bluuebunny/crossref_metadata_2025 huggingface dataset:
The behavior of hyperbolic heat equations’ solutions near their parabolic limits
Authors: Nagy Gabriel B. , Ortiz Omar E. , Reula Oscar A.
Published: July 2002

Standard energy methods are used to study the relation between the solutions of one parameter families of hyperbolic systems of equations describing heat propagation near their parabolic limits, which for these cases are the usual diffusive heat equation. In the linear case it is proven that given any solution to the hyperbolic equations there is always a solution to the diffusion equation which after a short time stays very close to it for all times. The separation between these solutions depends on the square of the ratio between the assumed very short decay time appearing in Cattaneo’s relation and the usual characteristic smoothing time (initial data dependent) of the limiting diffusive equation. The techniques used in the linear case can be readily used for nonlinear equations. As an example we consider the theories of heat propagation introduced by Coleman, Fabrizio, and Owen, and prove that near a solution to the limiting diffusive equation there is always a solution to the nonlinear hyperbolic equations for a time which usually is much longer than the decay time of the corresponding Cattaneo relation. An alternative derivation of the heat theories of divergence type, which are consistent with thermodynamic principles, is given as an appendix.
New methods and structures in the theory of the multi-mode Dicke laser model
Authors: Alli Giovanni , Sewell Geoffrey L.
Published: July 2002

We base a treatment of the dissipative, multi-mode version of Dicke laser model on the theory of completely positive dynamical semigroups and quantum Markov processes. This leads to new results at both the mathematical and physical levels. On the physical side, it provides a generalization of the Hepp–Lieb model that admits both chaotic and polychromatic laser radiation. On the mathematical side, it extends the theory of dynamical semigroups to a regime where the generators are perturbed by unbounded derivations.
Derivation of conservation laws from nonlocal symmetries of differential equations
Authors: Anco Stephen C. , Bluman George
Published: July 2002

An identity is derived which yields a correspondence between symmetries and conservation laws for self-adjoint differential equations. This identity does not rely on use of a Lagrangian as needed to obtain conservation laws by Noether’s theorem. Moreover, unlike Noether’s theorem, which can only generate conservation laws from local symmetries, the derived identity generates conservation laws from nonlocal as well as local symmetries. It is explicitly shown how Noether’s theorem is extended by the identity. Conservation laws arising from nonlocal symmetries are obtained for a class of scalar wave equations with variable wave speeds. The constants of motion resulting from these nonlocal conservation laws are shown to be linearly independent of all constants of motion resulting from local conservation laws.
Quantization of minisuperspaces as ordinary gauge systems
Authors: Simeone Claudio
Published: July 2002

Simple cosmological models are used to show that gravitation can be quantized as an ordinary gauge system if the Hamilton–Jacobi equation for the model under consideration is separable. In this situation, a canonical transformation can be performed such that in terms of the new variables the model has a linear and homogeneous constraint, and therefore canonical gauges are admissible in the path integral. This has the additional practical advantage that gauge conditions that do not generate Gribov copies are then easy to choose.
Quantum diffusion and tunneling in the solid hydrogens (a short review)
Authors: Meyer Horst
Published: July 2002

The first observations 30 years ago of molecular clustering via quantum diffusion in solid H2 in nuclear magnetic resonance (NMR) and pressure experiments are described. A previous review on quantum diffusion and tunneling up to 1986 is updated to reflect progress in the last ten years. In particular I review the effect of clustering on heat capacity in solid D2 and on the thermal conductivity in solid H2. The configurational relaxation time observed in D2 at 1.75 K is found to scale with that in H2 at the same temperature in terms of the predictions of ortho–para resonant conversion-induced hopping. The relaxation times measured simultaneously on the same sample in NMR and conductivity experiments reflect different configurational processes. The theory of molecular hopping and pairing in solid H2 is outlined and compared with experiments. The tunneling frequency of HD in solid H2 deduced from transverse and longitudinal NMR relaxation experiments between 0.03 and 14 K is discussed. The hopping of ortho-H2, invoked as a mechanism in the enhanced ortho–para conversion in presence of O2 impurities, is mentioned. Finally, recent tunneling results for H, D and H2− anions in solid H2 during the studies of low temperature reaction dynamics are also briefly described. In the Appendix, the hopping frequency determination in HD from NMR transverse relaxation time measurements is reviewed.
Rayleigh–Taylor instability in thin viscous films
Authors: Yiantsios Stergios G. , Higgins Brian G.
Published: July 2002

The behavior of a viscous fluid film bounded by a wall and a heavier overlying immiscible phase is examined in the limit of small Bond number. Evolution equations governing the behavior of the interface between the two fluids are derived for spatially periodic disturbances and studied numerically. The analysis shows that instability leads to a spectrum of steady-state interfacial shapes characterized by film rupture and formation of pendant drops, such that gravity and interfacial forces are in balance. An energy stability analysis reveals that one drop per wavelength is the most energetically favorable. An extension of the analysis, based on the boundary integral method, is described for arbitrary Bond number and creeping flow conditions, aimed at identifying a Bond number below which stable pendant drops are possible. Simulations are shown for Bond numbers in the range 0.4≤B≤10 for fluids of equal viscosity. When the Bond number is relatively large, the interface takes the form of a circular front that penetrates into the overlying fluid, followed by a trailing plume. A critical Bond number is found, which leads to steady-state shapes in the form of pendant drops, confirming the predictions of the asymptotic analysis.
Rarefied gas flow through a slit
Authors: Hasegawa Manabu , Sone Yoshio
Published: July 2002

