bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth behavior of carbon nanotubes on Fe-deposited (001) Si substrates
Authors: Sohn Jung Inn , Choi Chel-Jong , Lee Seonghoon , Seong Tae-Yeon
Published: July 2002

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to investigate the growth behavior of carbon nanotubes on the Fe-deposited Si (001) substrates by thermal chemical vapor deposition (CVD). The Fe films are deposited for 20 s–20 min by pulse-laser deposition. SEM results show that the growth characteristics of carbon nanotubes strongly depend on the Fe film deposition time. TEM results show that the CVD growth at 800 °C causes the continuous Fe films to be broken up into nanoparticles 10–50 nm across and discontinuous islands 100 nm–1.1 μm in size. It is shown that the Fe nanoparticles are essentially required for the formation of aligned carbon nanotubes. We show direct evidence that a base growth mode is responsible for the growth of carbon nanotubes in the present work.
First principles study of direct exchange coupling between the grains in NiMn antiferromagnets
Authors: Kai T. , Fujiwara H. , Schulthess T. C. , Butler W. H.
Published: July 2002

Exchange coupling between antiferromagnetic regions of tetragonal NiMn through a separation at a boundary was evaluated by first principles calculation to study the coupling between antiferromagnetic grains. It was assumed that the crystallographic orientation was assumed not to change across the boundary. The layer version of the Korringa–Kohn–Rostoker method was employed to calculate the total energy of the coupled system. The exchange coupling strength was estimated as the total energy difference between the two spin configurations of the two body system, parallel and antiparallel to each other. For the grains without any atomic lattice shift parallel to the plane (100) across the boundary, it was found that the coupling strength decreases more rapidly than that for ferromagnetic hexagonal cobalt with the increase of the separation and that it changes its sign at a separation length of a little greater than a half of the lattice constant. For the case with a boundary across which the lattice shifts by an atomic distance diagonally, the exchange coupling is reduced to about 1/3 of the original value and decreases rather slowly with the increase of the separation compared to the previous case. Those results are consistent with our previous report which predicted the existence of a weak exchange coupling between the grains in an antiferromagnetic polycrystalline layer based on the analysis of a characteristic feature often observed in torque curves for ferro/antiferromagnetic coupled layer systems.
Nanometer-scale measurements of photoabsorption spectra of individual defects in semiconductors
Authors: Hida Akira , Mera Yutaka , Maeda Koji
Published: July 2002

Photoabsorption measurements using scanning tunneling microscopy, in which a modulated component of the tunneling current induced by a wavelength-variable chopped light is detected, were conducted for a cleaved surface of GaAs to demonstrate that a simple scheme enables nanometer-scale imaging of individual subsurface defects isolated in the crystal with fingerprints of photoabsorption spectra associated with them. The origin of the signal modulation and the image contrast formation mechanism are discussed in terms of photothermal expansion caused by nonradiative recombinations at the defect, photoinduced defect transformation, and an electrostatic surface potential change due to a charge alteration of the defect.
Oxide-assisted growth and optical characterization of gallium-arsenide nanowires
Authors: Shi W. S. , Zheng Y. F. , Wang N. , Lee C. S. , Lee S. T.
Published: July 2002

This letter reports the synthesis and optical characterization of GaAs nanowires obtained by oxide-assisted laser ablation of a mixture of GaAs and Ga2O3. The GaAs nanowires have lengths up to tens of micrometers and diameters in the range of 10–120 nm, with an average of 60 nm. The nanowires have a thin oxide layer covering a crystalline GaAs core with a [1̄11] growth direction. Raman scattering and photoluminescence (PL) characterizations of GaAs nanowires reveal that the spectral peaks significantly shifted and broadened from those of bulk GaAs material. The changes in these spectra are mainly attributed to impurities, defects, and residual stress in the GaAs nanowires.
The grain charging and the dust acoustic wave instability
Authors: Varma Ram K.
Published: July 2002

The stability of the steady charging state of the assembly of dust grains in a plasma is analyzed using, besides the equations of continuity and momentum balance, also the equations of thermal energy balance with the grain charging terms for both the electron and ion species. The grain charging terms account for the energy exchange between the dust grains and the electron and ion fluids. The grains are taken to be immobile for the purpose of this analysis. Two limiting cases are analyzed: (i) f(≡4πndλD2a)≪1 and (ii) f≫1 (nd is the dust number density, λD plasma Debye length, and a, the grain radius). The steady grain charge state is found to be stable in the case f≪1, so that the steady state grain charge qo is unaffected. On the other hand, in the limit f≫1, the state is found to be unstable provided γq(≡qoe/aTe)<12 (Te−Ti)/Te (Te, Ti are electron and ion temperatures). A coherent charging of the dust grains results as a consequence of this instability until γq≈12 (Te−Ti)/Ti. Next, by letting the grain charges be mobile, so that the perturbation of dust number density is nonzero, we examine the stability of the dust-acoustic wave (DAW). The DAW is found to be unstable, also in the f≫1 case, while stable in the f≪1. The instability of the DAW also implies a concomitant grain charge growth, which would again be of a coherent nature.
Correlated roughness effects on electrical conductivity of quantum wires
Authors: Palasantzas G. , Barnaś J. , De Hosson J. Th. M.
Published: July 2002

