bluuebunny/crossref_metadata_2025 huggingface dataset:
Disordered-resistor network approach to the effective conductivity in inhomogeneous continua with substitutional disorder
Authors: Nagatani Takashi
Published: February 2003

A disordered-resistor network model is presented to analyze the effective (or macroscopic) conductivity in inhomogeneous continuum with a cellular-substitutional disorder, where local conductivity g(x) varies randomly from cell to cell. The perturbation expansion for the lattice model is given to derive the effective conductivity from the statistical information about the random field g(x). The two-cell approximation taking account into pair configurations can be obtained from the partial sum of two-vertex terms by means of a diagrammatic representation of the perturbation series. The expression for the effective conductivity is presented up to the second-order term of the volume concentration c. This is also rederived from the different method, by solving problems involving two cells and averaging over all possible pair configurations. The coefficient of c2 is numerically calculated for two models with the different pair configurations. The difference between pair configurations are clearly demonstrated by the present theoretical approach. It is shown that the calculated values agree with the experimental data of isotropic conducting paper into which square holes are punched at random.
Impact ionization of electrons in silicon (steady state)
Authors: Tang J. Y. , Hess Karl
Published: February 2003

Monte Carlo simulations of electron impact ionization in silicon are presented which include the pseudopotential band structure as well as collision broadening and higher order effects in the electron phonon interaction. Conduction in the two lowest conduction bands of silicon is considered. We also present new results for the impact ionization probability and deformation potential constants which are obtained by comparing our theory with a variety of experimental results.
Minority carrier lifetime in n-type Bridgman grown Hg1−xCdxTe
Authors: Pratt R. G. , Hewett J. , Capper P. , Jones C. L. , Quelch M. J.
Published: February 2003

Minority carrier lifetimes have been mapped on slices of n-type Hg1−xCdxTe (x∼0.3) grown by the Bridgman technique. The mean lifetime on a slice has been measured as a function of extrinsic carrier density and composition. Lifetimes at selected positions on slices have been measured as a function of temperature down to 30 K. Aging effects have also been investigated. We show that the lifetime variation with temperature cannot be explained by direct band-to-band recombination alone. The assumption that recombination also occurs via Shockley–Read type recombination centers, situated 10–30 meV below the conduction band edge, enables us to calculate theoretical values of the lifetime in good agreement with the experimental results. Such a model can also be used to explain the variation of lifetime with composition.
A new static method for measuring minority carrier lifetime
Authors: Manifacier J.-C. , Moreau Y. , Henisch H. K.
Published: February 2003

The paper describes the theory of a new static lifetime measurement, carried out by means of potential probes in the vicinity of a current-carrying contact on a high-lifetime semiconductor, with and without traps. It is based on recognition of the fact that, in the presence of minority carrier injection, a uniform field is obtained only for a particular current density, and that depends directly on the carrier lifetime.
Analysis of mixed conduction effects in semi-insulating gallium arsenide
Authors: Winter J. J. , Leupold H. A. , Ross R. L. , Ballato A.
Published: February 2003

Hall effect and conductivity measurements made on semi-insulating bulk GaAs are examined by a new approach to mixed conduction analysis. Based on Fermi level and electron mobility analyses of conductivity and Hall coefficient, it uses revised values of effective densities of states at the band edges and electron/hole mobility ratios recently adopted by other workers. The treatment provides a visual analysis of the system in terms of the electrical parameters and impurity densities, and establishes criteria for the onset of mixed conduction.
Multibarrier tunneling in Ga1−xAlxAs/GaAs heterostructures
Authors: Vassell M. O. , Lee Johnson , Lockwood H. F.
Published: February 2003

A theoretical study of resonant tunneling in multilayered Ga1−xAlxAs/GaAs structures is presented. The spectrum of resonant energies and its dependence on the barrier structure are analyzed from calculated profiles of barrier transparency versus energy, and from current–voltage characteristics computed at selected temperatures and Fermi levels. The present formalism is based on the effective mass approximation as done to date, but contains three significant improvements: a more realistic treatment of the spatial dependence of effective masses and band edges; the recognition of the special dynamical role played by the transverse energy as a consequence of the difference in itinerant two dimensional carrier motion from layer to layer; and the avoidance of plane-wave or WKB approximations for calculating the wave function in favor of direct numerical evaluation. It is shown that these revisions lead to quantitative differences with results of previous work.
Scanned light pulse technique for the investigation of insulator–semiconductor interfaces
Authors: Engström Olof , Carlsson Annelie
Published: February 2003

A new measurement method, scanned light pulse technique, for the investigation of the interface properties of metal–insulator–semiconductor (MIS) structures is introduced. The measured signal is the charge contents of current transients induced by light pulses applied to the investigated sample. This signal depends on surface potential, interface state density and voltage applied to the MIS structure. By analyzing the results of such measurements it is quantitatively demonstrated how insulator charge and interface state distribution influence the voltage dependence. By scanning a light spot across the surface of an MIS structure with transparent metal electrode it is further shown that pictures of the spatial variation of the surface potential and the interface state density can be obtained.
Fluxoid motion and electromagnetic phenomena of a superconductor in a longitudinal magnetic field
Authors: Matsushita T. , Hasegawa Y. , Miyake J.
Published: February 2003

