bluuebunny/crossref_metadata_2025 huggingface dataset:
Recombination lasing in a magnetoplasmadynamic arcjet
Authors: Campbell E. M. , Jahn R. G. , von Jaskowsky W. F. , Clark K. E.
Published: February 2003

The plasmadynamic recombination laser concept is verified experimentally in a high-power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s Ar II transitions are established by collisional-radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of seven such transitions, 5145, 4880, 4764, 4727, 4658, 4579, and 4545 Å, is observed spectrophotograpically and photoelectrically over the entire 1-msec discharge.
Simultaneous stimulated Raman scattering and optical frequency mixing employing a three-mirror Raman configuration
Authors: Ammann E. O.
Published: February 2003

The simultaneous occurrence of stimulated Raman scattering and optical frequency mixing in LiIO3 at kHz PRF’s (pulsed repetition frequency) has previously been investigated using a two-mirror internal Raman configuration. These simultaneous processes produce multiple visible outputs that are selectable by rotating the LiIO3 crystal. In this paper, the same simultaneous processes are investigated using a three-mirror configuration. It is found that the three-mirror configuration yields smaller average visible output powers, but larger peak powers, than the corresponding two-mirror configuration.
Raman-like scattering processes in metastable hydrogenic atoms
Authors: Heno Y. , Maquet A. , Schwarcz R.
Published: February 2003

Differential and total cross sections for various competing two-photon processes in metastable 2s hydrogenic atoms are given for several current laser frequencies. Exact calculations are performed within the framework of conventional time-dependent perturbation theory by using a Sturmian representation of the Coulomb Green’s function. Our results are useful for discussing a recent proposal for obtaining intense vacuum uv light sources from anti-Stokes Raman scattering.
The hollow-cathode helium-fluorine laser
Authors: Crane J. K. , Verdeyen J. T.
Published: February 2003

It is possible to obtain uniform stable long-pulse excitation (?100 μs) in gas mixtures involving highly electronegative constituents (SF6, CCl4, NF3, and I2). Such a system was used to investigate the atomic fluorine laser. In the hollow cathode, lasing on fluorine transitions in the doublet system lasted for up to 80 μs with no signs of the self-termination as reported previously in positive-column devices. The excitation process of the laser appears to depend heavily upon the fluorine donor utilized. For instance, a single-step process is involved when NF3 is used whereas a two-step process is evident for SF6. The details will be discussed.
Kinetic modeling of rotational nonequilibrium in chemical lasers. A comparison of three models applied to the Cl2/HI/He system
Authors: Reuven Yakir , Ben-Shaul Avinoam , Baer Michael
Published: February 2003

In this study three theoretical models which yield the temporal evolution of photon densities and population levels for a pulsed chemical laser are compared. The models are applied to the Cl2/HI/He chemical laser system. The simplest one is the well-known Boltzmann equilibrium model (BEQM) which assumes instantaneous rotational equilibrium throughout the lasing period. This assumption is removed in the detailed rotational nonequilibrium model (DRNM) which follows the time development of each vib-rotational population level separately. A third model, recently introduced by Baer, Top, and Alfassi, is an approximate rotational relaxation model (ARRM) which represents the rotational distribution in each vibrational level as a linear combination of three known functions with time-dependent coefficients. The main conclusions are as follows: (1) The BEQM is inadequate for providing the properties of a laser operating under low and intermediate inert-gas pressures. It can serve at most to derive an upper bound for the actual laser performance. (2) The ARRM provides very good estimates of total laser energy and efficiency as well as of more detailed properties, such as band intensities and the temporal behavior of the vibrational populations, for a wide range of pressures. (3) The use of the DRNM cannot be avoided if fine details, such as spectral distribution of output energy or rotational energy profiles, are required.
Surface wave scattering from elliptical cracks for failure prediction
Authors: Tittmann B. R. , Buck O. , Ahlberg L. , De Billy M. , Cohen-Tenoudji F. , Jungman A. , Quentin G.
Published: February 2003

The scattered radiation patterns from surface cracks irradiated by acoustic surface waves are interpreted to provide estimates of crack length and aspect ratio, geometric crack parameters needed to enable failure prediction. The technique is demonstrated for circular and elliptical cracks as small as 100 μm in depth with an accuracy of about 10%. The key features are the positions and spacing of peaks and nulls in angular frequency dependence of scattered surface wave intensity. A simple model based on optical diffraction theory is demonstrated on cracks in commercial hot-pressed silicon nitride studied at 100 MHz and on spark-eroded slots in commercial aluminum studied at 2–10 MHz. The results are used to calculate the stress intensity factors and to describe the direction of crack propagation for a variety of real and simulated cracks. Implications of the technique with respect to crack closure and effects of stress and time are also discussed.
Isotope separation in supersonic molecular beams using rf spectroscopy
Authors: Amirav Aviv , Even Uzi
Published: February 2003

Radiative isotope separation (without lasers) has been achieved using isotopic differences in the rf spectrum of paramagnetic molecules in a supersonic nozzle beam. The combination of molecular-beam magnetic resonance and supersonic molecular-beam techniques can be used for isotope separation on a large scale. The principle was demonstrated experimentally for molecular oxygen. The vastly larger isotope spectral differences, the tunability of the spectra by external fields, and the use of the well-developed technologies are promising starting points for this technique.
Experimentally determined absorption for spherical-shell targets
Authors: Segall Stephen B.
Published: February 2003

