bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct determination of kinetic fragility indices of glassforming liquids by differential scanning calorimetry: Kinetic versus thermodynamic fragilities
Authors: Wang Li-Min , Velikov V. , Angell C. A.
Published: November 2002

A calorimetric method of obtaining directly the fragility of liquids from the fictive temperatures of variably quenched glasses, is outlined. “Steepness indexes” m, have been determined for a group of molecular liquids of diverse character, and vary in the range 50–150. The values obtained mostly agree well with those from earlier studies using dielectric relaxation, heat capacity spectroscopy, and viscosity data. In our method there is the advantage that the fragility is determined from the relaxation process that is basic to the calorimetric glass transition temperature measurement, namely, that of the enthalpy. The calorimetric measurements also yield the liquid and glass heat capacities, and entropies of fusion, permitting relationships between thermodynamic and kinetic responses to be examined simultaneously. We study glycerol, dibutylphthallate, 9-bromophenanthrene, salol, orthoterphenyl, propylene carbonate, decalin and its nitrogen derivative decahydroisoquinoline, and find the latter two to be the most fragile liquids known, m =145 and 128 respectively. Surprisingly, of the liquids studied, decalin has the smallest increase in heat capacity at the glass transition. By contrast, the strongest liquid, glycerol, has the largest increase. However, the thermodynamic fragility of decalin, assessed from the scaled rate of increase of the excess entropy above Tg, is found to be high, due to the unusually small value of the excess entropy at Tg. Conversely, the entropy-based fragility for glycerol is the lowest. Thus the correlation of kinetic and entropy-based thermodynamic fragilities reported in recent work is upheld by data from the present study, while the basis for any correlation with the jump in heat capacity itself is removed.
Laser imprint reduction with a short shaping laser pulse incident upon a foam-plastic target
Authors: Metzler Nathan , Velikovich Alexander L. , Schmitt Andrew J. , Gardner John H.
Published: November 2002

In the previous work [Metzler et al., Phys. Plasmas 6, 3283 (1999)] it was shown that a tailored density profile could be very effective in smoothing out the laser beam nonuniformities imprinted into a laser-accelerated target. However, a target with a smoothly graded density is difficult to manufacture. A method of dynamically producing a graded density profile with a short “shaping” laser pulse irradiating a foam layer on top of the payload prior to the drive pulse is proposed. It is demonstrated that the intensity and the duration of the shaping pulse, the time interval between the shaping pulse and the drive pulse, and the density ratio between the foam and the payload can be selected so that the laser imprint of the drive pulse is considerably suppressed without increasing the entropy of the payload. The use of the foam-plastic target and a shaping pulse reduces the imprinted mass perturbation amplitude by more than an order of magnitude compared to a solid plastic target. The requirements to the smoothing of the drive and “shaping” laser beams and to the surface finish of the foam-plastic sandwich target are discussed.
A revised experimental absolute magnetic shielding scale for oxygen
Authors: Wasylishen Roderick E. , Bryce David L.
Published: November 2002

A revised absolute magnetic shielding scale for oxygen is established based on a recently reported highly precise experimental measurement of the O17 spin-rotation constant in carbon monoxide. The isotropic oxygen magnetic shielding constant for C12O17 at the equilibrium geometry, σe, is found to be −56.8±0.6 ppm. The experimental rovibrationally averaged value of the shielding constant at 300 K, 〈σ〉300 K, is −62.7±0.6 ppm, in excellent agreement with the ab initio value reported by Vaara et al. [J. Chem. Phys. 109, 8388 (1998)]. Based on the revised scale and on experimentally known oxygen chemical shifts, 〈σ〉300 K (H2O(l)) is 287.5±0.6 ppm and 〈σ〉300 K (H2O(g)) is 323.6±0.6 ppm.
Density functional theory for inhomogeneous polymer systems. I. Numerical methods
Authors: Frischknecht Amalie L. , Weinhold Jeffrey D. , Salinger Andrew G. , Curro John G. , Douglas Frink Laura J. , McCoy John D.
Published: November 2002

We present a new real space Newton-based computational approach to computing the properties of inhomogeneous polymer systems with density functional theory (DFT). The DFT is made computationally efficient by modeling the polymers as freely jointed chains and obtaining direct correlation functions from polymer reference interaction site model calculations. The code we present can solve the DFT equations in up to three dimensions using a parallel implementation. In addition we describe our implementation of an arc-length continuation algorithm, which allows us to explore the phase space of possible solutions to the DFT equations. These numerical tools are applied in this paper to hard chains near hard walls and briefly to block copolymer systems. The method is shown to be accurate and efficient. Arc-length continuation calculations of the diblock copolymer systems illustrate the care required to obtain a complete understanding of the structures that may be found with this polymer-DFT approach.
Density functional theory for inhomogeneous polymer systems. II. Application to block copolymer thin films
Authors: Frischknecht Amalie L. , Curro John G. , Douglas Frink Laura J.
Published: November 2002

