bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface acoustic waves with nearly dispersion-free propagation in a layered silicon configuration
Authors: Davis K. L.
Published: February 2004

Calculations have been made for the surface-wave velocity and the piezoelectric coupling constant in the multilayered system consisting of an Al2O3 film and a piezoelectric ZnO film on a silicon substrate. It was found that the addition of an Al2O3 film to the ZnO-on-Si configuration substantially reduced the surface-wave dispersion over a range of normalized acoustic wave numbers. A specific example considered gives phase-velocity variations of less than 0.8% over a 40% acoustic bandwidth, and less than 0.08% over a 10% acoustic bandwidth.
Ignition of hydrocarbons and the thermalization of electrical discharges
Authors: Barreto E. , Reynolds S. I. , Jurenka H.
Published: February 2004

Using propane-air mixtures, it is shown that the minimum ignition energy corresponds precisely to the amount that produces, in the discharge channel, the electron density (1017 cm−3) that changes the discharge from a cold streamer to a hot incipient arc. This electron density together with the minimum quenching distance are suggested as a physically meaningful criterion for ignition. The procurement of the critical electron density is also studied using a polyester film and water as examples of solid and deformable dielectric electrodes. It is found that thermalization is controlled by the rate of supply of charge into the discharge channel and that a stored minimum energy value applies only when two metal electrodes are involved. Ignition capability can be determined by the characteristics seen in the oscilloscope recordings of the current in the discharge. Electrode conduction effects are studied by varying the conductivity of a saltwater solution. It is found that either surface-charge accumulation or resistive effects may prevent ignitions depending on the conductivity of the solution. Also, that except for metals, ignitions are always invariably associated with nonuniform electric fields and the procurement of electrons by cold-streamer discharges. In the better dielectrics, surface charges prevent ignition independently of the energy supply. However, these same charges may be stored for a long time (days) and produce ignitions at very low voltages with polarity reversals. Finally, local thermalization is suggested as a necessary requirement for the propagation of long sparks characterized by stepping.
Acoustic wave propagation along a fluid-filled cylinder
Authors: Peterson Edward W.
Published: February 2004

Phenomena of elastic wave propagation from a point source located in a fluid-filled cylinder are investigated. Detailed consideration is given to the natural mode wave propagation for either fluid or elastic solid surroundings of infinite extent. Phase and group velocity dispersion curves are presented and the relative modal sensitivity, interference pattern, and decay rates are determined for typical sources having various dominant wavelengths. Curves showing actual waveforms including both axial and radial dependence are also presented for this coupled system.
Strain-amplitude-independent dislocation damping
Authors: Read M. P. , Brailsford A. D.
Published: February 2004

The equation of motion of a dislocation segment is derived and its solution used to determine the contribution to the absorption of energy from an incident sound wave. It is shown that, in a representation based upon the normal modes of an extensible string, neither the line tension nor effective mass of the of the dislocation is diagonal, and the numerical values of the low-index elements of these matrices are given. It is found, however, that this mode coupling has a negligible effect on the absorption. Additionally, for a distribution of segments of random length, the present analysis is shown to yield results in quantitative agreement with the predictions of the string model of Koehler and Granato and Lücke.
Carrier concentration and diffusion length measurements by 8-mm-microwave magnetophotoreflectivity in germanium and silicon
Authors: Fortini André , Lande Richard , Madelon Roger , Bauduin Philippe
Published: February 2004

The photoinduced reflectivity of millimeter waves (34 GHz) was measured as a function of an applied longitudinal magnetic field in Ge and Si samples. The results are analyzed with a detailed calculation of the magnetophotoreflectivity in a medium of exponentially decreasing conductivity. The comparison leads to consistent values of the excess carrier density near an illuminated surface, and of the diffusion length of minority carriers. With some further refinements the method could be of great interest in semiconductor technology.
Coupled-wave equations with three or more elements
Authors: Denger L. A.
Published: February 2004

An investigation has been made regarding the theoretical possibility of involving two or more spurious modes in the study of overmoded transmission systems. This is a departure from previous works as it considers more than one spurious mode in a more general manner.
Defect centers in a germanium-doped silica-core optical fiber
Authors: Friebele E. J. , Griscom D. L. , Sigel G. H.
Published: February 2004

The radiation-induced defect centers in a low-loss Corning germanium-doped optical fiber have been studied. In addition to silicon E′ centers, four germanium-related centers, corresponding to electrons trapped at the site of oxygen vacancies in s p3 orbitals of germanium ions with zero to three next-nearest-neighbor germaniums, were observed. A model which assumes Gaussian distributions in the excited-state energy-level splittings has been successfully used to computer simulate the ESR spectrum of the irradiated fiber.
(GaAl)P optical-waveguide modulators fabricated by liquid-phase epitaxy
Authors: Kleinknecht Hans P. , Widmer Alois E.
Published: February 2004