Energy absorbed by spherical-shell targets irradiated using the KMSF ellipsoidal-mirror illumination system at powers on target of up to 1.0 TW has been measured using a thermopile differential calorimeter. Data are presented for 1.06 and 0.532-μm laser light, for glass and low-atomic-number PVA targets, and for laser configurations with and without a plasma spatial filter.
Necessary conditions for the homogeneous formation of pulsed avalanche discharges at high gas pressures
Authors: Levatter Jeffrey I. , Lin Shao-Chi
Published: February 2003

The preionization level and other initial conditions necessary for the formation of spatially homogeneous pulsed avalanche discharges at high gas pressures are examined. Assuming properly shaped electrodes with no strong edge effects, the minimum preionization level required for homogeneous discharge initiation is found to depend on the voltage rise time across the electrodes as well as on the total pressure and various electrochemical properties of the gas mixture which govern the net rate of change of the first Townsend coefficient with respect to the local electric field strength. Our predictive results are found to be consistent with experimental observations.
Spatial distribution of plasma in a transverse-discharge supersonic nitrogen stream
Authors: Garcia M.
Published: February 2003

Experimental and theoretical studies were conducted on plasma in a supersonic channel containing a transverse plate discharge and localized pin-discharge ionizers. The goal was to determine the mechanism by which the plasma was created and distributed in such a discharge channel, where a nitrogen flow and both discharges operated continuously. Spatially resolved measurements of neutral density (N?1018 cm−3), flow velocity (u?540 m/s), voltage distribution between the discharge plates (voltage drop ?2 kV), and plasma density distributions have allowed for the determination of such plasma properties as the ratio of electric field to total number density (E/N?10−16 V cm2), the ambipolar diffusion coefficient (Da?40 cm2/s at N?1018 cm−3), and the average electron energy (ε?0.1 eV). The experimentally determined plasma density distributions are shown to be consistent with the predictions of a continuum quasineutral convection-diffusion model with pin-discharge source terms. The theory models all the major features of the plasma flow in the discharge channel, and can be used for future design studies of potential laser devices.
Relativistic electron-beam propagation in vacuum with ion acceleration
Authors: Taylor Peter L.
Published: February 2003

A self-pinched relativistic electron beam is injected through a thin foil into vacuum with no externally applied magnetic field. The beam is observed to propagate at currents well above the space-charge-limiting current (∼3 kA) but limited to the Alfven current (∼30 kA). Propagation results from charge neutralization of the beam by ions accelerated out of the anode plasma as confirmed by various ion diagnostics. Ions are collectively accelerated to greater than the electron energy. The experimental results are in qualitative agreement with a one-dimensional time-dependent computer simulation.
Interaction of CO2 laser radiation with a dense Z-pinch plasma
Authors: Neufeld C. R.
Published: February 2003

We present results obtained when a TEA-CO2 laser pulse is radially incident on a dense hydrogen Z-pinch plasma. Perturbations of the plasma column are visible on high-speed streak photographs. Spectral measurements indicate that stimulated Brillouin scattering in the underdense plasma regions is the dominant mechanism for the observed backscattering of laser radiation by the plasma column. The time behavior of the backscattered signal can be very complex, both prompt and delayed backscatter having been observed under ostensibly identical experimental conditions. The backscattered power is typically 1–2% of the incident laser power.
Trans-gauche concentration in crystalline polyethylene measured by the intensity of rocking mode vibrations of deuterated methylene groups
Authors: Reneker D. H. , Mazur J. , Colson J. P. , Snyder R. G.
Published: February 2003

Polyethylene with a low concentration of deuterated methylene groups displays an infrared band in the frequency region 646–651 cm−1. This band is attributed to a rocking normal mode of a CD2 group with one of the adjacent dihedral angles approximately trans and the other approximately gauche (tg). This mode vibrates at 620 cm−1 when the dihedral angles adjacent to the CD2 group are both trans (tt). In polyethylene crystals tg sequences can occur only in defects where constraints cause some of the dihedral angles to be approximately trans or gauche. Calculations of the rocking mode vibrational frequencies of CD2 groups in model chains which incorporate some of the typical defects showed that the bands were broadened but not completely disrupted by the distorted dihedral angles. Measurements of the relative intensities of the CD2 rocking bands show an increase in the concentration of tg sequences consistent with the thermal generation of defects which may be involved in transport of the polymer chain through the crystal. Confidence in the particular values of the concentration ratio is limited by uncertainties in the determination of the base line for the infrared bands of interest. Quantitative measurements of the concentration ratio tg/(tg+tt), determined from the integrated band intensities, fall between limits set by reasonable independent estimates of the concentration of folds and point dislocations.
The crystal structure of phase IV of poly(vinylidene fluoride)
Authors: Bachmann M. , Gordon W. L. , Weinhold S. , Lando J. B.
Published: February 2003

