bluuebunny/crossref_metadata_2025 huggingface dataset:
rf sputtering of ZnO shear-wave transducers
Authors: Lehmann H. W. , Widmer R.
Published: February 2004

Thin films of ZnO with a large degree of preferred parallel orientation have been rf bias sputtered onto sputtered indium-tin oxide (ITO) on quartz. The orienting effect of the ITO film is partly due to some limited chemical reaction at the ZnO/ITO interface and partly due to a surface microtexture. An x-ray pole figure analysis indicates that the (10.0) planes of the ZnO are parallel to the substrate surface within ± 5° and that the direction of the c axes is parallel to the target surface within ± 20°. The preferred orientation of the c axes is only observed if both the ITO and the ZnO are sputtered onto the substrate at the same oblique incidence. The ZnO films have resistivities of the order of 108 to 1010 Ω cm. If the ITO/ZnO film couple is deposited onto a well-conducting ground electrode, efficient shear-wave transducers can be obtained.
Elastic energy of wedge disclination loops in hexagonal crystals
Authors: Chou Tsu-Wei , Pan Yen-Cheng
Published: February 2004

The plane of the wedge disclination loop is assumed to be parallel to the basal plane in hexagonal-close-packed crystals. The rotation axis of the loop lies in the basal plane. Closed-form solutions have been obtained for the stress field and elastic energy of the disclination loop. Unlike the case of a twist disclination loop, there is a dilatational field associated with a wedge disclination. The strain energies of wedge disclinations are computed for some common hexagonal crystals. It is noted that for the same loop dimension and angle of rotation, the strain energy of a wedge disclination loop is generally larger than that of a twist disclination loop. This is mainly due to the fact that, for these materials, the Young's moduli along the C axes are higher than those in the basal planes.
Coalescence kinetics of migrating crystallites
Authors: Robertson David
Published: February 2004

Assuming that small crystallites can perform noninteracting random walks on a substrate, one may calculate the expected rate of collisions between them and the rate of decrease of their numbers. Comparison with experimental results for gold on potassium chloride at temperatures less than 150°C (for which coalescence is not observed despite large root mean square displacements) indicates either that those crystallites do not diffuse as entities or that coalescences are inhibited. It is suggested that inhibition be due to elastic interactions, electrostatic interactions, or impurity effects.
Acousto-optical light diffraction in thin films
Authors: Ohmachi Yoshiro
Published: February 2004

The diffraction of optical guided waves in thin films through an acousto-optic effect is treated. The diffraction of the bounded optical waves in thin films is a rather complicated phenomenon as compared with that of the free waves in bulk media. An expression for the diffraction efficiency has been derived using coupled-wave equations. Acousto-optical figure of merit and the mode coupling factor applicable to the diffraction in thin films are defined. The TE0 and TM0 waves in an As2S3 film deposited onto a LiNbO3 substrate were diffracted by Rayleigh waves with 93 and 72% efficiency at electrical input powers of 150 and 50 mW, respectively. The present experiment revealed that approximately 5% of the total acoustic power penetrated into the film and took part in the diffraction.
Partial discharges in solid dielectrics and corona discharge phenomena
Authors: Mayoux C. , Goldman M.
Published: February 2004

By using techniques developed by many workers to study streamer mechanism in air between metallic electrodes, the phenomena of partial discharges in insulating walls were studied. It is shown that the luminous evolution of partial discharges consisted of the development of a primary and a secondary streamer, for positive pulses. The velocity of propagation of the primary streamer was about 5 × 105 m/s as for metallic electrodes. The electrically induced pulses and photon pulses have shown a correspondence between electrical and luminous phenomena for positive pulses, while Trichel pulses were observed for negative pulses. A cathodic zone was shown, and then a mechanism of erosion of insulating materials was conceived.
Near-infrared radiation intensity from restrikes of exploding wires
Authors: Vlastós Antonios E.
Published: February 2004

The time variation of the near-infrared radiation intensity from restrikes of exploding wires was studied for different currents and wire materials. The results show that the peak near-infrared radiation intensity form the restrike is proportional to the first current maximum and that the radiation reaches its peak slightly after the first current maximum. By using the computed values of the particle density and the temperature of the discharge plasma, it was possible to show that the reason why the radiation from the discharge reaches its peak near the first current maximum may be that the ionized particle density in the discharge channel reaches its peak near the first current maximum.
Simulation of a transient dc breakdown in a Penning mixture between two closely spaced parallel electrodes
Authors: Lay Frank M. , Chu C. K.
Published: February 2004

The results of a numerical simulation of a dc gas discharge in a mixture of neon + 0.1% argon are presented. The simulation is based upon a Townsend avalanche mechanism (direct ionization) and the ion secondary effect. The effect of the delayed electron due to Penning collision (indirect ionization) in the mixture is fully accounted for. Comparisons with the experimental results of Penning and co-workers are also made.
Fundamental aspects of electron beam lithography. I. Depth-dose response of polymeric electron beam resists
Authors: Heidenreich R. D. , Thompson L. F. , Feit E. D. , Melliar-Smith C. M.
Published: February 2004

