bluuebunny/crossref_metadata_2025 huggingface dataset:
Trapping of Brownian particles by random spheres of different radii
Authors: Berezhkovskii Alexander M. , Makhnovskii Yurii A. , Weiss George H.
Published: July 2002

We analyze the survival of a Brownian particle moving among randomly distributed spherical traps of two different radii. All of the results known in the case of identical traps, the mean-field Smoluchowski solution, the lowest order correction of this solution, the cumulant expansion, and the long-time behavior, are generalized to the case of two types of traps. Our approach is readily extended to deal with trapping spheres having more than two different radii.
Mapping the orientation of exciton transition dipoles along individual nanostructures of molecular J-aggregates
Authors: Vacha Martin , Saeki Masaaki , Isobe Osamu , Hashizume Ken-ichi , Tani Toshiro
Published: July 2002

Modulation of the polarization state of incident light in reflection microspectroscopy is used to study locally the orientations of exciton transition dipole moments of fiberlike nanostructures of J-aggregates of pseudoisocyanine dyes. The lowest exciton state assumes a wide range of directions with respect to the long axis of the fibers, from parallel to perpendicular. This behavior is correlated with the onset of polariton-like character of the local reflectance spectra. The results imply that a new structural model has to be conceived to explain the observed phenomena.
Real-time evolution of trapped charge in a SiO2 layer: An electrostatic force microscopy study
Authors: Buh G. H. , Chung H. J. , Kuk Y.
Published: July 2002

Time-dependent motion of localized electrons and holes trapped in a SiO2 layer is visualized with electrostatic force microscopy. Both negative and positive charges of up to ∼1010 e/cm2 are trapped at a SiO2–Si interface in ∼500-nm-diam area with a voltage stress between the tip and the sample. There is a higher probability for trapped charges to spread out in the plane direction than to de-trap toward the Si substrate. The dynamics is explained with diffusion and drift of the charges induced by Coulombic interaction.
Energetic particles and magnetohydrodynamic activity in the Swarthmore Spheromak Experiment
Authors: Qin G. , Lukin V. S. , Cothran C. D. , Brown M. R. , Matthaeus W. H.
Published: July 2002

Results from the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] indicate that formation and partial merging of two spheromak plasmas can be described well by a magnetohydrodynamic (MHD) picture in which there is substantial evolution towards force free states within each vessel, while reconnection activity, also described reasonably well by MHD, occurs in the region of interaction. MHD simulations [V. S. Lukin et al., Phys. Plasmas 8, 1600 (2001)] support and provide further detail to this interpretation. In the present study, test particle equations are integrated using MHD data from SSX simulations to further understand the energetic particle fluxes that are observed experimentally. The test particle simulation is run with dimensionless parameters similar to the experiment, and particles are permitted to escape when they encounter the simulated SSX boundaries. MHD activity related to reconnection is responsible for accelerating charged particles. The process includes two phases—a strong but short duration direct acceleration in the quasi-steady reconnection electric field, and a weaker longer lived stochastic component associated with turbulence.
The energy distribution, angular distribution, and alignment of the O(1D2) fragment from the photodissociation of ozone between 235 and 305 nm
Authors: Dylewski Scott M. , Geiser Joseph D. , Houston Paul L.
Published: July 2002

Resonance-enhanced multiphoton ionization and time-of-flight product imaging have been used to study the O3(X̃ 1A1)+hν→O(1D2)+O2(1Δg) channel of the UV photodissociation of ozone at 235, 245, 255, 265, 275, 285, 298, and 305 nm. At all wavelengths, the vibrational populations, the spatial anisotropy parameter β, and the O(1D2)|mj| populations were determined. The corresponding vibrational populations of O2(1Δg) were peaked at v=0. The spatial anisotropy parameter was determined for each vibrational level and changed monotonically from about 1.2 at 235 nm to 1.7 at 298 nm. At all wavelengths, |mj| populations were peaked at |mj|=0. A full density matrix method was used to determine the aq(2)(p) parameters at 255 and 298 nm, where most of the signal was found to be from parallel, incoherent excitation. The data support a dissociation mechanism in which excitation occurs to a state of A′ symmetry and there is substantial bending of the ozone before dissociation.
Direct measurement of the slow α-relaxation modes of a metallic liquid near the glass transition
Authors: Wilde Gerhard
Published: July 2002

Modulated-temperature calorimetry measurements on the bulk glass-forming Pd40Ni40P20 alloy yielded the complex specific heat response of the deeply undercooled melt near the static glass transition. The imaginary contributions to the complex signal give direct access to the spectrum of slow α-relaxation modes of the undercooled liquid state that are frozen in upon vitrification. The results are discussed with respect to the kinetics of the glass transition and compared to results obtained from static equilibrium measurements.
Multicolor images acquisition by scanning near-field optical microscopy
Authors: Emonin S. , Held T. , Richard N. , Hollricher O. , Marti O.
Published: July 2002

A multicolor scanning near-field optical microscope (color-SNOM) has been developed to provide real color images of nanoscopic samples for biological and spectroscopical purposes. The sample illumination consists either of a single or a combined beam of different laser wavelengths. A common SNOM setup has been modified in a way that three photomultipliers for blue, green, and red light detection and color separating dichroic filters have been implemented. With this beam splitter device, it is possible to acquire simultaneously with the topography three color optical images on three different channels. In order to improve the signal-to-noise ratio, etched fiber tips with a high transmission intensity were used. Fluorescence experiments on latex beads labeled with two different dyes and transmission measurements on gold nanoparticles show a wavelength dependent optical contrast. The color-SNOM appears as a powerful tool for high resolution color spectroscopy.
On the classification of N-extended supersymmetric quantum mechanical systems
Authors: Pashnev A. , Toppan F.
Published: July 2002

