bluuebunny/crossref_metadata_2025 huggingface dataset:
Polaron effective mass in n-type cadmium sulfide
Authors: Kataria N. D. , Mathur P. C.
Published: February 2003

The effective mass of the large carriers in cadmium sulfide has been estimated by comparing Hall-effect measurements with theoretically computed mobility in the temperature range 77–300 °K. The relaxation-time approximation is assumed taking the scattering of the electrons due to the deformation potential, the piezoelectric potential, the ionized impurities, and the polar optical phonons, simultaneously.
Hall-effect noise in semiconductors
Authors: Vaes H. M. J. , Kleinpenning T. G. M.
Published: February 2003

The influence of magnetic induction on the noise voltage between two point electrodes in a homogeneous semiconductor has been investigated both theoretically and experimentally. Relations are derived, assuming that the conductivity fluctuations are caused either by mobility fluctuations or by free carrier density fluctuations. The theoretical results are compared with experimental results of 1/f noise in germanium. Using Hall-effect noise, one cannot discriminate between mobility and number fluctuations.
Electrical properties and conduction mechanisms of Ru-based thick-film (cermet) resistors
Authors: Pike G. E. , Seager C. H.
Published: February 2003

This paper presents an experimental study of the electrical conduction mechanisms in thick-film (cermet) resistor. The resistors were made from one custom and three commercially formulated inks with sheet resistivities ranging from 102 to 106 Ω/⧠ in decade increments. Their microstructure and composition have been examined using optical and scanning electron microscopy, electron microprobe analysis, x-ray diffraction, and various chemical analyses. This portion of our study shows that the resistors are heterogeneous mixtures of metallic metal oxide particles (∼4×10−5 cm in diameter) and a lead silicate glass. The metal oxide particles are ruthenium containing pyrochlores, and are joined to form a continuous three-dimensional network of chain segments. The principal experimental work reported here is an extensive study of the electrical transport properties of the resistors. The temperature dependence of conductance has been measured from 1.2 to 400 K, and two features common to all resistors are found. There is a pronounced decrease in conductance at low temperatures and a shallow maximum at several hundred Kelvin. Within the same range of temperatures the reversible conductance as a function of electric field from 0 to 28 kV/cm has been studied. The resistors are non-Ohmic at all temperatures, but particularly at cryogenic temperatures for low fields. At higher fields the conductance shows a linear variation with electric field. The thick-film resistors are found to have a small dielectric constant and a (nearly) frequency-independent conductance from dc to 50 MHz. The magnetoresistance to 100 kG, the Hall mobility, and the Seebeck coefficient of most of the resistors have been measured and discovered to be quite small. Many of the electrical transport properties have also been determined for the metal oxide particles which were extracted from the fired resistors. These results yielded a quantitative estimate of the metal oxide contribution to the total thick-film resistance. Using the results of our measurements we examine four broad categories of conduction mechanism models which have been previously suggested in the literature: uniform, uniform channel, nontunneling barrier, and tunneling barrier models. The first three categories are systematically rejected because of disagreements with the data. A tunnel barrier model is then developed which incorporates two features not ordinarily considered in simple tunneling theory. The small metal oxide particle size is shown to cause a small activation energy associated with electrostatic charging of the particles. Also, impurities within the tunnel barriers are presumed to act as resonant centers which increase the barrier transmission coefficient. The model is compared in detail to our experimental results and shown to be in excellent agreement.
Superconducting properties and microstructure in dilute copper alloys containing small amounts of V3Ga particles
Authors: Nagata Akihiko , Hirayama Hiroshi , Noto Kōshichi , Izumi Osamu
Published: February 2003

The superconducting properties (Tc and Jc) were investigated by the resistivity measurement, and the structure was observed by a transmission electron microscopy in the dilute copper alloys containing small amounts of V3Ga particles prepared by quenching from the liquid state and aging. No superconductivity could be observed at 4.2 K in as-quenched and/or in overaged samples. The highest Tc2 (=12.5 K), Tc1 (=9.6 K), and Jc (=525 A/cm2) were obtained by aging at 700 °C for 96 h and corresponded with the structure of fine V3Ga precipitates dispersed homogeneously in the copper matrix. Therefore, it is concluded that superconductivity in these alloys results from the superconducting path due to the proximity effect of the superconducting V3Ga particles.
Pinning of 180° Bloch walls at etched nuclear tracks in LPE-grown iron garnet films
Authors: Krumme J.-P. , Bartels I. , Strocka B. , Witter K. , Schmelzer Ch. , Spohr R.
Published: February 2003

