bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab initio pair potential and phase equilibria predictions for hydrogen chloride
Authors: Naicker Pavan K. , Sum Amadeu K. , Sandler Stanley I.
Published: February 2003

An ab initio intermolecular pair potential for hydrogen chloride has been computed using symmetry-adapted perturbation theory and an extended basis set at a level of theory equivalent to fourth-order Møller–Plesset perturbation theory. Three different site–site pair potential functions were used to fit the ab initio energies, and these were then used to calculate the second virial coefficient and in Gibbs ensemble Monte Carlo simulations to determine the vapor–liquid equilibria. The accurate predictions of the phase behavior compared to experimental data with only pairwise interactions suggest that these are the predominant contribution, and that nonpairwise additivity and quantum effects are not important for HCl. Our results are also compared with those of another ab initio-based pair potential previously reported in the literature.
Looking into overcharging in model colloids through electrophoresis: Asymmetric electrolytes
Authors: Martı́n-Molina A. , Quesada-Pérez M. , Galisteo-González F. , Hidalgo-Álvarez R.
Published: February 2003

Some theories claim that the Poisson–Boltzmann approach could fail to describe the electric double layer of colloids under certain conditions as a result of neglecting ion size correlations. For instance, if the surface charge density and/or the electrolyte concentration are high enough, the counterion local density in the vicinity of charged surface could become so large that the particle charge would be overcompensated. This phenomenon is theoretically known as overcharging and, sometimes, should involve a ζ-potential reversal. Accordingly, this work looks into overcharging through electrophoresis experiments. The electrophoretic mobility has been measured for latex particles with moderate and large surface charge density in solutions of asymmetric electrolytes z:1 (symmetric electrolytes have been studied in a previous work). In order to find out the relevance of ion size correlations, results are analyzed within the so-called hypernetted-chain/mean-spherical approximation (HNC/MSA) as well as a Poisson–Boltzmann approach. In the case of divalent counterions (z=2), the HNC/MSA seems to justify why a mobility reversal is hardly observed. For z=3, our results suggest that ion correlations could play an important role and be mostly (or partially) responsible for mobility reversal in certain cases.
Development of a niobium nanosuperconducting quantum interference device for the detection of small spin populations
Authors: Lam S. K. H. , Tilbrook D. L.
Published: February 2003

Electron-beam lithography and reactive ion etching have been used to fabricate thin-film Au/Nb bridges with widths ∼50 nm. The Au layer was used as both a mask for etching the Nb superconducting bridge and as a resistive shunt in the completed devices. Using these junctions, a dc superconducting quantum interference device (SQUID) design with a hole size of 200 nm×200 nm (nano-SQUID) has also been fabricated and characterized. A flux noise of approximately 7×10−6 Φ0/Hz1/2 at 4.2 K has been achieved, from which a calculated spin sensitivity of 250 spin/Hz1/2 is predicted.
Thermodynamic theory of diffusion−controlled bubble growth or dissolution and experimental examination of the predictions
Authors: Ward C. A. , Tucker A. S.
Published: February 2003

Although the evolution of a bubble in a liquid containing a single dissolved gas has been treated frequently in the past, a prediction of the time−dependent radius of a bubble in a liquid solution containing several dissolved gases, all diffusing simultaneously, has not been given previously. For this multiple solute case, the set of assumptions corresponding to those used in the single−component case leads to a set of undetermined equations so that these assumptions are insufficient to specify the bubble radius as a function of time. Here the assumption of near−equilibrium evolution is extended to include an assumption concerning the local rate of entropy production: it is assumed that the solute concentrations at the boundary of the bubble must be such as to minimize this local rate at each instant of the bubble evolution. This is shown to be sufficient to close the set of governing equations and thereby allow the prediction of the time−dependent bubble radius for the multiple−solute case. This general set of equations is then applied to predict the radius of a bubble dissolving in a water−oxygen−nitrogen solution. The predictions are compared with the results of a set of measurements and it is found that they agree well, thus giving confidence in the validity of the assumptions used in making the theoretical predictions.
X−ray topography of defects produced after heat treatment of dislocation−free silicon containing oxygen
Authors: Patel J. R. , Authier A.
Published: February 2003

In this investigation we have established the nature of defects produced by the heat treatment of initially dislocation−free silicon crystals containing oxygen. The defects observed by x−ray topography are of two types: (i) prismatic loops with Burgers vector along 〈110〉 and (ii) stacking faults with Burgers vector along 〈111〉. Fringe contrast has been observed in the partial dislocation loops. The contrast and geometrical nature of the fringes in section patterns has been analyzed using the results of dynamical theory of x rays for stacking faults. From detailed theoretical calculations and experimental observations of section topographs we have been able to establish the nature of the stacking faults. All of the faults investigated have been of the Frank extrinsic type. An important result of this investigation has been that the stacking fault fringe information on the section pattern can under certain circumstances be obscured on traverse topographs. Conclusions on the nature of the fault based solely on traverse topography can be erroneous and may lead to exactly the opposite conclusion to that based on section topographs. The importance of section topographs is underscored in this study.
Electrostatic forces between conducting spheres at constant potentials
Authors: Warren W. E. , Cuthrell R. E.
Published: February 2003

