bluuebunny/crossref_metadata_2025 huggingface dataset:
Low dielectric loss and enhanced tunability of Ba0.6Sr0.4TiO3 based thin films via material compositional design and optimized film processing methods
Authors: Cole M. W. , Nothwang W. D. , Hubbard C. , Ngo E. , Ervin M.
Published: May 2003

Low dielectric loss in conjunction with high tunability are simultaneous requirements for tunable device applications which have proved problematic to achieve. In this work, material compositional design and optimized film processing methods were employed to simultaneously lower the dielectric loss and enhance the dielectric tunability of Ba0.6Sr0.4TiO3 (BST) based thin films without compromising the device impedance matching (εr<500) and control voltage (<10 V) requirements. The films compositional design was achieved by Mg doping BST from 3 to 10 mol %. The Mg doped thin films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors and postdeposition annealing in an oxygen ambience at 750 °C for 60 min. The films dielectric loss at these doping levels was identical, tan δ∼0.007. In contrast, the films permittivity (339–220), leakage current density (2.55×10−8–2.43×10−9 A/cm2), tunability (21.3%–5.7%), and grain size (75.2–61.55 nm) were observed to decrease with increasing Mg concentration levels from 3 to 10 mol %, respectively. Device quality values of tunability, 40% and 32%, for the 3 and 7 mol % doped BST films, respectively, were achieved by elevating the applied bias from 237 to 474 kV/cm. This device quality tuning is compatible with voltage requirements of current semiconductor based systems. Our results suggest that the low level acceptor doping from 3 to 7 mol %, optimized precursor solution concentration (0.43 M), and oxygenated postdeposition thermal processing were found to work in concert to lower dielectric loss, limit defect density concentration, optimize film microstructure, and eliminate undesirable film/electrode interfacial phases. As a result, high quality BST thin films, with their resultant high breakdown fields, were realized. It is the excellent film quality (i.e., optimized composition and microstructure), which allowed the enhanced tunability at elevated dc bias to be achieved without risk of dielectric breakdown. The enhanced dielectric and insulating properties of the 3–7 mol % Mg doped BST thin films make them excellent candidates for integration into tunable devices.
Optimization of the microstructure and properties of Co-substituted Fe–Si–B–Nb–Cu nanocrystalline soft magnetic alloys
Authors: Ohnuma M. , Ping D. H. , Abe T. , Onodera H. , Hono K. , Yoshizawa Y.
Published: May 2003

The effect of Co replacement for Fe on the microstructure and soft magnetic properties of Fe78.8−xCoxNb2.6Si9B9Cu0.6 (x=5–60) nanocrystalline alloys has been studied for improving the soft magnetic properties of Fe–Si–B–Nb–Cu type alloys at a high frequency range. The magnetic anisotropy constant increases with x, but the coercivity increases when x exceeds 20, indicating that magnetic softness is degraded by replacing Fe with Co. Three-dimensional atom-probe observations have revealed that the number density of Cu-enriched clusters decreases with x, thereby decreasing the number density of the heterogeneous nucleation sites for bcc-Fe primary crystals. In addition, differential scanning calorimetry measurements show that the Cu clustering temperature shifts to a higher temperature with increasing x, suggesting that the kinetics for the Cu clustering decreases as Co content. These experimental results are discussed from the thermodynamical point of view, and the optimized Cu composition to achieve a low coercivity with 40 at % Co has been found. © 2003 American Institute of Physics.
Strong ion-sound parametric turbulence and anomalous anisotropic plasma heating in helicon plasma sources
Authors: Mikhailenko V. S. , Stepanov K. N. , Scime E. E.
Published: May 2003

Experimentally observed anisotropic ion heating in helicon plasma sources may result from the interaction of ions with ion-sound turbulence. The ion-sound turbulence develops due to excitation of the short scale, kinetic, parametric ion-sound instability. From the quasilinear equation for the ion distribution function, which includes the induced scattering of ion-sound waves by ions, the turbulent heating rate is determined. This anomalous ion heating is predominantly across the magnetic field and can lead to strong turbulence effects, such as the collective statistical effect of ion-sound turbulence on individual ion orbits (resonance broadening). Resonance broadening is a strong turbulence saturation mechanism for ion-sound turbulence. The energy density of the ion-sound turbulence in the saturated state, the ion and electron heating rates, as well as the effective collision frequency arising from the anomalous absorption of the helicon wave, are estimated and compared to experimental data.
Landau–Darrieus instability in an ablation front
Authors: Piriz A. R. , Portugues R. F.
Published: May 2003

An analytical model that shows the conditions for the existence of the Landau–Darrieus instability of an ablation front is presented. The model seems to agree with recently claimed simulation results [L. Masse et al., Proceedings of the 1st International Conference on Inertial Fusion Sciences and Applications (Elsevier, Paris, 2000), p. 220]. The model shows that the ablation front can be unstable in absence of gravity when the thermal flux is inhibited within the supercritical region of the corona.
Efficient evaluation of beam ion confinement in spherical tokamaks
Authors: Egedal J. , Redi M. H. , Darrow D. S. , Kaye S. M.
Published: May 2003

