bluuebunny/crossref_metadata_2025 huggingface dataset:
Random matrix averages and the impenetrable Bose gas in Dirichlet and Neumann boundary conditions
Authors: Forrester P. J. , Frankel N. E. , Garoni T. M.
Published: August 2003

The density matrix for the impenetrable Bose gas in Dirichlet and Neumann boundary conditions can be written in terms of 〈∏l=1n|cos φ1−cos θl||cos φ2−cos θl|〉, where the average is with respect to the eigenvalue probability density function for random unitary matrices from the classical groups Sp(n) and O+(2n), respectively. In the large n limit log-gas considerations imply that the average factorizes into the product of averages of the form 〈∏l=1n|cos φ−cos θl|〉. By changing variables this average in turn is a special case of the function of t obtained by averaging ∏l=1n|t−xl|2q over the Jacobi unitary ensemble from random matrix theory. The latter task is accomplished by a duality formula from the theory of Selberg correlation integrals, and the large n asymptotic form is obtained. The corresponding large n asymptotic form of the density matrix is used, via the exact solution of a particular integral equation, to compute the asymptotic form of the low lying effective single particle states and their occupations, which are proportional to N.
Lorenz integrable system moves à la Poinsot
Authors: Nucci M. C.
Published: August 2003

A transformation is derived which takes the Lorenz integrable system into the well-known Euler equations of a torque-free rigid body about a fixed point, i.e., the famous motion à la Poinsot. The proof is based on Lie group analysis applied to two third-order ordinary differential equations admitting the same two-dimensional Lie symmetry algebra. Lie’s classification of two-dimensional symmetry algebras in the plane is used. If the same transformation is applied to the Lorenz system with any values of the parameters, then one obtains Euler equations of a rigid body about a fixed point subjected to a torsion depending on time and angular velocity. The numerical solution of this system yields a three-dimensional picture which looks like a “tornado” the cross-section of which has a butterfly-shape. Thus Lorenz’s butterfly has been transformed into a tornado.
Quantum four-body system in D dimensions
Authors: Gu Xiao-Yan , Ma Zhong-Qi , Sun Jian-Qiang
Published: August 2003

By the method of generalized spherical harmonic polynomials, the Schrödinger equation for a four-body system in D-dimensional space is reduced to the generalized radial equations where only six internal variables are involved. The problem on separating the rotational degrees of freedom from the internal ones for a quantum N-body system in D dimensions is generally discussed.
Pulsed deposition of silicate films
Authors: He W. , Solanki R. , Conley J. F. , Ono Y.
Published: August 2003

A sequential pulsed process is utilized for deposition of nonstoichiometric silicate films without employing an oxidizing agent. The metal precursors were HfCl4, AlCl3, and ZrCl4, as well as Hf(NO3)4 and the silicon source was tris(tert-butoxy)silanol. Unlike atomic layer deposition, the growth per cycle was several monolayers thick, where the enhancement in growth was due to a catalytic reaction. The bulk and electrical properties of these films are similar to those of silicon dioxide. Silicon carbide devices coated with these films show good insulating characteristics.
Mathematical description of atomic layer deposition and its application to the nucleation and growth of HfO2 gate dielectric layers
Authors: Alam M. A. , Green M. L.
Published: August 2003

Alternate gate dielectrics will be necessary for continued scaling in the microelectronics industry, and atomic layer deposition is a likely technology for growth of such films. A phenomenological mathematical model of atomic layer deposition has been developed and applied to a large body of HfO2 growth data. The model is based on classical chemical kinetics theory, and assumes that OH groups are the nucleation sites for film growth. Two differential equations, one describing the deposition rate of HfO2 per cycle, and another the creation rate of new OH groups per cycle, completely describe the atomic layer deposition process. The entire body of HfO2 growth data can be explained by the model: linear growth behavior in the presence of large initial OH concentrations such as are present on chemical oxides; the ∼17 steric hindrance factor for linear growth, based on the size of the tetrahedral HfCl4 molecule, and a combination of adsorption modes; initial parabolic growth behavior in the presence of small initial OH concentrations such as are present on hydrogen (H)-terminated Si; and the transition from nonlinear to linear growth behavior after about 80 cycles of growth on H-terminated Si. Although applied to HfO2, for which the largest body of nucleation and growth data for thin atomic layer deposited films on differently treated substrate surfaces exists, the model is completely general and can describe any atomic layer deposition process. This is a comprehensive model of the atomic layer deposition process.
Comparison of HfO2 films grown by atomic layer deposition using HfCl4 and H2O or O3 as the oxidant
Authors: Park Hong Bae , Cho Moonju , Park Jaehoo , Lee Suk Woo , Hwang Cheol Seong , Kim Jong-Pyo , Lee Jong-Ho , Lee Nae-In , Kang Ho-Kyu , Lee Jong-Cheol , Oh Se-Jung
Published: August 2003

