bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and magnetic properties of the (Y, Sm, Lu, Ca)3(Ga, Ge, Fe)5O12 garnet films for bubble-memory applications
Authors: Jindal B. K.
Published: February 2003

Films of the (Y, Sm, Lu, Ca)3(Ga, Ge, Fe)5O12 garnet were grown on gadolinium gallium garnet substrates, using PbO-B2O3 flux. Comparing this garnet with the widely used (Y, Sm, Lu, Ca)3(Ge, Fe)5O12 garnet, we find the following: (1) It is considerably easier to grow with reproducible l values; the variation of the characteristic length l with the growth supercooling is less by a factor of ∼2–3. When growing films within a specified range of l values, this allows a 2–3 times larger variation in growth temperature. (2) The Ga addition results in a 10–20 °C decrease in Curie temperature. But, over the temperature range 0–100 °C, the variations of l, the anisotropic field (Hk−4πMs), and the collapse field H0 are not much different for the two materials. Therefore, over this temperature range the devices made from the Ga-Ca-Ge garnet should perform just as well as those made with the Ca-Ge garnet. (3) The coercivity for this material is always low, <0.20 Oe, whereas for the Ca-Ge garnet the coercivity tends to fluctuate from ∼0.1 to ∼1.0 Oe.
Observation of particle trajectories near a magnetized fiber
Authors: Treat Richard P. , Lawson William F. , Johnson Jack L.
Published: February 2003

The motions of 20–30-μm paramagnetic particles have been observed in the neighborhood of a 250-μm ferromagnetic fiber. The particles are entrained in nitrogen flowing down over a horizontal fiber. The particles and fiber are magnetized by a vertical magnetic field of strength up to 0.73 T. The free-stream velocities range from nearly zero to 1 m/sec. A Fastax movie camera is used to record the positions of the particles as they pass by or collide with the fiber. The particle trajectories thus observed determine the collision cross section as a function of field strength and free-stream velocity. Cross sections of over five diameters are observed. The cross sections and trejectories are compared and agree with the Newtonian theory of the particle motion. The theorey assumes potential flow over the fiber and accounts for the magnetic, viscous, and gravitational forces and particle inertia, all of these being significant in the range of conditions considered. The observed trajectories show details of the motion which are clear manifestations of particle inertia. The sharp particle shadows cast by the isolated fiber are a striking feature of the trajectory patterns. Such shadows should be the source of an intereference effect in multiple-fibr filters.
Silicone resin electrets
Authors: Perlman M. M. , Kao K. J. , Bamji S. S.
Published: February 2003

Corona charged electrets (both negative and positive) and thermoelectrets have been formed with Dow Corning silicone resin. Thermally stimulated discharge (TSD) measurements on charge and current and charge-decay measurements at ambient temperature have been carried out on each type of electret. The charge retention of the negative-corona-charged samples compares favorably with polypropylene. A theoretical analysis of the current TSD yielded lifetime estimates of many months. The thermoelectret shows promise of being even longer lived. Further work is needed to determined the optimum thermoelectret polarization and curing temperatures and times. A detailed study of the effects of humidity should also be made.
On the photoelastic shear constants of cubic ionic crystals
Authors: Smit Jan
Published: February 2003

A simple model for the strain-induced change in polarizability of the ions can account for the difference between the observed shear p’s and the contributions calculated in a previous publication arising from dipole-dipole interaction. The agreement is improved by leaving the nearest-neighbor dipole interaction unscreened.
Temperature and current dependence of degradation in red-emitting GaP LED’s
Authors: Ralston J. M. , Mann J. W.
Published: February 2003

Experimental studies have been performed on several aspects of the degradation of electroluminescent quantum efficiency in ZnO-doped GaP light-emitting diodes. The dependence of degradation on stress temperature, stress current (experienced during accelerated aging), and measurement current (at which quantum efficiency is evaluated) has been empirically determined from experiments on several lots of devices. It is shown that degradation is dominated by a decrease in bulk p-side radiative recombination efficiency. The degradation of other factors (such as injection efficiency and injection ratio) contributing to the overall electroluminescent efficiency has only a secondary effect. Moreover, it is shown empirically that the dependences of degradation on temperature and stress current are separable.
Laser-beam annealing of discharge-produced amorphous silicon
Authors: Staebler David L.
Published: February 2003

Amorphous silicon films prepared by dc glow discharge of silane on room-temperature substrates darken when exposed to a focused laser beam. The process is primarily thermal, has an activation energy of ∼1 eV, and is accompanied by the desorption of hydrogen. It also affects the etch rate in basic solutions. A bleaching effect, not reported before, is seen at low exposures. All coloration changes are permanent. Possible applications for optical storage of information are discussed.
The refractive-index distribution normal to the polished surface of fused quartz measured by ellipsometry
Authors: Fukuyo Hitohiro , Oura Nobunori , Kitajima Nobuyuki , Kono Hiromichi
Published: February 2003

One of the dominant factors influencing the frequency aging of a crystal oscillator is the amount of surface irregularity left by polishing upon its crystal resonator. This paper deals with the refractive-index distribution of fused quartz as a measure of polished layer depth. It is found that the refractive-index distribution can be expressed by a combination of an exponential function and a linear function. The refractive index decreases exponentially from a surface value of 1.736 to a certain value at a depth of 50±10 Å and from it decreases linearly to the bulk value of 1.460 at a depth of 2000±200 Å.
Spin-polarized photoelectrons from semiconductors with chalcopyrite structure: ZnSiAs2 and ZnGeAs2
Authors: Zürcher P. , Meier F.
Published: February 2003

