bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of equilibrium pressure of Ba by reduction of BaB6
Authors: Yamamoto Shigehiko , Honda Yukio , Aita Toshiyuki
Published: February 2003

The equilibrium pressure of Ba reduced from BaB6 is measured by using a tungsten surface ionizer. The semiempirical relation between the pressure P and the equilibrium temperature T is given as logP (mm Hg) =3.0(±0.1)−(15300±1000)/T in the range 1270<T<1670 °K. The pressure is found to increase by one or two orders of magnitude when impurities exist on the BaB6 surface.
Surface structure and stability of a tin-covered tungsten tip as observed in a field ion microscope
Authors: Nishikawa O. , Saadat R.
Published: February 2003

The deposition of tin on a tungsten emitter tip and subsequent heating above 700 °C results in a drastic change of the equilibrium shape of the emitter at an elevated temperature and the formation of a surface layer with unusual structure. The new surface layer requires a significantly higher external electric field to cause the migration of surface atoms than a bare tungsten surface layer. A tentative explanation is the formation of a closely packed two-dimensional alloy of transition and nontransition metals.
Heat capacity of sapphire between 2 and 10 K by ac technique
Authors: Viswanathan R.
Published: February 2003

The low-temperature heat-capacity data of small single crystals of sapphire obtained by an ac calorimetric technique are reported here. The lattice heat-capacity coefficient β is calculated to be 0.00172 mJ/g atom K4, giving a Debye temperature ϑD of 1042 K. This is in very good agreement with the published ϑD of 1035 K, on samples which were ∼1000 times larger.
Photoluminescence study of the shallow acceptor states in n-type GaAs
Authors: Bois D. , Beaudet D.
Published: February 2003

The 4 °K photoluminescence spectra of vapor phase epitaxial GaAs (n) layers with doping levels from 1013 to 3×1016 cm−3 have been studied. Taking into account the shift of the donor-acceptor (D-A) transitions lines versus the neutral donor concentration, it is shown that five shallow acceptor states are involved; their binding energies are determined, and compared with results obtained in other laboratories. Besides carbon (Ea=27 meV), zinc (31 meV), silicon (35 meV), and germanium (41 meV), there appears an acceptor level at 22 meV which had not previously been observed.
Oxidation of Si surfaces
Authors: Haas G. A. , Gray H. F.
Published: February 2003

The oxide thickness for Si wafers of different doping species and densities has been measured from 30 to 1000 Å for dry O2 oxidation at 900 °C. The transition from the linear to parabolic oxide growth rate occurs near 300 Å with measured rate constants of 6 Å/min and 2500 Å2/min, respectively. Carbon in graphitic form was found on the surface of the wafers prior to oxidation. This changed to a carbide-type form after oxidation and remained at the Si-SiO2 interface.
Space-charge effect on electrical conductivity in extrinsic semiconductor films
Authors: Covington D. W. , Ray D. C.
Published: February 2003

Theoretical expressions for electrical conductivity for thin semiconductor films are derived based on the Poisson and Boltzmann transport equations with the only restriction being that the charge carriers obey nondegenerate statistics. Earlier results based on symmetrical or quasisymmetrical charge distributions by the authors are shown to be a special case of this more general analysis. The derived expressions are solved numerically, and the results are presented in the form of universal curves of normalized film conductivity versus normalized film thickness. The curves are displayed as a function of representative surface and bulk potentials for accumulated n- and p-type films and weakly depleted n- and p-type films. As the surface layers become increasingly accumulated or depleted, appreciable variations are generally observed in the conductivity-vs-thickness curves for film thicknesses falling in the range 0.1L to 10L where L is the effective Debye length.
Scale parameters for thermal blooming and the occurrence of instabilities
Authors: Steverding B.
Published: February 2003

Thermal blooming of an intense light beam can be easily estimated by the determination of a characteristic scale length for the distribution of light intensity, refractive index, velocity of the medium, etc. This scale length is derived from the hydro-optical equations. The threshold conditions are determined above which thermal blooming will predominate as compared to linear absorption.
Mössbauer-effect study of Co57 and Fe57 impurities in ferroelectric LiNbO3
Authors: Keune W. , Date S. K. , Dézsi I. , Gonser U.
Published: February 2003

The Mössbauer effect observed with LiNbO3:Co57 (source) and LiNbO3:Fe57 (absorber) crystals showed the existence of high-spin Fe2+ and Fe3+ valence states. The Fe2+/Fe3+ ratio could be changed by reducing or oxidizing heat treatment. Fe3+ in sources and absorbers shows Mössbauer spectra which are typical for slow electronic relaxation between the crystal field states of the 6S5/2 state ion. For both Fe3+ and Fe2+, the principal axis of the electric field gradient is found to be parallel to the crystallographic c axis. For ferric iron Vzz is positive, while Vzz is negative and strongly temperature dependent for ferrous iron. The impurity site substitution and charge compensation mechanism are discussed.
An Al p-silicon MOS photovoltaic cell
Authors: Charlson E. J. , Lien J. C.
Published: February 2003

