bluuebunny/crossref_metadata_2025 huggingface dataset:
Consistency of elastic thermal coefficients of quartz
Authors: Shimony Uri
Published: February 2003

the symmetry of quartz implies six independent thermal coefficients of elasticity ofany order. A method is described in which the constraint on elastic elements 11, 12, and 66 is used to find from three inconsistent experimental values of the thermal coefficients more accurate values, of which only two are independent. Thus, a set of seven inconsistent values is reduced to six independent, as required by symmetry. Calculated results are provided, assuming experimental uncertainties for published data.
Use of intense relativistic electron beams to pump VUV lasers
Authors: Whitney K. G. , Davis J.
Published: February 2003

Evidence is given to suggest that intense relativistic electron beams will find application as energy sources for pumping high-power vacuum ultraviolet lasers. A simple model of a stationary oxygen plasma was set up. When pulse heated, the plasma underwent a temperature evolution in close correspondence with measured values obtained in a plasma-heating experiment using a pulsed relativistic electron beam. In addition, a transient gain sufficient to produce amplified spontaneous emission (ASE) was calculated for the 3p→3s transitions in O III. The width of the gain curve was comparable to the width of experimentally measured uv laser pulses produced from an oxygen plasma having roughly the same density as in the plasma-heating experiment.
Carrier lifetime of semi-insulating GaAs in the region of magnetoconcentration
Authors: Nomicos C. D. , Philadelpheus A. Th. , Euthymiou P. C.
Published: February 2003

The effect of a magnetic field on the photoconductivity of semi-insulating GaAs crystals mounted in the Voigt geometry has been investigated at room temperature. In the present experiment, the magnetic field deflects the photocarriers towards the illuminated surface of the specimen where their concentration increases. For weak electric fields an increase of the photoconductivity is obtained, whereas high electric fields produce a reduction of the photoconductivity. From the experimental results the carrier lifetime was determined as a function of the thickness of the magnetoconcentration region.
Investigation of the changes in the electron-state spectrum of plastically deformed silicon by the diode effect
Authors: Mil’shtein S. Kh.
Published: February 2003

A study was made of the effect of high-density dislocation clusters (108–1011 cm−2) on the electrical properties of plastically deformed n-type silicon. Inversion of the conductivity was found at room temperature in the deformed crystal regions. When current was passed through the deformed regions strong rectification was observed. The forward currents of the characteristics were larger than the reverse currents by three orders of magnitude. The effect of point defects and other extraneous factors was separated from the diode action of the dislocations. Band-theoretical concepts were used to locate the dislocation acceptor centers which gave rise to the observed effect. It was shown that it is in principle possible to interpret the spectrum of electron states in plastically deformed silicon on the basis of the diode effect.
Determination of the MOS oxide capacitance
Authors: McNutt M. J. , Sah C. T.
Published: February 2003

A simple and explicit formula is derived to give the oxide capacitance from MOS C-V data in the accumulation but nondegenerate range of surface potential. The effect of majority impurity deionization is shown to be unimportant due to a higher surface concentration of majority carriers than impurities in the accumulation range. A first-order correction is obtained to take into account the degenerate or Fermi statistics of the majority-carrier surface concentration for oxide capacitance determinations from C-V data in the strong accumulation and degenerate range of surface potentials.
Effect of transferred-electron velocity modulation in high-efficiency GaAs IMPATT diodes
Authors: Constant Eugène , Mircea Andréi , Pribetich Joseph , Farrayre Antoine
Published: February 2003

Numerical calculations, supplemented by detailed physical interpretation, show that the high (greater than 30%) output efficiencies, experimentally obtained with GaAs non-punch-through IMPATT devices, are only possible due to the specific features (related to the transferred-electron effect) of the electron velocity versus electric field dependence in this material. Comparison is made with experimental results. Based on this new understanding, suggestions are made for further improvement of IMPATT performance.
Generalized study on angular dependence of induced second-order nonlinear optical polarizations and phase matching in biaxial crystals
Authors: Ito Hiromasa , Naito Hatsuhiko , Inaba Humio
Published: February 2003

The induced second-order nonlinear coefficients in the noncentrosymmetrical biaxial crystals are formulated in a general way as functions of the their crystal symmetry and directions of propagation of optical waves in the crystal. The direction of light propagation is determined from the phase matching among three optical waves. The optimum operating condition is also derived analytically by investigating the effective nonlinearity under the phase-matched direction. This treatment is applied to the case of the second harmonic generation of Nd : YAG laser (1.064 μm), using α-iodic acid, lithium formate, sodium formate, and lithium-sodium formate crystals. Experimental results were compared quite favorably with the theoretical analysis given in this paper.
Field-induced tunnel diode in indium antimonide
Authors: Margalit S. , Shappir J. , Kidron I.
Published: February 2003

Tunneling in a field-induced diode in InSb operated at 77 °K is reported. The current-voltage characteristics is controlled by the gate of an MIS structure. Tunneling is observed in both forward and reverse modes of operation. For SiO2 insulator thickness of 1000 Å, tunneling threshold voltages of 4 and 0.6 V are measured for the two operating regions, respectively.
Anomalous weak-field magnetic hysteresis in plastically deformed and annealed gadolinium near the Curie temperature
Authors: Milstein Frederick , Baldwin John A. , Rizzuto Michael
Published: February 2003

