bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconducting Properties of Reactively Sputtered Thin-Film Ternary Nitrides, Nb–Ti–N and Nb–Zr–N
Authors: Bell H. , Shy Y. M. , Anderson D. E. , Toth L. E.
Published: February 2004

Superconducting critical fields, currents, and temperatures of reactively sputtered thin films of Nb–Ti–N and Nb–Zr–N ternary alloys have been determined as a function of composition, and these properties are compared with those of sintered bulk nitrides of the same composition. The thin films have substantially higher critical current densities, higher critical fields, but lower critical temperatures than the bulk samples. In fields as high as 136 kOe, the Jc characteristics of the nitride films compare favorably with the thin-film characteristics of Nb3Sn and V3Si. The Jc-H properties of the nitride films are relatively insensitive to the Nb:Ti(Nb:Zr) ratio, a characteristic which favors these materials for certain practical applications such as thin-film solenoids. An unusual temperature independence of the electrical resistance was found for several compositions.
Transient Currents in Semi-Insulating CdTe Characteristic of Deep Traps
Authors: Zanio K. R. , Akutagawa W. M. , Kikuchi R.
Published: February 2004

The transport of charge in single crystals of semi-insulating cadmium telluride has been studied under the influence of deep trapping and subsequent thermal release of carriers from traps. Trapping and detrapping times for electrons and holes are determined directly from the shape of the transient response of surface-barrier devices to alpha particles. Hole-trapping times are 60 nsec; electron-trapping times range from 30 to 90 nsec. The measurement of the detrapping times from −60° to 60° C indicates that an electron trap with an activation energy of 0.59±0.04 eV can exist below the conduction band in semi-insulating material. The present measurement of drift mobilities, trap densities, and trapping cross sections does not require observation of a transit time. Furthermore, pulse analysis is not limited to times less than the transit time, a restriction in previous drift measurements. The theoretical response which accounts for both the trapping and detrapping of charge was derived by solving the kinetic differential equations which represent charge conservation. This extends the small-signal theory of transient currents in insulators to times beyond the transit time. Excellent agreement is found between experimental traces and theoretical shapes using a single-level trap model. Limiting cases which allow convenient measurement of the material parameters are described. In addition, the energy required to form an electron-hole pair is redetermined and found to be 4.9±0.1 eV.
Amplitude Dependence of Internal Friction and Shear Modulus of Boron Fibers
Authors: Firle Tomas E.
Published: February 2004

The internal friction and shear modulus of vapor-deposited boron fibers were measured at room temperature in an inverted torsion pendulum at about 5 Hz. The amplitude dependence was determined from <6×10−7G to 2×10−3G, where G is the shear modulus. Two regions were observed: a relatively amplitude-independent range to about 10−4G and strong amplitude dependence for higher oscillatory stresses. The internal friction and modulus were found to be independent of the number of stress-strain cycles for amplitudes <4×10−4G; irreversible changes started within a few cycles at or above 10−3G. The changes are qualitatively similar to the depinning of dislocations in metals. Absolute values of the shear modulus were determined at a strain amplitude of 2×10−6 and typically were 1.4×1012 dyn/cm2 (2×107 psi).
Preparation and Properties of Chromium Films
Authors: Milgram A. A. , Lu Chih-shun
Published: February 2004

A study was made of the properties of chromium films formed by vacuum deposition techniques. It was found possible to obtain films that had nearly bulk characteristics by using specific deposition conditions. The resistivity was determined as a function of film thickness. The orientation of the films was determined using x-ray diffraction. The film orientation was found to be dependent upon the particular glassy material used as a substrate. The resistance anomaly associated with the antiferromagnetic-paramagnetic transition in bulk chromium was observed. The experimentally determined resistance-temperature relationships for the Cr films were explained in terms of the effects of stress on the magnetic transition temperature.
Magneto-Optic Readout Using Media Modulation
Authors: Treves D. , Smaller P.
Published: February 2004

In the conventional magneto-optic readout of digital information stored in a magnetic thin film, surface imperfections are a major source of noise. The readout method described here uses a low-coercivity overlay film modulated by an external magnetic field, thus circumventing this noise source by detecting those light changes that are due only to the magnetic information and not surface noise. Experimental results, including a comparison of the new and conventional readout techniques, demonstrate the superiority of the modulation method.
A Simple Method for Determining Magnetostatic Mode Frequency and Pattern
Authors: Thiessen C.
Published: February 2004

To survey all the magnetostatic modes in a sample of any form, modes are regarded as superpositions of spin waves. A rough estimation of mode pattern and frequency is obtained from the azimuthal (m), radial (r), and longitudinal (l=n-m-2r) indices with n, m, r after the notation of Fletcher and Bell. The well-known guided-wave solutions in thin disks and in long rods are briefly reviewed by the superposition idea and are combined to get the resonances of cylinders. These are determined by longitudinal as well as transversal boundary conditions, which may originate from internal cutoff conditions rather than from the reflecting sample surface. As an example, the resonances in normally magnetized thin disks are treated more extensively, and are investigated experimentally, in seven different resonator sites, at the frequency of 6525 MHz. The measured resonances have been identified in (m+2r)-groups by symmetry considerations which follow from the mode indices. The resonance fields have been checked theoretically within about 20 G. Intensity and broadness of various resonances indicate a strong coupling to the whole resonator mode with a partial breakdown of local fields. The main resonance is damped selectively by higher-order modes.
Surface Charging of Triglycine Sulfate
Authors: Robertson Glenn D. , Baily Norman A.
Published: February 2004