HfO 2 gate dielectric thin-films were deposited on Si wafers using an atomic-layer deposition (ALD) technique with HfCl4 and either H2O or O3 as the precursor and oxidant, respectively. Although the ALD reactions using either H2O or O3 were successfully confirmed at a deposition temperature of 300 °C, the structural and electrical properties of the HfO2 films grown using the two oxidants were quite different. The stronger oxidation power of the O3 compared to H2O increased the oxygen concentration in the HfO2 film and the rate of interfacial SiO2 formation even at the as-deposited state. Because of the larger oxygen concentration, the decrease in the capacitance density of the film grown with O3 after rapid thermal annealing at 750 °C under N2 atmosphere was slightly larger than that of the HfO2 film grown with H2O. Apart from this weakness, all the other electrical properties, including the fixed charge density, the interface trap density, the leakage current density and the hysteresis in the capacitance–voltage plot of the film grown with O3 were superior to those of the film grown with H2O. Therefore, O3 appears to be a better oxidant for the HfO2 film growth using the ALD method.
X-ray particle image velocimetry for measuring quantitative flow information inside opaque objects
Authors: Lee Sang-Joon , Kim Guk-Bae
Published: August 2003

An x-ray particle image velocimetry (PIV) technique was developed to measure quantitative information on flows inside opaque objects. To acquire x-ray images suitable for PIV velocity field measurements, refraction-based edge enhancement was employed using detectable tracer particles with the object and detector separated by an experimentally determined optimal distance. The x-ray PIV method was applied to a flow in an opaque Teflon tube. The resulting amassed velocity field data were in reasonable agreement with theoretical predictions.
Dynamics of dust particles in a magnetized plasma sheath in a fully ionized space plasma
Authors: Baishya S. K. , Das G. C.
Published: August 2003

The dynamics of negatively charged dust particles in sheath formed in plasma similar to those observed in moons, asteroids, and other atmospheres in planetary system have been studied. The ambient conditions are based on the consideration of a static magnetic field in the dynamical system. It is assumed that the dust has been injected into the sheath by the impact of meteorites. Some charged dust particles of very small size might be drawn into the sheath by the electrostatic levitation also. The forces on the dust particles are assumed to be from the electric field in the sheath, the static magnetic field and from gravitation. It is expected that the charged dust particles would describe a slanted helix with variable pitch in the sheath. The size of the dust particles is likely to influence the progress of the ejected dust particles in the sheath. The size of the charged dust particles should determine whether they escape the sheath or fall back to the ground or form a cloud in the sheath.
Blueshifts in the ultraviolet absorption spectra of cerium oxide nanocrystallites
Authors: Tsunekawa Shin , Wang Jian-Tao , Kawazoe Yoshiyuki , Kasuya Atsuo
Published: August 2003

Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The mechanism of the absorption is a charge-transfer optical transition. The relationships among the blueshift, valence state of cerium ions, and the particle size are formulated. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.
Effect of chain length on the tunneling conductance of gold quantum dots at room temperature
Authors: Chaki Nirmalya K. , Gopakumar T. G. , Maddanimath Trupti , Aslam M. , Vijayamohanan K.
Published: August 2003

Understanding the electronic structure of nanometer-sized metal particles which bridge the gap between the molecules and bulk materials is important due to the fabrication of many nanodevices, like single-electron transistors and molecular switches. Using a simple core-shell model, here, we investigate the variation of electrostatic charging properties of metallic nanoclusters with the chain length of the passivating molecule and cluster core size. The estimation of capacitance (Cc) and charging energy (Ec) as 2πε0εrRc/(1+2r/Rc) and e2(1+2r/Rc)/4πε0εrRc, respectively, as a function of the core size as well as the intercluster spacing, reveals that longer chains (8 to 10 methylene units) limit the electron transport beyond usefulness.
Thermal exfoliation and crystallographic transformation of single-crystal metal oxides induced by He-ion implantation
Authors: Moran P. D. , Levy M.
Published: August 2003

We report on the thermal exfoliation of 7 μm thick films from 3.8 MeV He ion-implanted single-crystal 0.955 Pb(Zn1/3Nb2/3)O3–0.045 PbTiO3 [(PZN–PT) with 4.5% PT] by rapid thermal processing. Comparison with z-cut LiNbO3 shows a significantly higher exfoliation threshold temperature in PZN–PT for the same implantation conditions. Unusually large strains in the through-implanted layer are induced in the relaxor ferroelectric PZN–PT upon ion implantation leading to a crystallographic phase transformation in that material that is not observed in LiNbO3. Depth profile analysis of the refractive index shows a much larger refractive index modulation due to nuclear collisions than in LiNbO3. The higher exfoliation temperature observed for PZN–PT, despite a larger impact of the ion implantation on material structure, suggests that the electronic polarizability and elastic response of relaxor ferroelectrics near the morphotropic phase boundary have a significant impact on the crack propagation process responsible for thermally induced exfoliation.
Origin of residual stress in the formation of boron nitride film by sputtering with Ar ions
Authors: Kim Hong-Suk , Park Jong-Keuk , Baik Young-Joon , Choi In-Hoon
Published: August 2003

It is demonstrated that the compressive residual stress in turbostratic boron nitride (tBN) film is caused by the incorporation of Ar atoms between the gap of tBN layers. The stress of the film is measured in situ during sputter deposition at various substrate bias voltages. The variation of the stress with increasing film thickness follows that of an Ar concentration profile in the films along the growth direction. This result reveals that the interstitial Ar atoms induce the evolution of the compressive residual stress in the tBN film. Cross-sectional transmission electron microscopic images of the films are examined to explain the penetration behavior of Ar ions during the deposition.
Characterization of deep levels in 6H-SiC by optical-capacitance-transient spectroscopy
Authors: Nakakura Y. , Kato M. , Ichimura M. , Arai E. , Tokuda Y. , Nishino S.
Published: August 2003

