bluuebunny/crossref_metadata_2025 huggingface dataset:
Fundamental and harmonic response voltages of a sinusoidally current-modulated ideal semiconductor laser
Authors: Joyce W. B. , Dixon R. W.
Published: February 2003

It appears that derivative techniques will become quite useful in the characterization of semiconductor lasers. This paper clarifies the signal responses expected with these techniques by calculating the fundamental and second-harmonic voltages which would be observed in the case of an ideal laser driven with a sinusoidally modulated current. The previously untreated nonanalytic lasing-threshold region is explicitly included and the results are exact for any modulation amplitude. The harmonic voltages are then related to the first and second voltage derivatives and to the parameters characterizing (Al,Ga)As double-heterostructure lasers.
Studies of a high-energy HF laser using an electron-beam-excited mixture of high-pressure F2 and H2
Authors: Gerber R. A. , Patterson E. L.
Published: February 2003

Chain-reaction lasing of mixtures of F2, O2, and H2 at pressure ratios of 1/0.3/0.25 with F2 pressures up to 800 Torr was initiated with an electron beam, and a parametric study of laser emission was performed. In one series of studies the F2 and O2 pressures were held constant while the hydrogen pressure was varied up to stoichiometric. Under some conditions, SF6 or He was added to the above mixtures. A maximum laser energy of 4.2 kJ was measured at the higher pressures. Chemical and electrical efficiencies of up to 11.4% and 180%, respectively, were obtained. Each of these efficiencies has been found to be dependent upon the gas pressure and composition. The measured laser energy was found to be proportional to the measured electron-beam energy deposited in the gas. Addition of an unstable resonator provided a beam with a 4-mrad divergence.
Optical energy extraction from electron-beam-initiated H2–F2 mixtures
Authors: Tisone G. C. , Hoffman J. M.
Published: February 2003

An oscillator, based on electric discharge in an SF6-H2 mixture and yielding 400-nsec pulses, was used to probe an HF amplifying medium produced by electron-beam initiation of H2-F2 mixtures. The oscillator produced 17 lines of the P1, P2, and P3 transitions. The oscillator power density at the input to the amplifier was about 2×104 W/cm2 at the time the H2-F2 mixture was initiated. The power gain of the amplifier was estimated to be 500. Results indicate that with 17 lines from the v′=1, v′=2, and v′=3 vibrational levels of HF, about 6% of the generated energy can be extracted by the oscillator beam. The results of the experiment have also beem compared with a model calculation.
The relation between deformation and thermoluminescent defect centers in LiF (TLD-100)
Authors: DeWerd L. A. , White R. P. , Stang R. G. , Stoebe T. G.
Published: February 2003

Plastic deformation after exposure to ionizing radiation is shown to increase the F-band absorption in LiF (TLD-100), while decreasing the absorptions at 310 and 380 nm which are related to thermoluminescent traps. The rate of change with deformation of the three bands indicates that F centers are created when 310- and 380-nm absorption centers are destroyed. The results are interpreted in terms of the removal of F centers from the defect complexes causing the 310- and 380-nm absorption bands; this implies that the F center may be an integral part of the thermoluminescent traps in this material.
Coil probe method for determining the electron density and electron collision frequency in a magnetoplasma
Authors: Basu J.
Published: February 2003

A nonimmersive coil probe method is reported for determining the electron density and electron collision frequency in a low-pressure plasma column in the presence of a longitudinal magnetic field. It is shown how the parameters can be obtained by measuring the rf impedance of the coil probe placed coaxially around the plasma column.
Determination of insulator bulk trapped charge densities and centroids from photocurrent-voltage charactersitcs of MOS structures
Authors: DiMaria D. J.
Published: February 2003

A new rapid technique for determining the density and centroid of trapped space charge in MOS structures is described. Photocurrent-voltage characteristics for both the metal-oxide and Si-oxide interfaces are used to determine the internal fields due to bulk trapped charge and, hence, its density and centroid. An experimental example of this technique is shown for a MOWOS (metal-SiO2-W-SiO2-Si) structure where a layer of approximately 1014 W atoms/cm2 deposited 80 or 42 Å from the Si-SiO2 interface and charged by internal photoemission is investigated. This technique is compared to others in terms of its direct, rapid, minimally perturbing, low-current and low-field characteristics.
Effect of gas composition on the pressure dependence of helium solubility in vitreous silica
Authors: Shelby J. E. , Keeton S. C. , Iannucci J. J.
Published: February 2003

Helium solubility in vitreous silica has been measured from 0.1 to 1360 atm for helium-nitrogen mixtures containing from 10 to 100% helium. The results support previous contentions that the solubility process can be adequately explained by a simple statistical thermodynamical model, i.e., Langmuir adsorption. This model indicates that there are 1.9×1021 solubility sites per cm3 of glass.
Threshold current variations and optical scattering losses in (Al,Ga)As double-heterostructure lasers
Authors: Nash F. R. , Wagner W. R. , Brown R. L.
Published: February 2003

