bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen dioxide and kerosene-flame soot calibration of photoacoustic instruments for measurement of light absorption by aerosols
Authors: Arnott W. Patrick , Moosmüller Hans , Walker John W.
Published: July 2002

A nitrogen dioxide calibration method is developed to evaluate the theoretical calibration for a photoacoustic instrument used to measure light absorption by atmospheric aerosols at a laser wavelength of 532.0 nm. This method uses high concentrations of nitrogen dioxide so that both a simple extinction and the photoacoustically obtained absorption measurement may be performed simultaneously. Since Rayleigh scattering is much less than absorption for the gas, the agreement between the extinction and absorption coefficients can be used to evaluate the theoretical calibration, so that the laser gas spectra are not needed. Photoacoustic theory is developed to account for strong absorption of the laser beam power in passage through the resonator. Findings are that the photoacoustic absorption based on heat-balance theory for the instrument compares well with absorption inferred from the extinction measurement, and that both are well within values represented by published spectra of nitrogen dioxide. Photodissociation of nitrogen dioxide limits the calibration method to wavelengths longer than 398 nm. Extinction and absorption at 532 and 1047 nm were measured for kerosene-flame soot to evaluate the calibration method, and the single scattering albedo was found to be 0.31 and 0.20 at these wavelengths, respectively.
Electric field effects on the ionic-neutral curve crossing of alkali halide molecules
Authors: Sousa Carmen , Domı́nguez-Ariza David , de Graaf Coen , Illas Francesc
Published: July 2002

The weakly avoided crossing between the two lowest Σ+4 electronic states of a series of alkali halide molecules has been studied by means of the recently reported multistate complete active space second-order perturbation theory, MS–CASPT2, method. For a large enough basis set and a complete active space self-consistent field that includes part of the radial and angular correlation of the outermost halide electrons, the calculated crossing distance is in very good agreement with that predicted from the Rittner empirical potential. The study of the relevant parameters corresponding to the crossing region on these molecules has been extended to include the effect of a uniform electric field and a generalization of the empirical Rittner formula that includes the electric field effects is presented. The predictions made by the MS–CASPT2 method are also in agreement with those derived from the generalized Rittner potential. Finally, the possible implications of the present work on electron transfer processes at metal electrodes are discussed.
Intramolecular energy transfer in highly vibrationally excited methanol. IV. Spectroscopy and dynamics of CH313OH
Authors: Chirokolava Andrei , Perry David S. , Boyarkin O. V. , Schmid M. , Rizzo T. R.
Published: July 2002

Rotationally resolved spectra in the 5ν1 region of CH313OH reveal strong vibrational splittings, which by analogy to CH312OH, we assign to a resonance between 5ν1 and 4ν1+ν2. Accordingly, the vibrational dynamics on a subpicosecond time scale are similar for the two isotopomers. Comparison of the secondary structure of the first-order states resulting from this strong resonance shows a distinct difference in the two isotopomers. While the CH12 species exhibits sharp secondary structure for the lower energy band resulting from weak coupling to the remaining bath of dark states, the CH13 species shows an equally complex pattern of couplings for both first-order states. The difference between the two isotopic species arises from the relative position of key dark background states. Despite a vibrational density of states of 100 per cm−1, only a small number of states seem to determine the secondary structure, and the difference in the positions of these states relative to the first-order states results in a difference in the vibrational dynamics on a picosecond time scale. What one might consider as statistical intramolecular energy transfer appears to occur on significantly longer time scales.
Microwaves in gyromagnetic waveguides
Authors: Wu Zhong , Wang Qi , Li Chun-Fang , Shi Jie-Long
Published: July 2002

Properties of transverse electric waves in the microwave frequency range on a plane interface between a nonlinear antiferromagnet and a linear ferromagnet are investigated. It is revealed that there are two different field distributions and powers. An exact analytical dispersion relation is obtained. On the basis of the dispersion relation, we have investigated the properties of surface waves in this waveguide and, theoretically, found that there exist passbands and stop bands, which can be controlled by varying the power in the nonlinear gyromagnetic waveguides.
Neoclassical theory for rotation and impurity transport in tokamaks with neutral beam injection
Authors: Stacey Weston M.
Published: July 2002

A self-consistent, first-principles neoclassical theory for rotation and impurity transport in tokamaks is presented. The implications of this theory for impurity transport in a tokamak are illustrated by a model problem calculation.
High undercooling of Ni59Nb41 alloy in a containerless electrostatic levitation facility
Authors: Robinson M. B. , Li D. , Rogers J. R. , Hyers R. W. , Savage L. , Rathz T. J.
Published: July 2002

Utilizing the containerless electrostatic levitation facility at NASA/MSFC, we were able to undercool the Ni59Nb41 (atomic) alloy by 210 K which was 160° farther than the results of previous flight experiments. Undercoolings were clustered around 200 K during the repeated melting–freezing cycles on a single sample. Prior to this work, a metastable liquid separation had been presumed to limit the undercooling of this alloy. However, microstructural observations have revealed that undercooling was limited by crystal nucleation.
Response to “Comment on ‘From Rouse dynamics to local relaxation: A neutron spin echo study on polyisobutylene melts’ ” [J. Chem. Phys. 113, 11396 (2000)]
Authors: Richter Dieter , Monkenbusch Michael , Pykhout-Hintzen Wim , Arbe Arantxa , Colmenero Juan
Published: July 2002