The influence of electron scattering by rough boundaries on electrical conductivity of quantum wires is studied in the diffuse transport limit within the kinetic Boltzmann equation approach. The considerations are restricted to the wires obtained by lateral confinement of a two-dimensional electron gas. Both intra- and interboundary roughness correlations are taken into account. It is shown that the cross correlations usually increase the conductivity, leaving the shape and phase of the quantum size oscillations almost unaffected.
Initial stages of SiC oxidation investigated by ion scattering and angle-resolved x-ray photoelectron spectroscopies
Authors: Radtke C. , Baumvol I. J. R. , Morais J. , Stedile F. C.
Published: July 2002

Initial stages of oxidation of single-crystal, Si-faced silicon carbide were investigated using ion scattering and angle-resolved x-ray photoelectron spectroscopies. The very first oxidation products are shown to be silicon oxycarbides (SiCxOy), while, for longer oxidation times, a mixture of SiCxOy and SiO2 is formed in the near-surface region of the growing oxide film. The composition of the near-surface region of such thin films is very similar to that reported in previous investigations for the near-interface region when thicker oxides films are grown on SiC.
Contribution of dangling-bond regeneration channels in the synchrotron-radiation-excited epitaxy of Si from SiH2Cl2
Authors: Akazawa Housei
Published: July 2002

The contribution of various dangling-bond regeneration channels during the synchrotron-radiation-excited epitaxial growth of Si has been investigated by using SiH2Cl2 as a source gas. When Si films are grown through the photoexcitation of SiH2Cl2 gas molecules alone at temperatures below 300 °C, ramified chains of higher-order silicon chlorides passivate the growing surface. The coverage of Cl decreases monotonically with increasing temperature and above 440 °C settles at a half monolayer, and this agrees with the saturation coverage when the self-limiting chemisorption of SiH2Cl2 is completed. The removal of Cl adatoms through reaction with incoming atomic H and SiHx is thus the only channel for surface activation. When both the surface and gas molecules are photoexcited, the coverage of Cl atoms is reduced to 20%–40% of the coverage without irradiation. This is due to photon-stimulated desorption, which increases the growth rate fourfold as compared with the growth rate when the surface is not excited.
Geodesic hierarchies and involutivity
Authors: Topalov Peter
Published: July 2002

We consider a special class of pseudo-Riemannian metrics that admit integrals in involution. A necessary and sufficient conditions for the complete integrability of the geodesic flows of the corresponding metrics is proved. Any of the metrics we consider lies in a big family (hierarchy) of metrics that also admit integrals in involution. Many classical and new examples of completely integrable metrics lie in such hierarchies.
Device performance of in situ steam generated gate dielectric nitrided by remote plasma nitridation
Authors: Al-Shareef H. N. , Karamcheti A. , Luo T. Y. , Bersuker G. , Brown G. A. , Murto R. W. , Jackson M. D. , Huff H. R. , Kraus P. , Lopes D. , Olsen C. , Miner G.
Published: July 2002

In situ steam generated (ISSG) oxides have recently attracted interest for use as gate dielectrics because of their demonstrated reliability improvement over oxides formed by dry oxidation. [G. Minor, G. Xing, H. S. Joo, E. Sanchez, Y. Yokota, C. Chen, D. Lopes, and A. Balakrishna, Electrochem. Soc. Symp. Proc. 99-10, 3 (1999); T. Y. Luo, H. N. Al-Shareef, G. A. Brown, M. Laughery, V. Watt, A. Karamcheti, M. D. Jackson, and H. R. Huff, Proc. SPIE 4181, 220 (2000).] We show in this letter that nitridation of ISSG oxide using a remote plasma decreases the gate leakage current of ISSG oxide by an order of magnitude without significantly degrading transistor performance. In particular, it is shown that the peak normalized transconductance of n-channel devices with an ISSG oxide gate dielectric decreases by only 4% and the normalized drive current by only 3% after remote plasma nitridation (RPN). In addition, it is shown that the reliability of the ISSG oxide exhibits only a small degradation after RPN. These observations suggest that the ISSG/RPN process holds promise for gate dielectric applications.
A novel imaging x-ray microscope based on a spherical crystal
Authors: Sanchez del Rio M. , Alianelli L. , Pikuz T. A. , Faenov A. Ya.
Published: July 2002

A novel, compact, large field, and spectrally tunable imaging x-ray microscope is presented. It is based on the use of an isotropic point x-ray source and a spherically curved crystal. The x-ray beam intensity is modulated by the object attenuation, then monochromatized and enlarged using a spherical crystal and, finally, imaged using a detector downstream from the crystal. We demonstrate by ray tracing simulations that this system allows microscopy studies with high spatial resolution, high magnification ratios, and large field of view. Microscopes using this model can be easily built using different x-ray sources, like conventional x-ray tube generators, x rays emitted by laser-generated plasmas or x-pinch plasmas, and also synchrotron radiation when used in combination with other condenser optics. Preliminary experiments are presented to demonstrate the feasibility of the proposed setup. High resolution (∼4 μm) monochromatic (δλ/λ∼10−5–10−3) images over a large field of view (few mm2) were recorded in the spectral range 8–14 Å using a laser-generated plasma source and a spherical mica crystal. Compared to x-ray crystal imagers used in relation with plasma sources, the new configuration produces high quality stigmatic images working at many different Bragg angles, thus improving the spectral tunability and allowing a more flexible design.
Study of growth hillocks in GaN:Si films by electron beam induced current imaging
Authors: Zaldivar M. Herrera , Fernández P. , Piqueras J.
Published: July 2002

