bluuebunny/crossref_metadata_2025 huggingface dataset:
Some recent results in interfacial critical phenomena (invited)
Authors: Jasnow David
Published: February 2003

Some recent developments pertaining to the behavior of interfaces near criticality are reviewed along with implications on some general questions regarding interface stability and scaling. The phenomenological approach to the case of scalar order parameter is reviewed briefly and compared to renormalization group results. Phenomenological and renormalization group approaches to the case of a domain wall in a weakly anisotropic n=2 system are also discussed.
Surface-induced order and disorder: Critical phenomena at first-order phase transitions (invited)
Authors: Lipowsky R.
Published: February 2003

Recent theoretical work about the influence of a surface on first-order phase transitions is reviewed. Several types of surface-induced disorder (SID) and surface-induced order (SIO) transitions are discussed. These transitions exhibit interface delocalization phenomena, long-range correlations, and critical behavior of local surface quantities. As a consequence, a variety of universal surface exponents can be defined although there are no bulk exponents. These surface exponents are calculated within Landau theory which is valid for space dimension d>3, and within effective interface models for d=2 and d=3. An estimate of finite size effects on SID and SIO is also given. Finally, it is discussed which critical effects at SID and SIO should be most easily accessible to experiments and to computer simulations.
Magnetic properties of Mo/Ni superlattices (invited)
Authors: Schuller Ivan K. , Grimsditch M.
Published: February 2003

We have studied the magnetic properties of Mo/Ni nonlattice matched superlattices. The dc magnetization was measured in the temperature range 5–300 °K and in magnetic fields up to 10 kG. The saturation magnetization and the Curie temperature behavior are consistent with expectations based on thin film effects. However, there are indications of ferromagnetic coupling across the nonmagnetic metal. Light scattering measurements were performed for the first time to study the magnon spectrum in superlattices. The Brillouin magnon spectra obtained from Mo/Ni superlattices show characteristic features associated with the collective behavior of the superlattice and are in good agreement with earlier theoretical predictions.
Magnetic susceptibility measurement method for thin films and surfaces
Authors: Moodera J. S. , Meservey R. , Tedrow P. M.
Published: February 2003

A new method is described for the measurement of the susceptibility of thin films of magnetic materials. This method uses the inductance change of a superconducting meander line as sensed by a tunnel diode oscillator and is specially suitable for measurements during deposition of the films on a cryogenically cooled substrate. The sensitivity of initial tests agree with design calculations and can detect 1% or less of the signal from a monolayer of Fe.
State of the art in design and technology of MSW devices (invited)
Authors: Castera J.-P.
Published: February 2003

Electronic warfare and telecom systems demands for increased bandwidths and operating frequencies for analog signal processing could be satisfied in the near future by the emergence of a novel technology based on magnetostatic waves (MSW) propagating in single crystal magnetic films such as the epitaxial yttrium iron garnet (YIG). Offering bandwidths up to 2 GHz at operating frequencies ranging from 0.5 to 20 GHz, MSW is, at the present time, the only available technology for analog signal processing directly at microwave frequencies. This paper will present an overview of the various techniques involved in the MSW area and of the possible device applications. In a first section, the growth of epitaxial YIG film, the propagation characteristics, the transduction, terminations, and temperature stability are briefly reviewed. Next, periodic structures obtained by ion beam milling, metal deposit, or ion implantation are considered. The following section is devoted to dispersive and nondispersive delay lines. Finally, the last part describes several major MSW devices with a particular emphasis on tunable MSW oscillators, a very promising application of MSW technology.
A new microwave ring resonator using guided magnetostatic surface waves
Authors: Poston T. D. , Stancil D. D.
Published: February 2003

A new microwave resonator based on guided magnetostatic surface waves is described. The waves are guided around a closed circular path by nonuniform in-plane fields. The ring resonator exhibits multiple resonances separated by approximately 10 MHz. Loaded Q’s as high as 1100 with 12 dB insertion loss and 1900 with 26 dB insertion loss have been observed. This resonator eliminates the fabrication complexity and losses associated with array reflector-type resonators and is potentially more compact since uniform fields over large sample areas are not required.
Breathing vibrations of a Néel wall
Authors: Slonczewski J. C.
Published: February 2003

One may sometimes regard a 180° Néel wall in a cubic ferromagnet as composed of two 90° subwalls or solitons. A spectrum of field-dependent natural frequencies for symmetric breathing of the subwall pair is derived from the Landau–Lifshitz equations in the limit of large uniaxial growth anisotropy and small spontaneous magnetization. The possibility of their excitation in the absence or presence of a Bloch line is discussed. Application to a garnet film of known characteristics predicts externally excitable modes with resonant frequencies near 2 GHz.
Bi-Sc doped bubble garnets supporting 0.35-μm diameter bubbles
Authors: Hosoe Y. , Andoh K. , Ohta N. , Sugita Y.
Published: February 2003

