bluuebunny/crossref_metadata_2025 huggingface dataset:
Onsager symmetry for inhomogeneous magnetized plasmas
Authors: Nambu Mitsuhiro
Published: July 2002

The symmetry properties of the linear dielectric function for an inhomogeneous magnetized plasma are studied based on the local mode approximation as well as on the modified local mode approximation. In the local mode approximation applied to the electrostatic or electromagnetic waves, the dielectric tensor lacks both the Hermitian symmetry and the symmetry of the Onsager relations. The lack of the symmetry properties arises because Fourier decomposition into plane waves is not a correct method for an inhomogeneous medium. The modified local mode approximation completely recovers the symmetry properties for the electromagnetic waves. However, it still lacks the symmetry properties for the electrostatic waves, due to the diamagnetic current. Some of the controversies previously given for an inhomogeneous plasma are also discussed.
Solitary kinetic Alfvén waves on the ion-acoustic velocity branch in a low-β plasma
Authors: Wu De-Jin , Wang De-Yu
Published: July 2002

Starting with an exact nonlinear equation governing solitary kinetic Alfvén waves (SKAWs), a new type of SKAW on the ion-acoustic velocity branch is obtained in a low-β plasma. It propagates in a direction oblique to the ambient magnetic field, has a dispersion originating from the finite perpendicular wavelength, and is accompanied by a density hump soliton similar to that of the SKAWs on the Alfvén velocity branch in the case of 1≫β≫me/mi. It has a perturbed electric field with the same order as that of the latter SKAWs, but its perturbed magnetic field is weaker by a factor of (β/2)1/2, and in the small amplitude limit, the analytical result also leads to the Korteweg–de Vries soliton.
Unstable particle drift across a magnetic field caused by oblique electric field gradients
Authors: Riyopoulos Spilios
Published: July 2002

The presence of a positive electric field gradient e dE/dx>0 oblique to a uniform magnetostatic field is shown to cause unstable particle motion across the magnetic lines. Both the drift velocity along ∇E and the E×B drift velocity exponentiate in time with growth rate proportional to |dE/dx|1/2 sin θ, where π/2−θ is the angle between E and B. Thus the cross-B transport due to ∇E is more severe than the ∇B and ∂E/∂t effects, that cause constant drift velocity under uniform field variation. The result has implications to a variety of situations involving oblique electric gradients, such as magnetized plasma sheaths, large amplitude drift waves, and possibly tokamak edge transport.
The breaking of up–down symmetry of trapped particle orbits by a toroidal electric field
Authors: Haines M. G. , Martín P.
Published: July 2002

A breaking of the up–down symmetry due to the inductive electric field Eφ is analyzed in detail for particles describing quasibanana orbits in the large aspect ratio approximation. Time-independent and time-dependent electric fields are considered. In the first case it is proved that the classical ∇B drift and the breaking of up–down symmetry due to Eφ lead to a net inward radial drift, which agrees with the well-known Ware pinch formula. The weak points of previous treatments of the Ware pinch, e.g. taking only leading terms in the Taylor expansion of Aφ, are discussed. Yet the results obtained here lead to the same pinch formula, even for banana orbits with a large amplitude of poloidal angle and for more general conditions than previously considered. A more general formula for a time-dependent Eφ has also been found. Our results show from a very general basis that the corresponding polarization type of drift does not play any role in the inward pinch; however, the second time derivative of the inductive electric field Eφ could significantly increase or decrease the usual Ware pinch.
Instability of the ion hybrid wave in the presence of superthermal alpha-particles
Authors: Lashmore-Davies C. N. , Russell D. A.
Published: July 2002

The stability of the ion hybrid wave in a plasma containing two thermal ion species present in comparable proportions and a low density population of superthermal alpha-particles is analyzed. A simple, model distribution function consisting of a ring distribution in the perpendicular velocity and a Maxwellian in the parallel velocity is used for the superthermal alpha-particles. This distribution function is relevant to the core plasma of a tokamak in the immediate post-birth phase before the alpha-particles have had time to relax collisionally and is therefore of interest to the alpha-channelling question. It has also been used to interpret ion cyclotron emission from fusion products in the edge plasma of large tokamaks. An approximate dispersion relation is derived which allows the conditions for instability to be explored and an analytic expression for the growth rate to be obtained. It is found that the ion hybrid wave can be unstable for v⊥0/cA≪1 where v⊥0 is the alpha-particle ring speed and cA is Alfvén speed for a plasma with two ion species. The instability conditions obtained from the analytic approximation are used to guide the solution of the exact dispersion relation. Numerical solutions for the specific cases of deuterium–tritium core and edge plasmas in the Tokamak Fusion Test Reactor (TFTR) [K. M. Young et al., Plasma Phys. Controlled Fusion 26, 11 (1984)] are given.
Direct magnetic field measurement of flow dynamics in magnetized coaxial accelerator channels
Authors: Black D. C. , Mayo R. M. , Caress R. W.
Published: July 2002

