bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling solvation of excited electronic states of flexible polyatomic molecules: Diatomics-in-molecules for I3 in argon clusters
Authors: Margulis C. J. , Coker D. F.
Published: July 2002

In this paper we calculate the lowest 216 electronic energy surfaces of the I3 argon cluster system. We use the same approach as in our previous paper [J. Chem. Phys. 113, 6113 (2000)], but we include the presence of a solvent environment. In the absence of solvent the electronic structure of this bending triatomic molecule can be block diagonalized, and the lowest block gives rise to the lowest 64 states of the I3 molecule, further constraining the geometry of the molecule to be linear simplifies the structure of the Hamiltonian to a 3×3 matrix [J. Phys. Chem. A 103, 9552 (1999)]. We show how the solvent couples the different angular momentum states in the different manifolds allowing for transitions between otherwise forbidden diabatic angular electronic states and we predict the shape of the potentials in the cluster. We also characterize the ground state geometrical structure and properties of some of these size selected clusters.
The transverse instability in a differentially heated vertical cavity filled with molecular radiating gases. I. Linear stability analysis
Authors: Borget V. , Bdéoui F. , Soufiani A. , Le Quéré P.
Published: July 2002

Radiation effects on the onset of the transverse instability in a differentially heated vertical cavity containing molecular emitting and absorbing gases in the so-called conduction regime is studied theoretically. Radiative transfer is treated using the full integro-differential formulation. The neutral stability curves are determined using a combined Galerkin-collocation method based on Chebyshev polynomials. A modified correlated-k model and the absorption distribution function model are used in order to take into account the spectral structure of the absorption coefficient for radiating molecules such as H2O and CO2. For transparent media, perfect agreement is found with the available data reported in the literature and, particularly, the principle of exchange of stability is found to hold for Prandtl number values less than 12.46. The study of gray media allows us to examine the basic mechanisms that yield to the onset of transverse instability as traveling waves. For real radiating gases, a parametric study for H2O and CO2 is reported. It is shown that the radiative transfer delays the onset of the transverse instability and this delay increases with temperature and decreases with boundary emissivities, while layer depth effects depend on the level of saturation of the gas active absorption bands. Whatever the gas considered, it is found that neither radiation effect on the basic flow nor the radiative power disturbances can be neglected.
Effect of growth temperature on Curie temperature of magnetic ultrathin films Co/Cu(100)
Authors: Kuo C. C. , Lin W. C. , Chiu C. L. , Huang H. L. , Lin Minn-Tsong
Published: July 2002

The magnetic and structural properties were investigated for the 2 ML Co/Cu(100) films grown at various temperatures from 125 to 350 K. By precisely controlling the film thickness, the influence of thickness on Curie temperature (TC) due to the finite size effect can be excluded. The Curie temperature of the 2 ML Co keeps almost invariant for the growth temperature (Tg) below 250 K, and drops drastically at Tg higher than 275 K. For Tg=340 K, TC dropped to 170 K which is only about half of 325 K for Tg=125 K. Accompanied with the increase of TC for the films grown at lower temperatures, the remanent Kerr signal as well as coercivity were enhanced. According to a simple theoretical estimation, the change of TC due to the variation of the magnetization and anisotropy was found to be consistent with the experimental results. The enhancement in TC or magnetization and anisotropy with various Tg should be traced back to the presence of island growth in the films grown at lower temperatures.
Enhancement of the inverse-cascade of energy in the two-dimensional Lagrangian-averaged Navier–Stokes equations
Authors: Nadiga Balasubramanya T. , Shkoller Steve
Published: July 2002

The recently derived Lagrangian-averaged Navier–Stokes equations model the large-scale flow of the Navier–Stokes fluid at spatial scales larger than some a priori fixed α>0, while coarse-graining the behavior of the small scales. In this communication, we numerically study the behavior of the two-dimensional (2D) isotropic version of this model, also known as the α model. The inviscid dynamics of this model exactly coincide with the vortex blob algorithm for a certain choice of smoothing kernel, as well as the equations of an inviscid second-grade non-Newtonian fluid. While previous studies of this system in 3D have noted the suppression of nonlinear interaction between modes smaller than α, we show that the modification of the nonlinear advection term also acts to enhance the inverse-cascade of energy in 2D turbulence and thereby affects scales of motion larger than α as well. This, we note, (a) may preclude a straightforward use of the model as a subgrid model in coarsely resolved 2D computations, (b) is reminiscent of the drag-reduction that occurs in a turbulent flow when a dilute polymer is added, and (c) can be qualitatively understood in terms of known dimensional arguments.
The evaluation of a Lagrangian model for turbulent transport and chemistry
Authors: van Dop Han
Published: July 2002

A Lagrangian two-particle model for the relative diffusion and mixing of two reactive species is proposed. It describes the relative motion of a pair of fluid particles and includes the possibility for chemical interaction. The model was tested for consistency in simple geometrical configurations and has been compared to experimental data, Eulerian first- and second-order closure models as well as to other Lagrangian models. The transport algorithm was adapted in order to accommodate dispersion in decaying grid turbulence so that a comparison could be made with a series of wind tunnel measurements of the reaction of NO with O3. Three chemical closures are formulated and compared with experimental results. It appears that the formation of the reaction product is sensitive for both the description of the dispersion process and the chemical closure and that an accurate assessment of chemical closures is only possible with an accurate description of the dispersion process.
Origin of abnormal temperature dependence of electroluminescence from Er/O-doped Si diodes
Authors: Hansson G. V. , Ni W.-X. , Du C.-X. , Elfving A. , Duteil F.
Published: July 2002

