bluuebunny/crossref_metadata_2025 huggingface dataset:
Line emission in AI XI as an optical diagnostic in laser-heated plasmas
Authors: Davis J. , Whitney K. G.
Published: February 2003

An extension of an earlier model of a laser-heated aluminum plasma is made to describe line emission in these plasmas from the lithiumlike Al XI ion. The model includes a satellite to the Heα-like line and the six most prominent lines originating from single excitations in Al XI. The core of the plasma is heated directly and cooled by thermal conduction losses to an equal volume of outer plasma, by a free hydrodynamic expansion, and by radiative losses principally from the hydrogen, heliumlike, and lithiumlike ionization stages. A study is made of the emission from plasmas initially at ion densities that, for a fully ionized plasma, would have critical electron densities for absorption of CO2, neodymium, and frequency-tripled neodymium laser radiation. Curves showing the integrated emission from different lines in Al XI are presented and correlated to the different plasma densities, peak average temperatures, and conduction loss rates.
Stimulated Brillouin scattering of CO2 laser radiation from underdense plasma
Authors: Offenberger A. A. , Cervenan M. R. , Yam A. M. , Pasternak A. W.
Published: February 2003

Results of detailed measurements undertaken to compare experiment and theory of stimulated Brillouin scattering of high-intensity CO2 laser radiation from underdense hydrogen and helium plasmas are reported. Spectral measurements confirm the ion acoustic wave as responsible for the backscatter. Ion Landau damping and collisions both contribute to spectral broadening. The maximum linear scattering growth rate γk was determined experimentally to be 6×1011 sec−1 in good agreement with a theoretical value calculated from random-phase wave scattering. The value derived assuming coherent-wave interaction was 1011 sec−1 which is a factor of 2 greater than the corresponding theoretical prediction. Temporal characteristics and reflectivity of the backscattered radiation are discussed.
Plastic bubbles and tamper 〈ρR〉 measurements for laser-driven fusion experiments
Authors: Mayer F. J. , Rensel W. B.
Published: February 2003

A new diagnostic technique is described which makes use of large-diameter (∼5 cm) thin-walled (∼10 μm) plastic bubbles to collect neutron-activated tamper material in a laser-driven fusion experiment. The plastic bubble and radioactive material are dissolved in a solvent and counted in a ?erenkov scheme to determine the average tamper 〈ρR〉 at peak compression conditions. The bubble energy flow and other plasma diagnostic characteristics are also briefly discussed.
Narrow-beam five-layer (GaAl)As/GaAs heterostructure lasers with low threshold and high peak power
Authors: Thompson G. H. B. , Henshall G. D. , Whiteaway J. E. A. , Kirkby P. A.
Published: February 2003

A variety of (GaAl)As/GaAs heterostructure injection lasers have been fabricated with two pairs of heterojunctions, the inner pair for carrier confinement and the outer pair for optical confinement. Asymmetrical versions of this design have given, at one extreme, threshold current density Jt at 300 K as low as 500 A/cm2 and at the other extreme far-field angular beam widths to the half-power point of 15° with Jt<1000 A/cm2, for 500-μm-long sawn cavity lasers with reflectors on one face. The incremental quantum efficiency from one end of 300-μm-long lasers with reflectors was over 40%. The peak optical power from lasers of 100 μm width was up to 3 W for 200-ns pulses. The temperature variation of threshold over the range 290–355 K was Jt355/Jt290∼1.5. Double-heterostructure lasers with narrow active layers and 20% AlAs confinement steps gave almost comparable performance in Jt and beam width (650 A/cm2 for 33° and 1200 A/cm2 for 15°), but the linearity of light versus current was poorer, the temperature sensitivity of threshold was Jt355/Jt290⩾2, and efficiency also dropped with temperature. The optical distribution has been calculated for various multilayer heterostructure waveguides and related both to the far-field beam width and to the threshold current. A universal gain/current density relation for the active layer has been deduced from the measurements and agrees reasonably with published theory.
Interfacial recombination at (AlGa)As/GaAs heterojunction structures
Authors: Ettenberg M. , Kressel H.
Published: February 2003

A determination has been made of the effective interfacial recombination at Al0.25Ga0.75As/GaAs and Al0.5Ga0.5As/GaAs heterojunctions. The recombination velocity was deduced from the dependence of the minority-carrier lifetime on junction spacing in heterojunction diodes. For heterojunction spacings in excess of about 1 μm, the interfacial recombination can be characterized by a recombination velocity of 4×103 and 8×103 cm/s for Al0.25Ga0.75As/GaAs and Al0.5Ga0.5As/GaAs heterojunctions, respectively. However, for double-heterojunction spacings below 1 μm, the minority-carrier lifetime is invariant, suggesting that the interfacial recombination velocity decreases with decreasing heterojunction spacing. No such effect is observed in single-heterojunction diodes.
Dielectric properties and a model of biphase water suspension at 9.4 GHz
Authors: Kraszewski A. , Kulinski S. , Matuszewski M.
Published: February 2003