An MOS photovoltaic diode, consisting of Al on p-type silicon with a thin interfacial layer of SiO2, has been found to have good conversion efficiency for solar radiation. Measurements of capacitance versus voltage, current versus voltage, and photocurrent per absorbed photon indicate a most probable surface barrier height of 0.85 eV, approximately twice as large as that for the normal Al p-type silicon diode. A single-layer antireflection coating of silicon monoxide or zinc sulfide was found to increase the short-circuit current by approximately 50%. Double-layer coatings of zinc sulfide over silicon monoxide gave nearly the same increase with a shift of the maximum diode response to the near infrared. Absolute light-conversion efficiencies of 8% at one sunlight level were obtained with short-circuit current densities as high as 26.5 mA/cm2.
Spectral acceptance for second-harmonic generation in CD*A
Authors: Taylor David J.
Published: February 2003

The efficiency of second-harmonic generation (SHG) in a crystal is reduced if the laser spectral width ΔλF is too large. This paper presents the measurement of the spectral acceptance width ΔλA in cesium dideuterium arsenate (CD*A) at the fundamental wavelength of 1.06 μm using a narrow-band tunable Nd : glass laser, with the result LΔλA=2.25 cm nm, where L is the crystal length. The theory presented here of SHG with a broad-band fundamental shows that SHG efficiency declines as ΔλA/ΔλF when ΔλF is increased beyond ΔλA. Achievement of 90% of the narrow-band SHG efficiency requires that a Q-switched Nd : glass laser be spectrally narrowed to 1.5 nm for a 1.5-cm CD*A crystal.
Damage in steel plates from hypervelocity impact. I. Physical changes and effects of projectile material
Authors: Shockey D. A. , Curran D. R. , De Carli P. S.
Published: February 2003

Microscopic details of physical changes occurring in steel plates impacted at hypervelocities by spherical projectiles of several materials are studied by means of metallographic examinations of polished and etched target cross sections. A hemispherical volume of material beneath the impact site undergoes the pressure-induced α?ε polymorphic phase change. The grain structure is heavily deformed and refined, and significant hardening occurs. The boundary between transformed and untransformed material can be made visible by etching; it corresponds to about a 13-GPa isobar. The occurrence of this phase change has a considerable effect on the stress history and on the rear-surface fracture damage, as is shown in the following paper, Paper II. Shear banding is a dominant deformation mechanism in the crater and near-crater regions. Furthermore, the numerous white-etching bands of very hard untempered martensite nearly always acquire brittle cracks along their length and, hence, shear banding strongly influences cratering behavior. The formation of crater ejecta, at least in later stages, is probably controlled by shear-band activity. Therefore, detailed predictions of near-crater fracture patterns and ejecta size distributions require a computational model for shear bands. Projectiles having lower shock impedance than the steel targets produce quite different crater shapes and near-crater fracture patterns than do higher-impedance projectiles. The downward and outward patterns of shear bands and associated cracks produce by the impact of nylon and water-filled polycarbonate, for example, are in direct contrast to the upward and outward patterns caused by steel and tungsten carbide spheres. This suggests that the maximum shear stress trajectories in the steel targets depend on the tendencies of the projectiles to penetrate or to reverse their direction upon impact. Several observed effects of projectile material on the extent of back-surface fracture damage are related to the relative shock impedances of projectile and target.
Microwave amplification with an intense relativistic electron beam
Authors: Granatstein V. L. , Sprangle P. , Herndon M. , Parker R. K. , Schlesinger S. P.
Published: February 2003

A linear microwave amplifier has been constructed using an intense relativistic electron beam (5 kA, 1.2 MV) as the active medium. Stable amplification of an externally applied 100-kW signal at ∼ 3-cm wavelength has been demonstrated with a spatial growth rate of 1 dB/cm and an over-all gain in this single-stage device of 16 dB. The amplifier appears to be a very wide band device having a bandwidth extending over several gigahertz. The measured characteristics of the amplifier have been compared with theoretical predictions for the relativistic electron cyclotron instability. Measurements of both the variation of amplifier gain with magnetic field strength and the linear spatial growth rate are in reasonable agreement with theoretical predictions.
Electrical properties of rich hydrocarbon flames
Authors: Sodha M. S. , Sagoo M. S. , Chandra Avinash , Ghatak A. K.
Published: February 2003

This paper presents measurement of electrical properties of rich hydrocarbon flames having colloidal carbon particles and comparison of the experimental results with the theory of colloidal plasmas. It is seen that in air-hydrocarbon flames the thermionic emission from colloidal carbon particles is the dominant process determining the electron density for temperatures around 1600 °K and above.
Diffuse streaks in the electron diffraction patterns from CdTe single crystals
Authors: Swaminathan V. , Narayanan G. H. , Copley S. M.
Published: February 2003

Transmission electron diffraction patterns from CdTe single crystals exhibit anomalous diffuse streaks and a number of extra spots. The orientation and temperature dependence of the intensity of the streaks and extra spots have been studied. It has been shown that the anomalous diffuse streaks can be interpreted as the intersections of {110} sheets of diffuse intensity in reciprocal lattice with the Ewalds sphere. The presence of {110} sheets of diffuse intensity is explained on the basis of thermal diffuse scattering of electrons by low-frequency acoustic phonons with wave vectors lying on {110} planes.
Dynamic behavior of twisted nematic liquid-crystal layers in switched fields
Authors: van Doorn C. Z.
Published: February 2003

