
Authors: Freudenthal J.
Published: February 2004

The neutral and ionic population of a plasma in a CO2 laser gas mixture was analyzed mass spectrometrically. Comparative measurements of the CO2 concentration at the cathode and anode side of the discharge show that the strongest regeneration of CO2 is at the cathode side. The oxidation mechanisms of CO (regeneration of CO2) in the He–N2–CO2 plasma is consistent with O(1D)+CO→CO2or alternatively O(1D)+CO2→CO3,CO3+CO→2CO2.If water vapor is added to the triple mixture, the CO2 is more effectively regenerated and the reaction OH+CO→CO2+H plays probably an important role. The molecule CO3 has been previously postulated, but has never been observed. In the mass spectra of the gas mixture with water vapor, mass 60 is observed and is assumed to be CO3.
Loss Lock-In in the Ring Laser
Authors: Aronowitz Frederick
Published: February 2004

In the ring laser, frequency synchronization between the oppositely directed traveling waves is usually attributed to mutual coupling by the mechanism of the backscattering of energy from each of the beams into the direction of the other. A new type of coupling is introduced where the standing wave state is shown to have less losses than the traveling wave state for rotations rates less than some critical lock-in threshold. The coupling mechanism is spacially varying losses over the cavity length. The minimum loss condition is also shown to determine the location of the nodes of the standing waves. In certain cases, lock-in thresholds due to nonuniform losses are shown to have the potential of being a few orders-of-magnitude greater than thresholds attributed to backscattering.
Pulse Velocity and Mode Pulling in a Laser with Equally Spaced Modes
Authors: Faxvog F. R. , Carruthers J. A.
Published: February 2004

Mode pulling and pulse velocity in an inhomogeneously broadened laser are examined starting from the assumption that the steady-state dispersion of the gain medium results in equally spaced modes. By summing the mode E-fields in the cavity it is found that the pulse velocity is less than that of light and equal to the classical group velocity dω/dk. The pulse shape is stable with time even in the presence of dispersion. The ratio of the intermode beat frequency to that of the empty cavity equals the ratio of the pulse velocity to that of light. Previous measurements on the He–He self-locked laser support these results.
Oscillator and Amplifier Characteristics of Lasers Based on Nd3+ Dissolved in Aprotic Solvents
Authors: Samelson H. , Kocher R. , Waszak T. , Kellner S.
Published: February 2004

Three different Nd3+ aprotic solvent laser solutions: Nd3+:SeOCl2:SnCl4; Nd3+:POCl3:SnCl4; and Nd3+:POCl3:ZrCl4 are considered in terms of their laser characteristics as oscillators and amplifiers. It is shown that such solutions have a loss that varies between 0.5 and 1.0% per centimeter and that their material efficiencies are at least comparable to those of an L.G. 55 (Schott) glass. As oscillators, the different solutions are shown to be equivalent to each other; as an amplifier only the SeOCl2 system was studied and this has produced gains of 18 dB in the small signal case.
Laser Characteristics of Neodymium-Doped Lithium Germanate Glass
Authors: Birnbaum Milton , Fincher Curtis L. , Dugger Cortland O. , Goodrum John , Lipson Herbert
Published: February 2004

The spectroscopic characteristics of Nd-doped lithium germanate glass are compared to those of Nd-doped silicate glasses; the laser characteristics of Nd-doped lithium germanate glass are compared to the corresponding properties of Nd-doped glass and YAG samples. The spectroscopic properties of the Nd-doped lithium germanate glass are similar in many respects to the familiar Nd-doped glass materials. The Nd-doped lasers were end pumped using the 5145-Å output of pulsed argon ion lasers and oscillated at ∼1.06 μ at room temperature. This technique enables a precise determination of the pump energy required to reach the oscillation threshold. Threshold energy, output power, spiking, fluorescent conversion efficiency, laser rod losses, and stimulated emission cross sections at 1.06 μ are compared. Stimulated emission cross-section values of the Nd:lithium germanate glass obtained by two methods are presented.
Energy Released by Flux Jumps in Superconductors
Authors: Iwasa Y. , Montgomery D. B. , Polzer H. W.
Published: February 2004

The energy released during a flux jump in single-core Nb–Ti wires and multifilament composite Nb–Ti superconductors has been measured. The evaporation of liquid helium produced by the flux jump was indirectly measured and for calibration was compared with that produced by a known energy input generated by a current pulse through a heater wire. The experiment has demonstrated that the equation derived for a slab geometry, relating the magnetization energy to the initial and final value of magnetization, is also valid for the wire samples, and (indirectly) for composite superconductors. For the composite superconductors with nontwisted filaments, the experiment has also shown that the configuration of filaments rather than their number or size is the principle determinant of the magnetization and thus the energy. The experiment further confirms that twisting the filaments along the axis increases the stability of composite superconductors.
Rotational Hysteresis Loss in High-Field Superconductors
Authors: Bean Charles P.
Published: February 2004

