bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of radiation induced relaxor behavior of poly(vinylidene fluoride-trifluoroethylene) copolymers
Authors: Stephanovich V. A. , Glinchuk M. D. , Kirichenko E. V. , Hilczer B.
Published: October 2003

We propose a theory of the dynamic dielectric response in the organic ferroelectrics polyvinylidene fluoride (PVDF), poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] copolymer before and after irradiation by fast electrons. For this purpose, we use our random field formalism. In the adopted model we consider the earlier polymers as the disordered ferroelectrics in a mixed ferroglass phase (FG) with a coexistence of polar short- and long-range order regions. Short-range order regions correspond to amorphous layers, while long-range order regions appears in the crystalline phase of all-trans conformation. In our formalism, we account for the change of VDF content as well as for the influence of the irradiation, by variation of the content of electric dipoles and other random field sources. The downward shift of the paraferroelectric phase transition temperature and gradual transformation of the mixed FG phase into a dipole glass state with the increase of the irradiation dose was shown to be related to the self-consistent change of parameters of random field distribution function. We were able to fit the low-temperature dynamic dielectric response related to the amorphous phase by Vogel–Fulcher (V–F) law with parameters close enough to those observed in the experiment. The coincidence between calculated and measured behavior (namely, almost complete disappearance of high-temperature maxima, corresponding to the ferroelectric phase transition, their submergence into low-temperature maxima and V–F law for the low-temperature maxima of absorption) of the irradiated samples speaks in favor of irradiation induced relaxor behavior of P(VDF/TrFE) copolymers. We also discuss the physical reasons for the choice of the parameters of material necessary to fit our theory to the experiment.
Stokesian dynamics of nonspherical particles, chains, and aggregates
Authors: Kutteh Ramzi
Published: October 2003

The microstructure and properties of suspensions of nonspherical particles are influenced by the specific particle shapes through hydrodynamic interactions, but here traditional numerical approaches of solving the Stokes equations are limited to small systems by computational cost, and often to special particle arrangements by symmetry requirements. On the other hand, the analytical development of a hydrodynamic mobility algorithm for Stokesian dynamics (SD) simulations of rigid nonspherical particles is mathematically involved, must be derived for each distinct particle shape needed, and cannot handle deformable particles. Hence we present algorithms for SD simulations of arbitrary shape particles, rigid or flexible, constructed with appropriate constraints among rigid spherical particles whose hydrodynamic mobility is computable by various available schemes, including ours [J. Chem. Phys. 112, 2548 (2000)]. The optimal algorithm also provides for rigid attachment among particles during simulation, by aggregation for example. Its implementation for a system with internal coordinate constraints is tested in simulations of aggregation of spheres and sedimentation of spheroids and chains in bounded and unbounded geometries.
Structures and optical properties of solid hydrogen at ultrahigh pressures
Authors: Nagara H.
Published: October 2003

The electronic energy bands in structures whose primitive cell contains up to four molecules are studied with full optimization of the structures on the basis of GGA and LDA band calculations. Above 250 GPa, the eventual optimal structure obtained by the GGA or the LDA calculation is Cmca, which is a layered structure with the molecular bonds lying in planes and which has a metallic band structure with no band gaps. The metallic property of the band structure remains unchanged even if the molecular bonds in the plane of the Cmca are inclined so that the atoms in the molecule lie out of the plane. The electronic bands of the Cmca structure and those of some other candidate structures are discussed in the light of recent experimental results. Effects of the occupation of electronic states on the predicted optimal structures are also studied.
Heat transfer by low-frequency phonons and “diffusive” modes in cryocrystal solutions: the Kr–Xe system
Authors: Konstantinov V. A. , Orel E. S. , Revyakin V. P.
Published: October 2003

The temperature and volume dependences of the thermal conductivity of the Kr1−ξXeξ solid solution are analyzed in a model in which heat is transferred by low-frequency phonons; above the phonon mobility edge this is done by “diffusive” modes migrating randomly from site to site. The phonon mobility edge ω0 is determined from the condition that the phonon mean free path limited by umklapp processes and scattering on point defects cannot be smaller than one-half the phonon wavelength. The Bridgman coefficient g=−(∂ ln Λ/∂ ln V)T is the weighted mean over these modes, whose volume dependences differ strongly. It is shown that the amount of heat transferred by the “diffusive” modes above 100 K is quite large even in pure Kr and it increases with rising temperature and impurity concentration.
Role of the orientational subsystem in the expansion of pure SF6, CHCl3, C6H6, CCl4, and N2O with Kr impurity
Authors: Zholonko N. N. , Tsibulin V. V. , Sarwar I.
Published: October 2003

The linear expansion coefficients of solid bulk samples of N2O with 5% Kr impurity are measured by an absolute dilatometric method in comparison with pure N2O in the temperature range 80–150 K. An additional unusual orientational effect is discussed. An analysis of the data from measurements of the linear expansion coefficients of pure solid SF6, CHCl3, C6H6, and CCl4 in comparison with solid Xe in the temperature range 80–170 K is carried out in order to determine the role of molecules’ orientational disordering in the thermal expansion of the given condensed systems. The results are discussed in connection with the problem of determining the contribution of orientational subsystems with different types of molecular symmetry to the total thermal expansion and its behavior in various temperature intervals of solid phase existence.
Properties of solid hydrogen doped by heavy atomic and molecular impurities
Authors: Galtsov N. N. , Prokhvatilov A. I. , Shcherbakov G. N. , Strzhemechny M. A.
Published: October 2003