The fluxoid motion during the process of applying the transport current to a superconductor in the longitudinal field configuration is visualized by solving the continuity equation of the fluxoid number. In this configuration, the force-free state described by rot B=αB is assumed. The obtained fluxoid velocity v contains the torsionally shearing component. The well-known relation E=B×v does not hold in the present field configuration. This fluxoid motion and the related phenomena are compared with those in the rotating transverse field configuration.
Spectroscopic measurement of hydrogen contamination in weld arc plasmas
Authors: Shea J. E. , Gardner C. S.
Published: February 2003

The introduction of hydrogen into metals during welding is known to cause hydrogen assisted cracking and embrittlement in certain situations. It has been shown that the weld metal hydrogen content is directly related to hydrogen concentration in the weld arc plasma. In this paper we describe a simple spectroscopic technique for measuring the arc plasma hydrogen concentration in real time when an argon shield gas is used. This technique is based on the fact that the intensity ratio of the hydrogen Balmer Alpha emission line at 6563 Å and an argon emission line at 6965 Å was observed to be an approximately linear function of hydrogen concentration in the weld arc plasma. This technique was experimentally verified under a variety of welding conditions for gas metal arc welding and found to have an error of less than 10% when measuring hydrogen concentrations in the arc plasma as low as 0.25% by volume. This method of hydrogen measurement is also applicable when welding with shield gases not containing argon so long as a suitable ratioing line is available.
Monte-Carlo simulation of electron properties in rf parallel plate capacitively coupled discharges
Authors: Kushner M. J.
Published: February 2003

Electron properties in a parallel plate capacitively coupled rf discharge are studied with results from a Monte-Carlo simulation. Time averaged, spatially dependent electron distributions are computed by integrating, in time, electron trajectories as a function of position while oscillating the applied electric field at rf frequencies. The dc component of the sheath potential is solved for in a self-consistent manner during the simulation. For conditions where the secondary emission coefficient for electrons from the electrodes is large, the electron distribution is spatially differentiated, being dominated by an e-beam component near the electrodes while being nearly in equilibrium with the applied electric field in the body of the plasma. The dc component of the sheath potential is found to be a function of the ratio λ/d, where λ is the electron mean free path and d is the electrode spacing.
Exact solutions for liquid crystal configurations and an improved boundary layer model
Authors: Thurston R. N.
Published: February 2003

The director configuration in a liquid crystal cell is basic to an understanding of both the optical contrast between states and switching dynamics. This paper treats the voltage dependence of nematic liquid crystal configurations in which the director orientation depends on a single space coordinate z, and there are equal but oppositely tilted boundary conditions on the two cell surfaces at z=±d/2. In the boundary layer model, configurations are approximated by joining together pieces of ‘‘boundary layer solutions,’’ which are solutions of the equations for equilibrium configurations in a half space with the boundary condition θ=constant at only one surface and θ=dθ/dz=0 at z=∞, where θ is measured from the normal to the surface. This paper (1) indicates exact solutions that satisfy the cell boundary conditions, (2) examines their high voltage asymptotes, (3) proves that the boundary layer solutions reproduce the essential features of these asymptotes, and (4) presents a way of fitting boundary layer solutions into a finite cell by joining them where θ=θmin such that θmin is the correct asymptotic function of voltage. Topologically distinct horizontal (H) and vertical (V) states are distinguished by the boundary conditions: if θ=θb at one surface, then at the other surface θ=−θb for V and π−θb for H. The H state can be symmetric (HS) or asymmetric (HA). All of these states are treated, with emphasis on the high voltage asymptotic behavior. Below the HA−HS threshold, HA is nonexistent, and HS is stable; above this threshold, HA is stable and HS is unstable [Julian Cheng, R. N. Thurston, and D. W. Berreman, J. Appl. Phys. 52, 2756 (1981)].
The rotational viscosity of nematic liquid crystal mixtures at low temperatures
Authors: Schad Hp.
Published: February 2003

An experimental setup is described for the determination of the rotational viscosity γ1 of nematic liquid crystals which operates at temperatures down to −60 °C. Using this setup we have determined γ1 of several liquid crystal mixtures over a wide temperature range and find significant deviations from Arrhenius behavior at lower temperatures.
Growth kinetics of platinum silicide
Authors: Wittmer Marc
Published: February 2003

The influence of substrate orientation and dopant on the growth kinetics of Pt2Si and PtSi have been studied. It was found that the growth of both silicides is diffusion limited and independent of substrate orientation. However, on substrates doped with an arsenic concentration of 5×1020 cm−3 the preexponential factor of the PtSi growth kinetics is lowered by a factor of 2, but the activation energy remains unchanged. This change in the preexponential factor is independent of the Si substrate orientation. The results are discussed in terms of possible diffusion mechanisms in PtSi.
Thermal aspects of magneto-optical recording
Authors: Mansuripur M. , Connell G. A. N.
Published: February 2003