Photoelectron spin polarizations of 50 and 17% have been obtained with the chalcopyrite-structure semiconductors ZnSiAs2 and ZnGeAs2, respectively, by irradiation with circularly polarized light. A comparison is made with the results obtained from GaAs, which has a zinc-blende structure. An analysis of the chalcopyrite electron-level structure shows that polarizations up to 100% can be expected for suitably chosen materials.
A study of surface stoichiometry and thermionic emission using LaB6
Authors: Storms E. K. , Mueller B. A.
Published: February 2003

The variables which influence the surface composition of vaporizing compounds have been studied using the behavior of LaB6 as an example. The thermionic work function of LaB6 has been determined as a function of surface stoichiometry. A nearly constant value of 2.93 eV for the effective work function was observed from the LaB6+LaB4 boundary up to approximately LaB6.06. A further increase in boron content caused a steep increase reaching 3.40 eV at the LaB6+LaB9 boundary at 1500 K. The interior composition which produces a surface composition having a high emission flux and the lowest attrition rate is in the high boron region near LaB6.5, not at the stoichiometric composition.
Short-time chemomechanical effects in MgO
Authors: Ahearn J. S. , Mills J. J. , Westwood A. R. C.
Published: February 2003

Dislocations were generated and moved in MgO in a single short-time (μs) stress event by dropping a steel ball onto freshly cleaved surfaces covered with either water, toluene, or dimethyl formamide. The results confirm that dislocation behavior in MgO is indeed environment sensitive under stressing conditions simulating those which occur in drilling.
Effect of GaAs or GaxAl1−xAs oxide composition on Schottky-barrier behavior
Authors: Garne C. M. , Su F C. Y. , Saperstein W. A. , Jew K. G. , Lee C. S. , Pearso G. L. , Spicer F W. E.
Published: February 2003

The electrical behavior of GaAs and other Schottky barriers is known to be affected by the presence of an oxide layer, but little is known of the effect of the oxide composition on the electrical characteristics (i.e., I-V and C-V). In this study, the surfaces of GaAs and AlxGa1−xAs were prepared in H2O, H2O2, and NH4OH, and electrical measurements were made of these Schottky barriers. The surface composition of these samples was studied with Auger electron spectroscopy and compared to the electrical behavior of the Schottky barriers. The presence of measurable amounts of As oxides in the oxide layer resulted in soft I-V characteristics. However, samples with predominantly Ga2O3 oxide layers (i.e., small amounts of As oxides) were found to exhibit more nearly ideal Schottky-barrier behavior, with conduction ideality values from 1.2 to 1.4.
Theoretical model of thin-film deposition profile with shadow effect
Authors: Yao S. K.
Published: February 2003

A theoretical model and a computational algorithm are presented for the shadow deposition of thin films through a generalized mask of finite dimensions in a vacuum environment. The computer model enables a theoretical study of the deposited-film-thickness profile from extended sources with shadow effect. Numerical evaluation of the masked deposition profile has been carried out to illustrate the film-profile dependences on several basic mask parameters. Using computer-aided design procedures, a deposition mask has been successfully constructed for the fabrication of precisely shaped thin-film Luneburg lenses for guided-optical-wave applications.
X-ray photovoltaic effect in undoped LiNbO3 and its correlation with ESR
Authors: Schirmer O. F.
Published: February 2003

X irradiation of undoped LiNbO3 causes a photovoltaic current along the crystal c axis, which declines at low temperatures. The ESR of Nb4+ and of trapped hole centers show parallel behavior. Illuminating a ’’saturated’’ crystal with visible light produces another decaying photovoltaic current, accompanied by ESR decrease. It is concluded that valence to conduction band transitions do not contribute essentially to the photovoltaic current.
Optical and electrical properties of evaporated amorphous silicon with hydrogen
Authors: Ghosh A. K. , McMahon T. , Rock E. , Wiesmann H.
Published: February 2003

The optical and electrical properties of evaporated amorphous silicon with hydrogen have been studied under various deposition conditions. Infrared measurements indicate that the hydrogen content of the films are comparable to a-Si : H films produced by other techniques. The optical-absorption coefficient below the band gap of ∼1.55 eV was measured to be ∼100 cm−1 for samples made at deposition temperatures of ∼275–325 °C. For these samples the photoresponse at room temperature and the temperature dependence of the conductivities were studied. Dark conductivities were found to be thermally activated for T≳300 K with activation energies of ∼0.75 eV. We found type-1 photoconductivity and investigated its dependence on the light intensity. When samples were heated to ∼175 °C in a vacuum and then exposed to air, they exhibited time-dependent increases in the dark conductivity and photoconductivity. This effect was reversible by a reanneal in a vacuum. High-temperature anneals to ∼450 °C increased the optical absorption below 1.4 eV and decreased the photoresponse significantly.
Frequency-dependent electrical behavior of polycrystalline trigonal selenium and its relationship to xerographic performance of selenium particle contact photoreceptors
Authors: Abkowitz M. , Enck R. C.
Published: February 2003