The Ericksen-Leslie equations, describing the dynamic behavior of nematic liquid crystals, have been applied to a twisted nematic layer and have been numerically solved for a number of cases. The results account well for the observed dynamic behavior of displays using a twisted nematic layer. In particular, an explanation is given for the ’’bounce’’ in the optical transmission of a twisted nematic cell between polarizers after switching off the applied field. Materials having a frequency dependence of the sign of the dielectric anisotropy show a reversal of twist after the frequency of the applied field has been switched. This can also be explained. It is shown that fluid motion is essential to the occurrence of these phenomena.
Effects of collisions and thermal pressure on the nonlinear excitation of the upper hybrid resonance
Authors: Chan V. S. , Seshadri S. R.
Published: February 2003

The nonlinear interaction of two ordinary modes (the pump wave and the idler or the scattered wave) and an extraordinary mode (the upper hybrid wave) propagating across the magnetostatic field in a uniform warm electron plasma is investigated. Using the parametric approximation, the threshold value of the pump wave electric field necessary for the excitation of the parametric instability near the upper hybrid resonance and the maximum growth rate of the instability are analyzed with respect to their dependence on the strength of the magnetostatic field and the relative directions of propagation. The choice of the physical parameters which will lead to the optimization of the energy transfer to the upper hybrid wave is examined. Omitting the damping of the waves, the time evolution of the amplitudes and the relative phase of the three interacting waves is determined. These amplitudes were found to vary periodically with the nonlinear period increasing with the increase in the strength of the magnetostatic field and the decrease in the amplitudes of the idler wave and the upper hybrid wave relative to that of the pump wave. The effect of the damping of the upper hybrid wave on the time evolution of the amplitudes of the three interacting waves in investigated. The amplitudes of the pump wave and the upper hybrid wave decrease to zero and that of the scattered wave increases to a saturation value either in an oscillatory or nonoscillatory manner according to whether the damping rate is below or above a critical value. The saturation amplitude of the scattered wave is found to decrease and that the coupling to the upper hybrid wave is found to increase if the extraordinary mode is excited slightly below the exact upper hybrid resonance.
Growth and optical properties of films sputtered from neodymium pentaphosphate
Authors: Quinn D. J. , Berak J. M. , Cullen D. E.
Published: February 2003

Amorphous thin-film waveguides having low scattering and absorption losses at 1.06 μm have been sputtered from a neodymium pentaphosphate target. A narrow range in substrate temperature for the growth of this phase was found and is reported along with the other deposition conditions. Fluorescence lifetime, stoichiometry, and the effect of lanthanum addition to the target were also investigated.
A hydrogen-sensitive Pd-gate MOS transistor
Authors: Lundström K. I. , Shivaraman M. S. , Svensson C. M.
Published: February 2003

An n-channel MOS transistor with palladium gate was fabricated. The threshold voltage of this transistor was found to depend on the partial pressure of hydrogen in the ambient atmosphere. At a device temperature of 150 °C, 10 ppm hydrogen in air is easily detected, and in nitrogen or argon the sensitivity is considerably larger. A model, based on hydrogen adsorption on the palladium–silicon dioxide interface, is proposed. This model explains the device behavior and is also able to predict the absolute sensitivity for hydrogen in argon.
Electrical properties of thin-film Al-CeF3-Al capacitors
Authors: Kalra A. D. , Simmons J. G. , Nadkarni G. S.
Published: February 2003

The ac electrical properties of thin-film Al-CeF3-Al samples are found to be extremely temperature and frequency dependent. Changes in capacitance are reported as high as 20 : 1 over a temperature range of 100 °C (at constant frequency) and a frequency range of a three decades (at constant temperature). At low temperatures and high frequencies the capacitance corresponds to the geometric capacitance, but at high temperatures and low frequencies the capacitance is independent of the film thickness. The results are explained in terms of Schottky barriers existing at the metal-insulator interfaces. Excellent agreement is found to exist between the experimental data and the theory and this correlation permits determination of the doping density (?2×1019 cm−3), the donor depth (?0.64 eV), and the width of the Schottky barriers (? 50 Å) among other properties of the films.
A technique for acoustic surface studies of nonpiezoelectric materials
Authors: Rockwell D. A. , Parks J. H.
Published: February 2003

A technique is described for fluid coupling acoustic surface waves onto an arbitrary nonpiezoelectric material to allow the study of its surface properties. In these surface studies the relevant experimental information is contained in an induced phase change of the acoustic wave. For this reason, the primary concern was to develop a reliable technique by which this phase could be transmitted through the fluid interface. This issue has not been considered in previous work on fluid coupling. A simple physical model of the coupling mechanism is given, followed by a detailed description of the apparatus and procedure. Experimental studies of the phase change using the fluid-coupling technique are compared with results obtained by direct surface-wave excitation with interdigital transducers. The comparison shows that nonvolatile low-viscosity fluids (e.g., water, xylene, and o-dichlorobenzene) consistently reproduce the direct coupling results over a large variation of fluid-coupling parameters. We present an example of the application of this technique to a problem of current research interest: alkali-halide surface absorption of CO2 laser radiation.
Dielectric alignment in an electrically conducting nematic liquid crystal
Authors: Gruler Hans , Cheung Lawrence
Published: February 2003