Photoluminescence studies have revealed that the active-layer waveguide of (Al,Ga)As double-heterostructure laser material often contains significant thickness variations which are introduced during the epitaxial layer growth. Examples of defects which may exist over substantial portions of an epitaxial wafer (12 mm×12 mm) are growth terraces and meniscus-dissolution lines. Observations of surface morphology alone are inadequate to gauge the actual active-layer deformations due to these defects. Angle-lap measurements permit a quantitative characterization of the growth defects. Both classes of defects can introduce several discrete optical-scattering disturbances within the gain volume of the laser. The works of Kogelnik and Marcuse are used to theoretically model the defects and compute optical scattering losses as functions of the parameters which describe the severity of the local waveguide deformations. When representative characterizations of observed defects are used in the calculations for scattering loss, it is found: (i) that significant threshold variations (tens to hundreds of percent) are predicted; (ii) that the computed range of threshold scatter agrees with the experimentally observed range of threshold scatter; and (iii) that in one specific instance the relatively elevated threshold of a particular laser agreed reasonably with the computed threshold based upon a knowledge of the defects actually present in the device.
Tolerance of laser-driven microshell targets to fluorescence and prepulse energy
Authors: Leonard Tom , Moncur N. K. , Sullivan David
Published: February 2003

Glass-shell targets currently being used for laser-fusion experiments are susceptible to damage by preenergy from the laser. This energy can result from amplified spontaneous emission (ASE) throughout the laser chain during the period of high-population inversion or it can take the form of a short prepulse nanoseconds before the main laser pulse. We point out the energy levels which a typical target can tolerate in the form of ASE and prepulses. These energies are low enough that special precautions must be taken to prevent significant perturbations of the target or its environment before the main laser pulse.
A new electrically controllable diffraction grating using polarization reflection
Authors: Sato Heihachi , Toda Kohji
Published: February 2003

An electrically controllable diffraction (ECD) grating using a polarization reflection from an electro-optic (EO) material is proposed and investigated in the experiments. The fundamental characteristics of this ECD grating are given experimentally for a He-Ne 0.63-μm laser. The grating used consists of a PLZT ceramic with ten pairs of interdigital electrodes having a period of 400 μm. Applying the electric field to the electrodes, the diffraction pattern can be changed due to the deviation of the reflectance of the EO material. Near the zeroth-order diffraction peak the maximum modulation degree of 33% was obtained with an applied peak voltage of 100 V at an incident angle 60°.
Hologram writing by the photorefractive effect with Gaussian beams at constant applied voltage
Authors: Moharam M. G. , Young L.
Published: February 2003

The problem of hologram writing with one-dimensional Gaussian beams incident on a finite crystal with finite dark conductivity is modelled for constant applied voltage and short transport length. Expressions are derived for the space-charge field during the initial linear and the final saturation stages plus a series solution covering the whole time development. It is shown that the ratio of light- to dark-carrier concentration and the ratio of crystal length to Gaussian beam width have important effects on the writing process.
Degradation of bulk luminescence in GaP : Zn,O induced by laser excitation
Authors: Daniel Dapkus P. , Henry C. H.
Published: February 2003

Bulk degradation of GaP : Zn,O LED material has been studied using above-band-gap laser light as the means of excitation. Significant bulk degradation can be induced at elevated temperatures by ?103 W/cm2 of 5145-Å laser excitation. The degradation is quite uniform and extends 20 μm into the crystal, conforming to the volume excited by the laser. SEM and luminescence studies show that the minority-carrier diffusion length changes only slightly during degradation, whereas the Zn-O luminescence decreases by as much as an order of magnitude. It is concluded that the degradation is due to the reduction of the Zn-O complex concentration.
Time dependence of environmental-contaminant-induced reactions in encapsulated metallurgy. I. Development of the model
Authors: Ferris-Prabhu A. V.
Published: February 2003

A one-dimensional model is presented to describe the diffusion of airborne environmental contaminants through the encapsulants in an integrated circuit package, and subsequent penetration to and reaction with the metallurgy. Equations are derived in terms of the physical parameters and geometry of the package, from which the critical time needed for the reaction to proceed till the metallurgy fails can be calculated.
Strain-amplitude–dependent damping in aluminum at a very low frequency
Authors: Goettler Hans J. , Nelson Carl W.
Published: February 2003

Strain-amplitude–dependent internal friction was measured in pure aluminum under forced vibrations at a frequency of 8.3×10−3 Hz. Using a modification of the torsional pendulum apparatus, the effects of time, cold work by bending, and changes in bias stress were investigated at room temperature. The dislocation damping theory by Granato and Lücke adequately describes the results. The frequency range in which this theory has been successfully applied is thus extended several orders of magnitude below the frequencies employed to date in experiments of this kind. Similar work at much higher frequencies by other investigators compares well with the present results.
AES study of electron-beam-induced interactions between oxygen and the Ge(111) surface
Authors: Margoninski Y.
Published: February 2003

For a Ge(111) surface irradiated by an electron beam of 1.5-keV energy and current density of 2 μA mm−2, it was found that beam-assisted oxygen adsorption at pressures <10−9 Torr always resulted in carbon-contaminated overlayers and was probably due to dissociation of physisorbed CO. The sticking coefficient s of CO was 0.08. At oxygen pressures ≳10−6 Torr, carbon-free coverages could be formed, even without irradiation. s for oxygen was 6×10−4 for beam-assisted and 1.5×10−4 for nonassisted adsorption. Electron impact desorption followed a first-order rate equation and the desorption cross section for oxygen was 6×10−20 cm2.
X-ray–induced electron emission from thin gold foils
Authors: Gaines J. L. , Hansen R. A.
Published: February 2003

