bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaky surface polariton
Authors: Seshadri S. R.
Published: July 2002

The characteristics of a leaky surface polariton existing on the surface of a free electron metal having the profile of an ordinary diffraction grating are investigated including the effects of the finite length of the grating and the slow spatial variation of the amplitude of the surface polariton. The radiative decay characteristics of the surface polariton and the characteristics of the antiresonance in the angular response of the reflectivity of light incident on the grating are discussed, and the effect of a small dissipation in the metal on these characteristics is also included.
Theory of high-field transport of holes in Al0.45Ga0.55As
Authors: Brennan Kevin , Hess Karl
Published: July 2002

Calculations of the high-field properties of holes in Al0.45Ga0.55As are presented based on the ensemble Monte Carlo technique. It is shown that the hole drift velocity in AlGaAs is significantly below that in GaAs until saturation occurs. Despite the much larger energy band gap in Al0.45Ga0.55As, the hole ionization rate approaches that of GaAs at very high electric fields, >600 kV/cm. No significant hole impact ionization is observed below 300 kV/cm in Al0.45Ga0.55As. This is of importance to superlattice avalanche photodiodes made from the GaAs/AlGaAs material system.
Effect of growth atmosphere on rare-earth iron garnets grown from PbO-based fluxes
Authors: Fratello V. J. , Slusky S. E. G. , Rana V. V. S. , Brandle C. D. , Ballintine J. E.
Published: July 2002

The growth atmosphere over a PbO fluxed melt can significantly affect the platinum and lead concentrations and the magnetic properties of rare-earth iron garnet films grown from that melt. We have investigated this effect using the simple composition (Gd2.5Eu0.5Fe5O12. The films were grown in N2, air, and O2 atmosphere on (111) MgCaZr substituted GGG substrates (substrate lattice parameter a0=12.497 Å) by conventional liquid-phase-epitaxy techniques from PbO and PbO/B2O3 fluxes. Lead is incorporated self-compensatingly from the flux as Pb2+ and Pb4+. The oxygen partial pressure of the growth atmosphere affects the platinum incorporation in the film through the equilibrium between neutral elemental Pt0 and ionic Pt4+ species in the melt. Incorporation of elemental species such as Pt0 in the film is unfavorable, but oxidized Pt4+ ions are accommodated in the lattice in concentrations that depend on their melt concentrations and distribution coefficients. Lead and platinum concentrations were determined by x-ray fluorescence. The incorporation of lead and platinum increased the lattice parameter and the index of refraction of these garnets. The diamagnetic octahedral substitution of Pt had a predictable effect on the magnetic properties, increasing the saturation magnetization and decreasing the Curie temperature, cubic anisotropy, and gyromagnetic ratio. Least-squares analysis and annealing studies showed that lead makes a positive contribution to the growth-induced anisotropy that seems to depend only on the concentration of the Pb2+ species. Platinum incorporation causes a negative contribution to the growth-induced anisotropy that can be annealed out at temperatures of 850–950 °C.
Thermoelectric amplification of phonons in semiconductors
Authors: Nunes O. A. C.
Published: July 2002

The damping coefficient of acoustical phonons interacting with charge carriers in semiconductors subjected to an external temperature gradient is calculated. It is shown that acoustic waves for which ql≫1 (q is the acoustic wave number and l is the electron-mean-free path) may be amplified by the carriers when the temperature gradient exceeds a certain threshold.
Observation of subdivided 180° Bloch wall configurations on iron whiskers
Authors: Hartmann U. , Mende H. H.
Published: July 2002

Subdivided 180° Bloch walls have been observed on iron whiskers using an improved colloid technique. Under the influence of a magnetic field applied vertical to the surface of a specimen the magnetization reversal of the complex wall is governed by Néel line motion. The field-induced conversion exhibits a characteristic ‘‘remanence’’ and ‘‘coercivity’’ of the wall. During a longitudinal magnetization cycle of a whisker the actual wall configuration has a substantial influence on the magnetization curve. The coercivity of the specimen is closely correlated to the initial mobility of the Néel lines. Discontinuities in the Néel line motion are responsible for small Barkhausen jumps, especially in the low-field region. The irregular segmentation of the complex wall in the remanent state appears to be an essential source of the remanent whisker magnetization.
Influence of magnetic history on flux jump fields
Authors: Sosnowski J.
Published: July 2002

A formalism describing the fields at which flux jumps occur in hard superconductors has been confirmed by the description of an experimentally observed shift of flux jump fields in the second hysteresis loop of a Nb3Al superconducting sample. By fitting the theoretical model to experimental data, values of the proportionality parameter between the stability limit and the flux jump field, the first stability limit, and the first penetration field have been estimated.
Aberrations in diverging electron beams caused by an inhomogeneous current density
Authors: van den Broek M. H. L. M.
Published: July 2002

For a diverging electron beam with parabolic space-charge density distribution, first-order perturbation theory is used to derive an analytic expression, yielding the aberrations as a function of the covered distance. Application of the derived expression shows that the performance of electrostatic projection TV guns may be severely degraded by the increase of the aberrations.
Splitting of domain of angles for incident wave vectors in elastic anisotropic media
Authors: Rokhlin S. I. , Bolland Ken , Adler Laszlo
Published: July 2002

