bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of dislocations on electrical conductivity of CdTe
Authors: Buch Fredrik , Ahlquist C. Norman
Published: February 2004

Simultaneous measurements of electrical conductivity and flow stress have been made on p- and n-type CdTe single crystals deformed in compression at room temperature. Observed changes in conductivity always correspond to a shift of the Fermi energy towards the conduction band and are consistent with the creation of an excess of dislocation donors. An energy-band diagram for the native point-defect states and dislocation states in CdTe is formulated based upon observed electrical, optical, and mechanical behavior.
Interface and doping profile characteristics with molecular-beam epitaxy of GaAs: GaAs voltage varactor
Authors: Cho A. Y. , Reinhart F. K.
Published: February 2004

Studies of the doping profile characteristics of molecular-beam epitaxy (MBE) of GaAs on GaAs substrates are reported. Highly resistive regions at the substrate—epitaxial-layer interface, and within the epitaxial layer, may occur if the growth is interrupted. It is shown that almost any arbitrary voltage dependence of the capacitance of such structures can be achieved by varying the dopant deposition rate during epitaxy. To illustrate the versatility of this growth technique, voltage-variable capacitors have been prepared with Schottky barriers on MBE GaAs layers with precisely controlled doping profiles. Low-frequency measurements (up to 100 MHz) demonstrate that capacitance variations in excess of a factor of 10 have been achieved by varying the applied bias voltage V from 0.3 V (with no significant forward conduction) to −1.0 V. The feasibility of frequency tuning diodes with C−1/2[sine wave]φ−V, where φ is the effective barrier height, is shown. At -3 V bias, cutoff frequencies >40 GHz have been measured. With an improved diode design, cutoff frequencies in excess of 200 GHz are expected at similar bias voltages.
Magnetoelastic Rayleigh waves on a YIG substrate magnetized normal to its surface
Authors: Parekh J. P. , Bertoni H. L.
Published: February 2004

The propagation characteristics of exchange-free magnetoelastic (ME) Rayleigh waves are treated for the case of propagation on a YIG substrate that is magnetized perpendicular to its surface. As a result of the wave anisotropy of the constituent ME plane waves, these waves differ substantially from the ME Rayleigh waves propagating on a YIG substrate along or obliquely to a tangential bias field. Computed dispersion and polarization properties are presented for a low saturation magnetization Ga-YIG substrate whose surface is either unmetallized or metallized with a thin perfectly conducting metallic film. In either case, the dispersion diagram consists of two branches, one of which represents bound surface waves for frequencies below a spectrum of frequencies given approximately by the magnetostatic bulk-wave spectrum, and the other branch represents bound surface waves for frequencies above this spectrum. Within the spectrum the surface waves are of the leaky variety, and can be used to obtain beam steering over an angle of 90 ° in the forward direction.
Lift and side forces on rectangular pole pieces in two dimensions
Authors: Brzezina W. , Langerholc J.
Published: February 2004

A closely spaced pair of nonsymmetrically opposing rectangular poles is reduced to a combination of opposing corners; the mutual forces between the poles can then be written in terms of the simple direct formulas obtained for the two-corner problem. The results obtained involve only elementary functions and do not require implicit solution of nonalgebraic equations.
Noncollinear three-phonon interactions in a multimode structure
Authors: Furgason E. S. , Newhouse V. L.
Published: February 2004

Excitation of Lamb waves in the five lowest-order modes is demonstrated on polarized plates of PZT by using interdigital transducers. It is shown that in this structure the nonlinear interaction of noncollinear phonons can produce sum- and difference-frequency beams at arbitrary angles. This is accomplished by interacting waves propagating in various combinations of the many available Lamb modes and by selecting frequencies and wave vectors that satisfy energy and momentum conservation. The phenomena described may have applications to acoustic signal processing.
Method of estimating stacking-fault energies in alkali halide crystals using creep data
Authors: Mohamed Farghalli A. , Langdon Terence G.
Published: February 2004

A method is presented of estimating the stacking-fault energies in alkali halide crystals using creep data. Using this procedure, the stacking-fault energies of NaCl, KCl, and LiF are estimated to be 235, 135, and 390 erg/cm2, respectively, in good agreement with the theoretical predictions for dissociation on {110} planes.
Thermally activated deformation. II. Deformation of sintered iron
Authors: Hanley T. O'D. , Krausz A. S. , Krishna N.
Published: February 2004

The atomic processes associated with the plastic deformation of commercial-quality sintered iron were investigated. Stress relaxation tests were carried out over the 17–19-kg mm−2 range of initial stress levels at room temperature. The experimental results were analyzed with the deformation kinetics theory discussed in Paper I. The analysis showed that the rate-controlling mechanism is associated with a system of two consecutive energy barriers. At high stress levels only the first barrier is effective. The corresponding activation volume of ∼ 200 b3, measured in these tests, suggested that the Peierls-Nabarro mechanism was rate controlling at this level. It is proposed that the second barrier is either the second half of the ``camel-hump'' Peierls-Nabarro barrier or the resultant of a series of dragging-point barriers controlling the spreading of the double kink.
Effect of the discreteness of the atomic structure on cleavage crack extension in brittle crystalline materials
Authors: Smith E.
Published: February 2004