We discuss the influence of thermal response on the magneto-optic readout performance of optically similar but thermally different quadrilayer media, using newly developed computational techniques for examining laser-induced heat flow in moving multilayer media. We first emphasize the importance of time scale for differentiating the write and read processes. We then show that the optimum design is a function of the medium velocity and available laser power for writing and is not normally one that provides maximum signal-to-noise ratio in the limit that laser heating during readout can be ignored. Finally, we describe a systematic approach to the selection of the best quadrilayer design for a given set of system conditions.
Self-pulsing and transients of a Fabry–Perot interferometer with quadratic nonlinear medium
Authors: Wedding Berthold , Gasch Armin , Jäger Dieter
Published: February 2003

The dynamic properties of a Fabry–Perot interferometer filled with a material exhibiting second-order dispersive nonlinearity are studied both theoretically and experimentally. The response of the medium is described by an intensity dependent phase constant as derived from self-action effects. Considering two relaxation times, that of the material and that of the cavity, the basic relations for the stability analysis and for the numerical calculations are obtained. Bistability and self-pulsing effects are predicted. Moreover, the transient behavior is characterized by anomalous switching properties like overshoot and alternate switching. The corresponding experiments performed on a nonlinear transmission line resonator confirm the theoretical results. In a final discussion, the relations to the field of nonlinear optics are outlined.
Measurements of energetic electrons in a magnetized hot filament discharge
Authors: Ellis R. F. , Arion D. N.
Published: February 2003

Measurements of the energy distribution function of primary electrons in a hot filament discharge in a magnetic field have been made. These results show a smooth distribution function which decreases monotonically with increasing energy up to a value approximately equal to the discharge voltage; the shape of the distribution is independent of other discharge parameters. An ionization kinetics model is used to estimate the energetic electron density, which is shown to vary linearly with plasma density, inversely with fill pressure, and decrease with increasing discharge voltage. At the highest plasma densities bulk heating, possibly due to coulomb drag on primary electrons, is observed.
On differential equations of nonlocal elasticity and solutions of screw dislocation and surface waves
Authors: Eringen A. Cemal
Published: February 2003

Integropartial differential equations of the linear theory of nonlocal elasticity are reduced to singular partial differential equations for a special class of physically admissible kernels. Solutions are obtained for the screw dislocation and surface waves. Experimental observations and atomic lattice dynamics appear to support the theoretical results very nicely.
Forward cw CO2-laser scattering on a high density plasma column
Authors: Lachambre J. L. , Decoste R. , Robert A. , Noel P.
Published: February 2003

Wave-number and frequency spectra S(k,ω) associated with spontaneous electrostatic fluctuations in a high-density (5×1021 m−3) current-driven plasma are measured using forward CO2-laser scattering with homodyne detection. Scattering measurements during the quiescent plateau phase of the discharge show fluctuation levels several orders of magnitude above the thermal level with k−4 and ω−2 spectral amplitude dependences. The fluctuations are found to be isotropic in a plane transverse to the magnetic axis with S(k∥,ω)≪S(k⊥,ω). The scattering apparatus is also shown to be a valuable diagnostic tool for basic studies of plasma current transport across magnetic field lines. In fact, a clear correlation is observed between the appearance of strong fluctuations and the rapid current penetration during fast plasma current reversal experiments. Finally, cw scattering results are used to find a set of experimental conditions suitable for the measurement of the ion temperature using a CO2 pulsed scattering system.
A Fourier series approach to magnetostatic field calculations involving magnetic material
Authors: Caldwell J. , Zisserman A.
Published: February 2003

The effect of iron on the uniformity of the field produced by an axisymmetric thick solenoid is considered. Using a Fourier series approach, an exact solution for the vector potential A is found and from this the magnetic induction B is derived. The results are compared with those obtained from previous approximate methods.
Electrostatic fields in an ionization chamber electret
Authors: Fallone B. G. , Podgorsak E. B.
Published: February 2003

The theory of linear systems is used to derive the potential and electric field in distance space in a cylindrical polarization/depolarization electret chamber. General solutions for the near, intermediate, and far regions are given and their domains of convergence discussed. On the axis of the chamber the solutions for the electret surface are equal to those obtained from Gauss’s and Kirchoff’s laws, and at large distances from the surface to those obtained from the introduction of a dipole layer model.
High voltage electric field and space-charge distributions in highly purified water
Authors: Zahn Markus , Takada Tatsuo
Published: February 2003

High voltage Kerr electro-optic field mapping measurements in highly purified water show significant field distortions due to injected positive space charge over the temperature range of 8–25 °C using parallel plane stainless steel electrodes stressed to average field strengths up to 150 kV/cm. The net space charge was always positive with density of ≂2 C/m3 which is about 40% of the background value of charge density of thermally generated hydronium and hydroxyl ions. Because measurements only showed a net positive space charge, a unipolar drift dominated conduction model was developed where positive charge would migrate in an ohmic medium. This model predicts the observed propagating charge front, electric field enhancement at the noncharge injecting electrode, and field decrease at the charge injecting electrode. The time of flight of positive charge between electrodes gave an estimate of the positive ion mobility of μ≂4×10−7 m2/(V s) which is inbetween the values of the hydronium ion mobility measured at low voltages and the electrohydrodynamic mobility which accounts for fluid convection effects due to the Coulombic force putting the fluid into motion. The dielectric relaxation time at T≂8 °C (τ≂320 μsec) measured at low voltage was much less than the measured charge transport time between electrodes, τmig ≂2 msec, so that the calculated effects of space charge were much less than measured because the charge relaxes quickly as it migrates. It was found that a dielectric relaxation time of τ≂1.6 msec would provide a good fit between analysis and experiments.
Study of ion-implantation damage in GaAs:Be and InP:Be using Raman scattering
Authors: Rao C. S. Rama , Sundaram S. , Schmidt R. L. , Comas J.
Published: February 2003