The rotational hysteresis loss in hard type II superconductors is calculated using the critical state model. For materials that can be characterized by a magnetic field-independent critical current density Jc the surface rotational loss is W(rot)s=[5/4π(6)]1/2(H03/Jc) erg/cm2−cycle.In this expression H0 is the amplitude in gauss of a rotating field applied parallel to the surface of a semi-infinite slab while Jc is measured in amperes per square centimeter. This loss is 3.84 times the equivalent loss for alternating fields. In addition, it is shown that by measurement of the hysteresis loss or hysteresis torque as a function of field, one may calculate the field dependence of the critical current.
Physical Theory of the Phonon Parallel Pump Instability
Authors: Sage J. P.
Published: February 2004

Previous theories of the phonon parallel pump instability, based on equations of motion for the coupled magnon-phonon system, have been very complicated and have not revealed the underlying physical phenomena. In this paper the steps in a simple, physically understandable, energy flow theory are outlined by means of a sample calculation which yields all of the principal results of the earlier calculations. In its most general development, this theory can be applied to any phonon wave vector for any direction and magnitude of applied static magnetic field. It can include the effects of magnetic, elastic, and magnetoelastic anisotropy. Moreover, the physical basis of the theory makes many conclusions possible without the necessity of detailed calculations.
Dependence of the Phonon-Instability Threshold for Parallel Pumping on Crystal Orientation and Magnetic Fieldstrength
Authors: Joseph R. I. , Schlömann Ernst
Published: February 2004

The theory of phonon instability under parallel pumping is extended by taking account of magnetocrystalline and magnetoelastic anisotropy. Previous results apply to real materials only when the magnetic field is along a [100] direction. Results are obtained for the instability threshold when the magnetic fields are along a [110] or a [111] direction. When magnetic loss is neglected the calculated threshold (minimum with respect to all directions of propagation) for all three principal crystal directions varies with dc field-strength in such a way that hcrit1/2 is approximately a linear function of the dc field, with the extrapolated intercept (zero threshold) at internal dc fields of −⅔Ha for [111], ½Ha for [110], and Ha for [100]. Here Ha=−2K1/M0 is the anisotropy field and it has been assumed that K1<0. For the [110] case the threshold is approximately hcrit1/2=(2γ/σQe)1/2(H−12Ha),where σ/γ=b22/C44M0 and Qe is the phonon Q. When magnetic loss is taken into account, hcrit1/2 still remains an approximately linear function of dc field, but the extrapolated intercept is moved to lower dc fieldstrengths.
Number Phase Relation for Elastic Scattering in Optics
Authors: Wohlleben Dieter
Published: February 2004

An elastically scattering optical object impresses a phase shift on the incident photon or electron beam. From this phase shift the scattering probability is derived and is used to determine the minimum number of incident particles necessary to detect the object. Then the accuracy is derived with which a phase shift can be measured at best from a given number of recorded particles. The results can be interpreted as a direct consequence of the number-phase uncertainty relation. In practice, the detection of elastically scattering objects always requires very much longer illumination times than expected from geometric optics, if the phase shifts are smaller than π.
Evidence for Photochemical Changes in Traps in CdS Crystals
Authors: Im Ho B. , Matthews Herman E. , Bube Richard H.
Published: February 2004

The dependence of trap filling on the intensity, temperature, and wavelength of the photoexcitation has been investigated for trapping centers in S–Se-annealed CdS–CdSe crystals and in crystals of CdS subjected previously to electron radiation damage and photoexcited annealing. For certain traps in both these kinds of crystals, it was found that trap filling was not only critically dependent on the temperature of excitation but also on the wavelength of excitation. In fact, for each process observed, a band of wavelengths is most effective, the maximum wavelength of this band being larger than the wavelength for maximum photoconductivity. This result makes previous attempts to explain this kind of phenomenon in terms of a Coulomb-repulsive trap less acceptable and provides additional evidence for the presence of photochemical changes at and below room temperature in CdS-like materials.
Photoconductivity in Neutron-Irradiated p-Type Si
Authors: Cheng L. J. , Swanson M. L.
Published: February 2004