For small deformations the local macroscopic electric field strength in a deformed uniaxial crystal is derived. For relative high frequencies (≫ σ/ε0ε) the electric field strength is determined by the anisotropic dielectric properties and for relative low frequencies (≪ σ/ε0ε) by the anisotropic electric conductivity. The local electric field strength is frequency independent if the dielectric and the electric conductivity tensor have the same anisotropy. The nonhydrodynamic deformation of a nematic liquid crystal under the influence of an electric field is derived from the torque balance equation in the small-angle approximation. This dielectric alignment is frequency dependent corresponding to the frequency dependence of the local electric field strength.
Conductance and capacitance studies in GaP Schottky barriers
Authors: Vincent G. , Bois D. , Pinard P.
Published: February 2003

A study of the conductance and capacitance associated with traps in Schottky barriers is described. A sample calculation of these two quantities is developed and compared with experimental data obtained in GaP VPE saples. It is shown that traps introduce peaks on the conductance-vs-temperatures curves; from them the concentration of each trap can be calculated. A study at different frequencies permits the determination of the characteristics of the traps. In GaP we have observed trapping effects in donor levels at Ec−Et?100 and 86 meV, the emission rates were found, respectively, to equal 2×1011 and 2×109 s−1 for these two levels. It is also shown that photoconductance effects occur at the oxygen deep levels.
Piezoelectric-magnetoelastic surface wave guided by interface between semi-infinite piezoelectric and magnetoelastic media
Authors: Tsutsumi Makoto , Bhattacharyya Tushar , Kumagai Nobuaki
Published: February 2003

This paper presents some useful discussions on the surface wave guided by the interface of two semi-infinite media in contact, of which one is piezoelectric and the other magnetoelastic. The dispersion relation has been derived and the distribution of the electric potential and the particle displacement as a function of the depth has been estimated numerically for the chosen media of ZnO and GaYIG. Subsequently, it has been shown that the nonreciprocal transmission characteristics in the narrow band can be obtained when two media have different elastic constants.
Solution strengthening of MgO crystals
Authors: Ahlquist C. Norman
Published: February 2003

The solution strengthening of MgO by dissolved transition metal cations is examined. Trivalent cations, Al3+, Cr3+, and Fe3+ harden MgO equally, while divalent cations Fe2+ and Ni2+ have little effect upon yield strength. The strengthening is inconsistent with the elastic theory of Fleischer for pinning of dislocations at tetragonal defects. The solution hardening by Al3+, Cr3+, and Fe3+ is quantitatively explained by a recent theory by Gilman. Strengthening in this theory results from the change in electrostatic energy that occurs when a trivalent ion−pair−cation−vacancy complex is sheared by a dislocation passing through the complex.
Simultaneous diffusion of two or more ions in the presence of internal electric fields
Authors: DeFord J. W. , Johnson O. W.
Published: February 2003

The theory of diffusion in the presence of internal electric fields developed in the preceding paper is generalized to the case of simultaneous diffusion of more than one species. It is shown that for the case of two chemically similar impurities, an experiment can be devised which virtually eliminates the effects of these internal fields, making possible accurate measurement of diffusion parameters. The theory is applied to H−D diffusion in rutile and it is shown that the main effect of the internal fields is to reduce the difference between the two diffusion coefficients while keeping the average nearly constant. Detailed calculations for the system are presented.
Study of the diffusion of Au and Ag in Be using ion beams
Authors: Myers S. M. , Langley R. A.
Published: February 2003

The diffusion of Au and Ag in single−crystal α−Be has been studied using ion beam techniques. The time−dependent diffusion profiles were monitored by ion backscattering. Diffusion couples were created both by ion implantation and by vapor deposition, with consistent results. Diffusion data were obtained at two temperatures, 665 and 780 °C, for both c and a crystallographic directions. Because of the low solid solubilities of Au and Ag in Be, ≲0.1 at.% at the above temperatures, a surface layer of ∼ 1000 Å thickness was always present in which the solubility was greatly exceeded. During annealing this layer served as a source from which the solute diffused into the underlying Be. The surface layer was characterized by transmission electron microscopy in the case of Au implantation. No evidence of precipitation was found following the room−temperature implantation, but subsequent annealing above about 300 °C caused regions of AuBe5 to form in the layer. In the underlying bulk, the observed diffusion behavior indicates that the dilute solute is migrating within the α−Be lattice without formation of an intermetallic compound, and that its concentration is limited by the solid solubility. By solving the diffusion equation with appropriate boundary conditions, the diffusion coefficients and solid solubilities in α−Be are extracted. The diffusion rates for Au in Be are found to be very similar to those for Cu in Be in magnitude, in temperature dependence, and in anisotropy (Dc/Da ?0.5 in both cases). However, for Ag the diffusion coefficients are larger by about an order of magnitude and have the opposite anisotropy (Dc/Da?2). This variation among the I B solutes is shown to correlate with pseudopotential parameters. Diffusion measurements were also made for Au in polycrystalline Be with a mean grain size of 10 μm. This effective diffusion coefficient is found to be much larger than in the single−crystal material, a factor of ∼100 at 665 °C, and to have a weaker temperature dependence.
Damage rates in electron−irradiated gold
Authors: Dworschak F. , Schepp H.−E. , Wollenberger H.
Published: February 2003

