bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced-Mode Radiation Detection by Superconducting Films
Authors: Bertin C. L. , Rose K.
Published: February 2004

In the course of investigating radiant-energy detection by high-resistance superconducting films [≈10 KΩ/square (□)] an unexpected enhanced mode of detection was observed at microwave frequencies. This mode was observed in addition to and differed significantly from the expected thermal or bolometer mode of detection. Since that time detailed measurements have been made of the dependence of the enhanced-mode response on bias current, incident power, temperature, and sample resistance; these are reported here. Correlation of the characteristics of the enhanced mode with the nonlinear VI (voltage-current) characteristics of the film is shown. This suggests that the enhanced mode is the result of a nonlinear response to currents induced in the film by the incident radiation, which explains the short wavelength cutoff associated with the enhanced mode. Physical mechanisms which might cause this response are considered and fabrication techniques for these films are presented in detail. Since the initial report, enhanced-mode responses have been observed with a responsivity per square (r=104 V/W) which is thousands of times greater than the peak bolometer responsivity. At the operating point, the film has a lower output impedance [<50Ω/square(□)] and responds with a time constant less than 0.1 nsec as estimated from heterodyning measurements at 9.4 GHz. At present, enhanced-mode devices with an active area of 1 cm2 can achieve a noise equivalent power of less than 10−13 W Hz−1/2. This compares quite favorably with other millimeter wave detectors such as InSb free carrier detectors, doped Ge detectors, and superconducting point-contact Josephson junction devices.
Study of the Energy Gaps in Bulk Gallium Single Crystals and Polycrystal Aluminum Films with High Impedance Tunnel Junctions
Authors: Keister J. C. , Straus L. S. , Gregory W. D.
Published: February 2004

Results are presented suggesting that fabrication procedures for bulk tunnel junctions can be relaxed provided one uses sample junctions with large barrier thicknesses and, consequently, large junction impedances. The results of a study conducted on Al–Al2O3–Pb film junctions, ranging in impedance from 10 Ω to 4 MΩ, show that one can obtain good I-V curves from high-impedance junctions and that the normalized energy gaps obtained from these data are the same as those measured with low-impedance samples. Bulk gallium tunnel junctions with impedances ranging from 1 kΩ to 20 MΩ exhibited energy gaps in the range of 3.4–3.8kTc for flat-surfaced specimens and from 2.9 to 3.5kTc for round-surfaced specimens. A best estimate for the anisotropy is 5% with an upper limit of 20%. Possible multiple gap structure, excess subharmonic currents, weak link behavior, and sample aging effects were observed.
Adhesion of Small Metal Spheres to Plane Metal Substrates
Authors: St. John Douglas F. , Montgomery D. J.
Published: February 2004

Small metal spheres (gold and silver, diameter 5–60 μ) dusted on plane metal substrates (gold, silver, nickel, stainless steel) were removed by application of centrifugal forces or electrostatic fields. For forces applied perpendicularly outward from the substrate, the force for removal by centrifuging was found to be much larger than that for removal by electrostatic fields. Analysis of these results shows that the spheres are not to be treated as particles, but rather as elastic or plastic bodies whose adhesion to a substrate is controlled by tangential as well as normal components of the applied force. To investigate the mechanism of removal, centrifuge runs were made with the removal force applied at varying angles with the normal to the plane. The dependence of force on angle is affected by the hardness of the substrate. For relatively soft substrates, the adhesion force reaches its minimum at angles greater than 90°, that is, when the sphere is actually pushed into the substrate. This surprising result can be interpreted on the basis of a plastic-deformation model.
Propagation of Stress Waves in a Laminated Plate Composite
Authors: Lundergan C. D. , Drumheller D. S.
Published: February 2004

The dispersion of a finite, dilatational stress wave propagating in a laminated composite was investigated both experimentally and analytically. The composite consisted of ten bilaminar plates oriented so that the plane of the plates was normal to the direction of the wave propagation. A flat plate accelerated by a compressed gas gun was used to induce a planar impact. Two one-dimensional wave-propagation codes were used to analyze the problem and to make comparisons with the experimental results. In general, the comparisons were good, indicating one-dimensional wave-propagation codes can be used to describe wave propagation in composites of this configuration. The analysis indicates the need to account for the influence of fracture and the nonlinearities of the constitutive materials in the description of the transmitted stress wave.
Effect of Pressure on the Fracture of Glass
Authors: Wiederhorn Sheldon M. , Johnson Harold
Published: February 2004

The fracture surface energy of three glass compositions was measured as a function of hydrostatic pressure and was found to be independent of pressure to 20 kbar. This suggests that no change in the fracture mechanism occurs. The brittle behavior of glass thus differs from plastics and metals which are observed to become stronger and more ductile with increasing pressure.
Nonlinear Optical Properties of Potassium-Lithium Niobates
Authors: Smith A. W. , Burns G. , Scott B. A. , Edmonds H. D.
Published: February 2004

