bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma heating in reversed field pinches at the fundamental ion cyclotron frequency
Authors: Svidzinski V. A. , Prager S. C.
Published: July 2002

The possibility of plasma heating in reversed field pinches (RFP) by radio-frequency (rf) waves at ω≈ωci is studied. A simple cylindrical RFP equilibrium which is symmetric in poloidal and axial directions is considered. RF fields are excited with given poloidal and axial wave numbers by a model antenna. The plasma dielectric properties are described by a hot plasma dielectric tensor in the limit of zero Larmor radius. Collisionless absorption by plasma ions is assumed. The power deposition distribution in the plasma is examined for different plasma parameters. Results demonstrate that effective heating of the central part of the plasma at ω≈ωci is possible for some range of parameters when the m=−1 poloidal mode is excited. This is a hot plasma effect; it disappears in the cold plasma limit.
A biased Monte Carlo technique for calculation of the density of states of polymer films
Authors: Jain Tushar S. , de Pablo Juan J.
Published: July 2002

A new Monte Carlo algorithm is implemented for simulation of the density of states of free-standing polymer films. The algorithm combines the original idea of conducting a random walk in energy space with advanced trial moves such as configurational bias and end-bridging. Excellent agreement is found between the results of this new method and those from simulations in the canonical ensemble, down to temperatures in the vicinity of the apparent glass transition. The efficiency of the new algorithm is studied as a function of the types of trial moves employed. It is found that, depending on the range of energy and density, certain localized moves fail to converge to the correct distribution of states.
Using masks to obtain uniform ion etch rates
Authors: Gnanarajan S.
Published: July 2002

For milling over large areas there is need for broad ion beam sources with a uniform etch rate profile. Currently uniform ion beam density is obtained in the central portion of the ion source by manipulating the grids and the magnets in the ion source. We have designed and implemented specially shaped hard masks to a rotating substrate holder. This mask is able to transform the Gaussian etch rate profile of a 150-mm-diam Oxford ion source to a flat profile. The flat profile decreases the etch rate in the central portion while maintaining the same etch rate along the edge. The deviation in the ion beam etch rate is within 5% in the flat region.
Simulation of short-chain polymer collapse with an explicit solvent
Authors: Polson James M. , Zuckermann Martin J.
Published: July 2002

We study the equilibrium behavior and dynamics of a polymer collapse transition for a system composed of a short Lennard-Jones (LJ) chain immersed in a LJ solvent for solvent densities in the range of ρ=0.6–0.9 (in LJ reduced units). The monomer hydrophobicity is quantified by a parameter λ∈[0,1] which gives a measure of the strength of attraction between the monomers and solvent particles, and which is given by λ=0 for a purely repulsive interaction and λ=1 for a standard LJ interaction. A transition from the Flory coil to a molten globule is induced by increasing λ. Generally, the polymer size decreases with increasing solvent density for all λ. Polymer collapse is induced by changing the hydrophobicity parameter from λ=0 to λ⩾0.5, where the polymer is in a molten globule state. The collapse rate increases monotonically with increasing hydrophobicity and decreases monotonically with increasing solvent density. Doubling the length of the chain from N=20 to N=40 monomers increases the collapse time roughly by a factor of 2, more or less independent of the hydrophobicity and solvent density. We also study the effect of conformational restrictions on polymer collapse using a chain model in which the bond angles are held near 109.5° using a stiff angular harmonic potential, but where free internal rotation is allowed, and find that the collapse times increase considerably with respect to the fully flexible polymer, roughly by a factor of 1.6–3.5. This increase is most pronounced for high solvent densities.
Radiation of horizontal electric dipole on large dielectric sphere
Authors: Margetis Dionisios
Published: July 2002

The electromagnetic field in air of a radiating electric dipole located below and tangential to the surface of a homogeneous, isotropic and optically dense sphere is studied anew. The starting point is the eigenfunction expansion for the field in spherical harmonics, which is now converted into series of integrals via the Poisson summation formula. A creeping-wave structure for all six components along the boundary is revealed that consists of waves exponentially decreasing through air and rays bouncing and circulating inside the sphere. The character of individual modes of propagation and the interplay between “electric” and “magnetic” types of polarization are investigated. Connections with and differences from standard ray optics and the cases of the radiating vertical dipole and scalar plane-wave scattering are outlined.
A simple weighted-density-functional approach to the structure of inhomogeneous fluids
Authors: Patra Chandra N. , Ghosh Swapan K.
Published: July 2002

A simple weighted-density-functional approach is developed for inhomogeneous fluids by approximating the excess free energy density functional by that of the corresponding uniform system evaluated at an effective density. This effective weighted density is obtained by a suitable local averaging procedure of the actual density distribution using a weight function which is evaluated only once at the bulk density, thus being decoupled from the weighted density. This approach does not involve any power series expansion or solution of any nonlinear differential equation at every point and each iteration, as is required in some of the analogous schemes. The new theory is applied to predict the structure of simple classical fluids, interacting with hard sphere, Coulombic as well as Yukawa potentials, under confinement in several geometries. The calculated results on the density profiles are shown to compare quite well with available simulation data.
Symmetric periodic solutions of the anisotropic Manev problem
Authors: Santoprete Manuele
Published: July 2002

