bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface reaction of NiO/NiFe and its influence on magnetic properties
Authors: Yu G. H. , Chai C. L. , Zhu F. W. , Xiao J. M. , Lai W. Y.
Published: July 2002

Ta/NiO/NiFe/Ta multilayers were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field between NiO and NiFe reached 120 Oe. The composition and chemical states at the interface region of NiO/NiFe were studied using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there are two thermodynamically favorable reactions at NiO/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. The thickness of the chemical reaction as estimated by angle-resolved XPS was about 1–1.5 nm. These interface reaction products are magnetic defects, and we believe that the exchange coupling field Hex and the coercivity Hc of NiO/NiFe are affected by these defects.
Effect of E×B flows on global linear ion temperature gradient modes
Authors: Maccio M. , Vaclavik J. , Villard L.
Published: July 2002

Strong electric fields generate an E×B rotation of the equilibrium plasma. Experiments have shown that this effect could lower the anomalous transport in tokamaks. The study of the effect of these flows on the linear stability of ion temperature gradient (ITG) modes has therefore been undertaken. The question is addressed solving the spectrum of the gyrokinetic equation in the full two-dimensional poloidal plane for a large aspect ratio tokamak with concentric circular magnetic surfaces. Results show a strong stabilizing effect of E×B flows on the ITG modes. Study with respect to different profiles of the flow shows that the so-called curvature of flow (second derivative) has no effect, while the intensity of flow itself produces the strongest effect. Study with respect to different magnetic shears did not allow the discovery of any particular behavior of the negative magnetic shear cases. Eventually, an experimental comparison was conducted.
Formation of planar optical waveguides in potassium titanyl phosphate by double implantation of protons
Authors: Bindner P. , Boudrioua A. , Loulergue J. C. , Moretti P.
Published: July 2002

The formation of planar waveguides in potassium titanyl phosphate by H+ ions implantation at low energy is presented and discussed. The energy and dose were (600+550) keV and (1+0.8)×1016 ions cm−2, respectively. The optogeometrical parameters deduced from the optical characterization are the following: −3% for each refractive index variation (nx, ny, and nz) and a guide thickness of 4.3 μm. A good agreement is found between the value given by the top of the nuclear damages profile obtained by transport of ions in matter code and the value given by the index fall position. Losses measured in nonannealed samples were estimated to be less than 5 dB cm−1.
The influence of aggregates and relative permeability on the magnetic birefringence in ionic magnetic fluids
Authors: Neto K. Skeff , Bakuzis A. F. , Morais P. C. , Pereira A. R. , Azevedo R. B. , Lacava L. M. , Lacava Z. G. M.
Published: July 2002

The static magnetic birefringence (SMB) of nickel-ferrite ionic magnetic fluid was investigated within the oscillating dipole-interaction anisotropy concept proposed by Xu and Ridler [J. Appl. Phys. 82, 326 (1997)]. The model was extended to include the magnetic texture of particle agglomerates and the field dependence of the magnetic permeability. The SMB data of samples subjected or not to a magnetic aging process and presenting particle concentration in the range of 2×1016 to 8×1016 particle/cm3 were successfully described. The particle size distribution obtained from the fit of the SMB data was discussed in comparison with the data obtained from transmission electron microscopy.
Competing isomeric product channels in the 193 nm photodissociation of 2-chloropropene and in the unimolecular dissociation of the 2-propenyl radical
Authors: Mueller Julie A. , Parsons Bradley F. , Butler Laurie J. , Qi Fei , Sorkhabi Osman , Suits Arthur G.
Published: July 2002

This paper presents product translational energy spectroscopy measurements of the primary photofragmentation channels of 2-chloropropene excited at 193 nm and of the unimolecular dissociation of the 2-propenyl radical. Tunable vacuum ultraviolet (VUV) photoionization of the products allows us to distinguish between the various product isomers formed in these processes. The data show evidence for three significant primary reaction channels in the dissociation of 2-chloropropene: An excited-state C–Cl fission channel producing fast Cl atoms, a C–Cl fission channel producing slow Cl atoms, and HCl elimination. A minor C–CH3 fission channel contributes as well. The measured branching of the major primary product channels is: [fast C–Cl]:[slow C–Cl]:[HCl elimination]=62%:23%:15%. The experiments also allow us to resolve selectively the product branching between the unimolecular dissociation channels of the 2-propenyl radical, a high energy C3H5 isomer; we measure how the branching ratio between the two competing C–H fission channels changes as a function of the radical’s internal energy. The data resolve the competition between the unimolecular H+allene and H+propyne product channels from the radical with internal energies from 0 to 18 kcal/mol above the H+propyne barrier. We find that the barrier to H+allene formation from this high-energy C3H5 radical is higher than the barrier to H+propyne formation, in agreement with recent theoretical calculations but in sharp contrast to that predicted for the most stable C3H5 isomer, the allyl radical. The experiments demonstrate a general technique for selectively forming a particular CnHm isomer dispersed by internal energy due to the primary photolysis, thus allowing us to determine the branching between unimolecular dissociation channels as a function of the selected radical isomer’s internal energy.
Effect of nonradiative recombination on light emitting properties of two-dimensional photonic crystal slab structures
Authors: Ryu Han-Youl , Hwang Jeong-Ki , Song Dae-Sung , Han Il-Young , Lee Yong-Hee , Jang Dong-Hoon
Published: July 2002