Crystals of composition (K2O)0.3(Li2O)0.7-x (Nb2O5)x with x in the range 0.515 to 0.55 have useful and unique nonlinear optical properties. These are transparent ferroelectric crystals having the tetragonal tungsten-bronze structure. Thus, they do not have to be detwinned, as does NaBa2Nb5O15. The dc halfwave voltage is about 1350 V at 6328 A, and the nonlinear constant d31 is 1.7d31 (LiNbO3). For x=0.515 the birefringence is very large. Thus, the phase-matching temperatures for harmonic generation without double refraction with the Nd-YAG laser is 450°C. For x=0.55, 140°C is obtained. With these crystals the GaAs injection laser emitting 0.90 μ can be phase matched above room temperature for the first time without double refraction.
Charge Transport and Photoconductivity in Amorphous Arsenic Trisulfide Films
Authors: Ing S. W. , Neyhart J. H. , Schmidlin F.
Published: February 2004

Charge transport and photoconductivity in As2S3 amorphous films have been investigated at a temperature of 25°C. It is found that holes are the mobile carriers in As2S3 whereas electrons are quite immobile in the material. The photoconductivity is mainly governed by the product of the photogeneration efficiency and the schubweg of the generated holes. Both of these quantities are electric field dependent. Carrier transport is essentially dominated by bulk trapping. The traps are distributed in energies above the hole conduction states. The release rate of the trapped charges varies since the rate is an inverse function of the trap energy. A theoretical model describing the transport process is presented to account for the experimental results. The photogeneration efficiency as a function of electric field at high fields (greater than 105 V/cm) has been determined for incident photon energies of 2.5–3.1 eV. The generation efficiency is observed to decrease in the same manner as the absorption coefficient with decreasing photon energy in the light wavelength range 4000–5000 Å.
Growth Rates and Stability Limits for Beam-Plasma Interaction
Authors: Self S. A. , Shoucri M. M. , Crawford F. W.
Published: February 2004

A treatment is given of the one-dimensional problem of beam-plasma interaction, including the effects of plasma and beam thermal velocities and momentum transfer collisions in the plasma. The conditions under which the Landau damping due to the plasma is negligible are first investigated. Neglecting this damping, a weak-beam approximation to the dispersion relation is derived, and conditions for its validity are established. Expressions are derived for the maximum temporal and spatial growth rates in the limits of cold and hot beams, and few and many collisions. The growth rates given by the weak-beam approximation are compared with those calculated from the full dispersion relation. The transition from a cold to a hot beam is discussed in terms of the topology of the roots of the dispersion relation, and also in terms of the location of the phase velocities of the most unstable waves relative to the bump in the distribution.
New S = 1 EPR Center in Irradiated Diamond
Authors: Kim Y. M. , Watkins G. D.
Published: February 2004

Electron spin resonance studies have been made of natural diamond crystals electron-irradiated at room temperature. A radiation-induced spectrum is identified as arising from a new anisotropic S=1 center. The S=1 center is characterized by: g1=2.0026, g2=2.0021, g3=2.0016; D1=∓27(10−4 cm−1), D2=∓25(10−4 cm−1), D3=±51(10−4 cm−1). Associated with each resonance line are four sets of weaker lines which are ascribed to hyperfine interaction with 13C (I=½, 1.1% abundant) at four nonequivalent sets of sites. The identity of the defect has not yet been established.
Electrical Conduction in Ferromagnetic Metal Oxide Junctions
Authors: Smeltzer R. K.
Published: February 2004

The electrical conduction from 4.2°K to room temperature in thin film Ni–NiOx-metal junctions was studied. Tunneling is the dominant conduction mechanism at low temperature; at high temperature, Schottky thermionic emission dominates. The effective barrier thickness determines at what temperature the conductivity changes from tunneling to Schottky emission. Atomic penetration into the oxide is important, and there appear to be broad transition regions at the metal-oxide interfaces. Using the conventional models, the barrier heights are approximately 0.2 eV.
Analysis of Impurity Distribution in Homoepitaxial n on n+ Films of GaAs which Contain High-Resistivity Regions
Authors: DiLorenzo J. V. , Marcus R. B. , Lewis R.
Published: February 2004

The occurrence of a high-resistivity region (i layer) at the interface of n-type GaAs films on n+ GaAs substrates has been a recurring problem in the halide synthesis transport growth of these films for microwave devices. Consistent success in the elimination of an i layer in the doping profile has been achieved by deposition of an n+ epitaxial film substrate prior to growth of the active n film, however the nature and cause of the i layer has remained unknown. It has been proposed by others that the i layer is caused by the presence of an impurity in that region. Under this assumption, a new analytical tool, the Direct Image Mass Analyzer (DIMA, Bell & Howell/CEC) has been used to obtain depth impurity profiles of known impurities through five homoepitaxial n-on-n+ GaAs film samples. These samples differed in the type of dopants used in the film and substrate, and in the magnitude of the i layers. The data were compared with doping profiles, and an analysis of this comparison has led to the following conclusions: (1) The impurities that are present in these samples include Si, K, Li, C, Na, Fe, F, Cl, and Mn; (2) the presence of an i layer is correlated with the presence of a high concentration (∼1×1021/cm3) of silicon in the i layer region; and (3) the origin of the silicon is probably external to the sample. The hardware of the reactor is a likely source of silicon, and a mechanism is proposed for the transport of the silicon into the growing film.
II. Auger Electron Conductivity in Silicon
Authors: Cuthbert J. D.
Published: February 2004

