bluuebunny/crossref_metadata_2025 huggingface dataset:
Comments on ’’Optical analysis of the interface between a moving arc and air at atmospheric pressure’’
Authors: Drouet Michel G.
Published: February 2003

Recent photographic and interferometric measurements, obtained by Mai et al., on an arc driven in air between parallel electrodes by a transverse magnetic field are examined. The interpretation, proposed by Mai, based on a continuous growth of a transition region in front of the moving arc is shown to be highly questionable. By contrast, the generally accepted existence of a double-vortex flow in the arc core is shown to account for the results.
Reply to ’’Comments on ′Optical analysis of the interface between a moving arc and air at atmospheric pressure′’’
Authors: Dimoff K. , Mai H. H.
Published: February 2003

A direct transfer of results developed for long arcs balanced magnetically against gas crossflows to explain the behavior of short high-power moving arcs can offer misleading conclusions if due care is not paid to fundamental assumptions of the models employed. A thermal wave description of the leading edge to arc systems traveling at a significant fraction of the sonic speed is defended as a reasonable alternative to arguments based upon analogy.
Surface accumulation of Te atoms in laser melted Te-implanted silicon
Authors: Campisano S. U. , Baeri P. , Grimaldi M. G. , Foti G. , Rimini E.
Published: February 2003

The fraction of Te atoms accumulated on the surface after pulsed laser melting of ion-implanted silicon depends on the implantation range. The experimental profiles can be fitted by a numerical calculation, taking into account the diffusion in the liquid phase, the interface velocity, and the interfacial distribution coefficient which is much higher than the equilibrium one. The comparison between the spatial extent of the initial transient, well-known from the standard theory of normal freezing, and the implantation range determines the fraction of surface accumulation.
Comments on the temperature dependence of mass and charge transport in single crystals of SrCl2
Authors: Hood G. M. , Morrison J. A.
Published: February 2003

The results of several independent investigations of tracer diffusion and/or ionic conductivity in single crystals of SrCl2 are reviewed briefly. It is shown that, despite the considerable experimental difficulties presented by this substance, good agreement is found for the majority of the results. Where disagreement exists, it seems probable that the experimental specimens were not chemically treated rigorously enough.
Test of coupled carrier theory under high-field, short-pulse conditions in thin-film amorphous chalcogenide semiconductors
Authors: Walsh P. J. , Thompson M. J.
Published: February 2003

The remarkable unity found in the high-field behavior of thin-film amorphous chalcogenides is illustrated by comparing pulse data ranging from nanosecond to millisecond duration. Sixteen long-pulse effects had earlier been described in detail by coupled carrier theory, which postulates one lower-energy carrier, localized by hopping or trapping below a band, and one higher-energy carrier, which is free within a band to ionize the localized carrier. Twelve new tests of this theory against short-pulse data are given in four materials and without the use of adjustable parameters. Very substantial agreement is found in both calculated magnitudes and in predicted functional dependences. The use of short pulses in unswitched materials renders joule heating negligible in all tests of theory against experiments reported here.
F-center fluorescence in neutron-bombarded sapphire
Authors: Jeffries B. , Summers G. P. , Crawford J. H.
Published: February 2003

The efficiency of the 3.0-eV photoluminescence band which results from optical excitation into the 6.1-eV F band in single-crystal sapphire is much weaker for F centers introduced by fast neutron bombardment than for those produced thermochemically (i.e., by either deliberate additive coloration or by coloration during growth). The luminescent efficiency has been monitored at room temperature following successive isochronal annealing stages up to 580 °C for samples exposed to ∼1017 neutrons cm−2. The relative emission intensity per F center increased rapidly as the F centers were thermally destroyed and reached a value at the upper end of the annealing range which was 40 times the preanneal value. It is suggested that the initial relatively weak emission is due to concentration quenching which results from the highly inhomogeneous distribution of lattice defects, i.e., displacement cascades, produced by fast neutron bombardment.
A computer analysis of heteroface solar cells with ultrathin window layer
Authors: Yoshikawa Akihiko
Published: February 2003

A computer analysis of heteroface solar cells with thin window layer has been performed regarding the effects of multiple reflections in the window layer, as well as in antireflection layers. It is shown that the thickness of the window layer greatly affects the reflection characteristic of the cell, and there is an optimum thickness for the window, so the window layer thickness must be defined so as to minimize the reflection loss, as well as the absorption loss by the window.
Silicon photodiode front region collection efficiency models
Authors: Geist Jon
Published: February 2003

The minority-carrier transport equations are solved numerically for a realistic model of the front region of a UV-enhanced silicon photodiode. Surface recombination is shown to be the dominant quantum efficiency reducing mechanism. Auger recombination is shown to be almost negligible for the type of diode under investigation.
Potential minimum determination for crossed-field electron guns
Authors: Rosenthal S. E. , Crawford F. W. , Harker K. J.
Published: February 2003

Four general functions are presented which determine self-consistently the potential minimum position and depth in planar space-charge-limited crossed-field electron guns.
Laser action in PrF3
Authors: Hegarty J. , Yen W. M.
Published: February 2003

