bluuebunny/crossref_metadata_2025 huggingface dataset:
Doppler-free spectroscopy of the ν2 band in 14NH3: Application to 16-μm generation
Authors: Bokor J. , Bischel W. K. , Rhodes C. K.
Published: February 2003

Several two-photon transitions leading to various (J,K) rotational sublevels of the ν2=2− state in 14NH3 have been observed using the high-resolution technique of Doppler-free two-photon spectroscopy. It is shown that these transitions can be both tuned into resonance with the optical Stark effect and saturated with intensities of order 1–10 MW/cm2, so that laser action on many wavelengths in the vicinity of 16 μm is obtainable. This method of excitation is generally applicable for the excitation of molecular systems in frequency-conversion processes.
Photoelastic waveguides and their effect on stripe-geometry GaAs/Ga1−xAlxAs lasers
Authors: Kirkby P. A. , Selway P. R. , Westbrook L. D.
Published: February 2003

This paper describes a new type of waveguide mechanism found in oxide-insulated stripe-geometry GaAs/Ga1−xAlxAs lasers. The photoelastic waveguide is formed by small variations of the refractive index of the active layer beneath the stripe contact of the laser. The refractive-index variations are caused by the effect of a strain field in the semiconductor surrounding the stripe window. The large photoelastic coefficients of III-V semiconductors cause significant changes in refractive index for relatively small strains. The strain field in the semiconductor is caused by the high compressive stress in the oxide film; it builds up to its highest value beneath the edges of the stripe window. The maximum calculated compressive strain in the active layer 2-μm beneath a stripe window 20 μm wide opened in an oxide film 2700 Å thick is 3×10−4. This strain reduces the dielectric constant of the active layer by approximately 10−2. The sign of the oxide stress, the stripe width, and the active layer depth determine whether a waveguide or antiwaveguide is formed. Experimental measurements have been carried out on two types of photoelastic waveguide at 1.15μm wavelength. The results confirm the theoretical calculations. These simply fabricated waveguides may be suitable for integrated optic applications. The effect of the photoelastic waveguide on operating stripe-geometry lasers has been determined by controlled experiments, which clearly indicate that it is the predominant builtin waveguide mechanism. The results also show that a reasonably strong builtin photoelastic waveguide is essential if well-behaved (’’kink’’-free) stripe lasers are to be made with stripe widths of about 20 μm.
Generalized expressions for the turn-on delay in semiconductor lasers
Authors: Dixon R. W. , Joyce W. B.
Published: February 2003

In semiconductor injection lasers the time delay between the application of a step function in current and the onset of lasing is widely used to extract the carrier lifetime. In this paper the common analysis of this effect is generalized to include the case in which radiative recombination significantly modifies the time delay. Expressions appropriate when a dc prebias is applied are included. Previously untreated ambiguities of interpretation of experimental data are discussed, and the possibility is suggested that time-delay measurements can be used to separately extract the radiative and nonradiative contributions to the lifetime.
Improved lasing performance of XeCl using Ar and Ne diluents
Authors: Sze Robert C.
Published: February 2003

The lasing-energy equivalent to KrF is extracted from XeCl in an electric avalanche discharge using argon or neon as the diluent gas. Parametric and electrical characteristics are interpreted in terms of changing electron-energy distributions as functions of changing E/N in the discharge volume.
Theory of paraxial self-focusing
Authors: Subbarao D. , Sodha M. S.
Published: February 2003

The phenomena of steady-state self-focusing and self-trapping have been analyzed in the paraxial approximation through a formalism utilizing a generalization of the angular-spectrum representation of electromagnetic beams. The method discards the a priori quasioptic approximation used in all previous theories; the effect of power loss from paraxial regions into beam aberrations during focusing and defocusing has also been incorporated. Results on self-trapping suggest greater dominance of nonlinear effects over beam-diffraction effects than predicted by earlier paraxial theories particularly in the region of nonlinear saturation. These results are in qualitative agreement with the moment theory of self-trapping. The present theory indicates certain periodic focusing solutions much different from the earlier paraxial theory.
High-efficiency coupling between phase-mismatched optical waveguides
Authors: Tsukada Noriaki , Tsujinishi Ryoko , Tomishima Kazunaru
Published: February 2003

Some properties of the power transfer between three coupled optical waveguides are discussed theoretically. It is shown that high-efficiency coupling is obtained when the effective propagation constants of the strong coupled two waveguides, which are proportional to the rms value of the coupling coefficient and the phase mismatching of the two-waveguide system, are equal to the propagation constant of the weakly coupled third waveguide.
Parametric study of a flash-initiated Cl2+HI chemical laser
Authors: Alfassi Zeev B. , Giniger Rina , Huler Eduardo , Reisler Hanna
Published: February 2003

The performance characteristics of a small flash-initiated HCl chemical laser pumped by the reaction between Cl and HI were determined. The variation of laser energy and peak power with total pressure, reagent concentration ratio, flash energy, and flash-pulse duration were obtained. The results are typical of a lasing system exhibiting strong relaxations.
Film-edge-induced stress in substrates
Authors: Hu S. M.
Published: February 2003

