bluuebunny/crossref_metadata_2025 huggingface dataset:
A statistical study of the reliability of oxide-defined stripe cw lasers of (AlGa)As
Authors: Ettenberg M.
Published: February 2003

In this report, we describe a statistical study of the reliability of oxide-defined stripe-contact cw injection lasers of (AlGa)As. These devices have one facet coated with Al2O3 and one facet coated with an Al2O3/Si dichroic reflector; the lasers are optimized for cw low-threshold currents at room temperature, with values typically about 50 mA. Lifetests were carried out at 70 °C ambient, in the cw mode of operation with about 5 mW output. Previous lifetests showed that the degradation rate followed a 0.95-eV activation energy so the 70 °C environment provides a degradation acceleration factor of 190 over that at room temperature. We have found that the device failures follow a log-normal distribution, characterized by a mean time before failure of 4200 h and a standard deviation of 1.3. This corresponds to a mean time to failure (MTTF) of 106 h at room temperature. Failure is defined here as the inability of the device to emit 1 mW of stimulated cw output at 70 °C, and assumes that optical feedback will be employed to adjust the laser current during operation. If a constant-current drive is envisioned, the failures for a 3-dB drop in light output also follow a log-normal distribution with a similar slope (standard deviation=1.1) and a MTTF of 2000 h at 70 °C (500 000 h at room temperature). The failures were found to be mainly due to bulk gradual degradation and not facet or contact failure. Careful study of lasers before and after lifetest showed a significant increase in contact thermal resistance. However, this increase accounts for only a small portion of the nearly 70% increase in room-temperature cw threshold after failure at 70 °C. After failure at 70 °C, we also noted a degradation in the near-field and associated far-field pattern of the laser.
Elastic interaction between a point defect and an edge dislocation
Authors: Johnson R. A.
Published: February 2003

The elastic interaction energy between a point defect and a stress field is determined for the case in which the point-defect displacement field has spheroidal symmetry, called the shape interaction. Results are given for the stress field of an edge dislocation, including a term from excluding the elastic interaction arising from the defect and dislocation core regions. With parameters appropriate to an fcc lattice it is then shown that a vacancy will tend to migrate around the dislocation to the compressional side, but that there is an energy barrier in the radial direction between the vacancy and the dislocation on the compressional side.
The determination of electronic stopping powers of light ions in metals from damage-rate measurements
Authors: Averback R. S. , Benedek R. , Merkle K. L. , Singer L. R.
Published: February 2003

We investigate a new technique for the determination of light-ion stopping powers in metals. The radiation-damage-induced resistivity change in thin films is measured as a function of ion energy. As the ion energy is raised, an increasing fraction of the energy passes through the back surface, thereby resulting in decreased damage production. This effect has been analyzed by comparison with predictions based on an Edgeworth expansion of the damage-distribution function, using the moments tabulated by Winterbon. Results are presented for He, Li, and C irradiations of silver films with thicknesses of 2640 and 3880 Å. The present results are compared with those of previous work. Other methods for calculation of the damage-distribution function are compared with the Edgeworth expansion.
Frequency factors for the annealing of the electrical resistance changes in deuteron-bombarded copper
Authors: Primak William
Published: February 2003

The results of attempting to fit the step-annealing data to an activation energy distribution indicate a dispersion of the frequency factor ranging from 107 to 1011 sec−1 which is explained as arising from diffusion processes. The distribution appears to rise gradually to a peak with the possible existence of a subsidiary peak, then a very sharp drop from the peak. This sharp drop indicates the annealing processes are first order. The beginning of the distribution is in accord with its being the residue from annealing during bombardment, subsequent treatment, and storage. It is hypothesized that the gradual rise is associated with the dispersion of the frequency factor.
Doping and electrical properties of Mg in LPE AlxGa1−xAs
Authors: Mukai Seiji , Makita Yunosuke , Gonda Shun-ichi
Published: February 2003

Mg-doped AlxGa1−xAs crystals with Al concentration 0⩽x⩽0.8 have been grown by the conventional LPE method. Doping characteristics of Mg and electrical properties of the crystals are studied using Hall measurements in the temperature range between 77 and 295 K. The results revealed are as follows. Magnesium works as an acceptor in AlxGa1−xAs. Its distribution coefficient is constant and about 0.6 for AlxGa1−xAs with x⩾0.1. Hole concentrations up to 1018 cm−3 are easily obtained for a high x of 0.65. The acceptor energy level Ei increases from 18 meV in GaAs to 40 meV in Al0.8Ga0.2As. The x dependence of Ei can be explained by the difference of effective hole masses and dielectric constants between GaAs and AlAs. Hole concentration, mobility, and resistivity, as well as their temperature dependences, are presented for various x values. These data show that Mg is a suitable acceptor in AlxGa1−xAs particularly with high x values.
Transient response of a cold lossy plasma half-space in the presence of a transverse static magnetic field
Authors: Prasad R. C. , Kalluri Dikshitulu
Published: February 2003

An analytical expression for the transient reflected field is given for the case of normal incidence of a linearly polarized impulsive plane electromagnetic wave on a cold lossy homogeneous plasma half-space in the presence of a transverse static magnetic field of arbitrary strength. Approximate expressions for small losses and small strength of the static magnetic field are also given.
The orienting action of ultrasound on liquid crystals related to the theorem of minimum entropy production
Authors: Dion Jean-Luc
Published: February 2003