The contactless microwave reflectivity technique was used to measure the transient free carrier density following the creation by a pulsed electron accelerator of electron-hole pairs in arsenic-doped silicon at 7°K. The experiments were directed at providing supporting evidence for the Auger recombination mechanism postulated by Nelson et al. as being operative in the decay of excitons bound at neutral donors in silicon. The results contrast distinctly with the results of similar experiments on semiconductors containing isoelectronic traps by showing a strong post excitation conductivity. Differential equations, describing the model of Auger decay and including the important effects of residual acceptors, are formulated and solved numerically. At high excitation levels the theoretical profiles depend weakly on unknown capture cross-sectional parameters and agree well with the experimental profiles. At lower excitation levels, the predicted profiles have a stronger dependence on the values of the unknown parameters, but, assuming reasonable values, good fits to the experimental data are obtained. It is therefore concluded that conductivity associated with Auger electrons has been observed.
Ultraviolet-Enhanced Oxidation of Silicon
Authors: Oren Ruben , Ghandhi Sorab K.
Published: February 2004

This paper describes the results of dry thermal oxidation of silicon under uv-irradiation conditions. A model is proposed to explain the enhanced oxidation and reduced surface-state charge density that occur under these conditions.
Impulse Excitation of GaP Electroluminescent Diodes
Authors: Jayson J. S. , Dixon R. W.
Published: February 2004

This paper introduces an impulse technique, utilizing either electrical or optical excitation, capable of giving new information concerning the properties of luminescent systems. An analysis is included for both types of excitation and experimental results utilizing electrical excitation are reported. In particular it is shown that minority carrier lifetime in the active electroluminescent region can be evaluated directly. The technique is applied to red emitting GaP (Zn–O) electroluminescent diodes excited with short, <2 nsec, current pulses. The resulting time-dependent luminescent response is then interpreted using a phenomenological model previously evolved. This model assumes that bound exciton radiation dominates the luminescent process at room temperature, where the experiments were carried out. Utilization of this theory allows the extraction of several of the important parameters of the radiative and nonradiative recombination processes. Minority carrier lifetimes between 3 to 10 nsec have been deduced for particular diodes, in good agreement with values previously reported. In addition, the experimental results can be interpreted as placing an upper bound on the hole equilibration time which is sufficiently small that it permits a significant simplification of the recombination kinetics in GaP.
Effect of Various Boundary Conditions on the Instabilities in Transferred Electron Bulk Oscillators
Authors: Shah Pradeep L. , Rabson Thomas A.
Published: February 2004

Transferred-electron bulk-negative-differential-conductivity devices with nonuniform geometry, field, and doping distributions are analyzed. Numerical solutions of the conduction equations was possible due to the novel scheme introduced to account for the area variation in the direction transverse to the electron flow. The simulation results show that the space-charge travel can be controlled with the applied bias voltage for concentric and some other nonuniform geometries. This results in the possibility of tuning the frequency over two octaves. The nature of the frequency control characteristic is shown to be dependent on the device geometry. Dipole space-charge nucleates due to nonuniform geometry without any necessity of initialization or doping fluctuations. Multiple space-charge formation is observed to occur in an oscillation cycle as a result of sequential decay processes. Space-charge modes in nonuniform geometries display polarity dependence. Divergent and convergent geometries are shown to favor dipole and accumulation-type space charges, respectively. Analysis of devices with doping gradients demonstrate the equivalence of these gradients to the geometry nonuniformities. The analytical solutions of the conduction equations indicate the simple dependence of the space-charge behavior on the geometry. The space-charge nucleation, growth, propagation, and decay are related to the time variation of the cathode field and the domain voltage.
Lamb-Mössbauer Factor of Sodium Ferrocyanide
Authors: Decker D. L. , Lortz L. E.
Published: February 2004

Using a set of commercially prepared sodium ferrocyanide absorbers enriched to 91.2% Fe57 the Lamb-Mössbauer factor was measured to be 0.28±0.03. The thickness of Fe57 for these absorbers was measured using x-ray absorption techniques and was found to be considerably smaller than that advertised by the manufacturer even after correcting for the size of the ferrocyanide particles in the absorbers.
Spectral Analysis of the Signal from the Laser Doppler Flowmeter: Time-Independent Systems
Authors: Edwards Robert V. , Angus John C. , French Michael J. , Dunning John W.
Published: February 2004

A method for prediction of the spectrum observed with the laser Doppler flowmeter (LDF) is developed. A detailed analysis of the spectrum observed with steady flows is presented. The effects of diffusive motion of the scattering centers, spatially varying velocities, finite transit time of the centers through the sample volume, and uncertainty in scattering vector are computed. The latter two effects are shown to be identical. A computation of the sample volume size and shape is made using the optical parameters of the system. The calculated linewidths and shapes are in good agreement with data taken on two independent LDF systems. The general formalism is also applicable to measurements made on turbulent fluids and diffusely reflecting solid objects. The special case of a static fluid (zero velocity) is considered in detail and the low angle correction to the conventional expressions used in laser ``beat-frequency'' spectroscopy is developed.
Analytical Equation of State for Water Compressed to 300 Kbar
Authors: Gurtman G. A. , Kirsch J. W. , Hastings C. R.
Published: February 2004