It is shown that the large deviations of the intermediate scattering function S(Q,t) from the prediction of the Rosue model as observed for polyisobutylene (PIB) chains in the melt cannot be explained by the stiff chain model. By presenting new data on polydimethylsiloxane with the same structural parameters but low internal barriers which follow the Rouse prediction over the full Q-range, the conclusion is reached that the PIB dynamics is slowed down by internal friction.
Interaction of sulfur with Pt(111) and Sn/Pt(111): Effects of coverage and metal–metal bonding on reactivity toward sulfur
Authors: Rodriguez José A. , Hrbek Jan , Kuhn Mark , Jirsak Tomas , Chaturvedi Sanjay , Maiti Amitesh
Published: July 2002

In the chemical and petrochemical industries, Pt-based catalysts are very sensitive to sulfur poisoning. Synchrotron-based high-resolution photoemission, thermal desorption mass spectroscopy (TDS), and first-principles density-functional slab calculations were used to study the adsorption of sulfur on Pt(111) and a p(2×2)-Sn/Pt(111) surface alloy. Our results show important variations in the nature of the bonding of sulfur to Pt(111) depending on the coverage of the adsorbate. For small coverages, θS<0.3 ML, atomic sulfur is the most stable species. The adsorbate is bonded to hollow sites, has a large adsorption energy (>75 kcal/mol), and desorbs as S. The Pt–S bonds are mainly covalent but sulfur induces a significant decrease in the density of Pt 5d states near the Fermi level. When the sulfur coverage increases on the surface, θS>0.4 ML, there is a substantial weakening in the Pt↔S interactions with a change in the adsorption site and a tendency to form S–S bonds. Desorption of S2 is now observed in TDS and the S2p core levels shift to higher binding energy. At coverages near a full monolayer, S2 is the most stable species on the surface and its adsorption energy is ∼45 kcal/mol. Similar trends are observed for the adsorption of sulfur on a p(2×2)-Sn/Pt(111) surface alloy, but the adsorbate↔substrate interactions are weaker than on Pt(111). The formation of Pt–Sn bonds reduces the reactivity of Pt toward sulfur. Electronic effects associated with bimetallic bonding can be useful for controlling or preventing sulfur poisoning.
Microstructure, structural defects, and piezoelectric response of Bi4Ti3O12 modified by Bi3TiNbO9
Authors: Sagalowicz Laurent , Chu Fan , Martin Pedro Duran , Damjanovic Dragan
Published: July 2002

Microstructure, structural defects, and piezoelectric response of bismuth titanate (Bi4Ti3O12)1−x and bismuth titanium niobate (Bi3TiNbO9)x solid solution with x=0.05 and 0.2 were investigated. Depending on x and on the sintering temperature different microstructures and piezoelectric responses were observed. For a low content in Bi3TiNbO9 (x=0.05) and a high sintering temperature (1130 °C), a coarse grain size is present, the number of structural defects within the grain is small, and there is a strong dependence of d33 on the ac pressure. For higher Bi3TiNbO9 (x=0.2) content or for lower sintering temperature (1080 °C) and x=0.05, the grain size is finer and a large number of structural defects is present within the grains. In particular, for x=0.2, high resolution transmission electron microscopy shows a high concentration of intergrowth defects which consist of Bi3TiNbO9 layers inserted in the Bi4Ti3O12 matrix in a more or less random way. In these samples, there is a very small dependence of d33 on the ac pressure and the piezoelectric hysteresis is likewise very small. The relation between microstructure and piezoelectric properties is discussed and it is shown that there is a good correlation between the dependence of the piezoelectric response on the ac pressure and the defect density. The piezoelectric response may be related to the structural defects present within the grain.
Nondestructive detection of stacking faults for optimization of CdSe/ZnSe quantum-dot structures
Authors: Passow T. , Heinke H. , Falta J. , Leonardi K. , Hommel D.
Published: July 2002

CdSe/ZnSe quantum structures were systematically investigated by high-resolution x-ray diffraction. The samples were grown at different growth temperatures on GaAs(001) substrates by molecular-beam epitaxy. A model is presented enabling the simulation and quantitative analysis of x-ray diffraction profiles influenced by stacking faults. This yields a fast and nondestructive method for the determination of stacking fault densities after calibration by transmission electron microscopy. A steep increase of the stacking fault density above a critical thickness was found. The critical thickness decreases with increasing growth temperature. Above this critical thickness, the amount of incorporated CdSe remains apparently constant.
Anomalous decay of shock impulses in laminated composites
Authors: Benson D. J. , Nesterenko V. F.
Published: July 2002

The decay of shocks in laminated composites is investigated with numerical modeling. An anomalous effect of the cell size on the leading shock amplitude was found. It is manifested in increased amplitude of the leading shock wave with the increase of the number of interfaces between the materials with different acoustic impedances crossed by a “long” shock wave in periodic laminar composites. The components in the fine composite are loaded by a larger number of shock waves than in the coarse composite, resulting in a higher residual temperature in the fine composite. The anomalous attenuation is not observed for “short” waves at the same depth from the impacted surface. The bonding strength between the layers has only a slight effect on the shock evolution.
Thermal and nonthermal ion emission during high-fluence femtosecond laser ablation of metallic targets
Authors: Amoruso S. , Wang X. , Altucci C. , de Lisio C. , Armenante M. , Bruzzese R. , Velotta R.
Published: July 2002