Single- and double-heterojunction structures of (GaAl)P have been grown by liquid-phase epitaxy using a rotary multiple-bin jig of alumina. A purity corresponding to net donor concentrations as low as 2 × 1016 cm−3 has been reached, and flat plane-parallel layers as thin as 1.5 μm have been made. p-n junctions were produced by doping with Mg during growth or by diffusion of Zn. These structures have been used as waveguides for 0.6328-μm light. The application of a reverse voltage produces an electro-optic modulation with retardations of about 90°, which corresponds to 70% intensity modulation. The measurements were done with edge-on coupling through flat faces cleaved perpendicularly to the guide plane. A special technique is used to eliminate the unguided background light from the result. The magnitude of the measured modulations agrees fairly well with simple theory. There is also good agreement with respect to the dependence of the modulation on geometry and, to a lesser degree, on voltage.
A flashlamp-pumped YAG : Nd3+ waveguide laser
Authors: Möckel P. , Oberbacher R. , Rauscher W.
Published: February 2004

YAG : Nd3+ waveguides of dimensions 50 mm by 4 mm by 30 μm, each optically contacted with a glass substrate, were realized by grinding and polishing. The effective refractive indices measured for the waveguide modes at the 0.6328-μm wavelength agreed well with theory. By coating the plane-parallel polished endfaces of one of the waveguides with dielectric mirrors, a YAG:Nd3+ waveguide laser was produced; the threshold of this laser in pulsed operation was 10 J. The pump efficiency (inversion density per pump energy) for this laser was estimated at η> 1012/J mm3, a value which is of the same order of magnitude as that for conventional YAG : Nd3+ lasers pumped in comparable pump systems.
Amorphous bismuth-germanium thin films: Infrared detector characterization
Authors: Vass R. W. , Anderson R. M.
Published: February 2004

Thin films of bismuth-germanium have been fabricated in vacuum by the method of codeposit vapor quenching. In this paper, the third of a three part series, the evaluation of a select set of amorphous bismuth-germanium thin films as infrared detectors is reported. The evaluation indicates that a -Bix Ge1−x thin films possess moderate potential as a new amorphous infrared detector material. The Bix Ge1−x system is found to be photoconductive in the range 0≤x≤0.037. Signal, noise, and signal-to-noise—ratio data at 300 and 162 °K are reported for various alloy concentrations. A clear maximum in the signal-to-noise plots is observed indicating an optimum bias regime. Photoresponse versus optical chopping frequency data indicate response times on the order of 1–2 msec at room temperature and at 162 °K. The specific spectral detectivity Dλ* for an a -Bi1.74Ge98.26 film at T = 162 °K shows a maximum in the vicinity of 1 μ with a maximum value in the range 107–108 cm Hz1/2 W−1.
Solid composition and gallium and phosphorus vacancy concentration isobars for GaP
Authors: Jordan A. S. , Caruso R. , Von Neida A. R. , Weiner M. E.
Published: February 2004

Thermodynamic calculations are presented which provide explicit expressions for the combined temperature and phosphorus partial pressure dependences of the Ga- and P-vacancy concentrations in GaP. This work extends the applicability of earlier results for the vacancy concentrations, obtained by an analysis of the solidus data, from solid-liquid (i.e., LPE and LEC growth) to solid-vapor equilibria (vapor growth, annealing, and diffusion). The calculations are represented in the form of Ga- and P-vacancy concentration and solid-composition isobars. In addition, the previously established correlation between the reciprocal of the nonradiative shunt-path lifetime (1/τn) and the relative Ga-vacancy concentration for GaP crystals prepared by a variety of techniques is transformed into a correlation with absolute vacancy concentrations. The electron-capture cross section of a Ga-vacancy behaving as a shunt path in p -type material is estimated to be ∼4.5×10−17 cm2. Finally, the Ga-vacancy concentration isobars and the 1/τn correlation are discussed in the context of LPE, vapor growth, and annealing processes for GaP.
Effects of pressure on optically pumped GaSb, InAs, and InSb lasers
Authors: Menyuk N. , Pine A. S. , Kafalas J. A. , Strauss A. J.
Published: February 2004

The pressure dependence of the energy gap has been determined at 63 and 77°K for GaSb, InAs, and InSb by tuning their laser-emission frequencies with hydrostatic pressures up to 8 kbar. The pressure variation of mode frequency and refractive index has also been measured for each semiconductor. The laser threshold and emission intensity are essentially independent of pressure in GaSb and InAs. For InSb, however, the application of pressure dramatically decreases the threshold and increases both spontaneous and stimulated emission. A number of experiments have been performed to determine the cause of these pressure effects. The data are consistent with a mechanism involving nonradiative recombination between nearly overlapping bandtails within the energy gap which separate with pressure.
Effect of shock loading on transparency of sapphire crystals
Authors: Urtiew P. A.
Published: February 2004

Single-crystal sapphire was found to lose some of its original transparency in the near infrared (0.9 μm) when subjected to strong dynamic compression in the pressure range between 100–130 GPa (1–1.3 Mbar). Experimental evidence of this phenomenon is presented and discussed in relation to some of the other known properties of the crystal.
Mode conversion in periodically disturbed thin-film waveguides
Authors: Elachi C. , Yeh C.
Published: February 2004