The temperature dependencies of the current–voltage characteristics and the electroluminescence (EL) intensity of molecular beam epitaxy grown Er/O-doped Si light emitting diodes at reverse bias have been studied. To minimize the scattering of electrons injected from the p-doped Si1−xGex electron emitters, an intrinsic Si layer was used in the depletion region. For many diodes, there is a temperature range where the EL intensity increases with temperature. Data are reported for a structure that shows increasing intensity up to 100 °C. This is attributed to an increasing fraction of the pumping current being due to phonon-assisted tunneling, which gives a higher saturation intensity, compared to ionization-dominated breakdown at lower temperatures.
Coulomb suppression of surface noise
Authors: Kochelap V. A. , Sokolov V. N. , Bulashenko O. M. , Rubı́ J. M.
Published: July 2002

We have generalized the model of the surface noise taking into account the self-consistent electrostatic interaction and transverse electron transport in a conductive channel. Analyzing this model, we have found that the Coulomb correlations between trapped and conducting electrons considerably suppress the surface noise. The suppression effect is shown to be frequency dependent and especially large for noisy conducting channels.
Energy- and angle-resolved pump–probe femtosecond photoelectron spectroscopy: Molecular rotation
Authors: Arasaki Yasuki , Takatsuka Kazuo , Wang Kwanghsi , McKoy Vincent
Published: July 2002

We have incorporated a classical treatment of molecular rotation into our formulation of energy- and angle-resolved pump–probe photoelectron spectroscopy. This classical treatment provides a useful approach to extracting the photoelectron signal primarily associated with vibrational dynamics in cases where rotational motion is slow and the coupling between rotational and vibrational motion is weak. We illustrate its applicability with pump–probe photoelectron spectra for wave packets on the Σu+1 double-minimum state of Na2.
High-performance InAs/GaSb superlattice photodiodes for the very long wavelength infrared range
Authors: Mohseni H. , Razeghi M. , Brown G. J. , Park Y. S.
Published: July 2002

We report on the demonstration of high-performance p-i-n photodiodes based on type-II InAs/GaSb superlattices with 50% cut-off wavelength λc=16 μm operating at 80 K. Material is grown by molecular beam epitaxy on GaSb substrates with excellent crystal quality as evidenced by x-ray diffraction and atomic force microscopy. The processed devices show a current responsivity of 3.5 A/W at 80 K leading to a detectivity of ∼1.51×1010 cmHz1/2/W. The quantum efficiency of these devices is about 35% which is comparable to HgCdTe detectors with a similar active layer thickness.
A multipole second order Møller–Plesset solvent reaction field method
Authors: Nielsen Christian B. , Mikkelsen Kurt V. , Sauer Stephan P. A.
Published: July 2002

The multipole solvent reaction field model is formulated within Møller–Plesset perturbation theory. The solvent is described as an isotropic dielectric medium characterized by a dielectric constant. Interactions between the solvent and the solute give rise to a modified Schrödinger-equation which is nonlinear with respect to the wave function. This leads to an iteration-scheme in order to obtain the solvent-modified correlation coefficients. Sample calculations are performed for a series of small neutral molecules and we compare the results with other correlated solvent methods. In the case of geometries no considerably changes are observed and the inclusion of electron correlation is crucial for describing the molecular properties of a solute. Total energies and energy-differences are very dependent on the dielectric medium. Furthermore, we outline future use of the model.
Direct observation of a critical length effect in dual-damascene Cu/oxide interconnects
Authors: Ogawa Ennis T. , Bierwag Alexander J. , Lee Ki-Don , Matsuhashi Hideki , Justison Patrick R. , Ramamurthi Anup N. , Ho Paul S. , Blaschke Volker A. , Griffiths David , Nelsen Anne , Breen Mark , Havemann Robert H.
Published: July 2002

Electromigration results have provided clear evidence of a short or “Blech” length effect in dual- damascene, Cu/oxide, multilinked interconnects. The test structure incorporates a repeated chain of Blech-type line elements and is amenable to failure analysis tools such as focused ion beam imaging. This large interconnect ensemble provides a statistical representation of electromigrationinduced damage in the regime where steady-state interconnect stress is manifest. Statistical analysis yields a critical length of 90 μm for interconnects with line width 0.5 μm at j=1.0×106 A/cm2 and T=325 °C.
Electron energy barriers between (100)Si and ultrathin stacks of SiO2, Al2O3, and ZrO2 insulators
Authors: Afanas’ev V. V. , Houssa M. , Stesmans A. , Heyns M. M.
Published: July 2002

Electron energy barriers between the valence band of (100)Si and the conduction bands of ultrathin SiO2, Al2O3, ZrO2 insulators and their stacks were determined using internal photoemission of electrons. For SiO2, the barrier of 4.25±0.05 eV was found unchanged down to the oxide thickness of ≈1 nm. The barriers for Al2O3 and ZrO2 are substantially lower: 3.25±0.08 and 3.1±0.1 eV, respectively. Thermal oxidation at 650–800 °C enhances the barriers at the Si/Al2O3 and Si/ZrO2 interfaces but does not reduce the high density of band tail states in the insulators, suggesting the formation of silicates.
Role of oxygen in the film growth and giant magnetoresistance of Co/Cu multilayers
Authors: Miura Satoshi , Tsunoda Masakiyo , Takahashi Migaku
Published: July 2002

