bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonstoichiometry and Crystal Growth of Lithium Niobate
Authors: Carruthers J. R. , Peterson G. E. , Grasso M. , Bridenbaugh P. M.
Published: February 2004

Deviations from stoichiometry occurring during the crystal growth of lithium niobate have been studied by 93Nb NMR and by shifts in the ferroelectric transition temperature. The high-temperature phase equilibria of nonstoichiometric lithium niobate were accurately determined by these techniques together with DTA and crystal-growth experiments. The congruently melting composition is located at 48.6 mole% Li2O and the solid-solution region at room temperature extends from 48% to 50% Li2O. The implications of growth at noncongruently melting compositions on the compositional uniformity of lithium niobate are discussed in detail.
Longitudinal Piezoresistance of AlxGa1−xAs
Authors: McGroddy J. C. , Lorenz M. R. , Smith J. E.
Published: February 2004

Samples of n-type AlxGa1−xAs were prepared by liquid phase epitaxy on a GaAs substrate. When x≳0.4 the material has the indirect band structure characteristic of AlAs. Longitudinal piezoresistance measurements were performed on this material with stress along the 〈100〉 and 〈111〉 crystallographic directions. The results indicate that the lowest conduction-band minima in the alloy, and by inference in pure AlAs, lie along the 〈100〉 directions in k space as in silicon.
Analysis of the 3-Tube Symmetrical Electrostatic Unipotential Lens
Authors: El-Kareh A. B. , Sturans M. A.
Published: February 2004

The 3-tube symmetrical electrostatic unipotential lens was analyzed in great detail. Starting from a mathematical expression for the axial potential distribution, the cardinal points and coefficients of spherical and chromatic aberration were obtained with the help of a digital computer. Values for S/R, the separation between the tubes, were taken equal to 0.25, 0.375, 0.5, 0.75, and 1.00 and the length of the central electrode, L/R, was varied from 0.25 to 2.00 in steps of 0.25. It was shown that the accelerating lens has a lower coefficient of spherical aberration than the decelerating lens. A comparison was made between the data obtained using the mathematical model and the relaxation technique. The agreement was excellent.
Effect of Wire Parameters on the Emission of Hard X Rays from Exploding Wires
Authors: Stenerhag B. , Händel S. K. , Göhle B.
Published: February 2004

Tungsten wires, 20–80 mm in length and 0.05–0.20 mm in diameter, were exploded in vacuum (1×10−5 Torr) by means of a 0.4-μF capacitor charged to 30 kV. A pronounced dip and peak in the dI/dt and voltage oscillograms, respectively, corresponded in time to each other and to an ultrafast x-ray pulse. Calculations showed that the wire temperature reached melting point at the same moment. It was found that for a constant wire length, the magnitude of the voltage peak attained a weak maximum at a diameter of about 0.10 mm. In addition, for a constant wire diameter, this magnitude increased with increasing wire length. The x-ray output was measured by a scintillator-photomultiplier (PM) combination and an x-ray film. The PM pulses (half-width 20 nsec) depended only slightly on the wire parameters. Their peak values plotted against wire length and diameter showed the same feature as the peak voltage diagram did. Furthermore, studies of the film blackening indicated that various wire dimensions gave rise to various rates of blackening. It was also found that the higher the voltage peak (or PM pulse) the more dense the blackening on the film. A model, based on Ohmic heating of the wire with accompanying thermionic electron emission, which qualitatively explains the generation of the ultrafast x-ray pulse, is presented. In addition, it was found that the electron currents which gave rise to the x-ray burst were up to 10 times higher than those predicted by Richardson's formula.
Channeling of an Ionizing Electrical Streamer by a Laser Beam
Authors: Koopman David W. , Wilkerson T. D.
Published: February 2004

Long electrical spark discharges have been directed through air along predetermined paths defined by a concentrated laser beam. At apparent optical power densities of 50–100 giga W/cm2, 35-nsec half-width laser pulses at 10 600 Å have been effective in channeling streamer discharges from a 350-kV positively charged electrode for distances up to 28 cm in a total streamer length of 71 cm. The average E field required to obtain a discharge between electrodes was reduced from 7.3 to 5.5 kV/cm with the laser powers employed.
Organic Dye Laser Threshold
Authors: Peterson O. G. , Webb J. P. , McColgin W. C. , Eberly J. H.
Published: February 2004