The structural characteristics of normal and para hydrogen crystals doped with Ar, Kr, N2, and O2 impurities are studied by powder x-ray diffraction over the range from 5 K to the melting point of the hydrogen matrix. It is established that in spite of the very low solubility of the dopants in solid hydrogen, these impurities appreciably affect the structural characteristics. In particular, only nitrogen impurities do not change the molar volume of the matrix; the other three make the matrix expand. The Ar and Kr impurities also change the c/a ratio of the hcp matrix. The fact that both Ar and O2 have smaller molar volumes than hydrogen may be regarded as evidence that these impurities form van der Waals complexes with the hydrogen lattice environment.
Influence of cut-off truncation and artificial periodicity of electrostatic interactions in molecular simulations of solvated ions: A continuum electrostatics study
Authors: Bergdorf Michael , Peter Christine , Hünenberger Philippe H.
Published: October 2003

A new algorithm relying on finite integration is presented that solves the equations of continuum electrostatics for truncated (and possibly reaction-field corrected) solute–solvent and solvent–solvent interactions under either nonperiodic or periodic boundary conditions. After testing and validation by comparison with existing methods, the algorithm is applied to investigate the effect of cut-off truncation and artificial periodicity in explicit-solvent simulations of ionic solvation and ion–ion interactions. Both cut-off truncation and artificial periodicity significantly alter the polarization around a spherical ion and thus, its solvation free energy. The nature and magnitude of the two perturbations are analyzed in details, and correction terms are proposed for both effects. Cut-off truncation is also shown to induce strong alterations in the potential of mean force for ion–ion interaction. These observations help to rationalize artifacts previously observed in explicit–solvent simulations, namely spurious features in the radial distribution functions close to the cut-off distance and alterations in the relative stabilities of contact, solvent-separated and free ion pairs.
Characteristics of laser-produced plasmas in a gas filled chamber and in a gas jet by using a long pulse laser
Authors: Kim J. U. , Lee H. J. , Kim C. , Kim G. H. , Suk H.
Published: October 2003

The dynamics of the laser-produced plasma in a gas filled chamber and in a gas jet were investigated using a relatively low intensity laser (I⩽5×1012 W/cm2) with long pulse duration (7 ns). Visualization methods such as the Mach–Zehnder interferometry and the shadow imaging were employed to characterize the shock velocity, electron densities, and temperatures in the laser-produced plasma. The electron density depletion on the laser propagation axis was observed in a gas jet but not in the gas filled chamber. Qualitative analysis for the density depletion is discussed by employing a fluid theory for the ambipolar diffusion of the plasma species. In the gas filled chamber, increase of the laser energy, and applied gas pressure results in faster and further propagation of the shock front with the distance-time relation of Rs∝t2/5, implicating an instantaneous energy release at a point. However, the plasma produced in a gas jet shows a rather linear relation of Rs∝t at early time (t⩽10 ns).
Nanometer precision metrology of submicron Cu/SiO2 interconnects using fluorescence and transmission x-ray microscopy
Authors: Xu Guangyong , Eastman D. E. , Lai B. , Cai Z. , McNulty I. , Frigo S. , Noyan I. C. , Hu C. K.
Published: October 2003

We used hard x-ray fluorescence and soft x-ray transmission microscopy to quantitatively measure “in situ” Cu/SiO2 interconnect dimensions down to 0.3 μm dimensions. We describe methods and analysis techniques for measuring submicron linewidths, lengths, and thicknesses with accuracies of 30–60 nm precision. The dimensions and shape of submicron Cu vias, W lines, and a 20 nm Ta liner and an electromigration defect (void) were determined by these methods. These nondestructive techniques promise to be useful for nanometer precision metrology studies of a variety of materials systems.
Fluorescence detected microwave Stark effect measurements in excited vibrational states of H2CO
Authors: Theulé Patrice , Callegari Andrea , Rizzo Thomas R. , Muenter J. S.
Published: October 2003

We describe a microwave-optical double resonance experiment designed for Stark effect measurements on molecules in excited vibrational energy levels of ground electronic states. This technique, which employs pulsed laser excitation and laser induced fluorescence detection, has been used to measure electric dipole moments in the 11, 51, and 52 vibrational states of formaldehyde. In addition, a Stark induced quantum beat experiment is briefly described.
Polymer-mediated adhesion: A statistical approach
Authors: Allegra Giuseppe , Raos Guido , Manassero Carlo
Published: October 2003

The statistical behavior of linear chains confined in a thin slab is investigated theoretically as a model of polymer-mediated adhesion. We apply transition-matrix methods to two lattice models of the polymer: model A consists of end-grafted monodisperse polymer chains, model B of randomly grafted infinitely long chains. We evaluate both the elongational and the tangential moduli, the first being generally larger than the latter. We also derive by a Flory–Huggins approach the contribution to the elongational modulus of the polymer compressibility or of a swelling solvent.
Magnetic properties of ultrathin Co/Ag/Pt(111) films
Authors: Su C. W. , Tzeng C. L. , Ho H. Y. , Shern C. S.
Published: October 2003