In this paper some properties of the irreducible multiplets of representation for the N=(p,q)-extended supersymmetry in one dimension are discussed. Essentially two results are presented. At first a peculiar property of the one dimension is exhibited, namely that any multiplet containing 2d (d bosonic and d fermionic) particles in M different spin states is equivalent to a {d,d} multiplet of just two spin states (all bosons and all fermions being grouped in the same spin). Later, it is shown that the classification of all multiplets of this kind carrying an irreducible representation of the N-extended supersymmetry is in one-to-one correspondence with the classification of real-valued Clifford Γ-matrices of Weyl type. In particular, p+q is mapped into D, the space–time dimensionality, while 2d is determined to be the dimensionality of the corresponding Γ-matrices. The implications of these results to the theory of spinning particles are analyzed.
Mathematical analysis of coaxial disk cellular shear loading devices
Authors: Wendl Michael C.
Published: July 2002

Coaxial disk devices are widely used at low Reynolds numbers to simulate cellular shear loading. Here, we develop a mathematical theory for analyzing fluid behavior in these instruments. It improves upon classical results by accounting for both unsteady dynamics and wall drag effects. All previous models are shown to be special cases of the present one. Most devices utilize a low aspect ratio, for which we find wall effects to be limited to small regions near the periphery. In these cases, classical theory yields acceptable precision over most of the domain. Investigators commonly simulate pulsatile effects using low-frequency sinusoidal forcing. Results indicate that fluid motion remains essentially harmonic, permitting the exact solution to be approximated by a simple separable expression. This approximation should be useful in analyzing specific configurations. A wavelike flow mode conjectured to exist at high Strouhal numbers is also discussed.
The influence of molecular shape on chemical reaction thermodynamics
Authors: Ben-Amotz Dor , Omelyan Igor P.
Published: July 2002

Hard body fluid theoretical and computer simulation results are combined to predict the influence of both solute and solvent shape on the excess free energy, entropy, and enthalpy of model chemical reactions. The reactions studied include model dissociation, isomerization and association processes carried out in hard body fluids composed of either spherical atoms or diatomic (homonuclear dumbbell) molecules. The effects of molecular shape on the solvent excess chemical reaction thermodynamic functions are compared with both bonded-hard-sphere (BHS) predictions and predictions obtained by approximating the solvent and solute molecules as spheres of appropriately defined effective hard sphere diameters. The results suggest that solvent composed of nonspherical hard body molecules may be accurately represented by a hard sphere fluid of the same pressure, and a nonspherical solute may be represented as a sphere whose effective hard sphere diameter depends on the magnitude and surface-area-to-volume ratio of the corresponding solute–solvent excluded volume, as prescribed by the excluded volume anisotropy (EVA) model. Furthermore, general hard body fluid thermodynamic expressions are combined with simulation results to quantify local (solvation shell) and nonlocal (macroscopic) contributions to excess reaction thermodynamic functions, and the results are compared with estimates of cohesive (and internal partition function) contributions to chemical reactions.
Ab initio study of spectroscopic and radiative characteristics of ion-pair states of the Cl2 molecule
Authors: Kokh D. B. , Alekseyev A. B. , Buenker R. J.
Published: July 2002

Electronic structure and radiative characteristics of low-lying ion-pair states of Cl2 converging to the Cl+(3P, 1D)+Cl−(1S) limits are studied. Ab initio calculations of potential energy curves for the valence and ion-pair states and dipole moments for transitions between them are carried out employing the multireference single- and double-excitation configuration interaction (MRD-CI) method, including spin–orbit coupling. It is shown that the lowest two pairs of the Ω=0u+, 1u ion-pair states arise from an avoided crossing between the Σu−3 and Πu3 parent Λ−S states, which leads to notably anharmonic shapes of the corresponding potential curves and their mixed Λ−S nature. This causes significant radial coupling, resulting in the strongly perturbed character of the 0u+ and 1u states observed experimentally. In contrast, their gerade counterparts run parallel to one another and exhibit much less perturbation. Spectroscopic properties of the computed adiabatic curves are in very good agreement with the available experimental data. Dipole moments have been calculated for parallel ion-pair–valence state transitions and radiative lifetimes have been obtained for the adiabatic ion-pair states. A reanalysis of the experimental bound–free emission spectra from the D0u+(3P2) state [N. K. Bibinov et al., Chem. Phys. 254, 89 (2000)] is given.
Infrared and visible luminescence properties of Er3+ and Yb3+ ions codoped Ca3Al2Ge3O12 glass under 978 nm diode laser excitation
Authors: Lihui Huang , Xingren Liu , Wu Xu , Baojiu Chen , Jiuling Lin
Published: July 2002