A derivation in the bispherical coordinate system is presented for the electrostatic force between conducting spheres at a constant potential difference. The theoretical results are compared with experimentally measured forces.
Dynamics of gas-fluidized beds
Authors: Garg S. K. , Pritchett J. W.
Published: February 2003

Governing equations for the motion of gas-fluidized beds are derived within the framework of the theory of interacting continua. Steady-state solutions for two simple cases (incompressible fluid, isothermal ideal gas) are outlined in detail. The stability of these steady-state solutions is examined by conventional linear hydrodynamic stability analysis. Finally, some numerical results illustrating the effects of various physical parameters are presented.
Molecular dipole electrets
Authors: Mopsik Frederick I. , Broadhurst Martin G.
Published: February 2003

The total polarization due to molecular dipoles in a glassy electret is computed using an Onsager cavity approach. From this result, all the possible contributions to the piezoelectric and pyroelectric coefficients are considered. It is shown that there are major contributions from the variation in dielectric constant and, for pyroelectricity, from thermal motion. These results account well for experimental data for polyvinyl chloride.
The morphology and thermal response of high-temperature–crystallized poly(vinylidene fluoride)
Authors: Prest W. M. , Luca D. J.
Published: February 2003

In this study, optical microscopy, differential scanning calorimetry, and infrared spectroscopy are used to study the high-temperature isothermal crystallization of high-molecular-weight poly(vinylidene fluoride). It is shown that there exists a temperature domain in which both the α and β phases of PVF2 can be grown concurrently and in competition with each other to form two distinct populations of spherulites which are characterized by different diameters, band periods, and melting points. In addition, a time- and temperature-dependent crystal-crystal transition from the α phase to the γ form can be induced in this high-temperature crystallization region to produce spherulites which melt 15–20 ° above the melting point of the original α phase. This transformation exhibits nucleation and propagation characteristics which in some regions can compete with the normal growth of the α phase to produce unique ’’wagon-wheel’’ spherulitic structures.
Optical damage in transition-metal-doped LiTaO3
Authors: Tsuya Hideki
Published: February 2003

The results of a detailed study of the optical damage in transition-metal (Fe, Cu, Mn, V, Cr, and Ni) -doped LiTaO3 are presented. The relationship between the sensitivity of the optical damage and the nominal concentration of dopants is analytically discussed based on the modified rate equations introducing trapping centers. The observed results of the dependence of sensitivity on nominal concentration, poling procedure, and heat treatment, and of the activation energy of the thermal decay and the distribution coefficients of examined transition metals in LiTaO3 are reported. The role of transition metals on optical damage is discussed using the results of electron paramagnetic resonance (EPR) and optical spectra in addition to the above results. It is found that Fe2+, Cu+, and oxygen vacancies, which stem from reduction or from off-stoichiometry, are mainly responsible for donors, and Fe3+, Cu2+, Mn3+, and V3+ play the role of trapping centers. In LiTaO3, the migration of oxygen vacancies by poling is very important, and is discussed in detail for Fe-doped LiTaO3. The optical damage for double-doped LiTaO3 containing Fe+Mn and Cu+Mn is also examined.
Double mode locking of dye lasers
Authors: Yasa Z. A.
Published: February 2003

The concept of double mode locking of dye lasers is introduced. A pair of laser dyes with the absorption spectrum of one coinciding with the fluorescence spectrum of the other is shown to become mode locked about two different wavelengths simultaneously. Numerical calculations predict rapid development of subpicosecond pulses.
Shock-compression and release behavior near melt states in aluminum
Authors: Asay J. R. , Hayes D. B.
Published: February 2003

The response of porous aluminum (ρ0=1.6 g/cm3) when shock-compressed to states of partial melting and then released has been investigated. There are no detectable changes in any of the Hugoniot properties in the region where melting should occur. However, release wave speeds in the completely compacted state of the porous aluminum specimens were found to depend critically upon the magnitude of the initial shock loading. For impact stresses below about 7 GPa, the measured release-wave velocity is well described by the assumption that the initial release is elastic. For initial impact stresses above 7 GPa, the speed of the release wave is observed to be about 20% lower than the elastic wave velocity and approaches the bulk sound speed predicted by equilibrium thermodynamics. All calculations of wave speeds were made with a complete equation of state which was obtained by constructing semiempirical free-energy functions for both solid and liquid pure phases. These were developed by first assuming self-consistent forms for the second derivatives of the Helmholtz free energy and then adjusting coefficients in the second derivatives using known quasistatic thermodynamic properties for each phase until agreement with all available data was achieved. Calculation of the intersection of the Hugoniot with the melt boundary (7.5 GPa, 1340 K) using this equation of state when compared with the observed change in sound speed gives strong support to the assumption that melting occurred in these experiments. The release-wave technique shows promise for measuring phase boundaries in regions of pressure and temperature not accessible by ordinary quasistatic techniques.
Capacitance properties of MIS tunnel diodes
Authors: Green M. A. , Shewchun J.
Published: February 2003