The application of a phenomenological depth-dose theory to the exposure of negative electron resists is described in detail. The model predicts a cross-linking rate dnc/dt=(Gc/100) × (J0/e)(Va/RG)Λ(f) cm−3 sec−1, where Gc is the number of crosslinks produced per 100 eV lost in the polymer. Jo is the incident current density, Va the initial kinetic energy, RG the electron Grun range, and Λ(f) the depth-dose function in terms of the normalized penetration f=z/RG. Since the G value of a negative resist decreases with exposure, it is suggested that a more meaningful parameter characterizing a negative resist is the absorbed energy required to gel the polymer at the resist-substrate interface. This interface or threshold gel energy density, Eg(i), is independent of the beam parameters and varies from about 1022 eV cm−3 for polyvinyl ferrocene to 3.8×1018 eV cm−3 for epoxidized polybutadienes. The model predicts that the threshold sensitivity should vary as Va0.75 which agrees reasonably well with published experimental values. It also predicts that at a given accelerating voltage, there is a unique initial resist thickness at which the top surface and interface receive identical doses. This unique thickness turns out to be roughly the electron diffusion range RD. The transverse resolution or linewidth for negative resists has been investigated as a function of accelerating voltage and found to be given by twice the diffusion range. Since RD decreases with decreasing Va, the linewidth likewise decreases as the accelerating voltage is lowered. The optimum operating conditions for a 500-nm resist film for electron lithography are predicted to be Va≈5 kV exposed to yield about a 400-nm film after development. It should be noted that these conditions result in a maximum crosslink density per incident electron and a minimum linewidth. However, there may be specific applications where other sets of operating conditions are useful. A geometric model is suggested which appears to account for the observed behavior of sensitivity of negative resists.
Morphology and mechanical properties of crystalline polymers. II. Spherulitic polyethylene
Authors: Wang Tsuey T.
Published: February 2004

The elastic moduli of bulk polyethylene having a spherulitic structure are determined by the multistep method described in a previous paper. It is pointed out that the properties of the regular symmetrical spherulite are spherically isotropic (that is to say, the properties are the same in all directions tangent to a series of concentric spheres) and can be characterized by the same elastic constants as those of a cylindrical spherulite. The effective moduli of spherulitic polyethylene are then computed from the properties of individual spherulites by the self-consistent scheme of Hershey, Kerner, and Kroner. The results agree very well with existing experimental data for Young's modulus and shear modulus. The predicted bulk modulus is found to be strongly dependent on the estimated Poisson's ratio of amorphous polyethylene.
Measurements of refractive index step and of carrier confinement at (AlGa)As–GaAs heterojunctions
Authors: Kressel H. , Lockwood H. F. , Butler J. K.
Published: February 2004

The refractive index difference at the GaAs lasting wavelength of [inverted lazy s] 9000 Å has been experimentally determined, from the measured beam profile, for a range of (AlGa)As–GaAs heterojunctions of practical interest. Good agreement is found with values calculated from the change in band gap with increasing Al in (AlGa)As. We have also shown by direct measurement that the loss of electron confinement at p+-p heterojunctions follows a thermally activated process with activation energy equal to the difference in band gap at the heterojunction.
cw degradation at 300°K of GaAs double-heterostructure junction lasers. I. Emission spectra
Authors: Paoli Thomas L. , Hakki Basil W.
Published: February 2004

Spectral changes in the spontaneous emission from stripe-geometry GaAs double-heterostructure junction lasers have been observed to occur during their noncatastrophic degradation under continuous operation at room temperature. As a result of prolonged continuous operation, the optical wavelength for maximum external spontaneous emission increases significantly as the degradation progresses. In some lasers the wavelength shift has been observed to occur only in the emission from one mirror of the laser with the spectral emission from the other mirror remaining unchanged. The observed changes in rapidly degrading lasers are interpreted in terms of the formation of a localized region of high optical absorption within the active region. The absorbing region is identified by visual observation through the n substrate of a degraded laser as a volume in which little or no spontaneous emission occurs near the lasing wavelength. In addition, the absorption is shown to be dispersive, exhibiting a sharply increasing absorption edge with increasing energy.
Stress and temperature analysis for surface cooling or heating of laser window materials
Authors: Sparks M.
Published: February 2004

