bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice Trapping of Fracture Cracks
Authors: Thomson Robb , Hsieh C. , Rana V.
Published: February 2004

Continuum treatments of lattice defects such as dislocations and fracture cracks do not predict the resistance to the defect mobility which is due to the Peierls energy in the case of the dislocation. The discrete character of the lattice in the case of the fracture crack leads to a stress stability range for the crack above and below the Griffith stress over which the crack is stable or ``lattice trapped''. We develop here two essentially qualitative theoretical treatments of the lattice structure of cracks. In the first, we carry out a lattice sum of the bond energies of atoms facing each other across the crack plane under certain assumptions regarding the crack shape and atomic force laws. In the second, we introduce a one-dimensional lattice model of a crack which can be solved exactly. In both of these treatments the range of stress over which the crack is lattice trapped appears to be of the order of magnitude of the Griffith stress itself. As in the case of dislocations the lattice trapping is a strong function of the ``width'' of the elastic singularity at the tip, and our prediction is that one should expect materials to exist in which lattice trapping is not only observable, but is an important effect. We also find that because of lattice trapping, the true surface energy is a lower bound to the mechanical surface energy as expressed in the Griffith-stress relation.
Kinetics of Hydriding and Allotropic Transformation in SmCo5
Authors: Raichlen Joel S. , Doremus Robert H.
Published: February 2004

Previous work on the rapid formation of a hydride of SmCo5 at room temperature is confirmed. It is shown that the rate of release of hydrogen is related to the rate of transformation of the hydride to the unhydrided compound, rather than by bulk diffusion of hydrogen. The rate-controlling step is probably the allotropic transformation from the hydride to the SmCo5 phase, so that the kinetics of such transformations can be studied from hydrogen desorption from the hydride.
Superconducting Thin-Film Detector of Nuclear Particles
Authors: Crittenden E. C. , Spiel Donald E.
Published: February 2004

Superconducting films of tin and indium on supporting substrates have functioned successfully as detectors of individual nuclear particles. The films are sufficiently thin and narrow that individual α-particle impacts initiate superconducting to normal transitions which spread, in the presence of a transport current, to span a full film cross section. The transitions are observed by means of the ir drop produced by a transport current. For low current densities self-terminating voltage pulses of a few nsec duration are observed. At higher current densities the boundaries of a normal region initiated by an α particle propagate by Joule heating to the ends of the film. The range of the 5.3-MeV α particles utilized for these experiments greatly exceeds the 0.1 μm thickness of the films and the resulting deposition of energy in the substrate affects the response of any film which is in direct contact with its substrate. The introduction of a thin thermally insulating layer of varnish between the film and its substrate, which in these experiments was either glass or crystalline quartz, increases the thermal decay constant to the extent that the film is thermally isolated from its substrate for a period comparable to that of pulse formation. The variation of count rate with film current has been studied and is shown to be consistent with the variation of critical current density along the length of the film. This model, coupled with classical heat diffusion within the film, accounts for the observed behavior of the thermally isolated films.
Numerical Tabulation of Integrals of Fermi Functions Using k lim →·p lim → Density of States
Authors: Bebb H. Barry , Ratliff C. R.
Published: February 2004

A generalized Fermi-Dirac integral F(ε,η), is evaluated. The density of states used is derived from k lim →·p lim → perturbation theory. Tables are presented for parameters ε and η over the ranges 0.01≤ε <∞ and −5≤η≤10, where ε = EG/KT is the reduced band gap and η = F/KT is the reduced Fermi energy. Computational formulas are developed for ε > 2 and ε < 0.01 which evaluate F(ε,η) for all ε and all η≤10 which are not included in the tables. The region of validity of the approximate formulas overlaps the range of the tables making possible cross checks on accuracy.
Partial Recovery of GaAs Tunnel Diodes after Stress-Induced Degradation
Authors: Marconato Roberto , Anderson R. L.
Published: February 2004

Partial recovery of stress-induced degradation in GaAs tunnel diodes was investigated. The room-temperature recovery rate is rapid immediately after removal of stress and decreases with time, becoming exponential with a time constant of about 5 h at longer times. It is thought that this partial recovery results from annealing of Frenkel defects created from recombination of injected electrons.
Shock-Wave Behavior and Properties of Solids
Authors: Huang Y. K.
Published: February 2004

Shock-wave behavior and properties of solids are described on the basis of a quadratic representation for the shock velocity and with results of considerable generality and simplicity. An implicit treatment is provided by coupling the Hugoniot adiabat with the isentrope in the Grüneisen equation of state for solids. This also leads to correlations between data and results of shock and hydrostatic measurements for high pressures.
Frequency Dependence of the Optical Saturation of Vibration-Rotation Transitions
Authors: Djeu N. , Wolga G. J.
Published: February 2004

The optical saturation of a vibration-rotation transition in a molecular gas generally cannot be described by any of the saturation formulas obtained with the assumption of fixed pump rates. Its explicit form is derived here by treating rotational relaxation into each of the radiatively interacting levels as a variable pump rate dependent upon the degree of saturation. The formula exhibits a collision-induced power-broadening feature which is distinct from the well-known homogeneous power broadening in form as well as in physical origin. This effect has been observed indirectly in a CO2 laser.
Collision of Stress Pulses with Obstacles and Dynamics of Fracture
Authors: Steverding B. , Lehnigk S. H.
Published: February 2004