A detailed correlation between the xerographic performance of trigonal selenium binder layers and the dc and low-frequency ac dark conductivity of these photoreceptors and of polycrystalline compactions fabricated from identical starting materials has been established. Studies of the temperature dependence of the ac conductivity of compactions and of xerographic layers as functions of thermal history and ambient gas exposure indicate that heating (∼150 °C) the pigment in oxygen (but not argon or nitrogen) is required to achieve adequate xerographic sensitivity. This heat treatment also converts the original simply activated conductivity to a complicated function of temperature, characterized by a local conductivity maximum near room temperature. From this result a large decrease in xerographic sensitivity (a factor of 2–3) with increasing temperature from 20 to 40 °C was first predicted and subsequently observed. Evidence that these effects are not due to absorption and desorption of weakly bound gases is presented. The frequency and ambient gas dependence of the ac conductivity of compactions and layers indicate that their dc and low-frequency ac conductivity (and thus the layer xerographic properties) are primarily controlled by interparticle barriers and that the thermal history and ambient gas effects modulate these barriers. Key requisites of models constructed to explain this behavior are discussed.
Determination of dopant-concentration diffusion length and lifetime variations in silicon by scanning electron microscopy
Authors: Chi Jim Y. , Gatos Harry C.
Published: February 2003

Compositional variations in Czochralski-grown silicon doped at levels above 1018/cm3 were observed with SEM in the EBIC mode employing large-area shallow p-n junctions. The EBIC contrast attributed to minority-carrier diffusion-length variations was related to dopant-concentration variations. Quantitative determination of dopant concentration, diffusion length, and lifetime variations on a microscale was obtained from the analysis of electron-beam-induced current measurements employing a model based on steady-state low-level excitation of minority carriers by the electron beam and on a phenomenological depth-dose function.
Solar-cell characteristics and interfacial chemistry of indium-tin-oxide/indium phosphide and indium-tin-oxide/gallium arsenide junctions
Authors: Bachmann K. J. , Schreiber H. , Sinclair W. R. , Schmidt P. H. , Thiel F. A. , Spencer E. G. , Pasteur G. , Feldmann W. L. , SreeHarsha K.
Published: February 2003

The preparation of indium-tin-oxide (ITO)/p-InP and ITO/p-GaAs solar cells via ion-beam deposition, rf sputtering, and magnetron sputtering of ITO onto single-crystal InP and GaAs substrates is described. The properties of these solar cells are strongly affected by the fabrication conditions and are related to chemical modifications of the junctions. The solar power conversion efficiencies at air mass 2 of ITO/p-GaAs and ITO/p-InP solar cells are ?5 and ?14.4%, respectively.
Computer simulation of charge dynamics in electron-irradiated polymer foils
Authors: Berkley David A.
Published: February 2003

A computer simulation is described which allows the study of charge motion in thin polymer films of the type used for electret transducers. The simulation operates with a variety of possible boundary conditions and can include nonlinear transport terms as well as time-varying radiation-induced conductivity. Electron-irradiation parameters, including radiation-induced conductivity and electron deposition profiles, are computed using a single-scattering Monte Carlo model of the polymer. The time-dependent charge-transport equations are solved by direct discretization of the partial differential equations. Using a fast minicomputer, the charge-transport solutions run approximately in real time for realistic polymer parameters. Results are discussed for open- and short-circuit irradiation and for charge recall experiments.
Theoretical efficiency of SnO2/Si solar cells
Authors: Ghosh Amal K. , Fishman Charles , Feng Tom
Published: February 2003

At present SnO2/Si solar cells with efficiencies greater than 12% have been fabricated. The maximum theoretical efficiency attainable with such cells is of great interest and is reported in the present paper. The cells behave very much like MIS devices. The insulating oxide and surface density of states at the interface affect the performance of the device mainly through the diode constant and the barrier height φB. The theoretical maximum short-circuit photocurrent, the open-circuit photovoltage, and the fill factor are 36 mA/cm2, 0.66 V, and 0.84, respectively. They yield a maximum theoretical efficiency of 20%.
Transport theory of high-frequency rectification in Schottky barriers
Authors: Tsang D. W. , Schwarz S. E.
Published: February 2003

A theory based on the Boltzmann equation is used to study rectification by Schottky barriers at frequencies as high as infrared. This theory is concerned only with effects originating inside the space-charge region, the voltages across this region being regarded as given. Thus, we confine our attention to transport mechanisms and exclude what are known as ’’circuit effects.’’ Typically, it is found that rectification is nearly constant from zero frequency to the plasma frequency of the bulk semiconductor, then drops as ω−2. A reversal of the sign of the rectification current is predicted near ωp. The small-signal impedance of the junction is calculated as a function of frequency. The theory is extended to mixing of two weak signals, and mixer output is calculated as a function of beat frequency. It is found that this output can be much larger than the value one would estimate from the ideal-diode equation.
The use of the electron-beam-induced current mode of the SEM for observing emitter/collector pipes in bipolar transistors
Authors: Ashburn P. , Bull C. J. , Beale J. R. A.
Published: February 2003