An anomalous phenomenon in the reflection and refraction of elastic waves on an interface between anisotropic crystals is analyzed. Due to the deviation of the ray (energy flow) direction from the wave normal for elastic waves in crystals, the domain of permissible incident angles splits into disjoint pieces for certain crystal cuts. This may lead to the existence of grazing angles at three different wave-vector angles. The grazing angle is defined as the angle at which the ray vector of the incident wave is parallel to the interface. To clarify this interesting phenomenon, numerical calculations were made for the (001) plane of a Ni crystal, based on a calculational procedure developed previously for study of the reflection and refraction of elastic waves in crystals. For each of the two split domains of incident angle there appear two branches of the reflection coefficient for the slow quasi-transverse wave corresponding to the same slowness surface. The value of the energy conversion of the incident wave into each of these reflected waves depends on the closeness of the direction of the displacement vector in these waves to the incident displacement direction.
Method-of-moments solution of a parallel-plate waveguide aperture system
Authors: Jarem John M.
Published: July 2002

The aperture fields which are excited in a ground-plane slot which is fed by a parallel-plate waveguide containing a TEM wave is solved by a K-space moment-method technique. The moment-method equations are derived using a boundary-value approach. A numerical example giving the matrix solution, aperture admittance, and electric field for the above waveguide-fed slot problem is presented. The far-field radiation pattern of the method-of-moments aperture field is calculated.
Transmission characteristics of the birefringent filter system, where a retarder-rotator combination is used at each stage
Authors: Chakraborty Biswajit
Published: July 2002

Polarizers and retarders have long been known as the basic building blocks of Lyot and Solc filters. Recently the use of an optically active medium along with polarizers and retarders has been found to be useful for modifying the transmission characteristics of the birefringent filter system. In this paper, the effect of using an optically active medium as the interstage element of a Solc filter has been studied. The idea of a birefringent band suppression filter has been found and the tuning procedures of these fixed-type filters have also been discussed.
Computer simulation of thin-film nucleation and growth: The multilayer mode
Authors: Salik Joshua
Published: July 2002

The computer simulation of thin-film nucleation and growth, which was previously performed for the case of single monolayer, has been extended to the case of multilayer growth. The simulation results show that the kinetics of multilayer growth is nearly identical to that of monolayer growth. The cluster density resulting from the multilayer mode is similar to that resulting from the monolayer mode at low coverage. At high coverage, multilayer growth results in substantially higher cluster density than that resulting from monolayer growth.
Transient electronic response in hydrogenated amorphous silicon
Authors: Silver Marvin , Snow Eric , Adler David
Published: July 2002

We analyze the problem of the transient response after a photogeneration pulse in a time-of-flight geometry in a material in which the density of localized states is characterized by a weakly decaying exponential just below the mobility edge and a more rapidly decaying exponential at lower energies. We find that it is then possible to observe essentially nondispersive transport over wide ranges of time and temperature, due to the finite trapping times to some of the deeper states. With this approach, we are able to understand some recent nondispersive time-of-flight data on films of hydrogenated amorphous silicon, provided that the band mobility of electrons is large (≊100 cm2/V s), ballistic transport predominates, and the trapping cross section is small (∼1016 cm2).
Nanosecond evolution of a low-inductance air spark
Authors: Najafzadeh Reza , Bergmann Ernest E.
Published: July 2002

The expansion of the shock front of a laser-triggered, atmospheric air spark was studied by shadow photography with a transversely excited atmospheric UV nitrogen laser. It was found that the shock front of the short spark (0.5 mm) was cylindrical. Within a few nanoseconds of spark formation the diameter of the spark channel grows linearly with time and the index of refraction is less than in the surrounding gas. The shock velocity was measured to be 7 km/s (Mach 20).
Optimal crystal cuts and propagation directions for excitation of acoustic waves in LiNbO3
Authors: Chen W. H. , Fu F. C.
Published: July 2002

Acoustic power flow in a LiNbO3 single crystal was calculated to find the optimal crystal cutting orientation and the wave propagation direction for the efficient excitation of acoustic waves in the crystal. By solving the stiffened Christoffel equations and calculating the acoustic Poynting vectors with piezoelectric effect included, maximum longitudinal acoustic power flow in a 30° Z-rotated, Y-cut LiNbO3 crystal was found.
Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs
Authors: Walukiewicz W. , Wang Le , Pawlowicz L. M. , Lagowski J. , Gatos H. C.
Published: July 2002

We show that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 cm2/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.
Mössbauer study of insoluble Fe-Ag coevaporated thin film
Authors: Kita Eiji , Kainosho Keiji , Tasaki Akira , Saegusa Norio , Takao Masatoshi
Published: July 2002