We show how the theorem of minimum entropy production of irreversible thermodynamics may be used to confirm the reality of the torque exerted on oriented liquid crystal molecules by an ultrasonic wave. This torque has previously been related to the anisotropy of acoustic attenuation. The analogy with the Langevin radiation pressure is underlined, and the possible existence of an ultrasonic-type Frederiks transition is discussed.
Impurity segregation by pulsed laser irradiation
Authors: White C. W. , Narayan J. , Appleton B. R. , Wilson S. R.
Published: February 2003

Changes in profiles of implanted impurities in siliconand associated microstructural changes as a result of high-power laser pulses have been studied using ion- scattering channeling and transmission electron microscopy. The results show a significant segregation in the form of precipitates at and away from the dislocations in the near-surface regions for impurities such as copper and iron in silicon which have very low equilibrium solubilities and equilibrium distribution coefficients.
Type conversion in electron-irradiated GaAs
Authors: Farmer J. W. , Look D. C.
Published: February 2003

The unambiguous type conversion of GaAs by electron irradiation is reported here for the first time. Several high-quality n-type vapor-phase epitaxial layers (ρ?3 Ω cm and μ?7000 cm2/V sec at 300 K) were converted by 1-MeV electrons to high-quality p-type layers (ρ?30 Ω cm and μ?400 cm2/V sec). Temperature-dependent Hall-effect data show energy levels at 0.5, 0.3, and about 0.1 eV above the valence band. Evidence is presented to indicate that the failure of some of our samples (and, perhaps, other samples reported in the literature) to convert to low-resistivity p type is due to a rather high concentration of as-grown deep levels which pin the Fermi level near midgap.
Determination of lattice mismatch in Ga1−xAlxAs LPE layer on GaAs substrate by using a divergent x-ray source
Authors: Chang Shih-Lin , Patel Navin B. , Nannichi Y. , de Prince F. C.
Published: February 2003

A new method of determining lattice mismatch in LPE heterojunction systems has been developed by utilizing a divergent x-ray source. The experimental arrangements and operation procedures are much simpler than those of the usual x-ray methods.
Exciton energy at 300 K in direct-gap semiconductors from luminescence reabsorption
Authors: Sermage Bernard , Voos Michel
Published: February 2003

We investigate here the reabsorption of the free-exciton luminescence in CuGaS2, AgGaSe2, and ZnSe at room temperature. For that purpose we use a model described in a previous paper to analyze our experimental data. Thus, we get the free-exciton energies at 300 K, and this allows us to determine the temperature coefficient of the band gap. Our method can, therefore, be used at 300 K as well as at low temperatures, and we believe that it can be helpful in other cases.
Comment on ’’A simple measurement of absolute solar cell efficiency’’
Authors: Dalal Vikram L. , Rothwarf Allen
Published: February 2003

In a recent paper, Shay et al. have described a simple indirect method for measuring absolute cell efficiency based upon using low-light-level quantum-efficiency measurements. We show in this paper that such an indirect method can lead to erroneous results. The error can arise because of at least four physical mechanisms: infrared quenching, recombination-center saturation, trapping-enhanced interface field, and Dember plasma field effects. A simple method to check for these effects is described.
Comment on thermal effects in superconducting proximity-effect bridges
Authors: Dharmadurai G. , Ratnam B. A.
Published: February 2003

Self-heating hot spots in long Ag-Sn proximity-effect bridges on glass substrates appear to dramatically affect the bridge electrical and critical current hysteresis characterstics. Our observations seem to complement a recent observation of Decker and Palmer. Further, the compatibility of our experimental results with predictions of the SBT hot-spot model provides an alternative method for estimating the heat-transfer coefficient.
Parametric amplification on rf-induced steps in a Josephson tunnel junction
Authors: Soerensen O. H. , Pedersen N. F. , Mygind J. , Dueholm B.
Published: February 2003

Parametric effects including amplification in a singly degenerate mode have been observed in Josephson tunnel junctions at dc bias points on rf-induced steps. Net gain at 9 GHz was achieved with a bias on the fundamental 18-GHz step and subharmonic self-oscillations were seen on 18 and 70-GHz rf-induced steps even at voltages approaching the energy gap. A qualitative explanation of the results is presented.
Measurement of mobilities of particles in liquids by optical and electrical transients
Authors: Novotny V.
Published: February 2003

A new optical transient technique was developed to measure the mobilities of particles suspended in liquids. The optical method is based on the detection of light scattered from charged particles moving through a suspending medium under the influence of an external field. Sweepout and transient variants of this technique are outlined and a semiquantitative description of the optical signals is developed which permits the evaluation of the size, mobility, charge, and particle-substrate interactions, as well as estimates of the distributions of these quantities. Extensive testing of the method using dispersions of highly scattering charged particles in nonaqueous media was undertaken before applying the technique to other nonaqueous dispersions. Simultaneous measurements of the electrical transients showed that our currents were dominated by the excess ions in solution and that the charged particles contributed significantly to the current only at high particle concentration.
Theory of conduction in ZnO varistors
Authors: Mahan G. D. , Levinson Lionel M. , Philipp H. R.
Published: February 2003

