bluuebunny/crossref_metadata_2025 huggingface dataset:
On the determination of the fourth-order elastic constants
Authors: Markenscoff Xanthippi
Published: February 2003

Starting from the equations of small-amplitude waves superposed on a state of homogeneous static deformation (due to hydrostatic pressure or uniaxial stress), exact expressions for the second derivative of the wave velocity with respect to the statically applied stress—at constant temperature—are derived. These equations involve the mixed (adiabatic-isothermal) fourth-order elastic constants, and the equations can be used for their determination. The mixed fourth-order elastic constants lack full symmetry in their indices. Their relations to the adiabatic and isothermal ones are derived.
Loss of coherency across an interface
Authors: Jagannadham K. , Marcinkowski M. J.
Published: February 2003

The loss of coherency across a two-phase interface was studied by invoking a dislocation model of the two-phase interface. In particular, the interface consists of periodically arranged misfit dislocations with interface dislocations distributed in between the misfit dislocations. A coherent interface consists of uniformly distributed interface dislocations and becomes noncoherent by rearrangement of the interface dislocations. This rearrangement of interface dislocations was studied by the techniques of continuously distributed dislocations and by the method of discrete distributions of dislocations. The atomic step produced across the interface is related to the physical properties of the two phases and to the magnitude of the frictional stress across the interface.
Theoretical analysis on radiation and reception characteristics of an oblate spheroidal antenna for electron plasma waves
Authors: Ohnuki Shigeo , Adachi Saburo , Ohnuma Toshiro
Published: February 2003

The radiation and reception characteristics of the oblate spheroidal antenna for electron plasma waves are theoretically investigated. The analysis is carried out as a boundary-value problem. The formulas for the radiation and reception characteristics such as radiation impedance, electron charge distributions, radiated wave potential, directional properties, and receiving voltage of the oblate spheroidal antenna are analytically obtained. As a result, it is concluded that the radiation and reception characteristics of the antennas are not uniquely determined by kpa (kp is the wave number of an electron plasma wave, and a is the radius of the circular-plate antenna), but are determined by two out of three factors, kpa, ζ (radius divided by Debye length), and ω/ωp (angular signal frequency to angular plasma frequency). This conclusion is in marked contrast to the conventional theory in which the charge distribution on the antenna is assumed a priori as uniform and, thus, the antenna characteristics are uniquely determined by kpa. It is claimed that the experimental results obtained hitherto support the present new theory.
Effect of electrode geometry on the tanh conductivity arc model
Authors: Choudhury Bejoy K. , Cohen Ira M.
Published: February 2003

Conservation of energy for the temperature field is solved jointly with conservation of charge for the electrostatic potential for an arc in which the effects of convection and radiation are neglected. The electrical conductivity is modeled by a hyperbolic tangent function. Prolate spheroidal coordinates are used to emphasize the effects of electrode shape. Electrodes are chosen as hyperboloids of revolution (varying from needlelike to planar) and the bounding wall is a prolate spheroid. Approximate solutions are obtained by Galerkin’s method. Current-voltage characteristics, arc shapes, and heat transfer to the electrodes and bounding wall are obtained. We find that current-voltage characteristics are sensitive to electrode geometry and temperature. Blunt and hot electrodes yield monotonically increasing characteristics. Cooling the electrodes and increasing their tip curvature both act to increase the voltage to drive a given current, especially for small currents, giving characteristics with distinct maxima and minima. The blunter the cathode, the larger the potential difference to drive a given current. The results also indicate that equipotentials are very close to coordinate lines, justifying an assumption of a one-dimensional electric field made elsewhere.
Thermal and electrical characteristics of a two-dimensional tanh-conductivity arc
Authors: Ayyaswamy P. S. , Das G.C. , Cohen I. M.
Published: February 2003

The two-dimensional variable-property arc has been studied through the use of the tanh-conductivity model. Results that describe the thermal and electric arc characteristics for various values of the electrode temperatures and aspect ratios are given. The numerical evaluation is carried out by the use of a Galerkin technique. The results exhibit several novel and interesting features depending on the arc parameters. For large aspect ratios (ratio of the interelectrode distance to that between the bounding walls) and small electrode temperatures, the current–electric-field characteristics tend toward those of a slender arc. However, at a given aspect ratio with large enough electrode temperatures, the distinct minimum noted in the slender-arc characteristics does not occur. Also, for a given aspect ratio and large enough differences in electrode potential, the electric-field–current characteristic is nearly linear and is independent of the electrode temperature. The transverse electrostatic potential is found to have no significant variation in cross-sectional planes. The qualitative nature of the thermal characteristics are similar to those of a constant-property arc although significant differences in quantitative results exist. Wall and electrode heat transfer rates are provided.
Calculation of reduced intensity functions for model amorphous structures, including coupling of thermal vibrations
Authors: Federman S. R. , Betts F.
Published: February 2003