The 3P0-3H6(1) transition of Pr in PrF3 was observed to undergo laser action under direct pulsed excitation at low temperature with a high conversion efficiency. Comparison with such behavior in other types of material is made and the usefulness of this stimulated emission behavior as a spectroscopic tool in characterizing concentrated materials is discussed. The parameters describing threshold conditions, linewidths, and energy conversion are measured and compared to theory.
Measurement of the energy distribution of a gallium liquid metal ion source
Authors: Swanson L. W. , Schwind G. A. , Bell A. E.
Published: February 2003

Total energy distribution (TED) curves of ions emitted from a gallium liquid metal ion source exhibit full width at half maximum (FWHM) value that increases from 5 to 30 eV with an increasing total current of 1–30 μA. An energy deficit of 4 eV at threshold supports a field evaporation mechanism of ion formation. The lowest TED FWHM value of 5 eV corresponds to a source angular brightness of 20 μA/sr.
Experimental measurement of increased neutral beam divergence due to a transverse magnetic field
Authors: Conrad J. R. , Horne S. F. , Pirkle D. R. , Moyer R. A. , Peranich L. S.
Published: February 2003

The deflection and increased divergence of a neutral beam due to a magnetic field perpendicular to the gas-cell neutralizer has been measured. The hydrogen neutral beam energy was 5.0 keV. The observed neutral beam deflection and divergence were in good agreement with results obtained from solutions of a coupled set of kinetic equations for the transverse velocity distribution functions for energetic ions and neutrals in the neutralizer volume.
Pressure dependence of fluorescent and photolytic interferences in HO detection by laser-excited fluorescence
Authors: Hard T. M. , O’Brien R. J. , Cook T. B.
Published: February 2003

In the measurement of HO concentrations by laser-excited fluorescence, expansion of the sampled air offers a way to reduce fluorescent and photolytic interference by other species. The decrease in [HO] upon expansion is balanced by an increase in HO fluorescence yield over a wide range of pressures. Background air fluorescence is reduced if the responsible species have fluorescence yields higher than those of HO. Preliminary experiments indicate that most of the fluorescence observed in laboratory air is due to such species. Upon expansion, the suppression of fluorescent interference can be no greater than the reduction in pressure, whereas the suppression of photolytic interference can be no less.
Multiple scattering of electromagnetic waves by random distributions of discrete scatterers with coherent potential and quantum mechanical formalism
Authors: Tsang L. , Kong J. A.
Published: February 2003

An experimental observed fact in scattering of electromagnetic waves by dense distribution of discrete scatterers is that the assumption of independent scattering leads to overestimation of scattering effects. To account for this phenomenon in the present paper, the method of coherent potential is applied to the study of multiple scattering of electromagnetic waves by random distribution of discrete scatterers. Comparisons are made with results obtained by using the effective field approximation and the quasicrystalline approximation. Numerical results of the effective dielectric constant and the scattering attenuation rates, as a function of the fractional volume occupied by the scatterers, are illustrated using parameters frequently encountered in the microwave remote sensing of snow and soil moisture. It is shown that the coherent potential method as applied to quasicrystalline approximation is superior to the other approximations in accounting for the overestimation factor.
Production of annular electron beams by foilless diodes
Authors: Miller R. B. , Prestwich K. R. , Poukey J. W. , Shope S. L.
Published: February 2003

A number of important aspects of the production of annular electron beams by foilless diodes are examined, both theoretically and experimentally. The theories of Ott, Antonsen, and Lovelace (OAL) and Chen and Lovelace (CL) are compared, and the CL theory is extended to include the effect of an axial gap in an approximate fashion. For the case of finite magnetic field strengths, Larmor orbits are examined and radial oscillations of the beam profile are predicted from a beam envelope analysis. Experimental results obtained with both low- and high-impedance sources have been compared with the theory, and based on such studies, the design and construction of an intense hollow beam generator are described. Experimental results obtained with the new diode compare favorably with both the analytic theory and the results of numerical simulations. The device currently produces 2-MeV electrons at beam currents of 65–70 kA.
Fabrication of optical strip waveguides with nearly circular cross section by silver ion migration technique
Authors: Viljanen J. , Leppihalme M.
Published: February 2003

Circular optical waveguides have been fabricated from vacuum-deposited Ag layers by ion migration technique into soda-lime substrate glass. In this method two different guide patterns, one of which is the mirror image of the other, are made. Later the guide patterns are placed on top of each other and circular guides are thus obtained. The ends of the guides are studied by optical microscope and the near-field scanning method. The optical loss spectrum is measured from 450 to 1600 nm.
Plasma heating by an electron beam from a foilless diode
Authors: Robertson Scott , Fisher Amnon
Published: February 2003

Intense relativistic electron beams (1 MV, 125 kA, 50 nsec) launched from foil and foilless diodes have been used to heat mirror-confined hydrogen plasmas of density 2×1013 and 1.6×1014 cm−3. Electrical shorts in the foilless diodes were prevented by locating the diode outside the magnetic mirror in a region of lower plasma density. The plasma heating by the foilless diode was found to be slightly greater than that of the foil diode. This agrees qualitatively with the theory of Thode which predicts that foil scattering decreases the strength of the beam-plasma interaction. E/T;8052.40.Mj, 52.50.Gj, 07.77.+p, 61.80.Fe
Microstructure of tellurium films
Authors: Chakrabarti B. , Chaudhuri S. , Malhotra G. L. , Pal A. K.
Published: February 2003