The Rayleigh parameters of cold-worked and annealed polycrystalline gadolinium have been measured at 10 °C. In contrast with the usual findings, they are relatively insensitive to the state of lattice disorder. The small-signal hysteresis loop differs qualitatively from the usual Rayleigh loop in that remanence is proportional to the first power, rather than the square, of the field amplitude.
Effect of electron irradiation on domain wall pinning defects in 50-50 NiFe
Authors: Baldwin John A. , Milstein Frederick , Smith Paul Wesley
Published: February 2003

A magnetic measuring technique which sorts out defects according to a distribution function n was used to study the influence of electron irradiation on 50-50 NiFe. The distribution function is determined in terms of the maximum force fm that a defect can exert on a forward moving domain wall, or equivalently, the range z0, which is the distance the mean position of the wall may move past the defect before the wall snaps free from the pinning action of the defect. The range and maximum force are related by a spring constant k, viz., fm=kz0. The quantity n (z0) dz0 gives the number of defects per unit volume having a range between z0 and z0+dz0. Distribution functions were determined before and after electron irradiation. The irradiation was for 100 min with 18-MeV electrons with a dose of 1.1×1017 e/cm2. Following irradiation, there was a substantial decrease in the number of short-range defects (i.e., defects capable of pinning a domain wall only over a relatively short range); there was an increase in the number of long-range defects; and the total number of defects N0 with which a steadily moving wall interacts at a given instant was found to decrease. Although the coercive force decreased, the Barkhausen noise power increased following irradiation. It has been shown by Baldwin and Milstein that the contribution to Barkhausen noise power from defects of a given range z0 is proportional z30; hence the increase in Barkhausen noise is understood in terms of the increase in long-range defects. The experimental results can be understood in terms of the effects of long-range crystallographic ordering which occurs in NiFe alloys which are subjected to electron irradiation.
Parametric amplification by unbiased Josephson junctions
Authors: Feldman M. J. , Parrish P. T. , Chiao R. Y.
Published: February 2003

The theory of parametric amplification by a series of unbiased Josephson junctions is presented. The various regimes of operation are explored. This device is in many ways different from the usual varactor parametric amplifier. In particular, a very small pump power is required and a large bandwidth is obtained. Comparison with experimental data is made.
Liquid-crystal twist cell dynamics with backflow
Authors: Berreman Dwight W.
Published: February 2003

We describe and present results of a numerical method we have used to solve the hydrodynamic equations with negligible rates of change of momentum and angular momentum, but without other approximations, in a liquid-crystal twist cell. We verify that the ’’bounce’’ in transmission of normally incident light that is observed when the electric potential across the cell is turned off is an effect of shear flow (backflow) which causes temporary reverse rotation of directors in the middle of the cell. It is not an inertial effect. Inertial effects would have transient times much shorter than the times associated with the optical bounce. When fluid flow is omitted, as in our previous papers, molecules do not tilt backward and the ’’optical bounce’’ occurs only for light that is obliquely incident in one quadrant. A qualitative explanation of the optics of the bounce is given, in addition to numerical results.
Initiation of dislocation multiplication in lithium fluoride monocrystals under impact loading
Authors: Flinn J. E. , Duvall G. E. , Fowles G. R. , Tinder R. F.
Published: February 2003

An experimental impact technique is described for exposing materials to small amplitude stresses in states of uniaxial strain for small times. It is applied to single crystals of LiF containing ∼8 ppm Mg, and multiplication of screw dislocations is measured. For shear impulses exceeding about 40 dyn sec/cm2, multiplication is adequately described by multiple cross glide with multiplication coefficient m= (2–4) ×109 cm−2. For shear impulses less than 20 dyn sec/cm2, no multiplication is observed. Stress amplitude and duration are varied independently.
Damage in steel plates from hypervelocity impact. II. Numerical results and spall measurement
Authors: Bertholf L. D. , Buxton L. D. , Thorne B. J. , Byers R. K. , Stevens A. L. , Thompson S. L.
Published: February 2003

Comparisons of calculated solutions with experimental results for the impact of a 9.53-mm-diam nylon sphere on a 12.7-mm-thick steel plate at 5.182 km/sec are presented. Numerical solutions are difficult to obtain with existing Eulerian codes because of the need for accurate treatment of material strength and the definition of both the material interface and the free surfaces. The large distortion of the nylon sphere and the steel near the impact crater lip also make this a difficult problem for Lagrangian codes unless frequent rezoning is used. Newly developed Eulerian and Lagrangian rezoning codes are used. They give essentially the same solution. The computational results show that in order to obtain agreement with the experiment, it is necessary to account for the α (bcc) ?ε (hcp) polymorphic phase change for iron. Calculations also indicate the need to obtain experimentally the correct spall strength for the steel and and a description of this measurement is included. Treatment of elastic-plastic response, a good numerical model for fracture, and a high degree of numerical resolution are also shown to be necessary in order to predict accurately the back-surface spallation observed in the experiment.
Growth morphology and surface-acoustic-wave measurements of AIN films on sapphire
Authors: Liu J. K. , Lakin K. M. , Wang K. L.
Published: February 2003