Coupling of thermal vibrations was introduced into the calculation of the reduced intensity function for two model amorphous structures by using coupling coefficients which are a function of interatomic distance. A microcrystallite model of amorphous silicon and an ion cluster model of amorphous calcium phosphate were examined. Since coupling factors appropriate to these materials were not available, data from several different materials was used to estimate the importance of such coupling. Splitting of certain peaks in the diffraction pattern at high angles was found to be reduced, giving better agreement between calculated patterns and measurements on actual materials. These results suggest that coupled thermal vibrations and other random perturbations which affect large interatomic distances more than smaller ones may have a significant affect on the diffraction pattern.
Analysis of compression of frequency-chirped optical pulses using dispersive bulk and surface phonon-polariton propagation modes at CO2 laser frequencies
Authors: McMullen J. D.
Published: February 2003

An analysis is given for the compression of linearly chirped optical pulses propagating in dispersive absorbing media. Numerical calculations are reported for frequency-chirped CO2 laser pulses which propagate as phonon polaritons in α-quartz or as surface phonon polaritons on BeO, including the influence of thin dielectric films on the surface propagation mode. Quantitative evaluation is made of the use of these modes to form dispersive optical pulse delay lines. It is shown that absorption limits both the usable propagation length and the curvature of the dispersion curves. For the materials considered, this approach is restricted to 10-psec pulses having THz chirp bandwidths, with large accompanying absorption losses.
Studies of annealing of neutron-produced defects in silicon by transconductance measurements of junction field-effect transistors
Authors: Tokuda Yutaka , Usami Akira
Published: February 2003

Annealing behavior of neutron-produced defects in silicon was studied by measuring the phase angle ϑ of the small-signal transconductance of the junction field-effect transistors (JFET’s). Three deep levels (N-1, N-2, and N-3 levels) in n-type silicon and two deep levels (P-1 and P-2 levels) in p-type silicon, introduced by irradiation, annealed gradually. Their energy levels and capture cross sections have been already reported by us. Three deep levels (P-3, P-4, and P-5 levels) were observed in annealed p-type silicon in the temperature range 150–300 °C. For these defects, ϑ was measured as a function of frequency to obtain the time constant. From the temperature dependence of the time constant, assuming that capture cross sections are independent of temperature, the energy levels of P-3, P-4, and P-5 were estimated to be Ev+0.21, Ev+0.40, and Ev+0.30 eV, respectively. The calculated hole capture cross sections of these levels were 2.2×10−15, 8.7×10−14, and 1.2×10−14 cm2, respectively. Comparison with other published data was made. It was found that N-3 and P-2 levels corresponded to the divacancy. Furthermore, it seemed that P-3, P-4, and P-5 levels corresponded to the high-order vacancy defects.
Isothermal compression of bcc transition metals to 100 kbar
Authors: Ming Li-chung , Manghnani Murli H.
Published: February 2003

Pressure-volume relationships for the bcc transition metals in the groups VB (V, Nb, and Ta) and VIB (Cr, Mo, and W) were determined under hydrostatic pressure to 100 kbar at room temperature by means of x-ray diffraction, employing diamond-anvil pressure cell and the ruby (R1 line) fluorescence calibration technique. Using the measured ultrasonic K′0 values, where K0 is the bulk modulus at ambient pressure, for five metals and the deduced shock-wave K′0 value for Cr, the values of K0 for V, Nb, Ta, Mo, W, and Cr are calculated to be 1.54, 1.71, 1.94, 2.67, 3.07, and 1.93 Mbar, respectively, by least-squares fit of the experimental P-V data to the Birch-Murnaghan equation. The K0 values thus determined are in good agreement with the ultrasonic and shock-wave values for V, Nb, Ta, Mo, and W. For Cr, the K0 value (1.93 Mbar) is in agreement with the shock-wave value (1.92 Mbar) but not with the ultrasonic value (1.65 Mbar). This discrepancy can be explained in view of the paramagnetic→antiferromagnetic transition in Cr in the temperature proximity of the ultrasonic measurements (Neel temperature TN∼311 °K at 1 bar) and by the negative pressure dependence of TN.
Interferometry and luminosity measurements on a CO2 laser plasma focus
Authors: Saint-Hilaire G. , Szili Z.
Published: February 2003

This paper presents an interferometry study of a CO2 laser plasma focus created in a 1-cm copper annular target. The average electron density measured on the plasma axis is approximately ne∼1.6×1018 cm−3. Spatial and temporal plasma luminosity measurements suggest a simple model for the plasma motion. This laser-produced plasma has an axis and a plane of symmetry which make it an interesting subject for further studies on laser plasma interactions.
Spatially resolved EUV emission from focused REB discharges into thin targets
Authors: Johnson David J. , Oliphant Willis F. , Doschek George A. , Feldman Uri
Published: February 2003

The EUV emission from 10- to 100-mg/cm2-thick planar targets (Z=6–79) exposed to 60-nsec-duration focused relativistic electron beams was examined at current densities of 0.4–1.0 MA/cm2. Spatially resolved spectra were obtained with a stigmatic near-normal incidence spectrograph, in the wavelength range 500–2100 Å, along axial and radial directions. Time-resolved EUV data were obtained with windowless photoelectric diodes operated unfiltered and filtered with 0.5-μm-thick aluminum. The axial views show copious emission from the diode gap associated with late-time impedance collapse. Radial views show continuum radiation which is emitted from the region of the target exposed to the focused REB and line radiation which originates from a lower-density (approximately 1019 cm−3) more-extended late-time plasma resulting from foil expansion. The region of the foil exposed to the focused REB radiates as a blackbody source with a peak temperature of 2–6 eV. These temperatures are a factor of 2 below the calculated temperatures for classical deposition in the foils exposed to the focused beam assuming no hydrodynamic foil expansion.
Optical measurements of laser-detonated shock waves in thin lithium wires
Authors: Samson J. C.
Published: February 2003

