bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen bonding in polyamides
Authors: Schroeder L. R. , Cooper S. L.
Published: February 2003

An infrared thermal analysis technique was used to measure the enthalpy of dissociation of hydrogen bonds in various polyamides and to test the influence of the type of nylon, annealing time, and moisture content on the strength of hydrogen bonding. Nearly all of the NH groups were found to be hydrogen bonded at room temperature for every nylon tested. Enthalpies of dissociation ranged from about 8–12 kcal/mole. Tensile tests were also performed to determine the effects of the same variables on Young’s modulus of the polyamides. The results show that while the enthalpy of dissociation of the hydrogen bonds was not significantly changed by the type of nylon or any of the tested variables, the modulus was strongly affected by several of the treatments. Since factors which do not affect the strength of hydrogen bonding do have a large effect on the modulus and failure mode, it may be inferred that hydrogen bonding does not play a primary role in determining the mechanical properties of polyamides.
Dislocation velocities and electronic doping in silicon
Authors: Kulkarni S. B. , Williams Wendell S.
Published: February 2003

Measurements of velocities of dislocations in silicon as a function of temperature and type of electronic impurity doping using Lang x-ray topography are reported. Doping with n- and p-type impurities results in an increase of the dislocation velocity and a decrease of the activation energy for both screw and 60° dislocations. The double kink nucleation and migration model of Gerk that takes kink motion to be limited by Auger electron-hole recombination-generation processes yields a satisfactory description of the experimental results.
An x-ray study of diffusion in the Cu-Ag system
Authors: Unnam J. , Houska C. R.
Published: February 2003

The interdiffusion coefficients for both solid phases of the Ag-Cu system have been determined from x-ray diffraction and electron microprobe data. Specimens containing 3.2 μm of Ag on a (111) -oriented Cu crystal were used for the x-ray studies, while a 15-μm deposit of Ag was used for the probe specimens. Composition profiles for each phase were obtained from the x-ray intensity bands and a new iterative one-dimensional model was applied to determine the composition-dependent diffusion coefficients. The average diffusion coefficients for both phases are nearly equal at about 10−10 cm2/sec at 750 °C, the diffusion temperature. Also, the solubility for the Ag-rich phase is about three times the solubility for the Cu-rich phase. These conditions result in interface reversal, i.e., the interface first moves into the substrate and later moves toward the free surface. Structural damage resulting from atomic diffusion was found to be much smaller for the Ag-Cu system than for other single-phase Cu-base specimens that have been examined. Both crystal misorientation (tilt) and subgrains are formed as a result of diffusion. The subgrain shape in the plating depends upon the ratio of the thickness to the initial grain size of the plating.
Elastic properties of UO2 at high pressure
Authors: Fritz I. J.
Published: February 2003

The elastic constants of UO2 have been measured as a function of pressure up to 20 kbar (2.0 GPa) at 23 °C. To within experimental uncertainty, the constants are linear functions of pressure, and no pressure-induced phase transitions occur in this 20-kbar pressure range. The elastic constant data are used to estimate the various polycrystalline elastic moduli and their pressure dependences, and the zero-pressure moduli are compared with data from polycrystalline material. Isothermal moduli are calculated from the adiabatic values. The elastic-constant data are also used to discuss the separation of the ’’pure’’ volume and temperature contributions to the (isobaric) temperature dependences of the elastic constants as well as to estimate the Grüneisen constant, Debye temperature, and equation of state of this material.
Proton-bombardment–induced blistering of vanadium
Authors: Hultgren P. J. , Scott T. E.
Published: February 2003

Samples of annealed and severely cold-rolled vanadium were bombarded at room temperature with 150-keV H+ ions at fluxes from 1.2×1015 to 1.2×1016 H+/cm2 sec to doses of from 3.6×1017 to 3.2×1019 H+/cm2. All samples irradiated to doses greater than 1.1×1019 H+/cm2 exhibited blistering in spite of the fact that temperatures never exceeded the peak miscibility gap temperatures below which vanadium hydride is stable with respect to gaseous hydrogen even at low hydrogen partial pressures. Niobium also blistered under similar conditions. This unexpected observation must be reconciled by any acceptable theory of radiation blistering.
Dielectric relaxation studies in n-butyl-4,5,7-trinitrofluorenone-2-carboxylate/LexanR polycarbonate solid solutions
Authors: Pochan J. M. , Hinman D. F. , Turner S. R.
Published: February 2003

The α and combined low-temperature dielectric relaxations of n-butyl-4,5,7-trinitrofluorenone-2-carboxylate (BuTNF)/LexanR polycarbonate solid solutions have been studied. It has been shown that only in the specific case of the β relaxations in the components does a correlated motion exist. For the α (Tg) relaxations, the relaxation modes are shown to coexist and are dependent upon composition. The intensity of the dielectric Tg relaxation is dominated by BuTNF. The sub-Tg relaxations of the system are different. At intermediate compositions, a correlated β relaxation of the polymer–small-molecule combination is observed. With the exception of the correlated β relaxation, the individual intensities appear to be relative functions of the molar concentrations. This study indicates that BuTNF acts as a plasticizer for the α and γ relaxations of polycarbonates and interacts directly with the phenyl group of the polycarbonate producing a correlated motion. This interaction affects the potential field causing the relaxation, but does not plasticize the relaxation.
Annealing characteristics of ultraoriented high-density polyethylene
Authors: Mead W. T. , Porter Roger S.
Published: February 2003

