bluuebunny/crossref_metadata_2025 huggingface dataset:
Segregation of Carbon to the (100) Surface of Nickel
Authors: Blakely J. M. , Kim J. S. , Potter H. C.
Published: February 2004

The reversible segregation of carbon to the (100) surface of nickel has been observed. The surface was studied at temperature through measurements of work function changes and observations of LEED patterns and Auger spectra. The work function increases with temperature by about 0.63 eV in the temperature range 500°–800°K. This difference is close to that obtained from reported values of the work function for Ni (100) and for carbon. Below about 650°K the diffraction pattern contains rings characteristic of a graphite layer with its basal plane parallel to the substrate. In contrast with previous LEED observations of graphite precipitation at single-crystal surfaces, the segregation described here is reversible under temperature cycling.
Surface Morphology of Sublimated Crystals of Cadmium and Zinc Sulfides
Authors: Munir Z. A. , Hirth J. P.
Published: February 2004

The surface structure of (0001)- and (101̄0)-oriented single crystals of ZnS and CdS sublimated under controlled variable vapor pressure was investigated. The results were found to be consistent with the terrace-ledge-kink model of sublimation. Possible revisions to the theory of the effect of charged carrier concentration on sublimation of II-VI compounds are suggested.
Theory of Isoperibol Calorimetry for Laser Power and Energy Measurements
Authors: West E. D. , Churney K. L.
Published: February 2004

Laser power and energy measurements are commonly made in calorimeters operating in a constant temperature environment. Calorimeters of this type are analyzed in terms of the first law of thermodynamics and the boundary value problem describing heat flow in the calorimeter. This theory of the measurement suggests design features of the calorimeter, sources of error to be avoided in design and operation, and tests to demonstrate experimentally the adequacy of the design. The analysis shows how time—temperature data can be used to allow for the temperature gradient on the calorimeter and the heat exchange due to transients in the temperature.
Thermodynamics and Calculation of the Liquidus-Solidus Gap in Homogeneous, Monotonic Alloy Systems
Authors: Steininger Jacques
Published: February 2004

A general expression for the thermodynamic relationship between liquidus and solidus equilibrium compositions is derived for systems which are nonideal but homogeneous and monotonic. For a number of typical systems, the nonideal term in this expression is found to be very small, thus indicating that the ideal form of the general expression can be used to calculate one of the boundaries of the two-phase field when the other one and the enthalpies of fusion of the pure components are known. For many of the systems examined (InAs–GaAs, InSb–InAs, InSb–GaSb, GaSb–AlSb, InSb–AlSb, CdTe–ZnTe, CdTe–CdSe, HgTe–CdTe, GeTe–MnTe, PbBr2–PbCl2), the solidus curves calculated by this method are in good to excellent agreement with the published experimental values; for the Ag–Au, InAs–InP, SnTe–PbTe, and PbTe–PbSe systems they confirm the results of the more recent and more dependable investigations; for the Cu–Ni, Ge–Si and HgTe–HgSe systems however, they suggest the need for a critical reevaluation of the presently available data. In the absence of pertinent experimental data, calculated solidus and liquidus curves, respectively, are also presented for the ZnTe–ZnSe and HgTe–ZnTe systems.
Acousto-Optic Properties of Crystalline Germanium
Authors: Abrams R. L. , Pinnow D. A.
Published: February 2004

The acousto-optic properties of crystalline germanium have been measured, including a complete and accurate characterization of the photoelastic tensor. The results of this work indicate that germanium has a substantially larger acousto-optic figure of merit, (n6p2/ρV3), than other known infrared materials, with the exception of crystalline tellurium. Because germanium has superior optical and mechanical properties, it should be preferred to tellurium for many infrared modulation and deflection applications. In addition, we propose that germanium be used as a standard for future infrared acousto-optic material studies in the same way that fused silica has been used in the visible and near visible portion of the spectrum.
Propagation of Piezoelectric Surface Waves on Cubic and Hexagonal Crystals
Authors: Campbell James J. , Jones William R.
Published: February 2004

The propagation of surface waves on free and metallized surfaces of cubic and hexagonal crystals is investigated numerically. Surface wave velocity curves and relative differential velocity curves are presented for propagation on typical surfaces of four selected crystals (gallium arsenide, bismuth germanium oxide, zinc oxide, and cadmium sulfide). Special attention is paid to degenerate modes wherein decoupling among the various components of mechanical displacement and the electric field occurs.
Burgers Vector of Dislocations Generated for Dislocation Velocity Measurements in Semiconductors
Authors: Patel J. R. , Freeland P. E.
Published: February 2004

Dislocation motion in crystals is usually measured on loops generated from a deliberately introduced nucleating center such as a scratch. In germanium crystals it has been noticed that motion of an individual loop is usually asymmetric as observed by etch-pit techniques. The asymmetry has been assumed to arise from motion of dislocations having different character. The validity of this assumption was tested directly by x-ray topographic contrast experiments on crystals of germanium and silicon. From appropriate reflections that give either a strong or vanishing contrast it is possible to determine the Burgers vector of the dislocation loop. For both bending and compression tests, dislocation loops generated from a scratch and subsequently moved have a Burgers vector in the maximum resolved shear stress direction. Thus, for the specimen orientation 〈123〉 commonly used in velocity experiments both ends of the dislocation loops intersecting the surface of observation have the same character. In some cases the asymmetry may be due to the shape of the loop. The x-ray evidence refutes the conclusions reached by previous workers that asymmetrical motion is due to dislocations of different character.
Diffusion of Selenium-75 in Lead Chalcogenides
Authors: Ban Y. , Wagner J. Bruce
Published: February 2004