The crystal structure of phase IV (polar α or δ phase) poly(vinylidene fluoride) was studied by x-ray diffraction. Oriented phase IV was obtained by orienting phase II (α phase) and then corona poling at approximately 2 MV/cm. The resulting material is a mixture of phases I, II, and IV. Infrared spectra indicate that phase IV has the same chain conformation (TGTG′) as phase II. The reflections of phase IV can be indexed to an orthorhombic unit cell with lattice constants similar to the phase II lattice constants, a=0.496 nm, b=0.964 nm, and c (chain axis)=0.462 nm. There are two chains in this unit cell. The two chains pack with the chain dipole moments parallel. Three different ways of packing the chains were investigated: both chains up, one up and one down, and a statistical up-down packing. It was found that to within a 97% confidence level, the chains pack with a statistical up-down packing.
Pressure dependence of the glass transition and related properties of Solithane 113 elastomer
Authors: Questad D. L. , Pae K. D , Newman B. A. , Scheinbeim J. I.
Published: February 2003

Several studies have been carried out on a polyurethane elastomer (Solithane 113). At atmospheric pressure, dielectric methods were used to study ε″ over the temperature range from −180 to +20 °C. Three peaks in ε″ were observed: an α peak associated with the glass transition and two low temperatures peaks ( β and γ). Mechanical tests were peformed to osberve the effect of the pressure-induced glass transition Pg on the Young’s modulus. The glass transition was studied of pressure from 1 bar to 6.5 k bar by observing the shift as a function of the dielectric α peak with pressure and also by volumetric methods. A densification of the glass and a resultant shift in the glass-transition temperature could be achieved by forming the glass at high pressures (Tg) as opposed to pressuring the glass formed at 1 bar (T*g). It was found that Δβ/Δα≳dTg /dP, but Δβ/Δα?dT*g /dP. At high pressures, dTg /dP reached a limiting value of 10.4 °C/kbar.
Molecular deformation of polypropylene
Authors: Wool R. P. , Boyd R. H.
Published: February 2003

Molecular deformation of polypropylene (PP) was investigated by stress infrared experiments on ultraoriented isotactic PP samples, and the results were compared with single chain deformation calculations. A nonlinear stress-strain curve of PP was determined in a strain range of 8% which resulted in an average chain modulus, Ec ?40 GPa, and an initial Ec ?30 GPa. PP chain stretching was accompanied by considerable C-C bond stretching and valence angle bending in addition to torsional angle changes. Vibrational frequency shifts Δν with stress were calculated using both harmonic and anharmonic potential energy functions for C-C stretching. The harmonic results incorrectly predicted a considerable number of Δν’s to higher frequencies in addition to lower frequencies. Experimentally, only one band shifted to higher frequencies, and shifts to lower frequencies generally increased with increasing temperature. These results are in agreement with the anharmonic calculation in which the majority of vibrations shifted to lower frequencies. Detailed valence coordinate changes and vibrational frequency shifts with stress and temperature are presented and discussed.
Evaluation of the stress-relaxation modulus for materials with rapid relaxation rates
Authors: Lin K. S. C. , Aklonis J. J.
Published: February 2003

The stress-relaxation modulus E(t) is defined in terms of an experiment involving an instantaneously applied strain; such experiments are, in practice, impossible. We have critically investigated several methods which have been suggested in the literature to extract E(t) from experimental stress values used to bring about a constant-strain rate followed by a constant strain; such strain histories are easy to realize in the laboratory. Strengths and weakness of the various methods are analyzed in terms of data generated via an appropriate analytical expression. In addition, an alternative technique for converting experimental data to E(t), which involves a direct fit of this analytical expression to experimental data, is suggested. The accuracy of this last method has been assessed using stress-relaxation data for polystyrene in the primary (glass to rubber) transition region.
On a coupled set of nonlinear diffusion equations
Authors: Lonngren Karl E. , Johnson Stevens F.
Published: February 2003

We show that the set of coupled nonlinear diffusion equations nt =μnxx−d [(n/s)sx]x and st =Dsxx−AnsB admits a self-similar solution. These equations have been used in biology to model the migration of bacteria into a substrate. An asymptotic solution in the limit of large η≡x/(4xt)1/2 is obtained.
Measuring the pulse energy of a nitrogen laser with a potassium ferrioxalate actinometer
Authors: Grüter Hans
Published: February 2003

The article describes the application of a chemical actinometer system to the measurement of UV pulses from a nitrogen laser. The procedure, which is easy to carry out, shows in linear form the absorbed energy in the range of approximately 10–900 mJ. No change in the quantum yield was observed up to a pulse power of 108 W/cm2.
The dispersion of powders by intense electrostatic fields. I. Experimental studies
Authors: Szirmai S. G. , Morton D. H. , Potter E. C.
Published: February 2003