Electrons of various energies are emitted when thin gold foils (0.19–0.95 mg/cm2 thick) are irradiated by monoenergetic x rays in the range 1.5–8 keV. In this experiment, the total electron yield, the high-energy electron yield, and the low-energy secondary electron yield are measured as a function of foil thickness, target angle, and x-ray energy. The total electron yield from a 7.62 ×10−4-cm-thick beryllium foil plated with 0.019 mg/cm2 of gold was also measured.
Acoustohydrodynamic instability in nematic liquid crystals
Authors: Scudieri F. , Bertolotti M. , Melone S. , Albertini G.
Published: February 2003

The hydrodynamic effects of ultrasound in the nematic liquid crystal MBBA are studied. The conditions for the formation of rolls or disclinations are given. The roll patterns are then examined and found to be produced at very low ultrasound intensities.
Dielectric-loss measurements of interfacial polarization at silver halide–insulator interfaces
Authors: Hoyen Harry A.
Published: February 2003

The role of Ag+-interstitial and Ag+-vacancy transport across silver halide surfaces is important for both ionically blocking and nonblocking interfaces. One technique to evaluate the nature of a blocking silver halide surface is to measure the alternating-current dielectric loss of silver halide microcrystals in contact with an insulating dry-gelatin phase. From the results of these measurements, the availability of the potential-determining Ag+ interstitial was determined as a function of silver halide type, crystal size and morphology, and the addition of divalent cations within the silver halide phase and adsorbed at the surface. The results on small crystals (0.2 μm) and, analogously, for very thin films, where the Debye length is comparable to the linear thickness, indicated that the Ag+-interstitial concentration is a critical function of the surface properties of the silver halide. Consequently, the transport of ionic carriers across the silver halide is not only dependent on bulk solid-state properties, but also on the nature of the surface and the ionic space-charge layer just below the surface.
Dielectric and thermal properties of Pb2Nb2O7 at low temperature
Authors: Siegwarth J. D. , Lawless W. N. , Morrow A. J.
Published: February 2003

Measurements of the dielectric constant, polarization, zero-field specific heat, and field-dependent specific heat of polycrystalline Pb2Nb2O7 at low temperatures are reported. No evidence for a phase transition at 15 K was found, contrary to previous suggestions of an antiferroelectric transition at 15 K based on dielectric data. The peak in the dielectric constant appears to be due to relaxation phenomena.
Practical antireflection coatings for metal-semiconductor solar cells
Authors: Yeh Y. C. M. , Ernest F. P. , Stirn R. J.
Published: February 2003

The metal-semiconductor solar cell is a potential candidate for converting solar energy to electrical energy for space and terrestrial application. In this paper, a method for obtaining parameters of practical antireflection (AR) coatings for the metal-semiconductor solar cells is given. This method utilizes the measured equivalent index of refraction obtained from ellipsometry, since the surface to be AR coated has a multilayer structure. Both the experimental results and theoretical calculations of optical parameters for Ta2O5 AR coatings on Au-GaAs and Au-GaAs0.78P0.22 solar cells are presented for comparison.
Electrical transpoet properties of SiGe thermoelectric alloys doped with As, P, and As+P
Authors: Heller M. W. , Nasby R. D. , Johnson R. T.
Published: February 2003

The Hall coefficient RH, Seebeck coefficient, and electrical resistivity have been measured on hot-pressed SiGe alloys (80 at.% Si) from 4 to 300 K. The alloys were doped with As, P, or As+P from 5×1018 to 1.75×1020 cm−3. Only slight differences in transport properties with dopant type were observed. Studies of dopant solubilities were pursued, and the results suggest that the limiting electrical active As concentrations are below those of P. In the analysis of the transport data the standard treatment of ionized impurity scattering was found to be inadequate. The theory, when modified to include the energfy dependence of the screening factor, gives an adequate description of our data. Hall factors were determined from RH data and dopant concentrations obtained from chemical analysis. Hall factor were also determined from analysis of the transport data and were about 20% smaller than those based on dopant concentrations deduced from chemical analysis.
Behavior of a manganin coil at elevated temperatures and pressures
Authors: Weiss Jonathan D. , Decker D. L. , Vanfleet H. B.
Published: February 2003

We have determined the temperature dependence in the first-order pressure coefficient of a manganin coil to be dβ/dT= (4.2±0.8) ×10−7 (kbar °C)−1 in the equation R (T,P) =R (T,0)(1+βP+γP2), where R (T,P) is the coil resistance at temperature T and pressure P. The measurements were performed by simultaneously measuring the coil resistance and temperature at the transitions of mercury and bismuth, which were observed by differential thermal analysis.
Effect of substrate temperature on composition ratio x in molecular-beam-epitaxial GaAs1−xPx
Authors: Gonda Shun-ichi , Matsushima Yuichi
Published: February 2003