Mode conversion in a periodically perturbed thin-film optical waveguide is studied in detail. Three different types of perturbations are considered: periodic index of refraction of the film, periodic index of refraction of the substrate, and periodic boundary. The applications in filters, mode converters, and distributed feedback lasers are discussed.
Holography of submerged objects
Authors: Palais J. , Biemer J. , Kaufman I.
Published: February 2004

Holograms of diffuse opaque objects which are submerged in water are difficult to obtain using a cw laser if the object is to be viewed from the top of the container. Experiments and theory are described which indicate that the major cause of the problem is excitation of unstable surface waves. When the object and container are on a stabilized table suitable for normal holography, these waves are excited by small residual oscillations of the table. Surface wave amplitudes can be of sufficient height and frequency to ruin the hologram. A simple solution to this problem is presented.
Effects of diffusion current on galvanomagnetic properties in thin intrinsic InSb at room temperature
Authors: Fujisada H.
Published: February 2004

Theoretical and experimental investigations have been made on the galvanomagnetic properties in very thin single-crystal InSb (4.6–26.4 μ in thickness) at room temperature, ranging from Ohmic to high-electric-field regions. Two kinds of surface are prepared by chemical etching and mechanical lapping. A transverse magnetic field of up to 15 kG is applied parallel to the surface of the samples to deflect intrinsic electrons and holes to one of the surfaces. The thin sample shows a small magnetoresistance in the Ohmic region, a linear electric field dependence of the conductance in a small electric field, and a current saturation in a high electric field. From these phenomena, bulk lifetimes and surface recombination velocities are estimated. It is shown that the bulk lifetimes and the saturation current can be explained by the Auger process. Surface recombination velocity of about 104 cm/sec for etched surfaces and of the order of 105 cm/sec for lapped surfaces are obtained. Theoretical calculations include the case of an intermediate magnetic field which is important for InSb at room temperature.
Ferrite prisms and lenses
Authors: Mueller R. S.
Published: February 2004

Microwave components incorporating ferrite elements are primarily waveguide devices. Success with these devices has yielded a wide range of useful commercial products. However an underdeveloped area for microwave ferrite application is microwave optics. Due to the complexity of design and observed anomalous behavior, ferrites have not found popularity as refraction elements. The present paper presents an initial assault into the analysis of refracting ferrite prisms and lenses. The anisotropic indices of refraction and angles of deviation were calculated for an isosceles ferrite prism magnetized in three orthogonal directions and the focal lengths of an axially magnetized thin double-convex ferrite lens were evaluated for various values of saturation magnetization.
Effects of high nonstoichiometry on EuO properties
Authors: Massenet O. , Capiomont Y. , Van Dang Nguyen
Published: February 2004

Electric, magnetic, and electron paramagnetic resonance (EPR) measurements have been performed on thin EuO films prepared either by reactive evaporation of Eu at 400°C or by oxidation of a Eu metal thin film at 200–250°C. The films obtained by reactive evaporation have electrical and magnetic properties very similar to those reported for EuO single crystals of various degrees of nonstoichiometry. The films prepared by oxidation of Eu films at 200–250°C are characterized by a much higher-valued Curie temperature (Tc≃148 K), while their resistivity is in the range 10−2−1 Ω cm. The EPR signal can be attributed to Eu spins, which shows that in these films there exist fluctuations of Eu doping due to nonstoichiometry. We analyzed the high concentration of oxygen vacancies in the bound magnetic polaron (BMP) model. A high level of defects and oxygen vacancies, inhomogeneously distributed in the film, can account for both their electrical and magnetic properties.
Magnetic order in Ni3Mn alloys
Authors: Patton Carl E. , Baker Glenn L.
Published: February 2004

Recent measurements reveal significant changes in the magnetic moment and superparamagnetic Curie point during the initial stages of atomic order in Ni3Mn alloys. The rate of increase of the induced moment at 8 kG and 300°K with annealing time at 400°C exhibits a discontinuity at about 1.5 h. The superparamagnetic Curie temperature is also found to increase from 145°K for the disordered alloy to 250°K after an extremely brief (20 min) anneal. These results show that significant atomic rearrangement is actually taking place rather quickly during the initial stages of ordering, contrary to the previously accepted model of homogeneous long-range-order development which saturates only after extremely long annealing times (1000 h or more), proposed by Marcinkowski and Brown. The discontinuity at 1.5 h is tentatively associated with the short-range-order saturation observed for anneals at higher temperatures, also at about 2 h, and the peak in the field-induced uniaxial anisotropy after 2 h of annealing.
Effect of thermal cycling on the magnetic domain structure of directionally solidified Co–Co3Nb eutectic
Authors: Arnson H. L. , Albright D. L.
Published: February 2004

Two groups of unidirectionally solidified Co–Co3Nb eutectic samples containing small differences in nickel content were analyzed for their magnetic domain structures using TEM. The two groups showed no observable domain structures in the as-solidified condition, but the group of samples containing the lower nickel content (<0.01 wt%) developed a strip-type domain structure when the samples were thermally cycled. When favorable crystallographic and defect structures existed, the thermal agitation of the heat treatment cycles was able to assist in nucleating the magnetic domain structures that were observed.
Scaling laws for flux pinning in Nb and NbTi multifilamentary conductors
Authors: Mathur M. P. , Ashkin M. , Deis D. W.
Published: February 2004