Aluminum nitride epitaxial films of thicknesses greater than 10 μ with excellent mechanical and chemical stability have been grown on R-plane sapphire substrates. The orientation relationship of single-crystal AlN on sapphire is discussed. Examination of the as-grown AlN film surface with a scanning electron microscope identifies the growth morphology and enables differentiation between good and poor quality films. The surface-acoustic-wave coupling constant K2 and propagation velocity Vs are measured out to a thickness-to-wavelength ratio t/λ=0.75 with typical K2 values of 0.8% and Vs of 6.1 km/sec. Preliminary results also indicate that AlN-sapphire interfacial strain extends about 1 μ into the AlN film.
Diffraction of light by sound waves of arbitrary standing-wave ratio
Authors: Mahajan Virendra N.
Published: February 2003

The Raman-Nath equation for diffraction of light by a sound wave of arbitrary standing-wave ratio is derived, and its solutions are obtained in the Raman-Nath and Bragg regions of diffraction. A Fourier analysis of the diffracted amplitudes is carried out to show that light in an even (odd) diffraction order is composed of light waves whose frequencies are shifted from the frequency of the incident light by even (odd) multiples of the acoustic frequency. Variation of the Bragg-diffracted irradiance with time is plotted for various values of the standing-wave ratio.
Generalization of computer simulation of dislocation emission under constant rate of stress application
Authors: Yokobori A. T. , Yokobori T. , Kamei A.
Published: February 2003

Generalization of computer simulation of dislocation groups emission with the dislocation velocity-stress relation of power type: v=Mτm under constant rate of stress application has been attempted, such as for the value of m ranging between 1 and 6.4. For metals in which the velocity of an isolated dislocation is given by a thermally activated process, the number of dislocations emitted up to time t is expressed in terms of single apparent rate process and the activation energy is a constant multiple [such as (m+1)/(m+2) or m/(m+2)] of the activation energy for the motion of an isolated dislocation. The mean mobile dislocation density along one slip plane was obtained, and its temperature and strain rate dependence are in good agreement with the semiexperimental results in literature.
Arc constriction in lamps containing mercury and iodine
Authors: Zollweg R. J. , Lowke J. J. , Liebermann R. W.
Published: February 2003

Quantitative calculations indicate that the mechanism by which iodine causes constriction of arcs in mercury vapor lamps is the emission of molecular radiation from HgI. Calculated arc temperature profiles from the energy balance equation for various mixtures of mercury and iodine are found to agree with measured profiles when allowance is made for the emission and self-absorption of radiation from all atomic and molecular species. Approximate emission coefficients for HgI molecular radiation and atomic iodine radiation have been determined as a function of temperature. Molecular radiation emitted from the plasma at temperatures between 2500 and 4500 °K is found to be the major cause of arc constriction for plasma pressures of the order of a few atmospheres.
Elastic and dielectric constants in mixtures of nematic liquid crystals
Authors: Meyerhofer Dietrich
Published: February 2003

The dielectric constants and two elastic constants were measured for a series of mixtures of two nematic liquid crystals, MBBA and PEBAB. The materials covered the range from 0 to 10% PEBAB. The parameters were calculated from the measured voltage dependence of capacitance. The dielectric constants vary linearly with PEBAB concentration and the anisotropy changes from negative to positive at 1.7%. The elastic constants remain fixed over most of the range, but are reduced in mixtures of small anisotropy. The results differ significantly from recent measurements of Michel and Smith, the probable reason being that we take any nonideal alignment at the surface explicitly into account in the calculations.
Bypassing of a barrier by dissociated and superlattice dislocations
Authors: Karihaloo B. L.
Published: February 2003

Very simple procedures are used to calculate the upper and lower bounds for the applied stress required for the leading extended (superlattice) dislocation in a group of n coplanar screw dislocations of like sign with Burgers vector b to bypass a noncoplanar perfect screw dislocation with Burgers vector mb (m≪n). Since these bounds are very close to each other, especially for small m, the long-range flow stress can be estimated accurately. The critical spacing between the parallel slip planes at the moment of bypass is determined in a natural way by studying the stability of equilibrium of the leader in the mobile group. Particular attention is paid to the effect of the stacking-fault (the antiphase boundary) energy and the barrier strength m on the bypass stress.
Ignition and maintenance of subsonic plasma waves in atmospheric pressure air by cw CO2 laser radiation and their effect on laser beam propagation
Authors: Fowler Michael C. , Smith David C.
Published: February 2003