Garnet films of (BiSmLu)3(FeSc)5O12 supporting very small diameter (≲0.4 μm) bubbles have been grown on (111) oriented Nd3Ga5O12 substrates by liquid phase epitaxy. The saturation induction 4πMs is increased up to 2100 G by doping Sc in the octahedral site and Bi in the dodecahedral site. At the composition of Bi0.5Sm1.6Lu0.9Fe4.9Sc0.1O12, 4πMs is 2040 G and the bubble diameter can be decreased to 0.35 μm. The anisotropy energy Ku is 2.73×105 erg/cm3 and the quality factor Q (=Ku/2πMs2) is 1.65. Both Sm–Lu pair and Bi contribute to Ku. Bubbles with 0.35-μm diam are considered to be the smallest possible in garnets since 4πMs can hardly exceed 2100 G.
Diffraction characteristics of laser-induced acoustic waves in liquids
Authors: Terzić Mira , Sigrist Markus W.
Published: February 2003

The effect of diffraction on the temporal shape of laser-excited plane acoustic waves propagating in liquids is studied both theoretically and experimentally. Two different boundary conditions corresponding to a constrained and a free surface of the liquid are considered. The main features are the development of a rarefaction zone behind the pure compression pulse in the first case and the appearance of a second compression zone following the original compression/rarefaction signal in the second case. Experiments have been performed in distilled water with a hybrid CO2 laser and piezoelectric detection of the acoustic transients. A good agreement between theory and experiment is found.
Power characteristics of single-mode semiconductor lasers
Authors: Wilcox Jaroslava Z. , Casperson Lee W.
Published: February 2003

The basic aspects of power calculations for high-gain semiconductor lasers are briefly reviewed, and a straightforward one-dimensional model is described. The relative importance of spontaneous emission, distributed losses, band-to-band absorption, and high single-pass gain are investigated in detail.
Techniques of flash radiometry
Authors: Leung W. P. , Tam A. C.
Published: February 2003

We analyze in detail flash radiometry techniques for the remote sensing of spectroscopic and physical properties of thin condensed matter samples. Such techniques rely on the transient infrared radiation from the sample heated by a short-duration pulsed radiation. Exact analytical solutions for the conventional transmission radiometry technique (in which the excitation source and the infrared detector are on opposite sides of the sample) as well as the new backscattering radiometry technique (in which the excitation source and the detector are on the same side of the sample) are presented with the effect of heat loss neglected. The analysis allows the determination of the thermal diffusivity or thickness, as well as the absorption coefficients at the excitation wavelength and at the detecting wavelength of the sample from the experimental radiometry profile. The effects of excitation pulse duration and finite rise time of the detection system are discussed. Experiments with pulsed radiometry measurements on thin-film samples are performed to verify some of these theoretical predictions. Radiation loss and lateral heat diffusion loss are shown to be negligible for thin-film samples.
Electron energy loss spectroscopy of ion irradiated Ni-Al alloys
Authors: Grunes L. A. , Barbour J. C. , Hung L. S. , Mayer J. W. , Ritsko J. J.
Published: February 2003

Ion beam modifications to thin-film, polycrystalline Ni-Al alloys have been investigated using high resolution [0.1 eV full width at half maximum (FWHM)] transmission electron energy loss spectroscopy (EELS). The ion-induced modification of Ni3Al, NiAl, Ni2Al3, and NiAl3, as measured by EELS, is compared to concurrent electron microscope diffraction analyses. The EELS core level spectra corroborate the NiAl3 to amorphous phase transition observed by diffraction, while the EELS valence spectra provide a signature for the Ni2Al3 to NiAl phase transformation. These results reflect the changes in the electronic states caused by changes in the crystal structure. In addition, perturbations to the electronic states are measured even when no change appears in the diffraction pattern (irradiated NiAl). Thus, high-resolution EELS is shown to be a sensitive analytical technique for studying ion irradiated materials.
Photoacoustic spectroscopy of thick powdered or porous samples at low frequency
Authors: Monchalin J.-P. , Bertrand L. , Rousset G. , Lepoutre F.
Published: February 2003

This paper sets forth a self-contained theoretical description of the photoacoustic effect in a thick powdered or porous sample at low modulation frequencies where the sample medium can be considered homogeneous from the point of view of heat diffusion. It is shown that the photoacoustic signal results from two contributions: the heat flux from the sample to the gas plus the expansion of the interstitial gas and that the pressure is essentially uniform throughout the sample. Scattering effects are introduced with a Kubelka–Munk modified model and an expression is first given for the conventional partially filled cell. We discuss of these results and their application to the explanation of several texture effects and to the analysis of experimental data. Using a sample composed of chrysotile asbestos powder, we present experimental data and perform an approximate analysis to retrieve the absorption spectrum. Several experimental results are also presented and thoroughly discussed for a cell completely filled with powder. The relationships between photoacoustic spectra and diffuse reflectance spectra are given for both cases.
Neutral beam line ion beam raster scanning with a dipole magnet
Authors: Dagenhart W. K. , Tucker T. C.
Published: February 2003