Magnetization measurements M(H,T) are made on several commercially drawn Nb–Cu and NbTi–Cu multifilamentary conductors as a function of applied magnetic field and temperature. The samples are distinguished by their filament sizes or the amount of cold work. From these measurements the pinning force Fp(H,T) and the critical current characteristics Jc(H) are deduced for all samples. Using this information Kramer's scaling laws for flux pinning in multifilamentary conductors were tested. It is found that the model with some reservations seems to account for most of the observed behavior in the Nb–Cu and NbTi–Cu systems.
Exact solution of electrostatic problem for a system of parallel cylindrical conductors
Authors: Alessandrini V. , Fanchiotti H. , Canal C. A. García , Vucetich H.
Published: February 2004

The problem of the calculation of the electric field distribution of a system of infinite parallel cylindrical conductors in the presence of a grounded plane is reexamined. The exact solution of a class of two-dimensional harmonic problems in multiply connected domains proposed by Burnside in 1893 is reviewed. This is shown to agree with recent generalizations of the method of images. An improved version of the exact solution which is more convergent than the conventional methods when the conductors are very close to one another is presented. The potential usefulness of the theoretical ideas and the mathematical apparatus used here for technological applications is emphasized.
Thick specimens in the CEM and STEM. I. Contrast
Authors: Crewe A. V. , Groves T.
Published: February 2004

Calculations have been performed on the contrast available in thick specimens. Ten modes of operation have been considered, six in the conventional electron microscope (CEM) and four in the scanning transmission electron microscope (STEM). Electrons passing through the specimen fall into four categories, elastically scattered, inelastically scattered, unscattered, and those scattered both elastically and inelastically. For the various operation modes these groups are taken in combinations to form practical signal intensities. In the calculation of practical intensities, the angular distribution of plurally scattered electrons is considered. The fraction of each scattered group passing through the microscope aperture has been calculated for various types of illumination. The practical intensities are used to calculate the contrast available in stained and unstained specimens. For very thick specimens bright field offers the best combination of contrast and signal intensity. Other contrast modes show a reversal in the sign of contrast for thicknesses close to one mean free path for elastic scattering. The equations for signal intensity and contrast are quite general, and apply to all values of voltage and instrumental resolution.
Thermal expansion of tetrathiofulvalinium tetracyanoquinodimethane
Authors: Cook J. W. , Glocker D. A. , Skove M. J.
Published: February 2004

The thermal expansion along the growth axis of crystalline TTF-TCNQ was determined between 5 and 300 K. The total change in length over this range was found to be approximately 3%.
Subthreshold velocity-field characteristics for bulk and epitaxial InP
Authors: Majerfeld A. , Potter K. E. , Robson P. N.
Published: February 2004

The subthreshold electron velocity-field characteristic has been measured at room temperature for a range of bulk and epitaxial samples of n-type InP having low-field Hall mobilities in the range 3600–4950 cm2/V s. The threshold field for current instabilities is found to be between 10.5 and 11.5 kV/cm and the peak velocity is 2.5×107 cm/s.
Superconductivity in metastable simple cubic alloys
Authors: Johnson William L. , Poon S. J.
Published: February 2004

Results of resistivity measurements and x-ray studies of four additional superconducting metastable simple cubic alloys are presented. It is found that, in general, superconducting phases with simple cubic structure occur at average valence electron concentrations of 4.5 and 6.5 valence electrons per atom, and average valence electron densities of 0.16 and 0.26 electrons/Å3. An inverse relation between the transition temperature Tc and the lattice spacing is pointed out which applies generally for both antimony- and tellurium-base alloys.
Preparation of nonequilibrium solid solutions of (GaAs)1−xSix
Authors: Noreika A. J. , Francombe M. H.
Published: February 2004

A method using coincident rf sputtering and rf discharge decomposition is shown capable of producing single-crystal, epitaxial, nonequilibrium solid solutions of Si in GaAs with the composition of Si far exceeding the limits reported for the bulk equilibrium phase diagram. Measured values of alloy composition and lattice parameter indicate close correspondence to Vegard's law. High-temperature annealing of epitaxial films demonstrates the ultimate instability of the alloys.
Some electrical properties of AgGaS2
Authors: Yu Phil Won , Manthuruthil J. , Park Y. S.
Published: February 2004

Results of Hall-effect and resistivity measurements on semi-insulating undoped AgGaS2 are reported. Both shallow (∼0.11 eV) and deep (∼0.72 eV) acceptor levels were observed from p-type crystals. Crystal resistance is not readily changed by heat treatment.
Electron-beam damage in cathodochromic sodalite
Authors: Bhalla R. J. R. S. B.
Published: February 2004