In order to clarify the effect of oxygen in the sputtering atmosphere on the microstructure and giant magnetoresistance, Co/Cu multilayers were fabricated under a sputtering atmosphere into which regulated impurity oxygen gas was introduced. After being pumped down the sputtering chamber to the ultimate pressure (less than 1×10−10 Torr), oxygen was introduced into the chamber until its content in processing Ar gas was about 0.1 ppm to 0.1%. The magnetoresistance (MR) ratio drastically increased from less than 20% to 54% when the content of impurity oxygen was slightly increased from 20 to 80 ppm, then nearly vanished when the content became more than 200 ppm. In the former region where the MR ratio steeply increased, the root mean square roughness of the multilayers decreased from 6.5 to 4.5 Å accompanied by a reduction in grain size as the oxygen content was increased. The partial oxidation of the multilayers is the most probable mechanism by which the flattening of the interfaces in the multilayer can be explained. We conclude that the impurity oxygen in the sputtering atmosphere serves as an obstruction of grain growth in the multilayer, not as a surfactant for the film growth.
Magnetoresistance of Mn:Ge ferromagnetic nanoclusters in a diluted magnetic semiconductor matrix
Authors: Park Y. D. , Wilson A. , Hanbicki A. T. , Mattson J. E. , Ambrose T. , Spanos G. , Jonker B. T.
Published: July 2002

We have fabricated a thin film magnetic system consisting of nanoscale Mn11Ge8 ferromagnetic clusters embedded in a MnxGe1−x dilute ferromagnetic semiconductor matrix. The clusters form for growth temperatures of ∼300 °C with an average diameter and spacing of 100 and 150 nm, respectively. While the clusters dominate the magnetic properties, the matrix plays a subtle but interesting role in determining the transport properties. Variable range hopping at low temperatures involves both nanoclusters and MnGe sites, and is accompanied by a negative magnetoresistance attributed in part to spin-dependent scattering analogous to metallic granular systems.
Local environment of rare-earth dopants in silica–titania–alumina glasses: An extended x-ray absorption fine structure study at the K edges of Er and Yb
Authors: d’Acapito F. , Mobilio S. , Santos L. , Almeida Rui M.
Published: July 2002

We have applied extended x-ray absorption fine structure (EXAFS) spectroscopy to the K edge of rare earths (RE) in a study of the local environments of diluted Er and Yb dopants in silicate glasses, prepared by sol-gel processing. Silica–titania–alumina glasses, doped with RE ions at and above the luminescence quenching concentration were investigated and EXAFS spectra were recorded in a wide k range up to 160 nm−1 not obtainable when working at the LIII edge. No direct RE–RE correlations were found, providing a strong support for previous studies. A model of RE aggregation derived from these observations is also discussed.
High-resolution photoelectron spectroscopic study of the first electronic states of Kr2+
Authors: Signorell R. , Hollenstein U. , Merkt F.
Published: July 2002

The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of Kr2 has been recorded between 103 500 cm−1 and 118 000 cm−1. Photoelectronic transitions to four [the I(1/2u), I(3/2u), II(1/2u), and II(1/2g) states] of the first six electronic states of Kr2+ have been observed. The photoelectronic transition to the ground I(1/2u) state consists of a long progression of vibrational bands, starting at v+=0. From the resolved isotopic substructure of vibrational levels with v+⩾15, the absolute numbering of the vibrational quantum number could be determined. The analysis of the spectrum has led to improved values of the adiabatic ionization potential [IP(I(1/2u))=(103 773.6±2.0) cm−1], the dissociation energy [D0+(I(1/2u))=(9267.8±2.8) cm−1] and to the determination of an analytical potential energy curve that reproduces the experimental data from v+=0 to beyond 81% of the dissociation energy. The transitions to vibrational levels of the I(1/2u) state with v+⩽30 and v+⩾65 have vanishing Franck–Condon factors for direct ionization from the ground neutral state and gain intensity from transitions to low Rydberg states that belong to series converging on excited electronic states of Kr2+. In the region immediately below the first dissociation limit of Kr2+, a second progression was observed and assigned to a photoelectronic transition to the I(3/2u) state. The adiabatic ionization potential [IP(I(3/2u))=(112 672.4±2.0) cm−1], the dissociation energy [D0+(I(3/2u))=(369.1±2.8) cm−1] and vibrational constants could be extracted for this state. Two further progressions were observed below the second dissociation limit of Kr2+ and assigned to transitions to the II(1/2u) and II(1/2g) states. The adiabatic ionization potentials [IP(II(1/2u))=(117 339.7±2.0) cm−1, IP(II(1/2g))=(117 802.6±2.0) cm−1] and the dissociation energies [D0+(II(1/2u))=(1071.7±2.8) cm−1, D0+(II(1/2g))=(608.8±2.8) cm−1] were determined for these two ionic states. In the region just below the ionic dissociation limits, artifact lines are observed in the PFI-ZEKE photoelectron spectra at the position of transitions to Rydberg states of the krypton monomer. At the lowest threshold, collisional and associative ionization of the long lived atomic Rydberg states leads to the formation of ZEKE electrons; at the upper threshold, the rapid autoionization of the atomic Rydberg states forms high ion concentrations, and the electrons that remain trapped in the ion cloud are released by the delayed pulsed field used to produce and extract the PFI-ZEKE electrons.
Magnetism and superconductivity in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices
Authors: Prieto P. , Vivas P. , Campillo G. , Baca E. , Castro L. F. , Varela M. , Ballesteros C. , Villegas J. E. , Arias D. , León C. , Santamarı́a J.
Published: July 2002