The annealing characteristics of ultraoriented high-density polyethylene fibers have been studied using differential scanning calorimetry, thermomechanical analysis, and tensile testing. The melting point of unannealed fibers was estimated to be 130 °C using a 10 °C min −1 heating rate. Fiber annealing between 126 and 132 °C split the melting endotherm into two peak melting at 132 and 139 °C. The weight fraction of fiber which had reorganized to the lower melting point increased with annealing time, finally attaining a constant value. However, annealing of laterally constrained fibers below 136 °C did not result in structural changes as detected by calorimetry. Melting-point variations with heating rates≳0.625 °C min−1 indicated the equilibrium melting point of the unconstrained fiber at zero heating rate as 138 °C, while a similarly extrapolated value using heating rates <0.625 °C was ∼132 °C. The linear expansion coefficients rapidly increased near 132 °C and were attributed to the structural reorganization detected by calorimetry. Fiber annealing markedly decreased the tensile modulus from 50 GPa towards the 1 GPa observed for the unoriented polyethylene. The annealing behavior was consistent with the thermal instability associated with the anisotropy of the surface free energies of the ultraoriented crystalline fibers as well as sources of melting-point reduction such as defects.
KxRb1−xTiOPO4: A new nonlinear optical material
Authors: Zumsteg F. C. , Bierlein J. D. , Gier T. E.
Published: February 2003

KxRb1−xTiOPO4, a new nonlinear optical material with coefficients comparable to BaNa2Nb5O15, has been prepared as optically perfect single crystals which are transparent from 350 to 4500 nm. We have shown that the material is phase matchable over its entire transparency range and that 1060-nm radiation can be doubled with minimal beam walk-off. The material is free from optical damage for power densities at least as large as 150 MW/cm2. Also, it is chemically stable and easily polished.
Growth of thick liquid-phase epitaxial GaAs : Si layers and their characterization
Authors: Kachare A. H. , Spitzer W. G. , Whelan J. M. , Narayanan G. H.
Published: February 2003

In this study we compare some of the characteristic properties of liquid-phase epitaxial (LPE) layers of heavily Si-doped GaAs with those of melt-grown GaAs : Si. LPE layers are grown isothermally at 750, 840, and 910 °C. All the layers are p type and have room-temperature carrier concentrations between 4.2×1017 and 4.8×1018 cm−3. Low-temperature photoluminescence measurements of the layers show a single broad band peaked near 1.32 eV, the peak shifting slightly to lower energy after annealing at 1100 °C. Infrared absorption measurements at ∼80 °K of electron-irradiated layers showed SiGa, SiAs, and SiGa-SiAs localized vibrational modes. The integrated absorptions indicate that the Si site distribution is not compatible with p-type conduction and a new acceptor defect is required. Transmission electron microscopy indicates that the layers have very few vacancy-type prismatic dislocation loops and are essentially free of stacking faults. It is concluded that the LPE layers are basically different than melt-grown GaAs : Si in that different acceptor species, other than SiAs, are present in the two materials and the characteristics of these different acceptors are discussed.
Analysis of the ac SQUID with low inductance and low critical current
Authors: Soerensen O. H.
Published: February 2003

The properties of the ac SQUID magnetometer has been analyzed. The results are valid in the low-inductance low-critical-current regime, where the Lri0 producted is belowthe value at which the relation between the enclosed and externally applied magnetic dc flux becomes reentrant. The effects of the screening current circulating in the SQUID ring as well as of the SQUID-ring time constant, τ-Lr/R9 are taken into account. Here LR IS THE SQUID-ring inductance, and R is the shunt resistance in the shunted junction model assumed to describe the weak link. It is shown that for finite values of ωτ, where ω/2π is the pump frequency, the magnetometer response is due to both the flux dependence of the dispersion and f the dissipation in the tank circuit, and that, generally, the two mechanisms contribute simultaneously. Furthermore, for appropriately chosen ac bias conditions theyt may add constriuctively with the result that the optimal response occurs at a definite and finite value of ωτ. If ωτ is increased beyond this optimal value the weak link behavior is dominated by the Ohmic current channel implying that only if the shunt conductance contains a term depending on the superconducting phase-as the so-called cosine-phji term predicted by tunneling theory-the SQUID will stay sensitivity to magnetic fiels for large ωτ. The influence of the cosine-phi term has been included in the analysis, and as expected it is found to play a significant role particularly fior large ωτ. It is, however, also shown that it is nontrivial to ext ract its magnitude from experiments based on the behavior of the ac SQUID, and that the recently published observations using this technique must be reinterpreted.
Analysis of contact pressures attainable using indentors which are bodies of revolution
Authors: Ruoff A. L. , Chan K. S.
Published: February 2003

The elastic behavior of a conical indentor with a rounded tip pressed against a flat anvil has been analyzed. It is found that when the radius of contact extends beyond the rounded tip, the contact radius increases much more rapidly as the pressure increases than it does for the case of a fully spherical or parabolic tip. Consequently, the pressure achieved for a rounded conical tip for a given applied force is considerably less than for a spherical or paraboloidal tip.
Pulse evolution in CO2 lasers
Authors: Casperson Lee W. , Herbst M. J. , Turechek John J.
Published: February 2003