An analytical form for the equation of state of water in the region 0.5–300 kbar is presented. The functional form of the equation was first proposed by Born to characterize the melting of crystalline solids, and is applied to water in the thermodynamic vicinity of the Hugoniot. The derived equation is equivalent to the Mie-Grüneisen equation of state if the specific heat at constant volume CV is taken as a constant. This restriction results in a simple expression for internal energy in terms of temperature and specific volume. This expression contains an undefined function of volume which is shown to be calculable from the available experimental data. The resulting formulation agrees with existing data for condensed states of water to a high degree of accuracy in the region from 0.5 to 300 kbar.
Parametric Studies of the Iodine Photodissociation Laser
Authors: O'Brien Dennis E. , Bowen J. Ray
Published: February 2004

Experimental data for the iodine photodissociation laser are presented over the following ranges of operating conditions: CF3I pressure, 0.4–500 Torr; argon pressures, 5–200 Torr; and flash energy, 225–1764 J. Peak powers of 400 W and optimal gains of 45 dB/m were observed. The experimental results for CF3I pressures less than 200 Torr and for the first 25 μsec of lasing action are within 10% of the predictions from a four-level kinetic model of the laser. These results indicate the utility of kinetic models for describing pumping, radiative, and collisional processes.
Pumping Mechanism of CO2 Laser and Formation Rate of CO2 from CO and O
Authors: Chen Che Jen
Published: February 2004

The pumping mechanism of a high-current pulsed CO2 laser has been investigated. It was found that there is a time delay of the laser pulse behind the current pulse. From the dependence of the time delay on the plasma parameters, such as electron density, electron temperature, gas temperature, gas pressure, and emission of oxygen atomic line (7771 Å), it can be shown that during the current pulse, the CO2 is totally dissociated into CO and O. The subsequent recombinations of CO and O into CO2 are responsible for the pumping of the upper level of the CO2 laser (10.6 and 9.4 μ). The time delay between the current pulse and laser pulse is thought to be due to the time required for CO and O to recombine to reach the threshold population for lasing for the particular optical cavity. The threshold upper level population is obtained by knowing the Q value of the optical cavity, wavelength of the laser line, and linewidth of the radiation line. By equating the amount of CO2 formed during the delay time to the threshold upper laser population, the reaction rate of CO+O→CO2 is thus obtained. The agreement between the rate obtained and previously determined supports the proposed pumping mechanism.
Stimulated Emission Spectra of CdS Platelets under Various Excitation Levels
Authors: Era Koh , Langer Dietrich W.
Published: February 2004

The stimulated emission of CdS platelets excited by light pulses from a N2 laser is investigated at 2° and 77°K, as a function of the level of excitation and for differently prepared crystals. Pure and perfect crystals show peaks due to exciton-exciton interactions (P), and due to the recombination of a free exciton with simultaneous emission of one or two LO phonons [(Ex-LO) and (Ex-2L)]. Platelets grown in an atmosphere of excess S or Cd show up to five additional stimulated emission lines, located between P and Ex-LO. Imperfect crystals show a broad emission band extending from P to beyond Ex-LO. At low excitation levels only P appears in the stimulated emission spectra. With increasing level of excitation the intermediate impurity lines (JJ) in Cd- and S-rich crystals also show stimulated emission and the maximum emission intensity shifts from the P peak sequentially through all JJ lines always toward the next peak at lower wavelengths. At still higher excitation levels, Ex-LO, the next peak at lower wavelengths, gains maximum intensity and in one observation even Ex-2LO grew to become the dominant stimulated emission line. In imperfect crystals the maximum of the broad emission band shifts from a position near P to Ex-LO with increasing level of excitation. Further, the P line is found to split in a magnetic field H⊥C. The intensity ratio of the upper to the lower P branch changes with the excitation intensity, such that with lower excitation intensity the higher energetic branch dominates the emission while at higher excitation intensity the lower energetic branch has higher emission intensity than the other branch. A reasonable explanation of the dependence on excitation intensity is given in terms of electron-assisted transitions which increase the absorption in the tail region of the absorption edge, and thus spoil the necessary gain for stimulated emission.
Calculation of Nd:YAlG Cavity Dumping
Authors: Chesler R. B. , Maydan D.
Published: February 2004

Calculations based on the rate equations for an idealized 4-level system indicate that efficient repetitive cavity dumping of Nd:YAlG lasers is possible at repetition rates above about 100 kHz. Analytical forms for the field and inversion variables are derived. A numerical example illustrates the resulting operation.
Production of Net Fusion Energy from Laser-Heated Target Plasmas
Authors: Johnson Roy R. , Hall Richard B.
Published: February 2004