We report on the magnetic and superconducting properties of La0.7Ca0.3MnO3/YBa2Cu3O7 (LCMO/YBCO) superlattices. For a constant LCMO layer thickness of 6 unit cells (u.c.), resistance and susceptibility measurements show superconductivity for YBCO layer thickness in excess of 4 unit cells. The critical temperature increases with YBCO thickness, and a Tc of 58 K is found for a YBCO thickness of 10 unit cells. Magnetization measurements show a ferromagnetic transition at 100 K in a (LCMO6 u.c./YBCO5 u.c.)15 bilayer superlattice, and a depressed value of the saturation magnetization of 20 emu cm−3. These results are discussed in terms of interface disorder (analyzed by x-ray diffraction and transmission electron microscopy) and of the possible interaction between magnetism and superconductivity.
One-dimensional model of the plasma flow in a Hall thruster
Authors: Ahedo E. , Martı́nez-Cerezo P. , Martı́nez-Sánchez M.
Published: July 2002

A macroscopic model which accounts for the complex interactions between electrostatic, thermal, and kinetic effects in a Hall thruster is presented. The analysis establishes the one-dimensional steady structure of the flow as consisting of an anode sheath, a long electron free-diffusion region, with reverse ion flow, a thin ionization layer, and the acceleration region, which extends into the plume. The ion flow presents a forward sonic point around the exit of the ionization layer, which can be either internal, with a smooth sonic transition, or localized at the channel exit. The supersonic plume is included via a simple expansion model, allowing closure of the formulation and calculation of thruster performance. The results indicate good agreement with experimental data for the case of an internal sonic point, and they delineate the existence and nonexistence regions in the space of externally controllable parameters. They also unveil the importance of the electron pressure, the reverse flow of ions, and the ionization rate in shaping the plasma structure, whereas, contrary to common perception, the details of the magnetic field profile influence weakly that structure.
Stabilization effect of magnetic shear on the diocotron instability
Authors: Kondoh Shigeo , Tatsuno Tomoya , Yoshida Zensho
Published: July 2002

The diocotron instability in a magnetized non-neutral plasma is a close cousin of the Kelvin–Helmholtz instability. A sheared magnetic field brings about coupling between the diocotron modes and the Langmuir waves that propagate along the magnetic field. The motion of electrons parallel to the magnetic field cancels the electric charge produced by the diocotron modes, resulting in stabilization of the diocotron instability.
On the existence of resonances in the H+D2→HD(v′=0,j′=7)+D reaction at collision energies 0.6–1.3 eV
Authors: Aoiz F. J. , Bañares L. , Castillo J. F.
Published: July 2002

Well-converged (total angular momentum J⩽33) quantum mechanical scattering calculations have been performed for the H+D2(v=0,j=0) reaction at 0.6–1.3 eV collision energies on the BKMP2 potential energy surface. The present integral and differential cross sections for the reaction yielding HD(v′=0,j′=7)+D indicate that no evidence of resonance structure is found once a fully converged calculation is carried out.
Photonic band-gap properties of opaline lattices of spherical colloids doped with various concentrations of smaller colloids
Authors: Gates Byron , Xia Younan
Published: July 2002

Monodispersed polystyrene beads have been organized into highly ordered, three-dimensional (3D) lattices using a self-assembly procedure recently demonstrated by our group. Such a 3D periodic structure consisting of high and low dielectric regions exhibits a pseudo-band gap (or a stop band) in the optical regime, with the position of this gap mainly determined by the size of the polymer beads. Doping of this 3D crystalline lattice with polymer beads of a smaller size was found to have a profound influence on the order (and thus the photonic band-gap properties) of the lattice. When the concentration of the dopant reached a certain level, phase segregation occurred which led to the formation of samples with relatively smaller domain sizes. In accordance, the attenuation (or rejection ratio) of the stop band also decreased monotonically as the doping level was increased.
Comment on “Finding finite-time invariant manifolds in two-dimensional velocity fields” [Chaos 10, 99 (2000)]
Authors: Lapeyre G. , Hua B. L. , Legras B.
Published: July 2002

This note serves as a commentary of the paper of Haller [Chaos 10, 99 (2000)] on techniques for detecting invariant manifolds. Here we show that the criterion of Haller can be improved in two ways. First, by using the strain basis reference frame, a more efficient version of theorem 1 of Haller (2000) allows to better detect the manifolds. Second, we emphasize the need to nondimensionalize the estimate of hyperbolic persistence. These statements are illustrated by the example of the Kida ellipse.
The triplet He2* Rydberg states and their interaction potentials with ground state He atoms
Authors: Eloranta J. , Apkarian V. A.
Published: July 2002