We use polymer reference interaction site model (PRISM)-based density functional theory (DFT) to study the structures and morphologies of block copolymer thin films. The polymers are modeled as freely jointed chains, allowing numerical solution of the nonlinear DFT equations. The use of PRISM with DFT allows the inclusion of compressibility and local packing effects due to the finite size of the monomers. We also employ a pseudo-arclength continuation algorithm to locate phase transitions and new morphologies. We study symmetric diblock copolymers confined between two parallel surfaces which both attract one component of the diblock, for two different values of AB segregation strength and for various surface interactions. The predicted equilibrium morphologies are in good qualitative agreement with previous self-consistent field calculations and are consistent with experiment. We are able to resolve the detailed packing structure near the surfaces. We find that packing effects enhance the stability of the perpendicular morphologies.
Monte Carlo simulation for the hard-core two-Yukawa fluids and test of the two-Yukawa equation of state
Authors: Lin Yang-Zheng , Li Yi-Gui , Lu Jiu-Fang , Wu Wei
Published: November 2002

A recently proposed analytical equation of state (EOS) for the hard-core two-Yukawa fluids is tested against the results of Monte Carlo (MC) simulation in six cases. One range parameter in the two-Yukawa potential is taken as 1.8 or 2.8647, and another is taken as 2.0, 4.0, 8.0, or 13.5485. Attractive and repulsive dominant cases of the potential outside the core are all considered. The simulation conditions selected ensure that, the interaction between two particles is attractive at enough long distance. Some of the cases can give the similar potential as that between charged colloid particles. The hard-core two-Yukawa fluid with parameters, which are obtained from fitting the Lennard-Jones potential, is also studied. The two-Yukawa EOS results fit very well with that of the MC simulation except for some points at high density (as ρ*=0.9), which is found to be crystal state. It is found that the two-Yukawa EOS can be used to study the fluid–fluid equilibrium of hard-core two-Yukawa fluid.
Vibrational predissociation of NeBr2 (X, v=1) using an ab initio potential energy surface
Authors: Prosmiti Rita , Cunha Carlos , Buchachenko Alexei A. , Delgado-Barrio Gerardo , Villarreal Pablo
Published: November 2002

Quantum mechanical calculations on the vibrational predissociation dynamics of NeBr2 are performed using an ab initio (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) potential energy surface. Energy positions, lifetimes, and final rotational state distributions are determined for vibrational predissociation from the two lowest linear (n=0) and T-shaped (n=1) van der Waals levels of NeBr2 (X, v=1). Comparison with the experimental assumption as regards the energy transfer to rotation provides information about the type of isomer involved in the experimental vibrational predissociation process, suggesting that it was the linear one.
Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study
Authors: Boudjada A. , Meinnel J. J. , Boucekkine A. , Hernandez O. J. , Fernández-Diaz M. T.
Published: November 2002

First the conformations of various ortho and di-ortho substituted toluenes calculated by quantum chemistry methods are discussed as well as the hindering potentials deduced from the latter results and those established experimentally by microwaves and fluorescence techniques. It appears that methyl (Me) groups are much less hindered in di-ortho than in ortho substituted compounds. Then the study of the 1,3,5-triiodo-2,4,6-trimethylbenzene (triiodomesitylene or TIM) is reported. Density functional theory (DFT) calculations indicate that two conformations of the TIM molecule have the same formation energies. One has C3h symmetry, the other with the Cs symmetry is obtained from the C3h by a rotation of 60° for one Me. Experimentally, the TIM structure has been determined at 15 K using single-crystal neutron diffraction data. TIM crystallizes in the triclinic space group P−1. Molecules are stacked in an antiferroelectric manner along the oblique a axis. For two Me groups the experimental conformation is close to the Cs one, but the third Me group has a C–H bond nearly orthogonal to the ring plane. Such conformation is unstable in the gas state, but it is stabilized in the crystal by intermolecular interactions, nevertheless DFT predicts accurate bond lengths and angles when the Me conformations are constrained to the experimental ones. The three Me groups, having different environments, experience different hindering potentials, this explains why they are tunnelling at different energies as found by inelastic neutron scattering (INS). Using INS results, we deduced the potentials hindering the Me groups rotation in the crystal. The proton probability densities (PPD) calculated from these potentials are in concordance with the crystallographic results. Hence the quantum origin of the broad spreading of PPD observed at 15 K is established. Moreover, it is demonstrated that the crystal field is responsible for the larger part of the potentials hindering the Me groups in the solid state.
Phase behavior of symmetric rod–plate mixtures revisited: Biaxiality versus demixing
Authors: Varga Szabolcs , Galindo Amparo , Jackson George
Published: November 2002