Explicit formulas are examined for the development of optical pulses in gain-switched or Q-switched laser oscillators and for the distortion of such pulses in succeeding stages of laser amplification. The results are compared to data obtained with a TEA CO2 oscillator-amplifier system.
Linewidth measurement and population calculation of a He-Cd laser
Authors: Watanabe Shuntaro , Kuroda Kazuo , Ogura Iwao
Published: February 2003

The radiative linewidth and pressure broadening of Cdii 4416-Å transition have been found to be 56±6 MHz and 8.7±2.9 MHz/Torr from the Lamb dip in a single-mode He-Cd laser. The population densities of the He metastables and Cd upper laser levels and the small-signal gains of the Cdii 4416- and 3250-Å transitions are calculated under the various conditoins of a positive column He-Cd laser through the rate diagram involving most of the important collisional and radiative processes. The calculated results are in trhe fair agreement with the experiments reported by other authors. The saturation of the laser output with an increasing discharge current can be explained by the rapid increase of stepwise excitation from the He metastable and the comparatively slow decrease of the electron temperature. Based on the measured linewidth and$rate diagram, the possibility of high-power pulsed He-Cd laser in a high-pressure region is proposed.
A 2.75-GHz tunable CO2-laser infrared source
Authors: Magerl Gottfried , Bonek Ernst
Published: February 2003

By mixing a tunable millimeter-wave signal with a fixed-frequency CO2 laser beam in an electro-optic crystal inside the laser cavity, a tunable 10-μm signal of high spectral purity was obtained. The continuous tuning range achieved was 2.75 GHz, maximum output power was 0.8 mW.
Darkening mechanisms in silver-halide photochromic glasses: Flash photolysis and ESR studies
Authors: Marquardt C. L. , Giuliani J. F. , Williams R. T.
Published: February 2003

The darkening and subsequent fading of silver-halide photochromic glass upon irradiation with a Q-switched laser pulse has been investigated. Together with new steady-state optical measurements and ESR observations of photolytic Cu++, the data reveal three major components of the darkening at room temperature: prompt (τ<20 nsec) visible absorption due to Cu++ ions in the silver-halide crystallites, slower-rising (τ?7 μsec) absorption due to silver colloids in the crystallites, and a prompt uv band tail due to ions in the matrix glass. The Cu++ component makes a significant contribution to the photochromic darkening at all excitation intensities, whereas that due to ions in the matrix glass becomes significant only for I≳105 W/cm2. Dependence of fading characteristics on intensity of the excitation pulse is shown to be due in part to variation in the relative magnitudes of the three components. Observations on the growth kinetics and temperature dependence of silver colloid formation are found to be consistent with transport properties of silver-halide thin films, supporting the hypothesis that photochromic action takes place primarily in a noncrystalline surface region surrounding the silver-halide crystallites.
Rise kinetics of light-induced modulation of absorption for a CdS crystal
Authors: Long Edward R. , Conway Edmund J.
Published: February 2003

An experimental study has been made of the rise kinetics for changes in optical absorption in a single crystal of CdS which was bulk excited by pulsed laser light. The experimental data were compared to calculations from a simple model involving a bimolecular process. Experimental and calculated values agreed to within the experimental error and confirmed that light-induced modulation of absorption is a bimolecular process.
InP/SiO2 MIS structure
Authors: Messick L.
Published: February 2003

Metal-insulator-semiconductor (MIS) structures were produced by the pyrolitic deposition of SiO2 on InP. The insulating layers were hard and glasslike with a room-temperature resistivity ≳1015 Ω cm at a field of 106 V/cm. Breakdown field strengths are typically between 5×106 and 107 V/cm. The electrical properties of the InP-SiO2 interface were found to exhibit a strong dependence on the SiO2 deposition process parameters. For optimum conditions capacitance/voltage (C/V) measurements suggest that the average interface state density is ∼2×1011 cm−2 eV−1 with flat band occurring at a gate voltage of approximately −0.1 V. Triangular waveform bias sweep frequencies of ≲10−3 Hz are required to attain equilibrium C/V conditions.
Drift mobility determinations using surface-potential decay in insulators
Authors: Perlman M. M. , Sonnonstine T. J. , St. Pierre J. A.
Published: February 2003

Open-circuit dark surface-potential decay characteristics have been measured in positively corona-charged films of solution-cast low-density polyethylene. For initial fields of about 5×105 V/cm, the surface potential V (t) decays linearly for a period of time, after which it is curvilinear. As a result, the time derivative of the surface potential −dV/dt is constant for a period of time, then abruptly decays. This transition is marked by a cusp, and the time it takes this cusp to appear is interpreted as the transit time through the sample of the leading front of carriers, implying a drift mobility of 2×10−10 cm2/V sec. As the initial field is increased, the corresponding −dV/dt decreases and then increases before the cusp appears. Further, the mobility appears to decrease with increasing initial field. The latter two phenomena are interpreted in terms of a mathematical model in which field ionization of centers in the bulk creates trapped space-charge layers, through which the surface layer of carriers then moves. Additional effects due to succesive corona charging and exposure to laboratory air and vacuum are discussed.
Thermodynamics of internal variables in the presence of internal forces
Authors: Valanis K. C.
Published: February 2003