Elliott's model of a straight-fronted cleavage crack is used to conduct an analytical Peierls-Nabarro-type calculation appropriate for a two-dimensional lattice where the atomic spacings are respectively a and b normal and parallel to the cleavage crack. The analysis enables the effect of the discreteness of the atomic structure on brittle cleavage crack extension to be assessed and circumvents some of the limitations in a previous analysis due to Thomson, Hsieh, and Rana. The general conclusion emerging from the present work is that the magnitude of the discreteness effect, reflected in the ratio between the crack extension stress and that predicted by the continuum-based Griffith relation, is greater the smaller the crack front width which thereby substantiates Thomson, Hsieh, and Rana's inferences. Proceeding from this conclusion, the wider problem of relating the magnitude of the discreteness effect, crack front width, and the type of atomic bonding is discussed from an essentially physical viewpoint. As a result of such considerations it is suggested that, in general, the discreteness effect will be small and the crack front will be wide with a material that is more resistant to elastic shear than tension, as in a covalently bonded solid where the bonding is directional. Since dislocation mobility is difficult in such a material, it would therefore seem that existing arguments regarding brittle cleavage crack extension should not be significantly affected by the introduction of discreteness considerations and that very special circumstances are likely to be required to give a large discreteness effect, as would be reflected in a brittle crack extension stress markedly in excess of that predicted by the Griffith relation.
Detection and identification of microparticles occurring in a high-voltage vacuum-insulated gap using electron optical methods
Authors: Menon M. M. , Srivastava K. D.
Published: February 2004

According to Cranberg's hypothesis, tiny aggregates of metallic matter called microparticles, emanating from the electrode surfaces, are responsible for the breakdown of a vacuum gap under high dc stress. Experiments are carried out using a scanning electron microscope to see whether such particles appear within the interelectrode gap prior to breakdown. It was observed that micron- and submicron-sized particles are released in abundance well below the breakdown voltage. Investigations were continued to identify the microparticles with the electrode materials using an electron microprobe analyzer. It was found that the microparticles were composed of the electrode materials. Direct examination of the electrode surfaces, after application of the voltage, under the scanning electron microscope also showed features suggesting that the microparticles are released from the electrode surfaces.
Magnetohydrodynamic behavior of a laser-heated solenoid
Authors: Burnett N. H. , Offenberger A. A.
Published: February 2004

The problem of laser-induced heating and radial expansion of a low-density plasma in a solenoidal magnetic field has been examined by means of a Lagrangian computer code incorporating an exact solution of the relevant MHD equations plus thermal conduction. It is shown that for long-term heating with a realistic range of laser power and magnetic field strength, the resulting radial temperature and density profiles can be closely approximated by a quasistatic solution of these equations.
Mode control in GaAs large-cavity double-heterostructure lasers
Authors: Hakki B. W. , Hwang C. J.
Published: February 2004

Factors that are important in maintaining zero-order-mode operation at high power in large-cavity GaAs double-heterostructure lasers are described. In the first place, it had previously been shown that the electronic gain of the zero-order mode is larger than that of high-order modes when gain is restricted to two-thirds of the waveguide thickness, and the remaining one-third is kept lossy. In practice, this is realized by the LPE growth of a heteroboundary within the cavity such that (a) by the addition of a small amount of aluminum the band gap of the umpumped region is made larger (≈40 meV) than that of the gain region and (b) the umpumped region is doped with a donor concentration larger than the electron concentration in the gain region at lasing threshold. The second factor that is useful in maintaining zero-order-mode operation at high power levels is the use of a zero-order-mode antireflective (AR) coating that increases the mirror transmission loss for the undesired high-order modes. This zero-order-mode selective AR coating consists of layers of ZnS and Al2O3 whose thicknesses are accurately controlled to provide maximum transmission loss at some prescribed angle of emergence relative to the normal axis. Experimental results obtained on zero-order-mode large-cavity PpnN lasers substantiate these design considerations.
Photodetection by light-induced barrier modulation in Cu-diffused Au–CdS diodes
Authors: Lubberts G. , Burkey B. C. , Bücher H. K. , Wolf E. L.
Published: February 2004

Modified Schottky barriers of the type Au–CdS : Cu were prepared by diffusing Cu to a depth of 0.1–0.2 μm into single crystals of CdS, prior to evaporating rectifying Au contacts. The electronic and photoelectronic properties of these junctions are adequately described by a simple model in which the Cu acts as an ionized acceptor, resulting in a ``humped'' potential barrier between the Au and the bulk CdS. Hole trapping by the acceptors under band-gap illumination reduces their ionization and, consequently, the hump height. The forward current density in the dark and under illumination can be accurately described by a thermionic emission model as J=A*T2 exp {—e[VB+VH(0)]/kT exp}(eV/βkT), where the hump potential VH (0) is light sensitive and where β (1<β<1.35) arises from a weak voltage dependence of the barrier height. Barrier height determinations, in the dark and under illumination with 5000-Å light, by means of internal photoemission, thermal activation energy, and J-V measurements unequivocally show that under saturating light conditions the hump in the potential barrier is reduced by 0.23±0.03 V. This barrier mechanism of photoconductive response results in steady-state electron/photon gains in excess of 106 at light intensities lower that 5×1011 photons cm−2 sec−1, where response times exceed 1 sec.
Nitrogen concentration in GaP measured by optical absorption and by proton-induced nuclear reactions
Authors: Lightowlers E. C. , North J. C. , Lorimor O. G.
Published: February 2004