A theory is presented which quantitatively accounts for the important features of conduction in ZnO-based metal-oxide varistors. This theory has no adjustable parameters. Using the known values of the ZnO band gap, donor concentration n0, and low-voltage varistor leakage-current activation energy, we predict a varistor breakdown voltage of ?3.2 V/grain boundary for n0=1017 carriers cm−3 and T=300 °K. This compares well with measurements on a single grain-grain junction. The highly nonlinear varistor conduction derives from electron tunneling ’’triggered’’ by hole creation in the ZnO when the conduction band in the grain interior drops below the top of the valence band at the grain interface. The theory predicts coefficients of nonlinearity α=d (lnI)/d (lnV) as high as 50, or even 100.
Thermally stimulated conductivity studies of trapping centers in alkali-borosilicate glasses
Authors: Catchings R. M.
Published: February 2003

Thermally stimulated conductivity studies have been performed on unirradiated borosilicate glasses made to contain various amounts of sodium, lithium, nickel, and iron oxides. Measurements were made between 77 and 570 °K. All the samples gave one or more conductivity peaks below room temperature. Analysis of the initial-rise slope of the conductivity peaks of the various samples gave trapping-level energies ranging from 0.1 to 1.9 eV. The shape and temperature of the maximum of most of the peaks changed on each measurement cycle. A few samples exhibited a common peak that formed on annealing.
Conductive strontium titanate layers produced by boron-ion implantation
Authors: Cooper Connie M. , Nayar P. S. , Hale Edward B. , Gerson Robert
Published: February 2003

The ion implantation of boron has been found to be an effective method for increasing the conductivity of strontium titanate. A highly conductive layer was formed by implantations at doses of 3.6×1016 to 1.0×1017 ions/cm2, using an accelerating voltage of 100 kV, corresponding to a boron range of about 300 nm. The conductivity of the implanted layer was found to be further enhanced by about four orders of magnitude after annealing at 225 °C. The surface resistivity attained was typically 1000 Ω/square at room temperature. The resistance increased with rising temperature between 77 and 500 K. All samples were found to be n type, as determined by Hall-effect and thermoelectric measurements. The measured Hall mobility range was from 100 cm2/V sec at 77 K, decreasing to 5 cm2/V sec at 300 K. The existence of several defect energy levels can be inferred from the electrical data.
Internal voltage in symmetric MIM junctions with even number of organic monolayers
Authors: Kapil A. K. , Singal C. M. , Srivastava V. K.
Published: February 2003

It has been shown that an internal voltage exists even in the case of symmetric metal/insulator/metal junctions with the insulating organic film having no net dipole moment. In the case of aluminum/barium-stearate/aluminum junctions, this voltage arises due to the polar nature of the thin alumina (Al2O3) film which is formed on the bottom electrode of aluminum during its exposure to the atmosphere, prior to the deposition of barium-stearate film.
Current-density distribution in Josephson tunnel junctions
Authors: Wang T. C.
Published: February 2003

An analysis of the relation between current-density distribution and the peak amplitude of Fiske modes in Josephson junctions is presented. It is shown that the peak value can vary through a large range of values, depending on whether the junction is ’’good’’ or ’’bad’’ in the sense of the uniformity of the oxidation barrier. By a close examination of the Fiske modes, it is possible to determine the barrier uniformity. However, for a nonuniform barrier junction, the current-density distribution corresponding to a particular field dependence of Fiske modes is no longer unique. A method of evaluating junctions for use as electronic devices is discussed.
Magnetostatic volume waves in dielectric layered structure: Effect of magnetocrystalline anisotropy
Authors: Bajpai S. N. , Rattan I. , Srivastava N. C.
Published: February 2003

This paper presents a theoretical investigation of the effect of magnetocrystalline anisotropy on the group delay of magnetostatic volume waves in a layered structure consisting of a normally magnetized ferrite slab (or film) supported on one side by a metal-backed dielectric slab. The cases of cubic, as well as hexagonal, planar anisotropy have been considered. Numerical calculations for YIG (yttrium-iron-garnet) (cubic) and Zn2Y (planar) ferrites show that, in general, the magnetocrystalline anisotropy leads to anisotropic propagation in the plane of the slab and also affects the frequency range of nondispersive delay as well as the overall magnitude of group delay time. In the case of cubic ferrites, the specific crystallographic orientations have been obtained for which the effect of magnetocrystalline anisotropy on propagation characteristics is negligible. In the case of the Zn2Y planar ferrite, the frequency range of allowed modes is found to be extremely large; it extends from about 3 to 12 GHz, with an effective bias field as low as 200 Oe.
Electric dipole moment measurements by internal-voltage technique
Authors: Kapil A. K. , Gupta S. K. , Singal C. M. , Srivastava V. K.
Published: February 2003

It has been shown that internal voltage in metal/insulator/metal structures can be used successfully to measure the electric dipole moment of organic compounds which can be built up in the form of monomolecular layers. Using this technique the dipole moment of stearic acid has been determined and compared with the known data for this fatty acid, and the agreement has been found to be good.
Microwave propagation in semiconductor powders: The Rayleigh limit
Authors: Sansonetti J. E. , Furdyna J. K.
Published: February 2003