Er 3+ and Yb3+ ions codoped calcium aluminum germanate glass has been synthesized by solid-state reaction. An intense infrared emission at 1534 nm, which corresponds to the minimum losses of silica based fibers used in optical communications, and visible emissions at 416, 490, 525, 548, and 660 nm, corresponding to the I13/24→I15/24, H9/22→I15/24, F7/24→I15/24, H11/22→I15/24, S3/24→I15/24, and F9/24→I15/24 transitions of Er3+ ions, respectively, were simultaneously observed in this glass under the excitation of a 978 nm diode laser at room temperature. These emissions are mainly attributed to energy transfer from Yb3+ ions to Er3+ ions. The up-conversion processes involve a sequential two-photon absorption for the red (660 nm), the green emissions (525 and 548 nm) and the blue emission (490 nm), and a sequential three-photon absorption for the violet-bluish emission (416 nm). The up-conversion fluorescence of Ca3Al2Ge3O12:Er,Yb glass can be used to detect 980 nm infrared laser light.
Conjecture of the lifetime of delocalized electrons in liquid helium
Authors: Schmidt Werner F. , Illenberger Eugen , Khrapak Alexey G. , Sakai Yosuke
Published: July 2002

From an analysis of data on the drift velocity of electron bubbles in He(l) as a function of the electric field strength we deduce a lifetime for delocalized electrons of approximately 5 ns at 72 kV/cm.
Overview of insertion device controls at the Advanced Photon Source
Authors: Ramanathan Mohan , Smith Martin , Grimmer John , Merritt Michael
Published: July 2002

The Advanced Photon Source (APS) is a third-generation synchrotron with major emphasis on insertion device (ID) sources. Currently, there are 25 sectors instrumented out of a possible 35 ID sources. Most of the insertion devices are undulators. Beamlines have been using the ID radiation at the APS for more than five years. The control system of choice at the APS is the experimental physics and industrial control system (EPICS) (http://www.aps.anl.gov/epics). Based on operational experience, the ID control system has been completely revamped. During user operations, the beamline user has complete control of the insertion device. Various interfaces, from RS-232 to EPICS channel access, have been provided for the users to control the IDs. The control system software has been designed to accommodate scanning of the insertion device synchronized to each user’s beamline monochromator. The users have the option of operating the device in a tapered mode. The control software allows the users to control the undulators in energy space from the fundamental to the seventh harmonic. The design philosophy of the insertion device control system will be discussed. The implementation and operational experience will be presented in detail.
VME insertion device control at the Advanced Photon Source
Authors: Smith M. , Ramanathan M. , Grimmer J. , Merritt M.
Published: July 2002

The Advanced Photon Source (APS) currently has 29 insertion devices (IDs) installed and operating. The need to remotely diagnose and correct problems has become increasingly important. This has been accomplished through the development of a new control system with greatly enhanced input/output (I/O) capabilities specifically targeted to this control task. The system features a custom VME control card and three rack-mounted interface chassis for ID control, encoder interface, and motor drive shutdown. The card provides device interlocks, limit switch logic, motor axis selection, digital I/O, and status feedback. This VME insertion device control was designed to operate with an eight-axis intelligent motor controller and a stepper-motor drive that accepts step and direction inputs. The front panel of the card has two connectors for all of the control signals for the stepper-motor drives. There is a third connector for the ID limit switch inputs and the emergency stop circuit, and a fourth connector provides 23 bits of digital outputs and 16 bits of digital inputs. Light-emitting diodes indicate which motions are inhibited by the limit switch logic. An experimental physics industrial control system (EPICS) (http://www.APS.ANL-GOV/EPICS) device driver was developed to access all the registers on the VME control card. Using standard EPICS records, the insertion device status can be viewed remotely. This minimizes downtime for APS ID beamline users by allowing faster resolution of any problems preventing a user from operating the insertion device. This new insertion device control has been in use at the APS since July of 1999. The design features of the control system and rationale for them will be presented, along with our experience in building, testing, installing, and operating the control system.
Thermally assisted formation of silicon islands on a silicon-on-insulator substrate
Authors: Legrand B. , Agache V. , Mélin T. , Nys J. P. , Senez V. , Stiévenard D.
Published: July 2002

We report the self-formation of nanometer-size silicon islands on a silicon-on-insulator (SOI) substrate that is associated with simple thermal treatment in the range of 500–900 °C. We study the island formation process versus the temperature of the thermal annealing, the thickness of the top silicon layer, and the presence of a native oxide on this top layer. The island size distribution is also studied. To follow the chemical evolution of the top layer, we used in situ Auger electron spectroscopy in an ultrahigh vacuum chamber. The island morphology is studied using ex situ atomic force microscopy (AFM). The formation temperature increases with the thickness of the top silicon layer and can be explained by thermal stress induced at the Si/SiO2 interface. From a technological point of view, this study shows the limitation of a SOI substrate with a thin silicon top layer under thermal treatment. On the other hand, it opens up an easy way in which to build silicon dots on an insulator. Finally, we present preliminary data that show the possibility of charging these nanocrystallites with an AFM tip.
Determination of performance on tunnel conduction through molecular wire using a conductive atomic force microscope
Authors: Sakaguchi Hiroshi , Hirai Atsushi , Iwata Futoshi , Sasaki Akira , Nagamura Toshihiko , Kawata Etsuya , Nakabayashi Seiichiro
Published: July 2002

Performance of nonresonant tunnel conduction through a self-assembled monolayer of conjugated molecules fabricated on gold (111) was determined by virtue of nanometer-scale electrical probe measurement using a conductive atomic force microscope. Electrical measurements with nanometer spatial resolution enabled mapping of tunnel current as well as efficiency of tunnel conduction through molecular wire by analyzing length dependence on current. A series of conjugated molecules with different numbers of oligothiophene rings proved to possess a high tunnel-conduction efficiency.
Line statistics: Stretching rate of passive lines in turbulence
Authors: Kida Shigeo , Goto Susumu
Published: July 2002