An optical-capacitance-transient spectroscopy (O-CTS) method was used to characterize defects in epitaxial 6H-SiC. The O-CTS measurements enable us to estimate the optical ionization energy and the optical cross section of these defects. By the deep level transient spectroscopy (DLTS), three peaks were observed, and two of them were identified as E2 and R centers which have been previously reported. We measured the optical cross section for both the centers. By fitting the experimental data with theoretical curves for the optical cross section, we obtained optical ionization energy of 1.58 eV for the R center and 1.0 eV for the E2 center. From the DLTS measurements, the thermal activation energy of the R center is 1.30 eV and that of the E2 center is 0.43 eV. From these results and the previously reported capture energy barrier, the Franck–Condon shift, dFC is estimated to be 0.28 eV for the R center and 0.62 eV for the E2 center.
Defective states induced in CdTe and CdZnTe detectors by high and low energy neutron irradiation
Authors: Cavallini A. , Fraboni B. , Dusi W. , Zanarini M.
Published: August 2003

We present a study of the effects of high and low energy neutron irradiation on CdTe and CdZnTe high resistivity detector grade material. The evolution of the defect states under increasing irradiation fluence has been monitored by means of photoinduced current transient spectroscopy analyses. Particular attention is placed on the comparison and correlation between the results from the two materials under the two different neutron irradiation energies. The behavior of the observed deep traps associated with defect states allowed us to attribute an origin to most of them and to understand the role they play in the charge carrier collection process and in the degradation of material spectroscopic capabilities.
Magnetohydrodynamic simulation of dynamical behavior of a field-reversed configuration during magnetic mirror reflection
Authors: Kanki T. , Okada S. , Goto S.
Published: August 2003

A two-dimensional magnetohydrodynamic (MHD) simulation of the reflection dynamics of a field-reversed configuration (FRC) plasma is performed by numerically modeling a confinement region of the FRC Injection Experiment [H. Himura et al., Phys. Plasmas. 2, 191 (1995)] machine. The FRC plasma is reflected by a downstream magnetic mirror field at the end of the confinement region without severe destruction of the closed magnetic flux surfaces even when injected at supersonic velocity into the magnetic mirror region, showing the robustness of the FRC against external perturbations. By examining the details of FRC motion, it is also predicted for any translation velocities that the FRC might eventually settle down in the confinement region and approach a MHD equilibrium condition. Interestingly, it is observed that the formation of a discontinuous wave front is caused by a shock when the FRC at supersonic velocity is reflected by the magnetic mirror.
Intense electron-beam ionization physics in air
Authors: Strasburg S. , Hinshelwood D. D. , Schumer J. W. , Mosher D. , Ottinger P. F. , Fernsler R. F. , Slinker S. P.
Published: August 2003

In this paper we study, experimentally and theoretically, the interactions of an intense electron beam with an initially-neutral background gas. The Naval Research Laboratory’s Gamble II generator [J. D. Shipman, Jr., IEEE Trans. Nucl. Sci. NS-18, 243 (1971)] was used to drive an annular 900 kV, 800 kA beam, whose effects on background air in the pressure range ∼0.01 to 10 Torr were studied. Experimental diagnostics included a sophisticated two-color interferometer for time-resolved measurements of the background electron density, B-dot monitoring of the global net current, and x-ray pinhole images of the beam location. Data obtained were compared to extensive simulations using three numerical models that incorporated complex beam physics, atomic processes, and the capability for simulating strongly-disturbed gases. Good simulation agreement with net current and electron density as a function of pressure was obtained using a scaled pressure. Simulated and experimental net current fractions (at peak beam current) for the 1–10 Torr collision-dominated transport regime were on the order of 10%, while ionization fractions after the beam pulse were 20% for 10 Torr, rising to nearly 100% at the lower pressure of 0.5 Torr. More advanced model development is underway to better understand the important physics of beam–gas interactions.
Instabilities of Ar/SF6 inductive plasma discharges
Authors: Tuszewski M. , White R. R.
Published: August 2003

Relaxation oscillations are studied in three low-pressure inductive plasma discharges operated with argon and sulfur hexafluoride gas mixtures. Two distinct phenomena, downstream instabilities and source oscillations, occur in certain domains of gas pressure, radio frequency power, and electronegative gas chemistry. The downstream instabilities develop at some location well below the plasma source. They are consistent with ion two-stream instabilities, in inductively coupled plasmas (ICPs) with sufficiently long downstream regions. Source oscillations consist of large amplitude density variations within the ICP plasma. They are consistent with capacitive to inductive mode transitions, in ICPs with sufficiently large capacitive currents.
Ultrathin silicon-on-insulator vertical tunneling transistor
Authors: Zaslavsky A. , Aydin C. , Luryi S. , Cristoloveanu S. , Mariolle D. , Fraboulet D. , Deleonibus S.
Published: August 2003

We have fabricated silicon-on-insulator (SOI) transistors with an ultrathin Si channel of ∼5 nm, tunneling gate oxide of ∼1 nm, and 100 nm gate length. In addition to good transistor characteristics, these same devices exhibit additional functionality at low temperature. The drain current ID exhibits steps near the turn-on threshold voltage as a function of the backgate VBG bias on the substrate. When operated as a gate-controlled tunneling device, with source shorted to drain and IG originating from tunneling from the gate to the channel, we observe structure in the IG(VBG) due to resonant tunneling into the quantized channel subbands. In the future, as SOI device fabrication improves and the buried oxide thickness is reduced, these quantum effects will become stronger and appear at lower VBG, offering the prospect of ultralarge scale integration-compatible devices with standard transistor operation or quantum functionality depending on the electrode biasing.
Nonlinear saturation of stimulated Brillouin scattering for long time scales
Authors: Divol L. , Cohen B. I. , Williams E. A. , Langdon A. B. , Lasinski B. F.
Published: August 2003