Shock-heated plasmas were produced by focusing 1-ns 1.06-μm laser pulses to intensities of 2×1012 W/cm2 on 100-μm-diam lithium wires. Interferograms and shadowgrams produced with 1-ns 0.53-μm pulses indicate two distinct phases in the plasma expansion. The first phase is a spherical core of dense plasma produced by a shock propagating through the wire, normal to the axis of the wire, and along the laser beam. Interferometric measurements of the expansion and drift velocity of this phase indicate that the initial pressure behind the shock was 1.4–1.9 Mbar, the compression was 2.6–4.2, the shock velocity was (2.1–2.2) ×106 cm/s, and the fluid velocity was (1.3–1.6) ×106 cm/s. The second phase is an approximately cylindrical column of partially ionized material produced by shocks propagating along the wire. Shadowgrams show that the velocities of these shocks were greater than 1.7×106 cm/s.
Particle and x−ray energy measurements in laser-plasma interaction experiments
Authors: Rupert V. C. , Gunn S. R. , Holzrichter J. F.
Published: February 2003

The energy carried by particles and low-energy x rays resulting from irradiation of laser fusion targets with 0.5–1-TW 1.06-μm lasers has been measured. The energy distributions were obtained from measurements at discrete locations using plasma calorimeters. The data have been integrated to obtain the absorbed energy, and these values compared to scattered-light calorimetry and optical-energy balance.
Reaction kinetics of molybdenum thin films on silicon (111) surface
Authors: Guivarc’h A. , Auvray P. , Berthou L. , Le Cun M. , Boulet J. P. , Henoc P. , Pelous G. , Martinez A.
Published: February 2003

Silicon-metal systems are highly susceptible to solid-solid reactions which modify their electrical and mechanical properties. Although many works are dealing with silicide formation, the molybdenum-silicon system has not yet been investigated in detail to our knowledge. In this paper we present a He+ ion backscattering study of the molybdenum-silicide formation by interaction of a thin molybdenum layer and a silicon 〈111〉 wafer. The silicide phases Mo3Si and MoSi2 have been identified by x-ray diffraction and transmission electron microscopy. Surface transformations were observed by scanning electron microscopy. For an 800-Å Mo layer sputter deposited on silicon, we have found a time-square growth rate for MoSi2 with an average activation energy of 2.4 eV in the temperature range 475–550 °C. The fundamental roles of the cleaning of the silicon surface, of the substrate temperature during sputtering, and of the stresses in the layer are pointed out.
Effects of substrate bias and annealing on the properties of amorphous alloy films of Gd-Co, Gd-Fe, and Gd-Co-X (X=Mo,Cu,Au)
Authors: Heiman Neil , Kazama N. , Kyser D. F. , Minkiewicz V. J.
Published: February 2003

We have examined the dependence of various properties of sputter-deposited amorphous GdCo, GdFe, and GdCoX (X=Mo,Cu,Au) films upon substrate bias and annealing. Particular interest was directed to changes in magnetization, anisotropy, composition, x-ray diffraction patterns, and Ar content of the films. In the case of the binary films, we applied substrate bias voltages to 400 V. We found that for the GdCo system, Ku rises with increasingly negative bias voltage to about Vb=−200 V. Further increases in Vb cause Ku to decrease, so that Ku?0 for Vb?−400 V. Furthermore, it was found that the Ar content of the films tends to correlate with Vb, reaching a maximum for Vb?−200 V. X-ray diffraction patterns of these films also appear to correlate with Ku but in a more subtle manner than has been suggested by other workers. The results for amorphous GdFe films were considerably different. In particular, it was found that Ku was large for Vb?0 but decreased rapidly with negative bias. The behavior of ternary GdCoX films was similar to that of the binary GdCo films, except that the x-ray diffraction patterns showed little dependence on Vb. On being annealed for 4 h at 200 °C, the binary films show no change in magnetization, composition, or x-ray diffraction profile, but do experience a decrease in Ku by about a factor of 2. The situation is similar for the GdCoCu and GdCoAu films except that the temperature dependence of the magnetization also changes dramatically. In contrast to these results, amorphous GdCoMo films undergo little or no change on annealing. Our results suggest that the incorporation of Ar into the films is closely related to the mechanism responsible for Ku in these materials; however, there exist data which conflict with this interpretation, so that the origin of Ku remains in doubt. On the other hand, we have established the limits to the effects of Vb on the material’s properties, and we present a comprehensive collection of empirical facts which will prove useful for preparing this class of materials with desired properties.
Selective absorption properties of lead sulfide–aluminum coatings as a function of lead sulfide thickness
Authors: Marchini Robert , Gandy Rex
Published: February 2003

The dependence of the absorptivity and emissivity of lead sulfide films on thickness was investigated. Theoretical calculations were made using the bulk–lead sulfide model. Reflectance measurements in the visible and infrared regions of the spectrum were made to determine absorptivity and emissivity values. Both the theoretical and experimental results predict optimum a/e values for the lead sulfide thickness range 300–800 Å.
Effect of multiple internal reflections on Faraday rotation in multilayer structures
Authors: Višňovský Š. , Prosser V. , Krishnan R.
Published: February 2003