The heating of a small particle of deuterium-tritium by laser radiation is considered and conditions for energy gain determined. The size of the D-T particle for a balance of energy input and neutron energy output is computed as a function of initial plasma temperature. The electrical energy required for this breakeven condition is shown and increases as the inverse fourth power of laser efficiency. Because electrons are first heated by the laser radiation and then must transfer their energy to ions by collisions, a computation of electron-ion thermalization is presented. These results show that electron-ion thermalization through collisions applies a severe limitation on most cases for producing net fusion energy and must be considered in a consistent manner for smaller particles.
Electroluminescence in Liquid-Phase Epitaxial GaSb Diodes
Authors: Blom G. M.
Published: February 2004

Electroluminescence in GaSb liquid-phase epitaxial diodes has been studied. Optical and electrical measurements were done between 65° and 300°K. Two emission bands are observed, which are both due to transitions between the conduction band and different acceptor levels. The peak photon energy of band I is stationary with applied voltage and is due to a thermal injection mechanism. The low-energy band II shifts with applied voltage and is described by theories of photon-assisted tunneling. It is demonstrated that for both emission bands the intensities and peak photon energies are directly related to the applied voltage.
Influence of a Continuous Activation Energy Spectrum on the Aging Behavior of Magnetic Thin Films
Authors: Pfrenger Eberhard
Published: February 2004

Skew aging and its dependence on stabilization treatments have been investigated in cylindrical electroplated Permalloy films by annealing in hard-axis magnetic fields. The skew field Hβ was measured using the Belson test method. Plots of Hβ vs a logarithmic time scale show nearly straight lines over a range of four decades for temperatures between the ambient temperature and 200°C. This behavior may be explained by assuming that the activation energies of the relaxation processes have a continuous distribution between 0.8 and 1.6 eV, independent of the stabilization treatment. The frequency factor is found to be a function of the stabilization temperature, lying between 109 and 1010 sec−1. These values can be interpreted as being due to first-order kinetic processes, which is not possible if discrete activation energies are assumed. The reason for the distribution is the highly defected structure of thin films, especially at grain boundaries and dislocations and around impurities. Stabilization treatments reduce the total volume of these regions and the vacancy concentration. Only the Fe–Fe pair ordering mechanism is necessary to interpret the annealing data if one assumes that pairs in local defected regions also contribute to the anisotropy.
Growth of MnBi Films on Mica
Authors: Unger W. K. , Stolz M.
Published: February 2004

Films of Bi and Mn were evaporated successively onto freshly cleaved mica and subsequently annealed. By this method one gets homogeneous, oriented MnBi films with a large specific Faraday rotation (80 to 120 deg/μm at a wavelength of 632.8 nm). The specific Faraday rotation depends on the Bi to Mn ratio in a reproducible manner. The growth of oriented MnBi was observed by means of electrical, magneto-optical, and electron microscopical methods. The growth takes place in two main steps: During deposition, the Bi film grows epitaxially on mica, with (0001)Bi ∥ (0001)mica and [1000]Bi ∥ [1000]mica. During annealing, the Mn atoms diffuse into the lattice of the Bi film. The resulting MnBi lattice has the same orientation as the Bi lattice grown first. The reproducibly large specific Faraday rotation may thereby be explained.
Dispersion of Finite Amplitude Ultrasonic Waves in InSb
Authors: Miller J. G. , Bolef D. I.
Published: February 2004

The dispersion of finite-amplitude ultrasonic standing waves in single crystal InSb is reported. The observed dispersion was found to be proportional to the square of the voltage applied to the transducer, in agreement with the predictions of a simple model which is proposed to account for the effect. An enhanced sensitivity to the detection of harmonics of the ultrasonic wave results from the use of a standing wave technique.
Variational Bounds of the Elastic Moduli of Two-Phase Materials
Authors: Yeh Robert H. T.
Published: February 2004

Previously derived variational bounds [R. H. T. Yeh, J. Appl. Phys. 41, 3353 (1970).] for Young's modulus are compared with experimental results on WC–Co alloy. The agreement is satisfactory. Numerical examples are given to illustrate the usefulness of these bounds for fiber-reinforced materials.
Finite-Strain Theory of Crystalline Elastic-Inelastic Materials
Authors: Kratochvil J.
Published: February 2004

The thermodynamics of elastic-viscoplastic materials developed in two previous papers is extended to account for finite strains. The description of the geometry of a body subjected to finite deformation is based on the kinematic of a continuum with dislocations suggested by Fox.
Determination of Three-Dimensional Density Fields from Holographic Interferograms
Authors: Matulka Robert D. , Collins Daniel J.
Published: February 2004

The successful application of holographic interferometry, and an associated mathematical reduction process, to the determination of an asymmetric three-dimensional density field of an aerodynamic phenomenon is reported. An integral inversion method from the field of plasma physics has been extensively evaluated by applying it to the determination of functions, both axisymmetric and asymmetric, which simulate aerodynamic density fields. The application of holographic interferometry has been extended to provide multiple holograms about a test region, with sufficient coverage to provide interferometric data for the successful solution of the density field. The analytical and experimental methods developed were applied to an experimental axisymmetric test field, the supersonic flow from a free jet, and shown to be comparable to a previous solution obtained by the Abel inversion method. Further, the free jet was tilted to provide a test field which was asymmetric in the plane of solution. Comparison of the resulting asymmetric solution was shown to be consistent with the previously obtained axisymmetric solution.
Magnetooptic Properties of Magnetite Films
Authors: Borrelli N. F. , Murphy J. A.
Published: February 2004