The interaction of stress pulses with obstacles is considered not from the aspect of ``wave stability'' (scattering), but from the aspect of ``obstacle stability'' (fracture). For this purpose the equation of motion for a penny-shaped crack which is subjected to stress pulses is derived directly from Hamilton's principle of least action. This way was chosen in order to make an important result of this work, the least-action theorem for crack stability, directly traceable to this first principle of mechanics. The indicated quantum interpretation can be made plausible in this way. It is also shown that crack stability can be treated as an eigen-value problem. A cross section for material-wave interaction is derived. From the law that the action density of the pulse σ2τ/E has to be at least approximately πγ/a to fracture materials, a few applications are drawn. The conditions for supersonic fracture are indicated.
Thermal Expansion of Tungsten at Low Temperatures
Authors: Shah Jayant S. , Straumanis M. E.
Published: February 2004

Lattice parameters, thermal expansion coefficients, and Grüneisen parameters of tungsten are determined by an x-ray method in the temperature range of 180–40 K without the use of liquid gases. Lattice parameters are expressed as a function of temperature. Thermal-expansion coefficients decrease with temperature and show no anomaly in contrast to a hypothesis proposed by Featherston and Neighbours. Grüneisen parameters γ are decreasing with temperature in accordance with the theoretical predictions.
Relation between Dislocations and Disclinations
Authors: deWit R.
Published: February 2004

The theory of disclinations contains the equation ∂iαij +ejmnθmn=0, where α and θ are the dislocation and disclination density tensors, respectively. This expression is interpreted to mean that dislocations can end on twist disclinations. A concrete example in a hexagonal crystal is discussed to illustrate this concept. It contains a 60° wedge disclination normal to the basal plane. By basic geometrical construction it is shown how a dislocation can be made to end on a jog in the wedge disclination. This jog is a small segment of twist disclination. Several ramifications of this concept are that disclinations can act as sources and sinks of dislocations, that dislocations change their Burgers vectors as they glide around disclinations, that a dislocation which crosses a disclination remains connected to it by a dislocation, that dislocations encircling a disclination must have a node, and that the local Burgers vector is not conserved on following a dislocation around a disclination.
Strain Energies of Disclination Loops
Authors: Liu Gaines C. T. , Li James C. M.
Published: February 2004

Some stress components in the plane of a twist and a wedge disclination loop and the strain energies of these loops outside the core region are calculated based on isotropic elasticity theory. These results complement previous results for the stress fields at large distances.
Prismatic Dislocation Loops in Aluminum-Magnesium Alloys
Authors: Kritzinger S.
Published: February 2004

Various types of prismatic dislocation loops were produced by quenching in silicone oil of aluminum containing nominally 1 and 7 wt% magnesium, respectively. The annealing behavior of the loops was studied by transmission electron microscopy of thin foils of the quenched material. Direct experimental proof is given for the conversion of hexagonal perfect loops to diamond-shaped loops, as well as for the rotation of perfect loops to different planes. The mechanism responsible for the coalescence of perfect loops is determined, and the nature of perfect loops evolving from climb sources is determined by their annealing behavior.
Analytical Expressions for the Composition Dependence of Stacking Fault Energies and Probabilities in Binary Silver Systems
Authors: Liu Y. C. , Gallagher P. C. J.
Published: February 2004

The following straight-line relationship between the stacking-fault probability α and alloying concentration has been obtained by fitting published data: lnα=lnα0+Kα [C/(1+C)]. In this expression, C=X/X*, where X is the alloying concentration and X* is the solubility limit (both in atomic percent) at either the peritectic or the eutectic temperature, α0 is the stacking-fault probability for pure silver and Kα is an experimental constant. The value of α0, obtained by extrapolation, is 3.13±0.14×10−3; Kα is usually within the range 6.2±0.5, but is lower in those binary systems alloyed with the hcp elements Mg, Zn, and Cd. Similarly, an analytical expression relating stacking-fault energy γ and alloying concentration may be written as lnγ=lnγ0+Kγ [C/(1+C)]2,where γ0 is the stacking-fault energy of silver. The value of Kγ for the Ag–Sn, Ag–In, and Ag–Al systems ranges from −10.0 to −10.5, but is −6.5 in the Ag–Zn system. The relationship between α and γ is discussed on the basis of these equations.
Fluctuation of Arc Potential Caused by Metal-Vapor Diffusion in Arcs in Air
Authors: Boddy P. J. , Utsumi T.
Published: February 2004

It was found that arc potential rises discontinously when the separation between two electrodes reaches a critical distance which has a certain functional dependence on the ambient gas pressure and the arc current. This phenomenon is discussed quantitatively as being caused by diffusion of metal vapor from the cathode spot to the surrounding gas in hemispherical geometry.
Thermal Migration of Liquid Droplets through Solids
Authors: Anthony T. R. , Cline H. E.
Published: February 2004

