bluuebunny/crossref_metadata_2025 huggingface dataset:
A high energy synchrotron x-ray study of crystallographic texture and lattice strain in soft lead zirconate titanate ceramics
Authors: Hall D. A. , Steuwer A. , Cherdhirunkorn B. , Mori T. , Withers P. J.
Published: October 2004

The lattice parameters and crystallographic texture in La, Sr-doped soft lead zirconate titanate ceramics were examined using high-energy synchrotron x-ray diffraction. The preferred orientations in poled tetragonal and rhombohedral ceramics near the morphotropic phase boundary, caused by ferroelectric domain switching, were determined by monitoring the (002)∕(200) and (111)∕(111¯) intensity ratios, respectively. The lattice strains were also monitored using the {111} and {200} plane spacings in tetragonal and rhombohedral ceramics, respectively. The diffraction experiments were carried out in transmission, enabling the true “bulk” state to be characterized. It was observed that for the tetragonal phase both the lattice spacing d{111} and the intensity ratio R{200} varied linearly as a function of sin2Ψ,Ψ being the angle between the plane normal and the macroscopic polar axis. Similar observations were made for d{200} and R{111} in rhombohedral ceramics. The results are interpreted in terms of the remanent macroscopic strain state due to poling and the resulting relative misfit between any given grain and the surrounding matrix, which creates significant intergranular stresses. The tetragonal {111} and rhombohedral {200} plane spacings were identified as important monitors of intergranular stress, since the elongation of a grain along the tetragonal ⟨111⟩ or rhombohedral ⟨200⟩ directions, respectively (due to non-180° domain wall motion), is zero in the absence of the constraint imposed by neighboring grains. As a result, the tetragonal {111} or rhombohedral {200} reflections are sensitive only to the macrostrain of the polycrystal. It is proposed that the nonlinear and hysteretic piezoelectric response of the lattice strain reported in previous studies is primarily a result of coupling between the extrinsic non-180° ferroelectric domain switching mechanisms and the intrinsic lattice strain.
Femtosecond and ultraviolet laser irradiation of graphitelike hexagonal boron nitride
Authors: Kanaev Andrei V. , Petitet Jean-Pierre , Museur Luc , Marine Vladimir , Solozhenko Vladimir L. , Zafiropulos Vassilis
Published: October 2004

The effect of the femtosecond and nanosecond UV laser irradiation (below the ablation threshold) on graphitelike hexagonal boron nitride (hBN) has been studied. Experiments were carried out with the compacted powder under high vacuum at room temperature using the excimer KrF laser (248nm). In the nanosecond operation mode, the laser-induced fluorescence spectra are found strongly modified depending on the integrated doze, which is attributed to a progressive enrichment of the surface layer by an elemental boron. A slow sample recovery after the laser irradiation has been observed. On the other hand, in the femtosecond mode, the fluorescence spectra depend on the laser fluence, and the changes are reversible: low-energy fluorescence spectra are restored immediately when the laser energy decreases. This effect can be explained by a material bleaching, which favors a bulk centers emission. The ablation threshold has been determined as 78mJ∕cm2 in the femtosecond laser operational mode.
Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films
Authors: Cao Zhiqiang , Zhang Xin
Published: October 2004

The structural relaxation of plasma-enhanced chemical-vapor-deposited (PECVD) silane-based silicon oxide films during thermal cycling and annealing has been studied using wafer curvature measurements. These measurements, which determine stress in the amorphous silicon oxide films, are sensitive to both plastic deformation and density changes. A quantitative case study of such changes has been done based upon the experimental results. A microstructure-based mechanism elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then used to explain a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD silicon oxide films with a thickness varying from 1to40μm were studied, as certain demanding applications in microelectromechanical systems require such thick films serving as heat∕electrical insulation layers.
Scintillator probe for lost alpha measurements in JET
Authors: Baeumel S. , Werner A. , Semler R. , Mukherjee S. , Darrow D. S. , Ellis R. , Cecil F. E. , Pedrick L. , Altmann H. , Kiptily V. , Gafert J. ,   JET-EFDA Contributors
Published: October 2004

Good confinement of alpha particles in a large magnetic fusion device is a precondition for building a magnetic fusion reactor. The direct measurement of alpha particle losses is of particular interest. Appropriate diagnostics are now being prepared for the Joint European Torus tokamak: a scintillator probe and a set of Faraday cups. Both systems are capable of measuring charged fusion products and ion cyclotron resonance heating tail ions. The design of the lost alpha particle scintillator probe is in the scope of this article. It will allow the detection of particles with a gyroradius between 20 and 140 mm (15% resolution) and a pitch angle between 30° and 86° (5% resolution). As scintillating material P56 will be used. The light emitted by the scintillator caused by charged particles that pass the collimator and hit the scintillator will be detected via a set of optical lenses and a coherent image fiber bundle with a charge coupled device camera and a photomultiplier array. In the following the present design of the scintillator probe with emphasis on the performance of the system, structural resistance against plasma disruptions, and the requirements on the heat protection against plasma and neutral beam induced thermal loads will be described.
Progress on neutron pinhole imaging for inertial confinement fusion experiments
Authors: Grim G. P. , Morgan G. L. , Wilke M. D. , Gobby P. L. , Christensen C. R. , Wilson D. C.
Published: October 2004