Powder dispersion by electrostatic fields above 0.20 kV/mm has been studied at ambient temperature in a vacuum, air, sulphur dioxide, and insulating liquids, with both conducting and nonconducting powders. All the conducting powders examined were dispersible, but only some of the insulating materials (e.g., alumina) reacted to the field. Alumina was studied in some detail using different media and various electrode geometries. It was concluded that dispersion of insulating powders occurs as a result of a conducting surface film, indicating that charging of the particles is mostly by conduction electrons from the bed. Effects of the dispersing medium were also detected, especially through the use of current-voltage curves. When liquids were used instead of air, for example, pronounced hysteresis occurred, an effect ascribed to the increased settling rate of the particles. Differences in behavior were also demonstrated from one gaseous medium to another, e.g., particulate clouds, which normally show pronounced turbulence in high-voltage air dispersion, became much more uniform in pure sulphur dioxide. In addition, some powders such as lycopodium, which is unreactive to the field in air, dispersed well in sulphur dioxide. This was traced back to the corona-suppressing properties of this gas, demonstrating that production of gaseous ions at field concentrations (such as those produced by sharp electrodes or angular particles) is detrimental to electrodispersion, since ions tend to act as charge carriers in preference to the particles. Further evidence of this came from gamma ray attenuation studies used for measuring cloud densities as a function of the applied field.
The dispersion of powders by intense electrostatic fields. II. A theoretical model
Authors: Szirmai S. G. , Morton D. H. , Potter E. C.
Published: February 2003

A mathematical model is presented of the electrodispersion of a monodisperse bed of spherical metallic particles, and an expression for the charge of a particle at the moment of its dispersion was deduced. Using this formula, both the motive force and the restraining force due to electrical images in the bed at the bed surface. Using the one identifiable configuration for each type that leads to minimum attraction between the charged particle and its image, the minimum dispersing field (MDF) was derived as E0=[rρg/ε0k(3−0.473k)] 1/2, where k is a numerical constant now known to be experimentally accessible. The usefulness of the mathematical model was demonstrated by comparing the predictions from this formula with published measurements of E0. Extending the model to polydisperse systems was found to further imply the necessity for in-flight charge exchanges as well as segregation in the densely dispersed cloud.
Abrupt degradation of three types of semiconductor light emitting diodes at high temperature
Authors: Ueda Osamu , Imai Hajime , Fujiwara Takao , Yamakoshi Shigenobu , Sugawara Tomonobu , Yamaoka Toyoshi
Published: February 2003

Abrupt degradation of three types of semiconductor light emitting diodes (LED’s), Ga1−xAlxAs double-heterostructure (DH) LED’s, Ga1−xAlxAs/ GaAs DH LED’s, and LED-operated Ga1−xAlxAs/ GaAs DH lasers operated at high temperature, was studied by electroluminescence topography, photoluminescence topography, and transmission electron microscopy. The following results were obtained from all types of the diodes. Dark regions which included 〈100〉 dark-line defects (DLD’s) and/or 〈110〉 DLD’s were often observed in the electronluminescence or photoluminescence patterns of the active regions. Two phenomena were associated with this type of degradation as follows: (i) generation of high density of dislocations and dislocation loops (in some cases, stacking faults) by dislocation glide motion due to the relaxation of the stress concentrated in the active region. (ii) subsequent development of dislocation dipoles from the glided dislocations (often accompanied with many small dislocation loops). In some of the degraded diodes, the phenomenon (ii) did not occur. There might be a certain threshold for the phenomenon (ii).
The effect of surface nucleation on the crystallization of the α phase of poly(vinylidene fluoride)
Authors: Weinhold S. , Litt M. H. , Lando J. B.
Published: February 2003

Transcrystalline films of the α polymorph of poly(vinylidene fluoride) have been prepared. X-ray diffraction shows that such films have a high degree of crystallographic orientation normal to the surface. The orientation shows that the b axis of the α phase unit cell is the principal crystal-growth direction. As is well established for other systems, it was found that the formation and growth of a transcrystalline layer requires relatively dense surface nucleation combined with sparse nucleation in the interior of the film. Experimental variables which favor the formation of surface nuclei include high polymer molecular weight, a mold surface which acts as a nucleating agent (such as Teflon), and a temperature gradient through the film during crystallization. Films exhibiting virtually no nucleation in the interior could be prepared from very pure PVF2 synthesized in our lab, while samples prepared from biaxially oriented films showed very dense internal nucleation. Annealing at high melt temperatures drastically decreased the internal nucleation in these films. An explanation to account for the behavior is proposed.
Direct observation of domain nucleation in GdCo5 single crystals
Authors: Uehara Mitsuru
Published: February 2003

Magnetization reversal in GdCo5 single crystals was studied by domain observations and magnetization measurements. Dendritelike domains appear after reversal at the nucleation field. These patterns suggest that the first reversed domain nucleates at one point and spreads out through the entire sample. The lifetime of moving walls of the dendritelike domain increases with the increasing diameter of the spheric or spheroidal samples along the easy axis of magnetization. The velocity of wall tips is estimated to be approximately 5 m/sec at room temperature except for extremely small samples.
Temperature-dependent small-angle x-ray scattering from poly(vinylidene fluoride)
Authors: Schultz J. M. , Lin J. S. , Hendricks R. W. , Lagasse R. R. , Kepler R. G.
Published: February 2003