A miniature magnetic probe array, consisting of ten spatially separated coils, has been used to obtain profile information on the time-varying magnetic field within the 2.54 cm wide flow channel of the Coaxial Plasma Source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. Two-dimensional (2-D) current profiles within the annular flow channel, which were constructed from the time-varying magnetic field data, reveal several complex features reflecting the influence of gun inductance, the Hall effect, and the applied magnetic field. When an external, electrode linking magnetic field is applied, the evolution of the 2-D current profile shows evidence of an ionizing shock front identified by a narrow current sheet propagating through the channel during the first few microseconds of the discharge. The thickness of this current sheet is on the same order as both the collisional mean-free path and the ion electromagnetic skin depth. In this applied field case, the plasma is prevented from advancing ahead of the current sheet by the applied magnetic field, which turns the ions and electrons without collisions. In the absence of an applied field, plasma is able to advance ahead of the current sheet, where it may initiate ionization downstream before the advance of the ionization front.
Fishbone mode excitation in the ion kinetic regime
Authors: Shi Bingren , Sui Guofang
Published: July 2002

By solving the dispersion relation in the ion kinetic regime, it is found that the threshold of the plasma beta value for exciting the ion-fishbone mode is lowered. Thus, for most of the present-day tokamaks where the Bussac criterion [Bussac et al., Phys. Rev. Lett. 35, 1638 (1975)] is not satisfied, it will still be possible to excite the ion-fishbone mode.
Electron transport fluxes in potato plateau regime
Authors: Shaing K. C. , Hazeltine R. D.
Published: July 2002

Electron transport fluxes in the potato plateau regime are calculated from the solutions of the drift kinetic equation and fluid equations. It is found that the bootstrap current density remains finite in the region close to the magnetic axis, although it decreases with increasing collision frequency. This finite amount of the bootstrap current in the relatively collisional regime is important in modeling tokamak startup with 100% bootstrap current.
Theory of high-frequency guided waves in a plasma-loaded waveguide
Authors: Ganguli A. , Akhtar M. K. , Tarey R. D.
Published: July 2002

The theory of high-frequency guided waves in a plasma-loaded waveguide is presented. The formulation is based on kinetic theory. The theory includes the effects of finite electron/ion temperatures and radial gradients in the plasma density and particle temperatures. The inclusion of gradients into the formalism results in three, coupled, second-order, ordinary differential equations in the plasma fields. These equations show a singularity on the plasma axis (r=0); regularization of the field equations at the singular point leads to constraints on the plasma fields that yield the necessary boundary conditions at r=0. Using the vacuum solutions, and the boundary conditions at r=0 and the plasma–vacuum interface, the field equations are solved as a two-point boundary-value problem. The numerical methods used are also discussed. Solutions are presented in the form of dispersion curves (plots of vphase vs ω/Ωe) and radial profiles of the field polarizations for the m=±1 modes near electron cyclotron resonance (ECR).
Refraction of the ordinary wave near the electron cyclotron fundamental
Authors: McDonald D. C. , Cairns R. A. , Lashmore-Davies C. N. , Le Clair G.
Published: July 2002

Detailed ray tracing, of wave propagation in a plasma near electron cyclotron resonances, suggests that refraction can lead to reduced absorption, in some cases. By studying the full wave equation for the ordinary wave near the fundamental, in a slab model, it is shown that such refraction does indeed reduce absorption, for this particular case, but that wave energy tunnelling can significantly modify the result.
Simulation of ion extraction from laser-induced plasma by electromagnetic fields
Authors: Zhidkov A. G.
Published: July 2002

The particle-in-cell (PIC) method is extended to allow for particle elastic collisions through the use of the Langevin equation. The one-dimensional, in cylindrical space coordinates, and three-dimensional in velocity coordinates (1D3V), electromagnetic PIC model is used to simulate the dynamics of a plasma produced in the system of two coaxial cylinders by selective laser photoionization in external fields. The electromagnetic fields and the plasma dynamics are solved in a self-consistent manner. Elastic electron–atom, electron–ion, and charge exchange collisions are included in the model. The extraction of ions from the weakly collisional plasma by the electrostatic, crossed electrostatic, and magnetic (E×H), rf, and alternating magnetic fields have been explored to compare the characteristics of various extractors relevant to atomic vapor laser isotope separation (AVLIS).
Instability criterion of tearing mode for arbitrary magnetic shear configuration
Authors: Li Ding
Published: July 2002

A new expression of Δ′ and instability criterion for m⩾2 tearing modes is derived for arbitrary magnetic shear configuration in the low beta and large aspect ratio limit. Local solutions of an ideal external kink equation are solved analytically by means of proper expansion and transformation. An analytic expression of the criterion parameter Δ′ results from the analytic solutions. The instability criterion obtained depends on the location of the resistive layer, and on a dimensionless parameter λ related to the ratio of the gradients of the equilibrium current density and of the rotational transform. Strauss’s Δ′ formula and the previous instability criterion are recovered as a special case in the large-m limit without a conducting wall. Considering both the boundary conditions at the plasma core and the conducting wall, the expression of Δ′ is extended to include the stabilizing effect of the conducting wall. The properties of tearing instability are analyzed based on the expression of Δ′.
Self-consistent removal of sawtooth oscillations from transient plasma data by generalized singular value decomposition
Authors: Dudok de Wit T. , Erba M. , Mattioli M. , Ségui J.-L.
Published: July 2002

This paper addresses the problem of removing sawtooth oscillations from multichannel plasma data in a self-consistent way, thereby preserving transients that have a different physical origin. The technique which does this is called the generalized singular value decomposition (GSVD), and its properties are discussed. Using the GSVD, spatially resolved electron temperature measurements are analyzed. Special attention is paid to transient regimes in which the temperature is perturbed either by the laser blow-off injection of impurities or by pellet injection. Nonlocal transport issues are briefly discussed.
Alight a beam and beaming light: A theme with variations
Authors: Chattopadhyay Swapan
Published: July 2002