Structural change and accompanied magnetic properties corresponding to the annealing of insoluble Fe-Ag coevaporated thin films were studied with Mössbauer spectroscopy. The observed linewidth of the absorption peaks of the spectra was remarkably large and implies that the hyperfine field of the Fe atom was largely distributed for as-deposited Fe49Ag51 film. After the successive heat treatment, crystallization of the thin film gradually proceeded up to 150 °C annealing and finished at 200 °C annealing. The coercive force of the film was several oersteds for as-deposited film and increased rapidly with an increase of annealing temperature. It suggests the growth of the segregated particles.
Relations between isothermal and adiabatic third-order material constants of piezoelectric and pyroelectric crystals
Authors: Kittinger Erwin , Tichý Jan
Published: July 2002

Depending on measurement conditions different choices of independent variables are used in the phenomenological description of piezo- and pyroelectricity. Eight different sets of material constants arise in this way on the basis of the commonly employed field variables resulting in a vast number of different but related third-order constants. To cope with this fact a generalized notation is introduced for them. Starting from the proper rotationally invariant form of the electric Gibbs function and the electric enthalpy, the relations between isothermal and adiabatic third-order material constants are derived. A numerical estimate for the nonlinear piezoelectric constants of α-quartz is presented.
Trapping of deuterium in krypton-implanted nickel
Authors: Frank R. C. , McManus S. P. , Rehn L. E. , Baldo P.
Published: July 2002

Krypton ions with energy 600 keV were implanted in nickel to fluences of 2 × 1016 cm−2 under three different conditions. Deuterium was subsequently introduced into the implanted regions by electrolysis at room temperature. After the diffusible deuterium was permitted to escape, the 2H(3He,1H)4He nuclear reaction was used to analyze for the trapped deuterium during an isochronal annealing program. The region implanted at 100 °C with no higher temperature anneal had the largest number of traps; the region implanted at 100 °C and annealed for 100 min at 500 °C had considerably less; the region implanted at 500 °C had the least. Electron diffraction patterns confirmed the existence of solid crystalline krypton in all three regions. Transmission electron microscope studies revealed precipitates with an average diameter of 8 nm in the region implanted at 500 °C. The two regions implanted at 100 °C contained smaller precipitates. Trap binding enthalpies were obtained by math modeling. In addition to the traps with binding enthalpy of 0.55 eV reported earlier by other investigators for helium implanted in nickel, a smaller number of traps with binding enthalpies up to 0.83 eV were also found. The trapping of deuterium by various types of imperfections, including the solid krypton precipitates, is discussed.
Electromagnetic scattering by periodic arrays of particles
Authors: Waterman P. C. , Pedersen N. E.
Published: July 2002

Employing self-consistency, the multiple-scattering problem is formulated for periodic arrays of particles having constitutive parameters distinct from those of the embedding material. A T-matrix description of individual particle scattering is employed, so that particles need not be spherical. Explicit analytical and numerical results are obtained for the effective complex dielectric constant ε̄ and permeability μ̄ in the quasistatic and infinitesimal lattice limits for several lattice geometries, and shown to agree with existing static computations under appropriate conditions. Random arrays are also considered briefly, and the role of single-particle resonance effects is examined. Finally, longitudinal electric and magnetic waves are predicted to exist at certain discrete frequencies where ε̄ or μ̄ vanish.
Study of Au-n-type GaAs Schottky contacts on a single-crystal part of large-grained polycrystalline GaAs
Authors: Hattori K. , Ohtani T. , Fujii T.
Published: July 2002

Gold-n-type GaAs Schottky contacts have been fabricated on a single-crystal part of polycrystalline GaAs with grain size of about 1 cm. The current-voltage (I-V) characteristic has been measured over the temperature range 120–380 K. The barrier height is evaluated from the Richardson plot as 0.57 eV, and discussed by taking account of the effects of an interfacial layer between the metal and semiconductor. The capacitance-voltage (C-V) characteristic has been measured at 0.1, 1, and 100 kHz over the temperature range 120–500 K. A frequency dispersion is observed in the C-V characteristic. It is explained by the frequency dispersion in the dielectric constant of the interfacial layer and the capacitive response of trapping states in the interfacial layer and single-crystal parts of polycrystalline GaAs.
Propagation characteristics of millimeter waves in the H guide loaded with yttrium iron garnet films
Authors: Maheri H. , Tsutsumi M. , Kumagai N.
Published: July 2002

The propagation characteristics of millimeter waves in an H guide loaded with yttrium iron garnet films are investigated. A perturbation theory is used for evaluating the dispersion curve. Theoretical results are confirmed by experiments carried out in the millimeter wave frequency range 40–50 GHz using yttrium iron garnet films. Dispersion characteristics for a laminated structure of yttrium iron garnet films are also examined. The gyromagnetic resonance behavior with a higher quality factor is observed when the dielectric slab is loaded on both sides with yttrium iron garnet films.
The role of bulk pinning in the Clem valley in hysteresis losses in type II superconductors
Authors: LeBlanc M. A. R. , Fillion G. , Lorrain J. P.
Published: July 2002