The maximum reduction in the average temperature 〈T〉z=b−1 ∫0b d z T of a slab of thickness b that can be obtained in both a short period of time, typically [inverted lazy s]1 sec, and a long period of time (steady-state approached) without causing material failure is calculated. The slab is originally at a constant temperature, and 〈T〉z is the temperature that determines the optical properties of a normally illuminated slab. The results indicate that Ge28Sb12Se60 glass can be cooled rapidly enough for use in laser systems at relatively high power levels (several hundred W/cm2) in the pulse mode of operation discussed previously, in contrast to previous beliefs. There is a time constant τs for the nonexponential approach of the surface temperature Ts of a semi-infinite medium to the temperature Tc of the coolant. Consider the thermally thin-disk case of τb≪τs, where τb is time required for heat to diffuse across the thickness b, roughly speaking. The value of 〈T〉z then approaches Tc exponentially with a time constant τc, which is much smaller than τs. For the thermally thick-disk case of τs≪τb, 〈T〉z[inverted lazy s](t/τc)Tc for t≪τs; 〈T〉z≃(t/τb)1/2 Tc for τs≪t≪τb; and 〈T〉z≃Tc for t≫τb. The solution to the heat-flow equation for T is known in simple closed form for the case of a semi-infinite medium. The result is quite accurate for finite disks, both thermally thick and thin, when t≪τb is satisfied. For this case of t≪τb, the maximum value of the magnitude of the stress component |σxx|(=|σyy|) is determined by the surface temperature Ts only. For a given temperature difference across the disk, the maximum value of |σxx| is less for the case of t≥τb than for the case of t≪τb. Two examples, GaAs and Ge28Sb12Se60 glass, are considered.
Controlled adjustment of bubble domain parameters in epitaxial garnet films by thermal annealing
Authors: Smith D. H. , Hagedorn F. B. , Hewitt B. S.
Published: February 2004

Controlled adjustment of the bubble domain collapse field has been demonstrated in epitaxial garnet films of nominal composition Y2.6Sm0.4Ga1.2Fe3.8O12 using a thermal annealing technique to redistribute gallium ions between the tetrahedral and octahedral sites in the garnet lattice. This technique involves annealing each film at two different temperatures, the first of which establishes equilibrium at a known temperature. Analysis, based on bubble domain theory, shows that the measured parameters after thermal equilibration can be used to calculate the change in saturation magnetization which will lead to the desired values of the bubble domain collapse field. The change in magnetization can be related to the required change in the equilibrium annealing temperature, Ta, from the derivative d(4πMs)/dTa. The value of d(4πMs)/dTa has been found to be approximately constant for 900≲Ta≲1200 °C and is equal to 0.35≲G/°C. By using this technique, the bubble domain collapse field can be changed by more than 10 Oe with a precision of a few tenths of an Oersted if the annealing temperatures are controlled to a fraction of 1°C.
Influence of solute oxygen and nitrogen on superconducting niobium cavities
Authors: Giordano S. , Hahn H. , Halama H. J. , Varmazis C. , Rinderer L.
Published: February 2004

The influence of solute oxygen and nitrogen on the magnetic breakdown and residual losses of superconducting niobium cavities was investigated experimentally by exposing the cavities to these gases at pressures up to 10−5 Torr during the heat treatment at 2100 K. We have collected evidence that the oxygen exposure increases the residual losses and, at bulk concentrations of about 0.1 at.%, the breakdown field is substantially lowered. Penetration depth measurements seem to indicate high values of the Ginzburg-Landau parameter κ ≈ 4.4 in the surface sheath which could explain the low rf breakdown observed.
Compositional dependence of cubic and uniaxial anisotropies in some mixed rare-earth garnets
Authors: Heilner E. J. , Grodkiewicz W. H.
Published: February 2004

We have measured the cubic and growth-induced uniaxial anisotropies of two series of bulk flux-grown garnets, Gd3−xEuxFe5O12 and Y3−xSmxFe5O12, at room temperature. In both series, the cubic anisotropy is approximately a linear function of composition between the end members, while the uniaxial anisotropy varies quadratically with composition.
Radiation-induced doping effects in a-tin
Authors: Gardiner R. B. , Myhra S.
Published: February 2004

An n → p transition has been observed for α-tin filaments irradiated with 0.675-MeV electrons at 5 K. Resistance and thermoelectric emf measurements were used to establish that the electron dose needed to effect the n → p transition is roughly proportional to the impurity concentration for n-type material. No transition was observed for p-type material. The data are interpreted in terms of radiation-induced trapping levels.
Electron spin resonance in argon-ion-implanted silicon
Authors: Chu Keh-Chang , Hurren Weiler R. , Hale Edward , Reigle John
Published: February 2004

A new paramagnetic center with g = 2.0029 is observed, in both n- and p-type silicon after they are heavily implanted (higher than 1017 ions/cm2) with 150-keV argon ions.
Waveguide dye laser amplifier
Authors: Burlamacchi P. , Pratesi R. , Salimbeni R.
Published: February 2004

A single-stage flash-lamp-pumped waveguide dye laser amplifier is presented. A Pyrex cylindrical dye cell filled with a rhodamine 6G solution in ethanol acts as an active hollow dielectric waveguide for the light to be amplified. Over-all efficiency and absolute energy gain are about one order of magnitude larger than for a conventional single-pass dye laser amplifier. Such a device can be conveniently used when inserted, with suitable couplers, in an optical waveguide system.
Phase transformation in bismuth under shock loading
Authors: Romain J. P.
Published: February 2004

The behavior of bismuth under shock loading was studied by means of a shock-detection technique based on the electrical response of bimetallic junctions and on the polarization effect of thin dielectric sheets under shock. The experiments were performed in the pressure range 50–180 kbar. A new shock-induced phase transformation was found to take place at about 70 kbar. A rough estimate of the temperature increase associated with shock loading, and comparison with data of static compression experiments suggest that this new shock-induced phase change in bismuth corresponds to the Bi III-V transformation, previously observed only under static pressure loading.
Compaction of ion-implanted fused silica
Authors: EerNisse Errol P.
Published: February 2004