The Faraday and longitudinal Kerr effects, respectively, were characterized for thin chemically deposited magnetite films. The Faraday rotation was determined to be 3.9×104 deg/cm and the Kerr rotation 2–3 min of arc. Magnetooptical readout of digital magnetic information was achieved on a magnetite-coated disk.
Charge-Carrier Dynamics Following Pulsed Photoinjection
Authors: Batra I. P. , Kanazawa K. Keiji , Schechtman B. H. , Seki H.
Published: February 2004

The transient behavior of charge carriers generated by pulse illumination of arbitrary intensity is investigated. The configuration treated is that in which one surface of a photoinsulating sample is grounded and the other charged to an initial potential V0 and left floating. Within the framework of the assumed model, expressions have been derived which completely describe the spatial and temporal dependence of the carrier density, electric field, and conduction current density. These expressions provide a physical picture of the charge-carrier dynamics within the photoinsulator and allow a qualitative discussion of possible trapping effects. Solutions are also obtained for the physically observable surface potential and its time rate of change. The geometry considered here is that usually employed in electrophotographic applications of photoinsulators for information copying and image conversion devices.
Cone Formation on Metal Targets during Sputtering
Authors: Wehner G. K. , Hajicek D. J.
Published: February 2004

When a Cu surface is sputtered by ion bombardment under the condition that Mo atoms arrive at the Cu surface during sputtering an unexpected phenomenon can arise: The surface of the Cu target becomes covered with microscopic cones. The cone density increases with increasing flux density of arriving Mo atoms. When the cones are closely spaced they give the target a velvet-like black appearance. The result of dense cone coverage is a lower sputtering yield and a more oblique ejection of sputtered material. The cone tops seem to consist of Mo nuclei which are constantly replenished via surface migration and protect the underlying Cu from being sputtered.
Point Contact MOM Tunneling Detector Analysis
Authors: Green Samuel I.
Published: February 2004

The responsivity and its frequency dependence are derived for an asymmetrical tunneling contact in terms of area, thickness, mean barrier height, and asymmetry. This analysis applies to the point contact metal-oxide-metal diodes which are used as detectors and heterodyne mixers in the submillimeter wavelength and far infrared regions and are the fastest detectors yet conceived. Analytical results show that the best detector will have a small contact area. This is best achieved by using base metals with extremely thin insulating surface layers in order to prevent flattening of the whisker tip. This conclusion led to the development of the tungsten-gold film diode used as a mixer and detector in the far infrared. Video detection is demonstrated at 27.97-μ wavelength in response to a water vapor laser.
Crystal Growth of Silicon Arsenide
Authors: Chu T. L. , Kelm R. W. , Chu Shirley S. C.
Published: February 2004

Silicon arsenide crystals have been prepared by chemical vapor growth and melt-growth techniques. The reaction of silicon, arsenic, and iodine in a closed tube has produced ribbon-shaped silicon arsenide up to 20×4.5×0.18 mm in size. They were found to be twinned crystals of monoclinic structure with twinning about a {2̄01} plane. The growth direction was parallel to the b axis, and the main faces were also of {2̄01} orientations. The room-temperature optical energy gap of silicon arsenide was determined to be about 2 eV. The dissociation pressure of silicon arsenide at its melting point was estimated to be 2 atm from vapor pressure measurements. Single crystals of silicon arsenide, up to 9 mm in diameter, have been grown by the Bridgman technique under an arsenic pressure of 3 atm. The growth direction was also parallel to the b axis, and the crystals cleaved readily along {2̄01} planes.
Output Pulse Amplitude from Lithium-Drifted Detector-Amplifier Combination under Conditions of Carrier Diffusion and Bulk and Surface Recombination
Authors: Tuzzolino A. J.
Published: February 2004

A calculation has been made of the output pulse amplitude obtained from an idealized lithium-drifted detector-amplifier combination under conditions where an incident charged particle generates a charge distribution in the field-free region of the detector which is a general function of position. An expression is derived for the probability P that a hole initially generated at a given position diffuses out of the field-free region as a function of position, bulk lifetime, and surface recombination velocity. For an amplifier with a ``long'' time constant, one obtains directly from P and the initial charge distribution the maximum amplitude of the output pulse. The output pulse amplitude is evaluated for actual charge distributions generated in the detector by incident charged particles. In principle, from measurements with charged particles and the results presented, the depth of the lithium-diffused region and the magnitude of the surface recombination velocity may be determined.
Carbide Contamination of Silicon Surfaces
Authors: Henderson R. C. , Marcus R. B. , Polito W. J.
Published: February 2004