Measurements of hysteresis losses W(h0, Hb) at several fixed amplitudes h0 versus a static bias magnetic field Hb collinear to h0 and directed along the length or the width of a VTi ribbon which exhibits significant magnetic anisotropy, are reported and are very well reproduced exploiting bulk pinning alone hence neglecting equilibrium diamagnetism and surface barriers. Families of curves of D≡W(h0, Hb)/W(h0,0) vs z≡Hb/h0 at various fixed h0 were calculated for planar and cylindrical geometry, neglecting surface steps, using the simple formulas μ0 jc=dB/dx=α/B, α/B0.5, α/B0.1, α[1−(B/Bc2)], and α/(B+Δ) for the bulk critical current density. For slab geometry and the first four functions listed, the curves of D vs z are independent of h0/H* when h0<H* (the first full penetration field) and z<zd with zd dependent on h0/H*. This decoupling of D from h0 occurs when xp, the maximum penetration of the flux disturbance during the cycle of the applied field, does not reach the midplane X. Closed form expressions for W(h0, Hb) developed for slab geometry using dB/dx=α/B confirm this by showing that under these circumstances h0 factors out of the formulas for D. Pursuing the condition xp=X, analytic expressions linking zd and h0/H* are obtained. Graphs of zmin, the locus of the valley minimum and of Dmin, the ratio of Wmin, the losses at the valley minimum to that at Hb=0 are presented. The edge of plateaus displayed by such graphs is determined by letting zmin=zd in the formulas for zd(h0/H*).
Behavior of phosphine in a focused CO2 laser beam
Authors: Blazejowski J. , Lampe F. W.
Published: July 2002

The energy absorption and decomposition of PH3 in a focused CO2 laser beam exhibit a threshold nature. The effect of laser frequency, pulse energy, pressure of PH3, and the presence of a foreign gas (neon) on the energy absorption and decomposition threshold were studied. The absorption of radiation increases sharply at threshold and is always accompanied by a visible luminescence. All the experimental facts can be explained in terms of an electron avalanche process, driven by inverse bremsstrahlung absorption of energy from the field of a focused IR laser beam. The simplified phenomenological theory of the dielectric breakdown of gases was applied to the explanation of the threshold phenomena. The decomposition of phosphine was studied as a function of laser frequency, pressure of PH3, and in the presence of foreign gases. The only products of the decomposition found were H2 in the gas phase and a solid deposit PHx. The partition of hydrogen between the gas and solid phases depends on the experimental conditions. A reaction scheme is presented which accounts satisfactorily for the experimental facts.
Diffusion of boron in Mo silicide films
Authors: Kato Juri , Fujisawa Akira , Asahina Michio , Shimura Hidetsugu , Yamamoto Yasuhiro
Published: July 2002

The diffusion of boron in MoSi2 films has been studied. The diffusion is determined by a combination of two factors: the low diffusivity in the bulk of grains and the much higher diffusivity in the grain boundaries. The diffusivity in the bulk of grains was 1×10−14 cm2/s and 8×10−13 cm2/s for furnace annealing at 950 °C and halogen lamp annealing at 1060 °C, respectively. The diffusivity in the grain boundaries was over two orders of magnitude higher than that in the bulk of grains. High-temperature annealing of MoSi2 films reduce the solubility and diffusivity of boron in the films because of grain growth.
A modified nucleation and growth model for ferroelectric switching in Form I poly(vinylidene fluoride)
Authors: Takase Y. , Odajima A. , Wang T. T.
Published: July 2002

The analytical description of transient switching characteristics in Form I poly(vinylidene fluoride) has previously been confined to the narrow time range where the switching current displays a modest peak under an applied dc field. We show here that this range can be broadened to include the entire switching process by considering the process to be composed of two successive events, the first involving only the nucleation of microdomains and the second entailing the random nucleation and two-dimensional growth. The model has been successfully applied to data obtained at temperatures between 20 and −80 °C from a sample that had been either unirradiated or irradiated with γ rays (10 Mrad). Furthermore, our analysis revealed that the irradiation, which enhances the retention characteristics of piezoelectric property at elevated temperatures, primarily affects the main switching process by suppressing the rate of nucleation.
Time-dependent fracture strength of oriented polymers
Authors: Mun M. S. , Hsiao C. C.
Published: July 2002

A statistical consideration based upon a theory of microscopic molecular kinetics is developed to describe the time-dependent fracture process for oriented polymers. The interrelation between the macroscopic fracture strength and the microscopic behaviors is formulated with the aid of a double Fourier series expansion. The microscopic behavior in the vicinity of a point is expressed in the form of a spherical function which can be expanded into a series of symmetric tensorial terms. Subsequently, the fracture strength of polymers is evaluated in terms of both time and molecular orientation. By taking account of the individual values of the directional fraction of integrity, the time to fracture and the most probable direction of fracture within any volume element in a medium are predicted.
Random sampling: Distortion and reconstruction of velocity spectra from fast Fourier-transform analysis of the analog signal of a laser Doppler processor
Authors: Boyer L. , Searby G.
Published: July 2002