The magnetic properties of Co on Pt(111) with 1 ML Ag buffer layer were studied by magneto-optical Kerr effect. The easy axis of the magnetization of Co deposited on 1 ML Ag/Pt(111) switches from the out-of-plane to the in-plane direction when the coverage of Co is larger than 1 ML. The easy axis can transform from the in-plane to the out-of-plane direction after high temperature annealing for 2–7 ML Co/1 ML Ag/Pt(111). The study of Auger electron spectroscopy shows that the spin reorientation transition occurs when 1 ML Ag atoms diffuse to the top layer. The perpendicular magnetic anisotropy is significantly enhanced after further annealing at higher temperatures. The enhancement of the perpendicular magnetic anisotropy is attributed to the formation of Co–Pt alloy after the atomic exchange between Co and Ag. The possible mechanisms for the spin reorientation transition and the enhancement in the perpendicular magnetic anisotropy are discussed.
Vibrational, single-particle-like, and diffusive dynamics in liquid Se, Te, and Te50Se50
Authors: Chiba Ayano , Ohmasa Yoshinori , Yao Makoto
Published: October 2003

Neutron scattering measurements were carried out for liquid Se, liquid Te, and liquid Te50Se50. The results are discussed in the context of semiconductor-to-metal transition. As to liquid Te50Se50, the vibrational modes show a remarkable change when the semiconductor-to-metal transition occurs by temperature increase. A soft stretching mode was observed for the metallic phase and it shows the structural change; the appearance of long bonds in the metallic phase. The vibrational modes for liquid Se and liquid Te were obtained and agreed well with former works. The crossover from collective to single-particle-like regime was also observed for all liquid samples and the transition ranges (Q=4.5–8 Å−1) are presented. The diffusive features in the low-Q region and single-particle-like properties in the high-Q region are discussed and are shown to be consistent with the results for the vibrational modes.
Structural and magnetic characterization of CoxNi1−x nanoparticles in yttria-stabilized zirconia single crystals
Authors: Zhu S. , Sun K. , Zhang Q. Y. , Zu X. T. , Wang L. M. , Ewing R. C.
Published: October 2003

Oriented CoxNi1−x nanoparticles were synthesized by sequential implantation of 90 keV Co and Ni ions at room temperature in the near surface of an yttria-stabilized zirconia single crystal. Transmission electron microscopy and a superconducting quantum interference device magnetometer as well as a vibrating sample magnetometer were utilized to characterize the structural and magnetic properties of the implanted layer. Typical nanoparticles range from 3 to 10 nm in diameter, and some elongated precipitates as long as 25 nm were formed by joining the nanoparticles with nanotwins. Hysteresis loops were measured at both 300 and 10 K, and showed coercivity of 100 or 250 Oe, respectively. Magnetization versus temperature in zero-field-cooled and field-cooled fields was measured. No obvious superparamagnetism was detected below 300 K.
Modulated and ordered defect structures in electrically degraded Ni–BaTiO3 multilayer ceramic capacitors
Authors: Yang G. Y. , Dickey E. C. , Randall C. A. , Randall M. S. , Mann L. A.
Published: October 2003

Structural defects formed on {111} planes of BaTiO3 during the degradation of high performance multilayer Ni–BaTiO3 X7R ceramic capacitors are studied using transmission electron microscopy and electron energy loss spectroscopy (EELS). Regular pseudocubic barium titanate grains are present in as-produced (virginal) base-metal electrode capacitors. However, there is a coexistence of regular, modulated, and long-range ordered structures in intentionally electrically degraded devices. The EELS analysis demonstrates that the concentration of oxygen vacancies in barium titanate with modulated or ordered structures is higher than that in the regular perovskite grains. The clustering or accumulation of oxygen vacancies in the structural framework of BaTiO3 gives rise to the formation of new metastable structures. These observations are consistent with earlier models for degradation, but demonstrate that the details of the process may be more complex than originally assumed. Here we introduce new details on the nature of the reduction process and the manner in which the lattice accommodates the enhanced oxygen vacancy concentration towards the failed regions of the capacitors and in the vicinity of the “blocking” cathodic electrodes.
On the generalized problem of the Boltzmann equation and the moment method in kinetic theory of gases
Authors: Chen M.
Published: October 2003

In this paper we formulate the generalized problem of the Boltzmann equation based on the kinetic entropy balance equation in conjunction with the maximum entropy principle. First we prove that the solution of this generalized problem is unique. We then prove that the entropy balance equation obtained by Eu in extended irreversible thermodynamics is valid, if, and only if, the one-particle distribution function fa is the solution of this generalized problem. As a by-product of this result, we also obtain a statistical expression of the thermodynamic entropy balance equation that shares the same formula as the kinetic entropy balance equation.
Characteristics of Schottky contacts on n-type 4H–SiC using IrO2 and RuO2
Authors: Han Sang Youn , Lee Jong-Lam
Published: October 2003