In this paper we have proposed an extension to the current theory of irreversible thermodynamics by introducing the concept of internal force. Within the resulting new framework we show that the phenomenon of creep enhancement, by neutron irradiation, can be explained physically and can be evaluated quantitatively by theoretical means. It is shown that the essential predictions of the theory agree well with experimental observations in the instance cited.
Absence of atomic ordering in Fe-31 at.% Ni alloy
Authors: Veeraraghavan V. G. , Eagen C. F. , Harrison H. R. , Winchell P. G.
Published: February 2003

Atomic ordering in bulk austenitic single-crystal samples of composition Fe-31 at.% Ni was investigated using x-ray and neutron diffraction techniques. Samples were annealed between 450–550 °C for time periods between 1.5 h and 55 days. No superlattice peak was observed in any case providing no evidence of long-range order in these samples. X-ray studies on martensitic samples of the same composition revealed a tetragonality of about 0.4% which was increased insignificantly by the ’’ordering’’ heat treatment given to the austenite prior to the martensitic transformation. If martensite tetragonality is linearly related to the difference in the first and second short-range order parameters of the austenite (as seems likely in this alloy) this observation supports and extends the results of the studies on the austenitic single crystals.
Effect of nuclear radiation on the elastic moduli of zircon
Authors: Özkan Hüsnü
Published: February 2003

Zircon crystals that have been damaged by a naturally occurring radioactive contaminant, referred to as metamict zircons, have density values ranging from 4.70 to 3.90 g/cm3. The present work is a study of the effect of the damage on the single-crystal elastic moduli. A systematic and very marked decrease (i.e., up to 69%) of the elastic moduli with density have been observed. All the longitudinal and the shear elastic moduli decrease with radiation damage and approach two common saturation values of 1.5×1012 and 0.49×1012 dyn/cm2, respectively. Present observation of the elastic moduli of the radiation-damaged zircon crystals confirms Warren’s theoretical predictions concerning the effect of different pore geometries on the compressibility. Qualitative correlation of the elastic moduli with the structural changes arising from radiation damage in zircon crystals suggests that the marked decrease of the elastic moduli in the radiation-damaged zircons is caused by the nonspherical defect clusters, microcracks, and pores generated during radiation damage. Thermal annealing, x-ray diffraction, elastic moduli, and density measurements on the zircon samples confirm the ’’three-stage’’ process proposed for the metamict transformation of zircons, but the final product of metamictization does not seem to be a mixture of ZrO2 and SiO2 crystallites.
Piezoresistive properties of polycrystalline silicon
Authors: Seto John Y. W.
Published: February 2003

The piezoresistive gage factor of boron-doped CVD polysilicon films deposited with a boron-to-silicon ratio of 2×10−4–1.2 ×10−2 on an aluminum-oxide-insulated molybdenum substrate is found to be between 15 and 27. Annealing increases the gage factor. The higher the doping, the lower is the gage factor. Over the range 20–140 °C, the gage factor is not temperature sensitive if the boron-to-silicon ratio is higher than 2×10−3 during deposition. The temperature dependence increases as the doping concentration is decreased. Our analysis shows that the piezoresistive properties in polysilicon is mainly due to the bulk crystallites.
Low-temperature polarization in impure SrTiO3 ceramics
Authors: Siegwarth J. D. , Morrow A. J.
Published: February 2003

Measurements of the temperature dependence of the dielectric constant and polarization in a constant field have been made on nominally pure SrTiO3 ceramics and SrTiO3 ceramics containing vanadium and niobium impurities. The peaks in the dielectric constant and the remanent polarization observed are apparently not due to a ferroelectric or antiferroelectric transition but rather to the presence of a thermoelectret state existing for permanent dipoles in the materials. It is suggested that the permanent dipoles have an origin similar to the impurity-vacancy dipoles found in alkali halides.
On the stability of electric arc discharges
Authors: Whitman A. M. , Ayyaswamy P. S. , Cohen Ira M.
Published: February 2003

The stability of electric arc discharges has been explored through the use of an energy balance coupled with charge conservation. In order to facilitate this analysis, a new model for the electrical conductivity function has been proposed. Asymptotic solutions for the arc governing equations have been obtained. Stability criteria have been developed from both the linear theory (infinitesimal size disturbance) and from a minimizing solution point of view for finite size disturbances. The results delineate an open region in the stability diagram where arc instabilities may be possible.
Use of probes to measure ion flux in a weakly magnetized plasma
Authors: Rudmin J. W.
Published: February 2003

Experimental investigations undertaken to examine the constancy of plasma density along magnetic field lines in a toroidal multipole field led to the following conclusions: The I-V curves of Langmuir probes differ in regions of strong and weak magnetic fields. In regions of weak magnetic field, a Langmuir probe must be thoroughly cleaned for ion current to saturate, and even the clean probe saturates poorly both theoretically and experimentally, thus introducing ambiguity into the determination of ion flux. A new type of probe was developed for the measurement of ion flux, which is simple to construct and to use. This probe appears to measure ion flux reliably and unambiguously, and confirmed the constancy of plasma density along field lines in a levitated toroidal multipole.
Measurements of alpha particles and protons in laser-driven fusion studies
Authors: Goforth R. R. , Mayer F. J. , Brysk H. , Cover R. A.
Published: February 2003