A transparent solid and liquid were chosen to study the thermomigration of liquid droplets through solids. Irreversible processes associated with the transfer of atoms between the solid and the liquid phases at the solid-liquid interface of the droplet were found to have a profound influence on the migration behavior of the liquid droplets. For large droplets, these interface kinetics cause the droplet to disintegrate in a thermal gradient. In smaller droplets where the containing effects of surface tension are relatively greater, the droplets experience a prolonged transient period of thermomigration during which there is a monotonic increase in the velocity of the droplet and a gradual distortion of the droplet shape. Following this transient period, the smaller drops enter a steady-state period during which both their shape and velocity remain constant. The steady-state velocity of droplets in this region decreases with decreasing droplet volume and falls to zero below a critical droplet size. This variation of droplet velocity with size produces an increased rate of collision and coalescence of droplets during thermomigration.
Ionic Jump Distance and Glass Transition of Polyvinyl Chloride
Authors: Kosaki Masamitsu , Sugiyama Koichi , Ieda Masayuki
Published: February 2004

The electrical conduction of polyvinyl chloride was measured from low electric field to high field near breakdown below, in, and above a glass transition region. Ionic conduction was found to hold up to the field near breakdown. The estimated jump distance of a charge carrier changes considerably in the glass transition region, while it remains constant (12 Å) at a temperature fairly below the glass transition Tg(=87°C) and seems to reach a saturation value (30 Å) above Tg. The elongation of substantial jump distance may be explained by the change in the shape and height of potential barriers against ionic migration due to the liberation of micro-Brownian motion of main chains in the glass transition region.
Gas-Dynamic CO2 Laser Pumped by Combustion of Hydrocarbons
Authors: Tulip J. , Seguin H.
Published: February 2004

The expansion of a hot mixture of CO2, N2, and H2O through a Laval nozzle is analyzed. Mixtures appropriate to the stoichiometric combustion of acetylene and propane are used. The calculations indicate that, despite the large quantities of water vapor present, the expansion will result in a population inversion on the CO2 laser transition for both fuels. The predicted maximum gain for these conditions is 3 dB/m which occurs for a reservoir temperature of 2000 °K. Design curves for this type of laser are given.
Simplified Theory of Picosecond Pulses in Lasers
Authors: Creighton John R. , Jackson Julius L.
Published: February 2004

A physical model of the generation of picosecond pulses from a laser is developed from self-consistent equations for cases in which a modulator or a nonlinear element is inserted in the laser cavity. Pulse widths are obtained by consideration of the variances of the pulse, modulator, and filter functions. An analytic solution for the pulse is obtained for a Lorentzian line shape and arbitrary amplitude-modulation waveform.
Time-Resolved Absorption Spectroscopy in the 10−12 -sec Range
Authors: Topp M. R. , Rentzepis P. M. , Jones R. P.
Published: February 2004

A technique is described for a single-shot time resolution of picosecond events. Some examples are given which demonstrate the feasibility of this method for making accurate measurements with a time resolution of ∼ 10−12 sec.
Electronic Structure and Luminescence Processes in In1−xGaxP Alloys
Authors: Onton A. , Lorenz M. R. , Reuter W.
Published: February 2004

The conduction-band structure of In1−xGaxP has been studied by cathodoluminescence (CL) and photoluminescence (PL). An accurate determination of the direct energy gap (± 10 meV) as a function of alloy composition (Δx = ± 0.025) is achieved by the simultaneous electron probe microanalysis of alloy composition and spectral measurements of the CL excited by the microprobe electron beam. Similar measurements in InP, GaAs, and GaAs1−xPx, as well as absorption edge measurements and the temperature dependence of the PL spectrum, indicate that essentially free-carrier recombination is observed in the PL and CL measurements of lightly n-type In1−xGaxP at 300 °K. These results indicate that the ``cross over'' between the direct and indirect conduction-band minima occurs at the composition x = 0.74 and energy gap = 2.26 eV.
Structural and Magnetic Characteristics of Th–Co and Th–Fe Compounds
Authors: Buschow K. H. J.
Published: February 2004

The Th–Co and Th–Fe systems were studied by x-ray diffraction methods. Five intermetallic compounds were observed in each system. For each of these compounds the lattice parameters were determined. The magnetic properties of the various compounds were investigated at temperatures between 4.2 and 1200 K with magnetic field strengths up to 30 kOe. In the Th–Co system the compounds Th2Co17 and ThCo5 are ferromagnetic; the Curie temperature and the cobalt moment decrease rapidly with Th-content. The compounds Th2Co7, ThCo, and Th7Co3 are paramagnetic. In the Th–Fe system the compounds Th2Fe17, ThFe5, Th2Fe7, and ThFe3 are ferromagnetic; with increasing Th content the Curie temperatures and iron moments first rise, then decrease. The compound Th7Fe3 is paramagnetic. A comparison is made with the magnetic properties of rare-earth-iron and -cobalt compounds. Magnetic data are reported for La3Co, Y3Co, and YCo2 which are paramagnetic. Curie temperatures are also given for YCo3 and YCo5.
Initial Susceptibility Study of Thermal Hysteresis in Gd in the Neighborhood of the Curie Region; Frequency Dependence of the Magnetization
Authors: Gerstein B. C. , Olander F.
Published: February 2004