New efficient methods are developed for the determination of the confined fraction of beam ions in standard and spherical tokamaks. The particle motion is described in the guiding center approximation and finite Larmor radius effects are included in the determination of the prompt orbit losses. A new code, CONBEAM, utilizes these methods and provides rapid evaluation of the beam confinement. Losses due to nonadiabatic changes in the magnetic moment are also evaluated. Due to the conservation of the canonical angular momentum, it is shown that changes in magnetic moment will not lead to a significant reduction in the confinement of co-injected beam ions.
Charge trapping in and electrical properties of pulsed laser deposited Sm2O3 films
Authors: Yang Dongfang , Xue Li Jue , Devine R. A. B.
Published: May 2003

The electrical properties of pulsed laser deposited Sm2O3 films have been studied. The dielectric constants are 9.6 and 12.8 for samples deposited at 400 and 683 °C, respectively. The presence of substantial densities of mobile positive charge and significant negative charge trapping has been evidenced. The leakage current densities are, typically, 10−4 A cm−2 for electric fields ∼0.24 MV cm−1.
Diffraction stress analysis of macroscopically elastically anisotropic specimens: On the concepts of diffraction elastic constants and stress factors
Authors: Welzel Udo , Mittemeijer Eric J.
Published: May 2003

A unifying, rigorous treatment has been given for the diffraction stress analysis of both macroscopically elastically isotropic specimens and macroscopically elastically anisotropic specimens. The applicability ranges of so-called diffraction elastic constants and diffraction stress factors have been discussed. It has been shown that the diffraction stress factors, originally introduced for the diffraction stress analysis of textured specimens, can be generally used in the diffraction stress analysis of macroscopically elastically anisotropic specimens exhibiting direction-dependent grain interaction, independently of the presence of texture. The grain-interaction tensor has been introduced and investigated for various grain interaction models. The notion surface anisotropy of bulk specimens has been revisited as a special case of direction-dependent grain interaction.
Fluence- and temperature-dependent studies of carrier dynamics in radiation-damaged silicon-on-sapphire and amorphous silicon
Authors: Lui K. P. H. , Hegmann F. A.
Published: May 2003

We study the effects of lattice damage level, pump fluence, and temperature on carrier dynamics in thin silicon films. Two samples of radiation-damaged silicon-on-sapphire (RD-SOS) and one amorphous silicon thin film on sapphire were investigated. The first RD-SOS sample was O+ implanted with doses of 1×1013 cm−2 at 100 and 200 keV; the second RD-SOS sample was O+ implanted with a dose of 1×1015 cm−2 at 100 and a second dose of 2×1015 cm−2 at 200 keV; the third sample was a nonhydrogenated amorphous-silicon thin film grown by electron-beam evaporation. Carrier concentrations up to 7.4×1020 cm−3 were injected into the samples with 100 fs, 400 nm pump pulses, while the transient optical properties were probed with subpicosecond-wide terahertz (THz) pulses. Using a thin film Drude model, we derived the carrier relaxation time and effective carrier mobility for the three samples. The increase of lattice damage decreased both the relaxation time constant and the carrier mobility. A slight increase in relaxation time was observed for increasing pump fluence, but mobility values were not affected. No change in relaxation time or mobility was found for temperatures from 5 to 300 K. We find average relaxation time constants of 5.5 ps in the first sample, 1.4 ps in the second sample, and 0.58 ps in the third sample, and average carrier mobility values of 383, 44, and 4.4 cm2/V s, respectively. The presence of a single relaxation time constant is consistent with a trap-influenced relaxation mechanism and not of Auger recombination for carrier concentrations <1021 cm−3, indicative of the absence of thermally activated processes in the relaxation mechanism.
Ion implantation range distributions in silicon carbide
Authors: Janson M. S. , Linnarsson M. K. , Hallén A. , Svensson B. G.
Published: May 2003

The first to fourth order distribution moments, Rp, ΔRp, γ, and β, of 152 single energy H1, H2, Li7, B11, N14, O16, Al27, P31, Ga69, and As75 implantations into silicon carbide (SiC) have been assembled. Fifty of these implantations have been performed and analyzed in the present study while the remaining implantation data was compiled from the literature. For ions with a limited amount of experimental data, additional implantations were simulated using a recently developed binary collision approximation code for crystalline materials. Least squares fits of analytical functions to the distribution moments versus implantation energy provide the base for an empirical ion implantation simulator using Pearson frequency functions.
Resistive magnetohydrodynamic transport model for a reversed field pinch. I. The model
Authors: Bruno A. , Freidberg J. P. , Hastie R. J.
Published: May 2003

A self-consistent transport model has been developed for an ohmically heated reversed field pinch (RFP). The model predicts, with no adjustable fitting parameters, the magnitude and radial dependence of the anomalous perpendicular thermal diffusivity as well as the macroscopic scaling relations for τE and βp. Qualitatively, the model extends Taylor’s theory of relaxation to driven systems with an external heating source, ohmic heating in the case of an RFP. The presence of such a heating source creates a finite nonzero pressure gradient in contrast to the zero pressure gradient predicted by Taylor’s fully relaxed state. In the driven case, the magnitude of the pressure gradient is determined by assuming the pressure increases in magnitude and adjusts its shape until the entire profile is marginally stable to all resistive magnetohydrodynamic modes. This paper (paper I) of this two-paper sequence describes the development of the model and the numerical procedure for obtaining quantitative results.
Effect of crystal orientation on the implant profile of 60 keV Al into 4H-SiC crystals
Authors: Wong-Leung J. , Janson M. S. , Svensson B. G.
Published: May 2003