Laser supported combustion (LSC) waves, subsonically propagating plasma, are ignited from solid targets and maintained in atmospheric pressure air using focused high−power, as high as 15 kW, cw CO2 laser radiation. The intensity necessary to ignite LSC waves, Ii, is measured for steel and aluminum targets as a function of beam focal spot diameter and wind velocity transverse to the beam axis as is the intensity needed to maintain such waves in atmospheric pressure air, Im. In the absence of a transverse wind, the quantities Ii and Im are essentially identical for diameters smaller than 0.1 cm, but Ii is substantially larger at larger diameters. The reason for this is discussed in terms of the ignition mechanism itself. In the presence of a 20−m/sec transverse wind, Im and Ii are essentially identical at 0.2 cm, the largest diameter for which Ii was determined. The measurements of Im extend to 0.5 cm beam diameter and indicate, in the absence of the transverse wind, that while thermal conduction determines the value of Im at small (0.007 cm) beam diameters, radiative losses are important at the larger diameters considered. An interferometric technique is utilized to obtain spatially resolved LSC wave plasma properties, and the latter are used to calculate the decrease in focal spot laser intensity due to absorption and refraction by the plasma. The calculated results, as well as those obtained from independent experiments, indicate that while inverse bremsstrahlung absorption can account typically for a 50% loss in focal spot intensity, scattering or beam blooming by the plasma has a significantly greater effect as the LSC wave propagates away from the focal spot.
Analog Monte Carlo studies of electron−photon cascades and the resultant production and transport of photoneutrons in finite three−dimensional systems
Authors: Hansen E. C. , Bartoletti C. S. , Daitch P. B.
Published: February 2003

A major computer program has been written to perform Monte Carlo studies of electron−photon cascades and the resultant production and transport of photoneutrons in finite three−dimensional systems. It is programmed in FORTRAN and is explicitly designed to be easily used and extended to yield a fast, adaptable, and versatile computer program that has wide application to problems in solid−state, nuclear, and reactor physics. It combines a simple but accurate procedure for sampling from an arbitrary differential probability distribution with efficient cross−section representations to perform complicated single−particle of many−particle calculations. The calculations of Alsmiller and Moran at ORNL and the experiments of Barber and George at the Stanford High Energy Physics Laboratory have been compared with results of the new computer code. The comparisons indicate that the results of the new Monte Carlo studies are in good agreement with the ORNL calculations of the photoneutron yield in cylindrical targets of Cu, Ta, Pb, and U for a wide variety and 100 MeV. The comparisons also yield good agreement with the Stanford experiments of the photoneutron yield in rectangular targets of Cu, Ta, experiments of the photoneutron yield in rectangular targets of Cu, Ta, experiments of the photoneutron yield in rectangular targets of Cu, Ta, Pb, and U for a wide variety of target thicknesses for incident electron energies ranging from 10 to 34 MeV. A series of Rensselaer Polytechnic Institute LINAC ’’bare’’ target experiments have been analyzed with the Monte Carlo program. The computational studies and the experimental results are in good agreement. In particular, there is excellent agreement on the angular distributions of photoneutrons from the tree spherical Pb targets as measured using foil detectors. the calculated results predicted quite faithfully the observed improvement in the angular distributions as the design of the spherical Pb target was modified to obtain a more isotropic distribution.
Etching study of microdomains in LiNbO3 single crystals
Authors: Ohnishi Norio , Iizuka Takashi
Published: February 2003

Microdomains in LiNbO3 single crystals have been investigated in considerable detail by the etch technique. Etch features, such as etch hillocks on the negative c surface, etch pits on the positive c surface, and needle−shaped etch patterns on the Y surface, have been examined by optical and electron microscopy. The results of detailed observations of the features lead to the conclusion that a common source of these patterns is a reverse polarized needlelike microdomain, less than 1 μm in diameter and 300 μm in length, lying parallel to the c axis, namely the polarization axis of LiNbO3. Mechanical scratching on the c surface and the subsequent chemical etching produce new hillocks on the negative surface and etch pits on the positive surface. It has been proposed that the polarization reversal takes place on a microscopic scale by scratch−induced stress.
Cross−sectional structure of Bi films and its phenomenological analysis
Authors: Namba Yoshikatsu , Mori Toshio
Published: February 2003

The cross−sectional structure of evaporated Bi films has been investigated using electron microscopy and a replica technique. The conditions of films formation were varied by using a range of substrate temperatures and deposition rates. It was found that a critical stage in the growth process is reached when the film becomes continuous. Whether the surface structure existing at this stage is maintained or becomes smooth during further growth is determined principally by the deposition rate. Based on these results a phenomenological analysis was made, assuming that changes in the surface roughness occur as a result of the surface diffusion of adatoms. It has been shown that this theoretical description of surface roughness as a function of temperature and deposition rate agrees well with the experimental observations.
Small−angle x−ray−scattering study of microstructure of polyvinylchloride
Authors: Neilson G. F. , Jabarin S. A.
Published: February 2003

Small−angle x−ray−scattering (SAXS) measurements were made on polyvinylchloride films which were stretched and/or annealed. The SAXS data showed only monotonically decreasing continuous−type scattering which varied according to the time and temperature of thermal treatment and to the amount of film extension. It was concluded from the analysis of these data that annealing and stretching have a relatively small effect on the size of the scattering regions, the major effect being due to the variation in electron density difference between regions. The results were interpreted assuming a two−phase system containing ordered and disordered regions. It was thus concluded that annealing mainly increases the degree of order in those regions which were initially partially ordered, whereas orientation from stretching causes chain alignment and hence partial ordering within the initially disordered regions. This latter conclusion was found to be consistent with the interpretation of the results obtained from infrared dichroism measurements.
Excitation in electron−metastable helium collisions
Authors: Flannery M. R. , Morrison W. F. , Richmond B. L.
Published: February 2003