This paper describes the results of an investigation of the interrelated physical parameters that determine laser threshold for three organic dyes: rhodamine B, rhodamine 6G, and fluorescein. Not only are these dyes (rhodamine 6G in particular) among the most widely used and important laser dyes, but insights into the threshold condition derived from our studies of these particular dyes should be generally applicable to future dye laser research. Our detailed characterization of threshold for these dyes and our novel insights result from the use of triplet state spectral data in a thorough and quantitative way for the first time, coupled with the physically realistic approximation that the triplet population is proportional to the singlet excited state population. For the case of self-tuning of the laser emission wavelength, solutions to the threshold equations are presented that establish relations between all the parameters affecting lasing: critical inversion, emission wavelength, extrinsic losses, dye concentration, length of active medium, and triplet to excited singlet population ratio. For reasonably high extrinsic cavity losses, the critical inversion is a simple power law function of extrinsic loss, and the emission wavelength is self-tuned in such a manner that the ratio of extrinsic losses to intrinsic singlet absorption losses is substantially constant. There exists a region of low, but still physically realizable, cavity losses, where laser action is determined exclusively by intrinsic characteristics of the dyes (triplet absorption, singlet emission, and absorption). Asymptotic limits on the maximum wavelength of emission and on the minimum critical inversion appear in this region, beyond which there is no point in reducing extrinsic cavity losses. The fraction of triplet state molecules also determines long wavelength cutoffs for an externally tuned laser. Methods are outlined for measuring the ratio of triplet state to excited singlet state populations for dyes with known triplet absorption spectra and for determining semiquantitatively the triplet effects in dyes where this information is not known. A final interesting conclusion is that molecular modifications of rhodamine 6G cannot be expected to improve its threshold characteristics as a laser dye by much more than a factor of 4.
GaAs–AlxGa1−xAs Double Heterostructure Injection Lasers
Authors: Hayashi I. , Panish M. B. , Reinhart F. K.
Published: February 2004

Double heterostructure GaAs–AlxGa1−xAs junction lasers which have very low thresholds and which have been operated continuously at and above room temperature have been fabricated by liquid phase epitaxial growth. The threshold current density of these lasers decreases approximately linearly with the thickness of the active region from 3 to at least 0.5 μm. This is interpreted as the result of near perfect carrier and optical confinement as the result of large steps in the energy gap and index of refraction at the heterojunctions in these diodes. The gain in these lasers is very high and its dependence upon current density is superlinear. Loss is very low and almost that expected from free carriers. Complete polarization of the lasing mode was observed. This latter is interpreted to be the result of an increased reflection coefficient for the T E mode.
Efficiency of Red, Green, and Blue Infrared-to-Visible Conversion Sources
Authors: Geusic J. E. , Ostermayer F. W. , Marcos H. M. , Van Uitert L. G. , van der Ziel J. P.
Published: February 2004

Efficiencies of ∼1%, 0.1%, and 0.01% have been achieved, respectively, in the red, green, and blue with simple infrared-to-visible conversion sources. Saturation effects observed in the blue-emitting phosphor Y0.65Yb0.35Tm0.001F3 have been explained. The first and second cross-transfer coefficients for this Yb, Tm system have been determined to be 1.3×10−17 and 8.3×10−15 cm3 sec−1.
Dynamics of Magnetic Bubble Domains with an Application to Wall Mobilities
Authors: Callen Herbert , Josephs Richard M.
Published: February 2004

By introducing a rather simple functional approximation for the magnetostatic energy in the bubble-domain theory of Thiele, we obtain explicit expressions for static properties such as the collapse field and the bubble size in a given bias field. The theory is extended to dynamic properties as well. In particular, we obtain a simple expression for wall mobility based on the bubble collapse technique introduced by Bobeck. We have carried out bubble size and mobility measurements on orthoferrite platelets, and we find excellent agreement with the functional form of the theory.
Fracture Marks Associated with Transition-Region Behavior of Slow Cracks in Glass
Authors: Varner J. R. , Fréchette V. D.
Published: February 2004

Techniques of fractography employed in a study of slow-crack behavior in edge-cracked glass sheets have led to the discovery of previously unreported fracture marks. The physical appearance of these marks and the mechanism of their formation is postulated to be a result of mixed stress-corrosion dependent/stress-corrosion independent effects in the transition region of slow-crack propagation in glass.
Geometric Optics Theory of Parametric Image Upconversion
Authors: Chiou Walter
Published: February 2004

This paper describes a general geometric optics theory of visible or near-visible image formation in parametric upconversion. A formula is derived that relates the location of the image to the locations of the object and the pump. Aberrations are caused by the finite thickness of the nonlinear material; these aberrations vanish when both the pump waves and the object waves are parallel plane waves. The primary factor that limits the field of view of parametric image upconversion is the phase-match condition.
Bubble Nucleation Induced in Liquid Films by Irradiation
Authors: Kato Ryuhei
Published: February 2004

An attempt is made to explain the mechanism of rupture by irradiation for thin liquid films. The author proposes a visualized model for the rupture. The model shows as follows; when liquid films, whose main component is water, are irradiated, first the microbubble formation occurs as in bubble chambers and second, if the diameter is more than about 0.3 times the film thickness, the film is broken. If the diameter is less than this, the microbubble will immediately disappear without any change in the film. Calculations for the radius and for the probability of rupture of a film are given by the author. The author has tried various experiments to affirm his picture, and some experimental evidences available for this model are also shown. Moreover, it was found that the agent responsible for film rupture consists of recoil oxygen nuclei rather than delta-rays or recoil hydrogen nuclei. The threshold energy for film rupture slightly exceeds about 1.1×105 eV.
Determination of Surface Impurity Concentration Profiles by Nuclear Backscattering
Authors: Ziegler James F. , Baglin John E. E.
Published: February 2004