A simple procedure is presented for computing optical transmission and Faraday-rotation optical density (OD) planar layered structures when all internal reflections are taken into account. The procedure makes use of the Mueller matrix technique and assumes that interference effects, Faraday ellipticity, and boundary magneto-optical effects, e.g., Kerr effect, are not important. The general formulas are applied to the case of the three-layer structure from which two examples of some practical interest are derived, i.e., a single absorbing layer on a nonabsorbing substrate and two identical absorbing layers on either side of a nonabsorbing substrate. The solutions are substantially simplified when Faraday-rotation angles are small.
The efficiency of grating solar cells
Authors: Kong Anthony K. , Green Martin A.
Published: February 2003

Computer simulation of grating solar cells is used to compare the performance of this type of device with more conventional cell geometries. Criteria for the grating design and their dependence upon substrate properties are discussed. The nature of the back contact to the cell is shown to play an important role in determining the cell efficiency. In order for the grating cell to be competitive in efficiency with the normal cell geometry, the back contact must have minority-carrier blocking properties. The efficiency of cells with ideal Ohmic back contacts is limited by geometrical effects. Recent experimental results are analyzed in terms of the results of the theoretical investigation.
Intermodulation distortion and spin waves in thin ferromagnetic resonators
Authors: Moll N. J.
Published: February 2003

The generation mechanism for intermodulation products in thin ferromagnetic resonators is examined. A sketch of classical theory provides a physical picture of this mechanism. Using this theory as a base, the effect of spin-wave scattering on intermodulation is then predicted by treating the resonant mode and spin waves as magnons; spin-wave scattering is found theoretically to increase the intermodulation products. A comparison of the full theory with experimental results on bandpass filters made with thin YIG resonators shows good agreement.
The effects of a weak axial magnetic field on the total energy output of the CuCl double-pulse laser
Authors: Cross Lee A. , Jenkins Robert S. , Gokay M. Cem
Published: February 2003

Measurements of the effects of a weak axial magnetic field on the output energy of a CuCl double-pulse laser have been made. It was anticipated that the application of a weak 290-G magnetic field could serve to stabilize the discharge in the laser tube and to, therefore, increase the output energy of the laser. Such increases were observed for large values of the delay time between the two successive electrical discharges but not for the optimum delay of 175 μsec, and a reduction in the output of the laser occurs for very small time delays. The mechanism by which the magnetic field enhances (or reduces) the laser output is not presently well understood but two alternatives are discussed.
High-pulse-rate 10-W KrF laser
Authors: Fahlen T. S.
Published: February 2003

A discharge-pumped KrF excimer laser, utilizing a rapid recirculation of atmospheric-pressure gas, has generated 10 W of average output power at a pulse repetition rate of 1 kHz. The usual spark gap was replaced with a hydrogen thyratron for the switch in the pulse-forming network, and a corona discharge was used as the source for discharge preionization. Operating at 30 psi (absolute) and at a pulse rate of 2 Hz, a similar device has generated output pulse energies of 100 mJ at 1% efficiency and 80 mJ at 1.6% efficiency.
Analysis and operation of UHF SQUID with tapped tank circuit
Authors: Jackel L. D. , Stoeckenius J. H. W. , Epworth R. W.
Published: February 2003

We have analyzed the operation of a UHF biased SQUID circuit in which it is possible to achieve near-perfect coupling of all the available SQUID signal power to a room-temperature amplifier. An experimental version of this circuit has attained a measured intrinsic energy resolution of 5×10−30 J H−1z.
Single and multiple thin-layer (L
z≲400 A) In1−xGaxP1−zAsz-InP heterostructure light emitters and lasers (λ∼1.1 μm, 77 °K)
Authors: Rezek E. A. , Holonyak N. , Vojak B. A. , Shichijo H.
Published: February 2003

Liquid-phase epitaxial (LPE) single and multiple thin quaternary layer In1−xGaxP1−zAsz laser diodes (x∼0.13, z∼0.28; λ∼1.1 μm, 77 °K) that exhibit quantum size effects (QSE) are described. LPE quaternary active layers approaching Lz∼200 A have been achieved. As a prototype for the behavior of multilayer heterostructures, the operation of single In1−xGaxP1−zAsz potential wells, or recombination layers, located a small distance into the p side of an InP p-n junction, is considered. Almost all the carrier recombination is observed to occur in the quaternary potential well, and little absorption occurs in the single-active-layer structure, consistent with the small change in the effective index of refraction measured in a large range (1500 A, 150 meV). This general behavior, i.e., single-well recombination, is observed also in thin-active-layer multilayer heterostructures in which the InP layers between quaternary layers are relatively thick (400–1000 A). In multilayered diode structures, distributed feedback may contribute, along with QSE, to modulation of the longitudinal (Fabry-Perot) modes.
Optical rise-time measurements on KD*P transmission-line Pockels cells
Authors: Johnson B. C. , Guinn K. R. , Martin W. E. , Fountain Wm. D.
Published: February 2003