InGaAsP-based two-dimensional photonic crystal light emitting structures are fabricated by employing wafer fusion and characterized optically. The structure does not contain defect regions and the whole area of the photonic crystal is used for light generation and extraction. The effect of nonradiative recombination is studied as a function of pump power. The relative contribution of surface recombination can be as low as 10% as pump power increases since carrier recombination is dominated by Auger recombination. In spite of the large surface-to-volume ratio of the photonic crystal pattern, over four-fold enhancement of photoluminescence extraction efficiency is observed.
Efficient ab initio sampling methods in rate constant calculations for proton-transfer reactions
Authors: Iftimie Radu , Schofield Jeremy
Published: July 2002

In this article, the classical potential based importance Monte Carlo sampling method of Iftimie et al. [J. Chem. Phys. 113, 4852, (2000)] is applied to an ab initio simulation of the proton transfer tautomerization reaction of malonaldehyde in an aprotic, nonpolar solvent. It is demonstrated that ad hoc bond-energy bond-order relations derived from bond evolution theory combined with Pauling’s valence bond ideas can be used to construct a molecular mechanics guidance potential for the simulation of the proton transfer reaction which improves the statistics of the calculation by three orders of magnitude. The sampling method is extended to simulations in which quantum effects are treated using the imaginary time path-integral representation. A new algorithm based on multiple Markov chain theory is introduced by which it is possible to obtain very short integrated correlation lengths in calculations of quantum static correlation functions.
Low frequency stability of geotail plasma
Authors: Wong H. Vernon , Horton W. , Van Dam J. W. , Crabtree C.
Published: July 2002

The local flux surface stability of magnetic dipole configurations is investigated in the magnetohydrodynamic (MHD) and drift frequency regimes. Solutions of the plasma equations in the very high beta limit are discussed. A novel procedure is developed for discussing stability in terms of the frequency ratio: the orbit averaged ion drift frequency divided by the ion diamagnetic frequency. This procedure is used to examine the stability of magnetospheric flux surfaces in the neighborhood of the equatorial plane at 6–10 Earth radii (where the plasma beta is ∼5 and where the onset of plasma instabilities may be responsible for triggering magnetic storms) with the following results: (1) MHD ballooning modes are predicted to be stable unless κvxp⩽2/5 where xp is the plasma pressure gradient scale length and κv the vacuum field line curvature at the equatorial plane; (2) drift modes may also be unstable unless η∼2/3, where η is the density gradient scale length divided by the temperature gradient scale length.
Ferromagnetic resonance study of Fe superparamagnetic nanoclusters on GaAs(100)
Authors: Zhai Y. , Xu Y. X. , Long J. G. , Xu Y. B. , Lu M. , Lu Z. H. , Zhai H. R. , Bland J. A. C.
Published: July 2002

The fundamental magnetism of the Fe film of 4 ML thick epitaxially grown on GaAs(100) was studied using ex situ ferromagnetic resonance (FMR) at room temperature. In parallel geometry the resonance fields were found to be strikingly different along [01̄1] (2170 Oe) and [011] (3360 Oe) direction, exhibiting a large uniaxial anisotropy with the easy and hard directions along [01̄1] and [011], respectively. For perpendicular geometry the data of FMR show an abnormally low resonance field of 5050 Oe. It implies a pronounced reduction of effective magnetization. This can be explained by a combination of the shape anisotropy of the nanoclusters with their large perpendicular anisotropy. The g factor of these nanoclusters is even smaller than the bulk value. The linewidth is also obviously anisotropic, 220 Oe in easy direction, [01̄1] and smaller by 50% in hard direction, [011].
Refrigeration by combined tunneling and thermionic emission in vacuum: Use of nanometer scale design
Authors: Hishinuma Y. , Geballe T. H. , Moyzhes B. Y. , Kenny T. W.
Published: July 2002

We consider new possibilities for cooling by vacuum tunneling. We examine a nanogeometry and find that large cooling currents can be obtained by a combination of energy selective tunneling of electrons and thermionic emission. The energy selective tunneling is a result of the special form of a potential barrier which has wider gap for low energy electrons, which results in electrons above the Fermi level being the principal tunneling component. Numerical calculations show that available material with work functions about 1.0 eV are useful for cooling. For gaps of 5–15 nm, which are well within the present state of the art, only a small external voltage (1–3 V) is required to create large currents and a useful Peltier coefficient of about 0.3, and cooling power of 100 W/cm2.
Simultaneous axial and rotational electron beam velocity measurement using a phosphor scintillator
Authors: He W. , Cooke S. J. , Cross A. W. , Phelps A. D. R.
Published: July 2002