The interaction of light (coherent and incoherent) with charged particle beams is explored in various configurations: incoherent scattering of coherent light (laser) from an incoherent particle beam (high temperature), coherent scattering of coherent light (laser) from a “cold” (bunched) beam, femtosecond generation of particle and light beams via “optical slicing” and Thomson/Compton scattering techniques, etc. The domains of ultrashort temporal duration (femtoseconds) as well as ultrashort wavelengths (x rays and shorter), with varying degrees of coherence, are explored. The relevance to a few critical areas of research in the natural sciences, e.g., ultrafast material, chemical and biological processes, protein folding, particle phase space cooling, etc. are touched upon. All the processes discussed involve proper interpretation and understanding of coherent states of matter and radiation, as well as the quality and quantity of information and energy embedded in them.
Role of flow shear and flow curvature in the suppression of low-frequency fluctuations
Authors: Sen S. , Sharma P. K. , Bora D.
Published: July 2002

The crucial question of whether it is the shear [V(r)′] or the curvature [V(r)″] in the flow profile [V(r)], which plays the dominant role in suppressing the low-frequency (ω<ωi, where ωi is the ion gyrofrequency) fluctuations is investigated. The role of flow curvature is found to have a robust effect on the fluctuations. For a positive value in the flow curvature, fluctuations are suppressed, whereas a negative flow curvature excites fluctuations. Flow shear, on the other hand, plays an insignificant role in this matter. These experimental findings are in complete agreement with the theoretical predictions.
Quasilinear damping of ion Bernstein waves on the harmonic resonant layer
Authors: Cardinali A. , Castaldo C. , Cesario R. , De Marco F.
Published: July 2002

The damping of an ion Bernstein wave (IBW) across a resonant layer of the minority species of the plasma is calculated within the framework of quasilinear theory. The model uses the analytical solution of the one-dimensional Fokker–Planck equation for the ion distribution function. A greater reduction of the damping has been found in this case compared with the one obtained with the linear model. This allows the wave to penetrate further towards the plasma core. In addition, a particle flux induced by the sharp spatial gradient of the distribution function across the resonant layer, due to the IBW field, has also been evaluated. This shows that modification of the distribution function generates a flux of particles from the outside which tends to increase the particle density in the vicinity of the resonance itself.
Enhanced transport via Kirchhoff radiation
Authors: Puri Satish
Published: July 2002

Momentum transfer via Kirchhoff radiation of electrostatic electron and ion-cyclotron-harmonic waves contributes an enhanced collisionality far in excess of that given by the Fokker-Planck term in the existing neoclassical models. The resultant particle and thermal transport resembles the observed anomalous transport in ohmically heated toroidal plasmas.
Numerical simulation of short laser pulse relativistic self-focusing in underdense plasma
Authors: Chessa Piero , Mora Patrick , Antonsen Thomas M.
Published: July 2002

Existing experimental results on relativistic self-focusing are interpreted by means of the particle code WAKE using the ponderomotive approximation to describe the laser–plasma interaction [P. Mora and T. M. Antonsen, Jr., Phys. Plasmas 4, 217 (1997)]. Novel features of the code, such as gas medium ionization and an enhanced paraxial approximation, allow more confidence in data interpretation. Simulations where the pulse power is less or close to the critical value match the experimental data. The transmitted pulse spectrum is shown in this case to shift towards longer wavelengths. The pulse is shown to focus over the vacuum diffraction limit, while the energy is slowly depleted. Simulations of pulses above the critical power match experiment with reduced precision. This can be ascribed to beam filamentation. High energy depletion is expected in this case due to Raman instability.
One-over-polynomial approximation for linear kinetic dispersion and its application to relativistic cyclotron resonance
Authors: Nakamura Tadas K. , Hoshino Masahiro
Published: July 2002

In this paper we propose a new method to calculate the plasma dispersion relation for a wide variety of distribution functions with a complicated resonance mechanism. An approximation with a one-over-polynomial function enables us to apply the residue theorem for integration, and gives an analytical form of the dispersion equation. The solution is highly accurate with typical error less than 10−4 when applied to the ordinary plasma dispersion function (Z function). Application of this method is not limited to the dispersion functions that can be expressed by the Z function; it can be applied to much wider class of problems with arbitrary velocity distributions. One example is the general solution to the dispersion equation for a weakly relativistic magnetized plasma.
A numerical study of density limit mechanisms in tokamaks
Authors: Stacey Weston M.
Published: July 2002

A core particle and power balance model with radiative cooling, a ballooning-mode-limit pedestal model, a “two-point” plasma divertor model with radiative and atomic recycling cooling, and a two-dimensional (2-D) neutral transport model have been combined to model the coupled plasma core-edge physics in a tokamak. This model has been applied to examine the physical mechanisms which limit the attainable core density. The first limitation is fueling rate and core penetrability. For fueling that is able to penetrate the core, the core density increases with a fueling rate up to a limit set by one of two other mechanisms. When a sufficient impurity concentration is present, the mechanism that limits the maximum density attainable in the core seems to be an impurity-driven thermal instability that produces a thermal collapse of the core plasma. At lower impurity concentrations, the buildup of plasma density in the divertor and the associated increase in atomic recycling and ionization cooling causes a collapse of the divertor plasma temperature, leading to a thermal collapse of the core plasma. An increase in core heating input power or in plasma confinement extends the point of thermal collapse to higher density.
Exact Green’s function for a class of parametric instabilities
Authors: Kanaev A. V. , McKinstrie C. J.
Published: July 2002