Thermally stable Schottky contacts on n-type 4H–SiC with high Schottky barrier height were demonstrated by annealing the rare earth metal contacts (Ir and Ru) under O2 ambient. The formation of rare earth metal oxides (IrO2 and RuO2) after O2 annealing led to the increase of Schottky barrier height (>1.9 eV) and a low reverse leakage current (∼10−9 A/cm2). Synchrotron radiation photoemission spectroscopy showed that the work function of IrO2 is higher about 0.23 eV than that of Ir and the binding energies of Si 2p and C 1s shifted toward lower binding energies by 0.12 eV in both O2 and N2 annealed samples. The oxidation annealing caused predominant Si outdiffusion to the IrO2 (RuO2), leaving Si vacancies behind, leading to the shift of surface Fermi level to the energy level of Si vacancy. Both the formation of oxide and the Fermi level movement played a role in forming the Schottky contact with high barrier height and excellent thermally stability.
Electron mobility in double gate silicon on insulator transistors: Symmetric-gate versus asymmetric-gate configuration
Authors: Gámiz F. , Roldán J. B. , Godoy A. , Cartujo-Cassinello P. , Carceller J. E.
Published: October 2003

We have studied electron mobility behavior in asymmetric double-gate silicon on insulator (DGSOI) inversion layers, and compared it to the mobility in symmetric double-gate silicon on insulator devices, where volume inversion has previously been shown to play a very important role, being responsible for the enhancement of the electron mobility. Poisson’s and Schroedinger’s equations have been self-consistently solved in these structures to study and compare the distribution of the electrons. We show that the lack of symmetry in the asymmetric DGSOI structure produces the loss of the volume inversion effect. In addition, we show that as the silicon thickness is reduced the conduction effective mass of electrons in asymmetric devices is lower than that in the symmetric case, but that the greater confinement of electrons in the former case produces a stronger increase in the phonon scattering rate, and in the surface roughness scattering rate. We have solved the Boltzmann transport equation by the Monte Carlo method, and have evaluated the electron mobility. The electron mobility curves in asymmetric DGSOI devices are shown to be considerably below the mobility curves corresponding to symmetric devices, in the whole range of silicon thicknesses. The difference is greater in the range 5–25 nm, where electron mobility in symmetric DGSOI inversion layers is greatly improved by the volume inversion effect. We show that mobility in symmetric devices could be 2.5 times greater than that for their asymmetric counterparts.
An extension of Fourier analysis for the n-torus in the magnetic field and its application to spectral analysis of the magnetic Laplacian
Authors: Sakamoto Makoto , Tanimura Shogo
Published: October 2003

We solved the Schrödinger equation for a particle in a uniform magnetic field in the n-dimensional torus. We obtained a complete set of solutions for a broad class of problems; the torus Tn=Rn/Λ is defined as a quotient of the Euclidean space Rn by an arbitrary n-dimensional lattice Λ. The lattice is not necessary either cubic or rectangular. The magnetic field is also arbitrary. However, we restrict ourselves within potential-free problems; the Schrödinger operator is assumed to be the Laplace operator defined with the covariant derivative. We defined an algebra that characterizes the symmetry of the Laplacian and named it the magnetic algebra. We proved that the space of functions on which the Laplacian acts is an irreducible representation space of the magnetic algebra. In this sense the magnetic algebra completely characterizes the quantum mechanics in the magnetic torus. We developed a new method for Fourier analysis for the magnetic torus and used it to solve the eigenvalue problem of the Laplacian. All the eigenfunctions are given in explicit forms.
Enhancement of thermal and electrical properties of carbon nanotube polymer composites by magnetic field processing
Authors: Choi E. S. , Brooks J. S. , Eaton D. L. , Al-Haik M. S. , Hussaini M. Y. , Garmestani H. , Li D. , Dahmen K.
Published: October 2003

We show that the thermal and electrical properties of single wall carbon nanotube (CNT)-polymer composites are significantly enhanced by magnetic alignment during processing. The electrical transport properties of the composites are mainly governed by the hopping conduction with localization lengths comparable to bundle diameters. The bundling of nanotubes during the composite processing is an important factor for electrical, and in particular, for thermal transport properties. Better CNT isolation will be needed to reach the theoretical thermal conductivity limit for CNT composites.
Exchange coupling between ferromagnetic and laminated antiferromagnetic layers and its application
Authors: Li Kebin , Wu Yihong , Han Guchang , Luo Ping , An Lihua , Qiu Jinjun , Guo Zaibing , Zheng Yuankai
Published: October 2003

Exchange bias (Hex) and coercivity (Hc) of the NiFe layer in the NiFe/IrMn system can be tuned by inserting either spacer layers such as Cu, Ru, and Ta or ferromagnetic layers such as CoFe into IrMn since the antiferromagnetic spin structure of IrMn is altered in consequence. Hex usually decreases while Hc increases when the thin discontinued spacer layers are inserted into IrMn. The crossover from the unidirectional exchange-biased coupling to the uniaxial exchange-spring coupling has been successfully observed in the NiFe/[IrMn/CoFe(t)]3/IrMn (here, 3 means the number of the repeated periods of IrMn/CoFe double layer) system when the thickness of CoFe layer t exceeds 1 nm. It indicates that much of the physics and reversal mechanisms in the exchanged-biased systems are similar to that observed in exchange-spring systems where the hard layer replaces the antiferromagnetic layer as the biasing layer. Uniaxial spin valves (both of current in the plane and current perpendicular to the plane modes) and uniaxial magnetic tunneling junctions have been successfully fabricated by using this uniaxial exchange-spring system.
Study of dynamical process of heat denaturation in optically trapped single microorganisms by near-infrared Raman spectroscopy
Authors: Xie Changan , Li Yong-qing , Tang Wei , Newton Ronald J.
Published: October 2003