Initial susceptibility measurements as a function of frequency and field have been made on two samples of polycrystalline gadolinium in the range 200–296 °K at frequencies of 20–200 Hz and fields of 2–25 Oe. Both samples exhibited thermal hysteresis in both real and imaginary susceptibilities between 260 and 290 °K. The absorption was more sensitive to the hysteresis than was the dispersion by a factor of 5. The nature of the susceptibility - temperature - frequency surface was delineated for both the real and imaginary components. A driven oscillator model failed to account for the frequency dependence of the susceptibility, the failure in the model being qualitatively similar to that observed in similar results obtained for holmium.
Instability of Vehicles Levitated by Eddy Current Repulsion-Case of an Infinitely Long Current Loop
Authors: Fink H. J. , Hobrecht C. E.
Published: February 2004

The coordinates which will assure translational and rotational equilibrium of an infinitely long current loop moving parallel to a metallic sheet of thickness d are found. It is found that two distinct equilibrium positions exist for a given loop velocity, current, and weight. It is also found that the equilibrium positions are unstable. The primary manifestation of this instability appears to be a run away in velocity coupled with oscillations in height and angle of tilt. End effects of the current loop and aerodynamic drag forces could hopefully stabilize a real vehicle supported by magnetic levitation.
Asymptotic Lift-to-Drag Ratios for Magnetic Suspension Systems
Authors: Burnham David C.
Published: February 2004

The asymptotic high-velocity lift-to-drag ratios L/D are calculated for the general case of continuous sheet track and for one case of loop track. For sheet track, (L/D)2 is proportional to λeff, the effective length of the train magnet. The use of loop track offers only a modest improvement in L/D compared to sheet track. The asymptotic L/D ratio is a convenient way of comparing different systems on an equal basis.
A Study of Thermomagnetic Remanence Writing on EuO
Authors: Wieder H. , Lavenberg S. S. , Fan G. J. , Burn R. A.
Published: February 2004

An improved method is described of measuring the temperature in a thermomagnetically written bit. It uses the temperature shift of absorption in the storage material to deduce the temperature from transmission changes measured during the application of a thermal pulse. The transmission kinetics which were measured in a film of EuO for several energy pulses supplied by a GaAs laser are presented. By fitting these curves to those generated by a computer program simulation of the experiment, details of the temperature profile within the bit are revealed. For moderate power levels, about half of the power absorbed by the bit is retained by it in the first 400 nsec, while radial losses do not produce significant thermal spreading in the same time period.
One-Dimensional Thermoelastic Response of Solids to Pulsed Energy Deposition
Authors: Oswald R. B. , McLean F. B. , Schallhorn D. R. , Buxton L. D.
Published: February 2004

A one-dimensional model for the thermoelastic response of materials exposed to pulsed energy deposition is presented. For the model presented, a generalized form of the Mie-Grüneisen equation of state was used to develop a description of the free-surface motion which includes the temperature dependence of the Grüneisen parameter Γ. This model was verified through free-surface motion measurements of solids exposed to a pulsed electron beam, over a temperature region where Γ may be considered constant. The measured time-dependent rear-surface displacement and velocity histories for a single crystal of Al are compared with those quantities predicted by the one-dimensional theory and found to agree very well. The measured thermoelastic response for Al, Ag, and Cu in both single and polycrystalline form, single crystals of Si, Ge, and InSb, and the polycrystalline alloy Kovar is presented in an equivalent form as a measurement of the Grüneisen parameter. The agreement between the measured Grüneisen parameters and their accepted value is within ± 7% for all materials studied. Empirical corrections have been made to the data to reflect the fact that the theoretical model neglects attenuation. It is concluded that the method is valid for determining the Grüneisen parameter of solids; however, it is restricted to materials for which (a) the deposited energy couples to the lattice phonons in times short compared to their acoustic relaxation time, (b) the Grüneisen parameter is relatively constant over the temperature range of the measurements, and (c) the thermal expansion of the materials is isotropic.
Temperature Dependence of the Dynamic Response of Si, Ge, and InSb to a Pulsed Electron Beam
Authors: McLean F. B. , Oswald R. B. , Schallhorn D. R. , Buxton L. D.
Published: February 2004

One material parameter used in describing the thermoelastic response of a material exposed to a pulsed energy deposition is the Grüneisen parameter. At room temperature this parameter is constant for many materials, but at lower temperatures it varies in both magnitude and sign for some materials, e. g., covalent-bonded cubic crystals. In this study, a generalized form of the Mie-Grüneisen equation of state was used to describe the response of that type crystal to pulsed electron-beam exposure as a function of initial temperature. In addition, the predicted responses of Si, Ge, and InSb are compared with the responses measured with a laser interferometer for several initial temperatures between 20 and 300 °K. The measured and predicted responses agree with each other well enough to indicate that an adequate response description using a temperature-dependent Grüneisen parameter was developed.
Quantum Tunneling as an Elementary Fracture Process
Authors: Gilman J. J. , Tong H. C.
Published: February 2004

A quantum-mechanical model for an elementary fracture process is proposed. The mechanism is driven by the local applied stress acting upon a chemical bond causing it to decompose. The bond tunnels from an initial bonded state to a final unbound state. The rate of this process is independent of temperature at low temperatures. It can be assisted, however, by phonons, photons, chemical potentials, and other excitations or driving forces. It is shown that the predictions of the model are in agreement with the effects of stress on rupture times, crack velocities, and rates of free radical formation. The observed temperature dependence of the fracture strength of Al2O3 is also predicted by the model.
Field Ion Microscopy of Graphite Fibers
Authors: Murr L. E. , Inal O. T.
Published: February 2004