Passive lines in a statistically stationary isotropic incompressible turbulent flow are tracked numerically. The line length increases exponentially in time as exp [γt] with the stretching rate γ=0.17 (Kolmogorov time)−1 which is larger, by about 30%, than the value estimated before by the arithmetic mean of the contributions from many passive vector elements. The underestimation in previous studies is attributed to the negligence of nonuniform probability weight due to nonuniform line stretching. If the effects of nonuniformity are taken into account, the true stretching rate is recovered in the early stage of evolution up to several Kolmogorov times. Thereafter, however, it is overestimated owing to the continual separation of initially adjacent vector elements.
Spherical grating monochromator with interferometer control and in-vacuum reference
Authors: Holly D. J. , Mason W. P. , Sailor T. , Smith R. E. , Wahl D.
Published: July 2002

Physical Science Laboratory’s new generation of spherical grating monochromators incorporates a laser interferometer to control scan angle and an in-vacuum absolute angle reference, as well as other improvements. The design accommodates up to six gratings which can be moved axially (under motor control, with encoder position readback) at any scan angle. The gratings are cooled by means of spring-loaded clamps which conduct heat to a water-cooled plate. The instruments feature hollow roller bearings on the scan axis to minimize bearing runout, and a pseudosine-bar drive for precise control of grating angle. The interferometer angle-measuring optics are mounted inside the vacuum chamber and measure the angle between the grating scan axis and the instrument’s granite base. The laser interferometer measures the grating angle with a resolution of approximately 0.02 arcsec over the entire scan range of 40°. To provide a reference for the interferometer angle measurement, we have built an in-vacuum optical reference which uses custom chrome-on-glass reticles mounted inside the vacuum chamber. Collimated light from a source outside the vacuum passes through the reticles to yield quadrature signals which precisely define an absolute reference angle for the interferometer. Repeatability of the grating angle is within a range of ±0.05 arcsec. Two of these instruments are in operation at SRRC (Taiwan) and a third instrument has been delivered to NSLS (Brookhaven).
Status of the Center for Advanced Microstructures and Devices (CAMD)-2001
Authors: Morikawa E. , Scott J. D. , Goettert J. , Aigeldinger G. , Kumar, Ch. S. S. R. , Craft B. C. , Sprunger P. T. , Tittsworth R. C. , Hormes F. J.
Published: July 2002

The current status of the Louisiana State University Center for Advanced Microstructures and Devices electron storage ring, beamlines, and the scientific program are described.
Chemical state imaging of iron in nerve cells from a patient with Parkinsonism-dementia complex
Authors: Ide-Ektessabi Ari , Fujisawa Shigeyoshi , Yoshida Sohei
Published: July 2002

X-ray fluorescence spectroscopy and Fe K-edge x-ray absorption near-edge structure spectroscopy were performed on postmortem human tissues containing nerve cells in order to investigate distributions and chemical states of iron. Specimens used in this study were obtained from the substantia nigra of a patient with Parkinsonism-dementia complex (PDC) of Guam and a control subject. Iron concentration was observed in the neuromelanin granules and in one of the glial cells surrounding the neuromelanin granules of the PDC patient. Iron was also detected in melanized neurons of the control subject. Chemical state imaging which separates Fe2+ and Fe3+ in iron compounds showed that the glial cell of the PDC patient has a higher concentration of Fe3+. Iron contained in the neuromelanin granules of the PDC patient was mixed states of Fe2+ and Fe3+.
Rabi oscillations in the dissociative continuum: Rotation and alignment effects
Authors: Granucci Giovanni , Magnier Sylvie , Persico Maurizio
Published: July 2002

We have simulated a set of experiments in which Rabi oscillations are induced in bound-free and free-free transitions of a diatomic molecule. Dissociative vibrational states belonging to different electronic terms are involved. We show analytically and confirm computationally that a simple relationship exists between the one-dimensional dynamics of a molecule with fixed orientation with respect to the polarization of the radiation field and the three-dimensional dynamics of a rotating system. It is demonstrated that sufficiently short laser pulses can induce oscillations in the probabilities of two coupled electronic states, and in the yields of the respective dissociation products, as functions of the radiation intensity. As a result of molecular rotation the oscillations are damped but not washed out. The initial thermal distribution on several rotational levels has a negligible effect on the photodissociation yields and other experimentally relevant quantities. Since the molecule undergoes a strong alignment along the polarization axis of the laser field, the ejection of atoms and ions is anisotropic. We have chosen the well known diatomic ion Na2+ as a convenient example.
Blistering of H-implanted GaN
Authors: Kucheyev S. O. , Williams J. S. , Jagadish C. , Zou J. , Li G.
Published: July 2002

Mechanisms of blistering of wurtzite GaN films implanted with H ions are studied. In particular, we report on the influence of the following parameters on the blistering process: (i) ion energy (from 20 to 150 keV), (ii) ion dose (up to 1.2×1018 cm−2), (iii) implantation temperature (from −196 to 250 °C), and (iv) annealing temperature (up to 900 °C). Results show that both the onset of blistering and blistering surface patterns strongly depend on implant conditions. This study may have significant technological implications for ion slicing and “etching” of GaN using high-dose implantation with H ions.
Elementary models with probability distribution function intermittency for passive scalars with a mean gradient
Authors: Bourlioux A. , Majda A. J.
Published: July 2002