A rarefied gas flow through a slit in an infinite plane wall, induced by a small pressure difference across the slit, is studied on the basis of the kinetic theory. The system of integral equations for the macroscopic variables (the velocity, density, and temperature of the gas), derived from the linearized Boltzmann–Krook–Welander equation with the diffuse reflection boundary condition, is solved by constructing the Neumann series numerically. The flow velocity, density, and temperature fields of the gas as well as the mass flux through the slit are obtained with good accuracy for various Knudsen numbers. The correction to the free molecular flow result for large but finite Knudsen numbers is also obtained analytically, which gives a continuous transition from the free molecular flow to the present numerical result.
A purely elastic instability in Dean and Taylor–Dean flow
Authors: Joo Yong Lak , Shaqfeh Eric S. G.
Published: July 2002

The linear stability of the viscoelastic flow of an Oldroyd-B fluid between rotating cylinders with an applied, azimuthal pressure gradient is considered. It is found that this Taylor–Dean flow is unstable in certain flow parameter regimes even in the limit of vanishingly small Reynolds number. The critical conditions and the structure of the vortex flow at the onset of instability are presented. These are determined in the limit as the channel width to radius of curvature becomes small. The present results reveal that the instability is a stationary mode when the pressure gradient becomes the dominant flow driving force, while it is an oscillatory instability when the shearing by the cylinder rotation is dominant. In addition, it is found that the direction of the pressure gradient controls the characteristics of the instability: A pressure gradient applied along the cylinder rotation destabilizes the flow, while if applied against the rotation, the flow is substantially stabilized. The mechanism of these instabilities is also investigated through an examination of the disturbance-energy equation. It is found that the mechanism of the elastic, stationary instability is associated with the coupling of the perturbation velocity field to the polymeric stree gradients in the base flow. To the authors’ knowledge this mechanism has not been reported elsewhere. In contrast, the mechanism for the elastic, oscillatory instability in Taylor–Dean flow involves the coupling between the disturbance polymeric stresses and the base state velocity gradients, as reported by Larson et al. [J. Fluid Mech. 218, 573 (1990)] for the elastic, oscillatory instability in Taylor–Couette flow.
Localized receptivity of boundary layers
Authors: Crouch J. D.
Published: July 2002

The boundary-layer receptivity resulting from acoustic forcing over a flat plate with a localized surface irregularity is analyzed using perturbation methods. The length-scale reduction, essential to acoustic receptivity, is captured within the framework of the classical stability theory. At first order, two disturbances are calculated: an unsteady disturbance resulting from the acoustic forcing and a steady disturbance resulting from the surface irregularity. These disturbance fields interact at second order to produce a traveling-wave field bearing the frequency of the acoustic wave and wave numbers associated with Fourier components of the surface irregularity. Components of the traveling-wave field scale linearly with both the acoustic forcing and the height of the surface irregularity. Receptivity occurs when the frequency and wave number of a traveling-wave component perfectly match the local eigenmode. Results are in general agreement with asymptotic analyses for irregularities in the neighborhood of branch I. Downstream of branch I, the current results show significant deviations from the asymptotic theory. Comparisons to experiments show good agreement for receptivity amplitudes when the height of the surface irregularity is small.
Time-dependent simulation of weakly nonideal plasmas in electrothermal launchers
Authors: Mohanti R. B. , Gilligan J. G. , Bourham M. A.
Published: July 2002

Simulation of electrothermal launchers is extended to include nonideal plasma effects. The simulation is compared to experimental data obtained from the SIRENS facility, for the measurable quantity of ablation depth as a function of the input discharge energy [IEEE Trans. Plasma Sci. PS-17, 386 (1989)]. The plasma model for nonideal plasma is based on the evaluation of a non-Debye radius due to incomplete screening of the shielding cloud around a charged particle. The consistent and necessary transport and thermodynamic functions for weakly nonideal plasmas are included in the time-dependent set of governing equations. In this paper a semiempirical scaling law for the fraction of blackbody radiation that is transmitted through the ablating vapor for Lexan insulators under high heat flux conditions is also presented.
Kinetic effects on the velocity-shear-driven instability
Authors: Wang Z. , Pritchett P. L. , Ashour-Abdalla M.
Published: July 2002

A comparison is made between the properties of the low-frequency, long-wavelength velocity-shear-driven instability in kinetic theory and magnetohydrodynamics (MHD). The results show that the removal of adiabaticity along the magnetic field line in kinetic theory leads to modifications in the nature of the instability. Although the threshold for the instability in the two formalisms is the same, i.e., VA∥<V0<Cs, the kinetic growth rate and the unstable range in wave-number space can be larger or smaller than the MHD values depending on the ratio between the thermal speed, Alfvén speed, and flow speed. When the thermal speed is much larger than the flow speed and the flow speed is larger than the Alfvén speed, the kinetic formalism gives a larger maximum growth rate and broader unstable range in wave-number space. In this regime, the normalized wave number (kL) for instability can be larger than unity, while in MHD it is always less than unity. The normal mode profile in the kinetic case has a wider spatial extent across the shear layer.
Test particle transport in stochastic magnetic fields modeled by stochastic processes
Authors: Hannibal Ludger
Published: July 2002