Microwave propagation in semiconductors in powder form is a potentially important technique for the characterization of semiconducting materials. The problem also contains valuable insights into the interaction of electromagnetic waves with inhomogeneous media in general. We have chosen powdered silicon to study the behavior of such an inhomogeneous system because of the wide range of electronic parameters available in this material and the ability to vary the permittivity of the grains by varying the temperature and/or the applied dc magnetic field. A series of samples, with grain size ∼100 μm and a wide range of resistivities, was investigated at temperatures from 77 to 300 °K and magnetic fields from 0 to 20 kG. We show that, for samples with room-temperature resistivities exceeding ∼15 Ω cm, the interaction can be satisfactorily formulated in terms of a theoretical model involving an effective depolarizing factor for the powder medium as a whole. The model becomes less quantitatively reliable for samples with lower resistivity, but still predicts all observed features qualitatively.
Photothermal conversion of solar energy by gold cermet coatings: applicability of the Bruggeman effective medium theory
Authors: Granqvist C. G.
Published: February 2003

Efficient photothermal conversion of solar energy requires high absorption at wavelengths λ≲2 μm and low absorption at λ≳2 μm. This absorptance profile can be achieved by coatings consisting of ultrafine metal particles in an insulating matrix. I compare available optical data for concentrated gold cermet films with calculations based on the non-self-consistent Maxwell Garnett theory and on the self-consistent Bruggeman theory. The latter is found to be superior for MgO+25 vol% Au and for Al2O3+18 vol% Au, whereas no firm conclusions can be drawn for MgF2+Au.
Raman scattering from boron-implanted laser-annealed silicon
Authors: Engstrom Herbert , Bates J. B.
Published: February 2003

Measurements of the line shape of the silicon optic mode in boron-implanted ruby-laser-annealed silicon were analyzed assuming a Fano-type interaction between the discrete optic mode and the continuous valence band states. The results yielded a utilization coefficient of 0.89±0.09 for the boron impurities. Measurements of the ratio of the intensity of the boron local mode to that of the silicon optic mode as a function of excitation wavelength are consistent with the conclusion of other workers that laser annealing is more effective than thermal annealing in reducing lattice damage.
Properties of high sensitivity GaP/InxGa1−xP/GaAs :  (Cs–O) transmission photocathodes
Authors: Fisher D. G. , Olsen G. H.
Published: February 2003

Negative electron affinity (NEA) GaAs photocathodes were vapor grown on GaP/InxGa1−xP substrates with 0.4<x<0.65. The dependence of cathode sensitivity, electron diffusion length, cathode back-interface recombination velocity, and surface-escape probability on buffer-layer composition was determined. The optimal InxGa1−xP composition for these samples was in the range of 52–55% InP. Indium unintentionally introduced into the GaAs causes a shift in the InxGa1−xP composition for good lattice match. SIMS and AES measurements were made to obtain the chemical and electronic structure of the epitaxial layers. The photosensitivity dependence on both Zn doping concentration and cathode thickness are presented. The highest transmission mode photosensitivity measured was 740 μA/lm.
Anomalous penetration of laser radiation in an overdense magnetoplasma
Authors: Sodha M. S. , Sharma J. K. , Kumar Santosh , Tripathi V. K.
Published: February 2003

A high-power Gaussian laser beam exerts a strong ponderomotive force on the electrons of a plasma, pushing them away from the axial region. This provides a passage to the beam through an otherwise overdense plasma. The depth of penetration, in the typical case of a linear density profile, increases with the power of the beam up to some critical value of power, beyond which the depth of penetration increases abruptly to very large values. The critical value of power corresponds to vd=vth, where vd and vth are the oscillatory velocity and thermal velocity of electrons, respectively. For a CO2 laser this corresponds to a power ?1011 W for fusion parameters. The effect of self-generated magnetic fields is to reduce the depth of penetration and to enhance the critical power.
Laser-beam characteristics of Phoenix, an HF oscillator-amplifier system
Authors: Patterson E. L. , Hays G. N. , Truby F. K. , Gerber R. A.
Published: February 2003

Energy-extraction and beam-quality measurements are reported for Phoenix, Sandia’s high-energy HF laser system. The final amplifier in this oscillator-amplifier chain used electron-beam initiation of high-pressure gas mixtures of H2-F2-O2. The oscillator and preamplifier utilized fast electric discharges in SF6-HI mixtures. Energy-extraction efficiency using this oscillator system was the same as that previously determined using an H2-F2-O2-fueled oscillator which produced a better spectral match to the amplifier but which yielded poorer beam quality. Lateral shearing interferograms showed no significant phase-front degradation of the beam by the final amplifier. Pinhole energy-transmission measurements using a short-focal-length parabolic mirror determined that the focal-spot diameter was 2.7 times the diffraction-limited diameter.
Holographic interferometry of a high-energy-density exploding lithium wire plasma
Authors: Rockett Paul D. , Bach David R.
Published: February 2003