We calculate the spectrum of a signal derived from a continuous signal by ‘‘sample and hold’’ random sampling. It is seen that an undistorted spectrum is obtained only if the mean sampling frequency is more than an order of magnitude greater than the highest frequency in the original signal. The cases of signal-independent and signal-dependent sampling probabilities are investigated. We show how to obtain a good estimate for the spectrum of the unsampled signal and determine the limitations of this form of processing.
Interferometric measurements of the complex amplitude of the defocus signal V(z) in the confocal scanning optical microscope
Authors: Hamilton D. K. , Sheppard C. J. R.
Published: July 2002

A confocal interference microscope incorporating an electro-optic phase modulator has been used to make simultaneous measurements of the inphase and quadrature components of the confocal signal as a reflecting surface is scanned axially, the so-called V(z) response. Comparison with previously published theoretical predictions is seen to be favorable.
Model of cw argon ion lasers excited by low-energy electron beams
Authors: Fetzer G. J. , Rocca J. J. , Collins G. J. , Jacobs R.
Published: July 2002

A model of cw argon ion lasers excited by low-energy (50–200 eV) direct current electron beams at current densities between 1 and 50 A/cm2 has been developed. The electron energy distribution in the electron-beam-created plasma is calculated by numerically solving the Boltzmann equation for electrons. Optical gains, powers, and laser efficiences were computed for the 4765-, 4880-, 4965-, and 4658-Å Ar ii transitions for a wide range of discharge conditions. Laser efficiencies comparable to those of a conventional Ar ii laser (∼3×10−4) are predicted for these laser transitions when electron beam excitation is used.
Electrical stress and inception voltage of discharges in gaseous cavities in an anisotropic dielectric material
Authors: Salama M. M. A. , Rizk M. S. , Hackam R.
Published: July 2002

The electric field stress and the inception voltage of discharges in a gaseous void present in an anisotropic dielectric material is developed from the solution of the Laplace equation. The relevant equations for the determination of the electric field and the inception voltage of discharges in voids are presented in a format that can be readily used. The electric field distribution within the void and the maximum field value are determined for two shapes of voids, rectangular and cylindrical cross sections, over wide ranges of anisotropy and sizes of voids. It has been found that the maximum electric field in the void increases with increasing width and decreases with increasing thickness of the void. The inception voltage of discharges is determined over a wide range of void dimensions. The minimum breakdown voltage of a slab of anisotropic dielectric material containing a void follows a U-shaped curve when plotted against the product of the length and width of the void.
Threshold voltage dependence on design parameters and layer uniformity in high electron mobility transistors
Authors: Svensson Stefan P. , Nilsson Boo J. L. , Willhite James R. , Swanson Alan W.
Published: July 2002

A threshold voltage sensitivity analysis of high electron mobility transistors (HEMTs) based on a self-consistent model for the electron distribution is presented. The calculated sensitivity values are related to experimentally obtained uniformity data on 2-in. wafers grown by molecular-beam epitaxy (MBE). The effect of doping concentration, compensation, and thickness of the doped and undoped (Al,Ga)As layers and the mole fraction are considered. Enhancement mode transistors are generally found to be less sensitive than transistors of depletion type. The analysis brings out that the most important design parameters to control are the thickness of the doped (Al,Ga)As layer and its doping concentration (compensation). Changes in the Al mole fraction are found to have a negligible influence. The effects of varying growth conditions are estimated and possible ways of improving the threshold uniformity are discussed.
Measurements of Al content in Ga1−xAlxAs using nuclear resonances
Authors: Wu S. C. , Cheng A. , Pao C. H.
Published: July 2002

The resonant nuclear reactions, 27Al( p,α) and 27Al( p,γ), were used to determine the Al distribution in GaAlAs samples. By varying the incident proton energy, the Al concentrations at different depths were measured. The results agree with concentrations measured with other methods. The present techniques serve as nondestructive, accurate methods of profiling Al in various materials.
Capture-to-emission ratios for multivalent traps
Authors: Landsberg P. T.
Published: July 2002

It is shown that a formula recently given for the ratio of emission to capture coefficient of a trap, en/cn=Nc  exp(−ΔG/kT), holds with only minor modifications also for traps which can capture several electrons. Auger effects and impact ionization can also readily be included.
Comparative evaluation of collisional relaxation mechanisms for gasdynamic lasers
Authors: Rolader Glenn , Desai Prateen
Published: July 2002

Three separate variations of a vibrational energy nonequilibrium flow of a supersonic expansion of a CO2-N2-H2O mixture through a gasdynamic laser nozzle are examined to demonstrate the relative importance of the error induced by neglecting various kinetic effects and anharmonicity. The significance of each important collisional relaxation mechanism is specifically demonstrated by comparing the error induced due to neglecting each effect, with the variation in the predicted inversion obtained by using three different sets of empirical relaxation time equations. Since the net effect of each relaxation mechanism is to drive the system towards equilibrium, thus decreasing the inversion, it is suggested that the application of the parallel mixture rule in a kinetic model to include different relaxation paths is incorrect. Two kinetic models are solved by first assuming the molecules to be harmonic oscillators and then using the Morse oscillator model to demonstrate the significance of anharmonicity. The influence of the reservoir temperature in establishing the significance of each kinetic effect on the inversion and small-signal gain is calculated.
Mode-transition characteristics and tunability of an AlGaAs laser
Authors: Hori Hirokazu , Endo Koji , Kono Eiji , Sakurai Takeki
Published: July 2002

