bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the repetitively pulsed dual-beam thermo-optical absorption spectrometer
Authors: Swofford Robert L. , Morrell James A.
Published: February 2003

An analysis is presented for the repetitively pulsed dual-beam thermo-optical absorption spectrometer, which has been used recently to determine the absorption strengths of several organic liquids in the visible spectral region covered by the cw tunable dye laser. The model succeeds in describing the development of the thermal lens on a pulse-by-pulse basis. The equations derived are then used to optimize the spectrometer design with respect to the parameters which are under the control of the experimenter. It is further demonstrated how one identifies the region of linear operation of the spectrometer. Finally, it is shown how the relative absorptivities of compounds may be determined.
Self-magnetic insulation in vacuum for coaxial geometry
Authors: Shope S. , Poukey J. W. , Bergeron K. D. , McDaniel D. H. , Toepfer A. J. , VanDevender J. P.
Published: February 2003

Magnetic insulation obtained by employing the magnetic field of the line current in coaxial vacuum-transmission lines is studied in experiments on two different relativistic electron-beam accelerators, spanning the voltage range 0.4–10 MV. Effective magnetic insulation at fields up to 1.3 MV/cm is demonstrated. The self-limiting impedance is measured and compared to a number of theories for magnetic insulation and it is found that none of the ’’standard’’ theories successfully describes the data. However, computer simulations using a self-consistent two-dimensional particle code give good agreement with the experimental data, as does a proposed modification of the parapotential flow model.
Long-lived lead-vapor lasers
Authors: Feldman D. W. , Liu C. S. , Pack J. L. , Weaver L. A.
Published: February 2003

Lead-laser operation has been demonstrated at 7229 Å in all-hot sealed-off quartz discharge tubes for 50-h cumulative operating times without tube degradation or failure. The maximum output energy of 230 μJ or 2.0 μJ cm−3 was obtained at ∼1.5 kHz, and the discharge efficiency was 0.12%. Average-power levels of 750 mW at 6 kHz were maintained under burst mode excitation conditions for extended periods at temperatures of ∼1050 °C. Lead-laser emission at ∼500 °C was also obtained using lead iodide as the starting material.
F2 absorption measurement in a combustion-driven chemical-laser nozzle
Authors: Spencer Donald J. , Clendening Charles W.
Published: February 2003

A sensitive F2 absorption diagnostic technique was used to determine F2 densities in the flow of a 10.2-cm-long combustion-driven chemical-laser nozzle. The diagnostic device was demonstrated to be readily transportable and operable in a combustion-driven chemical-laser field environment. Cold- and hot-flow measurements up to 970 K plenum temperature (i.e., no F2 dissociation cases) were in agreement; hence, the measurement technique appears to be reliable. The use of C2H4 as a combustor fuel did not result in particulate absorption or scattering of sufficient magnitude to affect the measurement. The flow dissociation level (α) was ≳0.8 for this nozzle. The measurement sensitivity achieved in these tests was ΔI/I0=6×10−4, which corresponds to an F2 density of 6.76×10−6 mole/l (i.e., 0.127 Torr F2 at 300 K) for a 10.2-cm path length.
Mirror-damage thresholds for laser-fusion pulse shapes
Authors: Howard James E. , Hunter T. O.
Published: February 2003

Mirror-surface-damage thresholds are calculated analytically for two temporal pulse forms relevant to laser-fusion experiments; a truncated Gaussian and the ’’ideal’’ isentropic pulse. The results show that 20% more laser energy/cm2 may be handled using a two e-folding Gaussian of the same FWHM as a square pulse of equal peak power. The surface-temperature rise is given in completely closed form for the isentropic pulse and applied to a conceptual laser-fusion design.
Laser generation by pulsed 2.45-GHz microwave excitation of CO2
Authors: Handy K. G. , Brandelik J. E.
Published: February 2003

A small CO2-N2-He laser excited by a pulsed microwave source at 2.45 GHz has been operated at low powers. Microwave power flux density was increased by using tapered sections to modify the aspect ratio. Pulsed microwave excitation of the gases resulted in laser output pulses characterized by time delays to threshold and long pulse lengths. The efficiency of conversion of microwave energy to laser energy was over 4%.
Transfer function for an acoustic source-receiver and target in a homogeneous fluid with distant boundaries
Authors: Hageman D. H.
Published: February 2003

The transfer function of the title is derived first for the case of a stationary source-receiver and a stationary target, with each in the far field of the other. Then, a quasi-transfer-function is constructed for the case in which the two bodies, separated as before, are moving at speeds which are small relative to the speed of sound, the flow around them being assumed to be derivable from velocity potentials. In both cases, the problem is formulated in terms of Helmholtz-Kirchhoff integrals. Conditions related to the distance to boundaries are deduced through the method of images. Theorems due to Blokhintsev and Oestreicher are used to treat the radiation, scattering, and reception of sound by a moving body.
Crack propagation in alkaline-earth fluorides
Authors: Becher P. F. , Freiman S. W.
Published: February 2003