Neutron imaging provides a powerful diagnostic for understanding the performance of inertial confinement fusion ignition capsules and the drive mechanism imploding them. To achieve the spatial resolution and fielding capability needed at the National Ignition Facility requires a staged approach that simultaneously pushes the limits of extant capabilities while developing new techniques that will extend to the National Ignition Facility regime. To this end, new pinhole assemblies have been designed and fabricated using very high-precision machining equipment. These assemblies have been fielded successfully at Laboratory for Laser Energetics, University of Rochester and have provided impetus for new aperture designs and new ideas for detectors, which are now the limiting element in the system resolution.
Response function measurement of layered type CVD single crystal diamond radiation detectors for 14 MeV neutrons
Authors: Kaneko J. H. , Teraji T. , Hirai Y. , Shiraishi M. , Kawamura S. , Yoshizaki S. , Ito T. , Ochiai K. , Nishitani T. , Sawamura T.
Published: October 2004

Response function measurement of layered-type chemical vapor deposition single crystal diamond radiation detectors for 14 MeV neutrons was carried out. The detector had a layered structure that was composed of a boron-doped diamond layer of 0.5 μm in thickness and a nondoped diamond layer of 20 μm on an inexpensive high pressure and high temperature-type Ib diamond substrate. The detector had energy resolution of 2.6% for 5.5 MeV α particles. This experiment was mainly carried out in order to understand the present status of the detector as a 14 MeV neutron spectrometer and an extent of charge trapping. As result, a peak caused by the C12(n,α0)9Be reactions was clearly observed; the best energy resolution of 6% as for a synthetic diamond radiation detector was achieved. Detection efficiency was 3.2×10−7 counts/unit neutron fluence. However, taking the energy resolution for α particles, etc., into account, the energy resolution for 14 MeV neutrons was not so high. Further improvement based on better crystal growth is indispensable.
Compact NE213 neutron spectrometer with high energy resolution for fusion applications
Authors: Zimbal A. , Reginatto M. , Schuhmacher H. , Bertalot L. , Esposito B. , Poli F. , Adams J. M. , Popovichev S. , Kiptily V. , Murari A. , program Contributors to the EFDA-JET work
Published: October 2004

Neutron spectrometry is a tool for obtaining important information on the fuel ion composition, velocity distribution and temperature of fusion plasmas. A compact NE213 liquid scintillator, fully characterized at Physikalisch-Technische Bundesanstalt, was installed and operated at the Joint European Torus (JET) during two experimental campaigns (C8-2002 and trace tritium experiment-TTE 2003). The results show that this system can operate in a real fusion experiment as a neutron (1.5 MeV<En<20 MeV) spectrometer with good energy resolution (ΔE/E<4% at En=2.5 MeV and ΔE/E<2% at En=14 MeV). First measurements performed under different plasma scenarios, including trace tritium experiments, are presented. The analysis of the pulse height data was carried out using a newly developed method based on maximum entropy unfolding. The results indicate that this efficient, inexpensive, and compact scintillator is suitable for use as a broadband spectrometer in large fusion devices (JET and the International Thermonuclear Experimental Reactor).
Improved charge-coupled device detectors for high-speed, charge exchange spectroscopy studies on the DIII-D tokamak
Authors: Burrell K. H. , Gohil P. , Groebner R. J. , Kaplan D. H. , Robinson J. I. , Solomon W. M.
Published: October 2004

Charge exchange spectroscopy is one of the key ion diagnostics on the DIII-D tokamak. It allows determination of ion temperature, poloidal and toroidal velocity, impurity density, and radial electric field Er throughout the plasma. For the 2003 experimental campaign, we replaced the intensified photodiode array detectors on the central portion of the DIII-D charge exchange spectroscopy system with advanced charge–coupled device (CCD) detectors mounted on faster (f/4.7) Czerny–Turner spectrometers equipped with toroidal mirrors. The CCD detectors are improved versions of the ones installed on our edge system in 1999. The combination improved the photoelectron signal level by about a factor of 20 and the signal to noise by a factor of 2–8, depending on the absolute signal level. The new cameras also allow shorter minimum integration times while archiving to PC memory: 0.552 ms for the slower, lower-read noise (15 e) readout mode and 0.274 ms in the faster, higher-read noise (30 e) mode.
Enhanced sensitivity beam emission spectroscopy system for nonlinear turbulence measurements
Authors: Gupta Deepak K. , Fonck Raymond J. , McKee George R. , Schlossberg David J. , Shafer Morgan W.
Published: October 2004