The nonlinear saturation of stimulated Brillouin scattering (SBS) in long beryllium plasmas (500 μm) and for long time (500 ps) is studied in detail through well-diagnosed one-dimensional (1D) hybrid particle-in-cell (PIC) simulations done using BZOHAR [B. I. Cohen, B. F. Lasinski, A. B. Langdon, and E. A. Williams, Phys. Plasmas 4, 956 (1997)]. Under conditions of interest, when the linear gain associated with the SBS growth is large, it is shown that following a first phase of large and bursty SBS reflectivity, SBS is suppressed by a self-induced spatial detuning due to inhomogeneous modifications of the (locally averaged) ion distribution function. This nonlinear evolution was observed over a range of laser intensities and plasma parameters.
On the vortex dynamics in fully relativistic plasmas
Authors: Eshraghi H.
Published: August 2003

Hydrodynamical equations for fully relativistic flows at high temperatures are used to investigate the generalized vortex dynamics. Relativistic versions of the Cauchy invariant, Kelvin’s Theorem, Weber transformation, Clebsh variables, Ertel’s Theorem and the helicity are investigated. Like the nonrelativistic flow, it is shown that the dynamics of the generalized vortex lines is determined by the normal component of the fluid velocity to the vortex line vn. Similar to the nonrelativistic case, the equation for vn is shown to be formally like a new charged fluid but (unlike the nonrelativistic flow) with a new formal thermodynamics. The relativistic incompressibility concept is used to establish its differences from the nonrelativistic treatment.
Growth-temperature-dependent (self-)annealing-induced blueshift of photoluminescence from 1.3 μm GaInNAs/GaAs quantum wells
Authors: Pavelescu E.-M. , Jouhti T. , Dumitrescu M. , Klar P. J. , Karirinne S. , Fedorenko Y. , Pessa M.
Published: August 2003

Growing the capping layer of a GaInNAs/GaAs quantum well at typical substrate temperature for GaAs growth by molecular-beam epitaxy, like 580 °C, was found to induce a blueshift of the quantum-well emission whose magnitude significantly increased as the quantum-well growth temperature was decreased. The growth-temperature-dependent (self-)annealing-induced blueshift is correlated with the presence of indium and occurs without observable changes in alloy macroscopic composition or quantum-well structure. The underlying cause for the increase in blue shift with decreasing quantum-well growth temperature appears to be an enhancement in the amount of In–N bonds formed by (self-)annealing, likely through a defect-assisted mechanism.
Thermally induced changes of magnetic coupling in a pinned artificial antiferromagnet used in magnetic tunnel junctions
Authors: Schmalhorst J. , Brückl H. , Reiss G. , Gieres G. , Wecker J.
Published: August 2003

The thermally induced changes of the magnetic coupling in an artificial antiferromagnet exchange biased by an antiferromagnetic layer in a magnetic tunnel junction (Mn–Ir/Co–Fe/Ru/Co–Fe/AlOx/Ni–Fe) is investigated for annealing temperatures up to 450 °C. Beside the usual increase of the tunneling magnetoresistance (TMR) by annealing (maximum TMR 43.9% at 325 °C) the degradation of the artificial antiferromagnet causes a well-defined 90° coupling of the Co–Fe layers in a narrow temperature window around 325 °C. At higher temperature, both Co–Fe layers are coupled ferromagnetically but the exchange biasing by the Mn–Ir is still present. This behavior results from an interplay of different coupling mechanisms of the two Co–Fe layers: (1) indirect antiferromagnetic interlayer exchange coupling across the Ru spacer, (2) ferromagnetic coupling by pinholes in the Ru spacer, and (3) exchange coupling between the lower Co–Fe layer and the antiferromagnet Mn–Ir. The importance of each contribution is discussed with respect to thermally activated diffusion processes.
Synthesis and characterization of superconducting single-crystal Sn nanowires
Authors: Tian Mingliang , Wang Jinguo , Snyder Joseph , Kurtz James , Liu Ying , Schiffer Peter , Mallouk Thomas E. , Chan M. H. W.
Published: August 2003

Single-crystal superconducting tin nanowires with diameters of 40–160 nm have been prepared by electrochemical deposition in porous polycarbonate membranes. Structural characterization through transmission electron microscopy and x-ray diffraction showed that the nanowires are highly oriented along the [100] direction. Although the superconducting transition temperature is close to the bulk value of 3.7 K, the effect of reduced dimensionality is clearly evident in the electrical transport properties of the thinnest wires (40 nm diameter). Magnetization measurements show that the critical field of the nanowires increases significantly with decreasing diameter to ∼0.3 T for the thinnest wires, nearly an order of magnitude larger than the bulk value.
Ion acoustic and drift wave vortices in electron–positron–ion plasmas
Authors: Haque Q. , Saleem H.
Published: August 2003

It is shown that two-dimensional large amplitude ion acoustic waves can give rise to dipolar vortex structures in magnetized homogeneous electron–positron–ion plasmas. In nonuniform plasmas they can couple with drift waves and similar structures can again be produced. A comparison with earlier works on pulse-like soliton formation of these waves in magnetized and unmagnetized electron–positron–ion plasmas is also presented.
Dynamical system approach to FRW models in higher-order gravity theories
Authors: Miritzis John
Published: August 2003