Measurements of the complex permittivity of clay-sand slurry containing fine-milled mineral particles suspended in water carried out at 9.4 GHz show a marked dependence on both temperature and moisture content. The character of these relations is similar to that obtained for pure water. Permittivity and specific gravity of a slurry in the range interesting for technical activity are little affected by its chemical composition. On the basis of measurements carried out for five kinds of technological slurries a simple model for quick analysis of their properties is presented. The model consists of two separate layers: water and dry mineral inclusions, the thickness of which is proportional to the volume content in the suspension. Resultant permittivity of the biphase water suspension is equal to the sum of square roots from permittivities of both constituents, multiplied by their volume filling factors. Experimental results agree with those calculated from such simple formula within accuracy of measurement (dielectric constant within 2%, loss factor within 5%).
A gigawatt CO2 laser with telescopic amplifier
Authors: Little V. I. , Selden A. C. , Stamatakis T.
Published: February 2003

The first production of gigawatt pulses form a 1-m CO2 telescopic amplifier with megawatt input is reported. This device has been used to generate 1-J pulses of 830 ps FWHM from a suitably gated source.
Pressure dependence of ultrasonic wave velocities and elastic stiffness moduli for a TiO2-SiO2 glass (Corning 7971)
Authors: Andreatch P. , McSkimin H. J.
Published: February 2003

A glass which is possibly useful as an optical and acoustical waveguide material was characterized. Ultrasonic wave velocities were measured as a function of hydrostatic pressure for Corning glass No. 7971, a TiO2-doped silica, and also for an undoped-specimen glass No. 7940. Pressure derivatives of the elastic stiffness moduli were determined.
Evidence of localized heating in CO2-laser-produced plasmas
Authors: Haas Roger A. , Boyle Michael J. , Manes Kenneth R. , Swain James E.
Published: February 2003

Polyethylene foils and parylene disks have been irradiated by CO2 (λ∼10.6 μm) and Nd : YAG-glass (λ∼1.06 μm) laser pulses focused to flux levels in the 1013- and 1014-W/cm2 range. X-ray pinhole photographs of the CO2-laser-produced plasmas exhibit intense localized emission regions whose characteristic dimensions are smaller than the nearly diffraction-limited focal spot of the laser. Corresponding photographs of the glass-laser-produced plasmas show no evidence of localized emission. These experimental results are consistent with theoretical predictions for laser-beam trapping and/or filamentation in laser-produced plasmas.
Improved transmission secondary emission from InxGa1−xP/GaAs self-supporting films activated to negative electron affinity
Authors: Martinelli Ramon U. , Olsen Gregory H.
Published: February 2003

Transmission secondary emission (TSE) gains as high as 540 at primary energies of 20 keV have been achieved in self-supporting InxGa1−xP/GaAs structures activated to negative electron affinity (NEA). Furthermore, a linear dependence of the gain on primary energy has been obtained in the range 4–20 keV. These improvements result from the long diffusion lengths (L) in the GaAs and the low interfacial recombination velocities (sb) at InxGa1−xP/GaAs interfaces which have small smounts of lattice mismatch (ε<3×10−3). Secondary emission yield curves along with corresponding cross-sectional transmission electron microscope micrographs from structures with lattice mismatches of 0, 3×10−3, and 1.2×10−2 are presented. Evidence from highly mismatched structures suggests that high densities of inclined dislocations degrade L and sb. Reflection secondary emission data support these conclusions.
Importance of the dependence of the secondary electron emission coefficient on E/p0 for Paschen breakdown curves in ac plasma panels
Authors: Sahni O. , Lanza C.
Published: February 2003

Apparent deviations from Paschen’s law, observed in ac plasma panels, have been resolved by generalizing the breakdown criterion to include the dependence of the secondary electron emission coefficient on E/p0. Incorporation of this dependence into the proposed effective coefficient involves consideration of both the back-diffusion phenomenon and the influence of E/p0 on the efficiency of metastable atom generation. Calculated voltage breakdown curves in pure neon and neon plus 0.1% argon mixture are in good agreement with experimental data for both the metal electrode dc discharges and the insulator-covered electrode discharges found in ac plasma panels.
Thermal warping of layered composites
Authors: Chow T. S.
Published: February 2003

The effect of shear deformation on a layered composite being heated to a prescribed temperature is analyzed according to a recently developed theory for unsymmetric laminated plates. Expanding the fundamental solutions of thermal stress and warping into a power series form, the first approximation gives us familiar formulas of classical plate theory. The second approximation leads to an equivalent Timoshenko’s plate equation. In addition to Timoshenko’s shear correction factor, a thermal shear correction parameter has to be introduced for thermal expansion problems.
Thermally induced bubblelike patterns in Fe-doped LiNbO3 single crystals
Authors: Yasuhira T. , Morikawa T. , Shimada J. , Sakurai K.
Published: February 2003

Bubblelike patterns associated with polar domains have been observed in Fe-doped LiNbO3 single crystals quenched with a temperature drop of approximately 50 °C or more. Exploitation of this effect for a nondestructive domain identification is indicated.
Influence of surface roughness on the intensity of elastically scattered low-energy noble-gas ions
Authors: Nelson G. C.
Published: February 2003

The influence of surface roughness on the intensity of elastically scattered low-energy noble-gas ions has been determined for surfaces whose surface displacements are normally distributed. This has been done by modeling the effect of shadowing on the scattered-ion intensity. The experimental results are in good agreement with the values predicted by the model.
A polarizing oriented smectic beam splitter
Authors: Cladis P. E. , White A. E.
Published: February 2003