An upgraded beam emission spectroscopy (BES) system has been deployed to access low amplitude turbulence regions near internal transport barriers on the DIII-D tokamak. Sixteen high sensitivity channels are being installed. A significant increase in total signal to noise is achieved by: (1) Increased spatial volume sampling tailored to known turbulence characteristics; (2) An increased throughput spectrometer assembly to isolate the local beam fluorescence, coupled to new large area photoconductive photodiodes; (3) A new sharp edge interference filter designed to optimize detection of the beam emission plus a significant fraction of the thermal deuterium charge exchange. A new data acquisition system has been installed, providing an eight times increase in integration time or an increased sample rate. Preliminary results from the upgraded system show a signal enhancement of greater than an order of magnitude. A clear broadband density fluctuation signal is observed in H-mode discharges with the upgraded BES system, demonstrating the significant performance enhancement.
Neutral beam diagnostics for the HT-7 tokamak
Authors: Hu L. Q. , Wan B. N. , Hu C. D. , Liu B. H. , Wu Z. W. , Huang J. ,   HT-7 DNB Team, Rowan William L. , Huang H. , Gentle K.
Published: October 2004

A diagnostic neutral beam will be added to the diagnostic set so that charge-exchange recombination spectroscopy (CXRS) can be used to acquire ion temperature and rotation, and to study the role of the ion thermal transport, the radial electric field, and turbulence in the high performance HT-7 plasma. In normal operation, the diagnostic neutral beam (DNB) can produce 5.5 A of extracted beam current in hydrogen at an energy of 50 keV with a pulse length of 0.1 s. D and He beams can be produced as well. The beam can be modulated at 0.5 kHz. The CXRS system will have 45 spatial observation chords and employ a spectrometer, which can acquire spectra at the rate of 100 Hz. In this article, the capabilities and implementation of the DNB and CXRS systems are presented.
Analysis of heavy ion beam probe potential measurement errors in the Madison Symmetric Torus
Authors: Zhang X. , Lei J. , Connor K. A. , Demers D. R. , Schoch P. M. , Shah U.
Published: October 2004

The heavy ion beam probe on the Madison Symmetric Torus is capable of measuring the plasma potential at radial locations from about ρ=r/a=0.3 to 0.75. Radial potential scans from two energy analyzer detectors have been used to assess measurement accuracy since they should produce identical profiles. The effects of analyzer characteristics, system alignment, sample volume locations and shapes, probing beam control, the quality of confining magnetic field information available, etc., have been assessed to determine the overall quality of the potential measurements. The accuracy of the measurements is found to be quite good relative to the potentials measured.
First MeV ion loss measurements using activation technique in reversed B experiments at JET
Authors: Bonheure G. , Popovichev S. , Bertalot L. , Murari A. , Conroy S. ,   JET-EFDA Contributors
Published: October 2004

Fast ions measurements become increasingly important as we move closer to the International Thermonuclear Experimental Reactor (ITER) or burning plasma experiments and further R&D is especially required in the field of fast ion loss measurements [Bonheure et al., Rev. Sci. Instrum. 74, 1726 (2003).] in the perspective of ITER. A boron target mounted on a manipulator was exposed to deuterium plasmas during reversed field experiments at the Joint European Torus (JET). Due to the B(p,α)10 Be7 reaction, Be7 is produced in the boron target by MeV protons escaping the plasma. The proton losses are deduced from measurements of the intensity of decay emission of Be7. Excellent agreement is found between measurements and prediction from fast ion classical drift losses. The MCORBIT Monte Carlo Simulation code was used to predict unconfined orbits fraction. Further developments are presented, including a new dedicated instrument to be used in experiments already planned at JET with ion cyclotron range of frequency accelerated alpha particles. The obtained results will be essential for the design of lost alpha diagnostics on ITER based on activation technique.
Generation of the transient electrical and spontaneous magnetic fields by solid state combustion
Authors: Martirosyan K. S. , Claycomb J. R. , Miller J. H. , Luss D.
Published: October 2004

Experiments revealed that transient electric field intensities up to 2.5V∕cm were generated during the initial period of combustion synthesis of the ferromagnetic products before the maximum temperature was reached. This occurred when the iron particles were partially oxidized and the reaction product was mainly magnetite (Fe3O4). The electromagnetic field caused spontaneous magnetization of the product in the postcombustion zone. Magnetic field values up to 4 μT formed after the sample temperature fell below the Curie temperature and the initial reactants were completely converted to the ferromagnetic phase PbFe12O19. Increasing the volume of the samples increases the absolute residual magnetic field magnitude after cooling. We present possible mechanisms of the electromagnetic field generation during the combustion.
Design of the collective Thomson scattering diagnostic for International Thermonuclear Experimental Reactor at the 60 GHz frequency range
Authors: Meo F. , Bindslev H. , Korsholm S. B. , Tsakadze E. L. , Walker C. I. , Woskov P. , Vayakis G.
Published: October 2004