The phase behavior of symmetric binary rod–plate mixtures has been investigated by numerical minimization of a free energy functional derived by Parsons [J. D. Parsons, Phys. Rev. A 19, 1225 (1979)] and Lee [S. D. Lee, J. Chem. Phys. 87, 4972 (1987)]. Both rod and plate molecules are represented by hard cylinders, with aspect ratios chosen so that the molecular and pair excluded volumes are equal; in this way symmetric phase diagrams in composition are found. The subtle competition between the packing entropy and the entropy of mixing rules out the possibility of a uniaxial nematic–biaxial nematic phase transition and instead favors a demixing phase transition between a rod-rich and a plate-rich nematic phase. It is shown that the biaxial nematic phase is unstable relative to demixing even for symmetric mixtures of very long rod and very flat plates, where the Parsons–Lee theory becomes identical with the Onsager theory. The contradictory predictions obtained in recent studies regarding the stability of the biaxial nematic phase have been resolved by examining the lowest aspect ratio of the rods (κ2) where the Parsons–Lee and Onsager theories become equivalent. It turns out that neglecting the lower order terms in the excluded volumes (so-called end effects) leads to a favoring of the biaxial nematic phases. Only two types of phase transitions are observed in this work: isotropic–nematic phase coexistence and demixing transitions involving either two isotropic or two nematic phases. The stability of the nematic region on mixing is found to be very sensitive to the aspect ratios of the molecules: for moderate aspect ratios of the rods (5<κ2<10), a destabilization of the nematic phase is observed relative to the isotropic phase, while for κ2>10 the opposite tendency is found. A demixing transition between rod-rich and plate-rich nematic phases takes place for all of the systems studied with a widening coexistence region for increasing aspect ratio. Isotropic–isotropic demixing is also observed for aspect ratios κ2>65.5. For the larger values of κ2 the regions of isotropic–isotropic and nematic–nematic demixing broaden, while the isotropic–nematic coexistence is progressively suppressed.
Ice 1h/water interface of the SPC/E model: Molecular dynamics simulations of the equilibrium basal and prism interfaces
Authors: Bryk Taras , Haymet A. D. J.
Published: November 2002

The basal and prism interfaces formed by ice 1h and water in equilibrium are studied using the rigid SPC/E model of water, in the temperature range of 220–240 K close to one atmosphere. Density, translational, orientational, and dynamic order parameters exhibit smooth, continuous changes from crystal to liquid across the interface. For both planes, the most stable interface is observed at 225±5 K. For higher temperatures the interfaces melt, while for lower temperatures strong changes in the normal and transverse components of the pressure tensor flag the beginning of growth into the supercooled water. We define new charge density profiles and their window averages. These are analyzed to understand both the local charge inhomogeneity at the intrinsic interface and the interaction of solutes with the broad interface.
Comparing experiments with modeling for light ion helicon plasma sources
Authors: Carter M. D. , Baity F. W. , Barber G. C. , Goulding R. H. , Mori Y. , Sparks D. O. , White K. F. , Jaeger E. F. , Chang-Dı́az F. R. , Squire J. P.
Published: November 2002

The ability to obtain high plasma densities with high fractional ionization using readily available, low-cost components makes the helicon a candidate plasma source for many applications, including plasma rocket propulsion, fusion component testing, and materials processing. However, operation of a helicon can be a sensitive function of the magnetic field strength and geometry as well as the driving frequency, especially when using light feedstock gases such as hydrogen or helium. In this paper, results from a coupled rf and transport model are compared with experiments in the axially inhomogeneous Mini-Radio Frequency Test Facility [Goulding et al., Proceedings of the International Conference on Electromagnetics in Advanced Applications (ICEAA 99), Torino, Italy, 1999 (Litografia Geda, Torino, 1999), p. 107] (Mini-RFTF). Experimental observations of the radial shape of the density profile can be quantitatively reproduced by iteratively converging a high-resolution rf calculation including the rf parallel electric field with a transport model using reasonable choices for the transport parameters. The experimentally observed transition into the high density helicon mode is observed in the model, appearing as a nonlinear synergism between radial diffusion, the rf coupling to parallel electric fields that damp near the plasma edge, and propagation of helicon waves that collisionally damp near the axis of the device. Power deposition from various electric field components indicates that inductive coupling and absorption in the edge region can reduce the efficiency for high-density operation. The effects of absorption near the lower hybrid resonance in the near-field region of the antenna are discussed. Ponderomotive effects are also examined and found to be significant only in very low density and edge regions of the Mini-RFTF discharge.
Fluctuation of the ambipolar equilibrium in magnetic perturbations
Authors: Spineanu F. , Vlad M.
Published: November 2002

Attention is drawn to the fast oscillatory deviations from the residual nonambipolarity in the case where electrons are driven by strong magnetic perturbations.
Relativistic effects on interaction-induced electric properties of weakly interacting systems: The HF…AuH dimer
Authors: Avramopoulos Aggelos , Papadopoulos Manthos G. , Sadlej Andrzej J.
Published: November 2002

The relativistic effect on interaction-induced dipole moment and polarizability in the HF…AuH dimer is studied in the framework of the long-range perturbation theory model and by using the supermolecular approach. The perturbation treatment is limited to the lowest multipole-expanded form known as the dipole–induced-dipole (DID) approximation. Although the long-range DID model may be useful in elucidating the origin of the relativistic effect on interaction-induced electric properties, it fails to predict the correct magnitude of this effect for all but very large separations between the two subsystems. At intermediate monomer separations the supermolecular model predicts a substantial relativistic contribution to interaction-induced dipole moments and a rather moderate relativistic effect on induced polarizabilities. It has also been found that the vibrational contribution to the interaction-induced polarizability estimated in the double harmonic approximation may dominate over the changes in the pure electronic term. However, sufficiently accurate calculations of the vibrational contribution to electric properties of a weakly bound dimer, which would confirm this finding, appear to be unlikely at present.
Dynamics of OH formation in the dissociation of acrylic acid in its (n,π*) and (π,π*) transitions excited at 248 and 193 nm
Authors: Upadhyaya Hari P. , Kumar Awadhesh , Naik Prakash D. , Sapre Avinash V. , Mittal Jai P.
Published: November 2002