The Raman spectra of GaAs and InP implanted with Be ions with fluences ranging from 5×1012 to 1×1016 cm−2 were investigated. A marked difference in the behavior of the TO and LO modes with respect to broadening with fluence was observed and the results indicate that this is caused by frequency dependent anharmonic damping constants. The Raman spectra of high fluence samples are interpreted in terms of disorder-induced first-order Raman spectra due to phonons with nonzero wave vectors. The similarities between our ‘‘Reduced Raman Spectra’’ of the disordered form and the theoretical one-phonon density of states, are presented without introducing Gaussian broadening as suggested by earlier authors studying amorphous materials. The observations support the conclusion that the form essentially retains the short-range order of the crystalline phase; the phonon spectrum of the crystal is largely determined only by near-neighbor interactions; and the existence of a frequency-dependent coupling constant for the scattering intensity at least in the low frequency region.
Yield point and dislocation mobility in silicon and germanium
Authors: Schröter Wolfgang , Brion Hans Georg , Siethoff Hans
Published: February 2003

Measurements of the lower yield point in silicon and germanium, covering wide ranges of temperature and strain rate, are presented. The results indicate that Haasen’s model for the beginning of the plastic deformation of semiconductors has to be modified for germanium, while it is confirmed for silicon.
The surface energy of zinc
Authors: Bilello J. C. , Dew-Hughes D. , Pucino A. T.
Published: February 2003

The influence of temperature and associated dislocation microstructure on the energetics of basal plane cleavage in zinc crystals has been investigated using the method of Hull, Beardmore, and Valentine (HBV). A marked temperature dependence was observed in the zinc surface energy, over the range 77–298 °K, contrary to previous expectations. Plastic relaxation was associated with crack initiation at 77 °K, but not propagation; while at room temperature a plastic zone of 1200–1500 μm in depth was produced by crack extension. The surface energy could be estimated, independent of the usual Griffith analysis, by measuring the energy dissipation in a fully relaxed deformed zone associated with an explosively formed precursor crack. This method yielded surface energies of 0.066 to 0.079 J m−2 which was in good agreement with previous work. It is demonstrated that the cleavage surface energy of zinc is well below the thermodynamic surface energy and that this discrepancy is not related to plastic deformation.
Thermal generation of confocal domains in a smectic A liquid crystal
Authors: Chou N. J. , Depp S. W. , Eldrige J. M. , Lee M. H. , Sprokel G. J. , Juliana A. , Brown J.
Published: February 2003

The effects of vacuum-deposited SiOx alignment layers on the thermal generation of focal conic centers in a smectic A liquid crystal were investigated using controlled thermal cycles. Surface defects were found to promote focal conic formation. Focal conic density increases with cooling rate for a given alignment layer, and with the deposition angle of the alignment layer for a fixed cooling rate. An attempt was made to fit these findings to heterogeneous nucleation theory in an effort to better understand the effects of selected thermodynamic properties on the focal conic formation process
Heterogeneous bubble nucleation and conditions for growth in a liquid–gas system of constant mass and volume
Authors: Ward C. A. , Johnson W. R. , Venter R. D. , Ho S. , Forest T. W. , Fraser W. D.
Published: February 2003

The conditions are considered under which heterogeneous bubble nucleation takes place in a conical pit in the boundary of a constant size volume containing a liquid–gas solution, and the size to which the nucleate bubble grows is predicted. Four possible equilibrium states are found for the nucleate bubble: two unstable, one metastable, and one stable. The unstable state corresponding to the smallest equilibrium size is the one that acts as the threshold size that must be exceeded in the nucleation event. The metastable and second unstable state are encountered as the nucleate bubble emerges from the conical pit and the stable state corresponds to the largest equilibrium size. It arises from the bubble being in a finite volume with fixed mass. The pressure produced in the volume by the growth of the bubble depends on the final state it attains (i.e., either the metastable or stable state). The theoretical expressions obtained from the analysis are applied to predict the conditions under which bubble nucleation and growth take place within a type of bone cell, and the results are used to explain certain types of damage to the bone of animals undergoing decompression from high pressures that have been previously reported in the literature. The expressions are also applied to predict the superheat necessary to produce bubble emergence from a conical pit and are shown to be in agreement with results previously reported.
Laser microspeckle technique in displacement measurement near a crack tip
Authors: Tang Z. Q. , Wu K. C. , Cheng C. H. , Chern S. S. , Hsiao C. C.
Published: February 2003