The diffusion of Se-75 has been studied in crystals of PbS, PbSe, and PbTe annealed under argon at 700°C. The relative diffusivities were D(PbS)≈D(PbSe)⪝D(PbTe). Adding bismuth to PbSe yields a higher diffusivity than in undoped crystals of PbSe while additions of silver do not change the diffusivity. At 700°C the diffusivity of selenium in PbSe was studied as a function of selenium partial pressure. For 10−4 ≤ pSe2 ≤ 80 Torr, D ∝ pSe21/4 while for pSe2 > 80 Torr, D ∝ pSe21/2. For pSe2 < 10−4 Torr, the diffusivity was not a function of selenium pressure.
Electronic Conduction and Space Charge in Amorphous Insulating Films
Authors: Pulfrey D. L. , Shousha A. H. M. , Young L.
Published: February 2004

Steady-state high-field electron conduction characteristics have been computed for a model in which the film contained electron traps with distributed binding energy and a compensating positive charge. Electron injection was taken to occur by the Schottky effect, trapping was considered as field independent, and detrapping as governed by the Poole-Frenkel equation. The results illustrate various types of behavior according to the values of some of the model parameters.
Concept of Transverse-Mode Pattern in Gyromagnetic Waveguides
Authors: Tully J. W. , Tao T. F.
Published: February 2004

The mode concept of a waveguide containing isotropic medium must be generalized when it is applied to waveguide containing gyromagnetic medium. For ferrite- or YIG-rod waveguides, three families of surface waves are found to exist. They are named as dynamic, surface, and volume modes. Dynamic modes are forward waves. Both surface and volume modes become backward waves when their phase velocities are much smaller than the velocity of light, i.e., large β values. The transverse-field vectors are generally elliptically polarized. Therefore, a stationary observer is not able to see the azimuthal and radial variations of a mode. Only by an observer rotating at radian frequency ω/n can a constant transverse-mode pattern be recognized. Using both amplitude and serrodyne-phase measurements, the differences between the mode concepts of an isotropic rod and a gyromagnetic YIG-rod waveguide are demonstrated. The same concepts are shown to be applicable to both the gaseous- and semiconductor-plasma waveguides.
Experimental Investigation of the Selective Deposition of Photoemitters by Nucleation
Authors: Doyle R. J.
Published: February 2004

Deposition of monoalkali and bialkali photoemitters has been controlled to preselected sites within a variety of vacuum device configurations by nucleating them on a thin (80%–98% optical transmission) predeposited metal layer having a heat of sublimation greater than that of the photoemitter evaporants. The nucleations were performed at elevated temperatures (typically 275°C for antimony) where the reevaporation rate of the evaporants was less than the arrival rate at the nucleation sites, and greater than the arrival rate at all other sites. Experiments are described where photoemitters were deposited by nucleation on preselected areas of surfaces in line of sight of the source materials, out of line of sight of the source materials, and in narrow confined spaces. Simultaneous selective deposition of more than 6000 separate 0.001-in.-diam photoemitters on a tungsten-pin matrix is also described.
Recovery of Deformed Polymers. I. Retraction of Cold-Drawn Polycarbonate, Polyethylene, and Polypropylene
Authors: Park J. B. , Uhlmann D. R.
Published: February 2004

A study is reported of the similarities and differences in the cold drawing and annealing behavior of amorphous polycarbonate (PC) and semicrystalline polyethylene (PE) and polypropylene (PP). The recovery data for all three polymers cover a range of temperature and initial strains. From these kinetic data, activation-energy spectra characterizing the recovery process are derived using an analysis for processes distributed in activation energy. These spectra are centered about 22–24 kcal/mole for PC, 22 kcal/mole for PE, and 15 kcal/mole for PP, treating recovery in the temperature ranges 170°–150°C for PC, 70°–60°C for PE, and 90°–80°C for PP. The mean activation energies do not vary with the initial strain but seen to decrease with increasing recovery temperature.
Effect of Helium on Population Inversion in the Helium-Neon Laser
Authors: Young R. T. , Willett C. S. , Maupin R. T.
Published: February 2004

Measurements are given of the ratio of the excitation due to helium to the excitation due to electrons for the 3s and the 2s levels (Paschen notation) of neon. The ratio was obtained from spectral intensity measurements on dc discharges in pure neon and in helium-neon mixtures with the electron temperature the same in the two cases. The excitation ratios for the Ne 3s levels at a discharge current density of 130 mA cm−2 in a 5:1 He–Ne mixture are 3s2−72, 3s3−4, 3s4−7, and 3s5−7; and for the Ne 2s levels in a 10:1 He–Ne mixture, 2s2−11, 2s3−20, 2s4−5, and 2s5−10.
Energy Levels and Spectral Broadening of Neodymium Ions in Laser Glass
Authors: Mann M. M. , DeShazer L. G.
Published: February 2004