A technique has been developed for determining the optical-transmission rise times of subnanosecond switching KD*P electro-optic modulators. Optical streak-camera data with 15-psec overall resolution and 30-psec resolution electrical sampling measurements taken on several commercial devices are reported.
Nonlinear interaction of surface polaritons
Authors: Bonsall Lynn , Maradudin A. A.
Published: February 2003

We present a Green’s function theory of the nonlinear interaction of surface polaritons propagating along the plane interface between vacuum and a noncentrosymmetric dielectric medium. These nonlinear effects are induced by the nonlinear polarization of the dielectric medium. The nonlinear effects considered are second harmonic generation of a surface polariton, the nonlinear mixing of two surface polaritons, and optical rectification of a surface polariton. Numerical estimates for the magnitudes of these effects are presented for GaAs, for which the necessary second-order susceptibilities in the infrared have been determined.
A stochastic model for microplasma noise
Authors: Ellouze N. , Hoffmann J. C. , Lacaze B.
Published: February 2003

Taking a simple branching process as model of the carrier multiplication in reverse junctions, the turn-on probability of a microplasma is determined. Considering the variation of the voltage and current in the diode, the distribution of the off-state time interval is deduced. Finally, expressions for the amplitude distribution as well as the rate of discharges in units of time are developed in the case where the on-time is negligible.
Threshold behavior of (GaAl)As-GaAs lasers at low temperatures
Authors: Hwang C. J. , Patel N. B. , Sacilotti M. A. , Prince F. C. , Bull D. J.
Published: February 2003

The temperature dependence of the threshold current, differential quantum efficiency, and internal loss have been measured in the temperature range 10–293 °K. The threshold current increases relatively slowly with temperature above 100 °K and is independent of the impurity concentration. Theoretical calculation shows that this behavior is to be expected for a band-to-band transition that follows k selection. The threshold behavior at low temperatures (? 80 °K) depends strongly on the type and concentration of the impurity. The relatively fast decrease in threshold below 100 °K shows saturation for an active layer with n-type impurities or with high-concentration p-type impurities. The saturation is attributed to the carrier diffusion length becoming smaller than the active-layer thickness. The internal differential quantum efficiency is near unity and is independent of temperature. The internal loss, however, decreases with temperature due to reduction in free-carrier absorption.
Contact electrification of polymers: A quantitative model
Authors: Duke C. B. , Fabish T. J.
Published: February 2003

An explicit model of contact-charge exchange in polymers is proposed in which the steady-state exchanged charge resides in intrinsic molecular-ion states. The eigenvalue spectra of these states are inferred from metal/polymer contact-charge measurements using a theoretical formalism constructed for this purpose. This model of metal/polymer contact-charge exchange is extended to encompass the description of polymer/polymer contact-charge exchange as well. Utilizing the metal/polymer contact-charge-exchange spectra as input data, the model predicts correctly both the sign and order of magnitude of measured contact-charge exchange between polystyrene and copolymers of styrene and methyl methacrylate.
The viscous drag on mobile dislocations in type-II superconductors
Authors: Pang C. S. , Lin T. H. , Galligan J. M.
Published: February 2003

The difference in the stress for plastic deformation between the mixed state and the superconducting state has been measured in a series of lead-indium crystals. These measurements show that the change in drag stress between the two states varies in the same manner as does the ultrasonic attenuation in a type-II superconductor. Quantitative agreement between the present results and Maki’s theory of transport properties in dirty superconductors is found for higher solute concentration crystals. These results show that dislocation motion in these lead-indium alloys can be treated as an underdamped oscillator.
Nonequilibrium superconductivity induced by normal-current injection
Authors: Sugahara Masanori
Published: February 2003

Theoretical investigations based on the Ginzburg-Landau theory and the consideration of the lifetime of normal particles and superparticles yields a new acceleration equation of superparticles and a diffusion-type equation for normal current in nonequilibrium superconductors. Derived relations are used to examine the experiments on normal-current injection in supernormal junctions and on the effective capacitance in superconducting microbridges. Good agreement is found between theory and experiment.
Critical-current densities of bronze-processed Nb3(Sn1−xGax) wires up to 23.5 T
Authors: Dew-Hughes D. , Suenaga M.
Published: February 2003

Gallium additions to the Cu-Sn bronze matrix in the production of Nb3Sn wires by solid-state diffusion raise Hc2(4.2 K) of the resulting compound to ∼25 T. This increase in Hc2, which is not accompanied by any significant increase in Tc, is associated with the incorporation of gallium into the A-15 compound which has the approximate composition Nb3(Sn0.9Ga0.1). Critical currents in a variety of Ga-containing wires, all reacted at 700 °C, have been measured in fields up to 23.5 T. This is the highest field at which steady-state current measurements have yet been made. The pinning force is found to be closely proportional to h1/2 (1−h)2, where h is the reduced field.
Detailed pulse-shape measurements of a TEA-CO2 laser mode locked by positive germanium
Authors: Gellert B. , Kronast B.
Published: February 2003