We report ab initio potential energy curves for the interaction of ground state He atoms with the triplet He2* excimers. Fully converged, unrestricted, open-shell, coupled-cluster method including singles, doubles, and perturbative treatment of triples substitutions (UCCSD(T)) is used to compute the He2*–He potential energy curves for the a(3Σu) and c(3Σg) states. The internally contracted multireference configuration interaction method (ICMRCI) is used to compute the potential energy curves for a(3Σu), b(3Πg), d(3Σu), e(3Πg), f(3Σu), and f(3Πu) states. Where they can be compared, at the potential minima, the ICMRCI and UCCSD(T) methods agree to within 1 cm−1. The method reproduces the diatomic He2 potential with an accuracy of 0.8 cm−1. An accuracy of ∼2 cm−1 is estimated for all reported He2*–He potentials. Calibrations based on Li–He and H2–He interactions are consistent with this expectation. Calculations on tetratomics, He–He2*–He, are carried out to assess the nonadditivity of potentials in various states. At short range, nonadditivity arises from polarization effects, while at long-range its nonadditivity is due to the distortion of the Rydberg electron density by the ground state He atoms. Besides potential energy points, electron density plots are provided.
Hydrodynamic modes of a sheared granular flow from the Boltzmann and Navier–Stokes equations
Authors: Kumaran V.
Published: July 2002

The initial growth rates for the hydrodynamic modes of the shear flow of a three-dimensional collection of inelastic spheres is analyzed using two models. The first is the generalized Navier–Stokes equations, derived for the shear flow of inelastic spheres using the Chapman–Enskog procedure, where the energy equation has an additional dissipation term due to inelastic collisions. The second is the solution of the linearized Boltzmann equation, where the distribution function in the base state is determined using a Hermite polynomial expansion in the velocity moments. For perturbations with variations in the velocity and gradient directions, it is found that the solutions obtained by two procedures are qualitatively similar, though there are quantitative differences. For perturbations with variations in the vorticity direction, it is found that there are qualitative differences in the predictions for the initial growth rate of the perturbations.
Convergence behavior of the symmetry-adapted perturbation theory for states submerged in Pauli forbidden continuum
Authors: Patkowski Konrad , Korona Tatiana , Jeziorski Bogumil
Published: July 2002

The polarization expansion and the symmetry-adapted perturbation theory (SAPT) in the symmetrized Rayleigh–Schrödinger (SRS) and the Hirschfelder–Silbey (HS) formulations are applied through high order to the medium- and long-range interaction of the ground-state lithium and hydrogen atoms. The interaction energies obtained by perturbation theory are compared with the counterpoise-corrected full configuration interaction results. It is shown that the SRS and HS expansions diverge as a result of the presence of the Pauli forbidden continuum in which the physical eigenstates of the perturbed Hamiltonian are submerged. Despite this divergence, the SAPT expansions give accurate results in low orders and excellent results when summed up in a standard way of assigning a sum to an asymptotically convergent series. The polarization expansion is found to diverge as well, with its asymptotic limit equal to the arithmetic mean of singlet and triplet energies. Unlike the case of simpler systems, for the interaction of lithium and hydrogen atoms the Hirschfelder–Silbey method does not provide any improvement over the much simpler SRS approach.
An experimental measure of anharmonicity in the bending of DCO+
Authors: Foltynowicz Robert J. , Robinson Jason D. , Grant Edward R.
Published: July 2002

Rydberg series of DCO have been rovibrationally isolated by double resonance and extrapolated to produce a map, with sub-wave-number accuracy, of individual rotational level positions in the bending fundamental and first overtone of DCO+. Analysis of this structure determines fundamental frequencies, rotational constants, and low-order anharmonicities associated with the bending mode of the cation. Rotational properties of excited DCO+ found by Rydberg extrapolation are observed to agree well with quantities measured by microwave spectroscopy. The CASSCF–MRCI potential energy surface of Puzzarini and co-workers, which yields fundamental frequencies that agree with experiment for HCO+, is shown to conform well with these first measurements of the bending frequencies of DCO+.
Rotation of chromophores in amorphous polymer hosts of arbitrary disorder
Authors: Binks D. J. , West D. P.
Published: July 2002

The rotational response of chromophores to an applied electric field is generalized for the case of an amorphous polymer host of arbitrary disorder. A time-dependent diffusion coefficient corresponding to a partially disordered system determines the solution of the rotational diffusion equation in response to the step function introduction of a poling field. This results in a transient that, in general, consists of two stretched exponential terms. In the limiting cases of complete order and disorder, the transient becomes a biexponential and a bi-power law, respectively. The degree of disorder is quantified to be consistent with the Scher–Montroll method of describing disorder in amorphous charge-transporting materials. Excellent agreement has been found between the theoretical dynamic and experimental measurement. This arbitrary disorder description is found to be consistently more accurate than assuming complete disorder. The effect of plasticization on the disorder is also studied.
Injection currents and effect of negative capacitance in porous TiO2
Authors: Kytin V. , Dittrich Th. , Koch F. , Lebedev E.
Published: July 2002

Transient dark and photocurrents and the frequency-dependent capacitance were investigated in porous (por-) TiO2 (anatase) layers. The current transients consist of a fast part being characteristic for a transit of charge and of a slow part which increases strongly in time for high applied potentials up to a saturation level. The drift mobility of injected electrons is 5×10−5 cm2/V s. The saturation current is described by space-charge-limited current (SCLC) in the presence of traps with an exponential energy distribution (exponential parameter, 80 meV). At high injection currents, SCLC causes slow polarization of the medium, which leads to a time-dependent capacitance and strong inductive behavior of the dark current transients.
Potential energy surfaces for CH(A 2Δ)–Ar and analysis of the A 2Δ–X 2Π band system
Authors: Kerenskaya Galina , Kaledin Alexey L. , Heaven Michael C.
Published: July 2002