Energy levels, linewidths, and oscillator strengths for trivalent neodymium ions in a commercial laser glass were determined from the fluorescence and absorption spectra. The spectra were composed of broad groups of overlapping lines and were deciphered from spectral variations produced by changes in glass temperature from 4° to 300°K. No thermal variation of the peak wavelengths and linewidths of the component lines was observed in this temperature range. The free ion levels of neodymium were completely split into J+½ Kramers doublets by the perturbation of the glass environment on the ion. The splitting patterns correlated closely with those determined from Nd2O3 crystals, indicating that the rare-earth ion locates in an environment in glass much like the sesquioxide crystal environment.
Effect of Junction Geometry on Maximum Zero-Voltage Josephson Current
Authors: Johnson W. J. , Barone A.
Published: February 2004

Tin-tinoxide-tin Josephson junctions have been fabricated by glow discharge oxidation of films evaporated in the 10−7−10−8-Torr range. Saturation of the maximum zero-voltage current with increasing junction length has been observed for a crossed film geometry, and a linear increase of maximum zero-voltage current with junction length has been observed for an overlap geometry. Approximate agreement with the theory of Owen and Scalapino has been obtained.
Pressure Dependence of the Second-Order Elastic Constants of ZnTe and ZnSe
Authors: Lee B. H.
Published: February 2004

Pressure dependences of the second-order elastic constants of ZnTe and ZnSe (zinc-blende structure) have been measured at 295°K as a function of hydrostatic pressure up to 6 kbar by means of ultrasonic pulse-echo method. The pressure derivatives evaluated at zero excess pressure for C11, C12, C44, and Bs (bulk modulus) are, respectively, 4.81±0.07, 5.12±0.1, 0.45±0.03, and 5.04±0.18 for ZnTe and 4.44±0.07, 4.93±0.1, 0.43±0.03, and 4.77±0.8 for ZnSe.
Visible and Infrared Faraday Rotation and Birefringence of Single-Crystal Rare-Earth Orthoferrites
Authors: Tabor W. J. , Anderson A. W. , Van Uitert L. G.
Published: February 2004

Faraday rotation and birefringence for propagation parallel to the magnetization, if single-crystal Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, and Lu orthoferrite have been measured from 0.6 to 1.8 μ at room temperature. The parameter δ, the relative phase per unit length, and χ, a parameter that relates the strength of the Faraday rotation to the birefringence, have been measured using transmission techniques. From these parameters θ, the intrinsic Faraday rotation, is calculated and found to be nearly the same for all of the orthoferrites except for samarium. In the wavelength region examined the intrinsic Faraday rotation is about three times greater than that in yttrium iron garnet. The optical axis for Eu, Tb, and Yb orthoferrite have been measured at a wavelength of 0.6 μ. The difficulties in using a material with both Faraday rotation and birefringence in devices is discussed.
Photovoltaic Effect Induced by Two-Photon Excitation in p-n Junction Devices
Authors: Yee Jick H.
Published: February 2004

The open-circuit voltage, the short-circuit current, and the efficiency of a p-n junction photovoltaic cell excited by the two-photon process is derived theoretically. Boundary conditions concerning the intensity of the light just inside the surface of the cell are discussed. As an application of the theory an order-of-magnitude calculation is carried out for a GaAs p-n junction device.
Method of Determining Ion Temperatures in Laser-Produced Plasmas
Authors: Allen F. J.
Published: February 2004

A method is derived for obtaining ion temperatures in a plasma produced by irradiation of a solid target with a Q-switched laser beam. Ion temperatures are then obtained from published data. For an incident intensity of 6×1010 W/cm2, ion temperatures in the range of 10–40 eV are found. These values are consistent with values of electron temperatures found by others.
Noise Emission from Indium Antimonide
Authors: Thompson A. H. , Kino G. S.
Published: February 2004

We have arrived at a new explanation for the noise emission radiated from InSb when an electric field is applied to it in the presence of a magnetic field. Our theory is based on the existence of localized high electric field regions at the contacts or corners of the sample. These high field regions cause local electron avalanche; the resulting electron-hole plasma appears to be the source of the noise emission. Our probe measurements of the dc and rf potentials and measurements of bandgap light radiation due to avalanching are in good agreement with the theory. The theory is also in agreement with experimental results on noise emission in the literature.
Propagation of Guided Electromagnetic Waves in Semiconductors in a Longitudinal Magnetic Field
Authors: van Dalen P. A.
Published: February 2004

The propagation of electromagnetic waves in a circular waveguide, filled over a finite distance with a longitudinally magnetized semiconducting medium, is studied both theoretically and experimentally. The existing theory of the propagation of guided electromagnetic waves in gyromagnetic media is extended by consideration of the attenuation of the wave by the medium. It follows from the theory presented that analytical expressions for the dependence of the propagation on the magnetic field can only be derived if the gyromagnetic properties of the semiconductor are sufficiently weak. It is shown that values of the concentration N, the mobility μ and the scattering time τ (and hence the effective mass m*) of the charge carriers can be found by measuring the Faraday rotation, as well as by measuring the attenuation of a plane-polarized wave due to the charge carriers in the medium. Furthermore, these two measurements are shown to provide a convenient way of determining the dielectric constant of a semiconductor in the microwave region. In order to verify the theory experiments were carried out on n-type GaAs. Both the Faraday rotation and the attenuation of the wave were measured, taking into account the influence of interferometer effects due to the finite length of the semiconducting medium. The experimental results obtained for the Faraday rotation and the attenuation were consistent with each other and were in excellent agreement with the theory. The dielectric constant εl of GaAs was found to be 12.77±0.1.
Hot-Electron Anisotropy of Microwave Conductivity in Nonparabolic Semiconductors
Authors: Kaw P. K. , Dubey P. K. , Chakravarti A. K.
Published: February 2004