GaAs1−xPx crystals were grown by molecular-beam epitaxy with parametric variation of substrate temperature Ts (540–580 °C) and of the ratio of beam intensity of P to that of As (2–11). The rate of decrease of composition ratio x with temperature, −dx/dTs, is 0.003 °C−1 for all ratios of beam intensity. The sticking coefficient of P is found to vary inversely proportional to the substrate temperature in this temperature range. This fact indicates the possibility of writing two-dimensional patterns on the surface by a partial temperature rise.
Capacitance and ellipsometrically determined oxide thickness of Nb-oxide-Pb Josephson tunnel junctions
Authors: Basavaiah S. , Greiner J. H.
Published: February 2003

The capacitance of Nb-oxide-Pb Josephson tunnel junctions was determined from the self-resonance phenomenon in the Josephson
Role of Joule heating in the electrostatic spraying of liquids
Authors: Crowley Joseph M.
Published: February 2003

Electrostatic spraying from a liquid cone is associated with a high electric current density at the tip of the cone. For all nonmetals, and for some metals, the Joule heating produced by this current is sufficient to poil the liquid. It is suggested that boiling, rather than electrostatic force, is responsible for the liquid droplets which appear in electrostatic spraying. This suggestion is confirmed by comparison of the expected temperature with the observed mode of spraying for various metals and nonmetals.
Influence of dynamic yield point in multimaterial impact
Authors: Gordon Paul , Karpp Robert , Sanday S. Carlos , Schwartz Milton
Published: February 2003

The impact of two in-series metal cylinders on rigid targets was studied experimentally and analytically. An analytical method was developed to determine the dynamic yield strengths of each material in the composite cylinder. This technique, which is numerical in nature, represents an extension of that recently advanced by Wilkins and Guinin for single-material yield point determinations. The basis of this new method is a comparison of various simulations with the postmortem experimental geometry. The method was applied to composite cylinders of 4340 steel and a tungsten alloy, for which the dynamic yield points were determined.
Multichannel laser light scattering diagnostics for density profile measurements in belt pinch plasmas
Authors: Protz R. , Söldner F. , Steuer K.-H.
Published: February 2003

A multichannel laser light scattering system with high sensitivity has been applied to Thomson scattering measurements of electron density profiles by a single laser shot. The problems inherent to radial profile measurements of toroidal plasmas were overcome and the stray light level could be lowered to ne =1013 cm−3 equivalent. This diagnostics was used for optimizing the preheating discharge in the Garching High-Voltage Belt Pinch at low densities ne?1013 cm−3.
Electromagnetic properties of thin epitaxial Bi films in magnetic fields up to 85 kG
Authors: Asahi Hajime , Baba Shigeru , Kinbara Akira
Published: February 2003

Electromagnetic measurements on thin epitaxial Bi films (thickness: 350–6350 Å) were carried out in magnetic fields up to 85 kG. The transverse magnetoresistance had a tendency of saturation with increasing magnetic fields. The tendency was stronger for thinner films. This behavior was attributed to the scattering at the grain-boundary planes parallel to the electric field. In the measurements of longitudinal magnetoresistance, the momentum value of carriers estimated from the positions of peaks or shoulders in the magnetoresistance–vs–magnetic-field curve was about 0.8×10−21 g cm/sec and agrees with the bulk Bi value. The appearance of peaks or shoulders can be interpreted by the partial diffuse scattering of carriers at film surfaces. Shubnikov–de Haas oscillations were observed in (dρ/dH) -H measurements. The oscillation period Δ (H−1) was found to depend on film thickness and the dependence was attributed to the thickness dependence of carrier densities in films. The oscillations caused by quantum size effect were not observed.
Note on the effects of finite ion mass and electron thermal velocity spread on the aperiodic instabilities of a space-charge-neutralized electron beam in a planar diode
Authors: Yuan K.
Published: February 2003

A hydrodynamic analysis of the aperiodic instabilities of a neutralized drifting electron stream in a short-circuited planar diode is given in this work. The results of this investigation indicate the following: (i) An electron stream can be aperiodically unstable only if the electron stream’s Mach number exceeds unity in the diode space. The change from a monoenergetic electron beam to a dispersive electron beam results in a modification of the instability condition, a reduction of the growth rate, and a smaller value of critical current flowing through the diode. (ii) The aperiodic instability imbedded in the immobile ion background, i.e., the Pierce instability, cannot be eliminated by the first-order motion of ions. The effect of the finite ion mass is not only to reduce the maximum growth rate of the Pierce instability and to increase the diode critical current, but also to introduce new aperiodic instabilities with growth rates generally smaller than that of the Pierce instability.
Graded-composition semiconductors as tunable narrow-band optical filters
Authors: Laurenti J. P. , Rustagi K. , Rouzeyre M. , Rufer H. , Ruppel W.
Published: February 2003