The single-point probability distribution function (PDF) for a passive scalar with an imposed mean gradient is studied here. Elementary models are introduced involving advection diffusion of a passive scalar by a velocity field consisting of a deterministic or random shear flow with a transverse time-periodic transverse sweep. Despite the simplicity of these models, the PDFs exhibit scalar intermittency, i.e., a transition from a Gaussian PDF to a broader than Gaussian PDF with large variance as the Péclet number increases with a universal self-similar shape that is determined analytically by explicit formulas. The intermittent PDFs resemble those that have been found recently in numerical simulations of much more complex models. The examples presented here unambiguously demonstrate that neither velocity fields inducing chaotic particle trajectories with positive Lyapunov exponents nor strongly turbulent velocity fields are needed to produce scalar intermittency with an imposed mean gradient. The passive scalar PDFs in these models are given through exact solutions that are processed in a transparent fashion via elementary stationary phase asymptotics and numerical quadrature of one-dimensional formulas.
Investigation of the mechanism of current density increase in volume sources of hydrogen negative ions at cesium adding
Authors: Goretsky V. P. , Ryabtsev A. V. , Soloshenko I. A. , Tarasenko A. F. , Shchedrin A. I.
Published: July 2002

In the present article the influence of adding cesium into the volume and on the surface of an ion source on its emission characteristics is studied both theoretically and experimentally. It is shown that cesium in the volume at conditions of a real ion source brings in a significant contribution to kinetic processes, but weakly influences the current of H− ions extracted from the source. It is shown both theoretically and experimentally that an observed increase of the current of H− ions with cesium added is due to the conversion of fast particles at the anode surface.
Dielectric and optical properties of BaTiO3/SrTiO3 and BaTiO3/BaZrO3 superlattices
Authors: Tsurumi Takaaki , Ichikawa Tomoyoshi , Harigai Terukiyo , Kakemoto Hirofumi , Wada Satoshi
Published: July 2002

BaTiO 3  (BTO)/SrTiO3 (STO), and BaTiO3/BaZrO3 (BZO) artificial superlattices were fabricated by the molecular beam epitaxy process and their dielectric properties and refractive indices were measured. Superlattices formed on Nb-doped STO substrates showed large leakage currents in comparison with those on pure STO substrates. This indicated that Nb-doped substrates were not suitable for bottom electrodes in dielectric measurements. Dielectric properties were therefore measured for films on pure STO substrates using planar interdigital electrodes. Superlattice films were so thin (32 nm) that fine planer electrodes were necessary to reduce the penetration of electric flux into the substrate. Interdigital electrodes with the interdigital width of 5 μm were formed by electron beam lithography. Dielectric permittivity of superlattices was determined from admittance data using an electromagnetic field analysis. It was found that the dielectric permittivities of [(BTO)10/(STO)10]4 and [(BTO)10/(BZO)10]4 were εr=720 000 and εr=330 000, respectively. A large Debye type dielectric dispersion was observed in the [(BTO)10/(BZO)10]4 superlattice. The refractive index of the superlattices was measured by spectroscopic ellipsometry. It was found that the refractive index of the superlattices changed with their structures and those of [(BTO)10/(STO)10]4 and [(BTO)10/(BZO)10]4 superlattices were larger than other superlattices. This indicated that the superlattice structure affected not only on the ionic polarization but also the electronic structure or chemical bonding nature of the superlattices.
Band gap and band discontinuities at crystalline Pr2O3/Si(001) heterojunctions
Authors: Osten H. J. , Liu J. P. , Müssig H. J.
Published: July 2002

We report the experimental results on the band alignment of Pr2O3 films on Si(001) as prepared by molecular beam epitaxy. Using x-ray photoelectron spectroscopy, we obtain a valence band offset at the Pr2O3/Si(001) interface of (1.1±0.2) eV. High field tunneling was used to extract the conduction band offset of (0.5–1.5) eV. Thus, the Pr2O3/Si(001) interface band alignment is symmetric, desired for applying such materials in both n- and p-type devices. The band gap of bulk Pr2O3 should be between 2.5 and 3.9 eV. Using scanning tunneling spectroscopy, we find a surface-state band gap of about 3.2 eV for monolayer coverage. In agreement with recent pseudopotential calculations, the electron masses in the oxide appear to be very large. This effect, together with the suitable band offsets lead to the unusually low leakage currents recently measured.
Rotationally resolved photoionization dynamics of hot CO fragmented from OCS
Authors: Rijs Anouk M. , Backus Ellen H. G. , de Lange Cornelis A. , Janssen Maurice H. M. , Westwood Nicholas P. C. , Wang Kwanghsi , McKoy Vincent
Published: July 2002