The (n,π*) and (π,π*) transitions in acrylic acid (H2C=CHCOOH) are excited by KrF (248 nm) and ArF (193 nm) laser pulses, respectively, and the dynamics of its photodissociation to give OH fragments is studied using laser induced fluorescence technique. At both the photolysis wavelengths, the OH fragments produced are vibrationally cold, but have different rotational state distributions. To get an insight into the potential energy surface involved in the dissociation process, spin–orbit and Λ-doublets ratios are also measured. Average relative translational energy partitioned into the photofragments is determined using linewidth of the Doppler profiles to be 13.2±3.1 and 10.2±2.8 kcal/mol at 193 and 248 nm excitations, respectively. High percentage of translational energy released into the photofragments suggests the presence of an exit barrier for the dissociation. On 248 nm excitation, the OH radicals are formed instantaneously during the laser pulse, while on 193 nm excitation, a risetime of ∼2 μs is seen. Another difference between the photodissociation at 193 nm and 248 nm is the observation of an intense fluorescence in UV–visible region at the former, and no fluorescence at the later wavelength. Our experimental results are compared with those obtained by recent ab initio calculations by Fang and Liu. It is concluded that when (π,π*) transition of acrylic acid is excited at 193 nm, the initially prepared S2 state undergoes nonradiative transitions to S1 and T2 states, and from where the molecule subsequently dissociates, while excitation to (n,π*) transition at 248 nm leads to dissociation solely from the initially prepared S1 state.
Mean field theory of the coherent to random-phase state transition in three-wave interactions
Authors: Drysdale P. M. , Robinson P. A.
Published: November 2002

The crossover of three-wave interactions from the coherent monochromatic limit to the wide bandwidth random-phase limit is investigated as the bandwidth of the waves is varied in a system exhibiting nonlinear three-wave oscillations. A recently observed sudden transition between the coherent and incoherent interaction is confirmed. As the bandwidth is increased from the monochromatic limit, it is found that the coherence of the interaction decreases slowly. At the transition point of the interaction the coherence then falls abruptly and nonlinear oscillations cease. An analytic mean-field approach is used to model the transition. Below the transition point, each frequency component of the wave spectra oscillates at its own individual frequency about the aggregate quasicoherent oscillation of the wave as a whole. It is when the frequency component at the spectral edge cannot sustain such oscillations that the system switches to random phase behavior. The analytic model’s estimate of the transition point and other interaction properties agrees semiquantitatively with numerical solutions of the full equations.
The stability of propagating slab electron holes in a magnetized plasma
Authors: Jovanović D. , Schamel H.
Published: November 2002

The stability of a propagating, one-dimensional solitary, slab electron hole in a magnetized plasma is studied using the linearized Vlasov description of the small perturbations. The plasma regimes characteristic to the magnetosphere and to the Earth’s magnetotail are considered. A destabilization of the electron hole by the resonant interaction of the wave with the trapped and the marginally free particles is found, and the expressions for the corresponding growth rates are given. In the case of a cyclotron wave–particle resonance, the instability manifests predominantly in the emission of linear waves. For the low-frequency resonance, when the wave frequency is comparable to the electron bounce frequency, larger growth rates are obtained, and the possibility of the breakup of the hole into smaller structures is found.
13–30 micron diameter microdischarge devices: Atomic ion and molecular emission at above atmospheric pressures
Authors: Park S.-J. , Eden J. G.
Published: November 2002

Cylindrical microdischarge devices having cavity diameters as small as 13 μm and volumes as low as several nanoliters have been fabricated in metal/polymer structures with and without screen electrodes. These devices produce stable glow discharges in Ne, Xe, air, Xe/O2, and Ne/air mixtures at total pressures up to the maximum investigated, 1200 Torr. Neon discharges in 30 μm diameter devices are well behaved for pNe above 700 Torr (pd>2.1 Torr cm) and generate strong emission in the UV from singly charged Ne-ion transitions at above-atmospheric pressures. Fluorescence in the visible from Xe+ and Xe2+ as well as molecular features in the green (∼530 nm) and blue (∼484 nm) that appear to be attributable to the neutral dimer are also observed from Xe in the 650–1100 Torr range. Discharges in air (100–740 Torr) and Ne/air mixtures produce strong N2(C→B) and N2+(B→X) emission in the near-UV and violet. The lowest observed operating voltage for Ne discharges in 30 μm devices is 87 V (pNe=1200 Torr). Discharges in microcavities of dimensions below 50 μm represent a unique spectroscopic tool.
Modeling of stochastic magnetic flux loss from the edge of a poloidally diverted tokamak
Authors: Evans T. E. , Moyer R. A. , Monat P.
Published: November 2002

A field line integration code is used to study the loss of edge poloidal magnetic flux due to stochastic magnetic fields produced by an error field correction coil (C–coil) in DIII–D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] for various plasma shapes, coil currents and edge magnetic shear profiles. We find that the boundary of a diverted tokamak is more sensitive to stochastic flux loss than a nondiverted tokamak. The C–coil has been used to produce a stochastic layer in an ohmic diverted discharge with characteristics similar to those seen in stochastic boundary experiments in circular limiter ohmic plasmas, including (1) an overall increase in recycling, (2) a broadening of the recycling profile at the divertor, and (3) a flattening of the boundary profiles over the extent of the stochastic layer predicted by the field line integration code. Profile flattening consistent with field line integration results is also seen in some high performance discharges with edge transport barriers. The prediction of a significant edge stochastic layer even in discharges with high performance and edge radial transport barriers indicates that either the self-consistent plasma response heals the stochastic layer or that edge stochastic layers are compatible with edge radial transport barriers.
Self-similar decaying profiles for reversed-field pinches
Authors: Nebel R. A. , Schnack D. D. , Gianakon T. A.
Published: November 2002