A time-of-flight detector employing magnetic deflection was used to measure α particles and protons from fusion reactions generated by laser implosion of microshells containing a mixture of deuterium and tritium gases. The density-radius product of the imploded microshell and the ion temperature of the thermonuclear fuel are estimated from the measurements.
Electromagnetic radiation from line sources interacting with a moving magnetoplasma half-space
Authors: Mukherjee P. K.
Published: February 2003

The problem of electromagnetic radiation from the electric and the magnetic line sources interacting with a cold collisionless moving magnetoplasma half-space has been treated. The ambient magnetic field lies parallel to the line source and is oriented normal to the direction of medium motion. For the configuration, the E and H modes become independent, being capable of becoming excited, respectively, by a magnetic and an electric line source. Using the saddle-point method of integration, we have obtained the far-zone radiation fields and the radiation patterns for both line sources. It is found that the fields radiated by an electric line source remain unaffected by the presence of an ambient magnetic field. Numerical results for the far-zone radiation pattern, referring to a magnetic line source, are presented for several values of the parameters characterizing the electron-plasma density, the local magnetic field, and the velocity of the moving medium.
Application of magnetic pinch force to arc plasma processes
Authors: Bhattacharyya D. , Gauvin W. H.
Published: February 2003

An investigation is carried out to estimate the importance of magnetic pinch force in arc plasma devices for heterogeneous processing. This magnetic force is quite appreciable in dc arc devices. A theoretical analysis is presented for its evaluation as a function of the operating parameters. Examples are given for three such cases. Estimated values of pinch force, MHD streaming velocity, mass flow rate, circulation, required generator power, and other related values are presented. The magnetic pinch force has a small effect over the entire volume of plasma but it is significant near the arc root (theoretically, near any constriction) and may be advantageously used in directing solid reagents along the magnetohydrodynamic lines of force into the bulk of the arc, with the help of an external flow.
Resonance Raman study of annealing in cadmium-implanted cuprous oxide
Authors: Hesse J. F. , Abbi S. C. , Compaan A.
Published: February 2003

A resonance Raman scattering study is presented of the annealing behavior of Cu2O implanted with 180-keV Cd++ ions to a dose of 1×1014 ions/cm2. As annealing progressed, large changes were observed in the Raman spectra which were obtained with the 488- and 476.5-nm lines of an argon laser to provide excitation nearly resonant with the 1S ’’blue’’ exciton at 480 nm. A detailed comparison is made of the spectra obtained during annealing with spectra previously reported on unannealed samples implanted with doses ranging from 1.5×1011 to 1.5×1015 ions/cm2. The analysis indicates a strong annealing stage at −250°C, after which apparently less than 1% of the implantation-produced damage remains.
A GaAs/SixOyNz MIS FET
Authors: Messick L.
Published: February 2003

GaAs MIS field effect transistors (FET) have been fabricated using silicon oxynitride (SixOyNz) as the gate insulator. These devices display very little hysteresis and exhibit effective mobilities in excess of 2000 cm2/V sec. This paper reports on both the characteristics of the dielectrics used and on the resulting devices.
LPE of GaAsxSbyP1−x−y continuously graded composition layer
Authors: Nagai Haruo , Noguchi Yoshio
Published: February 2003

GaAsxSbyP1−x−y continuously graded composition layers were grown on GaAs substrate by the LPE method. This technique improves the quality of subsequently grown III-V mixed crystals which have larger lattice constant than GaAs.
Laser action in krypton fluoride and N2 in a fast pin laser
Authors: Sze R. C. , Scott P. B.
Published: February 2003

Fifty μJ of uv laser energy in a krypton fluoride excimer laser and 4.5 mJ of uv energy in the superradiant nitrogen laser have been obtained in a fast pin discharge using transmission-line excitation techniques.
The electric field due to stripline conductors
Authors: Geer James F.
Published: February 2003

The problem of determining the electromagnetic fields about conductors surrounded by various dielectric materials, such as in the analyses of transmission line configurations, computer circuit boards, or, more recently, electro-optic effects in crystals, is studied. A slab of dielectric material of finite thickness is bounded above and below by a second (different) dielectric material of infinite extent. A finite number of infinitely thin stripline conductors are arranged along two parallel planes within (or on the surface of) the middle dielectric in such a way that the geometry of the conductors is symmetric about the center plane of the dielectric. Low-frequency charging of the conductors is assumed so that the electric potential can be computed as for static fields. A singular integral equation is derived for determining the surface charge density on each conductor. This equation is reduced to a Fredholm integral equation which is solved by successive approximations. Expressions for the coefficients of capacitance and induction are derived and an example is given. The general technique of solution seems to be applicable to boundary value problems that have a finite number of parallel material interfaces on which boundary conditions must be met.
Electronic properties of calcium borate glasses containing iron oxide
Authors: Gawish M. , Saleh M. N.
Published: February 2003