Field ion microscopy of pyrolytic graphite produced image streaks resulting from gross surface irregularities as a result of the etching characteristics in tip preparation. The streaks were observed to contract with a decrease in imaging voltage and to remain relatively stable. Commercial high-modulus graphite fibers could be electropolished to fine tips, and single image points (occurring as double spots) were observed for the first time in the field ion microscope. These image points were interpreted to represent the carbon atoms in the corner of a single graphite platelet. It is concluded from these experiments that the possibility of studying graphite by field-ion microscopy might be viewed with a little more optimism.
Faraday Rotation in Birefringent Crystals
Authors: Kurtzig A. J.
Published: February 2004

Birefringence complicates the use and measurement of the Faraday effect. The Faraday rotation in nonbirefringent materials increases linearly with path length of the light propagation. However, the observed Faraday rotation in birefringent crystals oscillates about zero as a function of the light path length. A new experimental technique has been developed for measuring the intrinsic Faraday rotation and the birefringence of noncubic materials. The measurements are based on mathematical curve fitting of the oscillatory variation of the Faraday rotation as a function of the angle between the light-propagation direction and an optic axis in a sample with fixed uniform magnetization. The birefringence can be determined from the periods and the intrinsic Faraday rotation from the amplitudes of the oscillations. The oscillatory variations of the Faraday rotation in birefringent crystals suggest ways of optimizing the usefulness of the rotation.
Refractive Index of AlAs
Authors: Fern R. E. , Onton A.
Published: February 2004

The refractive index of AlAs at 300 °K has been measured in the 0.5- to 2.2-eV range of photon energy. The long-wavelength dielectric constant with lattice vibrations neglected ε∞ is determined to be 8.16 ± 0.02, and the resulting static dielectric constant ε0 is 10.06 ± 0.04.
Dispersion of Electro-Optic Effect in BaTiO3
Authors: Johnston Alan R.
Published: February 2004

The dispersion of both the quadratic and linear electro-optic effects in flux-grown crystals of BaTiO3 has been measured polarimetrically between 0.4 and 1.0 μ yielding (g11 - g12) and rc =r33 - (na/nc)3 r13. A strong dispersion was found: (g11 - g12) increases to double its long-wavelength limit at 0.4 μ. Both unclamped (low frequency) and clamped measurements were made. Birefringence and the principal indices were also determined. A two-oscillator Sellmeier model, in which one oscillator frequency is polarization dependent, was shown to represent closely all the data. The unclampled polarization potential, which specifies the magnitude of the oscillator frequency shift, was 3.9 eV m4 C−2, while its clamped value was one-third as large. Ultraviolet reflectivity calculated from the model assuming reasonable values of empirical damping agrees with the observations of Cardona and Gahwiller.
Mechanism of Photoconductivity in Chemically Deposited Lead Sulfide Layers
Authors: Espevik Svein , Wu Chen-ho , Bube Richard H.
Published: February 2004

Many of the classical problems involved in the mechanism of photoconductivity in chemically deposited PbS layers have been resolved by a combination of (a) materials control, (b) measurements of conductivity, photoconductivity, Hall effect, thermoelectric effect, and oxygen sorption, and (c) analysis of an inhomogeneous model. The dark conductivity process, characterized by a small thermally activated mobility, is the same for samples without added oxidant in the deposition and for samples with added oxidant, and is dominated by intergrain barriers to free-hole transport. Carrier densities derived from Hall measurements are equal to those derived from thermoelectric power measurement and are therefore interpreted to be equal to the carrier density in the grains of the PbS layer. Layers prepared without added oxidant are only very weakly photosensitive, corresponding to sensitizing centers lying 0.13 eV below the conduction band, whereas layers prepared with added oxidant are strongly photosensitive, corresponding to sensitizing centers lying 0.22 eV below the conduction band. In all cases photoconductivity results primarily from an increase in free hole density, with some small contribution from an increase in hole mobility. Increases in hole mobility caused either by photoexcitation or by photoadsorption of oxygen are attributed to an increase in hole tunneling through intergrain barriers as the results of decreased depletion layer widths. Oxygen adsorbed on the free surface of the layer increases the free-hole density without appreciably affecting the mobility; oxygen which is adsorbed on the surface and then diffuses to intergrain barriers increases the free-hole density, and also to a lesser extent the hole mobility and the hole lifetime. In several ways the results following from photoexcitation and photoadsorption of oxygen are similar, and they may both be described in terms of the same inhomogeneous model.
Curvature Stabilization of the Universal Instability
Authors: Emmert Gilbert A.
Published: February 2004

A graphical technique for determining the influence of the drift velocity in a magnetic well on wave-particle resonance is presented and applied to the universal instability. It is seen that the curvature drift velocity can strongly affect the number of resonant ions and lead to increased stabilization of the wave.
Predicted Arc Properties in Sulfur Hexafluoride
Authors: Lowke J. J. , Liebermann R. W.
Published: February 2004