Remote electron beam induced current (REBIC) measurements have been carried out to investigate electrically active regions in Si doped GaN films. REBIC bright–dark contrast has been observed in the border of growth, round or pyramidal, hillocks, while pyramidal hillocks also show bright contrast at the center. The results are explained by the inhomogeneous distribution of charged point defects and impurities at the hillocks.
High-speed 1.55 μm Fe-doped multiple-quantum-well saturable absorber on InP
Authors: Marceaux A. , Loualiche S. , Dehaese O. , Lambert B.
Published: July 2002

Excitonic saturable absorption on iron-doped InGaAs/InP multiple-quantum-well structures is studied by Fourier transform infrared spectroscopy and pump-probe measurement in the 1.55 μm wavelength range. The recovery time of the excitonic absorption bleaching is improved by iron doping and is found to vary from 7 ns on the undoped sample to 7 ps on the highest doped sample. The samples exhibit high optical switching with a differential optical transmission coefficient of more than 20% and a saturation fluence smaller than 47 μJ/cm2. Furthermore, we notice no degradation of the contrast ratio due to iron doping.
Energy migration of the local excitation at the Eu3+ site in a Eu–O chemical cluster in sol-gel derived SiO2:Eu3+ glasses
Authors: Hayakawa Tomokatsu , Nogami Masayuki
Published: July 2002

By using the fluorescence line-narrowing technique, we observed a broad fluorescence band in the vicinity of a resonant line of the D05→7F0 transition in an Eu3+-doped SiO2 glass synthesized by a sol-gel process. The comparison with a similar line in an Al2O3–SiO2:Eu3+ sol-gel glass revealed the existence of a chemical cluster of Eu3+ and O2− in the tetrahedral SiO4 network. The broad fluorescence band was attributable to an energy migration among the Eu3+ ions for the site-selectively received excitation energy. Also, based on Yokota–Tanimoto’s energy diffusion model, the fluorescence decay curves for the D05→7F2 transition were closely correlated with the energy migration and gel–glass transformation. The gel-shrinkage and reduced interatomic distance between Eu3+ ions due to a thermal treatment at higher temperature definitely resulted in a decrease in the associated lifetime of the initial decay.
A new high sensitivity magnetic system for microposition measurement
Authors: Choi Dong-June , Kim Soo Hyun
Published: July 2002

This article presents a new design of a magnetic system which can be used as a position sensing system for precision measurements. The proposed system consists of driving coils, position-detecting coils, movable cores, and magnetic blocks. The cores are put into the position-detecting coils to draw the flux. As the cores move in a motion proportional to the input position, induced voltages arise in the position-detecting coils. The turns ratio and the air-gap dimensions between the magnetic blocks and the movable cores are selected in such a way as to have high sensitivity. To decrease the flux loss and produce the strong flux density, a symmetric and closed loop form is adopted. The elements that affect the system characteristics and sensitivity are turns ratio, air-gap dimension, capacitance effect, excitation frequency, and so forth. The sensitivity of the newly designed system is greater than 2000 mV/(V mm) and the linearity error is below ±0.10% in the range of ±200 μm. The repeatability standard deviation in this system is below 50 nm.
Computational formulas for symmetry-forbidden vibronic spectra and their application to n–π* transition in neat acetone
Authors: Shiu Y. J. , Hayashi M. , Mebel A. M. , Chen Yit-Tsong , Lin S. H.
Published: July 2002

In this study theoretical expressions are derived to investigate the non-Condon effect for symmetry-forbidden optical transition using displaced–distorted harmonic potential energy surfaces. These expressions can efficiently cope with multipromoting modes and multielectronic states involved in the non-Condon effect at a finite temperature. Ab initio and molecular dynamics calculation results can be directly invoked into the formulas. Based on the proposed formulas, the temperature dependence of the interference effects of multipromoting modes on the non-Condon optical linear spectra is investigated. To demonstrate the computational formulas, the optical absorption and dispersion fluorescence spectra for the forbidden transition of neat acetone, A11–A21(n–π*), are also studied. Simulation results indicate that the vibrational frequency of CH3 torsion mode of acetone plays an important role in the optical spectra. Moreover, the electronic energy gap (adiabatic transition), the Stokes shift caused by environmental interaction, and the average Huang–Rhys factor for intermolecular modes in neat acetone are obtained as 29 900 cm−1, 5400 cm−1, and 0.607, respectively.
On electrostatic acceleration of plasmas with the Hall effect using electrode shaping
Authors: Wang Zhehui , Barnes Cris W.
Published: July 2002

Resistive magnetohydrodynamics (MHD) is used to model the electromagnetic acceleration of plasmas in coaxial channels. When the Hall effect is considered, the inclusion of resistivity is necessary to obtain physically meaningful solutions. In resistive MHD with the Hall effect, if and only if the electric current and the plasma flow are orthogonal (J⋅U=0), then there is a conserved quantity, in the form of U2/2+w+eΦ/M, along the flow, where U is the flow velocity, Φ is the electric potential, w is the enthalpy, and M is the ion mass. New solutions suggest that in coaxial geometry the Hall effect along the axial plasma flow can be balanced by proper shaping of conducting electrodes, with acceleration then caused by an electrostatic potential drop along the streamlines of the flow. The Hall effect separation of ion and electron flow then just cancels the electrostatic charge separation. Assuming particle ionization increases with energy density in the system, the resulting particle flow rates (Jp) scales with accelerator bias (Vbias) as Jp∝Vbias2, exceeding the Child–Langmuir limit. The magnitude of the Hall effect (as determined by the Morozov Hall parameter, Ⅺ, which is defined as the ratio of electric current to particle current) is related to the energy needed for the creation of each ion–electron pair.
Self-trapping of a rotating ion ring
Authors: Albright B. J. , Faehl R. J.
Published: July 2002