Growth and structure of tellurium films deposited by molecular beam technique onto NaCl single-crystal and glass substrates were studied by TEM. It was observed that films deposited onto NaCl substrate have a structure similar to those obtained by other workers. The films deposited on glass at a substrate temperature of 150 °C have an altogether different structure showing a definite c-axis orientation with needle-shaped crystallites lying parallel to the substrate plane.
Theoretical study for a 16-μm CO2 gasdynamic laser
Authors: Suzuki K. , Saito S. , Obara M. , Fujioka T.
Published: February 2003

The possibility of obtaining high-power 16-μm radiation from a conventional gasdynamic CO2 laser (GDL) has been evaluated theoretically by means of a modified Anderson’s time-dependent method. The analysis showed that up to 2.5% cm−1 gain can be achieved on the P(15) line of the (0200)–(0110) transition by injecting a fast 9.4-μm pulse at a position 15 cm downstream of the nozzle throat to populate the upper laser level. For a gas mixture of CO2:N2:H2=20:73:7(%) and a nozzle area ratio of 100, the optimum reservoir temperature and pressure were calculated to be 1200 K and 15 atm. Because of its high repetition rate and high average-power capabilities, such a conventional GDL could easily provide the power levels required for industrial applications of 16-μm radiation.
Temperature characteristics of threshold current in InGaAsP/InP double-heterostructure lasers
Authors: Yano M. , Nishi H. , Takusagawa M.
Published: February 2003

Temperature dependence of threshold current in InGaAsP/InP double-heterostructure (DH) lasers was studied from the standpoint of the effect of carrier leakage from the quaternary active region into the InP confining layers. The carrier-confinement coefficient, defined as the ratio of confined carriers to total injected carriers in the active region, was connected with other oscillation characteristics such as emission efficiency, carrier lifetime, and internal quantum efficiency in three different ways. These variations, as a function of ambient temperature, were measured and the temperature variation of the carrier-confinement coefficient was evaluated and compared with that of threshold current. These results demonstrated that the carrier leakage was the dominant mechanism on temperature dependence of threshold current in InGaAsP/InP DH lasers. Moreover, we too discussed the other possibilities such as the effects of interfacial recombination at heterojunctions and laser parameters.
Self-sustained pulsations in semiconductor lasers: experimental results and theoretical confirmation
Authors: Chik K. D. , Dyment J. C. , Richardson B. A.
Published: February 2003

New experimental results on self-sustained pulsations in semiconductor lasers are presented and compared with theoretical predictions. These results show that laser diodes with high external differential quantum efficiency (ηext) and low coefficient of spontaneous emission coupled into lasing modes (β) have a significantly higher probability of developing pulsations, which is in good agreement with theoretical predictions. Furthermore, these results provide strong evidence that the laser cavity contains defects which act as optically saturable absorbing centers. These may be incorporated into the active layer of the laser during crystal growth and/or subsequent fabrication.
Detection of latent scratches and swirl on silicon wafers by scanned surface photoresponse
Authors: Hill Dale E.
Published: February 2003

Latent scratches, surface effects, and swirl on silicon wafers can be nondestructively detected by the scanned surface photoresponse technique with results that are similar to those obtained with the usual destructive method of oxidation and preferential etching. In addition, scanned surface photoresponse can provide information on the depth of the damage related to latent scratches and surface effects by noting the effect of bias on the signals observed. The nondestructive nature of the measurement allows one to study phenomena which are not normally accessible such as the change in swirl patterns on a silicon wafer with heat treatment.
Furnace annealing behavior of phosphorus implanted, laser annealed silicon
Authors: Miyao Masanobu , Itoh Kazuo , Tamura Masao , Tamura Hiroshi , Tokuyama Takashi
Published: February 2003

The furnace annealing characteristics of supersaturated solutions produced by P+ implantation (50 keV, 8×1015 cm−2) and Q-switched pulse by ruby laser annealing (0.3–1.5 J/cm2) are investigated. Observed phenomena are classified into two regions. In the region of laser energy ?0.8 J/cm2, the concentrations of supersaturated solutions decrease monotonically to, and remain at thermal equilibrium values during furnace annealing. In the region of laser energy <0.8 J/CM2, the concentrations decrease at first to below the thermal equilibrium values with furnace annealing. However, with continued furnace annealing, the solution concentrations increase and approach the equilibrium value. These results are discussed in relation to the crystal quality after laser annealing and formation of dislocation loops durin subsequent furnace annealing.
An annealing study of electron irradiation-induced defects in GaAs
Authors: Pons D. , Mircea A. , Bourgoin J.
Published: February 2003

Isochronal and isothermal annealing experiments on defects produced by 1-MeV electron irradiation at room temperature have been performed on n-type GaAs (vapor phase epitaxy layers). In addition to the previously reported irradiation-induced defects E2 to E5, three new traps have been observed (P1 to P3) and their thermal behavior has been studied together with the thermal behavior of the traps E2–E5. The trap E2 is shown to exhibit an annealing kinetics which can be decomposed into the sum of two first-order kinetics, the first one having the same annealing rate as the annealing kinetics of the traps E3 and E5. These observations lead to an interpretation of the annealing mechanism: annihilation of vacancy-interstitial pairs or vacancy-antisite defect pairs, and E2 is tentatively identified as a vacancy.
Conduction mechanisms in ZnO varistors
Authors: Vanadamme L. K. J. , Brugman J. C.
Published: February 2003