The spatiotemporal evolution of stimulated Brillouin scattering and stimulated Raman scattering is studied analytically without recourse to the envelope approximation on the time scale of the plasma oscillations. In their regimes of validity, the standard approximate Green’s functions for weak coupling and strong coupling describe the growth of the scattered light wave accurately. However, in the transition period between the two regimes, which can be a significant fraction of the duration of an experiment, the approximate solutions cannot be applied and the exact Green’s function, which is valid for all times, is required.
Surface waves in a magnetized plasma
Authors: Janaki M. Sita , Dasgupta Brahmananda
Published: July 2002

Electrostatic surface waves propagating along the interface between a warm magnetized plasma and vacuum are investigated by deriving the relevant dispersion relations using a fluid model. The general dispersion relation for arbitrary orientation of the magnetic field and the propagation vector is derived in a closed form and certain special cases (when the magnetic field is directed parallel and perpendicular to the boundary surfaces) are analyzed numerically.
Wave and Joule heating in a rotating plasma
Authors: Amatucci W. E. , Ganguli G. , Walker D. N. , Duncan D.
Published: July 2002

Laboratory experiments were conducted to investigate ion energization by the wave and Joule heating mechanisms in plasma with a radial electric field and an axial magnetic field subjected to increasing ion–neutral collision frequency. Wave and Joule heating regimes were isolated and a transition between the two regimes was observed as the ion–neutral collision frequency was varied. The data show that the dissipation of energy occurs via the mechanism operating on the shortest time scale.
Turbulent magnetohydrodynamic dynamo based on alpha and cross-helicity effects, with special reference to geomagnetic fields
Authors: Yoshizawa Akira , Yokoi Nobumitsu , Kato Hirofumi
Published: July 2002

Magnetohydrodynamic (MHD) state in a wide-gap spherical shell mimicking the earth’s outer core is examined with resort to the mean-field or turbulent-dynamo theory. In the dynamo, the induced mean magnetic field is in a quasi-force-free state under a large alpha effect. The saturation level of the field is determined through the alignment with the mean velocity under a cross-helicity effect. On this basis, the following characteristics of the induced field are elucidated: The energy of the magnetic field becomes much larger than the kinetic one of the fluid motion driven by buoyancy force; the Lorentz force coming from the field remains less dominant than the buoyancy force; the toroidal component of the field is larger than the poloidal one.
Nonlinear dynamics of upper-hybrid waves in dusty magnetoplasmas
Authors: Shukla P. K. , Stenflo L.
Published: July 2002

The nonlinear propagation of upper-hybrid waves in a magnetized dusty plasma is considered. Several sets of Zakharov-like coupled equations are derived. They exhibit the nonlinear coupling between the high-frequency waves and various low-frequency electrostatic dusty plasma fluctuations. These nonlinear mode coupling equations are needed in forthcoming studies of modulational instabilities, envelope soliton formation, and wave collapse in dusty magnetoplasmas.
Breakdown properties of high-pressure electrical discharge
Authors: Uhm Han S. , Choi Eun H. , Cho Guangsup
Published: July 2002

A simple scaling law of the electrical breakdown is obtained. Introducing the normalized net ionization-rate ξ, the electrical breakdown phenomenon is uniquely described in terms of the ionization properties of the gas, the second ionization coefficient γ at cathode, and the gas pressure pd. The electron attachment process plays a decisive role in breakdown phenomenon for a high-pressure gas, whereas it is not important in low-pressure discharge.
Optical investigation of modulation-doped In0.53Ga0.47As/In0.48Al0.52As multiple quantum well heterostructures
Authors: Penna A. F. S. , Shah Jagdeep , Pinczuk A. , Sivco D. , Cho A. Y.
Published: July 2002

We present the results of the first optical studies of modulation-doped In0.53Ga0.47As/ In0.48Al0.52As multiple quantum well heterostructures. By a combination of luminescence and absorption measurements, we have distinguished between intrinsic and extrinsic luminescence processes. We show that the intrinsic luminescence dominates above 70 K and results from recombination of two-dimensional electron plasma with photoexcited holes. Spectral line shape analysis yields important sample parameters. The use of As2 source appears to enhance the purity of the material as compared to the material grown with As4 source.
High resolution ultraviolet photoablation of SiOx films
Authors: Fiori C. , Devine R. A. B.
Published: July 2002

The ability of UV laser radiation at 248 nm to cause the photoablation of SiOx films is demonstrated. Given the relatively low doses necessary to ablate significant SiOx thicknesses and the excellent etched wall verticality obtained, it appears that SiOx might be a viable UV photoresist. A brief discussion of the mechanisms leading to SiOx photoablation is presented.
Observation of new common emissions in GaAs produced by ion implantation of four acceptor impurities
Authors: Takeuchi Yoshinori , Makita Yunosuke , Kudo Kazuhiro , Nomura Toshio , Tanaka Hideki , Irie Katsuhiro , Ohnishi Nobukazu
Published: July 2002