The theory of stochastic processes is applied to analyze the effect of magnetic-field perturbations on the motion of classical charged particles. For arbitrary field fluctuations along the path of a particle, an approximate diffusion equation is obtained by means of the cumulant technique. The limit of white noise, in which the model is exact, and the difference between adiabatic and nonadiabatic motion are discussed. These cases relate results obtained for astrophysical plasmas and tokamak plasmas. It is shown that large longitudinal perturbations give rise to a new regime for diffusion perpendicular to the mean magnetic field.
Effects of a weak ion beam on grid-launched ion-acoustic waves
Authors: Raychaudhuri Santwana , Lonngren Karl E.
Published: July 2002

Experimentally observed multiple ion-acoustic wave excitation in a weak ion beam plasma system is described. An additional anomalous signal was observed to form and propagate hundreds of Debye lengths from the grid in a large quiescent plasma. The existence of this signal is interpreted to be caused by the grid excitation mechanism, and it can be used to ascertain the dimension of the sheath surrounding the grid.
Nonlinear saturation of single-mode trapped ion instability
Authors: Kim S. Y. , Sen A. K.
Published: July 2002

The trapped ion instability appears as a single mode in the Columbia Linear Machine and is expected to appear as such in tandem mirrors. Using three-wave, nonresonant mode coupling of radially nonlocal eigenfunctions, two mode-coupling equations for the unstable fundamental and stable first-order radial harmonics are derived and solved. Mode coupling to the damped higher-order radial harmonics is the principal physical saturation mechanism of the unstable fundamental mode.
Expansion of dense particle clouds in magnetically confined plasmas
Authors: Lengyel L. L.
Published: July 2002

A single-cell Lagrangian model has been developed for calculating the ionization and expansion dynamics of high-density clouds in magnetic fields or in magnetically confined plasmas. The model was tested by means of data from magnetospheric barium cloud experiments and approximately reproduced such global characteristics as expansion rate, stopping radius, stopping time, and magnetic cavity lifetime. Detailed calculations were performed for hydrogen clouds associated with the injection of frozen hydrogen pellets into tokamak plasmas. The dynamic characteristics of the cloud expansion, such as ionization radius, stopping time, lifetime, oscillation frequencies, and amplitudes, etc., are computed as functions of the magnetic field strength, the background plasma temperature, and the cloud mass. The results are analyzed and compared with experimental observations.
An experimental observation of low-dimensional dynamics in an open channel flow
Authors: Madden F. N. , Mullin T.
Published: July 2002

We present the results of an experimental study of dynamical phenomena in the fluid flow through a symmetric nominally two-dimensional channel expansion. The particular phenomena of interest are observed as a result of modulating the flow rate through the system. In the absence of modulation, the flow downstream of the expansion is found to be steady at low Reynolds numbers. It then loses stability to a high-dimensional dynamical state for Reynolds numbers above a critical value. However, when a small periodic modulation is added to the flow rate new low-dimensional dynamical phenomena emerge. In some parameter ranges this novel temporal behavior arises at Reynolds numbers below those at which the transition to irregular fluid flow occurs in the unforced system. In other regions of parameter space the low-dimensional dynamics suppress the irregular flow of the unforced system. Moreover, the dynamics are organized by the underlying solution structure and show evidence for a subharmonic resonance, quasiperiodicity, and homoclinicity.
Rarefied gas flow through a slit. Influence of the boundary condition
Authors: Sharipov Felix
Published: July 2002

A rarefied gas flow through a thin slit caused by a small pressure difference is studied on the basis of the kinetic equation. The Bhatnagar–Gross–Krook model equation is solved numerically by the optimized discrete velocity method. The gas–surface interaction is assumed diffuse-specular. It is shown that the dependence of the mass flow rate on the gas–surface interaction law is negligibly small at any Knudsen number. Analytical formulas for the flow rate embracing the whole range of the Knudsen number are obtained.
Convective instability boundary of Couette flow between rotating porous cylinders with axial and radial flows
Authors: Kolyshkin A. A. , Vaillancourt Rémi
Published: July 2002

The convective instability boundary of a circular Couette flow in the annular region bounded by two co- or counter-rotating coaxial cylinders with angular velocities ω1 and ω2, respectively, is studied in the presence of an axial flow due to a constant axial pressure gradient and a radial flow through the permeable walls of the cylinders. A linear stability analysis is carried out for positive and negative radial Reynolds numbers corresponding to outward and inward radial flows, respectively. Axisymmetric and non-axisymmetric disturbances are considered. In the particular case of no axial flow, the Couette flow is stabilized by an inward, or a strong outward, radial flow, but destabilized by a weak outward radial flow. Non-axisymmetric disturbances lead to instability for some negative values of μ=ω2/ω1. Bifurcation diagrams for combined radial and axial flows are more complicated. For particular values of the parameters of the problem, the Couette flow has regions of stabilization and destabilization in the parameter space. Computational results are compared with experimental data.
Numerical prediction of laminar, transitional and turbulent flows in shrouded rotor-stator systems
Authors: Randriamampianina A. , Elena L. , Fontaine J. P. , Schiestel R.
Published: July 2002