Single-wavelength holographic interferometry was applied to the study of an exploding lithium wire plasma. The wire was 1 mil in diameter, extruded in vacuum. A holographic-quality ruby-laser probe produced a 16-ns FWHM pulse at λ=694.3 nm with 45 mJ in the TEM00 mode. A temperature-controlled resonant reflector restricted laser operation to essentially a single-longitudinal mode. Linear charge density measured from Abel inverted interferograms implied that a significant amount of neutral or un-ionized lithium was present in a cold core. Peak electron density reached 1.4×1019 e−/cm3 and 2<Te<10 eV, but significant neutral contribution prevented accurate electron density determination near the core. Three characteristic periods of plasma development were identified and compared to time-resolved streak photographs of the luminous plasma front and optical spectra. Of special interest, a period of localized neutral ’’cloud’’ formation was observed with densities reaching 8×1017 cm−3, forming after self-pinching and before peak discharge current.
Waveguide modes of a warm isotropic drifting electron plasma
Authors: Kalluri Dikshitulu , Prasad Ramjee
Published: February 2003

The dispersion relation for the guided waves in a warm isotropic drifting electron plasma is derived using relativistic electrodynamics. TE modes are unaffected by the temperature and the drift velocity but these parameters have a significant effect on the TM modes. The phase characteristics of the fast, slow, and waveguide waves of the TM modes are discussed and presented as graphs.
Electrically active stacking faults in CMOS integrated circuits
Authors: Dishman J. M. , Haszko S. E. , Marcus R. B. , Murarka S. P. , Sheng T. T.
Published: February 2003

The origin and nature of anomalous leakage currents in CMOS (complementary metal-oxide-semiconductor) integrated circuits are investigated. Studies of the voltage dependence of the leakage on both devices and p/n junctions show that device leakage originates from individual junctions, and is very similar to that found from electrically active stacking faults (EASF’s) studied by other workers.1 In particular, a power-law dependence (IR∝VnR) is observed with exponents ranging from n=3–7.5. The onset of the anomalous leakage occurs at reverse-bias voltages ranging from 2–8 V. Etching studies of junctions with and without the anomalous leakage indicate a high correlation between the presence of the leakage and the occurrence of stacking faults intersecting the p/n junction boundary at the silicon surface. This correlation is confirmed by scanning electron microscope studies in the electron-beam-induced-current (EBIC) mode. Every junction showing the anomalous leakage exhibits one or more EBIC sites along the perimeter defined by the intersection of the p/n junction boundary and the silicon surface. A detailed investigation of these sites using transmission electron microscopy reveals that in every case they are associated with a decorated stacking fault crossing the junction at this point. In no case has an undecorated stacking fault been identified as a leakage site. Implications of this result for reducing the anomalous leakage by gettering are discussed.
Electrolytical doping of silicon with lithium
Authors: Antula J.
Published: February 2003

The results of the depth-profile analysis of p-type silicon, electrolytically doped with lithium, show in semilogarithmic representation a straight-line depth profile. The slope of this profile is in good agreement with the calculated Debye length, as would be expected from the theory presented here.
Lead depth profiles in binary mixtures
Authors: Congendo T. , Rudolph H.
Published: February 2003

Backscattering of 18-MeV α particles was used to measure concentration profiles of lead in bindary lead silicate glasses after they had been etched by acid. Lead removals extracted from these profiles are in good agreement with values measured by atomic absorption spectroscopy.
Field-induced volume diffusion in a two-phase system
Authors: Stark J. P.
Published: February 2003

When an applied field causes solute diffusion, second-phase redistribution is found for a two-phase system. The solute will diffuse in the primary phase with a tendency to maintain that phase saturated. However, particularly for small volume fractions, external surfaces provide flux discontinuities which can cause significant withdrawals from solute saturation. Thus, second-phase depletion, or the converse, may be totally dominated by a large withdrawal of the solute from what is expected with saturation. The general equations for such a process are derived and a detailed example is developed for electromigration.
Gaussian curvature of the slowness surface for piezoelectric surface waves on a cubic crystal
Authors: Shirasaki Hirokimi , Makimoto Toshio
Published: February 2003

The Gaussian curvature of the slowness surface for piezoelectric surface waves propagating on the Z-cut metal-coated surface of a semi-infinite cubic crystal (class 4̄3m or 23) is calculated. It is shown numerically that the points of zero curvature on the slowness surface correspond to the cusps in the wave surface. It is also shown analytically and numerically that these points correspond to the points satisfying ∂ε/∂ϑ=−1 on the ε−ϑ curve, where ϑ is the phase propagation angle and ε is the deviation angle, i.e., the angle which the phase velocity vector makes with the energy velocity vector.
Laser-to-microwave frequency division using synchrotron radiation
Authors: Wineland D. J.
Published: February 2003

Calculations are made to demonstrate the feasibility of obtaining one-step frequency division from optical or infrared laser frequencies to a subharmonic in the microwave spectral region. The cyclotron orbit of a single relativistic electron in a Penning trap is driven with a Gaussian laser beam focused to a spot diameter ∼λ; the laser subharmonic frequency is measured from the electron synchrotron radiation. The uncertainty in orbit dimensions is limited to λ/2 by radiative cooling and the technique of motional sideband excitation.
Catalytic control of the gas chemistry of sealed TEA CO2 lasers
Authors: Willis C. , Purdon J. G.
Published: February 2003

Sealed operation of TEA CO2 lasers is demonstrated using external catalytic control of the laser gas chemistry. With copper catalysts, although the level of oxygen is maintained at very low levels, the level of CO is sufficient that some increase in instability is anticipated. With platinum-on-alumina catalysts the levels of both CO and O2 are very low and it is anticipated that indefinite laser gas lifetime is feasible even for high-repetition-rate high-power devices.
Wave amplitude variation and energy flow in autoresonant collective ion acceleration
Authors: Godfrey Brendan B. , Newberger Barry S.
Published: February 2003

