bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Temperature, Charge Exchange, and Coulomb Collisions in an Argon Plasma Column
Authors: Hudis Martin , Chung K. , Rose D. J.
Published: February 2004

Ion temperatures in a highly ionized argon plasma column have been measured with a Fabry-Perot interferometer. Plasma-column conditions were altered over a range of parameters from 10% to 70% ionized, electron temperature Te=2–10 eV, and magnetic field 1400–2800 G. In general, Ti is about one-tenth Te, determined by the balance between electron heating and charge-exchange cooling. The measured values of Ti agree fairly well with those calculated, using accepted values of Coulomb collision and charge-exchange cross sections. Alternately, the present data are processed to derive approximate values of the charge-exchange cross section to neutral argon as a function of Ar+ ion energy in the range 0.1–1.0 eV. It can also be concluded that the theoretical rate for electron-ion energy relaxation is not seriously in error.
Ion Current to a Langmuir Probe in Very Low Density Flowing Plasmas for Electron-Density Determinations
Authors: Chen Sin-Li , Goodings J. M.
Published: February 2004

The mechanism for ion-current collection by Langmuir probes and the validity of electron-density determinations using ion-current characteristics are examined for low-density (Ne=109−105 cm−3) flowing plasmas in various gases (He, Ar, N2, and air) for the pressure range 0.05–1 Torr. When h≫rp (where h=electron Debye length, and rp=probe radius), both cylindrical and ring probes show spherical-probe behavior; the experimental ion current Ii varies almost linearly with the probe voltage Vp. The results are compared with Su and Lam's collision-dominated theory. Experimental ratios of the electron to the ion current Ie/Ii agree with those predicted by the plasma ``sheath criterion'' for Ne>108 cm−3. But for Ne<106 cm−3, Ii increases so that Ie/Ii is low by an order of magnitude, and Ii cannot be used for Ne determinations. Explanations are offered in terms of the method used to evaluate the ion current, interference of the discharge-tube wall, and, at higher pressure, the release of electrons from the probe surface by collisions of metastables (or photons).
Diffusion of Carbon in TiC
Authors: Sarian S.
Published: February 2004

The self-diffusion coefficients of carbon-14 in TiC have been measured as a function of composition in the temperature range 1450° to 2280°C, and can be represented by the expressions: D*0.970=6.98±1.24 exp (−95 300±700/RT) and D*0.887=45.44±5.12 exp (−106 800±400/RT) cm2/sec. The effect of composition on the self-diffusion coefficients is discussed and the tracer coefficients are compared with apparent diffusion coefficients calculated from steady-state creep measurements and the kinetics of TiC compound formation.
Effect of Mobility Gradient in Inhomogeneously Doped Semiconductors
Authors: Ho B. L. , Cho C. C.
Published: February 2004

Based on a theoretically predicated impurity distribution, it has been shown that the lower minority carrier lifetime in a diffused semiconductor as compared to that measured in a uniform bulk semiconductor was solely due to the effect of electrostatic field gradient. In fact, the true impurity distribution in a diffused region has never been determined. Investigation of the effects of mobility gradient in the diffused region with assumed impurity distribution of a complementary error and an exponential function has been performed. The results showed that (1) the effect of mobility gradient contributes to the effective minority carrier lifetime with an equivalent lifetime of the order of 10−10 to 10−12 sec, and (2) the lower minority carrier lifetime in the diffused region may be explained more commonly in terms of the effect of mobility gradient than that of the electrostatic field gradient.
Noise of a Self-Sustaining Avalanche Discharge in Silicon: Studies at Microwave Frequencies
Authors: Haitz Roland H. , Voltmer Fred W.
Published: February 2004

The studies of avalanche noise reported by Haitz are extended to frequencies up to and above the avalanche frequency ωa. It is found that the open-circuit spectral voltage density is flat within ±5% from less than 100 Hz up to frequencies approaching ωa. Near ωa the open-circuit spectral voltage density increases with frequency, goes through a maximum at ωa and then decreases rapidly. The spectral power density is similarly flat but fails to exhibit an expected maximum at ωa. For ω≫ωa the spectral power density decreases with ω−4. The experimental results are in good agreement with Hines' theory of avalanche noise for ω≪ωa and ω≫ωa. The discrepancies observed near ωa are thought to be caused by an oversimplification in Hines' theory which neglects internal diode losses. Compared with conventional noise sources such as temperature-limited diodes or gas discharge tubes, avalanche diodes have several advantages: larger noise output, larger bandwidth, lower 1/f noise, low power consumption, small size, and low weight.
Semiconducting Properties of InSb–InAs Alloys
Authors: Kudman I. , Ekstrom L.
Published: February 2004

Hall coefficient and conductivity of InSb–InAs alloys have been measured from approximately 300° to 700°K. The 0°K energy gaps determined from the intrinsic carrier concentrations were found to reach a minimum of 0.195 eV at 90 mole % InSb. The electron mobilities were found to vary significantly from sample to sample and are interpreted as arising from ionized impurity plus inhomogeneity scattering.
Time-Domain Treatment of a Spherical Boundary-Value Problem
Authors: Granzow Kenneth D.
Published: February 2004