We have investigated the emission of positive ions from metallic targets irradiated with intense, ultrashort laser pulses (≈120 fs) at 780 nm, in both S and P polarized states. The measured energy spectra show the presence of a nonthermal, high-energy (several keV) ion component accompanying low-energy ions (tens of eV) produced by a thermal mechanism. The yield of the high-energy component shows a strong dependence on both laser fluence and light polarization. For the low-energy component a higher ablation efficiency was observed for P polarization, and ascribed to a more effective absorption mechanism active during the laser–target interaction.
Parallel Douglas–Kroll energy and gradients in NWChem: Estimating scalar relativistic effects using Douglas–Kroll contracted basis sets
Authors: de Jong W. A , Harrison R. J. , Dixon D. A.
Published: July 2002

A parallel implementation of the spin-free one-electron Douglas–Kroll–Hess (DKH) Hamiltonian in NWChem is discussed. An efficient and accurate method to calculate DKH gradients is introduced. It is shown that the use of a standard (nonrelativistic) contracted basis set can produce erroneous results for elements beyond the first row elements. The generation of DKH contracted cc-pVXZ(X=D,T,Q,5) basis sets for H, He, B–Ne, Al–Ar, and Ga–Br is discussed. The effect of DKH at the Hartree–Fock level on the bond distances, vibrational frequencies, and total dissociation energies for CF4, SiH4, SiF4, and Br2CO is discussed. It is suggested that the predominant effect of the scalar relativistic correction on the total dissociation energy can be calculated at the Hartree–Fock level if an adequate basis set is used.
A strategy for analysis of (molecular) equilibrium simulations: Configuration space density estimation, clustering, and visualization
Authors: Hamprecht Fred A. , Peter Christine , Daura Xavier , Thiel Walter , van Gunsteren Wilfred F.
Published: July 2002

We propose an approach for summarizing the output of long simulations of complex systems, affording a rapid overview and interpretation. First, multidimensional scaling techniques are used in conjunction with dimension reduction methods to obtain a low-dimensional representation of the configuration space explored by the system. A nonparametric estimate of the density of states in this subspace is then obtained using kernel methods. The free energy surface is calculated from that density, and the configurations produced in the simulation are then clustered according to the topography of that surface, such that all configurations belonging to one local free energy minimum form one class. This topographical cluster analysis is performed using basin spanning trees which we introduce as subgraphs of Delaunay triangulations. Free energy surfaces obtained in dimensions lower than four can be visualized directly using iso-contours and -surfaces. Basin spanning trees also afford a glimpse of higher-dimensional topographies. The procedure is illustrated using molecular dynamics simulations on the reversible folding of peptide analoga. Finally, we emphasize the intimate relation of density estimation techniques to modern enhanced sampling algorithms.
Detection of O(1D) produced in the photodissociation of O2. II. Identification of the Σu-3 and Πu3 Rydberg states in 105–113 nm
Authors: Lee P. C. , Nee J. B.
Published: July 2002

The production of O(1D) from O2 by photodissociation was measured in the 105–113 nm wavelength region. The quantum yields of O(1D) were employed to identify the excited states as Σu-3 or Πu3, where the former correlated with the production of O(1D) and the latter production of O(3P) only. Many bands of E, E′ of Σu-3 and F, F′ Πu3, were found with their vibrational states identified. Several bands had mixed states, such as the (0,0) and (1,0) bands of D′ 3Σu−←X 3Σg− transition which had smaller than unity quantum yields of O(1D) due to the perturbation caused by the nearby states D′ 3Σu+(v′=1,2) at 112.0 and 110.0 nm. The bands of npσu 3Πu state in the region of 105–110 nm are in agreement with the assignments of other works, and a band near 107.3 nm is consistent with the predicted band position of the F 3Πu(v′=6) upper-state.
Predicted thermal stresses in a bimaterial assembly adhesively bonded at the ends
Authors: Suhir E.
Published: July 2002

The interfacial shearing and “peeling” stresses in an elongated bimaterial assembly, adhesively bonded at the ends and subjected to the change in temperature, are predicted, based on an approximate structural analysis (strength-of-materials) model. The stresses in the bonded joints due to the thermal expansion (contraction) mismatch of the adherend materials within the bonded areas (“local” mismatch), as well as the stresses, caused by the thermal mismatch of the adherend materials within the unbonded midportion of the assembly (“global” mismatch), are considered. The interaction of the “local” and the “global” stresses is evaluated and analyzed. It is shown that if the bonded joints are made long enough, the maximum stresses in the assembly will not be different from the stresses in an assembly with a continuous adhesive layer, no matter how long the unbonded midportion of the assembly might be. The obtained results can be helpful in the stress–strain evaluations and physical (mechanical) design of bimaterial assemblies in electronic and photonic packaging.
Structure and magnetism of Co1−xMnx alloys epitaxially grown on GaAs(001)
Authors: Wu D. , Liu G. L. , Jing C. , Wu Y. Z. , Dong G. S. , Jin X. F.
Published: July 2002