Photoluminescence studies of C+, Mg+, Zn+, and Cd+ ion-implanted GaAs layers were carried out at 2 K. Two conspicuous emissions denoted by g and [g-g] were observed to be situated between bound exciton and band to acceptor emissions. It was found that these two are common emissions among the above acceptor impurities, and that they can be explicitly observed only when the background impurity concentration is extremely small.
Growth of single crystal bcc α-Fe on ZnSe via molecular beam epitaxy
Authors: Prinz G. A. , Jonker B. T. , Krebs J. J. , Ferrari J. M. , Kovanic F.
Published: July 2002

Molecular beam epitaxy methods have been used to grow high quality single crystal films of bcc α-Fe on fcc (zinc blende) ZnSe (001) epilayers on GaAs (001). These films were characterized by reflection high-energy electron diffraction, Auger electron spectroscopy, ferromagnetic resonance (FMR), and vibrating sample magnetometry. The FMR linewidth and measured coercive field are significantly smaller than previously reported for single crystal Fe films.
AlGaAs heterojunction visible (700 nm) light-emitting diodes on Si substrates fabricated by metalorganic chemical vapor deposition
Authors: Hashimoto A. , Kawarada Y. , Kamijoh T. , Akiyama M. , Watanabe N. , Sakuta M.
Published: July 2002

AlGaAs visible surface light-emitting diodes (LED’s) on silicon substrates have been successfully fabricated by use of the metalorganic chemical vapor deposition technique. The emission spectrum of the LED peaked at 700 nm with a half-width of 45 nm at the forward current of 100 mA at room temperature. The external efficiency was 0.3%.
Epitaxial growth of LiInSe2 on {111}A oriented GaP by a hot wall technique
Authors: Kuriyama K. , Igarashi Y. , Nakamura F. , Okada A.
Published: July 2002

LiInSe2 films were grown on GaP substrates using a hot wall technique. Reflection high-energy electron diffraction analysis showed that LiInSe2, having a β-NaFeO2 (wurtzitelike) structure, grows epitaxially on a 〈111〉A oriented GaP at substrate temperatures ranging from 360 to 400 °C and at the wall temperature of 650 °C with the compensation of Se. The crystalline quality of the epitaxial layers on substrates was investigated by Rutherford backscattering (RBS). The depth profile of RBS-aligned spectrum showed the relative low minimum yield of backscattered particles except for that near the interface. Auger electron spectroscopy measurements showed that the atomic concentration ratio of Se and In in films was 2.
Reversibility of recombination-induced defect reactions in amorphous Si:H
Authors: Redfield David
Published: July 2002

Recombination-induced defect reactions are reversible in principle; i.e., any recombination (or trapping) process that induces defect formation can also induce recovery of that defect. This reversibility principle applies to crystalline and amorphous semiconductors. Although the rates in the two directions are generally quite different, evidence is cited indicating that in hydrogenated amorphous silicon they may be comparable, and offer new explanations for several observations. Illustrative rate equations are presented along with a series of testable experimental predictions.
Longitudinal mode selection in hybrid CO2 laser for subthreshold operation of cw discharge section
Authors: Sinha Sucharita , Gupta Pradeep K.
Published: July 2002

The relative mode intensities in the hybrid CO2 laser output are investigated for subthreshold operation of cw gain section. The rate equation model developed for the purpose provides estimates in very satisfactory agreement with experimental results. The model also predicts the existence of an optimum pressure and length for the cw discharge section and shows that very good longitudinal mode discrimination is possible even when cw discharge section gain is only a tenth of that required for oscillation.
Simultaneous depth profiling of constituents and impurities by elastic proton scattering in amorphous hydrogenated silicon films
Authors: Schwarz R. , Kolodzey J. S. , Wagner S. , Kouzes R. T.
Published: July 2002

Depth profiles of various constituents and impurities of thin films were obtained simultaneously by a nuclear coincidence method. The energy spectrum of elastically scattered 12 MeV protons, measured by a high-resolution magnetic spectrometer, was used for constituent identification and total content determination. Constituents of interest were selected by software pulse height discrimination and their depth profiles were obtained from the recoil energy spectrum, measured by a surface barrier detector telescope. Thin films of Teflon, of carbon, and of amorphous hydrogenated silicon were measured. The best possible depth resolution is about 20 nm for carbon and is limited by the beam energy spread and the energy resolution of the solid state detectors.
Shallow n+ diffusion into InP by an open-tube diffusion technique
Authors: Ghandhi Sorab K. , Parat Krishna K.
Published: July 2002

Very shallow n+ layers have been obtained in InP by using gallium sulfide as a source for sulfur diffusion, and chemically vapor deposited SiO2 as a cap. Diffusions were carried out from 585 to 725 °C in an open-tube system with a nitrogen ambient. The doping profile of sulfur in InP is estimated to be of the complementary error function type with a surface concentration of 5.6×1018/cc and a diffusion constant of 1.1×10−14 cm2/s at 670 °C. Diodes made on n+-p junctions obtained by this diffusion technique show ideality factors close to unity and saturation current densities as low as 3.4×10−15 A/cm2, signifying the presence of a defect-free junction. These diffusions, with junction depths in the 400–700 Å range, are ideal for solar cell applications.
Cascade-driven migration of structural interfaces: A new type of irradiation-induced phase transformation
Authors: Allen C. W. , Rehn L. E. , Wiedersich H.
Published: July 2002