For increasing the magnetic-wall coercivity Hwc in liquid-phase epitaxial (LPE) ferrimagnetic garnet films of composition (Gd,Bi)3(Fe,Al,Ga)5O12, magnetic-wall ’’traps’’ are formed via bombardment by xenon ions with 180-MeV/ion energy and doses between 106 and 108 cm−2. For efficient wall pinning, the width of the nuclear damage tracks associated with the ion trajectories in the film have been enlarged to about the wall width by using a selective (chemical) etchant that makes use of the drastically increased etching rate in the damaged track volume. Therefore, channels of cylindrical or prismatic cross section are created having a width of a few 102 to about 103 Å and a length of more than 10 μm at the given etching conditions. The pinning capability of such channels can be further enhanced in films that are grown under planar compressive or tensile misfit strain. Then, strain relaxation occurs in the vicinity of these channels which results in steep gradients of the magnetic-wall energy via magnetostriction. These strain halos extend sufficiently beyond the channels so that efficient wall pinning is observed, even if the channel cross section is small compared with the wall width. Thermomagnetic compensation-point writing in LPE garnet film, that were treated accordingly, yield a pattern of stable magnetic domains of down to 8 μm in diameter in 3-μm-thick layers. The effect of etched nuclear tracks on the magnetic-wall coercivity can be interpreted satisfactorily with present models on Hwc.
Evolution of ferroelectricity in ultrafine-grained Pb5Ge3O11 crystallized from the glass
Authors: Glass A. M. , Nassau K. , Shiever J. W.
Published: February 2003

By controlled crystallization of the ferroelectric crystalline phase of Pb5Ge3O11 from the glass of the same composition, the evolution of ferroelectric behavior has been studied as a function of grain size. The large-grained material (≳1 μm) exhibits normal ferroelectric behavior. However, during the initial growth of grains of about 10-nm dimensions the polarization is unstable and no dielectric anomaly is observed. The behavior of this fine-grained material can be understood in terms of large dipolar clusters which can be frozen into ferroelectriclike order at low temperatures in the presence of an electric field, but which are too small to stabilize spontaneous ferroelectric order.
Current runaway in insulators affected by impact ionization and drift
Authors: Kashat I. , Klein N.
Published: February 2003

Current runaway in insulators as affected by impact ionization and drift was treated rigorously by O’Dwyer. The theory did not result in explicit relations for the current runaway field Fr, and approximate relations derived later were based on rather arbitrary assumptions. To avoid these difficulties, in this report an approximate theory is developed which results in simple relations for Fr and for times to breakdown. The Fr values calculated are only a few percent smaller than those obtained with the rigorous theory. The approximate theory is presented for small and large rates of ionization, for the cases of trapping and field ionization, and for steady states and transients. To help with the identification of the breakdown mechanism on the basis of experimental observations, the properties of various breakdown models are compared and tabulated.
Analysis of alternating current excitation of a wire rope by a toroidal coil
Authors: Hill David A. , Wait James R.
Published: February 2003

An idealized magnetic sheet current model for a toroidal coil which encircles a conducting ferromagnetic rope is analyzed. This configuration is suitable for the nondestructive testing of wire ropes and cables. Numerical results for the axial electric current density induced in the rope reveal that low frequencies on the order of 10 Hz are required to produced a uniform current in a typical rope. For a toroidal coil which does not completely encircle the rope, the azimuthal symmetry is lost and harmonics in φ are produced. These harmonics are large but decay rapidly away from the source.
Thermionic return currents in contact electrification
Authors: Ruckdeschel F. R. , Hunter L. P.
Published: February 2003

It is demonstrated that the contact electrification process is generally a nonequilibrium phenomenon. The electrochemical potential is considered for the case of ion transfer between insulators. It is shown that the thermionic return currents are significantly dependent on the physical separation and the dielectric constants of the materials. A nonequilibrium chemical kinetics formulation is presented in which dielectric constants and surface separation rates are explicitly accounted for. The predictions of the theory are shown to correlate with electrification experiments performed on various glass, lead zirconate, and aluminum oxide beads rolled in an aluminum oxide coated rotating cylinder.
Stability limits of high-power ion-laser discharges
Authors: Lüthi H. R. , Seelig W.
Published: February 2003

Highly ionized plasmas (degree of ionization 0.1,...,0.5) with electron temperatures kTe≳4 eV are required for high-power generation from ion lasers. In stationary low-pressure arcs, however, these requirements are limited by discharge instabilities. The stability limits are investigated in the case of Ar and Hg low-pressure discharges. It is shown that the main limitation processes are due to neutral gas depletion by ionization and axial plasma inhomogeneities. The stability ranges of ion-laser discharges are represented using the geometry-independent parameters jR and pR ( j: discharge current density; p: filling pressure; R: discharge radius). These instabilities, together with saturation effects in the laser mechanism, limit the output power of ion lasers by restricting the operational range of the discharges.
Nonlinear imaging of an edge in the scanning acoustic microscope
Authors: Wickramasinghe H. K. , Yeack Celia
Published: February 2003

When harmonics are produced in the scanning acoustic microscope, the resultant images have a complex appearance which requires interpretation. A theoretical calculation of the distribution of harmonic radiation has been made for the case of a focused beam scanning across the edge of an object such as a Mylar sheet suspended in water. The results show that most of the harmonic signal is generated in the water, and that diffraction causes the appearance of fringes in the image. Experimental results agree with the theory.
Scattering of relativistic electron beams by magnetic field errors and beam-induced waves
Authors: Benford Gregory
Published: February 2003

Relativistic electron beams propagating in long plasma columns must be well focused to cause efficient plasma heating. Expansion of the beam area due to scattering lowers efficiency. We calculate the beam spreading expected from errors in the ambient magnetic field. We then include scattering from both electrostatic and magnetic waves generated by the beam itself. All these effects can be important in contemplated experimental regimes. However, it may prove possible to ’’tune’’ beam-plasma heating processes to avoid significant beam spreading.
Anisotropic production of laser-plasma soft x rays and fast electrons from thin plastic targets
Authors: Violet C. E. , Petruzzi J.
Published: February 2003