The structure and magnetism of Co1−xMnx films grown on GaAs(001) substrates were characterized by reflection high energy electron diffraction and magneto-optical Kerr effect measurements. It is found that the Co-rich and Mn-rich films exist in body-centered-cubic and face-centered-cubic structures, respectively. Meanwhile, the Co1−xMnx films show ferromagnetism whenever the structure is bcc, but they show antiferromagnetism or paramagnetism whenever the structure is fcc. This strong correlation established between the structure and magnetism was further studied and confirmed by an ab initio electron linearized augmented-plane-wave calculation with the local-spin-density approximation.
Microstructural contributions to hole transport in p-type GaN:Mg
Authors: Rice A. K. , Malloy K. J.
Published: July 2002

We present an analysis of hole transport in p-type Mg-doped GaN grown on sapphire substrates by metalorganic chemical vapor deposition. We find that the experimental Hall mobility cannot be described by numerically solving the Boltzmann transport equation. We attribute this discrepancy to the microstructure of GaN:Mg grown on sapphire and present a microstructure-oriented model of the transport of holes in p-type GaN:Mg grown on sapphire. This model provides a simplified picture of the microstructure consisting of two distinct microstructural phases in GaN on sapphire. Using this model for the experimental mobility, the extracted parameters from hole transport measurements suggest a weak direct correlation with the microstructural parameters determined from x-ray diffraction measurements. The experimental mobility of p-type GaN:Mg grown on sapphire can be described as dependent upon the acceptor doping, impurity compensation, and microstructure, including dislocation density, columnar grain size, and grain boundaries.
Fast-scanning shear-force microscopy using a high-frequency dithering probe
Authors: Seo Yongho , Park June H. , Moon Jin B. , Jhe Wonho
Published: July 2002

We have demonstrated high-speed scanning shear-force microscopy using a fiber tip attached to quartz crystal vibrating at 2.0 MHz resonance frequency. With a high-frequency dithering probe, we have obtained clear images at the scanning speed of 1.2 mm/s and it takes only 0.5 s to image the surface area of 55 μm2 for 64×64 pixels without any compromise of spatial lateral resolution. This speed is more than five times faster than that obtained by other topographic imaging methods and can be further improved to realize real-time shear-force probe microscopy.
Molecular dynamics computer simulations of solvation dynamics at liquid/liquid interfaces
Authors: Michael David , Benjamin Ilan
Published: July 2002

The solvent dynamic response to electronic transitions at several liquid/liquid interfaces is studied using molecular dynamics computer simulations. The interfaces examined are between water and one of four different organic liquids. The electronic transitions involve a change in the permanent dipole of a dipolar solute located at the interface. Two locations of the solute relative to the interface are studied and are compared with the same process in each of the bulk liquids. The different organic liquids are 1-octanol, 1,2-dichloroethane, n-nonane, and carbon tetrachloride. They are selected to give a range of polarity and of interface structure. The solvent dynamic response at the interface is much more complex than in the bulk. The total relaxation involves multiple time scales corresponding to contributions from both solvents and from the unique structural and dynamic properties of the interface. In particular, interfacial water relaxation may contain a slow component not present in the bulk nor at the water liquid/vapor interface.
Modeling stimulated Raman scattering for smoothed laser–solid target interaction at 0.53 μm
Authors: Mourenas D. , Divol L. , Casanova M. , Rousseaux C.
Published: July 2002

The behavior of stimulated Raman backscattering in an inhomogeneous plasma at subcritical density is investigated in the context of inertial confinement fusion. A refined independent hot spots model has been introduced in a laser interaction postprocessor to hydrodynamical code simulations. The model is shown to reproduce most experimentally observed trends, provided that the Langmuir waves damping is reduced on axis, due to the presence of trapping, inverse bremsstrahlung heating, or perpendicular self-generated magnetic fields. The experiments were carried out at 0.53 μm at the Phébus laser facility, and Raman scattering was measured as a function of laser intensity and relative bandwidth, as well as solid target composition.
Diffusion of implanted beryllium in silicon carbide studied by secondary ion mass spectrometry
Authors: Henkel T. , Tanaka Y. , Kobayashi N. , Tanoue H. , Hishita S.
Published: July 2002

The diffusion behavior of beryllium implanted in silicon carbide has been investigated by secondary ion mass spectrometry. The shape of the as implanted profile changed considerably after annealing at temperatures above 1300 °C due to redistribution processes. In addition, strong out diffusion into the annealing ambient and in diffusion into the bulk material was observed. Moreover, beryllium diffuses faster in epitaxial layers than in bulk crystals grown by sublimation. Effective diffusion coefficients with an activation energy of 3.1 eV were determined in bulk crystals in the temperature range 1500–1700 °C. Beryllium is suggested to diffuse via interstitial sites.
Observation of the crystal-field splitting related to the Mn-3d bands in spinel-LiMn2O4 films by optical absorption
Authors: Kushida K. , Kuriyama K.
Published: July 2002