A method is described for the determination of the nitrogen concentration in GaP crystals from optical absorption measurements. The method has been calibrated by measuring the absolute nitrogen concentration by nuclear reaction quantitative analysis in the same samples for which the optical absorption was measured. The relationships between the nitrogen concentration, the integrated absorption of the A line (2.3172 eV), and the optical absorption at Ax (2.3275 eV) at 4.2°K are given by [N] cm−3=8.5×1014∫αA d E=3.4 ×1016αAx, where α is measured in cm−1 and d E in meV. Previous formulas which have commonly been used to determine the nitrogen concentration in terms of optical absorption overestimate the nitrogen concentration by about a factor of 5. Also the application of these formulas has varied between laboratories. Section I describes the determination of nitrogen concentrations by nuclear microanalysis. Measurements have been made in the range from [inverted lazy s]5×1016 to [inverted lazy s]1018 cm−3 in GaP grown by the liquid encapsulated Czochralski process in a nitrogen-pressurized crystal puller and in nitrogen-doped GaP grown by liquid phase epitaxy at [inverted lazy s]1000°C. Two distinct charged-particle techniques have been employed. In crystals containing nitrogen of normal isotopic composition, the 14N concentration was determined by proton activation using the reaction 14N(p,α)11C with proton energies in the range 6–10 MeV. The reaction product, 11C, was chemically separated after irradiation. The 11C is a positron emitter, and the γ rays from the positron annihilation were measured. Boron interference through the reaction 11B(p,n)11C was independently determined by measuring the prompt α-particle emission from the reaction 11B(p,α1)8Be*→2α2 during irradiation with 685-keV protons. In 15N-doped LPE layers, the 15N concentration was determined by measuring the prompt α-particle emission from the reaction 15N(p,α)12C during irradiation with 685-keV protons. Section II describes the optical absorption measurements and the correlation with the nuclear measurements. The temperature dependence of the integrated absorption and the line shape of the A line have also been measured. For determination of the nitrogen concentration, the A-line absorption measurements should be made at a temperature at which the absorption line shape is amenable to accurate integration. The integrated absorption can then be corrected to its value at 4.2°K and the nitrogen concentration calculated from the above relationship.
Electron-beam-irradiated discharges considered for initiating high-pressure pulsed chemical lasers
Authors: Hofland R. , Lundquist M. L. , Ching A. , Whittier J. S.
Published: February 2004

Volumetric irradiation by a short-pulse electron beam has been used to trigger long-duration spatially uniform electric discharges in gas mixtures of He and F2 or SF6. Uniform energy deposition to 300 J/liter has been observed for atmospheric F2–He mixtures at nominal electron-beam currents of 3 A/cm2 and discharge currents up to 20 A/cm2. Operation suitable for efficient initiation of pulsed HF/DF chain lasers appears possible over a wide range of E/N and mixture ratios, limited by breakdown at large E/N and negligible field enhancement at low E/N. Approximate analytical plasma models are presented and used in conjunction with time-resolved afterglow current measurements to obtain rate constants for F−-ion F2+−ion recombination and F2+−ion electron recombination. Estimates of F2 dissociation fractions achieved in the experiments imply the possibility of scalable and efficient initiation of pulsed chemical lasers with such discharges.
Measuring rotationally symmetric potential profiles with an electron-beam probe
Authors: Black W. M. , Robinson James W.
Published: February 2004

An electron-beam probe has been developed to measure the potential profile of a plasma within a spherical grid structure which was designed to trap charged particles. The potential was obtained from observed deflections of a collimated beam of electrons incident upon the device at selected impact parameters. The beam consisted of conversion electrons of 62.2 and 84.2 keV from a Cd109 source. Deflections of the beam through the plasma were measured relative to the beam trajectory without voltage applied to the grids. A movable detector allowed angular resolution to within 0.08 deg for maximum deflections of 7 deg. The inversion of the nonlinear singular integral relating potential and deflection is accomplished in an iterative manner with appropriate series expansions about the singular points. Simulations using postulated potential profiles show this procedure to give accuracy typically better than 4% with 20 deflection samples. Beam deflection measurements in spherical electrostatic systems without plasma show this probe technique to be very accurate. For a variety of experimentally controlled plasma parameters, no measurable departures from electrostatic potential profiles were observed.
Stress waves generated in thin metallic films by a Q -switched ruby laser
Authors: Yang L. C.
Published: February 2004

Vacuum-deposited thin films of B, C, Mg, Al, Si, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Mo, Ag, In, Sn, Sb, Pt, Au, Pb, and Bi in several thicknesses, confined between glass substrates, were irradiated by a uniform Q-switched ruby laser beam. The laser pulse was 15 ns in duration, with a maximum energy of 5 J in an area 6.35 mm in diameter. The stress waves were studied using the piezoelectric response of X-cut quartz-crystal disks of the same diameter. The peak stresses are presented as a function of the energy fluence, with possible interpretations of the phenomenon.
Losses in laminar composite Nb3Sn at 60 Hz
Authors: Snowden D. P. , Meyer C. H. , Sterling S. A.
Published: February 2004