Two-dimensional intermolecular potential energy surfaces for the CH(A 2Δ)–Ar complex (CH bond fixed at equilibrium) have been calculated at the multireference singles and doubles configuration interaction/correlation-consistent valence quadruple zeta level of theory. These surfaces are of 2 2A′ and 2 2A″ electronic symmetry. Both potentials define a linear CH–Ar equilibrium structure (Ar…H∼3 Å), with a secondary minimum for the Ar–CH linear geometry (Ar…C∼4 Å). The global minimum is ∼117 cm−1 below dissociation. Side-on approach of the Ar atom breaks the orbital degeneracy of the Δ2 state, but this splitting is relatively small near the equilibrium separation, only about 10 cm−1. The potential surfaces have been used in simulations of the A–X bands of CH/D–Ar. The correlation between the simulated and observed spectra was sufficient for assignment of the latter. Systematic adjustment of the A state average potential, defined as Va=(VA′+VA″)/2, was made to obtain a surface that reproduces the vibrational energy spacings and rotational constants of CH/D–Ar.
Molecular dynamics of interfaces in opposing fields
Authors: Toxvaerd S. , Stecki J.
Published: July 2002

Equilibrium binary liquid mixture below its upper critical consolute temperature, confined between opposing walls, is investigated by molecular dynamics simulations. The wall potentials are chosen strong enough to ensure that both walls are wet and therefore the interface is delocalized. The interfacial widths (W) are determined from density profiles and from order parameter profiles for a series of wall to wall distances (D). Early saturation of the width with increasing D is found already for D∼20σ and data at the other end are consistent with the theoretical prediction of linear dependence of W2 on D. Also, the error function complement is found slightly superior to the hyperbolic tangent, on the basis of a new test of consistency proposed.
Coherent nanoscale islands on La0.5Ca0.5MnO3 thin films and the enhancement of magnetoresistance
Authors: Gong W. Z. , Zhao B. R. , Cai C. , Lin Y.
Published: July 2002

A low cost reproducible fabrication process has been developed to prepare La0.5Ca0.5MnO3 (LCMO) films with well distributed uniform nanoscale dots using pulsed-laser deposition. It was found that the growth of the dots was closely related to the strain in the film during the growth process. The diameter and density of dots could be controlled within the range of 30–120 nm and 2×108–2×109/cm2, respectively. The magnetoresistance effect of such LCMO films is also enhanced, which may be caused by the spin-dependent scattering of carriers due to the existence of the dots.
Analysis of solvation structure and thermodynamics of ethane and propane in water by reference interaction site model theory using all-atom models
Authors: Cui Qizhi , Smith Vedene H.
Published: July 2002

Following our previous paper on methane [Cui and Smith, J. Chem. Phys. 113, 10240 (2000)], we study the solvation structures and thermodynamics of ethane and propane in water at the infinite dilution limit by using the hypernetted chain closure reference interaction site model (HNC-RISM) theory with all-atom representations for solute molecules. At four thermodynamic states: temperature T=283.15, 298.15, 313.15, 328.15 K and the corresponding bulk water density ρ=0.9997, 0.9970, 0.9922, 0.9875 g cm−3, all the atomic solute–solvent radial distribution functions are obtained, and the corresponding running coordination numbers and the hydration free energies, energies, enthalpies, and entropies are calculated with the radial distribution functions as input. The hydration structures of ethane and propane are presented and analyzed at the atomic level in terms of the atomic solute–solvent radial distribution functions. With the optimized nonbonded potential parameters based on the CHARMM96 all-atom model for alkanes [Yin and Mackerell, J. Comput. Chem. 19, 334 (1998)], the ethane and propane hydration thermodynamic properties predicted by the HNC-RISM theory are improved in the specified temperature range (10–55 °C).
An ab initio molecular dynamics study of S ketene fragmentation
Authors: Forsythe Kelsey M. , Gray Stephen K. , Klippenstein Stephen J. , Hall Gregory E.
Published: July 2002

The dynamical origins of product state distributions in the unimolecular dissociation of S0 ketene, CH2CO (X̃ 1A1)→CH2(ã 1A1)+CO, are studied with ab initio molecular dynamics. We focus on rotational distributions associated with ground vibrational state fragments. Trajectories are integrated between an inner, variational transition state (TS) and separated fragments in both the dissociative and associative directions. The average rotational energy in both CO and CH2 fragments decreases during the motion from the TS to separated fragments. However, the CO distribution remains slightly hotter than phase space theory (PST) predictions, whereas that for CH2 ends up significantly colder than PST, in good agreement with experiment. Our calculations do not, however, reproduce the experimentally observed correlations between CH2 and CO rotational states, in which the simultaneous formation of low rotational levels of each fragment is suppressed relative to PST. A limited search for nonstatistical behavior in the strong interaction region also fails to explain this discrepancy.
Ab initio, variational transition state theory and quasiclassical trajectory study on the lowest A′2 potential energy surface involved in the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) atmospheric reaction
Authors: González Miguel , Miquel Irene , Sayós R.
Published: July 2002