In recent years sodalite, Na8Al6Si6O24X2, where X is Cl, Br, or I, has received wide attention as a cathodochromic material. The utility of sodalite, however, is severely restricted because of damage produced after repeat write-erase cycles. This damage was investigated and found to be of two kinds. The first kind was considerable loss of potential color centers, i.e., after a certain number of write-erase cycles the material would not color up to the original optical density. The second kind was build up of permanent coloration which could not be removed on exposure to bleaching light but could be removed by heat. Electron microprobe, electron spectroscopy for chemical analysis, thermogravimetric analysis, x rays, and a variety of other analytical tools were used to understand the causes of damage. Considerable loss of sodium and a smaller loss of halogen ions on continued electron-beam irradiation was found to be closely associated with the damage. Possibility of heat generated by the electron beam was discounted as the source of damage.
Amplification of Bleustein-Gulyaev waves in tetragonal and hexagonal crystals
Authors: Soluch W.
Published: February 2004

This paper presents the results of calculations for the amplification coefficient and the velocity of Bleustein-Gulyaev waves in tetragonal and hexagonal crystals (classes 4 and 6) which are coupled with a semiconductor through an infinitesimally small vacuum gap. The conditions for existence of these waves are discussed. Detailed calculations of the amplification coefficient and velocity are performed for the system which consists of silicon and lithium iodate.
Ion-channeling and optical absorption studies of implantation disorder in germanium
Authors: Picraux S. T. , Stein H. J.
Published: February 2004

Ion-channeling and optical absorption measurements are reported for lattice disorder in Ge after ion implantation at 90 K. An anneal stage is observed by ion channeling at 175 K for low-fluence Zn implants (3×1012/cm2). The annealing occurs over a much narrower temperature range (∼50 K) than is observed for low-temperature implantation disorder in Si. The Ge anneal stage measured by ion channeling is shown to correlate closely with that observed by near-band-edge optical absorption measurements for these low-disorder-density implants. For high-disorder-density implants (e.g., ≳3×1013 Zn/cm2) ion-channeling measurements saturate due to a loss of long-range order, while near-edge absorption measurements are still sensitive to further changes in the disorder. Following high-disorder-density implants near-edge absorption shows appreciable recovery below room temperature, while ion channeling shows recovery of the long-range order at temperatures ≳450 K. Thus, ion-channeling and optical absorption measurements of ion-induced disorder in Ge are shown to correlate for low-disorder-density implants and provide complementary information for high-disorder-density implants.
Electron energy losses in thin graphite layers on the (111) face of nickel
Authors: Patil H. R. , Blakely J. M.
Published: February 2004

Equally spaced multiple losses of 29±1 eV were observed accompanying 700–1500-eV electrons elastically reflected from epitaxial graphite layers formed by segregation to a Ni(111) surface. Both the loss spectra and the structure in the ``true secondary'' region from the thin segregated layers were indistinguishable from those obtained with bulk pyrolytic graphite. The relative loss peak intensities agree well with the theoretical predictions of Lucas and Sunjic.
Determination of diffusion velocities in argon and helium plasmas
Authors: Pytlinski J. T. , Jones W. D. , Oleson N. L. , Flynn R. W.
Published: February 2004

Some results of the investigation of plasma diffusion velocity in collisionless argon plasma and collision-dominated helium plasma in the steady state are presented. The experiment was performed for argon pressures of 1.25×10−3, 3.8×10−3, and 8.0×10−3 Torr and for helium pressures of 2.4×10−2, 3.3×10−2, and 4.6×10−2 Torr. It is shown that in the hot-cathode-type steady-state discharge a plasma diffusion velocity obtained by using an ion acoustic wave technique represents only a sort of average value in the region of measurement and that actually it increases with radial distance.
Nonlinear scattering from a warm plasma column
Authors: Larsen J-M.
Published: February 2004

When a plane electromagnetic wave impinges normally on a plasma column, with its magnetic field vector parallel to the axis of the column, a series of (Tonks-Dattner) resonances are excited which have been described previously in the linear regime, by a warm plasma analysis using a scalar electron pressure and an inhomogeneous radial electron density profile. In this paper, the theory is extended to the weakly nonlinear regime, assuming a parabolic electron density profile. The nonlinear scattered power is obtained. The excitation of dipole resonances at two different frequencies produces a predominantly quadrupolar radiation pattern with minima in the direction of the incident wave vectors and approximately at right angles to it. In general, there is no nonlinear power radiated in the forward and backward directions. Numerical results for the nonlinear scattering coefficients are obtained in the special case of second-harmonic generation at dipole resonance.
Plasma-wave production by two laser beams in an inhomogeneous plasma
Authors: Beaudry G.
Published: February 2004

The problem of plasma-wave production by two beating laser beams is examined in that case of a linear density profile plasma. We assume that convection of the plasma wave dominates over dissipation. We show that the energy transferred to the plasma wave strongly depends on initial laser-beam intensities and on the density gradient scale length. For initial conditions leading to Raman backscattering we obtain an expression for the spatial growth of the reflected beam.
Analytic solution for transient heat flow in a shocked composite slab
Authors: Swan G. W. , Dick J. J.
Published: February 2004