The theoretical capacitance properties of the metal-insulator-semiconductor (MIS) tunnel diode are described. It is shown that devices with relatively thick insulating layers display properties similar to conventional MIS capacitors, while those with thinner insulating layers differ appreciably. Frequency-dependent features can occur in the characteristics of these devices as a result of a delayed inversion layer response. The presence of such features in experimental devices provides support for the inversion layer clamping process predicted theoretically. Because of these frequency-dependent features, it is shown that caution must be exercised when using MIS tunnel diodes for obtaining surface-state information.
Angular and temperature dependence of viscosity coefficients in a plane normal to the direction of flow in MBBA
Authors: Summerford J. W. , Boyd J. R. , Lowry B. A.
Published: February 2003

The temperature dependence of the viscosity coefficients η1 and η3 of the liquid crystal MBBA has been measured. The temperature range was from 23 to 50 °C. A magnetic field was used to orient the liquid crystal. The results are η1=1.54 P and η3=0.79 P at 23 °C in disagreement with earlier studies. Possible factors contributing to this disagreement are discussed. The angular dependence of the viscosity coefficient in a plane normal to the flow direction is found to be in good agreement with Leslie’s theory of anisotropic fluids. The method employed is a direct measurement of viscous force at a very low shear rate.
Theoretical description of ac arcs in mercury and argon
Authors: Lowke J. J. , Zollweg R. J. , Liebermann R. W.
Published: February 2003

The energy balance and circuit equations, together with Ohm’s law, are solved numerically to obtain temperature profiles, current, and voltage as functions of time for wall−stabilized ac arcs. Experimental measurements of current and voltage oscillograms and also temperature profiles have been made for 1.5− and 7.5−A rms arcs in mercury vapor. Derived net emission coefficients of radiation as a function of temperature for the 1.5− and 7.5−A arcs are consistent with one another; furthermore, the experimental temperature profiles for both arcs are in good agreement with our theoretical predictions. Theoretical current and voltage waveforms and central temperatures for a 20−A rms arc in argon are in good agreement with the experimental results of Detloff and Uhlenbusch. Radial convection has little influence on these results. An approximate criterion for arc extinction or reignition at current zero is given in terms of the steady−state V−I characteristic and the arc time constant. By relating the present analysis to methods using the Cassie−Francis and the Mayr equations, expressions are derived for the undetermined constants used in these equations for arcs dominated by thermal conduction losses.
Epitaxial silicon solar cell
Authors: Dalal V. L. , Kressel H. , Robinson P. H.
Published: February 2003

A new design for silicon solar cells employing epitaxial deposition is presented. It is shown that the use of epitaxial solar cells may result in higher efficiencies for converting solar energy into electricity. Preliminary experiments are reported which show the feasibility of making near−ideal junctions with high quantum yields.
A wide bandwidth detection and display system for use with TEA CO2 lasers
Authors: Gibson A. F. , Kimmitt M. F. , Maggs P. N. D. , Norris B.
Published: February 2003

A photoconductive detector based on intravalence band transitions in p−type germanium is described. The detector responsivity is sufficient to drive a travelling−wave oscilloscope (Tektronix 519) without amplification, and consequently has an over−all bandwidth sufficient to display 300−ps−duration pulses from a mode−locked TEA CO2 laser.
Photovoltaic effects in semi−insulating GaAs
Authors: Zucca R. , Wood E. J.
Published: February 2003

Photovoltaic effects at junctions between semi−insulating and low−resistivity GaAs, and at Al Schottky barriers on semi−insulating GaAs are reported. Changes of photovoltage polarity as the photon energy crosses the band−gap energy are interpreted by extension of the behavior of n− and p−type GaAs.
On indentation dislocation rosettes in silicon
Authors: Hu S. M.
Published: February 2003

The structure of dislocation rosettes generated by microindentation in 〈100〉 silicon is discussed and then verified experimentally. Dislocation loops in the rosettes move on glide prisms that are formed by two {111} planes and the surface plane, the width of the prism being equal to the size of the indent. The size of the dislocation rosette is also discussed using a rudimentary model.
Effect of atmospheres on arsenic diffusion into silicon from the doped oxide layer
Authors: Itoh Tadatsugu , Shinada Kazuyoshi , Ohmura Yamichi , Kirita Kei
Published: February 2003

The backscattering method is employed to investigate the effect of atmospheres on arsenic diffusion into silicon from the doped oxide layer. An effect of the coating of undoped silicon oxide and silicon nitride upon the surface of the doped oxide layer is also investigated. Arsenic atoms diffused more efficiently into silicon in oxygen atmosphere than in nitrogen atmosphere. An additional oxide layer was formed by oxidation of the silicon surface during the thermal diffusion in oxygen atmosphere and this layer exists between the doped oxide layer and the silicon substrate. It is considered that such an additional oxide layer may play an important role in the thermal diffusion of arsenic atoms into the silicon substrate.
Electrical relaxation and exoelectron emission on the fresh mica surface
Authors: Metsik M. S. , Golub L. M.
Published: February 2003