A detailed study has been made of the ac loss in cylindrical samples of Nb3Sn carrying a transport current at 60 Hz. Samples were prepared by a vacuum codeposition process. At low currents, up to 550 A/cm at 4.2 °K in some samples, the loss is dominated by a surface fluxoid pinning mechanism, varies no faster than the square of the current, and in many cases less rapidly, and is temperature independent. At higher currents, the loss is described by the critical-state model. Formation of the superconductor in cylindrical layers separated by another material provides enhanced bulk fluxoid pinning, thereby increasing the critical current density and decreasing the loss at high currents. The magnitude of the ac loss in this material up to 10–12 °K is comparable to that reported in niobium at 4.2 °K.
Refractive index of GaAs0.62P0.38 between 1.2 and 2.0 eV
Authors: Casey H. C.
Published: February 2004

The refractive index of GaAs0.62P0.38 has been determined from double-beam reflectance measurements. Near the peak emission energy of GaAs0.62P0.38 light-emitting diodes, the refractive index is 3.68.
Fluorescence quenching of the 4F3/2 state in Nd-doped yttrium aluminum garnet (YAG) by multiphonon relaxation
Authors: Liao P. F. , Weber H. P.
Published: February 2004

Quenching of the fluorescence from the 4F3/2 state (upper state of 1.06-μm laser transition) of YAG : Nd by multiphonon relaxation is investigated. Measurements of the temperature dependence of fluorescence lifetime and relative fluorescence efficiency are compared with an established model for multiphonon processes. An upper limit of 0.2 and a most probable value of 0.02 are obtained for the room-temperature efficiency of this quenching process.
Optical reflectivity of aggregated silver surfaces—MG approach
Authors: Tokarsky R. W. , Marton J. P.
Published: February 2004

A simple working model is formulated to describe the reflectivity of aggregated Ag surfaces. It is based on the Maxwell Garnett film theory and compared to specially fabricated films representative of rough surfaces. Experimantally determined aggregate dielectric constants are used in the model and point to possible errors in the use of bulk values for such surfaces. Particular aggregated surfaces are shown to correspond closely to surface plasmons. The model is suggested to be applicable to other metals and alloys.
Magneto-optics and motion of the magnetization in a film-waveguide optical switch
Authors: Tien P. K. , Schinke D. P. , Blank S. L.
Published: February 2004

We discuss magnetic properties of iron-garnet films and the use of these films as film-waveguide optical switches. Our experimental study involves the observation of magnetic domains, measurements of Faraday rotation constants, coercive forces and anisotropy fields, and a detailed investigation of the switching process between 0 and 300 MHz. Our theoretical study includes magneto-optics in film waveguides, and analysis of the serpentine circuit, and an extensive calculation of the motion of the magnetization. For low driving fields, the process of optical switching is the formation of periodic domains and the subsequent motion of domain walls. For higher driving fields, the process is rotation of the magnetization in unison. The switching field required for 100% modulation is several times the anisotropy field in the film, which can be as small as 0.1 Oe.
Domain wall motion in Ga: YIG films
Authors: de Leeuw F. H.
Published: February 2004

The motion of an isolated straight magnetic domain wall established in a Ga : YIG film (Y2.9La0.1Fe3.8Ga1.2O12) by a gradient field of 2.4 kOe/cm and driven by a homogeneous pulse field Ho is studied experimentally. The measurements are performed at different pulse fields in the presence of a static field of 400 Oe in the plane of the film. At low pulse fields (Ho ≤4.1 Oe), the reduced Landau-Lifshitz damping constant and the wall mobility are obtained λ/γ2 = (2.9 ± 1.2) × 10−9 Oe2s and μ=(1.4±0.4)×104 cm/s/Oe, respectively, from the fit with numerical solutions of the Landau-Lifshitz-Slonczewski (LLS) equations of wall motion. At pulse fields Ho >4.1 Oe, it is found that the wall velocity reduces within a few nanoseconds to a constant value of 110 m/s when a ``critical'' velocity of about 400 m/s is reached. The critical velocity is lower than the peak wall velocity from the LLS formalism by a factor of 2.4 and is reached after 15–40 ns of wall motion, depending on the pulse field.
Correlation functions for predicting properties of heterogeneous materials. I. Experimental measurement of spatial correlation functions in multiphase solids
Authors: Corson Peter B.
Published: February 2004

Recent interest in the use of statistical continum theories to predict the properties of heterogeneous materials has created a need for experimentally measured spatial correlation functions related to the geometries of microscopic phases. This paper describes an experimental method for the measurement of such spatial correlation functions. The method consists of taking microphotographs of material cross sections and generating statistical data from the microphotographs. The data developed may be used to construct correlation functions of any order. Statistical checks on the quality of the data are also presented.
Small-angle scattering of x rays from groups of nonrandomly oriented ellipsoids of revolution of low concentration
Authors: Hamzeh F. M. , Bragg R. H.
Published: February 2004