An expression for the energy of small-amplitude waves in a radially inhomogeneous cold-fluid unneutralized relativistic electron beam is obtained in terms of the wave amplitudes. The result is employed together with conservation of wave energy to determine how the axial electric field strength and beam-edge modulation associated with slow cyclotron waves change with position in an electron beam propagating along the adiabatically spatially decreasing magnetic guide field of an autoresonant collective ion accelerator. The resulting axial profiles are found to depart markedly from those of earlier radially homogeneous beam calculations. Possible impacts of these findings on a planned autoresonant acceleration feasibility experiment are discussed.
Light scattering by dielectric needles and disks
Authors: Schiffer R. , Thielheim K. O.
Published: February 2003

Light-scattering properties of very thin or flat dielectric particles are approximately calculated by means of a method which combines Rayleigh-Gans and Rayleigh scattering. For the approximation to be valid the shortest diameter of the particle, Rmin, must be small compared to the longest diameter Rmax and to the wavelength λ of the incident radiation. The method is applied to needles and circular disks and yields the scattering matrix and the differential and total scattering cross section in the lowest order of Rmin/Rmax and Rmin/λ. For the disks the total cross section is calculated only in the limiting cases of long and short wavelengths.
Power flow along a 40-kV multimegawatt neutral beam line
Authors: Menon M. M. , Dagenhart W. K. , Davis R. C. , Gardner W. L. , Haselton H. H. , Kim J. , Ryan P. M. , Schechter D. E. , Stirling W.L. , Tsai C. C. , Whealton J. H.
Published: February 2003

The results of a systematic investigation of the power flow along the Oak Ridge National Laboratory/Princeton Large Torus (ORNL/PLT) neutral beam line, using an intense modified duoPIGatron source with a 22-cm active grid diameter and 1799 circular apertures that provide 53% transparency, are reported. The variation of power deposited on the different components of the beam line is measured over a wide range of perveance values. The maximum efficiency for beam power transmitted through a 20×25-cm aperture located 4.1 m downstream was found to be 41%. This efficiency was raised to 53% when a voltage of about 175 V was applied to preaccelerate the ions entering the extraction apertures. Transmission efficiencies approaching 60% were obtained using shaped apertures on the plasma grid. Higher efficiencies should be attainable when used for PLT injection since the acceptance angle for the Princeton tokamak is 11% higher than that of the test facility. Detailed analysis of the results using straight circular apertures without precel voltage suggests that the power-deposition profiles have broad wings that significantly affect the transmission efficiency. The results allow optimization of the performance of the beam line and provide guidelines for designing future multimegawatt neutral beam lines.
Magnetocardiography in weak dc ambient magnetic fields
Authors: Boismier G. , Hlatky L. , Tepley N.
Published: February 2003

The magnetic field detectable outside the chest arising from the heart is analyzed using Maxwell’s equations. It is shown to consist of two contributions: (i) the field arising from the heart’s electrical activity, commonly known as the magnetocardiogram, and (ii) a contribution occurring only in the presence of an external magnetic field arising from the motion of diamagnetic material, principally blood. The latter contribution has been studied by means of a superconducting gradiometer in model circulatory systems consisting of plastic or rubber ventricles filled and emptied by pumps and tubing, and has been shown to be readily detectable in magnetic fields comparable to that of the earth. The effect has also been measured with human subjects, suggesting the possibility of clinical application of our results.
An asymmetric electrostatic lens for field-emission microprobe applications
Authors: Orloff J. , Swanson L. W.
Published: February 2003

The properties of a physically asymmetric three-element electrostatic lens have been calculated numerically for voltage-symmetric and voltage-asymmetric cases. The lens has low chromatic aberration, Cc∞/f < 0.5, when operated in the voltage-asymmetric mode with voltage ratios Vfinal/Vinitial as low as 2. Calculations of beam diameter versus current with realistic field electron emission parameters of dI/dΩ=1 mA sr−1 and ΔE=2 eV at 5 kV emitter voltage show that at 30-kV final-beam voltage 250 nA current could be focused into a 0.25-μm spot at 5 cm working distance, with an emitter-lens separation of 1.5 cm. It is shown that while the two-element immersion lens is inappropriate for high-current microprobe applications, the three-element asymmetric lens is well suited for this work.
Theoretical gain-optimization studies in CO2–N2 gasdynamic lasers. I. Theory
Authors: Reddy N. M. , Shanmugasundaram V.
Published: February 2003

Based on a method proposed by Reddy and Daum, the equations governing the steady inviscid nonreacting gasdynamic laser (GDL) flow in a supersonic nozzle are reduced to a universal form so that the solutions depend on a single parameter which combines all the other parameters of the problem. Solutions are obtained for a sample case of available data and compared with existing results to validate the present approach. Also, similar solutions for a sample case are presented.
The independence on preload and afterload of the contraction variable for the heart muscle. Thermodynamic and clinical consequences
Authors: Klip Willem , Janicki Joseph S. , Reeves Russell C. , Klip Dorothea A.
Published: February 2003