The wavelength characteristics of a transverse-junction-stripe AlGaAs laser were precisely measured for a wide range of diode temperatures and injection currents. A very simple rule was found in the mode transition characteristics. Typical features of mode competition, such as mode-competition noise, mode hopping with and without hysteresis phenomenon, and a tristable state of the lasing wavelength, were successively observed for a single diode sample. The characteristics were analyzed theoretically by using a two-mode intensity equation of laser oscillation under the assumption of a homogeneously broadened gain spectrum. The results were in good agreement with the experiment.
Laser melting of solids—An exact solution for time intervals greater than the transit time
Authors: El-Adawi M. K. , Shalaby S. A.
Published: July 2002

The thickness of the molten layer and the rate of melting of a solid slab are obtained for time intervals greater than the transit time. Two cases are considered: one for targets with a thermally insulated rear surface and the other for targets with cooling at the rear surface. A simple suggested model for the melting process together with the integral form of the heat diffusion equation and an appropriate boundary condition at the interfacial boundary between the liquid and solid phases are used to derive the required results. Computations are carried out on a slab of aluminum of thickness l=10−3 m subjected to constant laser irradiance q0=1011 W/m2, at different values for the heat transfer coefficient at the rear surface.
Space-charge-limited current flow in a spherical double sheath
Authors: Wei Ronghua , Wilbur Paul J.
Published: July 2002

Solutions to the problem of counterflowing, space-charge-limited, negatively and positively charged particle currents between two spherical surfaces are presented. They show that the current magnitudes exhibit the usual 3/2 power dependence on driving potential difference and square root dependence on particle charge-to-mass ratio. The magnitude of either current is strongly dependent on the radius ratio of the two spherical surfaces. The relative magnitudes of the two counterflowing currents are related by the square root of the mass ratio of the two charged particle species and a radius ratio factor that lies in the range ∼0.1–1.0.
Hollow oval magnetron for large-area low-energy ions
Authors: I Lin , Wu Ming-Shing
Published: July 2002

A novel device, the ‘‘hollow oval magnetron,’’ was designed and characterized. The device has a hollow electrode with an oval cross section. It sustains a large-area uniform plasma with low-energy ions under low pressure and moderate rf power (Ni ∼1011 cm−3, Γi ∼0.5 mA/cm2, Ei ∼30 eV, and P∼5 mTorr). The energy distribution of ion current onto the hollow electrode has a broad spread ΔEi /Ēi ∼1 in the rf mode, and a narrow peak ΔEi/ Ēi ∼0.1 with a low-energy tail in the dc mode. The device is a good candidate for low-energy high-rate plasma-material processing.
Inner-shell x-ray line spectra of highly ionized titanium, chromium, iron, and nickel and their application to laboratory plasmas
Authors: Lemen J. R. , Phillips K. J. H. , Doschek G. A. , Cowan R. D.
Published: July 2002

The intensities of x-ray lines due to inner-shell 1s-2p transitions in O i-, N i-, and C i-like ions of Ti xv–xvii, Cr xvii-xix, Fe xix-xxi, and Ni xxi-xxiii seen in tokamak plasmas are calculated. The lines are assumed to be formed by dielectronic recombination and inner-shell excitation. The present calculations are an extension of previous work for iron alone. The dielectronic contribution for iron was found to be more important, and this is true for the ions of titanium, chromium, and nickel considered here. The dielectronic rates were calculated using a suite of computer programs developed by one of us. The inner-shell contribution was estimated by van Regemorter’s formula. The considered ion stages have two or more fine-structure levels in the ground configuration, which gives rise to a density dependence of both dielectronic and collision excitation mechanisms at densities between 1011 and 1016 cm−3, a range suitable for tokamak plasmas. A means for determining the density of high-temperature plasmas is presented for when no other density diagnostics are available. Finally, the present calculations were applied to the problem of radial ion diffusion in tokamaks. Spectra were calculated by integrating along various lines of sight to simulate what might be observed by an actual spectrometer viewing a tokamak plasma. The assumed temperature and density profiles and two diffusion models were taken from a recent calculation. A method for determining the diffusion coefficient from tokamak observations is discussed.
Equation of state for strong electrolytes
Authors: Zener Clarence
Published: July 2002

I develop an equation of state for strong electrolytes (nonassociated) by combining the Debye–Hückel electrostatic interaction with the van der Waals excluded volume for hard elastic spheres. This equation of state gives essentially perfect agreement with published data up to 5M negative ion concentration for all the systems I have studied: HCl, LiCl; MgCl2, CaCl2, SrCl2; AlCl3. I use two adjustable parameters: the Debye–Hückel closest distance of approach a0 between positive and negative ions, and the van der Waals’ excluded volume b0 at infinite dilution. These two parameters approximately satisfy an equation stating that all the water of hydration is absorbed by the small positive ion.
Image processing algorithm for automatic detection and position assignment of monodispersed polystyrene spheres from microscope images
Authors: Dyrdal Idar
Published: July 2002