A beam of unpolarized light is shown to be split into three distinct polarized beams when it passes through the core region of a smectic liquid crystal which is oriented so that its planes form concentric cylinders. In N-p-cyanobenzylidene-p-octylozyaniline (CBOOA) the angle between two adjacent exit beams is ∼22° whereas for N-p-cyano-p-octylbiphenyl (COB) it is ∼14°. Knowing this angle, we are able to deduce the ratio of the extraordinary to ordinary index of refraction, ne/no, for CBOOA and COB.
Measuring small-area Si/SiO2 interface stress with SEM
Authors: Conru H. W.
Published: February 2003

A method for measuring small-area Si/SiO2 interface stress with the scanning electron microscope (SEM) has been developed. The method consists of cleaving a Si wafer (chip) through the desired area and selectively etching the Si back from the broken edge. The compressive stress in the remaining SiO2 shelf is thus released. When viewed on edge by a SEM, the sample conveniently shows the resulting sinusoidal shape of SiO2. Direct measurement of the arc length and its corresponding straight-line distance can then be used to calculate the Si/SiO2 stress. The technique is particularly suited for measuring stress in local areas of thin SiO2. Stress calculations obtained from SiO2 films 500–700 Å thick at local regions only 4 μ wide have shown the compressive stress to be as high as 5.1×1010 dyn/cm2. The lower limit of film thickness to which this technique may be applied is governed by the resolving power of the SEM or the ability of the thin film to support itself. The upper limit of film thickness is dependent upon the length and thickness of the strut and the actual compressive stress, all of which affect the critical value that will cause the unsupported film to buckle.
Response time of Ge-doped (Al,Ga)As-GaAs double-heterostructure LED’s
Authors: Zucker J. , Lauer R. B. , Schlafer J.
Published: February 2003

The response time of the spontaneous emission of planar double-heterostructure LED’s has been measured as a function of the majority-carrier concentration in the active layer. The response time was found to decrease from a value of 15.5 ns at p0?2×1017 cm−3 to a value of 1.6 ns at p0?2×1019 cm−3. These rise times imply amplitude-modulation bandwidths for these LED’s in excess of 200 MHz. Based on the experimental values of the response time, the diffusion length of the minority carriers in the active layer of the LED can be calculated. Values of the minority-carrier diffusion length are found to range from 10.0 μm for p0?3×1017 cm−3 to 1.45 μm for p0?2×1019 cm−3.
Low-voltage tunnel-injection blue electroluminescence in ZnS MIS diodes
Authors: Walker L. G. , Pratt G. W.
Published: February 2003

Tunnel-injection green and blue electroluminescence in ZnS tunnel MIS diodes with alkali halide insulator layers is reported. Complete films down to 59 Å average thickness and external quantum efficiencies up to 1.1×10−5 have been achieved. The trend of the data is an increase in external quantum efficiency for a decrease in insulator layer thickness. The measured interface state density is on the order of 1014 cm−2 eV−1.
Grain size and film thickness of Nb3Sn formed by solid-state diffusion in the range 650–800 °C
Authors: Shaw Bevil J.
Published: February 2003

A simple etching and replication technique for the determination of grain size in thin films of Nb3Sn has been established. The resulting data compares well with previous reports of grain size as a function of reaction temperature and of the pinning force Fpmax as a function of grain size. The possibility of an optimum grain size for Fpmax is indicated.
Scattering of spin waves by pores in ferrimagnetic materials
Authors: Sawado E.
Published: February 2003

The differential cross section of spherical pores in ferrimagnetic materials is calculated by using the Born approximation in scattering theory. Using this scattering cross section, the theory is developed for evaluating the wave-vector dependence of the spin-wave linewidth. The wave-vector dependence of the spin-wave linewidth is 1/k in the long-wavelength region and is proportional to k for the short-wavelength region, where k is the wave vector of the spin waves. It is concluded that the spin-wave linewidth is a function of both the number of pores and their radius. Agreement between the theoretical formula and the experimental results is good except in the region of very long wavelength.
A technique for measuring, displaying, recording, and modifying the spatial uniformity of implanted ions
Authors: Hammer W. N. , Michel A. E.
Published: February 2003

This paper describes a technique for the continuous ’’on line’’ measurement of the spatial distribution of implanted ions. The method employs a multichannel analyzer to record the digitized integrated ion current and beam position and to generate a three-dimensional topographic display. The technique is applicable to apertured beams on mechanically rastered targets or to swept beams on stationary targets. The implant uniformity can be examined from either an isometric or a contour-type display on the multichannel analyzer or the data can be transferred to a digital computer for more sophisticated analysis. The uniformity can be examined prior to removal of the sample from the target chamber and ’’fill in’’ techniques employed to improve the uniformity.
Angular properties of particle fluxes for strongly forward-peaked scattering
Authors: Strickland D. J. , Bernstein I. B.
Published: February 2003

An equation of transfer for elastic scattering and the corresponding Fokker-Planck equation are solved for strongly forward-peaked scattering. The cross sections employed are appropriate to kilovolt electrons scattering off light nuclei. Results are shown for which the backscattered flux calculated with the transfer equation is sensitive to the cross section at large angles, indicating that single large-angle scattering can be important even though the cross section for it may contribute but a small fraction of the total cross section. Solutions of the Fokker-Planck equation agree well with those of the counterpart integral equation, provided sufficient scatterers are present to make multiple small-angle scattering dominant. For thin systems, the Fokker-Planck results for backscatter fall below the integral-equation results. The integral equation of transfer has been solved both numerically and in terms of its eigenfunctions and eigenvalues. Solutions by the two distinct methods agree to at least three significant places, thereby establishing the accuracy of the applied numerical techniques.
Log-normal size distributions from magnetization measurements on small superconducting Al particles
Authors: Buhrman R. A. , Granqvist C. G.
Published: February 2003