By studying the precipitation of charged particles obtained from powder clouds, dielectrical suspension, and electrostatic separation in vacuum, we have found that isolated positively charged centers of activity are preserved on freshly cleaved mica surfaces for a long time after neutralization of the primary electrostatic mosaic. They induce negative charges in neighboring regions. Upon heating the mica to 400 °C three maxima of exoelectron emission which coincide with maxima of surface electrical activity are observed. The centers of electrical activity are associated with surface defects. The epitaxial crystallization on the surface is connected with these centers.
Macroscopic engineering properties of polycrystalline materials: Elastic properties
Authors: Gubernatis J. E. , Krumhansl J. A.
Published: February 2003

We outline the formal application of integral equation methods (Green’s function techniques) to the systematic computation of the effective elastic properties of polycrystalline materials from the specification of the statistical distribution of elastic properties of the constituent grains (or pores). These methods are not entirely new, but by the use of recent developments in theory of the physics of the electronic porperties and lattice dynamics of disordered solids, we can place various methods on a common footing and indicate their limitations. Some details for the computational application of these methods are also presented.
Molecular beam epitaxy of II-VI compounds
Authors: Smith Donald L. , Pickhardt Vincent Y.
Published: February 2003

The II-VI compounds are desirable for integrated optics due to their high electro-optic coefficients, wide transparency range from the visible to beyond 10 μm, and the continuously adjustable refractive index offered by their ternary alloys. Films of waveguide thickness (1/2–2 μm) were grown here by evaporation, under ultrahigh vacuum, of the constituent elements (Zn, Cd, Se, Te) from separately liquid-nitrogen-shrouded graphite Knudsen cells onto temperature-controlled chemomechanically polished single-crystal substrates. A quartz-crystal deposition monitor operating at the growth temperature was used in a novel way to determine the group-VI/II impingement rate ratio which would produce stoichiometric films, by measuring deposition rate as a function of the impingement rate ratio. Dissociative reevaporation of growing films sets an upper limit to growth temperature; 1 μm/h reevaporation rates were calculated to be reached at 400 °C for CdTe, 470 °C for ZnTe and CdSe, and 570 °C for ZnSe. At impingement rates corresponding to about 1 μm/h, ZnSe ceased to deposit at 125 °C below that point and the other three compounds at 50 °C below that point. Over a 50 °C range below the cessation of deposition, epitaxy was obtained for all II-VI compounds, as determined by in situ LEED. Film surface topography was examined by Nomarski differential-interference-contrast microscopy. Crystallographic quality depended slightly and surface smoothness depended very strongly on substrate orientation in the following decreasing order of quality: (1) GaAs(100); (2) GaAs(110); (3) CdS(0001), CdSe(0001). On GaAs, ZnTe and Zn(SeTe) films were much smoother than ZnSe films, 1-μm-thick films being smooth to tens of angstroms. The following system is recommended for integrated optics: ZnTe waveguide on Zn(SeTe) to optically isolate the waveguide from the high-index substrate, InAs(100) for 0.6% lattice constant mismatch.
Stored energy function and compressibility of compressible rubberlike materials under large strain
Authors: Peng Stevens T. J. , Landel Robert F.
Published: February 2003

By using new invariants in the theory of finite elasticity an expression is obtained for the stored energy function of slightly compressible materials in which the effects of the distortional change (change of shape) and of the volume change are clearly separated. The volume-related terms are expressed as a function of the third invariant Γ3, the classical compressibility K0, and an induced anisotropy of the effective compressibility which is due to the large deformations. After evaluating the terms, using data on pressure, volume, uniaxial stress-strain, and ΔV/V0 versus strain data on natural rubber from the literature, it is shown that the volume change contribution to the total stress observed in a simple tensile experiment can be clearly separated from the distortional contribution, even at finite strains.
Space-charge-limited currents in electron-irradiated dielectrics
Authors: Nunes de Oliveira L. , Gross Bernhard
Published: February 2003

This paper develops the theory of steady-state currents generated in a dielectric placed between positively or negatively biased electrodes and irradiated with a partially penetrating electron beam. The dielectric is divided into an irradiated region (IR), which extends from the electrode of incidence to the extrapolated range of the beam, and a nonirradiated region (NIR). In the IR the primary beam generates an electron-hole plasma. Its end plane acts as a virtual electrode embedded in the dielectric. Currents are space-charge limited in the NIR and Ohmic in the IR which is characterized by a uniform radiation-induced conductivity. Depending on the polarity of the electrode bias, electrons or holes are drawn from the IR into the NIR. The theory correctly predicts an apparent threshold effect for the inset of steady-state currents: the current amplitudes remain small as long as the electron range is smaller than half the sample thickness, and increase strongly only afterwards. Calculated current curves for different beam energies are in satisfactory agreement with experimental results. The role of the electron beam as a virtual electrode is discussed.
Calculations of the energy loss of 4He ions in solid elements
Authors: Chu W. K. , Moruzzi V. L. , Ziegler J. F.
Published: February 2003