The physics feasibility study [H. Bindslev et al., ITER Report Contract No. EFDA 01.654, 2003, www.risoe.dk/euratom/CTS/ITER] concludes that the frequency option below the electron cyclotron resonance was the only system capable of meeting the International Thermonuclear Experimental Reactor (ITER) measurement requirements for the fusion alphas, with present or near term technology. This article presents the design of the collective Thomson scattering diagnostic for ITER at the 60 GHz range. The system is capable of measuring the fast ion distribution parallel and perpendicular to the magnetic field at different radial locations simultaneously. The design is robust technologically with no moveable components near the plasma. The article includes the upgrade requirements to provide temporally and spatially resolved measurements of the fuel ion ratio.
Evaluation of energetic particle confinement using CXNPA with NB-blip experiments on Large Helical Device
Authors: Osakabe M. , Seki T. , Takeiri Y. , Tanaka K. , Narihara K. ,   LHD-experimental Group, Murakami S. , Sasao M.
Published: October 2004

A new experimental technique to investigate the particle confinement of energetic ions during their slowing-down process is developed for charge exchange neutral particle diagnostics. The method is based on the maximum entropy and the maximum likelihood method and is used for the neutral beam short pulse experiment. The method assumes that the energy loss of the fast ions is given by the classical deceleration rate at their birth orbit. It will not require the bulk neutral distributions and the energetic ion distribution in plasmas. The method provides the spatial distribution of confinement time of energetic particles on their orbit during the slowing-down processes. The method of the analysis is described and the application to the experimental data is shown in this article.
Neutral particle analyzer diagnostic on the National Spherical Torus Experiment
Authors: Medley S. S. , Roquemore A. L.
Published: October 2004

The neutral particle analyzer (NPA) diagnostic on the National Spherical Torus Experiment (NSTX) utilizes a PPPL-designed EIIB spectrometer that measures the energy spectra of minority hydrogen and bulk deuterium species simultaneously with 39 energy channels per mass specie and a time resolution of 1 ms. The calibrated energy range is E=0.5–150 keV and the energy resolution varies from ΔE/E=3%–7% over the surface of the microchannel plate detector. The NPA measures Maxwellian spectra of residual hydrogen to obtain ion temperatures and measures the energetic ion spectra produced by injection of up to 100 keV deuterium neutral beams into deuterium plasmas. The NPA views across the coinjection paths of the three neutral beam sources on NSTX which localizes the measured charge exchange effux to the intersection region. The incorporation of horizontal scanning for the NPA over a sightline tangency range of Rtan=125–−75 cm has enabled measurement of the anisotropic energy distribution of the beam ions. Vertical scanning allows measurements to be made from the horizontal midplane through an angle of 26° downward. A description of the NPA diagnostic on NSTX will be presented along with illustrations of measurement capability.
Novel compact electrostatic ion-current detector using a self-collection method for secondary-electron suppression
Authors: Hirata M. , Tokioka S. , Cho T. , Kohagura J. , Yoshida M. , Miyake Y. , Numakura T. , Yokoyama N. , Fukai T. , Tomii Y. , Nakashima Y. , Miyoshi S. , Kondoh T.
Published: October 2004

For the purpose of observations of the absolute values of ion-end-loss currents for plasma confinement studies in open-field plasma devices, a compact-sized electrostatic ion-current detector is proposed on the basis of a self-collection principle for suppressing the effects of secondary-electron emission from a metal collector. For employing this specific method, it is worth noting that no further additional magnetic systems except ambient open-ended magnetic fields are required for the proposed detector structure. This characteristic property provides a compactness of the total detector system and availability for its use in a plasma confinement device without disturbing plasma-confining magnetic fields. The detector consists of a set of parallel metal plates with respect to lines of ambient magnetic forces of a plasma device for analyzing incident ion currents along with a grid for shielding the collector against strays due to the metal-plate biasing. Availability of the detector is clearly demonstrated in the GAMMA 10 plasma experiments.
Two-dimensional potential profile and density measurements by use of an improved gold neutral beam probe
Authors: Takemura Y. , Ishii K. , Kojima A. , Hagisawa K. , Miyata Y. , Masuda Y. , Yamaguchi T. , Itakura A. , Cho T.
Published: October 2004

An improved gold neutral beam probe system has been developed in order to measure both the potential profile and the electron density profile simultaneously at the central cell of the tandem mirror GAMMA10. A gold film detector was also developed in order to measure the plasma density profile. The yield curves of secondary electrons were measured as a function of the incident angle and electron energy using both the gold neutral beam and ultraviolet ray injection. Time evolution of the plasma line density was measured by adjusting the incident angle and adding a beam chopping method. The result is in good agreement in comparison with the line density measured using a microwave interferometer. It was found that this film detector is very useful for simultaneous measurements of the electrostatic potential and plasma density.
Use of spherically bent crystals to diagnose wire array z pinches
Authors: Shelkovenko T. A. , Pikuz S. A. , Hammer D. A. , Ampleford D. J. , Bland S. N. , Bott S. C. , Chittenden J. P. , Lebedev S. V.
Published: October 2004

Spherically bent mica and quartz crystals have provided time-integrated spectra and monochromatic images in self-radiation of wire array z-pinch implosions on the MAGPIE generator (1 MA, 240 ns) at Imperial College. Diagnostics based on spherically bent crystals offer higher efficiencies than those based on flat or convex dispersion elements, allowing positioning far from the pinch with good debris shielding. A mica crystal spectrometer produced an image of the pinch in each emission line with about 100 μm axial resolution. Combining the results of monochromatic imaging and spectra confirmed the presence of bright spots, probably generated by energetic electrons inside the pinch.
Measurements of the counting statistics on RAR-2497 and DEF x-ray film
Authors: Dunham Greg , Rochau G. A. , Lake P. , Nielsen-Weber L. , Schuster D.
Published: October 2004