Field-dependent magnetization of superconducting fine Al particles has been measured down to 0.5 K with a SQUID system. The results can be explained in considerable detail by the existence of a log-normal distribution of particle size.
Dielectric properties of pyrophyllite as a function of water vapor pressure
Authors: Timco G. W. , Dvorak Z. , Schloessin H. H.
Published: February 2003

The effects of water vapor pressure on the dielectric constant and dissipation factor of pyrophyllite have been measured in the frequency range 0.05–10 kHz. Both the dielectric constant and dissipation factor increase with increasing vapor pressure and decreasing measuring frequencies. This result has application in electrical measurements made in pyrophyllite-media high-pressure devices.
How many data establish a model? Electrical transport in amorphous As2Te3 and polycrystalline PbS
Authors: Bube Richard H.
Published: February 2003

The transport properties of amorphous sputtered films of As2Te3 show a striking similarity to the transport properties of chemically deposited polycrystalline PbS. An investigator, without certain critical pieces of data, would feel strongly reinforced by this similarity in applying the same model to both materials. It is a case, however, where it can be readily shown that the similarities are only coincidental, and that quite different models are needed for the two materials. A lesson in deciding for or against choice of a model is contained in these observations.
Fluorine-atom probe techniques for chemical lasers
Authors: Schlossberg Howard
Published: February 2003

The infrared absorption coefficient and Raman scattering cross sections of the fluorine-atom 2P3/2→2P1/2 transition at 404 cm−1 are estimated. The results are discussed in terms of probing fluorine-atom concentrations in chemical lasers. It is shown that absorption and coherent anti-Stokes Raman scattering can give sensitivity better than 1015 atoms/cm3.
Storage and examination of high-resolution charge images in Teflon foils
Authors: Feder J.
Published: February 2003

High-resolution charge patterns at various charge densities were written on Teflon TFE foils using a 10-kV electron beam with a 1/2-μm spot diameter. Resolutions of 50–100 line pairs/mm were observed by examination with an electron beam and use of xerographic development techniques. Charge spreading in the Teflon and the examination processes were among the factors limiting resolution. Development of stored patterns up to 3 months after their writing showed that resolutions of 100 line pairs can be maintained for this period. Comparison of the results for heat-sealed samples with those for nontreated samples showed an absence of any marked pattern deterioration due to heat sealing.
Optical dielectric constant of Pb1−xSnxTe in the narrow-gap region
Authors: Lowney J. R. , Senturia S. D.
Published: February 2003

The optical dielectric constant ε∞ of Pb1−xSnxTe has been measured for Sn fractions x of 0.0, 0.24, 0.36, 0.39, and 0.40 in the temperature range 6–120 K and at 300 K. The value of ε∞ increases from 33 for PbTe at 300 K to 60 for Pb0.61Sn0.39Te at 6 K. This maximum value appears to occur at a composition and temperature close to the L-point band inversion. However, the relative insensitivity of ε∞ to carrier concentration suggests that this increase in ε∞ near band inversion arises from motion of the bands throughout the Brillouin zone rather than from a change in L-point ionicity, as suggested by Wemple.
Temperature distribution on thin-film metallizations
Authors: Chaug Yi-Shung , Huang Huei Li
Published: February 2003

The time-dependent temperature distribution of a thin-film stripe has been solved rigorously using two successive Laplace transforms on both time and coordinate. For a good conducting stripe with a δ-shaped crack it is shown that the temperature distribution can be very adequately described by the steady-state solution provided only that the time scale involved is of the order of 10−3 sec or longer. No localized hot spot is possible, for whatever reasons, for a good conductor. However, if heat generation outpaces heat conduction, as would be the case for a poor conductor, a localized temperature becomes quite realizable. Finally, if stripe cracking is developed via grain-boundary grooving processes somewhere along the stripe, in particular near the anode, void formation there is simply a natural consequence of the temperature-grandient effect.
Positive and negative hydrogen ions backscattered from Au, Ta, and ThO2 in the energy range up to 15 keV
Authors: Verbeek H. , Eckstein W. , Datz S.
Published: February 2003

Samples of polycrystalline Au, Ta, and ThO2 were bombarded by 5–15-keV beams of H+1, H+2, H+3, D+1, and D+3 ions. The backscattered positive and negative hydrogen ions were energy analyzed by a spherical condenser. For Au and Ta both the positive and the negative spectra start with zero intensity at zero energy and reach maxima, whose position depends on the primary energy and the ion species. For ThO2 the positive spectrum is similar but the number of negative ions shows no maximum and is largest at energies below 1 keV and continues to decrease with increasing energy. With decreasing work functions of the target materials the number of backscattered negative ions increases. The ratio of negative-to-positive backscattered ions is larger than unity at low energies in the cases of Au and ThO2. A comparison of proton and deuteron results shows that the ratio is equal for ions of equal velocities. For Ta and ThO2 this ratio is considerably larger when the targets are bombarded with molecular ions as H+2, H+3, D+2, and D+3 than when bombarded with the corresponding atomic ions H+ and D+ with equal energies per atom.
Modeling of enhanced diffusion under ion irradiation
Authors: Myers S. M. , Amos D. E. , Brice D. K.
Published: February 2003