Mn  3d bands in spinel-LiMn2O4 films, synthesized on SiO2-glass substrates by a sol-gel method, were studied using an optical absorption method. Two absorption peaks were observed at around 1.63 and 2.00 eV at room temperature. These peaks were associated with two d–d transitions: One is the Mn t2g to the lower Mn eg bands transition and the other the Mn t2g to the upper Mn eg bands one. A large absorption was also observed above 3.0 eV, indicating a transition from the O 2p valence band to the Mn 3d bands. The d–d transitions showed the blueshifts of 20–30 meV at 77 K comparing with those at room temperature. The observed electronic structure was consistent with the calculated one.
Magneto-optical characteristics of SiN/GdFe films
Authors: Shen Z. C. , Wang S. Y. , Li J. , Li H. Y. , Jin Q. Y. , Zhang R. J. , Zhou S. M. , Chen L. Y.
Published: July 2002

The magneto-optical and optical properties of GdFe single layer films, which are covered with a thin Si3N4 layer, were studied in the visible wavelength region. A Kerr rotation peak and a reflectivity drop were observed near 4.1 eV in GdFe alloyed films and attributed to the Gd element. Compared with the single thick GdFe film, the Kerr effect of SiN/GdFe bilayers was enhanced, due to the optical interference between Si3N4 and GdFe. The Kerr rotation of GdFe films showed a nonlinear function of the compositions in the whole measured wavelength range. Magneto-optical measurements directly evidence the spin–flip in the GdFe films as the Gd content increased from 20.7 to 24.2 at. %, which showed advantages over conventional magnetometry.
Investigation of the P–As substitution at GaAs/Ga0.51In0.49P interfaces by photoluminescence under pressure
Authors: Aurand A. , Leymarie J. , Vasson A. , Mesrine M. , Massies J. , Leroux M.
Published: July 2002

Substitution of As atoms by P ones during the growth of GaAs/Ga0.51In0.49P quantum wells (QWs) is investigated by photoluminescence (PL) as a function of temperature and under hydrostatic pressure. We have studied a series of samples, grown by chemical beam epitaxy, in which this substitution is achieved by changing the exposure time of GaAs surface to cracked PH3. The emision lines related to the QWs are blueshifted when the time of exposure to PH3 increases; this is due to the formation of Ga(As,P) monolayers by P–As exchange. Two samples are examined by PL under hydrostatic pressure at 5 K. The Γ–X crossover, which corresponds to the transfer of electrons from the Γ conduction band states of the QWs to X valley states of the Ga(As,P) interfacial layers occurs at 3.2 GPa for the sample grown with the shortest exposure time (5 s). In contrast, it occurs at 2.4 GPa for the the sample with the longest exposure time (35 s). The data obtained by PL under pressure give evidence of the formation of a GaP-rich layer up to 2 monolayers thick at the Ga0.51In0.49P on GaAs interface. Calculations allow us to estimate the modifications of the P concentration profile among the samples.
Nonadiabatic effects in the lowest +(3P) ion-pair states of CIF
Authors: Kokh Daria B. , Li Yan , Buenker Robert J. , Alekseyev Aleksey B. , Liebermann Heinz-Peter , Alekseev Vadim A.
Published: July 2002

Nonadiabatic calculations of vibrational energies and wave functions are carried out for the E(0+, 3P2) and f(0+, 3P0) ion-pair states of the ClF molecule. It is shown that strong radial coupling between these 0+ states is caused by a significant variation of their 3Σ− and 3Π Λ-S contributions with internuclear distance and results in vibrational energy shifts as well as changes in the corresponding adiabatic vibrational wave functions. Both resonance and nonresonance interactions between vibronic levels of these two adiabatic states are found to be important, but significant mixing of the adiabatic wave functions can occur only for the nearly resonant levels located around f,v=3; E,v=7 and f,v=8; E,v=13. Nonadiabatic interactions are found to be responsible for the appearance of long-wavelength maxima in the f,v=3,4 emission spectra that was the subject of the discrepancy between theoretical and experimental data discussed in the previous paper [A. B. Alekseyev, H.-P. Liebermann, R. J. Buenker, and D. B. Kokh, J. Chem. Phys. 112, 2274 (2000)]. Inclusion of nonadiabatic effects leads to notably better agreement between the calculated and measured bound-free emission spectra.
Detachment and divertor temperature and density redistribution
Authors: Stacey Weston M.
Published: July 2002

A theoretical model is developed for large scale-length, one-dimensional thermal instabilities along the field lines in tokamak divertors. Calculated growth rates predict a divertor thermal instability under the conditions (low-plasma temperature and density and high-neutral densities at the divertor plate) at which detachment followed by large-scale divertor temperature and density redistributions are observed in several DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159] discharges.
Dusty plasma near a conducting boundary with dust-neutral collisions
Authors: Mahanta M. K. , Goswami K. S.
Published: July 2002

Using the usual fluid model the behavior of an unmagnetized dusty plasma near a conducting boundary with dust-neutral collisional effect is studied. The plasma consists of electrons, ions, negatively charged micron size dust particles, and neutrals. The Sagdeev potential for collisionless case is also calculated and found that it has different structure for plasmas with and without dusts. An expression for gradient of potential (i.e., the electric field) for collisional dusty plasma with dust–neutral collisions is calculated. The relation between the dust acoustic velocity and the collisionality has been discussed.
Analytic treatment of weak-turbulence Langmuir wave electrostatic decay
Authors: Edney S. D. , Robinson P. A.
Published: July 2002