An ion beam raster scanning method utilizing a wide gap dipole magnet has been developed at the Oak Ridge National Laboratory that can reduce the time-averaged amplitude of the ion beam power density on the ion beam dump by factors of 3 to 6. Time-varying in-phase and out-of-phase modulation current components are used in the dipole magnet coils in order to generate a time-varying magnetic field shape and magnitude whose magnetostatic central surface position oscillates between the two magnet iron poles. This time-varying three-dimensional (3-D) magnetic field shape deflects the ion beam onto an ion dump and can be programmed to produce a raster scan pattern that depends on the coil current modulation pattern. The 3-D magnetic field produced by an iron yoke system has been computed for different coil current ratios using a finite-element integral method. Ion orbit equations do not need to include the small space-charge forces present in the beam used for these purposes. The time-averaged amplitude of beam dump power densities should be lowered by a factor of 6 by sharing the beam impact pattern over a larger area with a short raster scan period compared to the ion dump thermal time constant.
Efficient XeF(C→A) laser oscillation using electron-beam excitation
Authors: Nachshon Y. , Tittel F. K. , Wilson W. L. , Nighan W. L.
Published: February 2003

Significantly improved XeF(C→A) laser energy density and efficiency have been obtained using electron-beam excited Ar-Xe gas mixtures at pressures up to 10 atm which contain both NF3 and F2. Maximum blue-green laser pulse energy density in excess of 1.0 J/liter was obtained, corresponding to an intrinsic electrical-optical energy conversion efficiency estimated to be in the 0.5%–1.0% range. Comprehensive, time-resolved absolute measurements of XeF(C→A) fluorescence, laser energy, and gain were carried out for a wide variety of experimental conditions. Analysis of these data has resulted in identification of the dominant transient absorbing species in the laser medium. For the laser mixtures investigated in this work, the primary blue/green absorption processes have been identified as photoionization of the 4p, 3d, and higher lying states of Ar, and of the Xe 6p and 5d states, and photodissociation of Ar2(3∑+u) and Ar+3.
Theory of thermal behavior of laser operation in In0.53Ga0.47As
Authors: Takeshima Masumi
Published: February 2003

A theory is given of thermal behavior of laser operation in In0.53Ga0.47As through rigorous calculation of laser parameters concerning the intervalence-band absorption, the Auger recombination, the radiative recombination, and the gain. The theory is based on a realistic band model, where anisotropic nonparabolic bands are considered. We use the Green’s function formalism, into which a phonon scattering effect is incorporated in order to take into account the electronic level broadening from the first principle. Experimental results on the laser parameters are well explained by the present theory. It is found that strong temperature dependences of the threshold currents and the differential quantum efficiencies, which are observed especially above room temperature, can be explained neither by the intervalence-band absorption nor the Auger recombination. Some possible models are proposed as alternatives to the previous theory based on the intervalence-band absorption.
A new class of thermionic electron emitters: Cesium tungsten bronzes, CsxWO3
Authors: Zocchi F.
Published: February 2003

A polycrystalline sample of Cs0.305WO3 was heated in the temperature range 390–630 °C in a UHV chamber. The values for the work function and thermionic constant are, respectively, 2.12±0.01 eV and 115 A/cm2 K2. The use of cesium tungsten bronzes as thermionic cathodes is limited to temperatures up to 630 °C, since at higher temperatures these materials deteriorate because of considerable loss of cesium. Tungsten bronzes, however, are suitable materials for systematic studies of the dependence of the work function on composition and structure.
Electron spin resonance identification of isolated Fe3+ in CdTe
Authors: Brunthaler G. , Kaufmann U. , Schneider J.
Published: February 2003

A new electron spin resonance (ESR) spectrum has been observed and identified in CdTe. The analysis of data taken at 9.5 and 35 GHz shows that the defect involved has cubic symmetry and spin S=5/2, and most likely corresponds to isolated Fe3+. Photo ESR results indicate that isolated iron is a deep donor with an ionization energy of (1.0±0.1) eV. Since the Fe3+ ESR has been observed in several nominally undoped samples it is concluded that iron is a common residual impurity in high-purity CdTe.
Photoluminescence study of the damage distribution in proton-bombarded (Al,Ga)As-GaAs-(Al,Ga)As double heterostructure
Authors: Swaminathan V. , Schwartz B. , Singh S. , Zilko J. L.
Published: February 2003

The damage distribution in proton-bombarded (Al,Ga)As-GaAs-(Al,Ga)As double heterostructure was studied via changes in the photoluminescence intensity of the GaAs layer as a function of proton energy in the range 50–300 keV for a constant fluence of 3×1015 cm−2. It was found that the intensity decreased monotonically with proton energy greater than 175 keV and at an implant energy of 225 keV it degraded by a factor of 4 even though the projected range of the protons ended ∼0.7 μm above the layer. The luminescence changes at low implant energies are attributed to the damage created by those protons in the tail of the distribution even though their number has decreased by two to three orders of magnitude from the peak value. In light of our results the implications of using protons to form the current-confining stripe in (Al,Ga)As lasers are discussed.
Carrier lifetime in argon-implanted silicon
Authors: Willander M.
Published: February 2003