The photoionization dynamics of rotationally hot CO, photodissociated from OCS, have been studied using laser photoelectron spectroscopy via the intermediate B 1Σ+ Rydberg state leading to the X 2Σ+ of the ion. The photodissociation of OCS near 230 nm produces rotationally hot, but vibrationally cold CO (X 1Σ+,N″,v″=0,1) fragments along with S (1D) atoms. These high rotational levels show photoelectron spectra with a very strong ΔN=0 transition and weaker ΔN=±1, ±2, and ±3 transitions. Agreement between measured and calculated spectra is good and suggests that there is significant angular momentum coupling in the photoelectron orbital. In the ionization step not only Δv=0, but also off-diagonal, non-Franck–Condon (Δv≠0) transitions are observed. The intensities of these transitions vary strongly within the region studied and can be explained by the excitation of superexcited Rydberg states with an A 2Π core.
Dielectric properties of 1 MeV electron-irradiated polyimide
Authors: Alegaonkar P. S. , Bhoraskar V. N. , Balaya P. , Goyal P. S.
Published: July 2002

The dielectric parameters of 50-μm-thick polyimide samples irradiated in air with 1 MeV electrons and in BF3 solution with Co-60 gamma rays were studied. The dielectric constant of polyimide was found to decrease with increasing electron fluence and dose of gamma rays. At an electron fluence of ∼1015 e/cm2, the dielectric constant decreased from its virgin value of 3.15 to 2.4, measured at a frequency of ∼7 MHz. Furthermore, by irradiating polyimide samples in BF3 solution with gamma rays, boron and fluorine diffused into each polyimide sample from both sides. In these polyimide samples, the dielectric constant decreased further to ∼2.1 (7 MHz). In a plot of dielectric loss, ε″, vs log (f ), two peaks were observed over a frequency range 100 Hz–7 MHz, in virgin as well as in the electron- and gamma-ray-irradiated polyimide samples. The dielectric loss increased with increasing electron fluence or dose of gamma rays. The refractive index (632.8 nm) of polyimide decreased from the virgin value of 1.74 to 1.69, at an electron fluence of ∼1015 e/cm2. The observed decrease in the dielectric constant and the refractive index can be attributed to the induced changes in the polarization and density of the irradiated polyimide samples.
Status of the LCLS x-ray FEL program (invited)
Authors: Arthur John
Published: July 2002

The Linac Coherent Light Source (LCLS) program involves a collaboration of several U.S. National Laboratories and universities with the goal of designing and building the first fourth-generation hard x-ray source, an x-ray free-electron laser (FEL). This FEL will utilize extremely short, intense, low-emittance electron pulses created by the high-energy linear accelerator at the Stanford Linear Accelerator Center. The FEL radiation produced will feature unprecedented peak brightness, short pulse length, and spatial coherence, tunable over an energy range of 0.8–8 keV. With favorable funding, major construction will begin by 2004 and the LCLS will be operating late in 2006. The LCLS facility will include experimental stations for carrying out groundbreaking experiments in several scientific fields. Current research and development efforts are directed at experimentally studying the physics of high-gain FELs, and refining the details of the plan for the LCLS facility. The FEL experiments, at Argonne and Brookhaven National Labs (along with experiments carried out at the German laboratory DESY), have confirmed the basic physical concepts upon which LCLS is based, and have demonstrated that many of the stringent technical requirements can already be met.
Pixel array detectors for time resolved radiography (invited)
Authors: Renzi M. J. , Tate M. W. , Ercan A. , Gruner S. M. , Fontes E. , Powell C. F. , MacPhee A. G. , Narayanan S. , Wang J. , Yue Y. , Cuenca R.
Published: July 2002

Intense x-ray sources coupled with efficient, high-speed x-ray imagers are opening new possibilities of high-speed time resolved experiments. The silicon pixel array detector (PAD) is an extremely flexible technology which is currently being developed as a fast imager. We describe the architecture of the Cornell PAD, which is capable of operating with submicrosecond frame times. This 100×92 pixel prototype PAD consists of a pixelated silicon diode layer, for direct conversion of the x rays to charge carriers, and a corresponding pixellated complementary metal–oxide–semiconductor electronics layer, for processing and storage of the generated charge. Each pixel diode is solder bump bonded to its own pixel electronics consisting of a charge integration amplifier, an array of eight storage capacitors and an output amplifier. This architecture allows eight complete frames to be stored in rapid succession, with a minimum integration time of 150 ns per frame and an interframe deadtime of 600 ns. We describe the application of the PAD to capture an x-radiograph movie of the mass-density distribution of the spray plume from internal combustion engine fuel injectors.
A cryogenically cooled channel-cut crystal monochromator using a helium refrigerator and heat exchanger
Authors: Berman Lonny E. , Siddons D. Peter , Montanez Paul A. , Lenhard Anthony , Yin Zhijian
Published: July 2002

Silicon crystals at room temperature employed as x-ray monochromators on synchrotron radiation beamlines, when subjected to high-power-density loading, suffer thermal distortions which compromise their x-ray diffraction efficiency and result in a reduction of the inherent brilliance of the synchrotron beam. At cryogenic temperatures however (below 150 K), silicon crystals suffer little or no thermal distortions under high-power-density loading. The design and implementation of a channel-cut silicon crystal monochromator which is cooled to as low as 50 K, using a commercial helium refrigerator and circulation system and a custom-designed heat exchanger for the monochromator crystal, are described. Test results have been obtained on the National Synchrotron Light Source X13B in-vacuum undulator beamline as well as the higher power X25 wiggler beamline.
Amplitude scaling of asymmetry-induced transport in a non-neutral plasma trap
Authors: Eggleston D. L. , Carrillo B.
Published: July 2002