X-ray scattering measurements over the angular range 2–30 mrad are reported for a uniaxially oriented poly(vinylidene fluoride) film containing the phase I crystal polymorph. Each intensity profile exhibits at ∼10 mrad an interference peak arising from quasiperiodic variation in electron density between crystalline and amorphous phases of the polymer. Over the temperature range 25–72 °C, reversible changes of 23% in peak intensity and 6% in peak position are observed. These reversible changes in x-ray scattering are analyzed in terms of a one-dimensional stack of alternating crystalline and amorphous layers. These model calculations show that the observed changes in the interference peak cannot be explained solely by thermal expansion within the two phases. In accordance with previous studies on other semicrystalline polymers, this discrepancy between observed scattering results and the predictions for thermal expansion is taken to be evidence that the crystallinity changes reversibly over the investigated temperature range. This evidence for reversible crystal melting is consistent with a hypothesis proposed by Kepler and Anderson to explain the pyroelectric response of polarized, phase I poly(vinylidene fluoride) films.
Optical heating in semiconductors: Laser damage in Ge, Si, InSb, and GaAs
Authors: Meyer J. R. , Kruer M. R. , Bartoli F. J.
Published: February 2003

A comprehensive theory developed previously for optical heating in semiconductors is applied to the calculation of laser damage thresholds in Ge, Si, InSb, and GaAs. The calculated thresholds agree well with the experimental values over a broad range of laser wavelengths and pulse durations. The results demonstrate that the dynamic nature of the material’s optical and transport properties with changing temperature and laser-generated carrier density has a significant effect on the heating process, particularly at short pulse durations.
Defects in crystalline SiO2:Optical absorption of the aluminum-associated hole center
Authors: Koumvakalis Nicholas
Published: February 2003

Radiation-induced optical absorption in crystalline SiO2 has been investigated in a number of synthetic quartz crystals. The dominant visible absorption band peaks at 2.5 eV and correlates directly with the paramagnetic resonance signal of the (Ale+)0 center. Similarities in behavior with the V− center in MgO suggest that a small polaron theory is applicable.
Shear wave excitation in a solid by longitudinal wave contact transducers
Authors: Chou C. H. , Liang K. , Khuri-Yakub B. T. , Kino G. S.
Published: February 2003

Longitudinal wave piezoelectric transducers of finite diameter which are placed in contact with a buffer rod or a material under test excite weak spurious shear wave modes. We have used a spatial frequency analysis to predict the level of the shear-longitudinal and shear-shear mode as compared to the level of the main longitudinal mode of interest. We find good agreement between theory and experiments for 50-MHz transducers made with PZT, PSN, or LiNbO3 on a quartz buffer rod.
Thermocouple temperature measurements in shock-compressed solids
Authors: Bloomquist D. D. , Sheffield S. A.
Published: February 2003

The emf produced by 5-μm-thick foil thermocouples when subjected to shock loading was studied over a stress range from 0.5 to 10 GPa. Thermocouples of either copper and constantan or chromel and alumel were embedded in the host materials, polymethyl methacrylate (PMMA), Epon 828 epoxy, single-crystal Al2O3, or vitreous SiO2. The observed emf history rises to a plateau in a period that varied from less than 100 ns for Al2O3 to about 500 ns for PMMA. Temperatures inferred from the constant-voltage portion of the records using standard thermocouple tables (corrected for pressure) compare favorably with calculated temperatures for PMMA and epoxy below 2.0 and 4.5 GPa, respectively. Above these threshold stresses, the observed temperatures increase rapidly with compression, which may indicate an exothermic reaction. Inferred temperatures for the two types of thermocouples are in good agreement. The shape of the response history, and agreement with predicted temperatures for PMMA and epoxy, indicate that the thermocouple and host material come to thermal equilibrium during the transient portion of the response. In the elastic materials Al2O3 and SiO2, the observed temperatures are better correlated with temperatures predicted for shock compression of the thermocouple materials than those predicted for the host materials, indicating that thermal equilibration is not achieved in the available test time.
Metal-containing fluoropolymer films produced by simultaneous plasma etching and polymerization: Effects of hydrogen or oxygen
Authors: Kay E. , Dilks A. , Seybold D.
Published: February 2003

The formation of metal-containing fluoropolymer films by simultaneous plasma etching and polymerization in a radiofrequency diode reactor configuration is investigated as a function of additive scavenger gases. The addition of oxygen to plasmas excited in tetrafluoroethylene or perfluoropropane is found to enhance the etching rate at the excitation metal electrode and diminish the polymer film deposition rate at the grounded electrode. The overall effect is to increase the metal content of the films. The addition of hydrogen to plasmas excited in tetrafluoromethane or perfluoropropane has the opposite effect. X-ray photoelectron spectroscopy is employed to determine the composition and structure of the films, and this coupled with mass spectrometric analysis of the plasma gas phase chemistry has allowed the identification of the likely precursors to plasma polymerization for the systems studied.
Domain size effect on the coherent precession mode wall motion in magnetic bubble materials
Authors: Honda Shigeo , Fukuda Nobuo
Published: February 2003

The twist spin angle φ1 in the wall associated with an isolated strip domain is calculated as a function of the strip domain width assuming Schlömann’s trial function φ1 sin[ 1/2 πζ] for wall structure, where ζ is the coordinate normal to film plane normalized with film thickness. The wall motion associated with a strip domain is analyzed as a function of the domain width based on the coherent precession model using the above trial function. It was found that the wall motion changes from the ’’Walker mode’’ to the ’’2π mode’’ through the ’’quasi-π-mode’’ with increasing strip width. The peak velocity decreases slightly from Walker’s critical velocity 2πMγΔ in the quasi-π-mode region, and above this region increases approaching to 2.36πMγΔ with increasing domain width, where M is the saturation magnetization, γ is the gyromagnetic ratio, and Δ is the wall width parameter. These calculations are adapted to the radial motion of the bubble domain wall.
Monte Carlo simulation of real-space electron transfer in GaAs-AlGaAs heterostructures
Authors: Glisson T. H. , Hauser J. R. , Littlejohn M. A. , Hess K. , Streetman B. G. , Shichijo H.
Published: February 2003