4H-SiC wafers of orientations (0001) and (112̄0) were implanted with 60 keV Al− in different major axial, planar, and low symmetry (“random”) directions to ascertain the degree of channeling and to determine the optimum tilt conditions for ion implantation. Significant channeling was observed for all axial directions with the [112̄0] channel exhibiting the deepest channeling with a maximum penetration depth 45 times greater than the projected range of the random implants. Significant channeling was observed for the {112̄0} and especially the {0001} planar channels while the implants in the {101̄0} planar channels did not differ from the corresponding random implants. To minimize channeling in (0001) crystals, our results show that beam alignment normal to the surface is advisable for off-axis (0001) wafers with the miscut toward 〈112̄0〉, while tilting of the wafer is necessary when the miscut is toward 〈101̄0〉. For the (112̄0) material, channeling can be minimized by a tilt of ≳10° toward the [0001] direction.
Energy losses of charged particles moving parallel to the surface of an overlayer system
Authors: Kwei C. M. , Hwang S. J. , Li Y. C. , Tung C. J.
Published: May 2003

An energetic charged particle moving parallel to the surface of an overlayer system was studied. This system was composed of a thin film on the top of a semi-infinite substrate. Based on the dielectric response theory, the induced potential was formulated by solving the Poisson equation and matching the boundary conditions. The stopping force was built-up using the energy-momentum conservation relations and the extended Drude dielectric functions with spatial dispersion. Surface (vacuum–film) and interface (film–substrate) excitations were included in the formulations of the interaction between charged particles and the overlayer system. Results of the wake potential were presented for protons moving parallel to a vacuum–copper–silicon system. Dependences of the induced potential and the stopping force on film thickness, distance of the proton from surface, and proton velocity were investigated.
Junction area scaling and statistical description of dc breakdown of ferromagnetic tunnel junctions
Authors: Nakajima K. , Asao Y. , Saito Y.
Published: May 2003

Magnetoresistive random access memory (MRAM) with ferromagnetic tunnel junctions (MTJs) has been recognized as a successful candidate for next generation solid-state memory. There are, however, still significant problems to realize MRAM. In particular, reliability of an ultrathin dielectric layer composing tunnel junctions is of great importance for MRAM developments. In this article, we performed systematical studies of the dielectric breakdown of MTJs. The samples have a double tunnel barrier structure with IrMn/CoFe/AlOx/CoFe/AlOx/CoFe/IrMn. Its width is ranging from 0.4 to 30 μm. Different from previous reports, the breakdown voltage gradually decrease with decreasing junction area. The breakdown voltage only shows weak dependence on junction area in the sub-μm region. In addition, the breakdown voltage is inversely proportional to the junction perimeter. Results of time-dependent failure measurements demonstrate that, within the limit of this experiment, the failure function of the MTJs obeys a Weibull distribution. The shape parameter of the Weibull distribution is less than unity, indicating early device to failure. We consider that process-induced defects at the sidewall of the junctions may serve a certain role in their early failure and lead the failure of the junction area scaling of the breakdown voltage.
Diffusion-induced beam bending in hydrogen sensors
Authors: Yang Fuqian , Li J. C. M.
Published: May 2003

The diffusion-induced bending of both single-layer and bilayer beam structure is analyzed by using linear elastic beam theory and the Moutier theorem. A closed form solution of the radius of curvature due to diffusion is obtained. For the single-layer beam structure, the radius of curvature is inversely proportional to the bending moment created by nonuniform concentration distribution. For the bilayer beam structure, the curvature is a linear function of the mismatch strain between the two layers and the bending moment introduced by diffusion. The mismatch strain depends on the concentration and the partial molar volume of the diffusing component in both layers. Application to microelectromechanical systems hydrogen sensors with a layer of Pd is shown.
Comment on “A quantitative numerical model of multilayer vapor-deposited organic light emitting diodes” [J. Appl. Phys. 86, 3895 (1999)]
Authors: Song Su-Bin , Lee Joo Hwa , Oh Jun-Sik
Published: May 2003

In an article of numerical modeling and simulation of organic light emitting diodes [J. Appl Phys. 86, 3895 (1999)], Staudigel et al. solved a one-dimensional Poisson equation to get an electric field at each monolayer, which is incorrect. The corrected solution of the Poisson equation can give a quantitatively different numerical result if the differences of dielectric constants among the layers are not negligible.
Thickness dependence of magnetic blocking in granular thin films with interacting magnetic particles
Authors: Wang Jian-Qing , Zhao Zhi-Dong , Whittenburg Scott. L.
Published: May 2003