A novel method which measures beam axial and rotational velocity for any large-orbit beam with a common guiding center is described. Time-integrated beam velocity information is obtained using a beam block and phosphor scintillator. Results using this method are compared to capacitive probe measurements and trajectory modeling for the electron beam for a cyclotron autoresonance maser oscillator.
Electronic and geometric properties of exohedral sodium- and gold-fullerenes
Authors: Palpant B. , Negishi Y. , Sanekata M. , Miyajima K. , Nagao S. , Judai K. , Rayner D. M. , Simard B. , Hackett P. A. , Nakajima A. , Kaya K.
Published: July 2002

The electronic and geometric properties of gas-phase exohedral C60NaN−, C70NaN−, and C60AuN− cluster anions are investigated. Time-of-flight mass spectrometry and photoelectron spectroscopy (PES) reveal complex-specific arrangements of the sodium and the gold atoms on the fullerene cage. The electron affinity of C60AuN clearly shows even–odd alternation with the number of Au atoms, which suggests a “dry” structure where Au atoms aggregate as a cluster on the C60. In contrast, C60NaN and C70NaN show a “wet” structure having the Na atoms packed into stable trimers on the surface. For C60NaN (N=0 to 4), PES experiments at a high photodetachment energy (5.81 eV) allow us to deduce the net charge transferred from the sodium atoms to the lowest unoccupied molecular orbital of the fullerene. For larger C60NaN, moreover, a metallic transition is shown to occur at N∼13, and analysis of the adiabatic electron affinity variations allows the identification of the first magic sizes corresponding to electronic shell closure in the sodium layer.
Donor and acceptor concentration dependence of the electron Hall mobility and the Hall scattering factor in n-type 4H– and 6H–SiC
Authors: Iwata Hisaomi , Itoh Kohei M.
Published: July 2002

Theoretical calculation of the electron Hall mobility and the Hall scattering factor in 4H– and 6H–SiC is performed based on the low-field transport model. Our mobility calculation as a function of temperature, net-doping concentration ([ND]-[NA]), and compensation ratio ([NA]/[ND]), where ND and NA are the donor (nitrogen) and acceptor concentrations, respectively, provides the theoretical values of the electron Hall mobility expected for the high quality SiC crystal. The results can be used for the evaluation of the crystalline quality of a given SiC sample. We also present the ratio of the Hall and drift mobility, i.e., the Hall scattering factor, which is needed to make a bridge between the experimentally measured Hall mobility and the theoretically calculated drift mobility using, for example, Monte Carlo simulation. Our calculations of both the electron Hall mobility and the Hall scattering factor are in very good agreement with the experimental results.
Band parameters for III–V compound semiconductors and their alloys
Authors: Vurgaftman I. , Meyer J. R. , Ram-Mohan L. R.
Published: July 2002

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.
Electron transport, ionization, and attachment coefficients in C2F4 and C2F4/Ar mixtures
Authors: Goyette A. N. , de Urquijo J. , Wang Yicheng , Christophorou L. G. , Olthoff J. K.
Published: July 2002

Measurements of electron transport, effective ionization, and attachment coefficients are reported for C2F4. In addition, measurements of the electron drift velocity and the effective ionization coefficient as a function of the density-reduced electric field E/N are reported for mixtures of C2F4 with Ar. The measured effective ionization coefficients in C2F4/Ar mixtures indicates a contribution to these coefficients from Penning ionization in dilute C2F4/Ar mixtures. The rate constant for electron attachment to C2F4 as well as the product of the longitudinal electron diffusion coefficient and the gas number density NDL in mixtures of C2F4 with Ar as functions of E/N are also reported.
Raman scattering and photoluminescence studies on Si/SiO2 superlattices
Authors: Benyoucef M. , Kuball M. , Sun J. M. , Zhong G. Z. , Fan X. W.
Published: July 2002

Photoluminescence and Raman scattering experiments were performed on Si/SiO2 superlattices grown by radio frequency magnetron sputtering on Si, quartz and glass substrates. Increasing the Si layer thickness in the Si/SiO2 superlattice gave rise to an increased photoluminescence signal and a Raman signature for nanocrystalline Si. Annealing the superlattice at 1000 °C in nitrogen atmosphere also resulted in a significantly increased photoluminescence intensity that correlated with the formation of nanocrystalline Si in the Si/SiO2 superlattice. Relationships between the emergence of nanocrystalline Si and changes in the photoluminescence properties of Si/SiO2 superlattices are discussed.
Crystal-field splitting of Pr3+ (4f 2) energy levels in GaN
Authors: Gruber John B. , Zandi Bahram , Lozykowski H. J. , Jadwisienczak W. M. , Brown I.
Published: July 2002

We have calculated the crystal-field splitting of the energy levels of Pr3+ in GaN and have compared these results to an analysis reported recently of the photoluminescence and the cathodoluminescence spectra of Pr3+ implanted in GaN by metal organic chemical vapor deposition on sapphire substrates. The lattice location of Pr in GaN determined recently by the emission channeling technique, provides direct evidence that substitutional Ga sites are thermally stable lattice positions for Pr. The lattice-sum calculations with Pr occupying Ga sites include effective ionic charges, multipole polarizabilities, and structural information also available in the literature. From the calculations, we conclude that the majority of the reported emission spectra is associated with Pr3+ ions in a common site with transitions from excited P30 and P31 states to crystal-field split multiplets, H34 (the ground state), J3J, and G14.
Luminescence lifetimes of single molecules in disordered media
Authors: Donley Elizabeth A. , Plakhotnik Taras
Published: July 2002