An analytical solution and computational procedure has been obtained for transient heat flow in a three-slab finite-length composite solid with symmetry about the center. Each material has different initial temperatures and there are constant temperatures on the boundaries. The solutions are of interest in thermal quenching procedures and in the shock compression of sandwich configurations of materials. The results of a computation corresponding to the temperatures reached in shock-wave compression indicate that there is significant heat flow into a metal foil, which is sandwiched between two epoxy layers, in less than 1 μsec of heat flow. This paper presents a mathematical discussion of the heat-flow problem along with sample computational results. One conclusion from these results is that they demonstrate the important effect of heat flow on electrical resistance changes in certain geometries of shock-wave compression of metals.
Excitation of parametric instabilities in statically stable and unstable fluid interfaces
Authors: Hoffmann F. M. , Wolf G. H.
Published: February 2004

By enforcing an oscillatory motion on superimposed fluids perpendicular to their interface, one can excite parametric instabilities, i.e., the unstable growth of interface or surface modes. Both the oscillation parameters and the wavelengths of the excited parametric instabilities depend on the viscosity and the surface tension of the fluids. This has been measured for the interface between air and various liquids and compared with theoretical predictions from Troyon and Gruber. The position of the liquids was either normal (air upon liquid) or inverted (liquid superimposed upon air). In the latter case the oscillation parameters had to be limited to those beyond the threshold for dynamic stabilization of the Rayleigh-Taylor instability. The applied frequencies were in the range between 30 and 4000 Hz, the surface tension was varied between 10 and 100 dyn/cm, and the viscosity between 10−2 and 10 P. Typical liquids were mineral oils, water, and gasoline.
Shock-wave compaction of porous aluminum
Authors: Butcher B. M. , Carroll M. M. , Holt A. C.
Published: February 2004

Experimental data on the shock-wave compaction of 78% dense porous aluminum are presented and compared with theoretical predictions from a mathematical theory of time-dependent pore closure for ductile materials with isolated spherical voids. A recently modified form of the theory was used which includes deviatoric stresses and material viscosity. Incorporation of the work-hardening properties of the solid resolved previous discrepancies between measured hydrostats and predictions assuming elastic-perfectly plastic deformation of the matrix. Generally good agreement was also observed between experimental quasistatic and shock data, although there was some evidence that the quasistatic data were strain-history dependent. Finally, a satisfactory check of the theory was obtained by comparing predicted steady-wave rise times with measured stress-wave profile data. These results suggest that the current version of the theory is a significant improvement over past models, because it permits a more accurate estimate of the influence of both pore size and the plastic deformation characteristics of the metal matrix on shock compaction.
Ionization dilatation effects in fused silica from 2 to 18-keV electron irradiation
Authors: Norris C. B. , EerNisse E. P.
Published: February 2004

We have used low-energy electron irradiations in conjunction with a bending-cantilever-plate technique to investigate the volume dilatations produced by ionization effects in fused silica. Our irradiations generally cause compaction in agreement with previous data from high-energy electron irradiations, but we consistently observe a slowly saturating compaction-dose relationship rather than the sublinear power-law relationship seen in the high-energy data. Our results show agreement with the apparent ionization compaction effect extracted from low-dose-rate 1H+-ion-implantation experiments. We find no dose-rate dependence in the electron ionization compaction effect, in marked contrast with the apparent ionization compaction effect in the implantation experiments. We therefore conclude that the enhancement of the apparent ionization compaction effect at high dose rates in the implantation experiments results from an interaction between the ionization and the atomic displacements accompanying the implanation. By probing to various depths at a constant dose and dose rate, we find that the electron irradiation compaction effect is generally enhanced within several hundred angstroms of the sample surface. There is no apparent threshold for onset of the compaction mechanism for incident electron energies between 2.2 and 18 keV. Finally, we observe the low-fluence expansion effect in impure fused silica as seen by other workers but establish here that it is primarily an ionization-stimulated phenomenon that occurs only when the irradiation current varies with time.
How much Al in the AlGaAs–GaAs laser?
Authors: Rode D. L.
Published: February 2004

Maintenance of higher doping levels in the AlxGa1−xAs barrier layers of double-heterostructure lasers permits one to use smaller molar fractions x, thereby minimizing the lattice mismatch between AlxGa1−xAs and GaAs. We estimate conduction-band and valence-band parameters of AlxGa1−xAs and show the relationship between laser threshold current and doping level.
Metallic aluminum particle concentration in aluminum oxide thin films
Authors: Birey Hülya
Published: February 2004

Two different methods based on (a) the tunneling junction model and (b) the optical model are used to determine the metallic aluminum particle concentration in aluminum oxide thin films prepared by thermal evaporation of pure aluminum under appropriate vacuum conditions. The concentration determined from these two models agree with each other at high concentrations and show considerable deviation at low concentrations.
Hall effect in high-purity and p-doped germanium crystals
Authors: Yee Jick H. , Swierkowski Stefan P. , Armantrout Guy A. , Wichner Ronald
Published: February 2004

Experimental and theoretical investigations of the Hall effect were carried out in high-purity (1010-cm−3 carrier concentration) germanium crystals. Optical phonon scattering, which was not included in the previous work on the calculation of the Hall coefficient factor θ̂, is included in the present calculation. Extensive numerical calculations were performed for θ̂ vs 1/T for both the spherical-band model and the anisotropic model of Beer and Willardson. Measurements and calculations of the Hall coefficient vs 1/T are in excellent agreement.
Low-frequency characteristics of the impedance of germanium avalanche diodes
Authors: Takeshima Masumi
Published: February 2004

The impedance characteristics of germanium avalanche diodes are analyzed in the frequency range 0.5 MHz-4.5 GHz. The analysis is made taking into account the capture of impact-ionized carriers via deep centers contained in a depletion layer. It is shown that the present model explains well the experimental results.
Analysis of ring distributed-feedback lasers
Authors: Wang Shyh , Tsang Won-Tien
Published: February 2004

Here a structure for ring distributed feedback (DFB) lasers is proposed and analyzed. The threshold condition for such lasers is derived and compared with that for plain DFB lasers. It is shown that the etalon and feedback effects provided by the uniform section of a ring DFB laser should narrow the laser bandwidth and lower the threshold gain.
Proton bombardment and isochronal annealing of p-type Pb0.76Sn0.24Te
Authors: Wang C. C. , Tao T. F. , Sunier J. W.
Published: February 2004

The effects of low-energy proton bombardment (200–450 keV) on the electrical properties of p-type Pb0.76Sn0.24Te have been investigated. The carrier concentrations were generally found to be reduced by the bombardment. Carrier conduction from p to n type, which depended upon the initial carrier concentrations, was also observed. Samples with an initial hole concentration in the range of low 1017 holes/cm3 were changed to n type after a proton dose of approximately 5 × 1013 protons/cm2. Type conversion was not consistent for samples with higher initial carrier concentrations. Mobilities were found to increase for type-converted samples. A slight decrease was observed for samples which did not change their type. Isochronal annealing was performed for type-converted samples. A major annealing stage was found to occur in the temperature range 90–140°C in which the converted samples changed their conduction back to p type. This seems to limit the applicability of proton bombardment as a process to produce reliable devices.
Recombination in high-resistivity n-type Zn-compensated silicon
Authors: Rabie S. , Rumin N.
Published: February 2004

The photocurrent decay following pulsed band-gap excitation has been measured in the temperature range 230–300°K on n-type zinc-compensated silicon samples containing approximately 1016 cm−3 of arsenic and having room-temperature resistivities between 3 and 150 kΩ cm. Sensitization of photoconductivity due to the addition of zinc was observed, and the decay time increased by several orders of magnitude over its value before compensation. From an analysis of the possible recombination mechanisms in such high-resistivity samples, we conclude, in light of our measurements, that in the specified temperature range and under low-level excitation conditions (i) the lower zinc level has a negligible effect on recombination time, (ii) thermal quenching of photoconductivity is an unlikely process, (iii) unipolar conductivity prevails due to the giant hole-capture cross section of the zinc ions, and (iv) the photodecay is largely influenced by a deep-lying αtype electron trap. The density and location of this trap are estimated to be, respectively, 1.3×1013 cm−3 and 0.4 eV below the conduction band edge. Resistivity measurements in the range 180–300°K yield a value of 0.49 eV for the location of the zinc-sensitizing level E2 with respect to the conduction band edge. This tends to support other recent independent studies over earlier ones which placed E2 at 0.55 eV. No differences were observed in any of our measurements between Czochralski and float-zone silicon.
Analytic expressions for ultrashort pulse generation in mode-locked optical parametric oscillators
Authors: Becker M. F. , Kuizenga D. J. , Phillion D. W. , Siegman A. E.
Published: February 2004

We obtain simple analytic solutions for ultrashort pulse generation in a degenerate mode-locked optical parametric oscillator pumped synchronously by a mode-locked laser. Very short pulses (∼1 psec) are predicted at steady state very close to threshold where pump depletion is negligible; but the parametric pulses broaden to the same order as the pumping laser pulses as soon as pump pulse depletion becomes significant. In the transient buildup regime, where pump depletion is again negligible, pulse widths approximately a quarter of the pump pulse width are obtained.
Do ferromagnets have a true coercive force?
Authors: Baldwin John A. , Milstein Frederick
Published: February 2004

The subject of slow domain wall motion in thin films is reviewed. The thermal activation theory of this motion is sketched and criticized. In particular, that theory predicts a qualitatively wrong temperature dependence for the after-effect field, Hn. An alternative theory, employing quantum-mechanical tunneling of walls past pinning centers, is developed. This theory gives a qualitatively correct temperature dependence for Hn. Also, unlike the thermal activation theory, it predicts zero velocity in zero field. However, it predicts wall motion in any nonzero field. In other words, it says that there is no such thing as an absolute coercive force below which wall motion does not occur. However, for some samples, the wall velocity at half the high-frequency coercive force is as small as 10−77 times a characteristic velocity, u0. By human standards this is zero. A sample's tunneling behavior is a very sensitive function of a parameter Z*≜Z/l0. Here Z is the characteristic range of the pinning centers, while l0 is approximately the tunneling length (decay constant of the harmonic-oscillator wave function). Experimental data of Scheibe, and of Olmen and Mitchell are interpreted in terms of this theory. The former data give Z* in the range 43–63. The latter give Z*≃11.4.
A single mechanism for slow domain wall motion in both ferroelectrics and ferromagnets
Authors: Baldwin John A. , Milstein Frederick
Published: February 2004