The thermionic emission enhanced by barrier lowering and the Zener tunnelling in ZnO varistors are discussed. Capacitance versus voltage, reverse current versus temperature, and 1/f noise measurements have been performed on commercial varistors. A model is proposed from which follows a diffusion voltage VD which is consistent both with the 1/C2 vs V plot and with the thermal activation energy obtained from the reverse current versus 1/T. The empirical law β=d log V/dlog I= constant, is explained by Zener breakdown. The 1/f current noise is proportional to the square of the current and independent of the conduction mechanism across reversely biased barriers.
Hologram decay in LiNbO3 : Fe with a time varying conductivity
Authors: Bienvenu M. P. , Woodbury D. , Rabson T. A.
Published: February 2003

Hologram decay results are presented concerning a time varying decay rate which can be explained on the basis of a time dependent conductivity given by σ=σ0+σ1 exp(−t/τT). An analysis based on this assumption describes the data well, giving strong support for the existence of a persistent photoconductivity component during decay. The effective time constant τeff ? lnη/∂t)−1 is dicsussed in terms of this component and the dark conductivity.
Semiconductor properties of polyacetylene p-(CH)x : n-CdS heterojunctions
Authors: Ozaki M. , Peebles D. , Weinberger B. R. , Heeger A. J. , MacDiarmid A. G.
Published: February 2003

T r a n s:(CH)x:n-CdS heterojunctions have been fabricated and used to study the properties of undoped trans-polyacetylene. The I-V data show rectifying behavior characteristic of a p-n junction diode, thus confirming that as-grown polyacetylene is p type. From C-V characteristics we infer a residual acceptor concentration in as-grown films of p-(CH)x of NA?2×1018 cm−3. Depletion has been studied in the polymer by using CdS of different doping concentrations. Detailed studies of the photovoltaic response at energies below Eg for (CH)x imply the existence of a meta-stable deep trap in the polymer with energy near the center of the gap. The threshold energy for pumping into this level provides an independent measurement of the energy gap, Eg=1.45 eV.
Electrical properties of particle migration microfilm
Authors: Josefowicz Jack Y. , Yang C. C.
Published: February 2003

Using photostimulated transient current measurements, the charge transport mechanism involved in the imaging process of particle migration microfilm has been elucidated. It was found that the illumination of a microfilm, across which an electric field had been applied, results in photogenerated electron-hole pairs which separate within the Se particles followed by charge injection out of the particles across the Se-styrene hexylmethacrylate interface. This injection results in negatively charged Se particles due to the more efficient transfer of holes relative to the electrons. The excitation spectrum of the Se spheres within the microfilm reflects the photoresponse of bulk amorphous Se which agrees with the photographic sensitivity of the particle migration microfilm.
Influence of growth conditions on tin incorporation in GaAs grown by molecular beam epitaxy
Authors: Alexandre F. , Raisin C. , Abdalla M. I. , Brenac A. , Masson J. M.
Published: February 2003

Intentional perturbations applied to the growth parameters of Sn-doped GaAs layers grown by molecular beam epitaxy have been performed in order to investigate the tin incorporation mechanism. The start, the interruption, and the end of growth as well as a variation of fluxes or substrate temperature have been studied, using either the Auger electron spectroscopy (AES) measurement of tin accumulation on the surface, or C-V derived free-carrier concentration profile versus any of these growth parameters. The theoretical model proposed by Wood and Joyce, based on a time-delayed incorporation mechanism, has been found to fit the observed results, especially for As-rich surface, provided that an incorporation mechanism of second order is assumed. For Ga-rich conditions (Ts≳580 °C), a new result has been recognized, i.e., a significant reduction of carrier concentration as Ts is increased. The assumption of a partially acceptor nature of tin incident atoms under these growth conditions does not seem to fully explain this result. On the other hand, this may be better understood assuming a certain amount of tin atoms being re-evaporated in the high substrate temperature range. This behavior induces a temporarily weaker accumulation at the surface, and hence a relatively smaller incorporation rate.
Study of Nb-based Josephson tunnel junctions
Authors: Matsuda Azusa , Inamura Takahiro , Yoshikiyo Haruo
Published: February 2003

Nb-based Josephson junctions are photographically fabricated with an improved lift-off method. Aging properties of Nb/Pb junctions are studied and the possible origin of aging was pointed out, using the shape dependence and IJ-H characteristics. The I-V characteristics of Nb/Pb junctions were analyzed quantitatively using a proximity effect model based on McMillan’s tunneling model. Maximum Josephson current was calculated incorporating the strong coupling correction. Theory and experiment agreed well for both pair and quasiparticle density of states.
Theory of modelocking of a laser diode in an external resonator
Authors: Haus H. A.
Published: February 2003