The 21,3P, 31,3S, 31,3P, 31,3D and 41,3P excitations arising from e−He(21,3S) collisions are examined by application of the Born and of the Vainshtein, Presnyakov, and Sobel’man approximations. Total excitation cross sections are calculated for the above transitions for electron impact energy E up to 500 eV. Contrary to expectation, excitation to the 31,3D and 31,3S states dominate the 31,3P and 41,3P excitations except at incident energies above 100 eV.
Photoemission electron microscopy of oxide fracture at slip steps on metals
Authors: Baxter William J. , Rouze Stanley R.
Published: February 2003

The surface deformation of metals and the concomitant mechanical behavior of the surface oxide film may be observed simultaneously by photoemission microscopy. This is illustrated by photoemission micrographs of steel and aluminum plastically deformed in either tension or compression. During tensile deformation of both metals the ’’natural’’ thin surface oxide is ruptured by the emerging slip steps. This reveals the bare metal surface of the step itself, which appears on the micrographs as a line of enhanced photoemission (exoelectrons). On the other hand, compressive deformation of ?4% rarely enhances the photoemission, the majority of the slip lines exhibiting only topographical contrast. This difference is related to the geometry of the slip steps as well as to the behavior of the surface oxide. In compression the oxide on aluminum does not fracture at the slip steps, and no exoelectron emission is observed. The oxide on steel clearly does fracture, but few slip steps emit exoelectrons because they are difficult to illuminate.
Temperature and pressure dependence of the elastic properties of RbAg4I5
Authors: Graham L. J. , Chang R.
Published: February 2003

An ultrasonic pulse superposition technique was used to measure the velocities of the three pure-mode waves which propagate along [110] in a single crystal of rubidium tetra-silver pentaiodide. The temperature was varied from 25 °C, through a phase transformation at −65 °C, and to a second phase transformation at −151 °C. There was a peak in the ultrasonic attenuation at the −65 °C transition for the longitudinal and one of the shear waves, and the attenuation and velocity of all of the waves were completely reversible upon cycling the temperature through this transition. The lower-temperature phase was generally several percent softer elastically than the room-temperature phase. Attempts to make measurements through the −151 °C transition were not successful. The pressure dependence of the wave velocities were determined at 25 °C. The adiabatic second-order elastic constants and their temperature and pressure derivatives at 25 °C which were determined from these measurements are as follows. The values of Cij (1011 dyn/cm2), C−1ij (∂Cij/∂T) (10−4 °K−1), and ∂Cij/∂P for C11 are 1.648±0.002, −3.54±0.12, and +8.73±0.11, respectively; for C12, 0.934±0.002, −3.73±0.13, and +6.29±0.11, respectively; and for C44, 0.4892±0.0005, −4.17±0.05, and +0.884±0.015, respectively. The Debye temperature of 90 °K and the thermal expansion coefficient of 0.566×10−4 °K−1 calculated from these values agree very well with values determined by other means.
Damping of elastic surface waves by density fluctuation on solid surfaces
Authors: Nakayama Tsuneyoshi , Sakuma Tetsuro
Published: February 2003

We investigate theroetically the damping rate of elastic surface waves due to density fluctuation on solid surfaces. A formula for the damping rate is presented using the Green’s function. The frequency and correlation length dependence of the rate is calculated. The results show a frequency and correlation length dependence quite different from that of the bulk phonon case.
Multi-control-volume analysis of elastic and plastic wave fronts in composite materials
Authors: Tsou F. K. , Chou P. C. , Singh I.
Published: February 2003

A multi-control-volume method is developed to predict the wave velocities and stresses in the elastic and plastic regions of layered composites. From the method, the wave velocities and stresses may be calculated from the constitutive relations of its constituents. The interfacial shearing force may then be computed. Two composites boron/aluminum and graphite/C-7 epoxy have been used for sample calculations. The results from the boron/aluminum composite indicate that the elastic and plastic waves may merge to form a shock at large impact velocities.
High-energy ions from a CO2 laser-produced plasma
Authors: Ehler A. W.
Published: February 2003

A time-of-flight ion collector was used to measure the energy of ions from the plasma produced by a high-power CO2 laser pulse focused on a flat polyethylene target. At laser irradiances exceeding 5×1012 W/cm2 at the target, high-energy ion current spikes appeared in addition to the ion current from an expanding thermalized plasma. The measured arrival time of these spikes was consistent with the assumption that ions of different charge and mass were accelerated by a high potential during the laser pulse which was produced by a steep pressure gradient at the plasma surface. The accelerating potential (equal to the measured energy of a singly charged ion) was proportional to the laser irradiance at the target to the 2/3 power. At an irradiance of 2×1014 W/cm2, the H+ ion energy was 140 keV. About 90% of the total ion energy appeared as high-energy ions.
Absorption of CO2 laser radiation in an exploded lithium wire plasma
Authors: DeBoo James C. , Bach David R.
Published: February 2003