The differential equations which govern enhanced diffusion under ion irradiation are solved using recently developed numerical techniques. Accurate time-dependent profiles for vacancies, interstitials, and diffusing atoms are generated thereby with minimal computer time. The theoretical description is improved further by incorporating refined calculations of the atomic displacement rate by energetic ions. Three representative cases of enhanced diffusion are treated in detail: Al diffusion in Al under 100-keV Al irradiation, Al diffusion in Al under uniform irradiation, and W diffusion in W under 100-keV proton irradiation. It is shown that more information may be obtained from the diffused atomic profiles if the irradiation damage rate varies with depth in a known way over the diffusion region. Under this condition, both the shape and the time dependence of the atomic profile are sensitive to the rate coefficient for point-defect annihilation. When the annihilation coefficient is so determined, the point-defect creation rate can be uniquely related to the enhanced atomic diffusion coefficient. Under irradiation with a limited range, the atomic profiles typically pass through a complicated form, but ultimately reach a flat shape with a relatively abrupt drop-off at greater depths. This end condition is qualitatively independent of the detailed structure of the irradiation profile, but the sharpness of the drop-off is a function of the rate coefficient for point-defect annihilation.
Light scattering from smectic liquid-crystal waveguides
Authors: Giallorenzi T. G. , Weiss J. A. , Sheridan J. P.
Published: February 2003

Light scattering properties of smectic-A liquid-crystal thin-film waveguides are studied both theoretically and experimentally. A Green’s function analysis of the depolarized light scattering induced by thermal fluctuations in the average molecular alignment is presented. Scattered power distributions and scattering coefficients for mode conversion and for scattering out of the guide are derived. It is shown that the power distributions for scattering from nematic and smectic waveguides differ greatly and that scattering losses in smectic-A liquid-crystal waveguides are several orders of magnitude lower than those encountered in nematic guides. Power loss in these waveguides, due to light scattering arising from thermally induced dynamical distortions of the smectic planes, is calculated to be on the order of 2 dB/cm and is experimentally verified.
Computer simulation of x-ray diffraction topographs of stacking faults
Authors: Wonsiewicz B. C. , Patel J. R.
Published: February 2003

A group of programs are described which will simulate a photograph of arbitrary contrast ratio or exposure. We have used these programs to simulate x-ray topographs of stacking faults as described by Authier’s spherical wave treatment of a perfect crystal with a stacking fault. Intrinsic and extrinsic faults are examined with a range of different wavelengths, fault orientations, diffraction conditions, specimen thicknesses, and absorption coefficients. In cases where experimental topographs are available, they correspond closely to the simulations, thereby indicating the basic correctness of Authier’s theory. The simulations illustrate the separation of the complex diffraction pattern into three components. Only one component carries information on the nature of the fault. The simulations clearly delineate the conditions for identifying the fault type; namely, the critical value of μd for adequate visibility of the I3 fringes is in the range 1<μd<2. Traverse patterns are demonstrated to be an unreliable guide to the nature of the fault.
An improved low-pressure dc discharge
Authors: Spielman R. B. , DeGroot J. S. , Rasmussen D. A.
Published: February 2003

We describe a scheme in which the primary beam electrons are electrostatically confined in a low-pressure dc discharge plasma which can substantially improve the density (300 or 400% in our case). The electrons are heated to 2 eV with a fraction thermalized to ∼10 eV by the extended presence of the primary beam electrons. Ion noise observed was not changed substantially from that without confinement. (It was slightly better than unconfined.) The plasma noise is strongly dependent on filament geometry. We also describe a second electrostatic confinement scheme in which both the primary electrons and the plasma are confined, resulting in a further density increase.
Net ionization coefficient in boron trifluoride
Authors: Davies D. Kenneth
Published: February 2003

Values of the net ionization coefficient λ1 in BF3 have been determined from spatial current growth measurements in uniform electric fields E over the range 1.07×10−15⩽E/N⩽17.0 ×10−15 V cm2 for gas densities N in the range 4.07×1016 ⩽N⩽348×1016 cm−3. For the limited range 1.07×10−15⩽E/N⩽1.70×10−15 V cm2, values of the ionization and effective attachment coefficients have also been determined. Within the limits of experimental uncertainty all the coefficients are found to be functions of E/N only. The limiting value of E/N at which λl=0 is found to be 1.13×10−15 V cm2.
The two-dimensional constant-property arc
Authors: Cohen Ira M. , Whitman Alan M.
Published: February 2003

The theory of the (one-dimensional) constant property arc has been extended to a planar arc in two dimensions. This makes use of the canal model where the canal boundary temperature T*, at which the electrical conductivity jumps discontinuously from zero to a constant value σ* characteristic of the gas, is specified as a gas property. The Elenbaas-Heller equation is solved for arc temperature distributions subject to Ohm’s law and current conservation. Temperatures on the bounding walls and electrodes are specified. The principal parameters of this study are the length (interelectrode distance) to width (between bounding walls) ratio (a) and the conducting spot size (or maximum temperature) on the electrodes (F0). For a≳1, the central plane electric field is nearly coincident with the one-dimensional value. As a increases beyond 2.0, temperature maxima and arc thickness maxima appear near the electrodes. As F0 increases, arc temperatures increase at each point for fixed current.
Laser-induced shocks and their capability to produce fracture
Authors: Steverding B. , Dudel H. P.
Published: February 2003