Tunable narrow-band optical filters over a wide spectral range are constructed. These use the efficient coupling of orthogonally polarized optical waves near the isotropic wavelength in graded-composition mixed crystals of CdS1−x Sex and Zn1−x Cdx S. In one crystal of CdS1−x Sex, x varied continuously between 0.04 and 0.29 and the central wavelength λi of the corresponding tunable filter from 5130 to 5700 Å. In one sample of Zn1−xCdx S, x varied from 0.41 at one end to 0.70 at the other and λi shifted from 4272 to 4584 Å. In both cases the transmission spectra were narrow peaks with peak transmission of 10–20% and widths at half-maximum of approximately 10 Å.
A continuous HF chemical laser: Production of fluorine atoms by a microwave discharge
Authors: Bertrand L. , Gagné J. M. , Mongeau B. , Lapointe B. , Conturie Y. , Moisan M.
Published: February 2003

We have used a slow-wave structure to dissociate SF6 and obtain the fluorine atoms for a cw hydrogen fluoride chemical laser. The laser output power has been observed to increase linearly with the absorbed microwave power. The effect of rare gases in the mixture is discussed. It is shown that the laser power increases linearly with their ionization potentials. Those features indicate that electron collisions are essential for the generation of fluorine atoms. In this respect, contributions involving metastable atoms are negligible. No simple relation is observed between the intensity of the fluorine spectral lines in the discharge and the laser power.
H2O, NO, and N2O infrared lasers pumped directly and indirectly by electronic-vibrational energy transfer
Authors: Petersen A. B. , Braverman L. W. , Wittig C.
Published: February 2003

Pulsed infrared molecular lasers are reported in which pumping is via electronic-vibrational energy transfer from Br(42P1/2). H2O and NO lasers are pumped directly by E-V transfer and operate on a variety of transitions not previosuly seen in stimulated emission. The N2O laser operates near 10.9 μm and is pumped by a two-step process involving E-V transfer to an intermediate molecule and subsequent V-V transfer from that molecule to N2O. This latter technique extends the applicability of E-V pumping to molecules which do not interact directly with the electronically excited species.
Spontaneous emf associated with shape memory effect in TiNi
Authors: Johnson A. D. , Katz P. I.
Published: February 2003

A transient emf of approximately 0.1 mV lasting for about 100 msec is observed at the ends of a cold-stressed TiNi wire when a central portion of the wire is rapidly heated to above its shape memory transition temperature. A pulse of opposite polarity is observed during cooling through the transition temperature when the temperature change is coincident with a shape change. The polarity of the voltage is inverted when the electrical leads are reversed, implying that the wire is itself polarized. The observed emf is enhanced in a wire which has been ’’trained’’ so that it displays a double memory.
Effect of hydrogen on the temperature dependence of the elastic constants of tantalum single crystals
Authors: Stewart W. L. , Roberts J. M. , Alexandropolous N. G. , Salama K.
Published: February 2003

An investigation was undertaken to determine whether or not a significant Snoek relaxation mechanism exists when hydrogen is dissolved in tantalum. The experimental approach involved the determination of the changes in the absolute values and the temperature (in the range 136–298 °K) dependence of the elastic constants of single crystals charged with varying amounts of hydrogen up to 10.3 at %. Changes in the absolute values of the elastic constants, as a function of hydrogen concentration, were found to be linear, with positive slopes for C11, CL, and C44, and a negative slope for C′. The small negative slope of C′ yields the distortion parameter (λ1−λ2) value of 0.0274. The bulk modulus and the Voight average Young’s modulus were found to increase when hydrogen was introduced into the crystal lattice. The elastic constants exhibit no change in their temperature dependence when either the temperature (in the range 245–298 °K) or the hydrogen concentration (in the range 0–10.3 at.%) was varied. It is concluded that a Snoek relaxation attributed to tetrahedral symmetry of the locally distorted tantalum cubic lattice by hydrogen is insignificant.
Slow magnetic domain-wall motion and tunneling
Authors: Baldwin John A. , Milstein Frederick , Wong Russel C. , West James L.
Published: February 2003

Slow motion of magnetic domain walls in grain-oriented 50-50% NiFe is studied experimentally and theoretically. There is a region in which velocity u is approximately exponentially dependent on field H. It is found that all of the data may be fit by a theoretical expression derived from the spring model, and the assumption of quantum-mechanical tunneling as the mechanism responsible for slow motion. However, the values of the parameters derived from the best fit lead to a value of the separation, at breakaway, between the midpoints of an average pinning center and that portion of a wall pinned by it which is about 4×10−13 lattice constants, which is unrealistically small. It is tentatively concluded that tunneling is not the mechanism behind slow wall motion, at least not at room temperature.
Magnetic properties of rare-earth vanadites L
nVO3
Authors: Sakai Takaaki , Adachi Gin-ya , Shiokawa Jiro , Shin-ike Tsutomu
Published: February 2003

The perovskite-type oxides LnVO3 (Ln=La-Lu and Y) containing a trivalent rare-earth ion and a trivalent vanadium ion were prepared. Magnetic susceptibilities of 15 LnVO3 were measured in the temperature range 60–300 °K. The measurement for DyVO3 was made down to 2 °K, in which the magnetic ordering of the Dy3+ ion was found. All LnVO3 except GdVO3 were antiferromagnets at low temperature. The paramagnetism of GdVO3 persisted down to 60 °K. Most of the materials investigated showed a weak ferromagnetism with an ordering temperature of 88–150 °K.
Spin-wave resonance spectra of inhomogeneous bubble garnet films
Authors: Hoekstra B. , van Stapele R. P. , Robertson J. M.
Published: February 2003

