bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface plasmon resonance method for probing interactions in nanostructures: CdS nanoparticles linked to Au and Ag substrates by self-assembled hexanedithiol and aminoethanethiol monolayers
Authors: Hutter E. , Fendler J. H. , Roy D.
Published: July 2002

Self-assembled hexanedithiol (HDT) and aminoethanethiol (AET) monolayers (SAMs), ∼0.4–0.8 nm in thickness, are used to link ∼5 nm diam CdS nanoparticles covalently and electrostatically onto Au and Ag substrates. The resulting nanostructures are probed with scanning electron microscopy (SEM) and surface plasmon resonance (SPR) measurements. The CdS nanoparticle–SAM–substrate interactions manifesting themselves in the dielectric functions of the multilayered systems, are detected in the SPR data, and are discussed in terms of a phenomenological six-layer model. The SPR response of the Ag substrate is more sensitive to neighboring interactions than the Au substrate. The SEM images show that the CdS, connected either by HDT or AET onto Ag substrates, forms crystalline structures. The interactions responsible for this crystallization are absent in samples employing Au substrates, in which case only ∼5 nm diam CdS nanoparticles are detected by SEM. The experimental results of the present article, analyzed in detail using Fresnel and Maxwell equations, demonstrate how the SPR technique can be used to characterize layered nanostructured materials.
Shifting and broadening in the fundamental band of CO highly diluted in He and Ar: A comparison with theory
Authors: Luo Caiyan , Wehr R. , Drummond J. R. , May A. D. , Thibault F. , Boissoles J. , Launay J. M. , Boulet C. , Bouanich J.-P. , Hartmann J.-M.
Published: July 2002

We present measurements of the shifts and widths of the rovibrational lines of the fundamental band of CO highly diluted in He and Ar at 296 K. The shifts are decomposed into parts odd and even in the line number, m. These are then compared with close coupled calculations carried out with the best known interaction potentials. There is general agreement between the calculated and measured values of the broadening and shifting. Furthermore, the results illustrate that the decomposition of the shifts into parts, odd and even in m, is a powerful tool for separating out the relative contributions of the isotropic and anisotropic part of the interaction to the shifts and which part needs to be corrected if there is a discrepancy. Thus, shift measurements can be added to the list of experiments that may be used to determine reliable interaction potentials. The results also show, given a potential, that close coupled calculations are accurate and could be used to confirm or establish empirical models of the temperature dependence of the broadening or shifting, etc. Such modeling is important at atmospheric physics.
Microstructural properties of (Ba, Sr)TiO3 films fabricated from BaF2/SrF2/TiO2 amorphous multilayers using the combinatorial precursor method
Authors: Takeuchi I. , Chang K. , Sharma R. P. , Bendersky L. A. , Chang H. , Xiang X.-D. , Stach E. A. , Song C.-Y.
Published: July 2002

We have investigated the microstructure of (Ba, Sr)TiO3 films fabricated from BaF2/SrF2/TiO2 amorphous multilayers. Rutherford backscattering spectroscopy and x-ray diffraction studies show that a controlled thermal treatment can interdiffuse the multilayers so as to create predominantly single-phase epitaxial (Ba, Sr)TiO3 films. A high resolution cross-sectional transmission electron microscopy investigation of the processed films shows that they consist of large epitaxial grains of (Ba, Sr)TiO3 with atomically sharp interfaces with the LaAlO3 substrates. In addition, we have identified regions where polycrystalline and transient phases exist in small pockets in the film matrix. The results here indicate that the combinatorial thin-film synthesis using precursors can produce (Ba, Sr)TiO3 films in combinatorial libraries which exhibit properties similar to those films made by conventional techniques.
Emission in a SnS2 inverted opaline photonic crystal
Authors: Romanov S. G. , Maka T. , Sotomayor Torres C. M. , Müller M. , Zentel R.
Published: July 2002

The photoluminescence of a dye embedded in the three-dimensional SnS2 inverted opal has been studied. Changes of the emission spectrum compared with the free-space dye emission was observed in the stop-band frequency range in accord with reflectance/transmission spectra of this photonic crystal. The angular-dependent component, due to the Bragg stop band, and the angular-independent component, which is, possibly, related to the minimum in the density of photon states, have been distinguished in the dye emission spectrum.
Analytic torsion of all vector bundles over an elliptic curve
Authors: Berthomieu A.
Published: July 2002

The spectrum of the Hodge–Laplace operator of all holomorphic vector bundles (with parallel curvature metrics) over a flat elliptic curve is shown to be the union of the spectra of some infinite set of (explicit) finite rank matrices. The analytic torsion is then deduced by direct computation. Another evaluation of the analytic torsion is then performed using Bismut, Gillet, and Soulé’s comparison formula for short exact sequences of vector bundles. This is a test for this method which could be useful when direct calculation is hopeless.
Viscous fingering in a magnetic fluid. II. Linear Hele–Shaw flow
Authors: Pacitto G. , Flament C. , Bacri J.-C.
Published: July 2002