In separate experiments incident pulses from two different Nd-glass lasers and a CO2 laser were fired at planar targets of thin plastic, and the angular distributions of the soft x rays and fast electrons were measured. The focused power densities of the first Nd-glass laser and the CO2 laser were 2×1012 W/mm2, of the second Nd-glass laser, 2×1013 W/mm2. The electron efficiency of the CO2 laser plasmas is strongly peaked antiparallel to the incident pulse, the backward-to-forward ratio being 100. The electron efficiency of both Nd-glass lasers is less than 150% of their x-ray efficiency. The x-ray efficiencies of the Nd-glass laser plasmas are at least an order of magnitude greater than that of the CO2 laser plasmas. The x-ray efficiency of the first Nd-glass laser was isotropic. The x-ray distribution for both the second Nd-glass laser and the CO2 laser plasmas had the backward-to-forward ratio of 4.
On the field effect of the electrical conductance of discontinuous thin metal films
Authors: Uozumi K. , Nishiura M. , Kinbara A.
Published: February 2003

In the activated tunneling model of electrical conductance of discontinuous thin metal films, non-Ohmic conductance has thus far been explained by a field-dependent activation energy at a high electric field. We point out that this interpretation is not appropriate. Alternatively, the field effect should be ascribed to the non-Ohmicity of the tunneling current density at a high electric field. Results of the computation are presented.
Critical current enhancement in Nb3Sn by low-temperature fast-neutron irradiation
Authors: Colucci S. L. , Weinstock H. , Suenaga M.
Published: February 2003

An advanced type of Nb3Sn composite wire was irradiated at ∼6 K with fast neutrons. The short-section critical current jc was measured at 4.2 K (after annealing to 77 K) in transverse magnetic fields up to 10 T. Before irradiation, jc at 4 T was 1.6×106 A/cm2. A fluence of 1.8×1018 n/cm2 increased jc for H≳2T, the enhancement increasing with field to 85% at H=10 T. After annealing to 540 K, roughly one-half the enhancement remained. These results are compared with those for an earlier similar material, but with a smaller jc before irradiation. For comparable fluences, the relative enhancement in the earlier material was unexpectedly less than in the improved samples.
Calculation of heating and burst phenomena in electrically exploded foils
Authors: Logan J. D. , Lee R. S. , Weingart R. C. , Yee K. S.
Published: February 2003

A method is presented for computing the transient current and temperature distributions in electrically exploded foils. The model employed is applicable up until the time of burst. Calculations are presented for Al, Cu, and Au foils showing good agreement with experimental current waveforms and burst times over a wide range of capacitor-bank charging voltages and for varying foil cross sections. The two-dimensional nature of the calculation permits investigation of effects associated with nonuniform heating of the foil and gives an estimate of the simultaneity of burst.
Saturation characteristics of SF6 absorption at the 10.53-μm CO2 P (14) line
Authors: Taylor R. S. , Ballik E. A. , Garside B. K.
Published: February 2003

Measurements are reported of the saturation characteristics of SF6 absorption at the P (14) CO2 line (10.53 μm) using a pulsed CO2 laser. The data is successfully interpreted in terms of a four-level non-steady-state transmission model.
Continuous high-power uv laser
Authors: Lüthi H. R.
Published: February 2003

An Ar low-pressure high-current discharge (length=1.7 m, diameter=12 mm) was used for continuous high-power operation of uv laser lines (λ=351.1 nm, 363.8 nm). The measured maximum output power of 18 W for both lines combined was restricted by thermal mirror degradation. Based on gain measurements, a maximum power of 35 W is predicted. It appears that this value is limited by discharge instabilities.
SQUID instruments and shielding for low-level magnetic measurements
Authors: Zimmerman James E.
Published: February 2003

We have used a thick-walled aluminum enclosure to provide low-frequency shielding for biomagnetic studies with SQUID magnetic gradiometers. The shield provides an attenuation proportional to frequency above 1/3 Hz. A 24-hole fractional-turn SQUID gradiometer has been used in the enclosure to carry out studies of magnetoencephalography on humans. An ’’asymmetric’’ configuration for a second-derivative gradiometer has been developed which provides a significant increase in sensitivity and resolution over more conventional symmetric arrays.
Energy and spatial distribution of an electron trapping center in the MOS insulator
Authors: Kapoor V. J. , Feigl F. J. , Butler S. R.
Published: February 2003

The energy and spatial distributions of electrons trapped in the silicon-dioxide layer of a metal-oxide-semiconductor structure have been determined. Visible–near-uv trap photodepopulation techniques have been used measure these electron distributions through a series of reductions of the oxide layer thickness by chemical etching. Electron trapping centers which could be emptied by visible–near-uv light were distributed uniformly throughout the oxide volume, with a volume density of order 1014 cm−3. These trapping centers produced a bell-shaped distribution of localized electrons states within the SiO2 band gap. The width of this distribution was 0.42 eV (FWHM), and the peak was located 2.4–2.5 eV below the SiO2 conduction edge. The peak location (trap depth) increased systematically as the oxide layer was reduced in thickness. Trapped electrons which could not be released by visible–near-uv light were determined to have an average concentration of 1015–1016 cm−3. These electrons had a significant excess concentration in the vicinity of the SiO2-Si and SiO2-Al interfaces (1017 cm−3). The midfilm concentration of these trapped electrons was approximately 2×1015 cm−3.
Anatomy of the transferred-electron effect in III-V semiconductors
Authors: Ridley B. K.
Published: February 2003