A fluid model is presented that describes the linear evolution of a thin layer of beam ions in a conducting cylindrical cavity with a narrow rotating beam layer, and a dispersion relation is computed for the low-frequency electromagnetic response of the system. For a broad range of ion ring parameters this configuration is found to be unstable to the generation of Alfvénic fluctuations. Simple estimates are provided of the time needed for these fluctuations to self-trap the ion beam.
Phase noise transfer in resonant optical cavities
Authors: Bienfang Joshua C. , Teehan Russell F. , Denman Craig A.
Published: July 2002

We study theoretically and experimentally the field circulating in a resonant optical cavity when the phase of the incident field and the length of the cavity exhibit fluctuations about their mean values. With a simple model we derive transfer functions which relate the spectral density of phase noise of both the input field and the cavity length to that of the circulating field. In agreement with the standard steady state result, we find that phase noise in the incident field is low pass filtered by the cavity. Cavity length fluctuations are found to be high pass filtered in their transfer to the circulating field. These results are used to present a control loop model of the cavity-laser system. We verify the model experimentally with a Pound–Drever–Hall discriminator and apply it to a discussion of the stability of a frequency reference at 532 nm.
Kinetic model of electrons in drift-Alfvén current-vortices
Authors: de Blank Hugo J.
Published: July 2002

Current-vortex filaments in magnetized plasmas are investigated analytically using a kinetic model for the electron motion parallel to the magnetic field. This Hamiltonian system can be considered as the minimal kinetic extension of the three-field drift-Alfvén model for collisionless plasmas. Stationary current-vortex solutions are presented. They are shown to maintain their coherence in the presence of slowly changing background electro-magnetic fields due to the adiabatic response of electrons confined inside the structure.
Study of electromagnetic instabilities driven by ion temperature gradient and parallel sheared flows in high-β plasmas
Authors: Gao Zhe , Dong J. Q. , Liu G. J. , Ying C. T.
Published: July 2002

The local electromagnetic modes driven by ion temperature gradient (ITG) and parallel sheared flows, including parallel velocity shear (PVS) of ions and plasma current, are studied for any β (plasma pressure/magnetic pressure) plasma. It is shown that a finite β not only weakens the driving mechanism directly but also reverses the effect of the current on the modes from weakly destabilizing to stabilizing. However, the local kinetic ITG–PVS modes are unstable in a high-β plasma with a parallel sheared ion flow (positive or negative). The plasma current and current gradient make nearly opposite contributions to the modes. As ηi (the parameter for ion temperature gradient) increases, the effects of the current and current gradient are weakened and then reversed.
Resistive drift modes in general geometry
Authors: Kleiber R.
Published: July 2002

A global approach for calculating resistive drift modes is developed, which does not use a ballooning formalism but solves the three-dimensional eigenvalue problem directly. The drift-wave model is based on linearized two-fluid equations with cold ions and electrostatic perturbations. For an axisymmetric model equilibrium results from the global approach are compared to those following from a ballooning approximation. For consistent equilibria the global approach is used to investigate the structure of resistive drift modes in tokamak configurations with positive/negative shear as well as in straight and toroidal l=2-stellarator configurations.
The 4pπ 3Πg–a 3Σu+ system in Ne220 and Ne222
Authors: Conway J. A. , Shen F. , Herring C. M. , Eden J. G. , Ginter Marshall L.
Published: July 2002

Excitation spectra for the 4pπ 3Πg–a 3Σu+ system in Ne220 and Ne222 have been used to characterize the v=0 through v=3 levels in both electronic states. This is the first time levels with v>1 have been characterized experimentally in either dimer. Rotational analyses lead to Be- and αe-values of 0.5638 cm−1 and −0.9000×10−2 cm−1 and of 0.5113 cm−1 and −0.6651×10−2 cm−1 for the a 3Σu+ states in Ne220 and Ne222, respectively. The Be- and αe-values are, respectively, 0.5716 cm−1 and −0.6429×10−2 cm−1 (20Ne2) and 0.5201 cm−1 and −0.4172×10−2 cm−1 (22Ne2) for the 4pπ 3Πg state. The vibrational parameters ωe, xωe are found to be 556.2, 10.2 cm−1, and 593.2, 7.5 cm−1 for the a 3Σu+ state and 4pπ 3Πg state, respectively, in Ne220 with corresponding values of 529.5, 9.75 cm−1, and 567, 7.5 cm−1 in Ne222. The observed vibrational level differences [ΔG(v+1/2)-values] for the 4pπ 3Πg state are within 0.5% of analogous spacings for the ground electronic state (X 2Σu+) of Ne2+ reported by Kim et al. [Phys. Rev. Lett. 68, 1311 (1992)].
Impact of surface discharge plasmas on performance of a metallized film capacitor
Authors: Kong M. G. , Lee Y. P.
Published: July 2002