Viscous fingering phenomenon in a linear channel is studied for a magnetic fluid subjected to an external magnetic field. The competition between the hydrodynamic effects and the capillary effects leads to the formation of an interface between the air and the fluid which has a finger shape. It is the so-called Saffman–Taylor instability (STI). The influence of the magnetic effects depends on the direction of the applied field: it is possible either to enhance or to reduce the destabilizing phenomena. We study the onset of the STI and compare the experimental results with the linear analysis including the magnetic contribution. In the nonlinear regime, the measurement of the width of the finger as a function of the direction and the amplitude of the magnetic field is understood using a phenomenological approach.
Structure and stability of endohedral fullerene Sc3N@C80: A Raman, infrared, and theoretical analysis
Authors: Krause M. , Kuzmany H. , Georgi P. , Dunsch L. , Vietze K. , Seifert G.
Published: July 2002

Structure and stability of endohedral fullerene Sc3N@C80 were studied by temperature-dependent Raman and infrared spectroscopy as well as by quantum-chemical [density-functional-based tight-binding] calculations. The material showed a remarkable thermal stability up to 650 K. By both theory and experiment, translational and rotational Sc3N modes were found. These modes give a direct evidence for the formation of a Sc3N–C80 bond which induces a significant reduction of the ideal Ih–C80 symmetry. From their splitting pattern a crystal structure with more than one molecule in the unit cell is proposed. According to our results: (i) a significant charge transfer from the Sc3N cluster to the C80 cage; (ii) the strength of three Sc–N bonds; (iii) the chemical bond between triscandium nitride cluster and C80 cage; and (iv) a large HOMO–LUMO gap are responsible for the high stability and abundance of Sc3N@C80.
Electrical and optical characterization of semiconducting Ru2Si3 films and single crystals
Authors: Lenssen D. , Carius R. , Mantl S. , Birdwell A. G.
Published: July 2002

Recently, Ru2Si3 has been predicted to be a direct semiconductor with a band gap of ≈0.8 eV. Since the corresponding wavelength of this potential light emitter coincides with the absolute absorption minimum of glass fibers of 1.5 μm, considerable attention has been attracted. Measurements of the temperature dependence of the electrical resistivity of silicide films on insulating substrates were carried out in van der Pauw geometry. The results were explained by assuming carrier hopping over grain boundaries. The optical absorption coefficient was measured on thin films grown on various substrates, on self-sustaining films, where the substrate was partly removed and on a single crystal by photothermal deflection spectroscopy. A direct band gap at 0.84 eV was found. The absorption coefficient is very low up to ≈1.5 eV, likely due to a low density of states, and then strongly increases at higher energies. The experimental results qualitatively confirm the predictions of the band structure calculations.
Direct heteroepitaxy of crystalline Y2O3 on Si (001) for high-k gate dielectric applications
Authors: Dimoulas A. , Travlos A. , Vellianitis G. , Boukos N. , Argyropoulos K.
Published: July 2002

This work focuses on the microstructural characteristics of Y2O3 thin films and interfaces, which is related to their suitability as high-k replacement for SiO2 gate dielectrics in future transistor devices. The films were grown directly on silicon (001) substrates by electron-beam evaporation in a molecular beam epitaxy chamber under ultrahigh vacuum conditions. At an optimum growth temperature, ∼450 °C, high crystalline quality films were obtained, albeit with a heteroepitaxial relationship Y2O3 (110)//Si (001) and Y2O3 [001]//Si 〈110〉, which favors the formation of a potentially harmful complex microstructure. The latter consists of large (submicron-sized) domains containing smaller (10–30 nm) inclusions with perpendicular crystal orientations. Despite predictions for thermodynamic stability and low O2 partial pressure in the chamber, the chemical reaction of Y2O3 with Si could not be avoided. Indeed, a nonuniform interfacial amorphous layer with thickness 5–15 Å was observed, while YSi2 was formed at a moderate growth temperature (610 °C).
Understanding singularities in Cartan’s and null surface formulation geometric structures
Authors: Forni D. M. , Iriondo M. S. , Kozameh C. N. , Parisi M. F.
Published: July 2002

In this work we establish a relationship between Cartan’s geometric approach to third-order ordinary differential equations and the three-dimensional null surface formulation. We then generalize both constructions to allow for caustics and singularities that necessarily arise in these formalisms.
Perpendicular-current exchange-biased spin valve structures with micron-size superconducting top contacts
Authors: Slater R. D. , Caballero J. A. , Loloee R. , Pratt W. P.
Published: July 2002

We describe an optical-lithography-based sample preparation technique for measuring the current-perpendicular-to-plane (CPP) magnetoresistance with micron-size current-contact areas on top of magnetic multilayer samples of millimeter in-plane size. We use Permalloy and Co91Fe9 exchange bias spin valves to show that the CPP specific magnetoresistance (area times change in resistance) is independent of the contact area size A over the range 4 μm2⩽A⩽1 mm2.
Hydrogen-exchange reactions via hot hydrogen atoms produced in the dissociation process of molecular hydrogen on Ir{111}
Authors: Moritani Kousuke , Okada Michio , Nakamura Mamiko , Kasai Toshio , Murata Yoshitada
Published: July 2002

Adsorption and reaction of hydrogen (deuterium) on the Ir{111} surface has been studied with temperature-programmed desorption and direct measurements of desorbing molecules using a quadrupole mass spectrometer at ∼100 K. H2 exposure of the D-precovered Ir{111} surface was found to induce the desorption of HD and D2 molecules. This result suggests that energetic H atoms (hot H atoms) produced in the dissociation process of incident H2 molecules react with preadsorbed D atoms and desorb as HD molecules or produce secondary energetic D atoms via energy transfer. Secondary energetic D atoms (secondary hot D atoms) also induce the associative reactions with preadsorbed D atoms and desorb as D2 molecules. We will discuss the hot-H-atom-mediated reaction based on both empirical and steady-state approximation models for interpreting the present experimental results.
A cylinder-to-sphere Fourier view factor model for azimuthal asymmetry studies in cylindrical hohlraums
Authors: Giorla J. , Poggi F. , Paillard D.
Published: July 2002