A tunneling theory of slow wall motion in ferromagnets is applied to BaTiO3 using the data of Miller and Savage. It is shown that, over seven decades of velocity for which the approximations are valid and for which data are available, the theory fits the data well and even gives the appreciable change of slope in the lnu -versus-l/E plot found experimentally. A material will or will not behave as though it had a true coercive force, below which wall motion does not occur, depending on whether a quantity called Z* is large or small, respectively. Z* is the average range of pinning centers in the crystal, normalized to the (approximate) tunneling length. For BaTiO3 it was determined that Z*=6; u0, a characteristic tunneling velocity, was 2.72 cm/s; Ec, the classical coercive field, was 763 V/cm. It is concluded that domain wall motion in ferromagnets and ferroelectrics proceeds by the same mechanism.
Two-dimensional arrays of Josephson weak links
Authors: Hansma Paul K. , Kirtley John R.
Published: February 2004

Two-dimensional arrays of Josephson weak links can be produced by evaporating metals in air or argon at reduced pressures onto insulating substrates. Below the superconducting transition temperature of the metal, these arrays enter a coherent state, capable of carrying a maximum supercurrent Ic, which has a temperature dependence similar to that for a single oxide barrier tunneling junction. The multiply connected nature of the arrays is most clearly demonstrated by a multiply periodic dependence of Ic on magnetic field applied perpendicular to the array. A simple model for the arrays with m current paths in parallel with n Josephson weak links in series is proposed. This model is used as a basis of a computer program which generates detailed I(V) curves for several assumed probability distributions of critical currents and two current-voltage characteristics for the individual weak links in the array. These computer-generated curves are compared with experiment. The model is also used to explain other aspects of the experimental observations, such as why the outermost current paths do not screen the applied magnetic field from inner paths. Some experimental results on the interaction of the arrays with electromagnetic radiation in the far infrared and microwave regions are included.
Effect of thermal annealing and ion radiation on the coercivity of amorphous Gd–Co films
Authors: Hasegawa R. , Gambino R. J. , Cuomo J. J. , Ziegler J. F.
Published: February 2004

Ferrimagnetic amorphous Gd–Co films deposited by rf sputtering with uniaxial perpendicular anisotropy were annealed at about 200 °C with or without a magnetic field of 3 kOe applied perpendicularly to the film plane. Data taken using the polar Kerr magneto-optic effect show a significant decrease in the value of the wall-motion coercivity Hc. A reduction of Hc by an order of magnitude was generally attained in films having compositions in the vicinity of the magnetic compensation point. Similar results were obtained in a film irradiated with 2.5-MeV argon ions. These data are discussed in terms of fluctuations in various parameters contributing to the resultant coercivity. The results indicate that the fluctuations in the exchange stiffness constant dominate over the others and, consequently, are most affected by the postdeposition treatments. The results for the ion-irradiated film suggest that the origin of the uniaxial anisotropy is due to pair ordering of Co atoms.
Interaction of domain walls with localized stress fields in magnetostrictive films
Authors: Dishman J. M. , Pierce R. D. , Roman B. J.
Published: February 2004

The interaction of magnetic bubble domains with overlying patterned metallizations is described in terms of a model in which local stress fields from the metal edges perturb the energy of domain walls through inverse magnetostriction. Examined in detail is the case in which a straight wall passes under the edge of a metal film deposited in either tension or compression. Using a simple form for the stress field generated at such a boundary, we show that the domain-wall energy is substantially perturbed in the immediate vicinity of the edge. This gives rise to either an attractive or repulsive interaction, depending on the signs of the stress and of the magnetostriction coefficients. The predictions of the model are examined by observing experimentally the interaction of straight domain walls and bubbles with metal stripes under compression. Comparison of the predicted and observed forces required to pull the domain walls away from the metal edges verifies the model calculations over almost two decades of metal stress. The use of a space layer to reduce the stress in the magnetic material is found to significantly lower the bubble-metallization interaction, thereby permitting improved device performance.
Spatial distribution of backscattered electrons in the scanning electron microscope and electron microprobe
Authors: Murata Kenji
Published: February 2004

Monte Carlo calculations have been applied to the electron scattering theory in scanning electron microscopy. These calculations are based on a single-scattering model in which the screened Rutherford expression for single-scattering cross section and the continuous energy-loss equation of Bethe are used. The surface distribution of backscattered electrons is obtained for Al and Au targets at 20 keV, with 0° and 45° incidence. From these results the exit areas of the backscattered electrons are discussed and compared with experiment. The penetration depths of the backscattered electrons are given at 0° incidence. Everhart's model for backscattering was modified, taking into account the calculated results. The proportion of the singly backscattered electrons to the total backscattered electrons was estimated by the modified model. The result shows that about half of the total backscattered electrons are caused by large-angle single-scattering events. This is consistent with the previous results of Cosslett and Thomas.
Thermal noise in the trap-filled diode
Authors: Sharma Y. K. , Srivastava B. B.
Published: February 2004

An expression for the thermal noise, based on the method of regional approximation, has been calculated for a trap-filled diode; while the current is smaller than the critical value.