We study the late time evolution of positively curved FRW models with a scalar field which arises in the conformal frame of the R+αR2 theory. The resulted three-dimensional dynamical system has two equilibrium solutions corresponding to a de Sitter space and an ever expanding closed universe. We analyze the structure of the first equilibrium with the methods of the center manifold theory and, for the second equilibrium, we apply the normal form theory to obtain a simplified system, which we analyze with special phase plane methods. It is shown that an initially expanding closed FRW space–time avoids recollapse.
Propagation of magnetic islands in the Er=0 frame of co-injected neutral beam driven discharges in the DIII-D tokamak
Authors: La Haye R. J. , Petty C. C. , Strait E. J. , Waelbroeck F. L. , Wilson H. R.
Published: August 2003

Measurements are made of the propagation frequency ω of tearing mode magnetic islands in the local Er=0 frame in co-injected neutral beam heated H-mode discharges in the DIII-D tokamak [J. L. Luxon et al., Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. Propagation is found to be in the ion diamagnetic drift direction with a frequency more than that of the diamagnetic drift frequency ωi* for modes near the axis and less than ωi* off-axis. This is consistent with the predicted stabilizing polarization current threshold for neoclassical tearing modes for all modes observed only if the condition 0<ω<ωi* is modified by |ωe*| or ηi effects, for example.
Electrostatic method to accelerate nanoshells to extreme hypervelocity
Authors: Wang Zhehui , Kline J. L.
Published: August 2003

Using an acceleration voltage of less than a few hundred kilovolts, it is unlikely that a charged solid object larger than a few micron (10−6 m) in all three dimensions can be accelerated to more than 10 km/s. Quasi-two-dimensional (Q2D) objects are unique forms of matter with two macroscopic dimensions, while the third approaches atomic dimensions. Well-known examples of Q2D objects are thin films. Another example of a Q2D object will be a sphere with a nm thick shell (nanoshell). In this letter, it is predicted that nanoshells can be accelerated to 100 km/s (extreme hypervelocity, or EHV) and above using the electrostatic method. The maximum velocity is limited by field emission and material strength. The two limits only allow a certain number of charges on a nanoshell before it starts to emit ions or electrons, or to break. “Table-top” EHV nanoshell beams can be used for high-temperature plasma diagnostics and fueling. EHV nanoshells can also be used to study hypervelocity-impact phenomena in a momentum space not accessible in the past.
Cylindrical Penning trap for the study of electron plasmas
Authors: Amoretti M. , Bettega G. , Cavaliere F. , Cavenago M. , De Luca F. , Pozzoli R. , Romé M.
Published: August 2003

The ELTRAP device installed at the Department of Physics of the University of Milan is a Malmberg–Penning trap, with a magnetic field up to 0.2 T, equipped with charge coupled device optical diagnostics. It is intended to be a small scale facility for electron plasma and beam dynamics experiments, and in particular for the study of collective effects, equilibrium states, and the formation of coherent structures in these systems. The device features a relatively long solenoid, corrected by 4 shims and 16 dipole coils, in order to obtain a large uniform magnetic field region. The modular electrode design allows several variations of the experimental configuration. The first experiments which assess the operation of the facility are described. Plasma confinement times up to several minutes have been obtained and an electron temperature of 4–8 eV has been measured.
Diffractometer for soft x-ray resonant magnetic scattering
Authors: Grabis J. , Nefedov A. , Zabel H.
Published: August 2003

We report on the design and construction of a new diffractometer for soft x-ray resonant magnetic scattering which has been built at the Ruhr-University Bochum. The ultrahigh vacuum-compatible diffractometer comprises a two-circle goniometer and works in horizontal scattering geometry. Rotation of the detector and sample is realized by two differentially pumped rotating platforms with motors and gears external to the vacuum. The sample environment consists of a closed-cycle He cryostat that allows heating up to 600 K and applying a magnetic field of ±2.5 kOe. All functions of the experimental setup have been extensively tested at the BESSY II Synchrotron (beamline PM3). The experimental results demonstrate the performance of the instrument.
Self-oscillating tapping mode atomic force microscopy
Authors: Manning L. , Rogers B. , Jones M. , Adams J. D. , Fuste J. L. , Minne S. C.
Published: August 2003

A piezoelectric microcantilever probe is demonstrated as a self-oscillator used for tapping mode atomic force microscopy. The integrated piezoelectric film on the cantilever serves as the frequency-determining component of an oscillator circuit; oscillation near the cantilever’s resonant frequency is maintained by applying positive feedback to the film via this circuit. This new mode, which is a step towards more compact and parallel tapping mode AFM imaging, is demonstrated by imaging an evaporated gold film on a silicon substrate. A self-oscillating frequency spectrum and a force–distance curve are also presented.
Recirculation cell for the small-angle neutron scattering investigation of polymer melts in flow
Authors: Bent Julian F. , Richards Randal W. , Gough Tim D.
Published: August 2003