The fracture potential of pulsed laser light is investigated for brittle and ductile fracture. The occurrence of fracture depends on the power density of the beam, the pulse duration, the target thickness, and a number of material parameters, ranging from the plasma state to the solid state of the target material. An essential part of the fracture analysis is the attenuation of the induced shock, which is rapid for short pulses. Using aluminum as a target material it will be shown that fluence levels of 104 J/cm2 are necessary to break targets of centimeter thickness, assuming that the pulse duration is 10−7 sec. It appears that an optimal situation for the achievement of fracture exists, since the peak pressure is inversely proportional to a power of pulse duration, whereas attenuation is proportional to pulse duration.
The behavior of nitric oxide in glow discharges
Authors: Kuehn D. G. , Chanin L. M.
Published: February 2003

Mass spectrographic analyses were conducted to determine the positive ions and neutral species in glow discharges containing NO for pressures from 10 to 75 Torr. The three gas mixtures investigated included 1.0% NO in He, 0.55% NO in N2, and 2.5% each of CO and CO2 plus 0.55% NO in N2. Various means were utilized for the application of electrical power: directly coupled dc and 60 Hz ac, capacitively coupled 60 Hz ac, and inductively coupled 3.0 MHz rf. Nitric oxide was readily dissociated in the discharges, resulting in the formation of N2 and O2—or N2 and CO2 when CO was present initially. Introduction of the minimum excitation necessary to maintain a uniform glow discharge was most effective; increasing the applied power beyond this minimum point served primarily to induce secondary reactions among the products of the NO decomposition.
Wave structure measurement and analysis in hypervelocity impact experiments
Authors: Lipkin J. , Kipp M. E.
Published: February 2003

The impact of a single low-density sphere on an aluminum target was analyzed with two-dimensional finite difference wave propagation codes. The results of these analyses are compared with experimental measurements of the target back-surface velocity history. An improved basis for establishing how closely a given equation-of-state and failure description represent the real material behavior is thereby achieved. In the experiments, measurements were made with the diffuse surface velocity interferometer. The experimental technique was sufficiently refined so that a sphere impacted within a 6-mm radius of the aiming point after a free flight of ∼15 m at ∼5 km/s. Sphere diameter and target thickness were varied in constant ratio so that a single calculation could be scaled to provide numerical results for comparisons with three different experiments. The final target configurations in these experiments make it clear, however, that uniform geometric scaling does not apply in the present case.
Model for the shape of polymer spherulites formed in a temperature gradient
Authors: Lovinger Andrew J. , Gryte Carl C.
Published: February 2003

A model is presented to account for the spherulitic morphology obtained during the oriented crystallization of a polymer in a moving temperature gradient. The model considers the sample to be divided into a series of narrow isothermal regions and, using an analogy to Snell’s law, correctly predicts the observed fibrillar curvature. Computer simulation of the proposed model yields spherulitic shapes that are consistent with the experimental results. A mechanism is proposed to account for the shapes observed, and the factors which affect them are discussed.
Yellow In1−xGaxP1−zAsz double-heterojunction lasers
Authors: Coleman J. J. , Holonyak N. , Ludowise M. J. , Wright P. D.
Published: February 2003

Improved yellow-spectrum double-heterojunction In1−xGaxP1−zAsz laser diodes constructed by LPE on VPE GaAs1−yPy substrates are described. The lattice-matched LPE quaternary alloy growth process is outlined, as well as the need for complete melt removal between the growth of each heterojunction layer, which is more difficult for In-rich melts than for Ga-rich melts when lattice match is a problem. Over two times lower threshold current densities are demonstrated (Jth?3.6×103 A/cm2, λ?5920 Å, 77 °K) than for the first reported diodes of this type. The temperature dependence of laser threshold current density is presented in the range 4.2–200 °K. The threshold current density can be approximated as Jth∝exp(T/T0) with T0?52 °K in the range 50–175 °K, which compares well with red-orange AlGaAs double heterojunctions (T0?42 °K) having greater heterobarriers. Laser operation in the yellow-orange portion of the visible spectrum at ∼200 °K is demonstrated. These results on thick (1.5 μm) active layer diodes, having relatively small heterobarriers (ΔE∼65 meV), indicate that further improvement and control of the quaternary growth process will lead to still lower threshold currents and higher-temperature operation in the orange-yellow.
1/f noise measurements for characterizing multispot low-Ohmic contacts
Authors: Vandamme L. K. J. , Tijburg R. P.
Published: February 2003

The patchiness of contacts can be determined from measurements of 1/f noise and contact resistance on a number of contacts of different diameters made by the same method. If a contact consists of k conducting spots with average radius a, k and a can be determined if the distance between the spot centers is at least 2.5 times the spot diameter. Using the developed multispot contact model, the results of the 1/f noise analysis are in good agreement with multispot parameters obtained from microscopic investigations.
Comments on ’’Griffith fracture equation—An experimental test’’
Authors: Bansal Girraj K.
Published: February 2003

The Griffith equation was originally derived for relatively sharp cracks. The equation can also be applied to round cracks provided a characteristic fracture surface energy value associated with the particular crack-tip radius is used.
Polarity-dependent memory switching and behavior of Ag dendrite in Ag-photodoped amorphous As2S3 films
Authors: Hirose Yooichi , Hirose Haruo
Published: February 2003