The problem of film-edge-induced stress in substrates has been analyzed self-consistently by allowing a distributed force in the film. The distributed force arises from the relaxation of the film strain, which is complementarily coupled to the substrate strain under the film force. The results are compared to those from a concentrated-edge-force approximation.
Thermal convection in a uniformly heated fluid between vertical parallel plates
Authors: Ellerbroek Brent , Kolin Alexander
Published: February 2003

In methods of continuous-flow-deviation electrophoresis, a basic element of the apparatus is a conductive fluid sheet sandwiched between two closely spaced parallel vertical plates which are maintained at a constant temperature while the fluid is uniformly heated by an electric current flowing parallel to the plates. A horizontal temperature gradient is established with a maximum temperature in the midplane of the fluid sheet. The velocity distribution of the resulting thermal convection is calculated in two steps: (1) in the general case for plates whose separation is negligible compared to their lateral dimensions, and (2) for the physical conditions encountered in fluid-sheet electrophoresis which justify the approximations that the effect of viscosity variations is negligible and that the density is a linear function of temperature. The resulting expression for the velocity distribution is a fourth-order polynomial in z (distance of a point from the midplane between the plates). The function has three extrema—a positive one at the midplane and two negative ones intermediate between the central plane and the walls.
Comment on ’’Transverse 1/f noise in InSb thin films and the signal-to-noise ratio of related Hall elements’’
Authors: Kleinpenning T. G. M. , Vandamme L. K. J.
Published: February 2003

The experiments of Kotera et al. on InSb thin-film Hall elements can be interpreted with existing noise calculations on four-probe configurations.
Domain-wall energies in thin magnetic films
Authors: Middleton Barry K.
Published: February 2003

Recent estimates of domain-wall energies, obtained from domain-tip-motion threshold fields in thin magnetic films, have been analyzed. It is revealed that either the theoretical understanding of domain-tip motion is inadequate or that measurements of anisotropy in thin films do not reflect the true effective anisotropy experienced by domain walls.
A note on the origin of pyroelectricity in polyvinylidene fluoride
Authors: Glass A. M. , Negran T. J.
Published: February 2003

A study of the low-temperature pyroelectric behavior of polyvinylidene fluoride (PVF2) supports the finding that pyroelectricity is largely due to thermal expansion of the piezoelectric polymer.
Study of the interface changes during operation of nCdTe-electrolyte solar cells
Authors: Vázquez-López C. , Sánchez-Sinencio F. , Helman J. S. , Peña J. L. , Lastras-Martínez A. , Raccah Paul M. , Triboulet Robert
Published: February 2003

Previous work has shown that while nCdTe-electrolyte solar cells are low cost and efficient, their photocurrent decays after a few hours of operation. We ave systematically analyzed the changes that take place at the interface. Auger spectroscopy measurements have shown out-diffusion of Cd2+ and the formation of a Te layer at the surface. Electroreflectance (ER) and electroluminescence measurements have further shown that this process results in the formation of a p-type region. The evolution of the ER spectra as the p-type region develops was followed and fully analyzed. This technique offers the advantage of easy control and optimization of the p-n junction growth parameter. The influence of the Te layer on the cell performance was determined from spectral response measurements.
Investigation of the production of singly charged ions in a rf quadrupole ion trap
Authors: Schuessler H. A. , Holder C. H.
Published: February 2003

A three-dimensional rf quadrupole ion trap has been constructed to study ion production by electron-impact ionization. Gases and atoms in an atomic beam can be investigated. The method can be extended to the study of photon ionization and of the production of multiply charged ions by a single collision and/or by step-by-step ionization. Total electron-impact ionization cross sections of helium have been measured and are σe(350 eV) =0.26(6) ×10−16 cm2 and σe(500 eV) =0.21(4) ×10−16 cm2. Equations are derived to operate the rf ion trap in the symmetric storage mode.
Comments on the spectroscopic analysis of a high-density plasma
Authors: Finken K. H.
Published: February 2003

The spectroscopic analysis of high-density plasmas poses difficulties because broad-line radiation and continua merge. The difficulties are discussed and published data are reanalyzed.
Ferromagnetic resonance study of the anisotropy field and nonmagnetic regions in implanted layers of bubble garnet films
Authors: Komenou K. , Zebrowski J. , Wilts C. H.
Published: February 2003

The effects of implantation dose and annealing on the anisotropy field of the implanted layer in bubble garnet films were investigated by ferromagnetic resonance. For large implantation dose, the existence of a nonmagnetic layer inside the implanted layer was verified and its boundaries were located. For smaller doses, the implanted region remains magnetic, but the negative shift in anisotropy field increases and the exchange constant decreases with increasing dose. For intermediate dose an internal nonmagnetic layer is created with a surface magnetic layer which resonates as an uncoupled region. The nonmagnetic layer extends to the surface at higher dose, and its thickness increases with increasing implantation dose.
Schottky-barrier ellipsometric electroreflectance in GaAs
Authors: Tachi S. , Moritani A. , Nakai J.
Published: February 2003