The interaction of gold interstitials with other point defects has been investigated by damage rate measurements in gold at irradiation temperatures between 5.2 and 220 K. At all irradiation temperatures the damage rate intially shows a strong nonlinear decrease with radiation−induced defect density which approximates a linear decrease at higher defect densities. At all irradiation temperatures the initial damage rate is reduced by quenched−in vacancies. Although these observations are consistent with several generally discussed interstitial production mechanisms, the results of irradiation doping experiments represent a serious contradiction against all models, which have been discussed before. A hypothesis, which overcomes this difficulty, is presented.
The structure of a single step on the surface of a Kossel crystal in equilibrium: A Monte Carlo simulation
Authors: van Leeuwen C. , Mischgofsky F. H.
Published: February 2003

Until now the equilibrium structure and properties of a monatomic step on a crystal surface have been described by statistical theories excluding overhanging ledge configurations and kink correlation. At higher temperatures the validity of these approximations is questionable. For these temperatures we have studied the (01) step of a (001) vicinal surface of a Kossel crystal using the Monte Carlo simulation technique for a one− and two−dimensional computer model. In our temperature region the ledge overhang density varies exponentially with ω according to h=29 exp(−5.8ω). The jump density distribution and the ledge roughness are in good agreement with statistical theories. There is no apparent kink correlation except a trivial one due to ledge overhangs. The ledge width originating from clustering at the ledge increases strongly with step length and temperature. For ω=1.0 it reaches a mean and maximal value of 7 and 40 units, respectively, for a step length of 960 units. With the help of modern techniques, these are visible dimensions.
Probe and spectroscopic measurements in a high−density dc argon arc plasma
Authors: Pasternak A. W. , Offenberger A. A.
Published: February 2003

A steady−state magnetized argon arc plasma device operating in the multi−Torr pressure region is described. Diagnostic techniques involving electrostatic probes and spectroscopic methods are discussed and subsequent information on plasma arc parameters is presented. Electron densities of ∼2.5×1015 cm−3 and electron temperatures of ∼3.5 eV are derived from probe data, while Ar II Doppler line broadening and Zeeman line splitting yield ion temperatures of ∼2.0 eV and peak magnetic field strength of ∼2.5 kG.
Aerosol−induced air breakdown with CO2 laser radiation
Authors: Smith David C. , Brown Robert T.
Published: February 2003

The breakdown threshold with 10.6−μ wavelength CO2 laser radiation induced by particles is reported. Single solid particles of different materials and sizes were suspended electrodynamically at the focus of a pulsed TEA laser and the thresholds for vaporization and also for particle−induced breakdown were measured. Th threshold intensity for breakdown is of the order 108 W/cm2, independent of particle size and material and represents the limiting intensity that can be propagated through an aerosol−laden atmosphere.
Electron microscopy of fine holes in polyethyleneterephthalate films irradiated by fission fragments
Authors: Komaki Yoshihide , Otsu Hitoshi , Izui Kazuhiko , Tsujimura Shigeo
Published: February 2003

Fine holes in polyethyleneterephthalate films prepared by exposing to fission fragments and chemical etching were observed with an electron microscope. Transmission electron micrographs of the films 6−9 μm in thickness were taken using a high−voltage electron microscope. Hole densities ahd hole diameters were determined and found to agree with the values calculated from the irradiating condition and those obtained from the measurements of gaseous diffusion through the films, respectively.
Interatomic distance functions obtained by electron diffraction from the polyethylene melt: Possible errors in the interpretation of radial distribution functions
Authors: Voigt−Martin I. , Mijlhoff F. C.
Published: February 2003

These investigations were undertaken in order to study in more detail problems regarding the distribution of molecules in the polymer melt, specifically the question concerning the existence of short−range order. The specimens studied in greatest detail were high−density polyethylene. The technique employed was that of electron diffraction, using the sector apparatus now common in gas electron diffraction work. Photographic densities were transformed to intensities (Itot), interpolated on an s scale {s=4π sin[(1/2) ϑ]λ−1], divided by the theoretical atomic scattering Ib, and a smooth background IB(s) (chosen by applying the usual criteria, e.g., smoothness and a flat zero line in the radial distribution function), yielding a quantity defined as 1+i (s). A radial distribution function is obtained by Fourier sine transform of si (s): φ (r) = (2/π)1/2 ℱsmaxsmin si (s) exp(−bs2) sin(rs) ds, where the damping factor b is chosen to reduce the termination error due to the lacking intensity data beyond s=smax. Great emphasis has been placed in this investigation on improving the accuracy and objectivity of the method, regarding both the diffraction technique and estimation of the background as well as the calculating method. It was thus possible to obtain radial distribution curves with good resolution up to about 10 Å. The limitations set by the experimental method do not allow any conclusions to be drawn about molecular configuration beyond this value.
Crack and dislocation propagation in an idealized crystal model
Authors: Weiner J. H. , Pear M.
Published: February 2003