Ion-bombardment-induced compaction of fused silica is measured using a cantilever plate technique for H, He, O, Ne, and A ions with a variety of ion energies. A phenomenological theory is developed which is based on the superposition of two independent compaction mechanisms, one proportional to the density of energy deposited into atomic collisions and the other dependent on the density of energy deposited into electronic excitations. All the present experimental data can be fit to within experimental error with the model using only three adjustable parameters and ion-energy partitioning calculations. Further substantiation of the present energy partitioning calculations and model are provided by showing the proportionality between the density of energy deposited into atomic collisions and other workers' published results for ion-bombardment-induced index-of-refraction changes in quartz and fused silica. It is concluded that the atomic-collision-induced-compaction and index-of-refraction changes are ion independent. Finally, a dose-rate dependence of the ionization-induced compaction is noted for the first time.
Energy-level structure and carrier transport in the poly(N-vinyl carbazole): trinitrofluorenone charge-transfer complex
Authors: Mort J. , Emerald R. L.
Published: February 2004

The photoinjection of electrons and holes from a sensitizing layer of amorphous selenium into films of the poly(N-vinyl carbazole) : trinitrofluorenone, PVK : TNF, charge-transfer complex has been studied by means of xerographic discharge techniques. The observed discharges are interpreted as being space-charge limited and thus allow a determination of the carrier mobilities as a function of TNF loading. The mobilities determined in this way are consistent with measurements reported which used the time-of-flight technique. The asymmetries of discharge observed depending on whether electrons or holes are injected from the selenium are thus associated with mobility limitations and not to significant energy barriers between the transport states in amorphous selenium and PVK : TNF. An upper limit can therefore be inferred for the separation between the transport states for electrons and holes in this charge-transfer complex.
Effect of Coulomb scattering on silicon surface mobility
Authors: Cheng Y. C. , Sullivan E. A.
Published: February 2004

Experimental results are presented and analyzed in order to demonstrate the importance of scattering by charge centers at or near the Si/SiO2 interface in the determination of the transport properties of inversion layer carriers in MOS structures. The measured mobility behavior clearly shows the relative importance of the effects of charges as a function of temperature and applied bias. The observations are compared with the existing theory of Coulomb scattering, and an attempt is made to present a theory which more correctly predicts the experimentally determined behavior.
Photovoltaic and rectification properties of Al/Mg phthalocyanine/Ag Schottky-barrier cells
Authors: Ghosh Amal K. , Morel Don L. , Feng Tom , Shaw Robert F. , Rowe Charles A.
Published: February 2004

The photovoltaic and rectification properties of Al/Mg phthalocyanine/Ag sandwich cells are reported. At low voltages, the current in the forward direction varies exponentially with voltage. A charge density of [inverted lazy s]1018/cm3 is estimated from C-V measurements. The short-circuit photocurrent JscαFm (m [inverted lazy s]0.5), where F is the incident light intensity. The open-circuit photovoltage Vocα logF as expected for a Schottky barrier or p-n junction. The J-V curve in the photovoltaic mode is characteristic of a cell with large series resistance. From the photovoltaic action spectra, the electron diffusion length is estimated to be [inverted lazy s]1.5×10−6 cm. The action spectrum is dependent on the direction of the incident radiation. A theory is presented which explains the results. The junction is attributed to a Schottky barrier of Vd ∼ 0.6 eV and width ∼ 2.5 × 10−6 cm estimated from C-V measurement. The values determined from photovoltaic measurements are in agreement. The lifetime of electrons is estimated to be ∼ 10−9 sec and the mobility ∼ 0.1 cm2 /V sec. The quantum efficiency for carrier generation is ∼ 1.5 × 10−3. At 690 nm, with light incident on the Al side, the photovoltaic efficiency is about 0.01%, one of the highest ever reported for organic photovoltaic cells.
Mode gain and junction current in GaAs under lasing conditions
Authors: Hakki B. W.
Published: February 2004

Although it is known that the small-signal gain calculations are in agreement with experimental results of lowest threshold for the zero-order mode in the thick-cavity PpnN junction laser, the theory for lasing mode stability under large-signal conditions has not been previously investigated. In this paper, a study is given of the geometrical conditions under which the best dynamic stability is obtained for the lasing mode in a structure capable of supporting several modes. Solutions are obtained for the carrier and gain spatial profiles in the active region of an injection laser under large-signal conditions by accounting for both spontaneous and stimulated recombination. The effect of stimulated emission in a lasing mode on the gain of a nonlasing mode is calculated. It is found that, for certain positions of the p-n junction within the optical cavity, an increase in lasing power in the zero-order mode suppresses the gain in higher-order modes. The optimum geometry for dynamic stability of the lasing zero-order mode is obtained when the gain region is two-thirds of the waveguide thickness, consistent with the condition for lowest zero-order mode threshold. In addition, the results also show that the quasi-Fermi level in the gain region changes as a function of stimulated power in such a way as to keep its spatially ``averaged'' value nearly constant. However, the position of the quasi-Fermi level at the p-n interface increases with increased optical power, thereby leading to a finite and positive junction differential resistance. Finally, for a double-heterostructure (DH) laser the calculated internal conversion efficiency, which is the ability of the stimulated field to extract power from the junction, is shown to decrease significantly when the thickness of the active region exceeds a carrier diffusion length.
Granular metal-semiconductor Schottky barriers
Authors: Wronski C. R. , Abeles B. , Daniel R. E. , Arie Y.
Published: February 2004