High cyclical reproducibility in polarity-dependent switching and memory function was obtained. Switching and memory effect seem to occur when both electrodes (Mo and Ag) are bridged by Ag dendrite which originates as the result of Ag photodoping. The combination of Ag electrode and another kind of electrode material may be responsible for the polarity-dependent switching and memory by the help of appropriate voltage shapes. Behavior of Ag dendrite was observed in relation to the similar electrical characteristics in a modified device structure. No thermal effects may be contained in the functional processes. Temperature dependence and frequency characteristics of the device resistances are measured and found to support the existence of the Ag dendrite and its role in the function in the original device. Switching transients in addition to the durability show the availability of the device in the compatibility with the magnetic core memory.
Spatial dependence of time delay in light-emitting diodes
Authors: Daino B. , Piazzolla S. , Spano P. , Bordoni Fondazione U. , Bertolotti M.
Published: February 2003

Some measurements performed on the spatial and temporal distribution of the light intensity emitted by various LED’s are described. The diodes are found to emit light in a nonuniform distribution with different delays along the emitting surface. A simple model of the diodes in the form of a transmission line gives theoretical results in agreement with the experimental data.
Two-dimensional growth of laser-driven waves in a hydrogen free jet
Authors: Thompson H. M. , Daiber J. W. , Rehm R. G.
Published: February 2003

A Q-switched ruby laser has been used to irradiate a free jet of hydrogen. The propagation of the luminous wave which originated in the breakdown spark has been monitored using an optical system which permitted simultaneous observation of the motion along and perpendicular to the coincident axes of the focused laser beam and the free jet. Correlation of the luminous frontal wave and the late-time shock wave (made visible with a schlieren system) with the third root of the ratio of laser power to free-jet plenum pressure was found to hold over a range of several orders of magnitude.
Photoluminescence of the Cr accepotr in boat-grown and LPE GaAs
Authors: Stocker H. J. , Schmidt Martin
Published: February 2003

Accurate photoluminescence measurements of both LPE and boat-grown GaAs show that the Cr acceptor has a binding energy of 838.0+0.2 meV at T=4.2 K. The spectra have a no-phonon line at that energy and a broad structure due to phonon emission, with the TA phonon replica dominating.
Charge exchange in zinc-neon
Authors: Chubb Donald L.
Published: February 2003

Excitation of the 4d and 5p levels of Zn+ by charge exchange between Ne+ and Zn was investigated. From measured electron temperature and line intensity ratios it was concluded that charge exchange is the dominant mechanism for populating the 4d 2D5/2 level of Zn+. Comparison of Zn-Ne and Zn-Ar results imply the same conclusion. No evidence for charge exchange as the dominant pumping mechanism for the 5p 2P1/2, 5p 2P3/2, or 4d 2D3/2 levels was obtained.
Impurity-induced first-order Raman spectra of KI and KBr in the fcc and sc phases
Authors: Ganguly B. N. , Nicol Malcolm
Published: February 2003

The pressure dependences of the impurity-induced Raman spectra of KI and KBr have been measured for both fcc and sc structures, up to 30 kbar. Both materials have been observed to undergo phase transition at about 18 kbar. Four phonon bands have been observed for KI and three distinct peaks for KBr in the sc phase. From the measurement of the temperature dependence of the band intensities for KI between 300 and ∼80 K, these bands have been identified with first-order processes. The mode Grüneisen parameters for the two acoustic Eg modes in fcc phase and two acoustic and one optic mode in sc phase have been measured for both KI and KBr. The impurity-induced phonon bands of KI and KBr in both phases have also been correlated to the corresponding phonon branch singularity or singularities for most peaks.
Coherent emission from Ho3+ ions by pumping into the YIG absorption band
Authors: Stafford R. G. , Masui H. , Farrow R. L. , Chang R. K. , van Uitert L. G.
Published: February 2003

Coherent emission from Ho3+ ions (2.1 μm) in a YIG host at 77 °K has been observed by optical pumping into the electronic absorption bands of the YIG host material, using (i) a pulsed Nd : glass laser to pump into the tail of the 6A1g→4T1g band (which has an absorption coefficient α=0.18 cm−1 at 1.06 μm) or (ii) a pulsed ruby laser (0.6943 μm) to pump the 6A1g→4T2g band near its peak (where α=300 cm−1). The Ho3+ emission from an illuminated slab 30–40 μm was investigated as a function of input pump energy. The electronic absorption bands of YIG are strong, broad, and have good energy-transfer efficiency to the upper laser level of the Ho3+ ions.
Experimental study of effects from two laser pulses
Authors: Maher W. E. , Hall R. B.
Published: February 2003

In order to investigate approximately the target-zone effects of repetitively pulsed laser beams, two CO2 lasers which were focused on the same spot were used in experiments with an adjustable temporal separation between their pulses. There are reported here studies at 1 atm of the effects of two laser pulses including high-speed photographic and interferometric observations of laser-produced plasmas, shocks, and target vapor; target damage evaluations; and investigations of impulse absorbed by the target. New effects were seen; the most significant of these was the dependence of several of these phenomena on the separation time. The interaction of the second laser pulse with the target is increased when it starts within a window 30 to 70 μsec after the start of the first laser pulse.
Deep-diode arrays
Authors: Anthony T. R. , Cline H. E.
Published: February 2003