Interparticle interaction among single domain nanosize magnetic particles embedded in nonmagnetic matrix was studied. Attention was paid to concentrated Cu–Co granular thin films with a fixed magnetic volume fraction (20%). By analyzing theoretical models and comparing with experimental results, a dimensional constraint on the magnetic properties was found. As the film thickness reduces toward the thin limit the interparticle interaction plays important roles in modifying the magnetic behavior. The dipolar interaction energy was calculated among magnetic particles including far-neighbor interaction for films with different thickness values. When magnetization variation is included in the calculation, the resulting calculated interaction energy versus film thickness shows remarkable agreement with the variation of experimental observed peak temperature derived from magnetic blocking curves.
Spontaneous magnetization generated by spin, pulsating, and planar combustion synthesis
Authors: Martirosyan K. S. , Claycomb J. R. , Gogoshin G. , Yarbrough R. A. , Miller J. H. , Luss D.
Published: May 2003

The motion of the high temperature front during combustion synthesis of ferrite materials generates residual magnetization in cylindrical product samples. The combustion wave created a current density of up to 10 A/cm2, which influenced the magnetization distribution. The measured peak magnetic field intensity was up to 8 μT. Qualitatively different magnetic field maps were generated in ferrite samples synthesized by different combustion modes. The average magnetization vector generated by either planar or pulsating combustion was oriented at a smaller angle with respect to the pellet axis (φ⩽45°) than those generated by spin combustion (60°⩽φ⩽80°). We estimate that an internal transient magnetic field of up to 5 mT formed in the postcombustion region when its temperature was below the Curie temperature. This explains why the Earth's field had no impact on the spontaneous magnetization field. Model calculations reproduce the qualitative features of the measured field maps.
Resistive magnetohydrodynamic transport model for a reversed field pinch. II. Results
Authors: Bruno A. , Freidberg J. P. , Hastie R. J.
Published: May 2003

The second paper of this series presents a wide range of results and comparisons obtained by numerically solving the resistive magnetohydrodynamic marginal stability model described in paper I [Phys. Plasmas 10, 2330 (2003), preceding paper]. The topics covered include the following. Many simulations have been carried out from which it has been possible to perform a regression analysis leading to macroscopic scaling relations for τE and βp as functions of I, a, n, and the pinch parameter θ. The scaling relations are used to compare with data from the Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] and the Reversed Field Experiment (RFX) [G. Rostagni, Fusion Eng. Des. 25, 301 (1995)], various near-analytic theoretical models, numerical simulations, and an empirical observation first pointed out by Werley concerning the “best” performance of reversed field pinch’s (RFP). The present model, which represents the most comprehensive scaling relations to date, agrees reasonably well with both the limited experimental data available and full three-dimensional nonlinear simulations. It makes more accurate predictions than any of the simpler near-analytic models. Finally, a comparison is made between the projected values for nTτ in an RFP and a tokamak. The scaling is surprisingly similar although the numerical coefficient is about a factor of 30 higher (i.e., more favorable) for the tokamak.
Ab initio lattice dynamics and structural stability of MgO
Authors: Oganov Artem R. , Gillan Michael J. , Price G. David
Published: May 2003

Using density-functional perturbation theory, we have studied lattice dynamics, dielectric and thermodynamic properties, and P–T stability fields of the NaCl- (“B1”) and CsCl- (“B2”) structured phases of MgO. The results compare well with available experiments and resolve the controversy between earlier theoretical studies of the phase diagram of MgO. We predict that at all conditions of the Earth’s mantle the B1 structure is stable. Static calculations predict the B1–B2 transition to occur at 490 GPa; zero-point vibrations lower this pressure by 16 GPa. The B2-structured phase is dynamically unstable below 110 GPa, but becomes dynamically stable at higher pressures. On the contrary, the B1 phase does not display soft modes at any of the studied pressures. MgO remains an insulator up to ultrahigh pressures: we predict metallization of the B2-structured phase of MgO at 20.7 TPa.
The complex structure of the reconnecting magnetopause
Authors: Mozer F. S. , Phan T. D. , Bale S. D.
Published: May 2003

Electric and magnetic fields observed in a one-of-a-kind example of a Polar satellite magnetopause crossing are consistent with static guide magnetic and electric fields, Hall magnetohydrodynamic (MHD) electric and magnetic fields, and a Z-component of the magnetic field that varied from −80 nT to +80 nT across the magnetopause [F. S. Mozer, S. D. Bale, and T. D. Phan, Phys. Rev. Lett. 89, 015002 (2002)]. In spite of this excellent agreement with simulations, other features of the data were unanticipated. An empirical model, based on these measured fields and the assumption that the parallel electric field was zero, is developed to explain such features by showing that (1) Postreconnection E×B/B2 flows, carrying electrons, magnetic field lines, and Poynting flux towards the X-line rather than away from it, occur at some locations. (2) The model and measured tangential electric fields varied significantly through the magnetopause. If the magnetopause was a time stationary structure, Faraday’s law requires that it be three-dimensional on a spatial scale in the Y-direction of a few ion skin depths. This three-dimensionality may explain why only one example having fields that agree with Hall MHD simulations has been found. (3) There were regions within the magnetopause where electromagnetic energy may have been generated (in the normal incidence frame tied to the magnetopause). (4) Significant conversion of electromagnetic energy can occur inside the magnetopause in the absence of an electron diffusion region, parallel electric fields, or the electrons being decoupled from the magnetic field. It is emphasized that these properties are consequences of the Hall MHD and guide electric and magnetic fields in the absence of any additional non-MHD processes.
X-ray scattering from solid density plasmas
Authors: Glenzer S. H. , Gregori G. , Rogers F. J. , Froula D. H. , Pollaine S. W. , Wallace R. S. , Landen O. L.
Published: May 2003