We consider the Manev potential in an anisotropic space, i.e., such that the force acts differently in each direction. Using a generalization of the Poincaré continuation method we study the existence of periodic solutions for weak anisotropy. In particular we find that the symmetric periodic orbits of the Manev system are perturbed to periodic orbits in the anisotropic problem.
Multidimensional Schrödinger equations with Abelian potentials
Authors: Buchstaber V. M. , Eilbeck J. C. , Enolskii V. Z. , Leykin D. V. , Salerno M.
Published: July 2002

We consider two- and three-dimensional complex Schrödinger equations with Abelian potentials and a fixed energy level. The potential, wave function, and the spectral Bloch variety are calculated in terms of the Kleinian hyperelliptic functions associated with a genus two hyperelliptic curve. In the special case in two dimensions when the curve covers two elliptic curves, exactly solvable Schrödinger equations are constructed in terms of the elliptic functions of these curves. The solutions obtained are illustrated by a number of plots.
Path integral simulations of quantum Lennard-Jones solids
Authors: Chakravarty Charusita
Published: July 2002

Path integral simulations are used to study the thermodynamic and structural properties of quantum Lennard-Jones solids as a function of the degree of quantum delocalization or the de Boer parameter. Simulations in the isothermal–isobaric ensemble are performed using a Fourier path integral Monte Carlo technique. Among the more striking trends in the properties of quantum solids which emerge from this study is the strong dependence of the number density on the degree of delocalization, rather than the temperature. The large lattice expansions, under NPT conditions, associated with quantum solids, are necessarily accompanied by significant decreases in the binding energies. The kinetic energies per particle indicate that even a semiclassical Lennard-Jones solid is far from the classical equipartition regime at temperatures as high as 70% of the melting temperature. The Lindemann index, the bond orientational order parameters and the structure factors are used to monitor the degree of solidlike order. The Lindemann index increases sharply with the de Boer parameter and is accompanied by a substantial decrease in the average coordination number. This local disorder in the solid phase has a significant effect on the second-order bond-orientational order parameters, but leaves the third-order rotational invariants unchanged. The intensity of structure factors dies out very rapidly as the magnitude of the wave vector increases. Trends in lattice rigidities and the deviation of typical instantaneous configurations from the equilibrium lattice geometry as a function of quantum effects are estimated from the instantaneous normal mode spectra. It is also shown that configurational properties of the quantum path centroids, when compared with observable values based on averaging over instantaneous configurations, provide insights into the relation between local disorder and the relative magnitude of thermal and quantum fluctuations.
Anomalies in the self-diffusion coefficient near the critical point
Authors: Cherayil Binny J.
Published: July 2002

In this paper we calculate the contribution Ds to the self-diffusion coefficient D0 from the coupling of solute motion to solvent density fluctuations in an infinitely dilute near-critical binary mixture using the methods of fully renormalized kinetic theory in the disconnected approximation. The expression for Ds is found to be similar to mode-coupling expressions for diffusion coefficients in dense or supercooled liquids. As a function of the solvent density ρ, and along the critical isotherm, D0 exhibits an anomalous decrease in the vicinity of the critical point that originates in the vanishing of Ds according to the scaling relation Ds∼(ρ−ρc)2, where ρc is the critical density. An analogous decrease in D0 has recently been observed in the simulations of Drozdov and Tucker [J. Chem. Phys. 114, 4912 (2001)] on a neat liquid of Lennard-Jones particles, and has been ascribed to local density inhomogeneities in the medium.
Vacuum ultraviolet laser pulsed field ionization photoelectron study of cis-2-butene
Authors: Woo H. K. , Zhan Jiping , Lau K.-C. , Ng C. Y. , Cheung Yu-San
Published: July 2002

The vacuum ultraviolet pulsed field ionization-photoelectron spectra of supersonically cooled cis-2-butene (cis-CH3CH=CHCH3) have been measured in the photon energy range of 73 560–75 460 cm−1. Using the ab initio theoretical rotational constants of cis-CH3CH=CHCH3 and its cation (cis-CH3CH=CHCH3+) and a semiempirical simulation scheme, we have obtained a good fit of the origin vibrational band with partially resolved contours of rotational branches. After taking into account the Stark shift, the ionization energy of cis-CH3CH=CHCH3 is determined to be 73 595.0±1.5 cm−1. Guided by ab initio vibrational frequency calculations, we have also assigned the vibrational bands observed for cis-CH3CH=CHCH3+ in its ground state.
Plasma velocity in hydromagnetic dynamos
Authors: Núñez Manuel
Published: July 2002

Hydromagnetic dynamos are plasma configurations generating for some time an exponentially increasing magnetic field. By using a number of functional inequalities, we estimate the rate of increase of magnetic energy in terms of the plasma resistivity and diferent norms on the plasma velocity. Our bounds are proved to be optimal as far as the powers of the relevant magnitudes are concerned.
Scaling properties of a turbulent passive scalar field
Authors: Feng Q. Z.
Published: July 2002