The laser speckle method has been found quite useful in obtaining in-plane displacement measurements. It is especially useful if the displacement field in a small region can be effectively determined. By obtaining directly the speckle patterns at higher magnifications, a better distinction of the displacements in the vicinity of a crack tip is possible. In this short report some results are obtained and compared with those calculated from linear fracture mechanics and the finite element method for an aluminum crack.
Temporal measurement of the gain of a CuCl laser
Authors: Kuroda Kazuo , Takeda Minoru , Chihara Masao , Ogura Iwao
Published: February 2003

The temporal behavior of the population inversion density of a CuCl laser was investigated using the gain method. The amplifier model which included the effect of the pumping during the amplification was discussed and used to analyze the experimental data. The populations of the laser transition levels were inverted during about 50 ns in our laser. The mechanism of the construction and destruction of the population inversion was discussed using the numerical model fo a CuCl laser, and the variation of the electron temperature would be the main cause of the behavior of the population inversion density.
Theoretical simulation of a pulsed HF optical resonance transfer laser
Authors: Yamaguchi Shigeru , Kumamoto Kenji , Kannari Fumihiko , Obara Minoru , Fujioka Tomoo
Published: February 2003

The high-efficiency pulsed HF Optical Resonance Transfer Laser (ORTL) is described in this paper. The multiline laser output, pulse shape, pulse width, and efficiency were all calculated by using the HF computer codes which have been developed in our laboratory. Parametric studies were also done to optimize system efficiency and, as a result, the ratio of laser output energy to pumping energy was as large as 56%. The lasing lines of the ORTL covered the wavelength region between 3.0 and 3.8 μm. Comparison of the results of this simulation with the experiments of cw-ORTL shows that the pulsed ORTL could be more efficient operation.
Flashlamp-pumped iodine monobromide laser characteristics
Authors: Zapata L. E. , De Young R. J.
Published: February 2003

The operating characteristics of a flashlamp-pumped IBr laser were investigated to evaluate its suitability for solar-pumped laser applications. A peak power of 350 W/cm2 at 2.7 μm was achieved at 12-Torr IBr pressure. At 500-J flashlamp energy, the IBr output saturated; a gain of 0.17% cm−1 was measured for IBr. Neon was found to be effective for enhancing the recombination of the photodissociation products. With neon as a buffer gas, the laser pulse length was extended to 53 μsec. The termination of the laser pulse, within the flashlamp pulse, is thought to be due to the temperature rise in the gas. Increasing the IBr initial temperature decreased the lasing output. At 300 °C, output dropped to approximately one-half the room temperature value. The dominant quencher is thought to be atomic iodine. IBr was found to couple better to the flashlamp energy than C3F7I.
Secondary electron emission in the scanning electron microscope
Authors: Seiler H
Published: February 2003

This paper surveys experimental results concerned with secondary electron emission of surfaces bombarded by primary electrons with respect to scanning electron microscopy. The energy distribution, the angular distribution, and the yield of secondary electrons from metals and insulators are reviewed as well as the escape depth of the secondary electrons and the contribution of the backscattered electrons to the secondary electron yield. The different detectors for secondary electrons in the scanning electron microscope are described. The contrast mechanisms in the scanning electron microscope, material, topography, voltage, magnetic, and crystallographic orientation contrast based on secondary electron emission, as well as the lateral resolution, depending among other things on the spatial distribution of the emitted secondary electrons, are discussed.
Limitations of surface photovoltage measurements
Authors: Ghosh Amal K. , Haberman Joel I. , Feng Tom
Published: February 2003

Surface photovoltage measurement used to measure the diffusion length of minority carriers in solar cells does not yield the correct value even when the cell thickness is much greater than the diffusion length. Under the best conditions the measured diffusion length is at least 10% lower than the actual value. The discrepancy increases as the ratio of diffusion length to thickness increases.
Theoretical gain optimization studies in 10.6 μm CO2–N2 gasdynamic lasers. IV. Further results of parametric study
Authors: Reddy K. P. J. , Reddy N. M.
Published: February 2003

Based on a method proposed by Reddy and Shanmugasundaram, similar solutions have been obtained for the steady inviscid quasi-one-dimensional nonreacting flow in the supersonic nozzle of CO2–N2–H2O and CO2–N2–He gasdynamic laser systems. Instead of using the correlations of a nonsimilar function NS for pure N2 gas, as is done in previous publications, the NS correlations are computed here for the actual gas mixtures used in the gasdynamic lasers. Optimum small-signal optical gain and the corresponding optimum values of the operating parameters like reservoir pressure and temperature and nozzle area ratio are computed using these correlations. The present results are compared with the previous results and the main differences are discussed.
Coherent mode conversion by grooved arrays in layered media
Authors: Bandyopadhyay S. , Datta S. , Martin S. J. , Gunshor R. L.
Published: February 2003