Using the equilibrium distribution function obtained from the Boltzmann transport equation, and the collision term given by Matz [D. Matz, Solid State Commun. 4, 491 (1966); J. Phys. Chem. Solids 28, 373 (1967)], expressions have been derived for microwave conductivity (in parallel and perpendicular orientations to an externally applied, high-dc electric field) in III-V semiconductors with nonparabolic energy bands. Electron scattering with phonons, via the polar optical mode and with ionized impurities, has been considered to be the dominant scattering mechanism. Numerical evaluation of the results for a typical case of n InSb shows that, for the same dc field, the perpendicular microwave conductivity is always greater than the parallel one. An interesting reduction to the case of parabolic-band semiconductors has also been made for the sake of comparison; it reveals that the band nonparabolicity has the effect of reducing the magnitude of conductivity anisotropy.
Transport Processes in Amorphous Cr2O3 Films
Authors: Barbe D. F. , Herman D. S.
Published: February 2004

The transport processes in amorphous Cr2O3 films, nominally 1000-Å thick, are studied experimentally in the temperature range 21°–300°C and in the electric field range 3.5×104−6.5×105 V/cm. For electric fields below 105 V/cm, the thermally activated hopping of carriers between localized states dominates the conduction process. Above 105 V/cm, the electric-field-assisted thermal ionization of donor-type states located 0.442-eV below the edge of the conduction band dominates the conduction process. A novel method of examining the pre-exponential factor in the Poole-Frenkel equation is presented. Based on these results and optical absorption data, an energy-band model for amorphous Cr2O3 is proposed.
Rectification and the Anomalous Photovoltaic Effect in ZnS Crystals
Authors: Shachar G. , Brada Y.
Published: February 2004

The current-voltage characteristics of insulating ZnS crystals were measured for various monochromatic excitations. A rectification dependent on crystallographic polarity was observed. The spectral dependence of the rectification ratio is similar to the spectral dependence of the positive anomalous photovoltage. The rectification is attributed to the action of the same internal fields which were investigated by electro-absorption measurements and which cause the generation of the anomalous photovoltaic effect. The electrical characteristics were correlated with other photoelectric properties of ZnS crystals and with the gross structure of the crystals, i.e., with the structure of the various regions of which a given crystal is composed. The origins of the internal fields and the mechanism of the negative photovoltage generation are also discussed.
Temperature Dependence of the Hall Mobility and Carrier Concentration in Silicon-on-Sapphire Films
Authors: Dumin D. J. , Ross E. C.
Published: February 2004

The temperature dependence of the Hall mobility and carrier concentration in thin n- and p-type silicon-on-sapphire films is described. The effects of both shallow and deep levels acting as compensating centers are discussed. The electrical properties of the thin silicon-on-sapphire films are compared with bulk silicon. It is shown that both shallow compensating donors and acceptors and deep levels can lower the Hall mobility below bulk values and can cause the carrier concentration to drop more quickly with decreasing temperature than observed in bulk silicon.
Theoretical Shock Properties of Porous Aluminum
Authors: Pastine D. John , Lombardi M. , Chatterjee A. , Tchen W.
Published: February 2004

Purely theoretical predictions are made of the states achieved by the passage of stable shocks through porous aluminum. This is done by combining a theoretical equation of state and a theoretical description of the compaction process with the current theory of shock propagation in porous materials. The results show very good agreement between theory and experiment, adding further justification to the presently accepted theory of shocked porous substances.
Nucleation of Multiply Twinned Particles at an Early Stage of Vapor Deposition
Authors: Sato H. , Shinozaki S.
Published: February 2004

The study of nuclei of Au deposited on NaCl substrates cleaved in the ultrahigh vacuum shows that most small deposits on the flat parts of the substrate are multiply twinned particles, whereas, at the cleavage steps there are epitaxial particles of definite shapes with either (100) or (111) orientation. From the dependence of the shape of small deposits on the magnitude of the interfacial interaction and from the stability of the multiply twinned particles, it is concluded that the predominant existence of multiply twinned particles is an indication of negligible interfacial interaction while the existence of epitaxial particles at the steps is due to the creation of nucleation sites by surface defects. The loss of epitaxy of Au on NaCl cleaved in an ultrahigh vacuum is explained as the result of negligible interfacial interaction between the deposits and substrates.
Dislocation Cell Formation in Metals
Authors: Holt David L.
Published: February 2004

It is shown by an analysis similar to that for the spinodal decomposition of a supersaturated solution that an array of dislocations, modelled by parallel screw dislocations, of uniform density, is unstable; the dislocations move to form a structure having a modulated dislocation density. It is suggested that the instability grows ultimately into a dislocation cell structure and that the cell size is given by the dominant wavelength of the density modulation. This wavelength λm is found to be proportional to ρ−1/2 and furthermore the wavelength is given by λm ≈ Kc·ρ−1/2=rc, where Kc is a constant, ρ is the dislocation density and rc is defined as a dislocation-dislocation interaction distance. Data in the literature relating to cell size are shown to support this result. Restrictions on the applicability of the analysis are discussed.
Ferrite-Filled Elliptical Waveguides. I. Propagation Characteristics
Authors: Salmond W. E. , Yeh C.
Published: February 2004