The roles played by band structure, ionicity, and phonon energies in the transferred-electron (TE) effect in III-V compound semiconductors at 300 K are analyzed within a simple transport model. Expressions are obtained for the threshold field, the peak velocity, the frequency limit, the valley velocity, the breakdown field, and the relative noise level. These exhibit a powerful dependence on the magnitudes of relevant phonon energies and also on ionicity. The dependence on individual band structures is relatively weak. A figure of merit for TE materials is suggested, on which basis InP emerges as over three times better than GaAs.
Magnetostriction of FeII ions in yttrium iron garnet
Authors: Hansen P.
Published: February 2003

The temperature dependence of the magnetostriction constants λ100 and λ111 has been studied for FeII : Y3Fe5O12 single crystals by ferromagnetic resonance in the temperature range 4.2⩽T⩽500 K. The contributions Δλ100/z and Δλ111/z at T=4.2 K are found to be 2.7×104 and 2.9×104, respectively. The experimental data are compared with calculations based on the single-ion theory.
Optical study of the metamagnetic hysteresis in FeCl2
Authors: Chen E. Yi , Dillon J. F. , Guggenheim H. J.
Published: February 2003

Recently we reported measurements of magneto-optical rotation of FeCl2 as a magnetic field was slowly swept (102 Oe/sec) at T?4.2 K across the lower boundary of the metamagnetic transition. This paper contains further rotation studies combined with direct microscope examination. The fields used are sufficient to sweep across the whole transition. The microscopy reveals the mechanisms responsible for various aspects of the hysteresis, e.g., (1) the hysteresis is seen to arise from the different texture of the minority phase on entering and leaving the mixed phase and (2) at low temperatures an important class of nucleation sites disappears after an excursion to the paramagnetic state.
The effect of an applied electric field on the laser-induced damage of silicon
Authors: Vitali G. , Stagni L.
Published: February 2003

The damage produced by irradiating silicon single crystals with a free-running ruby laser is found to be influenced by an applied electric field E. For an average irradiation flux slightly higher than the damage threshold, and a carrier lifetime of 2 ms, surface cracking disappears when E is increased from 0 to about 20 V/cm. Larger values of E lead to a decrease of the surface corrugation. These results may be accounted for by the recombination volume increase caused by an applied electric field.
Inclusions in cadmium telluride: Estimates for damage thresholds
Authors: Bennett Herbert S. , Cantrell C. D.
Published: February 2003

One problem frequently encountered in high-power laser systems is the thermal extrinsic damage to the laser materials, which arises from absorbing inclusions. Absorbing inclusions are impurities with physical and optical properties which differ substantially from those of the host material. Such inclusions may absorb sufficient radiation from the incident laser beam to produce major stresses within the host. In this paper, estimates of the maximum tensile stress as a function of inclusion size, laser pulse width, and laser power are computed for the common precipitates in CdTe. Our computations suggest that the heating of such precipitates when subjected to power densities of about 100 MW/cm2 may produce stresses comparable to or greater than the breaking strength of the CdTe host.
Interaction of ultrasonic waves incident at the Rayleigh angle onto a liquid-solid interface
Authors: Breazeale M. A. , Adler Laszlo , Scott Gerald W.
Published: February 2003

The behavior of a Gaussian ultrasonic beam incident on a liquid-solid interface at the Rayleigh angle, the angle at which surface waves are excited on the interface, has been studied in some detail. The reflected beam is displaced in the manner predicted by Schoch; however, the ’’Schoch displacement’’ in general is too large. Good agreement is obtained between experimental results and the theory of Bertoni and Tamir, which assumes that the incident beam couples resonantly into a leaky surface wave at the Rayleigh angle and that the energy reradiated from this leaky surface wave interferes with specularly reflected energy. The propagation distance of the ultrasonic beam is explicitly included in describing the ultrasonic wave reflection at the Rayleigh angle.
Role of structural defects in electron transport properties of copper films
Authors: Chopra K. L. , Suri Ritu , Thakoor A. P.
Published: February 2003

Kinetics of annealing of the electrical resistivity (ρ), Hall coefficient RH, mobility μ, and thermoelectric power TEP of thin (160–5000 Å) copper films deposited at temperatures ranging from 80 to 600 K have been studied. The activation energy for the associated recovery process has been obtained from the observed isothermal and isochronal changes in the resistance of the films. This energy increases from a value of 0.7 eV at 2000 Å to 1.4 eV at 180 Å for room-temperature-deposited Cu films. Changes in ρ, RH, and μ on annealing are found to decrease with film thickness and deposition and annealing temperatures. On the other hand, changes in TEP due to annealing increase with film thickness up to 3000 Å; the rate of change depends sensitively on deposition temperature. With decreasing temperature of deposition, the reduction in TEP occurs at successively higher annealing temperature. Annealing does not affect the temperature dependence of RH and TEP. These results, together with the information on the microstructure of the films and the known scattering behavior of structural defects in the bulk, lead us to conclude that (1) the reduction in ρ, RH, and μ on annealing is due to the annihilation of vacancies; (2) the corresponding changes in TEP are due to the decrease in the concentration of vacancies as well as the density of dislocations. Quantitative effects of vacancies and dislocations on RH and TEP have been deduced from the observed data. The enormously large contributions of the defects may be understood qualitatively in terms of the variations in the density of holelike states and/or the energy dependence of conductivity (at the Fermi surface), caused by changes in the extent and/or degree of curvature of the necks at the Fermi surface.
Study of electron-beam-produced plasmas by fast photography and emission spectroscopy
Authors: Wei P. S. P. , Adamski J. L. , Beymer J. R.
Published: February 2003