Surface breakdown discharges are one probable failure mechanism of metallized polymeric film capacitors used in power systems, traction drives, and other technological applications. To assess whether surface breakdown discharges may undergo considerable elongation on the electrode surface to affect significantly capacitor performance, an equivalent electric circuit model is developed for metallized polymer film capacitors under the thermal equilibrium condition. With the aid of a surface field gradient mechanism, propagation of surface plasmas is studied and the necessary condition for their possible elongation is obtained. Numerical examples of a metallized film capacitor are used to demonstrate that surface breakdown plasmas and their elongation are unlikely to affect capacitor performance in a significant fashion. Then the generic problem of plasma propagation is restudied under thermally nonequilibrium conditions. Based on a heat conduction formulation in the one-dimensional limit, a temperature gradient mechanism is proposed to explain the possible elongation of breakdown plasmas on an electrode surface. Numerical examples are again used to deduce that thermally nonequilibrium surface plasmas are unlikely to evolve into catastrophic flashover arcs to fail film capacitors.
Ion channeling, high resolution x-ray diffraction and Raman spectroscopy in strained quantum wells
Authors: Siddiqui Azher M. , Rao S. V. S. Nageswara , Pathak Anand P. , Kulkarni V. N. , Murthy R. Keshav , Williams Eric , Ila Daryush , Muntele Claudiu , Chandrasekaran K. S. , Arora B. M.
Published: July 2002

InGaAs strained epitaxial layers on GaAs are of considerable interest in semiconductor devices. An important feature is the critical thickness of the epitaxial layer beyond which relaxation occurs, affecting the device performance. With this in view, a series of such structures have been grown by organometallic vapor phase epitaxy and characterized by ion channeling, high resolution x-ray diffraction and Raman spectroscopy. The results of these three techniques are compared for the samples in this study which are fully strained, nominally and by experimental measurements. Beam steering effect that occurs at low energy channeling is also addressed.
Excimer laser annealing of Er-implanted GaN
Authors: Rhee Seuk Joo , Kim Sangsig , Sterner Christopher W. , White Jeffrey O. , Bishop Stephen G.
Published: July 2002

Thin films of Er-implanted GaN are annealed with pulses of 31 ns duration from a KrF excimer laser. The degree of annealing is evaluated by measuring the Er photoluminescence at 1540 nm. The implantation dose is 4×1013–4×1015 cm−2. The laser fluence is 0.15–0.88 J/cm2. The number of laser pulses is 102–5×104. A total heating time on the order of 1 ms is long enough to produce good structural reordering, and short enough to avoid decomposition. The results are compared with a numerical simulation of the heating as a function of time and depth in the sample.
Magnetic and velocity shear effects on ηi-modes in plasmas with ion temperature anisotropy
Authors: Dong J. Q. , Long Y. X. , Avinash K.
Published: July 2002

Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using fluid and kinetic theories, for plasmas with ion temperature and temperature gradient anisotropy. The sheared slab geometry model (nonlocal scheme) is employed. The effects of a parallel velocity shear and a perpendicular velocity shear on the modes are investigated. It is shown that the anisotropy in ion temperature gradient enhances (reduces) the stabilization from a magnetic shear for η⊥>η∥ (η⊥<η∥). An anisotropy of T⊥>T∥ in ion temperature is found to give an overall stabilizition (destabilization) for low (high) magnetic shear, ŝ∼0.1 (ŝ∼0.4). Parametric dependence of the instabilities is systematically analyzed. Previous results from the shearless toroidal model are confirmed with a sheared torus.
Experimental study of photoionization of ozone in the 12 to 21 eV region
Authors: Mocellin A. , Wiesner K. , Burmeister F. , Björneholm O. , Naves de Brito A.
Published: July 2002

The total and partial ion yield of ozone using time-of-flight is presented. The measurements were done using multicoincidence between a photoelectron and a photoion (PEPICO). Comparison with the photoelectron spectrum and previous measurements using other techniques allowed the assignment of most broad features in the spectra. Kinetic energy released is obtained for O+ and O2+ ions. A discussion about the dissociation channels is included.
Density and temperature sensitive line ratios in plasmas generated by laser ablation
Authors: Pérez-Tijerina E. , Bohigas J. , Machorro R.
Published: July 2002

Solving the statistical equilibrium equations we find line intensity ratios of C III, N III, O III, Si III, and Al III in the visible and ultraviolet range, that are sensitive to electron density and/or temperature in the regime commonly found in pulsed laser deposition. For thin film deposition, the plasma density is between 1012 and 1018 cm−3 and the temperature is close to 104 K. Our results are consistent with experimental data on Al II and Al III, previously reported in the literature. These line intensity ratios are a promising tool to diagnose the physical state of plasmas generated through laser ablation in thin film deposition techniques.
The low temperature reactive tunneling in condensed phase. I. The rate expression
Authors: Basilevsky M. V. , Davidovitch G. V.
Published: July 2002

We study how the quantization of energy levels affects the deep tunneling rate expression for a double-well system immersed in a harmonic bath. The model of tunneling transitions implies that the energy of a tunneling system is not conserved during a transition because its interaction with the environment is explicitly taken into account. The Golden Rule approach invoked usually cannot be directly applied for such a model. We consider its modification in which the expression for the rate constant depends symmetrically on spectral line shapes of energy levels in both reactant and product wells. The derivation is based on the Breit–Wigner resonance expansion of a dynamical transition probability which is extended on condensed phase systems and averaged at the next stage over fluctuations of the energy levels promoted by system/environment interactions. Test computations for a one-dimensional model case demonstrate novel features inherent to this approach which are clearly revealed in the low-temperature kinetic regime.
Novel method to estimate solubility of small molecules in cis-polyisoprene by molecular dynamics simulations
Authors: Kikuchi Hiroaki , Kuwajima Satoru , Fukuda Mitsuhiro
Published: July 2002