The electronic properties of calcium borate glasses containing iron oxide have been investigated. It was found that glasses with an Fe2O3 content less than 20 mole% were amorphous, while those above 20 mole% were devitrified. It was observed that increasing the iron molar content in the amorphous samples caused an increase in their dc conductivity, ac conductivity, dielectric constant, and in the frequency of the dielectric loss peak. Thermoelectric power measurements in the temperature range 400–800 °K indicate that all glasses were n type. The experimental results support the idea of hopping of electrons between the iron ions in the different valence states. An attempt to explain the dc and ac conductions of this system on the basis of a band model and structural changes is presented.
Stress-induced birefringence of solids transparent to 1- to 12-μm light
Authors: Szczesniak J. P. , Cuddeback D. , Corelli J. C.
Published: February 2003

The application of a variation of intensity method using static uniaxial compressive stress and polarized light to measure stress-induced birefringence in the infrared wavelength region (?1 to 12 μm) is described. The measurements were made at 296 °K for the following materials: KCl, KBr, KI, NaCl, LiF, ZnS, ZnSe, SrF2, CaF2, MgF2, and a chalcogenide glass TI-1173; for the alkali halides the values of the stress optic coefficients obtained are in the range ∼1–4 Brewsters, while for the nonoxide glasses values of 9–14 Brewsters were measured. Comparisons of measurements from experiments with a theoretical model which predicts the wavelength dispersion of stress birefringence cannot be fitted better than a factor of ∼2.
Pulse shaping in the iodine laser
Authors: Olsen J. N.
Published: February 2003

The equations for coherent pulse propagation in an iodine laser are numerically solved for various combinations of saturable absorber and amplifier sections. The intention is to translate recent progress in iodine lasers into design of a 80-J subnanosecond laser suitable for use in target irradiation studies. The interaction between saturable amplification and absorption, coherent transient responses, and relaxation of the lower hyperfine levels offer many pulse-shaping possibilities; particular attention is given to pulse shortening and prepulse suppression. For a mode-locked 1.0-nsec oscillator the best balance between performance and complexity suggests three amplifiers of varying bandwidths and one absorber, shortening the pulse to 0.34 nsec. Single element calculations are also shown which clarify the characteristics of these nonlinear components and allow some intuitive understanding.
Correlations of the 4.77–4.28-eV luminescence band in silicon dioxide with the oxygen vacancy
Authors: Jones Colin E. , Embree David
Published: February 2003

A luminescence band observed at 4.77 eV (260 nm) in crystalline and at 4.28 eV (290 nm) in amorphous silicon dioxide has been found to correlate with optical and spin resonance measurements of oxygen vacancy concentrations in a series of irradiated samples. The 4.28-eV (290-nm) band has also been observed in the silicon dioxide layer of metal-oxide-semiconductor (MOS) devices. The intensity of the bands can be increased by chemical reduction in carbon monoxide vapor or decreased by heating in oxygen or water vapor. The 4.28-eV (290-nm) luminescence intensity in the MOS samples also seems to be related to the trapped positive charge in the silicon dioxide. These facts all support a model for the luminescence center as being the oxygen vacancy.
Evidence for the direct impact excitation of Mn centers in electroluminescent ZnS:Mn films
Authors: Tanaka Shyosaku , Kobayashi Hiroshi , Sasakura Hiroshi , Hamakawa Yoshihiro
Published: February 2003

In order to clarify the excitation mechanism of Mn luminescent centers in ZnS:Mn electroluminescent thin films, time-resolved emission spectra in photoluminescence and electroluminescence were measured. In photoluminescence, both emissions arising from ZnS host and Mn centers were observed. For the emission arising from Mn centers, the time delay showing energy transfer from ZnS host to Mn centers was recognized. In electroluminescence, contrary to this, the emission from the ZnS host was hardly observed, and the emission from Mn centers was observed immediately after excitation. These experimental results strongly suggest that the excitation mechanism of Mn centers in electroluminescence is due to the direct impact excitation of Mn centers by hot electrons accelerated in the high electric field in the Zns host. These results are also supported by efficiency measurements.
Determination of conduction band edge and electron affinity in surface potential measurements of BaO
Authors: Haas G. A. , Shih A. , Thomas R. E.
Published: February 2003

A technique is described which utilizes low-energy electron reflections (LEER) to determine the electron affinity and to simultaneously locate the position of the conduction band edge with respect to the Fermi level at the surface. The method involves the use of very-low-energy incident electrons (<10 V) and subsequent analysis of relections using a kinematical approximation for the interference phenomena. The good agreement between the LEER analysis for thin epitaxial films of BaO and low-energy electron diffraction (LEED) lattice spacings indicates the validity of the kinematic approximation for this case. An electron affinity of ∼0.6 eV is obtained which is also in good agreement with previously assumed values. Examples of changes in LEER patterns due to changes in electron affinity are correlated with changes in surface stoichiometry from Auger spectroscopy results, while changes in conduction band edge are found to result from changing the temperature or altering the donor density. Because of the depth resolution which is in the range of five to six atomic layers, LEER can be a suitable complementary surface analysis technique to Auger and LEED studies.
Electron mobility and energy gap of In0.53Ga0.47As on InP substrate
Authors: Takeda Yoshikazu , Sasaki Akio , Imamura Yujiro , Takagi Toshinori
Published: February 2003