The small-angle scattering from low concentrations of ellipsoids of revolution is examined. For monodisperse ellipsoids having axes of 2a, 2a, and 2b and a fixed common orientation, it is shown that the scattering is equivalent to that of a ``Guinier sphere'' whose radius is H = (a2 sin2γ + b2 cos2γ)1/2, where γ is the angle between the axis of symmetry and the plane of observation. This affords a simple geometric interpretation of the ``average inertial distance'' of Guinier and also of the quantity analagous to the surface area in the Porod approximation. By analyzing the experimental data in the Guinier region for γ=0 and π/2, independent determinations of a and b are obtained. Comparisons of the data in the Porod region provide an independent determination of a/b. For ellipsoids having an orientation distribution described by a probability function, the scattering is equivalent to that of a group of Guinier spheres of radii in the range a to b. The general case of ellipsoids having both an orientation and size distribution is also treated. Methods of correction for beam height and the interpretation of experimental data are presented, along with an application to oriented inhomogeneities in pyrolytic graphite.
Electron avalanche and surface charging on alumina insulators during pulsed high-voltage stress
Authors: Brainard J. P. , Jensen Dal
Published: February 2004

This paper describes a model for insulator surface charging in high-voltage ceramic vacuum diodes. The model involves electron emission from the insulator-cathode-vacuum junction followed by electron avalanches on the insulator surface which leave the wall positively charged. Experiments were performed to measure (i) the triple-junction (cathode-vacuum-insulator interface) emission and its relation to the initiation of the avalanche, (ii) the dynamic current in the avalanche, and (iii) the saturated surface charge resulting from the avalanche. The experimental results were interpreted by computer simulation in terms of the model and were found to be in close agreement with the predictions.
Nonlinearly generated harmonics and attenuation of Rayleigh waves on crystalline quartz
Authors: Gibson John W. , Meijer Paul H. E.
Published: February 2004

Measurements have been made of the nonlinearly generated harmonics and attenuation of Rayleigh acoustic surface waves at microwave frequencies on crystalline quartz. The Rayleigh waves were generated using an interdigital transducer deposited on the x-z surface of the quartz crystal aligned so that the surface wave propagates in the pure-mode x direction. Attenuation coefficients α were measured using the laser diffraction technique at frequencies of ∼160, ∼280, and ∼492 MHz with resulting typical values of α=0.083 dB/μsec, α=0.206 dB/μsec, and α=0.812 dB/μsec, respectively. These results agree with previously reported values and with theoretical predictions. The growth and decay of nonlinearly generated harmonics of Rayleigh waves with a fundamental frequency of 281 MHz were observed also using the laser probe technique. A description of the variation of the Rayleigh waves' intensity for each of the three harmonics observed is provided by a set of coupled amplitude equations modified to include dispersion effects. It was not possible to describe the data using the coupled amplitude equations without including terms containing dispersion. Surface imperfections are assumed to be responsible for the dispersion as well as to contribute to the residual values for the attenuation coefficients. The small amount of dispersion needed for a good fit is determined. The nonlinearities are characterized by a set a nonlinear coefficients Γ. A computer program was written in order to solve the coupled amplitude equations and to determine a set of Γ values which provide a best description of the experimental data.
The column of a dc arc burning in a metal halide atmosphere
Authors: Fischer E.
Published: February 2004

Starting from energy and mass balance (diffusion equation), temperature distributions and plasma compositions are calculated for metal halide discharges in closed cylindrical vessels with and without mercury (buffer gas). Special interest is given to arcs in tin halide atmospheres. While for pure tin halide discharge radiation can be neglected, the energy transfer by radiation must be considered in discharges containing larger amounts of mercury. The results obtained for electrical data as well as for thermal data of Sn–I arcs are in reasonable agreement with the experiments.
Crystallization of amorphous selenium films. II. Photo and impurity effects
Authors: Kim K. S. , Turnbull D.
Published: February 2004

Superposition of illumination with white light on thermal treatments of amorphous films, formed by deposition of high-purity Se on mica, had the following effects on crystallization: (i) interface cylindrites thickened much more rapidly but their radial growth rates were not detectably changed; (ii) the number density of interface cylindrites was sharply increased—this result may signify that the transition of single to cylindritic crystals, and not necessarily primary nucleation, is photoenhanced; (iii) surface cylindrites grew at much higher radial rates and developed a concentric ``hill-and-valley'' surface topology. The radial growth rates of interface cylindrites were reduced markedly by small amounts of certain impurities (e.g., Te or As) in the films and they are photoenchaned but not to the rates in the highest-purity films without illumination. In general, our results suggest that the primary effect of photoillumination on the crystal growth rates was to reduce the restraining action of impurities and mechanisms for this are considered.
Ignition of laser detonation waves
Authors: Steverding B.
Published: February 2004

The ignition of laser-supported detonation waves is caused by the thermomechanical response of the target. The blown-off material acts as an accelerating piston creating a shock wave in air. The small amount of free electrons created by the shock wave is cascaded to plasma densities by light absorption. The theory explains a number of conclusions which have been experimentally verified. Numerical results agree with observed data.
Growth and properties of CdS epitaxial layers by the close-spaced technique
Authors: Yoshikawa Akihiko , Sakai Yoshio
Published: February 2004