A novel method to predict gas solubility in cis-1,4-polyisoprene is developed using molecular dynamics (MD) simulations under constant particle number, constant pressure and constant temperature (NPT) conditions. Analogous to the experimental sorption technique, the binary-phase model constructed of gas/polymer was prepared. In order to maintain external pressure of the whole system during long NPT-MD runs, the vapor phase was filled with virtual liquid which has no interaction with the gas molecules and has only a repulsive interaction with the polymer. After attaining equilibration of the system, the solubility of oxygen and carbon dioxide in the polymer phase were estimated in the temperature range from 273 K to 373 K by counting the number of gas molecules inside the polymer phase. The average solubility linearly increased with the increase in the external pressure, indicating that Henry’s Law was satisfied. The solubility coefficient obtained from the present method showed good agreement with the experimental data. Concentration profiles of gas molecule showed that it was significantly higher near the interface than both in the gas phase and inside the polymer phase. The distinction between “adsorbed” and “absorbed” gas molecules and also their effect on the solubility was discussed.
Proposal for a spin-polarized solar battery
Authors: Žutić Igor , Fabian Jaroslav , Das Sarma S.
Published: July 2002

A solar cell illuminated by circularly polarized light generates charge and spin currents. We show that the spin polarization of the current significantly exceeds the spin polarization of the carrier density for the majority carriers. Based on this principle, we propose a semiconductor spin-polarized solar battery and substantiate our proposal using analytical arguments and numerical modeling.
Integral equations for molecular fluids based on the interaction site model: Density-functional formulation
Authors: Sumi Tomonari , Imai Takashi , Hirata Fumio
Published: July 2002

An integral equation for rigid-body molecules with respect to site-density distribution function under arbitrary external fields is derived by the density-functional theory. Using a grand canonical partition function of molecular systems, we extend original Percus’ idea to molecular fluids. The extended Percus’ idea provides a relation between the site–site pair distribution function and site–density distribution function under an external field composed of the site–site interaction potentials of a molecule fixed at the origin. The site–density integral equation combined with the extended Percus’ relation to molecular fluids gives a closure relation of reference interaction site model equation. The site–site pair distribution functions of homonuclear diatomic Lennard-Jones fluids obtained by the integral equation agree well with those of Monte Carlo simulation.
Minority additive distributions in a ceramic metal-halide arc lamp using high-energy x-ray induced fluorescence
Authors: Curry J. J. , Adler H. G. , Shastri S. D. , Lawler J. E.
Published: July 2002

X-ray induced fluorescence is used to measure the elemental densities of minority additives in a metal-halide arc contained inside a translucent ceramic envelope. A monochromatic x-ray beam from the Sector 1 Insertion Device beamline at the Advanced Photon Source is used to excite K-shell x-ray fluorescence in the constituents of a ceramic metal-halide arc lamp dosed with DyI3 and CsI. Fluorescence and scattered photons are collected by a cryogenic energy-resolving Ge detector. The high signal-to-noise spectra show strong fluorescence from Dy, Cs, and I, as well as elastic scattering from Hg. Radial distributions of the absolute elemental densities of Dy, Cs, and I are obtained.
Accurate ab initio spectroscopic and thermodynamic properties of BBrx and HBBrx (x=0, +1, −1)
Authors: Peterson Kirk A. , Flowers Bradley A. , Francisco Joseph S.
Published: July 2002

The near-equilibrium potential energy functions (PEFs) of BBr, its ions, BBr+ and BBr−, and HBBr and its ions, HBBr+ and HBBr−, have been determined using the singles and doubles coupled cluster method including a perturbational correction for connected triple excitations, CCSD(T), together with systematic sequences of correlation consistent basis sets. A wide range of spectroscopic constants have been derived from the calculated PEFs as a function of basis set, including results obtained at the extrapolated complete basis set (CBS) limit. After the explicit inclusion of relativistic and core–valence correlation effects, the agreement with the available experimental values is excellent at the CCSD(T)/CBS level of theory. Accurate predictions for the spectroscopic constants of the ions are made. The 0 K adiabatic ionization potentials and electron affinities are predicted to be (in kcal/mol) 224.8, 4.3 (BBr) and 172.8, 22.2 (HBBr). The 0 K proton affinity of BBr is calculated to be 203.7 kcal/mol, while ΔHf0(0 K) of BBr and HBBr are predicted to be 62.3 and 51.1 kcal/mol, respectively. The dipole moments and infrared intensities of the ions are calculated to be relatively large, which should facilitate their characterization by experimental methods.
The binding energies of p-difluorobenzene–Ar,–Kr measured by velocity map imaging: Limitations of dispersed fluorescence in determining binding energies
Authors: Bellm Susan M. , Moulds Rebecca J. , Lawrance Warren D.
Published: July 2002