Granular metal-semiconductor barriers were investigated on n-type Si, GaAs, and CdSe single crystals. The barriers were formed by cosputtering metals, Au or Ni, and insulators, SiO2 or Al2O3, onto the semiconductor surface. By varying the relative volume fraction of the insulator over the range 0–90%, the structure of the granular metal changed from that of a continuous metal to that of isolated small ([inverted lazy s]20  Å ) metallic particles embedded in the insulator. Even with as little as 10% by volume of the metal, the granular metal contacts were found to behave as metal-semiconductor Schottky barriers. In the composition range 60–90% insulator in the granular metal, the barrier heights were independent of composition and their values were 0.57, 0.58, and 0.65 eV on Si, GaAs, and CdSe, respectively. In the case of Si and GaAs, the barriers are significantly lower than those observed for the pure metals; in the case of CdSe no such difference is found.
Optical properties of vapor-grown Inx Ga1−xAs epitaxial films on GaAs and Inx Ga1−xP substrates
Authors: Enstrom R. E. , Zanzucchi P. J. , Appert J. R.
Published: February 2004

The absorption coefficients for Inx Ga1−xAs epitaxial n - and p-type films have been determined for the composition range 0 < x < 0.25. The optical absorption coefficient is a parameter in the operation of negative electron affinity (NEA) photoemissive devices, and the experimentally determined absorption coefficient will be useful in the interpretation of NEA photoemissive device characteristics. In general, the optical absorption properties of n - and p-type Inx Ga1−xAs alloys vary smoothly with increasing indium content. The effect of lattice parameter mismatch between the Inx Ga1−xAs epitaxial film and GaAs or Inx Ga1−xP substrates on the optical absorption properties is shown to be negligible. Doping with zinc acceptor impurities ([inverted lazy s]1019 cm−3) does, however, apparently change slightly the characteristics of the Inx Ga1−xAs absorption curves, particularly at low In compositions. Two nondestructive methods of determining the acceptor density of zinc-doped GaAs epitaxial layers have been compared. The plasma minimum method is useful for acceptor concentrations above about 5 × 1018 cm−3, while the free-carrier absorption method gives quantitative values in the 1017–1019-cm−3 range.
Effect of gamma-ray irradiation on the surface states of MOS tunnel junctions
Authors: Ma T. P. , Barker R. C.
Published: February 2004

γ-ray irradiation with doses up to 8 × 106 rad produces no significant change on either the C(V) or the G(V) characteristics of MOS tunnel junctions with intermediate oxide thicknesses (40–60 Å), whereas the expected flat-band shift toward negative electrode voltages occurs in control thick oxide capacitors. A simple tunneling model would explain the results if the radiation-generated hole traps are assumed to lie below the valence band of the silicon. The experiments also suggest that the observed radiation-generated interface states in conventional MOS devices are not due to the radiation damage of the silicon surface.
GaAs–AlxGa1−xAs heterostructure laser with separate optical and carrier confinement
Authors: Casey H. C. , Panish M. B. , Schlosser W. O. , Paoli T. L.
Published: February 2004

Heterostructure injection lasers in which the GaAs active region is the center layer of a five-layer dielectric slab waveguide have been investigated. The GaAs active layer is bounded on each side by an AlxGa1−xAs layer to confine the carriers. The two outside layers which are AlyGa1−yAs(y > x) confine the optical field. Lasers with this structure have been fabricated and room-temperature threshold current densities Jth300 as low as 650 A/cm2 have been obtained for 1-mm cavity lengths. Differential quantum efficiencies ηD for these separate optical and carrier confinement heterostructure (SCH) lasers were higher than generally encountered for double-heterostructure (DH) lasers with values as high as 65% for [inverted lazy s]300−μ−long cavities. The external quantum efficiency of several typical units was determined as a function of input current, and for one representative unit a maximum value of 39% was obtained at about four times Jth300. Emission in the fundamental TE mode was obtained for symmetrical structures with optical waveguide thicknesses in excess of 1 μ at currents many times Jth300. The angle of beam divergence perpendicular to the junction plane was found to depend on the thickness of the optical waveguide w with half-power point values varying from 51° to 33° for w between 0.8 and 1.56 μ. Calculation of the optical intensity distributions for the symmetrical SCH structure demonstrated the influence of the AlAs mole fraction and layer thickness on confinement of the optical intensity and suggest that it should be possible to achieve still lower threholds.
Applications of the gyrocoupling vector and dissipation dyadic in the dynamics of magnetic domains
Authors: Thiele A. A.
Published: February 2004