This paper deals with electromagnetic wave propagation in a longitudinally magnetized, ferrite-filled elliptical waveguide. Using the wave equations and boundary conditions for a ferrite-filled waveguide of arbitrary cross-sectional shape, it is shown that for an elliptical cross section the characteristic equations for the propagation constant take the form of even and odd infinite determinants. Solutions for the characteristic equations are obtained for various values of applied field strength, saturation magnetization, and waveguide ellipticity. The existence of three types of cutoff conditions is demonstrated.
Photoemission from Amorphous Selenium
Authors: Leiga Algird G.
Published: February 2004

Photoemission yield measurements were made on amorphous selenium from about 6 to 21 eV. The yield curve exhibits a change in slope at about 7.8 eV corresponding to a maximum in the imaginary dielectric constant. The photoemission threshold is obtained by using a threshold law equation derived by Kane, Y = C (E − Et)n, where Y is the yield, E and Et are the photon energy and threshold energy, and C and n are constants. The yield data up to 8 eV are best represented by the equation with n=52 resulting in an extrapolated photoemission threshold of 5.86 eV for amrophous selenium.
Mechanisms Controlling the Positive Ion Emission from Heated Fe Filaments
Authors: Stefanakos E. K. , Dresser M. J. , Tinder R. F.
Published: February 2004

Positive ions emitted from heated iron filaments consist mainly of the alkali-metal atoms, such as lithium, sodium, and potassium, which are present in iron as trace impurities. Changes in the work function with different applied partial pressures of oxygen and hydrogen have been recorded. From the results of measurement it is concluded that the effect of oxygen on the work function of iron is much stronger than that of hydrogen. Kinetic data representing the emission of Na and K ions from Fe were obtained in the temperature range of 1050°–1350°K. Diffusion and ion desorption are discussed as possible rate-controlling processes. Activation energies, believed to represent the diffusion of Na and K atoms in Fe, are found to be approximately 38 kcal/mole (1.7 eV) and 53 kcal/mole (2.3 eV), respectively. The Richardson work function of iron varies from φ≃4.0 eV at P02≃10−9 Torr to φ≃5.6 eV at P02≃10−5 Torr. When a diffusion-controlled process is assumed, the difference between the activation energies, for the above two oxygen pressure conditions, is found to be the same as the difference (I - φ); that is, the difference between the first ionization potential of the atom and the work function of the metal surface. The experimentally determined values of (I - φ)exD for K and Na agree within experimental error with the calculated values.
Effect of Radio-Frequency Fields on the Electrical Breakdown of Vacuum-Insulated Electrodes
Authors: Kustom Robert L.
Published: February 2004

Five possible mechanisms of dc vacuum breakdown are analyzed for rf electric fields. The theories which are considered are the vaporization of a micron-sized cathode irregularity due to joule heating by field-emitted electrons, vaporization of the anode due to bombardment by field-emitted electrons, field-emission current instability created by the presence of anode ions, exchange of electrode ions, and microparticle vaporization. The analysis indicates that mechanisms which do not involve anode ions in gaps of 0.2–1.0 cm will not be strongly influenced by rf fields in the frequency range of 20–120 MHz. Under similar conditions, the theories involving anode ions predict a very sizable increase in the voltage capability of vacuum-insulated electrodes. Experimental ratios of vacuum breakdown voltage at 21.5 MHz to that for 60 Hz were experimentally determined for highly polished tungsten electrodes with separations between 0.18 and 0.61 cm. The rf voltages obtained experimentally were less than the values predicted by theory, although the cathode whisker vaporization and ion perturbation by light ions were within experimental uncertainties. From the differences seen in spark conditioning of electrodes, it would appear that micron-sized particles are involved in the spark threshold at 60 Hz.
Phenomenological Approach to Low-Frequency Electrical Noise
Authors: Teitler S. , Osborne M. F. M.
Published: February 2004

A phenomenological description of excess noise in a nonequilibrium system is presented. The development involves two basic physical ideas. Firstly, the excess noise is ascribed to the fluctuation of the local reference level to which equilibrium and other white fluctuations are compared. Secondly, it is assumed that excess low-frequency noise involves a nonlinear process. This implies the noise power in different frequency regions are coupled. A further simple assumption requires the integral of the power spectral density over specially chosen intervals to be a constant. This leads to a 1/f spectrum for the power spectral density. Possible generalizations that provide for other spectral laws are also mentioned.
Stability Analysis of a Levitated Superconducting Current Ring Stabilized by Feedback and Eddy Currents
Authors: Woods C. H. , Cooper R. K. , Neil V. K. , Taylor C. E.
Published: February 2004

A stability analysis is presented for the superconducting levitron stabilized partly by feedback and partly by magnetic coupling to metal plates placed symmetrically above and below the current ring. The system is so designed that eddy currents in the plates provide sufficient damping to limit the velocity of the ring to safe values in case of loss of control. The magnetic field associated with the feedback system must diffuse through the plates, which tends to handicap the feedback process and complicate the stability analysis. While levitated current rings stabilized by feedback normally require a component of stabilizing current proportional to the ring velocity to produce artificial damping, the present system is found to be stable without such a velocity-dependent component.
Correlation between Photoluminescence and Electroluminescence Time Decay in Red-Emitting GaP Diodes at Room Temperature
Authors: Hackett W. H. , Bhargava R. N.
Published: February 2004