X-ray film is commonly used to diagnose high temperature plasmas. Quantitative analysis of the recorded film exposure requires knowledge of the counting statistics inherent to each particular film type. To address this issue, RAR-2497 and DEF film were exposed on a Manson x-ray source for multiple fluence values and photon energies. The fluctuations in the measured intensity were found by determining the statistical distribution of the recorded photon intensity using Henke’s calibration tables to relate the net film density to the incident intensity. The resulting measurements of the statistical fluctuations in photon intensity are presented for each film type.
Operation of a single-photon–counting x-ray charge-coupled device camera spectrometer in a petawatt environment
Authors: Stoeckl C. , Theobald W. , Sangster T. C. , Key M. H. , Patel P. , Zhang B. B. , Clarke R. , Karsch S. , Norreys P.
Published: October 2004

The use of a single-photon–counting x-ray charge-coupled device (CCD) camera as an x-ray spectrometer is a well-established technique in ultrashort-pulse laser experiments. In single-photon–counting mode, the pixel value of each readout pixel is proportional to the energy deposited from the incident x-ray photon. For photons below 100 keV, a significant fraction of the events deposits all the energy in a single pixel. A histogram of the pixel readout values gives a good approximation of the x-ray spectrum. This technique requires almost no alignment, but it is very sensitive to signal-to-background issues, especially in a high-energy petawatt environment. Shielding the direct line of sight to the target was not sufficient to obtain a high-quality spectrum, for the experiments reported here the CCD camera had to be shielded from all sides with up to 10 cm of lead.
Design and construction of a fast ion loss Faraday cup array diagnostic for Joint European Torus
Authors: Darrow D. S. , Bäumel S. , Cecil F. E. , Kiptily V. , Ellis R. , Pedrick L. , Werner A.
Published: October 2004

A thin foil Faraday cup array is being built to measure the loss of 3.5 MeV alpha particles and MeV ion cyclotron heating tail ions on Joint European Torus. It will consist of nine detectors spread over five different poloidal locations and three radial positions. They will measure the poloidal distribution and radial scrape off of the losses. The detectors will be comprised of four layers of thin (2.5 μm) Ni foil, giving some resolution of the lost particle energy distribution as different ranges of energies will stop in different layers of the detector. One detector will utilize eight thinner (1.0 μm) foils to obtain a better-resolved energy distribution. These detectors will accept particles incident up to 45° from the normal to the foils.
An improved Abel inversion method modified for tangential interferometry in tokamak
Authors: Ha J. H. , Nam Y. U. , Cheon M. S. , Hwang Y. S.
Published: October 2004

An improved Abel inversion technique has been developed for an accurate reconstruction of the electron density profile in the tangential interferometer system. A conventional slice-and-stack method has been modified in various ways for tangential interferometer data, and their results are compared with various density profiles. Among them, an improved inversion technique of double linear density method shows good reconstructions of all those density profiles even with measurement errors accounted. Especially, it provides better-reconstructed profiles at the edge. This technique has been successfully applied to KSTAR (Korea superconducting tokamak advanced research) tokamak for the design of the KSTAR tangential interferometer system.
D
3
He
-proton emission imaging for inertial-confinement-fusion experiments (invited)
Authors: Séguin F. H. , DeCiantis J. L. , Frenje J. A. , Kurebayashi S. , Li C. K. , Rygg J. R. , Chen C. , Berube V. , Schwartz B. E. , Petrasso R. D. , Smalyuk V. A. , Marshall F. J. , Knauer J. P. , Delettrez J. A. , McKenty P. W. , Meyerhofer D. D. , Roberts S. , Sangster T. C. , Mikaelian K. , Park H. S.
Published: October 2004

Proton emission imaging cameras, in combination with proton spectrometers and a proton temporal diagnostic, provide a great deal of information about the spatial structure and time evolution of inertial-confinement fusion capsule implosions. When used with D3He-filled capsules, multiple proton emission imaging cameras measure the spatial distribution of fusion burn, with three-dimensional information about burn symmetry. Simultaneously, multiple spectrometers measure areal density as a function of angle around the imploded capsule. Experiments at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have already proven the utility of this approach. An introduction to the hardware used for penumbral imaging, and algorithms used to create images of the burn region, are provided here along with simple scaling laws relating image resolution and signal-to-noise ratio to characteristics of the cameras and the burn region.
Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)
Authors: Mackinnon A. J. , Patel P. K. , Town R. P. , Edwards M. J. , Phillips T. , Lerner S. C. , Price D. W. , Hicks D. , Key M. H. , Hatchett S. , Wilks S. C. , Borghesi M. , Romagnani L. , Kar S. , Toncian T. , Pretzler G. , Willi O. , Koenig M. , Martinolli E. , Lepape S. , Benuzzi-Mounaix A. , Audebert P. , Gauthier J. C. , King J. , Snavely R. , Freeman R. R. , Boehlly T.
Published: October 2004

Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.
The saturation current of silicon bipolar transistors at moderate stress levels and its relation to the energy-band structure
Authors: Creemer J. F. , French P. J.
Published: October 2004

Mechanical stress has a pronounced influence on the saturation current of bipolar transistors, which is called the piezojunction effect. This effect has been adequately modeled from band theory for stresses over 1 GPa. However, this is not the case for stresses below 200 MPa, which are frequently encountered in electronic engineering. This paper presents a band model for this stress range which reproduces measurements in a successful way. The model is based on the idea that the saturation current depends on the conductivity of minority charge carriers in thermodynamic equilibrium. This conductivity is expressed in terms of the energy bands. The influence of stress on the bands is calculated from the deformation potential theory. With this approach calculations are also made of the changes in the mobility and the intrinsic carrier concentration. The presented model naturally includes the theory of the piezoresistive effect, which is well established. It also includes our previous engineering model of the piezojunction effect. This is used to numerically calculate the coefficients of the piezoresistive and the piezojunction effect, which are in good agreement with literature values and measurement results.
Temperature- and electric-field-dependent polarization rotations in (211)-cut Pb(Mg1∕3Nb2∕3)0.69Ti0.31O3 (PMNT31%) single crystal
Authors: Tu Chi-Shun , Hung L.-W. , Chien R. R. , Schmidt V. Hugo
Published: October 2004

Polarization rotations of temperature- and electric-field-dependent phase transformations in a (211)-cut Pb(Mg1∕3Nb2∕3)0.69Ti0.31O3 (PMNT31%) single crystal were observed by means of polarizing microscopy. Dielectric permittivity was also measured as a function of temperature and frequency. Below 380 K domains are mostly rhombohedral (R) phase mixed with monoclinic (M) domains. As temperature increases above 380 K, polarizations of the rhombohedral domains begin to rotate toward the cubic (C) phase through monoclinic distortions, i.e., R→M→C, associated with a long-range percolation of monoclinic phase near 380 K. However, the tetragonal phase was not observed apparently. Electric-field-dependent domain structures show that a long-range R→M phase transformation takes place in the range of 3–5kV∕cm as electric field increases. The crystal cannot reach a monodomain as the electric field reaches 26kV∕cm. A hysteresis loop of polarization versus electric field was also measured for comparison with electric-field-dependent observation of polarizing microscopy.
Bounds on elastic constants for random polycrystals of laminates
Authors: Berryman James G.
Published: October 2004

A well-known result due to Hill provides an exact expression for the bulk modulus of any multicomponent elastic composite whenever the constituents are isotropic and the shear modulus is uniform throughout. Although no precise analog of Hill’s result is available for the opposite case of uniform bulk modulus and varying shear modulus, it is shown here that some similar statements can be made for shear behavior of random polycrystals composed of laminates of isotropic materials. In particular, the Hashin-Shtrikman-type bounds of Peselnick, Meister, and Watt for random polycrystals composed of hexagonal (transversely isotropic) grains are applied to the problem of polycrystals of laminates. An exact product formula relating the Reuss estimate of bulk modulus and an effective shear modulus (of laminated grains composing the system) to products of the eigenvalues for quasicompressional and quasiuniaxial shear eigenvectors also plays an important role in the analysis of the overall shear behavior of the random polycrystal. When the bulk modulus is uniform in such a system, the equations are shown to reduce to a simple form that depends prominently on the uniaxial shear eigenvalue—as expected from physical arguments concerning the importance of uniaxial shear in these systems. Applications of the analytical results presented here include benchmarking of numerical procedures used for studying elastic behavior of complex composites, and estimating coefficients needed in upscaled equations for elasticity and∕or poroelasticity of heterogeneous systems.
Microstructural bonding features of cold sprayed face centered cubic metals
Authors: Borchers C. , Gärtner F. , Stoltenhoff T. , Kreye H.
Published: October 2004

Cold spraying is a coating technique, in which the formation of dense, tightly bonded coatings occurs only due to the kinetic energy of high velocity particles of the spray powder. These particles are still in the solid state as they impinge on the substrate. This study correlates physicomechanical properties of the fcc metals Al, Cu, and Ni with the respective microstructures of their cold sprayed coatings in the light of scanning and transmission electron microscopical investigations. It is found that the microstructures of these coatings differ substantially from each other, and the results are discussed in the light of melting temperatures and stacking fault energies.
Filters display inverse limit spaces
Authors: Urías Jesús
Published: October 2004

A rigorous proof that linear filters display the inverse limit spaces of chaotic maps is given.
Doping-induced strain and relaxation of Al-doped 4H-SiC homoepitaxial layers
Authors: Huh S. W. , Chung H. J. , Benamara M. , Skowronski M. , Sumakeris J. J. , Paisley M. J.
Published: October 2004