This work addresses the analytical calculation of the irradiation coming from a cylindrical surface to a spherical one. This exact solution of the x-ray transport equation allows one to connect the emitted and the received fluxes, expanded as Fourier modes, by coefficients called Fourier view factors. Such a calculation is well suited to a symmetry study in the Laser Megajoule configuration [P.-A. Holstein, M. André, M. Casanova et al., C. R. Acad. Sci. Paris 1, 693 (2000)] where a cylindrical hohlraum and a spherical capsule are irradiated. Indeed, this 60 quad laser system induces an azimuthal asymmetry of the hohlraum lighting depending on the laser focal spot size. Thus, the Fourier view factors allow one to express the modes of the capsule irradiation as functions of the elliptic spot dimensions.
Potential profiles obtained from applied dust cloud perturbations
Authors: Thomas Edward
Published: July 2002

This paper details an experimental investigation of the local potential structure within a cloud of suspended microparticles—a “dusty” or “complex” plasma—using particle image velocimetry (PIV) techniques. Applied perturbations, synchronized to the PIV measurements, are used to force a cloud of suspended microparticles to become unconfined. From the free-streaming motion of the particles during the loss of confinement and subsequent reformation of the dust cloud, an analysis of the potential is performed. Furthermore, a new method of analyzing the potential structure from the motion of free-streaming microparticles in the plasma is presented.
Role of the shear flow profile on the stability of magnetic islands
Authors: Smolyakov A. I. , Lazzaro E. , Coelho R. , Ozeki T.
Published: July 2002

Plasma flow affects the stability of a magnetic island via modification of the ion inertial current. It is shown here that certain profiles of plasma velocity with shear may provide a stabilizing influence on the magnetic island. Such profiles of the plasma flow are characterized by inite plasma circulation inside a magnetic island.
Nonlinear theory of propagation of intense laser pulses in magnetized plasma
Authors: Wadhwani Navina , Kumar Punit , Jha Pallavi
Published: July 2002

A one-dimensional nonlinear theory of propagation of intense laser pulses in cold underdense plasma is presented. The linearly polarized radiation propagates in the presence of a constant magnetic field applied perpendicular to both the electric vector and the direction of propagation. Dispersion of the incident radiation and generation of its harmonics are studied. The axial electric wakefield and potential are evaluated.
Theory of the momentum flux probability distribution function for drift wave turbulence
Authors: Kim Eun-jin , Diamond P. H.
Published: July 2002

An analytical theory of the tails of the probability distribution function (PDF) for the local Reynolds stress (R) is given for forced Hasegawa–Mima turbulence. The PDF tail is treated as a transition amplitude from an initial state, with no fluid motion, to final states with different values of R due to nonlinear coherent structures in the long time limit. With the modeling assumption that the nonlinear structure is a modon (an exact solution of a nonlinear Hasegawa–Mima equation) in space, this transition amplitude is determined by an instanton. An instanton is localized in time and can be associated with bursty and intermittent events which are thought to be responsible for PDF tails. The instanton is found via a saddle-point method applied to the PDF, represented by a path integral. It implies the PDF tail for R with the specific form exp[−cR3/2], which is a stretched, non-Gaussian exponential.
An adaptive, kink-based approach to path integral calculations
Authors: Hall Randall W.
Published: July 2002

A kink-based expression for the canonical partition function is developed using Feynman’s path integral formulation of quantum mechanics and a discrete basis set. The approach is exact for a complete set of states. The method is tested on the 3×3 Hubbard model and overcomes the sign problem seen in traditional path integral studies of fermion systems. Kinks correspond to transitions between different N-electron states, much in the same manner as occurs in configuration interaction calculations in standard ab initio methods. The different N-electron states are updated, based on which states occur frequently during a Monte Carlo simulation, giving better estimates of the true eigenstates of the Hamiltonian.
Gas temperature equation in a high-frequency argon plasma column at low pressures
Authors: Palmero A. , Cotrino J. , Barranco A. , González-Elipe A. R.
Published: July 2002

Using a collisional-radiative model and taking into account an energy balance equation in a surface-wave-produced and -sustained argon plasma, it is possible to obtain the dependence of the gas temperature on the plasma parameters. If only heat conduction and radiative losses are considered for the neutral system, as well as the interaction with the electrons, the plasma parameters that determine the gas temperature will be the elastic absorbed power per electron and the electron number density. In a first approximation the axial dependence of the neutral gas temperature can be considered lineal with the product of these two parameters.
Effect of coverage and temperature on the kinetics of nitrogen desorption from Rh(111) surfaces
Authors: Zaera Francisco , Gopinath Chinnakonda S.
Published: July 2002