The expressions in the time domain representing the general solution of the wave equation in spherical polar coordinates are summarized. The boundary-value problem where the tangential component of E is given as a function of time on the surface of a sphere is solved for outward-moving waves. This problem embodies the transient spherical-antenna problem as a special case. Since the solution involves solving ordinary linear differential equations with constant coefficients, it is similar to that of a transient circuit problem and Laplace transforms can be employed in a similar way.
Point-Defect Pinning of Dislocations during Initial Period of Continuous Low-Level Gamma Irradiation: Application to Stage III in Copper
Authors: Meisel L. V. , Thompson D. O.
Published: February 2004

The pinning of dislocations by point defects formed during continuous low-level irradiation is studied for short times. On the basis of stress-assisted diffusion theory it is shown that the number of point defects which arrive at dislocations should be proportional to the 5/3 power of the irradiation time (for short times). These results are applied to stage III measurements in copper. The migration energy and (formation) volume determined from the transient data are 0.61±0.04 eV and (0.45±0.23)×10−23 cm3, respectively.
Measurement of the Faraday Rotation of a Laser Beam Passing through a θ-Pinch Plasma
Authors: Falconer I. S. , Ramsden S. A.
Published: February 2004

Faraday rotation of a beam of light is discussed as a means of determining the magnetic field within a plasma and the relative merits of various detection systems are considered. Apparatus is described for measuring the rotation of the plane of polarization of a He–Ne laser beam at 6328 Å on passing through a small θ-pinch plasma. Using a differential detection system of risetime 0.3 μsec, an observed peak rotation of 1.0 mrad can be measured to an accuracy of 10%. Deviation of the beam by electron-density gradients within the plasma is shown to be small and readily compensated for. Good agreement is obtained between the measurements of Faraday rotation and independent measurements of the magnetic field using magnetic probes.
Correlation of the Physical Location of Crystal Defects with Electrical Imperfections in GaAs p-n Junctions
Authors: Tretola A. R. , Irvin J. C.
Published: February 2004

A thermal-mapping technique is presented which, when applied to a p-n junction, can locate hot spots that are only slightly warmer than surrounding regions. Among the Zn-diffused GaAs devices to which this method has been applied, these hot spots have always been found to be associated with an irregularity (usually a microplasma) in the I-V characteristic. Furthermore, etching has revealed a crystal imperfection coinciding with each hot spot. Selective etching at these sites causes the removal of the imperfect region and a corresponding significant improvement in the diode reverse characteristic, though less than 4% of the total diode area has been removed.
Etching and Regrowth of Cuprous Chloride
Authors: Chase A. B. , Wilcox W. R. , Teviotdale J. R.
Published: February 2004

Partial dissolution in hydrochloric acid followed by gentle rinsing in water allowed individual grains and twins in cuprous chloride to be distinguished easily with the naked eye. It was found that regrowth occurred during rinsing because of dissociation of the soluble CuCl2− complex. This regrowth resulted in the formation of a shingled surface which served to reflect light quite differently from different grain orientations. Polished surfaces were found to result from etching with 50:50 nitric acid-water for times up to 30 sec at room temperature. Dislocation etch pits were revealed by placing cuprous chloride in hydrochloric acid for times up to 5 sec, followed by spraying with acetone.
Preparation and Properties of Noncrystalline Silicon Carbide Films
Authors: Mogab C. J. , Kingery W. D.
Published: February 2004

Noncrystalline silicon carbide films have been formed by physical sputtering of a hexagonal single crystal of silicon carbide. Electron-microscopy and electron-diffraction studies indicate that the films undergo a transition to polycrystalline cubic silicon carbide (β-SiC) in the temperature interval 850°–900°C. The noncrystalline films were p type and exhibited an irreversible diminution of conductivity by about two orders of magnitude when annealed in the range 200°–600°C. Isothermal annealing in this temperature range produced a decrease in conductivity approximately proportional to the logarithm of annealing time. This kinetic behavior is consistent with the occurrence of thermally activated processes having a distribution of activation energies. An approximate activation energy range for annealing was determined as 0.4–2.3 eV. The irreversible change in conductivity of the noncrystalline films is interpreted as arising from the annealing of structural defects having acceptor-like properties. Since a distribution of activation energies for annealing is observed, it is inferred that a variety of defect types or configurations must be present corresponding to a range of localized energy levels in the forbidden gap.
Polarization-Dependent Rayleigh Scattering in a Coarse-Grained Ferroelectric Ceramic
Authors: Nettleton R. E.
Published: February 2004

Visible light intensity transmitted by a polarized ferroelectric crystallite of diameter ≥2 μ has been observed to decrease markedly when the direction of polarization Ps is shifted from parallel to perpendicular to the direction of incidence. This is explained by regarding the 180° domain structure as constituting a displacement field, in which ions are shifted relative to a cubic reference phase. The Fourier wavevectors of this field shift with Ps, causing an increase in backscattering when Ps is normal to the light. This property is demonstrated for tetragonal, orthorhombic, and rhombohedral phases of a perovskite, and in all cases scattered intensity is proportional to Ps4. Selection rules affecting depolarization of the light are derived from the polarizability theory of Raman processes. This theory supposes that the incident radiation polarizes the atoms, which then emit dipole radiation whose amplitude is proportional to the polarizability α. The latter depends on the displacement field whose symmetry, combined with the cubic symmetry of the reference phase, requires certain tensor components of α to vanish. This imposes no important limits on backscattering, but it predicts that α should be isotropic in the rhombohedral phase, thus preventing the domain structure from providing a significant source of forward depolarization. Grain-boundary scattering and reflections must be invoked to explain the latter.
Local Atomic Arrangements in a Nickel—10 Atomic Percent Tungsten Alloy
Authors: Ammons A. M. , Spruiell J. E.
Published: February 2004