Existing bivariate log-normal model [C. W. Van Atta, Phys. Fluids 14, 1803 (1971)] and bivariate log-Poisson model [N. Cao and S. Chen, Phys. Fluids 9, 1203 (1997)] for the scaling exponent of the pth order scalar structure function becomes a decreasing function of p as p is large enough and ultimately tends to −∞. Therefore the passive scalar cannot be bounded. However, in the frame of the hierarchical structure theory [Z. S. She and E. Leveque, Phys. Rev. Lett. 72, 336 (1994)] we can rechoose the values of some basic parameters to avoid the above shortcoming. The revised scaling law of a turbulent passive scalar field is in agreement with existing experimental data. The interesting prediction of the revised model is the saturation of the scaling exponents of the scalar structure functions as p→∞.
Inviscid dynamics of a wet foam drop with monodisperse bubble size distribution
Authors: McDaniel J. Gregory , Akhatov Iskander , Holt R. Glynn
Published: July 2002

Motivated by recent experiments involving the acoustic levitation of foam drops, we develop a model for nonlinear oscillations of a spherical drop composed of monodisperse aqueous foam with void fraction below 0.1. The model conceptually divides a foam drop into many cells, each cell consisting of a spherical volume of liquid with a bubble at its center. By treating the liquid as incompressible and inviscid, a nonlinear equation is obtained for bubble motion due to a pressure applied at the outer radius of the liquid sphere. Upon linearizing this equation and connecting the cells at their outer radii, a wave equation is obtained with a dispersion relation for the sound waves in a bubbly liquid. For the spherical drop, this equation is solved by a normal mode expansion that yields the natural frequencies as functions of standard foam parameters. Numerical examples illustrate how the analysis may be used to extract foam parameters, such as void fraction and bubble radius, from the experimentally measured natural frequencies of a foam drop.
Many-body effects in the stimulated Raman response of binary mixtures: A comparison between theory and experiment
Authors: Jansen Thomas l. C. , Pugzlys Audrius , Crı̂nguş Gheorghe Dan , Snijders Jaap G. , Duppen Koos
Published: July 2002

The subpicosecond dynamics of binary mixtures of carbon disulfide and alkane have been studied using third-order time-resolved Raman techniques. Both the anisotropic and the isotropic responses were investigated. These depend differently on many-body contributions to the first-order susceptibility and probe different modes in the liquid. The anisotropic response is dominated by single molecule effects, whereas the isotropic response is completely determined by many-body contributions since the single molecule response vanishes. To interpret the experimental results, molecular dynamics simulations were performed on model mixtures. The effect of dilution on the subpicosecond response cannot be explained by many-body effects in the first-order susceptibility alone. Aggregation due to permanent quadrupole moments on the carbon disulfide molecules and density changes upon dilution are also inadequate explanations for the observed effect. Apparently the character of the many-body dynamics itself is modified by the change of the molecular force fields, when carbon disulfide molecules are replaced by alkanes.
Noncommutative tori and universal sets of nonbinary quantum gates
Authors: Vlasov Alexander Yu.
Published: July 2002

We address the problem of universality in simulation of evolution of quantum system and in theory of quantum computations related with the possibility of expression or approximation of arbitrary unitary transformation by composition of specific unitary transformations (quantum gates) from given set. In an earlier paper application of Clifford algebras to constructions of universal sets of binary quantum gates Uk∈U(2n) was shown. For application of a similar approach to nonbinary quantum gates Uk∈U(ln), in present work we used rational noncommutative torus T1/l2n. A set of universal nonbinary two-gates is presented here as one example.
Photoluminescence and photoluminescence excitation studies of as-grown and P-implanted GaN: On the nature of yellow luminescence
Authors: Huang H. Y. , Chuang C. H. , Shu C. K. , Pan Y. C. , Lee W. H. , Chen W. K. , Chen W. H. , Lee M. C.
Published: July 2002

We have studied optical and electronic properties of isoelectronic P-implanted GaN films grown by metalorganic chemical vapor phase epitaxy. After rapid thermal annealing, a strong emission band around 430 nm was observed, which is attributed to the recombination of exciton bound to isoelectronic P-hole traps. From the Arrhenius plot, the hole binding energy of ∼180 meV and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, the implantation process likely introduced NI and P-related defects. By using photoluminescence excitation technique, we found that the P-implantation-induced localized states not only increase the yellow luminescence but also suppress the transitions from the free carriers to deep levels.
Laminar boundary layer flow of saturated vapor and its condensate over a horizontal tube
Authors: Smyrnaios D. N. , Pelekasis N. A. , Tsamopoulos J. A.
Published: July 2002