Recent experiments have shown that a periodic array of grooves and strips on a layered medium provides efficient conversion between Rayleigh and Sezawa modes supported by the medium; these novel mode converting reflectors have been used to construct surface wave resonators. This paper presents a theoretical analysis of the mode conversion process starting from material parameters. A first-order perturbation theory is used to construct a four-port scattering matrix for each strip in the array. The scattering matrices are then converted to transmission matrices and cascaded to provide the overall scattering characteristics of the array. The predicted characteristics are in close agreement with experimentally measured values.
An investigation of ‘‘stable extension of crack’’ in Mo single crystals under unidirectional loading
Authors: Ha K. F. , An Z. Z.
Published: February 2003

An x-ray diffraction topographic method is used to observe the fracture surfaces during the cracking processes of Mo single crystals under a unidirectional loading. A special attention is paid to study the stable extension of crack (S.E.O.C.). The so-called S.E.O.C. is found to be caused by a forward spreading quasi-fracture formed by the alignment of the subgrains and the local lattice planes in the fracture surface through structural rotation. The phenomenon is somewhat similar to crazing in polymers. Therefore there exists an unstable brittle fracture of the deformed crystal instead of a stable extension of crack.
Surface studies of dielectric materials used in spark gaps
Authors: Jackson G. , Hatfield L. , Kristiansen M. , Hagler M. , Marx J. , Donaldson A. L. , Leiker G. , Curry R. , Ness R. , Gordon L. , Johnson D.
Published: February 2003

Dielectric materials commonly used as insulators in spark gaps (lexan, nylon, lucite,macor, boron nitride, delrin, and G-10) have been exposed to the byproducts of arcs in three different spark gap experiments. The first was a 60-kV, 0.05-C/shot spark gap using copper-tungsten or graphite electrodes at various pressures of N2 and SF6 gas. The second was a 5–30-kV, 4–25-kA, 0.1–0.6-C/shot, unipolar, pulsed spark gap using graphite, copper-graphite, copper-tungsten, brass, and stainless steel electrodes in N2 gas or air. The third was a 45-kV, 0.009-C/shot surface discharge switch. Surface analysis of these insulators indicates that most become coated with a thick layer of electrode material depending upon the type of gas, electrode, and insulator material used, and the conditions of the arc. However, lucite insulators inserted in the second spark gap using graphite electrodes and air showed no indications of deposited electrode material on the surface but did show small particles of graphite imbedded in the surface. The self-breakdown voltage (Vsb) statistics for spark gaps with insulator inserts show significant deviations from the Vsb statistics for spark gaps without insulator inserts, which may be due to deposits of insulator material onto the electrodes.
Nonequilibrium noise of InSb hot electron bolometers
Authors: Brown Elliott
Published: February 2003

Noise spectra of a InSb hot electron bolometer at 4.2 K bath temperature are measured and compared with theory. Bolometer phonon noise and Johnson noise are included in the analysis. A nonequilibrium Johnson noise model, due to Mather, gives good agreement with experiment over the frequency range 0.2–1.1 MHz. This model incorporates an elevated electron gas temperature and electrothermal feedback from the bias supply.
A method of determining electrical properties of geophysical media
Authors: Freundorfer Alois , Iizuka Keigo , Ramseier René
Published: February 2003

A method to measure the loss tangent and relative dielectric constant of geophysical media at ultrahigh frequencies was proposed and implemented. An analytic expression which is useful to derive the electrical properties of the medium was obtained from that of the field of a monopole immersed in such a medium. The measurements were made using sand and clay loam soils to validate the proposed method. The behavior of electrical properties of both kind of soils were studied with frequency and moisture content as the parameters.
Formation of MO+ ions from metal oxides bombarded by 10-keV Ar+ ions
Authors: Okajima Yoshiaki
Published: February 2003

The yields of MO+ molecular ions emitted from 26 metal oxides were measured by bombardment with argon ions accelerated at 10 kV. The yields were obtained by dividing the peak intensity of MO+ by the intensity of M+, a method which negated variations in absolute peak intensity due to surface roughness of the specimen and variations in the ion current of the primary beam. The difference in the yields of MO+ from metal oxides was investigated on the basis of their binding energies, and the following empirical expression for the yield of MO+ ions was obtained: I(MO+)/I(M+)=K(−ΔH0f×mt)n, where I(MO+) and I(M+) are the peak intensity of MO+ and M+ ions, ΔH0f the heat of formation of oxides used as a binding energy, mt the mean mass of the oxides, and K and n constants. The values of n were approximately 2, 3, and 4 for MO-, M2O-, and MO2-type oxides, respectively, which was equal to the valence number of the metal atom in the oxides, calculated by assigning a valence number of −2 to oxygen.
Transport coefficients of SF6 and SF6-N2 mixtures from revised data
Authors: Novak J. P. , Fréchette M. F.
Published: February 2003