A helical TEA-CO2 laser was mode locked by inserting a positive germanium plate close to the plane mirror of a hemiconfocal type of resonator. Single pulses of the emitted sequence of nanosecond spikes were recorded with high time resolution. Best fitting the experimental curves to a Gaussian and (cosh)−2 time dependence revealed that the temporal pulse shape corresponds with great accuracy to the (cosh)−2 behavior as it is predicted in a theoretical treatment of Haus. Since this theory is dealing primarily with steady-state saturable absorber mode locking, it is also pointed out that it can be applied to the above case.
Fabrication and properties of high-temperature weak links and SQUID’s
Authors: Wu C. T. , Falco Charles M.
Published: February 2003

We present our latest results on the fabrication and properties of high-Tc Nb3Sn thin-film weak links and SQUID’s prepared by radiation damage of localized regions. Using radiation damage, we have successfully fabricated high-temperature thin-film weak links with current-voltage characteristics similar to those produced either by proximity effect or ion-implantation techniques. The critical current of these weak links obey a relation Ic∝ (T′c-T)3/2 for T<T′c, and Ic∝exp(−γT) for T≳T′c, where T′c is the intrinsic transition temperature of the radiation-damaged region. High-temperature (operation temperature ≳14.5 K) Nb3Sn thin-film SQUID’s with sensing area ∼3 mm2 have been successfully fabricated using these weak links.
Effects of metal on dispersion relations of magnetostatic volume waves
Authors: Yukawa Toshinobu , Ikenoue Jun-ichi , Yamada Jun-ichi , Abe Kenji
Published: February 2003

The dispersion relation of the magnetostatic volume wave in a normally magnetized ferromagnetic slab placed between two metal plates is analyzed. When the normalized spaces A=D1/S and B=D2/S, where D1 and D2 are the spaces between the slab and the metals and S is the slab thickness, are finite, the cutoff frequency Ωc exists in the dominant mode and becomes {ΩH[ΩH+1/(A+B+1)]}1/2, where ΩH =Hi/4πMs, Hi is the internal magnetic field, and 4πMs is the saturation magnetization. This frequency Ωc gives the lower limit of the frequency region in which the magnetostatic volume wave exists and varies with A+B from ΩH to [ΩH(ΩH+1)]1/2. The experimental values on the change of Ωc with A+B have agreed well with the theoretical results.
Voltage oscillations in switching VO2 needles
Authors: Fisher B.
Published: February 2003

Voltage oscillations observed in switching VO2 needles are associated with traveling semiconductor domains driven by the Peltier effect at their boundaries. The model is supported by the dependence on current of the two time constants characterizing the rectangular synchronous oscillations.
Influence of annealing on the surface-acoustic-wave velocity increase induced by ion implantation in quartz
Authors: Hartemann P.
Published: February 2003

A surface-acoustic-wave velocity increase is induced by implantation of helium ions at 100 keV in Y- and ST-cut quartz substrates. An important decrease of this velocity variation has been found after an annealing at about 560 °C, and it depends on the annealing time. After annealing, the features of the quartz layer perturbed by implantation of 1.3×1016 4He+/cm2 are close to those of vitreous silica at room temperature. Experimental and calculated results of the influence of an annealing on the surface wave velocity variation and the density of the perturbed layer are reported and discussed.
Elasticoviscous flow along a plane wall with periodic suction
Authors: Acharya B. P. , Tripathy U. K.
Published: February 2003

The flow of an elasticoviscous liquid past an infinte wall with periodic suction is discussed. Approximate solutions of the velocity fields and the pressure field have been obtained. The effect of the parameters Re (Reynolds number) and Rc (elastic parameter) on the quasi-two-dimensional corrections in the case of the velocity fields, pressure field, and skin friction have been discussed.
The role of chemisorption in plasma etching
Authors: Winters Harold F.
Published: February 2003

It is shown that the sticking probability (i.e., the probability for dissociative chemisorption plus the probability for nondissociative chemisorption where E≳20 kcal/mole) for CF4, CF3H, and CF3Cl on polycrystalline films of SiO2, Si3N4, and silicon is less than 10−7. The sticking probability for CF2Cl2 and CCl4 is detectable on some of these surfaces but still less than 10−6. Electron collisions with nondissociatively adsorbed molecules (E≳20 kcal/mole) are shown to result in the rapid buildup of adsorbed carbon and chlorine which will then remain on the surface indefinitely. It is further shown that CFx radicals have sticking probabilities between 0.08 and 0.75 on clean silicon. Based on these results, it is concluded that the dissociative chemisorption of stable gases is probably not important in plasma etching while radiation-induced-dissociative chemisorption and the chemisorption of CFx radicals are expected to play an important role.
Comparative study of annealed neon-, argon-, and krypton-ion implantation damage in silicon
Authors: Cullis A. G. , Seidel T. E. , Meek R. L.
Published: February 2003

Comparative annealing studies were carried out upon Si layers implanted with Ne+, Ar+, and Kr+ ions. Ion doses were in the range 6×1014/cm2–6×1015/cm2, and ion energies were chosen so that the matrix damage had approximately the same depth for each ion type. Annealing was carried out in a N2/dilute O2 ambient or in vacuum at 600, 900, or 1100 °C. Implanted layer structures were studied using electron-microscope and ion-backscattering techniques. The orientation of the Si substrate and ion-beam heating effects were found to be important in determining layer-annealing behavior. The latter depended weakly, if at all, upon the nature of the annealing ambient. Layer recrystallization was studied as a function of implanted ion type and dose, and the effects of inert gases trapped in the Si lattice were examined. The suitability of implantations for device gettering applications were considered. Crystallographic defects produced by annealing ranged from polycrystals and microtwins to simple dislocation networks. Faceted gas bubbles invariably occurred in annealed layers, and their geometry gave information regarding low-energy planes in Si. Electron diffraction and He+-ion channeling effects produced by twins in recrystallized layers have also been examined.
Viscoelastic characterization of isotropic solids using harmonic dispersion of longitudinal resonances
Authors: Galkiewicz R. K. , Karasz F. E.
Published: February 2003