The development of laser traps has made it possible to investigate single cells and record real-time Raman spectra during a heat-denaturation process when the temperature of the surrounding medium is increased. Large changes in the phenylalanine band (1004 cm−1) of near-infrared spectra between living and heat-treated cells were observed in yeast and Escerichia coli and Enterobacter aerogenes bacteria. This change appears to reflect the change in environment of phenylalanine as proteins within the cells unfold as a result of increasing temperatures. As a comparison, we measured Raman spectra of native and heat-denatured solutions of bovine serum albumin proteins, and a similar change in the phenylalanine band of spectra was observed. In addition, we measured Raman spectra of native and heat-treated solutions of pure phenylalanine molecules; no observable difference in vibrational spectra was observed. These findings may make it possible to study conformational changes in proteins within single cells.
Distinct nonequilibrium plasma chemistry of C2 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas
Authors: Gordillo-Vázquez F. J. , Albella J. M.
Published: October 2003

We show that the concentrations of the species C2 (X 1Σg+), C2 (a 3Πu), and C2H exhibit a significant increase when the argon content grows up to 95% in medium pressure (0.75 Torr) radio frequency (rf) (13.56 MHz) produced C2H2 (1%)/H2/Ar plasmas of interest for the synthesis of nanodiamond thin films within plasma enhanced chemical vapor deposition devices. In contrast, the concentrations of CH3 and C2H2 remain practically constant. The latter results have been obtained with an improved quasianalytic space–time-averaged kinetic model that, in addition, has allowed us to identify and quantify the relative importance of the different underlying mechanisms driving the nonequilibrium plasma chemistry of C2. The results presented here are in agreement with recent experimental results from rf CH4/H2/Ar-rich plasmas and suggest that the growth of nanodiamond thin films from hydrocarbon/Ar-rich plasmas is very sensitive to the contribution of C2 and C2H species from the plasma.
Integrated predictive modeling of high-mode tokamak plasmas using a combination of core and pedestal models
Authors: Bateman Glenn , Bandrés Miguel A. , Onjun Thawatchai , Kritz Arnold H. , Pankin Alexei
Published: October 2003

A new integrated modeling protocol is developed using a model for the temperature and density pedestal at the edge of high-mode (H-mode) plasmas [Onjun et al., Phys. Plasmas 9, 5018 (2002)] together with the Multi-Mode core transport model (MMM95) [Bateman et al., Phys. Plasmas 5, 1793 (1998)] in the BALDUR integrated modeling code to predict the temperature and density profiles of 33 H-mode discharges. The pedestal model is used to provide the boundary conditions in the simulations, once the heating power rises above the H-mode power threshold. Simulations are carried out for 20 discharges in the Joint European Torus and 13 discharges in the DIII-D tokamak. These discharges include systematic scans in normalized gyroradius, plasma pressure, collisionality, isotope mass, elongation, heating power, and plasma density. The average rms deviation between experimental data and the predicted profiles of temperature and density, normalized by central values, is found to be about 10%. It is found that the simulations tend to overpredict the temperature profiles in discharges with low heating power per plasma particle and to underpredict the temperature profiles in discharges with high heating power per particle. Variations of the pedestal model are used to test the sensitivity of the simulation results.
Nanopowder management and control of plasma parameters in electronegative SiH4 plasmas
Authors: Denysenko I. B. , Ostrikov K. , Xu S. , Yu M. Y. , Diong C. H.
Published: October 2003

Management of nanosize powder particles via control of plasma parameters in a low-pressure SiH4 discharge for silicon microfabrication technologies is considered. The spatial profiles of electron and positive/negative ion number densities, electron temperature, and charge of the fine particles are obtained using a self-consistent fluid model of the electronegative plasmas in the parallel plate reactor geometry. The model accounts for variable powder size and number density, powder-charge distribution, local plasma nonuniformity, as well as UV photodetachment of electrons from the nanoparticles. The relations between the equilibrium discharge state and powder properties and the input power and neutral gas pressure are studied. Methods for controlling the electron temperature and SiH3− anion (here assumed to be the powder precursor) density, and hence the powder growth process, are proposed. It is shown that by controlling the neutral gas pressure, input power, and powder size and density, plasma density profiles with high levels of uniformity can be achieved. Management of powder charge distribution is also possible through control of the external parameters.
Some results on the eigenfunctions of the quantum trigonometric Calogero–Sutherland model related to the Lie algebra D4
Authors: Fernández Núñez J. , Garcı́a Fuertes W. , Perelomov A. M.
Published: October 2003

We express the Hamiltonian of the quantum trigonometric Calogero–Sutherland model related to the Lie algebra D4 in terms of a set of Weyl-invariant variables, namely, the characters of the fundamental representations of the Lie algebra. This parametrization allows us to solve for the energy eigenfunctions of the theory and to study properties of the system of orthogonal polynomials associated with them such as recurrence relations and generating functions.
Effects of charge non-neutrality and finite β on the electron temperature gradient mode
Authors: Hirose A.
Published: October 2003