The three-wave decay of beam-driven Langmuir waves into ion-sound waves, and backscattered Langmuir waves is analyzed. Realistic approximations are used for the spectra of Langmuir and ion-sound waves to enable calculations of growth rates of ion-sound and backscattered Langmuir waves in terms of a single well behaved integral. This integral is evaluated numerically, and approximated analytically and the results are compared with previous estimates. The case of intense beam-driven Langmuir waves decaying amid a weak thermal background of pre-existing Langmuir and ion-sound waves is examined in detail and the analytical approximation in this case is found to reproduce the numerical results accurately.
Persistent photoconductivity in InGaN/GaN multiquantum wells
Authors: Yang H. C. , Lin T. Y. , Chen Y. F.
Published: July 2002

Optical properties of undoped InGaN/GaN multiquantum wells (MQWs) have been investigated by photoconductivity, photoluminescence, and photoluminescence excitation measurements. We report the observation of persistent photoconductivity (PPC) in InGaN/GaN MQWs and show that the PPC effect arises from In composition fluctuations in the InGaN well layer. From the analysis of the decay kinetics, the localization depth caused by composition fluctuations has been determined. Compared with the results of complementary absorption and photoluminescence measurements, it is found that the quantum-confined Stark effect due to piezoelectric field and composition fluctuations both exist in the InGaN/GaN MQWs. These two effects are responsible for the photoluminescence Stokes’ shift in the InGaN well layers. Here, we provide a unique way to distinguish the individual contribution to the Stokes’ shift for the piezoelectric field and composition fluctuations.
Selective ablation of AlN ceramic using femtosecond, nanosecond, and microsecond pulsed laser
Authors: Hirayama Yoichi , Yabe Hiroyuki , Obara Minoru
Published: July 2002

The microsecond, nanosecond, and femtosecond laser ablation of AlN ceramic with a transversely excited atmospheric (TEA) CO2 laser, KrF excimer laser, and Ti:sapphire laser is demonstrated. It is shown that the laser-induced thermal decomposition process occurs with a microsecond TEA CO2 laser and a nanosecond KrF excimer laser. With the microsecond and nanosecond laser-induced thermal decomposition process, the conductive aluminum line can be directly fabricated and very low resistance can be obtained with a TEA CO2 laser. In the case of femtosecond Ti:sapphire laser ablation, there are two different regimes of ablation rate-like metals. In addition, a nonthermal process without a chemical composition change of the ablated surface can be achieved successfully, which is evident from scanning electron microscopy observation and x-ray photoelectron spectroscopy analysis of the ablated surface.
Correlation between Si–H/D bond desorption and injected electron energy in metal–oxide–silicon tunneling diodes
Authors: Lin C.-H. , Lee M. H. , Liu C. W.
Published: July 2002

Metal–oxide–silicon tunneling diodes with SiO2/Si interface passivated by hydrogen or deuterium are stressed under various constant current conditions. When the energy of injected electrons exceeds a threshold value (∼3 eV), both hydrogen and deuterium passivated devices reveal similar soft breakdown behaviors. On the contrary, when the injected electrons with low energy (<3 eV) at high current density stress, a giant isotope effect is observed in the deuterated devices due to the resonance between the Si–D bond bending mode and the transverse optical phonon of bulk silicon.
Potential flow issuing from a two-dimensional curved nozzle
Authors: Toison Fabrice , Hureau Jacques
Published: July 2002

We consider the two-dimensional potential flow of a liquid issuing from a nozzle, for which the far upstream flow tends to be uniform and horizontal. The problem is solved by mapping the potential plane ( f ) onto a unit disk and then solving a mixed boundary problem. Using an iterative process, we can consider either polygonal walls or arbitrary curved walls. By considering polygonal walls, our method is first validated by comparison with results already published for weightless fluid. It is next applied to arbitrary curved walls, with or without gravity.
Dispersion in three-dimensional fracture networks
Authors: Huseby O. , Thovert J.-F. , Adler P. M.
Published: July 2002

Dispersion in three-dimensional networks of polygonal fractures is determined by triangulating the network and solving the two-dimensional convection-diffusion equation in each fracture or by performing random walks. The general triangulation methodology and the numerical solution are summarized. The influence of the Péclet number, of the fracture density and of the fracture shape are systematically studied. Moreover, fracture networks are shown to belong to the same universality class as bond percolation networks.
Energy modulation of nonrelativistic electrons in an optical near field on a metal microslit
Authors: Ishikawa R. , Bae J. , Mizuno K.
Published: July 2002