Results are presented of computer simulation studies of crack dynamics in an idealized two-dimensional crystal model. It is based on a model introduced by Sanders which permitted crack extension and has been modified here to permit dislocation generation and propagation as well. The studies indicate that, depending on the parameter values, the model exhibits either brittle or ductile behavior. In the former case it is found that, except at very high stress levels, the crack reaches a steady subsonic terminal velocity whose value is stress dependent. Supersonic crack velocities are observed at very high stress levels in accord with the theoretical prediction of Sanders. The effect of temperature on crack speed is found to be small. For the parameters which lead to ductile behavior, the crack does not extend but is blunted by dislocation generation from its tip.
X-ray-induced electron emission from metals
Authors: Dolan K. W.
Published: February 2003

Energy and angular distributions of electrons (energies greater than 5 keV) emitted from metals irradiated by photons in the x-ray energy range were measured with a lithium-drifted silicon detector. The data presented here characterize electron emission distributions for normal photon incidence. They provide a systematic set of absolute distributions for quantitative comparisons to theoretical treatments of the combined photon and electron transport process. X-ray bremsstrahlung spectra with mean photon energies of 30 and 54 keV were used to induce electron emission from aluminum, copper, silver, and tantalum. Angular distributions for the higher-Z materials are found to be nearly cosine distributions in both the forward and backward emission directions, while the distributions for lower-Z materials deviate from a cosine distribution, tending to be more isotropic. Energy distributions are observed to change very little as a function of emission angle. Energy and angular distributions calculated by Monte Carlo and analytic techniques show good correlation with the measured distributions. Calculated forward and back (2π) emission efficiencies agree with experimental values within the uncertainties of these quantities (±15 to 20%). The generally good agreement between the experimental and theoretical results establishes the validity of the present techniques for calculating high-energy (greater than 5 keV) x-ray-induced electron emission from metals.
Maintenance of a gas breakdown in argon using 10.6-μ cw radiation
Authors: Moody Carlton D.
Published: February 2003

An experimental study on a sustained optical discharge in argon was made. The discharge was initiated by using the high-power radiation from a pulsed CO2 laser and was maintained by using the 10.6-μ radiation from a low-power cw laser. An extensive pressure range, where the discharge can be maintained indefinitely, is found to exist. The discharge exhibits four distinct characteristics in the pressure range 2–17 atm. It is also found that the minimum cw power required to maintain the discharge is several orders of magnitude smaller than the power to initiate it and has a p−2 dependence on the gas pressure at low pressures. This dependence came from the ambipolar diffusion losses. An electron production and loss rate balance equation is found to adequately describe this minimum maintenance power dependence on the gas pressure.
Nonlinear response of a plasma to superposed electric fields
Authors: Willett Joseph E.
Published: February 2003

An analysis is presented which describes the nonlinear response of the electrons in a weakly ionized plasma to superposed time-dependent electric fields. Two or more uniform fields with frequencies ω+nΩ, where ω≫Ω and the n are small positive and/or negative integers, are considered. A method of calculating the current density is developed which is based upon solution of the Boltzmann equation by use of a single Fourier series in a quasiperiodic approximation. Measurement of the amplitude and phase shift of the nonlinear current density at frequency ω is proposed as a diagnostic technique.
Diamagnetic loops in beam-plasma heating experiments
Authors: Striffler C. D. , Kapetanakos C. A.
Published: February 2003

The effect of an electron beam on the output signal of a diamagnetic loop, used in beam-plasma heating experiments, is studied by examining the diffusion of a magnetic field pulse through a cylindrically symmetric plasma column. The source of the magnetic field pulse in the calculations is a thin rotating E layer which has a trapezoidal shape in time. Exact analytical expressions are obtained for the electric and magnetic fields and for the integrated output of a diamagnetic loop placed outside the plasma column. It is shown that only for low plasma conductivity does the diamagnetic signal at all resemble the shape of the beam current pulse. The results are not sensitive to the shape of the beam current pulse.
Electrostatic potential due to a finite number of double laminae in free space
Authors: Pasha Mohammed Latif
Published: February 2003

The potential problems due to a finite number of double laminae in the form of disks and spherical caps are considered. The solution of each problem is reduced to the solution of some Fredholm integral equations of the second kind and Volterra integral equations of the first kind which are easily invertible. Detailed solutions are presented for the particular case of a pair of double laminae and the expressions for some physical quantities such as the total charge on the laminae are derived. Even some of the limiting results obtained from the analysis of the particular case seem to be new. At the end of the paper some numerical solutions of the problem are obtained.
Room−temperature cw Nd3+ : CeCl3 laser
Authors: Singh S. , Chesler R. B. , Grodkiewicz W. H. , Potopowicz J. R. , Van Uitert L. G.
Published: February 2003

Room−temperature cw laser operation has been achieved in Nd : CeCl3 at a threshold 0.6 times that of Nd : YAG, in excellent agreement with theoretical predictions.
Energy loss of 0.3−2.0−MeV 4He ions in aluminum
Authors: Feng J. S.−Y.
Published: February 2003