The Monte Carlo method has been used to simulate electron transport in GaAs/AlGaAs heterostructures with an electric field applied parallel to the heterojunction interface. The simulations indicate that a unique physical mechanism for negative differential conductivity is provided by such layered heterostructures, which is analogous in many respects to the Gunn effect. This mechanism has been termed ’’real-space electron transfer’’ since it involves the transfer of electrons from a high-mobility GaAs region to an adjacent low-mobility AlGaAs region as the applied electric field intensity is increased. The simulations further indicate that the important details of the resulting velocity-field characteristics for these layered heterostructures can be controlled primarily through material doping densities, layer thicknesses, and the material properties of the individual layers. Thus, the phenomenon of real-space electron transfer potentially provides the ability to ’’engineer’’ those basic material properties which influence the performance of negative resistance devices.
rf annealing mechanisms in metal-oxide-semiconductor structures—an experimental simulation
Authors: Ma T. P. , Chin M. R.
Published: February 2003

The mechanisms of rf (radio frequency) annealing have been studied using an experimental simulation, in which the three essential ingredients in the annealing process—the rf field, the ionizing radiation source, and the wafer temperature—can be independently controlled. The results have confirmed the importance of the simultaneous presence of all three components, whose cooperative effect leads to the effective annihilation of the oxide defects. From an analysis of the activation energy associated with the annealing process, an annealing mechanism based on the recombination-enhanced defect reactions is discussed.
Characterization of plasma-deposited silicon nitride films
Authors: Yokoyama S. , Kajihara N. , Hirose M. , Osaka Y. , Yoshihara T. , Abe H.
Published: February 2003

Structural and electrical properties of plasma-deposited silicon nitride (SiN) have been investigated. The compositional ratio of Si to N estimated by Auger analysis is found to be uniform in the direction of the film thickness. The numbers of Si-H and N-H bonds of the order of ∼1021/cm3 have been obtained by calculating the vibrational spectra. The two types of trapping states which are responsible for the Poole-Frenkel conduction are found in SiN from the current DLTS measurement. The barrier height at the SiN/Si interface determined by the internal photoemission ranges from 1.7 to 2.5 eV, being dependent on the film thickness. From these results, current transport mechanisms through SiN films are quantitatively discussed, and it is demonstrated that the carrier transport is dominated by the Fowler-Nordheim tunneling at low temperatures and by the Poole-Frenkel conduction at high temperatures.
Superconductivity of ductile Ti-Nb-Si amorphous alloys
Authors: Inoue A. , Kimura H. M. , Masumoto T. , Suryanarayana C. , Hoshi A.
Published: February 2003

Amorphous superconducting alloys with high strength and good ductility have been found in rapidly quenched alloys of the Ti-Nb-Si system. Continuous ribbons of these alloys were produced about 2 mm wide and 0.04 mm thick using a modified single roller quenching apparatus. The silicon content in the amorphous alloys was limited to the range between about 13 and 21 at. % and the niobium content was in the range 0–43 at. %. The alloys containing more than 10 at. % niobium showed a superconducting transition above the liquid-helium temperature (4.2 K). The transition temperature Tc increased with increasing niobium content or with decreasing silicon content. The highest value obtained was 5.1 K for Ti45Nb40Si15. The upper critical magnetic field Hc2 and the critical current density Jc were of the order of 1.6×106 A/m at 4.2 K and 300 A/cm2 at zero applied field and 4.2 K.
Magnetic transition temperatures of ion-implanted layers on bubble garnet films
Authors: Maartense I. , Searle C. W.
Published: February 2003

By means of susceptibility measurements, it has been found that the magnetic ordering temperatures of ion-implanted layers are depressed relative to those of the original garnet films. Implantation of 1015 Ne+ ions/cm2 at 100 keV brings the ordering temperature of the layer down to ∼30 °C, in the film composition which was investigated. Such behavior explains why implanted films can become ’’nonmagnetic’’ near room temperature, as is reported in the literature. Thus it appears unnecessary to invoke an overdamage mechanism which is qualitatively different than that of implanted layers normally used for hard bubble suppression. Annealing raises a layer’s transition temperature, as expected, but high-temperature annealing results in an anomalous behavior which suggests that healing of the radiation damage does not restore a low-damage structure.
Effects of ion implantation on the temperature coefficient of bubble collapse field in magnetic bubble garnet materials
Authors: Blunt R. T.
Published: February 2003

Significant changes in the temperature coefficient of bubble collapse field (αHcoll) for magnetic bubble garnets in the SmLuYCaGe:IG system have been observed after ion implantation and subsequent thermal annealing. This change can be reduced to insignificant levels by changes in the garnet composition or by increasing the implantation energy used.
The electronic properties of the metal-insulator contact: Space-charge induced switching
Authors: Hughes R. C.
Published: February 2003