The effects of argon-ion implantation upon the carrier lifetime in lightly phosphorus-doped silicon (ρ=600 Ω cm) are deduced by an analysis of the shape of the photoconductivity transients induced in the material by irradiation with picosecond laser pulses. The results obtained for samples subjected to 250-keV ion doses in the range 1013 −1015 cm−2, show that the carrier lifetime is reduced within a region which is considerably greater than the volume affected directly by the ions. Furthermore, deep-level transient spectroscopy measurements at the depths 2 and 3 μm reveal the creation of at least two new recombination centers in the band gap at the energy levels Ec −0.46 eV and Ev +0.44 eV, respectively. These levels are attributed to dislocations. Finally, other measurements show that, next to the surface, n-doped material can be converted into p type by this kind of implantation.
On continuous distributions of dislocations in nonlocal elasticity
Authors: Eringen A. Cemal
Published: February 2003

A linear, nonlocal continuum theory of dislocations is developed. The field equations are given for the dislocation density and the stress field due to continuous distribution of dislocations. Green’s functions are obtained for two- and three-dimensional media and an integral formula is given for line distribution of dislocations generalizing Peach–Koehler formula of the classical (local) theory. Unlike the classical theory, no stress singularities occur so that self-stress and energies of dislocation loops can be calculated involving no divergences. Exact solutions given for the line and circular distributions of dislocations verify these expectations.
Kinetics of thermal donor generation in silicon
Authors: Mao B.-Y. , Lagowski J. , Gatos H. C.
Published: February 2003

The generation kinetics of thermal donors at 450 °C in Czochralski-grown silicon was found to be altered by high-temperature preannealing (e.g., 1100 °C for 30 min). Thus, when compared with as-grown Si, high-temperature preannealed material exhibits a smaller concentration of generated thermal donors and a faster thermal donor saturation. A unified mechanism of nucleation and oxygen diffusion-controlled growth (based on solid-state phase transformation theory) is proposed to account for generation kinetics of thermal donors at 450 °C, in as-grown and high-temperature preannealed Czochralski silicon crystals. This mechanism is consistent with the main features of the models which have been proposed to explain the formation of oxygen thermal donors in silicon.
Epitaxial growth of Al on Si(111) and Si(100) by ionized-cluster beam
Authors: Yamada I. , Inokawa H. , Takagi T.
Published: February 2003

Epitaxial Al films were deposited on clean Si(111) and Si(100) by ionized-cluster beam at room temperature. Crystalline orientation was studied by reflection electron diffraction during and after the deposition of the 360-nm-thick Al films. Ion channeling spectra, optical reflectance spectra, and scanning electron micrographs were taken to evaluate the properties of the deposited films and to elucidate the effects of acceleration of ionized clusters. It was found that the films did not give rise to hillock and alloy penetration at the interface after 450 °C thermal treatment.
Optical properties of iron doped AlxGa1−xAs alloys
Authors: Wang Zhan-Guo , Ledebo L-Å. , Grimmeiss H. G.
Published: February 2003

Photocapacitance measurements were used to study the photoionization cross-section spectra of holes in iron doped Alx Ga1−xAs. The spectra are well described by the crystal field theory giving a nearly constant crystal field splitting of about 0.36 eV for all compositions studied. As a result of an extended range of composition (0≤x≤0.76), it was possible to show that the binding energy of the dominant iron center increases linearly with composition and that the relative position of the center is not related to any of the conduction band minima. The variation of the energy for Γ1(5E)→Γ5(5T2) transition in Fe2+(3d6) is discussed for different host crystals.
The image-force effect at a metal-semiconductor contact with an interfacial insulator layer
Authors: Tugulea Andrei , Dascǎlu Dan
Published: February 2003

The theory of image-force lowering of the potential barrier at a metal-semiconductor contact has sometimes been incorrectly applied to the metal-insulator-semiconductor system. In this paper the image-force potential is derived for a finite-thickness insulator bounded by a metal at one side and another insulator (or semiconductor) at the other side. The exact solution corresponds to an infinite series of images of the electron with respect to both interfaces. If the interfacial insulator permittivity is lower than that of the semiconductor, then the image force in the vicinity of the insulator-semiconductor interface will pull the electron away from the metal.
Study of microscopic heat sources in semiconducting barium titanate ceramics
Authors: Mader Gerhard , Meixner Hans , Kleinschmidt Peter
Published: February 2003

If high electric fields are applied to semiconducting barium titanate ceramics, the rapid temperature rise caused by power dissipation makes it difficult to separate the field dependence of the resistance from its temperature dependence. For that reason the microscopic temperature rise during a voltage pulse was calculated by a theoretical model for the heat production and the heat flow inside a single grain. In addition, the local temperature behavior was measured experimentally by means of an infrared radiometric microscope. The fast temperature rise during a voltage pulse (350 V/mm; 400 μs) and the cooling off immediately after the end of the pulse prove that there are significant heat sources at the grain boundaries. In ceramics with relatively large grains (30–60 μm) temperature differences up to 50 K within a single grain were measured.
Destruction mechanism of ZnO varistors due to high currents
Authors: Eda Kazuo
Published: February 2003

The destruction process of ZnO varistors caused by high currents is described. When high currents were applied to ZnO varistors, two kinds of destruction modes were found: a cracking mode and a puncture mode. The puncture mode is caused by melting of the region where current concentrates. The puncture process was simulated by a computer, solving a set of heat transfer equations. The relationships among the destruction energy, uniformity of the sintered body and nonohmic I-V characteristics were obtained. The simulated results are consistent with the experimental results and show that the destruction energy depends strongly on the uniformity.
Ion channeling studies of regrowth kinetics of disordered surface layers on graphite
Authors: Venkatesan T. , Elman B. S. , Braunstein G. , Dresselhaus M. S. , Dresselhaus G.
Published: February 2003