The paper deals with numerical prediction of laminar, transitional and turbulent regimes in confined flow between rotating and stationary discs. For the laminar and transitional flows, a spectral tau-Chebyshev method associated with a multistep time scheme is used. This approach allows accurate prediction of the two laminar regimes mentioned by Daily and Nece (1960) in their experimental studies. For the geometry under consideration (1/11 aspect ratio), the transition to unsteady motion occurs abruptly without any oscillatory behavior. Thus, the instabilities develop in a region localized near the external shroud, primarily along the stator side, according with experimental findings. For calculating turbulent flow regimes, one point second-order transport modeling has been implemented in a finite volume code. The superiority of advanced Reynolds stress transport models over the classical k−ε model is decisive for predicting such a complex flow. This is particularly important in order to get a precise delineation of the adjacent turbulent and relaminarized regions within the cavity. This level of closure was crucial to produce numerical results in good agreement with experimental data.
Kinetic theory and molecular dynamics simulations of microscopic flows
Authors: Din Xue-Dong , Michaelides Efstathios E.
Published: July 2002

This study aims at the understanding of the viscosity distributions near a solid wall in microscopic pores. The pair-correlation function is derived from the density distribution function, which in itself is obtained from molecular dynamics simulations. The revised Enskog equation for the shear flow of strongly inhomogeneous hard-sphere fluids is solved by the Chapman–Enskog method and the viscosity coefficients are obtained by keeping all the high-order derivatives of the density and pair-correlation functions. The molecular dynamics method is used in order to simulate the Couette flow of a Lennard-Jones fluid in a micropore, with weak or strong wall–fluid interactions. Under the weak interaction, slip is observed near the wall and the fluid in the contact layer exhibits higher viscosity than the fluid in other regions. Under the strong interaction, a layer of fluid always adhered to the wall is observed. A low viscosity valley often exists next to the high viscosity region, where apparently the flow commences. It is observed that the molecular dynamics simulations predict higher viscosity than the kinetic theory of the hard-sphere model, as it is expected. However, the distributions obtained from both methods are in qualitative agreement. The present study suggests that, provided the bulk viscosity and appropriate boundary conditions are used, the Navier–Stokes equations are valid at a distance of two to three molecular layers from the wall.
Statistics and structures of pressure in isotropic turbulence
Authors: Cao Nianzheng , Chen Shiyi , Doolen Gary D.
Published: July 2002

Statistics and structures of pressure in three-dimensional incompressible isotropic turbulence are studied using high-resolution direct numerical simulation for Taylor microscale Reynolds numbers up to 220. It is found that the probability distribution function (PDF) of pressure has negative skewness due to both kinematic and dynamic effects, in contrast to the statistics of the pressure head, whose PDF is almost symmetric. The statistical relations among pressure, vorticity, dissipation and kinetic energy are investigated using conditional averaging. The averaged pressure, conditional on the local enstrophy, shows a linear dependence on enstrophy in the high-enstrophy region. Structure relations between pressure and other physical quantities are qualitatively examined using three-dimensional visualization of iso-surfaces. It is found that the high-vorticity regions are strongly correlated with the low-pressure regions. However, it appears that experimental visualization techniques for detecting high-intensity vortices using microbubbles in low-pressure regions might only be valid for those very-high-vorticity regions where the local enstrophy is at least five times higher than the root mean square enstrophy. The scaling law of the pressure structure function is also presented for both conventional and extended self-similarity. It is found that the pressure increment, δrp, scales with the velocity increment, δru, for the Reynolds numbers studied: δrp∼δru. For flows at moderate Reynolds numbers, it is demonstrated that the extended self-similarity gives better pressure scalings than results from traditional similarity solutions.
Strong collisions and response function for two-component plasmas
Authors: Röpke G. , Redmer R. , Wierling A. , Reinholz H.
Published: July 2002

The dielectric function for a two-component (hydrogen) plasma at arbitrary degeneracies is considered in the entire (k,ω)-space. Applying a generalized linear response theory, it is expressed in terms of determinants of equilibrium correlation functions which allow for a systematic perturbative treatment. The relation to dynamical local-field factors is given. Collisions are treated in Born approximation leading to a (k,ω)-dependent collision integral. The link to the conductivity is given in the long-wavelength limit. Strong collisions are included in the frequency dependent conductivity. Sum rules are discussed.
Multi-layered flyer accelerated by laser induced shock waves
Authors: Tanaka Kazuo A. , Hara Motohiko , Ozaki Norimasa , Sasatani Yasufumi , Anisimov Sergei I. , Kondo Ken-ichi , Nakano Motohiro , Nishihara Katsunobu , Takenaka Hisataka , Yoshida Masatake , Mima Kunioki
Published: July 2002

Multi-layered flyer (aluminum–polyimide–tantalum) is designed as a high speed flyer making use of shock impedance matching and reverberation techniques. The designed three layered targets have been irradiated using a 20 J laser beam. Flyer velocities are measured by observing the flyer impact emissions on glass step targets within a 500 μm laser focal spot at laser intensities 5×1012–2×1013 W/cm2. Thin (0.5–1.0 μm) Ta layers of the flyers are accelerated via shock reverberations between the thick polyimide and thin Ta layers for the first time using laser induced shock waves. Their velocities are measured to be more than 13 km/s with a good hydrodynamic stability. The obtained velocity is faster than the ones obtained by a conventional flyer method such as a double gas gun.
Nuclear fusion in gases of deuterium clusters heated with a femtosecond laser
Authors: Ditmire T. , Zweiback J. , Yanovsky V. P. , Cowan T. E. , Hays G. , Wharton K. B.
Published: July 2002

Recent experiments on the interaction of intense, ultrafast pulses with large van der Waals bonded clusters have shown that these clusters can explode with substantial kinetic energy. Producing explosions in deuterium clusters with a 35 fs laser pulse, deuterium ions were accelerated to sufficient kinetic energy to drive deuterium–deuterium (DD) nuclear fusion. By diagnosing the fusion yield through measurements of 2.45 MeV fusion neutrons, over 104 neutrons per laser shot were measured when 100 mJ of laser energy is used.
Photoluminescence of a Cd0.55Mn0.45Te-CdTe multiple quantum well structure in a magnetic field
Authors: Petrou A. , Warnock J. , Bicknell R. N. , Giles-Taylor N. C. , Schetzina J. F.
Published: July 2002

The photoluminescence of a Cd0.55Mn0.45 Te-CdTe multiple quantum well structure grown by molecular beam epitaxy has been studied. Both emission and excitation spectra were obtained at T=1.8 K and T=70 K with the specimen in a magnetic field ranging from 0 to 15 T.
Amorphous carbon coatings prepared by high rate rf plasma deposition from fluorinated benzenes
Authors: Sah R. E. , Dischler B. , Bubenzer A. , Koidl P.
Published: July 2002

Amorphous carbon films were prepared by radio frequency plasma deposition from benzene and fluorinated benzenes: C6H6−mFm with m=0–6. The films have been characterized spectroscopically. The infrared spectrum shows that besides hydrogen, fluorine is incorporated in the films. With increasing m the concentration of fluorine in the film increases while the amount of chemically bonded hydrogen decreases and vanishes for m>3. The properties of these hydrogenated fluorinated amorphous carbon films (a-C:H,F) are qualitatively similar to those of hard carbon coatings (a-C:H) prepared from benzene. However, the deposition rate has been found to rise significantly (up to 900 nm min−1) with increasing fluorine content, m, in the substituted benzene. Optical data and protective properties of the films are reported.
Failure temperature of amorphous Cu-Ta alloys as diffusion barriers in Al-Si contacts
Authors: Saris F. W. , Hung L. S. , Nastasi M. , Mayer J. W. , Whitehead B.
Published: July 2002

Self-supporting films of amorphous Cu20Ta80 alloys have a crystallization temperature as high as 800 °C, yet they fail as diffusion barriers in aluminum-silicon contacts at much lower temperature because of compound formation. On Si(100) the a-Cu20Ta80 films react above the temperature at which TaSi2 forms (650 °C). In contact with aluminum, Al3Ta starts to form at 500 °C, which is also the failure temperature of a-Cu20T80 as diffusion barrier between Al and Si(100). The reaction characteristics of the barrier constituents with the surrounding elements as well as the crystallization temperature determine the thermal stability of amorphous alloy diffusion barriers.
Rapid thermal annealing of Al-Si contacts
Authors: Pai C. S. , Cabreros E. , Lau S. S. , Seidel T. E. , Suni I.
Published: July 2002

Contact formation of Al on n+-Si by rapid thermal annealing has been investigated. It was found that contact resistivity of the order of 6×10−7 Ω cm2 can be reproducibly achieved. The uniformity of the contact area morphology is much improved due to the limited Si migration into the Al metallization. Flat contact morphology can be obtained with a combined technique of ion mixing and rapid thermal annealing.
Capless annealing of ion implanted GaAs in automatically evaporated vapor
Authors: Lee C. T.
Published: July 2002

A simplified automatic vapor capless annealing technique for ion implanted GaAs wafers is demonstrated. The basic method is to put an implanted GaAs wafer in a partially sealed quartz crucible which is filled with GaAs powder. The measured Hall mobility of the implanted sample annealed by this method is almost the same as those obtained by the other usual annealing methods, but the transition region can be reduced significantly. Furthermore, the surface morphology is better than that obtained by dielectric encapsulant annealing methods.
Role of resonant laser enhanced surface kinetics in the low substrate temperature molecular beam epitaxial growth of compound semiconductors: A Monte Carlo study
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

The role of resonant laser enhanced cation surface kinetics in low-temperature molecular beam epitaxial (MBE) growth of compound semiconductors is examined using Monte Carlo techniques. At low temperature, due to reduced cation surface migration, conventional MBE growth produces films with rough surfaces and consequently heterojunctions with rough interfaces. Resonant coupling of photons to bonds of cations at nonkink sites of the growing surface can enhance the cation surface migration rate and thus produce films with smooth surfaces and sharp interfaces. Results of our simulations are presented to establish the potential of resonant laser enhanced surface migration in the MBE growth of compound semiconductors and conditions necessary to achieve this potential are identified.
Raman spectroscopy of reactive ion etching induced subsurface damage
Authors: Tsang J. C. , Oehrlein G. S. , Haller Ivan , Custer J. S.
Published: July 2002

Raman spectroscopy has been used to characterize the surface modifications introduced into Si(100) by reactive ion etching with a CF4/H2 plasma. Both Raman scattering due to the destruction of crystalline long range order by lattice damage and the stretching modes of protons bonded to Si atoms have been observed without any special sample preparation. Our results are consistent with backscattering and nuclear reaction profiling studies of similarly prepared samples and Raman studies of Si(100) bombarded by low-energy protons and Ar ions.
Studies of Ag photodoping in GexSe1−x glass using microlithography techniques
Authors: Leung W. , Cheung N. W. , Neureuther A. R.
Published: July 2002

Using microlithographic techniques to define the Ag sensitized area, the lateral profile of Ag diffusion in GexSe1−x (x≊0.1) glass is made directly visible with an optical microscope. Experimental measurements have verified that Ag photodoping in Ge0.1Se0.9 glass obeys Fick’s diffusion law with a constant diffusivity. Light absorption in the Ag2Se region has little effect on Ag photodoping. Ag photodoping is caused mainly by light absorption in the Ge0.1Se0.9 near the boundary between the Ag-containing and the non-Ag-doped region. Light absorption in Ge0.1Se0.9 glass has a long range effect which causes Ag photodoping to occur even when light irradiation is away (up to 3 μm) from Ag-containing region.
Deep level photoluminescence commonly present in undoped Czochralski grown GaAs
Authors: Tajima Michio
Published: July 2002

Photoluminescence (PL) under the below band-gap excitation with the 1.32-μm line of a yttrium aluminum garnet laser has been measured for undoped, semi-insulating Czochralski grown GaAs crystals. A Gaussian band with a peak at 0.67 eV and a half-width of 120 meV has been found to appear commonly, regardless of the groups of crystals classified according to their dominant PL band measured under the above band-gap excitation. The occurrence of the PL fatigue effect, the positive correlation of the PL intensity with the dislocation density, and the spectral shape indicate that the main deep donor EL2 is involved in the transition responsible for the 0.67-eV band.
Silicon interstitial generation by argon implantation
Authors: Bronner G. B. , Plummer J. D.
Published: July 2002

In this letter we show that damaged layers in silicon created by argon implantation act as a source of silicon interstitials. This effect is shown to cause orders of magnitude increase in the diffusion coefficient of phosphorus at temperatures less than 800 °C. This creation of interstitials is shown to be long lasting. The value of this is discussed in understanding the role of point defects on dopant diffusion.
Fast shrinkage of oxidation-induced stacking faults in silicon at the initial stage of annealing in nitrogen
Authors: Nishi Kenji , Antoniadis Dimitri A.
Published: July 2002

The shrinkage of oxidation-induced stacking faults (OSF′s) in silicon has been studied in the temperature range of 950–1100 °C in nitrogen ambient. Abnormally fast OSF shrinkage with activation energy of 2.3 eV has been observed at the initial stage of annealing. This fast shrinkage regime becomes more pronounced as the annealing temperature is reduced. It is proposed that the fast OSF shrinkage rate is due to the fact that initially the shrinkage is dominated by the rate of self-interstitial capture at the silicon/silicon dioxide interface, while the subsequent lower rate with activation energy of 4.3 eV is due to the traditionally accepted diffusion-limited mechanism. Because of the difference in activation energies, as temperature increases above about 1100 °C the latter mechanism becomes dominant and the fast shrinkage regime disappears.
Fabrication and performance characteristics of 1.55-μm InGaAsP multiquantum well ridge guide lasers
Authors: Dutta N. K. , Wessel T. , Olsson N. A. , Logan R. A. , Koszi L. A. , Yen R.
Published: July 2002

We report the fabrication and performance characteristics of InGaAsP ridge waveguide lasers with multiquantum well (MQW) active layers emitting near 1.55 μm. The active region has four active wells (1.55 μm InGaAsP) and three barriers (1.3 μm InGaAsP). The thicknesses of the active wells and the barrier layers are ∼250 Å. The 360-μm-long lasers have threshold currents in the range 60–80 mA at 30 °C, external differential quantum efficiency ∼25% at 30 °C, and T0∼70 K. The modulation bandwidths of the lasers are ∼1.5 GHz and they exhibit less frequency chirping than similar lasers with conventional double heterostructure (DH) active layer. Since frequency chirp limits the performance of high bit rate long haul fiber communication system at 1.55 μm, we believe MQW lasers offer an advantage over conventional DH lasers.
Evidence for optical bistability in millimeter gas cells
Authors: Harrison R. G. , Al-Saidi I. A. , Cummins E. J. D. , Firth W. J.
Published: July 2002

Optical bistability, limiting, and other pulse shaping effects are observed in compact Fabry–Perot resonators containing SF6. The gas, in cells as short as 1 mm, is excited with smooth 100-ns transversely excited atmospheric CO2 laser pulses. The optical nonlinearity responsible for these effects is well described by a four-state kinetic model with unsaturable excited state absorption.
Optical diagnostics of positive column dc discharge by Rydberg state spectroscopy
Authors: Ganguly B. N. , Garscadden Alan
Published: July 2002

High resolution measurements of the Stark broadening of very high Rydberg 1P states in helium provide a resolution in electric field of approximately 1 V cm−1. The tunable laser-induced optogalvanic signal experiments were performed in a low pressure, low current discharge. The high sensitivity permits, for the first time, the net electric field to be obtained by a spectroscopic technique. The relative metastable density profile and indirectly, the electron density profile are also obtained from the magnitudes of the optogalvanic signals.
Lateral transport of hot electrons on a spherical target by 10.6-μm CO2 laser irradiation
Authors: Terai K. , Daido H. , Fujita M. , Miki F. , Nakai S. , Yamanaka C.
Published: July 2002

Lateral transport of hot electrons on a spherical target irradiated with two beams of CO2 laser (4.8×1014 W/cm2) is studied by spatially resolved Kα x-ray measurements. The hot-electron energy and spatial distribution in the target are found to depend on the method of irradiation: tight and overlapped focusing conditions.
Temporally resolved imaging of silicon surfaces melted with intense picosecond 1-μm laser pulses
Authors: Boyd Ian W. , Moss Steven C. , Boggess Thomas F. , Smirl Arthur L.
Published: July 2002

The reflectivity of crystalline silicon irradiated by intense 46-ps pulses at 1 μm has been measured using an optical pump-probe technique and also by imaging the irradiated sample surface on to a vidicon. We clearly resolve dramatic fluence-dependent reflectivity changes across the profile of the melted region that are consistent with rapid melting within the pulse duration and the formation of a superheated liquid layer.
Transmission electron microscopy of liquid phase epitaxial Hg1−xCdxTe layers on CdTe substrates
Authors: Wood Susan , Greggi J. , Takei W. J.
Published: July 2002

Epitaxial Hg1−xCdxTe films were grown on (111)A CdTe substrates by the tellurium solvent, horizontal tube slider liquid phase epitaxy technique. Their microstructures were subsequently investigated by both planar and cross-sectional transmission electron microscopy (TEM). Planar TEM showed the top surface of the films to be precipitate free with a general dislocation density <106/cm2 except for localized regions containing high dislocation densities associated with linear surface features on the Hg1−xCdxTe. Cross-sectional TEM showed the interface region to be nonplanar due to meltback during epilayer growth. A three-dimensional dislocation structure was confined to a band in the interface region having a graded Hg composition.
A new pulsed cryogenic proton source cooled by liquid helium
Authors: Takahashi T. , Horioka K. , Yoneda H. , Kasuya K.
Published: July 2002

A new cryogenic proton source with liquid helium cooling system is presented. The anode is cooled down to about 4.2 K. A hydrogen ice is produced on the surface and used as the ion source. Proton beams of a current density 21 A/cm2 at 200 kV are extracted with good reproducibility. This new ion source is expected to be a proton source without contamination by nonprotonic ions.
Light-hole conduction in InGaAs/GaAs strained-layer superlattices
Authors: Schirber J. E. , Fritz I. J. , Dawson L. R.
Published: July 2002

We report the first observation of light-hole band carriers in In0.2Ga0.8As/GaAs strained-layer superlattices by direct measurements of their effective mass (m*mo=0.14) using oscillatory magnetoresistance data. Preferential population of light-hole states, due to splitting of the degenerate bulk valence bands by built-in strain, allows this direct observation.
High efficiency 3-J mercury bromide discharge laser
Authors: Znotins T. A. , Fisher C. H. , DeHart T. E. , McDaniel J. P. , Ewing J. J.
Published: July 2002

Operation of a large volume x-ray preionized avalanche discharge mercury bromide laser is reported. Output energies in excess of 3 J have been obtained; the best efficiency is 2.1% at an output energy of 2.2 J.
Critical currents and flux cutting in thin superconducting films
Authors: Blamire M. G. , Evetts J. E.
Published: July 2002

Experiments have been performed on thin films with the magnetic field applied parallel to the sample current (the force-free state). Plots of the flux-flow critical current versus magnetic field show a pronounced temperature independent structure which is sensitive to the film thickness. This structure is interpreted in terms of flux vortex arrangements that are matched to the sample geometry. A flux-cutting model for the dynamic behavior of vortices in this system is proposed and shown to be in qualitative agreement with the results.
Very low threshold buried ridge structure lasers emitting at 1.3 μm grown by low pressure metalorganic chemical vapor deposition
Authors: Razeghi M. , Blondeau R. , Kazmierski K. , Krakowski M. , Duchemin J. P.
Published: July 2002

GaInAsP-InP buried ridge structure lasers emitting at 1.3 μm have been fabricated on material grown completely by low pressure metalorganic chemical vapor deposition. These lasers have low threshold (11 mA), exhibit linear (kink-free) light-current characteristics up to high powers (10 mW/facets), and can be operated at high temperatures (70 °C). Excellent uniformity over 10 cm2 has been obtained, and an external quantum efficiency of 60% for two faces has been measured.
Low-temperature ion beam mixing of Pt and Si markers in Ge
Authors: Kim Sung-Joon , Nicolet M-A. , Averback R. S. , Baldo P.
Published: July 2002

The mixing of Pt and Si marker atoms in Ge during 750-keV Xe irradiation was measured at temperatures between 6 and 500 K. The low-temperature measurements show that the mixing parameter for Pt is nearly twice that for Si. This result is in strong contradiction to the collisional theory of ion beam mixing. A weak temperature dependence in the mixing is found for both markers.
Effect of coupling gas viscosity on the photoacoustic signal
Authors: Korpiun P. , Büchner B. , Tam A. C. , Wong Y. H.
Published: July 2002

The phase angle φ of a gas-coupled photoacoustic (PA) signal has been measured as a function of coupling gas column thickness lg for a ‘‘one-dimensional’’ PA cell. The PA signal is excited by a modulated continuous laser beam incident on an opaque solid surface of silicon. We show that the observed data can be explained in a PA model including the consideration of a residual volume in the PA cell, together with the consideration of viscous damping of the PA signal at small lg.
Raman microprobe analysis of tungsten silicide
Authors: Codella Peter J. , Adar Fran , Liu Yung S.
Published: July 2002