The steady two-dimensional laminar flow of a stream of saturated vapor flowing over a tube that is kept at a uniform temperature, below the saturation temperature, is examined. Owing to the temperature difference between the vapor stream and the solid surface a film of condensate is generated that flows along the surface due to shear, pressure-drop, and gravity. In the limit as the boundary layer and film thickness remain smaller than the radius of curvature of the surface a simplified lubrication-type formulation describes the temperature and flow fields in the film, whereas the usual boundary layer formulation is applied in the vapor boundary layer. The case of flow past a horizontal cylinder of radius R is investigated numerically with the oncoming stream aligned with gravity. The parameters that control momentum and heat transfer in this problem are the viscosity ratio, μcs/μss, the density ratio, ρcs/ρss, the Prandtl number, Pr=cpcsμcs/kcs, the Froude number, Fr=U∞2/(gπR), and finally the thickness ratio between the condensate and the vapor boundary layer, ε, which is also a measure of the temperature difference between the vapor stream and the tube wall. Then, the Nusselt number and the skin friction coefficient, averaged over the upper half of the cylinder, are calculated for a wide parameter range. When Fr is very small and ε relatively large the flow remains attached until the trailing stagnation point of the cylinder. As the effect of adverse pressure drop becomes more pronounced (Fr increases or ε decreases) it is shown that the solution exhibits two different types of singularity in the rear part of the cylinder. The first one is a typical Goldstein singularity because it appears at the tube wall and it is associated with vanishing skin friction (wall shear) and rapidly increasing film thickness. The second one takes place near the interface between the vapor stream and the film of condensate in a region where very small velocities prevail in conjunction with vanishing shear rate. The latter has not been reported so far and it is expected to affect the flow locally, as opposed to the Goldstein singularity which is known to lead to massive separation in the case of a cylindrical surface. Upon proper rescaling of Fr and ε, Fr′=Fr ρss/ρcs, ε′=ε6(μss/μcs)7/2(ρcs/ρss)7/2, a critical curve is produced in the (Fr′,ε′) plane that marks the boundary curve separating the two types of singular behavior for most of the numerical data obtained herein for the steam–water system, irrespective of the saturation temperature.
Charge transfer in hyperthermal surface collisions of C60 and C60−: Experiment and model calculations
Authors: Bekkerman A. , Tsipinyuk B. , Kolodney E.
Published: July 2002

In this paper we address the issue of electron exchange between a large molecular projectile and a surface during a hyperthermal collision. Hyperthermal neutral C60 molecules with well-defined average vibrational energy Ev=8±0.5 eV were scattered from a graphitized (monolayer-covered) nickel surface for both near normal and near grazing incidence angles. The yield of C60− negative ions was measured for the impact energy range 8–33 eV and was found to scale exponentially with the inverse of the normal component of the scattered molecule velocity. Normal and tangential velocities of the scattered C60 are very low, (1.3–5.6)×10−4 and (0.8–3.1)×10−4 a.u. correspondingly. The fact that nearly the same slope (characteristic velocity) was extracted from the semilog plots for both near normal and near grazing incidence angles shows that tangential velocity effects are negligible. The rate of electron tunneling from C60− to the surface was calculated quasi-classically assuming that the excess (active) electron in C60− is moving in the highly screened short range attractive potential of the neutral C600 core, which is approximated by a radial delta function (Dirac bubble). The transmission coefficient was calculated for C60− located at the center of a spherical metallic cavity with image charge potential barrier for the active electron. The preexponential frequency factor was obtained by solving the quasi-stationary Shrödinger equation for the same system but without the image charge barrier. Finally, the decay rate was corrected for the case of C60− in front of a conducting plane. The experimental results were analyzed using the calculated tunneling rates and a critical ion formation distance was obtained. Independence of the scattering dynamics and negative ion yield on the incoming charge state is demonstrated by using incident C60− at the impact energy range of 40–100 eV. The same relative energy losses were measured for incident C60− ions as for neutral C600 thus extending the range of linear dependence of the scattered kinetic energy on impact energy up to 100 eV.
CF 3 I on a silicon surface: Adsorption, temperature-programmed desorption, and electron-stimulated desorption
Authors: Sanabia Jason E. , Moore John H. , Tossell John A.
Published: July 2002

CF 3 I adsorption on a silicon surface and the effect of low-energy electron bombardment of a CF3I-covered silicon surface are relevant to plasma etching. Dissociative chemisorption of CF3I on Si(100) surface is observed at 370 K. Uptake measurements corroborated by work-function change measurements and temperature-programmed desorption (TPD) gives a sticking probability of at least 0.34±0.05. Molecular orbital calculations yield an adsorption energy greater than 3 eV for dissociative chemisorption of CF3X (X=F, Cl, Br, and I) on Si(100) (modeled by Si9H12) with X transferred to a silicon atom. We conclude that the variation in the sticking probability across the CF3X family is a consequence of the activation energy barrier for C–X bond cleavage. In TPD, SiF4 desorbs at 370 and 840 K, SiF3 radical at 770 K, and atomic iodine at 790 K. The parent CF3I does not desorb. Electron-stimulated desorption (ESD) yields F+, F− and a trace of I+. The threshold for the appearance of F+ is 20 eV and for F− is 29 eV. Dissociative ionization and dipolar dissociation are possible mechanisms for ESD of F+. Dipolar dissociation and harpooning are possible mechanisms for ESD of F−. There is evidence that iodine on the surface quenches the electronically excited states that lead to desorption of F−.
A three-dimensional polymer growth model
Authors: Vogt Marc , Hernandez Rigoberto
Published: July 2002

A three-dimensional model for polymerization processes in nonequilibrium environments has been constructed as an extension of an earlier two-dimensional polymer-growth-Hamiltonian model [M. Vogt and R. Hernandez, J. Chem. Phys. 115, 1575 (2001)]. The extension to three dimensions will permit a direct comparison with experiments, and presently allows us to observe the effects of reduced conformational trapping as one scales from two to three dimensions. The three-dimensional model exhibits surprisingly similar equilibrium and dynamic behavior to the two-dimensional model with the exception that it grows large polymers which are more compact. The radius of gyration scales weaker with the polymer size in three dimensions as has been seen in other models. The effects of temperature ramping and jumps on the dynamics of cross-polymerization have also been examined and exhibit a switch over from linear to nonlinear response for larger perturbations.
Vibrational effects in a weakly-interacting quantum solvent: The CO molecule in He4 gas and in He4 droplets
Authors: Paesani F. , Gianturco F. A.
Published: July 2002