An experimental technique utilizing the dispersion of the harmonics of longitudinal resonances is employed to measure Young’s modulus, Poisson’s ratio, and the logarithmic decrement simultaneously as a function of temperature. A knowledge of the temperature behavior of these three quantities completely characterizes the viscoelastic response of a material in the kilohertz frequency region. Measurements performed on the borosilicate glass KG-33 Kimax are presented for different sample geometries and temperatures and are compared with previous results in the literature.
Estimation of surface-layer structure from Rayleigh-wave dispersion. III. Sparse data case—Interpretation of experimental data
Authors: Tittmann B. R. , Richardson J. M.
Published: February 2003

Elastic surface waves penetrating into solids to a depth proportional to the wavelength are expected to be dispersive in the presence of gradients in physical properties such as density, chemical composition, internal stress, or metallurgical microstructure. This paper presents the results of studies to use this phenomenon to determine physical property profiles in a nondestructive manner. In a previous paper, a mathematical model was presented giving, for discrete data sets, a probabilistic description of the possible results of measurement, including measurement errors. The model also yields auxiliary measures pertaining to bias, data-vs-model dominance, resolution, and a posteriori variance. Here, the model is applied to actual experimental data consisting of the phase velocities of Rayleigh surface waves measured as a function of frequency for three typical profiles: a thin layer on a thick substrate, a thin layer embedded near the surface of a thick substrate, and a smoothly and monotonically varying profile. The estimated profile is compared with independent (destructive) measurements. As a test, the theory is also applied at a discrete set of frequencies to a set of synthetic data calculated from an assumed profile. The above auxiliary measures giving properties of the estimator are also discussed.
Controlled variation of rag-domain garnet film properties under oxygen annealing
Authors: Menegalli S. , Paroli P. , Tesei E.
Published: February 2003

Thermal treatments in oxygen atmosphere offer a convenient way of varying the properties of ’’rag’’-domain garnet films (namely, films showing macroscopic unperiodical domains because of the vicinity of the compensation temperature to room temperature). Substantial changes are obtained in the following parameters relevant for the application of rag-domain films to magnetic writing and magnetooptic displays: anisotropy field, domain nucleation field, optical transmission, and compensation temperature. The last can be changed in a range of 65 °C around the as-grown value. The temperature behavior of the magnetization and the transitions between rag and strip domains are studied.
Metastable Pb1−xCdxS epitaxial films. III. Optical properties
Authors: Sood Ashok K. , Zemel Jay N.
Published: February 2003

The optical properties of metastable epitaxial films of Pb1−xCdxS on NaCl were measured at room temperature for 0⩽x⩽0.38. The refractive index, high-frequency dielectric constant, susceptibility effective mass, and band gap were measured over this range. It was found that the fundamental absorption edge Eg(Pb1−xCdxS) could be written as Eg(Pb1−xCdxS) =Eg(PbS)+1.80x.
Pulsed laser heating of thick opaque targets in air
Authors: Robin James E.
Published: February 2003

An analytical model has been developed which describes the surface heating of a thermally thick opaque target in air when subjected to irradiation from a high-power pulsed laser. Both single pulsed and repetitively pulsed irradiation effects were examined. Effects due to the formation of a laser-supported absorption wave (LSAW) above the target surface are explicitly included in this model. The results show that despite the increase in thermal coupling due to the presence of the LSAW, the retarded heating effects experienced by tightly focused beams due to energy spreading as the LSAW expands over the target surface can be quite severe. This model shows that for small incident beam diameters the rate of temperature rise at the target surface can become negative during the pulse deposition time due to the combined effects of energy spreading and axial heat conduction.
Double-mesa reach-through avalanche photodiodes with a large gain-bandwidth product made from thin silicon films
Authors: Ataman Attila , Müller Jörg
Published: February 2003

A new geometry for an avalanche photodiode is presented which allows both a large gain-bandwidth product (300 GHz) at high frequencies and a high quantum efficiency in the 0.4–1-μm wavelength range. It is a thin-silicon-film double-mesa-shaped structure, which utilizes light reflection at the back metallic contact. The advantages of such a structure are discussed, and the fabrication steps and typical electrical and optical data of these diodes are presented.
Rayleigh-Brillouin light-scattering study of atactic polyethylmethacrylate (PEMA)
Authors: Mahler D. S. , Coakley R. W. , Stevens J. R. , Hunt J. L.
Published: February 2003