The Boltzmann equation for the electron energy distribution has been solved for N2, SF6, and SF6-N2 mixtures. Calculated transport coefficients for N2 have been found to agree well with published experimental values and with previously published calculations. Using the comparison between theoretical and experimental transport coefficients for SF6, available data for momentum transfer and attachment cross sections have been reviewed and excitation cross sections evaluated. The set of representative cross sections thus derived yields good agreement between calculated and measured ionization and attachment coefficients and drift velocities for pure SF6, while on the other hand calculated diffusion coefficient-to-mobility ratios are about 30% high. In the case of N2-SF6 mixtures the theoretical effective ionization coefficients were consistent with those obtained experimentally by Itoh et al. [J. Phys. D 12, 2167 (1979)]. However, for attachment coefficients agreement between theory and the experimental results of Siddagangappa et al. [J. Phys. D 15, L83 (1982)] is poor, and numerous attempts to resolve this discrepancy so far have failed.
Polarized radial magnetic fields and outward plasma fluxes during shallow-reversal discharges in the ZT-40M reversed-field pinch
Authors: Jacobson Abram R. , Rusbridge Michael G. , Burkhardt Louis C.
Published: February 2003

The characteristics of edge-region electromagnetic disturbances and of pulsed radial fluxes of plasma to the liner as well as the detailed interrelationship among these processes have been studied on the ZT-40M reversed-field pinch in its normal, shallow-reversal operating regime. The dominant magnetic disturbances are spiky (pulsewidth ∼5–10 μs) low-amplitude (‖Br/Bθ‖≲10−2) poloidally symmetric radial-field structures intersecting the vacuum wall and precessing toroidally in the anti-Iφ sense. The effect of even slight toroidal-field reversal (‖Bφ(a)‖≊Bθ(a)/10) is to polarize these radial-field spikes preferentially positive (i.e., Br>0) and to increase the speed of the minority (Br<0) while decreasing the speed of the majority (Br>0) spikes. Synchronous with the polarized Br spikes are intense radially outward fluxes of plasma (instantaneously ≳1022 m−2 s−1) leading to recurrent, large amplitude (‖Δn/n≳25%) depletion of the density in the outer quarter of minor radius. The resulting time-averaged global loss-rate per particle is significant (∼103 s−1). The toroidal wavenumbers (kφ≊3 m−1) of the radial-field spikes are sufficiently low to cause radially extensive (Δr∼a/4) magnetic islands which could account for the observed pulsed depletions of density in the same radial zone. The propagation and polarization of the coupled radial field/plasma loss process cannot be explained on the basis of known single-fluid plasma models.
Radial electron beam autoaccelerator for inertial confinement fusion
Authors: Poukey J. W. , VanDevender J. P. , Quintenz J. P. , Lockner T. R.
Published: February 2003

A possible approach to particle-beam fusion is to use a series of electron-beam driven coaxial cavities as an autoaccelerator to produce a short, high-energy electron pulse which in turn drives an ion diode. A theoretical study of such a system is made, using an electromagnetic particle code, and an equivalent circuit model for the whole system. The particle simulations indicate that a beam-to-wave conversion efficiency of up to 70% is possible for a single cavity, with careful design. Circuit modeling studies suggest that this implies an overall system efficiency which is somewhat low for reactor applications, but of possible interest for single pulse laboratory experiments.
Influence of gap length on the field increase factor β of an electrode projection (whisker)
Authors: Miller H. Craig
Published: February 2003

β, the increase of the macroscopic electric field at the tip of a projection, varies with the gap length. The sign and magnitude of this variation depends upon how the gap length is defined. If gap length is defined as x, the distance from the projection tip to the opposing electrode, then β is a strong function of x and may be approximated by β(x)=β∞x/(x+h) [h=projection height] in the region where x/h>10/β∞. If gap length is defined as d, the interelectrode distance ignoring the projection, then β is a weak function of d and may be set equal to β∞ in the region d/h>2.
Damage-resistant LiNbO3 waveguides
Authors: Jackel J. , Glass A. M. , Peterson G. E. , Rice C. E. , Olson D. H. , Veselka J. J.
Published: February 2003

The photorefractive effect (‘‘optical damage’’) severely limits the application of LiNbO3 in visible wavelengths. We have found that proton exchanged LiNbO3, in which up to 70% of the Li ions are replaced by protons, exhibit no measurable index change with average intensities of visible light up to 5 kW/cm2 or peak pulse intensities of ∼5×108 W/cm2 in the guide. These experiments demonstrate that the photorefractive sensitivity of proton exchanged waveguides is at least four orders of magnitude lower than that of conventional titanium diffused guides. Similar results are obtained with titanium diffused waveguides which are subsequently proton exchanged.
Optical study of cylindrically converging blast waves
Authors: Matsuo Hideo , Ebihara Kenji , Nagayama Kunihito
Published: February 2003

Cylindrically converging blast waves have been produced by detonating cylindrical explosive shell. Formation of shock waves has been observed adopting the laser shadowgraphy. Spectroscopic measurements have also been made with a monochromator combined with a photomultiplier. A temperature of 12 000±2000 K has been observed, which is 10 000 K lower than that estimated from the propagation velocity of the shock wave.
Influence of plastic deformation on the magnetic transition temperature of L12-type materials
Authors: Ikeda Kôki , Takahashi Seiki
Published: February 2003

The influence of plastic deformation on the magnetic transition temperature in L12-type materials is explained in terms of the modified slip-induced directional-order model with consideration of the magnetic interactions between the neighboring atoms. The calculation based on the pair-interaction model predicts that the magnetic transition temperature changes in proportion to the dislocation density at the early stage of plastic deformation and to the square root of it at the advanced stage. The numerical estimation is given for four alloys with the L12-type superstructure: i.e., Pt3Fe, Pt3Co, Fe3Pt, and Ni3Mn.
Morphology and thermal properties of solvent-cast arsenic sulfide films
Authors: Norian K. H. , Chern G. C. , Lauks I.
Published: February 2003