The crystallization of disordered surface layers on highly oriented pyrolytic graphite (HOPG) has been studied by Rutherford backscattering spectrometry and channeling techniques. Disordered layers (∼1000–3000 Å thick) are produced on the surface of HOPG by the implantation of various ions. The disordered layers are regrown by thermal annealing of the samples in an inert environment. Isochronal anneals reveal two distinct regrowth processes: one, a rapid process of low activation energy (Ea∼0.15 eV) which is observed primarily in regions where the disorder is sufficient to prevent the channeling of the ions, but insufficient to totally destroy the graphitic structure. This low activation energy may indicate annealing of the damage by migration of interstitials where the interstitials are the knock-on carbon atoms produced by the primary ions. A regrowth process with higher activation energy (Ea∼1.2 eV) occurs primarily in regions where the disorder is close to the saturation disorder produced by ion implantation. Both regrowth processes are epitaxial in nature and the epitaxial nature of the process may explain the much lower activation energy for three-dimensional AB layer stacking as measured in ion-implanted graphite when compared with results on the bulk graphitization of pyrocarbons. The time dependence of the annealing process shows a depth dependence and thus the regrowth cannot be uniquely interface or diffusion limited. In the case of the damaged layer produced by As ion implantation, the ability of the lattice to retain As atoms after high-temperature anneals increases with the extent of damage in the lattice. With the advent of three-dimensional ordering, most of the As is squeezed out of the lattice.
Flux-flow-type Josephson oscillator for millimeter and submillimeter wave region. II. Modeling
Authors: Nagatsuma T. , Enpuku K. , Yoshida K. , Irie F.
Published: February 2003

A theoretical study is made of a travelling-wave-type oscillator, which utilizes a flux flow in a long Josephson junction for use as a local oscillator in the integrated superconducting receiver system. An internal electromagnetic field of the oscillator junction in the flux-flow state is investigated both numerically and analytically. It is shown that the voltage amplitude of the internal oscillation increases gradually in the direction of the flux flow and reaches a maximum value at the junction end. An equivalent circuit of the oscillator is also obtained, which gives dependences of the emitted radiation on frequency, magnetic field, and load. It is shown that the output power attains the value of the order of 10−6 W in the frequency range between 100 and 500 GHz, and that the output power and the radiation frequency can be controlled by both the bias voltage and the applied magnetic field. These theoretical results explain quantitatively the experimental ones with a Pb-alloy long junction of length 24 λJ.
Phenomenological aspect of particle trapping by dielectrophoresis
Authors: Benguigui L. , Lin I. J.
Published: February 2003

We studied experimentally the trapping of particles by action of the dielectrophoretic force, in a matrix of glass beads in an inhomogeneous electric field. A phenomenological analysis of the trapping process is presented.
Computer analysis of ion elastic backscattering: An iterative fitting method
Authors: Rauhala E.
Published: February 2003

A new approach towards the computer analysis of ion elastic backscattering is introduced, in which the spectrum synthesis method is extended to an automatic iterative procedure. Instead of fitting the spectrum as a whole, parameters such as signal areas, widths, and leading-edge heights, often readily determined from an experimental spectrum, are fitted by corresponding parameters of computer generated theoretical spectra. Usually fewer signals of the elements of the sample are needed than in alternative methods, and the beam dose may be ignored. The number of layers or the number of elements in a layer is not limited. Regardless of the choice of initial approximations, only a few iterations generally suffice to reproduce accurately the given parameters. As a result of successful analysis, the depth profiles of the elements and a theoretical energy distribution identical in all relevant aspects to the experimental spectrum is produced, thus verifying the initial assumptions about the sample. The accuracy of the procedure exceeds or is equal to that of conventional data analysis.
Determination of the dynamic phase transitions in bismuth with in-material manganin gauges
Authors: Rosenberg Z.
Published: February 2003

We performed planar impact experiments with in-material manganin gauges in order to record the multiple wave structure resulting from the BiI-II and BiII-III phase transformations. Our values are somewhat higher than the static values (28 kbar for BiI-II and 32.5 kbar for BiII-III) but they agree with other dynamic measurements. The release portion of the stress signal shows a complicated structure which results from the multiplicity of waves in the target and their interactions. Our measured wave amplitudes and Lagrangian velocities are in good agreement with those obtained by free-surface velocity measurements, thus demonstrating the usefulness of manganin gauges in planar impact experiments.
Fluorescence emission from Nd:yttrium aluminum garnet laser amplifier
Authors: Uppal J. S. , Gupta P. D. , Bhawalkar D. D.
Published: February 2003

Study of on axis emission from a Nd:YAG (yttrium aluminum garnet) laser amplifier is reported. At high input energies, the fluorescence pulse shows a sharp peak and its intensity keeps on increasing with the pump energy. This is attributed to superposition of parasitic oscillations from the laser amplifier in the axial direction on the amplified fluorescence intensity.
PbSnTe diode lasers incorporating passive waveguides
Authors: Kapon Eli , Zussman A. , Katzir A.
Published: February 2003

PbSnTe diode lasers with an unpumped section were fabricated. It was found that this section was virtually transparent at the lasing frequency. Such unpumped regions can serve as integrated waveguides for integrated optics applications in the midinfrared.
Modifications of the Fourier approach for magnetic field calculations to include axial shields in superconducting magnets
Authors: Caldwell J.
Published: February 2003

Martinelli and Morini have used an analytical method for calculating values and distribution of the magnetic field in superconducting magnets. Using Fourier series the magnetic field is determined by carrying out a series expansion of the current density distribution of the system of coils. This Fourier method can be modified to include axial iron to a far greater accuracy (for finite permeability) by incorporating the image series approach of Caldwell and Zisserman. Also an exact solution can be obtained for the case of infinite permeability. A comparison of the results derived from the expansion of Martinelli and Morini with the exact solution of Caldwell and Zisserman shows excellent agreement for the iron-free case but the accuracy deteriorates as the permeability μz increases. The exact solution should be used for infinite permeability and also gives satisfactory results for permeability μz >100. A symmetric geometry is used throughout the communication for simplicity of presentation.
Electrically stimulated optical switching of NbO2 thin films
Authors: Lee J. C. , Durand W. W.
Published: February 2003

For the first time, electrically stimulated optical modulation in a thin-film NbO2 device is demonstrated. NbO2 thin-film deposition by reactive ion-beam sputtering, device fabrication, and device performance as a 120-Hz continuous-wave modulator are described.
InGaAsP/InGaP buried heterostructure lasers at 810 nm
Authors: Wakao K. , Isozumi S. , Nishi H. , Ohsaka S.
Published: February 2003

InGaAsP/InGaP buried heterostructure lasers emitting at 810 nm have been grown on GaAs substrates using two-step liquid-phase epitaxy. A threshold current of 79 mA and an external differential quantum efficiency of 26% are obtained. Fundamental transverse mode operation up to 3 mW is achieved in the laser with the active region of 3.5 μm wide.
Technique for measurement of the gain spectra of semiconductor diode lasers
Authors: Cassidy Daniel T.
Published: February 2003

A simple technique for determining the gain spectra of semiconductor lasers from measurements of the emission spectra of the laser is presented. The technique is insensitive to the response function of the device used to determine the emission spectra of the laser. Accurate estimates of the gain can be obtained from data which have been convolved with an instrument response function of ≲0.5 Å FWHM for a cavity free spectral range of 2.5 Å. Two applications of the gain data obtained by the technique are presented.
Thermodynamic limits to nonlinearity. II. Purely-resistive, dissipative systems
Authors: Gupta Madhu S.
Published: February 2003

This paper deals with the nonlinearity of a class of idealized thermodynamic systems, such as electrical resistors and semiconductor junction diodes, in which energy is dissipated when the flow of an extensive quantity takes place through them, and the extensive variable is not stored in the system. A thermodynamic model of such a system is constructed by representing it as a weak coupling between two storage systems described by a Master equation. The lowest-order dimensionless measure of nonlinearity, defined as the second derivative of the force variable with respect to the flow, normalized with respect to the flow and the first derivative, is shown to have a lower bound of −2. The proof is based on the assumptions that the force and flow variables are functionally related, and the system is homogeneous, stable, and has a single flow in it.
Conductivity and permeability from microgeometry
Authors: Koplik J. , Lin C. , Vermette M.
Published: February 2003

We show how the electrical conductivity and the fluid flow permeability of a disordered random medium may be calculated from the microscopic geometry of the pore space. Serial sections of the pore space are used to determine an equivalent random network of cylinders, the transport coefficients of this network are related to the conductivity of an analog random resistor network, and the latter is calculated using an effective medium approximation. The procedure is illustrated by detailed analysis of a Massilon sandstone.
A hollow cathode arc in neon: Simultaneous laser probing and molecular-beam sampling of metastable atoms as a plasma diagnostic
Authors: Verheijen M. J. , Beijerinck H. C. W. , Berkers P. W. E. , Schram D. C. , Verster N. F.
Published: February 2003

The mean free path of metastable rare-gas atoms in a plasma can be determined by simultaneous sampling of a beam of metastable atoms through an orifice in the wall and optically pumping of the metastable atoms in the plasma with a cw dye laser beam perpendicular to the atomic beam axis. This method gives very accurate results for the absolute value and the velocity dependence (using a time-of-flight detection technique) of this mean free path. With a simple model the contributions of collisions with electrons and with heavy particles to the experimental mean free path can be determined from the velocity dependence. We have applied this method to the external plasma column of a hollow cathode arc in neon. The experimentally determined mean free path of 2–10 mm points unambiguously to a surprisingly low degree of ionization of 2% or less. At these conditions the plasma column is fully transparent for the background atoms in the vacuum chamber. This all means that the character of the plasma of a hollow cathode arc in neon is totally different from argon and helium, which is probably caused by the isotope composition of neon.
Ozone formation behind pulsed-laser-generated blast waves in oxygen
Authors: Stricker J. , Parker J. G.
Published: February 2003

The formation of ozone behind blast waves in oxygen generated by a pulsed laser has been investigated both experimentally and theoretically, over cell pressure range of 0.68–27 atm. Ozone buildup formed by successive pulses was monitored by recording UV absorption at 2540 Å. It was found that, as the number of pulses increase, the rate of ozone formation decreased until finally an equilibrium concentration was reached. This equilibrium magnitude was determined by the condition that the number of ozone molecules produced by the wave equals the number decomposed by the same wave. The decomposition and formation of O3 during a single pulse were monitored by time-resolved UV absorption measurements. In order to provide a fundamental basis for interpretation of the mechanism of ozone formation, a mathematical model was developed. Although qualitatively measurements and theory agree, the data, mainly on the number of O3 molecules produced per pulse, is in significant disagreement. Several possible explanations of this discrepancy are given.
Shortening of electron conduction pulses by electron attachers O2, N2O, and CF4
Authors: Lee L. C. , Li F.
Published: February 2003

A uniform electron density is produced by two-photon ionization of trace trimethylamine in the N2 buffer gas of atmospheric pressure using ArF laser photons. The transient conduction pulses induced by the electron motion between parallel electrodes under various applied electric fields are observed. The duration of the electron transient pulse is shortened when the electron attacher O2, N2O, or CF4 is added to the buffer gas. Electron attachment rate constants are obtained from the ratios of the transient current with and without attachers at various times after the laser pulses. For O2 and N2O, the electron attachment rate constants measured in this experiment agree with previous values measured by different methods. The apparent rate constants for the attachment of low-energy electrons by CF4 are measured. The electron drift velocity is found to increase when CF4 is added to N2. The present method is applicable for the measurement of the electron attachment rate associated with the production of short-lived negative ions.
Gradient B drift transport of high current electron beams
Authors: Lee James R. , Backstrom Robert C. , Halbleib John A. , Quintenz Jeffrey P. , Wright Thomas P.
Published: February 2003

A 1-MeV, 200-kA electron beam was transported 89 cm in a low pressure background gas via gradient B drift in the 1/r azimuthal magnetic field of a current carrying wire. The electron drift velocity was measured and found to be in good agreement with theory. Measurements of x-ray production in the target indicated high transport efficiency.
Stress profiles in rail-gun projectiles with distributed armatures
Authors: Batteh Jad H.
Published: February 2003

The one-dimensional steady-state momentum equation for rail guns is used to develop an analytic model for the acceleration stresses which arise in rail-gun projectiles. The model is applicable to the case where several armatures are embedded throughout the projectile and provides an expression for the stress as a function of integrals of the electrical conductivity and density distributions in the projectile. This expression is used to derive the conductivity profile which minimizes the stress in the projectile. Stress profiles are calculated for several distributed armature designs. The investigation indicates that, for both solid and arc armatures, the peak stress in a projectile with N uniformly distributed, discrete armatures is proportional to 1/N.
Infrared and visible emission analysis of 20% CO–He radio-frequency discharges
Authors: De Benedictis Santolo , d’Agostino Riccardo , Cramarossa Francesco
Published: February 2003

Radio-frequency discharges fed with 20% CO-He have been studied in a reactor with liquid–nitrogen-cooled walls, at 2 Torr of pressure, using various diagnostics techniques (infrared and visible emission spectroscopy and mass spectrometry). Highly-extended vibrational distributions of CO have been observed even at long residence times. The importance of the various energy exchange processes and dissociation channels, together with the vibrational deactivating action of some species, have been examined.
Scattering by lossy dielectric nonspherical objects with nonvanishing magnetic susceptibility
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: February 2003

Using the recently formulated iterative extended boundary condition method (IEBCM) it is shown that the absorption mechanisms in a lossy dielectric object are enhanced by the presence of a nonvanishing magnetic susceptibility. In addition, there is a corresponding reduction in the backscattering cross section. The conditional convergence of the IEBCM algorithm is also proved.
Wavelength-modulated reflectivity spectra of MnxCd1−xTe alloys at the Γ and Λ points
Authors: Montegu B. , Laugier A. , Triboulet R.
Published: February 2003

MnxCd1−xTe alloys are studied by wavelength modulation reflectivity for the composition range 0<x<0.75. Optical transitions around Γ and Λ critical points are investigated from T=10–300 K. In all the composition ranges the nature of the transitions appears to be the same as in CdTe: E0=Γv8−Γc6, E1=Λc6−(Λ4+Λ5)v, E1+Δ1=Λc6−Λv8. The energy position of these structures changes linearly with x.
Heavy-atom effects in laser properties of 9-acetoxy-10-acetoxyhalogenophenylanthracene derivatives
Authors: Heldt Janina R. , Szczepański Jan , Heldt Józef
Published: February 2003

Laser emission has been found for eight new 9-acetoxy-10-acetoxyhalogenophenylanthracene. For these compounds the absorption threshold power, laser output energy, and lasing region have been determined. It has been found that derivatives possessing –OAc or heavy-atom substituents in position 2′ or 6′ of the phenyl ring show laser properties differing distinctly from those compounds which have them in positions 4′, 3′ or 5′. These differences can be explained throughout by ‘‘internal heavy-atom’’ effects and interaction—hydrogen bonding—of the substituted phenyl ring with the anthracene skeleton. This interaction shifts the triplet levels causing a decrease of T1–Tn absorption losses.
Effect of pressure on the height of the Schottky barrier (φB) for several semiconductors
Authors: Peanasky M. J. , Drickamer H. G.
Published: February 2003

This paper contains the first measurements of the effect of pressure on the Schottky barrier (φB) at a metal-semiconductor interface. Results are presented for CdS, CdSe, and ZnO together with measurements of the absorption edges for CdSe and ZnO. These results are used in conjunction with previously published flat-band potential measurements on GaAs and InP to relate the change in energy of the top of valence band Ev relative to the Fermi level of the metal to the ionicity of the semiconductor. These measurements are compared to correlations of the change of φB with work function of the metal which have previously appeared in the literature.
A surface integral approach to determine the effects of iron on axisymmetric coil systems
Authors: Caldwell J. , Zisserman A. , Saunders R.
Published: February 2003

The scalar potential of any system of axisymmetric conductors can be expanded in terms of Legendre polynomials. This paper describes a method for including the effects of a spherical iron shell into the Legendre polynomial expansion. The scalar potential is found using a surface integral approach by dividing the iron surface into elements over which the potential is constant and then using point collocation. Numerical results are obtained for a range of values of permeability by varying the number of elements and are found to agree well with the analytical results.
Effects of platinum silicide thickness and annealing temperature on arsenic redistribution
Authors: Lew Peter W. , Helms C. R.
Published: February 2003

Arsenic redistribution due to PtSi formation was studied with Auger sputter profiling. Pt was sputter-deposited onto As-doped Si wafers (1.7×1020 cm3) with Pt thicknesses of 200, 500, and 1000Å. Samples of each Pt thickness were annealed at 400 °C for 30 min in a forming gas ambient and another set of samples were annealed at 550 °C for 30 min in forming gas. In all cases, As appeared at the PtSi surface and at the PtSi-Si interface. More As was found at the surface for the higher temperature anneal and more As redistribution occurred overall for the thicker Pt films. The As redistribution is modeled by an initial pileup at the PtSi-Si interface followed by As outdiffusion to the PtSi surface
Formation of artificial superlattice composed of ultrathin layers of CoO and NiO by reactive evaporation
Authors: Terashima Takahito , Bando Yoshichika
Published: February 2003

Films composed of alternating ultrathin layers of CoO and NiO have been prepared by reactive evaporation. The structure was investigated by x-ray diffraction and transmission electron microscopy (TEM). The CoO-NiO multilayered films deposited on the (100) plane of NaCl at 250 °C were single crystal, having the NaCl structure with lattice constants intermediate between the ones of CoO and NiO when each layer was ultrathin (<5 nm). The stacking sequence could be directly observed by the cross-sectional TEM method. The artificial periodicity in the films was also confirmed by the low angle Bragg diffraction and the satellite peaks appearing around the (200) peak. It was found that the films had an artificial superlattice consisting of coherently stacked CoO and NiO single-crystal layers. This structure resulted from alternate epitaxial deposition of these oxides. An artificial superlattice formed also on glass substrates although they were polycrystal films.
Study of electrical resistivity of lithium-indium thin films
Authors: Chandra Gyanesh , Katyal O. P.
Published: February 2003

Experimental results are presented on the electrical resistivity of lithium-indium films. The resistivity has been studied as a function of temperature (150–300 K), thickness of the films (570–3300 Å) and concentration of Li (11.0–58.7 at. %). The resistivity is observed to be minimum for samples having a Li concentration of 25 and 50 at. %. In general, resistivity varies linearly with temperature but resistivity versus temperature plot shows two distinct regions which have different slopes, i.e., dρ/dT. The role of lithium in indium-lithium films is discussed.
Annealing of selenium-implanted GaAs
Authors: Barrett N. J. , Grange J. D. , Sealy B. J. , Stephens K. G.
Published: February 2003

The electrical and structural properties of 1×1014 Se+ cm−2, 100–400 kV and 5×1012 Se++ cm−2, 350-kV implants into (100) semi-insulating GaAs have been studied. Peak carrier concentrations of 5×1018 cm−3 have been measured and mobilities >4000 cm2 V−1 s−1 obtained for low-dose implants (n=1–2×1017 cm−3) by annealing samples on a graphite strip heater. Si3N4 and AlN have been used as encapsulants. Comparisons are made with capless annealing in an arsine ambient.
Solar cell junction profiles in ion-implanted texture-etched surfaces
Authors: Keavney C. J. , Spitzer M. B.
Published: February 2003

An experiment was conducted to determine the dopant profile in ion-implanted solar cell emitters formed on texture-etched silicon wafers. To overcome the difficulties inherent in profiling the variable pyramids that characterize the texture-etched surface, it was necessary to simulate junction formation by implantation of a polished (111) wafer equivalently oriented with respect to the phosphorus ion beam. It is found that the doping profile in the equivalent surface is nearly identical to profiles obtained by ion implantation of a standard (100) polished surface.