A CASSCF and CASPT2 ab initio study has been carried out for the lowest A′2 potential energy surface (2 2A′ PES) that correlates reactants and products of the N(2D)+O2→O(3P)+NO reaction. All the stationary points have been characterized and along with a grid of more than 600 ab initio points have been fitted to an analytical function. Afterwards, this analytical PES has been employed to study the kinetics [variational transition state theory (VTST) and quasiclassical trajectory (QCT) methods] and dynamics (QCT method) of the reaction. Concerning the rate constants, a good agreement with the experimental values corresponding to the global deactivation of N(2D) has been obtained. This suggests that this reaction is responsible of most of the reactivity of the N(2D)+O2 system. NO vibrational distributions have also been calculated. Although there is not a good agreement between the theoretical and experimental values, preliminary results show that they can become quite close by taking into account the contribution of the 1 2A″ PES.
Current density functional theory for optical spectra: A polarization functional
Authors: de Boeij P. L. , Kootstra F. , Berger J. A. , van Leeuwen R. , Snijders J. G.
Published: July 2002

In this paper we present a new approach to calculate optical spectra, which for the first time uses a polarization dependent functional within current density functional theory (CDFT), which was proposed by Vignale and Kohn [Phys. Rev. Lett. 77, 2037 (1996)]. This polarization dependent functional includes exchange-correlation (xc) contributions in the effective macroscopic electric field. This functional is used to calculate the optical absorption spectrum of several common semiconductors. We achieved in all cases good agreement with experiment.
The effect of bond length on the structure of dense bead–spring polymer melts
Authors: Abrams Cameron F. , Kremer Kurt
Published: July 2002

We explored the effect of the ratio of bond length to excluded volume bead diameter, l0/d0, of simple bead–spring homopolymer chains on the resulting liquid structure of dense, monodisperse polymer melts. We conducted NVT molecular dynamics simulations of both bulk and planar confined polymer liquids. We find that both pressure and surface tension increase with l0/d0. We attribute this sensitivity to the reduction in short range liquid ordering, classically observed for simple fluids, when l0/d0<1, and its persistence and even enhancement when l0/d0>1. We explain this by examining specific correlations between bond orientations and monomer density. This leads to a better understanding of how intramolecular constraints influence intermolecular structure in molecular liquids.
Alfvén wave propagation in a helicon plasma
Authors: Hanna Jeremy , Watts Christopher
Published: July 2002

Alfvén wave propagation in a helicon plasma is being studied in the Auburn Linear Experiment for Space Plasma Investigations. The helicon discharge provides the high-density plasma necessary to propagate Alfvén waves. Shear Alfvén waves are produced in this discharge by means of an inductive coil positioned to oscillate the magnetic field perpendicular to the background field lines. The waves are detected by means of a second inductive coil positioned down the plasma column. Initial investigations demonstrate the propagation of shear Alfvén waves within the plasma through the localization of the oscillations along the magnetic-field lines and the expected phase velocity of the waves.
Ferroelectric order in positionally frozen dipolar systems
Authors: Klapp S. H. L. , Patey G. N.
Published: July 2002

We discuss the possibility of long-range ferroelectric order in an amorphous dipolar system. Our model consists of spheres with frozen positions and freely rotating three-dimensional dipole moments. Correlation functions are calculated by means of the hypernetted-chain integral theory combined with the replica method. Our results suggest that inhomogeneities in the frozen spatial structure induce a gradual local freezing of the dipole axes upon decreasing temperature. However, at sufficiently high densities and dipole moments, the long-range interactions dominate the short-range frustration, resulting in a ferroelectric transition. The estimated transition temperatures depend strongly on the degree of spatial correlation in the underlying system of frozen spheres. For a randomly frozen system, we find that the transition temperature is considerably lower than that predicted by mean field theory, and also lower than the temperature where simulations indicate the onset of glass-like behavior. Strong positional correlations can push the transition toward temperatures higher even than those observed for dipolar fluids.
Nickel clusters: The influence of adsorbed CO on magnetic moments
Authors: Knickelbein Mark B.
Published: July 2002

Stern–Gerlach magnetic deflection measurements were performed on Nin and NinCO (n=8–18) in a molecular beam experiment. Adsorbed carbon monoxide was found to reduce the magnetic moments of most nickel clusters in this size range. For Ni8, the reduction was ∼5 bohr magnetons, while smaller reductions were observed for the other clusters. The present results are in qualitative accord with previous experiments and calculations of the magnetization quenching effects of CO on both nickel nanoparticles and thin nickel films. The magnitude of the changes in cluster magnetic moments of Ni8, Ni15, and Ni18 were larger than those predicted by the local quenching (bond number) model, indicating that the CO-induced perturbation to cluster electronic structure in these clusters is distributed among many nickel atoms.
Study of the strain relaxation in InGaN/GaN multiple quantum well structures
Authors: Bai J. , Wang T. , Sakai S.
Published: July 2002