It is shown how the electron-beam-induced current (EBIC) mode of the SEM can be used to study the sites of emitter/collector pipes in bipolar transistors. In initial experiments the EBIC signal is collected across the collector and emitter of a bipolar transistor with the base floating, and it is observed that the pipes appear white (higher induced current) in comparison with the surrounding region. The way in which the state of the base affects the contrast is studied by collecting the EBIC signal across the collector and emitter with the base shorted to either collector or emitter. In the former case, white contrast is obtained from the pipes and, in the latter case, black contrast is obtained. The relative magnitudes of the various types of contrast are obtained by recording y-modulated line scans across the pipes. A description is given of the way in which the emitter/base and collector/base junctions behave, in the presence of the electron/hole pairs generated by the electron beam and under the various experimental conditions described above. This shows how the contrast from the emitter/collector pipes arises.
Investigation of heterojunctions for MIS devices with oxygen-doped AlxGa1−xAs on n-type GaAs
Authors: Casey H. C. , Cho A. Y. , Lang D. V. , Nicollian E. H. , Foy P. W.
Published: February 2003

Metal-insulator-semiconductor (MIS) structures were prepared with high-resistivity oxygen-doped Al0.5Ga0.5As layers on n-type GaAs. These layers were grown by molecular-beam epitaxy (MBE). Capacitance-voltage measurements of MIS structures on both conducting and high-resistivity substrates demonstrate the achievement of deep depletion for reverse-bias and a near-flatband condition at zero bias. Measurement of the output characteristics of a majority-carrier depletion mode MISFET illustrates the application of this MIS technique to three terminal devices. The presence of a 2000-Å-thick O-doped Al0.5Ga0.5As layer on n-type GaAs was found to enhance the photoluminescent intensity of the n-GaAs layer by 52 times over that of an exposed GaAs surface. The measurements described here demonstrate that the use of single-crystal lattice-matched heterojunctions of O-Al0.5Ga0.5As–n (GaAs) avoids large interface state densities. Admittance spectroscopy measurements permitted assignment of the dominant deep level in O-doped Al0.5Ga0.5As as 0.64±0.04 eV.
Two-stage process for buildup of radiation-induced interface states
Authors: Winokur P. S. , Boesch H. E. , McGarrity J. M. , McLean F. B.
Published: February 2003

The interface-state buildup in wet-oxide MOS capacitors under positive bias was studied as a function of time following pulsed e-beam irradiation. The buildup was found to be a two-stage process. The first stage, which occurs during the time required for holes to transport to the SiO2/Si interface, determines the final or saturation value of interface states and was found to be field dependent and temperature independent. The second stage, which begins after the holes have reached the SiO2/Si interface and continues for several thousand seconds, determines the time scale for the buildup and was found to be both field and temperature dependent.
Microwave response of superconducting variable-thickness microbridges
Authors: Octavio M. , Skocpol W. J.
Published: February 2003

We report on the microwave response of variable-thickness tin and lead microbridges, the best of which can show microwave-induced Josephson steps up to 4.2 mV at low temperatures, limited primarily by heating effects. By examining the temperature dependence of the number of steps observed, we find agreement with the theory of such heating effects of Tinkham, Octavio, and Skocpol. We also show that the size and periodicity with microwave power of the steps at low voltages can be affected by heating. Finally, we show that closely spaced pairs of such variable-thickness microbridges can couple strongly together, and apparently can synchronize their oscillations on a Josephson step over a wider range of currents than can single bridges.
Wall effects in a diamond-anvil pressure-cell falling-sphere viscometer
Authors: Munro R. G. , Piermarini G. J. , Block S.
Published: February 2003

A geometric correction factor γ due to the close proximity of the walls and sphere in a diamond-anvil pressure-cell falling-sphere viscometer is evaluated in order to determine a liquid’s viscosity μ from the measured apparent viscosity μA. μ=γμA. Approximate values of γ are presented for a finite right circular cylindrical cell in which a sphere falls along a centrally located diameter. The results are used in conjunction with measurements on a fluid of known viscosity to estimate that the accuracy obtainable in a diamond-anvil pressure-cell falling-sphere viscometer is better than 30%.
On the diffusion approximation of the Boltzmann equation for slow electrons
Authors: Jacob J. H. , Srivastava B. N. , Rokni M. , Mangano J. A.
Published: February 2003

In this article we investigate the validity of the lowest-order diffusion or P1 approximation of the Boltzmann equation. This is done by considering a narrow band of electrons in energy space. The analysis shows that if the spatial derivative can be neglected, i.e., for a distributed source of electrons, the P1 approximation is valid all the cases considered (for e.g., N2). When the spatial derivative cannot be neglected, which is the case for a spatially localized source of electrons, then the region of validity of the P1 approximation is much more restrictive. High-pressure discharges are examples of a distributed source. Electrons generated for swarm experiments are examples of a spatially localized source of electrons.
Temporally and spatially resolved harmonic emission from spherical laser fusion targets
Authors: Leonard Thomas A. , Cover Ralph A.
Published: February 2003

An electro-optic streak camera was used to record 2ω0 and (3/2) ω0 harmonic emission from glass microsphere targets irradiated with a 0.3-TW Nd : glass laser. These two harmonic frequencies are produced at the critical and quarter-critical surfaces, respectively, and thus provide a measure of these electron-density trajectories. After applying a refraction correction to the data, the trajectories were compared with predictions from the KMSF TRHYD code. It was found that hydrodynamic development in the critical-density region was accurately depicted by the temporal behavior of the 2ω0 emission. In addition, observed periodic fluctuations in (3/2) ω0 emission along a meridian give direct evidence of density rippling in the underdense corona.
Annealing behavior of neutron-transmutation doped silicon—As studied by EPR
Authors: Kaufmann U. , Mitlehner H.
Published: February 2003

The EPR spectrum of the neutral substitutional phosphorus donor has been observed in originally undoped float-zone silicon after irradiation with thermal neutrons. The EPR intensity has been measured as a function of annealing temperature between 250 and 1100 °C. The minimum temperature required to achieve full phosphorus activity is near 700 °C if the material is irradiated in a purely thermal neutron beam. If the thermal and fast-neutron doses are comparable, this limit is near 800 °C. Observed annealing stages at 350, 600, and 700 °C correlate with published recovery data for specific defects.
Effects of pulsed ruby-laser annealing on As and Sb implanted silicon
Authors: White C. W. , Pronko P. P. , Wilson S. R. , Appleton B. R. , Narayan J. , Young R. T.
Published: February 2003

The effects of pulsed (Q-switched) ruby-laser annealing of arsenic- and antimony-implanted silicon (1×1015 to ∼2×1016 cm−2) has been studied by Rutherford ion backscattering, TEM, and ion channeling. The laser pulses were of ∼50-nsec time width and of 1.5–1.7 J/cm2 energy density. Analysis of the dopant profiles before and after annealing leads to the conclusion that the dopants diffuse under normal kinetics in a melted silicon layer over an average time interval of about 0.27-μsec after the laser power has been absorbed. Recrystallization of the melt layer is by liquid-phase epitaxial regrowth from the substrate. The recrystallized zone is found to be free of significant structural defects for all specimens except the very highest antimony doses, in which case some near-surface (∼400 Å) precipitation at dislocations is observed. Atom-location measurements reveal that 98–99% of the retained dopant is in substitutional lattice sites even when the dopant concentration greatly exceeds the limit of solid solubility. Only in the high-dose (≳1016 cm−2) antimony case was significant loss of dopant (20–35%) observed as a consequence of laser processing. The high-dose antimony also had a lower substitutional fraction (∼87%) compared to the other specimens.
Electrical measurements and optical activation studies in Mg-implanted GaAs
Authors: Yeo Y. K. , Park Y. S. , Yu Phil Won
Published: February 2003

Mg ions were implanted in Cr-doped semi-insulating GaAs at 120 keV to doses of 3×1012 to 1×1015/cm2 at room temperature. Surface-carrier concentrations and mobilities have been measured at various postimplantation anneal temperatures using the van der Pauw Hall-effect/sheet-resistivity technique. Detailed profiles of depth as a function of ion dose and anneal temperature are presented. Also, the results of a study of the integrated intensity of Mg emission at various annealing temperatures and of depth profiles of the relative emission intensity of the ions obtained by the photoluminescence method are compared with results obtained from electrical measurements. In addition, compensation-level analysis and a comparison of theoretical diffusion profiles with depth-profile data have been made. p-type layers have been produced for all except the lowest dose of 3×1012/cm2 after capping only (no postimplantation annealing) with pyrolytic Si3N4 encapsulants. Subsequent annealing up to 600 °C does not alter the electrical behavior appreciably. The electrical-activation efficiencies obtained were as high as 85% for the sample having a dose of 1×1013/cm2 annealed at 800 °C and 51% for the sample having a dose of 3×1014/cm2 after capping only. In general, the depth profiles are very sensitive to annealing temperature and ion dose, broadening dramatically at or above the 700 °C annealing temperature, and producing an active layer which extends to roughly twice the projected range of the original implant.
Transmission electron microscopy study of microdefects in dislocation-free GaAs and InP crystals
Authors: Kamejima Taibun , Matsui Junji , Seki Yasuo , Watanabe Hisao
Published: February 2003

The transmission electron microscopy study has been carried out to characterize the structural defects in heavily impurity-doped LEC-grown GaAs and InP crystals which are free from native dislocations. The microdefects in S- and Te-doped GaAs crystals were found to be mainly Frank-type stacking faults and prismatic dislocation loops. Diffraction contrast analysis revealed that all the microdefects were of interstitial type. However, in Zn-doped GaAs and Zn-, S-, and Te-doped InP crystals, the microdefects were hardly observed, which suggests that those crystals could be useful substrates for electronic devices. The appearance, especially in GaAs : S, of microdefects and also of helical dislocations associated with the effects of impurities on reducing dislocations are discussed.
Twofold orientations and hysteresis properties of nematic liquid crystals in strong magnetic fields
Authors: Motooka T. , Fukuhara A.
Published: February 2003

The effects of a magnetic field on director orientation in nematic liquid crystals between parallel electrodes with the director and the applied field in a plane perpendicular to the electrodes are studied theoretically; electric capacitance is computed to show changes in orientation. For a fixed field direction, capacitance is twofold for stronger magnetic fields and onefold for weaker fields. The former case corresponds to two types of orientations and the latter to a single type; the boundary is the boundary between the stable and unstable domains of one of the two types of orientation. In the twofold region, the actual selection of one orientation depends on the history of the applied magnetic field: it may happen that the orientation comes to the domain boundary and jumps to the other type. Such transitions have been experimentally observed.
Elastic constants of Fe(Ni,Co) -B glasses
Authors: Chou C.-P. , Davis L. A. , Hasegawa R.
Published: February 2003

Densities and Poisson’s ratios are reported for two series of metallic glasses, (FeCo)80B20 and (FeNi)80B20. These results are combined with extensional acoustic-wave velocity measurements, previously reported, to provide a characterization of the elastic stiffnesses of these glasses. The Poisson’s ratios for both series of alloys peak at intermediate compositions, reflecting essentially similar sharp peaks in the bulk stiffnesses. Shear stiffnesses are relatively insensitive to composition, especially for the Fe-Co-B alloys. The hardnesses of the alloys appear to vary in proportion to their shear stiffnesses.
Laser scanning measurement of the density distribution of confined 6Li+ ions
Authors: Knight R. D. , Prior M. H.
Published: February 2003

The density distribution of metastable 1s2s 3S1 Li+ ions confined in a radio-frequency quadrupole ion trap has been studied using a laser scanning technique. The laser beam, resonant with the 5485-Å 1s2s 3S1–1s2p 3P1 transition, is scanned in a plane normal to the trap z axis. Intercombination photons, 1s2 1S0–1s 2p 3P1 at 202 Å, are counted and stored as a function of laser-beam position. Application of the Abel transform to the data gives the density profile in the plane of the scan. In all cases, the density profiles were consistent with a Gaussian distribution of ions. The radial and axial widths of the distribution were measured as a function of the number of ions and potential well depth and shape. The results are discussed in terms of a model in which the ions are in thermal equilibrium at a temperature of several thousand degrees Kelvin.
Two-dimensional distribution of refractive-index changes in Ti-diffused LiNbO3 strip waveguides
Authors: Minakata Makoto , Saito Shoichi , Shibata Masashi
Published: February 2003

A method is reported for determining the two-dimensional distribution of refractive-index changes in Ti-diffused LiNbO3 strip waveguides. The measurement process was as follows. Distributions of diffused Ti concentration in LiNbO3 were measured using an x-ray microanalyzer. Using calibration curves the Ti concentrations were then converted into refractive-index changes. To obtain high spatial resolution in the two-dimensional XMA measurement the electron beam position was fixed and the sample was moved at a constant velocity. Lateral sliding of the sample perpendicular to the scanning direction was peformed mechanically, and the measured XMA data were corrected for edge effects. The results obtained for the Y-cut LiNbO3 waveguide diffused at 1000 °C for 10 h with a 10-μm-wide 500-Å-thick Ti strip showed that lateral diffusion of Ti was marked. The contour with a refractive-index change of 1×10−3 is of approximate depth 3.5 μm and width 40 μm. The maximum values of Δne and Δn0 were 1×10−2 and 8×10−3, respectively.
Optical modulation of second-harmonic generation in tellurium
Authors: Quint D. W. , Johnson L. M. , Jain K. , Pratt G. W.
Published: February 2003

Modulation of second-harmonic generation in tellurium by a 5.3-μm signal beam is analyzed. The signal beam in combination with the other beams in the process (10.6 μm doubling to 5.3 μm) generates free carriers by two-photon absorption. The resultant free carriers decrease the refractive index and increase the loss tangent of the material, thereby interfering with the second-harmonic generation process. The process is examined here both theoretically and experimentally. It is shown that the modulation efficiency can be as great as 100%. The prospect of achieving a usable power gain in a simple crystal of tellurium is shown to be unlikely, but the analysis points to promising alternatives.
Effects of transient and permanent optical confinement on the far-field radiation pattern from electron-beam-pumped semiconductor lasers
Authors: Gouin F. , Shewchun J. , Garside B. K.
Published: February 2003

The dynamic behavior of electron-beam-pumped semiconductor lasers can change drastically depending on whether transient or permanent waveguiding predominates. Measurements of the far-field diffraction patterns at lasing threshold from GaAs bulk crystal and GaInAs heteroepitaxial layers of various thicknesses are reported. The refractive-index step at the interface between the epi-layer and the substrate due to the changes in material composition results in optical confinement of the laser radiation within the GaInAs layer. A theoretical model for such a laser cavity is introduced to investigate the dependence of the diffraction loss and the transverse distribution of the radiation on the cavity parameters. The effects of the confining surface decrease as it becomes less accessible to the laser radiation. The critical parameters are the thickness of the passive region, the optical losses in that same region, and the refractive-index difference between active and passive regions. The analysis permits the determination of the specific conditions under which the effects of the back-reflecting surface become negligible.
Modes of operation of waveguide TE CO2 lasers
Authors: Wood II O. R. , Maloney P. J. , Adams C. R. , Smith P. W.
Published: February 2003

We have developed a particularly rugged waveguide TE CO2 laser structure that can be usefully operated in several distinctly different discharge modes. A short-pulse mode provides 0.4-μsec-duration gain-switched pulses, a quasicontinuous mode provides 20-μsec output pulses of over 200 W/cm3 of discharge volume, and the high-average power mode provides average power outputs of over 17 W/cm3.
A theory of quasielastic laser light scattering by polymer gels
Authors: Nossal Ralph
Published: February 2003

New theory is developed for interpreting periodic time correlations of coherent light scattered from soft polymer gels. Scattering is assumed to be caused by time-varying refractive-index changes which occur when a polymer lattice is distorted by macroscopic displacement waves. The frequencies of these waves are found to depend on the elastic moduli, material density, and dimensions of a sample, and are identical with central frequencies of resonances which would be noted in self-beat light-scattering spectra. The effects of friction between polymer strands and surrounding solvent, and of internal energy dissipation by the polymer lattice, also are investigated. Expressions are obtained for the widths of spectral resonances which are induced when a gel is excited by a sound field deriving from a sweep generator. Comparison with experimental results (reported elsewhere) leads to the conclusion that our previously proposed light-scattering scheme—involving mechanical excitation of a sample—measures the shear modulus of bulk gel rather than the rigidity of the polymer lattice alone.
Characteristics of a SAW filter with three inclined and tapered transducers
Authors: Tsukamoto Masahide
Published: February 2003

Inclined and tapered three-transducer configuration (ITTT configuration) is proposed which consists of three tapered interdigital transducers, a central IDT for an input and two outer IDT’s for an output which are inclined with respect to the central IDT. Characteristics of a surface-acoustic-wave filter having the ITTT configuration were calculated and compared with those of a filter having a conventional configuration. It was found that the ITTT configuration brings about smaller ripple in the amplitude response and in the group delay, and also wider tolerances for source and load impedances. Experiments were carried out using a piezoelectric ceramic. The results agreed well with calculations. An insertion loss of 10 dB and a ripple of group delay less than 50 nsec were attained, experimentally.
Ba2Si2TiO8 for surface-acoustic-wave devices
Authors: Yamauchi Hisao , Yamashita Kunio , Takeuchi Hiroshi
Published: February 2003

Characteristics of piezoelectric fresnoite (Ba2Si2TiO8) for surface-acoustic-wave (SAW) devices are calculated. In general, the SAW characteristics of this material are located between those of LiNbO3 and LiTaO3. It always has nonzero temperature coefficients of delay (TCD’s). The lowest TCD is approximately 38×10−6/K, corresponding to the Bleustein-Gulyaev wave on the Z-axis cylinder cuts. A layered structure of Ba2Si2TiO8 thin film deposited on a fused-quartz substrate is expected to have excellent SAW characteristics, e.g., k2a (electromechanical coupling factor when the interdigital transducers are formed on the surface of the layer) =0.0158–0.0165, and TCD=0–25×10−6/K for kh (where k is the wave number and h is the layer thickness) =2.0–3.2. A comment is made in the Appendix on an additional contribution to the formula for the power flow, and this contribution is taken into account in the present calculation.
Stress distributions in the vicinity of a neck
Authors: Jones S. E. , Gillis P. P. , Shalaby A. H.
Published: February 2003

The Bridgman analysis gives the stress distribution at the minimum cross section in a neck in a round tensile specimen. Consequently, the Bridgman analysis is essentially one dimensional since only radial variation (at constant axial position) is considered. In the present analysis the assumptions made by Bridgman are assumed valid for other cross sections close to the neck. A method suggested by Kaplan is then used to extend the Bridgman analysis to obtain the stresses as a function of both radial and axial position.
Anisotropy study of electrical conduction in oriented polymers. I. Analysis of bulk electrical conduction parallel to the surface of film
Authors: Hirota Sumio
Published: February 2003

A method of measuring current flow parallel to the film surface which is related to bulk conductivity is developed in the case of a four-electrode system attached symmetrically on both sides of a film. Two-dimensional analysis is carried out for potential and current distribution in the film with realistic boundary conditions. An apparent conductivity parallel to the film surface is defined using electrode geometry, applied potential, and total current. A relation between the apparent and the true conductivities of the film is obtained theoretically as a function of electrode geometry and is compared with the experimental results. It is shown that there is a good coincidence between them in the case where the thickness of the film is larger than the gap between the electrodes. With the aid of the method proposed here, it becomes possible to measure the anisotropy of conductivity in films.
Anisotropy study of electrical conduction in oriented polymers. II. Anisotropy of electrical conduction in uniaxially oriented polymers
Authors: Hirota Sumio
Published: February 2003

Conductivity σ (γ) in uniaxially oriented polymers is presented as a function of the angle γ between the orientation axis and electric field, resulting in the form σ (γ) ∝1+h cos2γ, where h is given as a function of both orientation and conductivity of the polymer crystallite. The anisotropy of conductivity is obtained in uniaxially oriented samples of poly-γ-methyl-L-glutamate (PMG) and of Nylon 12 (N12). Conductivity is largest parallel to the orientation axis in PMG and is largest perpendicular to the orientation axis in N12. These correspond to the direction of the hydrogen bonding orientation. This is very obvious evidence that charge carriers flow along a direction parallel to hydrogen bonding. Anisotropy of conductivity in crystallite is estimated using an orientation parameter and anisotropy of the observed conductivity.
Resonance-ionization velocimeter
Authors: Edelstein S. A. , Cooke W. E.
Published: February 2003

A technique is described in which flow velocities are measured by monitoring the ions produced in a laser-excited metal-vapor stream. The technique uses low-power lasers and low metal densities (∼10−3 Torr). It is used here to measure a flow velocity to an estimated uncertainty of 3%.
Excitation of the slow cyclotron and space-charge waves in a relativistic electron beam
Authors: Providakes G. , Nation J. A.
Published: February 2003