Measurements of the microscopic properties of dense matter have been demonstrated by applying spectrally resolved multi-keV x-ray scattering. The scattering spectra from solid density beryllium show the inelastic Compton-down shifted feature that is spectrally broadened when heating the solid density plasmas isochorically and homogeneously to temperatures of several times the Fermi energy. The spectral shape of the inelastic scattering component provides an accurate measurement of the temperature, and the intensity ratio of inelastic to elastic scattering measures the ionization balance. These measurements extend the powerful technique of Thomson scattering [S. H. Glenzer et al., Phys. Plasmas 7, 2149 (1999)] to the x-ray regime for independent measurements of the plasma parameters of solid density and super dense laboratory plasmas. This new technique has wide applications to investigate the previously inaccessible regimes of dense matter, from Fermi degenerate, to strongly coupled, to high temperature ideal gas plasmas.
Cd doping at the CuInSe2/CdS heterojunction
Authors: Liao Dongxiang , Rockett Angus
Published: May 2003

The chemical composition of the CuInSe2/CdS heterojunction interface is investigated by angle resolved x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy in combination with selective etching of CdS. We demonstrate that ∼0.8 monolayer of Cd is incorporated into the first 1–3 atomic layers of the CuInSe2. This is accompanied by significant Cu depletion with respect to In in the same region. The results suggest that CdCu defects heavily dope CuInSe2 surface n type and cause the observed large band bending on the CuInSe2 side of the heterojunction.
Guided modes with imaginary transverse wave number in a slab waveguide with negative permittivity and permeability
Authors: Wu Bae-Ian , Grzegorczyk Tomasz M. , Zhang Yan , Kong Jin Au
Published: May 2003

The guidance conditions of modes with both real and imaginary transverse wave numbers inside a dielectric slab with negative permittivity and permeability are solved. We show that for real transverse wave numbers, cutoffs exist for all modes, unlike in conventional media where the first even mode is always propagating. In addition, we also show that guided modes exist for imaginary transverse wave numbers, with the power concentrated at the interfaces instead of having maxima inside the slab. A graphical method of determining the imaginary transverse wave numbers of the guided modes is introduced which clearly identifies the different conditions of propagation depending on the properties of the slab. In particular, propagation of guided waves inside less dense negative media is shown to be possible.
Heat transfer mapping in 3–5 μm planar light emitting structures
Authors: Malyutenko V. K. , Malyutenko O. Yu. , Dazzi A. , Gross N. , Ortega J.-M.
Published: May 2003

We report on the heat distribution inside a p+-InAsSb(Zn)/n-InAsSbP/n-InAs planar structure, emitting at 4.3 μm at 300 K. The experimental setup consists of both an infrared scanning microscope and a fiber tip as remote heat sensors (spatial resolution of some μm) operating in a time-resolved (10 μs temporal resolution) manner in the 3–5 μm spectral range. By comparing light and heat maps, we show that current crowding generates local hot regions (somewhat like heat traps) and remarkable temperature gradients (up to 3000 °C/cm) inside the emitting structure.
Effect of high magnetic fields on the morphology of soft magnetic α′-FeN films
Authors: Wang H. Y. , Mitani S. , Motokawa M. , Fujimori H.
Published: May 2003

The effect of high magnetic field on the microstructure and magnetic properties of α′-FeN films has been studied. The application of a high magnetic field during sputter deposition has a significant influence on the microstructure of α′-FeN films. In particular, the grain growth and the surface roughness are suppressed, and concurrently the coercivity becomes much lower. α′-FeN films deposited in magnetic fields of 2 and 4 T exhibit smooth surfaces with root-mean-square (rms) roughness of, respectively, 0.38–1.53 nm, saturation magnetization of 2.25–2.32 T and coercivity of 1.6–2.6 kA/m, while α′-FeN films deposited at H=0 T show rough surfaces with rms roughness of 6.0–6.8 nm, saturation magnetization of 2.13–2.15 T and coercivity of 9.8–12 kA/m. This effect of high magnetic field on the surface morphology is expected to be widely used to improve various properties of thin films.
Broken symmetries in the entanglement of formation
Authors: Benatti Fabio , Narnhofer H. , Uhlmann A.
Published: May 2003

We compare some recent computations of the entanglement of formation in quantum information theory and of the entropy of a subalgebra in quantum ergodic theory. Both notions require optimization over decompositions of quantum states. We show that both functionals are strongly related for some highly symmetric density matrices. Indeed, for certain interesting regions the entanglement of formation can be expressed by the entropy of a commuting subalgebra, and the corresponding optimal decompositions can be obtained one from the other. We discuss the presence of broken symmetries in relation with the structure of the optimal decompositions.
Chamber transport of “foot” pulses for heavy-ion fusion
Authors: Sharp W. M. , Callahan D. A. , Tabak M. , Yu S. S. , Peterson P. F.
Published: May 2003