The time dependence of the contraction variable (Qc) for dog hearts was found to be largely independent of preload and afterload. This appears to make its clinical determination by pressure-volume measurements not unfeasible and could have important diagnostic consequences. The independence of the function Qc=?c(t) on the deformation variable (Q) led also to the derivation of some thermodynamic formulas for this contractile material.
Variable-thickness-type microbridges made of thin Nb films
Authors: Kuriki S. , Gundlach K. H.
Published: February 2003

In a study of a Nb thin-film microbridge it is found that thinning a part of constriction of the short bridge is effective in localizing the weak region. Such variable-thickness-type bridges, typically thinned from 400 to 250 Å and 0.5-μ long and wide, have a normal resistance of 1–4 Ω and show the temperature variation of critical current of the type of Ginzburg-Landau depairing current. Microwave-induced current steps are observed up to 360 μV and down to T/Tc=0.56 in a low critical current bridge. The data of microwave response imply that heating is limiting the high-voltage operation.
The elastic moduli and their pressure derivatives for tungsten carbide with different amounts of cobalt binder
Authors: Gerlich D. , Kennedy George C.
Published: February 2003

The elastic moduli and their pressure derivatives for polycrystalline tungsten carbide containing different amounts of cobalt binder have been measured. No clear-cut correlation between the values of the elastic moduli or their pressure derivatives and the cobalt content can be detected. From the measured data, an equation of state for the material is computed, and the various mode Grüneisen γ’s are evaluated. All the latter are in the range 1–2. The results are compared to the experimentally measured compression and Grüneisen constant.
Radiation effects in hydrogen-impregnated vitreous silica
Authors: Shelby J. E.
Published: February 2003

γ irradiation of vitreous silica normally leads to the formation of a large number of optical defects and to an increase in density. Irradiation of hydrogen-impregnated vitreous silica suppresses the formation of these optical defects, but does result in the formation of large quantities of bound hydroxyl and hydride. This process is accompanied by the expansion (density decrease) of the glass. The rates of hydroxyl and hydride formation and the density decrease all are proportional to the square root of the applied dose. The mechanism responsible for these results is not clear at this time.
Molecular-weight dependence of developed contours in poly- (methyl methacrylate) electron resists
Authors: Atoda Nobufumi , Komuro Masanori , Kawakatsu Hisazo
Published: February 2003

In order to study effects of initial molecular weight, developed profiles in poly- (methyl methacrylate) (PMMA) films are simulated by use of the Monte Carlo method coupled with a time-dependent solubility model. The solubility rate measured in PMMA with molecular weights of up to 1.6×107 is used. The induction period observed before the beginning of dissolution is taken into consideration at the surface layer of the resist film. With increase in the initial molecular weight, the minimum usable dose can be lowered while the required development time is increased. The influence of the molecular weight becomes considerably slight in the region of molecular weight higher than about 1×105. The minimum linewidth obtainable at high dose is determined by the electron scattering and is almost independent of the initial molecular weight. The long development time required at the low-dose region, causing the significant thickness loss and lateral spread of the profile, is mainly due to the decrease in the solubility rate in the deeper part of the resist film. By decreasing the initial molecular weight with the film depth, the decrease in the solubility rate of the deeper portion can be compensated for and consequently the usable exposure dose is lowered without loss of resolution.
The effect of neutron irradiation on the lattice parameter and anomalous x-ray transmission of silicon
Authors: Baldwin Thomas O. , Thomas James E. , Haldeman James K.
Published: February 2003

This paper reports the effects of fast-neutron irradiation on the lattice parameter and anomalous x-ray transmission of silicon. A monochromator first suggested by Hart was used to make precision measurements of the lattice parameter and measurements of integrated intensities simultaneously on the same sample. Isochronal annealing results of both quantitites are related to earlier studies and to each other. Two dominant annealing regions centered at about 180 and 550 °C were observed, although the precise location of these regions appeared to be dependent upon neutron dose and the physical quantity (lattice parameter or anomalously diffracted intensities) being measured. Some additional evidence was found for reverse annealing behavior at temperatures greater than 650 °C; this behavior was attributed to the formation of defect clusters.
Shallow defect levels in neutron-irradiated p-type extrinsic silicon
Authors: Young M. H. , Marsh O.J. , Baron R.
Published: February 2003

Two new acceptor levels, at 0.027±0.001 eV and 0.039±0.004 eV from the valence band, have been observed by measurements of Hall effect versus temperature in neutron-irradiated float-zone-grown Si : Ga. The presence of these very shallow electronic energy levels was also indicated by photoconductive spectral response measurements at 5 K. The purpose of neutron irradiation was to counterdope residual boron by neutron transmutation for infrared detector applications. These shallow acceptors are observed after anneals at temperatures as high as 625 °C, but annealing at 700–850 °C reduces their concentration below detectable levels. Shallow levels are also observed in neutron-irradiated Si : Al and Si : In grown by the floating-zone method. Results indicate that formation of these shallow defects depends upon the presence of column-III dopant atoms (Ga, In, Al).
Analysis of ’’Comments on ’Electrochemical effects as the source of emf in metal(1) -polymer-metal(2)’ ’’
Authors: Vijh Ashok K.
Published: February 2003