Initial experiments on asymmetry-induced transport in the Occidental non-neutral plasma trap found the radial particle flux at small radii to be proportional to φa2, where φa is the applied asymmetry amplitude. Other researchers, however, using the global expansion rate as a measure of the transport, have observed a φa1 scaling when the rigidity (the ratio of the axial bounce frequency to the azimuthal rotation frequency) is in the range of 1–10. In an effort to resolve this discrepancy, measurements have been extended to different radii and asymmetry frequencies. Although the results to date are generally in agreement with those previously reported (φa2 scaling at low asymmetry amplitudes falling off to a weaker scaling at higher amplitudes), some cases have been observed where the low amplitude scaling is closer to φa1. Both the φa2 and φa1 cases, however, have rigidities less than 10. Instead, the φa1 cases are characterized by an induced flux that is comparable in magnitude but opposite in sign to the background flux. This suggests that the mixing of applied and background asymmetries plays an important role in determining the amplitude scaling of this transport.
First measurements and observations from the new permanent magnet undulator at the SRC
Authors: Wallace D. J. , Bisognano J. J. , Bissen M. , Eisert D. , Green M. A. , Kubala T. , Rogers G. C. , Trzeciak W. S.
Published: July 2002

In December of 2000 the University of Wisconsin Synchrotron Radiation Center (SRC) installed a new, state-of-the-art undulator in long straight section 2 of the Aladdin storage ring. This undulator replaced the first Aladdin undulator, which was on loan from the Stanford Synchrotron Radiation Laboratory and had been in use since 1986 [K. Halbach et al., IEEE Trans. Nucl. Sci. NS-28, 3136 (1981); H. Winick et al., Nucl. Instrum. Methods Phys. Res. A 208, 127 (1983); M. A. Green et al., Nucl. Instrum. Methods Phys. Res. A 266, 91 (1988)]. The new undulator was designed, constructed, and tested by Danfysik (Danfysik A/S, Moellchaves 31A, DK-4040 Jyllinge, Denmark). The undulator uses NdFeB permanent magnets for the magnetic structure and is 3.52 m long with 50 periods, each of 68.3 mm. The new undulator is intended to provide high flux from 7.8 to 500 eV. To cover this wide energy range we use the first through ninth odd harmonics. The magnetic structure has been phase-corrected to better than 2° rms and should provide fidelity better than 90% through the ninth harmonic. The resulting undulator flux will support an extreme ultraviolet nano-lithography beamline, a low energy Wadsworth beam line, and a high energy VLS-PGM beam line. Some coherence experiments are also anticipated. The undulator radiation has been analyzed using an existing HTM [M. C. Hettrick, Nucl. Instrum. Methods Phys. Res. A 266, 404 (1988)] monochromator, a durable filter-pinhole detector, and computer controlled, cooled, scanning apertures. We present measurements of the undulator harmonic content, energy and spatial structure of the undulator beam, and undulator beam position stability.
The double-tailed normal-incidence-monochromator beamline at CAMD
Authors: Evans Cherice M. , Scott John D. , Morikawa Eizi
Published: July 2002

A high-resolution, high-intensity 3 m normal-incidence-monochromator beamline at the J. Bennett Johnston Sr. Center for Advanced Microstructures and Devices is described. The beamline was designed primarily for high-resolution photoelectron spectroscopy utilizing a Scienta electron analyzer, which is permanently placed as an endstation at the beamline. In order to expand utilization of the beamline, an additional beamline tail also has been designed. Optical design of the beamline and preliminary performance results are discussed.
Monolithic I-beam crystal monochromator
Authors: Bagnasco J. , Van Campen D. G. , Rabedeau T.
Published: July 2002

Curved crystal, focusing monochromators featuring cubed-root thickness profiles typically employ side-clamped cooling to reduce thermally induced overall bend deformation of the crystal. While performance is improved, residual bend deformation is often an important limiting factor in the monochromator performance. A slightly asymmetric “I-beam” crystal cross section with cubed-root flange profiles has been developed to further reduce this effect. Physical motivation, finite-element modeling evaluation, and performance characteristics of this design are discussed. Reduction of high mounting stress at the fixed end of the crystal required the soldering of an Invar support fixture to the crystal. Detailed descriptions of this process along with its performance characteristics are also presented.
Design and performance of the double crystal monochromator beamline at the Canadian Light Source
Authors: Yates B. W. , Hallin E. L.
Published: July 2002

The medium energy x-ray double crystal monochromator (DCM) is currently being designed at the Canadian Light Source (CLS). Design goals for the DCM are to provide photons between 1750–5500 eV with a resolving power better than 3000 and photon flux better than 5×1010 photons/s/0.1% bandwidth for 500 mA beam current. A set of indium antimonide crystals [InSb(111)] will be used over the energy range of 1750–3700 eV, with resolution ranging from 0.52–1.05 eV. Although InSb allows one to probe the important silicon K edge at ∼1840 eV, it has the disadvantage of poor thermal conductivity. Exposure to high heat loads from the CLS synchrotron on the first crystal (∼56.5 W of power for 2 mrad of horizontal bending magnet radiation, ∼0.54 W/mm2 power density) will cause crystal distortion and thereby intensity/resolution degradation. A second set of silicon crystals [Si(111)] are proposed for the energy range of 3700–5500 eV. Resolution ranges linearly from ∼0.41 to ∼0.70 eV over this energy range. A harmonic filter mirror has been included in the design to reject higher harmonic orders. SHADOW ray-tracing results show that the experimental focus should be 334 μm [horizontal full width at half-maximum (FWHM)]×296 μm (vertical FWHM) when the CLS is operational under 2008 conditions.
Electromagnetic wave radiation by current-driven magnons in magnetic multilayers (invited)
Authors: Tsoi M.
Published: July 2002