The luminous events produced by a drifting relativistic electron beam (REB) (1–2 MeV, 100 kA, 40 nsec) have been photographed with an image converter of 5-nsec gate time. Coupled with a transmission spectrograph, time-gated snapshots (1 μsec) of the spectra have been recorded. For air pressure between 0.1 and 0.3 Torr, the beam is self-focused and it yields a spark spectrum containing mainly N+, with some O+ and N++ lines. In 0.8–1 Torr of air, the beam is unfocused and it yields the N2 (B←C) but not the (A←B) bands. In the presence of a target, the unfocused beam may again produce an air breakdown. A slitless spectrum then yields a two-dimensional image of the event, which may be related to the spatial distribution of the beam. The results are discussed in connection with REB and ion acceleration research. In addition, Lichtenberg-type discharge tracks in a Plexiglas disk irradiated by 2-MeV beams are photographed and compared with the fluorescence lifetime of the N2 (B←C) bands.
Interaction of electromagnetic waves with bounded plasmas moving perpendicular to the plane of incidence
Authors: Kalluri Dikshitulu , Prasad R. C.
Published: February 2003

This paper describes the reflection and transmission of obliquely incident electromagnetic plane waves by an isotropic and uniaxially anisotropic plasma half-space moving perpendicular to the plane of incidence. Results for both the parallel and perpendicular polarizations of the incident wave have been obtained. The mechanism of power transmission into the plasma for each of the cases is examined. The effect of the dispersive nature of the plasma medium is illustrated by presenting numerical results of the power reflection coefficient versus incident wave frequency for various values of the medium velocity.
The disintegration and vaporization of plastic targets irradiated by high-power laser pulses
Authors: Greig J. R. , Pechacek R. E.
Published: February 2003

We have studied the disintegration of polyethylene and polystyrene targets irradiated by 100-J 40-nsec Nd/glass laser pulses. At power densities of ≲1012 W/cm2 relatively massive targets (6×10−5 to 5×10−4 cm3) are totally disintegrated to produce finely divided target material and un-ionized vapor. Both the size of the target and the presence or absence of a laser prepulse strongly influence the proportions of finely divided target material and un-ionized vapor, especially within the first few microseconds after peak laser power. This disintegration is always preceded by the emission of a hot fully ionized plasma, but only 1% of the target material is contained in the hot plasma. Typically, (1–3) ×1019 atoms of un-ionized vapor are released as a slowly expanding (v∼105 cm/sec) cold dense gas cloud (no≳1019 cm−3) surrounding the initial target position. This cloud of target material has subsequently been heated by absorption of a 300-J 100-nsec CO2 laser pulse to produce an approximately fully ionized plasma.
Microstructural investigation of polycrystalline iron whiskers
Authors: Lashmore D. S. , Jesser W. A. , Schladitz D. M. , Schladitz H. J. , Wilsdorf H. G. F.
Published: February 2003

The microstructure of polycrystalline iron whiskers, produced by chemical vapor decomposition in a magnetic field, is found to consist of a core extending the length of the whiskers surrounded by a series of approximately cylindrical layers made up of particles whose diameters are about 1000–3000 Å. These layers of particles are arranged to form a series of nearly concentric cylinders centered on the core. The grain size in both the core and the surrounding particles is found to be between 50 and 200 Å. The very high strength of these whiskers, 800 MPa, is considered a result of extreme grain refinement strengthening.
Stage I
E recovery of electron-irradiated pure silver and of its dilute alloys with cadmium and indium
Authors: Rizk R. , Vajda P. , Maury F. , Lucasson A. , Lucasson P.
Published: February 2003

Irradiations of silver specimens with electrons in the energy range 0.4–1.7 MeV were performed at liquid-helium temperatures. A subthreshold phenomenon has been observed which is taking over below ∼750 keV. After separation of this effect, we have studied the annealing spectra of pure silver and of AgCd (25 and 50 ppm Cd) and AgIn (15 and 50 ppm In) diluted alloys following irradiation with different doses of 1.7-MeV electrons and after irradiation doping. The stage IE recovery has been analyzed in terms of the chemical reaction rate theory. The corresponding rate equations have been solved numerically yielding the following values for the capture radii of a silver self-interstitial atom by a Cd and an In impurity: rCdAg=0.15rv, rInAg= (0.05–0.10) rv, where rv is its annihilation radius at a vacancy. The best fit was obtained with a value of Em=88 meV for the migration energy of a self-interstitial.
Estimation of surface layer structure from Rayleigh wave dispersion: Dense data case
Authors: Richardson J. M.
Published: February 2003