Energy modulation of nonrelativistic electrons with a laser beam using a metal microslit as an interaction circuit has been investigated. An optical near field is induced in the proximity of the microslit by illumination of the laser beam. The electrons passing close to the slit are accelerated or decelerated by an evanescent wave contained in the near field whose phase velocity is equal to the velocity of the electrons. The electron–evanescent wave interaction in the microslit has been analyzed theoretically and experimentally. The theory has predicted that electron energy can be modulated at optical frequencies. Experiments performed in the infrared region have verified theoretical predictions. The electron–energy changes of more than ±5 eV with a 10 kW CO2 laser pulse at the wavelength of 10.6 μm has been successfully observed for an electron beam with an energy of less than 80 keV.
Spatial distributions of trapped microparticles in a plasma sheath
Authors: Wang Dezhen , Wang Xiaogang
Published: July 2002

The density distributions of trapped microparticles under the interaction of electrostatic, gravitational, ion-drag, and pressure gradient forces in a cathode sheath are investigated in a self-consistent model. It is found that instead of a δ-function distribution for cold microdust particles, the distribution for the particles with a finite temperature has a thermal broadening throughout the trapping region. The region where the microparticles are trapped is wider for a higher dust temperature or a smaller particulate radius and much narrower for a much lower dust temperature or a bigger particulate radius. For a very low temperature, the distribution exhibits a sharp peak. The peak can shift from the edge into the sheath region as the particulate radius increases.
Rotational spectrum and molecular structure of OCS–N2O
Authors: Leung Helen O. , Osowski Anne M. , Oyeyemi Olayinka A.
Published: July 2002

The rotational spectra of four isotopomers of OCS–N2O, including nuclear quadrupole hyperfine structure in the N14-containing isotopomers, have been observed in the 6.5–19 GHz region with a Fourier transform microwave spectrometer and analyzed using the Watson A-reduced Hamiltonian with the inclusion of nuclear quadrupole coupling interactions where applicable. The effective structure of the complex, obtained by fitting the structural parameters to the moments of inertia of each isotopomer, is approximately slipped parallel, with oxygen in N2O and sulfur in OCS occupying the obtuse vertices of the quadrilateral formed by the two subunits. The intermolecular distance is 3.5166(2) Å, with N2O and OCS forming angles of 68.5(3)° and 99.6(2)° with the intermolecular axis, respectively. This structure is also supported by a Kraitchman analysis. Comparisons of the structure of OCS–N2O with those of OCS–CO2 and CO2–N2O show that the isoelectronic N2O and CO2 behave similarly in their intermolecular interactions with OCS while the difference between the isovalent OCS and CO2 in their interactions with N2O mainly arises from steric effects. The nuclear quadrupole coupling constants of the two nitrogen nuclei in OC32S–14N2O do not definitively indicate a perturbation of the electronic distribution of N2O in the complex. However, an electrostatic calculation of the electric fields at the N2O atomic positions due to OCS shows that the perturbation is small and is therefore rendered unobservable due to the large uncertainties in the nuclear quadrupole coupling constants of the central nitrogen.
Magnetization process in thin Ni sheets: Effect of cold-rolling and recrystallization annealing
Authors: Asti G. , Solzi M. , Sarzi Sartori S. , Beatrice C. , Fiorillo F.
Published: July 2002

Reversible and irreversible magnetization processes have been investigated in thin Ni sheets by means of flux-metric and alternating-gradient-force magnetometer techniques. Cold-rolled samples exhibit a rotation-dominated process at low fields, and the value of the associated susceptibility, related to the stress-induced and the magnetocrystalline anisotropies, can provide an estimate of the residual stress in the material. Reversible displacements of the domain walls come into play and combine with rotations in the annealed samples. A method is devised, by which domain-wall and rotational contributions to the reversible susceptibility can be singled out. The Rayleigh law always accounts for the behavior of hysteresis loops and losses at low fields, but rotations engender some peculiar evolution of the related parameters and their relationship with the coercive field. Magnetic softening by stress relief is assessed, as a whole, through Preisach analysis. It is found that the local stochastic coercive fields can be described by means of a Lorentzian distribution function, whose relative width is minimum in the cold-rolled material. By removing the internal stresses through recrystallization annealing, the contribution of grain boundaries and surface effects to coercivity is put in evidence, with the latter apparently posing the major restraints to domain-wall motion for grain sizes larger than the sheet thickness.
Stimulated blue emission in reconstituted films of ultrasmall silicon nanoparticles
Authors: Nayfeh M. H. , Barry N. , Therrien J. , Akcakir O. , Gratton E. , Belomoin G.
Published: July 2002

We dispersed electrochemical etched Si into a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-photon process at 780 nm, the emission exhibits a sharp threshold near 106 W/cm2, rising by many orders of magnitude, beyond which a low power dependence sets in. Under some conditions, spontaneous recrystallization forms crystals of smooth shape from which we observe collimated beam emission, pointing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si–Si phase found only on ultrasmall Si nanoparticles. The Si–Si phase model provides gain coefficients as large as 103–105 cm−1.
Magnetic properties of Mn-doped ZnO
Authors: Fukumura T. , Jin Zhengwu , Kawasaki M. , Shono T. , Hasegawa T. , Koshihara S. , Koinuma H.
Published: July 2002

We report on the magnetic properties of an oxide-diluted magnetic semiconductor (DMS), Zn0.64Mn0.36O. The temperature dependence of the magnetization shows a spin-glass behavior with the large magnitude of the Curie–Weiss temperature, corresponding to a stronger antiferromagnetic exchange coupling than other II–VI DMSs. The small effective Mn moment (x̄∼0.02) under high field also represents a strong antiferromagnetic exchange coupling in this compound.
The stationary non-Poissonian collision model of energy relaxation and stochastic motion in condensed phase processes
Authors: Shushin A. I.
Published: July 2002