The kinetics of molecular nitrogen desorption from Rh(111) single-crystal surfaces covered with atomic nitrogen were characterized by both isothermal and temperature-programmed experiments. A complex kinetic behavior was observed for this system not describable by typical Arrhenius expressions even if coverage-dependent activation energies are considered. In fact, the possibility of developing an analytical expression for those desorption rates is voided by the fact that they depend not only on surface temperature and nitrogen coverage but also on the mode of preparation of the system. Isotope labeling experiments support the idea of the formation of surface nitrogen islands and of preferential recombination and desorption at their edges. Coadsorbed oxygen, a typical by-product in NO reduction catalysis, behaves kinetically in a way similar to surface nitrogen as far as N2 desorption is concerned. The recombination of two surface nitrogen atoms is typically slower than the reaction between one nitrogen and one adsorbed NO molecule, and therefore the catalytic reduction of NO most likely occurs via the latter pathway.
Implications of the electrostatic approximation in the beam frame on the nonlinear Vlasov–Maxwell equations for intense beam propagation
Authors: Davidson Ronald C. , Lee W. Wei-li , Qin Hong , Startsev Edward
Published: July 2002

This paper develops a clear procedure for solving the nonlinear Vlasov–Maxwell equations for a one-component intense charged particle beam or finite-length charge bunch propagating through a cylindrical conducting pipe (radius r=rw=const), and confined by an applied focusing force Ffoc. In particular, the nonlinear Vlasov–Maxwell equations are Lorentz transformed to the beam frame (“primed” variables) moving with axial velocity Vb=βbc=const relative to the laboratory. In the beam frame, the particle motions are nonrelativistic for the applications of practical interest, already a major simplification. Then, in the beam frame, the electrostatic approximation (Es′=−∇′φ′, ET′≃0≃Bs′) is made, which fully incorporates beam space-charge effects, but neglects any fast electromagnetic processes with transverse polarization (e.g., light waves). The resulting Vlasov–Maxwell equations are then Lorentz transformed back to the laboratory frame, and properties of the self-generated fields and resulting nonlinear Vlasov–Maxwell equations in the laboratory frame are discussed.
Photoluminescence properties of amorphous silicon-based oxygen and hydrogen alloys
Authors: Umezu Ikurou , Yoshida Ken-ichi , Sakamoto Naomichi , Murota Takatoshi , Takashima Yoshiaki , Inada Mitsuru , Sugimura Akira
Published: July 2002

We prepared hydrogen and oxygen alloys of a-Si by the method of rf sputtering and found similarities in their photoluminescence (PL) features. Depression of PL intensity at high temperature is reduced by alloying and results in a larger PL intensity at room temperature. Nonradiative recombination processes in the alloys are discussed in terms of the temperature dependence of the PL intensity. It is concluded that band gap fluctuations induced by alloying reduce transitions to nonradiative defect centers in these systems.
Self-assembled dye-DNA network and its photoinduced electrical conductivity
Authors: Gu Jianhua , Tanaka Shinnichi , Otsuka Youichi , Tabata Hitoshi , Kawai Tomoji
Published: July 2002

DNA molecules [poly(dG-dC).poly(dG-dC)] were modified with acridine orange (AO). Direct measurement of the electrical characteristics of the AO-DNA network were performed using a conducting atomic-force microscope (AFM) with a gold coated tip, a second gold electrode being electrically contacted to the dye-DNA/mica surface. Enhancement of electrical conductivity was observed while irradiating the sample with visible light. The results indicated that excited AO obtains an electron from the G site and eventually a hole is generated.
Millimeter-wave cavity ringdown spectroscopy
Authors: Gopalsami N. , Raptis A. C. , Meier J.
Published: July 2002

Laser-based cavity ringdown techniques have demonstrated ultrahigh sensitivities for trace gas detection in the optical and infrared wavelength regions. We have investigated the applicability of the cavity ringdown technique in the millimeter wave region, which is rich in the rotational spectra of molecules. The millimeter-wave system uses a tunable Fabry–Perot cavity that is excited by a continuous-wave, phase-locked source at the W band; a fast PIN diode switch that turns off the excitation after the cavity is tuned to resonance; and a diode detector that records the resonance decay. Proof of concept has been established by measuring the ringdown times with absorbing materials in the cavity and comparing them with theoretical prediction.
Soft x-ray excited optical luminescence: Some recent applications
Authors: Hu Y. F. , Tan K. H. , Kim P. S. , Zhang P. , Naftel S. J. , Sham T. K. , Coulthard I. , Yates B. W.
Published: July 2002

X-ray excited optical luminescence (XEOL) studies of several classes of light emitting materials excited using soft x rays (photon energy ranging from 10 to 2500 eV) are presented. We show that XEOL with soft x rays (short penetration depths) is often site specific and is ideally suited for the study of light emitting thin films and devices. Several examples including porous silicon, organic light emitting diode materials, and CdS based nanostructures are used to illustrate the unique properties of XEOL and its applications in the soft x-ray energy region.
On separable Pauli equations
Authors: Zhalij Alexander
Published: July 2002

We classify (1+3)-dimensional Pauli equations for a spin-12 particle interacting with the electro-magnetic field, that are solvable by the method of separation of variables. As a result, we obtain the 11 classes of vector-potentials of the electro-magnetic field A(t,x⃗)=(A0(t,x⃗), A⃗(t,x⃗)) providing separability of the corresponding Pauli equations. It is established, in particular, that the necessary condition for the Pauli equation to be separable into second-order matrix ordinary differential equations is its equivalence to the system of two uncoupled Schrödinger equations. In addition, the magnetic field has to be independent of spatial variables. We prove that coordinate systems and the vector-potentials of the electro-magnetic field providing the separability of the corresponding Pauli equations coincide with those for the Schrödinger equations. Furthermore, an efficient algorithm for constructing all coordinate systems providing the separability of Pauli equation with a fixed vector-potential of the electro-magnetic field is developed. Finally, we describe all vector-potentials A(t,x⃗) that (a) provide the separability of Pauli equation, (b) satisfy vacuum Maxwell equations without currents, and (c) describe non-zero magnetic field.
Solution of a second order difference equation using the bilinear relations of Riemann
Authors: Legault Stéphane R. , Senior Thomas B. A.
Published: July 2002