Laser diodes modelocked to date are gain modulated in an external resonator. The reflection from the diode face internal to the resonator causes a dependence of gain upon frequency that cannot be described by a simple bell-shaped function. Previous analyses treating modelocking by modulation of loss are generalized to treat modulation of gain with a general frequency dependence. We arrive at a limit on pulse width achievable with gain modulation of a laser diode in an external resonator and evaluate the limit for typical parameters.
Single-mode fiber wavelength multiplexer
Authors: Sheem S. K. , Moeller R. P.
Published: February 2003

Wavelength multiplexer for single-mode optical communication is reported. The multiplexer is made of all single-mode fibers and exhibits excellent stability. The separation between the multiplexed wavelengths was about 3.5 nm.
Theory of three-dimensional photoacoustic effect with solids
Authors: Chow H. C.
Published: February 2003

The photoacoustic signal from a finite cylindrical solid sample under excitation by an arbitrary incident source is derived and is in general a complicated function of the beam profile, optical, thermal, and geometrical properties of the gas, sample, and backing material in the cell. For sufficiently high chopping frequency or for a sample with large lateral dimension, the signal is similar to its one-dimensional counterpart. Departure from one-dimensional theoretical predictions occurs at chopping frequency for which the lateral dimension is of the order of the thermal diffusional length of the gas. Spot size plays a relatively insignificant role in affecting the signal. These predictions as well as quantitative calculations based on the present theory are in agreement with several recently reported experiments.
The role of inertia in the fracture of rock
Authors: Passman S. L. , Grady D. E. , Rundle J. B.
Published: February 2003

A theory for the accumulation of damage in one dimension in fast deformation of a brittle material is developed. The theory is consistent with thermodynamics and takes crack inertia into account. The problem of damage accumulation due to a step pulse in strain is solved, and shows good agreement with experimental results.
Theoretical transient currents from space-charge swarms in fluids
Authors: Henson Bob L.
Published: February 2003

The mathematical problem of transient currents that are produced by space-charge swarms after they are injected into liquids or gases is solved using a field-independent mobility model for the charge carriers. Only one species of charge carrier is assumed to be present in the fluid-containing drift space defined by parallel-plane constant potential electrodes. An integral-differential equation is derived for arbitrary initial charge distributions in the drift space. From its solution, the transient current waveform can be determined. When the initial current is in a steady state, the integral-differential equation reduces to a nonlinear ordinary differential equation which is valid for initial currents that may or may not be space-charge limited. This final equation is solved for the special case of small space-charge fields. The analysis is also expected to apply to conduction in solids in some cases.
Structural origin of the light scattering from a phase-separated glass
Authors: Kerwawycz J. P. , Tomozawa M.
Published: February 2003

The light scattering from many phase-separated glasses is characterized by a peculiar scattered intensity profile that increases with increasing scattering angle, as measured relative to the incident beam direction. This is in contrast to the typical diffractionlike situation where the scattered intensity is found to decrease with increasing scattering angle. Physical origins proposed as an explanation have included diffusion zone, internal stress, and interparticle interference. A detailed investigation of the light scattering from a borosilicate glass is described. Using x-ray small-angle scattering data and transmission electron micrographs as supporting evidence, it is concluded that the source of scattering in this glass is interparticle interference. However, the interparticle scattering predicted from two existing x-ray scattering models is shown to be inappropriate in describing the light scattering. A coherent interparticle interference model is proposed for the light-scattering case. A discrete Fourier analysis of the interparticle interference based upon the experimental scattered-light amplitude curves and the electron micrographs was performed. The results of this analysis produce a very plausible refractive-index profile which predicts a scattered intensity that is essentially the same as the one observed experimentally.
An empirical study of electron backscattering from thin films
Authors: Sogard M. R.
Published: February 2003

Empirical fits to data are obtained which determine the backscattered electron coefficient for films of arbitrary thickness and electrons of normal incidence over the energy range 20–53 keV for the elements Al, Cu, Ag, Au, and Bi. From this is derived a ’’universal’’ fit which describes with reasonable accuracy the backscattered electron coefficients of Be, Al, Cu, Ge, Ag, Au, Pb, and Bi over a somewhat larger energy range. By extension, it should predict the coefficients of other elements over at least the atomic number range Z=4–83. An expression is suggested for predicting the backscattered electron coefficient for films of arbitrary thickness and composed of compounds of several elements. Approximate agreement with experiment is obtained.
Identification of Auger spectra induced by Ar+ and Kr+ ion impact on transition metals
Authors: Legg K. O. , Metz W. A. , Thomas E. W.
Published: February 2003

The production of Auger electrons from Cr, Mn, Fe, and Co by 20–200-keV Ar, 100-keV Kr, and 3-keV electrons has been studied. The metal M23M45M45 and the Argon LMM peaks are clearly identifiable, the latter broadened consistent with electron emission from backscattered Argon ions. Various other features are produced which cannot be due to target or projectile Auger emission. These are believed to result from interatomic transitions between the ions of the beam and those of the target.
Sintering and varistor characteristics of ZnO-Bi2O3 ceramics
Authors: Wong Joe
Published: February 2003