The x-ray diffuse scattering from both single-crystal and polycrystalline samples of a Ni—10 at.% W alloy has been measured and interpreted to yield information about local atomic arrangements in the alloy as a function of heat treatment and cold deformation. The short-range-order parameters for a sample which had been quenched from 950°C agreed well with those computed from a model based on long-range-ordered Ni4W. The degree of short-range order gradually decreased as the alloy was cold worked, but could be recovered at annealing temperatures well below the recrystallization temperature. An attempt was made to use these results to explain the anomalous behavior of the electrical resistivity upon plastic deformation.
Thermal Conduction near a Metal Surface Exposed to Blackbody Radiation
Authors: Harrington R. E.
Published: February 2004

A method of calculating thermal conductivity near the surface of a metal is proposed. Kinetic theory is used to show that the thermal conductivity decreases near the surface and becomes zero at the surface if there is no heat flow across the surface. Kinetic theory is also applied to the problem of heat conduction in the surface region of a metal exposed to blackbody radiation. The resultant temperature distribution is exponential. From a practical standpoint, a useful consequence of the theory is that the absorption depth for blackbody radiation should equal the mean free path of electrons in metals. In the layer of a metal which absorbs incident radiation, the electrons possess increments of energy from both absorbed radiation and thermal conduction. The fraction of the electron's energy lost per collision is taken from the kinetic theory of gases as a first approximation. Thus, thermal conduction is reduced by factors of 10-5 to 10-6 in the surface region of the metal. The factor is not needed for the conduction process in the bulk of the material because the energies entering and leaving an elemental layer are independent of each other, permitting random walk to equilibrate the energy. Application of the theory to the heating rate of a tantalum sample exposed to 1500 W/cm2 leads to results consistent with the experimental data available.
Electron Multiplication and Surface Charge on Zinc Oxide Single Crystals
Authors: Williams R. , Willis A.
Published: February 2004

Electron multiplication has been observed in ZnO using reverse-biased electrolyte contacts to n-type conducting crystals. Measurements have also been made of the surface potential of the free surface charged by a negative corona discharge in air. The surface charge is discharged by illumination. Under certain conditions electron multiplication contributes to the discharge process. The amount of surface charge discharged by illumination has been measured as a function of the energy of the light. This gives an approximate energy-level spectrum for the localized electrons on the surface.
Normal Spectral Emissivity of Ta–W and Nb–Mo Alloys
Authors: Thomas Ludwig K.
Published: February 2004

Measurements of the normal spectral emissivity of Ta–W and Nb–Mo alloys are reported. The emissivities were measured at 2000°, 2200°, and 2400°K in the wavelength range 0.4 to 4 μm. The emissivities of the alloys generally lie between the values of the pure constituents. The temperature coefficient and the x-point wavelength of Ta–W alloys change in a characteristic way. The measurements support the validity of the rigid band model.
Infrared Absorption in Single-Crystal Stannic Oxide: Optical Lattice-Vibration Modes
Authors: Summitt Robert
Published: February 2004

The ir reflection spectrum of single-crystal stannic oxide has been observed at room temperature in the region 2000 to 100 cm−1, and analyzed by classical dispersion theory to give values for the transverse and longitudinal optical-mode frequencies. For the cassiterite structure, four lattice-vibration modes may interact with infrared radiation, three of these with radiation polarized perpendicular to the c axis, and the remaining one with radiation polarized parallel to the c axis. The oscillator frequencies found for the best fit to the experimental reflection curves are: E⊥c, 243, 284, and 605 cm−1; E ∥ c, 465 cm−1. Low-frequency dielectric constants are estimated from this analysis to be 13.5 and 9.58 for E⊥c and E ∥ c, respectively, which are about half the literature values. The E⊥c value was confirmed directly in a substitution bridge measurement yielding 15±1 for the frequency range 102 to 106 Hz.
Electron Microscopy of Yttrium Aluminum Garnet (YAG)
Authors: Ashbee K. H. G. , Thomas G.
Published: February 2004

A transmission electron microscopy study has been made of defects in yttrium aluminum garnet (YAG). Three kinds of planar defect were observed: antiphase boundaries generated by slip on {110} planes, antiphase domain boundaries separating regions of crystal which appear to have slightly different lattice parameter, and orientation twins.
Relation between Third-Order Elastic Constants of Single Crystals and Polycrystals
Authors: Barsch G. R.
Published: February 2004