A recently proposed technique to solve a class of second order functional difference equations arising in electromagnetic diffraction theory is further investigated by applying it to a case of intermediate complexity. The proposed approach is conceptually simple and relies on first obtaining well-defined branched solutions to a pair of associated first order difference equations. The construction of these branched expressions leads to an equation system whose solution requires relationships akin to Riemann’s bilinear relations for differentials of the first and third kinds; their derivation necessitates the application of Cauchy’s theorem on Riemann surfaces of, in this particular instance, genera one and three. Branch-free solutions of the second order difference equation are then obtained by taking appropriate linear combinations of the branched solutions of the first order equations. Analysis and computation demonstrate that the resulting expressions have the desired analytical properties and recover known solutions in the appropriate limit.
Micromagnetic modeling of low noise perpendicular media
Authors: Shukh Alexander , van Ek Johannes
Published: July 2002

The effect of magnetic anisotropy constants and inter-granular exchange coupling on properties of hcp CoCrX perpendicular media was studied by micromagnetic modeling. It was found that the second anisotropy constant K2 reduces the energy barrier, coercivity HC, saturation field HS and, as a result, promotes writeability of the media for fixed anisotropy field HK. HC inversely decreases with the increase of K2/K1 ratio. Exchange coupling modifies a domain structure of the media in a virgin state and slope of hysteresis loop by reducing the coercivity and saturation field, and marginally increasing the nucleation field. Magnetic domains were found even in the decoupled media. The minimal domain size is about 2.5⋅dG, where dG is an average grain size of the media. The domain size increases exponentially with the inter-granular exchange. The transition parameter and dc noise is reduced with increased exchange coupling. At a specific exchange coupling the dependence of the transition parameter on the exchange almost disappears, approaching a minimum value of dG/3.
First principles studies of intergrain exchange coupling
Authors: MacLaren J. M. , Willoughby S. D.
Published: July 2002

Self-consistent electronic structure calculations are used to study how exchange interactions are altered at the interface between two magnetic grains. The work focused on a systematic study of the variation of intergrain exchange in a Co1Pt5 superlattice and the influence of a rough Cr layer at the boundary between two Co grains. The choice of boundary in a Co1Pt5 superlattice was guided by high resolution transmissions electron microscopy studies that provided partial structural information. Our calculations show that the exchange coupling falls off quickly as the misorientation between the grains increases. As is found experimentally, Cr acts to decouple the intergrain exchange energy, especially for a rough interface. These calculations are aimed at developing a more realistic description of magnetic thin films that takes into account details of the microstructure and provide salient input to micromagnetic simulations.
Adding twist to anisotropic fluids
Authors: Krisch J. P. , Glass E. N.
Published: July 2002

We present a solution generating technique for anisotropic fluids which preserves specific Killing symmetries. Anisotropic matter distributions that can be used with the one parameter Ehlers–Geroch transform are discussed. Example space–times that support the appropriate anisotropic stress-energy are found and the transformation applied. The 3+1 black string solution is one of the space–times with the appropriate matter distribution. Use of the transform with a black string seed is discussed.
Effects of flow rate of hydrogen on selective growth kinetics and magnetic induction in thin-gauged 3% Si–Fe strip
Authors: Chai K. H. , Heo N. H. , Cho S. S. , Na J. G. , Lee S. R.
Published: July 2002

During final annealing, microalloyed sulfur in thin-gauged silicon steel segregates to the strip surface and on grain boundaries and thus affects the texture development. With increasing flow rate of hydrogen, the profile of magnetic induction was shifted to a shorter annealing time, and the time range of lower magnetic induction was drastically shortened. This is ascribed to the faster depletion of surface-segregated sulfur that accelerates surface-energy-induced selective growth of (110)[001] Goss grains. After final annealing for 14.4 ks, the strips showed a high magnetic induction of about 1.9 T. By controlling the surface segregation behavior of sulfur, it is possible to achieve the surface-energy-induced selective growth of grains favorable for magnetic induction in thin-gauged silicon steel.
Anisotropy of magneto-optical spectra in ultrathin Fe/Au/Fe bilayers
Authors: Gřondilová J. , Rickart M. , Mistrı́k J. , Postava K. , Višňovský Š. , Yamaguchi T. , Lopušnı́k R. , Demokritov S. O. , Hillebrands B.
Published: July 2002

Molecular beam epitaxy grown Au(5 nm)/Fe(1.1 nm)/Au(t)/Fe(1.1 nm)/Au(100 nm)/Fe(1 nm)/MgO(001) structures with t between 1 and 2.5 nm were the subject of optical and magneto-optical (MO) ellipsometry studies at photon energies between 1.5 and 5.4 eV. Both the optical ellipsometry and MO polar Kerr rotation spectra can be explained with a multilayer model based on the bulk optical and MO data for Fe and Au. However, the longitudinal MO Kerr effect spectra depart from the model prediction showing an additional well-resolved structure between 3 and 4 eV. This demonstrates a stronger effect of interfaces on the electronic properties at in-plane magnetization in ultrathin magnetic films. On a macroscopic level the effect can be accounted for by a reduced symmetry of the linear MO tensor.
Thermal annealing effect on FeCoB soft underlayer for perpendicular magnetic recording
Authors: Yu Jun , Chang Chunghee , Karns Duane , Ju Ganping , Kubota Yukiko , Eppler Walter , Brucker Charles , Weller Dieter
Published: July 2002