A theory and an experimental method of Schottky-barrier ellipsometric electroreflectance (or electric-field-modulated ellipsometry) at sufficiently low fields are presented. The real part and the imaginary part of field-induced changes in the dielectric function of GaAs in the vicinity of the E1 transition have been determined, independently and simultaneously, by the present theory without use of the Kramers-Kronig relation. Spectra obtained are analyzed by the low-field electroreflectance theory. Resulting energy-band parameters are as follows: the energy band gap Eg=2.928±0.003 eV and the broadening energy Γ=57±2 meV for the E1 transition (M1 type), and Eg=3.152±0.003 eV and Γ=78±3 meV for the E1+Δ1 transition (M1 type) at room temperature. Effects of linear electroreflectance upon the present Schottky-barrier ellipsometric electroreflectance spectra have been discussed.
Neon spectral line broadening as a diagnostic for compressed laser-fusion targets
Authors: Auerbach J. M. , Bailey D. S. , Glaros S. S. , Koppel L. N. , Pan Y. L. , Richards L. M. , Slivinsky V. W. , Thomson J. J.
Published: February 2003

Experiments have been conducted on the JANUS laser system to measure fuel density in imploded laser-fusion targets filled with deuterium, tritium, and neon. An x-ray crystal spectrometer was used to record the line emission of the 1s-2p line of the Ne+9 ion. Simultaneous measurement of the linewidth and the neutron yield indicated that symmetrically irradiated exploding pusher targets reached fuel densities of approximately 1 g/cm3.
Collection efficiency measurements on a-Si : H solar cells
Authors: Crandall Richard S. , Williams Richard , Tompkins B. E.
Published: February 2003

The collection efficiency ηc for photoexcited carriers is an important factor in solar cell efficiency. We have measured ηc for a-Si : H-Pt Schottky-barrier solar cells and shown how it changes with the thickness of the barrier-depletion layer. The results show that carrier generation requires an electric field in addition to light.
Comment on ’’Diamond: An efficient source of soft x rays for high-resolution x-ray lithography’’
Authors: Burgemeister E. A.
Published: February 2003

Measurements of the thermal conductivity of type-IIb diamond indicate that the heat transfer estimates in a paper by Nelson and Ruoff [J. Appl. Phys. 49, 5365 (1978)] are very conservative.
Reply to the ’’Comment on ’The significance of the distribution of hot spots on the interpretation of laser-produced plasma experiments’ ’’
Authors: Arad B. , Eliezer S.
Published: February 2003

We disagree with the conclusion reached by Goel, Gupta, and Bhatnagar that the effect of hot spots is not significant in analyzing scaling laws using transformed variables. We believe they have overlooked the main points of our analysis.
Defect studies in multilayer epitaxial GaAs by transient capacitance
Authors: Rodine E. T. , Farmer J. W. , Langer D. W.
Published: February 2003

Majority-carrier defects, induced by 1-MeV-electron irradiation in n-type epitaxial GaAs were studied by deep-level-trap spectroscopy. The samples were fabricated in the form of FET-like devices on the epitaxial active and buffer layers. Anomalies in the DLTS response such as the appearance of double peaks, a rapid growth of transient response, and lack of exponential behavior as the depletion width extends into the buffer are discussed in terms of the planar geometry, the series resistance, and the multilayer nature of the devices.
Evolution of two-phase dispersions by volume diffusion
Authors: Stark J. P.
Published: February 2003

A set of simultaneous equations is given for the evolution of a regular morphology of a second phase of spheres or rods as described by a distribution function. The precipitates may dissolve and reprecipitate or migrate as a consequence of an applied field or simultaneously coarsen as a consequence of interface effects. A linearization of the set is integrated for a rodlike morphology in an electric field.
Radiation effects in 1.06-μm InGaAs LED’s and Si photodiodes
Authors: Barnes C. E.
Published: February 2003

Because of the low-intrinsic and radiation-induced attenuation losses in glass fibers in the wavelength range 1.0–1.3 μm, emitters and detectors operating in this range are of practical importance for radiation-environment applications. We have studied the effects of both γ and neutron irradiation on the properties of InGaAs LED’s emitting at 1.06 μm and Si photodiode detectors optimized for this wavelength. While the preirradiation light output of the InGaAs LED’s is low relative to many GaAs LED’s, the InGaAs devices exhibit less sensitivity to radiation than the most radiation-hardened GaAs LED’s. No significant neutron-induced light-output degradation is observed below 1×1013 n/cm2, while 2×107 Co-60 rads are required before any γ-induced degradation is observed. In addition, a significant portion of the γ-induced light-output degradation can be recovered by applying forward-bias currents of the order of 50 mA in magnitude. Although γ irradiation up to 2×108 rads has essentially no effect on the photodiodes, neutron fluences above 2×1014 n/cm2 cause a reduction in responsivity. Analysis of the neutron-induced increases in the photodiode leakage current with the guard ring attached reveals a lifetime-damage constant product of 4×10−12 cm2/n. Laboratory isolators made up of these emitters and detectors have typical preirradiation current-transfer ratios of 5×10−4 which decrease by a factor of 10 after an irradiation of 1.5×1014 n/cm2.
Channeling and backscattering studies of the crystalline perfection and the thermal stability of epitaxial PtSi films on Si
Authors: Ishiwara Hiroshi , Hikosaka Kohki , Furukawa Seijiro
Published: February 2003

Ion-channeling and backscattering techniques, with some addition of reflection electron-diffraction analysis, have been employed to study the crystalline perfection and thermal stability of epitaxial PtSi films on (111)Si substrates. It was found that a preferred orientation of crystallites in the films strongly depends on film thicknesses above 300 Å. It was also found that the annealing temperature affects the spread in preferred orientation. The angular and energy-dependence measurements of backscattering yields have shown that the angular spreads in crystallite orientations in the PtSi films are larger than 0.5° for annealing times of 0.5–8 h, temperatures of 400–750 °C, and film thicknesses of 100–1600 Å. Epitaxial PtSi films on (111)Si are more stable than nonepitaxial ones on (100)Si up to temperatures 100 °C greater. It was concluded that the stability of the epitaxial films originates in the preferred orientation of crystallites in the films.
The surface barrier Rayleigh wave transducer
Authors: Bjerkan L. , Fossum J. O. , Fossheim K.
Published: February 2003

The electromechanical properties of the metal-dielectric contact have been studied theoretically and experimentally, and a transducer for Rayleigh wave generation and detection has been developed. This transducer introduces a new principle for excitation and detection of acoustic surface waves in dielectrics. Its properties have been studied with particular emphasis on nonpiezoelectric materials. Experiments are reported on KTaO3, SrTiO3, and BaTiO3. Experimental and theoretical investigations of photosensitivity were carried out. The acoustic intensity can be fully controlled by band-gap illumination. We propose that the mechanism studied here is responsible for the electroacoustic properties of many electrets.
Electrical and photoelectronic properties of Cr-doped semi-insulating GaAs
Authors: Kitahara K. , Nakai K. , Shibatomi A. , Ohkawa S.
Published: February 2003

The variation of I-V characteristics and photoconductivity spectra with Fermi-level energy is studied for as-grown or heat-treated Cr-doped semi-insulating GaAs. The I-V characteristics are classified into two types, and the relation among I-V characteristics, Fermi-level energy, and the ionization energy of deep levels is briefly explained with the space-charge-limited current model. On the basis of the dependence of the photoconductivity spectrum and the quenching effect on Fermi-level energy, it is deduced that the photocurrent peak at 0.88 eV is explained by two optical processes, i.e., photoabsorption of the Cr acceptor and the quenching effect causing by the photoinduced electron transition from the valence band to deep level, located at about 0.9 eV above the valence band.
Thermally stimulated polarization current technique for measuring the electrical conductivity of vitreous solids
Authors: Hong Chi-Ming , Day Delbert E.
Published: February 2003

The electrical conductivity of glasses determined by TSPC agrees well with that measured by conventional ac or dc techniques. The TSPC technique is a rapid and easy method of measuring the dc conductivity over the range 10−15–10−7 (Ω cm)−1 and is especially suited for conductivities <10−12 (Ω cm)−1. Polarization at the electrodes is easily detected and avoided.
Coupling losses in various outer normal layers surrounding the filament bundle of a superconducting composite
Authors: Turck B.
Published: February 2003

In multifilamentary composites submitted to a changing external field, coupling currents between the filaments give rise to the so-called coupling losses. These losses can be reduced by using a three-component matrix in the filament bundle itself. However, in the outer normal-conducting layer surrounding the bundle of filaments, significant extra losses from azimuthal coupling currents exist if the thickness of the layer is not small. One can expect a reduction of these losses by introducing a cupronickel shell. The losses are calculated in the three particular cases involving one, two, and three concentric layers of different resistivity.
Nonradiative recombination in GaAlAs proton-bombarded stripe-geometry lasers
Authors: Nelson R. J. , Rode D. L.
Published: February 2003

Nonradiative recombination processes in GaAlAs double-heterostructure lasers are examined using luminescence time-response measurements. Photoluminescence time-decay data for proton-bombarded (PB) isotype (p-type) heterostructures give an effective recombination velocity for the PB region of (7±1) ×105 cm/sec. Electroluminescence decay times of laser devices indicate that the interfacial recombination velocity of the anisotype interface (p-GaAs/N-GaAlAs) is 1500±500 cm/sec compared with 400±100 cm/sec for isotype (p-type) interfaces. The contribution of each important recombination process to the laser threshold current is calculated. For devices in which the PB region penetrates into the active layer, recombination in the PB region and interfacial recombination are the major nonradiative paths.
Illumination and energy deposition in a multibeam laser-fusion system
Authors: Scannapieco A. J. , Brysk H.
Published: February 2003

Calculations are presented for multibeam laser-fusion systems illuminating spherical targets. Both the illumination pattern and the energy deposition on the surface of the target are obtained, with the beam focus in general displaced from the center of the target. The absorptivity (which depends on angle of incidence and polarization) is discussed from experimental and theoretical evidence. Numerical results are displayed for two LASL laser systems. They illustrate the distinction between the symmetry of the illumination and of the energy deposition. They also demonstrate, as a function of the relative size of the target and of the (finite) focal spot, that the absorption can be enhanced by displacing the beam axis from the center of the target.
Mirror degradation in AlGaAs double-heterostructure lasers
Authors: Yonezu H. , Endo K. , Kamejima T. , Torikai T. , Yuasa T. , Furuse T.
Published: February 2003

Degradation mechanism and the related change in lasing characteristics for a mirror degradation were investigated in AlGaAs double-heterostructure lasers with uncoated mirror surfaces. In constant optical-power operation, mirror degradation was classified into three phases. The lasing-characteristics degradation in the initial stage of phase I was well explained in the excitation-enhanced oxidation model. Dark-line defects, originating from mirror surfaces, were found in the final stage of phase III, following phase II with a low degradation rate. The mechanism of the optical-power dependence was also investigated. Marked improvement in operating life was confirmed by the dielectric film coating and in a new-structure laser with little excitation in the vicinity of mirror surfaces.
Experimental aspects of the Born approximation theory for elastic-wave scattering from flaw
Authors: Lewis K. D. , Adler Laszlo
Published: February 2003

In order to study ultrasonic-wave scattering from hidden defects in metals an experimental system was developed to study the relationships between the various parameters of the scattered field and the scattering centers. Experimental results were analyzed based on Born approximation theory recently developed for elastic-wave scattering [J.E. Gubernatis, E. Domany, and J.A. Krumhansl, J. Appl. Phys. 48, 2804–2811 (1977); 48, 2812 (1977)]. For an incident longitudinal wave the scattered longintudinal and shear waves from various shapes and sizes of ellipsoidal cavities in titanium were analyzed. It appears that the Born approximation theory agrees reasonably well with experiment.
The infinite planar baffles problem in acoustic radiation and its experimental verification
Authors: Delannoy B. , Lasota H. , Bruneel C. , Torguet R. , Bridoux E.
Published: February 2003

In acoustics, the analysis of pressure distribution in a field of surface sources is most frequently performed using the assumption that the source constitutes a part of an infinite planar rigid baffle (Rayleigh’s approximation). However, in many practical cases of ultrasonic echography, assumption of a soft pressure-release baffle (the Rayleigh-Sommerfeld approximation) or of free-field conditions (the Kirchhoff approximation) seemed to be better matched to real conditions. A theoretical survey of the planar baffles problem is given in this paper, and its practical aspects in acoustic source radiation are discussed. Some experiments, showing the influence of different boundary conditions onto radiation patterns, verify the theoretical predictions.
Transient surface heating of metals by CO2 laser pulses with air-plasma ignition
Authors: McKay J. A. , Schriempf J. T.
Published: February 2003

The ignition of an air plasma by a laser pulse at the surface of a metal target may yield a large increase in the heat deposition in the target. The target surface temperature during the pulse is determined by the thermal flux from the plasma, rather than the laser-pulse parameters. The plasma prevents direct observation of the surface temperature. We show how the surface temperature can be calculated using plasma thermal-coupling models based on thermal conduction from a radially expanding plasma (due to Robin) and on thermal emission from a axially propagating plasma. The two unknown parameters of the models, the thermal-coupling coefficient and the propagation or expansion speed, can be evaluated with simple measurements of the total heat and spot-center thermal fluence depositions. The model calculations are applied to an experimental example using a 137-J 30-μs CO2 laser pulse. No discrepancy between the calculated peak surface temperatures and the observed absence of surface melting is found. The calculated values of plasma propagation and expansion speed are in fair agreement with the observed plasma development early in the pulse. The models therefore appear to be reliable for calculation of the surface thermal transient.
Closed-form solution for transient reflection from a lossy plasma half-space for TM polarization
Authors: Stanić Bo?idar V. , S̊korić Milo? M.
Published: February 2003

Closed-form solution for transient reflection from an isotropic cold lossy plasma half-space for TM-type polarization is obtained in the form of an infinite power series of a modified Bessel function of the first kind. The delta, unit step, and rectangular pulse excitations were considered. The obtained results are valid for an arbitrary value of the lossy parameter αν=ν/ωp≳0. Numerical results are presented to illustrate the effects of the incident angle and lossy parameter on the reflected waveform. Early time response at the incident angle ϑi=π/4 is related to the time-domain Brewster angle.
Diagnostics of dense argon plasmas by two-wavelength optical absorption
Authors: Phillips M. G. R. , Pugatschew A. A.
Published: February 2003

A diagnostic method using optical absorption at two different wavelengths to determine simultaneously the electron density and temperature in an argon plasma is described. One wavelength is chosen to lie in the continuum, while the other (488 nm) is resonant with a plasma transition. Examples of measurements made in a dense plasma produced by a reflected shock wave are discussed together with the main systematic errors.
Reflex triode with unidirectional ion flow
Authors: Bromborsky A. , Brandt H. E. , Kehs R. A.
Published: February 2003

Experimental results are reported which show that the ion beam generated by a simple reflex triode can be made almost totally unidirectional toward the virtual cathode. This ion flow is accomplished by constructing the triode so that a controlled surface flashover generates plasma on only one side of the dielectric anode foil.
Measurements of the molecular stopping cross sections of organic ring compounds
Authors: Brown R. B. , Powers D.
Published: February 2003

The molecular stopping cross sections of the organic ring compounds cyclopentane, cyclohexane, cyclooctane, cyclopentene, cyclohexene, 1,3-cyclohexadiene, benzene, toulene, phenylacetylene, cyclohexanone, and p-dioxane have been measured for helium ions with energies from 0.3 to 2.0 MeV. It is found that the ring structure of molecules with less than six CH2 groups in the ring as well as the nature of the bonds involved correlate with deviations from Bragg’s rule as great as 14.7%. Evidence of resonance in the ring structure which correlated with the stopping cross section of the compound benzene is also observed. A qualitative relationship between chemical bond strain and deviations from Bragg’s rule is given.
The functional form of energy-differential cross sections for carbon using transmission electron energy-loss spectroscopy
Authors: Maher D. M. , Joy D. C. , Egerton R. F. , Mochel P.
Published: February 2003

Measurements have been made of the functional form of the energy-differential cross sections for carbon, using transmission electron energy-loss spectroscopy. It is shown that both the characteristic K edge and the background, prior to the K edge, can be represented accurately by functions of the form AE−r, where E is the energy loss and A and r are constants. The values of the exponent in this expression for the K edge have been compared with calculated values derived from a hydrogenic model and good agreement has been obtained.
Electromagnetic interaction between a conducting cylinder and a solenoid in relative motion
Authors: Wait James R. , Hill David A.
Published: February 2003

An analysis is presented for the mutual impedance between two solenoids that are coaxial with a conducting cylinder in relative motion. The formulation is based on the first-order Lorentz transformation and the results obtained are sufficiently general to encompass any such situation that could arise in nondestructive-testing schemes. A numerical example, relevant to steel-wire ropes of 2-cm radius used in mine hoists, indicates that even with relative velocities as high as 10 m/s, the mutual impedance at 10 Hz differs little from that calculated for zero velocity. However, the nonreciprocal effects could be significant for higher velocities and/or for more highly conducting and larger ropes.
Kinetics of decomposition of amorphous hydrogenated silicon films
Authors: McMillan J. A. , Peterson E. M.
Published: February 2003

The decomposition kinetics of amorphous hydrogenated silicon films have been studied by thermomanometric analysis at constant heating rate. rf and dc-biased rf glow-discharge films, as well as films deposited by reactive sputtering, have been analyzed and the results used to determine the thermodynamic parameters characterizing the activation barriers for decomposition of the =SiH2 and ≡SiH centers. Conclusions regarding the structure of these films are presented on the basis of kinetic evidence and parallel infrared absorption studies.
Single-thermal-source formation of ZnxCd1−xS thin films
Authors: Burton L. C. , Hench T. L. , Meakin J. D.
Published: February 2003

Thermal sublimation of atomically homogeneous ZnxCd1−xS powders from a single source results in films that are nonuniform in a direction normal to the substrate. This is attributed to initial preferential sublimation of Cd from the charge and is verified by energy dispersive x-ray analyses of film cross sections and of the charge residue. These results are related to the utility of this technique for forming ZnxCd1−xS films for photovoltaic applications.
Optical properties of boron hydride BHx
Authors: Pankove J. I. , Hough W. V.
Published: February 2003

Boron hydride emits a broad band of yellow light at 2.1 eV when excited optically. The emission is nearly temperature independent from 78 to 300 °K. An external power efficiency of 5×10−3 is obtained. The luminescence exhibits fatigue at room temperature. An absorption edge is found above 1.2 eV.
On pulsed-laser heating of thin targets in air
Authors: Robin James E.
Published: February 2003

A simple analytical model has been developed which describes the heating of a thin opaque target in air when subjected to irradiation from a high-power pulse laser. Effects due to the formation of a laser-supported absorption wave (LSAW) above the target surface are explicitly included in this model. The effective on-target flux distribution is assumed to be described by a radially expanding Gaussian profile in order to simulate the effects of enhanced coupling dominated by uv emission from the hot expanding LSAW plasma. Target heating inside as well as outside the incident beam-spot region is described. This model is an improvement over the previous approach [J.E. Robin, Appl. Phys. Lett. 30, 401 (1977)] which employed a radially expanding uniform flux distribution that was based on the assumption of a thermal-conduction-dominated enhanced-coupling mechanism.
Reply to ’’Comments on ’Efficiency of the solid-state engine made with Nitinol memory material’ ’’
Authors: Golestaneh A. A.
Published: February 2003

In reply to the comments of Mohamed and Banks, we outline the conditions under which a Ni-Ti shape-memory element operates in a solid-state engine. The expression for the energy output of this element, which was used in the original paper, is derived here, and further aspects of the efficiency formula for this engine are explained.
On rotational equilibrium in infrared laser cavities
Authors: Steverding B.
Published: February 2003

In scale-up problems for chemical lasers the question arises, ’’how much can the light intensity in the cavity be increased before rotational nonequilibrium effects confine further intensity increases?’’ A critical light intensity is determined above which deviations from thermal equilibrium become pronounced. This critical intensity is given for Doppler-broadened as well as pressure-broadened lines. Nonequilibrium effects are much more serious restrictions in the Doppler regime.
A reciprocating magnetic refrigerator for 2–4 K operation: Initial results
Authors: Barclay J. A. , Moze O. , Paterson L.
Published: February 2003

The basic theory and design of a reciprocating magnetic refrigerator to pump heat from 2.2 to 4.2 K is presented. The results of initial experiments are shown. These results include conduction losses, eddy current losses, frictional losses, and mixing losses. Two cooling cycles were attempted and a net cooling power of 52 mW was observed at 1/60 Hz. The key problems in this design are identified and discussed.
Permanent local modification of the magnetic bubble properties of epitaxial garnet films by laser annealing
Authors: Schultz L. , Giess E. A. , Hodgson R. T. , Sedgwick T. O.
Published: February 2003

Ga-substituted magnetic garnet films are laser annealed with annealing times of several milliseconds by scanning a cw argon laser beam across the film. Locally the bubble collapse field and the saturation magnetization increase, and the domain width decreases permanently unless conventional furnace annealing is used to restore the material to its initial state. We attribute the observed effects to a crystallographic site redistribution of the Ga and the Fe atoms in annealed regions which support mobile bubbles. The site distribution is changed from a state quenched in from the growth temperature to a higher-temperature state representative of the laser-annealing treatment. The effect does not involve melting.
Effects of interfacial polarization and loading factor in dielectric-loss measurements of composites
Authors: Mickish Daniel J.
Published: February 2003

The effect of the loading factor (the ratio of the conductive volume to the total volume) of a composite can lead to errors of 20% if not considered when interpreting dielectric-loss measurements. Free-carrier interfacial polarization is shown to be unimportant in the interpretation of the Maxwell-Wagner effect for certain classes of composites contrary to currently accepted thought, whereas it can be important in the interpretation of the Dember effect for the same materials. Non-Debye loss in cases where free-carrier interfacial polarization is unimportant is shown to be caused by an additional frequency-dependent component of the conductivity, e.g., that caused by dipole reorientation or conformational rearrangement.
Time-resolved site-selection spectroscopy investigation of Y3(Al1−xGax)5O12 : Nd3+ crystals
Authors: Zokai Masud , Powell Richard C. , Imbusch G. F. , DiBartolo B.
Published: February 2003

We have used selective laser excitation techniques to investigate the spectroscopic properties of Nd3+ ions in Y3(Al1−xGax)5O12 crystals and found the mixed crystal nature of the host produced both distinct structure and inhomogeneous broadening in the Nd3+ spectra. We employed time-resolved spectroscopy measurements to characterize energy transfer between Nd ions in nonequivalent crystal field sites and the results are consistent with the migration of energy among Nd ions in the dominant type of site with trapping occurring at Nd ions in defect sites. The migration and trapping processes require thermal activation and are consistent with a two-phonon assisted energy transfer mechanism. The efficiency of energy transfer is greater in mixed crystals than in unmixed garnet hosts, and it is shown that this is associated with the increase in the transition matrix elements in the mixed crystals.
Electrochromic effects in solid phosphotungstic acid and phosphomolybdic acid
Authors: Tell B. , Wudl F.
Published: February 2003

The electrochromic performance of all solid-state cells employing phosphotungstic acid and phosphomolybdic acid is reported. These cells employ SnO2 as the viewing electrode and graphite as the back electrode. Diffuse reflectivity changes of ∼50% are readily achieved in ∼10 msec. The cells, in the bleached state, can be made white to red, and become black in the colored state.
Comparison of the momentum densities of glassy carbon and graphite
Authors: Urban J. P. , Weick D.
Published: February 2003

Compton profiles of glassy carbon and polycrystalline graphite were measured with AgKα-fluorescence radiation and a LiF 400 analyzer at a scattering angle of 160°. After some corrections, the projections of the momentum densities for the valence electrons as well as the radial-momentum densities are obtained. The valence electron configurations show differences by comparing the individual profiles. A comparison with free-atom Hartree-Fock calculations demonstrates that the electronic state of glassy carbon is closer to the free atomic model than graphite.
Electroluminescent energy transfer from terbium to neodymium trifluoride in zinc sulphide
Authors: Stewart J. M. , Dresser M. J.
Published: February 2003

Terbium (+3) ions doped into zinc sulphide in the presence of neodymium trifluoride were excited by an electroluminescent process. The ZnS host lattice was in the form of a thin film made by vacuum deposition. Metallic electrodes attached to the ZnS film allowed a voltage to be applied to the device. Electroluminescence was observed through one of the electrodes after a short voltage pulse was applied. Measurements were made on the decay time of the 5D4-7F5 line of the Tb+3 ions. Changes in the decay time of this line were observed when the concentration of NdF3 was varied. Photon-counting techniques were used to measure the decay of the excited Tb+3 ions. A decay-rate theory based on resonance energy transfer between impurity ions in substitutional sites of the ZnS lattice was found to be in good agreement with the experimental data.
Optically induced anisotropy in photochromic glasses
Authors: Borrelli Nicholas F. , Chodak Jan B. , Hares George B.
Published: February 2003

Optical anisotropy and color adaptation are induced in certain silver-halide photochromic glasses by optical bleaching with polarized visible light. These induced optical effects have been found to be reversible and present after thermal fading. An explanation of the induced effects is given in terms of preferential optical bleaching of anisotropically shaped silver specks on the halide microcrystal. A simple model is presented which predicts the correct order of magnitude of the induced dichroic effect.
Photolysis of Se2 by uv lasers: Application to kinetics of group-VI laser systems
Authors: Gower M. C. , Kearsley A. J. , Webb C. E.
Published: February 2003

Experimental studies of the photolysis of selenium vapor were performed using a variety of high-power pulsed uv lasers. The results have direct relevance for the kinetic modeling of high-energy-storage laser systems based on metastable group-VI atomic species. Quenching rates and radiative lifetimes of the Se2 B3Σ−u states have been measured, as well as those for an as yet unidentified state Se*2 produced in the reaction Se(1S0)+OCSe→Se*2+CO. It was discovered that a mixture of Se2 and CO, when photolyzed with ArF laser radiation at 1933 Å, produced significant yields of Se(1S0).
Dependence of the decrease in contrast ratios on the intensity of the laser pulse for two-photon fluorescence
Authors: Venable D. D. , Taboada J.
Published: February 2003

The contrast ratio for two-photon fluorescence (TPF) is found to depend on the laser pulse intensity. The peak-to-background ratio is observed to decrease from the ideal value of 3 to about 2.1 as the intensity of the single Nd-glass laser ultrashort pulse is increased from 15 to 60 GW/cm2. Parametric analysis of the autocorrelation function for the pulse amplitude shows that this effect can be explained by two-photon attenuation of the laser pulse by the TPF medium.
Doping profiles in Zn-implanted GaAs after laser annealing
Authors: Inada T. , Kato S. , Maeda Y. , Tokunaga K.
Published: February 2003

Differential Hall-effect and sheet-resistivity measurements have been carried out to investigate electrical properties of p-type layers formed by implanting 100-keV Zn ions into Cr-doped semi-insulating GaAs at room temperature and by subsequent laser irradiation (Nd : YAG, λ=1.06 μm) using chemical-vapor-deposited (CVD) Si3N4 films as the encapsulant. It has been shown that very shallow (approximately 0.3 μm) and highly doped (pmax=4×1019 cm−3) p-type GaAs layers can be fabricated by Zn implantation with an ion dose of 1.0×1015 cm−2 followed by laser irradiation at a beam energy density of 1.5 J cm−2.
Transmission electron microscope observations of damage in InP induced during handling
Authors: Comer J. J.
Published: February 2003

Damage observed in InP specimens following thinning and mounting in a specimen holder for transmission electron microscopy consisted of two kinds. In one case microcracks were observed in {110} cleavage planes. These contained edge dislocations with Burgers vectors of the type b= (a/2) 〈110〉. A second kind consisted of dislocation clusters which gave rise to slip and stacking-fault formation during examination in the microscope. The results suggest that extreme care is essential in handling this material during device processing.
Fractional uptake technique for determining diffusion coefficients
Authors: Glasser M. L.
Published: February 2003

A procedure is given for determining the diffusion constant D when the rate of uptake (or loss) of the diffusing material can be measured at any one time.
Dislocation slip-band mobility in ordered Cu3Au
Authors: Liang Shwu-Jian , Pope D. P.
Published: February 2003

Dislocation slip-band velocities were measured at 77- and 300-K in well-ordered Cu3Au single crystals. The results of the 77 and 300 K experiments were very similar: No slip-band motion is produced at stresses below a critical stress approximately equal to the macroscopic-yield stress, and bands that were produced during one-load pulse were never observed to move during subsequent load applications. The slip-band velocity increases very rapidly in a small stress range above the critical stress.
Activation volume for self-diffusion and for the diffusion of impurities in lead
Authors: Falter C. , Zierau W. , Varotsos P.
Published: February 2003

A recently derived representation of the Gibbs free energy of a defect process in terms of the thermoelastic properties of the host crystal is shown to be applicable to the calculation of the activation volume for the diffusion of impurities in solids. The experimental data for the diffusion of several metals (Ag, Au, Cu, Hg, Zn, Sn, Tl, Ni, Pd) in lead and the self-diffusion are discussed showing a fair agreement with the theoretically determined activation volumina.
The formation of vanadium silicides at thin-film interfaces
Authors: Schutz R. J. , Testardi L. R.
Published: February 2003

Previous results have shown, in agreement with the silicide-growth theory of Walser and Bené, that VSi2 is the first silicide phase to nucleate and grow at single-crystal-Si–V interfaces. We have found that with sputtered thin-film-V–crystalline-Si or amorphous-Si diffusion couples we can reproducibly cause either VSi2 or V3Si, respectively, to nucleate and grow. V3Si and VSi2 are never observed together, suggesting that bistable growth can be triggered by the initial interface. The V3Si growth was found to have a t1/2 dependence and V was found to be the dominant diffusing species. This implies that unlike the case of VSi2, in V3Si the diffusion constant of V is much larger than Si and growth occurs at the Si-V3 Si interface. Deposition parameters and initial sample properties such as structure and impurity content which may control the nature of the reaction phase are discussed. We also find oxygen to be rejected by a growing A-15 phase. Samples were studied by Rutherford backscattering, Seeman-Bohlin x-ray diffraction, and electrical-resistivity–vs–temperature measurements.
Electrical properties of Ge-doped p-type AlxGa1−xAs
Authors: Zukotynski S. , Sumski S. , Panish M. B. , Casey H. C.
Published: February 2003

The Hall effect and conductivity of Ge-doped p-type AlxGa1−xAs has been studied in the temperature range from 77 to 500 K. The experimental results have been analyzed to yield the acceptor and donor concentration and the Ge activation energy. The samples have been found to be heavily compensated with an average compensation ratio of about 0.4. The activation energy was found to increase strongly with Al content for x<0.6 and to decrease with Ge concentration.
Gallium arsenide films and solar cells on graphite substrates
Authors: Chu Shirley S. , Chu T. L. , Lan M. S.
Published: February 2003

Gallium arsenide films have been deposited on graphite substrates by the reaction of gallium, hydrogen chloride, and arsine in a hydrogen flow. The structural and electrical properties of gallium arsenide films have been investigated. The interface between undoped gallium arsenide and graphite exhibits rectifying characteristics; however, a heavily doped interlayer reduces the interface resistance to a tolerable level. MOS-type solar cells prepared from n-GaAs/n+-GaAs/graphite structures have AM1 efficiencies of higher than 6%.