An analysis has been made to extract the concentration profiles of impurities in the upper two microns of a substrate surface. The technique used is nuclear backscattering. Since the stopping power of materials is nonlinear with energy, detailed calculations are necessary to unfold the impurity distributions. The calculations were tested by analyzing arsenic impurities in silicon. Four MeV helium was used as the projectile. Because the reaction 28Si(α, α)28Si at 2–4 MeV occurs in a region of many energy levels in 32S, a fitting technique was used to extract cross sections from an optical-model calculation of the reaction cross section. The experimental data were corrected by the technique of deconvolution for detector and electronic noise to obtain a final depth resolution of about 200 Å. The extracted impurity profile is shown to be as accurate as those obtained from neutron-activation profiling, differential Hall measurements, and differential resistivity measurements.
Acoustoelectric Effects in Indium Antimonide
Authors: Fleming W. J. , Rowe J. E.
Published: February 2004

The acoustoelectric interaction in InSb is developed and investigated on the basis of a hydrodynamical theory. Comparison of numerical results obtained from this theory with the corresponding numerical results from more detailed microscopic theories reveals that the essential features of the microscopic theories are also present in the simpler hydrodynamical theory. In particular, the hydrodynamical theory accounts for the existence of two distinct modes of acoustic domain formation and for the reduction of peak acoustic gain at low values of magnetic field. Valuable insight into the physical basis of the acoustoelectric effect is obtained and it is shown that in the limit of large electron drift velocities and small transverse magnetic field strengths, the Mode I-type acoustoelectric interaction arises from a drift-enhanced quenching of electron diffusion effects. Moreover it is found that the frequency of maximum acoustoelectric gain, as given by the hydrodynamical theory of the present paper, does not occur at the fixed frequency f0 = (ωRωD)1/2/2π, but rather, it is dependent upon the exact values of drift velocity and magnetic field strength. Several computer-generated plots are presented and discussed in order to fully illustrate the results of this investigation.
Gunn Effect in InAs Under Hydrostatic Pressure
Authors: Smith John E. , Camphausen Don L.
Published: February 2004

We have studied the high electric field conductivity of n-type InAs at pressures up to 29 kbar. Carrier multiplication due to impact ionization of valence band electrons is the predominant phenomenon at lower pressures, while the Gunn effect is observed at higher pressures. Above about 25 kbar no carrier multiplication is observed below the threshold electric field for Gunn effect. The bulk negative differential conductivity underlying the Gunn effect is presumed to be due to the transferred carrier mechanism. From the change in character of the high-field transport near 25 kbar, and from some recently published studies on the In1-xAlxAs alloy system, we eliminate the subsidiary minima involved in the carrier transfer to lie about 1.2±0.05 eV above the top of the valence band at atmospheric pressure, and to have L1 symmetry. The results are compared with an earlier report of Gunn effect in InAs under uniaxial stress.
GaAs Epitaxy by a Molecular Beam Method: Observations of Surface Structure on the (001) Face
Authors: Cho A. Y.
Published: February 2004

The epitaxial growth of GaAs by a molecular beam deposition method on bromine-methanol etched (001) GaAs substrate has been studied in situ in an ultrahigh vacuum high-energy electron diffraction system. GaAs (001)−C(2×8) and (001)−C(8×2) surface structures were observed during growth: one is arsenic stabilized, the other is gallium stabilized, and they are rotated 90° about the [001] axis from each other. Which surface structure is present during growth is a function of the ratio of the arsenic to gallium intensity in the molecular beam and the substrate temperature. For a given As2/Ga ratio, there is a transition from growth with the arsenic-stabilized (001)−C(2×8) to the gallium-stabilized (001)−C(8×2) with an increase in substrate temperature. In the case of a constant substrate temperature, the same transition can be achieved by varying the As2/Ga ratio. Without the molecular beam impinging on the surface, a gallium-stabilized (001)−C(8×2) surface structure quenches to a (001)−6 structure while the arsenic-stabilized (001)−C(2×8) structure remains unchanged.
Method for Doping Thin Insulating Films and the Comparison between the Electrical Characteristics of Undoped and Doped Films
Authors: Antula Jovan
Published: February 2004

A technique has been developed for doping thin dielectric films with either positive or negative ions from aqueous solution. The experimental investigations were made on 60–400-Å thick aluminum oxide films. The influence of doping on Schottky or Poole-Frenkel emission was shown by comparison of the electrical characteristics of the doped and undoped films. The predominating mechanisms are, for thin (<100 Å) films, Shottky emission; for thick (400 Å) films, Poole-Frenkel emission; and for films of intermediate thickness (∼200 Å) Poole-Frenkel and Schottky for doped and undoped, respectively.
Electrical Properties of Gold at the Silicon-Dielectric Interface
Authors: Brotherton S. D.
Published: February 2004

The influence of gold has been examined at the Si/SiO2 interface, and it has been found that the results are consistent with gold introducing an acceptor surface state close to the valence band edge. A study of the formation kinetics of these centers has indicated that they result from a surface-reaction-limited process rather than from a gold diffusion-rate-limited process. It is suggested that the surface reaction is between the gold and interfacial disorder centers, such that the density and availability of these centers determine the resulting density of active gold centers. Gold has also been found to introduce the same type of acceptor center at the interface between silicon and deposited layers of both silicon nitride and silica. Finally, a number of other metals were examined for action similar to gold at the Si/SiO2 interface. Only platinum was found to behave in this manner, and it was assumed that the same mechanism was operative in the formation of this center as with the gold centers.
Hydrodynamics of Explosively Generated High-Velocity Fluid Jets
Authors: Politzer Jay L. , King Walter F.
Published: February 2004

High-velocity fluid jets can be explosively generated by firing a piston into a liquid-filled gun barrel fitted with a convergent nozzle. A simple equation is derived in Lagrange's approximation for the motion of the piston and fluid for a one-dimensional model which includes the effects on the flow due to the firing chamber and nozzle. Calculations using parameters typical of a 105-mm howitzer indicate the feasibility of producing a high-velocity jet flow with a relatively low terminal piston velocity, thereby allowing it to be stopped without damage to the nozzle.
Analysis of a High-Explosive Shock-Tube Experiment
Authors: Glenn H. David , Crowley Barbara K.
Published: February 2004

A shock-tube experiment was performed with 5.5 kg of high explosives to generate and to drive an air shock down a steel pipe 7.8-cm i.d. and ∼25-m length. Fiber optics and pressure transducers were installed at specific locations to record optical and pressure time of arrival of the air shock and pressure histories in the pipe. The initial∼Mach 30 air shock attenuated to∼Mach 6 at the end of the pipe. A numerical simulation of this experiment was performed. This paper presents the experimental arrangement and results, and briefly describes the numerical models used. The calculation results are compared with the data. During the interval of approximately 8 msec required for the shock to travel the length of the 25-m pipe, the calculations indicated that the predominant factors in attenuating the time of arrival of the shock were heat transfer and friction, respectively.
Transitions from the 4T2 State in Pink Ruby
Authors: Everett Patrick N.
Published: February 2004

In this investigation it was determined by direct measurements that the 4T2 lifetime is less than 2 nsec at temperatures between 2° and 300°K. No fluorescent emission from the 4T2 state was observed although extremely high excitation powers and sensitive detecting equipment were used. It was demonstrated that the nonradiative transitions 4T2→2E occur with a frequency which is greater by a factor of at least 3×105 than that of the fluorescent 4T2→4A2 transitions. If the 4T2→4A2 transitions are considered to be purely electronic, it is shown that the lifetime of the 4T2 state must be less than 45 psec. In the more likely event that the transitions are vibrationally assisted it is shown that the lifetime must be less than 10 psec. Luminescence was observed as the result of a two-photon absorption process.
Single-Crystal Folded-Path Delay Lines Utilizing Ultrasonic Pure Shear Modes
Authors: Brugger K. , Thurston R. N.
Published: February 2004

We describe the principle of folded-path single-crystal delay lines for pure shear modes, utilizing the fact that in most crystal classes there exist special planes with the following properties: (1) A pure shear wave with polarization normal to such a plane can propagate along any direction in it. (2) Upon reflection of this wave on a boundary normal to the plane, no mode conversion occurs. Hence, in a crystal with two or more boundary surfaces normal to such a special plane, a pure shear wave can be reflected back and fourth between these boundaries without reflection loss. Moreover, with an entire plane of propagation directions available, the design can be optimized by selecting the path giving either the largest delay, or, if the attenuation for all propagation directions is known, giving the lowest loss per unit delay. Examples for the propagation and reflection of pure shear modes in cubic and rhombohedral crystals are presented.
Morphology of Migrating Bubbles in KCl Crystals
Authors: Nadeau J. S. , Carter R. E. , Rosolowski J. H.
Published: February 2004

Gas bubbles migrating under the influence of a temperature gradient in KCl gradually evolve stable shapes which have a low length (in the direction of migration) to width ratio and are bounded by cube planes (100). The shape is determined by evaporation-condensation kinetics and not by the equilibrium surface energies. A significant part of the bubble volume is left behind in a trail of very fine bubbles resulting in as much as a fivefold increase in bubble surface area. Most of the observed phenomena can be correlated with the detailed temperature distribution around a migrating bubble.
Low-Frequency Dielectric Constants of the Alkaline Earth Fluorides by the Method of Substitution
Authors: Andeen Carl , Fontanella John , Schuele Donald
Published: February 2004

The 1000-Hz 300°K dielectric constants of the alkaline earth fluorides were measured to an accuracy of 0.01% by the method of substitution. Reproducibly different values for various crystals of the same type were obtained which varied beyond the experimental error. The ranges of results for various crystals of each type measured along with further separation by manufacturer are: CaF2, Harshaw, 6.7984–6.7988, Optovac, 6.8074–6.8432; SrF2, Harshaw, 6.4647–6.4664, Optovac, 6.4700–6.4703; and BaF2, Harshaw, 7.3590–7.3595, Optovac, 7.3606–7.3630. The spread for each type of crystal is thought to be attributable to random trace impurities.
Temperature Dependence of the Elastic, Piezoelectric, and Dielectric Constants of Lithium Tantalate and Lithium Niobate
Authors: Smith R. T. , Welsh F. S.
Published: February 2004

The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase-velocity measurements, the measured resonant and antiresonant frequencies of a single length-extensional bar resonator, and the measured low-frequency capacitances of two thin flat-plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4/°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4/°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4/°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4/°C. The dielectric or permittivity temperature derivatives are positive for both materials.
Properties of Vacuum-Insulated Single-Crystal Tungsten Electrodes in High Electric Fields. Part II. Nature of Prebreakdown Currents
Authors: Fabiniak T. J. , Jedynak L. , Dodd R. A.
Published: February 2004

The nature of the emission currents associated with electropolished single-crystal tungsten electrodes in vacuum insulation has been studied. Schottky-Richardson curves indicate that the emission current is thermionic at voltages above 1.5 kV, this conclusion being supported by Fowler-Nordheim curves which show no evidence for field emission. It is uncertain whether the emission currents below 1.5 kV are of the thermionic or field-emission type. The origin of the thermionic currents can be associated with various surface structures on the electrodes, notably slip plane ledges and surface hole ledges, as discussed in Part I. Polycrystalline electrodes were not studied in detail, but appear to be associated with field emission.
Temperature Dependence of the Effective Diffusion Coefficient for Zinc in Gallium Arsenide
Authors: Ting C. H. , Pearson G. L.
Published: February 2004

The temperature dependence of the effective diffusion coefficient D̄ of Zn in GaAs has been measured at fixed temperatures between 600° and 1000°C. The isoconcentration diffusion technique was used throughout this investigation. It was found that D̄ is essentially temperature independent over the entire range. The relationship is revealed only when the total zinc concentration is held constant since D̄ is strongly concentration dependent. At a fixed Zn concentration of 2×1019 cm−3 the measured value was 9.0×10−10 cm2sec−1 with a standard deviation of 1.15. This experimental result is interpreted in terms of the interstitial-substitutional diffusion model.
Transition Radiation from a Modulated Electron Beam
Authors: Marcuse D.
Published: February 2004

It appears most natural to try to explain the Schwarz-Hora effect as transition radiation that is emitted when a modulated beam enters a target composed of either a good metallic conductor or a dielectric material. This study comes to the conclusion that the signal-to-noise ratio at the beam current reported by Schwarz and Hora is so small that transition radiation could not be observed. One is thus led to the conclusion that transition radiation cannot explain the light emission that Schwarz and Hora have observed.
Correlation of Electrical Breakdown and Centers of Strong Electron Emission on a Zone-Refined Iron Cathode in Vacuum
Authors: Farrall G. A.
Published: February 2004

The present work is a study of the whiskerlike protuberances upon the surface of a ½-in-diam zone-refined electrode in vacuum. The experimental technique employs a phosphor screen parallel to the electrode surface. The electron emission from the surface protuberances are projected upon this screen. The experiment consisted of more than 40 trials, each trial involving the recording of an emission pattern, the determination of a Fowler-Nordheim plot, and the application of 60-cycle high voltage sufficiently large to produce occasional breakdown. Further, the electrode surface was photographed directly during each application of 60-cycle voltage so that the locations of individual breakdown events could be recorded. In general, good correlation was found between the location of emitters as determined from the phosphor screen display and the locations of breakdowns.
Analysis of Nonequilibrium Plasmas in Close-Spaced Thermionic Converters
Authors: Shaw D. T. , Wu F. T.
Published: February 2004

The effects of varying interelectrode spacings, current outputs, and cesium pressures on the spatial profiles of the electron temperature and density are determined for an ignited thermionic converter. A new method is introduced for the determination of the boundary conditions of the three transport equations which describe the electron and ion diffusion and the electron energy transport in the interelectrode plasma. Special emphasis is placed on the change of plasma properties as the interelectrode spacing varies from large values to very small values.
Minimal Energy Dissipation and Maximal Error for the Computational Process
Authors: Landauer Rolf , Woo James W. F.
Published: February 2004

In a preceding paper, the execution of elementary logic steps was analyzed for minimal energy requirements and for bounds on the unavoidable error probabilities. This was done with the aid of a hypothetical device involving the use of a particle held in a time-modulated potential well, and coupled through springs to other such particles. The previous analysis was limited to the case of wells modulated very slowly compared to the relaxation time for particle redistribution. The present analysis extends these studies to the case of computations proceeding at arbitrary velocity. The same hypothetical device is invoked, with minor modifications for analytical tractability. Energy dissipation is found to be minimal for potential wells endowed with critical damping and the dissipation is roughly proportional to computing rate. The error rate also increases with computing velocity and is lowered by critical damping, but is less sensitive to these parameters, and is largely dependent on the magnitude of the interaction potentials between wells.
Improved Thermal Diffusivity Method Applied to TiB2, ZrB2, and HfB2 from 200°–1300°C
Authors: Branscomb T. M. , Hunter O.
Published: February 2004

The thermal diffusivities of dense polycrystalline TiB2, ZrB2, and HfB2 were measured by a laser flash method over the temperature range 200°–1300°C. An investigation of the effects of radial heat flow was performed and a special sample shape was used to comply with the assumption of one-dimensional heat flow. The values of the diffusivities were found to be described by the empirical equations αTiB2=0.1290+[39.26/T(∘K)]cm2/secαZrB2=0.1424+[81.17/T(∘K)]αHfB2=0.1436+[35.97/T(∘K)].Values of thermal conductivity computed from the diffusivity data were found to be described by λTiB2=0.7867+[10.30/T(∘K)]W/cm degλZrB2=0.8235+[108.2/T(∘K)]λHfB2=0.7157+[34.24/T(∘K)].
Inferences from the Transfer Function of Maser Media
Authors: Schulz-DuBois E. O.
Published: February 2004