The effect of energy dissipation on transport and activated rate processes in condensed phase is analyzed in detail within the non-Poissonian collision model (NPCM). The NPCM is a generalized variant of the collision model (CM) describing the instantaneous change of the velocity of probe particles induced by random collisions with particles of a medium. Unlike the conventional CM, the NPCM assumes the non-Poissonian collision statistics. In this work we concentrate on the stationary variant of the NPCM (SNPCM), which differs from the nonstationary NPCM (NNPCM) discussed in previous studies by the proper treatment of the collision statistics ensuring the time homogeneity of the process. The SNPCM is shown to be free of inconsistencies inherent in the NNPCM. In particular, the SNPCM reproduces the physically natural relations between the average parameters (the average displacement and velocity, correlation functions, etc.) well known in the transport theory. The SNPCM describes properly the specific features of the processes under study, for example, the kinetic cage effect predicted earlier. Within the SNPCM the analytical expressions for the rate of passage over a parabolic barrier, valid in the intermediate-to-strong friction limit, are derived for some particular values of the parameters of the model. The expressions obtained are analyzed in detail.
Rate coefficient calculation for diffusion-influenced reversible reactions with longer-range reactivities
Authors: Naumann Wolfgang
Published: July 2002

The chemically relevant so-called phenomenological forward and reverse rate coefficients of reversible bimolecular solution reactions, for nonlocal reactivities defined via attributed irreversible diffusion-kinetic schemes [W. Naumann and A. Molski, J. Chem. Phys. 103, 3474 (1995)], are exactly expressed by formal operator expressions. It is shown that this rate coefficient definition corresponds to the so-called integral encounter theory by Gopich, Kipriyanov, and Doktorov [J. Chem. Phys. 110, 10888 (1999)], an isolated reactive pair approximation. Assuming detailed balance, for the bimolecular isomerization A+B⇌B+C the operator expressions lead to exact relations with the rate coefficients of the irreversible partial reactions A+B→B+C and A+B←B+C. Generalizations of the well-known Noyes formula to reversible reactions result when the corresponding Wilemski-Fixman closure approximations of the irreversible and reversible rate coefficients are inserted.
Preparation and photoluminescence of highly ordered TiO2 nanowire arrays
Authors: Lei Y. , Zhang L. D. , Meng G. W. , Li G. H. , Zhang X. Y. , Liang C. H. , Chen W. , Wang S. X.
Published: July 2002

Highly ordered TiO2 nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and F+ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the F+ centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls.
High-field transport in a dense two-dimensional electron gas in elementary semiconductors
Authors: Dmitriev A. P. , Kachorovskii V. Yu. , Shur M. S.
Published: July 2002

We calculate the dependence of the electron temperature T and the drift velocity vd on the applied electric field E for a two-dimensional electron gas in elementary semiconductors. We consider the case of high electron concentrations when the energy dependence of the electron distribution function is governed by electron–electron collisions. We show that, in the one-valley approximation, T should tend to infinity at a certain value of the electric field E=Ec. This result is linked to the “runaway” effect, which takes place in the two-dimensional case, even for the deformational phonon scattering. Transitions of hot electrons into the upper valleys with larger densities of states limit the growth of T. As a result, a two-dimensional electron gas should exhibit a negative differential mobility, just as in the previously discussed case of noninteracting electrons.
Current transport in ramp-type junctions with engineered interface
Authors: Heinsohn J.-K. , Dittmann R. , Contreras J. Rodrı́guez , Scherbel J. , Klushin A. , Siegel M. , Jia C. L. , Golubov S. , Kupryanov M. Yu.
Published: July 2002

The transport properties of “interface-engineered” edge-type YBa2Cu3O7 Josephson junctions are investigated in detail. We have investigated the dependence of the current–voltage characteristics on external magnetic field, temperature, and microwave irradiation and compare them to the resistively shunted junction model. The temperature dependence of the critical current and the normal resistance allows us to draw conclusions to the transport of quasiparticles and Cooper pairs in the investigated “interface-engineered” junctions. We have studied the properties of junctions for which La doped YBa2Cu3O7 is used for the superconducting electrodes. We will propose a model for the undoped and the La doped case which takes into account a barrier which consists of a series connection of a normal conducting layer and an insulator, containing superconducting microconstrictions.
Phosphorus-doped thin silica films characterized by magic-angle spinning nuclear magnetic resonance spectroscopy
Authors: Jakobsen Hans J. , Skibsted Jørgen , Kristensen Martin , Zauner Dan A.
Published: July 2002

Magic-angle spinning nuclear magnetic resonance spectra of 31P and 29Si have been achieved for a thin silica film doped with only 1.8% 31P and deposited by plasma enhanced chemical vapor deposition on a pure silicon wafer. The observation of a symmetric 31P chemical shift tensor is consistent with a three-fold symmetric (–O–)3P=O chemical structure. We find that the glass structure is very similar to that found in fiber preforms.