The techniques of grazing angle reflection high-energy electron diffraction (RHEED), mass spectroscopy, and electron microscopy have been used to study carbide contamination of silicon samples heated in ultra-high vacuum. The RHEED data showed that the surfaces of silicon crystals heated between 800°–1000°C were covered with β-SiC crystallites well oriented with respect to the substrate. Heating between 1000°–1100°C formed a nonoriented β-SiC phase, and further heating above 1100°C removed the surface carbide. CO and CO2 evolution was observed when samples were heated above 800°C. The carbide reappears with heating to 800°C if the carbide free surface is exposed to atmosphere or left in the vacuum environment for a sufficient time. Electron micrographs of platinum-shadowed carbon replicas from samples contaminated with β-SiC indicated that the carbide existed within protuberances at the surface. Data from samples heated to 950° and 1050°C showed particles ∼400 Å in size, of cylindical shape and tapering towards the top; the surface density of the protuberances was observed to vary from 2×107 to 6×109/cm2. In all cases of carbide formation, the carbide results from the chemical reaction of a carbon-containing adsorbate with the silicon surface. Although a gaseous origin for an adsorbate has been demonstrated, additional adsorption probably also results from chemical cleaning of the sample. Surface steps on the silicon are correlated with the presence of β-SiC protuberances (or other artifacts) and appear to have been pinned by these particles.
Observation of Surface Defects in Electrolytically Etched Silicon by Infrared Microscopy
Authors: Bellin P. H. , Zwicker W. K.
Published: February 2004

Infrared microscopy has been used to observe tunnel networks in anodically etched silicon. The etch networks on (111) silicon originate at surface defects and lie along 〈110〉 directions in (111) planes. The technique described offers considerable promise as a quick and simple room-temperature method for surface evaluation. A comparison is made of the defect structure revealed using electrolytic etching with that revealed by high-temperature copper-decoration techniques.
Shape of Modulation-Broadened Unsaturated Lorentzian Magnetic Resonance Transitions. III. Absorption, aIIIL (Third Harmonic)
Authors: Buckmaster H. A. , Skirrow J. D.
Published: February 2004

The effect of modulation broadening on the shape of unsaturated Lorentzian absorption lines is examined. The closed analytic expression for the Fourier coefficients anL due to Wahlquist [H. Wahlquist, J. Chem. Phys. 35, 1708 (1961)] is employed to derive exact formulas relating the location and amplitude of the extrema, the amplitude extrema ratio, the location and amplitude of the slope extrema, the slope extrema ratios and the location of the zeros of the observed aIIIL to the true half-width for arbitrary modulation amplitude [normalized modulation amplitude (1/β)]. This Fourier coefficient is recorded when synchronous demodulation is employed at the third harmonic of the magnetic-field modulation frequency. It is of considerable experimental interest since it has two zeros symmetrically located with respect to a central zero and the total amplitude of the pairs of antisymmetric peaks is approximately the same as for the two antisymmetric peaks of aIL when the modulation amplitude is near optimum. It is shown that linewidth measurements can be made more precisely and easily under conditions of near-maximum sensitivity using aIIIL than either aIL or aIIL since zero crossings can be located more accurately than the amplitude extrema. Graphs of the various results of experimental interest are included.
Magnetoacoustoelectric Effects in InP
Authors: Carlson D. G. , Mosekilde E. , Woodall J. M.
Published: February 2004

The observation of acoustoelectric current saturation and domain propagation in n-type InP single crystals is reported. The electromechanical coupling constant K and the dominant acoustic frequency f are obtained from the variation of the incubation time for current decay with applied drift field. K2 = 1.0×10−3 and f = 17 GHz. The enhancement of acoustic gain in a transverse magnetic field is examined and compared to the predictions of the microscopic theory. Semiquantitative agreement can be obtained by assuming a slight scan of the dominant accoustic frequency with magnetic field.
Equivalence of Sturm-Liouville-Type Distributed-Parameter Systems
Authors: Yamamoto Sadahiko , Makimoto Toshio
Published: February 2004

This paper analyzes equivalence properties of linear distributed-parameter systems characterized by Sturm-Liouville-type differential equations. The approach taken here may be regarded as an application of the method of independent-variable transformation to those fundamental equations. In accord with the meaning of equivalence used for lumped-parameter systems, distributed-parameter systems are considered here as equivalent when they possess the same terminal behavior. The principal result is an equivalence theorem which establishes a general method of equivalent transformation of Sturm-Liouville systems. The fact that we can generate any number of equivalent parameter distributions from a given one is not only of theoretical interest but also of practical importance, because it offers a flexibility in the design of distributed-parameter structures. The derivation of the transformation function which plays a central role in the equivalent transformation is briefly described. Discussion is also given to the quantities which are invariant under the equivalent transformation. In the later part of the paper applications of the general theory to several problems of practical interest are considered, which include guiding systems for electromagnetic and space-charge waves such as nonuniform transmission lines, lens-like media, and nonuniform drift regions. The physical meanings of the transformation function, the parameters introduced, and various transformation invariants are discussed in detail. A simple example of equivalent systems is also illustrated in the case of nonuniform transmission lines.
NMR Spin-Echo Flow Measurements
Authors: Grover Thomas , Singer J. R.
Published: February 2004