The problem of determining subsurface structure of a material from the measured dispersion of Rayleigh surface waves is obviously important in nondestructive testing and in the operation of surface acoustic wave devices. As is typical of many inverse problems this one is ill-posed and thus the use of special approaches is indicated. One approach is to represent possible profiles of the subsurface structure by trial functions containing a finite set of adjustable parameters and then find the parameter values giving the best fit to the dispersion data. Here we present an approach using a nonparametric version of estimation theory. This involves a mathematical model representing measurement errors and all possible profiles with reasonable a priori probability weightings. The present paper is limited to the case in which the dispersion data are dense (i.e., in a practical sense the data points are sufficiently dense on the frequency axis that interpolation can be performed with impunity). Later related papers will deal with the sparse data case. To elucidate the nature of the ill-posedness, a formal solution of the inverse problem is given in closed form. The application of estimation theory yields tractable estimator which corresponds to the inclusion of a convergence factor in the formal solution. The properties of the estimator are given by a set of auxiliary measures relating to statistical bias, model vs data dominance, resolution and reduction of variance. Because of the present lack of actual data sufficiently dense in a practical sense, synthetic test data, with and without simulated measurement noise, are used to investigate the performance of the estimator.
Limitations of the direct-indirect transition on In1−xGaxP1−zAsz heterojunctions
Authors: Holonyak N. , Chin R. , Coleman J. J. , Keune D. L. , Groves W. O.
Published: February 2003

Because In1−xGaxP1−zAsz is the highest-energy direct-gap alloy employed in laser diodes, we attempt to establish where the direct-indirect transition (xc+0.516yc=1.235, 77 °K) hinders or possibly even limits the use of this sytem in large-barrier (ΔE∼250 meV) double-heterojunction (DH) structures. The behavior at 300 and 77 °K of the I-V characteristics of single-heterojunction and homojunction structures employing high Ga composition (x?0.72, z≲0.01) wide-gap In1−xGaxP1−zAsz layers, lattice matched on GaAs1−yPy substrates, show that the nature of the direct-indirect transition of the ternary boundary In1−xGaxP (x∼xc, y=1 or z=0) acts as a limiting factor on the DH diode and laser performance of the quaternary system. As in GaAs1−yPy, donor states associated with subsidiary minima (X) cause a premature onset of the direct-indirect transition, and limit the growth of lattice-matched large-barrier In1−xGaxP1−zAsz (ΔE∼250 meV) DH lasers, with all layers direct, to substrates of composition y≲0.40.
High-pressure luminescence studies of alkali–halide phosphors doped with Pb++ and Sn++
Authors: Bieg K. W. , Woracek D. L. , Drickamer H. G.
Published: February 2003

The effect of pressure to 140 kbar has been measured on the luminescent properties of a series of alkali halides doped with Pb++ and Sn++ in both the fcc and simple cubic (sc) phases. In a few cases absorption or excitation data are also presented. For selected cases the results are analyzed in terms of a single-configuration coordinate diagram and the possibilities and limitations are discussed. For three sodium halides and three potassium halides (the latter in the sc phase) a comparison of peak-shift data are made for Pb++, Sn++, and previously published data on Tl+ and In+. The analysis is based on the effect of ionic radii and anion polarizability on the ratio of the force constants for the excited and ground states. Some aspects of the spectra, including intensity changes, are discussed in terms of Jahn-Teller splitting.
Line narrowing and tuning of high-power Nd : glass laser using an an intracavity brewster-angle birefringent filter
Authors: Liu Yung S.
Published: February 2003

We discuss the properties of a Brewster-angle briefirngent filter (BBF) using inside a laser cavity for line narrowing and tuning of a high-power low-gain laser, in particular, a Nd : glass laser. The free-spectral range (FSR) and t he dispersion function are found to be strongly angle dependent. This tuning method is found to be extremely simple, rugged, almost lossless, and to have a high finesse.
Berlinite, a temperature-compensated material for surface acoustic wave applications
Authors: Jhunjhunwala A. , Vetelino J. F. , Field J. C.
Published: February 2003

The surface and pseudosurface acoustic wave properties of berlinite (α-AlPO4) have been theoretically predicted in order to evaluate the merit of using this material in related surface acoustic wave devices. The surface and pseudosurface acoustic wave velocities, an estimate of the electromagnetic to acoustic coupling, the temperature coefficient of delay, the powerflow angle, and the attenuation have been determined for several standard crystallographic cuts. These results supplement the results given by Carr and O’Connell. This material is shown to possess several temperature-compensated cuts and about four times the coupling of α-quartz. It is pointed out that α-AlPO4 may be only one of many potentially temperature-compensated materials with a silica derivative-type structure.
Location of positive charges in SiO2 films on Si generated by vuv photons, x rays, and high-field stressing
Authors: DiMaria D. J. , Weinberg Z. A. , Aitken J. M.
Published: February 2003

The location of positive trapped charge in the dry thermally grown films of SiO2 on Si in MOS structures has been investigated by combining the internal photoemission-voltage dependence from both interfaces with the capacitance-voltage technique. Trapped holes have been produced in the SiO2 by vacuum ultraviolet (vuv) photons, x rays, and high-field stressing. After irradiation under positive gate bias, trapped holes have been found to reside near the Si-SiO2 interface with an upper limit of about 50 Å determined for their centroid from this interface. After irradiation under negative bias, a similar situation was found to occur near the Al-SiO2 interface; and in addition some positive charge was found approximately at the Si-SiO2 interface. After high-field stressing under negative bias, positive charge was found approximately at the Si-SiO2 interface. The charge locating technique is described in detail as well as the implications of the results to radiation damage and insulator breakdown.
cw GaAs/GaAlAs DH lasers grown by Peltier-induced LPE
Authors: Daniele J. J. , Cammack D. A. , Asbeck P. M.
Published: February 2003