Deep-diode arrays consist of geometric arrays of long narrow columnar p-n junctions extending through a thick semiconductor wafer. These arrays are produced by the thermomigration of large arrays of appropriately doped metal-rich droplets through semiconductors. The processing techniques to make deep-diode arrays are described and the various electrical properties of these arrays are discussed. Applications of deep-diode arrays in the areas of semiconductor-device manufacturing, planar integrated-circuit technology and x-ray and infrared detection are discussed.
Lattice superdilation phenomena in doped GaAs
Authors: Mullin J. B. , Straughan B. W. , Driscoll C. M. H. , Willoughby A. F. W.
Published: February 2003

A lattice superdilation phenomenon in doped GaAs is reported. Measurements of lattice parameter on GaAs doped with tin and tellurium have revealed this effect, which is an exceptional rate of lattice expansion (about 14 times that predicted by simple substitution) which occurs when the doping exceeds a critical concentration of ∼3×1018 cm−3. Below this critical concentration simple substitution on arsenic sites appears to occur. Possible defect models which might explain this phenomenon are discussed.
Operation of the SUPARAMP at 33 GHz
Authors: Chiao R. Y. , Parrish P. T.
Published: February 2003

A 9-mm degenerate parametric amplifier has been constructed using a linear series array of unbiased Josephson junctions as the active nonlinear element. We used a balanced diode mixer as a synchronous detector, with a single source serving both as the pump and as the mixer local oscillator. A stable net gain of 15 dB in an instantaneous bandwidth (FWHM) of 3.4 GHz has been achieved. We measured a system noise temperature of 220±5 K (DSB) with a SUPARAMP contribution of only 20±10 K. Output saturation, however, has been observed. This complicates the interpretation of our noise-temperature measurements and may render them upper limits. Comparison is made with the results of an earlier 3-cm SUPARAMP. The data are in substantial agreement with theoretical predictions.
rf SQUID’s in the nonhysteretic mode: Detailed comparison of theory and experiment
Authors: Rifkin Robert , Vincent Daniel A. , Deaver Bascom S. , Hansma Paul K.
Published: February 2003

A simple analytic theory for the operation of rf SQUID’s in the regime where the current I in the superconducting ring is a continuous function of the applied flux (nonhysteretic mode) has been extended to include the effects of screening flux LI, where L is the inductance of the ring. A comparison of calculated results with detailed measurements of the response of a rf SQUID using a toroidal Nb ring containing a Nb point contact shows excellent agreement both in cases when screening flux is significant and when it can be neglected.
Relation between coercive force and microstructure of sintered SmCo5 permanent magnets
Authors: den Broeder F. J. A. , Zijlstra H.
Published: February 2003

The coercive force of a sintered SmCo5 permanent magnet is found to depend reproducibly on the temperature of heat treatment. In order to find out the origin of this, the mechanism of the demagnetization was studied by magnetic-domain observation, using the polar Kerr effect. It appears that the highest coercive forces which are obtained by heat treating at 850–950 °C and quenching are due to difficult nucleation of reverse domains and strong pinning of domain walls by the grain boundaries. After quenching from higher temperature (∼1100 °C) the coercive force decreases owing to weaker pinning of the domain walls. The drop of the coercive force which is found to occur upon heating at lower temperature (∼700 °C) comes from an easy nucleation of reverse domains. Indirect evidence is presented which supports the assumption that this easy reverse-domain nucleation occurs on Sm2Co17 precipitates. The Sm2Co17 precipitation is governed by the Co-rich SmCo5 phase boundary and its metastable extension below the eutectoid temperature of SmCo5. The state of the grain boundary which may be responsible for the strong pinning is discussed.
Photoelectrolysis of water: Si in salt water
Authors: Candea Rodica M. , Kastner Marc , Goodman R. , Hickok N.
Published: February 2003

Current-voltage measurements are reported for heavily p-type Si electrodes in NaCl solution. The zero current voltage depends logarithmically on light intensity, indicating that photoelectrolytic devices are solar cells in series with electrolytic cells. The catalytic efficiency of the electrode is enhanced by illumination, but Si is a poor hydrogen electrode, probably because of its surface oxide.
Scattering noise of hot holes in space-charge-limited current flow in p-type Si
Authors: Gisolf A. , Zijlstra R. J. J.
Published: February 2003

Experimental data are presented for the spectral density of the scattering fluctuations of hot holes in space-charge-limited current flow in p-type Si. Measurements have been made in the temperature range 100–300 K for electric field strengths up to 106 V/m. To avoid excessive heating of the lattice, measurements were performed under pulsed bias conditions. The experimental curves are compared with those calculated for thermal carriers. At room temperature no hole heating effects are observed for electric field strengths up to 4.5×105 V/m. Above this limit hole heating sets in. A noise temperature Tn is defined which is a proper measure for departures from the thermal equilibrium carrier-velocity distribution. The field strength which marks the onset of hot-hole phenomena gradually decreases with decreasing lattice temperature T and reaches the value 1.5×103 V/m at 100 K. At this temperature noise temperatures of 3T are observed for fields up to 106 V/m. Evidence is put forward for the presence of a hole trapping energy level 0.3 eV above the valence band with hole capture cross section (2.0±1.0) ×10−19 m2.