Linewidth measurements for single terrylene molecules in polyethylene at a temperature of 30 mK indicate that there is a distribution of lifetimes for the terrylene molecules with a relative standard deviation of ∼20%. An analysis of the linewidth–line area correlation shows that the variations arise from approximately equal radiative and nonradiative contributions. A simple model suggests that the distribution of radiative lifetimes in disordered media is a general effect caused by the same interactions responsible for inhomogeneous broadening. In addition to the transition frequency, the luminescence lifetime of a probe molecule can be used to study the nano-environment of the probe.
Interaction of an external rotating magnetic field with the tearing mode in a plasma surrounded by a resistive wall
Authors: Guo S. C. , Chu M. S.
Published: July 2002

The nonlinear dynamics of a tearing mode interacting with an externally applied rotating field and a resistive wall is studied. A pair of coupled equations describing the evolution of the amplitude and frequency of a single tearing mode is derived and used in this study. The equations are valid for both tokamaks and reversed field pinches (RFP). Numerical analysis is applied on the RFP configuration. Bifurcated stationary states of the tearing mode are found. Transition between these stationary states is studied by time dependent integration. This investigation shows that the dynamics of the tearing mode is substantially affected by the external applied field. For example, a tearing mode locked to the resistive wall can be unlocked to rotate with the external field; the required amplitude and frequency of the external field are presented. Finally, the possibility of utilizing the external resonant magnetic field to enhance the amplitude of an unlocked single helicity state in the RFP is discussed.
Effects of interface roughness and phonon scattering on intersubband absorption linewidth in a GaAs quantum well
Authors: Unuma Takeya , Takahashi Teruyuki , Noda Takeshi , Yoshita Masahiro , Sakaki Hiroyuki , Baba Motoyoshi , Akiyama Hidefumi
Published: July 2002

We experimentally and theoretically study the effects of interface roughness and phonon scattering on intersubband absorption linewidth in a modulation-doped GaAs/AlAs quantum well. Quantitative comparisons between experimental results and theoretical calculations make it clear that interface roughness scattering is the dominant scattering mechanism for absorption linewidth in the temperature range below 300 K. Even at room temperature, phonon scattering processes contribute little to linewidth, while polar-optical phonon scattering limits electron mobility.
Bosonic M theory
Authors: Horowitz Gary T. , Susskind Leonard
Published: July 2002

We conjecture that there exists a strong coupling limit of bosonic string theory which is related to the 26 dimensional theory in the same way that 11 dimensional M theory is related to superstring theory. More precisely, we believe that bosonic string theory is the compactification on a line interval of a 27 dimensional theory whose low-energy limit contains gravity and a three-form potential. The line interval becomes infinite in the strong coupling limit, and this may provide a stable ground state of the theory. We discuss some of the consequences of this conjecture.
Collective electronic oscillator/semiempirical calculations of static nonlinear polarizabilities in conjugated molecules
Authors: Tretiak S. , Saxena A. , Martin R. L. , Bishop A. R.
Published: July 2002

The collective electronic oscillator (CEO) approach based on the time-dependent Hartree–Fock approximation is combined with INDO/S, MNDO, AM1, and PM3 semiempirical Hamiltonians. This technique is applied to compute and analyze the static nonlinear polarizabilities of a series of donor/acceptor substituted oligomers. To mimic the experimental conditions, polarizabilities in substituted molecules are calculated for the isolated complex and in a dielectric medium, wherein the solvent contributions are incorporated using the self-consistent reaction field approach. The dielectric environment significantly increases second and third order static polarizabilities and considerably improves the agreement with experimental data. We find that calculated spectroscopic observables agree well with experimental values. We conclude that the CEO/semiempirical approach is an inexpensive and numerically efficient method of computing nonlinear molecular properties.
Effect of amphiphilic block copolymers on the structure and phase behavior of oil–water-surfactant mixtures
Authors: Endo H. , Mihailescu M. , Monkenbusch M. , Allgaier J. , Gompper G. , Richter D. , Jakobs B. , Sottmann T. , Strey R. , Grillo I.
Published: July 2002

The effect of amphiphilic diblock copolymers of several molecular weights on the structure and phase behavior of ternary amphiphilic systems (water, oil, and nonionic surfactant) is investigated. Small amounts of amphiphilic block copolymer polyethyleneoxide–polyethylpropylene lead to a dramatic decrease of the amount of total surfactant needed to solubilize given equal volumes of water and oil in a bicontinuous microemulsion. Neutron scattering experiments employing a high-precision two-dimensional contrast variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane. Based on these observations, we propose a mechanism for the enhancement of swelling behavior, which is due to the variation of the membrane curvature elasticity by polymer mushrooms anchored to the interface.
Nuclear motion driven by the Renner–Teller effect as observed in the resonant Auger decay to the X̃2Π electronic ground state of N2O+
Authors: Miron C. , Simon M. , Morin P. , Nanbu S. , Kosugi N. , Sorensen S. L. , Naves de Brito A. , Piancastelli M. N. , Björneholm O. , Feifel R. , Bässler M. , Svensson S.
Published: July 2002