The technique of velocity map imaging has been used to determine the dissociation energies of the van der Waals complexes p-difluorobenzene–Ar and p-difluorobenzene–Kr. The values determined for the S0, S1, and D0 states, respectively, are 337±4, 367±4, and 572±6 cm−1 for p-difluorobenzene–Ar and 398±7, 445±7, and 720±6 cm−1 for p-difluorobenzene–Kr. An ionization potential of 73 549±4 cm−1 for p-difluorobenzene–Kr has been determined by velocity map imaging of photoelectrons. The dissociation energies determined here are inconsistent with dispersed fluorescence spectra of the complexes when these are assigned in the usual way. The issue is that spectra for levels below dissociation show bands where free p-difluorobenzene emits, suggesting that dissociation is occurring from these levels. For the dispersed fluorescence and velocity map imaging results to be consistent, these fluorescence bands must arise from transitions of the van der Waals complexes shifted such that they appear at the free p-difluorobenzene wavelengths. It is proposed that these bands are due to emission from highly excited van der Waals modes populated by intramolecular vibrational redistribution from the initially excited level. From calculations performed for the related benzene–Ar system [B. Fernandez, H. Koch, and J. Makarewicz, J. Chem. Phys. 111, 5922 (1999)], the emitting levels are most likely above the barrier separating different p-difluorobenzene–partner configurations. The fluorescence observations are consistent with those of other techniques if the p-difluorobenzene–partner interaction is the same in the ground and excited electronic states for such highly excited levels. Emission then occurs at the p-difluorobenzene monomer position since the energy shift is the same for the initial and final states. Deducing van der Waals binding energies from the observation of spectral transitions at the free chromophore position following excitation of the complex can be confounded by such an effect. The dispersed fluorescence spectra reveal that the rate of intramolecular vibrational redistribution is reduced for the Kr complex compared with the Ar complex.
Metalorganic vapor-phase epitaxial growth and photoluminescent properties of Zn1−xMgxO(0⩽x⩽0.49) thin films
Authors: Park W. I. , Yi Gyu-Chul , Jang H. M.
Published: July 2002

High-quality Zn1−xMgxO(0.00⩽x⩽0.49) thin films were epitaxially grown at 500–650 °C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy. By increasing the Mg content in the films up to 49 at. %, the c-axis constant of the films decreased from 5.21 to 5.14 Å and no significant phase separation was observed as determined by x-ray diffraction measurements. Furthermore, the near-band-edge emission peak position showed blueshifts of 100, 440, and 685 meV at Mg content levels of 9, 29, and 49 at. %, respectively. Photoluminescent properties of the alloy films are also discussed.
Multi-resolution analysis and fractional quantum Hall effect: An equivalence result
Authors: Bagarello F.
Published: July 2002

In this article we prove that any multi-resolution analysis of L2(R) produces, for some values of the filling factor, a single-electron wave function of the lowest Landau level (LLL) which, together with its (magnetic) translation, gives rise to an orthonormal set in the LLL. We also discuss the inverse construction. Moreover, we extend this procedure to the higher Landau levels and we discuss the analogies and the differences between this procedure and the one previously proposed by J.-P. Antoine and the author.
Simulations of Cerenkov wake radiation sources
Authors: Spence N. , Katsouleas T. , Muggli P. , Mori W. B. , Hemker R.
Published: July 2002

The Cerenkov wakes stimulated by various drivers (an intense laser pulse, a train of laser pulses or beats and a relativistic particle bunch) propagating transverse to a dc magnetic field in a plasma are analyzed. In each case, the wake generated couples to the electromagnetic radiation of approximate frequency ωp at the plasma-vacuum boundary. The radiation amplitude is ωc/ωp times the amplitude of the wake excited in the plasma (for a sharp boundary). Two- and three-dimensional particle-in-cell simulations are used to verify the scaling laws. For the parameters of current plasma wake field accelerator experiments the results predict that generation of high-power (GW) coherent microwave to terahertz radiation is possible.
Sums of spherical waves for lattices, layers, and lines
Authors: Enoch S. , McPhedran R. C. , Nicorovici N. A. , Botten L. C. , Nixon J. N.
Published: July 2002

We consider the connections between sums of spherical wave functions over lattices, layers, and lines. The differences between sums over lattices and those over a doubly periodic constituent layer are expressed in terms of series with exponential convergence. Correspondingly, sums over the layer can be regarded as composed of a sum over a central line, and another sum over displaced lines exhibiting exponential convergence. We exhibit formulas which can be used to calculate accurately and efficiently sums of spherical waves over lattices, layers, and lines, which in turn may be used to construct quasiperiodic Green’s functions for the Helmholtz equation, of use in scattering problems for layers and lines of spheres, and for finding the Bloch modes of lattices of spheres. We illustrate the numerical accuracy of our expressions.
Relaxor single crystals in the (Bi1/2Na1/2)1−xBaxZryTi1−yO3 system exhibiting high electrostrictive strain
Authors: Sheets Sossity A. , Soukhojak Andrey N. , Ohashi Naoki , Chiang Yet-Ming
Published: July 2002

Single crystals have been grown in the (Bi1/2Na1/2)1−xBaxZryTi1−yO3 perovskite system by a self-flux method over the range of compositions y=0.04 and x=0.06–0.012. Rhombohedral (x⩽0.08) and tetragonal phase (x⩾0.09) crystals have been obtained that do not show polarization or field-induced strain hysteresis characteristics of a ferroelectric. However, a frequency-dispersive dielectric response characteristic of a relaxor ferroelectric, and predominantly electrostrictive actuation, is observed across the range of compositions tested, with Q11=(2.8–3.3)×10−2 m4/C2. Due to induced polarizations that do not saturate at fields beyond 50 kV/cm, high electrostrictive strains are obtained. Rhombohedral phase crystals exhibit d33 up to 1180 pC/N and strains of S3=0.3% before electrical breakdown, while tetragonal phase crystals exhibit d33 up to 2000 pC/N and S3 up to 0.45% strain. These crystals show the highest electrostrictive strains yet reported for an inorganic compound. The unusually high electrostriction is discussed in relation to an energy landscape that allows ferroelastic and ferroelectric distortions to be simultaneously accessible at the nanometer scale.
Rapid thermal annealing of InAs/GaAs quantum dots under a GaAs proximity cap
Authors: Babiński Adam , Jasiński J. , Bożek R. , Szepielow A. , Baranowski J. M.
Published: July 2002