The approximations by Voigt, Reuss, and Hill for calculating the elastic constants of polycrystals from the elastic constants of single crystals are extended to the third-order elastic constants. The general relations including the expressions for the third-order elastic compliances are presented and given explicitly for cubic symmetry. They are used to calculate the polycrystalline third-order elastic constants of eleven cubic materials. For cubic symmetry, relations for the pressure derivatives of the second-order elastic constants in the approximations of Voigt, Reuss, and Hill are also presented, and the anisotropy of the third-order elastic constants is discussed. It is found that for all materials considered, the anisotropy for the third-order elastic constants is much larger than the anisotropy of the second-order elastic constants, and that a weak correlation exists between the anisotropy of the third-order elastic constants and of the second-order elastic constants.
Resistivity Estimates for Some Shocked Ferroelectrics
Authors: Halpin W. J.
Published: February 2004

It has been observed previously that the shape of the current pulse delivered to an external short circuit by a shock-loaded ferroelectric ceramic specimen undergoes an abrupt change when a sufficiently high shock stress level is reached. This change was explained qualitatively as being due to the onset of electrical conduction in the specimen. Here a quantitative analysis of short-circuit current waveshapes from some typical ferroelectric materials is made on the basis of a previously developed model that has been extended to include the effect of conduction. Finite resistivity is assumed in the stressed region of a specimen and evaluated in terms of the various model parameters and experimental quantities, particularly the short-circuit current itself. With the analysis an estimate is made that the resistivity of the ferroelectric materials under shock stress in the range of 25 to 35 kbar is of the order of a 100 Ω·cm with accompanying fields greater than about 20 000 V/cm.
A Digital Computer Program for Computing Ion-Saturation Currents from a Plasma of Uniform Density in a Two-Dimensional Geometry
Authors: Harrison John L.
Published: February 2004

The shape of the surface from which ions are extracted is a major factor in determining the tractability of an ion beam for fine focusing. In duoplasmatron-type ion sources the extraction is made from a plasma, and the shape of the plasma surface has been difficult to define. The paper describes a computer program which both determines the shape of a plasma surface in a known extraction geometry with known current density at the surface and calculates trajectories of particles leaving this surface.
Magnetization of Superconducting Cu–Pb Alloys
Authors: Livingston J. D.
Published: February 2004

Magnetization curves have been measured on as-cast and annealed Cu–Pb alloys and correlated with microstructural observations. Magnetic hysteresis and trapped flux are observed and related to a multiply connected lead network. Critical fields are lower than for bulk lead and are lowest for the as-cast monotectic alloy, where the lead is most finely dispersed. Both a surface energy effect and the proximity effect contribute to this result. Proximity-effect calculations are extended to the cases of rodlike and spherical superconducting particles and are compared with experiment.
Redistribution of Diffused Layers during Epitaxy and Other Process Steps
Authors: Hu S. M.
Published: February 2004

Analysis and numerical solution are given for the redistribution of a diffused layer during epitaxial growth. The results show that at a relative epitaxial rate of r>2 [r=at/2 (Dt)1/2, where α is the linear rate constant of epitaxial growth], the problem can be regarded as diffusion in an infinite medium. Approximate analytic expressions in closed form are presented for redistribution during various sequential process steps, and are compared with exact numerical calculations.
Oscillations at the Anode of Alkali-Vapor Arc Plasmas
Authors: Robertson Harry S.
Published: February 2004

The theory of the anode sheath for quasineutral collision-dominated arc plasmas is developed, both for the steady state and for behavior following emission of a burst of ions from the anode surface. It is shown that the decay time constant for such a burst is related to the ambipolar diffusion time, τ=Λ2/Da, where Λ is the appropriate diffusion length. The ion burst, a consequence of field emission from the anode surface, causes a local sharp decrease in the electric field strength, followed by a gradual increase as the ion cloud dissipates. A new burst of field-emitted ions begins another cycle. A summary is given of experimental work on anode-spot oscillations, some of which supports the predictions of the theory.
Josephson-Effect Far-Infrared Detector
Authors: Grimes C. C. , Richards P. L. , Shapiro Sidney
Published: February 2004

Superconducting point contacts, bridges, and tunnel junctions are all capable of carrying a zero-voltage current; i.e., no voltage appears across the device until the current exceeds a finite critical value. The critical value of the zero-voltage current is changed when microwave radiation is incident on such a junction. Thus such a device can be used as a detector of radiation. Experiments have been carried out demonstrating that this detection mechanism extends well into the far-infrared, is highly sensitive, and has inherently high speed. Junctions were formed by pressing together the ends of two superconducting wires, one of which was flat, the other pointed. The spectral response of such point contact junctions was studied by using them as detectors in a far-infrared Fourier transform spectrometer in which they were irradiated by broadband, incoherent radiation. The response of Nb–Nb junctions was found to extend to frequencies above 40 cm−1 (λ<250 μ), i.e., to about twice the superconducting energy gap. Measurements using a klystron source at 2.5 cm−1 (λ=4 mm) yielded a value of 5×10−13 W for the noise equivalent power in a one-cycle bandwidth and showed the junction detector could follow a pulsed signal which had a risetime of 10 nsec. Preliminary experiments using a monochromatic laser source at 32.2 cm−1 showed the appearance of constant-voltage steps in the voltage-current characteristic of the junction, as is well known at microwave frequencies. These experiments demonstrate the existence of the Josephson effect at frequencies up to and beyond the superconducting energy gap, and show that over this range of frequencies, Josephson junction detectors exhibit both high sensitivity and high speed when compared with other helium-temperature far-infrared detectors.
MnBi Thin Films: Physical Properties and Memory Applications
Authors: Chen D. , Ready J. F. , Bernal G. E.
Published: February 2004