The transfer function for transmission through a maser medium is derived. It is valid within the dynamic range of linear maser response and under the assumption of weak dispersion. All signal distortions due to propagation in a maser medium may be canceled by subsequent propagation in a complementary absorbing medium. The signal leaves the cascaded media undistorted with a delay corresponding to propagation at the vacuum velocity of light. This possibility of recovering the speed of light makes it difficult to talk of the propagation of information in a dispersive medium as taking place at a signal velocity below that of light. A potentially useful scheme is shown in which a severely distorting low-noise maser amplifier is used. After further amplification the signal distortions are eliminated by transmission through a complementary absorbing medium. The mathematical form of the transfer functions also leads to a new integral formula involving Bessel functions.
Quantitative Control of Surface Pinning in a Low-κ Type II Alloy
Authors: Morrison D. D. , Rose R. M.
Published: February 2004

Quantitative control of surface pinning in the case of In–2% Bi foils was achieved by pressing diffraction gratings into the foil surfaces. The resulting grooves were effective pinners when they were 8.4ξ or wider and ineffective when 4ξ or narrower; the critical Lorentz force for flux flow was consistent with simple static calculations based on the groove geometry. No pinning occurred for flux flow along the grooves. Near Hc2, the strength of pinning decreased linearly with H, and was essentially constant at lower fields. The Jc(H) peak effect was found to depend on pinner spacing.
Electroluminescence in GaAsxP1−x, InxGa1−xP, and AlxGa1−xP Junctions with x≲0.01
Authors: Logan R. A. , Dean P. J. , White H. G. , Wiegmann W.
Published: February 2004

The addition of low concentrations (≲1%) of As, In, or Al to the p side of GaP junctions, where exciton recombination at N or Zn, O centers generates green and red electroluminescence (EL), respectively, drastically decreases the quantum efficiency η of the junctions. The decrease in η is due to increased nonradiative recombination at deep centers in the junction space charge, while recombination outside the space charge is unchanged according to measurements of the EL decay time. Low-temperature photoluminescence efficiency measurements confirm that recombination in the bulk semiconductor is unaffected by the presence of these low concentrations of As, In, and Al. The junctions were formed using liquid epitaxial techniques. Using InxGa1−xP layers, where the alloy composition was accurately determined using radioactive tracer techniques, the composition dependence of the transition energies of the N and S bound excitons was measured by low-temperature absorption and luminescence studies.
Growth and Some Magnetic Properties of GdIG Films
Authors: Stein B. F.
Published: February 2004

The growth and magnetic properties of GdIG films grown by chemical vapor deposition on YIG and GdGaG substrates is described. Various aspects of the deposition technique including the design of a concentric tube reactor, hydrodynamics of the gas flow, substrates, and deposition parameters are discussed in detail. GdIG films have been grown at rates as high as 16 μ/h. They are epitaxial and are of the same orientation as the substrate. The films are strained because of mismatch between the film and substrate. A Faraday effect hysteresigraph has been used to measure the coercive force and the compensation temperature. The remanence has been measured as a function of temperature from −40° to 60°C and has been correlated with strains in the film. Diffusion has been observed between the film and substrate. This can be minimized by increased growth rates and by preheating substrates.
Permalloy Rail-Cylindrical Magnetic Domain Systems
Authors: Goldstein R. M. , Copeland J. A.
Published: February 2004

Recently proposed bubble-memory designs employing Permalloy rails are examined to determine an optimization of their geometries. This is done by determining the interaction force of Permalloy films with cylindrical domains. The appropriate rail geometry is shown to yield a bistable condition for the bubbles; that is, the reading of a one or zero is insured by the fact that the bubbles will not ride directly underneath the rail but only on one side of the rail. Calculations of the forces between bubbles and various geometric shapes (squares, circles, etc.) are also given. The results enable a determination of the geometric shape required to propagate bubbles along the rails with the least expense of energy when a single-phase drive circuit is used. General design considerations resulting from the mutual repulsive force between bubbles and the effects of demagnetizing fields are included in the above analyses.
Shear-Strength and Friction Measurement on Thin Layers under High Pressure
Authors: Towle Laird C.
Published: February 2004

Rotating-anvil type shear presses have been used by several investigators in studies of shear strength and friction on thin samples. The essential design features and operating procedures used by previous investigators are briefly reviewed. A new apparatus of this general type is then described which incorporates a high-sensitivity, strain-gauge instrumented, combination load and torque cell. The new device was designed specifically for measurements on very weak solids at pressures up to about 20 kbar. Operation of the apparatus is illustrated with measurements at pressure up to 5 kbar on thin sheets of the polymer polyvinylidene fluoride. The results are interpreted in terms of the friction and shear strength of the sample material by making use of concepts from the adhesion theory of friction.
Pressure Dependence of the Elastic Constants of SrTiO3
Authors: Beattie A. G. , Samara G. A.
Published: February 2004

The effects of hydrostatic pressure between 0 and 22 kbar on the elastic constants of SrTiO3 were measured at 295°K. All constants increased linearly with pressure in this range. The pressure derivatives of the adiabatic constants dCij/dP are: 10.21±0.15, 3.51±0.15, and 1.24±0.05 for C11, C12, and C44, respectively. These pressure derivatives, in conjunction with the recent second-harmonic generation results of Mackey and Arnold, allow us to determine the complete set of third-order elastic constants. The results, in units of 1012 dyn/cm2, are: C111=−49.6±4.3, C112=−7.7±1.6, C123=+0.2±4.3, C144=−8.1±2.4, C166=−3.0±1.2, and C456=0.9±2.7. Combined with the temperature derivatives of the (second-order) elastic constants at constant pressure, the pressure results allow a determination of the explicit volume and temperature dependences of these constants. In addition, the present results allow us to calculate the acoustic mode Grüneisen parameters, an approximate value of the limiting Grüneisen constant, γ0=1.52, and the coefficients of the polynominal and logarithmic (Murnaghan) forms of the high-pressure equation of state of SrTiO3.
Chemical Kinetics of Plastic Deformation
Authors: Krausz A. S. , Eyring H.
Published: February 2004

An argument is presented in which it is shown that the deformation process in a crystal is identical with the isomerization of a giant molecule and that the study of plastic flow is part of chemical kinetics. This view leads to a general expression for the rate constant which describes the kinetics of the thermally activated dislocation movement associated with a system of consecutive and parallel energy barriers. The application of the kinetic equation is illustrated with several specific examples.
Internal Fracture of Glass under Triaxial Tension Induced by Thermal Shock
Authors: King C.-Y. , Webb W. W.
Published: February 2004

Glass spheres were stressed internally in triaxial tension by thermal shock induced by up quenching from 77°K in liquid nitrogen to about 1000°K in liquid tin to obtain rather uniform hydrostatic tension stress of about 3×109 dyn cm−2. Among some 200 tested specimens, only 28, each of which contained a visible preexisting defect, were fractured. The rest showed strengths in excess of about 4.5×109 dyn cm−2 since no fractures nucleated either internally or at internal bubbles which concentrate the stress by a factor of 1.5. The fracture-initiating stress correlated with the size of the initial defect and with the size of the fracture surface prior to division. By applying Griffith's criterion, the apparent specific surface energy of clean soda-lime glass at 77°K in vacuum was found to be 1.6×104 erg cm−2 substantially larger than values previously obtained with fracture nucleii exposed to atmospheres. However, this value is subject to several uncertainties. Crack division due to ``relativistic'' distortion of the stress field was observed and roughness of the fracture surfaces were attributed to multiple nucleation of new secondary fractures ahead of the main cracks.
Photocurrents Due to Pulse Illumination in the Presence of Trapping. II
Authors: Seki H. , Batra I. P.
Published: February 2004

The transient photodischarge process in a photoconductor-dielectric sandwich structure due to pulsed light is analyzed. It is assumed that the light is absorbed at one of the surfaces of the photoconductor layer and its duration is short compared to the transit time of the leading edge of the charge carriers. The theory is developed for one type of trap but can be extended to multiple trap types. Time dependent approximations which give the upper and lower limits of the observable parameters are derived up to the transit time and beyond in some cases. It is shown that the two limits are sufficiently close to each other under a rather wide range of experimental conditions so that important transport properties such as mobility, lifetime, and trapping times can be experimentally determined. Examples of calculated results are given by cases involving one type of trap and two types of traps.
Space-Charge Waves on Plasma Columns in a Weak Magnetic Field
Authors: Sugai H. , Sato N. , Hatta Y.
Published: February 2004

Effects of the thermal motion on the space-charge waves propagating along plasma columns in a weak magnetic field is measured by using a unique experimental method. Good agreement is obtained between the experiment and the theory.
Electromagnetic Energy Absorption at the Upper Hybrid Resonance
Authors: Baldwin D. E. , Henderson D. M. , Ignat D. W.
Published: February 2004

A method of calculating the bulk response of an inhomogeneous plasma in the zero-temperature approximation is extended to include the presence of a uniform magnetic field where again the process of resonant absorption is of prime importance. Calculations are presented which show the transmission and reflection coefficients of a cylindrical plasma in a parallel plate waveguide. Experimental results obtained in rectangular waveguides are given to demonstrate the degree to which the zero-temperature models and the solution of the resultant singular equations may predict physically realizable values for the plasma admittance.
Alloy Sputtering Studies with in situ Auger Electron Spectroscopy
Authors: Tarng M. L. , Wehner G. K.
Published: February 2004

Triode sputtering and Auger electron spectroscopy were combined in an uhv apparatus for in situ studies of the composition of ion-bombarded surfaces of alloy targets and of sputter-deposited films. The changes in surface composition of a 55 Cu–45 Ni alloy (Constantan) target were studied under Ar+-ion bombardment as a function of bombarding energy. Below 150 eV ion energy, the Cu/Ni sputtering ratio increases steeply with decreasing ion energy. This causes the nickel to become much enriched in the target surface. By ion bombarding a substrate during film deposition (biasing) one can produce a film which has an altered composition throughout. By varying in our geometry the bias voltage we were able to change the film composition from that of the target to one in which the Cu concentration was only 5% that of the Ni. The depleted species in this case appears as enrichment in films at other less biased surfaces (such as at the anode in triode systems).
Charge Exchange Cross Sections for Electron Loss from B+, P+, and N+ on N2
Authors: Moline R. A.
Published: February 2004