Spin-wave resonance at 10 GHz has been observed in thin (? 5 μm) garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12. The films were grown by LPE on [111]-oriented gadolinium gallium garnet substrates, both from a nonstirred melt (vertical mode of dipping) and a stirred melt (horizontal dipping, applying axial substrate rotation). The spectra exhibit large numbers of strongly excited modes with large deviations from quadratic spacing, which are interpreted in terms of a volume inhomogeneity of the uniaxial anisotropy constant Ku. Two models are used to explain the experimental spectra. In one model the film is considered as being built up of exchange coupled layers having different uniaxial anisotropy constants Ku. In the second model it is assumed that Ku varies linearly with the distance from the substrate, but with different slopes in different regions. No pinning is assumed at the surfaces. A simple graphical method is presented for determining the normal modes of films with these types of variations. It is shown that the normal modes can be separated into two types. The low-order modes are localized modes, which are wavelike in only part of the film. These are strongly excited and their spacing is nonquadratic. High-order modes are volume modes, which are sinusoidal throughout the films, though with varying wave vector. These are weakly excited. The low-order modes bear information on the variations of Ku within the thickness. The nature of these variations is determined experimentally by examining the changes of these modes when the films are thinned down by chemical etching. Examples are given of films which are homogeneous except for a narrow (? 1 μm) region next to the substrate and of films whose anisotropy varies linearly throughout the major part of the thickness. The high-order modes are only slightly affected by the variations. From their positions, using the universal numbering scheme n = 0,1,2,... for all the modes, the exchange stiffness constants have been determined.
Use of image restoration and enhancement to improve x-ray pinhole camera resolution
Authors: Toepfer A. J. , Demuth H. B.
Published: February 2003

Numerical image processing techniques are applied to the restoration of x-ray pinhole photographs of solid targets irradiated by intense relativistic electron beams. The numerical and analytic bases for image restoration are briefly described. An experimentally determined point-spread function for the pinhole camera is utilized to eliminate the effects of high-energy x-ray degradation of pinhole resolution. It is shown that penetration by hard x rays from filtered spectra through the pinhole edges can lead to apparent broadening of the electron-beam pinch on high-Z targets. Elimination of x-ray shine-through also permits determination of photon intensity from high-Z target ablation products, and improves spatial resolution of the x-ray source.
A mechanism of Br2 formation in Ar/Br2 laser systems
Authors: Kolts J. H. , Setser D. W.
Published: February 2003

The reaction of electronically excited state Br* (4p4, 5s) atoms with Br2 and BrI produces electronically excited Br*2, which gives a complex emission system in the 190–350-nm region. In both cases the excitation reaction probably involves bromine atom transfer with formation of Br*2. Similar reactions may be expected between other excited np4(n+1) s halogen atoms and suitable halogen donor molecules. These experiments were done in a flowing-afterglow apparatus at 1–8 Torr; the Br* atoms were generated from interaction of the precursor molecules with metastable argon atoms or with metastable helium atoms. Under high-pressure excitation conditions, formation of Br*2 by reaction of Br* with Br2 followed by vibrational relaxation may contribute to the excitation mechanism for the Br*2 laser system initiated by e-beam or discharge pumping of Br2/Ar mixtures.
Dislocation distribution introduced into soft copper crystals by ultrasonic irradiation
Authors: Jackson P. J. , Nathanson P. D. K.
Published: February 2003

Soft copper crystals in the form of specimens oriented for single glide in tensile tests were immersed in an ultrasonic cleaning bath. By etch-pitting {111} planes, it was found that irradiation had introduced dislocations which lay preferentially on the main glide plane. The dislocations produced more hardening on a plane which they intersected than on the plane on which they lay and the character of slip was different on the two planes.
Broad-band radioluminescence in electron-irradiated ionic compounds
Authors: Green B. A. , Passenheim B. C.
Published: February 2003

It is found that the magnitude of the broad-band radioluminescent efficiency in electron-irradiated ionic materials varies exponentially with both temperature and lattice frequency, and that the general features of the data can be explained by longitudinal optical phonon-assisted emission.
Growth of PbTe films under near-equilibrium conditions
Authors: Lopez-Otero A.
Published: February 2003

Using a vacuum evaporation method, we have deposited, on BaF2 substrates, PbTe films which are free of significant strains and have Hall mobilities as large as 2.5×106 cm2/V sec at 13 °K. This was accomplished by putting the emphasis on growth under near-equilibrium conditions rather than on growth under ultraclean conditions.
Persistence of a surface film on a liquid in the presence of disturbance propagation
Authors: Dudeck M. , Prud’Homme R.
Published: February 2003

An impermeable film (such as oil) can be used to prevent gas entrainment by the free surface of a liquid. This film, lying on the liquid, is modeled as a continuous viscoelastic two-dimensional medium. Cohesion and sufficient thickness of this medium are necessary to ensure effective protection. The authors study the evolution of the system in the case of a progressive surface wave of low amplitude. A theory of linearized disturbances is used to obtain the propagation equation of the wave. The solution of this equation gives the film thickness and the surface tension during the movement and leads to determination of the protection conditions of the liquid.
Effects of truncated Gaussian-beam variations in laser saturation spectroscopy
Authors: Sargent Murray
Published: February 2003