Thin films of MnBi possess many unusual physical properties and are particularly suitable for memory applications using laser Curie-point writing and magneto-optical readout. Films prepared on mica substrates have the easy direction of magnetization perpendicular to the film plane. They typically have a specific Faraday rotation of 5×105 deg/cm, and an absorption coefficient of 3.8×105 cm−1 for 6328 Å wavelength, permitting a readout rate of 109 bits/sec at 1 mW laser power level using available detectors. Curie-point writing and erasing of a spot a few microns in diameter in a 1000 Å thick film with a 4 μsec pulse from a 13 mW Gaussian laser beam have been achieved. For a 106 bits/cm2 packing density, heating at adjacent spots is negligible. Calculations show that the writing magnetic field can be reduced to less than 10 Oe by using a memory plane consisting of discrete squares of MnBi. Analytical and experimental results as well as memory design considerations are presented.
Measurements of Transport Phenomena of Dilute Impurities in Metals
Authors: Hehenkamp Theodor
Published: February 2004

Transport phenomena in solid metals under the influence of external forces such as electric fields or temperature gradients have been determined mostly by means of marker or sectioning techniques so far. Sectioning techniques permit simultaneous measurements of transport shifts and transport rate-controlling diffusion and are therefore preferred for the more precise measurements. For brittle or soft materials sectioning is not feasible. It is shown that use of an electron microprobe for transport profile analysis avoids these difficulties and improves the accuracy of impurity transport measurements remarkably. This is due to the much better linear resolution and the nondestructive analysis without any deformation of the sample. For dilute impurities the results are virtually free of analytical errors. A review of measurements and techniques, particularly steady-state profile determinations, is given.
Monte Carlo Simulation of the Low-Voltage Arc Mode in Plasma Diodes
Authors: Salinger S. N. , Rowe J. E.
Published: February 2004

A statistical simulation of the low-voltage arc mode of plasma diodes is carried out on a large-scale digital computer to ascertain the importance of various thermalization and transport mechanisms. The computer experiment is two-dimensional and utilizes Monte Carlo techniques to study the low-voltage arc in neon at p=2 Torr, current=4 A, and diode spacing=2.37 cm. Results on the potential distribution, electron-density distribution, and electron-energy density function are presented and discussed. The theoretical results are correlated with experimental results.
Behavior of Divalent Impurities in Sodium Chloride Crystals
Authors: Kao K. C. , Giles L. J. , Calderwood J. H.
Published: February 2004

Electric conductivity measurements in the temperature range from 100° to 500°C were made on sodium chloride crystals doped separately with magnesium, calcium, strontium, and barium as divalent impurities, and on undoped crystals. The results indicate that the mobility of the cation vacancies, the binding energy of the complex and the solubility of impurity in the crystal lattice are dependent on the divalent ion radius, but the jump activation energy is not affected by the impurities. The concentration of unavoidable impurities in the undoped crystal is estimated to be of the order of 7×10−6 molar fraction and they are likely to be calcium. The analysis also shows that to determine the concentration and mobility of vacancies in an undoped crystal by measuring the conductivity as a function of the concentration of divalent ions artificially dissolved in the crystal, it is necessary to use the divalent ions whose physical parameters are close to those of the unavoidable impurity ions.
Selected-Area Diffraction Patterns and Magnified Laue-Diffraction Images by X-Ray Microscopy
Authors: Kozaki Shigeru , Ohkawa Tokio , Hashimoto Hatsujiro
Published: February 2004

An ``x-ray microscope'' which can take both x-ray diffraction patterns and magnified Laue-diffraction images of selected areas of the specimen under microscopic observation has been constructed. Resolving power of the microscope is 0.3 μ and the minimum diameter of the selected area of the specimen is about 10 μ. A decontamination device for the target is incorporated into the instrument. Some applications of the methods of x-ray microscopy, selected-area diffraction, and magnified Laue diffraction are described. It is shown that the selected-area diffraction patterns are useful for the identification of the components of the specimen with complicated structure. It is also shown that the magnified Laue-diffraction images are useful for the study of imperfections and local distortions in crystals.
Suppression of Close-Lying Modes in Ring Lasers and Related Devices
Authors: Bass M. , Statz H. , deMars G. A.
Published: February 2004

In ring lasers and certain other devices one is dealing with modes which are split by only very small frequency differences. In general the modes under investigation have the same spatial dependence and thus derive their energy from the same active centers. Due to the shape of the gain-vs-frequency curve, the split modes experience a small difference in gain. It is shown that in ring lasers and similar devices one of the modes may thus have much reduced output and may even be so weak as to be unobservable. An experiment is reported in which a longitudinal mode of a Nd3+-doped YAG laser is split into counter-rotating circularly polarized modes by a Faraday rotator. It is observed that one of the split-off modes will not even oscillate when the modes are split by a sufficient amount to overcome the locking effects due to intermode scattering.
The Elastic Constants of Gallium Phosphide
Authors: Weil Raoul , Groves Warren O.
Published: February 2004