This paper extends the theory of magnetic domains with emphasis on recent developments in ``hard bubbles''. A spin configuration of a planar Bloch wall containing periodic Bloch lines is presented which minimizes the magnetostatic energy to first order in the parameter 2πMs2/Ku for arbitrary period. The form of this solution is found to suggest the form of the dynamic breakdown of this spin configuration. The remainder of the paper consists of applications of the gyrocoupling force and vector, fg = g × v and g = − (Ms/|γ|)sinθ(▿θ) × (▿φ), respectively, and the dissipation force and dyadic, fa = d · v and d = − α(Ms/|γ|)[(▿θ)(▿θ) + sin2θ(▿φ)(▿φ)]. The use of fg and fa produces results with fewer assumptions and with less calculation than with previous methods. The magnitude of g is found to be an invariant local measure of the ``hardness'' of the domains. Integrating fg and fα produces a general planar wall response function from which the hard bubble dynamic equation is obtained. It is found that the difference between the hard bubble and normal bubble damping parameters can be accounted for by examination of the hard bubble spin-wave spectrum. An estimate of the velocity required for the production of horizontal Bloch lines is made using fg. This velocity is a substantial fraction of the Walker velocity. The vector g is used as an aid in the visualization of the mechanism by which ion implantation suppresses hard bubbles. From the point of view of both mobility and hard bubble suppression, materials having a large in-plane anisotropy are found to be desirable.
Interaction of a magnetic domain wall with an electric current
Authors: Charap S. H.
Published: February 2004

The electromagnetic interaction between a wall separating two magnetic domains and an impressed electric current is studied in quasistatic approximation. In this case, unlike the related eddy-current loss problem, the wall velocity calculation requires explicit consideration of magnetic losses which limit the wall velocity, otherwise the wall velocity v would reach the carrier drift velocity vD. For a magnetic bubble in a material having wall mobility μω and coercive force Hc, we calculate ν=[1−(4/π)(Hc/Hd0)]νDνm/(νD+νm), where Hd0 is a calculated drive field and νm=μωHd0.
Flux kinetics and heat flow during flux jumps in type-II superconductors
Authors: Harrison Robert B. , Wright Laurie S. , Wertheimer Michael R.
Published: February 2004

The Faraday-rotation technique in combination with high-speed cinephotography has been used to study flux kinetics and heat flow associated with flux jumps in type-II superconductors. It has been shown that at ``runaway'' velocities, flux motion can be better described in terms of an exponential rather than a diffusion law. Transients observed to exist in the flux-penetrated region and thought to represent a flux relaxation or redistribution following the jump have been shown to be associated with heating effects in the Faraday glass. Heat flow and its relationship to the flux kinetics was studied for the particular case of a Nb–25%Zr disk sample at 1.4 K in different thermal environments; that is, in a vacuum or immersed in liquid-helium II. In the latter case, heat transfer to the bath was about three orders of magnitude more important than thermal conduction within the sample. Nevertheless, the assumption that flux jumps take place under essentially adiabatic conditions, made for purposes of analysis, turns out to be approximately correct; this supports the theoretical treatments of Swartz and Bean and Wipf.
Neutron small-angle scattering investigation of voids in irradiated materials
Authors: Mook H. A.
Published: February 2004

Neutron small-angle scattering has been used to measure the distribution of voids in irradiated aluminum crystals. The scattering measurements were obtained with a spectrometer utilizing the focusing properties of nearly perfect germanium crystals. Direct inversion of the scattering data yields void distributions very close to those obtained with electron microscopes for similar aluminum samples.
Penetration and energy deposition of electrons in thick targets
Authors: Jacob J. H.
Published: February 2004

The transport and energy deposition of fast electrons in multilayer targets are investigated. For a highly peaked distribution function of electrons impinging on a target, it is necessary to use a high-order diffusion theory to adequately represent the distribution function. To a first approximation the energy loss is neglected in any given layer. The average energy loss per layer is then calculated using the Bethe stopping power and knowledge of the electron multiple scattering. Once the beam penetrates a distance of about one-fifth the transport mean free path, it becomes possible to use the Bethe age diffusion equations provided that the atomic number ≥ 13 and the electron energies are below 1 MeV. A combination of the diffusion and high-order diffusion theory is also used to compute the backscattered current and energy. Limitations and regions of validity of the above theories are also discussed.
Effect of magnetic field upon plasmas produced by laser-induced gas breakdown
Authors: Loter N. G. , Raff G. J. , Cohn D. R. , Halverson W.
Published: February 2004

The effect of a magnetic field upon the properties of a plasma created by CO2 laser-induced gas breakdown in helium has been investigated. Spatially and temporally resolved temperatures in the 7–20-eV range were observed using the spectral-line ratio technique, in particular the He II 468.6-nm line-to-continuum ratio. The continuum measurements were also employed to obtain relative values of electron density. The temporal dependences of electron density and temperature indicate that energy is lost from the plasma by an adiabaticlike expansion. The presence of the magnetic field significantly decreases both the energy and density loss rates.
Amorphous structure heat: Molecular mechanisms from solution heats of poly(2,6-dimethyl-p-phenylene oxide) in orthodichlorobenzene
Authors: Filisko F. E. , Raghava Ram S.
Published: February 2004