Very uniform In0.53Ga0.47As was grown on InP by liquid phase epitaxy. The electron mobility is 8450 cm2/V sec at 300 K and 27700 cm2/V sec at 77 K. The mobility increases with decreasing temperature from 300 to 77 K in contrast to the results of In1−xGaxAs grown directly on GaAs by vapor phase epitaxy. The energy gap of this high-mobility material is 0.750 eV at room temperature.
Physical models for photoactive pigment electrophotography
Authors: Hartmann G. C. , Marks L. M. , Yang C. C.
Published: February 2003

The photographic characteristics of photoactive pigment electrographic imaging systems are investigated by analysis of two model configurations. The results establish which physical parameters control the photographic characteristics. An analysis of electrophoretic display devices is also presented. The models give estimates for the ultimate performance of these systems and make it possible to correlate photographic measurements with related physical phenomena.
Application of synchrotron radiation to x-ray lithography
Authors: Spiller E. , Eastman D. E. , Feder R. , Grobman W. D. , Gudat W. , Topalian J.
Published: February 2003

Synchrotron radiation from the German electron synchrotron DESY in Hamburg has been used for x-ray lithography. Replications of different master patterns (for magnetic bubble devices, Fresnel zone plates, etc.) were made using various wavelengths and exposures. High-quality lines down to 500 Å wide have been reproduced using very soft x rays. The sensitivities of x-ray resists have been evaluated over a wide range of exposures. Various critical factors (heating, radiation damage, etc.) involved with x-ray lithography using synchrotron radiation have been studied. General considerations of storage ring sources designed as radiation sources for x-ray lithography are discussed, together with a comparison with x-ray tube sources. The general conclusion is that x-ray lithography using synchrotron radiation offers considerable promise as a process for forming high-quality-submicron images with exposure times as short as a few seconds.
Early growth of silicon on sapphire. I. Transmission electron microscopy
Authors: Abrahams M. S. , Buiocchi C. J. , Smith R. T. , Corboy J. F. , Blanc J. , Cullen G. W.
Published: February 2003

The early growth of Si on (011̄2) -oriented sapphire has been examined by transmission electron microscopy. The Si was deposited at 1000 °C by pyrolyzing silane in H2. The nominal growth rate was 0.4 μm/min. The morphology of the initial Si growth islands was determined after 0.5, 1.0, 2.5, and 3.5 sec of growth. The basic Si orientation is (100) with [01̄1] Si∥[2̄110] Al2O3. Extensive faulting and twinning is observed leading to {221} orientations. These defects apparently form at coalescence sites of adjacent islands. Also present are four {110} orientations occuring as twin-related pairs. The observation of isolated {110} domains indicates that they nucleate on the sapphire independently of the (100) domains. The {110} and (100) domains grow at about the same rate. Eventually, the {110} domains become trapped by the surrounding (100) domains. The volume percentage of the {110} domains is constant with growth time and equals 7% up to coverages of 90%.
Annealing characteristics of boron- and phosphorus-implanted polycrystalline silicon
Authors: Seto John Y. W.
Published: February 2003

Polycrystalline silicon films implanted with 1×1012 to 7.8×1015/cm2 doses of boron and phosphorus were isochronally annealed up to 1100 °C. Annealing below 600 °C removes the radiation damage created by the implantation process. For doses higher than 1×1014/cm2 an abrupt decrease in sheet resistance takes place between 650 and 700 °C. Hall measurements show that this decrease is the result of a large increase in both the carrier concentration and mobility. Electron-reflection diffraction patterns show that recrystallization takes place within this temperature range. Annealing above 700 °C only causes a small further decrease in the sheet resistance.
Calculation of reflection and transmission coefficients in one-dimensional wave propagation problems
Authors: Mur G. , Nicia A. J. A.
Published: February 2003

One-dimensional electromagnetic wave propagation problems can be formulated exactly in terms of an integrodifferential equation of the Fredholm type. The numerical solution of this equation is often complicated and time consuming. In this paper a method is described of transforming this equation into an integral equation of the Volterra type. The solution of the latter equation can be carried out easily and within a short time.
Secondary electron emission from beams of polystyrene latex spheres
Authors: Hall T. D. , Beeman W. W.
Published: February 2003

Polystyrene latex spheres suspended in a carrier gas of nitrogen are accelerated through a nozzle-skimmer system into a vacuum chamber and ionized in a crossed electron beam. Measurements of the particle beam current as a function of the primary electron energy and current give information on the secondary electron emission yield of the spheres and on the energy distribution of the secondaries. The positively charged spheres provide their own retarding potential for the energy scan of the secondaries. For 260-eV primaries the distribution in energy of the secondaries from polystyrene peaks between 1 and 2 eV. At 5 eV it has fallen to about 40% of its peak value. The yield per incident primary of secondaries (or scattered primaries) whose energy is greater than 5 eV is unity. Some advantages and limitations of the method are discussed.
Effects of transpiration on MHD boundary layers
Authors: Chuang Hsing
Published: February 2003

A steady two-dimensional MHD boundary-layer flow on a flat plate with a uniform transpiration through the plate is considered. The shearing stress at the wall is found to increase with the magnetic interaction number and the transpiration number. Injection will cause a shearing stress reduction and eventually a flow separation which can be suppressed by increasing the magnetic interaction number. The velocity profile is substantially altered by both magnetic interaction and transpiration.
Physical properties of thin-film field emission cathodes with molybdenum cones
Authors: Spindt C. A. , Brodie I. , Humphrey L. , Westerberg E. R.
Published: February 2003