The elastic constants of GaP have been determined by the ultrasonic phase-comparison method. The frequency range and temperature for the measurements were 8–20 MHz and 300°K, respectively. The compressibility, Debye temperature, and average longitudinal sound velocity in GaP are calculated. The elastic constants of GaP are found to agree with the regularities established from the measurement of these constants in other III–V compounds.
Cesium Ion Emission from a Small Hole in Single-Crystal Tungsten
Authors: Kuskevics Guntis
Published: February 2004

Cesium-ion emission from a 50–75 μ diam hole in the (110) face of a tungsten single crystal was studied in a surface ionization microscope. At low cesium flow rates and high tungsten temperatures the ion emission is entirely from within the hole. For increased cesium flow or reduced surface temperature, the ion emission shifts to an annular front surface region around the hole. This annular region moves along the front surface away from the hole as the flow is increased.
Some Physical Properties of Single Crystals of Normal and Deuterated Potassium Dihydrogen Arsenate. II. Electro-optic and Dielectric Properties
Authors: Adhav R. S.
Published: February 2004

The electro-optic and dielectric constants of single crystals of potassium dihydrogen arsenate, grown in H2O, and potassium dideuterium arsenate, grown in D2O, have been measured. On deuteration, the relative dielectric constant K33 is increased from 24 to 31 and K11 is increased from 60 to 70, measured at 25°C. The half-wave retardation voltage Vλ/2, measured at 500 nm is decreased from 5.9 to 3.3 kV, and the electro-optic constant γ63 in increased from 11.0×10−10 cm/V to 19.5 cm/V on deuteration. The loss tangent tanδ33 measured at 1 kHz and at 25°C is about 0.30 for KDA and 0.18 for D-KDA. The specific resistivity ρ33 for KDA is 7.2×108Ω·cm, and that for D-KDA is 5.1×108Ω·cm, measured at 25°C. The input power requirement using these crystals in an electro-optic modulator is compared to that of KDP.
The Microwave Magneto-Kerr Effect in Silicon and Germanium. II. Determination of Relaxation Time and Effective Mass
Authors: Hauge Peter S. , Champlin Keith S.
Published: February 2004

This paper analyzes microwave (8.6 GHz) measurements of complex conductivity and Hall factor in order to investigate the temperature dependence of the momentum relaxation time and effective mass of majority carriers in near-intrinsic n- and p-type Si and Ge. The analysis uses scattering models which include ionized impurity scattering, intravalley acoustic- and optical-mode scattering, and intervalley scattering. For n- and p-type Ge and n-type Si, the conductivity effective mass is found to be virtually independent of temperature in the range 77° < T < 160°K and to agree favorably with results calculated from microwave cyclotron resonance measurements at 4°K. Because of inadequancy of the model for p-type silicon, the measurements do not yield an unambiguous value of the effective mass but do indicate constancy with temperature.
Recombination Lifetimes in Gamma-Irradiated Silicon
Authors: Hewes Ralph A.
Published: February 2004

Photoconductivity decay measurements on a wide variety of silicon crystals (boron- and phosphorusdoped, Czochralski and float-zone grown, 20≤ρ≤200 Ω·cm) irradiated with 60Co gamma rays indicate that a separate system of levels controls the radiation-induced lifetime in n- and p-type specimens. In n-type material the introduction rates for two recombination active defects (the A center and a deeper level) were seen to be nearly independent of oxygen and donor concentrations in the range encountered in the experiment, while the introduction rate of a second deep level, the E center (vacancy-phosphorus pair), was seen to be inhibited by the presence of oxygen and to increase with increasing donor concentrations. The behavior of the lifetime was studied after the samples were annealed and it was found that a shallow level 0.23 eV from the conduction band edge was introduced. Hole-capture cross sections for the two deep levels were obtained from Hall and lifetime measurements. In p-type material recombination levels at Eν+0.18 eV and Ec−0.3 eV were introduced by irradiation. The introduction rate of the level nearest the conduction band was strongly inhibited by the presence of oxygen and dominated the lifetime only in float-zone material. Low-temperature annealing was seen to occur in the defects having levels at Ec−0.3 eV with the subsequent creation of defects with levels at Eν+0.18 eV in some materials. In other materials a second type of defects with levels at Ec−0.3 eV was created, while in some materials a simple annealing with no creation of new defects was found.
Elastic Moduli of Gallium Antimonide under Pressure and the Evaluation of Compression to 80 kbar
Authors: McSkimin H. J. , Jayaraman A. , Andreatch P. , Bateman T. B.
Published: February 2004

Ultrasonic wave velocities in GaSb have been measured at 25°C as a function of hydrostatic pressure to 2 kbar. The adiabatic ``zero-field'' stiffness moduli calculated from these velocities (for 1 atm) are as follows: c11 = 8.839±0.008, c12 = 4.033±0.010, c44 = 4.316±0.004, and Bs (bulk modulus) = 5.635±.012. All moduli are in units of 1011 dyn/cm2 and are based on a density of 5.6137 g/cm3 taken as exact with respect to estimates of errors. Hydrostatic pressure derivatives for c11, c12, c44, and Bs are, respectively, 4.96±0.10, 4.64±0.15, 1.01±0.02, and 4.75±0.15. The static compression of GaSb to 80 kbar has been evaluated using the isothermal bulk modulus (BT) of 5.614×1011 dyn/cm2 and (∂BT/∂P) of 4.78.
An Experimental Determination of the Drag on a Sphere at Low Reynolds Numbers
Authors: Pruppacher H. R. , Steinberger E. H.
Published: February 2004