The stopping power of aluminum for 0.3−2.0−MeV 4He ions has been remeasured. The present results do not differ significantly from those previously reported by Porat and Ramavataram.
Magnetization of amorphous Gd-Co-Ni films
Authors: Hasegawa R. , Taylor R. C.
Published: February 2003

The temperature dependence of magnetization from 4.2 to 500 °K for amorphous Gd-Co-Ni films obtained by evaporation is found to be satisfactorily described by a two-sublattice model in wihch the two 3d transition metals form one sublattice interacting antiferromagnetically with the Gd sublattice. The unique magnetization behavior observed is attributed to an intersublattice exchange interaction which is small in comparison to the transition-metal intrasublattice exchange interaction.
An accurate and sensitive method for the determination of the depth distribution of light elements in heavy materials
Authors: L’Ecuyer J. , Brassard C. , Cardinal C. , Chabbal J. , Deschênes L. , Labrie J. P. , Terreault B. , Martel J. G. , St.-Jacques R.
Published: February 2003

A method for the determination of the depth distribution of light elements in heavy materials is described. It involves the detection of light elements recoiling under the bombardment by a 35Cl beam. A resolution of 300 Å was achieved for the lithium present in a thin sample. The measures were done with layers of 1016 atoms/cm2 and it is estimated that quantities as small as 1014 atoms/cm2 can be located without much difficulty.
Radial profiles of upper-laser-level emission in an oscillating Ar II laser
Authors: Ihjima Toshiyuki , Karatsu Osamu , Ogura Iwao
Published: February 2003

Radial profiles of the emission from upper-laser-level ions have been investigated in an oscillating Ar II laser and a significant dip in the tube center is observed.
Amplification of magnetostatic surface waves in a layered structure consisting of metals, dielectrics, a semiconductor, and YIG
Authors: Chang Nion S. , Yamada S. , Matsuo Y.
Published: February 2003

The amplifying characteristics of magnetostatic surface waves (MSSW) propagating in a layered structure consisting of metal plates, dielectrics, a semiconductor, and a YIG slab are given. The dispersion relation of the system is derived under the condition of magnetostatic approximation. From the results of computer solution for the dispersion equation, we conclude that a growing MSSW occurs only when the carrier drift velocity is greater than phase velocity of the MSSW. The effect of YIG loss on the wave instability is considered. Also, the influence of a gap between the semiconductor and the YIG slab on the amplifier is discussed.
Quasistatic deformation of porous beryllium and aluminum
Authors: Schock R. N. , Abey A. E. , Duba A.
Published: February 2003

Loading and unloading of two types of porous beryllium and a porous aluminum under conditions of uniaxial strain, proportional loading, and hydrostatic pressure indicate that yielding is dominated by porosity. Analysis of the data prior to yielding indicates that aspherical pores cause increased compressibility on initial loading. All materials exhibit enhanced compaction when loaded under nonhydrostatic stress conditions. Models which treat the collapse of spherical pores do not agree with the beryllium data, probably because of the influence of aspherical pores and pore-size distribution.
Phase identification in titanium-rich Ti-Fe system by Mössbauer spectroscopy
Authors: Stupel M. M. , Ron M. , Weiss B. Z.
Published: February 2003

Various phases of the titantium rich part of the Ti-Fe binary system were obtained by thermal treatments and were identified by Mössbauer spectroscopy and x-ray diffraction. Room-temperature Mössbauer parameters were derived for the following phases: αm, α, ϑ, ω, β, and TiFe. The range of concentrations for which an athermal ω phase appears upon quenching was found to be 2.7⩽CFe⩽5 wt%. The athermal ω phase disappears during aging at 285 °C for 15 h, when the alloy contains CFe⩽4.0 wt%. Martensite αm was found to form when Fe concentrations were ⩽2.7 wt.%. After quenching from the β field, the β phase retains when the Fe content of the alloy is ⩾2.7 wt.%. The ϑ phase forms during aging at temperatures above 280 °C, for alloys with a Fe content ⩽2.7 wt.%. Room-temperature Mössbauer parameters are given to enable phases to be indentified and analyzed by means of Mössbauer spectroscopy.
Transition radiation by a charged particle moving across a plasma sheet
Authors: Sharma S. R. , Swami K. C.
Published: February 2003

Expressions are derived for the transition radiation fields due to a charged particle passing across a dielectric layer surrounded by media of different dielectric constants. Transition radiation for a cold plasma sheet is discussed in detail and radiation patterns on both sides of the sheet are presented for different values of the particle velocity and the thickness of plasma sheet. The radiation patterns are found to depend sensitively on these parameters.
Estimation of mechanical transients in ’’tuned-circuit’’ levitators by employing steady-state impedances
Authors: Kaplan B. Z.
Published: February 2003

Investigations of a relatively new magnetic levitation device are described. This device uses an electromagnet, which is the inductive part of a resonant circuit. If the circuit is properly tuned, static stability is attainable. ’’Tuned-circuit’’ levitators are characterized by typical transients of the suspended object which are difficult to analyze. The work described here is a contribution towards simplifying the calculations of such transients. The analysis presented in the paper relies on calculating the impedance of the tuned circuit for each position of the suspended object. Though the impedance obtained in this way is merely the ’’steady-state’’ impedance of the circuit, it enables one to predict some of the parameters characterizing the mechanical transients of the suspended object. The frequency of mechanical oscillations is the main parameter to be predicted in this way. Investigations were conducted where the predicted mechanical frequency of oscillations was compared with that obtained experimentally. The results of the experiments were usually close to those expected by theory.
Production of intense proton fluxes in a magnetically insulated diode
Authors: Dreike P. , Eichenberger C. , Humphries S. , Sudan R.
Published: February 2003