Monodispersed polystyrene spheres have recently been introduced as a two-dimensional model system for studying phase transition phenomena. For quantitative studies coordinates must be assigned to each sphere in a microscope sample containing hundreds or thousands of spheres. This paper describes a digital image processing technique for automatically determining the sphere positions from an image of the microscope sample. Results are given for some sample images.
Analysis of the near-intrinsic and extrinsic photocapacitance due to the EL2 level in boron-implanted GaAs
Authors: Morante J. R. , Samitier J. , Pérez A. , Altelarrea H. , Gourrier S.
Published: July 2002

A detailed analysis of the photocapacitance signal at the near-band and extrinsic energetic ranges in Schottky barriers obtained on horizontal Bridgman GaAs wafers, which were implanted with boron at different doses and annealed at several temperatures, has been carried out by using the optical isothermal transient spectroscopy, OITS. The optical cross sections have been determined as well as the quenching efficiency of the EL2 level which has been found to be independent of the annealing temperature. Moreover, the quenching relaxation presents two significant features: (i) a strong increase of the quenching efficiency from 1.35 eV on and (ii) a diminution of the quenching transient amplitude in relation with that shown by the fundamental EL2 level. In order to explain this behavior, different cases are discussed assuming the presence of several energy levels, the existence of an optical recuperation, or the association of the EL2 trap with two levels located, respectively, at Ev+0.45 eV and Ec−0.75 eV. The theoretical simulation, taking into account these two last cases, is in agreement with the experimental photocapacitance data at low temperature, as well as at room temperature where the EL2 filling phototransient shows an anomalous behavior. Moreover, unlike the previous data reported for the EL2 electron optical cross section, the values found using our experimental technique are in agreement with the behavior deduced from the theoretical calculation. The utilization of the OITS method has also allowed the determination of another level, whose faster optical contribution is often added to that of the EL2 level when the DLOS or standard photocapacitance is used.
Determination of surface-spin orientations of rare-earth iron garnet films by depth-selective Mössbauer spectroscopy
Authors: Itoh J. , Saneyoshi K. , Toriyama T. , Hisatake K.
Published: July 2002

Spin orientations of a rare-earth iron garnet film grown by a liquid-phase-epitaxial method on a gadolinium gallium garnet substrate were determined as a function of depth by means of the depth-selective conversion electron Mössbauer spectroscopy. The spin-tilt angle from the surface normal was found to increase from the bulk value up to 30° at the top of the surface. This phenomenon can be explained by the widening of the domain wall width toward the surface.
Characteristics and boron doping effect of hydrogenated amorphous carbon films
Authors: Noda Kenji , Nakajima Atsushi , Itoh Tadatsugu
Published: July 2002

Hydrogenated amorphous carbon films (a-C:H) have been formed by the electron beam decomposition of 100% acetylene (C2H2). The optical and electrical properties of the films depend on the substrate temperature (Ts). Insulating, translucent, and hard films were obtained at Ts≤250 °C. Only sp3C–H and sp3C–H2 stretch were observed by infrared absorption spectroscopy. The a-C:H films deposited at 250 °C were doped by incorporation of B2H6 during growth, and the doping effects of B in the films formed on indium-tin-oxide/glass substrates were investigated. The photo- and dark conductivities strongly dependend on the B doping level.
Interphase characterization at the n–CuInSe2/I−–I2 acidic electrolyte contact
Authors: Lewerenz H. J. , Kötz E. R.
Published: July 2002

The chemical nature of a photoelectrochemically formed film at the n–CuInSe2/I−–I2–HI–Cu+ electrolyte interface is determined. Grazing incidence x-ray diffraction reveals a phase consisting of polycrystalline CuISe3 with elemental Se patches. Ultraviolet photoelectron spectroscopy (UPS) identifies the interphase as a p-type semiconductor. Evidence for the film character of p–CuISe3–Se0 is presented. Flat-band potential, net acceptor density in the film, and the respective band bending in the substrate/film structure are determined assuming a n-p junction between n–CuInSe2 and p–CuISe3–Se0. Electronic properties of the three-phase junction substrate/film/electrolyte are deduced and the validity of the derived energy-band diagram of the junction in contact is discussed.
Lowering of grain-boundary barrier heights by grain curvature
Authors: Schöll E.
Published: July 2002

A model is presented for the potential barrier height at grain boundaries in polycrystalline semiconductors, which takes into account a curved grain boundary under equilibrium and nonequilibrium conditions, assuming flat quasi-Fermi levels. An analytical method to calculate the reduction of the potential barrier due to the grain curvature, without using the depletion approximation, is developed and applied to compute the barrier lowering as a function of the bulk doping concentration, interface state density, and the grain radius in silicon. The barrier height can vary along a grain boundary, due to different local curvatures, being lowest at corners of grains.
Measurement of SF6 ions with a Gerdien ion counter
Authors: Novak J. P. , Ellena G. , Nguyen D. H.
Published: July 2002