It is shown that photoluminescent and electroluminescent decay times are equal in a wide variety of red-emitting GaP diodes grown by liquid-phase epitaxy. In general, the luminescent decay times depend strongly on the Zn concentration in the bulk p region. For high Zn concentrations (≥5×1017 cm−3) the decay times vary approximately inversely with Zn concentration. The equality of the photoluminescent and electroluminescent decay times for the wide variation of decay times and Zn concentrations provides additional evidence that the luminescence occurs in the bulk Zn- and O-doped p region.
Energy Spectrum of the Domain Structure of Metal Platelets Under Stress
Authors: Kaczér Jan
Published: February 2004

The domain structure of thin metal platelets having positive cubic anisotropy constants K1 changes discontinuously on application of external stress. The paper deals with the calculation of the eigenvalues of the stress and of the wall energy corresponding to these discrete domain configurations determined by the finite size and shape of the platelets.
Tensile Plastic Instability at an Elevated Temperature and Its Dependence upon Strain Rate
Authors: Wray P. J.
Published: February 2004

Observations have been made of the changes in shape that develop in initially cylindrical specimens of In–0.5% Pb and In–5.0% Pb alloys extended axially at overall strain rates in the range 1.2×10−7−1.7×10−1 sec−1 at a temperature of 0.69Tm. To deal with the dynamic nature of neck formation and with the possibility that necks once formed may become dormant, the concept of neck activity is introduced. Two types of instability are observed. The first instability is related to the initiation of several active necks in a uniformly deforming specimen. It may occur at small strains (<0.05) and apparently is strain-rate sensitive. The second instability occurs at large strains and involves the unequal rate of growth of concurrently active necks, resulting in the final ascendancy of a single neck. The second instability is related to elevated temperature ductility. At high strain rates, where work hardening is dominant, it corresponds approximately to Considère's criterion, but at low strain rates, where viscous effects are significant, a postponement with respect to the Considère condition is observed, the ductility increasing with decreasing strain rate.
Variational Principles of the Elastic Moduli of Composite Materials
Authors: Yeh Robert H. T.
Published: February 2004

Variational principles and variational bounds are obtained for the effective elastic moduli of quasiisotropic composite materials.
Effect of a Reactive Environment on the Hertzian Strength of Brittle Solids
Authors: Langitan F. B. , Lawn B. R.
Published: February 2004

Hertizan fracture theory, previously developed for ideal brittle solids fractured under essentially environment-free conditions, is here modified to allow for an interaction between the growing cone crack and a reactive environment. Two alternative models, both of which account for the observed detrimental effect of an environment on the Hertzian strength but which predict slight differences in the growth of the cone crack, are offered. The first is based on a surface-energy-lowering concept and the second on a subcritical-crack-growth concept. The theoretical implications of these two models are examined in the light of Hertzian fracture experiments on abraded glass slabs in different test environments. Observations of the growth of the cone crack in fatigue experiments favor the second model for glass. The advantages of the Hertzian test as a tool for the study of environmental effects on the fracture strength of brittle solids in general are discussed in relation to more conventional fracture tests.
Elastic Constants of Compression-Annealed Pyrolytic Graphite
Authors: Blakslee O. L. , Proctor D. G. , Seldin E. J. , Spence G. B. , Weng T.
Published: February 2004

The elastic constants of pyrolytic graphite which has been highly ordered by annealing under compressive stress have been determined by ultrasonic, sonic resonance, and static test methods. Ultrasonic tests yielded the elastic constants c11, c12, c33, c44 = 1/s44, and the stress derivative of c33. The moduli 1/s11 and c44 were determined from the free flexural resonant vibrations of bars, and the shear modulus c44 also was determined from the fundamental torsional resonance of the bars and from the resonance of compound torsion oscillators composed of thin graphite disks with steel end pieces. Static tension, compression, and torsion tests on the pyrolytic graphite yielded a complete set of compliances (s11, s12, s13, s33, and s44). The following self-consistent set of elastic constants (cij in units of 1011 dyn/cm2; sij in 10−11 cm2/dyn) has been deduced from the results: c11 = 106±2, c12 = 18±2, c33 = 3.65±0.10, c13 = 1.5±0.5, c44 = 0.018 to 0.035, 1/s11 = 102±3, 1/s33 = 3.65±0.10, s12 = −0.0016±0.0006, s13 = −0.0033±0.0008, and s66 = 0.023±0.002; with the possible exception of c44, these constants are expected to be typical of the graphite single crystal. The shear strength for shear between basal planes was found to be in the range of 90–250 g/mm2.
Elastic Constants and Electron-Microscope Observations of Neutron-Irradiated Compression-Annealed Pyrolytic and Single-Crystal Graphite
Authors: Seldin E. J. , Nezbeda C. W.
Published: February 2004