It is shown that the short wavelength electron temperature gradient mode in tokamaks has a threshold in the plasma density (or the ballooning parameter α) through the charge non-neutrality. The growth rate peaks at k/kDe≃0.7 insensitive to plasma β and temperature. Electromagnetic finite β stabilization of the mode only occurs at a large ballooning parameter α comparable to that required for drift reversal.
Dynamics of domain walls within two interacting wires
Authors: Krupińska G. , Gawroński P. , Blanco J. M. , González J. , Kułakowski K.
Published: October 2003

We propose a modified setup of the conventional induction method to investigate the coupling between ferromagnetic bistable wires. The idea is to prevent the saturation by an application of two additional coils near the wire ends in a conventional measurement of the hysteresis loop of the wires. In this way, the fluctuations of the switching field are eliminated. Theoretically, the system is described by phenomenological equations of motion, one equation per wire. The hysteresis loop calculated numerically agrees qualitatively with the experimental results. The comparison allows to evaluate the value of the magnetostatic coupling between the wires.
Prompt and delayed secondary excitons in rare gas solids
Authors: Kirm M. , Vielhauer S. , Zimmerer G. , Kisand V. , Sombrowski E. , Steeg B.
Published: October 2003

Direct and indirect creation of excitons in rare gas solids has been investigated with reflectivity and luminescence spectroscopy. For the heavy rare gas solids Kr and Xe, new and more reliable exciton parameters have been deduced. With time-resolved luminescence spectroscopy, fast and delayed secondary-exciton creation has been established and separated. Thermalization of photocarriers and their delayed recombination have been analyzed, including a first attempt to investigate the influence of excitation density on the carrier dynamics. The existence of excitonic sidebands of the ionization limits Ei (either band-gap or inner-shell ionization limits) in prompt secondary exciton creation has been established. The threshold energies of these sidebands are given by Eth≈Ei+nEex (n is an integer, Eex is the exciton energy). The sidebands are ascribed to the formation of electronic polaron complexes, superimposed on the inelastic scattering of photoelectrons.
The vibration–rotation of H2O and its complexation with CO2 in solid argon revisited
Authors: Michaut X. , Vasserot A. M. , Abouaf-Marguin L.
Published: October 2003

Fourier-transform infrared spectroscopy in the frequency range 400–4000 cm−1 has been used to investigate the absorption of H2O and H2O:CO2 complex isolated in solid argon. Thanks to the lowest temperature reached in our experiment, temperature effects and nuclear spin conversion studies allow us to propose a new assignment of the rovibrational lines in the bending band ν2 for the quasi-freely rotating H2O. An additional wide structure observed in this band shows two maxima around 1657.4 and 1661.3 cm−1, with nuclear spin conversion of the high-frequency part into the low-frequency one. This structure is tentatively attributed to a rotation–translation coupling of the molecule in the cage. However, the equivalent effect is not observed in the vibrational stretching bands ν1 and ν3. Finally, in double doping experiments with CO2 important new structures appear, allowing us to unambiguously extract the frequencies of the lines of the H2O:CO2 complex.
Three-dimensional electrostatic particle-in-cell simulation with open boundaries applied to a plasma beam entering a curved magnetic field
Authors: Hurtig Tomas , Brenning Nils , Raadu Michael A.
Published: October 2003

Three-dimensional electrostatic particle-in-cell simulations of a laboratory experiment with an elongated plasma cloud entering a curved magnetic field are presented. A moving grid is used to follow the plasma motion from a region with longitudinal magnetic field, through a “transition region” where the field curves, and into a region where the magnetic field has a constant angle of 45° to the flow direction. In order to isolate the physics from disturbing boundary effects a method to create open boundary conditions has been implemented. As a result the boundaries are essentially moved to infinity. The simulation reproduces and gives physical insight into several experimental results concerning the plasma’s macroscopic behavior in the transition region, which have earlier been only partly understood. First, the deformation of the plasma from a cylinder to a slab; second, the formation of strong currents along the sides of the plasma cloud in the transition region, which continue into field-aligned currents in the (upstream) flow-parallel field region, and close across the magnetic field both in the front and in the back of the penetrating cloud; and, third, the formation of a potential structure including (in the transition region) magnetic-field-aligned electric fields, and (both in, and downstream of, the transition region) a potential trough structure in the plasma’s rest frame. It is found that all these macroscopic phenomena are intimately linked and can be understood within one consistent physical picture. The basic driving mechanism is the azimuthal electric field that is induced when, in the plasma’s rest frame, the transverse magnetic field grows in time. The plasma’s response is complicated by the fact that penetrating plasma clouds are in a parameter range where currents are not related to electric fields by a local conductivity: the ion motion is instead determined by the macroscopic potential structure.
Statistical analysis of turbulent flux and intermittency in the nonfusion magnetoplasma Blaamann
Authors: Fredriksen A. , Riccardi C. , Cartegni L. , Draghi D. , Trasarti-Battistoni R. , Roman H. E.
Published: October 2003