Rayleigh-Brillouin light-scattering studies have been carried out on atactic polyethylmethacrylate thermally polymerized under vacuum from extremely clean monomer. The scattered intensity ratio for the VV polarization geometry varies from 2 (at high temperatures) to 5 and appears to be a function of T−1 with a broad discontinuity in the temperature range 40–70 °C. Depolarization intensities have also been measured and, in particular, it is found that ρH equals unity. These results agree with those previously obtained for polybutylmethacrylate and are also compared with reports on polystyrene. Other characteristics of this glass are discussed.
Hypersonic attenuation in the n-alkanes
Authors: Patterson G. D. , Lindsey C. P.
Published: February 2003

The Brillouin spectra of n-dodecane, n-hexadecane, n-docosane, n-octacosane, and n-hexatriacontane are studied as a function of temperature. The Brillouin linewidths increase monotonically as the liquids are cooled toward the freezing point. The results are analyzed quantitatively in terms of frequency-dependent volume and shear viscosities.
The formation of the γ phase from the α and β polymorphs of polyvinylidene fluoride
Authors: Prest W. M. , Luca D. J.
Published: February 2003

Thermal, optical, infrared, and x-ray techniques are used to demonstrate that the γ phase of polyvinylidene fluoride can be obtained from existing α- and/or β-phase crystallites by either an annealing-induced solid state α→γ phase transformation or as the result of a slow melting and recrystallization process. It is shown that certain surfactants modify the melting behavior of the α and β phases in a manner that accelerates the rapid recrystallization of the γ form. PVF2 samples that contain only the γ polymorph can be produced by this surfactant-controlled technique. It is postulated that the surfactant delays the diffusion of molecules freed in the melting process and thus increases the probability of the stabilization of conformational fluctuations that result in the γ phase.
The aging of glassy polymers as determined by scanning calorimeter measurements
Authors: Robertson Richard E.
Published: February 2003

A model successfully applied to explain the volumetric relaxation of amorphous polymers near the glass transition has been used to predict the behavior in a scanning calorimeter of amorphous polymers annealed or aged below their glass transition. Although the predictions are incomplete because of the uncertainty of several critical parameters, the calculations indicate that caution is needed in interpreting scanning calorimeter data. Possible problems interpreting such data include (1) underestimation of the conformational heat capacity, (2) incorrect comparison of specimens aged at different temperatures, and (3) uncertain energy of the quenched state, against which aging is often compared.
Neutron-scattering studies of bulk polyethylene at intermediate Q values
Authors: Anderson J. E. , Bai S. J.
Published: February 2003

We report SANS studies of bulk polyethylene (PE) samples crystallized from the melt at different rates. All samples contained both protonated and deuterated PE. Substantial isotopic concentration fluctuations are present in slow-cooled samples. This is seen as large differences in the low-angle (low-Q) SANS. At larger Q values, the SANS data from both materials is approximately identical. We interpret this in terms of an exponential radial correlation function for composition fluctuation whose correlation length is comparable to lamellar dimensions. Numerical calculations show that concentration fluctuations have minimal effect in the intermediate Q region.
Piezoelectricity and pyroelectricity in polyvinylidene fluoride—A model
Authors: Broadhurst M. G. , Davis G. T. , McKinney J. E. , Collins R. E.
Published: February 2003

A description is given of the molecular and morphological structure of polyvinylidene fluoride and from this description a classical model is proposed for calculating the piezoelectric and pyroelectric properties. The model consists of an array of crystal lamellae with a net moment from aligned dipoles in the crystals and compensating space charge on the crystal surfaces. The results for no compensation and complete compensation essentially bracket experimentally observed results and indicate that the largest contribution to the activity of this polymer arises from bulk dimensional changes rather than from changes in molecular dipole moments.
Dynamic mechanical properties of collagen film and collagen film containing β-galactosidase
Authors: Yau B-J. , Woodward A. E. , Gilbert S. G.
Published: February 2003

The dynamic mechanical properties of strips of film prepared from cattle hide collagen film impregnated with the enzyme, β-galactosidase, were studied as a function of water content and temperature using a torsion pendulum at 0.4–1 Hz. In the temperature range of 120 to 300 °K four mechanical loss peaks are observed for collagen and the collagen-enzyme system. The temperature, position, and magnitude of these peaks depend on the water content and the presence of the enzyme. The results of this study are compared with those obtained earlier on various types of collagen. The molecular assignments for the four peaks and the location and behavior of the β-galactosidase in the system are discussed.
Neutron radiographs using the ionographic process
Authors: Scott P. B. , Johnson S. E. , Watson G. W. , Berger Harold
Published: February 2003

Thermal neutron radiographs have been made using ionographic techniques. With a fluence of 107 neutrons/cm2 at the image plane, image resolution of three line pairs per mm was demonstrated. The apparatus for these demonstration experiments is described, and alternative modes of operation are discussed. It appears possible to make ionographic neutron radiographs using a transmitted fluence of 106 neutrons/cm2.
Stark effect in high-frequency fields for resonant modulation
Authors: Kim S. H. , Chung Hae Yang
Published: February 2003

We solved in closed form the resonant-modulation problem for the effect of the high-frequency electric field on the absorption spectra of the three-level system. It is shown that an electric field whose frequency is made resonant with the separation between two upper levels should give rise to the two absorption lines of equal intensity disposed symmetrically in pairs about the allowed line. The separation between these two lines is linearly proportional to the intensity of the electric field. The positions and the property of equal intensity of these lines are the same in both the laser absorption spectrum and the ordinary absorption spectrum.