High-resolution Auger spectroscopy applied under resonant Auger Raman conditions is shown to be a powerful tool for characterizing complex potential energy surfaces in core-excited systems. Using the example of Nt 1s−1π*→X̃2Π resonant Auger transition in nitrous oxide we emphasize the interplay between the nuclear motion and the electronic decay. We show how the choice of excitation energy allows selection of core-excited species of different geometries. The nuclear dynamics of these species are mapped by measuring the resonant Auger decay spectra. In addition to the changes in vibrational structure observed for the resonant Auger decay spectra, a strong influence of nuclear motion on the electronic decay is revealed, inducing the so-called “dynamical Auger emission.” The experimental results are supported by ab initio quantum chemical calculations restricted to a linear geometry of the core-excited state.
Monopoles and dyons in SO(3) gauged Skyrme models
Authors: Brihaye Y. , Hartmann B. , Tchrakian D. H.
Published: July 2002

Three-dimensional SO(3) gauged Skyrme models characterized by specific potentials imposing special asymptotic values on the chiral field are considered. These models are shown to support finite energy solutions with nonvanishing magnetic and electrix flux, whose energies are bounded from below by two distinct charges—the magnetic (monopole) charge and a noninteger version of the Baryon charge. Unit magnetic charge solutions are constructed numerically and their properties characterized by the chosen asymptotics and the Skyrme coupling are studied. For a particular value of the chosen asymptotics, charge-2 axially symmetric solutions are also constructed and the attractive nature of the like-monopoles of this system are exhibited. As an indication toward the possible existence of large clumps of monopoles, some consideration is given to axially symmetric monopoles of charges 2,3,4.
Case study of an InAs quantum dot memory: Optical storing and deletion of charge
Authors: Pettersson H. , Bȧȧth L. , Carlsson N. , Seifert W. , Samuelson L.
Published: July 2002

We have studied self-assembled InAs quantum dots embedded in an InP matrix using photocapacitance and photocurrent spectroscopy. These dots are potentially promising for memories due to the large confinement energy for holes. In this work we have realized simple quantum dot memory by placing the dots in the space–charge region of a Schottky junction. Our measurements reveal that a maximum of about one hole can be stored per dot. We also find that illumination for an extended period deletes the stored charge. We show that these limitations do not reflect the intrinsic properties of the dots, but rather the sample structure in combination with deep traps present in the sample.
Influence of surface processing and passivation on carrier concentrations and transport properties in AlGaN/GaN heterostructures
Authors: Dang X. Z. , Yu E. T. , Piner E. J. , McDermott B. T.
Published: July 2002

The influence of surface chemical treatments and of deposition of a SiO2 surface passivation layer on carrier distributions and mobility in AlxGa1−xN/GaN heterostructure field-effect-transistor epitaxial layer structures is investigated. Surface chemical treatments are found to exert little influence on carrier distribution and mobility. Deposition of a SiO2 surface passivation layer is found to induce an increase in electron concentration in the transistor channel and a decrease in mobility. These changes are largely reversed upon removal of the SiO2 layer by wet etching. These observations are quantitatively consistent with a shift in Fermi level at the AlxGa1−xN surface of approximately 1 eV upon deposition of SiO2, indicating that the AlxGa1−xN/SiO2 interface has a different, and possibly much lower, density of electronic states compared to the AlxGa1−xN free surface.
Electrospinning and electrically forced jets. II. Applications
Authors: Hohman Moses M. , Shin Michael , Rutledge Gregory , Brenner Michael P.
Published: July 2002

Electrospinning is a process in which solid fibers are produced from a polymeric fluid stream (solution or melt) delivered through a millimeter-scale nozzle. This article uses the stability theory described in the previous article to develop a quantitative method for predicting when electrospinning occurs. First a method for calculating the shape and charge density of a steady jet as it thins from the nozzle is presented and is shown to capture quantitative features of the experiments. Then, this information is combined with the stability analysis to predict scaling laws for the jet behavior and to produce operating diagrams for when electrospinning occurs, both as a function of experimental parameters. Predictions for how the regime of electrospinning changes as a function of the fluid conductivity and viscosity are presented.
Hot-hole lasers in III–V semiconductors
Authors: Kinsler P. , Wenckebach W. Th.
Published: July 2002

Following the success of p-Ge hot-hole lasers, there is potential for using other semiconductor materials, notably III–V materials such as GaAs and InSb. Previous analysis had suggested that a large effective mass ratio between the heavy and light holes is advantageous, which implies that InSb would make an excellent hot-hole laser. Using our Monte Carlo simulation of both GaAs and InSb hot-hole lasers in combination with a rate equation model, we see that previously accepted criteria used to predict performance are not always reliable, and we suggest suitable alternatives. The simulation results include gain and gain bandwidth as a function of field strength and laser frequency, and alternative field orientations and photon polarizations are considered. Comparisons are made with bulk p-Ge systems. The optimum conditions predicted by our simulation could then be used in the design of quantum-well hot-hole lasers.
Benchmark calculations of electron affinities of the alkali atoms sodium to eka-francium (element 119)
Authors: Landau Arie , Eliav Ephraim , Ishikawa Yasuyuki , Kaldor Uzi
Published: July 2002