A small-scale flow cell has been developed and used for small-angle neutron scattering (SANS) investigations of polymer melts in Poiseuille flow through a 4:1 contraction. The cell enables the investigation of polymer melt flow subject to a volumetric flow rate of up to 6 cm3 s−1, at pressures up to 10 MPa, temperatures up to 230 °C, and a melt viscosity up to 65 000 Pa s. The cell has recirculating flow path and a relatively small capacity (circa 200 g of polymer) so that polymers with novel and well-defined molecular architectures may be investigated. The details of its construction and operation are described. When two walls of the cell are composed of zero order birefringent sapphire, both small-angle neutron scattering and birefringence studies can be undertaken in the same cell providing a link between macroscopic and molecular level descriptions of the influence of melt flow. Both birefringence and the first melt flow SANS data for a monodisperse, linear polystyrene are presented. These demonstrate the capability and potential of the apparatus to provide data which provide a crucial test for molecular theories of the rheology of entangled polymer melts. However, the use of sapphire windows limits the maximum flow rate that can be used and higher flows necessitated an all aluminum flow cell to cope with the higher pressures developed in flow. Clear evidence of a stretching of the molecule in the direction of the melt flow and a contraction perpendicular to the flow direction has been provided.
A system for cryogenic hydrogen pellet high speed inboard launch into a fusion device via guiding tube transfer
Authors: Lang P. T. , Cierpka P. , Gehre O. , Reich M. , Wittmann C. ,   ASDEX Upgrade Team, Lorenz A. , Frigione D. , Kalvin S. , Kocsis G. , Maruyama S.
Published: August 2003

Particle deposition deep inside the hot target plasma column by cryogenic hydrogen pellet injection is required for efficient particle refueling of fusion devices such as tokamaks. As the ablation plasmoid is subject to a strong outward drift in hot plasmas, pellet launch from the tokamak inboard side is more useful than from the outboard. The depth of the pellet particle deposition depends on density and temperature of the target plasma, and on the pellet mass and velocity. Plasma operation determines density and temperature values, the maximum affordable density perturbation limits the pellet mass. Consequently, the pellet speed remains the only technically variable parameter allowing improvement of the refueling performance. To achieve this an inboard high-speed pellet injection system based on looping type geometry was designed and built at the midsize tokamak ASDEX Upgrade, and first fueling studies had validated the potential for the required injection velocity increase. Throughout the last two years experimental efforts focused on careful step-by-step optimization of the different system hardware components and the operational procedures. Introducing amongst other features a well pumped, rectangular guide track section, the feasibility for the inboard launch scheme up to an injection velocity of 1 km/s was successfully demonstrated. Detailed off-line tests have confirmed that pellets can withstand controlled mechanical and thermal impact even at this high speed, albeit for the sacrifice of increasing and significant mass losses. In a first application to plasma refueling deep penetration into hot target plasmas and hence, high fueling performance was achieved by deeper pellet born particle deposition and hence enhanced particle sustainment times.
Characterization of laser ablation as a means for doping helium nanodroplets
Authors: Claas P. , Mende S.-O. , Stienkemeier F.
Published: August 2003

Helium nanodroplets are doped with metal atoms by means of laser evaporation. The material is evaporated directly in front of the helium nozzle by a pulsed laser. In comparison with conventional pickup from an oven we deduce that the droplets can be loaded with more than one atom per droplet on average. Conditions and efficiencies for loading are evaluated. Furthermore, metal ions can be attached to helium droplets by this method, allowing isolation of charged particles at temperatures below 1 K. In this way we can directly measure size distributions of helium nanodroplets which are compared to results using other techniques.
Optical detection system for biochips using plastic fiber optics
Authors: McMullin J. N. , Qiao H. , Goel Sanket , Grundmann A.
Published: August 2003

An instrument for the detection of optical signals from microfluidic biochips is described. The light detection system uses a LabView™-controlled photomultiplier tube with a programmable gain of 104–107. Plastic optical fibers (POFs) of 1 mm diameter are used to deliver light to and from the microfluidic systems. The detection system is demonstrated by detecting fluorescence from 15 μm polystyrene spheres in commercial biochips and micropipettes using a custom POF launch and detect tip. The spatial response of the tip allows dynamic measurements of the velocities of the microparticles to be made.
ac nanocalorimeter for measuring heat capacity of biological macromolecules in solution
Authors: Yao Haruhiko , Ema Kenji , Fukada Harumi , Takahashi Katsutada , Hatta Ichiro
Published: August 2003

A precise calorimeter has been developed to measure the heat capacity of a small amount of liquid using a novel ac calorimetric method in which the effect of heat loss from a sample cell is corrected using the phase of the ac temperature. The sample cell is made of a fine glass tube, whose outer surface is plated with a nickel film as an ac heater. The ac temperature of the sample is detected precisely with a microbead thermistor attached to the middle of the tube. The resistance of the thermistor is measured with an ac Wheatstone bridge which is composed of resistors with a low temperature coefficient of ±1 ppm/K. The unbalance ac signal of the bridge is measured with a lock-in amplifier. To reduce the drift of measured values caused by the variation of room temperature, the amplifier and measuring instruments with temperature coefficients of >1 ppm/K are kept at constant temperature. Moreover, the gain of the amplifier is calibrated at every measuring point. Consequently, the heat capacity of 10 μl liquid can be determined with an extremely high sensitivity of ±0.001%, which corresponds to heat capacity changes of ±300 nJ/K. A test of the performance was made of the heat capacity measurement during thermal denaturation of lysozyme dissolved in buffered solution. This method is particularly useful for studying thermal properties of biological macromolecules in solution, since the heat capacity of macromolecules can be measured with a 10 μg sample.
Sufficient cusp magnetic field for designing a novel electron cyclotron resonance ion source
Authors: Rashid M. H. , Bhandari R. K.
Published: August 2003