In Ti-Cr alloys containing both the Laves phase (ordered TiCr2) and the β phase (bcc solid solution), 1 MeV Kr+ irradiation at temperatures <250 K amorphizes the Laves phase but not the β phase. The irradiation-induced amorphous material transforms into polycrystalline β upon warming to room temperature. In contrast, irradiation at room temperature causes the β phase to grow by migration of the β/Laves interface; no change in local composition across the migrating interface is observed. The β phase also grows during prolonged irradiation at 100 K, but the velocity of the β/amorphous interface per unit calculated atomic displacement rate is more than three orders of magnitude lower than that of the β/Laves interface at room temperature. An interpretation of this new type of irradiation-induced phase transformation is presented in terms of displacement cascade formation and dynamic recovery at the structural interface that exists between the two phases.
Effect of heat treatments on the electrical resistivity of polycrystalline silicon films implanted with antimony
Authors: Komem Y. , Harrison H. B.
Published: July 2002

Polycrystalline silicon films, ion implanted with antimony to a dose of 1–3×1015/cm2 at an energy of 100 keV, were heat treated by means of rapid thermal or conventional furnace techniques. It was found that the electrical resistivity is a function of time, reaching a minimum value that is relatively lower at 600 than 900 °C for heat treatment times that are short enough to avoid significant lattice diffusion, and then increasing with time. However, in cases where longer times at high temperatures (between 860 and 975 °C) are used in order to provide sufficient atom movement, the resistivity increases with decrease in temperature. The results are explained on the basis of recrystallization, diffusion, and segregation processes.
Ga0.47In0.53As/InP superlattice avalanche photodiode grown by metalorganic chemical vapor deposition
Authors: Beltram F. , Allam J. , Capasso F. , Koren U. , Miller B.
Published: July 2002

We report the operation of the first Ga0.47In0.53As/InP superlattice avalanche photodiode grown by metalorganic chemical vapor deposition. The undoped region of the p-i-n structure consists of 100 periods of alternating InP and Ga0.47In0.53As layers 100 A˚ thick with no intentional doping. dc multiplication higher than 20 and high-speed response with full width at half-maximum of 200 ps have been measured.
Studies of texture in thin films using synchrotron radiation and energy dispersive diffraction
Authors: Hart M. , Parrish W. , Masciocchi N.
Published: July 2002

High resolution, energy dispersive patterns are obtained with parallel beam x-ray optics, synchrotron radiation, a step scanning incident beam channel monochromator, and independently selectable specimen and detector angles, which are fixed during the scan. This permits decoupling of the specimen and detector geometry (which would cause defocusing in conventional methods) and makes it possible to measure the intensities at several incidence angles to determine the preferred orientation of the crystallites in a thin film. The method is illustrated by patterns of a Pd/Xe thin film.
Dual laser diode array emission coherently summed in an external cavity
Authors: Hemmati Hamid , Abshire James B.
Published: July 2002

The output power from two ten-element laser diodes arrays has been efficiently summed in an external cavity to obtain a coherent, continuous wave beam. In this technique, laser emission from each front surface antireflection coated diode array is stimulated by injection of emission from a second such array. This method was also applied to single-element diode lasers. The output beam characteristics such as spectral distribution, far-field and near-field beam patterns, and overall efficiency have been measured.
Universal relationship between resonant frequency and damping rate of 1.3 μm InGaAsP semiconductor lasers
Authors: Olshansky R. , Hill P. , Lanzisera V. , Powazinik W.
Published: July 2002

Analysis of the measured frequency response of 1.3 μm InGaAsP vapor phase regrown buried heterostructure lasers shows that there is a universal linear relationship between damping rate and resonant frequency squared with a proportionality factor of 0.32×10−9 s. This result can be explained by the intraband relaxation model of nonlinear gain.
Formation of submicron epitaxial islands of Pd2Si on silicon
Authors: Boothroyd C. B. , Stobbs W. M. , Tu K. N.
Published: July 2002

It has been found that annealing Pd-Er deposits on a (001) silicon surface results in the formation of isolated submicron islands of Pd2Si with two epitaxially oriented habits. By contrast, when Pd is annealed on a (111) silicon substrate, Pd2Si is formed with full coverage and a specific epitaxy.
Effects of reactive ion etching on chemical vapor deposition
Authors: Wong C. Y. , Batson P. E.
Published: July 2002

Silicon surfaces were exposed to reactive ion etching with CCl2F2, followed by low pressure chemical vapor deposition of silicon nitride. Examination with transmission electron microscopy shows a 5-nm homogeneous layer with interfacial roughness about the order of the layer thickness between the nitride and the silicon substrate. Analysis with spatially resolved electron energy loss scattering indicates that this phase is Si2N2O. The causes for the formation of this layer and its implication on very large scale integration technology are discussed.
Nb/GaAs and NbN/GaAs Schottky barriers
Authors: Wu X. W. , Zhang L. C. , Bradley P. , Chin D. K. , Van Duzer T.
Published: July 2002