The relationship between strain relaxation and quantum well number in InGaN/GaN multiple quantum well (MQW) structures has been investigated by x-ray diffraction (XRD) and low-temperature photoluminescence (PL) measurements. At low temperature, the PL emission energy of a MQW monotonically decreases with increasing quantum well number, and the large pumping induced blueshift of the emission energy decreases rapidly with an increasing quantum well number. Based on an excitation power dependent PL measurement and a previous calculation that was made assuming a fully strained InGaN/GaN MQW, it is found that only a two-period MQW shows no strain relaxation. Furthermore, the residual strain in a MQW with different quantum well numbers is estimated, which is used for an x-ray diffraction kinetic simulation. The simulation agrees well with our measured XRD data, which in turn supports the conclusion based on the PL measurement. Our results indicate that the strain relaxation starts from a three-period InGaN/GaN MQW. Since the strain relaxation generally has a strong influence on the performance of the optical devices, the results presented should definitely be taken into account in designing InGaN/GaN MQW based optical devices.
Single-electron transistor with metallic microstrips instead of tunnel junctions
Authors: Krupenin V. A. , Zorin A. B. , Savvateev M. N. , Presnov D. E. , Niemeyer J.
Published: July 2002

A single-electron transistor (SET) comprising highly resistive Cr thin-film strips (sheet resistance ∼4 kΩ) instead of traditional tunnel barriers is reported. Two such strips (∼1 μm long) connect two Al outer electrodes to an Al island 1 μm in length equipped with a capacitively coupled gate. This transistor with a total asymptotic resistance of 110 kΩ showed a perfect Coulomb blockade and strictly e-periodic reproducible modulation by the gate in wide ranges of bias (V) and gate (Vg) voltages. In the Coulomb-blockade region (|V|⩽ about 0.5 mV), we observed a strong suppression of the transport current, allowing modulation curves V(Vg) with appreciable amplitude to be measured at a fixed bias current value I as low as 100 fA. The background-charge noise of our SET was found to be similar to that of typical Al/AlOx/Al tunnel-junction single-electron transistors, namely δQ≈5×10−4e/Hz at 10 Hz. The electron transport mechanism is discussed.
High temperature stability in lanthanum and zirconia-based gate dielectrics
Authors: Maria J.-P. , Wicaksana D. , Kingon A. I. , Busch B. , Schulte H. , Garfunkel E. , Gustafsson T.
Published: July 2002

Gate dielectrics composed primarily of lanthana and zirconia were prepared by reactive evaporation. The stability of the layers during high temperature anneals was investigated. By controlling the oxygen partial pressure during heat treatment, lanthana and zirconia films could be protected against reaction with the underlying Si substrate and against the growth of low-ε interface layers. The electrical thickness of the dielectrics could be maintained after a 900 °C exposure. The critical oxygen pressure at 900 °C for low-ε interface formation beneath ZrO2 and La2O3 dielectrics was ∼2e−4 Torr. The interfaces that formed beneath the ZrO2 and La2O3 layers are distinctly different. The sub-ZrO2 interface, influenced primarily by phase separation, tends towards pure SiO2, while the sub-La2O3 interface, influenced primarily by silicate formation, tends towards a La–Si–O alloy. For both materials, reducing the oxygen pressure to values below 10−7 Torr resulted in rapid degradation of the metal oxide. This dielectric degradation is believed to be linked to SiO evaporation. These results suggest that at high temperatures, a window of optimal oxygen partial pressure exists in which the stability of many oxides in contact with silicon can be achieved.
A study of aqueous solutions of lanthanide ions by molecular dynamics simulation with ab initio effective pair potentials
Authors: Floris Franca Maria , Tani Alessandro
Published: July 2002

Infinitely dilute aqueous solutions of Nd3+, Gd3+, and Yb3+ have been studied with molecular dynamics simulations, using ab initio effective ion–water pair potentials based on the polarizable continuum model. Structural results, as first peak positions of g(r) are in good agreement with experimental data. We obtain a coordination number of 9 for all the cations. This value agrees with experimental measurements for Nd3+ and Gd3+ but overestimates them for Yb3+. Significant differences between Yb3+ and the other two ions have however been observed in a detailed analysis of the solvation shell structure, based on the diagonalization of the inertia tensor. A similarity index based on a linear combination of the inertia tensor eigenvalues is proposed. Going from Nd3+ to Yb3+, structures like a capped square antiprism (CSQA) are more favored than a tricapped trigonal prism. In contrast to the lanthanide contraction observed for the most probable ion–oxygen distances, in CSQA structures the distance from the center of mass of the polyhedron to the capped O increases from Nd3+ to Yb3+. Dynamics of internal rearrangements has been studied and residence times of waters in the first and second hydration shell have been calculated. Diffusion coefficients for the ions appear somewhat underestimated with respect to the experimental data, which agree with the value we obtain for hydration shell waters. Linear and angular velocity correlation functions and spectra of first shell waters show a large increase of intensity at high frequency compared to bulk solvent. The Yb3+ solution consistently presents these features in enhanced form.
The Enskog theory for classical vibrational energy relaxation in fluids with continuous potentials
Authors: Bagchi Biman , Srinivas Goundla , Miyazaki Kunimasa
Published: July 2002

The recently developed Enskog theory for binary friction for fluids with continuous potentials, such as the Lennard-Jones, has been extended to calculate the frequency dependence of this friction, ζE(ω). This ζE(ω) is then applied to study vibrational energy relaxation of low-frequency modes via the Landau–Teller expression. The agreement with simulation results is found to be satisfactory. In the present approach we provide an exact prescription for the binary friction and thus remove a lacuna in this area. ζE(ω) shows an interesting structure with a hump at low frequency, the signature of which has already been seen in many simulation studies.