We have calculated the energy loss of 4He ions in a number of elemental and rare-gas solids in the energy range from 0.4 to 4.0 MeV. The calculations are based on the Lindhard-Winther energy-loss formalism and use solid-state charge densities for the target atoms. Stopping cross sections εα are presented as a function of projectile energy and are compared with the Hartreee-Fock-Slater isolated-atom calculations and semiempirical cross sections. It is found that the solid-state charge densities generally produce a somewhat better energy dependence than the atomic charge densities but that neither produces an adequate fit in the low-energy region. In particular, solid-state effects of Ne and Ar lead to a 4–10% increase over the atomic calculations.
Origin of secondary-electron-emission yield-curve parameters
Authors: Dionne Gerald F.
Published: February 2003

From an analysis of the one-dimensional constant-loss theory of secondary electron emission, maximum yield (δm), primary electron energy at maximum yield (Eom), and both crossover energies EIoc and EIIoc are shown to depend on the surface and bulk properties of the emitting material through simple relations. In particular, the results strongly suggest that the first crossover energy can be very dependent on surface properties, whereas the energy at maximum yield is entirely controlled by bulk properties. Refinement of the low-energy part of the reduced yield curve by means of the results of the more realistic three-dimensional theory leads to the development of the expression EIoc=0.51Eomδm−1.32. Comparison between theory and experiment for several secondary-emitting materials is presented to demonstrate the accuracy of this useful relation. Finally, the implications of these results for different classes of materials are discussed in terms of basic physical properties, such as density, electrical conductivity, work function, and band gap.
Two-idler parametric amplification with Josephson junctions
Authors: Kanter Helmut
Published: February 2003

A self-pumped Josephson junction can be operated in a mode which is described in first order by a two-idler parametric amplifier analysis for a sinusoidal elastance variation. Thus the analysis and operation follows the two-idler negative resistance behavior predicted by Penfield and Rafuse for varactor diodes. Experimental observations on parametric negative conductance excitations at 9 GHz by a Josephson point contact are readily explained by the two-idler model. A total signal power gain of 12 dB was achieved with an experimental device consisting of a niobium titanium point contact in a shallow rectangular cavity coupled through a room-temperature circulator.
Measurement of energy band gap using an electrolyte-semiconductor junction: Water–gallium indium arsenide alloys
Authors: Baliga B. Jayant , Bhat Rajaram , Ghandhi Sorab K.
Published: February 2003

Energy band gaps of semiconductors are usually obtained by optical transmission measurements through bulk samples. Such measurements on epitaxial layers are difficult due to absorption in the substrate. A technique utilizing the photogeneration of carriers at an electrolyte-semiconductor junction is described for the measurement of the energy gap of epitaxial layers. Results of measurements of the band gap of GaInAs alloy films on GaAs substrates are presented.
Domain wall dynamics in ferroelectric/ferroelastic molybdates
Authors: Flippen R. B.
Published: February 2003

The effects of electrical field and mechanical stress on domain wall motion have been quantitatively determined for gadolinium molybdate (GMO) and similar compounds. The ratio of the stress driven wall mobility μτ to the electrical field driven wall mobility μE is shown to be equal to the ratio of the spontaneous strain γ0 to the spontaneous polarization P0 and to have the numerical value 1.53×104 cm2/C. The dynamics of domain wall motion in GMO are discussed in relation to the crystal structure of this material.
Photoconductivity from shallow negative donor ions in silicon: A new far-infrared detector
Authors: Norton P.
Published: February 2003

Shallow donor impurities in silicon at low temperatures are able to bind two electrons, forming negative donor ions, analogous to atomic H− ions. The second electron has a binding energy of only a few meV. Far-infrared radiation can be used to excite these electrons into the conduction band, giving a photoconductive signal. This mechanism is the basis of a new type of far-infrared detector, with promising applications for heterodyne detection at wavelengths on the order of 300 μm. The nature of the negative donor ion is discussed, in part from the effective mass analogy with H− atomic ions, and also with H−2 molecular ions. The theory of how this detector will perform as a function of such variables as bias voltage, background intensity, signal level, and signal speed has been examined. Response speeds on the order of 1 nsec are expected, for operation at temperatures ?2 K, with bias voltage as high as 100 V/cm. With unfiltered 300-K background radiation, the NEP is estimated to be on the order of 10−11 W/(Hz)1/2 at the response peak. In the heterodyne mode of operation, the theoretical noise level will be only fractionally larger than the noise level of a conventional impurity photoconductor. Unlike GaAs far-infrared detector material which is only available in relatively thin epitaxial layers, silicon detectors can be made thick enough to absorb the radiation effectively, and should have much higher quantum efficiency. The wavelength dependence of the photosignal as a function of temperature indicates that for samples doped on the order of 1016 cm−3, a distribution of binding energies exists for an electron bound to a group of randomly spaced donors. Such a distribution of binding energies may be related to excitonic spectra seen at similar doping densities.
On the theory of acoustic surface-wave to bulk-wave scattering by grooves
Authors: Ro/nnekleiv A. , Souquet J.
Published: February 2003