Some have used a cusp modified minimum-B field configuration for designing an electron cyclotron resonance ion source (ECRIS) for 2.45 GHz μ-wave (microwave) frequency. A few ECRIS of this type were tested for >2.45 GHz also but later on converted into the conventional ones because of their poor performance. In this note is an attempt to understand the problems of the old cusp field ECRIS. They are mitigated using a highly permeable midiron disk and negatively biased metal ring and disk in the midplane and at the injection end to design and construct a compact and cost-effective ECRIS of the future.
A fast star sensor for balloon payloads
Authors: Nati Federico , de Bernardis Paolo , Iacoangeli Armando , Masi Silvia , Benoit Alain , Yvon Dominique
Published: August 2003

We developed a system to reconstruct the attitude of balloon borne spinning experiments, where high accuracy (about 1′) and high rotation speed (up to tens of degrees per second) are required. It is based on a stellar sensor, and gathers together hardware simplicity, cheap components, high resolution, and sensitivity. It is composed of an optical mirror (diameter 40 cm), an array of 46 fast and sensitive photodiodes, and low noise readout electronics. It was designed for the Archeops experiment, a balloon borne millimetric telescope whose goal is to generate high resolution maps of large regions of the sky, to study the temperature anisotropies of the cosmic background radiation.
An improved continuous compositional-spread technique based on pulsed-laser deposition and applicable to large substrate areas
Authors: Christen H. M. , Rouleau C. M. , Ohkubo I. , Zhai H. Y. , Lee H. N. , Sathyamurthy S. , Lowndes D. H.
Published: August 2003

A method for continuous compositional-spread (CCS) thin-film fabrication based on pulsed-laser deposition (PLD) is introduced. This approach is based on a translation of the substrate heater and the synchronized firing of the excimer laser, with the deposition occurring through a slit-shaped aperture. Alloying is achieved during film growth (possible at elevated temperature) by the repeated sequential deposition of submonolayer amounts. Our approach overcomes serious shortcomings in previous in situ implementation of CCS based on sputtering or PLD, in particular the variation of thickness across the compositional spread and the differing deposition energetics as a function of position. While moving-shutter techniques are appropriate for PLD approaches yielding complete spreads on small substrates (i.e., small as compared to distances over which the deposition parameters in PLD vary, typically ≈1 cm), our method can be used to fabricate samples that are large enough for individual compositions to be analyzed by conventional techniques, including temperature-dependent measurements of resistivity and dielectric and magnetic properties (i.e., superconducting quantum interference device magnetometry). Initial results are shown for spreads of (Sr1−xCax)RuO3.
Observation of Cu surface inhomogeneities by multiphoton photoemission spectromicroscopy
Authors: Cinchetti M. , Oelsner A. , Fecher G. H. , Elmers H. J. , Schönhense G.
Published: August 2003

The spatially resolved energy distribution of electrons emitted from a polycrystalline copper surface has been studied by multiphoton photoemission. Electron emission was induced by femtosecond laser excitation and detected by an emission electron microscope combined with a time-of-flight detector to allow spatially resolved energy analysis. The energy distributions obtained from small spots with strongly enhanced electron emission yield (so-called hot spots) turned out to be different from those measured for homogeneous surface regions. The latter directly reflect two photon photoemission spectra from Cu as was previously observed in spatially averaging experiments. The hot spots, however, are characterized by a slightly lower work function and a strongly enhanced intensity if excited by s-polarized light. The peak positions of these spectra do not depend on the photon energy as is characteristic for a true secondary process. This indicates a different electron emission mechanism in the hot spots compared to homogeneous surfaces.
Spectroscopic ellipsometry study of epitaxially grown Pb(Mg1/3Nb2/3)O3–PbTiO3/MgO/TiN/Si heterostructures
Authors: Tsang W. S. , Chan K. Y. , Mak C. L. , Wong K. H.
Published: August 2003

0.65 Pb(Mg 1/3 Nb 2/3 ) O 3 –0.35 PbTiO 3 (PMN–PT) thin films have been grown on MgO/TiN-buffered Si(001) substrates using pulsed laser deposition. Their structural properties and surface morphology were examined by x-ray diffraction and scanning electron microscopy, respectively. All PMN–PT films grown at 670 °C show a cube-on-cube epitaxial relationship of PMN–PT(100)∥MgO(100)∥TiN(100)∥Si(100). Discernable interfaces between layers in the heterostructures and crack-free surfaces are evident. A spectroscopic ellipsometer was used to study the optical characteristics of the films. It was revealed that the refractive index of the PMN–PT is ∼2.50 as measured at 635 nm. This value is only slightly less than that of the PMN–PT single crystal of 2.60. Our results suggest that the PMN–PT/MgO/TiN/Si heterostructure has an excellent potential for use in integrated optical waveguide devices.
Quantitative analysis of highly transient fuel sprays by time-resolved x-radiography
Authors: Cai Wenyi , Powell Christopher F. , Yue Yong , Narayanan Suresh , Wang Jin , Tate Mark W. , Renzi Matthew J. , Ercan Alper , Fontes Ernest , Gruner Sol M.
Published: August 2003