Field emission cathodes fabricated using thin-film techniques and electron beam microlithography are described, together with effects obtained by varying the fabrication parameters. The emission originates from the tip of molybdenum cones that are about 1.5 μm tall with a tip radius around 500 Å. Such cathodes have been produced in closely packed arrays containing 100 and 5000 cones as well as singly. Maximum currents in the range 50–150 μA per cone can be drawn with applied voltages in the range 100–300 V when operated in conventional ion-pumped vacua at pressures of 10−9 Torr or less. In the arrays, current densities (averaged over the array) of above 10 A/cm2 have been demonstrated. Life tests with the 100-cone arrays drawing 2 mA total emission (or 3 A/cm2) have proceeded in excess of 7000 h with about a 10% drop in emission current. Studies are presented of the emission characteristics and current fluctuation phenomena. It is tentatively concluded that the emission arises from only one or a few atomic sites on the cone tips.
Electron-collisional excited-state kinetics in argon and mercury electrical discharges
Authors: Judd O.
Published: February 2003

The effects of inelastic electron-collisional processes on the efficiency for population of electronic states in atomic argon and mercury in an electrical discharge have been studied theoretically as a function of excited-state population fraction. Electron impact excitation rates for the lowest-lying electronic states and rates for ionization from these states have been determined through the use of the Boltzmann transport equation for the range 5×10−17?E/N?10−15 V cm2. It was found that the electron distribution functions are highly non-Maxwellian. Also, the electron excitation rates from the ground state, and consequently the efficiency for populating these states by electron impact, can be reduced significantly as the excited-state population fraction X* is increased; in Ar this occurs for X*≳10−5. These effects impose fundamental limitations on the efficiency and power extraction that can be obtained from electrical-discharage-excited visible and uv lasers that use electronic states in the noble gases for pumping the lasing species.
High-field Ohmic contacts to semiconducting SrTiO3 single crystals
Authors: Jefferies D. J.
Published: February 2003

We have demonstrated a reliable way of making Ohmic contacts to semiconducting strontium titanate using evaporated titanium films. The contacts are Ohmic in low and high electric fields and can support current densities of 108 A/m2. It is possible to form Ohmic contacts on strontium titanate having a wide range of carrier concentrations produced by a number of different techniques. Using these contacts we have observed current saturation in high applied electric fields at low temperature.
Persistence of n-beam dynamical effects in the high-voltage electron diffraction from single thin paraffin microcrystals
Authors: Dorset Douglas L.
Published: February 2003

The theoretically predicted persistence of n-beam dynamical effects in the electron diffraction from single crystals at high voltages due to relativistic effects is experimentally verified. Crystal structure analysis of an orthorhombic paraffin structure was carried out using single-crystal diffraction data obtained at accelerating voltages from 100 to 1000 kV.
Preparation of polished substrates of BaF2
Authors: Bis R. F. , Farabaugh E. N. , Muth E. P.
Published: February 2003

The utilization of Pb1−xSnxTe epitaxial films in high-density forward-looking infrared (FLIR) arrays has been hampered thus far by cleavage steps in the substrates. We have developed a chemical-mechanical polishing technique for the (111) surface of BaF2 which leaves this substrate material single crystal and almost damage free. X-ray data on the polished BaF2 and the Pb0.8Sn0.2Te epitaxial film indicate single-crystal surfaces with very little damage. Furthermore, the electrical properties of the Pb0.8Sn0.2Te epitaxial film are sufficient for FLIR applications.
Estimation of surface energies from phonon frequencies for bcc and fcc metals
Authors: Tyson W. R.
Published: February 2003

The Orowan-Polanyi approach to the calculation of surface energy is modified to incorporate information on interplanar force constants derived from phonon frequencies. Models using interatomic interactions to second and first nearest neighbor respectively for bcc and fcc crystals are found adequate to give acceptable results for dispersion curves and surface energies.
Concentration-dependent absorption and spontaneous emission of heavily doped GaAs
Authors: Casey H. C. , Stern Frank
Published: February 2003

A model for the calculation of the absorption and emission spectra for GaAs at carrier concentrations in excess of 1×1018 cm−3 is described. This model utilizes a Gaussian fit to Halperin-Lax band tails for the concentration-dependent density of states and also includes an energy-dependent matrix element. The calculated absorption and emission spectra are compared to previous experimental results. All results are for 297 K. For p-type GaAs, the agreement is very good. The concentration dependence of the effective energy gap is obtained and can be expressed as Eg (eV) =1.424−1.6×10−8 [p (cm−3)]1/3. The concentration-dependent thermal equilibrium electron-hole density product n0p0 and the radiative lifetime τr are calculated for p-type GaAs. The value of n0p0 increases from the low-concentration value of 3.2×1012 cm−6 to 1.2×1013 cm−6 at p=1.6×1019 cm−3. This value of n0p0, together with the thermal generation rate obtained from the experimental absorption coefficient, gives τr as 0.37 nsec at p=1.6×1019 cm−3.