We study the noise performance of amorphous FeCoB soft underlayers (SULs) with radial magnetic anisotropy. 200 nm thick FeCoB films are sputter deposited and optionally postannealed for 8 s at different annealing powers. The correlation of SUL read-back noise with the magnetic and structural properties is studied using spin stand testing, in-plane magneto-optical Kerr effect measurements, magnetic force microscopy, and x-ray diffraction. The effects of annealing to achieve low read-back noise are examined. It is found that as-prepared films show large dc noise associated with stripe domains due to stress-induced perpendicular anisotropy. Thermal annealing reduces the internal stress and the films become magnetically anisotropic in the radial direction. The SUL-induced dc noise drops to the electronic noise floor. dc noise is found to decrease with an increase in annealing power until the films start to crystallize.
Analytical method for two dimensional current crowding effect in magnetic tunnel junctions
Authors: Chen Jian , Li Yun , Nowak Janusz , de-Castro Juan Fernandez
Published: July 2002

An analytical method was developed to compute the current crowding effect in two dimensions when the lead width and length are much larger than the tunnel junction radius. In a typical four-terminal geometry, current crowding gives rise to an extra lead resistance which can result in a larger measured resistance and lower tunneling magnetoresistance ratio than the intrinsic values of the magnetic tunnel junction. This extra lead resistance is approximately Rlead,4-terminal∼0.1×(Rsheet,Top+Rsheet,Bottom)×ln(lead−width/junction−radius), where Rsheet,Top/Bottom is the sheet resistance of the top/bottom lead.
Optical near-field enhancement at a metal tip probed by a single fluorophore
Authors: Kramer A. , Trabesinger W. , Hecht B. , Wild U. P.
Published: July 2002

The optical near-field in the vicinity of a metal tip is mapped using a single-molecule optical probe. We observe an enhancement of the fluorescence signal by a factor of 5.7±0.3, clearly larger than the fourfold enhancement that can arise from constructive interference if the tip acts as a simple mirror. Considering the tip apex as a nanoparticle of nonregular shape, we suggest that, in the case of gold tips, the enhancement is due to resonant plasmon excitation. Consistently, no enhancement has been observed using Pt/Ir tips.
Barkhausen noise measurements in materials with vanishing magnetoelastic anisotropies
Authors: Santi L. , Denardin J. C. , Dotto M. R. , Schelp L. F. , Sommer R. L.
Published: July 2002

In this work, Barkhausen noise measurements are shown for a series of amorphous ribbons: Metglas 2605TCA, Metglas 2705M, and Finemet materials with composition Fe73.5Cu1Nb3Si18.5B4 under different stress (σ) and annealing temperature (TA) conditions. The dynamical state of the system is characterized by the power spectra and amplitude distribution functions as well as by the Minkowski–Bouligand dimension for each set of samples. Special attention has been paid to the ranges of vanishing anisotropies: low applied stress for the Metglas samples and the nanocrystallized phase of Finemet materials.
Analysis of hybrid stepping motor using 3D equivalent magnetic circuit network method based on trapezoidal element
Authors: Kim Youn Hyun , Jin Chang Sung , Kim Sol , Chun Yon Do , Lee Ju
Published: July 2002

The permanent magnet in a hybrid stepping motor (HSM) is magnetized in the axial direction. Accordingly, 2D analysis methods such as the 2D finite element method cannot guarantee accurate analysis. In this article, the characteristics of HSM are analyzed using the 3D equivalent magnetic circuit network method (3D EMCNM). The 3D EMCNM supplements the magnetic equivalent circuit by a numerical technique using distributed magnetic circuit parameters. Formerly, the 3D EMCNM based on the hexahedron element or the fan shaped element has usually been applied for linear motor analysis or rotary machine analysis. However, the use of these elements carries a serious permeance calculation error in complex shaped machinery such as a HSM. Therefore, to overcome this weakness, a new trapezoidal element is used.
Magnetism and structure of ZnxFe3−xO4 films processed via spin-spray deposition
Authors: Taheri Mitra , Carpenter E. E. , Cestone V. , Miller M. M. , Raphael M. P. , McHenry M. E. , Harris V. G.
Published: July 2002

Zn-ferrite films, ZnxFe3−xO4 where the Zn:Fe ratio ranges from 0.36 to 0.76, were grown on glass substrates using a spin spray technique. Films are shown using scanning electron microscopy and atomic force microscopy to be dense and granular with an average grain size ∼0.3 μm. X-ray diffraction indicates that the films are a Fd3m symmetry consistent with a pure spinel ferrite phase. The films’ coercive fields have a strong positive correlation with the film roughness indicating the dominance of a physical domain wall pinning mechanism. The films are smooth and magnetically soft near the ZnFe2O4 stoichiometry. All films, including those near the ZnFe2O4 stoichiometry, display ferrimagnetic behavior with compensation temperatures well above the bulk Neel temperature of 9.5 K; this is attributed to the cation disorder measured in the Zn cation distribution.
f-sum rule for the spin conductivity in itinerant magnets
Authors: Fishman R. S. , Jarrell M.
Published: July 2002