CdS layers were epitaxially grown on GaAs in an atmosphere of hydrogen gas by the close-spaced technique. Then the thermodynamics of the reaction, the morphology, and electrical properties of the CdS epitaxial films were studied. Examinations of the temperature dependence of the evaporation rate of source CdS powder, of film growth rates, and of surface morphology demonstrated that the growth kinetics are between the mass-transfer control case and the surface-reaction control case, but closer to the former. The electrical properties of the films were greatly influenced by growth conditions, especially by substrate temperature. Film resistivity increased from 10−3 to 1 Ω cm as a function of substrate temperature, and the carrier concentration in the film increased exponentially as the temperature of the substrate was raised: Carrier concentration = 1.31×1029 exp (−1.98/kTsub) cm−3. The dominant donor species in CdS films was shown to originate from the autodoping of Ga by the GaAs substrate. Electron mobility in the films also increased as the temperature of the substrate was raised, which was attributed to the superior crystallinity in the films grown at a rather high substrate temperature.
Effect of cubic, tilted uniaxial, and orthorhombic anisotropies on homogeneous nucleation in a garnet bubble film
Authors: Hubert A. , Malozemoff A. P. , DeLuca J. C.
Published: February 2004

We have studied domain nucleation phenomena in a (111)-oriented garnet bubble film in the presence of in-plane fields. From visual observations we have found that as the in-plane field is lowered from saturation, a homogeneous stripe nucleation occurs at a critical easy axis bias field H∥n, leading to a ``mixed polarity state'' at remanence. For bias fields different from H∥n, inhomogeneous bubble nucleation occurs which is dependent on the defect distribution in the sample and which can give rise to a bubble lattice at remanence. The bias field H∥n depends on the azimuthal angle φ of the in-plane field in the sample plane; it has threefold (cos3φ) and onefold (cosφ) symmetry components which can be related to cubic and tilted uniaxial anisotropy, respectively. The tilt of the uniaxial anisotropy is found to be along the same direction as, but significantly larger than, the actual tilt of the crystallographic axis, perhaps indicating a large sensitivity of growth anisotropy to misalignment. An orthorhombic anisotropy component is observed in the in-plane nucleation field. These results are compared to the results of photometric measurements of the type previously proposed by Shumate, Smith, and Hagedorn, and by Krumme, Hansen, and Haberkamp. A phase theory, modified to include finite-thickness effects phenomenologically, is developed to determine the conditions for second-order (stripe) nucleation in the presence of cubic, tilted uniaxial, and orthorhombic anisotropy. Analytical expressions are found for H∥n which can be used to evaluate the anisotropies from the data. The results are consistent with independent measurements of these anisotropies on the same specimen.
Correction to the velocity-per-fringe relationship for the VISAR interferometer
Authors: Barker L. M. , Schuler K. W.
Published: February 2004

A Doppler shift in wavelength can result in a very slight change in the index of refraction of a transparent material due to disperison. This effect, if not accounted for, produces an error of a few percent in the velocities determined using the recently developed velocity interferometer for diffusely reflecting surfaces.
Twinning of Zn and Sn during ultrasonic deformation
Authors: Jon M. C. , Beshers D. N. , Mason W. P.
Published: February 2004

Zn and Sn have been deformed plastically by an ultrasonic system operating at 22.5 kHz. The amplitude dependence of the internal friction was correlated with the presence or absence of twins. Friedel's relation between the dimensions of a twin formed in a burst from a single source was found to hold for Zn but not for Sn. Assuming that each twin forms during a single stress pulse, the rate of operation of a Frank-Read source is found to be physically reasonable for Zn, with a dislocation velocity approaching the speed of sound, but too high for Sn. We conclude that the assumption that twins form in a single burst is justified for Zn, giving a linear growth rate ≳3×102 m/sec, but not for Sn, implying a slower growth rate.
Oxidation of Nb as studied by the uv-photoemission technique
Authors: Lindau I. , Spicer W. E.
Published: February 2004

The initial stages in the oxidation of Nb have been studied by the uv-photoemission technique for photon energies below 12 eV. Changes of structure in the electron distribution curves for different oxygen exposures and temperatures are correlated with formation of different types of Nb oxides. Electronic structure changes due to formation of at least three different oxides or mixtures of oxide have been observed. NbO2 and the NbO oxides seem to form first as a thin protective layer. The pentoxide, Nb2O5, is obtained after heavy oxidation. Practical implications of the formation of NbO in the interface between Nb2O5 and Nb metal are discussed.
SEM observation and contrast mechanism of stacking faults in an epitaxial silicon layer
Authors: Kato T. , Koyama H. , Matsukawa T. , Shimizu R.
Published: February 2004

The stacking-fault tetrahedron in an epitaxial Si layer was observed in the electron-beam-induced current mode using the scanning electron microscope. The contrast mechanism involved in the stair-rod partial dislocations of the stacking-fault tetrahedron was analyzed on the basis of a simplified model. The calculation seems to fit the experiment since good agreement was obtained between the observed and calculated results.
Structure of vapor-deposited GaxIn1−xAs crystals
Authors: Nagai Haruo
Published: February 2004

Deformation of the crystal lattice of layers of GaxIn1−xAs (0.5 < x < 1.0) grown onto GaAs substrates by a chemical vapor deposition process was investigated. For this study, Ga and In were transported as chlorides with HCl and AsH3 was the source of As. It was observed that the lattice constant along the direction of the film thickness was larger than that along the surface. This fact indicates that the crystal lattice of GaxIn1−xAs is compressed along the substrate surface as a result of lattice mismatch. The influence of both the composition of the epitaxial layers and the crystal plane of the substrate surface on the degree of this deformation was investigated. It was also found that the epitaxial orientation grew inclined to the substrate crystal when the crystal surface of the substrate was {100} or {110}.
Microparticle-initiated vacuum breakdown—Some possible mechanisms
Authors: Menon M. M. , Srivastava K. D.
Published: February 2004