A magnetically insulated diode has been used to produce intense fluxes of protons with high efficiency. Currents in excess of 4 kA with current density greater than 50 A/cm2 have been produced in a 50-nsec bursts at energies up to 200 keV. The system appears to be easily scalable to higher parameters. The extraction of the beams, as well as geometries in which current densities of kA/cm2 may be realized, are discussed.
Nonlinear modulation of TM waves in a circular waveguide
Authors: Asfar Omar R. , Nayfeh Ali H.
Published: February 2003

The method of multiple scales is used to derive a nonlinear Schrödinger equation for the temporal and spatial amplitude and phase modulations of TM waves in a perfectly conducting guide containing a nonlinear isotropic medium. This equation is used to show that monochromatic waves are stable if the mechanism producing the nonlinearity is an electric or magnetic polarization and unstable if the nonlinearity is due to electrostriction or magnetostriction. It is also used to determine the amplitude dependence of the cutoff frequencies.
Radiation pressure of light in a refractive medium
Authors: Weiss Richard A.
Published: February 2003

The radiation pressure and energy density of light in a refractive medium is calculated in terms of the index of refraction of the medium. The factor equal to the cube of the index of refraction that occurs in the expressions for the energy density and pressure of light in a refractive medium is shown to arise from the basic thermodynamic nature of the photon system and from the volume dependence of the index of refraction. It is shown that a mechanical pressure exists in a refractive medium which is in equilibrium with the blackbody radiation of the vacuum.
Double mass transfer during polymer-polymer contacts
Authors: Salaneck W. R. , Paton A. , Clark D. T.
Published: February 2003

Double mass transfer has been observed spectroscopically and nondestructively for the first time using the x-ray photoemission technique to examine both halves of polymer films touched to other polymer films. A careful selection of polymers according to their peculiar x-ray photoemission spectra enabled the unambiguous identification of polymer fragments on the respective surfaces. The use of the nondestructive XPS or ESCA technique makes possible the observations involving both halves of the contacting pair, and especially the detection of fragments of one polymer on the surface of another. The amount of material transferred is much larger than that necessary to explain triboelectric charging phenomena in terms of mass transfer on a basis of one electronic charge per atom.
Elastic interactions between ’’voids’’ induced by solute segregation
Authors: Nolfi F. V.
Published: February 2003

Expressions are derived for the elastic interaction energy between void-solute shell composites. These composites consist of spherical void cores surrounded by spherically symmetric solute shells containing a uniform concentration of irradiation segregated solute. The solutes are assumed ’’misfitting’’ and as such represent sources of internal stress. The elastic interaction energy between composites arises because of the so-called inhomogeneity interaction and has minimum values at certain composite separations and solute shell thickness. The existence of these minima obtains largely because the misfit of the composites increases as the composite separation R increases. For a constant misfit, the interaction energy would decrease monotonically approximately as R−6. The surface stress of voids is taken to be zero in the calculations so that the only source of interaction between composites is the stress induced by solute segregation. The calculations are performed for both two-composite and N-composite interactions, and we show that, primarily, only nearest-neighbor interactions are significant. The calculations are compared with experimental investigations of void ordering in an Ni ion-irradiated Nb-1Zr alloy containing 0.0038 atom fraction of oxygen as an impurity. Given experimentally determined void sizes and auxiliary data, the correct void lattice parameter is predicted when the solute shell thickness is ∼30% of the composite radius. In pure Nb, it is found the O, C, or N impurities are necessary for void ordering, which supports the main thesis of the present paper, viz., solutes/impurities are a primary cause of void ordering.
Ingot-nucleated Pb1−xSnxTe diode lasers
Authors: Lo W. , Montgomery G. P. , Swets D. E.
Published: February 2003

Large high-quality Pb1−xSnxTe single crystals (x=0.13) have been grown by a horizontal vapor-growth process in which the horizontal temperature gradient is adjusted to produce nucleation on the source ingot. The crystals are free of metallic inclusions, low-angle grain boundaries and voids, and have bulk dislocation densities as low as 2×104/cm2. Diode lasers having up to 400-μW single-mode cw power near 10.6 μm have been fabricated from these crystals. Material quality, particularly dislocation density, appears to be the major factor governing device performance.
Drift mobility of holes in n-type germanium bombarded by fast neutrons
Authors: El-Difrawi A. A. , Yeh T. H. , Christopher J. E. , Gossick B. R.
Published: February 2003

A surface effect which depends on exposure to fast neutrons is introduced. This effect makes the apparent drift mobility of holes in germanium increase under certain conditions following irradiation by fast neutrons, but the bulk mobility never increases. Thus, contrary to a simple model for disordered regions in n-type germanium, these regions do not act like short circuits for holes.