Niobium and niobium nitride films have been deposited on n-GaAs substrates using dc magnetron sputtering to form Nb/GaAs and NbN/GaAs Schottky diodes. Current-voltage(I-V) measurements were made on the diodes and the metal/GaAs interfaces were studied by Rutherford backscattering spectrometry. For the Nb/GaAs Schottky diodes, without rapid thermal annealing and after annealing for 10 s at temperatures up to 600 °C, the ideality factor and the Schottky barrier height as measured by the current-voltage technique vary slightly from 1.01 to 1.03 and from 0.75 to 0.78 V, respectively. For annealing above 750 °C, evidence of interdiffusion between Nb and GaAs is observed. In contrast to the Nb/GaAs diodes, the NbN/GaAs Schottky diodes have poor characteristics without high-temperature annealing; however, after annealing at 800 °C, the diodes show excellent forward I-V characteristics with an ideality factor of 1.06 and a barrier height of 0.73 V. No trace of interdiffusion between NbN and GaAs is found after annealing up to 800 °C.
High power, AlGaAs buried heterostructure lasers with flared waveguides
Authors: Welch D. F. , Cross P. S. , Scifres D. R. , Streifer W. , Burnham R. D.
Published: July 2002

High power, buried heterostructure laser with flared waveguide horns have been grown by a two-step metalorganic chemical vapor deposition process. Powers up to 120 mW cw in a single longitudinal and transverse mode have been obtained from a single stripe laser. The flared waveguides decrease the lateral far-field divergence from 25° to 11° while supporting only the lowest order transverse mode.
Nonequilibrium boron doping effects in low-temperature epitaxial silicon films
Authors: Meyerson B. S. , LeGoues F. K. , Nguyen T. N. , Harame D. L.
Published: July 2002

We report the first preparation of in situ boron-doped epilayers by a low-temperature chemical vapor deposition process (T=550 °C). Boron incorporation is approximately linear in source gas concentration, and active levels of boron incorporation exceeding 1×1020 B/cm3 have been achieved in as-deposited 550 °C epilayers. This value exceeds solid solubility limits for boron in silicon at these temperatures by two orders of magnitude, and highlights the nonequilibrium nature of this process. High resolution transmission electron microscopy lattice imaging of this material shows it to be free of boron precipitates, while both plane view transmission electron microscopy and x-ray topography fail to reveal extended defects. Utilizing low-temperature processing throughout, p/n junctions have been fabricated in several of the in situ doped layers, with essentially ideal junction quality factors (n=1.0 –1.05) found for junctions of 1×106 μm2.
Josephson effect above 77 K in a YBaCuO break junction
Authors: Moreland John , Goodrich L. F. , Ekin J. W. , Capobianco T. E. , Clark A. F. , Braginski A. I. , Panson A. J.
Published: July 2002

We have observed the Josephson effect in a YBaCuO break junction. Critical currents as high as 10 mA were measured at 4 K for break junctions with a point contact within the fracture of a sample. The junction was susceptible to microwave radiation showing Shapiro steps with the ratio of V/f of 2.04±0.05 μV/GHz compared to the pair tunneling value of h/2e=2.068 μV/GHz. These steps were clearly visible in the current-voltage characteristics at tempertures up to 85±5 K.
Interferometric generation of high-power, microwave frequency, optical harmonics
Authors: Eichen Elliot
Published: July 2002

A new technique for sinusoidal intensity modulation of light at microwave frequencies using a frequency modulated semiconductor laser and an interferometer is described. This technique can be more efficient than direct amplitude modulation and, since sidebands at harmonics of the modulation frequency are generated, is capable of reaching higher frequencies than direct modulation. The highest observed frequency (18 GHz) was generated by direct modulation of a laser diode at 9 GHz, and was limited by the bandwidth of available detectors. Frequencies in excess of 100 GHz can be obtained using suitable detectors.
Dynamic observation of magnetic domains in amorphous ferromagnetic ribbons driven at line frequencies
Authors: Mase H. , Shimizu R. , Ikuta T.
Published: July 2002

The recently developed dynamic observation technique of R. Shimizu and T. Ikuta [Appl. Phys. Lett. 44, 811 (1984)] for scanning electron microscopy, ‘‘line-sampling stroboscopy,’’ was used for the observation of magnetic domains in an amorphous ferromagnetic ribbon. The image-processing technique introduced turned out to be very useful, allowing the behavior of domain walls, which is often obscured by topological contrast, to be clearly observed.
Transport and structural properties of the Ho1Ba2Cu3O9−δ superconductor
Authors: Lee Sung-Ik , Golben John P. , Song Yi , Lee Sang Young , Noh Tae W. , Chen Xiao-dong , Testa Joe , Gaines J. R. , Tettenhorst Rodney T.
Published: July 2002

The compound Ho1Ba2Cu3O9−δ has been found to be a high Tc superconductor. The onset of the superconducting transition is 88 K with zero resistance achieved at 87 K. The x-ray diffraction spectrum of this material shows it to be a single-phase perovskite similar to the Y1Ba2Cu3O9−δ compound but different from the K2NiF4 perovskite which is believed to be the superconducting phase for the La2(1−x) Ba2xCuO4−δ system. Possible oxygen deficiencies in several of the unit cell planes are discussed. The room-temperature resistance, the superconducting onset temperature, and the emergence of the single phase all depend upon the sample preparation firing conditions.
High-power (1.4 W) AlGaInP graded-index separate confinement heterostructure visible (λ∼658 nm) laser
Authors: Bour D. P. , Shealy J. R.
Published: July 2002