It is shown that our previous model suggesting the paramount importance of the metal-oxide reaction (and thence the metal/metal-oxide potentials) in determining the magnitudes of emf observed in metal(1) -polymer-metal(2) systems is consistent with, and supported by, all the available experimental data. Specifically, the model is not invalidated by the presence of a voltage under a ’’presumed’’ vacuum, the influence of the polymer upon the measured voltages, and the increase in voltage at approximately 80 °C. Electrode oxidation will play a prominent role as long as electrodes have access to the traces of ambient moisture, oxygen, or oxygenated ionic species (e.g., OH−, RCOO−, and H+3O) arising from the polymer. Such a surface oxidation can be eliminated only under a very high vacuum (10−9 Torr) on noble metals (i.e., Au) that are not in contact with any oxidizing species; such conditions are almost never realized in the work on metal(1) -polymer-metal(2) systems.
GaP negative-electron-affinity cold cathodes
Authors: Sukegawa Tokuzo , Kan Hirofumi , Nakamura Tsutomu , Katsuno Hironobu , Hagino Minoru
Published: February 2003

A new GaP junction structure for negative-electron-affinity (NEA) cold cathodes is proposed in order to obtain a higher emission efficiency and a narrower energy distribution of the emitted electrons. Highly efficient GaP NEA cold cathodes with the proposed junction structure were fabricated by improving material technology. A typical efficiency of electron emission for a (100) -oriented GaP surface was about 0.7%. The energy distribution of the emitted electrons from the cold cathode had a full width at half-maximum of about 0.3 eV. At present, the cold cathodes have been operating continuously in excess of 3000 h at an emission current density of about 10−3 A/cm2.
Direct measurement of diffusion coefficients of sputtered atoms in Ar
Authors: Mase H. , Tanabe T. , Miyamoto G.
Published: February 2003

The diffusion coefficients of sputtered particles through Ar are directly measured by using a rotating collector of particles sputtered in a pulsed discharge. The total amount of diffusing substance W (t) as a function of time is obtained from the deposit on the collector. The asymptote of W (t) has the intercept t0 on the t axis given by t0=L2/6D, so that D can be determined by an observation of t0. The experimental results show that the coefficient of diffusion varies inversely with the square root of the mass of the sputtered particle and the value of Dp is 35 cm2 Torr/sec for Cu in Ar.
Kinetic momentum quantum effect in a superconducting closed loop composed of Josephson junctions
Authors: Yamashita Tsutomu , Ogawa Yasuhiko , Onodera Yutaka
Published: February 2003

Superconducting closed loops composed of N series Josephson junctions are discussed. The conditions to achieve the n quantum state of a fluxoid in the loop are analyzed. It is found that the n quantum state exists in Josephson loops having more than 4n pieces of junctions even if it is assumed that the inductance L in the loop is negligibly small. This n quantum state is achieved by an asymmetric current feed to the Josephson loop. The properties of the loop are easily explained by using a pendulum analog.
Diffraction contrast behavior of grown-in dislocations in V3Si single crystals
Authors: Nakahara S. , Mahajan S. , Wernick J. H. , Chin G. Y.
Published: February 2003

The diffraction contrast behavior of grown-in dislocations in V3Si single crystals has been examined in detail by transmission electron microscopy. It is inferred that the Burgers vectors of these line imperfections are 〈100〉. The observed image features are rather complex and are compared with computer-simulated dislocation images. It is suggested that the likely glide systems in V3Si are 〈100〉 {001}. Since these slip systems yield only three independent systems, the observed lack of ductility in polycrystalline aggregates may be rationalized.
Electron spectroscopy studies on amorphous GdFe and GdCo alloys
Authors: Terzieff Peter , Lee Kenneth
Published: February 2003

I n situ XPS photoelectron studies on amorphous thermally evaporated GdFe and GdCo films have been made under UHV conditions. The results were used to test the conventional concept of charge transfer, which had been applied to the materials under discussion. The XPS binding energies were found to be identical in the pure elements and the alloys, suggesting that the core levels in a-GdFe and a-GdCo are not very sensitive to a change in the chemical environment. Thus, it was concluded that the transfer of charge from Gd to the transition metal d bands, if existing at all, must be smaller than one electron per Gd atom. The preferential oxidation of Gd in GdFe and GdCo films was found to be characteristically reflected in the low-energy transitions of the Auger spectra, which hence were used to distinguish between the clean and the oxidized state of Gd. The influence of oxidation from the Gd 4d and 4f levels was characterized in some separate experiments on pure Gd.
Domain-wall dynamics in the presence of an in-plane field in bubble garnet material
Authors: Vural K. , Humphrey F. B.
Published: February 2003

Domain-wall dynamics in the presence of an in-plane field (HI) have been investigated in bubble garnet material using transient photography during high drive radial expansion. For HI?100 Oe, the velocity is approximately constant with respect to the effective drive field He. This saturation velocity increases as HI increases. At higher HI’s the velocity is drive-field dependent at first with saturation at higher drives. There is a significant anisotropy between the velocity of the wall along HI and the wall normal to HI with the latter moving slower. This anisotropy decreases an HI increases. Implantation generally decreases the velocities by about 25%. The wall normal to HI exhibits a dynamic structure change for high fields, whereas the wall parallel to HI does not. The experimental results are compared with the predictions of existing theories and no agreement is found.