Calculations of spectral absorptivities of sulfur hexafluoride for continuum radiation ranging from the far ir to 300 Å have been made as a function of temperature and pressure. These values are used together with theoretical values of thermal and electrical conductivity to derive temperature profiles of arcs in sulfur hexafluoride, taking into account effects due to self-absorption of radiation, but assuming local thermal equilibrium. The temperature profile for a 100-A arc is in good agreement with the experimental measurements of Motschmann. The sensitivity of the derived temperature profile to the input material functions is examined. It is predicted that radiation losses at the arc center are dominated by radiation of wavelengths in the region of 1000 Å. Using the theoretical material functions, an estimate is made of central arc temperatures and electric field strengths for currents of up to 60 000 A and arc radii of up to 2 cm for gas pressures of 1 and 8 atm.
Ion-Implanted Phosphorous in Silicon: Profiles Using C-V Analysis
Authors: Moline R. A.
Published: February 2004

Depth distributions are presented for 200-, 300-, and 600-keV phosphorus ions either channeled along the 〈111〉 axis or implanted away from any major axis or plane in silicon. The profiles were obtained using the differential capacitance technique, and the technique is discussed along with a description of an automatic data-acquisition system which allows precise C-V data to be accumulated. The ``random''-direction implant profiles exhibit a definite exponential tail on the deep side of the implant. The characteristics of this tail appear to be material dependent but independent of the implantation energy. Thus, the tail probably results from an anomalous diffusion mechanism. The observed projected range for the random implants is 1.1 μm/MeV, with a range straggle nearly equal to that predicted by the range theory of Lindhard, Scharff, and Schiott (LSS). The channeled profiles exhibit a near flat characteristic to a depth of 2.2 μm/(MeV)1/2.
Precipitation in High-Purity Silicon Single Crystals
Authors: Nes E. , Washburn J.
Published: February 2004

Precipitation in high-purity Lopex (low-oxygen dislocation-free) silicon has been examined by x-ray diffraction topography and transmission electron microscopy. It has been found that the impurity concentration in the as-grown silicon crystals is sufficient to cause precipitation of a second phase if the specimens are annealed in the temperature range 700–1000°C, followed by a critical cooling rate. The precipitating phase has been tentatively identified as α Fe3Si. The precipitates appear in colonies. Each colony has a three-dimensional starlike configuration, where the different arms are planar arrangements of precipitates enveloped by a dislocation loop. The precipitates have a blocky shape and the dislocation loops are of interstitial edge type and both 12−a 〈110〉 and a 〈100〉 Burgers vectors are involved. The nucleation of colonies is heterogeneous and the presence of small silica particles as nucleation centers is suggested.
Transport Properties of the Gold Germanium Gallium Arsenide Metal Semiconductor System
Authors: Pruniaux B. R.
Published: February 2004

In an attempt to improve Ohmic contacts to gallium arsenide, we undertook the characterization of the gold germanium contact by measuring its barrier height. The intrinsic barrier height of the system was found to be 0.74±0.01 eV and independent of the carrier concentration in the semiconductor. However, it can be considerably decreased if the metal is deposited on a heated substrate, leading to a reduced Ohmic resistance of the contact on low-resistivity gallium arsenide.
Alloying Behavior of Au and Au–Ge on GaAs
Authors: Gyulai J. , Mayer J. W. , Rodriguez V. , Yu A. Y. C. , Gopen H. J.
Published: February 2004

Although Au–Ge has often been used in making Ohmic contacts to GaAs, the alloying behavior of this system has not been well characterized and understood. In this paper the behavior of Au and Au–Ge layers on GaAs was investigated as a function of processing temperature (400–600°C) and time by backscattering and channeling-effect measurements with 2-MeV 4He ions. Scanning electron microscopy and current-voltage evaluations were also made. Similarities are found in both systems: There is a deeply penetrating component of Au into the GaAs that remains essentially unaltered once the surface Au has been consumed; a disordered region near the surface is found, the amount of which increased with increased process times. No significant amount of Au is found on substitutional or tetrahedral interstitial sites within about 3000 Å of the surface. The presence of the Ge does have a significant effect: Complete alloying occurs at lower temperatures, and Ohmic contacts are formed. Scanning-electron-microcope displays indicate that surface pits are formed; the depth of these increase with increased amounts of Au. Optical micrographs of a sectioned sample indicate a deep Au penetration.
Charge Transfer in Charge-Coupled Devices
Authors: Kim Choong-Ki , Lenzlinger Martin
Published: February 2004

The transfer characteristics of charge-coupled devices have been investigated theoretically and simulated experimentally. The transport of minority carriers along the Si–SiO2 interface can be described by a diffusion equation where the effective diffusion coefficient is composed of two terms representing the drift and the diffusion currents. There are two time constants associated with the two current components. For typical operating conditions, the drift time constant is about 100 times smaller than the diffusion time constant. The charge transfer can theoretically be separated into a charging and a discharging process, and the final stages are described by the drift and the diffusion time constants, respectively. Transfer efficiencies for charge-coupled devices have been calculated from the discharging phenomena. The drift current increases the transfer efficiency significantly. For high transfer efficiencies (>99%), however, the increase of the transfer efficiency with transfer time is limited by the diffusion time constant. A simple scheme which overcomes this limitation is described. Experimentally, the charging and discharging conditions have been simulated by using gated diodes. Good agreement between theory and experiment has been found by a reasonable adjustment of the surface mobility alone.
X-Ray Excited LMM Auger Spectra of Copper, Nickel, and Iron
Authors: Yin L. I , Yellin E. , Adler I.
Published: February 2004