The coupling between the intermolecular motion and the internal vibrational coordinate in the He–CO system is computed at the post-Hartree–Fock level using the DFT+DISP model already employed by us for similar systems and reviewed here in the main text. The quality of the computation of such weak effects is compared with other, earlier model calculations and then used for the evaluation of the vibrational relaxation cross sections of the CO molecule diluted in He4 gas. A further assessment of the vibrational coupling is carried out by computing, with a stochastic approach that employs the Diffusion Monte Carlo method, the effects on the vibrational frequency of the CO impurity from its immersion in He4 droplets of variable size. Both sets of results are analyzed and discussed to gauge the reliability of the computed coupling vis-à-vis one of those suggested by earlier calculations. This study provides further evidence on the difficulty of quantitatively obtaining from calculations the extremely small effects connected with molecular vibrational features in this system and caused by the weak interaction between the title molecule and a quantum solvent like He4.
Probe diagnostics of high pressure microwave discharge in helium
Authors: Talukder M. R. , Korzec D. , Kando M.
Published: July 2002

A method for the determination of electron temperature and plasma density in high pressure helium plasmas is established using numerical results of the continuum probe model by Cohen [Phys. Fluids 6, 1492 (1963)]. Simple algebraic functions are derived to approximate the probe characteristics of high pressure plasmas calculated by Cohen and are applied to use iterative procedures for the determination of plasma parameters. The proposed fitting technique has allowed one to obtain reasonable plasma parameters even for the probe characteristics strongly affected by large secondary electron emission currents from the probe. Fitting of the ion saturation current may possibly be used to estimate the ion temperature, provided that the electron temperature and plasma density are known. Finally high pressure helium microwave discharges have been produced by moderate microwave power of 400 W and investigated by the present method.
Semiclassical IVR treatment of reactive collisions
Authors: Elran Y. , Kay K. G.
Published: July 2002

We generalize a recently-developed semiclassical uniform initial value representation (IVR) treatment of the S-matrix [Y. Elran and K. G. Kay, J. Chem. Phys. 114, 4362 (2001)] to chaotic nonreactive and reactive collinear scattering. The present modifications allow one to determine the phase of the complex IVR integrand in a unique and practical manner even when the integrand is discontinuous or rapidly varying. The method is applied to the collinear H+H2 exchange reaction on the Porter–Karplus surface. A strategy is introduced for adapting the integration over the chaotic chattering zones to the fractal nature of the integrand. The results indicate that the technique is capable of good accuracy while requiring a relatively small number of trajectories per energy.
Fast time response from Si–SiGe undulating layer superlattices
Authors: Buca D. , Winnerl S. , Lenk S. , Buchal Ch. , Xu D.-X.
Published: July 2002

We have grown Si–Si1−xGex undulating layer superlattices with x=0.39 and 0.45 by molecular-beam epitaxy on top of epitaxial implanted CoSi2 layers and fabricated vertical metal–semiconductor–metal detectors. The detectors show a quantum efficiency of 5% for the wavelength of 1320 nm and 0.9% for 1550 nm. We performed temporal response measurements, using a Ti:sapphire laser and an optical parametric oscillator which generates ultrafast pulses at infrared wavelengths. An electrical response time of 16 ps full width at half maximum was obtained at a wavelength of 1300 nm.
Conductance fluctuations and quantum chaotic scattering in semiconductor microstructures
Authors: Marcus C. M. , Westervelt R. M. , Hopkins P. F. , Gossard A. C.
Published: July 2002

We review recent experiments on aperiodic conductance fluctuations in ballistic GaAs/AlGaAs microstructures in the shape of a stadium billiard and a circle with point-contact leads, measured at millikelvin temperatures. Much of the observed behavior can be analyzed within a semiclassical approach to quantum chaotic scattering. After a brief review of the Landauer–Büttiker formulation of coherent transport, a variety of novel experimental phenomena and comparisons to semiclassical theory are presented. In particular, we discuss quantum-enhanced backscattering, the power spectrum of conductance fluctuations, crossover to the high-magnetic-field and tunneling regimes, and an application allowing the rate of phase-randomizing scattering to be measured in chaotic ballistic microstructures.
An advanced investigation of interaction of allocated quasi-two-dimensional vortices
Authors: Danilov S. D. , Dolzhanskii F. V. , Dovzhenko V. A. , Krymov V. A.
Published: July 2002

This work should be regarded as a natural development of the investigations by Dolzhanskii, Krymov and Manin [Sov. Phys. Usp. 33, 495–520 (1990); J. Fluid Mech. 241, 705–722 (1992); Russ. J. Comput. Model. 1, 107–118 (1993)] of quasi-two-dimensional (Q2D) flows in which the linear and weakly nonlinear stability theory based on the 2D hydrodynamic equations with the Rayleigh (Ekman) friction term imitating the influence of the bottom on the motion of upper fluid layers was corroborated with laboratory and observational data. The applicability of the Q2D approach to describe self-oscillating supercritical regimes was even more vague as Batchaev’s experiments [Izv. AN SSSR Fiz. Atmos. Okeana 25, 434–439 (1989); Z. Prikl. Mech. Tech. Fiz., No. 4, 85–91 (1990)] on modeling the four vortex self-oscillations in a thin fluid layer by the magnetohydrodynamics method (the so called hydrodynamical clock [Obukhov, Dolzhanskii and Batchaev, Topological Fluid Mechanics, Proceedings of the IUTAM Symposium, Cambridge, 13–18 August 1989 (Cambridge University Press, Cambridge, 1989), pp. 304–314]) did not find an appropriate theoretical explanation. To remove earlier uncontrolled effects the supplementary detailed measurements of the experimental flow characteristics were implemented, including the spatial spectral composition of the external vorticity sources and free surface 2D velocity fields. Satisfactory agreement is found between experimentally measured flow characteristics and the results of numerical simulations. The frequency of self-oscillations was found to be greatly susceptible to the spectral composition of the external vorticity sources and fluid layer thickness, which should be taken into account in designing laboratory experiments to simulate the natural Q2D processes observed in the ocean and atmosphere. Applicability conditions of the Q2D approach and the influence of geometrical parameters of vortices on their nonlinear interplay are also discussed.
Magnetic properties of CdxZnyMnzTe alloys
Authors: Donofrio T. , Lamarche G. , Woolley J. C.
Published: July 2002

Low-field measurements of magnetic susceptibility χ have been made as a function of temperature in the range 4–150 K on polycrystalline samples of the alloy system CdxZnyMnzTe (x+y+z=1). Values of Tg, the spin-glass transition temperature, have been obtained from the cusp in the χ vs T curves and values of the Curie-Weiss θ obtained by extrapolation of the 1/χ vs T line at the higher temperatures. When the various values of Tg vs composition are fitted to a straight line they all extrapolate to a percolation limit of 0.18±0.01. However, it is shown that the plot proposed by Escorne et al. of ln Tg vs az−1/3, where a is the lattice parameter, also gives a straight line variation within the limits of experimental error. This indicates that for z≤0.2, the variation of Tg with z must deviate from linearity. The extrapolated value of 0.18±0.01 is attributed to nearest neighbors only and for z≤0.2 more distant neighbors become relatively more important. For both the Tg vs z and ln Tg vs az−1/3, a change in slope occurs at z≊0.6. This probably represents the change from spin glass to antiferromagnetic behavior and may be due to an additional exchange effect becoming important.
A pulsed thermoelastic analysis of photothermal surface displacements in layered materials
Authors: Rousset G. , Bertrand L. , Cielo P.
Published: July 2002

A pulsed photothermal method is proposed for the detection of delaminations in layered materials. The surface of the material is heated by a focused laser pulse to a few degrees above the ambient temperature, and the induced thermoelastic displacement is detected by a laser interferometer. Unbonded areas are characterized by their thermoelastic bending behavior, in addition to their thermal expansion, because of the induced temperature gradients both in the radial and axial directions. A theoretical analysis and an experimental investigation of this behavior are described in order to point out the most significant parameters. An application of the nondestructive inspection of Al-epoxy honeycomb panels is presented.
Theoretical studies of the electron scattering effect on developed pattern profiles in x-ray lithography
Authors: Murata Kenji
Published: July 2002

Monte Carlo calculations of the photo and Auger electron production by a monochromatic x ray of Al Kα have been performed to study the effect of their diffusion in a 1.0-μm polymethyl methacrylate resist film on replicated patterns both with and without the Si substrate. Based on both the calculated spatial distribution of the absorbed energy density and the solubility rate for mixture developers of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA), investigations were carried out on the x-ray resist sensitivity, the ultimate resolution, and the mask contrast effect on developed profiles. Typically, the ultimate resolution was found to be 1000 Å with MIBK and to be 400 Å with MIBK : IPA=1 : 3. There was no significant influence of the Si substrate on the developed patterns.
FMR linewidth measurements in bismuth-substituted YIG
Authors: Vittoria C. , Lubitz P. , Hansen P. , Tolksdorf W.
Published: July 2002

The ferromagnetic resonance linewidth ΔH has been measured on films of Y3−xBixFe5O12 with x values of 0, 0.41, and 1.03 and for temperatures from 5 to 550 K. The measurements were made at 9.3 GHz, with the applied field perpendicular to the film plane. The films are about 1 μm thick. We find that for T near the Néel temperature, ΔH is about 1.5 Oe for x=1.03 as opposed to 3.5 Oe for pure YIG. The minimum value of ΔH for the pure LPE YIG is about 1/3 Oe at room temperature. The minimum linewidth for x=1.03 is 0.4 Oe at 160 K while for x=0.41 the narrowest linewidth observed was 0.2 Oe at 2.5 K. For this sample the linewidth was a monotonically increasing function of temperature while for x=0 and 1.03, maxima occurred at about 50 K.
Rapid thermal and pulsed laser annealing of boron fluoride-implanted silicon
Authors: Narayan J. , Holland O. W. , Christie W. H. , Wortman J. J.
Published: July 2002