An absorption experiment was performed with a pulsed TEA CO2 laser incident upon a partially ionized plasma created by exploding a 0.0025-cm-diam lithium wire in vacuum. Stark broadening of the Li I 6104-Å line and line intensity ratios of the same line to the Li II 5485−Å line were used to extract the density and temperature from time-resolved emission spectra. The neutral density was found from absorption measurements at 6328 Å and compared well with particle conservation calculations. In order to explain the strong observed absorption of both 10.6-μ and 6328-Å radiation, the plasma was assumed to consist of a hot peripheral region containing electrons and singly ionized lithium ions and a colder central region of excited neutrals. The model was supported by computer calculations and spectroscopic observations. Absorption of the 10.6-μ radiation was dominated by inverse bremsstrahlung in the field of ions and in the presence of neutrals.
Passive vibration isolator with sharp cutoff
Authors: Lorrain Paul
Published: February 2003

It is shown that the addition of a small auxiliary mass to a vibration isolator using partial damping can reduce its transmissibility at low frequencies by one or two orders of magnitude. It is also shown that parasitic damping, such as air damping on the mass isolated from ground vibrations, has quite a large effect on the transmissibility curve and must, therefore, be taken into account.
Effect of Au nucleation centers and deposition rate on crystallinity and electronic properties of evaporated Te films.
Authors: Okuyama Katsuro , Yamamoto Hiromu , Kumagai Yasuji
Published: February 2003

The effect of Au nucleation sites, deposition rates, and the film thickness on the crystallinity and electronic properties of evaporated Te films has been investigated. It has been found that to obtain large−grain Te films there exists an optimum conditoin in the coating ratio of Au nucleation sites and the film thickness of Te, and that a fast deposition rate of Te results generally in large−grain Te films with preferred orientation. The best films obtained have shown a grain size of 20−30 μ diameter with the c axis parallel to the substrate and a Hall mobility of 170 cm2 V−1 sec−1.
Hydroxyl ions and the 200−nm absorption band in Mg− and Ti−doped thermoluminescent LiF single crystals
Authors: Vora H. , Jones J. H. , Stoebe T. G.
Published: February 2003

A study of the distribution of the optical absorption coefficient of the 200−nm band in Mg− and Ti−doped LiF single−crystal boules, grown from monocrystalline starting materials of varying purity, indicates that this absorption band is due to titanium−hydroxyl complexes. The measurements of ionic conductivity and infrared absorption on the starting materials and in doped crystals indicate that each titanium ion probably interacts with several hydroxyl ions to form these complexes, and that the association of hydroxyl ions is stronger with titanium ions than with magnesium ions. Since earlier work has shown that the 200−nm band is involved in the thermoluminescent recombination process, it is indicated that hydroxide impurities may be essential constituents in dosimetry grade LiF.
The origin of internal stress in low−voltage sputtered tungsten films
Authors: Sun R. C. , Tisone T. C. , Cruzan P. D.
Published: February 2003

The internal stress can be of importance in the tungsten metallization process used for the fabrication of large−scale integrated circuits. The present work is an extension of an earlier study on the dependence of the stress in low−voltage triode sputtered tungsten films upon deposition conditions and substrate materials. As a function of film thickness, the stress was found to decrease with increasing thickness at various substrate temperatures. The effect of higher substrate temperatures is just to change from large compressive stress to smaller compressive stress and finally into tension. For example, the stress in a 5000−Å film decreases from 1.6×1010 dyn/cm2 in compression to 5×109 dyn/cm2 in tension as substrate temperature increases from 370 to 850 °C. Generally, no gross difference was found for films deposited on SiO2, Al2O3, or Si3N4 at higher substrate temperatures. As a function of deposition rate, the stress can be described in three regions. The stress was found to be small and relatively constant in the low−deposition−rate region. However, as the deposition rate increased to the transition region, a sharp stress increase was found. Finally, above a critical deposition rate, the large internal stress remains constant again. By measuring the stress and characterizing the microstructure of the film, it is concluded that the grain size is the dominant factor determining the stress. These experimental results are discussed in light of the grain boundary relaxation model of Finegan and Hoffman and annealing of disorder proposed by Klokholm and Berry.
Localized vibrational mode absorption of ion−implanted Be in ZnTe
Authors: Vodopyanov L. K. , Kachare A. H. , Spitzer W. G. , Wilson R. G.
Published: February 2003

Results of infrared measurements made at 300 and 80 °K are given for samples of ZnTe which were Be doped either during crystal growth or by ion implantation. The local mode frequency for BeZn, Be substitutional on the Zn sublattice, is in agreement with the previously measured frequency and with theory. Comparison of spectrochemical analyses with optical data indicates that in the melt−doped samples [Be]≫[BeZn]. The ion−implanted sample was annealed isochronally in 100 °K steps from 373 to 773 °K with no appreciable change in the integrated absorption of the BeZn band indicating no substantial change in [BeZn]. The linewidth decreases with annealing but is significantly larger than that observed in melt−doped material. Raman local−mode measurements were unsuccessful. Previously reported Raman scattering measurements of other ion−implanted materials show damage−induced line broadening of the optical phonon bands. However, no change in optical phonon linewidths is observed in ZnTe after Be implantation.
Temperature dependence of surface flashover voltage of polyethylene in vacuum
Authors: Ohki Y. , Yahagi K.
Published: February 2003