Reversible changes (switching) in the magnitude of the leakage current through a metal-insulator-metal (semiconductor) structure can be induced by the excitation of electron-hole pairs in the insulator. The switching behavior in metal-polyethyleneterephthalate (PET) metal capacitors is given as a function of the variables: excitation rate, applied electric field, film thickness, and metal work function. The switching is interpreted by a simple model which requires knowledge of the bulk transport of electrons and holes in the insulator, and a high density of hole (or electron) traps near the contact only. The switching occurs when the trapped space charge induces injection from the contact, and saturation is achieved by recombination of the injected carriers with the trapped carriers. Both the time dependence and magnitude of switching is predicted for published switching data in MOS devices with good agreement. Since the model requires knowledge of the current-voltage characteristic for the contact in question, new data for leakage currents in PET is given, with a discussion of the nonfit of the data to the standard injection theories. A fit of the model to the PET switching data is given and the first measurement of the magnitude and field dependence of the recombination coefficient is presented.
Infrared absorption spectra of SiO2 precipitates of various shapes in silicon: calculated and experimental
Authors: Hu S. M.
Published: February 2003

It is shown that the infrared absorption band at 1230 cm−1, observed under certain conditions of oxygen precipitation in silicon, is the LO mode of SiO2. The LO mode, which is normally infrared inactive, becomes infrared active under the condition of polarization of small (<0.36 μm) platelets in an appropriate dielectric matrix (silicon). Infrared absorption spectra of SiO2 particles of various shapes, imbedded in silicon, have been calculated. For platelet SiO2 precipitates, the spectrum shows an absorption band at 1215 cm−1, which is reasonably close to the observed band at 1230 cm−1. For SiO2 precipitates of other shapes the spectra do not exhibit this absorption band. Instead, they exhibit a slightly weaker primary absorption band at 1095 cm−1, the TO mode, and a very weak band at 1170 cm−1, which is a mixed mode of longitudinal and transverse optical phonons.
Observations on the hexagonal form of MoSi2 and WSi2 films produced by ion implantation and on related snowplow effects
Authors: d’Heurle F. M. , Petersson C. S. , Tsai M. Y.
Published: February 2003

MoSi2 and WSi2 films produced by As-ion implantation through the respective metallic films deposited on Si substrates were analyzed by backscattering and x-ray diffraction. The backscattering results indicate that As atoms are snowplowed into Si during the formation of the silicides. Crystallographic observations on similar samples both before and after various heat treatments provide evidence for the existence at low temperatures of the hexagonal phase of WSi2, presumably unreported up to now, which is similar to the corresponding phase of MoSi2. In the case of the W disilicide, however, the temperature for the transition, hexagonal to tetragonal, is so low that the low-temperature phase is unlikely to be obtained by the usual diffusion-controlled mechanisms.
Effect of metalloidal elements on the microhardness of iron-base glasses
Authors: Naka M.
Published: February 2003

The microhardness of Fe85-x B15Nx, Fe80B20-xNx,Fe85-xP15Nx, and Fe80P20-xNx glasses has been investigated, where N is B, C, Si, P or Ge. The average change of microhardness with the concentration of 1 at.% metalloidal elements, dHv/dX, is 24, 17, 11, 6, and 4 for B, C, Si, P, and Ge, respectively. The hardness of the iron-base glasses is related to the valence, the average outer electron concentration, the atomic size, the atomic conhesive energy, and the melting point of the constituent metalloids. An increase in the valence, the electron concentration and the atomic radius of metalloidal elements decreases the dHv/dX in the glasses. A decrease in the value of dHv/dX is attributed to the decrease in the strength of bonding between metals and metalloids in the glasses.
Influence of hydrogen on superconducting niobium cavities
Authors: Isagawa S.
Published: February 2003

The influence of the solute hydrogen on rf properties of superconducting niobium cavities is investigated experimentally. Chemical polishing and too much electropolishing decrease the energy gap and rf breakdown fields. High-temperature vacuum firing in a UHV furnace decrease the residual loss and recovers the energy gap. Annealed cavities are, however, easily degraded not only by a short period of exposure to hydrogen, but also by a long term storage in air. Chemically polished cavities also show a great enhancement of the penetration depth λ0. These effects can be ascribed to hydrogen which is picked up from etchants or from atmosphere.
Electron diffusion and electrochromism in MoO3 amorphous films
Authors: Zelaya-Angel O. , Menezes Cornelius , Sánchez-Sinencio F. , Ferreira G. F. Leal
Published: February 2003

Coloration by electron diffusion and electrochromism was studied in HxMoO3 amorphous films following the technique of Crandall and Faughnan et al. in HxWO3. The measured diffusion coefficient for electrons was D=7.5×10−4 cm2/sec and the emf of the cell Cu-In-glycerol +H2SO4-HxMoO3-SnO2-Cu was measured as a function of x. The dynamics of the coloration process induced by small changes of the potential across the HxMoO3-electrolyte interface was studied by a photometric method.
Birefringence of viscoelastic in the unloading process under combined stresses
Authors: Nishitani T. , Yasuda T.
Published: February 2003