Virgin crystals of triglycine sulfate were found to emit light when heated through the ferroelectric Curie temperature. This light comes from electrical discharges into the surrounding atmosphere, and both the first negative and the second positive band spectra of nitrogen have been observed. The crystal will repeat the phenomenon only if it is exposed to a humid environment. The moisture layer responsible for the sparking phenomenon does not exceed 50 Å in thickness.
Photoelectronic Evaluation of Electron Radiation Damage in CdS Crystals
Authors: Im Ho Bin , Bube Richard H.
Published: February 2004

The effects of electron radiation damage for electrons with energy between 75 keV and 2 MeV have been investigated in CdS single crystals by measurements of dark conductivity, photoconductivity vs temperature, spectral response of photoconductivity, optical quenching of photoconductivity, and thermally stimulated conductivity. The major effect of electron radiation damage is to decrease the electron lifetime in high-resistivity photosensitive crystals if the electron energy is 400 keV or higher. Relatively minor effects are also observed in dark conductivity, optical quenching, and thermally stimulated conductivity. Low-temperature annealing of irradiated crystals under illumination removes the effects of damage on the electron lifetime. After such annealing, however, all irradiated crystals exhibit a distinctly different trap distribution from nonirradiated crystals, prominent in which is the 289°K trap previously investigated and described as a repulsive trap in CdS and CdSSe crystals.
High-Temperature Internal Friction and Transport Mechanisms in Sodium Silicate Glasses
Authors: Field M. B.
Published: February 2004

Recent experimental evidence in favor of a vacancy model of ionic transport in glasses is discussed. The model is applied to new internal friction data on binary sodium silicate glasses. The second, high-temperature peak in the internal friction spectra of these glasses is apparently due to the stress-induced diffusion of singly-bonded oxygen ions. These ions diffuse into vacancies or interstitial sites whose concentration is thermally activated. Approximately 1012 cm−3 free sites are frozen into the glass below 200°C.
Observation of Parallel Arrays of Pure Edge Dislocations in Silicon
Authors: Green D. , Glaenzer R. H. , Jordan A. G. , Noreika A. J.
Published: February 2004

A four-point bending technique is used to plastically deform silicon slices. The silicon samples are oriented so that the resolved shear stress is greatest along a single family of (111) crystallographic planes. The operation of a single slip system is observed both optically and with a scanning electron microscope when bending is done at temperatures greater than 1000°C. At lower temperatures, multiple slip occurs. Transmission electron microscopy shows the dislocations to be arranged in parallel arrays where single slip predominates and classifies them as pure edge.
Electrical Resistance of Thin Triode-Sputtered Gold Films
Authors: Toombs P. A. B. , Bennett P.
Published: February 2004

Freshly prepared triode-sputtered gold films thicker than 200 Å on glass substrates exhibited a constant resistivity, about four times that of bulk gold, up to 4000 Å, the thickest films made. Annealing at 300°C for 4 h reduced their resistivity to twice that of bulk gold. Resistivity vs temperature curves were linear and parallel to the bulk gold curve.

Nucleation of the films were extremely rapid: Films deposited onto substrates at 70°C had resistivity only twice the final value at <70 Å thickness. The gold also appeared to renucleate on grown parts of the film, since 2000 Å thick films exhibited no preferred orientation and had small crystals, 100 to 200 Å in the plane of the film, probably ∼60 Å thick. Film resistivity attained its final value as soon as a film became continuous, at about 100 Å with substrate at 70°C and about 250 Å at 250°C. This cannot be explained by invoking lamellar crystals, where the thickness of a single crystal is to be considered and not that of the whole film, since this would call for much higher film resistivity than observed. The alternative is that the film surfaces reflect conduction electrons specularly. This behavior is in marked contrast to that observed for solid films prepared by other techniques. The differences in behavior are fully discussed and reasons for the discrepancies are suggested.
Possibility of Observing Negative Thermally Stimulated Conductivity
Authors: Bräunlich P.
Published: February 2004

Experiments are discussed which suggest that in compounds such as CdS, hole traps are likely to influence thermally stimulated rate processes. One of the interesting effects attributable to hole traps is negative thermally stimulated conductivity (NTSC). A phenomenological theory of NTSC has been developed. Conditions necessary for the effect to occur and experimental techniques to be employed for its possible observation are described.
Laser-Produced Plasmas from Solid Deuterium Targets
Authors: Colin C. , Durand Y. , Floux F. , Guyot D. , Langer P. , Veyrie P.
Published: February 2004

A 2 GW laser interacts with a solid deuterium target. Framing and streak pictures give the evolution of the plasma for different cases of focusing. A tentative interpretation is suggested.
Undegassed and Degassed Exploding Tungsten Wires in Vacuum
Authors: Holmström I. , Händel S. K. , Stenerhag B.
Published: February 2004