Photoelectron and Auger-electron spectra are both obtained with x-ray excitation. Using the photoelectron spectra as internal energy standards, the energies of the prominent LMM Auger lines in Cu, Ni, and Fe have been accurately determined. In addition, the photoelectron spectra provide a measure of the vacancy distribution created by the x rays among the three L subshells. Thus, knowing both the energy values and the vacancy distribution, we have assigned the three prominent Auger lines of Cu, Ni, and Fe to be of type L3MM rather than L2MM.
Improvement of the Resolving Power and Transmission of Electrostatic Spectrometers
Authors: Roy D. , Carette J.-D.
Published: February 2004

A method proposed by Delage for the calculation of electron energy distributions has previously been generalized and applied to various types of electrostatic spectrometers, that is, to toroidal-type and mirror-type spectrometers. Thus, it has been found that spectrometers with wide angular apertures yield an asymmetric energy distribution which may have an important tail on the high-energy side. The analysis of a typical distribution shows that this tail is caused by the angular dispersion of the trajectories; because of the filtering action of slits and electrodes, the positive and negative angular components of the beam contribute unequally to the energy spectrum. By changing the way that the beam is filtered, it is possible to improve the energy distribution profile, without or with little loss of transmitted current. The improvement of the resolution may thus reach 30% or more, as the result of only a small displacement of the exit slit either on the exit equipotential, or toward the beam. Most of these results are new, principally in the case of the spectrometers of the toroidal type where the optimum deflection angle is greater than the focusing angle. Moreover, from Wollnik's conclusions about shielding from fringing field in toroidal spectrometers, supplementary calculations are performed to extend the validity of other results to more practical cases. Finally, results obtained for the cylindrical mirror are found in good agreement with conclusions presented before by Hafner, Kuyatt, and Simpson.
X-Ray Topographic Visualization of an Interface
Authors: Saccocio Edward J.
Published: February 2004

Asymmetric diffraction is used in transmission x-ray topography to sense the interfacial strain between a vapor-deposited aluminum film and a crystal substrate. Strain across the interface affects lattice planes inclined to the surface and produces additional contrast in the x-ray topograph over the entire surface area covered by the film. Comparisons are made with the normal topograph which shows contrast only at the edges of the film. The contrast over the interface is itself found to reflect an asymmetry with respect to the sense of the diffraction vector. It is learned that curvature of the diffraction planes near the interface is responsible both for the contrast and its asymmetry. The rule followed for the greater contrast is shown to be the same as with the edge-contrast asymmetry from normal topographs. Detailed topographic observations are presented along with a tenable argument as to the origin of the x-ray enhancement.
Structure and Topography of Monocrystalline Nickel Thin Films Grown by Vapor Deposition
Authors: Grenga Helen E. , Lawless Kenneth R. , Garmon Lucille B.
Published: February 2004

Monocrystalline nickel thin films were grown by vapor deposition onto heated rocksalt substrates. The (100)-, (110)-, and (111)-oriented nickel films were prepared by deposition onto (100)-, (110)-, and (111)-oriented rocksalt substrates, respectively. The structures of the films were examined by x-ray diffraction and electron diffraction and microscopy. These thin films (less than 1000 Å thick) were well oriented and continuous and contained relatively high densities (108−1011/cm2) of stacking faults, twins, and dislocations. Ledges parallel to the 〈001〉 were found on (100)-oriented films and {111} facets along 〈11̄0〉 were found on (110)- oriented films. The (111)-oriented films were quite rough with pits, mounds, and other ledges. These films were satisfactory for investigations on the initial stages of oxidation and catalysis.
Thermoelectric Power of Thin Gold Films
Authors: Lin Shing F. , Leonard William F.
Published: February 2004

The thermoelectric power and temperature coefficient of resistance of gold films has been measured and related to the energy dependence of both the mean free path of conduction electrons and the area of the Fermi surface. Values obtained for the quantities (dlnλ/dlnW)W=WF and (dlnA/dlnW)W=WF are − 0.60±0.04 and − 0.85±0.04, respectively. These quantities can be determined without knowing the surface-scattering coefficient or sample thickness if the films have the same structure as the bulk material.
Investigation of hypersonic properties of acrylic monomers using Brillouin spectroscopy
Authors: Papayoanou A. , Hart T. R. , Andrews R. D.
Published: February 2004

The Brillouin spectrum of laser light scattered by four acrylic and methacrylic monomer liquids was investigated. Measurements of Brillouin shifts and linewidths, obtained as a function of temperature, allow a determination of the temperature dependent velocity and attenuation of hypersonic acoustic waves. Analysis of the velocity data using Rao's empirical rule indicates that these liquids are unassociated. The attenuation of these liquids as a function of temperature reveals a common thermal relaxation effect. The relaxation mechanism is taken as due to a molecular rotation of an ester group about a C–C bond from one rotational isomeric state to a second isomeric state. This relaxation mechanism is believed similar to the well known Beta relaxation effect in the acrylic and methacrylic polymers.
Molecular beam study of polyatomic free radical reactions. Angular distributions
Authors: McFadden D. L. , McCullough E. A. , Kalos F. , Ross J.
Published: February 2004