This paper is concerned with analysis of the coherent scattering of surface acoustic waves into bulk waves by grooves. This scattering is important in devices such as reflective array devices because it leads to signal loss, and in devices such as grating scanners which make use of the scattered bulk waves. We show how published analysis of the scattering from a single groove, after suitable corrections, can be used to derive the scattering from infinite arrays of grooves, in agreement with other published results for this latter case. End effects in finite arrays are considered, together with comments on validity of calculations for grooves with steep walls.
Laser oscillation with optically pumped very thin GaAs-AlxGa1−xAs multilayer structures and conventional double heterostructures
Authors: Miller R. C. , Dingle R. , Gossard A. C. , Logan R. A. , Nordland W. A. , Wiegmann W.
Published: February 2003

Optically pumped laser oscillation from multilayer heterostructures (ML) grown by molecular beam epitaxy (MBE) that consist of many alternating thin layers of GaAs and AlxGa1−xAs has been studied in some detail over the temperature range 7–300 K. These samples which have GaAs layers 100–200 Å thick that act as one-dimensional potential wells for electrons and holes have thresholds for lasing that are generally a factor of 2 or more higher than conventional comparable GaAs-AlxGa1−xAs double heterostructures (DH) also grown by MBE. The quantum effects due to the GaAs wells of the ML samples are shown to exist under lasing conditions well above room temperature, but there is no evidence to date of the beneficial effects expected from the modified density of states of this type of structure. Also optically pumped conventional DH lasers grown by MBE and liquid phase epitaxy (LPE) have been compared. The DH lasers grown by MBE are found to have lasing thresholds that are consistently about a factor of 2 higher than their twins grown by LPE.
Ion scattering and Auger electron spectrometry of superconducting ’’Nb3Ge’’ sputtered films
Authors: Tongson Luis L. , Rogowski Donald A. , Knox Bruce E.
Published: February 2003

Low-energy ion scattering spectrometry (ISS) in conjunction with Auger electron spectrometry (AES) has been applied to the analysis of a series of superconducting ’’Nb3Ge’’ thin films deposited on alumina substrates by rf sputtering. ISS was used to determine the Nb/Ge ratio as a function of depth, while AES in combination with ISS was used to determine the impurities. No gradients in composition with depth were observed except in a thin (∼13% of the film thickness) niobium-deficient region near the film-alumina interface. The applicability of ISS to quantitative measurements of the Nb/Ge ratio was shown by comparing the variation of this ratio with lattice parameter a0 with a similar analysis performed on the same samples using electron microprobe (EMP) measurements on the Nb and Ge composition. Comparison of the Nb/Ge ratio determined by ISS with EMP data showed that no preferential sputtering of Ge from the films occurred during neon ion bombardment. The variation of Tc with the Nb/Ge ratios determined by ISS and EMP supports the idea that for ’’Nb3Ge’’, Tc increases as the composition approaches the stoichiometric ratio of 3:1.
Barrier voltage measurement in metal oxide varistors
Authors: Wong Joe
Published: February 2003

A combination of electrical and ceramic microstructural data has been used to determine the voltage drop across the ZnO-intergranular barrier in some simple and multicomponent ZnO-based varistors at the onset of high non-Ohmicity. The data are obtained by measuring the varistor breakdown field (V/mm) and average grain size of the conductive ZnO matrix systematically as functions of sintering temperature and time. Results show that the voltage drop in ZnO varistors is equal to the sum of the voltage drops vb across the ZnO-intergranular barriers. In the case of GE-MOVR varistors, vb is determined to be 2.3 V per barrier.
Pyroelectricity induced by space-charge injection in polymer electrets
Authors: Crosnier J. J. , Micheron F. , Dreyfus G. , Lewiner J.
Published: February 2003

Corona-charged polypropylene-film electrets are reported to give a reversible short-circuit electrical current when subjected to a change in temperature. This current varies as the time derivative of the temperature; we point out a linear dependence of the signal amplitude on the charge of the electret. We show that without specific assumptions concerning charge trapping, the sample expansion cannot account for this pyroelectric behavior. The results can be explained in terms of either a dipolar distribution or a noncentrosymmetry of the trapping centers.
Double-heterostructure PbS-PbSe-PbS lasers with cw operation up to 120 K
Authors: Preier H. , Bleicher M. , Riedel W. , Maier H.
Published: February 2003

Double-heterojunction PbS-PbSe-PbS lasers were fabricated by hot-wall epitaxy allowing cw operation for heat-sink temperatures up to 120 K and pulsed operation up to 180 K. The emitted wavelength can be temperature tuned from 8.5 to 6.5 μm for the cw and from 8.6 to 5.8 μm for the pulsed mode. Threshold current densities of less than 1 kA cm−2 were obtained at 77 K.
Photoluminescence of ion-implanted GaN
Authors: Pankove J. I. , Hutchby J. A.
Published: February 2003

Thirty-five elements were implanted in GaN. Their photoluminescence spectra were measured and compared to those of an unimplanted control sample. Most impurities emit a peak at about 2.15 eV. Mg, Zn, Cd, Ca, As, Hg, and Ag have more characteristic emissions. Zn provides the most efficient recombination center. A set of midgap states is generated during the damage-annealing treatment.
Thin-film interaction in aluminum and platinum
Authors: Murarka S. P. , Blech I. A. , Levinstein H. J.
Published: February 2003

The interdiffusion and intermetallic formation in thin-film sandwiches of platinum on preannealed aluminum has been investigated at temperatures in the range 200–500 °C. X-ray diffractometer studies, sheet-resistivity measurements, and microscopic studies were employed to follow the metallurgical reaction. It has been found that Al-Pt interact very rapidly, leading to the formation of several intermetallics. In heat-treated samples with thick aluminum (?6000 Å), Pt2Al3, PtAl2, PtAl3, and PtAl4 were present. In others with 4000 Å or less Al, platinum-rich phases Pt5Al3 and Pt3Al2 were detected. After prolonged or high-temperature anneals, phases comparatively richer in Al were found to grow at the expense of other phases formed earlier. The Al-Pt interaction rate was found to be dependent on the annealing ambient, being significantly higher in forming gas, argon, or helium than in vacuum or air. Also, the intermetallic formation resulted in large stress changes in the composite Al-Pt films due to a volume increase accompanying the formation of Al-rich phases, which led to the loss of adhesion.
Electrostatic metallic spray theory
Authors: Kelly A. J.
Published: February 2003

A statistical model for the description of an isolated cloud of electrostatically generated droplets is developed. The droplet charging process is assumed independent of droplet population density consistent with high fluid conductivity and maximal charging levels. It is found that charge distribution is describable by Fermi-Dirac statistics and droplet number distribution by Maxwell-Boltzmann statistics. Evaluation of molten copper sprays reveals that the smaller the droplet cloud mass the higher the overall charge-to-mass ratio will be. Charge-to-mass ratio is found to vary approximately as the inverse square of droplet radius. The smaller the droplet the closer it can in general approach the Rayleigh criterion charge limit. The influence of emission-limited charging was found to be unimportant for the cases studied. The model indicates the possibility that microscopic distributions of charge and mass can be inferred from knowledge of total charge and mass.
Reduction of ac losses of Nb3Sn by surface treatment
Authors: Bussière J. F. , Suenaga M.
Published: February 2003

Large reductions in the ac losses of Nb3Sn were obtained by surface treatment of thick layers of Nb3Sn formed by reacting Nb-1% Zr with liquid tin. The surface treatments studied were chemical etching, electropolishing, and mechanical polishing. The significant reduction in the losses is attributed to the removal, by polishing, of a porous outer layer of Nb3Sn which forms at the Nb3Sn–liquid-Sn interface and extends into the material. The porosity of this layer results in low surface and bulk current densities (hence high losses) compared to the material further away from the surface. Low losses (∼1 μW/cm2 at 500 rms A/cm) can be obtained by fine mechanical polishing, electropolishing, or chemical etching of the surface. Mechanical polishing can produce the smoothest surfaces but introduces damage beneath the surface which is detrimental to achieving very low losses. When this damaged layer is either etched away or annealed, however, the losses can be made smaller than 1 μW/cm2 at 500 rms A/cm. The lowest losses were obtained by annealing after rather coarse mechanical polishing. This behavior is attributed to the creation of new pinning centers near the surface after cold working and annealing.
Determination of energy spectra of backscattered electrons by use of Everhart’s theory
Authors: McAfee Walter S.
Published: February 2003

Everhart’s theory on the backscatter of electrons from solids is extended so as to yield the backscatter coefficient as a function of the retarding potential rejecting backscattered electrons having energies below a certain fraction of the energy of the primaries. From this function an analytical expression is obtained for the energy spectra of backscattered electrons with the atomic number of the target material as a parameter. Limited comparisons with experiments are included. The theory is found to give reasonable agreement with electron backscatter experiments for primary electron energies above about 1 keV and target materials having atomic numbers up to about 40. The upper energy limit of perhaps 100 keV is set by the relative importance of bremsstrahlung and relativistic effects which are not included in the Thomson-Whiddington law. Theoretical energy spectra display observed behavior of measured spectra under variation of the atomic number of the target. Energy spectra obtained from this theory give results which are in rather good agreement with experiment for backscattered electrons having energies in the range of about 0.25 to 0.90 of the energy of primary electrons.
Laser operation by dissociation of metal complexes: New transitions in As, Bi, Ga, Ge, Hg, In, Pb, Sb, and Tl
Authors: Chou Mau Song , Cool Terrill A.
Published: February 2003

New laser transitions at 24 wavelengths from 1.152–12.02 μ have been observed from nine metal atoms. Pulsed discharges have been employed for the production of the metal atoms by dissociation of metal halides, hydrides, and alkyls. This technique shows promise for application for pulsed chemical lasers based on electronic transitions in diatomic metal oxides and halides.
Pulse properties of the tunable dye laser pulse converter
Authors: Chan C. K. , Sari S. O. , Foster R. E.
Published: February 2003

Intensity correlation measurements of pulse widths are reported for a sheet-flow rhodamine dye laser mode locked by synchronous gain modulation by a pulsed 2-W argon laser. For pump pulses 1–2-ns long, the minimum dye pulse width obtained is 50 ps. The dye-laser outputs in this pump pulse regime are discussed as a function of cavity length, pump power, and rhodamine and saturable absorber dye concentration.
Excess noise in silicon avalanche photodiodes
Authors: Kaneda T. , Matsumoto H. , Sakurai T. , Yamaoka T.
Published: February 2003

The electric field dependence of the excess noise factor F in silicon reach-through avalanche photodiodes has been studied. The value of F is found to decrease with a decrease in the maximum electric field of the junction. This result shows sufficiently good agreement with a simplified calculation of McIntyre’s equation.
Corrections for nonuniform surface-heating errors in flash-method thermal-diffusivity measurements
Authors: McKay J. A. , Schriempf J. T.
Published: February 2003

The effects of nonuniform surface heating in the flash method of thermal-diffusivity measurement are investigated theoretically and experimentally. An expression for the temperature response with nonuniform surface heating is presented. Evaluation of this expression shows that 30% nonuniformity results in diffusivity errors of 0.1–7.4%, depending on the method of data reduction used. It is shown experimentally that corrections for nonuniform heating can be made with this expression given quantitative information about the nonuniformity, in this case reducing the error from 26% to zero.
Tables of stopping cross sections for 4He ions in solids
Authors: Ziegler J. F. , Chu W. K.
Published: February 2003

Tables are presented for proposed stopping cross sections of 4He ions in solid forms of N, O, F, Ne, Cl, Ar, Br, Kr, I, and Xe.
Lateral spread of damage formed by ion implantation
Authors: Matsumura Hideki , Furukawa Seijiro
Published: February 2003

The lateral distribution of damage introduced in semiconductors by ion implantation is studied theoretically using the theory of Lindhard et al. This theoretical study is experimentally verified by a backscattering measurement of the damage formed by ion implantation into a tilted target. It is found that the spread of lateral damage is largest at a position near to or deeper than the ion projected range, and that the ratio of the lateral damage spread from a mask edge to the longitudinal damage spread from the surface is less than unity even in the case of implantation of light ions. For instance, the ratio is about 20% in the case of 100-keV B+ implantation into Si. It is also found that the ratio becomes smaller as the energy of the implanted ions increases or as the ions become heavier.
Density perturbations caused by weak absorption of a laser pulse
Authors: Fader W. J.
Published: February 2003

Changes in pressure, temperature, and density associated with weak absorption of a short laser pulse are derived as closed solutions of the acoustic-wave equation and the heat-conduction equation for the case of a Gaussian radial intensity profile of the laser beam.
Variation of refractive index of polystyrene with pressure to 7 kbar
Authors: Vedam K. , Meyers J. A. , Mariner G. R.
Published: February 2003

The variation of refractive index with pressure (up to 7 kbar) for two polystyrenes of narrow molecular-weight distributions and in the glassy state has been measured using an interferometric technique. The refractive indices of polystyrenes S102 and S108, having weight-average molecular weights Mw of 82 500 and 267 000 and Mw/Mn ratios of 1.05 and 1.08, respectively (where Mn is the number-average molecular weight), are found to increase linearly with pressure with slopes of 0.1227×10−1 and 0.1219×10−1/kbar, respectively, up to 2 kbar; they thereafter increase sublinearly. However, the relationship between the increase of refractive index and Lagrangian strain is linear for both materials over the entire experimental range with a maximum volume strain of 11.9%. The values of ρ (dn/dρ) are 0.6486×10−2 and 0.6470×10−2 for the two polystyrenes, respectively. Combining the results of both hydrostatic and uniaxial pressure measurements, values of the individual elasto-optic constants p11 and p12 of S102 and S018 were determined. These values for S102 are p11=0.316 and p12=0.328 while for S108 they are p11=0.283 and p12=0.327.
Estimates on the ignition of high-explosives by laser pulses
Authors: Harrach Robert J.
Published: February 2003

The response of high-explosive materials to laser pulses is examined using a one-dimensional theory. Two distinct regimes of laser flux density I and pulse duration τp are identified, one concerned with a thermal initiation process and the other with an impulse or shock initiation process. For the thermal problem the competition between laser-induced ablation and thermal runaway is explored, and analytical formulas are found for an ignition time t* and maximum useful laser flux density I*. When I is below I* thermal initiation by the laser pulse is predicted to occur after an exposure time t* (I), but the rapid removal of material by laser-induced ablation can preclude this type of initiation when I exceeds I*. Values of I* are found to vary from 20 kW/cm2 for PETN to 0.05 kW/cm2 for TNT. The corresponding t* values are about 4 μs for PETN and 0.3 s for TNT. For decreasing flux densities I0 below I*, the ignition time t* increases approximately as I−1.80. For the impulse problem a self-regulating-ablation model is used to predict the pressure P exerted on the target surface as a function of the I and τp values of the pulse. This information is coupled with a P2τ ignition criterion for an HE to derive an inequality to be satisfied for impulse ignition: [τp(ns)]3/4[I0 (GW/cm2)]3/2≳17[P2 (kbar) τ (μs)]min. For pulse durations in the hundreds of ns region, this condition requires flux densities of tens of GW/cm2 for HE’s of interest.