The cross sections for electron loss from singly ionized B, N, and P ions at 100 keV, 200 keV, and 300 keV in collisions with N2 have been measured. The cross sections for a singly ionized projectile to become doubly ionized, σ12, are (10−16 cm2 per molecule): σ12 (B, 100 keV) = 2.0, σ12 (B, 200 keV) = 3.4, σ12 (B, 300 keV) = 4.4, σ12 (N, 100 keV) = 2.2, σ12 (N, 200 keV) = 3.4, σ12 (N, 300 keV) = 4.6, σ12 (P, 100 keV) = 4.3, σ12 (P, 200 keV) = 6.6, and σ12 (P, 300 keV) = 8.7. The cross sections for double electron loss were also measured. The observed cross section for P+→P2+ indicates that for a 1% contamination of a 300-keV P+ ion beam with P2+, the pressure times path length of the beam is 3.5×10−6 Torr m.
Optical Phonon Scattering, μH / μD, and Statistics of p-Type Zinc-Doped Silicon
Authors: Ashley K. L. , Brown R. T. , Blaske T. A.
Published: February 2004

Some ambiguity has been associated with the value of the degeneracy factor for the first acceptor level that is evident when zinc is diffused into silicon crystals. Both ½ and 2 have previously been reported. We obtain a confirmation of the latter figure by careful comparison of experimental data with theoretical relations. In addition, evidence is obtained which suggests that optical-mode scattering may become dominant above 320°K. For this region, we present an equation for the Hall-coefficient factor rp.
Vacuum Deposition of Hg0.8Cd0.2Te
Authors: Hohnke D. K. , Holloway H. , Logothetis E. M. , Crawley R. C.
Published: February 2004

Vacuum deposition of Hg0.8Cd0.2Te has been studied using both flash evaporation and separate molecular beams of the components. At substrate temperatures near 100°C there is considerable reevaporation of mercury from the growing layer. Consequently, deposition at these temperatures by flash evaporation of Hg0.8Cd0.2Te gives layers that consist of Hg1−xCdxTe with x>0.2, together with a second phase of unreacted tellurium. This effect imposes restrictions upon the use of flash evaporated layers for the study of composition-dependent properties. The loss of mercury may be compensated, either by adding a source of mercury to the flash evaporation system, or by using separate molecular beams with the mercury in excess. These techniques were used for growth at temperatures as high us 150°C. The conditions needed for growth of single phase Hg0.8Cd0.2Te are in agreement with a simple model for evaporation of mercury from the growing surface. Layers grown in the temperature range 70°–150°C are all n type with extrinsic conduction. This leads to the suggestion that, at low temperatures, Hg0.8Cd0.2Te exists stably, only as a Te-deficient phase.
Current Crowding in a Circular Geometry
Authors: Kohn Elliott S.
Published: February 2004

Current crowding, a phenomenon well known in transistors, is discussed in terms of its importance in cold-cathode structures. The solution to the problem of current crowding in one dimension is reviewed, and the analogous problem for a device with circular symmetry is solved. The solution is presented in terms of a dimensionless parameter for two important cases having circular symmetry. It is shown that the solution of the circular problem approaches the solution of the one-dimensional problem in the limit of severe crowding.
Bulk Negative Differential Conductivity in a Near Cathode Region in n-Type Germanium
Authors: Guion W. G. , Ferry D. K.
Published: February 2004

Sinusoidal current oscillations up to 0.2 A (rms) are observed in n-type germanium at 77°K. The oscillations occur at a frequency near 1 GHz and for an average threshold electric field of approximately 1 kV/cm. The germanium samples were cut from single crystal n-type germanium with carrier concentration 6×1014/cm3, and were approximately 2.0×0.5×0.5 mm. Using a capacitive probe, the oscillation is found to occur in a region of bulk negative differential conductivity which causes traveling high electric field domains. The domain movement confines itself to a 0.3-mm region starting 0.1 mm beyond the cathode contact. The electric field in this region, at the threshold applied voltage, is approximately 2800 V/cm, the same as that previously measured for bulk negative differential conductivity in germanium. A discussion of the effect of a cathode boundary electric field is included. It is shown that cathode boundary conditions can lead to a stable high electric field at the cathode, which in turn gives rise to traveling high-field domains which are confined to a region near the cathode.
Heteroepitaxial GaAs on Aluminum Oxide: Electrical Properties of Undoped Films
Authors: Thorsen A. C. , Manasevit H. M.
Published: February 2004

Measurements of the Hall coefficient and resistivity have been carried out on a large number of heteroepitaxial (111) GaAs/(0001) Al2O3 films grown by the trimethylgallium-arsine process. Nominally undoped films have been produced with average mobilities greater than 5000 cm2/V sec for carrier concentrations between 1015 and 1016 cm−3, the net donor concentrations in the films being determined primarily by the impurities in the reactant gases. The quality and conductivity type can be controlled by the deposition conditions. The GaAs near the Al2O3 interface is found to have inferior electrical properties, with the region nearest the interface exhibiting p-type conductivity. The dependence of the electrical properties on growth conditions, reactant gas purity, film thickness, and other variables is discussed.