Indirect-drive targets for heavy-ion fusion must initially be heated by “foot” pulses that precede the main heating pulses by tens of nanoseconds. These pulses typically have a lower energy and perveance than the main pulses, and the fusion-chamber environment is different from that seen by later pulses. The preliminary particle-in-cell simulations of foot pulses here examine the sensitivity of the beam focusing to ion–beam perveance, background-gas density, and pre-neutralization by a plasma near the chamber entry port.
Neoclassical nature of the radial electric field at the low-to-high confinement transition
Authors: Kiviniemi T. P. , Sipilä S. K. , Rozhansky V. A. , Voskoboynikov S. P. , Kaveeva E. G. , Heikkinen J. A. , Coster D. P. , Schneider R. , Bonnin X.
Published: May 2003

The radial electric field Er at the tokamak plasma edge is simulated both with a two-dimensional (2D) fluid code solving the most complete system of transport equations and with five-dimensional (three-dimensional in configuration space and 2D in velocity space) Monte Carlo particle following code. At low to high confinement transition conditions, the E⃗r×B⃗ shearing rate is found to be high enough for turbulence suppression even though the field is essentially neoclassical. Here, B⃗ is the magnetic field. No bifurcation of Er is found.
A Gordeyev integral for electrostatic waves in a magnetized plasma with a kappa velocity distribution
Authors: Mace R. L.
Published: May 2003

A Gordeyev-type integral for the investigation of electrostatic waves in magnetized plasma having a kappa or generalized Lorentzian velocity distribution is derived. The integral readily reduces, in the unmagnetized and parallel propagation limits, to simple expressions involving the Zκ function. For propagation perpendicular to the magnetic field, it is shown that the Gordeyev integral can be written in closed form as a sum of two generalized hypergeometric functions, which permits easy analysis of the dispersion relation for electrostatic waves. Employing the same analytical techniques used for the kappa distribution, it is further shown that the well-known Gordeyev integral for a Maxwellian distribution can be written very concisely as a generalized hypergeometric function in the limit of perpendicular propagation. This expression, in addition to its mathematical conciseness, has other advantages over the traditional sum over modified Bessel functions form. Examples of the utility of these generalized hypergeometric series, especially how they simplify analyses of electrostatic waves propagating perpendicular to the magnetic field, are given. The new expression for the Gordeyev integral for perpendicular propagation is solved numerically to obtain the dispersion relations for the electrostatic Bernstein modes in a plasma with a kappa distribution.
Laser synthesis of carbon-rich SiC nanoribbons
Authors: Salama I. A. , Quick N. R. , Kar A.
Published: May 2003

A nanosecond pulsed laser direct-write and doping (LDWD) technique is used for the fabrication of carbon-rich silicon carbide nanoribbons heterostructure in a single crystal 4H–SiC wafer. Characterization by high-resolution transmission electron microscope and selected area electron diffraction pattern revealed the presence of nanosize crystalline ribbons with hexagonal graphite structure in the heat-affected zone below the decomposition temperature isotherm in the SiC epilayer. The nanoribbons exist in three layers each being approximately 50–60 nm thick, containing 15–17 individual sheets. The layers are self-aligned on the (0001) plane of the SiC epilayer with their c axis at 87° to the incident laser beam. The LDWD technique permits synthesis of heterostructured nanoribbons in a single step without additional material or catalyst, and effectively eliminates the need for nanostructure handling and transferring processes.
Ultrasonic study of ferrimagnetic FeCr2S4: Evidence for low temperature structural transformations
Authors: Maurer D. , Tsurkan V. , Horn S. , Tidecks R.
Published: May 2003

The elastic properties of single crystalline FeCr2S4 have been investigated as a function of temperature and magnetic field. The temperature dependence of the sound velocity is characterized by three distinct anomalies, namely at the Curie temperature TC=167 K, at T∼60 K, and at T∼15 K. For T<TC the sound velocity and, thus, the shear modulus depend on the magnetic field. The concurrence of elastic and magnetic anomalies in the ferrimagnetic state suggests that they are of a common origin. From the experimental observations it is concluded that orbital ordering induces a lattice distortion below T=60 K.
Lower bound for the superheating field in the weak-κ limit: The general case
Authors: Del Castillo Pierre
Published: May 2003

We have constructed asymptotic matched solutions for the one dimensionnal Ginzburg–Landau system when κ is small [Math. Model. Num. Anal. 36, 971–993 (2002)]. We have deduced an expansion in powers of κ1/2 at all orders for the superheating field. In this paper, using these constructions, we propose to show that the superheating field admits for lower bound the expansion of the formal superheating field truncated at order n, for all n∈N. We generalize the proof given in Eur. J. Appl. Math. 13, 519–547 (2002), where this result is obtained for n=1. Then, we construct solutions of the Ginzburg–Landau system when the exterior magnetic field is near to the superheating field, and we give a localization of these solutions.
Modeling and application of plasma charge current in deep penetration laser welding
Authors: Zhang Xudong , Chen Wuzhu , Jiang Ping , Guo Jing , Tian Zhiling
Published: May 2003