Compression-annealed pyrolytic graphite and single-crystal graphite specimens were irradiated with neutrons for total exposures of 3 to 71×1017 neutrons/cm2 (nvt) at 50°C, 3 to 8×1019 nvt at 650°C and 1.2×1020 nvt at 1000°C. The elastic constants of the materials were determined before and after irradiation by ultrasonic-, sonic-resonance-, and static-test methods. The only elastic constant that changed significantly with irradiation was the shear modulus c44 although a small change was also seen in c33. The natural crystals after irradiation had shear moduli in the range of 0.16–0.46×1011 dyn/cm2, the modulus after irradiation showing no correlation with irradiation temperature, exposure, or modulus before irradiation. The average values of the shear modulus of the pyrolytic graphite were 0.22−0.40×1011 dyn/cm2 after irradiation at 50°C, 0.030−0.033×1011 dyn/cm2 after irradiation at 650°C, and 0.042×1011 dyn/cm2 after irradiation at 1000°C; the shear modulus c44 of graphite when all dislocations are pinned is thus equal to or greater than 0.40×1011 dyn/cm2. The results can be correlated with electron-microscope observations and interpreted in terms of nucleation theory of radiation damage in analogy to the interpretation of the electron-microscope observations of W. N. Reynolds and P. A. Thrower [Phil. Mag. 12, 573 (1965)] or in terms of a difference in the availability of sinks for the displaced atoms.
Experimental Observation of and Comments on Optical Parametric Oscillation Internal to the Laser Cavity
Authors: Smith R. G. , Parker J. V.
Published: February 2004

The theory of an optical parametric oscillator located internal to the cavity of the pump laser has recently been presented by Oshman and Harris. An oscillator of this type has been constructed and the details of its operation are presented here. Several features predicted by the theory have been observed; in particular a form of relaxation oscillation peculiar to the internal oscillator has been observed for the first time. In addition to the experimental results the question of the stability of the various modes of operation and factors affecting the pulse repetition rate of the pulsing solution are considered.
New Photovoltaic Response in the Surface of n-Type InSb
Authors: Axt Carl J. , Rogers C. G.
Published: February 2004

Previous studies of anodized InSb samples cooled in the dark to 77°K have shown that initially n-type surfaces are changed to p type upon visible illumination. For n-type bulk material an infrared photovoltaic response can be obtained from the inverted surface after such illumination. A new response has been found in n-type samples which was present initially but which then disappeared upon visible illumination. Measurements on both types of response have shown other distinguishing features, and several models are discussed.
Inverse Problem for Electrostatic Plasma Probes
Authors: Sajben M. , Lee P. H. Y.
Published: February 2004

Electrostatic probe theories are traditionally aimed at predicting probe characteristic curves for specified sets of plasma density, temperature, and potential. The inverse process of determining the plasma properties from a measured current-voltage curve is conventionally done in a fashion involving subjective judgement and resulting in one set of properties for one characteristic. A method is presented which eliminates subjective factors altogether and yields one set of properties for each point of the characteristic curve. By averaging, the accuracy and reliability of the data is considerably increased. The method is based on the replacement of conventional dimensionless variables by new, experimentally convenient ones and expressing the results of a given theory in terms of the new variables. The method is applied to a cylindrical probe in a collision-free Maxwellian plasma at rest. It is demonstrated, by way of an example, that the results of the inverse solution are consistent with the direct problem. The principle of the inversion is applicable to a wide variety of probe theories.
Production and Study of an Alkali Plasma with Negative Ions
Authors: Hashmi M. , van der Houven van Oordt A. J. , Wegrowe J.-G.
Published: February 2004

The method of contact ionization is used to produce a three-component plasma (Cs+, Cl−, e−) in the Q-device BARBARA using a beam of Cesium chloride. The end-plate temperature controls the concentration of Cl−, which can be varied in a wide range. The density of negative ions is obtained from the difference between the positive ion density given by a Langmuir probe and the electron density given by a microwave resonator. A high concentration of negative ions is achieved.
Kinetic Equation of Annealing in Lithium-Diffused Silicon
Authors: Fang P. H.
Published: February 2004

Some unusual annealing properties of the radiation damage in lithium-diffused silicon are discussed. These properties are (1) spontaneous room-temperature recovery, (2) the effect of oxygen content in silicon on the recovery, (3) the effect of the defect concentration on the recovery, (4) high damage effect on the recovery, and (5) redegradation. A kinetic equation is formulated by introducing the time dependence of free lithium concentration in the system to the kinetic equation of the repairing of the damage. The results successfully describe all the properties listed above.
Zinc Diffusion into Silicon by a Closed-Tube, Two-Temperature Technique
Authors: Zalar Stojan M.
Published: February 2004

The diffusion of zinc into silicon was investigated by a sealed-quartz-tube, two temperature method. The following diffusion variables were considered: time (15 min-16 h), silicon type (N and P), temperatures (900°–1100°C), zinc temperatures (600°–900°C), and the effect of chemical treatments. A value of 4.4×10−8 cm2/sec was computed for substitutional zinc diffusivity in silicon, with silicon wafers at 1000°C and zinc source at 700°C. While the diffusion of zinc followed the usual square root dependence on time, there was an initial time lag of several minutes very probably due to the ever present thin SiO2 films on the surface of silicon. When these SiO2 surface layers were made intentionally thicker zinc diffusion virtually stopped. In the pressure range between 50 and 760 Torr, the penetration of zinc was found to be a nonlinear function of the vapor pressure of zinc. The effects of heat treatments at 1000°C on electrical resistance of silicon with and without zinc were also studied and compared. Finally, zinc was diffused into N+-P power diode structures.
Pair Spectra Involving the Shallow Acceptor Mg in GaP
Authors: Dean P. J. , Schönherr E. G. , Zetterstrom R. B.
Published: February 2004