The surface flashover voltage over cylindrical spacers made of polyethylene in vacuum under impulse voltage application decreases monotonically with increasing temperature of the sample surface. This temperature dependence may be explained well by the mechanism that electrons injected from a cathode-insulator-vacuum junction bombard the sample surface to cause desorption of adsorbed gases and vaporization of sample material, thereby triggering surface flashover.
Luminescence in highly conductive n-type ZnSe
Authors: Bouley J. C. , Blanconnier P. , Herman A. , Ged Ph. , Henoc P. , Noblanc J. P.
Published: February 2003

We have studied the photoluminescence of ZnSe doped by diffusion of Al at high temperature (1000–1100 °C) or by Ga at low temperature (600 °C). The diffused samples are highly conductive (0.1<ρ<10 Ω cm). According to the doping conditions the luminescence, at 300 °K, is dominated by the well-known self-activated orange emission (6300 Å) or by a yellow-green band that we assign to Na-Al complexes. Annealing in zinc atmosphere was found to have a large influence on the photoluminescence of the Ga-doped samples only. Thus, at 300 °K, the annealed samples exhibit a blue intrinsic emission with a strong reduction of the orange or the yellow-green bands; at 77 and 4.2 °K the photoluminescence spectra are dominated by blue lines corresponding, respectively, to free-electron–acceptor or donor-acceptor recombinations. We show that the shallow acceptor involved is Na.
A steady-state high-density magnetized arcjet plasma column
Authors: Tang J. T. , Luhmann Jr. N. C. , Turechek J. , Jassby D. L.
Published: February 2003

A four-stage differentially pumped arcjet system generates a fully ionized current-free 1-m-long plasma column of uniform density 1013 ≲ne≲1015 cm−3 and temperature Ti∼Te∼1–7 eV confined by an axial magnetic field up to 9 kG. The first three stages consist of an arc chamber, a separation chamber, and an experimental chamber. The addition of a fourth stage converts the device into a double-ended differentially pumped system; it ensures the uniformity of the plasma column in high-density plasma operation. The properties of the four-stage differentially pumped plasma system are reported.
Laser focal spot measurements
Authors: Brannon P. J. , Anthes J. P. , Cano G. L. , Powell J. E.
Published: February 2003

The focal spot size for a high-powered neodymium laser has been determined by measuring the energy passing through pinholes of various sizes and also, by photographing the focused spot. A comparison of the two methods indicated that the photographic method could give misleading results. The spot size was also determined by measuring the absorbed energy by target pellets of various sizes. This method always gave a smaller value than the pinhole method. The difference was attributed to plasma effects.
Pulse propagation in a partially homogeneously broadened linear gas laser amplifier: Determination of line-shape parameters
Authors: Gamo Hideya , Sato Heihachi
Published: February 2003

A new method for determining the Lorentzian linewidth ΔνL, Doppler linewidth ΔνD, and gain parameter G of a partially homogeneously broadened linear laser amplifier is developed here. This method is based on the measurements of the following pulse propagation parameters: the incremental pulse intensity gain γI, the increments of pulse duration, and pulse delay time per unit plasma length ∂τ′/∂z and ∂T′/∂z, respectively. Assuming that the gain medium is uniformly distributed, the pulse width is narrower than the gain bandwidth, the waveform of an incident pulse is Gaussian and its mean frequency is tuned to the line center of the gain medium, the γI, ∂τ′/∂z, and ∂T′/∂z are expressed in terms of the Voigt function ψ (0,y), and its second derivative ψ″ (0,y), and the first derivative of its Hilbert conjugate φ′ (0,y), respectively. The parameter y= (ln2)1/2 ΔνL/ΔνD is obtained by solving a transcendental equation; S (0,y) =Q, where S (0,y) =ψ (0,y) ‖ψ″ (0,y) ‖/φ′ (0,y)2. The function S (0,y) is numerically tabulated and Q=γI(∂τ′2/∂z)/8 ln2(Λ T′/∂z)2 consists of the observable quantities. By substituting the values of ψ (0,y), ψ″ (0,y), and φ′ (0,y) for the y obtained in the numerical tables into the formulas for γI, ∂τ′/∂z, and ∂T′/∂z, we obtain ΔνL, ΔνD, and G. The line-shape parameters of the 3.5-μm high-gain xenon transition are determined by applying this pulse propagation method, where the experimental setup consists of a self-mode-locked xenon laser, a xenon laser amplifier with variable plasma lengths, infrared isolators, InAs photovoltaic detectors, and a sampling scope controlled by a signal-averaging computer. The results are consistent with those obtained by the cw method based on the line-narrowing and gain measurements.
Surface acoustic waves in strained media
Authors: Nalamwar A. L. , Epstein M.
Published: February 2003

Variations of elastic constants and density with strain and the introduction of stresses can significantly affect the propagation velocity of surface acoustic waves. Digital computation using iterative methods is employed to obtain the variations of propagation velocity with strain. It is found that while the individual contributions of the initial stresses, changes in elastic constants, and changes in density with strain can be considerable, their combined effect in some materials may be reduced by mutual cancellation. Computed results for YX quartz YZ LiNbO3 are compared with experimentally measured values.
Diffusion of mercury in Ag3Sn
Authors: Okabe T. , Hines A. L. , Hochman R. F.
Published: February 2003