Aluminum-doped 4H-SiC epilayers with Al concentrations in the 7.4×1018–3.8×1020cm−3 range were deposited on off-orientation (0001) wafers by chemical vapor deposition method and analyzed using high-resolution x-ray diffraction, transmission electron microscopy, and KOH etching. Reciprocal space maps of (0008) reflection revealed two distinct peaks originating from the substrate and doped epilayer. For Al concentration below 3.3×1020cm−3, 10μm thick layers were fully strained with the a-lattice parameter of the layer matching that of the substrate. The equilibrium c-lattice parameter change versus doping was determined to be 1.3±0.3×10−24cm3. The basal planes of the epilayers were tilted in respect to the substrate in the direction of the offcut with the tilt magnitude proportional to the doping concentration. The 10μm thick layers with Al concentration above 3.3×1020cm−3 underwent partial relaxation. The a-lattice parameter of the epilayer was higher than that of the substrate, the width of ω and 2θ scans of (0008) x-ray peaks broadened by a factor of 2 compared to strained layers, and the threading dislocation density increased by several orders of magnitude. Since no inclusions have been found in the relaxed epilayer, we interpret the above changes as due to strain relaxation by nucleation of dislocations.
Microwave loss mechanisms in Ba0.25Sr0.75TiO3 thin film varactors
Authors: Vorobiev A. , Rundqvist P. , Khamchane K. , Gevorgian S.
Published: October 2004

Parallel-plate Au(Pt)∕Ba0.25Sr0.75TiO3∕(Pt)Au thin film varactors were fabricated on high resistance Si substrates and characterized at dc, rf, and microwave frequencies. In the frequency range 10–45 GHz the varactors show relatively low losses, with loss tangent less than 0.025 at 45 GHz. Due to the thick and highly conductive Pt/Au electrodes the metal losses are less than 10%. However, the loss tangent of the ferroelectric film is still three to five times higher than that in Ba0.27Sr0.73TiO3 single crystal. The analysis of the dc field dependences of loss tangent and permittivity in a wide frequency range shows that these additional losses are mainly due to the charged defects. Extrapolation of measured low frequency (1 MHz) loss tangents to the microwave region using the power law ω1∕3 is in good agreement with experiment. The dc current through the varactor is found to be controlled by Schottky emission and Poole-Frenkel mechanisms depending on the polarity. The Poole-Frenkel mode is associated with field enhanced thermal excitation of charge carriers from internal traps. The trap activation energy (about 0.15 eV) determined from the Poole-Frenkel mode agrees well with the energy level of the oxygen vacancy. We assume that the oxygen vacancies within the grain boundaries of the ferroelectric film act as charged defects and cause additional (extrinsic) microwave losses. The possible correlation between the film’s internal strains and density of the oxygen vacancies are discussed. The knowledge of the extrinsic loss mechanism and corresponding microstructure defects is useful in optimization of the varactor design, deposition, annealing process, and further improvement of the varactor performance.
Effect of material structure on photoluminescence spectra from silicon nanocrystals
Authors: Orbons S. M. , Spooner M. G. , Elliman R. G.
Published: October 2004

The thickness of a silicon dioxide layer is shown to have a significant effect on the measured photoluminescence spectrum from silicon nanocrystals embedded in the layer. This can range from significant but subtle spectral distortions that are difficult to detect, including changes in intensity, peak position and peak width, to gross distortions that are readily apparent as a modulation of the measured spectrum. These distortions are shown to be a simple consequence of the wavelength dependent reflectivity of the sample structure but to have important implications for determining nanocrystal properties from such data.
Two-bands charge transport in silicon nitride due to phonon-assisted trap ionization
Authors: Nasyrov K. A. , Gritsenko V. A. , Novikov Yu. N. , Lee E.-H. , Yoon S. Y. , Kim C. W.
Published: October 2004

The charge transport in the amorphous Si3N4 is studied experimentally and theoretically. We have found, that widely accepted Frenkel model of the trap ionization gives the unphysical low value of the attempt to escape factor, and the enormously high value of the electron tunnel mass. Experimental data are well described by theory of the two-bands conduction and the phonon-assisted trap ionization in Si3N4.
Effect of fluorine implantation dose on boron thermal diffusion in silicon
Authors: El Mubarek H. A. W. , Bonar J. M , Dilliway G. D. , Ashburn P. , Karunaratne M. , Willoughby A. F. , Wang Y. , Hemment P. L. F. , Price R. , Zhang J. , Ward P.
Published: October 2004