Turbulent particle flux due to correlated fluctuations of density and E⃗×B⃗-drift velocity has been statistically characterized in the simple magnetized torus Blaamann [F. J. O/ynes, O. M. Olsen, H. L. Pécseli, A. Fredriksen, and K. Rypdal, Phys. Rev. E 57, 2242 (1998)]. The shape and width of the probability distribution functions (PDF) and how they change as a function of time resolution τ upon coarse-graining have been analyzed. The shape of the PDF is non-Gaussian with a sharp central peak and is strongly asymmetric. The resulting width, σ, scales as a power-law over about two decades in τ, σ∼τH, for τ>100 μs. As τ decreases the width tends to flatten, i.e., the effective Hurst exponent H increases continuously in the interval 0.5<H<1. The behavior of the PDF at small time scales seems to be ascribed to the presence of coherent structures, living in the torus generated by flux instability.
Tuning phase stability in nanocomposite multilayers
Authors: Thompson G. B. , Banerjee R. , Fraser H. L.
Published: October 2003

As thin-film layers in a multilayered stack are reduced in thickness, changes in phase stability can result within the individual layers. These changes in phase are expected to have a significant influence upon the functional properties of the nanostructured composite. The ability to engineer, or tune, phase stability at this nanometer length scale is of significant importance in order to maximize the functional properties of these materials. We report the prediction and experimental conformation of tuning the hcp to bcc phase stability in Ti for Ti/Nb multilayered nanocomposites. The prediction was based upon selective alloying of Ti with a bcc β stabilizing element using a new form of a thermodynamic phase diagram for predicting phase stability in thin-film multilayers.
Comparison of gyrokinetic stability code calculated critical ion temperature gradients and growth rates to DIII-D measured gradients and diffusivities
Authors: Baker D. R. , Staebler G. M. , Petty C. C. , Greenfield C. M. , Luce T. C.
Published: October 2003

The gyrokinetic equations predict that various drift type waves or modes can be unstable in a tokamak. For some of these modes, such as the ion temperature gradient mode and the electron temperature gradient mode, there exists a critical gradient, above which the mode is unstable. There are also drift type modes, such as the trapped electron mode, which do not have a critical ion temperature gradient, but have a threshold which depends upon a variety of parameters. Since the existence of unstable modes can cause increased transport, plasmas which are centrally heated tend to increase in temperature gradient until the modes become unstable. Here the measured ion temperature gradients are compared to the “critical” gradients as calculated by a gyrokinetic linear stability (GKS) code [M. Kotschenreuther et al., Phys. Plasmas 2, 2381 (1995)]. Also, the maximum linear growth rate as calculated by this code is compared to experimentally derived transport coefficients. The results show that for low confinement mode (L-mode) discharges, the measured ion temperature gradient is significantly greater than the GKS calculated critical gradient over a large region of the plasma. This is the same region of the plasma where the ion thermal diffusivity is large. For high confinement mode (H-mode) discharges the ion temperature gradient is closer to the critical gradient, but often still greater than the critical gradient over some region. For the best H-mode discharges, the ion temperature is less than or equal to the critical gradient over the whole plasma. In general, the position in the plasma where the ion thermal diffusivity starts to increase rapidly is where the maximum linear growth rate is greater than the E×B shearing rate.
High-efficiency visible photoluminescence from amorphous silicon nanoparticles embedded in silicon nitride
Authors: Wang Y. Q. , Wang Y. G. , Cao L. , Cao Z. X.
Published: October 2003

Confinement of silicon nanoparticles in silicon nitride instead of an oxide matrix might materially facilitate its potential applications as a light-emitting component in optoelectronics. We report in this letter the production of high-density (up to 4.0×1012/cm2 from micrographs) silicon nanoparticles in SiNx thin films by chemical vapor deposition on cold substrates. Strong room-temperature photoluminescence was observed in the whole visible light range from the deposits that were postannealed at 500 °C for 2 min. The Si-in-SiNx films provide a significantly more effective photoluminescence than Si-in-SiOx fabricated with similar processing parameters: for blue light, the external quantum efficiency is over three times as large. The present results demonstrate that the nanostructured Si-in-SiNx system can be a very competitive candidate for the development of tunable high-efficiency light-emitting devices.
Negative electron mobility under condition of the resonant optical excitation in gas mixtures
Authors: Gorbunov N. A. , Melnikov A. S. , Smurov I.
Published: October 2003

The negative electron mobility (NEM) effect has been analyzed in gas mixtures consisting of heavy inert gas (Ar, Kr or Xe), molecular nitrogen and lithium vapor. The mixture parameters, which are optimal for NEM observation, have been determined by using an analytical technique and simulating the Boltzmann equation for the nonequilibrium electron energy distribution function. It has been shown that NEM may be realized under condition of ionization evolution generated by selective optical excitation of resonant transition of lithium atom Li(2S)–Li(2P).
Selective formation of ZnO nanodots on nanopatterned substrates by metalorganic chemical vapor deposition
Authors: Kim Sang-Woo , Kotani Teruhisa , Ueda Masaya , Fujita Shizuo , Fujita Shigeo
Published: October 2003