Accurate measurements of the drag on a sphere falling in a viscous medium were carried out for Reynolds numbers between 0.001 and 10.0. When the fractional deviation (D/Ds) − 1 of the actual drag D from the Stokes drag Ds was plotted as a function of the Reynolds number, significant inconsistencies among the results of measurements previously reported in literature and significant differences between these and our own results were revealed. Our experimental results also deviated from most theories available; however, they were consistent with the theory of Proudman and Pearson for vanishingly small Reynolds numbers and at Reynolds numbers between 0.5 and 10 with Carrier's semiempirical modification of Oseen's theory.
The Effect of Gold on the Properties of the Si–SiO2 System
Authors: Collins D. R.
Published: February 2004

The admittance and surface-state density of metal-oxide-silicon structures are studied as a function of fabrication processing, emphasizing the effects of gold doping. Experimental investigations show that the process used in fabricating an MOS structure has as much effect on its surface-state density as the introduction of gold. The theoretical effect of gold in the bulk semiconductor on the C-V curves is derived. This theory must be used to evaluate the surface-state density in order to separate the bulk effects from the surface effects. A high-frequency theory for gold-doped structures is used to show that the gold which causes the experimentally observed positive shift in the MOS C-V curves can cause an increase in the surface-state density of 3×1011 states/eV·cm2. This gold is believed to be located at the silicon-silicon dioxide interface and has a continuous rather than a discrete energy distribution within the energy gap. The state of the gold is shown to be best described in terms of a bonding model rather than a band structure viewpoint. A low-frequency method of evaluating surface-state density gives excellent agreement with the high-frequency analysis for non-gold-doped structures. However, this low-frequency method does not give agreement in the gold-doped case nor do the experimental low-frequency gold-doped C-V curves agree well with the low-frequency capacitance theory, which is extended here to include the effect of gold in the bulk silicon. It is shown that this discrepancy may be caused by the gold introducing appreciable loss into the low-frequency admittance of the bulk silicon. This loss illustrates a limitation in the applicability of previous low-frequency capacitance theories.
Analogy between Concentrated Forces and Edge Dislocations
Authors: Dundurs J.
Published: February 2004

The stress induced by an edge dislocation in a finite body containing inhomogeneities can be obtained from the stresses caused by concentrated forces acting in the direction of the extra sheet of the dislocation. The results hold regardless of the topological intricacies of the composite body, but the relationship is restricted to plane deformations. When the forces are balanced by specified tractions that are proportional to the magnitudes of the forces and are independent of elastic constants, all boundaries are free of tractions for the dislocation. If the stress for the force is known through a formula, the dislocation stress is obtained by manipulating the elastic constants involved. Experimentally, dislocation stress can be obtained from two tests with concentrated forces. For a homogeneous body, two different Poisson's ratios must be used in the experiments with forces. If the magnitudes of the forces are properly scaled, the dislocation stress is found by extrapolating linearly to the value of Poisson's ratio equal to one.
Formation and Stability of Virtual Electrodes in a Cylinder
Authors: Hockney R. W.
Published: February 2004

Two-dimensional computer experiments have been performed to determine whether a stable virtual electrode can be formed inside an evacuated cylinder by the injection of charged particles from the outside. This question is important to the feasibility of certain inertial confinement schemes for fusion reactors. The charges are injected with constant velocity uniformly from the surface of the cylinder and directed at the axis. Above a certain current, depending on the injection velocity and dimensions, dc solutions exist corresponding to the formation of a virtual electrode at a calculable radius within the cylinder. Such analytic solutions involving virtual electrodes are not necessarily realized in practice as they were not in the one-dimensional computer experiments of Birdsall and Bridges on the short-circuited diode. The problem discussed here, although related to the diode, is different both in geometry and in the manner of injection. It is interesting that our computer experiments show the formation of a stable virtual electrode for a wide range of input current. Such variations of potential that do occur are transient and decay to less than ±2% after ten single-particle transit times. Experiments have also been conducted with the current injected from four separate guns. Stable virtual electrodes are formed in this case opposite each gun.
Influence of Growth Conditions and Tellurium Phase on the Thermoelectric Properties of Bismuth Telluride-Type Materials
Authors: Champness C. H. , Chiang P. T. , Grabowski K. , Muir W. B.
Published: February 2004

A study has been made in n-type Bi2Te3+x, n-type Bi2Se0.45Te3+x, and p-type Bi0.5Sb1.5Te3+x of the influence of segregated tellurium phase, determined metallographically, on the thermoelectric figure of merit (Z), electrical conductivity (σ), Seebeck coefficient (α), and thermal conductivity (κ). It was found that Z and σ at a given α value were reduced by excessive amounts of the Te phase. Calculation using an idealized two-phase model has shown that in this case circulating currents are unimportant. The effects appear to be due to a redistribution of electrical and thermal current by the Te phase located mostly between cleavage planes where any misalignment can have a strong influence. Zone melting of p-type Bi0.5Sb1.5Te3.13 at low speeds of about 0.1 cm/h produced an increase in the average value of Z and a decrease in the amount of Te phase.
Shock-Wave Generation in Rarefied Gases by Laser Impact on Beryllium Targets
Authors: Bobin J. L. , Durand Y. A. , Langer Ph. P. , Tonon G.
Published: February 2004