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both quenched and as-received polyphenylene oxide. The curves are linear below 110°C with slopes of 0.098 cal/g°C and linear above 110°C with slopes of 0.032 cal/g°C. The inflection at 110°C is attributed to a β transition. The plot for the as-received material is displaced vertically from that of the quenched material by 2.75 cal/g which is attributed to the fact that the as-received material contains about 27.5% crystallinity. The major component of the heats of solution is the exothermic contribution from the solvent-induced freeing or relaxation of the constrained molecular motions.
Fracture surface morphology of some crystalline block copolymers—propylene/ethylene and tetramethyl-p-silphenylenesiloxane dimethylsiloxane
Authors: Kojima M. , Magill J. H.
Published: February 2004

The fracture surface morphology of block copolymers of (i) tetramethyl-p-silphenylenesiloxane/dimethylsiloxane (TMPS/DMS) and (ii) propylene/ethylene (P/E) has been studied. The TMPS/DMS samples had compositions ranging from 90/10 to 30/70 wt% ratios. The ethylene content in the P/E samples ranged from 8 to 13%. A few polyolefin blends were also examined. Materials were fractured at liquid-nitrogen temperatures and studied under ambient conditions by scanning and transmission electron microscopy. X-ray methods and differential scanning calorimetry (DSC) techniques were also used. Copolymers with higher TMPS compositions exhibited a lamellar texture, but at high DMS contents fracture appeared ``glassy''. All TMPS/DMS samples exhibited spherulitic structures. Spherulites were mainly banded and were negatively birefringent. In samples with higher TMPS content, fracture occurred predominately between lamellar bands. The DMS component rejected by the crystalline TMPS hard segments is largely responsible for the observed fracture behavior and for the tensile properties of these copolymers particularly where this phase predominates. In the P/E copolymers both large and small globular particles are observed. Ethylene and propylene form separate crystalline phases. The interfacial characteristics between the large aggregates and the polypropylene matrix are believed to be responsible for impeding fracture porpagation in these materials, as assessed by impact tests. The influence of annealing conditions on the observed morphology has been investigated.
Theory of polymer crystal thickening during annealing
Authors: Sanchez I. C. , Peterlin A. , Eby R. K. , McCrackin F. L.
Published: February 2004

A previous theory of thickening has been extended to encompass the possible dependence of cooperative chain transport on lamella thickness and crystallinity changes during annealing. These have marked effects on the thickening rate leading to changes in slope and departures from straight-line behavior of the plots of lamella thickness versus the logarithm of time. The resulting curves bear a resemblance to many exprimental ones in the literature. Also brought out by the analysis is the important fact that the volumes of the coherently thickening domains are not known from experiment.
Holographic interferometry of crazes in polycarbonate
Authors: Peterson Timothy L. , Ast Dieter G. , Kramer Edward J.
Published: February 2004

Holographic interferometry has been used to determine the differential stress concentration at the tip of a craze as a function of over-all strain. The differential stress concentration factor δKσyy is unity at low strains. Upon further strain increase, δKσyy increases, passing through two maxima before it finally decreases again to approximately a value of unity before fracture. In addition, the differential craze opening displacements of, and stress increments borne by, various regions along the craze have been determined as a function of strain. It is found that the craze opens unevenly, with the base of the craze opening at lower applied stresses than the craze tip. As a result, the differential stress concentration in the craze at a point well behind the craze tip can be greater than that at the craze tip. The strain dependence of δKσyy is in qualitative agreement with that expected, given the nonlinear stress-strain curve of similar crazes measured by Kambour and Kopp. A detailed explanation of the stress concentration and the uneven craze opening requires consideration of the structural differences between craze fibers in the base and tip of the craze as well as the possibility of structure differences along individual fibers in the craze.
Nucleus growth rate of vacuum-deposited thin films
Authors: Fujiwara S. , Terajima H. , Ozawa S.
Published: February 2004

The nucleus growth rate in the initial stages of thin-film formation has been discussed on the basis of the collision theory of a two-dimensional gas and the diffusion theory of surface adatoms. It has been shown that, in the formulation of the area of the capture zone, the former theory is suitable for small nuclei (ρ < 0.27) and the latter for large nuclei (ρ > 0.27), ρ being the ratio of the nucleus radius to one half of the mean diffusion distance of single adatoms. The foregoing theoretical considerations were examined by the deposition experiment of bismuth films onto mica substrates. It has been found that the calculated deposition time, required for obtaining amount of deposits, agrees well with the observed one.
Finite-amplitude elastic-plastic wave propagation in fiber-reinforced composites
Authors: Hegemier G. A. , Gurtman G. A.
Published: February 2004

An approximate nonlinear theory is developed to describe waveguide-type propagation in unidirectional fibrous composites. The model, which is an extension of a previously developed laminate formulation, explicitly considers the effects of thermodynamics, finite deformations, and nonlinear (elastic-plastic) constitutive behavior. The theory contains microstructure and yields information on stress, deformation, and internal energy within individual components. The resulting equations assume the form of a one-dimensional binary mixture theory. Transient wave propagation solutions are obtained numerically, and are compared with essentially exact data from a well-known two-dimensional finite difference code in an effort to extract information concerning accuracy and computational economy of the mixture model.
Determination of coupling coefficient in second harmonic generation of acoustic surface waves
Authors: Alippi A. , Palma A. , Palmieri L. , Socino G.
Published: February 2004