It is known that micron- and submicron-sized metallic particles are released from the electrode surfaces when a vacuum gap is subjected to a high dc stress. It is also well known that larger particles (> 10 μm) are generated within the interelectrode gap when a vacuum gap is subjected to conditioning or severe prebreakdown current flow. This paper examines the role of such particles in inducing the breakdown of a vacuum gap. While the larger particles induce breakdown by way of a trigger discharge, it is shown that the smaller particles can initiate breakdown because of effects associated with impact. The various effects associated with the high-speed impact of a metallic microparticle on a target electrode, viz., cratering, production of metal vapor, and production of thermally generated plasma and their relative significance on vacuum breakdown, are examined.
Thermionic emission of boron- and lanthanum-coated boron filaments
Authors: Wolff E. G.
Published: February 2004

Thermionic emission from boron filaments exposed to a lanthanum metal vapor flux was studied with a view towards development of filamentary lanthanum hexaboride (LaB6) emitters. The emission was continually monitored in both stationary and continuous coating processes. A Richardson plot of uncoated-boron-filament emission data yields φ = 4.38 eV and A = 22 A/cm2°K2 for the temperature region 1550–1855°K. Current densities equivalent to LaB6 emission were obtained for optimally coated filaments. Coated-filament strength data, possible reaction mechanisms, and potential process limitations are also presented.
Properties of Zn-doped GaN. II. Photoconductivity
Authors: Pankove J. I. , Berkeyheiser J. E.
Published: February 2004

A drastic change is observed in the electron concentration and in the photoconductivity spectrum of GaN as the Zn concentration is increased. The photoconductivity peak shifts to higher energies by about 70 meV, the exponential edge of the spectrum steepens by a factor of 3, and the sensitivity to visible radiation disappears. These changes are tentatively attributed to an abrupt decrease in bandtailing when Zn preferentially occupies N sites above a critical Zn concentration.
Rapid degradation phenomenon in heterojunction GaAlAs–GaAs lasers
Authors: Petroff P. , Hartman R. L.
Published: February 2004

The rapid degradation phenomenon in Ga1−xAlxAs–GaAs DH lasers has been associated with the growth of a dislocation network during the device operation. The nature of these defects has been analyzed by transmission electron microscopy in an effort to understand their origin and growth mechanism. The propagation of the dislocation network is found to take place by successive climb of a dislocation crossing the n-Ga1−xAlxAs, p-GaAs, and p-Ga1−xAlxAs layers in the stripe area. The climb process leads to the formation of a three-dimensional dislocation dipole network which extends through the three epitaxial layers and remains confined to the stripe area. A tentative model which discusses the network growth process is presented. The source of the very large vacancy concentration involved in the climb process has been attributed to the interfaces between the binary and ternary layers. The fast climb rate has been related to large drift forces acting on the vacancies during the device operation. The dominant drift forces are thought to be electrical and elastic in nature.
Grain boundary diffusion and growth of intermetallic layers: Nb3Sn
Authors: Farrell H. H. , Gilmer G. H. , Suenaga M.
Published: February 2004

A study of the formation of Nb3Sn layers at the junction of pure Nb and a Cu–Sn alloy is presented, and the effect of grain boundary diffusion on the kinetics of the formation of the layers is assessed. Data at 700–800 °C imply that the layer thickness increases with a t0.35 time dependence. This deviation from the usual t1/2 law for a process whose rate is limited by volume diffusion through the growing layer had previously been explained using analytical expressions for grain boundary diffusion into a semi-infinite crystal. A numerical analysis of grain boundary diffusion with geometry appropriate to an intermetallic layer is presented, and the results imply that a fixed array of grain boundaries in the layer cannot cause appreciable deviation from a t1/2 law for most systems. The flux to the growth interface required to form the layer normally causes the diffusion processes in the layer to approach steady-state conditions, which, in the case of fixed boundaries, precludes a large deviation from the t1/2 law. Scanning electron micrographs of the layer at various stages of growth show that the average grain diameter increases with time at an appreciable rate. The measured grain growth rate is used in a simple steady-state layer growth expression to obtain a description which agrees with the experimental measurements. Other factors which can influence the formation rate of intermetallic layers are discussed.
Bubble domains in double garnet films
Authors: Lin Y. S. , Grundy P. J.
Published: February 2004

The properties of bubble domain lattices in magnetostatically coupled double garnet films are investigated. The calculated static properties of bubble lattices in both single and double garnet films are compared with the results of experiments on three double-film composites. The differences in behavior between the three composite structures, chosen to exhibit varying degrees of magnetostatic coupling, are explained quantitatively in terms of the interaction fields between bubble domains in the two magnetic films. The dependence of bubble diameter on the applied bias field has been investigated experimentally and agreement with theory is good. Stable bias field ranges for bubble lattices are also examined. Effects such as the ordering of double-bubble lattices, changes in bubble size upon coupling, and experimental observation of bubble repulsion and attraction effects are explained qualitatively. Some results on novel stacking arrangements of overlying bubble lattices and the dependence of bubble spacing in a lattice on the method of generation are briefly discussed.
Uranium Monosulfide. The Ferromagnetic Transition. The Heat Capacity and Thermodynamic Properties from 1.5° to 350°K
Authors: Westrum Edgar F. , Walters Robert R. , Flotow Howard E. , Osborne Darrell W.
Published: February 2004