The effects of possibly truncated Gaussian-beam variations in probe and saturator-wave intensities are studied analytically and numerically for saturation spectroscopy of homogeneously and inhomogeneously broadened systems. The measured saturation intensity is shown to be about 2.5 times greater for Gaussian beams than for uniform saturation. Systems characterized by the short dipole lifetime limit (T2≪T1) are treated, revealing sizeable modifications to the depths of coherent pulsation dips and Bennet holes. The equal lifetime case (T2=T1) is studied as well, showing substantial influence on the dynamic Stark effect.
Bounds on the energy and mean square fields in a heterogeneous dielectric
Authors: Mendelson Kenneth S.
Published: February 2003

A variety of upper and lower bounds are obtained on the energy and the mean square electric field and electric displacement in a heterogeneous dielectric subject to arbitrary Dirichlet or Neumann boundary conditions.
Low dark-current MOS photodiodes using GaAs0.6P0.4
Authors: Ahrenkiel R. K. , Moser F. , Coburn T. , Lyu S. L.
Published: February 2003

Anodic oxides have been grown on n-type GaAs0.6P0.4 and MOS capacitors have been fabricated. The thermal generation rate of minority carriers, and therefore the dark current, is very small in this material. Consequently, MOS photosensors typically have storage times of 500 sec but can be read out in submillisecond times by pulsing into accumulation. The intrinsic quantum efficiency of these structures is about unity and applications to sample-and-hold and low-light-level devices are suggested.
Grain-boundary electromigration in thin films. I. Low-temperature theory
Authors: Tai K. L. , Ohring M.
Published: February 2003

A Macroscopic mathematical theory is presented accounting for grain-boundary diffusion and electromigration in the presence of a simultaneous flux of atoms into the surrounding bulk lattice. The model employs a semi-infinite bicrystal geomettry with a constant source at the origin, and both integral and numerical solutions to the subsequent non-steady-state transport equations are given. ONly the case where V2/4Db-DL/δ2≳0, which is ttrue at low temperatures, is considered in detail. (V, Db, and aδ are the grain-boundary ion drift velocity, diffusivity, and width, respectively, while DL is the lattice diffusivity.). It is predicted that the time dependence of the displacement of a front of fixed concentration is linear only at short times and parabolic at longer times or with increasing amounts of atoms leakage into the bulk. In addition, the concentration profiles are predicted to have a plateau which becomes less apparent at higher temperatures. A comparison between the present theory and a previous treatment based on an extension of the Fisch analysis will be made. Application to recent results in thin films will be discussed.
Effects of electron-beam radiation on MOS structures as influenced by the silicon dopant
Authors: Scoggan G. A. , Ma T. P.
Published: February 2003

The flatband shift induced by 25-keV electron-beam radiation in unbiased MOS structures depends in great part on the type and concentration of the dopant in the silicon. The flatband shifts for n-type samples are less pronounced than those for p-type samples, and in general are in the opposite direction. The radiation-induced interface states, however, are independent of the dopant. The difference between the flatband shifts is shown to be best explained by a model based on the assumption that the interface states above midgap are acceptor-type states, and those below are donor-type states. A quantitative analysis made with this model indicates that the radiation-induced fixed oxide charge also is independent of the dopant. The dopant dependence of the flatband shifts can thus be attributed entirely to the charging effects of the interface states. By use of the same model, the apparent discrepancy between the shifts in the threshold voltage and in the flatband voltage of a MOSFET can also be readily resolved. A simple midgap method is implemented to obtain the fixed oxide charge without using interface-state information; the results agree well with those obtained by the more conventional flatband method, which must take the interface-state effects into account.
Study of thermally induced deep levels in Al doped Si
Authors: Marchand Raymond L. , Sah Chih-Tang
Published: February 2003

Deep levels in heat-treated aluminum-doped silicon were observed using thermally stimulated capacitance measurements. Three hole traps (1012–1014 centers/cm3) at EV+216 meV, EV+316 meV, and EV+402 meV, and an electron trap (1013 centers/cm2) at EC−389 meV were observed. Concentration profiles of these centers were measured and a comparison with levels observed in electron-irradiated and Al-doped Si was made.
Magnetic anisotropy in evaporated amorphous films of the ternary system Gdx(Fe1−yCoy)1−x
Authors: Taylor R. C. , Gangulee A.
Published: February 2003

Magnetic anisotropy has been determined for evaporated amorphous films of Gdx(Fe1−yCoy)1−x with 0.08<x<0.35 and 0.06<y<0.62. The anisotropy data were fitted with a dipolar equation of the form Ku=𝒥 CijMiMj in which Cij is a dipolar coupling constant for the i-j pair and Mi and Mj are sublattice magnetizations. The model satisfactorily described the experimental data for all films that were amorphous. The anisotropy could be attributed to pair ordering in which rare earth–transition metal pairs (Gd-Co) and Gd-Fe) contribute to in-plane anisotropy and rare earth–rare earth (Gd-Gd) and transition metal–transition metal (Fe-Fe, Co-Co, and Fe-Co) pairs contribute to perpendicular anisotropy. The Fe-Co pairs were the strongest contributor to perpendicular anisotropy with CFe-Co=2.809, CFe-Fe=0.992, and CCo-Co=0.660.
Circular magnetization of nickel and ferrite twisted tubular polycrystalline samples in axial magnetic fields
Authors: Cecchi G. C. , Drigo A. , Ronconi F.
Published: February 2003