Undegassed and degassed tungsten wires, initially coated with an impurity layer of tungsten oxide and graphite, have been exploded in a vacuum of 2×10−6 Torr and at an initial capacitor voltage of 20 kV. Correlated x-ray and electrical measurements of these wires indicate that the x-ray emission from the wires begins prior to the appearance of the shunting discharge. The hard x-ray burst emitted has a half-amplitude width of about 25×10−9 sec and is reproducible from explosion to explosion provided the initial conditions are identical. The emission of hard x rays but not the main discharge current is influenced by the gases initially adsorbed by the wire surface. Finally, the main discharge current, but not the emission of hard x rays, is influenced by the impurity layer.
Growth and Defect Structure of Lamellar Gold Microcrystals
Authors: Morriss R. H. , Bottoms W. R. , Peacock R. G.
Published: February 2004

A common nonequilibrium form exhibited by gold microcrystals grown from solution is a thin (111) platelet of trigonal or hexagonal symmetry. From moiré patterns it has been established that these crystals are essentially free of dislocations if the growth temperature is kept constant. Using both bright- and dark-field electron microscopy and electron diffraction at various crystal orientations it has been shown that the major imperfection is coherent twinning in the large (111) planes of the crystals. The layered growth can be explained on the basis of a twin-accelerated growth mechanism involving multiple twinning on parallel (111) planes. Anomalous ED spots of the type ⅓{4̄22} can be explained on the basis of a nonzero structure facture resulting from a stacking disorder in the (111) planes. An electron microscopic and diffraction study of various stages of growth indicates that multiple twinning occurs very early in the growth process. An intermediate structure is exhibited by the gold platelets during the initial 40% of the growth process. It is speculated that the intermediate phase involves a gold compound of the type Au2X.
Lithium Niobate: Effects of Composition on the Refractive Indices and Optical Second-Harmonic Generation
Authors: Midwinter J. E.
Published: February 2004

Crystals of lithium niobate have been grown with varying amounts of Li2O, Nb2O3, and MgO present in the melt. The refractive indices have been measured and the birefringence so obtained correlated with the phase-matching temperature for second-harmonic generation (SHG) and with the composition. The use of optical methods is decribed for the study of compositional uniformity and a method of correcting the effects of uniform composition gradients on SHG described.
Two Theoretical Considerations for the Ultrasonic Measurement of Third-Order Elastic Constants
Authors: Holt Albert C.
Published: February 2004

It is pointed out that the deviation of the energy-flux vector from the propagation direction for plane waves in anisotropic solids is an important factor in the design of ultrasonic wave-distortion experiments for measuring third-order elastic constants. An equation for the energy-flux vector is derived in terms of the quantities characterizing the plane waves, and the direction of the energy-flux vector is tabulated for a particular material. It is shown that wave-distortion experiments cannot yield a complete set of third-order elastic constants, for crystals of arbitrary symmetry.
Index of Refraction of ZnO
Authors: Park Y. S. , Schneider J. R.
Published: February 2004

Measurements of the refractive indices of ZnO single crystals are extended from room down to liquid-helium temperatures in the region between the absorption edge and 5500 Å for E⊥C and E∥C. The indices are calculated from the locations of interference maxima in transmission spectra caused by multiple reflections in thin (0.4–80 μ), plane-parallel platelets. The dispersion curves at room temperature are similar to those reported by Mollwo, but they are extended to include the optical isotropic point. At energies near absorption edge n∥n⊥, as is found in other II-VI materials of the wurtzite symmetry. The isotropic point and its variation with temperature was also determined by birefringence measurements.
Current-Voltage Characteristics of Semiconducting Barium Titanate Ceramic
Authors: Mallick G. T. , Emtage P. R.
Published: February 2004

The current-voltage characteristics of semiconducting BaTiO3 ceramic have been investigated with electric fields up to 2×104 V/cm. The results obtained are in agreement with Heywang's model for conduction in this material (other published models being unsatisfactory) provided that allowance is made for the Ohmic drop in the bulk material. It is found that most of the current is channeled through small pores (0.1–0.5 μ diam) in the intergranular boundaries.
The Kinetic Behavior of an Optical Wave Packet
Authors: Pomraning G. C.
Published: February 2004

The kinetic behavior of a wave packet in a dispersive medium is discussed. The equations of motion, based on the general eikonal method for waves, are identical in form to Hamilton's equations for a particle. The relationship of this description of wave-packet motion to the ray equation of geometric optics is pointed out. A general solution of the equations of motion is obtained in the special case of an isotropic, inhomogeneous dispersive medium with a time-independent refractive index whose spatial dependence is one dimensional. In particular, detailed results are given for the parabolic waveguide problem which has been extensively discussed in the literature.
Statistics of Carrier Recombination at Disordered Regions in Semiconductors
Authors: Curtis O. L.
Published: February 2004