Electron affinities of the alkali atoms sodium to eka-francium are calculated by the intermediate Hamiltonian Fock-space coupled cluster approach, which allows very large P spaces. Large basis sets are used (37s32p23d18f10g7h for most atoms), and many electrons are correlated (from 10 for Na− to 52 for E119−) to account for core polarization. While the usual Fock-space method gives errors of 5%–9% for K, Rb, and Cs, the intermediate Hamiltonian results agree with all known values to 5 meV or 1%. The EA of Fr, not known experimentally, is predicted at 491±5 meV. While EAs decrease from Li to Cs, the Fr value is 20 meV higher than that of Cs, with E119 EA being much higher at 662 meV. This trend reversal is due to relativistic stabilization of s orbitals, which has been shown [Eliav et al., Phys. Rev. Lett. 74, 1079 (1995)] to give the rare gas E118 positive electron affinity.
The miniature cylindrical mirror analyzer: A new tool for surface analysis
Authors: Grzelakowski K. , Man K. L. , Altman M. S.
Published: July 2002

The design and performance of a new miniature cylindrical mirror analyzer (CMA) are presented. The CMA comprises outer and inner cylinders, an integral on-axis electron gun, and a detector system consisting of ring aperture and channeltron, all mounted on a single 2.75 in. (70 mm o.d.) Conflat flange. Entrance angle, sample-to-detector distance, and polar cone angle were chosen, in consideration of second order focusing effects, which optimized analyzer transparency and resolution. Fringe field correction at the ends of the CMA is made by means of six rings precisely separated by sapphire insulators. The electron gun is a one-lens electrostatic system equipped with an x-y deflector for beam adjustment and scanning. A CeB6 low temperature cathode operating at up to −3.0 keV delivers emission current up to 100 μA. The energy range of analyzed electrons can be varied between 0 eV and 3.0 keV. The flange mounting also incorporates a high precision z-motion drive for optimization of the working distance. The control electronics and software permit operation of the instrument in pulse and analog phase sensitive detection modes. Results obtained with this new mini CMA for a W(100) surface demonstrate an energy resolution (ΔE/E) of 0.9%, which is comparable to larger 6 in. (152 mm) flange-mounted instruments. The very small size of the mini CMA permits its use in small or crowded ultrahigh vacuum chambers or where only 2.75 in. ports are available, thereby increasing flexibility in surface analysis.
Theoretical studies of the HO+O⇔HO2⇔H+O2 reaction. II. Classical trajectory calculations on an ab initio potential for temperatures between 300 and 5000 K
Authors: Troe J. , Ushakov V. G.
Published: July 2002

A comparably simple new analytical expression of the potential energy surface for the HO+O⇔HO2⇔H+O2 reaction system is designed on the basis of previous high precision ab initio calculations along the minimum energy path of the HO2→H+O2 and HO2→HO+O dissociations. Thermal rate constants for the reaction HO+O→H+O2 are determined by extensive classical trajectory calculations. The results depend on the policy to solve the zeropoint energy problem. We show that, with the chosen policy, there are nearly equal amounts of statistical and nonstatistical backdissociations HO+O←HO2 following HO+O→HO2; however, backdissociations become important only at temperatures above about 500 K. Below 500 K, the reaction is completely capture-controlled. Below 300 K, classical trajectory treatments become inadequate, because quantum effects then are so important that only the quantum statistical adiabatic channel model gives reliable results. For the reaction HO+O→H+O2 and the range 300–5000 K, a rate constant of k/10−11 cm3 molecule−1 s−1=0.026(T/1000 K)1.47+1.92(1000 K/T)0.46 is obtained from the trajectory calculations. Converting experimental results for the reaction H+O2→HO+O to the reverse reaction on the basis of the revised enthalpy of formation of OH, agreement between experiment and theory within better than 20% is obtained between 300 and 5000 K.
Lagrangian statistics in uniform shear flow: Direct numerical simulation and Lagrangian stochastic models
Authors: Sawford B. L. , Yeung P. K.
Published: July 2002