Photoconductivity spectra of p-type silicon after fission neutron irradiation at ∼13°K and isochronal annealing up to 360°K have been measured in the wavelength range 1.2–5 μ. Neutron irradiation increases the photoconductivity in the measured wavelength range. The 3.9-μ photoconductivity band, which has been correlated with the divacancy, appears immediately after the irradiation and starts to grow upon annealing around 170°K. The growth rate becomes rapid around 350°K. The energy level at Ev+0.42 eV, which has been correlated with interstitial dopant atoms, also appears immediately after the irradiation and grows upon annealing in the temperature range 250°–360°K. The results indicate that the neutron damage region is localized, and they are consistent with a model in which the outer part of the region consists of a divacancy-rich region surrounded by an interstitial-rich region. The presence of shallow traps in neutron-irradiated silicon has been assumed in order to explain the temperature dependence of the photoconductivity.
Electron Tunneling Through p-Type GaAs–Pb Point Contacts
Authors: Tsui D. C.
Published: February 2004

We have studied the variation with bias (to ± 150 mV) of the I, dV/dI, and d2I/dV2 of p-type GaAs point contacts on Pb single crystals at liquid-He temperatures. The results are examined and are compared with those obtained from p-type GaAs–Pb film tunnel junctions fabricated by conventional techniques. A small reduction of the energy gap and a shift in bias energy of the phonon-induced structure in the superconducting Pb tunneling characteristics have been observed, and we suggest these are due to pressure at the point contact. The effects of this pressure on the p-type GaAs tunneling characteristics are also observed and some qualitative explanations are suggested.
Superlinear Current Density vs Electric Field in p-Type Silicon-on-Sapphire
Authors: Ross E. C. , Warfield G.
Published: February 2004

The large internal stresses in epitaxial layers of silicon-on-sapphire remove the cubic symmetry of the silicon lattice. The valence-band degeneracy at k̄=0 is lifted and the valence bands are split by 0.015 eV. The band lowered in hole energy has a larger effective mass than the band which is raised in hole energy. A theoretical calculation predicts that a field induced redistribution of the equilibrium hole concentration will result in an effective hole mobility which increases with increasing electric field. Experimental results confirming the theoretical prediction are presented. The field-induced effect is observed to commence at a field strength of 150 V/cm. The effective hole mobility increases by 50% of its zero field value at a field strength of 3000 V/cm.
Calculation of Fermi Energy and Bandtail Parameters in Heavily Doped and Degenerate n-Type GaAs
Authors: Hwang C. J.
Published: February 2004

The second-order perturbation method of Parmenter and the theories of Kane and of Halperin and Lax are employed to calculate self-consistently the conduction band density of states in heavily doped n-type GaAs using a screened Coulomb potential for impurity atoms. The three models all show that the total number of states in the tail is small compared to the total number of electrons even though the detailed structure of the bandtails are substantially different. Consequently, the position of electron Fermi level relative to the shifted band edge and other bandtail parameters such as the carrier screening length and the bandshift due to Coulomb interaction can be calculated with sufficient accuracy using parabolic density of states. Because of omission of the kinetic energy of localization, Kane's theory predicts a larger density of states in the tail than does the theory of Halperin and Lax. The condition for the validity of the calculation is that the impurity concentration be approximately equal or greater than 6×1017 cm−3 at 300°K or 2×1017 cm−3 at both 77° and 20°K.
Electrothermal Initiation of an Electronic Switching Mechanism in Semiconducting Glasses
Authors: Böer K. W. , Ovshinsky S. R.
Published: February 2004

An analysis of the switching mechanism in semiconducting glasses is given which indicates that the actual switching involves electronic processes which prevent a thermal runaway. The rapid and reversible transition between the highly resistive and conductive states can have a thermal origin from Joule's heating of a current channel. Double tunneling, forced by the characteristic temperature profile, and current-density saturation are suggested as an explanation of the characteristics in the conductive state.
Thick Target Bremsstrahlung Produced by Electron Bombardment of Targets of Be, Sn, and Au in the Energy Range 0.2–2.8 MeV
Authors: Rester D. H. , Dance W. E. , Derrickson J. H.
Published: February 2004

Electron bremsstrahlung due to bombardment of Sn and Au targets at 0.2, 1.0, 2.0, and 2.8 MeV, Be targets at 0.2, 1.0, and 2.0 MeV, and Al and Fe targets at 0.2 MeV were measured. Angular distributions of bremsstrahlung intensity and total transmission spectra are derived from the measurements, which were carried out for perpendicular incidence of the electron beam to the target plane. Comparisons for Au and for previously reported Al and Fe spectra are made at 1.0 and 2.8 MeV to calculated spectra from the Monte Carlo program of M. J. Berger and S. M. Seltzer, ETRAN 15. Total external radiation emitted from the targets is represented by the function 1.4×10−3 T02.16 for Be, 1.6×10−2 T02.07 for Sn, and 2.3×10−2 T01.90 for Au, where T0 is the incident electron kinetic energy in MeV.