GaAs/GaAlAs DH lasers were grown for the first time by Peltier-induced LPE. Peltier-induced LPE is an LPE technique in which an electric current is passed through the semiconductor-solution interface and cools it by the Peltier effect. The growth takes place at constant furnace temperature and the growth rate is proportional to the applied current. In this way, widely different growth rates were used for each of the four layers in the double heterostructure and the active layer was grown at average rates of 100–200 Å/min. Mesa stripe lasers were made from the resulting material and lased in cw mode at room temperature. Tests on pulsed devices showed Jth/d?5 kA/cm2 μm for devices from several wafers. Measurements of characteristic temperature, external slope efficiency, internal quantum efficiency, optical loss, and minority-carrier lifetime yielded 150–160 °K, 22–30%, 50–66%, 20–45 cm−1, and 2.5–3.5 nsec, respectively. Thus, it was concluded that the Peltier-induced LPE results in material and laser devices of quality comparable to those produced by normal LPE.
Heterostructure by solid-phase epitaxy in the Si 〈111〉/Pd/Si (amorphous) system
Authors: Lau S. S. , Liau Z. L. , Nicolet M-A. , Mayer J. W.
Published: February 2003

When a thin film of Pd reacts with a 〈111〉 Si substrate, a layer of epitaxial Pd2Si is formed. It is shown that Si can grow epitaxially on such a layer by solid-phase reaction.
Trapping of hydrogen isotopes in molybdenum and niobium predamaged by ion implantation
Authors: Bo/ttiger J. , Picraux S. T. , Rud N. , Laursen T.
Published: February 2003

The trapping of hydrogen isotopes at defects in Mo and Nb have been studied. Ion beams of 11- and 18-keV He+, 55-keV O+ and Ne+, and 500-keV Bi+ were used to create defects. Subsequently H or D was injected at room temperature by use of molecular beams of 16-keV H+2 and D+2. Appreciable enhancements were observed in the amount of H and D retained within the near-surface region of predamaged samples compared to samples with no prior damage. The total amount of D retained within the near-surface region was measured by means of the nuclear reaction D(3He,p)4He, and H depth profiles were measured via a resonance in the nuclear reaction 1H(19F,αγ)16O. The H profiles correlate with the predicted predamaging ion profiles; however, appreciable tails to deeper depths for the hydrogen profiles are observed for the heavier predamaging ions. For a given predamage ion fluence, the amount of trapped deuterium increases linearly with incident deuterium fluence until a saturation in the enhancement is reached. The amount of deuterium trapped when saturation occurs increases with increasing predamage fluence. The experiments indicate that lighter ions, which create fewer primary displacements, are more effective per displacement in trapping hydrogen. An appreciable release of hydrogen is obtained upon annealing at 200 and 300 °C, and a preannealing experiment indicates this is due to detrapping rather than to any loss of traps. These temperatures suggest a much higher binding energy for the trapped hydrogen isotopes (∼1.5 eV) than the available evidence gives for simple H-defect binding energies (≲0.3 eV). The detailed trapping mechanism is not known. However, it is suggested on the basis of the high binding energies and the high concentrations of hydrogen which can be trapped that clusters of hydrogen may be formed.
Preparation and properties of ferroelectric PLZT thin films by rf sputtering
Authors: Ishida M. , Matsunami H. , Tanaka T.
Published: February 2003

Ferroelectric PLZT thin films were prepared onto Pt and fused-quartz substrates by the rf sputtering method using powder targets with a few wt% of excess PbO. The structures of films were analyzed by x-ray diffraction and classified into three types depending on substrate temperatures: the perovskite type (PLZT); the pyrochlore type, and the coexistence of both types. For the preparation of PLZT thin films, the substrate temperature was kept above 550 °C. Excess PbO seemed to act as a flux for crystal growth. The Curie temperature and hysteresis loops of thin films were investigated and it was confirmed that ferroelectric PLZT thin films could be obtained without annealing.
Thermoelectric power of gold-silver alloy films
Authors: Leonard W. F. , Lee S. C.
Published: February 2003

Thermoelectric power, resistivity, and temperature coefficient of resistance of annealed Au−Ag alloy films, covering the entire composition range, have been measured. Using size effects in the electron transport theory, the energy dependence of the mean free path U and the Fermi surface area V have been determined.
Strength of MgO and NaCl polycrystals to confining pressures of 250 kbar at 25 °C
Authors: Kinsland Gary L. , Bassett William A.
Published: February 2003