Plasma charge current distribution during deep penetration CO2 laser welding was analyzed theoretically and experimentally. The laser-induced plasma above the workpiece surface expands up to the nozzle, driven by the particle concentration gradient, forming an electric potential between the workpiece and the nozzle due to the large difference between the diffusion velocities of the ions and the electrons. The plasma-induced current obtained by electrically connecting the nozzle and the workpiece can be increased by adding a negative external voltage. For a fixed set of welding conditions, the plasma charge current increases with the external voltage to a saturation value. The plasma charge current decreases as the nozzle-to-workpiece distance increases. Therefore, closed-loop control of the nozzle-to-workpiece distance for laser welding can be based on the linear relationship between the plasma charge current and the distance. In addition, the amount of plasma above the keyhole can be reduced by a transverse magnetic field, which reduces the attenuation of the incident laser power by the plasma so as to increase the laser welding thermal efficiency.
Contextual viewpoint to quantum stochastics
Authors: Khrennikov Andrei
Published: May 2003

We study the role of context, complex of physical conditions, in quantum as well as classical experiments. It is shown that by taking into account contextual dependence of experimental probabilities we can derive the quantum rule for the addition of probabilities of alternatives. Thus we obtain quantum interference without applying the wave or Hilbert space approach. The Hilbert space representation of contextual probabilities is obtained as a consequence of the elementary geometric fact: cos-theorem. By using another fact from elementary algebra we obtain complex-amplitude representation of probabilities. Finally, we found contextual origin of noncommutativity of incompatible observables.
Dynamics of complex interfaces. I. Rheology, morphology, and diffusion
Authors: El Afif A. , De Kee D. , Cortez R. , Gaver D. P.
Published: May 2003

In this paper, we investigate, on two levels of description, the isothermal coupling: (i) between rheology and morphology in immiscible blends (A/B) and (ii) among rheology, morphology, and diffusion in mixtures consisting of an immiscible blend (A/B) and one simple fluid, s. The interface separating the phases A and B is described, on the kinetic level by an area density distribution function and on the mesoscopic level by a scalar and a traceless symmetric second order tensor. The nonlinear formulations are derived using the general equation for nonequilibrium reversible and irreversible coupling formalism which ensures the consistency of dynamics with thermodynamics. In addition to the non-Fickian character of mass transport, the coupled three-dimensional governing equations explicitly show the effects of the external flow and diffusion on the size and shape of the interface. New expressions for the stress tensor emerge naturally in the models including the contributions of the diffusion fluxes and the isotropic (Laplace) and anisotropic deformations of the interface. Asymptotic solutions of the governing equations also show that the transport coefficients (diffusivity, etc.) are explicitly dependent on the interfacial tension and on the velocity gradient of the applied flow. The latter dependence renders the process of mass transfer highly anisotropic even in the absence of internal stresses created by the deformation of the interface. The diffusion-free models of Doi–Ohta and Lee–Park are recovered as particular cases.
Dynamics of complex interfaces. II. Diffusion and morphology
Authors: El Afif A. , De Kee D. , Cortez R. , Gaver D. P.
Published: May 2003

In this contribution, we theoretically investigate the isothermal mass transport of a simple fluid into a blend of two immiscible Newtonian polymers. Using internal state variables, we derive a nonlinear formulation that addresses the effects of the diffusion/interface coupling on both the mass transport as well as on the morphology of the interface. The approach uses a scalar and a second-order tensor to directly track the dynamic changes of the size and shape of the interface. The mass flux governing equation includes new terms that lead to non-Fickian behavior attributed to the viscoelatic contribution of the interface. In turn, the size and shape of the interface are modified by diffusion. In one-dimensional analysis, we examine the nature of propagation of both nonlinear hyperbolic and linear dispersive waves. Explicit formulas for the characteristic speed, phase velocity, and attenuation are provided.
Phase diagrams of Zwanzig models: The effect of polydispersity
Authors: Martı́nez-Ratón Yuri , Cuesta José A.
Published: May 2003

The first goal of this article is to study the validity of the Zwanzig model for liquid crystals to predict transitions to inhomogeneous phases (like smectic and columnar) and the way polydispersity affects these transitions. The second goal is to analyze the extension of the Zwanzig model to a binary mixture of rods and plates. The mixture is symmetric in that all particles have equal volume and length-to-breadth ratio, κ. The phase diagram containing the homogeneous phases as well as the spinodals of the transitions to inhomogeneous phases is determined for the cases κ=5 and 15 in order to compare with previous results obtained in the Onsager approximation. We then study the effect of polydispersity on these phase diagrams, emphasizing the enhancement of the stability of the biaxial nematic phase it induces.
Effects of solvent model flexibility on aqueous electrolyte behavior between electrodes
Authors: Guymon Clint G. , Hunsaker Matthew L. , Harb John N. , Henderson Douglas , Rowley Richard L.
Published: May 2003