Characteristics of rapid thermal and pulsed laser annealing have been investigated in boron fluoride- (BF+2 and BF+3) -implanted silicon using cross-section and plan-view electron microscopy. The amorphous layers recrystallize by the solid-phase-epitaxial growth process, while the dislocation loops below the amorphous layers coarsen and evolve into a network of dislocations. The dislocations in this band getter fluorine and fluorine bubbles associated with dislocations are frequently observed. The secondary-ion mass spectrometry techniques were used to study concomitant boron and fluorine redistributions. The as-implanted Gaussian boron profile broadens as a function of time and temperature of annealing. However, the fluorine concentration peak is observed to be associated with dislocation band, and the peak grows with increasing time and temperature of annealing. The electrical properties were investigated using van der Pauw measurements. The electrical activation of better than 90% and good Hall mobility were observed in specimens with less than 500-Å dopant-profile broadening. In pulsed laser-annealed specimens, the boron profile broadens both toward the surface and into the deeper regions of the crystal. However, the fluorine concentration profile exhibits a decrease in peak concentration with only a limited broadening.
The effect of slight surface roughness on the scattering properties of convex particles
Authors: Schiffer R. , Thielheim K. O.
Published: July 2002

The average scattering cross section for reflection of electromagnetic waves by an ensemble of randomly oriented convex particles is calculated. The particles are assumed to be large compared to the incident wavelength and to have a slightly rough surface such that the deviations from a smooth surface are smaller than wavelength. A perturbation expansion resulting from the Rayleigh–Rice approach leads to incoherent and coherent corrections to the zero-order specularly reflected light. The quantity that in this limit completely determines the scattering behavior of the particles is the two-point correlation function ρ(r) of the roughness structure. The main effect of roughness is a diminution of the reflected intensity for a wide range of the scattering angle θ and a shifting of the maximum of the polarization curve to larger θ. It turns out that measurements of the backscattered intensity in some wavelength limits provide information on the correlation function ρ(r). For conducting material, knowledge of the cross-polarized backscatter intensity over a wide frequency range even enables one, at least in principle, to calculate the complete shape of the correlation function.
Quantized electron accumulation layers on ZnO surfaces produced by low-energy hydrogen-ion implantation
Authors: Yaron G. , Many A. , Goldstein Y.
Published: July 2002

Implantation of 100-eV hydrogen ions on the (0001̄) face of ZnO produces extremely strong electron accumulation layers on the surface. Calibrated argon-ion sputtering measurements indicate that the implanted ions (consisting mostly of protons) penetrate to a depth of 10–20 Å beneath the surface. They act as fully ionized donors giving rise to a free electron layer of comparable depth and of surface electron densities up to 2×1014 cm−2. The narrow width, combined with detailed transport measurements, show that the implanted accumulation layers closely resemble ordinary accumulation layers on ZnO surfaces obtained, for example, by exposing the surface to atomic hydrogen. Thus the implanted layers, just as the ordinary accumulation layers, constitute a quantized, two-dimensional electron gas system. The important advantage of the implanted over the ordinary accumulation layers, however, is that they are completely inert to oxygen or even to room air. Annealing experiments provide estimates for the activation energies for release of the hydrogen ions from the surface layer. The results indicate the presence of several different types of lattice sites for the implanted ions.
Transition-metal silicides formed by ion mixing and by thermal annealing: Which species moves?
Authors: Affolter K. , Zhao X.-A. , Nicolet M-A.
Published: July 2002

The moving species during the formation of Pt2Si, Ni2Si, and CrSi2 by both ion mixing with 300–600 keV Xe ions and thermal annealing is identified with inert markers using backscattering spectrometry. Samples of metal-on-silicon and silicon-on-metal have been used, evaporated on SiO2 substrates with two very thin markers (Mo for Pt2Si, W for Ni2Si and CrSi2) placed at the metal–silicon interface, and at the bottom interface with the SiO2 substrate. Monitoring the separation of the two markers as a function of the amount of silicide formed determines the ratio of atomic transport through the growing silicide layer. The results establish that the dominant moving species in both silicide formation processes is the same for the refractory metal-silicide CrSi2, e.g., Si, whereas different atomic transport ratios are found in the case of the near-noble metal silicides Pt2Si and Ni2Si. This outcome is discussed in terms of high-temperature effects during thermal formation of transition-metal silicides.
Mono- and disilicon radicals in silane and silane-argon dc discharges
Authors: Robertson Robert , Gallagher Alan
Published: July 2002

Measurements of monosilicon (SiHn) and disilicon (Si2Hn) radicals at the cathode surface of dc discharges in silane and silane-argon mixtures are reported. Silyl radical density per decomposed silane was constant for fixed flow conditions over a range of powers and silane-argon ratios. The relative densities for other monosilicon radicals SiHn/SiH3 decreased with increased fraction of silane in silane-argon mixtures. The density of disilicon radicals was observed to be comparable to some of the monosilicon radicals, with Si2H2 and Si2H4 the dominant Si2Hn species. Formation and destruction reactions are discussed for these radicals, disilane, and the deposited film. We deduce that disilane is formed primarily on surfaces and that sputtering is a significant source for radicals near the cathode.
Modeling nonlocal heat flow in laser-produced plasmas
Authors: Holstein P. A. , Delettrez J. , Skupsky S. , Matte J. P.
Published: July 2002