Microsecond time-resolved synchrotron x-radiography has been used to elucidate the structure and dynamics of optically turbid, multiphase, direct-injection gasoline fuel sprays. The combination of an ultrafast x-ray framing detector and tomographic analysis allowed three-dimensional reconstruction of the dynamics of the entire 1-ms-long injection cycle. Striking, detailed features were observed, including complex traveling density waves, and unexpected axially asymmetric flows. These results will facilitate realistic computational fluid dynamic simulations of high-pressure sprays and combustion.
Structural and morphological characteristics of planar (112̄0) a-plane gallium nitride grown by hydride vapor phase epitaxy
Authors: Haskell B. A. , Wu F. , Matsuda S. , Craven M. D. , Fini P. T. , DenBaars S. P. , Speck J. S. , Nakamura Shuji
Published: August 2003

This letter discusses the structural and morphological characteristics of planar, nonpolar (112̄0) a-plane GaN films grown on (11̄02) r-plane sapphire by hydride vapor phase epitaxy. Specular films with thicknesses over 50 μm were grown, eliminating the severely faceted surfaces that have previously been observed for hydride vapor phase epitaxy-grown a-plane films. Internal cracks and crack healing, similar to that in c-plane GaN films, were observed. Atomic force microscopy revealed nanometer-scale pitting and steps on the film surfaces, with rms roughness of ∼2 nm. X-ray diffraction confirmed the films are solely a-plane oriented with on-axis (112̄0) and 30° off-axis (101̄0) rocking curve peak widths of 1040 and 3000 arcsec, respectively. Transmission electron microscopy revealed a typical basal plane stacking fault density of 4×105 cm−1. The dislocation content of the films consisted of predominately edge component (bedge=±[0001]) threading dislocations with a density of 2×1010 cm−2, and mixed-character Shockley partial dislocations (b=13〈11̄00〉) with a density of 7×109 cm−2.
Fast optical nonlinearity induced by space-charge waves in dc-biased GaAs
Authors: Subačius L. , Kašalynas I. , Aleksiejūnas R. , Jarašiūnas K.
Published: August 2003

Time-resolved four-wave mixing in dc-biased GaAs crystals exhibit GHz frequency oscillations when the applied dc field and nonequilibrium carrier density are high enough to form a photorefractive high-field domain grating. Its propagation through the spatially modulated carrier density structure creates a photorefractive space-charge wave and leads to an oscillatory behavior of the probe-beam diffraction efficiency with period T=Λ/ν≈200 ps, determined by the grating spacing Λ and domain drift velocity ν. Formation of the space-charge wave in dc-biased GaAs was verified experimentally by using a picosecond transient grating technique. The experimental data were found to be in good agreement with numerical calculations based on the hot electron hydrodynamic model.
Radiation-induced nitrogen segregation during electron energy loss spectroscopy of silicon oxide–nitride-oxide stacks
Authors: Levin Igor , Leapman Richard D. , Kovler Mark , Roizin Yakov
Published: August 2003

Electron energy loss spectroscopy (EELS) in both fixed-probe transmission electron microscopy (TEM) and scanning TEM (STEM) was used to measure elemental profiles of Si, O, and N in the SiOx/SixNy/SiOx/poly-Si stacks deposited on silicon. The results revealed radiation-induced nitrogen segregation to both the Si/SiOx and SiOx/poly-Si interfaces; the extent of nitrogen segregation increased visibly with increasing the radiation dose. The nitrogen diffusion through the oxide layers apparently was accompanied by the diffusion of oxygen into the nitride. Low-noise artifact-free nitrogen profiles across the Si/SiOx interfaces were obtained in STEM by scanning the beam parallel to the layers. These measurements indicated lack of detectable nitrogen segregation to the interfaces.
Microstructures of poly (ethylene glycol) by molding and dewetting
Authors: Suh Kahp Y. , Langer Robert
Published: August 2003

We report on the fabrication of microstructures of poly (ethylene glycol) (PEG) using a soft molding technique. When a patterned poly (dimethylsiloxane) stamp is placed on a wet PEG film, the polymer in contact with the stamp spontaneously moves into the void space as a result of capillary action. Three types of microstructures are observed with the substrate surface completely exposed: a negative replica of the stamp, a two-dimensional projection of the simple cubic structure, and a two-dimensional projection of the diamond structure. A molding process is responsible for the first type and a dewetting process for the final two. A phase diagram is constructed based on the effects of molecular weight and concentration, which shows that mobility and confinement play a crucial role in determining the particular type of microstructure obtained. The PEG microstructure could be used as a lithographic resist in fabricating electronic devices and a resistant layer for preventing nonspecific adsorption of proteins or cells.
Efficient white and red light emission from GaN/tris-(8-hydroxyquinolato) aluminum/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin hybrid light-emitting diodes
Authors: Xiang Hai-Feng , Yu Sze-Chit , Che Chi-Ming , Lai P. T.
Published: August 2003

We report efficient white and red light emission from GaN light-emitting diode (LED)/tris-(8-hydroxyquinolato) aluminum (Alq3)/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin (PtF20TPP) hybrid LEDs. Alq3 was employed to enhance the efficiency of red and white luminescence conversion (LC) LEDs through energy transfer from Alq3 to PtF20TPP. In the white LC-LED, an intense, highly pure white-light emission with CIE_1931 coordinates at x=0.32 and y=0.31 is obtained. The LC-LEDs in this work have relatively high efficiencies, 3.3% for white LC-LED and 4.0% for red LC-LED. The color temperature (Tc), color rendering index (Ra) and luminous efficiency (ηL) of the white LC-LED at 20 mA are 6800 K, 90.6 and 10 lm/W, respectively.