In semiconductors, when a region of local disorder is produced (e.g., by neutron irradiation), the defects contained in the region affect the local equilibrium carrier densities and act as effective recombination centers. In this paper, expressions are given for the transient carrier lifetime at low excess carrier densities, and for the steady-state lifetime at low defect concentrations. Results agree well with experimental observations of neutron-irradiated silicon.
Interference of Characteristic Waves in Plasmas
Authors: Brand G. F. , Hooker C. A.
Published: February 2004

The interference between the two characteristic waves in a magnetized plasma has been studied for propagation both parallel and perpendicular to the magnetic field. A new microwave interferometer which has been used to measure electron densities is described. Besides having a simpler construction, it is more sensitive than existing interferometers in certain situations.
Surface Conductivity of Cleaved Germanium Surfaces
Authors: Grant J. T. P. , Webster D. S.
Published: February 2004

The surface conductivity of clean germanium surfaces obtained by partial cleavage in ultrahigh vacuum has been measured for 2.0Ω·cm n-type material at room temperature by a channel technique and found to be within ±50% of 290 μmho/square. Allowing for variations in the published values of the surface hole mobility, the position of the upper edge of the valence band at the surface has been estimated as 0.05±0.07 eV above the Fermi level. The surface conductivity has been measured as a function of exposure to molecular hydrogen and oxygen. The temperature dependence of the conductivity along recontacted clean surfaces has been measured between 300° and 2°K.
Identification of the Ionic Species in a Cesium Plasma Diode
Authors: Agnew L. , Reichelt W. H.
Published: February 2004

The identification of the dominant ionic species in the cesium plasma diode has been established experimentally as the atomic ion, Cs+, instead of the molecular ion, Cs2+. Values of the atomic ion density, Ni, have been determined spectrographically by measurements of the radiative recombination spectrum leading to the 6P state. Electron densities, Ne, were measured independently by the Stark broadening of selected cesium lines. Within experimental uncertainty for a broad range of diode operating conditions, Ni=Ne. Thus, not only are Cs+ ions directly observed, but any important concentrations of Cs2+ would violate plasma neutrality. The experimental results are consistent with the existence of local thermodynamic equilibrium.
Dynamics of Bubbles Moving in Liquids with Pressure Gradient
Authors: Yeh Hsu-Chieh , Yang Wen-Jei
Published: February 2004

The time history of the velocity, size, and deformation of a bubble moving in the flow field around a point source or sink is studied analytically. Consideration is given to the case where the changes in the bubble velocity, size, and deformation are caused by the dynamic forces of the fluid, rather than the initial perturbation of the bubble shape. The effect of viscosity and gravitation is neglected. The flow is considered irrotational and the velocity potential is assumed to exist. The gas, vapor, or their mixture inside the bubble undergoes a polytropic process. The governing equations for the translatory motion, size, and deformation of the bubble are derived by perturbation theory. The analysis is general and may be applied to an initially spherical as well as nonspherical bubble. It is disclosed that the time history of the bubble's translating velocity in a sink flow is monotonically increasing, while in a source flow it varies following two typical patterns depending upon the initial velocity. In a sink flow, an initially spherical bubble can maintain a nearly spherical shape over a rather long distance as it grows, while in a source flow, the bubble shape varies with time in various ways, depending on the initial velocity. The analysis may also predict, by means of numerical reduction, the moment corresponding to the threshold of instability from which the bubble will attain an irregular shape. The mechanisms leading to the photographically observed behavior of a cavitation bubble moving in a rectangular venturi tube diffuser by Ivany et al. (1966) are revealed, in that the flow in a section of such a diffuser (or nozzle) closely resembles source or sink flow.
Temperature Dependence of Dynamical Electron-Diffraction Intensities of Polycrystalline Foils. II
Authors: Albrecht W. W. , Niedrig H.
Published: February 2004

Measurements of the filtered electron-diffraction intensities of polycrystalline gold foils were carried out at different temperatures. The intensities of the primary beam and the low-order reflections vary strongly with temperature. The dependence of this temperature effect on the diffraction angle and on the electron energy shows quantitative agreement with the results of the dynamical theory.
Stress Relaxation in Nickel Single Crystals between 77°−350°K
Authors: Rohde R. W. , Pitt C. H.
Published: February 2004

Stress-relaxation tests were conducted in compression with nickel single crystals of various orientations and purities. The experiments were performed at five temperatures, 77°, 153°, 198°, 298°, and 350°K. The data are fit by the semilogarithmic equation, Δτ(kT/B) (In A′t+1), based on reaction rate theory. Crystals oriented to produce glide on intersecting slip planes exhibited no relaxation at the three lower test temperatures. This absence of relaxation is believed to be a result of the high activation enthalpy necessary to produce dislocation motion across the intersecting glide dislocations which would markedly reduce the rate of thermal activation. Crystals oriented to produce slip on a single set of planes had only one relaxation curve at low temperatures; no subsequent relaxation after the initial one could be induced. At higher temperatures, after relaxation had ended, new relaxation was easily initiated by increasing the stress slightly. The activated volumes obtained were almost independent of the crystalline purity and of strain, and volumes varied between 6.5×10−20 cm3 at 350°K to 0.5×10−20 cm3 at 77°K. These volumes were considerably larger and had a different temperature dependence than the activated volumes previously measured by etch-pitting methods which varied between 1.0×10−20 cm3 at 273°K to 0.2×10−20 cm3 at 77°K. The discrepancy is believed to result because the rate controlling mechanisms for dislocation motion in etch-pitting and stress-relaxation experiments are different. It is shown that during stress-relaxation dislocation-dislocation interactions are rate controlling. In the previous experiment where dislocation velocities were directly measured, dislocation-dislocation interactions are believed to be of only secondary importance. Thus, the stress relaxation test while providing a simple method for obtaining the activated volumes associated with macroscopic deformation does not seem applicable for the inference of the parameters for dislocation motion in nickel measured by etch-pitting techniques.
Vibrational Mode Behavior of Rotating Cruciform Gravitational Gradient Sensors
Authors: Bell Curtis C. , Morris J. Roger , Richardson John M. , Forward Robert L.
Published: February 2004