In this work, the circular component of magnetization in nickel and ferrite twisted tubular polycrystalline specimens has been measured. These data have been related to the magnetoelastic properties of the samples by means of an equation deduced from energetic considerations. Excellent agreement was found between measured and calculated values of circular magnetization whenever Joule magnetostriction data were obtainable. These results pointed out that the circular component of magnetization and its dependence on applied stress are mainly determined by magnetostrictive properties of polycrystalline samples. The applicability of this equation to magnetostriction measurements has been briefly considered.
Thermally assisted field emission near precipitates in p-n junctions
Authors: Busta H. H. , Waggener H. A.
Published: February 2003

Conductive precipitates imbedded in the space-charge region of a p-n junction give rise to localized high fields near the precipitates. For localized fields of approximately 106 V/cm or larger, the dominant current contribution is due to localized Fowler-Nordheim field emission which gives rise to a soft leakage behavior. By fitting soft leakage currents to a thermally assisted field-emission model, information about the local field enhancement at the precipitates and about the barrier height surrounding the precipitates was obtained. The model predicts that soft leakage currents which are generated in regions of high field enhancement (∼107 V/cm) are almost temperature independent (77–350 K), whereas in regions of moderate field enhancement (∼106 V/cm) the soft leakage currents are strongly temperature dependent.
(GaAl)As/GaAs heterojunction phototransistors with high current gain
Authors: Konagai Makoto , Katsukawa Kosho , Takahashi Kiyoshi
Published: February 2003

n-Ga1−xAlxAs/p-GaAs/n-GaAs heterojunction transistors with high Al concentrations have been fabricated by the conventional liquid-phase epitaxial method. Electrical measurements showed that the transistors have a common emitter current gain of up to 1600. The current gain varies with the emitter injection level because of the defect-current component, which is the recombination current in the depletion region. It has been made clear, however, that the effect of the defect current was reduced in transistors grown at low temperature (∼750 °C). The variation of the electron diffusion length Ln with the device operating temperature has been calculated by using the current gain at each temperature. Furthermore, the phototransistor characteristics have been widely investigated.
Speckle size in acoustic holograms and Bragg-diffraction imaging systems
Authors: Schlussler Larry
Published: February 2003

In acoustic holography and Bragg-diffraction imaging an object is almost invariably surrounded by a background of low-intensity speckle. This background noise may be caused by either spatially random acoustical or optical scatterers. It is shown that the size of this speckle is the same whether they are due to either acoustic or optical scatterers.
Experimental study of the influence of surface-potential variations on the measurement of the electron temperature of a plasma by an electrostatic probe
Authors: Bujor M.
Published: February 2003

The quantitative influence of controlled spatial variations of the surface potential of an electrostatic probe on the measurement of the electron temperature has been studied experimentally using an electrostatic probe with an interdigital structure. By statistical treatment of a large number of measurements in an on-line computer, it was possible to detect changes in the apparent electron temperature of as little as 2%. Such changes occurred when potentials of the order of the electron thermal energy were applied to the surface of the probe on spatial scales of the order of the Debye length in the plasma. For larger potential variations, the influence on the apparent temperature was very important, regardless of the spatial scale.
Particle distributions and early phases of ionization in proposed convergent neutral-beam experiments
Authors: Marx K. D. , Eggens C. J. , Post R. F.
Published: February 2003

The use of convergent neutral beams to create high-density plasmas is investigated. A detailed study is made of the evolution of the neutral distribution function and the neutral density for both spherical and cylindrical configurations. Ionization rates due to neutral-neutral and ion-neutral collisions are computed, and those due to electron-neutral collisions are estimated. It is concluded that densities of 1017 to 1018 cm−3 could be achieved in spherical systems and that densities of 1015 cm−3 are possible in cylindrical systems. The ionization rates are sufficiently low that the plasma will not be produced too soon, i.e., before the distribution converges to a final high density.
Molecular charge states and contact charge exchange in polymers
Authors: Fabish Thomas J. , Duke Charles B.
Published: February 2003

Observation of a new phenomenon, the reversible change in sign of charge transferred to a polymer upon sequential contacts with a series of metals, is reported. This observation is interpreted using a model which attributes the polymer charges to the occurrence of local intrinsic molecular-ion states. A phenomenological representation both of these charge states and of the metal/polymer contact charge exchange process is developed. The validity of this phenomenology is tested by comparing its predictions with a systematic study of the contact charging of poly(styrene), poly(methyl methacrylate), and copolymers thereof. Using the contact charge exchange spectra of poly(styrene) and poly(methyl methacrylate) to determine the input parameters, the phenomenological model successfully predicts the contact charge exchange spectra of the copolymers.