In a slightly dispersive y-cut sample of LiNbO3 the complex coupling coefficient between fundamental and second harmonic acoustic surface waves has been measured through the intensities of the light reflected from the corrugated surface into second diffraction orders. The values have been separately obtained for both +z and −z propagation directions.
An acoustically resonant system for detection of low-level infrared absorption in atmospheric pollutants
Authors: Goldan Paul D. , Goto Kenya
Published: February 2004

The use of acoustic detection for the measurement of infrared absorption in gases has been shown to be of value in measuring atmospheric pollutant gases. Further improvements in detection sensitivity may be achieved by the use of an acoustically resonant system and multipass optics wherein the incident laser radiation is reflected many times through the absorption sample. We have demonstrated acoustic Q's exceeding 750 and sensitivity increases of at least 10 using multipass optics. A microphone amplifier pair is described whose noise limitation approaches the thermal noise on the microphone diaphragm.
Theory for nonlinear coupling between a piezoelectric surface and an adjacent semiconductor
Authors: Otto Oberdan William
Published: February 2004

The problem of nonlinear coupling of surface waves in an insulating piezoelectric to an adjacent but mechanically isolated semiconductor is treated theoretically. A perturbation approach is used with a small-signal nonlinear field expansion to obtain nonlinear coupling equations in terms of the linear material parameters and geometry of the system. The limiting case of the linear solution is related to other linear coupling theories. The special case of the surface-wave convolver is treated and compared to other convolver theories.
Effects of electrode curvature, distance from glass insulator, and addition of hydrogen on field-emission currents and breakdown voltage in vacuum
Authors: Hackam R. , Salman S. K.
Published: February 2004

Measurements of the prebreakdown currents have been made for highly polished stainless-steel electrodes in an ultrahigh vacuum (UHV) at 10−9 Torr as a function of electrode separation in the range 0.5–3.81 mm. Three sets of electrodes are employed to investigate the dependence of the prebreakdown current on the radius of curvature of the electrodes and the electrodes-insulator distance. The breakdown potential is measured in UHV gaps over the gap length range 0.25–4.57 mm and in hydrogen, in the pressure range 3 × 10−9−1.5 × 10−2 Torr, over the gap length range 0.38–0.76 mm. It has been found that the breakdown voltage, the electric field enhancement factor, and the prebreakdown current are independent of electrode-glass-insulator distance in the range 1–12.65 mm for a fixed gap length and a fixed radius of curvature of the electrodes. On the other hand, increasing the radius of curvature of the edge of the flat electrodes, at a fixed gap length, results in (i) large increases in the prebreakdown currents, (ii) increase in the electric field enhancement factor at the cathode, and (iii) a decrease in the breakdown voltage. The addition of hydrogen causes an increase in both the prebreakdown currents and the field enhancement factor, at a fixed gap distance. The field enhancement factor at the cathode is determined from the Fowler-Nordheim field emission theory and was found, in all cases, to increase initially with increasing gap length until saturation is reached, and therein it remains constant. The breakdown potential of vacuum gaps is found to follow a linear field-emission dependence on gap separation up to 1 mm. At higher gaps a transition to the Cranberg clump mechanism is observed with a dependence law on distance to the power of 0.45. The critical electrical breakdown field at the cathode in high vaccum is determined to be (7.8 ± 1.3) × 109 V m−1.
Electromagnetic scattering by a three-dimensional conducting rectangular box
Authors: Tsai L. L. , Dudley D. G. , Wilton D. R.
Published: February 2004

The scattering problem of a perfectly conducting rectangular box illuminated by a linearly polarized electromagnetic plane wave is numerically solved through consideration of the vector magnetic field integral equation. Because the scattering obstacle is three-dimensional and possesses no rotational symmetry, the vector integral equations consist of coupled scalar integral equations, which are reduced by the method of moments. Numerical results are presented for broadside incidence where symmetry arguments are used to produce an eightfold reduction in matrix size. Calculated currents and radar cross sections for a square plate and a cube show good agreement with measurements found in the literature. Techniques for analyzing the case of arbitrary incidence are also included.
The theory of the transient behavior of a plasma injected into a trap-free semiconductor at constant current
Authors: Zee Benjamin , Lampert Murray A.
Published: February 2004

The theoretical problem of the transient behavior of a plasma injected, at constant current, into a trap-free semiconductor is solved exactly. Coincident with the arrival of the propagating injected-plasma front at the collecting electrode there is a cusp in the time-derivative-of-the-voltage-vs-time profile. At any instant of time, the relative field-intensity distribution within the injected plasma region is the same as in the steady state.
Electrocooling in gases
Authors: Kibler K. G. , Carter H. G.
Published: February 2004

Significant surface-temperature decreases may be achieved by generating a corona discharge near a heated object. We demonstrate that this electrocooling phenomenon may be ascribed to an electric wind which results from ionic drag and which produces a convective heat-transfer coefficient that is proportional to the fourth root of corona current.