The influence of annealing on solvent-cast arsenic sulfide films has been studied through its effect on morphology, structure, and optical properties. Transmission electron microscopy accompanied by electron and x-ray diffraction studies showed morphologic and structural transformations upon annealing. Thermal densification and effect of heat treatment on the ultraviolet/visible optical properties were also investigated. The results are in agreement with an evolving model for the solvent cast arsenic sulfides, in which 50-Å-diam macromolecules are deposited from solution and cross linked into a network glass during subsequent annealing.
Bulk and surface effects of heat treatment of p-type InP crystals
Authors: Wong C-C. Daniel , Bube Richard H.
Published: February 2003

Heat treatment of p-type InP crystals leads to major changes in bulk properties of InP:Zn crystals, and to major changes in surface properties for InP:Zn and InP:Cd crystals. An increase of hole density extending 60 μm into the bulk is observed for InP:Zn crystals after heat treatment between 300 and 500 °C. The data may be successfully described by the outdiffusion of interstitial Zn during heat treatment, reducing the compensation of substitutional Zn acceptors. Such bulk effects are absent for InP:Cd crystals. Preferential evaporation from the surface of InP leads to changes due to P loss that for high heating temperatures result in visually observable excess indium. Such preferential evaporation produces surface states on the InP that change the transport mechanism of Au/InP junctions from thermionic emission to tunneling controlled, and reduce the barrier height of the junction. Since these effects are surface related they occur similarly for InP:Zn and InP:Cd crystals.
Argon-ion assisted etching of silicon by molecular chlorine
Authors: Kolfschoten A. W. , Haring R. A. , Haring A. , de Vries A. E.
Published: February 2003

Argon-ion assisted etching of silicon by molecular chlorine has been investigated. The masses and some kinetic energy distributions of the neutral particles emitted from the surface have been determined by mass spectrometry and time-of-flight spectra. It is found that an important part of the silicon-containing particles consists of SiCl and SiCl2 molecules which have kinetic energies in the eV region. The observations exclude a simple evaporation of SiCl4 at the target temperature. A tentative model—consisting of a collision cascade like process parallel to thermal evaporation at the substrate temperature induced by a reduction of the effective surface binding energy during a sputtering event—is given to explain the observed kinetic energy distributions qualitatively.
Size effects in Pb-alloy Josephson junctions
Authors: DeLuca J. C. , Chi C. C. , Tsuei C. C. , Davidson A.
Published: February 2003

Five Pb-alloy Josephson junctions of various sizes were fabricated together and variations in their electrical parameters were studied. The dependence of the excess current on the junction geometric dimensions is demonstrated. As the area to perimeter ratio of the junction is increased, there is a proportional decrease in excess current density. A simple analysis indicates that there is an insignificant contribution to excess current through the interior planar area of the junction with most of the excess current generated at the edges.
Physics of amorphous silicon based alloy field-effect transistors
Authors: Shur M. , Hack M.
Published: February 2003

In this paper we develop a new theory to describe the characteristics of amorphous silicon based alloy field-effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap. The current-voltage and capacitance-voltage characteristics are related to the basic material parameters such as the distribution of localized states in the energy gap, band mobility, device geometry, channel doping, and series resistances. Our analysis shows that an on current in excess of 2×10−7 A/μm gate width can be obtained with a 10-μm gate length. We also demonstrate that even in the above threshold regime the field-effect mobility is dependent on the gate voltage. Our theory can be used to optimize the design of amorphous silicon based alloy field-effect transistors.
GaAs/GaAs1−ySby superlattice light emitting diodes
Authors: Klem J. , Fischer R. , Masselink W. T. , Kopp W. , Morkoç H.
Published: February 2003

We present the first report of light emitting diodes fabricated with GaAs/GaAs1−ySby superlattice active regions. Several device structures are investigated, including devices with and without AlxGa1−xAs confining layers. Preliminary measurements indicate peak optical intensities may be obtained at wavelengths near 1 μm, with an associated full width at half maximum ∼100 meV at 300 K. Room temperature forward I-V characteristics indicate an ideality factor of approximately two for these devices. Quantum efficiencies of ∼0.1% have been obtained for continuous operation.
Experiments in switching the bistable boundary layer liquid crystal display by the application of dc
Authors: Thurston R. N. , Boyd G. D. , Senft Donna Cowell
Published: February 2003

It has been previously reported that a liquid cystal display cell based on bistable boundary layer configurations can be switched between its bistable states by the application of dc. We report here the first experiments in the use of dc to switch an insulated cell. Included also are additional experiments with E7 in the cell of the previous report [R. B. Meyer and R. N. Thurston, Appl. Phys. Lett. 43, 342 (1983)] and a brief description of some observations with other materials. The results with the insulated cell are important because they show that the dc switching effect does not require charge transfer between the metallic electrodes and the liquid crystal.