We derive a rigorous f-sum rule for the spin conductivity D(ω), valid in the paramagnetic regime of any itinerant system with nearest-neighbor hopping, assuming only that the potential energy conserves the total spin at each site. Two such itinerant systems are the double-exchange and Hubbard models. According to the f-sum rule, the integral over D(ω) is proportional to the average, electronic kinetic energy and is inversely proportional to the static susceptibility. The elastic value D(0) can be obtained directly from the width of the quasielastic peak in neutron-scattering measurements. For infinite dimensions dynamical mean-field theory implies that D(ω) is proportional to the optical conductivity σ(ω) and that implies the f-sum rule for D(ω) reduces to the well-known optical sum rule for σ(ω). Our results place severe constraints on the appropriate model to describe the magnetoresistive manganites.
A laser-based instrument for the study of ultrafast chemical dynamics by soft x-ray-probe photoelectron spectroscopy
Authors: Nugent-Glandorf Lora , Scheer Michael , Samuels David A. , Bierbaum Veronica , Leone Stephen R.
Published: July 2002

A laser-based instrument is described for the study of femtosecond dissociation dynamics of gas phase molecules via time-resolved vacuum ultraviolet and soft x-ray photoelectron spectroscopy. Visible or UV pump pulses are generated with nonlinear crystal techniques on a Ti:sapphire laser output, while soft x-ray probe pulses are created via high-order harmonic generation of the same laser in rare gases. Here we describe the optical layout of the pump-probe system, the means for separation of the high-order harmonics in the soft x-ray probe beam, including a description of the two grating setup used to compress the high-harmonic pulses and the magnetic bottle photoelectron spectrometer used for data collection. The feasibility of using the generated high-harmonic pulses for an array of gaseous phase photoelectron spectroscopy experiments is established. These include measurements of valence shell and core-level photoelectron transitions in atoms and molecules, the tunability of the soft x-ray harmonic through Rydberg resonances, and the energy bandwidths of the harmonics. Cross correlations between the visible/UV and soft x-ray pulses, by above threshold ionization, are used to establish the pulse timing, pulse duration, and spatial overlap for ultrafast studies. The observed real time photodissociation of Br2 serves as a demonstration of the pump-probe ultrafast technique and the applicability to ultrafast time-resolved chemical dynamics.
Dielectric behavior of Co2Z hexagonal ferrites with multiple modifications
Authors: Zhang Hongguo , Li Longtu , Wang Yongli , Zhou Ji , Yue Zhenxing , Gui Zhilun
Published: July 2002

The dielectric characteristics of Co2Z hexagonal ferrites with Cu and Zn modifications are reported. Dielectric characterization experiments are performed in Z-type hexagonal ferrites having composition of Ba3Co2(1−x−y)Cu2xZn2yFe24−δO41, measuring the dielectric constant and loss tan(delta). Different dielectric behaviors are observed in the modified and pure Co2Z hexagonal ferrites, indicating that different kinds of carrier polarizations are involved in the ferrites. This conclusion is also indirectly supported by x-ray photoelectron spectroscopy experiments, where it is shown that the variation of iron ions features the different dielectric behaviors. The impact of iron deficiency and other possible mechanisms are also addressed.
A theoretical study of the vibrational spectrum of the CS2 molecule
Authors: Zúñiga José , Bastida Adolfo , Requena Alberto , Sibert Edwin L.
Published: July 2002

A theoretical study of the vibrational spectrum of the CS2 molecule is carried out. For that purpose, a new Morse-cosine potential energy function is determined by fitting to observed vibrational frequencies, using as a starting point an ab initio force field. Highly excited vibrational states for CS2 are then calculated up to 20 000 cm−1 using a DVR truncation-diagonalization method. Hyperspherical Radau coordinates, which are a set of normal curvilinear coordinates for linear symmetric triatomic molecules, are used in these calculations. The computed vibrational energy levels are shown to present an excellent agreement with the observed values up to 13 000 cm−1. Based on these calculations, some unassigned observed vibrational frequencies are identified and the assignments of others are reconsidered. Inspection is made of the vibrational wave functions computed for CS2 revealing a persistent regularity up to 13 000 cm−1. This regularity is found to be consistent with perturbation theory results for these energies. Van Vleck perturbation theory is used to derive effective Hamiltonians that contain polyad quantum numbers and that provide good agreement with the variational calculations. It is also shown that the asymmetric stretch is practically decoupled from the symmetric stretch and the bend in this range of energies. The nearest neighbor space distribution (NNSD) and the Δ3 spectral rigidity function show that the calculated vibrational spectrum of CS2 up to 20 000 cm−1 is essentially regular, in agreement with the most recent statistical analyses made of the spectroscopically observed frequencies.
An experimental and ab initio investigation of the low-frequency vibrations of coumaran
Authors: Watkins Mark J. , Belcher David E. , Cockett Martin C. R.
Published: July 2002