The effect of postgrowth rapid thermal annealing (RTA) on GaAs proximity-capped structures with self-assembled InAs/GaAs quantum dots (QDs) is investigated using transmission electron microscopy (TEM) and photoluminescence (PL). As can be seen from the TEM images, QDs increase their lateral sizes with increasing annealing temperature (up to 700 °C). QDs cannot be distinguished after RTA at temperature 800 °C or higher, and substantial thickening of the wetting layer can be seen instead. The main PL peak blueshifts as a result of RTA. We propose that in the as-grown sample as well, as in samples annealed at temperatures up to 700 °C, the peak is due to the QDs. After RTA at 800 °C and higher the PL peak is due to a modified wetting layer. Relatively fast dissolution of QDs is explained in terms of strain-induced lateral Ga/In interdiffusion. It is proposed that such a process may be of importance in proximity-capped RTA, when no group-III vacancy formation takes place at the sample/capping interface.
Electrical and thermal properties of hot pressed (Nd0.5Gd0.5)Se1.50−x, where x=0.01, 0.02
Authors: Cook B. A. , Harringa J. L.
Published: July 2002

Rare earth selenides, based on the composition (Nd0.5Gd0.5)Se1.50−x where 0.005⩽x⩽0.030, were prepared by vapor phase reaction, melting, and hot pressing. The transport properties of electrical resistivity, Seebeck coefficient, and thermal diffusivity were characterized between 300 and 1300 K. In addition, carrier concentration and mobility were measured at 300 K. Chemical composition and homogeneity were determined on several samples by electron microprobe and atomic emission spectroscopy. Partial substitution of Nd for Gd was found to stabilize the high temperature gamma (Th3P4-type) phase. This system is characterized by a low thermal conductivity, the temperature dependence of which indicates mixed scattering. Analysis of the Seebeck and carrier concentration data by a single band conduction model suggests the existence of a heavy electron band, responsible for the large thermopower in this system. Electrical resistivity and Seebeck coefficient data were combined in a Jonker analysis to determine a maximum power factor, (S2/ρ), of 5.4 μW/cm °C2, corresponding to a resistivity of 5.5 Ω cm and a Seebeck coefficient of −172.3 μV/°C.
X-ray photoelectron spectroscopic study of KrF excimer laser nitrided InP surface
Authors: Akane Toshimitsu , Sugioka Koji , Midorikawa Katsumi , Dubowski Jan J. , Aoki Naoko , Toyoda Koichi
Published: July 2002

Nitridation of InP is performed by KrF excimer laser irradiation in an NH3 ambient. The N–In and N–P bonds are formed in the irradiated area in proportion to the number of laser pulses. The x-ray photoelectron spectroscopy spectra of the nitrided samples contain a small concentration of oxide components after aging in an air atmosphere than nonirradiated samples
Effect of adsorbed water on perfluoropolyether-lubricated magnetic recording disks
Authors: Tyndall G. W. , Waltman R. J. , Pacansky J.
Published: July 2002

The impact of water on the hydroxyl-terminated perfluoropolyether, Zdol, and the amorphous carbon overcoats commonly used on magnetic recording disks was investigated via computer modeling, kinetic experiments, and surface energy measurements. Water is shown to interact via hydrogen bonding with the hydroxyl end groups of Zdol and the polar, carbon–oxygen functionalities on the carbon overcoat. The interaction between water and the hydrophobic perfluorinated backbone is, however, repulsive. The corrosion susceptibility of Zdol lubricated magnetic recording disks was also studied. Reduced levels of corrosion were observed when the total Zdol thickness, and/or the bonded thickness, were increased. The results are consistent with a heterogeneous corrosion mechanism in which electron transfer from the polar functionalities on the carbon overcoat to the surface adsorbed water is the rate limiting step. The disk lubricant inhibits the electrochemical conductivity of the disk surface by; (a) a screening of the electrochemically active surface sites by the hydrophobic perfluoropolyether backbone, and (b) a neutralization of the surface active sites by hydrogen bonding of the hydroxyl end groups of Zdol.
Nonlinearly optical–optical isomerization cycle in azobenzene liquid crystal polymers
Authors: Liang Zhongcheng , Ming Hai , Wang Pei , Zhang Jiangying , Xie Jianping , Zhang Qijing
Published: July 2002

A nonlinearly optical method to induce the birefringence in azo liquid crystal polymers by the optical–optical isomerization cycle (O–O cycle) process is proposed in theory and implemented by experiments. In the O–O cycle, the two isomerization steps of trans-cis and cis-trans are both induced by light. In the nonlinearly O–O cycle, at least one step involves the nonlinearly optical absorption. It has been demonstrated that the permanent birefringence was induced in azo polymer P–CN films with a visible light source at 532 nm wavelength by the nonlinearly O–O cycle. The nonlinear nature of the photoisomerization process in P–CN was verified and a high nonlinear absorption coefficient of 40 cm/W was measured by use of the Z-scan technique.