We report the detection of electromagnetic waves radiated by current-driven magnons in Co/Cu magnetic multilayers. The magnons were excited by means of a high current density ∼108 A/cm2 injected into the multilayer through a point contact. The point contact itself was used as a high frequency mixer to mix electromagnetic waves radiated by the current-driven magnons with externally generated microwave radiation. Here the external microwaves are used as a direct probe of the high-frequency behavior and partial phase coherence of the current-induced excitations. When the external frequency equaled the frequency of the magnons generated in the multilayer a dc voltage was found to develop across the contact. Investigation of how this voltage varies with exciting current, magnetic field, and microwave frequency provides detailed information on the spectrum of the current-driven magnons. Our observations support the feasibility of a spin-wave maser, or spin-wave amplification by stimulated emission of radiation (SWASER).
Test of ballistic spin-polarized electron transport across ferromagnet/semiconductor Schottky interfaces
Authors: Hirohata A. , Guertler C. M. , Lew W. S. , Xu Y. B. , Bland J. A. C. , Holmes S. N.
Published: July 2002

We previously reported highly efficient spin detection associated with spin filtering at single layer ferromagnet (FM)/GaAs interfaces (NiFe, Co, and Fe as the FM) using photoexcitation at room temperature, confirming that the Schottky barrier acts as a tunnel barrier. In order to consider explicitly possible background effects, e.g., magnetic circular dichroism, we therefore prepared antiferromagnetic (AF) Cr/GaAs structures as reference, using the same growth techniques as used for the FM structures. The Cr/GaAs samples showed very good Schottky characteristics and the difference in the helicity-dependent photocurrent was found to be negligible, indicating that no spin filtering occurs at the AF Cr/GaAs interfaces. These combined results conclusively show that high efficient spin detection can be achieved at room temperature.
Calculation of the magnetorefractive effect in giant magnetoresistive granular films
Authors: Kravets V. G. , Bozec D. , Matthew J. A. D. , Thompson S. M.
Published: July 2002

Calculations of the magnetorefractive (MRE) effect in giant magnetoresistive CoxAg1−x (GMR) granular films have been performed and compared with experimental data. At long wavelengths (λ>20 μm), there is a linear relationship between the GMR and MRE. As the wavelength is reduced (10<λ<20 μm), the value of ωτ↑(↓) becomes increasingly important requiring fitting of the spin dependent relaxation times. For λ<10 μm, optical constants such as εr become significant and the MRE curve becomes more complex. Spin dependence was introduced by modeling the optical conductivity using the model of Zhang and Levy. Both the calculation and experiment reveal that the MRE effect is an order of magnitude larger for s-polarized light than for p-polarized light at high angles of incidence.
On the Gauss law and global charge for quantum chromodynamics
Authors: Kijowski J. , Rudolph G.
Published: July 2002

The local Gauss law of quantum chromodynamics (QCD) on a finite lattice is investigated. It is shown that it implies a gauge invariant, additive law giving rise to a gauge invariant Z3-valued global charge in QCD. The total charge contained in a region of the lattice is equal to the flux through its boundary of a certain Z3-valued, additive quantity. Implications for continuum QCD are discussed.
Measurement of the localized iron loss in electromagnetic steel sheet by using the needle probe method
Authors: Hashimoto Y. , Enokizono M. , Mogi H.
Published: July 2002

Grain oriented silicon steel used for transformer cores has large crystal grains in comparison with nonoriented silicon steel used in rotational machines. Therefore, we need to consider the magnetic properties of each crystal grain and the influence of grain boundaries to reduce the iron loss of the grain oriented silicon steel cores. In this article, we make them clear and report the influence of the grain boundary to the local iron loss.
Observable effects and parametrized scaling limits of a model in nonrelativistic quantum electrodynamics
Authors: Hiroshima Fumio
Published: July 2002

Scaling limits of the Hamiltonian H of a system of N charged particles coupled to a quantized radiation field are considered. Ultraviolet cutoffs, λ̂1,…,λ̂N, are imposed on the radiation field and the Coulomb gauge is taken. It is the so-called Pauli–Fierz model in nonrelativistic quantum electrodynamics. We mainly consider two cases: (i) all the ultraviolet cutoffs are identical, λ̂1=⋯=λ̂N, (ii) supports of ultraviolet cutoffs have no intersection, supp λ̂i∩supp λ̂j=∅, i≠j. The Hamiltonian acts on L2(RdN)⊗F, where ℱ is a symmetric Fock space, and has the form H=Hel⊗1+B+1⊗Hquad. Here Hel denotes a particle Hamiltonian, Hquad a quadratic field operator, and B an interaction term. The scaling is introduced as H(κ)=Hel⊗1+κlB+κ21⊗Hquad, where κ is a scaling parameter and l⩽2 a parameter of the scaling. Performing a mass renormalization we consider the scaling limit of H(κ) as κ→∞ in the strong resolvent sense. Then effective Hamiltonians Heff in L2(RdN) infected with reaction of effect of the radiation field is derived. In particular (1) effective Hamiltonians with an effective potential for l=2, and (2) effective Hamiltonians with an observed mass for l=1, are obtained.