The residual-activity method was employed to evaluate the volume and grain-boundary diffusion coefficients of mercury in the Ag3Sn alloy at temperatures ranging from 50 to 245 °C. The volume diffusion coefficient obeys the relationship Dv*=1.87×10−5 exp(−8.25×103/RT) cm2/sec. The grain-boundary diffusion coefficient evaluated from Suzuoka’s exact solution varied from 10−3 cm2/sec at 50 °C to 10−1 cm2/sec at 245 °C. The large grain-boundary-diffusion coefficient was attributed to the increased grain-boundary width of the alloy caused by the corrosive nature of the mercury.
High-field transport in SiO2 on silicon induced by corona charging of the unmetallized surface
Authors: Weinberg Z. A. , Johnson W. C. , Lampert M. A.
Published: February 2003

A study has been made of high-field electronic transport in thermally grown SiO2 in which the injection and transport of carriers were induced by charging the exposed surface of the insulator with ions extracted from a corona discharge. This technique totally avoids destructive breakdown through weak spots in the insulator. Auxiliary developments included a comparison technique for measuring the steady-state potential difference across the unmetallized insulator and a p-n junction method for determining the sign of the principal charge carrier in the oxide. Using a corona discharge in dry air, breakdown fields of approximately 6.5 and 13.5 MV/cm were obtained for charging with positive and negative ions, respectively. Electrons were identified as the current carriers for both polarities of applied field. Measurements of the discharge of the samples, made with a Kelvin probe, yield results that are consistent with Fowler-Nordheim tunneling of electrons from the silicon into the oxide, with an electron effective mass in the oxide m*ox=0.48m. Positive charge accumulation was observed in the oxide after charging with negative corona to fields above 11 MV/cm.
On state of amorphous threshold switches
Authors: Petersen Kurt E. , Adler David
Published: February 2003

A detailed study of the on state of amorphous threshold switches has been performed. Transient and steady-state I-V characteristics have been investigated as functions of film thickness, pore size, and electrode material. Velocity saturation effects in amorphous/crystalline Si heterojunctions and threshold recovery curves were also studied. It is found that the on-state resistivity is approximately 0.08 Ω cm, independent of electrode material. The on state is that of a semiconductor whose electronic band structure and carrier mobility are essentially unchanged from the off state, but in which a concentration of about 7×1018 free electron/cm3 produces the high conductivity observed. The decay of the on state is due to a combination of diffusion of the free carriers out of the filament, together with direct carrier recombination. A major result of this work is the determination of the size of the conducting filament as a function of operating current. As expected, the current density in the filament is essentially independent of on-state current, provided the filament does not saturate the device pore. However, the filament turns out to be much larger than previous speculations, leading to the result that heating effects are negligible at currents below those for which the pore saturates.
Deep-level energy spectroscopy in p-type CdTe using TSC measurements
Authors: Martin G. M. , Fogarassy E. , Fabre E.
Published: February 2003

TSC measurements have shown the presence of up to eight deep traps in highly resistive compensated p-type CdTe, the corresponding energy levels range between 0.18 and 0.53 eV above the valence band. The effect of the barrier height has been investigated and comparison between different ways of excitation has yielded an estimation of the Fermi-level position in such a material.
Photoconductivity of amorphous As2Se3
Authors: Tutihasi Simpei
Published: February 2003

It is shown that a blocking contact on a-As2Se3 becomes injecting upon trapping photogenerated electrons. The blocking contact consists of a thin organic insulator layer between a semitransparent gold anode and the photoconductor. Gains exceeding unity have been observed. The dynamics of the blocking-to-injecting contact transition have been investigated, and its process has been interpreted in terms of thermally assisted tunneling. This effect, in which one observes a blocking contact and an injecting contact in one sample, allows one to study both the primary and the conduction photocurrents in a sequential manner in a-As2Se3. Applying this technique, the steady-state photoconductivity of a-As2Se3 has also been investigated in detail. The results of the steady-state photocurrent measurements are examined in terms of the classical photoconductivity theory.
Plasmon excitation energies in ZnO, CdO, and MgO
Authors: Hengehold R. L. , Pedrotti F. L.
Published: February 2003

A study has been made to experimentally determine the plasmon excitation energies in the oxides of Zn, Cd, and Mg using the reflection electron energy loss technique. The measurements were made on clean single-crystal surfaces using electrons of 250–1000-eV energy. Distinction was made between surface- and bulk-plasmon excitation by recording the changes which occurred in the energy loss spectrum as the surface was selectively contaminated. Surface-plasmon excitation energies of 17.0, 15.9, and 14.7 eV and bulk-plasmon excitation energies of 18.8, 22.8, and 22.0 eV were measured for ZnO, CdO, and MgO, respectively. Comparison is made with similar data obtained from optical reflectivity and transmission electron energy loss measurements.
Magnetization curling in a sphere
Authors: Eisenstein I. , Aharoni A.
Published: February 2003

Using simplifying assumptions, solutions for the magnetization distribution in the curling mode are obtained for a ferromagnetic sphere with a uniaxial anisotropy. These are used to obtain a magnetization curve for a vanishing anisotropy constant and the remanent domain configuration in a cobalt sphere. In the latter case it is shown that as the radius of the sphere increases, two cylindrically symmetric coaxial domains are being formed. Some features of this configuration are discussed and a comparison is made with previous literature.