Experiments are reported in which a relativistic electron beam, having an energy of 650 keV and carrying a beam current of about 0.8 kA, was used to excite slow (negative energy) space-charge and cyclotron waves. The waves, which yielded megawatt powers in the Ka and V bands, were generated as a result of the unstable interaction between a beam wave, a static rippled magnetic field, and a waveguide mode. The instability growth was observed to increase with both increasing guide and ripple magetic field strengths, and saturated when the ripple field was about 10% of the guide field. The observations are mainly consistent with theoretical predictions, although selection rules for excited modes violate predictions.
Negative magnetoresistance in heavily compensated ZnSe crystals
Authors: Mathur P. C. , Sethi B. R. , Sharma O. P.
Published: February 2003

Magnetoresistance (MR) measurements have been performed in the temperature range 300–77 K in two single crystals of In-doped ZnSe, one of which was annealed in molten zinc. The MR has been found to be negative in the In-doped sample in the entire temperature range. The MR in the Zn-annealed In-doped sample is found to be positive but with magnitude much less than expected on the basis of free-electron conduction. The measured data suggest the contribution of impurity band conduction in both the samples. The experimental results are discussed in the light of various existing theories for negative magnetoresistance.
Capacitance-vs-voltage characteristics of ZnO varistors
Authors: Mukae Kazuo , Tsuda Kouichi , Nagasawa Ikuo
Published: February 2003

Studies were made on the capacitance-vs-voltage characteristics of ZnO varistors which contain rare-earth metal oxides and cobalt oxide. On the basis of the symmetrical Schottky-barrier model of the grain-boundary region, the barrier height φ and donor concentration Nd of ZnO grains were obtained by the modified 1/C2-V plot reduced from observed C-V relations. φ and Nd were obtained as 0.72 V and 1.6×1018 cm−3, respectively, for a ZnO-Pr6O11-Co3O4 system and 1.00 V and 0.76×1018 cm−3, respectively, for a ZnO-Pr6O11-La2O3-Co3O4 system. These results support the validity of this model and the treatment.
Comment on ’’A note on the assumption of quasiequilibrium in semiconductor junction devices’’
Authors: Guckel H. , Thomas D. C. , Demirkol A.
Published: February 2003

The quasiequilibrium assumption for p-n junctions is used to simplify the analysis of junction devices. It is useful to know if this assumption can be used for arbitrary forward injection levels. A recent proof which insists that the assumption is restricted to low injection levels is shown to be in error. An alternative approach via quasi-Fermi levels yields the conclusion that the assumption can be verified only after the bulk behavior has been established.
Comment on ’’A note on the assumption of quasiequilibrium in semiconductor junction devices’’
Authors: Berz F.
Published: February 2003

It is shown that the quasiequilibrium approach leads to consistent results when one takes into account the difference between the applied potential ψa across the junction and the split Δφ of the quasi-Fermi levels at the junction (ψa=Δφ only at low injection).
Reply to ’’Comments on ’A note on the assumption of quasiequilibrium in semiconductor junction devices’ ’’
Authors: von Roos Oldwig
Published: February 2003

It is pointed out that recently published criticisms of my work are based on a misunderstanding.
Theoretical calculations of the minority-carrier diffusion length in high-internal-quantum-efficiency GaAs
Authors: Lastras-Martínez A.
Published: February 2003

An explicit expression for the GaAs minority-carrier diffusion length, taking into account phenomena of photon absorption reemission, is deduced. A simpler approximate expression, valid for internal efficiencies larger than 0.9 and introducing an error less than 10%, is also obtained. The application of the deduced expressions to practical devices is discussed. It is concluded that such application is not a straightforward matter, as we must take into account the probability that some of the generated photons leave the active region of the device.
Hydrogen-isotope separation in dc-arc plasma
Authors: Vukanović Vladimir , Coyle Edward L.
Published: February 2003

In an arc plasma (230 A) burning in an atmosphere of air and argon a vapor-probe mixture of D2O and H2O was introduced. Samples were taken with a Calprobe water-cooled probe from the plasma gas at the same axial position in the arc column, but at different radial distances. The results of mass-spectrometric analyses are presented in two groups: for the samples taken from arc regions having temperatures above 5900 K and for those taken below 3800 K. An isotope separation factor is found between these regions of higher and lower temperature: (D : H) (high temp.)  :  (D : H) (low temp.) =1.67±12%.
Correlation between simultaneous thermally stimulated conductivity and thermoluminescence transients-experimental case of stannic oxide monocrystals
Authors: Gasiot J. , de Murcia M. , Fillard J. P. , Chen R.
Published: February 2003

The general solution of thermally stimulated processes is known to need the complex formulation of a nonlinear functional. Classical solutions can yet be found in special cases of particular exchange mechanisms and using approximations. The implicit correlation between thermally stimulated conductivity (TSC) and luminescence (TSL) is an important element in the qualitative determination of the mechanism involved. In this paper we propose a method for deducing such information from a log(TSC) -vs-log(TSL) parametric plot. This method is expected to apply even in the complex situation of overlapping or low-level peaks. Typical cases are emphasized and an experimental illustration of the technique is proposed for stannic oxide monocrystals. The conclusions are shown to be in very good agreement with the results obtained from classical measurements of luminescence and photoconductivity.