This paper investigates how the thermal diffusion of boron in silicon is influenced by a high energy fluorine implant with a dose in the range 5×1014–2.3×1015cm−2. Secondary Ion Mass Spectroscopy (SIMS) profiles of boron marker layers are presented for different fluorine doses and compared with fluorine profiles to establish the conditions under which thermal boron diffusion is suppressed. The (SIMS) profiles show significantly reduced boron thermal diffusion above a critical F+ dose of 0.9–1.4×1015cm−2. Fitting of the measured boron profiles gives suppressions of the boron thermal diffusion coefficient by factors of 1.9 and 3.7 for F+ implantation doses of 1.4×1015 and 2.3×1015cm−2, respectively. The suppression of boron thermal diffusion above the critical fluorine dose correlates with the appearance of a shallow fluorine peak on the (SIMS) profile in the vicinity of the boron marker layer. This shallow fluorine peak is present in samples with and without boron marker layers, and hence it is not due to a chemical interaction between the boron and the fluorine. Analysis of the (SIMS) profiles and cross-section Transmission Electron Microscope micrographs suggests that it is due to the trapping of fluorine at vacancy-fluorine clusters, and that the suppression of the boron thermal diffusion is due to the effect of the clusters in suppressing the interstitial concentration in the vicinity of the boron profile.
Predictions of electronic, structural, and elastic properties of cubic InN
Authors: Bagayoko D. , Franklin L. , Zhao G. L.
Published: October 2004

We present theoretical predictions of electronic, structural, and elastic properties of cubic indium nitride in the zine-blende structure (c-InN). Our ab initio, self-consistent calculations employed a local density approximation potential and the Bagayoko, Zhao, and Williams implementation of the linear combination of atomic orbitals. The theoretical equilibrium lattice constant is 5.017Å, the band gap is 0.65eV, and the bulk modulus is 145GPa. The band gap is 0.74eV at an experimental lattice constant of 4.98Å.
Superconducting screening on different length scales in high-quality bulk MgB2 superconductor
Authors: Horvat J. , Soltanian S. , Pan A. V. , Wang X. L.
Published: October 2004

High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ∼1μm, ∼10μm, and whole of the sample (∼millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (Δm). The analysis of the field dependence of Δm for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to Δm. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to Δm in the intermediate fields (1T<H<4T at 20K) and they can be used to obtain the value of Jc from critical state model, which corresponds to the transport Jc. The stretched exponential field dependence of these currents is similar to the one obtained for high-temperature superconductors, and it seems to be connected with the percolation of the currents.
Supercritical density relaxation as a new approach of droplet vaporization
Authors: Préau Stéphane , Prud’homme Roger , Ouazzani Jalil , Zappoli Bernard
Published: October 2004

The isobaric density relaxation of a cold, slightly supercritical, fluid package in a hotter atmosphere of this same fluid at a near critical pressure is studied in this paper. We solve the Navier–Stokes equations describing the evolution of an initial density inhomogeneity in a supercritical van der Waals fluid. These numerical simulations allow exploring the whole range of surrounding conditions, including the slightly supercritical ones. Strong discrepancies are found from the classical decay of the squared diameter of the droplet observed in clearly subcritical conditions. We present a quasisteady analysis that allows neglecting unsteady terms in the equations that describe the problem, provided that the moving reference frame is well defined. The strong density gradient that follows the “droplet” as well as the time dependant mass flow rate location are considered with a particular attention. The obtained solutions of the equations match with the numerical results and generalize to near critical conditions the classical subcritical quasisteady analysis of droplet vaporization performed in the combustion science field.
Improved phase modulation for an en-face scanning three-dimensional optical coherence microscope
Authors: Hoeling Barbara M. , Peter Mary E. , Petersen Daniel C. , Haskell Richard C.
Published: October 2004

We have previously described an inexpensive method for modulating the interferometer of an en-face scanning, focus-tracking, three-dimensional optical coherence microscope (OCM). In this OCM design, a reference mirror is mounted on a piezoelectric stack driven at a resonance frequency of about 100 kHz. We perform a partial discrete Fourier transform of the digitally sampled output fringe signal. In the original design, we obtained the amplitude of the backscattered light by summing the powers in the fundamental (1ω) and first harmonic (2ω) of the modulation frequency. We used the particular piezoamplitude that eliminates the effects of interferometer phase drift. However, as the reference mirror was stepped to scan at different sample depths, variations in the back-coupled reference power added noise to the fringe signal at the fundamental piezodriving frequency. We report here a technique to eliminate the effects of this piezowobble by using instead the sum of the 2ω and 3ω powers as a measure of the backscattered light intensity. Images acquired before and after this improvement are presented to illustrate the enhancement to image quality deep within the sample.
Device for rapid sample insertion and extraction in thermal chemical vapor deposition tube furnace
Authors: McBride William S. , Ruoff Rodney S.
Published: October 2004

In this article, a simple and inexpensive device to allow the rapid insertion and withdrawal of samples from a tube furnace is described. The device operates in an atmosphere that is separate from ambient. This device shortens sample insertion and extraction times, which allows the study of the short time kinetics of chemical vapor deposition processes, and may allow for the growth of structures that could not be achieved using the conventional sample insertion and extraction procedure. The use of magnets to provide actuation through the walls of a quartz tube furnace is entirely general to any procedure using a tube furnace.
A versatile computer-controlled valve
Authors: Stiltner Sara , Zytkovicz Andrea , Rollefson R. J.
Published: October 2004

We have developed a computer-controlled valve based on the popular Nupro B-4HK bellows valve. The valve is actuated by a stepper motor. A modification to the Nupro valve necessary to achieve reproducible performance in setting the flow rate is described, and performance data on the coefficient of flow is presented. These valves have been cycled thousands of times without difficulties.