We have designed, constructed, and tested a gravitational mass sensor which uses a rotating resonant elastic system to detect the gravitational force gradient fields of a nearby mass. As part of the over-all program, we have carried out a detailed analysis of the vibrational mode behavior of a rotating cruciform-shaped spring-mass system supported on a spring mount. The behavior of the sensor modes as a function of the design parameters and the rotation speed agrees well with data obtained from actual sensors used in the experimental portion of the work. This theory can aid in the design of optimum sensors and sensor-mount structures.
The Negative Point-to-Plane Breakdown in a Free-Electron Gas
Authors: Hassoun Abbass M.
Published: February 2004

The breakdown of a point-to-plane gap in pure He, under conditions where electrons do not attach to form negative ions with steady potential, has been observed using the two-photomultiplier technique for pressures from 50 to 220 Torr. Using a dual-trace oscilloscope, oscillograms of luminosity and current, luminosity and potential, and potential and current as a function of time were made. Movement of luminosity across the gap with and without interference filters segregating direct electron-impact excitation from thermal ionization, together with still photographs of the arc, allowed a fairly complete diagnosis of the breakdown mechanism to be made. The breakdown initiates as a localized Townsend glow discharge that propagates axially as an initially restricted luminous potential-gradient front across the gap, at from 4×105 cm/sec to 1×106 cm/sec. The cathode fall has a positive ion sheath of 4.5×1011 electrons/cm3 maintaining ionization which spreads over the cathode surface, yielding an ion density in the restricted portion of the arc channel of the order of 1014 ions/cm3. Ion plasma oscillations of 7×10 Hz occur during growth. These are associated with striations in the transient glow-discharge phase of growth, the arc phase being controlled by external circuitry.
Negative-Resistance Current-Voltage Characteristics of an Indium Antimonide p+−p−n+ Diode
Authors: Nordman James E. , Kvinlaug Hans
Published: February 2004

The negative resistance volt-ampere characteristic of a solution-grown indium antimonide p+−p−n+ diode is presented. The curve can be understood through the use of crude models. A prebreakdown nonlinearity and the negative resistance are attributed to the growth of a high-conductivity plasma across the sample. A shallow negative resistance in the postbreakdown region is thought to be caused by lateral expansion of this plasma. Finally, a postbreakdown characteristic of the form I ∝ V3 is explained in terms of a double-injection recombination-limited current with a current-dependent effective diode length.
Electrical Resistivity of Some Dilute Gold-Rare-Earth Alloys
Authors: Edwards L. Roger , Legvold Sam
Published: February 2004

The electrical resistivity has been measured from 1.3° to 20°K on solid solutions of Gd, Tb, and Ho in Au. It was found that the resistivity decreased with decreasing temperature with no evidence of a resistance minimum. However, the resistivity showed a more pronounced decrease in the temperature range 6°–3.5°K. These results are discussed in terms of the Kondo theory. It was also found that the residual resistivity, ρ(4.2°K), is proportional to the concentration of rare earths for the Gd, Tb, and Ho alloys. Furthermore, the proportionality constant is the same for the three sets of alloys indicating ionic (trivalent) scattering as the main contribution to the residual resistivity.
Microwave Measurement of the Electron-Density Profile in a Mercury Plasma
Authors: Carlile R. N. , Swinford H. W.
Published: February 2004

An experimental method is described which permits the electron-density profile in a circular cylindrical plasma column in the absence of a magnetic field to be measured. The method involves the propagation of plasma surface waves. Two parameters which characterize the profile are determined: α, the parabolic rate of decrease of electron density from the system axis, and T, which is a measure of the plasma-sheath thickness. For our experimental system in which the plasma is the positive column of a mercury-vapor dc discharge we find α=0.76±0.07 and T=0.96±0.03. (The plasma-sheath thickness is 1−T times the discharge radius.) These results are in good agreement with Parker's theoretical prediction.
Effect of Numerical Aperture of Microscope Objectives on Film-Thickness Determinations
Authors: Pliskin W. A. , Esch R. P.
Published: February 2004