Direct numerical simulation calculations of Lagrangian statistics for homogeneous turbulence in uniform shear flow are used to test the performance of two different Lagrangian stochastic models of turbulent dispersion. These two models differ in their representation of Eulerian acceleration statistics. In particular one of the models imparts an excessively large mean rotation to the trajectories in the plane of the shear, while the other is nonrotational. We show that this rotation degrades the model’s prediction of Lagrangian statistics such as the velocity correlation function and the dispersion. Compared with the predictions of the nonrotational model, the excessive rotation reduces dispersion in the shear plane by up to a factor of 2 and introduces spurious oscillations into the velocity covariance. These differences are typical of those for shear flows at equilibrium, and may be even greater for flows not at equilibrium. The Eulerian differences thus also serve as a useful indication of the performance of these models in predicting Lagrangian statistics. We also show that for the present shear flow the behavior of the Lagrangian velocity structure function for time lags between the Kolmogorov and energy-containing time scales is consistent with corresponding analyses of forced isotropic turbulence. The present results are consistent with a revised value C0≈6 for the universal constant in the inertial subrange of the Lagrangian velocity structure function. This finding suggests that the artificial forcing of the isotropic turbulence simulations does not distort estimates of C0.
Time-dependent wave packet calculation for state-to-state reaction of Cl+H2 using the reactant-product decoupling approach
Authors: Zhang Yici , Zhang Jingfeng , Zhang Haiyan , Zhang Qinggang , Zhang John Z. H.
Published: July 2002

We present in this paper the application of the reactant-product decoupling (RPD) method [T. Peng and J. Z. H. Zhang, J. Chem. Phys. 105, 6072 (1996)] in a time-dependent wave packet calculation of the state-to-state reaction of Cl+H2→HCl+H on the G3 potential energy surface. In the RPD approach, the wave function is split into two components: the reactant ψR, which comprises the reagent and interaction regions, and the product ψP, which comprises the product region. The propagation of the reactant component ψR is separated (decoupled) from that of the product component ψP through the use of absorbing potential. The propagation ψP is entirely in the product space using the product Jacobi coordinates by using a coordinate transformation on the absorbed piece of wave function. The reaction probabilities from the ground state of H2 to specific rovibrational states of the product ClH are presented in detail. All calculations are done for total angular momentum J=0 on the G3 potential energy surface.
Formation of diluted III–V nitride thin films by N ion implantation
Authors: Yu K. M. , Walukiewicz W. , Wu J. , Beeman J. W. , Ager J. W. , Haller E. E. , Shan W. , Xin H. P. , Tu C. W. , Ridgway M. C.
Published: July 2002

Diluted III–Nx–V1−x alloys were successfully synthesized by nitrogen implantation into GaAs, InP, and AlyGa1−yAs. In all three cases the fundamental band-gap energy for the ion beam synthesized III–Nx–V1−x alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grown GaNxAs1−x and InNxP1−x alloys. In GaNxAs1−x the highest value of x (fraction of “active” substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850 °C. The highest value of x achieved in InNxP1−x was higher, 0.012, and the NP was found to be stable to at least 850 °C. In addition, the N activation efficiency in implanted InNxP1−x was at least a factor of 2 higher than that in GaNxAs1−x under similar processing conditions. AlyGa1−yNxAs1−x had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1−yNxAs1−x alloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.
Spatial variation of electrical properties in lateral epitaxially overgrown GaN
Authors: Hsu J. W. P. , Matthews M. J. , Abusch-Magder D. , Kleiman R. N. , Lang D. V. , Richter S. , Gu S. L. , Kuech T. F.
Published: July 2002

Using confocal Raman and scanning probe microscopies, we show that the electrical properties of lateral epitaxial overgrown GaN films vary at the submicron scale. Wing regions, which are located directly above the SiOx stripes, contain carrier densities ∼1020 cm−3, but possess a Fermi level deep in the band gap. This cannot be explained by having a high density of free electrons in the conduction band, but is consistent with high levels of compensation and impurity band transport. In the coalescence region, stripes of different electrical properties are evident, indicating the incorporation of impurities and defects being dictated by the growth dynamics.
Growth mode transition from layer by layer to step flow during the growth of heteroepitaxial SrRuO3 on (001) SrTiO3
Authors: Choi J. , Eom C. B. , Rijnders G. , Rogalla H. , Blank D. H. A.
Published: July 2002

We have observed the growth mode transition from two-dimensional (2D) layer-by-layer to step-flow in the earliest stage growth of heteroepitaxial SrRuO3 thin films on TiO2-terminated (001) SrTiO3 substrates by in situ high pressure reflective high energy electron diffraction (RHEED) and atomic-force microscopy. There is no RHEED intensity recovery after each laser pulse in the first oscillation when the growth mode is 2D layer-by-layer. On the other hand, it is getting more pronounced in the second oscillation, and finally reaches a dynamic steady state in which the growth mode is completely changed into the step-flow mode. The origin of the growth mode transition can be attributed to a change in the mobility of adatoms and switching the surface termination layer from the substrate to the film. SrRuO3 thin films with an atomically smooth surface grown by atomic layer control can be used in oxide multilayered heterostructure devices.
Control, with a rf field, of photon emission times by a single molecule and its connection to laser-induced localization of an electron in a double well
Authors: Makarov Dmitrii E. , Metiu Horia
Published: July 2002

We simulate an experiment in which a single molecule is simultaneously exposed to light resonating with a transition and to rf radiation. We show how the rf radiation can be used to control the statistical properties of the photon emission events (e.g., the time between successive photon emissions). This process is isomorphic with laser-induced localization of an electron in a semiconductor double well.
Oblique solitons in a cold magnetized plasma
Authors: McKenzie J. F. , Doyle T. B.
Published: July 2002