Shock waves in argon and in air have been observed when focusing a 0.8 J, 40 nsec, Q-switched ruby laser beam onto a beryllium target in the presence of gas at various pressures ranging fron 2×10−1 to 3 Torr. High-speed streak and framing camera as well as a prism spectrograph have been used as diagnostic tools. Space-resolved spectra show, besides an intense continuum, Stark-broadened lines from Be I and Be II. The reinforced argon lines when moving off the Be target surface are probably due to a shock wave driven by the Be plasma acting as a piston. A simple theoretical model taking this mechanism into account is proposed. Calculated curves for the outer radius variations of the shock front fit closely the experimental results.
Focusing of a Relativistic Electron Flow
Authors: Hsieh H. C. , Rowe J. E.
Published: February 2004

The trajectory differential equation governing the motion of relativistic electrons is derived in terms of the scalar and vector potentials of the system using the principle of least action. The conservation of energy and momentum are used to develop the paraxial-ray differential equation describing the beam radius of a laminar-flow relativistic electron beam. The focusing of the electron beam in drift and accelerating regions has been examined and the conditions for perfect balancing and nonspreading of a laminar-flow drifting beam are also derived. It is shown that the equilibrium condition for Brillouin flow is that 2ωL2−ωp2[1 − (uz/c)2]=01 where ωL is the Larmor precession frequency and ωp the electron-plasma frequency. uz and c denote, respectively, the axial beam velocity and the speed of light in vacuum. The variation of the normalized ripple amplitude and the scallop wavelength of a drifting beam is discussed. The profile of a beam accelerated in a uniform longitudinal electrostatic field is also illustrated.
Influence of Chemisorbed Films of Various Gases on Adhesion and Friction of Tungsten
Authors: Buckley Donald H.
Published: February 2004

An investigation was conducted to determine the effect of various absorbed gaseous species on the adhesion and friction of tungsten. Experiments were conducted in a vacuum of 10−10 Torr with a hemispherical rider specimen [(100) tungsten] contacting a flat. The atomic planes of tungsten examined on the flat included the (100), (110), and the (210). The gases absorbed to these tungsten surfaces included hydrogen, oxygen, carbon dioxide, hydrogen sulfide, and a homologous series of hydrocarbons (methane through decane), as well as ethylene and acetylene. The resùlts of the study indicate that the presence of any gas, even hydrogen, on the tungsten surface will reduce adhesion and friction. Less than a monolayer of oxygen adsorbed on tungsten is sufficient to reduce appreciably the friction of tungsten crystals. For hydrocarbons an increase in chain length (methane through decane) resulted in a progressive decrease in friction. Furthermore, with ethane, ethylene, and acetylene, friction decreased with an increase in the number of carbon-to-carbon bonds.
Thermoelectric-Thermomagnetic Energy Converter Staging
Authors: Kooi C. F. , Horst R. B. , Cuff K. F.
Published: February 2004

An exact theory of staging of heat engines or coolers is given for the case where the individual stage efficiencies or coefficients of performance are functions only of the fractional temperature difference ΔT/T between the hot and cold sides of the stage. In this case, it is exactly true that, for an extremum in efficiency or coefficient of performance, the fractional temperature differences of each stage are equal. For the constant ZT case of thermoelectric and thermomagnetic engines and coolers this extremum is a maximum. Z is the isothermal thermoelectric or the adiabatic thermomagnetic figure of merit and T is the absolute temperature. The cases α=constant, ρ ∝ T and κ=constant for the thermoelectric engine or cooler, and α ∝ T−1, ρ ∝ T−1 and κ=constant for the thermomagnetic engine or cooler are considered. Here α, ρ, and κ are, respectively, the appropriate thermopowers, resistivities, and thermal conductivities. Exact expressions are given for the efficiency and coefficient of performance for a single stage and for an infinitely staged device and also for the shape of the infinitely staged device. These expressions are the same for these two examples of constant ZT thermoelectric and thermomagnetic devices, thus simplifying device design.
Microwave Diagnostics for Measuring Very Low Electron Densities in Afterglow Plasmas
Authors: Weaver L. A. , Freiberg R. J.
Published: February 2004

An extension of conventional microwave cavity diagnostic methods is described which is capable of measuring very low electron densities occuring late in afterglow plasmas. Electronic signal sampling and pulse-stretching techniques are combined with phase-sensitive detection to provide a sensitive measure of the shift in cavity resonance during selected 0.5 μsec intervals of the afterglow. By employing a synchronous source frequency compensation scheme, electron densities as low as ne∼2×104 cm−3 were measured in helium afterglows at 0.4 and 4.0 Torr. A comparison with conventional cavity techniques for ne∼109 cm−3 shows good agreement between the two methods. The application of such low density measurements to transition diffusion studies is discussed.