The use of high-power magnification with large numerical aperture (N.A.) objectives in determining the thickness of transparent films requires a thickness correction due to the effective angle of incidence not being perpendicular to the substrate. The effective angle of incidence is dependent upon both the numerical aperture of the objective and the aperture diaphragm of the microscope. Under extreme conditions the uncorrected measured thickness can be as much as 10% smaller than the actual thickness. The error can be kept to less than 3% or 4% with reasonably high N.A. objectives by reducing the aperture diaphragm of the microscope. In many cases, the correction can be neglected depending on the precision required.
Second- and Higher-Order Effective Elastic Constants of Cubic Crystals under Hydrostatic Pressure
Authors: Barsch G. R. , Chang Z. P.
Published: February 2004

The concept of the pressure-dependent effective elastic constants of a cubic crystal under hydrostatic compression is extended to the effective higher-order elastic constants. These constants describe the non-linear elastic behavior of a cubic crystal in reference to arbitrary finite deformations which are performed in addition to the initial hydrostatic compression. The effective higher-order elastic constants are expressed in terms of pressure-independent actual higher-order elastic constants. Explicit expressions are given for the expansion coefficients of the effective second-, third-, and fourth-order elastic constants with respect to volume strain and pressure, up to terms involving the actual fifth-order elastic constants.
Thermionic and Tunnel Currents in Film-Covered Symmetric Contacts
Authors: Holm Ragnar
Published: February 2004

For calculating the current through a film-covered symmetric contact at a very small applied voltage, one can approximate the influence of the film by representing it as a rectangular potential barrier, with the height ψ volt=work function for emission of electrons from the metal into the film, and with the width s=thickness of the film; ψ depends on s. The tunnel current I1 flows below ψ; the thermonic current I2 flows above ψ. It is shown that, at a certain temperature Tc(ψ, s), I2 begins to exceed I1. In the case of a very small ψ and a relatively great s, Tc can appear below room temperature.
The Energy of Hexagonal Dislocation Arrays Forming Twist Boundaries
Authors: Hokanson J. L. , Winchell P. G.
Published: February 2004

The strain energy of low-angle twist boundaries has been computed using isotropic elasticity. The boundaries considered are hexagonal networks of dislocations whose Burgers vectors form an equiliateral triangle in the boundary plane. The Read-Shockley relationship for the dependence of grain-boundary energy on misorientation, θ, across the boundary, E=E0θ(A-lnθ), is valid for such boundaries. The parameter E0 is proportional to the sum of the self-energy contribution from each dislocation in the array; the parameter A was found by detailed calculation for the hexagonal networks of dislocations. A flat energy minimum was computed for the boundary consisting of an array of regular hexagons. For shapes not very different from this, the A parameter remained nearly constant. The energy increase over the minimum energy can be effectively estimated using a ``line-tension'' model. Observations of twist boundaries in twisted and annealed zinc single crystals show that some nearly regular hexagonal networks are present.
Origin of Short-Pulse Emission by Passively Switched Lasers
Authors: Fleck J. A.
Published: February 2004

The pulsed emission of passively switched lasers is analyzed in terms of traveling waves. Partial differential equations governing waves proceeding in opposite directions inside the laser cavity are derived by using a rate-equation approximation. The essential equivalence between the resulting model and theories based on normal mode expansions of the laser field is demonstrated. Numerical solution of the equations shows emission as a periodic train of short pulses for sufficiently short lifetimes of the upper absorber state. Single pulses in a round-trip time 2L/c occur if the saturable absorber is next to one mirror, whereas multiple pulses per round trip occur for absorber positions intermediate between the mirrors. The pulse patterns can be interpreted simply in terms of the nonlinear absorption properties of the saturable absorber.
Charged-Particle Emission upon Ruby Laser Irradiation of Transparent Dielectric Materials
Authors: Rousseau D. L. , Leroi G. E. , Falconer W. E.
Published: February 2004

Positive and negative charged particle currents induced in vacuo by high-power laser irradiation of transparent dielectric materials below the threshold for physical damage have been investigated. Soft glass, Pyrex, fused quartz, Supracil quartz, CaF2, LiF, and sapphire all show similar behavior. Currents as large as 1010 charged particles per pulse are obtained using ruby laser radiation with normal mode power levels of about 200 kW. For negative particle currents, two distinct signals have been time resolved using Q-switched pulses. The emission can be correlated qualitatively with that from laser irradiated metal surfaces. A phenomenological model is presented to account for the observed emission pulses. For the dielectric materials, currents are ascribed to laser heating of surface contaminants with subsequent production of high-energy photons and thermionic emission of electrons and ions. The emission of photons, electrons, and ions can be reduced, but not completely eliminated, by careful precleaning and repeated lasing on the dielectric surface. Much smaller emissions have been obtained from a ``clean'' surface than were previously considered to be intrinsic to the dielectric material.
Electro-optic and Piezoelectric Coefficients and Refractive Index of Gallium Phosphide
Authors: Nelson D. F. , Turner E. H.
Published: February 2004