In previous work it was shown that progress in attaining and maintaining stable mean reversed-field pinch (RFP) profiles can be made by abandoning the steady-state assumption and instead seeking solutions of the pressureless (force-free), one-dimensional transport equations that are separable in time and space [E. J. Caramana and R. A. Nebel, Phys. Fluids 31, 3322 (1988)]. Here these solutions have been extended to two dimensions and therefore the previous formalism is also applicable to toroidal and helical states as well as axisymmetric cylindrical states. Furthermore, the one-dimensional separable solutions are demonstrated to be three-dimensional attractors, provided that the separable profiles are stable to current-driven modes. The sensitivity of these states to the velocity boundary conditions and to dimensionless parameters such as the Lundquist number and the magnetic Prandtl number has been studied. The stability boundary between one-dimensional stable solutions and unstable rampdown solutions has also been explored. Simulations with finite pressure and self-consistent transport clearly show the improved confinement that can be achieved with plasma rampdown. Finally, reactor simulations demonstrate that self-similar tearing mode stable rampdown discharges can lead to pulsed systems that show significant net energy gain.
Linear and nonlinear thresholds of neoclassical tearing modes in tokamaks
Authors: Lütjens Hinrich , Luciani Jean-François
Published: November 2002

The understanding of the physics of neoclassical tearing modes (NTM) is important for the dimensioning of current drive systems used to stabilize these modes in International Thermonuclear Experimental Reactor (ITER) plasmas [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)]. Predictions by theoretical models for the dynamics of NTM’s are compared with full scale numerical magnetohydrodynamical simulations including bootstrap current and transport effects. It is shown that curvature currents are sufficient to generate a nonlinear stability threshold for NTM’s. Furthermore, it is emphasized that at large resistivity NTM’s behave as an ordinary linear instability, which suppresses this nonlinear stability threshold.
Electronic structure of the carbon nanotube tips studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy
Authors: Chiou J. W. , Yueh C. L. , Jan J. C. , Tsai H. M. , Pong W. F. , Hong I.-H. , Klauser R. , Tsai M.-H. , Chang Y. K. , Chen Y. Y. , Wu C. T. , Chen K. H. , Wei S. L. , Wen C. Y. , Chen L. C. , Chuang T. J.
Published: November 2002

Angle-dependent x-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed to differentiate local electronic structures of the tips and sidewalls of highly aligned carbon nanotubes. The intensities of both π*- and σ*-band C K-edge XANES features are found to be significantly enhanced at the tip. SPEM results also show that the tips have a larger density of states and a higher C 1s binding energy than those of sidewalls. The increase of the tip XANES and SPEM intensities are quite uniform over an energy range wider than 10 eV in contrast to earlier finding that the enhancement is only near the Fermi level.
Work function and thermal stability of Ti1−xAlxNy for dual metal gate electrodes
Authors: Cha Tae-Ho , Park Dae-Gyu , Kim Tae-Kyun , Jang Se-Aug , Yeo In-Seok , Roh Jae-Sung , Park Jin Won
Published: November 2002

Work function and thermal stability of reactive sputtered Ti1−xAlxNy films were investigated for a metal gate electrode using a metal–oxide–semiconductor (MOS) structure. It is found that the work function (ΦM) values of Ti1−xAlxNy are ranged from 4.36 to 5.13 eV with a nitrogen partial flow rate (fN2). The ΦM values of Ti1−xAlxNy films, 4.36 eV for nMOS (n-Ti1−xAlxNy) and 5.10–5.13 eV for pMOS (p-Ti1−xAlxNy), may be applicable to dual metal gate electrodes. Excellent thermal stability up to 1000 °C was obtained on SiO2 as observed by the negligible change of capacitance equivalent thickness and Al 2p core level spectra for p-Ti1−xAlxNy (y∼1.0,fN2=50%), whereas a limited stability was attained in case of n-Ti1−xAlxNy (fN2⩽40%). The p-Ti1−xAlxNy can be a good candidate for pMOS device feasibility because of good thermal stability, while the n-Ti1−xAlxNy may be applicable for nMOS gate electrode in low thermal devices using damascene gate process.
Organic polymeric thin-film transistors fabricated by selective dewetting
Authors: Chabinyc Michael L. , Wong William S. , Salleo Alberto , Paul Kateri E. , Street Robert A.
Published: November 2002

Thin-film transistors (TFTs) of polymeric semiconductors were fabricated using selective dewetting in the patterning process. The process consists of: (i) patterning the wettability of the substrate using a protective layer of printed wax and a self-assembled monolayer, and (ii) patterning a polymeric semiconductor by selective dewetting from an organic solution. The method has been used to fabricate small arrays of TFTs with a regioregular poly(thiophene) and poly(9-9′-dioctyl-fluorene-co-bithiophene). The TFTs exhibited mobilities of 0.5–1.0×10−3 cm2 V−1 s−1 and on-to-off ratios on the order of 104.
Substrate-free crystallization of distorted hexagonal barium titanate thin films
Authors: Stavitski N. , Lyahovitskaya V. , Nair J. , Zon I. , Popovitz-Biro R. , Wachtel E. , Feldman Y. , Lubomirsky I.
Published: November 2002

We show that substrate-free crystallized barium titanate (BaTiO3) films adopt a hexagonal structure, whereas substrate-supported films assume the commonly observed tetragonal phase. However, in contrast to the known hexagonal BaTiO3, the substrate-free crystallized films demonstrate a small but measurable pyroelectric effect, and do not exhibit phase transitions in the 25–423 K temperature range. Thus the substrate-free crystallized BaTiO3 represents a heretofore unreported crystallographic modification of BaTiO3.
Dynamics of stimulated emission in InAs quantum-dot laser structures measured in pump-probe experiments
Authors: Tartakovskii A. I. , Groom K. M. , Adawi A. M. , Lemaı̂tre A. , Fox A. M. , Mowbray D. J. , Skolnick M. S. , Hopkinson M.
Published: November 2002

Nonlinear carrier-photon dynamics are studied for optically pumped InAs quantum-dot (QD) laser structures, using excitation into the GaAs barrier by two degenerate pump and probe laser pulses. The nonlinear emission from QDs excited by the pump pulse is further amplified by the probe excitation. By varying the delay between the two pulses, a very fast decay of the QD excited state emission is measured. Notably slower dynamics for the QD ground state are observed, governed by state filling phenomena that result in gain saturation.
Nitrogen passivation of deposited oxides on n 4H–SiC
Authors: Chung G. Y. , Williams J. R. , Isaacs-Smith T. , Ren F. , McDonald K. , Feldman L. C.
Published: November 2002

Results for measurements of interface state density and breakdown field strength are reported for deposited oxides on n 4H–SiC following passivation with nitric oxide. Low-temperature oxides deposited by plasma-enhanced chemical vapor deposition and high-temperature oxides deposited at 950 °C were investigated. Nitrogen passivation of deposited oxides on n 4H–SiC is found to produce interface state densities of 1–2×1012 cm−2 eV−1 at Ec−E=0.1 eV, regardless of variations in oxide deposition procedures that affect the residual interfacial carbon concentration. Breakdown field strengths were higher for passivated high-temperature oxides compared to passivated low-temperature oxides at room temperature and 290 °C. We suggest that additional oxide growth during the NO passivation is the reason for the observed interface state densities.
On the effects of implantation temperature in helium implanted silicon
Authors: Oliviero E. , David M. L. , Beaufort M. F. , Barbot J. F. , van Veen A.
Published: November 2002

He + ions were implanted into silicon with a fluence of 5×1016 cm−2 at different temperatures ranging from 473 to 1073 K. Samples were analyzed by thermal helium desorption spectroscopy and by transmission electron microscopy. As far as cavity formation is concerned, the behavior can be divided into three stages depending on the implantation temperature. However, it is found that helium release from cavities is governed by a single mechanism regardless of the implantation temperature.
Magnetically and electrically tunable semiconductor quantum waveguide inverter
Authors: Gilbert M. J. , Akis R. , Ferry D. K.
Published: November 2002

In recent years, quantum computing and information theory has received a great deal of attention as a means of drastically improving the computational speed and resources traditionally associated with current binary implementations. We present an electrically tunable semiconductor quantum waveguide implementation of an inverter gate in a GaAs/AlGaAs heterostructure in which the output of the waveguide structure may be selected via the application of an appropriate magnetic field or electrical bias. The resulting behavior observed by our implementation shows a great deal of promise for an eventual semiconductor realization of this basic qubit structure.
Ultrathin zirconium silicate gate dielectrics with compositional gradation formed by self-organized reactions
Authors: Watanabe Heiji
Published: November 2002

Zirconium silicate gate dielectrics with compositional gradation in depth were fabricated by in situ reoxidation of thin metal layers on oxidized Si surfaces. The silicate is composed of a trilayer structure, in which Si-rich layers are formed both at the top and the bottom of the film. The zirconium element is localized at the center of the silicate and, thus, the advantages of the silicate material can be obtained, while keeping sufficient permittivity. The compositionally graded silicates show promising electrical properties, such as a leakage current of less than 0.11 A/cm2 for an equivalent oxide thickness of 1.1 nm and an improved flatband voltage shift that is a result of postdeposition annealing and oxidation.
Getting high-efficiency photoluminescence from Si nanocrystals in SiO2 matrix
Authors: Wang Y. Q. , Kong G. L. , Chen W. D. , Diao H. W. , Chen C. Y. , Zhang S. B. , Liao X. B.
Published: November 2002

Silicon nanocrystals in SiO2 matrix are fabricated by plasma enhanced chemical vapor deposition followed by thermal annealing. The structure and photoluminescence (PL) of the resulting films is investigated as a function of deposition temperature. Drastic improvement of PL efficiency up to 12% is achieved when the deposition temperature is reduced from 250 °C to room temperature. Low-temperature deposition is found to result in a high quality final structure of the films in which the silicon nanocrystals are nearly strain-free, and the Si/SiO2 interface sharp. The demonstration of the superior structural and optical properties of the films represents an important step towards the development of silicon-based light emitters.
Breaking and restoring a molecularly bridged metal|quantum dot junction
Authors: Hens Z. , Tallapin D. V. , Weller H. , Vanmaekelbergh D.
Published: November 2002

Nanometer-sized insulating quantum dots (CdSe and ZnO) have been attached to a Au(111) substrate, using molecular bridges with thiol and carboxylate end functions. We demonstrate that the quantum dots can be probed by a scanning tunneling microscope at negative substrate bias. At positive bias, however, the gold–sulfur bond is broken and the quantum dots are transferred to the tip. Individual CdSe quantum dots can be picked up by the tip and displaced on the substrate in a controlled way.
Thermal stress hardening of a-Si3N4/nc-TiN nanostructured multilayers
Authors: Xu Junhua , Yu Lihua , Azuma Yasushi , Fujimoto Toshiyuki , Umehara Hiroyuki , Kojima Isao
Published: November 2002

Amorphous/nanopolycrystalline Si3N4/TiN nanostructured multilayer films have been fabricated by radio-frequency reactive magnetron sputtering. The effects of deposition temperature, modulation period, and the layer thickness ratio on the hardness have been studied, in order to elucidate the hardening mechanisms in these multilayers. The hardness of the Si3N4/TiN multilayers is affected not only by the modulation periods, but also by the layer thickness ratio and deposition temperature. The hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500 °C and a modulation ratio (lSi3N4/lTiN) of 3/1. Based on the experimental results, it is suggested that the alternating stress field caused by thermal mismatch between Si3N4 and TiN is one of the main reasons for the superhardness effect in Si3N4/TiN nanostructured multilayers.
Electromigration-induced plastic deformation in passivated metal lines
Authors: Valek B. C. , Bravman J. C. , Tamura N. , MacDowell A. A. , Celestre R. S. , Padmore H. A. , Spolenak R. , Brown W. L. , Batterman B. W. , Patel J. R.
Published: November 2002

We have used scanning white beam x-ray microdiffraction to study microstructural evolution during an in situ electromigration experiment on a passivated Al(Cu) test line. The data show plastic deformation and grain rotations occurring under the influence of electromigration, seen as broadening, movement, and splitting of reflections diffracted from individual metal grains. We believe this deformation is due to localized shear stresses that arise due to the inhomogeneous transfer of metal along the line. Deviatoric stress measurements show changes in the components of stress within the line, including relaxation of stress when current is removed.
Thermal stability of polycrystalline silicon/metal oxide interfaces
Authors: Callegari A. , Gousev E. , Zabel T. , Lacey D. , Gribelyuk M. , Jamison P.
Published: November 2002

The thermal stability of polycrystalline silicon (poly-Si)/ZrO2 interface was significantly enhanced when the poly-Si was plasma deposited using silane heavily diluted in He. With regard to this process, transmission electron microscopy shows a sharp poly-Si/ZrO2 interface that is stable at 1000 °C. When the poly-Si was deposited by chemical vapor deposition using undiluted silane gas, transmission electron microscopy shows strong reactions at the poly-Si/ZrO2 interface when annealed at 1000 °C. The increased stability can be attributed to He dilution, which may prevent hydrogen from reducing the metal oxide. Another explanation may be directly related to He-excited plasma, which is known to produce denser and more stable films.
Probing the AlxGa1−xN spatial alloy fluctuation via UV-photoluminescence and Raman at submicron scale
Authors: Bergman Leah , Chen Xiang-Bai , McIlroy David , Davis Robert F.
Published: November 2002

We present a straightforward method for the study of alloy spatial compositional distribution at the submicron scale via photoluminescence and Raman spectroscopy. The spatial dependence of the band gap light-emission energy of AlxGa1−xN alloys at composition 0⩽x⩽1 was studied via deep UV-photoluminescence and Raman microscopy in order to address the issue of the spatial alloy fluctuation. The data were acquired in a random fashion from an area of ∼1 mm2 on the sample at steps of ∼1–200 μm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the photoluminescence emission energy exhibits random type variations depending on locality: the alloys of composition x=0.12, x=0.22, x=50, and x=0.70 exhibit average variations of ∼10, 30, 45, and 25 meV, respectively. The photoluminescence of the pure GaN exhibits no significant spatial fluctuation. The stress contribution to the observed photoluminescence fluctuations was investigated via Raman analysis and was taken into account in order to estimate the local compositional fluctuation Δx. Our results indicate that for the higher Al composition alloys x=0.50 and 0.70 the stress and the compositional fluctuation can be resolved, resulting in average spatial fluctuations of Δx=0.004 and 0.002, respectively.
Early locus of a linguistic variable in a fast priming task
Authors: Lee Chang H. , Katz Leonard
Published: November 2002

The syllable and the morpheme are known to be important linguistic variables, but is such information involved in the early stages of word recognition? Syllable‐morpheme information was manipulated in the early stage of word naming by means of the fast priming paradigm. The letters in the prime were printed in a mixture of lower‐ and upper‐case letters. The change from lower to upper case occurred either at a syllable‐morpheme boundary, before the boundary, or after it (e.g., reTAKE, rETAKE, or retAKE) creating either an intact pair or a broken one. The target was always in lower case (e.g., retake). The results of Experiments 1 and 2 revealed that intact syllable and morpheme information facilitated word naming at a short Stimulus Onset Asynchrony (below awareness) but not at a long SOA, suggesting that the use of such information is automatic. A second set of experiments attempted to determine if syllable information alone could facilitate word processing. In Experiments 3 and 4, monomorphemic words were divided either at, before, or after the syllable boundary (e.g., rePEL, rEPEL, or repEL). The primes were all pseudomorphemic in the sense that the initial syllables could appear as a morpheme in other words (e.g., restate) but were not morphemic in the target words (e.g., repel). The second syllable was neither morphemic nor pseudomorphemic. Using the same SOAs as in Experiments 1 and 2, intact syllables were found to be facilitative at the short SOA, but not at the long SOA. Thus, the syllable plays a role in an early stage of word recognition. Whether morphemes that are not syllables are facilitative is still to be determined in this paradigm.
Normative predictions of collectivist‐individualist intentions and behaviour of Indians
Authors: Sinha Jai B.P. , Vohra Neharika , Singhal Sushila , Sinha R.B.N. , Ushashree S.
Published: November 2002

Five hundred and thirty‐four college students, drawn from five distantly located cities in India that varied in affluence and infrastructural facilities, participated in a study designed to understand their normative predictions about people's responses to 20 situations. The responses consisted of five combinations: collectivist behaviour with collectivist intention (CC), individualist behaviour with individualist intention (II), collectivist behaviour with individualist intention to behave subsequently in an individualist way or to serve individualist intention (CI), individualist behaviour with collectivist intention to behave subsequently in a collectivist way or to serve a collectivist purpose (IC), and a mix of collectivist and individualist intention and behaviour (C&I). The findings indicated that the situations involving family members were reported to induce collectivism in behaviour as well as intentions. However, compelling personal needs were believed to lead to serve individualist interests, but by adopting collectivist behaviour. Further, collectives, compared to individuals, were reported to behave in collectivist way. Even when collectives behaved in individualist fashion, the ultimate aim was conjectured to serve a collectivist purpose. Females, like males, were perceived to meet compelling individual needs by resorting to collectivist behaviour. In less compelling matters that are less salient to their gender role, females were reported to remain collectivist in their behaviour as well as intentions. More affluent places with better infrastructure are believed to manifest either a mix of collectivist and individualist behaviour and intentions or a response pattern that enables individualist interests to be served through collectivist behaviour. A clear individualist pattern of behaviour and intention was rarely predicted to occur. The changing socioeconomic scenario has probably induced a shift towards cultivating individualist intentions that are still realized through collectivist behaviour. With the rate of change accelerating further, individualism is likely to get stronger, particularly in more affluent areas with better infrastructure. However, the combinations of collectivist and individualist behaviour and intentions are likely to remain complex.
Interleukin‐18 and CD30 serum levels in patients with moderate‐severe depression
Authors: Merendino Rosaria Alba , Di Rosa Antonio Enrico , Di Pasquale Giuseppe , Minciullo Paola Lucia , Mangraviti Carmela , Costantino Antonella , Ruello Antonella , Gangemi Sebastiano
Published: November 2002

Interleukin‐18 (IL‐18), a pro‐inflammatory cytokine that plays an important role in the T‐cell‐helper type 1 response, is a new member of the family of cytokines produced in the brain. CD30 is a marker of T‐cell‐helper type 2 lymphocytes. We evaluated IL‐18 and CD30 serum levels in 10 patients affected by moderate‐severe depression (MSD). We demonstrated for the first time that serum IL‐18 levels of MSD patients were significantly higher than those of healthy donors. On the contrary, no significant difference was found between serum CD30 levels of MSD patients compared with those of healthy donors. These data strengthen the hypothesis that MSD disease is associated with an inflammatory response, mainly T‐cell‐helper type 1, and suggest an important role for IL‐18 in the pathophysiology of MSD.
The effect of interleukin‐15 on the expression of killer‐cell immunoglobulin‐like receptors on peripheral natural killer cells in human
Authors: Kogure Toshiaki , Mantani Naoki , Goto Hirozo , Shimada Yutaka , Tamura Jun′ichi , Terasawa Katsutoshi
Published: November 2002

Interleukin (IL)‐15 has emerged as a key regulator of both natural killer (NK) cell differentiation and activation. The aim of the present study was to investigate the expansion of the population of cells expressing killer‐cell immunoglobulin‐like receptors (CD158a and CD158b) in human peripheral lymphocytes by treatment with IL‐15. One million peripheral lymphocytes were cultured in RPMI1640 medium alone or in medium containing IL‐2 at 100 U/ml or IL‐15 at 0.1, 1.0, or 10.0 ng/ml for 48 h. After each incubation, we assessed the natural killing activity and the population of CD16+CD158a+/b+ cells and CD8+CD158a+/b+ cells. IL‐15 increased the NK activity and expanded the populations of CD16+CD158a+/b+ cells and CD8+CD158a+/b+ cells. These actions were dose dependent, and the effects of IL‐15 at 1.0 ng/ml were close to those of IL‐2 at 100 U/ml. These findings suggest that IL‐15 induces the effector functions of resting NK cells throughout the body, and thereby plays a critical role in the activation of tissue‐associated immune responses.