The strengths of MgO and NaCl polycrystals under confining pressures to 250 kbar have been determined in a diamond-anvil high-pressure cell. The stresses in the samples are inferred from the strains determined by x-ray diffraction. The strength of MgO polycrystals is found to rise from a 1-bar confining pressure value of about 4 kbar to a maximum of 30±10 kbar at a pressure of 50±20 kbar and to remain constant at that value to a pressure of 250 kbar. The strength of NaCl polycrystals is found to rise from a 1-bar confining pressure value of about 0.3 kbar to a maximum of 4.0±1.5 kbar at a confining pressure of 250 kbar. The interpretation of the form of strength versus pressure for these two compounds is discussed in terms of a brittle-ductile transition. Preliminary transmission electron microscope data are presented.
Origin of magnetization-induced uniaxial anisotropy in evaporated Fe-Co and Ni-Co films
Authors: Srivastava R. S.
Published: February 2003

The contributions, from (1) strain-magnetostriction anisotropy due to substrate constraint and (2) directional ordering of atom pairs, to the magnetization-induced uniaxial anisotropy in evaporated Fe-Co and Ni-Co films are considered and their variation with concentration is studied. It is found that iron atoms in Fe-Co films are not so mobile as to form freely Fe-Fe pairs aligned parallel to the field applied at the time of deposition or annealing; hence the contribution from directional ordering of atom pairs is limited in these films. The compositional dependence of uniaxial anisotropy in Ni-Co films for the range 30–100% Ni can be explained by a linear combination of the two mechanisms. In Ni-Co films the directional ordering of atom pairs contributes more than 90% to the total anisotropy in the range 30–60% Ni. The constant a of Néel-Taniguchi theory is also found to depend on concentration.
Below-threshold waveguiding in a stripe-geometry junction laser
Authors: Paoli Thomas L.
Published: February 2003

Direct measurements of the intensity profile along the junction plane of a cw stripe-geometry junction laser are reported for currents extending from well below to above threshold. We find that the spatial profile of the optical intensity emitted at the wavelength of one Fabry-Perot mode exhibits a pronounced narrowing as the current is increased toward threshold. The observed behavior is shown to be consistent with an intensity distribution consisting of a Gaussian mode with current-independent width superimposed on a background of spontaneous emission. This interpretation suggests that waveguiding exists along the junction plane at currents as low as 50% below threshold and is at most weakly dependent on current.
Some remarks on selenium plates for xeroradiography
Authors: Borasi G. , Cubeddu R.
Published: February 2003

We report a calculation based on Donovan’s experimental data on selenium plates for xeroradiography showing that there is no discrepancy, at least from a qualitative point of view, between his results and the others reported in the literature.
Plasma response to ponderomotive forces from a laser pulse
Authors: Siegrist M. R.
Published: February 2003

The dynamic plasma response under the influence of ponderomotive forces from a laser pulse is investigated in connection with self-focusing. The resulting cone of the ion-acoustic compression wave can be used to contain backscattered and reflected radiation within the interaction region.
Drift mobility of holes in single-crystal β-AgI
Authors: Govindacharyulu P. A. , Bose D. N.
Published: February 2003

The drift mobility of photoexcited holes in single-crystal β-AgI has been measured between 260 and 312 °K. In this range the drift mobility μd increased with temperature due to trap-limited behavior. At 300 °K μd=12 cm2/V sec, the concentration and energy of the dominant traps being given by Nt=3×109 to 5×109/cm3 and Et=0.52 to 0.50 eV, respectively. Electron drift mobilities could not be determined due to low electron lifetimes.
Absolute linear thermal-expansion measurements on copper and aluminum from 5 to 320 K
Authors: Kroeger F. R. , Swenson C. A.
Published: February 2003

A linear absolute dilatometer based on a three-terminal parallel-plate capacitor design has been used to obtain thermal expansion data for high-purity copper and aluminum from 5 to 320 K. These data have an absolute accuracy of ±0.1% above 20 K for copper and above 30 K for aluminum, and agree well with published data at the higher temperatures. The disagreement which exists with other data below 5 K for copper and below 15 K for aluminum is believed to be sample dependent, but the mechanism is not known. The aluminum results in this region depend on the state of annealing of the sample.
Temporal stability of single-line cw HF chemical laser with unstable resonator
Authors: Turner E. B. , Chodzko R. A. , Mirels H.
Published: February 2003

The temporal stability of the output from a single-line cw HF chemical laser with an unstable resonator was investigated experimentally to determine if large-scale output-power fluctuations, associated with a ’’mode-medium’’ instability of the type originally postulated by Dreizin and Dykhne, would be observed. Cases where the gain at the resonator inlet was less than or greater than the threshold value were studied. In all cases, the output was found to be stable. For inlet gain less than the threshold value, this result is in accord with the theoretical prediction of Mirels.
A parametric study of the copper chloride laser
Authors: Nerheim Noble M.
Published: February 2003

A parametric study of the double-pulsed copper chloride laser is reported here. The effects of a wide range of variables on the laser energy density and on three characteristic time intervals (the minimum, maximum, and optimum delay time) between the two electrical discharge pulses were studied. The geometric variables investigated included the tube diameter from 2.3 to 40 mm and the tube length from 3 to 60 cm. Three buffer gases, helium, neon, and argon, were studied over the pressure range 0.5–50 Torr and the tube temperature was varied from 270 to 500 °C. The energy density and voltage of both the dissociation and pumping pulse were varied independently from less than 1 mJ/cm3 at 8.5 kV to over 500 mJ/cm3 at 20 kV. The optimum conditions for maximum laser energy density were found to be with 20 Torr neon in a 10-mm by 30-cm tube at 400 °C. The maximum energy density obtained was 22 μJ/cm3.