The heat capacity of uranium monosulfide was measured from 1.5° to 22°K by an isothermal (isoperibol) method and from 6° to 350°K by an adiabatic technique. The ferromagnetic transition at 180.1°K has a characteristic lambda shape and associated magnetic ordering entropy and enthalpy increments of 1.62 ± 0.2 cal °K−1mole−1 and 231 ± 20 cal mole−1, respectively, over the temperature range 0° to 230°K. The correlation of the thermal data with magnetic studies is discussed. The heat capacity below 9°K is represented by Cp = 5.588 × 10−3T + 2.627 × 10−4T3 / 2 + 6.752 × 10−5T3cal °K−1mole−1, in which the successive terms represent conduction electronic, magnetic, and lattice contributions. Values of the entropy [S°], enthaply function [(H° − H°0) / T], and Gibbs-energy function [(G° − H°0) / T] are 18.64 ± 0.005, 8.94 ± 0.002, and − 9.70 ± 0.02 cal °K−1 mole−1, respectively, at 298.15°K. The Gibbs energy of formation at 298.15°K is − 72.9 ± 3.5 kcal mole−1.
Phase Transition and Surface Tension in the Quasichemical Approximation
Authors: Parlange Jean-Yves
Published: February 2004

The statistical formulation of phase transition is derived for a three-dimensional Ising model using Guggenheim's approximation. As the temperature approaches the critical temperature, the difference equations governing the transition can be replaced by differential equations, easily integrated. Comparisons are made with the Cahn-Hilliard continuum model, and criticisms of that model by Widom are also examined.
Raman Spectral Studies of HDO in H2O
Authors: Walrafen G. E.
Published: February 2004

Argon-ion-laser and mercury-excited photoelectric Raman spectra have been obtained from a 6.2M solution of D2O in H2O in the temperature range of 16°-97°C and at frequencies from 2000-3000 cm−1. Examination of the OD stretching contours observed near 2500-2600 cm−1 revealed marked asymmetry, and a high-frequency shoulder was apparent in all cases. In addition, an isosbestic point was found at 2570 ± 5 cm−1.

The OD stretching contours were analyzed by means of a special-purpose analog computer, and two Gaussian components near 2510-2540 and 2630-2660 cm−1 were found to provide adequate fits of the contours in the temperature range involved, although some indication of a third weak Gaussian Raman component was found, and three Gaussian components were employed to fit the infrared-absorbance contours also obtained in this work. The integrated Raman intensities of the two principal Gaussian components were observed to have opposite temperature dependences, and the component intensities yielded a value of 2.5 ± 0.6 kacl/mole for the van't Hoff ΔH° associated with the disruption of one O–D···O unit in good agreement with the O–H···O values of 2.8 kcal/mole obtained from previous Raman studies of water and 2.4 kcal/mole obtained by Worley and Klotz from near-infrared studies of HDO in D2O. The presence of asymmetry in the form of a pronounced high-frequency shoulder, and of an isosbestic point, constitute the principal experimental observations indicating that the OD stretching contours observed in the Raman spectra are composed of two or more components. The opposite temperature dependences of the integrated Raman intensities of the principal Gaussian components considered to comprise the OD stretching band, the resulting ΔH° value, and agreements between ΔH° values from various methods provide additional support for the two-state model of water structure. No evidence was obtained in support of the continuum model proposed by some workers.
Magnetic Susceptibility and Nuclear Magnetic Resonance Studies of Transition-Metal Monophosphides
Authors: Scott B. A. , Eulenberger G. R. , Bernheim R. A.
Published: February 2004

The magnetic susceptibilities of the transition-metal monophosphides TiP, ZrP, HfP, VP, NbP, TaP, and CrP were measured between 78° and 400°K. Susceptibilities ranged from − 0.70 × 10−6 cg/gm for TaP to 3.4 × 10−6 cg/g in CrP. Although small temperature variations of χ were observed in some cases, magnetic ordering was absent in these materials over the temperature range investigated. Shifts of the 31P magnetic resonance relative to 85% H3PO4 were all to higher frequency (lower applied field) for the Group IVa and Va monophosphides, and temperature independent, varying from 0.001% in HfP to 0.059% for TiP. On the other hand, the 31P resonance in CrP exhibited an indirect Knight shift of K(297°K) = − 0.149% which varied linearly with bulk magnetic susceptibility. From K(T) vsχ (T) data a value of − 30 ± 3 kO/Bohr magneton was obtained for the phosphorus hyperfine field in CrP. Metal resonance shifts and quadrupole splittings were also measured in 51VP and 93NbP. Magnetic susceptibility results are shown to be consistent with the qualitative features of Goodenough's model in which narrow cation d bands lie in the energy gap between broad metal-phosphorus valence and conduction bands. The NMR findings in CrP and the isomorphic compounds MnP, FeP and CoP studied by previous workers suggest appreciable covalent mixing of phosphorus 3d± states with cation t2g sublattice bands, and support the concept that the eg states are collective in the monophosphides.