Pulsed operation of an AlGaInP graded-index separate confinement heterostructure laser grown by organometallic vapor phase epitaxy is reported. The laser active region consists of a single 100 Å Ga0.5In0.5P quantum well and 1600 Å graded index regions on both sides of the well. The graded index regions were produced by lattice-matched graded composition (AlyGa1−y)0.5In0.5P quaternary alloys. This structure reduces the broad-area threshold current compared to a double heterostructure laser, with pulsed thresholds as low as 1050 A/cm2. Total pulsed power of 1.4 W at 658 nm is available from an 80 μm×300 μm mesa-stripe laser. A differential quantum efficiency of ∼56% is measured. By examining the cavity length dependence of the threshold current density and quantum efficiency, it is apparent that the quantum well gain has not saturated in these structures. This suggests that devices containing a thinner single quantum well active region may result in a further reduction in threshold current density for visible lasers.
Relation between chirp and linewidth reduction in external Bragg reflector semiconductor lasers
Authors: Olsson N. A. , Henry C. H. , Kazarinov R. F. , Lee H. J. , Johnson B. H.
Published: July 2002

A 1.5-μm single longitudinal mode semiconductor laser, formed by butt coupling an external Bragg reflector to a standard Fabry–Perot laser, is shown to have greatly reduced wavelength chirp and emission linewidth. The linewidth reduction is found to be proportional to the square of the chirp reduction, in agreement with a previous theoretical prediction. The linewidth and chirp reduction factor can be varied by changing the operating point of the laser. With a 3-mm-long Bragg reflector, a linewidth of 1 MHz at 5 mW has been achieved.
Zn-diffusion-induced intermixing of InGaAs/InP multiple quantum well structures
Authors: Nakashima Kiichi , Kawaguchi Yoshihiro , Kawamura Yuichi , Imamura Yoshihiro , Asahi Hajime
Published: July 2002

The intermixing process of InGaAs/InP multiple quantum well structures by Zn diffusion at 550 °C is investigated. Secondary ion mass spectroscopy and x-ray analysis reveal that Zn diffusion induces the intermixing of group III atoms, but has little effect on group V profiles. However, resulting group III atom profiles are not completely uniform even after Zn diffusion. These results suggest that large lattice mismatch suppresses the intermixing process by Zn diffusion.
Room-temperature observation of resonant tunneling through an AlGaAs/GaAs quasiparabolic quantum well grown by molecular beam epitaxy
Authors: Chou S. Y. , Harris J. S.
Published: July 2002

We report the first room-temperature observation of resonant tunneling through a double-barrier diode with a 31.5-nm-wide AlGaAs/GaAs quasiparabolic quantum well grown by molecular beam epitaxy. As the bias voltage is scanned from 0 to 4 V, 11 resonant tunneling transitions are observed at room temperature. At 77 K, 13 resonant tunneling transitions are observed; 10 of them show negative differential resistance, and the highest peak-to-valley ratio is 1.4. At 4.2 K, 17 resonant tunneling transitions are observed; 15 of them show negative differential resistance, and the peak-to-valley ratio of the first tunneling peak is 3.6. Computer simulation indicates that for the 17 resonant tunneling transitions, the first 13 are likely due to resonant tunneling through quasibound states in the well, and the remainder are due to resonant tunneling through virtual states.
Shear-limited flux pinning studied in superconducting thin-film devices
Authors: Pruymboom A. , Kes P. H. , van der Drift E. , Radelaar S.
Published: July 2002

We report critical-current measurements on superconducting devices containing nanometer-scale artificially structured channels of low pinning which simulate microstructures in technical superconductors. Our observations uniquely demonstrate the role of the grain morphology for flux pinning in polycrystalline materials. The results are in very good agreement with a continuum model for the shear-limited pinning force.
Ultrahigh power 38 W continuous-wave monolithic laser diode arrays
Authors: Sakamoto M. , Welch D. F. , Harnagel G. L. , Streifer W. , Kung H. , Scifres D. R.
Published: July 2002

Continuous-wave output power levels of 38 W from one facet have been obtained from a 1 cm monolithic AlGaAs laser array with a 2 mm total active aperture width. One of the diodes has been operated under constant current conditions (initial output power of 5 W) at room temperature for over 1100 h.
Enhanced wear resistance by compressive strengthening: A novel combination of laser and ion implantation technology
Authors: De Beurs H. , De Hosson J. Th. M.
Published: July 2002

In general, neon implantation is not very effective in reducing wear rates. However, neon implantation into laser-melted steel turns out to reduce the wear rate substantially as a result of a conversion of residual tensile stresses into compressive ones. Nitrogen implantation, on the other hand, at a high dose of 3×1017 ions/cm2 at 90 °C exhibits a deleterious effect on the wear performance. A brittle layer of ε-Fe2(C,N)1−x nitrides is formed. At a lower dose of 1×1017/cm2 or implantation of nitrogen at 150 °C, the wear rate is also reduced.
Etching and cathodoluminescence studies of ZnSe
Authors: Clausen E. M. , Craighead H. G. , Tamargo M. C. , de Miguel J. L. , Schiavone L. M.
Published: July 2002

Epitaxial thin films of ZnSe grown on GaAs substrates were reactive ion etched using BCl3 /Ar gas mixtures. Using an optimized etching process, photolithographically defined micrometer sized structures were etched several micrometers deep with straight sidewalls and smooth surfaces. Cathodoluminescence was measured from both etched and unetched surfaces at room temperature. Luminescence intensities of etched surfaces are shown not to be degraded by the reactive ion etching process. Cathodoluminescence intensities of etched pixels with exposed sidewalls were found to be greater than the intensities measured from unetched flat surfaces. This suggests the possibility of efficient etched light-emitting structures.