Measurements of the constant-strain electro-optic coefficient of GaP between 0.56 and 3.39 μ wavelength were made using both pulsed electric field and optical heterodyne techniques. At 0.6328 μ wavelength its value is −0.97×10−12 m/V. A dispersion of only 10% is present between 0.56 and 3.39 μ. Approximate values of the piezoelectric coefficient and the constant-stress electro-optic coefficient are also obtained from the analysis of the experiments. For GaP the magnitude of the constant-stress coefficient is less than the constant-strain coefficient. The analysis also points out an often ignored effect: electro-optic measurements made with electric field frequencies in the range of resonant acoustic frequencies may not exhibit the expected symmetry of the crystal plus field but may also evidence effects from the crystal shape. Accurate refractive index measurements made on many GaP crystals between 0.545 and 0.70 μ wavelength are also reported.
Growth and Electrical Properties of Zinc-Cadmium Sulfide Graded-Band-Gap Crystals
Authors: Indradev  , Van Ruyven L. J. , Williams Ferd
Published: February 2004

Large quasi-single crystals of ZnxCd1−xS with increasing x along the growth direction, have been successfully grown by vapor-growth techniques. Typical dimensions are 15×3×4 mm. The growth mechanism is studied and, as a result, it is believed that the thermal conductivity plays a decisive role. Position-dependent optical and electrical studies on these crystals have revealed that the crystals with a slowly varying composition can be described by a graded band gap while the properties of crystals having a more abrupt change in composition are determined by lattice defects. Most of the crystals exhibit photoluminescence and high-field electroluminescence at low temperatures. From the optical and electrical data an energy-band diagram for graded ZnxCd1−xS is deduced with the position-dependent band gap accounted for by the position-dependent electron affinity.
The Effect of Strain on the Susceptibility of Polycrystalline Ni–Fe Films
Authors: Doyle W. D. , Finnegan T. F.
Published: February 2004

Various ripple effects in uniaxial polycrystalline magnetic films have been related by several authors to an effective single-grain crystalline anisotropy constant K. If either an isotropic planar stress σ or a uniaxial strain ε33 is applied to such a film, the ripple properties are altered. We develop a simple model which includes the effects of such stresses and strains. We thereby evaluate K as an effective crystalline anisotropy given by K=[(K1+Bsε33+¼Bσσ)2+(7/16)(Bσσ)2],1/2where K1 is the fourth order magneto-crystalline anisotropy constant, and B8 and Bσ are appropriate magnetoelastic coupling constants. A convenient ripple parameter is (HP-HK), where HK is the uniaxial anisotropy field of the film and HP is the field in the hard direction at which the in-phase component of the transverse differential susceptibility is a maximum. Measurements of (HP-HK) vs ε33 taken on electroplated cylindrical Ni–Fe films varying in thickness from 3000 Å to a 10,000 Å are presented. While the results are qualitatively in agreement with both Hoffmann's model and Torok's model, there are quantitative discrepancies with both models, particularly Torok's. In as-plated films, (HP-HK) increased more rapidly than expected and was found to be proportional to (ε33)8/3. Several possible mechanisms are proposed to explain this results. It is shown that measurements by several authors on dispersion and susceptibility in as-prepared and annealed films can be explained qualitatively using the proposed formulation for K.
Microwave Emission from Nonequilibrium Plasmas in InSb Subject to Magnetic Fields
Authors: Ancker-Johnson Betsy
Published: February 2004

This paper draws together a large amount of experimental information obtained by others as well as the author. Out of the maze of conflicting results one set of consistent characteristics of the microwave emission and its associated phenomena results. The reconciliation is obtained by means of a model for the spatial distribution of plasmas during emission. It shows why some samples emit preferentially for B ∥ E, others for B⊥E, and still others for intermediate orientation. Indeed, under the proper sets of conditions the same sample can be made to emit for all these various orientations in consonance with the model. The model also clarifies the various observed threshold dependencies. Why megahertz resistance oscillations of two different natures attend emission under some conditions and why under others such oscillations are totally absent is explained. Thus three characteristics of the emission and its associated phenomena can be consistently predicted, namely, the polar dependencies, the sometimes attendant megahertz resistance oscillations, and the threshold dependencies on E and B. It is concluded that the role of the B in the emission process is to place concentrated plasma within a radiation absorption length of a sample surface which is orthogonal to the direction of microwave propagation. It is argued that all observations of emission from InSb, at low and high electric fields, with and without magnetic fields, are caused by the same (unidentified) instability which is excited by the proper conditions of electric field and plasma density.
Measurements of the Density and Temperature of Electrons in a Reflex Discharge by Scattering of cw Ar+ Laser Light
Authors: Koons H. C. , Fiocco Giorgio
Published: February 2004

An experiment to measure the electron density and temperature in a low-density reflex discharge in helium, by scattering of cw argon-ion laser radiation at 4880 Å, has been successfully carried out. A synchronous detection scheme was used to distinguish the scattered radiation from all other radiation entering the detector. The scattering measurements indicated a density of 4.8×1018 m−3 and a temperature of 1.2 eV. These values are in good agreement with those obtained with a Langmuir probe.
Kinematics of Desorption by Emerging High-Energy Electrons
Authors: Danforth W. E. , Pollard John H.
Published: February 2004