Nonlocal heat transport is investigated under conditions relevant to laser-driven fusion. Results from the nonlocal transport model of Luciani and Mora are compared with results from Fokker–Planck codes and from local flux-limited diffusion simulations. No significant nonlocal effects are found in hydrodynamic simulations for irradiation with either 1.06 or 0.35 μm laser light. Over a large range of conditions, the transport is well modeled with a harmonic averaged flux-limiter between 0.1 and 0.2.
Characterization of GaAs and Si by a microwave photoconductance technique
Authors: Cummings K. D. , Pearton S. J. , Vella-Coleiro G. P.
Published: July 2002

A nondestructive microwave photoconductance technique has been employed to investigate the uniformity of electrical transport properties in semi-insulating, doped, or implanted GaAs. Although the measurement time is increased, the technique is also applicable to Si. A review of the advantages and limitations is discussed and some example applications to a variety of GaAs and Si structures are presented.
Frequency dependence of quasiparticle mixers
Authors: Danchi W. C. , Sutton E. C.
Published: July 2002

An analysis of the frequency dependence of superconductor-insulator-normal (SIN) and superconductor-insulator-superconductor (SIS) quasiparticle mixers is presented. Power-law expressions for conversion loss and mixer shot-noise temperature for the double-sideband SIN mixer are derived from the Tucker theory for the case of a source conductance which is small compared to the conductance of the junction. For an ideal SIN tunnel junction at T=0 the mixer conversion efficiency is shown to decrease approximately linearly with frequency up to  f=Δ/h. From  f=Δ/h to 2Δ/h the conversion efficiency remains approximately constant, while above  f=2Δ/h it rolls off as the inverse square of the frequency. Expressions for the shot-noise contribution to the mixer noise temperature are also derived. At frequencies up to  f=Δ/h the noise temperature rises as the square root of the frequency. From  f=Δ/h to  f=2Δ/h the noise temperature of the mixer increases linearly with frequency, whereas above  f=2Δ/h it rises as the cube of the frequency. Conversion efficiency and noise temperature are also calculated numerically for the SIN mixer. Good agreement is found between the frequency dependencies calculated analytically in the limit of small local oscillator power and the numerical calculations for optimal pumping. The frequency dependence of the nonideal SIS junction is also analyzed, and shown to yield similar results, with the characteristic frequencies Δ/h and 2Δ/h for a SIN mixer transformed into 2Δ/h and 4Δ/h, respectively. Expressions also are derived for the saturation power as a function of frequency.
Sensitivity of a 1200-kg three-mode gravitational radiation detector instrumented with a Clarke or IBM dc SQUID
Authors: Richard Jean-Paul
Published: July 2002

An analysis is made of a three-mode 1200-kg gravitational radiation detector operating at 1660 Hz and instrumented with a Clarke or IBM dc SQUID. The sensitivity projected for the detection of short pulses at 4.2 K and with optimum filtering is at the level of dh∼10−18 over a bandwidth of approximately 150 Hz.
Thermal and Si-beam assisted desorption of SiO2 from silicon in ultrahigh vacuum
Authors: Streit D. C. , Allen F. G.
Published: July 2002

We have measured the kinetic parameters for the removal of SiO2 films from silicon in ultrahigh vacuum using Auger electron spectroscopy and low-energy electron diffraction, both with and without a beam of atomic silicon incident on the surface. Due to the very low vapor pressure of SiO2, it is removed only through reduction to SiO by excess silicon. We find that the activation energy for the rate limiting step in the thermal desorption of SiO2 is 3.54±0.2 eV, so that at temperatures below ∼900 °C, thick films (∼25 Å) can scarcely be removed by thermal desorption alone, in agreement with earlier work. Very thin oxide films (∼5Å) can be readily removed at lower temperatures, since SiO formed at the Si-SiO2 interface encounters a negligible diffusion barrier and sublimes directly into vacuum. With a beam of silicon incident, SiO forms at the oxide surface and desorbs with an activation energy of only 0.84±0.2 eV. Oxide films on silicon can be removed at temperatures as low as 700 °C using an incident silicon beam flux of 3×1013 cm−2 s−1.
Effect of rapid thermal annealing on ion-implanted and neutron transmutation-doped GaAs
Authors: Wagner J. , Ramsteiner M. , Haydl W.
Published: July 2002

Raman spectroscopy with optical multichannel detection was used to study Se+ implanted and neutron-transmutation doped GaAs, both before and after rapid thermal annealing. Samples implanted at room temperature showed an amorphous surface layer, whereas those implanted at 320 °C exhibited Raman features of both amorphous and crystalline GaAs. After rapid thermal annealing, the material implanted at elevated temperatures showed a better structural recovery, as indicated by a lower intensity of forbidden phonon scattering. Using resonance Raman effects, we were able to discriminate between amorphous and crystalline features in the spectra. For the neutron-transmutation doped GaAs, the as-irradiated material showed a Raman spectrum similar to the one of undoped crystalline GaAs. The increase in electrical activation with increasing annealing temperature was monitored by Raman scattering from coupled plasmon-phonon modes, giving a carrier concentration comparable to the one obtained from Hall measurements.