A fully nonlinear theory for stationary waves, propagating obliquely to the ambient magnetic field in a cold plasma, has been developed. Soliton solutions, representing both compressions and rarefactions in the magnetic field, exist for sub-fast flow conditions and in certain cones of magnetic obliquity. The soliton is explicitly characterized, in terms of the wave speed and its obliquity, by a parameter m (the “soliton number”). Compressive (“bright”) solitons are found to have a maximum attainable compression amplitude of three, corresponding to the condition m=1. Rarefactive (“dark”) solitons attain complete rarefaction when m=4. The properties of these stationary waves are described both in terms of magnetic hodographs, and of a spatial structure equation, whose equilibrium points yield the maximum compression and rarefaction at the center of the waves. An analytic solution, in terms of elementary transcendental functions, is also presented and highlights the role played by the soliton number m in determining the speed, strength and width of the solitons.
Energy versus amplitude corrected coupled-cluster approaches. I
Authors: Li Xiangzhu , Paldus Josef
Published: July 2002

In the spirit of recently proposed renormalized CCSD(T) and CCSD(TQ) methods [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 5644 (2000), and references therein], we explore the additive, noniterative energy corrections for both the standard and reduced multireference (RMR) CCSD approaches. Our study is based on a simple asymmetric energy expression of the standard single reference (SR) coupled cluster theory and casts a new light on the RMR CCSD method and its relationship with the corresponding MR CISD and SR reference CCSD methods, thus interrelating the amplitude and energy corrected schemes. These developments are illustrated on two exactly solvable model systems, namely, on the DZP models of the H4 system and of the HF molecule. We find that appropriately projected CCSD provides an almost identical energies as does the RMR CCSD method.
Electric dipole polarizabilities of Ni12–58
Authors: Knickelbein Mark B.
Published: July 2002

The electric dipole polarizabilities of Ni12–Ni58 have been measured via a molecular beam deflection experiment. The majority of the clusters display polarizabilities α between 4 and 6 Å3 per atom, below the atomic value of 6.8 Å3 and above that predicted for ideal conducting spheres. Local extrema in α/atom are observed for certain Nin. In particular, those clusters that adopt closely packed or quasispherical structures (e.g., Ni38, Ni55) display local minima, while Ni21, Ni22, Ni25, and Ni49–54, each an icosahedron or polyicosahedron with “missing” atoms, display anomalously high values. The relationship between the polarizabilities of nickel clusters and their shapes and structures is discussed.
Kinetic stability of electrostatic plasma modes in a dipolar magnetic field
Authors: Simakov Andrei N. , Catto Peter J. , Hastie R. J.
Published: July 2002

An axially symmetric plasma immersed in a poloidal magnetic field with closed lines is considered. Low-frequency electrostatic modes are studied kinetically for an “intermediate collisionality” ordering, in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. This ordering is appropriate for the Levitated Dipole Experiment (LDX) [J. Kesner et al., 17th IAEA Fusion Energy Conference, Yokahama, Japan (IAEA, Vienna, 1999)] and some other closed field line devices. “High-frequency” magnetohydrodynamic-like and “low-frequency” entropy modes are found and stability boundaries are determined. Collisional effects are considered and the corresponding ion gyro-relaxation effects are evaluated. These effects introduce dissipation (or inverse dissipation) and are shown to modify the stability picture considerably, while leaving large stability regions in the d, η parametric space, where η is the ratio of the gradients of temperature and density and d is the ratio of the diamagnetic and magnetic drift frequencies.
Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors
Authors: Isler R. C. , Colchin R. J. , Brooks N. H. , Evans T. E. , West W. P. , Whyte D. G.
Published: July 2002

The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C2 under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discrimination of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C2 influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma.
Ac susceptibility studies of ferrimagnetic FeCr2S4 single crystals
Authors: Tsurkan V. , Hemberger J. , Klemm M. , Klimm S. , Loidl A. , Horn S. , Tidecks R.
Published: July 2002

Ac linear and nonlinear susceptibilities, χ0 and χ2, of ferrimagnetic FeCr2S4 single crystals were measured in the temperature range from 4.2 to 300 K for different driving ac and applied dc magnetic fields in the frequency range of 10−1–103 Hz. For high driving ac fields the real part of χ0 exhibits a cusp at around Tm≈60 K correlated with the onset of dc magnetization irreversibilities. The imaginary part of χ0 shows a strong increase below 100 K and nonmonotonic temperature dependence with a maximum shifted toward low temperatures with an increase in the driving field. Both real and imaginary parts of the linear susceptibility, χ0′ and χ0″, show a pronounced frequency dependence between 90 and 20 K with a maximal difference at around 60 K. Below the Curie temperature the real part of the nonlinear susceptibility, χ2, exhibits a broad negative peak which is strongly shifted towards low temperatures with an increase in the driving field. No clearly divergent behavior of χ2′ around Tm is observed. The field and temperature dependencies of χ0 and χ2 are explained by domain wall pinning. Spin-glass-like magnetic anomalies at temperatures below 60 K are attributed to changes in the domain structure and the appearance of additional pinning centers suggested to result from a structural lattice transformation.