The polyatomic free radicals CH3 and C2H5(R) were produced by thermal dissociation (1500°K) of R2Cd or R2Zn. A molecular beam containing about 7%–20% free radicals emerged from the source and collided with a hydrodynamic (nozzle) beam of halogen molecules. Angular distributions of the alkyl halide product were measured with a quadrupole mass spectrometer for the reactions CH3+Cl2, Br2, I2, ICl (both products), and C2H5+Br2. The reactive scattering is predominantly backwards in the c.m. system and the reaction cross sections, estimated within a factor of 3, are small, about 0.5 to 5 Å2. There is much similarity between these polyatomic free radical reactions and corresponding D atom reactions, except that there is much less forward scattering in the CH3 cases. The angular distribution of C2H5Br is peaked backwards and is remarkably narrow.
Hyperfine structure of furan
Authors: Tomasevich G. R. , Tucker K. D. , Thaddeus P.
Published: February 2004

The hfs of five rotational transitions of furan (C4H4O) has been resolved with a beam maser spectrometer with a resolution of about 500 Hz. All significant details of the observed structure are accounted for by the spin-spin and spin-rotation interactions of the four protons, and the coupling constants for these interactions have been determined to high precision. In particular, the diagnoal elements of the spin-rotation tensors have been determined to about 10 Hz.
Theory of transport in liquid metals. I. Calculation of self-diffusion coefficients
Authors: Protopapas P. , Andersen Hans C. , Parlee N. A. D.
Published: February 2004

An approach is presented for the theoretical calculation of self-diffusion coefficients of liquid metals. The basic assumption is that the self-diffusion coefficient of a liquid metal is equal to that of an appropriate hard sphere fluid. The hard sphere diameter is dependent upon temperature, and a method is developed for estimating this temperature dependence by exploring the relationship between the diameter and the interatomic potential energy function of the liquid metal. The theory gives accurate results for the magnitude and temperature dependence of the self-diffusion coefficient for many liquid metals. In addition, the physical basis for the theory is consistent with what has been learned about the liquid state from molecular dynamics calculations.
Observation of the Compton modified band for the scattering of keV electrons by H2, He, Ne, and Ar
Authors: Schmoranzer H. , Ulsh R. C. , Bonham R. A. , Ely J.
Published: February 2004

Measurements of the energy loss spectrum using keV electrons scattered from H2, He, Ne, and Ar at large scattering angles which define a portion of the Bethe surface are reported. The results are in good agreement with the theory of the Compton effect where the incident x-ray is replaced by a high-energy electron. The angular dependence of the inelastic scattering from H2, He, and Ne with 45 keV incident electrons is found to be in agreement with the first Born approximation including interference and exchange effects assuming weakly bound target electrons. The ratio of the inelastic peak height to the elastic peak height is compared with the results of the binary encounter theory using Hartree-Fock ground state wavefunctions and the results of experiment and theory are found to be in agreement within experimental uncertainties.
Reinvestigation of the molecular structure of gaseous p-benzoquinone by electron diffraction
Authors: Hagen Kolbjo/rn , Hedberg Kenneth
Published: February 2004

The molecular structure of gaseous p-benzoquinone has been studied by electron diffraction at a nozzle-tip temperature of 110–125°C. The molecule has D2h symmetry to within experimental error. The results for the more important distance (ra), bond angle, and rms amplitude (l) parameters are rC–H=1.089 Å (0.011), rC=O=1.225 Å (0.002), rC=C=1.344 Å (0.003), rC–C=1.481 Å (0.002), ∠C2C1C6=118.1° (0.3), ∠C3C2H=121.4° (assumed), lC–H=0.077 Å (assumed), lC=O=0.0424 Å (0.0020), lC=C=0.0446 Å (0.0024), and lC–C=0.0546 Å (0.0024). These values are in good agreement with those found in an early electron-diffraction study by Swingle, and except for the length of the carbon-carbon double bond, in excellent agreement with those found in the crystal by Trotter.
Bond orbital analysis of the hydrogen bond in the linear water dimer
Authors: Bowers Michael J. T. , Pitzer Russell M.
Published: February 2004

The hydrogen bond energy of the isolated linear water dimer has been investigated with the use of the bond orbital approximation. This approach provides a simple description of the relative contributions from electrostatic, overlap repulsion, and charge transfer effects. The basis set used is a minimum basis of Slater atomic orbitals. The hydrogen bond energy obtained is in reasonable agreement with the values obtained from SCF calculations.
Infrared and Raman spectra of lithium and ammonium nitrate solutions in liquid ammonia
Authors: Gardiner D. J. , Hester R. E. , Grossman W. E. L.
Published: February 2004

Vibrational spectra, most of them obtained from Raman scattering, are reported for LiNO3 and NH4NO3 solutions in liquid ammonia, ranging from dilute to the compositions LiNO3/1.6NH3 and NH4NO3/1NH3. All the spectra were obtained from solutions at ambient temperatures. Large changes in the N–H stretching region are correlated with the effects of the electrolytes on the solvent structure. Low-frequency bands associated with Li–NH3 modes are identified. Spectral features indicative of both solvent-separated and contact ion pairs involving Li+ and NO3− are analyzed. Contact ion pairing between NH4+ and NO3− ions in this solvent fails to produce any measurable splitting of the NO3− ν3(E′) or ν4(E′) modes.