Patterns of fluid flow are investigated by a technique utilizing NMR spin echoes. Spin-echo amplitudes are sensitive to the phase distribution of the resonating nuclei in the fluid, and the phase distribution is dependent upon the flow. A mathematical transformation of the spin-echo amplitudes observed provides a velocity distribution function which indicates the relative number of molecules flowing in any given velocity range when plotted. Experimental data are obtained from ordinary laminar flow, and blood flow in human fingers.
Effect of Solute Addition on the Formation of Vacancy Condensation Pits
Authors: Tariyal B. K. , Ramaswami B.
Published: February 2004

The effect of alloying elements in aluminum on the phenomenon of pit formation has been studied. It is suggested that alloying elements will affect; (1) the vacancy supersaturation, (2) the migration energy of the vacancies; and (3) the nature of the oxide-metal interface. It was found that there are four main types of effects of solute addition on the formation of pits. (a) Pits are not observed (Al–1.05% Mg alloy). (b) Pits appear with a larger ΔT than for pure aluminum, and ΔT decreases with increasing holding temperature (Al–1.07% Zn alloy and Al–0.57% Cu alloy). (c) Pits appear with a larger ΔT than that for pure aluminum and ΔT does not follow any regular trend (Al–0.0045% Sn alloy). (d) Pits are not observed, but a rippled structure appears on the surface of the specimen (Al–0.96% Sn alloy).
Theory of Dislocation Cells. II. Dislocation Multipoles
Authors: Moore J. , Kuhlmann-Wilsdorf D.
Published: February 2004

The stresses of infinite edge dislocation multipoles are investigated with the aid of a B5500 computer, and contour maps are obtained using the line printer. These multipoles consist of infinitely long, parallel edge dislocations of same strength, arranged so as to define a prism whose cross section is a regular polygon and with their Burgers vectors in radial orientation. As will be shown in Part III, multipoles are the prototypes of dislocation cells containing the same Burgers vectors, independent of cell shape, in the same way that the quadrupole, discussed in Part I, is the prototype of all cells composed of dislocations involving two mutually perpendicular Burgers vectors. It is found that the stress fields of τrr, τφφ, and τrφ all exhibit 2N similar leaves of alternating sign for a multipole of Nth order, except that τφφ of the dipole has eight rather than the expected four leaves. The magnitude of the stresses falls as 1/rN at large distances, except that τφφ of the dipole falls as 1/r4. Lastly, there exists a ``conservation of zero line'' rule to the effect that a fixed number of contours of vanishing stress passes each dislocation, independent of N, the order of the multipole, namely, six zero contours of τφφ and τrφ, and two of τrr, respectively.
Phonon Scattering by Impurity Atmospheres Surrounding Dislocations. III. Combined Mass and Distortion Scattering
Authors: Ackerman M. W. , Klemens P. G.
Published: February 2004

The inhomogeneous distribution of solute atoms in the presence of the strain field of dislocations causes additional phonon scattering in alloys. This nonuniformity results from the size difference between solute and solvent atoms. A previous theory considered the source of the scattering to be the mass difference between solute and solvent atoms. It is now shown that the size difference which causes the inhomogeneous distribution is, at the same time, an important additional source of scattering, which will always reinforce the anharmonic scattering of the strain field. The case of copper-aluminum alloys is considered because of recent measurements made on this system. At higher temperatures (shorter phonon wavelengths) scattering by the individual solute atoms becomes relatively more important.
Ultrasonic Third-Harmonic Generation in Strontium Titanate Single Crystals
Authors: Peters R. D. , Arnold R. T.
Published: February 2004

The ultrasonic harmonic generation technique employing fundamental and third harmonic wave amplitude measurements has been used to study the nonlinear elastic properties of SrTiO3 single crystals. A complete set of nonlinearity parameters calculated from room temperature data support the values recently reported for the harmonic generation technique in which fundamental and second-harmonic amplitudes were measured. The temperature variation of the third-order elastic constant C111 in the range 103°–300°K was also measured by third-harmonic generation methods and was found to agree well with the corresponding second-harmonic result. The experimental technique in most cases involved overlapped pulses in the pulse-echo wave train, and the results were found to agree well with measurements for the first pulse in the normal pulse-echo pattern.
Effect of Viscosity and Membrane on the Oscillations of Superposed Fluids
Authors: Puri K. K.
Published: February 2004

Two-dimensional small-amplitude viscous, as well as nonviscous, wave motion is considered in a medium consisting of two superposed incompressible fluids of finite depths, separated at the interface by a membrane. The upper one has a free surface and the lower one is bounded below by a rigid bottom. This is rather a crude model of a general problem in biology. Here one is interested in studying similar motions in a medium consisting of several layers of fluid separated by membranes across which there is migration of particles. It is found that the membrane affects the dispersion relation but does not lead to the damping of the waves. The frequency in the viscous case decreases with viscosity. The modulus of decay of the amplitude is 0{(ν1ν2)1/2/[ρ1(ν1)1/2+ρ2(ν2)1/2]},where ν1, ν2 are the viscosities and ρ1, ρ2 are the densities of the upper and the lower fluid, respectively.