Coumaran (2,3-dihydrobenzofuran) has been studied using a combination of (1+1′) resonantly enhanced multiphoton ionization (REMPI) and zero electron kinetic energy (ZEKE) studies, supported by ab initio molecular orbital calculations, in order to characterize the low wave number vibrational structure of the S1 neutral excited and D0 ionic ground states. These studies focus primarily on the modifying effects of electronic excitation and ionization on the balance of forces driving the S1 and D0 equilibrium structures toward or away from planarity. The results suggest that coumaran retains a puckered structure in the S1 state, having a barrier significantly smaller than that in the electronic ground state, but is apparently pseudo-planar or weakly puckered in the cation ground state. In each state the drive towards or away from planarity results from a competition between decreasing bond order in the aromatic system which increases torsional interactions thereby favoring a higher barrier and an increase in bond order in the furan ring which has the opposite effect. The lack of symmetry in coumaran lifts any restrictions on which out-of-plane modes can couple, resulting in a rich combination band structure in REMPI and ZEKE spectra, principally involving the ring twisting (44) and the ring pucker (45) vibrational modes. The butterfly mode (43) on the other hand shows surprisingly little activity.
Cubic nonlinear optical response of a molecule in an inhomogeneous solvation environment: A response theory formalism
Authors: Jørgensen Solvejg , Ratner Mark A. , Mikkelsen Kurt V.
Published: July 2002

A method for determining cubic response molecular properties of heterogeneously solvated molecules is presented. The molecule is either located at the surface of a metal or solvated alongside the surface of a metal. We represent the metal as a perfect conductor and the solvent as a dielectric medium. The electronic structure of the molecular systems is described both at the uncorrelated and correlated electronic structure levels. The latter is given by the multiconfigurational self-consistent field method. From this method it is possible to calculate fourth order molecular properties such as frequency-dependent second-order hyperpolarizabilities (γ), three-photon absorptions, two-photon absorption between excited states, and frequency-dependent polarizabilities of excited states. From the frequency-dependent second-order hyperpolarizabilities one can calculate for heterogeneously solvated molecules the third harmonic generation, the static electric field-induced second harmonic generation, the static electric field induced Kerr effect. Calculations of the frequency dependent second-order hyperpolarizability tensor for heterogeneously solvated CO are presented. The calculations show that the second-order hyperpolarizability tensor elements depend strongly on the heterogeneous solvent configuration.
InAs self-assembled quantum-dot lasers grown on (100) InP
Authors: Allen C. Nı̀. , Poole P. J. , Marshall P. , Fraser J. , Raymond S. , Fafard S.
Published: July 2002

Five stacked layers of InAs quantum dots (QDs) embedded in quaternary InGaAsP are grown on (100) InP substrate to form a laser diode. The QD ensemble has a density of 1.5×1010 cm−2 and emits light at ∼1.6 μm at 77 K. Lasing wavelength and threshold current density can be shifted by changing the cavity length of the laser diode and the latter reaches a value as low as 49 A/cm2 at 77 K for a gate size of 2000 μm×150 μm. Temperature dependence of the threshold current is observed implying the presence of thermionic emission increasing with temperature.
The global minimum structure of SiC3: The controversy continues
Authors: Sattelmeyer Kurt W. , Schaefer Henry F. , Stanton John F.
Published: July 2002

The linear triplet structure of SiC3 (with terminal Si) has been investigated using coupled cluster methods, including a perturbative treatment of triple excitations, and Dunning’s correlation-consistent polarized core-valence quadrupole zeta basis set (CCSD(T)/cc-pCVQZ). Based on the demonstrated convergence with respect to correlation and the large basis set employed, this triplet isomer appears to be energetically less stable than the two ring isomers, which have either a C–C (2s) or a Si–C (3s) transannular bond, by 7.5 and 1.3 kcal /mole, respectively.
In-plane lattice constant tuning of an oxide substrate with Ba1−xSrxTiO3 and BaTiO3 buffer layers
Authors: Terai K. , Lippmaa M. , Ahmet P. , Chikyow T. , Fujii T. , Koinuma H. , Kawasaki M.
Published: July 2002

Oxide thin films are usually grown on substrates which offer the smallest mismatch with the desired structure of the film. The choice of high-quality substrates with suitable lattice constants is unfortunately very limited. Coherently grown films are therefore always under tensile or compressive in-plane strain. We report on the growth of a Ba1−xSrxTiO3/BaTiO3 bilayer buffer on a SrTiO3 substrate. Changing the Sr/Ba ratio in the Ba1−xSrxTiO3 layer can be used to select a desired in-plane lattice constant in the 3.9 to 4.0 Å range. The thinner BaTiO3 film serves as a compliant layer while the thicker Ba1−xSrxTiO3 film determines the final surface lattice constant. This is achieved by a combination of low-temperature deposition and annealing at 1350 °C. X-ray diffraction and high-resolution transmission electron microscopy were used to show that the final buffer layer surface is fully relaxed, cubic, and essentially defect free, while all lattice mismatch between the substrate and the buffer is relieved by misfit dislocations at the compliant BaTiO3/SrTiO3 interface.
Equidistant spectra of anharmonic oscillators
Authors: Dubov S. Yu. , Eleonskii V. M. , Kulagin N. E.
Published: July 2002

Some representative potentials of the anharmonic-oscillator type are constructed. Some corresponding spectra-shift operators are also constructed. These operators are a natural generalization of Fok creation and annihilation operators. The Schrödinger problem for these potentials leads to an equidistant energy spectrum for all excited states, which are separated from the ground state by an energy gap. The general properties of the dynamic system generated by spectral-shift operators of third degree are analyzed. Several examples of such anharmonic oscillators are discussed. The relationship between the eigenvectors of the Schrödinger problem and a certain type of nonclassical orthogonal polynomials is established.