The sintering behavior of binary ZnO ceramics (containing 0.01–1 mol% of added Bi2O3) showed that densification in the initial stage of sintering and grain growth of the ZnO matrix are enhanced in the presence of a liquid Bi2O3 phase. Exaggerated grain growth of ZnO was observed above 1100 °C and in mixtures containing as low as 0.05 mol % Bi2O3. Volatilization loss of Bi2O3 during sintering affected the microstructure of the sintered ceramics and resulted in the loss of varistor property and return to Ohmic behavior and high conductivity (∼1 Ω−1 cm−1). A simple microstructural model which predicts that the minimum content of Bi2O3 required to maintain varistor behavior is proportional to the thickness of intergranular layer and inversely proportional to the average grain size of the ZnO.
Magnetic and transport properties of Metglas Fe40Ni38Mo4B18
Authors: Majumdar A. K. , Nigam A. K.
Published: February 2003

Systematic studies of the magnetic and the transport properties are lacking in Metglas 2826 MB (Fe40Ni38Mo4B18). Low-field magnetic susceptibility between 300 and 1000 K gives Tc=(591±2) K in the amorphous state. A thermal cycling up to 1000 K yields two crystalline magnetic phases with Tc=(760±10) K and (545±5) K. Differential thermal analysis shows that the crystallization temperature is about 810 K. The ferromagnetic anisotropy of resistivity (FAR) is very small and positive with a typical value of 0.1%. The average slope of magnetoresistivity changes from −(1.1×10−8) G−1 to −(0.55×10−8) G−1 from 300 K to 77 K. The transverse and the longitudinal magnetoresistances could be related to the tangent of the Hall angle for a number of Metglas alloys including 2826 MB by considering the normal anisotropic magnetoresistance as well as the reduction in resistance due to the removal of domain walls in a uniaxial ferromagnet.
On a possible connection between superconductivity and covalency
Authors: Schoijet Mauricio
Published: February 2003

An attempt is made to establish a correlation between superconductivity and the existence of a certain degree of covalency in metallic compounds on the basis of thermodynamic phase diagrams of some superconducting compounds.
Secondary ions from hydrogen ion bombardment of metal surfaces
Authors: McCaughan D. V. , Sloane R. H. , Geddes J.
Published: February 2003

The production of negative ions at metal surfaces under ion bombardment is of theoretical and practical interest. In this paper data for H+ and H− production at clean and hydrogen-covered tungsten surfaces under H+n bombardment are given, and the data interpreted. In the experimental apparatus primary ion beams of H+n are impacted on a tungsten target, from which secondary H+ and H− ions are emitted, and mass and energy are analyzed. It is found that the secondary H+ spectrum from H+n bombardment is a broad peak, reaching an Emax which is a function of the primary ion energy, independent of the state of hydrogen coverage of the tungsten surface. The H− yield has a peak and tail distribution, the peak being a function of the degree of surface coverage. The mechanism whereby the high-energy peak arises and the amount of hydrogen trapped in the lattice is related to multiple scattering process in the target. The low-energy peak of H− ions arises from surface atoms sputtered off the surface as H− ions. A new theory explaining the secondary H− production in terms of a two electron Auger process followed by resonant capture of an electron from a normally unoccupied state in the metal is presented.
Experimental and theoretical study of the equation of state of carbon using an intense beam of relativistic electrons
Authors: Peugnet C. , Roche M. , de Villers P. , Savy C. , Sibille G.
Published: February 2003

Methods designed for the simultaneous measurement of energy deposition and impulses allowed the study of the equation of state of a refractory material at energy levels exceeding 2000 cal/g. The principle involved consists of comparing the impulse delivered by the material whose thermodynamic behavior is to be determined with that delivered by a material with a known equation of state. The material investigated here is graphite 2239, with specific gravity 1.78. Reference materials are aluminum and sulfur. The experiments were conducted on the Sidonix accelerator, whose electrical characteristics are 1 MV, 0.8 MA, 80 ns.
Amorphous FeCoNi-SiB alloys having zero magnetostriction
Authors: Kohmoto O. , Ohya K. , Yamaguchi N. , Fujishima H. , Ojima T.
Published: February 2003

Zero magnetostriction compositions in the (FeaCo1−a−bNib)100−y(Si0.4B0. 6)y system in the range 20⩽y⩽30 and 0⩽b⩽0.6, the resultant magnetic properties, and the crystallization temperatures were systematically studied as functions of Ni content (b) and metalloid content ( y). The iron content (a=0.058−0.11) decreases with increasing metalloid content ( y), increases with Ni content (b), and then decreases with the addition of Ni. The effects of annealing on low-field magnetic properties were studied for two kinds of alloys; a high-Bs alloy and a high-μ alloy. For the high-Bs alloy, the effect of sample shape was also studied. The high remanence observed for a tape-wound toroid and the low remanence observed for a ring-laminated toroid in the as-quenched state are attributed to weak uniaxial anisotropy, whose origin may be due to local tension as well as atomic and impurity arrangement introduced during the quenching. By annealing at Tc <Ta <Tx , high-μ alloys with relatively low Hc and Br were obtained.
The role of B-site cation disorder in diffuse phase transition behavior of perovskite ferroelectrics
Authors: Setter N. , Cross L. E.
Published: February 2003

In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B-site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well-ordered by long annealing, dielectric measurements on single crystals show a normal first-order ferroelectric phase change at 13 °C and a maximum low-temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low-frequency dielectric dispersion in the transition range. X-ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single-crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.
Refractive index dependence on free carriers for GaAs
Authors: Mendoza-Alvarez J. G. , Nunes F. D. , Patel N. B.
Published: February 2003

This work reports on the influence of the injected free carriers on GaAs refractive index N at 297 °K. The variation of N caused by injected free carriers was theoretically calculated in a more complete way than has been performed earlier. New results were obtained rather than those of a reducing effect on N in a linearlike dependence on the injected free carrier concentration n. They are: (1) linearlike dependence of N on n occurs only beyond a certain value n1 and (2) an increasing effect on N is caused by the injected free carriers for concentrations in the range between n=0 and a certain value of n=nc (nc<n1) . In the range nc<n<n1 a nonlinear decreasing effect was obtained. Effect (2) has not been noticed up to now, so far as the authors know.
The application of elastobirefringence to the study of strain fields and dislocations in III–V compounds
Authors: Booyens H. , Basson J. H.
Published: February 2003

The basic relations between the strain fields in III–V crystals and their elastobirefringence transmission properties are derived. The results are applied in an analysis of the contrast phenomena observed in III–V crystals containing misfitting epitaxial structures as well as the contrast features due to dislocations using visible and infrared birefringence.
Distribution of electrically active Mg implants in GaAs
Authors: Choe Byung Doo
Published: February 2003

The electrical properties of Mg-implanted GaAs have been studied in detail using the van der Pauw technique. Mg ions were implanted in Cr-doped semi-insulating GaAs at 120 keV to doses of 1×1013–3×1015/cm2 at room temperature. The implanted samples were annealed with rf-plasma-deposited Si3N4 encapsulants at temperatures ranging from 600 to 850 °C. p-type layers have been produced for all dose levels. The maximum electrical activation occurred at an annealing temperature of 750 °C for all except the lowest dose of 1×1013/cm2. An electrical-activation efficiency as high as 85% was obtained for the sample implanted to a dose of 3×1013/cm2 and annealed at 750 °C. The dopant profiles were very sensitive to annealing temperature and ion dose, broadening significantly at or above 750 °C. Double peaks in the depth profiles have been observed for doses of ?1×1014/cm2, and the maximum carrier concentration obtained was as high as 2×1019/cm3.
Radiation-induced defects and their annealing behavior in cadmium telluride
Authors: Taguchi Tsunemasa , Inuishi Yoshio
Published: February 2003

Radiation-induced defects and their annealing behavior in p- and n-type CdTe irradiated with 2-MeV electrons, neutrons, and 60Co gamma rays have been investigated by means of photoluminescence, Hall, time-of-flight measurements, and the performance of CdTe gamma-ray detectors. The 1.1-eV emission band produced after electron irradiation at 77 K anneals at a stage centered around about 120 K and originates from a defect including Te vacancy. From the isothermal annealing experiment, an activation energy of about 0.2 eV is obtained for the annealing stage. The electron and gamma irradiation at 77 K with room-temperature anneal, and neutron irradiation at 300 K enhance 1.53- and 1.55-eV edge emission bands. It has been suggested that the 1.53-eV band is attributed to a complex involving Cd vacancies. On the other hand, the 1.55-eV band is attributed to a complex involving Te vacancies. An annealing stage centered at about 370 K is observed in electrical properties in relatively pure p-type crystals irradiated with electrons and gamma rays. It is found from the isothermal annealing that the annealing behavior of the stage obeys first-order kinetics. The activation energy for the migration of the defects is estimated to be about 0.8 eV and the pre-exponential factor is found to be about 108 sec−1, suggesting long-range migration of Cd vacancies. Electron-trap levels lying at 0.058 and 0.5 eV below the conduction band are observed in crystals irradiated with gamma rays. The 0.058-eV electron trap anneals at about 600 K and the origin is tentatively assigned to a complex involving Te vacancies as inferred from photoluminescence results. Electron-drift mobility at room temperature is remarkably reduced after gamma irradiation, possibly due to the introduction of an electron-trap level at about 0.5 eV below the conduction band. The 0.5-eV electron-trap level and the electron-drift mobility anneal in the vicinity of about 600 K. The effects due to successive detector irradiations with 60Co gamma rays markedly degraded the output pulse-height spectra until ultimately the 59.5-keV photopeak of the 241Am gamma ray can not be discerned. Following annealing at 600 K, the pulse-height spectrum recovers almost to the preirradiation value. This annealing behavior coincides with the recovery of the electron-drift mobility of bulk crystals.
Shear strength of shock-loaded polycrystalline tungsten
Authors: Asay J. R. , Chhabildas L. C. , Dandekar D. P.
Published: February 2003

Previous experiments have suggested that tungsten undergoes a significant loss of shear strength when shock loaded to stresses greater than 7 GPa. In order to investigate this effect in more detail, a series of experiments was conducted in which polycrystalline tungsten was first shock loaded to approximately 10 GPa and then either unloaded or reloaded from the shocked state. Analysis of measured time-resolved wave profiles indicates that during initial compression to 9.7 GPa, the shear stress in polycrystalline tungsten increases to a maximum value of 1.1 GPA near a longitudinal stress of 5 GPa, but decreases to a final value of 0.8 GPa for stresses approaching 10 GPa. During reloading from a longitudinal stress of 9.7 GPa to a final value of ∼14 GPa, the shear stress increases to a peak value of 1.2 GPa and softens to 1.0 GPa in the final state. During unloading from the shocked state, the initial response is elastic with a strong Baushinger effect. Examination of a recovered sample shows evidence for both deformation slipping and twinning, which may be responsible for the observed softening.
Deformation of depleted uranium - 0.78 Ti under shock compression to 11.0 GPa at room temperature
Authors: Dandekar Dattatraya P. , Martin Anthony G. , Kelley John V.
Published: February 2003

The present work on depleted uranium alloyed with 0.78% titanium by weight (i.e., U-0.8 Ti) describes the nature of deformation it undergoes when subjected to shock compression at room temperature. The principal results emerging out of the present work are: (1) The stress limits of elastic deformation are dependent on the thickness of U-0.8Ti. The stress limit decreases from over 3.0 GPa at the impact surface to 1.2 GPa at a depth of 9 mm in U-0.8 Ti; (2) The lower limit of the stress agrees with the static yield stress in U-0.8 Ti; (3) Above the elastic stress limit, the deformation of U-0.8 Ti proceeds in a manner of the ideal plastic solid; and (4) The pressure derivative of Lame’s parameter of U-0.8 Ti is estimated to be 3.8.
Diffusivity of carbon in iron and steels at high temperatures
Authors: Tibbetts Gary G.
Published: February 2003

Although the literature contains many measurements of the diffusivity of carbon in Fe and steels, recent progress in plasma carburizing has made this regime around 1050 °C and over 1% carbon concentration of great interest. We have measured the diffusivity of carbon in steel from 975 to 1075 °C up to 1.3% carbon concentration by the steady-state method. Our results are in agreement with previous measurements of Smith and Wells, Batz, and Mehl in the regime of low temperatures and carbon concentrations. Using activation energies determined over a wider temperature range by the latter authors, we derive as an empirical expression for D throughout the range of temperatures and concentrations investigated, D=0.47 exp (−1.6 C) ×exp[−(37 000−6600 C)/RT] cm2/sec. Here, C is expressed in weight percent carbon and the energies are in cal/mole.
Complexes due to donor-acceptor-type transitions in GaAs
Authors: Reynolds D. C. , Litton C. W. , Almassy R. J. , McCoy G. L. , Nam S. B.
Published: February 2003

A sharp line transition at 1.51385 eV has been observed in the photoluminescence spectra of an epitaxially grown crystal of GaAs. A Si3N4 cap was applied by plasma deposition and the crystal was then annealed at 850 °C for 15 min. The sharp emission line was observed after annealing. This transition was analyzed in perturbing magnetic and strain fields and is shown to result from a donor-acceptor-type complex. Three additional sharp line transitions are reported and the behavior of all of these transitions is compared with the behavior of similar transitions reported in the literature. Models for the complexes involved are re-examined and components of the complexes are suggested. All of the sharp line transitions were introduced in the growing process with the exception of the 1.51385-eV line which was introduced in the capping and annealing process.
Time-dependent radiation-induced conductivity in electron-irradiated Teflon foils
Authors: Gross Bernhard , West James E. , von Seggern Heinz , Berkley David A.
Published: February 2003

The radiation-induced conductivity (RIC) of 2.5×10−3 -cm-thick Teflon was measured using partially penetrating electrons with an energy of 40 keV. The behavior of the external currents generated during irradiation is expressed by a ’’generalized box model.’’ We explain, with this model, the experimentally observed buildup and decay of the RIC by using a time-dependent conductivity σ(t)=σ0 (1−et/τs), where σ0 is the steady-state conductivity and τs is the time constant of the RIC buildup. The time sequence in which voltage and irradiation are applied is found to give significantly different time effects; for irradiation first, the induced conductivity reaches a final value when the voltage is applied, while with voltage first, the conductivity increases with time after the radiation is turned on. Measurements are complex because the nonirradiated region of the foil is entirely blocking for electrons while it allows transport of holes. The peak value of the induced current, and thus of the induced conductivity, increases proportional to ‖I0‖0.79, while the initial slope of the current versus time is proportional to the electron beam current I0.
Carrier relaxation mechanisms in CdS0.5Se0.5 optoelectronic switches
Authors: Mathur V. K. , Mak P. S. , Lee Chi H.
Published: February 2003

A detailed investigation of carrier relaxation in CdS0.5Se0.5, which has potential in ultrafast switching applications, has been carried out. It has been concluded from these investigations that there are three mechanisms for carrier relaxation in this material. At low 1.06-μm radiation intensities the two-photon-induced photoconductivity decays slowly with a decay constant ?20 ms determined predominantly by bulk recombination of carriers. However, at high intensities this decay becomes very fast, with the recombination lifetime of the carriers estimated to be only a few nanoseconds. This drastic reduction in free-carrier lifetime may be due to stimulated radiative recombination at high carrier densities. Single-photon conductivity induced by low-intensity 0.53-μm radiation has been found to decay initially due to surface recombination of carriers.