Densities of the negative and positive ions of SF6 in a 110-liter Pyrex container were measured using a Gerdien ion counter. The current-voltage characteristics were obtained for gas flows ranging from 40 to 200 cm3 s−1. A quantitative model of the counter was developed to interpret the measured data. The model includes appropriate representation of the developing gas flow and the electric field distribution near the ends of the accelerating electrode. The best-fit value for the negative-ion mobility was μn =0.38 cm2 V−1 s−1, as derived from a comparison of the calculated and the measured characteristics. The mobility of the positive ions was found to equal that of the negative ions within the limits of dispersion of experimental data. The negative-ion density at a pressure of 760 Torr evaluated at the counter entry plane was 3000 cm−3; the value of the positive-ion density was practically identical.
Determination of the chain segment lengths involved in γ relaxation of low-density polyethylene by thermostimulated depolarization measurements
Authors: Audren P. , Ronarc’h D.
Published: July 2002

We determined the chain segment lengths involved in the γ process of low-density polyethylene by introducing linear alkanes of different chain lengths into the polymer. These alkanes possess at one end of the chain an electric dipole constituted by an ester group. Their influence on the γ relaxation of low-density polyethylene was observed by thermostimulated depolarization measurements. We found a correlation between the γ temperature peak position and the alkane chain length, while the activation parameters distributions determined by the thermal sampling technique were only slightly modified. This was explained by considering that the distribution in activation parameters is partly induced by a distribution in the chain segment length of the relaxing species. Adding a linear alkane to the polyethylene modifies the population of the mobile chain segments of a given length. We deduced that the γ1 subrelaxation is induced by the motion of chain segments having approximately between 10 and 20 carbon atoms. A compensation law was evidenced in the γ process of all samples studied. The slight modifications of the preexponential factor of relaxation time and the variation of compensation temperature with the alkane chain length are discussed considering a local order in the amorphous phase of low-density polyethylene.
Onset of instability in a pulsed, low-pressure, high-current hydrogen discharge
Authors: Penetrante B. M. , Kunhardt E. E.
Published: July 2002

It is shown how the transition from a positive to a negative voltage–current characteristic can be accomplished in a pulsed, low-pressure, high-current hydrogen discharge. This transition is observed to be related to the onset of instability in the discharge. The instability is characterized by the formation of non-steady-state, high-energy, high-mobility electrons similar to those occurring in arcs or sparks.
Photo Hall-effect characterization of closely compensated Ge:Be
Authors: Germer Thomas A. , Haegel Nancy M. , Haller Eugene E.
Published: July 2002

The temperature dependence of the free-carrier concentration in germanium doped with the double acceptor Be has been investigated using the photo Hall-effect technique and found to be strongly temperature dependent when the residual shallow impurities are closely compensated. Close compensation (NA≂ND) of shallow levels was achieved by controlling the concentration of a beryllium–hydrogen acceptor complex A(Be,H) which is present in crystals grown under a H2 atmosphere. This complex can be removed with high-temperature annealing. An increase of up to two orders of magnitude in free-carrier lifetime as a function of temperature is found to occur between 5 and 11 K in closely compensated material due to the population inversion of ionized centers created by optical pumping.
Changes of the principal directions of electrical resistivity caused by a magnetic field
Authors: Kyriakos D. S.
Published: July 2002

Magnetoresistance skewness effect (change of the principal directions of electrical resistivity) appears when a magnetic field of arbitrary direction is applied on the examined material. This effect is useful for the magnetoresistance coefficients determination. A complete investigation of the skewness effect requires additional experimental facilities, such as the rotation of the sample and the contact system, which in some cases are impossible or very difficult to obtain. In this work the importance of the (110) and (111) planes of cubic crystals for such measurements is shown. For this purpose the elements of the resistivity tensor in the systems of reference, used in these planes, are correlated with those in the basic system of the (001) plane.
Magnetic and magneto-optic properties of praseodymium- and bismuth-substituted yttrium iron garnet films
Authors: Hansen P. , Klages C.-P. , Witter K.
Published: July 2002

Garnet films of composition R3−x−yPrxBiyFe5O12 with R=Lu, Y, and 0≤x≤1.8, 0≤y≤1.7 have been grown from different melt compositions and under various growth conditions onto substituted gadolinium gallium garnet substrates with (100), (110), (111), and (211) orientation. The dependence on composition and temperature of the saturation magnetization Ms, the uniaxial anisotropy constant Ku, the Faraday rotation θF, and the Faraday ellipticity ψF, have been investigated. The change of Ms as compared to that of Y3Fe5O12 is essentially associated with the alignment of the Pr moment parallel to the net iron moment and the increase of the Curie temperature originating mainly from the bismuth. However, both contributions are negligible in the room-temperature range. The uniaxial anisotropy is strongly affected by both Pr and Bi. The anisotropy contributions ΔKu /x<0 and ΔKu/y>0 turn out to be approximately additive. Both Pr and Bi give rise to a pronounced enhancement of the magneto-optical effects. At λ=633 nm θF increases linearly with x and y yielding at T=295 K the contributions ΔθF/x =−3.8×105 deg m−1 and ΔθF/y=−20.6×105 deg m−1, respectively. The bismuth contribution compares well with that observed for various other Bi-substituted rare earth iron garnets.