The birefringent effect in the unloading process is fairly different from that in the loading process discussed in the previous paper. A birefringence relation in the unloading process for a nonlinear viscoelastic dielectric is theoretically deduced by using the procedure for the loading process of the previous paper. Moreover, the validity of the deduced relation in the unloading process is discussed in relation to the experimental results of creep and of simple loading tests performed under the combined stresses of tensile and hydrostatic pressure.
Silicon-ion implantation in InP and annealing with CVD SiO2 encapsulation
Authors: Nishioka Takashi , Ohmachi Yoshiro
Published: February 2003

Silicon-ion implantation in semi-insulating Fe-doped InP has been investigated. Chemical vapor deposited (CVD) SiO2 encapsulation film for annealing of the Si-implanted layer has been investigated by Auger electron analysis. It indicated that by selecting deposition condition, CVD SiO2 films can be used effectively as an annealing encapsulant of InP. The electrical activation of 80% was realized at 750 °C annealing for doses ranging from 6×1012 to 3×1014 cm−2 at 350 keV. Depth profiles after annealing were found to be close to the Lindhard-Scharff-Schiott (LSS) theory, with no redistribution of implanted Si by the annealing process. Anomalous behavior in activation efficiency was found at relatively low doses of the order of 1012 cm−2, and it is considered to be due to compensation by Fe in the substrate.
Low-temperature Lamb wave propagation in PVF2
Authors: Wagers R. S.
Published: February 2003

Lamb wave propagation in thin films of polyvinylidene fluoride PVF2 is examined as a function of temperature. Results are presented for frequencies from 10 to 70 MHz and temperatures from −50 to −175 °C. Lamb waves were excited in the 28.4-μm-thick films by interdigital transducers with a center frequency wavelength of 92 μm. At the fundamental wavelength, the first five Lamb modes were observed, while at the third harmonic of the transducer only the first two branches of the dispersion curves could be detected. The observed velocities of the seven modes are compared to the theoretical dispersion curves to obtain stiffness constants for the PVF2 film as a function of temperature. The results obtained for constants c33 and c55 are in agreement with previous literature. Values for the constants c11 and c13 are presented for the first time.
Diffusion of gallium in silicon
Authors: Haridoss S. , Bénière F. , Gauneau M. , Rupert A.
Published: February 2003

Neutron activation analysis and secondary ion mass spectrometry were used to measure gallium profiles resulting from the diffusion of Ga into intrinsic silicon. The diffusion of the impurity was measured between 700 and 1100 °C. The diffusion coefficient in this wide temperature range follows the expression D=0.005 exp[−(2.70/kT)] cm2 sec−1. The possible intervention of surface effects in the diffusion kinetics is discussed. An estimate of the enthalpy of association of Ga vacancy is deduced. The solid solubility of gallium in silicon was measured in the same range and at various concentrations of donors and acceptors.
Effects of the lapped surface layers on the dielectric properties of ferroelectric ceramics
Authors: Jyomura Shigeru , Matsuyama Iwao , Toda Gyozo
Published: February 2003

The effects of lapped surface layers on the dielectric properties of Ba- and Sr-modified lead titanate and lead zirconate ferroelectric ceramics are examined. Specimens with lapped surfaces show anomalous dielectric behaviors, namely, smaller dielectric constant, higher Curie temperature, smaller dielectric loss (below Curie point), and smaller remanent polarization than those of specimens whose surface layers are removed by chemical etching. This may be ascribed to the existence of a lapped surface layer, which seems to be a (0.1–2)-μm-thick nonferroelectric layer of small dielectric constant with a two-dimensional tensile stress of 5–15 kbars. The thinness of the layer results in a large capacitance on the order of 0.5 μF/cm2. The above model for lapped surface layer, especially involving the two-dimensional tensile stress, explains well the anomalous dielectric behaviors measured in this paper.
A steady-state constant capacitance method for the characterization of deep energy levels in semiconductors
Authors: Grimmeiss H. G. , Kullendorff N.
Published: February 2003

A steady-state constant capacitance technique is presented for the study of photoionization cross sections of deep energy levels. The analysis of the data obtained with this technique is less time consuming and more straightforward than transient measurements. The method is particularly suitable when the sample contains high concentrations of deep energy levels. The feasibility of the technique is exhibited by presenting data obtained in ZnSe:Cu and CdS:Cu.
Light scattering by point defects in insulating crystals
Authors: Mills D. L.
Published: February 2003

We examine the theory of light scattering by point defects in crystals through use of a model which includes scattering induced by the strain field near the defect, in addition to that caused by the change in electronic polarizability within the unit cell which contains it. The model applies to defects with the same valence as the missing host ion. We find the light-scattering cross section is given by an expression of the Rayleigh form, with overall magnitude influenced by interference between the two mechanisms considered. A rough estimate of the cross section shows, in agreement with recent data, that isoelectronic impurities present in alkali halide crystals at the part-per-million level should not influence the Landau-Placzek ratio.
Relations between geometrical factors for noise magnitudes in resistors
Authors: Weissman M. B.
Published: February 2003

A relation between the spatial weighting function for voltage fluctuations in the presence of a magnetic field and weighting functions determined in the absence of a magnetic field on four-probe resistors is demonstrated. The tensor character of conductivity fluctuations is shown to have a significant effect on the ratios of measurable fluctuations. The results are intended for use in determining the sources of 1/f noise in semiconductors.