With certain systems the cross section for desorption of surface atoms by low-energy electrons is negligibly small. Desorption will not take place unless the electrons have sufficient energy to impart the required momentum by direct exchange. The present paper is relevant to such systems. Given a high-energy electron traversing a solid and emerging from the surface, there exists a finite probability that the electron will suffer a deflection in the Coulomb field of the nucleus of a surface atom and thereby impart sufficient momentum to the atom to result in its desorption. Assuming that a value for the binding energy is given, the paper sets forth the several considerations which must have a part in the computation of the desorption cross section as a function of electron energy. Calculated values are presented for the case of adsorbed thorium over a wide range of assumed binding energies and for electron energies up to 2 MeV. Results of the mechanical integrations are plotted in such a form that cross sections for other atomic species can be obtained by simple calculation.
Occurrence and Mechanism of Rebinder Effects in CaF2
Authors: Westwood A. R. C. , Goldheim D. L.
Published: February 2004

A study has been made of the influence of adsorbed species on the room-temperature mobility of near-surface dislocations introduced into freshly cleaved {111} CaF2 surfaces by a diamond indenter. It was found that, in general, adsorbed surface-active ions or molecules decrease dislocation mobility, i.e., increase microhardness. Studies of the relaxation behavior of near-surface dislocations in CaF2 exposed to solutions of DMF in DMSO revealed that these environments also can influence dislocation mobility in the absence of stresses imposed by a loaded indenter. Moreover, for any particular DMSO-DMF environment, a correlation exists between the extent of dislocation motion induced by a loaded indenter and the amount of relaxation which occurs after the indenter is removed. From these and other observations it is concluded that indenter-lubrication effects do not play a fundamental role in the occurrence of Rebinder phenomena in CaF2. The results of this work are consistent, however, with the view that Rebinder effects in ionic solids are associated with chemisorption-induced changes in the state of ionization of near-surface point defects and dislocations. Such changes introduce variations in their mutual interactions which are then manifested as environmentally induced changes in the mobility of near-surface dislocations, and hence in microhardness.
Magnetization of Synthetic Filamentary Superconductors. B. The Dependence of the Critical Current Density on Temperature and Magnetic Field
Authors: Watson J. H. P.
Published: February 2004

Measurements of the magnetization of cylinders of synthetic high-field superconductors were made as a function of magnetic field and temperature. The superconductors were made by impregnating porous glass with indium. The porous glass can be characterized by the pore diameter; the critical field and the transition temperature depend strongly on the pore diameter. Assuming a critical-state model, the current density Jc was calculated from the magnetization versus field curves and was found to be of the form Jc=A−CB for magnetic fields B less than 0.3 of the critical field. In greater fields, Jc is almost independent of field. A and C depend upon temperature. For values of the ratio T/Tc between 0.9 and 0.5, A increases linearly with decreasing temperature. Several samples with different pore sizes have been measured; no systematic dependence on pore size was found.
Electron- and X-Ray-Diffraction Study of Cesium Antimonide Films Deposited on MnO and Other Substrates
Authors: McCarroll W. H.
Published: February 2004

Electron-diffraction data obtained from cesium antimonide cathodes deposited on oxidized manganese are consistent with a composite layer structure of Cs3Sb and MnO in which no appreciable chemical reaction occurs. In constrast, the low sensitivity cathodes obtained on unoxidized manganese can be attributed to the formation of MnSb when antimony is deposited. No change in the diffraction pattern of Cs3Sb is observed when the cathode is superficially oxidized as would be expected if only surface oxidation takes place. Direct evidence was also obtained for essentially complete order in annealed samples of Cs3Sb by x-ray diffraction. Although diffraction lines, indicative of order, were observed in the electron diffraction patterns of some simple Cs3Sb cathodes, their presence could not be correlated with any changes in photoelectric sensitivity.
Microwave Phonon Attenuation in Magnesium Aluminate Spinel
Authors: Lewis M. F. , Patterson E.
Published: February 2004

Measurements are reported of the attenuation of microwave phonons of various modes in magnesium aluminate spinel (MgAl2O4). The attenuation of certain modes is lower than in any other material measured and permits the observation of 9000 MHz echo patterns at room temperature. Some possible applications of this discovery are discussed. The attenuation at room temperature is interpreted in terms of an effective viscosity damping mechanism and approximate values of the components of the viscosity matrix are given.
Reverse-Biased Gallium Phosphide Diodes as High-Frequency Light Modulators
Authors: Reinhart F. K.
Published: February 2004

Reverse-biased gallium phosphide diodes have been successfully operated as high-frequency intensity and phase modulators of light at room temperature. The high-frequency modulation is fundamentally limited by the series resistance and the capacitance of the diodes. Cutoff frequencies as high as 7 GHz have been measured. Diode capacitance, typically less than 7 pF at the operating point, and driver impedance determine the broad-band characteristic. Intensity modulation measurements have been performed up to 500 MHz. The power consumption per MHz bandwidth for 40% intensity modulation was 2.7 mW for a diode only 0.7 mm long. A diode of 1.5 mm length used as a phase modulator needed only 1.5 mW of power per MHz bandwidth for a modulation index of 1 rad at a wavelength of 0.633 μ. This latter value corresponds to an intensity modulation depth of over 80%.