Molecular dynamics simulations have been carried out for aqueous electrolyte solutions between model electrode surfaces. The effect of solvent model flexibility on bulk and double layer properties was observed for electrode surface charge densities of 0, ±0.1, and ±0.2 C/m2 and ion concentrations of 0, 0.5, and 1 M. Two flexible models were used to isolate the effects of flexibility from the effects of a change in the condensed-phase dipole moment. Model flexibility increases the pure water self-diffusion coefficient while a larger liquid dipole moment substantially decreases it. There is an increase in ion contact adsorption and counter ion affinity with the flexible models, suggesting that the ions are less tightly solvated. This conclusion is consistent with observed enhancements of solvated ion densities near uncharged electrodes for the flexible water case. Mobile ions in high concentration quickly damp out the electric field even at high electrode charge densities, but for dilute ion concentrations the field may extend to the center of the cell or beyond. In these cases it is more appropriate to integrate Poisson’s equation from the electrode surface outward instead of the common method of assuming zero field at the center of the simulation cell. Using this methodology, we determine the voltage drop across the half-cell for both the rigid and flexible models. The half-cell voltage drop shows some dependence on ion concentration, but solvent flexibility has little effect on that behavior.
Experimental observation of a tripolar vortex in a plasma
Authors: Okamoto A. , Hara K. , Nagaoka K. , Yoshimura S. , Vranješ J. , Kono M. , Tanaka M. Y.
Published: May 2003

A tripolar vortex, three aligned vortices with alternate signs of polarity of rotation, has been observed in a plasma for the first time. The tripolar vortex always appears with a deep density depression in the neutral particles, and the rotation direction of each vortex is opposite to that of the E×B rotation due to the ambipolar electric field. It is shown that a net momentum transfer during the charge-exchange interaction produces an effective force acting on the ions. The present experiment shows that this effective force may dominate the ambipolar-electric field and drive the anti-E×B vortical motion of ions.
Structural, optical, and electronic properties of hydrogenated polymorphous silicon films deposited from silane–hydrogen and silane–helium mixtures
Authors: Saadane O. , Lebib S. , Kharchenko A. V. , Longeaud C. , Roca i Cabarrocas R.
Published: May 2003

Here we compare the hydrogen incorporation and the optoelectronic properties of hydrogenated polymorphous silicon (pm-Si:H) films deposited by the decomposition of either silane–hydrogen or silane–helium mixtures. The use of He dilution leads to higher deposition rate and films with a lower hydrogen content with respect to hydrogen dilution. On the contrary, hydrogen dilution leads to films with high hydrogen content that show a characteristic infrared stretching band at 2040 cm−1. We propose that this absorption band is due to hydrogen bonded at the surface of crystallites and clusters in a platelet-like configuration. This peculiar hydrogen bonding is related to low temperature hydrogen diffusion, which gives rise to a sharp hydrogen effusion peak at around 420 °C. Interestingly enough, the higher deposition rate in the films from the He-dilution series does not result in degradation of the film’s electronic and transport properties, which are strongly improved with respect to those of standard amorphous silicon. Finally, we report on improvement of the hole transport properties and their homogenization, independent of the deposition conditions, when the films are submitted to repeated light-soaking and annealing cycles.
Amorphous-to-crystalline transition during the early stages of thin film growth of Cr on SiO2
Authors: Hu Minghui , Noda Suguru , Komiyama Hiroshi
Published: May 2003

The growth of sputter-deposited Cr thin films on amorphous SiO2 during the early stages was studied using transmission electron microscopy. Amorphous three-dimensional islands were first formed, and then they grew with continuously increasing density and slowly increasing size as the deposition proceeded. When these islands began to coalesce at a nominal film thickness of 2.3–3.0 nm, they abruptly crystallized into randomly oriented crystalline nuclei. The depth profile analysis by x-ray photoelectron spectroscopy indicates the existence of interfacial Cr–O interactions. After excluding the possibilities of kinetic limitation and interfacial mixing, a thermodynamic model was employed to explain the size-dependent amorphous-to-crystalline transition. Our results suggest that the interfacial-interaction-induced strain relaxation at island/substrate interfaces might result in the thermodynamic stabilization of substrate-supported amorphous islands below a critical size.
Composition dependence of optical phonon properties and dielectric functions of group-III arsenide ternary and quaternary mixed crystals
Authors: Zheng Ruisheng , Taguchi Tsunemasa
Published: May 2003

Optical properties of group-III arsenide ternary and quaternary alloys are investigated theoretically by a generalized mixed crystal theory. On the basis of a modified random element isodisplacement approach, long-wavelength optical phonon energies, phonon mode strengths and dielectric functions of AlxGa1−xAs, AlxIn1−xAs, and GaxIn1−xAs ternary alloys, and also of AlxGayIn1−x−yAs quaternary alloys are calculated numerically in the whole compositional range. The results are discussed and compared with experimental results. It is confirmed that the optical phonon spectra of AlxGayIn1−x−yAs alloys will exhibit three optical phonon modes in most of the compositional range.
Microstructure of heteroepitaxial GaN revealed by x-ray diffraction
Authors: Chierchia R. , Böttcher T. , Heinke H. , Einfeldt S. , Figge S. , Hommel D.
Published: May 2003

The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy.