bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling of the resistive wall mode to liquid wall surface modes
Authors: Rappaport H. L.
Published: July 2002

An analysis of the resistive wall mode of a fusion plasma surrounded by a cylindrically symmetric rotating thin liquid metal shell is given. Coupling between the resistive wall mode and free fluid boundary surface modes is described. Consequences of fluid perturbations induced in the wall, on the wall mode growth rate, are found to be greater when the wall fluid has a vacuum–fluid interface than when the fluid is forced to flow between solid bounding shells. The effect of the fluid perturbations is always found to be destabilizing, except close to the wall mode/surface mode resonance. Criteria for resonance, an analytic solution to the dispersion relation for the wall mode in the resonance regime, and implications of this work for relevant experiments are given.
Electron trajectories in a free-electron laser with planar wiggler and ion-channel guiding
Authors: Mehdian Hassan , Esmelzadeh Mehdi , Willett Joseph E.
Published: July 2002

An analysis of quasi-steady-state electron trajectories in a planar wiggler with an ion channel and an axial magnetic field is presented. A tenth-degree polynomial equation for the average axial electron velocity and an equation for the function Φ, which determines the rate of change of axial velocity with energy, are derived. Numerical calculations are made to illustrate the effects of the two electron-beam guiding devices on the trajectories when applied separately and simultaneously. Some interesting effects of their simultaneous application include the existence of three groups of orbits, two singularities of the function Φ, and two negative mass regimes.
Retrofitted confocal laser scanner for a commercial inverted fluorescence microscope
Authors: Bigelow Chad E. , Harkrider Curtis J. , Conover David L. , Foster Thomas H. , Georgakoudi Irene , Mitra Soumya , Nichols Michael G. , Rajadhyaksha Milind
Published: July 2002

We describe the design and implementation of an inverted laser scanning confocal fluorescence microscope utilizing the commercial Nikon Diaphot TMD platform. An external confocal scanner was retrofitted through the video side port of the Diaphot. With 10×, 0.5 NA dry and 60×, 1.4 NA oil immersion objectives, the depth discrimination is 5.8 μm and 0.8 μm, respectively, as determined by derivatives of fluorescence edge responses measured in liquid samples of rhodamine 6G dissolved in DMSO. We present sample edge response curves and representative confocal fluorescence images of tumor cells in monolayer culture.
Dynamics of ion-ion plasmas under radio frequency bias
Authors: Midha Vikas , Economou Demetre J.
Published: July 2002

A time-dependent one-dimensional fluid model was developed to study the dynamics of a positive ion-negative ion (ion-ion) plasma under the influence of a rf bias voltage. The full ion momentum and continuity equations were coupled to the Poisson equation for the electrostatic field. Special emphasis was placed on the effect of applied bias frequency. Due to the lower temperature and greater mass of negative ions compared to electrons, the sheath structure in ion-ion plasmas differs significantly from that of conventional electron-ion plasmas, and shows profound structure changes as the bias frequency is varied. For low bias frequencies (100 kHz), the charge distribution in the sheath is monotonic (switching from positive to negative) during each half cycle. For intermediate frequencies (10 MHz), when the bias period approaches the ion transit time through the sheath, double layers form with both positive and negative charges coexisting in the sheath. For high frequencies (60 MHz), beyond the plasma frequency, plasma waves are launched from the sheath edge, and the sheath consists of multiple peaks of positive and negative charge (multiple double layers). For a relatively large range of bias frequencies (up to the plasma frequency), each electrode is bombarded alternately by high energy positive and negative ions during a rf bias cycle. For bias frequencies greater than the plasma frequency, however, the electrode is bombarded simultaneously by low energy positive and negative ions with ion energies approaching the thermal value. The ion energy was found to increase with the applied bias potential. Also, at relatively high pressures (20 mTorr), the ion energy at low frequencies (100 kHz) is limited by collisions. The peak ion energy may then be increased by using an intermediate bias frequency (10 MHz). At lower pressures, however, the effect of collisions is mitigated while the effect of ion transit time becomes significant as the bias frequency increases. In this case, a low bias frequency (100 s of kHz) is favorable for extracting high energy ions from the plasma.
Far-infrared absorption spectra of doped quantum well structures
Authors: Jiang P. , Kok W. C.
Published: July 2002

Infrared absorption line profiles associated with transitions between the 1s-like ground state and 2p− excited state of hydrogenic donors in a quantum well are calculated for x-polarized radiation. Various types of dopant distribution are considered as in the experimental studies. Similarity is drawn between the calculated quasi-Lorentzian line shapes and one derived from a transmission spectrum for a central 1/3 barrier doped multiple quantum well sample. Effects in a magnetic field applied perpendicular to the layers are also investigated and compared with experiment.
Relaxed plasma-vacuum systems
Authors: Spies G. O. , Lortz D. , Kaiser R.
Published: July 2002

Taylor’s theory of relaxed toroidal plasmas (states of lowest energy with fixed total magnetic helicity) is extended to include a vacuum between the plasma and the wall. In the extended variational problem, one prescribes, in addition to the helicity and the magnetic fluxes whose conservation follows from the perfect conductivity of the wall, the fluxes whose conservation follows from the assumption that the plasma-vacuum interface is also perfectly conducting (if the wall is a magnetic surface, then one has the toroidal and the poloidal flux in the vacuum). Vanishing of the first energy variation implies a pressureless free-boundary magnetohydrostatic equilibrium with a Beltrami magnetic field in the plasma, and in general with a surface current in the interface. Positivity of the second variation implies that the equilibrium is stable according to ideal magnetohydrodynamics, that it is a relaxed state according to Taylor’s theory if the interface is replaced by a wall, and that the surface current is nonzero (at least if there are no closed magnetic field lines in the interface). The plane slab, with suitable boundary conditions to simulate a genuine torus, is investigated in detail. The relaxed state has the same double symmetry as the vessel if, and only if, the prescribed helicity is in an interval that depends on the prescribed fluxes. This interval is determined in the limit of a thin slab.
Angle-resolved electron energy loss spectroscopy of valence-shell and Si 2p pre-edge excitation of SiF4: Bethe surface and absolute generalized oscillator strength measurement
Authors: Fan X. W. , Leung K. T.
Published: July 2002

Absolute generalized oscillator strengths (GOSs) of discrete transitions in the preionization-edge region of the valence and Si 2p inner shells of SiF4 have been determined as functions of energy loss and momentum transfer by using angle-resolved electron energy loss spectroscopy at 2.5 keV impact energy. The GOS profiles of the pre-edge features are generally consistent with the spectral assignments based on the term values of the virtual and Rydberg states from earlier valence and inner-shell studies. In particular, the GOS profiles for these low-lying preionization-edge features in the valence shell are found to be dominated by a strong maximum at zero momentum transfer, consistent with the proposed assignment of predominantly dipole-allowed Rydberg and mixed valence-Rydberg transitions. In the case of the lowest-lying preionization-edge 1t1→6a1 feature, which is formally dipole-forbidden, the present work shows that such a shape for the GOS profile is, however, not exclusive to just dipole-allowed transitions. In the Si 2p shell, the GOS profiles for the well resolved, intense σ* resonance and three higher-lying Si 2p pre-edge features have been determined and are found to be largely dominated by dipole-allowed (Rydberg) excitations. Differences in and between the GOS profiles for the valence-shell and Si 2p pre-edge features in SiF4 are identified. No discernible secondary extrema can be found in any of these GOS profiles. The present GOS results for SiF4 are compared with those reported for other cage-like molecules, including CF4 and SF6.
Effects of conduction band offset on spin-polarized transport through a semimagnetic semiconductor heterostructure
Authors: Zhai Feng , Guo Yong , Gu Bing-Lin
Published: July 2002

We investigate the role played by the zero-field conduction band offset in spin-dependent transport through a ZnSe/Zn1−xMnxSe heterostructure with a single paramagnetic layer. It is shown that the zero-field band offset can strongly affect features of spin-polarized transport: the spin polarization is greatly weakened for the negative zero-field offset while in the positive case it is drastically enhanced. The reason is that the polarization is determined by the discrepancy between the effective potential for spin-up electrons and that for spin-down ones. Furthermore, the magnitude of the effective potential as well as its configuration are conduction-band-offset dependent and field tunable.
Femtochemistry of mass-selected negative-ion clusters of dioxygen: Charge-transfer and solvation dynamics
Authors: Paik D. Hern , Bernhardt Thorsten M. , Kim Nam Joon , Zewail Ahmed H.
Published: July 2002

Femtosecond, time-resolved photoelectron spectroscopy is used to investigate the dissociation dynamics of mass-selected anionic molecular-oxygen clusters. The observed transient photoelectron signal for the clusters (O2)n− (n=3–5) shows the O2− production; for n=1 and 2, we observe no time-dependence at this wavelength of 800 nm. The observed transients are bi-exponential in form with two distinct time constants, but with clear trends, for all investigated cluster sizes. These striking observations describe the reaction pathways of the solvated core and we elucidate two primary processes: Charge transfer with concomitant nuclear motion, and direct dissociation of the O4− core-ion via electron recombination; the former takes 700–2700 fs, while the latter is on a shorter time scale, 110–420 fs. Both rates decrease differently upon increasing cluster size, indicating the critical role of step-wise solvation.
Defect clustering during ion irradiation of GaAs: Insight from molecular dynamics simulations
Authors: Nordlund K. , Peltola J. , Nord J. , Keinonen J. , Averback R. S.
Published: July 2002

Defect formation in compound semiconductors such as GaAs under ion irradiation is not as well understood as in Si and Ge. We show how a combination of ion range calculations and molecular dynamics computer simulations can be used to predict the atomic-level damage structures produced by MeV ions. The results show that the majority of damage produced in GaAs both by low-energy self-recoils and 6 MeV He ions is in clusters, and that a clear majority of the isolated defects are interstitials. Implications of the results for suggested applications are also discussed.
A priori and a posteriori tests of subgrid scale models for scalar transport
Authors: Jiménez C. , Valiño L. , Dopazo C.
Published: July 2002

A priori tests of subgrid scale (SGS) models for the transport of scalars by turbulence are performed by studying the transfer of scalar fluctuations between resolved and subgrid scales in a temporal mixing layer. They confirm that both forward and backward transfer are present, what can be best represented by mixed models (eddy-diffusivity+scale-similarity). However, a posteriori tests show that eddy-diffusivity models, even if only able to dissipate fluctuations from resolved to subgrid scales, give very similar results to mixed models, provided that an appropriate model is used for SGS stresses.
From binary and ternary to multicomponent nucleation: Atmospheric aerosol formation
Authors: Gorbunov B.
Published: July 2002

Multicomponent homogeneous nucleation is considered in the case of dominant and trace species (with respect to embryo composition). The free energy of embryo formation for multicomponent homogeneous nucleation has been derived for systems with several dominant species, e.g., water+sulfuric acid and a number of trace substances. This treatment is based on a differential version of the capillarity approximation. It is considered that an embryo is formed due to the condensation of several different gaseous compounds containing water, sulfuric acid, nitric acid, organic compounds, etc. Henry’s law is employed to describe the chemical potential of trace species in embryos. The case of the surface free energy influenced by amounts of trace species transferred into an embryo is considered. It was found that the free energy of embryo formation for multicomponent nucleation depends upon the ratios of the partial pressures of the trace species to the Henry’s law constants of the species. The nucleation rate for a multicomponent system is found to be a product of the dominant species nucleation rate (e.g., binary or ternary nucleation rate) and the correction factor that is influenced by the trace species. It was shown that the multicomponent nucleation correction factor is likely to be in the range from 3 to 1010. As an example of the approach developed, the formation of secondary atmospheric aerosols was considered as multicomponent homogeneous nucleation of water vapor, sulfuric acid, nitric acid, formic acid, and other hydrophilic compounds.
Transient filaments formation by nonlinear kinetic Alfvén waves and its effect on solar wind turbulence and coronal heating
Authors: Shukla Anita , Sharma R. P.
Published: July 2002

The nonlinear dynamical equation for the propagation of kinetic Alfvén waves has been derived in two dimensions using the two-fluid model of the plasma and by taking the adiabatic response for the background density in the presence of nonlinear electron heating and the ponderomotive force. Dynamically evolving filamentary structures are predicted. The effect of these filaments on solar wind turbulence and coronal heating has also been pointed out.
Nucleation and growth of Cu films during the initial stage of chemical vapor deposition
Authors: Chae Y. K. , Komiyama H.
Published: July 2002

The nucleation and growth of Cu nanoparticles during the initial stage of film growth by chemical vapor deposition was investigated using transmission electron microscopy and energy dispersive x-ray spectroscopy analysis. Cu nanoparticles did not migrate on the SiO2 surface because the Cu nanoparticles were deposited by autocatalytic reactions onto pre-existing nuclei, and therefore were strongly bonded to the surface. The initial growth mechanism of Cu nanoparticles appears to be that Cu particles deposit by surface reaction onto pre-existing nuclei, grow to become nanoparticles, and these nanoparticles form amorphous Cu islands. The amorphous Cu islands grow to become larger islands that consist of partially-crystallized Cu. The crystallized Cu particles then begin to form on the amorphous Cu phases. With increasing deposition time, the amorphous Cu phases completely convert into crystalline phases to form a crystalline film.
A converged calculation of the energy barrier to internal rotation in the ethylene–sulfur dioxide dimer
Authors: Resende Stella M. , De Almeida Wagner B. , van Duijneveldt-van de Rijdt Jeanne G. C. M. , van Duijneveldt Frans B.
Published: July 2002

Geometrical parameters for the equilibrium (MIN) and lowest saddle-point (TS) geometries of the C2H4⋯SO2 dimer, and the corresponding binding energies, were calculated using the Hartree–Fock and correlated levels of ab initio theory, in basis sets ranging from the D95(d,p) double-zeta basis set to the aug-cc-pVQZ correlation consistent basis set. An assessment of the effect of the basis set superposition error (BSSE) on these results was made. The dissociation energy from the lowest vibrational state was estimated to be 705±100 cm−1 at the basis set limit, which is well within the range expected from experiment. The barrier to internal rotation was found to be 53±5 cm−1, slightly higher than the (revised) experimental result of 43 cm−1, probably due to zero-point vibrational effects. Our results clearly show that, in direct contrast with recent ideas, the BSSE correction affects differentially the MIN and TS binding energies and so has to be included in the calculation of small energy barriers such as that in the C2H4⋯SO2 dimer. Previous reports of positive MP2 frozen-core binding energies for this complex in basis D95(d,p) are confirmed. The anomalies are shown to be an artifact arising from an incorrect removal of virtual orbitals by the default frozen-core option in the GAUSSIAN program.
The role of neoclassical convection in the confinement improvement of plasmas with impurity injection in DIII-D
Authors: Stacey Weston M.
Published: July 2002

A series of three otherwise identical DIII-D [J. L. Luxon, F. Batty, C. B. Baxi et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] L-mode (low confinement mode) plasma experiments with and without neon injection was analyzed with neoclassical theory. The measured increases in momentum and energy confinement times, central rotation speed, and E×B with increasing neon injection are predicted quantitatively by neoclassical theory, in particular by the predicted increase in the inward neoclassical convective momentum and energy fluxes with neon injection. This agreement between theory and experiment suggests that the physical mechanism by means of which neon injection improves the confinement of these L-mode DIII-D plasmas is to increase the inward neoclassical particle flux, and hence increase the inward convective momentum and energy fluxes.
Phase transformations of nanometer size carbon particles in shocked hydrocarbons and explosives
Authors: Viecelli J. A. , Bastea S. , Glosli J. N. , Ree F. H.
Published: July 2002

Estimates for the displacement of the phase equilibrium lines for small carbon particles containing from several hundred to several tens of thousands of atoms are made, and an error analysis of the uncertainties in these estimates is derived and evaluated using available experimental data. Hugoniot calculations for methane, benzene, polyethylene, and polybutene, based on a carbon particle surface energy adjusted equation of state, are in better agreement with shock pressure-volume and temperature data than those obtained with a bulk carbon equation of state. The results suggest that carbon particles, of order 103–104 atoms, can exist in the liquid state at lower temperatures than bulk carbon.
Weakly damped acoustic-like ion waves in plasmas with non-Maxwellian ion distributions
Authors: Gunell H. , Skiff F.
Published: July 2002

Dispersion relations for ion-acoustic-like waves in plasmas with and without superthermal particles are calculated using a simple pole expansion of the distribution function for the ions. It is found that slow weakly damped modes exist in two-temperature plasmas, and the conditions when these modes appear are investigated. For plasmas with equal ion and electron temperatures weakly damped modes are found when there is a depletion of the high-energy tails.
Zonal flow and field generation by finite beta drift waves and kinetic drift-Alfvén waves
Authors: Guzdar P. N. , Kleva R. G. , Das A. , Kaw P. K.
Published: July 2002

A study of the generation of zonal flows and zonal magnetic fields by finite beta drift waves and kinetic drift-Alfvén waves is presented. The analysis is a generalization of recent investigations of the modulational instability for zonal flow generation by electrostatic drift waves to finite beta drift waves and kinetic drift-Alfvén waves. The drift wave driven unstable zonal flows/fields are stabilized by finite β below a critical value, due to the finite beta modification of the drift wave pump and the drift sidebands. They are, however, destabilized by coupling to the zonal field for larger β. The drift-Alfvén branch driven zonal flows/fields are found to be completely stable below a critical β, and are destabilized for larger β. These new results can find applications in a variety of laboratory and space plasma situations.
Green’s function embedding approach to quantum conductivity of single wall carbon nanotubes
Authors: Andriotis Antonis N. , Menon Madhu
Published: July 2002

Quantum conductivity of carbon nanotubes is calculated using an efficient embedding Green’s function formalism that allows for a realistic nanotube-metal lead contacts. The details of the contact geometry is found to profoundly influence the I–V characteristics. Furthermore, the primary effect of defects in nanotubes is to smooth out the steplike features of the corresponding I–V curve of the pristine tube.
A system for performing simultaneous in situ atomic force microscopy/optical microscopy measurements on electrode materials for lithium-ion batteries
Authors: Beaulieu L. Y. , Cumyn V. K. , Eberman K. W. , Krause L. J. , Dahn J. R.
Published: July 2002

An atomic force microscope (AFM) equipped with an optical charge coupled device camera has been placed in an Ar filled glovebox for the purpose of studying the change in morphology of electrode materials as they react with lithium. In order to minimize noise induced by vibration, the AFM is mounted on granite blocks suspended from the ceiling of the glovebox by a combination of flexible rubber cords and metal springs. The AFM, which is equipped with an environmental chamber surrounding the sample, is then enclosed in a specially constructed draft shield that allows the circulation of Ar gas by the purification system during imaging. A special electrochemical cell was constructed to hold the working electrode under study. Repeated imaging with little drift is possible while electrodes are reacted with lithium for periods of many days. Examples of measurements made by this device will be given for the case of lithium alloying with sputter-deposited Si–Sn thin films. The optical and AFM images obtained as a function of lithium content in the films are assembled into time-lapsed “movies” showing the evolution of the morphology of the sample along with the corresponding electrochemistry. These movies are available for download through the Electronic Physics Auxiliary Publication Service (EPAPS).
White microbeam diffraction from distorted crystals
Authors: Barabash R. , Ice G. E. , Larson B. C. , Pharr G. M. , Chung K.-S. , Yang W.
Published: July 2002

We present a general description of white-beam (Laue) scattering from grains with dislocations. This approach is applied to examples with equal numbers of positive and negative Burger’s vectors (paired) and with unpaired dislocations of one sign (geometrically necessary). We find that streaking of the Laue reflections is sensitive to both long-range geometrical rotations introduced by unpaired edge dislocations and to local rotation fluctuations introduced by the total number of dislocations (paired and unpaired). We demonstrate the technique by analyzing the dislocation distribution in a nanoindented Cu single crystal.
Exciton linewidth in semiconducting cylindrical quantum wire structures due to scattering by polar optical phonons: Finite potential well model
Authors: Ham Heon , Spector Harold N.
Published: July 2002

In our previous work [H. Ham and H. N. Spector, Phys. Rev. B 62, 13599 (2000)], the contribution to the exciton linewidth due to scattering by polar optical phonons was calculated in semiconducting cylindrical quantum wire structures using the infinite confining potential well model. This model showed the linewidth steadily increasing as the wire radius decreased for both elastic and inelastic scattering of the exciton. The same calculation is repeated here using the finite confining potential well model which is more appropriate for small wire radii in quantum wires. We find in this case, that this contribution to the exciton linewidth initially increases with decreasing wire radius until a critical radius is reached, which depends upon the height of the confining potential barrier, and for smaller wire radii, the linewidth decreases. This is due to the fact that in narrow wires, the exciton is no longer completely confined.
Secondary electron emission characteristics of C(111) and the observation of double-peaked emission spectra
Authors: Yater J. E. , Shih A.
Published: July 2002

Secondary electron emission spectroscopy (SEES) is used to investigate the low-energy electron emission characteristics of the C(111) surface. A negative electron affinity (NEA) is observed at hydrogenated and cesiated C(111) surfaces, and very high secondary electron yields are measured from these surfaces. The emission from both surfaces is sharply peaked at low energy, although the cesiated surface produces greater energy spread than the hydrogenated surface. Yield measurements are uniform across the hydrogenated and cesiated surfaces, but energy distribution curves (EDCs) contain emission features that depend on the measurement position on the surface. Specifically, an intense secondary emission peak centered above Ec is observed in EDCs measured at all positions while a weaker peak lying completely below Ec appears only at specific regions of the surface. The intense peak is well understood and has been observed in EDCs taken from NEA surfaces of C(100) and chemical vapor deposited diamond. However, the weaker peak has not been observed in previous SEES studies of diamond. This peak corresponds to electron emission from surface or defect electronic states in the energy gap, and it is manifested in the EDCs only when χ is sufficiently lowered by the adsorption of H or Cs. Although the origin of the surface or defect states is not known, it appears to be associated with structural properties of the C(111) surface.
Micromagnetic studies of high frequency permeability in Fe–M–N thin films with macroscopic and mesoscopic sizes
Authors: Wei Dan , Wei Fu-lin , Yang Zheng
Published: July 2002

A micromagnetic model is established to analyze the permeability of Fe–Ta–N and Fe–Al–N thin films in a wide frequency range from 10 to 2200 MHz. The simulated real part of the permeability is about 2500 and 5000 at low frequencies for macroscopic Fe–Al–N and Fe–Ta–N films, respectively. It then decreases by a factor of 2 around 500 and 300 MHz. The corresponding imaginary part of the permeability increases from zero to a maximum value. In mesoscopic Fe–M–N films, huge magnetic poles on the edge of a layer play a significant role in the frequency response. As a result, the real part of the permeability in a mesoscopic film becomes much smaller than that in a macroscopic film. The spin patterns of mesoscopic Fe–M–N films in an external oscillatory field are also shown to understand the frequency response with strong magnetic poles.
Optimization of CoPt/B nanocomposite films for ultrahigh-density recording media
Authors: Karanasos V. , Panagiotopoulos I. , Niarchos D. , Okumura H. , Hadjipanayis G. C.
Published: July 2002

The microstructure and magnetic properties of nanocomposite CoPt/B films are investigated in view of their suitability as ultrahigh-density recording media. The as-made films have a disordered face-centered cubic structure and low coercivity (below 100 Oe). The granular structure is obtained after an aging heat treatment, which also leads to an increase of the coercivity due to the formation of the highly anisotropic face-centered tetragonal phase. The dynamics of the fct phase formation are found to depend on the boron content. For the sample with 50% vol boron concentration, annealing temperatures as low as 550 °C are sufficient to obtain useful coercivities. Transmission electron microscopy studies and x-ray diffraction show that minimum grain size is obtained for the 20% vol boron concentration for all temperatures. The “magnetic” grain size is found to coincide with the structural only for this particular sample.
Visible-light-induced persistent photoconductivity in perovskite manganite films of (La0.3Nd0.7)2/3Ca1/3MnO3
Authors: Dai J. M. , Song W. H. , Wang S. G. , Ye S. L. , Wang K. Y. , Du J. J. , Sun Y. P.
Published: July 2002

The persistent photoconductivity (PPC) induced by visible light of a He–Ne laser with a wavelength of 632.8 nm in perovskite manganite films of (La0.3Nd0.7)2/3Ca1/3MnO3 at low temperatures, below ∼50 K, was observed. Based on the measurements of transport and magnetic properties, it is suggested that the samples undergo a transition of cluster-glass state below ∼50 K. The PPC phenomenon can be qualitatively explained in terms of a photoinduced ferromagnetic cluster growth model.
Vitrification of emulsified liquid water under pressure
Authors: Mishima Osamu , Suzuki Yoshiharu
Published: July 2002

We cool emulsified liquid water below 130 K at a rate of 103–104 K s−1 at ≈0.5 GPa and vitrify it under pressure. We recover the produced glassy sample at 1 bar and 77 K, and examine it by Raman spectroscopy, x-ray diffraction, and visual observation. We find that the emulsified glassy water, when heated from 77 K at 1 bar, exhibits a distinct volume expansion around 130 K and becomes a second amorphous state. The second amorphous state becomes ice Ic at 160–170 K with a negligible volume change. This behavior of the high-pressure emulsified glassy water resembles that of high-density amorphous ice made by pressure-induced amorphization of ice Ih.
Suppression of lateral fluctuations in CdSe-based quantum wells
Authors: Kurtz E. , Schmidt M. , Baldauf M. , Wachter S. , Grün M. , Kalt H. , Klingshirn C. , Litvinov D. , Rosenauer A. , Gerthsen D.
Published: July 2002

We report a reduction of inhomogeneous broadening in CdSe-related quantum wells in ZnSe by employing a growth technique that uses a CdS-compound source instead of the standard Cd elemental source for molecular-beam epitaxy. Assisted by the low sticking coefficient of sulfur and possibly an exchange reaction between S and Se, only a small S contamination is observed. A comparison with standard layers reveals an increase in quality and homogeneity by a strong reduction of the photoluminescence (PL) linewidth. Samples obtained by our method show extremely little lateral confinement as indicated by a lack of sharp single dot emission lines in micro PL and the absence of the extensive redshift observed in temperature dependent PL of fluctuating well potentials.
The rates of redistribution of CCl3F clusters under subsaturation conditions
Authors: Cheng Zhikai , Pall Raman , Teitelbaum Heshel
Published: July 2002

Pure CCl3F (Freon-11) vapor, initially below its room-temperature saturated vapor pressure, was compressed behind weak incident shock waves. The initial pressure was varied from 26 to 747 mm Hg, and the shock speed was varied from 141 to 321 m/s. The equilibrium cluster-size distribution was thus perturbed to varying degrees. Under the present experimental conditions cluster-forming processes en route to homonuclear condensation were set into motion. The exothermic redistribution of cluster sizes at the new temperature and pressure was monitored using the laser-schlieren technique over a time period of 10–300 μs. A characteristic redistribution time scale was measured as a function of temperature and pressure. The measured temperature and pressure dependence of the redistribution times are different than the classical temperature and pressure dependence of lag times in supersaturated vapors. A negative activation energy is observed, indicative of a strong competition between cluster formation, redissociation, and stabilization. A stability analysis of the nonlinear kinetic mechanism leads to a criterion for the onset of oscillations, and provides a basis for extracting elementary rate constants from the observations.
Anharmonic vibrational frequencies of proton transfer coordinates in the clusters of aromatic molecules with water
Authors: Jansen A. , Gerhards M.
Published: July 2002

The vibrational frequencies of OH and NH groups which form hydrogen bonds to a water molecule are calculated using the complete active space self-consistent field (CASSCF) method and the second order perturbation theory based on the CASSCF reference (CASPT2). As model systems indole(H2O), phenol(H2O), and their corresponding cations are chosen. Furthermore, different isomers of the 3-aminophenol(H2O)+ and 4-aminophenol(H2O)+ clusters are considered. For all these clusters IR spectra are known, but the IR spectra of the ionic clusters in the region of the hydrogen-bonded OH and NH groups have not yet been well interpreted. Due to the strong anharmonicity of the OH and NH vibrations it is not possible to predict their frequencies by a simple scaling of harmonic values. By using different active spaces including both π-orbitals as well as σ-orbitals it is shown that the vibrational frequencies can be derived from potentials obtained from CASSCF single-point calculations along the OH and NH stretching modes. These vibrations can be regarded as proton-transfer coordinates. The calculated vibrational frequencies are in excellent agreement with the experimental values obtained for the investigated clusters. Furthermore, a strong shift of the OH stretching frequency is predicted by going from phenol(H2O)+ to aminophenol(H2O)+ clusters, explaining the completely different IR spectra of the investigated species.
A stable fluctuating-charge polarizable model for molecular dynamics simulations: Application to aqueous electron transfers
Authors: Ando Koji
Published: July 2002

A stable and efficient variant of the dynamical fluctuating charge (fluc-q) model for electronically polarizable molecular dynamics (MD) simulation is developed and applied to electron transfer (ET) reactions in water. The energy divergence problem often encountered with the original form of the fluc-q model is essentially removed by introducing an alternative functional form for the electronic self-energy term of hydrogen atoms without any additional parameters. In the application to the aqueous ET problem we find the following: For the present donor–acceptor (DA) model of moderate size, the induced dipole is slightly smaller in the first solvation shell than in the outer region even under the electrostatic field from the ion pair state of the DA, which suggests that the induced dipole is enhanced more in the solvent–solvent hydrogen-bonding structure. The structural aspects are also examined via radial distribution functions. The solvent reorganization energy is demonstrated to be renormalized, both in the magnitude and in the slope along the inverse DA distance, due to coupling with electronic polarization. In the time correlation and spectral density functions of the solvent reaction coordinate, the frequency of the librational coupling motion is slightly blue-shifted and its intensity is suppressed due to inclusion of the solvent electronic polarization. The impact of the electronic polarization on the scaled quantum energy gap law of the ET rate is found to be modest.
Nonvolatile reprogrammable logic elements using hybrid resonant tunneling diode–giant magnetoresistance circuits
Authors: Hanbicki A. T. , Magno R. , Cheng S.-F. , Park Y. D. , Bracker A. S. , Jonker B. T.
Published: July 2002

We have combined resonant interband tunneling diodes (RITDs) with giant magnetoresistance (GMR) elements so that the GMR element controls the switching current and stable operating voltage points of the hybrid circuit. Parallel and series combinations demonstrate continuous or two-state tunability of the subsequent RITD-like current–voltage characteristic via the magnetic field response of the GMR element. Monostable–bistable transition logic element operation is demonstrated with a GMR/RITD circuit in both the dc limit and clocked operation. The output of such hybrid circuits is nonvolatile, reprogrammable, and multivalued.
X-ray diffraction analysis of a selectively grown InGaAsP epitaxial layer
Authors: Nakashima Kiichi , Kawaguchi Yoshihiro
Published: July 2002

We analyzed compositional fluctuation with lattice relaxation in a selectively grown InGaAsP epilayer by x-ray diffraction measurement. A simple and deterministic analysis procedure is described for analyzing the distribution of lattice constants (Δa⊥,Δa∥). The method is based on the systematic analysis of hkl-dependence of x-ray peak profiles. The method makes the direct observation of the distribution of lattice constants easier and is suitable for analysis of selectively grown samples. The method is applicable to a selectively grown InGaAsP epilayer with a small strain under a dislocation-free condition. Clear lattice relaxation is experimentally confirmed in the epilayer and is identified as the elastic relaxation that is caused by the three-dimensional shape of the selectively grown region. This is a direct observation of elastic relaxation in a selectively grown dislocation-free structure by x-ray diffraction measurement. Distributions of both perpendicular and parallel lattice constants are estimated from the x-ray data. The result shows that both the composition and relaxation rate fluctuate in the sample.
Relaxation effect of electron inertial delay in an ion-beam plasma system
Authors: Dwivedi C. B. , Prakash Ram
Published: July 2002

In this article an interesting result has been reported to highlight the physical implication of finite nonzero electron inertial delay in acoustic oscillations of an ion-beam plasma system. A simple fluid model has been used to demonstrate the excitation of relaxation type resonant instability on the electron inertial delay time scale. Physical arguments have been included to understand and explain the driving mechanism of the instability and its utility to comprehend the ion-beam driven oscillations in plasma sheath experiments. The physical nature and origin of the potential relaxation instability has been correlated to the electron inertial delay effect in the ion current carrying plasma system.
Thermomechanical effects in the nematic liquid crystals
Authors: Akopyan R. S. , Alaverdian R. B. , Santrosian E. A. , Chilingarian Y. S.
Published: July 2002

Thermomechanical effects in hybrid and cylindrical-hybrid oriented nematic liquid crystals (NLC), as well as thermomechanical effects in NLC with a homogeneous director distribution induced by quasistatic or light electric fields, are observed and investigated theoretically and experimentally. It is postulated that these effects arise from a horizontal hydrodynamic flow in the NLC due to the vertical temperature gradient. There is good agreement between the theoretical calculations and the experimental results. The thermomechanical coefficient is measured. In the case where the hydrodynamic flow tends to strain the curvature of the “flexible ribbon,” an oscillatory motion is observed.
Femtosecond light scattering spectroscopy of single gold nanoparticles
Authors: Itoh Tamitake , Asahi Tsuyoshi , Masuhara Hiroshi
Published: July 2002

We have developed an ultrafast, light-scattering spectroscopic system combining a conventional microscope with a pump–probe setup. We successfully measured the surface plasmon resonance band for the individual gold particles with a mean radius of 40 nm. The results on the pump–probe experiment demonstrate that both the electron–phonon and the phonon–phonon coupling processes in the individual gold particles take place with the lifetimes of 4 ps and >25 ps, respectively.
A-site surface termination in strontium titanate single crystals
Authors: Schrott A. G. , Misewich J. A. , Copel M. , Abraham D. W. , Zhang Y.
Published: July 2002

It is well known that chemical etching of strontium titanate (SrTiO3) results in titanium-terminated (B site) surfaces. In this letter, we describe a facile method for generating strontium-terminated surfaces in SrTiO3. We demonstrate that a substrate treatment consisting of a low-power oxygen ashing followed by annealing yields a strontium (A site)-terminated surface in single-crystal SrTiO3 (100). This surface termination of the substrate allows the deposition of cuprate films with improved quality.
Photoluminescence investigation of phononless radiative recombination and thermal-stability of germanium hut clusters on silicon(001)
Authors: Dashiell M. W. , Denker U. , Schmidt O. G.
Published: July 2002

Intense photoluminescence (PL) originating from single layers of germanium hut clusters grown on silicon (001) is investigated using PL spectroscopy. We propose that the luminescence originates from phononless recombination within a spatially indirect, type-II neighboring confinement structure. Enhanced no-phonon (NP) luminescence is attributed to exciton localization at the Ge/Si interfaces. The PL intensity is sensitive to the growth temperature during interface formation, as well as to post-growth thermal annealing, illustrating the influence of atomic-level Si–Ge intermixing on exciton localization and NP enhancement.
Evanescent-wave acceleration of ultrashort electron pulses
Authors: Zawadzka Justyna , Jaroszynski Dino A. , Carey John J. , Wynne Klaas
Published: July 2002

High-power femtosecond laser pulses have been used to excite surface plasmons in 500 Å silver and gold films. Nonlinear excitation results in the emission of electron bunches through multiphoton excitation at low power and laser-induced field emission at high power. The energies of photoelectrons are found to extend as high as 0.4 keV. Calculations show that these high energies are due to ponderomotive acceleration in an evanescent field extending from the metal film out into the vacuum. The theoretical calculations suggest that femtosecond electron pulses with relativistic energies can be generated using longer wavelengths or by developing the surface morphology.
Improvement of the photoluminescence properties in a-SiNx films by introduction of hydrogen
Authors: Molinari M. , Rinnert H. , Vergnat M.
Published: July 2002

Photoluminescence properties of amorphous hydrogenated silicon nitride thin films with various compositions are presented. The as-deposited samples prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions exhibit visible photoluminescence at room temperature without any annealing treatment. The evolution of the photoluminescence properties with increasing nitrogen concentration in the films is correlated to structural investigations performed with Fourier-transform infrared spectroscopy and optical characterization obtained from transmission measurements in the ultraviolet-visible-near-infrared range. It is shown that the introduction of hydrogen is of prime importance to improve the photoluminescence intensity of the films.
Protein denaturation in vacuo: Mechanism for centrifugal unfolding of neutral lysozyme
Authors: Arteca Gustavo A. , Tapia O.
Published: July 2002

Experiments on anhydrous proteins diffusing in a low-pressure gas reveal transitions that share common features with the unfolding and refolding processes observed in solution. These phenomena force us to re-evaluate the specific role played by solvent on large-scale protein rearrangements. Computer simulations, in combination with tools for molecular shape analysis, provide insights into in vacuo processes. In this work, we deal with one particular aspect of this problem: the conditions and the mechanism for spontaneous unfolding in a globally neutral protein. When coupling the protein to a simulated thermal bath, the flow of energy between rotational modes and internal modes can produce a centrifugal effect leading to unfolding. Using hen lysozyme as a system, we study the reproducibility of the unfolding transition and its dependence on the bath relaxation constant. In addition, we monitor the evolution of large-scale molecular shape features (e.g., chain entanglements) that take place during unfolding. Our results show that a change in bath relaxation constant affects the time scale of the transition and the population of intermediates, without changing the basic unfolding mechanism. We also discuss possible cycles of unfolding–refolding transitions, and their implications for our understanding of the denatured state.
Crystallization of lithium cobalt oxide thin films by radio-frequency plasma irradiation
Authors: Kang Youn-Seon , Lee Ho , Kang Yong-Mook , Lee Paul S. , Lee Jai-Young
Published: July 2002

The crystallinity of lithium cobalt oxide thin films deposited by the radio-frequency (rf) reactive magnetron sputtering method has been improved by the rf plasma irradiation method. Compared with conventional thermal annealing, reaction to form crystalline lithium cobalt oxide via rf plasma irradiation is fast and does not need any additional external heat supply. It is found that the nucleation and the growth reactions are determined during the film deposition and the rf irradiation, respectively. The film composition does not change significantly, and severe mechanical damages such as resputtering or etching phenomena do not appear after the irradiation. A model showing the process of the crystallization by rf plasma irradiation is suggested on the basis of phenomenological analyses using secondary electron microscopy, high-resolution transmission electron microscopy, etc.
Ab initio studies of dissociation pathways on the ground- and excited-state potential energy surfaces for formyl chloride (HClCO)
Authors: Fang Wei-Hai , Liu Ruo-Zhuang
Published: July 2002

Potential energy surfaces of the HClCO dissociation to H+ClCO and Cl+HCO in the lowest three electronic states (S0, S1, and T1) have been investigated with ab initio molecular orbital method at the levels of the complete active space self-consistent-field, single- and multi-reference MP2. The results show that the C–Cl bond cleavage on the S1 surface is the most probable mechanism for the HClCO photodissociation at 230–320 nm. In comparison with formyl fluoride (HFCO), a significant difference was found in photodissociation dynamics between HClCO and HFCO, and this has been discussed in detail.
Slowly accreting ice due to supercooled water impacting on a cold surface
Authors: Myers T. G. , Charpin J. P. F. , Thompson C. P.
Published: July 2002

A theoretical model for ice growth due to droplets of supercooled fluid impacting on a subzero substrate is presented. In cold conditions rime (dry) ice forms and the problem reduces to solving a simple mass balance. In milder conditions glaze (wet) ice forms. The problem is then governed by coupled mass and energy balances, which determine the ice height and water layer thickness. The model is valid for “thin” water layers, such that lubrication theory may be applied and the Peclet number is small; it is applicable to ice accretion on stationary and moving structures. A number of analytical solutions are presented. Two- and three-dimensional numerical schemes are also presented, to solve the water flow equation, these employ a flux-limiting scheme to accurately model the capillary ridge at the leading edge of the flow. The method is then extended to incorporate ice accretion. Numerical results are presented for ice growth and water flow driven by gravity, surface tension, and a constant air shear.