The Raman spectrum of tungsten silicide has been observed and is reported for the first time. It was obtained on the MOLE■ Raman microprobe during the examination of an annealed sample of tungsten deposited over crystalline silicon. A similar examination of fine tungsten lines, 8 μm wide by 20 nm thick, selectively deposited on a crystalline silicon surface using laser-induced chemical vapor deposition techniques, produced an identical spectrum superimposed with that of the silicon substrate. This observation demonstrates the capability of the Raman microprobe to analyze the formation of solid silicide phases on a microscopic scale. The technique offers a rapid and nondestructive method for the identification of tungsten silicide either in the bulk or as a component in an integrated circuit.
Growth of molybdenum and tungsten on GaAs in a molecular beam epitaxy system
Authors: Bloch J. , Heiblum M. , Komem Y.
Published: July 2002

Thin films of Mo and W were grown on top of (100) GaAs in a molecular beam epitaxy system. Mo grew epitaxially between 200 and 450 °C with its (111) plane parallel to (100) GaAs plane. W grew as a random polycrystalline deposit. For both metals, interaction with the GaAs occurred during growth at 500 °C. Schottky barrier heights determined by current and capacitance measurements show that the electrical properties of the metal-GaAs interface do not strongly depend on the growth temperature and the microstructure of the films.
High resistivity InGaAs(Fe) grown by a liquid phase epitaxial substrate-transfer technique
Authors: Groves S. H. , Diadiuk V. , Plonko M. C. , Hovey D. L.
Published: July 2002

Reproducible growth of high quality InGaAs(Fe) by liquid phase epitaxy has been achieved by using long pregrowth bakes and a substrate-transfer apparatus. A mixed conduction model with fixed electron and hole mobilities is shown to explain the large variation of transport properties with Fe doping. This model predicts a maximum resistivity of 2500 Ω cm, and samples with resistivities within 5% of this value have been grown.
Excimer laser etching of Al metal films in chlorine environments
Authors: Koren G. , Ho F. , Ritsko J. J.
Published: July 2002

The etching of Al metal films on Si substrates in up to 1 Torr of Cl2 gas using the 308-nm XeCl laser pulses is reported. Etch rates of up to ∼1 μm per pulse were obtained which were laser fluence independent in the range 3≳φ≳0.25 J/cm2. The etch rates decreased, however, at high Cl2 pressures and high laser repetition rate. Processes such as redeposition of the ablated material and slowing down of the ablation at increased Cl2 pressures are considered as possible explanations of the observed results. By subsequently exposing the film to Cl2 and then irradiating it under vacuum, we found that the main etching mechanism is reaction in the absence of light to form an aluminum chloride layer followed by the ablation of this layer with the subsequent laser pulse.
Temperature dependence of the threshold of GaInAsP/InP surface emitting junction lasers
Authors: Uchiyama Seiji , Iga Kenichi
Published: July 2002

A GaInAsP/InP surface emitting (SE) laser has been fabricated with a round mesa structure. The minimum threshold current was 35 mA (77 K) and the operating temperature was raised to −21 °C. The characteristic temperature T0 was 100–120 K near 100 K, but decreased at higher temperatures. This is believed to be caused by the generation of heat at the p-side electrode. Room-temperature operation of the GaInAsP/InP SE laser is expected upon solving the ohmic contact problem.
Doppler shifted cyclotron maser radiation pumped by an asymmetric undulator
Authors: Shraga I. , Leibovitch C. , Eckhouse S. , Goren Y. , Gover A.
Published: July 2002

Super-radiant microwave emission pumped by the second harmonics of an asymmetric undulator has been investigated. Intense emission of TE mode electron cyclotron maser radiation was detected near the cyclotron resonance. It has been shown that an asymmetric undulator can be a suitable tool in producing high-frequency intense microwave radiation without any change in its fundamental period.
Acoustic Lamb wave-electric field nonlinear interaction in Y
Z LiNbO3 plates
Authors: Palma A. , Palmieri L. , Socino G. , Verona E.
Published: July 2002

The nonlinear electroacoustic effect has been investigated for acoustic Lamb wave propagation in a YZ LiNbO3 plate under a uniform bias electric field. A theoretical model is briefly outlined, which shows how the effect can be interpreted in terms of second and third order material constants. The strength of the nonlinear interaction has been experimentally evaluated through measurements of the change in phase velocity of Lamb modes produced by the bias field. The experiments were performed in the frequency range 8–33 MHz on most of the Lamb modes excited in a 1.25-mm-thick plate by an interdigital transducer with a periodicity λ=0.396 mm. The results evidence a strong dependence of the nonlinear effect on the order and symmetry of the analyzed modes.
Microplasma characteristics in InP-In0.53Ga0.47As long wavelength avalanche photodiodes
Authors: Magnea N. , Petroff P. M. , Capasso F. , Logan R. A. , Foy P. W.
Published: July 2002

Characterization of microplasmas has been performed on InP-In0.53Ga0.47As avalanche photodiodes using electron induced current and low-temperature cathodoluminescence measurements. Microplasmas are shown to be associated with a local increase of the electric field resulting from doping fluctuations which are tentatively associated with impurity segregation at crystal imperfections.