Type II donor-acceptor pair spectra involving the shallow group IIA acceptor Mg and the group VI donors S and Te have been observed from GaP crystals grown from Ga solution in an open-tube furnace system. Magnesium can be an optically active inadvertent contaminant in high-purity GaP. Crystals containing ∼1017 cm−3 of these desired impurities, added intentionally, exhibited sharp structure due to electron-hole recombinations at discrete donor-acceptor pairs, with negligible contamination from unwanted spectra. The transition energies in these spectra can be closely fitted for shell numbers m≳20 (pair separation ≳17 Å) by an expression which includes only the coulomb monopole term for the final state interaction and a van der Waals term for the initial state interaction, using low-temperature static dielectric constant. This analysis yields the activation energy of the Mg acceptor in GaP, (EA)Mg=53.5±1 meV, substantially different from previous estimates derived from electrical transport and impurity Raman scattering measurements. Trends in the activation energies of the three Ga-site acceptors and three P-site acceptors known in GaP are discussed qualitatively.
Effects of Surface Recombination on the Transverse Magnetoresistance of Thin InSb Layers
Authors: Lile Derek L.
Published: February 2004

The variation of current with magnetic field for constant applied electric field has been measured in thin films of InSb in which the transverse magnetic field is aligned both normal to and in the plane of the sample. These measurements have been performed for values of electric field both below and above that required for impact ionization of the lattice. The results are shown to be well explained by the magnetoresistance theories, of Wieder and Pikus, which indicate a maximum contribution of the surfaces to the measured magnetoresistance for a sample whose thickness is ∼1.4 times the bulk diffusion length. From the results it is estimated that the ratio of the recombination rates associated with the two surfaces of the films is ∼0.4, the larger recombination rate being associated with the free surface.
Hugoniot Elastic Limit of Single-Crystal Sodium Chloride
Authors: Murri William J. , Anderson Gordon D.
Published: February 2004

Single-crystal specimens (7- and 12-mm thick) of sodium chloride were impacted with flat-nosed, gas-driven projectiles, and the Hugoniot elastic limit (HEL) was determined by reducing quartz gauge measurements. The HEL for the [100], [110], and [111] crystal directions was 0.26, 0.77, and 7.4 kbar, respectively. Stress—time profiles for specimens shocked in the [100] and [111] direction show evidence of stress relaxation behind the elastic precursor. This phenomenon is more pronounced in 12-mm-thick specimens. The ratio of the resolved shear stress on the active slip systems for uniaxial strain (shock loading) conditions to that for uniaxial stress (static loading) indicates a strain-rate effect. This ratio increases from 3.1 for loading in the [100] direction to 8 for the [110] direction and to 21 for the [111] direction. The anisotropy of the HEL with crystal direction is related to the resolved shear stress on the primary and secondary slip systems in single-crystal sodium chloride. The large HEL for shock loading in the [111] direction is a consequence of the resolved shear stress on the primary slip systems being zero. Thus, for deformation by slip to occur, a secondary slip system (or systems) must be activated which will require a higher resolved shear stress. The experimental data for single crystals of copper and beryllium can also be explained in terms of the resolved shear stress.
Fluorescence Rise-Curve Technique for Measuring Nonradiative Transition Probabilities
Authors: Pollack S. A.
Published: February 2004

Several experimental techniques of measuring the nonradiative transition probabilities in condensed media are briefly reviewed and the fluorescence rise-curve technique is analyzed in detail from the theoretical and practical points of view. Some applications and experimental pitfalls are discussed.
Measurement of Silicon Epitaxial Layers Less Than 1-μ Thick by Infrared Interference
Authors: Schumann P. A. , Schneider C. P.
Published: February 2004

An analysis of the infrared-interference method of measuring epitaxial layer thickness is given which shows that the technique is useful for measurement of layers thinner than one micron. The connection between plasma resonance and infrared interference is established. A new method of interpreting the infrared spectra is given which produces both the layer thickness and substrate impurity concentration.
Observations of Spark-Erosion Damage in Copper Crystals
Authors: Guberman H. D. , Bachmann K. J. , Baldwin T. O.
Published: February 2004

The damage introduced by electrical discharge machining was investigated in low-dislocation copper single crystals with a view toward determining the acceptability of the technique for the preparation of nearly perfect crystals. The damage was observed by anomalous x-ray transmission, etch-pitting, and x-ray rocking curve halfwidths. It was concluded that with due care this technique could be used successfully, even for relatively soft crystals.
Molecular-Orbital Interpretation of the Soft X-Ray LII,III Emission and Absorption Spectra from Some Titanium and Vanadium Compounds
Authors: Fischer David W.
Published: February 2004

A molecular-orbital energy-level diagram is constructed and used to interpret the metal-ion LII,III x-ray emission and absorption spectra from the oxides, nitrides, carbides, and borides of titanium and vanadium. It is shown that the MO model provides a more accurate description of the experimental results than did the ionic model and crossover transition theory. Specific electronic transitions are assigned to spectral components. Anomalous emission peaks which fall on the low-energy side of the main LIII band are found to originate in molecular orbitals which are primarily associated with ligand 2p and 2s levels.