Selective formation of ZnO nanodots was accomplished by metalorganic chemical vapor deposition on nanopatterned SiO2/Si substrates. Self-organized ZnO nanodots were selectively formed in nanopatterned lines of Si created by etching of SiO2 with focused ion beam (FIB), whereas any nanodots were hardly observed on the SiO2 surface in the vicinity of the FIB-sputtered Si areas. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned lines is mainly attributed to the effective migration of Zn adatoms diffusing on the SiO2 surface into the Si lines followed by the nucleation at surface atomic steps and kinks created by Ga+ ion sputtering. Cathodoluminescence measurements confirmed that the emission originated from the selectively grown ZnO nanodots.
Single-crystal organic field effect transistors with the hole mobility ∼8 cm2/V s
Authors: Podzorov V. , Sysoev S. E. , Loginova E. , Pudalov V. M. , Gershenson M. E.
Published: October 2003

We report on the fabrication and characterization of single-crystal organic p-type field-effect transistors (OFETs) with the field-effect mobility μ∼8 cm2/V s, substantially higher than that observed in thin-film OFETs. The single-crystal devices compare favorably with thin-film OFETs not only in this respect: the mobility for the single-crystal devices is nearly independent of the gate voltage and the field effect onset is very sharp. The subthreshold slope as small as S=0.85 V/decade has been observed for a gate insulator capacitance Ci=2±0.2 nF/cm2. This corresponds to the intrinsic subthreshold slope Si≡SCi at least one order of magnitude smaller than that for the best thin-film OFETs and amorphous hydrogenated silicon (α-Si:H) devices.
Spin blockade in ferromagnetic nanocontacts
Authors: Zhuravlev M. Ye. , Tsymbal E. Y. , Jaswal S. S. , Vedyayev A. V. , Dieny B.
Published: October 2003

Using a free-electron model and a linear response theory we investigate spin-dependent electronic transport in magnetic nanocontacts in the ballistic regime of conduction. We emphasize the fact that in atomic-size ferromagnetic contacts it is possible to achieve the conductance value of e2/h, which implies a fully spin-polarized electric current. We explore some consequences of this phenomenon. In particular, we show that the presence of a nonmagnetic region in the nanocontact separating two ferromagnetic electrodes can lead to a spin blockade resulting in very large values of magnetoresistance.
Electric field screening in polymer light-emitting diodes
Authors: Lane P. A. , deMello J. C. , Fletcher R. B. , Bernius M.
Published: October 2003

Electromodulation (EM) spectroscopy has been used to probe the electric field distribution in polymer light-emitting diodes. Below the turn-on bias, the EM spectrum is dominated by electroabsorption of the emissive layer. The electroabsorption signal vanishes above the turn-on bias. Under operation, the EM spectrum is composed of bleaching of the emissive layer absorption and excited state absorption from trapped charge with no trace of the electroabsorption signal remaining. We conclude that the internal electric field is effectively screened by accumulation of trapped electrons at the anode.
Photoluminescence of GaN deposited on single-crystal bulk AlN with different polarities
Authors: Tamulaitis G. , Yilmaz I. , Shur M. S. , Gaska R. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Schujman S. B. , Schowalter L. J.
Published: October 2003

Photoluminescence (PL) properties of two GaN epilayers grown in identical conditions on substrates of Al face and N face of bulk single-crystal AlN are studied in the temperature range from 8 to 300 K under weak cw excitation and strong pulsed excitation up to the intensities when electron–hole heating and stimulated emission are observed. At low temperatures and pump intensities, PL of GaN on Al-face AlN is consistent with that of homoepitaxial Ga-face GaN, while GaN on N-face AlN exhibits features indicating the existence of tail localized states. At carrier densities high enough for band-to-band transitions to dominate, the room-temperature PL of GaN on N-face AlN is higher than that in GaN on Al-face AlN due to longer effective lifetime of photoexcited carriers.
The Impact of Personality on the End of the Cold War: A Counterfactual Analysis
Authors: Greenstein Fred I.
Published: October 2003

The end of the Cold War is examined with respect to the impact of Mikhail Gorbachev, Ronald Reagan, and their respective foreign secretaries. This discussion yields an approach to the systematic examination of counterfactual questions about the impact of political actors on historical outcomes.
After the Fall of the Wall: The Impact of the Transition on East German Women
Authors: Meyer Sibylle , Schulze Eva
Published: October 2003

This article addresses the impact of unification on East German families and on the situation of women in the East. The main hypothesis is that women are the losers of German unification, not only in terms of their decreasing participation in the labor force, but also in terms of their weakened position in partnerships and their increasing responsibilities in the domestic sphere. The findings are based primarily on personal interviews of different types of families. The first part of the article describes respondents' recollections of their everyday lives during the days of the former DDR (East Germany) and analyzes the specific family structures and relations between family members that prevailed. It focuses on the domestic division of labor and discusses the impact of high female employment on gender roles in the family and in the socialist society. The second part deals with the effects of German unification on families in East Germany.
Doubly Bound: The Impact of Gender and Race on the Politics of Black Women
Authors: Gay Claudine , Tate Katherine
Published: October 2003

Gender has been thought to be less salient than race among black women. Data from two national surveys of black Americans, conducted in 1984 and 1996, show that black women identify as strongly on the basis of their gender as their race, and that these gender and racial identities are mutually reinforcing. Nevertheless, among black women, their identification with their race more powerfully affected their political attitudes than did their identification on the basis of gender, except in instances where the interests of blacks directly conflict with the interests of women. These empirically based findings speak to the issue of why the attitudes of black women toward contemporary gender issues can sharply diverge from those of white women.