The fracture of CaF2, SrF2, and BaF2 crystals by {111} cleavage requires critical fracture energies (γIC) which increase with decrease in cation size, as would be predicted. The γIC of single crystals, however, can be affected by the crystallographic direction of crack propagation and by annealing treatment. The introduction of grain boundaries can also result in some increase in γIC, particularly for finer grain sizes. Slow crack growth, which is sensitive to the environment, is observed but differs from that noted in other brittle materials in that it is often accompanied by crack arrest. This observation, as well as the stair-step crack motion during slow crack growth in concentrated HF, indicates that dislocation motion at the crack tip is associated with the slow-crack-growth phenomenon. Because of the extremely strong influence of the stress intensity on crack growth velocity, the effects of delayed failure should be minimal in CaF2, SrF2, and BaF2.
Nonlinear development of the negative-mass instability and its effect on intense microwave generation
Authors: Goren Y. , Uhm H. , Davidson R. C.
Published: February 2003

The nonlinear development of the negative-mass instability is investigated for a thin E layer (Δ≪R0) located inside a cylindrical waveguide. A quasilinear analysis shows that the instability saturates by the development of an energy spread and a corresponding increase in thickness Δ of the E layer. The efficiency of microwave generation by this instability is also calculated.
Determination of the electron density in a high-pressure Na-Xe discharge from the profile of a Stark-broadened spectral line
Authors: Waszink J. H. , Flinsenberg H. J.
Published: February 2003

The electron density is derived from the half-width of an optically thin Stark-broadened spectral line. A small nonperturbing amount of K is introduced, and the emission profile of the K 6s-4p (6939 Å) is measured. The side-on intensity distribution is recorded with a scanning Fabry-Pérot interferometer. Fourier transformation and Abel inversion yields the local profiles. Thus, the electron density ne is found as a function of the radial coordinate. The plasma temperature is calculated from ne and the sodium pressure pNa. Axis values are ne= (1.0±0.2) ×1022 m−3 and T=4100±120 K for pNa=100 Torr; ne= (2.1±0.4) ×1022 m−3 and T=4350±120 K for pNa=200 Torr.
Field ion microscopy of polycrystalline iron whiskers
Authors: Lashmore D. , Melmed A. J.
Published: February 2003

Field ion micrographs of polycrystalline iron (steel) whiskers are presented. These micrographs indicate that the whiskers examined here possess a two-phase structure consisting of an ordered iron phase and a randomly imaging phase interpreted to be the iron carbide, Fe3C. The iron image indicates not only a high defect density but also the presence of twins.
Corona charging and the piezoelectric effect in polyvinylidene fluoride
Authors: Das-Gupta D. K. , Doughty K.
Published: February 2003

Biaxially stretched PVF2 films were poled by corona charging over a range of surface potentials not exceeding 10 kV. Studies of x-ray diffraction patterns are presented together with the measured values of the piezoelectric constant d31 of such films. The results indicate that the piezoelectricity in this polymer arises from the dipolar orientation of the polar crystallites.
A gnomonic method for the indexing of field ion micrographs
Authors: Henslee S.Paul , Margolis William S. , Johnson Robert M. , Wiseman Carl D.
Published: February 2003

A simplified and accurate method was found for the indexing of field ion micrographs. The procedure makes use of a gnomonic projection that is modified to fit the particular microscope and thus describes the ionic paths. A unique modification was incorporated into the microscope by allowance of a ±15° vertical rotation of the image screen. Calculations of ionic paths at several screen rotations proved that the ionic paths were accurately defined.
Anodic oxides on gallium phosphide for optoelectronic device and processing applications
Authors: Hasegawa Hideki , Sakai Takamasa
Published: February 2003

Properties of anodic oxides formed on GaP with anodization in a mixed solution of glycol and water (AGW) are studied for possible optoelectronic device and processing applications. A new interpretation of anomalous MOS C-V behaviors based on the ’’interface-state band model’’ is presented. Because of the wide band gap, the MOS diode shows a quasi-steady-state deep-depletion behavior and a remarkable charge memory capability. The estimated charge retention time is of the order of several hundred hours. It is demonstrated that light detection and emission can also be achieved with the GaP MOS structures. For processing applications, a new method of low-temperature selective Zn diffusion is presented, which uses anodic oxides as the diffusion source.
Room-temperature coloration of TiO2
Authors: González H. Jesús , González-Basurto J. , Sánchez-Sinencio F. , Helman J. S. , Reyes-Flotte A.
Published: February 2003

Coloration accompanied by an increase of several orders of magnitude in electrical conductivity can be induced at room temperature in rutile single crystals by contact with a Na amalgam. Sodium and hydrogen (which is present as an impurity of metallic sodium) diffuse during treatment. The crystals can be bleached by heating at temperatures T≳100 °C. The coloration process is highly anisotropic, being effective only along the c direction. Coloration is not observed in crystals previously irradiated with neutrons.
Thermoluminescence of LiF TLD-100: Glow-curve kinetics
Authors: Fairchild R. G. , Mattern P. L. , Lengweiler K. , Levy P. W.
Published: February 2003

The thermoluminescence kinetics have been determined for the 13 glow peaks contained in the glow curves obtained from LiF TLD-100 after exposure to 60Co irradiations. The glow curves were constructed from measurements made with recently developed equipment for recording emission spectra at closely spaced temperature intervals. In addition, the recorded data has been subjected to all corrections needed to make it suitable for reliable kinetic analysis. The recorded emission spectra can be described by a single Gaussian-shaped band whose width and peak-energy parameters vary erratically with temperature or, alternatively, by resolving the observed spectra into three Gaussian-shaped bands whose parameters vary with temperatures in accord with theoretical expressions relating the emission-spectra peak energy and full width at half-maximum to the sample temperature. The kinetics and kinetic parameters were independently determined for the two most intense resolved emission bands. All peaks are described by first-order kinetics and the independently determined parameters are in very good agreement. The glow curves for the least intense component are also described by the same kinetics and parameters. Inasmuch as the single-band emission is a superposition of the three components, the same kinetics and parameters apply to the glow curve constructed from unresolved spectra. The identification number, nominal peak temperature in °C (for a heating rate of 10.3 °C/min), the activation energy E (eV), and preexponential factor s (sec−1) for the 13 peaks are as follows: (1) 1.62, 1.04, and 1014; (2) 94, 1.07, and 1013; (3a) 112, 0.987, and 1011; (3) 137, 1.05, and 1011; (4) 170, 1.54, and 4×1015; (5) 190, 2.20, and 1022; (5a) 210, 1.61, and 1015; (6) 235, 1.70, and 1015; (7) 260, 1.79, and 1015; (8) 285, 1.96, and 5×1015; (9) 315, 2.10, and 1016; (10) 345, 2.19, and 1016; (11) 370, 2.27, and 1016. The unusual value of s=1022 for the 190 °C peak, previously reported by other authors, was obtained during this study. However, it appears that this value can be obtained from relatively simple mechanisms and one of these is described.
Intermediate infrared optical absorption in intrinsic tellurium
Authors: Ades S. , Champness C. H.
Published: February 2003

Measurements of the absorption coefficient α and reflectivity have been made on intrinsic tellurium samples between about 5- and 20-μm wavelength λ at room temperature. In all cases, the samples were thicker than 1/α and had their surfaces prepared by chemical polishing only, to minimize surface damage. The variation of transmittance with sample thickness d was found to be strictly inversely exponential, even for small αd, indicating nonobservance of multiple internally reflected rays. For E⊥c, high transparency was found in the intermediate infrared range, with α of the order of 0.1 cm−1 near λ=8 μm. With this orientation, α was found to be proportional to λ2, in accordance with the classical Drude theory for free-carrier absorption. It is shown that this result is also consistent with the quantum treatment of Schmidt, which assumes acoustic lattice scattering, and it is concluded that this mode may be dominant at room temperature. For E∥c, a broad absorption shoulder is found between 6 and 9 μm on the short-wavelength side of the well-known p band.
Secondary emission from multialkali photocathodes
Authors: Ghosh C. , Varma B. P.
Published: February 2003

The secondary emission from high-sensitivity multialkali photocathodes has been measured. The secondary emission from these photocathodes are found to be very high. A maximum value of 39 for the yield was obtained at a primary energy of 1800 eV. Such high yields have seldom been obtained in materials with positive electron affinity. The approximate escape depth of the secondary electrons was calculated by applying the phenomenological theory of secondary emission. The escape depth was found to be about 400 Å.
Endurance studies on MNOS devices
Authors: Schuermeyer Fritz L. , Young Charles R.
Published: February 2003

The effect of write-erase cycling on surface-state generation and on retentivity in MNOS devices was studied. Annealing behavior of surface states and of threshold-voltage-decay rates was investigated. It is concluded that the threshold-voltage-decay rate is not controlled by surface states but by the nitride conductivity.
Absolute efficiency of CsI : Na phosphor under fluoroscopy conditions
Authors: Nomicos Constantine D. , Giakoumakis George E. , Ravanos Christos E. , Euthymiou Paraskevi C. , Sandilos Panayotis X.
Published: February 2003

The absolute x-ray efficiency of CsI : Na phosphor screens was measured under fluoroscopy conditions, as a function of x-ray tube voltage and for different screen weights. The screens were prepared by evaporation. The critical concentration of Na was determined for which the efficiency of CsI : Na is maximum.
An efficient multielement cathode for high-power electric discharge laser applications
Authors: Seguin H. J. J. , Nam A. K. , Tulip J.
Published: February 2003

The design and operational characteristics of a multielement cathode, suitable for high-power electric discharge laser application is described. The compact structure utilizes a recirculating aqueous electrolyte for uniform current distribution, without the need for external resistive ballast. The simple and inexpensive geometry is suited for large-area scaling.
Annealing of Se-implanted GaAs with an oxygen-free CVD Si3N4 encapsulant
Authors: Inada T. , Miwa H. , Kato S. , Kobayashi E. , Hara T. , Mihara M.
Published: February 2003

Auger electron spectroscopy and differential Hall measurements have been employed to investigate CVD Si3N4 layers as encapsulants for annealing of Se-implanted GaAs. Carrier concentrations exceeding 4×1018 cm−3 can be achieved by implanting 100-keV Se ions into Cr-doped semi-insulating GaAs heated at 400 °C and by subsequent annealing at 900 °C using an oxygen-free CVD Si3N4 encapsulant, in which out-diffusions of Ga and As are sufficiently depressed.
Diffusion coefficient determination using a size-variation technique
Authors: Stark Walter A.
Published: February 2003

Conventional techniques for determining diffusion coefficients in solids measure the rate of approach to saturation. A alternative technique, which does not require saturation, determines the diffusion coefficient by a comparison of the solute uptake in two or more different size particles after some definite exposure time. A description of this procedure for spherical particles is presented, together with a working nomograph suitable for the planning and quick analysis of experiments.
Optical properties of uranium plasmas
Authors: Maceda Edward L. , Miley George H.
Published: February 2003

The opacity and radiative-energy current due to line radiation is calculated for a U235 plasma with a temperature range 5000–8000 °K. Also, a variation in the neutron flux of 2×1012 to 2×1016 neutrons/cm2 sec is considered. The plasma forms a cylinder with a diameter and height of 1 m. Because the electron states in uranium lie below 5 eV, recombination is the principal excitation mechanism. At and above 6000 °K, inversions are found and, at all temperatures, the line radiation at line center is greater than the corresponding blackbody radiation. An example of this is the 28763–5762-cm−1 transition in neutral uranium, where the Planck function at 5000 °K is 6.49×10−6 ergs/cm2, and the calculated radiative-energy current is 1.492×10−4 ergs/cm2. Negligible changes in the radiative-energy current are observed for changes in the neutron flux at a given temperature. The opacity at 5000 °K agrees with Parks’s previous calculations, and recombinational excitation explains the variation in the opacity with temperature.
Thomson scattering of EM pulses by random fluctuations in plasmas: Effect of self-focusing
Authors: Sodha M. S. , Maheshwari K. P. , Sharma R. P. , Kaushik S. C. , Krishan Vinod
Published: February 2003

In the present paper the authors have investigated the transient Thomson scattering of the EM pulses (having Gaussian intensity distribution in space and time) from a collisional plasma with random inhomogeneities. Because of a Gaussian intensity distribution of the pulse in a plane transverse to the pulse propagation, the electrons get redistributed and affect the scattering accordingly. When the power of the pulse is greater than the critical power for self-focusing, the backscattered power is found to exhibit a maximum at a particular time, dependent on the parameters of the pulse and the plasma.
Relativistic study of electromagnetic waves in the accelerated dielectric medium
Authors: Tanaka Kazuo
Published: February 2003

The problem of electromagnetic wave propagation in the linearly accelerated dielectric medium is studied by using the extended Maxwell-Minkowski theory. First, from the viewpoint of the extended Maxwell-Minkowski theory, the well-known problem of reflection and transmission of electromagnetic waves by the moving dielectric with constant velocity is studied by using the Galilean transformations instead of the Lorentz transformations. It is shown that the problem can be solved and the same results can be obtained as those obtained by using the Lorentz transformations. Then, with the aid of the covariant properties of Maxwell’s equations, a rigorous solution of the electromagnetic wave in a linearly accelerated dielectric is founded. The phenomena of bending of light rays in the accelerated system and the relativistic energy velocity and phase velocity addition law for the accelerated motion are derived from the rigorous solution obtained. The problem of reflection and transmission of the electromagnetic wave at normal incidence by a linearly accelerated dielectric interface is solved using the solution obtained. The reflected wave and the transmitted wave are obtained, and their interesting properties concerning the Doppler effect and drag effect are discussed in comparison with the case of constant-velocity motion.
On the determination of phase and group velocities of dispersive waves in solids
Authors: Sachse Wolfgang , Pao Yih-Hsing
Published: February 2003

A new technique is developed to determine the dispersion relation and the propagational speeds of waves in dispersive solids. The phase spectrum of a broadband pulse is linearly related to the dispersion relation of the dispersive medium. The method is simpler than the continuous-wave phase comparison technique. Application is made to measure the phase and group velocities of waves in fiber-reinforced composite materials and in thin wires. This technique is expected to be applicable to measurements of acoustic or electromagnetic wave speeds in other dispersive media.
Efficient coupling of LED and spherical-ended fiber
Authors: Hasegawa Osamu , Abe Masayuki , Yamaoka Toyoshi
Published: February 2003

A model of the coupling of a Lambertian LED and a spherical-ended fiber is proposed and analyzed by means of geometrical optics. The system of this optical coupling can be regarded as a simple optical system which consists of a light source, a principal plane, and an aperture stop. The model analyzed is that in which a light source and an aperture stop are on the anterior and the posterior focal planes, respectively. The maximum incident angle φm into the fiber is determined from the condition that the ray passing through the anterior focal point is not obstructed by the aperture stop, which has the same diameter as the core one. According to the theoretical analysis, the coupling efficiency for the Lambertian LED and the spherical-ended fiber is sin2φm provided that d0?dc and (dc/d0)2 sin2φm provided that d0≳dc, where d0 is the emitting diameter and dc is the critical diameter defined by the critical angle φc of the light propagation in the fiber. For two kinds of LED’s with emitting diameters of 35 and 85 μm, the coupling experiment was performed on spherical-ended fibers which had a numerical aperture NA of 0.14 and a core diameter of 85 μm. The spherical ends of fibers were fabricated to radii r from 75 to 170 μm. A good agreement between the theoretical and experimental results is obtained. In the case that the emitting diameter is 35 μm and the spherical radius is 75 μm, the calculated efficiciency is 6.3%, three times greater than that for a flat-ended fiber. It is shown that the coupling efficiency can be improved by using the spherical-ended fiber with the spherical radius less than about d1/(4NA), where d1 is the core diameter. It is also shown that the maximum coupling efficiency for the LED with the emitting diameter of d0 is obtained by the fiber with the spherical radius less than about d0/(4NA).
Ranges of 10–30-keV deuterons implanted into solids
Authors: Bo/rgesen P. , Bo/ttiger J. , Möller W.
Published: February 2003

Ranges of 10–30-keV deuterons implanted into amorphous C, and polycrystalline Al, Ni, and Zr have been measured via the D(3He,α)1H nuclear reaction. The finite depth resolution, which has been determined separately, was taken into account in the evaluation of the data. Monte Carlo computer calculations have been carried out for comparison with the experimental results. Generally, good qualitative agreement is observed.
Physical behavior of the neck-down region during furnace drawing of silica fibers
Authors: Paek U. C. , Runk R. B.
Published: February 2003

During the drawing of optical fibers, the maintenance of a uniform fiber diameter is a difficult task. Parameters affecting the diameter variations are the temperature and viscosity distributions within the neck-down region, the neck-down shape, and the fiber drawing tension. A physical model is presented that predicts the neck shape and temperature distribution within the neck-down region during the drawing of a high silica rod into a fiber. The model is formulated by an iterative technique to obtain solutions from the coupled equations of momentum and energy for given fiber-drawing conditions. It is demonstrated that the predicted values of the viscosity, neck shape, and drawing tension agree well with those of measured values.
Elastic properties of a lithia-alumina-silica glass-ceramic at high pressure
Authors: Fritz I. J.
Published: February 2003

Ultrasonic measurements have been made on a commercial glass-ceramic (Corning Pyroceram 9608) at high pressure. Pulse transit-time data taken at room temperature and at pressures up to 2.6 GPa (26 kbar) have been analyzed to determine the pressure dependences of the sample strain and various elastic parameters. Anomalous behavior is observed, with all the elastic parameters decreasing as a function of pressure up to ∼2.4 GPa and, thereafter, increasing with increasing pressure. Direct strain-gauge measurements are in agreement with the results obtained from the analysis of the ultrasonic data. The possibility that the anomalous behavior is caused by a pressure-induced phase transition is discussed.
Isothermal compression of Al and Ag to 120 kbar
Authors: Syassen K. , Holzapfel W. B.
Published: February 2003

Isothermal compression curves for Ag and Al have been determined by high-pressure x-ray diffraction studies in the 120-kbar range. The pressure-volume relations can be represented by a Birch equation with B0=727 kbar and B′0=4.30 for Al, and B0=1061 kbar and B′0=4.70 for Ag (B0 is the isothermal bulk modulus at ambient conditions and B′0= (dB/dP)P=0. Systematic errors of the PV relations are estimated to be ±2 kbar at 100 kbar relative to the NaCl pressure scale.
Volumetric study of the α→α′ phase transformation of cerium and its implications regarding the crystal structure of α′-cerium.
Authors: Bocquillon G. , Epain R. , Loriers C.
Published: February 2003

The volume change of cerium metal at the α→α′ phase transformation at 51 kbar is found to be (1.5±1) % from macroscopic measurements made in the sliding-anvil apparatus SAD 2. This value supports the proposal by Zachiarasen and Ellinger that the high-pressure forms of cerium above 51 kbar are a stable orthorhombic form with the α-uranium type of structure and a metastable monoclinic body-centered form with a deformed face-centered structure and invalidate all the other crystal structures reported so far for α′-cerium.
Superchanneling of accelerated ions through crystals with large channels
Authors: Goetzberger A. , Fritzsche C. R. , Diehl R.
Published: February 2003

350-keV protons were transmitted through beryl crystals of thicknesses up to 58 μm. The dependence of the output/input flux ratio upon the angle of incidence indicates the existence of a superchanneling effect caused by the large channel diameter. The channel effect is strongly dependent on purity and perfection of the crystals.
Nonlinear thermal redistribution of boron impurities in SOS device structures
Authors: Maldonado C. D. , Murphy W. D.
Published: February 2003

The redistribution of impurities in SOS (silicon-on-sapphire) -type structures during thermal oxidation is formulated and solved numerically for the nonlinear case when the diffusion coefficient depends on the impurity density. The method of lines is used to reduce the nonlinear boundary-value problem to a stiff system of initial-value ordinary differential equations, which is solved by Gear’s method. A computer program based on the numerical solution has been developed and applied to an illustrative example considered previously for the linear problem. The program was then applied to three realistic examples pertaining to the redistribution of ion-implanted boron impurities in SOS-type structures during thermal oxidation.
Tin-doping effects in GaAs films grown by molecular beam epitaxy
Authors: Wood C. E. C. , Joyce B. A.
Published: February 2003

The incorporation of Sn atoms as donor impurities in autoepitaxial GaAs films grown from beams of Ga and As4 by the process of molecular beam epitaxy (MBE) has been studied in several ways. The sticking coefficient of Sn, as measured directly by modulated beam techniques, is unity over a wide range of growth conditions, and the Sn diffusion rate is low up to the maximum growth temperatures used (820 K). In thick (?1 μm) films, away from the substrate-film interface, free-donor profiles are flat, with a free-carrier concentration proportional to the Sn flux. Electron mobilities at 300 and 77 K as a function of free-donor concentration are close to theoretical, assuming a fairly low level of compensation, although there is no evidence for Sn atoms being incorporated as acceptors. There is, however, a surface rate limitation to the incorporation of Sn atoms, so that until a steady-state surface population of Sn is formed, which can be as large as 0.1 monolayers, the free-donor density is not constant, but increases exponentially to a steady-state value. The rate constant associated with this process is strongly dependent on the As4 flux, and to a lesser extent on substrate temperature. At constant growth rate (Ga flux constant) and constant Sn flux, therefore, transients are observed in the free-donor concentration at the beginning of growth, or where the As4 flux or substrate temperature are changed during growth. A simple chemical model is shown to describe this behavior.
Characterization of niobium point contacts showing Josephson effects in the far infrared
Authors: Weitz D. A. , Skocpol W. J. , Tinkham M.
Published: February 2003

The high-frequency behavior of niobium cat-whisker point contacts has been studied using radiation from an optically pumped far-infrared laser. When the point contacts are classified on the basis of their high-frequency performance, their dc I-V curves fall into recognizable groups. We find that the ac Josephson effect has a strong correlation with the gap-related structure on the I-V curve, but none at all with the apparent excess current observed in all the contacts. For high-performance junctions, these and other features of the I-V curves are very reproducible from contact to contact, allowing a comparison with the available theories. The experimental evidence seems to suggest that our point contacts are best modeled as extremely small metallic constrictions.
Magnetic properties of amorphous and crystalline GdFe2
Authors: Vittoria C. , Lubitz P. , Ritz V.
Published: February 2003

The magnetic and structural properties of GdFe2 thin films prepared by electron beam coevaporation have been investigated. The measurements included magnetic resonance, magnetometer, the Mössbauer effect, x-ray diffraction, and Auger analysis. Comparisons were made between the properties of the as-deposited amorphous films and films annealed at various temperatures up to 500 °C, at which point crystallization is essentially complete. The measured magnetization for amorphous films was less than the magnetization measured in crystalline films at all temperatures. The magnetic moment of the Gd and Fe ions within their respective magnetic sublattices were determined to be 7.6 and 2.12μβ for crystalline GdFe2. The sublattice moments in the amorphous case do not change appreciably from the crystalline case. The sublattice g values were determined to be slightly temperature dependent below 77 K. The Landau-Lifshitz magnetic damping parameter was determined to be ∼1×107 and 2×107 Hz for amorphous and crystalline films, respectively. For amorphous thin films on a Si substrate overcoated with Si, the spin-wave mode field positions obeyed a n2 law with A/M=1.2×10−9 Oe cm2, in agreement with calculation.
Uniaxial-stress effects in a 95/5 lead zirconate titanate ceramic
Authors: Fritz I. J.
Published: February 2003

The response of a lead zirconate titanate ceramic to statically applied uniaxial stresses in the range 0–0.4 GPa has been investigated. The material studied was a niobium-doped composition with the chemical formula Pb0.99Nb0.02(Zr0.95Ti0.05)0.98O3. Properties measured as a function of stress include electrical charge release from poled specimens, ferroelectric hysteresis-loop behavior, macroscopic strains, and ultrasonic velocities. Data from the experiments exhibit anomalous behavior at low-stress levels (0.05–0.2 GPa). Comparison with similar data obtained under conditions of hydrostatic pressure indicate that the anomalies observed in the uniaxial-stress experiments are caused by domain-reorientation processes rather than by the ferroelectric to antiferroelectric phase transition. This transition occurs at 0.32 GPa under hydrostatic-pressure conditions, but no evidence for it is seen in the uniaxial-stress measurements to 0.4 GPa. The relationship of the present results to other uniaxial-stress studies and to shock-wave studies on ferroelectric ceramics is discussed.
On the supralinearity of Mg2SiO4 : Tb thermoluminescent dosimeters
Authors: Yamazaki T. , Tomimasu T. , Mikado T. , Chiwaki M.
Published: February 2003

The measurement of the response of Mg2SiO4 : Tb thermoluminescent dosimeter against radiation dose has been made and the result is presented. The supralinearity observed is characterized by (1) a clear power-law relation between the response and the dose and (2) a sharp transition from the linear to the supralinear region, a behavior which has not been found in other phosphors. A few existing models are shown to be insufficient to explain the above features. A new model seems to be appropriate.
Thermionic emission of alkali ions from zeolites
Authors: Pargellis A. N. , Seidl M.
Published: February 2003

The thermionic emission of positive alkali ions from zeolites has been investigated in the high-voltage pulsed regime. Current densities of up to 1 A cm−2 have been obtained using 2-μs-long 30-kV pulses. This is about two orders of magnitude larger than currents obtained in the low-voltage dc regime. There are two major reasons for this difference. First, the currents have a Schottky-type dependence on electric field, and second, the current rapidly decays in dc operation. The desorbed ion fluxes are up to a million times larger than those for neutrals for high-voltage pulses. The ratio of these two fluxes can be described by the Saha-Langmuir equation. This indicates that the alkali atoms and ions are in thermal equilibrium at the surface of the zeolite.
Tuning characteristics of parametric interactions in a three-dimensional LiNbO3 optical waveguide
Authors: Uesugi Naoshi , Daikoku Kazuhiro , Fukuma Masaharu
Published: February 2003

Tuning characteristics of parametric interactions in a three-dimensional LiNbO3 optical waveguide fabricated by a Ti in-diffusion process are revealed by experimenting on both second harmonic and sum frequency generation. The experimental results agree well with the theoretical results, where Sellmeier’s equation and Marcatili’s approximation are used to evaluate the tuning characteristics of parametric interactions. The waveguide parameters are decided by the experimental phase-matching temperature difference between the generated second harmonic fundamental and higher-order modes.
Precise determination of refractive-index changes in Ti-diffused LiNbO3 optical waveguides
Authors: Minakata Makoto , Saito Shoichi , Shibata Masashi , Miyazawa Shintaro
Published: February 2003

A new method for determining refractive-index changes in Ti-diffused LiNbO3 optical waveguides is reported. The measurement process was as follows: (1) Diffusion profiles and Ti concentrations in LiNbO3 optical waveguides were measured by an x-ray microanalyzer. (2) Ti concentrations in the samples were converted into refractive-index changes using calibration curves which gave the relation between Ti concentrations and refractive-index changes. The calibration curves were obtained from highly Ti-diffused LiNbO3 samples, as well as Ti-doped LiNbO3 single crystals. As an example, the maximum refractive-index changes of a Ti-diffused LiNbO3 optical waveguide made at 1000 °C for 10 h were determined to be Δne=1.05×10−2 and Δno=7.7×10−3.
Multidipole plasma density
Authors: Lang Alan , Hershkowitz Noah
Published: February 2003

The primary-electron bias voltage and the neutral-pressure dependence of plasma density in a multidipole device are investigated. Experimental data are described by a simple model which takes into account the production of multiple electron-ion pairs by each ionizing primary electron.
Boundary layer with a traveling magnetic field and Hall currents
Authors: Nageswara Rao B. , Mittal M. L.
Published: February 2003

The present analysis gives the influence of the Hall currents on the growth of a boundary layer in a parallel-plate channel in the presence of a transverse traveling magnetic field. The analysis is made by using a perturbation technique in terms of the iteraction parameter. The boundary layer thickness as well as the skin-friction coefficient decreases due to the Hall currents.
Dislocation interactions in cylindrical surface crystals
Authors: Ichikawa Masahiro , Chou Tsu-Wei
Published: February 2003

Cylindrical crystals are generally found in biological structures where the structural units are packed in two-dimensional lattices. Dislocations are believed to be responsible for the movement and shape changes of cylindrical crystals in many biological systems. We investigated the dislocation interactions in thin cylindrical crystals. The elastic field of a dislocation dipole with Burgers vectors normal to the cylinder axis is obtained by employing a first-order shallow-shell theory. The variation of climb force as a function of dislocation separation distance is expressed in a closed form. The significance of the present finding as related to the study of contractile mechanisms in biological systems is also discussed.
Light-activated storage device (LASD)
Authors: DiMaria D. J. , DeKeersmaecker R. F. , Young D. R.
Published: February 2003

A novel nonvolatile semiconductor memory called the light-activated storage device (LASD) is reported. It consists of a thin metal–silicon-dioxide–silicon (MOS) structure with the SiO2 layer ion implanted with impurities such as As or P which create light-sensitive traps. The sites resulting from the implantation are charged (’’write’’ operation) by using light and a moderate-voltage bias to photoinject carriers from the metal or silicon contacts into the SiO2 where some of the carriers are trapped on these sites as they traverse the oxide layer. It is discharged (’’erase’’ operation) by using light and a low-voltage bias to photoionize these trapped charges while blocking photoinjection from the contacts with the internal field of the trapped charges. The ’’write’’ and ’’erase’’ properties of this structure are investigated as a function of the ion used (As or P), ion fluence, ion energy, and oxide thickness. The LASD is shown to have reproducible cycling properties and excellent charge retention.
Mode degeneracy in magnetic garnet optical waveguides with high Faraday rotation
Authors: van Engen P. G.
Published: February 2003

TE-TM mode conversion was studied in LPE-grown garnet films with high Faraday rotation (up to 1800 °/cm at 1.15-μm wavelength) and positive uniaxial anisotropy. High conversion ratios (80–90%) were found for several modes. The phase matching is satisfactorily explained by the birefringence in the film resulting from the misfit stress.
Electron-beam-induced dislocation climb in ZnSe
Authors: Stacy W. T. , Fitzpatrick B. J.
Published: February 2003

Dislocations in solution-grown ZnSe were observed to climb when exposed to a focused 100-kV electron beam in an electron microscope. The resulting dislocation networks are complex and are generated in a three-step sequence: (1) existing dislocations extend their length by forming dipoles, (2) a thin layer of radiation-damaged material forms at the beam entry surface, and (3) dislocation loops originating at the damaged layer grow into the sample bulk. From a diffraction contrast analysis the loops were determined to be of the extrinsic type. From annealing experiments it is concluded that the beam-induced climb involves vacancy emission at the dislocation and that the process is energized by electron-hole recombination.
Anharmonicity and elastic hysteresis of fused SiO2 fibers
Authors: Kobayashi Hiroshi
Published: February 2003

For the purpose of obtaining load-elongation curves, fused SiO2 fibers a few μm in diameter, which were produced by Nichols’s method, were tested using the tensile-testing machine which was specially prepared by Hiki and the author. Load-elongation curves obtained showed nonlinearity which indicates that Young’s modulus becomes larger with increasing strain. Moreover, a distinct elastic hysteresis was observed in which increasing curves have different traces from decreasing ones and return to the origin smoothly. The nonlinearity of load-elongation curves is explained as the macroscopic appearance of anharmonic interaction between atoms. On the other hand, an elastic hysteresis which has not been observed in metal whiskers is assumed to be caused by complex deformation of a random network of fused SiO2 fibers.
Static and dynamic fatigue of high-strength glass fibers coated with a uv-curable epoxy-acrylate
Authors: Schonhorn H. , Wang T. T. , Vazirani H. N. , Frisch H. L.
Published: February 2003

The static and dynamic fatigue of high-strength glass fibers drawn with a 250-W CO2 laser and coated with a uv-curable coating is presented and analyzed with respect to current theories. Theories of Charles and those of Wiederhorn and Evans are shown to reduce to a simple expression which accounts for the static- and dynamic-fatigue data. Further, the strength of the coated glass fibers is directly proportional to the inverse temperature.
Stress-wave propagation in Al2O3-epoxy mixtures
Authors: Munson D. E. , Boade R. R. , Schuler K. W.
Published: February 2003

One-dimensional shock loading, attenuation, and recompression data from gas-gun experiments on mechanical mixtures of alumina powder and epoxy were used to develop model parameters for stress-wave propagation. Specimens with 0.42, 0.34, and 0.20 volume fractions of alumina were investigated. Calculations simulating the experiments were performed using an extension of a Maxwell rate-dependent model which requires definitions of the instantaneous, equilibrium, and relaxation functions as input. Experimental observations indicated the shock-loading behavior is identifiable with the equilibrium response, and the release wave behavior is closely related to the instantaneous response. To model these effects, for negative strain rates, indicative of expansion, a relaxation time of 0.25 μs was used; this value gave agreement between the calculated and measured release wave behavior. For positive strain rates, indicative of compression, the relaxation time was permitted to decrease to 0.03 μs, which caused the shock-loading response to be dominated by the equilibrium function. Hugoniot data determined from the stress-wave profiles were compared to effective modulus calculations. This comparison suggests a strength effect which can be interpreted as an interaction between the components. Analysis using a self-consistent scheme for spherical particles shows good correlation between calculated and measured ultrasonic and Hugoniot intercept wave velocities.
Thermoluminescent response of LiF (TLD-100) to 0.1–5-keV electrons: An energy-range relationship and comparison of the TL glow with TSEE glow curves
Authors: Lasky J. B. , Moran P. R.
Published: February 2003

Thermoluminescence from freshly cleaved TLD-100 exposed to monoenergetic electrons from 3 to 30 keV behaves as if the electrons induce the luminescence over an effective range which follows R (μm) =1.62×10−2E1.73. Between 0.1 and 1 keV the effective range is essentially constant at 0.3 μm. The glow curves for these crystals sampled with electrons at 1 keV and below are very similar to TSEE curves reported by others, provided similar annealings have been performed. Annealing in air alters these curves from that of the bulk response presumably because water vapor diffuses inward at the surface. We believe this diffusion is what has caused past disagreement in curve shape between TSEE and bulk thermoluminescence curves.
The analysis of casting conditions of amorphous alloys
Authors: Takayama S. , Oi T.
Published: February 2003

Processing conditions of Fe40Ni40B20 amorphous ribbon, 10 mm in width, have been investigated by employing a single roll-casting method. To explore the conditions, the temperature of the melt, the angular velocity of the roll, and the ejection pressure of the melt were varied in turn while holding the other quenching parameters constant. The thickness of the as-quenched glassy ribbon increases monotonically with increase of ejection pressure and decreases monotonically with increase in roll speed. A mathematical treatment of the conditions for obtaining good-quality glassy ribbon has been attempted, and shows a good accord with the present experimental data.
Efficient electron-beam-deposited ITO/n-Si solar cells
Authors: Feng Tom , Ghosh Amal K. , Fishman Charles
Published: February 2003

Indium tin oxide/silicon heterojunction solar cells with power conversion efficiencies of 10% in AM1 solar spectrum were fabricated. The indium tin oxide (ITO) films were deposited onto n-type silicon by electron-beam evaporation of a mixture of 90 : 10 molar% In2O3 : SnO2 powder. As in SnO2/n-Si cells, the efficiencies of these cells depend upon the angle of incidence of the ITO vapor stream to silicon. We have found the photovoltaic properties of these cells to be very similar to those of SnO2/n-Si devices.
Beam stability and current loss in magnetic insulation
Authors: Bergeron Kenneth D. , Poukey James W.
Published: February 2003

A two-dimensional electromagnetic particle code has been used to investigate the effect on magnetic insulation of a beam of electrons injected longitudinally into the coaxial vacuum gap. It is found that a parapotential beam, though force balanced at the input, does not propagate more than a short distance before being totally disrupted, apparently by beam instability. Even a very hollow beam is lost to the anode by a diffusion process which may explain the anomalous current leakage observed in some experiments.
Recombination structures and their effects in depleted low-pressure gas discharges
Authors: Hasker J.
Published: February 2003

Experiments have been performed on low-pressure sodium discharges with substantial radial ground-state depletion in both homogeneous and radial-dependent recombination structures. For the 35 W low-pressure sodium lamp the gain in lamp luminous efficacy is about 10% at optimum structure density. A simplified discharge model is presented and used to discuss and understand the experimental results. This model also provides insight into the influence of the radial-structure density distribution on the electron and ground-state density profiles as a function of the electron density.